Encyclopedia of Cancer [2 ed.]
 9783540368472, 9783540476481, 9783540476498, 2008921484

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  • eBook

Table of contents :
Front Cover
Title Page
Copyright Page
Preface To The First Edition
Preface To The Second Edition
Editor in Chief
Field Editors
List of Contributors
A
2ar
17-1A
A Disintegrin and Metalloprotease
A-Scan Ultrasonography
Definition
AAA+
Definition
AAMP
Definition
Characteristics
References
AAPC
AAV
Definition
Characteristics
AAV Genome Structure
AAV Life Cycles
Clinical Relevance
Are Wildtype AAVs Pathogenic in Humans?
Is There a Natural Connection Between AAV Infection and Cancer?
What are Recombinant AAV Vectors?
Is AAV Unique as a Human Gene Therapy Vector?
What are Recent Advances in AAV Vector Technology?
What are Clinically Relevant rAAV Applications in Cancer Treatment?
Anti-Angiogenesis
Immunotherapy
Tumor Suppressors
Suicide Gene Therapy
Drug Resistance
Repair Strategies
Purging of Tumor Cells from Autologous Transplants
RNAi
Future Applications
References
ABC Drug-Transporters
Definition
ABC (ATP-Binding Cassette) Superfamily
Definition
ABC Transporter
Definition
ABC Transporter Proteins
Definition
ABC-Transporters
Synonyms
Definition
Characteristics
Human ABC-Transporters
ABC-Transporters and Multidrug Resistance of Cancer
ABC-Transporters as Anticancer Drug Targets
References
ABC Transporters (ATP-Binding Cassette Transporters)
Definition
ABL
Definition
Ablation
Definition
ABLES
Definition
ABVD
Definition
Characteristics
References
Accelerated Phase
Definition
ACD
Definition
ACDC
Acetaldehyde
Definition
Acetaldehydehydrogenase
Definition
Acetylation
Definition
N-Acetylcysteine
Definition
Acetylsalicylic Acid
Definition
Acetyltransferase
Definition
N-Acetyltransferase
Definition
ACF
Definition
Acharan Sulfate (AS)
Definition
Achneiform Rash
Definition
Acid Rain
Definition
Acidosis
Definition
Acinar Cells
Definition
Acites
Definition
Characteristic
Pathophysiology
Diagnosis
Treatment
References
Aclarubicin
Definition
Acquired Immunodeficiency Syndrome
Definition
Acquired Mutation
Definition
Acromegaly
Definition
ACRP30
ACTH
Definition
Actin
Definition
Actin Cytoskeleton
Actin Filament Severing
Definition
Actinic Keratosis
Definition
Actinomycin D
Definition
Activated Fibroblasts
Activated Natural Killer Cells
Synonyms
Definition
Characteristics
Biology of NK Cells
Role of NK Cells in Human Cancer
Markers of NK Cells
NK Cell Receptors
NK Cell and Cytokines
Cytotoxicity of NK Cells against Tumor or Infected Cells
NK Cells and Cancer Immunotherapy
References
Activated Vitamin D
Activation Loop
Definition
Activator Protein-1 (AP-1)
Definition
Active
Active Cell Death
Active Immunity
Definition
Acute Granulocytic Leukemia
Acute Lung Injury (ALI)
Definition
Acute Lymphoblastic Leukemia
Synonyms
Definition
Characteristics
References
Acute Megakaryoblastic Leukemia
Synonyms
Definition
Characteristics
Epidemiology
Clinical and pathologic features
Cytogenetic and Biological Features
Prognosis and Treatment
References
Acute Myelogenous Leukemia
Acute Myeloid Leukemia
Synonyms
Definition
Characteristics
Classification
Epidemiology
Etiology
Signs and Symptoms of AML
Prognostic Factors
Therapy
References
Acute Myeloid Leukemia 1
Acute Nonlymphocytic Leukemia
Acute Promyelocytic Leukemia
Definition
Characteristics
Clinical and Laboratorial Presentation
Molecular Characterization
Modeling APL in Mice
Therapeutics
References
Acute Respiratory Distress Syndrome (ARDS)
Definition
Acute Toxicity Studies
Acyclovir
Definition
AD
Definition
ADAbp
ADA-CP
ADAM
Definition
ADAM10
Definition
ADAM17
Synonyms
Definition
Characteristics
Structure
Expression and Regulation
Biological Function
Clinical Relevance
Summary
References
ADAM Molecules
Synonyms
Definition
Characteristics
Metalloprotease Function
Adhesion Function
Signaling Function
Other Functions
References
Adaptive Immunity
Definition
Adaptive Response
Definition
Adaptor Proteins
Definition
ADAR
Definition
ADCC
Definition
Additive Effects
Definition
Adduct
Definition
Adducts to DNA
Synonyms
Definition
Characteristics
Rationale for Using DNA Adducts as Biomarkers for Exposure and Adverse Effects
Advantages and Disadvantages of DNA Adducts Compared to Other Biomarkers
Cellular Defense: Repair of DNA Adducts
Adduct Measurements in Disease Epidemiology
Association of DNA Adducts with Cancer Risk
Background DNA-adduct Levels: Sources, Variations and Cancer Risk Prediction
Contributions of DNA-adduct Measurements to Disease Etiology and Pathogenesis
References
Adenine Nucleotides
Definition
Adenocarcinoid
Definition
Adenocarcinoma
Definition
Adenomas
Adenomatous Polyposis Coli
Definition
Adenomatous Polyps
Adenomucinosis (DPAM)
Definition
Adenosine and Tumor Microenvironment
Synonyms
Definition
Characteristics
Adenosine Deaminase
Definition
Adenovirus
Definition
Characteristics
Infection and Viral Transcription
Adenoviral Functions and Oncogenesis
Gene Therapy: First- and Second-Generation Adenoviral Vectors
“Gutless” Adenoviral Vectors
Replication-Competent Adenoviral Vectors for Cancer Gene Therapy
Adenovirus Vectors for Genetic Vaccination
References
Adenylyl Cyclase
Definition
Adherens Junctions
Definition
Adherens Junctions
Synonyms
Definition
Characteristics
Implications in Cancer
References
Adhesion
Definition
Characteristics
Cell Adhesion Receptors
Adhesion and Cancer
Adhesion in Metastasis
Adhesion within The Tumor Mass
Malignant Tumor Cells in the Blood Stream: Adhesion to Blood Cells and Platelets
Adhesion in the Target Organ
Adhesion to Endothelial Cells (EC)
Adhesion to Extracellular Matrix Components
Adhesion and Drug Resistance
References
Adhesion Molecules
Definition
ADI
Adipocyte Complement-Related Protein of 30 kDa
Adipocyte C1q
Adipocytes
Definition
Adipocytic Tumors
Adipokine
Definition
Adiponectin
Synonyms
Definition
Characteristics
Adiponectin and Carcinogenesis
Prostate Cancer
Breast Cancer
Endometrial Cancer
Gastric and Colorectal Cancer
Leukemia
Mechanisms
AMPK
c-Jun N-Terminal Kinase (JNK) and Signal Transducer and’Activator of Transcription 3 (STAT3)
Glycogen Synthase Kinase (GSK) 3beta/beta-Catenin Signaling Pathway
Other Pathways
References
AdipoQ
Adipose Most Abundant Gene Transcript 1
Adipose Tumors
Synonyms
Definition
Characteristics
Benign Adipose Tumors
Malignant Adipose Tumors
References
Adjuvant
Definition
Adjuvant Chemoendocrine Therapy
Synonyms
Definition
Characteristics
Breast Cancer
Adjuvant Hormone Therapy
Adjuvant Chemotherapy
Planning the Adjuvant Treatment: Adjuvant Chemoendocrine Therapy
Prostate Cancer
References
Adjuvant Chemohormonal Therapy
Adjuvant Cytotoxic and Hormonal Therapy
Adjuvant Effect
Definition
Adjuvant Therapy
Definition
Characteristics
ADMET
Definition
ADMET Screen
Definition
Characteristics
References
Admixture Population
Definition
Adopted Orphan Nuclear Receptors
Adoptive Immunotherapy
Definition
Characteristics
Unmanipulated T Cells
Cytokine Induced Killer Cells
Lymphocyte Activated Killer Cells
Tumor Infiltrating Lymphocytes
Antigen-Specific Cytotoxic T Lymphocytes
NK Cells
Enhancing the Function of Adoptively Transferred’Cells
References
Adrenal Cortex
Definition
Adrencorticotropic Hormone
Definition
Adrenocortical Cancer
Synonyms
Definition
Characteristics
Epidemiology of Adrenocortical Cancer
Pathophysiology of Adrenocortical Cancer
IGF-II (Insulin-Like Growth Factor II)
beta-Catenin Activation in Adrenocortical Cancer
TP53
Diagnosis and Treatment of Adrenocortical Cancer
Clinical and Hormonal Investigations
Imaging of Adrenocortical Cancer
Pathology and Molecular Analysis
Prognosis of Adrenocortical Cancer
Treatment of Adrenocortical Cancer
References
Adrenocortical Tumors
Definition
Adrenomedullin
Definition
Characteristics
Adrenomedullin: Peptide and Gene Structure
Signal Transduction
AM Serves as a Common Language Between the Different Cellular Components of the Tumor Microenvironment
Concluding Remarks
References
Adriamycin
Synonyms
Definition
Characteristics
Chemical Properties
Clinical Aspects
Therapeutic Applications
Pharmacokinetics
Clinical Toxicities
Pharmacological Mechanisms
Mechanisms of Action
Mechanisms of Resistance
Mechanisms for Development of Cardiotoxicity
References
Adult-Onset Diabetes
Definition
Adult Stem Cells
Synonyms
Definition
Characteristics
Therapeutic Potential
Cancer Stem Cells
References
Adult T-cell Leukemia
Definition
Adult Tissue Stem Cells
Definition
Advanced Breast Cancer
Definition
AEL
Definition
Aerobic Glycolysis
Aesthetic and Reconstructive Surgery of the Breast
Definition
Afaxin
Definition
Affinity-Matured IgG Response
Definition
Aflatoxin B1
Definition
Aflatoxins
Definition
Characteristics
Biotransformation
Carcinogenesis
Repair
Species/Tissue Susceptibility
References
Aflatoxin B1
Definition
AFP
AFP-L3
Definition
Agammaglobulinemia
Definition
AGEs
Definition
Aggressive Fibromatosis
Aggressive Fibromatosis in Children
Synonyms
Definition
Characteristics
Clinical Presentation
Diagnostic Approach
Pathogenesis
Treatment
Side Effects in Survivors
Conclusion
References
Aging
Definition
Characteristics
Aging
Epithelial Cancers
Cellular Senescence
Alterations in the Microenvironment
Tumor Progression in Aging
Implications for Treatment
References
Aging-Associated Inflammation
Synonyms
Definition
Characteristics
References
Agnogenic Myeloid Metaplasia
Agranulocytosis
AHNP
Definition
AHR
Definition
AI
Definition
AIB1
AIE2
AIF
Definition
AIK
AIK2
AIK3
AIM1
AIM-1
AIPC
Definition
AIs
Definition
AIT
Definition
AJCC
Definition
Ajuba
Definition
AKT
Definition
Akt Signal Transduction Pathway
Synonyms
Definition
Characteristics
Akt in Human Malignancy and Different Function of Akt Family Members
Signal Transduction
Akt Pathway as a Target for Cancer Intervention
References
ALA
Definition
5-ALA
ALAD
Definition
Alcohol Consumption
Definition
Characteristics
Epidemiology
Cancer of the Upper Aerodigestive Tract
Hepatocellular Cancer (HCC)
Breast Cancer
Colorectal Cancer
Mechanisms of Alcohol Mediated Carcinogenesis
Acetaldehyde
Oxidative Stress
Altered Methyl Transfer
Reduced Retinoic Acid
Specific Mechanisms (Cirrhosis, Gastroesophageal Reflux Disease, Estrogens)
References
Alcohol Dehydrogenase (ADH)
Definition
Alcohol Mediated Cancer
Definition
Alcoholic Beverages Cancer Epidemiology
Definition
Characteristics
Epidemiology of Alcohol-Related Cancer
Mechanisms of Alcohol Carcinogenicity
Conclusions
References
ALD
Definition
Aldehyde Dehydrogenases
Definition
Aldehydes
Definition
Aldo-Keto Reductase
Definition
Aldose Reductase
Definition
Alemtuzumab
Definition
ALK
Definition
ALK Protein
Synonyms
Definition
Characteristics
ALK Protein – Structure, Distribution and Function in Normal Tissues
ALK Protein and Cancer
Full Length ALK
ALK Fusion Proteins
Therapeutic Options
References
Alkeran
Definition
Alkyl
Definition
Alkylating Agents
Definition
Characteristics
Classification
Mechanism of Action
DNA Cross-Links
Molecular Pharmacology, Drug Resistance and Clinical Efficacy
Metabolism:
Toxicology
References
ALL
Definition
Allele Imbalance
Definition
Allelic Association
Allelic Loss
Definition
Allergen
Definition
Allergen-Specific Immunotherapy
Definition
Allergic Asthma
Allergic Disease
Definition
Allergic Rhinitis or Conjunctivitis
Allergy
Synonyms
Definition
Characteristics
Epidemiological Studies
Biological Details
References
Allodynia
Definition
Allogeneic
Definition
Allogeneic Bone Marrow Transplantation
Allogeneic Cell Therapy
Synonyms
Definition
Characteristics
Rationale
Procedure
Mechanisms
Clinical Aspects
References
Allogeneic Cellular Immunotherapy
Allogeneic Hematopoietic Stem Cell Transplantation
Allograft
Definition
Allograft Rejection
Definition
Allopurinol
Definition
Allylic Structures
Definition
Alpha-Actinin
Definition
Alpha1-Fetoglobulin
Alpha-Fetoprotein
Definition
Alpha-Fetoprotein – Historical
Synonyms
Definition
Characteristics
Immunochemical Techniques
AFP in Pathology
Fetuin versus AFP
AFP in laboratory Animals
References
Alpha-Fetoprotein – Modern
Synonyms
Definition
Characteristics
References
Alpha-Particles
Definition
Alpha-SMA
Definition
Alternative Lengthening of Telomeres (ALT)
Definition
Alternative Reading Frame
Alternative RNA Splicing
Definition
Alu Elements
Definition
Characteristics
Structure
Function
Role in Human Cancer
References
ALVAC-CEA
Definition
Alveolar Soft Part Sarcoma
Definition
AMAP1
Definition
AME Transcription Factor
Synonyms
Definition
Characteristics
References
Amenorrhea
Definition
Ames Assay
Definition
Amidation
Definition
Amifostine
Definition
Amine Oxidases
Definition
Characteristics
Functions
References
D-Amino Acid
Definition
Amino Terminal End
Definition
Amino-Bisphosphonate
Aminoflavone
Definition
5-Aminolevulinic Acid
Definition
delta-Aminolevulinic Acid
Definition
AML
Definition
AML1
AML1/ETO
AML-1/ETO/CBFbeta/TEL in Chromosomal Translocations
Definition
AML1/EVI-1
AML1/MTG8
AMN107
Amosite
Definition
Amph II
Amphibian Gastrin-Releasing Peptide
Amphipathic
Definition
Amphiphysin II
Amphiphysin-like
Amphiregulin
Synonyms
Definition
Characteristics
Amphiregulin Structure, Expression, and Function
References
Amphitropic Proteins
Definition
AMPK
Definition
AMPL
Amplaxin
Amplification
Definition
Characteristics
Cellular Regulation
Clinical Relevance
References
Amplified in Breast Cancer 1
Synonyms
Definition
Characteristics
Molecular Structure and Functional Domains
Functional Mechanisms
Physiological Function
Role in Cancer
References
Amrubicin
Synonyms
Definition
Characteristics
Preclinical Studies
Clinical Studies
Amrubicin Monotherapy
Amrubicin Combination Chemotherapy
Conclusion
References
Anaerobic
Analgesic
Definition
Analytic Epidemiological Study
Definition
Anaphase-Promoting Complex
Definition
Anaphylactic Shock
Definition
Anaplasia
Definition
Anaplastic Astrocytoma
Definition
Anaplastic Carcinomas
Anaplastic Large Cell Lymphoma
Synonyms
Definition
Characteristics
Diagnosis
Genetics
Therapy
References
Anaplastic Lymphoma Kinase
Definition
Anatomic Pathology
Definition
Anchorage-Independent
Definition
Anchorage-Independent Cell Growth
Definition
Anchorage-Independent Cell Transformation
Definition
Androgen
Definition
Androgen Insensitivity Syndrome (AIS)
Androgen Receptor
Synonyms
Definition
Characteristics
Structure–Function Relationships between Different Domains of Androgen Receptor that are Required for its Transcriptional Acti
Regulation of Unliganded AR
Regulation of Ligand-Bound AR
Nongenomic Function of AR
Androgen Receptor in Human Physiology and Pathology
References
Androgen-Independent Prostate Cancer
Definition
Androgens
Definition
Anemia
Definition
Anergy
Definition
Aneugen
Definition
Aneuploidy
Definition
Aneuploidy
Definition
Characteristics
Aneuploidy in Cancer
Aneuploidy as a “Driving Force” and not a “Consequence” in Cancer
Genetic Mechanisms of Aneuploidy in Cancer
Conclusions
References
Angiogenesis
Synonyms
Definition
Characteristics
Clinical Aspects
References
Angiogenesis Inhibiting Agents
Angiogenic Factors
Definition
Angiogenic Switch
Definition
Angiogenic/Angiostatic Chemokines
Angiosarcoma
Definition
Angiostatin
Definition
Angiotensin
Angiotensin II Signaling
Synonyms
Definition
Characteristics
Angiotensin II Signaling in Carcinogenesis
Clinical Aspects
Epidemiological Study of the Effect of ACE Inhibitors on Cancer Risk
References
Aniline
Definition
Aniridia
Definition
Ankyrin Repeat
Definition
ANLL
Ann Arbor Staging System
Definition
Anoikis
Synonyms
Definition
Characteristics
Mechanisms
Anoikis
Definition
Anomalous Pancreaticobiliary Ductal Junction
Definition
Anorexia
Definition
Anoxia
Synonyms
Definition
Characteristics
In vitro Creation of Hypoxia and Anoxia
Causes and Consequences of Tumor Anoxia
The HIF and p53 Interaction Relevant to the Hypoxic and Anoxic Cellular Fate
Oxygen Sensing/Signaling Pathways Relevant to Anoxia
Therapeutic Implications of Anoxia
References
Anoxic
Ansamycin Class of Natural Product Hsp90 Inhibitors
Synonyms
Definition
Characteristics
Anti-Tumor Activity
References
Ansomia
Definition
Antagonism
Definition
Anterior Pituitary Gland
Definition
ANTH
Definition
Anthocyanins
Definition
Anthracycline
Definition
Anthropogenic Activity
Definition
Anti-Angiogenic Drugs
Definition
Anti-HER2/Neu Peptide Mimetic
Synonyms
Definition
Receptor Characteristics
Her2 Regulation
AHNP Characteristics
Rational for Design of AHNP
AHNP
AHNP Analogs
AHNP as a Drug Carrier
AHNP in Breast Cancer Diagnosis
Relevance to Cancer Therapy
Conclusions
References
Anti-human p185neu Receptor Immunoglobulin G1
Anti-idiotype Vaccination
Anti-Idiotypic Antibodies
Definition
Anti-Inflammatory Drugs
Synonyms
Definition
Characteristics
Steroid Anti-Inflammatory Drugs
Nonsteroidal Anti-Inflammatory Drugs
Side Effects of NSAIDs
References
Anti-Ro/SSA and Anti-La/SSB Antibodies
Definition
Antiangiogenesis
Definition
Characteristics
Rationale for Antiangiogenesis for Therapy
Molecular and Cellular Players in Angiogenesis: Potential Targets for Antiangiogenesis
The Antiangiogenesis Strategy in Cancer Patients
Antiangiogenesis for Ocular Diseases
Mechanisms of Action of Antiangiogenic Agents
Biomarkers of Antiangiogenesis
Toxicity of Antiangiogenesis
Future Directions in Antiangiogenesis
References
Antiangiogenic
Definition
Antibodies to Self Antigens
Antibody
Definition
Antibody-Dependent Cell Mediated Cytotoxicity
Definition
Antibody Fragments
Definition
Antibody Microarray
Definition
Anticancer Therapeutic Synergy
Definition
Anticipation
Definition
Antiestrogens
Definition
Antigen
Definition
Antigen of the Cromer blood group
Antigen-Presenting Cells (APCs)
Definition
Antigen–Antibody Complexes
Definition
Antihormonal Therapy
Definition
Antihormones
Definition
Antilipid Peroxidation
Definition
Antimetabolite
Definition
Antinuclear Antibody
Definition
Antioxidant
Definition
Antioxidant Capacity
Definition
Antioxidant Defenses
Definition
Antioxygen
Definition
Antiproliferative
Definition
Antipyretic
Definition
Antiradical
Definition
Antisense DNA Therapy
Definition
Characteristics
Target Choice and Oligonucleotide Design
Delivery, Subcellular Trafficking, and Pharmacodynamics of ODNs
Clinical Applications of Antisense ODNs in Hematological Malignancies
Prospects for Antisense DNA Therapy
References
Antisense Nucleic Acid
Definition
Antiserum
Definition
Antitoxins
Definition
Antitumor Vaccines
Definition
Antizyme Inhibitor
Definition
Characteristics
References
AP-1
Definition
Characteristics
General Structure of the AP-1 Subunits
DNA Binding Domain
Transactivation Domain
Transcriptional and Posttranslational Control of AP-1 Activity
Transcriptional Activation
Regulation of AP-1 Activity
AP-1 in Physiology and Pathology
AP-1 Subunits in Cancer
Acknowledgments
References
AP2
Definition
Apactin (mouse)
APAF-1
Definition
APAF-1 Signaling
Synonyms
Definition
Characteristics
APAF-1 Gene Structure and Regulation
APAF-1 Protein Structure
Assembly and Structure of the Apoptosome
Positive and Negative Regulation of Apoptosome’Function
APAF-1 Expression and Apoptosome Regulation in Cancer
Apoptosome-Dependent and -Independent Pathways of Apoptosis in Normal and Neoplastic Cells
References
AP2-alpha
Definition
APC
Definition
APC/beta-Catenin Pathway
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
APC Gene in Familial Adenomatous Polyposis
Synonyms
Definition
Characteristics
Genotype–phenotype Correlations
References
APC-Min Mouse
Definition
Apheresis
Definition
Aphidicolin
Definition
API4
Apical Surface
Definition
APL
Definition
apM1
APO-1
Definition
APO2 ligand
APO2L
Apoptogenic Death
Definition
Apoptosis
Synonyms
Definition
Characteristics
Cellular Regulation
Clinical Relevance
References
Apoptosis-inducing Factor (AIF)
Definition
Apoptosis-Induction for Cancer Therapy
Definition
Characteristics
Re-activation of Intracellular Pro-Apoptotic Systems
Inhibition of Intracellular Anti-Apoptotic Systems
Selective Delivery of Additional External Pro-Apoptotic Stimuli
Perspectives for Selectively Tipping the Apoptotic Balance in Cancer
Reference
Apoptosis Inhibitor 4
Apoptosis Pathways
Definition
Apoptosis Regulator Bcl2
Apoptosis Signaling
Synonyms
Definition
Characteristics
Death Receptor Signaling
Mitochondrial Regulation of Apoptosis
Endoplasmic Reticulum Regulation of Apoptosis
Regulation of Apoptosis by Tumor Suppressors and Oncogenes
Apoptosis Regulation During Cancer Treatment
References
Apoptosome
Definition
Apoptotic Protease Activating Factor-1
Appendiceal Epithelial Neoplasms
Synonyms
Definition
Characteristics
Epithelial Appendiceal Neoplasms
Pseudomyxoma Peritonei Syndrome
Treatment
Management in Absence of Peritoneal Dissemination
Management of Mucinous Neoplasms with Peritoneal Dissemination
Outcomes
Approaches to Management
A New Standard of Care
Summary of Changes in Management of Appendiceal Epithelial Neoplasms
References
Appendiceal Mucinous Tumor’of Uncertain Malignant Potential
Appendix
Definition
Appraisal Consultation Document
Definition
Aptamer
Definition
Aptamer Bioconjugates for Cancer Therapy
Characteristics
References
Apudomas
Definition
AR
Definition
9-beta-D-Arabinosyl-2-fluoroadenine (F-ara-A) Monophosphate
Arachidonic Acid
Definition
Arachidonic Acid Pathway
Synonyms
Definition
Characteristics
Fatty Acids as Dietary Precursors
Production of Eicosanoids – from AA and EPA by COX and LOX Pathways
Signaling by Eicosanoids
NSAIDS and Eicosanoid Signaling
Interactions with Cancer Signaling Pathways
References
Archaea
Definition
ARE
ARF
Definition
ARF Tumor Suppressor Protein
Synonyms
Definition
Characteristics
p53-Dependent Functions of ARF
The ARF–MDM2–p53 Pathway
ARF and Replicative Senescence
p53-Independent Functions of ARF
ARF Negatively Regulates Ribosome Biogenesis
ARF and the Control of Transcription
Conclusion
References
Argentaffin Carcinoma
Arginase
Definition
Arginine
Definition
Characteristics
Arginine Metabolism
Nitric Oxide, Polyamines, Carcinogenesis, and Chemoprevention
Arginine and Cancer: Experimental Studies
Arginine and Cancer: Epidemiologic Studies
Arginine and Cancer: Clinical Aspects
References
Arginine-Depleting Enzyme Arginine Deiminase
Synonyms
Definition
Characteristics
Sensitivity of Cancer Cells to ADI-Treatment
Mechanisms of Anti-Tumor Activity of ADI
Clinical Trials
References
Argininosuccinate Lyase
Definition
ARK1
ARK2
Armadillo Family
Definition
Armed Viruses
Aromatase
Definition
Aromatase and its Inhibitors
Synonyms
Definition
Characteristics
Composition
Distribution and Regulation
Expression
Aromatization Reaction
Type I Inhibitors of Aromatase
Formestane
Exemestane
Type II Inhibitors of Aromatase
Applications and Indications
References
Aromatic Amine
Definition
Aromatic Hydrocarbon
Definition
Arp2/3
Definition
Arp2/3 Complex
Definition
Array-based Comparative Genomic Hybridization
ArrayCGH
Synonyms
Definition
Characteristics
Clinical Applications
References
Arrhenoblastoma
Definition
Arsenic
Definition
Characteristics
History of Use
Paradox of Arsenic
Mechanisms of Action – Cancer Causing Effects of’Arsenic
Genotoxicity
Possible Involvement of Reactive Oxygen Species (ROS)
Aberrations in Signal Transduction
Arsenic as a Therapeutic Agent
References
Arsenic Trioxide
Definition
Aryl Hydrocarbon Receptor
Synonyms
Definition
Characteristics
Historical Perspective
Xenobiotic Stress
Physiological Effects
A Link Between Environment and Cancer?
The Signaling Pathway
Gene Expression and Biological Pathways
Mechanisms of Carcinogenicity of AhR Ligands
AhR as a Pharmacological Target
References
Aryl sulfatase C
Arylamine
Definition
Arylamine N-Acetyltransferases
Synonyms
Definition
Characteristics
Acetylation Polymorphism
Clinical Relevance
References
Asbestos
Definition
Characteristics
Carcinogenic Action of Iron
Asbestos: A Vehicle for Iron
Asbestos: Usage and Banishment
References
ASK1
Definition
Askanazy
Definition
Askin Tumor
Definition
Asparagine
Definition
Aspiration Cytology
Aspirin
Definition
Asrocytoma
Definition
Assessment of Anaplasia of a Tumor
Assessment of the Degree of Tumor Differentiation
Association Study
Definition
Aster
Definition
Asthma
Astrocyte
Definition
Astrocytoma
Definition
Asymmetric Cell Division
Definition
Asymmetric Cytokinesis
Definition
Ataxia Telangiectasia
Definition
Ataxia-telangiectasia Mutated (ATM)
Ataxia-telangiectasia Variant 1 and Variant 2
ATF2
Definition
ATF6
Definition
Atheromatous Plaques
Definition
Atherosclerosis
Definition
ATL
Definition
ATM
Definition
ATM Protein
Synonyms
Definition
Characteristics
Cellular Functions and Molecular Regulation
Clinical Relevance
References
Atopic Dermatitis
Atopic Disorders
Definition
Atopy
Atorvastatin
Definition
ATP
Definition
ATP-Binding Cassette Transporters
Definition
ATPase
Definition
ATR
Definition
Atrasentan
Definition
Attenuated Adenomatous Polyposis Coli
Attributable Fraction
Definition
Attributable Risk
Definition
Attrition
Definition
Atypia
Definition
Atypical Congenital Mesoblastic Nephroma
Atypical Mole Syndrome
Definition
Atypical Neurocytoma
Atypical Nevi (dysplastic nevi)
Definition
Atypical Teratoid/Rhabdoid Tumor
Definition
AUC
Definition
AURA
AurB
AurC
AURKB
AURKC
AURORA2
Aurora-A
Aurora-B
Definition
Aurora-C
Aurora Kinases
Synonyms
Definition
Characteristics
Mechanisms
Aurora Kinase as Target for Cancer Intervention
References
Autoantibodies
Definition
Characteristics
Autoantibodies Can Produce Tissue Injury and May Influence Tumor Behavior
Autoantibodies as Diagnostic and Prognostic Serologic Biomarkers of Cancer
References
Autoantigens
Definition
Autocrine
Definition
Autocrine Growth Factors
Definition
Autocrine Signaling
Definition
Autocrine Stimulation
Definition
Autografts
Definition
Autoimmune Diseases
Definition
Autoimmune Hemolytic Anemia
Definition
Autoimmune Lymphoproliferative Syndrome
Definition
Autoimmune Response
Definition
Autoimmune Thyroid Disease
Definition
Autoimmunity
Definition
Autoimmunity and Prognosis in Cancer
Synonyms
Definition
Characteristics
Evidence for Autoreactivity in Patients with Cancer
Regulation of Autoreactivity
Immunotherapy May Induce Autoimmunity
Autoantigens as a Link Between Cancer and Autoimmunity
References
Autologous Bone Marrow Transplantation
Autologous (hematopoietic) Stem Cell Transplantation
Autologous Typing
Definition
Autonomic Nervous System
Definition
Autophagic Body
Definition
Autophagocytosis
Autophagosome
Definition
Autophagy
Synonyms
Definition
Characteristics
Cell Biology of Autophagy
Signal Transduction
Autophagy and Programmed Cell Death
Autophagy and Cancer
References
Autoreactivity
Definition
Autosomal Dominant
Definition
Autotaxin
Definition
Auxiliary Tissue
Definition
Auxilin-2
Auxotrophy
Definition
Avian Erythroblastic Leukemia Viral Oncogene Homolog 2
Awd in Drosophila
Definition
Axin
Definition
Axon Guidance
Definition
Axonal Growth Cone
Definition
Aza-arenes
Definition
5-Azacytidine
Definition
5Upsi-Aza-2Upsi-Deoxycytidine
Definition
5-Azadeoxycytidine
5-aza-2′ Deoxycytidine
Synonyms
Definition
Characteristics
History
Contemporary Research
Clinical Research
References
Aza-epothilone B
Azathioprine
Definition
Aziridine
Definition
Azoxymethane
Definition
B
B Cell
Definition
B-1 Cells
Definition
B7 Molecules
Definition
B Symptoms
Definition
BAC
Definition
BACH1 Helicase
Synonyms
Definition
Characteristics
BACH1 and Hereditary Breast Cancer
BACH1 was Identified by its Direct Interaction with BRCA1
BACH1 is Mutated in Hereditary Breast Cancer Patients
BACH1 is Important for Mediating the DNA Damage Response
BACH1 is Required for DSBR
BACH1 and Fanconi Anemia
References
Bacillus Calmette-Guérin
Synonyms
Definition
Characteristics
Microbiological Background on BCG and Tuberculosis Vaccination
BCG in Cancer Immunotherapy
Mode of Action in Antitumor Activity
References
Bacteriophage
Definition
Bacteriophage Display
Baculoviral IAP-repeat Containing Protein 5
Baculovirus
Definition
BAD
Definition
BAF47
Bak
Definition
BAK1
Definition
BALT
Definition
Bannayan-Riley-Ruvalcaba Syndrome
Definition
BAR Domain
Definition
BARD1
Synonyms
Definition
Characteristics
BARD1 Structure, Conservation, and Expression
Functions of the BARD1–BRCA1 Heterodimer
BRCA1-Indendent Tumor Suppressor Function of BARD1
BARD1 in Mitosis
Clinical Relevance
BARD1 Mutations in Cancer
References
Barrett Esophagus
Definition
Barrett High-grade Dysplasia
Definition
Basal Cell Carcinoma
Definition
Characteristics
Risk Factors and Therapy
Squamous Cell Carcinoma
Risk Factors and Therapy
References
Basal Cell Nevus Syndrome (BCNS)
Definition
Basal-like Breast Cancer
Synonyms
Definition
Characteristics
Molecular Etiology
Diagnosis
Clinical Features
Treatment
References
Basal Phenotype Breast Cancer
Basal-subtype Breast Cancer
Basal-type Breast Cancer
Basalioma
Definition
Base Excision Repair (BER)
Definition
Basement Membrane
Definition
Basic FGF
Definition
Basic Fibroblast Growth Factor (bFGF)
Basic Helix-Loop-Helix Domain
Definition
Basolateral Surface
Definition
Basophil
Definition
BAX
Definition
bbc3
BCC
Definition
BCDF
B-cell CLL/lymphoma 2
B-cell Differentiation Factor
B-cell Interferon
B-cell Leukemia/Lymphoma-2 Gene (Bcl2)
B-cell Leukemias
B-cell Lymphoid Neoplasm
B-cell Lymphoma
Definition
B-cell Lymphoma Protein 2
B-cell lymphoproliferative Disorders/Diseases
B-cell Malignancy
B-Cell Response
Definition
B-cell Stimulating Factor-2
B-cell Tumors
Synonyms
Definition
Characteristics
What is a B-lymphocyte?
Immunoglobulin Gene Rearrangement
Somatic Mutation and Class Switching
What is a B-cell Tumor?
Characteristics of B-cell Tumors
Immunogenetics of B-cell Lymphomas
References
BCG
Definition
Bcl2
BCL2
Synonyms
Definition
Characteristics
Functions
Regulation
Bioactivity
References
Bcl-2 Binding Component 3
Bcl-2 Family Proteins
Definition
BCL3
Definition
Characteristics
Structure and Molecular Function
Regulation
Expression
Physiological Function
Oncological Relevance
References
BCL-6
Definition
BCL6 Translocations in B-cell Tumors
Synonyms
Definition
Characteristics
The BCL6 Gene and Gene Product
BCL6 Translocation Affecting the IG Loci
BCL6 Translocations Affecting Non-IG Loci
The 5´ Non-coding Region of BCL6 Undergoes Somatic Hypermutation
Clinical Relevance
References
BCL-x
Definition
Bcl-XL
Definition
BCNS
Definition
BCR-ABL1
Definition
Characteristics
A Somatic Mutation of Bone Marrow Progenitor Cells
Molecular Features of BCR-ABL1 Recombination
Complex BCR-ABL1 Rearrangements
Translocation-Associated Genomic Deletions
Detection of BCR-ABL1
What Causes BCR-ABL1?
BCR-ABL1 in Healthy Individuals
Why Breakpoint Cluster Regions?
Molecular Consequences of BCR-ABL1
Clinical Relevance
Anti-BCR-ABL1 Therapies
References
BCSG1
Definition
BDNF
Definition
Beckwith-Wiedemann Syndrome
Definition
Beckwith-Wiedemann Syndrome Associated Childhood Tumors
Definition
Characteristics
Diagnostic Criteria
(Epi)-Genetics
BWSCR1
BWSCR2
Diagnostics
BWS Associated Tumors
Wilms Tumor
Adrenocortical Carcinoma
Rhabdomyosarcoma
Hepatoblastoma
Common Genetic Pathways
References
Beclin 1
Definition
Becquerel
Definition
Behcet Disease (BD)
Definition
Benign Tumor
Definition
Benzene and Leukemia
Definition
Characteristics
Benzene Toxicity and Carcinogenicity
Benzene Metabolism and Toxicity
Benzene, Chromosome Changes and Leukemia
References
Benzidine
Definition
Benzo(a)pyrene
Definition
Benzol
Definition
Benzo[a]pyrene Diol Epoxide (BPDE)
Definition
Benzoquinone ansamycin
Benzpyrene
Definition
Berlin Breakage Syndrome
Beta-2 Microglobulin (beta2 Microglobulin)
Definition
Beta-glucosidase
Beta Subunit of Human Chorionic Gonadotropin (beta-hCG)
Definition
Betacellulin (BTC)
Definition
Betel Quid
Definition
Betulin
Definition
Betulinic Acid
Definition
Characteristics
References
Bevacizumab
Definition
bFGF
Definition
BGP, Biliary Glycoprotein
BH
Definition
BH3
Definition
BH3 Binding Pocket
Definition
BH3-Interacting Death Domain Agonist (Bid)
Definition
BH3-interacting Domain Death Agonist
BHD Syndrome
bHLH
Definition
bHLH-PAS Proteins
Definition
Biallelic Mutations
Definition
Bias
Definition
Bicalutamide
Definition
Bid
Synonyms
Definition
Characteristics
The Bid Molecule
Bid is a Pro-Death Sensor for Specific Protease Activation
Activation of Mitochondria by Bid
Bid as a Pro-Life Sensor for Cell Cycle Progression and’DNA Damage
Role of Bid in Oncogenesis
Summary
References
Bidirectional Differentiated Malignant Tumors
Definition
2,3´-Biindolinylidene-2,3´-diones
BIK Proapoptotic Protein
Synonyms
Definition
Characteristics
Discovery
Protein Structure and Molecular Functions
Gene Structure, Expression, and Phenotypes
Relevance to Cancer Genetics and Therapy
References
Bilateral Acoustic Neurofibromatosis
Bile
Definition
Bile Acids
Definition
Characteristics
Toxicity of Bile Acids
Effects of Bile Acids on Organs
Upper Gastrointestinal Tract
Lower Gastrointestinal Tract
Liver, Gallbladder, and Bile Ducts
Pancreas
References
Bile Duct
Definition
Bile Duct Adenoma
Bile Duct Carcinoma
Bile Duct Hamartoma Biliary Cystadenoma
Bile Duct Neoplasms
Synonyms
Definition
Characteristics
Benign Bile Duct Neoplasms
Malignant Bile Duct Neoplasms
References
Biliary Glycoprotein
Definition
Bin1
Synonyms
Definition
Characteristics
References
BING2
Bioactivation
Definition
Bioactive Lipids
Bioavailability
Definition
Biochip
Bioconjugate
Definition
Biodribin
Biogenic Amines
Definition
Bioinformatics
Definition
Biologic Therapy
Definition
Biological Clock
Definition
Biological Markers
Biological Monitoring
Biological Response Modifiers
Definition
Biological Therapy
Biologically Effective Dose (BED)
Definition
Biologicals
Definition
Bioluminescence Imaging
Synonyms
Definition
Characteristics
About Luciferases
How is In Vivo Bioluminescence Detected?
Considerations to Maximize In Vivo Imaging Sensitivity
Oncology Model Applications
References
Bioluminescent Reporter Gene Assays
Biomarkers
Definition
Characteristics
Background
Types of Biomarkers
Biomarker Techniques and Fields of Application
References
Biomonitoring
Synonyms
Definition
Characteristics
Biomarkers of Exposure
Biomarkers of Effect
Biomarkers of Susceptibility
Ethical and Social Implications
References
Biopsy
Definition
Bioreductive Drug
Definition
Biosensor
Definition
Biosynthesis
Definition
Biotechnology
Definition
Biotechnology Derived Therapeutic Proteins
Biotin
Definition
Biotransformation
Definition
BiP/GRp78
Definition
BIR Domain
Definition
BIRADS
Definition
Birbeck Granule
Definition
BIRC5
Birt–Hogg–Dubé Syndrome
Synonyms
Definition
Characteristics
Diagnostic Criteria
BHD Gene Mutations
Screening and Possible Treatment for BHD
References
Bispecific Antibodies
Definition
Characteristics
Generation of Bispecific Antibodies
Effector Cell Retargeting
Clinical Experience with Bispecific Antibodies
References
Bisphosphoglycerate
Definition
Bisphosphonates
Definition
Characteristics
Mechanism of Action
Pharmacokinetic
Clinical Use
Hypercalcemia of Malignancy (HCM)
Treatment of Bone Metastases
Prevention of Bone Metastases
Osteoporosis
Side Effects
References
BL
Definition
Bladder Cancer
Definition
Characteristics
Clinical Epidemiology and Risk Factors
Tumor Biology and Genetics
Characteristics of Nonurothelial Cell Carcinomas
Clinical Presentation
Diagnosis and Staging
Management of Noninvasive Disease
Management of Invasive and Metastatic Disease
References
Blast Crisis
Definition
Characteristics
Clinical Features
Biological Basis
References
Blast Phase
Definition
Blastocyst
Definition
Bleomycin
Definition
BLI
BLL
Definition
Blood–Brain Barrier
Synonyms
Definition
Characteristics
The BBB Junctional Complexes
Permeability Properties of the BBB
In Vitro BBB Models
BBB in Disease
References
Blood Stasis due to Vital Energy Stagnancy
Definition
Bloom Syndrome
Synonyms
Definition
Characteristics
Clinical Description
BLM-Deficient Cells
BLM Gene
Frequency
BLM Protein
Mouse Models
Genetic Counseling
Therapy
References
Bloom-Torre-Mackacek Syndrome
Blue Dye
Definition
BM-40
BMP
Definition
BMS-247550
Body Mass Index
Definition
Bombesin (BBS)
Definition
Bone Loss, Cancer Mediated
Synonyms
Definition
Characteristics
Types of Bone Metastasis
Bone Physiology: Control of Normal Bone Remodeling
Bone is a Unique Environment for Metastasis
The Vicious Cycle of Osteolytic Metastasis
The Vicious Cycle of Osteoblastic Metastases
Osteolytic Multiple Myeloma
Osteolytic Metastasis from Breast Cancer
Osteoblastic Metastasis in Prostate Cancer
References
Bone Marrow
Definition
Bone Marrow-Derived Mesenchymal Stem Cells (MSC)
Definition
Bone Morphogenetic Protein
Definition
Bone Neoplasms
Bone Resorption
Definition
Bone Sarcomas
Bone-seeking Malignant Phenotypes
Bone Sialoprotein
Bone Tropism
Synonyms
Definition
Characteristics
Blood Circulation Patterns
Cellular Adhesive Interactions
Chemoattraction of Cancer Cells
Tissue Conditions Supporting the Growth of Cancer Cells
Alteration of Bone Microenvironment by Cancer Cells
References
Bone Tumors
Synonyms
Definition
Characteristics
Etiology
Diagnosis
Staging and Prognosis
References
Borderline Appendiceal Mucinous Tumor
BORIS
Synonyms
Definition
Characteristics
BORIS Functions
BORIS in Cancers
Clinical Aspects
BORIS as a Cancer Biomarker
BORIS as a Target for Cancer Immunotherapy
References
Bortezomib
Synonyms
Definition
Characteristics
Mechanism of Action
Pharmacology
Clinical Aspects
In Cancer
In Graft Versus Host Disease and Immune Disorders
Other Uses
Future Directions
References
Bovine Papillomavirus
Definition
Characteristics
BPV Gene Products
E5
E6
E7
L1 and L2
BPV and Papillomas
BPV and Cancer
BPV and Equine Sarcoids
References
Bowen Disease
Definition
Bowman-Birk Inhibitor (BBI)
Definition
Boyden Chambers
Definition
53BP
Definition
BR 27-29
Brachytherapy
Synonyms
Definition
Characteristics
Dose Rate
Dose Calculations
Implantation Techniques
Clinical Applications of Brachytherapy
Gynecologic Malignancies
Prostate Cancer
Other
References
Bracken Fern
Definition
Bradykinin
Definition
B-raf-1
BRAF1
B-Raf Signaling
Synonyms
Definition
Characteristics
Physiological Aspects of B-Raf Signaling
B-Raf Signaling and Tumor Development
B-Raf Structure and Regulation
B-Raf as a Therapeutic Target
References
B-Raf Somatic Alterations
Definition
Characteristics
History of the BRAF Proto-Oncogene
Chromosomal Aberrations
Somatic and Germ-Line Point Mutations
Amplification
References
Bragg (Curve) Peak
Definition
Brain Capillaries
Brain Microvascular Endothelial Cells
Brain Tumors
Definition
Characteristics
Classification and Pathology
Clinical Presentation of Brain Tumor Patients
Clinical Management of Brain Tumor Patients and’Prognosis
Complications of Therapy
References
Brain-Derived Neurotrophic Factor
Definition
Branching Morphogenesis
Definition
BRCA1-associated Ring Domain (Gene/Protein) 1
BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk
Definition
Characteristics
Clinical Characteristics
Molecular and Cellular Characteristics
Tumor Suppressor Genes
Expression of BRCA1 and BRCA2
Clinical Relevance
When to Take the DNA-test?
Why Take the DNA-test?
Interpreting a Negative Test Result
References
BRCT Domain
Definition
Breakpoint
Definition
Breakpoint Cluster Region
Definition
Breast Cancer
Definition
Characteristics
Epidemiology
Screening
Genetics
Molecular Biology
Treatment
New Treatments
References
Breast Cancer Genes BRCA1 and BRCA2
Definition
Characteristics
Protein
Cellular and Molecular Regulation
Role in the Cellular Response to DNA Damage
Other Functions
Tumor Suppression by BRCA1 and BRCA2
Clinical Relevance
Breast Cancer Resistance Protein
Definition
Breast Conservation
Definition
Breast Imaging Reporting and Data System
Definition
Breast Implant
Definition
Breast Reconstruction
Definition
Breast Reduction
Definition
Breast Regressing Protein 39 Kd
Breast Stem Cells
Definition
Breast Surgery
Definition
Breast Transillumination
Breslow Depth
Definition
BRG- and BRM-associated Factor, 47 kDa
Brilliant Yellow S
BRIP1
BRIT1 Gene
Synonyms
Definition
Characteristics
Significance of BRIT1 in the Development of Cancer
BRIT1 Function in DNA Damage Response
BRIT1 Function in Cell Cycle Control
References
BRM
Definition
BRMS1
Definition
Characteristics
Cellular and Functional Characteristics
Clinical Relevance
References
BRN-5547136
Broder Histological Classification
Definition
Bromodeoxyuridine (BrdU)
Definition
Bromodomain
Definition
Bronchogenic Carcinoma
Brother of the Regulator of Imprinted Sites
Brown Adipose Tissue
Definition
brp-39
Brush Border
Definition
Bryostatin-1
Definition
Characteristics
Rationale for Targeting the PKC
Preclinical Activity of Bryostatin-1
Single Agent Activity of Bryostatin-1
Bryostatin-Based Combinations
Future Directions
References
BSA
Definition
B-Scan Ultrasonography
Definition
BSF-2
BTAK
BUB1
Definition
Bulk Minerals
Definition
Bulky
Definition
Burkitt Lymphoma
Definition
Burkitt Lymphoma Cell Lines
Definition
Bystander Effect
Definition
C
C33
C75
Definition
c-Abl
Definition
C.elegans cell death 4 homolog
CA19-9
Definition
CA125
Definition
Ca2+-activated Phospholipid Dependent Protein Kinase
Ca2+ ATPase
Definition
Ca2+-Release Channels
Definition
CaBP3
Cachexia
Definition
Characteristics
Weight Loss
Poor Appetite
Increased Metabolism and Energy Expenditure
Loss of Adipose Tissue
Loss of Muscle Protein
Treatment
References
Cachexia-inducing Agent
Caco-2
Definition
Cadherin 1
Definition
Cadherins
Definition
Cafe Au Lait Spots
Definition
Cajal Bodies
Synonyms
Definition
Characteristics
References
CAK1 Antigen
Cal
Definition
Calcineurin
Definition
Calcitonin
Definition
Characteristics
Biosynthesis
Biological Actions
Actions on Bone
Renal Actions
Central Actions
Other Actions
CT in Cancer
Mechanism of CT Action
Receptors
Receptor Isoforms
Modulation of CTR Specificity
CTR Signaling
G protein-Mediated Signaling
G Protein-Independent Signaling
Significance of CT–CTR axis in Cancer: Clinical Aspects
CT is “Oncogene” for Prostate Cancer but “Tumor Suppressor” for Breast Cancer
CT is an Angiogenic Factor
References
Calcitriol
Synonyms
Definition
Characteristics
Calcitriol and Cancer
Mechanisms
Role of Vitamin D or Calcitriol in Cancer Prevention or Therapy
Colon Cancer
Breast Cancer
Prostate Cancer
Other Malignancies
Note Added in Proof
References
Calcium-Binding Proteins
Definition
Characteristics
EF-Hand Motif Calcium-Binding Proteins
Annexins and Other non-EF-Hand Motif Proteins
Calreticulin-like Proteins
References
Calcium-binding Reticuloplasmin of Molecular Weight 55 kDa
CALI
Calnexin
Definition
Calpain
Definition
Characteristics
Calpain and Cell Proliferation
Calpain and Cell Migration
Calpain and Apoptosis
References
Calpastatin
Definition
Calreticulin
Definition
Calreticulin
Synonyms
Definition
Characteristics
Structure of CRT
Functions of CRT in the Cell
CRT, a Lectin-like Molecular Chaperone in the ER
CRT, a Regulator of Ca2+ Homeostasis in the ER
Other Miscellaneous Functions of CRT In and Out of the ER
CRT and Development
CRT and Cancer
Expression of CRT in Cancer
Pathophysiological Relevance of CRT in Malignant Disease
CRT as a Tool for Cancer Therapy
References
Calsequestrin-like Protein
CAM
Definition
cAMP
Definition
cAMP Response Element Binding Protein (CREB)
Definition
Campath-1H
Definition
Camptothecin
Definition
CAMs
CAMTA1
Definition
Characteristics
Clinical Relevance
References
Canale-Smith Syndrome
Definition
Canals of Hering
Definition
Cancer
Definition
History
Characteristics
Types of Genetic Damage
Cellular Aspects
Sporadic Versus Familial Cancer
Polygenic Determinants of Risk
Cancer and Cadmium
Definition
Characteristics
References
Cancer Antigen
Definition
Cancer Antigen 15-3 (CA 15-3)
Definition
Cancer Associated Antigen 19-9 (CA 19-9)
Definition
Cancer Associated Antigen 27-29 (CA 27-29)
Definition
Cancer of B-lymphocytes
Cancer Cachexia Syndrome (CCS)
Definition
Cancer Causes and Control
Synonyms
Definition
Characteristics
Tobacco
Trends
Physical Activity
Trends
Weight Control and Obesity Prevention
Trends
Dietary Improvements
Dietary Fat
Red Meat
Calcium
Excess Caloric Intake
Whole Grains
Vitamin A and Carotenoids
Selenium
Vitamin D
Trends
Limitation of Alcohol Use
Safer Sex and Decreased Viral Transmission
Trends and Disparities
Sun Protection
Screening
Trends and Disparities
Conclusion
References
Cancer Cell-platelet Microemboli
Cancer Epidemiology
Synonyms
Definition
Characteristics
References
Cancer Epigenetics
Definition
Characteristics
DNA Hypermethylation
Histone Modification
DNA Hypomethylation
Epigenetic Alterations as Targets for Diagnosis and Therapeutic Intervention
Cancer Genome Project
Definition
Cancer Germline Antigens
Synonyms
Definition
Characteristics
Identification
Nomenclature
Regulation of Expression
Function
Clinical Studies
References
Cancer of the Large Intestine
Cancer-mediated Bone Loss
Cancer Networks
Definition
Cancer-Prone Genetically Modified Mouse Models
Definition
Cancer Registry
Definition
Cancer Stem Cells
Definition
Cancer Stem-Like Cells
Synonyms
Definition
Characteristics
References
Cancer Testis Antigens
Definition
Cancer (or Tumor) Stroma
Cancer Vaccines
Definition
Characteristics
T Lymphocytes
Tumor Cells
Peptides and Carbohydrates
Recombinant Vaccines Expressing Tumor Antigens
Anti-idiotype Vaccines
Dendritic Cell-based Vaccines
Conclusion
References
Cancer Without Disease
Cancers of Hormone-responsive Organs or Tissues
Cancer-Testis-Antigens
Definition
Candidat of Metastasis 1
Cannabinoids
Synonyms
Definition
Characteristics
Signaling Pathways Modulated by Cannabinoid Receptors
Palliative Effects of Cannabinoids in Cancer
Mechanism Involved in the Antiemetic Effect of Cannabinoids
Mechanism Involved in Appetite Stimulation by Cannabinoids
Mechanism Involved in the Analgesic Effect of Cannabinoids
Antitumoral Effects of Cannabinoids
Induction of Apoptosis
Inhibition of Tumor Angiogenesis
Therapeutic Potential of Cannabinoids as Antitumoral Agents
References
Cap
Definition
Cap-Binding Complex
Definition
Cap-Dependent Translation
Definition
Capecitabine
Definition
CapG
Definition
Capillary Hemangioblastoma
Definition
CAR
Carbonyl Reductases
Carboplatin
Definition
Carboxylesterase
Definition
Carboxypeptidase
Definition
Carcinoembryonic Antigen
Synonyms
Definition
Characteristics
Protein Structure
The CEA Gene Family
Function of CEA in Normal and Cancerous Tissue
Clinical Aspects
References
Carcinoembryonic Antigen (CEA)
Definition
Carcinofetal Proteins
Carcinogen
Definition
Carcinogen Dosimetry
Definition
Carcinogen Macromolecular Adducts
Definition
Characteristics
Carcinogen Metabolism Leading to Macromolecular Adduct Formation
Structural Modification of DNA to Form Carcinogen-DNA Adducts
Methods to Measure Carcinogen-DNA Adducts
Importance of DNA Adducts in Chemical Carcinogenesis
Significance of Carcinogen-Protein Adducts
Methods to Measure Carcinogen-Protein Adducts
Significance of Protein-Adducts
References
Carcinogen Metabolism
Definition
Characteristics
History
Metabolism
Mechanisms
Cancers
References
Carcinogenesis
Definition
Characteristics
Causes
Molecular Genetics
Clinical Relevance
Prevention
References
Carcinogenicity Studies
Definition
Carcinoid
Carcinoid Syndrome
Definition
Carcinoid Tumors
Synonyms
Definition
Characteristics
References
Carcinoma
Definition
Carcinoma In Situ
Definition
Carcinoma of the Adrenal Cortex
Carcinoma with Amine Precursor Uptake Decarboxylation Cell Differentiation
Carcinomatosis
Synonyms
Definition
Characteristics
Etiology of Peritoneal Carcinomatosis
Diagnosis
Treatment
References
CARD
Definition
Cardiac Dysrhythmia
Definition
Cardiac Myxoma
Definition
Cardiac Tumors
Definition
Characteristics
Incidence
Clinical Features
Primary Tumors
Benign
Malignant
Secondary or Metastatic Tumors
Therapy and Prognosis
References –
Cardio-Facial-Cutaneous (CFC) Syndrome
Definition
Cardiomyopathy
Definition
Cardiotoxicity
Definition
Caretaker Genes
Definition
Caries
Definition
Carney Complex
Synonyms
Definition
Characteristics
References
Carotene 15,15´-Oxygenase
Definition
beta-Carotene
Definition
Carotenes
Definition
Carotenoids
Definition
Characteristics
References
Cas
Definition
Case Control Association Study
Synonyms
Definition
Characteristics
Potential Problems in Association Studies
References
Case–Control Association Analysis
Case–Control Study
Definition
CASH
CASP-8
Definition
Caspase
Definition
Caspase-3
Definition
Caspase-8
Synonyms
Definition
Characteristics
Structure and Physiological Functions of Caspase-8
Caspase-8 and Cancer
References
Caspase-eight-related Protein
Caspase-9
Definition
Caspase Homologue
Caspase-like Apoptosis-regulatory Protein
CASPER
CASTing
Definition
Catalytic Domain
Definition
Catalytic Pocket
Definition
Catastrophe Promoter
Definition
Catechin
Catechins
Definition
Catechol Estrogen
Definition
Catenate
Definition
beta-Catenin
Definition
beta-Catenin Stabilization
Definition
Cathepsin-D
Definition
Characteristics
Apoptosis
Regulation
Cancer
Clinical Aspects
References
Cathepsins
Definition
Catheters
Definition
Caveolae
Definition
Caveolins
Definition
Characteristics
Clinical Aspects
References
C-Bandless Chromosome
Definition
CBFA2
CBP/p300
Definition
CBP/p300 Coactivators
Definition
Characteristics
References
CBs
Definition
CCAAT/Enhancer-Binding Protein α (CEBPA)
Definition
CCCTC-Binding Factor
Synonyms
Definition
Characteristics
CTCF Functions
Clinical Aspects
References
CCI-779
CCL5/RANTES
Definition
CCL20/MIP-3alpha
Definition
CCND1
Definition
CCR4
Definition
CCR6
Definition
CCRG-81045
CCV
Definition
CD1a
Definition
CD2AP
Definition
CD3 Complex
Definition
CD4
Definition
CD4+T-Cells
Definition
CD5 B Cells
Definition
CD8
Definition
CD8+ Cytotoxic T-Cells
Definition
CD8 T Cells
Definition
CD14
Definition
CD15
Definition
CD20
Definition
CD24
Definition
CD26
CD26/DPPIV in Cancer Progression and Spread
Synonyms
Definition
Characteristics
CD30
Definition
CD33
Definition
CD34
Definition
CD39
Definition
CD44
Synonyms
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
CD45
Definition
CD52
Definition
CD55
CD57
Definition
CD62E
CD66a
Definition
CD73
Definition
CD82
Definition
CD95
Definition
CD95
Definition
CD99
Definition
CD156b Antigen
CD184
CD246
CD314
CD Antibody Microarray
Definition
CD Antigens
Synonyms
Definition
Characteristics
CD Antigens Provide Immunophenotypes of Leukocytes
Classification of Leukemias Using CD Antigens
CD Antigens as Targets for Therapeutic Antibodies
Methods for Identification of CD Antigens
References
CdA
2-CdA
CDC
Definition
CDC7
Definition
CDC20
Definition
CDC25
Definition
CDC37
Definition
CDC42
Definition
CDDP
CD66e
CDH1
Definition
CDK
CDK1 Kinase
CDK2/cyclin A-associated protein p45
CDK4I
CDK Inhibitors
Definition
CDKN2
CDKN2A
Definition
CDKN2A
Synonyms
Definition
Characteristics
Identification of CDKN2A
Gene Structure of CDKN2A
Tumor Suppressor
P16 is a CDK Inhibitor
Role of the Alternative Reading Frame (ARF) Product
Senescence
Mouse Models
Clinical Aspects
CDKN2A Mutations and Melanoma
Multiple Primary Melanoma
CDKN2A Mutations and Non-Melanoma Cancers
Modifiers of Penetrance of CDKN2A Mutations
CDKN2a Polymorphisms as Low Risk Factors
CDKN2A and the Atypical Mole Syndrome
References
cDNA chips
CEA
CEA Gene Family
Synonyms
Definition
Characteristics
Expression and Functions of CEA Family Members in Normal and Tumor Tissues
Expression and Functions of CEACAM1
Transcriptional Regulation
The Next Frontier
References
CEA-related Cell Adhesion Molecule 1
CEA-Vaccine Virus
Definition
Ceacam1, Ceacam6, Ceacam7, Ceacam8
Definition
CEACAM1=BGP, C-CAM, CD66a
CEACAM5
CEACAM5=CEA,CD66e
CEACAM6=NCA, CD66c
CEACAM7=CGM2
CEACAM8=CGM6, CD66b
CEACAM1 Adhesion Molecule
Synonyms
Definition
Characteristics
Properties of CEACAM1
CEACAM1 in Cancer
Loss of CEACAM1 Expression in Tumorigenesis and Tumor Progression
Upregulation of CEACAM1 Expression in Malignant Diseases
CEACAM1 and Tumor Angiogenesis
Studying CEACAM1 in Cancer: Animal Models
References
C/EBPalpha
Definition
C/EBP Homologous Protein
Definition
CED
CED-3
Definition
CED-4
Definition
Celastrol
Synonyms
Definition
Characteristics
Biological Properties
Potential Molecular Targets
Clinical Relevance
References
Celebra
Celebrex
Celecoxib
Synonyms
Characteristics
References
Cell Adhesion Molecules
Synonyms
Definition
Characteristics
Cell Adhesion Molecules and the Cytoskeleton
Classification of Cell Adhesion Molecules
Cadherins
Integrins
The Ig Superfamily
Selectins
Proteoglycans
Role of Adhesion Molecules in Cancer
The Metastatic Cascade
Adhesive Events in Metastasis
Other Cancer-Related Functions of Cell Adhesion Molecules
References
Cell-Adhesion Molecules (CAM)
Definition
Cell Adhesion Receptors
Cell Biology
Definition
Characteristics
The Cell
Cell Division and Reproduction
Cell Proliferation
Cell Cycle
Regulation of Cell Cycle Progression
Programmed Cell Death
Apoptosis
Necrosis
Autophagy
Signal Transduction
Signaling Targets
Systems Biology
Cell Motility and Migration
Cytoskeleton
Signaling Regulation
Tumor Biology
Initiation and Promotion
Progression
Metastasis
Stem Cell Biology
Self-Renewal and Clonality
Potency
Environmental Regulation
Social Implications
References
Cell Block
Definition
Cell Cycle
Definition
Cell Cycle Arrest
Definition
Cell-Cycle Checkpoint
Definition
Cell-Cycle Targets for Cancer Therapy
Definition
Characteristics
Restriction Point Control
Checkpoint Control
Clinical Relevance
References
Cell Differentiation
Definition
Cell Division
Definition
Cell Fate
Definition
Cell-free Circulating Nucleic Acids
Cell Lines
Definition
Cell Locomotion
Cell-Mediated Immunity
Definition
Cell Membrane
Definition
Cell Migration
Cell Motility
Cell Movement
Cell Polarity
Definition
Cell Scattering
Definition
Cell Signaling
Definition
Cell-Surface Receptors
Definition
beta-Cell Tumor of the Islets
Cellular Antigens
Cellular Atypia
Definition
Cellular Immortalization
Definition
Cellular Immunity
Definition
Cellular Self-Cannibalism
Cellular Senescence
Definition
Cellular Transformation Assay
Definition
CENP-E
Definition
Censoring
Definition
Central Cleavage
Definition
Central Nervous System
Definition
Central Neurocytoma
Central Neurofibromatosis
Centrocytic (Mantle Cell) Lymphoma
Centromere
Definition
Centrosome
Synonyms
Definition
Characteristics
Structure and Function
Centrosome Duplication
Abnormal Amplification of Centrosomes and Chromosome Instability in Cancer
Loss of Tumor Suppressor Proteins and Centrosome Amplification
Centrosome Amplification and Cancer Chemotherapy
References
Ceramide
Definition
Characteristics
Formation of Ceramide
Ceramide-Induced Changes of Biological Membranes
Ceramide in Receptor-Mediated Signaling
Signaling Molecules Regulated by Ceramide
Ceramide in Mitochondria and Cell Death
Genetic Evidence for a Function of Ceramide in Apoptosis
Ceramide in gamma-Irradiation- and UV-A Light-Induced Apoptosis
Ceramide and Chemotherapy
Short Chain Ceramide
References
Ceramide Kinase (CerK)
Definition
Ceramide-1-Phosphate (C1P)
Definition
C-erb-B2
Cerebral Edema
Definition
Cerulenin
Definition
Cervical
Definition
Cervical Cancers
Definition
Characteristics
Symptoms
Pathology
Staging
Prognosis
Therapy
References
Cetuximab
Definition
c-FLICE-like Inhibitory Protein
Definition
c-FLIP
Definition
CG
cGMP
Definition
CGP57148
z Chain
Definition
Channels
Definition
Chaperone
Definition
Chaperonins
Definition
Charged Particle Therapy
Checkpoint
Definition
Checkpoint Kinases
Definition
Chelation Therapy
Chelator
Definition
Chelators as Anti-Cancer Drugs
Synonyms
Definition
Characteristics
Iron Metabolism in Cancer Cells
Desferrioxamine, an Iron Chelator with Some Anti-Cancer Activity
Other Chelators with Anti-Cancer Potential
PIH Chelators
The DpT Chelators: Dp44mT
Iron Chelation and Cell Cycle Control Molecules
Conclusions
References
Chemical Biology
Definition
Chemical Biology Screen
Chemical Carcinogenesis
Definition
Characteristics
Normal Cell Types in Animals and the Tumors They Give Rise to
Carcinogens
Mechanisms of Chemical Carcinogenesis
Insights into Mechanisms of Chemical Carcinogenesis from Studies of Chemically Induced Neoplastic Transformation
Significance of Chemical Carcinogenesis
References
Chemical Castration
Definition
Chemical Genetic Screen
Chemical Mutagenesis
Chemical Tool
Definition
Chemically Induced Cell Transformation
Definition
Characteristics
Normal Growth of Normal Cells
Carcinogens
Chemically Induced Cell Transformation – Description and Mechanisms
Significance of Chemically Induced Neoplastic Transformation
References
Chemoattractant
Definition
Chemoattractant Cytokine
Chemoattraction
Synonyms
Definition
Characteristics
Chemokines
Chemokines and Cancer
Chemoattraction: A Key Process to Attract Cancer Cells to New Biological Niches
Other Biological Effects of Chemokines on Cancer Cells Apart from Chemoattraction
Chemokines can Contribute to Regulate the Growth of Cancer Cells
Chemokines can Contribute to Regulate the Survival of Cancer Cells
Chemokines can Contribute to Regulate the Adhesion to New Sites in Cancer Cells
Chemokines can Contribute to Control Protease Secretion in Cancer Cells
Chemokines can Contribute to Control Angiogenesis in Cancer Cells
Therapeutical Aspects
Summary and Final Conclusions
References
Chemoembolization
Definition
Chemokine
Synonyms
Definition
Characteristics
References
Chemokine Receptor CXCR4
Synonyms
Definition
Characteristics
Chemokines
Definition
Chemokinesis
Chemoprevention
Definition
Chemoprotectants
Synonyms
Definition
Characteristics
Synthetic Chemoprotectants
Natural Chemoprotectants
References
Chemoprotection
Chemoradiation
Chemoradiotherapy
Synonyms
Definition
Characteristics
Chemoradiotherapy for Non-Small Cell Lung Cancer
Chemoradiotherapy for Small Cell Lung Cancer
Chemoradiotherapy for Cervical Cancer
Chemoradiotherapy for Head and Neck Cancer
Chemoradiotherapy for Esophageal Cancer
Chemoradiotherapy for Gastric Cancer
Chemoradiotherapy for Rectal Cancer
Chemoradiotherapy for Anal Cancer
Concluding Remarks
References
Chemorepulsive Cues
Definition
Chemoresistance
Definition
Chemosensibilization
Synonyms
Definition
Characteristics
Chemosensibilization of Tumors by Targeting P-gp
Inhibitors of P-gp Activity
Other Strategies to Inhibit P-gp
Chemosensibilization of Tumors by Triggering Apoptosis
References
Chemotactic
Definition
Chemotactic Cytokine
Chemotactic Factors
Definition
Chemotaxis
Definition
Chemotherapy
Definition
Chemotherapy of Cancer
Definition
Characteristics
The Challenge
The Agents
Clinical Strategies
Supportive Care
Long Term Effects of Cancer Treatment
Conclusions
References
Chest Tube
Definition
xi-(Chi)-Like Sequence
Definition
CHI3L1
Child-Pugh Score
Definition
Childhood Adrenocortical Carcinoma
Definition
Characteristics
Incidence
Causes
Normal Physiology and Tumor Biology
Clinical Manifestations
Testing
Treatment
Prognosis
Concluding Remarks
References
Childhood Cancer
Definition
Characteristics
Incidence
Causes and Risk Factors
Genetic and Chromosomal Syndromes
Clinical Presentation and Diagnosis
Treatment
Outcome and Late Effects
References
Chimeric
Definition
Chimeric Antibodies
Definition
Chimeric Antigen Receptor on T Cells
Synonyms
Definition
Characteristics
Background on Manipulating T-Cell Responses to Cancer
Tumor-Specific CAR Development
Clinical Application of CAR-Specific T Cells
Improved Therapeutic Potential of CAR+ T Cells
Future Challenges
Conclusion
References
Chimeric Genes
Chimeric Oncogenes
Chimeric Oncoproteins
Definition
Chimeric T Cell Receptors
Synonyms
Definition
Characteristics
The TCR Format
The Single Chain Format
Chimeric T Cell Receptors with Primary and Costimulatory Signal
Clinical Aspects
References
Chimeric Transcripts
Chinese Medicine, Traditional Chinese Medicine, Oriental Medicine
Chinese versus Western Medicine
Synonyms
Definition
Characteristics
Developing History
Theories and Principles
Etiology and Pathogenesis
Diagnostic Methods
Treatment Modalities
References
Chitinase-3-like-1
CHK1
Definition
CHK2
Definition
2-chlorodeoxyadenosine
2-chloro-2´-deoxyadenosine
CHO Cells
Definition
Cholangiocarcinoma
Synonyms
Definition
Characteristics
Etiology
Biology
Diagnosis
Treatment and Prognosis
References
Cholangiocarcinoma
Cholangiocellular Carcinoma
Cholangiocytes
Definition
Cholangiosarcoma
Cholecystectomy
Definition
Cholecystitis
Definition
Cholecystokinin (CCK)
Definition
Cholera Toxin
Definition
Cholestasis
Definition
Cholesterol
Definition
Chondrex
Chondroitin Sulfate (CS)
Definition
Chondrosarcoma
Definition
Characteristics
Diagnosis
Therapy
Genetics
References
CHOP
Definition
Choroidal Melanoma
Christmas Factor
Definition
Chromate
Chromatid
Definition
Chromatin
Definition
Chromatin Modification
Chromatin Remodeling
Synonyms
Definition
Characteristics
Mechanisms and Clinical Aspects
Chromatin Remodeling Complex
Histone Modifications
Histone Variant
Epigenetic Therapy
References
Chromium(VI)
Chromium Carcinogenesis
Synonyms
Definition
Characteristics
Chromium, The Chemical Element, and its Ionic Species and Chemical Compounds
Important Commercial Uses of Nickel and Nickel Compounds
Biological Aspects of the Essentiality of Chromium (III) in Mammalian Cells
Exposure of Humans to Chromium Compounds
Genotoxicity of Chromium Compounds
Chromium-Induced Cell Transformation
Chromium Carcinogenesis
Mechanisms of Chromium Carcinogenesis
References
Chromium-induced Carcinogenesis
Chromium-induced Cell Transformation
Chromium Tumorigenesis
Chromocenter
Definition
Chromodomain
Definition
Chromogranin A
Definition
Chromophore
Definition
Chromophore-Assisted Laser Inactivation
Synonyms
Definition
Characteristics
Advantages
Limitations
Application
Current Applications
Future Applications
Conclusions
References
Chromosomal Aberrations
Definition
Chromosomal Imbalance
Definition
Chromosomal Instability
Synonyms
Definition
Characteristics
Historical Background
Chromosome Segregational Defects Lead to Chromosomal Instability
A Defective Response to DNA Damage Leads to Chromosomal Instability
Telomere Dysfunction May Lead to Chromosomal Instability
Cell Cycle Disturbances Result in Chromosomal Instability
References
Chromosomal Rearrangement
Definition
Chromosomal Translocation t(9;22)
Definition
Chromosomal Translocation t(8;21)
Synonyms
Definition
Characteristics
Cytogenetics and Morphology
AML1/MTG8
AML1/MTG8 in Leukemogenesis
Clinical Relevance and Therapy
References
Chromosomal Translocations
Definition
Characteristics
Biology
Clinical Relevance
References
Chromosome
Definition
Chromosome Abnormality
Definition
Chromosome Band
Definition
Chromosome Condensation
Definition
Chronic Bronchitis
Definition
Chronic Granulomatous Disease (CGD)
Definition
Chronic Idiopathic Myelofibrosis
Chronic Liver Disease
Definition
Chronic Lymphocytic Leukemia
Synonyms
Definition
Characteristics
Diagnosis
Epidemiology
Etiology
Pathogenesis
Risk Prediction in CLL
Symptoms and Signs of Active CLL
Treatment Strategies in CLL
Allo-HCT in CLL
Chronic Lymphocytic Thyroiditis
Definition
Chronic Lymphoproliferative Disorders
Definition
Chronic Myeloid Leukemia (CML)
Definition
Chronic Obstructive Pulmonary Disease and Lung Cancer
Definition
Characteristics
COPD
Lung Cancer
Link to Decline in FEV1
COPD and Lung Cancer Associations
Possible Mechanisms of the COPD - Lung Cancer Risk
Summary
References
Chronic Obstructive Pulmonary Disease (COPD)
Definition
Chronic Phase
Definition
Chronic Ulcerative Colitis
Definition
Chronotherapeutics
Definition
CHRPE
Definition
Chrysotile
Definition
Chuvash Polycythemia (CP)
Definition
Chylothorax
Definition
C.I. 75300
Ciclosporin
Definition
Cilia
Definition
Ciliary Body Melanoma
CIN
Cip-Interacting Zinc Finger Protein 1 Ciz1
Definition
Characteristics
References
Circadian
Definition
Circadian Clock
Definition
Circadian Clock Induction
Definition
Characteristics
Relevance of Circadian Disruption for Cancer Processes
Circadian Clock Control of Cell Cycle
Circadian Disruption in Cancer Tissues
Physiologic Clock
Tumor Clock
Circadian Clock Induction
References
Circadian Disruption
Definition
Circadian Pacemaker
Definition
Circadian Rhythm
Definition
Circular Dorsal Ruffles
Definition
Circulating Endothelial Cells (CECs)
Definition
Circulating Nucleic Acids
Synonyms
Definition
Characteristics
Biological Aspects
Clinical Aspects
References
Circulating Progenitor Cells (CPCs)
Definition
Circulating Tumor Cells
Definition
Characteristics
CTC Detection and Characterization
Clinical Impact of CTC Detection
References
Circulating Tumor Microemboli (CTM)
Definition
Cirrhosis
Definition
CIS
Definition
Cis2His2 Zinc Finger
Definition
Cis-Diamminedichloroplatinum
Cis-Dichlorodiammineplatinum(II)
Cisplatin
Synonyms
Definition
Characteristics
Mechanisms of Action
Cisplatin and Cancer Treatment
Cisplatin-Induced Resistance
Inhibition of Drug Uptake and Decreased Intracellular Accumulation
Increased DNA Repair
Development of Cisplatin Analogs
References
Cisplatin-refractory Germ Cell Tumors
Cisplatin Resistant Germ Cell Tumors
Cis-Platinum II
c-Jun N-terminal Kinase (JNK)
Definition
CK I
Definition
CK II
Definition
CKI
Definition
c-Kit
Cladribine
Synonyms
Definition
Characteristics
Administration and pharmacokinetics
Clinical activity
Toxicity and adverse effects
References
Clark Level
Definition
CLARP
Class II Tumor Suppressor Genes
Definition
Characteristics
Evidence for a Class II Tumor Suppressive Activity
Class II Tumor Suppressor Identification
Mechanisms of Inactivation
Clinical Relevance
References
Class III Histone Deacetylases
Class Switching
Definition
Classifier
Definition
Clastogen
Definition
Clastogenesis
Definition
Clathrin
Definition
Clathrin-mediated Endocytosis
Clear Cell Sarcoma of Soft Tissue
Definition
Clear Cell Sarcoma of the Kidney (CCSK)
Definition
Clearance
Definition
Cleavable Complex
Definition
Clinical Cancer Biomarkers
Synonyms
Definition
Characteristics
Diagnostic Tumor Markers
Prognostic/Predictive/Markers
Surrogate/Monitoring Markers
Miscellaneous Markers
References
Clinical Pathology
Definition
Clinical Studies
Definition
Clinical Trial
Definition
CLL
CLN
Clonal
Definition
Clonal Proliferation
Definition
Clone
Definition
Clonogenic Survival Assay (CSA)
Definition
Clonorchis Sinensis
Definition
Cluster of Differentiation 44
Cluster of Differentiation (CD) Molecules
Definition
Clustering
Definition
CMC
Definition
CMF
Definition
CML
Definition
CMM2
CMMoL
Definition
c-Myc
Definition
CNAs
CNC
CNDF
cNOS
Definition
Coactivator ACTR
Coactivators
Definition
Coagulation Factor II Receptor
Coagulation Factor II Receptor-like 1
Coagulation Factor II Receptor-like 2
Coagulation Factor II Receptor-like 3
Coagulation Pathway
Definition
Coagulopathy
Definition
Characteristics
References
Co-chaperone
Definition
Cockayne Syndrome
Definition
Coding Region
Definition
Codon
Definition
Codon-Optimization
Definition
COE
Cofactor
Definition
Coffee Consumption
Definition
Characteristics
Coffee Constituents
Coffee Association with Cancer
References
Cohesins
Definition
Cohort Study
Definition
Coiled Bodies
Coiled-Coil Domain
Definition
Colchicine
Definition
Cold Surgery
Coley Toxin
Definition
Collagen
Definition
Collapsin
Collective Cell Invasion
Definition
Collier-Olf-EBF
Colloid Carcinoma
Colon Cancer
Synonyms
Definition
Characteristics
Screening Strategies for the Average Risk Population
FOBT (Fecal Occult Blood Test)
Sigmoidoscopy
Colonoscopy
Double Contrast Barium Enema
Cancers of the Cecum and Ascending Colon
Cancers of the Right Flexure and the Proximal Transverse’Colon
Cancers of the Transverse Colon
Tumors of the Left Colonic Flexure
Tumors of the Descending Colon and Proximal Sigmoid Colon
Tumors of the Middle and Distant Sigmoid Colon
Further Constellations Influencing Surgical Strategy
Classification of Colorectal Cancers
Cellular and Molecular Features
Perspective
References
Colonoscopy
Definition
Colony-Forming Unit (CFU)
Definition
Colony Stimulating Factor-1
Definition
Colorectal Premalignant Lesions
Synonyms
Definition
Characteristics
Adenomas
Adenoma–Carcinoma Sequence
Hyperplastic Polyps
Hamartomatous Polyps
Aberrant Crypt Foci
Inflammatory Bowel Diseases
References
Combination Therapy
Definition
Combinatorial Chemistry
Definition
Combinatorial Libraries
Definition
Combinatorial Selection Methods
Synonyms
Definition
Characteristics
CASTing
REPSA
SELEX
References
Combined Modality Treatment
Comet Assay
Synonyms
Definition
Characteristics
Modifications
Areas of Application
Genotoxicity Testing
DNA Repair
Biomonitoring
Cancer Susceptibility
References
Committed
Definition
Common Bile Duct
Definition
Common Fragile Sites
Definition
Common Melanocytic Nevi
Definition
Comorbidity
Definition
Comparative Genomic Hybridization (CGH)
Definition
Comparative Genomics
Definition
Comparative Oncology
Definition
Characteristics
History
Scientific Advancements
Need for New Models of Drug Development
Clinical Applications
References
Complement
Definition
Complement Cascade
Definition
Complement-Dependent Cytotoxicity
Definition
Complement-Mediated Cell Death
Definition
Complementarity Determining Region
Definition
Complementation Groups
Definition
Complete Cytoreduction
Definition
Complete Hematologic Remissions
Definition
Complex Karyotypic Changes
Definition
Compound Screen
Compounds from Organisms
Computed Tomography
Definition
Concatamerization
Definition
Concomitant
Definition
Conditionally Replicating Adenovirus
Conditionally Replicative Adenovirus
Conduit
Definition
Confidence Interval
Definition
Confocal Laser-Scanning Microscopy In Vivo
Definition
Characteristics
Clinical Relevance
References
Conformational Diseases
Definition
Confounding
Definition
Congenic Animal
Definition
Congenics
Congenital
Definition
Congenital Hypertrophy of the Retinal Pigment Epithelia
Definition
Congenital Lymphedema
Definition
Congenital Mesoblastic Nephroma
Congenital Telangiectatic Erythema
Conjugated Double Bonds
Definition
Conjugated Linoleic Acid (CLA)
Definition
Conjugated Linolenic Acids
Synonyms
Definition
Characteristics
In-Vitro Studies
In-Vivo Studies
References
Conjugation
Definition
Conn Syndrome
Definition
Connexins
Definition
Characteristics
Connexins as Tumor Suppressors
Connexins as a Therapeutic Target
References
Connexon
Definition
Conservative Surgery
Definition
Conserved Region
Definition
Constant Region
Definition
Constitutive
Definition
Contact Inhibition
Definition
Contact Inhibition of Cell Division
Definition
Contact Normalization
Synonyms
Definition
Characteristics
References
Contralateral
Definition
Contralateral Breast Cancer
Contrast Agents
Definition
Convection Enhanced Delivery
Synonyms
Definition
Characteristics
Clinical Application
Future Directions
References
Convection-Enhanced Delivery
Definition
Convergent Extension
Definition
COP1 (Constitutively Photomorphogenic 1)
Definition
Core Binding Factor A2
Core Fucose
Definition
Corepressor
Definition
Corin
Definition
Coronary Artery Disease
Definition
Cortactin
Synonyms
Definition
Characteristics
Structure and Binding Partners
Function
Regulation
Role in Cancer
References
Cortical Bone
Definition
Cortical Neurons
Definition
Corticosteroids
Definition
Corticotrophin
Definition
Corticotrophin-Releasing Hormone
Definition
Cortisol
Definition
Corynebacterium Diphtheriae
Definition
Cosinor
Definition
Costello Syndrome
Definition
Costimulation
Definition
Costimulatory Signal
Definition
Coumestans
Definition
gamma-Counter
Definition
Cowden Disease
Cowden Syndrome
Synonyms
Definition
Characteristics
Molecular Features
Clinical Aspects
References
COX
COX-2
Cox-2 inhibitors
Cox Proportional Hazards Model
Definition
Coxibs
Definition
CPD
Definition
CpG
Definition
CpG Islands
Synonyms
Definition
Characteristics
Preservation of CpG Islands
Clinical Relevance
Normal, Developmentally Regulated, CpG Island Methylation
Aberrant CpG Island Methylation in Cancer
References
CPT-11
Cr(VI)
Cr6+
c-Rmil
cRaf
C-Raf
Cre/loxP
Definition
C-Reactive Protein
Definition
CREB-Binding Protein (CBP)/p300
Definition
CREB/cAMP Signaling
Definition
Cre-Lox Recombination
Definition
Cremophor EL
Definition
Cripto-1
Synonyms
Definition
Characteristics
Structure of Cripto-1, a Member of the EGF-CFC Protein’Family
Cripto-1 During Embryonic Development and in Embryonic Stem (ES) Cells
Cripto-1 in Mammary Gland Development
Cripto-1 in Transformation, Tumorigenesis and Angiogenesis
Transgenic Mouse Models Overexpressing CR-1 in the Mammary Gland
Expression of CR-1 in Human Carcinomas and Premalignant Lesions
References
Cripto-1 (Cr-1)
Definition
Crk
Definition
CRLR
Definition
Crocidolite
Definition
Crohn Disease
Synonyms
Definition
Characteristics
Chemoprevention of IBD-Related CRC
Wnt/beta-Catenin Pathway (Wnt Signaling)
Conclusions
References
Cross-links
Definition
Cross Match
Definition
Cross Priming
Definition
Cross-Sectional Study
Definition
Cross Talk
Definition
Crow-Fukase Syndrome
Definition
CRP55
CRP-ductin (mouse)
CRT
Cryofibrinogen
Definition
Cryosurgery
Definition
Cryosurgery in Bone Tumors
Synonyms
Definition
Characteristics
Cryobiology
Tumors, Suitable for Cryosurgical Treatment
Indications for Cryosurgery
Cryosurgical Technique
Results of Treatment
Complications
Wound Infection
Venous Gas Embolism
Fracture
Epiphyseal Damage
Degenerative Osteoarthritis
Damage to Nerves
Prospects to the Future
References
CSA
Definition
CSC
CSF
Definition
Csk
Definition
Csk-Binding Protein (Cbp)
Definition
c-Src
CT
Definition
CT4
CT Scan
Definition
C-Tail
Definition
CTCAE
Definition
CTCF
Definition
CTCFL
Definition
CTCF-T
Definition
CTL
Definition
C-type Lectins
Definition
CUB Domain
Definition
CUL4A (Cullin4A)
Definition
CUP
Definition
Curative
Definition
Curcumin
Synonyms
Definition
Characteristics
Anti-Carcinogenic Activities
Effect on Cell Signaling Pathways
Clinical Trials
References
Curie
Definition
Cushing Syndrome
Definition
Characteristics
Diagnostic Guidelines
References
Cutaneous Desmoplastic Melanoma
Synonyms
Definition
Characteristics
Epidemiology
Microscopic Features
Clinical Features
Management
References
Cutaneous T-Cell Lymphoma (CTCL)
Definition
CX3CL1/Fractalkine
Definition
CX3CR1
Definition
Cx26
Definition
Cx32
Definition
CXC Chemokines
Synonyms
Definition
Characteristics
Angiogenesis and Tumor Growth
Tumor Cell Invasion and Metastasis
References
C-X-C Motif Chemokines
Definition
CXCL11/I-TAC
Definition
CXCL12
Definition
Cyclin B
Definition
Cyclin D
Definition
Characteristics
Regulation of D Cyclins
CDK-Independent Activities of D Type Cyclins
Clinical Relevance
References
Cyclin-dependent Kinase
Cyclin-dependent Kinase Inhibitor 2A
Cyclin Dependent Kinases
Synonyms
Definition
Characteristics
The Discovery of CDKs
Members of the CDK Family
CDKs in Cancer and Other Human Diseases
References
Cyclin G-Associated Kinase
Synonyms
Definition
Characteristics
GAK and the Androgen Receptor
GAK and Prostate Cancer Progression
References
Cyclins
Definition
Cyclobutane Pyrimidine Dimer
Definition
Cyclooxygenase
Cyclooxygenases (COX)
Definition
Cyclooxygenase-2 (COX-2)
Definition
Cyclooxygenase-2 in Colorectal Cancer
Synonyms
Characteristics
Cyclooxygenase-2 and Colorectal Cancer Prevention
Summary
References
Cyclooxygenase-prostaglandin Endoperoxide Synthase
Cyclopamine
Definition
Cyclophosphamide
Definition
Cyclosporin A
Definition
CYFRA 21-1
CYLD
Definition
Cylindromatosis
Definition
CYP
Definition
CYP2E1
Definition
CYP450
CYP 450arom
CYP P-450 2D6
Definition
Cystadenocarcinoma
Cystatins
Synonyms
Definition
Characteristics
Domain Structure
Gene Structure & Evolution
Function
Role in Cancer
Conclusion
References
Cystatins A, B
Cystectomy
Definition
Cysteine Proteases
Definition
Cystic Fibrosis
Definition
Cystic Nephroma
Definition
Cytarabine (1-arabinofuranosylcytosine)
Definition
Cytochalasin B
Definition
Cytochrome c
Definition
Cytochrome c Oxidase
Definition
Cytochrome P450
Synonyms
Definition
Characteristics
Detoxification
Using CYPs to Improve Therapy
Genetic Polymorphisms
CYP2B6
CYP2C8
CYP2C9
CYP2C19
CYP2D6
CYP3A4
CYP3A5
Cancer Incidence
References
Cytochrome P450 (CYP)
Definition
Cytochrome p450 2 E1 (CYP2E1)
Definition
Cytochrome P-4502E1
Definition
Cytochrome P450 CYP-P450 3A4
Definition
Cytochrome P450 Enzymes
Definition
Cytogenetic
Definition
Cytogenetic Alteration
Definition
Cytogenetic Analysis
Definition
Cytogenetic Karyotype
Cytogenetics
Definition
Cytokeratin 19 Fragments (CYFRA 21-1)
Definition
Cytokeratins
Definition
Cytokine
Definition
Cytokine Gene Transfer
Definition
Cytokine Receptor
Definition
Cytokine Receptor as the Target for Immunotherapy and Immunotoxin Therapy
Synonyms
Definition
Characteristics
Cytokine Receptor as the Target for Immunotherapy
Cytokine Receptor as the Target for Immunotoxin Therapy
References
Cytokinesis
Definition
Cytologist
Definition
Cytology
Definition
Cytolytic Synapse
Definition
Cytometry
Definition
Cytomorphology
Definition
Cytopathologist
Definition
Cytopenia
Definition
Cytoplasmic Scaffolding Apoptotic Protease Activating Factor
Cytoplasmic 7SL RNA
Definition
Cytoprotective Adjuvant
Definition
Cytoreduction
Definition
Cytoreductive Surgery
Definition
Cytoreductive Surgery
Definition
Cytoskeleton
Definition
Cytosol
Definition
Cytosolic Transglutaminase
Cytostasis
Definition
Cytostatic
Definition
Cytotactin
Cytotechnologist
Definition
Cytotoxic Carcinogen
Definition
Cytotoxic Chemotherapy
Definition
Cytotoxic T Cells (CTLs)
Definition
Cytotoxic T Lymphocytes
Definition
Cytotoxins
Definition
Cytovilin
D
DAC
Dacogen
DAF
DAG
Definition
Diadzein
Definition
Daltons
Definition
Damage Response
DAMP
Definition
Danazol
Definition
DAP6
DAP-10
Definition
DAP-12
Definition
DARC
Darier Sign
Definition
Dasatinib
Definition
Data Over-Fitting
Definition
Daughter Cells
Definition
Daunorubicin
Definition
Daxx
Synonyms
Definition
Characteristics
Basic Information
Subcellular Distribution of Daxx Protein
Daxx Mediates Stress-Induced Cell Death
In Unstressed Cells, Daxx Seems to Play an Antiapoptotic Role
References
DBCCR1
Definition
DCC
Definition
DCIS
Definition
DcR3
DCX
Definition
D-Dimer
Definition
DDP
DDS
De novo
Definition
Deacetylation
Definition
Death-associated protein 6
Death Domain
Definition
Death-Effector-Domain
Definition
Death-Inducing Signaling Complex
Definition
Death Receptor-3
Definition
Death Receptor Apoptosis Pathway
Definition
Death Receptors
Definition
Debulking Surgery
Definition
Decatenation G2 Checkpoint
Definition
Characteristics
Molecular Biology
Clinical Implications
References
Decay-Accelerating Factor
Synonyms
Definition
Characteristics
Actions of DAF in Cancer (Tab.1)
Perspectives in Cancer Therapy (Table 2)
References
Decay-accelerating Factor For Complement
Decitabine
Decoy Receptor 3
Synonyms
Definition
Characteristics
Tissue Expression and Decoy Function of DcR3
Decoy Unrelated Novel Actions of DcR3 (Figure 1)
New Action Mechanisms of DcR3 (Figure 1)
References
DED
Definition
Dedifferentiation
Definition
Deeply Infiltrating Endometriosis
Definitive Therapy
Definition
Delayed Type Hypersensitivity Reaction
Definition
Deleted in Malignant Brain Tumours 1
Synonyms
Definition
Characteristics
Functional Characteristics
DMBT1 and Innate Immunity/Mucosal Protection
DMBT1 and Epithelial/Stem Cell Differentiation and Regenerative Processes
DMBT1 and Tumorigenesis
References
Deleted in Pancreatic Carcinoma Locus 4
Synonyms
Definition
Characteristics
TGFβ-Smad Signaling Cascade
Transcriptional Regulation through Smads
What makes DPC4/Smad4 Unique among the Other Smad Family Members?
Which Human Tumors Show Alterations of the DPC4 Gene?
How are Naturally Occurring DPC4 Mutations Interfering with the Smad Signaling Cascade
Does DPC4 Contribute to the Familial Risk for Pancreatic Cancer?
How does DPC4 Contribute to Tumor Formation?
References
Deletion
Definition
Dendrimer
Definition
Dendritic Cell-Based Tumor Vaccines
Definition
Dendritic cells
Definition
Characteristics
Origin and Function
Dendritic Cell-Based Immunotherapy
Dendritic Cells in Cancers
References
Densitometric
Definition
Dental Pulp
Definition
Dental Pulp Neoplasms
Definition
Characteristics
History
Inflammatory Pulp Reactions
Chead3
Radiotherapy
Animal Investigations
Clinical Relevance
References
Dentin
Definition
Denys-Drash Syndrome
Definition
Deoxyazacytidine
2′-Deoxy-5-azacytidine
Deoxycytidine Kinase
2-Deoxy-D-Glucose
Definition
Dermoid Cyst
Definition
DES
DES Daughters
Definition
DES Mothers
Definition
DES Sons
Definition
Descriptive Epidemiology
Definition
Desert
Definition
Des-Gamma-Carboxy Prothrombin
Definition
Designer Foods
Desmocollin
Definition
Desmoglein
Definition
Desmoglein-2
Synonyms
Definition
Characteristics
Cell Junctions
Desmosome
Adherens Junctions
References
Desmoid Tumor
Synonyms
Definition
Characteristics
Pathology
Aetiology
Clinical Features
Treatment
References
Desmoplakin
Definition
Desmoplasia
Synonyms
Definition
Characteristics
References
Desmoplastic
Definition
Desmoplastic Medulloblastoma
Definition
Desmoplastic Melanoma
Desmoplastic Small Round Cell Tumor
Synonyms
Definition
Characteristics
Clinical and Pathological Features
Molecular Diagnosis
Molecular Genetics
References
Desmosomal Cadherins
Definition
Desmosomes
Synonyms
Definition
Characteristics
Desmosomal Cadherins
Armadillo Family
Plakin Family
Null Mutations in Mice
Clinical Relevance
References
Destruction Box
Definition
Detachment-induced Cell Death
Determination of Tumor Extent and Spread
Detoxification
Synonyms
Definition
Characteristics
Genetic Variation
Cellular Regulation
Clinical Relevance
References
Detoxication
Definition
De-ubiquitinase
Definition
De-ubiquitinating Enzymes
Definition
Development of New Lymphatic Vessels
Dexrazoxane
Definition
Dexrazoxane
Definition
Dezocitidine
dFdC
DHT
Definition
DIA
Diabetes
Definition
Diabetes Type 2
Definition
Diabody
Synonyms
Definition
Characteristics
Structure
Pharmacokinetics and Distribution
Agonistic Activity
Application of Diabodies
Future Directions
References
Diacylglycerol
Definition
Diagnostic Biomarkers
Definition
Diagnostic Pathology
Dibasic Processing Enzyme
Dicer
Definition
DIE
Diet
Definition
Dietary Essential Minerals
Dietary Micronutrient
Definition
Dietary Supplement
Definition
Diethylstilbestrol
Synonyms
Definition
Characteristics
Pharmacology
Initial Use and Early Epidemiologic Studies
Animal Studies
Neoplastic Effects in Humans
Non-Neoplastic Effects in Humans
Mechanism of Toxicity
Summary
References
Diferuloylmethane
Differentiation
Definition
Diffuse, Small Cleaved Cell Lymphoma
Diffuse Large B-Cell Lymphoma
Synonyms
Definition
Characteristics
Diagnosis
Therapy
Genetics
Subtypes of Diffuse large B-cell Lymphoma
Mediastinal (thymic) Large B-Cell Lymphoma
Intravascular Large B-Cell Lymphoma
Primary Effusion Lymphoma
Lymphomatoid Granulomatosis
References
Diffuse Neuroendocrine System
Definition
Diffusion
Definition
Diffusional Flux
Definition
2prime,2prime-Difluoro-2prime-deoxycytidine
Difluoromethylornithine
Definition
Dihydrogen Dioxide
Dihydrotestosterone Receptor
1α,25-Dihydroxyvitamin D3
2-Dimensional Gel Replicon Mapping
Definition
Dimer Formation
Definition
Dimesna
Definition
Dimethyl Benz(a)anthracene
Definition
7, 12 Dimethylbenz[a]anthracene
Definition
Dimethylfumarate
Definition
Chemistry and Pharmacodynamics
Characteristics
Biological Effects of FAEs In vitro
Drug Formulations of Currently Used Fumaric Acid Esters (FAEs)
Biological Effects of FAEs In vivo
Clinical Aspects and Future Perspectives
References
Dioxin
Synonyms
Definition
Characteristics
Carcinogenic Activity
Mechanisms
Clinical Relevance
References
Dioxin Receptor
Dipeptidyl Peptidase IV
Diphtheria Toxin
Definition
Diploid
Definition
Diplopia
Definition
Dipropyl-acetic Acid
Direct Repeats
Definition
Direct-Acting Carcinogen
Definition
Directed Migration
Directed Motility
DISC
Definition
Disintegrin Metalloproteases
Disordered Domain
Disposition
Definition
Distamycin-A
Definition
Distribution
Definition
Disulfide
Definition
Dithiol
Definition
dJ889N15.2
DKFZ
Definition
DKK
Definition
DLBCL
Definition
DLC1
Definition
Characteristics
Functions of DLC1
Negative Regulation of Cytoskeleton
Tumor Suppressive Effect
Clinical Relevance
Genetic Alteration
Epigenetic Silencing
References
DLT
Definition
DM
Definition
D-MAPP
Definition
DMBA
Definition
DMBA/TPA Mouse Skin Carcinogenesis Model
Definition
DMBT1
Definition
DNA
Definition
DNA Adducts
Definition
DNA Amplification
Definition
DNA Aptamers
Definition
DNA-Binding Domain
Definition
DNA-bound Carcinogens
DNA Damage
Synonyms
Definition
Characteristics
Agents Causing Bulky, Structurally Distorting DNA Adducts
Nucleotide Base Damage
Single and Double Strand Breaks
Cancers Associated with Failure to Signal DNA Damage
Therapeutic Approaches
References
DNA Damage Responses
Definition
Characteristics
Sources of Damage
Checkpoint Pathway
G1 Checkpoint
Intra-S-phase Checkpoint
G2/M Checkpoint
DNA Repair Responses
Excision Repair
Double Strand Break Repair
Translesion Synthesis Repair
Interstrand DNA Crosslink Repair
Arrest, Repair, or Die?
p53-Dependent Mechanisms
p53-Independent Mechanisms
Cancer Susceptibility
References
DNA-Damage Tolerance
Synonyms
Definition
Characteristics
Mechanism
Nonreplicative DNA Polymerases
Translesion DNA Synthesis
Association with Cancer
References
DNA Damage Triggered Death Signaling Pathways
DNA Damage-Induced Apoptosis
Synonyms
Definition
Characteristics
Summary
Physiological Role of Apoptosis Induced by DNA Damage
References
DNA Demethylation
DNA Double Strand Breaks
Definition
DNA Double-Strand Break Repair
Definition
DNA Flexibility
Definition
DNA Glycosylase
Definition
DNA-Interstrand Crosslinks
Definition
DNA Lesion Bypass
DNA-Methyl-Transferases
Definition
DNA Methylation
Definition
DNA Microarray
Definition
DNA Mismatch Repair Mechanism
Definition
DNA Photoproduct
Definition
DNA-PK
Definition
DNA Repair
Definition
DNA Repair and Damage Processing
DNA Repair Capacity
Definition
DNA Replication
Definition
DNA Topoisomerases II
Definition
DNA Undermethylation
DNA Vaccination
Synonyms
Definition
Characteristics
Mechanisms of Action
Adjuvant Activity of DNA
Tailoring Immune Responses by DNA Vaccine Design
Formulation
Mixed Modality Vaccines
Results from Clinical Trials
References
DnaJ (Hsp40) Homolog Subfamily C Member 15
DNAJC15
DNAJD1
DNF15S2
DNMTs
Definition
Docetaxel
Synonyms
Definition
Characteristics
Pharmacokinetics
Toxicity
Dosage
Indications
References
DOCK180/ELMO
Definition
Docking Proteins
Definition
Domain
Definition
Domain Structure
Definition
Dominant
Definition
Dominant Negative
Donor Lymphocyte Infusion
Definition
Dopamine
Definition
Doppler Ultrasound
Definition
Dormancy
Synonyms
Definition
Characteristics
Blocked Angiogenesis
Maintenance of Tumor Dormancy by Endogenous Angiogenesis Inhibitors
Escape from Tumor Dormancy by a Switch to the Angiogenic Phenotype
Experimental Analysis of the Angiogenic Switch in Human Dormant Cancers
Molecular Mechanisms of Angiogenic Switching in Dormant Cancers
Other Forms of Tumor Dormancy
Immune Surveillance as a Cause of Tumor Dormancy
Hormonal Depletion as a Cause of Tumor Dormancy
Dormancy of Single Metastatic Tumor Cells
Future Directions
Biomarkers to Detect Dormant Tumors
References
Dose-Dense Chemotherapy
Definition
Dose-Density
Definition
Dose Fall-off
Definition
Dose Homogeneity
Definition
Dose-Limiting Toxicity
Definition
Dose Rate
Definition
Dose-Response Curve
Definition
Double Minute
Definition
Double Strand Break
Definition
Doublecortex
Doublecortin
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
Double-Strand Break DNA Repair
Definition
Doxorubicin
Definition
DPC4
DPPIV
DR4 Antibodies
DR5
Definition
DR5 Antibodies
Draining Lymph Node
DRF
Drg-1
Definition
Drosophila Melanogaster
Definition
Drug Biodistribution
Definition
Drug Carrier
Definition
Drug Delivery Systems for Cancer Treatment
Synonyms
Definition
Characteristics
Characteristics of Vascular Walls of Cancer
Drug Carriers
Targeted Drug Delivery
References
Drug Design
Synonyms
Definition
Characteristics
Identification and Validation of Molecular Targets
Characterization of Molecular Targets
Compound Screening and Optimization
Pre-Clinical Optimization
Clinical Evaluation
References
Drug Development
Drug Latency to Withdrawal
Definition
Drug Metabolism
Drug Resistance
Definition
Drug Resistant
Definition
Drug Targeting
Drug Tolerance
Definition
Dry Eyes Syndrome
Dry Mouth Syndrome
Dsg2
DSS1
Definition
DT40
Definition
Ductal Carcinoma In Situ
Synonyms
Definition
Characteristics
Diagnosis
Risk Factors
Classification
Treatment
DCIS in Men
Recurrence
References
Ductal Carcinomas
Definition
Duffy Antigen Receptor for Chemokines
Synonyms
Definition
Characteristics
References
DUG
Definition
Dukes Classification
Definition
dUTP
Definition
DVL
Definition
Dwell Positions
Definition
Dynamic Contrast-Enhanced Magnetic Resonance Imaging
Definition
Characteristics
T1 and T2* DCE-MRI Techniques
Data Acquisition
Data Analysis
Clinical Findings
Evaluation of Angiogenesis Inhibitors
Conclusion
References
Dynamic Instability
Definition
Dynamin
Definition
Dysgerminoma
Definition
Dyskeratosis Congenita
Definition
Dysmenorrhea
Definition
Dysmyelopoietic Syndrome
Dysphagia
Definition
Dysphonia
Definition
Dysplasia
Definition
Dyspnea
Definition
Dystroglycan
Definition
E
E1-Activating Enzyme
Definition
E2F
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
E2F Transcription Factor
Definition
E3 Ubiquitin Ligase
Definition
E4 Ubiquitin Ligase
Definition
E5
Definition
E7
Definition
E11 Antigen, RTI40
E100
E-Cadherin
Synonyms
Definition
Characteristics
E-cadherin and the Formation of Adhesion Junctions
Signals Elicited by the Loss of Cell Adhesion
E-Cadherin in Animal Models of Cancer
E-Cadherin in Human Cancer
Clinical Relevance
References
E2-Conjugating Enzyme
Definition
E Motif
E-Selectin
Definition
E-Selectin-Mediated Adhesion in Cancer
Synonyms
Definition
Characteristics
Mechanisms
Clinical Relevance of E-selectin and its Ligands in Cancer
References
Eag
EAOC (Endometriosis Associated Ovarian Cancers)
Definition
EAP1
E2A-PBX1
Definition
Characteristics
Clinical Aspects
Wild-type E2A and PBX1 Gene Products
Structure and Function of E2A-PBX1
References
Early B-cell Factors
Synonyms
Definition
Characteristics
Potential Roles in Cancer
References
Early Detection
Definition
Characteristics
Biomarker Consortium
Approaches
Early Detection Markers
References
Early Detection Biomarkers
Definition
Early Genes of Human Papillomaviruses
Definition
Characteristics
Clinical Relevance
References
Early Menopause
Definition
Early Virus Genes
Definition
Eaton-Lambert Syndrome
Definition
EBF
Ebnerin (rat)
E-Box
Synonyms
Definition
Characteristics
Genes Containing E-Boxes and the bHLH Proteins that Control them
Genes and Gene Products that are Related to Growth Control and Cancer
How do bHLH Proteins Bind to E-Boxes?
References
4E-BP1
Definition
4EBP-1
Definition
EBV
Definition
EC 2.7.11.1
EC50
Definition
Ecchymosis
Definition
ECM
Definition
ECMRIII
ECOG Performance Status
Definition
Ecological Study
Definition
ECSA
Ecteinascidin 743
Ectodermal
Definition
Ectodermal Dysplasias
Definition
Ecto-Enzymes
Definition
Ectopic Expression
Definition
Eczema
Edelfosine
Definition
Edible Salt
EDN
EDTA
Definition
EEN
Definition
EF-Hand
Definition
EF-Hand Proteins
Definition
Effectors
Definition
Efflux Pumps
Definition
Efflux Ratios
Definition
Eg5
EGF
Definition
EGF-CFC Protein Family
Definition
EGF Family
EGF-like Ligands
EGFR
Definition
EGFR Transactivation
Definition
EGP-2
EGP34
Egr-1 (Early Growth Response-1)
Definition
EH
Definition
Eicosanoid Signaling
Eicosanoids
Definition
Eicosapentaenoic Acid
Definition
eIF4A
Definition
Eker Rat
Definition
ELAM-1
Electrical Coupling
Definition
Electrolytes
Definition
Electromagnetic (EM) Heating
Definition
Electromagnetic Fields
Definition
Characteristics
Epidemiological and Clinical Evidence
Experimental Evidence
Clinical Relevance
References
Electrophiles
Definition
Electroporation
Definition
Electrospray Ionization (ESI)
Definition
Electrostatic Interaction
Definition
Elimination
Definition
ELISA
Definition
ELISPOT
Definition
Elk-1
Definition
Elongin
Definition
Elongin BC Complex
Definition
Characteristics
The VHL Tumor Suppressor Complex
SOCS-box Proteins and the Elongin BC Complex
Clinical Relevance
References
ELR+ /ELR-chemokines
Emboli
Definition
Embolization
Definition
Embryo-specific alpha-Globulin
Embryo-specific Alpha-Globulin
Embryonal Serum alpha-Globulin
Embryonal Serum Alpha-Globulin
Embryonic Stem Cells
Definition
EMI Domain
Definition
Emphysema
Definition
EMS1
EMT
Definition
Enchondroma
Definition
End Replication Problem
Definition
Endocan
Synonyms
Definition
Characteristics
References
Endocannabinoids
Endochondral Ossification
Definition
Endocrine Ablation
Definition
Endocrine or Antihormonal Therapy
Synonyms
Definition
Endocrine-Related Cancers
Synonyms
Definition
Characteristics
Pathogenesis
Prevalence
Clinical Presentation and Pathology
Pituitary Tumors
Thyroid Tumors
Parathyroid Tumors
Endocrine Pancreatic Tumors
Adrenal Tumors
Ovarian Tumors
Testicular Tumors
Multiple Endocrine Gland Tumors
Carcinoids
Secondary Endocrine Malignancies
Ectopic Hormone Syndromes
Treatment
Prognosis
Cancers of Endocrine Target Tissues
References
Endocrine-responsive Cancers
Endocurietherapy
Endocytosis
Synonyms
Definition
Characteristics
Endocytosis and Signaling
Molecular Mechanisms
Clinical Relevance
References
Endodermal
Definition
Endogenous
Definition
Endogenous Retrovirus
Definition
Endolysosomal Pathway
Endometrial Cancer
Definition
Characteristics
Risk Factors
Classification
Pathogenesis Mechanisms
Treatment
Surgery
Radiation Therapy
Hormonal Therapy
Progestogens
Aromatase Inhibitors
References
Endometrial Carcinoma
Definition
Endometrioma
Definition
Endometrioma-benign Endometriotic Ovarian Cysts
Endometriosis
Synonyms
Definition
Characteristics
Pathological Studies
Epidemiological Studies
Molecular Genetic Studies
References
Endometrium
Definition
Endoplasmic Reticulum (ER)
Definition
Endoplasmic Reticulum Stress
Synonyms
Definition
Characteristics
Molecular Mechanisms
Signal Transduction by the Three Arms of the UPR
Clinical Relevance
References
Endoplasmic Reticulum Stress Response
Definition
Endoproteolysis
Definition
Endoscopic-Ultrasound Guided Fine Needle Aspiration (EUS-FNAB)
Definition
Endosomal Compartments
Synonyms
Definition
Characteristics
Clinical Aspects
References
Endosomal Protein Sorting
Endostatin
Definition
Characteristics
Discovery
Structure and Function
Mechanism of Action
Genetic Variations
Preclinical Studies
Clinical Trials
References
Endothelial Cell Specific Molecule-1
Endothelial Cells
Definition
Endothelial Derived Gene-1
Synonyms
Definition
Characteristics
Mechanisms
EG-1 in Human Cancer
Translational Aspects
References
Endothelial Leukocyte Adhesion Molecule-1
Endothelial Progenitor Cells (EPCs)
Definition
Endothelial Transglutaminase
Endothelin (ET)
Definition
Endothelin-2
Endothelin Converting Enzyme (ECE)
Definition
Endothelins
Synonyms
Definition
Characteristics
Endothelin Expression in Cancer
References
Endothelium
Definition
Endotoxins
Definition
Enediynes
Definition
Energy of Photon
Definition
Engineered Antibody
Enhancer
Definition
eNOS
Definition
Enterohepatic Recirculation
Definition
ENU
Definition
Enucleate
Definition
Enucleation
Definition
Environmental Tobacco Smoke
Definition
Enzyme
Definition
Enzymic Mouth to Mouth Feeding
EOC
Definition
Eosinophil
Definition
Eosinophilic Granuloma
Definition
Ep
EPA
Definition
EpCAM
Synonyms
Definition
Characteristics
Structure and Function
Structure
Tissue Morphogenesis
Pattern of Tissue Expression
Normal Tissue
Abnormal Tissue
Paradox of Expression with Advance in Carcinomas
EpCAM Targeted Immunotherapy
Mechanism of Tumor Inhibition
Clinical Trials (Table 1)
Monospecific Murine Antibody
What are the Solutions?
Humanized Antibody
Bispecific Antibodies
In-vitro Cytotoxicity
Prolonged Anti-Tumor Immunity in-vivo
Clinical Trials (Table 2)
References
Ep-CAM
Ependyma
Definition
Ependymoma
Definition
Eph Receptors
Definition
Characteristics
Normal EPH Signaling
EPH Signaling in Cancer
References
Epidemiologic Studies
Definition
Epidemiology of Cancer
Synonyms
Definition
Characteristics
Study Design
Risk Factors
References
Epidermal Growth Factor Inhibitors
Definition
Characteristics
EGFR Activation and Downstream Signaling
Molecular Mechanisms of Targeted Therapies
EGFR Mutations
EGFR Inhibitors in GI Tumors
EGFR Inhibitor in Lung Cancer
References
Epidermal Growth Factor Receptor
Definition
Epidermal Growth Factor-like Ligands
Synonyms
Definition
EGF-Like Ligands and Cancer
Brain Cancer
Breast Cancer
Carcinoma of the Lung
Colorectal Cancer
Head and Neck Squamous Cell Carcinoma (HNSCC)
References
Epidermodysplasia Verruciformis (EV)
Definition
Epidermoid
Definition
Epidermoid Carcinoma
Epigallocatechin
Synonyms
Definition
Characteristics
Cellular and Molecular Targets of EGCG
General Anticancer Effects of Green Tea Polyphenols
Direct Molecular Targets of EGCG
Clinical Relevance
References
Epigastric
Definition
Epigen
Definition
Epigenetic
Definition
Epigenetic Asymmetry
Definition
Epigenetic Changes
Definition
Epigenetic Event
Definition
Epigenetic Gene Silencing
Definition
Characteristics
Epigenetics and Cancer
DNA Methylation
Histone Modifications and Chromatin Remodeling
Clinical Relevance
References
Epigenetic Mechanism
Definition
Epigenetic Modifications
Definition
Epigenetic Reprogramming
Definition
Epigenetic Therapy
Definition
Characteristics
DNA Methylation and Histone Deacetylation
Epigenetic Abnormalities in Cancer
DNA Methyltransferase and Histone Deacetylase Inhibitors
Epigenetic Therapy in Cancer
References
Epigenome
Definition
Epigenomics
Definition
Epilepsy
Definition
Epiphysis
Definition
Epipodophyllotoxins
Definition
Epiregulin
Definition
Epirubicin
Definition
Epistaxis
Definition
Epithelial Cadherin
Epithelial Cell
Epithelial Cell Adhesion Molecule
Epithelial Growth Factors
Definition
Epithelial Tumorigenesis
Definition
Epithelial-to-Mesenchymal Transition
Definition
Characteristics
Mechanisms
Clinical Relevance
References
Epithelioid
Definition
Epithelioid Hemangioendothelioma (EH)
Definition
Epithelioid Sarcoma
Definition
Epitope
Definition
Epitope Spreading
Definition
Epo
Epoetin
Epothilone B Analogue
Synonyms
Definition
Characteristics
Introduction
Preclinical Testing
Phase I Studies in Cancer Patients
Phase II Studies in Cancer Patients
Summary and Future Outlook
References
Epothilones
Definition
Epoxide Hydrolase
Definition
Epoxides
Definition
EPR
Definition
EPR Effect
Definition
EpRE
Definition
EPSCC
Definition
Epstein-Barr Virus
Synonyms
Definition
Characteristics
In vitro Immortalization of Primary B Cells by EBV: The Growth Transcription Program
EBV Biological Cycle in Vivo
Viral Productive Cycle
Clinical Relevance
References
Epstein–Barr Virus Latent Membrane Protein 1
Definition
Characteristics
Mechanisms
References
ER
Definition
ER-Associated Protein Degradation
Definition
ER Quality-Control
Definition
ER Stress
ERBB2
ERG
Definition
Erionite
Definition
ERK
Definition
ERK/MAP Kinase (ERK/MAPK)
Definition
Erlotinib
Synonyms
Definition
Characteristics
References
ERM Proteins
Synonyms
Definition
Characteristics
History, Structure, and Sequence
Regulation
Function, Distribution, Localization
The Expression and Functions of ERM Proteins in Cancer
References
ERp57
Definition
ERp60
Erythema
Definition
Erythema Multiforme Major
Definition
Erythematous Pruritic Macropapular Rash
Definition
Erythrocytosis
Definition
Erythroid Colony Stimulating Activity
Erythroleukemia
Definition
Erythroplakia
Definition
Erythropoiesis
Definition
Erythropoiesis Stimulating Factor
Erythropoietin
Synonyms
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
Erythropoietin Receptor
Definition
ES
Definition
ESA
Definition
ESF
ESFT
Definition
ESM-1
Esophageal Cancer
Definition
Characteristics
References
ESR2
Estradiol
Definition
Characteristics
Mechanism of Action
Sources of Estrogens
Role of Estrogens in Human Breast Carcinogenesis
Receptor-Mediated Pathway
Oxidative Metabolism of Estrogen
Estrogens as Inducers of Aneuploidy
References
17beta-Estradiol
Definition
Estramustine
Definition
Estrogen Receptor
Synonyms
Definition
Characteristics
History
Molecular Mechanisms of Action
What have We Learned from ER Knock-Out Mice?
Involvement of Estrogen Receptors in Physiology and Cancer
References
Estrogen Receptor Alpha ESR1
Estrogen Receptor Beta
Estrogen Synthase
Estrogenic Hormones
Definition
Characteristics
Etiology
Breast Cancer
Uterine, Cervical and Ovarian Cancer
Vaginal Adenocarcinoma
Hepatoma
Therapy
Breast Cancer
Uterine and Cervical Cancers
References
Estrogens
Definition
ET
Definition
ET-18-OCH3
Definition
ET-2
ET-743
ET-RA
Definition
ET-RB
Definition
Eta-1
Ethanol
Definition
Ether à-go-go Potassium Channels
Synonyms
Definition
Characteristics
Oncogenic Potential of h-Eag1 Channels
Eag1 as a Diagnostic Marker
Eag1 as a Therapeutic Target
Mechanisms of Oncogenicity
Outline
References
Etiology
Etk
Definition
Etoposide
Definition
Ets
Definition
ETS (Environmental Tobacco Smoke)
Definition
Ets Transcription Factors
Definition
Characteristics
Ets Factors and Development
Regulation of Ets Protein Activities
Ets Proteins and Cancer
References
ETV6
Synonyms
Definition
Characteristics
Discovery
Protein Domains
ETV6 Fusion Partners in Cancer
Protein Tyrosine Kinase Fusion Partners of ETV6
Transcription Factors and Other Fusion Partners of ETV6
“Unproductive” ETV6 Fusions
Putative Tumor Suppressor Gene and Physiological Function
References
Euchromatin
Definition
Eukaryotic Initiation Factors (eIF)
Definition
Eutectic Temperature
Definition
Evans Syndrome
Definition
Everolimus
Definition
EVI-1
Definition
Ewing Sarcoma
Synonyms
Definition
Characteristics
Cytogenetics and Gene Alterations
Aetiology
Therapy
References
Ewing Sarcoma Family Tumors
Ewing Tumor
EWS
Definition
EWS-FLI (ets) Fusion Transcripts
Definition
Characteristics
Structure
Properties of the EWS-FLI1 Fusion Transcript and Protein
EWS and Other Specific Human Translocations
Genesis of the Translocation
The EWS-FLI1 Fusion and the Pathogenesis of Ewing Sarcoma
Clinical Relevance
EWS-FLI1 (ets) in Diagnosis
EWS-FLI1 (ets) Fusion Type and Prognosis
EWS-FLI1 (ets) and Detection of Minimal Residual’Disease
EWS-FLI1 (ets) and Therapeutics
References
Ex Vivo Culture
Definition
Excentric Cleavage
Definition
Excess Relative Risk (ERR)
Definition
Exchange Factors
Definition
Exchangeable Apolipoprotein
Definition
Excipient Culture
Definition
Excitation
Definition
Excretion
Definition
Excretory Urography
Definition
Exfoliation of Cells
Synonyms
Definition
Characteristics
Mechanisms
Cell Exfoliation in Neoplasia
Clinical Aspects
References
Exfoliative Erythroderma
Definition
Exobiotics
Exon
Definition
Exonic Splicing Enhancer (ESE)
Definition
Experimental Carcinogenesis
Experimental Metastasis
Definition
EXT Genes
Definition
External Granular Layer (EGL)
Definition
Extra Eleven-Nineteen Gene
Definition
Extracellular Domain (ECD)
Definition
Extracellular Matrix
Definition
Extracellular Matrix Remodeling
Definition
Characteristics
References
Extracellular Nucleic Acids
Extracellular Signal-Regulated Kinase (ERK)
Definition
Extracorporeal Photochemotherapy
Definition
Extrahepatic
Extralesional Excision
Definition
Extramedullary
Definition
Extramedullary Hematopoiesis
Definition
Extrapulmonary Small Cell Cancer
Synonyms
Definition
Characteristics
Epidemiology
Pathology
Clinical Features
Diagnosis and Staging
Management
Prognosis
Genitourinary Tract
Urinary Bladder
Prostate
Gynecological Sites
Cervix
Gastrointestinal Tract
Esophagus
Colon and Rectum
Head and Neck Region
Larynx
References
Extrarenal
Definition
Extrarenal Rhabdoid Tumor
Definition
Extraskeletal Myxoid Chondrosarcoma
Definition
Extravasation
Definition
Extreme Hypoxia
Extrinsic Membrane Proteins
Definition
Extrinsic Pathway of Apoptosis
Definition
Ezrin-Radixin-Moiesin (ERM) Family
Definition
F
4F9
F-box and Leucine-rich Repeat Protein 1 – Fbxl1
FAB Classification
Definition
Fab Fragment
Definition
FAC
Definition
FACS
Definition
Factor Ia
Definition
Factor V
Definition
Factor VII
Definition
Factor VIII
Definition
Factor IX
Definition
Factor X
Definition
Factor XI
Definition
Factor XII
Definition
D-factor
FAD
Definition
FADD
Definition
FADD-like Antiapoptotic Molecule 1
FADD-like ICE
FAE
Definition
FAK
Familial Adenomatous Polyposis
Definition
Familial Breast Cancer
Definition
Familial Cancer
Definition
Familial Cancer Syndrome
Definition
Familial (constitutional) Panmyelocytopathy (type) Fanconi
Familial Hypoplastic Anemia Fanconi
Familial Polyposis Coli
Definition
FAMP
FANC Genes
Definition
FANCJ
Fanconi Anemia
Synonyms
Definition
Characteristics
Myelodysplastic Syndromes (MDS)
Leukemia
Solid Tumors
Squamous Cell Carcinoma of the Head and Neck (HNSCC)
SCC of the Vulva and Cervix
Liver Tumors
Other Tumors
FA Gene Involvement in Neoplastic Disease of Non-FA Individuals
References
FAP
Definition
Farnesyl Lipid
Definition
Farnesylated
Definition
Farnesyltransferase
Definition
FAS
Definition I
Definition II
Fas-associated Death Domain
Fas Associated with a Death Domain
Definition
FAS I
Definition
FAS II
Definition
Fas Ligand
Definition
Fasciclin I
Definition
Faslodex
Definition
FASN
FAT
Definition
Fatty Acid Synthase
Synonyms
Definition
Characteristics
Structure and Function
FAS in Normal Tissues
FAS and Cancer
FAS Inhibitors as Potential Cancer Chemotherapeutic Agents
References
Fatty Acid Transport
Definition
Characteristics
Characteristics - Tumor
Mechanisms
References
n3 Fatty Acids
Definition
Fbl1
FcR
Definition
FDA
Definition
FDG
Definition
Fecal Immunochemical Test
Synonyms
Definition
Characteristics
Fate of Hemoglobin in the Gastro-Intestinal Tract
Uses for FIT
Quantifiable FIT
Types of FIT Currently Available
Stool-Sampling Procedures
Biology of Bleeding from Colorectal Neoplasia
References
Fecal Occult Blood Test
Definition
Felty Syndrome
Definition
Female Sex Hormones
Definition
Feminization
Definition
Fenestration
Definition
FERM
Definition
FERM Domain
Definition
Fermentation Products
Definition
Ferredoxin Reductase
Definition
Ferritin
Definition
Ferruginous Bodies
Definition
FET
Definition
Fetal Hamartoma of the Kidney
alpha1-fetoglobulin
alpha-Fetoprotein
Definition
alpha-feto-protein
Feto-specific Proteins
Fetuin
Fetuin-A
FEV1
Definition
Fever
Definition
Fever of Obscure Origin
Fever of Unexplained Origin
Fever of Unknown Origin
Synonyms
Definition
Characteristics
Cancer and Fever of Unknown Origin
Diagnosis
Prognosis of Cancer Associated with Fever of Unknown’Origin
Conclusion
References
FEV1/FVC Ratio
Definition
FGD1
Definition
FGF
Definition
FGFR3
Definition
FH
FHIT
Definition
Fibrin Degradation Products
Definition
Fibrin
Definition
Fibrinogen
Definition
Characteristics
References
Fibroadenoma
Definition
Fibroblast
Definition
Fibroblast Growth Factor 2
Definition
Fibroblast Growth Factors
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
Fibroblasts
Definition
Fibrofolliculomas with Trichodiscomas and Acrochordons
Fibrogenesis
Definition
Fibroid
Definition
Fibromas
Fibromyoma
Fibronectin
Definition
Characteristics
Forms of Fibronectin
Functions
Structure
Fibronectin Polymorphism
Post-Translational Modifications
Alternative Splicing
Biological Significance of ED-B
Fibronectin Isoforms in Disease
Fibronectin Isoforms and Cancer
References
Fibrous Dysplasia
Definition
Fibulins
Synonyms
Definition
Characteristics
Fibulin-1
Fibulin-2
Fibulin-3
Fibulin-4
Fibulin-5
Fibulin-6
Conclusion and Perspective
References
Field Cancerization
Definition
Field Defect
Definition
Field Effect
Definition
FIGO
Definition
Filipodia
Definition
Final Appraisal Document
Definition
Finasteride
Definition
Fine Needle Aspiration Biopsy
Synonyms
Definition
Characteristics
Background
What is FNAB?
What Cellular Characteristics Do Cytologists Study in Order to Make a Microscopic Diagnosis of Cancer?
Method
Palpation-Guided Aspirates
Deep Seated Aspirations
Complications and Contraindications
Diagnostic Accuracy and Yield
Diagnostic Utility of FNAB
Limitations of the FNAB Method of Study
References
Fine-Needle Aspiration Cytology
Definition
Firestorm Pattern
Definition
Characteristics
Contrast with Other Forms of Gene Amplification
Mechanism of Firestorm Formation
Relation of Patterns to Clinical Outcome
References
First-echelon Node
First-tier Node
FISH
Definition
FIT
Five Elements
Definition
FK-506
Definition
FKHL-16
FLAME-1
Flavin Monooxygenases
Definition
Flavonoids
Definition
Flavopiridol
Definition
Fli1-1
Definition
FLICE
FLICE Inhibitory Protein
Synonyms
Definition
Characteristics
Function
Modulation of c-FLIP Level
Role in Carcinogenesis
Implications in Cancer Therapy
References
Flow Cytometry
Definition
Characteristics
The Technology
Applications
Immunophenotyping (IP)
Transplant Support
DNA Ploidy and S Phase Fraction
Determining Treatment Efficacy
Newer and Future Applications
References
FLT
Definition
Fludarabine
Synonyms
Definition
Characteristics
Clinical and Cellular Pharmacology
Mechanisms of Anti-Cancer Activity
Clinical Applications
References
Fludarabine Phosphate
Fluid Phase Endocytosis
Fluorescein Angiography
Definition
Fluorescence
Definition
Fluorescence Cystoscopy
Definition
Fluorescence Diagnostics
Synonyms
Definition
Characteristics
Application
Detection of Early Lung Cancer by Fluorescence Bronchoscopy
Urinary Bladder
Other Organ Sites
References
Fluorescence in Situ Hybridization
Definition
Fluorescence Resonance Energy Transfer
Fluorochrome
Definition
Fluorodeoxyglucose-Positron Emission Tomography
Definition
Fluorouracil
Synonyms
Definition
Characteristics
Mechanisms of Action
Determinants of Cell Sensitivity to 5-FU
Toxic Side-Effects
Capecitabine, an Orally Administered Prodrug of Fluorouracil
References
5-Fluorouracil (5-FU)
Definition
Fluoxetine
Synonyms
Definition
Characteristics
Multiple Drug Resistance
MDR Reversal by Chemosensitization
Fluoxetine as a Multi-pump Chemosensitizer
In Vitro Studies
In Vivo Studies
Conclusions
References
Fluvastatin
Definition
FOBT
Definition
Focal Adhesion
Definition
Focal Adhesion Kinase
Synonyms
Definition
Characteristics
FAK Phosphorylation and Regulation
Focal Contact
Regulation of Focal Contacts
Signaling Pathways in Cancer
Cell Migration
Invasion
Cell Survival
Growth and Proliferation
Tumor Progression
Metastasis
FAK Overexpression
Cancer Therapy
References
Focal Complex
Definition
Focal Contact
Definition
Folate
Definition
FOLFIRI
Definition
FOLFOX
Definition
Folinic Acid
Definition
Follicle Stimulating Hormone
Definition
Follicular Adenoma, Oncocytic Variant
Follicular Adenomas
Follicular Carcinoma
Follicular Carcinoma, Oncocytic Variant
Follicular Lymphoma
Definition
Follicular Thyroid Tumors
Synonyms
Definition
Characteristics
Classification
Etiology
Diagnosis
Treatment
Genetics
References
Folliculin
Food-derived Heterocyclic Amines
Definition
Food for Specified Health Use
FOR
Foreign Substances
Forkhead
Definition
Forkhead Box M1
Synonyms
Definition
Characteristics
References
Formalin-fixed Paraffin-embedded Tissue
Definition
Formation of New Blood Vessels
Forward Chemical Genetics
Definition
FOS
Definition
Fossil Tree
FOX
Definition
FOXC2
Definition
FOXO1A
Definition
FOXO 3A
Definition
FPC
FRA3B
Definition
FRA16D
Definition
Fragile Histidine Triad
Synonyms
Definition
Characteristics
The Gene
The Protein
Bioactivity
Clinical Relevance
References
Fragile Sites
Definition
Characteristics
Categories of Fragile Site
Rare Fragile Sites
Common Fragile Sites
Molecular Basis of Fragile Site Expression
Rare Fragile Sites
Common Fragile Sites
Cellular Regulation of Common Fragile Site Instability
Clinical Relevance
Rare Fragile Sites
Common Fragile Sites
References
Fragile-X Syndrome
Definition
Fragilomics
Definition
Fragment Analysis
Definition
Frameshift Mutation
Definition
Free Radicals
Definition
Freeze Surgery
FRNK
Definition
FTC
Definition
5-FU
Fucosylation
Definition
Characteristics
Regulation of Fucosylation
Core Fucosylation and alpha-Fetoprotein
Fucosylation and Lewis Antigen
Fucosylated Haptoglobin and Pancreatic Cancer
References
alpha1-6 Fucosyltransferase
Definition
Fucosyltransferases
Definition
Fucoxanthin
Definition
Characteristics
Effect on Cancer Cell Growth
Apoptosis
Mechanism
Combination with Troglitazone
References
Fulvestrant
Synonyms
Definition
Characteristics
Mode of Action
Current Utilization of Fulvestrant
Administration and Tolerability
Future Uses of Fulvestrant
Summary
References
Fumarase
Fumarate Hydratase
Synonyms
Definition
Characteristics
Clinical Features of HLRCC/MCUL
Mutations in the FH Gene
References
Functional Foods
Functional Vascular Stabilization
Fungus
Definition
Funnel Factors
Definition
Characteristics
Background of Molecular Human Carcinogenesis
Cell Signaling in Human Tumors
Searching for Funnel Factors: p-4E-BP1
Funnel Factors in Other Oncogenic Pathways
References
Furin
Synonyms
Definition
Characteristics
References
Fusin
Fusion Genes
Synonyms
Definition
Characteristics
Formation Of Fusion Genes
Clinical Relevance
References
Fusion Oncogenes
Fusion Proteins
FVC
Definition
FX
Definition
FZD
Definition
G
G1/S Transition
Definition
G Antigen
G2 Checkpoint Abrogation
Definition
G-protein Couple Receptor
Definition
G-Proteins
Synonyms
Definition
Characteristics
Molecular and Cellular Regulation
Clinical Relevance
References
GA733-2
GABA
Definition
GADD45
Definition
GADD153
Definition
Gadolinium
Definition
GAGE Proteins
Synonyms
Definition
Characteristics
References
Gain of Function p53
Definition
Characteristics
Molecular Mechanisms
Clinical Aspects
References
Gain-of-Function Mutation
Definition
GAK
Galactorrhea
Definition
Galectin-3
Definition
Gallbladder Cancer
Definition
Characteristics
Descriptive Epidemiology
Risk Factors
Conclusions and Perspectives
References
Gallstones
Definition
GALT
Definition
Gametic Phase Disequilibrium
Definition
Gametogenic
Definition
Gamma-Aminobutyric Acid
Definition
Gamma Delta (gammadelta) T Cells
Definition
Gamma-Glutamylcysteine Synthetase
Definition
Gamma Knife
Definition
Gamma-Ray Detection Probe
Definition
Gamma-Ray Induced Cancer
Ganciclovir
Ganglioneuroblastoma
Definition
Ganglioneuroma
Definition
Ganglioside Secretion
Definition
Gangliosides
Synonyms
Definition
Characteristics
Structure
Cellular Ganglioside Expression in Cancer
Ganglioside Shedding in Cancer
Functional Properties
Immunosuppression
Growth Factor-Induced Cell Signaling
Cell Proliferation and Angiogenesis
Conclusions
References
Gankyrin
Synonyms
Definition
Characteristics
pRB and Gankyrin
p53 and Gankyrin
Miscellaneous
Clinical Aspects
References
GAP
Definition
Gap Junctions
Definition
Characteristics
Clinical Relevance
References
Galphaq
Definition
Gardner Syndrome
Definition
Galphas
Definition
Gastric Cancer
Synonyms
Definition
Characteristics
Epidemiology
Etiology
Molecular Biology of Gastric Cancer
Familial Clustering of Gastric Cancer
Hereditary Diffuse Gastric Cancer
Diagnosis and Detection
Management
References
Gastric Carcinoma
Gastrin
Definition
Gastrin-Releasing Peptide
Synonyms
Definition
Characteristics
GRP Receptors
Physiological Functions of GRP
GRP and Cancer
GRP and Lung Carcinoma
GRP and Prostate Carcinoma
GRP and Breast Cancer
GRP and Gastric Carcinoma
GRP and Pancreatic Carcinoma
GRP and Colorectal Carcinoma
GRP and Gastrointestinal Carcinoid Tumors
Clinical Significance
References
Gastrinoma
Synonyms
Definition
Characteristics
Diagnosis
Therapy
Genetics
References
Gastroesophageal Reflux Disease
Definition
Gastrointestinal Hormones
Gastrointestinal Stromal Tumor
Synonyms
Definition
Characteristics
Epidemiology and Clinical-Pathological Features of GIST
Diagnosis
Oncogenic Signaling Pathways in GIST
Cytogenetics and Molecular Cytogenetic Alterations
Therapy
References
Gastrulation
Definition
Gatekeeper
Definition
Gatekeeper Position
Definition
Gaucher Disease
Definition
GBM
GBP28
GCL
Definition
GC-MS
Definition
GC/Post-GC Type B-Cell Tumors
Definition
GCSF
Definition
GCV
Definition
GDEPT
GDF
Definition
GDF15
GDP
Definition
GDP-Fucose
Definition
GEF
Definition
Gefitinib
Definition
Gelatin-Binding Protein 28
Gelatinase B
Geldanamycin
Definition
Gelsolin
Definition
Characteristics
Gelsolin and Cancer
Gelsolin Considered as a Tumor Suppressor
Gelsolin Considered as a Tumor Enhancer
References
Gelsolin Family
Definition
Gemcitabine
Synonyms
Definition
Characteristics
Mechanism of Action and Resistance
Clinical Profile
Toxicity
Indications
Clinical Pharmacology
Future Perspective
References
Gemtuzumab Ozogamicin
Definition
GEMZAR
Gene Amplification
Definition
Gene Battery
Definition
Gene Directed Enzyme-Prodrug Therapy
Gene Expression Cassette
Definition
Gene Expression Profile
Definition
Gene Expression Profiling
Definition
Gene Gun
Definition
Gene Knockout
Definition
Gene Profile
Definition
Gene Therapy
Definition
Characteristics
Transfer of Genes
Clinical Relevance
Reference
Gene Transfection
Definition
Gene-Environment Interaction
Definition
Genetic Association
Definition
Genetic Association Study
Genetic Epidemiology
Definition
Genetic Haplotype
Definition
Genetic Immunization
Genetic Instability
Definition
Genetic Knock-out
Definition
Genetic Polymorphism
Definition
Genetic Recombination
Definition
Genetic Susceptibility
Definition
Genetic Toxicology
Synonyms
Definition
Characteristics
Genetic Toxicology
Chemical, Viral, and Radiation Carcinogens
Chemical Carcinogenesis
Chemically Induced Morphological and Neoplastic Transformation and the Molecular Biology of Carcinogenesis/Cell Transformation and Human Cancer
References
Genetically Engineered Mice
Genetically Engineered Model
Definition
Genistein
Synonyms
Definition
Characteristics
Soy and Cancer
Cancer Prevention by Genistein
Mechanisms of Action of Genistein
Bioavailability and Safety
Other Indications
References
Genomic Imbalance
Definition
Characteristics
Genomic Imbalance Concept
Cancer as a Genetic Disease
Cause of Genomic Imbalance in Cancer
References
Genomic Imprinting
Definition
Characteristics
Imprinted Genes and their Regulation
Imprinting and DNA Methylation
Loss of Imprinting (LOI) in Cancer
References
Genomic Instability
Definition
Genomics
Definition
Genotoxic
Definition
Genotoxic Carcinogen
Definition
Genotoxicity Tests
Definition
Genotype
Definition
Geranylgeranyl
Definition
Geranylgeranylation
Definition
Germ Cell Layers
Definition
Germ Cell Tumors
Synonyms
Definition
Characteristics
Incidence
Risk Factors
Histological Classification
Clinical Presentation and Diagnosis
Staging and Risk Stratification
Management
Seminomas
Non-Seminomatous Germ Cell Tumors (NSGCT)
Conclusions
References
Germinal Center
Definition
Germinal Stem Cells
Definition
Germinoma
Definition
Characteristics
Diagnosis
Treatment
Surgery
Radiotherapy
Chemotherapy
Genetics
References
Germline Mutation
Definition
GI
Definition
Giant Cell Tumor
Definition
Gilbert Syndrome
Definition
Ginkgo Biloba
Synonyms
Definition
Characteristics
G. biloba Seeds
G. biloba Extract
References
Ginkgo Tree
Ginseng
Definition
GIST
GISTs
Definition
GJIC
Definition
GlcCer
Definition
Gleason Grading
Definition
Characteristics
Clinical Aspects
References
Gleevec
Definition
GLFG Bodies
Definition
Gli
Definition
GLI-Kruppel Family Member
GLI Proteins
Synonyms
Definition
Characteristics
Regulation of GLI Activity in Response to HH Signaling
GLI Proteins in Cancer
References
Glioblastoma
Definition
Glioblastoma Multiforme
Synonyms
Definition
Characteristics
Introduction
The Genomic Abnormalities in GBM Tumors
Treatment of GBM Tumors
Current Status of GBM Research
References
Glioma
Definition
Glioma Retinae
Glivec
Definition
gamma Globulins
Definition
Glucagon
Definition
Glucagonoma
Definition
Glucocorticoids
Definition
Glucose
Definition
Glucuronic Acid
Definition
beta-Glucuronidase
Definition
Glucuronidation
Definition
Glut1
Definition
Glut4
Definition
Glutamate Carboxypeptidase II
Definition
gamma-Glutamylcystein Synthetase
Definition
Glutathione
Definition
Glutathione Conjugate Transporter RLIP76
Synonyms
Definition
Characteristics
Discovery of RLIP76
Clinical Significance
Drug Resistance
Heat-shock and Oxidative Stress
Radiation Toxicity
References
Glutathione Conjugates
Definition
Glutathione-S Transferase
Synonyms
Definition
Characteristics
Catalytic function
Signaling regulation
Cancer related
References
N-Glycan Chain
Definition
Glycans
Definition
Glycobiology
Definition
Characteristics
Glycan Structural Diversity is Theoretically Immense but Genetically Restricted
Glycans Evoke Antibody Responses
Glycans are Clinically Useful as Cancer Markers
TACAs are Recognized by Lectins on Antigen-Presenting Dendritic Cells
Human Retrovirus HTLV-1 (Human T-cell Leukemia Virus) Induces Specific Glycan Biosynthesis
Selectin–Glycan Interactions Initiate Adhesion of Malignant Cells to Vascular Endothelium
Drugs may Inhibit Metastases by Blocking Selectin–Glycan Interactions
Concluding Sweet Remarks
References
Glycocalyx
Definition
Glycoconjugates
Definition
Glycoforms
Definition
Glycogen Synthase Kinase-3
Definition
Glycolipids
Definition
Glycolysis
Definition
Glycoprotein
Definition
Glycoprotein-340
Glycosaminoglycans
Definition
Glycoside
Glycosphingolipids
Definition
Glycosyl Phosphatidyl Inositol
Definition
Glycosylation
Synonyms
Definition
Characteristics
Glycosylation Alterations and Functions in Cancer
Glycans Used as Serological Markers in Cancers
Therapeutic Applications of Glycans in Cancers
References
Glycosylation, Aberrant
Definition
N- and O-Glycosylation
Definition
O-Glycosylation
Definition
Glycosylphosphatidylinositol Linkage
Definition
Glycosyltransferase
Definition
Glycyrrhetinic Acid
Definition
Glypican 1
Definition
G2/M Arrest
Definition
G2/M Checkpoint
Definition
G2/M Cyclins
Definition
G2/M Transition
Definition
Characteristics
Structural Changes at the G2/M Transition
Triggering G2/M Transition
References
GMEM
GnRH
Definition
GnRH Analogs
Definition
Goldberg-Hogness Box
Definition
Gompertzian Growth Curve
Definition
Gonadal Mosaicism
Definition
Gonadal Neoplasms
Gonadotropes
Definition
Gonadotropin-Releasing Hormone
Synonyms
Definition
Characteristics
References
Good Laboratory Practices
Definition
Characteristics
Principles
Subpart A: General Provisions
Subpart B: Organization and Personnel
Subpart C: Testing Facility
Subpart D: Equipment Design
Subpart E: Testing Facility Operation
Subpart F: Test and Control Article Characterization
Subpart G: Protocol and the Conduct of the Non-clinical Laboratory Study
Subpart H & I: (Reserved)
Subpart J: Records and Data Reporting
Subpart K: Disqualification of Testing Facilities
References
Good Manufacturing Practices
Definition
Characteristics
Quality Assurance
Documentation and SOPs
FDA Quality Initiatives
Pharmaceutical Quality for the Twenty-First Century
Process Analytical Technology (PAT)
ICH Q8 Pharmaceutical Development
ICH Q9 Quality Risk Management
Quality System Approach to Pharmaceutical Good Manufacturing Practices
ICH Q10 Pharmaceutical Quality Systems
References
Gordon-Kosswig Melanoma System
Gorlin Syndrome
Definition
Government Drug Regulatory Agencies
Definition
gp36
gp90Hermes
gp170
GPCR
Definition
G6PD
Definition
gp-Fy
GPI PLD
Definition
GPI-Anchored Protein
Definition
GPI-Linked
Definition
Gp38k
Grade IV Astrocytoma
Grading of Tumors
Synonyms
Definition
Characteristics
Basic Principles
Methods of Grading
Future Perspectives
References
Graft Acceptance and Rejection
Definition
Characteristics
Cellular and Molecular Mechanisms
Clinical Relevance
References
Graft Acute Cellular Rejection
Definition
Graft Acute Vascular Rejection
Definition
Graft Chronic Rejection
Definition
Graft Hyperacute Rejection
Definition
Graft Primary Non-Function
Definition
Graft Tolerance
Definition
Graft-Versus-Host Disease
Definition
Graft-Versus-Leukemia/Tumor
Definition
Granulocyte Elastase
Granulocyte-Colony Stimulating Factor
Definition
Granulocytes
Definition
Granulocytopenia
Granulosa Cell Tumors
Definition
Characteristics
Clinical Aspects
References
Granzymes
Definition
Grape Seed Extract
Definition
Characteristics
Biological Activity
Health Beneficial Effects
Cardiovascular Diseases
Other Health Conditions
Anticancer and Cancer Preventive Efficacy
Clinical Studies
Conclusions
References
Grape Seed Proanthocyanidins
Definition
Graves Disease
Definition
GRB2
Definition
Grb2 Adaptor Protein
Definition
Green Tea
Definition
Green Tea Catechins
Definition
Green Tea Polyphenol
Groucho
Definition
Growth Arrest
Definition
Growth Factor
Definition
Growth Factor Receptors
Definition
Growth Guidance Cue
Growth Hormone
Definition
G-SE
Definition
GSH
Definition
GSK3
Definition
GSL
Definition
GSP
Definition
GST
Definition
GTP
Definition
GTP-Binding
Definition
GTP-Binding Proteins
GTPase
Synonyms
Definition
Characteristics
The Ras Family
The Rho Family
The Rab Family
The Arf Family
The Ran Family
Regulation of GTPases
Clinical Implications
Signaling Pathways
References
GTPase-Activating Protein
Definition
Guanine Nucleotide Exchange Factor
Definition
Guanylate Cyclase
Definition
Guidance Cues
Definition
Gut Peptides
Synonyms
Definition
Characteristics
Overview
Gastrin
Gastrin-Releasing Peptide
Neurotensin
Somatostatin
References
Gynaecomastia
Gynecomastia
Synonyms
Definition
Characteristics
References
Gynecomazia
Gyrus
Definition
H
H-2
Definition
H60
Definition
H-CAM
H Enzyme
Definition
H731 (Human PDCD4 Variant 2, Cancer-related)
H3 (Rhesus Monkey)
HA
Definition
HACBP
Hageman Factor
Definition
Hairy Cell Leukemia
Definition
Half-life
Definition
Halsted Radical Mastectomy
Definition
Hamartin
Synonyms
Definition
Characteristics
References
Hamartoma
Definition
Hamartomatous Polyposis
Definition
HAND Gene Family
Definition
Hand–Schüller–Christian Disease
Definition
Haploinsufficiency
Definition
Characteristics
Mechanism of Disease Initiation Involving Haploinsufficiency
References
Haplotype
Definition
Haptens
Definition
Haptoglobin
Definition
Haptotaxis
Definition
Hardy–Weinberg Law
Definition
HARP
HAS
HAS1
Definition
HAS2
Definition
HAS3
Definition
Hashimoto Thyroiditis
Definition
HAT
Definition
HAUSP
Definition
HAUSP De-Ubiquitinase
gammaH2AX
Definition
Hay Fever
HBBM
HB-EGF
Definition
Characteristics
Clinical Relevance
References
HB-GAM
HBGF
HBGF-8
HBNF
HBNPF
HC-11 Cells
Definition
HC gp39
HCAEC
Definition
HCC
Definition
HCV
HD
Definition
HDAC Inhibitors
Definition
HDACs
Definition
HDM
HDMVEC
Definition
H&E Stain
Definition
HEA125
Health Technology Appraisal
Definition
Heat Shock Protein 90
Heat Shock Protein 70
Definition
HECT
Definition
Hedgehog
Definition
Hedgehog Signaling
Definition
Characteristics
Hedgehog Signaling and Cancer
Hedgehog, Stem Cell Renewal and Cancer
Targeting Hedgehog Signaling for Therapeutics
References
HEK 293
Definition
HeLa Cells
Definition
Helicase
Definition
Helicobacter Pylori
Definition
Helix-Loop-Helix Domain
Definition
Helper CD4 T Cells
Definition
Helper T (Th) Cells
Definition
Hemagglutinating Virus of Japan
Definition
Hemangioblastoma
Definition
Hemangioendothelioma
Definition
Hemangioma
Definition
Hemangiosarcoma
Definition
Hematological Malignancies, Leukemias and Lymphomas
Definition
Characteristics
The Hematopoietic System
The WHO Classification
Major Myeloid Subclasses within the WHO Classification
Major Lymphoid Subclasses within the WHO Classification
Diagnosis
Treatment
References
Hematopoiesis
Definition
Hematopoietic Niche
Definition
Hematopoietic Progenitors
Definition
Hematopoietic Stem Cell
Definition
Hematopoietic Stem Cell Transplants
Definition
Hematopoietic System
Definition
Hematoporphyrin Derivative
Definition
Hematoxylin and Eosin
Definition
Hematuria
Definition
Heme
Definition
Heme-Oxygenase 1
Definition
Hemichannel
Definition
Hemihypertrophy
Definition
Hemizygous
Definition
Hemizygous Deletion
Definition
Hemochromatosis
Definition
Hemoglobin
Definition
Hemoglobinopathy
Definition
Hemosiderin
Definition
Henle–Koch Postulates
Hensin (Rabbit)
Heparan Sulfate
Definition
Heparan Sulfate Proteoglycans
Definition
Heparanase
Definition
Characteristics
Heparan Sulfate Proteoglycans (HSPGs)
Molecular Properties
Preferential Expression in Human Tumors
Involvement in Tumor Metastasis
Involvement in Tumor Angiogenesis
Clinical Relevance
References
Heparanase Inhibitors
Definition
Characteristics
Inhibitors Targeting the Heparanase Substrate
Heparin, Chemically Modified Derivative and Nonanticoagulant Heparin
Sulfated Phosphomannopentaose
Oligomannurarate Sulfate-JG3
Suramin
Noncarbohydrate Substrate Mimetic Polymers
Inhibitors Targeting Heparanase
Small Molecules
Peptides Competing with the Heparin/HS Binding Domains of Heparanase
Antiheparanase Antibodies
Conclusions and Perspectives
References
Heparin
Definition
Heparin-affin Regulatory Peptide
Heparin-binding Brain Mitogen
8-kDa Heparin-binding Glycoprotein
Heparin-binding Growth Associated Molecule
Heparin-binding Growth Factor 8
Heparin-binding Growth Factors
Heparin-binding Neurite Promoting Factor
Heparin-binding Neurotropic Factor
Hepatic Acinus
Definition
Hepatic Carcinoma
Hepatic Epithelioid Hemangioendothelioma
Synonyms
Definition
Characteristics
Etiology
Diagnosis
Therapy
Clinical Outcome
References
Hepatic Ethanol Metabolism
Definition
Characteristics
References
Hepatic Excretion
Definition
Hepatic Leukemia Factor (HLF)
Definition
Hepatic (Liver) Fixed Macrophages
Hepatic Stellate Cell
Definition
Hepatitis
Definition
Hepatitis B Virus
Definition
Hepatitis B Virus x Antigen Associated Hepatocellular Carcinoma
Synonyms
Definition
Characteristics
References
Hepatitis C Virus
Synonyms
Definition
Characteristics
Untranslated Regions
Structural Proteins
Non-structural Proteins
Cellular and Molecular Regulation
Clinical Relevance
References
Hepatoblastoma
Definition
Characteristics
Pathological Classification
Staging
Therapy and Outsome
Predictive Factors
Genetic and Molecular Characteristics
Cellular Characteristics
References
Hepatocellular Carcinoma
Synonyms
Definition
Characteristics
Epidemiology
Risk Factors
Diagnosis
Prognosis
Prognostic Staging System
Treatment
Prevention
References
Hepatocellular Carcinoma – Etiology, Risk Factors and Prevention
Synonyms
Definition
Characteristics
Etiology
Oncogenic and Environmental Factors
High-Risk Non-viral Liver Diseases
Viral Hepatitis-Induced HCC
Molecular Aspects of Hepatocarcinogenesis (Fig. 1)
Diagnosis
Treatment
Prognosis and Prevention
References
Hepatocyte
Definition
Hepatocyte Activator Inhibitor-1
Definition
Hepatocyte Growth Factor
Definition
Hepatocyte Growth Factor-like Protein
Hepatocyte Stimulating Factor
Hepatocyte Stimulating Factor-III
Hepatolithiasis
Definition
Hepatoma
Hepatomegaly
Definition
Hepatosplenomegaly
Definition
Hepsin
Definition
HER2
Definition
HER-2/neu
Synonyms
Definition
Characteristics
References
HER3
Definition
Herceptin
Synonyms
Definition
Characteristics
Clinical Activity
Mechanisms of Activity
Molecular Level
Cellular Level
Mechanisms of Resistance
Insulin-like Growth Factor-I Signaling
Akt Signaling
Extracellular Domain and Truncated Forms of HER-2
New Directions
References
Hereditary Breast Cancer
Definition
Hereditary Hamartosis Peutz-Jeghers
Hereditary Leiomyomatosis and Renal Cell Cancer
Definition
Hereditary Nonpolyposis Colon Cancer
Definition
Hereditary Nonpolyposis Colorectal Cancer
Heregulin
Definition
HERG
Definition
Herniorrhaphy
Definition
Herpes Simplex Virus
Definition
Herpesvirus-Associated Ubiquitin-Specific Protease
Definition
Herpesvirus-Associated Ubiquitin-Specific Protease De-ubiquitinase
Synonyms
Definition
Characteristics
p53-Mdm2 Pathway
Implications in Cancer Therapy
References
Heterochromatin
Definition
Heterocromatic Regions
Definition
Heterocyclic Amines
Definition
Heterodimer
Definition
Heterodimeric Complex
Definition
Heteroduplex Analysis
Definition
Heterokaryon
Definition
Heterologous Growth Control
Hetero-oligomers
Definition
Heteroplasmy
Definition
Heterotrimeric G-Proteins
Definition
Heterotrimeric GTP-binding Proteins
Heterotrimeric Guanine Nucleotide-binding Proteins
Heterozygosity
Definition
Heterozygous
Definition
Hexabrachion
Hexavalent Chromium
Synonyms
Definition
Characteristics
Uses and Sources
Epidemiology
Animal Studies
Cell Culture Studies
Role of Valence State, Uptake and Metabolism
Role of Solubility
Mechanism of Carcinogenicity
References
Hexavalent Chromium-induced Carcinogenesis
HFH-11B
HGF
Definition
HGF Activator
Definition
HGFL
gammaH2AX
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
HHV4
HHV8
Definition
HHV-8
Definition
HIF1
Definition
HIF-1
HIF1α
Definition
High Affinity Ca2+-binding Protein
High Content Screen
Definition
High-dose (Myeloablative) Chemotherapy
High-Dose Therapy with Stem-Cell Support
Definition
High Endothelial Venules
Definition
High-flow Microinfusion
High-frequency Ultrasound Imaging
High-Grade
Definition
High Grade/Undifferentiated MEC
High Mobility Group
Definition
High Throughput Screen
High Throughput Screening
High Throughput Screens
Definition
HILDA
Hindgut
Definition
HIPK2
Definition
HIP1r
Definition
Hirschsprung Disease
Definition
Hirsutism
Definition
Histiocytoid
Definition
Histiocytosis X
Histo-blood Group Lewis Antigens
Histocompatibility
Definition
Histocompatibility Antigens
Definition
Histocompatibility Testing
Definition
Histocultures
Definition
Histogram
Definition
Histologic Grading
Histology
Definition
Histone
Definition
Histone Acetylation
Definition
Histone Acetyltransferases
Definition
Histone Deacetylases
Synonyms
Definition
Characteristics
Functional Roles of Histone Deacetylases (HDACs)
HDACs and Cancer
HDAC Family Members
HDAC Inhibitors
Epigenetic Therapy
References
Histone Deacetylation
Definition
Histone Demethylases
Definition
Histone H4
Definition
Histone H2AX Phosphorylated at Serine 139
Histone Methylation
Definition
Histone Methyltransferase
Definition
Histone Modification
Definition
Characteristics
Histones and Chromatin
Histone Modifications
Histone Modifications and Cancer Prognosis
Epigenetic Therapy: HDAC Inhibitors
References
Histone Modifying Enzymes
Definition
Histone Proteins
Definition
Histones
Definition
Histopathological
Definition
HIV
Definition
HLA
Definition
HLA Class I
Definition
Characteristics
Bioactivity
Altered HLA Class I Phenotypes in Tumors
Functional Significance of HLA Class I Loss: Implications for Immune Evasion
References
HLH Domain
Definition
hMAWD: Human MAPK Activator with WD Repeats
HMEC-1
Definition
HMG-CoA Reductase
Definition
HMG-I/Y
Definition
HMGA1
Definition
HMGA2
Definition
HMTs
4-HNE
Definition
HNPCC
Definition
hnRNP M
Definition
HO-1
Definition
Hoarseness
Definition
Hodgkin Disease
Definition
Characteristics
References
Hodgkin Disease, Clinical Oncology
Synonyms
Definition
Characteristics
Pathology
Basic
Clinical
References
Hodgkin Lymphoma
Definition
Hodgkin and Non-Hodgkin Lymphomas
Hodgkin and Reed/Sternberg Cell
Definition
Characteristics
Associated Pathologies
Cellular Origin
Immunophenotype
Cell Differentiation and Function
Transforming Mechanisms of HRS Cells
References
Hoechst-33342 Dye
Definition
Hollow Fiber Assay
Definition
Characteristics
Methodology
References
Homeobox
Definition
Homeobox Genes
Definition
Characteristics
Hox Genes and Leukemia
Homeobox Genes and Solid Tumors
References
Homeostasis
Definition
Homeotic Genes
Definition
Homer Wright Rosette
Definition
Homing Peptides and Vascular Zip Codes
Definition
Characteristics
Biological Significance
Clinical Significance
References
Homing receptor
Homo Sapiens Mitotic Arrest Deficient-like 1 Protein
Homodimer
Definition
Homo- or Heterodimers
Definition
Homogeneously Staining Region
Definition
Homogenous Assays
Homogenous Time Resolved Fluorescence
Homolog
Definition
Homologous Recombination Repair
Definition
Characteristics
Cellular Regulation
Clinical Relevance
References
Homologue of Synaptopodin
Homomeric Complex
Definition
Homophilic and Heterophilic Adhesion
Definition
Homoplasmy
Definition
Homotypic and Heterotypic Adhesion
Definition
Homozygous Deletion
Definition
Horizontal Gene Transfer (HGT)
Definition
Hormonal Carcinogenesis
Definition
Characteristics
Mechanisms
References
Hormonal Therapy
Definition
Hormonal Treatments
Definition
Hormone-induced Cancers
Hormone-Refractory Prostate Cancer
Definition
Hormone-related Cancers
Hormone Replacement Therapy
Definition
Hormone-Responsive Element
Definition
Hormones
Definition
Characteristics
Mechanisms
The Receptor Concept
Endogenous Metabolic Activation of Steroids
Epidemiology and Animal Studies
Steroid Hormones
Prolactin
Insulin
Gastrointestinal Hormones
Thyroid Hormones
Hormonal Management of Cancer
References
Hornstein–Knickenberg syndrome
HOX
Definition
HOXA5 gene
Definition
HOXA9
Definition
HpaII Tiny Fragments (HTF) Islands
HPAEC
Definition
HPD
Definition
HPRT
Definition
hPTTG1
HPV
HRPC
Definition
HS1
Definition
HSC
Definition
HSD18
HSF
HSF-III
hSNF5
HSNF5/INI1
Definition
hSNF5/INI1/SMARCB1 Tumor Suppressor Gene
Synonyms
Definition
Characteristics
The Chromatin Remodeling and the SWI/SNF Complex
hSNF5/INI1 Gene and Protein Structures
Biological Roles of hSNF5/INI1
Genetic Alterations of hSNF5/INI1 in Human Malignancies
Pathological and Clinical Aspects of hSNF5/INI-Deficient Tumors
Conclusion
References
HSP
Definition
Hsp60
Definition
Hsp90
Synonyms
Definition
Characteristics
Mechanism
Clinical Aspects
As a Single Modality
In Combination with Radiotherapy
References
HSPG
Definition
HSR
Definition
HSV-TK/Ganciclovir Mediated Toxicity
Synonyms
Definition
Characteristics
Toxicity to HSV-TK-Expressing Cells
Toxicity to Non-HSV-TK-Expressing Cells (Bystander Effect)
Characteristics in Vivo
Experimental Tumors in Animals
Mechanism of the Bystander Effect in Vivo
Clinical Relevance
Improving Cancer Therapy with HSV-TK/GCV
References
hTERT
Definition
HTLV-1
Definition
HUCE
Definition
Human Cancer Epidemiology
Definition
Human Cartilage Glycoprotein-39
Human ESP1-associated Protein 1
Human Herpes Virus 4
Human Herpesvirus 6
Definition
Characteristics
Clinical Aspects
References
Human Immunodeficiency Virus
Definition
Human Kallikrein 3
Human Lymphocyte Antigen
Definition
Human Non Sucrose Fermenting 5
Human Papillomaviruses
Synonyms
Definition
Characteristics
Virus Particle
Virus Replication
Pathogenesis of Papillomavirus Infection
Bioactivity
Clinical Relevance
References
Human Pituitary Tumor-transforming Gene 1
Human Podoplanin
Human Symbols for Snail1 and Snail2: SNAI1,SNAI2
Human T-cell Leukemia Virus
Synonym
Definition
Characteristics
Leukemia
Clinical Presentation
Pathology
Neurologic Disease
Clinical Presentation
Pathology
References
Human T-lymphotropic Virus (HTLV)
Human Umbilical Vein Endothelial Cells
Definition
Human Wart Virus
Humanized Antibodies
Definition
HUMARA
Humoral Immune Response
Definition
Humoral Immunity
Definition
Huntingtin Interacting Protein 1 (HIP1)
Definition
Characteristics
Future
Significance
References
Hurthle Cell
Definition
Hurthle Cell Adenoma and Carcinoma
Synonyms
Definition
Characteristics
Current and Past Controversies
References
Hutchinson-Weber-Peutz-Syndrome
HUVEC
Definition
HVEM
Definition
HVJ
Definition
HVJ-Envelope Vector
Definition
HVJ-Liposomes
Definition
Hyaluronan
Definition
Hyaluronan Receptor
Hyaluronan Synthases
Synonyms
Definition
Characteristics
Hyaluronan Synthases and Hyaluronan
Hyaluronan Synthases and Hyaluronan in Cancer
Proliferation and Tumor Growth
Invasion and Metastasis
Multidrug Resistance
References
Hyaluronic Acid
Definition
Hyaluronic Acid synthases
Hyaluronidase
Definition
Characteristics
HAase Expression in Cancer
HAase Functions in Cancer
Regulation of HAase Activity
Clinical Importance of HAase
Summary
References
Hybrid Genes
Hybrid Positron Emission Tomography/Computed Tomography
Hybridomas
Definition
Hydrogen Dioxide
Hydrogen Nuclei
Definition
Hydrogen Peroxide
Synonyms
Definition
Characteristics
Carcinogenic Effects
Clinical Relevance
References
Hydrophilic
Definition
Hydroquinone
Definition
Hydroxyapatite
Definition
Hydroxybutyrate Dehydrogenase
5-HydroxyIndoleacetic Acid (5-HIAA)
Definition
Hydroxyl Group
Definition
Hydroxylapatite
Definition
14-Hydroxyldaunorubicin
4-Hydroxynonenal
Definition
13-Hydroxyoctadecadienoic Acid (13-HODE)
Definition
2-Hydroxyoleic Acid
Definition
7-Hydroxystaurosporine
7-Hydroxystaurosporine, NSC 638850
Definition
Hydroxysteroid Dehydrogenases
Hyperalgesia
Definition
Hypercalcemia
Definition
Hyperchlorhydria
Definition
Hyperdiploidy
Definition
Hypergastrinemia
Definition
Hyperglycemia
Definition
Hypericin
Synonyms
Definition
Characteristics
Physical Properties
Clinical Applications
PDD of Cancers
PDT of Cancers
Preclinical Investigations
References
Hyperlipidemia
Definition
Hypermethylation
Definition
Hyperplasia
Definition
Hyperplastic growth
Definition
Hypersensitivity
Hypersensitivity Reaction
Definition
Hyperthermia
Definition
Characteristics
Cytotoxic Effects
Physiologic Effects
Immunological Effects
Hyperthermia Physics
Delivery Modalities
Thermometry
Thermal Dosimetry
Clinical Hyperthermia
Radiation Therapy and Hyperthermia
Chemotherapy and Hyperthermia
Clinical Trials
References
Hypertrophy
Definition
Hypertrophy of Male Breast
Hypervariable Region
Definition
Hypodiploidy
Definition
Hypoechoic
Definition
Hypogammaglobulinemia
Definition
Hypomethylation
Definition
Hypomethylation of DNA
Synonyms
Definition
Characteristics
References
Hypospadias
Definition
Hypothalamus
Definition
Hypoxia
Synonyms
Definition
Characteristics
Phenotypes of Hypoxic Cells
Gene Regulation in Hypoxic Cells: Implications for Tumorigenesis
References
Hypoxia Inducible Factor
Definition
Hypoxia Inducible Factor-1
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Hypoxic
Definition
Hysterectomy
Definition
I
IA4
IAP
Definition
IARC
Definition
IARC TP53 Database
Definition
Characteristics
TP53 Gene Mutations in Human Cancers
Database Structure and Content
Web Site and New Search Tools
Recommendation to Users
References
IkappaB
Definition
IkappaBalpha
Definition
IC50
Definition
ICAMs
Definition
Id1
Definition
Id Proteins
Definition
Idarubicin
Definition
Idiopathic Bone Infarction
Definition
Idiopathic Myelofibrosis
Idiotype
Definition
Idiotype Vaccination
Synonyms
Definition
Characteristics
Field of Application
Formulation
Production
Clinical Aspects
Open Questions
References
Idiotypic Vaccination
IDO
I-FLICE
IFN
Definition
iFOBT
IgE-Mediated Hypersensitivity
IGF
Definition
IGF-2
Definition
IGF-I
Definition
IGs
Definition
IHC
IISRE
Definition
IL-1
Definition
IL-12
Definition
Illegitimate Recombination
Definition
Image Cytometry
Definition
Imaginal Discs
Definition
Imatinib
Synonyms
Definition
Characteristics
BCR-ABL and CML as a Target for Imatinib
Activity of Imatinib in CML
Mechanisms of Relapse/Resistance to Imatinib
Activity of Imatinib in Other Diseases
Conclusion
References
Imatinib Mesylate
Imiquimod
Definition
Immature B Cells
Definition
Immediate Early Genes
Definition
Immediate Early Stress Response
Immortalization
Definition
Immortalized
Definition
Immortalized Cells
Definition
Immune Adjuvants
Definition
Immune Complex
Definition
Immune Deviation
Definition
Immune Escape
Definition
Characteristics
Host Ignorance
Tumor Cell Adaptation
References
Immune Escape of Tumors
Definition
Immune Response
Definition
Immune Responses to Autoantigens
Immune Surveillance of Tumors
Definition
Immune System
Definition
Immunoassay
Definition
Immunoblotting
Definition
Immunochemical Fecal Occult Blood Test
Immunocompetent
Definition
Immunocytochemistry
Definition
Immunodeficient Nude Mice
Definition
Immunodiffusion
Definition
Immunoediting
Definition
Characteristics
History
The Role of Interferons and Other Immune Components
The Role of Induced Immune Pressure
Evidence of Immunoediting in Human Cancer
References
Immunogenicity
Definition
Immunoglobulin
Definition
Immunoglobulin E (IgE)
Definition
Immunoglobulin Genes
Definition
Immunoglobulin Libraries
Definition
Immunoglobulins
Definition
Immunohistochemistry
Synonyms
Definition
Characteristics
History
Techniques
Uses
Use in Research
Clinical Uses
Diagnosis
Intermediate Filaments
Nuclear Transcription Factors
Carcinoma
Melanoma
Sarcoma
Lymphoma
Infectious Agents
Tumor Stage and Occult Metastases
Prognosis
Treatment Response
Targeted Therapy
References
Immunohistology
Immunoliposomes
Definition
Characteristics
Immunoliposome Types and Antibody Formats
Drugs and Targets
References
Immunologic Tolerance
Definition
Immunological Fecal Occult Blood Test
Immunophenotype
Definition
Immunophenotypic Determinants
Immunophenotyping
Definition
Immunophilins
Definition
Immunoprevention
Synonyms
Definition
Characteristics
Immunoprevention of Viral Tumors
Immunoprevention of Tumors Unrelated to Infectious Agents
Immune Mechanisms of Cancer Prevention
Target Antigens of Cancer Immunoprevention
Clinical Developments
The Risks of Cancer Immunoprevention
References
Immunoprophylaxis
Immunoreceptor
Immunoreceptor Tyrosine-based Activation Motif
Definition
Immunoregulatory Aberrations
Immunoscreening cDNA Expression Libraries
Definition
Immunostimulatory Molecules
Definition
Immunosuppressed
Definition
Immunosuppression
Definition
Immunosuppressive Drugs
Definition
Immunotherapy
Synonyms
Definition
Characteristics
Nonspecific Immunotherapy
Specific Immunotherapy
References
Immunotoxin
Definition
Importin-Alpha-3
Definition
Importins
Definition
Imprinted Gene
Definition
Imprinting
Definition
Characteristics
Cellular and Molecular Aspects
Clinical Relevance
References
In Situ Breast Cancer
In Situ Cancer or Carcinoma
In Situ Carcinoma
In Vitro
Definition
In Vitro Genetics
Definition
In Vivo
Definition
Inbred Lines
Inbred Strain
Definition
Incidence
Definition
Incidence Rate
Definition
Independent Prognostic Factor
Definition
Indian
Definition
Indirubin and Indirubin Derivatives
Synonyms
Definition
Characteristics
History
Mechanism
Structure/Activity
References
Individual Susceptibility
Definition
Individualized Treatment
Individually Mutated Tumor Antigens
Definition
Indoleamine
Definition
Indoleamine 2,3-Dioxygenase
Synonyms
Definition
Characteristics
Enzymatic Properties, Tissue Distribution, and Regulation of Expression
IDO and Immune Suppression
IDO and Cancer
Clinical Relevance
IDO as a Prognostic Indicator for Human Cancer
Targeting IDO as a Therapeutic Strategy for Cancer Treatment
Implication of IDO for DC-based Cancer Immunotherapy
References
Indolent Lymphoma
Definition
Induction
Definition
Induction Chemotherapy
Synonyms
Definition
Characteristics
Solid Tumors
Leukemia
References
Infection
Definition
Infectious Mononucleosis
Definition
Infiltration
Inflammation
Definition
Characteristics
References
Inflammatory Response and Immunity
Definition
Characteristics
An Overview of Inflammation
An Overview of Cancer
Interrelationship Between Inflammation and Cancer
Examples of Inflammation-Associated Cancers
Immunotherapeutic Strategies Against Cancer
References
Inflammatory Bowel Disease-associated Cancer
Definition
Characteristics
IBD-Associated CRC
Small Bowel Adenocarcinoma in Crohn Disease
Cancer risk Associated to Immunosuppressive Therapy in IBD
References
Inflammatory Cytokines
Definition
Inflammatory Response
Definition
Infratentorial Primitive Neuroectodermal Tumor
Inherited Human Polycystic Kidney Disease
Inhibin
Definition
Inhibitor of Apoptosis Family
Definition
Inhibitor of Cyclin-Dependent Kinase
Definition:
Inhibitor of FLICE
Inhibitors
Definition
Initial Area Under the Gadolinium Contrast Agent Concentration–Time Curve
Definition
Initiation
Definition
Initiation and Promotion
Definition
Initiation Codon
Definition
Initiation Factors
Definition
Initiator Caspases
Definition
INK4a
Definition
Characteristics
Structure of INK4b/ARF/INK4a Locus and Molecular Functions of INK4s/ARF
Roles in Tumorigenesis
Roles in Senescence
Activators of the p15INK4b/ARF/p16INK4a
Ras–Raf–p38MAPK Pathway
E2F
Myc Oncogene
Suppressors of p15INK4b/ARF/p16INK4a
AML1/ETO
p53
Polycomb Proteins
Future Directions
References
Innate Immune System
Definition
Innate Immunity
Definition
Innexins
Definition
iNOS
Definition
Inosine
Definition
Inositol Lipids
Definition
Characteristics
Hydrolysis of PtdIns(4,5)P2 to Generate Second Messenger Molecules
Binding of PtdIns(4,5)P2 to Specific Proteins
Generation of PtdIns(3,4,5)P3 and Other 3-Phosphorylated Inositol Lipids and Their Binding to Specific Intracellular Targets
Clinical Relevance
References
Inositol Polyphosphates
Definition
Inositol Tetrakisphosphate
Definition
Inositol 1,4,5-trisphosphate
Definition
Inositoltrisphosphate
Definition
Insertional Mutagenesis
Definition
Insulator
Definition
Insulin
Definition
Insulin Receptor
Definition
Characteristics
Regulation
Clinical Relevance
References
Insulin Receptor Substrate Proteins
Definition
Insulin Resistance
Definition
Insulin-like Growth Factor Binding Proteins
Definition
Insulin-like Growth Factors
Definition
Characteristics
IGFs
IGF Receptors
IGFBPs
Mechanisms
Altered Expression of the IGF System Components in Tumor Cells
Syndrome of Hypoglycemia
Clinical Aspects
References
Insulinoma
Synonyms
Definition
Characteristics
Diagnosis
Differential Diagnosis
Treatment
Malignant Insulinoma
References
Integral Membrane Protein
Definition
Integrated Positron Emission Tomography/Computed Tomography
Integrin
Definition
beta3 Integrin
Definition
Integrin-Mediated Death
Integrin Signaling
Definition
Characteristics
Signaling
Growth and Differentiation
Motility and Invasion
Survival
References
Intensity-modulated Radiation Therapy
Definition
Intercellular Junctions
Definition
Interferon
Definition
Interferon-alpha
Synonyms
Definition
Characteristics
Malignant Melanoma
Pancreas Carcinoma
Renal Cell Carcinoma/Leukemia/Multiple Myeloma
Hairy Cell Leukemia
Direct Effects of IFN-alpha
Radio- and chemosensitizing Effects
Antiangiogenic Effects
Immunogenic Effects
Immunomodulation
References
Interferon Gamma
Definition
Interferons Type I
Definition
Interleukin
Definition
Interleukin-1
Definition
Interleukin-1 beta
Definition
Interleukin-2
Definition
Interleukin-4
Definition
Characteristics
Bioactivity
Clinical Relevance
IL-4 and Allergic and Inflammatory Diseases
Human Severe Combined Immunodeficiency (SCID)
References
Interleukin-6
Synonyms
Definition
Characteristics
Genes
Clinical Relevance
References
Interleukin-8
Definition
Interleukin-12
Definition
Intermediate
Definition
Intermediate Endpoint
Intermediate Junction
Internal Dose
Definition
Internalization
International Agency for Research on Cancer
Definition
Interphase Cytogenetics
Definition
Characteristics
References
Interstitial Cells of Cajal
Definition
Interstitial Space
Definition
Interstitual Microinfusion
Interstrand Cross Link
Definition
Intervention Study
Definition
Intestinal Absorption
Definition
Intestinal Permeability
Definition
Intestinal Type Adenocarcinoma
Definition
Intrabodies
Definition
Intracerebral Clysis
Intracerebral Microinfusion
Intraductal Carcinoma
Intraductal Papillary Mucinous Tumors
Intralesional Excision
Definition
Intraocular Melanoma
Intraperitoneal Chemotherapy
Definition
Intravasation
Definition
Intravesicular Instillation
Definition
Intrinsic Pathway of Apoptosis
Definition
Intrinsically Disordered Proteins
Intrinsically Unfolded Proteins
Intrinsically Unstructured Proteins
Synonyms
Definition
Characteristics
Identification of Unstructured Proteins
Unstructured Proteins and Cancer
Other Roles in Cancer Biology
References
Intron
Definition
Invadopodia
Definition
Invasion
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Invasive Ductal Carcinoma
Definition
Inverse PCR
Definition
Inversion
Ion Channels
Definition
Ionization
Definition
Ionizing Radiation
Definition
Ionizing Radiation Induced Cancer
Ionizing Radiation Therapy
Synonyms
Definition
Characteristics
References
IPL1
IPT/TIG Domain
Definition
IQGAP1 Protein
Synonyms
Definition
Characteristics
Functions
IQGAP1 and Cancer
References
IRE1
Definition
IRES
Definition
IRF1
Definition
Irinotecan
Synonyms
Definition
Characteristics
Mechanism of Action
Position of Irinotecan
Adverse Effects
Metabolism and Excretion
Dosage Individualization
Role of Genetic Screening
References
gamma-irradiation
Definition
IRS
Definition
Ischemia
Definition
ISEL
Definition
Islet Cell Tumor
Definition
Islets of Langerhans
Definition
Isochromosome
Definition
Isodose
Definition
Isoflavones
Definition
Characteristics
History
Examples
Metabolism
Mechanisms
Diseases
References
Isoform
Definition
Isografts
Definition
Isopeptide Bonds
Definition
Isoprenoid
Definition
Isoprostanes
Definition
Isothiocyanates
Definition
Isotope
Definition
ITAM
Definition
Itch
Definition
ITIM
Definition
Ixabepilone
J
J1 220/200
JAK
Definition
JAK2
Definition
Japanese Silver Apricot
Jasmonates in Cancer Therapy
Definition
Characteristics
Anticancer Activities of Jasmonates In Vitro and In Vivo
The Mechanisms of Action of Jasmonates in Cancer Cells
Biochemical Outcomes Shared by Jasmonate-Treated Plant and Animal Cells
Conclusions
References
Jaundice
Definition
Jaw Osteonecrosis
Definition
J-Domain
Definition
Jelly Belly
JFY1
JNK
JNK1
JNK2
JNK3
JNK Cascade
Definition
JNK Subfamily
Synonyms
Definition
Characteristics
References
JNK-Interacting Protein
Definition
JUN
Definition
Jun N-terminal kinase
Definition
Junctional Complex
Definition
K
Ktrans
Definition
K Cells
K Lymphocyte
KAI1
Kallikrein-related Peptidases
Kallikreins
Synonyms
Definition
Characteristics
The Kallikrein Genes
The Role of Kallikreins in Tumor Progression
Kallikreins as Diagnostic and Prognostic Markers
References
Kaplan–Meier Product Limit Estimator
Kaplan-Meier Survival Analysis
Synonyms
Definition
Characteristics
Censoring
Parametric, Semi-Parametric and Nonparametric Survival
Kaplan–Meier Product Limit Estimator
Comparing Survival Functions
References
Kaposi Sarcoma
Definition
Characteristics
Histology
Virus Involvement
Viral Strains
KSHV Latent Proteins
Neoplasms Associated with KSHV
KSVH and Immunity
Anti-Herpesviral Drugs
Treatment for KS
References
Karnofsky Performance Score
Definition
Karyoplast
Definition
Karyotype
Definition
KCNH1
KCS
Keap1
Definition
Kennedy Disease
Keratinocyte
Definition
Keratoconjunctivitis Sicca
Keratodermas
Definition
Keratosis
Definition
Ket
Kew Tree
Ki-1
Ki1 Lymphoma
Ki-67
Definition
KIAA0413
Killer Cells
Kin-Cohort Study
Definition
Kinase
Definition
In vitro Kinase Assay
Definition
Kinesin
Definition
Kinesin-5
Kinesin Spindle Protein
Kinesin-like Protein KIF11
Kinetic Parameters
Definition
Kinetochore
Definition
Kinetochore Outer Plate
Definition
Kininogen
Definition
KiSS1
Definition
Characteristics
Does KiSS1 Suppress Metastasis of Other Human Cancers?
How Does KiSS1 Suppress Metastasis?
Is KiSS1 a Marker of Metastasis?
Clinical Relevance
References
KIT
Definition
Kit/SCF-R
Kit/Stem Cell Factor Receptor in Oncogenesis
Synonyms
Definition
Characteristics
Molecular and Cellular Regulation
Clinical Relevance
Mastocytosis/Mast Cell Leukemia
Gastro-Intestinal Tumors
Acute and Chronic Myeloid Leukemias
Germ Cell Tumors
Malignant Melanoma
Other Neoplastic/Malignant Lesions
Gene Transfer, Immunotherapy, Vaccination
References
Klatskin Tumors
Synonyms
Definition
Characteristics
History and Classification
Epidemiology
Etiology and Risk Factors
Biology
Diagnosis
Treatment
Survival
References
KLK3
KLRK1
Knobloch Syndrome
Definition
Knock-Down
Definition
Knock-in
Definition
Knock-Out
Definition
Knock-out Mice
Knock-Out Mouse
Definition
Knockdown
Definition
Knudson Hypothesis
Definition
Koch’s Postulates
Synonyms
Definition
Characteristics
References
Kostmann Syndrome
Definition
Kringle Domain
Definition
KSA
KSP
KSP Mitotic Spindle Motor Protein
Synonyms
Definition
Characteristics
Regulation
Relevance to Cancer
References
Ku70
Definition
Kulchitsky Cell Carcinoma
Kunitz Trypsin Inhibitor
Definition
Kupffer Cells
Synonyms
Definition
Characteristics
Kupffer Cells and Liver Disease
Relationship of Kupffer Cells to Primary and Secondary Liver Cancers
Kupffer Cell Cancers
References
Kuzbanian
Definition
Kv10.1
L
L-PAM
Definition
L&H
Definition
L&H Cells
Definition
Label-Free Analysis
Definition
Labile Factor
Definition
Lactate
Definition
Lactate Dehydrogenase
Definition
Lactoferricin Antiangiogenesis Inhibitor
Definition
Characteristics
Clinical Perspectives
References
Lactoferrin
Definition
LAIR1
Definition
LAK
LAMB
Lamellar Phase
Definition
Lamellipodia
Definition
Laminin
Definition
Laminin-Receptor
Definition
Laminin Signaling
Definition
Characteristics
Laminin Signaling
Laminin Receptors
Integrins
Nonintegrin Receptors
67 kDa Laminin Receptor and Integrins
Dystroglycan
References
Langerhans, Islets of
Definition
Langerhans Cell
Definition
Langerhans Cell Histiocytosis
Synonyms
Definition
Characteristics
Epidemiology
Etiology
Pathophysiology
Clinical Manifestations
Pathology and Diagnosis
Prognosis
Treatment
Late Sequelae
References
Langerin
Definition
LAP
Definition
Laparoscopy
Definition
Lapatinib
Definition
Large Cell Calcifying Sertoli Cell Tumor
Definition
Large Cell Medulloblastoma
Definition
Large-Cell Undifferentiated Carcinoma
Definition
Large Granular Lymphocyte
Large Tumor Suppressor Gene
Laryngeal Carcinoma
Definition
Characteristics
Genetic Changes in Laryngeal Carcinomas
Chromosome Abnormalities in Laryngeal Carcinomas
Fluorescence in Situ Hybridization (FISH)
Molecular Genetic Findings
References
Laser
Definition
Laser Capture Microdissection
Definition
Laser Diagnostics
Definition
Characteristics
References
Laser-induced Fluorescence Diagnosis LIFD
Latent TGF-beta Binding Protein
Definition
Lateral Gene Transfer
Definition
Lats in Growth Regulation and Tumorigenesis
Synonyms
Definition
Characteristics
Clinical Relevance
References
LD
LD50
Definition
LDL
Definition
LDL Receptor
Definition
Lead Chromate
Definition
Lead Exposure
Definition
Characteristics
Sources of Lead Exposure
Biological Markers of Lead Exposure
Lead Carcinogenesis: Possible Etiologic Mechanisms
Lead Exposure and Cancer Epidemiology
References
Lead Generation
Definition
Lead Optimization
Definition
Characteristics
Physicochemical Optimization
Pharmacokinetic Optimization
Toxicological Optimization
References
Leakage Radiation
Definition
Lean Body Mass
Definition
LECAM-2
Lecithin
Definition
Lectin
Definition
Leiomymatous Harmatoma of the Kidney
Leiomyoma
Definition
Leiomyomata
Leiomyosarcoma
Definition
Lentigines
Definition
Lentiginosis
Definition
Lentiginosis polyposa Peutz
Leptomeningeal Carcinomatosis
Definition
Leptomeningeal Disease
Leptomeningeal Dissemination
Synonyms
Definition
Characteristics
Symptoms
Diagnosis
Neuroimaging
Laboratory Findings
Treatment
References
Leptomeningeal Metastasis
Leptomeningeal Seeding
Leptomeninges
Definition
Lesion on Tongue, Lip and Other Areas in the Mouth
LET
Definition
Letterer–Siwe Disease
Definition
Leucopenia
Definition
Leucovorin
Definition
Leukemia
Definition
Leukemia Diagnostics
Definition
Characteristics
Introduction
Methods Applied in Leukemia Diagnostics
Cytomorphology and Cytochemistry
Immunophenotyping
Cytogenetics
Importance of Chromosome Analysis, Indication
Material
Conventional Chromosome Analysis Using Banding Techniques
Nomenclature – ISCN Cytogenetics
Comparative Genomic Hybridization (CGH)
Fluorescence In Situ Hybridization (FISH)
Interphase FISH
Metaphase FISH
Molecular Genetics
PCR
RT-PCR
Nested PCR
Real Time PCR
Mutation Screening
Fragment Analysis (Genescan)
Sequence Analysis
Diagnostic Procedures in Leukemia
Diagnostic Workup of AML
Monitoring of Minimal Residual Disease (MRD)
Cytogenetics
Fluorescence In Situ Hybridization
Molecular Genetics
Cytomorphology
Immunophenotyping
Cytogenetics
Fluorescent In Situ Hybridization
Molecular Genetics
Cytomorphology
Immunophenotyping
Cytogenetics
Fluorescence In Situ Hybridization
Molecular Genetics
Cytomorphology
Immunophenotyping
Cytogenetics
Fluorescence in Situ Hybridization
Molecular Genetics
Cytomorphology
Immunophenotyping
Cytogenetics
Fluorescence In Situ Hybridization
Molecular Genetics
Diagnostic Algorithm in AML
Diagnostic Algorithm in ALL
Diagnostic Algorithm in CML
Diagnostic Algorithm in CLL
Diagnostic Algorithm in MDS
References
Leukemia Inhibitory Factor
Synonyms
Definition
Characteristics
LIF
LIF Receptor
LIF Over Expression and LIF Knockouts
Pleiotropic Effects of LIF
LIF and Oncogenesis
Clinical Aspects
References
Leukocyte Elastase
Leukocyte Endothelial Cell Adhesion Molecule-2
Leukocyte Functional Antigens
Definition
Leukocyte Homing
Definition
Leukocyte Interferon
Leukocytes
Definition
Leukopenia
Leukoplakia
Definition
Leukotriene Receptors
Definition
Leukotrienes
Definition
Characteristics
References
Leustatin
Lewis Antigens
Synonyms
Definition
Characteristics
Lewis Antigens in Cancer
References
Lewis Enzyme
Definition
Lewisx
Definition
Lexatumumab
Definition
LFS
Definition
LH-RH
Definition
LHRH
Definition
LHRH Agonists
Definition
LI Element
Definition
Li-Fraumeni Syndrome
Definition
Characteristics
Diagnostic Criteria
Genetics
TP53 Germline Mutations
Type and Origin of TP53 Mutations
Tumor Spectrum in TP53 Mutation Carriers
Age Distribution in Relation to Tumor Type
Gender Distribution of Patients with TP53 Germline Mutations
Functional Consequences and Phenotype of Germline Mutations
Mutation Detection Methods and Results Interpretation
References
Lichenification
Definition
Lichenoid Dermatitis
Definition
Licorice
Definition
LIF
Life Table Estimates
Ligament of Treitz
Definition
Ligands
Definition
Steel Ligand Receptor
Light-Induced Fluorescence Endoscopy
Definition
Light Tomography
LIM Domain
Definition
LIM Domain Containing Preferred Translocation Partner in Lipoma
LIMD1
Definition
LINE
Definition
LINE-1 Elements
Definition
Characteristics
Structure
Genomic Impact
Role in Human Cancer
References
Lineage
Definition
Lineage Differentiation Tumor Antigens
Definition
Lineage Restriction
Definition
Linear Accelerator
Definition
Linearly Patterned Programmed Cell Necrosis
Definition
Lingual Cancer
Linkage
Definition
Linkage Disequilibrium
Synonyms
Definition
Characteristics
Introduction to Linkage Disequilibrium
Measures of Linkage Disequilibrium
Estimation of Linkage Disequilibrium
Haplotype Blocks
Linkage Disequilibrium versus Linkage
Origins of Linkage Disequilibrium
Linkage Disequilibrium in Human Populations
Using Linkage Disequilibrium to Select Informative Markers
Utility of Linkage Disequilibrium to Genome-wide Association Studies
Other Uses of Linkage Disequilibrium in Cancer Research
References
N-Linked Glycan
Definition
O-Linked Oligosaccharide
Definition
Linoleic Acid
Definition
Characteristics
References
Lipid Mediators
Synonyms
Definition
Characteristics
References
Lipid Peroxidation
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Lipid Phosphatases
Definition
Lipid Raft
Definition
Lipid Second Messengers
Lipid Therapy
Lipogenesis
Definition
Lipoma
Definition
Lipoma Preferred Partner
Synonyms
Definition
Characteristics
LPP and Tumors
Cell Biological Characteristics of the LPP Protein
LPP as a Transcriptional Coactivator
LPP as a Smooth Muscle Marker
References
Lipomas
Lipomatous Tumors
Lipophilic
Definition
Lipophilicity
Definition
Lipoprotein
Definition
Liposarcomas
Liposomal Chemotherapy
Synonyms
Definition
Characteristics
The Magic Bullet Concept
Drug Delivery Technology
Sterically Stabilized (Stealth) Liposomes
Ligand-Targeted Stealth Liposomes
Future Perspectives for Liposomal Chemotherapy
References
Liposomes
Definition
Lipoxygenase
5-Lipoxygenase (5-LO)
Definition
Lisch Nodules
Definition
Liver
Definition
Liver Cancer
Liver Cancer – Molecular Biology
Definition
Characteristics
Epidemiology
Etiology
Role of Viral Factors
Direct Mutagenic Role
Oncogenic Potential of the HBx Transactivator
Immunopathogenesis
Chromosomal Aberrations
Tumor Suppressor Genes and Oncogenes
Oncogenic Pathways
Conclusions
References
Liver Cell Carcinoma
Liver Cirrhosis
Definition
Liver Flukes
Definition
Liver Resection
Definition
Liver Transglutaminase and Gh
Liver Transplantation
Definition
LMP2
Definition
Lob 1
Definition
Lobular Involution
Synonyms
Definition
Characteristics
Anatomy of the Human Breast
Involution
Age-Related Lobular Involution
Factors Affecting Involution
Measurement of Involution
Failure to Involute
References
Local Ablation Therapy
Local Therapy
Definition
Local Treatment
Definition
Locoregional Therapy
Synonyms
Definition
Characteristics
Transarterial Chemoembolization (TACE)
Percutaneous Ethanol Injection (PEI)
Percutaneous Acetic Acid Injection (PAI)
Radiofrequency Ablation (RFA)
Microwave Coagulation Therapy (MCT)
Comments
References
Locus
Definition
Log-Kill Hypothesis
Synonyms
Definition
Characteristics
References
LOH
Definition
LOI
Definition
Long Dispersed Nuclear Element
Definition
Long Terminal Repeat
Definition
Loss-of-Function Mutation
Definition
Loss of Heterozygosity
Definition
Lovastatin
Definition
Low Density Lipoprotein
Definition
Low Grade/Well Differentiated MEC
Low Molecular Weight G-Proteins
Low-Grade
Definition
LOX
LPP
LRF
Definition
LRP
LRP5/6
Definition
LS-80558
LTBP
Definition
LTR
Definition
Lucifer Yellow
Definition
Luciferase Reporter Gene Assays
Synonyms
Definition
Characteristics
References
Lugol Unstained Lesion
Definition
Characteristics
Carcinogenesis (Precursor of ESCC)
Multiple LULs
References
Luminal Epithelial Cells
Definition
Lunasin
Definition
Characteristics
References
Lung Cancer
Synonyms
Definition
Characteristics
Pathology
Etiology
Biology and Molecular Pathogenesis
Activation of Dominant Oncogenes
Inactivation of Tumor Suppressor Genes
Autocrine Growth Factors
Clinical Presentation
Treatment
References
Lung Carcinoma
Lung Colony Formation Assay
Definition
Lung Resistance-related Protein
Lupus Erythematosus
Definition
Luteotropic Hormone
Luteotropin
Lycopene
Definition
Lymph
Definition
Lymph Node
Definition
Lymph Node Metastases
Definition
Lymphadenopathy
Definition
Lymphangiogenesis
Synonyms
Definition
Characteristics
Molecular Regulation
Clinical Relevance
References
Lymphangioleiomyomatosis
Definition
Lymphangitic Carcinomatosis
Definition
Lymphatic Mapping
Definition
Lymphatic System
Definition
Lymphatic Vessels
Definition
Characteristics
Clinical Relevance
References
Lymphedema
Definition
Lymphedema-Distichiasis
Definition
Lymphoblastoid Cell Lines
Definition
Lymphocytes
Definition
Lymphocytic and Histiocytic Cells
Definition
Lymphoepithelioma
Lymphogenic Metastatic Spread
Definition
Lymphoid Organs
Definition
Lymphokine-Activated Killer
Definition
Lymphokine-Activated Killer Cell
Definition
Lymphokines
Definition
Lymphoma
Definition
Lymphoscintigraphy
Definition
Lymphotoxin
Definition
Lymphovascular Invasion
Definition
Lymphovenous Shunt
Definition
Lynch Syndrome
Synonyms
Definition
Characteristics
History
References
Lysolecithin
Lysophosphatidate
Definition
Lysophosphatidylcholine
Synonyms
Definition
Characteristics
Signaling Mechanisms
Clinical Aspects
References
Lysosome
Definition
Lyve-1
Definition
M
Mphi
Definition
M&B 39831
MA-3, TIS (mouse Pdcd4)
Mach
MACH-related Inducer of Toxicity
Machado-Joseph Disease
Definition
Macro- and Microminerals
Macroautophagy
Macrolide
Definition
Macrometastasis
Definition
Macropain
Definition
Macrophage Stimulating 1 Receptor
Macrophage-Stimulating Protein
Synonyms
Definition
Characteristics
Structure
Biological Activities and Targets
Cellular and Molecular Regulation
MSP Receptor Signaling
Clinical Relevance
References
Macrophages
Definition
Characteristics
References
Maculae Adherents
MAD
Definition
MAD1
MAD1L1
Mad (Mxd)
Definition
MADH4
Magic Bullet
Definition
Magicin
Magnetic Resonance Imaging
Definition
Magnetic Resonance Imaging-Guided Focused Ultrasound Surgery
Definition
Maidenhair Tree
Major Histocompatibility Antigens
Definition
Major Histocompatibility Complex
Definition
Major Histocompatibility Complex (MHC) Class I-related Chain Molecules
Major Life Event
Definition
Major Microtubule Organizing Center
Major Vault Protein
Synonyms
Definition
Characteristics
The Vault Complex
Major Vault Protein (MVP)
Drug Resistance
Prognostic Significance
References
Malignancy-Associated Changes
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Malignancy of Small Round Blue Cell Type
Malignant Adrenocortical Tumor
Malignant Endocrine Tumors
Malignant Lymphoma: Hallmarks and Concepts
Definition
Characteristics
Classification
The Molecular Genetic Basis of NHL
Antigen Receptors in NHL
Immunoglobulin Receptor of B Cells:
T Cell Receptors in Peripheral T Cell Lymphomas:
Gene Expression Profiling
Etiology
Cell Biological Features of Hodgkin Lymphoma
Basic Clinical Features of Malignant Lymphoma
References
Malignant Melanoma
Malignant Mesenchymal Nephroma of Infancy
Malignant Mesothelioma
Malignant Neoplasias Originating in Endocrine Tissues or their Target Organs
Malignant Neoplastic Changes of the Colon
Malignant Peripheral Nerve Sheath Tumor
Definition
Malignant Pleural Effusion
Definition
Malignant Progression
Definition
Malignant Salivary Gland Cancer
Malignant Tumor
Definition
Malignant Tumors of the Endocrine Glands
MALT Lymphoma
Definition
Mammalian Target of Rapamycin
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
40 kDa Mammary Gland Protein
Mammographic Breast Density and Cancer Risk
Definition
Characteristics
Effect of Mammography Screening
Benefits and Harms
Public Health Screening Recommendations
References
Mammographic Density
Definition
Characteristics
Mammographic Density and Risk of Breast Cancer
Factors Associated with Variations in Mammographic Density
Heritability of Mammographic Density
Summary and Conclusions
References
Mammotropic Hormone
Mammotropin
Mann–Whitney U-test
Definition
Mantle Cell Lymphoma
Synonyms
Definition
Characteristics
References
MAP Kinase
Definition
Characteristics
Members of the MAP Kinase Family
Structure of MAP Kinase Cascades
Signaling Via the MAP Kinase Cascades
The ERK1/2 Cascade
The p38 and JNK Cascades
The ERK5 Cascade
Regulation and Specificity Determination of MAP Kinases
Involvement of MAP Kinases in Cancer
References
Mapatumumab
Definition
MAPK
Definition
MAPK8
MAPK9
MAPK10
MAPs
MAR
Marginal Excision
Definition
Marginal Zone B-Cell Lymphomas
Definition
Characteristics
Histology
Pathogenesis
Genetics
Deregulation of NF-kappaB: The Unifying Concept for MALT Lymphomagenesis?
Clinical Features, Prognosis and Therapy
References
Marijuana
MAR-syndrome
Maspin
Definition
Characteristics
The Role of Maspin in Epithelial Pathophysiology
The Molecular Mechanisms of Maspin
References
Mass Recovery
Mass Spectrometry
Definition
Mast Cell Growth Factor
Mast Cells
Synonyms
Definition
Characteristics
MC and Tumor Growth
MC and Tumor Angiogenesis
Conclusions
References
Mast Zellen
Mastectomy
Definition
Mastocytosis
Definition
Characteristics
Diagnosis
Classification
Therapy
References
Matricellular Proteins
Definition
Matrigel
Definition
Matriptase
Definition
Matriptase: Epithin, MT-SP1, suppression of tumorigenicity 14
Matrix-Assisted Laser Desorption/Ionization
Definition
Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF)
Definition
Matrix Metalloproteinase
Matrix Metalloproteinase 2
Definition
Matrix Metalloproteinase 3
Matrix Metalloproteinase-7, -9
Definition
Matrix Metalloproteinase Inhibitor
Matrix Metalloproteinases
Synonyms
Definition
Characteristics
Domain Structure
Zymogen Activation
Inhibition
Substrate Cleavage
Control of MMP Gene Expression
Clinical Relevance
References
Matrixins
Maturation Promoting Factor
Mature B-cell Tumors
Definition
Max
Definition
Maximum Tolerable Dose
Definition
Maximum Tolerated Dose (MTD)
Definition
MCA
Definition
MCC
Definition
Mch5
MCJ
MCL
Mcl-1
Definition
Mcl Family
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
MCM/P1 Proteins
Definition
MCP-1
Definition
MCPH1
Definition
MCT-1 Oncogene
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
MCTS1
MDC
MDC1
Definition
MDM2
Definition
MDM Genes
Synonyms
Definition
Characteristics
MDM2
MDM2 and Human Tumors
MDM4
MDM4 and Human Tumors
References
MdmX
Definition
MDR
Definition
Mdr1 protein
MDS
Definition
2ME
2ME2
MEA II
Measles Virus
Definition
Mechanical Properties
Definition
Mechanical Stress
Definition
Mechanosensor
Definition
Mechanotransducer
Definition
Med28
Mediastinum
Definition
Medical Foods
Medullary Breast Carcinoma
Definition
Medullary Thyroid Carcinoma
Definition
Medulloblastoma
Synonyms
Definition
Characteristics
Clinical Significance
Medulloblastoma Stem Cells
Molecular Genetics and Biology
References
Melanin
Definition
Melanocortin Receptor
Definition
Melanocyte
Definition
Melanocyte-Stimulating Hormone
Definition
Melanocytic Nevus
Melanocytic Tumors
Synonyms
Definition
Characteristics
References
Melanocytoma
Melanoma
Synonyms
Definition
Characteristics
Genetics of Melanoma Susceptibility (Genetic Disorders Associated with Cancer Predisposition and Chromosomal Instability)
Molecular Abnormalities in Melanoma
Immunology
Rational Therapies
References
Melanoma Antigens
Synonyms
Definition
Characteristics
Background
Classification
Tumor Specific Antigens
Tumor Specific Shared Antigens (CTA)
Antigens Encoded by Genes Overexpressed in Tumor Cells
Antigens Encoded by Differentiation Genes
Clinical Implications
References
Melanoma Associated Antigens
Melanoma-Associated Retinopathy
Synonyms
Definition
Characteristics
Pathogenesis
Clinical Aspects
Diagnostic Procedure
Therapy
Prognostic Relevance
References
Melanoma Vaccines
Synonyms
Definition
Characteristics
Historical Background
Tumor Immune Defence against Transplantable Tumors in Mouse Models
Culture of Melanoma-Specific Human T Cells and Identification of Melanoma Antigens
Rational Development of Melanoma Vaccine Strategies in Animal Models
Efficacy of Melanoma Vaccines in Clinical Trials
Barriers for the Successful Implementation of Therapeutic Melanoma Vaccines
Summary and Future Perspective
References
Melanosomes
Definition
Melanotic Medulloblastoma
Definition
Melanotic Schwannoma
Definition
Melatonin
Definition
Characteristics
Melatonin Anticancer Action and Mechanisms
Nocturnal Melatonin Suppresson by Light at Night and Human Breast Cancer Risk
Clinical Cancer Trials with Melatonin
Summary and Conclusions
References
Melatonin Receptors
Definition
Melphalan
Definition
Melting Point Analysis
Definition
Membrane Fluidity
Definition
Membrane-Linked Docking Protein
Definition
Characteristics
Mechanism of Signal Transduction by MLDP
Roles of Individual MLDP Family in Normal and Cancer Cells
FRS2/SNT
Dok
Transmembrane Adaptor Proteins (TRAPs)
Gab
IRS
References
Membrane Lipid Structure
Definition
Membrane-Lipid Therapy
Synonyms
Definition
Characteristics
Heterogeneity of Membrane Lipids and Lipid Structures
Lipid-Protein Interactions in Membranes
Development
References
Membrane Permeability Transition
Definition
Membrane Potential
Definition
Membrane Transport Proteins
Membrane Transporters
Synonyms
Definition
Characteristics
General Features
Pharmacological Relevance of Membrane Transporters
Role of Membrane Transporters in Drug Resistance
References
MEN 1
MEN 2
MEN II
Mendelian Distribution
Definition
Meningeoma
Definition
Meningioma
Definition
Menopausal Symptoms After Breast Cancer Therapy
Definition
Characteristics
Introduction
Treatment Options
Synthetic Hormonal Compound
Nonhormonal Therapies
Treatment of Urogenital Atrophy and Related Symptoms
Treatment of Bone Loss
Cardiovascular Complications
Conclusion
References
Menopause
Definition
Merlin
Synonyms
Definition
Characteristics
References
Mesalazine
Definition
Mesenchymal Stem Cells
Definition
Mesenchymal Tumors
Definition
Mesenchyme
Definition
Mesenteric Fibromatosis
Mesna
Definition
Mesoblastic Nephroma
Synonyms
Definition
Characteristics
Diagnosis
Histology and Genetics
Treatment
Prognosis
References
Mesoderm
Definition
Mesothelial Cells
Definition
Mesothelin
Synonyms
Definition
Characteristics
Tissue Expression
Regulation
Function
Diagnostic Marker
Therapeutic Applications
References
Mesothelioma
Synonyms
Definition
Characteristics
Pathogenesis
Asbestos
SV40
Chromosome Changes
Tumor Suppressor Genes
Diagnosis
Clinical Approaches
References
MET
Definition
Characteristics
Cellular and Molecular Features
Clinical Relevance
References
MET, 11C-Methionine
Definition
Metaanalysis
Definition
Metabolic Activation
Definition
Metabolic Capability
Definition
Metabolic Cooperation
Definition
Metabolic Detoxification
Definition
Metabolic Polymorphisms
Definition
Metabolic Polymorphisms and Cancer Susceptibility
Definition
Characteristics
History
Important Genetic Factors
Relevance of Pharmacogenetics
Ethnic Differences
Future
References
Metabolic Regulation of Cancer During Cellular Oxygen Deprivation
Metabolic Trapping
Definition
Metabolism
Definition
Metabolite
Definition
Metal Chelating
Definition
Metalloenzymes
Definition
Metalloprotease
Definition
Metalloprotease Disintegrin Cysteine-Rich
Metalloproteases
Definition
Metallothionein Enzymes
Definition
Metanephrogenic Blastema
Definition
Metaphysis
Definition
Metaplasia
Definition
Metastasis
Synonyms
Definition
Characteristics
Mechanisms
References
Metastasis Signaling
Definition
Characteristics
The Process of Metastasis
The TGF-beta Pathway and Other Well Established Metastasis Signaling Networks
Signaling Pathways Involved in Cytoskeletal Remodeling
Adhesion Molecules and Metastasis Signaling
Perspectives and Summary
References
Metastasis Suppressor Gene
Definition
Characteristics
How are Metastasis Suppressor Genes Identified?
Clinical Relevance
References
Metastasis Suppressor KAI1/CD82
Synonyms
Definition
Characteristics
Mechanism
References
Metastatic Cancer
Metastatic Colonization
Synonyms
Definition
Characteristics
References
Metastatic Tumors
Definition
Methazolastone
Methemoglobinemia
Definition
Methotrexate
Definition
Methoxyestradiol
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
2-Methoxyestradiol
Methyl Groups
Definition
Methylation
Definition
Characteristics
Cellular and Molecular Aspects
Aberrant DNA Methylation in Cancer
Hypomethylation
Hypermethylation
References
Methylation-Controlled J Protein
Synonyms
Definition
Characteristics
References
Methylation-Specific PCR
Definition
Methylation Status
Definition
Methylator Phenotype
Definition
Metrorrhagia
Definition
Mevalonate
Definition
Mga
Definition
MGC34538
MGC126245
MGC126246
MGC126806
MGC138284
MGF
MGP-40
MGUS
Definition
MHC
Definition
MHC I or MHC II
Definition
MHC-Restricted Antigen Recognition
Definition
MHF
Definition
MIC-1
Synonyms
Definition
Characteristics
Regulation of MIC-1 Gene Expression
Serum MIC-1 Measurement as a Clinical Tool
Role of MIC-1 in Tumor Biology
References
MIC Molecules
Synonyms
Definition
Characteristics
Clinical Aspects of MIC Expression by Tumors
Clinical Aspects of Soluble MIC Molecules in Blood
Soluble MIC in Diagnosis of Cancer Disease
Soluble MIC in Staging of Cancer Disease
Soluble MIC in Cancer Prognosis and Monitoring of Cancer Disease
References
MICA, MICB
Definition
Micelles
Definition
Michaelis-Type Addition
Definition
Microadenomas
Microarray (cDNA) Technology
Synonyms
Definition
Characteristics
cDNA Microarray Construction
Hybridization with Labeled cDNA
Scanning the cDNA Microarray Using a “Reader”
Image Analysis and Generation of cDNA Microarray’Data
Analysis of Large Scale cDNA Microarray Data
Application
Clinical Relevance
References
Microautophagy
Definition
Microbes
Definition
Microbubbles
Definition
Microcell
Definition
Microcell Hybrid
Definition
Microcell--Mediated Chromosome Transfer
Definition
Characteristics
References
Microcephalin
Microcirculation
Definition
Microcytoma
Microenvironment
Microenvironmental Niche
Definition
Microfold Cells
Definition
Microglia
Definition
Micrometastasis
Definition
Characteristics
Detection Techniques
Immunocytochemistry
Molecular Techniques
EPISPOT Assay
Cellular and Molecular Biology
Clinical Relevance
Bone Marrow
Peripheral Blood
Lymph Nodes
References
Microminerals
Definition
Micronucleus
Definition
Micronucleus Assay
Definition
Characteristics
Clinical Aspects
References
Microprocessor Complex
Definition
MicroRNA
Definition
Characteristics
miRNAs and Cancer
miRNAs as Tumor Suppressors and Oncogenes
miRNA Profiling and Cancer Diagnosis
References
Microsatellite
Definition
Microsatellite Instability
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
Microsomes
Definition
Microspikes
Definition
Microtubule
Definition
Microtubule Associated Proteins
Synonyms
Definition
Characteristics
MAPs and Cancer
Cancer Predisposition
Cancer Development
Cancer Diagnosis and Prognosis
Cancer Sensitivity/Resistance to Microtubule Targeting Drugs
References
Microtubule-Associated Proteins
Definition
Microtubule Binding Proteins
Microtubule Network
Definition
Microtubule Stabilizing/Destabilizing Proteins
Microtubules
Definition
Micro-ultrasound Imaging
Midgut
Definition
Midkine
Definition
MIG-6
Migfilin
Definition
Migration
Synonyms
Definition
Characteristics
Mechanisms of Cell Migration: Rho-GTPases are Key Players
Rac
Cdc42
Rho
Summary
Acknowledgement
References
Milieu
Definition
Milky Spots
Mimetic Peptide
Definition
Min
Definition
Mind Bomb Homolog 2 (Mib-2)
Mineral Nutrients
Synonyms
Definition
Characteristics
Mineral Nutrients and Cancer
References
Mineralocorticoid
Definition
Minichromosome Maintenance
Definition
Minimal Residual Disease
Synonyms
Definition
Characteristics
Methods of Detecting MRD
Clinical Relevance
References
Minisatellite
Definition
Minodronate
Synonyms
Definition
Characteristics
Effects of Minodronate on Endothelial Cells (ECs)
Effects of Minodronate on Tumor Cells in vitro
Effects of Minodronate on Tumor Cells in vivo
References
Minodronic Acid
Minor Histocompatibility Antigens
Definition
Mismatch Repair in Genetic Instability
Definition
Characteristics
Biological Consequences
Clinical Relevance
References
Missense Mutation
Definition
Mitochondria
Definition
Mitochondria Apoptogenic Factors
Definition
Mitochondria Apoptosis Pathway
Definition
Mitochondrial DNA
Definition
Characteristics
References
Mitochondrial Intrinsic Pathway
Definition
Mitochondrial Membrane Permeabilization in Apoptosis
Synonyms
Definition
Characteristics
Mechanisms of MMP
Regulation of MMP
MMP and Cancer
Therapeutic Implications
References
Mitochondrium
Definition
Mitogen
Definition
Mitogen-Activated Protein Kinase
Definition
Mitogen-Inducible Gene 6 in Cancer
Synonyms
Definition
Characteristics
Signaling Regulation
Clinical Relevance
References
Mitogenic Carcinogen
Definition
Mitomycin C
Synonyms
Definition
Characteristics
Form
Bioreductive Activation
Enzymatic Bioreductive Activation of MMC
NQO1
NQO1 and Mitomycin C In vitro
NQO1 and Mitomycin C in Anaerobic Conditions
NQO1 and Mitomycin C In vivo
Xanthine Oxidase/Dehydrogenase
NADPH-Cytochrome C P450 Reductase
Other Reductases
Analogues of MMC
Pharmacokinetics
Clinical Use of MMC
Side Effects of MMC
References
Mitosis
Definition
Mitosis Promoting Factor
Definition
Mitotane
Definition
Mitotic Accumulation & Inhibition of Microtubule Polymerization
Definition
Mitotic Arrest-Deficient Protein’1
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Mitotic Catastrophe
Synonyms
Definition
Characteristics
Cellular and Molecular Aspects
Clinical Relevance
References
Mitotic Cell Death
Mitotic Checkpoint
Definition
Mitotic Spindle
Definition
Mixed Gliomas
Mixed Lineage Leukemia Protein
Definition
Miz-1
Definition
MJ
Definition
MK-1
MK-0683, SKI390
MLH1/3
Definition
MLL-ELL Leukemia
Definition
MLPLI
MLS/RCLS
Mlx
Definition
MM
Definition
MMAC1
Definition
MMP
Definition
MMP-3
MMPs
MNA
Definition
Mnt
Definition
Model Selection
Definition
Model Testing
Definition
Modifier Loci
Synonyms
Definition
Characteristics
Rodent Models
Humans
Mechanisms
Perspectives
References
Modular Recombinant Transporters
Modular Transporters
Synonyms
Definition
Characteristics
Objectives
Principles
Features
References
Module
Definition
Mohs Micrographic Surgery
Definition
Mole
Molecular Cancer Epidemiology
Definition
Molecular Chaperones
Definition
Characteristics
HSP90 as an Anticancer Drug Target
References
Molecular Epidemiology
Definition
Molecular Genetics
Definition
Molecular Imaging
Definition
Molecular Memory
Definition
Molecular Mimicry
Definition
Molecular Morphology
Molecular Pathology
Synonyms
Definition
Characteristics
Historical and Clinical Background
Immunohistochemistry
In Situ Hybridization
Polymerase Chain Reaction
Future Developments
References
Molecular Shape
Definition
Molecular Therapy
Definition
Characteristics
Gene Therapy
Nucleic Acid Constructs
Small Molecule Drugs
Antibody Therapy
References
Mom1
Definition
MOMP
Definition
Monoclonal Antibodies
Definition
Monoclonal Antibody Therapy
Definition
Characteristics
Antibody Structure
Monoclonal Antibody Generation
Clinically Relevant Anticancer Monoclonal Antibodies
Approved Anticancer Monoclonal Antibodies
Unmodified Monoclonal Antibodies
Immunoconjugates
Radioimmunoconjugates
Toxin Immunoconjugates
Drug Immunoconjugates
References
Monoclonal Gammopathy of Undetermined Significance
Definition
Characteristics
Epidemiology
Etiology
Pathogenesis
Diagnosis
Predictors of Progression from MGUS to MM
Distinguishing MGUS, SMM, and MM
MGUS Variants
Association of MGUS with Other Diseases
Antibody Activity of Mig and Associated Diseases
Aggregation and Deposition of Mig and Associated Diseases
Management of MGUS
References
Monocyte
Definition
Monogenic
Definition
Monokines
Definition
Monolayer Culture
Definition
Monomeric GTPases
Definition
Mononeuropathy
Definition
Monosomy
Definition
Monoubiquitination
Definition
Morpheaform
Definition
Morphogenesis
Definition
Morphogenic Differentiation
Definition
Morphological Cell Transformation
Definition
Mortality Stage
Definition
Mosaic
Definition
Mosaic Vessels
Definition
Mother Against Decapentaplegic, Drosophila, Homolog of 4
Motif
Definition
Motility
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Mouse
Mouse Double Minute 2
Definition
Mouse Double Minute Gene
Mouse Mammary Tumor Virus
Definition
Mouse Models
Synonyms
Definition
Characteristics
History
Biological Relevance
Genetically Engineered Mice
Transgenic Animals
Conditional Transgenics
Inducible Systems
Spontaneous Recombination
Genetic Susceptibility
Inbred Strains
Mapping of Susceptibility Genes
Congenics
Recombinant Inbred-Lines and Other Types of Inbred Mice
Outbred Strains
Therapeutics
Xenografts
Molecular Imaging
References
Mouse Podoplanin
MPF
MPO
Definition
MPP2
MPS1
Definition
MRE11
Definition
MRI
Definition
MRIT
mRNA
Definition
mRNA Profiling
Definition
MRP
Definition
MSC
Definition
MSH2–6
Definition
MSP
MST
Definition
MST1
MST1R
MSTS Functional Evaluation System
Definition
MTOC
mTOR
Definition
MTS1
MTT Assay
Definition
MUC1
Definition
MUC1–20
Definitions
Mucin
Definition
Mucinous Cystadenocarcinoma
Definition
Mucinous Neoplasms
Definition
Mucins
Definition
Characteristics
References
Muclin (Mouse)
Mucocellular Layer
Definition
Mucoepidermoid Cancer
Synonyms
Definition
Characteristics
Historical Data
Histological Features
Epidemiology
Etiology
Staging Parameters
Treatment
References
Mucosa Associated Lymphatic Tissue Lymphoma
Definition
Mucosal-Associated Lymphoid Tissue
Definition
Mucositis
Definition
Mullerian Inhibiting Hormone
Definition
Multi-domain Transporters
Multi-Marker Panels
Definition
Multicellular Layers
Definition
Multicellular Spheroids
Definition
Multidrug Resistance
Definition
Multidrug Resistance Proteins
Definition
Multidrug Resistance Transporters
Multidrug Transporter
Multilayered Post-Confluent Cultures
Definition
Multimeric Antibody Fragments
Multiple Cutaneous and Uterine Leiomyomatosis
Definition
Multiple Endocrine Adenopathy Type 1
Multiple Endocrine Neoplasia Type 1
Synonyms
Definition
Characteristics
Genetics
MEN1 Mutations in Hereditary Endocrine Disorders
MEN1 Mutations in Sporadic Non-MEN1 Endocrine Tumors
Function of the MEN1 Protein (Menin)
Mouse Models for MEN1
Clinical Application
Acknowledgements
References
Multiple Endocrine Neoplasia Type 2
Synonyms
Definition
Characteristics
Cellular and Molecular Disease Aspects
Clinical Aspects
References
Multiple Hamartoma Syndrome
Multiple Myeloma
Definition
Multiple Osteochondromas
Definition
Multiplex Profiling Technologies
Definition
Multipolar Spindles
Definition
Multipotent
Definition
Multipotent Stem Cells
Definition
Multistep Development
Definition
Characteristics
History
Participating Genes
Minimum Requirements for Tumor Development
Clinical Relevance
References
Multivariate Statistics
Definition
Murine Double Minute 2
Definition
Mutagen
Definition
Mutagen Sensitivity
Definition
Characteristics
Overview of Human DNA Repair System
Inter-Individual Variations in DNA Repair Capacity Within General Population
Development of Mutagen Sensitivity Assay
Heritability of Mutagen Sensitivity
High Mutagen Sensitivity is a Genetic Susceptibility Factor for Cancer Development
References
Mutagenic
Definition
Mutated in Multiple Advanced Cancers 1
Definition
Mutation
Definition
Mutation Rate
Definition
Characteristics
Summary
References
Mutator Phenotype
Definition
Characteristics
Mutations and Cancer
Chromosomal Alterations in Human Cancers
Point Mutations in Human Cancer
Rarity of Spontaneous Mutations in Normal Cells
Historical Perspective
Tumor Evolution
Implications of a Mutator Phenotype
References
mutHLS
Definition
MUTYH-Associated Colorectal Polyposis
Definition
Characteristics
Inherited Predisposition to Colorectal Cancer
Inherited Mutations in MUTYH Predispose to Colorectal Tumors
The Pathway of MAP Tumorigenesis
The Phenotype of MAP
MUTYH Mutation Spectrum
Genetic Testing and Clinical Management of MAP
References
MVP
Definition
Myalgia
Definition
MYB
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Aspects
References
Myc-associated Protein X
Definition
N-myc Downstream-Regulated Gene
Synonyms
Definition
Characteristics
References
N-myc Downstream-regulated Gene, NDRG1
MYC Family
Definition
Myc Oncogene
Definition
Characteristics
Myc Structure and Function
Post-Translational Modifications and Regulation of Myc Turnover
Other Members of the Max-Interacting Network
Effects of Myc Activation
Consequences of Myc Deregulation
Tumors Associated with Myc
Targeting Myc as an Approach to Treat Cancer
Conclusion
References
MYCL
Definition
MYCN
Definition
Mycobacterium
Definition
Mycobacterium bovis BCG
Mycoplasma
Definition
MyD88
Definition
Myeloablative Megatherapy
Synonyms
Definition
Characteristics
Therapeutic Concept
Timing of Megatherapy within a Treatment Strategy
Which Drugs Can be Used for Megatherapy?
References
Myelocytomatosis
Definition
Myelodysplasia
Definition
Myelodysplastic Syndromes
Synonyms
Definition
Characteristics
Treatment Options
References
Myelofibrosis with Myeloid Metaplasia
Myeloid
Definition
Myeloid Leukemia of Down Syndrome (DS-ML)
Myeloid Suppressor Cells
Definition
Myeloperoxidases
Definition
Myeloproliferative Disease
Definition
Myelosuppression
Definition
Characteristics
Hematopoietic Growth Factor Support
Regulation of Neutrophil Cell Death
Conclusion
References
Myocardium
Definition
MyoD
Definition
Myoepithelial Cells
Definition
Myofibroblasts
Definition
Myofibromas
Myoma
Definition
Myomectomy
Definition
Myometrium
Definition
Myopodin
Synonyms
Definition
Characteristics
Myopodin Gene Expressed in Prostate but Deleted or Down Regulated in Prostate Cancer
Myopodin Expression and Relapses of Prostate Cancer
Mechanism of Myopodin Mediated Tumor Suppression
Myopodin Expressed in Muscles
References
Myotendinous Antigen
Myrosinase
Definition
Myxoid Liposarcoma
Synonyms
Definition
Characteristics
Genetics
Etiology
Diagnostics
Treatment
Prognosis
References
Myxoid Tumors
Definition
Myxoma
Definition
MZCL
Definition
MZL
Definition
N
NAALADase
NAD(P)H-Quinone Oxidoreductase
Definition
NADPH Oxidase
Definition
Naevoid Basal Cell Carcinoma Syndrome
Definition
NAG-1
NAME
Nanometer
Definition
Nanoparticles
Definition
Nanoparticles in Diagnosis and Treatment
Synonyms
Definition
Characteristics
Types of Nanoparticles
Nanoparticles in Tumor Diagnostics
Tumor Detection
Profiling of Tumor Biomarkers
FISH
Nanoparticles in Anti-tumor Therapy
Liposomal Based Drug Delivery
Gene Delivery
References
Nanoshell
Definition
Nanotechnology
Definition
Characteristics
Nanoparticles
Nanoscale Cancer Imaging Contrast Agents
Nanoscale Cancer Therapeutics
Laboratory Nanoscale Cancer Diagnostics
Current Applications of Nanotechnology in Clinical’Medicine
References
Nano-treatment
Nano-typing
Nasopharyngeal Carcinoma
Synonyms
Definition
Characteristics
Diagnosis
Treatment
References
NAT
National Institute for Health and Clinical Excellence
Synonyms
Definition
Characteristics
The Overall Purpose of NICE
Why Was NICE Established?
What Sort of Guidance Does NICE Produce?
Why Has NICE Been Controversial?
How Does NICE Reach Its Decisions?
What Impact Has NICE Had in Oncology?
References
Native Conformation
Definition
Natural Chemoprotectants
Definition
Natural Killer Cell Activation
Synonyms
Definition
Characteristics
Cytokine Activation of NK cells
Activation of Natural NK Cytotoxicity by Tumor Cells
Activated NK Cells in Cancer Therapy
Acknowledgments
References
Natural Killer Group 2D
Natural Products
Synonyms
Definition
Characteristics
Natural Products Drug Discovery
Natural Product Anticancer Drugs
References
Natural Yellow 3
Naturally Disordered Proteins
Naturally Occurring Antibodies
Definition
Naturally Unfolded Proteins
Naturally Unstructured Proteins
NBCCS
Definition
NBS1
Definition
NBT
Definition
NCA-160
Definition
NCI 60 Cell Line Screen
Definition
NCoA3
Ndks
NDP Kinases
NDPKs
NEBD
Definition
Neck Dissection
Definition
Necrosis
Definition
Neddylation
Definition
Needle Aspiration Biopsy
Needle Biopsy
Negative Feedback Mechanism
Definition
Negative Predictive Value
Definition
Negative Resection Margins
Definition
Nek2
Definition
Characteristics
References
Nemosis
Definition
Characteristics
Possible Significance of Nemosis
References
Neoadjuvant
Definition
Neoadjuvant Chemotherapy
Neoadjuvant Therapy
Synonyms
Definition
Characteristics
Neoangiogenesis
Definition
Neobladder
Definition
Neocarcinostatin
Definition
Neocentromere
Definition
Neohormone
Definition
Neoplasia
Definition
Neoplasms with Perivascular Epithelioid Cell Differentiation
Definition
Neoplastic Cell Transformation
Definition
Neoplastic Development
Definition
Neoplastic Meningitis
Neovascularization
Definition
Nephroblastoma
Synonym
Definition
Characteristics
Genetics
Clinical Aspects
Treatment
References
NER
Definition
Nerve Growth Factor
Definition
Nested PCR
Definition
NET
Neurabin II
Definition
Neural Stem Cells
Definition
Neuro-Cardio-Facial-Cutaneous Syndromes
Definition
Neuro-Oncology: Primary CNS Tumors
Synonyms
Definition
Characteristics
Epidemiology
Classification
Clinical and Radiological Presentation
Etiology
Molecular Pathogenesis
Current Management
Future Directions
Molecular Therapy: Molecular Based Diagnostics-Prognosis-Targeted Therapy
Adjuvant Therapy: Novel Biologicals and Therapeutic Delivery
Biological Imaging
Conclusions
References
Neuroblastoma
Definition
Characteristics
References
Neurocytoma
Synonyms
Definition
Characteristics
Diagnosis
Therapy
References
Neuroectodermal Tumor
Neuroendocrine Carcinoma
Synonyms
Definition
Characteristics
Classification
Epidemiology
Natural History
Carcinoids
Neuroendocrine Tumors of the Pancreas (Islet Cell Tumors)
Diagnosis of Neuroendocrine Carcinomas
Treatment of Neuroendocrine Carcinomas
References
Neuroendocrine Cells
Definition
Neuroendocrine Gland
Definition
Neuroendocrine Tumors
Definition
Characteristics
Diagnostic Criteria for Entering the NET Category
Prognostic Classification Concepts of NETs
Genetics
NETs of the Pancreas
NETs of the Stomach and the Oesophagus
NETs of the Small Intestine, Colon and Rectum
NETs of the Lung
Carcinoid Tumors
Small Cell Lung Carcinoma
Large Cell Neuroendocrine Carcinoma
Thymic NETs
Medullary Thyroid Carcinoma (MTC)
NET (Merkel Cell Carcinoma) of the Skin
References
Neuroendocrine Tumors of the Pancreas
Neuroepithelioma
Definition
Neurofibroma
Definition
Neurofibromatosis 1
Synonyms
Definition
Characteristics
Diagnostic Criteria and Clinical Aspects
Genetics
Neurofibromin
Gene Mutations in NF1 Related Tumors
NF1 Gene Mutations in Cancer
References
Neurofibromatosis 2
Synonyms
Definition
Characteristics
Diagnostic Criteria and Clinical Aspects
Genetics
Merlin Protein
References
Neurofibromin
Definition
Neurologically Eloquent
Definition
Neuromedin
Definition
Characteristics
NMB in Human Cancer
NMU in Human Cancer
Clinical Relevance
References
Neuronectin
Neuropathy
Definition
Neuropeptide Y
Definition
Neuropeptides
Neuropilin
Definition
Neuropilin Ligand
Neurotensin
Definition
Neurotoxicity
Definition
Neurotransmitters
Definition
Neurotrophic factors
Neurotrophins
Synonyms
Definition
Characteristics
Clinical Relevance
References
Neutropenia
Synonyms
Definition
Characteristics
Hematopoiesis
Neutrophil Disorders
Neutrophil Growth Factors
References
Neutrophil
Definition
Neutrophil Elastase
Synonyms
Definition
Characteristics
NE Gene and Its Variations
NE and Cancer Development
NE and Cancer Progression and Prognosis
NE as Cancer Therapeutic Target
Possible Mechanisms of NE in Cancer Development and Progression
Carcinogen Exposure Enhancer
Apoptosis Inhibitor
Invasion and Metastasis Promoter
Cancer Promoting Gene Derepressor
NE Suppresses Granulopoiesis of Hematopoietic Cells
References
Neutrophil Granulocytes
Definition
Neutrophil Polymorphonuclear Granulocytes
Definition
Neutrophils
Definition
Nevi
Definition
Nevocellular Nevus
Nevoid Basal Cell Carcinoma Syndrome
Definition
Nevus
Definition
Nevus of Ota
Definition
Newcastle Disease Virus
Definition
NFkappaB
Definition
NF1
NF2
NF2 Gene Product
NGF
Definition
NGF Family
NHL
Definition
NHS
Definition
Nibrin
Definition
NICE
Definition
NICE Blight
Definition
Nickel Carcinogenesis
Synonyms
Definition
Characteristics
Nickel, the Chemical Element, and its Ionic Species and Chemical Compounds
Important Commercial Uses of Nickel and Nickel Compounds
Exposure of Humans to Nickel Compounds
Genotoxicity of Nickel Compounds
Nickel-Induced Cell Transformation
Nickel Carcinogenensis
Mechanisms of Nickel Carcinogenensis
References
Nickel-induced Cell Transformation
Nickel Oxide
Definition
Nickel Subsulfide (Ni3S2)
Definition
Nickel Tumorigenesis
Nicotine
Definition
Nicotine Addiction
Synonyms
Definition
Characteristics
The Nicotine Withdrawal Syndrome
Drug Tolerance
Early Onset of Addiction
References
Nicotine Dependence
Nicotine Withdrawal Syndrome
Definition
NIH-3T3 Cells
Definition
NIH3T3 Transformation Assay
Definition
Nijmegen Breakage Syndrome
Synonyms
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
Nilotinib
Synonyms
Definition
Characteristics
Implications of Nilotinib in Treatment of Imatinib-Resistant CML
Development and Preclinical Studies with Nilotinib
Nilotinib Resistance
Clinical Assessment of Nilotinib
Future Prospects
References
Nipple Construction
Definition
Nitric Oxide
Definition
Characteristics
Chemistry and Biological Synthesis of NO
Biochemical Basis of NO Action
Cancer and NO
Role of NO in Initiating Cancer
Role of NO in Cancer Cell Proliferation and Tumor’Growth
NO and Tumoricidal Activity
Action of NO on Cellular Respiration
Clinical Relevance
References
Nitric Oxide Synthases
Definition
Nitrogen-containing Bisphosphonate
Nitrogen Mustards
Definition
N-Nitrosamine
Definition
Nitrosamines
Definition
Nitrosoureas
Definition
NK
Definition
NK Cell Induction
NK Cell Stimulation
NKG2D
NKG2D Receptor
Synonyms
Definition
Characteristics
The NKG2D Receptor
NKG2D Ligands
NKG2D and Cancer Immunosurveillance
Tumor Escape
References
NM23 Metastasis Suppressor Gene
Synonyms
Definition
Characteristics
NM23-H1 and Family Members
Mechanism of Metastasis Suppression
Biochemical Activities
Binding Proteins
Downstream Gene Expression Alterations
Translational Development
References
NMP22
Definition
NMR
Definition
NNK
Definition
Nodal Involvement
Definition
NOD-SCID
Definition
Non-adaptive Immunity
Definition
Non-essential Amino Acid
Definition
Non-genotoxic Carcinogen
Definition
Non-Hodgkin Lymphoma
Definition
Non-homologous End Joining
Definition
Non-Insulin Dependent Diabetes
Definition
Non-invasive Breast Cancer
Non-ionizing Radiation
Definition
Non-Lamellar Phase
Definition
Non-myeloablative
Definition
Non-receptor Tyrosine Kinases
Definition
Non-Rhabdomyosarcoma Soft Tissue Sarcomas
Definition
Characteristics
Clinical Diagnosis and Staging
Pathology and Biology
Treatment and Outcome
Particular Histotypes
Future Issues
References
Non-small Cell Lung Cancer
Definition
Non-syntenic
Definition
Non-Viral Vector for Cancer Therapy
Definition
Characteristics
Liposomes
Polymers
Virosomes
Fusion-Liposomes
HVJ-Envelope Vector
References
Nonparametric
Definition
Nonseminomatous Germ Cell Tumor
Nonsense Mutation
Definition
Nonspecific Cross Reacting Antigen
Definition
Nonsteroidal Anti-inflammatory Drugs
Definition
Characteristics
Types of NSAIDs
Mechanism of Action
Cancer Chemoprevention
Colorectal Cancer
Breast Cancer
Prostate Cancer
Bladder Cancer
Lung Cancer
Conclusions
References
Noonan Syndrome
Definition
Nootropic
Definition
Normoxia
Definition
Norton-Simon Hypothesis
Definition
Characteristics
The Log-kill Model
Gompertzian Growth Kinetics
Norton-Simon Hypothesis
References
Notch Signaling
Definition
Notch/Jagged Signaling
Definition
Characteristics
Bi–Directional, Jagged1-Mediated Signaling
Clinical Relevance
T-Cell Leukemia
Cervical Carcinoma
B-Cell Leukemia
Mammary Carcinoma
Prostate Carcinoma
Feline Leukemia Virus (FeLV) Induced T-Cell Leukemia
Cross-Talk Between Signaling Pathways
Notch as a Potential Therapeutic Target
References
NPM
Definition
NPM–ALK
Definition
NQO1
Definition
4-NQO
Definition
NR1C
NR3C4
Nrf2
Definition
NSC-638850
NSC-684766
NSC-710428
NSC-312887
NSC-362856
NSC-10514-F
NSCLC
Definition
Nuclear Atypia
Definition
Nuclear Envelope Breakdown
Definition
Nuclear Export Signal
Definition
Nuclear Factor-kappaB
Definition
Characteristics
Regulation
Clinical Relevance
References
Nuclear Hormone Receptors
Definition
Nuclear Imaging
Definition
Nuclear Localization Signal
Definition
Nuclear Magnetic Resonance
Definition
Nuclear Magnetic Resonance Spectroscopy
Definition
Nuclear Pore Complex
Definition
Nuclear Receptor
Definition
Nuclear Receptor Coactivator 3
Nuclear Translocation
Definition
Nucleolin
Definition
Characteristics
Regulation of Nucleolin Function as a Phosphoprotein
Nucleolin Function of Cell Cycle and Ribosomal Biogenesis
The Role for Nucleolin in Cancer
Role of Nucleolin in B-cell Lymphomas
Nucleolin’s Interaction with Cellular Protein, p53, and Rb
Nucleolin’s Interaction with Other Factors
References
Nucleolus
Definition
Nucleophile
Definition
Nucleoporin
Definition
Characteristics
The Nucleocytoplasmic Transport
Nucleoporins
Nucleoporins and Cancer
References
Nucleoside Analogs
Definition
Nucleoside Diphosphate Kinases
Nucleoside Transporters
Definition
Nucleosomal DNA Fragments
Nucleosome Remodeling
Nucleosomes
Definition
Characteristics
Structure and Function of Nucleosomes
Origin of Circulating Nucleosomes
Metabolism of Circulating Nucleosomes
Relevance of Circulating Nucleosomes
Clinical Aspects of Circulating Nucleosomes in Blood
Circulating Nucleosomes in Noncancerous Diseases
Circulating Nucleosomes in Diagnosis and Staging of Cancer Disease
Circulating Nucleosomes in Prognosis of Cancer Disease
Circulating Nucleosomes in Therapy Monitoring of Cancer Disease
References
Nucleotide Base
Definition
Nucleotide Excision Repair
Definition
Characteristics
Cellular Regulation
Global Genome Repair
Transcription-Coupled Repair
Excision and Gap Filling
Clinical Relevance
References
Nude Mice
Definition
NUP98-HOXA9 Fusion
Definition
Characteristics
Mouse Models of Leukemogenesis
Human Models of NUP98-HOXA9 Leukemogenesis
Proposed Mechanism of Leukemic Transformation by the NUP98-NUP98 Fusion
Aberrant Transcriptional Activity
Stabilization of HOXA9 Protein Expression
Depletion of NUP98 from the NPC in Cells Expressing NUP98-HOXA9
References
NUPR1
Nur77
Definition
Nutraceuticals
Synonyms
Definition
Characteristics
Nutraceuticals and Cancer
References
Nutrition Assessment
Definition
Nutrition Screening
Definition
Nutrition Status
Definition
Characteristics
Mechanisms
Assessment of Nutrition Status
Nutrition Intervention
Benefit of Maintenance of Nutrition Status
References
NWTSG
Definition
O
O/E
O6-Alkylguanine-Alkyltransferase
Definition
Oat Cell Carcinoma
Oat Cell Lung Cancer
Definition
Obesity
Definition
Obesity and Cancer Risk
Definition
Characteristics
Trends in Obesity
Obesity and Cancer Risk
Obesity-Related Cancers
Cancers Likely Related to Obesity
Other Cancers
Mechanisms Linking Obesity to Cancer Risk
References
Observational Study
Definition
Occult Cancer
OCP
Definition
Octreotide
Definition
Oculodermal Melanocytosis
Definition
ODC
Definition
Odontoblasts
Definition
Odynophagia
Definition
8-OHdG
Definition
Okadaic Acid
Definition
OKT3
Definition
Oleanolic Acid
Definition
Olefins
Definition
Olf
Olfactory Neuronal Transcription Factor
Olfactory/Early B-cell Factors
Oligoastrocytomas
Synonyms
Definition
Characteristics
References
Oligodendrocyte
Definition
Oligodendroglioma
Definition
Characteristics
History
Epidemiology
Clinical Presentation
Radiologic Appearance
Pathologic Features
Tumor Grading
Mixed Gliomas
Genetics
Therapy
References
Oligomerization Domain
Definition
Oligonucleotide
Definition
Oligosaccharides
Definition
Ollier Disease
Definition
OM
Definition
Omega-3 Fatty Acids
Definition
Omental Immune Aggregates
Synonyms
Definition
Characteristics
Structure and Cellular Composition
Vascularization
Function
Tumor Cell Adherence and Metastases
References
Omentum
Definition
Omentum-associated Lymphoid Tissue
Omeprazole
Definition
Oncoantigen
Definition
Oncocyte
Definition
Oncodevelopmental Proteins
Oncofetal Antigen
Definition
Characteristics
Alpha-Fetoprotein: Role as an Oncofetal Antigen
Carcinoembryonic Antigen: Role as an Oncofetal Antigen
5T4 Oncofetal Antigen
References
Oncofetal Antigens
Oncogene
Synonyms
Definition
Characteristics
Oncogene Cooperation
References
Oncogene Addiction
Synonyms
Definition
Characteristics
Multistage Carcinogenesis and Oncogene Addiction
Evidence for Oncogene Addiction
Mechanisms of Oncogene Addiction
Future Directions and Clinical Applications
Identification of the Critical Oncogene or “Achilles’ Heel” in Specific Human Cancers
Combination Therapy
Conclusion
References
Oncogene-induced Senescence
Definition
Oncogene Transduction
Oncogenic Viruses
Definition
Oncologic Surgical Pathology
Oncolytic Adenovirus
Synonyms
Definition
Characteristics
General Description
Mechanism
Clinical Applications
Future Directions
References
Oncolytic Therapy with Viruses
Oncolytic Virotherapy
Synonyms
Definition
Characteristics
Viruses as Therapeutics: Clinical Trials of Oncolysis
Targeting Viruses to Tumor Cells
“Armed” Oncolytic Viruses
Perspectives
References
Oncolytic Virus
Definition
Oncolytic Virus
Synonyms
Definition
Characteristics
Selectivity and Cancer-Targeting Mechanisms
Efficacy and Anti-Cancer Mechanisms
Virus Species
References
Onconase
Definition
Oncopeptidomics
Definition
Characteristics
Peptides
Peptide Biomarker
Peptide Biomarker Discovery
Challenges and Limitations in Oncopeptidomics
Conclusion
References
Oncoplastic Surgery
Definition
Characteristics
Historical Background
Clinical Impact of Oncoplastic Surgery
Summary
References
Oncoprotein 18
Definition
Oncostatin M
Synonyms
Definition
Characteristics
Oncostatin M Protein Structure
Oncostatin M Ligand-Receptor Interactions
Oncostatin M Signaling
Clinical Relevance of Oncostatin M in Cancer
References
Oncostatin M Precursor
ONYX Vector
Definition
Oocyte
Definition
Open Biopsy
Open Reading Frame
Definition
Opportunistic Infections
Definition
Opsonin
Definition
Opsonization
Definition
Opsonize
Definition
OptiBerry
Definition
Optic Glioma
Definition
Optical Mammography
Synonyms
Characteristics
Description
Application
References
Oral Cancer
Synonyms
Definition
Characteristics
Etiology
Progression
Genetics
Treatment
References
Oral Squamous Cell Carcinoma
Synonyms
Definition
Characteristics
Epidemiology
Etiology
Genetics
Premalignancy
Clinical Features
Pathology
Treatment and Management
Future Directions
References
Orchiectomy
Definition
ORG 2766
Definition
Organ Cultures
Definition
Organotypic Cultures
Definition
Origin of Replication
Definition
Origin Replication Complex
Definition
Orlistat
Definition
Ornithine Cycle
Definition
Ornithine Decarboxylase
Definition
Ornithine Transcarbamylase
Definition
Orphan GPCR
Definition
Orphan Nuclear Receptors
Synonyms
Definition
Characteristics
Mechanism
Clinical Aspects
References
Orthologue
Definition
Orthotopic
Definition
Orthotopic Model
Definition
OSF-1
OSM
Osmotic Pump
Definition
Osteoblast
Definition
Osteoblast Specific Factor
Osteoblast-specific Factor-2
Osteoblastic Bone Disease
Osteoblastic Bone Lesion
Definition
Osteoblastic Metastasis
Definition
Osteochondroma
Definition
Osteochondromyxoma
Definition
Osteoclast
Definition
Osteogenic Sarcoma
Osteolysis
Definition
Osteolytic Bone Disease
Osteolytic Metastasis
Definition
Osteoma
Definition
Osteomimicry
Definition
Osteonectin
Definition
Osteopetrosis
Definition
Osteopontin
Synonyms
Definition
Characteristics
OPN Gene Structure and Regulation of Gene Expression
OPN Protein Structure and Interaction with Other Proteins
Functions of OPN in the Context of Cancer
OPN-Mediated Cell Adhesion
OPN-Mediated Cell Migration and Invasion
OPN-Mediated Cell Survival/Resistance to Apoptosis
OPN and Angiogenesis
OPN and Metastasis
OPN Expression in Human Tumors and Prognostic Significance
References
Osteoporosis
Definition
Osteoprotegerin
Definition
Osteosarcoma
Synonyms
Definition
Characteristics
Epidemiology
Clinical Course
Treatment
Metastases
Recurrence
Genetics
Future
References
Osteosynthesis
Definition
Ototoxicity
Definition
Outer Edge of the Tumor Mass
Definition
Ovarian Ablation
Definition
Ovarian Adenocarcinomas
Definition
Ovarian Cancer
Definition
Characteristics
References
Ovarian Function Suppression
Definition
Ovarian Steroid Hormones
Definition
Ovarian Stroma
Definition
Ovarian Surface Epithelium
Definition
Ovarian Teratoma
Definition
Ovarian Tumors During Childhood and Adolescence
Synonyms
Definition
Characteristics
Epidemiology
Histology and Biology
Clinical Diagnosis
Surgical Therapy
Adjuvant Therapy
References
Overexpression
Definition
Ovulation
Definition
Oxaliplatin
Definition
Oxidation
Definition
Oxidative DNA Damage
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Oxidative Metabolism
Definition
Oxidative Phosphorylation
Definition
Oxidative Stress
Definition
Characteristics
Oxidative Stress is Involved in Oncogenesis
Increased Oxidative Stress in Cancer Cells
Therapeutic Perspectives of Oxidative Stress Modulation
References
Oxidized
Definition
Oxidized Phospholipids
Definition
Oxidoreductase
Definition
8-Oxoguanine
Definition
Oxygen Free Radicals
Definition
Oxygen Partial Pressure Distribution in Tumor
Oxygen Tension Distribution in Tumor
Oxygenation of Tumors
Synonyms
Definition
Characteristics
Pathomechanisms of Tumor Hypoxia
Methods of Measurement
Clinical Relevance
Tumor Oxygenation as a Prognostic Parameter
Modulation of Tumor Oxygenation
References
Oxygenation Status and Tumor Oxygen Level
P
P6 Protocol
Definition
p8
p8 Protein
Synonyms
Definition
Characteristics
Tumor Establishment and Progression
p8 and Cell Cycle Regulation
p8 and Apoptosis
Conclusion
References
p14ARF
Definition
p16
p16INK4
p16INK4A
p19ARF
Definition
p21 (Waf1/Cip1/Sdi1)
Synomyms
Definition
Characteristics
Cell Cycle Inhibition by p21
Positive Regulation of Proliferation by p21
Binding of p21 to Target Proteins
Regulation of p21 Expression and Activity
Role of p21 in p53 Pathway
Role of p21 in Differentiation and Senescence
Role of p21 in Apoptosis
Tumor-Suppressing Function of p21
Clinical Relevance
References
p28
p40AIS
p51
p53
Definition
p53 Family
Synonyms
Definition
Characteristics
Molecular Structure and Function
Roles in Development
Role in Cancer: Tumor Suppressor or Oncogene?
Clinical Relevance p63 and p73-Prognosis and Chemosensitivity
Concluding Remarks
References
p63 – TP63
p73
Definition
p73 – TP73
p94
p185neu
p300
Definition
p300/CBP-interacting Protein
p/CIP
P-glycoprotein
Synonyms
Definition
Characteristics
Expression
Cellular and Molecular Regulation
Clinical Relevance
References
PAC
Definition
PACE
Paclitaxel
Definition
Characteristics
Mechanism of Action
Mechanism of Resistance
Pharmacokinetics
References
Paget Disease
Definition
PAH
Definition
Paired Basic Amino Acid Cleaving Enzyme
PAK1
Definition
PALB2
Definition
Palliative
Definition
Palliative Care
Palliative Therapy
Definition
Characteristics
Palliative Radiotherapy
Palliative Chemotherapy
Hormonal Therapy
Conclusion
References
Palmitoylated
Definition
PAMPA
Definition
Pancreas
Definition
Pancreas Cancer, Clinical Oncology
Definition
Characteristics
Anatomy
Etiology (Cause of the Disease)
Pathology
Symptoms
Making the Diagnosis
Staging of the Disease
Prognosis
Treatment
Familial Pancreatic Cancer
References
Pancreatic Cancer, Basic and Clinical Parameters
Definition
Characteristics
Pathology
Staging
Genetics
Cytogenetics
Oncogenes
Tumor Suppressor Genes
Epigenetic Changes
Hereditary Pancreatic Cancer
Diagnosis of Pancreatic Cancer
Abdominal Ultrasound
Computed Tomography (CT)
Magnetic Resonance Imaging (MRI)
Endoscopic Retrograde Cholangiopancreatography (ERCP)
Therapy of Pancreatic Cancer
References
Pancreatic Cancer: Molecular Targets for Therapy
Definition
Characteristics
Oncogenes
K-Ras Oncogene
Signaling Pathways of Ras
Raf-MAPK
Phosphoinositide 3-Kinase (PI3K) Pathway
Nuclear Factor kappaB
Ras Family GTPases
Tumor Suppressor Genes
CDKN2A/INK4A/p16
SMAD4 and TGF-beta
p53
Growth Factors
Epidermal Growth Factor Receptor (EGFR)
Vascular Endothelial Growth Factor Receptor (VEGFR)
Cytoplasmic Tyrosine Kinases
Matrix Metalloproteinases
References
Pancreatic Cancer Stem Cells
Definition
Characteristics
References
Pancreatic Ductal Adenocarcinoma
Definition
Pancreatic Islet Cells
Definition
Panitumamab
Definition
Pannexins
Definition
Characteristics
References
Panzem
PAP Smear
Definition
Papain
Definition
Papanicolaou Test
Definition
Papillary Carcinoma
Papillary Carcinoma, Oncocytic Variant
Definition
Papillary Thyroid Carcinoma
Definition
Papilloma
Definition
PAR
Definition
PAR1
PAR1
PAR2
PAR3
PAR4
Paracentesis
Definition
Paracetamol
Definition
Paracrine
Definition
Paracrine Stimulation
Definition
Paraesthesia
Definition
Parallel Gene Expression Analysis
Paralogue
Definition
Parametric
Definition
Paraneoplastic Neuropathy
Definition
Paraneoplastic Syndromes
Definition
Parathyroid Glands
Definition
Parathyroid Hormone-Related Protein
Synonyms
Definition
Characteristics
Protein Structure
Regulation of PTHrP Expression
Normal Functions
PTHrP and Cancer
References
Paresthesia
Definition
Parity
Definition
Parkinson Disease
Definition
Parosteal Lipoma
Definition
PARP
Definition
PARP Inhibitors
Definition
Particle-induced Cancer
Definition
Introduction
Particle Size and Form
Deposition and Clearance of Particles in the Lungs
Mechanisms
References
Particulate Matter
Definition
Parvovirus
Definition
Passive Cell Death
Definition
Passive Immunity
Definition
Passive Targeting
Definition
Patch-Clamp Technique
Definition
Patched
Definition
Pathogen-Associated Molecular Pattern
Definition
Pathogenesis
Definition
Pathological Tumor Cell-Platelet Interaction
Pathology
Synonyms
Definition
Characteristics
Pathologic Factors Involved in the Prognostication of Human Neoplasms
Techniques in Diagnostic Pathology
References
Pathway Addiction
Patient Generated Subjective Global Assessment
Definition
PAX
Definition
PAX5
Definition
Paxillin
Definition
PBPC
Definition
PBX
Definition
PCNA
Definition
PCP
Definition
PCR
Definition
PCSK3
PCT
Definition
PD-ECGF
PDCD4/Pdcd4
PDD
Definition
PDF
PDGF
Definition
PDGFR
Definition
PDK1
Definition
PDMP
Definition
PDZ Domain
Definition
PDZ Ligand
Definition
PEA3
Definition
PEBP2αB
PEComas
Definition
PEG
Definition
Pegylated Interferons
Definition
Pegylation
Definition
Pemphigus
Definition
Penetrance
Definition
Pentakisphosphate
Definition
Characteristics
Inositol Phosphates Family
Inositol Pentakisphosphate (IP5)
IP5 Intracellular Functions
IP5 Anti-Cancer Properties
Mechanism of Action of IP5
Clinical Perspective of IP5
References
PEP Syndrome
Definition
Peptide
Definition
Peptide Vaccines for Cancer
Synonyms
Definition
Characteristics
Principles of Antitumor Immunity
Tumor Antigens for T Lymphocytes
Selection of Peptides for Vaccination
Immunization Strategies Using Synthetic Peptides
Remaining Challenges for Developing Effective Antitumor Peptide Vaccines
References
Peptidomimetic
Definition
Perforin
Definition
Performance Status
Definition
(Peri-) Hilar Cholangiocarcinoma
Pericardium
Definition
Pericellular Matrix
Definition
Pericyte
Definition
Periodontium
Definition
Periostin
Synonyms
Definition
Characteristics
References
Peripheral Lymph Node Addressin Molecule
Definition
Peripheral Lymphoid Organs
Definition
Peripheral Membrane Proteins
Definition
Peripheral Nervous System
Definition
Peripheral Neurofibromatosis
Definition
Peripheral Neuropathy
Synonyms
Definition
Characteristics
Mononeuropathies and Plexopathies
Paraneoplastic Neuropathies
Toxic, Treatment-Related Neuropathies
References
Peripheral Primitive Neuroectodermal Tumor
Peritoneal Carcinomatosis
Peritoneal Debulking Surgery
Definition
Peritoneal Dissemination
Definition
Peritoneal Malignancy
Peritoneal Metastasis/Dissemination
Peritoneal Mucinous Carcinoma
Definition
Peritoneal Tumor
Peritonectomy
Definition
Peritoneovenous Shunt
Definition
Peritoneum
Definition
Peritoneum as the First Line of Defense
Definition
PERK
Definition
Perlman Syndrome
Definition
Permeases (for Import Systems)
Peroxisome
Definition
Peroxisome Proliferator-Activated Receptor
Synonyms
Definition
Characteristics
PPARα
PPARbeta/bdelta (NUC1, FAAR)
PPARgamma
References
Peroxisome Proliferator-Activated Receptors
Definition
Personalized Cancer Medicine
Synonyms
Definition
Characteristics
Why is Personalized Medicine Important in Cancer?
To what Extent is Cancer Medicine Already Personalized?
The Future of Personalized Medicine in Cancer
The Challenges for Achieving Personalized Medicine
Summary
References
Personalized Medicine
Definition
Pertussis Toxin
Definition
PEST Sequence
Definition
PET
Definition
PET/CT, Integrated Positron Emission Tomography/Computed Tomography
Definition
Petechiae
Definition
Peutz-Jeghers-Syndrome
Synonyms
Definition
Characteristics
Lentiginosis (Pigment Spots)
Hamartomatous Polyposis
Increased Risk for Malignant Tumors
Pathogenesis
Therapy
Screening Recommendations
References
Peutz-Touraine-Syndrome
Peyer Patches
Definition
pgp-1
PH Domain
Definition
Phaeochromocytoma
Definition
Phage
Definition
Phage Display
Synonyms
Definition
Characteristics
Development of Therapeutic and Imaging Agents for’Cancer
Identification Cancer-Specific Antigen, Interacting Partners and Immune Response
References
Phagemid
Definition
Phagocyte
Definition
Phagocytic Glycoprotein-1
Phagocytosis
Definition
Phakomatoses
Definition
Pharmacodynamics
Definition
Pharmacogenetics
Definition
Pharmacogenomics in Multidrug Resistance
Definition
Characteristics
Single Nucleotide Polymorphism (SNP)
ABC Transporters
ABCB1 (P-glycoprotein/MDR1)
ABCC1 (MRP1/GS-X pump) and ABCC2 (MRP2/cMOAT)
ABCG2 (BCRP/MXR1/ABCP)
Perspectives
References
Pharmacogenotype
Definition
Pharmacokinetic Profile
Definition
Pharmacokinetics
Definition
Pharmacokinetics and Pharmacodynamics in Drug Development
Definition
Pharmacokinetics
Pharmacodynamics
Characteristics
Pharmacokinetics
Pharmacodynamics
Demonstrating the PK-PK-Clinical Relationship
Conclusions
References
Pharmacophore
Definition
Characteristics
References
Pharmafoods
Phase I and II Clinical Trials
Definition
Phase 1 Enzymes
Definition
Phase I Metabolism
Definition
Phase II Biotransformation Enzymes
Definition
Phase 2 Detoxification Enzymes
Definition
Phase 2 Drug-Metabolizing Enzymes
Definition
Phase 2 Enzymes
Synonyms
Definition
Characteristics
Regulation
References
Phase II Metabolism
Definition
Phase 2 Proteins
Definition
Phenomics
Definition
Phenotype
Definition
Phenotype-Orientated Screens
Definition
Phenylalanine Mustard
Definition
Phenylalanine Nitrogen Mustard
Definition
Phenylaminopyrimidine
Definition
Pheocromocytoma
Definition
Philadelphia Chromosome
Definition
Phlegm Dampness
Definition
Phorbol Ester
Definition
Phorbol 12-Myristate 13-Acetate
Definition
Phosphatase and Tensin Homolog Deleted on Chromosome 10
Definition
Phosphatase
Definition
Phosphatidic Acid
Definition
Phosphatidyl Inositol 3-Kinase
Definition
Phosphatidylinositol-3,4,5-trisphosphate
Definition
Phosphatidylinositol 3-kinase
Phosphatidylinositol Lipids
Definition
Phosphatidylserine
Definition
Phosphodiesterase
Definition
Phosphoinositide-Dependent Kinase-1
Definition
Phosphoinositide 3-kinase
Phosphoinositides
Definition
Phospholipase
Definition
Phospholipase A1
Definition
Phospholipase A2
Definition
Characteristics
Function
Regulation
Cancer Relevance
References
Phospholipase C
Definition
Phospholipase D
Definition
Phospholipid Bilayer
Definition
Phospholipids
Definition
Phosphoprotein Enriched in Diabetes/Phosphoprotein Enriched in Astrocytes-15kDa
Definition
Phosphorylation
Definition
Photoactivation
Definition
Photocarcinogenesis
Synonyms
Definition
Characteristics
Ultraviolet Radiation and Skin Cancer
Ultraviolet Radiation-induced Skin Cancer or Photocarcinogenesis
Oxidative Stress and Photocarcinogenesis
DNA Damage and Photocarcinogenesis
p53 and Photocarcinogenesis
Inflammation, Immunosuppresion and Photocarcinogenesis
Defects in Signaling Pathways and Photocarcinogenesis
Conclusions and Recommendations
References
Photochemical Reaction Type-I
Definition
Photochemical Reaction Type-II
Definition
Photochemoprevention
Definition
Characteristics
References
Photodamage
Definition
Photodynamic Diagnostic
Definition
Photodynamic Laser Therapy
Photodynamic Therapy
Synonyms
Definition
Characteristics
Historical Perspective
Principle of PDT
Available Photosensitizers
Principles of Clinical Application
Molecular Mechanisms
References
Photodynamic Tumor Therapy
Photofrin
Definition
Photolithography
Definition
6,4-Photoproduct
Definition
Photosensitivity
Definition
Photosensitizer
Definition
Photothermal Ablation
Definition
Phthalocyanines
Definition
Phytoalexin
Definition
Phyto-Cannabinoids
Phytochemicals in Cancer Prevention
Synonyms
Definition
Characteristics
Cancer Chemopreventive Mechanisms
References
Phytoestrogens
Definition
Characteristics
Potential Benefits of Phytoestrogens
Potential Drawbacks of Phytoestrogens
References
PIAS
Definition
PIBIDS
Definition
PI3-K
Definition
PI3K Signaling
Synonyms
Definition
Characteristics
PI3K Classification and Signaling Pathways
Class IA PI3K
Class IB PI3K
Class II PI3K
Class III PI3Ks
Class I PI3Ks
Class II PI3Ks
Class III PI3Ks
PI3K Signaling Pathways
Negative Regulation of PI3K Signaling Pathways
Main Phenotypes Induced by PI3K Signaling Pathways
PI3K Signaling and Cell Growth
PI3K Signaling, Tumorigenesis, and Cancers
PI3K, Insulin Signaling, and Diabetes
Future Directions
References
PIK3CA Oncogene
Synonyms
Definition
Characteristics
Genetics
Clinical Relevance
References
PI3-Kinase
PIM-1
Definition
PIN
Definition
Pineal Gland
Definition
p16INK4A
Definition
Pinocytosis
PI-PLC
Definition
Pirarubicin
Definition
Pituitary Tumor-Transforming Gene 1
PJS
PKA
Definition
PKB
Definition
PKC
Definition
PL74
PLA2
Definition
PLAB
Placebo
Definition
Placenta Growth Factor
Synonyms
Definition
Characteristics
Clinical Relevance
References
Placental-derived Growth Factor
Definition
Placental Growth Factor
Placental Site Trophoblastic Tumor
Synonyms
Definition
Characteristics
Clinical Features
Pathological Features
Molecular Etiology
References
Plakin Family
Definition
Plakoglobin
Definition
Plakophilin
Definition
Plant-derived Agents
Plaques
Definition
Plasma Cell Neoplasm
Plasma Cells
Definition
Plasma Membrane
Definition
Plasma Thromboplastin Antecedent
Definition
Plasmacytoma
Synonyms
Definition
Characteristics
References
Plasmalemma
Definition
Plasmamembrane Microdomains
Definition
Plasmin
Definition
Plasminogen Activating System
Definition
Characteristics
The Plasminogen Activating System in Cancer Progression
Clinical Significance of PAS Components Expression in’Cancer
PAS as Target for Anticancer Therapy
References
Plasminogen-Related Growth Factors
Definition
Plasticity
Definition
Platelet
Definition
Platelet-Activating-Factor
Definition
Platelet-derived Endothelial Cell Growth Factor
Platelet-Derived Growth Factor
Definition
Characteristics
Genes
Bioactivity
Clinical Relevance
References
Platelet Derived Growth Factor Receptor
Definition
Platinating Agents
Platinum Antitumor Agents
Platinum Antitumor Compounds
Platinum Complexes
Synonyms
Definition
Characteristics
Mode of Action
Bioactivation
Formation of Platinum-DNA Adducts
Cellular Response
Mechanisms of Resistance
Reduced Accumulation
Increased Inactivation
Increased Adduct Tolerance and Failure of Apoptotic Pathways
Increased Repair
Approved Platinum Complexes
Cisplatin
Carboplatin
Oxaliplatin
Nedaplatin
Lobaplatin
Heptaplatin
New platinum Complexes Under Development
Platinum(IV) Complexes
Sterically Hindered Platinum Complexes
Multinuclear Platinum Complexes
Platinum Complexes with Bioreactive Ligands
References
Platinum Drugs
Platinum-Refractory Testicular Germ Cell Tumors
Synonyms
Definition
Characteristics
Mechanisms of Platinum Resistance
Treatment of Patients with Cisplatin-Refractory GCTs
Drugs with No or Minor Activity in Refractory GCTs (Table 1)
Active Agents (Table 2)
Salvage Surgery
References
Platyfish-Swordtail Melanoma
Pleckstrin Homology Domains
Definition
Pleiotrophin
Synonyms
Definition
Characteristics
References
Pleiotropy
Definition
Pleura
Definition
Pleural Biopsy
Definition
Pleural Effusion
Synonyms
Definition
Characteristics
Clinical Manifestations and Diagnosis
Thoracentesis
Treatment
Therapeutic Thoracentesis
Chest Tube Drainage
Pleurodesis
Mechanical Pleurodesis
Other Treatment Options
References
Pleurectomy
Definition
Pleurodesis
Definition
Pleuroperitoneal Shunting
Definition
Plexiform Neurofibroma
Definition
Plexin Ligand
Plexins
Synonyms
Definition
Characteristics
Plexin Function
Plexins in Tumor Biology
Plexin D1
B-Plexins
References
Plexopathy
Definition
PlGF
PLK
Definition
Ploidy
Definition
PLP
Pluripotency
Definition
Pluripotent
Definition
Pluripotent Stem Cells
Definition
PLXN
PMA
Definition
PML
Definition
PML Bodies
Definition
PML Nuclear Bodies
Definition
PML-RARalpha
Definition
PMS1/2
Definition
PNAd
Definition
PNET
Definition
Pneumothorax
Definition
Podophyllotoxins
Definition
Podoplanin
Synonyms
Definition
Characteristics
Podoplanin Expression in Human Tumors
Regulation
Podoplanin and Tumor Invasion
Podoplanin and Metastasis
Podoplanin as a Marker for Tumor-Associated Lymphatic Vessels
Conclusions
References
POEMS Syndrome
Definition
Point Mutation
Definition
Polo-Like Kinase
Definition
Poly (ADP-Ribose) Polymerase
Definition
Poly(ADP-Ribosyl)ation
Definition
Characteristics
Catalytic Function of PARP-1 and Life Cycle of Poly (ADP-Ribose)
Molecular Functions Related with Regulation of DNA Strand Breaks and of DNA Repair
Molecular Functions Related with the Maintenance of Genomic Stability
Molecular Functions Related with DNA Replication
Molecular Functions Related with Gene Expression
Molecular Functions Related with Energy Metabolism and Mitochondrial Changes
Cellular Functions
Clinical Relevance
Genetic Cancer Risk Assessment
Therapy
References
Poly-Drug Chemotherapy
Definition
Polyadenylation
Definition
Polyamines
Definition
Polyaromatic Compounds
Polyaromatic Hydrocarbons
Definition
Polychlorinated Biphenyls
Definition
Polycomb
Definition
Polycomb Group
Definition
Characteristics
PcG Protein Complexes
PcG Proteins and Stem Cell Maintenance
PcG Proteins in Human Malignancies and Their Clinical Relevance
References
PolyComb Group Genes
Definition
Polycyclic Aromatic Hydrocarbons
Synonyms
Definition
Characteristics
Anthropogenic Origin and Carcinogenicity
Molecular Mode of Action
References
Polycystic Kidney Disease
Synonyms
Definition
Characteristics
Clinical Features
ADPKD
ARPKD
Molecular Basis
ADPKD
ARPKD
Cilia and PKD
Animal Models
Therapy and Perspective
References
Polycythemia
Synonyms
Definition
Characteristics
References
Polycythemia Vera
Definition
Polygenic
Definition
Polygenic Diseases
Definition
Polymers
Definition
Polymorphism
Definition
Polymorphonuclear Leukocyte Elastase
Polyneuropathy
Definition
Polypeptide
Definition
Polyphenols
Definition
Characteristics
Cellular and Molecular Studies
Clinical Studies
References
Polyubiquitination
Definition
Polyunsaturated Fatty Acid
Definition
Population-based Cancer Research
Population Candidate Gene Association Study
Porfimer Sodium
Definition
Porphyrin
Definition
Portal Hypertension
Definition
Positional Cloning
Definition
Positive Nodes
Definition
Positive Predictive Value
Definition
Positron Emission Tomography
Synonyms
Definition
Characteristics
Principle of Positron Emission Tomography (PET)
Radiolabeled Biomarkers for PET Imaging Specifically Addressing Metabolic Pathways or Target Molecules
Clinical Applications of PET and PET/CT
Differentiation of Benign from Malignant Tumors and’Detection of the Primary Tumor (Cancer of Unknown Primary)
Staging of Cancer, Prognostic Potential of PET
Assessment of Response to Therapy
Restaging of Cancer, Detection of Recurrence
Radiation Treatment Planning
PE……T for Anticancer Drug Development
References
Post Surgical Systemic Therapy
Postcode Prescribing
Definition
Postirradiation Sarcoma
Postischemic Reperfusion
Definition
Postlabeling
Definition
Postnatal Stem Cells
Postreplication Repair
Posttranslational Modification
Definition
Pou Transcription Factors
Definition
Pox Viruses
Definition
pp60c-Src
pp60v-Src
PPARgamma
Definition
PPARs
Definition
ppb
Definition
ppm
Definition
PPNAD
Definition
pPNET
Definition
PR
Definition
pRb
Definition
Pre-invasive Breast Cancer
Pre-mRNA
Definition
Pre-mRNA Splicing
Definition
Characteristics
Spliced Forms in Cancer
Therapeutic Intervention
References
Pre-replicative Complex
Definition
Precancerous Lesions
Definition
Preclinical Drug Safety Evaluation
Preclinical Imaging
Definition
Preclinical Safety Testing
Preclinical Studies
Definition
Preclinical Testing
Synonyms
Definitions
Characteristics
Discovery Phase
Phase I Clinical Study
Phase II and III Clinical Studies
References
Predictive Biomarkers
Definition
Prednisone
Definition
Preleukemia
Premature Menopause
Definition
Preneoplastic Changes
Definition
Preneoplastic Lesions
Definition
Characteristics
Some Experimental Models of Preneoplastic Lesions
Human Preneoplasia
Genetic Predisposition to Neoplasia
Clinical Relevance
References
Prentice Criteria
Definition
Prenylation
Definition
Preoperative Chemotherapy
Prevalence
Definition
Prevention
Primary Biliary Cirrhosis
Definition
Primary Cancer Prevention
Definition
Primary Cancer Site
Definition
Primary Care Trust
Definition
Primary Chemotherapy
Primary Cilium
Definition
Primary Dissemination
Definition
Primary Hepatic Carcinoma
Primary Liver Cancer
Primary Lymphedema
Definition
Primary Myelofibrosis
Synonyms
Definition
Characteristics
Background
Historical Perspective
Disease Mechanisms
Clinical and Laboratory Characteristics
Diagnosis
Prognosis and Treatment
References
Primary Pigmented Nodular Adrenocortical Disease
Definition
Primary Sclerosing Cholangitis
Definition
Primary Systemic Therapy
Primitive Neuroectodermal Tumor
Definition
Proaccelerin
Definition
Procarcinogen
Definition
Procaspase
Definition
Processed Pseudogene
Definition
Processing
Definition
Proconvertin
Definition
Prodrug
Definition
Progenitor Cells
Definition
Progesterone
Definition
Progesterone Receptor
Definition
Progesterone Response Elements
Definition
Progestin
Synonyms
Definition
Characteristics
Mechanisms
Clinical Significance
References
Progestogens
Definition
Prognosis
Definition
Prognostic Biomarker
Definition
Programmed Cell Death
Definition
Programmed Cell Death 4
Synonyms
Definition
Characteristics
Tumor Suppressor Activity
Control of Translation
Transcriptional Controls
Induction of Apoptosis
Roles in Cell Differentiation
Clinical Aspects
References
Progression
Definition
Characteristics
Tumor Stem Cell and Metastasis
The Tumor Stroma and Metastasis
The Metastatic Cascade: Effector and Suppressor Molecules
Clinical Relevance
References
Progressive Myoclonus Epilepsy
Definition
Prohormone Convertase
Prolactin
Synonyms
Definition
Characteristics
Pituitary Prolactin Secretion and Its Regulation
Prolactin Structure and Activation of Cellular Signaling
Biological Effects of Prolactin
Disease States Related to Prolactin
Hyperprolactinemia and Prolactinoma
Prolactin and Breast Cancer
References
Proliferation
Definition
Proline
Definition
Promoter
Definition
Promoter Hypermethylation
Definition
Promotion
Definition
beta Propeller
Definition
Prophylactic Mastectomy
Definition
Prophylactic Vaccine Therapy
Definition
Proproteins
Definition
2-Propylpentanoic Acid
Prosome
Definition
Prospective Study
Definition
Prostaglandins
Definition
Prostaglandins
Definition
Characteristics
Biosynthesis
Regulation of Prostaglandins Synthesis and Degradation
Prostaglandin Signaling Pathway
Prostaglandin Signaling Pathway in Cancer
References
Prostanoid
Definition
Prostate Cancer, Clinical Oncology
Definition
Characteristics
Clinical Epidemiology and Risk Factors
Etiology
Tumor Biology and Genetics
Clinical Presentation
Diagnosis and Staging
Management
References
Prostate-Specific Membrane Antigen
Synonyms
Definition
Characteristics
PSMA Expression
Enzymatic Functions of PSMA
Does PSMA have a Signaling Function?
PSMA and Imaging
PSMA as a Therapeutic Target
References
Protease Activated Receptor Family
Definition
Characteristics
Melanoma
Breast Cancer
Prostate Cancer
Pancreatic Cancer
Lung Cancer
Colon Cancer
References
Protease Activated Receptors
Synonyms
Definition
Characteristics
References
Protease Signaling
Definition
Proteases
Definition
Proteasomal Cleavage
Definition
Proteasome
Definition
Proteasome Inhibitors
Definition
Characteristics
Mechanisms Mediating Bortezomib-Induced Apoptosis in MM Cells
Clinical Relevance
New Proteasome Inhibitor NPI-0052
References
Proteasome (prosome, macropain) 26S subunit, non-ATPase, 10
26S Proteasome
Definition
26S Proteasome Regulatory Subunit p28
Protein Array
Protein DATA Bank
Definition
Protein Disulfide Reductase
Protein Disulphide Isomerase
Definition
Protein-fragment Complementation Assays
Definition
Protein Kinase
Definition
Protein Kinase B
Definition
Protein Kinase C
Definition
Characteristics
Mechanism of Activation
PKC-Binding Proteins
Bioactivity
PKC in Cancer
Clinical Relevance
References
Protein Kinase C Family
Synonyms
Definition
Characteristics
Regulation
PKC Expression in Cancer
PKC Activation in Carcinogenesis
Targets of PKC and its Cancer-Related Functions
PKC as a Target in Cancer Therapy
References
Protein Microarray
Definition
Protein Stabilization
Definition
Protein-tyrosine Kinase Inhibitors
Proteinase
Definition
Proteinase-Activated Receptor-1
Synonyms
Definition
Characteristics
References
Proteinase-Activated Receptor 2
Synonyms
Definition
Characteristics
Proteinase-Activated Receptor-3 (PAR3)
Synonyms
Definition
Characteristics
Proteinase-Activated Receptor-4
Synonyms
Definition
Characteristics
Proteinase-Activated Receptors
Definition
References
Proteinchip
Synonyms
Definition
Characteristics
Technologies
Analytical Approaches
Applications in Cancer Research
Challenges and Perspectives
References
Proteins
Definition
14-3-3 Proteins
Definition
Proteoglycan
Definition
Proteoglycanase
Proteoglycans
Definition
Proteolysis
Definition
Proteolytic Processing
Definition
Proteome
Definition
Proteomic Techniques
Definition
Proteomics
Definition
Characteristics
Subproteomes and their Advantages
Common Protein Profiling Methods
Proteome Informatics
Clinical Aspects
References
Prothrombotic, Proinflammatory, and Proadhesive Endothelium
Definition
Protoadjuvant Therapy
Proton Beam Therapy
Synonyms
Definition
Characteristics
Physical Properties
Biological Properties
Clinical Aspects
Uveal (choroidal) Melanoma
Sarcomas of the Skull Base and Spine
Head and Neck Cancers
Lung Cancer
Hepatocellular Carcinoma
Prostate Cancer
Childhood Cancers
Miscellaneous
Facilities and Costs for Proton Beam Therapy
References
Proton Radiation Therapy
Proton Therapy
Proto-oncogene
Definition
Protoporphyrin IX
Definition
Provirus
Definition
Prox-1
Definition
Proximal-type Epithelioid Sarcomas
Definition
Proximate Carcinogen
Definition
Prozac
Prune
Definition
Characteristics
Regulation
Clinical Relevance
Inhibition
References
PS 341
PSA
Synonyms
Definition
Characteristics
Clinical Aspects
PSA as Diagnostic Marker
Percent free PSA
PSA, %fPSA for Staging and Grading
PSA for Recurrence of PCa
Monitoring After Radical Surgery
Use of PSA to Monitor Radiation Therapy
PSA monitoring After Androgen Deprivation Therapy
Conclusion and Future
References
Pseudarthrosis
Definition
Pseudogene
Definition
Pseudokinase
Definition
Pseudomonas Aeruginosa
Definition
Pseudomonas Exotoxin
Definition
Pseudomyxoma Peritonei
Definition
Pseudomyxoma Peritonei
Synonym
Definition
Characteristics
Epidemiology
Historical Perspective
Natural History
Appendiceal Origin
Pathological Classification
Presentation
Staging Systems
Cytoreductive Surgery
Rationale for Intra-Peritoneal Chemotherapy
Prognosis
Palliative Treatment Options
Basic Science
References
PSG1–11
Definition
PSI Domain
Definition
PSMA
PSMD10
PSTT
Ptaquiloside
Definition
PTB Domain
Definition
PTC
Definition
PTCH
Definition
PtdIns
Definition
PtdIns 3-kinase
P-TEFb
Definition
PTEN
Synonyms
Definition
Characteristics
Somatic Mutation of PTEN
Germline Mutation of PTEN
Biochemical Functions
Phosphoinositide-3 Kinase Signaling
How is the Pathway PI3K/PTEN Relevant to Cancer?
Conservation of the PI3K/PTEN Pathway in Caenorhabditis Elegans
Loss of PTEN Deregulates PI3K Signaling
PTEN as a Cell Cycle Regulator
PTEN as a Regulator of Cell-Death
PTEN as a Regulator of Cell Motility and Adhesion
PTEN as a Regulator of Angiogenesis
Clinical Relevance and Therapeutic Implications
References
PTEN Hamartoma Tumor Syndrome
Pterophyllus Salisburiensis
PTGF-beta
PTHLH
PTHrP
PTKIs
PTPase
Definition
PTPC
Definition
PTTG1
Definition
Pulsed Dye Laser
Definition
PUMA
Synonyms
Definition
Characteristics
Discovery and Function
Regulation
Clinical Considerations
References
Purging
Definition
Purine Analogues
Putative NF-kappa-B-activating protein 002N
PVHL
Definition
Pyelography
Definition
Pyrexia of Unknown Origin
Pyrimidine
Definition
Pyrophosphate
Definition
Q
Qi
Definition
Qigong
Definition
QSAR
Quadriradial Chromosomes
Definition
Quality Adjusted Life Year
Definition
Quality of Life
Definition
Quantitative Structure Activity Relationship
Synonyms
Definition
Characteristics
References
Quantitative Trait Loci
Quantum Dots
Definition
Quasispecies
Definition
Quaternary Structure
Definition
Quercetin
Definition
Quinones
Definition
R
R2
Rab
Definition
Rac
Definition
RAC3
RACE
Definition
RAD50
Definition
RAD51
Definition
RAD54
Definition
Radiation Biology
Definition
Radiation Carcinogenesis
Synonyms
Definition
Characteristics
Radiation
Interaction of Radiation with Matter
Interaction with Living Cells
Clinical Issues
References
Radiation Dose
Definition
Radiation-Induced Neoplastic Transformation
Radiation-Induced sarcomas
Radiation-Induced Sarcomas After Radiotherapy
Synonyms
Definition
Characteristics
Carcinogenesis
Dose–Effect Relation
Megavoltage or Orthovoltage Radiotherapy
Latent Period
Histological Findings
Age and RIS
Incidence
Genetic Findings
Treatment
Conclusion
References
Radiation Oncology
Synonyms
Definition
Characteristics
References
Radiation Pneumonitis
Definition
Radiation-Resistant DNA Synthesis
Definition
Radiation Sensitivity
Synonyms
Definition
Characteristics
Clinical Radiation Sensitivity or “Adverse Radiation Effects”
References
Radiation Therapy
Definition
Radical
Definition
Radical Mastectomy
Definition
Radio-Immunodetection
Definition
Radio-Isotope Therapy
Radio-Labeled Tracer
Definition
Radioactive Seed Therapy
Radioactivity
Definition
Radiobiology
Definition
Radiochemotherapy
Radioimmunoconjugates
Definition
Radioimmunotherapy
Synonyms
Definition
Characteristics
Principle of RIT
Tumor Characteristics
Monoclonal Antibody and Tumor Antigen
Radionuclides
RIT in Malignant Lymphoma
References
Radiological Response Criteria
Definition
Characteristics
Historical Developments
Strengths of Radiological Response Criteria
Limitations of RECIST
Future Developments and Possible Solutions
References
Radiomimetic
Definition
Radionuclide
Definition
Radioresistant DNA Synthesis
Definition
Radiosensitivity
Definition
Radiosensitization
Definition
Characteristics
Evaluation of a Radiosensitization Effect
Mechanisms of Radiosensitization
References
Radiosensitizer
Definition
Radiotherapy
Definition
Radon
Synonyms
Definition
Characteristics
Occurrence
Exposure Situations
Population Under Risk
Health Hazards
Mechanisms
References
Radon Daughter Products
Radon Decay Products
Radon Progeny
Rae-1
Definition
RAEB
Definition
RAET
Definition
Raf
Definition
Raf-1
Raf Kinase
Synonyms
Definition
Characteristics
Raf Signaling
Raf Function
Raf in Cancer
Raf Pathway Inhibitors
References
RAFB1
Rafts
Definition
RAGE
Definition
Ral
Definition
Ral Interacting Protein 76kDa
Raman Scattering
Definition
Ran
Definition
Randomization
Definition
RANK–RANKL Signaling
Synonyms
Definition
Characteristics
RANK(L) Function in Bone Remodeling
RANK(L) Signaling
RANK(L) and the Vicious Cycle of Bone Metastases
Additional Functions of RANK(L) in Cancer Cells
References
RANKL
Definition
Rap1
Definition
Rap1 and Sipa-1
Definition
Characteristics
Biological Functions of Rap1
Interference with Ras-Mediated ERK Activation
Activation of MAP Kinases and Other Signaling Pathways
Regulation of Cell Adhesion and Migration
Regulation of Rap1 Signal by Spa-1
Rap1 and Spa-1 in Leukemia
Rap1 and Spa-1 in Cancer Metastasis
Clinical Aspects
References
Rapamycin
Synonyms
Definition
Characteristics
Discovery of Rapamycin
Mechanism of Action
Mechanism(s) of Sensitivity and Resistance
Clinical Activity of Rapamycins
References
Rare Fragile Sites
Definition
RAS
Definition
Characteristics
Structure
Cellular and Molecular Regulation
Clinical Relevance
References
RAS Activation
Definition
Characteristics
Clinical Aspects
References
Ras Association Domain Family 1
Synonyms
Definition
Characteristics
RASSF1A as a Tumor Suppressor Gene
RASSF1A Methylation as a Cancer Biomarker
Functional Characterization of RASSF1A
Conclusion
References
RAS Gene
Definition
Ras-Homologous Proteins
RAS Transformation Targets
Synonyms
Definition
Characteristics
Background
RAS Proteins Affect Gene Transcription via Cytoplasmic Effectors
Identification of RAS Transformation Targets
A Selected List of RAS Transformation Targets
Clinical Relevance
References
Rasburicase
Definition
RasGEF
Definition
RAS-Regulated Genes
Ras-Related Small GTPases
RAS-Responsive Genes
RASSF1
Rat Podoplanin
RB1
Definition
RB2/p130
Definition
Reactive Oxygen Species
Synonyms
Definition
Characteristics
Chemistry of Major ROS
Generation and Scavenger of ROS
Oxidative Stress
Clinical Aspects
References
Reactive Species Overload Diseases
Definition
Reactive Stroma
Definition
Real-Time PCR
Definition
RecA
Definition
RecA/Rad51-like Proteins
Definition
Recall Bias
Definition
Receptor
Definition
Receptor-Associated Coactivator 3
Receptor Clustering
Definition
Receptor Cross-Talk
Synonyms
Definition
Characteristics
Survival Signaling/p53 and Suppressor Cross-Talk
Signaling to Angiogenesis
Integrin: Growth Factor Receptor Cross-Talk
References
Receptor Interactions
Receptor-Mediated Endocytosis
Receptor Protein Tyrosine Phoshatase Beta/Zeta
Definition
Receptor for Stromal Cell-Derived Factor-1 alpha
Receptor for TNF-Related Apoptosis-Inducing Ligand
Definition
Receptor Tyrosine Kinases
Synonyms
Definition
Characteristics
Physiological RTKs Activation
Deregulation of RTKs in Malignant Cells
Clinical Relevance
References
Receptors with Empty Ligand-Binding Pockets
Receptors with no Ligand-Binding Pocket
Receptors Regulated by Ligands
Receptors with Structural Ligands
Recessive
Definition
Recessive Oncogenes
Reciprocal Translocation
Definition
RECK Glycoprotein
Synonyms
Definition
Characteristics
Regulation
Clinical Relevance
References
Recombinant
Definition
Recombinant Inbred
Definition
Recombinant T Cell Receptor
Recombinant Therapeutics
Synonyms
Definition
Characteristics
References
Recombinase Activating Gene-2
Definition
Recombination
Definition
Record-Linkage Study
Definition
Recurrence
Definition
Recycling
Definition
Redifferentiation
Definition
Redistribution
Definition
Redox Cycling
Definition
Redox Reaction
Definition
Reduced
Definition
Reduced Intensity Conditioning (RIC) Allogeneic Stem-Cell Transplantation
Definition
Reduced Penetrance
Definition
Reductases
Synonyms
Definition
Characteristics
Carbonyl Reduction by SDRs and AKRs
The “Pro”
Reductases Protect Against Lung Cancer
Clinical Aspects
The “Contras”
Reductases in Chemotherapy Resistance
Cardiotoxicity
Clinical Aspects
References
Reduction
Definition
Reduction/Oxidation
Definition
Reed-Sternberg Cells
Definition
Regeneration
Synonyms
Definition
Characteristics
References
Regional Disease
Definition
Regulator of Extracellular Matrix Integrity
Regulatory T Cells
Synonyms
Definition
Characteristics
Molecular Markers of Treg Cells
Treg Cell in Cancer and their Antigen Specificity
Suppressive Mechanisms of Treg Cells
Manipulation of the Number or Suppressive Function of Treg Cells
References
REL
Synonyms
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Aspects
References
Relapse
Definition
Relative Risk
Definition
Relaxation
Definition
Relaxin
Definition
Characteristics
References
Remission
Definition
Remodeling
Definition
Renal Carcinoma
Definition
Characteristics
Early Diagnosis
Treatment
Types of Renal Cancer
Renal Cancer Genes
Types of Inherited Renal Cancer
Clinical Features of Renal Cancer Suggesting Hereditary Renal Cancer
Mechanisms of Development of Inherited Renal Cancers
References
Renal-Cell Carcinoma
Definition
Renal Excretion
Definition
Reovirus
Definition
Reoxygenation
Definition
Repair of DNA
Definition
Characteristics
Reversal of Base Damage
Removal of Damage
Repair of DNA and Cancer
Repair of DNA Strand Breaks
References
Repeat Dose Toxicity Studies
Definition
Reperfusion
Definition
Repetitive DNA
Definition
Replication
Definition
Replication-Activated Adenovirus
Replication-Competent Adenovirus
Replication-Dependent Histone Genes
Definition
Replication Factories and Replication Foci
Synonyms
Definition
Characteristics
Protein Composition of Replication Factories
Regulation of the Formation of Replication Factories
Clinical Relevance
References
Replication Fork
Definition
Replication Licensing System
Definition
Characteristics
Molecular Composition
Regulation
Clinical Relevance
References
Replication Origin
Definition
Replication-Selective Adenovirus
Replication-Selective Viruses
Replication Sites
Replicative DNA Lesion Bypass
Replicative DNA Polymerase
Definition
Replicon
Definition
Replisome
Definition
Reporter Gene Assays
Definition
Repressor Complex
Definition
Reproductive Toxicology Studies
Definition
REPSA
Definition
Reserve Cell Carcinoma
Residual Disease
Resistance
Definition
Resistance Modulation
Resistance Reversion
Respiration Rate
Definition
Respiratory Burst
Definition
Respiratory Chain
Definition
Response Elements
Definition
Restenosis
Definition
Resting Energy Expenditure
Definition
Resting NK Cell
Definition
Restriction Landmark Genomic Scanning
Definition
Characteristics
Application
Identification of Low Level DNA Amplification in Human Cancers
Global Scanning for DNA Methylation Changes in Human Cancers
Detection of Imprinted Genes
References
Restriction Point
Definition
Resveratrol
Synonyms
Definition
Characteristics
Mechanism of Action
Clinical Relevance
References
RET
Definition
Characteristics
Cellular and Molecular Regulation
Knockout Mice
Clinical Relevance
Mutations Found in Medullary Thyroid Carcinoma
Mutations Found in Papillary Thyroid Carcinoma
References
Rete Ovarii
Definition
Reticulin
Retinoblastoma
Synonyms
Definition
Characteristics
Clinical Aspects
Diagnosis of Rb
Presentation and Family History
Therapy and Prognosis
Second Tumors
Molecular Genetics
Rb is Caused by Two Mutations
Structure of the RB1 Gene
Spectrum of RB1 Gene Mutations
Genotype–Phenotype Associations
Genomic Alterations Associated with the Progression of Rb
Risk Prediction and Genetic Testing
References
Retinoblastoma Protein, Biological and Clinical Functions
Synonyms
Definition
Characteristics
The RB1 Gene Encodes the pRB Protein
pRB is Post-Translationally Modified
Phosphorylation of pRB
Acetylation of pRB
Functions of pRB
Cell Cycle Control
Differentiation and Development
Apoptosis
Clinical Relevance
Inactivation of RB1 Initiates Retinoblastoma Development
RB1 Loss in Other Cancers
References
Retinoblastoma Protein, Cellular Biochemistry
Definition
Characteristics
pRb and Its Family Members
Cell-Cycle Regulation of pRb
Role in Terminal Differentiation
Other Targets of pRb
Animal Models
Summarizing Remarks
References
Retinoic Acid
Definition
Characteristics
Regulation
Clinical Relevance
References
Retinoic Acid Receptors
Definition
Retinoid Receptor Cross-Talk
Synonyms
Definition
Characteristics
Retinoids
Retinoid Receptors
Retinoid Acid Receptors (RARs)
Rexinoid Receptors (RXRs)
Retinoid Receptors Cross-talk During Carcinogenesis
References
Retinoid X Receptor
Definition
Retinoids
Definition
Retinol
Definition
Retromer
Definition
Retroperitoneum
Definition
Retrospective Study
Definition
Retrotransposition
Definition
Retroviral Insertional Mutagenesis
Synonyms
Definition
Characteristics
History
Provirus Structure
Tumor Types
LTRs Regulate Transcription of Host Genes Near the Insertion Site
Promoter Insertion
Enhancer Activation
Protein Fusion
Transcript Stabilization
Cloning of Insertion Sites
Common Integration Sites
Randomness of Insertion
References
Retroviral Insertional Tagging
Retroviral Transduction
Retrovirus
Definition
Reverse Chemical Genetics
Definition
Reverse Transcriptase
Definition
Reverse Transcription PCR
Definition
Reverse Transcription-Polymerase Chain Reaction
Definition
Rexinoids
Definition
RGD
Definition
RGD, 18F-Galacto-RGD
Definition
RGS Proteins
Definition
Rhabdoid Tumor
Definition
Characteristics
Genetics
References
Rhabdomyosarcoma
Definition
Characteristics
References
RHAMM
Definition
Rheb
Definition
Rheumatoid Arthritis
Definition
Rheumatoid Factor
Definition
Rho
Definition
Rho Family Proteins
Synonyms
Definition
Characteristics
Cellular and Molecular Regulation
Functions
Clinical Relevance
References
Ribavirin
Definition
Ribonucleotide Reductase
Definition
Ribosomal Protein S6 Kinase1
Definition
Ribosome
Definition
Richter Syndrome
Definition
Rigaud and Schmincke Types of Lymphoepithelioma
RING
Definition
RING Finger Domain
Definition
RIS
RISC
Definition
Risk Factor
Definition
Rituximab
Synonyms
Definition
Characteristics
Mechanism of Action
Administration
Indications
Adverse Events
Clinical Trials with Rituximab Monotherapy
Clinical Trials with Rituximab Combination Regimens
References
RLIP76
Definition
RNA Interference
Synonyms
Definition
Characteristics
RNA Interference as a Research Tool
RNA Interference as a Novel Therapeutic Agent Against Cancer
Prospects and Obstacles Regarding RNAi Therapeutics
References
RNA Silencing
Definition
RNA Tumor Virus
Definition
RNAi
RNP Complex
Definition
Robo
Definition
ROCK
Definition
ROD-ZW10-Zwilch Complex
Definition
ROI
Definition
RON
Definition
Ron Receptor
Synonyms
Definition
Characteristics
Expression and Function
Ligand
Signaling Through Ron
Ron Overexpression in Multiple Tumor Types
Ron Variants
Ron-Dependent Transformation
Transgenic Mouse Models Overexpressing Ron
Ron Loss in Murine Tumor Models
Oncogenic Ron Signaling
Ron as a Therapeutic Target in Human Cancer
References
ROS
Definition
ROS Accumulation
Definition
ROS Scavenger
Definition
Rothmund-Thomson Syndrome
Definition
RT-PCR
Definition
Rule of Five
Definition
Runx1
Synonyms
Definition
Characteristics
Expression and Regulation
RUNX1 in Leukemia
References
Runx-1
Definition
RUNX1/CBFA2T1
RUNX1/MDS1/EVI1
RUNX1/RUNX1T1
S
S1P
Definition
S-9
Definition
S-Phase
Definition
S-Phase Checkpoint
Definition
S-Phase Damage-Sensing Checkpoints
Definition
Characteristics
References
S-Phase Kinase-associated Protein 2
S-Phase Promoting Factor
Definition
S-100 Protein
Definition
SAAB
Definition
SAGE
Definition
SAHA
Definition
Salisburia Adiantifolia
Salisburia Macrophylla
Salivary Agglutinin (SAG, Human)
Salivary Gland Malignancies
Definition
Characteristics
Epidemiology/Risk Factors
Staging/Classification
Diagnosis
Treatment
References
Salmonella typhi and paratyphi
Definition
Salt Intake
Synonyms
Definition
Characteristics
Nasopharyngeal Carcinoma
Gastric Cancer
References
Salting
Sanctuary Site
Definition
Sandwich ELISA
Definition
SAPKalpha
SAPKbeta
SAPKgamma
Sarcoid
Definition
L-Sarcolysin
Definition
Sarcoma
Definition
SBP
Definition
SCA1
Definition
Scaffold Proteins
Definition
Scatter Factor
Synonyms
Definition
Characteristics
The SF Family
SF Receptor (The c-Met Proto-oncogene Product)
Cellular and Molecular Regulation
SF Producer and Responder Cell Types
Regulation of SF Production
Biologic Responses Induced by SF and Their Regulation
SF and c-Met Participate in Various Physiologic and Pathologic Processes
Development
Oncogenesis
Angiogenesis
Clinical Relevance
References
Scavenge Free Radicals
Definition
Scavenger Cells
Definition
SCF
Definition
SCF-R
scFv
Definition
SCH52365
Schirrous (archaic)
Schistosomas Hematobium
Definition
Schwannoma-derived Growth Factor
Schwannomin
SCID
Definition
Scid Mice
Definition
SCID Mouse Model
Definition
Scintigraphy
Definition
SCLC
Definition
Sclerosing Angiogenic Tumor
Sclerosing Endothelial Tumor
Sclerosing Epithelioid Angiosarcoma
Sclerosing Interstitial Vascular Sarcoma
Screening Toxicity
Definition
SDF-1
Definition
SDF-1alpha
SDGF
SEA Domain
Definition
Seckel Syndrome
Definition
Second Malignant Neoplasm (SMN)
Second Messenger
Definition
Second Primary Cancers
Second Primary Malignancy (SPM)
Second Primary Tumors
Synonyms
Definition
Introduction
Causal and Risk Factors
Shared Etiologic Exposure
Genetic Predisposition
Therapy-Related Risk Factors
Diagnosis
Treatment
Prevention
References
Second-Tier/Third-Tier Lymph Node
Definition
Secondary Amenorrhea
Definition
Secondary Cancer Prevention
Definition
Secondary Cancer Site
Definition
Secondary Dissemination
Definition
Secondary Hypogonadism
Definition
Secondary Lymphedema
Definition
Secondary Lymphoid Organs
Definition
Secondary Metabolites
Secondary Structure
Definition
Secondary Tumor
Secondhand Tobacco Smoke
Definition
Secosteroid
Definition
Secretagogues
gamma-Secretase
Definition
Secreted Phosphoprotein 1
Secreted Protein Acidic and Rich in Cysteine
Synonyms
Definition
Characteristics
Gene Organization
Protein Structure
Functional Properties
Animal Models
SPARC in Cancer
References
Secretor Enzyme
Definition
Securin
Synonyms
Definition
Characteristics
Securin Function
Securin Function in Tumor Development
References
“Seed and Soil” Theory of Metastasis
Definition
Characteristics
Historical Development of the “Seed and Soil” Theory
Recent Evidence Shows that the “Seeds” Can Even Prepare the “Soils”
References
Seer
Definition
SELDI-TOF MS
Definition
Selectins
Definition
Selection Template
Definition
Selective Estrogen Receptor Modulator
Definition
Selective Serotonin Reuptake Inhibitors SSRIs
Selenium
Definition
Characteristics
References
Selenocysteine
Definition
Selenoenzyme
Definition
SELEX
Definition
Self-Renewal
Definition
Self-Sufficiency in Growth Signals
Definition
Sella Turcica
Definition
SEMA
SEMA Domain
Definition
Semanová II syndrome
Semaphorin
Synonyms
Definition
Characteristics
Subclasses
Structure and Processing
Brief History of the Semaphorin Family
Semaphorins and the Composition of their Receptors
Neuropilins
Plexins
Plexin Signaling
Brief History of Semaphorins in Cancer Research
Different Mechanisms may Account for Semaphorin Functions in Cancer Biology
References
Semaphorin Receptors
Seminomatous Germ Cell Tumor
Sendai Virus
Definition
Senescence
Definition
Senescence Accelerated
Definition
Senescence and Immortalization
Definition
Characteristics
Senescence
Immortalization
Relevance of Senescence and Immortalization to Cancer
A Cell Division Counting Mechanism
Telomerase
Alternative Lengthening of Telomeres (ALT)
Tumor Suppressor Genes
Clinical Relevance
References
Senescence-associated Chronic Inflammation
Senile Involution
Sensorineural
Definition
Sentinel Lymph Nodes
Synonyms
Definition
Characteristics
General anatomy and physiology of the lymphatic system
The Sentinel Node
Lymphatic Mapping
Sentinel Node Biopsy
Breast Cancer
Melanoma
Concluding Remarks
References
Sentinel Node
Synonyms
Definition
Characteristics
Sentinel Node Procedure
Clinical Relevance
Immunology of the Sentinel Node
References
Sentinel Node Biopsy
Definition
Sentinel Vessels
Definition
SEP
Definition
Separin
Definition
Sequence Identification
Definition
Sequestered
Definition
Ser/Thr-Phosphorylation
Definition
SERCA
Definition
Serex
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
Serine Elastase
Serine Protease
Definition
Serine Protease Inhibitor
Definition
Serine Protease Inhibitor-like Domain
Serine Proteases (Type II) Spanning the Plasma Membrane
Synonyms
Definition
Characteristics
Regulation of Activity
Biological Responses
Expression in Cancer
Clinical Relevance
References
Serine/Threonine Kinase
Definition
Serine-Threonine Kinase Receptor-Associated Protein
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects
References
Serological Analysis of cDNA Expression Libraries
Definition
Seropositive
Definition
Serotonin
Definition
Serotypes
Definition
Serpin
Definition
Sertoli Cell
Definition
Sertoli-Leydig Cell Tumor
Definition
Serum
Definition
Serum-Ascites Albumin Concentration Gradient
Definition
Serum Biomarkers
Synonyms
Definition
Characteristics
Alpha-Fetoprotein (AFP)
Beta Subunit of Human Chorionic Gonadotropin (β-„hCG)
Cancer Antigen 15-3 (CA 15-3)
Cancer Associated Antigen 19-9 (CA 19-9)
CA 27-29
CA-125
Carcinoembryonic Antigen (CEA)
Cytokeratin 19 Fragments
Lactate Dehydrogenase (LDH)
Matrix Metalloproteinase-9 (MMP-9)
Placental Alkaline Phosphatase (PLAP)
Prostate-Specific Antigen (PSA)
YKL-40
References
Severe Combined Immunodeficiency Disease
Definition
Severe Combined Immunodeficient Mice
Definition
Severe Hypoxia
Sex Cord Stromal Tumors
Definition
Sex Hormone
Definition
Sex Hormone Dependent Cancers
Definition
Sezary Syndrome
Definition
Characteristics
Staging and Treatment
References
sFRP
Definition
SH2/SH3 Domains
Synonyms
Definition
Characteristics
Clinical Relevance
References
SH2/src Homology 3
SH2 Domain
Definition
SH3 Domain
Definition
SHANK
Definition
Shark Cartilage
Definition
Characteristics
References
Shc
Definition
Shedding of Cells
Shimada System
Definition
Short Hairpin RNA
SHP-1
Definition
SHP-2
Definition
SH3P9
shRNA
Sialoglycoconjugates
Definition
Sialyl Lewis-a/x Determinants
Definition
Sialyltransferases
Definition
Sicca Complex
Definition
Sicca Syndrome
Signal Sequence
Definition
Signal Transducer and Activator of Transcription
Signal-Transducer Proteins
Definition
Signal Transducers and Activators of Transcription in Oncogenesis
Synonyms
Definition
Characteristics
STATs in Cytokine and Growth Factor Induced Signaling
Bioactivity
STAT Activation During Progression of Human Cancer
Targeting STATs for Cancer Therapy
Targeting the Tumor Cell
Targeting the Tumor Microenvironment
Summary
References
Signal Transduction
Definition
Characteristics
Receptors
Targets of Signaling Pathways
Signal Transduction in Cancer Pathogenesis
Signal Transduction in Cancer Therapy
References
Signal Transduction Cross-Talk
Definition
Signal Transduction Inhibitor-571
Signaling Cascades
Definition
Signalosome
Definition
Silencing Mediator of Retinoid and Thyroid Hormone Receptor
Definition
Simian Virus 40
Definition
Simulation
Definition
SIN3A
Definition
Single Cell Gel Electrophoresis Assay (SCGE)
Single Cell Invasion
Definition
Single Cell Microgel Electrophoresis Assay
Single-chain Fv Dimer
Single-Chain Fv Fragment
Definition
Single Dose Toxicity Studies
Definition
Single Nucleotide Polymorphism
Definition
Single Stranded Conformation Analysis
Definition
Siomycin A
Definition
SIOP
Definition
Sipa-1 (Spa-1)
Definition
Sipple Syndrome
Sir2-like Proteins
siRNA
Definition
siRNA
Definition
Characteristics
Clinical Aspects
Delivery
Nonspecific Immune Stimulation
Off-Target Interference
References
SIRS
Definition
SIRTs
Sirtuins
Synonyms
Definition
Characteristics
Biochemical Features of Sirtuins
Cellular Functions of Sirtuins
Sirtuins and Cancer
Sirtuin Inhibitors and Activators
References
Sister Chromatid Exchange
Definition
Sister-Chromatids
Definition
Site-Directed Mutagenesis
Definition
Site-specific Drug Delivery
Sivelestat
Definition
Characteristics
Mechanisms of Action
Clinical Aspects
Clinical Application in Practice
Application to Cancer Treatment as Molecular Targeting Therapy
References
Sjögren Syndrome
Synonyms
Definition
Characteristics
Incidence
Etiology
Clinical Manifestations
Presentation
Involvement of Exocrine Glands
Extraglandular Involvement
Diagnosis
SS is Diagnosed on the Basis of Either European Classification
Laboratory Abnormalities
Anti-Ro/SSA and anti-La/SSB Antibodies
Anti-CENP-H Antibodies and SS
Pathogenesis
Immunopathology
Humoral Immunity
Cellular Immunity
Immune-Mediated Tissue Destruction
Immunopathogenesis (Summary)
Treatment and Prognosis
SS and HCV
SS Cause Lymphoma?
SS and Lymphoproliferative Disorders
Future Directions
References
Skeletal Complications (skeletal-related events)
Skeletal-Related Events
Definition
Skeletal Secondary Tumors
Skeletrophin
Synonyms
Definition
Characteristics
Clinical Aspects
References
Ski
Definition
Skin Cancer
Definition
Skin Carcinogenesis
Definition
Characteristics
Genetic Basis of Skin Carcinogenesis
Initiation
Promotion
Cellular and Molecular Basis
Relevance to Human Disease
References
Skin Prick Testing
Definition
Skin-Sparing Mastectomy
Definition
Skinny Needle
Skipper-Schabel Model
Skipper-Schabel-Wilcox Model
Skp2
Definition
SL-1
SLD
Definition
SLE
Definition
SLex
Definition
Slit
Definition
Characteristics
Slit function in the Nervous System
Slit-Robo Signaling
Slit function Outside the Nervous System
Slit proteins and Cancer
Slit and Medulloblastoma
References
Sloughing of Cells
Slu
Slug
Definition
SM
Definition
SM-5887
SMA
Definition
SMA- and MAD-related Protein 4
SMAC/Diablo
Definition
SMAD
Definition
SMAD4
Smad Binding Element
Definition
SMAD-4/DPC4
Smad Proteins in TGFbeta Signaling
Definition
Characteristics
Cellular and Molecular Regulation
Clinical Relevance
References
Small Animal Positron Emission Tomography
Small Bowel Mesentery
Definition
Small Cell Carcinomas
Definition
Small Cell Lung Carcinoma
Definition
Small Cell Neuroendocrine Carcinoma
Small GTPases
Definition
Small GTP-binding Proteins
Small Interfering RNA
Definition
Small Molecule
Definition
Small Molecule Drugs
Definition
Characteristics
Differences to Large Molecule Drugs
High Throughput Screening
Structure Determination and Modeling
Physicochemical Properties and Drug Uptake
Drug Formulations
Side Effects
Some Examples for the Mechanism of Cancer Drug Action
Systemic Effects of Tumor Growth
References
Small-Molecule Inhibitors
Definition
Small Molecule Screens
Synonyms
Definition
Characteristics
Types of Screens
“Small” Molecules
Screening Technology and Tools
Screening Assays
The Screening Epilog
Conclusions
References
Small Round-cell Tumor
SMARCB1
Definition
SMAX1
Smelting
Definition
SMN
Definition
Smoking
Definition
Smoothened
Definition
SMR (Soluble Mesothelin-related Proteins)
SMRT Co-repressor
Definition
SN-38
Definition
Sna
SNAG
Definition
Snail Transcription Factors
Synonyms
Definition
Characteristics
Structural Organization
Transcriptional Repression
Regulation of Expression and Functional Activity
Additional Snail Functions
Clinical Significance
References
SNAILH (Human)
SNCA
Definition
SNCB
Definition
SNCgamma
Definition
snoRNA
Definition
SNP
Definition
SNP Array
Definition
snRNA
Definition
snRNP
Definition
SOCS
Definition
SOD
Definition
Sodium Chloride
Solar Light Induced Cancer
Solar Ultraviolet Light
Definition
Characteristics
Effects of Exposure to Solar Ultraviolet Light on Skin
DNA Damage Induced by Solar Ultraviolet Light
Mutations Induced by Solar Ultraviolet Light
Protection Against Photocarcinogenesis
Hereditary Disorders with Increased Photocarcinogenesis
References
Solitary Bone Plasmacytoma
Solitary Extramedullary/Extraosseous Plasmacytoma
Solitary Plasma Cell Myeloma
Solute Carrier Transporters
Definition
Somatic Cells
Definition
Somatic Cross-Over Point Mapping
Definition
Somatic Hypermutation
Definition
Somatic Recombination of V, D’and J Segments
Somatic Stem Cells
Somatic Tissue
Definition
Somatostatin
Synonyms
Definition
Characteristics
Somatostatin Secretion and Gene Expression
Somatostatin Receptors (sst)
Molecular Basis of Somatostatins Antiproliferative Effects
Clinical Relevance
Somatostatin Analogue Therapy
Somatostatin Receptor Imaging and Radiotherapy
General Clinical Applications
References
Somatostatin Receptor Scintigraphy
Definition
Somatostatinoma
Definition
Somatostatinoma Syndrome
Definition
Somatotropin Release Inhibiting Factor
Sonic
Definition
Sonic Hedgehog
Definition
Sorafenib
Definition
SOX18
Definition
Soy Isoflavonoids
Definition
Soy Phytoestrogen
Soy Proteins
Definition
Sp
Definition
Sp-Like Proteins
Definition
SPARC
SPB, in Yeast
SPC1
Specific Immunotherapy for Melanoma
Specificity
Definition
Spectral Karyotyping
Definition
Characteristics
Advantages of SKY
Disadvantages
Clinical Significance
References
Spectral Unmixing
Definition
Spermatocytes
Definition
Spheroids
Definition
Sphinganine
Definition
Sphingolipid Metabolism
Definition
Characteristics
Poly-Drug Chemotherapy and Multi-Drug Resistance
Chemotherapy via Ceramide Control
Immunological Attack Against Cancer Cells
Mechanisms of Sphingolipid Antineoplastic Action
References
Sphingolipids
Definition
Sphingomyelinase
Definition
Sphingomyelins
Definition
Sphingosine
Definition
Sphingosine-1-Phosphate
Definition
Spinal and Bulber Muscular Atrophy (SBMA)
Spindle Assembly Checkpoint
Definition
Spindle Pole Apparatus
Definition
Spindle Pole Body
Spinocerebellar Ataxia Type 1
Definition
Spinophilin
Definition
Spirometry
Definition
Spleen
Definition
Spleen Tyrosine Kinase
Splenic Marginal Zone Lymphoma
Definition
Splice Variant
Definition
Spliceosome
Definition
Splicing
Definition
Spontaneous Bacterial Peritonitis
Definition
Sporadic
Definition
Sprouty
Synonyms
Definition
Characteristics
Mechanisms of Action
Regulation of the Activity of Sproutys
Deregulation of Spry Expression in Cancer
Ability of Sprys to Inhibit Cancer
References
Spry
Sputum Cytology
Definition
Squamous Cell Carcinoma
Synonyms
Definition
Characteristics
Etiology
Diagnosis and Clinical Features
Disease Management
Molecular Aspects
References
SR Proteins
Definition
Src
Synonyms
Definition
Characteristics
Domain Structure
Subcellular Localization
Interacting Proteins
Cellular and Molecular Aspects
Clinical Relevance
References
SRC-3
Src8
Src Family Tyrosine Kinase
Definition
Src Homology 2
Src Homology Domain
Definition
Src Kinase
Definition
SRC-Homology Domains
Definition
SRCR Superfamily
Definition
SREBP
Definition
SRF
Definition
srGAPs
Definition
SRIF
St. John’s Wort
Definition
Stage
Definition
Staging of Tumors
Synonyms
Definition
Characteristics
Purpose
Methods
Perspectives
References
Standardization
Definition
STAT
Definition
Stathmin
Definition
Statins
Definition
Characteristics
Cellular Effects of Statins in Vitro
Statins in the Prevention and Treatment of Cancer
References
Staurosporine
Definition
Characteristics
Kinase Inhibition
Staurosporine in Apoptosis
Anti-tumor Activity
References
Stefins
Synonyms
Definition
Characteristics
Physiological and Pathological Roles
Stefins in Cancer
References
Stem Cell
Definition
Stem Cell Factor
Definition
Stem-Cell Harvest and Purging
Definition
Stem Cell Hypothesis in Cancer
Definition
Stem Cell Markers
Definition
Characteristics
Methods Used to Detect Stem Cell Markers in Cancer Biology
Clinical Applications
References
Stem Cell Niche
Definition
Stem Cell Plasticity
Synonyms
Definition
Characteristics
Metaplasia
The Bone Marrow and Tumor Stroma: Clinical Relevance
References
Stem Cell Telomeres
Synonyms
Definition
Characteristics
References
Stem Cells
Definition
Characteristics
Tissue Renewal and Models of Cellular Hierarchy
Stem Cell Division
Stem Cell Markers and Identification Problems
Stem Cell Location and the Niche
The Concept of Stemness and “Immortal” DNA Strands
Regulation of Stem Cell Numbers
Properties of Stem Cells Which Favor Tumorigenesis
Evidence that Human Tumors Arise from Stem Cells
Cancer Stem Cells
Clinical Implications of Cancer Stem Cells
References
Stem-like Cancer Cells
Synonyms
Definition
Characteristics
Identification
Clinical Implications
Stent
Definition
Steradian
Definition
Stereocenter
Definition
Stereotactic Radiosurgery
Definition
Sterile-alpha-Motif
Steroid Hormone Receptor Coactivators
Definition
Steroid Hormone Receptors (SHR)
Definition
Steroid Receptor Coactivator-3
Steroid-Refractory Graft-Versus-Host Disease
Definition
Steroid Sulfatase
Synonyms
Definition
Characteristics
Regulation of STS
STS in Hormone-Dependent Breast Cancer (HDBC)
STS Inhibitors
References
Steroid Sulfohydrolase
Steroidogenesis
Definition
Steryl Sulfohydrolase
Stevens-Johnson Syndrome
Definition
STI-571
Synonyms
Definition
Characteristics
Physicochemical Properties
Pharmacology and Pharmacokinetics
Clinical Applications
Chronic Myeloid Leukemia (CML)
Gastrointestinal Stromal Tumors (GISTs)
Other Diseases
Side Effects
Resistance to STI-571
Low Concentrations in the Central Nervous System (CNS)
References
STI571 STI-571
Sticker Sarcoma
Definition
Stilbenes
Definition
STK5
STK6
STK7
STK12
STK13
STK15
STMY1
Stomach Cancer
Stomatitis
Definition
STR1
STRAP
Streptavidin
Definition
Stress
Definition
Characteristics
Possible Pathways of an Association of Stress and Cancer Risk
Methodological Problems
Findings
Conclusion
References
Stress-activated Protein Kinase
Stress Response
Synonyms
Definition
Characteristics
Cellular Regulation
Clinical Relevance
References
Stressful Life Event
Definition
Stressor
Definition
Striatonigral Medium Spiny Neurons
Definition
Stroma
Definition
Stromagenesis
Synonyms
Definition
Characteristics
References
Stromal Cell Response
Stromal Cells
Definition
Stromal-derived Factor 1 Alpha (SDF1alpha)
Definition
Stromal Progression
Stromatogenesis
Stromelysin-1
Synonyms
Definition
Characteristics
Enzymatic Properties of Stromelysin-1
Regulation of Stromelysin-1
Stromelysin-1 and Cancer
References
Structural Biology
Definition
Characteristics
References
Structural Maintenance of Chromosomes Protein
Definition
Structural Vascular Stabilization
STS
Stuart-Prower Factor
Definition
Subacute Toxicity Studies
Definition
Subarachnoid Space
Definition
Subarachnoidal Spread
Subcellular Compartments
Definition
Suberoylanilide Hydroxamic Acid
Definition
Substrate Channeling
Synonyms
Definition
Characteristics
The Key Features
The Prototypical Paradigm
Details
Mechanisms
References
Subtractive Hybridization
Definition
Subtype AML-M7
Subunit Vaccine
Definition
Sugar-Remodeling System
Definition
Sugarbaker
Definition
SUI1 Domain
Definition
Suicide Gene
Definition
Suicide Gene Therapy
Definition
Sulcus
Definition
Sulfasalazine
Definition
Sulfatases
Definition
Sulfate Group
Definition
Sulfatide
Definition
Sulfation
Definition
6-Sulfatoxymelatonin
Definition
Sulfokinases
Sulforaphane
Synonyms
Definition
Characteristics
Actions and Pharmacology
Mechanisms of Action
Metabolism and Pharmacokinetics
Summary
References
Sulfotransferases
Synonyms
Definition
Characteristics
Sulfotransferases and Cancer
References
SULT
Definition
SULT1A1
Definition
SULT1E1
Definition
Sumoylation
Definition
Sun Light Induced Cancer
Sunbeds
Definition
Sunitinib
Definition
Superantigens
Definition
Supercooled Phase
Definition
Supercooling
Definition
Superoxide Dismutase
Definition
Superoxide Radical
Definition
Supervised Classification
Synonyms
Definition
Characteristics
Clinical Relevance
Caveats and Recommendations
References
Supervised (Machine) Learning
Supportive Care
Synonyms
Definition
Characteristics
Supportive Care Needs Require an Individualized Approach
Patients and Carers are Key Members of the Supportive Care Team
A Multidisciplinary and Coordinated Approach
The Development of an Evidence Base to Interventions to Improve Supportive care Outcomes
Conclusion
References
Suppressive T Cells
Suppressor of Fused
Definition
Suppressor of Invasion, Metastasis, and Angiogenesis
Suppressor T Cells
Definition
Suppressors of Cytokine Signaling
Synonyms
Definition
Characteristics
Role of SOCS-1 in Cancer
SOCS-3 in Human Cancer
SOCS-2 in Malignant Diseases
References
Suprachiasmatic Nucleus
Definition
Supraparamagnetic Nanoparticle
Definition
Suramin
Definition
Surface-Enhanced Laser Desorption/Ionization Time of Flight Mass Spectrometry
Definition
Surface Glycoproteins
Definition
Surface Molecules
Surface Plasmon Resonance
Definition
Characteristics
Detection Principle of SPR Biosensor
Properties of the SPR Biosensor
Biomedical Applications
Biomolecular Interaction Analysis (BIA)
High-Throughput Screening (HTS)
Proteomics Research
References
Surgery
Definition
Surgical Biopsy
Definition
Surgical Debulking
Definition
Surgical Menopause
Definition
Surgical Pathology
Surgical Trauma and Cancer Recurrence
Definition
Characteristics
Trauma and Inflammation
Laboratory Investigations
Clinical Applications
References
Surrogate Endpoint
Synonyms
Definition
Characteristics
Role of Surrogate Endpoints in Cancer Research
Methods of Validation
Caveats in the Use of Validated Surrogate Endpoints
References
Surrogate Endpoint Biomarker
Surrogate Endpoints
Surrogate Outcome
Survival
Survivin
Synonyms
Definition
Characteristics
Functional and Cellular Characteristics
Clinical Relevance
References
Susceptibility Loci
Sustained Release
Definition
SV40
Synonyms
Definition
Characteristics
Replication
Clinical Relevance
References
SVA Repeat
Definition
SWI/SNF
Definition
SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin subfamily b, member1
SWISS-PROT
Definition
Syk
Syk Tyrosine Kinase
Synonyms
Definition
Characteristics
Distribution and Function
Experimental Evidence for a Tumor/Metastasis Suppressor Role of Syk
Mechanism of Syk Activation and Signaling
Clinical Studies of Syk Expression and Activity
References
Sympathetic Ganglia Neurons
Definition
Symptom Management
Definition
Synaptic Vesicle Recycling
Definition
Synaptopodin
Definition
Synchronizer
Definition
N-Syndecan
Definition
Syndecans
Definition
Synergism
Definition
Synergistic
Definition
Syngeneic
Definition
Synovial Sarcoma
Definition
Characteristics
References
Syntenic
Definition
Synthetic Cannabinoids
Synthetic Chemoprotectants
Definition
Synuclein
Definition
Characteristics
Synuclein Expression in Cancer
Role in Tumor Progression
References
Synuclein alpha
Definition
Synuclein beta
Definition
Synuclein gamma
Definition
Systemic Antibody-directed Radionuclide Therapy
Systemic Chemotherapy
Definition
Systemic Clearance
Definition
Systemic Inflammatory Response Syndrome
Definition
Systemic Lupus Erythematosus
Definition
Systemic Spread of Cancer
Systemic Therapy
Systemic Treatment or Therapy
Definition
Systems Biology
Definition
T
T
Definition
T Cell
Definition
T Cell Receptor Complex
Definition
TH1 Cells
Definition
TH2 Cells
Definition
TH3 Cells
Definition
T Helper
Definition
T Helper Lymphocytes
Definition
T-Helper 1 Response
Definition
T-Loop
Definition
T Lymphocyte
Definition
T-lymphoma Invasion and Metastasis
T-PLL
Definition
T-Prolymphocytic Leukemia (T-PLL)
Definition
TAA
Definition
TACE
Definition
TAK
Definition
Takatsuki Disease
Definition
Tall Cell Variant of Papillary Carcinoma
Definition
TAM
Definition
Tamoxifen
Definition
Characteristics
Background
Adjuvant Therapy
Chemoprevention
Mechanism of Action
Side Effects
References
Tamponade
Definition
Tankyrase-2: TNKL, TNKS2, TANK2
Tankyrases
Synonyms
Definition
Characteristics
Structure
Intracellular Distribution
Binding Partners
Functions
Telomere Elongation
Cell Division Control
Insulin-Stimulated Glucose Uptake
Clinical Aspects
References
TAP
Definition
TARC
Definition
Tarceva
Target Cells
Definition
Target-Based Screen
Definition
Targeted Deletion
Definition
Targeted Drug Delivery
Synonyms
Definition
Characteristics
Intratumoral Drug Administration
Liposomal Drug Delivery
Tumor-Activated Prodrug Therapy (TAP)
Antibody-Directed Enzyme Prodrug Therapy
Gene-Directed Enzyme Prodrug Therapy
Folate-Targeted Drug Delivery
Transferrin Targeted Drug Delivery
Albumin-Drug Conjugate for Targeted Delivery
References
Targeted Drug Design
Targeted Radioimmunotherapy
Targeted Therapy
Definition
Targeted Viruses
Definition
Targeting, Active
Definition
Tat
Definition
TAT Protein of HIV
Definition
Characteristics
Transcriptional Regulation: Control of HIV Replication
AIDS-Associated Pathologies: A Direct Contribution by Tat
Conclusion
References
TATA Box
Definition
TATI
Definition
Tau
Definition
Taurodont
Definition
Tax
Definition
Tax Binding Protein-181
Tax Helper Protein (GLI2)
Taxane
Definition
Taxol
Definition
Characteristics
Mode of Action
Clinical Pharmacology
Antitumor Activity
Absorption and Excretion
Toxicity
Structurally and Functionally Related Compounds
Structurally Related Compounds
Nontaxane, Microtubule-Stabilizing Agents
References
Taxotere
Synonyms
Definition
Characteristics
Chemistry
Mechanisms of Action
Clinical Use
References
TBI
Definition
T-body
TBP
Definition
TCDD
2,3,7,8-TCDD
T-Cell ALL
Definition
T-Cell Antigen Receptor
Definition
T-Cell Clone
Definition
T-Cell Hybrids
Definition
T-Cell Receptor
Definition
T-Cell Response
Definition
Characteristics
References
T-Cell Zones
Definition
T-cells Recognizing Autoantigens
Tcf/LEF
Definition
TCL1
Definition
Characteristics
Clinical Characteristics of the T-PLL
Cytogenetic and Molecular Characteristic of the TCL1 Locus
Animal Models
TCL1 Protein
TCL1 Expression in Normal and Pathological Tissues
Conclusions
References
TCR
Definition
TCRα and TCRβ
Definition
TDA
Definition
TDGF-1
Technical Knockout
Definition
Characteristics
Isolation of Genes in Apoptosis
Clinical Aspects
References
TEL
Definition
TEL-AML1
Definition
Telangiectasia Macularis Eruptive Perstans
Definition
Telomerase
Definition
Characteristics
What Are Telomeres and What Do They Do?
Why Do Telomeres Shorten?
What is Cellular Senescence?
If You Can Stop the Shortening of Telomeres Will This Prevent Cellular Aging?
Can Telomerase be Used as a Product to Extend Cell Lifespan?
Cell and Molecular Regulation
Clinical Relevance
Could Telomerase be the “Achilles Heel” of Cancer?
Will Inhibiting Telomerase Restore the Senescence Program in Cancer Cells and if so Will This Therapy Cure Cancer?
Will Telomerase Activity be Useful in Cancer Diagnostics?
Have any Telomerase Therapeutic Agents been Identified and what are the Potential Complications of such Strategies?
References
Telomere
Definition
Telomere Length
Definition
Telomeric Repeats of Stem Cells
TEM7
Definition
Temodal
Temodar
Temoget
Temozolomide
Synonyms
Definition
Characteristics
Temozolomide and MGMT
Mismatch DNA Repair and Temozolomide Response
Repair of N7-Methylguanine and N3-Methyladenine DNA Lesions
References
Temsirolimus
Synonyms
Definition
Characteristics
Mechanism of Action
Activity in Cancer Models
Activity in Clinical Trials
References
Tenascin-C
Synonyms
Definition
Characteristics
Molecular Organization
Induction and Processing
Interaction Partners
Cell Rounding and Tumor Cell Proliferation
Metastasis
Angiogenesis
Phenotype of Tenascin-C Knockout Mice and Cancer
Clinical Aspects
References
Tensin2
Definition
Tensional Homeostasis
Definition
Characteristics
References
TEP1
Definition
Teratocarcinoma
Definition
Teratocarcinoma-derived Growth Factor-1
Teratogenic
Definition
Teratoma
Definition
N- or C-Terminal Processing
Definition
Terminally Differentiated Cells
Definition
Tertiary Cancer Prevention
Definition
Tertiary Structure
Definition
Testicular Cancer
Synonyms
Definition
Characteristics
Diagnosis
Therapy
Non-Seminomatous Germ-Cell Tumors (NSGCT)
Low-Stage (IIA/B) NSGCT
Clinical Stages IIC and III
Seminomatous Germ-Cell Tumors
Clinical Stage I Seminoma
Low-Stage (Clinical Stage IIA/B) Seminoma
Clinical Stage IIC and III
Salvage Chemotherapy, High-Dose Chemotherapy
Genetics
Future Directions in TC
References
Testicular Feminization TFM
Testicular Germ Cell Tumor
Testicular Tumors
Testosterone
Definition
2,3,7,8-Tetrachlorodibenzo-p-dioxin
Tetracopeptide Repeat TPR Domains
Definition
Tetraploidization
Definition
Tetraspanin
TF
Definition
TFF
TFIIH
Definition
TG2
Definition
TGc
TGF
Definition
TGFalpha
Definition
TGF-beta
Definition
TGF-β Activation
Definition
TGF-β-Regulated and Epithelial Cell-Enriched Phosphatase
Definition
TGF-β Superfamily
Definition
Th1
Definition
Th2
Definition
Th1 Immune Response
Definition
Th2 Immune Response
Definition
Thalidomide and its Analogues
Synonyms
Definition
Characteristics
Mechanisms of Action
Multiple Myeloma
Myelodysplastic Syndromes (MDS)
Solid Malignancies
Future Directions
References
Therapeutic Active Targeting
Definition
Therapeutic Cloning
Definition
Therapeutic Efficacy
Definition
Therapeutic Passive Targeting
Definition
Therapeutic Vaccine Therapy
Definition
Therapeutic Viruses
Thiazolidin
Synonyms
Characteristics
References
Thiazolidinediones
Definition
Thiazolidinone
Thin Needle
Thiol
Definition
Thiol-Protease Inhibitors (Cytoplasmic alpha- and beta-TPIs)
Thioredoxin
Definition
Thioredoxin is Identical to ADF Adult T cell Leukemia Derived Factor
Thioredoxin Reductase
Definition
Thioredoxin System
Synonyms
Definition
Characteristics
References
Thiostatins
Thiotepa
Definition
Third-Generation Bisphosphonate
Third-Generation Nitrogen-containing Bisphosphonate
Thoracentesis
Definition
Three-Dimensional Conformal Radiation Therapy
Definition
Three-Dimensional Tissue Cultures
Definition
Characteristics
Multicellular Spheroids
Culture
Diffusion Limited Growth, ECM and Differentiation
Dissociation, Histology and Other Study Methods
Cell Proliferation
pH and Metabolite Gradients
Cancer Biology
Drug Effects and Multicellular Resistance
Drug Transport
Individualized Therapy
Multicellular Layers (MCL, Multilayered Cell Cultures, MCC)
Multilayered Post-Confluent Cultures (MPCC)
Co-Cultures of Tumor and Normal Cells
Histocultures
Organotypic Cultures
Organ Cultures and Tissue Engineering
Conclusions and Future Directions
References
Three-Stage Phenomenon
Definition
Thrombin
Definition
Thrombin Receptor
Thrombin Receptor-like 1
Thrombin Receptor-like 2
Thrombin Receptor-like 3
Thrombocyte
Definition
Thrombocytopenia
Definition
Thrombocytopenic Purpura
Definition
Thrombopoietin
Definition
Thrombosis
Definition
Thrombospondin
Definition
Characteristics
Classification
Mechanism
References
Thrombotic Cancer Cell Emboli
Definition
Thromboxane
Definition
Thrombus
Definition
Thymidine Phosphorylase
Synonyms
Definition
Characteristics
References
Thymocytes
Definition
Thymoma
Definition
Characteristics
Diagnosis
Classification
Treatment and Prognosis
References
Thymus
Definition
Thymus-Dependent Lymphocyte
Definition
Thyroglobulin
Definition
Thyroid Carcinogenesis
Definition
Characteristics
General Features
Role of Ionizing Radiation
Genetic Aberrations
RET Gene Changes
References
Thyroid Follicle
Definition
Thyroid Hormone Receptor Activator Molecule 1
Thyroid Hormone Receptors
Definition
Thyroid Lobectomy
Definition
Thyroid Receptor Interacting Protein 6
Definition
Thyroidectomy
Definition
Tiam1
Synonyms
Definition
Characteristics
References
Tight Junction
Definition
Characteristics
References
Tight Junction Protein-1
TIG-IPT
Definition:
TIL
Time-of-Flight
Definition
Time Resolved Fluorescence
Time-Resolved Fluorescence Resonance Energy Transfer Technology in Drug Discovery
Synonyms
Definition
Characteristics
References
Time-to-Event Analysis
TIMP
Tissue Engineering
Definition
Tissue Factor
Definition
Tissue Inhibitors of Metalloproteinases
Synonyms
Definition
Characteristics
References
Tissue Kallikreins
Tissue Proliferation
Tissue Regeneration
Definition
Tissue Spectroscopy
Tissue Stem Cells
Tissue-transglutaminase
Tissue-Type Plasminogen Activator
Tissue Typing
Definition
TJP-1
TKO
Definition
TLR4
Definition
TMPRSS1
Definition
TMPRSS10
Definition
TMPRSS2/ERG Fusions
Definition
Characteristics
References
TNF
Definition
TNF-alpha
Definition
TNF-alpha in HIV Infection
Definition
Characteristics
Physiopathological Role of TNF-alpha in HIV Infection
Relationships Between HIV Replication and TNF-alpha
Role of TNF-alpha in NeuroAIDS
Role of TNF-alpha in Cachexia, Opportunistic Infections and Tumors
Clinical Relevance of Molecules Inhibiting TNF-alpha Synthesis
References
TNF-Related Apoptosis Inducing Ligand
Synonyms
Definition
Characteristics
Introduction
TRAIL and Its Cell Surface Receptors
Organization of TRAIL-Induced Apoptotic Signaling
Mechanisms to Attenuate TRAIL-Induced Apoptosis
Augmentation of TRAIL-Induced Apoptosis
Clinical Potential for TRAIL Therapy
Perspectives
References
Tobacco
Definition
Tobacco Addiction
Tobacco Carcinogenesis
Definition
Characteristics
Tobacco Products and Human Cancer
Tumor Induction in Laboratory Animals
Chemistry of Tobacco Smoke
Mechanisms of Tumor Induction
References
Tobacco Dependence
Tobacco-Related Cancers
Definition
Characteristics
Tobacco as a Carcinogen
Cancers Related with Tobacco
Evidence for Other Cancers
Passive Smoking
Conclusions
References
Tobacco-Related Lung Cancer
Definition
Tobacco-Specific N-Nitrosamines
Definition
Tolbutamide
Definition
Tolbutamide Intravenous Test
Definition
Tolerance
Definition
Tolfenamic Acid
Definition
Toll-Like Receptors
Definition
Characteristics
TLRs and Cancer Treatment
References
Tongue Cancer
Synonyms
Definition
Characteristics
Epidemiology
Pathology and Genetic Aberration
Clinical Features
Subclinical Nodal Metastasis
TNM Staging and Prognostic Factors
Pretreatment Assessment
Treatment Options
Controversy of Elective Neck Dissection Versus Observation of N0 Neck
Outcome of Treatment
References
Tonsils and Adenoids
Definition
Topoisomerase II
Definition
Topoisomerase II-DNA Cleavage Complexes
Definition
Topoisomerase III
Definition
Topoisomerases
Definition
TOR
Definition
Torisel
Definition
Torsade de Pointes
Definition
Totipotent
Definition
Totipotent Stem Cells
Definition
Toxic Epidermal Necrolysis
Definition
Toxicity
Definition
Toxicity Testing
Toxicokinetics
Definition
Toxicological Carcinogenesis
Synonyms
Definition
Characteristics
History
References
Toxicological Pathologist
Definition
Toxicology
Definition
TP
TP53
Synonyms
Definition
Characteristics
Upstream of p53: Signaling of DNA Damage
Downstream of p53: Cell-Cycle Control, Apoptosis and DNA Repair
Clinical Relevance
References
TP73L
tPA
Definition
TPA
Definition
TR-FRET
TRA-8
Trabectedin
Synonyms
Definition
Characteristics
Structural and Biophysical Characterization of Trabectedin-DNA Adducts
Biological Activity
Clinical Studies
References
Trabecular Bone
Definition
Trace Elements
Definition
TRAF-1
Definition
TRAF2
Definition
Traffic ATPases
TRAIL
Definition
TRAIL Receptor Antibodies
Synonyms
Definition
Characteristics
Clinical Aspects
Mapatumumab (anti-DR5)
Lexatumumab (anti-DR5)
TRA-8 (CS1008)
Perspectives
TRAM-1
Trans-Golgi Network
Definition
Transabdominal Metastasis/Dissemination
Trans Activating Protein
Definition
Transactivation
Definition
Transactivation Domain
Definition
Transarterial
Definition
Transarterial Chemoembolization
Definition
Transcoelomic Metastasis
Synonyms
Definition
Characteristics
Mechanisms of Transcoelomic Metastasis
Models of Metastasis
Cell Detachment
Peritoneal Fluid and Anatomy
Ascites: A Metastatic Milieu
Immune Evasion
Tumor Implantation
Clinical Aspects
References
Transcript
Definition
Transcription
Definition
Transcription-Coupled Repair
Definition
Transcription Factor
Definition
Transcription Factory
Definition
Transcriptional Complex
Definition
Transcriptional Coregulators
Definition
Transcriptional Memory
Definition
Transcriptional Regulation
Definition
Transcriptional Silencing
Definition
Transcriptome
Definition
Transdifferentiation
Definition
Transduction
Definition
Transduction of Oncogenes
Synonyms
Definition
Characteristics
Identification of Cellular Oncogenes
Mechanism of Oncogene Transduction
Lessons from Retroviral Transduction of Oncogenes
References
Transfection
Definition
Transformation
Definition
Transforming Gene
Transforming Growth Factor Alpha
Definition
Transforming Growth Factor Beta
Definition
Characteristics
TGF-beta Receptors and Signaling Mechanisms
Latency TGF-beta
Matrix Association and Release of TGF-beta
LTBPs: Expression and Functions
Activation of Soluble and Extracellular Matrix Forms of Latent TGF-beta
TGF-Beta and LTBP Knockout Mice
Perspective
References
Transforming Retroviruses
Definition
Transgene
Definition
Transgenic
Definition
Transgenic Animal
Definition
Transgenic Mice
Definition
Transglutaminase-2
Synonyms
Definition
Characteristics
TG2 and Apoptosis
TG2 in Drug Resistance and Metastasis
Clinical Relevance
References
Transglutaminase Type-2
Transient Amplifying Cells
Definition
Transin-1
Transit Amplifying Cells
Definition
Transition
Definition
Transition Metals
Definition
Transitional Carcinoma
Transitional Cell Carcinoma
Synonyms
Definition
Characteristics
Epidemiology
Etiology
Signs and Symptoms
Evaluations
Staging (1997 AJCC-UICC, TNM Staging)
Treatment of Superficial Bladder Cancer
Treatment of Invasive Bladder Cancer
Treatment of Metastatic Bladder Cancer
References
Transitional Cell Carcinoma of Bladder
Transitional Cell Carcinoma of Renal Pelvis
Transitional Cell Carcinoma of the Urinary Bladder
Transitional Cell Carcinoma of Ureter
Transjugular Intrahepatic Portosystemic Shunt
Definition
Translation
Definition
Translation Initiation Complex
Definition
Translesion DNA Polymerases
Definition
Characteristics
References
Translesion Synthesis
Definition
Translin
Definition
Translocase
Definition
Translocation
Definition
Translocation ETS Leukemia Gene
Translocation Non-homologous
Definition
Translocation Reciprocal
Definition
Translocation t(14;18)
Definition
Transmembrane
Definition
Transmembrane 4 Superfamily Protein
Transmembrane Domain
Definition
Transmembrane Protein Type I
Definition
Transmembrane Protein Type II
Definition
Transmembrane Signaling
Definition
Transmigration Assay
Definition
Transphosphorylation
Definition
Transplacental Carcinogen
Definition
Transporter Nomenclature
Definition
Transporters
Definition
Transposon
Definition
Transpupillary Thermal Therapy
Definition
Transurethral Resection
Definition
Transversion
Definition
Trastuzumab
Definition
betaTrCP
Definition
Treatment-refractory Germ Cell Tumors
Trefoil Factors
Synonyms
Definition
Characteristics
TFF Discovery and Expression
TFF in Mucosal Repair and Protection
TFF in Chronic Inflammation and Cancer Progression
Aberrant Expression of TFF as Clinical Markers of the Neoplasia
Conclusions
References
Trefoil peptides
Treg
Definition
Tremolite
Definition
TRF1-interacting, ankyrin-related ADP-ribose polymerases
TbetaRI and TbetaRII
Definition
Tribbles Homologue 3
Definition
Trichilemmoma
Definition
Trichostatin A
Definition
Trichothiodystrophy
Definition
Trident
Trifunctional Antibody
Definition
Triglyceride
Definition
4´,5,7-Trihydroxyisoflavone
3,4´,5-Trihydroxystilbene
Trinucleotide Repeat
Definition
Triple Negative Breast Cancer
Definition
Tripterine
Trisomy
Definition
Trivalent Chromium (Cr+3)
Definition
Trk Family Tyrosine Kinase Receptors
Definition
TRK-A
Definition
Troglitazone
Definition
TROP-1
Trophoblast
Definition
Tropism
Definition
Tropomyosin
Definition
Trousseau Syndrome
Definition
Trp63
Trp73
Trx
Definition
Trypsin
Definition
Tryptase
Definition
TSC
Definition
TSC1
TSH
Definition
TSH
Definition
TSH Receptor
Definition
TSP
Definition
TSR
Definition
TTF-1
Definition
tTGase
Tuberin
Definition
Tuberous Sclerosis Complex
Synonyms
Definition
Characteristics
Clinical Aspects
Identification and Characterization of the TSC Genes
TSC1 and TSC2 Act as Tumor Suppressor Genes
Lymphangioleiomyomatosis and Pulmonary TSC
Role of hamartin and Tuberin in the mTOR Pathway
mTOR and other Hamartoma Syndromes
Rodent Models of Tuberous Sclerosis
References
Tuberous Sclerosis Complex 1
Tuberous Sclerosis Syndrome
Definition
Tubulin
Definition
Tubulin Interacting Proteins
Tubulogenesis
Definition
Tumor
Definition
Tumor Antigens
Definition
Tumor-Associated Angiogenesis
Definition
Tumor-Associated Antigen
Definition
Tumor Associated Carbohydrate Antigens
Definition
Tumor-Associated Fibroblasts
Definition
Tumor-Associated Macrophages
Definition
Characteristics
Macrophages
Tumor-Associated Macrophages
TAM Recruitment
TAM Express Selected M2 Protumoral Functions
Modulation of Adaptive Immunity by TAM
Conclusion
References
Tumor-Associated Stromal Progression
Tumor Cell Invasion
Tumor Cell-Induced Platelet Aggregation
Synonyms
Definition
Characteristics
Mechanisms
Clinical Aspects and Therapy
References
Tumor Cell-platelet Aggregate
Tumor Cell-Platelet Interaction
Tumor Endothelial Cell
Definition
Tumor–Endothelial Communication
Tumor–Endothelial Cross-talk
Synonyms
Definition
Characteristics
Adhesion Molecules in Tumor–Endothelial Cross-talk Mediating Extravasation
Tumor–Endothelial Cross-talk Leading to Prothrombotic Endothelial Activation
Conclusion
References
Tumor Glucose Metabolism
Tumor Grading
Tumor-Induced Platelet Aggregation
Tumor-Infiltrating Lymphocytes
Definition
Tumor Infiltrating T Cells
Definition
Tumor-Initiating Cells
Tumor Lysis Syndrome
Definition
Tumor Markers
Definition
Tumor Matrix
Definition
Tumor Metabolism
Definition
Tumor Microenvironment
Synonyms
Definition
Characteristics
References
Tumor Necrosis Factor
Definition
Tumor Necrosis Factor-α
Definition
Tumor Necrosis Factor-Alpha Converting Enzyme
Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand
Definition
Tumor Pathology
Tumor Progenitors
Tumor Progression
Definition
Tumor Promoter
Definition
Tumor Promotion
Definition
Tumor-Reinitiating Cells
Tumor-Repopulating Cells
Tumor-Specific Stroma
Definition
Tumor Spread
Tumor Staging
Definition
Tumor Stroma
Definition
Tumor Suppression
Definition
Characteristics
Clinical Aspects
References
Tumor Suppressor
Definition
Tumor Suppressor Genes
Synonyms
Definition
Characteristics
What was the Evidence for Tumor Suppressors?
Retinoblastoma – The First Suppressor
Are There Other Tumor Suppressors and What Cellular Role do They Normally Play?
Clinical Relevance
References
Tumor-Transforming 1
Tumor Typing
Tumor Vessel Density
Definition
Tumor Xenografts
Definition
Tumoricidal
Definition
Tumorigenesis
Definition
TUNEL
Definition
Tunicamycin
Definition
Characteristics
Structure and Function
Anti-viral Effect of Tunicamycin
Apoptosis Induction by Tunicamycin
Tunicamycin Increases Effects of Anti-cancer Agents
Tunicamycin Enhances Death Ligand TRAIL-Induced Apoptosis
Normal Cellular Toxicity of Tunicamycin
References
Turban Tumor Syndrome
Definition
Turcot Syndrome
Definition
Characteristics
Clinical Criteria
Genetics
PMS2 Gene
Microsatellite Instability
Clinical Aspects
References
Turmeric Yellow
TUTR1
Two-Hit Model
Definition
Two-Step Carcinogenesis
Definition
TXBP181
Type I Cystatins
Type-1 Hypersensitivity
Type I Interferon
Type I Programmed Cell Death
Typical Neurocytoma
Tyrosine
Definition
Tyrosine Kinase
Definition
Tyrosine Kinase Inhibitors
Synonyms
Definition
Characteristics
References
Tyrosine Kinase Receptors
Definition
Tyrosine Phosphorylation
Definition
U
Ubiquitin
Definition
Ubiquitin-directed Protein Degradation
Definition
Ubiquitin Ligase
Definition
Ubiquitin Ligase SCF-Skp2
Synonyms
Definition
Characteristics
Regulation
Clinical Significance
References
Ubiquitination
Definition
Characteristics
Cellular Regulation
Clinical Relevance
p53 and HPV-Associated Cervical Carcinoma
von Hippel Lindau (VHL) Disease
beta-Catenin Turnover in Colorectal Tumors
Degradation of p27, a CDK Inhibitor
Cbl and Receptor Tyrosine Kinase Degradation
Fanconi Anemia
Proteasome inhibitors
Summary
References
Ubiquitous
Definition
Ubiquitous Immunopoietc Polypeptide
Definition
UCH
Definition
UCN-01 Anticancer Drug
Synonyms
Definition
Characteristics
Inhibition of Chk1 Kinase and G2 Checkpoint Abrogation by UCN-01
Mechanisms of UCN-01 Induced Tumor Cell Death
References
UDP
Definition
UDP-Glucuronosyl Transferase
Definition
UGT
Definition
Ulcerative Colitis
Definition
Ultimate Carcinogen
Definition
Ultrasound
Definition
Ultrasound Biomicroscopy
Ultrasound Micro-Imaging
Synonyms
Definition
Characteristics
Two- and Three-Dimensional Anatomical Imaging
Doppler Blood Flow Imaging
Contrast-Enhanced Imaging
References
Ultratrace Minerals
Definition
Ultraviolet Light
Definition
Ultraviolet Radiation
Definition
Ultraviolet Radiation Induced Cancer
Umbilical Cord Blood
Definition
Uncertain or Unknown Histogenesis Tumors
Definition
Characteristics
Distinctive Tumors of Uncertain Histogenesis
Synovial Sarcoma
Epithelioid Sarcoma
Alveolar Soft Part Sarcoma
Clear Cell Sarcoma of Soft Tissue
Extraskeletal Myxoid Chondrosarcoma
Desmoplastic Small Round Cell Tumor
Extrarenal Rhabdoid Tumor
Neoplasms with Perivascular Epithelioid Cell Differentiation (Pecomas)
Ewing Sarcoma/Primitive Neuroectodermal Tumor (Pnet)
Capillary Hemangioblastoma
Angiomatoid Fibrous Histiocytoma
Myxoid Tumors
Other (Benign) Tumors
References
Uncoupling Protein-1
Definition
Unfolded Domain
Unfolded Protein Response
Definition
Unipotent Stem Cells
Definition
Unrip: Unr-interacting Protein
Unstructured Domain
Untranslated Region
uPA
Definition:
p53 Upregulated Modulator of Apoptosis
Definition
Uranium
Definition
Uranium Miners
Definition
Characteristics
Uranium Mining
Miners’ Cohorts
Exposures
The Risk of Lung Cancer
Histopathologic Findings
The Risk of Cancers Other than Lung Cancer
Conclusion
References
Urea Cycle
Definition
Uridine Diphosphate-Glucuronosyltransferase
Definition
Urine Cytology
Definition
Urokinase-Type Plasminogen Activator
Definition
Uroplakins
Definition
Urothelial Cancer
Definition
Urothelial Carcinoma
Synonyms
Definitions
Characteristics
Distribution, Histology, and Clinical Course
Causes
Therapy
Diagnosis and Monitoring
Molecular Genetics
References
Urothelial Carcinoma, Clinical Oncology
Synonyms
Definition
Characteristics
Diagnosis
Therapy
Genetics
References
Urothelial Carcinoma In Situ
Definition
Urothelial Nodular Invasive Carcinoma
Definition
Urothelial Papillary Superficial Carcinoma
Definition
Urothelial Tumor
Urothelium
Definition
Ursolic Acid
Definition
Urticaria Pigmentosa
Definition
USP
Definition
USP44
Definition
Uterine Artery Embolization
Definition
Uterine Fibroid
Definition
Uterine Leiomyoma
Synonyms
Definition
Characteristics
References
Uterine Leiomyoma, Clinical Oncology
Synonyms
Definition
Characteristics
Incidence
Gross Features
Microscopic Features
Symptoms
Diagnosis
Treatment
Cytogenetic Changes
References
Utrafine Particles
Definition
UV Radiation
Definition
Characteristics
Cancers of the Skin
Epidemiological Evidence of the Carcinogenic Potential of UV Radiation
Host Factors
UV Radiation as an Environmental Risk Factor
Intraocular Melanoma
Biological Effects of UV Radiation Relevant to Carcinogenesis
DNA Damage
Cellular Damage
Differential Effects of UVA and UVB
Changes in the Immune Response
Drug-Induced Photosensitivity
Cancer Preventive Effects of UV Radiation
Indoor Tanning and Cancer
References
UVC Light
Definition
Uveal Melanoma
Synonyms
Definition
Characteristics
Epidemiology
Risk Factors
Clinical Diagnosis
Signs and Symptoms
Diagnostic Modalities
Treatment Options
Pathology
Systemic Evaluation and Metastasis
Prognostic Factors
Systemic Therapy and Future Directions
References
Uveal Tract
Definition
Uvomorulin
UV-Signature Mutation
Definition
V
V-erb-B2
V-raf Murine Sarcoma Viral Oncogene Homolog B1
Vaccine Therapy
Definition
Valproic Acid
Synonyms
Definition
Characteristics
Valproic Acid Affects Cell Behavior by Multiple Mechanisms
Valproic Acid Inhibits Histone Deacetylase Activity
Valproic Acid Interferes with MAPK Signaling
Valproic Acid Affects the Beta-Catenin Pathway
Valproic Acid may Influence Additional Pathways
References
Vanadium
Definition
Characteristics
Vanadium in Cancer Treatment
Chemopreventive/Anticancer Mechanisms
Future Direction
References
VANGL
Definition
Variable Number Tandem Repeats
Definition
Variant Allele
Definition
Variant Isoforms
Definition
Vascular Disrupting Agents
Synonyms
Definition
Characteristics
Vascular Disrupting Agents
The Biologic Approach
Small Molecule VDAs
Flavonoids Agents
Tubulin Binding Agents
VDAs as Adjuvants to Conventional Therapy
References
Vascular Endothelial Growth Factor
Synonyms
Characteristics
VEGF Family
VEGF-Receptor Family
VEGF in Vasculogenesis and Physiological Angiogenesis
Clinical Relevance
VEGF in Pathophysiological Angiogenesis
VEGF/VEGF Receptor System: Therapeutic Opportunities
References
Vascular Maturation
Vascular Normalization
Definition
Vascular Permeability Factor
Vascular remodeling
Vascular Stabilization
Synonyms
Definition
Characteristics
Normal Vascular Hierarchy
Vascular Destabilization and Activation of Angiogenesis
Vascular Stabilization
Clinical Implications
References
Vascular Targeted Therapies
Vascular Targeting Agents
Synonyms
Definition
Characteristics
Background
Mechanisms
Clinical Aspects
References
Vascular Targeting Agents
Vasculogenesis
Definition
Vasculogenic Mimicry
Definition
Characteristics
Introduction
Current Status of Studies on VM in Tumors
Molecular Mechanisms Underlying VM
Dedifferentiation of Tumor Cells is the Key to Formation of VM Channels
Linearly Patterned Programmed Cell Necrosis and Three-Stage phenomenon
The Effect of Local Tumor Microenvironment on the Formation of VM Channels
Clinical Significance of VM
Advances and Challenges
VM and Lymphagenesis in Tumors
VM-Targeted Therapy
References
Vasoactive Intestinal Contractor
Vasoconstrictor
Definition
Vasodilation
Definition
Vasostatin
Definition
VCAM-1
Definition
V(D)J Recombination
Synonyms
Definition
Characteristics
Mechanism
Clinical Aspects
References
VE-Cadherin
Definition
Vector
Definition
VEGF
Definition
VEGF-C
Definition
VEGFR
Definition
VEGFR-2
Definition
VEGFR-3
Definition
Verapamil
Definition
Verner-Morrison Syndrome
Definition
Vesicle Trafficking
Definition
V-Gene
Definition
VHL
Definition
Video-assisted Thoracoscopic Surgery
Definition
Villin 2
Vinblastine
Definition
Vinca Alkaloids
Definition
Vincristine
Definition
Vinorelbine
Definition
VIPoma
Definition
Viral Oncogene
Definition
Viral Oncology Epigenetics
Definition
Characteristics
Host Epigenetic Changes Due to Viruses and Virus-Associated Cancers
Kaposi Sarcoma Associated Herpesvirus
Epstein Barr Virus
Hepatitis B Virus
Human Papillomavirus
Polyomaviruses (SV40, BK Virus and JC Virus)
Adenovirus
Human T Cell Lymphotrophic Viruses
Epigenetic Alterations in the Virus Due to the Host
Conclusions
References
Viral Vector-mediated Gene Transfer
Synonyms
Definition
Characteristics
References
Virilization
Definition
Virology
Definition
Characteristics
Tumor Virus Epidemiology
Immunosurveillance and Viral Oncogenesis
Tumor Viruses
Herpesviridae
Epstein-Barr Virus
EBV-Encoded microRNAs
Burkitt Lymphoma
Nasopharyngeal Carcinoma
Hodgkin Lymphoma
Lymphoproliferative Disease in Immunosuppressed Patients
Other Tumors
Kaposi Sarcoma Herpesvirus
Polyomaviridae
Papillomaviridae
Hepadnaviridae
Hepatitis B Virus
Flaviviridae
Hepatitis C Virus
Retroviridae
Human T lymphotropic Virus-1
References
Virosomes
Definition
Virotherapy
Synonyms
Definition
Characteristics
Oncolytic Adenoviruses and Cancer Gene Therapy
CRAds in Human Clinical Trials and the Limitations
CAR-Deficiency on Tumor Cells Results in the Poor Infectivity of Ad Agents
Infectivity Enhanced CRAd Agents-Retargeting CRAds to Tumor Cells
Tumor Specific CRAd Agents – Using a Tumor Specific Promoter to Drive Specific Viral Replication
A Double Targeted CRAd for Ovarian Cancer
Future Directions for Improvements
References
Virtual High Throughput Screen
Definition
Virus-like Particles
Definition
Virus Therapy of Cancer
Virus Vector
Definition
Virus Vector-mediated Gene Transfer
Viruses
Definition
Vital
Definition
Vitamin A
Definition
Vitamin C
Definition
Vitamin D
Definition
Characteristics
Mechanisms
Conclusions
References
Vitamin D Receptor
Definition
Vitamin E
Definition
Vitiligo
Definition
Vitrification
Definition
VLP
Definition
VM-targeted Therapy
Definition
VNTR
Definition
Volume of Distribution
Definition
von Hippel-Lindau
Von Hippel-Lindau Disease
Definition
von Hippel-Lindau Tumor Suppressor Gene
Synonyms
Definition
Characteristics
Molecular Features
Role in Diseases – Clinical, Molecular and Cellular Characteristics
Clinical and Molecular Features
Classical Clinical Definition
Germline Mutations
Genotype/Phenotype Correlation
Sporadic Tumors
Somatic Mutations
Cellular/Functional Features
Applications in Diagnosis and Clinical Management
Remaining Questions
References
von Recklinghausen Disease
Definition
von Willebrand Factor
Definition
Vorinostat
Synonyms
Definition
Characteristics
Background
Mechanism of Antitumor Action
Clinical Studies
Activity of Vorinostat in Non-oncology Indications
References
Voxel
Definition
v-Src
vWF
Definition
W
WA
WAGR Syndrome
Definition
Waldenstrom Macroglobulinemia
Definition
Walker A Motif
Definition
Warburg Effect
Synonyms
Definition
Characteristics
Mitochondrial DNA Mutations and the Warburg Effect
Tumor Suppressors and the Warburg Effect
Oncogenic Activation of the Warburg Effect
Does the Warburg Effect Contribute to Tumorigenicity?
Clinical Aspects and Summary
References
Warts (wts) – Drosophila lats
WARTS (WTS) – mammalian LATS1
N-WASp
Definition
WD Repeats
Definition
Wegener Granulomatosis
Definition
T1- and T2-Weighted Images
Definition
T1-Weighted
Definition
T2-Weighted
Definition
Well-differentiated Neurocytoma
Wermer syndrome
Wharton Jelly
Definition
Whey Acidic Protein
Definition
Whipple Triad
Definition
White Blood Cell
Definition
WHO
Definition
WHO Grade IV Astrocytoma
Wide Excision
Definition
Wild-type
Definition
Wilms Tumor
Definition
Characteristics
How Common is Wilms Tumor?
What Causes Wilms Tumor?
Clinical Characteristics
Is Wilms Tumor One Disease?
Molecular Characteristics of Wilm Tumor
Treatment of Relapsed Wilms Tumor and Future Therapeutic Possibilities
Heritability and Screening
References
Wilms Tumor Anaplasia
Definition
Wilms Tumor Suppressor Gene
Definition
WIN
Wiskott-Aldrich Syndrome
Definition
Withaferin A
Synonyms
Definition
Characteristics
References
muMEN1
Wnt
Definition
Wnt/beta-Catenin Pathway
Definition
Wnt Signaling
Definition
Characteristics
Wnt Proteins
Wnt Signaling Pathways
Other Ligands and Receptors that Directly Regulate Wnt Signaling
References
Working Level
Definition
Working Level Month
Definition
Working Level Months (WLM)
Definition
Wound Healing
Definition
Wound Healing Assay
Definition
Wox1
Wright-Giemsa Stain
Definition
WT1
Definition
WTIP
Definition
WW Domains
Definition
WWOX
Synonyms
Definition
Characteristics
The Gene
The Protein
Biological Role
References
X
X Chromosome Inactivation
Definition
Xanthine Oxidase
Definition
Xanthophylls
Definition
Xenobiotic Biotransformation
Xenobiotic Metabolism
Xenobiotic Receptor
Xenobiotic
Definition
Xenobiotics
Synonyms
Definition
Characteristics
Origin of Xenobiotics
Metabolism of Xenobiotics
Effects of Xenobiotics
Interactions
Individual Variability
Xenobiotics and Cancer
Exploitation of Knowledge about Xenobiotics and XMEs
References
Xenogeneic
Definition
Xenograft
Definition
Xenograft Models
Xeroderma Pigmentosum
Definition
Characteristics
Xeroderma Pigmentosum (XP) Subgroups
Clinical Aspects
Cellular Parameters
Molecular Parameters
Animal Models
Other NER-Related Syndromes
References
Xerophthalmia
Xerostomia
XIAP
Definition
Xiphophorus
Synonyms
Definition
Characteristics
Genetics of Melanoma Formation
The Xmrk Oncogene
UV-Induced Tumors
Carcinogen-Induced Tumors
Further Information
References
XME
Definition
X-Ray Crystallography
Definition
X-ray Induced Cancer
XRF
Definition
Y
YAC
Definition
Yin and Yang
Definition
Yinxing
YKL-40
Definition
YM-529
YM-529/ONO-5920
Yondelis
Z
Z′ factor
Zeolite
Definition
Z-Factor
Synonyms
Definition
Characteristics
Connections to Other Assay Data Quality Indicators
Z′-factor and Lower Limit of Detection of an Assay
References
Zinc-Finger Proteins
Definition
Zinc Transporters
Definition
ZO-1
Definition
Zoledronic Acid
Definition
Characteristics
Structural Characteristics
In vitro Activities of Zoledronic Acid and Mechanisms of Action
Antitumor and Bone Resorption Activity of Zoledronic Acid in Preclinical Models
Clinical Aspects
References
Zollinger-Ellison Syndrome
Definition
Zonula Adherens
Zonula Occludens Protein-1
Synonyms
Definition
Characteristics
Molecular Biology of ZO-1
Regulation and Function of ZO-1
ZO-1 in Cancer
References
ZRP1
Definition
Zymogen
Definition
Zyxin
Definition
ZZANK1

Citation preview

Encyclopedia of Cancer (2nd edition)

M ANFRED S CHWAB (Ed.)

Encyclopedia of Cancer (2nd edition)

With 979 Figures* and 210 Tables

*For color figures please see our Electronic Reference on www.springerlink.com

Editor: Manfred Schwab Professor for Genetics Director Division of Tumour Genetics (B030) German Cancer Research Center (DKFZ) Im Neuenheimer Feld 280 69120 Heidelberg Germany

A C.I.P. Catalog record for this book is available from the Library of Congress ISBN: 978-3-540-36847-2 This publication is available also as: Electronic publication under ISBN 978-3-540-47648-1 and Print and electronic bundle under ISBN 978-3-540-47649-8 Library of Congress Control Number 2008921484 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg New York 2008 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. THIS PARAGRAPH FOR MEDICAL TITLES ONLY: Product liability: The publishers cannot guarantee the accuracy of any information about the application of operative techniques and medications contained in this book. In every individual case the user must check such information by consulting the relevant literature. Springer is part of Springer Science+Business Media springer.com Printed on acid-free paper SPIN: 150231 2109 — 5 4 3 2 1 0

Preface To The First Edition

Cancer, although a dreadful disease, is at the same time a fascinating biological phenotype. Around 1980, cancer was first attributed to malfunctioning genes and, subsequently, cancer research has become a major area of scientific research supporting the foundations of modern biology to a great extent. To unravel the human genome sequence was one of those extraordinary tasks, which has largely been fuelled by cancer research, and many of the fascinating insights into the genetic circuits that regulate developmental processes have also emerged from research on cancer. Diverse biological disciplines such as cytogenetics, virology, cell biology, classical and molecular genetics, epidemiology, biochemistry, together with the clinical sciences, have closed ranks in their search of how cancer develops and to find remedies to stop the abnormal growth that is characteristic of cancerous cells. In the attempt to establish how, why and when cancer occurs, a plethora of genetic pathways and regulatory circuits have been discovered that are necessary to maintain general cellular functions such as proliferation, differentiation and migration. Alterations of this fine-tuned network of cascades and interactions, due to endogenous failure or to exogenous challenges by environmental factors, may disable any member of such regulatory pathways. This could, for example, induce the death of the affected cell, may mark it for cancerous development or may immediately provide it with a growth advantage within a particular tissue. Recent developments have seen the merger of basic and clinical science. Of the former, particularly genetics has provided instrumental and analytical tools with which to assess the role of environmental factors in cancer, to refine and enable diagnosis prior to the development of symptoms and to evaluate the prognosis of patients. Hopefully, even better strategies for causal therapy will become available in the future. Merging the basic and clinical science disciplines towards the common goal of fighting cancer, calls for a comprehensive reference source to serve both as a tool to close the language gap between clinical and basic science investigators and as an information platform for the student and the informed layperson alike. Obviously this was an extremely ambitious goal, and the immense progress in the field cannot always be portrayed in line with the latest developments. The aim of the Encyclopedia is to provide the reader with an entrance point to a particular topic. It should be of value to both basic and clinical scientists working in the field of cancer research. Additionally both students and lecturers in the life sciences should benefit highly from this database. I therefore hope that this Encyclopedia will become an essential complement to existing science resources. The attempts to identify the mechanisms underlying cancer development and progression have produced a wealth of facts, and no single individual is capable of addressing the immense breadth of the field with undisputed authority. Hence, the ‘Encyclopedic Reference of Cancer’ is the work of many authors, all of whom are experts in their fields and reputable members of the international scientific community. Each author contributed a large number of keyword definitions and in-depth essays and in so doing it was possible to cover the broad field of cancer-related topics within a single publication. Obviously this approach entails a form of presentation, in which the author has the freedom to set priorities and to promote an individual point of view. This is most obvious when it comes to nomenclature, particularly that of genes and proteins. Although the editorial intention was to apply the nomenclature of the Human Genome Organisation (HUGO), the more vigorous execution of this attempt has been left to future endeavours. In the early phase of planning the Encyclopedia, exploratory contacts to potential authors produced an overwhelmingly positive response. The subsequent contact with almost 300 contributory authors was a marvellous experience, and I am extremely grateful for their excellent and constructive cooperation. An important element in the preparation of the Encyclopedia has been the competent secretarial assistance of Hiltrud Wilbertz of the Springer-Verlag and of Ingrid Cederlund and Cornelia Kirchner of the DKFZ. With great attention to detail they helped to keep track of the technical aspects in the preparation of the manuscript. It was a pleasure to work with the Springer crew, including Dr. Rolf Lange as the Editorial Director (Medicine) and Dr. Thomas Mager, Senior Editor for Encyclopedias and Dictionaries. In particular I wish to thank Dr. Walter Reuss, who untiringly has mastered all aspects and problems associated with the management of the numerous manuscripts that were received from authors of the international scientific community. It has been satisfying and at times comforting to see how he made illustration files come alive. Thanks also to Dr. Claudia Lange who, being herself a knowledgeable cell biologist, has worked as the scientific editor. Her commitment and interest have substantially improved this Encyclopedia.

vi

Preface To The First Edition

As a final word, I would like to stress that although substantial efforts have been made to compose factually correct and well understandable presentations, there may be places where a definition is incomplete or a phrase in an essay is flawed. All contributors to this Encyclopedia will be extremely happy to receive possible corrections, or revisions, in order for them to be included in any future editions of the ‘Encyclopedic Reference of Cancer’. Heidelberg, September 2001 MANFRED SCHWAB

Preface To The Second Edition

Given the overwhelming success of the First Edition of the Cancer Encyclopedia, which appeared in 2001, and the amazing development in the different fields of cancer research, it has been decided to publish a second fully revised and expanded edition, following the principle concept of the first edition that has proven so successful. Recent developments are seeing a dynamic merging of basic and clinical science, with translational research increasingly becoming a new paradigm in cancer research. The merging of different basic and clinical science disciplines towards the common goal of fighting against cancer has long ago called for the establishment of a comprehensive reference source both as a tool to close the language gap between clinical and basic science investigators and as a platform of information for advanced students and informed laymen alike. It is intended to be a resource for all interested in information beyond their specific own expertise. While the First Edition had featured contributions from approximately 300 scientists/clinicians in one Volume, the Second Edition includes more than 1000 contributors in 4 Volumes with an A–Z format of more than 7000 entries. It provides definitions of common acronyms and short definitions of both related terms and processes in the form of keyword entries. A major information source are detailed essays that provide comprehensive information on syndromes, genes and molecules, and processes and methods. Each essay is well-structured, with extensive cross-referencing between entries. Essays represent original contributions by the corresponding authors, all distinguished scientists in their own field, Editorial input has been carefully restricted to formal aspects. A panel of Field Editors, each an eminent international expert for the corresponding field, has served to ensure the presentation of timely and authoritative Encyclopedia entries. These new traits are likely to meet the expectance that a wide community has towards a cancer reference works. An important element in the preparation of the Encyclopedia has been the competent support by the Springer crew, Dr. Michaela Bilic, Saskia Ellis and, lately, Jana Simniok. I am extremely grateful for their excellent and pleasant cooperation. The Cancer Encyclopedia, Second Edition, will be accessible both in print and online versions. Clinicians, research scientists and advanced students will find this an amazing resource and a highly informative reference to cancer. Heidelberg, March 15, 2008 MANFRED SCHWAB

Editor in Chief

Manfred Schwab Tumor Genetics German Cancer Research Center, DKFZ Heidelberg Germany [email protected]

Field Editors

S TEFAN B ARTH Department of Pharmaceutical Product Development, Fraunhofer-Institute for Molecular Biology and Applied Ecology Aachen Germany [email protected] PAOLO B OFFETTA Lifestyle, Environment and Cancer Group International Agency for Research on Cancer Lyon France [email protected] G RAHAM A. C OLDITZ Washington University in St. Louis St. Louis, MO USA [email protected]

Houston, TX USA [email protected] J OSEPH R. L ANDOLPH Departments of Molecular Microbiology and Immunology, and Pathology; USC/Norris Comprehensive Cancer Center, Keck School of Medicine; Department of Molecular Pharmacology and Pharmaceutical Sciences, School of Pharmacy Health Sciences Campus University of Southern California Los Angeles, CA USA [email protected] H ENRY LYNCH Preventive Medicine and Public Health Hereditary Cancer Institute Creighton University Omaha, NE USA [email protected]

R OY J. D UHÉ Department of Pharmacology and Toxicology University of Mississippi Medical Center Jackson, MS USA [email protected]

PAUL G. M URRAY CRUK Institute for Cancer Studies The Medical School University of Birmingham Birmingham UK [email protected]

K ENT H UNTER Metastasis Susceptibility Section Laboratory of Cancer Biology & Genetics CCR/NCI/NIH Bethesda, MD USA [email protected]

S AUL S USTER The Ohio State University Columbus, OH USA [email protected]

J ESPER J URLANDER Department of Hematology and the Leukemia Laboratory Rigshospitalet Copenhagen Denmark [email protected] R AKESH K UMAR Molecular and Cellular Oncology The University of Texas MD Anderson Cancer Center

A NDREW T HORBURN University of Colorado at Denver and Health Sciences Center Aurora, CO USA [email protected] M ARTIN T OBI University of Pennsylvania School of Medicine Chief GI Section Philadelphia VAMC Philadelphia, PA USA [email protected]

List of Contributors

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List of Contributors V ESA A ALTONEN Department of Anatomy Institute of Biomedicine University of Turku Turku Finland [email protected]

FARRUKH A FAQ Department of Dermatology University of Wisconsin Medical Sciences Center Madison, WI USA [email protected]

C ORY A BATE -S HEN Center for Advanced Biotechnology and Medicine UMDMJ – Robert Wood Johnson Medical School Piscataway, NJ USA [email protected]

C HAPLA A GARWAL Department of Pharmaceutical Sciences, School of Pharmacy University of Colorado Health Sciences Center Denver, CO USA [email protected]

P HILLIP H. A BBOSH Department of Pathology and Laboratory Medicine Indiana University School of Medicine Indianapolis, IN USA [email protected] F RITZ A BERGER Department of Molecular Biology University of Salzburg Salzburg, Austria [email protected] H INRICH A BKEN Tumor Genetics, Clinic I Internal Medicine and Center for Molecular Medicine Cologne, University of Cologne Cologne, Germany [email protected] A MAL M. A BU -G HOSH Departments of Pediatric Hematology and Oncology Lombardi Comprehensive Cancer Center Georgetown University Washington DC, NW USA [email protected] R OSITA A CCARDI Infections and Cancer Biology Group International Agency for Research on Cancer Lyon France [email protected] F ILIPPO A CCONCIA Molecular and Cellular Oncology The University of Texas M. D. Anderson Cancer Center Houston, TX USA IFOM The FIRC Institute for Molecular Oncology Milan Italy

R AJESH A GARWAL Department of Pharmaceutical Sciences, School of Pharmacy University of Colorado Health Sciences Center Denver, CO USA [email protected] PATRIZIA A GOSTINIS Catholic University of Leuven Leuven Belgium [email protected] T ERJE A HLQUIST Department of Cancer Prevention Rikshospitalet-Radiumhospitalet Medical Centre Oslo Norway [email protected] S HAHID A HMED Saskatoon Cancer Center University of Saskatchewan Saskatoon, SK Canada [email protected] J OOHONG A HNN Department of Life Science Gwangju Institute of Science and Technology Buk-Gu, Gwangju Korea [email protected] C EM A KIN University of Michigan Ann Arbor, MI USA [email protected] E NRIQUE DE A LAVA Centro de Investigación del Cáncer-IBMCC Salamanca Spain [email protected]

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List of Contributors

A MI A LBIHN Department of Microbiology Tumor and Cell Biology (MTC) Karolinska Institutet Stockholm Sweden [email protected] A DRIANA A LBINI IRCCS Multimedica Milano Italy [email protected] J ÉRÔME A LEXANDRE Faculté de Médecine Paris – Descartes UPRES 18-33, Groupe Hospitalier Cochin – Saint Vincent de Paul Paris France [email protected] S HADAN A LI Karmanos Cancer Institute Wayne State University Detroit, MI USA [email protected] M ALCOLM R. A LISON Centre for Diabetes and Metabolic Medicine Queen Mary’s School of Medicine and Dentistry Institute of Cell and Molecular Science London UK [email protected] C ATHERINE A LIX -PANABIERES University Medical Center, Lapeyronie Hospital Montpellier France [email protected] A LISON L. A LLAN Cancer Research Laboratories, London Regional Cancer Program; and Departments of Oncology and Anatomy and Cell Biology, Schulich School of Medicine and Dentistry University of Western Ontario, London, ON Canada [email protected] PAOLA A LLAVENA Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected] A NGEL A LONSO Deutsches Krebsforschungszentrum Heidelberg Germany [email protected]

G IANFRANCO A LPINI Departments of Medicine and Systems Biology and Translational Medicine, Central Texas Veterans Health Care System, Scott & White Hospital and Texas A&M University System Health Science Center Temple TX USA [email protected]

M ARIE -C LOTILDE A LVES -G UERRA The Wistar Institute Molecular and Cellular Oncogenesis Program Philadelphia, PA USA [email protected] P IERRE Å MAN LLCR, Department of pathology, Institute of Biomedicine Sahlgrenska Academy Goteborg University Gothenburg Sweden [email protected] K UROSH A MERI University of Stanford School of Medicine Department of Surgery/Surgical Oncology Stanford, CA USA [email protected] M OUNIRA A MOR -G UÉRET Institut Curie – UMR 2027 CNRS Orsay Cedex France [email protected] K ENNETH C. A NDERSON Department of Medical Oncology The Jerome Lipper Multiple Myeloma Center Dana-Farber Cancer Institute Harward Medical School Boston, MA USA [email protected] P ETER A NGEL Deutsches Krebsforschungszentrum Division of Signal Transduction and Growth Control Heidelberg Germany [email protected] A NDREA A NICHINI Department of Experimental Oncology Fondazione IRCCS Istituto Nazionale per lo Studio e la Cura dei Tumori Milan Italy [email protected]

List of Contributors

P ETER D. A PLAN Genetics Branch, Center for Cancer Research National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected]

E LIAS S. J. A RNÉR Department of Medical Biochemistry and Biophysics Karolinska Institutet Stockholm Sweden [email protected]

N ATALIA A PTSIAURI Hospital Universitario Virgen de las Nieves Granada Spain [email protected]

S TEFANO ATERINI Department of Experimental Pathology and Oncology University of Firenze Firenze Italy [email protected]

R AMI A QEILAN Molecular Virology, Immunology and Medical Genetics The Ohio State University, Comprehensive Cancer Center Columbus, OH USA [email protected]

M ARC A UMERCIER Institute of Biology of Lille, Pasteur Institute of Lille Universities of Lille 1 and Lille 2 Lille France [email protected]

T SUTOMU A RAKI Departments of Obstetrics and Gynecology Nippon Medical School Kawasaki and Tokyo Japan [email protected]

R ICCARDO A UTORINO Clinica Urologica Seconda Università degli Studi Napoli Italy [email protected]

S ANCHIA A RANDA School of Nursing The University of Melbourne Carlton, VIC Australia [email protected]

M ATIAS A. AVILA Division of Hepatology and Gene Therapy, CIMA University of Navarra Pamplona Spain [email protected]

D IEGO A RANGO Molecular Biology and Biochemistry Research Center (CIBBIM) Valle Hebron Hospital Research Institute Barcelona Spain [email protected]

H AVA AVRAHAM Division of Experimental Medicine Beth Israel Deaconess Medical Center Harvard Institutes of Medicine Boston, MA USA [email protected]

D AVID J. A RATEN NYU School of Medicine NYU Cancer Institute, and the New York VA Medical Center New York, NY USA [email protected]

S HALOM AVRAHAM Division of Experimental Medicine Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine Boston, MA USA [email protected]

VALENTINA A RCANGELI Department of Oncology Infermi Hospital Rimini Italy [email protected]

S ANJAY AWASTHI United States Longview Cancer Center Longview, TX USA [email protected]

G EMMA A RMENGOL Department of Pathology Vall d’Hebron University Hospital Barcelona, Spain [email protected]

Y OGESH C. AWASTHI Department of Human Biological Chemistry and Genetics University of Texas Medical Branch Galveston, TX USA [email protected]

xv

xvi

List of Contributors

M ATHIJS B AENS Centre for Human Genetics, Molecular Genetics-Flanders Interuniversity Institute for Biotechnology University of Leuven Leuven Belgium [email protected] D EBASIS B AGCHI Department of Pharmacy Sciences Creighton University Medical Center Omaha, NE USA [email protected] X UE -TAO B AI State Key Laboratory for Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital School of Medicine Shanghai Jiao Tong University Shanghai, People's Republic of China [email protected]

L AURENT B ALENCI INSERM Unité Mixte 873 Grenoble Cedex 09 France [email protected] S USHANTA K. B ANERJEE Division of Hematology and Oncology, School of Medicine Kansas University of Medical Center Kansas City, KS USA [email protected] M ICHAL B ANIYASH The Lautenberg Center for General and Tumor Immunology The Hebrew University-Hadassah Medical School Jerusalem Israel [email protected]

J ÜRGEN B AJORATH Department of Life Science Informatics B-IT University of Bonn, Bonn Germany [email protected]

R ACHEL B AR -S HAVIT Department of Oncology Hadassah-University Hospital Jerusalem Israel [email protected]

S TUART G. B AKER Biometry Research Group National Cancer Institute Bethesda, MD USA [email protected]

A DITYA B ARDIA Department of Internal Medicine Mayo Clinic College of Medicine Rochester, MN USA [email protected]

E LIZABETH K. B ALCER -K UBICZEK Department of Radiation Oncology University of Maryland School of Medicine Baltimore, MD USA [email protected]

R AFIJUL B ARI Vascular Biology Center, Cancer Institute, and Departments of Medicine and Molecular Sciences University of Tennessee Health Science Center Memphis, TN USA [email protected]

E NKE B ALDINI Department of Experimental Medicine University of Rome “Sapienza” Rome Italy [email protected] G RAHAM S. B ALDWIN Department of Surgery University of Melbourne Austin Health Melbourne, VIC Australia [email protected] S HERRI B ALE GeneDx, Rockville, MD USA [email protected]

D R N ICOLA L. P. B ARNES Department of Academic Surgery South Manchester University Hospital Manchester UK R OBERT B AROUKI INSERM UMR-S 747, Université René Descartes Paris Paris, France [email protected] JM B ARROS -D IOS Department of Preventive Medicine and Public Health University of Santiago de Compostela C/San Francisco Spain [email protected]

List of Contributors

H ARRY B ARTELINK Department of Radiotherapy The Netherlands Cancer Institute–Antoni van Leeuwenhoek Hospital Amsterdam The Netherlands [email protected] S TEFAN B ARTH Department of Pharmaceutical Product Development Fraunhofer-Institute for Molecular Biology and Applied Ecology Aachen Germany [email protected] H ELMUT B ARTSCH Division of Toxicology and Cancer Risk Factors German Cancer Research Center (DKFZ) Heidelberg Germany [email protected] T HOMAS B ARZ Max-Panck-Institut für Psychiatrie München Germany [email protected] H OLGER B ASTIANS Philipps University Marburg Institute for Molecular Biology and Tumor Research (IMT) Marburg Germany [email protected] A. B ATISTATOU Ioannina University Medical School Ioannina Greece [email protected] F. B ATTEUX Faculté de Médecine Paris – Descartes UPRES 18-33, Groupe Hospitalier Cochin – Saint Vincent de Paul Paris France [email protected] J ACQUES B AUDIER INSERM Unité Mixte 873 Grenoble Cedex 09 France [email protected] PAUL B AUER Pfizer Research Technology Center Cambridge, MA USA [email protected]

xvii

PAIGE J. B AUGHER Department of Cancer Biology Vanderbilt University Medical School Nashville, TN USA [email protected] A SNE R. B AUSKIN Centre for Immunology, St. Vincents Hospital and Department of Medicine University of New South Wales Sydney, NSW Australia [email protected] N ICOLE B EAUCHEMIN McGill Cancer Centre McGill University Montreal, Quebec Canada [email protected] J OHN F. B ECHBERGER Department of Cellular and Physiological Sciences The University of British Columbia Vancouver, BC Canada [email protected] G ERHILD B ECKER Department of Internal Medicine II (Gastroenterology, Hepatology, Endocrinology) University Hospital Freiburg Freiburg, Germany [email protected] H EINZ B ECKER Department of General and Visceral Surgery University Medical Center Göttingen Germany [email protected] M ARIE E. B ECKNER Department of Pathology University of Pittsburgh School of Medicine Pittsburgh, PA USA [email protected] C LAUS B ELKA Department of Radiation Oncology University Tübingen Tübingen Germany [email protected] M AURIZIO B ENDANDI University Clinic and Center for Applied Medical Research University of Navarra Pamplona Spain [email protected]

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List of Contributors

YAACOV B EN -D AVID Division of Cancer Biology, Sunny brook Health Sciences University of Toronto Toronto, ONT Canada [email protected] S UZANNE M. B ENJES Cancer Genetics Research Group, University of Otago at Christchurch Christchurch, New Zealand [email protected] C ARMEN B ERASAIN Division of Hepatology and Gene Therapy, CIMA University of Navarra Pamplona Spain [email protected] A LAN B EREZOV Department of Pathology and Laboratory Medicine & Abramson Cancer Center University of Pennsylvania Philadelphia, PA USA [email protected] R OB J. W. B ERG University Medical Center Utrecht Utrecht The Netherlands [email protected]

S ANCHITA B HADRA Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology The University of Texas at Austin Austin, TX USA [email protected] K UMAR M. R. B HAT Department of Dermatology University of Wisconsin School of Medicine and Public Health Sciences Madison, WI USA [email protected] M ALAYA B HATTACHARYA -C HATTERJEE University of Cincinnati and The Barrett Cancer Center Cincinnatti, OH USA [email protected] C ATERINA B IANCO Mammary Biology and Tumorigenesis Laboratory National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected] J EAN -M ICHEL B IDART Institut de Cancérologie Gustave-Roussy Villejuif and Université Paris-Sud 11, Paris France [email protected]

C ORINNA B ERGELT Institute of Medical Psychology University Medical Center Hamburg-Eppendorf Hamburg Germany [email protected]

J ACLYN A. B IEGEL The Children’s Hospital of Philadelphia Philadelphia, PA USA [email protected]

R ENE B ERNARDS The Netherlands Cancer Institute Amsterdam The Netherlands [email protected]

M ARGHERITA B IGNAMI Istituto Superiore di Sanita’ Rome Italy [email protected]

Z WI B ERNEMAN Laboratory of Experimental Hematology Antwerp University Hospital Edegem Belgium [email protected]

I RENE V. B IJNSDORP Department of Medical Oncology VU University Medical Center Amsterdam The Netherlands [email protected]

J ÉRÔME B ERTHERAT Assistance Publique Hôpitaux de Paris, Hôpital Cochin Department of Endocrinology Reference Center for Rare Adrenal Diseases Paris France [email protected]

C HEN B ING Division of Cellular and Metabolic Medicine, School of Clinical Sciences University of Liverpool Liverpool UK [email protected]

List of Contributors

M ARC B IRKHAHN Departments of Urology and Pathology University of Southern California Keck School of Medicine Los Angeles, CA USA [email protected] G IOVANNI B LANDINO Rome Oncogenomic Center, Department of Experimental Oncology Regina Elena Cancer Institute Rome Italy [email protected] D AVID E. B LASK Bassett Research Institute The Mary Imogene Bassett Hospital Cooperstown, NY USA [email protected] J ONATHAN B LAY Department of Pharmacology Dalhousie University Halifax, NS Canada [email protected] A DRIAN J. B LOOR The Christie NHS Trust Manchester UK [email protected] J ULIAN B LOW Wellcome Trust Biocentre University of Dundee Dundee, Scotland UK [email protected] P ETER B LUME -J ENSEN Serono Reproductive Biological Institute Randolph, MA USA

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PAOLO B OFFETTA Gene-Environment Epidemiology Group International Agency for Research on Cancer Lyon France [email protected] S TEFAN K. B OHLANDER Medizinische Klinik und Poliklinik III, Klinikum Großhadern Universität München München Germany [email protected] VALENTINA B OLLATI Department of Occupational and Environmental Health “Clinica del Lavoro L. Devoto” University of Milan Milan Italy [email protected] M ARIA G RAZIA B ORRELLO Department of Experimental Oncology IRCCS Istituto Nazionale Tumori Foundation Milan Italy [email protected] G IUSEPPE B ORZACCHIELLO Department of Pathology and Animal health University of Naples Federico II Naples Italy [email protected] VALERIE B OSCH Forschungsschwerpunkt Infektion und Krebs, F020 German Cancer Research Center (DKFZ) Heidelberg Germany [email protected] C HRIS B OSHOFF Cancer Research Campaign Viral Oncology Group Wolfson Institute for Biomedical Research University College London London UK [email protected]

S ARAH B OCCHINI Department of Experimental Medicine University of Rome “Sapienza” Rome Italy [email protected]

F RANCK B OURDEAUT Département de pédiatrie INSERM 830, Biologie et génétique des tumeurs Institut Curie Paris France [email protected]

A NN M. B ODE The Hormel Institute University of Minnesota Austin, MN USA [email protected]

J EAN -P IERRE B OURQUIN Pediatric Oncology University Children’s Hospital Zurich Zurich Switzerland [email protected]

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J UDITH V. M. G. B OVÉE Department of Pathology Leiden University Medical Center Leiden The Netherlands J.V.M.G. [email protected]

K ATJA B ROCKE -H EIDRICH Institute of Clinical Immunology and Transfusion medicine University Hospital of Leipzig Leipzig Germany [email protected]

N ORMAN B OYD Campbell Family Institute for Breast Cancer Research Ontario Cancer Institute Toronto, ONT Canada [email protected]

A NGELA B RODIE University of Maryland School of Medicine Baltimore, MD USA University of Maryland Greenebaum Cancer Center Baltimore, MD USA [email protected]

S VEN B RANDAU Department of Otorhinolaryngology University Duisburg-Essen Essen Germany [email protected] B URKHARD H. B RANDT Institute for Tumour Biology University Medical Centre Hamburg Germany [email protected] H ILTRUD B RAUCH Dr. Margarete Fischer-Bosch-Institute of Clinical Pharmacology and University Tuebingen Stuttgart Germany [email protected] S AMUEL N. B REIT Centre for Immunology, St. Vincents Hospital and Department of Medicine University of New South Wales Sydney, NSW Australia [email protected] E DWIN B REMER Groningen University Institute for Drug Exploration (GUIDE), Department of Pathology & Laboratory Medicine Section Medical Biology, Laboratory for Tumor Immunology Groningen The Netherlands [email protected]

C HRISTOPHER L. B ROOKS Institute for Cancer Genetics, and Department of Pathology College of Physicians and Surgeons, Columbia University New York, NY USA M AI N. B ROOKS Surgical Oncology, School of Medicine University of California Los Angeles, CA USA [email protected] D AVID A. B ROWN Centre for Immunology, St. Vincents Hospital and Department of Medicine University of New South Wales Sydney, NSW Australia [email protected] K AREN B ROWN Cancer Biomarkers and Prevention Group Department of Cancer Studies, University of Leicester Leicester UK [email protected] K EVIN B ROWN University of Florida College of Medicine Gainesville, FL USA [email protected]

C ATHERINE B RENNER University of Versailles/SQY CNRS UMR 8159, Versailles France [email protected]

D IEDERIK DE B RUIJN Department of Human Genetics Radboud University Nijmegen Medical Centre Nijmegen The Netherlands [email protected]

D AVID J. B RENNER Department of Radiation Oncology Columbia University New York, NY USA [email protected]

T ILMAN B RUMMER Cancer Research Program Garvan Institute of Medical Research Sydney, NSW Australia [email protected]

List of Contributors

A NTONIO B RUNETTI Department of Experimental and Clinical Medicine G. Salvatore University of Catanzaro Magna Græcia Catanzaro Italy [email protected] A NDREAS K. B UCK Department of Nuclear Medicine Technical University of Munich Munich Germany [email protected] L ASZLO B UDAY Department of Medical Chemistry Semmelweis University Medical School Budapest Hungary [email protected] M ARIE A NNICK B UENDIA Oncogenesis and Molecular Virology Unit Inserm U579 Institut Pasteur, Paris France [email protected] R ALF B UETTNER City of Hope National Medical Center and Beckman Research Institute Duarte, CA USA [email protected] N IGEL J. B UNDRED Department of Academic Surgery South Manchester University Hospital Manchester UK [email protected] I RINA B U ß Institute of Pharmacy University of Bonn Bonn Germany [email protected] A LEXANDER B ÜRKLE Department of Biology University of Konstanz Konstanz Germany [email protected] J ADISH B UTANY Laboratory Medicine and Pathobiology University Health Network/Toronto Toronto, ON Canada [email protected]

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N EVILLE J. B UTCHER School of Biomedical Sciences University of Queensland St Lucia, QLD Australia [email protected] T IMON P. H. B UYS Department of Cancer Genetics and Developmental Biology British Columbia Cancer Research Centre Vancouver, BC Canada [email protected] Y I C AI Department of Pathology Baylor College of Medicine Houston, TX USA Y IQIANG C AI Section of Nephrology Yale University School of Medicine New Haven, CT USA [email protected] B RUNO C ALABRETTA Thomas Jefferson University Kimmel Cancer Institute Philadelphia, PA USA [email protected] D ANIELE C ALISTRI Molecular Laboratory Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori Meldola (Forlì) Italy [email protected] J AVIER C AMACHO Pharmacology Division Centro de Investigación y de Estudios Avanzados del I.P.N. Mexico City, Mexico [email protected] W ILLIAM G. C ANCE Departments of Surgery University of Florida College of Medicine Gainesville, FL USA [email protected] A MPARO C ANO Departamento de Bioquímica Facultad de Medicina, UAM, Instituto de Investigaciones Biomédicas “Alberto Sols” CSIC-UAM Madrid Spain [email protected]

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S HARON C ANTOR Assistant Professor of Cancer Biology UMASS Medical School Worcester, MA USA [email protected]

E STEBAN C ELIS H. Lee Moffitt Cancer Center and Research Institute University of South Florida Tampa, FL USA [email protected]

A NTHONY J. C APOBIANCO The Wistar Institute Molecular and Cellular Oncogenesis Program Philadelphia, PA USA [email protected]

H O M AN C HAN Division of Biochemistry and Molecular Biology University of Glasgow Glasgow UK

S ALVATORE J. C ARADONNA University of Medicine and Dentistry of New Jersey Stratford, NJ USA [email protected] M ICHELE C ARBONE Cancer Research Center of Hawaii University of Hawaii Honolulu, HI USA [email protected] N EIL O C ARRAGHER Advanced Science and Technology Laboratory AstraZeneca R&D Charnwood Loughborough UK [email protected] M ICHELA C ASANOVA Pediatric Oncology Unit Fondazione IRCCS Istituto Nazionale Tumori Milano Italy [email protected] W OLFGANG H. C ASELMANN Medizinische Klinik und Poliklinik I Rheinische Friedrich-Wilhelms-Universität Bonn Germany [email protected] R OBERTO C ATTANEO Molecular Medicine Program and Virology and Gene Therapy Track Mayo Clinic College of Medicine Rochester, MN USA [email protected] W EBSTER K. C AVENEE Ludwig Institute for Cancer Research, UCSD La Jolla, CA USA [email protected]

D AWN S. C HANDLER Department of Pediatrics, Columbus Children’s Research Institute, Center for Childhood Cancer The Ohio State University School of Medicine and Public Health Columbus, OH USA [email protected] M AU -S UN C HANG Department of Medical Research Mackay Memorial Hospital Taipei County 251 Taiwan [email protected] M EI -C HI C HANG Biomedical Science Team Chang Gung Institute of Technology Taoyuan Taiwan [email protected] J ANE C.-J. C HAO School of Nutrition and Health Sciences Taipei Medical University Taipei Taiwan [email protected] C HRISTINE C HAPONNIER Department of Pathology and Immunology University of Geneva Geneva Switzerland [email protected] K ONSTANTINOS C HARALABOPOULOS Ioannina University Medical School Ioannina Greece [email protected] M ALAY C HATTERJEE Department of Pharmaceutical Technology Jadavpur University Calcutta, West Bengal India [email protected]

List of Contributors

S UNIL K. C HATTERJEE University of Cincinnati and The Barrett Cancer Center Cincinnatti, OH USA [email protected] G AUTAM C HAUDHURI Department of Molecular and Medical Pharmacology and Department of Obstetrics and Gynecology David Geffen School of Medicine at UCLA Los Angeles, CA USA [email protected] M. A SIF C HAUDRY University Department of Surgery Royal Free and University College London Medical School London UK [email protected] D HARMINDER C HAUHAN Department of Medical Oncology The Jerome Lipper Multiple Myeloma Center Dana Farber Cancer Institute Harvard Medical School Boston, MA USA [email protected] J EREMY P. C HEADLE Institute of Medical Genetics Cardiff University Heath Park, Cardiff UK [email protected] S AI -J UAN C HEN State Key Laboratory for Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital School of Medicine Shanghai Jiao Tong University Shanghai, People's Republic of China [email protected] TAOSHENG C HEN New Leads, Bristol-Myers Squibb Wallingford, CT USA [email protected] Z HU C HEN State Key Laboratory for Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital School of Medicine Shanghai Jiao Tong University Shanghai, People's Republic of China [email protected] G EORGE Z. C HENG Mount Sinai School of Medicine New York, NY USA [email protected]

J IN Q. C HENG Molecular Oncology and Pathology, H. Lee Moffitt Cancer Center & Research Institute University of South Florida College of Medicine Tampa, FL USA [email protected] L IANG C HENG Department of Pathology and Laboratory Medicine Indiana University School of Medicine Indianapolis, IN USA [email protected] YA -H UI C HI National Institute of Allergy and Infectious Disease, NIH Bethesda, MD USA [email protected] M ARTYN A. C HIDGEY Division of Medical Sciences University of Birmingham Clinical Research Block Queen Elizabeth Hospital Birmingham UK [email protected] Y OUNG -W ON C HIN College of Pharmacy The Ohio State University Columbus, OH USA [email protected] S UDHAKAR C HINTHARLAPALLI Department of Veterinary Physiology and Pharmacology Texas A&M University College Station, TX USA [email protected] A LEXANDRE C HLENSKI The Robert H. Lurie Comprehensive Cancer Center Northwestern University Feinberg School of Medicine Chicago, IL USA [email protected] W ILLIAM C HI -S HING C HO Department of Clinical Oncology Queen Elizabeth Hospital Kowloon Hong Kong [email protected] M ICHAEL C HOPP Neurology Research Henry Ford Health System Detroit, MI USA [email protected]

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P EI -L UN C HOU Division of Allergy-Immunology-Rheumatology, Department of Internal Medicine Lin Shin Hospital Taichung Taiwan

P IER PAOLO C LAUDIO Department of Surgery Marshall University Huntington, WV USA [email protected]

C LAUS C HRISTENSEN Department of Cancer Genetics Danish Cancer Society Copenhagen Denmark [email protected]

E LIZABETH B. C LAUS Department of Epidemiology and Public Health Yale University School of Medicine New Haven, CT USA [email protected]

R IKKE C HRISTENSEN Anatomy and Neurobiology, Institute of Medical Biology University of Southern Denmark Odense, Denmark [email protected]

PASCAL C LAYETTE SPI-BIO, Service de Neurovirologie, CEA, CRSSA, EPHE Fontenay aux Roses Cedex France [email protected]

G ERHARD C HRISTOFORI Department of Clinical-Biological Sciences, Centre of Biomedicine Institute of Biochemistry and Genetics, University of Basel Basel Switzerland [email protected]

S TEVEN C. C LIFFORD Northern Institute for Cancer Research Newcastle University Newcastle upon Tyne UK [email protected]

R ICHARD I. C HRISTOPHERSON School of Molecular and Microbial Biosciences University of Sydney Sydney, NSW Australia [email protected]

K EVIN A. C OCKELL Nutrition Research Division Health Canada Ottawa, ON Canada [email protected]

B ONG H YUN C HUNG BioNanotechnology Research Center Korea Research Institute of Bioscience and Biotechnology Yuseong, Daejeon Republic of Korea [email protected]

S USAN L. C OHN Clinical Sciences The Institute for Molecular Pediatric Sciences University of Chicago Chicago, IL USA [email protected]

F UNG -L UNG C HUNG Department of Oncology, Lombardi Comprehensive Cancer Center Georgetown University Medical Center Washington, DC USA [email protected]

G RAHAM A. C OLDITZ Washington University in St. Louis St. Louis, MO USA [email protected]

J ACKY K. H. C HUNG Department of Medical Genetics and Microbiology University of Toronto Toronto, Ontario Canada [email protected]

PAOLA C OLLINI Anatomic Pathology Department Fondazione IRCCS Istituto Nazionale Tumori Milano Italy [email protected]

S UE C LARK The Polyposis Registry St Mark’s Hospital Harrow UK [email protected]

A NDREW R. C OLLINS Department of Nutrition University of Oslo Oslo Norway [email protected]

List of Contributors

J OAN W. C ONAWAY Stowers Institute for Medical Research Kansas, MO USA [email protected] R ONALD C. C ONAWAY Stowers Institute for Medical Research Kansas, MO USA [email protected] N ATHALIE C OOLS Laboratory of Experimental Hematology Antwerp University Hospital Edegem Belgium [email protected] H ELEN C. C OONEY UCD School of Biomolecular and Biomedical Science UCD Conway Institute University College Dublin Dublin Ireland [email protected] K UMARASEN C OOPER Department of Pathology University of Vermont Burlington, VT USA [email protected] L AURENCE J. N. C OOPER Division of Pediatrics, Department of Immunology M.D. Anderson Cancer Center Houston, TX USA [email protected] P ETER J. C OOPMAN CRBM/CNRS UMR 5237, Univ Montpellier II, Montpellier France [email protected] R ICHARD J. C OTE Departments of Urology and Pathology University of Southern California Keck School of Medicine Los Angeles, CA USA [email protected] M ARCUS V. C RONAUER Institute of General Zoology and Endocrinology University of Ulm Ulm Germany [email protected]

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S IDNEY C ROUL Department of Pathology, UHN University of Toronto ON Canada [email protected] V INCENT L. C RYNS Department of Medicine, Feinberg School of Medicine Northwesten University Chicago, IL USA [email protected] R ONALD G. C RYSTAL Department of Genetic Medicine Weill Medical College of Cornell University New York, NY USA [email protected] J IUWEI C UI Department of Medical Biophysics University of Toronto Toronto, ONT Canada [email protected] E DNA C UKIERMAN Basic Science/Tumor Cell Biology Fox Chase Cancer Center Philadelphia, PA USA [email protected] Z ORAN C ULIG Department of Urology Innsbruck Medical University Innsbruck Austria [email protected] D AVID T. C URIEL Departments of Medicine, Pathology, Surgery, Obstetrics and Gynecology and the Gene Therapy Center, Division of Human Gene Therapy University of Alabama at Birmingham Birmingham, AL USA [email protected] YATARO D AIGO Institute of Medical Science The University of Tokyo Tokyo Japan [email protected] A NGUS G. D ALGLEISH St. George’s Hospital Medical School London UK [email protected]

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List of Contributors

A SHRAF D ALLOL Department of Medical and Molecular Genetics, Institute of Biomedical Research University of Birmingham Birmingham UK [email protected] TAMAS D ALMAY School of Biological Sciences University of East Anglia Norwich UK [email protected] I VAN D AMJANOV Department of Pathology University of Kansas School of Medicine Kansas City, KS USA [email protected] V INCENT D AMMAI Hollings Cancer Center and Department of Pathology and Laboratory Medicine Medical University of South Carolina Charleston, SC USA [email protected] C HENDIL D AMODARAN Department of Clinical Sciences University of Kentucky Lexington, Kentucky USA [email protected] J ANET E. D ANCEY Division of Cancer Treatment and Diagnosis National Cancer Institute Rockville, MD USA [email protected] C HI V. D ANG Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins Johns Hopkins University School of Medicine Baltimore, MD USA [email protected] A LLA D ANILKOVITCH -M IAGKOVA National Cancer Institute-FCRDC Frederick, MD USA [email protected] M ASSIMINO D’A RMIENTO Department of Experimental Medicine University of Rome-Sapienza Rome Italy [email protected]

K AUSTUBH D ATTA Department of Urology Research, Department of Biochemistry and Molecular Biology Mayo Clinic College of Medicine Rochester, Minnesota USA [email protected] P RAN K. D ATTA Departments of Surgery and Cancer Biology Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine Nashville, TN USA [email protected] L EONOR D AVID IPATIMUP (Institute of Molecular Pathology and Immunology of the University of Porto) and Medical Faculty of the University of Porto Porto Portugal [email protected] H ELEN D AVIS Oxford University Medical School John Radcliffe Hospital Oxford UK [email protected] A LEXEY D AVYDOV Fox Chase Cancer Center Philadelphia, PA USA [email protected] R OBERT D AY Department of Pharmacology, Institut de Pharmacologie Faculté de Médecine Université de Sherbrooke Sherbrooke, QC Canada [email protected] J OCHEN D ECKER Bioscientia Institute Center for Human Genetics and University of Mainz Ingelheim Germany [email protected] A MIR R. D EHDASHTI Division of Neurosurgery University of Toronto Toronto, ON Canada [email protected]

List of Contributors

M ARYSE D ELEHEDDE INSERM U774 Institut Pasteur de Lille Lille France [email protected] B ERNA D EMIRCAN University of Florida College of Medicine Gainesville, FL USA [email protected] D AVID A. D ENNING Department of Surgery Marshall University Huntington, WV USA [email protected] S YLVIANE D ENNLER The Netherlands Cancer Institute Amsterdam The Netherlands [email protected] C HANNING J. D ER University of North Carolina at Chapel Hill Chapel Hill, NC USA [email protected] B ARBARA D ESCHLER Medical Center, Department of Hematology-Oncology University of Freiburg Freiburg Germany [email protected] C HANTAL D ESDOUETS Institut Cochin Université Paris Descartes, CNRS Paris France [email protected] P ETER D EVILEE Leiden University Medical Center Leiden The Netherlands [email protected] M ARK W. D EWHIRST Department of Radiation Oncology Duke University Durham, NC USA [email protected]

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M ARC D IEDERICH Laboratoire de Biologie Moléculaire et Cellulaire du Cancer (LBMCC) Hôpital Kirchberg Steichen Luxembourg [email protected] J OSEPH D I F RANZA Department of Family Medicine and Community Health University of Massachusetts Medical Center Worcester, MA USA [email protected] M ARTIN D IGWEED Institute of Human Genetics Charité – Universitätsmedizin Berlin Berlin Germany [email protected] P ETER T EN D IJKE The Netherlands Cancer Institute Amsterdam The Netherlands [email protected] G ERARD D IJKSTRA University Medical Center Groningen University of Groningen Groningen The Netherlands [email protected] H ELEN D IMARAS Ontario Cancer Institute/Princess Margaret Hospital Toronto, ON Canada [email protected] J IAN D ING State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai P. R. China [email protected] J ÜRGEN D ITTMER Clinic for Gynecology University of Halle, Halle Germany [email protected] H ENRIK J. D ITZEL Medical Biotechnology Center Institute of Medical Biology University of Southern Denmark Odense C Denmark [email protected]

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List of Contributors

C HOLPON S. D JUZENOVA Klinik für Strahlentherapie der Universität Würzburg Würzburg Germany [email protected]

B RIAN J. D RUKER Oregon Health & Science University Cancer Institute Portland, OR USA [email protected]

C HRISTIAN D OEHN Department of Urology University of Luebeck, Medical School Luebeck Germany [email protected]

R AYMOND N. D U B OIS Provost and Executive Vice President M.D. Anderson Cancer Center Houston, TX USA [email protected]

YASUFUMI D OI Department of Environmental Medicine Graduate School of Medical Sciences Kyushu University Fukuoka Japan [email protected]

D AN G. D UDA Steele Laboratory for Tumor Biology Department of Radiation Oncology Massachusetts General Hospital and Harvard Medical School Boston, MA USA [email protected]

Q IHAN D ONG Central Clinical School The University of Sydney, Department of Endocrinology and Sydney Cancer Centre, Royal Prince Alfred Hospital NSW Australia [email protected]

J AQUELIN P. D UDLEY Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology The University of Texas at Austin Austin, TX USA [email protected]

Z IGANG D ONG The Hormel Institute University of Minnesota Austin, MN USA [email protected]

R OY J. D UHÉ Department of Pharmacology and Toxicology University of Mississippi Medical Center Jackson, MS USA [email protected]

Q. P ING D OU The Prevention Program, Barbara Ann Karmanos Cancer Institute and Department of Pathology, School of Medicine Wayne State University Detroit, MI USA [email protected]

I GNACIO D URAN Department of Medical Oncology and Hematology Robert and Maggie Bras and Family New Drug Development Program Princess Margaret Hospital Toronto, ONT Canada [email protected]

T OMMASO A. D RAGANI Fondazione IRCCS Istituto Nazionale Tumori Milan Italy [email protected] K ENNETH D RAKE Department of Chemistry and Biochemistry University of Texas at Arlington Arlington, TX USA [email protected] M ARTIN D REYLING Department of Internal Medicine III University of Munich, Großhadern München Germany [email protected]

S TEPHEN T. D URANT University of Oxford Oxford UK [email protected] M EENAKSHI D WIVEDI Department of Life Science Gwangju Institute of Science and Technology Buk-Gu, Gwangju Korea [email protected] B EHFAR E HDAIE University of Virginia Charlottesville, VA USA [email protected]

List of Contributors

J USTIS P. E HLERS Department of Ophthalmology and Visual Sciences Washington University School of Medicine St. Louis, MO USA [email protected] C. H. J. VAN E IJCK Department of Surgery Erasmus MC Rotterdam The Netherlands [email protected] G ERHARD E ISENBRAND Department of Chemistry, Division of Food Chemistry and Toxicology University of Kaiserslautern Kaiserslautern Germany [email protected]

A NDREAS E NGERT Hematology and Oncology University Hospital of Cologne, Department of Internal Medicine I Cologne Germany [email protected] C OCAV A. E NGMAN Department of Medicine Dartmouth Hitchcock Medical Center Lebanon, NH USA [email protected] M ARICA E OLI Unit of Clinical Neuro-Oncology Istituto Neurologico Besta Milano Italy

PATRICIA V. E LIZALDE Institute of Biology and Experimental Medicine (IBYME) CONICET Buenos Aires Argentina [email protected]

S ÜLEYMAN E RGÜN Institute of Anatomy University Hospital Essen Essen Germany [email protected]

B ASSEL F. E L -R AYES Karmanos Cancer Institute Wayne State University Detroit, MI USA [email protected]

PABLO V. E SCRIBÁ Department of Biology-IUNICS University of the Balearic Islands Palma de Mallorca Spain [email protected]

M ITSURU E MI Departments of Obstetrics and Gynecology Nippon Medical School Kawasaki and Tokyo Japan [email protected]

F RANCISCO J. E STEVA Breast Cancer Translational Research Laboratory The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected]

C AROLINE E ND Division of Molecular Genome Analysis, DKFZ Heidelberg Germany [email protected] M ANON VAN E NGELAND Department of Pathology Research Institute for Growth and Development (GROW) Maastricht University Hospital Maastricht The Netherlands [email protected] R AINER E NGERS Institute of Pathology University Hospital Düsseldorf Düsseldorf Germany [email protected]

M ARK F. E VANS Department of Pathology University of Vermont Burlington, VT USA [email protected] B. M ARK E VERS Department of Surgery, University of Texas Medical Branch Galveston, TX USA [email protected] C RISTINA M ARIA FAILLA Laboratory of Molecular and Cell Biology, IDI-IRCCS Rome Italy [email protected]

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List of Contributors

M ARCO FALASCA Department of Medicine University College London London UK [email protected] FANG FAN Department of Pathology University of Kansas School of Medicine Kansas City, KS USA [email protected] S AIJUN FAN Long Island Jewish Medical Center Albert Einstein College of Medicine Bronx, NY USA B INGLIANG FANG Department of Thoracic and Cardiovascular Surgery The University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected] L EI FANG Dermatology Branch National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected] VALERIA R. FANTIN Merck Research Laboratories Boston, MA USA [email protected]

A NDREW P. F EINBERG Department of Medicine and Center for Epigenetics Institute for Basic Biomedical Sciences Johns Hopkins University School of Medicine Baltimore, MD USA [email protected] M ARK A. F EITELSON Department of Pathology, Anatomy and Cell Biology Thomas Jefferson University Philadelphia, PA USA [email protected] D AVID F ELDMAN Division of Endocrinology Department of Medicine, Stanford University School of Medicine Stanford, CA USA [email protected] F RANCESCO F EO Department of Biomedical Sciences Division of Experimental Pathology and Oncology Sassari Italy [email protected] M ARIE F ERNET INSERM U612, Institut Curie-Recherche Orsay France [email protected] A NDREA F ERRARI Pediatric Oncology Unit Fondazione IRCCS Istituto Nazionale Tumori Milano Italy [email protected]

O MID C. FAROKHZAD Laboratory of Nanomedicine and Biomaterials, Department of Anesthesiology Brigham and Women’s Hospital Boston, MA USA [email protected]

L ORENA L. F IGUEIREDO -P ONTES Medical School of Ribeirão Preto University of São Paulo Ribeirão Preto Brazil [email protected]

W ILLIAM L. FARRAR National Cancer Institute – Frederick Frederick, MD USA [email protected]

D ANIEL F INLEY Department of Cell Biology Harvard Medical School Boston, MA USA [email protected]

A LESSANDRO FATATIS Department of Pharmacology and Physiology Drexel University College of Medicine Philadelphia, PA USA [email protected]

G AETANO F INOCCHIARO Istituto Nazionale Neurologico Besta Unit of Experimental Neuro-Oncology Milano Italy [email protected]

List of Contributors

P IER PAOLO D I F IORE IFOM, the FIRC Institute of Molecular Oncology Milan Italy [email protected]

R ICCARDO F ODDE Department of Pathology Josephine Nefkens Institute Erasmus MC, Rotterdam The Netherlands [email protected]

PAUL B. F ISHER Departments of Urology, Pathology and Neurosurgery Columbia University Medical Center College of Physicians and Surgeons New York, NY USA [email protected]

J UDAH F OLKMAN Children’s Hospital and Harvard Medical School Boston, MA USA [email protected]

J AMES F LANAGAN Wolfson Institute for Biomedical Research University College London London UK [email protected]

H AMIDREZA F ONOUNI Department of General Visceral and Transplantation Surgery University of Heidelberg Heidelberg Germany [email protected]

M ICHAEL F LEISCHHACKER Charité-Universitätsmedizin Berlin CCM, Berlin Germany [email protected]

K ENNETH A. F OON The Pittsburgh Cancer Institute Pittsburgh, PA USA [email protected]

E LIEZER F LESCHER Department of Human Microbiology, Sackler Faculty of Medicine Tel Aviv University Tel Aviv Israel [email protected] J ONATHAN A. F LETCHER Albany Medical College Albany NY [email protected] B ARBARA D. F LORENTINE Department of Pathology Henry Mayo Newhall Memorial Hospital Valencia, CA and Keck School of Medicine, University of Southern California, Los Angeles, CA USA [email protected] R OKA F LORIAN Department of Surgical Oncology The University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected] TAMARA F LOYD Cancer Vaccine Branch, National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected]

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A LESSANDRA F ORNI EPOCA Epidemiology Research Center, “Clinica del Lavoro L. Devoto” University of Milan Milan Italy [email protected] PAUL F OSTER Department of Endocrinology and Metabolic Medicine, Imperial College Faculty of Medicine St. Mary’s Hospital London UK [email protected] D AVID A. F RANK Dana-Farber Cancer Institute and Harvard Medical School Boston, MA USA [email protected] S TUART J. F RANK Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine University of Alabama at Birmingham Birmingham, AL USA [email protected] S TANLEY R. F RANKEL Merck Research Laboratories Upper Gwynedd, PA USA

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A LEKSANDRA F RANOVIC Department of Cellular and Molecular Medicine Faculty of Medicine, University of Ottawa Ottawa, ONT Canada [email protected]

ATSUKO F UJIHARA Department of Gene Therapy Science Osaka University, Graduate School of Medicine Suita, Osaka Japan [email protected]

M ICHAEL R. F REEMAN Urological Diseases Research Center Children’s Hospital Boston, Harvard Medical School Boston, MA USA [email protected]

J IRO F UJIMOTO Department of Obstetrics and Gynecology Gifu University School of Medicine Gifu City Japan [email protected]

E MIL F REI III Dana-Farber Cancer Institute Boston, MA USA [email protected] J EAN -N OËL F REUND INSERM, U682 Université Louis Pasteur Strasbourg France [email protected] E RROL C. F RIEDBERG University of Texas Southwestern Medical Center Dallas, TX USA [email protected] S TEVEN M. F RISCH Mary Babb Randolph Cancer Center and Department of Biochemistry West Virginia University Morgantown, WV USA [email protected] PAUL F RÉNEAUX Département de Pathologie Institut Curie Paris France [email protected] M ICHAEL C. F RÜHWALD Department of Pediatric Hematology and Oncology University Children’s Hospital Muenster Muenster Germany [email protected] A NDREW M. F RY University of Leicester Leicester UK [email protected]

J UN F UJITA Department of Clinical Molecular Biology, Graduate School of Medicine Kyoto University Kyoto Japan [email protected] K ENJI F UKASAWA Molecular Oncology Program H. Lee Mofitl Cancer Center & Research Institute Tampa, FL USA [email protected] S IMONE F ULDA University Children’s Hospital, University of Ulm Ulm Germany [email protected] K YLE F URGE Van Andel Research Institute Grand Rapids, MI USA [email protected] M UTSUO F URIHATA Department of Pathology Kochi Medical School Kochi Japan [email protected] R HOIKOS F URTWÄNGLER Division of Pediatric Hematology and Oncology Saarland University Hospital Homburg/Saar Germany [email protected] B ERNARD W. F UTSCHER Department of Pharmacology and Toxicology, Arizona Cancer Center and College of Pharmacy University of Arizona Tucson, AZ USA [email protected]

List of Contributors

S HIRISH G ADGEEL Karmanos Cancer Institute Wayne State University Detroit, MI USA [email protected]

A NDREI L. G ARTEL Department of Medicine University of Illinois at Chicago Chicago, IL USA [email protected]

F EDERICO G AGO Departamento de Farmacología Universidad de Alcalá Alcalá de Henares, Madrid Spain [email protected]

R ONALD B. G ARTENHAUS The University of Maryland Marlene and Stewart Greenebaum Cancer Center Baltimore, MD USA [email protected]

W ILLIAM M. G ALLAGHER UCD School of Biomolecular and Biomedical Science UCD Conway Institute University College Dublin Dublin Ireland [email protected]

T HOMAS A. G ASIEWICZ University of Rochester Medical Center Rocheser, NY USA [email protected]

B ERNARD G ALLEZ Biomedical Magnetic Resonance Université Catholique de Louvain Brussels Belgium [email protected] B RENDA L. G ALLIE Ontario Cancer Institute/Princess Margaret Hospital Toronto, ON Canada [email protected]

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PATRIZIA G ASPARINI Molecular-Cytogenetic Unit, Department of Experimental Oncology Istituto Nazionale Tumori Milano Italy [email protected] G RÉGORY G ATOUILLAT Laboratory of Biochemistry IFR53, Faculty of Pharmacy Reims cedex, France [email protected]

P ING G AO Division of Hematology, Department of Medicine Johns Hopkins University School of Medicine Baltimore, MD USA [email protected]

A DI F. G AZDAR Hamon Center for therapeutic Oncology Research and Departments of Pathology, Internal Medicine and Pharmacology University of Texas Southwestern Medical Center Dallas, Texas USA [email protected]

R OY G ARCIA City of Hope National Medical Center and Beckman Research Institute Duarte, CA USA [email protected]

C HRISTIAN G EISLER The Leukemia and Lymphoma Marker Laboratory Department of Hematology, The Finsen Centre Rigshospitalet, Copenhagen Denmark [email protected]

L AWRENCE B. G ARDNER The NYU Cancer Institute New York University School of Medicine New York, NY USA [email protected]

S PYROS D. G EORGATOS Department of Basic Sciences The University of Crete, School of Medicine Heraklion, Crete Greece [email protected]

C ATHIE G ARNIS MIT Center for Cancer Research Cambridge, MA USA [email protected]

J ULIA M. G EORGE Department of Molecular and Integrative Physiology University of Illinois at Urbana-Champaign IL, USA [email protected]

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List of Contributors

A RMIN G ERGER Department of Internal Medicine, Division of Oncology Medical University Graz Graz Austria [email protected]

M ICHAEL K. G IBSON University of Pittsburgh Cancer Institute Pittsburgh, PA USA [email protected]

U LRICH G ERMING Klinik für Hämatologie Onkologie und Klinische Immunologie Heinrich-Heine-Universität Düsseldorf Germany [email protected]

M ICHAEL Z. G ILCREASE Department of Pathology, Breast Section M. D. Anderson Cancer Center Houston, TX USA [email protected]

J EFFREY E. G ERSHENWALD Department of Surgical Oncology The University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected]

M.B. G ILLESPIE Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA

A NDREAS J. G ESCHER Cancer Biomarkers and Prevention Group Department of Cancer Studies, University of Leicester Leicester UK [email protected]

F RANÇOIS N OËL G ILLY Department of Digestive Oncologic Surgery Hospices Civils de Lyon–Université Lyon 1 Lyon France [email protected]

C HRISTIAN G ESPACH INSERM U. 673, Paris, France; Laboratory of Molecular and Clinical Oncology of Solid tumors, Faculté de Médecine Université Pierre et Marie Curie-Paris 6 Paris France [email protected]

T HOMAS D. G ILMORE Biology Department, Boston University Boston, MA USA [email protected]

B. M ICHAEL G HADIMI Department of General and Visceral Surgery University Medical Center Göttingen Germany [email protected]

O LIVER G IMM Department of Surgery University Hospital Linköping Sweden [email protected]

R ICCARDO G HIDONI Laboratory of Biochemistry and Molecular Biology San Paolo Medical School University of Milan Milan Italy [email protected] R ONALD A. G HOSSEIN Department of Pathology Memorial Sloan-Kettering Cancer Center New York, NY USA [email protected] L ORENZO G IANNI Department of Oncology Infermi Hospital Rimini Italy [email protected]

L UTZ G ISSMANN DKFZ, Heidelberg Germany [email protected] M ORTEN F. G JERSTORFF Department of Oncology Odense University Hospital Odense C Denmark [email protected] S HANNON S. G LASER Departments of Medicine and Research and Education Scott & White Hospital and Texas A&M University System Health Science Center Temple, TX USA [email protected]

List of Contributors

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H ANSRUEDI G LATT German Institute of Human Nutrition (DIfE) Potsdam-Rehbruecke Nuthetal Germany [email protected]

S USANNE M. G OLLIN Department of Human Genetics University of Pittsburgh Graduate School of Public Health Pittsburgh, PA USA [email protected]

O LIVIER G LEHEN Department of Digestive Oncologic Surgery Hospices Civils de Lyon–Université Lyon 1 Lyon France [email protected]

R OY M. G OLSTEYN Senior Scientist, Cancer Research Division Institut de Recherches Servier Croissy-Sur-Seine France [email protected]

A LEKSANDRA G LOGOWSKA Department of Human Anatomy and Cell Science University of Manitoba Winnipeg, MB Canada

E LLEN L. G OODE Mayo Clinic College of Medicine Rochester, MN USA [email protected]

T HOMAS W. G LOVER Department of Human Genetics University of Michigan Ann Arbor, MI USA [email protected]

G REGORY J. G ORES Miles and Shirley Fiterman Center for Digestive Diseases Division of Gastroenterology and Hepatology Mayo Clinic College of Medicine Rochester, MN USA [email protected]

U LRICH G ÖBEL Clinic of Pediatric Oncology Hematology and Immunology Heinrich-Heine-University Düsseldorf Düsseldorf Germany [email protected] J. G ODDARD Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA [email protected] A NDREW K. G ODWIN Department of Medical Oncology Fox Chase Cancer Center Philadelphia, PA USA [email protected] G ARY S. G OLDBERG Molecular Biology University of Medicine and Dentistry of New Jersey Stratford, NJ USA [email protected] I TZHAK D. G OLDBERG Long Island Jewish Medical Center Albert Einstein College of Medicine Bronx, NY USA

T OBIAS G ÖRGE Department of Dermatology University of Münster Münster Germany [email protected] N ORIKO G OTOH Institute of Medical Sciences The University of Tokyo Minatoku, Tokyo Japan [email protected] S TEPHANIE G OUT Le Centre de recherche en cancérologie de l’Université Laval Québec, QC Canada [email protected] A MMI G RAHN Department of Clinical Chemistry and Transfusion Medicin Institute of Biomedicine Sahlgrenska academy at Göteborg University Göteborg Sweden [email protected] P ETER G REAVES Department of Cancer Studies and Molecular Medicine University of Leicester Leicester UK [email protected]

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List of Contributors

M ARK I. G REENE Department of Pathology and Laboratory Medicine & Abramson Cancer Center University of Pennsylvania Philadelphia, PA USA [email protected] W. M. U. VAN G REVENSTEIN Department of Surgery Erasmus MC Rotterdam The Netherlands [email protected]

VALENTINA G UARNERI Department of Oncology and Hematology University of Modena and Reggio Emilia, Policlinico via del Pozzo, Modena Italy [email protected] W EI G U Institute for Cancer Genetics, and Department of Pathology College of Physicians and Surgeons, Columbia University New York, NY USA [email protected]

A RJAN W. G RIFFIOEN Angiogenesis Laboratory, Department of Pathology Maastricht University Maastricht The Netherlands [email protected]

L ILIANA G UEDEZ Extracellular Matrix Pathology Section, Cell and Cancer Biology Branch National Cancer Institute Bethesda, MD USA [email protected]

D IRK G RIMM University of Heidelberg, Cluster of Excellence Cell Networks BIOQUANT Heidelberg, Germany [email protected]

F. P ETER G UENGERICH Department of Biochemistry and Center in Molecular Toxicology Vanderbilt University School of Medicin Nashville, TN USA [email protected]

M ATTHEW J. G RIMSHAW Breast Cancer Biology Group, King’s College London School of Medicine, Guy’s Hospital London UK [email protected] S TEPHEN R. G ROBMYER Department of Surgery, Division of Surgical Oncology University of Florida Gainesville, FL USA [email protected]

A BHIJIT G UHA Division of Neurosurgery University of Toronto ON Canada [email protected] K ATHERINE A. G UINDON Department of Pharmacology and Toxicology Queen’s University Kingston, ONT Canada [email protected]

B ERND G ROSCHE Department of Radiation Protection and Health Bundesamt für Strahlenschutz (Federal Office for Radiation Protection) Oberschleissheim Germany [email protected]

E RICH G ULBINS Department of Molecular Biology University of Duisburg-Essen Essen Germany [email protected]

H ANS H. G RUNICKE Biocenter, Division of Medical Biochemistry Medical University of Innsbruck Innsbruck Austria [email protected]

B ILL G ULLICK Department of Biosciences University of Kent at Canterbury Canterbury, Kent UK [email protected]

J ULIANA G UARIZE Department of Thoracic Surgery European Institute of Oncology Milan Italy [email protected]

U RSULA G ÜNTHERT Department of Clinical and Biological Sciences Institute for Medical Microbiology, University of Basel Basel Switzerland [email protected]

List of Contributors

J AMES F. G USELLA Molecular Neurogenetics Unit Massachusetts General Hospital Charlestown, MA USA [email protected] G RAEME R. G UY Signal Transduction Laboratory Institute of Molecular and Cell Biology Singapore [email protected] M ANUEL G UZMÁN Department of Biochemistry and Molecular Biology I School of Biology Complutense University Madrid Spain [email protected] G EUM -Y OUN G WAK Department of Medicine Samsung Medical Center Sungkyunkwan University School of Medicine Gangnam-gu, Seoul South Korea [email protected] C LAUDIA H AFERLACH MLL Munich Leukemia Laboratory Munich Germany [email protected] T ORSTEN H AFERLACH MLL Munich Leukemia Laboratory Munich Germany [email protected] S TEPHAN A. H AHN University of Bochum Bochum Germany [email protected] J ÖRG H AIER Department of General Surgery University Hospital Münster Münster Germany [email protected] N UMSEN H AIL Department of Pharmaceutical Sciences The University of Colorado at Denver and Health Sciences Center Denver, CO USA [email protected]

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P IERRE H AINAUT Group of Molecular Carcinogenesis and Biomarkers International Agency for Research on Cancer World Health Organization Lyon cedex 08 France [email protected] B RETT M. H ALL Department of Pediatrics Columbus Children’s Research Institute The Ohio State University Columbus, OH USA [email protected] J ANET H ALL INSERM U612, Institut Curie-Recherche Orsay France [email protected] J OYCE L. H AMLIN Department of Biochemistry and Molecular Genetics University of Virginia School of Medicine Charlottesville, VA USA [email protected] R ASHA S. H AMOUDA National Institutes of Health Bethesda, MD USA, [email protected] J. W ILLIAM H ARBOUR Department of Ophthalmology and Visual Sciences Washington University School of Medicine St. Louis, MO USA [email protected] M ARK H ARLAND Section of Epidemiology and Biostatistics Cancer Research UK Clinical Centre, Leeds Institute of Molecular Medicine, St. James’s University Hospital Leeds UK [email protected] A DRIAN L. H ARRIS University of Oxford, Cancer Research UK Weatherall Institute of Molecular Medicine, John Radcliffe Hospital Headington, Oxford UK [email protected] U ZMA H ASAN Infections and Cancer Biology Group International Agency for Research on Cancer Lyon France [email protected]

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List of Contributors

M IA H ASHIBE Gene-Environment Epidemiology Group International Agency for Research on Cancer Lyon France [email protected]

O LAF H EIDENREICH Northern Institute for Cancer Research Newcastle University Newcastle upon Tyne UK [email protected]

M ASAHARU H ATA Department of Radiology Yokohama City University, Graduate School of Medicine Yokohama, Kanagawa Japan [email protected]

D AVID G. H EIDT Department of Surgery University of Michigan Medical Center Ann Arbor, MI USA

J OHN . D. H AYES Biomedical Research Centre, Ninewells Hospital and Medical School University of Dundee Dundee, Scotland UK [email protected] L ILI H E Molecular Oncology and Pathology H. Lee Moffitt Cancer Center & Research Institute Tampa, FL USA [email protected] L I -Z HEN H E Memorial Sloan-Kettering Cancer Center Weill Cornell Graduate School of Medical Sciences NY USA [email protected]

W ERNER H ELD Ludwig Institute for Cancer Research Lausanne Branch, and University of Lausanne Epalinges Switzerland [email protected] C ARL -H ENRIK H ELDIN Ludwig Institute for Cancer Research Uppsala Sweden [email protected] W IJNAND H ELFRICH Groningen University Institute for Drug Exploration (GUIDE), Department of Pathology & Laboratory Medicine, Section Medical Biology, Laboratory for Tumor Immunology Groningen The Netherlands [email protected]

R UTH H E Georgetown University Lombardi Comprehensive Cancer Center Washington, DC USA [email protected]

D EBBY H ELLEBREKERS Department of Pathology Research Institute for Growth and Development (GROW) Maastricht University Hospital Maastricht The Netherlands [email protected]

S TEPHEN S. H ECHT The Cancer Center University of Minnesota Minneapolis, MN USA [email protected]

PAUL W. S. H ENG Department of Pharmacy National University of Singapore Singapore Singapore [email protected]

A HMED E. H EGAB Department of Geriatric and Respiratory Medicine Tohoku University Hospital Sendai Japan [email protected]

K AI -O LIVER H ENRICH DKFZ, German Cancer Research Center Heidelberg Germany [email protected]

A XEL H EIDENREICH Division of Oncological Urology, Department of Urology University of Köln Köln Germany [email protected]

M ARIE H ENRIKSSON Department of Microbiology Tumor and Cell Biology (MTC) Karolinska Institutet Stockholm Sweden [email protected]

List of Contributors

E LIZABETH P ETRI H ENSKE Fox Chase Cancer Center Philadelphia, PA USA [email protected] D ONALD E. H ENSON The George Washington University Cancer Institute Washington, DC USA [email protected] M EENHARD H ERLYN The Wistar Institute Philadelphia, PA USA [email protected] B LANCA H ERNANDEZ -L EDESMA Dept of Nutritional Sciences and Toxicology University of California Berkeley, CA USA [email protected] W OLFGANG H ERR Department of Medicine III, Hematology and Oncology Johannes Gutenberg-University of Mainz Mainz Germany [email protected] H ELEN E. H ESLOP Center for Cell and Gene Therapy, Baylor College of Medicine Texas Children’s Hospital, and The Methodist Hospital Houston, TX USA [email protected] J OCHEN H ESS Deutsches Krebsforschungszentrum Division of Signal Transduction and Growth Control Heidelberg Germany [email protected] M ARRY M. VAN DEN H EUVEL -E IBRINK Department of Pediatric Oncology/Hematology Erasmus MC-Sophia Children’s Hospital Rotterdam The Netherlands [email protected] D OMINIQUE H EYMANN Physiopathologie de la Résorption Osseuse et Thérapie des Tumeurs Osseuses Primitives University of Nantes Nantes France [email protected]

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M ARTHA H ICKEY Department of Gynaecology, School of Women’s and Infants’ Health WIRF and University of Western Australia Crawley, WA Australia [email protected] J AMES H ICKS Cold Spring Harbor Laboratory Cold Spring Harbor NY USA [email protected] K EVIN O. H ICKS Auckland Cancer Society Research Centre The University of Auckland Auckland New Zealand [email protected] I AN D. H ICKSON ICRF, Institute of Molecular Medicine University of Oxford John Radcliffe Hospital, Oxford UK [email protected] C OLIN K. H ILL Department of Radiation Oncology USC Keck School of Medicine Los Angeles, CA USA B OAZ H IRSHBERG Cardiovascular and Metabolic Diseases, Pfizer Inc Groton, CT USA [email protected] A RI H IRVONEN Finnish Institute of Occupational Health Helsinki Finland [email protected] YASUYUKI H ITOSHI Departments of Pediatrics and of Genetics, Norris Cotton Cancer Center Dartmouth Medical School Hanover, NH USA [email protected] R ICARDO H ITT Medical Oncology Service University Hospital 12 de Octubre Madrid Spain [email protected]

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List of Contributors

E ISO H IYAMA Natural Science Center for Basic Research and Development Department of Pediatric Surgery, Hiroshima University Hospital Hiroshima University Hiroshima Japan [email protected] FALK H LUBEK Department of Pathology Ludwig-Maximilians-University of Munich Munich Germany [email protected] S TEVEN N. H OCHWALD Departments of Surgery Departments of Molecular Genetics and Microbiology University of Florida College of Medicine Gainesville, FL USA [email protected] M ICHAEL H ODSDON Department of Laboratory Medicine Yale University School of Medicine New Haven, CT USA [email protected] K ASPER H OEBE Department of Immunology The Scripps Research Institute San Diego, CA USA [email protected] L ORNE J. H OFSETH Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy University of South Carolina Columbia, SC USA [email protected] PANCRAS C. W. H OGENDOORN Department of Pathology Leiden University Medical Center Leiden The Netherlands [email protected] S TEFAN H OLDENRIEDER Institute of Clinical Chemistry University Hospital of Munich Ludwig-Maximilians-University Munich Germany [email protected]

P ETRA D EN H OLLANDER Molecular and Cellular Oncology The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected] C AROLINE L. H OLLOWAY BC Cancer Agency Centre for the Southern Interior Kelowna, BC Canada [email protected] A RNE H OLMGREN Department of Medical Biochemistry and Biophysics Karolinska Institutet Stockholm Sweden [email protected] JUN HYUK HONG The Cancer Institute of NJ, Robert Wood Johnson Medical School Division of Urologic Oncology New Brunswick, NJ USA C HRISTINE H ORAK Women’s Cancers Section, Laboratory of Molecular Pharmacology, Center for Cancer Research National Cancer Institute Bethesda, MD USA [email protected] A DÍLIA H ORMIGO Department of Neurology Memorial Sloan-Kettering Cancer Center New York, NY USA [email protected] J. H ORNIG Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA M ICHAEL R. H ORSMAN Department of Experimental Clinical Oncology Aarhus University Hospital Aarhus Denmark [email protected] A NDREA K RISTINA H ORST Institute of Clinical Chemistry University Medical Center Hamburg Eppendorf Hamburg Germany [email protected]

List of Contributors

D AVID W. H OSKIN Departments of Pathology, and Microbiology and Immunology Dalhousie University Halifax, NS Canada [email protected]

M AUREEN B. H UHMANN Department of Primary Care, School of Health Related Professions, University of Medicine and Dentistry of New Jersey The Cancer Institute of New Jersey New Brunswick, NJ USA [email protected]

A NDREAS F. H OTTINGER Department of Neurology Memorial Sloan-Kettering Cancer Center New York, NY USA [email protected]

W EN -C HUN H UNG Institute of Biomedical Sciences National Sun Yat-Sen University Kaohsiung, Taiwan Republic of China [email protected]

P ETER J. H OUGHTON Department of Molecular Pharmacology St. Jude Children’s Research Hospital Memphis, TN USA [email protected]

K ENT H UNTER Laboratory of Population Genetics, CCR/NCI/NIH Bethesda, MD USA [email protected]

A NTHONY H OWELL CRUK Department of Medical Oncology University of Manchester, Christie Hospital NHS Trust Manchester UK [email protected] S HIE -L IANG H SIEH Department of Microbiology and Immunology National Yang-Ming University Immunology Research Center, Taipei Veterans General Hospital Genomics Research Center Academia Sinica, Taipei Taiwan [email protected] C HENG -L ONG H UANG Department of Second Surgery Kagawa University Kagawa Japan [email protected] K AY H UEBNER Department of Molecular Virology Immunology and Medical Genetics, Ohio State University Comprehensive Cancer Center Columbus, OH USA [email protected] P ERE H UGUET Department of Pathology Vall d’Hebron University Hospital Barcelona, Spain [email protected]

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T ONY H UNTER Salk Institute Molecular and Cell Biology Laboratory La Jolla, CA USA [email protected] T EH -I A H UO Institute of Pharmacology, School of Medicine National Yang-Ming University Taipei, TAIWAN and Department of Medicine Taipei Veterans General Hospital Taipei, TAIWAN People’s Rebublic of China [email protected] J ACQUES H UOT Le Centre de recherche en cancérologie de l’Université Laval Québec, QC Canada [email protected] D OUGLAS R. H URST Department of Pathology and Comprehensive Cancer Center University of Alabama at Birmingham Birmingham, AL USA [email protected] K AREN L. H UYCK Department of Pathology Brigham and Women’s Hospital Boston, MA USA [email protected] S AM T. H WANG Dermatology Branch National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected]

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List of Contributors

B RANDY D. H YNDMAN Department of Pathology and Molecular Medicine Queen’s University Cancer Research Institute Queen’s University Kingston, ON Canada [email protected] TAKAFUMI I CHIDA Department of Hepatology and Gastroenterology Juntendo University School of Medicine, Shizuoka Hospital Shizuoka Japan [email protected] Y OSHITO I HARA Department of Biochemistry and Molecular Biology in Disease, Atomic Bomb Disease Institute Nagasaki University Graduate School of Biomedical Sciences Nagasaki Japan [email protected] H ITOSHI I KEDA Department of Pediatric Surgery Dokkyo Medical University Koshigaya Hospital Koshigaya, Saitama Japan [email protected] K AZUHIKO I NO Department of Obstetrics and Gynecology Nagoya University Graduate School of Medicine Nagoya Japan [email protected] J UAN I OVANNA INSERM, Stress Cellulaire, Parc Scientifique et Technologique de Luminy Marseille Cedex France [email protected] I RMGARD I RMINGER -F INGER Molecular Gynecology and Obstetrics Laboratory, Department of Gynecology and Obstetrics Geneva University Hospitals Geneva, Switzerland [email protected]

T OSHIHISA I SHIKAWA Department of Biomolecular Engineering Graduate School of Bioscience and Biotechnology Tokyo Institute of Technology Meguro-ku Tokyo [email protected] M ARK A. I SRAEL Departments of Pediatrics and of Genetics, Norris Cotton Cancer Center Dartmouth Medical School Hanover, NH USA [email protected] A NTOINE I TALIANO Laboratory of Solid Tumors Genetics Nice University Hospital and CNRS UMR 6543, Faculty of Medicine Nice France [email protected] N ORIMASA I TO University of Pittsburgh, Departments of Surgery and Bioengineering Pittsburgh, PA USA [email protected] M ICHAEL I TTMANN Department of Pathology Baylor College of Medicine Houston, TX USA [email protected] R ICHARD I VELL Head of School of Molecular and Biomedical Sciences The University of Adelaide SA Australia [email protected]

M EREDITH S. I RWIN Cell Biology Program and Division of Hematology-Oncology Hospital for Sick Children University of Toronto Toronto, ON Canada [email protected]

N OBU I WAKUMA Department of Surgery, Division of Surgical Oncology University of Florida Gainesville, FL USA [email protected]

P LO I SABELLE INSERM U790, Hématopoièse et cellules souches Institut Gustave Roussy–PR1 Villejuif France [email protected]

S HAI I ZRAELI Pediatric Hemato-Oncology Sheba Medical Center and Tel Aviv University Ramat Gan Israel [email protected]

List of Contributors

PAOLA I ZZO Dipartimento di Biochimica e Biotechnologie Medicine a Chirurgia, Facoltà di Medicina Università di Napoli Federico II Napoli Italy [email protected] M ARK J ACKMAN Wellcome/CRC Institute Cambridge UK [email protected]

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G ORDON C. J AYSON Cancer Research UK Department of Medical Oncology Christie Hospital Manchester UK [email protected] K UAN -T EH J EANG National Institute of Allergy and Infectious Disease, NIH Bethesda, MD USA [email protected]

A LAN J ACKSON Imaging Science University of Manchester Manchester UK [email protected]

J IIANG -H UEI J ENG Laboratory of Pharmacology and Toxicology, School of Dentistry National Taiwan University Hospital and National Taiwan University Medical College Taipei Taiwan [email protected]

D EBORAH J ACKSON -B ERNITSAS Department of Systems Biology, The University of Texas M.D. Anderson Cancer Center Houston, TX USA [email protected]

E LWOOD V. J ENSEN National Institute of Health Bethesda, MD USA [email protected]

U LRICH J AEHDE Institute of Pharmacy University of Bonn Bonn Germany [email protected]

L IN J I Department of Thoracic & Cardiovascular Surgery The University of Texas M.D. Anderson Cancer Center Houston, TX USA [email protected]

D AVID J AMIESON School of Clinical and Laboratory Sciences Newcastle University Newcastle upon Tyne UK [email protected]

Y UFEI J IANG Cancer Vaccine Branch, National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected]

P IDDER J ANSEN -D ÜRR Institute for Biomedical Ageing Research Austrian Academy of Sciences Innsbruck Austria [email protected]

C HARLOTTE J IN Departments of Clinical Genetics University Hospital Lund, Sweden [email protected]

S IEGFRIED J ANZ Department of Pathology University of Iowa, Carver College of Medicine Iowa City, IA USA [email protected] D ANIEL G. J AY Tufts University School of Medicine Boston, Ma USA [email protected]

A NDREW K. J OE Department of Medicine Herbert Irving Comprehensive Cancer Center New York, NY USA [email protected] A LAN L. J OHNSON Walther Cancer Research Center University of Notre Dame Notre Dame, IN USA [email protected]

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List of Contributors

S ARA M. J OHNSON Department of Surgery University of Texas Medical Branch Galveston, TX USA [email protected] F LORIS A ART DE J ONG Department of Medical Oncology Erasmus University Medical Center Rotterdam Rotterdam The Netherlands [email protected] W ON -A J OO The Wistar Institute Philadelphia, PA USA [email protected] V. C RAIG J ORDAN Fox Chase Cancer Center Philadelphia, PA USA [email protected] S ERENE J OSIAH Shire Pharmaceuticals Cambridge, MA USA [email protected] R ICHARD J OVE City of Hope National Medical Center and Beckman Research Institute Duarte, CA USA [email protected] J AROSLAW J OZWIAK Department of Histology and Embryology Medical University of Warsaw Warsaw, Poland [email protected] J ESPER J URLANDER Department of Hematology The Finsen Centre Rigshospitalet, Copenhagen Denmark [email protected]

TADAO K AKIZOE National Cancer Center Tokyo Japan [email protected] T UULA K ALLUNKI Apoptosis Department Institute of Biological Cancer Research Danish Cancer Society Copenhagen Denmark [email protected] TAKEHIKO K AMIJO Division of Biochemistry Chiba Cancer Center Research Institute Chuoh-ku, Chiba Japan [email protected] YASUFUMI K ANEDA Department of Gene Therapy Science Osaka University Graduate School of Medicine Suita, Osaka Japan [email protected] K AZUHIRO K ANEKO Second Department of Internal Medicine Showa University School of Medicine Tokyo Japan [email protected] I NKYUNG K ANG Department of Surgery University of California San Francisco, CA USA [email protected] D AVID E. K APLAN Division of Gastroenterology University of Pennsylvania Philadelphia, PA USA [email protected]

C HAIM K AHANA Department of Molecular Genetics Weizmann Institute of Science Rehovot Israel [email protected]

M ICHALIS V. K ARAMOUZIS Department of Biological Chemistry Medical School University of Athens Goudi, Athens Greece [email protected]

B ERND K AINA Department of Toxicology University of Mainz Mainz Germany [email protected]

A DAM R. K ARPF Department of Pharmacology and Therapeutics Roswell Park Cancer Institute Buffalo, NY USA [email protected]

List of Contributors

N ILESH D. K ASHIKAR Departments of Surgery and Cancer Biology Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine Nashville, TN USA [email protected] J UHAYNA K ASSEM Division of Pulmonary and Critical Care Medicine Weill Medical College of Cornell University New York, NY USA [email protected]

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S TANLEY B. K AYE Section of Medicine Institute of Cancer Research, The Royal Marsden Hospital London UK [email protected] R ICHARD K EFFORD Westmead Institute for Cancer Research and Sydney Melanoma Unit, University of Sydney Westmead, NSW Australia [email protected]

M ATILDA K ATAN CRC Centre for Cell and Molecular Biology Institute of Cancer Research London UK [email protected]

E VAN T. K ELLER Departments of Urology and Pathology University of Michigan Ann Arbor, MI USA [email protected]

S ASSER A. K ATE Department of Pediatrics Columbus Children’s Research Institute, The Ohio State University Columbus, OH USA [email protected]

S TEPHEN K ENNEDY Nuffield Department of Obstetrics and Gynaecology Oxford University John Radcliffe Hospital, Oxford UK [email protected]

W ILLIAM K. K AUFMANN Department of Pathology and Laboratory Medicine University of North Carolina at Chapel Hill Chapel Hill, NC USA [email protected]

D ANIEL K EPPLER Department of Cell Biology & Anatomy and Feist-Weiller Cancer Center LSUHSC-School of Medicine Shreveport, LA USA [email protected]

M ANJINDER K AUR Department of Pharmaceutical Sciences School of Pharmacy University of Colorado Health Sciences Center Denver, CO USA [email protected]

W OLFGANG K ERN MLL Munich Leukemia Laboratory Munich Germany [email protected]

I NGO K AUSCH Department of Urology University of Luebeck, Medical School Luebeck Germany [email protected] K OJI K AWAKAMI Graduate School of Medicine and Public Health Kyoto University Kyoto Japan [email protected] F REDERIC J. K AYE National Cancer Institute NIH and National Naval Medical Center Bethesda, MD USA [email protected]

J ORMA K ESKI -O JA Departments of Pathology and of Virology Haartman Institute, University of Helsinki Helsinki, Finland [email protected] A D G EURTS VAN K ESSEL Department of Human Genetics Radboud University Nijmegen Medical Centre Nijmegen The Netherlands [email protected] K HANDAN K EYOMARSI Department of Experimental Radiation Oncology Department of Surgical Oncology Unit 66, University of Texas, MD Anderson Cancer Center Houston, TX USA [email protected]

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List of Contributors

C HAND K HANNA National Cancer Institute, Center for Cancer Research Comparative Oncology Program Bethesda, MD USA [email protected]

S EONG J IN K IM Laboratory of Cell Regulation and Carcinogenesis, National Cancer Institute Bethesda, MD USA [email protected]

S AMIR K HLEIF Cancer Vaccine Branch, National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected]

S U Y OUNG K IM Pediatric Oncology Branch, Center for Cancer Research National Cancer Institute Bethesda, MD USA [email protected],gov

R OYA K HOSRAVI -FAR Department of Pathology Harvard Medical School, Beth Israel Deaconess Medical Center Boston, MA USA [email protected] T OBIAS K IESSLICH Department of Molecular Biology University of Salzburg Hellbrunnerstrasse 34, 5020 Salzburg Austria [email protected] F UMITAKA K IKKAWA Department of Obstetrics and Gynecology Nagoya University Graduate School of Medicine Nagoya Japan [email protected] N ERBIL K ILIC Department of Hematology and Oncology University Hospital Hamburg-Eppendorf Germany [email protected] I SAAC Y I K IM The Cancer Institute of NJ, Robert Wood Johnson Medical School Division of Urologic Oncology New Brunswick, NJ USA [email protected] J UNG - WHAN K IM Division of Hematology, Department of Medicine Johns Hopkins University School of Medicine Baltimore, MD USA [email protected] M OONIL K IM BioNanotechnology Research Center Korea Research Institute of Bioscience and Biotechnology Yuseong, Daejeon Republic of Korea [email protected]

A DI K IMCHI Department of Molecular Genetics Weizmann Institute of Science Rehovot Israel [email protected] A. D OUGLAS K INGHORN College of Pharmacy, The Ohio State University Columbus, OH USA [email protected] D AVID K IRN Jennerex Biotherapeutics Inc. San Francisco, CA USA [email protected] Y OULIA M. K IROVA Department of Radiation Oncology Institut Curie Paris France [email protected] S HINICHI K ITADA Burnham Institute for Medical Research La Jolla, CA USA [email protected] K AREL K ITHIER Department of Pathology Wayne State University School of Medicine Detroit, MI USA [email protected] C ELINA G. K LEER Department of Pathology and Comprehensive Cancer Center University of Michigan Medical School MI USA [email protected] G EORGE K LEIN Microbiology, Tumor and Cell Biology Karolinska Institute Stockholm Sweden [email protected]

List of Contributors

M ICHAEL J. K LEIN Center for Metabolic Bone Disease The University of Alabama at Birmingham Birmingham, AL USA [email protected]

L IN K ONG Department of Radiation Oncology Cancer Hospital of Fudan University Shanghai China [email protected]

E LENA K LENOVA Department of Biological Sciences University of Essex Colchester Essex, UK [email protected]

R OLAND E. K ONTERMANN Institute of Cell Biology and Immunology University of Stuttgart Germany [email protected]

T HOMAS K LONISCH Department of Human Anatomy and Cell Science University of Manitoba Winnipeg, MB Canada [email protected] E LIZABETH K NOBLER Department of Dermatology Columbia College of Physicians and Surgeons New York, NY USA [email protected] R OBERT K NOBLER Department of Dermatology Medical University of Vienna Vienna Austria [email protected] B EATRICE K NUDSEN Divisions of Public Health Sciences, Human Biology and Clinical Sciences Fred Hutchinson Cancer Research Center Seattle, WA USA [email protected] S TEFAN K OCHANEK Division of Gene Therapy University of Ulm Cologne Germany [email protected]

J ANKO K OS Department of Pharmaceutical Biology University of Ljubljana Ljubljana Slovenia [email protected] M ARTA K OSTROUCHOVA Laboratory of Molecular Biology and Genetics Institute of Inherited Metabolic Disorders, 1st Faculty of Medicine, Charles University Prague Czech Republica [email protected] H EINRICH K OVAR Children’s Cancer Research Institute St. Anna Kinderkrebsforschung, Vienna Austria [email protected] C RAIG K OVITZ Department of Medical Oncology University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected] B ARNETT S. K RAMER Office of Disease Prevention National Institutes of Health Bethesda, MD USA [email protected]

C HRISTIAN K OLLMANNSBERGER Division of Medical Oncology, British Columbia Cancer Agency, Vancouver Cancer Centre University of British Columbia Vancouver, BC Canada [email protected]

B ARBARA K RAMMER Department of Molecular Biology University of Salzburg Salzburg Austria [email protected]

Y UTAKA K ONDO Division of Molecular Oncology Aichi Cancer Center Research Institute Nagoya Japan [email protected]

H ENK J. VAN K RANEN National Institute of Public Health and Environment Bilthoven The Netherlands [email protected]

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T HOMAS K RAUSZ Department of Pathology University of Chicago Chicago, IL USA [email protected]

D EEPAK K UMAR Department of Biological and Environmental Sciences University of the District of Columbia Washington, DC USA [email protected]

J ÜRGEN K RAUTER Department of Haematology Haemostasis and Oncology Hannover Medical School Hannover Germany [email protected]

H IROKI K UNIYASU Department of Molecular Pathology Nara Medical University School of Medicine Kashihara, Nara Japan [email protected]

B ERNHARD K REMENS Department of Pediatric Hematology Oncology and Respiratory Medicine, University Hospitals of Essen Essen Germany [email protected] A RUNA K RISHNAN Division of Endocrinology Department of Medicine, Stanford University School of Medicine Stanford, CA USA [email protected] B IN B. R. K ROON Department of Surgery The Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital Amsterdam The Netherlands [email protected] YASUSEI K UDO Department of Oral and Maxillofacial Pathobiology Division of Frontier Medical Science Graduate School of Biomedical Sciences Hiroshima University Hiroshima Japan [email protected] R AKESH K UMAR Molecular and Cellular Oncology The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected] PARVESH K UMAR Department of Radiation Oncology USC Keck School of Medicine Los Angeles, CA USA [email protected]

S IAVASH K. K URDISTANI Department of Biological Chemistry David Geffen School of Medicine at UCLA Los Angeles, CA USA [email protected] R ALF K ÜPPERS Institute for Cell Biology (Tumor Research) University of Duisburg-Essen, Medical School Essen Germany [email protected] E LENA K URENOVA Departments of Surgery University of Florida College of Medicine Gainesville, FL USA [email protected] K EISUKE K UROSE Departments of Obstetrics and Gynecology Nippon Medical School Kawasaki and Tokyo Japan PAULA M. K UZONTKOSKI Departments of Pediatrics and of Genetics, Norris Cotton Cancer Center Dartmouth Medical School Hanover, NH USA [email protected] R OBERT M. K YPTA Cell Biology and Stem Cells Unit CIC bioGUNE, Derio, Bilbao, Spain; Imperial College London London UK [email protected] J UAN C ARLOS L ACAL Instituto de Investigaciones Biomedicas CSIC, Madrid Spain [email protected]

List of Contributors

J AMES C. L ACEFIELD Departments of Electrical and Computer Engineering and Medical Biophysics University of Western Ontario London, ONT Canada [email protected] S TEPHAN L ADISCH Children’s Research Institute, Children’s National Medical Center, The George Washington University School of Medicine Washington, DC USA [email protected] H ERMANN L AGE Charité Campus Mitte Institute of Pathology Berlin Germany [email protected]

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J OSEPH R. L ANDOLPH Departments of Molecular Microbiology and Immunology, and Pathology; USC/Norris Comprehensive Cancer Center, Keck School of Medicine; Department of Molecular Pharmacology and Pharmaceutical Sciences, School of Pharmacy, Health Sciences Campus University of Southern California Los Angeles, CA USA [email protected] R OBERT L ANGER Department of Chemical Engineering and Center for Cancer Research Massachusetts Institute of Technology Cambridge, MA USA [email protected] PAOLA L ARGHI Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected]

C HARLES P. K. L AI Department of Cellular and Physiological Sciences The University of British Columbia Vancouver, BC Canada [email protected]

J AMES M. L ARNER Department of Therapeutic Radiology and Oncology University of Virginia School of Medicine Charlottesville, VA USA [email protected]

D ALE W. L AIRD Department of Anatomy and Cell Biology University of Western Ontario London, ON Canada [email protected]

G ÖRAN L ARSON Department of Clinical Chemistry and Transfusion Medicine Institute of Biomedicine Sahlgrenska Academy at Göteborg University Göteborg Sweden [email protected]

J ANICE B. B. L AM Department of Medicine and Genome Research Center University of Hong Kong Hong Kong, China [email protected]

S USANNA C. L ARSSON Division of Nutritional Epidemiology, Institute of Environmental Medicine Karolinska Institutet Stockholm Sweden [email protected]

WAN L. L AM Department of Cancer Genetics and Developmental Biology British Columbia Cancer Research Centre Vancouver, BC Canada [email protected] H UI Y. L AN Department of Medicine The University of Hong Kong Li Ka Shing Faculty of Medicine Hong Kong China [email protected]

P HILIPPE L ASSALLE INSERM U774 Institut Pasteur de Lille Lille France [email protected] FARIDA L ATIF Department of Medical and Molecular Genetics, Institute of Biomedical Research University of Birmingham Birmingham UK [email protected]

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V IRPI L AUNONEN Department of Medical Genetics, Biomedicum Helsinki University of Helsinki Helsinki Finland [email protected]

W ILLIAM P. J. L EENDERS Department of Pathology Radboud University Nijmegen Medical Center Nijmegen The Netherlands [email protected]

V INCENZO DE L AURENZI Department of Experimental Medicine and Biochemical Sciences University of Tor Vergata Rome Italy [email protected]

A NDREAS L EIBBRANDT Institute of Molecular Biotechnology of the Austrian Academy of Sciences Vienna Austria [email protected]

G WENDAL L AZENNEC INSERM Montpellier France [email protected]

M ANUEL C. L EMOS Academic Endocrine Unit, Nuffield Department of Clinical Medicine, University of Oxford, Oxford Centre for Diabetes Endocrinology and Metabolism (OCDEM), Churchill Hospital Headington, Oxford UK [email protected]

G AIL S. L EBOVIC Director of Women’s Services The Cooper Clinic Dallas, TX USA [email protected] D AVID P. L E B RUN Department of Pathology and Molecular Medicine Queen’s University Cancer Research Institute, Queen’s University Kingston, ON Canada [email protected] C HEONG J. L EE Department of Surgery University of Michigan Medical Center Ann Arbor, MI USA J ONG -H EUN L EE Women’s Cancers Section, Laboratory of Molecular Pharmacology, Center for Cancer Research National Cancer Institute Bethesda, MD USA [email protected]

E RIC J. L ENTSCH Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA [email protected] Y UN -C HUNG L EUNG Lo Ka Chung Centre for Natural Anti-cancer Drug Development and Department of Applied Biology and Chemical Technology The Hong Kong Polytechnic University Hung Hom, Kowloon, Hong Kong China [email protected] F RANCIS L ÉVI INSERM, Rythmes Biologiques et Cancers Hospital Paul Brousse, Villejuif Cedex France Université Paris Sud XI Orsay France [email protected]

S EAN B ONG L EE Genetics of Development and Disease Branch, National Institute of Diabetes & Digestive & Kidney Diseases National Institutes of Health Bethesda, MD USA [email protected]

J AY A. L EVY University of California, School of Medicine San Francisco, CA USA [email protected]

S TEPHEN L EE Department of Cellular and Molecular Medicine Faculty of Medicine, University of Ottawa Ottawa, ONT Canada [email protected]

K AIYI L I Department of Surgery Baylor College of Medicine Houston, TX USA [email protected]

List of Contributors

D AIQING L IAO Department of Anatomy and Cell Biology, Shands Cancer Center University of Florida College of Medicine Gainesville, FL USA [email protected] E MMANUELLE L IAUDET-C OOPMAN INSERM U826 CRLC Val d’Aurelle Parc Euromédecine, Montpellier Cedex 5 France [email protected] R OSSELLA L IBÈ INSERM U567, Institut Cochin Endocrinology, Metabolism and Cancer Department Paris France K E L IN Department of Haematology Royal Liverpool University Hospital Liverpool UK [email protected] S HENG -C AI L IN Department of Biomedical Sciences, School of Life Sciences Xiamen University, Xiamen Fujian China [email protected] S HIAW-Y IH L IN Department of Systems Biology, The University of Texas M.D. Anderson Cancer Center Houston, TX USA [email protected] WAN -WAN L IN Department of Pharmacology College of Medicine National Taiwan University Taipei Taiwan [email protected] J ANET C. L INDSEY Northern Institute for Cancer Research Newcastle University Newcastle upon Tyne UK [email protected] C HRISTOPHER A. L IPINSKI Scientific Advisor, Melior Discovery Waterford USA [email protected]

J OSEPH L IPSICK Stanford University Stanford, CA USA [email protected] F EI -F EI L IU Department of Medical Biophysics, Princess Margaret Hospital/Ontario Cancer Institute University Health Network University of Toronto Toronto, ON Canada [email protected] X IANGGUO L IU Winship Cancer Institute Emory University Atlanta, GA USA [email protected] T ING L ING L O Signal Transduction Laboratory Institute of Molecular and Cell Biology Singapore [email protected] V ICTOR L OBANENKOV Section of Molecular Pathology, NIAID National Institutes of Health Bethesda, MD USA [email protected] H OLGER N. L ODE Charité University Medicine Berlin Pediatrics, Berlin Germany [email protected] L AWRENCE A. L OEB University of Washington Seattle, WA USA [email protected] R OBERT L OEWE Department of Dermatology, Division of General Dermatology Medical University of Vienna Vienna Austria [email protected] S TEFFEN L OFT Institute of Public Health Department of Occupational and Environmental Health University of Copenhagen, København K Denmark [email protected]

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D IETMAR L OHMANN Institut für Humangenetik Universitätsklinikum Essen Essen Germany [email protected] M ATTHIAS L ÖHR Molecular Gastroenterology Unit, German Cancer Research Center (dkfz E180) Heidelberg and Department of Medicine II, Mannheim Medical Faculty University of Heidelberg Heidelberg Germany [email protected] V INATA B. L OKESHWAR Department of Urology, Cell Biology and Anatomy Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine Miami, FL USA [email protected] A LEXANDRE L OKTIONOV Colonix Medical Limited Babraham Research Campus Cambridge UK [email protected] E LIAS L OLIS Department of Pharmacology Yale University School of Medicine New Haven, CT USA [email protected] P IER -L UIGI L OLLINI Section of Cancer Research Department of Experimental Pathology University of Bologna Bologna Italy [email protected] M IGUEL L OPEZ -L AZARO Department of Pharmacology Faculty of Pharmacy, University of Seville, Seville Spain [email protected] C HARLES L. L OPRINZI Division of Oncology Department of Internal Medicine Mayo Clinic College of Medicine Rochester, MN USA [email protected]

J OCHEN L ORCH Dana Farlur Cancer Institute Head and Neck Oncology Program Boston, MA USA [email protected] E DITH M. L ORD Department of Microbiology & Immunology University of Rochester School of Medicine and Dentistry Rochester, NY USA [email protected] G IUSEPPE D I L ORENZO Cattedra di Oncologia Medica, Dipartimento di Endocrinologia e Oncologia molecolare e clinica Università degli Studi “Federico II” Napoli Italy [email protected] R EUBEN L OTAN Department of Thoracic Head and Neck Medical Oncology The University of Texas, MD Anderson Cancer Center Houston, TX USA [email protected] R AGNHILD A. L OTHE Department of Cancer Prevention Rikshospitalet-Radiumhospitalet Medical Centre Oslo Norway [email protected] M ICHAEL T. L OTZE University of Pittsburgh, Departments of Surgery and Bioengineering Pittsburgh, PA USA [email protected] C HRYSTAL U. L OUIS Center for Cell and Gene Therapy, Baylor College of Medicine Texas Children’s Hospital, and The Methodist Hospital Houston, TX USA [email protected] D MITRI L OUKINOV Section of Molecular Pathology NIAID NIH WT-I bldg Rockville, MD USA [email protected] D AVID B. L OVEJOY Department of Pathology University of Sydney NSW Australia [email protected]

List of Contributors

J IADE J. L U Department of Radiation Oncology Cancer Hospital of Fudan University Shanghai China [email protected]

J IAN -H UA L UO Department of Pathology University of Pittsburgh Pittsburgh, PA USA [email protected]

T ZONG -S HI L U Division of Experimental Medicine Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine Boston, MA USA [email protected]

G ARY H. LYMAN Cancer Center University of Rochester Medical Center Rochester, NY USA [email protected]

Y UANAN L U Department of Public Health Science University of Hawaii Honolulu, HI USA [email protected]

H ENRY LYNCH Hereditary Cancer Institute Creighton University Omaha, NE USA [email protected]

I RINA A. L UBENSKY National Cancer Institute National Institutes of Health Bethesda, MD USA [email protected]

E LSEBETH LYNGE Institute of Public Health University of Copenhagen Denmark, Copenhagen [email protected]

D ARIO D I L UCA Department of Experimental and Diagnostic Medicine University of Ferrara Ferrara, Italy [email protected]

S COTT K. LYONS Molecular Imaging Group CRUK Cambridge Research Institute, Li Ka Shing Centre Cambridge UK [email protected]

J ARED L UCAS Divisions of Public Health Sciences, Human Biology and Clinical Sciences Fred Hutchinson Cancer Research Center Seattle, WA USA [email protected]

M ICHAEL M AC M ANUS Department of Radiation Oncology Peter MacCallum Cancer Institute East Melbourne, VIC Australia [email protected]

A NDREAS L UCH Federal Institute for Risk Assessment Berlin Germany [email protected]

B RITTA M ÄDGE DKFZ Heidelberg Germany

B EN O. DE L UMEN Dept of Nutritional Sciences and Toxicology University of California Berkeley, CA USA [email protected]

C LAUDIE M ADOULET Laboratory of Biochemistry IFR53, Faculty of Pharmacy Reims Cedex France [email protected]

M ARIA L I L UNG Department of Biology and Center for Cancer Research Hong Kong University of Science and Technology Clearwater Bay Kowloon, Hong Kong (SAR) People's Republic of China [email protected]

F ÉLIX F ERNÁNDEZ M ADRID Department of Internal Medicine Karmanos Cancer Institute and Center for Molecular Medicine and Genetics, Wayne State University Detroit, MI USA [email protected]

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R OLANDO F. D EL M AESTRO Brain Tumour Research Centre, Montreal Neurological Institute, McGill University Montreal, QC Canada [email protected] B RINDA M AHADEVAN Department of Environmental and Molecular Toxicology Oregon State University Corvallis, OR USA [email protected] C SABA M AHOTKA Institute of Pathology Heinrich Heine Universität Düsseldorf Germany [email protected] S OURINDRA N. M AITI Division of Pediatrics, Department of Immunology M.D. Anderson Cancer Center Houston, TX USA [email protected] C ÉDRIC M ALICET INSERM, Stress Cellulaire, Parc Scientifique et Technologique de Luminy Marseille Cedex France [email protected] A LESSANDRA M ANCINO Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected] E VELYNE M ANET INSERM U758, Ecole Normale Supérieure de Lyon Lyon France [email protected] S RIDHAR M ANI Department of Medicine, Oncology and Molecular Genetics Albert Einstein College of Medicine NY USA [email protected] M ARCEL M ANNENS Academic Medical Centre, University of Amsterdam Amsterdam The Netherlands [email protected]

A LBERTO M ANTOVANI Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected] A SHLEY A. M ANZOOR Department of Radiation Oncology Duke University Durham, NC USA [email protected] L UCIA M ARCOCCI Department of Biochemical Sciences “A. Rossi Fanelli” Sapienza University of Rome Rome Italy [email protected] D IETER M ARMÉ Tumor Biology Center Institute of Molecular Oncology Freiburg Germany [email protected] D EBORAH J. M ARSH Kolling Institute of Medical Research University of Sydney NSW Australia [email protected] J OHN L. M ARSHALL Georgetown University Lombardi Comprehensive Cancer Center Washington, DC USA [email protected] R ENÉE M. M ARSHALL The Wistar Institute Molecular and Cellular Oncogenesis Program Philadelphia, PA USA [email protected] A NGELA M ÄRTEN National Centre for Tumour Diseases, Department of Surgery University Hospital Heidelberg Heidelberg Germany [email protected] E DMUND M ASER Institute of Toxicology and Pharmacology for Natural Scientists University Medical School Kiel Germany [email protected]

List of Contributors

T HOMAS E. M ASSEY Department of Pharmacology and Toxicology Queen’s University Kingston, ONT Canada [email protected]

J OSEPH H. M C C ARTY University of Texas, M.D. Anderson Cancer Center Houston, TX USA [email protected]

N ORIYUKI M ASUDA Department of Respiratory Medicine Kitasato University School of Medicine Sagamihara, Kanagawa Japan [email protected]

K ATHERINE A. M C G LYNN Division of Cancer Epidemiology and Genetics National Cancer Institute National Institutes of Health Bethesda, MD USA [email protected]

ATSUKO M ASUMI National Institute of Infectious Diseases, Musashimurayama-shi Tokyo Japan [email protected]

W. G LENN M C G REGOR James Graham Brown Cancer Center University of Louisville School of Medicine Louisville, KY USA [email protected]

YASUNOBU M ATSUDA Department of Hepatology and Gastroenterology Juntendo University School of Medicine, Shizuoka Hospital Shizuoka Japan

I AIN H. M C K ILLOP Department of Biology The University of North Carolina at Charlotte Charlotte, NC USA [email protected]

S ACHIKO M ATSUHASHI Department of Internal Medicine Saga Medical School Saga University Saga Japan [email protected]

R OGER E. M C L ENDON Department of Pathology Duke University Medical Center Durham, NC USA [email protected]

TAKAYA M ATSUZUKA Department of Anatomy and Physiology Kansas State University Manhattan, KS USA [email protected]

D ONALD C. M C M ILLAN University Department of Surgery Royal Infirmary Glasgow UK [email protected]

M ALGORZATA M ATUSIEWICZ Department of Medical Biochemistry Wroclaw Medical University Wroclaw Poland [email protected]

A RIANEB M EHRABI Department of General Visceral and Transplantation Surgery University of Heidelberg Heidelberg Germany [email protected]

WARREN L. M AY Department of Preventive Medicine University of Mississippi Medical Center Jackson, MS USA [email protected] M ATTHEW A. M C B RIAN Department of Biological Chemistry David Geffen School of Medicine at UCLA Los Angeles, CA USA [email protected]

A NIL M EHTA Maternal and Child Health Sciences University of Dundee Dundee UK [email protected] K APIL M EHTA The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected]

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List of Contributors

R EKHA M EHTA Toxicology Research Division, Bureau of Chemical Safety Food Directorate, HPFB, Health Canada Ottawa, ONT Canada [email protected] E LVIRA DE M EJIA Department of Food Science and Human Nutrition University of Illinois Urbana-Champaign, IL USA [email protected] B AR -E LI M ENASHE Department of Cancer Biology The University of Texas, M.D. Anderson Cancer Center Houston, TX USA [email protected] H EATHER M ERNITZ Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University Boston, MA USA [email protected] J ENNIFER A. M ERTZ Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology The University of Texas at Austin Austin, TX USA [email protected] K ARL -H EINZ M ERZ Department of Chemistry, Division of Food Chemistry and Toxicology University of Kaiserslautern Kaiserslautern Germany [email protected] J UN M I Department of Therapeutic Radiology and Oncology University of Virginia School of Medicine Charlottesville, VA USA [email protected] D ENNIS F. M ICHIEL Biopharmaceutical Development Program SAIC-Frederick, Inc. National Cancer Institute-Frederick Frederick, MD USA [email protected]

S TEPHAN M IELKE Hematology Branch, National Heart, Lung and Blood Institute (NHLBI) National Institutes of Health (NIH) Bethesda, MD USA [email protected] TAKEO M INAGUCHI Department of Obstetrics and Gynecology Toranomon Hospital Tokyo Japan [email protected] N AGAHIRO M INATO Department of Immunology and Cell Biology Graduate School of Medicine, Kyoto University Kyoto Japan [email protected] R ODNEY F. M INCHIN School of Biomedical Sciences University of Queensland St Lucia, QLD Australia [email protected] J OHN D. M INNA Hamon Center for Therapeutic Oncology Research and Departments of Pathology, Internal Medicine and Pharmacology University of Texas Southwestern Medical Center Dallas, TX USA [email protected] C LAUDIA M ITCHELL Institut Cochin Université Paris Descartes, CNRS Paris France [email protected] K AZUO M IYASHITA Department of Bioresources Chemistry, Faculty of Fisheries Sciences Hokkaido University Hakodate Japan [email protected] E IJI M IYOSHI Department of Biochemistry Osaka University Graduate School of Medicine Suita Japan [email protected]

List of Contributors

J UN M IYOSHI Department of Molecular Biology Osaka Medical Center for Cancer and Cardiovascular Diseases Osaka Japan [email protected] T OSHIHIKO M IZUTA Department of Internal Medicine Saga Medical School Saga Japan [email protected] K. T HOMAS M OESTA Klinik für Chirurgie und Chirurgische Onkologie Robert Rössle-Klinik, Charité Berlin-Buch, Berlin Germany [email protected] S ONIA M OHINTA Department of Medical Microbiology, Immunology and Cell Biology Southern Illinois University, School of Medicine Springfield, IL USA [email protected] J AN M OLLENHAUER Division of Molecular Genome Analysis, DKFZ Heidelberg Germany [email protected] M ICHAEL B. M ØLLER Department of Pathology, Division of Hematopathology Odense University Hospital Odense Denmark [email protected] B RUNO M ONDOVÌ Department of Biochemical Sciences “A. Rossi Fanelli” Sapienza University of Rome Rome Italy [email protected] A LESSANDRA M ONTECUCCO Istituto di Genetica Molecolare CNR via Abbiategrasso, Pavia Italy [email protected] R UGGERO M ONTESANO Courmayeur Italy [email protected]

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W OLTER J. M OOI Department of Pathology VU Medical Center Amsterdam The Netherlands [email protected] A MY C. M OORE Vanderbilt University Medical Center Nashville, TN USA [email protected] M ALCOLM A. S. M OORE Department of Cell Biology Memorial-Sloan-Kettering Cancer Center New York, NY USA [email protected] C ESAR A. M ORAN Department of Pathology M D Anderson Cancer Center Houston, TX USA [email protected] J AQUELINE M ORENO Division of Endocrinology Department of Medicine, Stanford University School of Medicine Stanford, CA USA [email protected] S ERGIO M ORENO Instituto de Biología Molecular y Celular del Cáncer CSIC/Universidad de Salamanca Campus Miguel de Unamuno, Salamanca Spain [email protected] FABIOLA M ORETTI Institute of Neurobiology and Molecular Medicine, National Council of Research/Molecular Oncogenesis Laboratory “Regina Elena” Cancer Institute Rome Italy [email protected] E IICHIRO M ORI Department of Biology Nara Medical University School of Medicine Kashihara, Nara Japan [email protected] A KIRA M ORIMOTO Department of Pediatrics Kyoto Prefectural University of Medicine Kyoto Japan [email protected]

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List of Contributors

PAT J. M ORIN Laboratory of Cellular and Molecular Biology National Institute on Aging, NIH Baltimore, MD USA [email protected]

H. K. M ÜLLER -H ERMELINK Institute of Pathology University of Würzburg Würzburg Germany [email protected]

C HRISTINE M. M ORRIS Cancer Genetics Research Group University of Otago at Christchurch Christchurch New Zealand [email protected]

L OIS M. M ULLIGAN Department of Pathology & Molecular Medicine Queen’s University Kingston, ON Canada [email protected]

G ABRIELA M ÖSLEIN Chefärztin für Allgemein- und Viszeralchirurgie Bochum Germany [email protected] C YNTHIA C. M ORTON Department of Pathology Brigham and Women’s Hospital Boston, MA USA [email protected] J USTIN L. M OTT Miles and Shirley Fiterman Center for Digestive Diseases Division of Gastroenterology and Hepatology Mayo Clinic College of Medicine Rochester, MN USA [email protected] S PYRO M OUSSES Cancer Genetics Branch National Human Genome Research Institute, NIH Bethesda, MD USA [email protected] S EBASTIAN M UELLER Department of Medicine Salem Medical Center, Heidelberg, Center of Alcohol Research Liver Disease and Nutrition and University of Heidelberg Heidelberg, Germany [email protected] S USETTE C. M UELLER Lombardi Comprehensive Cancer Center Georgetown University Medical Center Washington, DC USA [email protected] R OLF M ÜLLER Institute of Molecular Biology and Tumor Research (IMT) Philipps-University Marburg Marburg Germany [email protected]

R AMACHANDRAN M URALI Department of Pathology and Laboratory Medicine & Abramson Cancer Center University of Pennsylvania Philadelphia, PA USA [email protected] K ENJI M URO Department of Neurological Surgery, Northwestern University Feinberg School of Medicine Robert H. Lurie Comprehensive Cancer Center Chicago, IL USA [email protected] E DWARD L. M URPHY University of California, School of Medicine San Francisco, CA USA [email protected] PAUL G. M URRAY CRUK Institute for Cancer Studies, Molecular Pharmacology, Medical School University of Birmingham Birmingham UK [email protected] M ARKUS M ÜSCHEN Leukemia and Lymphoma Program, Norris Comprehensive Cancer Center University of Southern California Los Angeles, CA USA [email protected] R UTH J. M USCHEL Radiation Oncology and Biology University of Oxford Oxford, UK [email protected] A KIRA N AGANUMA Laboratory of Molecular and Biochemical Toxicology Graduate School of Pharmaceutical Sciences Tohoku University Sendai Japan [email protected]

List of Contributors

S HIGEKAZU N AGATA Osaka University Medical School Osaka Japan [email protected] R ITA N AHTA Department of Breast Medical Oncology The University of Texas MD Anderson Cancer Center Houston, TX USA Breast Cancer Translational Research Laboratory The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected] A KIRA N AKAGAWARA Chiba Cancer Center Research Institute Chiba Japan [email protected] T ETSUYA N AKATSURA Section for Frontier Medicine, Investigative Treatment Division, Research Center for Innovative Oncology National Cancer Center Hospital East Kashiwa City, Chiba Prefecture Japan [email protected] PATRIZIA N ANNI Section of Cancer Research Department of Experimental Pathology University of Bologna Bologna Italy [email protected] Z VI N AOR Department of Biochemistry, The George S. Wise Faculty of Life Sciences Tel Aviv University Ramat Aviv Israel [email protected] K EVIN T. N ASH Department of Pathology and Comprehensive Cancer Center University of Alabama-Birmingham Birmingham, AL USA [email protected] C HRISTIAN C. N AUS Department of Cellular and Physiological Sciences The University of British Columbia Vancouver, BC Canada [email protected]

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T IM S. N AWROT Division of Lung Toxicology Department of Occupational and Environmental Medicine (T.S.N.) and the Studies Coordinating Centre (J.A.S.) Division of Hypertension and Cardiovascular Rehabilitation Department of Cardiovascular Diseases University of Leuven Leuven Belgium [email protected] D AVID F. N ELLIS Biopharmaceutical Development Program SAIC-Frederick, Inc. National Cancer Institute-Frederick Frederick, MD USA [email protected] P ETER N ELSON Divisions of Public Health Sciences, Human Biology and Clinical Sciences Fred Hutchinson Cancer Research Center Seattle, WA USA [email protected] K ENNETH P. N EPHEW Medical Sciences Indiana University School of Medicine Bloomington, IN USA [email protected] K ORNELIA N EVELING Department of Human Genetics University of Wurzburg Wurzburg Germany [email protected] B RAD W N EVILLE Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA [email protected] K LAUS N EUHAUS Department of Operative, Preventive and Paediatric Dentistry School of Dental Medicine, University of Bern Bern Switzerland [email protected] I RENE O. L. N G Department of Pathology The University of Hong Kong Hong Kong [email protected]

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List of Contributors

D UC N GUYEN Associate Research Scientist Yale University School of Medicine New Haven, CT USA [email protected]

L ARRY N ORTON Breast Cancer Medicine Service Department of Medicine Memorial Sloan-Kettering Cancer Center New York, NY USA [email protected]

C AROLE N ICCO Faculté de Médecine Paris – Descartes UPRES 18-33, Groupe Hospitalier Cochin – Saint Vincent de Paul Paris France [email protected]

F RANCISCO J. N OVO Department of Genetics University of Navarra Pamplona, Spain [email protected]

S ANTO V. N ICOSIA Molecular Oncology Program & Research Institute, H. Lee Moffitt Cancer Center University of South Florida College of Medicine Tampa, FL USA [email protected]

R USLAN N OVOSYADLYY Division of Endocrinology, Diabetes and Bone Diseases Departmant of Medicine Mount Sinai School of Medicine New York, NY USA [email protected]

A NNE T. N IES Division of Tumor Biochemistry German Cancer Research Center Heidelberg Germany [email protected] M. A NGELA N IETO Instituto de Neurociencias de Alicante CSIC-UMH Sant Joan d’Alacant Spain [email protected] O MGO E. N IEWEG Department of Surgery The Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital Amsterdam The Netherlands [email protected] J ONAS N ILSSON Department of Clinical Chemistry and Transfusion Medicin Institute of Biomedicine Sahlgrenska academy at Göteborg University Göteborg Sweden [email protected] E WA N INIO INSERM UMRS Université Pierre et Marie Curie-Paris Paris France [email protected] D OUGLAS N OONAN University of Insubria Varese Italy [email protected]

N OA N OY Department of Pharmacology Case-Western Reserve University School of Medicine Cleveland, OH USA [email protected] H ALA H. N SOULI Department of Epidemiology and Biostatistics The George Washington University School of Public Health and Health Services Washington, DC USA [email protected] L AUREN M. N UNEZ Department of Cell Biology & Anatomy and Feist-Weiller Cancer Center LSUHSC-School of Medicine Shreveport, LA USA [email protected] A NDRÉ O BERTHÜR Department of Pediatric Oncology and Hematology Children’s Hospital University of Cologne Cologne Germany [email protected] TAKAHIRO O CHIYA Section for Studies on Metastasis National Cancer Center Research Institute Chuo-ku, Tokyo Japan [email protected]

List of Contributors

J AMES P. B. O’C ONNOR Imaging Science University of Manchester Manchester UK james.o'[email protected] S ARAH T. O’D WYER Department of Surgery University of Manchester Christie Hospital NHS Foundation Trust Manchester UK [email protected] S TEFAN O FFERMANNS Institute of Pharmacology, University of Heidelberg Heidelberg Germany [email protected] A NAT O HALI Cancer Vaccine Branch, National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected] TAKEO O HNISHI Department of Biology Nara Medical University School of Medicine Kashihara, Nara Japan [email protected] H ITOSHI O HNO Department of Internal Medicine, Faculty of Medicine Kyoto University Kyoto Japan [email protected] K EVIN R. O LDENBURG MatriCal, Inc. Spokane, WA USA [email protected] M AGALI O LIVIER Group of Molecular Carcinogenesis and Biomarkers International Agency for Research on Cancer World Health Organization Lyon Cedex 08 France [email protected] M ILITSAKH O N Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA [email protected]

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R UTH M. O’R EGAN Winship Cancer Institute Emory University Atlanta, GA USA [email protected] G ERTRAUD O REND Departement Klinisch-Biologische Wissenschaften (DKBW) Center for Biomedicine, Institute of Biochemistry and Genetics University of Basel Basel Switzerland [email protected] M AKOTO O SANAI Department of Pathology Sapporo Medical University School of Medicine Sapporo Japan [email protected] E DUARDO O SINAGA Departamento de Inmunobiología, Facultad de Medicina Universidad de la República Montevideo Uruguay [email protected] F RANCISO R UIZ -C ABELLO O SUNA Hospital Universitario Virgen de las Nieves Granada Spain [email protected] G. O TT Institute of Pathology Robert-Bosch Krankenhaus Stuttgart Germany [email protected] C HRISTIAN O TTENSMEIER CRC Wessex Oncology Unit, Southampton General Hospital and Tenovous Laboratory Southampton University Hospital Trust Southampton UK [email protected] I WATA O ZAKI Health Administration Center Saga Medical School Saga University Saga Japan [email protected]

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S HUJI O ZAKI Department of Medicine and Bioregulatory Sciences The University of Tokushima Graduate School of Health Biosciences Tokushima Japan [email protected] H ELEN PACE Department of Molecular Virology Immunology and Medical Genetics, Ohio State University Comprehensive Cancer Center Columbus, OH USA [email protected] S IMON C. PACEY Cancer Research UK Center for Cancer Therapeutics The Institute of Cancer Research Sutton, Surrey UK [email protected] P IER PAOLO PANDOLFI Memorial Sloan-Kettering Cancer Center Weill Cornell Graduate School of Medical Sciences NY USA [email protected] K LAUS PANTEL Universitäts-Krankenhaus Eppendorf Hamburg Germany [email protected] M ELISSA C. PAOLONI National Cancer Institute, Center for Cancer Research Comparative Oncology Program Bethesda, MD USA [email protected],gov E VANGELIA PAPADIMITRIOU Department of Pharmacy University of Patras Patras Greece [email protected] ATHANASIOS G. PAPAVASSILIOU Department of Biological Chemistry, Medical School University of Athens Goudi, Athens Greece [email protected] S ABITHA PAPINENI Department of Veterinary Physiology and Pharmacology Texas A&M University College Station, TX USA [email protected]

B EN H O PARK The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University Baltimore, MD USA [email protected] G EOFF J. M. PARKER Imaging Science University of Manchester Manchester UK [email protected] S ARAH J. PARSONS University of Virginia Charlotteville, VA USA [email protected] O NEEL PATEL Department of Surgery University of Melbourne, Austin Health Melbourne, VIC Australia [email protected] PATRIZIA PATERLINI -B RÉCHOT INSERM Unit 807, Faculté de Médecine Necker Enfants Malades, Paris V, Paris France [email protected] Y VONNE PATERSON Professor of Microbiology University of Pennsylvania Philadelphia, PA USA [email protected] K ONAN P ECK Institute of Biomedical Sciences Academia Sinica Taipei Taiwan Republic of China [email protected] F LORENCE P EDEUTOUR Laboratory of Solid Tumors Genetics Nice University Hospital and CNRS UMR 6543 Faculty of Medicine Nice France [email protected] D AN P EER Departments of Anesthesia and Immunology, CBR Institute for Biomedical Research Harvard Medical School Boston, MA USA [email protected]

List of Contributors

M IGUEL A. P EINADO Institue of Predictive and Personalized Medicine of Cancer (IMPPC) Badalona Barcelona, Spain [email protected]

G ODEFRIDUS J. P ETERS Department of Medical Oncology VU University Medical Center Amsterdam The Netherlands [email protected]

A NGEL P ELLICER Department of Pathology New York University School of Medicine New York, NY USA [email protected]

M ARLEEN M. R. P ETIT Department of Human Genetics University of Leuven Leuven Belgium [email protected]

J UHA P ELTONEN Department of Anatomy, Institute of Biomedicine University of Turku Turku Finland [email protected]

P ETER P ETZELBAUER Department of Dermatology, Division of General Dermatology Medical University of Vienna Vienna Austria [email protected]

S IRKKU P ELTONEN Department of Dermatology University of Turku Turku Finland [email protected]

C LAUDIA P FÖHLER Department of Dermatology Saarland University Medical School Homburg/Saar, Germany [email protected]

J OSEF M. P ENNINGER Institute of Molecular Biotechnology of the Austrian Academy of Sciences Vienna Austria [email protected]

M ICHAEL P FREUNDSCHUH Klinik für Innere Medizin I Universität des Saarlandes Homburg Germany [email protected]

M AIKEL P. P EPPELENBOSCH University Medical Center Groningen University of Groningen Groningen The Netherlands [email protected]

P HILIP A. P HILIP Karmanos Cancer Institute Wayne State University Detroit, MI USA [email protected]

M ÓNICA P ÉREZ -R ÍOS Department of Preventive Medicine and Public Health University of Santiago de Compostela C/San Francisco Spain [email protected]

M ARCO A. P IEROTTI Scientific Director IRCCS Istituto Nazionale Tumori Foundation Milan Italy [email protected]

F RANCISCO G. P ERNAS National Institute on Deafness and Other Communication Disorders and National Cancer Institute NIH Bethesda, MD USA

PAOLA P IETRANGELI Department of Biochemical Sciences-A. Rossi Fanelli Sapienza University of Rome Rome Italy [email protected]

S ILVERIO P ERROTTA Department of Pediatrics Second University of Naples Naples Italy [email protected]

T ORSTEN P IETSCH Institut für Neuropathologie Universitätskliniken Bonn, Bonn Germany Kinderchirurgie [email protected]

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M ICHAEL P ISHVAIAN Georgetown University Lombardi Comprehensive Cancer Center Washington, DC USA [email protected] E LLEN S. P IZER Laboratory of Cellular and Molecular Biology National Institute on Aging, NIH Baltimore, MD USA C HRISTOPH P LASS German cancer Research cener (DKFZ) Heidelberg Germany [email protected] L EONIDAS C. P LATANIAS Robert H. Lurie Comprehensive Cancer Center and Division of Hematology-Oncology, Department of Medicine Northwestern University Medical School Chicago, IL USA [email protected] J EFFREY L. P LATT Transplantation Biology and the Departments of Surgery Immunology and Pediatrics Mayo Clinic Rochester, MN USA [email protected] M ARK R. P LAYER Johnson & Johnson Pharmaceutical Research & Development Exton, PA USA [email protected] I RIS M. C. VAN DER P LOEG Department of Surgery The Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital Amsterdam The Netherlands [email protected] K LAUS P ODAR Department of Medical Oncology, Jerome Lipper Multiple Myeloma Center Dana-Farber Cancer Institute Boston, MA USA [email protected] M IRIAM C. P OIRIER National Cancer Institute, NIH Bethesda, MD USA [email protected]

J EFFREY W. P OLLARD Department of Developmental and Molecular Biology, Center for the Study of Reproductive Biology and Women’s Health Albert Einstein College of Medicine Bronx, NY USA [email protected] S IMONA P OLO University of Milan, Medical School Milan Italy [email protected] B RUCE A. J. P ONDER Department of Oncology University of Cambridge Cambridge UK [email protected] M IRCO P ONZONI Differentiation Therapy Unit, Laboratory of Oncology G. Gaslini Children’s Hospital Genoa Italy [email protected] B EATRICE L. P OOL -Z OBEL Nutritional Toxicology Friedrich-Schiller-University of Jena Jena Germany [email protected] C HRISTOPHER S. P OTTEN Epistem Ltd and School of Biological Sciences University of Manchester Manchester UK [email protected] A NNEMARIE P OUSTKA Division of Molecular Genome Analysis, DKFZ Heidelberg Germany [email protected] M ARISSA V. P OWERS Cancer Research UK Centre for Cancer Therapeutics The Institute of Cancer Research Sutton, Surrey UK [email protected] G ARTH P OWIS Department of Experimental Therapeutics M.D. Anderson Cancer Center Houston, TX USA [email protected]

List of Contributors

G RAZIELLA P RATESI Fondazione IRCCS Istituto Nazionale dei Tumori Milan Italy [email protected] G EORGE C. P RENDERGAST Department of Pathology, Anatomy and Cell Biology Jefferson Medical School Lankenau Institute for Medical Research Wynnewood, PA USA [email protected] V ICTOR G. P RIETO Department of Pathology The University of Texas M.D. Anderson Cancer Center Houston, TX USA [email protected] K EVIN M. P RISE Centre for Cancer Research and Cell Biology Queen’s University Belfast Belfast UK [email protected] K ATHY P RITCHARD -J ONES Institute of Cancer Research/Royal Marsden Hospital Sutton, Surrey UK [email protected] A MANDA H. P ROWSE Nuffield Department of Obstetrics and Gynaecology Oxford University John Radcliffe Hospital Oxford UK [email protected] C HING -H ON P UI St. Jude Children’s Research Hospital Memphis, TN USA [email protected] K AREN P ULFORD Department of Clinical Laboratory Sciences University of Oxford, John Radcliffe Hospital Oxford UK [email protected] T ERESA G ÓMEZ D EL P ULGAR Instituto de Investigaciones Biomedicas CSIC, Madrid Spain

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C HAO -N AN Q IAN Laboratory of Cancer Genetics Van Andel Research Institute Grand Rapids, MI USA [email protected] J IAHUA Q IAN Cancer Vaccine Branch, National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected] H ARTMUT M. R ABES Institute of Pathology University of Munich Munich Germany [email protected] D IRK R ADES Department of Radiation Oncology University Hospital Schleswig-Holstein Campus Luebeck Germany [email protected] J ERALD P. R ADICH Clinical Research Division Fred Hutchinson Cancer Research Center Seattle, WA USA [email protected] N ORMAN S. R ADIN Department of Psychiatry University of Michigan Ann Arbor, MI USA [email protected] F ULVIO D ELLA R AGIONE Department of Biochemistry and Biophysics Second University of Naples Naples Italy [email protected] RYAN L. R AGLAND Department of Human Genetics University of Michigan Ann Arbor, MI USA [email protected] AYYAPPAN K. R AJASEKARAN Department of Pathology and Laboratory Medicine University of California Los Angeles, CA USA [email protected]

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List of Contributors

S IGRID A. R AJASEKARAN Department of Pathology and Laboratory Medicine University of California Los Angeles, CA USA [email protected] J AYADEV R AJU Toxicology Research Division, Bureau of Chemical Safety Food Directorate, HPFB, Health Canada Ottawa, ONT Canada [email protected] S. R AMAKRISHNAN Department of Pharmacology University of Minnesota Minneapolis, MN USA [email protected] K OTA V. R AMANA Dept of Biochemistry and Molecular Biology University Of Texas Medical Branch Galveston, TX USA [email protected] S ANTIAGO R AMÓN Y C AJAL Department of Pathology, Vall d’ Hebron University Hospital Barcelona Spain [email protected] G IORGIA R ANDI Department of Epidemiology Institute for Farmacological Research Mario Negri Milan Italy [email protected] M ARIUSZ Z. R ATAJCZAK Stem Cell Institute at James Graham Brown Cancer Center University of Louisville Louisville, KY USA [email protected] A NKE R ATTENHOLL Department of Dermatology University of Münster Münster Germany [email protected] A LBERTO R AVAIOLI Department of Oncology Infermi Hospital Rimini Italy [email protected]

M IRA R. R AY Department of Urologic Sciences The Prostate Centre at Vancouver General Hospital Vancouver, BC Canada [email protected] R OGER R EDDEL Children’s Medical Research Institute Westmead, NSW Australia [email protected] M AY R EED Department of Medicine, Division of Geriatric Medicine University of Washington Seattle, WA USA [email protected] E DUARDO M. R EGO Medical School of Ribeirão Preto University of São Paulo Ribeirão Preto Brazil [email protected] R EUVEN R EICH Department of Pharmacology, School of Pharmacy, Faculty of Medicine The Hebrew University of Jerusalem Jerusalem Israel [email protected] J EAN -M ARIE R EIMUND Service d’Hépato-Gastro-Entérologie et Nutrition, Centre Hospitalier Universitaire de Caen Université de Caen-Basse Normandie Caen France [email protected] C ELSO A. R EIS Institute of Molecular Pathology and Immunology of the University of Porto Medical Faculty of Porto Porto Portugal [email protected] L ING R EN National Cancer Institute, Center for Cancer Research Pediatric Oncology Branch Bethesda, MD USA [email protected] ANDREW G. RENEHAN Department of Surgery University of Manchester Christie Hospital NHS Foundation Trust Manchester UK [email protected]

List of Contributors

M ARCUS R ENNER Division of Molecular Genome Analysis, DKFZ Heidelberg Germany [email protected] PAUL S. R ENNIE The Richard Ivey School of Business University of Western Ontario London, ONT Canada [email protected] D OMENICO R IBATTI Department of Human Anatomy and Histology University of Bari Medical School Bari Italy [email protected] R AUL C. R IBEIRO Department of Oncology St. Jude Children’s Research Hospital Memphis, TN USA [email protected] D ES R. R ICHARDSON Department of Pathology University of Sydney NSW, Australia [email protected] A NN R ICHMOND Department of Cancer Biology Vanderbilt University Medical School Nashville, TN USA [email protected] V ICTORIA M. R ICHON Merck Research Laboratories Boston, MA USA [email protected]

C ARRIE R INKER -S CHAFFER Department of Surgery, Section of Urology The University of Chicago Chicago, IL USA [email protected] TADEUSZ R OBAK Department of Hematology Medical University of Lodz Lodz Poland [email protected] F REDIKA M. R OBERTSON The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected] C RISTINA R ODRÍGUEZ National Cancer Institute of Research (CNIO) Madrid Spain J OSE L UIS R ODRÍGUEZ -F ERNÁNDEZ Departamento de Fisiología Celular y Molecular Centro de Investigaciones Biológicas Madrid Spain [email protected] C ARLOS RODRIGUEZ-GALINDO Department of Oncology St. Jude Children’s Research Hospital Memphis, TN USA [email protected]

J USTIN L. R ICKER Merck Research Laboratories Upper Gwynedd, PA USA

D EREK L E R OITH Division of Endocrinology, Diabetes and Bone Diseases Departmant of Medicine Mount Sinai School of Medicine New York, NY USA [email protected]

T HOMAS R IED Genetics Branch, Center for Cancer Research, National Cancer Institute, NIH Bethesda, MD USA [email protected]

W OLF C. R OLAND Biomedical Research Centre University of Dundee Dundee UK [email protected]

M AARTJE C. VAN R IJK Department of Surgery The Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital Amsterdam The Netherlands [email protected]

Z E ’ EV R ONAI Signal Transduction Program Burnham Institute for Medical Research La Jolla, CA USA [email protected]

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L UCA R ONCUCCI Department of Medicine University of Modena and Reggio Emilia Modena Italy [email protected]

L UCA R UBINO Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected]

I GOR B. R ONINSON Department of Molecular Genetics University of Illinois at Chicago Chicago, IL USA [email protected]

M ARCO R UGGIERO Department of Experimental Pathology and Oncology University of Firenze Firenze Italy [email protected]

E LIOT M. R OSEN Long Island Jewish Medical Center Albert Einstein College of Medicine Bronx, NY USA [email protected] C AROL L. R OSENBERG Boston Medical Center and Boston University School of Medicine Boston, MA USA [email protected] S TEVEN A. R OSENZWEIG Department of Cell and Molecular Pharmacology and Experimental Therapeutics Medical University of South Carolina Charleston, SC USA [email protected] A NGELO R OSOLEN Department of Pediatrics, Hemato-oncology Unit University of Padua Padova Italy [email protected] J EFFREY S. R OSS Albany Medical College Albany, NY USA [email protected]

Z ORAN R UMBOLDT Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA T HOMAS M. R ÜNGER Department of Dermatology Boston University School of Medicine Boston, MA USA [email protected] E RKKI R UOSLAHTI Vascular Mapping Center, Burnham Institute for Medical Research at University of California Santa Barbara, CA USA [email protected] D ARIO R USCIANO Friedrich Miescher Institute Basel Switzerland [email protected] G IANDOMENICO R USSO Istituto Demopatico dell’Immacolata Instituto di Ricovero e Cura a Carattere Scientifico Roma, Italy [email protected]

T HEODORA S. R OSS Department of Internal Medicine University of Michigan Ann Arbor, MI USA [email protected]

I RMA H. R USSO Breast Cancer Research Laboratory Fox Chase Cancer Center Philadelphia, PA USA [email protected]

A LBERTO R UANO -R AVINA Department of Preventive Medicine and Public Health University of Santiago de Compostela C/San Francisco Spain [email protected]

J OSE R USSO Breast Cancer Research Laboratory Fox Chase Cancer Center Philadelphia, PA USA [email protected]

List of Contributors

J. RYAN Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA

T OSHIYUKI S AKAI Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science Kyoto Prefectural University of Medicine Kyoto Japan [email protected]

J AMES T. R UTKA The Arthur and Sonia Labatt Brain Tumour Research Centre The Hospital for Sick Children The University of Toronto Toronto, ONT USA [email protected]

B ODOUR S ALHIA Cancer and Cell Biology Division The Translational Genomics Research Institute Phoenix, AZ USA [email protected]

A NNE T HOUSTRUP S ABER National Research Centre for the Working Environment Copenhagen Denmark [email protected]

H ELMUT R AINER S ALIH Department of Internal Medicine II University Hospital of Tuebingen Eberhard-Karls-University Tuebingen Germany [email protected]

G AURI S ABNIS University of Maryland School of Medicine Baltimore, MD USA [email protected] M OHAMAD S EYED S ADR Brain Tumour Research Centre, Montreal Neurological Institute, McGill University Montreal, QC Canada [email protected] S TEPHEN S AFE Department of Veterinary Physiology and Pharmacology Texas A&M University College Station, TX USA [email protected]

B ETH A. S ALMON Department of Pharmacology and Therapeutics University of Florida Gainesville, FL USA [email protected] H OWARD W. S ALMON Department of Radiation Oncology North Florida Radiation Oncology Gainesville, FL USA [email protected] R AED S AMARA Cancer Vaccine Branch, National Cancer Institute National Institutes of Health Bethesda, MD USA [email protected]

X AVIER S AGAERT Department of Pathology University Hospitals of K.U. Leuven Leuven Belgium [email protected]

J ULIAN R. S AMPSON Institute of Medical Genetics Cardiff University Heath Park, Cardiff UK [email protected]

A SIM S AHA University of Cincinnati and The Barrett Cancer Center Cincinnatti, OH USA [email protected]

M ANORANJAN S ANTRA Neurology Research Henry Ford Health System Detroit, MI USA [email protected]

K UNAL S AIGAL National Institute on Deafness and Other Communication Disorders and National Cancer Institute NIH Bethesda, MD USA [email protected]

F RANK S ARAN Department of Radiotherapy and Paediatric Oncology Royal Marsden Hospital NHS Foundation Trust Sutton, Surrey UK [email protected]

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D EVANAND S ARKAR Departments of Urology, Pathology and Neurosurgery Columbia University Medical Center College of Physicians and Surgeons New York, NY USA [email protected] FAZLUL H. S ARKAR Karmanos Cancer Institute Wayne State University Detroit, MI USA [email protected] D EBASHIS S ARKER Cancer Research UK Center for Cancer Therapeutics The Institute of Cancer Research Sutton, Surrey UK [email protected] S TEPHANIE S ASSE Hematology and Oncology University Hospital of Cologne, Department of Internal Medicine I Cologne Germany [email protected] L EONARD A. S AUER Bassett Research Institute Cooperstown, NY USA [email protected] C HRISTOBEL S AUNDERS School of Surgery and Pathology, QEII Medical Centre University of Western Australia Crawley, WA Australia [email protected] C ONSTANCE L. L. S AW Department of Pharmacy National University of Singapore Singapore [email protected]

R ON H. N. VAN S CHAIK Department of Clinical Chemistry Erasmus University Medical Center Rotterdam The Netherlands [email protected] M ANFRED S CHARTL Biozentrum, Universität Würzburg Würzburg Germany [email protected] H UUB S CHELLEKENS Department of Innovation Studies Central Laboratory Animal Institute Utrecht University, TD Utrecht The Netherlands [email protected] D ETLEV S CHINDLER Department of Human Genetics University of Wurzburg Wurzburg, Germany [email protected] P ETER M. S CHLAG Klinik für Chirurgie und Chirurgische Onkologie Robert Rössle-Klinik, Charité Berlin-Buch Germany [email protected] M ARTIN S CHLUMBERGER Institut de Cancérologie Gustave-Roussy, Villejuif and Université Paris-Sud 11, Paris France [email protected] P ETER S CHMEZER Division of Toxicology and Cancer Risk Factors German Cancer Research Center (DKFZ) Heidelberg Germany [email protected]

A NURAG S AXENA Department of Pathology and Laboratory Medicine Royal University Hospital, Saskatoon Health Region/ University of Saskatchewan Saskatoon, Saskatchewan Canada [email protected]

A NNETTE S CHMITT-G RAEFF Institute of Pathology University Hospital Freiburg Freiburg Germany [email protected]

R EINHOLD S CHÄFER Molecular Tumor Pathology Institute of Pathology Berlin Germany [email protected]

D OMINIK T. S CHNEIDER Clinic of Pediatrics Klinikum Dortmund Dortmund Germany [email protected]

List of Contributors

S TEFAN W. S CHNEIDER Department of Dermatology University of Münster Münster Germany [email protected]

M ARKUS S CHWAIGER Department of Nuclear Medicine Technical University of Munich Munich Germany [email protected]

S USANNE S CHNITTGER MLL Munich Leukemia Laboratory Munich Germany [email protected]

E DWARD L. S CHWARTZ Department of Oncology Albert Einstein College of Medicine Bronx, NY USA [email protected]

N ATHALIE S CHOLLER Center for Research on Early Detection and Cure of Ovarian Cancer, School of Medicine University of Pennsylvania Biomedical Research Building (BRB) II/III Philadelphia, PA USA [email protected] A XEL H. S CHÖNTHAL University of Southern California Keck School of Medicine Los Angeles, CA USA [email protected] Y VONNE M. S CHRAGE Department of Pathology Leiden University Medical Center Leiden The Netherlands [email protected] H. W. B ART S CHREUDER Department of Orthopaedics Radboud University Medical Centre Nijmegen The Netherlands [email protected] L AURA W. S CHRUM Department of Biology The University of North Carolina at Charlotte Charlotte, NC USA [email protected] W OLFGANG A. S CHULZ Department of Urology Heinrich-Heine University Düsseldorf Germany [email protected] M ANFRED S CHWAB Tumour Genetics German Cancer Research Center, DKFZ Heidelberg Germany [email protected]

D IETRICH VON S CHWEINITZ Universitäts-Kinderspital beider Basel (UKBB) Basel Switzerland B ÉATRICE S ECRETAN IARC/WHO, Group Carcinogen Identification and Evaluation Lyon Cedex France [email protected] R ONY S EGER Department of Biological Regulation Weizmann Institute of Science Rehovot Israel [email protected] G AIL M. S EIGEL Department of Ophthalmology University at Buffalo Buffalo, NY USA [email protected] H IROYUKI S EIMIYA Division of Molecular Biotherapy, Cancer Chemotherapy Center Japanese Foundation for Cancer Research Koto-ku, Tokyo Japan [email protected] PAULE S EITE Pôle Biologie Santé University of Poitiers Poitiers cedex France [email protected] H ELMUT K. S EITZ Department of Medicine Salem Medical Center, Heidelberg, Center of Alcohol Research Liver Disease and Nutrition and University of Heidelberg Heidelberg, Germany [email protected]

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W ILLIAM R. S ELLERS Harvard Medical School Dana-Farber Cancer Institute Boston, MA USA [email protected] P ERIASAMY S ELVARAJ Department of Pathology Emory University School of Medicine Atlanta, GA USA [email protected] M ARIE G. S ELZER Department of Urology, Cell Biology and Anatomy Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine Miami, FL USA [email protected] S UBRATA S EN Department of Molecular Pathology (Unit 951) The University of Texas, M.D. Anderson Cancer Center Houston, TX USA [email protected] V ITALYI S ENYUK Department of Medicine (M/C 737), College of Medicine Research Building University of Illinois at Chicago Chicago, IL USA [email protected] N EDIME S ERAKINCI Anatomy and Neurobiology Institute of Medical Biology University of Southern Denmark Odense Denmark [email protected] C HRISTINE S ERS Institute of Pathology University Medicine Charité Berlin Germany [email protected] V IJAYASARADHI S ETALURI Department of Dermatology University of Wisconsin School of Medicine and Public Health Sciences Madison, WI USA [email protected]

J OHN F. S EYMOUR Peter MacCallum Cancer Center and the University of Melbourne Melbourne, VIC Australia [email protected] R ABIA K S HAHID Saskatoon Cancer Center University of Saskatchewan Saskatoon, SK Canada [email protected] G IRISH V. S HAH Department of Pharmacology University of Louisiana College of Pharmacy Monroe, LA USA [email protected] A. S HARMA Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA R ICKY A. S HARMA Radiation Oncology and Biology University of Oxford Churchill Hospital Oxford UK [email protected] J ERRY W. S HAY University of Texas Southwestern Medical Center Dallas, TX USA [email protected] S HIJIE S HENG Department of Pathology, Wayne State University School of Medicine Karmanos Cancer Institute Detroit, MI USA [email protected] D ONNA S HEWACH Department of Pharmacology University of Michigan Medical School Ann Arbor, MI USA [email protected] I E -M ING S HIH Department of Pathology Johns Hopkins University School of Medicine Baltimore, MD USA [email protected]

List of Contributors

K ENTARO S HIKATA Department of Environmental Medicine Graduate School of Medical Sciences Kyushu University Fukuoka Japan [email protected] Y OSEF S HILOH Sackler School of Medicine, Tel Aviv University Tel Aviv, Israel [email protected] H YUNSUK S HIM Department of Hematology/Oncology Winship Cancer Institute, Emory University Atlanta, GA USA [email protected] Y UTAKA S HIMADA Department of Surgery Graduate School of Medicine Kyoto University Kyoto Japan [email protected] Y ONG -B EOM S HIN BioNanotechnology Research Center Korea Research Institute of Bioscience and Biotechnology Yuseong, Daejeon Republic of Korea [email protected]

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A NTONIO S ICA Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected] G ENE P. S IEGAL Departments of Pathology, Cell Biology, and Surgery and the Gene Therapy Center University of Alabama at Birmingham Birmingham, AL USA [email protected] D IETMAR W. S IEMANN Department of Radiation Oncology University of Florida Gainesville, FL USA [email protected] C HRISTINE L. E. S IEZEN National Institute of Public Health and Environment Bilthoven The Netherlands [email protected] A LEXANDRA C. S ILVEIRA Department of Pathology and Comprehensive Cancer Center University of Alabama at Birmingham Birmingham, AL USA [email protected]

T OSHI S HIODA Massachusetts General Hospital Center for Cancer Research Charlestown, MA USA [email protected]

D IANE M. S IMEONE Department of Surgery University of Michigan Medical Center Ann Arbor, MI USA [email protected]

J ANET S HIPLEY The Institute of Cancer Research, Sutton Surrey UK [email protected]

H ANS -U WE S IMON Department of Pharmacology University of Bern Bern, Switzerland [email protected]

G IRJA S. S HUKLA Department of Surgery, Vermont Comprehensive Cancer Center, College of Medicine University of Vermont Burlington, VT USA [email protected]

A MRIK J. S INGH Department of Pathology Harvard Medical School, Beth Israel Deaconess Medical Center Boston, MA USA [email protected]

A RTHUR S HULKES Department of Surgery University of Melbourne, Austin Health Melbourne, VIC Australia [email protected]

S HREE R AM S INGH Mouse Cancer Genetics Program National Cancer Institute at Frederick Frederick, MD USA [email protected]

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V INEETA S INGH School of Surgery and Pathology Sir Charles Gairdner Hospital, QEII Medical Centre Nedlands, WA Australia [email protected]

J OSEF S MOLLE Department of Dermatology Medical University Graz Graz Austria [email protected]

L ILLIAN L. S IU Department of Medical Oncology and Hematology Robert and Maggie Bras and Family New Drug Development Program Princess Margaret Hospital Toronto, ONT Canada [email protected]

LYNN S NIDERHAN Department of Microbiology and Immunology University of Rochester Rochester, NY USA [email protected]

A NITA S JÖLANDER Cell and Experimental Pathology, Department of Laboratory Medicine Lund University, Malmo University Hospital Malmo Sweden [email protected]

R OBERT W. S OBOL Department of Pharmacology University of Pittsburgh School of Medicine, Hillman Cancer Center, University of Pittsburgh Cancer Institute Pittsburgh, PA USA [email protected]

J. S KONER Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA K EITH S KUBITZ Division of Hematology, Oncology and Transplantation University of Minnesota Medical School Minneapolis, MN USA [email protected] C HRISTOPHER S LAPE Genetics Branch, Center for Cancer Research National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected] K EIRAN S. M. S MALLEY The Wistar Institute Philadelphia, PA USA [email protected]

A LEXANDER S. S OBOLEV Department of Molecular Genetics of Intracellular Transport Institute of Gene Biology Russian Academy of Sciences Moscow Russia [email protected] G RAZIELLA S OLINAS Department of Immunology Fondazione Humanitas per la Ricerca Rozzano, Milan Italy [email protected] T OSHIYA S OMA Department of Surgery Graduate School of Medicine Kyoto University Kyoto Japan [email protected]

L UBOMIR B. S MILENOV Department of Radiation Oncology Columbia University New York, NY USA [email protected]

PAVEL S OUCEK Group for Biotransformations, Center of Occupational Medicine National Institute of Public Health Prague Czech Republic [email protected]

B RUCE F. S MITH Scott-Ritchey Research Center College of Veterinary Medicine Auburn University Auburn, AL USA [email protected]

T HOMAS D. S OUTHGATE Paterson Institute for Cancer Research University of Manchester Manchester UK [email protected]

List of Contributors

L ORENZO S PAGGIARI Department of Thoracic Surgery European Institute of Oncology Milan Italy [email protected] D AVID W. S PEICHER The Wistar Institute Philadelphia, PA USA [email protected] VALERIE S PEIRS Leeds Institute of Molecular Medicine University of Leeds Leeds UK [email protected] D IETMAR S PENGLER Max-Panck-Institut für Psychiatrie München Germany [email protected] P HILLIPPE E. S PIESS Department of Urologic Oncology University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected] C HRISTOPH S PRINGFELD Department of Internal Medicine IV University of Heidelberg Hospital Heidelberg Germany [email protected]

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M. S HARON S TACK Northwestern University Medical School Chicago, IL USA [email protected] J AN A. S TAESSEN Division of Lung Toxicology Department of Occupational and Environmental Medicine (T.S.N.) and the Studies Coordinating Centre (J.A.S.) Division of Hypertension and Cardiovascular Rehabilitation Department of Cardiovascular Diseases University of Leuven Leuven Belgium [email protected] L. J OE S TAFFORD Department of Pathology and Comprehensive Cancer Center University of Alabama-Birmingham Birmingham, AL USA [email protected] E RIC S TANBRIDGE Department of Microbiology and Molecular Genetics University of California Irvine, CA USA [email protected] B ARRY S TAYMATES Department of Pathology Henry Mayo Newhall Memorial Hospital Valencia, CA USA [email protected] S TACEY S TEIN Center for Advanced Biotechnology and Medicine UMDMJ – Robert Wood Johnson Medical School Piscataway, NJ USA

L AKSHMAIAH S REERAMA Department of Chemistry St. Cloud State University St. Cloud, MN USA [email protected]

M ARTIN S TEINHOFF Department of Dermatology University of Münster Münster Germany [email protected]

S ATISH K. S RIVASTAVA Dept of Biochemistry and Molecular Biology University Of Texas Medical Branch Galveston, TX USA [email protected]

A LEXANDER S TEINLE Department of Immunology Institute for Cell Biology Eberhard-Karls-University Tuebingen Germany [email protected]

S UDHIR S RIVASTAVA Division of Cancer Prevention National Cancer Institute Rockville, MD USA [email protected]

C ARSTEN S TEPHAN Department of Urology, Charité Universitätsmedizin Campus Charité Mitte Berlin Germany [email protected]

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List of Contributors

P ETER L. S TERN Cancer Research UK Immunology Group Paterson Institute for Cancer Research Manchester, UK [email protected] W ILLIAM G. S TETLER -S TEVENSON Extracellular Matrix Pathology Section, Cell and Cancer Biology Branch National Cancer Institute Bethesda, MD USA [email protected] R ICHARD G. S TEVENS University of Connecticut Health Center Farmington, CT USA [email protected] F REDA S TEVENSON CRC Wessex Oncology Unit, Southampton General Hospital and Tenovous Laboratory Southampton University Hospital Trust Southampton UK W ILLIAM P. S TEWARD Cancer Biomarkers and Prevention Group Department of Cancer Studies, University of Leicester Leicester UK [email protected] C ONSTANTINE A. S TRATAKIS Department of Pediatric Endocrinology NICHD, NIH Bethesda, MD USA [email protected] A LEX Y. S TRONGIN Burnham Institute for Medical Research La Jolla, CA USA [email protected] G ARNET S UCK Health Sciences Authority Centre for Transfusion Medicine Singapore [email protected] PAUL H. S UGARBAKER Washington Cancer Institute, Washington Hospital Center Washington, DC USA [email protected] M AXWELL S UMMERHAYES Roche Products Limited Welwyn Garden City UK [email protected]

B AOCUN S UN Department of Pathology Tianjin Cancer Hospital and Tianjin Cancer Institute Tianjin P.R of China [email protected] D UXIN S UN Division of Pharmaceutics, College of Pharmacy The Ohio State University Columbus, OH USA [email protected] S HI -Y ONG S UN Winship Cancer Institute Emory University Atlanta, GA USA [email protected] Z HIFU S UN Department of Health Sciences Research Mayo Clinic College of Medicine Rochester, MN USA [email protected] S AUL S USTER The Ohio State University Columbus, OH USA [email protected] S RILATHA S WAMI Division of Endocrinology Department of Medicine, Stanford University School of Medicine Stanford, CA USA [email protected] R USSELL S ZMULEWITZ Department of Medicine, Section of Hematology/Oncology The University of Chicago Chicago, IL USA [email protected] D AY TA Head and Neck Tumor Program Hollings Cancer Center Medical University of South Carolina Charleston, SC USA [email protected] D IRK TAEGER Berufsgenossenschaftliches Forschungsinstitut für Arbeitsmedizin (BGFA) Institute of Ruhr University Bochum Bochum Germany [email protected]

List of Contributors

M ASATOSHI TAGAWA Division of Pathology Chiba Cancer Center Research Institute Chiba, Chuo-ku Japan [email protected]

M ASAAKI TAMURA Department of Anatomy and Physiology Kansas State University Manhattan, KS USA [email protected]

Y OSHIKAZU TAKADA UC Davis School of Medicine Sacramento, CA USA [email protected]

TAKUJI TANAKA Deaprtment of Oncologic Pathology Kanazawa Medical University Kanazawa Japan [email protected]

A KIHISA TAKAHASHI Department of Biology Nara Medical University School of Medicine Kashihara, Nara Japan [email protected] T SUTOMU TAKAHASHI Laboratory of Molecular and Biochemical Toxicology Graduate School of Pharmaceutical Sciences Tohoku University Sendai Japan [email protected] Y OSHIMI TAKAI Osaka University Graduate School of Medicine/Faculty of Medicine Suita Japan [email protected] TAKASHI TAKATA Department of Oral and Maxillofacial Pathobiology, Division of Frontier Medical Science, Graduate School of Biomedical Sciences Hiroshima University Hiroshima Japan [email protected] TAMOTSU TAKEUCHI Department of Pathology Kochi Medical School Kochi Japan [email protected] C ONSTANTINE S. TAM The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected] H ARALD TAMMEN Digilab BioVisioN GmbH Hannover Germany [email protected]

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D AVID S. P. TAN Section of Medicine Institute of Cancer Research, The Royal Marsden Hospital London UK [email protected] D EAN G. TANG Department of Carcinogenesis, The University of Texas M.D Anderson Cancer Center Science Park-Research Division Smithville, TX USA [email protected] N IZAR M. TANNIR Department of Genitourinary Medical Oncology University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected] W EIKANG TAO Department of Cancer Research Merck Research Laboratories West Point, PA USA [email protected] C HI TARN Department of Medical Oncology Fox Chase Cancer Center Philadelphia, PA USA [email protected] C LIVE R. TAYLOR Departments of Urology and Pathology University of Southern California Keck School of Medicine Los Angeles, CA USA [email protected] J ENNIFER TAYLOR Committee on Cancer Biology The University of Chicago Chicago, IL USA [email protected]

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List of Contributors

A NDREW R. T EE Institute of Medical Genetics Cardiff University Heath Park, Cardiff UK [email protected] AYALEW T EFFERI Division of Hematology Mayo Clinic College of Medicine Rochester, MN USA [email protected] B IN T EAN T EH Laboratory of Cancer Genetics Van Andel Research Institute Grand Rapids, MI USA [email protected] V IGGO VAN T ENDELOO Laboratory of Experimental Hematology Antwerp University Hospital Edegem Belgium [email protected] J OSEPH R. T ESTA Fox Chase Cancer Center Philadelphia, PA USA [email protected] J OHN T HACKER Medical Research Council Radiation and Genome Stability Unit Harwell, Oxfordshire UK [email protected] R AJESH V. T HAKKER Academic Endocrine Unit, Nuffield Department of Clinical Medicine, University of Oxford, Oxford Centre for Diabetes Endocrinology and Metabolism (OCDEM), Churchill Hospital, Headington Oxford UK [email protected] N ICHOLAS B. L A T HANGUE Division of Biochemistry and Molecular Biology Davidson Building University of Glasgow Glasgow UK [email protected] D AN T HEODORESCU Department of Urology University of Virginia Charlottesville, VA USA [email protected]

PANAYIOTIS A. T HEODOROPOULOS Department of Basic Sciences The University of Crete, School of Medicine Heraklion, Crete Greece K ARL -H EINZ T HIERAUCH Therapeutic Research Group Oncology Bayer Schering Pharma AG Berlin Germany [email protected] M EGAN N. T HOBE University of Cincinnati College of Medicine Cincinnati, OH USA [email protected] G ARETH J. T HOMAS Institute of Cancer, Bart’s and the London School of Medicine and Dentistry Queen Mary University of London London UK [email protected] N ATALIE T HOMAS Department of Biochemistry and Molecular Biology Monash University Melbourne, VIC Australia [email protected] P ETER T HOMAS Departments of Surgery and Biomedical Sciences Creighton University Omaha, NE USA [email protected] S VEN T HOMS Department of Paediatrics and Paediatric Neurology University of Göttingen Göttingen Germany [email protected] A NDREW T HORBURN University of Colorado at Denver and Health Sciences Center Aurora, CO USA [email protected] M AGNUS T HÖRN Department of Surgery (MT) Karolinska Institutet Stockholm Sweden [email protected]

List of Contributors

D ERYA T ILKI Department of Urology University Hospital Groβhadern Munich Germany [email protected]

M ASSIMO T OMMASINO Infections and Cancer Biology Group International Agency for Research on Cancer Lyon France [email protected]

D ONALD J. T INDALL Department of Urology Research, Department of Biochemistry and Molecular Biology Mayo Clinic College of Medicine Rochester, Minnesota USA [email protected]

A NTONIO T ONINELLO Department of Biochemical Sciences “A. Rossi Fanelli” Sapienza University of Rome Rome Italy [email protected]

U MBERTO T IRELLI National Cancer Institute Aviano Italy [email protected] M ARTIN T OBI Section of Gastroenterology Detroit VAMC, Detroit MI USA [email protected] P EIKERT T OBIAS Division of Pulmonary and Critical Care Medicine Department of Internal Medicine Mayo Clinic College of Medicine Rochester USA [email protected] P HILIP J. T OFILON Department of Interdisciplinary Oncology, Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute University of South Florida Tampa, FL USA [email protected] H ENRIK T OFT S ØRENSEN Department of Clinical Epidemiology Aarhus University Hospital Aarhus C Denmark M ASAKAZU T OI Department of Surgery (Breast Surgery) Graduate School of Medicine, Kyoto University Bunkyo-ku, Kyoto Japan [email protected] A MANDA E WART T OLAND Division of Human Cancer Genetics The Ohio State University Columbus, OH USA [email protected]

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J EFFREY A. T ORETSKY Departments of Pediatric Hematology and Oncology Lombardi Comprehensive Cancer Center, Georgetown University Washington DC, NW USA [email protected] J ORGE R. T ORO National Institutes of Health Bethesda, MD USA [email protected] T IFFANY A. T RAINA Breast Cancer Medicine Service Department of Medicine Memorial Sloan-Kettering Cancer Center New York, NY USA [email protected] L UBA T RAKHTENBROT Head of Molecular Cytogenetics Laboratory Institute of Hematology, The Chaim Sheba Medical Center Tel Hashomer, Israel [email protected] P IERRE -L UC T REMBLAY Le Centre de recherche en cancérologie de l’Université Laval Québec, QC Canada [email protected] G REGORY J. T SAY Department of Medicine, Institute of Immunology Chung Shan Medical University Taichung Taiwan [email protected] A POSTOLIA -M ARIA T SIMBERIDOU Department of Investigational Cancer Therapeutics, Division of Cancer Medicine The University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected]

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List of Contributors

K UNIHIRO T SUCHIDA Division for Therapies against Intractable Diseases Institute for Comprehensive Medical Science (ICMS) Fujita Health University Toyoake Japan [email protected]

S PECKS U LRICH Division of Pulmonary and Critical Care Medicine Department of Internal Medicine Mayo Clinic College of Medicine Rochester USA [email protected]

N OBUO T SUCHIDA Department of Molecular Cellular Oncology and Microbiology Tokyo Medical and Dental University Bunkyo-ku Tokyo Japan [email protected]

N ICK U NDERHILL -D AY School of Biosciences University of Birmingham Birmingham UK [email protected]

M EHMET K EMAL T UR Department of Experimental Medicine and Immunotherapy Helmholtz Institute for Biomedical Engineering University Hospital RWTH Aachen Aachen Germany [email protected] G REG T URENCHALK Senior Bioinformatics Developer 454 Life Sciences Branford, CT USA [email protected] A NDREW S. T URNELL Cancer Research UK Institute for Cancer Studies The Medical School The University of Birmingham Birmingham UK [email protected] M ICHELLE C. T URNER McLaughlin Centre for Population Health Risk Assessment Institute of Population Health University of Ottawa Ottawa, ON Canada [email protected]

R OSEMARIE A. U NGARELLI Boston Medical Center and Boston University School of Medicine Boston, MA USA [email protected] A NTTI VAHERI Haartman Institute University of Helsinki Helsinki Finland [email protected] K EDAR S. VAIDYA Department of Pathology and Comprehensive Cancer Center University of Alabama at Birmingham Birmingham, AL USA [email protected] I LAN VAKNIN The Lautenberg Center for General and Tumor Immunology The Hebrew University-Hadassah Medical School Jerusalem Israel [email protected] A NNE M. VAN B USKIRK Department of Surgery The Ohio State University Colombus, OH USA [email protected]

T HOMAS T ÜTING Laboratory for Experimental Dermatology Department of Dermatology University of Bonn Bonn Germany [email protected]

M ICHAEL W. VAN D YKE Department of Molecular and Cellular Oncology The University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected]

S ALVATORE U LISSE Department of Experimental Medicine University of Rome-Sapienza Rome Italy [email protected]

C ARTER VAN WAES National Institute on Deafness and Other Communication Disorders and National Cancer Institute NIH Bethesda, MD USA [email protected]

List of Contributors

G EORGE F. VANDE W OUDE Van Andel Research Institute Grand Rapids, MI USA [email protected] W IM VANDEN B ERGHE Lab of Eukaryotic Gene Expression LEGEST-University Gent Gent Belgium [email protected] S AKARI VANHARANTA Department of Medical Genetics Biomedicum Helsinki University of Helsinki Helsinki Finland [email protected] R OBERTA VANNI Department of Biomedical Science & Technology University of Cagliari Monserrato (CA), Italy [email protected] J UDITH A. VARNER Moores UCSD Cancer Center University of California San Diego La Jolla, CA USA [email protected] A IKATERINI T. VASILAKI University Department of Surgery Royal Infirmary Glasgow UK [email protected] P ETER VAUPEL Institute of Physiology and Pathophysiology University of Mainz Mainz, Germany [email protected]

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M ARCEL V ERHEIJ Department of Radiotherapy The Netherlands Cancer Institute–Antoni van Leeuwenhoek Hospital Amsterdam The Netherlands [email protected] M UKESH V ERMA Analytical Epidemiology Research Branch, Epidemiology and Genetics Research Program, Division of Cancer Control and Population Sciences National Cancer Institute, Bethesda MD USA [email protected] R AKESH V ERMA Antisoma Research Laboratories, St. George’s Hospital Medical School London, UK [email protected] S RDAN V ERSTOVSEK MD Anderson Cancer Center University of Texas Houston, TX USA [email protected] R ENÉ P. H. V ETH Department of Orthopaedics Radboud University Medical Centre Nijmegen The Netherlands [email protected] GJ V ILLARES Department of Cancer Biology The University of Texas, M.D. Anderson Cancer Center Houston, TX USA A KILA N. V ISWANATHAN Brigham and Women’s/Dana-Farber Cancer Center Boston, MA USA [email protected]

G UILLERMO V ELASCO Department of Biochemistry and Molecular Biology I School of Biology Complutense University Madrid Spain [email protected]

K RIS V LEMINCKX Department of Molecular Biology Ghent University – VIB Ghent Belgium [email protected]

A SHOK R. V ENKITARAMAN Hutchison/MRC Cancer Research Centre Cambridge UK [email protected]

I SRAEL V LODAVSKY Department of Oncology Hadassah Hospital, Jerusalem Israel [email protected]

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List of Contributors

M ARTINA V OCKERODT Department of Pediatrics I, Children’s Hospital Georg-August University of Goettingen Goettingen Germany [email protected]

D ONGMEI WANG Georgetown University Lombardi Comprehensive Cancer Center Washington, DC USA [email protected]

C HARLES L. V OGEL Sylvester Cancer Center, School of Medicine University of Miami Plantation, FL USA [email protected]

G ANG WANG Department of Neurology and Neuroscience Weill Medical College of Cornell University New York, NY USA [email protected]

T ILMAN V OGEL Department of Surgery Krankenhaus Maria Hilf Mönchengladbach Germany [email protected]

J IANGHUA WANG Department of Pathology Baylor College of Medicine Houston, TX USA

U LLA V OGEL National Research Centre for the Working Environment København Ø Denmark [email protected] D ANIEL D. VON H OFF Arizona Cancer Center Tucson, AZ USA [email protected] A LIREZA V OSOUGH Department of Radiotherapy Royal Marsden Hospital NHS Foundation Trust Sutton, Surrey UK [email protected] C HRISTOPH WAGENER Institute of Clinical Chemistry University Medical Center Hamburg Eppendorf Hamburg Germany [email protected] S ABINE WAGNER Department of Pediatrics Klinik St. Hedwig, Krankenhaus der Barmherzigen Brüder Regensburg Germany [email protected] H ÅKAN WALLIN National Research Centre for the Working Environment København Ø Denmark [email protected] S USAN E. WALTZ Shriner’s Hospital for Children Cincinnati, OH USA [email protected]

R ONG -F U WANG Departments of Pathology and Immunology Center for Cell and Gene Therapy Baylor College of Medicine Houston, TX USA [email protected] X IANG -D ONG WANG Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University Boston, MA USA [email protected] X IANGHONG WANG Department of Anatomy The University of Hong Kong Hong Kong China [email protected] Y U WANG Department of Medicine and Genome Research Center University of Hong Kong Hong Kong, China [email protected] PATRICK WARNAT Department of Theoretical Bioinformatics German Cancer Research Center Heidelberg Germany [email protected] K OUNOSUKE WATABE Department of Medical Microbiology, Immunology and Cell Biology Southern Illinois University, School of Medicine Springfield, IL USA [email protected]

List of Contributors

VALERIE M. W EAVER Department of Surgery University of California San Francisco, CA USA [email protected] S COTT A. W EED Department of Neurobiology and Anatomy, Mary Babb Randolph Cancer Center West Virginia University Morgantown, WV USA [email protected] O LIVER W EIGERT Department of Internal Medicine III University of Munich, Großhadern München Germany [email protected] E UGENE D. W EINBERG Biology and Medical Sciences Indiana University Bloomington, IN USA [email protected] I. B ERNARD W EINSTEIN Columbia University New York, NY USA [email protected] E LLEN W EISBERG Department of Medical Oncology Dana Farber Cancer Institute Boston, MA USA [email protected] L AWRENCE M. W EISS Division of Pathology City of Hope National Medical Center Duarte, CA USA [email protected] D ANNY R. W ELCH Department of Pathology and Comprehensive Cancer Center University of Alabama at Birmingham Birmingham, AL USA [email protected] S ARAH J. W ELSH Harris Manchester College University of Oxford Oxford UK [email protected]

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TANIA M. W ELZEL Division of Cancer Epidemiology and Genetics National Cancer Institute National Institutes of Health Bethesda, MD USA [email protected] C LAUDIA W ENDEL Department of General Surgery University Hospital Münster Münster Germany [email protected] TAMRA E. W ERBOWETSKI -O GILVIE McMaster Stem Cell and Cancer Research Institute Hamilton, ON Canada [email protected] F RANK W ESTERMANN German Cancer Research Center Department of Tumour Genetics Heidelberg Germany [email protected] A INSLEY W ESTON National Institute for Occupational Safety and health, CDC Morgantown, WV USA [email protected] L INDA C. W HELAN UCD School of Biomolecular and Biomedical Science UCD Conway Institute University College Dublin Dublin Ireland [email protected] R OBERT P. W HITEHEAD Department on Medicine, Division of Hematology/Oncology University of Texas Medical Branch Galveston, TX USA [email protected] T HERESA L. W HITESIDE University of Pittsburgh Cancer Institute and University of Pittsburgh School of Medicine Pittsburgh, PA USA [email protected] A NDREAS W ICKI Department of Clinical-Biological Sciences, Centre of Biomedicine Institute of Biochemistry and Genetics, University of Basel Basel Switzerland [email protected]

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List of Contributors

C AROL W ICKING Institute for Molecular Bioscience The University of Queensland St Lucia, QLD Australia [email protected]

C HRISTIANE D E W OLF -P EETERS Department of Pathology University Hospitals of K.U. Leuven Leuven Belgium [email protected]

E DWIN VAN W IJNGAARDEN Department of Community and Preventive Medicine University of Rochester School of Medicine and Dentistry Rochester, NY USA [email protected]

C. M. W ONG Department of Pathology The University of Hong Kong Hong Kong [email protected]

E LIZABETH D. W ILLIAMS Cancer Metastasis Laboratory Monash Institute of Medical Research, Monash University Clayton, VIC Australia [email protected] J AMES P. W ILMOT Cancer Center University of Rochester Medical Center Rochester, NY USA O LA W INQVIST Department of Medicine (OW) Karolinska Institutet Stockholm Sweden [email protected] J OHN P IERCE W ISE Department of Applied Medical Sciences, Maine Center for Toxicology and Environmental Health University of Southern Maine Portland, ME USA [email protected] O LAF W ITT CCU Pediatric Oncology German Cancer Research Center Heidelberg Germany [email protected]

D ORI C. W OODS Walther Cancer Research Center University of Notre Dame Notre Dame, IN USA [email protected] PAUL W ORKMAN Cancer Research UK Centre for Cancer Therapeutics The Institute of Cancer Research Sutton, Surrey UK [email protected] T HOMAS W ORZFELD Institute of Pharmacology, University of Heidelberg Heidelberg Germany [email protected] X IFENG W U Department of Epidemiology The University of Texas MD Anderson Cancer Center Houston, TX USA [email protected] G UANG -H UI X IAO Fox Chase Cancer Center Philadelphia, PA USA [email protected]

I SAAC P. W ITZ Department of Cell Research and Immunology Tel Aviv University Tel Aviv, Israel [email protected]

J IANMING X U Department of Molecular and Cellular Biology Baylor College of Medicine Houston, TX USA [email protected]

I DO W OLF Institute of Oncology and the Cancer Research Center, Chaim Sheba Medical Center and the Sackler Faculty of Medicine Tel Aviv University Tel Aviv Israel [email protected]

T IAN X U Professor and Vice Chair of Genetics Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT USA [email protected]

List of Contributors

J UDY W. P. YAM Department of Pathology The University of Hong Kong Hong Kong [email protected]

H ELEN L. Y IN Department of Physiology University of Texas Southwestern Medical Center Dallas, TX USA [email protected]

S HO - ICHI YAMAGISHI Division of Cardiovascular Medicine, Department of Medicine Kurume University School of Medicine Kurume Japan [email protected]

X IAO -M ING Y IN Department of Pathology University of Pittsburgh School of Medicine Pittsburgh, PA USA [email protected]

M ICHIKO YAMAMOTO Department of Respiratory Medicine Kitasato University School of Medicine Sagamihara, Kanagawa Japan [email protected]

Z HIMIN Y IN College of Life Sicence Nanjing Normal University Nanjing People’s Republic of China [email protected]

H AINING YANG Cancer Research Center of Hawaii University of Hawaii Honolulu, HI USA

K ENNETH W. Y IP Burnham Institute for Medical Research La Jolla CA USA [email protected]

H ONG YANG Cancer Vaccine Branch, National Cancer Institute, National Institutes of Health Bethesda, MD USA [email protected]

H ARRY H. Y OON Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins Baltimore, MD USA [email protected]

P ING YANG Department of Health Sciences Research Mayo Clinic College of Medicine Rochester, MN USA [email protected]

J UNG -H WAN Y OON Department of Internal Medicine Seoul National University College of Medicine Chongno-gu Seoul South Korea [email protected]

M ASAKAZU YASHIRO Department of Surgical Oncology Osaka City University Graduate School of Medicine Osaka Japan [email protected]

K AZUHIRO Y OSHIDA Department of Surgical Oncology Gifu University School of Medicine Gifu Japan [email protected]

W. A NDREW Y EUDALL Philips Institute of Oral and Craniofacial Molecular Biology Virginia Commonwealth University Richmond, VA USA [email protected]

TATSUSHI Y OSHIDA Department of Molecular-Targeting Cancer Prevention Graduate School of Medical Science Kyoto Prefectural University of Medicine Kyoto Japan

M AKSYM V. Y EZHELYEV Winship Cancer Institute Emory University Atlanta, GA USA [email protected]

A NAS Y OUNES Department of Lymphoma and Myeloma M. D. Anderson Cancer Center Houston, TX USA [email protected]

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List of Contributors

G RAEME P. Y OUNG Flinders Cancer Control Alliance Flinders University Adelaide, SA Australia [email protected]

L AURA P. Z ANELLO Department of Biochemistry University of California-Riverside Riverside, CA USA [email protected]

X IAO Y UAN Research and Development Center, Wuhan Botanical Garden Chinese Academy of Science Wuhan, Hubei People’s Republic of China [email protected]

U WE Z ANGEMEISTER -W ITTKE Department of Pharmacology University of Bern Bern, Switzerland [email protected]

J IAN Y U Departments of Pathology and Pharmacology University of Pittsburgh Cancer Institute University of Pittsburgh School of Medicine Pittsburgh, PA USA [email protected]

YAN P ING Y U Department of Pathology University of Pittsburgh Pittsburgh, PA USA [email protected]

YU YU Department of Pathology University of Sydney NSW Australia [email protected]

A NTHONY P O -W ING Y UEN Division of Otorhinolaryngology Department of Surgery, The University of Hong Kong Hong Kong, SAR China [email protected]

L EO R. Z ACHARSKI VA Hospital White River Junction VT USA [email protected]

G ERARD P. Z AMBETTI Department of Biochemistry St. Jude Children’s Research Hospital Memphis, TN USA [email protected]

A NDREW C. W. Z ANNETTINO IMVS Main Laboratory Adelaide, SA Australia [email protected] B ERTON Z BAR Laboratory of Immunobiology NIH – Frederick Frederick, MD USA [email protected] H ERBERT J. Z EH III University of Pittsburgh, Departments of Surgery and Bioengineering, Pittsburgh, PA USA [email protected] J ASON A. Z ELL Cancer Prevention Program Division of Hematology/Oncology and Epidemiology Department of Medicine School of Medicine, Chao Family Comprehensive Cancer Center, University of California Irvine, CA USA [email protected] D ANFANG Z HANG Department of Pathology Tianjin Cancer Hospital and Tianjin Cancer Institute Tianjin P.R of China [email protected] H AO Z HANG The University of Texas M. D. Anderson Cancer Center Houston, TX USA [email protected] H ONG Z HANG Biogen Idec San Diego, CA USA [email protected]

List of Contributors

J I -H U Z HANG Lead Discovery Center Novartis Institute for Biomedical Research Cambridge, MA USA [email protected] J INPING Z HANG Departments of Pathology and Immunology, Center for Cell and Gene Therapy Baylor College of Medicine Houston, TX USA L IN Z HANG Biogen Idec San Diego, CA USA [email protected] L IN Z HANG Departments of Pathology and Pharmacology University of Pittsburgh Cancer Institute University of Pittsburgh School of Medicine Pittsburgh, PA USA [email protected] R UIWEN Z HANG University of Alabama at Birmingham Birmingham, AL USA [email protected]

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Y UESHENG Z HANG Roswell Park Cancer Institute Buffalo, NY USA [email protected] W EILING Z HAO Department of Radiation Oncology and Brain Tumor Center of Excellence Wake Forest University School of Medicine Winston-Salem, NC USA [email protected] G UANG -B IAO Z HOU State Key Laboratory for Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital School of Medicine Shanghai Jiao Tong University Shanghai, People's Republic of China [email protected] ZENG B. ZHU Departments of Medicine, Pathology, Surgery, Obstetrics and Gynecology and the Gene Therapy Center, Division of Human Gene Therapy University of Alabama at Birmingham Birmingham, AL USA [email protected] M. Z IGLER Department of Cancer Biology The University of Texas, M.D. Anderson Cancer Center Houston, TX USA

S HIWU Z HANG Department of Pathology Tianjin Cancer Hospital and Tianjin Cancer Institute Tianjin P.R of China [email protected]

M ARGOT Z OELLER DKFZ Heidelberg Germany [email protected]

X IN A. Z HANG Vascular Biology Center, Cancer Institute, and Departments of Medicine and Molecular Sciences University of Tennessee Health Science Center Memphis, TN USA [email protected]

M ASSIMO Z OLLO Department of Genetics Faculty of Biotechnological Science Federico II, Naples CEINGE, Biotecnologie Avanzate Naples Italy [email protected]

X UEFENG Z HANG Beth Israel Deaconess Medical Center and Harvard Medical School Boston, MA USA [email protected]

E NRIQUE Z UDAIRE NCI Angiogenesis Core Facility, National Cancer Institute National Institutes of Health Advanced Technology Center Gaithersburg, MD USA [email protected]

Y U -W EN Z HANG Laboratory of Molecular Oncology Van Andel Research Institute Grand Rapids, MI USA [email protected]

C ARSTEN Z WICK Klinik für Innere Medizin I Universität des Saarlandes Homburg Germany [email protected]

A

2ar ▶Osteopontin

AAA+ Definition Superfamily of proteins characterized by a segment of ~220 aminoacids (the AAA domain) containing several conserved motifs including those necessary for ATP binding and hydrolysis.

17-1A

▶APAF-1 Signaling

▶EpCAM

AAMP M ARIE E. B ECKNER

A Disintegrin and Metalloprotease ▶ADAM Molecules

A-Scan Ultrasonography Definition Ophthalmologic ultrasound that provides singledimension information on the ultrasonic echogenicity of the ocular tissues providing information regarding axial length, size of intraocular structures (such as tumor height), and homogeneity of individual tissues within the eye. ▶Uveal Melanoma

Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA

Definition AAMP stands for angio-associated migratory cell protein and its gene is found on chromosome 2q35. ▶HUGO nomenclature symbol is AAMP. AAMP has been conserved in evolution, is distributed intracellularly in many cells and also extracellularly on vascular cells, shares an ▶epitope with motility-related proteins (▶alpha-actinin and a fast twitch skeletal muscle protein) and contains potential heparin binding and thrombin cleavage sites. Antibody and antisense studies have indicated compartment (intracellular or extracellular) specific roles for AAMP in angiogenesis, cell-cell and cell-matrix interactions, and cell migration.

Characteristics The cDNA derived from mRNA encoding AAMP was originally cloned from a human melanoma cell library (A2058) in a search for migration-related proteins. AAMP has been found in the cytoplasm of many

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nucleated cells, in an extracellular mesh-like network on monolayers of endothelial and vascular-associated smooth muscle cells, and on the apical membranes of endometrial glandular cells. AAMP expression when normalized for tissue source has shown the highest levels of distribution in the esophagus (7.17% of tissue clones) (http://smd.stanford.edu/cgi-bin/source/sourceImage? File = Hs.83347). Local homologies discovered initially to human immunodeficiency viral proteins led to identification of two immunoglobulin-like ▶domains in AAMP. In addition to melanoma, expression of AAMP has been observed in a variety of malignant cells, including poorly differentiated colon adenocarcinoma within lymphatics, gastric adenocarcinoma, Jurkat lymphoma, gastrointestinal stromal tumors with mutated ▶c-kit, breast cancer cell lines and ductal adenocarcinoma in situ with necrosis, and brain tumor cells. Co-culture of astrocytes with endothelial cells (without physical contact) led to increased amounts of extracellular AAMP associated with the endothelial cells. Stimulation of T lymphocytes and monocytes by a ▶phorbol ester led to greatly increased AAMP expression, 1.6 kb message and 52 kDa protein. Hypoxia increased expression of the AAMP gene in a breast carcinoma cell line. AAMP has demonstrated compartment-specific effects on endothelial cell migration. Affinity-purified antibodies, that interacted with the extracellular form of AAMP on non-permeabilized endothelial cells, inhibited cell migration and endothelial tube formation. However, anti-sense oligonucleotides, that decreased total AAMP expression, paradoxically increased cell migration, presumably via loss of intracellular AAMP. The structure of AAMP was initially characterized as having two immunoglobulin-like domains and six ▶WD repeats. Now eight WD repeats have been identified in AAMP, UniProt KB/Swiss-Prot Q13685. AAMP has been conserved in evolution. Comparisons of reference sequences for human AAMP (433 aa) with related forms in mouse (434 aa), rat (471 aa), chicken (419 aa), frog (438 aa), and zebrafish (408 aa) have shown 99.5, 98.9, 86.7, 76.5, and 69.0% identity, respectively (UniGene, NCBI, NIH). An acid box (short contiguous run of glutamic or aspartic acid residues) has been identified in the amino terminal regions of several AAMP homologs. They are comprised of seven glutamic acids in human, eight glutamic acids in mouse and rat, and six aspartic acid residues in the zebrafish forms of AAMP. AAMP contains a strongly immunoreactive ESESES epitope at its ▶amino terminal end that has been used to generate an anti-peptide antibody. Under normal reducing conditions, the epitope is immunoreactive for AAMP only in lysates of human brain and activated T lymphocytes. AAMP (52 kDa) shares this epitope with non-skeletal alpha-actinin (100 kDa) and an

unidentified fast twitch skeletal muscle fiber protein (23 kDa), as demonstrated with anti-RRLRRMESESES (anti-P189) and related anti-peptide antibodies. The ESESES epitope is linear in AAMP but is discontinuous or conformational (formed by ▶secondary structure) in alpha-actinin. The fast twitch skeletal muscle fiber protein with immunoreactivity for anti-P189 was found in the periodic bands (Z discs). An alternatively spliced, slightly longer form of AAMP (452 aa) includes coding sequence upstream from MESESES. The immediate upstream sequence, RRLRR, potentially functions as a heparin binding site. In addition to an alternative initiating methionine, the upstream human coding sequence differs by only two of seventeen codons when compared to an even longer form of AAMP in rat. The coding sequence of AAMP in rat includes the sequence GRFRRMESESES that corresponds to RRLRRMESESES in the alternative form of human AAMP. In peptide studies, the bipolar RRLRRMESESES sequence was strongly self-aggregating, sensitive to thrombin digestion, and displayed binding to heparin and cells as either an immobilized, single peptide or as an aggregated peptide, without affecting cell viability or adhesion to collagen. Peptide sequencing verified the presence of RLRR in recombinant AAMP translated in Escherichia coli following thrombin digestion that cleaved the first R. Although anti-P189 (RRLRRMESESES) did not demonstrate reactivity with the RRLRR epitope in tissue that displayed reactivity with ESESES, the lack of reactivity for RRLRR could have been due to interference by strongly adherent ▶glycosaminoglycans. Thus initial studies of AAMP’s distribution and structure are supportive of a role for this protein in cell migration and angiogenesis.

References 1. Beckner ME, Krutzsch HC, Stracke ML et al. (1995) Identification of a new immunoglobulin superfamily protein expressed in blood vessels with a heparin-binding consensus sequence. Cancer Res 55:2140–2149 2. Allander SV, Nupponen NN, Ringner M et al. (2001) Gastrointestinal stromal tumors with KIT mutations exhibit a remarkably homogeneous gene expression profile. Cancer Res 61:8624–8628 3. Adeyinka A, Emberley E, Niu Y et al. (2002) Analysis of gene expression in ductal carcinoma in situ of the breast. Clin Cancer Res 8:3788–3795 4. Beckner ME, Jagannathan S, Peterson VA (2002) Extracellular angio-associated migratory cell protein plays a positive role in angiogenesis and is regulated by astrocytes in coculture. Microvasc Res 63:259–269 5. Beckner ME, Krutzsch HC, Klipstein S et al. (1996) AAMP, a newly identified protein, shares a common epitope with alpha-actinin and a fast skeletal muscle fiber protein. Exp Cell Res 225:306–314

AAV

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AAPC ▶APC Gene in Familial Adenomatous Polyposis

AAV D IRK G RIMM University of Heidelberg, Cluster of Excellence Cell Networks, BIOQUANT, Heidelberg

Definition Adeno-associated viruses (AAV) are small DNAcontaining viruses that belong to the family of Parvoviridae. Thus far, 11 ▶serotypes of adeno-associated viruses (AAV-1 to AAV-11) have been cloned from humans and primates, and multiple further isolates were identified in various other species, including birds, bovines, mice, rats and goats. According to current knowledge, none of these naturally occurring viruses are pathogenic in humans. AAV type 2 (AAV-2) has been studied for over 40 years and is the best characterized AAV isolate, hence its frequent referral as the AAV prototype. All AAV serotypes are currently being developed and evaluated as gene transfer ▶vectors for the human ▶gene therapy of various inherited or acquired diseases, including different types of cancer.

Characteristics

As typical members of the ▶Parvovirus family, AAV are characterized by non-enveloped, icosahedral capsids of about 18–24 nm in diameter. These capsids carry linear single-stranded DNA genomes of ~4.6–4.8 kb. The genomes of all known AAV serotypes have been cloned and sequenced. With the exception of AAV-4 and -5, which are distinct (>30%) from the other serotypes at both the nucleotide and amino acid level, all human and primate AAV genomes are related and highly homologous (>80%). Accordingly, their genomic structure and organization are also very similar. AAV Genome Structure As an example, the organization of the 4,681 nucleotide AAV-2 prototype genome is described (Fig. 1). The AAV-2 genome consists of two large ▶open reading frames (orf), one at the left end encoding the nonstructural proteins (replication, rep orf), and one at the right end encoding the structural proteins (capsid, cap orf). In addition, a single intron sequence is found in the

AAV. Figure 1 Structure of the AAV-2 genome. The 4,681 nucleotide single-stranded genome is depicted as a solid line; by convention, AAV genomes are drawn in 3′-5′ orientation. Shown are the locations of the rep and cap orfs and the single intron (caret), as well as the position of the three promoters (p5, p19, p40) and the polyA signal, which is used for polyadenylation of all AAV-2 transcripts. Further depicted at the ends of the genome are the palindromic inverted terminal repeat (ITR) sequences in their hairpin configuration.

center of the genome, where the rep and cap orfs overlap. The AAV-2 rep gene encodes four closely related proteins (Rep proteins) with partially shared amino acid sequences. On the basis of their molecular weights, these proteins were designated Rep78, Rep68, Rep52 and Rep40. Unspliced and spliced transcripts originating from a ▶promoter located at map unit 5 (p5) are translated into the two large Rep proteins, Rep78 and Rep68. Rep52 and Rep40 are expressed from similarly spliced mRNAs that initiate from a second promoter, p19. The third AAV-2 promoter, p40, controls transcription of the cap gene. Translation of differentially spliced cap mRNAs results in expression of the three proteins that form the AAV-2 capsid, VP1, VP2 and VP3 (in a 1:1:10 ratio). The two viral genes are flanked by short (AAV-2: 145 nucleotides) inverted terminal repeats (ITR), palindromic sequences that are able to fold into T-shaped stem loop structures. The ITRs are necessary and sufficient for replication and encapsidation of the viral genome during a productive infection of cells. Moreover, they are important for integration and rescue of the AAV DNA into, or from, the genome of latently infected cells, respectively. Thereby, the ITRs serve as minimal cis-acting sequences during the two different AAV life cycles (see also below). AAV Life Cycles AAV serotypes belong to the Parvovirus genus Dependovirus, indicative of their dependence on an unrelated helpervirus to undergo a productive infection of cells. In fact, AAV genomes can only express their genes, replicate and become encapsidated if the cell is simultaneously co-infected by one of these helperviruses. The typical helpervirus for AAV-2 is human ▶Adenovirus type 2 or 5, but many other human viruses can also provide full or partial helper functions, including Herpes simplex virus, Vaccinia virus and Cytomegalovirus.

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In the case of Adenovirus, one of the major helper functions is to stimulate AAV gene expression, by trans-activating the AAV-2 promoters. Additional help for the AAV life cycle is mediated at the posttranscriptional level, where adenoviral proteins and RNAs help to facilitate the cytoplasmic transport of AAV-2 mRNAs. Concurrently, adenoviral functions help to stabilize replicated AAV-2 genomic DNA later in the AAV infection. Notably, once expressed in the infected cell, AAV-2 Rep proteins subsequently further regulate and coordinate gene expression from the AAV promoters. They also play important roles for AAV DNA replication, as well as for packaging of viral genomes into empty new capsids (assembled from AAV-2 VP proteins). To mediate these diverse functions, Rep proteins bind to the AAV-2 ITRs and to sequences located in the AAV-2 promoters. They also interact with various cellular proteins, e.g. the TATAbox binding protein ▶(TBP), as well as with each other and the AAV-2 VP proteins. The final step in a productive AAV-2 infection is the helpervirus-mediated lysis of the infected cell. This results in cell death and release of both new AAV-2 and helpervirus particles. In contrast to this productive (or lytic) phase, AAV2 can establish latency in the absence of any helpervirus. Rather than replicating, the AAV-2 DNA then integrates into the target cell genome, where it stably persists as a so-called provirus. Important to point out, wildtype AAV-2 integration is not random, as is the case for retroviruses (▶Retroviral Insertional Mutagenesis) and other integrating viruses. Instead, it is targeted to a specific region on the long arm of human chromosome 19 (19q13.3-ter). The large Rep proteins (albeit only weakly expressed in the absence of a helpervirus) mediate this site-specific integration through binding to the AAV-2 ITRs, as well as to homologous sequences (AAVS1) located in chromosome 19. However, if a latently AAV-infected cell is later super-infected with a helpervirus, AAV-2 gene expression is induced and the AAV-2 genome is rescued from its integrated state. From this point on, a typical productive AAV-2 infection will occur. Thus, the helpervirus can act as an efficient switch between the two different phases that characterize the AAV-2 life cycle, lytic and latent. Clinical Relevance In theory, due to its inherent anti-tumor properties (see below), wildtype AAV-2 (and probably other serotypes alike) could be used as a therapeutic agent for the treatment of human cancers. However, more widely studied and applied are ▶recombinant vectors derived from wildtype AAVs. Typically, these vectors are generated by replacing the two viral genes (rep and cap) with a foreign ▶gene expression cassette, encoding RNAs or proteins that mediate an anti-tumor effect (if used for cancer therapy). The general clinical relevance of

wildtype and recombinant AAVs is briefly discussed below; for more depth, the reader is referred to recent excellent reviews on the use of AAV for the treatment of human disease (see References below). Are Wildtype AAVs Pathogenic in Humans? According to the bulk data available, wildtype AAV serotypes are believed to be non-pathogenic in humans. In fact, despite estimates that up to 80% of adults are ▶seropositive for AAV-2, no human disease has ever been causally linked to infection with the wildtype virus. This is even more remarkable considering that AAV-2 can infect a large variety of cells from diverse organs and tissues. Yet, although without gross pathological consequences for the cell, a latent AAV-2 infection can induce subtle changes in the cell ▶phenotype. Examples are an increased ability to respond to stress factors, or a perturbation of the cell cycle, resulting in retarded cell growth. Most probably, these various effects are mediated by the large AAV-2 Rep proteins, even at the low expression levels typical for the latent stage. Is There a Natural Connection Between AAV Infection and Cancer? One frequently reported observation is that AAV-2infected cells exhibit an increased resistance to ▶oncogene- or tumorvirus-induced transformation. It is moreover known that AAV-2 infection can inhibit the proliferation of cultured cells derived from human cancers, e.g. ▶melanomas. Cumulatively, these data strongly suggest that wildtype AAV-2 is not only nonpathogenic, but in fact has oncosuppressive properties. Moreover, certain human cancer cell lines become more sensitive to gamma irradiation (▶Ionizing Radiation Therapy) and chemotherapeutic drugs (▶Chemotherapy of Cancer, Progress and Perspectives) upon experimental infection with wildtype AAV-2, as compared to noninfected controls. From a clinical point of view, these findings are of particular interest, since a major limitation of cancer chemotherapies is increasing resistance of transformed cells towards the drugs used. The observations of AAV-2-mediated cell sensitization therefore suggest that wildtype AAV might help to improve cancer chemotherapy, when applied in combination with conventional drugs. What are Recombinant AAV Vectors? Recombinant AAV (rAAV) vectors are derivatives of wildtype AAV which lack the rep and cap genes, and instead carry a foreign gene expression cassette inserted between the two viral ITRs. By definition, AAV vectors are thus “gutless” or “gutted” (i.e., devoid of any viral genes). The generation of rAAV vectors is technically feasible and simple, due to the wide availability of molecular clones of the various wildtype viruses. These clones are easily modified using standard molecular

AAV

laboratory techniques. Particularly beneficial is that wildtype and recombinant AAV are very small as compared to all other viruses developed as vectors, which aids in their experimental manipulation. Except for the replacement of the wildtype genes with a recombinant DNA, AAV vectors are identical in structure and organization to wildtype viruses and thus also function alike. In fact, AAV vectors will infect the target cell via the same molecular and cellular pathways as the wildtype virus. Ultimately, this will lead to expression of the encapsidated recombinant gene in the cell and thus to the intended therapeutic effect. As gene transfer vehicles, AAV vectors hold enormous promise for therapeutic intervention for a multitude of human acquired or innate genetic diseases, including cancer. Is AAV Unique as a Human Gene Therapy Vector? AAV vectors possess a multitude of advantages over all other virus-derived gene transfer vectors currently in (pre-)clinical development. One asset already mentioned is the lack of pathogenicity of the wildtype virus, which is in stark contrast e.g. to Adenovirus, another commonly used virus for gene therapy. Consequently, the production and handling of AAV vectors requires the lowest biosafety levels (S1, i.e., causing minimal risks for humans and the environment). The safety of AAV vectors is further increased by their “gutted” nature, precluding the expression of viral gene products which could cause cellular immune responses in the treated patient (a frequent adverse reaction to adenoviral vectors). A third unique asset, and a further difference to other viral vectors, is the availability of a wide spectrum of human, mammalian and nonmammalian natural serotypes. These isolates typically differ in their ▶tropism, i.e., the range of cells and tissues they can infect. Fortunately, it is technically very simple to generate recombinant AAV vectors which carry the same expression cassette, but differ in the viral capsid. This process is called “pseudotyping” and allows for the targeted delivery of a given recombinant DNA to virtually any desired cell or tissue, provided it can be infected by a known wildtype AAV (or a mutant thereof, see below). A plethora of reports have already demonstrated the power of this approach, to use AAV vectors for therapeutic and specific gene transfer to all clinically relevant target organs, including liver, muscle, lung, eye and brain. Last but not least, AAV vectors also differ from all other viral vectors by their capability to mediate persistent and long-term gene expression, both in actively dividing and in quiescent (i.e., non-dividing) cells, and most importantly, without integrating into the host chromosome. Instead, the vector forms stable but extra-chromosomal DNA molecules, which are not capable of perturbing chromosome structures and thus do not pose a mutational risk. This is clinically most pertinent, as many gene therapy

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applications will require stable gene expression, ideally for the life-span of the patient. The only other viral vectors able to mediate long-term gene expression (and in non-dividing cells) are derived from retroviruses or lentiviruses (HIV). However, these vectors are associated with drastically higher concerns about biosafety, due to the inherent pathogenic nature of the parental wildtype virus, as well as due to their propensity for integration into the human genome. The latter can readily result in insertional mutagenesis, i.e., activation of endogenous oncogenes, or vice versa, inactivation of ▶tumor suppressor genes. In both cases, the result is malignant transformation of the infected cell. This potentially serious adverse event from the use of retroviral vectors has indeed been observed in a recent clinical study, where multiple children developed leukemias, and some even died. Likewise, adenoviral vectors and the associated immune response have been blamed for the death of a patient in an early gene therapy trial in 1999. In striking contrast, thus far, none of the over 30 clinical trials using AAV vectors has yielded any evidence for a tumorigenic or lethal potential of this particular vector system. What are Recent Advances in AAV Vector Technology? In the early years, AAV vectors have been criticized for their small size (preventing packaging and therapeutic transfer of recombinant DNA >5kb in length), their relatively slow transduction kinetics (resulting from the single-stranded DNA genome and its need for conversion into a transcriptionally active DNA duplex), and their restricted cell and tissue tropism (based on the sole availability of the AAV-2 capsid in the early phase of AAV vector development). Nonetheless, even with those presumed limitations, AAV-2 vectors have been tested successfully in various large animal models and in human patients, addressing diverse diseases such as cystic fibrosis or hemophilia B. Most importantly, all three initial limitations of the AAV vector system have now been overcome, leading to the rapid expansion of AAV-based human gene therapy, especially for cancer treatment. First of all, the issue of limited packaging capacity has been solved with the creation of “split” AAV vectors which exploit the virus’ natural propensity for ▶concatamerization. In an infected cell, rAAV genomes frequently recombine with each other, resulting in large “head-to-tail” concatamers (i.e., multiple copies of an rAAV genome in the same orientation). This can be exploited experimentally, by splitting a large recombinant DNA (e.g., a gene and its promoter) into two halves, each of which is then delivered by a separate rAAV vector. This strategy effectively doubles the packaging limit of AAV vectors to up to 10 kb, which is sufficient even for large DNAs such as the factor VIII gene (encoding a blood clotting factor missing or defect in hemophilia A patients). Secondly, the inherently slow transduction kinetics of AAV

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have been overcome with the development of selfcomplementary or double-stranded vectors. In these, two copies of a foreign gene expression cassette are cloned and packaged in an inverted format, only separated by a minimal version of an AAV ITR. In the transduced cell, these two inverted copies then rapidly anneal with each other without the need for conversion into a duplex AAV DNA molecule. This results in an extremely rapid onset as well as maximum efficacy of gene expression, both far superior to what is obtained with conventional single-stranded AAV vectors, or most other viral vector systems. Thirdly, the limited host range of AAV-2 was readily overcome with the engineering of the over 100 alternative naturally occurring AAV serotypes as vectors. This approach has not only substantially broadened the range of cells and tissues that can now be infected with AAV vectors, but it has also alleviated concerns over the prevalence of neutralizing antibodies against the AAV-2 prototype in the human population. In fact, a wealth of studies have shown that AAV vectors derived from non-type2 serotypes are functional in many tissues that are refractory to AAV-2 infection, and most importantly, transduction readily occurred in the (experimentally induced) presence of anti-AAV-2 antibodies, mimicking the situation in most humans. Moreover, very recent work demonstrated the feasibility to create synthetic AAV capsids which are further unique from the AAV2 prototype, as well as from any of the naturally occurring isolates. Multiple strategies are currently being pursued, including the random mutagenesis of the AAV(-2) cap gene, the insertion of peptide pools into exposed regions of the AAV-2 capsid (hoping the peptides will mediate re-targeting to unknown cellular receptors), or the creation of libraries of “shuffled” viruses, in which capsid genes from several parental viruses are mixed and recombined. Most importantly, all of these new approaches and designs remain fully compatible with already established AAV vector technology, allowing for their rapid and straightforward pre-clinical evaluation. In fact, current AAV vector production methodologies are highly advanced and permit the generation of high titer stocks (>1 × 1014 recombinant particles per batch) in a very short amount of time (~10 days) (Fig. 2). As a result, AAV vectors have entered clinical evaluation and are currently being studied in about 30 ongoing trials in human patients. What are Clinically Relevant rAAV Applications in Cancer Treatment? The sum of assets described above – safety, versatility, efficacy, specificity – makes AAV an ideal vector for multiple and diverse therapeutic applications in humans. With particular respect to cancer, the use of AAV vectors is still in its infancy, but increasing preclinical data suggest that this vector system holds

AAV. Figure 2 Streamlined protocol for rAAV production. Cultured cells are transfected with two plasmids: The vector plasmid containing the foreign gene to be packaged into the viral particles, flanked by the AAV-2 ITRs, and the helper plasmid carrying the AAV-2 rep and cap genes to supply the Rep and VP proteins, respectively. In addition, the helper contains all adenoviral (Ad) genes which encode proteins with supportive function for AAV vector production, but it does not yield Adenovirus after transfection. Helpervirus infection is thus superfluous, and the resulting AAV-2 vectors are free of contaminating Adenovirus. Following a 2-day incubation of the transfected cells, the rAAV particles are harvested, purified and quantified. Note that there are numerous modifications to this basic protocol, e.g., in the number of plasmids (1–3, depending on the arrangement of AAV and adenoviral sequences).

enormous potential also for this specific application. Thus far, the approaches can be divided into strategies that either target the tumor cell directly or that modify host mechanisms. In more detail, AAV vectors have been employed in the following major categories: Antiangiogenesis, ▶immunotherapy, tumor suppressors, suicide gene therapy, drug resistance, repair strategies, and, last but not least, purging of tumor cells. For many of those categories, a currently emerging therapeutic modality which is also still in its infancy is RNA interference or RNAi (▶RNA interference and Cancer). This term describes the natural phenomenon of gene silencing mediated by short double-stranded RNAs.

AAV

The latter can be expressed from AAV vectors and thus be used to effectively and specifically suppress, for instance, expression of cellular or virally-encoded oncogenes. RNAi will likely become a valuable and crucial aspect of AAV-based cancer therapy in the near future, and will complement or perhaps even replace many of the currently existing strategies. Anti-Angiogenesis The efficacy of ▶angiogenesis inhibitors to undermine tumor ▶neovascularization and to block cancer progression as well as formation of metastases (▶metastasis) has been established in many animal models. However, this cancer therapy requires that the inhibitors are chronically administered as recombinant proteins, which is usually associated with severe problems. Therefore, AAV vectors with their unique ability to mediate sustained gene expression should prove particularly useful for this type of tumor therapy. Especially promising will be the future combination with synthetic AAV capsids that have been evolved to target the vasculature. Thus far, mostly AAV-2-based vectors have been used to deliver and express various antiangiogenesis factors in small animals, typically mice. A first important example is angiostatin, which has been expressed from AAV-2 in multiple mouse models of human cancers, including gliomas (▶Glioblastoma Multiforme) and liver cancers (▶Liver Cancer, Molecular Biology]. In all reported cases, this led to suppression of in vivo tumor growth and to substantial improvements in tumor-free survival rates. Similarly impressive are results with the related anti-angiogenic peptide ▶endostatin, whose expression from AAV2 vectors inhibited the establishment or growth of various human cancers in mice, including liver, ovarian (▶Ovarian Cancer), pancreatic (▶Pancreas Cancer, Clinical Oncology) and colorectal (▶Colon Cancer) tumors. Even better results have been obtained with the co-expression of both angiostatin and endostatin from a single or from two separate AAV vectors, exemplifying the potential for synergistic effects from combinatorial AAV therapies. Other examples for antiangiogenic AAV therapies already evaluated include the expression of a truncated form of the ▶vascular endothelial growth factor receptor (renal tumors), or of tissue inhibitors of ▶matrix metalloproteases. Immunotherapy Failure of the immune system to recognize cancer antigens can substantially contribute to tumor manifestation and progression. Although tumors can illicit strong immune responses in the early stages, this effect is frequently lost in later phases, eventually allowing for aggressive and metastatic tumor growth. Gene transfer protocols involving AAV (or other viral) vectors have thus been developed which aim to potentiate the patient’s

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antitumor responses, by either targeting the tumor cells directly, or by transducing host-derived immune effector cells. Examples for already reported tumor celldirected therapies include AAV-mediated delivery of ▶interferon genes to ex vivo cultured cancer cells, or via intra-tumoral injection (gliomas). Likewise, AAV2 has been used to express tumor necrosis factor-related ▶apoptosis-inducing ligand (▶TRAIL) in colorectal, lung and liver tumor models, resulting in significantly inhibited tumor growth and, in some cases, even in regression. Targeting cells of the host immune system, on the other hand, is a promising alternative approach and could eventually be developed into a vaccination therapy. Already, AAV-2 vectors have been used to deliver dominant tumor epitopes to antigen-presenting cells, such as CD40 ligand which was expressed in B-cells from ▶chronic lymphocytic leukemia (CLL) patients, leading to specific proliferation of ▶HLA Class I-matched allogeneic T-cells. Another potential vaccine could be AAV vectors expressing an HPV16 (▶Human Papillomaviruses) E7 CTL (cytotoxic T-cell) epitope/heat shock fusion protein, based on reports that infected mice became immunized against E7expressing tumor cells. Last but not least, encouraging studies have identified ▶dendritic cells (DC), the most potent antigen-presenting cells, as an attractive target for AAV-based cancer immunotherapies. For instance, DCs transduced with AAV vectors encoding HPV16 E6 or E7 genes caused a stark CTL response against cervical cancer cell lines, while in another study, DCs transduced with CD80-expressing AAVs induced high levels of CD8+ T-cells. Together, these findings suggest that AAV can be used to trigger strong anti-tumor CTL responses, and that AAV-based immunotherapy has substantial clinical potential for cancer treatment. Tumor Suppressors Highly attractive targets for AAV-mediated cancer therapy are oncogenes and tumor suppressor genes, respectively, whose expression is frequently dysregulated in malignant human cancers. An important example for a tumor suppressor involved in cellular checkpoint control is p53 (▶p53 Protein, Biological and Clinical Aspects), which normally prevents passage of cells with DNA damage through the cell cycle. Consequently, expression of p53 from AAV vectors was consistently found to block the growth of cancer cells in vitro and in vivo, and to mediate apoptosis and cytotoxicity. Similar results were obtained after expression of the fragile histidine triad tumor suppressor (▶FHIT), which delayed the growth of human pancreatic tumor ▶xenografts and extended longterm animal survival. In a third example, delivery of the gene encoding the monocyte chemoattractant protein MCP-1 from AAV vectors suppressed expression of the HPV E6 and E7 proteins in cervical cancer cell lines, as well as in tumors derived from these cells.

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Suicide Gene Therapy This approach is based on the idea to bio-activate a prodrug within tumor cells to a toxic species, triggered by the tumor-directed delivery of the activating enzyme from AAV vectors. The best studied example for this category is the Herpes simplex virus-encoded enzyme thymidine kinase (tk) in combination with gancyclovir. This system has already been used successfully from AAV vectors to inhibit tumor growth in a variety of human xenograft models, including liver cancer, gliomas and ▶oral squamous carcinomas. Notably, the specificity of this approach can be enhanced by the use of tissueand/or tumor-specific promoters, such as those only active in liver or melanoma cells. Moreover, the overall efficacy of the AAV/tk vectors was shown to increase following treatment of transduced cells with irradiation or topoisomerase inhibitors, both known to enhance AAV infection (in addition to their direct effects on cells). Drug Resistance Development of multiple drug resistance (MDR) is a major issue with cancer chemotherapies and is often associated with over-expression of the ▶P-glycoprotein (an ATPase that pumps chemotherapeutic drugs out of the cancer cell). One recently reported, highly effective approach to reverse the MDR phenotype is to use double-stranded AAV vectors to express anti-Pglycoprotein short hairpin RNAs (effectors of RNAi). In human ▶breast cancer and oral cancer cells, this led to a substantial sensitization to chemotherapy, suggesting a high potential to overcome the MDR obstacle with this approach. Another application is expression of the MDR1 gene from AAV vectors in ▶hematopoietic progenitors. This should confer myeloprotection in patients undergoing high-dose chemotherapy for advanced tumors, and thus prevent myelosuppresssive effects (▶Myelosuppression) from the chemotherapeutic regimen, such as infection or hemorrhaging. However, this strategy has not been fully explored in animal models yet. Repair Strategies ▶Telomerase (the enzyme maintaining and stabilizing the integrity of telomeres, i.e., chromosome ends) is an example for a therapeutically relevant target for repair strategies. Its activity is often elevated in tumor cells, and it was shown that delivery of telomerase antisense molecules [Antisense DNA Therapy] via AAV vectors (in this particular case hybrids with adenoviral vectors) can reduce tumor cell proliferation, as well as induce apoptosis. Purging of Tumor Cells from Autologous Transplants Autologous grafts (▶Graft Acceptance and Rejection), e.g. peripheral blood progenitor cells, are used for treatment of many solid human cancers. However, they can be contaminated with tumor cells that give rise to

relapse after ▶myeloablative megatherapy and graft transplantation. There is recent evidence that following infection of such contaminated grafts with recombinant AAV-2, the contaminating tumor cells are preferentially infected, while the hematopoietic progenitors are spared. Indeed, infection of sarcoma cells with AAV/tk vectors (see above) extended the survival of transplanted mice (over non-treated controls), while the same vector was unable to transduce and kill human peripheral blood progenitors. However, it remains to be proven that this strategy can indeed be applied to selectively purge tumor cells from autologous transplants. RNAi RNA-mediated silencing of gene expression (RNAi) will clearly become a major part of anti-tumor therapies in the future, as proof-of-concept for the efficacy of this approach is already overwhelming. In combination with AAV, there have only been a few reports thus far, but this field will certainly expand. One described application is to use AAV vectors to deliver short hairpin RNAs against the hec1 gene, which is highly expressed in mitotic cells where it represents a vital component of the ▶kinetochore outer plate. Transduction of glioma cells with anti-hec1 AAV vectors resulted in selective cell death, while mitotically inactive control cells were unaffected. Likewise, infected xenografts showed lower densities and were highly fibrotic, as a result of AAV treatment. It can generally be predicted that virtually any over-expressed gene that contributes to transformation can be an AAV/RNAi target, including virally-encoded (see above, e.g., HPV E6/7) or cellular oncogenes. Future Applications With the current state-of-the-art technology, the AAV vector system is already one of the most powerful and promising toolkits for development as anti-tumor bioreagents. In the future, the versatility of this system will further increase with the discovery and creation of new natural or synthetic capsids, respectively. Likewise, the field will benefit from the engineering of novel tumor- and tissue-specific gene expression cassettes, and from the design of safer and more effective therapeutic sequences, e.g., for the induction of anti-cancer RNAi. A very important approach will be to merge the different strategies into combinatorial therapies, e.g., by mixing immunotherapies with RNAi vectors, or suicide gene expression with repair approaches. Examples for such multimodality cancer therapies with AAV vectors have already been reported, and their numbers will increase in the future. Last but not least, it will also be crucial to combine AAV (or other viral) vectors with further anti-cancer effectors, such as new classes of compounds including proteasome (▶Proteasomal Inhibitors) and histone deacetylase (▶Histone Deacetylases) inhibitors.

ABC Transporter Proteins

References 1. Grimm D (2002) Production methods for gene transfer vectors based on adeno-associated virus serotypes. Methods 28:146–157 2. Grimm D, Kay MA (2004) From virus evolution to vector revolution: use of naturally occurring serotypes of adenoassociated virus (AAV) as novel vectors for human gene therapy. Curr Gene Ther 3:281–304 3. Grimm D, Pandey K, Kay MA (2005) Adeno-associated virus vectors for short hairpin RNA expression. Methods Enzymol 392:381–405 4. Li C, Bowles DE, van Dyke T et al. (2005) Adenoassociated virus vectors: Potential applications for cancer gene therapy. Cancer Gene Ther 12:913–925 5. Warrington KH, Herzog RW (2006) Treatment of human disease by adeno-associated viral gene transfer. Hum Genet 119:571–603

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▶Fluoxetine ▶Glutathione Conjugate Transporter RLIP76 ▶Major Vault Protein ▶Vault Complex

ABC (ATP-Binding Cassette) Superfamily Definition ABC (ATP-binding cassette) superfamily contains both uptake and efflux transport systems. These proteins bind ATP and hydrolyze it to energize transport of molecules outside or inside the cells.

ABC Drug-Transporters Definition Synonym ABC Transporter, ABC (ATP-Binding Cassette) Superfamily. The adenosine-triphosphate (ATP) binding cassette (ABC) transporters form the largest family of transmembrane proteins that use ATP-derived energy to transport various substances over cell membranes. Primary-active transporters, driven by energy released from ATP by inherent ATPase activity, that export substrates from the cell against a chemical gradient, Based on the arrangement of the nucleotide binding domain and the topology of its transmembrane domains, human ABC-transporters are classified into seven distinct families (ABC-A to ABC-G), including ABCB1 (P-glycoprotein), ABCC1 (MRP1), ABCC2 (cMOAT; MRP2), ABCC4 (MRP4), and ABCG2 (ABCP; MXR; BCRP). Structural characteristics based on their ▶Walker motif (ATP binding domain) and their nucleotide-binding folds across the membrane are responsible for their classification into this superfamily. Their localization pattern over the body suggests that they have an important role in the prevention of absorption as well as the excretion of potentially toxic metabolites and xenobiotics, both on a systemic and a cellular level. ABC drug-transporters (may) show substrate-overlap. Examples of mammalian ABC transporters include ▶P-glycoprotein, MRP (▶multidrug resistance protein), ▶cystic fibrosis transmembrane conductance regulator (CFTR) and the transporter associated with antigen processing (TAP). ▶P-glycoprotein ▶Irinotecan

ABC Transporter Definition ABC transporters are a superfamily of prokaryotic and eukaryotic proteins. They are usually involved in membrane transport and share a homologous nucleotidebinding domain, ABC (ATP-binding cassette). In addition to the ABC domain, ABC transporters contain or interact with hydrophobic domains containing multiple transmembrane segments. Examples of mammalian ABC transporters include P-glycoprotein, MRP (multidrugresistance protein), cystic fibrosis transmembrane conductance regulator (CFTR) and the transporter associated with antigen processing (TAP).

ABC Transporter Proteins Definition ABC transporter proteins are a superfamily of proteins responsible for transporting a broad range compounds across membranes in cells. Structural characteristics based on their Walker domains (ATP binding domain) and their nucleotide-binding folds across the membrane are responsible for their classification into this superfamily.

A

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ABC-Transporters

ABC-Transporters H ERMANN L AGE Charité Campus Mitte, Institute of Pathology, Berlin, Germany

Synonyms Multidrug resistance transporters; Traffic ATPases; Permeases (for import systems)

Definition ABC (ATP-binding cassette)-transporters are membraneembedded proteins with a characteristic ABC domain that utilize the energy from ATP hydrolysis for the transport of their substrates across a cellular membrane.

Characteristics The superfamily of ABC-transporters comprises one of the most abundant protein families in nature. These transporters are believed to date back in evolutionary time more than 3 billion years and are distributed in all three kingdoms of living organisms, archaea, eubacteria, and eukaryotes. ABC-transporters have to be distinguished from ABC-proteins. Both types of proteins are defined by the presence of a highly conserved ~215 amino acids consensus sequence designated as ABC domain or nucleotide-binding domain (NBD). The domain contains two short peptide motifs, a glycine-rich Walker A and a hydrophobic Walker B motif, both involved in ATP binding and commonly present in all nucleotide-binding proteins. A third consensus sequence is named ABC signature and is unique in ABC domains. ABC-containing proteins couple the phosphate bond energy of ATP hydrolysis to many cellular processes and are not necessarily restricted to transport functions. However, the proper meaning of the term ABC-transporter is satisfied when the ABC-protein is in addition associated with a hydrophobic, integral transmembrane domain (TMD) forming a translocation path. TMDs are usually composed of at least six transmembrane (TM) α-helices. They are believed to determine the specificity for the substrate molecules transported by the ABCtransporter. The minimal structural requirement for a biological active ABC-transporter seems to be two TMDs and two NBDs [TMD-NBD]2 (Fig. 1). In fullsize transporters, this structural arrangement may be formed by a single polypeptide chain and in multiprotein complexes by more than one polypeptide chain. In prokaryota, ABC transport systems are often halfsize transporters having only one TMD fused to one NBD [TMD-NBD]. Half-size transporters probably dimerize to form a full-size transporter [TMD-NBD]2 to mediate mainly the influx of essential compounds such

ABC-Transporters. Figure 1 Schematic representation of the predicted domain arrangement of (a) half-size transporters having only one TMD fused to one NBD [TMD-NBD], e.g., ABCG2 (BCRP); and (b,c) full-size transporters [TMD-NBD]2, whereby (b) shows the predicted structure of ABCB1 (MDR1), and (c) the structure of ABCC1 (MRP1) containing an additional TMD (TMD0) of unknown function. Half-size transporters probably dimerize to form a biological active ABC-transporter. These three ABC-transporters are the most important drug extrusion pumps in multidrug-resistant cancers. TMD, transmembrane domain consisting of six α-helices; NBT, nucleotidebinding domain. It should be noted that the orientation of ABCG2 is reverse to that of ABCB1 and ABCC1.

as sugars, vitamins, and metal ions into the cell. Eukaryotic ABC-transporters commonly function as exporters mediating the efflux of compounds from the cytosol to the extracellular space or to the inside of intracellular membrane-bound compartments, i.e., endoplasmic reticulum, mitochondria, peroxisomes, or vacuoles. The range of physiologically transported compounds includes lipids and sterols, ions, diverse small molecules, oligo- and polypeptides. Human ABC-Transporters In humans, 48 ABC-transporters distributed to seven subfamilies have been identified (Table 1). Although the number of human ABC-transporters is much smaller than found in bacteria, many of them are of clinical significance. Currently, 18 human genes encoding ABC-transporters have been associated with genetic diseases. Even though the majority of the members of the human ABC-transporter family are active transporters, there are some exceptions in which the energy of ATP hydrolysis is utilized to control alternative biological processes. Thus, ABCC7 (CFTR), well known as mutated in patients suffering on ▶cystic

ABC-Transporters ABC-Transporters. Table 1

Family of human ABC-transporters

Subfamilay

HUGO-nomenclature

Common names

ABCA

ABCA1 ABCA2 ABCA3 ABCA4 ABCA5 ABCA6 ABCA7 ABCA8 ABCA9 ABCA10 ABCA12 ABCA13 ABCB1 ABCB2 ABCB3 ABCB4 ABCB5 ABCB6 ABCB7 ABCB8 ABCB9 ABCB10 ABCB11 ABCC1 ABCC2 ABCC3 ABCC4 ABCC5 ABCC6 ABCC7 ABCC8 ABCC9 ABCC10 ABCC11 ABCC12 ABCD1 ABCD2 ABCD3 ABCD4 ABCE1 ABCF1 ABCF2 ABCF3 ABCG1 ABCG2 ABCG4 ABCG5

ABC1 ABC2 ABC3, ABCC ABCR

ABCB

ABCC

ABCD

ABCE ABCF

ABCG

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ABCX

MDR1, PGY1 TAP1 TAP2 MDR3, PGY3 MTABC3 ABC7 MABC1 TABL MTABC2 BSEP, SPGP MRP1, MRP MRP2, cMOAT MRP3 MRP4 MRP5 MRP6 CFTR SUR1 SUR2 MRP7 MRP8 MRP9 ALD, ALDP ALDL1, ALDR PXMP1, PMP70 PXMP1L, P70R RNASELI, OABP ABC50

ABC8, White BCRP, MXR White2 White3

Location 9q31.1 9q34 16p13.3 1p22.1-p21 17q24.3 17q24.3 19p13.3 17q24 17q24.2 17q24 2q34 7p12.3 7q21.1 6p21.3 6p21.3 7q21.1 7p15.3 2q36 Xq12-q13 7q36 12q24 1q42 2q24 16p13.1 10q24 17q22 13q32 3q27 16p13.1 7q31.2 11p15.1 12p12.1 6p21.1 16q12.1 16q12.1 Xq28 12q11-q12 1p22-p21 14q24.3 4q31 6p21.33 7q36 3q27.1 21q22.3 4q22 11q23.3 2p21

A Size [AA]

Function

2261 2436 1704 2273 1642 1617 2146 1581 1624 1543 2595 5058 1280 808 653 1279

Cholesterol-, PS transport

842 752 718 723/766 738 1321 1531 1545 1527 1325 1437 1503 1480 1581 1549 1464 1382 1359 745 740 659 606 402 807 623 709 638 655 627 651

Iron transport Iron-, Sulfur- cluster transport

Surfactant production N-retinylidene-PE transport

MDR Peptide transport Peptide transport PC transport

Bile salt transporter MDR, organic anion transporter MDR, organic anion transporter Organic anion transporter Organic anion transporter Organic anion transporter Chloride transport Regulation Regulation

FA-, FA AcylCoA transport FA-, FA AcylCoA transport FA-, FA AcylCoA transport FA-, FA AcylCoA transport

Cholesterol transport MDR Sterol transport

AA, amino acids; FA, fatty acids; MDR, multidrug resistance; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PS, phosphatidylserine.

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ABC Transporters (ATP-Binding Cassette Transporters)

fibrosis, appears as a chloride ion channel; ABCC8 (SUR1) and ABCC9 (SUR2) are both regulatory subunits of the regulatory sulfonylurea receptor (SUR). Other members of the ABC-transporter family couple ATP binding and hydrolysis to the control of translation or ▶DNA repair. Although the active transporters have dedicated functions involving the transport of specific substrates, the complex physiological network of ABC-transporters may also have an important role in host detoxification and protection against xenobiotics. This general function is revealed by their tissue distribution. ABC-transporters are highly expressed in important pharmacological barriers, such as the epithelium that contributes to the blood–brain barrier (BBB), the brush border membrane of intestinal cells, the biliary canalicular membrane of hepatocytes, or the lumenal membrane in proximal tubules of the kidney. Anyway, this xenobiotics pump function is the basis for the pivotal role of ABC-transporters in ▶multidrug resistance (MDR) of cancer. ABC-Transporters and Multidrug Resistance of Cancer MDR is defined as the simultaneous resistance of a tumor against a variety of antineoplastic agents with different chemical structure and mode of action. Thus, MDR is a major obstacle in clinical management of cancer by ▶chemotherapy. Although various mechanisms have been identified to mediate a multidrugresistant phenotype to malignant diseases, the enhanced drug extrusion activity of the ABC-transporter ABCB1 or ▶P-glycoprotein (MDR1; PGY1) was the first mechanism that was demonstrated to be the reason for MDR. The substrates of ABCB1 include first and foremost natural product-derived anticancer drugs, such as ▶anthracyclines, ▶epipodophyllotoxins, ▶taxans, and ▶vinca alkaloids, but not clinically important drugs like platinum-containing compounds or ▶antimetabolites. Besides ABCB1, in particular, ABCC1 (MRP1) and ABCG2 (BCRP) were found to be associated with a multidrug-resistant phenotype, but also alternative ABCtransporters can pump drugs from the inside to the outside of a cancer cell, e.g., ABCC2 (MRP2) is a platinum drug transporter. ABCB1, ABCC1, and ABCG2 have partial overlapping but not identical substrates. ABC-Transporters as Anticancer Drug Targets Following the identification of ABCB1 as a pivotal MDR-mediating factor, tremendous efforts were undertaken to identify ABCB1-interacting agents that inhibit its pump activity and, therewith, reverse the MDR phenotype. Such drugs are commonly designated as chemosensitizers or MDR modulators. Although many compounds, e.g., ▶verapamil and ▶ciclosporin derivatives, were identified as ABCB1 inhibitors or inhibitors of alternative MDR-mediating ABCtransporters, so far all of them failed in clinical trials.

References 1. Gottesman MM, Fojo T, Bates SE (2002) Multidrug resistance in cancer: role of ATP-dependent transporters. Nat Rev Cancer:2:48–58 2. Higgins CF (1993) ABC transporters: from microorganisms to man. Annu Rev Cell Biol 8: 7–113 3. Holland IB, Cole SPC, Kuchler K, Higgins CF (eds) (2003) ABC proteins from bacteria to man. Academic Press, an imprint of Elsevier Science, London (UK) and San Diego (CA, USA) 4. Lage H (2003) ABC-transporters: implications on drug resistance from microorganisms to human cancers. Int J Antimicrob Agents 22:188–199

ABC Transporters (ATP-Binding Cassette Transporters) Definition Primary-active transporters, driven by energy released from ATP by inherent ATPase activity, that export substrates from the cell against a chemical gradient, including P-gp, MRP, and BCRP.

ABL Definition The ABL gene encodes a nuclear tyrosine kinase that is involved in chromosomal translocations in chronic myeloid leukemia (CML). ▶BCR-ABL1 ▶Chromosomal Translocations

Ablation Definition In cancer therapy, the surgical removal or destruction of tumor tissue. ▶Photothermal Ablation

ABVD

ABLES Definition Adult Blood Lead Epidemiology and Surveillance. ▶Lead Exposure

ABVD A NAS YOUNES Department of Lymphoma and Myeloma, M.D. Anderson Cancer Center, Houston, TX, USA

Definition Doxorubicin, bleomycin, vinblastine, and dacarbazine combination chemotherapy used for the treatment of patients with Hodgkin lymphoma.

Characteristics ABVD (doxorubicin, bleomycin, vinblastine, and dacarbazine) is the most widely used regimen for the treatment of early and advanced stage Hodgkin lymphoma (HL). Treatment of patients with early stage classical HL evolved over the last three decades. Radiation therapy alone as the single treatment modality is no longer practiced. Today, the most widely used approach is combined modality therapy (chemotherapy plus involved field radiation therapy). In general, 2 (for favorable early stage) to 4 (for unfavorable early stage) cycles of ABVD plus 30 Gy of involved field radiation therapy is the most widely used standard of care approach. Using this approach, more than 90% of the patients are expected to be cured of their disease. Patients with bulky stage II disease, (especially with bulky mediastinal mass), or stage II with B-symptoms are usually treated similar to those with advanced stage HL with 6–8 cycles of ABVD followed by involved field radiation therapy to the bulky area. Use of chemotherapy alone has recently been proposed for a selected group of patients with early stage classical HL. The rationale for this approach is to reduce radiation-induced morbidity and mortality, including second malignancies and cardiac complications. While this approach is appealing, it will need to be further examined after prolonged follow-up. For now, it seems appropriate to treat young female patients with non-bulky early stage classical HL (especially those with mediastinal or axillary adenopathy) with chemotherapy alone to reduce the risk for breast cancer. The risks and

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benefits of combined modality versus chemotherapy alone should be discussed with patients before making a final treatment recommendation. Based on several randomized studies comparing ABVD with other multi-drug regimens, ABVD became the most widely used combination regimen for the treatment of patients with advanced HL. Chemotherapy alone (6–8 cycles) is usually considered sufficient for treating patients with advanced stage classical HL. However, involved field radiation therapy is frequently added at the end of chemotherapy to areas of bulky disease. This combined modality approach has been recently compared with chemotherapy (MOPP/ABV) alone in a randomized trial in patients with advanced stage classical HL, and showed no survival advantage, especially in those who achieved complete remission after the completion of chemotherapy. Furthermore, meta-analysis review of fourteen clinical trials comparing chemotherapy with combined modality also showed no survival advantage for those receiving the combined modality approach. Newer treatment programs such as Stanford V and BEACOPP have shown successful results, but remain less widely used compared with ABVD. Although BEACOPP has been shown to be superior to ABVDlike regimens in large-scale randomized trials, the superiority of Stanford V over standard ABVD has not yet been established. Because ABVD may cure only 50–65% of patients with poor risk advanced stage HL, more intensive programs such as BEACOPP may add benefit, despite the increased toxicity. Patients with good risk features have a high cure rate with ABVD, so the use of more intensive and more toxic regimens in this patient population should be used with caution, and preferably within a clinical trial. In fact, a recently published randomized study demonstrated that early intensification with autologous stem cell transplantation after four cycles of ABVD-like chemotherapy did not improve the outcome in patients with advanced stage HL compared with conventional chemotherapy, perhaps because many patients did not have poor risk features as identified by the international prognostic score for HL.

References 1. Bonadonna G, Bonfante V, Viviani S et al. (2004) ABVD plus subtotal nodal versus involved-field radiotherapy in early-stage Hodgkin’s disease: long-term results. J Clin Oncol 22:2835–2841 2. Meyer RM, Gospodarowicz MK, Connors JM et al. (2005) Randomized comparison of ABVD chemotherapy with a strategy that includes radiation therapy in patients with limited-stage Hodgkin’s lymphoma: National Cancer Institute of Canada Clinical Trials Group and the Eastern Cooperative Oncology Group. J Clin Oncol 23:4634–4642 3. Straus DJ, Portlock CS, Qin J et al. (2004) Results of a prospective randomized clinical trial of doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD) followed by radiation therapy (RT) versus ABVD alone for

A

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Accelerated Phase

stages I, II, and IIIA nonbulky Hodgkin disease. Blood 104:3483–3489 4. Canellos GP (1996) Is ABVD the standard regimen for Hodgkin’s disease based on randomized CALGB comparison of MOPP, ABVD and MOPP alternating with ABVD? Leukemia 10(Suppl 2):s68 5. Diehl V, Thomas RK, Re D (2004) Part II: Hodgkin’s lymphoma – diagnosis and treatment. Lancet Oncol 5:19–26

Acetaldehydehydrogenase Definition

The enzyme which oxidizes ▶acetaldehyde. ▶Alcohol Consumption

Accelerated Phase Definition

Occurs between chronic phase and ▶blast crisis. Characterized by 10–19% myeloblasts and >20% basophils in blood or bone marrow and cytogenetic evolution; also increasing splenomegaly, platelet count, or white blood cells if unresponsive to treatment. ▶Nilotinib

Acetylation Definition The reversible, covalent attachment of an acetyl group to the lysine residue of proteins. Acetylation and deacetylation of histones play an important role in transcriptional regulation ▶Histone Deacetylases

ACD Definition

N-Acetylcysteine

Abbreviation for Appraisal Consultation Document. ▶National Institute for Health and Clinical Excellence (NICE)

ACDC ▶Adiponectin

Acetaldehyde Definition Highly reactive chemical compound (CH3CHO) that forms following ethanol metabolism. Toxic, mutagenic and carcinogenic. ▶Alcohol Consumption ▶Hepatic Ethanol Metabolism

Definition A pharmacological agent used mainly as a mucolytic and in the management of ▶paracetamol overdose and is available in different dosage forms for different indications: solution for inhalation – inhaled for mucolytic therapy or ingested for nephroprotective effect; i.v. injection – treatment of paracetamol overdose; or oral solution – various indications. ▶Chemoprotectants

Acetylsalicylic Acid Definition ASA/aspirin; one of the most successful drugs in combating reactive species overload diseases, and the ▶chemoprevention of cancers such as ▶colon cancer. ▶Inflammation

Acinar Cells

Acetyltransferase

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inhibits tumor growth by binding the ▶nucleolin protein on the surface of cancer cells.

Definition An enzymic activity that catalyzes the transfer of an acetyl moiety from acetyl CoA to a specific amino acid on a substrate protein. CBP and p300 are lysine (K)directed acetyltransferases. ▶CBP/p300 Coactivators

Achneiform Rash Definition Is a pustular rash with usual distribution over the face, scalp, and upper trunk. ▶Erlotinib (Tarceva®)

N-Acetyltransferase Definition Is an acetyl-CoA requiring enzyme that catalyses the acetylation of ▶xenobiotics that are aromatic amines or contain a hydrazine group. It participates in the ▶detoxification of a plethora of hydrazine arylamine drugs and is also able to bioactivate several known carcinogens. (Vatsis KP, Weber WW, Bell DA et al (1995) Nomenclature for N-Acetyltransferases. Pharmacogenetics 5:1–17) ▶Detoxification

ACF

Acid Rain Definition Is formed by absorption of acidic gases as SO2 or NOx by water droplets in clouds Precipitation then increases the acidity of the soil, and affects the chemical balance of surface water bodies. ▶Xenobiotics

Acidosis

Definition

Definition

Aberrant crypt foci; Putative precursors of colon cancer ▶Preneoplastic lesions.

Is present in a tissue whenever the pH is below 7.0 (or the H+-concentration is higher than 10–7 mol/L).

▶Trefoil Factors ▶Colon Cancer ▶Conjugated Linolenic Acids

▶Oxygenation of Tumors

Acinar Cells Acharan Sulfate (AS) Definition Definition Is isolated from the giant African snail Achatina fulica, responsible for inhibitory effect of tumor growth. AS

Key cell in the exocrine pancreas. These are arranged around a central lumen and form the bulk of the pancreatic gland. They contain digestive enzymes usually found in the apical region of the cells.

A

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Acites

Acites G ERHILD B ECKER Department of Internal Medicine II (Gastroenterology, Hepatology, Endocrinology), University Hospital Freiburg, Freiburg, Germany

Definition

Ascites is derived from the Greek word ασκóς (gr. sack, wineskin) and is defined as accumulation of protein rich fluid in the peritoneal cavity. It occurs mainly in ▶cirrhosis of the liver, but also in heart failure, tuberculosis and malignancy. Malignant ascites occurs in association with a variety of neoplasms and is defined as the abnormal accumulation of fluid in the peritoneal cavity caused by cancer.

Characteristic Malignant ascites accounts for around 10% of all cases of ascites and occurs in association with a variety of neoplasms. Malignant effusion is the escape of fluid from the blood or vessels into tissues or cavities, and is a common problem in patients with cancer. All types of cancer can metastasize to any of the body’s serous cavities and result in malignant effusion. In the Western World the most common cause of malignant ascites is ▶ovarian cancer. Other common primary sites are the pancreas, stomach and uterus, with breast, lung, and lymphoma representing the commonest extra-abdominal sites. Up to 20% of all patients with malignant ascites have cancer of unknown primary origin (▶CUP). Except in breast and ovarian cancer, the presence of malignant ascites in patients with neoplastic disease frequently signalizes the terminal phase of cancer. The mean survival time for ovarian cancer is 30–35 weeks and for tumors of lymphatic origin 58–78 weeks, whereas for cancers of the gastrointestinal tract the mean survival is only 12–20 weeks. In patients with CUP the median survival shows a great variability ranging from 1 week to 3 months in different series. Pathophysiology Fluid accumulation in the peritoneal cavity is dependent on the amount of fluid generated and the rate at which it leaves the abdominal cavity. When fluid production exceeds its clearance, free transudate will accumulate. Under physiologic conditions, transudation of plasma through capillary membranes of the peritoneal serosa continuously produces free fluid to lubricate the serosal surfaces. This fluid production is under the influence of portal pressure, plasma oncotic pressure, sodium and water retention, hepatic lymph production, and

microvascular permeability for macromolecules. Under physiologic conditions, at least two-thirds of the peritoneal fluid reabsorbs into open-ended lymphatic channels of the diaphragm and is propelled cephalad by the negative intrathoracic pressure. This fluid proceeds through mediastinal lymph channels into the right thoracic duct and empties into the right subclavian vein. The ability of the healthy subject to resorb fluid is much greater than the fluid generated, with the result that there is normally only a small volume of approx. 50 mL of fluid in the peritoneal cavity. Ascites as an abnormal accumulation of fluid in the peritonal cavity can be induced by several causes. In principle, four types of causes can be identified. (i) Ascites due to raised hydrostatic pressure, caused by cirrhosis, congestive heart failure, inferior vena caval obstruction, or hepatic vein occlusion. (ii) Ascites due to decreased osmotic pressure, caused by protein depletion (e.g. nephrotic syndrome), reduced protein intake (malnutrition) or reduced protein production (cirrhosis of the liver). (iii) Ascites due to fluid production exceeding resorptive capacity, caused by infections or malignancies. (iv) Chylous ascites, caused by obstruction and leakage of the lymph channels draining the gut. The pathophysiology of malignant ascites is multifactorial and is yet incompletely understood. Ascites may result from obstruction of lymphatic drainage by tumor cells that prevent absorption of intraperitoneal fluid and protein as often seen in lymphomas and breast cancer. Since the ascites of many patients with malignant ascites has a high protein content, alteration in vascular permeability has been implicated in the pathogenesis of ascites production. The tumor induces increasing production of peritoneal fluid due to increased microvascular permeability of tumor vasculature and the amount of ascites production correlates with the extent of neovascularization. Aside from mechanical obstruction and cytokines, the pathophysiology of malignant ascites also consists of hormonal mechanisms. Due to decreased removal of fluid as a consequence of obstructed lymphatics, the circulating blood volume is reduced and this activates the reninangiotensin-aldosterone system, leading to sodium retention. Therefore, reduced sodium intake together with diuretics is often used to treat malignant ascites, but there is no consensus on effectiveness. Available trials considering diuretics often include different patients groups with varying dose regimens and there are no randomized controlled trials to asses the efficacy of diuretics in malignant ascites. Diagnosis In most cases, ascites can be diagnosed by careful physical examination and taking a detailed history. The main clinical symptoms of ascites include abdominal

Acites

distension, ankle edema, continuous abdominal discomfort or pain, nausea, vomiting, shortness of breath and decreased mobility. Greater quantities of ascites cause abdominal distension, bulging flanks that are dull to percussion, shifting dullness and a fluid wave. Ultrasound is able to detect free peritoneal fluid if its volume is greater than 100 mL. CT and MRI are also able to detect little quantities of ascites. Malignant diagnosis is indistinguishable by physical examination from ascites caused by non-malignant conditions. Ascites detected by ultrasound, CT or MRI in the presence of typical imaging features of a malignant tumor is strongly suggestive of a malignant ascites. Diagnosis is confirmed by positive cytology of malignant cells in the fluid. A positive cytology result has a specificity of nearly 100%, but it is not very sensitive with only about 60% of malignant aspirates being cytologically positive. Compared to ascites caused by cirrhosis, malignant ascites usually contains more white blood cells and a higher level of lactate dehydrogenase. Fibronectin, cholesterol, lactate dehydrogenase, sialic acid, proteases, and antiproteases have been studied with fibronectin performing best in differentiating between malignant and non-malignant acites in most series. However, at present there is no single test available to be used routinely to differentiate between malignant and non-malignant ascites. Tumor markers, especially ▶CEA and CA-125 can be useful in diagnosing the primary tumor in malignant ascites, although they lack specificity. In case of doubt abdominal ▶paracentesis with chemical and cytologic analysis of the ascitic fluid should be used. The cell count provides immediate information about possible bacterial infection. Samples with a predominance of a least 250 neutrophils per cubic millimeter of ascitic fluid are suggestive of infection. Gram stains and culture for bacterial, fungal, and acid fast organisms are mandatory. ▶Spontaneous bacterial peritonitis is characterized by the spontaneous infection of ascitic fluid in the absence of an intra-abdominal source of infection and involves the translocation of bacteria from the intestinal lumen to the lymph nodes, with subsequent bacteremia and infection of ascitic fluid. Third-generation cephalosporins are the treatment of choice. Ascitic fluid amylase content helps to detect pancreatic ascites and gut perforation. 80% of all cases of ascites are caused by cirrhosis of the liver. The chief factor contributing to ascites in liver cirrhosis is ▶portal hypertension. Patients with ascites caused by liver disease usually have a ▶serum-ascites albumin concentration gradient (calculated by subtracking the albumin concentration of the ascitic fluid from the albumin concentration of a serum specimen obtained on the same day) ≥1.1 g/dL. If serum albumin: ascites albumin gradient is less than 1.1g/dL, portal hypertension can be safely ruled out.

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Treatment In general, practice of managing malignant ascites seems to be influenced by the evidence obtained in the context of non-malignant ascites, especially ascites caused by liver disease. Malignant ascites only accounts for approximately 10% of all cases of ascites whereas over 80% of cases are caused by chronic liver disease. So, most evidence in treatment of ascites is obtained in the context of liver disease. In ascites caused by liver cirrhosis the most important treatments are the restriction of dietary sodium intake and the use of oral diuretics because patients with liver cirrhosis retain sodium and water as a result of the renin-angiotensinaldosterone pathway. In ascites due to liver disease there is good evidence for the efficacy of a combined therapy with the diuretics spironolactone and furosemide supported by several randomized controlled trials. Treatment options for the minority of patients who are resistant to standard therapy with diuretics are therapeutic paracentesis, ▶peritoneovenous shunting, ▶transjugular intrahepatic portosystemic shunt (TIPS), extracorporal ultrafiltration of ascetic fluid with reinfusion and liver transplantation. Of these, ▶transjugular portosystemic stent shunts, extracorporal ultrafiltration and liver transplantation are specific to liver diseases, whereas abdominal paracentesis and peritoneovenous shunting are often used in managing malignant ascites. In contrast to the treatment of underlying cancer, there is no generally accepted gold standard for the management of malignant ascites so far. There are two principle approaches in managing malignant ascites. The first attempts to treat the cancer as the underlying cause of the ascites. The main treatments are systemic or intraperitoneal chemotherapies, biological therapies like intraperitoneal α or β ▶interferon, tumor necrosis factor TNF or administration of infectious agents in non pathogenic form like corynebacterium parvum or OK-432, a penicillinand heat-treated powder of Su-strain streptococcus pyogenes A3 in peritoneal cavity. Octreotide, a somatostatin analogue known to decrease the secretion of fluid by the intestinal mucosa and to increase water and electrolyte reabsorption, was used successfully in some case reports of malignant ascites. Novel therapies are radiolabeled monoclonal antibodies and radiocolloids. In tumors associated with increased activity of ▶vascular endothelial growth factor (VEGF) like ovarian, gastric, colon, pancreatic carcinomas and omental or hepatic metastatic malignancies, a new concept is to reduce the production of ascites by the inhibition of neovascularization. This is achieved via inhibition of vascular endothelial growth factor (VEGF) or inhibition of ▶matrix metalloproteinases, which are a family of enzymes present within the normal healthy individuals, but produced in high

A

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Aclarubicin

concentrations by a variety of tumors. However, these concepts are comparatively new and are based on experimental results or only partially investigated in Phase I trials and have not yet been evaluated in randomized controlled trials. The second approach in managing malignant ascites is palliative and relies upon reducing the volume of fluid through a variety of approaches like paracentesis, diuretics, or peritoneovenous shunts. Paracentesis is indicated for those patients who have symptoms of increasing intra-abdominal pressure. Available data show good, although temporary relief of symptoms in most patients. Symptoms seem to be significantly relieved by drainage of up to 5 L of fluid. When removing up to 5 L, intravenous fluids seem to be not routinely required. If the patient is hypotensive, dehydrated or known to have severe renal impairment and paracentesis is still indicated, intravenous hydration should be considered. The only investigated therapy in malignant ascites is infusion of dextrose 5%. There is no evidence of concurrent albumin infusions in patients with malignant ascites. To avoid repeated paracenteses, a peritoneovenous shunting may be considered. Major complications like pulmonary edema, pulmonary emboli, infection or clinically relevant disseminated intravascular coagulation have to be expected in about 6% of patients. There are no randomized trials assessing the efficacy of diuretic therapy. The available data are controversial and there are no clear predictors to identify which patients would benefit. Therefore, the use of diuretics should be considered in all patients with malignant ascites, but has to be evaluated individually. Patients with malignant ascites due to massive hepatic metastasis seem to respond more likely to diuretics than patients with malignant ascites caused by peritoneal carcinomatosis or chylous ascites. Choice of diuretics is also not sufficiently evaluated. As available data suggest that the efficacy of diuretics in malignant ascites depends on plasma renin/aldosterone concentration, aldosterone antagonists like spironolactone should be used, either alone or in combination with a loop diuretic.

References 1. Becker G, Galandi D, Blum HE (2006) Malignant ascites: systematic review and guideline for treatment. Eur J Cancer 42(5):589–597 2. Adam RA, Adam YG (2004) Malignant ascites: past, present and future. J Am Coll Surg 198(6):999–1011 3. Smith EM, Jayson GC (2003) The current and future management of malignant ascites. Clin Oncol 15:59–72 4. Gines P, Cardenas A, Arroyo V et al. (2004) Management of cirrhosis and ascites. N Engl J Med 350(16):1646–1654 5. Parsons SL, Watson SA, Steele RJC (1995) Malignant ascites. Br J Surg 83:6–14

Aclarubicin Definition Is an anthracycline anticancer agent; Synonym aclacinomycin A. ▶Adriamycin

Acquired Immunodeficiency Syndrome Definition AIDS; A life-threatening disease caused by he human immunodeficiency virus (▶HIV) and characterized by breakdown of the body's immune defenses.

Acquired Mutation Definition A mutation (a genetic change) acquired by a somatic cell after conception. ▶Gastrointestinal Stromal Tumor

Acromegaly Definition

The name “acromegaly” comes from the Greek words for “extremities” (acro) and “great” (megaly), because one of the most common symptoms of this condition is abnormal growth of the hands and feet. A hormonal disorder that most commonly occurs in middle-aged men and women. The prevalence of acromegaly is approximately 4,676 cases per million population, and the incidence is 116.9 new cases per million per year. The symptoms of acromegaly can vary and they

Actinomycin D

develop gradually over time; therefore, a diagnosis of this condition may be difficult. Early detection is a goal in the management of acromegaly because the pathologic effects of increased growth hormone (GH) production are progressive.

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Actin Cytoskeleton The actin cytoskeleton is a dynamic structure of ▶actin bundles and networks in the cytoplasm that provides a framework to maintain cell shape, protects the cell and enables cell locomotion. It also plays an important role in intra-cellular transport.

ACRP30 ▶Adiponectin

Actin Filament Severing Definition

ACTH

The breakage of noncovalent bonds between ▶actin molecules within an actin filament. ▶Geloslin

Definition Adrencorticotropic Hormone. ▶Corticotrophin

Actinic Keratosis Definition

Actin Definition A protein that is found abundantly in all eukaryotic cells. The protein exists in monomeric (globular or Gactin) and polymeric forms (filamentous or F-actin). Filamentous actin bundles to form long fibers known as Actin Microfilaments or stress fibers. Actin is a globular structural protein that polymerizes in a helix to form an actin filament. Actin filaments determine the cell shape, stabilize the cell mechanically, enable cell movements, and participate in contraction of the cell during ▶cytokinesis. Monomers of the protein actin polymerize to form long, thin fibers about 8 nm in a globular protein found in all cells. It is a major component in microfilaments and forms the contractile filaments in muscle cells. ▶Huntingtin Interacting Protein 1 (HIP1) ▶Micronucleus Assay ▶Migration ▶Tight Junction

Scaly, erythematous patches found on the skin in sun-exposed areas. Radiation induced keratosis (hornification) of the skin. It represents a precancerous lesion also known as solar keratosis or senile keratosis. May undergo malignant progression to form squamous cell carcinoma. ▶Epidermoid Carcinoma ▶Squamous Cell Carcinoma ▶Photodynamic Therapy

Actinomycin D Definition Synonym Dactinomycin. An antineoplastic antibiotic used for Nephroblastoma, Rhabdomyosarcoma, and trophoblastic disease in women. ▶Placental Site Trophoblastic Tumor (PSTT)

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Activated Fibroblasts

Activated Fibroblasts ▶Myofibroblasts

Activated Natural Killer Cells N ORIMASA I TO, H ERBERT J. III Z EH , M ICHAEL T. L OTZE University of Pittsburgh, Departments of Surgery and Bioengineering, Pittsburgh, PA, USA

Synonyms K cells; killer cells; K lymphocyte; large granular lymphocyte; lymphokine activated killer; LAK

Definition White blood cells that kill tumor and virus-infected cells as part of the body’s immune system (Unified Medical Language System). A type of white blood cell that contains granules with enzymes that can kill tumor cells or microbial cells (National Cancer Institute). A circulating cellular biosensor, regulating immunity through release of cytokines, maturation of dendritic cells, and recognition and lysis of stressed cells, allowing sampling of cellular contents for delivery to phagocytic cells (our definition).

Characteristics Biology of NK Cells ▶Natural Killer cells comprise 10–15% of circulating lymphocytes in normal adults and are also found in peripheral tissues, including the liver, peritoneal cavity, lymph nodes, and placenta. NK cells were first reported by Wunderlich, Herberman, and Sendo and others in the early 1970s. They were first discovered on the basis of their nonspecific killer activity, disturbing attempts to generate tumor-specific, ▶MHC-restricted cytotoxic T lymphocytes (CTLs). NK cell belongs to the innate immune system, bridging ▶adaptive immunity in concert with ▶dendritic cells. NK cells play a major role in the host defense against tumors and infected cells. NK cells mediate cytolysis of cultured tumor cells, and when lymphokine activated (LAK activity), against freshly acquired tumor cells. “Natural killer” suggests the initial notion that they do not require activation in order to kill target cells. NK cells are large granular lymphocytes (LGL). The targets of NK cells are stressed cells expressing either “nonself” or “the self that changed in quality,” prompting their recognition.

NK cells, when activated, can recognize cells which fail to express cognate self MHC molecules and simultaneously express (stress-induced) ligands recognized by activating NK receptors. These ligands include MICA/ MICB ULPBs, PVR, and Nectin-2 in humans or Rae-1 in mice. NK cytolytic activity is almost nonexistent at birth, increases until 15 years of age, and then gradually reduces through old age. Natural killer cells (NK cells) lack the ability to destroy tumor cells at the time of birth, acquiring cytolytic capacity following recognition. Given their ready acquisition from the peripheral blood, multiple studies have evaluated their activity in various clinical studies; for example, chronic mental stress, fatigue, and physical exertion suppress NK activity. Reduced NK activity may be related to increasing cancer risk. Patients deficient in NK cells prove to be highly susceptible to early phases of herpes virus infection. Many studies indicate that NK activity is reduced in patients with advanced cancer. Tumor infiltrating NK cells of pediatric cancer are significantly less in number than that observed in adult cancers, prompting the notion that this creates a major nosologic difference of adult and pediatric neoplasms. Role of NK Cells in Human Cancer NK cells induce tumor cell death when NK cells recognize tumor cells with NK cell activating receptors. NK cells produce many cytokines including ▶IFNs and ▶TNF-α and suppress proliferation of tumor and cells and drive type 1 immunity. NK cells help dendritic cells to mature into DC1. NK cells have some suppressive roles against cancer. NK cells have inhibitory receptors. They become tolerant to tumor cells when inhibitory receptors are stimulated with their ligands (Fig. 1). Markers of NK Cells NK cells express CD16 (FcγRIII), CD56, ▶CD57, CD94, or CD158a. They do not express ▶T-cell receptor (TCR) or the pan T cell marker ▶CD3 or surface immunoglobulins (Ig) B cell receptor (▶CD20). NK cells recognize specific polysaccharide on target cells with NK receptor (CD161; NKR-P1) and expression of MHC class I molecules. NK Cell Receptors There are two main types of receptors for MHC class I on NK cells including the KIR (killer cell immunoglobulin-like receptors, one of the immunoglobulin superfamily) and NKG2 receptor (CD94, type C lectin family). In both, there are activating and suppressing forms that accelerate or suppress NK activity. Two explanations for NK-cell self-tolerance have been proposed: first, NK cells from MHC-class-Ideficient hosts have a lower activation potential, owing to decreased activating-receptor expression and/or

Activated Natural Killer Cells

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A

Activated Natural Killer Cells. Figure 1 Role of NK cells in tumor immunity. NK cells play multiple roles in tumor immunity. They recognize stressed cells or those failing to express cognate Class I major histocompability molecules, both lysing targets and serving as a source of cytokines important in initiation and perpetuation of the inflammatory response is carried out by them. They serve as helper cells, promoting immune interaction with both T and dendritic cells, critically being required for initiation of the TH1 response. Their absence may also be important in limiting autoimmunity as revealed by their critical absence in the NOD mouse strain, susceptible to autoimmune diabetes. When lysing cells, normal cells capable of undergoing apoptotic or autophagic00128 death, Types I and II death, do so. Many virally infected or transformed cells fail to undergo such death because of block of these pathways, and when lysed, undergo necrotic cell death causing DC maturation and promoting recruitment of additional inflammatory cells. In the absence of viral or bacterial pathogen signals, such chronic necrotic cell death is associated with inhibition of immune effectors and promotion of a wound repair phenotype with angiogenesis and stromagenesis, characteristic of many tumors.

function; or second, NK cells are kept self-tolerant by interactions between non-MHC-dependent receptor– ligand pairs CD94: NKG2, a C-type lectin family receptor, is conserved in both rodents and primates and identifies nonclassical (also nonpolymorphic) MHC I molecules including HLA E. Though indirect, this is a means to survey the levels of classical (polymorphic) HLA molecules. Expression of HLA E at the cell surface is dependent upon the presence of classical MHC class I leader peptides. Ly49 is a relatively ancient, C-type lectin family receptor. Humans have only one pseudogenic Ly49; the receptor for classical MHC I molecules. KIRs belong to a multigene family of more recently evolved Ig-like extracellular domain receptors. They are present in nonrodent primates and are the primary receptors for both classical MHC I (HLA A, HLA B, HLA C) and nonclassical HLA G in primates. KIRs are specific for certain HLA subtypes. ILT or LIR (leucocyte inhibitory receptors) are recently discovered members of the Ig receptor family. ▶Carcinoembryonic antigen related cell adhesion molecule 1

(▶CEACAM1 Adhesion Molecule) is an inhibitory receptor and its ligands are CEACAM1 itself and CEACAM5, known as CEA. Sialic acid binding immunoglobulin-like lectins (SIGLECs) have a V-set immunoglobulin domain, which binds sialic acid, and varying numbers of C2-set immunoglobulin domains. IRp60, KLRG1, and LAIR1 are other inhibitory receptors recently discovered (Table 1). NK Cell and Cytokines NK cells are capable of producing many cytokines including IFN-γ (▶Interferon-f γ), IFN-α, IFN-β, and TNF-α. They suppress proliferation of tumor and virally infected cells and regulate immune responses. IFN-γ (Interferon-f γ) increases NK activity as a positive feedback mechanism. NK cytolytic activity is increased by IFN-α, IFN-β, and IFN-γ (Interferon-f γ) (produced by T and NK cells), IL-2\(produced by T cells), IL-10, IL-12, and IL-15 (produced by B cell, monocyte/ macrophage, or dendritic cells). NK cytolytic activity is inhibited by IL-4 (▶Interleukin-4). IL-15 induces

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Activated Natural Killer Cells

Activated Natural Killer Cells. Table 1 receptors

Inhibitory and Activating NK Cell Receptors and their Ligands Activating NK cell

Receptors 2B4 NKp44 NKp30 NKp46 CD16 NKG2D02396 NKp80 DNAM Inhibitory NK cell receptors ILT2 KIR3DL2 KIR3DL1 KIR2DL4 KIR2DL1,2,3 CD94 CEACAM102441 IRp60 KLRG1 LAIR1 SIGLEC7 SIGLEC9

Ligands CD48 Influenza/unknown Influenza/unknown IgG MICA, MICB CD112/CD155 MHC01094-A, B, G MHC01094-A MHC01094-B MHC01094-A, B, G MHC01094-C MHC01094-C CEACAM102441, CEACAM5 Unknown Unknown Unknown Sialic acid Sialic acid

NK cell proliferation. IL-12 induces IFN-γ (Interferonf γ) production by NK cells. IFN-α, IFN-β, IFN-γ (Interferon-f γ), and TNF-α produced by NK cells activate monocyte/macrophage, vascular endothelial cells, neutrophils, and induce a local inflammation response. Cytotoxicity of NK Cells against Tumor or Infected Cells NK cells release ▶perforin from intracellular granules when they bind to target cells, along with granules containing serine proteases known as ▶granzymes. Perforin attaches to the membrane inducing an autophagic (▶Autophagy) repair process, inducing uptake of vesicles containing granzymes and associated molecules that can target cells for lysis, with perforin allowing escape through pore formation once intracellular. Granzyme induce apoptosis to the target cells utilizing various intracellular pathways. NK cells also induce ▶apoptosis to target cells by expressing apoptosis inducing molecules such as FAS ligands or ▶TRAIL on the cell surface. The distinction between apoptosis and ▶necrosis is important in cancer immunology – necrotic cells release danger/damage associated molecular pattern molecules (DAMPs) such as high-mobility group box 1 (HMGB1) protein, whereas apoptosis leads to retention of HMGB1 within the cells or apoptotic nuclei.

NK Cells and Cancer Immunotherapy Their rapid cytolytic action and broad target range suggest that NK cells may be promising candidates for cancer cell therapy. The clinical application of ex vivo manipulated cells, including NK cells, is referred to as ▶adoptive immunotherapy (AIT). The first clinical AIT trial exploited autologous ex vivo expanded and interleukin 2 (IL-2) stimulated ▶lymphokine activated killer (LAK). Although this approach produced nearly 15–20% partial and complete responses in initial trials, subsequent studies showed that a similar antitumor effect could be achieved with administration of high dose IL-2 alone. Purification and enrichment of NK cells on a clinical scale may improve therapeutic outcomes. Alternatively, stimulation of LAK cells with IL-15 or IL-21 instead of IL-2 might increase efficacy. Myeloid ▶dendritic cells (mDCs) support the tumoricidal activity of NK cells, while cytokinepreactivated NK cells activate DCs and induce their maturation and cytokine production. NK–DC interactions promote the subsequent induction of tumorspecific responses of CD4+ and CD8+ T cells, allowing NK cells to act as nominal “helper” cells in the development of the desirable type-1 responses to cancer. NK–DC interaction provides a strong rationale for the combined use of NK cells and DCs in the immunotherapy of patients with cancer. Clinical trials that are being

Acute Lung Injury (ALI)

implemented at present should allow evaluation of the immunological and clinical efficacy of combined NK–DC therapy of melanoma and other cancers.

References 1. Arnon TI, Markel G, Mandelboim O (2006) Tumor and viral recognition by natural killer cells receptors. Semin Cancer Biol 16:348–358 2. DeMarco RA, Fink MP, Lotze MT (2005) Monocytes promote natural killer cell interferon gamma production in response to the endogenous danger signal HMGB1. Mol Immunol 42(4):433–444 3. Lotze MT, Line BR, Mathisen DJ, et al. (1980) The in vivo distribution of autologous human and murine lymphoid cells grown in T cell growth factor (TCGF): implications for the adoptive immunotherapy of tumors. J Immunol 125 (4):1487–1493 4. Ito N, Demarco RA, Mailliard RB, et al. (2007) Cytolytic cells induce HMGB1 release from melanoma cell lines. J Leukoc Biol 81(1):75–83 5. Moretta A, Bottino C, Vitale M, et al. (1996) Receptors for HLA-class I-molecules in human Natural Killer cells. Annu Rev Immunol 14:619–648

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transcription factors activate various genes critical in the initiation of DNA synthesis. In ▶mesothelioma, it is thought that the persistent induction of these transcription activators following ▶asbestos exposure enhances cell division and favors malignant growth. ▶Mesothelioma ▶Polyphenols ▶Retinoid Receptor Cross-talk ▶Simian Virus 40 ▶SV40

Active ▶Melanoma Vaccines

Active Cell Death Activated Vitamin D ▶Calcitriol

▶Apoptosis

Active Immunity Definition

Activation Loop

Immunity produced by the body in response to stimulation by a disease-causing organism or a vaccine.

Definition A 20–25-residue segment within the catalytic domain of protein kinases that functions to regulate their kinase activity. ▶B-Raf Signaling

Activator Protein-1 (AP-1) Definition A dimeric complex that contains members of the c-jun, c-fos, ATF and MAF protein families. The ▶AP-1

Acute Granulocytic Leukemia ▶Acute Myeloid Leukemia

Acute Lung Injury (ALI) Definition A distinct form of acute respiratory failure characterized by diffuse pulmonary infiltrates, progressive hypoxemia, reduced lung compliance, and normal hydrostatic

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Acute Lymphoblastic Leukemia

pressures. ALI is caused by any stimulus of local or systemic inflammation, principally sepsis. ▶Sivelestat

Acute Lymphoblastic Leukemia C HING -H ON P UI St. Jude Children’s Research Hospital, Memphis, TN, USA

Synonyms Acute lymphoblastic leukemia; ALL

Definition Acute lymphoblastic leukemia (ALL) is a malignant disease that arises from several cooperative genetic mutations in a single B or T-lymphoid progenitor, leading to altered blast cell proliferation, survival, and maturation, and eventually to the lethal accumulation of leukemic cells. Although cases can be subclassified further according to the stages of T or B-cell maturation, these distinctions are not therapeutically useful, except for the recognition of a mature B-cell, B-cell precursor, or T-cell stage.

Characteristics ALL accounts for about 12% of all childhood and adult leukemias diagnosed in developed countries and for 60% of those diagnosed in persons younger than 20 years. It is the most common cancer in children (25% of all cases) and has a peak incidence in patients between the ages of 2 and 5 years, with a second, smaller peak in the elderly. The factors predisposing children and adults to ALL remain largely unknown. Fewer than 5% cases are associated with inherited genetic syndromes defined by chromosomal instability and defective DNA repair. Ionizing radiation and mutagenic chemicals have been implicated in some cases of ALL, but their contributions appear negligible. Nonetheless, evidence collected over the past two decades has revealed that ALL is essentially a disease of acquired genetic abnormalities. Specific genetic abnormalities are found in the leukemic cells of approximately 75% of patients with ALL to date, and in all likelihood, will be identified in all cases with the improved genetic techniques. These include chromosomal translocations and chromosomal gains or losses, resulting in ▶hyperdiploidy or ▶hypodiploidy, respectively. Chromosomal translocations often

activate transcription factor genes, which in many cases control cell differentiation, are developmentally regulated, and frequently encode proteins at the tops of critical transcriptional cascades. These “master” oncogenic transcription factors, which can exert either positive or negative control over downstream responder genes, are aberrantly expressed in leukemic cells as a single gene product or as a unique fusion protein combining elements from two different transcription factors. Recently, activating mutations of ▶NOTCH1, a gene encoding a transmembrane receptor that regulates normal T-cell development, and mutations of ▶PAX5, a gene essential for B-lineage commitment and maintenance, have been identified to be most frequent cooperative mutations in T-cell and B-cell precursor ALL, respectively. Although most leukemias begin in the bone marrow and spread to other parts of the body, some may arise in an ▶extramedullary site, such as the thymus or intestine, and subsequently invade the bone marrow. The presenting features of ALL generally reflect the degree of bone marrow failure and the extent of extramedullary spread. Common signs and symptoms are . Fever . Fatigue and lethargy . Dyspnea, angina, and dizziness (older patients mainly) . Limp, bone pain, or refusal to walk (young children) . Pallor and bleeding in the skin or mouth cavity . Enlarged liver, spleen, and lymph nodes (more pronounced in children) . Anemia, low neutrophil count, and low platelet count . Metabolic abnormalities (e.g., high serum uric acid and phosphorus levels) The diagnosis of ALL is based on a morphologic examination of bone marrow cells (Figs. 1–3) and immunophenotype of cells from the same sample.

Acute Lymphoblastic Leukemia. Figure 1 Small regular blasts with scanty cytoplasm, homogeneous nuclear chromatin, and inconspicuous nucleoli.

Acute Lymphoblastic Leukemia

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Acute Lymphoblastic Leukemia. Figure 2 Admixture of large blasts with moderate amounts of cytoplasm and smaller blasts. Such cases may be mistaken for acute myeloid leukemia, emphasizing the importance of immunophenotyping and genotyping to corroborate the differential diagnosis.

Karyotyping, fluorescence in situ hybridization (FISH), and molecular genetic analysis by RT-PCR (reverse transcriptase-polymerase chain reaction) are now routinely performed by many centers to identify subtypes of ALL with prognostic and therapeutic significance, for example: . BCR-ABL fusion gene due to the t(9;22), or ▶Philadelphia chromosome – 25% of adult cases and 3–4% of childhood cases (dismal prognosis) . ▶TEL-AML1 fusion gene due to a cryptic t(12;21) – 22% of childhood cases (favorable prognosis) . Hyperdiploidy (more than 50 chromosomes per cell) – 25% of childhood cases (favorable prognosis) . Hypodiploidy (fewer than 45 chromosomes per cell) – 1% of childhood cases and 2% of adult cases (unfavorable prognosis) Contemporary risk-directed treatment can cure 80% or more of children and up to 40% of adults with ALL. Cases are generally classified as standard or high risk in adults and as low, standard, and high risk in children. Factors used to determine the relapse hazard include the presenting leukocyte count, age at diagnosis, gender, immunophenotype, ▶karyotype, molecular genetic abnormalities, initial response to therapy, and the amount of “minimal residual leukemia” upon achieving a complete ▶remission. Multidrug remission induction regimens almost always include a glucocorticoid (prednisone, prednisolone, or dexamethasone), vincristine, and at least a third agent (L-asparaginase or anthracycline), administered for 4–6 weeks. Some treatments rely on additional agents to increase the level of cell kill, thereby reducing the likelihood of the development of drug resistance and subsequent relapse. However, several studies suggest

Acute Lymphoblastic Leukemia. Figure 3 Mature B-cell ALL blasts characterized by intensely basophilic cytoplasm, regular cellular features, prominent nucleoli, and cytoplasmic vacuolation.

that intensive remission induction therapy may not be necessary for low or standard-risk patients, provided that they receive postinduction intensification therapy. Remission induction rates now range from 97 to 99% in children and from 78 to 93% in adults. Complete clinical remission is traditionally defined as restoration of normal blood cell formation with a blast cell fraction of less than 5% by light microscopic examination of the bone marrow. With this definition, some patients in complete remission may harbor as many as 1 × 1010 leukemic cells in their body. With sensitive and specific methods developed to measure minimal residual disease, it is now recognized that most patients actually have less than 0.01% of residual leukemia after 4–6 weeks of remission induction therapy, and they have excellent treatment outcome. By contrast, patients with 1% or more leukemic cells after remission induction treatment have a poor prognosis and may be candidates for hematopoietic stem cell transplantation. To improve treatment outcome, most protocols specify an intensification (or consolidation) phase in which several effective antileukemic drugs are administered in high doses soon after the patients attain a complete remission. Reinduction treatment, essentially a repetition of the initial induction therapy administered during the first few months of remission, has become an integral component of successful ALL treatment protocol. Regardless of the intensity of induction, consolidation or reinduction therapy, all children require 2–3 years of continuation treatment, usually methotrexate and mercaptopurine, with pulses of vincristine and dexamethasone for low-risk cases, and multiagent intensive chemotherapy for standard and high-risk cases. The need for continuation therapy in adults is less clear, although in most cases it is discontinued after 2–2½ years of complete remission. The central nervous system can be a ▶sanctuary site for leukemic cells, requiring intensive,

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Acute Megakaryoblastic Leukemia

intrathecally administered chemotherapy that begins early during the remission induction phase, extending through the consolidation phase and into the continuation phase. Once considered standard treatment, cranial irradiation is now reserved for less than 10% of patients who are at very high risk of relapse in the central nervous system. For selected high-risk cases, such as patients with Philadelphia chromosome-positive ALL, and those who require extended therapy to attain initial complete remission, hematopoietic stem-cell transplantation is currently the treatment of choice. In light of the development of new therapeutics, the indications for transplantation should be continuously evaluated. For example, therapy with imatinib mesylate (Gleevec; Novartis) or second-generation tyrosine kinase inhibitors has improved the duration of remission of patients with Philadelphia chromosome-positive ALL, but whether this therapy will increase the cure rate remains to be determined. Finally, the optimal clinical management of patients with ALL requires careful attention to methods for the prevention or treatment of metabolic and infectious complications, which may otherwise be fatal.

References 1. Pui C-H, Relling MV, Downing JR (2004) Acute lymphoblastic leukemia. N Engl J Med 350:1535–1548 2. Vitale A, Guarini A, Chiaretti S et al. (2006) The changing scene of adult acute lymphoblastic leukemia. Curr Opin Oncol 18:652–659 3. Pui C-H, Evans WE (2006) Treatment of acute lymphoblastic leukemia. N Engl J Med 354:166–178 4. Pui C-H, Jeha S (2007) New therapeutic strategies for the treatment of acute lymphoblastic leukaemia. Nat Rev Drug Discov 6:149–165 5. Mullighan CG, Goorha S, Radtke I et al. (2007) Genomewide analysis of genetic alterations in acute lymphoblastic leukemia. Nature 446:758–764

Acute Megakaryoblastic Leukemia J EAN -P IERRE B OURQUIN 1 , S HAI I ZRAELI 2 1

Pediatric Oncology, University Children’s Hospital Zurich, Zurich, Switzerland 2 Pediatric Hemato-Oncology, Sheba Medical Center and Tel Aviv University, Ramat Gan, Israel

Synonyms Acute Myeloid Leukemia; Subtype AML-M7 according to the French-American-British (FAB) Classification; Myeloid Leukemia of Down Syndrome (DS-ML); WHO classification: Acute Megakaryoblastic Leukemia (M7)

Definition Acute Megakaryoblastic Leukemia (AMKL) is defined as a malignant ▶clonal proliferation of immature hematopoietic cells of the megakaryocytic lineage. AMKL is a subtype of Acute Myeloid Leukemia (AML). The biologic features of AMKL are heterogeneous and ongoing characterization of the disease pathogenesis is likely to lead to a novel clinically meaningful classification of the disease.

Characteristics Epidemiology AMKL is diagnosed in 7–10% of infants and children with AML without Down syndrome (DS). In most pediatric cases the disease occurs de novo and subgroups can be identified based on cytogenetic features or biological features as described later. In contrast, AMKL is rare in adults, occurring in 1–2% of all AML cases and is frequently associated with antecedent hematological disorder such as myelodysplastic syndrome. Children with DS have a markedly increased risk to developing AMKL and represent up to 10 % of children with AML. A large proportion of Children with DS (estimated 10%) are born with a unique transient form of AMKL, often called transient myeloproliferative disorder (TMD) or transient abnormal myelopoiesis (TAM). This congenital leukemia resolves spontaneously in most of the patients. Up to 20% of those patients will relapse with a full blown AMKL by the age of 4 years. Thus the leukemia of DS represents a unique clinical entity of multistep leukemogenesis (Fig. 1). Clinical and pathologic features Typical features at diagnosis include hepato-splenomegaly, anemia, thrombocytopenia and myelofibrosis. The fibrosis is probably caused by soluble factors (such as TGF-β) secreted from the malignant megakaryoblasts. Infants with DS may exhibit marked liver failure that sometimes may be life threatening. The liver failure is secondary to liver fibrosis caused by the infiltration of leukemic cells. ▶Flow cytometry is the preferred method for ▶immunophenotypic characterization of AMKL, although in some cases the diagnosis can only be made from bone marrow or liver biopsies due to extensive myelofibrosis. Typically, the leukemic blasts express at least one megakaryoblastic antigen [CD41(GPIIb)/ CD42b(GPIbalpha) or CD61]. Coexpression of the T-lineage marker CD7 is frequently observed, suggesting pathogenic mechanism that could lead to aberrant regulation of lymphoid genes. Expression of erythroid markers (e.g. glycophorin A) and of CD36 (thrombospondine receptor) characterize the AMKL of DS. Because AMKL blasts may display low expression levels of the panhematopoietic CD45 antigen, the distinction from metastatic solid tumours may be challenging.

Acute Megakaryoblastic Leukemia

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Acute Megakaryoblastic Leukemia. Figure 1 Multistep evolution of AMKL in Down Syndrome. Mutation in GATA1 is acquired during fetal liver hematopoiesis in cells carrying a germline trisomy 21 results in congenital clonal megakaryoblastic proliferation (TMD). In almost all patients TMD resolves spontaneously leading to cure. However in about 20% of the patients additional postnatal acquired mutations in residual cells from the resolved TMD results in the development of full blown acute megakaryocytic leukemia (AMKL) during early childhood.

Cytogenetic and Biological Features Increasing evidence suggest that distinct subtypes of AMKL can be identified based on genetic and molecular characteristics. Recurrent cytogenetic abnormalities are specifically associated with AMKL and at least in part convey a prognostic significance. The megakaryoblastic disorders associated with DS (both AMKL and TMD) are characterized by the presence of an acquired mutation in the ▶transcription factor GATA1. The mutations occur in exon 2 or in the beginning of exon 3 and uniformly results in the production of a short GATA1 protein (GATA1s) that lacks the amino-terminal of the full length GATA1. GATA1 is a major regulator of normal megakaryopiesis. GATA1s blocks terminal differentiation and enhances proliferation of immature fetal megakaryoblasts. The mutations occur during ▶fetal liver hematopoiesis. The initiation of the leukemia during fetal liver hematopoiesis explains the frequent liver dysfunction observed in DS newborns with TMD. Strikingly, GATA1 is located on chromosome X and is mutated only in AMKL with trisomy 21. The precise mechanism by which trisomy 21 promotes the survival of cells with acquired mutation in GATA1 is presently unknown. One hypothesis suggests that genes on chromosome 21 code proteins that enhance fetal megakaryopoiesis. This developmental pressure of megakaryopoiesis coupled with differentiation arresting mutation in GATA1 cause clonal accumulation of megakaryoblasts diagnosed at birth as TMD. GATA1 mutation is necessary and probably sufficient for the development TMD, but additional mutations are required for the occurrence of full blown AMKL in DS patients. Why TMD spontaneously resolves and which mutations cause further evolution to AMKL is largely unknown. There are several biological subgroups among patients with AMKL that do not have DS. The most

frequent recurrent chromosomal aberration detected in non-DS AMKL is the translocation t(1;22), which typically occurs in infants and very young children that present with hepatosplenomegaly and pronounced myelofibrosis. This translocation fuses RBM15/ OTT1, an RNA export factor to MKL1/MAL1, a cofactor of the transcription factor SRF (Serum Response Factor). Less commonly fusion translocations between the MLL gene and different partners, often AF10, have been reported in AMKL. Interestingly, a second translocation involving AF10, the translocation t(10;11) which results in the fusion of CALM (clathrin-assembly protein-like lymphoid myeloid) with AF10 was reported in several cases. This translocation was also identified in other AML subtypes and in cases of T-cell ALL. In a mouse model, infection of bone marrow cells with a retroviral vector to express CALMAF10 results in a transplantable AML, demonstrating that this fusion gene represents a fundamental leukemogenic event. By ▶gene expression profiling, at least two distinct classes of non-DS AMKL could be discriminated based on their molecular phenotype. Approximately one third of the cases display an erythroid expression pattern coupled with expression of CD36 and higher expression levels of the transcription factor GATA1 in absence of detectable mutations. Interestingly this gene expression signature is reminiscent to the increased expression of erythroid markers detected in AMKL from DS patients, which are characterized by increased expression levels of mutated GATA1s. The second subtype of non-DS AMKL samples include all cases with recurrent translocation t(1;22). Interestingly, samples that share similar expression profiles with the samples positive for the translocation t(1;22) are characterized by increased expression levels of another SRF cofactor, HOP,

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Acute Myelogenous Leukemia

suggesting that similar regulatory pathways may be involved. This second class is associated with higher levels of expression of the surface antigen CD44, which was associated with worse outcome in other type of malignancies and coexpressed on the leukemia initiating cells from patients with AML. It is currently not possible to determine if the distinction of these two classes by expression profiling has a prognostic significance due to the small numbers of patients that were treated on different therapeutic protocols. A prospective study using selected genes from the AMKL signature will be required to determine if this information could be used as prognostic marker to guide selection of treatment intensity. Prognosis and Treatment Treatment results from several international study groups, including the European AML-BFM study group and UK-MRC cooperative groups, and the north american SJCRH and CCG cooperative groups show a marked difference in treatment outcome between DS and non-DS AMKL. Reduction of treatment intensity for patients with DS resulted in a marked decrease in treatment related mortality and an excellent treatment outcome (91% event free survival at 5 years in the AMLBFM 98 study), strongly suggesting a distinct leukemia biology between DS and non-DS AMKL patients. AMKL blasts from patients with DS are extremely sensitive to the chemotherapy drug Cytosine Arabinoside (ARA-C), probably due to a decrease in its cellular degradation caused by an enzyme regulated by GATA1. The results for patients with AMKL excluding patients with DS are still poor, despite of intensification of AML treatment regimens. The 5–year event free survival (EFS) reported for the most recent treatment regimen correspond to results obtained for other AML subtypes, with EFS of 42% reported for the AML-BFM93/98 trials and of 47% reported by the UKMRC 10 and 12 trials. Further research is necessary to identify new treatment modalities and biomarkers to guide treatment intensification, including the indication for bone marrow transplantation for patients at highest risk of relapse. Recent data in mouse models suggest that targeted therapy with antibodies directed against the surface marker CD44 may be a future therapeutic.

References 1. Bourquin JP, Subramanian A, Langebrake C et al. (2006) Identification of distinct molecular phenotypes in acute megakaryoblastic leukemia by gene expression profiling. PNAS 103:3339–3344 2. Ge Y, Stout ML, Tatman DA et al. (2005) GATA1, cytidine deaminase, and the high cure rate of Down syndrome children with acute megakaryocytic leukemia. J Natl Cancer Inst 97:226–231

3. Izraeli S (2006) Down’s syndrome as a model of a preleukemic condition. Haematologica 91:1448–1452 4. Oki Y, Kantarjian HM, Zhou X et al. (2006) Adult acute megakaryocytic leukemia: an analysis of 37 patients treated at M.D. Anderson Cancer Center. Blood 107:880–884 5. Reinhardt D, Diekamp S, Langebrake C et al. (2005) Acute megakaryoblastic leukemia in children and adolescents, excluding Down’s syndrome: improved outcome with intensified induction treatment. Leukemia 19: 1495–1496

Acute Myelogenous Leukemia ▶Acute Myeloid Leukemia

Acute Myeloid Leukemia B ARBARA D ESCHLER Medical Center, Department of Hematology-Oncology, University of Freiburg, Freiburg, Germany

Synonyms Acute myelogenous leukemia; Acute nonlymphocytic leukemia; ANLL; Acute granulocytic leukemia

Definition Acute myeloid leukemia (AML) is part of a group of hematological malignancies (▶hematological malignancies) in the bone marrow involving cells committed to the ▶myeloid line of cellular development. It is defined by the malignant transformation of a bone marrow-derived, self-renewing stem cell or progenitor (▶stem cells and cancer) which demonstrates a decreased rate of self-destruction and aberrant ▶differentiation. Uncontrolled growth of such cells, named blasts, is the result of ▶clonal proliferation. Blasts accumulate in the bone marrow and other organs. As a result, mature cells of ▶hematopoiesis are suppressed. For the leukemia to be called acute, the bone marrow must include greater than 20% leukemic blasts.

Characteristics Classification The first comprehensive morphologic-histochemical classification system for AML was developed by the French-American-British (FAB) Cooperative Group. This classification system categorizes AML into eight major subtypes (M0 to M7) based on morphology and

Acute Myeloid Leukemia

immunohistochemical detection of lineage markers. This classification of AML was recently revised under the auspices of the World Health Organization (WHO) (see list 1). While elements of the older FAB classification were preserved, the WHO classification incorporates and interrelates morphology, cytogenetics, molecular genetics, immunologic markers, and clinical features in an attempt to define categories that are biologically homogeneous and that have prognostic and therapeutic relevance. The most significant difference between the WHO and FAB classifications is that the minimum blast percentage for the diagnosis of AML is at least 20% blasts in the blood or bone marrow (the FAB scheme required the blast percentage to be at least 30%). What was known as “refractory anemia with excess blasts in transformation” (RAEB-t) of myelodysplastic syndromes (▶MDS), is now included within the broader category of “AML with multilineage dysplasia” as “AML with multilineage dysplasia following a MDS.” List 1 – WHO classification of AML (the older FAB classifications are given in parentheses where appropriate): . AML with characteristic genetic abnormalities – AML with t(8;21)(q22;q22); (AML/ETO) – AML with inv(16)(p13q22) or t(16;16)(p13; q22); (CBFβ/MYH11) – Acute promyelocytic leukemia (AML with t(15;17)(q22;q12); (PML/RARα) and variants) – AML with 11q23 (MLL) abnormalities . AML with multilineage dysplasia – AML with prior MDS – AML without prior MDS . AML and MDS, therapy-related – Alkylating agent-related AML and MDS – Topoisomerase II inhibitor-related AML . AML not otherwise categorized – Acute myeloblastic leukemia, minimally differentiated (FAB M0) – Acute myeloblastic leukemia without maturation (FAB M1)

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– Acute myeloblastic leukemia with maturation (FAB M2) – Acute myelomonocytic leukemia (AMML) (FAB M4) – Acute monoblastic leukemia and acute monocytic leukemia (FAB M5a and M5b) – Acute erythroid leukemias (FAB M6a and M6b) – Acute megakaryoblastic leukemia (FAB M7) – AML/transient myeloproliferative disorder in Down syndrome – Acute basophilic leukemia – Acute panmyelosis with myelofibrosis – Myeloid sarcoma . Acute leukemias of ambiguous lineage Epidemiology AML is infrequent but highly malignant, responsible for a large number of cancer-related deaths. AML accounts for approximately 25% of all leukemias in adults in industrialized countries and, thus, is the most frequent form of leukemia. Worldwide, the incidence of AML is highest in the United States, Australia, and Western Europe. The age-adjusted incidence rate of AML in the United States in the years 1975–2003 has been relatively stable at approximately 3.4 per 100,000 persons (=2.5 per 100,000 when age-adjusted to the world standard population). The American Cancer Society estimates that 11,930 individuals will be diagnosed with AML in 2006 in the United States. Patients that are newly diagnosed with AML have a median age of 65 years. From 2000 to 2003, the U.S. incidence rate in people under the age of 65 was only 1.8 per 100,000, while the incidence rate in people aged 65 or over was 17 per 100,000 (Fig. 1). AML is thus primarily a disease of later adulthood with an age-dependent mortality of 2.7 to nearly 18 per 100,000. The incidence of AML varies to a small degree depending on gender and race. AML in adults is slightly more prevalent in males in most countries. In the US in 2000, AML was more common in Whites with 3.8 per 100,000 than in Blacks (3.2 per 100,000).

Acute Myeloid Leukemia. Figure 1 Age-specific incidence of AML (USA: 2000–2003) (Source: SEER).

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Acute Myeloid Leukemia

Acute Myeloid Leukemia. Table 1

Risk factors

Genetic disorders

Down syndrome Klinefelter syndrome Patau syndrome Ataxia telangiectasia Shwachman syndrome Kostman syndrome Neurofibromatosis Fanconi anemia Li–Fraumeni syndrome Physical and chemical Benzene exposure Drugs as pipobroman Pesticides Cigarette smoking Embalming fluids Herbicides Radiation Exposure Non-/therapeutic radiation Chemotherapy Alkylating agents topoisomerase II inhibitors Anthracyclines Taxanes

Etiology The development of AML has been associated with several risk factors summarized in Table 1. Generally, only a small number of observed cases can be traced back to known risk factors. These include age, antecedent hematological disease, genetic disorders as well as exposures to radiation, chemical or other hazardous substances (e.g., benzene), and previous chemotherapy (e.g., treatment with ▶alkylating agents). Leukemogenesis, like ▶carcinogenesis is a multistep process that requires the susceptibility of a hematopoietic progenitor cell to inductive agents at multiple stages. The different subtypes of AML may have distinct causal mechanisms, suggesting a functional link between a particular molecular abnormality or mutation and the causal agent. Most cases of AML arise without objectifiable leukemogenic exposure. Signs and Symptoms of AML AML can cause different uncharacteristic signs and symptoms such as weight loss, unusual fatigue, and fever. Many patients feel a loss of well-being. Most symptoms can be traced back to bone marrow insufficiency: Anemia, immunodeficiency caused by neutropenia, and thrombocytopenia. Diagnostic procedures and types of specimen necessary to reach the diagnosis of AML are the following:

Acute Myeloid Leukemia. Figure 2 Myeloid blasts in peripheral blood detected by light microscopy.

. Blood cell counts and microscopic blood cell examination (Fig. 2) . Bone marrow aspiration and biopsy . Routine microscopic exam of bone marrow . Flow cytometry . Immunocytochemistry . Cytogenetics . Molecular genetic studies The peripheral blood count may reveal a decreased white blood cell count (leukopenia) as well as leukocytosis (increased white blood cell count). Leukemia cells do not protect against infection and may cause congestion of blood vessels (leukostasis). Thrombocytopenia, a decrease of platelets, can lead to excessive bruising, ▶petechiae, and bleeding. When leukemia cells spread outside the bone marrow, it is called extramedullary manifestation. Small pigmented spots that look like common rashes may indicate skin involvement. A tumor-like collection of AML cells is called chloroma or granulocytic sarcoma. AML sometimes causes enlargement of the liver and spleen. Prognostic Factors AML is a curable disease; the chance of cure for a specific patient depends on a number of prognostic factors. Some of the strongest prognostic information can be obtained by ▶cytogenetic analysis. Normal cytogenetics indicates average-risk AML. Cytogenetic abnormalities that suggest a good prognosis include translocations t(8;21) and t(15;17), as well as inv(16). Patients with AML that is characterized by deletions of the long arms or monosomies of chromosomes 5 or 7; by translocations or inversions of chromosome 3, t(6;9), t(9;22); or by abnormalities of chromosome 11q23 have particularly poor prognoses. Further adverse prognostic factors include central nervous system involvement with leukemia, elevated

Acute Nonlymphocytic Leukemia

white blood cell count (>100,000/mm3), treatmentinduced AML, and a history of MDS. Leukemias in which cells express the progenitor cell antigen CD34 and/or the P-glycoprotein (MDR1 gene product) have an inferior outcome. Due to a higher relapse rate, patients with AML associated with an internal tandem duplication of the FLT3 gene (FLT3/ITD mutation) have a poorer outcome. Beyond these disease-specific factors, patient-specific parameters like comorbidities and frailty have a strong impact on the course of the disease and treatment tolerability, as reflected by the age-dependent surge in mortality. Therapy Therapeutic approaches can be differentiated as curative (aimed at long-term cure) or palliative (principally aimed at achieving best quality of life) (▶palliative therapy). Curative intensive chemotherapeutic treatment (▶chemotherapy of cancer, progress and perspectives) for AML is considered the standard procedure, usually divided in two phases, induction and consolidation (post-remission) therapy. It is traditionally based on two substances, cytarabine (cytosine arabinoside) and anthracycline. The objective of a curative treatment approach is to rapidly eliminate the cancer cells with induction chemotherapy, called remission. Complete remission occurs in 60–80% of patients. More than 15% of adults with AML (about 25% of those who attain complete remission) can be expected to survive 3 or more years and may be cured. Remission rates in adult AML are inversely related to age, with an expected remission rate of >65% for those younger than 60years. Duration of remission may be shorter in older patients. Increased morbidity and mortality during induction appear to be directly related to age. This is associated with several factors including the ability to tolerate intensive treatment approaches. Without treatment, the average life expectancy is about 3 months. Complications during treatment include relapse of the disease, severe infections, or life-threatening bleeding. During this time, supportive care consists of patient isolation to prevent infection, antibiotics to treat infections, and transfusion of blood products. After remission is achieved, further treatment is known as consolidation and is necessary in order to achieve a permanent cure. Consolidation may consist of either further chemotherapy or a bone marrow, or stem cell transplantation. The aforementioned treatments are appropriate for all subtypes of AML except for one type of AML known as ▶acute promyelocytic leukemia (APL). Newer treatments, especially for those patients not tolerating intensive chemotherapy, include monoclonal antibodies, demethylating agents, and experimental

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drugs given in clinical trials. Thus, while the diagnosis of AML in itself does not represent a therapeutic mandate for intensive chemotherapy in all cases, the latter is the only curative approach to treatment. Decisions whether to treat patients with intensive chemotherapy, new agents, or solely best ▶supportive care should be based on a sum of patient factors (including age, previous history of MDS, ▶comorbidity, frailty, and patients’ preferences), in addition to the blast count and the above-described prognostic factors. Careful consideration of these factors is especially relevant in older, multimorbid patients with AML. ▶Acute Megakaryoblastic Leukemia ▶Nucleoporin

References 1. Brunning RD, Matutes E, Harris NL et al. (2001) Acute myeloid leukaemia: introduction. In: Jaffe ES, Harris NL, Stein H et al. (eds) Pathology and genetics of tumours of haematopoietic and lymphoid tissues. IARC Press, Lyon, France. World Health Organization Classification of Tumours, 3, pp 77–80 2. Ries LAG, Harkins D, Krapcho M et al. (eds) (2006) SEER cancer statistics review, 1975–2003. National Cancer Institute, Bethesda, MD 3. Parkin DM, Whelan SL, Ferlay J et al. (eds) (1997) Cancer incidence in five continents, vol 7. IARC Scientific publications, Lyon, France 4. Grimwade D, Walker H, Harrison G et al. (2001) The predictive value of hierarchical cytogenetic classification in older adults with acute myeloid leukemia (AML): analysis of 1065 patients entered into the United Kingdom Medical Research Council AML11 trial. Blood 98 (5):1312–1320 5. Deschler B, de Witte T, Mertelsmann R et al. (2006) Treatment decision-making for older patients with highrisk myelodysplastic syndrome or acute myeloid leukemia: problems and approaches. Haematologica 91(11): 1513–1522

Acute Myeloid Leukemia 1 ▶Runx1

Acute Nonlymphocytic Leukemia ▶Acute Myeloid Leukemia

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Acute Promyelocytic Leukemia

Characteristics

Acute Promyelocytic Leukemia L I -Z HEN H E 1,3 , LORENA L. F IGUEIREDO -P ONTES 2 , E DUARDO M. R EGO 2 , P IER PAOLO PANDOLFI 1,3 1

Memorial Sloan-Kettering Cancer Center, Weill Cornell Graduate School of Medical Sciences, NY, USA 2 Medical School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil 3 Cancer Genetics Program, Beth Israel Deaconess Cancer Center and Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02155

Definition Acute promyelocytic leukemia (APL) is a distinct subtype of ▶acute myeloid leukemia (AML) characterized by the expansion of leukemic cells blocked at the promyelocytic stage of myelopoiesis. According to the French–American–British (FAB) classification of acute leukemia, APL corresponds to the M3 and M3-variant subtypes, and according to World Health Organization classification (2001) it corresponds to the subtype: AML associated with translocations involving chromosomes 15 and 17 [t(15;17)] and variants. APL accounts for 5–10% of adult AML patients in Caucasian populations and for 20–30% among patients with Latino ancestry. Invariably, APL leukemic cells harbor ▶chromosomal translocations involving the retinoic acid receptor α (RARα) gene on chromosome 17 (Table 1), which may be fused to one of five possible partner genes: promyelocytic leukemia (PML), promyelocytic leukemia zinc finger (PLZF), nucleophosmin (NPM), nuclear mitotic apparatus (NuMA), and signal transducer and activator of transcription 5B (STAT5b). This leads to the generation of fusion genes encoding distinct fusion proteins. The sensitivity of APL to the differentiating action of all-trans retinoic acid (ATRA) is differentially mediated by the various fusion proteins (see Molecular Characterization).

Acute Promyelocytic Leukemia. Table 1

Molecular genetics of acute promyelocytic leukemia

Translocation t(15;17) t(11;17) t(5;17) t(11;17) t(17;17)

Clinical and Laboratorial Presentation The symptoms of APL are similar to those of other subtypes of AML such as weight loss, fatigue, weakness, pallor, fever, and bleeding. These symptoms manifest acutely and are accompanied by petechiae, bruising, oral bleeding, or epistaxis as well as symptoms and signs related to specific bacterial infections. Patients with APL are particularly susceptible to disseminated intravascular coagulation (DIC) and extensive bleeding is common at onset. The most common sites of clinically overt extramedullary leukemic infiltration include superficial lymphonodes, liver, and spleen. The leukocyte counts are usually lower than those observed in other AML subtypes and the differential counts reveal a variable percentage of blasts in the majority of patients. In most cases, anemia and thrombocytopenia are present at diagnosis. Abnormal promyelocytes constitute more than 20% of marrownucleated cells or more than 20% of leukocytes in peripheral blood. Leukemic blasts are morphologically characterized by the presence of distinctive large cytoplasmic granules, frequent multiple Auer rods, and a folded nucleus. The hypogranular variant (M3-variant) is characterized by the expansion of blasts containing large number of small granules that may be difficult to distinguish by light microscopy, and may be wrongly classified as monoblasts. However, both in the classical and variant M3 subtypes the cells are strongly positive for myeloperoxidase staining. A more rare hyperbasophilic variant has been described. The diagnosis is usually suspected upon the morphological examination of bone marrow and peripheral blood smears. The immunophenotypic profile suggestive of APL is composed by heterogenous intensity of expression of the CD13 surface marker associated with a homogenous expression of CD33; HLA-DR is negative in the majority of cases, and the expression of CD15 and CD34 is mutually exclusive and usually dim. The genetic confirmation of gene rearrangements involving the RARα locus is mandatory and can be done by classical cytogenetics, FISH, or RT-PCR. The

Fusion proteins PML–RARα PLZF–RARα NPM–RARα NuMA–RARα STAT5b–RARα

RARα–PML RARα–PLZF RARα–NPM RARα–NuMA? RARα–STAT5b?

Response to RA Good Poor Good Good Poor?

Acute Promyelocytic Leukemia

pattern of immunofluorescence staining using an antiPML antibody is also useful for a rapid diagnosis of APL. In APL cells a nuclear microspeckled pattern is observed in contrast to other subtypes of AML in which larger and less numerous dots (nuclear bodies) are evident. DIC occurs in 75% of M3 patients accompanied by secondary fibrinolysis. The cause of coagulopathy is complex, resulting from a combination of tissue factors and cancer procoagulant-induced activation of the coagulation, exaggerated fibrinolysis due predominantly to enhanced expression of annexin II on APL blasts, and blast cell production of cytokines. Laboratory evidence of DIC (prolonged prothrombine time and partial thromboplastin time, decreased fibrinogen and increased fibrin degradation products) should be examined in all APL patients. Molecular Characterization APL has been well characterized at the molecular level and has become one of the most compelling examples of aberrant transcriptional regulation in cancer pathogenesis. Due to reciprocal translocations, the RARα gene on chromosome 17 is fused to one of five distinct partner genes (for brevity, hereafter referred as X genes; Table 1). In the vast majority of cases, RARα fuses to the PML gene (originally named myl) on chromosome 15. In a few cases RARα fuses to the PLZF gene, to the NPM gene, to the NuMA gene, or to the STAT 5B gene located on chromosomes 11, 5, 11, or 17, respectively. The various translocations result in the generation of X–RARα and RARα–X fusion genes and the coexpression of their chimeric products in the leukemic blasts. The characterization of the genetic events of APL, and the availability of techniques such as FISH and RT-PCR, render it possible to confirm the diagnosis at the molecular level and to monitor minimal residual disease. RARα is a member of the superfamily of nuclear receptors, which acts as a retinoic acid (RA)-dependent transcriptional activator in its heterodimeric form with retinoid-X-receptors (RXR). In the absence of RA, RAR/ RXR heterodimers can repress transcription through histone deacetylation by recruiting nuclear receptor corepressors (SMRT), Sin3A, or Sin3B, which in turn, form complexes with histone deacetylases (HDAC) resulting in nucleosome assembly and transcription repression. PML–RARα represses transcription not only through HDAC, but also via interactions with DNA methyltransferases (DNMTs) leading to hypermethylation at target promoters. The epigenetic changes induced by PML–RARα are stable and maintained throughout cell divisions. ATRA causes the disassociation of the corepressor complex and the recruitment of transcriptional coactivators to the RAR/RXR complex. This is

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thought to result in terminal differentiation and growth arrest of various types of cells, including normal myeloid hematopoietic cells. The X–RARα fusion proteins function as aberrant transcriptional repressors, at least in part, through their ability to form repressive complexes with corepressors such as NCoR and HDACs. PLZF–RARα can also form, via its PLZF moiety, corepressor complexes that are less sensitive to RA than the PML–RARα corepressor complexes, thus justifying the poorer response to RA-treatment observed in these patients (see also Therapeutics). The X–RARα oncoproteins retain most of the functional domains of their parental proteins and can heterodimerize with X proteins, thus potentially acting as double-dominantnegative oncogenic products on both X and RAR/RXR regulated pathways. Recently, it has been demonstrated that APL blasts present a marked defect in TGF-β signaling including Smad2/3 phosphorylation and nuclear translocation, which is similar to that in Pml null primary cells. Remarkably, RA-treatment, which induces PML–RARα degradation, resensitizes the cells to TGF-β. It is plausible that PML–RARα may inhibit TGF-β signaling through direct inhibition of the interaction between Smad3 and the cytoplasmic form of PML (cPML). Modeling APL in Mice The transgenic approach in mice has been used successfully in modeling APL and in generating faithful mouse models harboring various APL fusion genes. In vivo, transgenic mice (TM) harboring X–RARα oncoproteins develop leukemia after a long latency suggesting that the fusion proteins are necessary, but not sufficient to cause full-blown APL. In the PML–RARα TM model, mice develop a form of leukemia that closely resembles human APL, presenting blasts with promyelocytic features that are sensitive to the differentiating action of RA. A similar phenotype was observed in NuMA–RARα TM, in which leukemia was also preceded by a period of latency, but displayed a higher penetrance. On the contrary, the leukemia developed by the PLZF–RARα TM lacked the distinctive differentiation block at the promyelocytic stage, morphologically resembling more a chronic myeloid leukemia (CML) type of disease, while NPM–RARα TM developed myelomonocytic leukemia. This analysis demonstrated that the X–RARα fusion protein plays a critical role in determining leukemic phenotype as well. Moreover, it is the X moiety of the X–RARα product to determine sensitivity to ATRA, since leukemia in PML–RARα, but not in the PLZF–RARα TM, is responsive to ATRA treatment. Modeling APL in TM contributed to the understanding of the important role of the reciprocal RARα–X fusion proteins. RARα–PML

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Acute Respiratory Distress Syndrome (ARDS)

and RARα–PLZF TM do not develop overt leukemia. However, the coexpression of RARα–PML with PML– RARα increases the penetrance and the onset of leukemia development in double mutants. Strikingly, in the PLZF–RARα TM model, the coexpression of RARα–PLZF with PLZF–RARα metamorphoses the “CML-like” leukemia in PLZF–RARα TM to a leukemia with classical APL features. In addition, RARα–PLZF renders the leukemic blasts even more unresponsive to the differentiating activity of RA. At the transcriptional level, RARα–PLZF acts as an aberrant transcription factor that can interfere with the repressive ability of PLZF. Therefore, RARα–X and X–RARα fusion products act in combination to dictate the distinctive phenotypic characteristics of each APL subtype disease. Modeling of APL in the mouse is thus allowing a better comprehension of the molecular mechanisms underlying the pathogenesis of APL as well as the development of novel therapeutic strategies. Therapeutics The exquisite sensitivity of APL blasts to the differentiating action of RA makes APL a paradigm for therapeutic approaches utilizing differentiating agents. This therapeutic approach conceptually differs from the treatments involving drug and/or irradiation therapies, because instead of eradicating the neoplastic cells by killing them, it reprograms these cells to differentiate normally. The utilization of ATRA in APL patient management has reduced early death from DIC-related complications and dramatically improved the prognosis. However, treatment with ATRA alone in APL patients induces disease remission transiently and relapse is inevitable if remission is not consolidated with chemotherapy. Most contemporary therapy protocols incorporate an anthracycline (e.g., dauno or idarubicin) with ATRA during induction, followed by consolidation therapy with ATRA, anthracyclines and cytarabine, followed by maintenance therapy. Leukocyte and platelet counts at diagnosis are frequently used as risk factors for relapse: patients presenting with more than 10,000 leukocytes/μl have high risk in contrast with those with less than 10,000/μl and platelet counts higher than 40,000/μl. In the majority of cases, relapse is accompanied by RA resistance. Unlike t(15;17)/PML–RARα APL, t(11;17)/PLZF–RARα leukemias show a distinctly worse prognosis with poor response to chemotherapy and little or no response to treatment with RA, thus defining a new APL syndrome. Up to 50% of patients treated with ATRA alone develop an “ATRA syndrome” characterized by a rapid rise in circulating polymorphonuclear leucocytes and associated with weight gain, fever, occasional renal failure, and cardiopulmonary failure, which may be life threatening in some patients. The combination of ATRA and chemotherapy in the induction and

consolidation treatment phases has been proven to be an effective strategy to prevent “ATRA syndrome” and achieve long-term disease-free survival. Arsenic trioxide (As2O3), a chemical used in Chinese medicine, is also extremely effective in the treatment of APL. About 90% of APL patients treated with As2O3 alone achieve complete remission, especially in relapsed patients who are resistant to RA and/or conventional chemotherapy. RA triggers blast differentiation while As2O3 induces both apoptosis and partial differentiation of the leukemic blasts. Utilizing PML–RARα and PLZF–RARα transgenic mouse models of APL, it has been demonstrated that the association of RA and As2O3 is effective in the former but not in the latter. Considering the importance of HDAC-mediated transcriptional repression in APL pathogenesis, the utilization of histone deacetylase inhibitors (HDACIs) such as suberanilohydroxamic acid (SAHA) or sodium phenylbutyrate (SPB) in combination with RA may represent a promising experimental therapeutic approach. Preclinical studies in transgenic mouse models of APL suggest that in fact HDACIs work as growth inhibitors and inducers of apoptosis, and that these effects are potentiated by RA.

References 1. Scaglioni PP, Pandolfi PP (2007) The theory of acute promyelocytic leukemia revisited. Curr Top Microbiol Immunol 313:85–100 2. Lin H-K, Bergmann S, Pandolfi PP (2005) Deregulated TGF-β signaling in leukemogenesis. Oncogene 24:5693–5700 3. Sanz M (2006) Treatment of acute promyelocytic leukemia. Hematology Am Soc Hematol Educ Program 147–155 4. Rego EM, Ruggero D, Tribioli C et al. (2006) Leukemia with distinct phenotypes in transgenic mice expressing PML/RAR alpha, PLZF/RAR alpha or NPM/RAR alpha. Oncogene 25(13):1974–1979 5. Rego EM, Pandolfi PP (2002) Reciprocal products of chromosomal translocations in human cancer pathogenesis: key players or innocent bystanders? Trends Mol Med 8:396–405

Acute Respiratory Distress Syndrome (ARDS) Definition A severe lung disease caused by a variety of direct and indirect insults. It is characterized by ▶inflammation of the lung parenchyma leading to impaired gas exchange

ADAM17

with concomitant systemic release of inflammatory mediators causing inflammation, hypoxemia, and frequently resulting in multiple organ failure. ▶Sivelestat

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ADAM Definition A Disentegrin and Metalloprotease; ADAM Molecules.

Acute Toxicity Studies ADAM10 ▶Single Dose Toxicity Studies

Definition

Acyclovir Definition A deoxyguanosine analog lacking the equivalent of 2υ and 3υ hydroxyl groups; commonly used in the treatment of herpesvirus infections. ▶HSV-TK/Ganciclovir Mediated Toxicity ▶Human Herpesvirus 6

ADAM10, synonym kuzbanian, is a member of a family of zinc-dependent transmembrane metalloproteases, involved in neuronal development in vertebrates and Drosophila and expressed in all epithelial tissues. Kuzbanian ADAM10 ▶Doublecortin ▶ADAM Molecules

ADAM17 A LEKSANDRA F RANOVIC , S TEPHEN L EE

AD Definition Androgen-dependent. ▶Cyclin G-Associated Kinase

Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ONT, Canada

Synonyms TACE; Tumor necrosis factor-alpha converting enzyme; CD156b antigen

Definition

ADAbp ▶CD26/DPPIV in Cancer Progression and Spread

ADAM17 is a zinc-dependent ▶metalloprotease belonging to the ▶ADAM (A disintegrin and metalloproteinase) family of type I transmembrane proteins. ADAM17 is involved in the ectodomain shedding of a wide variety of membrane-bound ligands and cytokines that are implicated in diverse biological processes including growth and ▶inflammation.

Characteristics

ADA-CP ▶CD26/DPPIV in Cancer Progression and Spread

Structure The 50 kb ADAM17 gene, which is located at chromosome 2p25, consists of 19 exons and encodes an 824 amino acid protein. ADAM17 is synthesized as an inactive precursor protein consisting of five domains: the

A

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ADAM17

pro-, metalloprotease, cysteine-rich, transmembrane and cytoplasmic domains. Prior to ADAM17 maturation, a conserved cysteine residue within the pro-domain interacts with the active site zinc atom maintaining the enzyme biologically inert. The active site of the metalloprotease domain contains a histidine consensus sequence (HExxHxxGxxH) that coordinates zinc atoms and water required for the enzymatic processing of ADAM17 substrates. Removal of the pro-domain occurs through a ▶furin cleavage site (RVKR), by an unidentified furin or proprotein convertase, enabling the active site zinc to interact with the required histidine residues and to generate the active protease. While the structural and functional aspects of the pro- and metalloprotease domains have been studied extensively and are well defined, the precise functions of the remaining ADAM17 domains are still somewhat obscure. The cysteine-rich domain consists of two subdomains: the disintegrin and EGF-like domains. A role in cellular ▶adhesion has been proposed for the disintegrin domain. In support of this hypothesis, ADAM17 has been shown to interact with at least one ▶integrin (α5β1) and modulate cell migration as a result of this interaction. It has also been demonstrated that the cysteine-rich domain is indispensable for the ectodomain shedding of select ADAM17 substrates and thus, might function in substrate recognition through the recruitment of accessory proteins or direct contact with the substrates themselves. The transmembrane domain tethers mature ADAM17 in the cell membrane where it exerts most of its physiological functions. Finally, the cytoplasmic domain comprises several ▶Src homology 2 (SH2) and 3 (SH3) domain binding sites as well as phosphorylation sites, and is likely involved in regulatory ▶signal transduction pathways. Expression and Regulation ADAM17 mRNA is ubiquitously expressed in most adult tissues, albeit at lower levels than those observed in fetal tissues at various stages of development. The ADAM17 zymogen is synthesized in the rough endoplasmic reticulum and is processed in the late Golgi compartment to produce the mature protease lacking the inhibitory pro-domain. This maturation step seems to entail a constitutive process as the majority of cellular ADAM17 exists in its mature form. The greater part of ADAM17 protein is localized in the perinuclear area while the remaining fraction resides at the cell surface, as expected. Notably, it appears that the membrane-bound ADAM17 population is exclusively in the processed form. This surface pool of ADAM17 is relatively stable with a half-life of ~8 h. The mechanism by which ADAM17 function is regulated is not entirely clear, however, two methods by which the protease can be activated have been described. The first method involves the activation of

ADAM17 by growth factors, such as the ▶fibroblast growth factor (FGF) and the ▶platelet-derived growth factor (PDGF). ADAM17-mediated ligand shedding can also be induced by non-physiological stimuli such as phorbol esters (▶Phorbol myristate acetate). Treatment of cells with phorbol esters, such as ▶PMA, results in increased ligand shedding without affecting the quantity or localization of endogenous ADAM17 in the cell. There is conflicting evidence with respect to the mechanism by which this stimulation occurs. One study demonstrated that PMA exerts its effects by activating the ▶extracellular signal-regulated kinase (ERK) signaling pathway, which results in the phosphorylation of ADAM17 at Thr735 in its cytoplasmic tail, while another group showed that the cytoplasmic tail of ADAM17 is not required for PMA-induced ligand shedding. Although there is no evidence that phorbol esters regulate ADAM17 activity in vivo, the ▶ERK signaling pathway has also been implicated in growth factor stimulated ADAM17 activation. For this reason, the ERK signaling pathway will likely be the focus of future studies aimed at delineating the mechanisms involved in the positive regulation of ADAM17 activity. In addition to stimulating ADAM17-mediated ligand cleavage, the treatment of cells with PMA also triggers the establishment of a negative feedback mechanism. Following an increase in ADAM17 activity and ligand shedding, the protease itself is internalized and degraded in response to prolonged treatment with PMA. This negative regulatory mechanism is probably in place to prevent over-stimulation of ligand-activated signaling pathways. In attempt to identify potential regulators of ADAM17 activity, two ADAM17 binding partners were uncovered by yeast two-hybrid screens: synapse associated protein 97 (SAP97) and protein tyrosine phosphatase PTPH1. Overexpression of either molecule results in decreased ligand shedding implicating them in the negative regulation of ADAM17 activity. Whether either of these two proteins regulates ADAM17 activity in vivo remains to be seen. The only known endogenous inhibitor of ADAM17 is the tissue metalloprotease inhibitor, TIMP3. The mechanism by which TIMP3 expression results in reduced ADAM17 activity is unknown. Biological Function ADAM17 was initially identified as the secretase responsible for the cleavage of tumor necrosis factor-alpha (TNFα), a pro-inflammatory cytokine. The generation of transgenic mice expressing ADAM17 lacking the zinc-binding sequence in its metalloprotease domain (ADAM17ΔZn/ΔZn) allowed for the identification of a multitude of additional ADAM17 substrates. The vast majority of the ADAM17ΔZn/ΔZn mice die at birth as a result of severe deficiencies in skin, muscle, lung and

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neuronal system development that cannot be entirely attributed to loss of TNFα shedding. This indicates the existence of other biologically relevant ADAM17 substrates. Interestingly, the few animals that do survive display a phenotype that is comparable to that of ▶transforming growth factor alpha (TGFα) or ▶epidermal growth factor receptor (EGFR) knockout mice. This includes the failure of eyelids to fuse as well as defects in skin and hair follicle development. Upon further investigation it was confirmed that ▶TGFα, an ▶EGFR ligand, is in fact an ADAM17 substrate. Moreover, ADAM17 appears to be the major convertase of several ▶EGFR ligands which are involved in a variety of cellular processes including cellular proliferation, survival, migration, and differentiation. The bulk of ADAM17 substrates, including the EGFR ligands, are involved in cell development and differentiation. Other examples include the neurogenic signaling molecule ▶Notch, the neurotrophin receptor TrkA, and the EGFR-family receptor HER4. The remaining substrates can be classified as those involved in cellular immunity and regulation of immunogenic responses, like TNFα. These substrates include the TNF receptors (TNF-RI and TNF-RII), the chemokine fractalkine, and the leukocyte adhesion molecule L-selectin to name a few. While many ADAM17 substrates have been identified to date, there is no obvious sequence or structural homology between their cleavage sites. How ADAM17 achieves substrate specificity is a key question that remains to be answered. Nonetheless, it is evident that ADAM17 substrates play an important role in a broad range of fundamental cellular processes.

malignancy. Thus ADAM17 is most highly expressed in advanced tumors, suggesting that ADAM17 and its substrates play a role in tumor progression. In accordance with these observations, there is a growing amount of evidence supporting the use of antiADAM17 drugs in the treatment of cancer. Several studies have shown that inhibition of ADAM17 activity using a variety of approaches is sufficient to inhibit EGFR ligand release and to prevent the proliferation, migration, and survival of squamous cell, ▶kidney cancer, ▶bladder cancer and ▶breast cancer cell lines in vitro. It was recently demonstrated that ▶siRNAmediated silencing of ADAM17 inhibits the release of soluble TGFα in highly malignant ▶renal carcinoma cells, thereby abolishing their ability to form tumors in nude mice. This was the first in vivo evidence that ADAM17-mediated ligand cleavage is a pivotal step in the establishment of the TGFα/EGFR autocrine ▶(Autocrine signaling) growth stimulatory loop and thus in tumorigenesis. Another study revealed that targeting ADAM17, using a ▶small molecule inhibitor, prevents ▶heregulin cleavage and hence ▶HER3 activation in non-small cell lung cancer cells. Not only did this inhibition abolish tumor growth in vivo but it also enhanced the sensitivity of the cancer cells to gefitinib, an anti-EGFR based therapy. This result suggests that the concomitant inhibition of ADAM17 and EGFR should improve patient responsiveness to such agents and increase survival. Thus targeting ADAM17 is a promising new alternative to traditional EGFR-based therapies in the treatment of human cancer.

Clinical Relevance Due to its involvement in TNFα processing, ADAM17 is considered to be a central mediator in human inflammatory diseases such as rheumatoid arthritis. Direct inhibition of TNFα or ADAM17 in arthritis-affected cartilage has been shown to reduce inflammation. For these reasons ADAM17-based therapies, such as zincchelating sulfonamide hydroxamates, are in use for the treatment of such diseases. In addition to its role in inflammatory diseases, ADAM17 is becoming increasingly implicated in the development and progression of cancer as a result of its role in the processing of EGFR ligands. The upregulation of EGFR expression and signaling is a common feature in human cancer. Unfortunately, ▶EGFR inhibitors have rendered disappointing results in ▶clinical trials and there is an apparent resistance of several cancer cell lines to these agents. Importantly, ADAM17 is also overexpressed in several neoplastic tissues including ▶breast carcinomas, ▶colon carcinomas, pancreatic ductal adenocarcinomas, and ▶ovarian carcinomas. There is also a positive correlation between ADAM17 expression and the aggressiveness of the

Summary ADAM17 was originally characterized for its role in TNFα processing and the regulation of inflammatory responses. It has since been demonstrated that ADAM17 is also a physiological convertase of a wide variety of signaling molecules implicated in the development and progression of cancer. The importance of ADAM17 in these oncogenic pathways is highlighted by the finding that silencing of ADAM17 is sufficient to abolish tumor formation in vivo. These results validate ADAM17 as a rational therapeutic target and endorse the use of ADAM17 inhibitors in the treatment of human cancer.

References 1. Blobel CP (2005) ADAMS: Key components in EGFR Signalling and Development. Nat Rev Mol Cell Biol 6:32–43 2. Franovic A, Robert I, Smith K et al. (2006) Multiple acquired renal carcinoma tumor capabilities abolished upon silencing of ADAM17. Cancer Res 66:8083–8090 3. Lee DC, Sunnarborg SW, Hinkle CL et al. (2003) TACE/ ADAM17 processing of EGFR ligands indicates a role as a

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physiological convertase. Ann New York Acad Sci 995:22–38 4. Seals DF, Courtneidge SA (2003) The ADAMs family of metalloproteases: multidomain proteins with multiple functions. Genes Dev 17:7–30 5. Zhou BS, Peyton M, He B et al. (2006) Targeting ADAMmediated ligand cleavage to inhibit HER3 and EGFR pathways in non-small cell lung cancer. Cancer Cell 10:39–50

ADAM Molecules J O¨ RG R INGEL 1,2 , M ATTHIAS LO¨ HR 2 1

Department of Medicine A, University of Greifswald, Greifswald, Germany 2 Molecular Gastroenterology Unit, German Cancer Research Center (DKFZ E180) Heidelberg and Department of Medicine II, Mannheim Medical Faculty, University of Heidelberg, Heidelberg, Germany

Synonyms A disintegrin and metalloprotease; Disintegrin metalloproteases; Metalloprotease disintegrin cysteine-rich; MDC

Definition A disintegrin and metalloprotease (ADAM) molecules share a common domain structure: a propeptide (prodomain), a metalloproteinase domain, a disintegrin domain, a cysteine-rich region, an epidermal growth factor (EGF)-like domain, a transmembrane region, and a cytoplasmatic domain (Fig. 1). Several ADAMs exist in both membrane-bound and secreted isoforms; the functional significance of this, in most cases, is still unclear. A subset of the presently known ADAM molecules shows catalytic activity. To date, at least 40 ADAMs have been identified in a variety of species.

A large proportion (13 ADAMs) is exclusively expressed in the male reproductive system, and only a minority can be found throughout all tissues.

Characteristics ADAM molecules, with their unique potential to combine ▶adhesion, ▶proteolysis, and signaling, are involved in a variety of cellular functions. Some have been shown to play an important role in diverse biological processes such as fertilization, myogenesis, cell signaling, inflammatory response, and cell–cell/ cell–matrix interactions. However, the respective key function has remained elusive for most ADAMs. Dysregulation of ADAM molecules has been shown in various diseases. However, there is a growing amount of reports about the role of ADAM molecules in malignant tumors. Metalloprotease Function To regulate biological activity, in normal as well as in malignant cells a wide variety of proteins are synthesized as inactive precursors that are subsequently converted to their mature active forms by ADAM molecules. A well-studied member of the ADAM molecules is ADAM17/▶TACE, which was originally described as being responsible for the proteolytic cleavage of the soluble form of ▶TNF-α. Subsequent studies have shown that ADAM17/TACE is also involved in the shedding of other biologically active proteins, including growth factors (erbB4/HER-4 and ▶transforming growth factor (TGF)-α), surface molecules (L-selectin), and interleukin (IL) receptors (IL-R; IL-1R type II and IL-6R; Fig. 2). TACE cleavage function in the activation of EGF receptor (EGFR) and EGFR signaling systems, which regulate the proliferation and motility of ▶squamous cell carcinoma cells in vitro. The key role of the EGFR/ EGFR ligand system for cancer development is wellknown. In this context, the transactivation of EGFR via ADAM17/TACE is of special interest. ADAM

ADAM Molecules. Figure 1 Domain structure of ADAMs. The ADAMs consist of a propeptide domain, a metalloprotease domain, a disintegrin domain, a cysteine-rich region, a EGF-like, a transmembrane domain, and a cytoplasmatic domain.

ADAM Molecules

metalloproteases such as ADAM9 and ADAM17/ TACE regulate G protein-coupled receptor induced cell proliferation and survival. Aberrant expression of a proteolytic active ADAM17/TACE has been reported in pancreas ▶cancer cells. The increasing prevalence of ADAM17/TACE expression with higher pancreatic intraepithelial neoplasia (PanIN) grade as precursor lesions underlines the role of this molecule in ductal pancreatic adenocarcinoma development. Gene silencing experiments showed a critical role of ADAM17/TACE in the invasion process of pancreatic cancer cells. The aberrant expression of proteolytically active ADAM17/TACE may result in an uncontrolled turnover of activated target molecules, such as TNF-α, TGF-α, and MUC1 (▶mucius).

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Silencing of ADAM17 in human renal carcinoma cell lines corrects critical features associated with cancer cells, including growth autonomy, tumor inflammation, and tissue invasion. In addition, these cells fail to form in vivo tumors in the absence of ADAM17. It has also been shown that ADAM17/ TACE is overexpressed in mammary cancer and other cancer types (Table 1). ADAM12, which is upregulated, for example, in breast and gastric cancer (Table 1), is expressed in two splice forms, the transmembrane ADAM12-L and the soluble ADAM12-S. In a mouse breast cancer model, ADAM12 decreased tumor cell apoptosis and increased stromal cell apoptosis. The shedding of heparin-binding EGF by ADAM12 was shown to

ADAM Molecules. Figure 2 Schematic overview about the published functions and interactions of ADAM17/TACE.

ADAM Molecules. Table 1 as published ADAM molecule ADAM2 ADAM8 ADAM9 ADAM10 ADAM11 ADAM12 ADAM15 ADAM17/TACE ADAM19 ADAM21 ADAM22 ADAM23 ADAM28 ADAM29

Overview about the aberrant expression of ADAM molecules in different human cancer types

Human cancer type Renal Brain, prostate, lung adenocarcinoma Prostate, colon, pancreas, liver, gastric, nonsmall cell lung cancer, renal Breast, colon, prostate, pheochromocytoma, neuroblastoma Glioma, breast Breast, gastric, glioblastoma, liver, aggressive fibromatosis, giant cell tumor of the bone, brain Prostate, breast, lung, ovarian, gastric, brain, bladder Pancreas, renal, breast, colon, liver, brain, squamous cell carcinoma cells Brain ADAM21-like (ADAM21-L) T-cell leukemia Brain Brain, gastric, breast (pancreas) Nonsmall cell lung carcinoma Chronic lymphocytic leukemia

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promote human ▶glioblastoma. In addition, in liver cancers, ADAM12 and ADAM9 expression is associated with tumor aggressiveness and progression. ADAM9 is also described to shed heparin-binding EGF. Overexpression of cytoplasmatic ADAM9 in pancreatic cancer is associated with poor differentiation and shortened survival. It is of particular interest for cancer development that ADAM molecules reported to shed cell-associated adhesion molecules such as L-selectin, MUC1, and glycoprotein (Gb) 1bα. In general, the metalloprotease protease function might be involved in various processes of cancer cells and be relevant to promote cell migration and invasion. Adhesion Function ADAM molecules are potential ligands for ▶integrins due to the presence of binding sites within the disintegrin domain. Only one ADAM (ADAM15) contains the ▶RGD integrin-binding motif and it can therefore interact not only with the αvβ3 integrin but also with the αvβ5. Additional ADAM–integrin interactions have been reported: a large number of ADAMs (1, 2, 3, 9, 12, and 15) with α9β1; ADAM9 with α6β1 and αvβ5; and ADAM28 with α4β1. Considering the recently published data on the interaction of ADAM17/TACE with the α5β1 integrin in ▶HeLa cells, it is also conceivable that ADAM17/ TACE may influence the migration and invasion in other cancer types. We are beginning to gather insights into ADAM– integrin and ADAM–▶extracellular matrix (ECM) interactions. The interplay with integrins and ECM compounds might promote ADAM function in malignant cells. Thus, cell binding to ADAM12 via beta3 integrin results in the formation of focal adhesions. Furthermore, it was shown that the cystein-rich domain of ADAM12 supports tumor cell adhesion through syndecan. ADAM23 with its inactive metalloprotease domain is exclusively involved in cell-adhesion. It was demonstrated that the interaction between the disintegrin-loop of ADAM23 and the αvβ3 integrin promotes the adhesion of ▶neuroblastoma and ▶astrocytoma cells. In contrast to the described overexpression or de novo expression in various cancer types, downregulation of ADAMs might also promote cancer development. Thus, ADAM23 gene silencing in breast cancer by promoter ▶hypermethylation may result in abnormal cell–cell interactions favoring cell migration. Signaling Function Beside the involvement of ADAM molecules in the EGFR transactivation, only few data about the signaling function of ADAM molecules are known. It is

intriguing that interactions between integrins and/or ECM- and ADAM-binding domains may induce outside–in signaling. ADAM inside–out signaling pathways might regulate shedding and/or adhesion function of the molecules. However, many ADAM cytoplasmatic domains contain binding motives for the Src homology region 3 (SH3 Domain) of various intracellular proteins. Tyrosine residues could be substrates for tyrosine kinases or could act as ligands for phosphotyrosine-binding domains, when phosphorylated. A number of binding partners have been identified for the cytoplasmatic domains of various ADAM molecules. Interaction of the cytoplasmatic domain of ADAM9 and 15 with endophilin and SH3PX1are reported. ADAM12 and ADAM15 are associated with ▶Src protein-tyrosine kinases. However, the shedding of the L1 adhesion molecules in breast cancer cells might involve a Scr protein-tyrosine kinase. Furthermore, mitotic arrest-deficient-2 (▶MAD2) was found as binding partner of ADAM17/TACE and ADAM15; MAD2β is linked to ADAM9. To date, the physiological role of this interactions as well as the implication in malignancies is speculative. Other Functions Within the ADAM molecules, ADAM11 might play a special role in malignancies. ADAM11 represents a candidate tumor suppressor gene for human breast cancer. This is based on its location within a minimal region of chromosome 17q21 previously defined by tumor deletion mapping. Taken together, there are rapidly increasing data supporting a critical implication of ADAM molecules in malignancies. But there are still more questions than answers on the function of ADAMs in human cancer and cancer development.

References 1. Seals DF, Courtneidge SA (2003) The ADAMs family of metalloproteases: multidomain proteins with multiple functions. Genes Dev 17:7–30 2. Gschwind A, Hart S, Fischer OM et al. (2004) TACE cleavage of proamphiregulin regulates GPCR-induced proliferation and motility of cancer cells. EMBO J 22:2411–2421 3. Ringel J, Jesnowski R, Moniaux N et al. (2006) Aberrant expression of a disintegrin and metalloproteinase 17/tumor necrosis factor-alpha converting enzyme increases the malignant potential in human pancreatic ductal adenocarcinoma. Cancer Res 66(18):9045–9053 4. Iba K, Albrechtsen R, Gilpin BJ et al. (1999) Cysteine-rich domain of human ADAM 12 (meltrin a) supports tumor cell adhesion. Am J Pathol 54:1489–1501 5. Karan D, Lin FC, Bryan M et al. (2003) Expression of ADAMs (a disintegrin and metalloproteases) and TIMP-3 (tissue inhibitor of metalloproteinase-3) in human prostatic adenocarcinomas. Int J Oncol 23:1365–1371

Additive Effects

Adaptive Immunity

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Adaptor Proteins

Definition

Definition

Adaptive immune responses occur when the host comes into contact with immunogenic molecules or organisms. These stimulate the expansion of the antigenspecific lymphocytes, antibody secreting B cells and T cells of the cytotoxic and helper phenotypes, which recognize cells expressing foreign antigens. B cells and T cells are the effector cells of the adaptive immune response. They bear antigen specific receptors of great diversity that are generated by random rearrangement of gene segments and other mechanisms. This results in a vast array of antigen-specific receptors clonally distributed on T and B cells, which clonally expand on contact with antigen. As the immunogen is cleared these clonal populations shrink but leave behind longlived populations of memory cells that are easily recalled on subsequent exposure to the same immunogen. Unlike the innate immune response, adaptive responses are not immediate, requiring 3–5 days for clonal expansion and differentiation of effector lymphocytes. The adaptive immune system allows for a strong immune response as well as immunological memory, where a tumor antigen is “remembered.” The adaptive immune response is antigen-specific and requires the recognition of tumor antigens during a process called antigen presentation. Antigen specificity allows for the generation of responses that are tailored to cancer cells and the ability to mount these tailored responses is maintained in the body by “memory cells.” Cells of the adaptive immune system are B- and T-lymphocytes. Adaptive humoral responses are mediated by tumor specific antibodies.

lack any intrinsic enzymatic activity themselves but instead mediate specific protein-protein interactions leading to formation of protein complexes.

▶Immunoediting ▶Specific Immunity ▶Immunoprevention of Cancer ▶DNA Vaccination ▶Inflammation

▶RAS Activation

ADAR Definition

A family of “adenosine-deaminase-acting-on-RNA” enzymes that convert adenosines to inosines in double-stranded RNA substrates. This process, known as A → I RNA editing, changes the sequence of the target dsRNA molecule so that it differs from the parent DNA strand. At translation, the inosine is interpreted as a guanosine (G). ▶ALU Elements

ADCC Definition Antibody-dependent cell-mediated cytotoxicity. ▶Immunoprevention of Cancer ▶Diabody ▶EpCAM

Adaptive Response Additive Effects Definition The process of adaptation, which allows survival under adverse conditions, is called adaptive response ▶Detoxification

Definition

Additive effects mean that the effects of ▶xenobiotics simply summate.

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Adduct

Adduct Definition In biology, adduct is a complex that forms when a chemical binds to a biological molecule, such as DNA or protein. ▶Biomonitoring ▶Adducts to DNA

(▶surrogate markers). DNA adducts are mechanistically more relevant to ▶carcinogenesis than the internal dose of a carcinogen, since they take into account interindividual differences in metabolism and of DNA repair capacity (Fig. 1). Several hundred DNA adducts, many with miscoding properties, are known to be produced by some 20 classes of carcinogens and through endogenous oxidative processes. DNA adducts are used in human ▶biomonitoring as dosimeters of early biological effects and predictors of cancer risk. These ▶biomarkers also provide tools for studying disease pathogenesis, etiology and for verifying preventive measures in human cancer.

Characteristics

Adducts to DNA H ELMUT B ARTSCH Division of Toxicology and Cancer Risk Factors, German Cancer Research Center (DKFZ), Heidelberg, Germany

Synonyms DNA-bound carcinogens

Definition

DNA-adducts reflect the amount of a ▶xenobiotic that covalently reacts with nucleic acid bases at the target site (biologically effective dose) or in surrogate tissues

Rationale for Using DNA Adducts as Biomarkers for Exposure and Adverse Effects Evidence for the biological significance of DNA adducts in carcinogenesis is supported by the following: . Over 80% of identified or suspected human carcinogens react often after metabolic activation with nucleic acids and proteins to form macromolecular adducts . Carcinogen-DNA adducts represent the initiating events leading to mutations in ▶oncogenes and ▶tumor suppressor genes, and to ▶carcinogenesis . The carcinogenic potency of a large number of carcinogens is proportional to the extent they bind to rodent liver DNA . Humans with inherited or acquired defects in ▶DNA repair have an elevated risk of developing cancer

Adducts to DNA. Figure 1 Paradigm for the multistage process of ▶carcinogenesis with DNA adducts as initiating lesions. They are used mostly as biomarkers for the biologically effective dose both of exogenous carcinogens and of DNA-reactive agents produced by endogenous processes, such as chronic oxidative stress. Over the past 40 years emphasis has been placed on the development of accurate and sensitive methods for the detection and quantitation of DNA adducts.

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Biological effect markers are defined as indicators of irreversible genetic damage that result from genotoxic interactions at the target site. As DNA adducts do not often cause completely irreversible lesions, because the DNA undergoes repair (which may not be complete), they are not in the strict sense biological effect markers. However, as carcinogen dosage is linked to cancer outcome, and permanent mutations can be caused by DNA adducts, they are associated with cancer risk. This has been shown for many carcinogens and their DNA adducts, when critical toxico-kinetic parameters are taken into account. These include the steady state adduct concentration, the amount of the miscoding adduct compared to others of lesser biological relevance, the adduct half-life after carcinogen exposure has stopped, the organ, cell and gene selectivity of the adduct (Fig. 2).

and/or subpopulations of non-dividing cells can survive for several months or even years. Since somatic genetic or cytogenetic effect markers are neither chemical- nor exposure-specific, only macromolecular adducts allow identification of the structure and thus the determination of the genotoxic exposure sources. Also, cytogenetic markers are more easily affected by lifestyle and environmental components (confounders) that often act as uncontrolled or uncontrollable variables in biomonitoring and molecular epidemiology studies. In addition, at equal levels of carcinogen exposure, DNA adduct levels are a measure for the host’s capability of carcinogen metabolism and adduct repair and can be used to determine the overall effect of genetic polymorphisms on DNA damage and cancer susceptibility by a given carcinogen.

Advantages and Disadvantages of DNA Adducts Compared to Other Biomarkers For human biomonitoring both DNA and protein adducts can be used for exposure assessment as long as the response in target organs versus surrogate tissue is shown to be proportional. The latter has to be determined individually for each carcinogen. The advantage of certain protein adduct measurements is that they often reflect cumulative past exposure (of several months), while the majority of DNA adducts is rapidly repaired or lost after exposure has ceased. However, a small portion of DNA adducts either with slow repair

Cellular Defense: Repair of DNA Adducts DNA repair (▶repair of DNA) systems such as ▶base and ▶nucleotide excision repair, O6-alkylguanineDNA alkyltransferase and ▶mismatch repair operate in human cells to remove adducted and oxidatively damaged DNA bases. Deficiency in nucleotide excision repair genes cause ▶Xeroderma pigmentosum (XP) and a high-rate occurrence of skin cancers, as well as a high susceptibility to UV-light and ▶polycyclic aromatic hydrocarbon-induced carcinogenesis. A defective mismatch repair system causes hereditary non-polyposis colorectal cancer (HNPCC).

Adducts to DNA. Figure 2 Measurement of carcinogen-DNA adducts in target tissue and cells or in surrogates. The predictive value of DNA adducts for disease risk increases with the proximity of measurements to critical lesions. Accordingly, from right to left, the specificity of this biomarker increases for predicting disease outcome.

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Genetic defects in these DNA repair functions or inhibition of repair proteins may have dramatic consequences when DNA adducts, DNA mismatches and DNA loops are not repaired prior to cell replication and when damaged cells are not eliminated by apoptosis. Thus, characterization of germ-line and somatic mutations in DNA-repair genes can identify high-risk subjects who especially in the case of bi-allelic mutations suffer from functional defects of proteins that repair DNAadducts leading to genetic instability and cancer. Adduct Measurements in Disease Epidemiology Cross-sectional and longitudinal studies in cancer epidemiology assess the relationship between carcinogen exposures and biomarker (adduct) levels. Adduct measurement exposed in humans allow the detection, quantification and structural elucidation of specific DNA damage. Findings from such studies include the detection of background exposures manifested in “unexposed” populations and a significant interindividual variation in adduct levels in persons with comparable exposure. The latter is in part due to genetic variation in carcinogen metabolism and DNA-repair processes. Positive correlations between the extent of occupational and environmental exposures, adduct levels and adverse effects, e.g. mutations in oncogenes and tumor suppressor genes have been observed. For example, large-scale studies on geographical variations of ▶hepatocellular carcinoma and exposure to ▶aflatoxins have used aflatoxin-bound albumin adducts, urinary aflatoxin B1N7-guanine adducts, and mutational hotspots in the ▶TP53 gene as biomarkers. They revealed more than an additive interaction between the hepatocarcinogen and hepatitis B virus (▶hepatitis viruses) infection. ▶Case-control studies in disease epidemiology allow the evaluation of the role of biomarkers as cancer risk factors and the exploration of underlying mechanisms, but such studies cannot establish causality between biomarker response and cancer causation. This is especially the case when the latency period (between exposure and cancer) is long. Here, adduct measurements are of greater relevance for cancer risk estimation when exposure has been continuous. An optimal study design that can establish causality is a nested case-control study that uses questionnaire data and biological sample collection prior to disease manifestation. Once diagnosis of cancer has been made, cases are matched to appropriate controls and their stored samples analyzed. The predictive value in terms of specificity and sensitivity of a DNA adduct biomarker in biological samples can thus be determined. Association of DNA Adducts with Cancer Risk Not all types of DNA adducts are associated with the same cancer risk. Using alkylating agents, aflatoxins and aromatic amines (that induced 50% tumor

incidence) DNA adduct levels were compared in animal experiments. A 40- to 100-fold difference in the ability of DNA adducts to induce the same tumor incidence in target tissues was detected. Thus, it is difficult to predict the tumor induction potential of unknown DNA adducts. In the past, assays for DNA adduct determination provided mostly information on the total amount of adducts in bulk genomic DNA. However, new methods are capable of pinpointing adduct profiles in critical target genes (Fig. 2). Because of the multistage and complex nature of human carcinogenesis, carcinogenDNA adducts per se cannot precisely and quantitatively predict an individual’s cancer risk. At present risk estimation is limited to a group level. Background DNA-adduct Levels: Sources, Variations and Cancer Risk Prediction The major analytical challenge has been to detect levels of DNA adducts at a concentration of 0.1–1 adducts per 108 unmodified DNA bases using only low microgram amounts of DNA, and with high specificity and accuracy. Several methods are available including 32 P-postlabeling assays often in combination with immunopurification and liquid chromatography coupled to electrospray ionization-mass spectrometry. By using ultrasensitive detection methods background DNA adduct levels have been found in organs of unexposed humans and untreated animals. These are due to physiological lipid peroxidation (LPO) processes, whereby endproducts, such as 4-hydroxynonenal and malondialdehyde when formed in excess in the body, can react with DNA to yield background levels of a variety of exocyclic DNA adducts. These types of adducts generally increase with age, but are significantly increased in human subjects affected by risk cancer factors that induce chronic oxidative stress. These include chronic inflammatory processes and infections, nutritional imbalances, and metal storage disorders. In addition, oxidized DNA bases and LPO-derived DNA adducts occur more frequently in cells with impaired antioxidant defense. Exogenous carcinogens can also induce oxidative stress causing agent-specific DNA adducts and secondary oxidative DNA base damage. The biological relevance of both oxidative and LPOderived DNA damage is supported by the fact that these adducts are miscoding lesions which are recognized by specific DNA-repair enzymes. There is a growing evidence that both types of DNA lesions, either derived from exogenous and endogenous agents, play a role in the initiation and progression of the multistage carcinogenesis process, as well as other chronic degenerative diseases. Current research addresses some open questions: . What is the significance of endogenously formed DNA adducts in human cancer, particularly associated with chronic inflammatory conditions and also in relation to spontaneous tumors?

Adenocarcinoma

. Has the proportion of cancers that result from environmental agents been overestimated compared to those arising from endogenous DNA damaging processes? . Can one protect humans against endogenously derived DNA damage and prevent chronic degenerative diseases by administration of chemopreventive (antioxidative) agents, using DNA-adduct measurements to verify their efficacy? . Will LPO-derived DNA adducts serve as potential prognostic markers for assessing progression of chronic inflammatory cancer-prone diseases? Contributions of DNA-adduct Measurements to Disease Etiology and Pathogenesis New insights are gained since . Adduct analysis permits identification of hitherto unknown exogenous and endogenous DNA-reactive agents and of carcinogenic components in complex exposures, thus increasing the power to establish causal relationships in molecular epidemiology. . Highly exposed individuals can be more readily identified, and exposure to carcinogenic risk factors can be minimized or even avoided. . Subgroups in the population (so called pharmacogenetic variants) that are, due to genetic polymorphism of xenobiotic-metabolizing and DNA-repair enzymes, more susceptible to carcinogens, are identifiable by a combination of genotyping and DNA-adduct measurements. . Repeated applications of dosimetry methods for macromolecular adducts can evaluate the effectiveness of primary and secondary interventions, either by reduction of carcinogen exposure or through (chemo-)preventive strategies. . Incorporation of DNA-adduct measurements (and of other critical endpoints involved in carcinogenesis) can reduce (i) the enormous uncertainties currently associated with high-to-low dose and species-tospecies extrapolation and (ii) yield information on inter-individual risk assessment procedures. . The role of specific carcinogen exposures may be retrospectively implicated in cancer etiology by analyzing decades after the period of exposure, mutational fingerprints in tumors that arise from exogenous and endogenous agents after their reaction with DNA. Specific mutational signatures, detected in the tumor suppressor gene TP53, were associated with distinct past carcinogen exposures (e.g. tobacco smoke, aflatoxin B1, vinyl chloride, and UV-light) or inflammatory disease state (such as chronic inflammatory bowel diseases). . Adducts and derived mutations should allow to study pathogenesis and preventive approaches of chronic degenerative diseases other than cancer (e.g. atherosclerosis, Alzheimer disease).

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References 1. Toniolo P, Boffetta P, Shuker DEG et al. (eds) (1997) Application of biomarkers in cancer epidemiology. IARC Sci Publ 142. IARC, Lyon, pp 143–158 2. Gupta RC, Lutz WK (eds) (1999) Background DNA damage. Mutat Res 424:1–288 3. Vineis P, Perera F (2000) DNA adducts as markers of exposure to carcinogenesis and risk of cancer. Int J Cancer 88:325–328 4. Bartsch H, Nair J (2006) Chronic inflammation and oxidative stress in the genesis and perpetuation of cancer: role of lipid peroxidation, DNA-. damage and repair Langenbecks Arch Surg 391:499–510 5. Singh R, Farmer PB (2006) Liquid chromatographyelectrospray ionization-mass spectrometry: the future of DNA adduct detection. Carcinogenesis 27:178–196

Adenine Nucleotides Definition Energy-carrying molecules composed of the purine base adenine, the sugar ribose, and one (AMP), two (ADP) or three (ATP) covalently-attached phosphate groups. ▶Adenosine and Tumor Microenvironment

Adenocarcinoid Definition An appendiceal malignancy that contains both an epithelial neoplasm and a neuroendocrine (carcinoid) neoplasm simultaneously. ▶Appendiceal Epithelial Neoplasms ▶Carcinoid Tumors

Adenocarcinoma Definition A form of carcinoma that originates in glandular tissue. To be classified as adenocarcinoma, the cells do not necessarily need to be part of a gland, as long as they

A

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Adenomas

have secretory properties. This form of carcinoma can occur in some higher mammals, including humans. The term adenocarcinoma is derived from “adeno” meaning “pertaining to a gland” and “carcinoma” which describes a cancer that has developed in the epithelial cells, i.e. cells that line the walls of various organs. This type accounts for about 40% of ▶lung cancer. It is usually found in the outer part of the lung. ▶Vanadium ▶Bile Duct Neoplasms ▶Appendiceal Epithelial Neoplasms

Adenosine and Tumor Microenvironment J ONATHAN B LAY Department of Pharmacology, Dalhousie University, Halifax, NS, Canada

Synonyms Adenosine; Adenine nucleoside; purine nucleoside; adenine-9-β-D-ribofuranoside

Definition

Adenomas ▶Colorectal Premalignant Lesions

Adenosine is a small molecule that is released into tissue at high concentrations in response to a deficiency of oxygen, which occurs characteristically in solid tumors. Adenosine has multiple effects within the tumor, including controlling cancer cell growth, locally inhibiting the immune system, and increasing blood vessel formation.

Characteristics

Adenomatous Polyposis Coli Definition Familial Adenomatous Polyposis; APC.

Adenosine (adenine-9-β-D-ribofuranoside, Fig. 1) is a small organic molecule that plays an important part in general cellular biochemistry. Chemically, it is a purine nucleoside. Adenosine is abundant within all cells, predominantly in the form of ▶adenine nucleotides (AMP, ADP and ATP) which participate widely in cellular energy metabolism and act as precursor molecules in many processes. However, adenosine itself can exist in a free form both inside and outside of cells, and extracellular adenosine is responsible for the regulation of many processes throughout the body. Adenosine becomes particularly important when tissues become deprived of oxygen (a state known as

Adenomatous Polyps ▶Colorectal Premalignant Lesions

Adenomucinosis (DPAM) Definition An appendiceal epithelial neoplasm that is noninvasive so that peritoneal surfaces are coated by increasing quantities of a mucinous neoplasm. ▶Appendiceal Epithelial Neoplasms

Adenosine and Tumor Microenvironment. Figure 1 The chemical structure of adenosine. Adenosine is composed of a purine base (adenine) linked through a glycosidic bond to a sugar (ribose). Successive phosphate groups may be added at the position indicated by the arrow to give AMP (adenosine monophosphate), ADP (adenosine diphosphate) and ATP (adenosine triphosphate).

Adenosine and Tumor Microenvironment

▶hypoxia). This can happen in certain pathological situations, including cancer. It may occur suddenly when blood flow is interrupted, as takes place in a stroke within the brain or during a heart attack. In solid tumors however, hypoxia is a chronic condition because the blood vessels that the cancer forms to nourish itself are not well made and are unable to supply the tissue with sufficient oxygen and other nutrients. For cells to be well oxygenated, they need to be within a distance of about 150 μm of a properly functioning blood vessel. Tumor vessels are typically far apart, are irregular in both size and orientation and can be so poorly regulated that the blood flow may periodically change direction. Cancer cells respond to these harsher conditions by changing their metabolism. In hypoxic cancer tissues, the balance of energy metabolism in the cells becomes altered. Specific changes in the biochemical pathways of hypoxic cells dramatically change the fate of adenosine. Free adenosine is normally formed principally from adenine nucleotides by the enzyme 5′-nucleotidase inside the cell (some tissues have another pathway that also contributes), and adjacent to the exterior of the cell membrane by a series of proteins including ▶CD39 and ▶CD73, the latter of which also has 5′-nucleotidase activity (Fig. 2) In hypoxia, the 5′-nucleotidase pathways that lead to adenosine production from adenine nucleotides are activated, while the adenosine kinase enzyme which serves to convert adenosine to AMP is inhibited. These and other changes rapidly increase the concentrations of adenosine within and outside the cell. Since adenosine can pass freely into and out of the cell through various ▶nucleoside transporters in the outer membrane, any excess adenosine in the cytoplasm escapes from the cell and further accumulates in the extracellular space. These sources of adenosine contribute to very high extracellular adenosine concentrations in hypoxic tissues. In tumor tissue the average concentration of adenosine in the extracellular space is approximately 10 μM. Such high concentrations can be found in small tumor nodules of about 2–3 mm in diameter, so are likely to be present in the extracellular fluid of early cancers even before the ▶angiogenic switch. Furthermore, because the level of hypoxia varies through the tumor depending upon the proximity of blood capillaries, local levels can be much higher. Finally, adenosine concentrations are highly regulated by ▶ecto-enzymes such as adenosine deaminase (ADA) at the cell surface (Fig. 2), so that the ultimate effects of adenosine depend heavily on events at the cell surface. In normal tissues, where the concentrations of adenosine are low (in the nanomolar range), the principle pathway through which adenosine is metabolized involves phosphorylation to AMP by adenosine kinase. At higher adenosine concentrations, as are present

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Adenosine and Tumor Microenvironment. Figure 2 Adenosine production in and around the tumor cell. Adenosine is produced in the cell principally from AMP through the action of 5′-nucleotidase (5′-NT). This pathway is more active under hypoxic conditions, such as exist in solid tumors. Hypoxia also inhibits adenylate kinase (AK), which catalyzes the reverse reaction to convert adenosine to AMP. Outside the cell, adenosine is produced from ATP that is present in the extracellular fluid, by the sequential enzyme activities of CD39 and CD73. The major factor restraining the levels of adenosine that can be reached is the activity of the enzyme adenosine deaminase (ADA), which breaks adenosine down to inosine. This is present both within the cell, and as an enzyme outside of the cell (ecto-enzyme) that is held in place by an anchoring protein, CD26.

inside a tumor, the major route through which disposal of adenosine occurs is by deamination to ▶inosine through ADA. ADA is found both within the cell and in the external milieu. The ADA that is present in the extracellular fluid does not remain free, but is largely captured by a 110-kDa binding protein present at the surface of many cells, particularly those of epithelial origin. This ▶ADA-binding protein (ADAbp) is found embedded as a dimer in the outer membrane of many cancer cells, where it functions to hold ADA. There is also evidence that some ADA can bind directly to adenosine ▶receptors of A1 and A2B subtypes. ADA held in this way is then able to modify adenosine concentrations immediately next to the cell surface (where the adenosine receptors are located). One factor that complicates our understanding of how adenosine levels may be regulated within cancer tissue is the fact that adenosine has the capacity to regulate its own levels. This interesting complication arises because ADAbp (also known as CD26 or DPPIV) can be down-regulated at the cell surface by adenosine. That reduces the capacity of the cell to bind ADA at the cell surface and therefore the local rate

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of degradation of adenosine. This will extend the half-life of adenosine and increase the persistence of its action. As a result, in the high concentration environment of a tumor, adenosine has the capacity to suppress its own breakdown and enhance its actions still further. (See also ▶CD26/DPPIV in Cancer Progression and Spread.) Although adenosine is a common molecule and has a relatively simple structure, it is able to regulate cellular behavior by interacting with specific receptors. The different types of adenosine receptors are outlined in Table 1 There are four known types, all of which are ▶G-protein-coupled receptors with seven transmembrane segments in their structure, embedded in the outer membranes of responsive cells. Adenosine receptors may be found on any of the cell types within a tumor including the cancer cells, the supporting stromal cells, the endothelial cells within blood vessels, or inflammatory cells that are infiltrating the tumor. All four of the adenosine receptor subtypes have been shown to exist on cancer cells; indeed it is possible for a single cancer cell population to express all four forms of the receptor. However, adenosine receptor subtypes A3 and A2B are the most commonly observed in cancers. The adenosine concentrations that exist in tumors are sufficient to activate all four of the adenosine receptor subtypes. There are four different types of adenosine receptor Table 1, which differ in their affinity for adenosine and the signalling pathways to which they are linked through G proteins. All of the receptor subtypes are

Adenosine and Tumor Microenvironment. Table 1 The different types of cellular receptors for adenosine Receptor subtype

Signalling Affinity for Major Gα adenosine protein pathways used by (s) receptor

A1

High

Gi/o

A2A

High

Gs

A2B

Low

Gs, Gq/11

A3

Low

Gi/o, Gq/11

Adenylyl cyclase (↓ cAMP) Phospholipase C K+ channels Adenylyl cyclase (↑ cAMP) Phospholipase C Adenylyl cyclase (↑ cAMP) Phospholipase C Phospholipase A2 PI3K Adenylyl cyclase (↓ cAMP) Phospholipase C KATP Channels

able to act on adenylyl cyclase but may either increase or decrease the production of cAMP as shown. The receptors can also be coupled to phospholipase C (leading to calcium release and activation of protein kinase C), to phospholipase A2 (causing generation of arachidonic acid and subsequent production of eicosanoid lipid mediators), to phosphatidyl inositol 3-kinase (PI3K, leading to increased activity of the phospholipase D pathway) or in certain cell types can cause the activation of potassium (K) channels. The interaction of adenosine with its receptors on the different cell types in a tumor leads to a myriad of different cellular responses. Although it is at times difficult to extrapolate from the experimental approach to the disease itself, these are such as to generally favor the expansion and spread of the cancer (Fig. 3) There is evidence that synthetic agents which target individual receptor subtypes may have different actions to adenosine, sometimes not clearly directed through the adenosine receptor. When adenosine itself is studied at concentrations that are known to be present within the tumor extracellular fluid, it is typically shown to increase the growth of cancer cells. At very high concentrations of adenosine, cells may be triggered to undergo ▶apoptosis, although some tumor cells are resistant to this action of adenosine. In addition to effects on cancer cell growth and survival, adenosine acts on isolated cancer cell populations to increase cell motility, adhesion to the extracellular matrix, the expression of cell attachment proteins and receptors for molecules that can direct cell movement. The patchiness of hypoxia within tumor tissue leads to local areas of high adenosine concentrations that would be capable of influencing tumor cell behavior directionally in this way. While not yet proven, it is possible that within the context of the tumor itself, adenosine may have an influence on the distribution of cells within the tumor and perhaps their dissemination at the later stage of metastasis. Adenosine receptors are also found on endothelial cells, which are the flattened cells that line blood vessels and which are the major cellular component of the newly-formed vasculature that is formed to supply the expanding cell population with nutrients. Adenosine is able to promote endothelial cell division and motility, and has been shown to enhance the formation of blood vessels (▶angiogenesis) in experimental animal models. Adenosine may therefore have an ancillary role alongside other angiogenic factors such as ▶VEGF in regulating the formation of the tumor microvascular network. Probably the greatest potential role for adenosine in the context of cancer however, is as a local immunosuppressant within the tumor. It has long been known that the local tissue environment in cancer is capable of suppressing the immune response, and that this

Adenosine Deaminase

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Adenosine and Tumor Microenvironment. Figure 3 The multiple potential actions of adenosine within a tumor. This diagram summarizes the different ways in which adenosine might act to facilitate the survival and expansion of a malignant tumor. This figure is drawn based upon studies on individual tumor cell populations and other studies in vivo in which these responses have been observed.

is one of the factors that limits the capacity of our immune system to eliminate the cancer. Experimental studies have shown that a significant proportion of the immunosuppressive activity is mediated by soluble factors, that it increases in proportion to tissue bulk, and it is seen to decline substantially when the cancer tissue is removed from the animal or patient and dissociated into isolated cells. Adenosine is one of the possible factors responsible for this phenomenon of “metabolic suppression” of the anti-tumor immune response. The capacity for adenosine to act as an immunosuppressant is dramatically illustrated by a rare but well-known genetic disease involving a lack of ADA. In this disorder, levels of adenosine within lymphoid tissues rise and (through a combination of events involving both toxic metabolites and adenosine acting through its receptors) cause a severe immunodeficiency (well known because of the need to protect afflicted children from infection in “biobubble” tents). Adenosine is capable of interfering with the immune response at different levels and by acting on different cell types. It works through cell-surface adenosine receptors (principally A2A and A3 subtypes) to suppress various functions of T lymphocytes, natural killer (NK) cells, polymorphonuclear granulocytes, and phagocytic cells such as tissue macrophages that play a key role in recognizing the targets for immunological attack. In the case of T lymphocytes and NK cells, whose infiltration and activity is of key importance to the fate of the tumor and prognosis of the patient, adenosine suppresses successive stages in the evolution and function of the cells. It inhibits proliferation of the cells, the expression of key molecules on the cell surface that are needed to allow full activation, the extent of interaction with the cancer

cell, the release of toxic molecules involved in cell killing, and the overall capacity for killing of the cellular targets. Given the extensive effects of adenosine on nearly all of the cell types present in tumors, it would be appealing to attempt to use drugs that interfere with adenosine pathways as a way of interfering with the growth of the cancer cells, blocking the formation of new blood vessels to nourish the tumor, or relieving the immunosuppression that is due to adenosine. The challenge here lies in the fact that this is a primitive regulatory network in evolutionary terms, and adenosine has a role in the regulation of most organ systems in the mammal. Adenosine receptors of the four subtypes are found on cells throughout the body. Drugs that would a block adenosine’s action at its receptors (antagonists) or mimic its actions at a certain receptor subtype (selective agonists) run the risk of interfering with normal processes such as the control of blood flow or the transmission of nerve signals. Nevertheless, there is hope that careful targeting of certain receptors (particularly the A3 subtype) in cancer may prove to be a useful intervention.

Adenosine Deaminase Definition An enzyme involved in the metabolism of deoxyadenosine to deoxyinosine. Congenital deficiency of this enzyme results in the clinical syndrome of severe combined immunodeficiency.

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Adenovirus

Adenovirus S TEFAN KOCHANEK Division of Gene Therapy, University of Ulm, Ulm, Germany

Definition Adenoviruses were originally isolated as etiologic agents for upper respiratory infections. Their name is derived from the initial observation that primary cell explants from human adenoids were found to degenerate secondary to the infection by an, at the time, unknown virus. According to the current official taxonomy, there are four adenovirus genera (Mastadenovirus, Atadenovirus, Aviadenovirus and Siadenovirus), indicating that adenovirus is widely distributed in vertebrates. More than 50 human serotypes have been identified. The individual serotypes are distinguished by different parameters such as immunological properties, tumorigenicity, and DNA sequence. Some serotypes may cause more serious infectious diseases such as epidemic keratoconjunctivitis, gastroenteritis or hemorrhagic cystitis. The adenovirus particle is composed of an outer icosahedric protein capsid with an inner linear double-stranded DNA genome of approximately 36 kilobases (kb) size. There are eleven structural proteins, seven to form the capsid, among them hexon, penton base and fiber being the major constituents of the adenoviral capsid, and four that are packaged in the core. Internalization of the viral particle during infection requires the interaction of the fiber and the penton base with surface proteins (receptors) of the cell. Several virally encoded proteins are associated with the viral DNA. Adenovirus is being used as a gene carrier for ▶gene therapy. Most adenoviral vectors (see below) are derived from the serotypes 2 and 5 (Ad2, Ad5) which are frequent causes for mild colds. During childhood most individuals will become immunized against different adenoviral serotypes by natural infection. Ad2 and Ad5 are not oncogenic in humans Adenoviruses have a good safety record based on vaccination studies that have been performed in military recruits two to three decades ago. As detailed below, during natural infection of permissive cells the adenoviral DNA is transcribed, replicated, and packaged into capsids within the nuclei of infected cells. Similar to other DNA viruses, two main phases can be distinguished during infection: . An early phase that is characterized by the expression of the ▶early virus genes E1, E2, E3, and E4 . A late phase after onset of viral replication in which the viral structural proteins are produced

Characteristics Infection and Viral Transcription A productive infectious cycle takes approximately 2–3 days and under optimal conditions more than 50,000 particles are produced in every infected cell. In the case of most human adenvirus serotypes the infection begins with the attachment of the virus particle to the cell surface via interaction of the tip of the capsid fiber protein with the membrane protein CAR (Coxsackie– Adenovirus receptor). As it is apparent from the name, CAR is also used by some coxsackie viruses as receptor for entry. Naturally, CAR plays an important role in the interaction of neighboring cells. The adenoviral particle is internalized by receptor-mediated endocytosis into clathrin-coated pits requiring a secondary interaction of the penton base with an αv-integrin. Following endocytosis the viral particle is sequentially disassembled, initally losing the fiber proteins, later most of the other viral structural proteins. Finally, the viral DNA is released as a DNA–protein complex through nuclear pores into the nucleus of the host cell. Shortly thereafter, transcriptional activation of the early genes E1A and E1B initiates a complex transcriptional program designed to first replicate the viral DNA and later to generate new infectious viral particles (Fig. 1). The activation of early and late transcription units follows a relatively well understood transcriptional pattern. The gene products of the E1A and E1B genes are involved in the activation of both viral and cellular genes. Under certain conditions, in particular if infection of a cell does not result in a productive but rather abortive infection (abortive infection = the infectious cycle is blocked at an early stage following infection of the host cell) together with the rare event of integration of the viral DNA into the chromosome, cellular transformation may be a consequence. The E2A and E2B gene products are involved in the replication of the viral genome and include the viral DNA polymerase (AdPol), the terminal protein (TP), and the DNA-binding protein (DBP). The E3 and E4 gene products have diverse functions leading to transcriptional activation of other promoters, preferential export of viral RNAs out of the nucleus of infected cells and suppression of host defenses. With the begin of replication of the viral genome approximately 6 h after infection, late phase transcription units are activated. Most of the late phase proteins are capsid proteins or proteins that are involved in the organization and packaging of the viral genome inside the viral capsid. The most active promoter at this stage is the major late promoter (MLP) that directs the transcription of a large primary RNA transcript that covers more than two thirds of the viral genome. From this transcript five families (L1-L5) of structural proteins are generated by differential splicing and polyadenylation. During the course of an infection the metabolism

Adenovirus

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Adenovirus. Figure 1 Organization of the adenovirus genome and the different adenoviral vector types employed for gene transfer. Promoters are indicated by arrowheads, transcribed genes by arrows. The genes that are transcribed early during infection are the E1A, E1B, E2, E3, and E4 genes. The main gene products, generated late during infection, are transcribed from the Major Late Promoter (MLP), which directs a very long RNA message (MLTU = major late transcription unit). Different RNA species (L1-L5) that code for structural proteins are generated by alternative splicing and differential polyadenylation (for clarity not all adenoviral genes and gene products are indicated). First-generation adenoviral vectors are characterized by deletion of the E1 genes, second-generation adenoviral vectors by the additional deletion of the E2 and/or E4 genes. High-capacity adenoviral vectors have most of the viral genome removed and retain only the noncoding viral ends. In high-capacity adenoviral vectors, stuffer DNA is included in the vector genome for stability reasons.

of infected cells is redirected to support a predominant production and assembly of viral proteins. Adenoviral Functions and Oncogenesis Adenoviruses have played important roles as experimental tools in the discoveries of several fundamental principles in molecular biology, including RNA splicing and oncogenic transformation of cells. In fact, the 1993 Nobel Prize for Physiology or Medicine was awarded to Dr. Phillip Allen Sharp and Dr. Richard John Roberts for the discovery or RNA splicing and was based on their work with adenovirus RNA transcription. The induction of malignant tumors by injection of adenovirus type 12 in newborn hamsters was the first direct demonstration of a human virus causing malignant cellular transformation. This observation greatly stimulated the interest in using viruses as experimental systems in the study of the pathogenesis of cancer. While there is no epidemiological evidence

for an involvement of adenoviruses in the pathogenesis of human cancers, several serotypes have been shown to cause tumors in rodents. Some serotypes, such as Ad12 or Ad18 are highly oncogenic in animals, others, for example Ad4 or Ad5 have a low oncogenic potential. Based on several complementing observations cellular transformation is mediated by the viral E1A and E1B genes: In most virus-transformed cells the viral E1 genes are consistently found integrated into the cellular genome where they are expressed. Transfection of cells with the E1A and E1B genes is necessary and sufficient for cell transformation, and viruses with mutations in the E1 genes are defective for transformation. Several RNAs are transcribed from the E1A genes, the main species in Ad5 being the 12S and the 13S RNAs coding for E1A proteins of 243 and 289 amino acids. To a large extent, the E1A proteins exert their transforming activity by interaction with cellular proteins that are involved in cell cycle regulation such as the tumor

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Adenovirus

suppressor pRB. While E1A alone is capable of immortalizing cells, cooperation with E1B functions is required to achieve a full transformation phenotype. Two main proteins are produced from the E1B gene by alternative splicing. The 21 kD E1B protein that has been shown to inhibit apoptosis, and the 55 kD E1B protein that interacts with the tumor suppressor protein p53. The expression of additional viral functions may contribute to E1 mediated tumorigenesis. For example, a 19 kD protein expressed from the E3 region can decrease MHC class I levels in transformed cells, and certain functions expressed from the E4 region can cooperate with the transforming activity of the E1B 55 kD protein. Gene Therapy: First- and Second-Generation Adenoviral Vectors First-generation adenoviral vectors do not replicate in human cells under normal conditions because the E1A and E1B genes are deleted from the vector genome (Fig. 1). These vectors are produced in complementing cell lines that express the E1A and E1B genes. Firstgeneration vectors have been used for gene transfer in cultured cells, animals and even clinical trials in humans to express a large number of genes in different cell types and tissues. So far the results of experiments performed in animals and clinical studies in humans have been relatively disappointing. Several significant disadvantages of first-generation adenoviral vectors have been acknowledged: . Because first-generation vectors still contain a nearly complete set of viral genes, toxicity and antiviral immune responses are frequently observed resulting in the clearance of transduced cells. Consequently, gene expression is only transient. Contributing factors for short-term gene expression include immune responses directed to the transgenic proteins expressed from the vector, if the organism is not tolerant to that protein. . The upper DNA packaging limit for adenoviruses is about 38 kb. Because most viral genes are retained on the vector only about 7–8 kb of nonviral DNA can be incorporated into such vectors. However, in many conditions the therapeutic cDNAs are either large, additional elements have to be included to achieve regulated gene expression, or multiple genes need to be expressed to obtain a therapeutic effect. Thus, it is clear that the size constraints in first-generation adenoviral vectors may be a limiting factor for many potential applications. In order to further decrease expression of late viral proteins, adenoviral vectors with inactivation of the E2 and/or E4 functions in addition to the deletion of the E1 region have been generated. These vectors are produced in cell lines that complement both E1 and E2 and/or E4 functions.

Currently it is controversial whether these secondgeneration adenoviral vectors have any significant advantages over first-generation vectors and lead to a longer duration of gene expression. “Gutless” Adenoviral Vectors In an attempt to address several of the problems observed with first-generation adenoviral vectors a novel adenoviral vector has been developed that will be useful for the functional analysis of genes in vivo and clinical studies. This vector has been variably called “high-capacity (HC)” adenoviral vector, “gutless”, “gutted” or “helper-dependent (HD)” adenoviral vector. Because all viral genes are deleted from this vector the capacity for the uptake of foreign DNA is more than 30 kb. The current production system involves the use of an adenoviral helper virus and takes advantage of the Cre-loxP recombination system. In this production scheme a first-generation adenoviral vector carries two loxP-recognition sequences that flank the adenoviral packaging signal. The vector is produced in E1-complementing cells that express the Cre-recombinase of bacteriophage P1. After infection of these cells both by helper virus and vector the packaging signal of the helper virus is excised. Therefore, vector and only little helper virus is packaged. From several in vivo experiments performed in different animal species it is apparent that these new vectors have clear advantages compared to earlier versions of adenoviral vectors and are considerably improved in safety and expression profiles. Their increased capacity for foreign DNA allows gene transfer of several expression cassettes, large promoters and some genes in their natural genomic context, a significant advantage over first- and second-generation adenoviral vectors. Replication-Competent Adenoviral Vectors for Cancer Gene Therapy While the above mentioned adenoviral vectors have been widely used in preclinical and, with the exception of “gutless” adenoviral vectors, also in clinical studies to express a wide variety of transgenes including cytokines, p53 and thymidine kinase (TK), it would be desirable to achieve gene transfer into all or most neoplastic cells within a tumor. This is clearly not possible with current vector technology. Recently, a new concept has been proposed that is based on the use of an adenovirus that is both replication competent and tumor-restricted in its growth. This virus is based on an Ad5 mutant virus that has an inactivating deletion within the E1B gene and does not express the E1B 55 kD protein. Initially, it was thought that replication of the virus was dependent on the p53 status of the host cell and that the virus was able to grow only in cells deficient for function p53 expression. However, more recent results indicate that the growth of this virus is

Adherens Junctions

independent of the p53 status cells and may depend on other cell cycle related factors. Although clinical studies so far have not been or only partially been successful, such a virus has been approved in 2005 in China for cancer therapy and is currently used in combination with chemotherapy and/or radiotherapy. In addition, replication-competent adenovirus vector are being developed, in which expression of essential viral genes, in particular of E1A, is under control of a tumor-specific promoter. These vectors have been named CRADs (conditionally replicating adenoviruses). Adenovirus Vectors for Genetic Vaccination One of the most promising applications of adenovirus vectors is in the area of genetic vaccination. For many common diseases including AIDS or Malaria there are currently no vaccines available. Since adenovirus vectors have been found to induce strong cellular and humoral (antibody) immune responses against expressed genes, many preclinical studies have been performed with the aim of vaccine development. In these studies adenovirus vectors have been found to belong to the strongest inducers of antigen-specific immune responses against different antigens. Therefore, clinical studies have been initiated, in which adenovirus vectors, either alone or in combination with proteins or other vectors, are evaluated for their potential as a vaccine against different infectious diseases.

α-subunits and βγ-complexes as well as by Ca2+ or protein kinase C. ▶G-Proteins ▶Signal Transduction

Adherens Junctions Definition Adherens junctions are intercellular junctional structures, most prominent in epithelial cells. In the adherens junction, the cell-cell adhesion is mediated by Ca2+dependent cell adhesion molecules, the cadherins; the cytoplasmic tail of these cadherins is indirectly linked to the ▶actin cytoskeleton. Normally are located more basally than ▶tight junctions. ▶Cell Adhesion Molecules ▶E-Cadherin ▶Exfoliation of Cells

Adherens Junctions

References 1. Berk AJ (2007) Adenoviridae: the viruses and their replication. In: Bernard N. Fields, David M. Knipe, Peter M. Howley (eds), Fields virology, 3rd edn. LippincottRaven, Philadelphia, New York, pp 2355–2394 2. Wold WSM, Horwitz (2007) Adenoviruses. In: Fields virology, 5th edn. Lippincott-Raven, Philadelphia, New York, pp 2395–2436 3. Doerfler W, Böhm P (eds) (1995) The molecular repertoire of adenoviruses. Current topics in microbiology and immunology, vol 199/I–III. Springer, Berlin 4. Imperiale MJ, Kochanek S (2004) Adenovirus vectors: biology, design, and production. Curr Top Microbiol Imunol 273:335–357

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J UN M IYOSHI 1 , YOSHIMI TAKAI 2 1

Department of Molecular Biology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan 2 Osaka University Graduate School of Medicine/ Faculty of Medicine, Suita, Japan

Synonyms Zonula adherens; intermediate junction

Definition

Adenylyl Cyclase Definition Ubiquitous group of enzymes which catalyze the formation of the second messenger cAMP from ATP. Various mammalian isoforms have been identified which are differentially regulated through G-protein

Adherens junctions are specialized cell–cell attachments composed of transmembrane proteins and cytoplasmic proteins that anchor to the actin cytoskeleton (Fig. 1). Anchoring proteins are clustered with several actin-binding proteins in the cytoplasm adjacent to the junctional membranes. Adherens junctions form punctate or streak-like attachments in nonepithelial tissues, whereas they encircle the apical portion of adjacent epithelial cells below ▶tight junctions. Adherens junctions have prototypic roles in stabilizing the epithelium, establishing apical–basal polarity of epithelial cells, and

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Adherens Junctions

Adherens Junctions. Figure 1 Epithelial cells joined by the apical adhesion complex. Adherens junctions are located below tight junctions near the apical end of the lateral cell interface in epithelial cells. Nectin and E-cadherin-based cell adhesions are connected via several cytoplasmic proteins into belts of actin filaments that underlie adherens junctions. Nectins are localized to adherens junctions via afadin, and they are associated with integrin αvβ3 in the extracellular space. Afadin binds to the tail of nectin cis-dimers as well as F-actin directly, interacting with Rap1. β-catenin binds to the tail of E-cadherin cis-dimers directly, and then α-catenin binds to β-catenin. The catenins can mediate interactions to F-actin through binding to several actin-binding proteins such as ZO proteins, afadin, vinculin, α-actinin, VASP, formin-1, and Arp2/3 complex. c-Src, Rac, Cdc42, and FAK play roles in regulating dynamic changes of the actin cytoskelton, facilitated by E-cadherin and nectin clustering.

facilitating cell–cell communication that regulates cell proliferation and movement. Since most human cancers are of epithelial origin, disruption of adherens junctions is one of the hallmarks of cancer cells exhibiting malignant transformation.

Characteristics Adherens junctions are sites of mechanical attachment regulated by dynamic changes in the actin cytoskeleton, and they also serve as sites of cell–cell communication. Adherens junctions are abundant in many tissues that

Adherens Junctions

are subjected to mechanical stress. In epithelial cells, adherens junctions coalesce into the mature zonula adherens. In cooperation with the zonula occludens (tight junctions), the zonula adherens defines apical–basal polarity by physically separating the membrane into apical and basolateral membrane domains. In addition, adherens junctions mediate nuclear ▶signal transduction induced by cell contact. For example, molecules clustered at adherens junctions could mediate contact-dependent inhibition of cell proliferation and movement: the arrest of the cell cycle in G1 phase that occurs when cell density increases to confluence in culture. Thus, the coupling of cell contact and signaling at adherens junctions reflects structural and functional regulations involved in establishing multicellular organisms. Cadherins and nectins are two major ▶cell adhesion molecules in the extracellular space. Cadherins are a superfamily composed of classical cadherins, which are the main components of adherens junctions, and nonclassical cadherins, which include desmosomal cadherins and protocadherins. The classical cadherins share a motif of five cadherin repeats in the extracellular domain, and they are divided into several subtypes including epithelial ▶(E) cadherin, placental (P) cadherin, neural (N) cadherin, and vascular endothelial (VE) cadherin. On the other hand, nectins are immunoglobulinlike adhesion molecules composed of four members. Adherens junctions facilitate cell–cell adhesion through homophilic binding between cadherin molecules, as well as homophilic and heterophilic bindings between nectin molecules on adjacent cells. It remains controversial whether or not the extracellular domain of Ecadherin first binds to form cis-dimers on the surface of the same cells, and then promotes cell-cell contacts by forming trans-dimers in a Ca2+-dependent manner. On the other hand, each member of nectins forms cisdimers, and then promotes homophilic or heterophilic trans-dimer formation in a Ca2+-independent manner. Heterophilic trans-interactions have been detected between nectin-2 and nectin-3, between nectin-1 and nectin-3, and between nectin-1 and nectin-4. Importantly, heterophilic trans-dimers form stronger cell–cell attachment than homophilic trans-dimers, which actually determines the type of cell–cell adhesion. Namely, cadherins exclusively promote adhesion between homotypic cells, whereas nectins have a dual role in promoting adhesion between homotypic cells and between heterotypic cells. Heterophilic engagement of nectins may thus play key roles in cell recognition and sorting in vivo. The intracellular domain of cadherins is associated with a cytoplasmic complex consisting of α-catenin and β-catenin, and forms structural links to the actin cytoskeleton. α-catenin does not act as a stable link to filamentous actin (F-actin) but possibly acts as a molecular switch that regulates actin dynamics at

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adherens junctions. The catenins could also mediate interactions with F-actin via binding to proteins such as ▶ZO protein-1, afadin, vinculin, and α-actinin. The intracellular domain of nectins directly binds to afadin that links nectins to the actin cytoskeleton. Localization of nectins to adherens junctions depends on the presence of afadin. Thus, the catenins and afadin cooperatively contribute to form adherens junctions that are strong yet easily remodeled. Nectin-based cell–cell adhesions establish adherens junctions, both independently and cooperating with cadherin-based cell–cell adhesions. In Madin–Darby canine kidney (MDCK) cells in culture, nectins first form cell–cell adhesion and then recruit cadherins to the nectin-based cell–cell adhesion sites to establish adherens junctions. Nectins further promote formation of tight junctions in MDCK cells by recruiting JAM (junctional adhesion molecule)-A, claudin-1, and occludin. On the other hand, nectins and integrin αvβ3 are physically associated through their extracellular domains to cooperatively regulate cell movement, proliferation, adhesion, and polarization. Thus, nectins play roles in establishing apical junctional complex, as well as in communication between cell–cell and cell–matrix junctions. Trans-interacting E-cadherin induces activation of Rac small ▶G-protein, which stabilizes nontransinteracting E-cadherin on the cell surface by inhibiting endocytosis through the reorganization of the actin cytoskeleton. p120 catenin (p120ctn) also plays a role for inhibiting endocytosis of E-cadherin. In contrast, E-cadherin undergoes endocytosis when adherens junctions are disrupted by the action of an extracellular signal, such as hepatocyte growth factor/ ▶scatter factor. Activated c-Src enhances endocytosis of E-cadherin by inducing the tyrosine phosphorylation and ubiquitylation of the E-cadherin complex. On the other hand, trans-interaction of nectins activates Cdc42 and Rac, which promotes the formation of adherens junctions mediated by the ▶IQGAP1-dependent actin cytoskeleton. In addition, afadin and activated ▶Rap1 complex interacts with p120ctn to strengthen the binding between p120ctn and E-cadherin. Furthermore, the cell polarity proteins Par-3, Par-6, and aPKC that form a ternary complex could be implicated in the assembly of adherens junctions. They regulate the association of afadin with nectins in MDCK cells. These cell polarity proteins and afadin could play cooperative roles in the formation of adherens junctions and tight junctions although the mechanism is largely unknown. Thus, E-cadherin and nectin trans-interactions induce elaborate interactions between peripheral proteins to establish mature adherens junctions. β-catenin is able to translocate to the nucleus, where it binds to lymphoid enhancer factor–T-cell factor (LEF/ TCF) that regulates gene transcription. β-catenin is involved in several signaling pathways including the

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wingless-type mammary virus integration-site family (▶Wnt) ▶signaling pathway. When Wnt proteins bind their receptors, they inactivate the serine/threonine kinase GSK3β that phosphorylates β-catenin and targets it for destruction in the proteosome. Mutations involving the serine/threonine residues of β-catenin that are phosphorylated by GSK3β can stabilize the β-catenin protein or increase its nuclear localization. Furthermore, tyrosine phosphorylation of β-catenin also disrupts the association between E-cadherin and β-catenin, allowing β-catenin to transduce signals to the nucleus. Necl-5, a member of nectin-like cell adhesion molecules (Necls), originally identified as a poliovirus receptor, could mediate growth arrest that has been known as contact inhibition of cell proliferation and movement. Necl-5 is overexpressed in human colon carcinoma, as well as in NIH3T3 cells transformed by ▶Ras activation. Necl-5 colocalizes with integrin αvβ3 and growth factor receptors at leading edges of migrating cells and regulates growth factor induced cell migration. When Necl-5 interacts in trans with nectin-3 at cell–cell contacts in NIH3T3 cells, Necl-5

undergoes downregulation from the cell surface, resulting in reduction of cell proliferation and movement. Thus, nectins and Necls have roles in mechanical cell–cell adhesion as well as cell–cell communication. Implications in Cancer Adherens junctions control epithelial cell polarity while other adhesion apparatus tends to inhibit cell migration, which is crucial for the differentiation and morphogenesis of many tissues. Loss of adherens junctions, as well as aberrant signaling involving the Wnt pathway, could contribute to carcinogenesis and ▶metastasis by causing cell depolarization, loss of contact-dependent inhibition of proliferation, and increased ▶motility and invasiveness (Fig. 2). Cancer cells that show migratory properties undergo ▶epithelial to mesenchymal transition (EMT), with the induction of transcriptional repressor proteins, such as ▶snail transcriptional factor, slug, and Twist, that downregulate E-cadherin gene expression. EMT is a basic mechanism that mediates disruption of epithelial polarity and disintegration of cancer cell nests.

Adherens Junctions. Figure 2 Signaling induced by loss of E-cadherin. Disruption of adherens junctions is caused by mutation or transcriptional repression of E-cadherin and growth-factor signaling. Dissociation of homophilic binding of E-cadherin promotes the endocytosis of E-cadherin and the disassembly of the catenins. p120ctn further promotes cell motility by activating Rac and Cdc42 to form lamellipodia and filopodia, and inhibits Rho activity that leads to stress-fiber formation. β-Catenin dissociated from the E-cadherin and catenin complex accumulated in the cytoplasm. Part of β-catenin translocates to the nucleus and binds to TCF to activate transcription of key genes required for survival of detached cells, while the other part of β-catenin is modified by phosphorylation and ubiquitination, leading to proteosome degradation. The Wnt pathway promotes β-catenin signaling by repressing the phosphorylation of β-catenin mediated by GSK-3β.

Adhesion

Reduced E-cadherin levels in cancer cells are accomplished by genetic events such as somatic mutation and reduced gene expression mediated by repressor proteins or by methylation of the promoter region of the E-cadherin gene. The genetic defects of E-cadherin have been found in human lobular breast carcinomas and scirrhus-type ▶gastric cancers, both of which have highly metastatic potentials. Mutations of β-catenin also promote migration and ▶invasion of cancer cells by the loss of interaction of adherens junctions with the actin cytoskelton. Distributions of E-cadherin and β-catenin tend to change depending on sites of tumor remodeling. In epithelial structures in the centre of cancer, E-cadherin and β-catenin are mostly present in adherens junctions. However, solitary cells at the invasive front of cancer plates shows no signal for E-cadherin but often produce signals for nuclear β-catenin. Thus, decreased E-cadherin expression promotes the release of solitary cancer cells at the invasive front and increases the survival of cancer cells by stimulating β-catenin signaling. Strategy for restoring adherens junctions, as well as cell–cell and cell–matrix communication may prevent cancer-cell invasiveness. Therapeutic targets might be molecules involved in pathways affecting the adhesive properties of E-cadherin and the assembly of the adherens-junction complex: c-Src and other tyrosine kinases, tyrosine phosphatases such as PTP-LAR, Rho, Rac, and Rap small G-proteins, transcriptional repressor proteins, and ▶merlin and the ▶ERM proteins. For example, c-Src regulates both disruption of adherens junctions and focal-adhesion turnover that are required for cancer cell motility. Twist is highly expressed in human cancers with reduced E-cadherin mRNA expression levels. In contrast, podoplanin promotes cancer cell invasion in the absence of EMT, suggesting cancer cells can also migrate as a mass, not necessarily as a single cell. Restoring E-cadherin-mediated cell adhesion could be means of preventing EMT in cancer and metastasis although EMT is not essentially required for cancer-cell invasion.

References 1. Christofori G (2006) New signals from the invasive front. Nature 441:444–450 2. Kobielak A, Fuchs E (2004) Alpha-catenin: at the junction of intercellular adhesion and actin dynamics. Nat Rev Mol Cell Biol 5:614–625 3. Takai Y, Nakanishi H (2003) Nectin and afadin: novel organizers of intercellular junctions. J Cell Sci 116:17–27 4. Takeichi M (1993) Cadherins in cancer: implications for invasion and metastasis. Curr Opin Cell Biol 5:806–811 5. Thiery JP, Sleeman JP (2006) Complex networks orchestrate epithelial-mesenchymal transitions. Nat Rev Mol Cell Biol 7:131–142

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Adhesion DARIO R USCIANO Friedrich Miescher Institute, Basel, Switzerland

Definition Cell adhesion is a dynamic process that results from specific interactions between cell surface molecules and their appropriate ligands. Adhesion can be found between adjacent cells (cell-cell adhesion) as well as between cells and the ▶extracellular matrix (ECM) (cell-matrix adhesion). Besides keeping a multicellular organism together, cell adhesion is also a source of specific signals to adherent cells; their phenotype can thus be regulated by their adhesive interactions. In fact, most of the cell adhesion receptors were found to be involved in ▶signal transduction. By interacting with growth factor receptors they are able to modulate their signaling efficiency. Therefore, gene expression, cytoskeletal dynamics and growth regulation all depend, at least partially, on cell adhesive interactions (Fig. 1).

Characteristics Cell Adhesion Receptors Cell adhesion molecules were grouped into distinct classes according to structural and/or functional homologies. The following receptors have been directly implicated in the malignant phenotype of tumor cells. . Integrins represent a family cell surface ▶glycoproteins that depend on divalent cations and are important in cell-ECM and cell-cell adhesion. The non-covalent association of an alpha and a beta subunit results in heterodimers that span the plasma membrane, enabling contacts with elements of the ▶cytoskeleton and signal transducing intermediates. . The immunoglobulin superfamily of adhesion receptors is mainly involved in cell-cell adhesion. Named after a 90–100 amino acid domain that is also present in Ig molecules, these kind of receptors can be expressed either as plasma membrane-spanning molecules. However, some of them are alternatively spliced and are anchored to the cell membrane by covalent linkage to phosphatidylinositol. . ▶Selectins represent a class of structurally related monomeric cell surface glycoproteins that bind specific carbohydrate ligands via their ▶lectin-like domains. Since the ligands are expressed in a specific way by vascular endothelial cells, selectins are important in lymphocyte trafficking and homing of malignant tumor cells. . Cell surface ▶proteoglycans consist of ▶glycosaminoglycans (GAG) attached to core proteins through

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Adhesion. Figure 1 Cell adhesion in normal (a, b) and cancer (c, d) cells. Normal mesenchymal cells show regular actin stress fibers (a: stained with phalloidin) and focal contacts (b: stained with anti-vinculin antibodies). In contrast, cancer cells (a highly motile melanoma cell is shown) often present with a completely disorganized actin cytoskeleton (c) and few focal contacts (d). Vinculin is typically arranged in patches at the periphery of the cell (d) (Confocal micrograph courtesy of Dr. Jörg Hagmann, FMI, Basel).

an O-glycosidic linkage. They can mediate cell-cell and cell-ECM adhesion. . ▶CD44 comprises a large family of proteins generated from one gene by alternative splicing. Variants of CD44 (CD44v) differ from the standard form (CD44s) by their implementation of ten variant exons in various combinations. Some variants have been causally related to the metastatic spread of some tumor cells. Among the ligands for CD44 are hyaluronic acid (HA), fibronectin and collagen, and chondroitin sulfate-modified proteins. . ▶Cadherins are surface glycoproteins involved in cell-cell interactions. They are involved in the formation of adherens-type functions between cells. Through their cytoplasmic tail they interact with catenins, which are important for the signal transducing ability of cadherins. . ▶Connexins are gap junction-forming proteins that oligomerize into specialized intercellular channels, connecting apposing plasma membranes. They allow the exchange of low molecular weight metabolites such as second messengers that are important in signal transduction (Table 1).

Adhesion and Cancer The selective adhesion of one cell to another or to the surrounding ECM, is of paramount importance during embryonic development as well as for the maintenance of normal adult tissue structure and function. Severe perturbations of these interactions can be, at the same time, cause and consequence of malignant transformation and also play a fundamental role during malignant progression and metastatic dissemination (Fig. 1). . Adhesion to the ECM through integrin receptors is important for anchorage dependent cell growth and cell survival. Normal cells that are detached from the ECM are locked in the G1 phase of the cell cycle (by loss of activity of the cyclinE/cdk2 complex) and undergo apoptosis (anoikis). Transformed cells, in which integrin signaling is altered, acquire the ability to grow in suspension and do not succumb to anoikis. . Adhesion to neighboring cells, mediated by cell-cell adhesion molecules (e.g. N-CAM and C-CAM) and by gap-junctions, inhibits growth of normal cells (what is commonly known as “contact growth inhibition”). Loss of these contacts due to the

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disrupted function of the relative adhesion molecules may result in uncontrolled proliferation. . The differentiated state of mature cells (their “identity”) is also maintained through specific adhesion to the ECM and adjacent cells: a loss of identity is thus a likely consequence if specific contacts are lost, finally resulting in the ambiguous phenotype of many tumor cells (Fig. 2).

abnormal adhesiveness that is generally displayed by tumor cells appears to contribute to their metastatic behavior. Both positive and negative regulation of cell adhesion are required in the metastatic process, since metastatic cells must break away from the primary tumor, travel in the circulation where they can interact with blood cells and then adhere to cellular and extracellular matrix elements at specific secondary sites.

Certain genes that code for cell adhesion molecules may therefore be considered as ▶tumor suppressor genes or even ▶metastasis suppressor genes since their loss or a functional mutation can strongly contribute to the acquisition of the malignant phenotype.

Adhesion within The Tumor Mass The majority of normal adult cells are restricted by compartment boundaries that are usually conserved during the early stages of development of a tumor. Therefore, the detachment of malignant cells from the primary tumor is an essential step for the initiation of the metastatic cascade. During ▶tumor progression changes on the cell surface that lead to a weakening of the cellular constraints, contribute to the release of such mutant cells

Adhesion in Metastasis Adhesive interactions play a very critical role in the process of metastatic tumor dissemination, and the Adhesion. Table 1

Adhesion receptors

Family Integrins IgG superfamily Cadherins Selectins Connexins Cell surface proteoglycans CD44

Main members

Type of adhesion

Characterized by the different α- and β-subunits Cell-ECM cell-cell ICAM-1, V-CAM, N-CAM, CD2 (LFA2), LFA3, CD4, CD8, MHC (class Cell-ECM cell-cell I and II) E, P, L Cell-cell (adherens junction) E, P, N Cell-cell 26 (tumor suppressor) 32 (liver) 43 (glial cells) Cell-cell (gap junctions) Syndecan, glypican Cell-ECM cell-cell CD44s, CD44v

Cell-ECM cell-cell

Adhesion. Figure 2 Cell adhesion and maintenance of a normal differentiated phenotype: Detachment of a normal cell from the extracellular matrix (ECM) would normally lead to apoptosis. Normal cells that keep contact with the ECM are protected from apoptosis and may migrate and grow. Normal cells tend to be organized as sheets onto the ECM, which contributes to their polarization and differentiation. Extensive intercellular contacts among cells adhered onto the ECM lead to contact-mediated growth inhibition. Tumor cells do not undergo apoptosis when detached from the ECM and may grow, migrate and invade into the matrix, to enter the circulation and give rise to distant metastases.

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from the primary tumor mass. Indeed, it was found that tumor cells separate more easily from solid tumors than normal cells from corresponding tissues. . Cadherin expression has been shown to influence intercellular cohesion in direct correlation with invasive behavior. An increased cadherin expression in tumor lines, generally causes a tighter association of tumor cells. In vitro experiments have shown that cells which do not express cadherins or in which cadherins are functionally inhibited are more invasive than cells with normal cadherin activity. In cases where E-cadherin was involved, re-introduction of a wild type copy of the gene could revert the invasive phenotype. The loss of cadherin activity however, is not sufficient to make cells invasive. ▶Invasion also requires other cellular activities, such as ▶motility and protease production. In vivo, tumors expressing low levels of cadherins tend to be less differentiated and to exhibit higher invasive potential, although they are not necessarily more metastatic. In human cancer, a reduction in cadherin activity correlates with the infiltrative ability of tumor cells, a correlation that in many tumors is also retained in distant metastasis. . A different type of cellular constraint is provided by gap junction communication. Gap junctions play an essential role in the integrated regulation of growth, differentiation and function of tissues and organs. The disruption of gap junction communication can cause irreversible damage to the integrity of the tissue and finally contribute to tumor promotion and malignant progression by favoring local cell isolation. There is experimental evidence that a loss of intercellular junction communication affects the metastatic potential of cell lines. Normal cells use gap junctions to control the growth of tumor cells. Once gap junctional communication is lost, the signaling mechanism responsible for the exertion of such growth control is also lost. Both quantitative and qualitative changes in gap junction protein (connexins) expression were found to be associated with tumor progression during multistage skin carcinogenesis in the mouse model system as well as with tumorigenesis in a rat bladder tumor cell line. Malignant Tumor Cells in the Blood Stream: Adhesion to Blood Cells and Platelets Blood-borne tumor cells undergo various homotypic and heterotypic interactions, the effect of which will also influence their metastatic behavior. Some of these interactions may be detrimental to circulating tumor cells such as tumor cell recognition by natural killer (NK) cells, or by tumor infiltrating lymphocytes (TIL). Others may provide, to a certain extent, a protective effect and/or contribute to metastatic spreading, such as interactions with platelets or, in certain cases, with leucocytes.

. De novo expression of the cell adhesion molecule ICAM-1 by melanomas might lead to heterotypic adhesion between melanoma cells and leukocytes bearing the relative receptor (LFA-1). Such interaction might thus enhance tumor cell adhesion to migratory and invasive leukocytes, thereby contributing to further dissemination of malignant tumor cells. In this regard, it has been suggested that site specificity of cancer metastasis might be, at least partially, a consequence of the formation of “multicellular metastatic units” (MSU) consisting of tumor cells, platelets and leukocytes. A subset of leukocytes within the “MSU” would be responsible for sitespecific endothelium recognition, adhesion and stable attachment, thus serving as “carrier cells” targeting the metastatic “spheroids” to specific sites of secondary tumor foci formation. . Several lines of evidence have provided strong support for the concept that tumor cell-platelet interaction significantly contributes to hematogenous metastasis. Two categories of molecules can trigger tumor cell induced platelet aggregation (TCIPA) and activation; soluble mediators and adhesion molecules. The latter are likely to be responsible for the initial contact between tumor cells and platelet cells, and might later stabilize the interaction. P-selectin and αIIbβ3 integrin on the platelet surface may bind Lex carbohydrate determinants and fibrin on the surface of tumor cells, thus triggering platelet activation. Sialylation appears to be a general requirement for TCIPA, and ▶sialoglycoconjugates present on both tumor cells and platelets have been involved in tumor cell-platelet interactions. Mechanistically, platelets may contribute to metastasis by stabilizing tumor cell arrest in the vasculature, shielding tumor cells from physical damage, providing additional adhesion mechanisms to endothelial cells and subendothelial matrix, and serving as a potential source of growth factors. If tumor cell interaction with host platelets occurs while tumor cells are circulating, an organ-specific colonization ability of blood-borne tumor cells may be influenced. In fact, the resulting embolus will be more easily arrested in the vasculature of the first organ downstream from the primary tumor site. If this organ represents a favorable milieu for tumor growth, then interaction with platelets will enhance tumor metastasis at that site; if this is not the case, it may prevent tumor cells from reaching their preferred organ and thus cause a reduction of the metastatic potential. It seems, however, that in most cases platelets are involved only after tumor cells have arrested, and platelet activation may then stabilize the initial tumor cell arrest in the microvasculature.

Adhesion

Adhesion in the Target Organ Circulating tumor cells, either as single cells or most likely as homotypic and/or heterotypic aggregates that have escaped killing by the host immune system and lysis by mechanical shear forces associated with passage in the blood stream, need now to arrest in the microvasculature and extravasate into the organ parenchyma. In fact, the survival time of tumor cells entering the circulation is very short, usually less than 60 min. Therefore those cells that can rapidly arrest and are able to get out the blood stream might have a selective advantage in giving rise to metastatic colonies. Specific adhesion in the target organ has been proposed as a critical determinant of organ specific metastasis, and experimental data indicates that malignant tumor cells preferentially adhere to organ-specific adhesion molecules. Tumor cells, for instance, adhered more efficiently to disaggregated cells or to histologic sections prepared from their preferred site of metastasis than from other organs. These type of assays, however, do not accurately mimic the physiological situation in vivo, where the first contact of circulating tumor cells happens with the luminal surface of the vascular endothelium, and, after endothelial retraction, with the subendothelial ▶basement membrane. Adhesion to Endothelial Cells (EC) The arrest of tumor cells in the capillary bed of secondary organs and their subsequent extravasation occur through interactions with the local microvascular endothelium and the subendothelial matrix. . Biochemical heterogeneity of EC is related to both the heterogeneous microenvironment within tissues and the size of the vessel. Heterogeneity is seen in the differential expression of plasma membrane glycoproteins, cytoskeletal proteins and surface receptors in microvascular endothelium of different organs. Such heterogeneity of endothelium underscores the importance of using organ-specific capillary endothelium in studying the role of organ-specific tumor cell adhesion in metastasis. . The specificity of the adhesive interactions that depends on the heterogeneity of microvascular EC and tumor cells, may favor, in a selective way, the initial adhesive events in preferred metastatic sites. As a consequence it may also facilitate metastatic dissemination to those organs, in a way that is similar to extravasation of lymphocytes from high endothelial venules of lymphoid tissues. Infact, lymphocyte “homing” represents the paradigm for organ-specific cell adhesion and it has been shown to follow specific interactions between surface “homing” receptors on lymphocytes with vascular “addressins” expressed on the high endothelial venule surface. In a similar

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way, tumor cells express various combinations of cell surface molecules that may serve as ligands for EC surface receptors, which are typically induced upon stimulation by mediators of inflammation. A local inflammatory response might thus facilitate circulating tumor cells adhesion and arrest. The relevance of this type of interaction in directing tumor metastasis has been recently demonstrated in vivo using strains of transgenic mice that constitutively express cell surface E-selectin either in all tissues or in the liver alone. Metastatic tumor cells that do not express the ligand, colonized mostly the lung. However, following the induction of ligand expression, tumor cell colonization was redirected to the liver with tremendous efficiency. Adhesion to Extracellular Matrix Components Mammalian organisms are composed by a series of tissue compartments separated from one another by two types of extracellular matrix (ECM): basement membranes and interstitial stroma. ECM consists of three general classes of macromolecules, including collagens, proteoglycans and non-collagenous glycoproteins (such as fibronectin, laminin, entactin and tenascin among others), which are expressed in a tissue-specific fashion. Malignant cells arrested in the microcirculation sometimes do not migrate further into the organ parenchyma but grow locally in an expansive fashion until they rupture the vessel wall. In most cases however, the contact between tumor cells and the endothelium results in EC retraction with exposure of the underlying basement membrane, followed by invasion of tumor cells in the tissue. The presence of specific adhesion receptors on the membrane of metastatic cells, and the peculiar composition of the extracellular matrix at a given site will influence tumor cell retention, motility and invasion, and growth at target organs. . Electron microscopy observation on the formation of pulmonary metastasis has shown that tumor cells often adhere to regions of exposed basal lamina. The exposed subendothelial matrix is usually a better adhesive substrate for tumor cells than the endothelial cell surface. . In order to move through the ECM, tumor cells must make firm contacts with matrix molecules, be able to break these adhesive contacts as they move on and respond to chemotactic molecules that direct their movement. Interactions with the ECM may fulfill all these scopes, through the signaling effect of several cytokines (growth factors, motility factors, enzymes and enzyme inhibitors) that are stored bound to ECM molecules, and released upon interaction with tumor cells. Moreover, ECM macromolecules themselves may also function as motility attractants, and have

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been shown to stimulate both ▶chemotaxis and ▶haptotaxis. Haptotactic migration over insoluble matrix components may occur predominantly during the initial stages of metastatic invasion, while at later stages partially degraded matrix proteins, derived from proteolytic processing of the matrix, could be the major determinant of directed motility. . Finally, it has to be considered that some ECM components may actually impede cell adhesion and thus might influence directional tumor cell motility by promoting the localized detachment of the trailing edge of migrating cells. ECM-associated chondroitin sulfate proteoglycans such as decorin, or the glycoprotein tenascin, have been suggested to modulate tumor cell adhesion and motility in this way.

have domains that extend into both the extracellular space and the intracellular space. The extracellular domain of a cell adhesion protein can bind to other molecules that might be either on the surface of an adjacent cell (cell-to-cell adhesion) or part of the ▶extracellular matrix (cell-to-ECM adhesion).

Adhesion and Drug Resistance The malignant phenotype of tumor cells depends, at least partially, on the weakening of cell-matrix and cellcell interactions that occurs during tumor progression. However, late stage tumors maintain some level of intercellular adhesion, or even tend to reactivate certain adhesion mechanisms, indicating that modulation of cell adhesion is a dynamic process. Given the beneficial effect of cell adhesion on apoptosis resistance, an increased level of adhesion may facilitate survival of tumor emboli, and there is evidence that it can help tumor cells to evade the cytotoxic effects of anticancer therapy.

▶Arginine-Depleting Enzyme Arginine Deiminase

▶Furin ▶Sjögren Syndrome

ADI

Adipocyte Complement-Related Protein of 30 kDa ▶Adiponectin

References 1. Rusciano D, Welch DR, Burger MM (2000) Cancer metastasis: experimental approaches. Laboratory Techniques in Biochemistry and Molecular Biology, Volume 29, Elsevier Science B.V. 2. Yamasaki H, Omori Y, Zaidan-Dagli ML et al. (1999) Genetic and epigenetic changes of intercellular communication genes during multistage carcinogenesis. Cancer Detect Prev 23:273–279 3. Boudreau N, Bissell MJ (1998) Extracellular matrix signaling: integration of form and function in normal and malignant cells. Curr Opin Cell Biol 10:640–646 4. Ruohslahti E, Öbrink B (1996) Common principles in cell adhesion. Exp Cell Res 227:1–11 5. Hedrick L, Cho KR, Vogelstein B (1993) Cell adhesion molecules as tumor suppressors. Trends Cell Biol 3:36–39

Adipocyte C1q ▶Adiponectin

Adipocytes Definition Fat storing cells. ▶Signal Transduction ▶Adipose Tumors

Adhesion Molecules Definition Are transmembrane cell adhesion proteins which extend across the cell surface ▶membrane and typically

Adipocytic Tumors ▶Adipose Tumors

Adiponectin

Adipokine Definition refers to a cluster of adipocyte-secreted molecules, which consist of growth factors, metabolic hormones, and cytokines etc. Many adipokines, such as leptin, adiponectin, resistin, visfatin, and adipocyte fatty acid binding protein, play important roles in obesity and its related diseases. ▶Adiponectin

Adiponectin J ANICE B.B. L AM , Y U WANG Department of Medicine and Genome Research Center, University of Hong Kong, Hong Kong, China

Synonyms Gelatin-binding protein 28; GBP28; AdipoQ; Adipocyte complement-related protein of 30 kDa; ACRP30; Adipose most abundant gene transcript 1; apM1; Adipocyte C1q and collagen domain containing; ACDC

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Definition

Adiponectin is a major ▶adipokine secreted exclusively from adipocytes. This adipokine has been demonstrated to possess antidiabetic, antiatherogenic, antiinflammatory and, more recently, antitumorigenic properties.

Characteristics Adiponectin was originally identified as an adiposespecific gene dysregulated in ▶obesity. Human adiponectin gene is located on chromosome 3q27 and encodes a 244 amino acids polypeptide comprising of an NH2-terminal secretory signal sequence, followed by a hypervariable region, a collagenous domain, and a COOH-terminal globular domain (Fig. 1a). Circulating concentrations of adiponectin range from 3 to 30 μg/ml, which accounts for about 0.05% of total human blood proteins. Endogenous adiponectin is predominantly present as several characteristic oligomeric complexes. The basic building block of the adiponectin complex is a trimer or low molecular weight (LMW) oligomer, which is formed via hydrophobic interactions within its globular domain. Two trimers self-associate to form a disulfide-linked hexamer or middle molecular weight (MMW) oligomer, which further assembles into a bouquet-like high molecular weight (HMW) multimeric complex that consists of 12–18 monomers (Fig. 1b). Posttranslational modifications, including disulfide bond formation at a conserved cysteine residue and glycosylations occurred on several hydroxylated lysine residues within the collagenous domain, are involved in the assembly and stabilization of the

Adiponectin. Figure 1 Schematic representation of the primary structure (a) and the oligomeric complexes of adiponectin (b). Adiponectin contains a NH2-terminal signal sequence peptide and a hypervariable region, followed by a conserved collagenous domain and a COOH-terminal globular domain. A cysteine residue within the hypervariable region is involved in the disulfide bond formation. Several lysine residues located within the collagenous domain are hydroxylated and glycosylated. (b) Adiponectin exists as three oligomeric species, including the trimer (LMW), hexamer (MMW), and HMW. Disulfide bond formation and glycosylation are involved in its oligomeric formation. GG, glucosylα(1–2)galactosyl group; S−S, disulfide bonds.

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oligomeric structures. Different oligomeric complexes of adiponectin activate distinct signaling pathways and possess different biological functions. Two putative adiponectin receptors, termed AdipoR1 and AdipoR2, have recently been identified. AdipoR1 is highly expressed in skeletal muscle whereas AdipoR2 is most abundantly expressed in liver. Both receptors are integral membrane proteins containing seven transmembrane spanning domains. AdipoR1/R2 mediates the effect of adiponectin on activation of ▶AMP-activated protein kinase (AMPK) and stimulation of glucose uptake and fatty acid oxidation. T-cadherin, which is highly expressed in endothelium and smooth muscle, has been identified as an adiponectin coreceptor with preference for hexameric and HMW adiponectin multimers. Both adiponectin analogues and adiponectin receptor agonists represent the potential therapeutic targets for obesity-linked diseases. Adiponectin and Carcinogenesis Although adiponectin is secreted exclusively from fat cells, the circulating adiponectin levels are paradoxically reduced in obese individuals and obesity-related pathological conditions, such as ▶insulin resistance, type 2 diabetes, and atherosclerosis. Adiponectin has been proved to have insulin-sensitizing, antidiabetic, and antiatherogenic activities. In addition, growing evidence has demonstrated adiponectin to be a potent inhibitor of carcinogenesis. Numerous clinical studies have observed an inverse association between blood adiponectin concentrations and risks of several ▶obesity-related cancers, such as ▶prostate, ▶breast, ▶endometrial, ▶gastric, and ▶colorectal cancers. Prostate Cancer Obesity is associated with prostate cancer progression, increased tumor aggressiveness, and poor prognosis. Higher plasma adiponectin is associated with a marked reduction in risk of prostate cancer, independent of other risk factors. Additionally, blood adiponectin levels in those with high-grade prostate cancer are significantly lower than those in the low-grade and intermediate-grade groups, suggesting that plasma adiponectin levels are negatively associated with the histologic grade and disease stage of prostate cancer. Adiponectin has been shown to inhibit leptin- and/ or ▶insulin-like growth factor-1 (IGF-1)-stimulated DU145 androgen independent prostate cancer cell growth and dihydrotestosterone-stimulated growth of androgen-dependent LNCaP-FGC cells at subphysiological concentrations. In addition, adiponectin enhances the inhibitory effects of the cytotoxic chemotherapy agent, doxorubicin, on prostate cancer cell growth. These data suggest that adiponectin could play an important role in the pathogenesis of prostate cancer, and may be used as a drug target for therapeutic interventions.

Breast Cancer Excess adiposity over the pre- and postmenopausal years is an independent risk factor for the development of breast cancer, and is associated with late-stage disease and poor prognosis. Clinical studies have shown that low plasma adiponectin levels are significantly associated with an increased risk for breast cancer in both pre- and postmenopausal women, particularly in a low estrogen environment. Moreover, tumors from women with low plasma adiponectin levels are more likely to show a biologically aggressive phenotype. In line with these clinical findings, experimental evidence supports the role of adiponectin as an inhibitory factor for breast cancer development. Adiponectin at physiological concentrations suppresses the proliferation and induces ▶apoptosis in the ▶estrogen receptor (ER)-negative human breast carcinoma MDA-MB-231 cells and the ERpositive human MCF7 breast cancer cells. It also inhibits insulin- and growth factors-stimulated cell growth in another ER-positive T47D human breast cancer cells. Furthermore, adiponectin replenishment therapy suppresses mammary tumorigenesis of MDA-MB-231 cells in nude mice. Endometrial Cancer Adiponectin is decreased in obesity, insulin resistance, type 2 diabetes, and polycystic ovary syndrome, all of which are well-established risk factors for endometrial cancer. Several case-control studies have demonstrated an inverse correlation between plasma levels of adiponectin and the risk of endometrial cancer, independent of other obesity-related risk factors as well as the major components of the IGF system. Moreover, a stronger inverse association is observed among obese women than among nonobese women. Further studies are needed to investigate whether adiponectin deficiency plays a causative role in the pathogenesis of endometrial cancer. Gastric and Colorectal Cancer Low plasma levels of adiponectin have been observed in patients with gastric cancer, especially in those with upper gastric cancer. Furthermore, plasma adiponectin levels tend to decrease as the tumor size, depth of invasion, and tumor stage increases. Additionally, the negative correlation is more significant in undifferentiated forms than in differentiated forms of gastric cancers. These data raise the possibility that adiponectin might play a potential role in the progression of gastric cancer, especially in the upper stomach. Although colorectal carcinogenesis is related to abdominal obesity and insulin resistance, the associations between low adiponectin levels and colorectal cancer are not conclusive. Two independent studies have suggested that men with low plasma adiponectin levels have a higher risk of colorectal cancer,

Adiponectin

whereas another report does not support this association. Moreover, adiponectin has been reported to have growth-promoting and proinflammatory actions on HT-29 colonic epithelial cancer cells. Leukemia Adiponectin inhibits cell proliferation and induces apoptosis in myelomonocytic cell lines. Decreased levels of plasma adiponectin have been found to be associated with ▶childhood acute myeloblastic leukemia (AML), but not with ▶acute lymphoblastic leukemia of B (ALL-B) or T (ALL-T) cells. Adiponectin levels are also reported to be inversely associated with ▶chronic lymphocytic leukemia and myeloproliferative diseases. However, it is worthy to note that adiponectin concentrations can be modulated by various inflammatory cytokines and interferon therapy in these conditions. Thus, whether low adiponectin level is a causal factor of leukemia, or a secondary response to ▶inflammation, needs to be further clarified. Mechanisms As summarized above, both clinical and experimental evidence support the role of adiponectin as a suppressor of tumorigenesis. Adiponectin has direct antiproliferative effects in a number of cancer cell lines. Although the underlying mechanisms remain poorly understood, adiponectin has been shown to modulate several intracellular signaling cascades involved in regulating cell proliferation and apoptosis (Fig. 2). AMPK The phosphorylation-dependent activation of ▶AMPK is the major signal transduction pathway evoked by adiponectin. AMPK mediates the insulin-sensitizing effects of adiponectin in liver and muscle. It is also

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involved in the regulatory activities of adiponectin on endothelial cell functions and cardiac remodeling. AMPK is a negative regulator on cell growth. The upstream kinase LKB1 that activates AMPK is a ▶tumor suppressor. ▶Tuberous sclerosis complex 2 (TSC2), another tumor suppressor, is downstream of AMPK and a key player in regulation of the ▶mammalian target of rapamycin (mTOR) pathway. Through inactivation of ▶mTOR, AMPK negatively regulates protein synthesis and de novo fatty acid synthesis, two essential elements for rapid cancer cell growth. In addition, AMPK controls phosphorylation and activation of the ▶P53 tumor suppressor and expression of the cell cycle inhibitor ▶p21. These molecular events might represent the potential mechanisms through which adiponectin regulate carcinogenesis. Indeed, it has been reported that adiponectin at subphysiological concentrations can induce AMPK phosphorylation and reduce the cell growth in human breast cancer MCF-7 cells. c-Jun N-Terminal Kinase (JNK) and Signal Transducer and Activator of Transcription 3 (STAT3) Both ▶JNK and STAT3 are the important regulators of cell proliferation, apoptosis, and differentiation in various physiological and pathophysiological conditions. Constitutive activation of STAT3 is crucial in malignant transformation and cancer progression. It has been reported that adiponectin stimulates the phosphorylation of JNK in prostate cancer DU145, PC-3, and LNCaP-FGC cells, as well as in hepatocellular carcinoma HepG2 cells. On the other hand, adiponectin inhibits constitutive activation of STAT3 in DU145 and HepG2 cells, suggesting that activation of JNK and inhibition of STAT3 may contribute to the suppressive effect of adiponectin on carcinogenesis. In addition, the inactivation of p42/p44

Adiponectin. Figure 2 Adiponectin elicits its antitumorigenic activities through multiple mechanisms.

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AdipoQ

MAP kinase has been implicated in the antiproliferative effects of adiponectin in human beast carcinoma MCF7 and T47D cells. Glycogen Synthase Kinase (GSK) 3b/b-Catenin Signaling Pathway Hyperactivation of the canonical ▶Wnt/β-catenin pathway is one of the most frequent signal abnormalities in many types of cancers. The central event in this pathway is the stabilization and nuclear translocation of β-catenin, where it binds to the transcription factor TCF/LEF and consequently activates a cluster of genes that ultimately establish the oncogenic phenotype. β-catenin is phosphorylated by GSK3β and then modified by ▶polyubiquitination for ▶proteasome-mediated degradation. Adiponectin could modulate the GSK3β/ β-catenin pathway in human breast cancer cells. In MDA-MB-231 cells, prolonged treatment with adiponectin markedly reduces serum-induced phosphorylation of GSK3β, decreases intracellular accumulation and nuclear translocation of β-catenin, and suppresses ▶cyclin D1 expression. These effects can be inhibited by inhibitors of GSK3β. These data suggest that the cross-talk between adipokines and the Wnt signaling pathway might represent a key mechanism underlying the development of obesity-related cancers. Other Pathways In addition to its direct suppressive effect on cancer cell proliferation, as an insulin-sensitizing hormone, adiponectin could ameliorate tumorigenesis indirectly by alleviating ▶hyperglycemia and insulin resistance, the two established risk factors for many obesityrelated cancers. Furthermore, adiponectin possesses antiinflammatory activity and can inhibit the production of a number of inflammatory factors involved in promoting tumorigenesis, such as IL6, IL8, TNFa, and MCP-1. There is also evidence supporting the anti ▶angiogenesis activity of adiponectin. It inhibits tumor neovascularization in mice, through suppression of endothelial cell proliferation, migration, and tubular formation. Moreover, adiponectin can act as a decoy for several proangiogenesis growth factors, including basic fibroblast growth factor (bFGF), platelet-derived growth factor BB (PDGF-BB), and heparin-binding epidermal growth factor (HB-EGF). In this manner, adiponectin prevents these growth factors from activating their respective receptors and effectively impedes their tumor-promoting activities. In summary, both experimental and clinical evidences support the suppressive role of adiponectin in tumorigenesis. In humans, adiponectin deficiency is closely associated with increased risks of several obesity-related cancers. Therefore, adiponectin and its agonists might represent a novel class of the anticancer agent for the treatment of these malignant

tumors. Further studies are warranted to investigate the prospective associations between plasma adiponectin levels and the risk of several obesity-related cancers, and to elucidate the detailed molecular events underlying the antitumor activities of adiponectin.

References 1. Barb D, Pazaitou-Panayiotou K, Mantzoros CS (2006) Adiponectin: a link between obesity and cancer. Expert Opin Investig Drugs 15:917–933 2. Kelesidis I, Kelesidis T, Mantzoros CS (2006) Adiponectin and cancer: a systematic review. Br J Cancer 94: 1221–1225 3. Scherer PE, Williams S, Fogliano M et al. (1995) A novel serum protein similar to C1q, produced exclusively in adipocytes. J Biol Chem 270:26746–26749 4. Wang Y, Lam JB, Lam KS et al. (2006) Adiponectin modulates the glycogen synthase kinase-3β/β-catenin signaling pathway and attenuates mammary tumorigenesis of MDA-MB-231 cells in nude mice. Cancer Res 66:11462–11470

AdipoQ ▶Adiponectin

Adipose Most Abundant Gene Transcript 1 ▶Adiponectin

Adipose Tumors F LORENCE P EDEUTOUR , A NTOINE I TALIANO Laboratory of Solid Tumors Genetics, Nice University Hospital and CNRS UMR 6543, Faculty of Medicine, Nice, France

Synonyms Lipomatous tumors; Adipocytic tumors; Lipomas; Liposarcomas

Adipose Tumors

Definition Adipose tumors (AT) are mesenchymal neoplasms that form the largest group of human tumors. They include benign tumors, such as the very common lipomas, as well as rare malignant tumors with various degrees of clinical aggressiveness. Histologically, AT consist of adipocytic cells showing different levels of differentiation, from mature adipocytes in benign lipomas up to undifferentiated lipoblastic cells in high-grade ▶liposarcomas. The 2002 World Health Organization classification distinguishes seven entities of benign AT: lipoma, lipoblastoma/lipoblastomatosis, angiolipoma, myolipoma of soft tissue, chondroid lipoma, spindle cell/pleomorphic lipoma, and hibernoma. Malignant AT, also called liposarcomas, include three types: well differentiated liposarcoma/dedifferentiated liposarcoma, ▶myxoid/round cell liposarcoma, and pleomorphic liposarcoma. Except for the ordinary superficial lipomas, differential diagnosis between benign and malignant AT and between AT and other kinds of tumors is sometimes difficult. Studies based on tumor karyotypes have identified chromosomal abnormalities specific to benign and malignant AT and recent advances in molecular cytogenetics improved AT diagnosis. It is now possible to directly detect the genic rearrangements resulting from chromosomal alterations on interphase nuclei such as those in formalin-fixed and paraffin embedded tumor tissue sections using fluorescence in situ hybridization (FISH) (▶interphase cytogenetics) or polymerase chain reaction (PCR).

Characteristics Benign Adipose Tumors The most common benign AT are the so-called superficial “conventional lipomas.” The other types of benign AT are rare and may be the cause of diagnostic difficulties because of their clinical or histological resemblance to malignant soft tissue tumors. In most cases benign AT do not require any treatment. Surgical

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removal may be necessary in case of functional or cosmetic impairment. ▶Conventional lipomas are the most common soft-tissue neoplasm in adults. They occur mainly in the 5–7th decades of life and are generally located superficially in subcutaneous fat. They can also be situated deeply in muscles or on the surface of bones or rarely in visceral and other organ sites. Lipomas usually present as a small (200 g) with nuclear atypia, more than five mitoses on 50 high-power fields, vascular and capsular invasion, broad fibrous bands, and extensive necrosis are highly suggestive of carcinoma. Small tumors without the mentioned features are considered to be adenomas. In children, distinguishing between adenoma and carcinoma is difficult because the histologic features of small and large lesions overlap. Only about

Adrenomedullin (AM) is a member of the ▶calcitonin superfamily of peptides. It is produced in virtually every organ by many different cell types and it is secreted into the plasma where it occurs at picomolar concentrations. Over the past several years AM has increasingly received the attention of the scientific community by virtue of its implication in many normal and disease states.

Characteristics Adrenomedullin is a small peptide (52 amino acids) first isolated from a ▶pheocromocytoma in 1993. It was initially described as a hypotensive peptide although after more than a decade of research and about 2,000 published articles published, AM is now recognized as a pluripotent peptide-hormone implicated in many normal and pathological processes ranging from vascular tone and diabetes to ▶angiogenesis and embryogenesis/ ▶carcinogenesis. Adrenomedullin: Peptide and Gene Structure Adrenomedullin is generated as part of a larger precursor molecule named preproadrenomedullin (preproAM) (Fig. 1). PreproAM is 185 amino acids long and contains an N-terminal 21 amino acid signal peptide which is cleaved during the transport of the molecule across the cell membrane to produce the 164 amino acids prohormone proAM. Further processing of proAM by endopetidases generates four peptides termed proadrenomedullin N-terminal 20 peptide (PAMP), mid-regional pro-adrenomedullin (proAM 45–92), adrenomedullin (AM) and adrenotensin (proAM 153–185). From these, PAMP, ProAM 45–92 and AM are present in plasma and PAMP, AM and Adrenotensin are biologically active peptides. Both PAMP and AM peptides are produced as a ▶glycine (Gly)-extended inactive peptides which coexists in plasma with the active form generated

Adrenomedullin

upon enzymatic ▶amidation. AM shares homology with several vasoactive peptide members of the calcitonin superfamily including calcitonin, calcitonin gene related peptide (CGRP), amylin and intermedin. Members of this family share the presence of an intramolecular disulfide bond which generates a six-member ring structure and an amidated carboxy terminal, both of which are required for biological activity. In humans, the single locus of the adrenomedullin gene is located in the short arm of chromosome 11. The complete gene (2,319 bp) contains four exons and three introns which are ▶alternatively spliced during the transcription process to generate two different transcripts (Fig. 1). The shortest mRNA form includes exons 1–4 and therefore codes for a complete preprohormone which results in stoichiometric amounts of the four peptides referred above. The longest

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transcript incorporates the third intron that contains an early termination codon, resulting in a truncated preprohormone which only expresses PAMP. AM is an ancient gene that, based on our current knowledge, first appeared in the starfish with a potential dual function of neurotransmission and host defense. It shows a remarkable degree of conservation in genomic organization and peptide structure from fish to humans which supports its critical role in species survival. Signal Transduction As most soluble peptides, AM transduces its signal upon interaction with a receptor located in the cellular surface. The discovery of the AM receptor in 1998 represented a novel paradigm in the field of ▶G-protein couple receptor (GPCR) signaling. A functional receptor for AM requires physical interaction in the cellular

Adrenomedullin. Figure 1 Genomic organization of the AM gene.

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Adrenomedullin

membrane of the seven transmembrane domain receptor calcitonin-receptor-like-receptor (CRLR) and either the receptor-activity-modifying protein (RAMP) 2 or RAMP3. CRLR has two alternative pharmacological profiles that are conferred by association to the accessory proteins RAMP1 (producing the CGRP receptor) and RAMP2/3 (producing the AM receptor). Therefore, the expression pattern of functional AM receptors is determined by the presence of these two components. In healthy individuals, RAMP2/3 is equally expressed among most tissues, excluding lung, female reproductive system and adipocytes which show higher levels of expression. CRLR expression although lower, parallels that of RAMP2 which suggests that the majority of CRLR signaling units in the body are complexed with RAMP2 to produce adrenomedullin receptors. Modest but robust changes in the expression of the complex CRLR-RAMP2 have been reported in certain physiological and disease states such as pregnancy, sepsis and ▶cancer. The same physiological conditions are related to high levels of AM expression. Other stimuli which result in coordinated regulation of AM, CRLR and RAMP2 include hypoxia, endocrine hormones and inflammatory cytokines. Upon binding to its receptor AM induces cAMP elevation through an adenylyl cyclase-PKA mediated pathway. While multiple reports including the seminal paper by Kitamura have consistently demonstrated cAMP mediated effects of AM, other more scarce ones have shown cAMP independent actions such as vasodilation via elevation of Ca2+ and K+-ATP, and activation of endothelial nitric oxide synthase. AM also activates Akt, ▶mitogen-activated protein kinase and focal adhesion kinase in endothelial cells which mediate its angiogenic potential. AM Serves as a Common Language Between the Different Cellular Components of the Tumor Microenvironment Many disease states have been reported to modulate the expression of AM including cancer. As we mentioned before, AM was originally isolated from an adrenal gland tumor. A wealth of subsequent studies have found that AM and its receptor are overexpressed in many human cancers and tumor cell lines establishing an ▶autocrine loop mechanism that tumor cells exploit to maintain an autonomous proliferative state. AM is intimately intertwined at several levels in the multistep process of tumor development. At the initial stage of tumor growth, rapid accumulation of malignant cells results in the establishment of an avascular nutrientdepleted ▶hypoxic environment. Low oxygen tension within and surrounding the tumor body triggers a number of survival mechanisms which allow neoplastic cells to overcome this inhospitable microenvironment. Many of these encompass the upregulation of AM’s

expression. In fact one, if not the most important driving force for AM upregulation in tumor cells is hypoxia. Cellular responses to hypoxia are mediated through a well known hypoxia inducible factor (HIF)-dependent mechanism. HIF is a heterodimeric transcription factor which is stabilized under hypoxic conditions and binds to specific DNA sequences denoted hypoxia response elements (HRE) which are present in the ▶promoter regulatory region of the AM gene (Fig. 1). Hypoxia also upregulates the expression of the AM receptor gene in many tumor types hence establishing a rational explanation behind the aforementioned autocrine growth mechanism underlying carcinogenesis (Fig. 2). As tumor derived AM is released into the microenvironment it establishes a peptide gradient which ultimately disseminates to reach a teeming collection of cell types known to be able to respond to this peptide and to be involved in further development of the tumor, including the cancer cell itself. AM not only stimulates tumor cell proliferation via its mitogenic activity but also by involving an antiapoptotic state. Although the advantageous effects of AM for the tumor cell are apparent, its actions are not restricted to this compartment within the tumor. On the contrary, AM acts as an integrative molecule allowing the crosstalk between all different compartments within the tumor microenvironment. As an example, AM is a ▶migratory factor for different inflammatory cells, including ▶mast cells. Mast cells migrate towards the tumor mass following the preestablished tumor-derived AM gradient. Hence, as mast cells approach the tumor they are exposed to increasingly higher concentrations of AM. Only when certain concentration of AM is reached in the proximity of the tumor, mast cells degranulate liberating to their immediate milieu numerous inflammatory factors (including AM) which not only enhance the tumor progression but also perpetuate the inflammatory process. AM is also implicated as a potential immune system suppressor, inhibiting macrophage function and acting as a negative regulator of the complement cascade, protective properties which help cancer cells circumvent immune surveillance. One of the most significant features distinctive of hypoxic tumors is their ability to induce angiogenesis. Tumor-induced angiogenesis is a pathological condition that results in ectopic neovascularization. Of most therapeutic interest is the finding that AM is an essential factor that regulates normal and pathological vascularization. AM was first described as a potent hypotensive peptide although its connection to the normal and pathological biology of the vascular system is much deeper than initially thought. AM is an essential factor for the normal development of vasculature as revealed by mice lacking the AM gene in mice which is embryonically lethal due to abnormal vascularization. AM also induces pathological neovascularization via

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Adrenomedullin. Figure 2 Model of the AM/tumor cell/inflammatory cells relationship in human carcinogenesis. The microenvironment around the tumor is hypoxic and stimulates expression of AM by the tumor cells. Tumorderived AM is released into the microenvironment setting up a concentration gradient of peptide that contributes to angiogenesis and attracts distal MCs to infiltrate the tumor site. Neovasculature makes possible tumor metastasis and it is used as a point of entrance for inflammatory cells (i.e. MC). As MCs migrate up the peptide gradient, higher AM concentrations are reached stimulating MC-derived angiogenic factors (AM, VEGF, bFGF, MCP-1) expression and ultimately release at the tumor site. AM mediates a paracrine tumor survival effect (direct mitogen, angiogenic factor, and anti-apoptosis), and functions as a paracrine recruitment factor drawing additional MCs to the area, thus perpetuating the inflammatory process and enhancing tumor promotion.

CRLR-RAMP2 present in the endothelial cells. Angiogenesis is a multistep process which commences with the growth of endothelial cells which is enhanced by tumor derived AM. AM also prevents hypoxiatriggered apoptosis in endothelial cells enhancing the neovascularization process. Additionally, AM participates in the remodeling of the extracellular matrix and tridimensional rearrangement of endothelial cells in the tissue which results in the establishment of the new intratumoral vasculature by stimulating migration and tube formation of endothelial cells. AM increases the permeability of the endothelial cells in the newly established vasculature which supplies the tumor with the necessary nutrients for expansion additionally it creates an access route for inflammatory cells which are attracted to the tumor site and migrate in following gradients of ▶chemoattractant and migratory factors produced by the tumor, such as AM. The same route can simultaneously be utilized by tumor cells as the entrance point to the vascular system facilitating the

metastasis process. The invasive capability of tumor cells is thus enhanced by AM.

Concluding Remarks Conclusions gleaned from the studies carried over the past fourteen years portrait AM as a molecular connector with competence to entangle and allow communication between the different cellular components of the tumor machinery which conspire under the tumor cell direction to promote cancer. It is not only the direct effect that AM has on tumor cells but also its ability to interact with all these cellular elements which makes this peptide an attractive therapeutic target for cancer. The collective research effort is shifting from trying to discern whether AM is a causative agent of cancer to better understanding its central role as a multifaceted exchange currency among the multiple cellular players involved in tumor development. Strategies utilizing blocking agents aimed at disruption of this loop might be proven successful to impede tumor growth.

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Adriamycin

References 1. Kitamura K, Kangawa K, Kawamoto M et al. (1993) Adrenomedullin: a novel hypotensive peptide isolated from human pheochromocytoma. Biochem Biophys Res Commun 192:553–560 2. Zudaire E, Martinez A, Cuttitta F (2003) Adrenomedullin and cancer. Regul Pept 112:175–183 3. Cuttitta F, Portal-Nuñez S, Falco C et al. (2006) Adrenomedullin: An esoteric juggernaut of human cancers. In Kastin AJ (ed) Handbook of biologically active peptides. Elsevier

Adriamycin T SUTOMU TAKAHASHI , A KIRA N AGANUMA Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan

Synonyms Doxorubicin; 14-Hydroxyldaunorubicin

Definition

Adriamycin is an antineoplastic ▶anthracycline antibiotic isolated from cultures of Streptomyces peucetius var. caesius. It is widely used in the treatment of various different types of cancers. Proposed mechanisms for its antitumor activity include intercalation into DNA, inhibition of ▶topoisomerase II, and promotion of freeradical formation. However, the clinical utility of this drug is seriously limited by the development of cardiomyopathy and ▶myelosuppression.

Characteristics Chemical Properties Adriamycin is an orange–red compound, soluble in water and aqueous alcohols, moderately soluble in anhydrous methanol, and insoluble in nonpolar organic solvents. It consists of an aglycone (adriamycinone), a tetracyclic ring with adjacent quinone–hydroquinone groups in rings C-B, coupled with an amino sugar (daunosamine). It is generated by C-14 hydroxylation of its immediate precursor, ▶daunorubicin (see Fig. 1). Semisystematic derivatives of adriamycin include ▶epirubicin, an axial-to-equatorial epimer of the hydroxyl group at C-4′ in daunosamine, and ▶pirarubicin, 4′-O-tetrahydropyranyl-adriamycin, etc. Clinical Aspects Therapeutic Applications Adriamycin has a broad antitumor spectrum. It is used to treat hematopoietic malignancies such as leukemias,

lymphomas (non-Hodgkin disease, ▶Hodgkin disease) and ▶multiple myeloma, and different solid tumors (breast, thyroid, gastric, ovarian, bronchogenic, head and neck, prostate, cervical, pancreatic, uterine and hepatic carcinomas, as well as transitional cell bladder carcinomas, ▶Wilms tumor, ▶neuroblastoma, and soft tissue and bone sarcomas). Adriamycin is applied as a component of combination chemotherapy, rather than a monotherapy. Adriamycin-based combination chemotherapy regimens include ABVD (Adriamycin, Bleomycin, Vinblastine, Dacarbazine) for non-Hodgkin disease, CHOP (Cyclophosphamide, Adriamycin, Vincristine, Prednisone) for ▶Hodgkin disease, and M-VAC (Methotrexate, Vinblastine, Adriamycin, Cisplatin) for urothelial carcinoma. Pharmacokinetics Adriamycin is rapidly cleared from the plasma, quickly taken up and only slowly eliminated from organs such as the spleen, lungs, kidneys, liver, and heart. It does not cross the blood–brain barrier. Adriamycin is converted to an active metabolite, adriamycinol, through a twoelectron reduction of the side chain C-13 carbonyl moiety by NADPH-dependent cytoplasmic aldo/keto reductase or carbonyl reductase. It is converted to inactive metabolites in the liver and other tissues, and predominantly excreted in the bile. Clinical Toxicities The usual toxic side effects of adriamycin including stomatitis, nausea, vomiting, alopecia, gastrointestinal disturbance, and dermatological manifestations, are generally reversible. The dose-limiting side effects of the anthracyclines including adriamycin are myelosuppression and cardiotoxicity. Myelosuppression with leukopenia, neutropenia, and occasionally thrombocytopenia is dose-related and potentially life-threatening. Cardiotoxicity is characteristic of the anthracycline antibiotics, of which adriamycin is the most toxic. Adriamycin-induced cardiotoxicity can be acute, chronic, or delayed. The acute effect is not dose-related, and is characterized by sinus arrhythmias and/or abnormal electrocardiographic (ECG) changes (nonspecific ST-T wave change, prolongation of QT interval). Acute toxicity of this type is transient and rarely a serious problem. Chronic cardiotoxicity is a much more serious problem, being related to cumulative dose. It is irreversible and leads to dilative cardiomyopathy and congestive heart failure (CHF), usually unresponsive to cardiotonic steroids (digitalis) and β-blockers. The risk of developing CHF increases markedly at total cumulative doses in excess of 500 mg/m2. Moreover, the effects of this chronic cardiotoxicity may manifest precipitously without antecedent ECG changes. The risk of life-threatening cardiac dysfunction can be decreased by regular monitoring of endomyocardial

Adriamycin

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Adriamycin. Figure 1 Structures of adriamycin and its analogues.

(EM) biopsy histopathological changes and left ventricular ejection fraction (LVEF) as measured by the multigated radionuclide angiography (MUGA) method and/or echocardiography (ECHO). Finally, adriamycin can also cause delayed cardiotoxicity, possibly, related to the dose. This occurs after an asymptomatic interval, mostly in people who were treated as children. Several approaches have been proposed to overcome adriamycin cardiotoxicity and that of the anthracycline antibiotics generally. Administration by slow continuous intravenous infusion (over 48–96 h) rather than the standard bolus injection decreases the likelihood of chronic cardiotoxicity. ▶Dexrazoxane (ICRF-187), an iron chelator that prevents the formation of complexes between adriamycin and iron, and subsequent production of ▶reactive oxygen species (ROS), is sometimes used as a cardioprotectant. However, it may decrease antitumor activity. Liposomal encapsulation is designed to increase safety and efficacy by decreasing cardiac and gastrointestinal toxicity through decreased exposure of these tissues to the drug, while effectively delivering it to the tumor. Polyethyleneglycol-coated (Pegylated) liposomal adriamycin (Doxil (USA), Caelyx (UK)) is currently used for treating AIDS-related ▶Kaposi sarcoma, refractory ovarian cancer, and some other solid tumors. In order to improve therapeutic efficacy and decrease side effects by promoting drug accumulation inside tumors, the water-soluble N-(2hydroxypropyl) methacrylamide (HPMA) copolymer, magnetic targeted carriers, and ▶immunoliposome

conjugates with the specificity of whole monoclonal antibodies (e.g. antibodies against CD19 or MUC-1) or FAB’ fragments have been developed as carriers of adriamycin. In further efforts to decrease the risk of developing cardiotoxicity, several derivatives of adriamycin or daunorubicin, such as epirubicin, pirarubicin, ▶idarubicin, and ▶aclarubicin have been developed. Although these agents may be less cardiotoxic than adriamycin itself, they do have a decreased antitumor activity. Pharmacological Mechanisms Mechanisms of Action Several mechanisms appear to contribute to the cytotoxic effects of adriamycin, including inhibition of DNA replication and repair; inhibition of RNA and protein synthesis via intercalation of the aglycone portion of the molecule between adjacent DNA base pairs, especially G-C base pairs; promotion of the cleavage of DNA by formation of adriamycintopoisomerase II-DNA ternary complexes; inhibition of topoisomerase I; and direct binding to the cell membrane. Formation of free radicals is another major mechanism of cytotoxicity. One-electron reduction of the quinone moiety in the C ring of adriamycin by some flavin-containing enzymes (mitochondrial NADH dehydrogenase, microsomal NADPH-cytochrome P450 reductase, and xanthine oxidase) generates adriamycinsemiquinone radicals. These rapidly react with oxygen

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Adult-Onset Diabetes

to form superoxide anions, which then generate hydrogen peroxide and hydroxyl radicals in the presence of redox-active metals such as iron (III) and copper (II). The final result is DNA damage and lipid peroxidation. The semiquinone radical can be transformed into an aglycone C7-centered radical that also mediates cellular damage by DNA alkylation and lipid peroxidation. Adriamycin can bind to metal ions such as iron, copper, and manganese, by forming adriamycin–metal complexes, which may lead to generation of ROS and damage to cell membranes. Mechanisms of Resistance Development of resistance to the drug is a major obstacle in chemotherapy with adriamycin. Drug efflux pumps are important for defending cells against anticancer drugs. The acquisition of adriamycin resistance involves promotion of excretion of the drug by overexpressing the ATP-binding cassette (ABC) transporters ▶P-glycoprotein (P-gp)/ABCB1, ▶multidrug resistance-associated proteins (MRPs)/ABCC (MRP1, MRP2, and MRP6 etc.), and breast cancer resistance protein (BCRP)/ABCG2. P-gp transports hydrophobic compounds including adriamycin, while MRP1 and BCRP can extrude predominantly these glutathione conjugates. In addition, RalA-binding protein 1 (RALBP1)/Ral-interacting protein of 76 kDa (RLIP76) is a nonclassical ABC transporter involved in drug excretion. RALBP1 catalyzes ATP-dependent efflux of xenobiotics including adriamycin as well as its glutathione conjugates. In fact, the level of expression of these efflux pumps correlates with the clinical efficacy of adriamycin. ▶Glutathione-S transferases (GSTs) are a family of enzymes involved in the cellular detoxification of xenotoxins. Adriamycin and its metabolites (adriamycinol) are conjugated with glutathione by GSTs and transported by MRPs and BCRP, etc. Increased expression of GSTs, especially GSTπ, also confers adriamycin resistance by promoting detoxification. Lung resistance protein (LRP), the 110 kDa major vault protein (MVP), is a main component of vaults, which are multisubunit structures that may be involved in nucleocytoplasmic transport, and is involved in resistance to anticancer drugs including adriamycin. LRP may affect the intracellular distribution of adriamycin, but the detailed mechanisms remain unknown. Furthermore, a relationship between adriamycin resistance and qualitative and quantitative changes in the expression of topoisomerase II, a major target for adriamycin, has been reported. Mechanisms for Development of Cardiotoxicity The molecular mechanisms leading to adriamycininduced cardiotoxicity may include lipid peroxidation

by generation of ROS, abnormalities in intracellular calcium homeostasis through inhibition of sarcomeric reticulum Ca2+-ATPase (SERCA2), Na+-K+-ATPase and Na+-Ca2+ exchanger of sarcolemma, inhibition of mitochondrial creatine kinase, and interaction with cardiolipin, which is a phospholipid of the inner mitochondrial membrane in the heart. Adriamycin also promotes apoptosis by activation of p38 mitogen-activated kinases (▶MAPK) in cardiac muscle cells. Moreover, adriamycin downregulates the expression of genes for sarcomeric proteins (such as α-actin, myosin, troponin I, and myofibrillar creatine kinase) and for proteins involved in calcium homeostasis in the sarcomeric reticulum, such as SERCA2, cardiac muscle ryanodine receptor (RYR2), calsequestrin, and phospholamban, by suppression of transcription factors (e.g. MEF2C, HAND2, and GATA4) and/or activation of a the transcriptional repressor Egr-1. Adriamycinol (doxorubicinol), a secondary alcohol metabolite, may also be involved in the development of adriamycin-induced cardiotoxicity, via enhancing the inhibitory effects of SERCA2, Na+-K+-ATPase, and Na+-Ca2+ exchanger of sarcolemma. Adriamycinol also inhibits the iron-regulatory protein/ironresponsive element (IRP/IRE) system, which plays a crucial role in iron homeostasis, and may lead to cardiotoxicity.

References 1. Hortobagyi GN (1997) Anthracyclines in the treatment of cancer. An overview. Drugs 54 Suppl 4:1–7 2. Minotti G, Menna P, Salvatorelli E et al. (2004) Anthracyclines: molecular advances and pharmacologic developments in antitumor activity and cardiotoxicity. Pharmacol Rev 56:185–229 3. Nielsen D, Maare C, Skovsgaard T (1996) Cellular resistance to anthracyclines. Gen. Pharmacol. 27:251–255 4. Awasthi S, Sharma R, Singhal SS et al. (2002) RLIP76, a novel transporter catalyzing ATP-dependent efflux of xenobiotics. Drug Metab Dispos 30:1300–1310 5. Poizat C, Sartorelli V, Chung G et al. (2000) Proteasomemediated degradation of the coactivator p300 impairs cardiac transcription. Mol Cell Biol 20:8643–8654

Adult-Onset Diabetes Definition Diabetes Type 2.

Adult Stem Cells

Adult Stem Cells R IKKE C HRISTENSEN , N EDIME S ERAKINCI Anatomy and Neurobiology, Institute of Medical Biology, University of Southern Denmark, Odense, Denmark

Synonyms Somatic stem cells; Tissue stem cells; Postnatal stem cells

Definition An undifferentiated cell found in a differentiated tissue that can renew itself and (with certain limitations) differentiate to yield all the specialized cell types of the tissue from which it originated.

Characteristics

Adult ▶stem cells are defined as undifferentiated tissue-specific stem cells with extensive self-renewal capacity, which can proliferate to generate mature cells of the tissue of origin. The primary roles of adult stem cells are to maintain and/or regenerate the cells of damaged tissues. Adult stem cells were first described in organs and tissues characterized by high cell turnover, such as blood, gut, testis, and skin but have to date also been isolated from many other organs and tissues including brain, bone marrow, liver, heart, lung, retina, and skeletal muscle. Stem cells differ from ▶somatic cells with their different potentials and their proliferation ability. There are three kinds of stem cells: Embryonic, germinal, and adults stem cells that are classified according to their developmental potential ranging from totipotency to unipotency. The fertilized oocyte and the blastomere up to the 8-cell stage are considered as totipotent (▶totipotent stem cells) as they can differentiate to generate a complete organism. ▶Embryonic stem cells, the cells derived from the inner cell mass of the blastocyste, are pluripotent (▶pluripotent stem cells) and have the ability to differentiate into cells and tissues from all three germ layers: the endoderm, the ectoderm, and the mesoderm. ▶Germinal stem cells are also pluripotent and are derived from so-called primordial germ cells and give rise to the gametes (sperm and eggs) in adults. In contrast, adult stem cells are generally believed to be multipotent (▶multipotent stem cells) or unipotent (▶unipotent stem cells) which means that they can only give rise to progeny restricted to the tissue of origin. Hematopoietic stem cells (▶HSC), bulge stem cells in the hair follicle, and mesenchymal stem cells (▶MSC) are examples of multipotent stem cells, which can differentiate into multiple cell types of

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a single tissue, whereas epidermal stem cells, myosatellite cells of muscle, and endothelial progenitor cells are examples of unipotent stem cells, which only give rise to one mature cell type. Recently, some studies have shown that many adult tissues may contain cells with pluripotent capacity capable of generating differentiated cells from an unrelated tissue. This process is termed ▶stem cell plasticity. In most tissues/organs renewal is compensated by tissue-specific stem cells. The stem cells normally divide very rarely, but stimuli caused by damaged or injured tissue or a need to generate progeny to maintain the tissue can induce proliferation and produce daughter cells that can differentiate into the specific cell lineages of the respective tissue type. Stem cell division typically leads to the formation of committed progenitor cells with more limited self-renewal capacity as e.g., transit amplifying cells in the epidermis or lymphoid or myeloid progenitors in the bone marrow. Tissue progenitor or transit amplifying cells provides an expanded population of a proliferating tissue that differentiate into more mature and determined cells that eventually no longer proliferates and die. To maintain the balance in the adult tissues/organs, the number of progenitor/stem cells that proliferates must be equal to the number of cells that determinedly differentiate and die. If the number of proliferating cells is higher than the number of cells that maturate and die, it will give the primary feature of a cancer. Studies have shown that many of the pathways that regulate normal stem cell proliferation are dysregulated and cause neoplastic proliferation in cancer cells. Therefore, cancer may be considered a disease of dysregulated cellular self-renewal capacity. Adult stem cells reside in a special ▶microenvironment termed the stem cell niche. Stem cell niches are composed of a group of cells that provide a physical anchorage site and extrinsic factors that control stem cell proliferation and differentiation and enable them to maintain tissue homeostasis. Deregulation of the niche signals has been proposed to lead to cancer. A decrease in proliferation-inhibiting signals, or an increase in proliferation-promoting signals, may lead to excessive stem cell production and thereby development of cancer stem cells (see later). Investigation of the interaction between stem cells and their niche may reveal possible targets for cancer treatments. For example, the blocking of proliferation signals, enhancing of antiproliferative signals or induction of differentiation from the stem cell niche may be used to target the cancer stem cells. It has furthermore been suggested that targeting the stem cell niche may prevent cancer metastasis. Some cancers metastasize to sites that cannot be explained by circulation distribution, lymphatic drainage or anatomic proximity. These sites may, however, provide favorable niches that support the survival of the cancer stem cells.

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Much effort is put into the identification of ▶stem cell markers to be able to isolate the stem cells of interest. Isolation of stem cells makes it possible to enhance the knowledge of stem cell identity and to use them therapeutically. Therapeutic Potential Adult stem cell transplantation has been used in several years for the treatment of ▶hematological malignancies and lymphomas. The main purpose of stem cell transplantation in cancer treatment is to make it possible for patients to receive very high doses of chemotherapy and/or radiation. High-dose chemotherapy and radiation can severely damage or destroy the bone marrow while killing cancer cells. Before treatment, bone marrow or peripheral blood stem cells are harvested from the patient itself (for autologues transplantation) or from a donor (for allogen transplantation), frozen down, and then transplanted after the patient has received high doses of chemotherapy, radiation therapy, or both. The transplanted healthy stem cells replace the stem cells destroyed by high-dose cancer treatment and allow the bone marrow to produce healthy cells. Stem cells in general, due to their high proliferative capacity and long-term survival in comparison to somatic cells, make them very ideal candidates to use for regenerative medicine and cell replacement therapy. Lately, there has been an increasing interest in the potential use of adult stem cells in cell replacement strategies and in tissue engineering, including gene therapy. This current interest rose due to the discovery of adult stem cells with pluripotential capacity and/or transdifferentiating (▶transdifferentiation) ability, which means that cells from one tissue can differentiate into mature and functional cells of another tissue. There are reports that HSCs under certain conditions can evolve into cells of neural lineage, liver, muscle, skin, and endothelium; skeletal muscle stem cells can evolve into blood cells and neural cells; and hair follicle stem cells can evolve into neural lineage cells. Other adult stem cells that can be induced to a different cell type include MSCs, cardiac muscle stem cells, neural stem cells, and testis-derived stem cells. These cells have the advantage that they can be used as autologous transplants and have been proposed as an attractive alternative to ▶embryonic stem cells in genetic therapy. An alternative approach for therapeutic use of stem cells is to use them as cellular vehicles. It has been demonstrated that genetically modified MSCs can be used to target delivery of anticancer agents and ▶suicide gene therapy vectors to tumor cells. Upon administration, MSCs can target microscopic tumors, proliferate and differentiate, and contribute to the formation of a network of cells surrounding the tumor (tumor stroma). MSCs genetically modified to express interferon beta has, for example, been shown to inhibit

the growth of tumor cells by local production of interferon beta. MSCs are not the only stem cells that have been used as shuttle vectors for delivery of gene therapies into growing tumors. It has also been demonstrated that neural stem and progenitor cells migrate selectively to tumor loci in vivo in mice. These studies clearly suggest that a stem cell-directed prodrug therapy approach may have great use for eradicating tumors as well as to treat the residual cancer cells remaining after therapy. Genetic manipulation of adult stem cells may also be used to increase the functionality and proliferative capacity of these cells. HSCs are one of the most promising candidates for correction of single gene disorders as e.g., ▶cystic fibrosis and ▶hemoglobinopathies, due to their capability of targeting solid organs and high success rate in their isolation by using a combination of surface markers. Infants with forms of ▶severe combined immunodeficiency syndrome have successfully been treated with genetically engineered bone marrow stem cells. The stem cells were harvested from the patients, a functional gene inserted, and the genetically modified cells reintroduced to the same patient. To increase the success of chemotherapeutic treatment, drug resistant HSCs have been produced by introduction of the ▶multidrug resistance gene with the aim of limiting the myelosuppressive effects of standard chemotherapeutic agents on the stem cells. However, even though adult stem cells have shown to carry great potential to function as therapeutic agents for targeting human diseases such as cancer, degenerative and chronic diseases, they do have some restrictions such as having limited self-renewal capacity. This limitation can be overcome by the introduction of immortalizing genes that increases the cells proliferative capacity. ▶Telomerase has been, in this connection, highlighted among the numerous genes that are capable of immortalizing stem- or progenitor cells. However, suggested oncogenic potential of ▶immortalized cells release caution that before the therapeutic use of stem cells in the clinic, a thorough screen for transformation phenotype is required. Cancer Stem Cells The theory that cancer stem cells (▶cancer stem-like cells and ▶stem-like cancer cells) are involved in many types of cancer has recently gained popularity. There are many similarities between adult stem cells and cancer stem cells. Both have the ability to self-renew and differentiate into more mature diversified cells. Cancer stem cells and normal stem cells share many cell surface markers and utilize many of the same signal transduction pathways. Cancer stem cells have been identified in most types of hematopoietic malignancies, including acute myeloid leukemia, chronic myeloid leukemia, acute

Advanced Breast Cancer

lymphoblastic leukemia, and multiple myeloma. Recently, cancer stem cells have also been isolated from solid tumors such as breast, lung, and brain tumors. The cancer stem cells only represent approximately 1% of the tumor, making them difficult to detect and study. Studies have shown that cancer stem cells may cause tumors when transplanted into a secondary host indicating that the cancer stem cells can initiate and repopulate a tumor. A study of human leukemia shows that the normal hematopoetic stem cell and the neoplastic clone share common molecular mechanisms governing proliferation which is supportive of the normal hematopoetic stem cell being a target for transformation. Due to stem cells are able to divide over the lifespan of the individual they seem to allow accumulation of a number of mutations and perhaps epigenetic changes (▶epigenetics) that cause neoplastic development. In addition, it has been shown that adult stem cells can be targets for neoplastic transformation by introducing the telomerase gene into a purified stem cell. The transduced cell line showed characteristic alterations of neoplastic development such as contact inhibition, anchorage independence, and in vivo tumor formation in immunocompromised mice. All these findings give a very large support to the existence of cancer stem cells and the strong links between normal adult stem cells and cancer stem cells suggest that stem cells are targets for neoplastic transformation. Cancer stem cells may also be derived from differentiated cells. Loss of the ▶tumor suppressor genes p16Ink4 and p19Arf combined with constitutive activation of the EGF receptor (▶EGFR) caused loss of differentiation in mature brain astrocytes and the cells regained stem cell properties. The identification of cancer stem cells strongly suggests that these cells are the key targets for future therapeutic development as they fuel the replicative capacity of the cancer. Therefore, as much as understanding the nature of a cancer cell it is very crucial to understand the neoplastic potential of the stem cells. Analysis of the differences between adult stem cells and cancer stem cells is very important to be able to specifically target the cancer stem cells whilst sparing the normal stem cell population. Several studies indicate that some stem cell markers are expressed differently in normal and cancer stem cells and these may be potential targets in the development of future cancer treatments.

References 1. Pessina A, Gribaldo L (2006) The key role of adult stem cells: therapeutic perspectives. Curr Med Res Opin 22:2287–2300 2. Pan CX, Zhu W, Cheng L (2006) Implications of cancer stem cells in the treatment of cancer. Future oncol 2:723–731

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3. Lotem J, Sachs L (2006) Epigenetics and the plasticity of differentiation in normal and cancer stem cells. Oncogene 25:7663–7672 4. Tuan RS, Boland G, Tuli R (2003) Adult mesenchymal stem cells and cell-based tissue engineering. Arthritis Res Ther 5:32–45 5. Reya T, Morrison SJ, Clarke MF et al. (2001) Stem cells, cancer, and cancer stem cells. Nature 414:105–111

Adult T-cell Leukemia Definition ATL; A leukemia of mature T lymphocytes (▶T cells) developing in adults, resulting from infection with the ▶human T-cell leukemia virus (HTLV) and characterized by circulating malignant T-lymphocytes, skin lesions, lymphadenopathy (enlarged lymph nodes), hepatosplenomegaly (enlarged liver and spleen), hypercalcemia (high blood calcium), lytic (“punched out”) bone lesions, and a tendency to infection. There are four categories of ATL, based on the aggressiveness of the disease – smoldering, chronic, lymphoma, and acute.

Adult Tissue Stem Cells Definition These cells are set aside during development in order to provide a source for replenishment of tissue over time in response to damage or simply wear and tear. ▶Stem Cell Telomeres

Advanced Breast Cancer Definition Tumors of stage III or IV (larger than 5 cm and/or have metastasized). ▶Fulvestrant ▶Breast Cancer

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AEL

AEL

Aflatoxin B1

Definition

Definition

Acute erythro leukemia.

Aflatoxin B1 is a potent hepatocarcinogen produced by the mold Aspergillus flavus; ▶aflatoxins

▶ETV6

▶Detoxification ▶Carcinogenesis

Aerobic Glycolysis ▶Warburg Effect

Aflatoxins T HOMAS E. M ASSEY, K ATHERINE A. G UINDON Department of Pharmacology and Toxicology, Queen’s University, Kingston, ONT, Canada

Aesthetic and Reconstructive Surgery of the Breast

Definition

Surgical procedures that reshape the breast to improve their appearance.

Mycotoxins are contaminants of a number of agricultural products, including peanuts, corn, and other grains in warm and moist conditions. Human exposure to aflatoxins is primarily through ingestion and results in acute hepatic necrosis, marked bile duct hyperplasia, acute loss of appetite, wing weakness, and lethargy.

▶Oncoplastic Surgery

Characteristics

Definition

Afaxin Definition ▶Retinol.

Affinity-Matured IgG Response Definition Affinity is the strength of binding between a receptor, such as the antigen-binding site on an antibody and a ligand, as for example an epitope on an antigen. High titer, high affinity IgG antibodies are characteristic of an antigen-driven immune response ▶Autoantibodies

In the early 1960s, an outbreak of hepatotoxic disease in turkeys, which became known as turkey “X” disease, gained the attention of many investigators worldwide. This condition was characterized by acute hepatic necrosis, marked bile duct hyperplasia, acute loss of appetite, wing weakness, and lethargy. It was deduced that the condition was caused by consumption of peanut meal contaminated with a mycotoxin, which is a toxin of fungal origin. The culprit fungi in turkey “X” disease turned out to be strains of Aspergillus flavus, A. parasiticus, and A. nomius, and thus the term aflatoxins was coined for the toxic metabolites. More specifically, A. flavus and A. parasiticus can produce aflatoxins B1, B2, G1, G2, and M1. These mycotoxins can contaminate a number of agricultural products, including peanuts, corn, and other grains in warm and moist conditions. Human exposure to aflatoxins is primarily through ingestion. In addition to outbreaks of liver failure and gastrointestinal bleeding in Southeast Asia and Africa having been attributed to aflatoxins, ▶liver cancer incidence was observed to be elevated in regions with high endemic aflatoxin concentrations. The two major risk factors for human ▶hepatocellular carcinoma, the fifth most common cancer worldwide, are hepatitis B infection and ingestion of aflatoxins.

Aflatoxins

Aflatoxin B1 (AFB1), the most prevalent and carcinogenic of the aflatoxins, is classified as a group 1 carcinogen (carcinogenic to humans) by the International Agency for Research on Cancer. Although the majority of AFB1 research has focused on its hepatic effects, AFB1 also targets other organs, including the lung and the kidney. In the lung, exposure to inhaled AFB1, particularly from contaminated grain dusts, has been linked to ▶respiratory cancers (▶Lung cancer). Due to a significant proportion of ingested mycotoxin being excreted via the urine, the renal nephron is exposed to AFB1 and its metabolites. AFB1 accordingly alters kidney function, and is a known renal carcinogen. Biotransformation AFB1 is defined as a procarcinogen, as its bioactivation is required for carcinogenicity (Fig. 1). The initial

Aflatoxins. Figure 1 Biotransformation of AFB1.

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metabolism of AFB1 involves four types of reactions: O-dealkylation, hydroxylation, epoxidation, and ketoreduction. The enzymes responsible for the metabolism include members of the ▶cytochrome P450 family (CYPs), prostaglandin H synthase (PHS), lipoxygenase (LOX), and a cytosolic NADPH-dependent reductase. In experimental animals, CYPs involved in AFB1 bioactivation include members of 1A, 2B, 2C, and 3A subfamilies. In humans, there are multiple p450 isozymes implicated, including CYP1A2, CYP2A3, CYP2B7, CYP3A3, and CYP3A4. CYP3A4 is thought to play a predominant role in the metabolism of AFB1 in human liver; although CYP1A2 has the highest affinity for AFB1 at low concentrations, it is expressed at much lower levels than CYP3A4. PHS and LOX are involved in ▶xenobiotic bioactivation by catalyzing the oxidation of ▶arachidonic acid to produce lipid

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peroxyl radicals, which are known epoxidizing agents. Cooxidation by PHS and LOX may be a significant mechanism of AFB1 bioactivation in extrahepatic tissues such as lung, which has high PHS and LOX expression, but overall P450 activity is lower than that in the adult liver. Regardless of the enzyme catalyzing the reaction, epoxidation of AFB1 results in formation of AFB1-8,9epoxide, which can exist in both endo and exo conformations. The exo-epoxide is the isomer implicated in the ▶alkylation of DNA, with its reactivity being at least 1,000 fold greater than that of the endoepoxide. Hydroxylated metabolites of AFB1 include AFM1, AFQ1, AFP1, and AFB2a. The formation of aflatoxicol from AFB1 is reversible, and therefore aflatoxicol is considered to be a “reservoir” for AFB1 rather than a bioactivation or ▶detoxification product. The two pathways for AFB1-epoxide detoxification are glutathione conjugation and epoxide hydrolysis, with glutathione conjugation being quantitatively the most important (Fig. 1). Glutathione conjugation is catalyzed by ▶glutathione-S-transferases (GSTs), which can be highly polymorphic. Human GSTM1-1 (hGSTM1-1), which is absent in ~50% of individuals, has the highest activity towards AFB1 exo-epoxide, but the importance of this polymorphism in AFB1 carcinogenicity has not yet been clearly established. AFQ1, AFP1, and AFB2a are not highly mutagenic and therefore are considered to be detoxification products. They can form glucuronide or sulfate conjugates, which are excreted. AFM1, a metabolite of AFB1 identified in milk and urine, is less biologically active than AFB1, but regardless is a potent carcinogen. The AFM1-epoxide can also bind to DNA, forming AFM1-N7-guanine. Carcinogenesis AFB1 is considered to be a complete carcinogen, possessing activity as both an initiator and a promoter. Initiation occurs by ▶DNA damage, as well as cytotoxicity, which stimulates cell division, thus promoting tumor formation. There are many characteristics of AFB1 that makes it a useful tool for investigating ▶chemical carcinogenesis. First, the metabolites of AFB1 have been extensively investigated and their toxicity elucidated. Second, the toxicity of AFB1 is determined by a balance between bioactivation and detoxification of the AFB1-8,9-epoxide. Third, there exists multiple mechanisms of bioactivation that can be compared in terms of carcinogenic metabolites produced. Fourth, not only does the susceptibility of a species/tissue relate to ▶DNA repair capabilities (▶Repair of DNA), but AFB1 itself has effects on DNA repair activity. Fifth, the specific AFB1-DNA adduct formed can be used to predict the mutagenic responses. Finally, the parent compound and several metabolites fluoresce, facilitating detection.

The exo epoxide of AFB1 can alkylate proteins and ▶nucleic acids, with the second guanine from the 5′ end in guanine di- and trinucleotide sequences in DNA being the favored target. The major adduct formed by the exo-epoxide is 8,9-dihydro-8-(N7-guanyl)-9hydroxy AFB1, also known as AFB1-N7-Gua (Fig. 2). AFB1-N7-Gua can undergo three reactions: release of AFB1-8,9-dihydrodiol restoring guanine; depurination resulting in an apurinic site in DNA; and base-catalyzed hydrolysis to form the AFB1-formamidopyrimidine adduct (AFB1-FAPY). AFB1-FAPY, representing a significant proportion of AFB1 adducts in vivo, exists in equilibrium between two rotameric forms, designated AFB1-FAPY major and AFB1-FAPY minor. The structure of AFB1-FAPY has not been completely defined, although the proposed structure is presented in Fig. 2. It has also been shown that metabolism of AFB1 can lead to formation of 8-hydroxy-2′-deoxyguanosine in rat, duck, and woodchuck liver and in mouse lung. G to T transversion, the most frequently observed mutation induced by AFB1, results from DNA alkylation and subsequent AFB1-N7-Gua formation, and possibly by the ▶oxidative DNA damage as well. A proportion of mutations in DNA formed by AFB1 occurs at the base 5′ to the modified guanine, or even further away, due to helical distortion resulting from the AFB1 adduct. ▶P53, a ▶tumor suppressor gene considered the “guardian of the genome,” has controls on cell cycle, DNA repair, and ▶apoptosis. P53 is the most frequently targeted gene in human carcinogenesis, with a mutation frequency of 50% in most major cancers. In geographical regions with a high dietary exposure to AFB1, such as China and Sub-Saharan Africa, mutations in p53 have been implicated AFB1-induced human liver tumorigenesis. AFB1 produces mutations at the 3rd base of codon 249 in p53, causing a G→T transversion, and an amino acid substitution (arginine to serine), and thus a structural alteration of this tumor suppressor protein. This may result in deregulation of the cell cycle, and thus loss of tumor suppression by p53. The K-▶ras proto-▶oncogene, important in ▶signal transduction, is often implicated in human and mouse lung tumors. AFB1-induced point mutations at specific “hot spots” (e.g. codons 12 and 13) of the K-ras gene, which cause activation of the protein, occur in AFB1-induced mouse lung tumorigenesis and rat hepatocarcinogenesis. Repair In mammals, ▶nucleotide excision repair (NER) is important for protection against AFB1-induced carcinogenesis. NER is a DNA repair process that deals with a wide array of DNA helix-distorting lesions that affect normal base pairing, thus altering transcription and replication. In E. coli, NER is responsible for the repair of both AFB1-N7-Gua and AFB1-FAPY. In yeast, NER

Aflatoxins

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Aflatoxins. Figure 2 AFB1-exo-8,9-epoxide and DNA damage.

is also the main repair pathway, although ▶homologous recombination is also involved in the repair of AFB1induced damage. In mammals, NER is important in protection against AFB1-induced carcinogenesis. NER is the main repair mechanism for the AFB1-N7-Gua adduct. AFB1-FAPY is repaired less efficiently by mammalian NER than is AFB1-N7-Gua, an effect that is attributed to AFB1-FAPY being less distortive of DNA architecture. Apurinic sites generated by AFB1-DNA adduct formation are repaired by base excision repair (BER), although insertion of an incorrect base is a frequent occurrence. Species / Tissue Susceptibility Susceptibility to the toxic and carcinogenic effects of AFB1 varies between species, as well as between different tissue types. In humans, the liver is the main target for this toxin. In rat, duck, and trout, administration of AFB1 results in hepatocarcinogenesis, whereas this is not the case in the mouse, monkey, hamster, and mouse. The reason for this has been attributed to differences in AFB1 biotransformation and DNA repair. For example, the mouse is susceptible to pulmonary carcinogenesis by AFB1, regardless of the route of administration, but does

not develop hepatocarcinogenesis. The mouse liver expresses an alpha-class GST with high specific activity towards the exo-epoxide, and higher NER activity as compared to the rat liver. On the other hand, mouse lung has lower DNA repair activity than does liver. AFB1 is able to alter NER activity (by inhibition or elevation) in different animal species and organs, which may contribute to differential susceptibility to the mycotoxin’s carcinogenicity.

References 1. Bedard LL, Massey TE (2006) Aflatoxin B1-induced DNA damage and its repair. Cancer Lett 241(2):174–183 2. Eaton DL, Groopman JD (eds) (1994) The toxicology of aflatoxins: human health, veterinary, and agricultural significance. Academic Press, San Diego, pp3–148 3. Massey TE, Stewart RK, Daniels JM et al. (1995) Biochemical and molecular aspects of mammalian susceptibility to aflatoxin B1 carcinogenicity. Proc Soc Exp Biol Med 208(3):213–227 4. Massey TE, Smith GBJ, Tam AS (2000) Mechanisms of aflatoxin B1 lung tumourigenesis. Exp Lung Res 26:673–683 5. Wogan GN (1973) Aflatoxin carcinogenesis. Meth Cancer Res 7:309–344

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Aflatoxin B1

Aflatoxin B1 Definition A potent liver carcinogen produced by fungi that infest cereal grains.

diabetic conditions. AGEs are involved in various types of disorders mainly through the interaction with its receptor RAGE. ▶Minodronate ▶Inflammation

▶Carcinogen Metabolism

Aggressive Fibromatosis AFP

▶Aggressive Fibromatosis in Children ▶Desmoid Tumor

▶Alpha-Fetoprotein ▶Alpha-Fetoprotein – Historical ▶Alpha-Fetoprotein – Modern

Aggressive Fibromatosis in Children AFP-L3

M ARRY M.

VAN DEN

H EUVEL -E IBRINK

Department of Pediatric Oncology/Hematology, ErasmusMC-Sophia Children’s Hospital, Rotterdam, The Netherlands

Definition An AFP fraction, which binds to LCA (lens culinaris agglutinin) lectin because this type of AFP has a core fucose on the N-glycan. ▶Fucosylation

Agammaglobulinemia Definition An almost total lack of immunoglobulins, or antibodies.

Synonyms Aggressive fibromatosis; Desmoid tumor

Definition

▶Aggressive fibromatosis (AF) is a rare soft tissue tumor and rare in childhood with high potential for local invasiveness and recurrence. Primary ▶surgery with ▶negative margins is the most successful primary treatment modality for ▶children with ▶AF. Positive resection margins after surgery indicate a high risk for ▶relapse. Multicenter prospective (randomized) trials are necessary to clarify the role of and best strategy for ▶treatment in pediatric AF after ▶incomplete surgery. For this purpose, ▶chemotherapy or alternatively ▶radiotherapy can be considered, each with its own potential side effects in consequence.

Characteristics

AGEs Definition

▶AGEs are advanced glycation end products. The formation and accumulation of these senescent macroprotein derivatives progress under inflammatory or

Aggressive fibromatosis (AF) (▶Supportive care) is a soft tissue tumor, which arises principally from the connective tissue of muscle and the overlying fascia (aponeurosis). The previously most used synonym is ▶desmoid tumor. The histological pattern is characterized by elongated fibroblast-like cells. Although AF is a nonmetastasizing tumor with benign histological features, it has a significant potential for local invasiveness (▶Invasion) and ▶recurrence. The overall incidence of

Aggressive Fibromatosis in Children

AF in children is 2–4 new diagnoses per 1 million a year. Childhood AF has an age distribution peak at approximately 8 years (range 0–19 years) with a slight male predominance. Clinical Presentation The typical clinical presentation of AF is a painless, slowly growing, deep-seated mass. Predilection sites are shoulder, chest wall and back, thigh, and head/neck. Children with AF of head/neck have shown to be to be younger at diagnosis than children with AF at other sites. From 1986 until 2004, ten pediatric AF case series reported a total of 206 patients. In 64 of the reviewed patients site of involvement and age at diagnosis were specified. The children with AF of head/neck had a median age of 3.6 years at diagnosis (range 0.2–9.9 years), whereas the children with AF of trunk/limb had a median age of 7.8 years (range 0.0–15.7 years) (p400 ng/ml are highly associated with HCC, not all HCC secrete AFP. It may also be elevated in patients with cirrhosis,

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viral hepatitis, drug or alcohol abuse as well as pregnancy, and may be used for screening of fetal spinal cord defects and placental disease. ▶Serum Biomarkers ▶Hepatocellular Carcinoma

Alpha-Fetoprotein – Historical K AREL K ITHIER Department of Pathology, Wayne State University School of Medicine, Detroit, MI, USA

Synonyms AFP; Tumor markers; Oncodevelopmental proteins; Carcinofetal proteins; Feto-specific proteins; Oncofetal antigens

Definition AFP or alpha-fetoprotein is a serum protein of mammalian fetuses that is hardly detectable in healthy adults. Its re-occurrence in serum of adults may often attest to specific malignancy especially in high-risk patients, such as those with hepatocellular carcinomas (▶hepatocellular carcinoma, ▶hepatoblastoma) and chronic hepatitis B or C virus infection (▶hepatitis associated hepatocellular carcinoma). It also serves in evaluation (▶serum biomarkers, ▶surrogate endpoints) of therapy and disease progress in patients with embryonal carcinomas (▶germ cell tumors, ▶platinum refractory testicular germ cell tumors).

Characteristics The studies of fetal serum proteins came from different corners: from researchers interested primarily in the development of proteins and from those studying proteins of tumor-bearing laboratory animals. These two groups were at the beginning not very aware of each other’s results. The fetal protein history began with the physicochemical and biochemical studies of serum proteins, which depended, as this often happens in the laboratory endeavor, on the development, improvement and refinement of laboratory methods. In the field of serum proteins, the electrophoretic and immunochemical techniques (▶proteomics) were of crucial importance, especially in the case of fetal proteins, where usually only minute volumes of sera were available. Studies of electrophoretic patterns of serum proteins in human fetuses showed some considerable differences when compared with the sera of adults. Thus, in 1956

Bergstrand and Czar, using filter paper electrophoresis reported on the special fetal band, (called substance X) which was located between albumin and alpha-1 globulins. Substance X was absent from maternal sera and from sera of healthy adults. Also, Halbrecht and Klibanski reported similar findings in the same year. The first immunochemical studies of the substance X were done by Muralt and by Masopust in 1961 and 1962, respectively. Using antisera to fetal serum proteins (rabbits were immunized with the human fetal sera), an additional precipitin line with alpha globulin mobility was observed on immunoelectrophoresis (IEP) of human fetal serum, however, it was not present in adult sera. This fetal component was called independently “alpha-foeto-proteine” by Muralt and “fetoprotein” by Masopust. These findings resembled older observations in large animals; in 1944 Pedersen studied bovine fetal sera by ultracentrifugation and found a distinct gradient, not present in sera of adult animals. The fraction was named fetuin. Thus, it was believed by some that the human fetoprotein was related to fetuin and the term “human fetuin” was used in some papers on human fetoprotein. Physicochemical properties of fetuin, which was found to be a typical glycoprotein, were studied by a number of workers; its physiological and pathologic properties attracted much less interest. Because fetuin and fetoprotein were present in higher concentrations in fetuses and undetectable in adults, they were sometimes called “feto-specific proteins.” Immunochemical Techniques For the detection of feto-specific proteins, the immunochemical techniques became the methods of choice in the 1960s. Antisera to these proteins were prepared by the immunization of animals, usually rabbits, with fetal sera. To obtain specific antisera to feto-specific proteins, the antisera were absorbed with the sera of adult men or animals. The absorbed antisera should contain only the antibodies directed to the feto-specific protein(s) of a given species. In some cases, the absorbed antisera showed two to three precipitin lines on IEP of fetal serum. Sometimes, in human fetal sera, two lines with the absorbed antiserum were observed. The line in alpha zone of IEP was that of human fetoprotein, the other line, in beta position, was sometimes incorrectly, without justification, called beta fetoprotein. The lines showed no antigenic relationship each to other. For this reason, the original term “fetoprotein” was changed to “alpha fetoprotein” and consequently the abbreviation of AFP came to life. The term “betafetoprotein” ceased to be used since the beta protein was later identified as fetal ferritin. AFP in Pathology In 1964, a study of a possible occurrence of AFP in sera of patients was started. The putative presence of AFP was

Alpha-Fetoprotein – Historical

tested by double radial immunodiffusion (Ouchterlony test). After hundreds of negative results, a patient was identified, who had a definitely detectable serum concentration of AFP. The diagnosis of this patient, confirmed histopathologically at the autopsy, was that of hepatocellular carcinoma. In 1966 and 1967, the occurrence of AFP in four children with a malignant growth of embryonic character was reported. One of them was a 5 year-old boy with embryonal cell carcinoma of the left testicle (▶testis cancer, ▶childhood cancer, ▶germinoma) and another patient was a 14 year-old girl with malignant teratoblastoma of the right ovary (▶ovarian cancer, ▶ovarian tumors during childhood and adolescens). Also, Abelev published in 1967 the finding of “alpha fetal globulin” in patients with embryonal testicular cancer. Several pediatric patients with non-cancerous liver diseases, such as infectious hepatitis and some unspecified hepathopathies were identified, who had detectable AFP serum levels. A highly sensitive technique, radioactive single radial immunodiffusion (employing the second, 125 Iodinelabeled antibodies to the primary antiAFP immunoglobulin fraction), enabled to quantify previously undetectable levels of AFP in various body fluids. By such means, AFP serum levels of patients with hepatocellular carcinomas were studied in a correlation with their individual histopathologic findings. A further increased sensitivity of AFP quantitation was facilitated by the development of a radioimmunoassay. This technique made the quantitation of AFP in healthy persons such as pregnant women a routine test in clinical laboratories. In the 1970s, a number of reviews on AFP were published along the studies of AFP physicochemical properties. The first studies on serum concentrations of AFP and their changes in the course of diseases were done in those years. Thus, the impact of the therapy could be evaluated and monitored in some malignancies. Fetuin versus AFP In the early years, AFP was considered by some investigators to be a protein similar to bovine fetuin and therefore called “human fetuin.” Fetuin was isolated from fetal calf serum and the antisera were prepared to fetuin, and to serum proteins of human and bovine fetuses. With the use of absorbed antiserum to calf serum, an additional protein component was detected in alpha zone of bovine fetal serum, which was not detectable in sera of adult animals. This component could be considered as a “bovine fetoprotein.” Antiserum to this protein did not react with isolated fetuin and conversely the specific antiserum to fetuin did not react in immunodiffusion experiments with the “bovine fetoprotein.” The protein was not detected in adult healthy animals; it was, however, found in sera of two, out of four, adult cows with hepatocellular carcinomas (▶comparative oncology). No antigenic relationship was observed in double

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radial immunodiffusion and the precipitin lines of fetuin and “bovine fetoprotein” crossed each other, showing thus the pattern of antigenic non-identity. AFP in laboratory Animals Rat sera were studied electrophoretically already in the 1950s. A “fetal” protein was detected by Beaton (1961) in the macroglobulin fraction of starch gel electrophoresis. This protein migrated as an alpha-2 globulin in electrophoretic media without molecular sieve effect (filter paper) and slowly in starch gel. Therefore, it was called “alpha-2 slow globulin.” The protein was found in sera of rat fetuses and newborns, as well as in pregnant rats, but not in healthy, non-pregnant adult rats. It was present, however, in sera of tumor-bearing rats and in animals with various inflammatory processes, e.g. with turpentine abscess. Another alpha globulin was found by Darcy in fetal rat sera; it was also present in sera of pregnant animals and adult rats with tumors and/or with inflammations. Protein was also detectable in much lower concentrations in healthy, non-pregnant rats. Wise in 1963, using two-dimensional electrophoresis (filter paper-starch gel) demonstrated in rat fetal sera special proteins, named “fetal postalbumins” (two electrophoretic bands), which were not present in sera of adult animals. Altogether, at least three fetal components were reported in rats. To address this question, rabbit antiserum directed to rat fetal serum proteins was prepared. The absorbed antiserum (with the serum proteins of adult, healthy, non-pregnant animals) did not react with sera of adult, healthy non-pregnant rats, or with the protein described by Darcy. It did react, however, with three different proteins on IEP of fetal rat sera; two of them located in alpha-2, and one in alpha-1 globulin zone. The antibody to the protein in alpha-2 zone could be absorbed with the serum from an adult rat with turpentine abscess. This protein was also detected immunochemically in extracted proteins from macroglobulin position in starch gel electrophoresis of fetal serum. The protein obviously corresponded to alpha-2 slow globulin of Beaton. The other precipitin line in alpha-2 globulin zone was stainable with lipid stains (Red Oil and Sudan Black B), and represented most probably a lipoprotein-esterase found by Stanislawski–Birencwajg in fetal rat serum. The precipitin line in alpha-1 zone, present in sera of fetuses, absent from sera of adult rats, either healthy or with the acute inflammation, was considered to be a typical feto-specific protein, probably related to human AFP. However, no cross- reaction was seen by immunodiffusion between human AFP and antiserum to rat fetal proteins. To prepare a monospecific antiserum to alpha Ft protein, it was important to remove the antibodies to alpha-2 slow globulin, e.g. by using sera of adult rats with some inflammatory pathology. In 1963, Abelev reported the finding of “embryonal alpha globulin” in serum of adult mouse with transplatable

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hepatoma; the globulin was also present in sera of fetal mice (▶mouse models). Much progress has been done since the early modest beginnings of AFP research. Presently, a review of AFP literature shows almost fifteen thousand papers related to the topic (▶AFP-modern).

References 1. Abelev GI (1971) Alpha-fetoprotein in ontogenesis and its association with malignant tumors. Adv Cancer Res 14:295–358 2. Kithier K, Houstek J, Masopust J et al. (1966) Occurrence of a specific foetal protein in a primary liver carcinoma. Nature 212:414 3. Kithier K, Poulik MD (1972) Comparative studies of bovine alpha-fetoprotein and fetuin. Biochim Biophys Acta 278:505–516 4. Kithier K, Prokes J (1966) Fetal alpha-1 globulin of rat serum. Biochim Biophys Acta 127:390–399 5. Masopust J, Kithier K, Radl J et al. (1968) Occurrence of fetoprotein in patients with neoplasms and non-neoplastic diseases. Int J Cancer 3:364–373

Alpha-Fetoprotein – Modern DAVID E. K APLAN Division of Gastroenterology, University of Pennsylvania, Philadelphia, PA 19104

Synonyms AFP; Alpha1-fetoglobulin; Embryo-specific alphaglobulin; Embryonal serum alpha-globulin; Foetoprotein; Fetuin; Fetuin-A; α-feto-protein; α1-fetoglobulin; Embryo-specific α-globulin; Embryonal serum α-globulin

Definition Alpha-fetoprotein (AFP) is a 68.7 kDa plasma protein synthesized primarily by the fetal liver and embryonic yolk sac that is highly homologous with human albumin. Widely expressed in the fetal liver, AFP mRNA is downregulated in post-natal hepatocytes. Serum AFP levels are used clinically for detection, confirmation and follow-up of human ▶hepatocellular carcinoma (HCC) and non-seminomatous ▶germ cell tumors, although lack of sensitivity and specificity complicate its use.

Characteristics Alpha-fetoprotein (AFP) is a 590 amino-acid plasma protein that shares 40% amino acid and 40–44% nucleotide sequence homology with human serum albumin and is a member of the albumin gene superfamily. The AFP gene covers approximately

22 kB of DNA and has 15 exons and 14 introns. The human albumin gene lies 14.5 kB upstream to its AFP homologue. Regulation of AFP protein production occurs mainly at the transcriptional level. In human cells, the AFP enhancer region contains binding sites for several liver-enriched transcription factors (HNF1-4, C/EBP) which control tissue specific expression. Expression of AFP also appears to be positively regulated by NFκB, by steroids via retinoid X receptors as well as by interactions with extracellular matrix. AFP is normally expressed by villous trophoblasts in the human placenta during pregnancy and by fetal hepatoblasts. In fetal and newborn rats, AFP mRNA can be detected at low levels in the kidney, pancreas, heart and gastrointestinal tracts as well. In early postnatal life, AFP production is repressed in normal hepatocytes and silenced in non-hepatic parenchymal cells. The mechanisms for the repression or silencing of AFP expression have largely been characterized. In mice, an unlinked locus called alpha-fetoprotein regulator 1 (Afr1) on chromosome 15 appears to interact with the AFP promoter region; repression of Afr1 appears to be associated with postnatal repression of AFP expression. The AFP promoter may also interact with Ku inducing a hairpin tertiary structure that may abrogate HNF1 binding to the promoter. Postnatal repression of AFP expression in the liver has also been shown to be ▶p53- and ▶TGFβ1-dependent whereas genetic silencing primarily involves epigenetic mechanisms that concomitantly silence the upstream albumin gene. In the adult liver, AFP expression is present but repressed. In situ hybridization studies confirm the presence of minute quantities of AFP mRNA, but at levels generally below the sensitivity of immunohistochemical detection. In the setting of hepatocyte regeneration, e.g. ischemic injury, surgical resection, and chronic viral hepatitis, in ▶hepatoblastoma as well as in a subset of hepatocellular carcinoma (HCC) (and rarely ▶cholangiocarcinoma) AFP expression is de-repressed. AFP production also occurs in nonseminomatous germ cell tumors such as choriocarcinoma, mixed germ cell tumors and teratomas. In fetal and newborn rats, AFP mRNA can be detected at low levels in the kidney, pancreas, heart and gastrointestinal tracts as well. Rarely in adults, non-hepatic/non-germ cell malignancies such as ▶gastric cancer, pancreatic cancer, endometrial cancer, colon cancer, and ▶ovarian cancer are associated with loss of silencing of AFP expression. The critical activities of AFP in vivo remain poorly defined. Many cell types including vascular endothelium and T-cells express receptors for AFP. AFP administration in human cell lines has been associated with differential expression of FasL and ▶TRAIL relative to fas and ▶TRAIL receptor, leading to postulation of a role for AFP in escape from tumor immunosurveillance. AFP also appears to inhibit ▶TNF

Alternative Reading Frame

receptor 1-signalling-mediated tumor cell apoptosis. Paradoxically, some studies suggest a pro-apoptotic role for AFP in tumor cells lines via interactions with X-linked inhibitor of apoptosis protein (XIAP). Other studies postulate that AFP may mediate anti-inflammatory effects that suppress autoimmunity and anti-fetal immune responses during pregnancy, possibly via inhibition of CD4 T-cell proliferation. Serum AFP determinations has two main clinical uses. First, it is used to screen women during pregnancy for fetal developmental abnormalities. Second, AFP is used as a tumor marker for hepatocellular carcinoma (HCC) and non-seminomatous germ cell tumors. Serum AFP determinations have been used since the late 1960s to detect hepatocellular carcinoma despite limitations in its sensitivity and specificity. While AFP levels greater than 400 ng/ml are considered diagnostic of HCC, such elevations are rarely present. The sensitivity and specificity of AFP determinations also appears to be dependent on the underlying cause of liver disease that results in HCC development. Using a cutoff of 20 ng/ml, sensitivity ranges from 41% to 65% and specificity ranges from 80% to 94%. The role of serum AFP in screening programs for HCC in patients with cirrhosis remains controversial. It remains unclear if the addition of AFP determinations to routine imaging examinations, e.g. ultrasound every 6 months, provides any incremental benefit. Current guidelines from the United Network of Organ Sharing (UNOS) in the United States support the use of AFP levels greater than 400 ng/ml to confirm the presence of HCC when a hypervascular lesion on CT or MRI imaging is seen. Exception points may be petitioned from UNOS to provide the rare individual patients with AFP levels greater than 400 ng/ml but no visible tumor to increase the priority of such patients for liver transplantation. Several glycoforms (AFP-L1, -L2 and -L3) of AFP have been resolved based on differences in glycosylation groups. Lectin-reactive AFP (AFP-L3) in some studies has been associated with intrahepatic cholangiocarcinoma. In other studies a high percentage of total AFP made up of the L3 fraction has been associated with hepatocellular carcinomas. Measurement of specific glycoforms is not in routine clinical use.

Alpha-Particles Definition Helium nuclei produced as radioactive-decay products.

Alpha-SMA Definition Alpha-smooth muscle actin. ▶Stromagenesis

Alternative Lengthening of Telomeres (ALT) Definition Alternative lengthening of telomeres (ALT) is a telomere maintenance mechanism that does not involve telomerase, which probably involves recombination. It is found in a minority of cancers and immortalized cell lines. A minority of immortalized cell lines and cancers have no detectable telomerase activity and maintain their telomeres by an alternative mechanism. Although the details are not yet known, it is likely to be a recombinational mechanism in which one telomere uses another telomere (or itself via looping back) as a template for synthesis of new telomeric DNA. Cells that maintain their telomeres by ALT characteristically have very heterogeneous telomere lengths, ranging from undetectable to extremely long. ▶Senescence and Immortalization ▶Stem Cell Telomeres

References 1. Nahon JL (1987) The regulation of albumin and αfetoprotein gene expression in mammals. Biochimie 69:445–459 2. Abelev GI, Eraiser TL (1999) Cellular aspects of alpha-fetoprotein reexpression in tumors. Cancer Biol 9:95–107 3. Gupta S, Bent S, Kohlwes J (2003) Test characteristics of α-fetoprotein for detecting hepatocellular carcinoma in patients with hepatitis C. Ann Intern Med 139:46–50

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Alternative Reading Frame ▶ARF Tumor Suppressor Protein

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Alternative RNA Splicing

Alternative RNA Splicing Definition Alternative RNA splicing refers to the synthesis of different RNA molecules from a single product by differential usage of splicing junctions, which are the sequences surrounding the exon–intron boundaries. ▶Progestin

Alu Elements C HRISTINE M. M ORRIS Cancer Genetics Research Group, University of Otago at Christchurch, Christchurch, New Zealand

Definition The most abundant class of dispersed repeat elements in the human genome, and one member of the family of short interspersed repeat elements (SINEs). An estimated one million copies comprise about 10% of DNA in human cells.

Characteristics Structure Alu elements are 280 bp in length, and consist of two similar monomers that have homology to, and were originally derived from, the ▶7SL RNA gene (Fig. 1). Individual Alu elements are flanked by direct repeats, end in a 3′ A-rich tract, and the left monomer contains an internal RNA polymerase III promoter which directs

transcription initiation to the first residue of the element. Alu are ▶retrotransposable elements, and several subfamilies, mobilized from different “source” genes at different evolutionary times, can be recognized on the basis of their sequence divergence and diagnostic bases. Some of the more recently integrated subfamilies are polymorphic, occupying regions on some chromosomes that are not occupied at the same locus on others. Function The function of Alu elements has been subject to intense investigation, debate and speculation over the past two decades. Proposed roles include modulation of chromosome structure and packaging of DNA around ▶nucleosomes, initiation or switch sites for DNA replication, regulation of gene transcription through Alu-specific protein binding domains, RNA editing as preferential templates for adenosine-to inosine (A-to-I) substitution by the ▶ADAR family of enzymes, and regulation of translation by RNA transcribed from Alu elements. Although Alu expression increases in cells stressed by chemical agents or viral infection, most human Alu repeats are silent in somatic cells, with only the minor, evolutionarily younger subgroups actively transcribed. Consistent with the latter observations, CpG sites in the majority of Alu sequences are normally fully methylated in most somatic cell types, a state which is considered to suppress expression and therefore transposition. However, Alus located adjacent to CpG islands show sequence features amenable to an unmethylated state, and which may therefore have increased mobility. Alu elements are also differently methylated in male and female germ cells, with at least a subset of the recently integrated Alus being almost completely unmethylated in sperm DNA. Role in Human Cancer Alu-mediated gene rearrangement underlies several important constitutional diseases, including familial

Alu Elements. Figure 1 Alu elements have a dimeric structure that originated from 7SL RNA. Colored areas show 7SL sequences present in the Alu repeat consensus.

AME Transcription Factor

cancers. Different mechanisms for these rearrangements include recombination between homologous or non-homologous regions of Alu elements at different locations within a gene, or on the same or different chromosomes, expansion of 3′ polynucleotide tracts to form fragile sites, or disruption of coding regions of functional genes by transpositional insertion of actively transcribed Alu elements. Instability of 3′ polynucleotide tracts may also indicate a DNA ▶mismatch repair deficiency. Because of their high density in the human genome, non-random chromosomal distribution and the high degree of homology between individual elements, Alu repeats are also recognized candidates to mediate somatically acquired gene rearrangements with neoplastic potential. Specific underlying mechanisms for involvement of Alu in somatic rearrangements have only recently begun to be explored, with possibilities including promotion of DNA exchange by sequences within Alu that share homology with known recombinogenic ▶translin DNA-binding motifs or the ▶χ-like Alu core sequence, preferential recombination between DNA regions that are localized within Alu-rich clusters on the same or different chromosomes, or otherwise unknown features of individual Alu elements that predispose to recurrent recombination events associated with some ▶breakpoint cluster regions.

References 1. Hasler J, Katharin S (2006) Alu elements as regulators of gene expression. Nucleic Acids Res 34:5491–5497 2. Kolomietz E, Meyn MS, Pandita A et al. (2002) The role of Alu repeat clusters as mediators of recurrent chromosomal aberrations in tumours. Genes Chromosomes Cancer 35:97–112 3. Deininger PL, Batzer MA (1999) Alu repeats and human disease. Mol Genet Metab 67:183–193 4. Schmid CW (1998) Does SINE evolution preclude Alu function? Nucleic Acids Res 26:4541–4550 5. Schmid CW (1996) Alu: structure, origin, evolution, significance and function of one-tenth of human DNA. Prog Nucl Acid Res Mol Biol 53:283–319

ALVAC-CEA Definition A cancer vaccine constructed from canary pox virus (ALVAC) and combined with the human carcinoembryonic antigen (CEA) gene. ▶Carcinoembryonic Antigen (CEA)

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Alveolar Soft Part Sarcoma Definition Rare tumor of young people comprised of large epithelioid acidophilic cells arranged in alveolar structures separated by thin vessels. The cells show light atypia and contain crystalline inclusions. There are not specific markers. ▶Uncertain or Unknown Histogenesis Tumors

AMAP1 Definition A regulator of the small GTPase Arf6, which is involved in actin cytoskeletal remodeling. AMAP1 is overexpressed in invasive carcinomas and functions in invadopodia by binding to paxillin and ▶cortactin.

AME Transcription Factor V ITALYI S ENYUK Department of Medicine (M/C 737), College of Medicine Research Building, University of Illinois at Chicago, Chicago, IL, USA

Synonyms RUNX1/MDS1/EVI1; AML1/EVI-1

Definition AME is an aggressive oncoprotein (chimeric transcription factor) associated with several types of ▶acute myeloid leukemia (AML), myelodysplastic syndrome (MDS) and myeloproliferative disorders (MPD).

Characteristics The legendary discovery of chromosomal translocations by Janet D. Rowley in 1972 has revolutionized leukemia research and therapy by allowing biological interrogation and classification of these disorders. Several recurring translocations have been identified and the participating genes cloned and characterized at the molecular level. One such recurring abnormality is the balanced translocation between the long arms of chromosomes 3 and 21, t(3;21)(q26;q22), originally discovered in a patient with

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therapy-related chronic myelogenous leukemia (CML) which is classified as an MPD. The t(3;21) is a complicated chromosomal rearrangement that employs a mechanism of intergenic splicing to generate several ▶fusion genes of which AME is perhaps the best characterized and the most important. Among the less frequent translocations involving RUNX1 (also known as AML1, CBFA2, and PEBP2) AME is the only fusion gene that has been cloned and characterized at the molecular level. AME, obtained by in frame fusion of the truncated RUNX1 and MDS1/ EVI1 (ME) genes, is controlled by the RUNX1 promoter which becomes active during the execution of multiple steps of hematopoietic program, especially during the development of myeloid lineage. The t(3;21) is a relatively rare translocation infrequently seen in de novo leukemias. It was observed in ~1% of AML, MDS and MPD cases, and often associated with secondary leukemia that arises in patients previously treated with ▶alkylating agents or topoisomerase inhibitors for other malignancies. In particular, the t(3;21) was detected in the patients after administration of cytostatic drugs such as busulphan, teniposide, etoposide, hydroxyurea, ▶fludarabine, ▶5-fluorouracil and others. There is no unique clinical picture of t(3;21)-associated leukemias such as restriction to a certain FAB (French-American-British classification) category and it has been classified as M1, M2, M4 and M7 subtypes. The common morphologic feature of t (3;21)-positive AML is minimally differentiated blasts with prominent nucleoli and scant cytoplasm. There is no age or gender specificity for t(3;21)-associated diseases but, as for many other ▶cancers, older individuals are at higher risk. In contrast to many other translocations, the t (3;21) causes a very aggressive myeloid leukemia/▶blast crisis of CML characterized by a low response to the existing therapeutic treatments and a poor prognosis. In the largest clinical investigation of t(3;21) patients published to date, the majority of AML patients died between 1 week and 8.5 months (median 2 months) after presentation whereas MPD patients survived 1–21 months (median 6.5 months) after presentation. RUNX1 is a DNA-binding subunit of the transcription factor CBF which is essential for hematopoiesis

and is involved in several chromosomal abnormalities associated with human leukemias. RUNX1 consists of an N-terminal DNA-binding domain called Runt with homology to the product of the Drosophila segmentation gene Runt and a C-terminal activation domain. ME is a zinc-finger transcription factor related to the leukemia-associated protein ecotopic viral integration 1 site (EVI1) of unknown function. ME contains a conserved N-terminal region, called PR domain, two sets of DNA-binding zinc finger domains, a proline-rich central domain, and an acidic C-terminal domain. AME consists of the DNA-binding domain Runt of RUNX1 fused to almost the entire ME (Fig. 1). Forced expression of AME upregulates the cell cycle and blocks granulocytic differentiation of the murine hematopoietic cell line 32Dcl3, and delays the myeloid differentiation of normal murine bone marrow progenitors in vitro. The exact mechanisms of AME oncogenic activation are unknown and several possibilities exist. Also, as with many other oncoproteins, most probably AME alone is insufficient to transform a healthy normal cell into leukemic one and additional cooperating genetic abnormalities are necessary. It has been shown that the majority of AME-positive patients have, in addition to t(3;21), several other chromosomal abnormalities readily detected by cytogenetic analysis: translocations, deletions and duplications the most common of which is t(9;22)(q34;q11) found in CML patients. One of the first investigated properties of AME was its effect on a subset of target promoters regulated by both parent proteins. RUNX1 is generally considered a transcription activator through its C-terminus, which interacts with several transcription coregulators and regulates critical genes in hematopoiesis. ME is also considered a transactivator, and both parent proteins act as antagonists of AME. Therefore, it was suggested that AME could act as a bifunctional transcription factor possessing the ability to bind to and repress/deregulate both the RUNX1- and MEdependent promoters. In support of this hypothesis, it was shown that AME directly interacts with the corepressors C-terminal binding protein (CtBP) and ▶histone deacetylase 1 (HDAC1) which are often a

AME Transcription Factor. Figure 1 Diagram of ME, RUNX1 and the fusion protein AME. The Runt, PR and two zinc finger (ZnF) domains are shown. The vertical dashed line indicates the breakpoint fusion.

AME Transcription Factor

part of big repressor complexes transiently formed at the promoter sites. AME has distinct regions for HDAC1 and CtBP binding and, taking in consideration that both corepressors are able to dimerize and interact to each other, one AME molecule can recruit several molecules of the corepressors. AME represses the target promoters by CtBP-dependent and CtBPindependent mechanisms, probably reflecting the dual nature of this protein. In vitro CtBP enhances not only AME repression potential but also the ability of AME to upregulate growth and deregulate differentiation in murine hematopoietic cells, suggesting that AME repression is necessary for its oncogenic activity. However, the transcription properties of AME are more complicated because it also interacts with histone acetyltransferases p300/CBP-associated factor (P/CAF) and general control of amino-acid synthesis 5-like (GCN5), which are generally considered as co-activators of transcription. Both P/CAF and GCN5 efficiently acetylate the central region of AME in vivo, but the function of this modification and its role in oncogenesis are still unknown. Similar to many other fusion proteins that are activated by chromosomal translocations in human leukemia, AME is able to oligomerize and displays a complex pattern of self-interaction that involves at least three oligomerization regions, which are the proximal and the distal zinc finger domains and the Runt domain. The distal zinc finger domain is quite important in AME oligomerization because it mediates the interaction with the other two domains and an internal deletion that removes the three zinc finger motifs virtually sufficient to repair (though not completely) the self-renewal and differentiation programs of normal murine bone marrow progenitors in vitro. In vitro, this domain efficiently cooperates with CtBP in disrupting normal hematopoiesis and the internal deletion and a point mutation that abolishes CtBP binding re-establishes almost completely the hematopoietic differentiation in murine cells. Probably AME belongs to a growing group of chimeric transcription factors which inappropriately maintain high local concentration of corepressors at the specific promoter sites because of their ability to oligomerize, resulting in the deregulation of genes involved in differentiation, ▶apoptosis, and proliferation. It is highly possible that the aggressiveness of AME as an oncoprotein is in part mediated by AME ability to abrogate the growth-inhibitory effect of ▶transforming growth factor β (TGF-β) that controls cell expansion and inhibits proliferation of different cell types. The repression of TGF-beta signaling depends on the ability of the proximal zinc finger of AME directly interact with and repress ▶Smad3, an intracellular mediator of TGF-β signaling. It should be noted that in contrast to AME, ME co-operates with TGF-β and increases the sensitivity of hematopoietic cells to its stimulus.

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AME is also indirectly involved in deregulation of the hematopoietic program. It has been shown that CCAAT/enhancer-binding protein α (C/EBPα), a crucial transcription factor for normal granulopoiesis, is suppressed at translation level by more than 90% in AME-expressing U937 cells. In AML patients harboring t(3;21) the C/EBPα level is reduced even more whereas in AML patients without the t(3;21) C/EBPα is not affected. The mRNA levels remain unchanged in both cases indicating that AME does not affect C/EBPα transcription. Most probably AME acts through an intermediate effector, ▶calreticulin, a ubiquitous multifunctional calcium-binding protein, which expression is strongly correlated with both, AME expression and C/EBPα suppression. It has been shown in reporter gene assays and in Rat1 fibroblasts that AME stimulates activator protein 1 (▶AP-1) activity with dependence on the distal zinc finger domain. AP-1 activation may increase cell proliferation potentially contributing to AME oncogenic properties. A ▶mouse model of AME-positive leukemia, generated by bone marrow transplantation of AMEexpressing cells using BALB/c mice, showed that AME induces acute myeloid leukemia with a latency of 5–13 months indicating that additional genetic abnormalities are necessary for leukemogenesis. The disease was clonal in origin and resembled human acute myelomonocytic leukemia (AML FAB-M4). It has been also shown in this model that AME efficiently co-operates with breakpoint cluster region/abelson tyrosine kinase (▶BCR/ABL), a product of t(9;22) frequently seen in CML patients. Both proteins together are able to block myeloid differentiation during the pre-leukemia stage and induce AML within 1–4 months. The second mouse model for AME utilized bone marrow infection and transplantation using C57BL/6 mice. The animals displayed a variety of clinical features that are observed in essential thrombocythemia (ET) that resulted in their death after 8–16 months. The molecular etiology of ET, which is classified as an MPD, is poorly understood. Recently an activating somatic point mutation (V617F) of Janus kinase 2 (Jak2) was identified in MPD patients. Nonetheless, this mutation was not detected in ~50% of ET patients, indicating that some other molecular mechanisms exist and t(3;21) could be one of them. The differences between these two mouse models can be explained by taking into consideration that the BALB/c strain of mice is well known to have a higher tumor incidence as compared with C57BL/6 mice (because it has a mutated inhibitor of Cdk4/alternative reading frame (INK4a/ARF) locus that at least partially disables p16Ink4a, a ▶tumor suppressor protein which is frequently mutated in many cancers). A mouse model of AME knock-in has been also reported. The heterozygous mutant embryos obtained

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by breeding of AME chimeric male (ICR strain) and wild type female (C57BL/6 strain) were not viable and died of fetal liver hematopoiesis failure at around day 13.5E. Fetal liver hematopoietic progenitor cells from these mice displayed increased self-renewal capacity and impaired erythropoiesis. In addition, myeloid and megakaryocytic cells appeared dysplastic indicating that AME induces multiple defects in several myeloid lineages. Interestingly, the majority of AME chimeric mice demonstrated sudden death at the age of about 7 months without any significant signs of any disease whereas one of them developed a disease resembling megakaryoblastic leukemia at 5 months of age. Since 1987, when the t(3;21) was described for the first time, our knowledge about AME has increased vastly, however the prognosis of patients with this abnormality is still extremely poor. Hopefully, the cumulative efforts of different research groups will provide new approaches for the search of a treatment for this selected group of patients.

altered so that they are sensitive to mutagenic damage. Bacterial cell death due to mutagen is the assay readout. ▶ADMET Screen

Amidation Definition A process in which glycoxylate is removed from a precursor peptide (glycine-extended form) and an α-amide group is added. In cells this process is catalyzed by the amidation enzyme complex peptidylglycine α-amidating monooxygenase (PAM). ▶Adrenomedullin

References 1. Nucifora G, Rowley JD (1995) AMLl and the 8;21 and 3;21 translocations in acute and chronic myeloid leukemia. Blood 86:1–14 2. Nucifora G, Laricchia-Robbio L, Senyuk V (2006) EVI1 and hematopoietic disorders: history and perspectives. Gene 368:1–11 3. Rubin CM, Larson RA, Bitter MA et al. (1987) Association of a chromosomal 3;21 translocation with the blast phase of chronic myelogenous leukemia. Blood 70:1338–1342 4. Yin CC, Cortes J, Barkoh B et al. (2006) t(3;21)(q26;q22) in myeloid leukemia. Cancer 106:1730–1738

Amifostine Definition

A cytoprotective ▶adjuvant used in cancer chemotherapy involving DNA-binding chemotherapeutic agents. It is also used to decrease the cumulative nephrotoxicity associated with cisplatin and cyclophosphamide. ▶Chemoprotectants

Amenorrhea Definition Absence or cessation of menstruation. ▶Granulosa Cell Tumors ▶Prolactin

Ames Assay Definition Ames assay comprises a family of widely used bacterial assays to screen for mutagenicity. Bacteria are genetically

Amine Oxidases B RUNO M ONDOVI` 1 , PAOLA P IETRANGELI 1 , LUCIA M ARCOCCI 1 , A NTONIO T ONINELLO 2

Department of Biochemical Sciences “A. Rossi Fanelli”, Sapienza University of Rome, Rome, Italy 2 Department of Biological Chemistry, University of Padua, Italy 1

Definition Amine oxidases (AOs) are a class of enzymes which is heterogeneous in terms of structure, catalytic mechanisms, and substrate specificity. ▶Biogenic amines, mono, di, and polyamines as well as N-acetyl amines, are oxidatively deaminated by AOs in a reaction that consumes O2 to produce the corresponding aldehydes,

Amine Oxidases

ammonium ions, and ▶hydrogen peroxide (H2O2) according to the following reaction: þ Eox þ R  CH2  NHþ 3 ! Ered  NH3 þ RCHO þ Ered  NHþ 3 þ O2 ! Eox þ NH4 þ H2 O2

(Eox = oxidized enzyme Ered = reduced enzyme)

Characteristics Two classes of AOs can be described, which contain different prosthetic groups: the FAD-dependent AOs (FAD-AOs) containing the flavin adenin dinucleotide (FAD), and the copper-dependent AOs (Cu-AOs) containing copper and an organic cofactor produced by the copper self-catalyzed posttranslational oxidation of a tyrosine residue, i.e., TPQ (trihydroxyphenylalanine quinone). The FAD-AOs are subdivided in monoamine oxidase A and B (MAO A, MAO B), polyamine oxidase (PAO) and the recently discovered spermine oxidase (SMO). The two latter enzymes are cytosolic, catalyze the oxidation of secondary amino groups, and participate in the interconversion metabolism of polyamines. MAOs are tightly bound to a component of the mitochondrial outer membranes. Cu-AOs are often also named SSAO (semicarbazide sensitive amine oxidase) because of their inhibition by semicarbazide, which binds the organic cofactor. When strictly necessary, the name of the best substrate is used to characterize the enzymes. For instance, Cu-AOs, which oxidize diamine, histamine, and elastin, are named diamine oxidase (DAO), histaminase, and lysyl oxidase (LXAO), respectively. LXAO contains, instead of TOPA quinone, lysyl tyrosyl quinone. Sometimes, a single enzyme, such as the enzyme purified from pig kidney, may display both DAO and histaminase activities, so that the name may not imply a specific enzyme. The X-ray structure is available for several Cu-AOs, PAO, and MAO B. Functions A plethora of physiological functions, sometimes in contrast with one another, is ascribed to AOs. Although the exact molecular mechanism of their biological activity is not well-defined, a role of these enzymes in various processes through the action of either substrates or reaction products is postulated. Evidences have accumulated on the physiopathological relevance of polyamines, histamine, hydrogen peroxide, and aldehydes in cell death and ▶differentiation, ▶allergic diseases, and ▶postischemic reperfusion damage. Histamine is considered to be a main factor involved in allergic diseases. A plant Cu-AO, showing high histaminase activity, counteracts acute allergic asthma-like reaction in actively sensitized guinea pigs. The same

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enzyme modulates cardiac anaphylactic response in guinea pig. Protective effects of the plant enzyme were also observed in myocardial ischemia and reperfusion injury in in vivo rats. Bovine serum Cu-AO was shown to present an antioxidant effect, in vitro, against electrolytically induced ▶reactive oxygen species (ROS) ðO 2; 1 OH; O2 Þ . Among other physiopathological functions ascribed to AOs are, for example, the involvement of MAO in psychiatric diseases like schizophrenia, by regulating the dopamine metabolism, and of Cu-AOs in cataract, by the lens damaging effect of amine oxidation products. A primary involvement of AOs was demonstrated in cancer growth inhibition and progression, especially by means of aldehydes, H2O2, and other ROS, the AOsmediated products of biogenic amines oxidation. Aminoaldehydes were shown to interact with nucleotides or with DNA. Microinjection of Cu-AO into chick embryo fibroblast, rat cells, and glioma cells caused the inhibition of ▶DNA damage and protein synthesis. Tumor cells, with higher polyamines content than the normal controls, were more sensitive to the injected AOs. When an immobilized Cu-AO was injected into the peritoneal cavity of Swiss mice, 24 h after viable Ehrlich ascites tumor cells (▶ascites) transplantation or into a mouse (▶melanoma) model, a strong inhibition of tumor growth was observed. An induction of tumors in rat bowels (▶colon cancer) was observed on inhibition of DAO by aminoguanidine. An induction of tumors in rats was observed after carcinogenic treatment combined with PAO inhibition. Both H2O2 and aldehydes contribute to cytotoxicity, as demonstrated by incubation of Chinese hamster ovary cells with purified bovine serum AO in the presence of spermine. Catalase, the enzyme involved in H2O2 elimination, is absent in many tumor cells and thus ▶apoptosis occurs. The direct relationship between AOs, apoptosis, and cancer appears to be related to the regulation of biogenic amines and their metabolic products. H2O2 is considered to be a mediator of apoptotic cell death but the mechanism is unclear. H2O2 produced by MAO-catalyzed monoamines oxidation seems extremely important for apoptosis induction by considering the fact that MAO inhibitors are able to prevent apoptosis in human melanoma cells and that catalase inhibits the apoptosis induced by polyamines or their analogs and cathecolamines. The catalytic products of active amine oxidation are strong inducers of mitochondrial ▶membrane permeability transition (MPT). Taken together, these results indicate that active amines, operating as AO substrates, play a critical role in controlling apoptosis through their effects on MPT and the ▶respiratory chain activity by means of fluctuations in their concentrations. The conclusions of the above results may be that apoptosis is induced by polyamines through their oxidation products. Other studies exist demonstrating instead the ability of polyamines to protect

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D-Amino Acid

cells from apoptosis. This discrepancy can be explained by taking into account the protective effect of the same polyamines, probably due to a scavenging action of ROS. A crucial role of AOs in cancer promotion has also to be considered. High levels of DAO activity were occasionally found in rapidly growing tissues, while in some patients, even affected by metastatic tumors, the level of circulating DAO was unaltered. A strong correlation between serum AO activity and the factor responsible for ▶angiogenesis was recently found in non-small cell lung cancer patients. DAO activity in the small intestine mucosa was reported to increase in parallel with the degree of cell maturation, being highest in differentiated villus tip cells and lowest in the proliferative compartment. It was also found to increase in regenerating rat liver, with a peak between 16 and 48 h after partial hepatectomy. DAO activity peaks at the outset of growth and falls during the logarithmic growth phase of the cells. An increasing degree of malignancy associated with an increase of MAO A activity and decrease of MAO B and Cu-AOs activities in chemically-induced mammary cancer in the rat has been observed. Elevated activity of AO was found in skeletal metastases of prostatic cancer (▶Prostate cancer, clinical oncology). DAO and arginase, an enzyme that catalyses the synthesis of ornithine from arginine, increase in tumor tissues as compared with benign prostatic hyperplasia. A linear correlation between arginase and DAO activities was observed in patients with cancer. A high concentration of PAO and DAO was found in the cervical intraepithelial neoplasia. The rise from normal conditions seems to produce cytological changes and to play a role in the aethiology of ▶cervical cancer. DAO activity is present at high levels both in tumor tissues and in biological fluids of tumorbearing subjects. A correlation between the degree of tumor malignancy and their levels of AO activity has been observed in astrocytomas, where the activity is proportional to the degree of malignancy. The oxidation products of biogenic amines should also be carcinogenic. Acrolein, produced from the oxidation of spermine and spermidine by AOs, appears to be both carcinogenic and cytotoxic. This compound is considered to be a component of a universal cell growth regulatory system. It may act as mediator of cell transformation under oxidative stress when cells are pretreated with benzopyrene, a major carcinogenic found in cigarette smoke. The oxidation products of spermine, spermidine, and putrescine should be cofactors in the development of cervical cancer. The balance between the cell content of biogenic amine oxidizing enzymes and antioxidizing enzymes appears to be a crucial point for cancer inhibition or progression. As a general conclusion, the cancer inhibition/promotion effect of AOs might be explained by taking into consideration the full pattern of the

enzymes contained in the cells. A long-lasting imbalance of antioxidizing enzymes and AOs activity may be carcinogenic, while AOs are rapidly cytotoxic for cancer cells, because of their higher biogenic amines concentration in comparison with normal cells.

References 1. Toninello A, Pietrangeli P, De Marchi U et al. (2006) Amine oxidases in apoptosis and cancer. Biochim Biophys Acta 1765:1–13 2. Bachrach U, Eilon G (1967) Interaction of oxidized polyamine with DNA. I. Evidence of the formation of cross-links. Biochim Biophys Acta 145:418–426 3. Mondovì B (ed) (1985) Structure and functions of amine oxidases. CRC Press, Boca Raton, FL

D-Amino Acid Definition Is an optical isomer that is the mirror-image of the corresponding L amino acid. Only L amino acids are constituents of natural proteins. ▶Lactoferricin Antiangiogenesis Inhibitor

Amino Terminal End Definition The amino terminus (N-terminus) is the end of a polypeptide chain that carries an unreacted amino group. A ribosome synthesizes a polypeptide in the direction from the amino terminal end to the carboxyl terminal end. ▶AAMP

Amino-Bisphosphonate ▶Minodronate

AML1/MTG8

Aminoflavone Definition 5-Amino-2,3-fluorophenyl-6,8-difluoro-7-methyl-4H1-benzopyran-4-one. New cytostatic drug entering clinical trials. It requires bioactivation by ▶cytochromes P450 and sulfotransferases (SULTs). Its growth-inhibiting activity in 60 human tumor cell lines was primarily determined by the level of expression of SULT1A1. ▶Sulfotransferases

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AML1 ▶Runx1

AML1/ETO ▶Chromosomal Translocation t(8;21)

5-Aminolevulinic Acid Definition Is the precursor of protoporphyrin IX in the heme synthetic pathway. It is used as a photodiagnostic agent. ▶Fluorescence Diagnostics

d-Aminolevulinic Acid Definition A member of the heme biosynthesis pathway and a precursor of the photosensitizer protoporphyrin IX (PpIX). PpIX is the last reaction step before heme and its photochemical and fluorescent properties are used in photodynamic therapy/▶fluorescence diagnosis for treatment/diagnosis of malignant and nonmalignant diseases. ▶Photodynamic Therapy

AML-1/ETO/CBFb/TEL in Chromosomal Translocations Definition AML-1 has been renamed RUNX1. ETO is also known as MTG8 and is part of the RUNX1-MTG8 translocation, previously known as AML1-ETO. CBFβ binds RUNX1. TEL is also known as ETV6 and occurs in the t(12;21) translocation with RUNX1. ▶RUNX1 ▶Chromosome Translocation ▶Acute Myecloid Leukemia

AML1/EVI-1 ▶AME Transcription Factor

AML Definition

▶Acute myeloid leukemia. ▶ETV6 ▶Childhood Cancer

AML1/MTG8 ▶Chromosomal Translocation t(8;21)

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AMN107

AMN107 ▶Nilotinib

Amosite Definition

Is an amphibole form of ▶asbestos. The term refers to Asbestos Mines of South Africa. This mineral contains 31% iron; when inhaled, it is highly carcinogenic.

Amphiphysin-like ▶Bin1

Amphiregulin M AT I A S A. AVI LA , C AR M EN B ERASAIN Division of Hepatology and Gene Therapy, CIMA, University of Navarra, Pamplona, Spain

Synonyms Schwannoma-derived growth factor; SDGF

Definition

Amph II ▶Bin1

Amphibian Gastrin-Releasing Peptide

Amphiregulin (AR) is a growth factor that belongs to the ▶epidermal growth factor receptor (EGFR) family of ligands. AR was originally described as a regulator of cell growth present in the conditioned media of MCF-7 breast tumor cells. AR has been implicated in different physiologic processes including mammary gland and bone development, lung and kidney branching morphogenesis, and trophoblast growth. The expression of AR is upregulated in a variety of cancerous tissues, and signaling triggered by AR is believed to be important in tumorigenesis.

Characteristics ▶Gastrin-Releasing Peptide

Amphipathic Definition Amphipathic molecules contain both a hydrophilic and a hydrophobic moiety.

Amphiphysin II ▶Bin1

The AR human gene spans 10 kb in the genomic DNA and it is composed of six exons, upon transcription it produces a 1.4 kb mRNA. AR gene shows broad constitutive expression, being more prevalent in human ovary and placenta although it is also expressed in pancreas, cardiac muscle, testis, colon, breast, lung, spleen, and kidney, whereas it is undetectable in liver. Transactivation of AR promoter and AR gene expression can be induced by the ▶Wilms’ tumor suppressor and through the activation of the ▶protein kinase c (PKC), mitogen associated protein kinase (▶MAPK), and ▶cyclic AMP/protein kinase A (cAMP/PKA) pathways (Fig. 1). AR is synthesized as a 252-amino acid transmembrane glycoprotein, also known as transmembrane precursor or pro-form (Pro-AR) (Fig. 1). Pro-AR consists of a hydrophilic extracellular N-terminus (or ectodomain), a hydrophobic transmembrane domain (TM), and a hydrophilic cytoplasmic C-terminus (CT-tail) (Fig. 1). In the extracellular N-terminus we can distinguish an N-terminal pro-region containing glycosylation sites followed by a heparin-binding domain and an EGF-like region (Fig. 1). The EGF-like region is

Amphiregulin

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Amphiregulin. Figure 1 Transcription of the AR gene can be activated in response to the WT1 protein and the PKC, cAMP/PKA or MAPK signaling pathways. AR is synthesized as a membrane-anchored precursor (Pro-AR) encompassing an EGF-like domain, a heparin-binding domain (HB), a transmembrane region, and a carboxy-terminal cytosolic tail (CT-tail). Upon digestion by the protease TACE/ADAM17, soluble AR forms are shed from the cell surface and can interact with the EGFR in an autocrine or paracrine fashion, or bind to heparan-sulfate proteoglycans (HSPG) in the extracellular millieu. Alternatively, the yuxtacrine interaction of membrane-anchored Pro-AR with the EGFR is also possible. Shedding of AR by TACE/ADAM17 can be enhanced in response to activation of ▶G-protein coupled receptors (GPCRs). Binding and activation of the EGFR by AR triggers growth and survival signals essential for the tumor cell.

shared by other members of the ▶EGF family of ligands. At the plasma membrane Pro-AR undergoes proteolytic cleavage to release the mature soluble factor in a process known as “ectodomain shedding.” Cleavage of Pro-AR at two N-terminal sites gives rise to two major soluble forms of ~19 and ~21 kDa. Alternatively, Pro-AR cleavage can produce a larger 43-kDa soluble protein corresponding to the entire extracellular domain. Cleavage of Pro-AR at the cell surface can be mediated by tumor necrosis factor-α converting enzyme (TACE), a member of the disintegrin and metalloproteinase (ADAM) family also known as ▶ADAM17 (Fig. 1). Shedding of AR allows the autocrine or paracrine interaction of the mature ligand with its cognate receptor, the ▶EGFR (also known as ErbB1), a transmembrane protein endowed with tyrosine kinase activity, although

yuxtacrine interaction between membrane-bound ProAR and the EGFR has also been observed (Fig. 1). Binding of AR to EGFR triggers key intracellular signaling pathways, such as the mitogenic MAPK and survival ▶PI3K/Akt pathways, which have been demonstrated to participate in the transduction of AR effects (Fig. 1). Amphiregulin Structure, Expression, and Function AR was originally identified as a factor capable of inhibiting the growth of certain carcinoma cell lines, while stimulating the proliferation of normal cells, a fact that motivated its denomination. In fact, depending on its concentration and the nature of the target cell AR promotes the growth and survival of most cell types, both normal and transformed. AR gene overexpression

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Amphitropic Proteins

has been frequently demonstrated in cancerous tissues like colon, breast, bladder, prostate, pancreas, lung, ovary, squamous cell carcinomas, hepatocarcinoma, and myeloma cells. Besides changes in AR gene expression, different stimuli can also influence the availability of this growth factor through the stimulation of Pro-AR cleavage at the cell membrane. This is achieved by the activation of TACE/ADAM17 in response to agonists acting through GPCRs in a process termed ▶EGFR transactivation (Fig. 1). The existence of EGFR transactivation involving the release of AR has been demonstrated in a variety of cancer cells, suggesting that AR could be an important mediator between diverse stimuli acting on GPCRs and the activation of protumorigenic signals conveyed through the EGFR. Interference with AR production by means of specific antisense RNAs or ▶siRNAs, or treatment with AR neutralizing antibodies, has been shown to revert many of the neoplastic phenotypic traits of cancer cells in vitro, even though the expression of other EGFR ligands was preserved in these cells. This suggests that AR plays a nonredundant role in carcinogenesis. Observations performed in vivo also lend support to a role for AR in the initiation and maintenance of the neoplastic properties of tumor cells. For instance, tissue-specific transgenic overexpression of AR in pancreas results in enhanced cell cycle progression, and in mice older than 1 year it induces dysplastic changes and premalignant alterations. Although, so far most of the evidences that support a role for AR in cancer development and progression have been gathered under experimental conditions, there are also clinical studies that point in the same direction. In this regard, a significant correlation has been established between elevated tumor tissue AR mRNA levels and poor survival in bladder carcinoma patients, or elevated serum AR concentrations and increased mortality in non-small cell lung cancer patients. In summary, the current knowledge on AR in cancer suggests that increased availability of this growth factor can provide transformed cells with a selective advantage. Targeted inhibition of AR expression or action may therefore represent a useful therapeutic strategy for a wide variety of cancers. ▶Epidermal Growth Factor (EGF)-Like Ligands

3. Fischer OM, Hart S, Gschiwnd A et al. (2003) EGFR signal transactivation in cancer cells. Biochem Soc Trans 31:1203–1208 4. Sanderson MP, Dempsey PJ, Dunbar AJ (2006) Control of ErbB signaling through metalloprotease mediated ectodomain shedding of EGF-like factors. Grwoth Factors 24:121–136 5. Berasain C, Castillo J, Perugorria MJ et al. (2007) Amphiregulin: a new growth factor in hepatocarcinogenesis. Cancer Lett 254:30–41

Amphitropic Proteins Definition

▶Peripheral Membrane Proteins.

AMPK Definition

Synonym ▶5’AMP-activated protein kinase is a fuelsensing enzyme that plays a central regulatory role in cellular energy metabolism. It stimulates fatty acid oxidation and glucose uptake, inhibits cholesterol and triglyceride synthesis, and modulates cell growth and death. ▶Adiponectin ▶Autophagy

AMPL ▶Bin1

References 1. Lee DC, Hinkle CL, Jackson LF et al. (2003) EGF family ligands. In: Thomson AW, LotzeMT (eds) The cytokine handbook. Academic Press, London, pp 959–987 2. Normanno N, De Luca A, Bianco C et al. (2006) Epidermal growth factor receptor (EGFR) signaling in cancer. Gene 366:2–16

Amplaxin ▶Cortactin

Amplification

Amplification M ANFRED S CHWAB Tumour Genetics (B030), German Cancer Research Center, DKFZ, Heidelberg, Germany

Definition Amplification is the selective increase in DNA copy number either intracellularly, as a local genomic change, or experimentally, by polymerase chain reaction (▶PCR). Increase in the level of mRNA or protein should not be referred to as amplification.

Characteristics Intracellular amplification results in a selective increase in gene copy number with the consequence of elevated gene expression. Gene amplification has been seen in three different settings . Scheduled amplification as part of a developmental gene expression program, e.g. chorion genes in ovaries of the fruitfly Drosophila melanogaster or actin genes during myogenesis in the chicken . Unscheduled amplification during acquisition of cellular ▶drug resistance. For example; amplification of the

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gene encoding dihydrofolate reductase (DHFR) can result in up to 1,000 gene copies per cell with the consequence of cellular resistance against methotrexate. . Unscheduled amplification of cellular genes involved in growth control (▶oncogenes) during ▶tumor progression. Amplification of oncogenes can result in up to several hundred gene copies and enhanced gene expression. Usually large DNA stretches (from 100 Kb up to several Mb) are amplified, and therefore ▶syntenic genes in addition to the particular oncogene can be co-amplified due to their close linkage to the oncogene. Alternatively, different ▶non-syntenic oncogenes can amplify independently in the same cell. The prototypic human cancer with oncogene amplification is ▶neuroblastoma. Here, the amplified gene, MYCN, is a ▶biomarker for patient management. Amplified DNA can be visualized cytogenetically as a ▶homogeneously staining region within chromosomes (▶HSR), as ▶double minutes (▶DM) or as ▶C-bandless chromosomes (CM) (Fig. 1). Cellular Regulation Amplification can follow different pathways, the “onion skin model” and “breakage fusion-bridge” (BFB) cycles (Fig. 2) both fit experimental observations.

Amplification. Figure 1 Cytogenetics of MYCN amplification in neuroblastoma cells. Chromosomal fluorescence in situ hybridization (FISH). High-level MYCN amplification appears in human neuroblastoma cells as two alternative cytogenetic manifestations: (a). Double minutes (DMs) (left), this tumor cell has in addition to amplified MYCN (red) amplification of another oncogene MDM2 (green). The two oncogenes are non-syntenic (2p24, and 12q13–14, respectively), and the amplification is the result of two independent genetic events. (b). Homogeneously staining region (HSR) (right), multiple copies are amplified in an HSR on chromosome 12 (with strong signal), while single copy gene is retained on the two parental chromosomes (arrows). The retention of MYCN at 2p24 indicates that not the original MYCN gene but rather a copy, presumably the result of extra-replication, has been amplified. Note also the strong signal in interphase nuclei which allows detection of amplified MYCN in tumor biopsies when chromosomes cannot be prepared.

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Amplification

Little is known about genomic or environmental elements involved in amplification. Unscheduled amplification presumably is a sporadic event that can become stabilized under selective pressures, i.e. cytostatic drugs or if cells acquire a growth advantage within a certain tissue architecture.

Clinical Relevance Resistance against cytostatic drugs poses a big problem in cancer therapy. Amplified oncogenes contribute to tumor progression, many different oncogenes have been found amplified (e.g. ▶RAS, ▶MYC, ▶MYCN, ▶MYCL, HER-2 [▶HER-2/neu], ▶ABL, etc.), in some

Amplification. Figure 2 Breakage-fusion-bridge (BFB) cycles in early stages of amplification. (a). BFB cycles start from common ▶fragile sites, where a DNA break can occur in both ▶sister chromatids. DNA repair systems will be recruited to the break and may join the free DNA ends of the two sister chromatids to form a dicentric chromosome, one that has two centromers. At anaphase, where sister chromatids are moved to the daughter cells, the dicentric chromosome at some point will break. Of the two daughter cells, one will carry a deletion, the other an inverted duplication of DNA, which is equivalent to a low-level amplification. By subsequent BFB cycles, the level of amplification can increase. (b). Low level amplification as the result of BFB cycles. FISH image, where each color shows the position and copy-number of a particular DNA sequence.

Amplified in Breast Cancer 1

tumor types the oncogene status provides information about patient prognosis: Amplified MYCN indicates poor prognosis for stage 1–3 neuroblastoma; and amplified HER-2 indicates unfavorable outcome in a subgroup of ▶breast cancer. ▶REL

References 1. Schwab M (1998) Amplification of oncogenes in human cancer cells. BioEssays 20:473–479 2. Savelyeva L, Schwab M (2001) Amplification of oncogenes revisited: from expression profiling to clinical application. Cancer Lett 167:115–123 3. Schwab M, Westermann F, Hero B et al. (2003) Neuroblastoma: biology, and molecular and chromosomal pathology. Lancet Oncol 4:472–480

Amplified in Breast Cancer 1 J IANMING X U Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA

Synonyms Nuclear receptor coactivator 3; NCoA3; Steroid receptor coactivator-3; SRC-3; Receptor-associated coactivator 3; RAC3; Thyroid hormone receptor activator molecule 1; TRAM-1; Coactivator ACTR; p300/CBP-interacting protein; p/CIP; AIB1

Definition AIB1 is a 160 kDa intracellular protein that enhances gene expression though interacting with nuclear hormone receptors and some other transcription factors and serving as a transcriptional coactivator. The AIB1 gene is amplified and overexpressed in some human breast tumors.

Characteristics Molecular Structure and Functional Domains The human AIB1 gene is located in chromosome 20 and it encodes for a 160-kDa intracellular protein with 1402 amino acid residues. AIB1 is a member of the p160 steroid receptor coactivator (SRC) family that also includes SRC-1 and the transcriptional intermediary factor 2 (TIF2). AIB1 contains multiple structural and functional domains (Fig. 1). The N-terminal basic helixloop-helix/Per-Ah receptor nuclear translocator-Sim (bHLH/PAS) domain is the most conserved region in

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the molecule with ~70% sequence similarity to the respective regions of SRC-1 and TIF2. The bHLH/PAS domain contains a nuclear localization signal, which is required for AIB1 to get into the cellular nucleus where AIB1-regulated gene transcription takes place and where AIB1 degrades in a proteasome-dependent manner. The bHLH/PAS domain also can interact with certain transcription factors such as myogenin to mediate their transcriptional functions. The serine/threonine (S/T) rich domain contains many serine and threonine residues and some of these residues are targets of serine/ threonine kinases. The phosphorylation status of AIB1 is related to its interaction specificity and affinity with transcription factors and other coactivators. A sequence in the S/T domain is also found to interact with transcription factor E2F1. Through interaction and function with ▶E2F1, AIB1 can play a role in direct regulation of cell cycle. Following the S/T domain is the second conserved region of AIB1 with ~60% sequence similarity to SRC-1 and TIF2. This region contains three LXXLL (L, leucine, X, any amino acid) α-helix motifs that are responsible for interaction with the ligand-binding domain of nuclear receptors in a hormone binding-dependent manner. The third conserved region located in the C-terminus of AIB1 has ~50% sequence similarity to SRC-1 and TIF2 and contains two poly-glutamine stretches and a weak histone acetyltransferase activity. This domain can steadily interact with CREB (cAMP response elementbinding protein) binding protein (CBP) and p300, which are strong histone acetyltransferases. This domain also can interact with the coactivator-associated arginine methyltransferase (CARM1) and the protein arginine methyltransferase 1 (PRMT1), which are histone methyltransferases. Functional Mechanisms Two transcriptional activation domains of AIB1 have been identified. The first one is located in the region that interacts with CBP or p300 and the second one is located in the region that interacts with CARM1 or PRMT1 (Fig. 1). The transcriptional activation function of AIB1 is mainly executed through these acetyltransferases and methyltransferases, which are chromatin-remodeling enzymes. In the case of steroid hormone-regulated gene expression, hormone binding triggers a series of events for steroid receptors, including the dissociation of heat shock proteins, change of receptor conformation, receptor dimerization and DNA binding. Importantly, the hormone binding also induces the steroid receptors expose their coactivator-binding motifs in their ligand-binding domains and allows coactivators such as AIB1 to be recruited to the enhancer region of the nuclear receptor target genes. Through the further interaction of AIB1 with CBP, p300, the p300 and CBP-associated factor (p/CAF), CARM1 and PRMT1, a steroid receptor-directed

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Amplified in Breast Cancer 1

Amplified in Breast Cancer 1. Figure 1 Schematic presentation of the structure and function of AIB1. CR1, CR2 and CR3, conserved regions 1, 2 and 3 in the p160 SRC family; bHLH/PAS, the basis helix-loop-helix/Per-Ah receptor nuclear translocator-Sim domain; S/T, the serine and threonine-rich domain; L, L and L, the three LXXLL motifs responsible for interaction with nuclear receptors; Q and Q, the two glutamine-rich regions; HAT, the histone acetyltransferase domain; H, hormone; NR, nuclear receptors; CBP, the CREB (cAMP response element-binding protein) binding protein; p300, the 300 kDa protein homologous to CBP; p/CAF, the p300 and CBP-associated factor; CARM1, the coactivator-associated arginine methyltransferase 1; PRMT1, the protein arginine methyltransferase 1; TBP, the TATA binding protein; TAFIIs, TBP-associated general transcription factors (GTFs); Pol II, RNA polymerase II.

transcriptional activation complex is built up on the hormone response elements of their target gene. This protein complex uses its protein acetyltransferase and methyltransferase activities to remodel the chromatin structure, to facilitate the assembly of general transcription factors on the promoter and thereby to promote target gene transcription. In addition to steroid receptors and other nuclear receptors, AIB1 also serves as a coactivator for certain other transcription factors such as E2F1, AP-1 and Ets transcription factors. Physiological Function AIB1 mRNA is expressed in many different human tissues and cell lines when examined by Northern blot analysis. Detail analyses with mouse tissues revealed that AIB1 is mainly expressed in the mammary gland epithelial cells, oocytes, vaginal epithelial layer, hepatocytes, smooth muscle cells, endothelial cells, and the hippocampus and olfactory bulbs of the brain. At this time, our knowledge regarding the in vivo physiological function of AIB1 is mainly learned from the AIB1 knockout mice. AIB1-deficienct mice have a much lower levels of insulin like growth factor-I and 17β-▶estradiol in their circulation. Accordingly, these mice are smaller in size and they exhibit delayed puberty, retarded mammary gland development and reduced female reproductive function. In addition, AIB1 plays a beneficial role in estrogen and ▶estrogen receptor-mediated vascular protection after vessel injury by enhancing estrogen receptor function and contributes to the control of acute inflammatory responses by inhibiting the production of pro-inflammatory cytokines.

Role in ▶Cancer The AIB1 gene is amplified (or increased in the number of gene copies) in about 5–10% human breast tumors. The AIB1 mRNA is overexpressed in about 30–60% breast tumors, depending on the resources of reports. However, some study only found about 10% of breast tumors that have elevated AIB1 protein levels. AIB1 overproduction is observed in breast tumors both positive and negative to the estrogen receptor α. In ▶tamoxifen-treated patients, high levels of AIB1 are associated with the HER2/Neu expression, the tamoxifen resistance and the lower disease-free survival rates. In the cultured ▶breast cancer cells, AIB1, together with the estrogen and estrogen receptor, enhances ▶cyclin D1 expression and cell cycle progression. Down regulation of AIB1 in breast cancer cells inhibits cell proliferation, cell motility and anchorage-independent growth in the culture and tumor formation in the immune-deficient mice. Animal experiments further demonstrate that AIB1-deficient mice are resistant to either transgenic ▶oncogene- or chemical ▶carcinogeninduced mammary gland tumorigenesis. The transgenic v-Ha-ras oncogene can no longer induce mammary gland tumors in the ovariectomized AIB1 knockout mice, suggesting that inhibition of AIB1 function and removal of ovarian ▶hormones may be a potential strategy to control breast tumorigenesis. On the other hand, it has been demonstrated that overexpression of AIB1 in the mouse mammary epithelial cells is sufficient to induce a high frequency of mammary gland tumors, indicating that AIB1 is an oncoprotein. Similar to the role of AIB1 in breast cancer, AIB1 is also found to be overexpressed in certain human prostate

Amrubicin

tumors and to play a detrimental role in prostate epithelial tumorigenesis in mouse models.

References 1. Anzick SL et al. (1997) AIB1, a steroid receptor coactivator amplified in breast and ovarian cancer. Science 277:965–968 2. Xu J, Li Q (2003) Review of the in vivo functions of the p160 steroid receptor coactivator family. Mol Endocrinol 17:1681–1692 3. Xu J et al. (2000) The steroid receptor coactivator SRC-3 (p/CIP/RAC3/AIB1/ACTR/TRAM-1) is required for normal growth, puberty, female reproductive function, and mammary gland development. Proc Natl Acad Sci USA 97:6379–6384 4. Kuang SQ et al. (2004) AIB1/SRC-3 deficiency affects insulin-like growth factor I signaling pathway and suppresses v-Ha-ras-induced breast cancer initiation and progression in mice. Cancer Res 64:1875–1885 5. Torres-Arzayus MI et al. (2004) High tumor incidence and activation of the PI3K/AKT pathway in transgenic mice define AIB1 as an oncogene. Cancer Cell 6:263–274

Amrubicin M ICHIKO YAMAMOTO, N ORIYUKI M ASUDA Department of Respiratory Medicine, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan

Synonyms (+)-(7S,9S)-9-acetyl-9-amino-7-[(2-deoxy-β-D-erythropentopyranosyl)oxy]-7,8,9,10-tetrahydro-6,11-dihydroxy-5,12-naphthacenedione hydrochloride; SM-5887

Definition The anthracyclines tested clinically so far have been limited to those produced by fermentation or semisynthetic processes. In contrast, 9-aminoanthracycline, amrubicin is a fully synthetic drug. Amrubicin differs from daunosamine in that it contains a 9-amino group and a simple sugar moiety (Fig. 1).

Characteristics Amrubicin is converted to its active 13-hydroxy metabolite, amrubicinol, in the liver, kidney, and tumor tissue, through reduction of its C-13 ketone group to a hydroxy group. Despite the similarity of its chemical structure to that of a representative anthracycline, doxorubicin, amrubicin’s mode of action differs from that of doxorubicin. Amrubicin and amrubicinol are

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inhibitors of DNA topoisomerase II, which exert their cytotoxic effects by stabilizing a topoisomerase II-mediated cleavable complex (▶Topoisomerase enzymes as drug targets), and are approximately only onetenth as potent as doxorubicin in producing DNA intercalation. Preclinical Studies In in vitro experiments, amrubicin and its metabolite amrubicinol have been found to be active against a broad spectrum of human cell lines established from cancers of the lung, prostate, urinary bladder, colon, kidney, pancreas, and uterus. Amrubicinol has been shown to exhibit a 20- to 220-fold more potent antitumor activity in vitro than amrubicin itself, being as potent as doxorubicin. In addition, amrubicin and amrubicinol have also been demonstrated to show some degree of noncross resistance with doxorubicin. Amrubicin has been shown to be more effective against five human xenografts (one breast cancer, one ▶lung cancer, and three gastric cancers), equally effective against two gastric cancers, and less effective against two tumor (one lung and one gastric cancer). Amrubicin caused dose-dependent weight loss, ataxia, myelosuppression, and hair loss in mice after a single intravenous (i.v.) injection. The maximum tolerated (MTD) for such administration was estimated to be 25 mg/kg in four mouse strains. Cardiotoxicity is one of the dose-limiting toxicities of anthracyclines. However, amrubicin showed little delayed-type cardiotoxicity in rabbit and dog experimental models. Furthermore, amrubicin did not aggravate the doxorubicin-induced myocardial injury. Clinical Studies Amrubicin Monotherapy Phase I/II Trial of Amrubicin Given Daily for Three Consecutive Days Every 3 Weeks. Based on the finding that amrubicin exhibited enhanced antitumor efficacy against six of eight cell lines when it was given for five consecutive days instead of on a single day at the MTD dose, a phase I/II trial of amrubicin for three consecutive days was carried out in patients with advanced nonsmall cell lung cancer (NSCLC). In the phase I study, four patients were enrolled at dose level 1 (40 mg/m2/day) and four at dose level 2 (45 mg/m2/day). No dose-limiting toxicity (DLT) was observed at these dose levels. At dose level 3 (50 mg/m2/day), three of five patients experienced DLTs (leukopenia, neutropenia, thrombocytopenia, or gastrointestinal toxicities). The MTD and recommended dose (RD) were determined to be 50 and 45 mg/m2/day, respectively, from the results of this trial. Seven partial responses (PR) were observed in a total of 28 patients of the phase I/II study, with an overall response rate of 25%.

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Amrubicin

Amrubicin. Figure 1 Chemical structure of amrubicin and its active metabolite, amrubicinol.

Multicenter Phase II Study of Amrubicin in Patients with Advanced NSCLC. Sixty-one previously untreated patients with stage III or IV NSCLC were entered in this study. Amrubicin was administered by a single i.v. injection daily at the dose of 45 mg/m2/day for three consecutive days every 3 weeks. One complete response (CR) and 16 PR were observed, with an overall response rate of 27.9%. The median survival time (MST) was 9.8 months. The major toxicity was myelosuppression. The incidences of grade 3 or 4 toxicity were 72.1% for neutropenia, 52.5% for leukopenia, 23.0% for anemia, and 14.8% for thrombocytopenia. Phase II Study of Amrubicin in Previously Untreated Patients with Extensive-Stage Small Cell Lung Cancer. Thirty-five previously untreated patients with extensive-disease small cell lung cancer (ED-SCLC) were entered in the study. Amrubicin was given by daily i.v. infusion at the dose of 45 mg/m2/day for three consecutive days every 3 weeks. Of 33 eligible patients, 3 showed CR and 22 showed PR, with an overall response rate of 75.8% (95% confidence intervals (CI), 57.7–88.9%). The MST and 1-year survival were 11.7 months and 48.5%, respectively. The most common toxicity was hematologic toxicity. Phase II Trial of Amrubicin for the Treatment of Refractory or Relapsed Small Cell Lung Cancer: Thoracic Oncology Research Group Study 0301. SCLC patients with measurable disease who had been treated previously with at least one platinum-based chemotherapeutic regimen were entered into the trial.

Amrubicin was administered at a reduced dose of 40 mg/m2 per day × 3 days every 3 weeks, in view of the prior chemo- and radiotherapy. Sixty patients (16 refractory and 44 sensitive) were enrolled. The grade 3 or 4 hematologic toxicities comprised neutropenia (83%), thrombocytopenia (20%), and anemia (33%). Febrile neutropenia was observed in three patients (5%). The nonhematologic toxicities were mild. The overall response rates were 50% (95% CI, 25–75%) in the refractory group and 52% (95% CI, 37–68%) in the sensitive group. The overall survival and 1-year survival in the refractory group and sensitive group were 10.3 and 11.6 months, and 40 and 46%, respectively. Thus, it was concluded that amrubicin shows significant activity against SCLC, with predictable and manageable toxicities. Amrubicin Combination Chemotherapy Phase I-II Study of Amrubicin and Cisplatin for Previously Untreated Patients with Extensive-Stage Small Cell Lung Cancer. This trial was performed to determine the MTDs for combined amrubicin and cisplatin therapy and to assess the efficacy and safety of these drugs at their RD. Patients with histologically or cytologically proven measurable ED-SCLC, no previous chemotherapy, and good prognostic factors were entered into this trial. Amrubicin was administered on days 1–3 and cisplatin on day 1, every 3 weeks. Four patients were enrolled at dose level 1 (amrubicin 40 mg/m2/day and cisplatin 60 mg/m2) and three patients at dose level

Analytic Epidemiological Study

2 (amrubicin 45 mg/m2/day and cisplatin 60 mg/m2). The MTD and RD were found to be at level 2 and level 1, respectively. The response rate at the RD was 87.8% (36/ 41). The MST and 1-year survival rate were encouraging, 13.6 months and 56.1%, respectively. Phase I and Pharmacologic Study of Irinotecan and Amrubicin for Advanced NSCLC. We conducted a phase I trial of irinotecan (CPT-11), a topoisomerase I inhibitor, combined with amrubicin. The aim was to determine the MTD and DLT of amrubicin combined with a fixed dose of CPT-11 in patients with advanced NSCLC. Eleven patients were treated with amrubicin on days 1–3, combined with 60 mg/m2 of CPT-11 on days 1 and 8, every 3 weeks. The starting dose of amrubicin was 25 mg/m2, and the dose was escalated in 5 mg/m2 increments until the MTD was reached. The 30 mg/m2 of amrubicin dose was one dose level above the MTD, since three of the five patients experienced DLT, namely, diarrhea and leukopenia. Amrubicin did not affect the pharmacokinetics of CPT-11, SN-38, or SN-38 glucuronide. There were five PRs among the 11 patients, with an overall response rate of 45%. The RD for phase II studies was determined to be 60 mg/m2 for CPT-11 (days 1 and 8) and 25 mg/m2 for amrubicin (days 1–3), administered every 21 days. Conclusion The preclinical studies described above show that amrubicin has a unique mechanism of action as an anthracycline derivative and a broad spectrum of antitumor activity. The results of clinical studies of amrubicin as a single agent or as one of the drugs in combination regimens for lung cancer have been promising. To determine the exact usefulness of amrubicin in the treatment of SCLC, two randomized trials are now underway in Japan; one of cisplatin + amrubicin versus cisplatin + irinotecan in previously untreated patients of ES-SCLC, and one of amrubicin versus carboplatin + etoposide in elderly patients with ES-SCLC. Although amrubicin has been investigated over the last decade, many of its characteristics remain unclear. Further studies exploring the usefulness of amrubicin as a single agent or as an agent administered in combination with other cytotoxic agents as well as novel molecule-targeted drugs for the treatment of other malignancies are warranted. Lastly, since all the trials with amrubicin have been conducted in Japan, the results of clinical studies to define the benefits and risk associated with amrubicin for cancer therapy conducted overseas are eagerly awaited.

References 1. Sawa T, Yana T, Takada M et al. (2006) Multicenter phase II study of amrubicin, 9-amino-anthracycline, in patients with advanced non-small-cell lung cancer (Study 1): West

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Japan Thoracic Oncology Group (WJTOG) trial. Invest New Drugs 24:151–158 Yana T, Negoro S, Takada M et al. (2007) Phase II study of amrubicin in previously untreated patients with extensivedisease small cell lung cancer: West Japan Thoracic Oncology Group (WJTOG) study. Invest New Drugs 13: 25:253–258 Onoda S, Masuda N, Seto T et al. (2006) Phase II trial of amrubicin for treatment of refractory or relapsed small-cell lung cancer: Thoracic Oncology Research Group Study 0301. J Clin Oncol 24:5448–5453 Oh Y, Negoro S, Matsui K et al. (2005) Phase I-II study of amrubicin and cisplatin in previously untreated patients with extensive-stage small-cell lung cancer. Ann Oncol 16:430–436 Yanaihara T, Yokoba M, Onoda S et al. (2007) Phase I and pharmacologic study of irinotecan and amrubicin in advanced non-small cell lung cancer. Cancer Chemother Pharmacol 59:419–427

Anaerobic ▶Hypoxia

Analgesic Definition The drugs that prevent or reduce pain. ▶Nonsteroidal Anti-inflammatory Drugs

Analytic Epidemiological Study Definition A study in a human population designed to evaluate a specific causal relationship. ▶Allergy ▶Cancer Epidemiology ▶Epidemiology of Cancer

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Anaphase-Promoting Complex

Anaphase-Promoting Complex

Anaplastic Large Cell Lymphoma

Definition

A NGELO R OSOLEN

The anaphase is a phase of mitosis, during which the paired sister-chromatids (▶Sister-chromatids) are separated and drawn to the poles of the cell. This phase is initiated by a ubiquitin-mediated proteolytic pathway (▶Ubiquitination) resulting in the degradation of regulatory proteins. The anaphase-promoting complex (APC/C) functions as a protein ubiquitin ligase.

Department of Pediatrics, Hemato-oncology Unit, University of Padua, Padova, Italy

▶Securin

Anaphylactic Shock Definition A life-threatening allergic reaction characterized by a swelling of body tissues including the throat, difficulty in breathing, and a sudden fall in blood pressure.

Anaplasia Definition Refers o lack of cell differentiation in a tumor.

Anaplastic Astrocytoma Definition Astrocytic tumor characterized by an intermediate degree of histologic and clinical malignancy ▶Brain Tumors

Anaplastic Carcinomas ▶Follicular Thyroid Tumors

Synonyms Ki1 lymphoma

Definition Anaplastic large cell lymphoma (ALCL) was originally described in 1985 as a separate entity among the ▶nonHodgkin lymphomas (NHL); it is characterized by the cohesive proliferation of large cells expressing the CD30/Ki1 antigen on their membrane. The World Health Organization more recently stated that the term ALCL should be applied to tumors with a T-cell or null phenotype, thus further restricting the identification of this specific subtype of ▶lymphoma.

Characteristics

Systemic ALCL accounts for 2–8% of all ▶lymphomas (▶Malignant lymphoma, hallmarks and concept) but represents ~10–15% of NHL of childhood. In addition to the primary systemic disease, a form of ALCL limited to the skin is also recognized. Isolated cutaneous ALCL may spontaneously remit, but can also progress to a more aggressive disease. Systemic ALCL has some clinical features that are less common in other NHL subtypes: patients at diagnosis often have B-symptoms (fever, weight loss, sweats) as in Hodgkin lymphoma, mediastinal (▶Mediastinum) and extranodal involvement, including skin, bone, and soft tissues. Among lymph nodes, the inguinal nodes are often site of disease, particularly in childhood, and rather frequently lymphadenopathy may be painful. Central nervous system and bone marrow are rare sites of disease, although with more sensitive techniques bone marrow may have submicroscopic infiltration of lymphoma cells more often than previously expected. Clinical differences have been reported between ▶ALK (anaplastic lymphoma kinase)-positive and ALK-negative subtypes. Patients with ALK-positive ALCL are significantly younger and have a better prognosis that the negative counterpart, suggesting that ALK-positivity, rather than age, may confer distinct and relevant clinical features to systemic ALCL. Secondary ALCL may arise in the progression of other lymphomas, most commonly during the course of T-cell NHL, mycosis fungoides, Hodgkin lymphoma or lymphomatoid papulosis, and has a poor outcome. Except for the cases of very aggressive disease, ALCL may show multiple recurrences that respond to therapy, although eventually a considerable number of patients die despite intensive treatment.

Anaplastic Large Cell Lymphoma

Diagnosis Diagnosis of ALCL relies on histopathology and immunophenotyping, but for a complete characterization of the tumor, chromosomal analysis and molecular genetic studies are warranted. It is now clear that ALCL includes several variants: classical or common type (corresponding to the original description of the disease) that accounts for ~60–70% of the cases, lymphohistiocytic variant, giant cell-rich, small cell type, and mixed. The large cell-rich type is characterized by multinucleated cells, often with ReedSternberg-like features that make the differential diagnosis with Hodgkin lymphoma (▶Hodgkin disease) sometimes difficult. Irrespective of the histotype, neoplastic ALCL cells are characterized by a distinctive phenotypic profile. They express CD30, a cell membrane glycoprotein, found in activated lymphoid cells, the epithelial membrane antigen (EMA) and T-cell antigens including CD3. Perforin and granzyme B are also expressed in the majority of the cases and, together with absence of CD15 expression, they are useful markers in the differential diagnosis with Hodgkin disease. The development of antibody against the ALCL kinase (ALK) (▶ALK protein) has further refined the immunohistochemical analysis of ALCL. Expression of ALK occurs in tumors carrying ▶chromosomal translocations that involve the corresponding gene. The most common rearrangement between chromosome 2 and 5 causes strong ALK positivity of neoplastic cells in the nucleus and cytoplasm (Figs. 1 and 2), whereas other chromosomal translocations involving ALK produce accumulation of the translocation product at the cytoplasmic level only. ALK reactivity of tumor cells has diagnostic relevance given

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that ALK is not detected in normal lymphocytes or in Hodgkin lymphoma cells and only few cases of rare forms of lymphoma and nonlymphomatous tumors (inflammatory myofibroblastic tumors, rare neuroblastoma, and rhabdomyosarcoma) show ALK reactivity. Ultimately, combination of morphological, immunophenotypic, and genetic analysis allow the diagnosis of ALCL and the differentiation of this lymphoma from other tumors. A peculiar aspect to consider is the differentiation of cutaneous ALCL from other CD30-positive lymphoproliferative disorders including lymphomatoid papulosis. In this case, because the great majority of isolated cutaneous ALCL is ALK-negative, clinical observation and evolution of the disease are of foremost importance. In addition, because skin involvement in the context of a systemic ALCL may bear prognostic implications, suspect skin involvement must be documented through biopsy. Imaging procedures used in the diagnosis and staging of ALCL are similar to other NHL. Special attention should though be given to the examination of soft tissues and skin, given the relatively high frequency of involvement of those sites. Chest x-ray is usually sufficient to detect a mediastinal mass, but a CT scan of the neck, thorax, and abdomen should always be obtained to define the extent of disease. Ultrasound is routinely used for diagnosis and monitoring of lymph nodes, abdominal organ involvement, including liver, spleen, kidney, and soft tissues. This technique is easy to perform and can give accurate information not only for diagnostic purposes, but also to evaluate tumor response to treatment and during follow-up, once treatment is completed. Whole skeletal ▶scintigraphy may be useful, especially in cases with bone pain, and should be complemented with x-ray of positive bones.

Anaplastic Large Cell Lymphoma. Figure 1 This panel depicts the classic variant of anaplastic large cell lymphoma with numerous large tumor cells that often contain horseshoe- or kidney-shaped nuclei, distinct nucleoli and abundant cytoplasm.

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Anaplastic Large Cell Lymphoma. Figure 2 This panel immunohistochemical staining of anaplastic large cell lymphoma containing the chromosomal translocation t(2;5) originating the NPM–ALK fusion protein. Nuclear and cytoplasmic reactivity to an anti-ALK specific monoclonal antibody is detectable in most lymphoma cells (brownish color) Pictures were a courtesy of Dr. E. S. d’Amore, Institute of Pathology, University of Padua, Italy.

Brain MRI or CT scan are usually performed, but central nervous system involvement at diagnosis is infrequent in ALCL. More recently ▶positron emission tomography (▶PET) with 18-fluorodeoxyglucose (FDG) has been introduced in the routine evaluation of ALCL patients, mainly for staging. Lymphoma cells characteristically have a higher uptake of FDG compared with normal cells and this gives high activity features to the vital tumor mass. Because a high reactivity may also be seen in other nonmalignant tissues with high glucose metabolism, including reactive lymph nodes and inflammatory tissues, PET findings have to be interpreted with caution at present, until large prospective clinical studies where this recent technology is routinely applied are completed. To completely define the extent of the disease, as in other NHL, bone marrow biopsy and bone marrow smear should be performed and analyzed for the presence of tumor cells, as well as a lumbar puncture to exclude the presence of lymphoma cells in the central spinal fluid. Genetics The ▶chromosomal translocation t(2;5)(p23;q35) was originally reported in patients with malignant histiocytosis, which indeed represented ALCL cases diagnosed according to old criteria. Break of chromosome 2 and subsequent fusion to chromosome 5 in a reciprocal chromosome rearrangement is the main genetic feature of ALCL. As a result, the ALK gene on chromosome 2 is juxtaposed to the nucleophosmin (▶NPM) gene on chromosome 5. The ▶NPM–ALK fusion gene gives rise to a fusion protein composed of ALK and NPM domains that can be detected by ▶immunohistochemistry using an anti-ALK monoclonal antibody. While

ALK is not usually expressed in normal tissues, except in few neuronal cells, NPM gene encodes a shuttle protein that undergoes dimerization in the cytoplasm and in this conformation can move to the nucleus. In the cytoplasm of NPM–ALK-positive ALCL cells, heterodimers between NPM and NPM–ALK are formed that, while retaining the ability to move to the nucleus, are reactive against the anti-ALK antibody. This explains the cytoplasmic and nuclear reactivity of ALCL cells harboring the t(2;5) translocation. The wide use of antibodies to ALK protein revealed that about 10% of the ALK-positive ALCLs showed an immunohistochemical reactivity confined to the cytoplasm. Molecular genetic studies demonstrated that those cases were associated to a series of different chromosomal translocations, all involving the ALK gene, but with partners other than NPM. The deriving fusion genes all cause hybrid protein overexpression that lack the shuttling properties of NPM-containing fusion proteins, thus preventing them from nuclear localization. From the functional point of view, NPM–ALK can dimerize and as such it possesses constitutive tyrosine kinase activity, mimicking the normal functional activity of the ALK receptor in normal cells upon binding and oligomerization by its specific ligand. A number of experimental data suggest that NPM–ALK has a causative role in tumorigenesis of ALK-positive ALCL, although it may need concomitant events. In fact, NPM–ALK displays transforming activity in both hematopoietic and fibroblastic cell lines in vitro. Overall, ~90% of childhood ALCLs are positive for the ALK-hybrid protein, whereas this percentage is only 50–60% in adult ALCLs. As suggested by clinical studies, ALK-positivity, not only is a relevant tool in the

Anaplastic Lymphoma Kinase

diagnosis of ALCL, but represents also a prognostic marker in that ALK-positive ALCLs fare better than ALK-negative lymphomas in the adult population. Therapy Treatment of ALCL, similarly to other NHL, is almost exclusively based on chemotherapy. The therapeutic approach has witnessed a variety of chemotherapy regimens, ranging from acute lymphoblastic leukemiatype regimens lasting 24 months to shorter chemotherapy more frequently used in aggressive B-cell lymphomas. Differently from most European studies where ALCL is considered as a separate entity, in North America all large cell lymphomas, regardless of the histologic subgroup and ▶immunophenotype, are treated according to the same chemotherapy scheme. Primary systemic ALCL in adults has been treated mostly with CHOP (cyclophosphamide, vincristine, prednisone), CHOP-derived chemotherapy, and MACOP-B (methotrexate, adriamycin, cyclophosphamide, vincristine, prednisone, and bleomycin) regimens, but occasionally patients have been treated with Hodgkin lymphoma-type chemotherapy (e.g., ABVD regimen). Collaborative trials have been conducted in childhood and adolescence ALCLs. Overall results were comparable with very different treatment strategies, ranging from leukemia-like treatment, such as modified LSA2-L2 protocol, to chemotherapy regimes derived from B-cell NHL as the BFM (Berlin-Frankfurt-Munster) and the French and British Pediatric Hemato-Oncology Society protocols. The latter are based on the administration of short (usually 5-days) courses of rather high-intensive chemotherapy (based on the rotational use of corticosteroid, anthracyclines, cyclophosphamide or ifosfamide, cytarabine, methotrexate, epipodophyllotoxin) administered at intervals of ~3 weeks. With these treatments, 60–75% of patients obtain cure of their disease and do not experience disease recurrences. Similar results were obtained with the APO regimen in the Children’s Oncology Group (USA) that includes higher cumulative doses of anthracyclines without ▶alkylating agents (cyclophosphamide/ifosfamide) or epipodophyllotoxins. Treatment intensity and/or duration have been differentiated based on various risk factors. Although stage of disease has some relevance, in the adult population a high International Prognostic Index (IPI) score, high serum lactate dehydrogenase levels, ALKnegativity and expression of the surface antigen CD56 have been associated to a significant lower outcome. In children and young adults, possibly because of the very high frequency of ALK-positivity, ALK expression does not seem to be a relevant prognostic indicator, whereas high stage of disease, elevated lactate dehydrogenase levels, and specific site of disease, including liver, spleen, lung, and skin involvement, seem to be associated to a less favorable prognosis.

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A distinct clinical condition is represented by the isolated cutaneous ALCL. Once other disease localizations have been excluded, given that spontaneous regression of the lesions can occur, a strict monitoring of the patient is often preferred, postponing initiation of chemotherapy when signs of lymph nodes or other organ involvement is demonstrated. A peculiar aspect of ALCL is that most patients who relapse respond well to salvage therapies. Although early disease recurrences can be extremely aggressive, moderate intensity chemotherapy, including single drug treatment with vinblastine, can achieve long-lasting remission. In case of resistant disease or very aggressive relapse, high-intensive chemotherapy with bone marrow transplant has also been used both in children and adults. Further studies are needed to definitively establish the benefit of bone marrow transplant in ALCL and to identify the subpopulations of patients who may benefit from such a treatment approach.

References 1. Falini B (2001) Anaplastic large cell lymphoma: pathological, molecular and clinical features. Br J Haematol 114:741–760 2. Seidemann, K, Tiemann, M, Schrappe M et al. (2001) Short-pulse B-non-Hodgkin lymphoma-type chemotherapy is efficacious treatment for pediatric anaplastic large cell lymphoma: a report of the Berlin-Frankfurt-Munster Group Trial NHL-BFM 90. Blood 97:3699–3706 3. Brugieres, L, Deley, MC, Pacquement H et al. (1998) CD30(+) anaplastic large-cell lymphoma in children: analysis of 82 patients enrolled in two consecutive studies of the French Society of Pediatric Oncology. Blood 92:3591–3598

Anaplastic Lymphoma Kinase Definition Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) having an extracellular, a single transmembrane, and an intracellular domain containing the tyrosine kinase activity. ALK belongs to the insulin receptor subfamily of RTKs, most closely related to leukocyte tyrosine kinase receptor. It localizes mostly in neuronal cells and may play a role in the nervous system development and maintenance. ALK and some of the ALK partners or closely related genes are found implicated both in anaplasic large cell lymphoma and in inflammatory myofibroblastic tumors. ▶Pleiotrophin ▶ALK Protein

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Anatomic Pathology

Anatomic Pathology Definition

phenotype of the cell, such that the cells are now able to grow as colonies in three-dimensional suspension in soft agar. ▶Chemically Induced Cell Transformation

The study of gross and microscopic tissue features in disease diagnosis. ▶Molecular Pathology

Androgen Anchorage-Independent Definition The ability of cells to survive and multiply in the absence of a protein matrix for adhesion.

Definition An agent, usually a hormone (e.g. testosterone) that stimulates the activity of the accessory sex organs of the male. ▶Prostate-Specific Membrane Antigen (PSMA)

▶Syk Tyrosine Kinase ▶Adhesion Molecules

Androgen Insensitivity Syndrome (AIS) Anchorage-Independent Cell Growth

▶Androgen Receptor

Definition In vitro transformed cells and cancer-derived cells are able to survive and grow in the absence of anchorage to the ▶extracellular matrix (ECM) and their neighboring cells, termed anchorage independence of growth, correlates closely with tumorigenicity in animal models. This property of cancer cells presumably reflects the tendency of tumor cells to survive and grow in inappropriate locations in vivo. Such incorrect localization, as occurs in invasion and metastasis, is the characteristic that distinguishes malignant from benign tumors. ▶Sprouty

Androgen Receptor K AUSTUBH DATTA , D ONALD J. T INDALL Department of Urology Research, Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA

Synonyms AR; dihydrotestosterone receptor; testicular feminization TFM; spinal and bulber muscular atrophy SBMA; Kennedy disease KD; androgen insensitivity syndrome AIS; NR3C4; SMAX1; HUMARA

Definition

Anchorage-Independent Cell Transformation Definition The process by which carcinogenic chemicals, oncogenic viruses, or radiations change the genotype and

The androgen receptor or AR is a member of the steroid/ thyroid receptor superfamily, in which all members share basic structural and functional homology. The AR is an intracellular ligand (androgen)-dependent transcription factor, which regulates the expression of genes that control cell proliferation, ▶apoptosis, ▶angiogenesis and differentiation in many hormonally regulated tissues including the prostate. It is an important regulator of male sexual differentiation and maturation.

Androgen Receptor

Characteristics The biological function of androgen is mediated through the androgen receptor. Except for the spleen and bone marrow, the androgen receptor is ubiquitously expressed in human organs. The human androgen receptor gene is more than 90-kb long, and is present as a single allele located at chromosome Xq11.2–12. The AR gene has eight exons and possesses a coding region of 2757 bp. This region encodes a 110 KDa protein (919 amino acids) with four distinct functional domains: a conserved Zn-finger DNA-binding domain (exons 2 and 3), a hinge region (exon 4), a COOHterminal ligand-binding domain (exons 4–8), and a less conserved and structurally flexible amino (NH2)terminal transactivation domain (exon 1). Structure–Function Relationships between Different Domains of Androgen Receptor that are Required for its Transcriptional Activity Regulation of Unliganded AR Unbound AR in the cytoplasm remains in an inactive but androgen responsive state as part of a large dynamic heterocomplex composed of heat shock proteins, cochaperones, and tetratricopeptide repeat containing proteins. This large complex helps to modulate the ligandbinding domain (LBD) of AR into a relatively stable, partially unfolded, and inactive intermediate which has a high affinity for the potent biologically active androgen, dihydrotestosterone. The androgen-free LBD and the associated chaperone proteins inactivate the function of

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the transactivation domain of AR. This transactivation domain becomes constitutively active in the mutant AR lacking a ligand-binding domain (LBD). As such, this molecular chaperone complex and the LBD of AR prevent unwanted activation of AR in the absence of androgen Regulation of Ligand-Bound AR Because of their lipophilic nature, androgens cross the cell membrane, both passively, and actively via the transport protein, megalin. Once within the cell the androgen binds to the AR, which is stabilized and translocated into the nucleus. Within the nucleus the AR homo-dimerizes and recruits transcriptional cofactors to the promoters and enhancers of AR-target genes, thus facilitating their transcription (Fig. 1). Androgen binding to the LBD of AR induces an overall change in AR structure leading into an active conformation which is characterized by dissociation of the receptor– chaperone complex. However, molecular chaperones also play important roles in the events downstream of AR activation such as translocation to the nucleus, transcriptional activation, transcription complex disassembly and degradation. LBD relieves its inhibitory function upon androgen binding. AR LBD configuration is highly structured and resembles other steroid receptors’ ligand-binding domains. 1. AR DNA Binding Domain and Hinge Region: Androgen binding to the LBD initiates a conformational change of AR leading to several secondary effects important for AR transcriptional activity.

Androgen Receptor. Figure 1 A schematic diagram of AR structure and its functions.

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Androgen Receptor

One such effect is the unmasking of the bipartite nuclear-localization signal (NLS) that overlaps the DNA-binding domain and hinge regions (amino acid 625–671). Another weak NLS (amino acid 722–805) is present in the LBD of AR, which is also exposed upon androgen binding. The NLS is recognized by an import protein that mediates translocation of the AR through the nuclear-pore complex. AR homodimerization occurs in the nucleus upon treatment with ligand. Both the DNA and ligand-binding domains of AR are involved in subsequent receptor dimerization. The stronger hydrophobic interaction occurs between the ligand-binding domains.The binding of AR dimer to the specific androgen response elements (ARE) of a gene occurs in a co-operative manner. The DNA binding domains of AR, like other nuclear receptor superfamily members, consist of two zinc fingers that provide the structural basis required for ARE recognition in the promoter region of a gene. The consensus ARE is a 6 bp palindromic core sequence (5′-AGEACA-3′) separated by a three nucleotide spacer. Sequences outside the DNA binding domain also play a role in AR-DNA binding. 2. AR AF-2 Domain: A hydrophobic protein-protein interaction surface known as Activation Function-2, or AF2, is present at the carboxy-terminal, and also becomes accessible after androgen binding to AR. AF2 is the potential binding site for AR co-activators such as the p160 family (TIF2, SRC1, and AIB1). These co-activators enhance AR transcriptional activity by modulating AR conformation and by recruiting cofactors to the promoter. Ligand binding also induces interaction of AF2 with a specific motif (FXXLF) (F = phenylalanine, L = leucine and X = any aminoacid) in the NH2-terminal activation domain of AR. The interaction of NTD and LBD or N/C interaction is important for AR transcriptional activity. Although the mechanistic details of how this interaction leads to AR activity are not precisely known, it appears that ligand binding induces intramolecular folding of AR, leading to the interaction between NTD and LBD. This influences receptor dimerization in the nucleus and reduces ligand degradation from LBD, AR protein dissociation, AR chromatin binding ability and receptor transactivation. 3. AR N-Terminal Transactivation Domain: The Nterminal transactivation domain (NTD) of AR is longer and structurally different as compared to other steroid receptors. The highly flexible and disordered domain containing NTD is largely globular in nature. Association with coactivators and transcription factors helps to induce folding in the domains of the NTD to optimize efficient binding. Due to the allosteric nature of binding, the AR NTD is able to bind a broad spectrum of transcriptional coactivators, co-repressors and other factors.

Therefore the AR NTD may be responsible for mediating androgen-regulated expression of genes whose functions consist of protein folding, trafficking and secretion, metabolism, cytoskeletal rearrangement, cell cycle regulation and signal transduction. AF1 and AF5 Domain of NTD: There are two major overlapping activation functions present in the AR NTD, AF1 (amino acids 142–485) and AF5 (amino acids 351–528). These regions contain microsatellite repeats, protein-protein interaction surfaces, and phosphorylation and sumoylation sites. AF1 is considered the major transactivation domain that binds to basal transcription factors, co-regulators, cell cycle regulatory proteins, heat shock proteins etc. The interaction with molecules like TIFIIF increases folding in the AF1 domain and facilitates further protein-protein interactions for the formation of a transcriptionally competent receptor complex. Unlike AF1, activation of AF5 is ligand independent. An inhibitory domain within AF5 inhibits the DNA-binding domain of AR from binding to AREs. Glutamine and Glycine Repeats: AR NTD contains two polymorphic trinucleotide repeat segments that encode polyglutamine and polyglycine tracts. The first trinucleotide repeat sequence, CAG, spans amino acids ~58–78, and encodes the amino acid glutamine. The second stretch consists of GGN repeats that encode glycines and span amino acids ~449–472. Shortened trinucleotide repeat stretches result in increased AR activity and are often associated with prostate cancer predisposition. On the other hand, overexpansions of the CAG repeat (more than 40) correlate with a significant decrease in AR activity and are associated with diseases such as X-linked Spinal and Bulbar Muscular Atrophy (SBMA), also known as Kennedy’s disease. Both the polyglutamine and polyglycine repeat size appear to regulate the N/C interaction and thereby influence AR activity. FXXLF and WXXLF Motifs: The AR NTD also contains two short, highly conserved peptide motifs that mediate the liganddependent N/C interaction as discussed previously. These motifs are FXXLF (in humans FQNLF), ranging from amino acids 23–27 and WXXLF (in humans WHTLF), ranging from amino acids 434–438. AR Co-regulators: AR functions as a tripartite receptor system involving AR itself, the androgens and AR coregulators. AR interaction with either co-activators or co-repressors enhances or represses its transcriptional activity, respectively, without affecting the basal levels of transcription. Possible mechanisms of co-regulator function include modulation of chromatin structure, promotion of AR post-translational modifications and control of androgen/AR binding affinity, AR expression, AR stability, AR nuclear translocation, and AR recruitment of transcription machinery.

Androgen Receptor

4. Post-translational Modification of AR: Posttranslational modification of AR is one of the key mechanisms regulating its function. One of the major post-translational modifications of AR is phosphorylation. These phosphorylation sites may be the sites for possible cross-talk between peptide growth factors and the AR signaling axis, which is important for normal prostate epithelial cell growth and function as well as for the progression of cancer. Most of the phosphorylation sites reside in the NTD at different serine residues. However, recent findings suggest that Src kinase mediates phosphorylation at tyrosine 534 of AR, and therefore acts as a potential regulator of AR transcriptional activity. Another post-translational modification is acetylation of AR at the hinge domain (at lysine residues 630, 632 and 633) by Histone Acetyl Transferases such as p300, p/CAF, and TIP60. This modification regulates recruitment of co-regulators as well as the growth properties of the AR. Acetylation is also required for regulation of the AR by the AKT, PKA and JNK signaling pathways. Sumoylation of AR at two specific domains (NRM1 and NRM2 at NTD) also appears to be important for AR activation, localization and degradation. Nongenomic Function of AR Recently, a nongenomic mechanism for AR function independent of its transcriptional activity has been postulated. This nongenomic event is very rapid (2–15 min) and activates signaling events such as the Src/ Raf1/ERK, ▶PI3K-AKT, and IL-6-STAT3 pathways. Interestingly, membrane lipid rafts are considered to be the privileged site for this AR-mediated nongenomic signaling. Upon androgen binding most of the ARs translocate to the nucleus and act as transcription factors. The few remaining cytosolic ARs may then enter into ▶caveolin positive or negative rafts to initiate different signaling pathways. Androgen Receptor in Human Physiology and Pathology Androgen and AR are not only necessary for the initiation of prostate development; they are also important factors for the survival, proliferation, secretary function, morphology, angiogenesis and differentiation of the adult prostate gland. AR is also important for Wolffian duct development and spermatogenesis in males. Various clinical disorders due to functional abnormalities of AR have been reported, suggesting that a wide range of physiological responses and developmental processes are mediated by AR. Androgen Receptor and ▶Prostate Cancer: Approximately 80–90% of prostate tumors are dependent on androgen at the initial diagnosis, suggesting the importance of AR signaling in all stages of ▶prostate carcinogenesis. A recently developed bioinformatics

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approach known as Cancer Outlier Profile Analysis (COPA) together with standard genomic techniques has identified recurrent gene fusions of the 5′ untranslated region of the TMPRSS2 gene to ▶ETS transcription factors (ERG or ETV1) in human prostate cancer tissues. Interestingly, this gene fusion enables expression of the fused product under the control of AR, as the TMPRSS2 promoter contains an ARE. This ▶TMPRSS2-ETS fusion appears to be frequent in prostate cancer and might be an initiating event for prostate cancer, underscoring the importance of ARmediated signaling in prostate cancer. Both the tumor epithelia and adjacent stroma express AR. Retardation of tumor growth occurs in response to androgen ablation therapy. Until now, the primary therapy for advanced (locally extensive or metastatic) prostate cancer consists of androgen ablation by pharmacotherapeutic or surgical means. Eventually, the tumor recurs due to a transition from androgen-dependence to a highly aggressive and androgen-depletion-independent (refractory) phenotype. The detailed molecular mechanism underlying the development of the androgen refractory phenotype of prostate cancer is poorly understood. As such, it has been difficult to develop effective treatments for this stage of the disease. Disruption of androgen receptor function inhibits proliferation of androgen refractory prostate cancer, demonstrating the importance of AR even at subnormal physiological levels of androgen. Mechanisms for ligand-independent AR reactivation include AR mutation, gene amplification, increased stability and nuclear localization, co-regulators and cross talk between different signal transduction pathways. Recent studies also suggest an acquired capacity of recurrent prostate tumors to biosynthesize testicular androgens from adrenal androgens or cholesterol, thereby reactivating the AR. Targeting AR for Therapy: Androgen ablation therapy, which is achieved by pharmaco-therapeutic (steroidal and non-steroidal antiandrogens) or surgical (subcapsular or subepididymal bilateral orchiectomy) means, is the standard initial systemic therapy for locally advanced or ▶metastatic prostate cancer. This therapy is based on inhibiting the synthesis of active androgen or inhibiting the physiological androgen from binding to AR. Novel therapeutic strategies for the androgen-depletion-independent stage of prostate cancer will focus on inhibiting expression of AR, blocking the binding of AR coactivators, and enhancing the binding of AR co-repressors. Using intelligent high-throughput screening and structural and computational chemistry, it may be possible to develop peptide antagonists, ▶small molecules or antisense oligonucleotides that target AR-coactivator binding surfaces. Potential drugs targeting the N-terminal domain may also prevent or delay the progression of both hormonal-dependent and -independent prostate cancer.

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References 1. Shen HC, Coetzee GA (2005) The androgen receptor: unlocking the secrets of its unique transactivation domain. Vitam Horm 71:301–319 2. MacLean HE, Warne GL, Zajac JD (1997) Localization of functional domains in the androgen receptor. J Steroid Biochem Mol Biol 62:233–242 3. Dehm SM, Tindall DJ (2006) Molecular regulation of androgen action in prostate cancer. J Cell Biochem 99:333–344 4. Heinlein CA, Chang C (2004) Androgen receptor in prostate cancer. Endocr Rev 25:276–308 5. Debes JD, Tindall DJ (2004) Mechanisms of androgenrefractory prostate cancer. N Engl J Med 351:1488–1490

Anergy Definition A state of unresponsiveness, induced when the T cell antigen receptor is stimulated, which effectively freezes T cell responses pending a “second signal” from the antigen-resenting cell (▶costimulation).

Aneugen Definition

Androgen-Independent Prostate Cancer

Any agent that affects cell division and the mitotic spindle apparatus resulting in the loss or gain of whole chromosomes, thereby inducing ▶aneuploidy. ▶Micronucleus Assay

Definition AIPC. ▶Hormone refractory prostate cancer

Aneuploidy Definition

Androgens Definition Male sexual hormones that are mainly produced in the testicles. Testosterone is the principal androgen hormone. ▶Adjuvant Chemoendocrine Therapy

Anemia Definition Anemia is abnormally low hemoglobin concentration in the blood (females: 100 nm) and differ. For example, the peak emission of renilla luciferase is 480 nm, whereas firefly luciferase is 610 nm. Collectively, these factors ensure that bioluminescent signals from selected pairs of luciferase enzyme can be discerned upon the basis of substrate exclusivity as well as their spectral signature. This is highly useful as it enables the employment of powerful dual-labeled BLI studies, where the light generated by different luciferase enzymes can be detected sequentially to measure multiple parameters within the same cell or individual animal (e.g. viable tumor burden measured by renilla luciferase and the activation of a cellular process by firefly luciferase). The development of increasingly sophisticated ▶spectral unmixing image analysis techniques should soon make it possible to routinely discern the optical spectra from two different luciferases when both substrates are administered simultaneously. How is In Vivo Bioluminescence Detected? The intensity of light generated by luciferase labeled cells in a typical bioluminescence imaging experiment is sufficiently low that a highly sensitive light detector is needed to measure it. Such detectors are commercially available and typically comprise a cryogenically cooled CCD camera (Charge-Coupled Device; cooled to ≤−90°C to reduce thermal noise and increase light sensitivity) that is housed behind a lens within a completely light tight box. The non-visible levels of light associated with bioluminescence imaging can be detected by the pixels of the cold CCD, which results in a fully digitized and quantifiable 2-D map of light intensity across the field of view. An image of this light intensity map is then superimposed over a digital

Bioluminescence Imaging

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Bioluminescence Imaging. Figure 1 The above figure shows a series of bioluminescent images of an individual mouse taken at weekly intervals and shows the development of a spontaneous and bioluminescent prostate tumor. Note that the colors associated with these images and accompanying scale bar correspond to light intensity and do not reflect the color of detected light. This figure is reproduced with modification from Fig. 4A (Lyons SK, Lim E, Clermont AO et al (2006) Noninvasive bioluminescence imaging of normal and spontaneously transformed prostate tissue in mice. Cancer Res 66(9):4701–4707) by copyright permission of the AACR.

photograph of the subject (taken in normal light conditions immediately prior to bioluminescence acquisition) to indicate the regions of the subject where labeled cells reside (Fig. 1). In a manner analogous to conventional photography, the exposure time and aperture settings of the CCD camera can be adjusted to modify the sensitivity of bioluminescence acquisitions. This ensures that CCD pixels do not become saturated when imaging relatively bright subjects and maximizes sensitivity when imaging relatively dim subjects. Computer software can be used to add together (or “bin”) the signals detected by adjacent CCD pixels to further increase imaging sensitivity, but this gain is made at a cost to image resolution. Software tools are also used to create “regions of interest” to quantitatively measure light emission from any area of the image in fully calibrated physical units (i.e. photons/s/cm2/▶steradian). Considerations to Maximize In Vivo Imaging Sensitivity Currently BLI is considered one of the most sensitive non-invasive preclinical imaging modalities when used in conjunction with small animal models of disease. There are, however, several important factors that will affect the sensitivity of any in vivo BLI approach and so influence the minimum number of cells that can be detected or the ability to visualize the activity levels of a cellular process above noise. One obvious issue relates to the extent of luciferase enzyme expression in the target cell; labeled cells that express relatively low levels of luciferase will be harder to detect than an equivalent number of labeled cells that express greater amounts of luciferase.

Another key issue is the depth of signal, as the wavelengths of light produced by the commonly employed luciferases are prone to scatter and absorption as they pass through mammalian tissue. Red wavelengths of light (>600 nm) pass through tissue with greater efficiency than relatively bluer wavelengths (12 Gy/h. VLDR (very low dose rate) radiation is used in permanent radioactive seed implants, at a dose rate of less than 40 cGy/h. Temporary implants are placed into the tumor/adjacent tissues in order to deliver LDR, MDR, or HDR treatments. VLDR implants typically reside permanently in the tissue implanted, but decay over the course of a few months. In the delivery of LDR or MDR radiation, the temporary implant stays in place over several hours, whereas HDR treatments usually last only a few minutes. LDR techniques involve the static placement of radiation isotopes within the applicators for a period of time. 137Cesium (137Cs) for gynecologic brachytherapy or 192Iridium (192Ir) for ▶gynecologic cancers or sarcomas are most commonly used. The radiation is either manually afterloaded by a physician or can be remotely afterloaded if a cesium selectron afterloader (for gynecologic brachytherapy) is available. HDR treatments involve a single 192Ir source fixed to a wire that is guided remotely by a computer. The HDR afterloader attaches to individual applicators by transfer tubes. Computer programming determines the position of the radiation isotope within the applicator, and calculates a radiation ▶isodose curve that may be manipulated by altering the dwell times. ▶Dwell positions are defined along the applicators every

Characteristics of some commonly used radioisotopes in the United States

Isotope

Half-life

Energy (MeV)

137

30 years 74 days 60 days 17 days

0.66 0.29–0.6 0.028 0.023

Cesium 192 Iridium 125 Iodine 103 Paladium

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Brachytherapy

2.5–10 mm, and the isotope remains at designated dwell positions for a preset time as determined by the optimized plan. LDR radiation may have a ▶radiobiological advantage over HDR radiation, as the normal tissue is more likely to be able to repair sublethal damage. Additionally, the continuous dose may prevent repopulation of the tumor cells, and the longer period of time that the cells are exposed to radiation allows the cell cycle to move through radio-resistant and radiosensitive phases. HDR radiation may lead to an increase in normal tissue toxicity if the total dose delivered compared to LDR is not decreased. It is important to fractionate the HDR radiation sufficiently and deliver as small a fraction size as feasible depending on the tissue treated, the indications for treatments and the amount of normal tissue in proximity to the source. In ▶cervical cancer brachytherapy, packing the vagina can reduce the amount of normal tissue exposed to radiation. Pulsed dose rate (PDR) brachytherapy uses an HDR afterloader and source but attempts to mimic the radiobiologic effect of LDR by giving a large number of very small fractions over a longer period of time than HDR.

Dose Calculations Historically, the dose delivered to a treatment volume was hand-calculated, based on one of three methods of implantation. The Paris and Quimby systems place parallel sources with uniform spacing and source activity, to give a higher central dose compared with the periphery. The Paterson–Parker method utilizes higher peripheral radioactivity compared with the centers resulting in increased ▶dose homogeneity throughout the implant. These methods have been replaced in several radiation oncology clinics by computer programs that utilize information gathered from imaging techniques such as CT scans to define the target volume and identify the implant geometry within that volume to calculate the dose.

Implantation Techniques The placement of the radiation source in relation to the treatment volume is the most important determinant in the effectiveness of brachytherapy. Therefore the techniques used depend on the location of the tissue being targeted. Surface applicators involve sculpting a radiotherapy delivery system on or around the target surface area. A superficial dose may be delivered to lesions of the skin or intraoperatively to exposed tumor beds. Intracavitary radiation utilizes orifices within the human body to introduce applicators in close proximity to the tumor. Common examples of intracavitary

radiation include gynecologic malignancies, in which the vagina, cervical os, and uterine cavity allow for the relatively easy placement of applicators. Other intracavitary treatments include the bronchus, esophagus, and rectum. Interstitial radiation entails passing catheters through normal tissue to reach the target volume or placing tubes within a surgical bed at the time of operation.

Clinical Applications of Brachytherapy Brachytherapy may be administered alone or in combination with external beam radiation, chemotherapy, or surgery to provide either cure or palliation for the patient. The most common uses of brachytherapy are discussed below.

Gynecologic Malignancies The most common gynecologic malignancy treated with brachytherapy in the United States is ▶endometrial cancer. Intracavitary radiation targets the vaginal vault in women thought to be at high risk of local recurrence to the vagina following definitive surgery. This treatment involves the insertion of a cylinder into the vagina (Fig. 1). LDR or HDR radiation may be used. The dose and fractionation of the radiation depend on both the dose rate and the patient’s history of prior external beam radiation therapy. The dose may be prescribed at either the surface of the applicator or at a depth, typically 5 mm, from the applicator. Cervical cancer is treated using a combination of external beam radiation with or without chemotherapy and brachytherapy, commonly referred to as a tandem and ovoid application. A central uterine tandem is placed through the cervical os into the uterine cavity. Vaginal ovoids or a vaginal ring or cylinder are secured to the central tandem (Fig. 2). Historically, cervical cancer brachytherapy was administered using LDR radiation, most commonly using tandem and ovoids placed twice with one week between treatments. In most centers, plain films assess the location of normal tissue structures; however, several radiation oncology clinics have acquired CT imaging capability, allowing for 3D imaging of the normal tissues and more accurate dose calculation. In more recent times, several centers have incorporated HDR radiation into the management of cervical cancer. HDR tandem and ovoid dose is delivered in minutes, and most commonly requires four or five separate insertions, with each treatment lasting several minutes. The HDR isodose curve approximates a standard LDR loading (Fig. 3). Vulvar and vaginal cancers are rare, but their treatment may involve interstitial or intracavitary radiation after external beam radiation.

Brachytherapy

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Brachytherapy. Figure 1 A high dose rate vaginal cylinder is inserted into the vagina to treat the vaginal surface for patients who have had a hysterectomy for uterine or cervical cancer. The applicator is attached to a brachytherapy board for stabilization.

Brachytherapy. Figure 2 Low dose rate Fletcher–Suit– Delclos tandem and ovoid applicator will be loaded with 137 Cs. The central tandem is inserted into the uterus. The ovoids may have plastic caps placed over them in order to fill the vaginal fornices. A flange rests outside the external os of the cervix. The apparatus is held in place by vaginal packing.

▶Prostate Cancer Brachytherapy in prostate cancer may be the sole treatment for low-risk disease or in combination with external beam radiation as a form of dose escalation. VLDR brachytherapy places permanent radioactive seeds of either 125I or 103 Pd into the prostate through the perineal skin, under image guidance and using catheters. The seeds remain permanently within the prostate and deliver a low dose of radiation continuously until they have decayed. HDR brachytherapy for prostate cancer is currently being investigated in research protocols.

Brachytherapy. Figure 3 High dose rate tandem and ovoid isodose curve demonstrates the 100% isodose line optimized to point A, a point 2 cm above and lateral to the cervical os.

Other Other cancers that can be treated with brachytherapy as part of combined care include head and neck cancers, including nasopharynx and tongue, breast cancers, sarcomas, thoracics and some gastrointestinal cancers.

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Bracken Fern

References 1. Williamson JF (2006) Brachytherapy technology and physics since 1950: a half century of progress. Phys Med Biol 51(13):R303–R325 2. Hoskin PJ, Bownes P (2006) Innovative technologies in radiation therapy: brachytherapy. Semin Radiat Oncol 16(4):209–217 3. Rivard MJ, Nath R (2006) Interstitial brachytherapy dosimetry update. Radiat Prot Dosimetry 120(1–4):64–69 4. Stewart AJ, Viswanathan AN (2006) Current controversies in high-dose-rate versus low-dose-rate brachytherapy for cervical cancer. Cancer 107(5):908–915 5. Nag S (2004) High dose rate brachytherapy: its clinical applications and treatment guidelines. Technol Cancer Res Treat 31(3):269–287

Bracken Fern Definition A worldwide diffuse plant belonging to Pteridium genus known to cause cancer naturally in animals. Bracken fern eating is also related to human cancer.

Bradykinin Definition Bradykinin is an active peptide of the kinin protein group. It consists of nine amino acid residues and is a potent vasodilator. ▶Kallikreins

B-raf-1 ▶B-Raf Signaling

BRAF1 ▶B-Raf Signaling

B-Raf Signaling T ILMAN B RUMMER Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia

Synonyms v-raf murine sarcoma viral oncogene homolog B1; B-raf-1; BRAF1; EC 2.7.11.1; MGC126806; MGC138284; RAFB1; p94; c-Rmil

Definition B-Raf signaling comprises the activation of the protooncogene product B-Raf and its downstream effectors and represents a key regulatory step in the activation of the canonical ▶MAP kinase pathway by various extracellular stimuli and oncogene products such as ▶RAS and activated receptor tyrosine kinases like ▶NTRK and ▶RET. Aberrant B-Raf activity as a result of somatic mutations is observed in 8% of human cancers.

Characteristics Physiological Aspects of B-Raf Signaling B-Raf is a member of the ▶Raf kinase family and represents an important component of the Ras/Raf/ MEK/ERK MAP kinase signal transduction pathway, which plays a pivotal role in growth control and differentiation. Dysregulation of this pathway is observed in about 30% of human tumors and represents an established mechanism for tumorigenesis. In their role as gatekeepers of this pathway, Raf-kinases appear as attractive targets for therapeutic intervention. The Raffamily contains three genes in vertebrates, A-Raf, B-Raf and Raf-1 as well as D-Raf and LIN-45 in Drosophila und Caenorhabditis, respectively. While the RAF1 gene displays a ubiquitous and prominent expression pattern, B-Raf is predominantly expressed in neuro-ectoderm derived tissues, placenta, the hematopoietic system and the testis. However, gene targeting experiments in mice and ▶DT40 B cells revealed that B-Raf represents the major ERK activator, even if it is expressed at barely detectable levels, whereas Raf-1 serves as an accessory ERK activator. Among the three mammalian isoforms, B-Raf displays the highest affinity towards its substrate MEK and has the highest activities in biological and ▶in vitro kinase assays. In many cell types, B-Raf plays a non-redundant role in the maintenance of ERK signaling induced by various extracellular signals and thereby regulates directly, or in concert with other signaling pathways, the expression of important target gene products such as growth factors and cytokines. The importance of B-Raf for the efficient expression of ERK-regulated target gene products is most likely

B-Raf Signaling

explained by the fact that ERK activation is not only required for the induction of ▶immediate early genes transcription, but also for the stabilization of the resulting proteins by phosphorylation through sustained ERK signaling. The correlation between B-Raf expression and sustained ERK signaling has been implicated in various physiological processes such as lymphocyte activation, myelopoiesis, angiogenesis, development of extra-embryonic tissues as well as for the growth-factormediated survival of neurons and their effector functions. The discovery of germ-line mutations with mostly slight to moderate gain-of-function character in the SOS, KRAS, HRAS, SHP2/PTPN11, BRAF and MEK1/ 2 genes in patients suffering from the various ▶neurocardio-facial-cutaneous syndromes illustrates that tight control of this pathway upstream or at the level of the B-Raf/MEK interface is key to the normal development and homeostasis of many organs. B-Raf Signaling and Tumor Development The high biological relevance of B-Raf is also reflected in the discovery that ▶somatic alterations of the BRAF gene occur in about 8% of all human tumors with particular high frequencies in ▶melanoma (70%), ovarian (30%), thyroid (27%), colorectal and biliary tract carcinoma (both 15%). Many of the resulting mutant B-Raf proteins cause chronic ERK activation and transform a variety of cell types in vitro. Furthermore, the B-RafV600E oncoprotein, which is the most frequently found mutant and occurs in 7% of human tumors, induces neoplasms in transgenic mice and zebrafish. Apart from their established role as ERK activators, B-RafV600E and other oncogenic mutants have been shown to activate the ▶NF-κB pathway, although the exact mechanism for this oncologically relevant aspect of B-Raf sigaling remains elusive. Dysregulated B-Raf signaling in the absence of any BRAF mutations has been also implicated in various neoplastic diseases. For example, hyper-activation of wild type B-Raf has been observed in ▶Polycystic Kidney Disease. Similarly, over-expression and deregulation of B-Raf have been implicated in ▶Kaposi Sarcoma. Likewise, amplification and/or overexpression of the BRAF gene were described as alternative events to BRAF mutations in melanoma. Furthermore, B-Raf serves as an important signal transducer of upstream oncogene products such as RAS or activated receptor tyrosine kinases (RTKs) such as ▶RET, ▶NTRK, ▶Epidermal Growth Factor Receptor family members or the ▶Kit/Stem cell factor receptor. In many cell types where the chronic activation of the RAF/ MEK/ERK effector arm by these oncoproteins represents a major mechanism of cellular transformation, a mutual exclusivity is observed between mutations in BRAF or genes encoding its upstream activators. For example, gain-of-function mutations in either the

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▶RET, ▶NTRK, ▶RAS or BRAF proto-oncogenes account for 70% of papillary thyroid carcinoma and provoke similar transformed phenotypes indicating that the activation of B-Raf effectors such as ERK and NF-κB is a major driving force in thyrocyte transformation. Similar constellations have been described for RAS and BRAF in melanoma, colorectal and ovarian carcinoma. However, Ras and B-Raf transformed cells differ in their responsiveness to MEK-inhibitors showing that both oncoproteins, while having a large group of effectors in common, also trigger ▶oncogene addiction through distinct mechanisms. Oncogenic B-Raf not only mimics growth factor signaling, but also induces a variety of auto- and paracrine acting growth factors itself, e.g. ▶Heparin-Binding Epidermal Growth factor (EGF)-Like Growth Factor, chemokines and proinflammatory and angiogenic cytokines like ▶Vascular Endothelial Growth Factor A. Apart from tumor initiation, tissue culture experiments suggest that oncogenic B-Raf also contributes to tumor progression by inducing two additional key events in metastasis: the ▶Epithelial to Mesenchymal Transition of the oncogene-bearing cell and the ▶angiogenic switch in its environment through the aforementioned growth factors and cytokines. Aberrant B-Raf activity does not necessarily result in tumorigenesis unless profound changes in the regulatory network underlying cell cycle control have occurred. Through the ERK and NF-κB pathways, oncogenic B-Raf stimulates not only the production of positive cell cycle regulators such as Cyclin D1, but also induces negative regulators such as cyclin-dependent kinase inhibitors like p16INK4A. Consequently, chronic B-Raf/ ERK signaling ultimately results in cell cycle arrest and cellular ▶senescence. For example, melanocytes with an intact cell cycle control program become growth arrested by chronic B-Raf signaling and develop only into benign nevi. However, if important negative cell cycle regulators and tumor suppressor genes like ▶INK4A or ▶p53 are lost, oncogenic B-Raf signaling will trigger cell cycle progression and drive tumor development. B-Raf Structure and Regulation Like many other protein kinases, B-Raf is part of a large multi-protein complex or ▶signalosome in which the individual components regulate B-Raf conformation and activity through various protein-protein interactions in a dynamic spatio-temporal manner. Key to the understanding of the (dys-)regulation of B-Raf is the knowledge of its modular structure. B-Raf shares three highly conserved regions (CR) with the other members of the Raf-family (Fig. 1): the N-terminal CR1 contains the Ras-GTP binding domain, which initiates the interaction with activated Ras, and the Cystein-rich domain involved in the stabilization of

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B-Raf Signaling

B-Raf Signaling. Figure 1 Model of the B-Raf activation cycle. B-Raf contains three conserved regions: CR1 (blue) consisting of the Ras-binding domain (RBD) and the Cystein-rich domain (CRD), CR2 (green) and the kinase domain CR3 (blue). Inactive B-Raf resides in the cytoplasm in a closed, inactive conformation stabilized by 14-3-3. Interaction of B-Raf with a complex consisting of CK2 and the scaffold protein KSR results in phosphorylation of S446 (and perhaps S447) in the N-region thereby transferring B-Raf into a more open conformation. The constitutive basal phosphorylation of B-Raf at S446 suggests that a large fraction of B-Raf resides in this primed state. Interaction with activated Ras (Ras-GTP) leads to phosphorylation of T599 and S602 within the activation loop, which induces a conformational change within the CR3 and renders B-Raf active. B-Raf is supposedly inactivated by phosphatases, re-phosphorylation of the inhibitory residue S365 and transition into the closed conformation.

Ras/Raf interaction. The CR2 contains a negative regulatory serine residue (S365) that serves as a binding site for ▶14-3-3 proteins upon phosphorylation by ▶Akt and other kinases. The catalytic domain (CR3) harbors phosphorylation sites for Raf-regulating enzymes within two segments, the N-region and the ▶activation loop. B-Raf carries a second 14-3-3 binding motif around S729 at the C-terminal end of the CR3 domain, which is essential to couple B-Raf to its downstream effector MEK. Similar to the better-characterized Raf-1 isoform, B-Raf is activated by its interaction with small GTPases of the RAS family. Although no crystal structure for any of the full-length Raf-proteins is available, various experimental approaches imply that Raf activation is accompanied by a transition from a closed, autoinhibited into an open, active conformation in which the N-terminal lobe consisting of the CR1 and CR2 domains is displaced from the C-terminal lobe encompassing the CR3 (Fig. 1). The degree of auto-inhibition of B-Raf is influenced by the inclusion/exclusion of

amino acid sequences within the linker region between N- and C-terminal lobe, which are encoded by alternatively spliced, tissue-specific exons and various phosphorylation events. Among the latter, two phosphorylation sites within the CR3, the N-region and the activation loop, are of particular importance (Fig. 1). The introduction of negative charges into the N-region, which is located at the N-terminal end of the CR3 domain, plays a critical, multi-faceted role in Raf activation. While the N-region of Raf-1 is charged through phosphorylation of its S338SYY341-sequence in a RAS-dependent manner by Ser/Thr- and Tyr-kinases, the equivalent serine residues within the N-region of B-Raf (S446SDD449-motif) are phosphorylated in a constitutive and RAS-independent manner (Fig. 1). Although structural data are still missing, several lines of evidence propose that N-region phosphorylation primes B-Raf for activation at the membrane by reducing the affinity between N-terminal and C-terminal lobe. The significance of the aspartate residues, which are the functional equivalents of the phosphotyrosine residues in the SSYY-sequence of Raf-1, is

B-Raf Signaling

twofold: firstly the negative charge of the aspartate residues are supposed to prime B-Raf for N-region phosphorylation by Casein Kinase 2 (CK2). Secondly, the D448 residue stabilizes the conformation of activated B-Raf through the formation of a salt-bridge with R506 within the αC-helix of the CR3. The important role of the SSDD-sequence is highlighted by the fact that mutation of the serine and/or aspartate residues results in drastic reduction of the basal in vitro kinase and biological activities. Furthermore, it has been suggested that the different mechanisms that supply the N-region of B-Raf and Raf-1 with negative charges, account not only for the aforementioned isoform-specific differences in the enzymatic, biological and transforming activities, but also predispose the BRAF gene for oncogenic hits. However, while tissue culture experiments demonstrated that the rare B-Raf E586K mutant indeed requires an intact SSDDsequence to induce MEK/ERK activation and oncogenic transformation, the biological activity of the most frequently found mutant, B-RafV600E, is not affected by N-region neutralization, at least not in experimental approaches involving the ectopic expression of this oncoprotein. The interaction with Ras recruits B-Raf to the plasma membrane followed by the phosphorylation of the

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activation loop residues T599 and S602 (Fig. 2). This phosphorylation event presumably leads to the dislocation of the activation loop relative to the overall catalytic domain thereby resulting in full B-Raf activity. The importance of the activation segment phosphorylation is established by the fact that mutation of these phosphorylation sites to alanine residues renders B-Raf resistant to extracellular signals and even to strong activators like oncogenic RasG12V. Conversely, mutations that mimic the phosphorylation-induced dislocation of the activation segment, such as BRAFV600E, lock B-Raf in an active conformation and confer high constitutive enzymatic and transforming activities to B-Raf independent of RAS. Consequently, these activation loop mutations are frequently found as somatic alterations of the BRAF gene in human tumors. Intracellular B-Raf activity is also regulated by the phosphorylation-dependent recruitment of ▶14-3-3 proteins in an opposing manner (Fig. 1). Binding of 14-3-3 proteins to phospho-S729 at the C-Terminus of B-Raf is essential to couple B-Raf to the MEK/ERK pathway. In contrast, phosphorylation of S365 within the CR2 by Protein kinases A, Akt or Serum-andGlucocorticoid-induced kinase (SGK) generates a second binding site for 14-3-3 proteins, which negatively regulates B-Raf activity, most likely through the

B-Raf Signaling. Figure 2 Modulation of B-Raf signaling. Extracellular signals received by various receptor classes trigger the activation of Ras-GTPases by stimulating their loading with GTP. Activated Ras not only recruits B-Raf and promotes its phosphorylation by unknown activation loop kinases, but also stimulates its homo- and hetero-dimerisation. The activity of B-Raf (and Raf-1) is fine tuned by a multitude of positive and negative modulators. The longevity of B-Raf/Raf-1 heterodimers is determined by a rapid negative feedback loop from ERK. In a delayed negative feedback loop, sustained B-Raf/ERK signaling also induces the transcription of Sprouty-2, a negative regulator of B-Raf.

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stabilization of the auto-inhibited conformation through the simultaneous binding of the 14-3-3 dimer to S365 and S729 (Figs. 1 and 2). 14-3-3 proteins are also involved in the RAS-stimulated formation of homodimers of B-Raf and its hetero-dimerisation with Raf-1 (Fig. 2). Indeed, B-Raf/Raf-1 hetero-dimers represent the most potent form of Raf-activity within the cell. Activated ERK limits the longevity of these dimers by targeting an evolutionary conserved phosphorylation motif at the C-terminus of B-Raf (Fig. 2). In addition, B-Raf activity is modulated by other components of the signalosome such as the ▶HSP90/Cdc37 chaperone complex and ▶scaffold proteins like Kinasesuppressor-of-Ras (KSR) and Connector-and-enhancerof-KSR (CNK). Membrane phospholipids such as phosphatidylserine (PS) and phosphatidic acid (PA) are also discussed as important regulators of Raf activation. B-Raf is also negatively regulated by Sprouty-2 and Rafkinase-inhibitory protein (RKIP), two proteins, which are both often down-regulated in human cancer raising the possibility that their epigenetic silencing represents an alternative mechanism to gain-of-function mutations in genes linked to the Ras/Raf/MEK/ERK pathway in human cancer. Similarly, B-RafV600E and other activation loop mutants are incapable of interacting with Sprouty demonstrating that the V600E mutation not only uncouples B-Raf from positive (interaction with Ras, N-region and activation loop phosphorylation) but also negative regulatory mechanisms. B-Raf as a Therapeutic Target The growing importance of B-Raf in tumor biology has fostered the development of therapeutic strategies aiming at either reducing the expression or activity of B-Raf or its downstream effector MEK. Various MEK inhibitors are currently in clinical trials and experiments in tissue culture and xenograft models indicate that tumor cells harboring the BRAFV600E mutation, but not those with RAS mutations, are highly “addicted” to ERK activity and are consequently particularly sensitive towards MEK inhibition. Similar results have been obtained in experiments in which the expression of B-RafV600E but not of wild type B-Raf was specifically abolished by allele-specific ▶RNA interference illustrating the importance of this oncoprotein for the maintenance of the tumor phenotype. Recent strategies also target B-Raf directly. The orally available multikinase inhibitor BAY 43-9006 (also known as Sorafenib or Nexavar), which was originally designed to block Raf-1, inhibits B-Raf as well as several receptor tyrosine kinases (RTKs) involved in neo-angiogenesis and tumor progression. However, it is assumed that the inhibition of the latter kinase class or the simultaneous inhibition of several kinases, rather than the inhibition of Raf itself, is responsible for the anti-tumor activity of BAY 43-9006, in particular in renal cell

carcinoma. A third approach employs the requirement of the HSP90/Cdc37 chaperone complex for the stability of B-Raf. In this regard, the HSP90 inhibitor ▶Geldanamycin was shown to trigger the degradation of B-Raf by disrupting its association with the HSP90/ Cdc37 chaperone complex. The stability of most activated B-Raf mutants, including B-RafV600E, appears to be more reliant on the chaperone complex than those of wild type B-Raf suggesting that tumor cells driven by BRAF mutations will be particularly sensitive to Geldanamycin.

References 1. Brummer T, Martin P, Herzog S et al. (2006) Functional analysis of the regulatory requirements of B-Raf and the B-RafV600E oncoprotein. Oncogene 25:6262–6276 2. Galabova-Kovacs G, Kolbus A, Matzen D et al. (2006) ERK and beyond: insights from B-Raf and Raf-1 conditional knockouts. Cell Cycle 5:1514–1518 3. Ritt DA, Zhou M, Conrads TP et al. (2007) CK2 is a component of the KSR1 scaffold complex that contributes to Raf kinase activation. Curr Biol 17:179–184 4. Schreck R, Rapp UR (2006) Raf kinases: oncogenesis and drug discovery. Int J Cancer 119:2261–2271 5. Wellbrock C, Karasarides M, Marais R (2004) The RAF proteins take centre stage. Nat Rev Mol Cell Biol 5:875–885

B-Raf Somatic Alterations T ILMAN B RUMMER Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia

Definition Somatic alterations of the BRAF gene in cancer, either caused by point mutation or genomic rearrangement of the BRAF proto-oncogene.

Characteristics The Ser/Thr-kinase B-Raf, a product of the human BRAF proto-oncogene, plays a pivotal role in the activation of the classical ▶ERK/MAP kinase pathway that is involved in the control of proliferation and differentiation of various tissues. Consequently, alterations of the expression level or the activity of B-Raf are associated with malignancies like ▶polycystic kidney disease and various cancers. Proto-oncogenes can be converted into oncogenes by point mutations, amplifications, genomic rearrangement, e.g. translocation or inversion, or by retroviral transduction. Interestingly, all four mechanisms of oncogene activation have

B-Raf Somatic Alterations

been documented for the BRAF genes in human and/or animal tumors. History of the BRAF Proto-Oncogene The discovery of the raf-oncogenes originates back to the isolation of the chicken Mill Hill 2 (MH2) retrovirus by Begg in 1927. Genetic studies in the 1980s demonstrated that MH2 contains two unrelated retroviral oncogenes that were designated as v-myc and v-mil. Subsequent analysis of v-mil revealed a high sequence homology to the v-raf oncogene of the murine sarcoma retrovirus 3611. Further analyses showed that both v-mil and v-raf arose independently by retroviral transduction from the chicken c-mil and mammalian raf-1 genes, respectively. In 1988, a v-mil related oncogene was discovered in ▶transforming retroviruses that were generated by passaging the nononcogenic Rous-associated virus type 1 (RAV-1) on embryonic chicken neuroretina cells. Due to its origin in retinal cultures, this relative of v-mil was designated as v-Rmil. Subsequent studies showed that v-Rmil was generated by retroviral transduction from the

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proto-oncogene c-Rmil, which is related but distinct to the c-mil/raf-1 proto-oncogenes and represents the avian ▶orthologue of BRAF. Similar to the avian c-Rmil/B-raf gene, the BRAF genes of other vertebrates display a conserved exon/intron structure with 18–20 coding exons, in which the first eight exons encode the N-terminal autoinhibitory region (Fig. 1a). At the same time as v-Rmil was discovered, the human BRAF oncogene was identified in a ▶NIH3T3 transformation assay using ▶Ewing sarcoma DNA. Importantly and in striking analogy to v-Mil and v-Raf, both the v-Rmil and the B-Raf oncoprotein from the Ewing sarcoma isolate represent N-terminally truncated B-Raf proteins (Fig. 1b), which have lost the N-terminal regulatory lobe and consequently the ability for autoinhibition (▶B-Raf signaling). Therefore, all these Rafoncoproteins display constitutive activity and induce chronic activation of the ERK pathway. Thus, loss of exons encoding for the auto-inhibitory N-terminal moiety is a common mechanism of oncogenic activation of raf proto-oncogenes. This notion is further supported by recent experiments showing that the

B-Raf Somatic Alterations. Figure 1 B-Raf oncoproteins. (a) Situation for wildtype B-Raf. In its inactive state, the BRAF proto-oncogene product resides in a closed conformation stabilized by 14-3-3 proteins. Activation of B-Raf by activated RAS results in a displacement of the N-terminal auto-inhibitory region (Conserved region (CR) 1 in blue, CR2 in green) from the CR3 or kinase domain (red) allowing access of the activation loop kinase to the the TVKS-motif. Phosphorylation of T599 and S602 within this motif renders B-Raf active. (▶B-Raf signaling). (b) Schematic representation of v-Rmil. Due to the retroviral transduction event, the genome of RAV encodes for a fusion protein flanking the B-Raf (CR3) kinase domain with an N-terminal portion encoded by the env gene and a C-terminal moiety encoded by a portion of the gag gene. Both the env and gag genes are integral components of retroviral genomes. (c) Schematic representation of AKAP9-B-Raf. (d) Schematic representation of B-Raf proteins with point mutations as exemplified for the activation loop mutant B-RafV600E.

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murine Braf gene represents a frequent integration point for the Sleeping Beauty transposon. All transposon integrations were observed between exons 9 and 10 resulting in a disruption of the coding sequence of full-length B-Raf and expression of an N-terminally truncated B-Raf protein with an intact kinase domain and structural similarity to v-Rmil and v-Raf. However, it should be mentioned that neither retroviral B-Raf oncogenes nor transposon-mediated oncogenic activation of the BRAF gene have been observed in human beings. Likewise N-terminal truncations of B-Raf like those found in the original publication on the human B-Raf gene, which most likely represents a transfection artifact, have not been found in human tumors until recently. Nevertheless, the human BRAF protooncogene is affected by somatic alteration in about 7% of human tumors. The following alterations are observed in human tumors: Chromosomal Aberrations A recent study has identified an oncogenic BRAF allele in about 11% of papillary thyroid carcinomas (PTC) in children and adolescents that had been exposed to radiation following the Chernobyl nuclear power plant station accident in 1986. This oncogene was generated via a paracentric inversion of the BRAF locus on chromosome 7q34 resulting in an in-frame fusion with exons 1–8 of the A-kinase anchor protein 9 (AKAP9) gene on 7q21-22. The resulting AKAP9-B-Raf fusion protein is made up by exons 1–8 of AKAP9 and exons 9–18 of BRAF. Thus, this AKAP9-B-Raf protein contains an intact kinase domain, but the auto-inhibitory N-terminal regulatory domain of B-Raf is replaced by the AKAP9 moiety, which cannot confer autoinhibition (Fig. 1c). Consequently, the activity of this fusion protein is, similar to the situation in v-Rmil, unrestrained and able to transform NIH3T3 cells. Interestingly these mutations were only found in tumors that had developed within a short latency period suggesting that this chromosomal aberration is a driver of radiation induced PTC rather than being a secondary event. Another recent study has reported the occurrence of chromosomal translocations involving the human BRAF gene in two cases of large congenital melanocytic nevi, which can progress into malignant melanoma. In both cases and similar to the situation of the AKAP9B-Raf fusion protein, these translocations give rise to fusion proteins, which lack the exons encoding the auto-inhibitory N-terminal regulatory domain, but again contain an intact B-Raf kinase domain. Somatic and Germ-Line Point Mutations Although Raf proteins were implicated early on as important effectors of human oncoproteins, e.g. Ras, they were not considered as frequent mutational targets

in cancer. In 2002, however, the ▶cancer genome project (CGP) reported a high frequency of somatic point mutations in the human BRAF gene in malignant melanoma (27–70%). Subsequent studies also revealed high point mutation frequencies in thyroid (36–53%), ovarian (30%), biliary (14%) and colorectal cancer (522%) and lower frequencies in a wide range of other human tumors. It is estimated that the human BRAF gene bears somatic mutations in about 7% of all human cancers. In contrast to the aforementioned alterations of the BRAF gene, these point mutations do not affect the overall primary structure of B-Raf (Fig. 1d), but mostly bypass critical regulatory events required for the activation of wildtype B-Raf (▶B-Raf signaling). While mutations in the human CRAF gene are still considered as a very rare event, over 40 different somatic mutations, involving 24 different codons, have been identified in BRAF since 2002. Most alterations represent point mutations, however, codon deletions or in-frame insertions have been occasionally identified as well. A detailed overview on these mutations can be found on the CGP homepage (http://www.sanger.ac.uk/perl/genetics/ CGP/cgp_viewer?action =gene&ln=BRAF). Most mutations cluster within the activation loop codons and, to a lesser extent, within the nucleotide sequence encoding the glycine-rich loop (also known as P-loop; Fig. 1d). Among the activation segment mutations, the thymidine to adenine transversion at nucleotide 1799, which results in the substitution of valine 600 within the T599V600KS602-motif in the activation segment by glutamate, represents the most common mutation and is found in 6% of human cancers. Structural analysis of the B-Raf kinase domain suggests that the inactive conformation of B-Raf is stabilized by a hydrophobic interaction between the activation loop residues with the glycine rich loop, with V600 and F467 playing key roles in this process. Upon activation of wildtype B-Raf by activated Ras, T599 and S602 in the activation loop become phosphorylated by an unknown kinase resulting in the disruption of the inhibitory hydrophobic interaction between the activation and glycine rich loop and consequently full activation of B-Raf (Fig. 1a). In a similar way, any mutation in either the activation or glycine-rich loop mutation that disrupts this hydrophobic interaction, e.g. replacement of V600 by bulky and/or charged amino acids like glutamate, mimics the activated state and confers constitutive activity to B-Raf. As described in ▶B-Raf signaling, the current model of B-Raf activation proposes a sequence of positive regulatory events leading to a relief of auto-inhibition by the N-terminal lobe followed by activation loop phosphorylation and full B-Raf activation. According to this sequential model of B-Raf activation, the V600E mutation not only bypasses these events, but is also

Brain Microvascular Endothelial Cells

able to counteract auto-inhibition, which would explain why this mutation is so frequently found in tumors driven by chronic ▶B-Raf signaling. However, why the V600E mutation occurs more frequently than any other activation loop or glycine-rich loop mutations that would also disrupt the inactive conformation, remains controversial. The V600E codon might represent a mutational “hotspot” or, due to still unknown details of B-Raf activation, might be an extremely efficient oncogene that subjects B-RafV600E expressing cells to a particularly strong positive selection. It should be also mentioned that the occurrence of the BRAFV600E allele in colorectal cancer is correlated with ▶microsatellite instability (MSI) and widespread methylation of CpG islands in a highly statistically significant manner. However, it remains to be clarified as to whether the MSI phenotype that is caused by absence or hypo-activity of DNA mismatch repair genes and is characterized by a widespread methylation of CpG islands, reflects a cause or a consequence of dysregulated B-Raf signaling. In 2006, germ-line mutations in the human BRAF gene were found in patients suffering from the ▶cardiofacial-cutaneous (CFC) syndrome. Some of these mostly gain-of-function mutations in CFC patients are also found in cancer, however, mutations conferring high activity to B-Raf such as BRAFV600E have not been found. Indeed, knock-in experiments in mice have shown that ubiquitous expression of B-RafV600E confers early embryonic lethality suggesting that high levels of chronic B-Raf activity would not be tolerated during human development as well. However, it should be noted that not all of the point mutations found in cancer or CFC patients represent obvious gain-of-function mutations as some of them actually display impaired in vitro kinase activity. Nevertheless, these impaired activity mutants still appear to activate the ERK pathway within the cell, either through stimulating the activity of Raf-1 in Raf-1/B-Raf heterodimers or, potentially, by acting as a buffer against negative regulators, e.g. RKIP, or negative feedback loops controlling ▶B-Raf signaling. Amplification Amplification of the BRAF locus is another mechanism contributing to elevated B-Raf protein expression and activity. Studies in malignant melanoma have described the amplification of BRAF alleles with point mutations such as V600E at the expense of the wildtype BRAF allele. Genetic experiments have identified B-Raf as an important factor for ERK activation under basal and steady state conditions (▶B-Raf signaling). Experiments in various cell types have shown that increasing levels of wildtype B-Raf enhanced basal and steady state ERK signaling suggesting that over-expression of endogenous

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wildtype B-Raf might contribute to tumorigenesis. Indeed, amplification of the BRAF locus in the absence of any mutations in exon11 (Gly-rich loop) and exon 15 (activation loop) was described as an important contributor to the proliferation of malignant melanoma cell lines.

References 1. Ciampi R, Knauf JA, Kerler R et al. (2005) Oncogenic AKAP9-BRAF fusion is a novel mechanism of MAPK pathway activation in thyroid cancer. J Clin Invest 115:94–101 2. Collier LS, Carlson CM, Ravimohan S et al. (2005) Cancer gene discovery in solid tumours using transposon-based somatic mutagenesis in the mouse. Nature 436:272–276 3. Dessars B, De Raeve LE, Housni HE et al. (2007) Chromosomal translocations as a mechanism of BRAF activation in two cases of large congenital melanocytic nevi. J Invest Dermatol 127:1468–1470 4. Dhomen N, Marais R (2007) New insight into BRAF mutations in cancer. Curr Opin Genet Dev 17:31–39 5. Tanami H, Imoto I, Hirasawa A et al. (2004) Involvement of overexpressed wild-type BRAF in the growth of malignant melanoma cell lines. Oncogene 23:8796–8804

Bragg (Curve) Peak Definition A characteristic dose distribution of a single-energy charged particle beam (e.g. protons) with a sharp peak close to the end of the range. The range is a distance that particles travel inside the medium. ▶Radiation Oncology

Brain Capillaries ▶Blood–Brain Barrier

Brain Microvascular Endothelial Cells ▶Blood–Brain Barrier

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Brain Tumors

Brain Tumors YASUYUKI H ITOSHI , PAULA M. K UZONTKOSKI , M ARK A. I SRAEL Departments of Pediatrics and of Genetics, Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, NH, USA

Definition

Primary ▶brain tumors present most commonly as ▶meningioma or various grades of ▶astrocytoma. ▶Gliomas constitute 78% of all malignant brain and central nervous system tumors. It is estimated that 20,500 individuals will be diagnosed with cancer of the brain and nervous system in 2007, or about 1.4% of all newly occurring malignancies. Of those diagnosed, there will be 10% more men than women. Primary brain and nervous system cancers will account for 2.3% of the estimated 560,000 cancer deaths in 2007. Based on the most recent report of the Central Brain Tumor Registry of the United States, benign tumors of the CNS arise in numbers comparable to malignant brain tumors. In children and young adults, brain tumors are responsible for 25% of all cancer-related deaths, second only to leukemia in this age group. The estimated 5-year relative survival rate for malignant brain tumors is 29%, but there is much variation in survival, depending on tumor histology. The 5-year survival rate exceeds 91% for pilocytic astrocytomas, but is less than 4% for glioblastomas. Generally, survival decreases with increasing age at diagnosis.

Characteristics Classification and Pathology The cell of origin of commonly occurring brain tumors is not known, although recent evidence suggests that these tumors arise either from ▶neural stem cells or from other cells that take on many characteristics of neural stem cells as a result of malignant transformation caused by the

Brain Tumors. Table 1 Tumor type

activation of oncogenes and the inactivation of ▶tumor suppressor genes within the cells. Pathologically, these tumors are classified according to the World Health Organization (WHO) nomenclature and grading criteria. Tumors that share cytologic and histologic evidence of astrocytic differentiation are known as ▶astrocytoma and are the most frequent primary intracranial neoplasms. Their neuropathological appearance is highly variable. Tumors with evidence of oligodendroglial differentiation are known as ▶oligodendroglioma. Some tumors that have cells reminiscent of both lineages are known as ▶mixed oligo-astrocytomas. Each of these tumor types can be graded histologically according to a four-tiered system of increasing malignancy from Grades I through IV. Grade I, for example, has an excellent prognosis following surgical excision, and Grade IV, ▶glioblastoma multiforme, has multiple features of clinical aggressiveness and is typically incurable. Hypercellularity with evidence of high mitotic activity, nuclear and cytoplasmic atypia, endothelial proliferation, and necrosis correspond closely to tumor virulence and are most characteristically present in Grade IV tumors. The overwhelming majority of gliomas arising in adults are high-grade and arise in a supratentorial location. Highgrade tumors do not have a clear margin separating neoplastic and normal tissue. This finding is consistent with the observation that tumor cells usually have infiltrated adjacent normal brain by the time of diagnosis, when complete resection is oftentimes not possible. Tumor cells capable of initiating new tumor foci can now be recognized as tumor stem cells. Cytogenetic examination of chromosomes within the cells of a ▶brain tumor has revealed characteristic regions that tend to be altered in specific tumor types (Table 1). Frequent sites for chromosomal DNA loss in astrocytic tumors include chromosomes 17p, 13q, and 9. In oligodendroglioma, DNA from 1p and 19q is frequently lost, and in ▶meningiomas, 22q is often lost. Molecular genetic analysis can also reveal evidence of tumor-specific genetic alterations at sites where chromosomes appear normal upon cytogenetic

Cytogenetic and genetic alterations in brain tumors Chromosomal alteration

Genetic changes Oncogene

1p–, 7+, 9p–, de110, 11p–, 12q–, 12q+, 13q–, 13q+, 18p+, 17p–, 17q–, 19p–, 19q–, 22q–, DMsa Oligodendroglioma 1p–, 19q–, 7+, 10– Astrocytoma

Medulloblastoma a

EGFR, PDGFRA, KIT, CROS, MET, CDK4, NEU, RAS, MDM2, GLI, CMYC EGFR

5p+, 5p–, 5q–, del6, 8p–, 8q+, 9q–,10q–, GLI, CMYC, CTNNB1 17p–, 17q–, 17q+, 21q+

DMs, double minute chromosomes.

Tumor suppressor gene P53, RB1, NF1, PTEN, DMBT, CDKN2A, CDKN2D, RASSF1A TP53, PTEN, CDKN2A, CDKN2D, PIK3CA TP53, PTCH, SUFU, APC, RASSF1A

Brain Tumors

analysis. Using a variety of molecular technologies, it has been possible to document the alteration of many different genes in brain tumors, particularly astrocytic tumors (Table 1). While the particular constellation of genetic alterations that activate oncogenes and inactivate tumor suppressor genes varies among individual brain tumors that appear to be histologically indistinguishable, an accumulation of mutations is typically associated with increasingly aggressive malignant behavior. Glioblastoma multiforme (▶GBM) typically presents without evidence of a precursor lesion, referred to as de novo or primary GBM. These tumors typically have evidence for chromosome 10 deletions in the region where the tumor suppressor ▶PTEN is known to be located, and activation of the ▶epidermal growth factor receptor (▶EGFR) gene either by amplification or deletion of 275 amino acids from the extracellular domain of the receptor. This and closely related mutations occur in 60% of GBM. EGFR is the gene most frequently activated in malignant astrocytomas. EGFR amplification and activation by mutation occurs in 5% of low-grade astrocytomas and about 30% of GBM, indicating that this molecular change is principally associated with the progression from lowor intermediate-grade neoplasia to high-grade astrocytic neoplasia. In fewer than 20% of cases, GBM arises in association with progressive genetic alterations after the diagnosis of a lower-grade astrocytoma. These tumors are referred to as secondary GBMs. The most widely described alterations are amplification or overexpression of the ▶PDGF receptor, mutations of ▶p53 or ▶MDM2 and ▶INK4a, and loss of PTEN (Table 1). Deletion of the ▶CDKN2 gene, which encodes the cyclin-dependent kinase inhibitor p16, has been reported to occur in 40–70% of glioblastoma. The ▶RB1 tumor suppressor gene is homozygously deleted or mutated in about 30% of high-grade gliomas. The protein products of tumor suppressor genes are proteins that act to regulate or suppress cell growth or promote cell death. These genes are inactivated during tumorigenesis, and several such genes have been implicated in the development of astrocytoma. Occasionally, inactivation of one of these alleles in the germline can occur without disturbing development, and patients who carry germline mutations of some tumor suppressor genes can be predisposed to the development of cancer. Several inherited cancer-predisposition syndromes are known to be associated with the development of different brain tumors. Patients with ▶Li-Fraumeni syndrome, caused by an inherited constitutional p53 mutation, have a predisposition for the development of brain tumors. The p53 gene, located on chromosome 17p, has been found to influence multiple cellular functions thought to be important in tumorigenesis. p53 mutations have been reported in sporadically arising astrocytic tumors of all grades, occurring in 40% of astrocytomas,

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in 30% of ▶anaplastic astrocytomas, and in a slightly smaller fraction of GBM. Other brain tumor predisposition syndromes associated with the inactivation of one copy of a particular gene in the germline include ▶neurofibromatosis type 1 (NF1 gene), which is associated with meningioma and optic glioma; ▶neurofibromatosis type 2 (NF2 gene), which is associated with acoustic neuroma and glioma; familial ▶retinoblastoma (▶Rb gene), which is associated with retinoblastoma and pinealoblastoma; ▶von Hippel-Lindau syndrome (VHL gene), which is associated with cerebellar hemangioblastoma; ▶tuberous sclerosis (TSC1 and TSC2 genes), which is associated with subependymal giant cell astrocytoma; ▶Turcot syndrome (▶APC gene), which is associated with astrocytoma and ▶medulloblastoma; and Gorlin’s syndrome (PTCH gene), which is associated with desmoplastic medulloblastoma. The second most common primary brain tumor is oligodendroglioma, which has a more benign course than astrocytoma. Many ▶gliomas have mixtures of cells with astrocytic and oligodendroglial features. If this mixed histology is prominent, the tumor is termed a mixed glioma or an ▶oligoastrocytoma. Many investigators believe that the greater the oligodendroglial component, the more benign the clinical course. The presence of such histologic characteristics as mitosis, necrosis, and nuclear atypia generally is associated with a more aggressive clinical course. If these features are prominent, the tumor is termed a malignant oligodendroglioma. The highest grade oligodendroglioma are indistinguishable from glioblastoma multiforme. Other malignant primary brain tumors include ▶primitive neuroectodermal tumors (▶PNET) such as ▶medulloblastoma, ▶ependymoma, and ▶atypical teratoid/▶rhabdoid tumors; ▶germinomas; and CNS ▶lymphoma. Cerebral PNETs and medulloblastoma, a PNET that arises in the posterior fossa, are highly cellular malignant tumors thought to arise in neural precursor cells. These tumors are difficult to distinguish from one another and typically appear histologically as sheets of small round malignant cells. Germline mutation of PTCH and SUFU in rare patients has called attention to the importance of sonic hedgehog signaling in medulloblastoma. Similarly, APC germline mutations in rare patients implicate WNT signaling as well. These tumors most commonly occur in children. Ependymomas are rare tumors, and when these occur in children, they typically are within the fourth ventricle, where they are thought to arise from cells lining the fourth ventricle. In adults, they arise more frequently in the spinal cord. Patients with neurofibromatosis type 2 are at increased risk of developing ependymoma, and 30% of sporadically occurring tumors exhibit deletion of Ch22q where the NF2 gene is located. Histologically, these tumors exhibit diagnostic ependymal rosettes.

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Brain Tumors

Atypical teratoid/rhabdoid tumors histologically appear as fields of undifferentiated malignant neuroectodermal cells that are indistinguishable from PNET, except for infrequent cells that exhibit evidence of rhabdoid differentiation and the presence of mesenchymal and epithelial elements. Germinomas arise most commonly during the second decade of life at midline locations. Both malignant and benign variants occur frequently. These tumors present with hypothalamic–pituitary dysfunction and visual field deficits. Primary CNS lymphomas are most commonly seen in immunocompromised patients, and have a clinical presentation similar to other primary brain tumors with signs and symptoms referable to cerebral and cranial nerve involvement. Imaging studies typically demonstrate a uniformly enhancing mass lesion. Secondary CNS lymphoma almost always occurs in association with the progression of systemic disease. Several kinds of tumors that are most often benign also occur in the nervous system. ▶Meningiomas are derived from cells of the arachnoid membranes. They are more frequent in women than in men, with a peak incidence in middle age. Meningiomas rarely have histological evidence of malignancy. Other tumors that have a benign clinical course include giant cell astrocytomas, pleomorphic xanthroastrocytomas, neurocytomas, and gangliogliomas. Colloid cysts, dermoid cysts, and epidermoid cysts also occur in the brain. Clinical Presentation of Brain Tumor Patients The most common symptoms that bring patients with a tumor arising in the brain to their physician include a slow progressive focal neurological disability, or a nonfocal neurological syndrome such as headache, dementia, gait disorder, or seizure. Other systemic symptoms suggest a tumor from some other location that may have metastasized to the brain, since patients with primary brain tumors typically do not exhibit systemic symptoms. Patients with primary brain tumors rarely have any biochemical abnormalities; thus CT (Computerized Tomography) and MR (Magnetic Resonance) imaging are key diagnostic modalities for the identification of brain tumors. The characteristic imaging features of brain tumors are mass effect, edema, and contrast media enhancement. Positron emission tomography (PET) scanning and single photon emission computed tomography (SPECT) have ancillary roles in the imaging of brain tumors. Meningiomas and other slow-growing tumors may be found incidentally on a CT or MRI scan or they may present with a focal seizure, a slow progressive focal deficit, or symptoms of increased intracranial pressure. As described above, brain tumors are also recognizable in many inherited syndromes including von Recklinghausen syndrome (neurofibromatosis type 1), neurofibromatosis type 2, Li-Fraumeni syndrome,

▶Multiple endocrine neoplasia type 1, tuberous sclerosis, Turcot syndrome, and Gorlin syndrome. Clinical Management of Brain Tumor Patients and Prognosis Stereotaxic needle biopsy may establish the histological diagnosis of primary brain tumor, although open biopsy is also often utilized to establish the diagnosis. The primary modality of treatment for most primary brain tumors is surgery. The goals of surgery are to obtain tissue for pathological examination, to remove tumor, and to control mass effect. In the case of low-grade and benign tumors, the removal of tumor tissue can be curative or contribute substantially to extending the time to symptomatic progression. In higher-grade tumors, the role of surgery in contributing to curative therapy is less clearly defined, but in younger patients most surgeons aggressively pursue the removal of as much tumor as possible. Following total excision of an ependymoma, the prognosis is excellent. However, many ependymomas cannot be totally excised. Following surgery, ▶radiation therapy has been shown to prolong survival and improve the quality of life of patients with high-grade glioma, PNET, ependymoma, or meningioma when malignant histologic elements can be pathologically identified within the tumor. The medical management of most brain tumors is symptomatic, although a role for chemotherapy is clearly defined in oligodendroglioma and medulloblastoma. In patients with oligodendroglioma, a combination of procarbazine, lomustine, and vincristine has been shown to be most effective in patients with a deletion of Ch1p. Various combination therapies have been shown to contribute to the treatment of medulloblastoma, which has a propensity to spread throughout the neuroaxis. If medulloblastoma is limited to the posterior fossa and completely resected, this tumor has a good prognosis. Temozolomide given during radiation therapy for glioblastoma has been shown to contribute to longer overall survival time. Chemotherapy and radiation typically play a central role in the treatment of germinomas, although there is a role for surgery as well. Patients whose brain tumors are associated with surrounding edema benefit symptomatically from the administration of high doses of glucocorticoids. Anticonvulsants are useful in the control of seizures. Some glioma patients receive anticoagulation therapy to avoid complications of venous thrombosis that occurs in these patients. The prognosis for patients with primary brain tumors varies greatly as a function of the histology and location of the tumor. Benign tumors are often cured by surgery alone. ▶Germinomas and medulloblastomas are more sensitive to cytotoxic therapies than are other brain tumors, and the prognosis for patients with these tumors is generally better than for patients with high-grade

BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk

glioma. In modern studies, the median survival of patients with high-grade glioma is 1–2 years. Complications of Therapy Neurological damage associated with surgical intervention presents a key challenge in the management of brain tumors. Furthermore, the nervous system is vulnerable to injury by therapeutic radiation, and this is frequently manifested by neuropsychological compromise and disability, particularly in very young children who have been treated with high doses of radiation. Pathologically, there is demyelination, hyaline degeneration of small arterioles, and eventually brain infarction and necrosis. Endocrine dysfunction is also commonly seen when the hypothalamus or pituitary gland has been exposed to therapeutic radiation. Depending on the radiated field, secondary tumors such as glioma, meningioma, sarcoma, and thyroid cancer occur following radiation therapy. Toxicities associated with chemotherapy can be significant, but they are not usually different from the toxicities associated with comparable treatments for tumors arising elsewhere in the body. ▶Neuro-Oncology: Primary CNS Tumors

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the growth and differentiation of new neurons and synapses. In the brain, it is active in the hippocampus, cortex, and basal forebrain—areas vital to learning, memory, and higher thinking. BDNF was the second neurotrophic factor to be characterized after NGF.

Branching Morphogenesis Definition Branching morphogenesis refers to the formation of tree-like networks of epithelial tubes through reiterated cycles of branch initiation, branch outgrowth and branch arrest. This process relies on the precise spatio-temporal control of gene expression, cell proliferation and migration, and is essential for the physiological function of many organs including the lung, the vascular system and the kidney. ▶Sprouty

References 1. Central Brain Tumor Registry of the United States (2005) Statistical report: primary brain tumors in the United States, 1998–2002. Central Brain Tumor Registry of the United States, Illinois 2. Jemal A, Siegel R, Ward E et al. (2007) Cancer statistics. CA Cancer J Clin 57(1):43–66 3. Beger M, Prados M (2007) Berger M, Prados M (eds) Textbook of neuro-oncology. Elsevier Saunders, Philadelphia 4. World Health Organization Classification of Tumours (2000) Tumours of the nervous system. In: Kleihues P, Cavenee WK (eds) Pathology and genetics. International Agency for Cancer, Lyon 5. Bigner DD, McLendon RE, Bruner JM (1998) Russell OS, Rubinstein LJ (eds) Pathology of tumors of the nervous system. 6th edn. University Press, New York

BRCA1-associated Ring Domain (Gene/Protein) 1 ▶BARD1

BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk P ETER D EVILEE

Brain-Derived Neurotrophic Factor

Leiden University Medical Center, Leiden, The Netherlands

Definition Definition BDNF; Is a neurotrophin in the central nervous system (CNS), predominantly in the brain and the periphery. This is in contrast to ▶NGF acting predominantly in the peripheral nervous system. It acts on certain neurons of the CNS and the peripheral nervous system that helps to support the survival of existing neurons and encourage

Mutations in the ▶breast cancer genes BRCA1 and BRCA2 cause elevated risks to breast and ovarian cancer. BRCA1 maps to chromosome 17 (band q21), BRCA2 maps to chromosome 13 (band q12). At the genetic level there are interesting analogies between the two genes, even though they are not detectably related by sequence. Both genes are large (coding regions of 5.6 and 10.2 kb, respectively),

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complex (22 and 26 coding exons, respectively), and span about 80 kb of genomic DNA. Both have extremely large central exons encoding >50% of the protein. The majority of the mutations in both genes detected to date lead to premature termination of protein translation, presumably resulting in an inactive truncated protein. Gene changes are distributed nearly ubiquitously over the coding exons and immediate flanking introns. Even though more than half of all mutations are found only once, many mutations have been detected repeatedly in certain populations. For most of these, this has been shown to be the result of a founder effect: these mutations arose a long time ago, and have since spread in the population. Typical founder mutations are the 1185delAG and 15382insC in BRCA1 and 26174delT in BRCA2 that have a joint frequency of about 2.5% among individuals of Ashkenazi Jewish descent.

Characteristics Clinical Characteristics Female carriers of a deleterious BRCA1 mutation were estimated by the Breast Cancer Linkage Consortium (BCLC) to have an 87% cumulative risk to develop breast cancer before the age of 70, and 40–63% risk to develop ovarian cancer before that age (Fig. 1). The gene frequency of BRCA1 was estimated at 1 in 833 women, implying that 1.7% of all breast cancer patients diagnosed between the ages of 20 and 70 are carrier of such a mutation. The estimated cumulative risk of breast cancer conferred by BRCA2 reached 84% by age 70 years. The corresponding ovarian cancer risk was 27% (Fig. 1). These estimates imply that BRCA2

mutations are about as prevalent as BRCA1 mutations. It has been suggested that the ovarian cancer risks are dependent on the position of the mutation in the gene, for BRCA1 as well as BRCA2 mutations. There is also some evidence that cancer risks can be modified by other factors. For example, a strong variability in phenotype can be seen among families segregating the same mutation. This can range from early-onset breast cancer and ovarian cancer, to late-onset breast cancer without ovarian cancer. Even within a single pedigree, ages of onset of cancer can vary substantially. It seems likely that environmental and hormonally related factors (smoking, oral contraceptives) importantly co-determine disease outcome in carriers. Molecular and Cellular Characteristics Tumor Suppressor Genes The first clues to the roles of BRCA1 and BRCA2 in tumorigenesis were genetic. The fact that most germline mutations are predicted to inactivate the protein, and the observed loss of the wild type allele in almost all breast and ovarian cancers arising in mutation carriers, are strong indicators that BRCA1 and BRCA2 proteins act as tumor suppressors. This is supported by the finding that induced overexpression of wild type but not mutant BRCA1 in MCF-7 breast cancer cells leads to growth inhibition and inhibited tumor growth in nude mice. Expression of BRCA1 and BRCA2 In normal cells, BRCA1 and BRCA2 encode nuclear proteins, preferentially expressed during the late-G1/ early-S phase of the cell cycle, but down-regulated in quiescent cells. While apparently at odds with the

BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk. Figure 1 Overall penetrances of BRCA1 and BRCA2 for breast and ovarian cancer. Estimates were obtained by maximizing the LOD score with respect to all the different penetrance functions in those families with strong evidence of the breast and ovarian cancers being caused by the gene (done by linkage analysis). This is equivalent to maximizing the likelihood of the marker data, which is determined only by disease phenotype data. This will give an unbiased estimation of the penetrance irrespective of ascertainment of families on the basis of multiple affected individuals. Data were compiled from Ford et al. (1994) Lancet 343:692–695 and Ford et al (1998) Am J Hum Genet 62:676–689. The graphs can be read in such a way that, for example, an unaffected carrier of a BRCA1 mutation has a 50% risk to develop breast cancer before age 50.

BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk

above-mentioned observations that BRCA1 expression inhibits cellular proliferation, the proliferation-induced expression could represent a negative feedback loop tending to decrease breast cancer risk. However, BRCA1 expression can also be up-regulated in a proliferation-independent way in mammary epithelial cells induced to differentiate into lactating cells by glucocorticoids. Hence, BRCA1 might also play a role in controlling mammary gland development. In mice, expression of BRCA1 and BRCA2 is coordinately up-regulated with proliferation of breast epithelial cells during puberty, pregnancy and lactation. Intriguingly, BRCA1 might suppress estrogen-dependent mammary epithelial proliferation by inhibiting ER-α mediated transcriptional pathways related to cell proliferation. Whatever the cellular function of BRCA1, it appears to be regulated by phosphorylation: it becomes hyperphosphorylated at G1/S with dephosphorylation occurring at M phase. BRCA1 might regulate the G1/S checkpoint by binding hypophosphorylated retinoblastoma protein. BRCA1 and BRCA2 have also been suggested to regulate the G2/M checkpoint by controlling the assembly of mitotic spindles and the appropriate segregation of chromosomes to daughter cells. BRCA1- and BRCA2-Related Breast Cancer A close examination of the pathology of BRCA1- and BRCA2-related breast cancers has defined a typical pathology for each category, differing from that in sporadic cases. In general, cancers in carriers are of higher grade than age-matched controls (Fig. 2), and the

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BRCA1-cancers more frequently display a “medullary”-like appearance. This is due to a higher mitotic count and lymphocytic infiltrate. BRCA2-related breast cancers generally show fewer mitoses and less tubule formation. For both BRCA1- and BRCA2-related cancers, greater proportions of the tumor show continuous pushing margins. Although a role for BRCA1 and BRCA2 in non-inherited sporadic breast cancer is unclear, protein expression of BRCA1 was found to be reduced in most sporadic advanced (grade III) ductal breast carcinomas. BRCA1 and BRCA2 as Caretakers of the Genome To date, several biological roles for BRCA1 and BRCA2 have been demonstrated, and a number of observations indicate that they function in a similar pathway. Both maintain genomic stability through their involvement in homologous recombination, transcription-coupled repair of oxidative DNA damage and double-strand break repair. These roles are suggested by interactions of the Brca1 and/or Brca2 proteins with proteins known to be involved in DNA damage repair, most notably RAD50 and RAD51. Murine embryonic stem cells and mice in which both copies of BRCA1 or BRCA2 have been mutated show a repair deficiency and defects in cell-cycle checkpoints. BRCA1 and BRCA2 play a role in transcriptional regulation, through interactions or complex formation with RNA polymerase II and various transcriptional regulators, although this is presently more firmly established for BRCA1 than for BRCA2. A transcriptional response to DNA damage is well-documented,

BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk. Figure 2 BRCA1- and BRCA2-related breast cancers are generally of higher grade than age-matched controls. Histological sections from 118 breast tumors attributable to BRCA1, and 78 attributable to BRCA2, were evaluated by five histopathologists, all experts in breast disease. Every slide was seen by two pathologists. An age-matched group of 547 apparently sporadic female breast cancer cases served as control. The overall grade of both BRCA1 and BRCA2 breast cancers was significantly higher than that of controls (p < 0.0001 and p < 0.04, respectively). For BRCA1 breast cancers this was due to higher scores for all three grade indices, whereas for BRCA2 breast cancers the grade was only significantly higher for tubule formation. Data taken from The Breast Cancer Linkage Consortium (1997) Lancet 349:1505–1510.

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and identification of downstream targets of BRCA1/2mediated transcription regulation might help to further understand how BRCA1 and BRCA2 suppress tumor formation. Microarray-based screening of genes regulated by BRCA1 were recently found to fall into two categories, cell-cycle control genes and DNA damage response genes. Clinical Relevance When to Take the DNA-test? Diagnosis of gene defects became possible after the identification of BRCA1 and BRCA2 in 1994 and 1995, respectively. In many countries, testing for mutations is being offered to women with a high priori familial risk in Clinical Genetic Centres or multidisciplinary Cancer Family Clinics. A few studies have presented models to determine the prior probability that the counselee is a BRCA mutation carrier, by combining breast and ovarian cancer family history data with results from comprehensive mutation-testing. These models enable the genetic counselor to decide when a DNA-test is indicated. Why Take the DNA-test? A clear positive result of the DNA-test, i.e. the presence of a deleterious mutation, is being used to enter these women into early-detection cancer screening programs or in the decision for or against prophylactic surgery. A woman in which breast cancer has just been diagnosed can benefit from knowledge about gene carrier status, since the risks to the contralateral breast and ovaria must

be considered. The treatment of such cancer by lumpectomy will not reduce recurrence risks dramatically, as opposed to complete mastectomy. Healthy women who test positive can take action to prevent cancer developing, although the efficacy of the preventive options currently offered to a woman remains without formal supporting evidence. Chemoprevention is still controversial, and good prospective data on BRCA carriers will probably never become available, given the ethical and clinical difficulties surrounding randomization. Prophylactic surgery, intuitively the most secure way to reduce breast cancer risk to below population levels, is socially ill-accepted in many parts of the world, and formal proof of its preventive effect in BRCA carriers is also lacking. Clearly, this area is fraught with clinical dilemmas. Interpreting a Negative Test Result Paradoxically, a negative test result (the absence of a deleterious mutation) presently still has limited power in excluding the presence of a strong susceptibility allele. A negative test result is presently being found in 70–80% of all probands tested in most non-Ashkenazi Jewish populations. Among probands with a family history for ovarian cancer, a negative test result is found less frequently (although still in 40–60% of the cases). There are several levels of uncertainty. . The first is technical: no single mutation-detection method is 100% sensitive, and therefore only exhaustive testing, using a range of different methodologies sensitive to various types of mutation-mechanisms,

BRCA1/BRCA2 Germline Mutations and Breast Cancer Risk. Table 1 Mutation types in BRCA1 and BRCA2 and their predicted effects BRCA1 % of Total Mutation type Frameshifting Nonsense Splice-site In-frame del/ins Missense Neutral Intronic change Mutation effect Protein truncating Missense Neutral polymorphism Unclassified variant

% of Distinct

BRCA2 % of Total

% of Distinct

47.1 11.3 4.4 0.6 28.4 3.5 4.7

38.7 11.1 7.9 1.8 28.4 3.9 8.3

33.7 11.5 2.2 0.4 44.3 3.1 4.9

36.5 10.2 3.6 1.0 35.4 5.5 7.8

62.6 2.2 11.0 24.2

56.9 1.5 7.2 34.4

41.4 0.7 14.4 43.4

47.9 1.9 13.7 36.4

The entire Breast Cancer Information Core (BIC) database was down-loaded on March 1, 2000 from http://www.nhgri.nih.gov/ Intramural_research/Lab_transfer/Bic. There were 3,086 BRCA1 mutations and 1,892 BRCA2 mutations. The total numbers of distinct changes were 724 and 670, respectively.

Breakpoint Cluster Region

and investigating the entire coding regions and regulatory domains, can detect any changes. This is obviously very cost- and labor-intensive. . The second level of uncertainty relates to the interpretation of sequence changes that do not predict a truncated protein. Of the almost 5,000 BRCA1 and BRCA2 mutations submitted to the Breast Cancer Information Core (BIC) database, about one-third are either missense, in-frame deletions or insertions, base-substitutions not leading to an amino acid change (neutral changes) or intronic changes with unknown effect on mRNA-processing (Table 1). Only a small proportion of these have been unmasked as polymorphisms unrelated to disease outcome. They include missense changes and intronic variants, but, intriguingly, also a nonsense mutation in BRCA2. The K3326X mutation was found in 2.2% of over 400 controls tested. Only a few missense changes (e.g., BRCA1C61G) have been called a deleterious disease-related mutation, mainly because they reside in a validated functional domain of the protein or affect an evolutionary conserved residue. As a result, about 35% of all the distinct gene changes detected to date are lumped into the “unclassified variant” category, meaning that their relevance to disease outcome is uncertain. Almost certainly, a substantial proportion of these represent rare polymorphisms but equally certainly, a number of them will turn out to be true deleterious mutations. . A third reason for a negative test result is that the familial clustering of breast cancer in a family is due to an unknown gene or in fact is a non-genetic chance event. The proportion of truly missed, deleterious mutations is therefore difficult to gauge. A study by the BCLC has suggested that a combination of incomplete testing and missed or misinterpreted gene changes, causes false-negative test results in over 30% of all family types with some evidence of being linked to BRCA1. This proportion was independent of the mutation-screening methodology used.

4. Ponder B (1997) Genetic testing for cancer risk. Science 278:1050–1054 5. Welcsh PL, Owens KN, King MC (2000) Insights into the functions of BRCA1 and BRCA2. Trends Genet 16:69–74

BRCT Domain Definition Named after BRCA1 c-terminal repeat. The domain consists of a 90–100 amino acid unit that occurs as a single element or as multiple repeats in several proteins involved in the DNA-damage response. Heterodimerization between BRCT repeats promotes proteinprotein interactions. A subset of tandem BRCT repeats adopt a conserved head-to-tail structure. Such tandem repeats can function as a phospho-peptide binding module that binds proteins with specific phosphorylation motifs. ▶Fanconi Anemia ▶BRIT1 Gene ▶BRCA1/BRCA2 Germline orientation and Breast Cancer Risk

Breakpoint Definition Point of separation on a chromosome involved in translocation or other structural rearrangement. ▶E2A-PBX1 ▶Chromosomal Translocations

References 1. Devilee P (1999) BRCA1 and BRCA2 testing: weighing the demand against the benefits. Am J Hum Genet 64:943–948 2. Ford D, Easton DF, Stratton M et al. (1998) Genetic heterogeneity and penetrance analysis of the BRCA1 and BRCA2 genes in breast cancer families. Am J Hum Genet 62:676–689 3. Lakhani SR, Jacquemier J, Sloane JP et al. (1998) Multifactorial analysis of differences between sporadic breast cancers and cancers involving BRCA1 and BRCA2 mutations. J Natl Cancer Inst 90:1138–1145

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Breakpoint Cluster Region Definition A localized site of recurrent DNA breakage. ▶ALU Elements ▶BCR-ABL1

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Breast Cancer

Breast Cancer B ILL G ULLICK Department of Biosciences, University of Kent at Canterbury, Canterbury, Kent, UK

Definition Breast cancer may originate from more than one cell type in the breast as a result of different subsets of molecular changes. It is therefore a collection of diseases with different characteristics, different risks and different treatments. It occurs predominantly in women but it may also occur in men (0.5% of cases). In addition to invasive disease, several benign pre-malignant and noninvasive forms exist. Although the broad pathological categories are generally accepted there are several alternative systems of sub-categorization. . Benign conditions: include sclerosing conditions and obliterative mastitis; mild moderate and severe hyperplasias and atypical hyperplasias; fibrocystic conditions, fibroadenomas and related conditions (note that the Oxford Textbook of Pathology presents a “simplified nomenclature” of 50 subtypes of benign breast disease). . Non-invasive carcinoma: generally divided into Lobular Carcinoma in situ (LCIS) and Ductal Carcinoma in situ (DCIS). DCIS was originally sub-divided into comedo, cribriform, papillary, solid and clinging but has more recently been categorized as well, moderately and poorly differentiated. . Invasive carcinoma: broadly defined as of “special type” (30% of cases) and “no special type” (70% of cases).

Characteristics Epidemiology Breast cancer is the most common fatal malignancy in women in the Western world representing about 10% of all cancer deaths. It is however much less common in other countries probably as a result of environmental rather than genetic factors. Behavioral risk factors have been identified. Early pregnancy to term and multiple pregnancy are protective for breast cancer incidence probably due to a reduced exposure to estrogens. There are several reports of weak associations with diet and use of oral contraceptives. Screening In some countries mammographic screening is available to women to detect early disease, as it is likely that earlier treatment is beneficial for survival. Educational programs are also active, for instance in promoting selfexamination as a method of early detection. The value

of these approaches for improving patient survival is not yet fully established.

Genetics About 5–10% of breast cancer cases are associated with a genetic predisposition to the disease. Recently three genes have been identified where the inheritance of variants is associated with a very high incidence (penetrance) of the disease. The ▶BRCA1 gene was the first to be identified, and gene carriers are thought to have as much as a 70–80% chance of developing the disease, generally at an earlier age than women with “sporadic” (not genetically predisposed) disease. Subsequently a second gene called ▶BRCA2 was also found in other families that predisposes to breast and ovarian cancers. The particular risk in an individual gene carrier may be determined by the nature of the particular gene defect and by environmental and hormonal factors and by their background genetic makeup (▶breast cancer genes BRCA1 and BRCA2). A further inherited condition, called ▶Li-Fraumeni syndrome is associated with increased risk to breast and many other types of cancers. This is due to the inheritance of a rare mutant copy of the ▶p53 gene. Molecular Biology Breast cancer is the most studied form of human cancer, due to its common occurrence and to the availability of many immortal breast cancer derived cell lines that can be grown in tissue culture (in contrast to prostate cancer for instance). About 60% of breast cancers at diagnosis express the estrogen receptor. Several genes have been found to be altered by mutation or amplification in invasive cancer and in DCIS. The ▶HER-2 or ERBB2 gene (also known as c-erbB-2 and neu) is amplified in about 25% of invasive breast cancers leading to overexpression of the growth factor receptor which it encodes. The c-myc gene is similarly found to be amplified in about 20% of breast cancer also resulting in overexpression of the c-myc protein. The ▶cyclin D gene, which specifies a protein important in regulating the cell cycle, is also amplified in a proportion of breast cancers. The p53 gene has been found to be point mutated in 20% of invasive breast cancers and to be overexpressed in about 50% of cases. Other point mutations have been found in E-cadherin gene, which encodes a cell adhesion molecule. In this case the mutations are most common in lobular cancers. More subtle changes occur in the expression of apparently normal proteins including growth factors such as those in the epidermal growth factor (EGF) family and the FGF family of proteins, the receptor tyrosine kinase c-erbB-3 and the Src tyrosine kinase. Some of these altered proteins represent targets for new forms of treatments.

Breast Cancer Genes BRCA1 and BRCA2

Treatment Three methods of treatment are available, surgery, radiotherapy and chemotherapy/hormonal therapy. Benign disease and lobular carcinoma in situ are rarely treated but are observed, as they are associated with an increased risk of developing breast cancer. DCIS of the breast has often been treated by mastectomy as it is frequently quite widespread within the breast but may also be treated by local surgery. It is possible that the different pathologically defined forms of DCIS may be associated with different relative risks of recurrence and recurrence as invasive disease. Invasive disease is generally first treated by surgery, and lymph nodes are sampled to determine, by pathological diagnosis, if there is evidence of tumor spread. This procedure may be limited to a single node (called the sentinel node) or may involve a greater degree of surgery. Patients with invasive breast cancer are often treated with radiotherapy to the breast to reduce the chances of local recurrence. Even if the cancer has not apparently spread, patients are sometimes offered preventative or “adjuvant” therapy using drugs, as this helps to prevent recurrence of the disease. Chemotherapy or hormonal therapy are generally offered to patients where metastatic spread of the disease has occurred. Hormonal therapy is frequently offered to women whose tumors express the estrogen receptor. Specific methods of treatment still vary depending on the patient and the institution where it is given, although more generally agreed protocols are becoming accepted. New Treatments Breast cancer is frequently a hormonally dependent disease. Thus treatments with drugs such as tamoxifen, which binds to the estrogen receptor and reduces its activity, or other drugs that suppress the production of estrogen, such as aromatase inhibitors, are frequently employed. However, new drugs directed to known molecular changes in the cancer cells are under development. These include signal transduction inhibitors directed to molecules such as the epidermal growth factor receptor, monoclonal antibodies to the c-erbB2 receptor and drugs which inhibit proteolytic enzymes thought to be involved in the process of metastasis. Several of these are now in clinical trials that will determine their usefulness for the treatment of the disease.

References 1. Fisher B (1999) From Halsted to prevention and beyond: advances in the management of breast cancer during the twentieth century. Eur J Cancer 35:1963–1973 2. Gayther SA, Pharoah PD, Ponder BA (1998) The genetics of inherited breast cancer. J Mammary Gland Biol Neoplasia 3:365–376

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3. Gullick WJ, Srinivasan R (1998) The type 1 growth factor receptor family: new ligands and receptors and their role in breast cancer. Breast Cancer Res Treat 52:43–53 4. Hortobagyi G (2000) Adjuvant therapy for breast cancer. Annu Rev Med 51:377–392 5. O’D McGee, Isaacson PG, Wright NA (1992) The breast. In: Oxford textbook of pathology, Oxford University Press, Oxford, pp 1643–170

Breast Cancer Genes BRCA1 and BRCA2 A SHOK R. V ENKITARAMAN Hutchison/MRC Research Centre, Cambridge, UK

Definition

▶BRCA1 and ▶BRCA2 are cancer-predisposition genes, germline mutations in which are associated with a high risk of developing breast, ovarian and other cancers. Much information has been accumulated on the function of their large, nuclear-localized protein products, which implicates them in the cellular response to DNA damage, the control of mitotic cell division, and the regulation of gene transcription. BRCA1 and BRCA2 are very distinct genes, despite the similarity in their acronyms.

Characteristics

Roughly one-tenth of all ▶breast cancer cases exhibit a familial pattern of inheritance. Of these familial cases, germline mutations in either one of two genes, BRCA1 or BRCA2, occur in 20–60% (that is, in 2–6% of all cases). Somatic mutations in BRCA1 or BRCA2 do not appear to be a feature of non-familial (that is, sporadic) breast cancer, but there is evidence that epigenetic suppression of BRCA gene expression, or genetic alterations affecting the biological pathways in which they participate, can occur in sporadic breast cancer. BRCA1 and BRCA2 were first identified in 1994– 1995 through the analysis of families exhibiting a predisposition to early-onset breast cancer. Founder mutations affecting these genes occur in Iceland and amongst the Ashkenazim, where they confer a highly penetrant risk of breast, ovarian and other cancers (including cancers of the male breast, pancreas and prostate). In other populations, germline BRCA1 or BRCA2 mutations are found in the great majority (up to 80%) of families that suffer from multiple occurrences of breast plus ovarian cancer. Germline BRCA2

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Breast Cancer Genes BRCA1 and BRCA2

mutations affecting both alleles also occur in the rare D1 complementation group of Fanconi anaemia. The BRCA1 and BRCA2 genes have been assigned to human chromosomes 17q and 13q, respectively. In both genes, exon 11 (3.4 kb in BRCA1, or 5 kb in BRCA2) encodes a large portion of the protein. Overall, the murine and human genes are no more than 60% identical at the amino acid level, although small regions exhibit a much higher degree of conservation. Proteins encoded in alternative splice products, such as the IRIS protein encoded by the BRCA1 gene, also exist. Protein BRCA1 and BRCA2 encode large proteins (human BRCA1 is 1,863 amino acids long; and human BRCA2 is 3,418 amino acids) that localise to the nucleus in mitotic and meiotic cells (Fig. 1). They bear little resemblance to proteins of known function. At its N-terminus BRCA1 protein contains a RING-domain known to mediate hetero-dimerization with the RING domain of BARD1, forming an active E3 ubiquitin ligase. At its C-terminus, BRCA1 includes two copies of a 95 amino acid motif (the BRCT domain, for BRCA1 C-terminal) later detected in a number of different proteins implicated in DNA repair and cell cycle checkpoint control. This domain, whose atomic structure has been elucidated, mediates a number of protein-protein interactions with phosphorylated targets by serving as a phosphopeptide-binding module. Eight repeated sequences (the BRC repeats), each of about 30 amino acids, are encoded in BRCA2 exon 11. The BRC repeats, but not their intervening sequences, are conserved between several mammalian species suggestive of a conserved function. Indeed, the interaction of BRCA2 protein with RAD51, a mammalian homologue of bacterial RecA essential for genetic recombination, occurs through the BRC repeats. There is good evidence from genetic, structural and biochemical studies that the BRC repeats regulate the activity of RAD51 in reactions that lead to DNA repair by recombination. Two other regions of BRCA2 have been implicated in the control of recombination. A domain carboxyl-terminal to the BRC repeats interacts with

the small protein Dss1 to form a structure capable of binding junctions between single-stranded and doublestranded DNA, which can displace the ssDNA-binding protein RPA from recombination substrates, whereas an additional RAD51-binding region of uncertain function is located near the extreme C-terminus of BRCA2. Cellular and Molecular Regulation The transcripts and protein products encoded by BRCA1 and BRCA2 are expressed in dividing cells of many types. Expression is also high in meiotic cells. These expression patterns speak to the possible functions of BRCA1 and BRCA2 proteins. Role in the Cellular Response to DNA Damage Both BRCA1 and BRCA2 proteins localize to the nucleus. In meiotic cells, co-localisation has been reported to the synaptonemal complexes of developing axial elements. This is suggestive of a role in meiotic recombination, a process that is initiated by DNA double-strand DNA breakage. Similarly, there is good evidence that BRCA1 and BRCA2 are essential in mitotic cells for the repair of DNA double-strand breaks by homologous recombination. Several lines of evidence are indicative of such a role: . Cells in which BRCA1 or BRCA2 or their homologues in other species have been inactivated exhibit genotoxin hypersensitivity and chromosomal instability suggestive of defects in DNA double-strand break repair. . Second, homology-directed repair of double-strand DNA breaks introduced into chromosomal substrates is impaired by the disruption of BRCA1 or BRCA2, although pathways for non-homologous end joining remain largely unaffected. . Finally, BRCA1 and BRCA2 localize after DNA damage to nuclear foci where they interact with molecules implicated in DNA recombination, including RAD51, and the Fanconi anemia proteins. The precise mechanisms that may underlie such a function remain to be determined. BRCA2 interacts directly, and at a relatively high stoichiometry, with

Breast Cancer Genes BRCA1 and BRCA2. Figure 1 Structural features of the BRCA1 and BRCA2 proteins (not drawn to scale).

Breast Cancer Genes BRCA1 and BRCA2

RAD51, a protein essential for DNA repair by recombination, to modulate RAD51 activity or availability. The interaction of BRCA1 with RAD51 is less well defined, although both proteins co-localize – along with BRCA2 – to discrete nuclear foci following DNA damage. BRCA1 may participate in the cellular mechanisms that sense and signal DNA damage, culminating in the activation of cell-cycle checkpoints and the machinery for DNA repair. The protein kinases ATM (encoded by the gene mutated in Ataxia telangiectasia), ATR, chk1 and chk2 (mutated in ▶Li-Fraumeni syndrome) are proximal components of these sensing/ signaling mechanisms. ATM, chk1 and probably the other checkpoint kinases, phosphorylate BRCA1 following DNA damage, a modification essential for its proper function. These observations are important because they place BRCA1 – and by extension, possibly BRCA2 – in the same pathway as genes such as ATM (▶ATM protein), germline mutations in which are also associated with an increased risk of breast and other cancers. Thus, a common DNA damage response pathway may be defective in a significant fraction of breast cancers. BRCA1 and BRCA2 have also been implicated in the enforcement of cell cycle checkpoints during the G2 and M phases, and in the regulation of centrosome number. Additional functions have recently been described in the control of mitosis. BRCA1 regulates proteins such as MAD2 that act in the mitotic spindle assembly checkpoint, and has an essential function in directing the correct formation and function of the mitotic spindle, whereas BRCA2-deficient cells exhibit defects in the completion of cell division by cytokinesis. Thus, BRCA1 and BRCA2 appear to work in multiple processes responsible for maintaining the integrity of chromosome number as well as structure in dividing cells, which may help to explain why they are potent tumor suppressors. Other Functions It is difficult to reconcile the disparate nature and severity of the cellular and developmental defects induced by the disruption of murine homologues of BRCA1 and BRCA2, with functions exclusively in the response to DNA damage. Indeed, evidence is accumulating that BRCA1, in particular, can control gene transcription. Several proteins that interact with BRCA1 are known to regulate transcription or mRNA processing. Moreover, at least a fraction of the total intracellular pool of BRCA1 is linked to the general transcription machinery – the RNA polymerase II holoenzyme – through its RNA helicase subunit. Intriguingly, BRCA1 has been implicated in the control of X-inactivation in female cells, a process whose dysregulation is associated with breast cancer predisposition. How this function may be exerted is not clear, but it may work through the control of localization of the Xist product.

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In addition, roles for BRCA1 and possibly BRCA2 have been reported in the control of oestrogen receptor expression and signaling. Tumor Suppression by BRCA1 and BRCA2 Inheritance of a single defective copy of BRCA1 or BRCA2 confers cancer predisposition in humans. However, the second allele is almost invariably lost in the cancers that arise in predisposed individuals, indicating that BRCA1 and BRCA2 behave in some respects as ▶tumor suppressor genes. Abnormalities in growth or in DNA repair have not yet been reliably detected in murine or human cells heterozygous for BRCA1 or BRCA2 mutations. Thus, there is currently little to suggest that cancer predisposition arises solely from haplo-insufficiency, or a transdominant deleterious effect induced by a single mutant BRCA1 or BRCA2 allele. Rather, as has been proposed for other tumor suppressor genes, germline mutations in one allele may simply increase the likelihood that the gene is wholly inactivated by loss of the second allele through somatic mutation. However, aneuploidy as a consequence of abnormal cytokinesis has been reported in cells and tissues heterozygous for BRCA2 mutations, and the possibility that this effect of haplo-insufficiency contributes to carcinogenesis remains to be determined. Whatever the events that lead to loss-ofheterozygosity, inactivation of BRCA1 or BRCA2 would initiate genetic instability by destabilizing chromosome structure and number, allowing the rapid evolution of tumors due to increased somatic alterations in genes that control cell division, death or lifespan. Thus, BRCA genes are proposed to work as “caretakers” of genetic stability. This “caretaker” role is most likely to arise through the function of the BRCA proteins in DNA repair and mitosis. Cells that harbor disruptions in BRCA1 or BRCA2 accumulate aberrations in chromosome structure, reminiscent of diseases like Bloom syndrome or ▶Fanconi anemia, where chromosomal instability is associated with cancer predisposition. They also exhibit aneuploidy and defects in cell division. These defects could together elevate the rate of genomic instability, leading to somatic mutations or alterations in gene copy number that promote carcinogenesis. It is unclear why carcinogenesis accompanied by loss of the second BRCA gene allele in individuals who inherit one mutant allele should occur preferentially in tissues such as the breast or ovaries. Both BRCA1 and BRCA2 are widely expressed and appear to perform functions essential to all tissues. Currently there is little evidence to help distinguish between the several possible explanations that can be advanced. The chronology of the molecular events during carcinogenesis in BRCA gene mutation carriers is not known. Loss of the second allele is clearly very frequent, but it is unclear at what stage in tumor

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Breast Cancer Resistance Protein

evolution this may occur. However, the catastrophic cellular consequences of homozygous inactivation of BRCA1 or BRCA2, which quickly lead to cell death, does emphasize that other genetic alterations will be necessary. Current evidence favors the notion that the inactivation of cell-cycle checkpoint genes, particularly those that enforce mitotic checkpoints, is an important additional step during carcinogenesis in BRCA gene mutation carriers. Viewed in this way, it is conceivable that the tissue specificity of carcinogenesis represents differences in the ability of cells which have lost both alleles of BRCA1 or BRCA2 to survive for long enough to acquire these additional genetic alterations. For instance, BRCAdeficient cells in epithelial tissues such as the breast and ovary may take advantage of hormonal or local inter-cellular interactions to support survival until the accumulation of additional genetic alterations allows outgrowth. By contrast, BRCA-deficient cells in nontarget tissues may quickly be eliminated.

Clinical Relevance Germline mutations in BRCA1 or BRCA2 are frequently associated with familial, early-onset, breast and ovarian cancer, particularly in those families that suffer from multiple cases of cancer in both sites. This has obvious important implications for genetic testing and counselling in the clinic. The mutations have been estimated to carry a cumulative life-time cancer risk of between 40–70%. There is some evidence that the pathological features of breast and ovarian cancers associated with BRCA1 or BRCA2 mutations differ from those of sporadic tumors. So far, these differences seem to be insufficiently wellmarked to be of diagnostic significance. One notable association is that BRCA1-deficient cancers often exhibit a “basal-like” phenotype usually characterized by the expression of specific markers, and negativity for oestrogen receptor expression. It is also unclear if the prognosis of breast and ovarian cancers associated with BRCA1 or BRCA2 mutations will differ significantly from that of sporadic cases. Conflicting results have been reported in the literature, their interpretation made difficult by the varied study designs and by the relatively small numbers of cases that have been compared. Similarly, the value of prophylactic interventions, whether surgical or drug-based, in BRCA gene mutation carriers awaits evaluation. Emerging evidence suggests that the DNA repair defect inherent in BRCA-mutant tumors can be exploited in cancer therapy. Thus, both BRCA1 and BRCA2deficient cancers appear to be hypersensitive to the effect of DNA cross-linking agents such as carboplatin, and also to novel chemical inhibitors of the PARP1 enzyme.

Breast Cancer Resistance Protein Definition The breast cancer resistance protein is a plasma membrane transporter and member 2 of the subfamily G of ATP-binding cassette transporters. It is predominantly localized in the epithelium of small and large intestine, in hepatocyte canalicular membranes, in ducts and lobules of the breast, on the placental syncytiotrophoblast, and in the plasma membrane of stem cells. Physiological substrates include sulfated steroids. Transported xenobiotics are e.g., several dietary carcinogens, the chlorophyll breakdown product pheophorbide, and the receptor tyrosine kinase inhibitor imatinib. The breast cancer resistance protein is involved in conferring multidrug resistance. ▶Membrane Transporters

Breast Conservation Definition Surgical removal of cancer from the breast while preserving the remainder of the breast tissue. ▶Oncoplastic Surgery

Breast Imaging Reporting and Data System Definition BIRADS; http://www.birads.at/index.html

Breast Implant Definition Device placed into the body to enlarge or reconstruct the breast after removal. ▶Oncoplastic Surgery

BRIP1

Breast Reconstruction Definition

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Breast Transillumination ▶Optical Mammography

Surgical procedure to simulate the appearance of the breast after it has been removed for the treatment of cancer. ▶Oncoplastic Surgery

Breslow Depth Definition

Breast Reduction Definition Surgery to reduce the size of the breast. ▶Oncoplastic Surgery

Breast Regressing Protein 39 Kd

Referring to ▶cutaneous desmoplastic melanoma tumor thickness (according to Breslow). The single most important factor in predicting survival for patients with stage I/II melanoma. Is measured from the top of the granular layer (for non-ulcerated lesion) or from the ulcer base overlying the deepest point of invasion (for ulcerated lesions) to the deepest extension of the tumor using an ocular micrometer. According to the AJCCcriteria for malignant melanoma, tumor thickness and the presence or absence of ulceration are the primary criteria for the tumor classification. ▶Desmoplasia ▶Desmoplastic Melanoma

▶Serum Biomarkers

Breast Stem Cells Definition

BRG- and BRM-associated Factor, 47 kDa ▶hSNF5/INI1/SMARCB1 Tumor Suppressor Gene

Self-renewing cells in the breast that are capable of producing all of the breast epithelial cell types and likely play an important role in breast cancer. ▶Basal-like Breast Cancer

Brilliant Yellow S ▶Curcumin

Breast Surgery Definition Surgical procedures on the breast used to treat congenital deformities or to remove cancerous tissue. ▶Oncoplastic Surgery

BRIP1 ▶BACH1 Helicase

B

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BRIT1 Gene

BRIT1 Gene D EBORAH J ACKSON -B ERNITSAS 1 , K AIYI L I 2 , S HIAW-Y IH L IN 1 1

Department of Systems Biology, The University of Texas M.D., Anderson Cancer Center, Houston, TX, USA 2 Department of Surgery, Baylor College of Medicine, Houston, TX, USA

Synonyms Microcephalin; MCPH1

Definition BRCT-repeat inhibitor of hTERT expression.

Characteristics Significance of BRIT1 in the Development of Cancer ▶BRIT1 was first described through a genetic screen for transcriptional repressors of the catalytic subunit of ▶human telomerase, (hTERT). This catalytic subunit, hTERT, is the rate-limiting determinant of and is necessary for telomerase activity and thus is highly significant for cellular immortalization by preventing natural cellular senescence. Therefore, molecules that negatively control hTERT activity, such as BRIT1, directly influence the development of pre-cancerous and cancerous cells. The BRIT1 amino acid sequence matched a previously identified gene, ▶Microcephalin (▶MCPH1) that is implicated as one of the contributing factors in the autosomal recessive neuro-develomental disorder, primary microcephaly. Additional biological roles for BRIT1 in the DNA damage response pathway were suggested by the protein structure. The presence of three ▶BRCA1 carboxy-terminal (BRCT) domains within its structure connected BRIT1 with a group of proteins involved in DNA damage repair and checkpoint control such as ▶53BP1, ▶MDC1 and BRCA1. Proper cellular response to DNA damage is essential for the maintenance of genomic stability and is consequently crucial in prevention of neoplastic transformation. Depletion of BRIT1 by experimental manipulation abolishes normal DNA damage response and introduces chromosomal and centrosomal abnormalities. The reduction of BRIT1 expression in normal human mammary epithelial cells by experimental RNA interference generated chromosomal breaks, dicentric chromosomes and telomeric fusions. Additional chromosomal aberrations were introduced when BRIT-deficient cells were submitted to genotoxic insult. The resultant genomic instability generated from the loss of

an appropriate BRIT1-mediated checkpoint and DNA repair mechanism may contribute to tumor formation. Functional impairment or loss of proteins, such as BRIT1, may significantly contribute to tumorigenic development by allowing the perpetuation of damaged or mutated genes within a cell, resulting in the inappropriate expression and control of the affected genes. In addition to the influence on hTERT expression, BRIT1 appears to control the expression of two vital checkpoint-regulating proteins; BRCA1 and Chk1. BRCA1 and Chk1 protein levels are dramatically reduced in cells where BRIT1 has been experimentally reduced by RNA interference. A concurrent reduction in mRNA levels of BRCA1 and Chk1 were observed in BRIT1 knockdown cells suggesting that BRIT1 exercises an influence on the transcription of these genes. The significance of BRCA1 in breast cancer has been previously established. Whether BRIT1 functions directly as a specific transcription factor or as a chromatin modifying factor is unclear at this time, however, as a controller of these key players in the DNA damage checkpoint control network, BRIT1 is extremely important to the maintenance of normal cell function and thus in the prevention of tumorigenesis. Aberrations of BRIT1 have been identified in various different human cancers. BRIT1 mRNA and protein expression is aberrantly reduced in several breast cancer cell lines and is reduced in some human ovarian and prostate epithelial tumors as compared to the corresponding normal tissue. Reduction of BRIT1 gene copy number significantly correlated with genomic instability found in the specimens. Additionally, reduced BRIT1 expression correlated with the duration of the relapse-free intervals and with the occurrence of metastases in some breast cancer patients suggesting that BRIT1 deficiency may contribute to the aggressive nature of breast tumors. A mutant form of BRIT1, isolated from one human breast tumor specimen, lacked two C-terminal BRCT-domains of the protein. This shorter form of BRIT1 resulted in a loss-of-function with respect to DNA damage response when tested experimentally. Therefore, significant evidence exists to directly link defective or reduced BRIT1 protein expression to several forms of cancer and to implicate BRIT1 as a novel tumor suppressor gene.

BRIT1 Function in DNA Damage Response In the normal course of events, cellular DNA is subjected to a variety of endogenous and environmental factors that induce damage within its structure. In response to these insults, normal cells activate complex mechanisms to detect, signal the presence of and subsequently repair DNA damage when possible. Propagation of the DNA damage alarm progresses

BRIT1 Gene

through a complex signal transduction network that includes the BRIT1 protein. Initially, sensor proteins recognize the location of damaged or altered DNA structure and transmit a signal through mediator molecules to transducer proteins. The transducer proteins transmit the signal to numerous downstream effectors involved in specific pathways (Fig. 1). Two distinct DNA damage repair networks, both requiring BRIT1 activity, have been described. The ▶ATM (ataxia telangiectasia mutated) pathway is activated by doublestranded breaks in the DNA observed after exposure to ionizing radiation while the ▶ATR (ATM and Rad3related) pathway is activated by prolonged presence of single-stranded DNA induced by either ultraviolet radiation or stalled DNA replication. ATM and ATR are essential kinases that are responsible for phosphorylating numerous transducer and effector proteins in the DNA damage network. BRIT1 co-localizes with numerous molecules associated with these two signaling networks including ▶γH2AX, MDC1, 53BP, ▶NBS1, p-ATM, ATR, p-RAD17 and p-RPA34 after DNA damage is induced. In the absence of functional BRIT1, all of these molecules with the exception of γH2AX, fail to localize to sites of DNA damage strongly suggesting that the BRIT1 molecule is an essential mediator for the subsequent repair processes. However, BRIT1 expression does not influence the chromatin binding of proteins unrelated to DNA damage such as Orc-2 indicating that the BRIT1 function is highly specific. The depletion of BRIT1 inhibits the recruitment of phosphorylated ATM to double-stranded DNA broken ends and subsequently blocks the phosphorylation of multiple down-stream members of the ATM repair pathway including Chk2

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and NBS1. Depletion of BRIT1 also abolishes the UVinduced phosphorylation of RPA34 and reduces the levels of phosphorylated RAD17 indicating the importance of BRIT1 in the ATR signaling pathway. Based on these observations, it has been determined that BRIT1 is a pivotal protein in both of the DNA damage signaling networks and for this reason has great significance in the prevention neoplastic transformations of cells. Figure 1 illustrates a simple model for the function of BRIT1 based on current experimental evidence. After exposure to ionizing radiation, double-stranded breaks in DNA occur resulting in the recruitment the MRE11/RAD50/NBS1 (MRN) complex and MDC1 to the damaged site thus facilitating the recruitment and kinase activity of ATM. Activated p-ATM phosphorylates NBS1, H2AX and BRCA1 which localize to sites of DNA damage. Increased single-stranded DNA by exposure to ultraviolet radiation induces the coating of RPA on DNA leading to the recruitment of ATRIP and ATR to the sites of DNA damage. Activated ATR then phosphorylates critical downstream molecules such as Rad17 and Chk1 further propagating the DNA damage signal in the cell. BRIT1 appears to regulate the recruitment of NBS1, MDC1 and thus the MRN complex in the ATM pathway. BRIT1 also regulates the recruitment of RPA, which in turn recruits ATRIP/ ATR complex initiating the ATR signaling cascade. BRIT1 Function in Cell Cycle Control Normally, the progression of a cell through the cell division cycle is stalled to allow for its DNA repair and if the damage cannot be repaired, the cell enters programmed cell death (apoptosis). This retardation or cell cycle checkpoint is essential to maintain the

BRIT1 Gene. Figure 1 BRIT1 Function in DNA Damage and Cell Cycle Control.

B

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BRM

integrity of cellular DNA that insures normalcy in consecutive descendant cells. Key molecules involved in cell cycle arrest, (p53, chk1 and chk2), are all activated when phosphorylated by ATM or ATR. BRIT1 clearly impacts the activity of both ATM and ATR by affecting the association of these molecules to damaged DNA. Activated p53 induces cell cycle arrest at G1 while p-Chk1 and p-Chk2 negatively regulate Cdc25 phosphatases that promote transition through the cell cycle thereby inducing the execution of G1/S, G2/M and intra-S checkpoints of the cell cycle. BRIT1 is required for the activation of intra-S and G2/M cell cycle checkpoints after cellular exposure to ionizing radiation. The influence of BRIT1 on control of these cell cycle checkpoints may result from BRIT1’s regulation of three checkpoint regulator proteins, Chk1, BRCA1 and NBS1. In the absence of BRIT1, BRCA1 and Chk1 expression is significantly reduced and NBS1 fails to be phosphorylated. BRCA1 plays a significant role in homologous recombination DNA repair and possibly serves as a scaffold for ATM and ATR thus affecting phosphorylation of many downstream effectors proteins. Therefore the regulation of BRCA1 by BRIT1 dramatically affects multiple aspects of cell cycle control and DNA damage repair. The normal cellular response to ionizing radiation is to arrest the cell cycle also at G2, allowing for the initiation of DNA repair, however, BRIT1-depleted cells continue to progress through G2 indicating that BRIT1 is essential in the activation of this important cell cycle checkpoint. Additionally, BRIT1-depleted cells continue to synthesize DNA and proceed through mitosis unlike normal cells exposed to ionizing radiation. Replication of DNA damaged by ionizing radiation could easily result in the propagation of mutated or disrupted genes and contribute to tumorigenesis. BRIT1 also controls the cell’s entry into mitosis by affecting the stabilization of the cdc25A, a key phosphatase in cell cycle control. Cells derived from a microcephaly patient (BRIT1 defective) maintained a persistent level of the phosphatase, cdc25A following UV treatment. Cdc25A is targeted for degradation when phosphorylated by Chk1 kinase during normal cell division and its degradation is usually amplified by UV exposure. Degradation of cdc25A abolishes the activation of the Cdk2-cyclin complex inhibiting DNA synthesis. Conversely, inappropriate persistence of cdc25A allows for the continued DNA synthesis despite aberrations or damage in the structure. These BRIT1 mutant cells also harbor reduced levels of phosphorylated Cdk1-cyclin B complex that is essential for mitotic entry. It was proposed that the regulation of mitosis by BRIT1 is both ATR dependent through regulation of cdc25A stability and ATR independent through regulation of Cdk1-cyclin B phosphorylation.

The affect of BRIT1 on cell cycle control is therefore multi-faceted (Fig. 1). Complete loss of the BRIT protein results in reduced protein levels of BRCA1 and Chk1 and impairs the activity of a multitude of vital proteins through their diminished phosphorylation. Presence of a mutated BRIT1 protein allows for expression of BRCA1 and Chk1 but still blocks proper signal transduction by inhibiting the activities of both ATM and ATR kinases.

References 1. Xu X, Lee J, Stern DF (2004) is a DNA damage response protein involved in regulation of Chk1 and BRCA1. J Biol Chem 279:34091–34094 2. Lin S, Rai R, Li K et al. (2005) BRIT1/MCPH1 is a DNA damage responsive protein that regulates the BRCA1Chk1 pathway, implicating checkpoint dysfunction in microcephaly. PNAS 102:15105–15109 3. Rai R, Dai H, Multani AS et al. (2006) BRIT1 regulates early DNA damage response, chromosomal integrity and cancer. Cancer Cell 10:1–13 4. Chaplet M, Rai R, Jackson-Bernitsas D et al. (2006) BRIT1/MCPH1: A Guardian of the genome and an enemy of tumors. Cell Cycle 5(22):2579–2583 5. Alderton G, Galbiati L, Griffith E et al. (2006) Regulation of mitotic entry by Microcephalin and its overlap with ATR signaling. Nat Cell Biol 8:725–733

BRM Definition Biological response modifier.

BRMS1 A LEXANDRA C. S ILVEIRA , DANNY R. W ELCH Department of Pathology and Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, USA

Definition BRMS1 (Breast Metastasis Suppressor 1) is a human ▶metastasis suppressor gene that, when re-expressed, suppresses metastasis of human breast carcinoma, ovarian, and melanoma cell lines in immunocompromised mouse models.

BRN-5547136

Characteristics The BRMS1 gene is located on chromosome 11q13.1-q13.2. It spans over 8.5 kb and is comprised of ten exons, the first exon being untranslated. BRMS1 cDNA is 1485 base pairs and encodes a 246 amino acid protein (MW 28.5 kD, although it runs more slowly (35 kDa) by SDS-PAGE). It is highly conserved with the mouse ortholog (Brms1) having 95% homology at the amino acid level. Like human BRMS1, the mouse ortholog has suppresses metastasis in murine models of breast cancer. BRMS1 protein contains two nuclear localization sequences, two coiled-coil motifs and imperfect leucine zippers. It also contains a glutamic acid rich N-terminus and a potential endoplasmic retention signal. BRMS1 shows almost ubiquitous expression in human tissues; highest expression is in kidney, placenta, peripheral blood lymphocytes and testis and lowest expression in brain and lung. Subcellular fractionation and immunofluorescence studies have determined that BRMS1 protein is predominantly (>90%) nuclear. BRMS1 protein is stabilized by interaction with the chaperone protein, Hsp90, and is further regulated by proteasomal degradation. Cellular and Functional Characteristics BRMS1 re-establishes gap junctional cell-cell communication in human breast cancer cell lines. Studies using MDA-MB-435, MDA-MB-231, and the ovarian cancer cell line HO-8910PM show an inverse effect of BRMS1 expression on cell motility. Further, over-expression of BRMS1 in H1299 human lung carcinoma cells and MDAMB-435 cells results in suppressed growth in soft agar. Additionally, BRMS1 transfection increases apoptosis in suspended non-small cell lung carcinoma. The exact mechanism by which BRMS1 affects these phenotypes is as yet unknown. However, it is known that BRMS1 interacts with several different proteins and large (megadalton) protein complexes, most notably with class I and class II histone deacetylases (HDACs) and the transcription factor NFκB. BRMS1 is specifically a core member of mSin3-HDAC chromatin remodeling/transcriptional repression complexes but its involvement is implicated in other HDAC complexes. Additionally, BRMS1 and HDAC1 function as NFκB co-repressors; chromatin bound BRMS1 facilitates HDAC-1-mediated deacetylation and inactivation of NFκB. Studies also suggest that direct interaction of BRMS1 and the RelA/p65 subunit of NFκB represses the transactivation potential of NFκB. Further, BRMS1 leads to a reduction in NFκB translocation by inhibiting the phosphorylation and degradation of the NFκB inhibitor, IκB. Studies show reduced phosphoinositide signaling in BRMS1 transfected cells. Decreased phosphoinositide

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signaling results in decreased mobilization of intracellular calcium, a known regulator of metastasis. BRMS1 expression also downregulates fascin, an actin-bundling protein associated with cell motility. Further, repression of NFκB results in decreased expression of anti-apoptotic genes and two tumor-metastasis activators, osteopontin and urokinase-type plasminogen activator. Clinical Relevance BRMS1 is regulated at both the RNA and protein levels. To date, only a single study has examined levels of BRMS1 protein in patient samples to find a loss of BRMS1 in nearly 25% of 238 breast cancer cases. Further, the study showed loss of BRMS1 correlated with disease-free survival when stratified by loss of estrogen receptor, progesterone receptor, or Her2 overexpression. Other clinical studies have studied BRMS1 mRNA expression in human cancers compared to adjacent non-cancerous tissues or regional lymph nodes. Since BRMS1 is regulated at the protein level, looking exclusively at mRNA may be misleading. Nonetheless, the majority of studies show high levels of BRMS1 correlates with increased disease-free survival and diminished progression.

References 1. Samant RS, Clark DW, Fillmore RA et al. (2007) Breast cancer metastasis suppressor 1 (BRMS1) inhibits osteopontin transcription by abrogating NF-kappaB activation. Mol Cancer 6:6 2. Hicks DG, Yoder BJ, Short S et al. (2006) Loss of breast cancer metastasis suppressor 1 protein expression predicts reduced disease-free survival in subsets of breast cancer patients. Clin Cancer Res 12:6702–6708 3. Liu Y, Smith PW, Jones DR (2006) Breast cancer metastasis suppressor 1 functions as a corepressor by enhancing histone deacetylase 1-mediated deacetylation of RelA/p65 and promoting apoptosis. Mol Cell Biol 26:8683–8696 4. Meehan WJ, Samant RS, Hopper JE et al. (2004) Interaction of the BRMS1 metastasis suppressor with RBP1 and the mSin3 histone deacetylase complex. J Biol Chem 279:1562–1569 5. Hurst DR, Mehta A, Moore BP et al. (2006) Breast cancer metastasis suppressor 1 (BRMS1) is stabilized by the Hsp90 chaperone. Biochem Biophys Res Commun 348:1429–1435

BRN-5547136 ▶Temozolomide

B

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Broder Histological Classification

Broder Histological Classification

Brown Adipose Tissue

Definition

Definition

Refers to histological classification of differentiation in ▶squamous cell carcinoma. Devised by Broder. Grades 1, 2 and 3 denoted ratios of differentiated to undifferentiated cells of 3:1, 1:1 and 1:3, respectively. Grade 4 denoted tumor cells having no tendency towards differentiation.

BAT is present in many newborn or hibernating mammals, and its primary function is to generate heat. ▶Cachexia

brp-39 Bromodeoxyuridine (BrdU)

▶Serum Biomarkers

Definition A compound that, due to its chemical structure, can substitute for thymidine in DNA. ▶Fragile Sites

Brush Border Definition

Bromodomain Definition Conserved domain that specifically recognizes and binds to acetylated lysine residues that occur within a protein. ▶Histone Modifications

Bronchogenic Carcinoma ▶Lung Cancer

Is formed by the densely packed microvilli of the surface of columnar epithelial cells, e.g., in the intestine and in the proximal tubules of the kidney. Microvilli are small projections of the plasma membrane which greatly enlarge the surface area of the cell. Individual microvilli can only be distinguished using an electron microscope; in a light microscope, the microvilli are observed collectively as a fuzzy fringe at the surface of the epithelium which has, therefore, been termed brush border. ▶Membrane Transporters

Bryostatin-1 B ASSEL E L -R AYES Karmanos Cancer Institute, Wayne State University, Detroit, MI, USA

Brother of the Regulator of Imprinted Sites ▶BORIS

Definition Bryostatins are a class of macrocyclic lactones. Bryostatins are potent modulators of ▶Protein Kinase C (PKC). Bryostatin-1 was isolated from the marine invertebrate Bugula neritina. Bryostatin-1 is currently not available for commercial use.

Bryostatin-1

Characteristics Rationale for Targeting the PKC PKC is a family of homologous serine/threonine protein ▶kinases that transduce signals linked to diverse cellular processes including proliferation, differentiation, angiogenesis, and ▶apoptosis. The PKC family includes 12 isoforms subdivided into three major classes based on their co-factor requirements for activation. Aberrant regulation of the PKC enzymes activity has been demonstrated in a number of malignancies including: breast, colorectal, pancreatic and non-small cell lung cancer. Preclinical Activity of Bryostatin-1 Treatment of cancer cell lines with bryostatin-1 results in the activation of PKC. However, prolonged exposure to bryostatin-1 induces PKC inhibition most probably through ubiquitin-mediated degradation. Inhibition of PKC activity results in cell cycle arrest, apoptosis, cell differentiation and modulation of chemoresistance. Bryostatin-1 has been shown to potentiate the effects of several classes of cytotoxic agents including: vincristine in diffuse large cell lymphoma, melphalan in Waldenstrom’s macroglobulinemia, gemcitabine in pancreatic and breast cancer, paclitaxel and mitomycin C in gastric cancer cell lines. The synergism between bryostatin and cytotoxic agents is sequence dependent. Single Agent Activity of Bryostatin-1 Phase I trials of bryostatin-1 used two different schedules. The maximal tolerated doses were 25 μg/ m2 when infused over 24 h and 120 μg/m2 when infused over 72 h. The most common side effects included ▶myalgia. Other observed toxicities included headache, phlebitis, and transient ▶thrombocytopenia. Single agent bryostatin-1 has been studied in phase II trials for lymphoma, renal, colorectal, head and neck, sarcoma, and melanoma. Bryostatin-1 did not demonstrate single agent activity in any of these diseases. Bryostatin-Based Combinations Since PKC activation contributes to chemoresistance the combinations of bryostatin-1 and cytotoxic agents were tested. In Chronic Lymphocytic Leukemia (CLL) and indolent Non-Hodgkin Lymphoma, bryostatin-1 was evaluated in combination with fludarabine. Patients received fludarabine daily for 5 days and bryostatin-1 over 24 h infusion either before or after fludarabine. The combination was well tolerated. Partial and complete responses were observed in 6 and 2 patients (total number 27), respectively. Bryostatin-1 and vincristine was evaluated in patients with refractory B-cell lymphoma. Twenty four patients were enrolled on the study. The bryostatin-1 was well tolerated at a dose of 50 μg/m2 over 24 h infusion. The regimen had activity with five patients having objective response and five having stable disease.

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Bryostatin-1 was also evaluated in combination with cisplatin in two phase I trials. In the first trial, bryostatin-1 (30 μg/m2 over 24 h infusion), had no significant activity. In the second trial bryostatin-1 was administered at a dose of 15–55 μg/m2 over 72 h. In this study, three responses were reported. A phase I trial of gemcitabine and bryostatin-1 (25–35 μg/m2 over 24 h) revealed that the regimen was well tolerated and resulted in stable disease in 8 out of 36 patients. Bryostatin-1 (15–50 μg/m2 infused over 24 h) was evaluated in combination with paclitaxel. Partial responses were observed in patients with pancreatic and gastroesophageal cancer. The common finding in these trials is that bryostatin-1 can be combined safely with cytotoxic chemotherapy agents. Phase II trials evaluating the activity of bryostatin-1 with cisplatin in cervical cancer had disappointing results. Fourteen patients were enrolled on the trial and there were no treatment responses. Ajani et al. reported on thirty seven patients with gastroesophageal and gastric cancer treated with bryostatin-1 (40 μg/m2 infused over 24 h) and weekly paclitaxel (80 mg/m2). The response rate was 29% which is higher than the previously reported response rates with paclitaxel. In a phase II trial, bryostatin-1 (50 μg/m2 infused over 24 h) and weekly paclitaxel (90 mg/m2) were evaluated in patients with non-small cell lung cancer. Of eleven response evaluable patients, stable disease was seen in five patients. Therefore, the bryostatin-1 and paclitaxel combination did not demonstrate significant activity in lung cancer. Future Directions Mixed results have been observed in the trials evaluating bryostatin-1 and cytotoxic chemotherapy agents. The future challenges in the development of bryostatin-1 include, the identification of biomarkers that can predict activity and the development of combination therapy with other targeted agents. Another approach for the development of bryostatins is through the modification of the chemical structure in order to identify analogues with better safety or efficacy profiles than bryostatin-1.

References 1. Choi SH, Hyman T, Blumberg PM (2006) Differential effect of bryostatin 1 and phorbol 12-myristate 13-acetate on HOP-92 cell proliferation is mediated by downregulation of protein kinase Cdelta. Cancer research 66: 7261–7269 2. Deacon EM, Pongracz J, Griffiths G et al. (1997) Isoenzymes of protein kinase C: differential involvement in apoptosis and pathogenesis. Mol Pathol 50: 124–131 3. Kortmansky J, Schwartz GK (2003) Bryostatin-1: a novel PKC inhibitor in clinical development. Cancer investigation 21: 924–936

B

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BSA

BSA

BUB1

Definition

Definition

Body surface area; The current practice of using bodysurface area (calculated using a formula derived from height and weight) in dosing anticancer agents has been implemented in clinical oncology about half a century ago. By correcting for BSA, it was generally assumed that the interindividual variation in the pharmacokinetics of the drug administered would be reduced which would lower the risk of serious adverse effects without reducing the agent’s therapeutic effect. Recently, doubt has arisen to this hypothesis, and for many anticancer drugs the rationale for individualization of dosage based on BSA is lacking.

budding uninhibited by benzimidazoles 1 is a protein that is required for the spindle assembly checkpoint. BUB1 is a protein kinase; it phosphorylates CDC20 and inhibits ubiquitin ligase activity of APC/C. In mammals, BUB1 depletion causes embryonic lethality in mice.

▶Irinotecan ▶Pharmacokinetics/Pharmacodynamics

▶Mitotic Arrest-Deficient Protein 1 (MAD1) ▶Synucleius

Bulk Minerals Definition

B-Scan Ultrasonography Definition Ophthalmologic ultrasound the provides a two-dimensional ultrasound image of the echogencity of the ocular structures providing a cross-sectional view allowing the for the diagnosis and characterization of multiple disorders including retinal and choroidal detachments, vitreous hemorrhages, vitritis, and intraocular tumors. ▶Uveal Melanoma

Are mineral nutrients that are typically required to be ingested by humans in amounts of hundreds of milligrams to a few grams per day. This category includes calcium, phosphorus, and magnesium and, along with electrolytes, are sometimes referred to as macrominerals. ▶Mineral Nutrients

Bulky Definition A lymphoma is bulky if a nodal lymphoma mass with largest dimension of 10 cm or greater is present.

BSF-2

▶Diffuse Large B-Cell Lymphoma

▶Interleukin-6

Burkitt Lymphoma BTAK ▶Aurora Kinases

Definition

Burkitt lymphoma is caused by ▶Epstein-Barr virus (EBV) and occurs mainly in sub-Saharan Africa.

Bystander Effect

Burkitt Lymphoma Cell Lines

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Bystander Effect B

Definition

Definition

Burkitt lymphoma cell lines are EBV-infected B cell lines established from Burkitt lymphoma biopsies; these cells are tumorigenic in nude mice.

When cells are killed indirectly by virtue of neighboring cells that transfer toxic products to them.

▶BCL6 Translocations in B-cell Tumors ▶Epstein-Barr Virus

▶HSV-TK/Ganciclovir Mediated Toxicity

C

C33 ▶Metastasis Suppressor KAI1/CD82

C75 Definition Derivative of cerulenin inhibits fatty acid synthase activity by interfering with the binding of malonyl-CoA to the β-ketoacyl synthase domain of fatty acid synthase. ▶Fatty Acid Synthase

CA19-9 Definition Carbohydrate antigen 19-9 is used as a tumor-marker when measured in serum. It is thought to be a sialylated Lewis blood group antigen. CA19-9 levels are elevated in many gastrointestinal malignancies including cholangiocarcinoma and pancreatic cancer, as well as some non-malignant conditions such as cholangitis and peritoneal ▶inflammation/infection. Patients who have a genetic deficiency in a fucosyltransferase specified by the Le gene are Lewisa-b- and are unable to make this antigen; thus CA19-9 testing in Lewisa-b- patients can be falsely negative. ▶Cholangiocarcinoma ▶Fucosylation

CA125 c-Abl Definition A protein tyrosine kinase which activation leads to cell cycle arrest and apoptosis. A chromosomal translocation of c-Abl to the Bcr locus results in a fusion gene. Constitutively active tyrosine kinase Bcr/Abl expression associates with chronic myelogenic leukemia. ▶Protein Kinase C Family ▶BCR-ABL1

C.elegans cell death 4 homolog ▶APAF-1 Signaling

Definition CA125 (cancer antigen 125) is a mucin-like protein of high molecular mass estimated at 200–20,000 kDA. CA125 cell surface expression is upregulated when cells undergo metaplastic differentiation into a Mülleriantype epithelium. CA125 is the most extensively studied biomarker for possible use in ovarian carcinoma early detection. It is elevated in some cases of ▶endometriosis. ▶Mesothelin ▶Ovarian Cancer ▶Serum Biomarkers

Ca2+-activated Phospholipid Dependent Protein Kinase ▶Protein Kinase C Family

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Ca2+ ATPase

Ca2+ ATPase Definition ATPases are a class of enzymes that catalyze the hydrolysis of adenosine triphosphate (ATP) into adenosine diphosphate (ADP). The Ca2+ ATPase uses this process to transport Ca2+ against a concentration gradient (e.g., Ca2+ transported from the cytoplasm into the endoplasmic reticulum). ▶Celecoxib

Ca2+-Release Channels Definition Membrane receptors localized in the sarcoplasmic/ endoplasmic reticulum that once activated mediates the release of Ca2+ from the ER to the cytosol. ▶Endoplasmic Reticulum Stress

CaBP3 ▶Calreticulin

Cachexia C HEN B ING Division of Cellular and Metabolic Medicine, School of Clinical Sciences, University of Liverpool, Liverpool, UK

Definition

Cachexia came from the Greek “kakos” and “hexis” meaning “bad conditions.” Cachexia is a complex metabolic syndrome characterized by progressive weight loss with extensive loss of skeletal muscle and adipose tissue, which is secondary to the growing malignancy.

Characteristics Most cancer patients develop cachexia at some point during the course of their disease, and nearly one-half of all cancer patients have weight loss at diagnosis. Cachexia prevents effective treatments for cancer and predicts a poor prognosis because the severity of wasting inversely correlates with survival. The consequences of cachexia are detrimental and cachexia is considered to be the direct cause of about 20% of cancer deaths. The pathogenesis of cancer cachexia remains to be fully understood, but it is evidently multifactorial. Weight Loss Clinically, cachexia should be suspected if involuntary weight loss of more than five percent of premorbid weight occurs within a six-month period. Weight loss is not simply caused by competition for nutrients between tumor and host as the tumor burden may be only 1–2% of total body weight. The frequency of weight loss varies with the type of malignancy, being more common and severe in patients with cancers of gastrointestinal tract (▶gastrointestinal tumors) and lung (▶lung cancer). Gastric and pancreatic cancer patients may lose large amounts of weight, up to 25% of initial body weight. Over 15% of weight loss in patients is likely to cause significant impairment of respiratory muscle function, which probably contributes to premature death. Weight loss can arise from several metabolic changes that take place during malignancy, for example, reduced food intake, increased energy expenditure, and tissue breakdown. Poor Appetite Loss of the desire to eat or lack of hunger is common in cancer patients. It can be related to the mechanical effect of the tumor such as obstructions (especially of the upper gastrointestinal tract), side-effects of chemotherapy or radiotherapy (▶chemoradiotherapy), and emotional distress. Some tumors may secrete products which act on the brain to inhibit appetite. Regulation of food intake involves the integration of the peripheral and neural signals in the hypothalamus and other brain regions. In the hypothalamus, the orexigenic signals such as ▶neuropeptide Y (NPY), the most potent appetite stimulant, increase food intake, and the anorexigenic signals including the pro-opiomelanocortin/cocaine and amphetamine regulated transcript (POMC/CART) inhibit appetite. Dysregulation of NPY in the hypothalamic pathway can lead to decreased energy intake but higher metabolic demand for nutrients. It has been demonstrated that NPY-immunoreactive neurons in the hypothalamus are decreased in experimental model of cancer anorexia. In contrast, reduced food consumption can be restored to normal levels by blocking the POMC/CART pathway in tumor-bearing animals.

Cachexia

High level of leptin, a hormone primarily secreted by adipocytes, inhibits the release of hypothalamic NPY. In cancer cachexia the leptin feedback loop appears to be deranged, altering the signaling pathway of NPY. Cytokines such as interleukin 1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor α (TNFα) are implicated to be involved in cancer anorexia, possibly by stimulating corticotrophin-releasing factor, a neurotransmitter which suppresses food intake at least in rodents, and/or by inhibiting neurons that produce NPY in the hypothalamus.

Increased Metabolism and Energy Expenditure Maintaining normal body weight requires energy intake to equal energy expenditure. In some patients with cancer cachexia, energy balance becomes negative as reduced food intake is not accompanied by a parallel decrease in energy expenditure. For example, patients with lung and pancreatic cancers generally have higher ▶resting energy expenditure (REE) compared with normal control subjects; however, REE is usually normal in patients with colorectal cancer. The mechanisms of increased energy expenditure are not clear although studies suggest that it might be through the upregulation of uncoupling proteins, a family of mitochondrial membrane proteins, which are proposed to be involved in the control of energy metabolism. ▶Uncoupling protein-1 (UCP-1), which decreases the coupling of respiration to ADP phosphorylation thereby generating heat instead of ATP, is only expressed in ▶brown adipose tissue (BAT). UCP-1 mRNA levels in BAT are increased in mice bearing the MAC16 colon adenocarcinoma. Although BAT is uncommon in adults, the prevalence of BAT has been found to be higher in cancer cachectic patients than the age-matched control subjects. mRNA levels of UCP2 (expressed ubiquitously) and UCP-3 (expressed in skeletal muscle and BAT) in skeletal muscle are upregulated in rodent models of cancer cachexia. In humans, skeletal muscle UCP-3 mRNA levels are over fivefold higher in cachectic cancer patients compared with patients without weight loss and health controls. Elevated expression of UCP-2 and -3 has been suggested to contribute to lipid utilization rather than whole-body energy expenditure. Cytokines such as TNFα and/or other tumor products may be responsible for the changes in UCP expression at least in rodents. Additional energy consumption could arise from the metabolism of tumor-derived lactate via “futile cycles” between the tumor and the host. The main energy source for many solid tumors is glucose, which is converted to lactate and transferred to the liver to convert back into glucose. This “futile cycle” requires large amount of ATP, resulting in an extra loss of energy in cancer patients.

439

Loss of Adipose Tissue Fat constitutes 90% of normal adult fuel reserves and depletion of adipose tissue together with ▶hyperlipidemia becomes a hallmark of cancer cachexia. Computed tomography (CT) scanning has revealed that cachectic cancer patients with gastrointestinal carcinoma had significantly smaller visceral adipose tissue area than control subjects. Increased lipolysis is implicated in cancer-associated adipose atrophy. The activity of hormone-sensitive lipase, a rate-limiting enzyme of the lipolytic pathway, is increased in cancer cachectic patients, which causes elevated plasma levels of free fatty acids and triglycerides. Meanwhile, there is a fall in lipoprotein lipase (LPL) activity in white adipose tissue, thus inhibiting cleavage of triglycerides from plasma lipoproteins into glycerol and free fatty acids for storage, causing a net flux of lipid into the circulation. Finally, glucose transport and de novo ▶lipogenesis in the tissue are reduced in tumor-bearing state, leading to a decrease in lipid deposition. There is also evidence that loss of adipose tissue in cancer cachexia could be the result of impairment in the formation and development of adipose tissue. The expression of several key adipogenic transcription factors including CCAAT/enhancer binding protein alpha, CCAAT/enhancer binding protein beta, peroxisome proliferator-activated receptor gamma, and sterol regulatory element binding protein-1c are markedly reduced in adipose tissue of cancer cachectic mice. Various factors produced by tumors or the host’s immune cells, responding to the tumor can disturb lipid metabolism. TNFα has been shown to affect adipose tissue formation by inhibiting the differentiation of new adipocytes, causing dedifferentiation of mature fat cells and suppressing the expression of genes encoding key lipogenic enzymes. TNFα has also been associated with increased lipolysis probably through suppression of LPL activity in adipocytes. In addition, both TNFα and IL-1 are able to inhibit glucose transport in adipocytes and consequently decrease the availability of substrates for lipogenesis. Certain prostate, gut and pancreatic tumors secrete a lipid-mobilizing factor (LMF), also produced by a mouse adenocarcinoma model. LMF has been shown to be identical to the plasma protein zinc-α2-glycoprotein (ZAG). It is recently found to be secreted by human adipocytes and upregulated in adipose tissue of mice with cancer cachexia. ZAG causes rapid lipolysis in vitro and in vivo, possibly through activation of intracellular cyclic AMP. ZAG also stimulates expression of UCPs in brown fat of mice, which may contribute to increased energy expenditure as well as lipid catabolism during cachexia. Moreover, ZAG has been shown to reduce glucose metabolic rate in adipose tissue, consistent with a decrease in glucose transportor-4 transcript in white fat of mice bearing a ZAG-producing tumor.

C

440

Cachexia-inducing Agent

Loss of Muscle Protein Weakness, commonly seen in cancer cachectic patients, is directly related to wasting of muscle that accounts for almost half the body’s total protein and bears the brunt of enhanced protein destruction. Reduced protein synthesis together with enhanced proteolysis have been observed in experimental animal models and in muscle biopsies from cancer patients with cachexia, and whole-body protein turnover can be markedly increased in cachectic cancer patients. Some mediators and pathways of excessive protein breakdown have been incriminated in cancer cachexia. TNFα appears to be involved, as treatment with recombinant TNFα enhances proteolysis in rat skeletal muscle and activates the ubiquitin–proteasome system. Ubiquitin, an 8.6 kD peptide, is crucially involved in targeting of proteins undergoing cytosolic ATP-dependent proteolysis. There is an increase in ubiquitin gene expression in rat skeletal muscle after incubation with TNFα in vitro. Tumors also produce cachectic factors such as proteolysis-inducing factor (PIF), a 24 kD glycoprotein initially isolated from a cachexia-inducing tumor (MAC16) and the urine of cachectic cancer patients. PIF induces muscle protein breakdown by stimulation of the ubiquitin–proteasome proteolytic pathway. There is increasing evidence that both cytokines and PIF cause protein degradation by activation of ▶nuclear factor kappa B (NFκB), a transcription factor that regulates the expression of a number of proinflammatory cytokines. TNFα and PIF can upregulate components of the ubiquitin–proteasome pathway in an NFκB-dependent manner. Activation of NFκB by TNFα in murine muscle cells suppresses mRNA of the transcription factor ▶MyoD, inhibiting skeletal muscle cell differentiation as well as preventing the repair of damaged skeletal muscle fibers. Treatment Current treatment designed to ameliorate cancer cachexia has limited benefit. Nutritional supplementation (oral or parenteral) alone has little effect and, critically, does not restore muscle mass, improve quality of life or prognosis in cancer patients. Appetite stimulants such as megestrol acetate and medroxyprogesterone acetate are commonly used at present in the treatment of anorexia and cachexia. These agents are believed to stimulate orexigenic peptide NPY in the hypothalamus, and inhibit the synthesis and release of proinflammatory cytokines. Their effects on appetite and well being are short-termed and they do not influence lean body mass and survival. Cannabinoids (▶cannabinoids and cancer) have also been studied as potential appetite stimulants. However, dronabinol has failed to prevent progressive weight loss in patients with advanced cancer. Therapeutic interventions include anticytokines such as thalidomide (▶thalidomide and its analogs) with

multiple immunomodulatory properties. It suppresses the productionofTNFα, IL-1β, IL-12, and cyclooxygenase-2, which is probably through inhibiting NFκB activity. Thalidomide has been shown to attenuate total weight loss and loss of lean body mass in cachectic patients with advanced pancreatic cancer. ▶Eicosapentaenoic acid (EPA), a polyunsaturated fatty acid from fish oil, has attracted attention as a potential anticachectic agent. EPA has been shown to attenuate the increased expression of the components of the ubiquitin–proteasome proteolytic pathway in skeletal muscle of mice with cancer cachexia, and EPA can block PIF-induced protein degradation in vitro. In randomized clinical trials, cachectic patients with unresectable pancreatic cancer receiving EPA have shown a stabilization in the rate of weight loss, fat and muscle mass as well as the REE. Recent data from animal studies suggest that EPA combined with the leucine metabolite beta-hydroxy-betamethylbutyrate seems to be more effective in the reverse of muscleprotein wasting.

References 1. Tisdale MJ (2002) Cachexia in cancer patients. Nat Rev Cancer 2:862–871 2. Fearon KC, Moses AG (2002) Cancer cachexia. Int J Cardiol 85:73–81 3. Bing C, Brown M, King P et al. (2000) Increased gene expression of brown fat uncoupling protein (UCP)1 and skeletal muscle UCP2 and UCP3 in MAC16-induced cancer cachexia. Cancer Res 60:2405–2410 4. Bing C, Russell S, Becket E et al. (2006) Adipose atrophy in cancer cachexia: morphologic and molecular analysis of adipose tissue in tumour-bearing mice. Br J Cancer 95:1028–1037 5. Argiles JM, Busquets S, Lopez-Soriano FJ (2006) Cytokines as mediators and targets for cancer cachexia. Cancer Treat Res 130:199–217

Cachexia-inducing Agent ▶Leukemia Inhibitory Factor

Caco-2 Definition Caco-2 is an immortalized cell line originally derived from a human ▶colon cancer. It can be grown in-vitro in

Cajal Bodies

such a way as to mimic the gastrointestinal tract wall and is used in cell culture models to measure drug intestinal permeability. ▶ADMET Screen

Cadherin 1 Definition CDH1; synonyms Epithelial cadherin, Uvomorulin. ▶E-Cadherin

441

Cajal Bodies V INCENZO

DE

L AURENZI

Department of Experimental Medicine and Biochemical Sciences, University of Tor Vergata, Rome, Italy

Synonyms Coiled bodies

Definition

Small nuclear organelles (0.1–2.0 μM in diameter), present in all eukaryotic cells, involved in a number of different nuclear functions.

Characteristics

Cadherins Definition Cadherins are a family of cell adhesion receptor glycoproteins that are involved in the calcium-dependent cell-to-cell adhesion. E-, V-, and N-cadherins are distinct in immunological specificity and tissue distribution. They promote cell adhesion via their homophilic binding interactions. Class of type-1 transmembrane proteins important in cell adhesion. They are dependent on calcium (Ca2+) ions to function, hence their name. Cadherins play an important role in regulation of morphogenesis. Cadherins inhibit invasiveness of tumor cells. ▶Doublecortin ▶E-Cadherin ▶EpCAM ▶Tight Junction ▶Adhesion ▶Cell Adhesion Molecules

Cafe Au Lait Spots Definition Synonym Cafe-au-lait Macule; Coffee-with-milk-colored spots on the skin that are seen characteristically in the neurofibromatosis type 1 (NF1) syndrome.

The nucleus of eukaryotic cells contains a number of different highly specialized organelles. Unlike cytoplasmic organelles these nuclear structures are not delimited by a membrane but are by all means compartments that contain a number of specific proteins. Most of the organelles can be clearly identified trough immuno-staining using antibodies directed against specific marker proteins; however, it should be kept in mind that these organelles are highly dynamic structures that often exchange components and therefore many proteins can be found in more than one organelle. Among these organelles are Cajal Bodies (CBs), described over a century ago by Ramon y Cajal. CBs were originally described in neuronal cells but have since been described in a variety of cell types, both in animals and in plants, suggesting that they are involved in some fundamental cellular process. Due to their characteristic ultra-structural appearance as a tangle of coiled fibrillar strands they have also been called coiled bodies. They usually vary in size from 0.2 μM to 2 μM, but can be occasionally larger. The number of CBs is usually between 0 and4 in normal diploid cells; however, many more can be found in some cancer cells. The number of CBs per cell is regulated during the cell cycle. Indeed, CBs disappear in prophase nuclei, to reappear in G1 at the same time of the nucleolus. Their number is then doubled, usually reaching the number of four, in the S phase. It has been suggested that in these cells the number of CBs depends on the ploidy of the cells or more specifically on the number of chromosomes 1 and 6. CBs can be found associated with specific gene loci such as snoRNA, snRNA and histone gene clusters. In addition, CBs can also be found in association with other nuclear bodies such as cleavage bodies and ▶PML bodies, suggesting that there is an exchange of components between the different nuclear organelles.

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Cajal Bodies

CBs have a heterogeneous composition, containing different Small Nuclear Ribonucleoproteins (snRNPs), Small Nucleolar Ribonucleoproteins (snoRNPs), cell cycle regulating proteins, and transcription factors, as well as other proteins, whose function still needs to be determined. The generally recognized marker of CBs is p80 coilin. The function of this protein is still unknown, its deletion in mice results in reduced coilin –/– animal litters, suggesting a developmental defect; however surviving animals appear normal. Deletion of coilin results in residual bodies that still contain some components such as fibrillarin, Nopp140 and FLASH, but not others like splicing snRNPs. While their function is still in part elusive, recent work suggests that they are involved in several nuclear functions. CBs are supposed to be the site of assembly of the three eukaryotic RNA polymerases (pol I, pol II and pol III) with their respective transcription and processing factors that are then transported as multiprotein complexes to the sites of transcription.They are also involved in the modification of Small Nuclear RNAs (snRNAs) and Small Nuclear Ribonucleoproteins (snRNPs), which are important for spliceosome formation. Indeed CBs contain newly assembled snRNPs and snoRNPs that later accumulate in speckles and nucleoli and it has recently been suggested that CBs are sites of modification for snRNPs and particularly sites where 2′-O-methylation and pseudouridine formation occur. This process requires a novel class of CB specific small RNAs (scaRNAs) that pair with the snRNAs and function as guides for 2′-Omethylation. The reaction is probably mediated by the fibrillarin, a CB and nucleolar associated protein with methyl transferase activity. CBs have also been implicated in ▶replication dependent histone gene transcription, and a subset of CBs is physically associated with histone gene clusters on chromosomes 1 and 6. Phosphorylation of a CB component p220/NPAT by cyclinE/Cdk2 is required for activation of histone transcription, exit from G1 and progression through S phase of the cell cycle. Moreover it has been shown that another CBs component FLASH is essential for this function. Downregulation of FLASH results in structural alteration of CBs, reduction of replication dependent histone gene transcription, and block of cells in the S phase (▶S-phase damage-sensing checkpoints) of the cell cycle. In addition, CBs are involved in U7 snRNA dependent cleavage of the 3′ end of histone pre-mRNA before the mature mRNA can be exported to the cytoplasm. Finally, a role for CBs in regulating ▶telomerase function has been proposed. Based on the presence of the RNA component of telomerase (hRT) in CBs of cancer cells, it has been suggested that CBs play a role in the maturation of hRT or in the assembly of the telomerase complex. However, CBs might represent

only a site of accumulation of hRT; alternatively, this could be an altered localization only present in cancer cells; therefore further studies are required to clarify this potential CB function. Alteration of CB structure, as well as other nuclear structure alterations, has been observed in various diseases; however, in most cases it is not clear if these defects are a consequence of altered nuclear functions or play a role in the disease pathogenesis. CBs have been found associated with the aggregates formed in CAG triplet expansion diseases and ataxin-1; mutated in ▶Spinocerebellar ataxia type 1 (SCA1) it has been shown to interact with coilin. The role of these findings in the disease pathogenesis is yet to be established. Spinal Muscular Atrophy (SMA) is an autosomal recessive disease characterized by motor neuron degeneration associated with muscular atrophy and paralysis; it is usually caused by mutations of the surviving motor neurons 1 gene (SMN1). SMN is a 294 amino acid protein, ubiquitously expressed; it bears no homology to other known proteins and its function is still unknown. It is localized both in the cytoplasm and in the nucleus where it is found in two different nuclear organelles: Cajal bodies (CBs) and Gems (for Gemini of CBs). Pathogenesis of SMA is not clearly understood but reduction of SMN levels results in an alteration of CB structure. Alteration of CBs in cancer has not been thoroughly studied yet and a role for these organelles in cancer has not been clearly established. However cancer cell lines often show an increased number of CBs and some alteration of CBs can be found in specific cancers. In ▶MLL-ELL leukemia (▶Acute myeloid leukemia) the presence of the MLL-ELL fusion protein results in alteration of CBs structure and altered localization of coilin. The TLS/CHOP fusion protein generated by the t(12;16) translocation (▶Chromosome Translocations), found in liposarcomas shows high transforming capacity and is in part localized in CBs. In conclusion, while recent studies have started to shed light on the function of CBs and on the interrelationship between these organelles and other nuclear structures, more work is required to clearly understand the molecular mechanisms involved in their formation and clarify their different roles in nuclear function. This in turn will provide information on their potential role in the pathogenesis of a range of human diseases.

References 1. Gall JG (2000) Cajal bodies: the first 100 years. Annu Rev Cell Dev Biol 16:273–300 2. Ogg SC, Lamond AI (2002) Cajal bodies and coilin – moving towards function. J Cell Biol 159(1):17–21 3. Cioce M, Lamond AI (2005) Cajal bodies: a long history of discovery. Annu Rev Cell Dev Biol 21:105–131

Calcitonin

CAK1 Antigen ▶Mesothelin

Cal Definition

Is a member of the ▶zyxin family of proteins. Also known as migfilin. ▶Lipoma Preferred Partner

Calcineurin

443

Characteristics Almost all cells of human body synthesize and secrete procalcitonin (proCT), a precursor of the CT peptide, in response to infection/▶inflammation. Only cells of the thyroid and ▶neuroendocrine organs can process proCT to produce mature CT molecule. CT sequence among various species shows remarkable divergence. However, all sequences contain 32 amino acids, a carboxy-terminal proline amide, and a disulfide bridge between cysteine residues at positions 1 and 7. In addition to CT, other biologically and chemically diverse molecules such as CT gene-related peptide (CGRP), ▶adrenomedullin (▶ADM), and ▶amylin (AMY) are considered as CT family of peptides because of their ability to interact with CT receptor (CTR) and induce biological response. Each of these peptides displays selective tissue distribution and distinct physiological effects. For example, CGRP is predominantly present in central and peripheral nervous system, and is important for neurotransmission and neuromodulation. ADM is relatively abundant in vascular space, and plays an important role in the regulation of cardiovascular and respiratory functions, and CT is essential for calcium balance. However, CT does not regulate calcium in extrathyroidal tissues but is implicated to play an important role in cell growth, cell differentiation, and other regulatory functions.

Definition

Is a highly conserved, Ca2+/calmodulin-dependent serine/threonine phosphatase, also called protein phosphatase 2B (PP2B). Calcineurin is best known for its role in the Ca2+-dependent regulation of the nuclear factor of activated T-cells (NF-AT) pathway which is involved in T-cell activation. ▶Calreticulin

Calcitonin G IRISH V. S HAH Department of Pharmacology, University of Louisiana College of Pharmacy, Monroe, LA, USA

Definition Calcitonin (CT) is a 32-amino acid peptide synthesized in mammals by the C cells of the thyroid gland. Several extrathyroidal sites including the prostate gland, gastrointestinal tract, thymus, bladder, lung, pituitary gland, and central nervous system (CNS) also produce this peptide molecule.

Biosynthesis Four CT genes, CALC-I, CALC-II, CALC-III, and CALC-IV with significant nucleotide homologies have been identified. However, CT is encoded by only CALC-I gene. CALC-I and CALC-II encode two different forms of CGRP, CGRP-I and CGRP-2. CALC-III is thought to be a pseudo gene, and CALC-IV produces AMY. Human (h) CT (CALC-I) gene is located in the p14qter region of chromosome 11. CT gene encodes two distinct peptides CT and CGRP, which arise by tissue-specific alternative splicing of the same primary mRNA transcript. The primary mRNA transcript is spliced almost exclusively to CT mRNA in thyroid, and to CGRP in the nervous system. CT is synthesized as part of a larger precursor protein of 136 amino acids. The DNA sequence of the hCT gene predicts that the hormone is flanked in the precursor by N- and C-terminal peptides. Both N-terminal and C-terminal flanking peptides are detected in the plasma and thyroidal tissues of both normal and ▶medullary thyroid carcinoma (MTC) patients. However, no biological function for either of these two peptides has been conclusively determined. Cyclic adenosine monophosphate (cAMP), pentagastrin, and progesterone are potent stimulators of CT gene expression. In contrast, testosterone and estrogens have inhibitory effect.

C

444

Calcitonin

There is evidence for ▶polymorphisms in CALC-I gene that leads to increased risk for ovarian ▶cancer in carrier women (T-C 624 bp upstream of translation initiation codon); and 16 bp microdeletion polymorphism has been reported in a family multiple cases of unipolar and bipolar depressive disorders. Biological Actions Actions on Bone CT is the only hormone that inhibits bone resorption by direct action on osteoclasts in the bone. It is characterized by the rapid loss of osteoclast ruffled borders, reduced cytoplasmic spreading, decreased release of lysosomal enzymes, and inhibition of collagen breakdown. This role is physiologically more relevant at times of stress on skeletal calcium conservation such as pregnancy, lactation, and growth, when bone remodeling by osteoclasts and the consequent release of calcium stores in the bone need to be tightly regulated to prevent unnecessary bone loss. In normal adult humans, even large dose of CT has little effect on serum calcium. However, in pathologies created by increased bone turnover such as thyrotoxicosis, ▶metastatic bone disease, or Paget’s disease, CT treatment effectively inhibits bone resorption and lowers serum calcium. Renal Actions CT increases urinary excretion rate of sodium, potassium, phosphorus, and magnesium. CT also enhances 1-hydroxylation of 25-hydroxy vitamin D in the proximal straight tubule by stimulating the expression 25-hydroxy vitamin D 1-hydroxylase. Central Actions Central administration of CT produces analgesia, affects sleep cycles producing insomnia, major reduction in slow wave sleep and long period of alteration of rapid eye movement (REM) sleep and wakening. The centrally mediated actions of CT correlate well with the location of CT binding sites. CT also demonstrates multiple hypothalamic actions such as modulation of hormone release, decreased appetite, gastric acid secretion, and intestinal motility. Administration of CT in clinical situations of bone pain is very effective in ameliorating the pain symptoms. Other Actions CT and its receptors have been identified in a large number of other cell types and tissue sites suggesting multiple roles for CT–CTR axis. CTR binding sites have been identified in the kidneys, brain, pituitary, testis, prostate, spermatozoa, lung, and lymphocytes. There is evidence to suggest the involvement of CT in cell growth and differentiation, tissue development and tissue remodeling. CT appears to be important for

blastocyst implantation and development of the early blastocyst. CT in Cancer Overexpression of CT has been reported in cancerderived cells from ▶thyroid, ▶lung, ▶breast, ▶prostate, ▶pancreas, ▶pituitary, ▶bone (osteoclastoma, osteogenic sarcoma), and embryonal carcinoma, suggesting the deregulation of CT expression is an important event in several malignancies. The results from our laboratory have shown that CT and CTR are present in undifferentiated basal cells, but absent in differentiated secretory cells of normal human prostate gland. However, CT and CTR become detectable in malignant secretory epithelium suggesting malignancyassociated deregulation of CT/CTR expression. CT and CTR transcripts in malignant human prostate become detectable as early as high-grade ▶PIN, and progressively increase with increase in tumor grade. In human pancreas, CTR is present in benign as well as malignant regions but CT is exclusively detected in malignant sections of multiple pancreatic carcinomas, including ductal adenocarcinomas. Mechanism of CT Action Receptors CT acts by binding to receptors on the plasma membrane of responding cells. CTR cDNA has been cloned in multiple mammalian species. Analysis of the protein translated from CTR cDNA sequence reveals the size of approximately 500 amino acids, and the receptor belongs to the class B family of G protein-coupled receptors (▶GPCRs), which also includes numerous potentially important drug targets. The human CTR gene is located on chromosome 7 at 7q21.3. The CTR gene exceeds 70 Kb in length, comprises of at least 14 exons, separated by introns ranging in size from 70 nucleotides to >20,000 nucleotides. Multiple polymorphic sites in CTR gene have been identified, and several of them lead to lower bone mineral density in postmenopausal women. Receptor Isoforms Human CTR (hCTR) is known to exist in mutiple isoforms that arise from alternative splicing of the same primary transcript. The two most common hCTR variants arise by alternative splicing of intracellular domain 1. The most common variant (Type 1 hCTR) leads to the addition of a 16 amino acid insert in the first intracellular loop. Alternative splicing of this small exon leads to the expression of type 2 hCTR, which differs from type 1 hCTR (abundant in the brain and the kidneys) by the absence of a 16-amino acid insert in the first intracellular loop. Type 2 CTR is predominantly expressed in malignant prostate and pancreatic cells. It has been shown that the lack of 16-amino acid insert in

Calcitonin

445

first intracellular loop enables type 2 hCTR to coactivate both adenylyl cyclase and phospholipase C. In addition, another receptor referred as calcitonin receptor-like receptor (▶CRLR) has been reported.

CT coactivates protein kinases A and C, and pathways activated by these enzymes play an important role in CT-stimulated growth, invasiveness and tumorigenicity of prostate cancer cells.

Modulation of CTR Specificity CTR displays high affinity for CT, but low affinities for other CT family peptides. However, the ligand specificity of CTR is significantly altered when it binds to a ▶RAMP protein. Several ▶RAMPs have been identified but three (RAMP1, RAMP2, RAMP3) are investigated. hCTR displays low affinity for AMY, but association with RAMPs enables hCTR to bind AMY with high affinity. Similarly, ligand specificity of CRLR depends on the complexed RAMP. For example, CRLR-RAMP1 serves as CGRP receptor whereas CRLR-RAMP2 acts as ADM receptor. CRLR-RAMP3 displays high affinity for ADM as well as CT. This phenomenon opens up a possibility that ligand specificity of CTRs can be regulated by modulation of RAMPs expression.

G Protein-Independent Signaling Recent evidence suggests that GPCRs also activate G protein-independent signaling by interacting with proteins referred as GPCR interacting proteins (GIPs). GPCRs activate this signaling by binding to GIPs through one or more of structural interacting domains such as ▶Src homology 2 (SH2) and SH3, plackstrin homology, ▶PDZ and Eva/WASP homology (EVH) domains. Examination of CTR sequence reveals that the last four amino acids at the extreme C-terminus of the ▶C-tail form E-S-S-A tetramer (amino acids 447–50), which conforms to the canonical type I ▶PDZ ligand. A single serine-to-alanine substitution in the PDZ ligand of prostate CTR almost abolished CT-elicited increase in invasiveness and tumorigenicity of PC-3 prostate cancer cell line, raising a strong possibility that metastasizing ability of CTR is dependent upon its ability to interact with intracellular proteins containing ▶PDZ domain(s). CTR seems to induce ▶metastasis by disassembly of tight junctions on prostate cancer cells, which leads to the loss of cell polarity, activation of proteases such as urokinase type plasminogen activator, matrix metalloproteinases 2 and 9. These results raise a possibility that the prevention of interaction between CTR and its intracellular partner through the PDZ ligand can be an effective strategy to prevent CT-mediated metastasis. With current advances in medicinal chemistry and peptide mimetics, it should be possible to design a small peptide of 4–6 amino acids or a small molecule to prevent this interaction. CT also activates ▶phosphoinositol-3-kinase (PI3K)– Akt–Survivin pathway and induces chemoresistance and ▶apoptosis in multiple prostate cancer cell lines through as yet uncharacterized mechanism. CT activated protein kinase A plays a key role in multiple actions of CT on prostate cancer cell lines, suggesting that both, G proteindependent and G protein-independent actions of CTR may act in concert to increase oncogenicity of prostate cancer cell lines.

CTR Signaling G protein-Mediated Signaling The intracellular mechanisms by which CTR produces biological effects are still being elucidated. However, the signaling pathways appear to vary with cell type as well as animal species. As with most other GPCRs, the CTRs show coupling with multiple G proteins, which also depends on the isoform of CTR. For example, type I CTR preferentially couples to ▶Gαs, leading to the activation of adenylyl cyclase and elevation in the intracellular levels of cAMP. The inhibitory action of CT on osteoclasts is accompanied by increase in cAMP levels. Forskolin, a direct activator of adenylyl cyclase, as well as dibutyryl cAMP, which elevates intracellular cAMP levels independent of adenylyl cyclase, mimic CT actions on bone resorption. Similarly, CTR is known to activate adenylyl cyclase in kidney as well as in cancers of lung, breast, and bone. Unlike type 1 CTR, type 2 CTR simultaneously couples with Gαs and ▶Gαq, leading to the coactivation of adenylyl cyclase and phospholipase C. This results in the elevation of intracellular levels of cAMP, as well as inositol triphosphates, and thence increased cytosolic calcium levels. This, together with coliberated diacyl glycerols, activates protein kinase C. In brain tissue, CT couples to G proteins other than Gαs as indicated by limited activation of adenylyl cyclase in neural tissues. In hepatocytes, CT increases cytosolic calcium levels without activating adenylyl cyclase. In LLC-PK1 kidney cells, CT increases either intracellular cAMP levels or cytosolic calcium levels in a cell cycledependent manner; and in pituitary lactotrophs, CT inhibits TRH-induced increases in cytosolic levels and activation of protein kinase C. In ▶prostate cancer cells,

Significance of CT–CTR axis in Cancer: Clinical Aspects CT is “Oncogene” for Prostate Cancer but “Tumor Suppressor” for Breast Cancer Although growing body of evidence suggests elevated expression of CT and CTR in multiple cancers, extensive studies on CT actions have been conducted only in ▶prostate cancer and ▶breast cancer (▶tumor suppressor) cell lines. Interestingly, CT displays sexual dimorphism in these two cancers, raising a possibility

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of the modulatory role of sex hormones on CT actions in these two organs. For example, CT is a potent ▶oncogene for prostate cancer as indicated by the progressive increase in CT and CTR expression in primary prostate cancers with tumor progression, and potent stimulatory actions of CT on tumorigenicity of prostate cancer cell lines. In contrast, CT and CTR is constantly expressed in normal mammary ductal epithelium, the loss of CTR expression is associated with the progression of breast cancer to ▶metastatic phenotype, and CT inhibits growth of some breast cancer cell lines. Although opposing actions of CT on prostate and breast cancer cell lines remain to be thoroughly investigated, initial studies in the author’s laboratory suggest that CT protects junctional complexes in breast cancer cell lines, and estradiol attenuates the actions of CT in estradiol receptorpositive breast cancer cell lines. These results emphasize the importance of CTR actions on junctional complexes in cancer, and its significance in cancer cell growth and metastasis. CT is an Angiogenic Factor ▶Angiogenesis, the process of new vessel formation or neovascularization, has aroused increasing interest over last 25 years. Expansion of the tumor cell mass is dependent on both the degree of tumor vascularization and the rate of angiogenesis. Our recent results have demonstrated the presence of CTR in ▶HMEC-1 cell line, and that CT stimulates in vivo angiogenesis in nude mice, and directly stimulates all major phases of in vitro angiogenesis including endothelial cell migration, invasion, proliferation, and tube morphogenesis. The stimulatory actions of CT on in vitro angiogenesis are comparable to the actions of ▶vascular endothelial growth factor (VEGF). Importantly, silencing of CTR in HMEC-1 cells completely abolishes CT-induced tube morphogenesis. Furthermore, ▶prostate and thyroid cancer cell lines expressing high levels of CT form large, highly vascular tumors. In contrast, the silencing of CT expression in these cell lines markedly reduces tumor growth and vascularity. These results may also explain the findings that malignancies displaying high levels of CT expression (such as MTCs and ▶multiple endocrine neoplasias) also produce highly vascular tumors. Considering that therapeutic use of CT for pain relief is fairly widespread in cancers as well as other diseases, it will be important to consider oncogenic and angiogenic effects while determining CT therapy in these patients. In summary, CT and CTR expression has been wellinvestigated in ▶breast and prostate carcinomas. CT is a potent stimulator of tumor growth, angiogenesis, and metastasis in prostate cancer cell lines. In contrast, CTR expression is lost with breast cancer progression, and CTR attenuates growth of breast cancer cell lines.

Significant expression of CT and CTR has also been reported in MTCs, multiple endocrine neoplasias, and ▶carcinomas of lung, ▶pancreas, ▶gastrointestinal tract, ▶thymus, and ▶bladder. However, the significance of CT–CTR axis in these carcinomas remains to be investigated.

References 1. Findlay DM, Saxton PM (2003) Calcitonin. Henry HL, Normon AW (eds) Encyclopedia of hormones and related cell regulators. Academic Press, New York, NY, pp 220–230 2. Thomas S, Chigurupati SA Muralidharan, Girish S (2006) Calcitonin increases tumorigenicity of prostate cancer cells: evidence for the role of protein kinase A and urokinase-type plasminogen receptor. Mol Endocrinol 20(8):1894–1911 3. Han B, Nakamura M, Zhou G et al. (2006) Calcitonin inhibits invasion of breast cancer cells: involvement of urokinase-type plasminogen actor and uPA receptor. Int J Oncol 28(4):807–814 4. Ball DW (2007) Medullary thyroid cancer: therapeutic targets and molecular markers. Curr Opin Oncol 19 (1):18–23 5. Seck T, Pellegrini M, Florea AM et al. (2005) The delta e13 isoform of the calcitonin receptor forms six transmembrane domain receptor with dominant negative effects on receptor surface expression and signaling. Mol Endocrinol 19(8):2132–2133

Calcitriol DAVID F ELDMAN , A RUNA K RISHNAN , J ACQUELINE M ORENO, S RILATHA S WAMI Division of Endocrinology, Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA

Synonyms CALCITRIOL; Activated vitamin D; 1α,25-Dihydroxyvitamin D3

Definition Calcitriol, the hormonally active form of vitamin D, is the major regulator of calcium homeostasis in the body and is critically important for normal mineralization of bone. Calcitriol is produced by sequential hydroxylations of vitamin D in the liver (25-hydroxylation) and the kidney (1α-hydroxylation) to produce the active hormone. Like other steroid hormones, calcitriol, working through the vitamin D receptor (VDR), functions by a genomic mechanism similar to

Calcitriol

the classical steroid hormones to regulate target gene transcription. In other words, vitamin D is converted into a hormone that acts similarly to other hormones (steroids, thyroid hormone, retinoids, etc.) whose mechanism of action is via nuclear receptors. The traditional actions of calcitriol are to enhance calcium and phosphate absorption from the intestine in order to maintain normal concentrations in the circulation and to provide adequate amounts of these minerals to the bone-forming site to allow mineralization of bone to proceed normally. This action is critical to prevent rickets in children and osteomalacia in adults. However, in the past two decades, it has become increasing clear that calcitriol has many additional functions that implicate the hormone in a wide array of actions relating to bone formation as well as to other areas unrelated to bone or mineral metabolism including antiproliferative, prodifferentiating and immunosuppressive activities. Pharmaceutical companies and academic centers have actively studied analogs of calcitriol in an attempt to design a drug with increased potency to treat osteoporosis, cancer or autoimmune diseases while being less likely to cause hypercalemia and renal stones, the predictable sideeffects of high doses of calcitriol, Several recent reviews of the mechanism of action and function of calcitriol have been published as well as a comprehensive book addressing all areas of vitamin D.

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northern latitudes or other life-styles that limit vitamin D production. Calcitriol and Cancer A number of epidemiologic studies have found a protective relationship between vitamin D status and decreased risk of cancer. Higher rates of cancer mortality have been observed in regions with less sunlight UV-B radiation, among African-Americans and among overweight people, each associated with lower levels of circulating 25(OH)D, the precursor of calcitriol. These data suggest that there is a beneficial effect of vitamin D on cancer development and mortality. The preponderance of observational studies of vitamin D status in relation to the risk of colon, breast, prostate and ovarian cancers has found that vitamin D sufficiency lowers cancer risk. Several studies have demonstrated an inverse relationship between sunlight exposure and the incidence of colon and prostate cancers. Studies correlating the measured plasma levels of vitamin D metabolites with cancer incidence have shown an inverse relationship between plasma 25(OH)D levels and colorectal cancer whereas in the case of prostate cancer, the results have been variable. Several studies have also examined the association between polymorphisms in the VDR gene and the risk for colon and prostate cancers and the results have also been variable but suggestive that some forms of VDR alter the risk of developing cancer.

Characteristics Vitamin D exists in two forms, vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). When written without a subscript the designation vitamin D denotes either D2 or D3. Sunlight, in the form of UV-B rays, cleaves the B ring between carbon-9 and 10 to open the ring and create a secosteroid structure. By this process the precursor (provitamin) molecules, 7-dehydrocholesterol in animals and ergosterol in plants, are converted to the secosteroids, vitamin D3 and vitamin D2, respectively. The two secosteroids differ only in the presence of a methyl group at carbon 28 and a double bond between carbon 22 and 23 on the side chain of vitamin D2. Vitamin D2 and vitamin D3 are handled identically in the body and converted, via two hydroxylation steps, first in the liver and then in the kidney to the active hormones, 1,25(OH)2D2 or 1,25 (OH)2D3 (calcitriol). Calcitriol then acts in multiple target tissues throughout the body by binding to its nuclear receptor, the vitamin D receptor (VDR) to regulate gene expression. Since few dietary sources contain high levels of vitamin D, sunlight exposure or ingestion of supplements or vitamin D-supplemented food is essential to maintain adequate vitamin D levels. In recent years it is being increasingly recognized that vitamin D deficiency in many people is related to inadequate sunlight exposure, dark skin, living in

Mechanisms VDR, the receptor through which calcitriol exerts its actions, is expressed in many normal and malignant cell types indicating a wide array of previously unrecognized potential targets for calcitriol action. In many of these normal and malignant cells, calcitriol and its analogs exert pleiotropic actions to inhibit cell proliferation and promote differentiation. A number of important mechanisms have been implicated in calcitriol-mediated growth inhibition. A primary mechanism appears to be the induction of cell cycle arrest in the G1/G0 phase, due to an increase in the expression of cyclin-dependent kinase inhibitors such as p21Waf/Cip1 and p27Kip, inhibition of cyclin-dependent kinase activity and regulation of the phosphorylation status of the retinoblastoma protein (pRb). As the loss of the expression of cell cycle regulators has been associated with a more aggressive cancer phenotype and decreased prognosis and poorer survival, these observations suggest that calcitriol may be a suitable therapy to inhibit cancer progression. In addition, calcitriol induces apoptosis in some cancer cells and down-regulates anti-apoptotic genes like bcl-2. Other mechanisms include the stimulation of differentiation, modulation of growth factor actions and regulation of the expression and function of oncogenes and tumor

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suppressor genes. The inhibition of invasion and metastasis of tumor cells as well as the suppression of angiogenesis have also been shown to contribute to the anti-tumor effects of calcitriol. Recent studies in prostate cancer have revealed anti-inflammatory effects of calcitriol through the inhibition of prostaglandin synthesis and actions as well as the inactivation of stressinduced kinase signaling and down-stream production of inflammatory cytokines. Since inflammation and prostaglandins are associated with carcinogenesis and cancer progression, these anti-inflammatory actions suggest yet another role for vitamin D in cancer chemoprevention and treatment. Role of Vitamin D or Calcitriol in Cancer Prevention or Therapy Because of its actions to inhibit cell proliferation and promote differentiation, calcitriol has been considered a good candidate for possible “chemoprevention” or “differentiation” therapy in a number of malignant cell types that possess VDR. Colon Cancer VDR are present in the colon, in colon cancer cell lines as well as in surgically removed colon cancers. The possibility that calcium and/or vitamin D may be active in decreasing colon cancer has been examined by several groups and an adequate intake of calcium (in the range of 1,800 mg/day) and vitamin D (800–1,000 IU/ day) has been found in some studies to have a protective effect against the development of colon cancer. Studies in a number of colon cancer models have demonstrated the tumor inhibitory and pro-differentiation effects of calcitriol or its analogs both in vitro and in vivo. A recent study in the APC(min) mouse model has demonstrated that both vitamin D and calcium individually exert inhibitory effects on the development of precancerous polyps and exhibit a synergistic effect when used together. VDR expression correlates with colon cancer prognosis: high VDR levels are associated with favorable prognosis and VDR expression is down-regulated in high grade tumors. Breast Cancer VDRs are present in normal breast and breast cancer cell lines and in many human cancer specimens. Adequate calcium and vitamin D intake has been shown to enhance survival rates among breast cancer patients in some studies. Calcitriol suppresses the growth of human breast cancer cell lines in culture and also in vivo in xenografts of human breast cancer cells in nude mice and carcinogen-induced breast cancer in rats. A number of investigators have shown that calcitriol or its analogs exhibit antiproliferative effects in cultured breast cancer cells through a number of different mechanisms. Calcitriol has also been

shown to decrease estrogen receptor-alpha levels in breast cancer cells and inhibit estrogen stimulation of breast cancer cell growth. In addition to its antiproliferative effects, calcitriol stimulates apoptosis in some breast cancer cells and may enhance the responsiveness of breast cancer cells to conventional cytotoxic agents. Studies in VDR null mice (mice in which the VDR was genetically deleted) reveal that calcitriol participates in the negative growth control of normal mammary gland. Disruption of VDR signaling results in abnormal morphology of the mammary ducts, an increase in preneoplastic lesions and accelerated mammary tumor development suggesting that vitamin D compounds may play a beneficial role in the chemoprevention of breast cancer. Prostate Cancer In a prediagnostic study with stored sera, calcitriol blood levels were found to be an important predictor for palpable and anaplastic tumors in men over 57 years of age but not for incidentally discovered or well differentiated tumors. VDR are present in prostate cancer cell lines and in normal prostate. Calcitriol inhibits the growth of all these cell types in culture. Calcitriol and vitamin D analogs exert antiproliferative effects in multiple prostate cancer models and several mechanisms mediate these effects. The induction of apoptosis may also play some role in the growth inhibitory activity of calcitriol in some prostate cancer cells. One of the recently discovered molecular mechanisms mediating calcitriol effects in prostate cells is the inhibition of the synthesis and actions of growth-stimulatory prostaglandins, through multiple calcitriol actions including a decrease in the expression of the pro-inflammatory molecule, cyclooxygenase2 (COX-2). Moreover calcitriol has been shown to cause synergistic inhibition of prostate cell growth when combined with non-steroidal anti-inflammatory drugs (NSAIDs), suggesting that a combination of vitamin D or its analogs with NSAIDs may be useful in prostate cancer therapy. Calcitriol also induces the expression of MAP kinase phosphatase-5 in primary prostate cells leading to the inactivation of the stress kinase p38 and inhibition of interleukin-6 production. These new mechanisms of action support an antiinflammatory role for calcitriol in prostate cancer and suggest that it may have beneficial prostate cancer chemopreventive effects. The efficacy of calcitriol as a chemopreventive agent has recently been evaluated using mutant mice, that recapitulate stages of prostate carcinogenesis from the pre-cancerous lesion known as prostate intraepithelial neoplasia (PIN), to high-grade PIN, to adenocarcinoma. The findings reveal that calcitriol is beneficial at the early-stage preventing the development of high-grade PIN, providing support for its use in the chemoprevention of prostate cancer.

Calcium-Binding Proteins

Several vitamin D analogs exhibit greater antiproliferative potency than calcitriol, raising the possibility of the therapeutic potential of these drugs in the treatment of prostate cancer. Clinical trials have begun to address the utility of calcitriol or its analogs in treating prostate cancer patients. Recent studies have demonstrated that intermittent administration of very high doses of calcitriol are well tolerated by prostate cancer patients without significant toxicity or renal stones. In combination with the chemotherapy drug docetaxel, calcitriol given at extremely high doses once weekly, produced favorable effects on the time to disease progression and survival. An unanticipated benefit of the combination therapy was decreased side-effects of docetaxel. A phase III placebo-controlled randomized trial is currently under way testing the safety and efficacy of this combination in prostate cancer patients.

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4. Krishnan AV, Peehl DM, Feldman D (2005) Vitamin D and prostate cancer. In: Feldman D, Pike JW, Glorieux FH (eds) Vitamin D, 2nd ed., Vol. 2. Elsevier Academic Press, San Diego, pp 1679–1707 5. Feldman D, Pike JW, Glorieux FH (eds.) (2005) Vitamin D, 2nd ed. Elsevier Academic Press, San Diego, pp 3–1843

Calcium-Binding Proteins M EENAKSHI DWIVEDI , J OOHONG A HNN Department of Life Science, Hanyang University, Seoul, Korea

Definition Other Malignancies Calcitriol or other related vitamin D compounds have been shown to exhibit anti-cancer effects in multiple other malignancies as well. The growth inhibitory action of calcitriol on tumor cells was first demonstrated in human melanoma cells. Since then a large body of evidence has accumulated indicating the antiproliferative and pro-differentiation effects of calcitriol in melanocytes as well as malignant melanoma cells and melanoma xenografts. Evidence for a potential beneficial role of vitamin D compounds in hematologic, ovarian, pancreatic, and lung cancers has also been developed. Clinical trials employing calcitriol or vitamin D analogs are currently under way to evaluate the benefits of vitamin D therapy in chemoprevention or therapy of a number of cancer types. Note Added in Proof After this article was written the phase III trial in advanced prostate cancer patients to compare docetaxel plus calcitriol with docetaxel plus placebo was halted because of safety concerns in the clacitriol arm of the study. The details are not yet available to explain the nature of the problem.

References 1. Haussler MR, Whitfield GK, Haussler CA et al. (1998) The nuclear vitamin D receptor: biological and molecular regulatory properties revealed. J Bone Miner Res 13:325–349 2. Malloy PJ, Pike JW, Feldman D (1999) The vitamin D receptor and the syndrome of hereditary 1,25-dihydroxyvitamin D-resistant rickets. Endocr Rev 20(2):156–188 3. Nagpal S, Na S, Rathnachalam R (2005) Noncalcemic actions of vitamin D receptor ligands. Endocr Rev 26 (5):662–687

Calcium-binding proteins are ▶proteins that participate in calcium signaling pathways by binding to Ca2+. The most ubiquitous Ca2+-binding protein, found in all eukaryotic organisms including yeasts, is calmodulin. With their role in signal transduction, Ca2+-binding proteins contribute to all aspects of the cell’s functioning, from homeostasis to ▶cancer.

Characteristics Normal cell cycle division is a highly coordinated progression of molecular events that is subject to control mechanisms from both outside and inside the cell. Commitment to cell cycle initiation is made from outside and occurs as a response to extracellular signals such as growth factors. Inside the cell, control mechanisms exist to determine the timing of intracellular events such as nuclear and cytoplasmic cleavage. Under normal conditions, growth-regulating mechanisms endeavor to maintain homeostasis. Homeostasis within a cell is regulated by the balance between proliferation, growth arrest, and ▶apoptosis. Intracellular Ca2+ is an important modulator of a variety of biochemical processes associated with cell cycle progression. With few exceptions, the controls exerted by intracellular Ca2+ are transduced through sitespecific interactions with specialized Ca2+-binding proteins. There exist at least three main families of Ca2+-binding proteins. The first of these is represented by proteins that possess one or more EF-hand helix– loop–helix structural motifs predicting Ca2+-binding domains as typically found within calmodulin. The second class of Ca2+-binding proteins is known generically as annexins. A possible third family of Ca2+-binding proteins is the “calreticulin-like” group of proteins that include ▶calreticulin, Grp78, endoplasmin, and protein disulfide isomerase. Ca2+ has also been implicated in cell growth under pathological states. An

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altered cellular response to extracellular calcium ion concentration is one of the earliest changes induced in mouse epidermal cells by chemical carcinogens. However, whereas some human breast cancer cell lines and leukemia cell lines exhibit Ca2+-induced cell proliferation, other carcinoma cell lines exhibit retarded growth in the presence of Ca2+ or no sensitivity to Ca2+ at all. In a human breast cancer cell line, which is sensitive to Ca 2+, the administration of calcium channel antagonists lowered intracellular (Ca2+) and inhibited cell proliferation. A sustained physiological elevation of intracellular calcium ion concentration (Ca2+i) may be responsible for a loss of proliferative potential in neoplasmic keratinocytes. It appears from preliminary evidence that Ca2+ is not only important to cell cycling and growth in normal cells, but the abnormal regulation of Ca2+ may also contribute to changes in these processes in disease conditions like cancer.

EF-Hand Motif Calcium-Binding Proteins The ▶EF-hand protein structural motif was first discovered in the crystal structure of parvalbumin. It consists of two alpha helices positioned roughly perpendicular to one another and linked by a short loop region (usually about 12 amino acids) that often binds calcium ions. A consensus amino acid sequence for this motif has aided the identification of new members of this family that now has over 200 members. A few of these proteins are present in all cells, whereas the vast majorities are expressed in a tissue-specific fashion. Some members, like S100 family, calcineurin, calmodulin, etc. have proved to be useful therapeutic markers for a variety of cancers. Calcium-Binding Proteins. Table 1 S100 protein S100A2

S100A3

Previous name CAN19, S100L

S100E

S100 family: The S100 (“Soluble in 100% saturated solution with ammonium sulfate”) family, the largest family within the EF-hand protein, comprises at least 26 members, 19 of which (S100A1–16, profillagrin, trychohyalin, and repetin) are located in the epidermal differentiation complex situated at 1q21, while S100B, S100G, S100P, S100Z, and S100A7L2–S100A7L4 are present at other genomic locations (21q22, xp22, 4p16, 5q14, and 1q22, respectively). Their gene structure is highly conserved, in general comprising three exons and two introns, of which the first exon is noncoding. The S100 family is a remarkable group of proteins that acquired highly specialized functions during their evolution, even though they are small proteins (9–13 kDa acidic proteins) with a single functional domain. S100 proteins, which exhibit dramatic changes in the expression, are involved in tumor progression and include S100A1, S100A4, S100A6, S100A7, and S100B (11–14), whereas S100A2 has been postulated to be a tumor suppressor (Table 1). Such changes might be caused by rearrangements and deletions in chromosomal region, which are frequently observed in tumor cells. Although in most cases, the function of S100 proteins in cancer cells is still unknown, the specific expression patterns of these proteins can be used as a valuable prognostic tool. The other members of EF-hand motif Ca2+-binding family involved in cancer are calcineurin, recoverin, calretinin, oncomodulin, etc. (Table 2). Annexins and Other non-EF-Hand Motif Proteins Annexin (AnxA1) is a Ca2+-binding and acidic phospholipid binding protein with antiinflammatory properties. AnxA1 has been found in leukocytes, tissue

S100 proteins involved in cancer with characteristic features Cancer type Esophageal SCC Thyroid Oral SCC Laryngeal SCC Melanoma Skin tumors (other) NSCLC Lung SCC Gastric Lymphoma Prostate Ovarian Breast Astrocytomas

Characteristic features Function in carcinogenesis is dependent upon the context of tissue and associated tumor type as well as stage of malignancy

Marker of patient prognosis

Level of S100A3 protein expression identified pilocytic astrocytomas

Calcium-Binding Proteins Calcium-Binding Proteins. Table 1 S100 protein S100A4

Previous name CAPL, Calvasculin, MTS1, Metastasin, p9Ka, FSP1

S100 proteins involved in cancer with characteristic features (Continued) Cancer type Thyroid carcinoma NSCLC Colorectal Gastric Prostate Breast Gallbladder Bladder Pancreas Esophageal SCC Melanoma Oral SCC Meningioma

S100A5

S100D

S100A6

CABP, CACY, Calcyclin, MLN 4, Thyroid PRA, Prolactin receptorPancreas associated protein Breast Lung Melanoma Colorectal PSOR1, Psoriasin Breast Esophageal SCC Bladder SCC Melanoma Skin SCC Gastric Calgranulin A, MRP-8, MIF, NIF, Prostate P8, CFAG, CGLA, CP-10, Breast Calprotectin Esophageal SCC HNSCC Gastric Pancreas Bladder TCC Endometrial Ovarian Colorectal Calgranulin B, MRP-14, P14, Prostate Calprotectin Breast HNSCC Esophageal SCC Liver (hepatocellular) Gastric Lung Ovarian

S100A7

S100A8

S100A9

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Characteristic features Stimulate angiogenesis Overexpression is associated with many different cancer types Poor patient prognosis in breast, colorectal, NSCLC and bladder cancers

Expression can be associated with prognostic value in recurrence of meningiomas Upregulation of S100A6 appears to be an early event in progression towards pancreatic cancer

Potentially act as a predictor of clinical outcome Expression is restricted to keratinocytes and breast epithelial cells Overexpression has a role in early breast tumor progression Upregulated in PIN and in prostatic adenocarcinomas

Early involvement of the proteins in prostate cancer

Upregulated in PIN and in prostatic adenocarcinomas

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Calcium-Binding Proteins. Table 1 S100 protein

S100 proteins involved in cancer with characteristic features (Continued)

Previous name

Cancer type

S100A10 CAL1L, CLP11, GP11, p10, ANX2LG

S100A11 Calgizzarin, MLN70, S100C

S100A12 Calgranulin C, MRP6, p6, CAAF1, ENRAGE S100A14 BCMP84, S100A15, S114

NSCLC Gastric Renal cell carcinoma Lymphoma Breast Bladder Prostate Thyroid Lymphoma Gastric Colon

Characteristic features Annexin 2 protein ligand Overexpressed in human renal cell carcinoma

Downregulated at transcriptional level in malignant bladder cells Expression may be involved in tumor suppression and better prognosis

Esophageal SCC

Esophageal SCC Circulating tumor cells S100A16 S100F, DT1P1A7 Circulating tumor cells S100B S100, S100 protein (beta chain), Melanoma NEF S100P S100E, MIG9 NSCLC Pancreas Prostate Breast Colon

Cytoplasmic staining pattern in Papillary carcinomas Downregulated Used for CTC monitoring in peripheral blood

Used for CTC monitoring in peripheral blood Putative cancer biomarker Isolated from placenta Upregulation is early event in pancreatic cancer valuable marker for the prediction of clinically relevant early pancreatic lesions

SCC, squamous cell carcinoma; HNSCC, head and neck SCC; NSCLC, nonsmall cell lung carcinoma; TCC, transitional cell carcinoma; CTCC, circulating tumor cells.

Calcium-Binding Proteins. Table 2 EF-hand motif protein Recoverin Calretinin Sorcin Calcineurin B Oncomodulin/ Parvalbumin Calmodulin

Other EF-hand motif family members

Cancer type

Characteristic features

Cancer-associated retinopathy Colon adenocarcinoma and mesothelioma of epithelial type Ovarian carcinoma Squamous cell carcinoma of cervix, pancreatic cancer Carcinoma cell lines characterized by translocative activity Osteoclast apoptosis

Autoimmune response Belongs to the calbindin subgroup, autoantigen in a paraneoplastic disease Overexpression leads to paclitaxel resistance Calcineurin B subunit appears to be a significant biological response modifier due to its anticancer effects Related to motile behavior of carcinoma cells, can be a possible candidate for tumor marker Calcium ion receptor in neoplastic cells

macrophages, T-lymphocytes, and epithelial cells of the respiratory and urinary systems. Cellular functions of AnxA1 include regulation of membrane trafficking, cellular adhesion, cell signaling, and membrane fusion

in exocytosis and endocytosis. The AnxA1 protein is involved in maintaining normal breast biology. The AnxA1 gene expression may provide data about the future therapeutic plan of breast carcinomas. The

Calnexin

decreased expression of ANXA1 gene in normal histological sections of breast may warn the clinician that a malignant version of the cancer is about to form from the benign gland. This observation carries an important prognostic clinical value on microscopic reading of the surgical specimen, especially if these normal glands are adjacent to surgical margins. Similar result was reported as a prognostic factor with downregulation of AnxA1 and other Anxs in the development of the lethal prostatic carcinoma phenotype. The other major protein that belongs to this category is clusterin (CLU). CLU is a disulfide-linked heterodimeric protein associated with the clearance of cellular debris and apoptosis. In prostate, breast, and colorectal cancers, the CLU was found to have antior proapoptotic activity regulated by calcium homeostasis. Reports so far suggest “two faces” of CLU activity: the calcium-dependent cytoplasmic localization of CLU positively correlates with cell survival, whereas nuclear translocation of this protein promotes cell death in calcium-deprived cells. The cytoplasmic retention and high level of the 50-kDa CLU protect tumor cells from apoptotic stimuli induced by chemotherapeutic drugs or natural ligands, such as FasL, whereas its nuclear localization (nCLU) enhances cell apoptosis. The 50-kDa CLU isoform is mainly overexpressed in cancer cells and retained in the cytoplasm, promoting cancer progression and aggressiveness. Cytoplasmic CLU could easily translocate into the nucleus in the presence of various inducers, such as IR, chemotherapy, hormones, or cytokines, or depletion of cellular calcium. These findings support CLU as a valid therapeutic target in strategies employing novel multimodality therapy for advanced prostate cancer.

Calreticulin-like Proteins Calreticulin is a 46-kDa Ca2+-binding chaperone protein found across a diverse range of species. The human gene for calreticulin is located on chromosome 19 at locus p13.3–p13.2 and the homologous gene in the mouse maps to chromosome 8. Calreticulin at the cell surface may play a role in cell adhesion, cell–cell communication, and apoptosis. Calreticulin has also been implicated in the pathology of some cancers. The protein also plays an important role in autoimmunity and cancer. For example, it appears that calreticulin might be an excellent molecular marker for prostate cancer. The expression of calreticulin is downregulated in metastatic melanoma and ▶squamous cell carcinoma, whereas significantly upregulated in colon cancer. Further, the N-domain of the protein has been reported to have inhibitory effects on tumors and to inhibit ▶angiogenesis on endothelial cells. This observation is of great interest because the development of angiogenesis inhibitors is

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currently a highly promising approach in anticancer therapy.

References 1. Donato R (2003) Intracellular and extracellular roles of S100 proteins. Microsc Res Tech 60:540–551 2. Kretsinger RH, Tolbert D, Nakayama S et al. (1991) The EF-hand, homologs and analogs. In: Heizmann CW (ed) Novel calcium-binding proteins: fundamentals and clinical implications. Springer-Verlag, New York, pp 17–37 3. Pfyffer GE, Haemmerlit G, Heizmann CW (1984) Calcium-binding proteins in human carcinoma cell lines. Proc Natl Acad Sci USA 81:6632–6636 4. Pfyffer GE, Humbel B, Strauli P et al. (1987) Calciumbinding proteins in carcinoma, neuroblastoma and glioma cell lines. Virchows Archiv 412:135–144

Calcium-binding Reticuloplasmin of Molecular Weight 55 kDa ▶Calreticulin

CALI ▶Chromophore-Assisted Laser Inactivation

Calnexin Definition CNX is an 88-kDa type I membrane protein in the Endoplasmic Reticulum. CNX and ▶calreticulin (CRT) are ▶paralogs and both function as molecular chaperones for glycoproteins by binding through monoglucosylated N-linked oligosaccharides (Glc1Man5– 9GlcNAc2). ▶Calreticulin ▶Endoplasmic Reticulum Stress

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Calpain N EIL O. C ARRAGHER Advanced Science and Technology Laboratory, AstraZeneca R&D Charnwood, Loughborough, England, UK

Definition The calpains represent a unique class of intracellular protein degrading enzymes. This class of ▶proteases was named “calpains” to reflect their dependency upon calcium ions for proteolytic activity, and homology to the ▶papain family of cysteine proteases. In mammalian species, the calpain protein family is comprised of 15 members, of which nine are ubiquitously expressed in all tissues and the remainder are expressed in a tissuespecific manner. The ubiquitously expressed calpain 1 and calpain 2 are the most well characterized isoforms. Calpain 1 and calpain 2 function as heterodimeric enzymes composed of a large catalytic subunit (calpain 1 and calpain 2) bound to a small regulatory subunit (calpain 4). Calpain activity in vivo is tightly regulated by the ubiquitously expressed endogenous inhibitor ▶calpastatin. Calpains result in the proteolysis of a broad spectrum of cellular proteins. No unique consensus amino-acid sequence has been identified as a calpain-binding or -cleavage site, rather, it appears that calpains target substrates for cleavage by recognition of unidentified tertiary structure motifs. Another distinguishing feature of calpain proteases is their ability to confer limited cleavage of protein substrates into stable fragments, rather than complete proteolytic digestion. Thus, the calpain-calpastatin proteolytic system represents a major pathway of post-translational modification of proteins, that influences various aspects of cellular physiology. The recent application of pharmacological and molecular intervention strategies against calpain activity demonstrates a broad role for this class of proteases in the control of proliferation, ▶migration and ▶apoptosis in most cell types.

Characteristics Cell proliferation, migration and apoptosis are key processes that have to be tightly regulated in order to maintain optimal tissue homeostasis, required for development and viability of multicellular organisms. Deregulation of any of these cellular processes will ultimately result in pathological outcomes, such as cancer. A number of studies have identified a correlative link between modulation of calpain gene expression and/or activity with cancer development and progression in vivo. For example, in human renal cell carcinomas, significantly higher levels of calpain 1

expression are found in tumors that metastasized to peripheral lymph nodes relative to tumors that had not metastasized. In addition, elevated calpain activity was detected in breast cancer tissues relative to normal breast tissues and was determined to be greater in estrogen receptor (▶ER)-positive tumors than ER negative tumors. Calpain-mediated proteolysis of the tumor suppressor protein neurofibromatosis type 2 (NF2 or ▶Merlin) is associated with the development of schwannomas and menigiomas. Experimental studies performed in vitro demonstrate that total cellular calpain activity is elevated upon transformation induced by the v-src, v-jun, v-myc, k-ras and v-fos oncogenes. Furthermore, calpain activity is necessary for full cellular transformation induced by such oncogenes. A number of intervention studies utilizing small molecule inhibitors or oligonucleotides that impair calpain activity have demonstrated a role for calpain during tumor cell progression in vitro and in vivo. Cell proliferation, migration and apoptosis are controlled by a plethora of regulatory proteins that participate in complex biochemical signaling cascades, of which calpain is a pivotal regulator. Thus, targeting calpain activity may represent an effective strategy for cancer prevention and/or treatment. Calpain and Cell Proliferation Studies using pharmacological inhibitors of calpain activity, overexpression of calpastatin and cells expressing depleted levels of calpain activity have all implicated calpain in the promotion of cell proliferation. Sequential progression through G1, S, G2 and M phases of the cell-cycle is required for mitosis and cell proliferation. Several studies indicate that calpain can cleave a number of cell-cycle control proteins such as ▶cyclin D, cyclin E and p27kip1 all of which regulate progression through G1 and S phase. Calpain has also been demonstrated to cleave upstream regulators of cell-cycle control proteins such as p53 and p107. Consequently, elevated calpain levels and activity in tumors may contribute to cancer cell proliferation through cleavage of cell-cycle control proteins and deregulation of normal cell cycle control. More detailed mechanistic studies also demonstrate that calpain 2 is an important downstream component of many growth factor receptor and non-receptor tyrosine kinase signaling pathways that include signaling kinases such as, epidermal growth factor receptor (▶EGFr), platelet derived growth factor receptor (▶PDGFr), Src and ▶focal adhesion kinase (▶FAK). Such signaling molecules play an important role in transmitting extracellular signals to intracellular mediators that control cell proliferation, and are often constitutively activated in cancer cells. Activation of receptor and non-receptor kinases subsequently leads to activation of the Ras/▶MAPK pathway, which results in

Calpain

▶ERK-mediated phosphorylation of calpain 2 on a serine residue (Ser 50). Phosphorylation of calpain 2 on Ser 50 initiates a conformational switch culminating in enhanced proteolytic activity. This evidence, together with pharmacological and molecular intervention studies targeting calpain activity, suggests that activation of calpain, in part, mediates growth factor receptor and non-receptor induced cell proliferation and migration of cancer cells. Calpain and Cell Migration The interaction between cell surface adhesion receptors known as ▶integrins and their ▶extracellular matrix substrates controls the migration of all cells. Integrinlinked ▶focal adhesions are large complexes of structural and signaling proteins that provide both a structural and biochemical link between the extracellular environment and intracellular proteins. Dynamic spatial and temporal regulation of focal adhesion assembly and disassembly is required for optimal cell motility. Several studies indicate that calpains localize to integrinassociated adhesions. Furthermore, many of the protein components of focal adhesions are known substrates of calpain. Calpain-mediated cleavage of the focal adhesion components, FAK, paxillin, talin and possibly others promotes the disassembly of these complexes, contributing to reduced cell adhesion and increased migration. In fact calpain-mediated cleavage of talin has been reported to represent the rate-limiting step in adhesion turnover. In addition to mediating focal adhesion turnover, emerging evidence suggests a role for calpain in regulating components of the actin cytoskeleton involved in cell spreading and membrane protrusion, mechanisms that are also essential for persistent and directed cell migration. It is likely that calpain cleavage of actin-binding and -regulatory proteins such as, ezrin, rhoA and cortactin influences the dynamic formation and retraction of membrane structures known as ▶filipodia and ▶lamellipodia thereby influencing cancer cell migration and ▶invasion. Pharmacological and molecular inhibition of calpain activity has been shown to impair cancer cell migration across experimental two-dimensional substrates and invasion into threedimensional extracellular matrix substrates in vitro. Furthermore, a recent intervention study demonstrates that antisense-mediated suppression of calpain 2 gene expression reduced the invasion of prostate cancer cells both in vitro and in a mouse model in vivo. Thus, evidence strongly indicates that calpain activity contributes to the invasion and ▶metastasis of cancer cells. Calpain and Apoptosis Apoptosis is defined as the process of programmed cell death. Apoptosis often follows activation of the caspase family of cysteine proteases, which degrade numerous proteins that are essential for cell viability. Regulated

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apoptosis is critical for the development of multicellular organisms and also restricts the growth and spread of malignant cancer cells. Conflicting roles for calpain activity in the promotion and suppression of cell apoptosis have been proposed. Calpain activity has previously been shown to play a pro-apoptotic role through the activation of caspase 3 and caspase 12 and cleavage of Bax and ▶Bid proteins to their pro-apoptotic forms. Enhanced calpain activity has also been implicated as the major proteolytic pathway resulting in breakdown of essential proteins during caspase-independent mechanisms of apoptosis. Conversely, calpain-mediated cleavage of caspase 7 and caspase 9 has been found to suppress their activity and subsequent apoptosis. In addition, calpain-mediated cleavage of IκBα can lead to activation of the NFκB transcription factor resulting in subsequent expression of anti-apoptotic survival proteins. Many chemotherapeutic agents such as cisplatin induce their tumoricidal effect via inducing apoptosis of cancer cells. Tumor cell resistance to cisplatin-induced apoptosis is a common feature frequently encountered during chemotherapy of cancer patients. Inhibition of calpain activity has been shown to sensitize resistant tumor cells to cisplatin-induced death, whereas other studies suggest that calpain potentiates cisplatin induced cell death. Thus, the role of calpain during cell apoptosis is context dependent and determined by cell type, the apoptotic stimuli and status of intrinsic regulators of cell apoptosis. In contrast to the aforementioned studies suggesting a pro-tumorigenic role for calpain activity, an antitumorigenic role is also supported by studies indicating that calpain degrades a number of oncogene-generated protein products such as PDGFr, EGFr, c-Jun, c-Fos, c-Src, and c-Mos. Also, calpain-mediated cleavage of protein kinase C (▶PKC), a downstream effecter for tumor promoting phorbal esters, inhibits malignant transformation. Furthermore, specifically calpain 9 (nCL-4) activity contributes to the suppression of cell transformation in vitro and gastric tumors in vivo. Although the calpain 9 substrates that mediate this antitumor effect remain to be determined. A substantial body of evidence has accumulated demonstrating that activity of the calpain family of proteases plays a broad and important role in the physiology of both normal and cancer cells. Further investigation into the complex and multifaceted role of calpain in cancer may lead to the discovery of novel therapeutic approaches targeting calpain activity that may impact on the development, progression and prevention of cancer.

References 1. Goll DE, Thompson VF, Li H et al. (2003) The calpain system. Physiol Rev 83:731–801

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2. Carragher NO, Frame MC (2002) Calpain: a role in cell transformation and migration. Int J Biochem Cell Biol 34:1539–1543 3. Franco SJ, Huttenlocher A (2005) Regulating cell migration: calpains make the cut. J Cell Sci 118(17):3829–3838

Calpastatin Definition Is an endogenous protease inhibitor that acts specifically on calpain. It consists of four repetitive sequences of 120–140 amino acid residues (domains I, II, III and IV), and an N-terminal non-homologous sequence (L). ▶Calpains

Calreticulin Definition Is the molecular chaperone that binds initially to ▶MHC class I, MHC class II, and other proteins that contain immunoglobulin-like domains, such as the T-cell and B-cell antigen receptors. ▶Sjögren Syndrome ▶Molecular Chaperones

Calreticulin YOSHITO I HARA Department of Biochemistry, School of Medicine, Wakayama Medical University, Wakayama, Japan

Synonyms CRP55; calcium-binding reticuloplasmin of molecular weight 55 kDa; Calsequestrin-like protein; CaBP3; ERp60; HACBP; high affinity Ca2+ -binding protein; Reticulin; CRT

Definition

Calreticulin (CRT) is a Ca2+ -binding multifunctional ▶molecular chaperone in the endoplasmic reticulum

(ER). CRT is a 46-kDa soluble protein with a cleavable N-terminal amino acid signal sequence and the C-terminal sequence Lys-Asp-Glu-Leu (KDEL), a retrieval signal in the ER. ▶Calnexin (CNX), a membrane-binding paralog of CRT, shares the ▶chaperone function in the ER. CRT is expressed in a variety of tissues and organs, but its levels are particularly high in the pancreas, liver, and testis. It is also a highly conserved protein with over 90% amino acid identity in mammals including humans, rabbits, rats and mice. The CRT gene has been mapped to human chromosome 19 at p13.2, and its expression is upregulated by ER stress such as unfolded protein responses and deprivation of Ca2+ in the ER.

Characteristics Structure of CRT Based on structural and functional studies, CRT can be divided into three distinct domains; N-terminal [N], proline-rich [P], and C-terminal [C]. The prolinerich P-domain shows a characteristic structure with an extended and curved arm connected to a globular N-domain. The N-terminal region encompassing the N and P-domains of CRT interacts with misfolded proteins and glycoproteins, binds ATP, Zn2+, and Ca2+ with high affinity and low capacity, and is likely to be involved in the chaperone function of the protein. The C-domain binds Ca2+ with high capacity and plays a role in the storage of Ca2+ in the ER in vivo, though no structural information is available at present (Fig. 1). Functions of CRT in the Cell CRT is involved in a number of biological processes including the regulation of glycoprotein folding, Ca2+ homeostasis and intracellular signaling, cell adhesion, gene expression, and nuclear transport (Fig. 2). CRT, a Lectin-like Molecular Chaperone in the ER A molecular chaperone function of CRT has been reported for several protein substrates. In the biosynthesis of glycoproteins bearing ▶N-linked glycans in the ER, the oligosaccharide Glc3Man9GlcNAc2 (Glc, glucose; Man, mannose; GlcNAc, N-acetylglucosamine) is attached to the Asn residue contained in the consensus sequence Asn-X-Ser/Thr, of newly synthesized polypeptides. CRT or CNX binds the Glc1Man5– 9GlcNAc in glycoproteins after the processing of sugar chains. The N-domain of CRT and CNX is speculated to be the oligosaccharide-binding site (▶lectin site). If the glycoprotein is completely folded in the ER, the terminal glucose is removed by glucosidase-II and the glycoprotein is released from the CNX/CRT chaperone cycle. However, if the glycoprotein is not properly folded, the terminal glucose is once again attached by

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Calreticulin. Figure 1 Schematic structure of calreticulin.

Calreticulin. Figure 2 Functions of calreticulin in the cell. CRT is involved in a variety of cellular processes including the quality control of glycoprotein synthesis in the ER, Ca2+ homeostasis, intracellular signaling, gene expression, and nuclear transport. In cancer cells, the altered expression of CRT may lead to alterations in cellular characteristics, such as growth, adhesion, motility, immune responses, and susceptibility to apoptosis. Furthermore, extracellular CRT fragments (i.e., vasostatin) elicit antiangiogenic or tumor-suppressing activities.

the action of UDP-Glc: glycoprotein glucosyltransferase, which discriminates between folded and unfolded substrates. Together, CRT and CNX form a specific chaperone cycle for the biosynthesis of glycoproteins in the ER. Because of the preference of CNX/CRT for oligosaccharides as substrates, CNX and CRT are called “lectin-like chaperones.” CRT and CNX function with the help of other chaperones such as ▶ERp57 and ▶BiP/GRp78. The binding site for ERp57 has been identified in the P-domain of CRT or CNX. As a chaperone, CRT plays an important role in the formation of major histo-compatibility complex (▶MHC) class I to aid in antigen presentation.

CRT, a Regulator of Ca2+ Homeostasis in the ER The ER is the main reservoir of intracellular Ca2+ and plays an important role in Ca2+ homeostasis. CRT has two Ca2+ -binding sites and this characteristic contributes to the function of the ER as a Ca2+ reservoir. Ca2+ is released from the ER by receptors for inositol-1,4,5-trisphosphate (IP3) and ryanodine, and taken up into the ER by sarcoplasmic and endoplasmic reticulum Ca2+ -ATPase (SERCA). With respect to the regulation of the Ca2+ level, the involvement of CRT and SERCA2b or the IP3receptor has been reported. Furthermore, the storeoperated release of Ca2+ from the ER was shown to be suppressed by overexpression of CRT protein. These

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findings indicate that CRT is not only a reservoir of Ca2+ but also a regulator of Ca2+ -homeostasis in the ER.

Other Miscellaneous Functions of CRT In and Out of the ER CRT is involved in cell ▶adhesion by affecting integrinrelated cell signaling. In CRT-deficient embryonic stem cells, integrin-mediated Ca2+ influx was impaired leading to a decrease in cell adhesion to fibronectin and laminin. It is still not clear whether CRT affects integrin directly or indirectly to regulate cell adhesion signaling. Cell surface expression of CRT has also been reported in various cell types, and may be related with cell adhesion and ▶migration. The cell surface CRT may modulate cell adhesion by binding with extracellular matrix proteins, such as ▶fibrinogen, ▶laminin, and ▶thrombospondin. Furthermore, extracellular CRT is implicated in the pathological processes of autoimmune diseases. ▶Autoantibodies against CRT were found in 40% of patients with systemic lupus erythematosus, patients with secondary Sjogrens syndrome, rheumatoid arthritis, celiac disease, complete congenital heart block, and halothane hepatitis. CRT is known to bind to complement, C1q, and compete with antibodies for binding to C1q and inhibition of C1q-dependent hemolysis. In autoimmune diseases, impairment of the classical pathway of compliment causes a failure to clear immune complex, resulting in progression of the disease. Therefore, extracellular CRT may contribute to the progression of autoimmune diseases by preventing the clearance of immune complex. Furthermore, it has been reported that cellsurface CRT is involved in the mechanism for clearance of viable or apoptotic cells through the trans-activation of LDL-receptor-related protein (LRP) on phagocytes. However, it is still controversial whether CRT is exported from necrotic cells or apoptotic cells under pathologic conditions. Cytosolic CRT functions as an export factor for multiple nuclear hormone receptors, such as steroid hormone, non-steroid hormone, and orphan receptors. This function is consistent with previous findings that CRT suppresses the transactivation of nuclear hormone receptors including ▶androgen receptor and vitamin D. However, the mechanisms by which CRT molecules are transported into, and retained in, the cytosol/nucleus are not fully defined.

CRT and Development CRT is essential for cardiac and neural development in mice. CRT-deficient embryonic cells showed an impaired nuclear import of nuclear factor of activated T cell (NF-AT3), a transcription factor, indicating that CRT functions in cardiac development as a component

of the Ca2+/▶calcineurin/NF-AT/GATA-4 transcription pathway. Actually, cardiac-specific expression of calcineurin reversed the embryonic lethality of CRTdeficient mouse. CRT transgenic mice suffer a complete heart block and sudden death, and CRT-dependent cardiac block involves an impairment of both the L-type Ca2+ channel and gap junction ▶connexins (Cx40 and Cx43). Phosphorylated Cx43 was also decreased in CRT transgenic heart, suggesting that the functions of protein kinases are altered via the regulation of Ca2+ homeostasis. Collectively, CRT plays a vital role in cardiac differentiation and function, though how has not been fully clarified. CRT and Cancer Expression of CRT in Cancer In terms of the relationship between CRT and cancer, proteomic analysis has revealed a new functional role of CRT in the early diagnosis of cancers. CRT is proposed to be a new tumor marker of bladder cancer. In addition, it was reported that the expression of CRT is up-regulated in a variety of malignant cells or tissues including progressive fibrosarcoma cells, colorectal cancer cells, and pituitary adenomas. Furthermore, autoantibodies to CRT isoforms have utility for the early diagnosis of pancreatic cancer. These reactions are not indicative of malignant properties of CRT, but rather are markers of immunogenicity and anticancer responses. On the other hand, another report demonstrated that CRT is over-expressed in the nuclear matrix in ▶hepatocellular carcinoma, compared with normal liver tissue, suggesting a relationship between overexpressed CRT and malignant transformation. In contrast, it was also reported that CRT expression correlates with the differentiation of ▶neuroblastomas to predict favorable patient survival. Pathophysiological Relevance of CRT in Malignant Disease Susceptibility to ▶apoptosis is important in terms of cancer treatments including the use of antibiotics and irradiation. In embryonic fibroblasts from CRT knockout mice, susceptibility to apoptosis was significantly suppressed, indicating that CRT functions in the regulation of apoptosis. Furthermore, it was found that overexpression of CRT modulates the ▶radiation sensitivity of human glioma U251MG cells by suppressing ▶Akt/protein kinase B signaling for cell survival via alterations of cellular Ca2+ homeostasis. These findings suggest that the expression level of CRT is well correlated with the susceptibility to apoptosis. In contrast, overexpression of CRT provides resistance to oxidant-induced cells death in renal epithelial LLC-PK1 cells. The function of CRT in the regulation of apoptosis may differ in specific cell types, and is still controversial.

cAMP

As for cell adhesion, it was reported that CRT expression modulates cell adhesion by coordinating upregulation of N-cadherin and vinculin. Recently, it has been reported that overexpression of CRT induces ▶epithelial-mesenchymal transition (EMT)-like morphological changes and enhances cellular invasiveness in renal epithelial MDCK cells. The enhanced invasiveness mediated through ▶E-cadherin gene repression was regulated by the gene repressor, ▶Slug, via altered Ca2+ homeostasis caused by overexpression of CRT in MDCK cells. This study suggests that expression of CRT may play some causative role in the gain of invasiveness during the process of malignant transformation. In addition, it has been reported that cellular migration and binding to collagen type V are apparently suppressed in embryonic fibroblasts from CRT knock-out mice, indicating that the cellular level of CRT is important for the regulation of cell motility. Furthermore, CRT protein binds to GCN repeats in mRNA of the myeloid transcription factor ▶CCAAT/ enhancer-binding protein α (CEBPA), and thereby impedes translation of the CEBPA mRNA, suggesting that CRT plays a functional role in the differentiation block in ▶acute myeloid leukemia through suppression of CEBPA by the leukemic ▶fusion gene AML1-MDS1-EVl1. Together, these findings suggest that CRT is involved in the regulation of cancer characteristics, although the overall mechanisms are still not clear.

CRT as a Tool for Cancer Therapy CRT can form complexes with peptides in vitro to elicit peptide-specific CD8+ ▶T cell responses. In addition, peptide-bound CRT purified from tumor extracts elicits an antitumor effect specific to the source tumor. Antigen-specific cancer immunotherapy is an attractive approach to the eradication of systemic tumors at multiple sites in the body. It has been reported that vaccination with DNA encoding chimera for CRT and a tumor antigen, ▶human papilloma virus type-16 (HPV16) E7 [CRT/E7], resulted in a significant reduction in the number of lung tumor nodules in immunocompromised mice. All together, the use of CRT represents a feasible approach for enhancing tumor-specific T cellmediated immune responses. Therapeutic agents that target the tumor vasculature may prevent or delay tumor growth and even promote tumor regression or dormancy. As another approach to cancer therapy, CRT or a fragment thereof (amino acids 1–180) (i.e., ▶vasostatin) inhibits ▶angiogenesis and suppresses tumor growth. The combination of vasostatin and IL-12 as well as vasostatin and interferoninducible protein-10 had a suppressing effect on the cell growth of Burkitt lymphoma and colon carcinoma in

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mouse metastasis models. Although this suggests some potential for use in cancer therapy, the molecular mechanism of CRT actions at the cell surface is not fully understood.

C References 1. Eggleton P, Michalak M (2003) Introduction to calreticulin. In: Eggleton P, Michalak M, (eds) Calreticulin, 2nd edn. Landes Biosciences/Eurekah.com, Georgetown, TX, or Kluwer Academic/Plenum Publishers, New York, NY, pp 1–8 2. Gelebart P, Opas M, Michalak M (2005) Calreticulin, a Ca2+ -binding chaperone of the endoplasmic reticulum. Int J Biochem Cell Biol 37:260–266 3. Johnson S, Michalak M, Opas M et al. (2001) The ins and outs of calreticulin: from the ER lumen to the extracellular space. Trends Cell Biol 11:122–129 4. Michalak M, Corbett EF, Mesaeli N et al. (1999) Calreticulin: one protein, one gene, many functions. Biochem J 344:281–292 5. Williams DB (2006) Beyond lectins: the calnexin/ calreticulin chaperone system of the endoplasmic reticulum. J Cell Sci 119:615–623

Calsequestrin-like Protein ▶Calreticulin

CAM Definition Complementary alternative medicines are popular all over the world. The general concept that natural products are harmless by definition should be changed into a more realistic and responsible attitude.

cAMP Definition Cyclic adenosine monophosphate, second messenger induced in cells treated with various peptide hormones. ▶Suppressors of Cytokine Signaling

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cAMP Response Element Binding Protein (CREB)

cAMP Response Element Binding Protein (CREB)

CAMTA1 K AI -O LIVER H ENRICH , F RANK W ESTERMANN

Definition A transcription factor that is activated by serine phosphorylation triggered by increased intracellular levels of cAMP or calcium. ▶Signal Transduction

Campath-1H Definition A chimeric anti-CD52 monoclonal antibody regimen that has been successfully used for the treatment of refractory ▶Chronic Lymphocytic Leukemia. ▶Mcl Family

Camptothecin Definition Is a plant alkaloid isolated from Camptotheca acuminata (family Nyssaceae) with cytotoxic potential. Various (semi-)synthetic and water-soluble anticancer drugs, including 9-aminocamptothecin and 9-nitrocamptothecin, diflomotecan, topotecan, lurtotecan, and the prodrug ▶irinotecan have been derived from camptothecin. ▶Irinotecan ▶Membrane Transporters ▶Topoisomerases

CAMs ▶Cell Adhesion Molecules

DKFZ, German Cancer Research Center, Heidelberg, Germany

Definition

CAMTA1 is a candidate ▶tumor suppressor gene encoding a member of a protein family designated as calmodulin-binding transcription activators (CAMTAs). It resides within a distal portion of chromosomal arm 1p that is frequently deleted in a wide range of human malignancies.

Characteristics CAMTA1 maps to 1p36.31-p36.23 and its 23 exons are spread over 982.5 kb. The 6,582 bp cDNA encodes a protein of 1,673 amino acids. The protein’s primary structure contains a nuclear localization signal, two DNA-binding domains (CG-1 and TIG), a transcription activation domain, calmodulin binding motifs (IQ motifs), and ankyrin domains. Although the expression of CAMTA1 is seen in various organs, highest levels are found in neuronal tissues. Information on the physiologic roles of CAMTAs is scarce and most data derive from plant and drosophila studies. CAMTAs are transcription factors that typically bind to CGCG boxes via their CG-1 domain. An alternative mechanism of transcriptional activation has been described for CAMTA2, the second human CAMTA homolog. It acts as a coactivator of another transcription factor, Nkx2-5, to stimulate gene expression. This function is inhibited by binding of class II ▶histone deacetylases to the ankyrin-repeat region of CAMTA2. Upstream signaling components can activate CAMTA2 by promoting the export of class II histone deacetylases to the cytoplasm, relieving their repressive influence on CAMTA2. The sole fly homolog of CAMTA1 induces the expression of an ▶F-box gene, the product of which inhibits a Ca2+-stimulating ▶G-protein-coupled receptor (GPCR). The controlled deactivation of Ca2+-stimulating GPCRs is needed to tune Ca2+-mediated signaling and prevent abnormal cell proliferation. As CAMTA activity is increased by the Ca2+-sensor calmodulin, the Ca2+/ calmodulin/CAMTA/F-box protein pathway may mediate a negative feedback loop controlling the activity of Ca2+-stimulating GPCRs. This regulatory loop is of special interest taking into account the fundamental links between GPCR-mediated pathways and cancer biology. Clinical Relevance Deletions within 1p occur in various types of human malignancies, ranging from virtually all types of

Cancer

solid cancers to leukemias and myeloproliferative disorders. Functional evidence for a role of 1p in tumor suppression derives from experiments in which the introduction of 1p chromosomal material into ▶neuroblastoma cells resulted in reduced tumorigenicity. In neuroblastoma and other cancers, deletion of 1p36 is a predictor of poor patient outcome. Therefore, it is widely assumed that distal 1p harbors a gene (or genes) with tumor suppressive properties. To define the DNA, deleted from 1p, more precisely in pursuit of identifying the gene(s) of interest, substantial mapping efforts have been undertaken with the most detailed picture being worked out for neuroblastoma. In this tumor entity, the combination of ▶loss of heterozygosity (LOH) fine mapping studies allowed to considerably narrow down a smallest region of consistent deletion spanning only 261 kb at 1p36.3 and pinpointing the CAMTA1 locus. Sequence analysis revealed no evidence for somatic mutations in the remaining CAMTA1 copy of neuroblastomas with 1p deletion. However, a rare sequence variant leading to amino acid substitution within the ankyrin domain was seen in a subgroup of neuroblastomas. More importantly, low CAMTA1 expression is significantly associated with markers of unfavorable tumor biology and is itself a marker of poor neuroblastoma patient outcome. Moreover, CAMTA1 expression is a neuroblastoma predictor variable that is independent of the established molecular markers including 1p deletion. Thus, the measurement of this variable should allow an additional biological stratification of neuroblastomas and help to assign patients to the appropriate therapy. Additional evidence for a role of CAMTA1 in tumor development comes from ▶glioma and ▶colon cancer in which 1p is frequently deleted. In glioma, a 1p minimal deleted region spans 150 kb and resides entirely within CAMTA1. In colorectal cancer, a genome-wide analysis of genomic alterations revealed that loss of a 2 Mb recurrently deleted genomic region encompassing CAMTA1 has the strongest impact on survival when compared with other genomic changes. Furthermore, as in neuroblastoma, low expression of CAMTA1 is an independent marker of poor patient outcome. The high prevalence of CAMTA1 deletion in neuroblastoma, glioma, and colorectal cancer together with the independent predictive power of low CAMTA1 expression for neuroblastoma and colorectal cancer outcome are consistent with the idea that low CAMTA1 levels mediate a selective advantage for developing tumor cells.

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as a candidate tumor suppressor gene. Clin Cancer Res 11(3):1119–1128 Bouche N, Scharlat A, Snedden W et al. (2002) A novel family of calmodulin-binding transcription activators in multicellular organisms. J Biol Chem 277 (24):21851–21861 Henrich KO, Claas A, Praml C et al. (2007) Allelic variants of CAMTA1 and FLJ10737 within a commonly deleted region at 1p36 in neuroblastoma. Eur J Cancer 43 (3):607–616 Henrich KO, Fischer M, Mertens D et al. (2006) Reduced expression of CAMTA1 correlates with adverse outcome in neuroblastoma patients. Clin Cancer Res 12(1):131–138 Kim MY, Yim SH, Kwon MS et al. (2006) Recurrent genomic alterations with impact on survival in colorectal cancer identified by genome-wide array comparative genomic hybridization. Gastroenterology 131(6): 1913–1924

Canale-Smith Syndrome Definition

▶Autoimmune Lymphoproliferative Syndrome

Canals of Hering Definition Hepatocytes secrete bile into bile canaliculi which in turn drain into the canals of Hering – small ductules lined in part by cholangiocytes and in part by hepatocytes. ▶Cholangiocarcinoma

Cancer M ANFRED S CHWAB DKFZ, Tumour Genetics, Heidelberg, Germany

References 1. Barbashina V, Salazar P, Holland EC et al. (2005) Allelic losses at 1p36 and 19q13 in gliomas: correlation with histologic classification, definition of a 150-kb minimal deleted region on 1p36, and evaluation of CAMTA1

Definition Cancer is a deregulated multiplication of cells with the consequence of an abnormal increase of the cell number in particular organs. Initial stages of the developing

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Cancer

cancer are usually confined to the organ of origin whereas advanced cancers grow beyond the tissue of origin. Advanced cancers invade the surrounding tissues that are initially connected to the primary cancer. At a later stage, they are distributed via the hematopoetic and lymphatic systems throughout the body where they can colonize in distant tissues and form ▶metastasis. The development of cancers is thought to result from the damage of the cellular genome, either due to random endogenous mechanisms or caused by environmental influences. The origin of cancers can be traced back to alterations of cellular genes. Genetic damage can be of different sorts: . Recessive mutations in ▶tumor suppressor genes . Dominant mutations of ▶oncogenes . Loss-of-function mutations in genes, involved in maintaining genomic stability and ▶repair of DNA (resulting in ▶genomic instability) History Human cancer is probably as old as the human race. It is obvious that cancer did not suddenly start appearing after modernization or industrial revolution. The world’s oldest documented case of cancer comes from ancient Egypt, in 1500 BC. The details were recorded on a papyrus, documenting eight cases of tumors occurring on the breast. It was treated by cauterization, a method to destroy tissue with a hot instrument called “the fire drill.” It was also recorded that there was no treatment for the disease, only palliative treatment. The word cancer came from the father of medicine, Hippocrates, a Greek physician (460–370 BC). Hippocrates used the Greek words, carcinos and carcinoma to describe tumors, thus calling cancer “karkinos.” The Greek terms actually were words to describe a crab, which Hippocrates thought a tumor resembled. Hippocrates believed that the body was composed of four fluids: blood, phlegm, yellow bile and black bile. He believed that an excess of black bile in any given site in the body caused cancer. This was the general thought of the cause of cancer for the next 1,400 years. Autopsies done by Harvey in 1628 paved the way to learning more about human anatomy and physiology. By about the same time period, Gaspare Aselli discovered the lymphatic system, and this led to the end of the old theory of black bile as the cause of cancer. The new theory suggested that abnormalities in the lymph and lymphatic system as the primary cause of cancer. The lymph theory replaced Hippocrates’ black bile theory on the cause of cancer. The discovery of the lymph system gave new insight to what may cause cancer, it was believed that abnormalities in the lymphatic system was the cause. Other theories surfaced, such as cancer being caused by trauma, or by parasites, and it was thought that cancer

may spread “like a liquid” (Bentekoe, 1687; Heinrich Vierling, personal communication). The belief that cancer was composed of fermenting and degenerating lymph fluid was predominant. The discovery of the microscope by Leeuwenhoek in the late seventeenth century added momentum to the quest for the cause of cancer. By late nineteenth century, with the development of better microscopes to study cancer tissues, scientists gained more knowledge about the cancer process. It wasn’t until the late nineteenth century that Rudolph Virchow, the founder of cellular pathology, recognized that cells, even cancerous cells, derived from other cells. The early twentieth century saw great progress in our understanding of microscopic structure and functioning of the living cells. Researchers pursued different theories to the origin of cancer, subjecting their hypotheses to systematic research and experimentation. John Hill first recognized an environmental cause from the dangers of tobacco use in 1761 and published a book “Cautions Against the Immoderate Use of Snuff.” Percivall Pott of London in 1775 described an occupational cancer of the scrotum in chimney sweeps caused by soot collecting under their scrotum. This led to identification of a number of occupational carcinogenic exposures and public health measures to reduce cancer risk. This was the beginning of understanding that there may be an environmental cause to certain cancers. A virus causing cancer in chickens was identified in 1911 (Rous sarcoma virus). Existence of many chemical and physical carcinogens were conclusively identified during later part of the twentieth century. The later part of the twentieth century showed tremendous improvement in our understanding of the cellular mechanisms related to cell growth and division. The identification of ▶transduction of oncogenes with the discovery of the ▶SRC gene, the transforming gene of Rous sarcoma virus, led to formulating the oncogene concept of tumorigenesis and can be viewed as the birth of modern molecular understanding of cancer development. Subsequently, tumor suppressor genes were identified. Many genes that suppress or activate the cell growth and division are known to date, their number is ever growing. It is conceivable that in the end the confusing situation may arise to recognize that all genes of the human genome, in one way or another, take part in signaling normal or cancerous cellular growth.

Characteristics A large proportion of genetic changes appears to arise by mechanisms endogenous to the cell, such as by errors occurring during the replication of the ~3 × 109 base pairs present in the human genome. Environmental factors have a major role as well, predominantly as:

Cancer

. Chemical carcinogens (e.g. aflatoxin B1 in liver cancer (▶liver cancer, molecular biology), tobacco smoke in lung cancer; ▶tobacco carcinogenesis) . Radiation . Viruses (such as ▶hepatitis B virus (▶Hepatitis viruses) in liver cancer, or ▶human papillomavirus in cervical cancer) Types of Genetic Damage Damage to oncogenes and tumor suppressor genes can be of different sorts: . Point mutations resulting in the activation of a latent oncogenic potential of a cellular gene (e.g. ▶RAS) or in the functional inactivation of a tumor suppressor gene by generating an intragenic stop codon that leads to premature translation termination with the consequence of an incomplete truncated protein (e.g. ▶p53) or the failure for maintaining genomic stability (▶mismatch repair genes in ▶HNPCC) . ▶Amplification leading to an increase of the gene copy number beyond the two alleles normally present in the cell (copy number can reach 500 and more; example: ▶MYCN in human ▶neuroblastoma) . Translocation, which is defined as an illegitimate recombination between non-homologous chromosomes, the result being either a fusion protein (where recombination occurs between two different genes such as BCR-ABL in Chronic Myclogenous Leukemia) or in the disruption of normal gene regulation (where the regulatory region of a cellular gene is perturbed by the introduction of the distant genetic material such as ▶MYC in Burkitt lymphoma (▶Epstein-Barr virus)) . Viral insertion by the integration of viral DNA into the regulatory region of a cellular gene. This integration can occur after a virus has infected a cell. Viral insertion is well documented in animal tumors (HBV integration in the vicinity of ▶MYCN in liver cancer in experimental animals; liver cancer, molecular biology) Cellular Aspects Cancer in solid tissues (solid cancer) usually develops over long periods (often 20–30 years latency period) of time. An exception are solid cancers (such as neuroblastoma) in children, which often are diagnosed shortly after birth. Malignant cancers are characterized by their ability to develop metastasis (i.e. secondary cancers at distance from the primary tumor), often they also show multidrug resistance, which means that they hardly react to conventional chemotherapy. It is thought that the development of a normal cell to a metastatic cell is a continuous process driven by genetic damage and genomic instability, with the progressive selection of cells that have acquired a selective advantage within the particular tissue environment

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(▶multistep development). Studies of colorectal cancers have identified 6–7 genetic events required for the conversion of a normal cell to a cell with metastatic ability. This is in contrast to leukemias, which usually require one genetic event, most often a translocation, for disease development. Sporadic Versus Familial Cancer The vast majority of cancers are “sporadic,” which simply means that they develop in an individual. Descendants of this individual do not have an increased risk because the cellular changes that have resulted in cancer development are confined to this individual. In contrast, ~10% of cancer cases have a hereditary background, they show familial clustering (prominent examples include retinoblastoma (▶Retinoblastoma, ▶cancer genetics), ▶breast cancer, FAP (▶APC gene in Familial Adenomatous Polyposis) and HNPCC as familial forms of colorectal cancer (▶colon cancer), ▶melanoma). Familial cancers have been identified to result from germline mutation of genes. These germ line mutations do not always directly dictate cancer development, although they are considered “strong” hereditary determinants. They represent susceptibility genes that confer a high risk for cancer development to the gene carrier. The relative risk of the individual carrying the mutant gene can vary considerably. For instance, the risk of carriers of one of the breast cancer susceptibility genes ▶BRCA1 or ▶BRCA2 for breast cancer development can vary between approximately 60 and 90%. In reality this means that the risk for cancer development is difficult to predict, and individuals may not develop cancer at all in spite of the presence of a mutated gene in their germ line. The molecular basis for the differences in risk are unknown. Formally the activity of modifying factors, either environmental or genetic, has been suggested. Such modifying factors appear to be less important for some other familial cancers, such as retinoblastoma, where the risk is constant between 90 and 95% for gene carriers. Polygenic Determinants of Risk The relative risk of the individual for cancer development can also be determined by so called “weak” genetic factors. Normal cells contain a number of genes involved in ▶detoxification reactions. Different allelic variants of these genes exist in the human population that encode proteins with slightly different enzymatic activities. Although the exact contribution of individual allelic variants to cancer development is difficult to assess, it is reasonable to assume that individuals that have inherited “weak” enzymatic activities in different detoxification systems are likely to have a higher risk. It is likely, therefore, that the risk for such cancers is “polygenic.” ▶Toxicological Carcinogenesis

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Cancer and Cadmium

Cancer and Cadmium T IM S. N AWROT, J AN A. S TAESSEN Division of Lung Toxicology, Department of Occupational and Environmental Medicine (T.S.N.) and the Studies Coordinating Centre (J.A.S.), Division of Hypertension and Cardiovascular Rehabilitation, Department of Cardiovascular Diseases, University of Leuven, Leuven, Belgium

Definition Cadmium is a metal that has the symbol Cd and atomic number 48 in the periodic table. Cadmium has high toxic effects, an elimination half-life of 10–30 years, and accumulates in the human body, particularly the kidney. Roughly 15,000 tons of cadmium is produced worldwide each year for nickel-cadmium batteries, pigments, chemical stabilizers, metal coatings, and alloys.

Characteristics Urinary excretion of cadmium over 24 h is a biomarker of lifetime exposure. Exposure to cadmium occurs through intake of contaminated food or water, or by inhalation of tobacco smoke or polluted air. Occupational exposures can be found in industries such as electroplating, welding, smelting, pigment production, and battery manufacturing. Other exposures to cadmium can occur through inhalation of cigarette smoker. Gastrointestinal absorption of cadmium is estimated to be around 5–8%. Inhalation absorption is generally higher, ranging from 15 to 30%. Absorption after inhalation of cadmium fume, such as cigarette smoke, can be as high as 50%. Once absorbed, cadmium is highly bound to the metal-binding protein, metallothionein. Cadmium is stored mainly in the kidneys and also the liver and testes, with a half-life in the body of 10–30 years. In general, nonsmokers have urinary cadmium concentrations of 0.02–0.7 μg/g creatinine, which increase with age in parallel with the accumulation of cadmium in the kidney. Cadmium is a global environmental contaminant. Populations worldwide have a low-level intake through their food, causing an age-related cumulative increase in the body burden of this toxic metal. Environmental exposure levels to cadmium, that are substantially above the background, occur in areas with current or historical industrial contamination for instance in regions of Belgium, Sweden, UK, Japan, and China. As an environmental carcinogen, cadmium could have substantial health implications. Three lines of evidence explain why the International Agency for the Research on Cancer classified cadmium as a human carcinogen. First, as reviewed by Verougstaete and colleagues, several, albeit not all studies in workers showed a positive

association between the risk of lung cancer and occupational exposure to cadmium; discrepancies between these studies should not be ascribed to the better design of the more recent studies. Verougstraete and colleagues suggested that such inconsistencies might be attributed to the high relative risk of cancer in the presence of coexposure to ▶arsenic, nickel, or toxic fumes, and that the increasingly stringent regulations with regard to levels of exposure permissible at work might be a confounding factor (▶Lead exposure, nickel carcinogenesis). Second, data from rats showed that the pulmonary system is a target site for carcinogenesis after cadmium inhalation. However, exposure to toxic metals in animal studies have usually been much higher than those reported in environmentally exposed humans to toxic metals. Third, several studies done in vitro have shown plausible pathways, such as increased oxidative stress, modified activity of transcription factors, and inhibition of DNA repair. Most errors that arise during DNA replication can be corrected by DNA polymerase proof reading or by postreplication mismatch repair. In fact, inactivation of the DNA repair machinery is an important primary effect, because repair systems are required to deal with the constant DNA damage associated with normal cell functions. The latter mechanism might indeed be relevant for environmental exposure because Jin et al. found that chronic exposure of yeast to environmentally relevant concentrations of cadmium can result in extreme hypermutability. In this study the DNA-mismatch repair system is already inhibited by 28% at cadmium concentrations as low as 5 μM. For example, the prostate of healthy unexposed humans accumulates cadmium to concentrations of 12−28 μM and human lungs of nonsmokers accumulate cadmium to concentrations of 0.9−6 μM. Further, in vitro studies provide evidence that cadmium may act like an estrogen, forming high-affinity complexes with estrogen receptors, suggesting a positive role in breast cancer carcinogenesis. Along with this experimental evidence, two epidemiological studies in 2006 gave important positive input into the discussion on the role of exposure to environmental cadmium in the development of cancer in human beings. First, the results of a population-based case-control study noticed a significant twofold increased risk of breast cancer in women in the highest quartile of cadmium exposure compared with those in the lowest quartile. Second, we conducted a populationbased prospective cohort study with a median follow-up of 17.2 years in an area close to three zinc smelters. Cadmium concentration in soil ranged from 0.8 to 17.0 mg/kg. At baseline, geometric mean urinary cadmium excretion was 12.3 nmol/day for people in the high-exposure area, compared with 7.7 nmol/day for those in the reference (i.e, low exposure) area. The risk of lung cancer was 3.58 higher than in a reference population from an area with low exposure. 24-h urinary

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excretion is a biomarker of lifetime exposure to cadmium. The risk for lung cancer was increased by 70% for a doubling of 24-h urinary cadmium excretion. Confounding by coexposure by arsenic could not explain the observed association. Epidemiological studies did not convincingly imply cadmium as a cause of prostate cancer. Of 11 cohort studies, only 3 (33%) found a positive association. In conclusion, recent experimental and epidemiological studies strongly suggest environmental exposure to cadmium as a causal factor in the development of cancer of the lung and breast.

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cancers. Increased levels may be associated with pregnancy and lactation, benign breast or ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis. ▶Serum Biomarkers

Cancer Associated Antigen 19-9 (CA 19-9)

References 1. Verougstraete V, Lison D, Hotz P (2003) Cadmium, lung and prostate cancer: a systematic review of recent epidemiological data. J Toxicol Environ Health B Crit Rev 6(3):227–255 2. Jin YH, Clark AB, Slebos RJ et al. (2003) Cadmium is a mutagen that acts by inhibiting mismatch repair. Nat Genet 34(3):326–329 3. Jarup L, Berglund M, Elinder CG et al. (1998) Health effects of cadmium exposure – a review of the literature and a risk estimate. Scand J Work Environ Health 24 (Suppl 1):1–51 4. McElroy JA, Shafer MM, Trentham-Dietz A et al. (2006) Cadmium exposure and breast cancer risk. J Natl Cancer Inst 98(12):869–873 5. Nawrot T, Plusquin M, Hogervorst J et al. (2006) Environmental exposure to cadmium and risk of cancer: a prospective population-based study. Lancet Oncol7(2):119–126

Cancer Antigen Definition Cell surface proteins specific for cancer cells. ▶Cytokine Receptor as the Target for Immunotherapy and Immunotoxin Therapy

Definition Serum levels of CA 19-9, an intercellular adhesion molecule, was initially found in patients with colorectal cancer, and subsequently also identified in patients with pancreatic and biliary tract cancers, and less often in gastric, ovarian, lung, breast and uterine cancer. Noncancerous conditions that may elevate CA 19-9 include gallstones, cholecystitis, pancreatitis and cirrhosis of the liver. ▶Serum Biomarkers

Cancer Associated Antigen 27-29 (CA 27-29) Definition Cancer antigen 27-29 (synonym: BR 27-29) is a normal epithelial cell mucin-1 (MUC1) apical surface glycoprotein. Elevated serum levels are highly associated with breast cancer. However they can also be found in cancers of colon, stomach, kidney, lung, ovary, pancreas, uterus and liver and in a number of noncancerous conditions, including first trimester pregnancy, ▶endometriosis, ovarian cyst, benign kidney, liver and breast disease. ▶Serum Biomarkers

Cancer Antigen 15-3 (CA 15-3) Definition Carbohydrate antigen 15-3 is a tumor marker associated with breast cancer, and has much less specificity and sensitivity in patients with ovarian, lung, or prostate

Cancer of B-lymphocytes ▶B-cell Tumors

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Cancer Cachexia Syndrome (CCS)

Cancer Cachexia Syndrome (CCS) Definition Loss of weight in the form of lean body mass and fat which results from a complex interaction between cytokines and tumor factors. ▶Nutrition Status

Cancer Causes and Control G RAHAM A. C OLDITZ Washington University in St. Louis, St. Louis, MO, USA

Synonyms Etiology; Prevention

Definition The process of identifying causes of cancer and developing strategies to change cancer risk through health care providers, regulations that reduce risk, or individual and community level changes.

Characteristics Over 6 million people around the world die from cancer each year. There is overwhelming evidence that lifestyle factors impact cancer risk and that positive, populationwide changes can significantly reduce the cancer burden. Current epidemiologic evidence links behavioral factors to a variety of diseases, including the most common cancers diagnosed in the developed world – ▶lung cancer, ▶colorectal cancer, ▶prostate cancer and ▶breast cancer. These four cancers account for over 50% of all cancers diagnosed on western countries. As summarized in Fig. 1, ▶tobacco causes some 30% of cancer, lack of physical activity 5%, obesity 15%, diet 10%, ▶alcohol 5%, ▶viral infections 5%, and ▶UV light by excess sun exposure 3%. Because of the tremendous impact of modifiable factors on cancer risk, especially for the most common cancers, it has been estimated that at least 50% of cancer is preventable. Currently in the US not all risk factors are equally distributed across race and social class. Trends in risk factors should also be considered when assessing potential for prevention. To bring about dramatic reductions in cancer incidence, widespread lifestyle changes will be necessary.

Cancer Causes and Control. Figure 1 Causes of cancer.

Rose advocates the need for population approaches for prevention of chronic disease. He emphasizes that when the relation between a lifestyle factor or biological predictor of risk is continuous, the majority of cases attributable to the exposure will likely arise in those who are not classified as being at high risk. He illustrates this with examples of blood pressure and rates of coronary heart disease. Specifically, even small changes in blood pressure at the population level can translate into large reduction in the rates of coronary disease and stroke. To reduce the risk of disease in the populationsubstantial benefits can be achieved by a small reduction for all members of the society rather than just focusing on the high-risk groups. Because population wide trends in cardiovascular risk factors show continuing improvement, the rate of coronary heart disease incidence and mortality continues to decrease. When we consider population approaches to cancer prevention, we must address the etiologic process, which covers a different time course and sequence from coronary heart disease. Although cardiovascular disease is the end point of the chronic process of atherosclerosis, treatment focuses on the reversal and subsequent prevention of the acute thrombotic process of myocardial infarction. Cancer, on the other hand, is the result of a long process of accumulating DNA damage (▶multistep development), leading ultimately to clinically detectable lesions such as in situ and invasive cancer. For example, studies of the progression in ▶colon cancer from first mutation to invading malignancy suggest that DNA changes accumulate over a period of as long as 40 years. The goal of cancer prevention is to arrest this progression; different interventions interrupt carcinogenesis at different points in the process. Further, most cancers do not have a late “acute” event, analogous to thrombosis, which can be prevented with medical interventions. The benefits of cancer prevention and control programs take time to be observed. The fact that different

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interventions will impact at different points along the pathway to cancer, that can stretch over nearly half a century, has implications for when we can expect to see pay-off in terms of lower cancer rates. Research has demonstrated that those who initiate smoking during early adolescence greatly increase risk of lung cancer even when one takes into account both the dose and duration of smoking. If we could delay the age at which most adolescents first start to smoke, we would probably substantially reduce lung cancer rates, but this benefit will not be observable for 20–40 years after the intervention. Adult cessation, on the other hand, reduces risk more rapidly, but fails to address the continuing recruitment of the next generation of smokers. Recent declines in the incidence of lung cancer among younger men and women in the United States reflect reductions in the rate of smoking among younger adults. Other lifestyle interventions may act as preventive early in the DNA pathway to cancer. For example, ▶aspirin and ▶folate appear to act early in the pathway inhibiting colon cancer. Population-wide prevention strategies for cancer do work. For example, reductions in lung cancer rates in the United States mirror changes in cigarette smoking patters, with marked decreases seen first in young men, then older men, and finally in women. Introduction of the Papaniculou test for cervical cancer in the 1950s was followed by a dramatic decline in cervical cancer in those countries that made wide-spread ▶screening available. The decline in Australian ▶melanoma mortality for those born after 1950 is an additional example of effective intervention at the population level. Behavior change is possible and offers great potential for cancer prevention. The recommendations for cancer risk reduction include reducing tobacco use, increasing physical activity, maintaining a healthy weight, improving diet, limiting alcohol, avoiding excess sun exposure, utilizing safer sex practices, and obtaining routine cancer screening tests. Age is the dominant factor that drives cancer risk; for all major malignancies, risk rises markedly with age. The importance of age is exemplified by the fact that the aging U.S. population together with projected population growth will result in a doubling of the total number of cancer cases diagnosed each year by the year 2050, assuming that incidence rates remain constant. With this estimated growth in cancer from 1.3 million to 2.6 million cases per year, it is expected that that both the number and proportion of older persons with cancer will also rise dramatically. Tobacco Tobacco is the major cause of premature death around the world accounting for some 5M deaths each year. In the United States, adult smokers lose an average of 13 years of life because of smoking, and approximately

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half of all smokers die of tobacco-related disease. Smoking is well known to cause over 90% of lung cancers in addition to a range of other malignancies (▶tobacco carcinogenesis). It causes about 30% of all the cancer in the developed world, including lung cancer, ▶mouth cancer, larynx cancer, ▶esophagus cancer, ▶pancreas cancer, ▶cervix cancer, ▶kidney cancer, and ▶bladder cancer. Smoking also increased risk of cancers of the colon, stomach, cervix, liver, and prostate, as well as to leukemia. In addition, smoking leads to many other health problems, including heart disease, stroke, lung infections, emphysema, and pregnancy complications. Tobacco may act on multiple stages of carcinogenesis; it delivers a variety of carcinogens, causes irritation and inflammation, and interferes with the body’s natural protective barriers. The health risks of tobacco use are not limited to cigarette smoking. Cigar and pipe use increase the risk of disease, as does exposure to second-hand smoke and smokeless tobacco use. Avoiding initiation of tobacco use clearly offers the greatest potential for disease prevention. However, for those who use tobacco products, there are substantial health benefits that come with quitting. There are numerous effective cessation methods, and in the past 25 years, 50% of all living Americans who have ever smoked, have successfully quit. Quitting smoking has immediate and significant health benefits for men and women of all ages. For example, former smokers live longer than individuals who continue smoking. Those who quit before age 50 have approximately half the risk of dying in the next 15 years. This decline in mortality risk is measurable shortly after cessation and continues for at least 10–15 years. Strategies to assist smoking cessation and decreasing youth initiation from both a population and clinical perspective are essential steps to reducing the burden of cancer. Trends Current smoking among US adults has remained steady over the past decade. Once quite pronounced, gender disparity in smoking rates is now relatively small and has been stable since 1990. In 2002, 25.7% of men were current smokers compared to 20.8% of women. Given the profound impact of smoking on cancer, disparities in smoking rates and in access to effective cessation methods will continue to translate directly into differences in the burden of smoking-related cancers. Physical Activity Lack of physical activity causes over 2M deaths each year around the world. People in the US and in other developed nations are extremely inactive – over 60% of

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the US adult population does not participate in regular physical activity, which includes 25% of adults who are almost entirely sedentary. Fortunately, the negative effects of a sedentary lifestyle are reversible: increasing one’s level of physical activity, even after years of inactivity, can reduce mortality risk. Lack of physical activity increases the risk of colon and breast cancer and likely endometrial cancer, as well as diabetes, osteoporosis, stroke, and coronary heart disease. Overall, sedentary lifestyles have been linked to 5% of deaths from cancer. Among both men and women, high levels of physical activity may decrease the risk of colon cancer by as much as half. Using a variety of measures of activity, studies have consistently shown higher physical activity lowers risk of colon cancer. Physical activity also appears to lower the risk of large adenomatous polyps, precursor lesions for colon cancer, suggesting that it may influence the early stages of the adenoma-carcinoma sequence. In addition, the relationship between physical activity and breast and colon cancer are seen across levels of obesity, indicating that physical activity and obesity have separate or independent effects on cancer incidence. Growing evidence suggests that physical activity may also be protective against lung and prostate cancer. Several mechanisms have been proposed to explain these associations. Physical activity reduces circulating levels of insulin, a growth factor for colonic epithelial cells. Additionally, it is postulated that cancer risk is reduced through alterations in prostaglandin levels, improvement in immune function, and modification of bile acid metabolism. Potential mechanisms for the reduction of breast cancer risk include physical activity’s lowering of the cumulative lifetime exposure to circulating estrogens and improving immune pathways. The benefits of physical activity include the prevention of cancer and a large number of other chronic diseases. Increasing levels of physical activity, even after years of inactivity, reduces mortality risk. As little as 30 min of moderate physical activity (such as brisk walking) per day significantly reduces disease risk.

Trends One major determinant of activity level that has changed over time is the amount of activity required for work and daily living. With advances in technology and the development of labor-saving devices, there is now a greatly reduced need for physical activity for transportation, household tasks, and occupational requirements. Overall, the prevalence of physical inactivity in the United States is remarkably high; in 1996, about 28% of Americans reported absolutely no participation in leisure-time physical activity. In addition, physical activity in schools has declined, and almost half of

young Americans between the ages of 12–21 are not vigorously active on a routine basis. Given the trends in our society, it is unlikely that this decreasing energy expenditure will reverse rapidly. Accordingly, the burden of cancer due to lack of physical activity will increase in the years ahead unless new strategies to promote activity are rapidly implemented.

Weight Control and Obesity Prevention Overweight and obesity is increasing at epidemic rates in the United States, around the world, and is estimated to account for 2.6M deaths each year. Currently almost 65% of American adults are overweight (body mass index (BMI) ≥25 kg/m2), and over 30% are considered obese (BMI ≥ 25 kg/m2). Overweight and obesity cause a variety of cancers; colon, postmenopausal breast, endometrial, renal, and esophageal. The proportion of cancer caused by obesity ranges from 9% for postmenopausal breast cancer to 39% for endometrial cancer. One large US study suggested that obesity influences an even broader range of cancers, increasing the risk of death from cancers of the colon and rectum, prostate, breast, esophagus, liver, gallbladder, pancreas, kidney, stomach, uterus, and cervix in addition to non-Hodgkin’s lymphoma and multiple myeloma. Overall, obesity causes 14% of cancer deaths among men and 20% of cancer deaths among women. Excess body fat may act by altering levels of hormones and tumor growth factors. It is clear that excess weight has severe health consequences. In addition to raising the risk of cancer, overweight and obesity also increase the risk of a multitude of other diseases and chronic conditions, such as stroke, cardiovascular disease, type 2 diabetes, osteoarthritis, and pregnancy complications. The International Agency for Research on Cancer has proposed a comprehensive set of recommendations to address the issue of weight control at multiple levels, including steps by health care providers, regulatory approaches to create adequate access to safe places for exercise (including school, worksite, and community), and family and community level actions.

Trends In the U.S., the prevalence of overweight and obesity has increased so dramatically and so rapidly, it is frequently referred to as an obesity epidemic. The trend is also being seen among children and adolescents. This epidemic has affected people of all ages, races, ethnicities, socioeconomic levels, and geographic regions. Given limited long-term success in weight reduction programs, the cancer burden due to obesity will likely continue to follow the rising prevalence of this risk factor in the coming years.

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Dietary Improvements Fruit and vegetable intake has been most consistently evaluated as a cancer prevention strategy. The global burden of inadequate intake is estimated to account for over 2M deaths each year. While evidence for cardiovascular benefits and reduced risk of diabetes are clear, evidence for cancer risk reduction has become less convincing with the results of numerous prospective cohort studies showing weaker associations with cancer risk. Low intake of fruits and vegetables are probably related to increased risk of pancreas, bladder, lung, colon, mouth, pharynx, larynx, esophagus and stomach cancer. Although the effect of fruit and vegetable consumption on the risk of prostate cancer has been examined in nearly twenty studies, data remain inconsistent. The majority of studies suggest that overall fruit and vegetable intake has little effect if any on the risk of prostate cancer. However, individual fruits and vegetables may offer the potential for greater risk reduction, with tomatoes being the most promising, with a 40–50% reduction in risk among men who consumed large amounts of tomatoes and tomato products. The carotenoid ▶lycopene is hypothesized to be responsible for the protective effect. A number of mechanisms have been suggested to explain the protective effect of fruits and vegetables, but it is not known if specific agents, such as ▶carotenoids, folic acid, and vitamin C, or a special combination of factors create anticarcinogenic effects. It is also possible that diet in childhood and adolescence is more important than later in life in driving risk of cancer. A number of studies have found that as folate intake increases, the risk of colorectal cancer (as well as polyps) decreases. The Nurses’ Health Study found that a high intake of folate from fruits and vegetables was sufficient to lower risk but that supplementation with a multivitamin that contained folate offered even greater reductions. The underlying biologic role of folate and its interaction with the MTHFR gene add support to the causal relation between low folate and colon cancer. In addition to the reduction in risk of colon cancer, growing evidence points to folate also reducing the adverse effect of alcohol on breast cancer. Based on this evidence and the benefits for prevention of neural tube defect and cardiovascular disease, use of a daily vitamin supplement containing folate is recommended.

Fiber has been shown to reduce the risk of heart disease and diabetes, but it does not appear to offer protection against cancer. Long believed to help prevent colon cancer, the data do not support this hypothesis.

Dietary Fat Variations in international cancer rates have often been attributed to differences in total fat intake, yet evaluation has shown no clear link between dietary fat and breast, colon or prostate cancer. Although dietary fat overall does not appear to impact cancer risk, there is some evidence to suggest that certain types of fat, such as animal fat, may increase risk.

Vitamin A and Carotenoids Isolated ▶vitamin A and carotenoids are not likely to play a large role in cancer prevention. Some observational data support a probable inverse relation with lung cancer risk, but randomized trials of beta-carotene intake found either no effect or an increased risk of lung cancer. It has also been suggested that beta-carotene impacts breast cancer risk, however, it seems that at

Red Meat High intake of red meat, including beef, pork, veal and lamb is associated with an elevated risk of colorectal cancer. The mechanism of this increased risk is not well understood, but it may be related to the high concentrations of animal fat or to carcinogens such as heterocyclic amines produced when the meat is cooked at high temperatures. Calcium Higher calcium intake has been linked to a reduced risk of colorectal adenomas and colorectal cancer. However, increased dietary calcium is also associated with an increased risk of prostate cancer. Research indicates that there may be a moderate intake of calcium that provides protection against colorectal cancer risk without causing a large increase in prostate cancer risk. Excess Caloric Intake One consistent dietary finding is that excess calories from any source result in weight gain and increased cancer risk. As the obesity epidemic continues to spread, the importance of balancing caloric intake with caloric expenditure becomes even more evident for the prevention of cancer and other chronic diseases. Whole Grains Although grain products in general have not been shown to affect cancer risk, whole-grain foods may provide some protection against stomach cancer. Grains such as wheat, rice, and corn form the basis for most diets worldwide. Some grain products, such as wholewheat bread and brown rice, are consumed in the “whole-grain” form, while others, like white bread and white rice, are more refined. During the process of refining grain, most of the fiber, vitamins, and minerals are removed, thus whole-grain foods tend to be more nutrient-rich than refined foods and may offer more in terms of disease prevention. The benefits of wholegrain foods in reducing cardiovascular disease and ischemic stroke are well established.

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best, there is only a small decrease in breast cancer risk associated with a high intake of carotenoids.

drink per day for women and less than two drinks per day for men.

Selenium Ecological studies have suggested that increased ▶selenium intake is associated with decrease risk of colon and breast cancer. A randomized control trial of selenium for skin cancer prevention showed no effect of selenium on skin cancer incidence, however it did show a reduction in incidence of lung, colon and prostate cancer. Despite these promising results, the impact of selenium remains unclear. Fortification of the soil in Finland in the mid-1980s led to higher blood selenium levels, but no decline in incidence or mortality has been noted for prostate or colon cancer.

Safer Sex and Decreased Viral Transmission ▶Unsafe sex is responsible for 2.9M deaths each year, primarily due to the transmission of ▶HIV. However, unprotected sexual contact also results in the spread of multiple other sexually transmitted infections including oncogenic viruses. Some of these viruses may also be spread through exposure to blood and blood products. ▶Human papillomavirus causes cervical cancer, vulvar, penile and anal cancer; ▶hepatitis B virus and ▶hepatitis C virus cause ▶hepatocellular cancer; human lymphotropic virus-type 1 is associated with adult T cell leukemia (▶human T-cell leukemia virus); human immunodeficiency virus-type 1 causes ▶Kaposi sarcoma and non-Hodgkin lymphoma; and human herpes virus causes Kaposi sarcoma and body cavity lymphoma. Prevention strategies to contain the spread of these viruses should include behavioral and educational interventions to modify sexual behavior, and structural and regulatory changes to promote safer sex and make condoms readily available. Biomedical interventions to administer vaccines are also needed. For example, it is estimated that vaccination programs could reduce the global burden of liver cancer by 60%. Additional strategies to prevent viral spread include needle exchange programs for intravenous drug users; regulation of tattooing and acupuncture; screening of blood donors, and the development of artificial blood products.

Vitamin D Growing evidence relates lower levels of ▶vitamin D to increased risk of cancer and to poor survival after diagnosis. Trends The proportion of adults consuming the recommended five servings of fruits and vegetables a day varies between 8 and 32%. While these estimates are clearly low for the entire population, certain groups, as defined by gender, race/ethnicity, education, and income, are of particular concern. Given constraints due to both financial resources and physical access to markets that provide fresh fruit and vegetables, it remains likely that SES gradients in diet will continue. Interventions are needed to overcome these existing barriers and make healthy foods readily available to all. Limitation of Alcohol Use Globally, alcohol intake in excess is responsible for 1.8M deaths each year. Clear benefits of moderate alcohol intake have been shown in terms of reducing cardiac and diabetes risk, but alcohol remains a risk factor for cancer mortality. Alcohol is a known carcinogen that may raise cancer risk in several ways. For example, it may act as an irritant, directly causing increased cell turnover, or it may allow for improved transport and penetration of other carcinogens into cells. Alcohol use is a primary cause of esophageal and oral cancer, and it is associated with an increased risk of breast, liver, and colorectal cancer. Multiple other risks are also associated with alcohol use, including the risk of hypertension, addiction, suicide, accident, and pregnancy complication. To balance the cardiovascular benefits with the risks of cancer and other negative consequences, it is recommended that those who drink alcohol should do so only in moderation. Intake should be limited to less than one

Trends and Disparities Current U.S. data on the prevalence of these different viruses is not adequate to predict trends in cancer incidence. In addition, the recent development of new technologies such as vaccines against HPV, suggest a new era in prevention of cervical cancer. However, for success, such vaccines must be available and accessible to the entire population. Assuring access remains a policy priority to maximize the potential benefit of this cancer prevention strategy. Sun Protection The American Cancer Society estimates over 50,000 melanoma diagnoses each year in the U.S. The incidence of melanoma is rising more rapidly than that of any cancer in this country. Exposure to the sun (▶UV radiation) is the major modifiable cause of melanoma and other skin cancers. For most people, the majority of lifetime sun exposure occurs during childhood and adolescence, and migrant studies clearly show that age at migration to high-risk countries has a strong impact on risk of this malignancy. For this reason, early intervention has the greatest potential for prevention.

Cancer Causes and Control

The risk of melanoma and other less aggressive forms of skin cancer exists for all racial and ethnic groups, but skin cancers occur predominantly in the non-Hispanic white population. Constitutional characteristics including hair color, mole count, and family history contribute to risk of melanoma. However, studies show that established risk factors alone do not identify a sufficient proportion of cases to focus prevention efforts on only a subset of the population. Because identifying high-risk individuals will miss the majority of cases, population-based efforts provide greater protection. There is tremendous potential to substantially reduce the burden of this common malignancy through effective prevention efforts.

Screening Screening for cancer can provide protection in several ways. In the case of colorectal and cervical cancers, screening can detect premalignant changes that can be treated to prevent cancer from developing. This primary prevention has the potential to substantially reduce the burden of cancer. With colorectal screening the mortality from colon cancer is reduced by a half or more. If cancer is already present, screening can act as a secondary prevention (▶early detection), such as mammography for breast cancer, facilitating early diagnosis and treatment, thereby decreasing morbidity and mortality. This type of prevention is an added benefit of colorectal and cervical screening, and is the main goal of breast cancer and prostate cancer screening.

Trends and Disparities Trends in cervical cancer screening have been impacted by the breast cancer cervical cancer screening act which provided resources to states, via the Centers for Disease Control and Prevention, to bring screening services to low income women. Despite these efforts, national data suggest that low income and Hispanic women are less likely to be current with screening recommendations. Lack of access to care, defined as not having a usual source of health care, was associated with significantly lower compliance with cervical screening. Evidence from the 1998 Health Interview Survey indicates that all US born women have comparable and high compliance with screening for cervical cancer. Foreign born women, however, appear to be underscreened, accounting for the disparity among Hispanic women and suggesting a priority area for prevention as the U.S. continues to have a large immigrant population at risk of cancer. Surveys of colorectal screening suggest that the rates of screening have been rising and that Caucasians are more likely to be up to date with screening than other racial or ethnic groups.

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Conclusion Lifestyle changes offer tremendous potential for prevention of cancer and multiple other chronic conditions. This potential is often underestimated. To achieve the maximal benefit through behavioral change, interventions are necessary at multiple levels. Societal changes are needed to support and encourage the behavior modification of individuals. Approaches are needed to target individuals, communities, and systems, and create an environment less inductive to high-risk lifestyles. Social systems and regulatory efforts must complement individual behavior changes if these changes are to be sustained and the benefits of reduced disease burden realized. Overall, the major lifestyle factors considered here account for the majority of cancer and could be modified to prevent at least half of all cancers. However, the burden of cancer is not limited to just the major lifestyle factors considered here. For example, occupational and environmental exposures also account for a relatively small number of cancer cases compared to the lifestyle factors considered above. Yet the burden of exposure to these harmful agents may be disproportionately high among low-income populations, accentuating their cancer risk. In large part, these exposures can be prevented through adequate enforcement of regulatory changes, and this should remain a high priority. Small individual changes can result in large population benefits, but efforts to create prevention programs for only certain members of our society limits the potential for prevention. We must largely reframe our approach to the issue. Identifying risk factors and setting goals for reduction is only the beginning. Research and policy must now focus on bringing about population-wide lifestyle change, addressing the issues of disparities, and leaving no group or community behind.

References 1. Colditz GA, DeJong D, Emmons K et al. (1997) Harvard Report on Cancer Prevention. Volume 2. Prevention of Human Cancer. Cancer Causes Control 8:1–50 2. Curry S, Byers T, Hewitt M (2003) Fulfilling the potential of cancer prevention and early detection. National Academy Press, Washington, DC 3. International Agency for Research on Cancer (2002) Weight control and physical activity (Vol. 6). International Agency for Research on Cancer, Lyon 4. Rose G (1981) Strategy of prevention: lessons from cardiovascular disease. Br Med J (Clin Res) 282:1847–1851 5. U.S. Department of Health and Human Services (1996) Physical activity and health: A Report of the Surgeon General. US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Atlanta, GA

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Cancer Cell-platelet Microemboli ▶Tumor Cell-Induced Platelet Aggregation

Cancer Epidemiology

useful distinction among etiological studies concerns the nature of the information on exposure: while some studies use information routinely collected for other purposes, such as censuses and medical records, in other circumstances exposure data are collected ad-hoc following a variety of approaches including questionnaires, pedigrees, environmental measurements, measurement of biological markers. A method-oriented (rather than subject- or design-oriented) approach has lead to the identification of specific sub-disciplines such as ▶molecular epidemiology.

PAOLO B OFFETTA International Agency for Research on Cancer, Lyon, France

Synonyms Population-based cancer research

Definition Knowledge about causes and preventive strategies for malignant neoplasms has greatly advanced during the last decades. This is largely attributable to the development of cancer epidemiology. In parallel to the identification of the causes of cancer, primary and secondary preventive strategies have been developed. A careful consideration of the achievements of cancer research, however, suggests that the advancements in knowledge about causes and mechanisms have not been followed by an equally important reduction in the burden of cancer. Part of this paradox is explained by the long latency occurring between exposure to carcinogens and development of the clinical disease. In addition, the most important risk factors of cancer are linked to lifestyle, and their modification entails cultural, societal and economic consequences. The failure to identify valid biomarkers of cancer risk is another reason of the limited success in cancer control. Cancer epidemiology investigates the distribution and determinants of cancer in human populations. Although the main tool in cancer epidemiology is the ▶observational study, ▶the intervention study, of experimental nature, is conducted to evaluate the efficacy of prevention strategies, such as screening programs and chemoprevention trials (clinical trials are usually considered outside the scope of epidemiology). Intervention studies follow the randomized trial design. Observational epidemiology can be broadly divided in ▶descriptive epidemiology and analytical studies. Analytical studies can be based on data collected at the individual or population level. The former consist of ▶cohort study, ▶case-control study and ▶cross-sectional study (and a few variations on these themes), the latter of so-called ▶ecological study. Family-based studies are used in ▶genetic epidemiology to identify hereditary factors. An additional

Characteristics A distinctive feature of cancer epidemiology is the availability in many countries of a population-based ▶cancer registry, which allow the calculation of valid and reliable estimate of the occurrence of cancer (incidence, mortality, prevalence, survival). Typically, registries collect routinely demographic data of patients, which are used to generate statistics according to period of diagnosis, age, sex, and other characteristics. These studies of descriptive epidemiology have been critical in developing etiological hypotheses. One particular type of descriptive studies concerns migrants from low- to high-risk areas, or vice-versa: the repeated demonstration of rapid changes in the risk of many cancers among migrants (from that prevalent in the area of origin towards that of the host area) provided very strong evidence of a predominant role of modifiable factors in the etiology of human cancer. While cancer registries were initially established in high-resource countries, a growing number of population s in middle- and low-resource countries are now covered by good-quality registries, thus providing a solid infrastructure for most ambitious research projects. Other routinely collected data are used in epidemiology. Mortality statistics are available in many countries of the world, and provide a good approximation of the incidence of the most fatal cancers. In a growing number of populations, automatic linkage is possible between incidence or mortality data and other population-based registries (e.g., hospital discharges, use of medications). ▶Record-linkage study may represent an efficient alternative to investigations based on ad-hoc collection of data. The number of new cases of cancer which occurred worldwide in 2002 has been estimated at about 10,800,000. Of them, 5,800,000 occurred in men and 5,000,000 in women. About 5,000,000 cases occurred in developed countries (North America, Japan, Europe including Russia, Australia and New Zealand) and 5,800,000 in developing countries. Among men, lung, prostate, stomach, colorectal, and liver cancers are the most common malignant neoplasms, while breast, cervical, colorectal, lung and stomach cancers are the

Cancer Epidemiology

most common neoplasms among women. The number of deaths from cancer in 2002 was estimated at about 6,700,000 and that of 5-year prevalent cases at about 24,600,000. Epidemiology has been instrumental to identify the causes of human cancer. In several cases, the epidemiological results preceded the elucidation of the underlying mechanisms. In other areas, however, epidemiological techniques are not sufficiently sensitive and specific to lead to conclusive evidence on the presence or absence of an increased risk. As for other branches of the discipline, the observational nature of epidemiology represents an opportunity for bias, including that generated by confounding, to generate spurious results. Techniques have been developed to prevent, control and assessment the presence and extent of bias in epidemiological studies. Cancer epidemiology has lead to the identification of tobacco smoking and use of smokeless tobacco products, chronic infections, overweight, alcohol drinking and reproductive factors as major causes of human cancer. Other important causes include medical conditions, some drugs, perinatal factors, physical activity, occupational exposures and ultraviolet and ionizing radiation. A role of diet in cancer risk has been suggested, but for very few dietary factors there is conclusive evidence of an effect on cancer risk. With a few exception of little relevance in most populations, the role of pollutants on cancer is not established. Tobacco smoking is the main single cause of human cancer worldwide. It is a cause of cancers of the oral cavity, pharynx, esophagus, stomach, liver, pancreas, nasal cavity, larynx, lung, cervix, kidney and bladder, and of myeloid leukemia. The proportion of cancers in a population attributable to tobacco smoking depends on the distribution of the habit a few decades earlier. Therefore, in populations in which the tobacco epidemic has not fully matured (e.g., men in many low-income countries and women in most European countries), the full effect of tobacco smoking on cancer burden is not yet observed. The notion that genetic susceptibility plays an important role in human cancer is old, and genetic epidemiology studies have characterized familial conditions entailing a very high risk of cancer have been identified, such as the Li-Fraumeni syndrome and the familial polyposis of the colon, and have identified high-risk cancer genes responsible for these syndromes. However, such high-risk conditions explain only a small fraction of the role of inherited susceptibility to cancer. The remaining fraction of genetic predisposition is likely explained by the combination of common variants in genes involved in one or more steps in the carcinogenic process, such as preservation of genomic integrity, repair of DNA damage. The identification of such low-penetrance susceptibility genes and of their

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interactions with exogenous factors (so-called ▶geneenvironment interactions) represents a challenge to genetic epidemiology. Advances in molecular biology and genetics offer new tools for epidemiological investigations, and have lead to the development of new methodological approaches, broadly defined as molecular epidemiology. The application of biomarkers to epidemiology has lead to advances in the identification of human carcinogens (e.g., the role of aflatoxin in liver cancer) and in the elucidation of mechanisms of carcinogenesis (e.g., TP53 mutations in tobacco-related carcinogenesis). Exposure to most known carcinogens – at least in theory – be avoided or reduced. This is true in particular for tobacco smoking and chronic infections, the two major known causes of cancer. Tobacco control measures have been implemented in most countries, and effective vaccination is today available against two of the main carcinogenic viruses, Hepatits B and Human Papilloma. Control of workplace exposure to known and suspected carcinogens in high-resource countries is another example of successful primary prevention of cancer. In many instances, however, primary prevention of cancer would require major changes in lifestyle, which are difficult to achieve. Detection of preclinical neoplastic lesions before they have developed the full malignant phenotype, and notably the ability to metastasize is a highly appealing approach to control cancer. The effectiveness of screening has been demonstrated via epidemiological studies for cervical cancer (cytological smear), breast cancer (mammography) and colorectal cancer (colonoscopy). The development of effective strategies for the early detection of other neoplasms is an active area of research. Cancer epidemiology exemplifies the strengths and the weaknesses of the discipline at large. Cancer epidemiology has the privilege of using complete and good quality disease registries available in many populations and covering a broad spectrum of rates and exposures. In many occasions, cancer epidemiology has been the key tool to demonstrate the causal role of important cancer risk factors. The best example is the association between tobacco smoking and lung cancer, which lead in the early 1960s to the establishment of criteria for causality in observational research. These findings have brought important regulatory and public health initiatives as well as lifestyle changes in many countries of the world. These epidemiological “discoveries” share two important characteristics: they involve potent carcinogens and methods are available to reduce misclassification of exposure to the risk factor of interest and to major possible confounders. It has been therefore possible to demonstrate consistently an association in different human populations. Note that it is not necessary for the prevalence of exposure to

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be high (although this obviously has an impact on the population ▶attributable risk): examples are the many occupational exposures and medical treatments for which conclusive evidence of carcinogenicity has been established on the basis of epidemiological studies conducted in small populations of individuals with well characterized exposure. When these conditions are not met, however, the evidence accumulated from epidemiological studies is typically inconsistent and difficult to interpret. The history of cancer epidemiology presents many examples of premature conclusions, which have not been confirmed by subsequent investigations and have damaged the reputation of the discipline. Exposure misclassification, uncontrolled confounding, emphasis of positive findings generated by chance, and inadequate statistical power are the most common limitations encountered in epidemiological studies. Several solutions have been proposed to overcome these problems. First, epidemiological studies should be very large in size. This is achieved either by conducting multicentric studies including thousands of cases of cancer, or by performing pooled and meta-analyses of independently investigations. Second, as mentioned above, the use of biological markers of exposure and early effect might contribute to reduce exposure misclassification, increase the prevalence of the relevant outcomes and shed light on the underlying mechanisms. Finally, guidelines have been developed to improve and standardize the conduct are report of observational epidemiological studies. Although relatively young, epidemiology has become a key component in cancer research. Most cancer centers have an epidemiological research group, and cancer is a major subject of research in most academic departments of epidemiology. Epidemiologists are more and more often invited to meetings of clinicians and basic researchers not only to provide an introduction to the distribution and the risk factors of a given cancer, but to participate in interdisciplinary discussions on clinical, preventive or mechanistic aspects of the disease. The strongest cancer epidemiology groups in the world are those combining different lines of expertise, from biostatistics to molecular biology and genetics to medical oncology. Despite its limitations, cancer epidemiology remains one of the most powerful tools at the disposal of the research community to combat cancer at all levels.

3. Doll R, Peto R (2003) Epidemiology of cancer. In: Warrell DA, Cox TM, Firth TD, (eds) Oxford Textbook of Medicine. Fourth Edition. Oxford University Press, London: pp 193–218 4. STROBE Statement. STrengthening the Reporting of OBservational studies in Epidemiology (http://www. strobe-statement.org/)

Cancer Epigenetics B ERNA D EMIRCAN , K EVIN B ROWN University of Florida College of Medicine, Gainesville, FL, USA

Definition

▶Epigenetics is defined as chromatin modifications that can alter gene expression, are heritable during cell division, but do not involve a change in DNA coding sequence.

Characteristics

References

In the context of normal biological processes, epigenetic mechanisms establish regions within the genome containing transcriptionally active (termed euchromatin) and silent (termed heterochromatin) DNA. Further, epigenetic mechanisms are responsible for stably inherited patterns of gene expression such as X chromosome inactivation and genomic imprinting (i.e., selective expression of maternal or paternal alleles). Chromatin modifications that alter gene expression are both changes to the methylation state of DNA and post-translational modifications to histone complexes. It is well recognized that genetic mutations occur in cancer cells and that these events can exert profound and disease-associated changes in gene expression and/ or function. However, it is becoming widely accepted that cancer cells also exhibit aberrant epigenetic alterations and that these changes can play a prominent role in disease initiation and progression. Epigenetic changes are potentially as important as genetic mutations in causing cancer since chromatin alterations can exert an influence regional gene expression, thereby changing the transcriptional profile of multiple genes. In this chapter we summarize the principal epigenetic alterations that occur in cancer cells: regional DNA hypermethylation and ▶histone modifications, and global DNA hypomethylation.

1. Last JM (1983) A dictionary of epidemiology. Oxford University Press, New York 2. Ferlay J, Bray F, Pisani P et al. (2004) Globocan 2002 – cancer incidence, mortality and prevalence worldwide. IARC CancerBase No. 5, version 2.0. Lyon, IARC Press

DNA Hypermethylation Chromatin structure is influenced by cytosine ▶methylation, the only known naturally occurring base

Cancer Epigenetics

modification in DNA. Cytosine methylation occurs at 5′-CG-3′ dinucleotides (referred to as CpGs) and is catalyzed by a class of enzymes termed ▶DNA methyltransferases (DNMTs). Several DNMTs have been characterized in mammalian cells including DNMT1, DNMT3a and DNMT3b. These enzymes catalyze the transfer of a methyl group from Sadenosylmethionine (SAM) to the 5-carbon position of cytosine, forming 5-methycytosine. DNMT3a and DNMT3b appear to be principally involved in methylating previously unmodified cytosines (termed de novo methylation). In contrast, DNMT1 preferentially methylates hemimethylated DNA and is thus viewed as the DNA methyltransferase principally responsible for continuation of DNA methylation patterns in daughter cells (termed maintenance methylation). From a statistical standpoint, the human genome is depleted in CpG dinucleotides; however, 60% of genes in our genome are associated with regions ranging from 200 to 4,000 bases in length containing high density of CpG dinucleotides relative to the bulk genome. These regions are referred to as ▶CpG islands and are usually located within upstream promoter regions or gene transcriptional start sites. In normal somatic cells, gene-associated CpG islands are usually unmethylated and associated with genes in a transcriptionally active euchromatic state. In cancer cells, hypermethylation of such CpG islands is strongly correlated with the transcriptional silencing of genes. Thus, through this epigenetic mechanism, tumor cells can dramatically down regulate expression of numerous genes, including ▶tumor suppressor genes (TSGs). At present, numerous TSGs have been characterized as targets for epigenetic silencing through hypermethylation of associated CpG islands. Table 1 is a partial listing of characterized TSG whose promoter regions have been shown to be hypermethylated in various tumor types. Given the wide spectrum of tumor types that display

Cancer Epigenetics. Table 1 Gene

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epigenetic silencing of TSGs, mounting evidence clearly supports the assertion that epigenetic silencing is a prominent mechanism driving the process of tumorigenesis. Cancer cells often over express DNMTs. Compared to normal tissues, the expression of DNMT1 is almost always increased in tumors. However, since DNMT1 expression is normally regulated during the cell cycle with increased abundance paralleling entry into S-phase, much of this increased expression may simply reflect increased cell proliferation within the tumor. Although demonstrable in model experiments, it remains unresolved if increased expression of DNMT1 is responsible for aberrant methylation in cancer cells. In contrast, increased expression of DNMT3a and DNMT3b observed in some tumors is likely significant, since these enzymes are normally expressed at low levels in somatic cells. However, it is still unclear to what extent over expression of these enzymes is responsible for cancer-associated DNA hypermethylation especially when one considers that cancer cells exhibit overall genome hypomethylation (discussed below). Thus, it remains unclear how CpG islands associated with specific TSG are targeted for hypermethylation during the process of tumorigenesis. One mechanism by which DNA methylation can negatively impact gene expression is by simply blocking the binding of essential transcription factors to gene promoter sequences. While several examples of this are documented, it is also apparent that CpG methylation is also capable of directing transcriptional repression through promoting additional layers of chromatin alteration. Specifically, several proteins have been characterized that bind to methylated CpG dinucleotides and are capable of promoting further chromatin condensation and consequential transcriptional repression through recruitment of chromatin-modifying activities.

Genes subject to epigenetic silencing in cancer Function

Tumor types

APC BRCA1 CDH1 (E-cadherin) MGMT MLH1 CDKN2A (p16)

Regulation of β-catenin, cell adhesion DNA repair Homotypic epithelial cell–cell adhesion

Colorectal, gastrointestinal Breast, ovarian Bladder, breast, colon, liver

DNA repair DNA repair Cell cycle control

PTEN VHL

Regulation of cell growth and apoptosis Inhibits angiogenesis, regulates transcription DNA damage response

Brain, colorectal, lung, head and neck Colorectal, endometrial, ovarian Lung, brain, breast, colon, bladder, melanoma prostate Prostate, brain, endometrial, melanoma Renal cell carcinoma

ATM

Breast, colorectal, head and neck

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Histone Modification Owing to technical considerations, DNA methylation is the most widely analyzed type of epigenetic alteration in human tumors. However, another extremely important epigenetic modification capable of altering gene expression during carcinogenesis involves various types of histone modifications. The fundamental packing unit of chromatin within the nucleus is termed the ▶nucleosome. A single nucleosome unit contains 146 base pairs of DNA wrapped around eight histone subunits (histone octamer). The histone octamer contains two copies each of histones H2A, H2B, H3 and H4. Structural studies have determined that each histone possesses an aminoterminal tail rich in the amino acid lysine. These lysine residues can undergo a variety of post-translational modifications including acetylation, methylation, phosphorylation, and ubiquitination. Such modifications are recognized by various proteins and protein complexes and combinations of histone modifications constitute a proposed histone code important in establishing a given gene’s transcriptional profile. Perhaps the best-studied histone modifications is acetylation of the ε-amino group of lysine residues within the amino-terminal tail of H3 and H4 although acetylation of both H2A and H2B occurs as well. This is a reversible modification that is carefully controlled by two large enzyme families: histone ▶acetyltransferases (HATs) and ▶histone deacetylases (HDACs). The net positive charges carried by these lysine residues are proposed to contribute to the high affinity of histones for negatively charged DNA. Acetylation of lysine residues by HATs neutralizes this positive charge thus decreasing histone/DNA interaction. This raises molecular access to DNA and promotes gene transcription. Conversely, HDACs promote transcriptional repression by supporting chromatin condensation into a heterochromatic conformation. Several proteins that bind specifically to methylated CpG through a conserved methyl-binding domain (MBD) motifs have been discovered. The first such protein to be characterized, termed MeCP2, is capable of recruiting the co-repressor molecule mSin3 to the sites of methylated DNA. In turn, mSin3 binds to HDAC1 and HDAC2, thus promoting localized histone deacetylation. The importance of HDAC activity in transcriptional repression is underscored by the observation that repression of several gene promoters that can be partially relieved by HDAC inhibitors. A functionally similar complex termed MeCP1 binds to methylated DNA via an associated protein termed MBD2. The MeCP1 complex contains multiple subunits besides MBD2, including components of the NuRD complex, a characterized repressor complex containing both chromatin remodeling and HDAC activities.

In addition to acetylation, lysine residues within histone tails can be methylated and exist in either mono-, di-, or trimethylated states. Similar to the effects of histone acetylation/deacetylation, methylated lysine 4 of H3 (H3K4) is associated with transcriptionally active chromatin, while transcriptionally silent chromatin generally contains methylated lysine 9 of H3 (H3K9). H3K9 is methylated by a number of histone methyltransferases including ESET, Eu-HMTase, G9a, and the closely related methyltransferases SUV39-H1 and SUV39-H2. Histone methylation is likely a dynamic process since a histone demethylase, termed LSD1, was recently characterized. Methylated H3K9 binds to the chromodomain protein heterochromatin protein 1 (HP1) which promotes heterochromatin formation and gene silencing. Moreover, since H3K9 methylation cannot occur when this position is acetylated, it is clear that H3K9 acetylation and methylation represent opposing forces in determining chromatin conformation. In a broad view, it is reasonable to propose that CpG methylation and histone acetylation/deacetylation act synergistically in the progressive silencing of genes. One model that accounts for tumor-suppressor gene silencing by epigenetic mechanisms invoke abnormal hypermethylation of the promoter CpG island followed by recruitment of MBD proteins, including complexes such as MeCP2 and MeCP1 that recruit HDACs to the area of hypermethylation and promote further transcriptional repression through histone modification. An alternate model proposes that transcriptionally repressive histone modifications are the first event in gene silencing and subsequently promote CpG methylation resulting in further transcriptional repression. Experimental evidence supports both of these models and may be reflective of the variety of gene promoters and model systems used for study. Less equivocal is the fact that DNA methylation appears the dominant silencing mechanism since inhibition of DNA methylation generally restores gene expression while HDAC inhibitors generally exert more modest effects on gene silencing. DNA Hypomethylation While CpG islands associated with gene promoters are generally unmethylated in normal adult somatic cells, the majority of CpG dinucleotides elsewhere in the genome are generally methylated. Moreover, despite the fact that many CpG islands are subject to hypermethylation in cancer cells, it is equally well documented that tumor cells display an overall loss of methylated cytosines compared to normal tissue. This tumor-associated global DNA hypomethylation predominantly occurs in repetitive DNA sequences within the human genome although the molecular mechanisms responsible for this loss of DNA methylation are poorly understood.

Cancer Genome Project

Recent work on a human genetic disorder has underscored an important role for DNA methylation in maintenance of genome stability. The immunodeficiency, centromeric region instability, facial anomalies (ICF) syndrome is a rare autosomal recessive disease characterized by germline mutation of the DNMT3B gene. Loss of DNMT3B activity in ICF leads to hypomethylation of repetitive satellite DNA sequences within heterochromatin adjacent to the centromeric region of chromosomes. The loss of methylation is most prominent within the pericentric regions of human chromosomes 1 and 16 and leads to multiple chromosomal abnormalities including chromatin decondensation, chromosomal translocations and deletion, and multiradial chromosomal structures. These observations, as well as those made on cells with engineered disruption of DNMTs, clearly support the view that DNA methylation is critical in maintaining normal chromosome structure. Since cancer cells often show chromosomal rearrangements, it is likely that cancer-associated DNA hypomethylation allows for heightened rates of chromosomal instability. Retrotransposon sequences of the LINE (long interspersed nuclear element) and SINE (short interspersed nuclear element) classes as well as human endogenous retroviruses (HERVs) are major targets of tumorassociated DNA hypomethylation. Mobility of these DNA elements is kept in check in normal tissues owing, in part, to dense methylation of CpG dinucleotides within their genomic structure. It follows that increased mobility of these dormant mobile elements occurs as a result of cancer-associated DNA hypomethylation and there have been reports of retrotranspositionlike insertions involving LINE-1 sequences in tumors although retrotransposition of endogenous elements seemingly occurs more often in rodents than humans. In addition to the hypomethylation of CpG dinucleotides present within repetitive DNA elements, cancer-associated hypomethylation also occurs in regions of the genome encoding single-copy genes. Dysregulation of allele-specific methylation will result in the loss of imprinting (LOI) and allow for both maternal and paternal gene expression. Perhaps the best-studied example of this is the insulin-like growth factor 2 (IGF2) gene where LOI occurs in primary tumors and in patients with the inherited, cancer-prone ▶Beck-with-Wiedemann. While not as well-studied as gene silencing due to DNA hypermethylation, it is likely that additional examples of cancer-promoting increased gene expression stemming from DNA hypomethylation will be uncovered in the future. Epigenetic Alterations as Targets for Diagnosis and Therapeutic Intervention Sequencing data obtained from the human genome project are currently undergoing analysis to construct a

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human epigenetic map based on CpG content. This knowledge coupled with cross-species comparisons of the epigenome will be invaluable in deciphering the epigenetic elements involved in gene regulation. Epigenetic alterations typically occur early during the oncogenic process, and detection of such early abnormalities may aid in early diagnosis and/or preventing cancer progression through dietary alterations or pharmacological intervention. With increasing awareness of the importance of epigenetics in tumorigenesis, and the advent of sensitive laboratory approaches to analyze epigenetic alterations, it is likely that epigenetic profiles will ultimately be used in the clinical setting to provide information useful in predicting an individual’s predisposition to cancer, assisting in tumor staging, and guiding optimal therapeutic approaches. A promising feature of alterations in DNA methylation patterns and chromatin structure in cancer cells is their potential for reversibility, because these modifications occur without changing the primary nucleotide sequence. At present, two major pharmacological targets associated with these epigenetic changes are DNMTs and HDACs. The DNMT inhibitor 5-azadeoxycytidine (5-azadC) and related compounds cause transcriptional reactivation of endogenous genes with hypermethylated promoters. This drug, also termed Decitabine, is currently used to treat certain types of hematological malignancies, especially advanced ▶myelodysplastic syndromes (MDS). HDAC inhibitors, such as trichostatin A and sodium butyrate, have been shown to increase the level of histone acetylation in cultured cells, and to cause growth arrest, differentiation and apoptosis. Based on these observations, the potent HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) is in clinical trials.

Cancer Genome Project Definition The Cancer Genome Project (CGP) was founded at the Wellcome Trust Sanger Institute in 2000 and aims to establish an unbiased catalogue of mutations involved in human tumorigenesis by complete sequencing of candidate genes. By sequencing the human BRAF gene, the CGP discovered a hitherto unknown mechanism of oncogenic activation of B-Raf that is not only found in 7% of human cancers, but also provided more insight into the complex process of B-Raf activation. ▶B-Raf Somatic Alterations

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Cancer Germline Antigens A DAM R. K ARPF Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, NY, USA

Synonyms Cancer-testis (CT) antigens; CG antigens

Definition

CG ▶antigens (Cancer-testis (CT) antigens) are a class of immunogenic tumor antigens encoded by genes expressed in ▶gametogenic cells of the testis and/or ovary and in human cancer.

Characteristics Identification The main criterion for classification of a gene as a CG antigen pertains to its expression pattern in gametogenic, somatic, and tumor tissues. A gene is generally considered to be a CG antigen if it is expressed in the gametogenic cells of the testis or ovary (including fetal ovary) and in some proportion of human cancers, but is expressed in two or fewer normal somatic tissues. CG antigen genes are also commonly expressed in ▶trophoblast tissue. CG antigens were originally identified from searches for auto-antigens expressed in human cancer. The original method for antigen screening used ▶autologous typing, in which ▶T-cells (T-lymphocyte) from a ▶melanoma patient were screened for reactivity with tumor cells from the same patient; this method led to the identification of MAGE-A (named for ▶melanoma antigen)/CT1 genes. In later studies, another immunological assay was developed to identify tumor antigens and this method, ▶SEREX (Serological analysis of recombinant cDNA expression libraries), was used to successfully identify a variety of important CG antigen genes, including NY-ESO-1/CT6 and SSX/CT5. Recognition of the unique expression pattern of CG antigen genes has led to the use of gene expression analyses (including EST or SAGE database searching) to identify CG antigen genes. This method has led to the identification of additional CG genes, including XAGE-1/CT12 and SCP-1/CT8. Although formally classified as CG antigen genes, genes identified by the latter non-immunological method may not be antigenic in cancer patients. Nomenclature A nomenclature system for CG antigens has been devised, which is based on their chronology of discovery, and also accounts for the numerous family

members that exist for certain CG antigens. In this system, CG antigen genes are referred to by their original given names and also are assigned a separate CT identifier or CT#. Currently, over 40 CG antigen gene families are recognized, comprising more than 89 distinct mRNA transcripts. CG antigen genes have been assigned into two groups on the basis of chromosomal localization. ▶CG-X antigens: These genes reside on the X-chromosome where, interestingly, close to 10% of the total number of genes encode CG antigens. CG-X genes are typically members of large multigene families, e.g. MAGE-A/CT1, MAGE-B/CT3, and MAGE-C/CT7. In normal tissues, CG-X genes are often expressed in pre-meiotic spermatocytes in the testis. All of the current important targets of CG antigen ▶cancer vaccines are members of this group, including MAGE-A1/CT1.1, MAGE-A3/CT1.3, and NY-ESO-1/CT6.1. ▶Non-X CG antigens: A number of CG antigen genes are located on autosomal chromosomes. Unlike CG-X genes, these genes are highly dispersed in the genome and do not exist in multigene families. In normal tissues, non-X CG genes are often expressed during meiosis, where some members play roles in DNA recombination, including SCP-1/CT8 and SPO11/CT35. The members of this gene group do not include any currently validated cancer antigens, although certain members are expressed at high levels in cancer.

Regulation of Expression Certain cancer types appear to expresses CG antigen genes frequently, while others rarely express them. Tumor types that frequently express CG antigens include melanoma, lung, ovary, and ▶bladder cancer; tumors that rarely express CG antigens include ▶colon cancer, renal cancer, and leukemia/lymphoma. CG antigen genes show coordinate expression in human cancer. That is, the great majority of tumors either do not express CG antigen genes or express two or more CG antigen genes simultaneously, while relatively few tumors express only one CG antigen gene. Another characteristic of CG antigen gene expression in cancer (revealed by immunohistochemical staining) is that tumors that express CG antigens show heterogeneous expression within the tumor: often only focal staining is observed. The coordinate but heterogeneous expression of CG antigens in cancer has led to the intriguing hypothesis that CG antigen expression is indicative of the activation of a normally dormant gametogenic program in tumor cells (possibly corresponding to tumor stem cells). The observation of coordinate expression of CG antigen genes suggests that CG antigen gene activation may be controlled by a common molecular mechanism. Supporting this idea, a number of studies

Cancer Germline Antigens

have suggested a key role for ▶DNA methylation in regulating CG antigen gene expression. Promoter DNA hypermethylation has been observed to correlate with CG antigen gene repression in normal tissues and nonexpressing tumors, while treatment of tumor cell lines in vitro with DNA methyltransferase inhibitors such as ▶5-aza-2′-deoxycytidine (DAC) leads to CG antigen gene activation, coincident with promoter DNA ▶hypomethylation. Conversely, tumor cell lines and tissues that endogenously express CG antigen genes often display promoter DNA hypomethylation. Many CG antigen genes have CpG-rich promoter regions that serve as targets for regulation by DNA methylation. Other studies have shown that ▶histone deacetylase (HDAC) inhibitors can either augment DAC-mediated CG antigen gene activation or can activate CG antigen genes on their own. As DNA ▶methylation and ▶chromatin structure (in the form of histone modification status) are intimately linked, it is not surprising that both of these ▶epigenetic mechanisms serve as important regulators of CG antigen gene expression. Consistent with the model that epigenetic mechanisms regulate CG antigen gene expression is the observation that DNA hypomethylation occurs during gametogenesis, which is the normal setting for CG antigen gene expression.

Function CG antigens are a rare group of genes in that clinical studies designed to target these antigens for ▶immunotherapy of cancer are more advanced than is our basic knowledge of the function of the gene products. However, some information about CG antigen gene function has recently come to light. As mentioned earlier, many non-X CG antigens have roles in germ cell maturation, including mediating the structure of synaptonemal complexes (SCP1/CT8), facilitating DNA recombination during meiosis (SPO11/CT35), and contributing to spermatid function (ADAM2/CT15, OY-TES-1/CT23). In tumors, the function of CG antigen genes is less clear, but recent studies of the MAGE-type antigens, which share a region referred to as the MAGE homology domain (MHD), indicate that these proteins might serve as transcriptional repressors via interactions with other transcriptional regulatory proteins that themselves recruit co-repressors such as HDACs. CG antigen genes have also been reported to play a role in the evolution of ▶chemotherapy resistance in cancer cell lines, suggesting that the CG antigen gene products could serve as viable targets for anticancer therapy. An recent report appears to link these two observations by showing that MAGEA2/CT1.2 disrupts ▶p53 function by recruiting HDAC3 to p53, leading to chemotherapy resistance in cancer cells.

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Clinical Studies The identification of CG antigens as tumor-specific antigens has led to a great deal of interest in treating cancer by targeting CG antigens via vaccine-based immunotherapy. In particular, MAGE-A1/CT1.1, MAGE-A3/CT1.3, and NY-ESO-1/CT6.1 have been developed as targets for this approach. In early studies, the antigenic peptides from CG antigens that elicited ▶T-cell dependent responses were mapped, and these peptides were utilized for vaccination. Because responses to peptide-based vaccine formulations are limited by patient ▶HLA type, more recent vaccination approaches targeting CG antigens have utilized full-length ▶recombinant proteins. These recombinant proteins can be introduced using viral vectors, including vaccinia and fowlpox viruses. Alternatively, recombinant CG antigen proteins can be assembled with ▶adjuvants such as ISOMATRIX, which further enhances immune responses. A common finding in CG antigen vaccine clinical studies is that the treatment is safe and elicits both ▶antibody and T-cell mediated immune responses in vivo. In particular, NY-ESO-1/CT6.1 vaccine trials have shown encouraging results, with durable and multifaceted immune responses, as well as suggestive data indicating clinical benefit, in terms of disease stabilization and prolonged time to recurrence. Many of the patients targeted in these clinical trials have had malignant melanoma, and a proportion of these patients displayed evidence of immune recognition to the target antigen prior to vaccine therapy. In virtually all cases, patients have been selected for inclusion in CG antigen vaccine trials based on the expression of the antigenic target in tumor biopsies. To expand the patient population that would benefit from this immunotherapy approach, a number of investigators have proposed using DNA methyltransferase and/or HDAC inhibitors (which are FDA approved and known to augment CG antigen gene expression) in combination with CG antigen directed vaccines. The potential benefit of this multi-modality approach awaits clinical testing.

References 1. Simpson AJG, Caballero OL, Jungbluth A et al. (2005) Cancer/testis antigens, gametogenesis and cancer. Nat Rev Cancer 5:615–625 2. Scanlan MJ, Simpson AJG, Old LJ (2004) The cancer/ testis genes: review, standardization, and commentary. Cancer Immun 4:1–15 3. Scanlan MJ, Gure AO, Jungbluth AA et al. (2002) Cancer/ testis antigens: an expanding family of targets for cancer immunotherapy. Immunol Rev 188:22–32 4. Davis ID, Chen W, Jackson H et al. (2004) Recombinant NY-ESO-1 protein with ISOMATRIX adjuvant induces broad integrated antibody and CD4+ and CD8+ T cell responses in humans. Proc Natl Acad Sci USA 101:10697–10702

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Cancer of the Large Intestine

Cancer of the Large Intestine ▶Colon Cancer

Cancer-mediated Bone Loss ▶Bone Loss, Cancer Mediated

Cancer Networks

cancer registries typically contain demographic and clinical characteristics. ▶Cancer Epidemiology

Cancer Stem Cells Definition A minor population of cells within a tumor that is thought to be necessary for tumor growth and propagation. Like all stem cells, cancer stem cells are characterized by their capacity for self renewal and unlimited replication. ▶Stem Cells and Cancer

Definition Local management teams, responsible for population areas of about 500,000, whose role is to co-ordinate cancer service within the National Health Service in England and Wales. ▶National Institute for Health and Clinical Excellence (NICE)

Cancer Stem-Like Cells G AETANO F INOCCHIARO Istituto Nazionale Neurologico Besta, Unit of Experimental Neuro-Oncology, Milano, Italy

Synonyms

Cancer-Prone Genetically Modified Mouse Models Definition Transgenic or knockout mice prone to cancer development as a consequence of ▶oncogene activation or ▶tumor suppressor gene inactivation. ▶Oncomouse ▶Immunoprevention of Cancer

Cancer Registry Definition System of on-going registration of all newly diagnosed cases of cancer in a given population. The files of

Tumor initiating cells

Definition Cancer stem(-like) cells are those cells that possess the capacity for self-renewal and for causing the heterogeneous lineages of cancer cells that comprise the tumor.

Characteristics The definition follows a consensus at a workshop on cancer stem(-like) cells (CSC) organized by the American Association for Cancer Research (AACR). There is considerable debate and some controversy on the CSC concept, so that a consensus definition is required. The importance of the debate is proportional to its relevance to the change in our perception of cancer, intirinsic to the CSC paradigm, implying that not all cancer cells are equal but that only a small fraction of them is endowed with the properties of perpetuating the disease. This hierarchical model has not only important biological consequences but also relevant therapeutic implications, as we discuss in this essay.

Cancer Stem-Like Cells

The CSC paradigm fits in a model of cancer as a caricature of an organ that is already present in the literature as suggested by data published 30 to 40 years ago. In particular, Hamburger and Salmon established growth conditions for cancer cells in soft agar medium and found that tumor stem cell colonies, arising from different types of cancer with 0.001–0.1% efficiency, had differing growth characteristics and colony morphology. Studies by Dick and co-workers in the 1990s showed that in several forms of acute myeloid leukemia (AML) cells that could engraft in immunodeficient mice are restricted to a minority subpopulation defined as [CD34+/CD38neg]: these cells, therefore, shared a cell surface phenotype with normal human primitive hematopoietic progenitors, suggesting that they may have originated from normal stem cells rather than from committed progenitors. Also of interest was the observation that leukemic cells engrafted in NODSCID mice (non obese diabetic-severe combined immunodeficiency: an immunodeficient mouse strain characterized by lack of B, T and NK lymphocytes) showed similar phenotypic heterogeneity to the original donor: thus, [CD34+, CD38neg] retain the differentiating capacity necessary to give rise to CD38+ and Lin+ cells (lineage positive). The presence of CSC has also been demonstrated in chronic myeloid leukemia (CML). This disease has a chronic phase and a terminal stage; the blast crisis and molecular events underlying this evolution are not completely understood. In the chronic phase, the chromosomal translocation t(9:22)BCR-ABL, a diagnostic marker of CML, can be detected in most circulating mature lineages. In the blast crisis, however, highly undifferentiated BCR-ABL+ cells accumulate in the blood. In particular, an expansion of granulocytemacrophage progenitors (GMP) is present in blast cells, showing aberrant acquisition of self-renewal properties and nuclear expression (i.e. activation) of beta-catenin, a key, positive regulator of stem cell self-renewal. These observations imply that during progression of CML the GMP subfraction of leukemic progenitors acquire stem

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cell characteristics. Thus, the functional hierarchy of CSC can be modified during the natural history of this tumor as a result of its progression. The requirement for a periodical renovation is not only present in blood but also in the skin and epithelia of the respiratory, gastrointestinal, reproductive and genito-urinary systems. Other tissues like brain, previously considered as exclusively post-mitotic, contain stem cells that can be mobilized and activated under conditions of stress, such as hypoxia. Thus the CSC model could also be applied to solid tumors, and a series of recent papers report data supporting the identification of a stem cell population in different cancers (see Table 1). Initial data were gained in breast cancer where a small population of cells with a CD44+ /CD24 neg-low phenotype appears exclusively capable of tumor initiation. The most malignant of brain tumors, glioblastoma multiforme (GBM), was also found to contain a fraction of neoplastic cells identified and selected on the basis of CD133 expression. Not only could CD133+ cells self-renew and differentiate into different neural lineages but also, in vivo, only the CD133+ cells were able to reinitiate malignant gliomas with phenotype similar to the original tumor. The CSC paradigm may also help to explain intratumor heterogeneity, a frequent finding in most cancers: heterogeneity could be consequent to functional diversity of cells at different states of differentiation. On the other hand, the patterns of tumor heterogeneity and gene expression profiles can be highly similar in the original tumor and in distant metastasis. It is rather obvious that the existence of cancer stem cells may provide novel therapeutic targets of increased effectiveness in contrasting or even eliminating cancer. Brain tumors have provided a highly fertile ground to start verifying this hypothesis, as outlined in Table 2. Data are piling up indicating that CD133+ GBM CSC are highly pro-angiogenic, because of the high levels of VEGF expression, and have greater resistance to chemotherapy and radiotherapy. As a consequence,

Cancer Stem-Like Cells. Table 1 Tumor Acute Myeloid Leukemia Breast cancer Glioblastoma Myeloma Prostate cancer Melanoma Lung cancer Colon cancer Pancreatic cancer

Markers

Reference

CD34+/CD38neg CD44+/CD24-/neg CD133+ CD138neg CD44+/alpha2beta1 integrin high/ CD133+ CD20+ Sca-1+/ CD45neg/ Pecam neg/CD34pos CD133+ CD44+/CD24+/ESA (epithelial specific antigen)+

Bonnet and Dick 1997 Al-Hajj et al 2003 Singh et al 2003 Matsui et al 2004 Collins et al 2005 Fang et al 2005 Kim et al 2005 O’Brien et al 2007, Ricci-Vitiani et al 2007 Li et al 2007

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Cancer Stem-Like Cells. Table 2 Pathway/mechanism in CSC Angiogenesis-Increased production of VEGF Increased resistance to radiation Specific patterns of expression Cell cycle deregulation Resistance to chemotherapy

Potential treatment

Reference

Bevacizumab Chk1 and Chk2 inhibitor Dendritic cell targeting Bone Morphogenetic Protein 4 BCRP1/MGMT inhibition (?)

Bao et al Cancer Res 2006 Bao et al Nature 2006 Pellegatta et al 2006 Piccirillo et al 2006 Liu et al 2006

specific therapeutic strategies can be attempted and combined to overcome CSC. Upon radiotherapy CD133+ GBM CSC activate checkpoint kinases 1 and 2 and repair mechanisms more effectively than CD133neg cells. Resistance to chemotherapy can be linked to an intriguing aspect of the CSC phenotype, the side population (SP) phenotype. SP cells have the ability to extrude the DNA binding dye Hoechst 33342 via the drug transporter BCRP1/ABCG2. Interestingly, the BCRP1/ABCG2 pump can also effectively extrude chemotherapeutic drugs such as mitoxantrone. Also related, although of less immediate relevance in the clinical setting, are the observations reported by Pellegatta et al. using glioma neurospheres as a target for dendritic cell (DC, the most potent of antigen presenting cells) immunotherapy. Normal neural stem cells may grow as neurospheres (NS) in the absence of serum and in the presence of two critical growth factors, EGF and bFGF. NS are enriched in neural stem cells but also contain partially committed progenitors as well as a differentiated progeny. Oncospheres with similar characteristics were obtained from GBM but also from other solid tumors like breast or colon carcinomas. Pellegatta et al set up a murine model showing that DC loaded with GBM NS are much more effective in protecting mice against the GBM challenge than DC loaded with GBM cells where CSC are poorly represented. Thus, CSC targeting by immunotherapy is feasible and highly effective, opening new scenarios for clinical immunotherapy and supporting the idea that CSC are at the heart of malignant growth. Also of interest is the observation by Piccirillo et al. that treating GBM CSC with the differentiating factor BMP4 can block growth in vitro and avoid tumor formation in the majority of mice in vivo. Given the increasing number of observations supporting the CSC paradigm in different tumors, it is expected that more therapeutically relevant observations will be proposed in the near future. Together with therapeutic and clinical implications the CSC concept seems to have important consequences for our understanding of tumor biology. Modern genetics and molecular biology have given a definition of cancer as a genetic disease in which a growing

burden of mutations leads to a progressively more aggressive and ultimately lethal phenotype (Fig. 1). A Darwinian selection for these mutations, privileging those that can confer resistance to different challenges, like hypoxic stress or immune attack, appears to be the most plausible rationale for making sense of this evolutionary catastrophe. The hierarchical, CSC model seems to introduce an element of rigidity in this highly flexible scenario, implying that only cells endowed with stem cell properties can afford tumor perpetuation (Fig. 1). Are these two models different or are they compatible? A convincing answer to this tough question will undoubtedly require a lot of robust science in the time to come but comments can be given on the basis of data that are already available. One important issue that the CSC model addresses is that of the cell of origin for cancer(s): stem cells, because they are long-lived and self-renewing, are excellent candidates to play the “cell of origin” role. A stem cell hosting a critical mutation could be quiescent for years and then be engaged in a repair response requiring mobilization and proliferation. For example, hypoxic stress may activate the CXCR4 pathway that not only attracts stem cells but may also favour their proliferation, thus being the spark initiating the cancer fire. However, an initiating mutation could also arise in a more committed progenitor (see the integrated model in Fig. 1): acquisition of a stem-like phenotype could in this context be the consequence of environmental challenges; in vivo, for instance, hypoxia could play an important role in de-differentiation; in vitro, the modification of growth factors could have similar consequences. Epigenetic changes could play important roles in mediating rapid and genome-wide changes that can substitute for genetic mutations and lead to dedifferentiation. In the Darwinian model different mutations (M1 through M4) accumulate during evolution and confer heterogeneity. In the Hierachical model tumor arises in a stem cell, thus becoming a cancer stem cell (CSC): heterogeneity is conferred by asymmetrical divisions creating different types of cancer cells (CC1 through 4). In the Integrated model a first mutation (M1) can arise in a progenitor or even a committed cell. During progression, though, external stimuli may give rise

Cancer Vaccines

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Cancer Stem-Like Cells. Figure 1 Biological models for tumor evolution.

to a cancer stem cell that through asymmetric division will create other CSC as well as more differentiated tumor cells. ▶Stem-Like Cancer Cells

undetectable expression in normal tissues except germ cell. ▶BORIS

References 1. Clarke MF, Dick JE, Dirks PB et al. (2006) Cancer stem cells – perspectives on current status and future directions: AACR workshop on cancer stem cells. Cancer Res 66:9339–9344 2. Dalerba P, Cho RW, Clarke MF (2007) Annu Rev Med 58:267–284 3. Jamieson CH, Ailles LE, Dylla SJ et al. (2004) Granulocytemacrophage progenitors as candidate leukemic stem cells in blast-crisis CML. N Engl J Med 351:657–667 4. Sanai N, Alvarez-Buylla A, Berger MS (2005) Neural stem cells and the origin of gliomas. N Engl J Med 353:811–822 5. Feinberg AP, Ohlsson R, Henikoff S (2006) The epigenetic progenitor origin of human cancer. Nat Rev Genet 7:21–33

Cancer (or Tumor) Stroma ▶Tumor Microenvironment

Cancer Vaccines M ALAYA B HATTACHARYA-C HATTERJEE 1 , S UNIL K. C HATTERJEE 1 , A SIM S AHA 1 , K ENNETH A. F OON 2 1

Cancer Testis Antigens

University of Cincinnati and The Barrett Cancer Center, Cincinnati, OH, USA 2 The Pittsburgh Cancer Institute, Pittsburgh, PA, USA

Definition

Definition

Cancer Testis Antigens are genes that can be defined by predominant expression in various types of cancer and

A vaccine should activate a unique lymphocyte (B and/ or T cell) response, which has an immediate anti-tumor

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Cancer Vaccines

Cancer Vaccines. Figure 1 T-cell activation. T-cells recognize antigens as fragments of proteins (peptides) presented with major histocompatibility complex (MHC) molecules on the surface of cells. The antigen presenting cell processes exogenous protein from the vaccine or from the lysed tumor cell in to a peptide, and presents the 14/25 mer peptide to CD4 helper-T-cells on a class II molecule. There is also data that suggests that exogenous proteins can be processed into 9/10 mer peptides that may be presented on MHC class I molecules to CD8 cytotoxic T-cells. Activated Th1 CD4 helper T-cells secrete Th1 cytokines such as IL-2 that upregulate CD8 cytotoxic T-cells. Activated Th2 CD4 helper T-cells secrete Th2 cytokines such as IL-4, IL-5 and IL-10 that activate B cells.

effect as well as memory response against future tumor challenge (Fig. 1). The primary role of a cancer vaccine is the treatment of cancer or in prevention of recurrence in a patient with surgically resected cancer, rather than “prevention” of cancer in a person who has never had cancer. Therefore, cancer vaccines are not thought of in the traditional sense of vaccines that are used for infectious diseases. If the current cancer vaccines prove to be useful in the above respects, then they may have a future role in preventing cancer in persons who have never had cancer but are at high-risk for a particular type of cancer.

Characteristics The first and most obvious types of vaccines are prepared from autologous or allogeneic tumor cells. Alternatively, membrane preparations from tumor cells may be used. In some instances, tumor cell vaccines have been combined with cytokines such as granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin-2 (IL-2). More recently, with advances in molecular biological approaches, gene modified-tumor cells expressing antigens designed to increase the immune response, or gene modified to secrete cytokines have been an additional tool used in vaccination. In addition, increase in our knowledge of tumor associated antigens (TAA) have led to the use of purified TAAs, DNA-encoding protein antigens, and/or protein derived peptides. All of these approaches are currently being tested in the clinic.

Mechanistically, the ultimate aim of a vaccine is to activate a component of the immune system such as B lymphocytes, which produce antibodies or T lymphocytes, which directly kill tumor cells. Antibodies must recognize antigens in the native protein state on the cell’s surface. Once bound, these molecules can mediate antibody-dependent cellular cytotoxicity or complementmediated cytotoxicity, both mechanisms which are capable of destroying tumor cells. T lymphocytes, on the other hand, recognize proteins as fragments or peptides that vary in size, presented in the context of major histocompatibility (MHC) antigens on the surface of the cells recognized (Fig. 1). The proteins from which the peptides are derived may be cell surface or cytoplasmic proteins. MHC antigens are highly polymorphic, and different alleles have distinct peptide binding capabilities. The sequencing of peptides derived from MHC molecules have led to the discovery of allele-specific motifs that correspond to anchor residues that fit into specific pockets on MHC class I or II molecules. T Lymphocytes There are two types of T lymphocytes, helper T lymphocytes and cytotoxic T lymphocytes (CTLs) that recognize antigens through a specific T cell receptor (TCR) in close conjunction to the CD3 molecules, which is responsible for signaling. CD4 helper T cells recognize antigens in association with class II MHC gene products, and CD8 positive CTLs recognize

Cancer Vaccines

antigens in association with class I MHC gene products. CD4 helper T cells are activated by binding via their TCR to class II molecules that contain 14–25 amino acid peptides in their antigen-binding cleft. Specialized antigen presenting cells (APCs), such as dendritic cells (DCs), macrophages, and B lymphocytes, capture extracellular protein antigens, internalize and process them, and display class II-associated peptides to CD4 helper T cells. The CD8 positive CTLs are activated by binding via their TCR to class I molecules that contain 9–10 amino acid peptides in their antigen-binding cleft. All nucleated cells can present class I-associated peptides, derived from cytosolic proteins such as viral and tumor antigens, to CD8 positive T cells. There are two types of CD4 helper T cells capable of generating either antibody or cell-mediated immune responses, based on the type of signaling they receive. Th1 CD4 helper T cells stimulate cell-mediated immunity by activating CTLs through the release of cytokines such as IL-2. Th2 CD4 helper T cells mediate an antibody response through the release of cytokines such as IL-4 and IL-10. Tumor Cells The most straightforward means of immunization is the use of whole tumor cell preparations (either autologous or allogeneic tumor cells). The advantage of this approach is that the potential TAAs are presented to the immune system for processing and presentation to the appropriate T cell precursors. The difficulty with this approach lies in the availability of fresh autologous tumor material and the sparcity of well-characterized long-term tumor cell lines. Regardless, whole tumor cell vaccines have been an area of intense interest. A variety of trials using autologous tumors for colon cancer and malignant melanoma have been reported. In one trial, freshly thawed autologous colon cancer cells were inactivated with radiation, mixed with ▶BCG (bacille Calmette-Guerin) and injected into patients who had their primary colon cancer resected but were at risk for recurrence. This study did reveal disease-free survival and overall survival trends in favor of the vaccine arm. In a melanoma study, autologous tumor cells were mixed with dinitrophenyl (DNP) and mixed with BCG. Promising results were reported for patients with metastatic disease and for patients with locally resected melanoma. The weakness of autologous cell vaccines can be overcome with the allogeneic approach: First an allogeneic vaccine is generic and developed from cell lines selected to provide multiple TAAs and a broad range of HLA expression. Second, allogeneic cells are more immunogeneic than autologous cells. Third there is no requirement to obtain tumor tissue by surgical resection for a prolonged course of immunotherapy.

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A polyvalent melanoma cell vaccine called CancerVax developed for allogeneic viable melanoma cell lines has demonstrated promising results for patients with resected metastatic disease and for resected local disease. Randomized phase III studies are ongoing in the United States comparing CancerVax plus BCG versus BCG for patients with stage III melanoma. Another variation of cell vaccines is using “shed” antigen vaccines. These are vaccines that are prepared from the material shed by viable tumor cells into culture medium. The potential advantage is that it contains a broad range of antigens expressed on the surface of melanoma cells and the shed antigens are partially purified. Trials of such vaccines in melanoma patients have demonstrated specific humoral and cellular immune responses in patients and promising early clinical results. Another approach to tumor cell vaccines is the introduction of foreign genes encoding cytokines such as IL-2 and GM-CSF into tumor cells. Alternatively, molecules designed to increase the immunogenicity of the tumor cell such as CD80 and CD86. Gene transfer can be accomplished by transfection of plasmid constructs (electroporation) or transduction using a viral vehicle such as a retrovirus or an adenovirus. Another option tested for gene transfer is physical gene delivery in which a plasmid or “naked” DNA is delivered directly into tumor cells. There are a number of mechanisms to carry this out including liposomes as gene carriers, use of a “gene gun,” electroporation and calcium phosphate-mediated gene transfer. In one phase I trial, 21 patients with metastatic melanoma were vaccinated with irradiated autologous melanoma cells engineered to secrete human GM-CSF. Metastatic lesions resected after vaccination were densely infiltrated with T lymphocytes and plasma cells and showed extensive tumor destruction. Peptides and Carbohydrates An advantage to peptide vaccines is that they can be synthetically generated in a reproducible fashion. The major disadvantage is that they are restricted to a single HLA molecule and are not of themselves very immunogenic. To increase their immunogenicity, peptides may be injected with adjuvants, cytokines or liposomes or presented on DCs. Whole proteins have the advantage over peptides in that they can be processed for a wider range of MHC class I and II antigens. Mucins such as MUC I are heavily glycosylated high molecular weight proteins abundantly expressed on human cancers of epithelial origin. The MUC I gene is over-expressed and aberrantly glycosylated in a variety of cancers including colorectal cancer. MUC 1 is being widely used as a focus for vaccine development. Using expression-cloning techniques, several groups have cloned the genes encoding melanoma antigens

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recognized by T cells and have identified the immunogenic epitopes presented on HLA molecules. Ten different melanoma antigens have been identified. Direct immunization using the immunodominant peptides from the tumor antigens or recombinant viruses such as adenovirus, fowlpox and vaccinia virus encoding the relevant genes have been pursued to immunize patients with advanced melanoma. Initial results have demonstrated increased anti-tumor T cell reactivity in patients receiving peptide immunization. Immunization in melanoma patients with melanoma antigens have been reported. One study showed that immunization of melanoma patients with MAGE-1 peptide pulsed on DCs induced melanoma-reactive and peptide specific CTL responses at the vaccination sites and at distant tumor deposits. Administration of the gp-100 molecule in conjunction with high-dose bolus IL-2 to 31 patients with metastatic melanoma revealed an objective response of 42%. This is compared with the typical response of high-dose systemic IL-2 without peptide of only 15%. Based on these data, a randomized trial was initiated to compare the peptide vaccine plus IL-2 versus IL-2 alone in metastatic melanoma patients. Immunization against tumor-associated carbohydrate antigens has also been attempted. Carbohydrate antigens typically bypass T cell help for B cell activation. Investigators demonstrated that some carbohydrates may activate an alternative T cell pathway. Vaccine studies have been reported using the GM-2 ganglioside vaccine. Patients were pretreated with low dose cyclophosphamide. After a minimum follow up of 72 months, there was a 23% increase in disease-free interval and a 17% increase in overall survival in patients who produced antibody against GM-2. This suggested a benefit to the GM-2 ganglioside vaccine which has led to a current phase III trial. Recombinant Vaccines Expressing Tumor Antigens The carcinoembryonic antigen (CEA) is highly expressed on colorectal cancer and on a variety of other epithelial tumors, and is thought to be involved in cell-cell interactions. A recombinant vaccinia virus expressing human CEA (rV-CEA) stimulates specific T cell responses in patients. This was the first vaccine to demonstrate human CTL responses to specific CEA epitopes and class I HLA-2 restricted T cell mediated lysis, and demonstrated the ability of human tumor cells to endogenously process CEA to present a specific CEA peptide in the context of a MHC for T-cell mediated lysis. Anti-idiotype Vaccines The idiotype network offers an elegant approach to transforming epitope structures into idiotypic determinants expressed on the surface of antibodies. According

to the network concept, immunization with a given TAA will generate production of antibodies against these TAA, which are termed Ab1; the Ab1 is then used to generate a series of anti-idiotype antibodies against the Ab1, termed Ab2. Some of these Ab2 molecules can effectively mimic the three-dimensional structure of the TAA identified by the Ab1. These Ab2 can induce specific immune responses similar to those induced by the original TAA and therefore can be used as surrogate TAAs. Immunization with Ab2 can lead to the generation of anti-anti-idiotypic antibodies (Ab3) that recognize the corresponding original tumorassociated antigen identified by Ab1. The anti-idiotype antibody represents an exogenous protein that should be endocytosed by APCs and degraded to 14–25 mer peptides to be presented by class II antigens to activate CD4-helper T cells. Activated Th2 CD4-helper T cells secrete cytokines such as IL-4 that stimulate B cells that have been directly activated by Ab2 to produce antibody that binds to the original antigen identified by Ab1. In addition, activation of Th1 CD4-helper T cells secrete cytokines that activate T cells, macrophages and natural killer cells that directly lyse tumor cells, and in addition, contribute to ADCC. Th1 cytokines such IL-2 also contribute to the activation of a CD8CTL response. This represents a putative pathway of endocytosed anti-idiotype antibody. The anti-idiotype antibody may be degraded to 9/10 mer peptides to present in the context of class I antigens to activate CD8-cytotoxic T cells, which are also stimulated by IL-2 from Th1 CD4-helper T cells. Anti-idiotype antibodies that mimic distinct TAAs expressed by cancer cells of different histology have been used to implement active specific immunotherapy in patients with malignant diseases including colorectal carcinoma, malignant melanoma, breast cancer, B cell lymphoma and leukemia, ovarian cancer, or lung cancer. A murine monoclonal anti-idiotype antibody, 3H1 or CeaVac, which mimics CEA was developed by the authors and was used in a phase I clinical trial. Among 23 patients with advanced colorectal cancer, 17 patients generated anti-anti-idiotypic Ab3 responses, and 13 of these responses were proven to be true anti-CEA responses. The median survival of 23 evaluable patients was 11.3 months, with 44% 1-year survival. Toxicity was limited to local swelling and minimal pain. In another clinical trial, 32 patients with resected colorectal cancer were randomized to treatment with CeaVac. All 32 patients entered into this trial generated high-titer IgG anti-CEA antibodies, and ~75% generated CEA specific T cell responses. These data demonstrated that 5-fluorouracil based chemotherapy regimens did not have any adverse effect on the immune response developed by CeaVac. TriGem, an anti-idiotype monoclonal antibody that mimics the disialoganglioside GD2 was used as a vaccine in

Cancer Vaccines

clinical trial consisting of 47 patients with stage IV melanoma. Forty of 47 patients developed high-titer IgG anti-GD2 antibodies. Seventeen patients were stable on the study from 8 to 34 months. Disease progression occurred in 27 patients on the study from 1 to 9 months. For the 26 patients with soft tissue disease, the median overall survival has not been reached. For 18 patients with visceral metastasis, the median overall survival was 15 months. These results exceed historical controls with stage IV melanoma. Another anti-idiotype monoclonal antibody, TriAb, which mimics the human milk fat globule (HMFG) membrane antigen, is highly overexpressed on breast cancer cells and a variety of other cancer cells, including ovarian cancer, non small-cell lung cancer, and colon cancer. Immunizations with this anti-idiotype antibody elicited both anti-HMFG antibodies and idiotype specific T cell responses in patients with breast cancer in the adjuvant setting as well as in patients with advanced disease following autologous bone marrow transplantation. Although these initial clinical data are promising, active specific immunotherapy with antiidiotype antibodies need to be tested in combination with other conventional and experimental therapies to overcome the multiple mechanisms by which tumor cells escape immune recognition and destruction. The anti-idiotype vaccine therapy for patients with minimal residual disease might be curative in the adjuvant setting and may improve the quality of patients’ life. Dendritic Cell-based Vaccines DCs are the professional APCs of the immune system and are present in peripheral tissues, where they capture antigens. These antigens are subsequently processed into small peptides as the DCs mature and move towards the draining secondary lymphoid organs. There the DCs present the peptides to naïve T cells, thereby inducing a cellular immune response that involves both CD4 T helper 1 (Th1) cells and cytotoxic CD8 T cells. DCs are also important at inducing humoral immune response through their capacity to activate naïve and memory B cells. DCs can also activate natural killer (NK) cells and natural killer T (NKT) cells. Therefore, DCs can conduct all of the elements of the immune orchestra, and they are therefore a fundamental target and tool for vaccination. The development of ex vivo techniques for generating large numbers of DCs in vitro from mouse bone marrow cells supplemented with either GM-CSF alone or GM-CSF plus IL-4 allowed the approach of DC-based tumor vaccination to be fully exploited. Numerous studies in mouse tumor models have shown that DCs pulsed with tumor antigens can induce protective and therapeutic anti-tumor immunity. In 1996, Hsu et al reported the first DC-based clinical trial of follicular B cell lymphoma patients who were treated

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with peripheral blood-derived DCs pulsed with a tumorspecific idiotype (Id) protein. Of these ten patients, eight developed a proliferative cellular response to Id and one patient developed an Id-specific CTL response. However, tumor regression was not reported in these DC-vaccinated patients. In several other trials a correlation between immunological and clinical outcome has been demonstrated. However, the efficacy of therapeutic DC-based vaccination has been modest and these trials have had similar clinical outcome: mainly, immunized patients often demonstrate significant activation of adaptive immunity to the targeted tumor antigen(s) as shown by various methods such as tetramer analysis, IFN-γ ELISPOT, and 51Cr-release assay; but only a limited number of immunized patients demonstrate significant tumor regression. The complexity of the DC system requires rational manipulation of DCs to achieve protective or therapeutic immunity. Further research is needed to analyze the immune responses induced in patients by distinct ex vivo generated DC subsets that are activated through different pathways. These ex vivo strategies should help to identify the parameters for in vivo targeting of DCs. Overall, we remain optimistic that improved cancer vaccines will ultimately yield favorable clinical results, particularly after these approaches have been modified in a manner that integrates recent progress related to the physiology of DCs and our improved understanding of how tumors and the host immune system interact with each other. Conclusion There exist several promising immunologic approaches to vaccine therapy of cancer. The challenge of immunotherapy research is to determine which combination of approaches leads to a favorable clinical response and outcome. Several studies have shown enhanced survival of patients receiving vaccines; however, a randomized phase III clinical trial has yet to show a statistically significant improvement in the survival of such patients. ▶Cancer-Germline (CG) Antigens ▶Cytokine Receptor as the Target for Immunotherapy and Immunotoxin Therapy ▶T-cell Response

References 1. Emens LA (2006) Roadmap to a better therapeutic tumor vaccine. Int Rev Immunol 25:415–443 2. Dalgleish AG, Whelan MA (2006) Cancer vaccines as a therapeutic modality: the long trek. Cancer Immunol Immunother 55:1025–1032 3. Nestle FO, Farkas A, Conrad C (2005) Dendritic-cellbased therapeutic vaccination against cancer. Curr Opin Immunol 17:163–169

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4. Saha A, Chatterjee SK, Mohanty K et al. (2003) Dendritic cell based vaccines for immunotherapy of cancer. Cancer Ther 1:299–314 5. Bhattacharya-Chatterjee M, Chatterjee SK, Foon KA (2002) Anti-idiotype antibody vaccine therapy for cancer. Expert Opin Biol Ther 2:869–881

Cannabinoids G UILLERMO V ELASCO, M ANUEL G UZMA´ N Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, Madrid, Spain

Synonyms

Cancer Without Disease ▶Dormancy

Cancers of Hormone-responsive Organs or Tissues ▶Endocrine-Related Cancers

Phyto-cannabinoids; Endocannabinoids; cannabinoids; Marijuana

Synthetic

Definition Cannabinoids are a family of lipid molecules that comprises a series of metabolites produced by the hemp plant Cannabis sativa (the phyto-cannabinoids); several fatty-acid derivatives endogenously produced by most animals (the endogenous ligands for cannabinoid receptors), and different synthetic compounds structurally or functionally related with the natural cannabinoids. Activation of cannabinoid receptors by some of these molecules reduce the symptoms associated to cancer chemotherapy and inhibit the growth of tumor cells in culture and in animal models of ▶tumor xenografts.

Characteristics

Cancer-Testis-Antigens Definition Tumor antigens which are only expressed by malignant tumor cells as well as by germ line cells in the testes. The MAGE1 protein was one of the first cancer-testis antigen originally identified in melanoma cells but also expressed by various other tumor types. It belongs to a large family of “MAGE-related” proteins whose biological function is still unclear. It is thought that common epigenetic alterations in tumors lead to re-expression of genes which are normally only expressed in the germ line. ▶Melanoma Vaccines ▶Cancer Germline (GC) Antigens ▶GAGE Proteins

Candidat of Metastasis 1 ▶p8 Protein

The hemp plant Cannabis sativa produces approximately 70 unique compounds known as cannabinoids, of which Δ9-tetrahydrocannabinol (THC) is the most important owing to its high potency and abundance in cannabis. THC exerts a wide variety of biological effects by mimicking endogenous substances – the endocannabinoids anandamide and 2-arachidonoylglycerol – that bind to and activate specific cannabinoid receptors (Fig. 1a and b). So far, two cannabinoid-specific ▶G-protein-coupled receptors have been cloned and characterized from mammalian tissues: The CB1 receptor is particularly abundant in discrete areas of the brain, but is also expressed in peripheral nerve terminals and various extra-neural sites. In contrast, the CB2 receptor was initially described to be present in the immune system, although recently it has been shown that expression of this receptor also occurs in cells from other origins including many types of tumor cells. Signaling Pathways Modulated by Cannabinoid Receptors Most of the physiological, therapeutic and psychotropic actions of cannabinoids rely on the activation of CB1 and CB2 receptors (Fig. 1a and b). Extensive molecular and pharmacological studies have demonstrated that cannabinoids inhibit adenylyl cyclase through CB1 and CB2 receptors. The CB1 receptor also modulates ion channels, inducing, for example, inhibition of N- and

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Cannabinoids. Figure 1 Cannabinoids, cannabinoid receptors and its mechanisms of action. (a) Δ9-tetrahydrocannabinol (THC), the main active component of marijuana, and the endocannabinoids anandamide and 2-Arachidonoylglycerol are ligands of cannabinoid receptors. (b) Both CB1 and CB2 receptors belong to the family of G-protein-coupled receptors. Binding of cannabinoids to cannabinoid receptors leads, among other actions and depending on the cell context, to: inhibition of adenylyl cyclase, modulation of the activity of several ion channels, modulation of phosphatidylionsoitol-3 kinase (PI3K) and of mitogen activated protein kinase cascades, or stimulation of ceramide generation.

P/Q-type voltage-sensitive Ca2+ channels and activation of G protein-activated inwardly rectifying K+ channels. Besides these well-established signaling events that mediate – among others – the neuromodulatory actions of the endocannabinoids, cannabinoid receptors also modulate several pathways that are more directly involved in the control of cell proliferation and survival, including extracellular signal-regulated kinase, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase, ▶phosphatidylinositol 3-kinase/Akt and focal adhesion kinase. In addition, cannabinoids stimulate the generation of the bioactive lipid second messenger ceramide via two different pathways: sphingomyelin hydrolysis and ▶ceramide synthesis de novo. Palliative Effects of Cannabinoids in Cancer Cannabinoids have been known for several decades to exert palliative effects in cancer patients, and nowadays

capsules of THC (Marinol-TM) and its synthetic analogue nabilone (Cesamet-TM) are approved to treat nausea and emesis associated with cancer chemotherapy. In addition, several clinical trials are testing other potential palliative properties of cannabinoids in oncology such as appetite stimulation and analgesia.

Mechanism Involved in the Antiemetic Effect of Cannabinoids One of the most important physiological functions of the cannabinoid system is to modulate synaptic transmission. Thus, activation of cannabinoid receptors at presynaptic locations leads to reduced neurotransmitter release. As the CB1 receptor is present in cholinergic nerve terminals of the myenteric and submucosal plexus of the stomach, duodenum and colon, it is likely that cannabinoid-induced inhibition of digestive tract motility is due to blockade of acetylcholine release in

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these areas. There is also evidence that cannabinoids act on CB1 receptors localized in the dorsal vagal complex of the brainstem – the region of the brain that controls the vomiting reflex. In addition, endocannabinoids and their inactivating enzymes are present in the gastrointestinal tract and may play a physiological role in the control of emesis.

ganglia, peripheral terminals of primary afferent neurons). Endocannabinoids serve naturally to suppress pain by inhibiting nociceptive neurotransmission. In addition, peripheral CB2 receptors might mediate local analgesia, possibly by inhibiting the release of various mediators of pain and inflammation, which could be important in the management of cancer pain.

Mechanism Involved in Appetite Stimulation by Cannabinoids The endogenous cannabinoid system may serve as a physiological regulator of feeding behavior. For example, endocannabinoids and CB1 receptors are present in the hypothalamus, the area of the brain that controls food intake; hypothalamic endocannabinoid levels are reduced by leptin, one of the most prominent anorexic hormones; and blockade of tonic endocannabinoid signaling with the CB1 antagonist rimonabant – inhibits appetite and induces weight loss. CB1 receptors present in nerve terminals and adipocytes also participate in the regulation of feeding behavior.

Antitumoral Effects of Cannabinoids Cannabinoids have been proposed as potential antitumoral agents on the basis of experiments performed both in cultured cells and in animal models of cancer. A number of plant-derived, synthetic and endogenous cannabinoids are now known to exert antiproliferative actions on a wide spectrum of tumor cells in culture. More importantly, cannabinoid administration to nude mice curbs the growth of various types of tumor xenografts, including lung carcinoma, glioma, thyroid epithelioma, lymphoma, skin carcinoma, pancreatic carcinoma and melanoma. The requirement of cannabinoid receptors for this antitumoral activity has been revealed by various biochemical and pharmacological approaches, in particular by determining cannabinoid receptor expression in the tumors and by using selective cannabinoid receptor agonists and antagonists. Although the downstream events by which cannabinoids exert their antitumoral action have not been completely unraveled, there is substantial evidence for the implication of at least two mechanisms: induction of ▶apoptosis of tumor cells and inhibition of tumor ▶angiogenesis (Fig. 2a).

Mechanism Involved in the Analgesic Effect of Cannabinoids Cannabinoids inhibit pain in animal models of acute and chronic ▶hyperalgesia, ▶allodynia and spontaneous pain. Cannabinoids produce antinociception by activating CB1 receptors in the brain (thalamus, periaqueductal grey matter, rostral ventromedial medulla), the spinal cord (dorsal horn) and nerve terminals (dorsal root

Cannabinoids. Figure 2 Mechanism of cannabinoid antitumoral action. (a) Cannabinoid administration decreases the growth of tumors by several mechanisms, including at least: (i) reduction of tumor angiogenesis, (ii) induction of tumor cell apoptosis, and perhaps (iii) inhibition of tumor cell migration and invasiveness. (b) Cannabinoid treatment induces apoptosis of several types of tumor cells via ceramide accumulation and activation of an ER stress-related pathway. The stress-regulated protein p8 plays a key role in this effect by controlling the expression of ATF-4, CHOP and TRB3. This cascade of events triggers the activation of the mitochondrial intrinsic apoptotic pathway through mechanisms that have not been unraveled as yet. Cannabinoids also decrease the expression of various tumorprogression molecules such as VEGF and MMP2.

Cannabinoids

Induction of Apoptosis Different studies have shown that the pro-apoptotic effect of cannabinoids on tumor cells relies on the stimulation of cannabinoid receptors and a subsequent activation of the proapoptotic ▶mitochondrial intrinsic pathway. In glioma and pancreatic tumor cells, treatment with cannabinoids leads to accumulation of the pro-apoptotic sphingolipid ceramide which in turn leads to up-regulation of the stress-regulated protein ▶p8, which belongs to the family of ▶HMG-I/Y transcription factors. The acute increase of p8 levels after cannabinoid treatment triggers a cascade of events that involves the up-regulation of several genes involved in the ▶endoplasmic reticulum (ER) stress response including the activating transcription factor 4 (ATF-4) and the C/EBP-homologous protein (CHOP). These two transcription factors cooperate in the induction of the ▶tribbles homologue 3 (TRB3), a ▶pseudokinase that is involved in the induction of apoptosis (Fig. 2b). The processes downstream of ER stress activation involved in the execution of cannabinoid-induced apoptosis of tumor cells are not completely understood yet but include inhibition of the anti-apoptotic kinase Akt and activation of the mitochondrial intrinsic pathway. Of interest the pro-apoptotic effect of cannabinoids is selective of tumor cells. For instance, treatment of primary cultured astrocytes with these compounds does not trigger ceramide accumulation, induction of the aforementioned ER stress-related genes or apoptosis. Furthermore, cannabinoids promote the survival of astrocytes, oligodendrocytes and neurons in different models of injury, supporting the notion that cannabinoids activate opposite responses in transformed and non-transformed cells. Inhibition of Tumor Angiogenesis To grow beyond minimal size, tumors must generate a new vascular supply (angiogenesis) for purposes of cell nutrition, gas exchange and waste disposal, and therefore blocking the angiogenic process constitutes one of the most promising antitumoral approaches currently available. Immunohistochemical analyses in mouse models of glioma, skin carcinoma and melanoma have shown that cannabinoid administration turns the vascular hyperplasia characteristic of actively growing tumors to a pattern of blood vessels characterized by small, differentiated and impermeable capillaries. This is associated with a reduced expression of ▶vascular endothelial growth factor (VEGF) and other proangiogenic cytokines such as angiopoietin-2 and placental growth factor, as well as of type 1 and type 2 VEGF receptors, in cannabinoid-treated tumors. Pharmacological inhibition of ceramide synthesis de novo abrogates the antitumoral and antiangiogenic effect of cannabinoids in vivo and decreases VEGF

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production by glioma cells in vitro and by gliomas in vivo, indicating that ceramide plays a general role in cannabinoid antitumoral action. Other reported effects of cannabinoids might be related with the inhibition of tumor angiogenesis and invasiveness by these compounds (Fig. 2a and b). Thus, activation of cannabinoid receptors on vascular endothelial cells in culture inhibits cell migration and survival. In addition, cannabinoid administration to glioma-bearing mice decreases the activity and expression of ▶matrix metalloproteinase-2, a proteolytic enzyme that allows tissue breakdown and remodeling during angiogenesis and metastasis. In line with this notion, cannabinoid intraperitoneal injection reduces the number of metastatic nodes produced from paw injection in lung, breast and melanoma cancer cells in mice. Therapeutic Potential of Cannabinoids as Antitumoral Agents On the basis of these preclinical findings, a pilot clinical study of THC in patients with recurrent ▶glioblastoma multiforme has been recently run. Cannabinoid delivery was safe and could be achieved without significant psychoactive effects. Also, although the limited number of patients involved in the trial did not permit the extraction of statistical conclusions, median survival of the cohort was similar to other studies performed in recurrent glioblastoma multiforme with temozolomide and carmustine, the drugs of reference for the treatment of these tumors. In addition THC administration correlated with decreased tumor cell proliferation and increased tumor cell apoptosis. The significant antiproliferative action of cannabinoids, together with their low toxicity compared with other chemotherapeutic agents and their ability to reduce symptoms associated to standard chemotherapies, might make these compounds promising new antitumoral agents.

References 1. Mackie K (2006) Cannabinoid receptors as therapeutic targets. Annu Rev Pharmacol Toxicol 46:101–122 2. Guzman M (2003) Cannabinoids: potential anticancer agents. Nat Rev Cancer 3:745–755 3. Hall W, Christie M, Currow D (2005) Cannabinoids and cancer: causation, remediation, and palliation. Lancet Oncol 6:35–42 4. Carracedo A, Lorente M, Egia A et al. (2006) The stressregulated protein p8 mediates cannabinoid-induced apoptosis of tumor cells. Cancer Cell 9:301–312 5. Guzman M, Duarte MJ, Blazquez C et al. (2006) A pilot clinical study of Delta9-tetrahydrocannabinol in patients with recurrent glioblastoma multiforme. Br J Cancer 95:197–203

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Cap Definition Structure added to the 5′-end of nascent eukaryotic mRNA molecules. It aligns eukaryotic mRNAs on the ribosome during translation. ▶Funnel Factors

Cap-Binding Complex Definition A protein complex that recruits messenger RNA to the ribosome. ▶MCT-1 Oncogene

Cap-Dependent Translation Definition In eukaryotes, translation can usually be initiated at the 5′ end “cap” of the mRNA since cap-recognition is required for the assembly of the initiation complex. Most of the transcripts are translated by cap-dependent translation. Alternatively, some transcripts might be translated from an internal ribosome entry site.

family. The subcellular localization of CapG protein is largely nuclear, though other ▶gelsolin family members localize only in cytoplasm, suggesting that CapG may have a function in addition to cytoskeleton modulation. The human CapG gene, mapped at 2p11.2, is ubiquitously expressed in normal tissues, but down-regulation of the expression was observed in roughly one third of melanomas, stomach, and lung cancers. Furthermore, CapG has been shown to possess tumor suppressor activity when transfected into certain cancer cell lines. ▶Gelsolin family

Capillary Hemangioblastoma Definition Low-grade tumor comprised of stromal cells and abundant capillaries, preferentially occurring in the cerebellum. Multiple hemangioblastomas are associated with the Von-Hippel Lindau disease. ▶Uncertain or Unknown Histogenesis Tumors ▶Von Hippel-Lindau Tumor Suppressor Gene

CAR ▶Chimeric Antigen Receptor on T Cells

▶Rapamycin ▶Funnel Factors

Carbonyl Reductases Capecitabine ▶Reductases

Definition

Capecitabine is a 5-fluorouracil (Fu) oral ▶prodrug. ▶Erlotinib (Tarceva®)

CapG Definition Is, a 45-kDa protein composed of 348 amino acids, is a member of the gelsolin/villin actin-modulating protein

Carboplatin Definition Second-generation platinum compound with a broad spectrum of antineoplastic properties. Carboplatin contains a platinum atom complexed with two ammonia groups and a cyclobutane-dicarboxyl residue. This agent is activated intracellularly to form reactive platinum complexes that bind to nucleophilic groups

Carcinoembryonic Antigen

such as GC-rich sites in DNA, thereby inducing intrastrand and interstrand DNA ▶cross-links, as well as DNA-protein cross-links. These carboplatin-induced DNA and protein effects result in ▶apoptosis and cell growth inhibition. This agent possesses tumoricidal activity similar to that of its parent compound, ▶cisplatin, but is more stable and less toxic.

Carboxylesterase Definition Carboxylesterases, present in serum, in the epithelial lining of the intestines, in tumor tissue, and in high content in the liver, are enzymes responsible for metabolizing (hydrolysis) a wide variety of drugs and ▶xenobiotics. The carboxylesterase genes are located on chromosome 16q13-q22 and are supposed to be highly conserved during evolution. ▶Irinotecan

Carboxypeptidase Definition A type of protease or hydrolase that removes the amino acid at the free carboxyl end of a polypeptide chain. ▶Prostate-Specific Membrane Antigen

Carcinoembryonic Antigen P ETER T HOMAS Departments of Surgery and Biomedical Sciences, Creighton University, Omaha, NE, USA

Synonyms CEA; CD66e; CEACAM5

Definition CEA is a glycoprotein of approximately 150–180 kDa. It’s measurement in serum is used clinically as a ▶biomarker for a number of cancers (pancreas, breast, stomach, ovary, lung and medullary carcinoma of the thyroid) but its primary use is in monitoring cancers of the colon and rectum.

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Characteristics Protein Structure CEA was discovered in 1965 in ▶colon cancer and fetal tissue extracts and was described as an ▶oncofetal antigen. Many of the advances in tumor marker research lead directly back to the discovery of CEA The protein component of CEA is 79 kDa in size and the balance of 70–100 kDa is made from up to 28 complex N-linked multi-antennary carbohydrate structures containing N-acetyl-glucosamine, mannose, galactose, fucose and sialic acid. Low resolution X-ray studies have shown an elongated monomeric structure that could be described as a bottle brush. The molecule is composed of a series of six disulphide linked immunoglobulin like domains (IgC2-like) of either 93 (type A) or 85 (type B) amino acids and a seventh Ndomain of 108 amino acids which is an IgV (variable antigen recognition domain) structure without the stabilizing disulphide bridge. CEA can attach to the cell membrane and this is achieved by post translational modification of a small (26 amino acids) hydrophobic C-terminal domain to a ▶glycosyl phosphatidyl inositol linkage (see Fig. 1A). Cleavage of this linkage by ▶phospholipases releases CEA into the lumen of the intestine or other extra-cellular compartments. The CEA Gene Family The complete gene for CEA has been cloned and it includes a promoter region that confers cell type specific expression. The ▶CEA gene family comprises of 29 genes or pseudogenes located between the q13.1 and q13.3 regions of chromosome 19. The family can be divided into three groups: The CEA group of 12 genes, the pregnancy specific glycoprotein group (PSG) of 11 genes and a third group composed of 6 pseudogenes. Only 16 of the 29 genes are expressed. Sequence data has shown that the CEA family is a subset of the Immunoglobulin supergene family. Comparative sequence studies of the CEA gene family from various species suggest that the CEA family have a common ancestry and arose relatively recently in evolution. Function of CEA in Normal and Cancerous Tissue In general members of the CEA family subgroup have a ubiquitous distribution in adult tissues. However CEA itself has a more restricted expression being found only in colon, pyloric mucus cells, epithelial cells of the prostate, in sweat glands and in squamous cells in the tongue, cervix and esophagus. In the colon CEA is located at the apical surface of colonic enterocytes and is associated with the ▶glycocalyx or fuzzy coat. In the normal colon CEA is maximally expressed on columnar cells at the level of the free luminal surface. CEA is also found in goblet cells in association with mucins. The function of CEA in the normal individual is not well understood and has been the subject of much

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Carcinoembryonic Antigen. Figure 1 CEA Structure (a) Showing insertion of CEA into the plasma membrane (down arrow) the Ig domain structure and the position of the N-linked sugar chains. An arrow marks the position of the PELPK receptor recognition sequence. (b). Shows homotypic binding between two CEA molecules with attachment between the N and A3 domains. (Structures are modified from the CEA Homepage http://cea. klinikum.uni-meunchen.de)

speculation. It has been estimated that the normal person can produce 70 mg or more of CEA a day and excrete it in the feces. CEA has been shown to bind to various fimbriated gut pathogens and therefore it has been suggested that it has a function in protecting the gut epithelia. In cancer cells CEA may perform a number of functions. Unlike the normal colonocyte where CEA expression is highly polarized in cancers this polarity is lost and its expression occurs through the whole of the cell surface. It has been shown that CEA

can act as a Ca2+ independent homotypic adhesion molecule binding with itself through an interaction between the N and A3 domains (Fig. 1B) and causing aggregation of tumor cells. This allows the malignant epithelium to adopt a multi-layered structure and may disrupt the normal pattern of differentiation. CEA can also bind heterotypically to other members of the gene family including the ▶nonspecific cross reacting antigen (NCA, CD66c, CEACAM6) and the ▶biliary glycoprotein (BGP, CD66a, ▶CEACAM1) of which seven different forms have been identified. It is unlikely that CEA functions as a ▶cell adhesion molecule in the normal colon because of its apical expression. CEA is cleared from the circulation by the hepatic ▶macrophages (▶Kupffer cells). A cell surface receptor identical to the heterogeneous nuclear RNA binding protein ▶hnRNP M4 recognizes a penta-peptide (Pro– Glu–Leu–Pro–Lys (PELPK)) located at the hinge region between the N and first immunoglobulin loop domain (A1) of CEA. Patients with a mutation in the region coding for this peptide have extremely high circulating CEA levels presumably due to the inability of Kupffer cells to clear the protein from the blood. CEA has also been implicated in the development of hepatic ▶metastasis from colorectal cancers by the induction of a localized inflammatory response that affects retention and implantation in the liver. Cytokines produced also protect the tumor cells against the toxic effects of hypoxia. CEA producing cells therefore have a selective advantage for growth in the liver. Recent studies have also shown that CEA can protect cancer cells from a form of programmed cell death called ▶anoikis and this also seems to involve the PELPK motif and inhibition of Trail-R2 (▶DR5) signaling. CEA is also protective against other forms of ▶apoptosis including drug and UV light induced programmed cell death. The related protein CEACAM-1, however, is a pro-apoptotic protein. Clinical Aspects The main clinical use for CEA is as a tumor marker especially for cancers in the colon and rectum and approximately 90% of these cancers produce CEA. CEA has also been used as a marker for breast and small cell cancer of the lung. Approximately 50% of breast and 70% of small cell cancers express CEA. Accurate immuno-assays are commercially available for its measurement in body fluids. Immunohistochemistry on biopsy or resection specimens is also often carried out, for example the intensity of CEA staining has been associated with a worse prognosis for breast cancer. Normal serum levels are T (promotor) and c.IVS2-105A>G (intron). There are considerable differences in the frequencies and distribution of CDKN2A mutations across the world. Many mutations have been shown to arise from a common founder, and are more frequent in particular geographic locations. For example Sweden and the Netherlands have single predominant founder mutations (p.R112_L113insR, and p16 Leiden respectively) involving over 90% of families tested. The G101W mutation, common in Italy, France and Spain, has been calculated to arise from a single genetic event approximately 93 generations ago. Many additional mutations have been repeatedly reported, and where analysis has been performed these have invariably been shown to be due to common founders. The only exception to this appears to be a 24 bp insertion in exon 1a, that has arisen multiple times, presumably because of DNA slippage over a 24 bp repeat region.

Mutation of ARF Germline mutations affecting ARF but not p16INK4a have been reported in a small number (~3%) of melanoma families. Whereas the distribution of p16 mutation types (approximately 70% missense or nonsense, 23% insertion or deletion, 5% splicing and 2% regulatory) is consistent with that observed in the Human Genome Mutation Database, the reported ARF specific mutations are almost all either splicing mutations (affecting the 3′ splice site of exon 1b) or large deletions.

Penetrance The pattern of susceptibility in melanoma pedigrees is consistent with the inheritance of autosomal dominant genes with incomplete penetrance. The overall penetrance of CDKN2A mutations in melanoma families has been estimated to be 0.30 by age 50 years and 0.67 by age 80 years. There is significant variation in the penetrance of CDKN2A mutations with geographical location. By age 50 years penetrance was estimated to be; 0.13 in Europe, 0.5 in the United States, and 0.32 in Australia, by age 80 years; 0.58 in Europe, 0.76 in the United States, and 0.91 in Australia (Fig. 4). This indicates that the CDKN2A mutation penetrance varies with melanoma population incidence rates, thus the same factors that effect population incidence of melanoma may also mediate CDKN2A penetrance.

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Modifiers of Penetrance of CDKN2A Mutations The MC1R gene (16q24) which encodes for the melanocyte-stimulating hormone has been shown to be a risk factor in families with segregating CDKN2A mutations. MC1R variants have been shown to act as modifier alleles, increasing the penetrance of CDKN2A mutations and reducing the age of onset of melanoma.

CDKN2A. Figure 4 Age specific penetrance estimates for CDKN2A mutations. Penetrance is shown for melanoma pedigrees from Australia, Europe, America (US) and all geographic locations combined.

Multiple Primary Melanoma General characteristics of inherited susceptibility to many types of cancer are early age of onset and the development of multiple primary tumors. Hence the presence of multiple primary melanomas (MPM) in an individual may be a sign of them being a CDKN2A mutation carrier. This is the case for a small proportion (13/133, 10%) of MPM cases without a family history of the disease. In contrast, analysis of MPM cases with a family history of disease yields CDKN2A mutations in 55/139 (40%) of samples tested. The proportion of CDKN2A mutations in sporadic MPM cases increases with increasing number of melanomas (10/119 (8.5%) of cases with two primary melanomas, compared to 11/83 (33%) cases with 3 or more primary tumors). CDKN2A Mutations and Non-Melanoma Cancers Since CDKN2A is a tumor suppressor found to be inactivated in a wide range of different tumors, one might expect individuals carrying germline mutations of CDKN2A to be prone to cancers other than melanoma. ▶Breast, ▶prostate, ▶colon, and ▶lung cancers, have been suggested to be associated with CDKN2A mutations, however, these common cancers may occur in CDKN2A positive pedigrees by chance. Convincing evidence for susceptibility to another tumor type has been shown only for pancreatic cancer, which has been shown to be significantly associated with CDKN2A mutations in all regions except Australia, the reason for this is not yet understood. There appears to be no evidence of an association between neural system tumors (NSTs) and CDKN2A mutations involving p16. However, there is marginal evidence for the association of NSTs with ARF specific mutations.

CDKN2a Polymorphisms as Low Risk Factors The A148T variant, located in exon 2 of the CDKN2A gene has no observed effect on p16 function, and does not segregate with disease in melanoma pedigrees. The contribution of this polymorphism to melanoma risk remains unclear, an association with increase in risk has been seen in some populations, but not in others. The 500 C > G and the 540 C > T polymorphisms in the 3′ untranslated region of the CDKN2A gene have been shown to be associated with melanoma risk. The frequencies of the rare alleles at these loci have been shown to be higher in melanoma cases than in controls. It is possible that these variants might alter the stability of the CDKN2A transcript or the level of transcription, or that they may be in linkage disequilibrium with an unidentified variant which is directly responsible for melanoma predisposition. The contribution of these polymorphisms to melanoma risk is likely to be small in comparison to that of CDKN2A inactivating mutations.

CDKN2A and the Atypical Mole Syndrome Since the description of the “B-K mole syndrome” much debate has ensued regarding the association between melanoma and the ▶atypical mole syndrome (AMS). Several authors have concluded that atypical moles segregate independently of CDKN2A mutations, although individuals with high numbers of naevi in melanoma-prone families are three times more likely to be CDKN2A mutation carriers than those with a low number of naevi. Support for the notion that CDKN2A is naevogenic comes from a study of a large series of 12-year-old twins in which total naevus count was found to be tightly linked to CDKN2A. This finding has recently been corroborated by two independent genome wide association studies that have mapped loci responsible for naevi in twin cohorts. Both studies showed peaks of high linkage scores at 9p21 directly over the CDKN2A gene.

References 1. Bishop JN, Harland M, Randerson-Moor J et al. (2007) Management of familial melanoma. Lancet Oncol 8(1):46–54

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2. Goldstein AM, Chan M, Harland M et al. (2007) Features associated with germline CDKN2A mutations: a GenoMEL study of melanoma-prone families from three continents. J Med Genet 44(2):99–106 3. Hayward NK (2003) Genetics of melanoma predisposition. Oncogene 22(20):3053–3056 4. Sharpless E, Chin L (2003) The INK4a/ARF locus and melanoma. Oncogene 22(20):3092–3098 5. Sharpless NE (2005) INK4a/ARF: a multifunctional tumor suppressor locus. Mutat Res 576(1–2):22–38

cDNA chips ▶Microarray (cDNA) Technology

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contributes to progression of many ▶epithelial cancers and immune dysfunctions.

Characteristics The CEA gene family encodes a set of 22 genes and 11 pseudogenes clustered in a 1.8 Mb region on human chromosome 19q13.2 between the CY2A and D19S15 marker genes. The CEA genes encompass an N-terminal Ig variable domain followed by one to six Ig constant-like domains. A striking characteristic of these proteins is their extensive ▶glycosylation on asparagine residues with multi-antennary carbohydrate chains. CEA and CEACAM1 are further modified by addition of ▶Lewisx and sialyl-Lewisx high-mannose residues. The proteins differ however, in their C-terminal regions producing either secreted entities such as the pregnancy-specific glycoproteins (▶PSG1–11) or others, tethered to the cell surface by either a glycosyl phosphatidylinositol linkage (CEA, CEACAM6–8) or a bona fide transmembrane domain (CEACAM1, CEACAM3, CEACAM4, CEACAM18–21) (Fig. 1). The CEACAM1 gene is unique in this family in that it produces twelve different splicing variants. More information on the structural features of the CEA gene family members is available at http://cea.klinikum.unimuenchen.de. CEA is a monomeric protein adopting a

CEA Gene Family N ICOLE B EAUCHEMIN McGill Cancer Centre, McGill University, Montreal, Quebec, Canada

Synonyms CEACAM1=BGP, C-CAM, CD66a; CEACAM5=CEA, CD66e; CEACAM6=NCA, CD66c; CEACAM7=CGM2; CEACAM8=CGM6, CD66b

Definition The Carcinoembryonic Antigen (▶CEA) gene family comprises 33 genes, 22 of which are expressed. All family members share similar structural features encompassing immunoglobulin (Ig) variable and/or constant domains and therefore constitute members of the large immunoglobulin superfamily. These proteins are either secreted or membrane-bound. Several CEACAMs function as homophilic or heterophilic intercellular ▶cell adhesion molecules. CEA, ▶CEACAM1, ▶CEACAM6 and ▶CEACAM7 also play a significant role as regulators of tumor cell proliferation and differentiation and their overexpression (CEA and CEACAM6) or their down-regulation (CEACAM1 and CEACAM7)

CEA Gene Family. Figure 1 Schematic representation of some members of the CEA family. Most CEA family members, except the pregnancy-specific glycoproteins (PSG) that are secreted proteins, are associated with the cell membrane (depicted in grey). The immunoglobulin variable-like domains (the N domain) are shown in blue and the immunoglobulin constant-like domains are represented in orange. The N-linked glycosylation sites are indicated by sticks and balls, colored in dark orange. The glycosylphosphatidylinositol membrane anchors are represented by arrows. The CEACAM1 gene expresses many splice variants. However, only the CEACAM-4L isoform containing four Ig domains and the longer cytoplasmic tail is shown here.

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β-barrel cylindrical shape resembling a “bottle brush,” whereas CEACAM1 is present as both a monomeric and dimeric protein. Expression and Functions of CEA Family Members in Normal and Tumor Tissues Although not ubiquitous, CEA family members exhibit a wide tissue distribution. CEA and CEACAM6 are found mainly in columnar epithelial and goblet cells of the colon in the early fetal period and are maintained in adult life. In the colonic brush border, CEA, CEACAM1, 6 and 7 demonstrate maximal expression at the free luminal surface, although CEACAM1 and 7 are also found at the lateral membrane. In addition to its expression in epithelia, CEACAM1 is located on granulocytes, lymphocytes and on endothelial cells, whereas CEACAM6 is also expressed on granulocytes and monocytes. CEACAM3 and 8 are found exclusively on granulocytes. CEA, CEACAM1 and CEACAM6 are recognized as cell adhesion molecules contacting each other by antiparallel self-binding (homophilic). Some associations are exclusive, such as ▶CEACAM8-CEACAM6. The first Ig domain is crucial in these interactions. Various CEA family members also act as heterophilic partners for ▶E-selectin and ▶galectin-3. Another striking feature of CEA family members is their ability to act as pathogen receptors binding to outer membrane proteins of Neisseria gonococci and Haemophilus influenzae as well as fimbriae of Salmonella typhimurium and Escherichia coli. In addition, CEACAM1 is the receptor for the mouse hepatitis viruses. The bacterial and viral adhesin functions of the CEA family members confer strong immunosuppressive activity in T and B lymphocytes, whereas they enhance integrindependent cell adhesion in epithelial cells with concomitant increase of the TGF-β1 receptor CD105. Other functions for CEA and CEACAM6 include inhibition of cellular differentiation as demonstrated in a number of cellular systems and inhibition of the ▶apoptotic process of ▶anoikis by activation of β1 integrins. PSG1–11 are mainly expressed in syncytiotrophoblast during the first trimester of pregnancy where they act as immunomodulators and inhibit cell-matrix interactions. CEA is abundantly expressed in tumors of epithelial origin such as colorectal, lung, mucinous ovarian and ▶endometrial adenocarcinomas. For these reasons, CEA has a long history as a marker of colonic, intestinal, ovarian and breast tumor progression and its high expression is associated with poor prognostic and recurrence of disease post-surgically. High pre-operative CEA levels are indicative of a poor prognosis whereas low levels are associated with increased survival of the patients. The tumorigenic potential of CEA and CEACAM6 was recently clarified by

transgenic overexpression of a bacterial artificial chromosome fragment of 187 kb encoding the full CEA, CEACAM6 and CEACAM7 genes. When the CEABAC transgenic mice were treated with the azoxymethane ▶carcinogen to induce colon cancers, expression of CEA and CEACAM6 was increased by 2–20 fold, a situation reminiscent to that observed in the human cancer. Information on CEACAM7 expression in tumors is more limited. It is down-regulated in colorectal cancers, but increased in gastric tumors. CEACAM6 however, exhibits a broader distribution than in the cancers described above, as it is additionally found in gastric and breast carcinomas, and ▶acute lymphoblastic leukemias. In fact, overexpression of CEACAM6 in ▶pancreatic cancer confers increased resistance to anoikis and increased metastasis. It also modulates chemoresistance to the ▶gemcitabine agent, thereby suggesting that CEACAM6 determines cellular susceptibility to apoptosis. Expression and Functions of CEACAM1 CEACAM1 expression is more complex. It is downregulated in colon, prostate, hepatocellular, bladder, endometrial, renal cell and 30% of breast carcinomas, but overexpressed in gastric and squamous lung cell carcinomas and ▶melanomas. In thyroid carcinomas, CEACAM1 was shown to restrict tumor cell growth. However, it increases the thyroid cancer metastatic potential. Manipulation of CEACAM1 expression levels in colonic, prostatic and bladder tumor cell lines, negative for CEACAM1, has indeed confirmed that expression of the longer variant, CEACAM1-4L, produces reduction of tumorigenic potential in vitro and inhibition of tumor growth in xenograft mouse models. The importance of cell surface CEACAM1 expression for maintenance of normal epithelial cellular behavior has recently been confirmed in vivo; a Ceacam1-null mouse exhibits a significantly increased colon tumor load compared to the wild-type littermates upon carcinogenic induction of colorectal cancer. CEACAM1’s role as a modulator of tumor progression depends on the involvement of its cytoplasmic domain in signaling via its tyrosine and serine phosphorylation. Two Tyr residues are positioned within Immunoreceptor Tyrosine-based Inhibition Motifs (▶ITIM). The membrane-proximal Tyr488 is a phosphorylation substrate of Src-like kinases as well as of the Insulin and Epidermal growth factor receptors. Upon Tyr phosphorylation, CEACAM1-L associates with the tyrosine phosphatases SHP-1 and SHP-2. The SHP-1CEACAM1-L protein complex regulates its function in various tissues such as inhibition of epithelial cell growth, CD4+ T cell activation and insulin clearance from hepatocytes. CEACAM1-L ▶tyrosine phosphorylation also stimulates its association with the cytoskeletal proteins G-actin, tropomyosin and paxillin, thereby

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influencing cell adhesion, and with the ▶β3 integrin, hypothesized to influence cell motility. The CEACAM1L cytoplasmic domain also carries seventeen serine residues most of which lie in consensus sequences recognized by serine kinases. However, little is know about their functional implications apart from the CEACAM1-S Thr/Ser452 and Ser456, shown to modulate direct binding to G- and F-actin, tropomyosin and calmodulin, and CEACAM1-L’s Ser503 whose mutation to an Ala residue enhances colonic or prostatic tumor development in xenograph models. Additionally, Ser503 renders permissive Tyr488 phosphorylation by the insulin receptor. Transgenic mice overexpressing a Ser503Ala CEACAM1-L mutant in the liver developed hyperinsulinemia, secondary insulin resistance and defective insulin clearance. As a consequence of the decreased insulin receptor endocytosis and altered insulin signaling, the transgenic mice became obese demonstrating increased visceral adiposity, elevated serum free fatty acids and plasma and hepatic triglyceride levels. CEACAM1-L also contributes to important functions in the immune system. It functions as an inhibitory coreceptor in T lymphocytes. Its conditional deletion in these cells amplified TCR-CD3 signaling, whereas overexpression in T cells was responsible for decreased proliferation, ▶allogeneic reactivity and cytokine production in vitro, with delayed type hypersensitivity and inflammatory bowel disease in vivo. Regulation of this function involves the ITIM motifs and the SHP-1 tyrosine phosphatase. A similar function and mechanism have been described in B lymphocytes and natural killer cells. Indeed, CEACAM1-mediated intercellular adhesion between melanomas with increased CEACAM1 expression and NK cells allows inhibition of NK-cell-elicited killing, thereby conferring upon CEACAM1 a role in tumor immunosurveillance. Similarly, heterophilic engagement of CEACAM1 with CEA, overexpressed in many tumors, also inhibits lymphocyte-mediated and NK-cell-mediated killing having therefore detrimental effects on immune surveillance. In addition, increased expression of CEACAM1 on endothelial cells present in tumors in response to ▶VEGF activation and/or hypoxia provokes a pro-angiogenic switch with increased endothelial tube formation and invasion. Therefore CEACAM1’s contribution to cancer progression most likely depends on its positive or negative expression and signaling in epithelial tumor cells, on its systemic effects on metabolism and adiposity, on its role in immunosurveillance and most probably on endothelial proliferation and invasion.

and CAAT boxes and are considered members of the housekeeping gene family. Their distal promoter regions (> −500 bp) contain highly repetitive elements, whereas their proximal promoter regions are rich in GC boxes and SP1 binding sites. Five footprinted regions have been identified in the CEA promoter, the first three binding respectively, to the Upstream Stimulatory Factor (USF), and SP1 and SP1-like factors. Similarly, the human CEACAM6 promoter is regulated by the USF1 and USF2 as well as SP1 and SP3 transcription factors. A silencer element has also been located in its first intron. In contrast, the human CEACAM1 promoter does not bind the SP1 factors, but associates with an AP-2-like factor and the USF and HFN-4 transcription factors. The gene is additionally controlled by the hormonal changes (estrogens and androgens) and can be induced by cAMP, retinoids, glucocorticoids and insulin. Moreover, many genes of this large family are triggered by inflammation via interferons, tumor necrosis factors and interleukins. It has been reported more recently that expression of the CEACAM1 gene is influenced by TPA and calcium ionophore in endometrial cancers, the expression of ▶BCR/ABL in leukemias, the expression of the β3 integrin in melanomas and VEGF and hypoxia in angiogenic situations. In prostate cancer, there is an inverse correlation between the down-regulation of CEACAM1 and the increased expression of the transcriptional repressor Sp2 that acts to recruit histone deacetylase to the CEACAM1 promoter.

Transcriptional Regulation The upstream promoters of the CEA and CEACAM1 genes have been dissected to identify important binding sites responsible for their transcriptional regulation. These two genes do not encompass classical TATA

References

The Next Frontier The diversity of functions of the members of the CEA gene family and their dynamic expression patterns in normal and tumor tissues has slowed the development of effective targeted therapies. More recently, effective strategies have been devised using vaccination with CEA peptide-loaded mature dendritic cells that induced potent CEA-specific T cell responses in advanced colorectal cancer patients. Effective protection from tumor development have also been seen with delivery of adenoviral vectors encoding CEA fused to immunoenhancing agents such as tetanus toxin or the Fc portion of IgG1. Likewise, targeting of CEACAM6 in pancreatic cancer may result in decreased tumor load. The therapeutic and selective targeting of CEACAM1 in melanomas, gastric and lung carcinomas as well as its location in tumor endothelia may prove to be a favorable avenue of future interventions.

1. Hammarström S (1999) The carcinoembryonic antigen (CEA) family: structures, suggested functions and expression in normal and malignant tissues. Semin Cancer Biol 9:67–81

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2. Horst A, Wagener C (2004) CEA-related CAMs. Handb Exp Pharmacol 165:283–341 3. Gray-Owen SD, Blumberg RS (2006) CEACAM1: contact-dependent control of immunity. Nat Rev Immunol 6:433–446 4. Kuespert K, Pils S, Hauck CR (2006) CEACAMs: their role in physiology and pathophysiology. Curr Opin Cell Biol 18:1–7 5. Leung N, Turbide C, Marcus V et al. (2006) Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) contributes to progression of colon tumors. Oncogene 25:5527–5536

CEACAM5 ▶Carcinoembryonic Antigen

CEACAM5=CEA,CD66e ▶CEA Gene Family

CEA-related Cell Adhesion Molecule 1 ▶CEACAM1 Adhesion Molecule

CEACAM6=NCA, CD66c ▶CEA Gene Family

CEA-Vaccine Virus CEACAM7=CGM2 Definition A vaccine constructed from a recombinant vaccine virus containing the human carcinoembryonic antigen gene.

▶CEA Gene Family

▶Carcinoembryonic Antigen (CEA)

CEACAM8=CGM6, CD66b Ceacam1, Ceacam6, Ceacam7, Ceacam8

▶CEA Gene Family

Definition Carcinoembryonic antigen-related cell adhesion molecules. Members of the CEA family. ▶CEA Gene Family

CEACAM1 Adhesion Molecule A NDREA K RISTINA H ORST, C HRISTOPH WAGENER Institute of Clinical Chemistry, University Medical Center Hamburg Eppendorf, Hamburg, Germany

CEACAM1=BGP, C-CAM, CD66a ▶CEA Gene Family

Synonyms NCA-160, nonspecific cross-reacting antigen with a Mw of 160kD; BGP, biliary glycoprotein; CD66a, cluster of differentiation antigen 66 a; CEACAM1 CEA-related cell adhesion molecule 1

CEACAM1 Adhesion Molecule

Definition CEACAM1 (CEA-related cell adhesion molecule 1) belongs to the CEA (▶Carcinoembryonic antigen, ▶CEA gene family) family of cell surface glycoproteins, a subfamily of the immunoglobulin gene superfamily. The CEA family comprises two major groups, the CEA-related molecules and the PSG (pregnancy-specific glycoprotein)-related molecules. Additionally, a number of pseudogenes have been identified. To date, 29 genes are known, which are clustered on human chromosome 19 (19q13.1-19q13.2). The CEA-related members of the CEA family display a complex expression pattern on human healthy and malignant tissues. They are linked to the cell membrane via GPI anchors, or they are transmembrane proteins with a cytoplasmatic tail. The PSG-related molecules are soluble glycoproteins; their expression is restricted to the placenta, more specifically, to the syncytiotrophoblast, which is the outermost fetal component of the placenta. CEACAM1 has been structurally and functionally conserved in humans and rodents.

Characteristics Properties of CEACAM1 Human CEACAM1 has been originally identified in human bile due to its crossreactivity with CEA-antisera. It was therefore named biliary glycoprotein I or nonspecific cross-reacting antigen at first. Amongst the cluster of differentiation antigens on human leukocytes, CEACAM1 used to be referred as CD66a. However, with the latest revision of the nomenclature for the CEA family, CD66a, BGP, or NCA-160 became CEACAM1. Its structural similarities to CEA and the immunoglobulin superfamily proteins became apparent, once the cDNA sequence for CEACAM1 became available. CEACAM1 displays the broadest expression pattern amongst CEA family members; it has first been described as a cell–cell ▶adhesion molecule on rat hepatocytes. CEACAM1 is expressed on epithelia, endothelia, and on leukocytes. CEACAM1 is a heavily glycosylated molecule that exists in 11 known isoforms emerging from differential splicing and proteolytic processing. The two major isoforms of CEACAM1 consist of four extracellular Ig-like domains, a transmembrane domain, and either a long or a short cytoplasmic tail, referred to as the long (CEACAM1-4L) and the short isoform (CEACAM1-4S), respectively. In addition to these transmembrane isoforms, soluble CEACAM1 isoforms are found in body fluids, for example, in saliva, serum, seminal fluid, and bile. Glycans on the extracellular domains of CEACAM1 are linked to the protein backbone via N-glycosidic linkages. It is presently unknown whether all of the 19 motifs that may render N-linked

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▶glycosylation actually harbor sugar moieties. On human granulocytes, CEACAM1 is a major carrier of Lewisx glycans that are implicated in cellular adhesion to cognate lectins on blood vessels, within the extracellular matrix, or antigen presenting cells. CEACAM1 also elicits cell–cell adhesion via self-association in a homomeric fashion or via formation of heteromers with other CEA-family members and different adhesion molecules that are either located on the same cell or on neighboring cells. The resulting adhesive properties are modulated by differential expression ratios between the long and short CEACAM1 isoform, respectively. Through its long and short cytoplasmic tail, CEACAM1 mediates molecular interactions with cytoskeletal components or adapter proteins, which are integral parts of various key signal transduction pathways (▶Signal transduction, cell biology). These interactions are in part dependent on differential phosphorylation of the CEACAM1-4L cytoplasmic domain on tyrosine and serine residues. The overall phosphorylation status of the CEACAM1-4L cytoplasmic domain relays signals, which contribute to cellular motility and differentiation, and thus determine cell fate by promoting proliferation or cell death. Phosphorylation of CEACAM1-4L cytoplasmic tyrosines that are part of an imperfect ITIM (immune receptor tyrosine-based inhibition motif) and serine residues regulate the interaction with kinases, phosphatases, cellular receptors for insulin (▶Insulin receptor), the epidermal growth factor (▶Epidermal growth factor receptor ligand, epidermal growth factor receptor inhibitor), and other cellular adhesion molecules, for example, integrin αvβ3 (▶Integrin signaling and cancer). These qualities make CEACAM1 an important tool for cellular communication and they illustrate why so many different biological functions have been attributed to CEACAM1 in different biological contexts (Fig. 1).

CEACAM1 in Cancer The first report on CEACAM1, in the context of human pathological conditions, was on elevated serum levels of a biliary glycoprotein in patients with liver or biliary tract disease. Later, aberrant CEACAM1 expression in a broad variety of human malignancies has been reported. In the progression of malignant diseases, two general patterns in the changes of CEACAM1 expression levels have emerged. In the first group of tumors, CEACAM1 expression is downregulated in the course of progressing disease. In the second group of tumors, CEACAM1 expression appears to be upregulated; often, this upregulation of CEACAM1 expression is observed in the context with increased invasiveness (▶Invasion) of the primary tumor or is found on microvessels in progressing (▶Progression) tumor areas (Fig. 2).

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CEACAM1 Adhesion Molecule. Figure 1 Schematic representation of CEACAM1-4L and CEACAM1–4S and their participation in extracellular and intracellular communication. The two major CEACAM1 isoforms consist of four extracellular immunoglobulin-like domains, a transmembrane domain and either a long or a short cytoplasmic tail. The N-terminal domain (N) resembles a variable-like Ig domain but lacks the cystin bond usually found in Ig members. The A1, B1, and A2 domain resemble constant I-type-like Ig domains. Motifs for N-linked glycosylation are represented by lollipops. With its extracellular domains, CEACAM1 mediates recognition of various pathogens, such as Escherichia coli, Salmonella typhimurium, Moraxella catarrhalis, Neisseria gonorrhoeae, Neisseria meningitidis. The murine homologue of CEACAM1 is the receptor for the murine hepatitis virus: Additionally, CEACAM1 binds to galectin-3, DC-SIGN (dendritic cell ICAM3-grabbing nonintegrin), and integrin αvβ3. Tyrosine and serine residues involved in relaying CEACAM1-4L-mediated signal transduction are indicated by red and grey circles, respectively. Through its long cytoplasmic tail, CEACAM1-4L interacts with intracellular kinases of the SRC-family ▶(SRC), the tyrosine phosphatases SHP-1 and SHP-2, caspase-3 as well as with paxillin, filamin, and calmodulin. Differential phosphorylation of the CEACAM1-4L cytoplasmic domain is required for its interaction with the insulin receptor, regulating insulin receptor internalization and recycling, and for modulating immune responses elicited by lymphocytes, for example. The short cytoplasmic domain of CEACAM1–4S binds to actin and tropomyosin.

Loss of CEACAM1 Expression in Tumorigenesis and Tumor Progression Human cancers that show downregulation of CEACAM1 expression in the course of tumor progression are carcinomas of the liver (▶Hepatocellular carcinoma), colon (▶Colon cancer, colorectal premalignant lesions), kidney (▶Renal cell carcinoma, renal carcinoma), urinary bladder (▶Bladder cancer, bladder tumors), prostate (▶Prostate cancer, clinical oncology), mammary gland (▶Breast cancer), and the endometrium (▶Endometrial cancer). In general, downregulation and subsequent loss of CEACAM1 expression is more frequent in

high-grade tumors that are poorly differentiated, and often associated with a larger tumor size. On epithelia, especially those that form a lumen, CEACAM1 exhibits a pronounced apical expression, like in the entire gastrointestinal tract, breast, liver, prostate, bladder, and kidney. CEACAM1 expression has been implicated in morphogenesis of lumen formation. In the process of building an asymmetrical epithelium, lateral CEACAM1 expression on neighboring cells is lost and often becomes entirely apical once a lumen or a duct has been formed. The loss of CEACAM1 expression in the context of tumorigenesis

CEACAM1 Adhesion Molecule

CEACAM1 Adhesion Molecule. Figure 2 Dysregulation of CEACAM1 expression in human cancers. Changes of epithelial CEACAM1 expression in the course tumor progressison: In mammary carcinomas and carcinomas of the liver, colon, endometrium, kidney, bladder, and prostate, CEACAM1 expression is downregulated on tumor epithelium (▶Epithelial cancers). Downregulation of CEACAM1 levels often correlates with dedifferentiation of the tumor and loss of tissue architecture. In carcinomas of the thyroid, ▶non-small cell lung cancer (Lung cancer), pancreatic tumors (▶Pancreas cancer, clinical oncology), and malignant melanomas (▶Melanoma), CEACAM1 is induced or upregulated in the course of tumor growth. Here, CEACAM1 expression is found on the invasive front of the tumors and is related to development of metastatic disease (▶Metastasis) and poor prognosis. In pancreatic cancer, CEACAM1 has been identified as a novel biomarker (▶Biomarker, clinical cancer biomarker) that indicates presence of malignant disease.

has been studied most extensively in the context of breast, colonic, and prostate carcinomas. A hallmark of carcinomatous lesions is the loss of polarity of their epithelial structures. In colonic epithelium, for example, loss of polarity is accompanied by the loss of apical CEACAM1 expression that occurs in early adenomas and carcinomas. In these tumors, presence and absence of CEACAM1 correlate with normal and reduced apoptosis (▶Apoptosis, apoptosis signals), respectively. Furthermore, the naturally occurring process of ▶anoikis, once cells lose contact to their substratum, is compromised. This observation and the fact that the CEACAM1 gene is silenced in the

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course of aberrant cell growth prompted the hypothesis that CEACAM1 acts as a ▶tumor suppressor. In intestinal cells, presence of the long CEACAM1 isoform is required to suppress tumor growth, and lack of CEACAM1-4L expression is accompanied by a decrease in proteins that inhibit cell cycle progression. In human mammary epithelial cells, CEACAM1 expression is causally related to lumen formation and differentiation. In mammary glands, CEACAM1-4S is the predominating isoform, and only the short cytoplasmic tail induces apoptosis of the central cells and subsequently leads to lumen formation in mammary morphogenesis. During tumor progression, CEACAM14S expression is lost and acinar polarity no longer can be observed. However, since particular mutations or allelic loss of the CEACAM1 gene in human cancers has not been described so far, it is likely that dysregulation of CEACAM1 expression rather than irreversible loss of the CEACAM1 gene are linked to tumorigenesis and tumor progression in vivo. Hence, gene silencing may attribute to the loss of the tumor suppressive qualities of CEACAM1. Though there are no changes in promoter ▶methylation of the CEACAM1 gene linked to tumor progression, CEACAM1 promoter activity appears to be regulated by binding of the transcription factor Sp2. In high-grade prostate carcinomas, Sp2 is highly abundant, whereas CEACAM1 expression is lost. Sp2 localizes to the CEACAM1 promoter and imposes repression of gene transcription by recruiting ▶histone deacetylase.

Upregulation of CEACAM1 Expression in Malignant Diseases Opposed to its tumor suppressive functions, certain tumors gain CEACAM1 expression in the course of cancer development. In the case of malignant melanomas and thyroid carcinomas, expression of CEACAM1 correlates with an increase of tumor invasiveness and development of metastatic disease. In primary cutaneous malignant melanomas, for example, CEACAM1 expression is found at the invasive front of the tumors, and its coexpression with integrin αvβ3 indicates that CEACAM1 may directly promote on cellular invasion. In a follow-up study, CEACAM1 was identified as an independent prognostic marker, predicting the development of metastatic disease and poor survival. In this context, it is noteworthy that CEACAM1 on melanoma cells forms homophilic cell–cell contacts with CEACAM1 molecules on tumor-infiltrating lymphocytes, and leads to inhibition of their cytolytic function. Similarly, in human non-small cell lung cancer, CEACAM1 expression correlates with advanced disease, whereas it is not expressed on the normal bronchiolar epithelium; this CEACAM1 neoexpression

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was identified as an independent prognostic marker, indicating lower incidence of relapse-free survival. In pancreatic carcinomas, CEACAM1 has been identified as a novel serum biomarker, with an increased CEACAM1 expression on neoplastic cells of pancreatic adenocarcinomas and elevation of serum levels at the same time. Additionally, significant differences in CEACAM1 serum levels were found in patients with either pancreatic cancer or chronic pancreatitis. Opposed to the classical pancreatic tumor marker CA19-9, CEACAM1 was confirmed as an independent marker to distinguish between the presence of malignant disease and pancreatitis. CEACAM1 and Tumor Angiogenesis CEACAM1 expression on human blood vessels is restricted to newly formed vessels, and usually, no CEACAM1 is found on mature, large vessels. The first indication that CEACAM1 is related to ▶angiogenesis was the description of CEACAM1 neoexpression on newly formed vessels in the human placenta. Furthermore, CEACAM1 is expressed on vessels in wound healing tissues and on tumor vessels of human bladder carcinomas, the prostate, hemangiomas, and ▶neuroblastomas. CEACAM1 expression in endothelia is induced by VEGF (▶Vascular endothelial growth factor)-dependent pathways and appears to favor vessel maturation. In human prostate carcinomas, CEACAM1 shows divergent expression on tumoral blood vessels and the tumor epithelium. The presence of epithelial CEACAM1 is observed in the context of poor tumoral blood vessel growth and loss of epithelial CEACAM1 expression parallels enhanced tumor angiogenesis. Especially in high-grade prostate carcinomas, tumor proximal vessels are expressing CEACAM1. Contrary to prostate carcinomas, microvessels in human neuroblastomas are CEACAM1-positive only during tumor maturation, but absent in undifferentiated, high-grade tumors. In ▶Kaposi sarcomas, CEACAM1 upregulation is observed, indicating that CEACAM1 might be related to lymphatic reprogramming of the vasculature in these tumors. Studying CEACAM1 in Cancer: Animal Models In animal models investigating CEACAM1 function in tumorigenesis in vivo, the observations from human diseases could be confirmed. The focus of the mouse and rat models (▶Mouse model) studied to date was set largely on the tumor-suppressive effects or enhancement of metastatic disease of CEACAM1-4L on the progression of colonic cancer, prostate cancer, hepatocellular carcinomas, and malignant melanomas. In CEACAM1knockout mice, chemically induced colonic tumor growth was significantly increased in terms of tumor numbers and size opposed to CEACAM1-expressing

wild type littermates. In syngeneic and xenotypic transplantation of tumor cells of the colon, prostate, and hepatocellular carcinomas, the tumor-suppressive effects of CEACAM1-4L expression could also be validated. After xenotransplantation of human CEACAM1-expressing melanoma cell lines into immune-deficient mice, enhanced metastasis was observed when compared to transplantation of CEACAM1-negative cell lines.

References 1. Beauchemin N, Draber P, Dveksler G et al. (1999) Redefined nomenclature for members of the carcinoembryonic antigen family. Exp Cell Res 252:243–249 2. Prall F, Nollau P, Neumaier M et al. (1996) CD66a (BGP), an adhesion molecule of the carcinoembryonic antigen family, is expressed in epithelium, endothelium, and myeloid cells in a wide range of normal human tissues. J Histochem Cytochem 44:35–41 3. Gray-Owen SD, Blumberg RS (2006) CEACAM1: contact-dependent control of immunity. Nat Rev Immunol 6:433–446 4. Kuespert K, Pils S, Hauck CR (2006) CEACAMs: their role in physiology and pathophysiology. Curr Opin Cell Biol 18:565–571 5. Singer BB, Lucka LK (2005) CEACAM1. UCSD-nature molecule pages. Nature Publishing Group, doi:10.1038/ mp.a003597.01

C/EBPa Definition The transcription factor CCAAT enhancer binding protein-α is a tumor suppressor gene and a crucial regulator of granulopoiesis through inhibition of cJUN. Disruption of C/EBPα, including dominant negative mutations of C/EBPα, are found in acetyl myeloid leukemia. ▶NUP98-HOXA9 Fusion ▶Tumor Suppressor Gene ▶Chromosomal Translocation t(8;21)

C/EBP Homologous Protein Definition CHOP; synonym growth arrest and DNA damageinducible gene 153; Is a C/EBP family transcription factor which is involved in ▶endoplasmic reticulum stress-mediated ▶apoptosis.

Celastrol

CED ▶Convection Enhanced Delivery

CED-3 Definition One of three genes (Ced-3, -4, and -9) that control the process of programmed cell death in Caenorhabditis elegans. Ced-9 is homologous of mammalian ▶BCL-2 family members and acts upstream of Ced-3 and Ced-4. Ced-4 is homologous of APAF-1 and Ced-3 is homologous of the proapoptotic cysteine proteases known as caspases. ▶APAF-1 Signaling ▶Apoptosis

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9,12b,14a-hexamethyl-11-oxo-1,2,3,4,4a,5,6,6a,11,12b, 13,14,14a,14b-tetradecahydropicene-2-carboxylic acid

Definition Celastrol is a natural quione methide friedelane tripterene, widely found in the plant genuses of celastrus, maytenus and tripterygium, all of which are present in China. For example, celastrol is one of the active components extracted from tripterygium wilfordii Hook F, an ivy-like vine also known as “Thunder of God Vine,” which belongs to the family of celastraceae and has been used as a natural medicine in China for hundreds of years (Fig. 1).

Characteristics Biological Properties Celastrol has strong antifungal, anti-inflammatory and antioxidant effects. It has been shown that celastrol isolated from the roots of Celastrus hypoleucus (Oliv) Warb f argutior Loes exhibited inhibitory effects against diverse phytopathogenic fungi. Celastrol was also found to inhibit the mycelial growth of Rhizoctonia solani

CED-4 Definition Homologous of APAF-1 in C. elegans. CED-4 is one of three genes (Ced-3, -4 and -9) that control the process of programmed cell death in C. elegans. ▶APAF-1 Signaling ▶CED-3

Celastrol Q ING P ING D OU 1 , X IAO Y UAN 2 1

The Prevention Program, Barbara Ann Karmanos Cancer Institute and Department of Pathology, School of Medicine, Wayne State University, Detroit, MI, USA 2 Research and Development Center, Wuhan Botanical Garden, Chinese Academy of Science, Wuhan, Hubei, People’s Republic of China

Synonyms Tripterine; Quione methide friedelane tripterene (2R,4aS,6aS,12bR,14aS,14bR)-10-hydroxy-2,4a,6a,

Celastrol. Figure 1 The chemical structure and nucleophilic susceptibility of celastrol. (a) The chemical structure of celastrol is shown. (b) Nucleophilic susceptibility of celastrol analyzed using CAChe software. Higher susceptibility was shown at the C2 and C6 positions of celastrol.

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Kuhn and Glomerella cingulata (Stonem) Spauld and Schrenk in vitro. Furthermore, celastrol has good preventive effect and curative effect against wheat powdery mildew in vivo. Celastrol in low nanomolar concentrations suppresses the production of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) by human monocytes and macrophages. Celastrol also decreases the induction of class II major histocompatibility complex (▶MHC) expression by microglia. In macrophage lineage cells and endothelial cells, celastrol decreases induction of nitric oxide (NO) production. Celastrol also suppresses adjuvant arthritis in the rat, demonstrating in vivo anti-inflammatory activity. Low doses of celastrol administered to rats could significantly improve the performance of these animals in memory, learning and psychomotor activity. In an isolated rat liver assay of lipid peroxidation, the antioxidant potency of celastrol (IC50 7 µM) is 15 times stronger than that of α-tocopherol or vitamine E. Under in vitro conditions, celastrol was found to inhibit ▶cancer cell proliferation and induce programmed cell death (or ▶apoptosis) in a broad range of tumor cell lines, including 60 National Cancer Institute (NCI) human cancer cell lines. As a ▶topoisomerase II inhibitor, celastrol was 5-fold more potent than the wellknown topoisomerase inhibitor etoposide to induce apoptosis in HL-60 leukemia cells. Celastrol was also found to be a tumor ▶angiogenesis inhibitor. In a sharp comparison, celastrol can block neuronal cell death in cultured cells and in animal models. These unique features of celastrol suggest potential use for treatment of cancer and neurodegenerative diseases accompanied by inflammation, such as Alzheimer’s disease. Potential Molecular Targets Celastrol is a naturally occurring potent inhibitor of the ▶proteasome and nuclear factor kappa B (NFκB). Proteasome, or 26S proteasome, is a multicatalytic protease complex consisted of a 20S catalytic particle capped by two 19S regulatory particles. The ubiquitinproteasome pathway is responsible for the degradation of most endogenous proteins involved in gene transcription, cell cycle progression, differentiation, senescence and apoptosis. Inhibition of the proteasomal chymotrypsin-like, but not trypsin-like activity is associated with induction of apoptosis in tumor cells. Both computational and experimental data support the hypothesis that celastrol is a natural proteasome inhibitor. Atomic orbital energy analysis demonstrates high susceptibility of C2 on A-ring and C6 on B-ring of celastrol toward a nucleophilic attack. Computational modeling shows that celastrol binds to the proteasomal chymotrypsin site (β5 subunit) in an orientation and conformation that is suitable for a nucleophilic attack

Celastrol. Figure 2 Docking solution of celastrol. Celastrol was docked to S1 pocket of β5 subunit of 20S proteasome. Celastrol was shown in pink while β5 subunit was shown in purple. The selected conformation with 92% possibility showed the distances to the OH group of N-Thr from C6 and C2 were 2.96 Å and 4.16 Å, respectively.

by the hydroxyl (OH) group of N-terminal threonine of β5 subunit. The distances to the OH of N-terminal threonine of β5 from the electrophilic C6 and C2 of celastrol are measured as 2.96 Å and 4.16 Å, respectively. Both carbons, more probably C6, of celastrol potentially interact with N-terminal threonine of β5 subunit and inhibit the proteasomal chymotrypsin-like activity (Fig. 2). Celastrol potently and preferentially inhibits the chymotrypsin-like activity of a purified 20S proteasome with an IC50 value 2.5 μM. Celastrol at 1–5 μM inhibits the proteasomal activity in intact human prostate cancer cells. The inhibition of the cellular proteasome activity by celastrol results in accumulation of ubiquitinated proteins and three natural proteasome substrates, ▶IκB-α, Bax and p27, leading to induction of apoptosis in ▶androgen receptor (AR)-negative PC-3 cells. In AR-positive LNCaP cells, celastrol-mediated proteasome inhibition was accompanied by suppression of AR protein, probably by inhibiting ATP-binding activity of heat shock protein 90 (Hsp90) that is responsible for AR folding. Treatment of PC-3 tumor-bearing nude mice with celastrol (1–3 mg/kg/day, i.p., for 1–31 days) resulted in significant inhibition (65–93%) of the tumor growth. Multiple assays using the animal tumor tissue samples from both early and end time-points demonstrated in vivo inhibition of the proteasomal activity and induction of apoptosis after celastrol treatment. Antitumor activity of celastrol was also observed in a breast cancer mouse model. Celastrol inhibited 60% tumor growth in breast cancer xenograft through

Celecoxib

NFκB inhibition. NFκB inhibition by celastrol includes inhibition of its DNA-binding activity and inhibition of IκBα degradation induced by TNF-α or phorbol myristyl acetate. Further investigation showed that the cysteine-179 in the IκBα kinase was a potential target of celastrol-suppressed IκBα degradation. Since the proteasome is required for the activation of NFκB by degrading IκBα, the proteasome inhibition may also contribute to the NFκB inhibition by celastrol. TNF could send both anti-apoptotic and pro-apoptotic signals. The effects of celastrol on cellular responses activated by the potent proinflammatory cytokine TNF have also been investigated. Celastrol was able to potentiate the apoptosis induced by TNF and chemotherapeutic agents and inhibited invasion, both regulated by NFκB activation. TNF induced the expression of gene products involved in anti-apoptosis (IAP1, IAP2, ▶Bcl-2, Bcl-XL, c-FLIP, and survivin), proliferation (cyclin D1 and COX-2), invasion (MMP-9), and angiogenesis (VEGF), and celastrol treatment suppressed the expression of these genes. Celastrol also suppressed both inducible and constitutive NFκB activation. Furthermore, celastrol was found to inhibit the TNF-induced activation of IκBα kinase, IκBα phosphorylation, IκBα degradation, p65 nuclear translocation and phosphorylation, and NFκB-mediated reporter gene expression. Therefore, celastrol potentiates TNF-induced apoptosis and inhibits invasion through suppression of the NFκB pathway.

Clinical Relevance Due to its antioxidant or anti-inflammatory effects, celastrol has been effectively used in the treatment of autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus), asthma, chronic inflammation, and neurodegenerative diseases. As a bioactive component in Chinese traditional medicinal products from the extract of the roots of Tripterygium wilfordii Hook F, celastrol has been used since 1960s in China for autoimmune diseases, but has showed some side effects such as nausea, vomit, etc. Celastrol has not been used solely as a medication product. Celastrol has anti-tumor activities via inhibition of the proteasome and NFκB activation, indicating that celastrol has a great potential to be used for cancer prevention and treatment. This finding can be applied to various human cancers and diseases in which the proteasome is involved and on which celastrol has an effect.

References 1. Setty AR, Sigal LH (2005) Herbal medications commonly used in the practice of rheumatology: mechanisms of action, efficacy, and side effects. Semin Arthritis Rheum 34:773–784

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2. Sassa H, Takaishi Y, Terada H (1990) The triterpene celastrol as a very potent inhibitor of lipid peroxidation in mitochondria. Biochem Biophys Res Commun 172:890–897 3. Yang HJ, Chen D, Cui QZC et al. (2006) Celastrol, a triterpene extracted from the Chinese “Thunder of God Vine,” is a potent proteasome inhibitor and suppresses human prostate cancer growth in nude mice. Cancer Res 66:4758–4765 4. Hieronymus H, Lamb J, Ross KN et al. (2006) Gene expression signature-based chemical genomic prediction identifies a novel class of HSP90 pathway modulators. Cancer Cell 10:321–330 5. Sethi G, Ahn KS, Pandey MK et al. (2006) Celastrol, a novel triterpene, potentiates TNF-induced apoptosis and suppresses invasion of tumor cells by inhibiting NFκB-regulated gene products and TAK1-mediated NF-κB activation. Blood 109:2727–2735

Celebra ▶Celecoxib

Celebrex ▶Celecoxib

Celecoxib N UMSEN H AIL 1 , R EUBEN LOTAN 2 1

Department of Pharmaceutical Sciences, The University of Colorado at Denver and Health Sciences Center, Denver, CO, USA 2 Department of Thoracic Head and Neck Medical Oncology, The University of Texas, MD Anderson Cancer Center, Houston, TX, USA

Synonyms Celebrex; Celebra; 4-[5-(4-Methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] benzenesulfonamide

Characteristics Celecoxib, a diaryl-substituted pyrazole drug, was developed by G. D. Searle & Company, and is currently

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marketed by Pfizer Incorporated under the brand names Celebrex and Celebra. Celecoxib is a member of the class of agents known as ▶non-steroidal antiinflammatory drugs (▶NSAIDs). NSAIDs are the most commonly used therapeutic agents for the treatment of acute pain, fever, menstrual symptoms, osteoarthritis, and rheumatoid arthritis. Because of their ability to reduce tissue ▶inflammation, which is often associated with ▶tumorigenesis at various sites in the body (e.g., gastrointestinal tract and lung), celecoxib and certain other NSAIDs are also considered to have a potential in ▶cancer chemoprevention as exemplified by their ability to prevent the formation and decrease the size of polyps in ▶familial adenomatous polyposis (FAP) patients. Orally administered celecoxib exhibits good systemic bioavailability and tissue distribution with an estimated plasma half-life of approximately 11 h. Celecoxib binds to plasma albumin, and is metabolized primarily by hepatic enzymes prior to excretion. In humans, long-term exposures to celecoxib taken for arthritis pain relief at 100 mg twice daily caused no biologically significant adverse reactions. However, higher doses of 400 mg twice daily recommended for patients with FAP resulted in threefold increased risk of cardiovascular events (Fig. 1). ▶Cyclooxygenase Dependent Mechanisms for Cancer Chemoprevention by Celecoxib. Cyclooxygenases are enzymes that are indispensable for the synthesis of ▶prostaglandins. Prostaglandins are ▶hormones generated from ▶arachidonic acid, and they are found in virtually all tissues and organs. Prostaglandins typically act as short-lived local cell signaling intermediates that regulate processes associated with inflammation. In the early 1990s, cyclooxygenases were demonstrated to exist as two isoforms, cyclooxygenase-1 (COX-1), and cyclooxygenase-2 (COX-2). COX-1 is characterized as a constitutively expressed housekeeping enzyme that mediates physiological responses like platelet aggregation, gastric cytoprotection, and the regulation of renal

Celecoxib. Figure 1 The chemical structure of celecoxib.

blood flow. In contrast, COX-2 is recognized as the inducible cyclooxygenase isoform that is primarily responsible for the synthesis of the prostaglandins that are involved in pathological processes (e.g., chronic inflammation) in cells that mediate inflammation (e.g., macrophages and monocytes). COX-2 is inducible by ▶oncogenes (e.g., ▶RAS and ▶SRC), interleukin-1, ▶hypoxia, benzo[a]pyrene, ultraviolet light, epidermal growth factor, ▶transforming growth factor β, tumor necrosis factor α. Many of these inducers activate nuclear factor kappa B (NF-κB), which controls COX-2 expression and has been associated with tumorigenesis in various cell types. The COX-2 isoenzyme is frequently unregulated in cancer cells, as well as cells that constitute premalignant lesions, which are important targets for ▶cancer chemoprevention. The expression of the inducible COX-2 is enhanced in 50% of colon adenomas and in the majority of human ▶colorectal cancers, as opposed to COX-1, which typically remains unchanged. Thus, the increase in COX-2 expression, which is an early event in colon carcinogenesis, is believed to be necessary for tumor promotion. Aberrant COX2 expression has also been implicated in tumorigenesis in the lung, ▶prostate, esophagus, ▶breast, ▶liver, ▶pancreas, and ▶skin. The activity of COX-2 to produce arachidonic acid metabolites appears to enhance the proliferation of transformed cells and/or increases their survival through the suppression of ▶apoptosis. Furthermore, COX-2 expression by tumor cells can stimulate ▶angiogenesis at the tumor site and alter tumor cell adhesion to promote ▶metastasis. Celecoxib is a highly selective inhibitor of COX-2. Traditional NSAIDs (e.g., aspirin) inhibit both COX-1 and COX-2 isozymes. In contrast, celecoxib is approximately 20 times more selective for COX-2 inhibition compared to its inhibition of COX-1. This specificity allows celecoxib, and other selective COX2 inhibitors, to reduce inflammation while minimizing adverse drug reactions (e.g., stomach ulcers and reduced platelet aggregation) that are common with nonselective NSAIDs. This selectivity for COX-2 is also intimately associated with the putative cancer chemopreventive activity of celecoxib, which has been demonstrated in ▶colorectal cancer prevention. Epidemiological studies have shown that persons who regularly take aspirin have about a 50% lower risk of developing colorectal cancer. Celecoxib was the most effective ▶NSAID in reducing the incidence and multiplicity of colon tumors in a rat colon carcinogenesis model. Moreover, in a clinical setting celecoxib has been used effectively to suppress the development and/ or reduce the number of colorectal polyps in patients with FAP. This inflammatory disease often predisposes individuals to the development of ▶colorectal cancers. The anti-inflammatory mediated anticancer effects of

Celecoxib

celecoxib may be tissue-specific considering that celecoxib reduced lung inflammation in mice, but failed to inhibit the formation of chemically induced lung tumors in these animals. Cyclooxygenase Independent Mechanisms for Cancer Chemoprevention by Celecoxib. The results of several in vitro and animal studies suggest the celecoxib may suppress tumorigenesis through several COX-2independent mechanisms, which may account, at least in part, for celecoxib’s anti-cancer effects in humans. For example, celecoxib inhibited the proliferation of various cancer cell types in vitro irrespective of their expression of COX-2, including transformed haematopoietic cells and immortalized and transformed human bronchial epithelial cells that were deficient in COX2 expression. Celecoxib also inhibited the growth of human COX-2-deficient ▶colon cancer cells that were transplanted as xenografts in nude mice. Thus, the chemopreventive effect of COX-2-specific inhibitors like celecoxib may be due to their effect on COX-2 as well as targets other than COX-2. One putative COX-2 independent target for celecoxib is the ▶phosphatidylinositol 3-kinase (PI3K) pathway, which is often deregulated in tumor cells. Celecoxib appears to directly inhibit the phosphoinositide-dependent kinase-1 (PDK1), and its downstream substrate protein kinase B/AKT, in the ▶PI3K pathway. Protein kinase B/AKT inhibits apoptosis through the ▶phosphorylation, and thus inactivation, of the proapoptotic ▶BCL-2 family protein BAD. During apoptotic stimuli, BAD antagonizes BCL-2 and BCL-XL activity, which can promote ▶mitochondrial membrane permeabilization and cell death. The inhibition of the PI3K pathway by celecoxib is believed to be specific in its ability to promote apoptosis in transformed cells. For example, rofecoxib, another specific COX-2 inhibitor, had only marginal protein kinase B/AKT inhibitory activity in tumor cells during apoptosis induction. Another presumed COX-2 independent target of celecoxib in tumor cells is ▶sphingolipid metabolism. Celecoxib treatment increases the level of the ▶sphingolipid ceramide in murine mammary tumor cells irrespective of COX-2 expression. This increase in ▶ceramide was considered essential to apoptosis induction in these cells. Ceramide has been shown to mediate apoptosis in response to inflammatory cytokines like Fas and tumor necrosis factor α, and/or conditions associated with ▶oxidative stress. During conditions of cell stress, the deregulation of ceramide generating and/or utilizing processes are believed to cause a net increase in cellular ceramide that is sufficient to trigger apoptosis induction via a mitochondrial membrane permeabilization mechanism. Celecoxib treatment has also been shown to suppress the activity of the ▶Ca2± ATPase located in the

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endoplasmic reticulum of human ▶prostate cancer cells. The inhibition of the Ca2± ATPase by celecoxib disrupted Ca2+ homeostasis in the prostate cancer cells. This activity was highly specific for celecoxib, and was not associated with the exposure to other COX2 inhibitors, including rofecoxib. Microsome and plasma membrane preparations from the human prostate cancer cells showed that only the Ca2± ATPases located in the endoplasmic reticulum were the direct targets of celecoxib. The disruption of Ca2+ homeostasis played a central role in apoptosis induction in the prostate cancer cells because it was required for the activation of Ca2+-dependet hydrolyses that carried out cellular degradation. Moreover, mitochondrial membrane permeabilization, which releases cytochrome c to activate cell death, is sensitive to elevations in intracellular free Ca2+. Consequently, the celecoxibinduced inhibition Ca2± ATPases located in the endoplasmic reticulum may provide a link to mitochondrial membrane permeabilization for apoptosis induction much in the same way that Celecoxib inhibition of the PI3K pathway can regulate BAD phosphorylation to trigger mitochondrial-mediated cell death. It is apparent that the central hypothesis of a dominant role for COX-2 inhibition in cancer prevention by celecoxib may need re-examination. Furthermore, the COX-2 dependent and independent action of celecoxib in cancer prevention may be tissue specific. Since the aberrant expression of COX-2 is implicated in the pathogenesis of various types of human cancers, perhaps this inducible enzyme may be a useful surrogate ▶biomarker of the anticancer activity of celecoxib when evaluating the chemoprevention of cancer at various sites in the body. Although the precise molecular mechanism for its chemopreventive effects are still fairly unknown, celecoxib may be still useful as a chemopreventive agent for a variety of malignancies, especially since it triggers less toxicity and adverse side effects during long-tern use when compared to traditional NSAIDs. Celecoxib may be useful when combined with other cancer chemopreventive/ therapeutic agents to control the process of tumorigenesis.

References 1. Chun KS, Surh JY (2006) Signal transduction pathways regulating cyclooxygenase-2 expression: potential molecular targets for chemoprevention. Biochem Pharmacol 68:1089–1100 2. Grosch S, Maier TJ, Schiffmann S et al. (2006) Cyclooxygenase-2 (COX-2)-independent anticarcinogenic effects of selective COX-2 inhibitors. J Natl Cancer Inst 98:736–747 3. Kismet K, Akay MT, Abbasoglu O et al. (2004) Celecoxib: a potent cyclooxygenase-2 inhibitor in cancer prevention. Cancer detect Prev 28:127–142

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4. Schroeder CP, Kadara H, Lotan D et al. (2006) Involvement of mitochondrial and akt signaling pathways in augmented apoptosis induced by a combination of low doses of celecoxib and N-(4-hydroxyphenyl) retinamide in premalignant human bronchial epithelial cells. Cancer Res 66:9762–9770 5. Psaty BM, Potter JD (2006) Risks and benefits of celecoxib to prevent recurrent adenomas. N Engl J Med 355:950–952

Cell Adhesion Molecules K RIS V LEMINCKX Department of Molecular Biology, Ghent University, Department of Molecular Biomedical Research, VIB, Ghent, Belgium

Synonyms Cell adhesion receptors; Adhesion molecules; CAMs

Definition

Cell ▶adhesion molecules are transmembrane or membrane-linked glycoproteins that mediate the connections between cells or the attachment of cells to substrate (such as stroma or basement membrane). Dynamic cell-cell and cell-substrate adhesion is a major morphogenetic factor in developing multicellular organisms. In adult animals, adhesive mechanisms underlie the maintenance of tissue architecture, allow the generation of force and movement, and guarantee the functionality of the organs (e.g. to create barriers in secreting organs, intestines and blood vessels) as well as the generation and maintenance of neuronal connections. Cell adhesion is also an integrated component of the immune system and wound healing. At the cellular level, cell adhesion molecules do not function just as molecular glue. Several signaling functions have been attributed to adhesion molecules, and cell adhesion is involved in processes such as ▶contact inhibition, growth and ▶apoptosis. Deficiencies in the function of cell adhesion molecules underlie a wide variety of human diseases including cancer. By their adhesive activities and their dialogue with the ▶cytoskeleton, adhesion molecules directly influence the invasive and metastatic behavior of tumor cells, and by their signaling function they can be involved in the initiation of tumorigenesis.

Characteristics At the molecular level, cell adhesion is mediated by molecules that are exposed on the external surface of the cell and are somehow physically linked to the cell membrane. In essence, there are three possible

mechanisms by which such membrane-attached adhesion molecules link cells to each other (Fig. 1a). First, molecules on one cell bind directly to similar molecules on the other cell (▶homophilic adhesion). Secondly, adhesion molecules on one cell bind to other adhesion receptors on the other cell (▶heterophilic adhesion). Finally, two different adhesion molecules on two cells may both bind to a shared secreted multivalent ligand in the extracellular space. Also, cell-cell adhesion between two identical cells is called ▶homotypic (cell) adhesion, while ▶heterotypic (cell) adhesion takes place between two different cell types. In the case of cellsubstrate adhesion the adhesion molecules bind to the ▶extracellular matrix (ECM). Cell Adhesion Molecules and the Cytoskeleton Adhesion molecules can be associated with the cell membrane either by a glycosylphosphatidyl-inositol (GPI) anchor or by a membrane-spanning region. In the latter case the cytoplasmic part of the molecule often associates indirectly with components of the cytoskeleton (e.g. actin, intermediate filaments or submembranous cortex). This implies that adhesion molecules, which by themselves establish extracellular contacts, can be structurally integrated with the intracellular cytoskeleton, and they are often clustered in specific restricted areas in the membrane, the so-called ▶junctional complex (Fig. 1b). This combined behavior of linkage to the cytoskeleton and clustering, considerably strengthens the adhesive force of the adhesion molecules. In some cases, exposed adhesion molecules can be in a conformational configuration that does not support binding to its adhesion receptor. A signal within the cell can induce a conformational change that activates the adhesion molecule. Dynamic adhesion can also be mediated via regulated endocytosis of the adhesion molecules. These mechanisms of regulation allow for a dynamic process of cell adhesion that, amongst others, is required for morphogenesis during development and for efficient immunological defense. Classification of Cell Adhesion Molecules Based on their molecular structure and mode of interaction, five classes of adhesion molecules are generally distinguished; the ▶cadherins, ▶integrins, immunoglobulin (Ig) superfamily, selectins and ▶proteoglycans (Fig. 2). Cadherins Cadherins and proto-cadherins form a large and diverse group of adhesion receptors. They are Ca2+-dependent adhesion molecules, involved in a variety of adhesive interactions both in the embryo and the adult. Cadherins play a fundamental role in metazoan embryos, from the earliest gross morphogenetic events (e.g. separation of germ layers during gastrulation) to the most delicate

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Cell Adhesion Molecules. Figure 1 Different modes of cell-cell and cell-substrate adhesion and the mechanism of cytoskeletal strengthening. (a) Three possible mechanisms by which cell adhesion molecules mediate intercellular adhesion. A cell surface molecule can bind to an identical molecule (homophilic adhesion) on the opposing cell or can interact with another adhesion receptor (heterophilic adhesion). Alternatively, cell adhesion receptors on two neighboring cells can bind to the same multivalent, secreted ligand (linkermediated adhesion). Intercellular adhesion can take place between identical cell types (▶homotypic adhesion) or between cells of different origin (▶heterotypic adhesion), independently of the involved adhesion molecules. Cell-substrate adhesion molecules attach cells to specific compounds of the extracellular matrix. Cell-cell and cell-substrate adhesion can occur simultaneously. (b) Intercellular and cell-substrate adhesion can be strengthened by indirect intracellular linkage of the cytoplasmic tail of the adhesion molecules to the cytoskeleton and by lateral clustering in the membrane.

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Cell Adhesion Molecules. Figure 2 The five major classes of cell adhesion molecules and their binding partners. Cadherins are Ca2+-dependent adhesion molecules that consist of a varying number of cadherin repeats (five in case of the classical cadherins). The conformation and activity of cadherins is highly dependent on the presence of Ca2+-ions. In general, cadherin binding is homophilic. Integrins are functional as heterodimers and consist of an a- and b-subunit. They interact with members of the immunoglobulin superfamily or with compounds of the extracellular matrix (e.g. fibronectin, laminin). Members of the immunoglobulin superfamily (Ig-like proteins) are characterized by a various number of immunoglobulin-like domains (open circles). Membrane-proximal, fibronectin type III repeats are often observed (gray boxes). They can either bind to other members of the Ig-family (homophilic) or to integrins. Selectins contain an N-terminal Ca2+-dependent lectin domain (circle) that binds carbohydrates, a single EGF-like repeat (gray box) and a number of repeats that are related to those present in complement-binding proteins (ovals). Proteoglycans are huge molecules that consist of a relatively small protein core to which long side chains of negatively charged glycosaminoglycans are covalently attached. They bind various molecules, including components of the extracellular matrix.

tunings later in development (e.g. molecular wiring of the neural network). The extracellular part of vertebrate classical cadherins consists of a number of cadherin repeats whose conformation is highly dependent on the presence or absence of calcium ions. Homophilic interactions can only be realized in the presence of calcium, usually by the most distal cadherin repeat. Classical cadherins are generally exposed as homodimers, and their cytoplasmic domain can be structurally or functionally associated with the actin

cytoskeleton. Cadherins are the major adhesion molecules in tissues that are subject to high mechanical stress such as epithelia (▶E-cadherin) and endothelia (VEcadherin). However, finer and more elegant intercellular interactions, such as synaptic contacts, also involve cadherins. Integrins Integrins are another group of major players in the field of cell adhesion. They are involved in various processes

Cell Adhesion Molecules

such as morphogenesis and tissue integrity, homeostasis, immune response and inflammation. Integrins are a special class of adhesion molecules, not only because they mediate both cell-cell and cell-substrate interactions (with components in the ECM such as laminin, fibronectin and collagen) but also because they function as heterodimers consisting of an α- and β-subunit. To date, at least 16 α-subunits and 8 β-subunits have been indentified. Of the theoretical 128 heterodimeric pairings, at least 21 are known to exist. While most integrin heterodimers bind to ECM components, some of them, more particularly those expressed on leukocytes, are heterophilic adhesion molecules binding to members of the Ig superfamily. The α-subunit mostly contains a ligand-binding domain and requires the binding of divalent cations (Mg2+, Ca2+ and Mn2+, depending on the integrin) for its function. Interestingly, integrins may be present on the cell-surface in a non-functional and a functional configuration. The cytoplasmic domain appears to be responsible for the conformational change that activates the integrin. The Ig Superfamily Among the classes of adhesion molecules discussed here, the Ig superfamily is probably the most diverse. The main representatives are the neural cell adhesion molecules (NCAMs) and V(ascular)CAMs. As the name suggests, the members of this family all contain an extracellular domain consisting of different immunoglobulin-like domains. NCAMs sustain homophilic and heterophilic interactions that play a central role in regulation and organization of neural networks, specifically in neuron-target interactions and fasciculation. The basic extracellular structure consists of a number of Ig domains, which are responsible for homophilic interaction, followed by a discrete number of fibronectin type III repeats. This structure is linked to the membrane either by a GPI anchor or a transmembrane domain. The VCAM subgroup, including I(ntercellular) CAMs and the mucosal vascular addressin adhesion molecule (MAdCAM), are involved in leukocyte trafficking (or homing) and extravasation. They consist of membrane-linked Ig domains that make heterophilic contacts with integrins. Other members of this family that are associated with cancer are carcinoembryonic antigen (▶CEA), “deleted in colon cancer” (DCC) and platelet endothelial (PE)CAM-1. Selectins These types of adhesion molecules depend on carbohydrate structures for their adhesive interactions. Selectins have a C-type ▶lectin domain, that specifically binds to discrete carbohydrate structures present on cell-surface proteins. Intercellular interactions mediated by selectins

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are of particular interest in the immune system, where they play a fundamental role in trafficking and homing of leukocytes. Proteoglycans Proteoglycans are large extracellular proteins consisting of a relatively small protein core to which long chains of glycosaminoglycans are attached. Although poorly documented, proteoglycans may bind to each other or may be the attachment site for other adhesion molecules. Role of Adhesion Molecules in Cancer The Metastatic Cascade Cell adhesion molecules play an important role during the progression of tumors, more particularly in the metastatic cascade (Fig. 3). When a benign tumor becomes malignant, cells at the periphery of the tumor will lose cell-cell contact (step I) and invade the surrounding stroma (step II) (see also ▶invasion). Cells then extravasate and enter the vasculature or lymphatic system, where they are further transported. A fraction of the circulating tumor cells survives and is arrested at a distant site, attaches to the endothelium (step III) and extravasates through the blood vessel wall and into the surrounding tissue (step IV). Here the tumor cells grow, attract blood vessels and develop to a secondary tumor (▶metastasis). Adhesive Events in Metastasis All the classes of cell adhesion molecules play a role in the metastatic cascade. During the first step, tumor cells need to disrupt intercellular junctions in order to detach from the primary tumor. This step often involves suppression of cadherin function. The second step of ▶migration through the stroma and into the blood or lymphatic vessels requires dynamic cell-substrate adhesion, mostly mediated by integrins. In the third step, where cells arrest in the circulation by aggregation with each other or attachment to platelets, leukocytes and endothelial cells, critical roles have been attributed to cell adhesion molecules of the Ig superfamily, selectins, integrins and specific membrane-associated carbohydrates. The fourth step is similar to step II and mostly involves integrins. Details on the adhesive events associated with metastasis are outlined below. . In benign epithelial tumors, cells maintain firm intercellular adhesive contacts, mostly by formation of a junctional complex (including tight junctions, ▶adherens junctions and desmosomes). Establishment and maintenance of such a strong junctional complex requires expression and function of cadherins (more particularly E-cadherin). Loss of E-cadherin expression or function appears to be a hallmark of progression of a benign epithelial tumor (adenoma)

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Cell Adhesion Molecules. Figure 3 Cell adhesion processes involved in the metastatic cascade. A subset of cells (gray) growing in a primary tumor will reduce cell-cell contacts (Step I) and migrate in the surrounding stroma by increasing specific cell-substrate adhesion (Step II). These invasive tumor cells can extravasate into the circulation and, at distant sites, attach to the endothelial blood vessel wall through specific cell-cell interactions (Step III). Once these cells have extravasated through the vessel wall they use cell-substrate adhesion molecules to invade the surrounding stroma (Step IV). See text for details.

to a malignant one (carcinoma). Epithelial tumor cells often acquire invasive properties by mutational inactivation of E-cadherin or one of its cytoplasmic binding partners (catenins). It is important to keep in mind that cadherin-mediated adhesion is a dynamic process and that E-cadherin can be temporarily inactivated at the functional level, for example by phosphorylation or other posttranslational modifications. E-cadherin and other molecules of the junctional complex are very often suppressed or functionally modulated in the epithelial-mesenchymal transitions (EMT), a hallmark of malignant tumor progression. EMT can be a tumorintrinsic feature or can be induced by their microenvironment. Paracrine factors such as scatter factor or juxtacrine signaling via Ephrin/Eph receptor or via Semaphorins/plexins can affect adhesion via direct activity on the cell adhesion molecules or via regulation of the cytoskeleton. . Dynamic cell-substrate adhesion is a critical factor in the migration of invasive tumor cells into the surrounding stroma. Integrins are instrumental in this process. Several studies have correlated the migratory behavior of tumor cells either with an increased or decreased expression of particular integrins. This apparent paradox may be explained by the fact that firm but temporary cell-substrate contacts are required for cells to migrate on a substrate. In order to crawl directionally through the stroma, a cell needs to “grab” the ECM, release after pulling itself forward and then has to establish the next contact. Both inhibiting adhesion and preventing

release of the substrate contacts “locks” the cell in its position and prevents migration. It should be remembered that integrins may exist in two functional states and that signals passed through the cytoplasm determine whether membrane-exposed integrins are functional or not. . In the third step of the metastatic cascade, cell-cell interactions are again the most determining. Homotypic interactions between circulating tumor cells promote formation of aggregates that are preferentially retained in the capillary network. PECAM-1 is a cell adhesion molecule potentially involved in this process. It should be pointed out that (re)expression of the invasion-suppressor molecule E-cadherin would actually promote metastasis formation. Besides these homotypic interactions, heterotypic interactions are also of major importance in the metastatic process. Tumor cells can attach to the blood-vessel wall either directly or indirectly through platelets and leukocytes. The adhesion molecules involved in this process are similar to those involved in the “multistep adhesion cascade” observed during homing and extravasation of leukocytes or trafficking of lymphocytes. Cell adhesion events include interactions of tumor-associated lectins with selectins expressed on platelets, leukocytes and endothelium (P-, L- and ▶E-selectins, respectively). These adhesion molecules are also involved in the initial transient low-affinity interactions (rolling) of circulating leukocytes (and probably tumor cells) with the endothelium. Other and

Cell Biology

more stringent heterotypic heterophilic interactions in this metastatic stage include the binding of integrins on tumor cells to ICAMs expressed on the surface of the endothelial cells. . The fourth step in the metastatic cascade is extravasation and invasion at a distant site. This process is very similar to step 2 and the same adhesion molecules are likely to be involved. Specific interactions of the tumor cells with molecules present on the endothelial cells (e.g. N-cadherin) will facilitate the extravasation process.

Other Cancer-Related Functions of Cell Adhesion Molecules Recently, it has become clear that some cell adhesion molecules are involved in signaling processes that are relevant to cancer. Germline mutations in E-cadherin predispose patients to the development of diffuse gastric carcinomas, and in lobular breast carcinoma E-cadherin seems to act as a tumor suppressor. Interestingly, β-catenin, a protein cytoplasmically linked to cadherins, has a central role in ▶Wnt signaling and has oncogenic properties that are counteracted by the adenomatous polyposis coli (▶APC) gene product. Signaling by integrins can also be an important factor that prevents cells from undergoing apoptosis (apoptosis upon loss of cell adhesion is called ▶anoikis), which might be critical when tumor cells are traveling in the circulation. Interdisciplinary research has revealed new unexpected functions for known cell adhesion molecules. The suspected tumor suppressor DCC, a member of the Ig superfamily of adhesion molecules, turned out to be the receptor for netrin-1, an axonal chemoattractant crucial in neuronal development. Other molecules known to have adhesive or repulsive activities in the axonal growth cone or in migrating neural crest cells, turn out to have similar activities in tumor cells (see also the chapters on ▶EPH receptors, ▶Ephrin signaling in cancer, ▶Semaphorins and ▶Plexins).

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Cell-Adhesion Molecules (CAM) Definition Are cell-surface proteins that are involved in binding cells together in tissues and also in less permanent cell– cell interactions. ▶Adhesion

Cell Adhesion Receptors ▶Cell Adhesion Molecules

Cell Biology F ILIPPO A CCONCIA 1,2 , R AKESH K UMAR 1,3 1

Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA 2 IFOM, The FIRC institute for Molecular Oncology, Milan, Italy 3 Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA

Definition Cell biology deals with all aspects of the normal and of the tumor cell, their normal and abnormal multiplication, their differentiation, their stem origins, and their regulated cell death.

Characteristics References 1. Cavallaro U, Christofori G (2004) Cell adhesion and signalling by cadherins and Ig-CAMs in cancer. Nat Rev Cancer 4:118–132 2. Chothia C, Jones EY (1997) The molecular structure of cell adhesion molecules. Annu Rev Biochem 66:823–862 3. Hynes RO (2000) Cell adhesion: old and new questions. Trends Cell Biol 9:M33–M37 4. Mizejewski GJ (1999) Role of integrins in cancer: survey of expression patterns. Proc Soc Exp Biol Med 222:124–138 5. Sanderson RD (2001) Heparan sulfate proteoglycans in invasion and metastasis. Semin Cell Dev Biol 12:89–98

The Cell The intracellular environment is separated from the external environment by a lipid bilayer called plasma membrane. The plasma membrane controls the movement of substances in and out of the cell and it is important for the cell to sense the surrounding environment. Within the cell the nucleus occupies most of the space. The cell nucleus contains genes, which drive all cellular activities and processes. Genes are organized in chromosomes (i.e., genome) and are made of DNA. The genetic information is used to produce proteins, which are the critical effectors required for all cellular processes. The nucleus is separated from the rest of the cellular content by the nuclear membrane,

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which remains in contact with the cytoplasm as well as the nucleoplasm. In the cytoplasm, proteins are organized into specific functional structures and also connected with the structural network referred to as cytoskeleton network, which physically sustains the cell. Moreover several intracellular organelles are located in the cytoplasm (e.g., mitochondria, Golgi apparatus) and allow the cells to self sustain. To continuously adjust the intracellular processes and to promptly respond to the demands of the extracellular environment, cells need to exchange matter, energy, and information with the external milieu. Cell Division and Reproduction One of the unique features of cell is its ability to divide and produce two daughter cells that are an exact copy of their parental cell, by a process called “mitosis.” However, some differentiated cells undergo the process of meiosis. For simplicity, meiotic division can be considered as the sum of two successive mitotic divisions, which result in four daughter cells with half the number of chromosomes and rearranged genes. These specialized cells (i.e., gametes) serve as reproductive cells. The fusion of the female and male gametes (eggs and spermatozoa, respectively) results in a new cell called zygote. The zygote, by definition, is a stem cell. Following mitotic division, it becomes an embryo and, at the end of the embryonic development, results in a new organism. Cell Proliferation The physiological functions of an organ require maintenance of homeostasis, a process of regulated balance between cell proliferation and cell death (also known as ▶apoptosis), in the differentiated tissue. Indeed, a variety of extracellular stimuli activate specific ▶signal transduction pathways that affect the expression and activity of molecules involved in the control of cell proliferation or cell death. Thus, the balance between ▶cell cycle progression and apoptosis defines the cell fate, and this process depends on genetic factors as well as the kinetics of signal transduction pathways in exponentially growing cells. Cell Cycle In mammalian cells, one cell cycle takes about 24 h in most cell types and can be schematically divided into two stages: mitosis and interphase. Mitosis (M phase) consists of a series of molecular processes that result in cell division. On the other hand, the interphase can be subdivided into three major gaps (G1, S, and G2 phase). The G1 phase of the cell cycle separates the M and S phases. In G1 phase, cells express a specific pattern of gene products required for the DNA synthesis; the G2 phase of the cell cycle resides in between the S and M phases and is important for the

completion of processes that are necessary for mitosis. The G0 phase of the cell cycle is entered by the cells from the G1. In the G0 phase, cells are out of the cell cycle and into a quiescent state where they do not proliferate. Regulation of Cell Cycle Progression Cell cycle progression is achieved through a series of coordinated molecular events that allow the cells to transit across the restriction points, also known as cell cycle checkpoints. There are three main restriction points in the cell cycle (G2/M, M/G1, and G1/S, respectively). Broadly, these checkpoints are defined as points after which the cell is committed to progress to the next phase in a nonreversible manner. Therefore, the transition between the phases of the cell cycle is strictly regulated by a specific set of proteins. ▶Cyclindependent kinases (CDK) act in various phases of the cell cycle by binding to its activating proteins called cyclins. For example, both ▶cyclin D/CDK4 and cyclin E/CDK2 complexes regulate transition of the cells through G1/S phase whereas cyclin A/CDK1, cyclin A/ CDK2, and cyclin B/CDK1 complexes are active during the rest of the cell cycle. On the other hand, another class of regulatory proteins, the cyclin-dependent kinase inhibitors (CKI) (e.g., p21Cip/Kip; p19Ink4d) antagonizes the activation of CDK activity, thus impeding the progression of the cell cycle. Programmed Cell Death Programmed cell death (PCD) is a physiological process of eliminating a living cell. The PCD involves activation of specific intracellular programs that commit cells to a “suicidal route.” The process of PCD plays an important role in a variety of biological events, including morphogenesis, maintenance of tissue homeostasis, and elimination of harmful cells. To date, different forms of PCD have been described among which apoptosis, necrosis, and ▶autophagy are the most common. Apoptosis One of the critical events in apoptosis is the activation of cystein proteases, called caspases, upon a given signal. The initiator caspases (▶Caspase 8 and 9) are the first enzymes involved in the activation of the apoptotic cascade. Caspase 8 and 9 activate the downstream effector caspases (caspase 3, 6, and 7) by proteolytic cleavage which in turn results in the hydrolysis and inactivation of the enzymes involved in the processes of DNA repair such as by poly-ADPribose polymerase (PARP). Upon stimulation of apoptotic cascade, cells display a specific set of characters, which constitute the hallmark of apoptosis (DNA fragmentation, cell shrinkage, cytoplasmic budding, and fragmentation). The activation of caspases

Cell Biology

is achieved through two principle pathways – an extrinsic pathway that transduces signals from the plasma membrane directly to the caspases, and an intrinsic pathway that involves activation of caspases through a series of biochemical events leading to permeabilization of the mitochondrial membrane and release of cytochrome c (▶Cytochrome P450) in the cytoplasm. Apoptotic cells are eventually eliminated by the immune system without the activation of inflammatory reactions (▶Inflammation). Necrosis Necrosis results from a severe physical, mechanical, or metabolic cellular damage. The necrotic phenotype is very different from those of an apoptotic cells. Overall, the cell switches off its metabolic pathways and the DNA condenses at the margins of the nucleus and the cellular constituents start to degrade. In general, necrosis consists in a general swelling of the cell before it disintegrates. Furthermore, upon leakage of the intracellular content, necrotic cells stimulate an inflammatory response that usually damages the surrounding tissue. Autophagy Autophagy, i.e., autophagic cell death, occurs by sequestration of intracellular organelles in a double membrane structure termed autophagosome. Subsequently, the autophagosomes are delivered to the lysosomes and degraded. Autophagy is responsible for the turnover of dysfunctional organelles and cytoplasmic proteins and thus, contributes to cytosolic homeostasis. Autophagy can occur either in the absence of detectable signs of apoptosis or concomitantly with apoptosis. Indeed, autophagy is activated by signaling pathways that also control apoptosis. Signal Transduction Extracellular signals are transduced by the activation of a series of phosphorylation-dependent intracellular pathways initiated by cell surface receptors. Eventually, such signals feed into the nucleus, stimulate transcription factors, and regulate gene transcription. Signaling Targets Signaling pathways regulate gene transcription by triggering the promoter activity of the target gene. For example, regulation of cyclin D is critical for cell cycle progression. The extracellular signal-mediated activation of specific signal transduction pathways stimulates the activity of transcription factors such as AP-1, SP-1, and NF-κB, which coordinate the activation of the cyclin D1 promoter and thus lead to cyclin D1 expression. On the other hand, signaling molecules can also change the activity of a preexisting protein. For example, activation of p21-activated kinase (PAK) induces the

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phosphorylation of phosphoglucomutase (PGM) that stimulates its enzyme activity and the phosphorylation of ▶estrogen receptor alpha (ERα) thus inducing its transcriptional activity. One of the most studied signaling pathways is the extracellular-regulated kinase (ERK) (▶MAP kinase) cascade. It consists of three steps of sequential phosphorylations that impact on diverse cellular effectors. The ERK cascade is activated by mitogenic stimuli (e.g., growth factors (▶Fibroblast growth factors)) and plays a critical role both in cell proliferation and cell survival. Indeed, activation of ERK induces the activation of AP-1 transcription factor, which, in turn, regulates cyclin D1 expression in addition to many of other proliferative molecules. Further, ERK activity leads to an increased expression of the antiapoptotic protein ▶Bcl-2 and inactivation of the proapoptotic protein ▶Bad. Conversely, the JNK/SAPK (▶JNK subfamily and cancer) and the p38/MAPK (MAP kinase) pathways mediate stress and apoptotic stimuli (e.g., UV, ischemic-reperfusion damage). Activation of JNK/SAPK and p38/MAPK often results in an increased expression of proapoptotic proteins (e.g., Bax), and in the activation of the caspase cascade and cytochrome c release from the mitochondria. Systems Biology Systems biology represents a new analytical tool that has begun to emerge for balanced comprehensive analyses of cellular pathways at the level of genes and proteins. Signal transduction pathways often cross-talk and influence each other, and the functionality of the effector molecule is influenced by the overall outcome of a set of signaling pathways. Thus, cells form a web of intracellular interactions that are critical for a timely and dynamic response. The intracellular signaling network is considered a complex system rapidly adapting to extracellular challenges. Therefore, an additional level of complication is the evaluation of the network as a whole, rather than the individual pathway. Cell Motility and Migration ▶Motility and ▶migration are important components for the functionality of a variety of cell types, and are involved in physiologic processes such as embryonic development, immune response, as well as in pathologic processes such as ▶invasion and ▶metastasis. Cell motility and migration are coordinated physiological processes that allow the cells to move or to invade the surrounding tissues, respectively. They occur as a result of a complex interplay between the focal ▶adhesion sites (cell-to-substrate contacts) and the ▶extracellular matrix (ECM) (substrate). Phenotypically, migratory cells develop motile structures such as pseudopodia, lamellipodia, and filopodia. An ordered sequence of events (protrusion of motile structures, formation and disruption of focal contacts) generate the traction forces

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that drive the cell movement. Moreover, when migration is required, cells secrete specific proteolytic enzymes (matrix metalloproteinases, MMPs) that digest the ECM, thus opening a passage across the substrate. Cytoskeleton is critical for the correct occurrence of cell motility and migration. Cytoskeleton Cytoskeleton is a network of cytoplasmic proteins, which define the cell “bones.” Many different protein filaments are important for cytoskeleton functions. In particular, microtubules, built from different types of tubulin, originate from specific intracellular structures called microtubules organizing centers (MTOC). Dynamic changes in the polymerization and depolymerization of tubulin maintain microtubule integrity and resulting functions. Furthermore, actin microfilaments form a network of cytoskeleton-associated proteins and connect the focal adhesion with the intracellular cytoskeleton. The dynamic remodeling of microtubules and microfilaments has an impact on cell motility, migration and cell–cell adhesion, ▶endocytosis, intracellular trafficking, organelle function, cell survival, gene expression, and cell division. Signaling Regulation At the focal adhesion sites, cells accumulate receptors (e.g., growth factor receptors), adaptors (e.g., vinculin), and signaling molecules, as well as structural and motor proteins (e.g., actin, myosin). Migration-specific stimuli (e.g., integrins engagement of ECM, growth factor stimulation, and mechanical stimuli) activate specific biochemical pathways. ▶Focal adhesion kinase (FAK), integrin-linked kinase (ILK), PAK, and ▶Src play key roles in modulating cell migration and invasion. The FAK/Src complex regulates the assembly and disassembly of focal contacts, F-actin cytoskeleton remodeling, and the formation of lamellipodia and filopodia through the activation of specific downstream cytoskeleton-associated signaling pathways. Further, ILK is also implicated in cell motility and migration by linking integrins with cytoskeleton dynamics through the ▶PI3K signaling pathway. Also, PAK1 dynamically regulates cytoskeletal changes by coordinating upstream signaling with multiple effectors. By acting on actin reorganization, PAK1 drives directional cell motility and migration. Tumor Biology Cancer is a progressive disease that arises from the clonal expansion of a single transformed cell into a mass of uncontrolled proliferating cells. Tumorigenesis is a multistep process and involves progressive conversion of a normal cell into a malignant cell, which subsequently invades the surrounding tissues. The process of tumorigenesis consists of major steps

(initiation, promotion, and progression), each involving specific molecular mechanisms, often interlaced with each other, that drive tumor development. Initiation and Promotion In general, initiation of tumorigenesis is referred to as the first oncogenic stimulus. However, such as initial event is not sufficient for tumor induction. In most cases, a second oncogenic stimulus must occur in a restricted time frame, thus promoting an irreversible effect. Chemical (e.g., aromatic compounds (▶Polycyclic aromatic hydrocarbons)), physical (e.g., ▶UV radiation), as well as biological (e.g., viruses as ▶human papillomavirus) stress have impact on the cells and can induce DNA mutations (e.g., point mutations). In addition, gene deletion or duplication also alters gene function and contributes to the process of tumorigenesis. These genomic changes result in the production of proteins with altered functions or in the overexpression or downregulation of specific proteins, which affects the associated cellular functions. Protooncogenes or oncogenes are genes that encode for proteins involved in the induction of cell proliferation (e.g., cyclin D1, CDK, EGFR, Src, Ras, etc.) and whose overexpression or hyperactivation leads to an uncontrolled cell proliferation. On the other hand, tumor suppressor genes are genes encoding for proteins that negatively regulate cell proliferation (e.g., p53, PARP, CKI, etc.). Inactivating mutations or downregulation of tumor suppressor genes are also critical for enhanced cell proliferation. In addition to DNA damage, oncogenes and tumor suppressor genes, abnormal changes in the epigenetic cellular information (e.g., DNA▶ methylation) can also participate in clonal evolution of human cancers. Progression The modified balance between the growth-inhibitory programs and proliferative networks allow the cell to escape the physiological growth restrains. These selective growth advantages produce a population of more aggressive or transformed cells that resist clearance by the immune system (i.e., immune defense escape), and in turn, contributes to the accumulation of additional mutations and eventually, in tumor growth. In this context, an in situ tumor develops, that is the uncontrolled mass of transformed cells stays within the limit of the tissue in which the first cell resided. During this phase, tumor volume increases in parallel with an increased dedifferentiation of the cells that also secrete angiogenic factors (▶Angiogenesis) to promote blood vessels formation in the tumor. Metastasis Metastasis is the process by which highly vascularized tumor cells acquire the ability to invade the

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blood-stream and seed in distant organs. Deregulation of cytoskeleton-associated proteins and secretion of protein factors play a critical role in the functionality of the metastatic cells. Stem Cell Biology In 1998, the group of Prof. James Thomson reported the isolation of a human embryonic stem cell line from the blastocyst stage of a human embryo. This cell line showed stability in a specifically developed culture medium and, upon transplantation in the nude mice, had the ability to form tumor-like structures made up of all the major human tissue types. This pioneer study opened the field of stem cell biology. Since then, enormous research efforts have been focused on the understanding of stem cell biology as well as their potential medical and therapeutic implications. Nonetheless, although the last 10 years witnessed an enormous progress, the field of stem cell research is in its infancy. The first controversy is the definition of stem cell itself. For simplicity, a stem cell is a clonal self-renewing entity that is multipotent and can generate several different cell types. This definition introduces three major characteristic of the stem cells: selfrenewal, clonality, and potency. Self-Renewal and Clonality Self-renewal is the process by which a stem cell undergoes an asymmetric mitotic division that produces, rather than two identical daughter cells, one cell that is completely identical to the parental stem cell and another cell that is already committed to a more restricted developmental path and more specialized abilities. Thus, stem cells have both the ability to selfmaintain their clonal cell population and to produce a population of clones with more differentiated characteristics. In this way, stem cells form a hierarchy of potency.

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stem cell population or mutation that can lead to tumorigenesis. One possibility is that the asymmetric division produces two daughter cells and, because of intrinsic factors, such cells follow different fates in spite of residing in the same ▶microenvironment. Alternatively, the two daughter cells become functionally different because they are exposed to different extrinsic factors. Most likely, both intrinsic and extrinsic factors are integrated in the milieu of the surrounding microenvironment, also known as the stem cell niche. Signals from the niche determine the type of gene regulation that allows the asymmetric division to take place. In this model, one daughter cell stays in the niche and the other one moves out. Indeed, the importance of the microenvironment in stem cell biology is highlighted by the ability of a particular stem cell to transdifferentiate or to dedifferentiate when put in a different niche. Although the concept of plasticity is debated in the literature, it is part of the “stemness” of a cell, which is the hallmark for a cell to be defined as a stem cell. Social Implications The ability to scientifically manipulate the human embryo or human adult stem cells has opened new perspectives for treatment of several human diseases. However, it has also initiated intense philosophical and political debates on the ethical issues associated with the use of such potential tools in medical practice.

References 1. Pestell RG, Albanese C, Reutens AT et al. (1999) The cyclins and cyclin-dependent kinase inhibitors in hormonal regulation of proliferation and differentiation. Endocr Rev 20:501–534 2. Lowe SW, Cepero E, Evan G (2004) Intrinsic tumour suppression. Nature 432:307–315 3. Potten C, Wilson J (2004) Apoptosis – the life and death of cells. Cambridge University Press, New York 4. Gearhart J, Hogan B, Melton D et al. (2006) Essential of stem cell biology. Academic Press, London 5. Feinberg AP, Tycko B (2004) The history of cancer epigenetics. Nat Rev Cancer 4:143–153

Potency Stem cells have the ability to give rise to a population of daughter stem cells with a reduced differentiation. The totipotent cells are the first embryonic cells that can become any kind of cell type (e.g., zygote). These cells become pluripotent cells, which can differentiate in most but not all cell types (e.g., embryonic stem cells). Next, cells that are committed to produce only a certain lineage of cell types (e.g., ▶adult stem cells) are the multipotent cells. Some multipotent cells can only generate one specific kind of terminally differentiated cell type and thus, such cells are called unipotent cells.

Definition

Environmental Regulation The molecular mechanism by which regulatory processes occur in stem cells are not clear but are believed to be tightly regulated to avoid imbalance in

Consists of a paraffin block made from the cellular material of cytologic specimens (most commonly fine needle aspiration biopsies and body fluids) and is processed similar to histology. Can be a useful adjunct in cytology because it gives a better idea of tissue

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architecture and allows for multiple sections for ancillary stains. ▶Fine Needle Aspiration

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completed. It is a regulatory mechanisms that monitors the progression of the cell cycle, so that one phase is not started before another has finished. The activation of checkpoints, for example by damaged DNA, arrests cell cycle progression. ▶Hypoxia ▶HSP90 ▶Decatenation G2 checkpoint

Definition The sequence of cellular transformations that accompany transition from one mitotic cell division to another. The cell cycle is composed of four phases known as G1, S, G2 and M. S is the period of DNA synthesis, M is mitosis when sister chromatids are condensed and segregated to two daughter cells. G1 lies between M and S and is a phase of preparation for DNA synthesis, G2 is between S and M and is a phase of preparation for mitosis. G0 refers to a quiescent state into which some cells in multicellular organisms enter from G1. Cells typically achieve full differentiation in the G0 phase. ▶Decatenation G2 Checkpoint ▶Cell-Cycle Targets for Cancer Therapy ▶Cyclin Dependent Kinases ▶Chelators as Anticancer Drugs

Cell Cycle Arrest Definition

The halt of the ▶cell cycle, often as a result of cellular stress with physical or chemical treatment as a mechanism of cellular defense. ▶Sulforaphane

Cell-Cycle Checkpoint Definition The cell-cycle checkpoint is a mechanism for stopping progression through the cell cycle when a key event, such as DNA replication, is not completed or when the genome is damaged. It is a restriction point during the cell cycle in which a cell monitors if preceding events required for cell division have been correctly

Cell-Cycle Targets for Cancer Therapy R OLF M U¨ LLER Institute of Molecular Biology and Tumor Research (IMT), Philipps-University Marburg, Marburg, Germany

Definition Knowledge of the molecular mechanisms governing the mammalian ▶cell cycle and their dysfunction in cancer cells has grown considerably in the last decade. It is now clear that the cell utilizes two distinct kinds of regulatory mechanisms to control cell-cycle progression: while progression past the ▶restriction point in late G1 is solely governed by extracellular signals, ▶checkpoints sense cellular damage or dysfunctions that are not compatible with a proper cell division, such as DNA damage. The detailed knowledge of the underlying molecular mechanisms, pathways and molecules provides the basis for a new approach to cancer therapy.

Characteristics Cell-cycle progression in mammalian cells is controlled through fundamentally different regulatory pathways. Progression through G1 across the restriction point (R-point) is controlled by external signals that are transmitted, for example, by mitogens or through cell adhesion processes. Beyond this point, cell-cycle progression is governed by a genetic program that is largely independent of extracellular signals but regulated by internally controlled checkpoints. These checkpoints ensure proper DNA replication, DNA integrity, progression through G2 and mitosis. A central role in cell-cycle progression is exerted by the ▶cyclindependent kinases (CDKs), which are composed of a regulatory cyclin subunit (e.g., cyclin A, B, D or E) and a catalytic kinase subunit (e.g., CDK1, 2, 4 or 6). The activity of CDKs is controlled by phosphorylation, phase-specific expression and proteolysis as well as the

Cell-Cycle Targets for Cancer Therapy

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Cell-Cycle Targets for Cancer Therapy. Figure 1 The E2F pathway and its regulation by Rb and G1 CDKs.

association with CDK inhibitors (CDIs) belonging to the INK4 (p15, ▶p16, p18, p19) or KIP (p27, p57)/CIP (p21) families. Restriction Point Control The G1 CDK-cyclin complexes regulate progression across the restriction point through phosphorylation of the ▶retinoblastoma protein Rb and its kins p107 and p130. In early-mid G1 the transcription factor ▶E2F is found in complexes with Rb and ▶histone deacetylase (HDAC). These complexes actively repress transcription via E2F binding sites in the respective target genes. The phosphorylation of the E2F-RbHDAC complexes by ▶cyclin D-CDK4/6 and cyclin E-CDK in mid-late G1 leads to the disruption of these complexes and the generation of transcriptionally active “free” E2F, which results in the induction of numerous E2F target genes (Fig. 1). The relevance of R-point control for tumorigenesis is emphasized by the fact that the ▶INK4-cyclin D-CDK4-Rb pathway is defective in the vast majority of human tumors due to genetic alteration of its components (Fig. 2). Therefore, this pathway is of major interest with respect to therapeutic intervention. Checkpoint Control A major role in checkpoint control is exerted by the ▶p53 tumor suppressor pathway. In response to DNA damage (or other insults to the cell) p53 induces a number of genes that either invoke cell-cycle arrest (such as the CDI p21/CIP) or trigger apoptosis (Fig. 3). The activity and the steady-state level of p53 is regulated by ▶MDM-2, a oncoprotein that associates with p53, inhibits its transcriptional activity and targets

Cell-Cycle Targets for Cancer Therapy. Figure 2 Deregulation of E2F activity in cancer cells through impairment of the INK4-cyclin D-CDK 4–8211; Rb pathway.

p53 for degradation by the proteasome. MDM-2 itself is targeted for proteolysis by the tumor suppressor ▶p14ARF (or p19ARF in mice). The importance of this pathway is demonstrated by the fact that each of its components can be a target for genetic alterations in human tumors, and that a defective p53 pathway is found in more than 50% of all human malignancies. This emphasizes the relevance of p53 for the development of new anti-cancer therapies.

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Cell-Cycle Targets for Cancer Therapy. Figure 3 Loss of p53 function in human cancer cells.

Another checkpoint activated in G2 in response to DNA damage is governed by the checkpoint kinase-1 (▶CHK1; Fig. 4). CHK1 phosphorylates the CDC2 (CDK1) phosphatase CDC25C, which results in the association of CDC25C with a p53-induced specific isoform of 14–3–3. This renders CDC25C inactive, so that the cyclin B-CDC2 complex remains in its phosphorylated inactive form. As a consequence, progression into mitosis is prevented and DNA repair can occur. Since many anti-cancer drugs exert their function through DNA damage, this checkpoint may have a negative impact on their efficacy. An analogous checkpoint operating in G1 has recently been identified. This checkpoint is activated when the CDK2 phosphatase CDC25B is targeted for degradation in response to DNA-damage that will leave the cyclin E kinase in an inactive (phosphorylated) state. As a consequence, cell-cycle progression into S-phase is prevented. Clinical Relevance Cancer is clearly a proliferative disease resulting from deregulated cell-cycle progression. The inhibition of specific proteins driving the cell cycle is therefore an obvious strategy for the rational discovery of new anticancer drugs. In this context it is of particular interest that the interference with coordinated cell-cycle progression can result in apoptosis of tumor cells. This is exemplified by the observation that the deregulated expression of proteins, such as ▶Myc or E2F-1, in conjunction with a non-physiological cell-cycle block is

incompatible with cell survival. It has also been shown that the direct inhibition of CDKs, for example by CDIs or through ▶antisense nucleic acid, can trigger programmed cell death in tumor cells. These and other findings have laid the foundation for the definition of a new class of anti-tumor agents that function through a direct inhibition of proteins driving the cell cycle. One of the prototypes of this class of compounds is the synthetic flavone ▶Flavopiridol. Flavopiridol is a general inhibitor of CDKs, induces cell-cycle arrest and apoptosis, and is not influenced by many of the genetic alterations conferring resistance on human tumor cells. Accordingly, Flavopiridol has shown promising tumor responses in preclinical models and is currently undergoing clinical trials. Numerous other chemical CDK inhibitors have recently been identified and are currently being evaluated for their anti-tumor properties. It can be anticipated that CDK-inhibiting drugs will constitute a new class of powerful chemotherapeutics. Other interesting targets for therapeutic intervention are the proteins governing checkpoint control, for instance in response to DNA damage. Checkpoint control can invoke a transient cell cycle block, but can also trigger apoptosis. Both types of checkpoints are of relevance to tumor therapy. While the functionality of an apoptosis-inducing mechanism in response to drug- or radiation-induced cellular damage is desirable, checkpoint control leading to cell-cycle arrest is counterproductive for any therapy that relies on cell proliferation, such as radiation or conventional therapy. The p53 checkpoint is lost in many tumor cells, and thus the ability to undergo apoptosis in response to chemo- or radiotherapy. The restoration of this checkpoint could therefore sensitize many tumor cells to conventional therapies. Strategies along these lines involve the development of compounds that can reactivate mutant p53 or inhibit MDM-2, or the use of gene therapeutic approaches for the reintroduction of functional p53 genes. Other drug-based strategies aim to improve the efficacy of existing therapies that rely on DNA-damage, such as radiation or DNA-damaging chemotherapy. A prime candidate in this context is the kinase ▶CHK1 that regulates the G2 checkpoint (Fig. 4). First results obtained with an inhibitor of the G2 checkpoint, UCN01, suggest that this may indeed be the case. Numerous other mechanisms controlling cellcycle progression have been discovered, and approaches for therapeutic intervention are being developed, pointing to the great potential of targeting the cell cycle for the development of new anti-cancer drugs. It can be anticipated that this new class of anti-cancer drugs will lead to a clear advance in clinical oncology.

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Cell-Cycle Targets for Cancer Therapy. Figure 4 Regulation of the G2 checkpoint.

References 1. Jacks T, Weinberg RA (1998) The expanding role of cell cycle regulators. Science 280:1035–1036 2. Russell P (1998) Checkpoints on the road to mitosis. Trends Biochem Sci 23:399–402 3. Hueber AO, Evan GI (1998) Traps to catch unwary oncogenes. Trends Genet 14:364–367 4. Johnson DG, Walker CL (1999) Cyclins and cell cycle checkpoints. Annu Rev Pharmacol Toxicol 39:295–312 5. Mailand N, Falck J, Lukas C et al. (2000) Rapid destruction of human Cdc25A in response to DNA damage. Science 288:1425–1429 6. Sherr CJ, Roberts JM (1999) CDK inhibitors: positive and negative regulators of G1-phase progression. Genes Dev 13:1501–1512 7. Gray N, Detivaud L, Doerig C et al. (1999) ATP-site directed inhibitors of cyclin-dependent kinases. Curr Med Chem 6:859–875 8. Garrett MD, Fattaey A (1999) CDK inhibition and cancer therapy. Curr Opin Genet Dev 9:104–111

Cell Differentiation Definition This is a concept from developmental biology describing the process by which cells acquire a “type”. The morphology of a cell may change dramatically during differentiation, but the genetic material remains the same, with few exceptions. A cell that is able to differentiate into many cell types is known as pluripotent. These cells are called stem cells in animals and meristematic cells in higher plants. A

cell that is able to differentiate into all cell types is known as totipotent. In mammals, only the zygote and early embryonic cells are totipotent, while in plants, many differentiated cells can become totipotent with simple laboratory techniques. ▶Orphan Nuclear Receptors and Cancer

Cell Division Definition Synonym cell proliferation; Is the process of cell doubling by which a cell, called the parent cell, divides into two cells, called daughter cells. Cell division is a physiological process that occurs in almost all tissues. However, a process of pathological cell division can be seen in cancers. ▶Cell Cycle

Cell Fate Definition The ultimate differentiated state to which a cell has become committed. ▶Polycomb Group

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Cell-free Circulating Nucleic Acids

Cell-free Circulating Nucleic Acids ▶Circulating Nucleic Acids

Cell Migration A highly complex process, regulated by multiple gene pathways enabling the motility of cells through the adhesion and invasion of extracellular matrices. ▶Tissue Inhibitors Of Metalloproteinases (Timps)

Cell Lines Definition Are cell populations with the feature of dividing indefinitely when growing in culture. There are tumor and non-tumor cell lines from different organisms including humans.

Cell Motility ▶Migration ▶Motility

Cell Movement Cell Locomotion

▶Motility

▶Migration

Cell Polarity Cell-Mediated Immunity Definition Synonym Cell-mediated immune response describes any adaptive immune response in which antigenspecific T cells have the main role. It is defined operationally as adaptive immunity that cannot be transferred to a naïve recipient with serum antibody. ▶Sjögren Syndrome

Definition Cell direction or orientation to maintain the property of having two opposite poles, apical and basolateral domains. ▶Tight Junction

Cell Scattering Definition

Cell Membrane Definition

▶Plasma membrane

A common tissue culture assay used to monitor ▶Met receptor activation. When non-transformed dog kidney epithelial (MDKC) cells are grown in tissue culture, the cells spontaneously arrange themselves into tightly connected epithelial sheets. Following Met activation, these cell sheets breakdown and the individual cells migrate away from each other.

Cellular Senescence

Cell Signaling Definition

Synonym ▶signal transduction, refers to the process by which a cell converts one type of stimulus into another using ordered sequences of biochemical reactions.

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architecture, de-differentiation, loss of cellular adhesion, loss of cellular polarity, keratinization within the deeper areas of the epithelium. ▶Squamous Cell Carcinoma

Cellular Immortalization Cell-Surface Receptors Definition Are cell surface receptor is a cellular proteins embedded within the cell membrane that receive and respond to extracellular soluble ligands such as neurotransmitters, hormones, growth factors, or chemokines.

Definition The process by which cells cultured in vitro, or in the organism, escape from cellular senescence and grow forever. This can happen spontaneously, or can be caused by chemical carcinogens, oncogenic viruses, or radiations. ▶Chemically Induced Cell Transformation ▶Senescence and Immortalization

▶CXC Chemokines

Cellular Immunity b-Cell Tumor of the Islets ▶Insulinoma

Cellular Antigens ▶CD Antigens

Cellular Atypia

Definition Immune protection provided by the direct action of immune cells (as distinct from soluble molecules such as antibodies).

Cellular Self-Cannibalism ▶Autophagy

Cellular Senescence

Definition

Definition

Histological features associated with epithelial dysplasia, the degree of which is determined by the number of atypia present in the dysplastic lesion. Atypia include densely stained nuclei, pleomorphic nuclei, altered nucleus:cytoplasm ratio, aberrant mitosis, frequent mitosis, supra-basal mitosis, disorganized tissue

The process of programmed cell aging, by which cells die after a specific number of population doublings, usually 60 population doublings. ▶Chemically Induced Cell Transformation ▶Senescence and Immortalization

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Cellular Transformation Assay

Cellular Transformation Assay

Central Cleavage

Definition

Definition

Cell biological test to demonstrate oncogenic activity of a candidate gene. Typically the gene in question is cloned into a mammalian expression vector, transfected into appropriate recipient cells and expressed. The transforming activity is detected on the basis of morphological alterations such as the loss of the typical fibroblastic or epithelial cell shape, anchorage independent proliferation, as determined in semi-solid agar medium, or tumor formation following injection of transfected cells into nude mice. The classical cellular transformation assays were done with donor DNA prepared from tumors and pre-neoplastic mouse NIH/3T3 cells as recipients.

Central cleavage refers to the symmetric cleavage of ▶carotenoids at their central 15,15′ double bond by carotene 15,15′-oxygenase, a main pathway for vitamin A formation from provitamin A carotenoids.

▶RAS Transformation Targets

▶Brain Tumors

Central Nervous System Definition The brain and spinal cord.

Central Neurocytoma CENP-E ▶Neurocytoma

Definition Centromeric protein E; Is a kinetochore-associated kinesin-like motor protein that is responsible for chromosome movement and alignment in mitosis. In animal model, CENP-E deletion in mice causes early embryonic lethality, with embryos unable to implant or develop past implantation.

Central Neurofibromatosis ▶Neurofibromatosis 2

▶Mitotic Arrest-Deficient Protein 1 (MAD1)

Centrocytic (Mantle Cell) Lymphoma Censoring

▶Mantle Cell Lymphoma

Definition Censoring, particularly in survival studies, occurs when the outcome of interest is not measured fully as, for example, when a trial is ended after a specified period of time so that failure times are not precisely measured.

Definition

▶Kaplan–Meier Survival Analysis

Constricted portion of the chromosome. The centromere divides the chromosome into a short “p” and a

Centromere

Centrosome

long “q” arm. The centromere is a region of chromosomes with a special DNA sequence and structure. The centromere plays a role in cellular division and it is the region where sister chromatids join after doubling the chromosomes during prophase and metaphase of mitosis. ▶Micronucleus Assay

Centrosome K ENJI F UKASAWA Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute 12902 Magnolia Dr. Tampa, FL 33612-9416, OH, USA

Synonyms Major microtubule organizing center; MTOC; Spindle pole body; SPB, in yeast

Definition

The centrosome is a nonmembranous organelle (1–2 μm in diameter) normally localized at the periphery of nucleus, and its primary function is to nucleate and anchor microtubules.

Characteristics Structure and Function The centrosome in mammalian cells consists of a pair of centrioles and the surrounding protein aggregates consisting of a number of different proteins (known as pericentriolar material; PCM). The centrioles in the pair structurally differ from each other; one with a set of appendages at the distal ends (mother centriole) and another without appendages (daughter centriole).

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These appendages are believed to be important for nucleating and anchoring microtubules. The daughter centriole acquires the appendages in late G2-phase of the cell cycle. As the primary function of the centrosome is to nucleate and anchor microtubules, centrosomes organize the cytoplasmic microtubule network during interphase, which is involved in vesicle transport, proper distribution of small organelles, and establishment of cell shape and polarity. In mitosis, centrosomes become the core structures of spindle poles and direct the formation of mitotic spindles. (Fig. 1). Centrosome Duplication Upon cytokinesis, each daughter cell receives only one centrosome. Thus, the centrosome, like DNA, must duplicate once prior to the next mitosis. In other words, cells have either one unduplicated or two duplicated centrosomes at any given time point during the cell cycle. Since DNA and centrosome are the only two organelles that undergo semiconservative duplication once in a single cell cycle, cells are equipped with a mechanism that coordinates these two events, likely to ensure these two organelles to duplicate once, and only once. In late G1/early S-phase, the centrosome initiates duplication by physical separation of the paired centrioles, which is followed by the formation of a procentriole in the proximity of each preexisting centriole. During S and G2, the procentrioles elongate and two centrosomes continue to mature by recruiting PCM. By late G2, two mature centrosomes are generated. The coupling of the initiation of DNA and centrosome duplication is in part achieved by late G1-specific activation of cyclin-dependent kinase 2 (CDK2)/ cyclin E. CDK2/cyclin E triggers initiation of both DNA synthesis and centrosome duplication. The activation of CDK2/cyclin E is controlled by the late G1-specific expression of cyclin E as well as the basal level expression of p53 and its transactivation target p21Waf1/Cip1 (p21), a potent CDK inhibitor. Several

Centrosome. Figure 1 Structure and function of centrosomes. (a) The centrosome consists of a pair of centrioles and surrounding protein aggregates (PCM). (b and c) Mouse embryonic fibroblasts were immunostained for γ-tubulin (one of major centrosomal proteins, green – appearing in yellow) and α- and β-tubulin (primary constituents of microtubules, red). Cells were also counterstained for DNA with DAPI. Panel b: interphase cell, panel c: mitotic cell.

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potential targets of CDK2/cyclin E for centrosome duplication have been identified, including nucleophosmin, Mps1 kinase, and CP110. For instance, nucleophosmin localizes between the paired centrioles, likely functioning in the pairing of the centrioles. CDK2/ cyclin E-mediated phosphorylation promotes dissociation of nucleophosmin from the centriole pairs, leading to physical separation of the paired centrioles. (Fig. 2). Abnormal Amplification of Centrosomes and Chromosome Instability in Cancer The presence of two centrosomes at mitosis ensures the formation of bipolar mitotic spindles. Since chromosomes are pulled toward each spindle pole, the bipolarity of mitotic spindles is essential for the accurate chromosome segregation into two daughter cells during cytokinesis. Abrogation of the regulation underlying the numeral homeostasis of centrosomes (i.e., regulation of centrosome duplication) results in abnormal amplification of centrosomes (presence of >2 centrosomes), which in turn increases the frequency of mitotic defects (i.e., formation of >2 spindle poles) and chromosome segregation errors/chromosome instability (see [1] for the full description of the mechanisms for generation of centrosome amplification). Chromosome instability has been recognized as a hallmark of cancer, and contributes to multistep carcinogenesis by facilitating the accumulation of genetic lesions required for acquisition of various malignant phenotypes. To date, a

number of studies have shown that centrosome amplification is a frequent event in almost all types of solid tumors, including breast, bladder, brain, bone, liver, lung, colon, prostate, pancreas, ovary, testicle, cervix, gallbladder, bile duct, adrenal cortex, and head and neck squamous cell, to name a few. Centrosome amplification has also been observed in certain cases of leukemia and lymphoma. Many studies have also shown the strong association between the occurrence of centrosome amplification and a high degree of aneuploidy. Thus, centrosome amplification can be reasonably considered as a major contributing factor for chromosome instability in cancer. (Fig. 3). Loss of Tumor Suppressor Proteins and Centrosome Amplification In view of carcinogenesis, it is important to mention that loss or inactivating mutation of certain tumor suppressor proteins, most notably p53 and BRCA1, results in centrosome amplification. For both p53 and BRCA1, they were initially implicated in the control of centrosome duplication and numeral homeostasis of centrosomes by the observations that centrosome amplification and consequential mitotic aberrations were frequent in the embryonic fibroblasts (as well as various tissues) of p53-null mice as well as mice harboring BRCA1 mutation, which implies that destabilization of chromosomes due to centrosome amplification contributes to the cancer susceptibility

Centrosome. Figure 2 The centrosome/centriole duplication cycle. Late G1-specific activation of CDK2/cyclin E triggers initiation of both DNA and centrosome duplication. Centrosome duplication begins with the physical separation of the paired centrioles, which is followed by formation of procentrioles. During S- and G2-phases, procentrioles elongate, and two centrosomes progressively recruit PCM. In late G2, the daughter centriole of the parental pair acquires appendages (shown as red wedges), and two identical centrosomes are generated. During mitosis, two duplicated centrosomes form spindle poles, and direct the formation of bipolar mitotic spindles. Upon cytokinesis, each daughter cell receives one centrosome.

Centrosome

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Centrosome. Figure 3 Representative immunostaining images of centrosome amplification in human cancer. The touch preparations of G3 tumor grade bladder cancer specimens and the adjacent normal bladder epithelium samples were subjected to immunostaining for γ-tubulin (centrosome, green) and counterstained for DNA with DAPI (blue). No centrosome amplification can be seen in normal bladder epithelium (a), while a high frequency of centrosome amplification in the G3 tumors (b).

phenotype associated with loss or mutational inactivation of p53 as well as BRCA1. Centrosome Amplification and Cancer Chemotherapy In cells inhibited for DNA synthesis (i.e., by exposure to DNA synthesis inhibitors such as aphidicolin (Aph) or hydroxyurea (HU)), centrosomes undergo multiple rounds of duplication in the absence of DNA synthesis, resulting in abnormal amplification of centrosomes. However, this phenomenon preferentially occurs when p53 is either mutated or lost. In the presence of wildtype p53, centrosome duplication is also blocked by exposure to DNA synthesis inhibitors; p53 is upregulated upon prolonged exposure to Aph or HU, leading to transactivation of p21, which in turn blocks the initiation of centrosome duplication via continuous inhibition of CDK2/cyclin E. In contrast, in cells lacking p53, p21 fails to be upregulated in response to the cellular stress imposed by DNA synthesis inhibitors, allowing “accidental” activation of CDK2/ cyclin E, which triggers initiation of centrosome duplication. Considering the high frequency of p53 mutation in human cancer, it is important to address the effect of commonly used anticancer drugs targeting S-phase (DNA replication) on centrosomes. When p53null cells were exposed to subtoxic concentrations of the S-phase targeting chemotherapeutic agents (i.e., 5′-fluorouracil, arabinoside-C), centrosome amplification was efficiently induced. Moreover, after removal of drugs, these cells resumed cell cycling, and suffered dramatic destabilization of chromosomes. This finding may be significant in the context of cancer chemotherapy using the S-phase targeting drugs. During chemotherapy, not all cells in tumors receive a maximal dose of drugs – such cells may not be killed, but only arrested for cell cycling. If these cells harbor p53 mutations, centrosome amplification occurs during the drug-induced cell cycle-arrest. Upon cessation of chemotherapy, these cells resume cell cycling in the

presence of amplified centrosomes, and suffer significant mitotic aberrations and chromosome instability, which increases the risk of acquiring further malignant phenotypes. This may in part explain why the recurrent tumors after chemotherapy are often found to be more malignant than the original tumors. Many S-phase targeting anticancer drugs have been found to be effective, and there is no doubt that DNA duplication should be one of the major targets for future development of more effective anticancer drugs. However, the possibility that the S-phase targeting drugs may exacerbate a chromosome instability phenotype by inducing centrosome amplification should be taken into consideration. Another important issue to be addressed is the concept of centrosome duplication as a target of cancer chemotherapy. Like DNA replication, centrosome duplication occurs only in proliferating cells. Inhibition of centrosome duplication will not only suppress centrosome amplification and chromosome instability, but also block cell division and possibly induce cell death – cells with one centrosome fail to form bipolar mitotic spindles, and are often undergo cell death. Moreover, in contrast to genotoxic drugs which impose an increased rate of secondary mutations through interfering with DNA metabolisms, such side effects will likely be minimal in the protocol designed to block centrosome duplication. ▶Genomic Imbalance ▶Microtubule-Associated Proteins

References 1. Fukasawa K (2005) Centrosome amplification, chromosome instability and cancer development. Cancer lett 230:6–19 2. Hinchcliffe EH, Sluder G (2002) Two for two: Cdk2 and its role in centrosome doubling. Oncogene 21:6154–6160

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3. Tarapore P, Fukasawa K (2002) Loss of p53 and centrosome hyperamplification. Oncogene 21:6234–6240 4. Deng CX (2002) Roles of BRCA1 in centrosome duplication. Oncogene 21:6222–6227 5. Bennett RA, Izumi H, Fukasawa K (2004) Induction of centrosome amplification and chromosome instability in p53-null cells by transient exposure to sub-toxic levels of S-phase targeting anti-cancer drugs. Oncogene 23:6823–6829

Ceramide E RICH G ULBINS Department of Molecular Biology, University of Duisburg-Essen, Essen, Germany

Definition Ceramide belongs to the group of sphingolipids and is constituted by the amide ester of the sphingoid base D-erythro-sphingosine and a fatty acid of C16 through C32 chain length. At present, the differential biological function of different ceramide species is unknown and, thus, the term ceramide is used collectively to represent all long chain ceramide molecules.

Characteristics Formation of Ceramide Ceramide molecules are very hydrophobic and exclusively present in membranes. Sphingomyelin, the choline-ester of ceramide is hydrolyzed by acid, neutral and alkaline sphingomyelinases to release ceramide. Ceramide is also de novo synthesized via a pathway involving the serine-palmitoyl-CoA transferase. Under some circumstances ceramide can be also formed from sphingosine by a reverse activity of the acid ceramidase. Ceramide-Induced Changes of Biological Membranes The formation of ceramide within biological membranes results in a dramatic change of the biophysical properties of the lipid bilayer. Ceramide molecules have the tendency to self-associate and to form small ceramideenriched membrane microdomains. These membrane microdomains spontaneously fuse to large ceramideenriched membrane macrodomains that constitute a very hydrophobic and stable membrane domain. Furthermore, ceramide molecules seem to compete with and displace cholesterol from membrane domains. Ceramide-enriched membrane platforms serve to re-organize and cluster/ aggregate receptor molecules in the membrane resulting in a very high density of receptors within a small area of the cell membrane. At least for some receptors the transmembranous domain of the receptor determines its

preferential partitioning in ceramide-enriched membrane platforms. Ceramide-enriched membrane macrodomains are also involved in the recruitment or exclusion, respectively, of intracellular signaling molecules that mediate transmission of signals into the cell via a particular receptor. In general, clustering of receptors in ceramide-enriched membrane domains serves to amplify a weak primary signal. For instance, it was shown that ceramide-enriched membrane platforms amplify CD95 signaling ~100-fold. Ceramide in Receptor-Mediated Signaling Death receptors, in particular CD95 or DR5, activate the acid sphingomyelinase and trigger the translocation of the enzyme onto the extracellular leaflet of the cell membrane. Translocation of the acid sphingomyelinase onto the extracellular leaflet of the cell membrane may occur by fusion of intracellular vesicles that are mobilized upon receptor stimulation with the cell membrane. Surface exposure and stimulation of the acid sphingomyelinase results in very rapid release of ceramide in the cell membrane. Ceramide forms membrane platforms and mediates clustering of the death receptors, which is required for the induction of cell death via these receptors (Fig. 1). However, ceramide is not only involved in the mediation of apoptotic stimuli, but also many other stimuli trigger the release of ceramide including CD40, CD20, FcγRII, CD5, LFA-1, CD28, TNFα, Interleukin-1 receptor, PAF-receptor, infection with P. aeruginosa, S. aureus, N. gonorrhoeae, Sindbis-Virus, Rhinovirus, γ-irradiation, UV-light, doxorubicin, cisplatin, gemcitabine, disruption of integrin-signaling and some conditions of developmental death. Signaling Molecules Regulated by Ceramide Ceramide interacts with and activates phospholipase A2, kinase suppressor of Ras (KSR; identical to ceramide-activated protein kinase), ceramide-activated protein serine-threonine phosphatases, protein kinase C isoforms and c-Raf-1. Furthermore, ceramide inhibits the potassium channel Kv1.3 and calcium release activated calcium (CRAC) channels. Lysosomal ceramide specifically binds to and activates cathepsin D resulting in translocation of cathepsin D into the cytoplasm and induction of cell death via the pro-apoptotic proteins Bid, Bax and Bak. Ceramide in Mitochondria and Cell Death Besides a function of ceramide in the plasma membrane and lysosomes for the induction of cell death, ceramide is also generated in mitochondria via the de novo synthesis pathway, a reverse activity of the ceramidase and/or activity of the acid sphingomyelinase. Although at present the function of ceramide in the mediation of mitochondrial pro-apoptotic events is poorly defined,

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Ceramide. Figure 1 Receptors cluster in ceramide-enriched membrane domain to transmit signals into cells. The interaction of a ligand with its receptor results in translocation of the acid sphingomyelinase onto the extracellular leaflet and a concomitant release of ceramide. Ceramide spontaneously forms ceramide-enriched microdomains that fuse to large ceramide-enriched macrodomains. These domains trap activated receptor molecules finally resulting in clustering of many receptor molecules within a small area of the cell membrane. The high density of receptor molecules and associated intracellular molecules amplifies the primarily weak signal, permits the generation of a strong signal and, thus, efficient transmission of the signal into the cell. Modified from A. Carpinteiro et al. Cancer Letters.

it was suggested that C16-ceramide molecules form large channels in mitochondrial membranes that may permit the exit of cytochrome c from mitochondria to execute death. Genetic Evidence for a Function of Ceramide in Apoptosis The role of the acid sphingomyelinase and ceramide for CD95 and DR5-triggered apoptosis was evidenced by studies on acid sphingomyelinase-deficient cells or mice, respectively, that revealed a resistance of these cells to CD95- and DR5-triggered apoptosis, but also γ-irradiation- and UV-light- or P. aeruginosa-triggered cell death. Ceramide in g-Irradiation- and UV-A Light-Induced Apoptosis The acid sphingomyelinase and ceramide are critically involved in the response of cells to γ-irradiation. Animals or cells lacking the acid sphingomyelinase are resistant to γ-irradiation-induced cell death. In particular, endothelial cells in acid sphingomyelinasedeficient mice are resistant to γ-irradiation. Ceramide also plays a critical role for UV-light induced apoptosis. UV-A and UV-C light activate the acid sphingomyelinase, trigger the release of ceramide and the formation of large ceramide-enriched membrane domains in the cell membrane to initiate. Ceramide and Chemotherapy In addition to a central role of ceramide in γ-irradiationinduced cell death, ceramide is also critically involved in the induction of cell death by at least some chemotherapeutic drugs. Thus, doxorubicin-, cisplatin- und

gemcitabine-induced cell death of malignant and nonmalignant cells requires expression of the acid sphingomyelinase, release of ceramide and/or the formation of ceramide-enriched membrane platforms to trigger death. Rituximab, an anti-CD20 antibody, requires expression of the acid sphingomyelinase and the generation of ceramide to kill leukemic cells. Short Chain Ceramide Short chain ceramide molecules composed of a fatty acid chain with C2 through C12 length are water-soluble and, thus, very much differ from endogenous long ceramide molecules (C16-C32). However, they are very efficient reagents to kill tumor cells in vitro. Cationic pyridinium-ceramides seem to accumulate in mitochondria of tumor cells and may, thus, serve as a new class of anti-tumor reagents, although at present no convincing concepts are available to selectively target tumor cells in vivo by and to avoid effects of short chain ceramide on normal cells.

References 1. Fulda S, Debatin KM (2006) Extrinsic versus intrinsic apoptosis pathways in anticancer chemotherapy. Oncogene 25:4798–4811 2. Kolesnick RN, Goni FM, Alonso A (2000) Compartmentalization of ceramide signaling: physical foundations and biological effects. J Cell Physiol 184:285–300 3. Gulbins E, Kolesnick RN (2003) Raft ceramide in molecular medicine. Oncogene 22:7070–7077 4. Jaffrezou JP, Laurent G (2004) Ceramide: A new target in anticancer research? Bull Cancer 91:E133–E161 5. Ogretmen B, Hannun YA (2004) Biologically active sphingolipids in cancer pathogenesis and treatment. Nat Rev Cancer 4:604–616

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Ceramide Kinase (CerK)

Ceramide Kinase (CerK) Definition Ceramide kinase (CerK) has important roles in leukocyte functions, including the role in degranulation of mast cells and the phagocytosis of polymorphonuclear leukocytes. ▶Ceramide

irreversibly binding to the active site cysteine thiol in the β-ketoacyl-synthase domain of fatty acid synthase. ▶Fatty Acid Synthase

Cervical Definition Pertaining to the neck.

Ceramide-1-Phosphate (C1P) Definition Ceramide-1-phosphate (C1P) is a phosphorylated form of ▶ceramide and possesses antitumor properties. ▶Lipid Mediators

Cervical Cancers J IRO F UJIMOTO Department of Obstetrics and Gynecology, Gifu University School of Medicine, Gifu City, Japan

Definition

C-erb-B2 ▶HER-2/neu

Cerebral Edema Definition Is the accumulation of fluid in the brain, often as a result of a pathological condition. ▶Convection Enhanced Delivery (CED)

Cerulenin Definition An antifungal antibiotic isolated from several species, including Cephalosporium, Acrocylindrum, and Helicoceras. It inhibits the biosynthesis of fatty acid by

The regions of the uterus are the corpus and the cervix. Cancer originating from the cervix is defined as cancer of the cervix. When cancers are simultaneously detected in the cervix and corpus, squamous cell carcinoma (SCC) is designated as a cancer of the cervix and adenocarcinoma is designated as a cancer of the corpus. When cancer occupies both the cervix and vagina without the junctional area (the fornix), the cancer extending to the exocervix is recognized as a cancer of the cervix. Thus, cervical cancer is defined apart from cancer of the uterine corpus (cancer of the uterine endometrium) and cancer of the vagina.

Characteristics The main gynecological cancers originate from the cervix, endometrium, and ovary. Among them, cervical cancer is the most common malignancy in women. Main risk factors are . Young age at first intercourse, especially shortly after the menarche . High number of sexual partners . High number of sexual partners of the partner . High number of children . Excessive douching Smoking appears to increase the incidence of SCC, but not of adenocarcinoma or adenosquamous carcinoma. Immunosuppression by smoke-derived nicotine and its metabolite cotinine in the cervical mucus may enhance

Cervical Cancers

the effects of sexually transmitted disease (STD) including human papillomavirus (HPV) infection. Most epidemiological risk factors for cervical cancer are associated with STDs. HPV induces an STD, human venereal condyloma, which is associated with cervical, vaginal and vulvar dysplasia, and invasive carcinomas. HPV particles and DNA, especially HPV-16, HPV-18, and HPV-33, are detected in cervical and vulvar dysplasia and in invasive carcinomas. Additionally, it has been demonstrated that HPV transforms human cell lines. HPV infection of the cervix is a main etiology of cervical cancer. Symptoms Main symptoms of cervical cancer are . Vaginal bleeding, which may be recognized as postmenopausal bleeding, irregular menses, or postcoital bleeding . Abnormal vaginal (watery, purulent or mucoid) discharge In advanced cases, corresponding local symptoms occur. A Pap smear even in unsymptomatic cases is useful for the early detection of cervical dysplasia and cancers. Among women over the age of 18 who have had sexual intercourse, high-risk women should be screened at least yearly. Pathology Histopathological types in cervical cancers are mainly SCC and adenocarcinoma, which account for about 90% of all cervical cancers (adenosquamous carcinoma, glassy cell carcinoma, adenoid cystic carcinoma, adenoid basal carcinoma, carcinoid, small cell carcinoma, and undifferentiated carcinoma also occur). SCCs are keratinizing or nonkeratinizing in most cases and may be verrucous, condylomatous, papillary, or lymphoepithelioma-like carcinomas in a few cases. Adenocarcinomas are classified into mucinous, endometrioid, clear cell, serous, and mesonephric adenocarcinomas; mucinous adenocarcinomas are subclassified with endocervical type into adenoma malignum and villoglandular papillary adenocarcinoma, and intestinal type adenocarcinoma. Staging Clinical staging represents the degree of advancement of the tumor, and is defined by the FIGO classification established in 1994 and by the TNM classification of malignant tumors set by the UICC in 1997 as follows (classified by FIGO [TNM]): . Stage 0 (Tis): carcinoma in situ (preinvasive carcinoma). . Stage I (T1): cervical carcinoma confined to the uterus.

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. Stage II (T2): tumor invades beyond the uterus but not to the pelvic wall or to the lower third of the vagina. . Stage III (T3): tumor extends to the pelvic wall and/ or involves the lower third of the vagina and/or causes hydronephrosis or nonfunctioning kidney. . Stage IVA (T4): tumor invades the mucosa of the bladder or rectum and/or extends beyond the true pelvis. . Stage IVA (Ml): distant metastasis. Stage IA (TIa) has been further classified by microinvasive depth and width into stage IA1 (Tlal) (depth of stromal invasion ≤3 mm, horizontal spread ≤7 mm) and stage IA2 (Tla2) (depth of stromal invasion >3 mm, ≤5 mm; horizontal spread ≤7 mm). Stage IB (Tlb) has been further classified by tumor size into stage IB1 (Tlbl) (greatest dimension ≤4 cm) and stage IB2 (Tlb2) (greatest dimension >4 cm). In cases staged IA2 (Tla2) or less advanced, colposcopically directed biopsy in the transformation zone of the cervix, endocervical curettage or cervical conization are required. Prognosis Unfavorable prognostic factors include younger age, advanced clinical stage, certain histopathological types, vessel permeation, large tumor volume, parametrium involvement, and lymph node metastasis. Nodal metastasis is an especially critical prognostic factor after curative resection. Vascular endothelial growth factor (VEGF)-C and osteopontin contribute to the aggressive lymphangitic metastasis in uterine cervical cancers. Platelet-derived endothelial cell growth factor (PD-ECGF) contributes to the advancement of metastatic lesions as an agiogenic factors. PD-ECGF, VEGF-C, and osteopontin levels in metastatic lesions are prognostic indicators. Furthermore, serum PDECGF level reflects the status of advancement of cervical cancers and is recognized as a novel tumor marker for both SCC and adenocarcinoma of the cervix, while the tumor marker SCC is well known only as an indicator for SCC of the cervix. VEGF-C and osteopontin contribute to the aggressive lymphangitic metastasis in uterine cervical cancers. Therapy The treatment for cervical cancer consists mainly of surgery and radiation. Chemotherapy is performed in combination with surgery and/or radiation for advanced cases, and immunotherapy is an adjuvant treatment for surgery, radiation, and chemotherapy. The standard treatment for carcinoma in situ is cervical conization or total hysterectomy. The standard treatment for microinvasive carcinoma stage IA (Tla) is modified radical hysterectomy regardless of regional lymphadenectomy. The standard surgical treatment for

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invasive carcinoma is radical hysterectomy with regional lymphadenectomy. Although oophorectomy can be avoided in some cases during the reproductive period, ovarian metastasis must be considered especially in adenocarcinoma of the cervix. When ooporectomy is avoided, the ovary is better shifted out of radiation area. For patients who undergo oophorectomy, hormone replacement therapy can be useful. In more advanced cases, extended radical hysterectomy or pelvic exenteration is appropriate. After surgery external irradiation is followed in some cases. The standard radiotherapy without surgery for invasive carcinoma is intra-cavitary and/or external irradiation. Recently, neoadjuvant therapy (chemotherapy) has been tried in order to make surgery more successful, and concurrent radio-chemotherapy has been tested for the purpose of enhancing the effect of radiation.

References 1. Fujimoto J, Toyoki H, Sato E et al. (2004) Clinical implication of expression of vascular endothelial growth factor-C in metastatic lymph nodes of uterine cervical cancers. Br J Cancer 91:466–469 2. Fujimoto J, Sakaguchi H, Hirose R et al. (1999) Clinical implication of expression of platelet-derived endothelial cell growth factor (PD-ECGF) in metastatic lesions of uterine cervical cancers. Cancer Res 59:3041–3044 3. Fujimoto J, Sakaguchi H, Aoki I et al. (2000) The value of platelet-derived endothelial cell growth factor as a novel predictor of advancement of uterine cervical cancers. Cancer Res 60:3662–3665

Cetuximab

have been identified in several types of cancer, such as lung cancer and colorectal cancer. Cetuximab is approved for treatment of EGFRpositive, irinotecan-refractory ▶metastatic colon cancer. ▶Monoclonal Antibody Therapy ▶Epidermal Growth Factor Receptor Inhibitors

c-FLICE-like Inhibitory Protein Definition c-FLIP, also known as FLAME-1/I-FLICE/CASPER/ CASH/MRIT/CLARP/Usurpin, is a death-effectordomain (DED)-containing protein that exists in three different isoforms, FLIPL, FLIPS, and FLIPR. All cFLIP isoforms contain two N-terminal DEDs, whereas only FLIPL also harbors a C-terminal part of catalytically inactive caspase-like domains homologous to caspase-8. FLIPL, FLIPS, and FLIPR function as inhibitors of apoptosis by blocking caspase-8 activation at the death-inducing signaling complex (DISC). In addition, FLIPL may promote ▶apoptosis at low expression levels by facilitating autocatalytic activation of procaspase-8 and is also involved in nonapoptotic pathways, e.g., NF-κB or MAPK signaling. ▶c-FLIP ▶Usurpin ▶Caspase-8

Definition Is a chimeric IgG1κ monoclonal antibody specifically binding to epidermal growth factor receptor (EGFR). Epidermal growth factor receptor (EGFR) (EGFR; ErbB-1; HER1 in humans) is the cell-surface receptor for members of the epidermal growth factor family (EGF-family) of extracellular protein ligands. Ligands which induce activation of EGFR are epidermal growth factor and transforming growth factor α, for example. Upon activation by its growth factor ligands, EGFR undergoes a transition from an inactive monomeric form to an active homodimer. EGFR dimerization stimulates its intrinsic intracellular protein-tyrosine kinase activity resulting in activation of several signal transduction cascades which lead to DNA-synthesis and cell proliferation. EGFR mutations can lead to EGFR overexpression or overactivity and consequently result in uncontrolled cell division. Mutations of EGFR

c-FLIP Definition

▶c-FLICE-like Inhibitory Protein

CG ▶Cancer Germline Antigens

Checkpoint

cGMP

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Chaperone

Definition

Definition

Cyclic guanosine monophosphate.

Molecular chaperones are proteins that aid the proper folding and assembly of proteins incompletely folded under conditions of cellular stress or protein synthesis. Molecular chaperones include small Hsp, Hsp40, Hsp60, Hsp70, Hsp90, Hsp100, the calnexin/calreticulin families, and so forth.

▶Nitric Oxide

CGP57148

▶Calreticulin ▶Dioxin ▶Methylation-Controlled J Protein (MCJ) ▶Autophagy

▶STI-571 ▶Imatinib

Chaperonins z Chain Definition A transmembrane protein associated with key functional receptors of the immune system, the T cell antigen receptor (TCR) and NK killing receptors (NKP30, NKP46 and CD16). The ζ chain has a key role in receptor assembly, expression and signaling function. Down-regulation of ζ chain expression associated with immunosuppression has been shown in various chronic pathologies characterized by chronic inflammation, including cancer, autoimmune, and infectious diseases. ▶Inflammation

Channels

Definition

A family of conserved ▶chaperone proteins which have a characteristic multi-subunit ring structure. They function by enclosing a nascent protein and preventing its non-specific aggregation during assembly. ▶Molecular Chaperones

Charged Particle Therapy ▶Proton Beam Therapy

Checkpoint

Definition

Definition

Channels are pores in biological membranes that have a rather limited specificity. Substance flow through channels is controlled by the channels’ open probability so that high transport rates of 107–109 molecules per second can be achieved.

Checkpoints represent intrinsic mechanisms that are activated when cell-cycle progression would be detrimental to the cell, as in case of DNA-damage, incomplete DNA synthesis, metabolic dysfunctions or mitotic spindle damage. In such cases, cell-cycle progression is transiently halted until the respective problem is fixed, for instance by the DNA repair

▶Membrane Transporters

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machinery. Major checkpoints are governed by the tumor suppressor gene product p53 or the ▶check point kinases CHK1 and CHK2. Control mechanism that ensures that the next step in the cell cycle does not proceed until a series of preconditions have been fulfilled including the completion of all previous steps; this is particularly true for all pathways associated with DNA replication and chromosome formation; impaired chromosome checkpoints can result in chromosomal.

Chelators as Anti-Cancer Drugs DAVID B. LOVEJOY, Y U Y U, D ES R. R ICHARDSON Department of Pathology, University of Sydney, NSW, Australia

Synonyms Chelation therapy

▶Cell-Cycle Targets for Cancer Therapy ▶Fragile Histidine Triad ▶Chromosomal instability ▶Aneuploidy

Checkpoint Kinases Definition Checkpoint kinases are a group of at least four protein kinases (ATM, ATR, CHK1 and CHK2) and their relatives, which play an important role in the mechanisms that sense and signal DNA damage, culminating in the activation of cell-cycle checkpoints and DNA repair. ▶Checkpoint ▶Cell-Cycle Checkpoint

Chelation Therapy ▶Chelators as Anti-Cancer Drugs

Chelator Definition A chemical or drug capable of binding metal ions. ▶Chelators as Anticancer Drugs

Definition Iron is an element fundamental for life. Many vital cellular processes such as energy metabolism and DNA synthesis consist of reactions that require catalysis by iron-containing proteins. These proteins include ▶cytochromes, and ▶ribonucleotide reductase (RR). The latter is more significant in the context of cellular proliferation due to its role in catalyzing the rate-limiting step of DNA synthesis. Ultimately, the importance of iron is highlighted by the fact that iron-deprivation leads to G1/S ▶cell cycle arrest and ▶apoptosis. Cancer cells in particular, have a higher iron requirement because of their rapid rate of proliferation. In order to satisfy their iron requirement, some cancer cells have altered iron metabolism. In addition, iron ▶chelators also demonstrate the ability to inhibit growth of aggressive tumors such as ▶neuroblastoma. For these reasons, iron-deprivation through iron chelation is seen as an exploitable therapeutic strategy for the treatment of cancer.

Characteristics Iron Metabolism in Cancer Cells In order to attain more iron, cancer cells have higher numbers of the transferrin receptor-1 molecule (TfR1) on their cell surface. The TfR1 binds the serum iron transport protein, transferrin (Tf). Hence, cancer cells are able to bind more Tf, and thus, take up iron at a greater rate than their normal counterparts. This is reflected by the ability of tumors to be radiolocalized using a radioisotope of gallium, 67Ga, which binds to the iron-binding site on Tf for delivery via TfR1. 67 Ga can bind to iron-binding sites of Tf due to the similar atomic properties between gallium(III) and iron (III). Additionally, gene therapy by administration of anti-sense TfR1 targeted to the sequences of TfR1 mRNA also showed selective anti-cancer activity, further demonstrating the importance of TfR1 in mediating cancer cell growth. Apart from TfR1 up-regulation, the expression of the iron-storage protein ferritin is also often altered in neoplastic cells, especially neuroblastoma (NB) and breast carcinoma. In childhood NB, serum ferritin levels are elevated at stages III and IV of the disease.

Chelators as Anti-Cancer Drugs

In a longitudinal study, it was found that the elevated level was associated with a markedly poorer prognosis of the disease. In addition, serum ferritin levels also exceeded the normal limit in ▶hepatocellular carcinoma and were found to be directly related to axillary lymph node status, presence of metastatic disease (▶metastasis) and clinical stages of breast cancer. Desferrioxamine, an Iron Chelator with Some Anti-Cancer Activity Desferrioxamine (DFO) is a natural ligand secreted by the bacterium Streptomyces pilosus to selectively sequester iron for biological use (Fig. 1). DFO is used clinically for the treatment of iron overload disorders such as the transfusion-related iron overload in β-thalassemia. DFO is active against aggressive tumors including NB and leukemia in cell culture and clinical trials. The cytotoxicity of DFO in vitro was prevented by coincubation of the cells with iron or iron saturated DFO, indicating that its anti-proliferative activity was due to depletion of cellular iron. Furthermore, DFO induces a block in cell cycle progression. Therefore, it was proposed that the mechanism of action of DFO involved the depletion of cellular iron, leading to the inhibition of ribonucleotide reductase for DNA synthesis and cell cycle arrest. In human NB cells, 5 days of exposure to DFO resulted in approximately 90% cell death. In contrast, the effect of DFO was minimal on non-NB cells, suggesting that it had selective anti-NB activity. A clinical trial showed that seven of nine NB patients

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had up to 50% reduction in bone marrow infiltration after a course of DFO administered for 5 days. Other clinical trials using DFO as a single agent and in combination with other chemotherapeutic drugs confirmed the anti-cancer potential of this chelator. However, in some animal studies and clinical trials, DFO was found to exhibit limited or no activity. DFO also suffers a number of limitations as a result of its highly hydrophilic nature. It has poor gastrointestinal absorption and a short plasma half-life of about 12 min due to rapid metabolism. As a result, DFO is not orally active and needs to be administered via subcutaneous infusion for prolonged periods ranging from 8 to 12 h for five to seven times per week. The prolonged infusion results in pain and swelling, which consequently leads to poor patient compliance. DFO is also expensive to produce. Despite these limitations and mixed results in clinical trials, DFO nonetheless provides “proof of principle” that iron chelation therapy may be specific and useful for cancer treatment. Other Chelators with Anti-Cancer Potential The limitations of DFO as an anti-cancer agent have encouraged the search for other active iron-chelating drugs against cancer. Other experimental iron chelators include Triapine® (3-AP; Fig. 1), an iron-binding thiosemicarbazonebased drug currently in clinical trials for cancer therapy. Triapine® is a chelator that binds iron via a sulfur and two nitrogen donor atoms, and is suggested to be one

Chelators as Anti-Cancer Drugs. Figure 1 Chemical structures of the iron chelators desferrioxamine (DFO), N,N′,N″-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane (tachpyridine or tachpyr), 3-aminopyridine2-carboxaldehyde-thiosemicarbazone (3-AP or Triapine®), 2-hydroxy-1-napthaldehyde isonicotinoyl hydrazone (311) and di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone (Dp44mT) showing coordination to iron (Fe) through pyridyl nitrogen, aldimine nitrogen and thionyl sulfur donor atoms.

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of the most potent inhibitors of RR yet identified. In clinical trials, high doses of Triapine® (160 mg/m2/day) resulted in dose-limiting toxicities, including reduction in white blood cells, jaundice, nausea and vomiting. Lower doses of Triapine® administered as a 96-h iv infusion at 120 mg/m2/day every 2 weeks was found to be well tolerated. In clinical trials with patients with advanced cancer, Triapine® was combined with the cytotoxic cancer drug gemcitabine, which also targets DNA synthesis. Of the 22 patients examined after treatment with gemcitabine and Triapine®, three were observed to have an objective response, and one patient had evidence of tumor reduction. In this trial, Triapine® was suggested to cause oxidation of hemoglobin to methemoglobin. This may have led to or contributed to the hypoxia, acute hypotension, and electrocardiogram changes in patients receiving this chelator. An asymptomatic myocardial infarction was also observed in one individual administered Triapine® and this may also be related to its oxidative effects. Triapine® continues to be examined in clinical trials, particularly in combination with standard chemotherapy drugs. However, these deleterious effects must be considered when designing future studies with compounds of this class. Tachpyridine, (or tachpyr; Fig. 1) is a novel chelator based upon the framework of the triamine cis,cis1,3,5-triaminocyclohexane. Tachpyridine is cytotoxic to cultured bladder cancer cells with an activity approximately fifteen times greater than that of DFO. Although tachpyridine has the potential to chelate a number of metals, including calcium(II), magnesium (II), manganese(II), copper(II) and zinc(II), toxicity studies on tachypyridine complexes suggest that iron and zinc depletion mediates its cytotoxic effects. Similar to Triapine®, Tachpyridine induces apoptotic cell death independent of functional p53 (see Iron Chelation and Cell Cycle Control Molecules, below) (▶p53 gene family). In addition, tachpyridine-iron complexes produce toxic free-radicals (▶reactive oxygen species), which was also thought to contribute to its anti-tumor activity. Tachpyridine arrests cells at the G2 phase, whereas the majority of iron chelators arrest cells at the G1/S phase due to inhibition of ribonucleotide reductase. The G2 phase stage of the cell cycle is particularly sensitive to the effects of radiation. Ionizing radiation increases the sensitivity of tumor cells to the action of tachpyridine. Currently, tachpyridine is in preclinical development with the National Cancer Institute, USA. PIH Chelators The most comprehensively assessed alternate chelators for cancer treatment are the pyridoxal isonicotinoyl hydrazone (PIH) analogues. This class of chelators bind iron through the carbonyl oxygen, imine nitrogen, and phenolic oxygen (Fig. 1).

Originally conceived for the treatment of iron overload disorders, several chelators of the PIH class were found to inhibit the growth of cancer cells. In fact, the chelator 311 (Fig. 1) was found to be highly active against a range of cancer cells. These compounds also showed marked ability to remove Fe from cells and prevent cellular Fe uptake from transferrin. The marked anti-cancer activity of chelator 311 was attributed to its relatively high ▶lipophilicity, which facilitates entry into the cell. Indeed, a general trend observed with the PIH analogues was that anti-cancer activity increased as the chelator became more lipophilic. Mechanistically, PIH analogues have multiple modes of anti-cancer activity, aside from chelation of iron and inhibition of ribonucleotide reductase. Some members of the PIH class of chelators (e.g. DpT chelators, see below) increase the generation of toxic free-radicals (reactive oxygen species) in cancer cells and affect the expression of cell-cycle control molecules (see Iron Chelation and Cell Cycle Control Molecules, below). Additional studies with 311 have also shown that it can markedly induce the expression of the metastasis suppressor protein, ▶Drg-1 in tumor cells. The Drg-1 protein is known to play a critical role in suppressing tumor growth and metastasis. Hence, induction of Drg-1 by potent iron chelators such as 311 may significantly contribute to the anti-cancer activity of these analogues. The DpT Chelators: Dp44mT The DpT class of chelators are structurally-related to PIH analogues, but feature a sulfur donor atom instead of the hydrazone oxygen donor atom (Fig. 1). The chelator Dp44mT has recently been shown to be the most effective of the DpT series of ligands in terms of anti-cancer activity. It acts with selectivity against tumor cells and has much less effect on the growth of normal cells. Dp44mT also showed high iron chelation efficacy and prevented cellular uptake of iron from iron-labeled Tf. Another mechanism of its action involves the generation of toxic free-radicals (reactive oxygen species) when Dp44mT interacts with cellular iron pools. Initially, in vivo studies of Dp44mT in mice bearing chemotherapy-resistant M109 lung carcinoma showed a reduction in the size of the tumor by 53% after 5-days of treatment. A later investigation also found marked inhibition of the growth of human lung, neuroepithelioma and melanoma xenografts growing in mice. In fact, a 7-week administration of Dp44mT in mice bearing human melanoma xenografts resulted in the decrease of tumor growth to 8% of that in untreated control mice. At the dose given, no hematological abnormalities were detected, although at a higher dose, myocardial fibrosis was identified. This side effect at a high dose may be due to the marked redox activity of the Dp44mT-iron complex. However, at a lower dose

Chelators as Anti-Cancer Drugs

Dp44mT was well tolerated with no hematological abnormalities and less cardiotoxicity. Other studies with Dp44mT showed that it also markedly increased the expression of the metastasis suppressor protein, Drg-1 in tumor cells. Induction of Drg-1 could potentially be a very significant component of the anti-cancer mechanism of Dp44mT. Further development of DpT series chelators is currently underway. Iron Chelation and Cell Cycle Control Molecules Iron-deprivation generally leads to G1/S phase cell cycle arrest as a result of inhibition of ribonucleotide reductase. This has prompted many studies assessing the effect of iron chelation by DFO and chelator 311 on the expression of many cell cycle control molecules, namely, cyclins, ▶cyclin dependent kinases (cdks), cdk inhibitors and p53 (p53 gene family). Consistently, these studies found that iron chelation markedly decreased the expression of ▶cyclin D (D1, D2 and D3), and to a lesser extent cyclin A and B. The expression of cdk2 and cdk1, but not cdk4, were also decreased upon iron chelation. These effects were dependent on iron-deprivation, as iron-chelator complexes were unable to induce such effects. Cyclins D, E, A and cdks 2, 4 and 6 are involved in progression through the G1 phase, although cyclin E, A and cdk2 are also involved in S phase progression. The formation of the cyclin A-cdk2 complex is essential for G1/S progression. Cyclin B and cdk1 on the other hand, are important for mitosis. During the G1 phase, cyclin D and E bind to cdk4 and cdk2 respectively to phosphorylate (▶phosphorylation) the ▶retinoblastoma protein (pRb) (▶Biological and Clinical Functions). This results in the release of molecules such as the ▶E2F transcription factor from pRb that promotes the expression of genes for S phase. The decrease in the expression of these cyclins upon iron chelation causes hypophosphorylation of pRb, which in turn leads to the G1/S phase arrest. In addition to cyclins and cdks, iron chelation also affects the expression of cell cycle modulatory molecules. In particular, iron chelators caused a marked increase in the expression of the cyclin-dependent kinase inhibitor p21WAF1/CIP1 (▶p21(WAF1/CIP1/ SDI1)) at the mRNA level. p21WAF1/CIP1 mediates G1/S phase arrest by directly binding the cyclin-cdk complexes. It was speculated that the increased level of p21WAF1/CIP1 upon iron chelation was consistent with its potential role in the G1/S phase arrest. However, an increase of p21WAF1/CIP1 expression only occurred at the mRNA level, with either no change or a decrease in p21WAF1/CIP1 protein expression being observed. This was unexpected and it was subsequently demonstrated that p21WAF1/CIP1 protein level could be controlled by proteasomal (▶proteasome) degradation after iron chelation.

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In contrast, investigations examining p53 showed that its protein expression and DNA-binding activity were increased after chelation. p53 is a tumor suppressor and acts as a transcription factor that is involved in the transcription of a variety of genes involved in cell cycle arrest, differentiation, apoptosis and DNA repair. An increase in p53 after iron chelation may be the result of a decrease in deoxyribonucleotide levels due to inhibition of RR activity or changes in intracellular redox status. Despite the fact that p21WAF1/ CIP1 is a down-stream effector of p53, elevated expression of p21WAF1/CIP1 upon iron chelation occurs through a p53-independent pathway. The ability of chelators to potentially inhibit tumor cell growth by a p53-independent pathway is significant, since p53 is the most frequently mutated gene in cancer. This also explains why cells with wild-type or mutant p53 are similarly sensitive to the growth inhibitory effects of iron chelators. However, the function of increased p53 expression after chelation remains a subject for further investigation. Conclusions The demonstration that some iron chelators may be clinically useful for cancer treatment followed on from initial observations that rapid cancer cell proliferation requires iron. Currently, the iron chelator, Triapine®, is being examined in a variety of clinical trials, with focus on a potential role in combination chemotherapy. The search for more effective anti-cancer Fe chelators than DFO has also led to the development of other potent Fe chelators, including Dp44mT and tachpyridine, and significant progress has been made towards understanding their molecular targets. However, further in vivo experiments and pre-clinical studies will be necessary to build upon the promise of these agents.

References 1. Yu Y, Wong J, Lovejoy DB et al. (2006) Chelators at the cancer coalface: desferrioxamine to triapine and beyond. Clin Cancer Res 12:6876–6883 2. Buss JL, Greene BT, Turner J et al. (2004) Iron chelators in cancer chemotherapy. Curr Top Med Chem 4:1623–1635 3. Kalinowski D, Richardson DR (2005) Evolution of iron chelators for the treatment of iron overload disease and cancer. Pharmacol Rev 57(4):1–37 4. Le NTV, Richardson DR (2004) Iron chelators with high anti-proliferative activity up-regulate the expression of a growth inhibitory and metastasis suppressor gene: a novel link between iron metabolism and proliferation. Blood 104:2967–2975 5. Whitnall M, Howard J, Ponka P et al. (2006) A class of iron chelators with a wide spectrum of potent anti-tumor activity that overcome resistance to chemotherapeutics. Proc Natl Acad Sci USA 103:14901–14906

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Chemical Biology

Chemical Biology Definition The application of chemical tools and ideas to biological problems. ▶Small Molecule Screens

Chemical Biology Screen ▶Small Molecule Screens

Chemical Carcinogenesis J OSEPH R ICHARD L ANDOLPH , J R . Department of Molecular Microbiology and Immunology, and Dept. of Pathology; Cancer research Laboratory, USC/ Norris Comprehensive Cancer Center, Keck School of Medicine; Department of Molecular Pharmacology and Pharmaceutical Sciences, School of Pharmacy, Health Sciences Campus, University of Southern California, Los Angeles, CA, USA

Definition

▶Chemical carcinogenesis (▶carcinogenesis) is the process of the genesis of a ▶tumor (carcinoma), and the series of sequential steps that occur when lower animals or humans are treated with ▶chemical carcinogens that leads to tumor development. After all these steps are accomplished, the physiological mechanisms regulating control of growth in the normal cells are degraded, and the normal cells are degraded and converted into tumor cells. The tumor cells then grow in an unregulated fashion and evade the host immune system, leading to development of visible tumors.

Characteristics Normal Cell Types in Animals and the Tumors They Give Rise to During embryogenesis in mammals (warm-blooded animals), there are three primary germ layers of the early embryo which develop into all the basic cell types, tissues, and organs in the body. These are the ectoderm, the endoderm, and the mesoderm. The ectoderm and endoderm are epithelial layers. Most of the epithelial

organs in the body are derived from the endodermal and the ectodermal germ layers. The epidermis of the skin, the corneal epithelium, and mammary glands develop from the ectoderm. The endoderm layer develops into the liver, pancreas, stomach, and intestines. The mesoderm develops into the kidney and linings of male and female reproductive tracts. Three types of cells are important in chemical carcinogenesis. These cell types are (i) ▶epithelial cells, which form the coverings and internal parts of organs, (ii) ▶fibroblasts, which are connective tissue cells derived from primitive mesenchymal cells, and (iii) cells of the hematolymphopoietic series, which are derived from the blood-forming elements. These cell types all have special, specific characteristics. In humans, 92% of the tumors that arise are derived from epithelial cells (▶Epithelial cell tumors). These tumors are called carcinomas. The remaining 8% of the tumors are derived from a combination of tumors derived from fibroblasts, called sarcomas, and tumors derived from white blood cells, called leukemias (▶Leukemia diagnostics) and lymphomas. Carcinogens There are a group of molecules and radiations referred to as “carcinogens.” A ▶carcinogen (▶Carcinogen macromolecular adducts) is any molecule, or group of molecules, such as viruses (▶Virology), or radiation (▶Radiation carcinogenesis; ▶radiation oncology) that can cause tumors in lower animals and humans, when they are exposed to this agent. This happens when carcinogens cause normal cells to transform, or convert into transformed cells and tumor cells during experiments in vitro, called chemical transformation experiments. Chemicals referred to as chemical carcinogens (chemical carcinogenesis) can cause tumors in lower animals in humans exposed to them. Examples of chemical carcinogens are vinyl chloride, aflatoxin B1 (a metabolite and biocide of the fungus, Aspergillus flavus) (▶Aflatoxins), benzo(a)pyrene (a polycyclic aromatic hydrocarbon formed when organic matter is pyrolyzed in the absence of oxygen) (▶Polycyclic aromatic hydrocarbons), and beta-naphthylamine (an aromatic amine used to manufacture dyestuffs that causes bladder cancer in animals and humans) (▶Aromatic amines). Nitrosamines are another class of chemical carcinogens. An example is dimethylnitrosamine (DMN). Many nitrosamines are synthetic compounds. Some are believed to form in the stomach of humans when amines (derived from fish in the diet) contact nitrous acid (formed from the nitrate from fertilizer that is used to grow foodstuffs) in the acidic conditions (acid pH) of the stomach. Chemicals in all these classes of carcinogens can cause tumors in humans and in lower mammals.

Chemical Carcinogenesis

There are also a number of radiations that cause tumors in humans and lower animals. These include ionizing radiations, such as alpha particles (charged helium nuclei), beta particles (naked electrons), and gamma particles. There are also tumor viruses, consisting of RNA (RNA tumor viruses) and DNA (DNA tumor viruses). When animals are treated with these viruses, tumors are formed. Examples of RNA tumor viruses are the Rous sarcoma virus, the Abelson leukemia virus, and the Kirsten Ras virus. Examples of DNA tumor viruses are the polyoma virus, the SV40 (simian virus 40) (▶SV40) virus, the ▶Epstein Barr virus, and the human papilloma viruses 16 and 18 (▶Human papilloma viruses). Mechanisms of Chemical Carcinogenesis There are two broad mechanisms of chemical carcinogenesis. In the first type, which we refer to here as “▶complete carcinogenesis,” a mammal is treated with a large dose of a chemical carcinogen, such as 7,12-dimethylbenz(a)anthracene, and the animals treated eventually develop tumors. Carcinogenesis with complete carcinogens is usually dose-dependent, such that the higher doses of carcinogens that the animals are treated with, the high the yield of tumors per animal and in the percentage of animals with tumors. The second mechanism of chemical carcinogenesis, discovered by Dr. Isaac Berenblum of the Weizmann Institute in Israel, is referred to as ▶“two-step carcinogenesis,” or “initiation and promotion”. In initiation and promotion experiments, Berenblum treated mice on the skin of their shaved backs with chemical carcinogens at low doses and also with ▶tumor promoters. Berenblum was testing the hypothesis that carcinogenesis was due to irritation and inflammation. Hence, he used croton oil, a product of the plant, Euphorbia lathyris, which the plant uses as a biocide against insects. Croton oil is a very irritating substance, which is important in the plant’s use of it as a biocide against insects. When mice were treated with low doses of 7,12-dimethyl-benz(a)anthracene (DMBA, a carcinogenic PAH), one time, they exhibited no tumors. A second group of animals was treated with the tumor promoter, croton oil, once per week, and the animals also exhibited no tumors. When the mice were treated with a low dose of DMBA, and then once weekly with croton oil, they developed many tumors. If the latter treatment was reversed, i.e. the animals were treated first with croton oil once per week, and then later treated with a low dose of DMBA, the animals showed no tumors. If the animals were treated with a low dose of DMBA, then no treatment was performed for a significant amount of time, then the animals were treated with croton oil once per week, the animals also developed a high yield of tumors. In this system, treatment of the animals with the low dose of DMBA is referred to as the “initiation step,” and later

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treatment with croton oil is called the “promotion” step. Initiation is believed to be a ▶genotoxic event, likely a ▶mutation, and is an irreversible step. Initiated cells can be promoted to tumors cells if they are treated with croton oil long enough. The promotion step is believed to be due to the binding of tetradecanoyl-phorbol acetate (TPA, the most active constituent of the mixture of phorbol esters in croton oil), to protein kinase C, triggering signal transduction and cell division in cells bearing mutations in ▶proto-oncogenes. If promotion is interrupted, then tumorigenesis is reversible, i.e. the cellular death rate will equal the cellular growth rate, and the tumor will regress. If promotion is continued long enough, the tumor becomes fixed and will not regress. Eric Hecker of the German Cancer Research Center (Deutsch Krebs Forschung Zentrum) in Heidelberg, Germany, fractionated croton oil used by Berenblum, by high pressure liquid chromatography, and found that TPA was the most active tumor promoter in it. From experiments with high doses of chemical carcinogens, and experiments with initiation and promotion, we now have evidence that chemical carcinogens such as DMBA cause mutations in proto-oncogenes, such as ras genes, converting them into activated ▶oncogenes. In complete carcinogenesis experiments, further mutations in other proto-oncogenes can also occur, leading to activation of additional oncogenes. In addition, activated metabolites of the carcinogens (formed in the animals/ mammals by cytochrome P450 or other enzymes of metabolic activation), also cause mutational inactivation of ▶tumor suppressor genes, or breakage of chromosomes bearing them, leading to loss of these tumor suppressor genes. Together, activation of oncogenes and inactivation of tumor suppressor genes is believed to lead to the genesis of tumors in mammals. Insights into Mechanisms of Chemical Carcinogenesis from Studies of Chemically Induced Neoplastic Transformation Studies of the abilities of chemical carcinogens to convert normal cells into tumor cells in cell culture dishes have given us substantial insight into the molecular mechanisms of chemical carcinogenesis. In cell culture, normal fibroblasts and normal epithelial cells grow if they are fed properly, until they eventually fill the culture dish, and touch each other. Growth then ceases. This process is called contact inhibition of cell division. Cells can then be removed from the cell culture dish with a protease called trypsin, diluted, and replated into new cell culture dishes. This process can be repeated many times, until the population of total cells has undergone sixty population doublings. At this point, the cells senesce (▶Senescence and immortalization), or die. This is due to progressive shortening of telomeres (▶Telomerase), structures at the end of chromosomes, with each successive DNA replication

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and cell division. Telomere shortening acts as a cellular and molecular “clock,” to mark the lifetime of the cell. This process aids in the control of the normal physiology of the organism, by removing old cells which accumulated many mutations, which could eventually lead to cancer. ▶Chemically induced cell transformation is the process by which normal cells are treated with chemical carcinogens in vitro in a cell culture dish or flask, and then their growth control mechanisms degrade, converting or transforming them into transformed cells. There are two mechanisms by which cells can be converted by chemical carcinogens into transformed cells. Firstly, cells can be treated with genotoxic (DNAdamaging) (▶Genetic toxicology) chemical carcinogens. Many of these genotoxic carcinogens are ▶mutagens (▶Mutation rate). These carcinogens either already are direct mutagens (rare), or more commonly they are pre-carcinogens, and can be converted into mutagenic proximate carcinogens by ▶cytochrome P450 enzymes or other enzyme systems that activate the pre-carcinogens into mutagens. The carinogens (benzo(a)pyrene, aflatoxin B1, and nitrosamines are all examples of pre-carcinogens that are metabolically activated into mutagens by various types of cytochrome P450 enzymes. Most pre-carcinogens are hydrophobic (fat-loving) compounds that would bioaccumulate in the body, and cause alterations in the properties of enzymes and membranes in cells. Mammals must therefore derive strategies to eliminate hydrophobic pre-carcinogens. The cytochrome P450 enzyme system, and other enzyme systems, have evolved in order to metabolize these pre-carcinogens, to make them water-soluble, so they can be excreted in the urine and removed from the body. Since these compounds are inherently chemically inert, a necessary first chemical reaction step has evolved, in which cytochrome P450 enzymes attack pre-carcinogens like benzo(a)pyrene (BaP) with molecular oxygen and reducing equivalents (NADPH and NADH) to generate epoxides and diol epoxides from it. These metabolites are mutagens, and this step results in “metabolic activation.” In a second step, which is closely coupled to the first step, these active metabolites are reacted with and conjugated to, molecules of water by the enzyme, epoxide hydrolase, converting them to trans-dihydrodiols and tetraols, which are highly water-soluble, so they are excreted in the urine. The small amount of epoxides and diol epoxides derived from BaP then bind covalently to DNA bases, resulting in mutations in proto-oncogenes, activating them into oncogenes, and mutations in tumor suppressor genes, inactivating them. In a second mechanism of ▶carcinogenesis, chemicals called “non-genotoxic carcinogens,” transform normal cells into tumor cells in a different way, by non-mutagenic mechanisms. One example is the

chemical, 5-azacytidine, a chemical analog of a normal base. 5-azacytidine binds to DNA methyltransferases (▶Methylation), inhibiting them. This results in a loss of methylation of the cytidine in DNA. If this occurs in quiescent proto-oncogenes, then these can become transcriptionally activated, leading to cell transformation. Other examples of non-genotoxic carcinogens include hormones, such as testosterone and estrogen. Higher steady-state levels of testosterone and estrogen are believed to lead to aberrantly high numbers of cell divisions in prostate and breast tissue. The resultant spontaneous mutations that occur are believed to lead to prostate cancer and breast cancer, respectively. The process by which a normal cell is converted into a tumor cells, or chemically induced ▶neoplastic transformation (▶Neoplastic cell transformation), occurs in four steps. In the first step, when cells are treated with mutagenic chemical carcinogens, there occur mutations in proto-oncogenes, activating them to oncogenes, and mutations in tumor suppressor genes, inactivating them. The cells then develop the ability to grow in multi-layers, and form foci. This is particularly true for fibroblastic cells, less so for epithelial cells. This first step in cell transformation is called morphological cell transformation, or focus formation. Further genetic changes occur in the transformed cells. The second step that occurs is that the cells become immortal, and do not die or senesce. Some activated oncogenes (v-myc) can cause cells to become immortal. This step would be called transformation to cellular immortality. In the third step, cells develop the ability to grow in soft agar, in three dimensional suspension. This step is called anchorage-independent cell transformation, or transformation to anchorage independence. A final step that develops after further genetic change is that cells develop the ability to form tumors when injected into athymic (nude) mice. This step is called neoplastic transformation, or the ability of cells to be transformed so that they form neoplasms, or new growths, which we call tumors. Often, a number of activated oncogenes, two or more, may cooperate together to perturb normal cellular physiology, to cause neoplastic transformation of normal rodent or human cells in culture. It is now believed by scientists that activation of proto-oncogenes into oncogenes, and inactivation of tumor suppressor genes, such that approximately eight total genes are genetically altered, leads to the aberrant expression of approximately 150 genes or more in the tumor cells. This then leads to neoplastic transformation of cells in culture, hence to chemical cacinogenesis in the animal. We believe that chemically induced neoplastic transformation is a good model for how cells in the animal become converted (transformed) into tumor cells when the animal is treated with chemical carcinogens.

Chemical Tool

Significance of Chemical Carcinogenesis The significance of the process of chemical carcinogenesis is two-fold. Firstly, the assay for chemical carcinogenesis in lower animals, usually mice and rats, can be used to test chemicals to determine whether they are carcinogens by virtue of their ability to induce tumors in mice and rats. Those chemicals that are able to cause a reproducible, dose-dependent induction of tumors in mice and/or rats, are presumed to be human carcinogens. This presumption is due first to the relationship that rodents and humans are both warm-blooded animals, or mammals. As such, their biochemistry and physiology is similar. In addition, many chemical carcinogens were first found to be carcinogenic in rodent carcinogenesis bioassays, and later found to be carcinogens in humans. Almost all carcinogens that have been shown to be carcinogenic in humans are also carcinogenic in rodents (aflatoxin B1, vinyl chloride, asbestos, cigarette smoke, asbestos, polycyclic aromatic hydrocarbons). Secondly, the process of chemical carcinogenesis as studied in rodents has led to unique insights into the mechanisms of carcinogenesis. Investigators frequently use whole animal carcinogenesis bioassays to study how proto-oncogenes are activated into oncogenes, how tumor suppressor genes are inactivated by chemical carcinogens, and how oncogene activation and tumor suppressor gene inactivation leads to induction of tumors in mammals. Studying the mechanisms of carcinogenesis in rodents has also led to the identification of agents that interfere with this process, and may eventually be used to prevent the induction of cancer in humans. ▶Toxicological Carcinogenesis ▶Genetic Toxicology

References 1. Landolph JR Jr, Xue W, Warshawsky D (2006) Whole animal carcinogenicity bioassays, Chapter 2. In: Warshawsky D, Landolph JR Jr (eds) Molecular carcinogenesis and the molecular biology of human cancer. CRC/ Taylor and Francis Group, Boca Raton, FL, pp 25–44 2. Verma R, Ramnath J, Clemens F et al. (2005) Molecular biology of nickel carcinogenesis: identification of differentially expressed genes in morphologically transformed C3H/10T1/2 Cl 8 mouse embryo fibroblast cell lines induced by specific insoluble nickel compounds. Mol Cell Biochem 255:203–216 3. Warshawsky D (2006) Carcinogens and mutagens, Chapter 1. In: Warshawsky D, Landolph JR Jr (eds) Molecular carcinogenesis and the molecular biology of human cancer. CRC/Taylor and Francis Group, Boca Raton, FA, pp 1–24 4. Warshawsky D Landolph JR Jr (2006) Overview of human cancer induction and human exposure to carcinogens, Chapter 13. In: Warshawsky D, Landolph JR Jr (eds)

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Molecular carcinogenesis and the molecular biology of human cancer. CRC/Taylor and Francis Group, Boca Raton, FA, pp 289–302 5. Weinberg RW (2007) Multi-step tumorigenesis, Chapter 11. In: The biology of cancer. Garland Science, Taylor and Francis Group, LLC, New York, NY, pp 399–462

Chemical Castration Definition Removal of the gonads (ovary and testis) is required to ablate serum levels of sex steroids (progesterone, estrogen, and testosterone). As continuous administration of GnRH analogs removes the influence of the pituitary to regulate gonadal function, this inhibitory effect became known as “Chemical castration.” ▶Gonadotropin-Releasing Hormone

Chemical Genetic Screen ▶Small Molecule Screens

Chemical Mutagenesis ▶Genetic Toxicology

Chemical Tool Definition A chemical tool is a small, drug-like molecule that can be used to identify new targets in a ▶signal transduction pathway. The chemical tool is usually identified through the screening of a cell-based or in vivo assay, and then used as an affinity probe to identify its molecular target. The chemical tool provides the link between the target and the desired phenotype in the assay. ▶Luciferase Reporter Gene Assays

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Chemically Induced Cell Transformation

Chemically Induced Cell Transformation J OSEPH R ICHARD L ANDOLPH J R . Department of Molecular Microbiology and Immunology, and Pathology; Cancer Resaerach Laboratory, USC/ Norris Comprehensive Cancer Center, Keck School of Medicine; Department of Molecular Pharmacology and Pharmaceutical Sciences; Health Sciences Campus, University of Southern California, Los Angeles, CA, USA

Definition

▶Chemically induced cell transformation is the series of sequential steps that occur when mammalian cells are treated with ▶chemical carcinogens, and converted into tumor cells. The intermediate cell phenotypes (cell properties) are acquired one at a time, including first morphological ▶transformation (change in cell shape, leading to crisscrossing of cells in abnormal patterns), then anchorage independence (growth of cells as colonies or balls of cells in three dimensional suspension of agar, without attachment to the plastic dishes cells are usually grown on), and finally ▶neoplastic transformation (▶Neoplastic cell transformation), or the ability of cells to form tumors when injected into nude (athymic) mice.

Characteristics Normal Growth of Normal Cells In the mammalian organism (warm-blooded animals), there are many types of cells. In general, these cell types are divided into (i) ▶epithelial cells, which form the coverings of organs, (ii) ▶fibroblasts, which are connective tissue cells, and (iii) cells of the hematolymphopoietic series, which are derived from the bloodforming elements. These cell types all have special, specific characteristics. These three general cell types can be grown outside the body in an artificial situation, in cell culture medium in plastic cell culture dishes. This constitutes a model system in which the physiology of cells can be studied outside of the complicated conditions of the body. When grown in cell culture, epithelial cells and fibroblastic cells attach to the cell culture dish, by virtue of the surface charge of the cell relative to that of the plastic of the cell culture dish. These normal fibroblastic and epithelial cells must anchor to the bottom inside of the cell culture dish in order to be able to replicate their DNA and divide. This is called anchorage dependence of cell growth. These cells continue to grow if fed properly with cell culture medium, containing 5–10% fetal calf serum and cell culture medium. Cell culture

medium consists of sugars, amino acids, salts, and buffers, along with an indicator to detect the acidity of the culture medium (pH indicator), all dissolved in water. In cell culture, the normal fibroblasts and normal epithelial cells continue to grow if they are fed properly, until they eventually fill the culture dish, and touch each other. Growth then ceases. This process is called ▶contact inhibition of cell division. These cells can then be removed from the cell culture dish with a protease called trypsin, diluted, and replated into new cell culture dishes. This process can be repeated many times, until the population of total cells has undergone approximately 60 population doublings. This is called the “Hayflick Limit,” after Dr. Leonard Hayflick, who discovered it. At this point, the cells undergo ▶cellular senescence (▶Senescence and cellular immortalization), or die. This is due to progressive shortening of telomeres (▶Telomerase), structures at the end of chromosomes that are progressively shortened with each successive DNA replication and cell division. Hence, telomere shortening acts as a cellular and molecular “clock,” to mark the lifetime of the cell. This process is believed to aid in the control of the normal physiology of the organism, and to rid it of old cells which have many ▶mutations, which could eventually lead to cancer. If these normal cells are injected into mice lacking an immune system (athymic or “nude” mice), they will not grow and will not form tumors. In contrast, cells of the hemato-lymphopoietic series grow in three-dimensional suspension (the blood) in vivo. Hence, when grown in vitro (outside the body), these cells must also be grown in three-dimensional suspension. A common practice is to grow the cells in varying concentrations of agar. When injected into athymic or “nude” mice, these normal cells, whether cells of the hematopoietic (red blood cell) or lymphoid (white blood cell) lineages, will not form tumors. Carcinogens There are a group of molecules and radiations referred to as “carcinogens.” A ▶carcinogen (▶Carcinogen macromolecular adducts) is any molecule or group of molecules, such as viruses (▶Virology) or radiation (▶Radiation carcinogenesis; ▶radiation oncology) that can cause tumors in lower animals when they are treated with this agent. These agents can also cause normal cells to transform (convert) into transformed cells and tumor cells. There are a group of chemicals referred to as chemical carcinogens (▶Chemical carcinogenesis). These are specific chemicals that can cause tumors in animals treated with them. Examples of these are vinyl chloride, aflatoxin B1 (a metabolite and biocide of the fungus, Aspergillus flavus) (▶Aflatoxins), benzo(a)pyrene (a polycyclic aromatic hydrocarbon formed when organic matter is burned in the absence of

Chemically Induced Cell Transformation

oxygen) (▶Polycyclic aromatic hydrocarbons), and beta-naphthylamine (an aromatic amine used to manufacture dyestuffs that causes bladder cancer in animals and humans) (▶Aromatic amines). Another class of chemical carcinogens is called nitrosamines. An example is dimethylnitrosamine (DMN). Many nitrosamines are synthetic compounds. Some are believed to form in the stomach of humans when amines (derived from fish in the diet) contact nitrous acid (formed from the nitrate from fertilizer that is used to grow foodstuffs) in the acidic conditions (acid pH) of the stomach. Chemicals in all these classes of carcinogens can cause tumors in humans and in lower mammals. There are also a number of radiations (Radiation carcinogenesis) that can cause tumors in humans and lower animals. These include ionizing radiations, such as alpha particles (charged helium nuclei), beta particles (naked electrons), and gamma particles. In addition, there are also tumor viruses, consisting of RNA (RNA tumor viruses) and DNA (DNA tumor viruses). When animals are treated with these viruses, tumors are formed. Examples of RNA tumor viruses are the Rous sarcoma virus, the Abelson leukemia virus, and the Kirsten Ras virus. Examples of DNA tumor viruses are the polyoma virus, the SV40 (simian virus 40) (▶SV40) virus, the ▶Epstein Barr virus, and the human papilloma viruses 16 and 18 (▶Human papilloma viruses). Chemically Induced Cell Transformation – Description and Mechanisms Chemically induced cell transformation is the process by which normal cells are treated with chemical carcinogens in vitro in a cell culture dish or flask, and they then convert or transform into transformed cells. There are two mechanisms by which cells can be converted by chemical carcinogens into transformed cells. Firstly, cells can be treated with ▶genotoxic (DNA-damaging) (▶Genetic toxicology) chemical carcinogens. Many of these genotoxic carcinogens are ▶mutagens (▶Mutation rate). These carcinogens either already are direct mutagens (rare), or more commonly they are pre-carcinogens, and can be converted into mutagenic proximate carcinogens by ▶cytochrome P450 enzymes or other enzyme systems that activate the pre-carcinogens into mutagens. The Pre-carinogens benzo(a)pyrene, aflatoxin B1, and nitrosamines are all examples of pre-carcinogens that are metabolically activated into mutagens by various types of cytochrome P450 enzymes. The perspective for this process is that most pre-carcinogens are hydrophobic (fat-loving) compounds that would bioaccumulate in the body, and cause alterations in the properties of enzymes and membranes in cells. Hence, the organism must derive a strategy to eliminate these hydrophobic precarcinogens. Therefore, the cytochrome P450 enzyme system, and other enzyme systems, have evolved in order

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to metabolize these pre-carcinogens, to make them water-soluble, so they can be excreted in the urine and removed from the body. Since these compounds are inherently chemically inert, a necessary first chemical reaction step has evolved, in which cytochrome P450 enzymes first attack pre-carcinogens like benzo(a)pyrene (BaP) with molecular oxygen and reducing equivalents (NADPH and NADH) to generate epoxides and diol epoxides from it. These metabolites are mutagens, and this step results in “metabolic activation.” In a second step, which is closely coupled to the first step, these active metabolites are reacted with and conjugated to, molecules of water by the enzyme, epoxide hydrolase, converting them to trans-dihydrodiols and tetraols, which are highly water-soluble, so they are excreted in the urine. The small amount of epoxides and diol epoxides derived from BaP then go on to bind covalently to DNA bases, resulting in mutations in proto-oncogenes, activating them into ▶oncogenes, and mutations in ▶tumor suppressor genes, inactivating them. In a second mechanism of ▶carcinogenesis, chemicals called “non-genotoxic carcinogens,” transform normal cells into tumor cells in a different way, by non-mutagenic mechanisms. One example is the chemical, 5-azacytidine, a chemical analog of a normal base. 5-azacytidine binds to DNA methyltransferases (▶Methylation), inhibiting them. This results in a loss of methylation of the cytidine in DNA. If this occurs in quiescent proto-oncogenes, then these can become transcriptionally activated, leading to cell transformation. Other examples of non-genotoxic carcinogens include hormones, such as testosterone and estrogen. Higher steady-state levels of testosterone and estrogen are believed to lead to aberrantly high numbers of cell divisions in prostate and breast tissue. The resultant spontaneous mutations that occur are believed to lead to prostate cancer and breast cancer, respectively. The process of chemically induced neoplastic transformation, or the process of generating a tumor cell, falls into at least four steps. In the first step, when cells are treated with mutagenic chemical carcinogens, there occur mutations in proto-oncogenes, activating them to oncogenes, and mutations in tumor suppressor genes, inactivating them. The cells then develop the ability to grow in multi-layers, and form foci. This is particularly true for fibroblastic cells, less so for epithelial cells. This first step in cell transformation is called ▶morphological cell transformation, or focus formation. Further genetic changes occur in the transformed cells. The second step that occurs is that the cells become immortal, and do not die or senesce. Some activated oncogenes (v-myc) can cause cells to be come immortal. This step would be called transformation to cellular immortality. A third step that occurs is that the cells develop the ability to grow in soft agar,

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in three-dimensional suspension. This step is called ▶anchorage-independent cell transformation, or transformation to anchorage independence. A final step that develops after further genetic change is that the cells develop the ability to form tumors when injected into athymic (nude) mice. This step is called neoplastic transformation, or the ability of the cell to be transformed so that it forms neoplasms, or new growths, which we call tumors. Often, a number of activated oncogenes, two or more, may cooperate together to perturb normal cellular physiology, to cause neoplastic transformation of normal rodent or human cells in culture.

4. Verma R, Ramnath J, Clemens F et al. (2005) Molecular biology of nickel carcinogenesis: identification of differentially expressed genes in morphologically transformed C3H/10T1/2 Cl 8 mouse embryo fibroblast cell lines induced by specific insoluble nickel compounds. Mol Cell Biochem 255:203–216 5. Weinberg RW (2007) Multi-step tumorigenesis, Chapter 11. In: The biology of cancer. Garland Science, Taylor and Francis Group, LLC, New York, NY, pp 399–462

Significance of Chemically Induced Neoplastic Transformation The significance of the process of chemically induced neoplastic transformation is twofold. Firstly, the assay for chemically induced morphological cell transformation can be used an assay to detect chemical carcinogens. Those chemicals that have the ability to induce foci of morphologically transformed cells are highly likely to be able to induce tumors in animals. Hence, this assay can detect chemical carcinogens by virtue of their ability to induce foci of morphologically transformed cells. Secondly, the study of chemically induced morphological, anchorage-independent, and neoplastic transformation in vitro is frequently used as a model system to study the process of chemical carcinogenesis. Investigators frequently use these assays to study how proto-oncogenes are activated into oncogenes, and how tumor suppressor genes are inactivated by chemical carcinogens, and how oncogene activation and tumor suppressor gene inactivation leads to induction of morphological transformation, cellular immortality, anchorage-independent transformation, and neoplastic transformation.

Definition

References

Synonyms

1. Kumar V, Abbas AK, Fausto N (2005) Neoplasia, Chapter 7. In: Robbins and Cotran’s pathologic basis of disease, 7th edn. Elsevier Saunders, Philadelphia, PA, pp 269–342 2. Landolph JR Jr (2006) Chemically induced morphological and neoplastic transformation in C3H/10T1/2 mouse embryo cells, Chapter 9. In: Warshawsky D Landolph JR Jr (eds) Molecular carcinogenesis and the molecular biology of human cancer. CRC/Taylor and Francis Group, Boca Raton, FL, pp 199–220 3. Pitot HC, Dragan YP (2001) Chemical carcinogenesis, Chapter 8. In: Klaassen CD (ed) Casarett and Doull’s toxicology, the basic science of poisons, 6th edn. McGraw-Hill Medical Publishing Division, New York, NY, pp 239–320

Directed migration; Directed motility

Chemoattractant

A molecule that is capable of promoting cell movement by inducing ▶chemotaxis. ▶Chemokine Receptor CXCR4

Chemoattractant Cytokine ▶Chemokine

Chemoattraction J OSE LUIS R ODRI´ GUEZ -F ERNA´ NDEZ Departamento de Fisiología Celular y Molecular, Centro de Investigaciones Biológicas, Madrid, Spain

Definition Chemoattraction is the process whereby a cell detects a chemical gradient of a ligand called chemoattractant and, as a consequence, gets oriented and subsequently moves in the direction from a low to a high concentration of the chemoattractant. Chemoattraction is controlled by specific chemoattractant receptors that are able to detect selectively these ligands. Chemoattraction is called ▶chemotaxis or ▶haptotaxis when the chemical gradient of the chemoattractant is presented to the cell either in a soluble or bound to a substrate form,

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respectively. As it is not clear which one of these two types of motile processes takes place in vivo, it is more appropriate to refer to these directional motile processes with the more general term of chemoattraction.

Characteristics

Chemoattraction. Figure 1 Classical and new names of chemokines are included. Red identifies “inducible” or “inflammatory” chemokines, green “homeostatic” agonists and yellow ligands belonging to both realms. BCA, B cell activating chemokine; BRAK, breast and kidney chemokine; CTACK, cutaneous T-cell attracting chemokine; ELC, Epstein–Barr virus-induced receptor ligand chemokine; ENA-78, epithelial cell-derived neutrophil-activating factor (78 amino acids); GCP, granulocyte chemoattractant protein; GRO, growth-related oncogene; HCC, human CC chemokine; IP, IFN-inducible protein; I-TAC, IFN-inducible T-cell α chemoattractant; MCP, monocyte chemoattractant protein; MDC, macrophage-derived chemokine; Mig, monokine induced by gamma interferon; MIP, macrophage inflammatory protein; MPIF, myeloid progenitor inhibitory factor; NAP, neutrophil-activating protein; PARC, pulmonary and activation-regulated

Chemoattractants use specific chemoattractant receptors to guide different migratory cell types towards specific sites in the organism. These receptors, upon binding to the chemoattractant, transform the information of this ligand in intracellular signals that result in the movement of the migratory cell towards the positions where chemoattractant is present at high concentration. Therefore, the analysis, in a specific context, in one hand, of the type of chemoattractant receptors expressed by a certain migratory cell and, on the other hand, the position in the organism of the chemoattractants recognized by these receptors, allow to make predictions on the potential tissues where this cell can be attracted. Upon arrival to the position where the chemoattractant is at a high concentration, adhesive receptors may contribute to slow down (function largely performed by selectin adhesive receptors for cells in blood vessels) and eventually attach (cells use ▶integrin receptors for this function in most cell types) the cells to these sites. Chemoattractants can be conveniently classified according to the type of receptor that they bind. In this regard, the first and the largest group include chemoattractants that bind members of the ▶G-protein coupled receptor (GPCR) superfamily. In this first group is included the family of ▶chemokines. A second group is formed by chemoattractants that bind tyrosine kinase receptors (e.g. Epidermal Growth Factor (EGF), Platelet Derived Growth Factor (PDGF)). A third group includes ligands that bind receptors different of the two aforementioned families (e.g. laminin and fibronectin, which bind integrin receptors). This article deals mainly with the chemokines because they have been the chemoattractant family most studied in relation to ▶cancer and ▶metastasis. Chemokines Chemokines (chemotactic chemokines) are a family of peptides (60–100 amino acid (aa)) that includes some 50 members (Fig. 1). Based on the number and spacing

chemokine; RANTES, regulated upon activation normal T cell expressed and secreted; SCM, single C motif; SDF, stromal cell-derived factor; SLC, secondary lymphoid tissue chemokine; TARC, thymus and activation-related chemokine; TECK, thymus expressed chemokine.

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of the conserved Cystein (C) residue in the N-terminus of the protein, chemokines are subdivided in four families (C, CC, ▶CXC, CX3C), where X is any intervening amino acid between the cysteins. Chemokines receptors transmit intracellular signals that can control either chemoattraction or other functions (Fig. 1). The chemokine receptors (some 20 members) are included in the G-protein coupled receptor (GPCR) superfamily. They are classified based on the class of chemokines that they bind, i.e. receptors that bind C, CC, CXC, CX3C chemokines are called respectively to CR, CCR, CXCR and CX3CR receptors. Based largely on studies performed in the immune system, chemokines have been classified in three functional groups, homeostatic, inducible and dual function (Fig. 1). The first group, which includes chemokines constitutively produced by “resting cells” in specific organs or in tissues inside these organs, controls homeostatic migratory processes that determinate the correct location of different cell types in the organism under normal conditions. Inducible or inflammatory chemokines are secreted in different tissues in emergency situations and serve to attract to these places specialized cell types that contribute to the resolution of the emergency situation. A third group is formed by dual function chemokines, which can be either homeostatic or inducible depending on the context (Fig. 1). Although chemoattraction is the function most commonly regulated by chemokines, however, studies performed mainly on leukocytes have demonstrated that these peptides, acting through specific chemokine receptors, may control additional cellular functions, including proliferation, ▶adhesion, motility, survival or protease secretion, among other functions. By controlling these activities, chemokines may contribute to modulate the functions of leukocytes and other cell types. Chemokines and Cancer Cancer is a disease where cells have disrupted the mechanisms that regulate their normal growth and, consequently, proliferate without control. This affliction becomes life threatening when cancer cells become metastatic, that is, they acquire the ability to leave their original sites of growth (primary tumor) and invade other tissues or organs where the uncontrolled growing cells can form new colonies (▶metastases) that can interfere with vital functions. The process leading to metastasis formation has been divided into several steps. In a first step, the cancer cells detach from the substrate and from the neighboring cells and escape from the primary tumors. A second step involves the penetration of the cancer cells into the blood or lymphatic vessels and their ▶migration through these vessels. In the case of cells that migrate through the

afferent lymphatics, they migrate first to the lymph nodes from where they can exit through the efferent lymphatics, eventually ending up in the blood vessels. In a third stage, cancer cells extravasate from blood vessels and home into new sites in the organism where new metastatic colonies can be formed. During these migratory processes the cells undergo changes in their adhesive properties that are regulated by modulation of the activities and/or levels of integrin receptors. Moreover, cancer cells and/or associated stromal cells secrete proteases which, by degrading extracellular matrix (ECM) proteins of connective tissues facilitate the moving of the cells and the ▶invasion of other tissues. Finally, at the metastatic sites, the cancer cells attach and grow as secondary colonies. In addition, they may secrete chemokines and other soluble factors that induce new vascular vessel formation (▶angiogenesis) and contribute to maintain the growth of the metastatic cells. Although millions of cells may be shed into the blood from primary tumors, however only a reduced percentage of these cells are able form metastases, suggesting that metastatic cells develop mechanisms that increase their survival in the face of a hostile environment. Chemoattraction: A Key Process to Attract Cancer Cells to New Biological Niches Since the work of Stephen Paget in the second half of the nineteenth century, it is known that metastatic cells do not move randomly, displaying in contrast a marked tropism toward specific organs (Table 1). A variety of experimental data indicates that chemokines may play an important role in determining this bias of the metastatic cells. Analysis of the phenotype of multiple metastatic cell types shows that these cells express specific sets of chemokine receptors (Table 1). Furthermore, a clear correlation has been observed between the expression of a specific chemokine receptor by a metastatic cell and the presence of its respective ligands in the metastatic sites, suggesting the involvement of these receptors in the homing processes (Table 1). Finally, a direct role for chemokines and their receptors in the control of the tropism of metastatic cells is corroborated in studies that show that interference with the binding to the chemokine receptors impairs the ability to metastasis to specific organs. For instance, antibody neutralization of ▶CXCR4 in breast cancer cells reduced the ability of these cells to form metastases in the lung, both upon intravenous injection and after ▶orthotopic implantation of the cells. Conversely, over-expression of CCR7 in B16 ▶melanoma resulted in a dramatic enhancement in the ability of these cells to form metastases in the draining lymph nodes upon intravenous injection of the cells in mice. From these studies it has also emerged that CCR7 and

Chemoattraction Chemoattraction. Table 1

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Chemokine receptors involved in cancer metastases

Chemokine/s receptor/s/ligand/s

Site/s of metastases

CXCR3/CXCL9, -10, -11 CXCR4/CXCL12

Lung, bone, lymph node Lung, bone, lymph node

Cancer cell types

Acute lymphoblastic leukemia, Chronic myelogenous leukemia, colon, melanoma Breast, ovarian, prostate, glioma, pancreas, melanoma, esophageal, lung (small cell lung cancer), head and neck, bladder, colorectal, renal, stomach, astrocytoma, cervical cancer, squamous cell cancer, osteosarcoma, multiple myeloma, intraocular lymphoma, follicular center lymphoma, rhabdomyosarcoma, neuroblastoma, B-lineage acute lymphocytic leukemia, B-chronic lymphocytic leukemia, non-Hodgkin lymphoma, acute myeloid leukemia, thyroid cancer, acute lymphoblastic leukemia, chronic myelogenous leukemia CXCR5/CXCL13 Lymph node Head and neck, chronic myelogenous leukemia CXCR7/CXCL11, -12 Lymph node Breast, cervical carcinoma, glioma, lymphoma, lung carcinoma CCR4/CCL17, -22 Skin Cutaneous T-cell lymphoma CCR7/CCL19, -21 Lymph node Breast, Melanoma, lung (non-small cell lung cancer), head and neck, colorectal, stomach, chronic lymphocytic leukemia CCR9/CCL25 Small intes- Melanoma, prostate tine CCR10/CCL27 Skin Melanoma, cutaneous T-cell lymphoma

CXCR4 are the chemokine receptors most commonly expressed by metastatic cells. This finding contributes to explain the ability of multiple metastatic cell types that express these receptors to colonize the lymph node and other organs where CXCL12 (ligand for CXCR4 and CXCR7) and CCL19 and CCL21 (both ligands of CCR7) are expressed (Table 1). Premetastatic niche is the name given to the specific regions, whose formation is induced by soluble factors released by primary tumor cells, which eventually become colonized by distant metastatic cells from the primary tumors. It has been shown that chemokines expression may confer premetastatic niches the ability to attract metastatic cells from the distant primary tumor. In this regard, it has been shown that chemokines S100A8 and S100A9, expressed by myeloid and endothelial in premetastatic niches in the lung, are responsible of attracting incoming Lewis Lung carcinoma metastatic cells to these niches because neutralization of the chemokines with antibodies reduced the metastases in these areas. In sum, chemokine/chemokine receptor pairs are important factors that control the colonization of cancer cells to specific sites in the organism.

Function/s regulated by chemokine receptor Chemoattraction Chemoattraction, angiogenesis, survival, growth

Chemoattraction Adhesion, survival, growth Chemoattraction Chemoattraction

Chemoattraction Chemoattraction, growth, survival

Other Biological Effects of Chemokines on Cancer Cells Apart from Chemoattraction Chemokines may affect cancer not only by regulating chemoattraction, but also by regulating other functions that control cancer progression. Chemokines can Contribute to Regulate the Growth of Cancer Cells Uncontrolled growth is a hallmark of cancer cells. Considering that chemokines may control cell growth in different cell types, the effect of chemokines on the proliferation of cancer cells is not unexpected. The growth of tumor cells may be affected by chemokines that can be either released in an ▶autocrine signaling fashion by the cancer cells or secreted by the stromal tissues associated to the cancer cells. As an example of the first case, it is known that CXCL1, -2, -3, and -8, secreted as autocrine growth factors by melanoma, pancreatic and liver cancer cells, regulate the proliferation of all these cell types. As an example of the second case, it has been reported that CXCL12, which is secreted in lung and lymph nodes, leads to the increase in the growth of ▶glioma, ovarian, small cell lung, basal cell carcinoma and renal cancer, all cancer cells

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types that colonize the aforementioned organs. The effects of chemokines on growth can be complex because, for instance interference with CCR5 seems to increase the proliferation of ▶xenografts of human breast cancer, suggesting that CCR5 inhibits the growth of this cancer cells. Chemokines can Contribute to Regulate the Survival of Cancer Cells A reduced susceptibility to ▶apoptosis, leading to a concomitant extended survival, is also an important factor to explain the uncontrolled growth and the ability of cancer cells to form metastases. Chemokines have been involved in regulating survival in leukocytes and other cells, therefore these ligands may potentially contribute to regulate the carcinogenic phenotype by modulating this function. Stimulation of melanoma B16 cells expressing CCR10 with its ligand CCL27 enhances the resistance of these cells to the apoptosis induced by stimulation of the death receptor CD95. These in vitro results are consistent with in vivo experiments that show that the neutralization of CCL27 ligand with antibodies results in the blocking of tumor cell formation. Also, stimulation of glioma cells with CXCL12 protects these cells from the apoptosis induced by serum deprivation. Recently, it has been shown that, CXCR7, a novel second receptor for CXCL12, is expressed in a variety of cancer cells. It has been indicated that CXCR7 may regulate survival, growth and adhesion. Thus, it is possible that CXCR7 may also contribute to control all these functions in cancer cells. Chemokines can Contribute to Regulate the Adhesion to New Sites in Cancer Cells Migratory cancer cells experience changes in adhesion, including processes of attachment and detachment, as they move through the organism. Enhanced adhesion is particularly crucial at the final stages of cancer progression where these cells require attaching to the new metastatic sites. Stimulation of cancer cells with chemokines may change the adhesion of these cells either by increasing the activity of ▶integrins or by inducing changes in the expression levels on the membrane of these receptors. As an example of the first case, it has been observed that stimulation of B16 melanoma cells with CXCL12 leads to an increase in the affinity of the β1 integrin by the ligand VCAM-1 both in in vitro and in in vivo experiments. As an example of the second case, stimulation of prostate tumor cells with CXCL12 induces enhanced expression of the integrins α3 and β5. Chemokines can Contribute to Control Protease Secretion in Cancer Cells Metalloproteins are largely responsible for ECM remodeling and play key roles in solid tumor cell invasion. In

this regard, it has been shown that chemokines enhance in protease secretion in some cancer cell types. For instance, stimulation of myeloma cells with CXCL12 induces metalloproteinase secretion. Chemokines can Contribute to Control Angiogenesis in Cancer Cells At metastatic sites cancer cells induce formation of new vessels (angiogenesis), which allow the nourishment of the metastatic colonies. Angiogenesis is a finely orchestrated process where endothelial cells proliferate, secrete proteases, change their adhesive properties, migrate and, finally, differentiate into new vessels. Chemokines can act as positive or negative regulators of the angiogenesis in the tumor microenvironment. In this regard, the members of the ▶CXC chemokine family play an important role during this process. The CXC family has been divided into two groups. A first group that includes members that present the triplet Glutamic-Leucine-Arginine (ELR) before the first Cys (ELR+ CXC chemokines), and a second group that include the members that lack this three amino acids (ELR− CXC chemokines). Although there are exceptions, by and large, ELR+ CXC chemokines (including CXCL1, -2, -3, -5, -6, -7 and -8) play proangiogenic roles, promoting vessel formation through the stimulation of the CXCR2 receptor. For instance, in human ovarian carcinoma CXCL8 induces both angiogenesis and tumorigenesis. Furthermore, treatment of mice that bear CXCL8-producing non-small cell ▶lung cancer cells with anti-CXCL8 antibodies blunted the growth of these tumors in the mice. Exceptions to the rule ELR+ CXC=angiogenic chemokines are the ELR+ CXC members CXCL1 and 2, which are angiostatic i.e. they inhibit angiogenesis. ELR− CXC chemokines, including CXCL9, -10, -11, are generally angiostatic. For instance, CXCL9 and CXCL10 inhibit Burkitt’s lymphoma tumor formation probably by blocking blood vessel formation. An exception to the rule ELR− CXC = angiostatic chemokine is CXCL12 that is angiogenic, as suggested by CXCL12 and CXCR4 KO mice that display cardiovascular development defects. It is believed that the angiogenic effects of CXCL12 are mediated by the vascular endothelial growth factor (VEGF) that is secreted by endothelial cells upon stimulation with CXCL12. The latter chemokine can be secreted in the tumor microenvironment by both the cancer cells and associated stromal cells. Finally, apart from CXC chemokines, other chemokines families may also regulate angiogenesis. In this regard, the CC chemokine CCL21 is angiostatic. In contrast, three CC family members (CCL1, -2, -11) and one CX3C family member (CX3CL1) can induce angiogenesis. All these chemokines, secreted inside the tumor, may potentially regulate the growth of the metastatic cells.

Chemokine

Therapeutical Aspects The multiple points at which chemokines may regulate cancer progression make them attractive targets to develop anti-cancer drugs. Several strategies have been adopted to harness the power of chemokines against cancer, including the use of antibodies against the overexpressed chemokine receptors in the target cancer cells to induce apoptosis of these cells. One common strategy has been the development of inhibitors to block the binding of the chemokines to the receptors and consequently the function of these receptors. The fact that chemokine receptors are on the membrane and that much information is available on the sequences, both on the ligands and on the receptors, necessary for receptor-ligand binding have enabled the development of numerous peptide or small molecule inhibitors that interfere with chemokine function. Some of these inhibitors have been developed against CCR1, CCR5, CXCR7 and CXCR4. Most of these inhibitors relay on their ability to inhibit survival or angiogenesis in the target cells. As CXCR4 is one of the most broadly expressed chemokine receptor in cancer cells, at least six peptides or small molecule inhibitors of the function of CXCR4 have been developed and used in preclinical cancer models. CXCR4 is particularly interesting due to its pro-angiogenic functions. A variety of data indicate that the growth and persistence of tumors and their metastases depend on an active angiogenesis at the tumor sites. In this regard, interference with this process is a powerful strategy to inhibit tumor growth. Interference with CXCR4 has been used in several cancer models, including many of the cancers indicated in Table 1. Although peptide inhibitors of chemokine receptors may not have by itself ▶tumoricidal affects, however, along with other strategies may be a powerful therapy against tumors. Summary and Final Conclusions Upon becoming carcinogenic and metastatic, a variety of cancer cells up-regulate the expression of chemokine receptors. In this regard, the microenvironment conditions inside the tumors are also known to induce chemokine receptor expression in some cases. For instance, the low oxygen concentration (▶hypoxia) inside a tumor induces CXCR4 expression which concomitantly leads to a more aggressive metastatic phenotype in cancer cells. Chemokine receptors endow cancer cells with “postal codes” that determine their migration to tissues where the ligands of these receptors are expressed and therefore are important for the metastatic ability of these cells. In addition, these receptors may confer or modulate cancer cells functions that, by regulating different steps in cancer progression, may contribute to the carcinogenic and metastatic phenotype of these cells. The case of the Kaposi’s sarcoma herpesvirus (KSHV), which induces cancer lesions similar to that of Kaposi sarcoma, is a dramatic

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example that shows the important role that chemokines and their receptors may play in cancer. Interestingly, this virus encodes a constitutively active receptor that displays a high degree of sequence similarity to chemokine receptors CXCR1 and CXCR2 and which can even be further activated by the CXCR2 ligands CXCL1 and/or CXCL8. KSHV is also pro-angiogenic and induces survival effects in the cancer cells where is expressed. Further supporting a causative role of CXCR2 in cancer, a constitutive form of CXCR2 can induce cell transformation in susceptible cell types.

References 1. Balkwill F (2004) Cancer and the chemokine network. Nat Rev Cancer 4:540–550 2. Zlotnik A (2006) Chemokines and cancer. Int J Cancer 119:2026–2029 3. Sánchez-Sánchez N, Riol-Blanco L, Rodríguez-Fernández JL (2006) The multiples personalities of the chemokine receptor CCR7 in dendritic cells. J Immunol 176:5153–5159 4. Kakinuma T, Hwang ST (2006) Chemokines, chemokine receptors, and cancer metastasis. J Leukoc Biol 79:639–651 5. Ben-Baruch A (2006) The multifaceted roles of chemokines in malignancy. Cancer Metastasis Rev 25:357–371

Chemoembolization Definition Chemoembolization is a procedure in which the blood supply to a tumor is interrupted through mechanical or surgical interventions (embolization) and cytotoxic drugs are administered directly into the tumor. This technique is used in hepatocellular carcinoma and neuroendocrine carcinomas, among other cancers. ▶Neuroendocrine Carcinoma

Chemokine L EI FANG , S AM T. H WANG Dermatology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA

Synonyms Chemotactic cytokine; Chemoattractant cytokine

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Definition Chemokines are a large group of small proteins that play multiple biological roles, including stimulating directional migration (▶chemotaxis) of leukocytes and tumor cells via their membrane-bound receptors.

Characteristics Chemokines are divided into four subgroups (C, CC, CXC, and CX3C) based on the spacing of the key cysteine residues near the N terminus of these proteins. The CC and CXC families represent the majority of known chemokines. Chemokines signal through seventransmembrane-domain receptors, which are coupled to heterotrimeric Gi-proteins. Activation of phospholipase C (PLC) and ▶phosphatidylinositol-3-kinase γ (PI3Kγ) by βγ subunits of ▶G-proteins is well established. So far, approximately 50 chemokines and 18 chemokine receptors have been identified. Some chemokine receptors bind to multiple chemokines and vice versa, suggesting possible redundancies in chemokine functions. Chemokine receptors permit diverse cells to sense small changes in the gradient of soluble and extracellular matrix-bound chemokines, thus facilitating the directional migration of these cells toward higher relative concentrations of chemokines. While soluble chemoattractants can induce directional migration, chemokines (due to their net positive charges) will often be bound to and presented by negatively charged macromolecules such as endothelial cell-derived proteoglycans in vivo. Chemokine gradients bound to solid surfaces are capable of mediating ▶haptotaxis of leukocytes and other cells. Chemokine receptor activation can also trigger conformational changes in membrane ▶integrins, permitting strong cell–cell adhesion in the presence of appropriate integrin receptors. This signaling pathway is particularly

relevant in triggering cellular integrins found on leukocytes and cancer cells to bind to their respective receptors (e.g. ICAM-1) on vascular endothelial cells, facilitating stable binding and spreading of cells to endothelium. The stable binding of metastatic tumor cells to vascular endothelial cells at distant sites of metastasis is likely to be a crucial early step in the process of ▶metastasis. Circumstantial evidence supports the idea that tumor cells use chemokines to promote their own survival and metastasis through multiple mechanisms. For example, certain chemokines secreted by tumor cells contribute to tumor growth and ▶angiogenesis. Members of chemokines that contain an ELR motif (Glu–Leu–Arg) act as angiogenic factors, which are chemotatic for endothelial cells in vitro and can stimulate in vivo. In contrast, members without an ELR motif inhibit angiogenesis. Chemokine-mediated tumor cell activation through cellular kinases such as PI3K, ▶Akt kinase, and other downstream mediators (Fig. 1) influences tumor cell resistance to apoptotic death. For example, activation of the chemokine receptor CCR10 prevents ▶Fasmediated tumor cell death induced by cytolytic antigenspecific T cells. Selected chemokine receptors are upregulated in a large numbers of common human cancers, including breast, lung, prostate, colon, and melanoma. Chemokine receptors expressed on tumor cells coupled with chemokines preferentially expressed in a variety of organs are believed to play critical roles in cancer metastasis to vital organs as well as draining lymph nodes. CXCR4 is by far the most common chemokine receptor expressed on most cancers. In addition, CXCL12, the ligand for CXCR4, is highly expressed in lung, liver, bone marrow, and lymph nodes, which represent the common sites of metastasis of many

Chemokine. Figure 1 ▶Chemokine receptor signaling. Upon stimulation by chemokine, βγ subunits of G-protein are dissociated from Gαi subunit. βγ subunits activate phospholipase C (PLC) and phosphatidylinositol 3 kinase γ (PI3Kγ), Whereas Gαi subunit directly activates ▶Src-like kinase.

Chemokine Receptor CXCR4

cancers. Chemokine receptor expression on cancer cells may influence the conversion of small, clinically insignificant foci of cancer cells at metastatic sites to rapidly growing, clinically serious secondary tumors. Cancers that upregulate CCR7 expression also facilitate their entry into lymphatic vessels, which strongly express the CCR7 ligand (CCL21), and subsequent retention within CCL21-rich secondary lymphoid organs. Upregulation of chemokine receptors such as CCR7 may be a major reason for efficient lymph node metastasis observed in many epithelial cancers. Chemokines released by tumor cells have been shown to attract ▶regulatory T cells, thus suppressing host responses to invasive tumors. Moreover, chemokine and their receptors are involved in ▶dendritic cell maturation, B and T cell development, and ▶Th1 and ▶Th2 polarization of the T cell response. These actions suggest the possibility that chemokines may play a role in altering the magnitude and polarity of host immune responses to cancer cells. Although individual chemokine and chemokine receptor appear to affect many aspects of cancer cell survival, migration, angiogenesis, and the host response to cancer cells, it is still unclear which of these functions predominate in the multistep establishment of primary tumors and secondary metastases.

References 1. Thelen M (2001) Dancing to the tune of chemokines. Nature Immunol 2:129–134 2. Murphy PM (2002) International Union of Pharmacology. XXX. Update on chemokine receptor nomenclature. Pharmacol Rev 54:227–229 3. Rossi D, Zlotnik A (2000) The biology of chemokines and their receptors. Annu Rev Immunol 18:217–242 4. Kakinuma T, Hwang ST (2006) Chemokines, chemokine receptors, and cancer metastasis. J Leukoc Biol 79: 639–651 5. Müller A, Homey B, Soto H et al. (2001) Involvement of chemokine receptors in breast cancer metastasis. Nature 410:50–56

Chemokine Receptor CXCR4 J ONATHAN B LAY Department of Pharmacology, Dalhousie University, Halifax, NS, Canada

Synonyms Receptor for CXCL12; Receptor for stromal cellderived factor-1 alpha (SDF-1α); CD184; Fusin

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Definition CXCR4 is a cell-surface protein that acts as a receptor for the molecule CXCL12 (stromal cell-derived factor-1 alpha, SDF-1α). CXCL12 is one of a class of signaling molecules called chemokines that regulate the movement and other activities of cells throughout the body. Although CXCL12 and CXCR4 play major roles in regulating stem cells and cells of the immune system, CXCR4 is also found on many cancer cells and plays a part in metastasis, spread of the cancer cells being influenced by tissue levels of CXCL12.

Characteristics Chemokines are a class of peptide mediators that play important roles in controlling cellular homing and migration both in embryonic development and in the regulation of cell populations in the adult. There are at least forty different chemokines that fall into four classes depending upon their peptide structure. The different classes are “C”, “CC”, “CXC” and “CX3C” chemokines, for which characteristic sequence motifs involve residues of the amino acid cysteine (C) either in sequence or separated by one or three other amino acids (X or X3). The chemokines themselves are peptides that can exist freely in solution in biological fluids and act by binding to corresponding ▶receptors. In the language of molecular interactions a chemokine is therefore known as a ▶ligand. Chemokines are denoted by the letter L within their name. CXCL12 is thus a ligand, and a chemokine of the CXC class of chemokine mediators. The chemokine receptors are named according to the chemokine class of their binding partner (or ligand), with the letter “R” to designate their receptor status. CXCR4 is therefore a receptor. As for chemokines, the numbers serve to distinguish individual members of the overall family. The partnership between chemokine receptors and the chemokines is not monogamous, and some chemokine receptors may bind as many as ten different chemokines. However, most receptors have between one and three distinct partners. With very few exceptions, these partnerships are within a particular chemokine class (e.g., CXCL chemokines bind selectively to certain CXCR receptors). At this point, the only chemokine factor known to bind to CXCR4 is CXCL12, although CXCL12 itself is able to bind to an alternate receptor (CXCR7, previously known as RDC-1) as well as to CXCR4. Chemokine receptors such as CXCR4 are seventransmembrane, ▶G-protein-coupled receptors. The protein chain of CXCR4 therefore winds back and forth across the outer membrane of the cell so that it crosses the membrane a total of seven times. One end of the protein chain (the amino terminus) protrudes from the outside of the cell. This region of the protein,

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Chemokine Receptor CXCR4

together with certain parts of the three extracellular loops, forms the binding domain for CXCL12. The part of the receptor that protrudes from the inner face of the membrane (composed of the carboxy terminus and three intracellular loops) contains the characteristics that allow it to provoke a cascade of events within the cell (Fig. 1). These steps are initiated firstly by a linkage to one or more of a small family of proteins that interact directly with the receptor, called ▶G proteins (in this case primarily Gαi and Gαq). G protein involvement leads to the activation of three major signaling pathways: (i) the phospholipase C-diacylglycerol/IP3 pathway, (ii) the ras-raf-MAP kinase pathway, and (iii) the PI 3-kinase pathway. CXCR4 is a crucially important member of the chemokine receptor family. If CXCR4 or CXCL12 is absent during embryonic development, the organism is unable to survive. The key dependence on CXCL12 and CXCR4 reflects the importance of this signal/receptor pair in marshalling the correct formation of cells as tissues are formed from their more rudimentary cellular precursors in the embryo. The CXCL12:CXCR4 axis, as it is often called, is a central part of the normal development of the central nervous system (the brain itself) and the exquisitely organized tissue that replenishes the different cells of the blood through adult life (the ▶hematopoietic system). In addition, CXCR4 and CXCL12 seem to play a particular role in

the development of the gut, and their participation is important for the proper development of the blood vessel system that is required for efficient intestinal function in the adult. In adult organisms, CXCR4 and CXCL12 partly reprise their developmental role during tissue damage by participating in repair processes. Once the organism is fully formed, the most evident role for CXCR4 and CXCL12 in a normal individual is that of continued regulation of the hematopoietic system. This takes place mainly in the bone marrow, which acts as a reservoir for the ancestral cells (stem cells and other progenitor cells) that are needed for the continued production of various white cells (leukocytes) and other progeny that are required to ensure a proper defense against infection or injury, or to deal with replacement and remodeling of damaged tissues. These stem cells – which need to be maintained safely by the body until required to respond – are located within the protected environment of the bone marrow and are supported and nourished by a specialized grouping of cells that together are referred to as the “▶microenvironmental niche.” These supporting cells or “▶stromal cells” secrete a number of factors that serve to nourish the stem cells and to keep them within a safe environment in their primitive and “resting” state. Notable amongst these factors is CXCL12 (the “stromal cell-derived factor”), which can bind to CXCR4 on the stem cells. The binding of CXCL12

Chemokine Receptor CXCR4. Figure 1 The cellular signaling pathways of CXCR4. When the chemokine ligand CXCL12 binds to its receptor CXCR4, one or more of several pathways can be activated through initial links involving G proteins that associate with the receptor. These pathways, which are shown only in outline, involve a further network of interactions that eventually lead to a cellular response that may ensure cell growth, migration or survival.

Chemokine Receptor CXCR4

to its receptor has several effects on cell behavior, but the principal outcome is to attract cells toward the source of CXCL12. In the case of stem cells in the bone marrow, this results in retention within the microenvironmental niche, or directs migrant stem cells back to this location. This ability of the CXCL12:CXCR4 axis to direct cell movement is what underlies its key role in orchestrating tissue development and repair. The phenomenon can be demonstrated in experiments using isolated cells, such that cells that have the CXCR4 receptor can be induced to migrate through pores in an artificial filter in response to an upward concentration gradient of CXCL12 in the fluid. This is a cellular response known as ▶chemotaxis, and CXCL12 is referred to as a ▶chemoattractant. Unfortunately, this normal and very important process by which CXCL12 and CXCR4 assist directed cell movement has been subverted by cancer cells to assist the spread of a cancer, or metastasis. Normal tissues that are not subject to inflammation or repair processes typically have very low levels of CXCR4. However, when cancers are formed the affected cells frequently experience a dramatic increase (“upregulation”) of CXCR4. This has been shown for the common adult cancers (carcinomas of the breast, colon, lung, prostate, cervix etc), which arise in the membranous linings (epithelia) of certain organs; but CXCR4 levels are also elevated in cancers arising in bone (e.g., osteosarcoma), muscle (e.g., rhabdomyosarcoma), nervous tissue (e.g., glioblastoma) or white cells (various leukemias). This is such a consistent finding that in many cancers the level, or “expression,” of CXCR4 can be used as cancer ▶biomarker. The levels of CXCR4 that are present on the cells give an indication of how the cancer is likely to behave in the future, and what therapeutic steps might need to be considered. Levels are assessed using a technique called immunohistochemistry. In this approach very thin slices or “sections” – no more than 0.005 mm thick – are taken from the suspect tissue onto glass slides. Special protein reagents called ▶antibodies are used that recognize any molecules of CXCR4 in the tissue, and additional steps in the process generate color wherever the antibody has bound. The resulting picture under a microscope tells the pathologist not only about the architecture of the tissue and the characteristics of the cells, but whether or not they have high levels of CXCR4. High levels (expression) of CXCR4 are associated with cancer aggressiveness, a likelihood that the cancer will spread or metastasize, and means that the outlook for the patient is likely to be poorer. The link between cancer aggressiveness/metastasis exists because the CXCL12:CXCR4 axis has a similar role of “directing traffic” in cancer as it does in normal circumstances. In this situation it is the cancer cells that possess the receptor – CXCR4 – and have levels at

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the cell surface that are much greater than are found on their normal counterparts. The exact reasons for these elevated levels of the chemokine receptor are not fully understood. Undoubtably the genetic changes that are characteristic of cancer cells lead to alterations in ▶transcription of the CXCR4 gene that may provide certain subpopulations with greater amounts of the CXCR4 protein, and these cells have a selective advantage. However, there are also indications that factors within the environment of the tumor can make the situation worse by stimulating the cell to make even more CXCR4. The hypoxic nature of tumor tissue causes an increase in CXCR4 gene transcription through a pathway involving ▶hypoxia-inducible factor-1 alpha (HIF-1α). Various small-molecularweight and polypeptide mediators have also been shown to enhance the cellular expression of this chemokine receptor. The cancer cells are therefore equipped to be attracted toward sources of CXCL12 and to be captured within environments that are high in concentrations of CXCL12. Thus, it is no coincidence that the tissues that are high in CXCL12 are also those in which cancers form secondary tumors or metastases. Such tissues include the lymph nodes – central filters in the system that drains fluid from all tissues – as well as the liver, lung and bone marrow. CXCL12 is believed to be one of the major factors driving metastasis (Fig. 2). As a colorectal cancer develops in the large intestine, for example, and small groups of tumor cells are shed into the blood circulation and the lymphatic drainage, circulating cells will find an attractive home as they encounter lymph nodes in the mesenteric fat around the intestinal wall, when they are delivered to the liver through the portal circulation, or as they lodge in the capillary beds of the lung after traversing the systemic circulation. Conversely, they have a much reduced probability of taking up residence in sites such as the heart or skeletal (voluntary) muscle, which are low in CXCL12. In addition to being attracted and retained in tissues that have high concentrations of CXCL12, the CXCR4-bearing cancer cells may respond in other ways. Although this may not be the case for all cancers, in some types (carcinomas of the colon and prostate, for example) there is evidence that once the cells have settled in to their new location, the presence of CXCL12 acting through CXCR4 also enhances their ability to grow and colonize the tissue. In this way, CXCL12 can also be regarded as a growth factor, alongside other polypeptide growth stimulators that participate in tumor expansion. One additional factor that makes CXCR4 of interest for many different clinicians and researchers is that it is one of the two major coreceptors by which the AIDS virus infects human cells. One of the proteins that is

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Chemokine Receptor CXCR4. Figure 2 How CXCR4 and CXCL12 work together to facilitate metastasis. Tumor cells have increased levels of the receptor at their cell surface. When the tumor grows sufficiently for the cancer cells to find their way into the bloodstream, some cells lodge in tissues (e.g., lungs, liver and bone marrow) that have high concentrations of CXCL12, the molecule for which CXCR4 is the receptor. CXCL12 both encourages the entry of cells into the tissue and promotes growth of the cell population, facilitating metastatic spread. Tissues that have low levels of CXCL12 are much less likely to accept metastases.

present within the outer surface of the HIV-1 virus, called gp120, binds to CXCR4, although at a slightly different site to CXCL12. When the virus binds to its major target (the CD4 protein) on susceptible cells, it requires a coreceptor in order to complete its cellular attack. This allows it to complete the molecular changes that allow it to infect the cell. Depending on the exact cell and viral type, the coreceptor may be CXCR4 or another chemokine receptor, CCR5. While the link with AIDS has limited direct relevance to most cancers, the two fields of research have synergized to extend our present understanding of CXCR4.

well as other cells, and the more widely expressed CXCR4. The tropism of specific chemokine receptors is associated with HIV clinical effects, with CCR5 linked to infection and CXCR4 tropism linked to progression to AIDS. ▶TAT Protein of HIV

Chemokinesis Chemokines

▶Motility

Definition

The name comes from “Chemotactic cytokines,” these small cytokines induce migration of diverse immune cells. The family of the chemokines is quite numerous, as are the chemokine receptors, and often there is “promiscuity,” in that a single chemokine can active multiple receptors and multiple chemokines can activate a single receptor. These molecules direct trafficking of leucocytes. Two chemokine receptors are also the principal co-receptors for HIV involved in viral entry: CCR5, expressed on monocytes and macrophages as

Chemoprevention Definition Chemoprevention involves the use, in healthy people, of natural or laboratory made substances to prevent cancer or reduce cancer risk both in high-risk individuals as well as in the general population. The

Chemoprotectants

aim is to reduce the cancer burden in humans. Most work is being done to reduce the risk for ▶oral cancer, ▶prostate cancer, ▶cervical cancer, ▶lung cancer, ▶colorectal cancer, and ▶breast cancer. The first chemopreventive agent to reach the clinic – and possibly the best known – was ▶tamoxifen, which has been shown to cut breast cancer incidence in highrisk women by 50%. It was followed by ▶finasteride, found to reduce ▶prostate cancer incidence by 25% in men at high risk for the disease. However, the largescale trials that confirmed these benefits brought to light a troublesome issue: the drugs caused serious side effects in some patients. This is an issue of particular concern when considering long-term administration of a drug to healthy people who may or may not develop cancer. Obviously, this is raising a number of ethical issues. An effective chemopreventive agent should not significantly alter quality of life, and should be ideally inexpensive, safe, well tolerated, and effective in preventing more than one cancer. Experience with ▶celecoxib (Celebrex) and other ▶COX-2 inhibitors illustrates the importance of an assessment of the risk/benefit ratio for patients. COX-2 inhibitors have shown impressive efficacy in the prevention of colon cancer and several other forms of cancer, but they also increase the risk of serious cardiovascular side effects. Attention has focused on ▶nutraceuticals and ▶phytochemicals as chemopreventive agents. ▶Curcumin (found in the curry spice turmeric), has shown dramatic anticancer results in preclinical studies owing to its significant anti-▶inflammation properties. Curcumin has been used for thousands of years in the diets of people in the Middle and Far East and therefore is believed to have a low probability of serious side effects. Under investigation for their potential in breast cancer chemoprevention are ▶aromatase inhibitors, a class of ▶estrogen blockers, which are approved to treat metastatic breast cancer in post-menopausal women. While the idea of cancer chemoprevention is extremely attractive, much research remains to be done to make this a generally applicable option for reducing the human cancer burden. An important element will be to identify informative ▶biomarkers to assess individual cancer risk and to possibly provide information of patients tolerance towards individual chemopreventive agents. ▶Celecoxib ▶Chemoprotectants ▶COX-2 ▶Cyclooxygenase 2 ▶Detoxification ▶Photochemoprevention ▶Phytochemicals and Cancer Prevention

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Chemoprotectants D EBASIS B AGCHI Department of Pharmacy Sciences, Creighton University Medical Center, Omaha, NE, USA

Synonyms Chemoprotection; Chemoprevention

Definition

▶Chemoprotectants are natural or synthetic chemical compounds which exhibit the ability to ameliorate, mimic, or inhibit the toxic or adverse effects of structurally different chemotherapeutic agents, ▶radiation therapy, cytotoxic drugs, or naturally occurring toxins, without compromising the anticancer or antitumor potential of the chemotherapeutic drugs. Chemoprotectants shouldn’t affect the ▶therapeutic efficacy of the chemotherapeutic agents, radiation or drugs, disrupt the serum enzyme levels, or induce significant injury to the tissues/organs. These chemoprotectants include anticancer, antitumor, anti▶angiogenic, and antioxidant compounds and used as an adjuvant in cancer ▶chemotherapy.

Characteristics According to the World Health Organization (WHO), cancer accounts for 7.6 million (or 13%) of all deaths in 2005, and the incidence of cancer is expected to rise with an estimated 9 and 11.4 million deaths from cancer in 2015 and 2030, respectively. Cancer chemotherapy and radiation therapy are the most promising choice available for the cancer patients. The global outlook of cancer therapy has made dramatic improvement since the discovery of various ▶synthetic and ▶natural chemoprotectants which slows down the progress of this deadly disease and enhances the life span of the cancer patients. Chemoprotectants may exert toxic effects. Thus, it is very important to determine the right dosage and exposure scenario for each chemoprotectant prior to the exposure to demonstrate adequate safety. Synthetic Chemoprotectants Amifostine. A white powder, water-soluble organic thiophosphate compound, chemically known as 2[(3-aminopropyl)amino]-ethanethiol dihydrogen phosphate (ester) or 2-(3-aminopropylamino)ethylsulfanyl phosphonic acid or aminopropylaminoethyl thiophosphate (Fig. 1a), and used as a ▶cytoprotective adjuvant in cancer chemotherapy to reduce the incidence of ▶neutropenia-related fever and infection caused by

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Chemoprotectants. Figure 1 Structures and IUPAC nomenclature of (a) Amifostine, (b) Dexazoxane, (c) Glutathione, (d) Mesna, and (e) N-acetylcysteine.

DNA-binding chemotherapeutic agents including cyclophosphamide and cisplatin. ▶Amifostine (empirical formula C5H15N2O3PS; molecular weight 214.22; trade name Ethyol, synonyms: Ethiofos, Ethanethiol, Gammaphos, WR2721, NSC-296961) is used to decrease the cumulative nephrotoxicity caused by cisplatin in patients with ovarian or lung cancer, as well as to reduce the incidence of moderate to severe xerostomia (dry mouth) in patients undergoing radiotherapy for head and neck cancer. Amifostine is dephosphorylated by alkaline phosphatase in tissues to a pharmacologically active free thiol metabolite, which readily scavenge noxious reactive oxygen species (ROS) generated by exposure to either cisplatin or radiation, as well as detoxify reactive metabolites of platinum and other alkylating agents. Pharmacokinetic studies show that amifostine is rapidly cleared from the plasma with a distribution half-life of 3 g/day) are required for an adrenolytic effect. Although responses to mitotane alone may occur in 20–30% of cases, most responses are transient, and the prospect for long-term survival is uncertain. The antitumor effect of mitotane is influenced by its pharmacokinetics and by the duration of its therapeutic exposure. Serum concentration plateaus after 8–12 weeks of treatment, and antitumor responses occur only when a serum concentration of at least 14 μg/mL is maintained for a prolonged period. The severe gastrointestinal (nausea, vomiting, diarrhea, and

abdominal pain) and neurologic (somnolence, lethargy, ataxia, depression, and vertigo) toxic effects of mitotane reduce patient adherence. Because mitotane is adrenolytic, all patients receiving this agent should be considered to have severe adrenal insufficiency and treated accordingly. ▶Cisplatin-based regimens, usually including etoposide and doxorubicin, are used in combination with mitotane, although less than 40% of patients respond. The use of radiotherapy in pediatric ACT has not been consistently investigated, although ACT is generally considered to be radioresistant. Furthermore, because many children with ACT carry germline TP53 mutations that predispose them to cancer, radiation may increase the incidence of secondary tumors. For most patients with metastatic or recurrent disease that is unresponsive to mitotane and chemotherapy, repeated surgical resection is the only alternative. However, given the infiltrative nature of the disease, complete resection is difficult. Image-guided tumor ablation with radiofrequency currently offers a valid alternative for these patients. Prognosis Complete tumor resection is the single most important prognostic indicator. Patients who have distant or local with gross or microscopic residual disease after surgery have a dismal prognosis. Long-term survival (5 years or more after the diagnosis) is about 75% for children after complete tumor resection. Among those who undergo complete tumor resection, tumor size has prognostic value. The estimated event-free survival is 40% for those with tumors weighing more than 200 g and 80% for those with smaller tumors. Children whose tumors produce excess glucocorticoid appear to have a worse prognosis than children who have pure virilizing manifestations. Classification schemes or disease staging systems (Table 2) are still evolving. Prognosis will likely be further refined by adding other predictive factors, including those from gene expression studies. Concluding Remarks Adrenocortical tumors remain difficult to treat, and little progress has been made in developing effective chemotherapeutic regimens. The rarity of ACT hinders the opportunity to conduct adequately powered clinical trials, including biological studies. Therefore, efforts must be coordinated and resources must be consolidated to advance our understanding and treatment of ACT. In this regard, a long-standing international ACT registry and tissue bank has been established [http://www.stjude. org/international-outreach/0,2564,455_2265,00.html]. Short-term goals are to establish tissue culture, xenograft transplants, and genetically engineered mouse models to explore novel therapies. Clinical investigators,

Childhood Cancer Childhood Adrenocortical Carcinoma. Table 2

Staging criteria for childhood adrenocortical tumor

Stage I II III IV

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Description Tumor totally excised, tumor size = Smad 5 BMP > ; Smad 8 ) Smad 2 TGFb, Activin Smad 3

Common DPC 4/Smad 4

Inhibitory Smad 6 Smad 7

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able to form a heterodimeric or trimeric complex with the “common-mediator” DPC4/Smad4 which then translocates into the nucleus. Here it can either up- or down-regulate the transcription levels of target genes by interacting with other nuclear factors and by recruiting transcriptional co-activators or co-repressors. This signaling cascade can be negatively regulated by the I-Smads (Smad6 and Smad7). Whereas Smad7 acts as a more general inhibitor of TGFβ family signaling Smad6 seems to preferentially block BMP signaling. I-Smads can compete with R-Smads for type I receptor binding and can therefore prevent the phosphorylationdependent activation of R-Smads. Furthermore, Smad7 can interact with the E3 ubiquitin ligases Smurf 1 and 2. Once the Smad7/Smurf complex is bound to the TGFβ receptor it induces TGFβ receptor degradation. Direct binding of I-Smads to R-Smads has also been shown, yielding R-Smads inactive. The expression of I-Smads appears to be regulated by TGFβ and BMP via an autoregulatory feed back loop. Furthermore, it has been shown that ▶interferon-γ (interferon-γ) (IFN-γ) via the Jak1/STAT1 pathway, and tumor necrosis factor alpha (TNFα) and interleukin 1 through NFκB (▶nuclear factor κB) /RelA can induce the expression of I-Smads to antagonize TGFβ signaling. Transcriptional Regulation through Smads Since Smad proteins have no intrinsic enzymatic activity, they exert their effector function as transcriptional

Deleted in Pancreatic Carcinoma Locus 4. Figure 2 Functional domains and sites of identified DPC4 mutations. In addition to the mad homology domains MH1 and MH2, DPC4 carries a ▶nuclear localization signal (NLS) domain and a ▶nuclear export signal (NES) domain responsible for constant shuttling of DPC4 between nucleus and cytoplasm, thus helping the cell to constantly sense the TGFβ receptor activation state. A number of candidate phosphorylation target sites (P) for kinase pathways such as the MAPK (▶MAP-Kinase) pathway have been described within the linker region which for example may modify nuclear accumulation rates of DPC4. The numbered squares forming the schematic DPC4 molecule also depict the 11 known exons within the DPC4 transcript.

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Deleted in Pancreatic Carcinoma Locus 4

regulators either directly by binding to specific promoter consensus sequences termed ▶Smad-binding elements (SBE) and/or indirectly by associating with transcription factors already bound to the promoter. Therefore, many but not all Smad responsive promoters have two adjacent DNA sequences. One provides the binding site for transcription factors that are cooperating with the ▶Smad complex, the other allows direct binding of the Smad complex to the DNA. While R-Smads provide the interface for the binding to ▶transcription factors, DPC4 makes the contact to SBE elements. DPC4 thereby stabilizes the formation of a higher order DNA binding complex which is able to recruit transcriptional co-activators or co-repressors. Many of the factors that cooperate with the Smad complex are regulated independently by other signaling cascades. The function of an active Smad complex can therefore be described as a co-modulator of transcription. It can modulate gene expression positively as well as negatively by integrating various incoming signals -including those mediated by the TGFβ ligand family. Therefore, it is not surprising that currently more than 1,000 genes are described to be either directly or indirectly regulated by DPC4. In addition, many of these DPC4 target genes can only be found in a certain cell type and growth state, again illustrating how much the cellular differentiation and signaling state determines the net gene expression regulation pattern of a DPC4 containing transcription complex. What makes DPC4/Smad4 Unique among the Other Smad Family Members? . DPC4 is the only human Co-Smad that is currently known. . It seems particular to DPC4 that it is, almost without exception, essential for the establishment of a functional active Smad complex, a fact that emphasizes its role as a “master switch” in the regulation of TGF-β-like signals. . Most somatic and all germ line mutations in human Smad genes identified to date target DPC4. Only very few somatic mutations were found in the human Smad2 gene, none were found in the other members of the human Smad gene family. Which Human Tumors Show Alterations of the DPC4 Gene? Changes, resulting in the inactivation of the DPC4 gene were found in approximately 50% of pancreatic carcinomas (▶pancreas cancer). Research carried out in a variety of other cancer types suggested that DPC4 may contribute primarily to the formation of pancreatic neoplasia, and to a lesser extend to ▶colon cancer ▶cervical cancer and biliary cancer (▶bile duct neoplasia) as well as the induction of non-producing ▶neuroendocrine tumors. However, such changes appear to play

only a minor role in the development of other tumor types such as head and neck, ▶lung cancer ▶ovarian cancer ▶breast cancer and ▶bladder cancer. The frequency of DPC4 mutations is markedly increased in metastatic colorectal carcinoma (35%) compared to non-metastatic colorectal carcinomas (7%). Furthermore, during pancreatic carcinoma development, a high incidence of biallelic DPC4-inactivation is generally not present before the carcinoma-in-situ stage, suggesting the loss of DPC4 function is critical for the tumor cell to develop characteristics such as the ability to invade into the surrounding tissue and to form metastasis. In addition, germline mutations of the DPC4 gene have been identified in patients with familial juvenile polyposis, an autosomal dominant disorder that is characterized by a predisposition to hamartomatous polyps as well as an increased risk for gastrointestinal carcinomas. How are Naturally Occurring DPC4 Mutations Interfering with the Smad Signaling Cascade Most DPC4 mutations identified to date are located within the C-terminal MH2 domain. Functional studies identified the MH2 domain as providing the binding properties to R-Smads, the latter being important for a functionally active Smad complex. It is therefore likely that compromising mutations of the MH2 domain structure restrict the formation of a functional Smad complex, thus preventing signal transduction to downstream components. In addition, a few mutations have been identified within the N-terminal MH1 domain which was shown to mediate the direct binding of DPC4 to DNA promoter sequences. Such mutations might interfere with Smad signaling by rendering the formation of the higher order Smad-DNA complex unstable. Furthermore, some DPC4 ▶missense mutations targeting the MH1 domain result in an instable protein due to a mutation-induced poly-ubiquitination of DPC4 and its subsequent proteasomal degradation. Does DPC4 Contribute to the Familial Risk for Pancreatic Cancer? Although the DPC4 gene is most frequently altered in ▶sporadic pancreatic carcinoma, to date no germline mutations were found in families with an increased risk of this type of carcinoma. DPC4 is therefore unlikely to play an important role as a heritable genetic risk factor in pancreatic carcinoma. How does DPC4 Contribute to Tumor Formation? Although Smad signaling (including DPC4/Smad4) is regarded as central to the TGFβ pathway, there are now numerous examples illustrating that DPC4 inactivation is not simply abolishing TGFβ responsiveness and thus providing the cell a growth advantage. This

Dendritic Cell-Based Tumor Vaccines

can partly be explained by the ability of TGFβ to modulate also Smad-independent pathways such as the Ras (▶RAS) -ERK, PI3K (▶PI3KSignaling) –AKT (▶AKTSignal Transduction Pathway in Oncogenesis) and Rac/Rho pathways. Thus, loss of DPC4 function is not able to completely abrogate TGFβ signaling rather than shifting the balance between DPC4/Smad-dependent and DPC4/Smad-independent TGFβ signaling pathways towards the DPC4/Smad-independent pathways. The output of the latter is dependent on the successful activation of the latent form of TGFβ ligands and intactness of the TGFβ receptors. The cellular context will further modulate the signaling state of the DPC4/Smad-independent pathways through regulating the activity status of their pathway target genes by integrating signals from other signaling pathways. Thus, loss of DPC4 function has been shown cell type dependent to be involved in altering a number of different cell behaviors relevant to tumor formation such as, cell growth rate by modulating the cell cycle and/or the rate of ▶apoptosis, altering the extracellular matrix components (▶extracellular matrix remodeling), the cell adhesion (▶adhesion) properties, and supporting ▶epithelial to mesenchymal transition, thereby facilitating tumor ▶invasion and ▶metastasis, Furthermore, other experiments provided evidence that loss of DPC4 function might promote tumor ▶angiogenesis by causing an increase in the concentration of angiogenic factors and/or a decrease its corresponding inhibitors. Additional insight of DPC4 function was provided by targeted mutagenesis in mice. Mice with two mutated alleles for DPC4 die at embryonic day 7.5, a result that underlines the importance of DPC4 in early embryonic development. DPC4 heterozygous mice develop gastric and duodenal polyps which resemble human juvenile polyps. Furthermore, knockout mice experiments have demonstrated a functional cooperation between the DPC4 and the APC (APC) (adenomatous polyposis coli) gene. In mice that were carrying defect copies of both genes, compared to mice carrying only the mutated APC gene, the induced colonic tumors displayed a much more aggressive phenotype. Lastly, data from primary human tumors and from mice experiments provided evidence that haploinsufficiency of the DPC4 locus may also contribute to progression of cancer. These data clearly support the importance of DPC4 in the suppression of tumorigenesis.

References 1. Hahn SA, Schutte M, Hoque AT et al. (1996) DPC4, a candidate tumor suppressor gene at human chromosome 18q21.1. Science 271:350–353 2. Howe JR, Roth S, Ringold JC et al. (1998) Mutations in the smad/dpc4 gene in juvenile polyposis. Science 280:1086–1088

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3. Miyaki M, Iijima T, Konishi M et al. (1999) Higher frequency of Smad4 gene mutation in human colorectal cancer with distant metastasis. Oncogene 18:3098–3103 4. Takaku K, Oshima M, Miyoshi H et al. (1998) Intestinal tumorigenesis in compound mutant mice of both Dpc4 (Smad4) and Apc genes. Cell 92:645–656 5. Alberici P, Jagmohan-Changur S, De Pater E et al. (2005) Smad4 haploinsufficiency in mouse models for intestinal cancer. Oncogene 25:1841–1851

Deletion Definition Is the loss of a chromosomal segment or gene. A chromosomal deletion can be terminal, i.e., involve the end of a chromosome, or it can be interstitial, in which case a segment from within the chromosome is lost. A decrease in specific DNA fragment copy numbers. ▶ArrayCGH

Dendrimer Definition

A type of ▶nanoparticle that is a highly branched polymeric molecule synthesized from monomers in a reproducible fashion that may have applications for drug delivery and imaging. ▶Nanotechnology

Dendritic Cell-Based Tumor Vaccines Definition The system of dendritic antigen-presenting cells derive from hematopoetic precursors and reside as sentinels of the immune system in all tissues, particularly in skin and mucous membranes. They are able specifically equipped with pathogen recognition receptors which enable them to recognize harmful microbial infections and take up foreign antigens. Activation of ▶dendritic cells triggers (i) their ▶migration to the regional lymph

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nodes, (ii) antigen processing and (iii) functional maturation for optimal antigen presentation and stimulation of T cell proliferation. ▶Dendritic cells are the key regulators of cellular immunity against both infected as well as malignant cells. They are therefore targets of many ▶cancer vaccine strategies both ex vivo (using cultured dendritic cells) as well as in vivo. ▶Melanoma Vaccines

Dendritic cells N ATHALIE C OOLS , V IGGO VAN T ENDELOO, Z WI B ERNEMAN Vaccine and Infections Disease Institute (VIDI) Laboratory of Experimental Hematology, University of Antwerp, Belgium

Definition

Dendritic cells are a special subset of ▶leukocytes that form a complex network of ▶antigen-presenting cells (APC) throughout the body. They play a principal role in the initiation of immune responses to invading micro-organisms (bacteria, fungi and viruses), malignant cells and allografts, by activating naïve lymphocytes, by interaction with innate cells and by the secretion of cytokines. At certain developmental stages they grow branched projections, the dendrites, hence the cell’s name.

Characteristics Origin and Function Dendritic cells (DC) were characterised for the first time by Steinman in 1973 based on their distinct morphology with different cytoplasmic extensions, such as dendrites, pseudopodia and ▶lamellipodia, which give the cell its star-shaped feature. Due to their pronounced morphology, DC have a large surface, ensuring close contact with neighbouring cells. Variations among the tissue distribution of DC and differences in their phenotype and function, indicate the existence of heterogenous populations of DC. DC originate from different hematopoietic lineages in the bone marrow (Table 1). A myeloid progenitor cell can differentiate in vivo to different DC populations: ▶Langerhans cells that migrate to the skin epidermis and interstitial DC that migrate to the skin dermis and various other tissues (airways, liver and intestine). Circulating or migrating DC are found in the blood and in the afferent lymphatics, respectively (the latter called veiled cells). Interdigitating DC are found in

the paracortex of lymph nodes in close proximity with T cells. In addition, monocytes represent an abundant source of DC precursors during physiological stress. Another subset of DC, plasmacytoid DC (pDC) originate from a lymphoid progenitor cell in lymphoid organs. By contrast, follicular DC (FDC) are probably not of hematopoietic origin, despite similar morphology and function to the above mentioned subsets of DC. FDC are APC of the B cell follicles in lymph nodes and central players in humoral immunity. DC express several different types of membrane molecules that determine their phenotypic and functional characteristics: 1. DC display a high surface density of antigenpresenting molecules, such as CD1a, ▶major histocompatibility complex (MHC) class I and class II molecules. The level of expression of these molecules is 10- to 100-fold higher compared to other APC (e.g. B cells). 2. In addition, mature DC have high expression levels of costimulatory and ▶adhesion molecules: CD40, ICAM-1/CD54, ICAM-3/CD50, LFA-3/ CD58, B7-1/CD80 and B7-2/CD86. Binding of these molecules with their respective receptors on T cells results in T cell activation and subsequently stimulates the expression of cytokines, cytokinereceptors and genes for cell survival. 3. Several members of the integrin family are expressed by DC. ▶Cadherins contribute to the generation of cell contacts and selectins are important for the motility of DC. 4. DC also express pathogen-recognition receptors, e.g. DEC-205, a macrophage-mannose receptor capable of binding bacterial carbohydrates and ▶toll-like receptors (TLR), recognising a variety of pathogen-associated molecular patterns (PAMP), such as carbohydrates, nucleic acids, peptidoglycans and lipoteichoic acids. 5. Cytokine and chemokine receptors are also important for DC function, since growth, differentiation and migration of DC as well as antigen processing and presentation is tightly regulated by cytokines and/or chemokines. The widespread distribution of DC and their expression of a variety of membrane molecules underline their sentinel function: they patrol the body to capture invading pathogens and certain malignant cells in order to induce efficient anti-microbial or antitumour ▶T-cell responses. In their in vivo steady state condition, immature DC are specialised in capturing antigens, i.e. they efficiently take up pathogens, apoptotic cells and antigens from the environment by phagocytosis, macropinocytosis or ▶endocytosis. However, immature DC remain tissue-resident, expressing only small amounts of (MHC) class II and of

Dendritic cells Dendritic cells. Table 1

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Different subsets of dendritic cells CD34+ hematopoietic stem cell Myeloid progenitor cell

Phenotype CD11c CD1a CD123 Birbeck granules Factor XIIIa Function Endocytosis IL-10* IL-12* IFN-α*

Lymphoid progenitor cell

Monocyte-derived DC

Langerhans cells

Interstitial DC

Plasmacytoid DC

+ ± – – ±

+ + – + –

+ – – – +

– – + – –

+ + + –

+ + – –

+ + + –

+ + + +

*After application of danger signals.

costimulatory molecules, which leads to T cell unresponsiveness. After encounter of a “danger” signal (e.g. TLR ligand) immature DC mature and migrate to the secondary lymphoid organs. Mature DC are considered to be immunogenic, mainly due to the marked upregulation of MHC class II and costimulatory molecules. This maturation step is believed to be a crucial event to regulate DC function and makes DC potent inducers of T cell immunity.

granulocyte-monocyte colony stimulating factor (GMCSF), tumour necrosis factor (TNF-α), stem cell factor (SCF), interleukin (IL)-3 and ▶Interleukin-6. Second, DC can be generated starting from monocytes using GMCSF and ▶Interleukin-4. Finally, DC can be directly harvested from the peripheral blood of a patient, where they reside at low percentages (0,1%). Next, cultivated DC can be loaded with the tumour antigen of importance in different ways:

Dendritic Cell-Based Immunotherapy Despite our immune system’s function to protect us from malignant cells, tumour cells grow undisturbed and, unless treated, are fatal to the host. The reasons for the failure to eliminate tumour burden in a majority of patients can be the consequence of different tumour escape mechanisms. For example, tumour-derived inhibitory factors (e.g. IL-10 and/or TGF-β) or tumour cell-induced T regulatory cells (▶Treg) might be involved in downregulating or altering immune function. The goal of cancer ▶immunotherapy is to resolve or circumvent these problems and generate tumourspecific immune responses. It is important to realise that immunotherapies will likely only be successful after reducing tumour mass via primary therapies: surgery, radio- and/or chemotherapy i.e. in a ▶minimal residual disease (MRD) setting. Because of their pivotal immune-stimulating capacity and their ability to activate naïve tumour-specific T cells, DC-based ▶cancer vaccines could have important applications in the future treatment of cancer. For this, it was necessary to cultivate DC with high yields. Several cultivation protocols were developed for in vitro generation of DC. First, DC can be differentiated from CD34+ hematopoietic progenitor cells using

1. DC can be grown in vitro in the presence of ▶tumorassociated antigens (TAA). This technique is called peptide pulsing and results in direct binding of the immunodominant epitope on an empty MHC class I molecule on the DC membrane. This circumvents the need for antigen uptake and processing and ensures the stimulation of tumour specific cellmediated cytotoxicity. However, the number of known TAA is still restricted and highly dependent on the human leukocyte antigen (HLA) haplotype of the patient. 2. DC can also be fused with the patient’s tumour cells in vitro or pulsed with tumour cell lysates. The former method combines sustained tumour antigen expression with the antigen-presenting and immunostimulatory capacities of DC. DC-tumour cell hybrids will also stimulate an active anti-tumoural immune response. 3. Tumour antigen can also be loaded on DC using plasmid DNA transfection or ▶viral vector mediated gene transfer. The former method results in only low transfection efficiencies. On the other hand, viral transduction, for example by using adenoviral or lentiviral, vectors is very effective with regard to transfection efficiency. However, the immunogenic character of the viral vector itself is a serious

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disadvantage. In both cases, DC will transcribe and process the tumour antigen. This will result in a cytotoxic immune response, necessary for immunological defence against cancer cells. 4. It is also possible to transfect DC using in vitro transcribed mRNA coding for tumour antigens or total tumour RNA. It has been shown that electroporation of RNA is the most effective nonviral transfection method for DC (▶non-viral vectors for cancer therapy). mRNA is brought directly into the cytoplasm and the cell’s metabolism will translate mRNA into proteins, which can be presented onto MHC class I molecules after processing. This will guarantee a specific cellmediated anti-tumoural immune response. In a clinical context, in vitro cultured and activated DC loaded with appropriate tumour antigens could be administered to cancer patients in a therapeutic setting (active specific immunotherapy). The aimed generation of anti-tumour immunity, mediated by DC, could be of importance for both treatment (as adjuvant to conventional therapies) as well as to prevent relapse in a MRD setting. On the other hand, tumour antigen-loaded DC can also be used for the ex vivo generation of tumourspecific cytotoxic T lymphocytes (CTL) in an autologous system. These tumour-specific CTL can, in their turn, be administered, to the patient to exert a direct cytotoxic effect on the patient’s cancer cells (passive or adoptive immunotherapy). The impact of a DC-based cancer vaccine is clear: an antigen-specific anti-tumour vaccine would influence both morbidity and mortality of various cancers. Currently, several phase I-II or III ▶clinical trials using TAA-loaded DC are ongoing worldwide in order to stimulate the patient’s immune system against tumour antigens. A number of these trials demonstrated some clinical and immunological responses (as evidenced by T cell proliferation, IFN-γ ▶ELISPOT and ▶delayed type hypersensitivity [DTH reaction] reaction) without any significant toxicity. However, despite the presence of expanded antigen-specific T cells in patients after vaccination, only a minor population of these patients showed a beneficial biologically relevant clinical response, i.e. tumour regression and increased disease-free survival. Until now, clinical trials using DC have only shown moderate, if any, success. Since DC possess the exceptional capacity to stimulate the patient’s own immune system against cancer, the reasons for the failure to eliminate tumour burden in a majority of patients needs to be carefully examined in ongoing and future trials. Dendritic Cells in Cancers DC can also infiltrate human tumours where they are involved in the induction of anti-tumour immune

responses. It is likely that the establishment of tumour-specific immune responses depends on the migratory capacity of DC from the tumour microenvironment to the draining lymph nodes, where tumour antigen presentation to T cells takes place. Moreover, by their expression of costimulatory molecules and several cytokines, such as IFN-α and IL-12, DC also mediate T cell survival by preventing T cell ▶apoptosis. In addition, mature DC have been reported to cause direct lysis, apoptosis as well as cell cycle arrest of cancer cells through the secretion of soluble factors. As a consequence, the presence of a high number of DC in the tumoural or peritumoural area, as well as in the draining lymph nodes of various human tumours has been shown to correlate with patients’ survival and a better prognosis. Decreased numbers or dysfunction (e.g. decreased expression of costimulatory molecules) of DC are reported in poor-prognosis tumours. Furthermore, tumour cells can secrete certain factors (e.g. IL-10 and TGF-β) that counteract DC maturation and migration and thus actively contribute to DC dysfunction. Occasionally, neoplasms of accessory immune cells (antigen-presenting cells, dendritic cells) can occur. These are primarily found in lymph nodes and extranodal lymphoid tissues (lymph node interdigitating cell sarcoma), but are also reported from other sites such as the skin (▶Langerhans cell histiocytosis). The incidence of dendritic cell tumours is very rare: until now, only a few dozens of cases have been reported in literature.

References 1. Banchereau J, Steinman RM (1998) Dendritic cells and the control of immunity. Nature 392:245–252 2. Lotze MT, Thomson AW (2001) Dendritic cells, 2nd edn. Academic Press, London 3. Van Tendeloo VF, Van Broeckhoven C, Berneman ZW (2001) Gene-based cancer vaccines: an ex vivo approach. Leukemia 15:545–558 4. Ponsaerts P, Van Tendeloo VF, Berneman ZN (2003) Cancer immunotherapy using RNA-loaded dendritic cells. Clin Exp Immunol 134:378–384 5. Gilboa E (2007) DC-based cancer vaccines. J Clin Invest 117:1195–1203

Densitometric Definition Pertaining to measurement of optical density in a material (e.g. amount of stain). ▶Malignancy-Associated Changes

Dental Pulp Neoplasms

Dental Pulp Definition Forms a functional and interdependent unit together with ist adjacent tissue, the dentin. Physiologic or pathologic reactions in one compartment will affect the other compartment as well. Dentin and the dental pulp are of mesectodermal origin. They are also called “pulpdentin complex”or “pulp-dentin organ”. ▶Dental Pulp Neoplasms

Dental Pulp Neoplasms K LAUS N EUHAUS MMA Department of Operative, Preventive and Paediatric Dentistry, School of Dental Medicine, University of Bern, Bern, Switzerland

Definition Are tumors that are located in the dental pulp.

Characteristics Dental pulp neoplasms (DPNs) are rare tumors of the dental pulp tissue which is not exposed to the oral cavity. Two types of DPNs can be distinguished: Type 1 originates from the dental pulp itself (primary DPN) and type 2 originates from tissue outside of the tooth (secondary DPN). Most DPNs are somewhat incidental findings in patients with a known tumor anamnesis. Therefore the number of histologic examples of DPNs is rather limited, and one also has to take into account articles from old literature in order to draw a complete clinical picture. History In the late nineteenth century, when systematic dental care and oral hygiene in general were considerably more deficient than today, dentists encountered numerous teeth with deep ▶caries and sometimes massive exposed pulp tissue. This phenomenon was called “pulpitis chronica sarcomatosa”, a chronically inflamed dental pulp supposedly caused by a sarcoma. Later it was found out that this pulpal alteration was in fact nothing to do with a sarcoma but rather was the result of colonization of the exposed dental pulp by free epithelium cells of the gums. This entity is a so-called “dental pulp polyp”. However, the first true description of a type 1 DPN was made in 1904 by V. A. Latham from

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Rogers Park, Illinois. He presented the case of a 56-yearold woman presenting with an upper right canine with a greenish-white tinge. The tooth was vital, symptomless and caries-free, i.e. the dental pulp was not exposed to the oral environment. After tooth extraction (for prosthodontic reasons) and histological processing, this canine proved to have an epithelioma of the pulp. The extraction socket was curetted and subsequently cleaned with iodine and carbolic acid. According to his report, Latham thus seems to have cured the patient from a tumor by simply extracting the tooth. Until today, descriptions of type 1 DPNs are very rare. First descriptions of type 2 DPNs also date back to the early 20th century where reports of involvement of dental pulps in patients with ▶breast cancer, ▶lymphoma or neuroma have been given. Three to thirty percent of tumors of the head and neck region (HNR) are associated with involvement of the dental pulp. Carcinomas are more likely to be associated with DPNs than sarcomas or any other type of tumors of the HNR. The maximum incidence of DPNs lies between the fifth and sixth decade of life. Inflammatory Pulp Reactions A DPN causes inflammatory reactions (▶inflammation) in the dental pulp. Chronic inflammation of the pulp may either lead to calcification of parts of the dental pulp tissue or to resorption of the surrounding hard tissue, i.e. ▶dentin. Calcifications – as regularly observed histological findings in dental pulps with a neoplasm – can be explained by the behavior of primary and secondary ▶odontoblasts. These cells are determined to secrete dental hard substance. If a bacterial impact is directed towards the pulp (as is the case with dental caries), the primary odontoblasts immediately start to produce tertiary dentin in the targeted area. Thus increasing the distance between the bacteria and the pulp, an early opening of the pulp chamber in the course of the carious process is evaded. Meanwhile, the chronic inflammation of the dental pulp in slowly progressing caries may lead to the calcification of parts of the pulpal tissue via secondary odontoblasts. These particular cells are differentiations of former pulpoblasts. Pulpoblast differentiation can be modified by ▶bone morphogenetic protein (BMP) 2, 4, and 11, ▶GDF, ▶TGF-β, or high calcium concentrations, all of which are present in dentin. It can also be modified by certain medicaments, which originally were only used in periodontal regenerative therapy but have now also been introduced in endodontic therapy as well as dental traumatology as a means of direct pulp capping. Radiotherapy As an additional point of discussion the possibility of therapeutically induced DPNs by radiotherapy has to

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be mentioned. It is a given fact that one of the risks of radiotherapy of the HNR consists in radiation-induced tumors (▶radiation-induced sarcomas after radiotherapy). Establishing a causal connection is often difficult due to a latency period of several years. However, teeth after radiotherapy sometimes show calcifications of the dental pulps, which can be detected in postirradiation radiographs. Since there has not been a study distinguishing between bacterial and abacterial calcifications as signs of chronic inflammations of the dental pulp in postirradiated cases, no predication can be given about a higher risk of DPN after radiotherapy. Animal Investigations As to DPN-cases, the pulp tissue reaction with respect to calcifications seems to be the same as in cases of dentin caries. At this point, observations made in experimental animal models become of interest: After several days calcification of the dental pulp tissue (with a simultaneous breakdown of the odontoblast layer) can be detected when inoculating the dental pulps of rodents with virulent sarcoma cells. Regular findings in these studies consist in massive development of intrapulpal dental hard substance like denticles, osteoids, or pulp stones. Also destruction of pulpal cells, particularly of the odontoblasts, by tumor tissue has been described in an animal study. In none of these investigations do the dental pulps survive longer than three weeks. Nevertheless, it is a matter of speculation whether this effect is really due to the sarcoma cells or rather to the increased extravasal pressure of the inflamed pulpal tissue. In these animal models, the sarcomata are able to infiltrate the dental pulps and to proliferate to adjacent tissue like ▶periodontium, mandibular bone and masseteric muscle. In later stages, ▶metastasis in the regional lymph nodes as well as in the sublingual, submandibulary and parotid glands can be found. The fact that rodent teeth are substantially different from human teeth must not be neglected. While rodent teeth are growing lifelong and have a largely open apex, human tooth formation literally comes to an endpoint in a constriction at the tip of the root(s). Clinical Relevance Since systematic autopsies of the jaws are no longer common, the entity of DPNs have somewhat moved out of the focus of scientific attention. Type 1 DPNs are certainly of small clinical relevance. In the dental pulp, fibroblasts, subodontoblastic progenitor cells, pericytes, stem cells, and, occasionally, Malassez epithelium remainders of the Hertwig root sheath are cells with mitotic competence and thus are able to undergo neoplastic alteration. A relatively high grade of differentiation of the pulpal tissue limits further differentiation of purported neoplasms.

Due to the restricted anatomical macroenvironment of a tooth and possibly further due to ▶microenvironmental interactions a type 1 DPN is more or less self-limited. Concerning the formation of a DPN, the capability of the dental pulp to regularly form calcifications under certain circumstances as well as the fact that one encounters a terminal blood supply in the pulp play a crucial role. Growth of a neoplasm will increase extravasal pressure within the dental pulp and thus stimulate secondary odontoblasts to secrete irritation dentin. A large amount of irritation dentin might influence the blood supply of the dental pulp and thus will probably lead to a hemorrhagic infarct. A growing tumor in the root canal system will contribute to this effect. While becoming necrotic in such a way, the dental pulp does not necessarily have to show clinical symptoms (such as tooth ache). Teeth with necrotic pulps will normally receive endodontic treatment (i.e. root canal therapy) or they will be “cured” by tooth extraction. It can be acclaimed that the specialty about a type 1 DPN lies in its possibility to be removed successfully and in a relatively easy way. The anatomic prerequisite of the root canal system presents the unique fact that while growing atumor is already limiting its further existence. The risk of metastasis of a DPN is not given in normal-sized teeth. The volume of the dental pulp chamber and the root canal system do not provide sufficient space for a tumor to gain a critical cell mass in order to disseminate clonal cells. Only teeth with incomplete root formation (as in children or adolescents) or ▶taurodonts, i.e. teeth with an abnormally large crown and roots, might provide enough space allowing a tumor to gain a critical cell mass. Large animal teeth, whose pulp chambers can surely provide enough space for a tumor (for instance in large mammalians), are not systematically screened for dental pulp diseases. Type 2 DPNs seem to be mere incidental findings in patients with tumors mainly of the HNR. This leads to the assumption that DPNs are normally symptomless and of relatively small clinical relevance. Nevertheless, type 2 DPNs may also lead to toothrelated symptoms (pain) as has been described in single case reports. Far more often (and clinically more important) is the opposite case when seemingly healthy teeth with no sign of caries, filling or a positive trauma history mimic toothache. The projected toothache is thus drawing off the attention of a true HNR tumor, which often leads to unnecessary root canal treatment or tooth extraction. Therefore, apart from regular or ofacial neuropathic or nociceptive pain conditions, differential diagnosis therefore should always consider a neoplasm in the HNR.

DES Mothers

In common classifications of dental pulp diseases, inflammation of the dental pulp due to neoplasms are neglected. However, animal tumor models (▶mouse models) should be reinvestigated for changes within the dental pulp.

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Deoxycytidine Kinase The rate-limiting enzyme in cytarabine metabolism, converting ara-C to ara-CMP. Also catalyzes the conversion of F-ara-A to F-ara-AMP.

References 1. Neuhaus KW (2007) Teeth: malignant neoplasms in the dental pulp? Lancet Oncol 8:75–8 2. Zajewloschin MN, Libin SI (1934) Histologische Untersuchungen der Zähne bei Neubildungen der Kiefer. Virchows Arch Pathol Anat Physiol Klin Med 293:365–380 3. Stewart EE, Stafne EC (1955) Involvement of the dental pulp by malignant tumors of the oral cavity. Oral Surg Oral Med Oral Pathol 8:842–55

2-Deoxy-D-Glucose Definition A glucose analog that inhibits glycolysis. ▶Jasmonates in Cancer Therapy

Dentin Definition

Dental hard substance located between ▶dental pulp and enamel/cementum. ▶Dental Pulp Neoplasms

Denys-Drash Syndrome Definition DDS; Is a rare disorder consisting of the triad of congenital nephropathy, ▶Wilms tumor, and disorders resulting from mutations in the Wilms tumor suppressor (WT1) gene. Nephropathy is a constant feature. ▶Nephroblastoma

Deoxyazacytidine

Dermoid Cyst Definition

▶Ovarian Teratoma.

DES ▶Diethylstilbestrol

DES Daughters Definition

Women exposed in utero to ▶diethylstilbestrol.

▶A5-aza-2′ Deoxycytidine

DES Mothers 2´-Deoxy-5-azacytidine ▶A5-aza-2′ Deoxycytidine

Definition Women administered pregnancy.

▶diethylstilbestrol

during

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DES Sons

DES Sons Definition

Men exposed in utero to ▶diethylstilbestrol.

Descriptive Epidemiology Definition The branch of cancer epidemiology that deals with the collection and analysis of data on the incidence, mortality, and survival of cancer in populations.

Desmocollin Definition

Dsc; a protein belonging to the desmosomal ▶cadherin family of cell ▶adhesion molecules. In humans three desmocollins (Dsc1–3) are known. Each is encoded by a distinct gene that is located in the desmosomal cadherin gene cluster on chromosome 18q21. Each desmocollin gene encodes two closely related proteins (the larger Dsc “a” protein and the smaller “b” protein) that differ only in the length of their C-terminal tails. The desmocollins are membrane spanning constituents of ▶desmosomes and are essential for desmosomal adhesion.

▶Cancer Epidemiology ▶Epidemiology of Cancer

Desmoglein Desert Definition Gene in hedgehog signaling. ▶Hedgehog Signaling

Definition

Dsg; a protein belonging to the desmosomal ▶cadherin family of cell ▶adhesion molecules. In humans four desmogleins (Dsg1–4) are known. Each is encoded by a distinct gene that is located in the desmosomal cadherin gene cluster on chromosome 18q21. The desmogleins are membrane spanning constituents of ▶desmosomes and are essential for desmosomal adhesion.

Des-Gamma-Carboxy Prothrombin Definition (DCP); Has been reported to be useful in the diagnosis of ▶Hepatocellular Carcinoma (HCC). This marker is also known as a protein induced by vitamin K absence or antagonist-II (PIVKA-II), or abnormal prothrombin. DCP was originally found in the blood of patients who were deficient in vitamin K or who were receiving a vitamin K antagonist. In 1984, Liebman et al. reported for the first time that serum DCP was elevated in patients with HCC.

Desmoglein-2 M ASAKAZU YASHIRO Department of Surgical Oncology, Osaka City University Graduate School of Medicine, Osaka, Japan

Synonyms Dsg2

Definition

Designer Foods ▶Nutraceuticals

Dsg2 is one of the calcium-binding transmembrane glycoprotein components of the cell-cell ▶adhesion molecules of the ▶desmosomes. Dsg2 is one of the ▶cadherin cell adhesion molecule superfamily in vertebrate epithelial cells.

Desmoglein-2

Characteristics Cell Junctions Epithelial cell-cell junctions consists of four junctions, ▶tight junctions, ▶adherens junctions, ▶desmosomes, and ▶gap junctions (Fig. 1). Two adhering-type junctions, the adherens junctions and the desmosomes, are responsible for strong cell-cell adhesion. Each of these junctions consists of a transmembrane cadherin and a complex cytoplasmic plaque that serve to link cadherin to actin microfilaments or the intermediate filament cytoskeleton. Desmosome Intercellular junctions known as desmosomes are multimolecular membrane domains that provide intercellular adhesion and membrane anchors for the intermediate filament cytoskeleton. Desmosomes are essential adhesion structures in most epithelia that link the intermediate filament network of one cell to its neighbor, thereby forming a strong bond. Desmosomes contain the desmosomal cadherins, desmoglein (Dsg) and ▶desmocollin (Dsc) that are linked to the intermediate filament cytoskeleton through interactions with ▶plakoglobin and ▶desmoplakin (Fig. 2). Desmoglein and Cancer Epithelial cell-cell adhesion is important in tumor development. Dsgs are transmembrane glycoproteins of the desmosome, a cell-cell adhesive structure prominent in epithelial tissues, which have been reported to be associated with tumor development. cDNA and protein

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studies have revealed that there are subfamilies of Dsg (types 1, 2 and 3) and Dsc (types 1, 2 and 3) [3]. Dsg2 and Dsc2 are widely expressed and are found together in desmosomes of the basal layer of stratified epithelia, simple epithelia, and nonepithelial cells such as in the myocardium of the heart and lymph node follicles, whereas Dsg3/Dsc3 and Dsg1/Dsc1 are more restricted to complex epithelial tissues. Although considerable overlap is exhibited in the distribution of these isoforms in stratified tissues, their expression is clearly differentiation-dependent. Dsg2, but not Dsg1 or Dsg3, is expressed in stomach epithelia. ▶Gastric cancers have been classified into two histological types: intestinal-type and diffuse-type. Diffuse-type gastric cancers show decreased cell-cell adhesion, which is associated with metastatic potential. These histological features indicate that a decrease in adhesive junctions may be involved in the emergence of diffuse-type gastric cancers. A decrease in E-cadherin has been reported to be one cause of the decrease in adhesive junctions, but not all diffuse-type gastric cancers show such a decrease. Decreased expression of Dsg2 is associated with diffuse-type gastric cancers and poor ▶prognosis in gastric carcinoma. Adherens Junctions The adherens junction is composed of a classic cadherin (e.g. E-, P- or N-cadherin) linked to ▶β-catenin or plakoglobin [5]. Thus, plakoglobin is found in both adherens junctions and desmosomes, while β-catenin is restricted to the adherens junction. Alpha-catenin links the cadherin/catenin complex to the actin cytoskeleton

Desmoglein-2. Figure 1 Cell junctions. Epithelial cell-cell junctions consist of four junctions, tight junctions, adherens junctions, desmosomes, and gap junctions.

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Desmoid Tumor

Definition Desmoid (meaning tendon-like) tumors are a heterogeneous group of rare connective tissue neoplasms, which can occur at almost any anatomical location. Desmoids have been classified as fibromatoses, along with pathologies such as palmar fasciitis, which are due to proliferation of well differentiated fibroblasts and are locally infiltrative and tend to recur after excision, but do not metastasize.

Characteristics Desmoglein-2. Figure 2 Desmosomes. Desmosomes contain the desmosomal cadherins, desmoglein and desmocollin that are linked to the intermediate filament cytoskeleton through interactions with plakoglobin and desmoplakin.

through interactions with ▶α-actinin, vinculin, ZO-1 and actin filaments. Lost or reduced plakoglobin expression has been observed in tumor tissues and metastatic lesions, and has been linked to poor prognosis in a variety of tumors.

References 1. Wahl JKr, Nieset JE, Sacco-Bubulya PA et al. (2000) The amino- and carboxyl-terminal tails of (beta)-catenin reduce its affinity for desmoglein 2. J Cell Sci 113 (Pt 10):1737–1745 2. Tselepis C, Chidgey M, North A et al. (1998) Desmosomal adhesion inhibits invasive behavior. Proc Natl Acad Sci USA 95:8064–8069 3. Buxton RS, Cowin P, Franke WW et al. (1993) Nomenclature of the desmosomal cadherins. J Cell Biol 121:481–483 4. Yashiro M, Nishioka N, Hirakawa K (2006) Decreased expression of the adhesion molecule desmoglein-2 is associated with diffuse-type gastric carcinoma. Eur J Cancer 42:2397–2403 5. Jou TS, Stewart DB, Stappert J et al. (1995) Genetic and biochemical dissection of protein linkages in the cadherincatenin complex. Proc Natl Acad Sci USA 92:5067–5071

Desmoid Tumor S UE C LARK The Polyposis Registry, St Mark’s Hospital Harrow, UK

Synonyms Aggressive fibromatosis; Mesenteric fibromatosis; Gardner syndrome

Desmoids are rare, accounting for less than 0.1% of all tumors, and have an annual incidence of 2–4 per million. While most occur sporadically, 2% are associated with ▶familial adenomatous polyposis (FAP), an autosomal dominantly inherited cancer predisposition syndrome due to mutation of the tumor suppressor gene APC (▶APC gene in familial adenomatous polyposis). Desmoids are over 1,000 times more common individuals with FAP than in the population in general, occurring in about 10–20% of them, and are an important cause of death in this group. It is useful to classify desmoid tumors as being either sporadic or FAP-associated, and by their location into intra-abdominal, abdominal wall or extra-abdominal. Pathology Both sporadic and FAP-associated desmoids have been shown to be clonal proliferations of myofibroblasts. Those associated with FAP result from acquired mutations in the ▶wild-type copy of APC. Somatic loss of the β-catenin gene has been described in sporadic desmoids, and APC mutation has also been identified in some cases ▶APC/β-catenin pathway. Thus abnormal activation of the Wnt pathway seems to have an important role in desmoid tumorigenesis ▶Wnt Signaling. A variety of complex chromosomal abnormalities, including trisomy 8 and gain of 1q21, has also been found in some tumors. There is no true capsule, and the desmoid compresses and infiltrates surrounding tissues as it grows. Desmoids range in size from a few centimetres to large masses weighing several kilograms. A photograph of a mesenteric desmoid tumor taken at surgery can be found in ▶APC gene in familial adenomatous polyposis. Growth rates are very variable. There have been reports of spontaneous resolution, and some desmoids grow relentlessly. The majority, however, either display cycles of growth and resolution or stabilize. The cut surface is usually pale and whorled. There may be central hemorrhage, necrosis or cystic degeneration. Histologically desmoids consist of mature, highly differentiated spindle shaped fibroblasts in an abundant collagen matrix. The histological appearances are not

Desmoid Tumor

necessarily diagnostic, and need to be interpreted in the light of the macroscopic findings. Aetiology Trauma, sex hormones and genetics have all been implicated in their aetiology. Many sporadic abdominal wall desmoids seem to arise in women in pregnancy, perhaps as a result of low-grade trauma of stretching, coupled with high levels of ▶female sex hormones. There have been numerous reports of desmoids arising at sites of surgical wounds, although many, particularly at extra-abdominal sites, seem to occur in the absence of any previous trauma. The higher incidence of desmoids in females, association with pregnancy, presence of estrogen receptors, and results of some experimental studies on desmoid cell lines all suggest that estrogens may have a role in stimulating desmoid development. Desmoids are very much more common in individuals with FAP. Within this group some familial clustering has been observed, in part explained by a ▶genotype-phenotype correlation in which families with an APC mutation 3′ of codon 1444 have an attenuated colorectal phenotype but a high risk of desmoid development. There is also evidence of the influence of as yet unidentified modifier genes. Clinical Features Desmoids most commonly occur in young adults (mean age of onset around 30 years), but have been described in children and even babies. Sporadic desmoids are more frequent in women than men (reported gender ratio 2–5:1), but in FAP there is a less marked gender difference. Sporadic desmoids are found predominantly in the abdominal wall (50%) and at extra-abdominal sites (40%), whereas about 80% of desmoids associated with FAP are within the abdomen, most in the ▶small bowel mesentery. It is not uncommon for an individual to develop desmoids at multiple sites. Intra-abdominal desmoids characteristically arise in the small bowel mesentery. Potential “desmoid precursor lesions,” consisting of small plaques of peritoneal thickening, have been observed in patients with FAP. It is thought that these enlarge, causing a diffuse thickening and puckering of the mesentery which can be seen on ▶CT scans. In some cases a frank desmoid mass develops. Most extra-abdominal desmoids cause symptoms because of their bulk and resulting mechanical effects. At some sites, for example in the neck, they can compress nerves and blood vessels. The overlying skin may ulcerate and abdominal wall desmoids occasionally adhere to and erode abdominal organs. Intraabdominal desmoids can cause major morbidity and even death, usually due to ureteric obstruction, bowel

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obstruction or perforation, either due to direct erosion or to compromise of the vascular supply. ▶CT and ▶MRI are the most useful imaging modalities, showing both tumor size and relationship to neighboring structures. Signal intensity on T2 weighted MRI may reflect cellularity and is correlated with tumor growth. Treatment The treatment of desmoids is difficult and controversial. There are numerous case reports and small uncontrolled series in the literature, but these are difficult to interpret, particularly as the natural history of these tumors is so variable. The drugs most widely used are ▶non-steroidal antiinflammatory drugs (NSAIDs) (particularly sulindac), and anti-estrogens (▶tamoxifen or toremifene). Overall the response rates to a variety of drugs in these classes is claimed to be in the region of 50%, but in reality is likely to beconsiderably less thanthis. There have beena handful of reports of acute desmoid necrosis, with abscess formation or bowel perforation in some, occurring in the weeks after initiation of drug treatment. As NSAIDs have little in the way of adverse effects they are often used as first-line treatment. The mechanism of action in this setting is not clear, but there is some evidence that Cox-2 inhibition my inhibit desmoid growth ▶celecoxib, ▶cyclooxygenase-2 in colorectal cancer. There have been no trials of Cox-2 inhibitors used therapeutically. Anti-estrogens can be used alone or in combination with NSAIDs. Surgery is widely accepted as the first line treatment for extra-abdominal and abdominal wall tumors. Recurrence rates are high (20–80%), but unaffected by use of prosthetic mesh in reconstruction. Serious morbidity and mortality rates are generally very low, although some sites, such as the neck, pose particular challenges. There are some reports suggesting that radiotherapy given postoperatively might reduce recurrence rates. Excision of intra-abdominal desmoids is also associated with frequent recurrence, but carries a substantial risk of perioperative mortality or major morbidity. The commonest reason for this is that the tumors lie close to or encase the superior mesenteric blood vessels, so that the blood supply of a large part of the intestine may be damaged or deliberately sacrificed during surgery. This may result in the need for lifelong parenteral nutrition, and in a handful of cases small bowel transplantation has been performed in these circumstances. Careful case selection, using CT angiography and multiplanar reconstruction, together with accumulation of expertise in a specialized institution has been shown to produce better surgical results in the last 10 years. Generally, however, major resection of intra-abdominal desmoids should be avoided. Ureteric obstruction can be successfully overcome by ▶stenting, and intestinal obstruction

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or fistulation may be managed in many cases, at least acutely, by defunctioning. Cytotoxic chemotherapy has been used to treat life-threatening desmoids. Response rates of 50% have been obtained using doxorubicin and dacarbazine in combination, and also with a less toxic regimen of methotrexate and vinblastine. In view of the potential toxicity of this type of treatment, it should probably be reserved for progressive, inoperable desmoid tumors in which other treatments have failed. ▶Aggressive Fibromatosis in Children

References 1. Clark SK, Phillips RKS (1996) Desmoids in familial adenomatous polyposis. Br J Surg 83:1494–1504 2. Hosalkar HS, Fox EJ, Delaney T et al. (2006) Desmoid tumours and current status of management. Orthop Clin North Am 37:53–63 3. Okuno S (2006) The enigma of desmoid tumours. Curr Treat Options Oncol 7:438–443 4. Reitamo JJ, Scheinin TM, Hayry P (1986) The desmoid syndrome. New aspects in the cause, pathogenesis and treatment of the desmoid tumour. Am J Surg 151:230–237 5. Sturt NJH, Clark SK (2006) Current ideas in desmoid tumours. Fam Cancer 5:275–285

Desmoplakin Definition DP; a protein belonging to the plakin family of cytolinkers. Desmoplakin is found in ▶desmosomes and is essential for desmosomal adhesion. The desmoplakin gene encodes two closely related proteins (the larger DPI and the smaller DPII) that differ only in the length of their central rod domain.

Definition Desmoplasia is the formation of fibrous connective tissue by proliferation of ▶fibroblasts. Desmoplasia is a key component of solid tumor stroma (Fig. 1).

Characteristics Tumors have many parallels to wounds, including similar inflammatory and desmoplastic responses, and fibroblasts are the key cellular component in development of desmoplasia. Fibroblasts are recruited into the wound or tumor, secrete and remodel ▶extracellular matrix (ECM) (▶Extracellular Matrix Remodeling), and serve as scaffolding for other cell types in connective tissue. As fibroblasts incorporate into a tumor environment, they undergo a phenotypic change and acquire an “activated fibroblast” appearance, which are also known as a ▶myofibroblasts or tumor-associated fibroblasts. Myofibroblasts have similar markers to fibroblasts, but myofibroblasts upregulate proteins such as α-smooth muscle actin (α-SMA), fibroblast activation protein (FAP-1), and ▶fibronectin fibrils. During wound repair, the number of myofibroblasts return to a normal level upon wound resolution. In contrast to wound repair, ▶tumor microenvironments simulate a chronic wound in many ways. Thus, local fibroblasts and those that were recruited into the expanding stroma are continuously exposed to activation signals. Activated fibroblasts expand and contribute to an increased stromal response known as desmoplasia. Desmoplasia can be associated with increased tumor stage and poor prognosis in ▶breast cancer patients, but it is unclear whether fibroblasts are active inducers or passive participants in cancer progression. It is clear, however, that activated fibroblasts play a large role in the expanding tumor stroma (▶Stromagenesis). Fibroblastic stromal cells and desmoplasia have been linked to several activities that promote cancer growth

▶Desmosomes ▶Maculae Adherents

Desmoplasia S ASSER A. K ATE , B RETT M. H ALL Department of Pediatrics, Columbus Children’s Research Institute, The Ohio State University, Columbus, OH, USA

Synonyms Stroma; Stromal cell response; Schirrous (archaic)

Desmoplasia. Figure 1 Hematoxolin and Eosin (H&E) stain. Tumor fibroblasts (i.e., desmoplasia) appear pink.

Desmoplasia

and ▶metastasis (▶Seed and Soil) including ▶angiogenesis, ▶epithelial to mesenchymal transition (EMT), and progressive ▶genetic instability. Additionally, fibroblastic stromal cells can dysregulate anti-tumor immune responses, as exemplified by experiments demonstrating that ▶allogeneic murine tumor cells, when co-injected with fibroblastic stromal cells, can engraft across immunologic barriers. Together, these studies suggest that tissue-specific fibroblasts are influential players in progression of metastatic cancer. However, with the exception of promoting epithelial to mesenchymal transition, the direct biological impact on cancer cells themselves has been difficult to distinguish from indirect mechanisms such as enhanced support for angiogenesis or recruitment of inflammatory cells. The origins of desmoplastic fibroblasts are not fully understood. Some studies have suggested that stromal cell fibroblasts are recruited to the expanding tumor mass from local tissue fibroblasts. However, other experimental evidence supports that additional tumorassociated fibroblasts can be recruited from peripheral fibroblast pools, such as ▶bone marrow-derived mesenchymal stem cells (MSC) or fibrocytes. It has been shown that once fibroblasts are recruited into the expanding stroma they change their phenotype and may also undergo selective genetic alterations, which may drive additional tumor growth. Desmoplastic tumor fibroblasts have also been shown to carry unique genetic lesions when compared to those found

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in expanding tumor cells. These observations offer an additional insight into potential mechanisms for how genetic lesions can induce tumor cell expansion. The mechanism for recruitment of desmoplastic fibroblasts into a developing tumor remains poorly defined. Yet, several groups have shown that ▶plateletderived growth factor (PDGF) can contribute to the formation of desmoplasia. In a ▶xenograft model using the human breast carcinoma cell line MCF-7 expressing the cellular oncogene, c-ras, investigators demonstrated that blocking tumor PDGF inhibited the formation of desmoplasia. Others have shown that blocking TGF-α, TGF-β, IGF-I, and IGF-II had no effect on the desmoplastic response. Since these models used murine xenografts it remains unclear whether PDGF is as critical for development of desmoplasia in human carcinomas (▶Epithelial Tumorigenesis). One important way that desmoplastic fibroblasts can contribute to tumor growth and metastasis is through the production of multiple growth factors (▶Fibroblast Growth Factors). ▶Paracrine growth factors such as the stroma derived factor 1 (SDF-1/CXCL12) (▶angiogenesis), vascular endothelial growth factor (▶VEGF) (angiogenesis), ▶fibroblast growth factor (FGF) family, ▶hepatocyte growth factor (HGF), ▶transforming growth factor beta (TGF-β) family, ▶interleukin-6 (IL-6), and epidermal growth factor (EGF) have all been linked to increased tumor growth. Desmoplastic fibroblasts also contribute to tumor stroma through the

Desmoplasia. Figure 2 The tumor microenvironment is composed of many cell types that support tumor cell growth and survival.

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production of fibrous connective tissues and extracellular matrix proteins (▶Fibronectin) (▶Focal Adhesion Kinase (FAK)). ▶Collagen production is a hallmark feature of desmoplasia. As fibroblasts convert to myofibroblasts or tumor-associated fibroblasts, parallel increases in production of collagen are observed. A pathologist can readily visualize increased levels of tumor collagen using standard histology procedures (▶Pathology), and collagen types I and IV are the most prevalent forms of collagen found within most desmoplastic reactions. Collagen bundles interact with extracellular matrix and cell surface proteins such as ▶integrins (▶Cell Adhesion Molecules) (Focal Adhesion Kinase (FAK)) to influence the stiffness of a given tumor ▶microenvironment. Desmoplasia varies extensively between tumors and even within the same tumor. Some studies have suggested that desmoplasia is a defensive mechanism used to wall off the expanding tumor, but other data demonstrate that desmoplasia is associated with increased tumor growth, invasion, and metastasis. It is unclear, however, which underlying mechanisms determine the extent to which desmoplasia may promote tumor progression. As investigators continue to recognize the importance of the tumor microenvironment (Fig. 2), more detailed studies will allow clarification of the biological impact of desmoplasia in tumor development, survival and metastasis.

Desmoplastic Medulloblastoma Definition

Histological subtype of ▶medulloblastoma characterized by a network of reticulin fibers leaving pale islands of typical medulloblastoma cells. Predominant histological medulloblastoma variant in ▶BCNS or ▶Gorlin syndrome.

Desmoplastic Melanoma ▶Cutaneous Desmoplastic Melanoma

Desmoplastic Small Round Cell Tumor S EAN B ONG L EE

▶Cutaneous Desmoplastic Melanoma ▶Stromagenesis ▶Stem Cell Plasticity

Genetics of Development and Disease Branch, National Institute of Diabetes & Digestive & Kidney Diseases, National Institutes of Health, Bethesda, MD, USA

References

Synonyms

1. Bhowmick NA, Neilson EG, Moses HL (2004) Stromal fibroblasts in cancer initiation and progression. Nature 432:332–337 2. Mahadevan D, Von Hoff DD (2007) Tumor-stroma interactions in pancreatic ductal adenocarcinoma. Mol Cancer Ther 6(4):1186–1197 3. Walker RA (2001) The complexities of breast cancer desmoplasia. Breast Cancer Res 3:143–145 4. Zipori D (2006) The mesenchyme in cancer therapy as a target tumor component, effector cell modality and cytokine expression vehicle. Cancer Metastasis Rev 25:459–467 5. Kunz-Schughart LA, Knuechel R (2002) Tumor-associated fibroblasts (part I): active stromal participants in tumor development and progression? Histol Histopathol 17(2):599–621

Desmoplastic Definition A growth of fibrous or connective tissue around the tumor. ▶Desmoplastic Small Round Cell Tumor

Small round-cell tumor; Malignancy of small round blue cell type

Definition DSRCT; Is a rare and highly aggressive tumor occurring mostly in the abdominal peritoneal cavity of adolescents and young adults. In rare cases, the tumors can also be found in other sites such as pleural cavity, pelvis, bone, and head and neck region. DSRCT belongs to a group of undifferentiated small round cell tumors, which include ▶Ewing sarcoma/primitive peripheral neuroectodermal tumor (PNET)/Askin’s tumor and ▶rhabdomyosarcoma. DSRCT is invariably defined by a ▶chromosomal translocation involving chromosomes 11 and 22, t(11;22)(p13;q12), leading to a fusion of two unrelated genes, ▶EWS and ▶WT1, into a single ▶chimeric gene.

Characteristics Clinical and Pathological Features DSRCT was first described in 1989 and is a poorly understood cancer that primarily affects young adults in their second and third decades of life. DSRCT occurs

Desmoplastic Small Round Cell Tumor

predominantly in males than females but the reason for this is unknown. Symptoms of DSRCT are usually associated with abdominal pain or pain in the primary site of tumor involvement, distention, and palpable mass. Local invasion or metastasis to liver, lungs, and bone is commonly found at diagnosis. DSRCT displays distinct histological and immunological features. Most of DSRCT cases are presented as tumors in the serosal surface of abdominal cavity, displaying nests of tumor cells surrounded by dense stromal components (hence the term ▶desmoplastic) containing spindle-shaped fibroblasts and hyperplastic blood vessels. Though rare, the primary tumors in sites other than abdominal region have been documented. The tumors are positive for various cell lineage markers, such as epithelial membrane antigen, keratin (epithelial), desmin (muscle), and neuron-specific enolase (neural). Thus, the tumor cell origin of DSRCT is not known. DSRCT is a clinically aggressive tumor with a high risk of recurrence and an overall poor prognosis. The most recent report on the comparison of different treatments of DSRCT patients suggests that compared to patients who received conventional treatments, a multimodal therapy, which include high-dose multiagent chemotherapy, aggressive debulking surgery, and radiotherapy, can prolong overall survival at 3 years (55%) and may provide a possibility of achieving a long-term survival, albeit at a low rate. The two key elements of the multimodal approach are the use of high-dose polychemotherapy, so-called ▶P6 protocol, and greater than 90% removal of tumor by surgery. P6 protocol consists of seven courses of high-dose alkylating agents ▶cyclophosphamide, ▶doxorubicin, ▶vincristine, ifosfamide, and ▶etoposide. This is followed by aggressive ▶debulking surgery, which was shown to be the major determinant in patient survival. Postoperative radiotherapy also contributed to improved survival. Although the multimodal therapy can improve survival at 3 and 5 years, the prognosis of DSRCT still remains extremely low (median survival of 2.5 years).

Molecular Diagnosis Although clinical, histologic, and immunologic features of DSRCT are distinct, a definitive diagnosis of DSRCT can be provided by genetic techniques. FISH technique, using fluorescently labeled genomic DNA probes derived from EWS and WT1, can be used to identify the specific t(11;22)(p13;q12) translocation of DSRCT. Alternatively, a definitive DSRCT diagnosis can be made with the use of reverse transcriptase-polymerase chain reaction (▶RT-PCR) technique to amplify and detect the DSRCT-specific EWS/WT1 hybrid mRNA transcripts using DNA primers specific for EWS and WT1 genes. This is an extremely sensitive detection

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method that can provide accurate diagnosis with limiting tumor materials. Molecular Genetics Molecular genetic studies revealed that all cases of DSRCT harbor a balanced reciprocal chromosomal translocation, t(11;22)(p13;q12) (▶reciprocal translocation) (Fig.1). The breakpoint in chromosome 22 has been mapped to the intron 7 of Ewing sarcoma gene, EWS, (breakpoints in other sites of EWS, such as in introns 8 and 10, have also been observed in rare cases), while the other breakpoint in chromosome 11 has been invariably mapped to the intron 7 of ▶Wilms tumor gene, WT1. This DSRCT-specific chromosomal translocation between EWS and WT1 results in a fusion of the N-terminal domain (NTD) of EWS to the C-terminal DNA-binding domain of WT1. EWS gene was first isolated from the Ewing sarcoma chromosomal breakpoint, where the translocation generates a fusion between EWS and an ETS-family transcription factor gene, FLI-1. EWS encodes a putative RNA-binding protein with presumptive roles in transcription and splicing. The NTD of EWS mediates potent transcriptional activation when fused to a heterologous DNA-binding domain, while its C-terminal domain, which is lost in the translocation gene product, is involved in RNA recognition. WT1 encodes a transcription factor which is mutated in a subset of Wilms’ tumor, a childhood kidney cancer. WT1 encodes four Cys2-His2 zinc-fingers in the C terminus that mediate sequence-specific DNA binding and the NTD containing both transcriptional activation and repression domains. WT1 is subjected to two ▶alternative RNA splicing events, one of which involves the usage of two alternative splice donor sites at the end of exon 9, leading to inclusion or exclusion of three amino acids, lysine, threonine, and serine (termed KTS), between the zinc-fingers 3 and 4 (Fig.1). The KTS insertion leads to a markedly decreased DNA-binding affinity of WT1. In all EWS/WT1 translocations examined, only the last 3 exons of WT1 (exons 8–10) encoding the last three zinc-fingers are fused to the NTD of EWS (Fig. 1), while the first zinc-finger of WT1 is invariably lost. The alternative KTS splicing of WT1, however, is preserved. As a result, EWS/WT1 produces two isoforms: EWS/WT1(−KTS) and (+KTS) that differs in the DNA binding affinity and specificity (Fig. 1). In vitro study has shown that only the EWS/WT1(−KTS) isoform, but not the EWS/WT1(+KTS), possesses the oncogenic activity in ▶NIH3T3 ▶transformation assay. DSRCT is a rare disease and has been recognized only recently as a distinct cancer type. Therefore, not much is known about the mechanisms of DSRCT but molecular details are starting to emerge. The novel fusion protein EWS/WT1(±KTS) acts as an aberrant transcription factor to presumably initiate the oncogenic

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Desmoplastic Small Round Cell Tumor

Desmoplastic Small Round Cell Tumor. Figure 1 Schematic representation of DSRCT-specific chromosomal translocation. A reciprocal balanced chromosomal translocation that results in the fusion of EWS gene to WT1 gene is shown. The arrow indicates the promoter of EWS which drives the transcription of the fusion gene and the boxes mark the exons. Alternative KTS splicing (grey box, KTS) within the exon 9 of WT1 is shown. Two isoforms of the fusion product are shown separately. See text for details.

process. To date, a number of direct transcriptional targets of EWS/WT1(−KTS) have been identified, which include PDGF-A (platelet-derived growth factor A), IGFR1 (insulin-like growth-factor receptor 1), IL2RB (interleukin 2 receptor beta), BAIAP3 (BAI1-associated protein 3), a potential regulator of growth-factor release, and TALLA-1 (T-cell acute lymphoblastic leukemiaassociated antigen 1), a gene encoding a tetraspaninfamily protein. There is only one target gene identified for EWS/WT1(+KTS), which is LRRC15 (leucine-rich repeat containing 15), a gene implicated in cell invasion. All of these target genes are not transcribed by the native WT1 and thus represent EWS/WT1-specific transcripts. Identification of the EWS/WT1 target genes may provide clues to the molecular and cellular pathways that are central to DSRCT. For example, expression of IGFR1 and IL2RB can promote proliferation and survival of the tumor cells, while expression of PDGF-A and BAIAP3 by the tumor cells can enhance recruitment and proliferation of surrounding fibroblasts and stromal tissues, which may further enhance the growth of the tumor cells

and may explain the dense stroma (desmoplastic feature) associated with DSRCT. Some of these target genes may also have diagnostic and therapeutic values, but it will require further evaluation.

References 1. Gerald WL, Rosai J (1989) Desmoplastic small round cell tumor with divergent differentiation. Pediatr Pathol 9:177–183 2. Ladanyi M, Gerald WL (1994) Fusion of the EWS and WT1 genes in the desmoplastic small round cell tumor. Cancer Res 54:2013–2840 3. Gerald WL, Ladanyi M, de Alava E et al. (1998) Clinical, pathologic, and molecular spectrum of tumors associated with t(11;22)(p13;q12): desmoplastic small round cell tumor and its variants. J Clin Oncol 16:3028–3036 4. Lal DR, Su WT, Wolden SL et al. (2005) Results of multimodal treatment for desmoplastic small round cell tumors. J Pediatr Surg 40:251–255 5. Gerald WL, Haber DA (2005) The EWS-WT1 gene fusion in desmoplastic small round cell tumor. Semin Cancer Biol 15:197–205

Desmosomes

Desmosomal Cadherins Definition A sub-family of the cadherin super-family of cell ▶adhesion molecules. In humans, the desmosomal cadherin family comprises four ▶desmogleins and three ▶desmocollins. The desmosomal cadherins are constituents of desmosomes and are essential for desmosomal adhesion. ▶Desmosomes

Desmosomes M ARTYN A. C HIDGEY Division of Medical Sciences, University of Birmingham, Clinical Research Block, Queen Elizabeth Hospital, Birmingham, UK

Synonyms Maculae adherents

Definition Desmosomes are intercellular junctions that mediate cellular ▶adhesion and maintain tissue integrity. They are found in ▶epithelial cells, myocardial and Purkinje fiber cells of the heart, arachnoid cells of brain meninges and follicular dendritic cells of lymph nodes.

Characteristics Desmosomes are localized at sites of close cell-cell contact (Fig. 1a). They are less than 1 μm in diameter, have a highly organized structure at the ultrastructural level and act as anchoring points for intermediate filaments of the cell cytoskeleton (Fig. 1b). By linking intermediate filaments of adjacent cells desmosomes confer structural continuity and mechanical strength on tissues. Desmosomes are particularly prevalent in tissues, such as the epidermis and heart, that experience mechanical stress. The proteins that form desmosomes belong to three genes families, the ▶desmosomal cadherins, the ▶armadillo family and the ▶plakin family of cytolinkers. Desmosomal Cadherins The desmosomal cadherins are the membrane spanning ▶cell adhesion molecules of desmosomes. In humans there are seven, four ▶desmogleins (Dsg1–4) and three ▶desmocollins (Dsc1–3). Each desmoglein and

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desmocollin is encoded by a distinct gene that is located in the desmosomal cadherin gene cluster on chromosome 18q21. All three desmocollin genes encode a pair of proteins, a larger “a” protein and a smaller “b” protein, that are generated by alternative splicing; the role of the smaller protein in desmosomal adhesion is not yet clear. All desmosomes contain at least one desmoglein and one desmocollin and both are required for adhesion. The desmosomal cadherins show tissue-specific patterns of expression with Dsg2 (▶desmoglein-2 adhesion molecule) and Dsc2 ubiquitously expressed in tissues that produce desmosomes and the others largely restricted to stratified epithelial tissues. The extracellular domains of desmosomal cadherins produced by adjacent cells interact in the intercellular space. Within the cell desmosomal cadherin cytoplasmic domains associate with armadillo proteins (Fig. 1c). Armadillo Family Armadillo proteins that are found in desmosomes include ▶plakoglobin (γ-Catenin) and ▶plakophilins. Plakoglobin is indispensable for desmosome function and interacts with desmosomal cadherins, plakophilins and ▶desmoplakin. Plakoglobin is also found in ▶adherens junctions where it is interchangeable with a closely related armadillo protein, β-catenin. In addition to its structural role in adherens junctions, β-catenin acts as a signaling molecule in the ▶APC/β-catenin pathway. There is a strong possibility that plakoglobin also has a signaling function in this pathway although its role has yet to be fully defined. There are three plakophilins (PKP1–3) that exhibit complex tissuespecific patterns of expression. All three plakophilins show dual localization in desmosomes and in the nucleus. The plakophilins have an important structural role in desmosomes and, because of their nuclear localization and similarity to other armadillo proteins, it is possible that they act as signaling molecules. Plakin Family ▶Plakin family proteins bind intermediate filaments and several, including desmoplakin, plectin, envoplakin and periplakin, localize to desmosomes. Of these only the presence of desmoplakin is obligatory for normal desmosomal adhesion. It is a dumbbell shaped molecule with two globular domains separated by a coiled-coil rod domain and is thought to exist as a homodimer. The desmoplakin gene encodes two proteins (DPI and DPII) that are generated by alternative splicing and differ only in the length of their central rod domain; the role of DPII, the smaller of these proteins, is unclear. The N-terminal end of desmoplakin binds to plakoglobin and plakophilins whereas its C-terminal end binds to intermediate filaments. In epithelial tissues desmoplakin anchors keratin intermediate filaments to the membrane, but in myocardial and

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Destruction Box

Purkinje fiber cells it interacts with desmin intermediate filaments and in arachnoid and follicular dendritic cells it associates with vimentin intermediate filaments. Null Mutations in Mice ▶Genetic ablation studies in mice have shown the importance of desmosomes for embryonic development and normal tissue biology. ▶Knock-out mice of either Dsg2, Dsc3 or desmoplakin display early embryonic lethality at around implantation or before. Mice without either PKP2 or plakoglobin survive longer but die during mid-gestation as a result of heart defects. Embryonic survival is not affected by absence of either Dsg3, Dsg4 or Dsc1 but loss of these molecules does result in defects in keratinocyte adhesion and skin and hair abnormalities. Clinical Relevance Loss of desmosomal adhesion can result in skin blistering diseases. Pemphigus is an autoimmune blistering disease that is caused by pathogenic ▶autoantibodies against desmogleins. Staphylococcal scalded-skin syndrome is caused by toxins with serine protease activity that are released by the bacterium Staphylococcus aureus and specifically cleave Dsg1. Mutations in DNA encoding desmosomal constituents result in a variety of diseases that can affect the skin, hair and heart, and sometimes all three. No mutations in desmosomal cadherins, plakophilins or desmoplakin have been found so far in cancer. However, many reports have documented altered expression of desmosomal constituents in tumorigenesis. For example, loss of Dsg2, Dsc2 and Dsc3 occurs in ▶gastric ▶colorectal and ▶breast cancer respectively. By contrast Dsg2 is overexpressed in ▶skin cancer and Dsg3 is overexpressed in head and neck cancer. PKP3 levels are elevated in ▶lung cancer and loss of desmoplakin has been correlated with progression in a variety of epithelial tumors. A causal relationship between these changes and cancer has yet to be established. Mutations in plakoglobin, concomitant with strong nuclear accumulation, have been linked to the pathogenesis of prostate cancer. Nuclear accumulation and improper activation of transcriptional targets as a result of a failure to degrade cytoplasmic β-catenin has been implicated in FAP (▶APC gene in Familial Adenomatous Polyposis), a familial syndrome that predisposes to ▶colon cancer, and sporadic colon cancer. It remains to be seen whether plakoglobin has, in common with β-catenin, pro-proliferative effects in cancer. In many cancers loss of expression of plakoglobin has been observed and it may be that plakoglobin is anti-proliferative in some cell types. There is little doubt that plakoglobin plays a role in cancer but whether this is related to its participation in desmosomes remains unclear.

Overall it appears that the importance of desmosomes in cancer is twofold. Firstly, as mediators of cell-cell adhesion reduced expression of desmosomal constituents could lead to loss of cell-cell adhesion, ▶epithelialmesenchymal transition, increased invasiveness and metastasis. Secondly, desmosomes may act as signaling centers and variations in expression levels of desmosomal proteins could trigger intracellular signaling cascades that contribute to cancer pathogenesis.

References 1. Chidgey M (2002) Desmosomes and disease: an update. Histol Histopathol 17:1179–1192 2. Garrod DR, Merritt AJ, Nie Z (2002) Desmosomal cadherins. Curr Opin Cell Biol 14:537–545 3. Getsios S, Huen AC, Green KJ (2004) Working out the strength and flexibility of desmosomes. Nat Rev Mol Cell Biol 5:271–281 4. Green KJ, Gaudry CA (2000) Are desmosomes more than tethers for intermediate filaments? Nat Rev Mol Cell Biol 1:208–216 5. Kottke MD, Delva E, Kowalczyk AP (2006) The desmosome: cell science lessons from human diseases. J Cell Sci 119:797–806

Destruction Box Definition DB; Amino acid sequence that when present in a protein in appropriate location confers the ability to be recognized by ▶E3-ubiquitin ligases and the subsequent degradation by the ▶proteasome. Usually, DB sequences can act in heterologous contexts. ▶Snail Transcription Factors ▶Ubiquitination

Detachment-induced Cell Death ▶Anoikis

Determination of Tumor Extent and Spread ▶Staging of Tumors

Detoxification

Detoxification J OHN D. H AYES Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, Scotland, UK

Synonyms Detoxication; Drug metabolism; Xenobiotic metabolism; Carcinogen metabolism; Xenobiotic biotransformation

Definition Metabolic and transport processes used to chemically inactivate noxious compounds and eliminate them from cells for subsequent excretion from the body.

Characteristics Humans are continuously exposed to foreign chemicals (xenobiotics (▶Xenobiotic)) through administration of medicines, the consumption of food and drink, and air breathed. Protection against the detrimental effects of xenobiotics is achieved by the concerted actions of a battery of proteins that metabolize, transport and ultimately pump out of cells modified forms of the compounds originally encountered. This process is called detoxification, or detoxication (in instances where no toxicity occurs). Although detoxication occurs primarily in the liver, all cells possess some capacity to metabolize and eliminate unwanted chemicals. The xenobiotics subject to this process are numerous and include mycotoxins, phytoallexins, pesticides, herbicides, environmental pollutants, cytotoxic anti-cancer agents and many pharmacologically-active drugs. Detoxication processes also confer protection against harmful compounds of endogenous origin, many of which arise as a consequence of interaction with reactive oxygen species, such as the superoxide anion, produced normally in the body. Detoxication is achieved in two distinct stages, the first involving metabolism of the xenobiotic, and the second involving energy-dependent efflux of the xenobiotic from the cell. Historically, description of xenobiotic biotransformation has been divided into phase 1 and phase 2 metabolism, and consequently efflux of xenobiotics is referred to as phase 3 of detoxication. . Phase 1 drug metabolism involves an initial chemical modification of the xenobiotic that results in the introduction, or exposure, of a functional chemical group (e.g. –OH, –NH2, –SH, –COOH) into the compound. This usually entails enzyme-catalyzed oxidation reactions by ▶cytochrome P450 (CYP) or flavin monooxygenase. . Phase 2 drug metabolism often involves a second chemical alteration of the xenobiotic, usually at the

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same region of the molecule where the functional group was introduced. This is performed by enzymes catalyzing conjugation reactions (such as ▶glutathione S-transferase (GST), ▶N-acetyltransferase (NAT), ▶sulfotransferase (SULT) and ▶UDP-glucuronosyl transferase (UGT). It should be noted that use of the terms phase 1 and phase 2 to define the detoxication enzymes is somewhat arbitrary and does not necessarily reflect the pathway of biotransformation of all chemicals. Thus, a number of xenobiotics are subject to several modifications by the phase 1 CYP isoenzymes before serving as substrates for the phase 2 enzymes. Alternatively, some xenobiotics do not require modification by phase 1 enzymes before metabolism by phase 2 enzymes, and others are subject to modification by more than one phase 2 drugmetabolizing enzyme. As a result of differences in drug metabolism, the group of enzymes catalyzing reduction of hydrolysis reactions (e.g. ▶aldehyde dehydrogenase (ADH), ▶aldo-keto reductase (AKR), ▶epoxide hydrolase (EPHX) and ▶NAD(P)H-quinone oxidoreductase (NQO)) are variously referred to as phase 1 or phase 2 detoxication, depending on the individual xenobiotic being considered and the preferences of research workers. Clearly, these enzymes provide a highly flexible metabolic defense that has evolved to protect against a diverse spectrum of chemicals. . Finally, phase 3 of detoxication involves ATPdependent elimination of the parent compound or modified xenobiotic by proteins that are drug efflux pumps (e.g. ▶multidrug resistance protein (MDR) and ▶multidrug resistance-associated protein (▶Multidrug resistance protein) (▶MRP)). As a consequence of the combined actions of phase 1 and phase 2 enzymes, a diverse spectrum of xenobiotics acquires a limited number of molecular “tags” (i.e. acetate, glutathione, glucuronide or sulfate moieties) that are recognized by the MRP trans-membrane pumps. Furthermore, the xenobiotic metabolites produced by phase 1 and phase 2 are usually more soluble, and easily excreted, than the parent compound. Whilst the ability of CYP to oxidize xenobiotics is generally desirable, as it facilitates further metabolism and elimination of harmful chemicals, it can sometimes result in the generation of highly reactive products that may not be readily detoxified. In such instances, modification of intracellular macromolecules will occur resulting in necrosis, ▶apoptosis or malignant ▶transformation. As an example of the interplay between toxification and detoxification reactions, a scheme depicting metabolism of ▶aflatoxin B1 (AFB1), modification of macromolecules by AFB1 metabolites, and efflux of the AFB1-glutathione conjugate from a cell is shown in the illustration (Fig. 1).

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Detoxification. Figure 1 Detoxification pathways for aflatoxin B1. The mycotoxin is converted to the ultimate carcinogen AFB1-8,9-epoxide, by the actions of the hepatic phase 1 CYP enzyme system. The epoxidated AFB1 is highly reactive, and if it is not detoxified it will form DNA adducts that may cause hepatocarcinogenesis. The phase 2 GST enzymes can achieve detoxification of this unstable intermediate, and the resulting AFB1-glutathione conjugate is eliminated from the liver cell by MRP. In addition, AFB1-8,9-epoxide can rearrange to form a dialdehyde-containing metabolite which will covalently modify proteins by forming Schiff’s bases. The dialdehyde can be reduced by phase 2 AKR to yield a dialcohol that may be a substrate for SULTor UGT before being transported out of the cell, presumably by MRP.

Genetic Variation Numerous proteins have evolved that detoxify drugs, and certain of the families listed above comprise over twenty genes. In total, the human probably possesses between 100 and 150 genes encoding detoxication proteins. Substantial variation can occur in the levels of these proteins in tissues from different individuals, and

this can result in increased sensitivity of cells to chemical insult. In part, this inter-individual variation is due to ▶genetic polymorphisms. By definition, such differences must be present in at least 1% of the population in order to be considered a ▶genetic polymorphism. In some instances the variation involves deletion of detoxication genes with complete loss of

De-ubiquitinase

specific functions, whereas in other instances point mutations result in alteration of protein structure causing only a modest attenuation of activity. In other cases mutations alter the regulatory regions of genes causing altered expression of normal protein. Detoxication genes that are polymorphic in the human include those for the enzymes CYP3A4, CYP2C9, CYP2C19, CYP2D6, CYP2E1, AKR1C4, GSTM1, GSTP1, GSTT1, NAT2, SULT1A1, SULT1E1, SULT2A1, UGT1A1, UGT1A4, UGT1A6 and UGT2B7, EPHX and NQO1, as well as the MRP2 efflux pump. It is clear additional polymorphisms remain to be identified. Cellular Regulation In addition to genetic polymorphisms, induction of detoxication proteins by xenobiotics and environmental agents is a further mechanism that can cause interindividual differences in detoxification capacity. Induction of detoxication proteins represents an ▶adaptive response to chemical and ▶oxidative stress, which can be brought about by synthetic drugs or by naturally occurring compounds such as coumarins, indoles and isothiocyanates that are found in edible plants. Increased expression provides short-term resistance to toxic xenobiotics. Enzyme induction also results in increased metabolism of therapeutic drugs. Many of the enzymes and pumps such as CYP, GST, ADH, AKR, NQO and MRP are inducible, often by transcriptional activation of genes encoding the proteins. The promoters of these genes contain enhancers that enable a transcriptional response to a diverse spectrum of chemical agents. The enhancers that are involved in induction of detoxication proteins include ▶AP-1 binding sites, the antioxidant responsive element, the xenobiotic responsive element, the phenobarbital responsive enhancer module, progesterone X receptor and peroxisome proliferator-activated receptor enhancer. Clinical Relevance It is apparent from studies into the mechanisms of selective toxicity between species that variation in the activity of detoxication proteins influences sensitivity to chemical insult. Increasing evidence suggests that genetic polymorphisms in detoxication enzymes can confer an inherited predisposition to a number of malignant diseases that are influenced by environmental factors (e.g. lung and colorectal cancer). They may also confer a predisposition to adverse drug reactions. Induction of some phase 2 detoxication systems is believed to represent a major mechanism of cancer ▶chemoprevention, and is thought to explain in part the epidemiological data suggesting that consumption of diets rich in fruit and vegetables protect against certain malignant diseases.

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Acquired ▶drug resistance to chemotherapy is a major problem in the treatment of many cancers. There is overwhelming evidence that the overexpression of several detoxication proteins, particularly GST, MDR and MRP, contributes to the drug-resistant phenotype.

References 1. Guengerich FP, Shimada T (1991) Oxidation of toxic and carcinogenic chemicals by human cytochrome P-450 enzymes. Chemical Res Toxicol 4:391–407 2. Hayes JD, Pulford DJ (1995) The glutathione S-transferase supergene family: regulation of GST and contribution of the isoenzymes to cancer chemoprotection and drug resistance. Crit Rev Biochem Mol Biol 30:445–600 3. Klaassen CD (ed), Amdur MO, Doull J (eds emeriti) (1996) Casarett and Doull’s toxicology: the basic science of poisons. McGraw-Hill, New York 4. Dinkova-Kostova AT, Massiah MA, Bozak RE et al. (2001) Potency of Michael reaction acceptors as inducers of enzymes that protect against carcinogenesis depends on their reactivity with sulfhydryl groups. Proc Natl Acad Sci USA 98:3404–3409 5. Hayes JD, McLellan LI (1999) Glutathione and glutathionedependent enzymes represent a co-ordinately regulated defence against oxidative stress. Free Radic Res 31:273–300 6. Borst P, Evers R, Kool M et al. (2000) A family of drug transporters: the multidrug resistance-associated proteins. J Natl Cancer Inst 92:1295–1302

Detoxication Definition Synonym Detoxification; Process, or processes, of chemical modification which make a toxic molecule less toxic. ▶Toxicological Carcinogenesis

De-ubiquitinase Definition DUB; An enzyme that can specifically remove ▶ubiquitin proteins from substrates through an enzymatic cascade that cleaves an isopeptide bond. ▶Herpesvirus-Associated Ubiquitin-Specific Protease (HAUSP) De-Ubiquitinase ▶Ubiquitination

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De-ubiquitinating Enzymes

De-ubiquitinating Enzymes Definition Are a large family of enzymes that cleave chemical bonds formed at the C-terminus of ▶ubiquitin. By virtue of their action, the ▶ubiquitination of a given protein is reversible. Ubiquitin-protein conjugates are not always degraded by the proteasome, an alternative fate is the protein is spared from degradation through the activity of any of a large family of de-ubiquitinating enzymes. De-ubiquitinating enzymes can remove ubiquitin from ubiquitin-protein conjugates. These enzymes break down abundant multiubiquitin chains that are nor attached to any substrate and produce mature ubiquitin from the precursor forms in which it is synthesized. A second alternative fate for ubiquitinprotein conjugates is that ubiquitinated cell surface proteins may be targeted for endocytosis and eventual degradation via the lysosome rather than the proteasome.

Dezocitidine ▶A5-aza-2′; Deoxycytidine

dFdC ▶Gemcitabine

DHT Definition Dihydrotestosterone.

Development of New Lymphatic Vessels

▶Cyclin G-Associated Kinase ▶Dihydrotestosterone Receptor

▶Lymphangiogenesis

Dexrazoxane

DIA ▶Leukemia Inhibitory Factor

Definition Is an iron chelator, is a bisdioxopiperazine with cardioprotective and antineoplastic activities. ▶Adriamycin

Dexrazoxane Definition

A cyclic derivative of ▶EDTA used to protect the heart against the cardiotoxic side effects of anthracycline chemotherapy. ▶Chemoprotectants

Diabetes Definition Diabetes mellitus; People who are Type 1 Diabetes mellitus must use manufactured ▶insulin, usually in an injectable form, to replace the natural insulin that is no longer produced by their body (for instance as the result of beta-cell degeneration). People with Type 2 Diabetes sometimes need to use insulin when their cells become too resistant to the insulin that they produce naturally and when oral medications are no longer working.

Diabody

Diabetes Type 2 Definition Type 2 Diabetes, is a metabolic disorder characterized by insulin resistance, relative insulin deficiency, and hyperglycemia. A disorder of glucose and insulin metabolism that is characterized by inappropriately increased blood glucose levels and resistance of tissues to the action of insulin. Insulin levels are elevated during early stages of the disease. Previously referred to as adult-onset diabetes or non-insulin-dependent diabetes. ▶Obesity and Cancer Risk ▶Adiponectin

Diabody S HUJI O ZAKI Department of Medicine and Bioregulatory Sciences, The University of Tokushima Graduate School of Health Biosciences, Tokushima, Japan

Synonyms Engineered antibody; Single-chain Fv dimer; Multimeric antibody fragments

Definition Diabody is a noncovalent dimer of single-chain Fv (scFv) fragment that consists of the heavy chain variable (VH) and light chain variable (VL) regions connected by a small peptide linker. Another form of diabody is single-chain (Fv)2 in which two scFv fragments are covalently linked to each other.

Characteristics Advances in antibody technology are enabling the design of antibody-based reagents for specific purposes in cancer diagnosis and ▶monoclonal antibody therapy. First, to minimize the immunogenicity and enhance the efficacy in human use, mouse monoclonal antibodies are engineered to ▶chimeric antibodies or ▶humanized antibodies by grafting to the human constant region or framework. Moreover, fully human antibodies are developed by the use of ▶transgenic mice or phage display technology. Second, monoclonal antibodies are designed as immunoconjugates to deliver the cytotoxic agents such as chemotherapeutic drugs, toxins, enzymes,

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and radioisotopes. These therapeutic antibodies have emerged as potent agents and are used worldwide for cancer therapy. More recently, engineered antibody fragments have been investigated as alternative reagents because of their unique properties resulting from the structure. Structure A variety of antibody fragments are developed including single VH domain, Fab, scFv, and multimeric formats such as multivalent scFvs (diabody, triabody, and tetrabody), bispecific scFv, and minibody (scFv– CH3 dimer) (Fig. 1). In scFv fragments, the VH domain binds to its attached VL domain when the linker is flexible and long enough (a length of at least 12 amino acids). For example, the linker sequence of (Gly4Ser)3 provides sufficient flexibility for the VH and VL domain to form Fv comparable to the parent antibody. In contrast, when the linker is shortened to less than 12 residues (e.g., five amino acids of (Gly4Ser)), the VH and VL domains are unable to bind each other and instead the scFv fragment form a noncovalent dimer by another scFv molecule [(scFv)2 diabody]. Shortening of the linker length between the VH and VL domains (less than three residues) promotes the assembly of trimeric or tetrameric structures (triabody or tetrabody). However, this multimer formation also depends on the V-domain orientation either VH–VL or reverse VL–VH orientation in the scFv constructs. The bivalent Fv fragment can also be designed by linking two scFv domains covalently as a single chain version [sc(Fv)2 diabody]. The sc(Fv)2 version is more stable than (scFv)2, and this structure may form a noncovalent dimer [sc(Fv)2]2. The capacity of multivalent binding of these fragments offers a significant opportunity to design multifunctional antibody reagents. The diabody structure is used to form ▶bispecific antibodies by linking different VH and VL domains of two antibodies (e.g., VHA–VLB and VHB–VLA). However, when two different polypeptides are produced within a single cell, purification steps are necessary to obtain the active heterodimeric antibody among the inactive homodimers. Therefore, bispecific sc(Fv)2 version is developed by connecting two different scFv domains with the middle-length linker (e.g., VHA–VLB–VHB–VLA or VHA–VLA–VHB–VLB). Pharmacokinetics and Distribution The ▶pharmacokinetics of these antibody fragments is markedly different from intact IgG antibodies that exhibit prolonged circulation (t1/2 of up to 3 weeks). The lower molecular weight constructs (below than 60 kDa) are subject to be excreted by renal clearance, resulting in a shorter serum half-life than intact IgG. In most cases, the t1/2 values of scFv and diabody are extremely short such as 2 and 6 h, respectively.

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Diabody

Diabody. Figure 1 Schematic structure of intact IgG antibody and engineered antibody fragments. The variable regions of heavy (VH) and light chains (VL) contribute to the antigen binding. The VH and VL domains can be connected by a peptide linker to form single-chain Fv (scFv). The scFv fragments can form multimers such as (scFv)2 diabody, triabody, and tetrabody depending on the linker length and the V-domain orientation. The bivalent sc(Fv)2 can be generated by connecting two scFvs covalently. Bispecific diabodies can also be engineered by using two different Fv domains.

This rapid pharmacokinetics is the most favorable for imaging applications and ▶radioimmunotherapy because of the lower background levels in normal tissues. ▶Drug biodistribution studies of radiolabeled scFv and sc(Fv)2 have shown high tumor-to-blood ratios in xenograft models compared with intact IgG antibodies. The fast blood clearance of antibody fragments contributes to avoid undesired toxicity, and these fragments have the remarkable advantage for ▶targeted drug delivery of toxins or radioisotopes. In addition, antibody fragments show better penetration into the tumor mass, but these smaller constructs have shorter retention to tumor cells at the same time. Thus, the valance of penetration and retention of antibodies is an important factor for therapeutic use, especially in solid tumors. The Fab and scFv fragments are monovalent and exhibit poor retention on target cells, but multivalent forms of these fragments such as diabody, triabody, and tetrabody exhibit dramatically increased affinity and high tumor retention compared with the parent scFv. The ideal tumor-targeting reagents are intermediate-sized multivalent antibodies such as bivalent diabodies that show a longer half-life as well. In another approach, the Fc portion is fused to antibody fragments to control the serum levels of the antibody. The scFv–Fc or scFv–CH3 fusion antibodies (minibodies) are expected to have a more prolonged half-life and increased tumor accumulation in vivo. The serum half-life of antibody fragments can also be extended by modification such as linkage to polyethylene glycol (▶PEG).

Agonistic Activity In terms of mechanism of action, intact IgG antibodies kill tumor cells mainly by Fc-mediated effector functions such as ▶antibody-dependent cell-mediated cytotoxicity (ADCC) and ▶complement-dependent cytotoxicity. In contrast, antibody fragments have the compact structures without the Fc portion, and have unique characteristics for using cancer treatment. The two binding sites of diabodies are located at a distance of about 70Å less than half for those of intact IgG antibodies. Therefore, diabodies can place the antigens more closely to each other than by the parent IgG antibodies, which efficiently induces the ligation of target molecules on the cell surface. When the targets are functional receptors, the diabody can mediate a direct effect or signal transduction in tumor cells, including the stimulation of ▶apoptosis or cell death. For example, we and our collaborators have generated (scFv)2 and sc(Fv)2 diabodies that recognize CD47 or ▶HLA class I molecules. These diabodies can crosslink the target antigens and show the enhanced cytotoxic activities against hematological malignancies such as leukemia, lymphoma, and myeloma cells when compared with the original IgG antibodies. Thus, enhancement of the cross-linking potential is one of the important bioactivity of antibody fragments. Application of Diabodies A variety of target antigens have been evaluated for therapeutic purposes including CD19, CD20, CD22,

Dicer

epithelial cell adhesion molecule (Ep-CAM), epidermal growth factor receptor (EGFR), HER2, MUC1, and carcinoembryonic antigen (▶CEA). Several types of diabodies and minibodies are engineered for targeting these candidate antigens on tumor cells. Immunotoxins are also constructed to deliver the cytotoxic agents, radioisotopes, enzymes, cytokines, and liposomes by using antibody fragments. Previous studies have shown the effectiveness of these reagents in preclinical and clinical trials. ▶Bispecific antibodies that comprise two different binding specificities have been studied extensively in cancer diagnosis and therapy. Most of the bispecific reagents are designed for the retargeting of effector cells such as cytotoxic T lymphocytes and NK cells. Recombinant bispecific diabodies such as anti-CD19 x anti-CD3, anti-Ep-CAM x anti-CD3, and anti-HER2 x anti-CD3 have been used in the immunotherapy of ▶B-cell lymphoma ▶breast ▶ovarian and ▶colorectal cancer. Another strategy of bispecific antibodies is the recruitment of effector molecules including toxins, drugs, ▶prodrugs, ▶cytokines, and radionuclides in vivo. First, the tumor cells are targeted by the tumorspecific binding site of the diabody. After the unbound diabody is cleared from the serum, cytotoxic drugs or radiolabeled hapten are administered to be captured by another binding site of the bound diabody.

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Diacylglycerol Definition DAG; Is a lipid with two acyl chains esterified to sn-1 and sn-2 position of glycerol backbone; it is produced by phospholipase C and is involved in selective activation of isoforms of ▶protein kinase C (PKC). ▶Lipid Mediators ▶Protein Kinase C Family

Diagnostic Biomarkers Definition Markers to assess the presence or absence of cancer.

Diagnostic Pathology Future Directions In principle, selection of target molecules and modification of antibody constructs are key issues of antibodybased strategies in clinical utility. Based on the properties of pharmacokinetics, biodistribution, and manufacturing production, engineered antibody fragments have been investigated as alternative reagents to target cancer cells. Although the efficacy of these antibody fragments needs to be evaluated in clinical settings, the drastic potential of agonistic activity or multivalent activity of these reagents will provide new promises for development of the next generation of antibody drugs in cancer diagnosis and treatment.

References 1. Holliger P, Hudson PJ (2005) Engineered antibody fragments and the rise of single domains. Nat Biotechnol 23:1126–1136 2. Jain M, Kamal N, Batra SK (2007) Engineering antibodies for clinical applications. Trends Biotechnol 25:307–316 3. Beckman RA, Weiner LM, Davis HM (2007) Antibody constructs in cancer therapy. Cancer 109:170–179 4. Batra SK, Jain M, Wittel UA et al. (2002) Pharmacokinetics and biodistribution of genetically engineered antibodies. Curr Opin Biotechnol 13:603–608

▶Pathology

Dibasic Processing Enzyme ▶Furin

Dicer Definition An RNaseIII type enzyme that cleaves perfect or partially double-stranded RNA molecules. The hallmark of Dicer cleavage is the production of double-stranded short RNA molecules consisting of two 21 nucleotide RNA strands annealing to each other through 19 base pairs and have a two nucleotide overhang at the 3′-ends. Dicer produces ▶siRNAs from long double-stranded RNAs in lower

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animals and plants and generates ▶microRNA duplexes from stem-loop structure pre-miRNAs.

Dietary Micronutrient Definition

DIE ▶Endometriosis

Diet Definition Dietary factors may contribute to enhancing risks for the various cancers. These factors are heterogeneous. In many cases individual compounds have been suggested to be involved but little definitive evidence is available. The individual risk factors are specific for different tissues, and the state of current knowledge has recently been published. In general diets high in total fat or animal fat are considered causative for several common tumors including those arising from tissues of the gastrointestinal tract. In contrast, vegetables and fruits are considered to be protective for many tissues and for all cancers discussed in the review listed below. Phytoprotectants are implicated as contributing to risk reduction by different mechanisms, but it has not been possible to pinpoint individual compounds as the responsible factors. Tissues that seem to be most protected are esophagus, stomach, colon, lung, pancreas and bladder. The least clear cut protection is achievable in the hormone dependent tissues, prostate and breast, although a dietary component can not be excluded for these tumors. Altogether the estimates indicate that at least 35% of all human tumors are dietary related, which means a large proportion of tumors could be prevented by adequate dietary regimens; biomarkers See also: World Cancer Research Fund and American Institute for Cancer Research; Food, Nutrition and the Prevention of Cancer: a global perspective. Washington DC: American Institute for Cancer Research, 1997 ▶Biomarkers

Dietary Essential Minerals ▶Mineral Nutrients

A trace element, present in the diet that is required for maintenance of normal health. ▶Ultra trace Minerals

Dietary Supplement Definition An agent intended to supply nutrients, vitamins, minerals, and essential elements. ▶Chemoprotectants

Diethylstilbestrol R OSEMARIE A. U NGARELLI , C AROL L. R OSENBERG Boston Medical Center and Boston University School of Medicine, Boston, MA, USA

Synonyms DES

Definition Diethylstilbestrol is a synthetic non-steroidal estrogen with biological properties similar to endogenous estrogens such as estradiol-17-beta and estrone (▶Estradiol).

Characteristics Pharmacology Diethylstilbestrol is administered orally, is lipid-soluble, and readily absorbed from the proximal gastrointestinal tract. It is metabolized via the hepatic microsomal system to dienestrol, and quinone and epoxide intermediates. It crosses the placenta and is thought to be metabolized by the fetus. Initial Use and Early Epidemiologic Studies Diethylstilbestrol (DES), first manufactured by Dodds and associates in London in 1938, was used to treat several gynecologic conditions. In particular, it was

Diethylstilbestrol

prescribed for the treatment of frequent or threatened miscarriages. As early as 1953, Dieckmann and colleagues demonstrated that DES did not improve pregnancy outcomes. (In fact, in a later re-analysis of these data in 1978, Brackbill and Berendes showed that women exposed to DES had higher risks of premature births, perinatal death, and miscarriages than women who were given placebo.) Other studies also found DES to be ineffective in preventing adverse pregnancy outcomes, but physicians continued to prescribe the drug to try to maintain high-risk pregnancies because its use seemed logical and it was well-established. It was administered to approximately 5–10 million pregnant women in the United States between 1940 and 1971. It remained in use in Europe until the early 1980s. In 1971, Herbst and colleagues established a strong connection between DES exposure in utero and subsequent development of clear-cell adenocarcinoma of the vagina and cervix in young women, aged 14–21 years. The incidence of this cancer in women whose mothers had been administered DES during pregnancy (▶DES daughters) is estimated to range from 1.4 cases per 1,000 exposed to one case per 10,000 exposed persons (▶Cervical cancer). Previously, clear-cell adenocarcinoma of the vagina and cervix had been observed only rarely, primarily in post-menopausal women (over age 50) not exposed to DES. Consequently, the U.S. Food and Drug Administration issued a drug bulletin recognizing DES as a ▶transplacental carcinogen, and banned its use during pregnancy (▶Carcinogen). Since then, DES exposure has been observed to cause a range of teratogenic and neoplastic changes in humans and animals. It is used now mainly for treatment of a small subset of hormonally responsive refractory cancers. However, DES exposure can serve as a model for evaluating the potential effects of xenoestrogens (▶Hormonal carcinogenesis; ▶estrogenic hormones). Therefore, its investigation remains important and

Diethylstilbestrol. Table 1

DES Mothers DES Daughters

DES Sons

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should not be limited to the study of the consequences of a specific, unintentionally deleterious administration. Animal Studies DES has been studied extensively in animal models. In the Syrian hamster model, exposure to DES induces neoplasms of the liver and kidney, as well as aneuploidy (particularly chromosome gains) in the renal neoplasms (▶Aneuploidy, ▶chromosome instability). DES exposure in rats elicits tumors of the reproductive tract, pituitary and mammary glands. In addition, Green and colleagues have observed that DES metabolites produce DNA adducts (▶Adducts to DNA) and, ultimately, cancer in the breast of female ACI rats. Tumors of the reproductive tract and mammary glands are seen in the murine model as well, along with alterations in the genetic pathways governing uterine differentiation. Data from Newbold and colleagues suggest that an increased susceptibility to tumor formation is transmitted along the maternal lineage to subsequent generations, both male and female. Thus, not only is the developing organism sensitive to the endocrine-disrupting chemical, but transgenerational effects are plausible as well. Neoplastic Effects in Humans The only increased risk of hormone-dependent cancers observed in women who took DES during pregnancy (▶DES mothers) is ▶breast cancer (Table 1). Hatch and colleagues found that DES mothers had a 30% increased rate of breast cancer compared to the general population. In contrast, DES daughters have an increased risk of two types of hormone-dependent cancers, clear cell adenocarcinoma of the vagina and cervix (mentioned above) and breast cancer (▶Breast cancer). Clear cell adenocarcinoma of the vagina and cervix generally presents in these women when they are in their teens and twenties; however, because some women have been diagnosed in their thirties and forties, concerns have arisen about whether

Effects of diethylstilbestrol exposure Non-neoplastic effects

Neoplastic effects

Increased risk of • Adverse pregnancy outcomes Increased risk of • Adverse pregnancy outcomes • Infertility • Reproductive tract structural abnormalities • Vaginal adenosis Increased risk of • Epididymal cysts • Cryptorchidism • Testicular hypoplasia • Semen and sperm abnormalities

Increased risk of • Breast cancer Increased risk of • Clear-cell adenocarcinoma of vagina and cervix • Breast cancer over age 40

No increased risk of hormone-related cancers

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another increase in risk will occur as DES daughters approach the age at which this type of cancer is seen in the general population (the postmenopausal period). Until recently, there was a paucity of information on breast effects in DES daughters. However, the National Cancer Institute’s Continuation of Follow-Up of DESExposed Cohorts has proven a rich source of information to study the long-term effects of in utero estrogen exposure in humans. These cohorts include over 4,000 women who had documented in utero exposure to DES and more than 2,000 unexposed women from the same record sources; all have been followed from 1994 or earlier. As women exposed in utero to DES have begun to reach the ages at which breast cancer is more common, it appears that these women have an increased risk. In the most recent data from the National Cancer Institute collaborative follow-up study of DES health effects (Continuation of Follow-Up of DES-Exposed Cohorts), Palmer and colleagues found that at ages 40 and older, DES daughters had double the risk of breast cancer of unexposed women; no association was seen prior to age 40. To date, males exposed in utero to DES (▶DES sons) do not exhibit an increase risk of developing hormonerelated cancers. However, DES sons do display nonneoplastic abnormalities (see below) that place then at increased risk of developing testicular cancer regardless of DES exposure (▶Testicular cancer). Non-Neoplastic Effects in Humans In utero exposure to DES has been shown to elicit a variety of non-neoplastic reproductive tract abnormalities, including structural cervical, vaginal, or uterine abnormalities, in addition to changes in the vaginal epithelium such as adenosis (see Table 1). DES dosage and the stage of pregnancy during which the drug was administered appears to be directly linked to the severity of the adenosis, with the most severe manifestations seen in DES daughters whose mothers took the drug during their first trimesters. It is unclear whether these areas of adenosis progress to vaginal clear cell adenocarcinoma. DES daughters have an increased risk of poor pregnancy outcomes, such as ectopic pregnancy or miscarriage, and also have a higher incidence of infertility than the general population. DES sons are more likely than unexposed men to exhibit genital abnormalities such as epididymal cysts, cryptorchidism, and testicular hypoplasia. Although DES sons show an increased incidence of semen and sperm abnormalities, they have not demonstrated an increased risk of infertility, but this is still under investigation. Mechanism of Toxicity The mechanism by which estrogens in general, and DES in particular, exert their toxic and carcinogenic

effects is not fully understood. Both proliferative and genotoxic mechanisms have been postulated. Classically, estrogen exerts its effects through interaction with the estrogen receptor α (ERα), which stimulates cell proliferation and inhibits apoptosis (▶Estrogen receptor). ERα may also interact with other receptors (such as ERβ, insulin-like growth factor 1 receptor and epidermal growth factor receptor) to influence proliferation, or may act through non-genomic pathways, since it is found in non-nuclear subcellular fractions such as the plasma membrane and the mitochondria. An alternative or additional mechanism that may mediate estrogen’s and perhaps DES’ toxic effects is through the metabolites’ genotoxic capacity. ▶Estrogens, and specifically DES, can be oxidatively metabolized into potentially genotoxic intermediates. Estrogen and its metabolites have been reported to induce DNA damage (▶DNA damage), manifesting as ▶allele imbalance and ▶DNA amplification in human breast epithelial cells in vitro (▶Amplification). DES metabolites have been reported to produce DNA adducts and cancer in mammary glands of female rats. DES is a strong mitotic inhibitor in cell lines, blocking equatorial plate formation, tubulin polymerization, and spindle assembly. This may, in turn, induce ▶aneuploidy. Tumors associated with DES exposure exhibit ▶genetic instability, such as whole and partial chromosome gains in vitro and in vivo, in the Syrian hamster model. ▶Microsatellite instability has been reported in human vaginal clear cell adenocarcinomas associated with in utero DES exposure, as well as in murine endometrial carcinomas after DES treatment. In contrast to the substantial microsatellite instability seen in human vaginal clear cell adenocarcinomas associated with in utero DES exposure, breast neoplasms in DES daughters do not exhibit an increased amount of microsatellite instability. Breast tumors of DES mothers have not been investigated. In fact, little microsatellite instability was observed in breast tumors in both exposed and unexposed women, which is consistent with previous results from unselected human breast cancers, confirming that microsatellite instability is unusual in human breast cancers and suggesting that prenatal DES exposure does not affect ▶DNA mismatch repair mechanisms in the breast. Similarly, equivalent amounts of allele imbalance have been observed in breast tissue regardless of exposure, which differs from findings in animal models and in vitro systems. Therefore, the effect of in utero DES exposure may be tissue, timing and/or species specific, as is the case with other hormonal agents such as ▶tamoxifen, which has variable effects on human endometrium and mammary tissue. It remains under investigation as to whether the potential effects of in utero DES exposure on human breast carcinogenesis

Diffuse Large B-Cell Lymphoma

are mediated by enhanced proliferation, by alternative genotoxic effects, or by other pathways entirely.

Summary The unfortunate consequences of DES administration to pregnant women have yielded clinical and scientific insights into estrogen’s effects on developing and mature tissues. Its continued investigation should provide additional clinical and mechanistic information about these effects, and have relevance to understanding the effects of exposure to xenoestrogens.

References 1. Giusti RM, Iwamoto K, Hatch EE (1995) Diethylstilbestrol revisited: a review of the long-term health effects. Ann Int Med 122:778–788 2. Larson PS, Ungarelli RA, De Las Morenas A et al. (2006) In utero exposure to diethylstilbestrol (DES) does not increase genomic instability in normal or neoplastic breast epithelium. Cancer 107(9):2122–2126 3. Newbold RR, Padilla-Banks E, Jefferson WN (2006) Adverse effects of the model environmental estrogen diethylstilbestrol are transmitted to subsequent generations. Endocrinology 147(6 Supp1):S11–S17 4. Schrager S, Potter BE (2004) Diethylstilbestrol Exposure. Am Fam Physician 69:2395–2402 5. Yager JD, Davidson NE (2006) Estrogen carcinogenesis in breast cancer. New Eng J Med 354:270–282

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dramatically during differentiation, but the genetic material remains the same, with few exceptions.

Diffuse, Small Cleaved Cell Lymphoma ▶Mantle Cell Lymphoma

Diffuse Large B-Cell Lymphoma M ICHAEL B. M ØLLER Department of Pathology, Division of Hematopathology, Odense University Hospital, Odense, Denmark

Synonyms KIEL classification: Centroblastic, B-immunoblastic, B-large cell anaplastic; Working Formulation: Diffuse large cell, Large cell immunoblastic, Diffuse mixed small and large

Definition

Diferuloylmethane ▶Curcumin

Diffuse large B-cell lymphoma is a ▶non-Hodgkin lymphoma entity composed of malignant large lymphoid cells with blastic morphologic features, expression of B-cell markers, and with a diffuse growth pattern. The postulated cells of origin are germinal or post germinal centre B-cells. This lymphoma entity is morphologically, clinically and genetically heterogeneous.

Characteristics

Differentiation Definition A process whereby a cell undergoes morphological transition from a cell which is capable of undergoing cellular division to a state where the cell becomes postreplicative. Often accompanied by changes in cellular function. The process during which young, immature (unspecialized) cells take on individual characteristics and reach their mature (specialized) form and function. Describes the process by which cells acquire a “type or assignment.” The morphology of a cell may change

Diffuse large B-cell lymphoma is the most common type of lymphoma comprising 30–40% of adult nonHodgkin lymphomas and approximately 20% of non-Hodgkin lymphomas in childhood and adolescence. Diffuse large B-cell lymphoma can be seen in all age groups, but the incidence increases with age. The median age at diagnosis is approximately 65 years. There is a slight male preponderance. In most patients the tumor resides in lymph nodes, but 40% of patients have predominant extranodal disease. Virtually any extranodal site may be involved, but the most frequently involved organs include the gastrointestinal tract, soft tissue, thyroid, skin, central nervous system, liver, bone, gonads, breast, kidney, lung and salivary glands. So-called transformed diffuse large B-cell

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lymphomas arise from indolent lymphomas such as small lymphocytic lymphoma/▶chronic lymphocytic leukaemia, ▶marginal zone B-cell lymphoma and ▶follicular lymphoma. The aetiology of most diffuse large B-cell lymphoma cases is unclear. However, patients with immunodeficiency such as human immunodeficiency virus-infected patients or patients receiving immunosuppressive therapy are at increased risk of developing lymphoma. Diffuse large B-cell lymphoma is the most frequent lymphoma arising in this setting, and these lymphomas are often ▶EBV associated. Diagnosis The typical clinical presentation of diffuse large B-cell lymphoma patients with nodal disease is rapidly enlarging ▶lymphadenopathy. Patients with extranodal presentation of the disease often have symptoms related to dysfunction of the involved organ(s). One third of the patients have ▶B symptoms. Approximately half of the patients have localized lymphoma, i.e. Ann Arbor stage I or II, and the remainder have disseminated disease. The morphological diagnosis is based on the World Health Organization Classification. Diffuse large B-cell lymphoma typically consists of a diffuse proliferation of medium-sized to large transformed B-lymphoid cells with a nucleus at least twice the size a normal lymphocyte. These large cells are a mixture of cells that resemble either the centroblasts or the immunoblasts that normally reside in reactive germinal centres. The diffuse large B-cell lymphoma entity is morphologically quite heterogeneous with several morphologic variants. The two most common variants are the centroblastic variant which is dominated by centroblasts and the immunoblastic variant with >90% immunoblasts. In the T-cell/histiocyte rich variant the majority of cells are small T-cells and histiocytes and less than 10% of the cells are neoplastic B-cells. An anaplastic variant of diffuse large B-cell lymphoma is recognized which has a similar morphology and ▶CD30 expression as the T-cell lymphoma anaplastic large cell lymphoma. However, anaplastic diffuse large B-cell lymphoma is clinically and genetically unrelated to anaplastic large cell lymphoma. Other rare variants include plasmablastic diffuse large B-cell lymphoma and diffuse large B-cell lymphoma with expression of full-length ALK. Diffuse large B-cell lymphoma cells usually express CD45 and B-lymphoid markers such as CD19, CD20, CD22, CD79a and PAX5. The proliferation rate is high with most cases expressing the proliferation associated marker ▶Ki-67 in >40% of the tumor cells. In some tumors >95% of the malignant cells express Ki-67. The prognosis is variable with a 5-year overall survival rate for all patients of 45–50%. The International Prognostic Index is widely used for prognostication

of diffuse large B-cell lymphoma. It consists of five clinical factors (age, stage, performance score, serum lactate dehydrogenase, number of extranodal sites involved) each with independent prognostic value regarding overall survival. The index allocates 35– 40% of the patients to the low risk group with a 5-year overall survival rate of >70%, while 15–20% of the patients have high risk lymphoma and a 5-year overall survival rate of 150) accomplish the common functions of recognition, incision, excision, degradation, polymerization and ligation by associating in different combinations and acting to remove the damage during a period of cell cycle arrest. ▶Carcinogen Macromolecular Adducts ▶Mismatch Repair in Genome Stability ▶Toxicological Carcinogenesis

DNA Photoproduct Definition Type of DNA damage formed after excitation of the DNA molecule by solar ▶ultraviolet light and kovalent

DNA Repair and Damage Processing ▶DNA Damage-Induced Apoptosis

DNA Vaccination

DNA Repair Capacity Definition

DRC; All living organisms have a ▶DNA repair system to protect the integrity of genomic DNA against constant assault from a plethora of endogenous and exogenous sources. DNA repair capacity (DRC) has often been used in epidemiologic studies as an indicator of the functionality of an individual’s DNA repair system. Reduced DRC is associated with increased cancer risk. ▶Mutagen Sensitivity

DNA Replication

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DNA Vaccination H OLGER N. LODE Charité University Medicine Berlin, Pediatrics, Berlin, Germany

Synonyms Genetic immunization

Definition Vaccination with deoxyribonucleic acid (DNA) against cancer is the most basic type of vaccination that, rather than consisting of the tumor-associated antigen itself, provides genes encoding for the antigen. Once produced in vivo following DNA delivery, the antigen is presented to the immune system inducing an antigen specific immune response. This response is augmented by the immunological properties of the DNA itself, mediated by unmethylated ▶CpG sequences. This essay reviews accomplishments and challenges in this area.

Definition Duplication of chromosomes by synthesis of DNA restricted to the S-phase of the ▶cell cycle. ▶Mitosis

DNA Topoisomerases II Definition Are the essential enzymes that play a role in virtually every cellular DNA process catalyzing the transient breaking and rejoining of DNA strands. They are able to cleave both DNA strands at the same time, allowing one DNA duplex to pass through another. ▶Nutraceuticals ▶Topoisomerases ▶Topoisomerases II

DNA Undermethylation ▶Hypomethylation of DNA

Characteristics DNA vaccination represents a young field in cancer immunotherapy. It started with the observation that injection of plasmid DNA into a mammal resulted in the synthesis of the encoded protein. The unformulated or “naked” plasmid DNA containing a simple expression cassette, consisting of a promoter functioning in mammalian cells and of a gene encoding for a protein antigen, was injected into the muscle of mice. The subsequent induction of antigen specific ▶CD8+ cytotoxic T-cells and antibodies was effective in protecting mice from challenges with the pathogenic agent expressing the antigen. This observation was surprising, given the low amount of antigen produced, the apparent lack of transfection of professional antigen presenting cells (APC) and the absence of any replicative step. The robustness of the technology was demonstrated for a variety of disease models. Mechanisms of Action The method of DNA delivery critically affects the mechanisms involved in the induction of an immune response. Intramuscular injection of plasmid DNA leads to in vivo transfection of myocytes. Mechanistic studies revealed that antigen specific immune responses following intramuscular injection of DNA is a result from ▶cross priming. This mechanism describes production of the antigen by the myocyte and subsequent uptake and presentation by professional APCs. This was clearly demonstrated in bone marrow chimeric mice and in experiments with transfected myoblasts. In both systems,

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the induction of an antigen specific immune response depended on the antigen presentation by APCs, and not by the myocyte. The transfer of the antigen from myocyte to APC follows different routes, ranging from uptake of secreted protein, processed peptide alone or with heatshock proteins or apoptotic bodies by APCs. The transfer of DNA into the myocyte and subsequent induction of an antigen specific immune response can be largely improved by in vivo ▶electroporation. The technique involves the application of an electric field around the DNA injection site. There are also needle free systems available, injecting DNA in solution using high pressure liquid jets. Clinical devices were developed by the pharmaceutical industry for application in humans, which are well tolerated. Bombardment of the epidermis with plasmid loaded onto gold particles using the ▶gene gun directly transfers DNA into APCs of the skin called ▶Langerhans cells. Once the protein antigen is expressed, professional antigen presentation is mediated by this cell type. Efficient induction of an immune response occurs after migration of these APCs from the skin into regional lymph nodes.

Gene transfer of plasmid DNA into APCs is also accomplished by the use of life attenuated bacteria such as salmonella typhimurium or listeria monocytogenes. In both cases, these micro organisms are infectious, but not pathogenic, and therefore serve as in vivo carrier systems for plasmid DNA vaccines. After in vivo application, ▶Peyer patches and the spleen become infected. Subsequently, the carrier microbes die due to distinct mutations in their genome and liberate multiple copies of the plasmid DNA vaccines in these ▶secondary lymphoid organs. There, the DNAvaccines are expressed by APCs leading to the induction of an antigen specific immune response. A central role for induction of an immune response by DNA vaccines is antigen expression by APCs and subsequent presentation to CD8+T-cells, ▶CD4+ T-cells and B-cells (Fig. 1). Adjuvant Activity of DNA Plasmid DNA derived from bacterial expression systems naturally contain unmethylated DNA sequences called CpG motifs. These sequences bind to Toll-like receptor 9 and are strong activators of ▶innate immunity. This

DNA Vaccination. Figure 1 Mechanisms involved in the generation of antigen specific humoral and cellular immune responses upon DNA vaccination. Antigen specific activation of cytolytic T lymphocytes (CD8+T-cells) occurs after proteasome dependent antigen processing of intracytoplasmic proteins into peptides associated with newly synthesized MHC class I molecules. MHC class I/peptide complexes are presented on the surface of APCs in conjunction with costimulatory molecules to CD8+T cells. The activation of ▶CD4+T-cells is primarily achieved by exogenous protein antigens taken up by the endolysosomal compartment. After degradation, peptides associate with MHC class II molecules which are then translocated to the cell surface. Specific CD4+ helper T cells recognize these MHC class II/peptide complexes and are activated to produce cytokines. These cytokines have multivarious activities helping B-cells to mature into antibody producing plasma cells and CD8+T-cells to transform into cytolytic effector cells. For antibody responses, B-cells recognize and respond to antigens that are either present extracellularly or exposed extracellularly by being transmembrane proteins.

DnaJ (Hsp40) Homolog Subfamily C Member 15

receptor is also expressed on APCs leading to improved antigen processing and presentation as well as the release of pro-inflammatory cytokines and chemokines that help to shift ▶adaptive immunity responses from ▶Th2 immune response to ▶Th1 immune response. Th1 responses are required for most effective anti-tumor immunity. Therefore, CpG motifs in the DNA vaccine backbone can be considered endogenous adjuvants linking innate immunity with ▶adaptive immunity, which provides for robust and long lasting antigen specific immune responses. Tailoring Immune Responses by DNA Vaccine Design In order to improve antigen specific immune responses, the versatility of DNA vaccine design allows for the simultaneous expression of antigen, co-stimulatory molecules and chemoattractants. These include cytokines, chemokines, molecules of the B7 family and CD40 ligand. The design of the protein antigen itself can be altered to be secreted for induction of B-cell responses or to be targeted into the endopasmatic reticulum or the proteasomal degradation pathway for the generation of T-cell epitopes. Protein antigens can be redesigned as mini genes only encoding for immunodominant peptide antigens. In summary the versatility of DNA vaccines allows for specific tailoring of an optimized immune response following a rational vaccine design. Formulation The formulation of DNA vaccines to improve antigen specific immune responses includes transfectionfacilitating lipid complexes, nanoparitcles and classical adjuvants. Lipid complexes are varying combinations of DNA with cationic lipids. Microparticles are generated with DNA entrapped in biodegradable poly-lactide-coglykolactide or complexed with non-ionic block copolymers or polycations. Among the classical adjuvants, aluminium phosphate is noteworthy for its effectiveness and simplicity of preparation. Microparticles appear to improve the trafficking of DNA to APCs by facilitating the transfer of DNA into regional lymphnodes. Mixed Modality Vaccines A very promising strategy that is entering clinical trials is to combine DNA vaccines with other gene delivery systems. This is based on observations that if DNA encoding an antigen is given as a prime followed by another gene-based vector system as a boost such as recombinant viruses encoding the same antigen, most optimal immune responses and protection are achieved. The responses are significantly greater than using DNA or the virus for both the prime and the boost or if the order of the administration is reversed.

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Results from Clinical Trials First generation DNA vaccines have been evaluated clinically as a therapeutic vaccine approach for cancer. These vaccines encoded for viral epitopes from transforming viruses, self-antigens expressed on tumors, and tumor specific antigens. In most trials so far, the plasmid DNA was injected intramuscularly, intradermaly or intranodaly. Antigen specific humoral and cellular responses were observed in human cancer trials. However, this did not translate into clinical responses in the trial patient populations characterized by large tumor burden and progressive disease. The clinical trials so far have proved the principle that immune responses can be generated in humans. They also highlight the need to apply strategies to increase the potency of the technology as outlined above and to generate second generation DNA vaccines for future application in cancer patients. In summary, DNA vaccines hold great potential as immunotherapeutic tools to prevent and treat human cancer. Their advantages include cost effectiveness, versatility, safety, stability, ease of construction and mass production and most importantly ability to induce robust humoral and cellular immune responses. Lack of success in early clinical trials so far is similar to early clinical results with treatments based on monoclonal antibodies which are now established cancer therapeutics. To push for success, the next generation of DNA vaccines will have to incorporate multiple strategies to enhance plasmid DNA immunogenicity. Additional avenues may involve exploring the possibilities of combining adoptive cell therapies with DNA vaccines such as ex vivo gene transfer into autologous dendritic cells.

References 1. Liu MA, Ulmer JB (2005) Human clinical trials of plasmid DNA vaccines. Adv Genet 55:25–40 2. Donnelly JJ, Wahren B, Liu MA (2005) DNA vaccines: progress and challenges. J Immunol 175:633–639 3. Fest S, Huebener N, Weixler S et al. (2006) Characterization of GD2 peptide mimotope DNA vaccines effective against spontaneous neuroblastoma metastases. Cancer Res 66:10567–10575 4. Lowe DB, Shearer MH, Jumper CA et al. (2007) Towards progress on DNA vaccines for cancer. Cell Mol Life Sci 64:2391–2403

DnaJ (Hsp40) Homolog Subfamily C Member 15 ▶Methylation-Controlled J Protein

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DNAJC15

DNAJC15 ▶Methylation-Controlled J Protein

DNAJD1 ▶Methylation-Controlled J Protein

DNF15S2 ▶Macrophage-Stimulating Protein

DNMTs Definition DNA methyltransferase enzymes; Responsible for maintenance of ▶methylation as well as de novo methylation. ▶Epigenetic Gene Silencing

Docetaxel R ICARDO H ITT 1 , C RISTINA R ODRI´ GUEZ 2 1

Medical Oncology Service, University Hospital 12 de Octubre, Madrid, Spain 2 Human Cancer Genetics Programme, Spanish National Cancer Center (CNTO), Madrid, Spain

Synonyms ▶Taxotere

Definition Docetaxel is a new class of anticancer agent that exerts the cytotoxic effects on microtubules. It is a semisynthetic drug with significant activity in a broad range

of tumor types that are generally refractory to conventional therapies, including chemotherapyresistant epithelial ▶ovarian cancer, ▶breast cancer, ▶non-small cell lung cancer, head and neck cancer, ▶bladder cancer, and ▶gastric cancer.

Characteristics Docetaxel is derived semisynthetically from 10-deacetylbaccatin III, is more water soluble than ▶paclitaxel and is more potent antimicrotubule agent in vitro. Mechanism of Action: Docetaxel induces polymerization of ▶tubulin, ▶microtubule bundling in cells, formation of numerous abnormal mitotic asters. The cytotoxic effects of docetaxel are also severalfold greater than paclitaxel in vitro and in tumor xenografts. Docetaxel inhibit proliferation of cells by inducing a sustained mitotis block at the metaphase–anaphase boundary at much lower concentrations than those required to increase microtubule polymer mass and microtubule bundle formation. These inhibitory effects at low drug concentrations are associated with the formation of an incomplete metaphase plate of chromosomes and an arrangement of spindle microtubules resembling the abnormal organization that occurs at low concentrations of the ▶vinca alkaloids. Docetaxel primarily block cell-cycle traverse in the mitotic phases and prevents the transition from Go to S phase. The inhibitory effects in the nonmitotic cellcycle phases include the disruption of tubulin in the cell membrane and direct inhibitory effects on the disassembly of the interphase cytoskeleton. These effects may result in the disruption of many vital cell functions such as locomotion, intracellular transport, and transmission of proliferative transmembrane signals. After disruption of microtubules and other processes by docetaxel, the precise means by which cell death occurs is not clear. Morphologic features and a DNA fragmentation pattern (▶nucleosomal DNA fragments) that are characteristic of programmed cell death, or apoptosis, in docetaxel-treated cells indicate that this taxane trigger apoptosis as do many other chemotherapeutic agents. Whether docetaxel-induced ▶apoptosis requires a functional ▶p53 pathway is unclear and probably depends on the cell line under study. The consensus seems to be that in most cell lines, disruption of p53 has little effect on drug sensitivity. Mechanism of Resistance: Selection of taxaneresistant cells in vitro is associated with changes in β-tubulin isotype expression. Six different isotypes of β-tubulin are expressed in nonmalignant tissues, with the class I isotype comprising 80–99% of cellular β-tubulin. The β III isotype increase the dynamic instability of microtubules, impairs rates of microtubule assembly, and increases resistance to taxanes.

Docetaxel

A second mechanism of acquired taxane resistance fits the general pattern of ▶MDR. The particular species of Pgp found in taxane-resistant murine ▶macrophages is similar, but not identical, to that found in ▶vinblastine- and ▶colchicine-resistant cells derived from the same parental line. These cells are cross-resistant with many other natural products, and resistance to docetaxel conferred by ▶mdr-1 can be reversed by many classes of drugs, including ▶tamoxifen, ▶cyclosporine A, antiarrhytmic agent. Other changes in tumor cells selected for drug resistance have included upregulation of ▶caveolin-1, a principal component of membrane-derived vesicles involved in transmembrane transport of small molecules and in intracellular signaling. Pharmacokinetics The single 1-hour infusion every 3 weeks is the most common administration of docetaxel. The ▶pharmacokinetics behavior on 1 or 2 h schedules is linear at doses of 115 mg/m2 or less and optimally fits a threecompartment model. Docetaxel binds rapidly and avidly to plasma proteins (>90%), especially to albumin, α1acid glycoprotein, and lipoproteins. In addition, peak plasma concentrations generally exceed levels required to induce relevant biologic effects in vitro. Limited information is available about the distribution of docetaxel in humans. Immediately after treatment, tissue uptake of radioactivity is highest in the liver, bile, and intestines, a finding that is consistent with substantial hepatobiliary extraction and excretion. High levels of radioactivity are also found in the stomach, which indicates the possibility of gastric excretion, as well as in the spleen, bone marrow, myocardium, and pancreas. Docetaxel has hepatic metabolism and biliary excretion and urinary excretion accounts only 2%. Approximately 80% of the administered dose of total radioactivity is excreted in the feces within 7 days after treatment, with the majority of excretion occurring in the first 48 h. In the hepatic ▶cytochrome P450-mixed function, oxidases are responsible for the bulk of drug metabolism, and CYP3A, CYP2B, and CYP1A isoforms may play major roles in biotransformation. The main metabolic pathway consists of oxidation of the tertiary butyl group on the side chain at the C-13 position of the taxane ring as well as cyclization of the side chain. Toxicity ▶Neutropenia is the principal toxicity of docetaxel. At dose of 100mg/m2, neutrophil count nadirs are 10% of estimated total natural production of carotenoids. Further, fucoxanthin is the characteristic pigments of brown seaweeds (phaeophyceae) which are the largest occurring group among seaweeds. In South East Asian countries, some brown seaweeds containing fucoxanthin are often used as a food source (Fig. 1).

Characteristics Effect on Cancer Cell Growth Cell proliferation is the key in promoting and further progression of carcinogenesis. In a study screening the antiproliferative activity of seaweed extracts on tumor cells, fucoxanthin from the brown seaweed,

a1-6 Fucosyltransferase Definition Fut8; A glycosyltransferase that transfers fucose onto the innermost N-acetylglucosamine in N-glycans via an

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Fucoxanthin. Figure 1 Structure of fucoxanthin.

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Undaria pinnatifida, is found to be the active principle. When several cancer cells are cultured with fucoxanthin, the cell viability decreases. The antiproliferative activity of fucoxanthin on human cancer cells is generally higher than other carotenoids. Fucoxanthin exhibits the higher activity than β-carotene and astaxanthin on human ▶colon cancer cells (Caco-2, HT-29, DLD-1) and human leukemia cell (HL-60). Treatment of Caco2 cells with fucoxanthin induces morphological changes such as a diminished size and rounded shape. Also, the cell membrane has shrunk with a condensed cytoplasm. The stronger inhibitory effect of fucoxanthin is found in human prostate cancer cells (PC-3, DU 145, LNCap). In this case, the effect of 15 kinds of carotenoids (phytoene, phytofluene, ξ-carotene, lycopene, α-carotene, β-carotene, β-cryptoxanthin, canthaxanthin, astaxanthin, capsanthin, lutein, zeaxanthin, vioaxanthin, neoxanthin, and fucoxanthin) present in foodstuffs is evaluated on the grown of the cancer cell lines. Among the carotenoids, neoxanthin and fucoxanthin cause a remarkable reduction in the growth of prostate cancer cells. Apoptosis There is a wealth of information pertaining to apoptosis in anticancer research. ▶Macrophages recognize the cells undergoing apoptosis and engulf them without adversely affecting or damaging the neighboring cells. Apoptosis-inducing activities provide a novel means of ▶chemoprevention and chemotherapy in the treating cancer. In an investigation on the apoptosis-inducing activity of fucoxanthin, a DNA ladder, which is a characteristic feature of apoptotic cells, is clearly visible in HL-60 cells treated with fucoxanthin. Similar results can be obtained with ▶camptothecin, which is known to be a strong apoptosis-inducing agent. The fragmented DNA content designated as the enrichment factor as estimated by sandwich ▶ELISA, increases with the concentration of fucoxanthin in the medium. DNA fragmentation, indicating by in situ ▶TUNEL (Terminal deoxynucleotidyl transferase-mediated dUTP nick endlabeling), reveals that fucoxanthin reduces cancer cell viability by inducing apoptosis. Some apoptosisinducing agents are known to arrest a specific cell phase. Therefore, it can be presumed that fucoxanthin affects cell cycle. Mechanism Fucoxanthin suppresses expression of ▶Bcl-2 protein, which is responsible for suppression of programmed cell death as a survival factor. This is indicative of the fact that downregulation of Bcl-2 protein may contribute to fucoxanthin-induced apoptosis in cancer cells. DNA fragmentation induced by fucoxanthin is partially inhibited by a ▶caspase inhibitor Z-VAD-fmk. Further, fucoxanthin also regulates the redox signals,

and then facilitates the progression of apoptosis through Bcl-2 protein suppression, and caspase-dependent and-independent pathway. Combination with Troglitazone ▶Troglitazone is known to inhibit cell growth and induce apoptosis through the activation of ▶PPARγ. Oral administration of troglitazone inhibits the early stage of colon tumorigenesis. On the other hand, preincubation of cancer cells with fucoxanthin remarkably enhances the effect of troglitazone. Therefore, the combined action of PPARγ ligand such as troglitazone and fucoxanthin is more effective on chemoprevention of cancer than troglitazone, and possibly other agents, alone.

References 1. Hosokawa M, Wanezaki S, Miyauchi K et al. (1999) Apoptosis-inducing effect of fucoxanthin on human leukemia cell line HL-60. Food Sci Technol Res 5:243–246 2. Kotake-Nara E, Kushiro M, Zhang H et al. (2002) Carotenoids affect proliferation of human prostate cancer cells. J Nutr 131:3303–3306 3. Hosokawa M, Kudo M, Maeda H et al. (2005) Fucoxanthin induces apoptosis and enhances the antiproliferative effect of the PPARγ ligand, troglitazone, on colon cancer cells. Biochim Biophys Acta 1675:113–119

Fulvestrant A NTHONY H OWELL CRUK Department of Medical Oncology, University of Manchester, Christie Hospital NHS Trust, Manchester, UK

Synonyms Faslodex

Definition Was originally known as ICI 182,780 and is now marketed by AstraZeneca under the trade name Faslodex®. The chemical formula of fulvestrant is 7α-[9-(4,4,5,5,5-pentafluoro-pentylsulfinyl)nonyl]estra1,3,5(10)-triene-3,17β-diol. Fulvestrant, a steroidal 7α-alkylsulfinyl analog of 17β-▶estradiol, is an ▶estrogen receptor antagonist with no agonist effects. It is used as an endocrine treatment for postmenopausal women with hormonesensitive ▶advanced breast cancer.

Fulvestrant

Characteristics Mode of Action Currently, more than one million women worldwide are diagnosed with ▶breast cancer each year. In postmenopausal women, approximately 75% of breast tumors are hormone sensitive, expressing the estrogen receptor and/or progesterone receptor, and are stimulated to grow in the presence of estrogen. To understand the treatments for hormone-receptor positive breast cancer, we must first understand the role of ▶estrogen, a natural circulating hormone that has been shown to drive tumor growth. Once estrogen has bound to the ▶estrogen receptor, the receptors dimerize, before translocation to the nucleus, where the complex binds to specific DNA sequences (estrogen response elements) in target genes. Activating functions on the estrogen receptor (AF1 and AF2) recruit protein cofactors, allowing the transcription and expression of the target genes, resulting in increased cell division and tumor progression (Fig. 1). As an estrogen receptor antagonist, fulvestrant exhibits a high estrogen receptor binding affinity and produces a complete receptor blockade. Following binding of fulvestrant, dimerization of the estrogen receptor is impaired and the bound receptor is rapidly

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degraded, a process unique to fulvestrant amongst the ▶antiestrogen receptor agents. Nuclear localization is also disrupted, and both AF1 and AF2 are inactivated, leading to complete abrogation of estrogen signaling through the estrogen receptor (Fig. 1). This also means that fulvestrant has no estrogen agonist activity, which is important, since even partial agonist activity can lead to an increased incidence of endometrial abnormalities and cancer. As a steroidal analog of estradiol, fulvestrant is structurally distinct from the non-steroidal ▶tamoxifen, a selective estrogen receptor modulator, which is also used in the treatment of hormone receptor-positive breast cancer (Fig. 2). Although tamoxifen binds to the estrogen receptor, and permits dimerization and translocation, AF2 is not activated and so the transcription of estrogen-responsive genes is blocked (Fig. 1). However, this block is not complete, since AF1 continues to function, and therefore tamoxifen retains partial agonist activity, with the associated endometrial risks. Fulvestrant, with its unique mode of action, is fundamentally different from the third-generation ▶aromatase inhibitors such as anastrozole, letrozole or exemestane, which are used to treat breast cancer in an increasing proportion of postmenopausal women.

Fulvestrant. Figure 1 The mode of action of fulvestrant, tamoxifen and estradiol. (Reproduced from Dowsett et al. [2, Fig. 1]. Breast Cancer Res Treat 93:S11–S18 (2005). With kind permission of Springer Science and Business Media.)

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Fulvestrant. Figure 2 Chemical structure of fulvestrant.

Fulvestrant. Figure 3 Scheme showing how different endocrine therapies (fulvestrant, tamoxifen, aromatase inhibitors) work in breast cancer.

Following the menopause, most endogenous estrogen is produced via the conversion of adrenal androgens in peripheral tissues. Aromatase inhibitors work by blocking the aromatase enzyme, which catalyzes this conversion, thus reducing the levels of circulating estrogen available to bind to the estrogen receptor (Fig. 3). Current Utilization of Fulvestrant While treatment for hormone-sensitive early breast cancer aims to remove the tumor by surgical or radiological techniques followed by adjuvant ▶endocrine therapy, treatment for advanced disease is essentially palliative rather than curative, with the emphasis on extending life and preserving quality of life amongst patients. In postmenopausal women with hormone-sensitive advanced breast cancer, it is now standard practice to employ a sequence of endocrine agents, to slow the progression of the disease and delay for as long as possible the requirement for cytotoxic chemotherapy treatment. Consequently, novel endocrine agents that are both effective and lack crossresistance with existing therapies are required to extend the duration of the sequential treatment regimens. Fulvestrant is a new therapeutic option that can be added to the hormonal treatment sequence. Results from Phase III clinical trials showed that in postmenopausal

women with hormone-responsive advanced breast cancer who had progressed on previous antiestrogen therapy, fulvestrant was at least as effective as anastrozole, in terms of time to progression, objective response rates and survival. This evidence led to its regulatory approval and fulvestrant is currently licensed for use as a second-line endocrine treatment agent for advanced breast cancer after progression or recurrence on an antiestrogen. More recently, Phase III trial data have confirmed fulvestrant activity in the postaromatase inhibitor setting. Reflecting all these data, fulvestrant is considered in the National Comprehensive Cancer Network guidelines as an option after the failure of first-choice endocrine treatment (tamoxifen or an aromatase inhibitor). Thus, fulvestrant is a valuable addition to the endocrine armory. Importantly, due to its unique mechanism of action, analyses of patients progressing on fulvestrant have demonstrated continued sensitivity to subsequent endocrine therapies, indicating that fulvestrant lacks cross-reactivity with the ▶aromatase inhibitors and tamoxifen. Administration and Tolerability Instead of the daily oral dosing used with other endocrine therapies, fulvestrant is given as a monthly

Fumarase

250 mg/5 mL intramuscular injection, which provides slow release of the drug and sustained pharmacologic activity over the dosing interval (28 ± 3 days). The injection is well tolerated locally and may also help to assure treatment compliance. Once in the body, fulvestrant is predominantly bound to plasma proteins and metabolized by the liver, with negligible renal excretion, and it is not implicated in clinically significant drug–drug interactions, making it suitable for use in patients receiving polypharmacy for comorbid conditions. Fulvestrant is well tolerated, with most adverse events being mild to moderate in intensity. In clinical trials, the most commonly reported adverse events were nausea, asthenia and pain. Fulvestrant has potential tolerability benefits over some existing treatments, e.g. it is associated with less hot flashes than tamoxifen, and a lower incidence of joint disorders than anastrozole. Future Uses of Fulvestrant In recent years, the third-generation aromatase inhibitors, have been shown to be superior to tamoxifen for the treatment of both early and advanced breast cancer. Treatment guidelines currently recommend that an aromatase inhibitor should be used as either the primary endocrine therapy in postmenopausal women, or after 2–3 years of tamoxifen. However, even in this estrogen-deprived environment, some tumors will become resistant to treatment and begin to progress. Therefore, if cytotoxic chemotherapy is to be further delayed, an alternative endocrine therapy must be used. Indeed, as aromatase inhibitors continue to replace tamoxifen in the first-line setting, it is becoming increasingly important to identify agents that are effective after recurrence or progression on these drugs. As previously described, results from both Phase III and Phase II studies suggest that fulvestrant may be active after progression on aromatase inhibitors. Fulvestrant’s unique mode of action and lack of cross-reactivity also invites the possibility of potentially synergistic combinations with other treatment agents. Preclinical data suggest that the combination of fulvestrant with aromatase inhibitors will offer a more effective anti-tumor effect than either agent alone, and Phase III trials are underway to fully evaluate this treatment strategy. In addition, the epidermal growth factor (EGF) receptor-mediated pathway of gene transcription, which can provide an alternative growth stimulus for breast tumors in the absence of hormone receptors, has also been shown to cross-talk with the estrogen receptor-mediated pathway. This, in turn, has important implications for the development of resistance to endocrine therapy. As fulvestrant increases degradation

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of estrogen receptors, it may limit the potential for cross-talk with other pathways. Combination treatment with fulvestrant and an agent targeting growth factor receptors (such as gefitinib, lapatinib or trastuzumab) may therefore further limit cross-talk and potentially delay the time of onset of treatment resistance. Currently, several clinical trials are ongoing to investigate the activity of such combination therapy in patients with advanced breast cancer. Summary Fulvestrant, a steroidal analog of ▶estradiol, is an effective treatment for postmenopausal women with hormone-sensitive advanced breast cancer who have progressed on previous endocrine therapy. With its unique mode of action, fulvestrant provides a valuable addition to the endocrine treatment sequence, with significant benefits for patients. It is administered as a monthly intramuscular injection, and is well tolerated and associated with few adverse events. Fulvestrant may also have a potential use in combination treatment strategies, as the partner of choice with ▶EGF receptor inhibitors.

References 1. Howell A (2005) Fulvestrant (‘Faslodex’): current and future role in breast cancer management. Crit Rev Oncol Hematol 57:265–273 2. Dowsett M, Nicholson RI, Pietras RJ (2005) Biological characteristics of the pure antiestrogen fulvestrant: overcoming endocrine resistance. Breast Cancer Res Treat 93 (Suppl 1):S11–S18 3. Robertson JF, Osborne CK, Howell A et al. (2003) Fulvestrant versus anastrozole for the treatment of advanced breast carcinoma in postmenopausal women – a prospective combined analysis of two multicenter trials. Cancer 98:229–238 4. Chia S, Gradishar W, Mavriac L et al. (2008) Doubleblind, randomized, placebo-controlled trial of fulvestrant compared with exemestane after prior nonsteroidal aromatase inhibitor therapy in postmenopausal women with hormone receptor-positive, advanced breast cancer: Results from EFECT. J Clin Oncol Published online a head of print March 3, 2008 at http://jco.ascopubs.orglcgi/doi/ 10.1200/jco.2007.13.5822 5. Vergote I, Abram P (2006) Fulvestrant, a new treatment option for advanced breast cancer: tolerability versus existing agents. Ann Oncol 17:200–204

Fumarase ▶Fumarate Hydratase

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Fumarate Hydratase

Fumarate Hydratase S AKARI VANHARANTA , V IRPI L AUNONEN Department of Medical Genetics, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland

Synonyms FH; Fumarase

Definition Fumarate hydratase is an enzyme that functions in the mitochondrial citric acid cycle, catalyzing the reversible hydration/dehydration reaction in which fumarate is converted to malate.

Characteristics The human gene encoding fumarate hydratase is located in the chromosome segment 1q42.3-q43. It consists of ten exons that span over 20 kb of genomic DNA. The transcript is approximately 1.8 kb long and is predicted to encode a 510 amino acid polypeptide. The first exon of FH encodes a signal peptide that directs the protein to the mitochondrion. There the signal peptide is cleaved, and the remaining mature FH protein forms a functional homotetramer in the mitochondrial matrix. Some processed FH is also present in the cytosol, although the function of this cytosolic FH is unclear. In addition to the mitochondrial signal, the processed FH contains other domains such as alpha-helical and lyase domains. The alpha-helixes form a superhelical core for the tetramer. The functionally active FH enzyme converts fumarate to malate. This hydration reaction is a part of the citric acid cycle (also known as the tricarboxylic acid cycle or the Krebs cycle) which is an essential component of cellular carbohydrate metabolism. In the cytosol, fumarate is produced in the urea cycle and therefore FH is connected to protein metabolism as well. FH is well conserved, human FH sharing a 57% amino acid identity with the Escherichia Coli FumC protein, and it belongs to a protein superfamily which includes mostly other enzymes such as aspartase, adenylosuccinate lyase, and arginosuccinate lyase. The first clues as to the role of FH in human disease came from the identification of two siblings that presented with progressive encephalopathy, dystonia, ▶leucopenia, and ▶neutropenia. They had elevated levels of lactate in their cerebrospinal fluid and high fumarate excretion in their urine. A ▶homozygous mutation was discovered in a conserved region of the FH gene in both of these patients. Also, FH deficiency was shown to be present in all tissues studied in the patients, and their healthy parents were shown to carry

the mutation in a heterozygous form. Since then, about 20 families with FH deficiency have been reported in the literature. The symptoms are severe and the affected individuals usually die within a few months of birth. Evidence for yet another role of FH in human disease came from quite a different line of research. The genomic locus harboring the FH gene was independently mapped by genetic linkage analysis to segregate with inherited predisposition to ▶leiomyoma and ▶renal carcinoma; ▶Hereditary leiomyomatosis and renal cell cancer (HLRCC), and to ▶multiple cutaneous and uterine leiomyomatosis (MCUL). Soon after, these two conditions were shown to be variants of the same syndrome and the underlying gene was identified as FH. The tumors showed loss of heterozygosity (▶LOH) and retention of the mutated allele, therefore suggesting that the gene acted as a ▶tumor suppressor. Also, FH enzyme activity was shown to be reduced in the leukocytes and absent in the tumors of mutation carriers. Clinical Features of HLRCC/MCUL Since the first reports indicating the involvement of FH in tumorigenesis, more than 100 families with the HLRCC/MCUL phenotype have been reported in the literature (Fig. 1). Although no population-based studies have been carried out, it seems clear that the prevalence of HLRCC/MCUL is very low. There are reports of HLRCC/MCUL from all around the world, and there seem to be population differences in the phenotype. For example, HLRCC seems to be more common in Finland and North America, whereas in the UK, renal cell cancer is rarely detected in the families segregating heterozygous FH mutations. The most common manifestation of HLRCC/MCUL is cutaneous and/or ▶uterine leiomyomas. Early-onset renal cell cancer is significantly rarer and is typically of the papillary type II histology. Cutaneous leiomyomas are small benign tumors of the skin that show as multiple 0.5–2 cm skin-colored nodules, and their tissue of origin is thought to be the arrectores pili muscle of the hair follicle. They can manifest clinically as pain and paresthesias already in childhood, and the age of onset ranges from 10 to 50 in the HLRCC/MCUL families. Uterine leiomyomas (also known as ▶myomas or ▶fibroids) are smooth muscle cell tumors that arise within the smooth muscle lining of the uterus, the myometrium. They are some of the most common neoplastic tumors of women, and estimates of affected individuals range from 25% to up to 77% depending on the methods used for the diagnosis. Even though they are benign, they can cause severe morbidity such as aberrant bleeding, abdominal pain and even infertility. In families affected by HLRCC/MCUL, the onset of leiomyomas seems to be earlier than in the general

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F Fumarate Hydratase. Figure 1 Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an autosomal dominant tumor predisposition syndrome caused by germline mutations in the fumarate hydratase gene. The most common features are cutaneous and/or uterine leiomyomas. Predisposition to renal cell carcinoma is present in a subset of families. Typically, HLRCC renal cell carcinomas display papillary type 2 histology.

population. In these families, leiomyomas are also more often symptomatic and therefore they more commonly result in hysterectomy (i.e. the surgical removal of the uterus). In addition to typical leiomyomas, some HLRCC/MCUL patients develop atypical leiomyomas. These are rare variants of leiomyomas which are sometimes hard to discern from uterine leiomyosarcomas. Whether HLRCC/MCUL predisposes to malignant leiomyosarcoma is still a somewhat open question, although some studies suggest that this might indeed be the case. Familial clustering of ▶renal cell cancer was the key finding in the identification of the syndrome HLRCC. In the first family reported, four patients aged 33–48 were identified. Since then, additional cases of renal cell cancer have been detected in some HLRCC/MCUL families, the median age of onset being around 40. The natural history of HLRCC/MCUL renal tumors is malignant with early metastasis often leading to the demise of the patient. In the early reports, all renal cell cancers related to HLRCC/MCUL displayed a distinctive papillary type II histology, although other types of renal tumors, such as collecting duct and clear-cell carcinoma, have been later associated with HLRCC/ MCUL as well. HLRCC/MCUL renal tumors are typically unilateral, which is in contrast to other inherited forms of renal cell cancer such as von ▶Hippel-Lindau Syndrome (VHL), Hereditary Papillary Renal Carcinoma, and ▶Birt-Hogg-Dubé Syndrome (BHD), in which tumors often affect both kidneys. FH-mutation carriers might be at risk of developing ▶Leydig cell tumors and ovarian cystadenomas. Incidental cases of other tumors, such as breast and prostate cancer and some hematological malignancies, have also been reported in HLRCC/MCUL families,

although it remains unclear whether any of these are true manifestations of the germline FH mutations. Mutations in the FH Gene The syndrome HLRCC/MCUL is transmitted in an ▶autosomal dominant manner, and germline FH mutations have been detected in 85% of all the families displaying the HLRCC/MCUL phenotype. Altogether, 60 different mutations have been identified. The vast majority (70%) are single base pair substitutions, of which ▶missense mutations comprise about 60%; the rest are non-sense mutations. Small deletions and insertions as well as ▶splice site changes have been reported. In addition, whole gene FH deletions have been detected in some families. Mutations occur throughout the gene. The mutation R58X has been detected in four families of diverse ethnic and geographical backgrounds in North America. ▶Haplotype analysis has suggested that the mutation has occurred independently in these families, indicating that this might represent a mutational hot spot. The same mutation has also been detected in families from the United Kingdom and Australia. Other mutations that have been detected in several families of different geographical backgrounds are, for example, N64T and R190H, and these may represent mutational hot spots as well. The mutations in families with the renal cell cancer phenotype do not differ from those seen in families without these malignant tumors and, in fact, the same mutations have been detected in families with either of the two phenotypes. This has raised the question of whether an additional genomic locus could act as a modifier together with FH mutations. A ▶founder effect has been detected at least in populations of the Finnish and Iranian origin. Two

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mutations, H153R and a 2-bp deletion in codon 181, have both been identified in three different families in Finland. Similarly, a splice site mutation IVS6-1G>A has been detected in a common haplotype in several families of Iranian origin. Most tumors arising in HLRCC/MCUL families have a second somatic inactivating hit in the FH gene. This is often acquired through the loss of the wild-type FH by a partial or whole genomic deletion of chromosome arm 1q. FH mutations are also rarely seen in sporadic tumors. Inactivation of the FH gene has been detected in three tumors from the Finnish population, one soft-tissue sarcoma of the lower limb, and two uterine leiomyomas, all showing loss of the wild-type FH. However, despite mutation screens comprising hundreds of tumor specimen, no other somatic changes in FH have been detected in various tumor types including prostate, breast, colorectal, lung, ovarian, thyroid, head and neck cancers, pheochromocytomas, gliomas, and melanomas. Therefore, it is safe to say that, in general, somatic inactivation of the FH gene is a very rare occurrence in human tumors. As determined by microarray based gene expression analysis, as well as by traditional immunohistochemical methods, ▶uterine fibroids carrying FH mutations have distinct biological properties which seem to require two hits in the FH gene. The molecular mechanisms through which mutations in FH lead to tumorigenesis are still far from being well understood. Some evidence suggests that the disruption of FH activity would lead to the stabilization of the ▶hypoxia inducible factor-1 (HIF1) under normoxic conditions, thus activating several growth-promoting signaling cascades. The mutations detected in the recessively inherited developmental disorder FH deficiency are also mostly missense mutations, and they occur throughout the FH gene. The mutational spectrum of FH deficiency does not seem to be different from that of HLRCC/MCUL and, indeed, a phenotype compatible with HLRCC/ MCUL has been reported in some of the parents of the children affected by FH deficiency.

References 1. Gottlieb E, Tomlinson IP (2005) Mitochondrial tumour suppressors: a genetic and biochemical update. Nat Rev Cancer 5:857–866 2. Kiuru M, Launonen V (2004) Hereditary leiomyomatosis and renal cell cancer (HLRCC). Curr Mol Med 4:869–875 3. Tomlinson IP, Alam NA, Rowan AJ et al. (2002) Germline mutations in FH predispose to dominantly inherited uterine fibroids, skin leiomyomata and papillary renal cell cancer. Nat Genet 30:406–410 4. Vanharanta S, Pollard PJ, Lehtonen HJ et al. (2006) Distinct expression profile in fumarate-hydratase-deficient uterine fibroids. Hum Mol Genet 15:97–103

5. Wei MH, Toure O, Glenn GM et al. (2006) Novel mutations in FH and expansion of the spectrum of phenotypes expressed in families with hereditary leiomyomatosis and renal cell cancer. J Med Genet 43:18–27

Functional Foods ▶Nutraceuticals

Functional Vascular Stabilization ▶Vascular Stabilization

Fungus Definition Member of a class of relatively primitive vegetable organisms. Fungi include mushrooms, yeasts, rusts, molds, and smuts.

Funnel Factors G EMMA A RMENGOL , S ANTIAGO R AMON

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C AJAL

Department of Pathology, Vall d’Hebron University Hospital, Barcelona, Spain

Definition Is a molecule where several oncogenic signals converge and drive the proliferative signal downstream. This transformation-inducing signal inexorably passes and is canalized through the funnel factor. Funnel factors provide a clear reflection of the tumor’s transforming potential regardless of the triggering genetic alteration upstream. The level of expression of these factors should correlate with the degree of malignancy of the tumor and the most relevant clinical parameters, such as ▶metastasis and survival. Therefore, they may reflect the molecular information and transformation potential for each tumor.

Funnel Factors

Characteristics Background of Molecular Human Carcinogenesis Funnel factors are those final effectors that channel the malignant cellular growth signals, which are transduced through pathways or cascades that induce and mediate changes into the cell physiology. Several of these pathways or cascades are redundant, that is they can trigger a similar cellular effect. There are six acquired capabilities considered to be necessary for the malignant cellular growth: ▶self-sufficiency in growth signals, insensitivity to anti-growth signals, limitless replicative potential, resistance to ▶apoptosis, sustained ▶angiogenesis and, finally, the ability to infiltrate the surrounding tissue and metastasize. Each of these changes in cellular physiology can be brought about through dozens of signaling pathways or cascades, each implicating various genes or proteins. Many different oncogenic alterations may be involved in each biochemical route. This intricate molecular background and its biochemical consequences can help us to understand the great heterogeneity observed in tumors, with over 250 types of malignant human tumors with distinctive clinical and pathological characteristics and thousands of morphological and pathological tumor subtypes. So far, up to 300 mutated genes implicated in oncogenesis have been identified as human cancer genes. Many oncologists and pathologists ask whether all this information is really important for the management of individual cancer patients. The answer is unknown because only a few molecular targets have been identified in a small number of tumor types. For example, ▶amplification of ERBB2 is seen in 25–30% of ▶breast carcinomas, ▶EGFR mutations in less than 10% of ▶lung carcinomas, and ▶c-KIT in the rare ▶gastrointestinal stromal tumors; but in most carcinomas, there is no distinctive oncogenic target. In the near future, technological advances will allow us to study the complete genetic background, ▶mRNA profiling, and protein expression of individual tumors, and identify a myriad of genetic and biochemical alterations. But even then, attempts to inhibit or counteract single genetic alterations with the use of multiple specific agents would probably be chaotic. Nevertheless, dissection of the biochemical pathways is progressing. We now know which factors are the final growth signaling effectors that can control ▶transcription and protein synthesis. Then, it is logical to think that the level of expression of these final effectors, which channel the proliferation signal, can be associated with the real oncogenic role of a pathway in individual tumors. Cell Signaling in Human Tumors Among the acquired capabilities of tumor cells, a funnel factor has been described for self-sufficiency in growth signals. This essential oncogenic capability is one of the

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most extensively studied characteristics of tumor cells, and one that is constitutively activated in nearly all tumors. The process of converting extracellular signals into cellular responses, in this case cell growth and division, is called signal transduction. The growth signal transduction pathway is comprised of ▶growth factors, ▶growth factor receptors, factors transmitting the growth signal, and the final effector factors, some of which are located in the nucleus to activate ▶transcription factors and some in the ▶ribosomes to activate protein synthesis. The neoplastic cell, however, may be able to generate signals for survival or proliferation through various mechanisms without depending on exogenous signals. These mechanisms include alterations in the growth factors or receptors, or in the signaling pathways, themselves. Among the latter, the most highly recognized and important are the ▶RAS-▶RAF▶MAPK (ERK1/2) and ▶PI3K-▶AKT pathways, which regulate ▶mTOR. Specific molecular alterations are detected in these signaling cascades in the majority of tumors. Usually these are single alterations with an oncogenic impact, such as growth factor mutations or RAS mutations; other concomitant genetic alterations are not usually found in these biochemical pathways.

Searching for Funnel Factors: p-4E-BP1 In studies performed in various tumor types, the expression of key cell-signaling factors, including Her1 and Her2 growth factor receptors, as well as the RASRAF-MAPK and the PI3K-AKT-mTOR pathways were correlated with the associated clinico-pathological characteristics of these tumors. The downstream factors p70, S6, 4E-BP1, and EIF4E, which play a critical role in the control of protein synthesis, survival, and cell growth, were also analyzed. It was found that ▶phosphorylated ▶4E-BP1 (eukaryotic ▶translation initiation factor 4E binding protein 1) levels in breast, ovary, and prostate tumors were associated with malignant progression and an adverse prognosis, regardless of the upstream oncogenic alterations. Thus, p-4E-BP1 seems to act as a funnel factor for an essential oncogenic capability of tumor cells, self-sufficiency in growth signals, and could be a highly relevant molecular marker of malignant potential. The results showing that 4E-BP1 is associated with the prognosis in breast, ovary and prostate tumors, are supported by other data. In breast cancer, ▶phosphorylation of AKT, mTOR and 4E-BP1 has been associated with tumor development and progression; and in prostate cancer, one of the best biomarkers of the mTOR pathway is 4E-BP1, since overexpression of this factor has been highly associated with this type of tumor. Moreover, experimental studies have shown that 4E-BP1 is essential for cell transformation. Transfer of 4E-BP1 phosphorylation site mutants into breast carcinoma cells suppressed their tumorigenicity.

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4E-BP1 is a eukaryotic translation initiation factor 4E (EIF4E)-binding protein that plays a critical role in the control of protein synthesis, survival, and cell growth. During ▶cap-dependent translation, EIF4E binds to the mRNA ▶cap structure and promotes formation of the ▶translation initiation complex and ▶ribosome binding. When 4E-BP1 is active (non-phosphorylated 4E-BP1) it binds to EIF4E and impedes formation of the initiation complex; translation is then blocked, favoring apoptosis. However, when 4E-BP1 is phosphorylated, the affinity for EIF4E binding is reduced, EIF4E is released, and cap-dependent translation can initiate. 4E-BP1 has seven phosphorylation sites. It is likely that mTOR is the main phosphorylation pathway of 4E-BP1, although other ▶kinases may be implicated, such as ▶CDK1, ▶ATM, ▶PI3K-AKT, ▶ERK1/2, and perhaps other, still unidentified, kinases. Therefore, 4E-BP1 phosphorylation can be the consequence of many different oncogenic events occurring in several biochemical pathways, including amplification or mutation of growth factor receptors, loss of function or mutations in ▶PTEN, ▶ATM, ▶p53, ▶PI3K or ▶RAS, or other collateral mechanisms of cellular oncogenic activation (Fig. 1). Because of the elevated number

of genetic alterations that regulate 4E-BP1, we propose that the phosphorylated form of this protein can act as a “bottleneck” or funneling factor through which the transforming signals converge, channeling the oncogenic proliferative signal regardless of the upstream specific oncogenic alteration. The role of other 4E-BP ▶isoforms, such as 4E-BP2 and 4E-BP3, in human tumors is still unclear, and it is not known whether they can be activated in 4E-BP1negative tumors. Study of the EIF protein family will also be determinant when reliable antibodies allow us to analyze their expression in large series of tumors. Recent data have provided novel perspectives into the proliferative and oncogenic properties of EIF4E, since it has been shown to have an impact on nearly every stage of cell cycle progression. Earlier studies have shown that EIF4E levels are substantially elevated in several types of cancers. Funnel Factors in Other Oncogenic Pathways Extending the concept of funnel factor, there might be several funnel factors where the final biochemical effect converges for each of the oncogenic capabilities of tumor cells. For example, in the apoptosis pathways,

Funnel Factors. Figure 1 Schematic diagram showing how funneling factors channel the proliferation signal.

Furin

where the expression of certain proteins that inhibit apoptosis, such as survivin and livin, might be associated with resistance to apoptosis regardless of the activation of other antiapoptotic or proapoptotic genes that might be present. Study of the expression profiles of funnel factors from all the cell transformation pathways would allow us to obtain an individual functional-molecular signature for each tumor. This signature, combined with clinical and pathological data would help us to establish the malignant potential of each individual tumor and deduce its potential resistance to conventional chemotherapy and radiotherapy. Obviously, in addition to molecular characterization of tumors for prognostic purposes, it is necessary to study factors that might be potential therapeutic targets, currently one of the most promising areas in the field of cancer treatment. With this functional approach it seems worthwhile to investigate whether these funnel factors can be critical targets for cancer treatment.

References 1. Armengol G, Rojo F, Castellvi J et al. (2007) 4E-binding protein 1: a key molecular “funnel factor” in human cancer with clinical implications. Cancer Res 67:7551–7555 2. Avdulov S, Li S, Michalek V et al. (2004) Activation of translation complex eIF4F is essential for the genesis and maintenance of the malignant phenotype in human mammary epithelial cells. Cancer Cell 5:553–563 3. Hanahan D, Weinberg RA (2000) The hallmarks of cancer. Cell 100:57–70 4. Mamane Y, Petroulakis E, LeBacquer O et al. (2006) mTOR, translation initiation and cancer. Oncogene 25:6416–6422 5. Rojo F, Najera N, Lirola J et al. (2007) 4E-binding protein 1, a cell signaling hallmark in breast cancer that correlates with pathologic grade and prognosis. Clin Cancer Res 13:81–89

Furin R OBERT DAY 1 , A LEX Y. S TRONGIN 2 1

Department of Pharmacology, Institut de Pharmacologie, Faculté de Médecine, , Université de Sherbrooke, Sherbrooke, QC, Canada 2 Burnham Institute for Medical Research, La Jolla, CA, USA

Synonyms Furin; PACE; SPC1; PCSK3; Dibasic processing enzyme; Prohormone convertase; Paired basic amino acid cleaving enzyme

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Definition Furin (E.C. 3.4.21.75) is a highly specialized proteinase that cleaves the unique sequence motifs in a variety of proteins. Normally, following furin cleavage, the target protein is activated and, therefore, it can exhibit its biological activity. Because furin has been discovered first, currently it is the most studied enzyme of the proprotein convertase (PC) family of serine proteinases. Seven distinct proprotein convertases of this family (furin, PC2, PC1/3, PC4, PACE4, PC5/6, and PC7) have been identified in humans, some of which have ▶isoforms generated as the result of ▶alternative splicing. Structurally and functionally, furin resembles its evolutionary precursor: the prohormone-processing enzyme, kexin (EC 3.4.21.61), which is encoded by the KEX2 gene of yeast Saccharomyces cerevisiae. The polypeptide sequence of the furin ▶catalytic domain is homologous to that of Bacillus subtilisin, an evolutionary precursor of PCs. Furin and related PCs are involved in the limited ▶endoproteolysis (▶protease activated receptor) of inactive precursor proteins which occurs at the sites marked by paired or multiple basic amino acids.

Characteristics A wide variety of proteins are initially synthesized as parts of higher molecular weight, but inactive, precursor proteins. Specific endoproteolytic processing of these ▶proproteins is required to generate the regulatory proteins in a mature and biologically active form. A large majority of these active proteins, including ▶matrix metalloproteinases, growth factors, and ▶adhesion molecules are essential in the processes of cellular transformation, acquisition of the tumorigenic phenotype, and metastases formation. The enzyme furin, which is encoded by the fur gene, was the first and can be considered the prototype of a mammalian subclass of subtilisin-like proteases. The localization of the gene immediately upstream from the FES ▶oncogene (V-FES feline sarcoma viral oncogene homolog) generated the name FUR (for FES upstream region). Furin is similar to other PCs in that it contains a signal peptide, a prodomain, a subtilisin-like catalytic domain, a middle P domain, a cysteine-rich region, a transmembrane anchor, and a cytoplasmic tail (Figs. 1 and 2). Furin and PCs are normally N-glycosylated ▶glycoproteins (▶glycosylation). Phosphorylation of the cytoplasmic tail is required for the trans-Golgi localization of furin which in vivo exists as di-, monoand non-phosphorylated forms. Propeptide cleavage is a prerequisite for the exit of furin molecules out of the ▶endoplasmic reticulum. The second cleavage in the propeptide occurs in the ▶trans-Golgi network, which is followed by the release of the propeptide bound to furin and the activation of furin. Furin is expressed in all examined tissues and cell lines and is mainly localized in the trans-Golgi

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Furin

Furin. Figure 1 A modular domain structure of furin and six related PCs. The A and B isoforms of PC5/6 are encoded by the same gene. The structure includes (i) the N-terminal signal peptide, which directs proteins into the secretory pathway, (ii) a pro-domain, which maintains the inactive zymogen state of PCs and which also acts as an intramolecular chaperone for the proper folding, (iii) a catalytic domain with the active site that exhibits an Asp (D)-His(H)-Ser(S) catalytic triad and an additional Asn(N), (iv) a barrel-like structured P domain that regulates enzyme stability, (v) a C-terminal domain that contains membrane attachment sequences, a Cys-rich region and intracellular sorting signals. Adapted from [4].

network. Some proportion of the furin molecules cycles between the trans-Golgi and the cell surface. Furin represents the ubiquitous endoprotease activity within constitutive secretory pathways and normally it is capable of cleaving the Arg-X-(Lys/Arg)-Arg consensus motif, where X is any amino acid type (Table 1). Furin and related PCs are activating proteases and normally they do not inactivate polypeptides. Because of the overlapping substrate preferences and cell/tissue expression, there is a substantive level of redundancy in the PC functionality, albeit certain distinct functions of the individual PCs have also been demonstrated. Furin knockout, however, is lethal in mice. Furin null embryos die because they fail to accomplish ventral closure successfully and to form a looping heart tube. These processes require cellular migration and proliferation, both of which are regulated by furin. Through regulation of cellular migration and proliferation, furin plays an important, albeit incompletely understood role, in cellular transformation, acquisition of the tumorigenic phenotype, cancer progression and metastasis. The expression of furin, however, discriminates sharply between small cell lung cancers, which have no expression, and non-small cell lung cancers, in which furin is overexpressed.

The roles of furin and other PCs in cancer have been characterized as the result of many studies of gene expression and enzyme inhibition. Because of the redundancy, it is not always clear if all PCs present in cancer cell/tissue are directly relevant to tumorigenicity. An enhanced expression of furin and related PCs in cancer is not necessarily an indicator of a poor clinical outcome. There is, however, evidence that high levels of furin-related PCs contribute to tumor growth and metastasis by controlling the activation of key cancer-associated proteins, including matrix metalloproteinases and growth factors such as ▶VEGF, ▶TGFβ and ▶PDGF. The multiple effects of PCs on cell proliferation, motility, adhesion and invasion have led to a concept that in the course of tumor development and progression PCs act as “master switches” of the key tumorigenic protein functionality. If this concept is valid, then PCs could be identified as important therapeutic targets in a number of cancer types. The challenge remains to identify the functionally-relevant, target PC in each cancer type, because it is unlikely that broad-range PC inhibitors would have significant clinically beneficial effects. No natural protein inhibitors of furin are known. D-Arg-based peptides, α1-anti-trypsin Portland and,

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Furin. Figure 2 Furin structure. The 794-residue pre-profurin sequence contains a 24-residue signal peptide, an 83-residue prodomain, a 330-residue subtilisin-like catalytic domain, a 140-residue middle P domain (also termed the “homo B,” a 115-residue cysteine-rich region, a 23-residue transmembrane anchor, and a 56-residue cytoplasmic tail. Adapted from [1].

especially the synthetic peptidic inhibitor decanoylArg-Val-Lys-Arg-chloromethylketone, are used to inhibit furin in the cleavage reactions in vitro and in cell-based tests. Inhibition of furin results in a significant reduction in tumor cell invasion. This reduction appears to be associated with a processing blockade of proteins directly involved in the mechanism of invasion including matrix metalloproteinases, growth factors and adhesion signaling receptors such as integrins. PCs including furin are implicated in many pathogenic states because they process to maturity membrane fusion proteins and pro-toxins of a wide variety of both naturally occurring and weaponized bacteria and viruses, including anthrax and botulinum toxins and H5N1 bird flu, Marburg and Ebola viruses. After processing by furin and the subsequent internalization inthe complex with the respective receptor followed by acidification of the ▶endosomal compartment (▶endocytosis), the processed, partially

denatured, infectious proteins expose their membranepenetrating peptide region and escape into the cytoplasm. The intact toxins and viral proteins, however, are incapable of accomplishing these processes. Normally, the low pathogenicity viral subtypes have mutations in the cleavage site sequence and thus a reduced sensitivity to furin. Accordingly, proteolytic processing by furin is an important determinant in the overall pathogenicity of viruses and bacterial toxins. Based on these data, PCs, including furin, are promising targets for drug design in a variety of acute and chronic diseases including cancer and infectious diseases.

References 1. Molloy SS, Anderson ED, Jean F et al. (1999) Bi-cycling the furin pathway: from TGN localization to pathogen activation and embryogenesis. Trends Cell Biol 9:28–35

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Furin. Table 1

Furin targets and the sequence of the cleavage sites

Proteinases

P6 P4 P1↓P1′

FURIN

Furin, two autolytic cleavage sites

MMP-11 MMP-14 MMP-15 MMP-16 MMP-17 MMP-24 MMP-25 ADAM-9 ADAM-12 ADAM-19 ADAMTS1

Matrix metalloproteinase 11, stromelysin-3 Matrix metalloproteinase 14, MT1-MMP Matrix metalloproteinase 15, MT2-MMP Matrix metalloproteinase 16, MT3-MMP Matrix metalloproteinase 17, MT4-MMP Matrix metalloproteinase 24, MT5-MMP Matrix metalloproteinase 25, MT6-MMP A desintegrin and metallopeptidase domain 9 A desintegrin and metallopeptidase domain 12 A desintegrin and metallopeptidase domain 19 A desintegrin and metalloproteinase with thrombospondin type-1 motif, 1 A desintegrin and metalloproteinase with thrombospondin type-1 motif (aggrecanase-1), 4 A desintegrin and metalloproteinase with thrombospondin type-1 motif. 13 Bone morphogenetic protein 1 Bone morphogenetic protein 4 Meprin A alpha Beta-site APP-cleaving enzyme 1

ADAMTS4 ADAMTS13 BMP1 BMP4 Meprin-A BACE1 Serum proteins

Albumin VWF von Willebrand factor F9 Coagulation factor IX PROC Protein C Extracellular matrix FBN1 Fibrillin 1 ZPC3 Zona pellucida glycoprotein 3 Chaperone 7B2 Secretogranin V Receptors ITGA3 Integrin alpha chain, alpha 3 ITGA6 Integrin alpha chain, alpha 6 LRP1 Low density lipoprotein-related protein 1 NOTCH1 Notch1 INSR Insulin receptor DSG3 Desmoglein 3 MET Hepatocyte growth factor receptor c-met CUBN Cubilin/vitamin B-12 receptor SORL1 Sortilin-related receptor HGFR Hepatocyte growth factor/scatter factor receptor Growth factors and hormones IGF-1a Insulin-like growth factor 1a/somatomedin C NTF3 Neurotrophin 3 VEGFC Vascular endothelial growth factor C NPPB Natriuretic peptide B PTH Parathyroid hormone

RGVTKR↓SLSP KRRTKR↓DVYQ RNRQKR↓FVLS NVRRKR↓YAIQ RRRRKR↓YALT HIRRKR↓YALT QARRRR↓QAPA RRRNKR↓YALT VRRRRR↓YALS LLRRRR↓AVLP ARRHKR↓ETLK PRRMKR↓EDLN SIRKKR↓FVSS

75–76 107–108 97–98 111–112 131–132 119–120 125–126 155–156 107–108 205–206 207–208 105–206 252–253

PRRAKR↓FASL

212–213

RQRQRR↓AAGG 74–75 RSRSRR↓AATS RRRAKR↓SPKH PSRQKR↓SVEN GLRLPR↓ETDE

120–121 292–293 653–654 45–46

RGVFRR↓DAHK SHRSKR↓SLSC LNRPKR↓YNSG RSHLKR↓DTED

24–25 763–764 46–47 199–200

RGRKRR↓STNE ASRNRR↓HVTE

2731–2732 301–302

QRRKRR↓SVNP

181–182

PQRRRR↓QLDP NSRKKR↓EITE SNRHRR↓QIDR GGRRRR↓ELDP PSRKRR↓SLGD KRRQKR↓EWVK EKRKKR↓STKK LQRQKR↓SINL PLRRKR↓SAAL EKRKKR↓STKK

875–876 902–903 3943–3944 1665–1666 762–763 49–50 307–308 35–36 81–82 307–308

PAKSAR↓SVRA TSRRKR↓YAEH HSIIRR↓SLPA TLRAPR↓SPKM KSVKKR↓SVSE

119–120 138–139 227–228 102–103 31–32

Fusion Genes Furin. Table 1

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Furin targets and the sequence of the cleavage sites (Continued)

Proteinases

P6 P4 P1↓P1′

TGFB1 TNFSF12– TNFSF13 EDA-A2 NGFB

Transforming growth factor, beta 1 Tumor necrosis factor (ligand) member 12-member 13/proliferationinducing ligand APRIL Ectodysplasin a isoform β-Nerve growth factor Semaphorin 3A Viral envelope glycoproteins HO Hemagglutinin type H5 F Newcastle disease virus F fusion protein F Parainfluenza HPIV3 F fusion protein P130 Sindbis virus structural polyprotein p130 prM Flaviviral prM protein

SSRHRR↓ALDT RSRKRR↓AVLT

278–279 104–105

VRRNKR↓SKSN THRSKR↓SSSH KRRTRR↓QDIR

159–160 179–180 555–556

RRRKKR↓GLFG GRRQKR↓LIGA DPRTKR↓FFGG SGRSKR↓SVID SRRSRR↓SLTV

THRTKR↓STDG VQREKR↓AVGL SRRHKR↓FAGV TRRFRR↓SITE YFRRKR↓SILW GRRTRR↓EAIV LRRRRR↓DAGN

344–345 116–117 109–111 328–329 215–216, West Nile Virus 205–206, Dengue virus 460–461 498–499 115–116 537–538 435–436 501–502 432–433

RHRQPR↓GWEQ NSRKKR↓STSA KRRGKR↓SVDS GNRVRR↓SVGS KVRRAR↓SVDG ASRVAR↓MASD

304–305 196–197 398–399 218–219 455–456 273–274

HRREKR↓SVAL UL55 Cytomegalovirus/herpesvirus 5 protein UL55/glycoprotein B gp160 HIV-1 glycoprotein-160 Fo Measles virus fusion protein E2 Infectious bronchitis spike protein GP Marburg virus spike glycoprotein env Ebola envelope glycoprotein BALF4/GP110 Epstein-Barr virus/herpesvirus 4 Bacterial endotoxins ExoA Pseudomonas aeruginosa exotoxin A PA83 Anthrax protective antigen α-Toxin Clostridium alpha-toxin DT Diphtheria toxin Aerolysin Aeromonas aerolysin Shiga toxin Shigella shiga toxin I subunit A

2. Khatib AM, Siegfried G, Chretien M et al. (2002) Proprotein convertases in tumor progression and malignancy: novel targets in cancer therapy. Am J Pathol 160:1921–1935 3. Bassi DE, Fu J, Lopez de Cicco R et al. (2005) Proprotein convertases: ‘‘master switches’’ in the regulation of tumor growth and progression. Mol Carcinog 44:151–161 4. Thomas G (2002) Furin at the cutting edge: from protein traffic to embryogenesis and disease. Nat Rev Mol Cell Biol 3:753–766 5. Fugere M, Day R (2005) Cutting back on pro-protein convertases: the latest approaches to pharmacological inhibition. Trends Pharmacol Sci 26:294–301

Fusin ▶Chemokine Receptor CXCR4

Fusion Genes PATRIZIA G ASPARINI Molecular-Cytogenetic Unit, Department of Experimental Oncology, Istituto Nazionale Tumori, Milano, Italy

Synonyms Fusion proteins; fusion oncogenes; chimeric genes; chimeric oncogenes; chimeric transcripts; hybrid genes

Definition A hybrid gene created by joining portions of two different genes (to produce a new protein) or by joining a gene to a different promoter (to alter or deregulate a gene transcription).

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Fusion Genes

Characteristics A wide variety of recurrent molecular alterations has been associated with cancer including ▶polymorphisms, changes in gene copy number (amplifications and deletions), point mutations, ▶epigenetic modifications and gene fusions due to structural ▶chromosomal rearrangements, such as translocations and less frequently inversions. As for these last ones, the genes located at the breakpoints of the rearrangement may be structurally changed with dramatic effects on their products. Molecularly, two events of structural aberrations

can be generated: “promoter swapping” (the exchange of promoter control regions) or fusion gene. In detail (Fig. 1a) “promoter swapping” occurs when the regulatory elements of a gene (promoter and/or enhancer) become aberrantly juxtaposed to a protooncogene, thus driving deregulated expression of an oncogene. Molecularly, the breakpoints of the rearrangements occur upstream from the coding region of the partner gene resulting in two chimeric genes which have exchanged their promoter regions, and less frequently noncoding exons. At the genomic level, the

Fusion Genes. Figure 1 A schematic representation of two events of stuctural aberations: (a) Promoter swapping and (b) Fusion genes and Fusion proteins.

Fusion Genes

3′ partner gene B is placed downstream of the 5′ gene A promoter region. The chimeric transcript contains 5′ ▶untranslated regions (UTR) from the A gene and a coding region B that is intact and encodes a normal protein B. This mechanism can be exemplified by the three translocations that characterize Burkitt lymphoma: t(8;14), t(8;22), and t(2;8). All these rearrangements lead to the activation of MYC, located on 8q24, by juxtaposing the coding sequences of the gene to one constitutively active immunoglobulin (Ig) genes promoter or regulatory regions (IgH at 14q32, IgK at 2p12, and IgL at 22q11). Fusion genes (Fig. 1b) arise when the coding regions of the two genes are juxtaposed, resulting in a chimeric transcript that produces a fusion protein with a new altered activity. In detail, in the majority of cases, fusion genes are formed when DNA breaks occur within two different genes mainly within the introns, A and B, and the gene fragments are joined in erroneous combinations. In most cases, the results are two fusion genes: A-B and B-A. On genomic level, the 3′partner gene B is placed under the 5′ gene A promoter control region which dominates the transcription control of the fusion gene. As a result, in the fusion protein the functional domains from the A and B proteins are brought together in a new abnormal combination. In cancer, the genes that are often interrupted by a chromosomal rearrangement are oncogenes , thus harboring fusion oncogenes. An appropriate example of a fusion oncogene is ▶BRC/ ABL characterizing chronic myelogenous leukemia which is driven by t(9;22)(q34;q11), also known as the ▶Philadelphia chromosome, the first translocation to be molecularly characterized. In particular, the translocation fuses the ABL gene normally located on 9q34, with the BCR gene at 22q11. The BCR/ABL fusion created on the derivative chromosome 22 encodes a chimeric protein with an increased ▶tyrosine kinase activity and abnormal localization. Table 1 enlists molecularly characterized recurrent chromosomal rearrangements found in cancers. Formation Of Fusion Genes Several factors influence the formation of fusion oncogenes and their role in tumorigenesis. Firstly, the rate at which fusion genes are formed is important. Literature suggests that at least some fusion genes are found in healthy individuals, implying that at least some gene fusions emerge at a notable rate. The mechanisms behind fusions are unknown but the occurrence of several double strand breaks that coincide in time and space are important. The proximity of damaged partner genes at the moments of repair is critical and the localization of chromatin and genomic regions in the interphase nuclei may be critical. Secondly, the presence of a fusion gene in a cell is not enough to cause cancer. Additional genetic or epigenetic changes are

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also needed and the risk for these additional events to occur affects the outcome. Thirdly, once the fusion is formed, its penetrance, i.e. the proportion of fusion carriers that develop tumors, is determined by selected mechanisms. Interestingly, many fusion oncogenes demonstrate a strict specificity for tumor type. The risk of getting a certain translocation could depend on cell type-specific processes that make the specific genes or DNA regions involved vulnerable to the translocation. It is clear that tumor development in different cell types and tissues locations involves many pathways, distinct genes, and also exogenous factors. A common mechanism for early genetic changes can however be distinguished in a number of different tumor types by specific chromosome rearrangements. Moreover, the transcriptional orientation of fusion partner genes is essential in order to harbor functional fusion genes. At times, the partner genes are not oriented in the correct direction with regards to their transcriptional orientation, and more complex rearrangements are needed to fuse the partner genes into functional fusion genes. For instance, the EWS-ERG fusion is found in about 10% of Ewing sarcomas and it is the result of a complex rearrangement, a ▶translocation and an ▶inversion, given that the genes involved are not transcribed in the same centromeric/telomeric direction. This requirement and the necessary presence of critical functional protein parts seem to influence how frequently variant fusion genes are present in tumors. Moreover, to produce a functional fusion gene is necessary that the exons flanking the breakpoints can give rise to splicing events that maintain their reading frames. Overall, the factors that generate double-strand breaks are largely unknown. Clinical Relevance Studies over the past decades have revealed that recurring chromosome rearrangements leading to fusion oncogenes are specific features not only of leukemias and lymphomas, but also of certain epithelial tumors. Presently, over 600 recurrent balanced tumor-associated chromosomal rearrangements have been molecularly characterized. However, the data are strongly biased in favor of hematologic malignancies and sarcomas. An important example of a recurrent rearrangement which leads to the development of a targeted therapy is the t(15;17)(q22;q21) in ▶acute promyelocytic leukemia which fuses the ▶PML gene (15q22) with RARα gene at 17q21. The PML protein contains a zinc-binding domain called a “ring” finger that may be involved in protein– protein interaction. RARα protein encodes the retinoic acid alpha-receptor protein (▶retinoic acid receptors a member of the nuclear steroid/thyroid hormone receptor superfamily. Although retinoic acid binding is retained in the fusion protein, the PML/RARα may confer altered DNA-binding specificity to the RARα ligand

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Fusion Genes. Table 1

Molecularly characterized recurrent chromosome rearrangements and fusion genes in cancer

Disease Hematopoietic tumor Lymphoid ▶Anaplastic Large Cell Lymphoma

Affected gene

NPM-ALK TPM3-ALK TFG-ALK ATIC-ALK MSN-ALK CLTCL-ALK ▶Burkitt Lymphoma, B-cell acute lymphoid leukemia MYC (relocation of IgH locus) MYC (relocation of IgK locus) MYC (relocation of IgL locus) B-cell precursor ALL E2A-PBX1 E2A-HLF TEL-AML1 BCR-ABL MLL-AF4 IL£-IgH ▶Diffuse large B-cell lymphoma BCL2-IgH BCL6- variant partners BCL8-IgH FCGR2-Igλ MUC1-IgH NFKB2-IgH Extranodal mucosa-associated MALT1-API2 lymphoid tissue MALT1-IgH BCL10-IgH BCL10-Igκ Plasma cells myeloma FGFR3-IgH and MMSET MAF-IgH MAF-Igλ CCND1-IgH MUM/IRF4-IgH Pre-T cell lymphoblastic leukemia, lymphoma MYC (Relocation to TCR α/δ locus) LYL1 (Relocation to TCRα/σlocus) TAL2 (Relocation TCRβ locus) SCL (Relocation to TCR α/δ locus) OLIG2 (Relocation to TCR α/δ) LMO1(RBTN1) (Relocation to TCR α/δ) LMO2 (RBTN2) (Relocation to TCR α/δ) HOX11 (Relocation to TCR α/δ) HOX1-1L2 CALM-AF10 NUP98-RAP1GDS1 Myeloid ▶Acute promyelocytic leukemia PML-RARα NPM-RARα PLZF-RARα

Rerrangement

t(2;5)(q23;q35) t(1;2)(q25;p23) t(2;3)(p23;q21) inv(2)(p23q35) t(X;2)(q11-12;p23) t(2;17)(p23;q23) t(8;14)(q24;q32) t(2;8)(p12;q24) t(8;22)(q24;q11) t(1;19)(q23;p13) t(17;19)(q22;p13) t(12;21)(p12;q22) t(9;22)(q34;q11.2) t(4;11)(q21;q23) t(5;14)(q31;q32) t(14;18)(q32;q21) t(3;v)(q27;v) t(14;15)(q32;q11-13) t(1;22)(q22;q11) t(1;14)(q21;q32) t(10;14)(q24;q32) t(11;18)(q21;q21) t(14;18)(q32;q21) t(1;14)(p22;q32) t(1;2)(p22;p12) t(4;14)(p16;q32) t(14;16)(q32;q23) t(16;22)(q23;q11) t(11;14)(q13;q32) t(6;14)(p25;q32) t(8;14)(q24;q11) t(7;19)(q35;p13) t(1;14)(p32;q11) t(14;21)(q11;q22) t(11;14)(p15;q11) t(11;14)(p13;q11) t(10;14)(q24;q11) t(5;14)(q35;q32) t(10;11)(p13;q21) t(4;11)(q21;p15) t(15;17)(q21;q21) t(5;17)(q35;q21) t(11;17)(q23;q21)

Fusion Genes Fusion Genes. Table 1 (Continued)

1185

Molecularly characterized recurrent chromosome rearrangements and fusion genes in cancer

Disease

▶Acute myeloid leukemia Acute myeloid leukemia

Solid tumors Sarcomas Alveolar rhabdomyosarcoma

▶Alveolar soft-part sarcoma Angiomatoid fibrous histiocytoma Dermatofibrosarcoma protubeans Desmoplastic small round cell tumor Endometrial stromal sarcoma ▶Ewing sarcoma

Infantile fibrosarcoma Inflammatory myofibroblastic tumour

Low grade fibromyxoid sarcoma Myxoid chondrosarcoma

▶Myxoid liposarcoma ▶Synovial sarcoma

Soft-tissue clear cell sarcoma

Affected gene

Rerrangement

ETV6- variant partners NUP98-variant partners MLL-variant partners AML1-ETO CBFB-MYH11 FUS-ERG CEV14-PDGFRB P300-MOZ MOZ-TIF2 MOZ-CBP DEK-NUP214 RBM15-MKL MLF1-NPM1 AML1-EVI1

t(12;v)(p13;v) t(11;v)(p13;v) t(11;v)(q23;v) t(8;21)(q22;q22) inv(16)(p13q22) t(16;21)(p11;q22) t(5;14)(q33;q32) t(8;22)(q33;q32) inv(8)(p11q13)

PAX3-FKHR PAX7-FKHR TFE3-ASPL FUS-ATF1

t(2;13)(q3?;q14) t(1;13)(q36;q14) t(X;17)(p11;q25) t(12;16)(q13;p11)

COL1A1-PDGFB

t(17;22)(q13;q13)

EWS-WT1

t(11;22)(p13;q12)

JAZF1-JJAZ1 EWS-FLI EWS-ERG EWS-ETV1 EWS-E1AF EWS-FEV FUS-ERG ETV-NTRK3 TPM3-ALK TPM4-ALK CLTC-ALK FUS-CREB312 EWS-CHN TAF2N-CHN TCF12-CHN FUS-CHOP EWS-CHOP SYT-SSX1 SYT-SSX2 SYT-SSX4 EWS-ATF1

t(7;17)(p15;q21) t(11;22)(q24;q12) t(21;22)(q22;q12) t(7;22)(q22;q12) t(2;22)(q33;q12) t(17;22)(q12;q12) t(16;21)(p11;q22) t(12;15)(p13;q25) t(1;2)(q22;p23) t(2;19)(p23;p13) t(2;17)(p23;q23) t(7;16)(q33;p11) t(9;22)(q22;q12) t(9;17)(q22;q11) t(9;15)(q22;q21) t(12;16)(q13;p11) t(12;22)(q13;q12) t(X;18)(p11;q11)

t(6;9)(p23;q34) t(1;22)(p13;q13) t(3;5)(q25;q34) t(3;21)(q26;q22)

t(12;22)(q13;q13)

F

1186

Fusion Genes

Fusion Genes. Table 1 Molecularly characterized recurrent chromosome rearrangements and fusion genes in cancer (Continued) Disease Carcinomas ▶Follicular thyroid carcinoma ▶Papillary thyroid carcinoma

▶Prostate cancer ▶Renal-cell carcinoma

▶Salivary gland tumors (malignant) Secretory breast carcinoma ▶Non-small cell lung carcinoma

Affected gene PAX8-PPARγ H4-RET (PTC1) RIa-RET (PTC2) ELE1-RET (PTC3,4) RFG5-RET (PTC5) TPM3-NTRK1 (TRK) TPR-NTRK1 (TRK-T1) TFG-NTRK1 (TRK-T3) TMPRSS2-ERG TMPRSS2-ETV1 TMPRSS2-ETV4 PRCC-TFE3 ASPSCR1-TFE3 SFPQ-TFE3 NONO-TFE3 CTNNB1- PLAG1 TORC1-MAML2 ETV6-NTKR3 EMLH-ALK

complex. Leukemia patients with the PML/RARα gene fusion have an excellent response to the all-trans retinoic acid treatment, which stimulates the differentiation of promyelocytic leukemia cells. Similarly, the molecular characterization of the t(9;22)(q34;q11) in chronic myelogenous leukemia, which generates the fusion oncoprotein BCR/ABL, lead to the development of a successful targeted treatment of imatinib. In contrast to hematological neoplasia, our knowledge regarding fusion genes in solid tumors is very limited, due to the complexity and poor quality of their ▶cytogenetic karyotypes, yet they constitute only the 10% of known recurrent balanced chromosome rearrangements. However, fusion oncogenes may be more common in epithelial tumors than previously thought. Usually, translocations in solid tumors result in gene fusions that encode chimeric oncoproteins. The first chromosome abnormalities to be molecularly characterized in solid tumors were an inv(10)(q11.2; q21.2), as the more frequent alteration, and a t(10;17) (q11.2;q23), in ▶papillary thyroid carcinoma. These two abnormalities represent the cytogenetic mechanism which activate the proto-oncogene ▶RET on chromosome 10, by generating the fusion genes forming the oncogene RET/PTC1 and RET/PTC2, respectively. Moreover, other chromosomal rearrangements leading

Rerrangement t(2;3)(q13;p25) inv(10)(q11.2;q21) t(10;17)(q11.2;q23) inv(10)(q11q22) inv(1)(q21q22) inv(1)(q21q25) t(1;3)(q21;q11) inv(21)(q22.2;q22.3) t(7;21)(p21.2;q22.3) t(17;21)(q21;q22.3) t(X;1)(p11;q21) t(X;17)(p11;q25) t(X;1)(p11;p34) inv(X)(p11;q12) t(3;8)(p21;q12) t(11;19)(q21;p13) t(12;15)(p13;q25) inv(2)(p21;p23)

to RET activation were recently described and listed in Table 1. A great impact in the study of solid tumors is foreseen by the recent identification of a large subset of ▶prostate cancer harboring ▶TMPRSS2/ERG, fusions, TMPRSS2/ETV1 and TMPRSS2/ETV4, generated by inv(21)(q22.2;q22.3), t(7;21)(p21.2;q22.3) and t(17;21)(q21;q22.3) respectively. In particular, the gene fusion of the 5′ UTR of TMPRSS2 (a prostatespecific gene) to ERG or ETV1 (genes of the ▶ETS family), was identified in the majority of prostate cancer. Although the clinical significance of those fusions is unknown, recent investigations indicate that the expression of TMPRSS2/ERG among prostate cancer patients is a strong prognostic factor for disease progression. Although fusion proteins play an important role in oncogenesis, additional genetic alterations are essential in order to transform cells. Silencing the specific fusion genes that play fundamental roles for the corresponding tumor, blocking targets of fusion proteins and repressing the cooperating events are all promising therapeutic strategies that need to be further investigated. The detection of the intracellular targets of these fusions will harbor new and important insights into molecular pathways that underlie tumor development. Ultimately, a combination of these approaches with

FZD

conventional treatments may provide a powerful new approach to treat these fusion-positive tumors.

1187

FVC

References

Definition

1. Aman P (2005) Fusion oncogenes in tumor development. Semin Cancer Biol 15:236–243 2. Kuman-Sinha C, Tomlins SA, Chinnayan AM (2006) Evidence of recurrent gene fusions in common epithelial tumors. Trends Mol Med 12:529–536 3. Pierotti MA, Frattini M, Sozzi G et al. (2006) Oncogenes. In: Kufe DW, Bast RC, Hait WN, Hong DK, Pollock RE, Weichselbanum RR, Holland JF, Frej E (eds) Cancer Medicine. American Association for Cancer Research, London, pp 68–84 4. Xia SH, Barr FG (2005) Chromosome translocations in sarcomas and the emergence of oncogenic transcription factors. Eur J C Cancer 41:2513–2527 5. Vega F, Medeiros JL (2003) Chromosomal translocations involved in non-Hodgkin lymphomas. Arch Pathol Lab Med 127:1148–1160

Forced vital capacity. The volume of air that can be forcibly exhaled following maximal inspiration.

Fusion Oncogenes

▶Chronic Obstructive Pulmonary Disease and Lung Cancer

F FX Definition Human homologue of GDP-4-keto-6deoxymannose-3, 5-epimerase-4-reductase. This enzyme is rate-limiting in the GDP-fucose synthetic pathway. ▶Fucosylation

▶Fusion Genes

FZD Fusion Proteins ▶Fusion Genes

Definition Frizzled; seven-pass transmembrane Wnt receptors closely related to G protein-coupled receptors. ▶Wnt Signaling

G

Definition

They transduce an extracellular signal (through ligand binding) into an intracellular signal (G protein activation) and are involved in a wide variety of stimulusresponse pathways, from intercellular communication to physiological senses.

▶Myc Oncogene ▶Retinoblastoma Protein, Cellular Biochemistry

▶Endothelins ▶Protease Activated Receptor Family ▶Adrenomedullin ▶G-Proteins ▶Receptor Cross-Talk ▶Protease Activated Receptor ▶Chemoattraction ▶RHO Family Proteins

G1/S Transition Of the ▶cell cycle is when the cellular decision to start duplicating its DNA is initiated. Mediators regulating this process include ▶cyclins, ▶cyclin-dependent kinases (CDKs), and CDK-inhibitors together with the transcription factors ▶E2F and ▶pRb that control the ▶restriction point after which DNA replication is initiated.

G Antigen ▶GAGE Proteins

G2 Checkpoint Abrogation

G-Proteins T HOMAS WORZFELD, S TEFAN O FFERMANNS Institute of Pharmacology, University of Heidelberg, Heidelberg, Germany

Synonyms Heterotrimeric GTP-binding proteins; Heterotrimeric guanine nucleotide-binding proteins

Definition

Definition

A concept of anti-cancer therapy that relies on the inhibition of the G2 DNA damage ▶checkpoint by small molecules in the presence of ▶DNA damage. G2 checkpoint abrogation results in mitotic cell death.

G-proteins are named for their ability to bind and hydrolyze the guanine nucleotide ▶GTP. In the widest sense, the superfamily of guanine nucleotide-binding proteins comprises two structurally distinct classes, the monomeric GTP-binding proteins (also called ▶monomeric GTPases) which are involved in a variety of cellular processes, and the heterotrimeric GTP-binding proteins which are primarily involved in transmembrane ▶signal transduction by coupling membraneous receptors to various effector molecules. Traditionally, the term “G-protein” is only applied to the latter group, the heterotrimeric GTP-binding proteins.

▶UCN-01 Anticancer Drug

G-protein Couple Receptor Definition

Characteristics

GPCR; seven transmembrane receptor, 7TM receptor, is the largest protein family of transmembrane receptors.

Cellular functions in a living organism are regulated and coordinated by a huge variety of extracellular

1190

G-Proteins

signals including ▶hormones growth factors, paracrine factors, neurotransmitters, or sensory stimuli. Many of these signals are received by cells through receptors on the plasma membrane which convey the incoming information by coupling to G-proteins which are attached to the inner side of the plasma membrane. More than 1,000 genes coding for G-protein-coupled receptors (▶GPCR) have been identified making GPCRs one of the largest gene families of the mammalian genome. G-proteins activated through GPCRs regulate various effectors like enzymes and ion channels which produce intracellular signals resulting in specific cellular responses. G-protein functions are highly diverse due to their composition of different α-, β-, and γ-subunits, each of which are products of different genes. The α-subunit of the heterotrimeric Gprotein possesses structural and functional homologies to other members of the guanine nucleotide-binding protein superfamily. The β- and γ-subunits of heterotrimeric G-proteins form an undissociable complex and represent a functional unit. Some G-proteins are very specialized like those expressed only in sensory cells; others appear to have functions in a wide variety of cells and tissues. Many G-proteins seem to have overlapping distributions and functions indicating that complex functional relationships exist among different Gproteins.

Molecular and Cellular Regulation In order to convey a signal from an activated receptor to an effector, the heterotrimeric G-protein undergoes an activation–inactivation cycle which allows the G-protein to function as a regulatable molecular switch (Fig. 1). In the basal state, the βγ-complex as well as the GDP-bound α-subunit is associated. In this form, the G-protein can be recognized by an appropriate activated receptor which interacts with the G-protein heterotrimer. This interaction results in the dissociation of GDP from the α-subunit of the heterotrimeric G-protein. GDP is then replaced by GTP. Binding of GTP to the α-subunit induces a conformational change, which in turn leads to the dissociation of the α-subunit and the βγ-complex. The GTP-bound α-subunit as well as the βγ-complex is now able to interact with effector proteins. A ▶GTPase activity inherent to the G-protein α-subunit terminates the G-protein activation. The formed GDP remains bound to the α-subunit which now reassociates with the βγ-complex. The reassociation of the heterotrimeric G-protein induced by the hydrolysis of GTP represents the inactivation mechanism for the βγ-complex. Two bacterial toxins specifically interfere with the G-protein activation–inactivation cycle and have been useful tools in studying G-protein-mediated signaling. ▶Pertussis

G-Proteins. Figure 1 The G-protein cycle. Upon activation of a G-protein-coupled receptor by binding of an agonist, GDP is released from the α-subunit of the heterotrimeric G-protein and replaced by GTP. This in turn leads to the dissociation of the α-subunit and the βγ-complex which are now able to interact with effector proteins. A GTPase activity inherent to the G-protein α-subunit terminates the G-protein activation. The hydrolysis of GTP to GDP can be accelerated by regulators of G-protein signalling (RGS) proteins as well as by various effectors.

toxin blocks the interaction of activated receptors and various G-proteins whereas ▶cholera toxin leads to the constitutive activation of some G-proteins. A physiological regulation of the GTPase activity of the α-subunit occurs by several effector proteins which interact with the GTP-bound α-subunit and accelerate their GTPase activity leading to G-protein inactivation. In addition, a family of proteins called “regulators of G-protein signaling” (▶RGS proteins) are also able to increase the GTPase rate of the G-protein α-subunit. More than 20 G-protein α-subunits have been described in the mammalian system, and they can be divided into four subfamilies based on structural and functional homologies (Table 1). The main properties of individual G-proteins appear to be primarily determined by the identity of the α-subunit of the heterotrimeric G-protein. While some G-protein α-subunits show a very restricted expression pattern others are expressed in a wide variety of tissues and some G-protein α-subunits like Gαs, Gαq, Gα11, Gα12, and Gα13 appear

G-Proteins G-Proteins. Table 1

Mammalian G-protein α-subunits

Class

Subtype

Expression

Gαs

Gαsa Gαolf Gαi1 Gαi2 Gαi3 Gαoa Gαgust Gαt-r Gαt-c Gαz Gαq Gα11 Gα14 Gα15/16c Gα12 Gα13

Ubiquitous Brain, olfactory epithelium Widely distributed Ubiquitous Widely distributed Neuronal, neuroendocrine cells Taste cells, brush cells Retinal rods, taste cells Retinal cones Neuronal, platelets Ubiquitous Almost ubiquitous Kidney, lung, spleen, testis Hematopoietic cells Ubiquitous Ubiquitous

Gαi/o

Gαq

Gα12

1191

Effectors

▶Adenylyl cyclase ↑ Adenylyl cyclase ↑ Adenylyl cyclase ↓ Adenylyl cyclase ↓ Adenylyl cyclase ↓ VDCC ↓b, GIRK ↑b ▶Phosphodiesterase ↑ ? Phosphodiesterase ↑ Phosphodiesterase ↑ Adenylyl cyclase ↓ ▶Phospholipase C-β ↑ Phospholipase C-β ↑ Phospholipase C-β ↑ Phospholipase C-β ↑ PDZ-RhoGEF, LARG p115-RhoGEF, PDZ-RhoGEF, LARG

VDCC, voltage-dependent Ca2+ channel; GIRK, G-protein-regulated inward rectifier potassium channel. a Various splice variants. b Effector is regulated by βγ-subunits. c Species variants (Gα15, mouse; Gα16, human). ?, Regulation not shown directly.

to be expressed more or less ubiquitously. An individual cell expresses up to ten different G-protein α-subunits. Five G-protein β-subunits and 11 γ-subunits have been described in the mammalian system. With the exception of the β5-subunit which is expressed mainly in the central nervous system, the currently known β-subunits exhibit a high level of sequence homology (79–90%). In contrast, G-protein γ-subunits are much more heterogeneous. Similar to GTP-bound Gα, βγ-complexes can also regulate various effectors. The best examples of βγ-regulated effectors are particular isoforms of ▶adenylyl cyclase and ▶phospholipase C, as well as ion channels and ▶phosphoinositide-3kinase isoforms. With a few exceptions, there appear to be no major differences between different βγ-combinations with regard to their ability to regulate effector enzymes. Stimulatory regulation of adenylyl cyclases through GPCRs involves G-proteins of the Gs-family of which two main members are known, Gs and Golf. The Gαi/o-family members have been shown to mediate receptor-dependent inhibition of adenylyl cyclases. Since the cellular levels of these G-proteins are usually relatively high, they also represent an important source for βγ-complexes which can regulate a

variety of cellular effectors. The G-protein Go is the most abundant G-protein in the mammalian nervous system. Go is involved in the inhibitory regulation of voltage-dependent Ca2+ channels, a process which appears to be mediated by the βγ-complex of Go. Several G-protein α-subunits are primarily expressed in sensory cells and have been involved in the signal transduction of sensory stimuli. Rod-transducin (Gt-r) and cone-transducin (Gt-c) play well established roles in the phototransduction cascade in the outer segments of retinal rods and cones where they couple light receptors to downstream signaling components of the retinal phototransduction cascade. In contrast to the transducins, the function of gustducin (Gαgust) in taste cells is less well understood. Among the five taste qualities (sweet, umami, bitter, sour, and salty), sweet, umami, and bitter tastes appear to be transduced through heterotrimeric G-proteins. Gαq-family members mediate the pertussis toxin insensitive regulation of phospholipase C β-isoforms. The Gq-family consists of four members whose α-subunits are expressed from individual genes with different expression patterns. Gαq and Gα11 appear to be expressed more or less ubiquitously and are primarily responsible for coupling of receptors to phospholipase C β-isoforms. In contrast, the murine G-protein α-subunit Gα15 and its

G

1192

GA733-2

human counterpart Gα16 are only expressed in a subset of hematopoietic cells, and the expression of Gα14 is restricted to several organs, e.g., kidney, testis, and lung. Receptors activating Gq-family members in mammalian systems do not discriminate between Gq and G11. The G-proteins G12 and G13 constitute the G12family and appear to be expressed ubiquitously. G12/13 regulate the actin cytoskeleton through the activation of the monomeric GTPase Rho (▶Rho-family proteins). This activation is mediated by a subgroup of guanine nucleotide exchange factors (▶GEFs) for Rho including p115-RhoGEF, PDZ-RhoGEF, and LARG. In recent years, genes of almost all G-protein α-subunits have been inactivated in mice. The resulting phenotypes of Gα-deficient animals have provided insights into the biological role of G-proteins demonstrating that G-protein-mediated signaling processes are crucially involved in multiple processes during development as well as in the adult organism.

Clinical Relevance G-protein-mediated signaling processes are operating in all cells of the human organism. They are involved in many physiological and pathological processes. Many clinically relevant drugs function as agonists or antagonists of GPCRs and exert their effects through G-protein-mediated signaling pathways. Some diseases have been found to be caused by distinct defects in single G-protein α-subunits. Emerging experimental data indicate that GPCRs, e.g., the receptors for ▶thrombin (▶Protease-activated receptor), ▶prostaglandin E2 (PGE2) (▶Prostaglandins), lysophosphatidic acid (LPA), and sphingosine-1-phosphate (S1P), are crucially involved in tumor growth and ▶metastasis. ▶Gain-of-function mutations of the gene encoding Gαs (GNAS) give rise to the gsp oncogene (▶Oncogene) which has been found in almost 30% of thyroid toxic adenomas as well as in some thyroid carcinomas (▶Thyroid carcinogenesis) and growth hormone producing pituitary adenomas. The sporadic somatic mutation leads to the substitution of Arg201, the same residue which is ADP-ribosylated by cholera toxin, and results in a constitutively active form of Gαs by blocking its GTPase activity. This leads to activation of adenylyl cyclase independent of receptor agonists. The same sporadic mutation occurring early in embryogenesis results in a ▶mosaicism which is responsible for the ▶McCune-Albright syndrome characterized by polyostotic fibrous dysplasia of the bone, precocious puberty, and café-au-lait pigmentation of the skin. An analogous mutation of the gene encoding Gαi2 (GNAi2) (the gip2 oncogene) has been found in human

ovarian sex cord stromal tumors and adrenal cortical tumors (▶Adrenocortical cancer). In vitro studies indicate that expression of constitutively active forms Gαq and Gα11 can lead to transformation of fibroblasts when expressed at low levels. No transforming mutants of Gαq and Gα11 have been detected in human tumors, but various Gq/G11coupled receptors have been shown to be involved in the stimulation of proliferation in small lung cancer cells. The ▶Kaposi sarcoma-associated herpesvirus (KSHV/ HHV8) is suppose to encode a Gq/G11-coupled receptor and signaling via this receptor has been shown to lead to cell transformation, tumorigenicity, and angiogenesis, and thus to critically contribute to KSHV-mediated oncogenesis. GNA12 the gene encoding Gα12 was identified as an oncogene (the gep oncogene) in soft tissue sarcoma. Constitutively active mutants of Gα12 and Gα13 have been shown to exhibit potent transforming activity in different systems. No activating mutation of Gα12 or Gα13 has been found in human tumors so far, however, increased expression levels of both proteins have been detected in various human cancers. In addition to their role in the regulation of cellular growth and their transforming ability, signaling via Gα12/13-proteins has recently been implicated in the control of ▶invasion and metastasis of breast and prostate cancer cell lines. By regulating a subgroup of RhoGEF-proteins, both Gα12 and Gα13 can activate the small GTPase RhoA which has been suggested to play an important role in cancer ▶progression and invasion.

References 1. Wettschureck N, Offermanns S (2005) Mammalian G proteins and their cell type specific functions. Physiol Rev 85(4):1159–1204 2. Spiegel AM, Weinstein LS (2004) Inherited diseases involving g proteins and g protein-coupled receptors. Annu Rev Med 55:27–39 3. Kelly P, Moeller BJ, Juneja J et al. (2006) The G12 family of heterotrimeric G proteins promotes breast cancer invasion and metastasis. PNAS 103(21):8173–8178 4. Dorsam RT, GutkindJS, (2007) G-protein-coupled receptors and cancer. Nat Rev Cancer 7(2):79–94 5. Malliri A, Collard JG (2003) Role of Rho-family proteins in cell adhesion and cancer. Curr Opin Cell Biol 15 (5):583–589

GA733-2 ▶EpCAM

GAGE Proteins

GABA Definition

▶Gamma-Aminobutyric Acid ▶Photodynamic Therapy

1193

GAGE Proteins H ENRIK J. D ITZEL 1,2 , M ORTEN F. G JERSTORFF 1 1

Medical Biotechnology Center, Institute of Medical Biology, University of Southern Denmark, Odense C, Denmark 2 Department of Oncology, Odense University Hospital, Odense C, Denmark

Synonyms

GADD45

CT4; G antigen

Definition Definition

Growth arrest and DNA damage, a ▶p53-responsive protein that induces a ▶G2/M ▶checkpoint of the cell cycle. ▶Daxx ▶G2/M Transition

GADD153 Definition Growth Arrest DNA Damage 153 is a small nuclear protein that is capable of dimerizing with various ▶transcription factors. Under normal cellular conditions this protein is not expressed in detectable levels, but is highly upregulated during times of cellular stress such as ▶anoxia.

Gadolinium Definition A rare earth metal (lanthanide), gadolinium ions are chelated to form paramagnetic contrast agents for use in ▶magnetic resonance imaging (MRI). ▶Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Belong to the ▶cancer testis antigen (CTA) family and consist of at least 16 highly homologous proteins (GAGE 1, GAGE2A-E, GAGE10, GAGE12B-J, GAGE13).

Characteristics The 16 genes that encode GAGE proteins are located in an equal number of tandem repeats on chromosome X (p11.2-p11.4 region). GAGE 1 is unique among the GAGE proteins because of an exclusive C-terminal encoded by an exon that is interrupted in the other GAGE genes. The remaining GAGE members are composed of five exons encoding 116–117 amino acids with 98% identity, while GAGE1 consist of 138 amino acids. The molecular size of GAGE proteins is 26–29 kDa. In contrast to other CTAs, the expression of which in adult normal tissues is restricted to germ cells of testis, GAGE is also expressed in a subset of oocytes of resting primordial follicles and in maturing oocytes of ovaries. In the testicular seminiferous tubuli, GAGE expression is restricted to the spermatogonia and, to a lesser degree, the primary spermatocytes. GAGE gene transcripts have been found in numerous cancers, most frequently ▶malignant melanoma (24–42%), ▶lung cancer (19–54%) ▶thyroid cancer (30%) ▶breast cancer (26%) ▶hepatocellular cancer (38%) and ▶ovarian cancer (30%) sarcomas (19%) (▶Osteosarcoma, ▶rhabdomyosarcoma), and ▶bladder cancer (12%). Immunohistochemical studies have also identified GAGE in many cancers, but generally at a lower frequency than that observed by ▶RT-PCR, including bladder cancer (40%) [00187], ▶malignant melanoma (17%), ▶lung cancer (16%) ▶breast cancer (12%), and ▶thyroid cancer (10%). The staining pattern varied significantly among and within specimens, and most GAGE-positive tumors also contained cancer cells lacking GAGE expression. GAGE has been correlated to poor prognosis in ▶gastric cancer, ▶esophageal carcinoma and ▶neuroblastoma.

G

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Gain of Function p53

In vitro studies have shown that GAGE expression in tumors can be induced by the DNA methyltransferase inhibitor 5-aza-2′-deoxycytidine (▶Methylation), but the transcription of individual GAGE genes seems to be differently regulated, since the GAGE members are not always co-expressed. GAGE proteins are immunogenic and lead to antiGAGE antibody and ▶cytotoxic T lymphocyte (CTL) responses in some cancer patients. The GAGE 1 gene was originally identified as encoding an antigenic peptide, YRPRPRRY, which was presented on a human melanoma by the MHC class I molecules HLA-Cw6 and recognized by a CTL clone derived from the melanoma patient. From the same patient, another CTL clone recognizing the peptide YYWPRPRRY, which is encoded by GAGE2A-E and presented by HLA-A29 molecules, was also isolated. Anti-GAGE antibodies are present in 6% of melanoma patients, but not in pancreas cancer patients. Subcellular localization of GAGE in normal cells (e.g. germ cells) and cancer cells is similar; exhibiting weak cytoplasmic staining and variable nuclear staining. This suggests that GAGE, when expressed in cancer cells, is expressed in the natural context and thus may play a functional role therein. The nuclear localization of GAGE in spermatogonia and cancer cells suggests that GAGE may be a regulator of germline gene expression. Due to the restriction of GAGE expression to immunoprivileged normal tissues and their relatively frequent expression in different types of cancer, GAGE proteins are considered attractive candidates for T cellmediated, cancer-specific ▶immunotherapy. However, the lack of GAGE expression in subsets of cancer cells within GAGE-positive tumors, as also observed for other CTAs, may limit its value as a therapeutic target. Combining different CTA targets may compensate for the heterogeous expression of each CTA within cancers and improve the therapeutic potential. The function of GAGE members remains largely unknown, although one study has reported antiapoptotic properties of GAGE12 (formerly known as GAGE7). GAGE12-transfected cells were shown to be resistant to ▶apoptosis induced by ▶interferon-gamma or by the death receptor ▶Fas/APO-1/CD95. In the Fas pathway, the anti-apoptotic activity of GAGE12 maps downstream of ▶caspase-8 activation, and upstream of poly (ADP-ribose) polymerase (PARP) cleavage. Furthermore, GAGE12 renders the cells resistant to the chemo- and radio-therapeutic agents (▶Chemotherapy of cancer, progress and perspectives, ▶radioimmunotherapy), ▶Taxol and gamma-irradiation.

References 1. Van den Eynde B, Peeters O, De Backer O et al. (1995) A new family of genes coding for an antigen recognized by autologous cytolytic T lymphocytes on a human melanoma. J Exp Med 182(3):689–698

2. Simpson AJ, Caballero OL, Jungbluth A et al. (2005) Cancer/testis antigens, gametogenesis and cancer. Nat Rev Cancer 5(8):615–625 (Review) 3. Gjerstorff MF, Johansen LE, Nielsen O et al. (2006) Restriction of GAGE protein expression to subpopulations of cancer cells is independent of genotype and may limit the use of GAGE proteins as targets for cancer immunotherapy. Br J Cancer 94(12):1864–1873

Gain of Function p53 G IOVANNI B LANDINO Rome Oncogenomic Center, Department of Experimental Oncology, Regina Elena Cancer Institute, Rome, Italy

Definition Gain of function is the property of some proteins whose alterations determine the acquisition of novel functions mainly opposite to those exerted by the ▶wild-type counterparts.

Characteristics

The gene product of the tumor suppressor ▶p53 represents a paradigm of a protein whose alterations, mainly missense mutations, cause the acquisition of novel functions that contribute to the insurgence, the maintenance, the spreading and the ▶chemoresistance of certain tumors. p53 is a ▶transcription factor that can be roughly divided in three functional domains: (i) the N-terminus where resides the transcriptional activity; (ii) the central DNA binding domain that is responsible for the specific recognition of p53 binding sites; and (iii) the C-terminus domain that exerts oligomeric and autoregulatory activities. Half of human cancers bear p53 mutations that mainly occur within the specific DNA binding domain. The resulting proteins are characterized by the loss of the antitumoral activities of wild-type p53 (wt-p53) and, at least, for some of them by the gain of novel oncogenic activities. Many in vitro and, very recently, in vivo studies have shown that, at least, some of these mutant p53 proteins gain novel oncogenic functions that range from increased proliferation to enhanced chemoresistance to anticancer treatments. To date, the diverse mutant p53 proteins have been classified accordingly to their structural features. Indeed, they can be divided in two large classes: (i) DNA contact defective mutants whose missense mutation impacts on the region of the protein that contacts the DNA. The prototypes of this class of mutants are p53His273 and p53Trp248 that are also the

Gain of Function p53

most frequent p53 mutations found in human cancers. (ii) Defective structure mutants whose missense mutation resides within the region of the stabilization of the internal loops (L2 and L3) of p53 and consequently their overall structure is quite different than that of wt-p53. Despite many ongoing attempts, a functional classification of p53 mutations that resembles their structures features has not been identified yet. By comparing wild-type versus mutant p53 two peculiar differences can be revealed. While wt-p53 is a shortliving protein capable to activate target genes transcriptionally through the recognition of specific binding sites on their regulatory regions, mutant p53 is a very stable protein that is unable to bind wt-p53 consensus. There is scarce evidence on the molecular basis of the prolonged half-life of mutant p53 compared with that of wt-p53, but this peculiar feature might play a key role in gain of function. Molecular Mechanisms The molecular mechanisms underlying gain of function of mutant p53 proteins need to be clarified yet. To date, two scenarios can be proposed as molecular basis for mutant p53 gain of function. The first one relies on the prolonged half-life of mutant p53 proteins that are consequently very abundant in tumor cells. Thus,

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mutant p53 proteins can be engaged in many and multiple physical protein–protein interactions. One of the most studied is that with the newly discovered ▶p53 family members, p73 and p63 (Fig. 1a). The latter, despite their critical roles in development and differentiation, have been shown to recapitulate most of the wt-p53 tumor suppressor activities when exogenously expressed in p53+/+ and p53 null cells. Floating protein complexes involving mutant p53 and p73 or p63 have clearly evidenced in diverse tumor cell lines. The net result of these protein complexes is the severe impairment of p73/p63-mediated growth suppression and ▶apoptosis. Chromatin immunoprecipitation experiments have clearly shown that mutant p53 severely impairs the in vivo recruitment of both p73 and p63 to the regulatory regions of their target genes. The polymorphism at position 72 of mutant p53 has been shown to be a critical determinant of the strength of the protein complex mutant p53/p73. Indeed, the 72R (Arg) forms of p53Ala143 and p53His175 mutants bind to p73 and impairs p73-mediated gene target transcriptional activation more efficiently than the equivalent 72P (Pro) mutants. The biochemical analysis of the protein complex mutant p53/p73 has revealed that the interaction surface is composed by the core domain of mutant p53 and the specific DNA binding

Gain of Function p53. Figure 1 Schematic representation of two molecular scenarios underlying gain of function of mutant p53. (a) Mutant p53 proteins form protein complexes with the newly discovered p53 family members, p73 and p63 (▶p53 protein biological and clinical aspects). This results in the impairment of p73 or p63 recruitment on the regulatory regions of their target genes and of p73/p63-mediated apoptosis in response to DNA-damaging agents. (b-upper part) Mutant p53 binds directly to DNA through a consensus that remains to be identified yet; (b-lower part) Mutant p53 takes part to large protein complex facilitating the recruitment of the acetylase, p300. The final outcome is the transcriptional modulation of target genes responsible for the indicated biological effects.

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domain of p73. These findings have discovered a novel function for the core domain of mutant p53, such as, its ability to function as a protein–protein interaction platform. Is there any link between the selective pressure for p53 missense mutations in the core domain and gain of function activity of mutant p53 proteins? There is no sufficient evidence to make a conclusion. The vast majority of p53 mutant proteins are unable to bind wt-p53 binding sites present on the regulatory regions of its target genes and consequently are inefficient in the activation of wt-p53 mediated antitumoral effects. Opposite to such loss of function, mutant p53 proteins may acquire, through its mutated core domain, new properties that contribute to their gain of function. Despite many efforts, the presence of wt-p53/p73 protein complexes has not been identified in tumor cells. This might suggest that mutant p53 binds to a pool of selected proteins diverse than those bound by wt-p53. The presence of mutant p53 or wt-p53 in large and multiple protein complexes might represent a key determinant of their biological outputs. A paradigmatic example has been recently provided by the analysis of the transcriptional cross-talk between mutant p53 and the transcription factor NF-Y. The latter binds to both wt- and mutant-p53 but the transcriptional effects on NF-Y target genes are repression or activation, respectively. Is mutant p53 a bona fide transcription factor? (Fig. 1b) There is growing evidence accounting for transcriptional activity of mutant-p53 as molecular mechanism underlying its gain of function activity. This possibility mainly resides on the assumption that the N-terminus of mutant p53 in functionally intact and might exert specific transcriptional activity. To date, one of the key features of a bona fide transcription factor such as a specific DNA binding site for mutant p53 proteins has not been identified yet. This might suggest that mutant p53 can exert its transcriptional activity by engaging with DNA binding proteins, acetylases, deacetylases, and other proteins in the context of large protein complexes. If this hypothesis will be further demonstrated, as occurred for the transcriptional crosstalk mutant p53/NF-Y, it will mean that the plethora of the putative mutant p53 target genes is rather large, thereby providing the molecular basis underlying the diverse mutant p53-mediated oncogenic effects. There is scarce evidence on the role of mutant in these large protein complexes and specifically the contribution of its N-terminus transcriptional activation domain. It was originally shown that mutant p53 proteins, whose residues 22 and 23 were mutated, lost their oncogenic activity as well as their ability to transactivate specific target genes. Despite the molecular details need to be clarified yet, these findings strongly support a direct involvement of the N-terminus of mutant p53 in the activity of the large transcriptional competent protein

complexes. The biochemical analysis of the spatial and temporal events regulating the cross-talk between mutant p53 and NF-Y has revealed a different transcriptional contribution of mutant p53 proteins (p53 protein biological and clinical aspects). Indeed, it was found that mutant p53 facilitates the recruitment of p300 acetylase, thereby indicating that it might serve as scaffold protein whose contribution results in the stabilization and proper activation of the transcriptional competent protein complex. Recent evidence has shown an additional molecular mechanism for mutant p53 gain of function activity. It is based on the tight association of mutant p53 with the nuclear matrix in vivo, and with high affinity to nuclear matrix attachment region (MAR) DNA in vitro. These findings suggest that mutant p53 interacting with key structural components of the nucleus, exerts its gain of function activity through the perturbation of the nuclear structure and function. As described earlier, the molecular scenario(s) underlying gain of function of mutant p53 are rather complex. It might be reasonable that a combination of specific protein–protein interaction and direct transcriptional activity takes place in driving gain of function of mutant p53. Many questions regarding the contribution of cell context, type of p53 mutations, posttranslational modifications are still unanswered and might be determinant in the final outcome of mutant p53 activities.

Clinical Aspects Many in vitro and in vivo evidences have shown that the status of p53 is a key determinant of tumor aggressiveness and chemosensibility to common anticancer treatments. Tumors carrying p53 mutations are more resistant to the killing of anticancer agents and relapse more frequently than those bearing wt-p53. As a consequence of it, the overriding of mutant p53 gain of function might be extremely useful for treating mutant p53 tumors. Diverse approaches ranging from reactivation of mutant p53 to its wt-conformation as well as the elimination of mutant p53 have been undertaken in the last few years. In addition to them, the use of short peptides capable to specifically disassemble oncogenic protein complexes involving mutant p53 protein might be attempted to increase the chemosensibility of tumor cells. The well-established mutant p53/p73 protein complex could be a preferential target to be tackle with such approach. The amount of free and available p73 to be recruited in activating proapoptotic pathways in response to different anticancer treatments might be significantly increased by pretreating mutant p53 cells with short interfering peptides capable to disrupt the protein complex mutant p53/p73. These effects might render mutant p53 cells more prone to the killing of anticancer treatments.

Gallbladder Cancer

References 1. Strano S, Dell’Orso S, Di Agostino S et al. (2007) Mutant p53: an oncogenic transcription factor. Oncogene 26:2212–2219 2. Di Agostino S, Strano S, Emiliozzi V et al. (2006) Gain of function of mutant p53: the mutant p53/NFY protein complex reveals an aberrant transcriptional mechanism of cell cycle regulation. Cancer Cell 3:191–202 3. Soussi T, Beroud C (2001) Assessing TP53 status in human tumours to evaluate clinical outcome. Nat Rev Cancer 1:233–240 4. Sigal A, Rotter V (2000) Oncogenic mutations of the p53 tumor suppressor: the demons of the guardian of the genome. Cancer Res 60:6788–6793

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types and binds glycoconjugates on the cell surfaces and ▶extracellular matrix. ▶CEA Gene Family

Gallbladder Cancer G IORGIA R ANDI Department of Epidemiology, Institute for Farmacological Research Mario Negri, Milan, Italy

Gain-of-Function Mutation Definition Is any mutation of a gene that causes increased function and/or activity of its encoded protein or of a protein that is directly or indirectly regulated by the mutated gene. ▶Gain of Function P53 ▶Gastrointestinal Stromal Tumor

GAK ▶Cyclin G-Associated Kinase

Galactorrhea Definition Breast milk secretion at a time other than normal lactation. ▶Prolactin

Galectin-3 Definition Protein with an amino-terminal non-lectin domain and a carboxy-terminal lectin domain. Expressed in many cell

Definition The biliary tract consists of an interconnected system of intra- and extrahepatic ducts that transport ▶bile secreted from the liver to the digestive tract. The gallbladder is an important organ of the biliary system lying just under the liver, receiving, storing and then releasing the bile through bile ducts into the duodenum to help digesting fat. Gallbladder cancer (GC) is the most common type of cancer of the biliary tract.

Characteristics GC is a relatively rare neoplasm and despite being a non sex-related cancer is several-fold more frequent among women than among men. Detection of GC is quite difficult because symptoms and signs of GC are not specific and often appear late in the clinical course of the disease. For this reason, diagnosis is generally made when the cancer is already in advanced stages, and prognosis for survival is less than 5 years in 90% of cases. Descriptive Epidemiology GC incidence is characterized by a wide worldwide variation (Fig. 1) being low in several European countries and the United States of America (USA), relatively high in selected central European countries, and very high in some countries of Latin America and Asia. GC has been shown to be the first cause of cancer death among women in some areas of Chile. According to ▶incidence rates recorded by cancer registries in mid-1990s, the highest incidence rate worldwide was shown by women from Delhi, India (21.5/100,000), followed by South Karachi, Pakistan (13.8/100,000) and Quito, Ecuador (12.9/100,000). Cancer registries reporting high GC incidence rates were in Far East Asia (Korea and Japan), Eastern Europe (Slovakia, Poland, Czech Republic and Yugoslavia), and South America (Colombia). In Western Europe, elevated incidence rates were shown in Granada, Spain. Although

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Gallbladder Cancer. Figure 1 Worldwide incidence of gallbladder cancer among women. Geographic areas according to incidence rates of mid-1990s from 40 selected cancer registries: areas in red are characterized by very high incidence rates (age-standardized rates ≥ 10 per 100,000 women); areas in yellow are characterized by high incidence (age-standardized rates between 6 and 10 per 100,000 women); areas in green are characterized by medium incidence rates (age-standardized rates between 2 and 6 per 100,000); areas in blue are characterized by low incidence rates (age-standardized rates < 2 per 100,000 women). *Countries in Europe were not specified because of space reasons: Germany, Italy, France, Slovenia, Croatia, Lithuania, Russia, Estonia shown medium incidence rates; Latvia shown low incidence rate. **No official incidence rate was available for Chile, but GC has been shown to be the first cause of cancer death among women in some areas of the country.

systematically lower than in women, high incidence rates among men (ranging between 4.4 and 8.0/100,000) were found in some areas of Asia and Eastern Europe. Low incidence rates (below 3/100,000 women and 1.5/100,000 men) emerged for most registries from Northern Europe, with the partial exception of Sweden, and from the USA (SEER), and Canada. The female to male (F/M) incidence ratio of GC incidence rates varied greatly: it was more than 5 in several high-risk areas (e.g., Pakistan, India, Colombia and Spain) as well as in low-risk areas (e.g., Denmark), but was typically between 2 and 3 in the majority of countries. F/M ratio was close to 1 in Korea, Japan and some part of China. Incidence rates of GC in various ethnic groups from selected cancer registries in the USA confirmed the worldwide pattern, as GC was substantially more

frequent among Hispanic than non-Hispanic white women and remarkably elevated among Korean and Chinese men. Very high incidence was also reported by men and women among American Indians in New Mexico. Also the F/M ratio reflected the worldwide situation being high among Hispanic whites, and close to 1 among Koreans, Filipinos, Japanese and Chinese. Risk Factors ▶Carcinogenesis of gallbladder is still poorly understood, and limited number of ▶epidemiologic studies have been published on this issue because of (i) the rarity of GC in countries where most medical research is funded and performed, (ii) the difficulties of histological identification of GC, (iii) the lack of relevant animal models and tumor cell lines for GC, (iv) the lack of comprehensive national or international registries

Gallbladder Cancer

for information on GC cases. ▶Risk factors for GC include genetic predisposition, geographic variation and ethnicity, increasing age, female gender, chronic inflammation, congenital abnormalities, low socio-economic status, low frequency of ▶cholecystectomy for gallbladder diseases and exposure to certain chemicals. History of ▶gallstones and ▶cholecystitis are considered the major risk factors for GC. Several cohort and case-control studies found strong association between history of benign gallbladder diseases (mainly gallstones) and GC risk. Cholesterol and mixed gallstones (containing more than 50% of cholesterol) account for 80% of the all gallstones found, and pigment stones (composed largely of calcium bilirubinate) account for the remaining fraction. The etiology of cholesterol gallstones is thought to involve the interaction of genetic factors (e.g. modification of MDR3 and CYP7A1 genes, and numerous lithogenic genes) and several environmental factors (age, female gender, ▶obesity, multiple pregnancies, a family history of gallstones and low levels of physical activity). The worldwide distribution of gallstone prevalence shows a strong geographic and ethnic variation, and a positive correlation with the incidence rates of GC. High gallstone prevalence (≥50%) among women was found among American Indians in the USA, and among Mapuche Indians in Chile, both populations presenting very high GC incidence rates. Other areas with high or medium prevalence of gallstones were identified in South America, in Eastern and Western Europe. Very few is known about some regions of the world like India where high incidence of symptomatic gallstones has been observed, but results from ultrasound-based studies are not available. Low-risk areas for gallstones (i.e., prevalence 100 ng/l), abnormal secretin stimulation test (increment in fasting serum level of gastrin >200 ng/l after intravenous secretin), and an elevated basal level of gastric acid output (>10 mEq/h). Gastrinomas are thought to originate from gastrinproducing (G) cells that are normally dispersed in gastric antral and upper duodenal mucosa (▶Gastrointestinal tumors; ▶Gastrointestinal hormones). However, there is no direct correlation between the distribution of G cells in the digestive system and frequency of gastrinoma location. The tumors commonly arise in ectopic sites such as pancreas (the second most common location) that is normally devoid of G cells. More than 50% of gastrinomas arise in the duodenum. Ninety percent of all gastrinomas are located in the “gastrinoma triangle” (the anatomic junction of cystic and common bile ducts, second and third portion of the duodenum, and neck and body of the pancreas). Solitary pancreatic or duodenal gastrinomas are characteristic for sporadic ZES cases. Location of the tumors in proximal duodenum and their multiplicity are common in ZES-MEN1 patients. Cases of gastrinoma located solely in periduodenal and peripancreatic lymph nodes have been reported, and clinical cure has been achieved following surgical excision of regional lymph nodes in some of such cases. Microscopically, gastrinomas are composed of small, uniform cells with abundant eosinophilic cytoplasm, and small uniform nuclei with inconspicuous nucleoli. Correlation between histologic features and malignant behavior is poor. Mitotic activity and nuclear pleomorphism, when rarely present, are unreliable predictors of prognosis in gastrinoma. Despite their small size and lack of invasion into adjacent organs, duodenal gastrinomas demonstrate high malignant potential with propensity for regional lymph node and distant metastases. Because gastrinoma may be an initial manifestation of ▶MEN1 in up to one third of familial ZES cases, it is currently recommended to evaluate all ZES patients for medical and family history of the endocrine neoplasms and assess their parathyroid and pituitary function. The differentiation of patients with familial ZES-MEN1 from patients with sporadic ZES is important because of the differences in natural history of ZES, need for family screening, difficulty in controlling acid hypersecretion, and need for exploratory laparotomy for cure. Gastrinomas are reported to be malignant in 60–90% of cases. About 34% of patients with ZES have metastatic disease at the time of diagnosis. Periduodenal and peripancreatic lymph nodes, liver, and bone are the most common sites of metastases. Gastrinomas in

MEN1-ZES and sporadic ZES patients have similar rates of metastases. Therapy Since ZES can be cured only by excision of a gastrinoma in the early stage of the disease, the exact tumor localization may be crucial in successful management of ZES patients. Duodenal gastrinomas are frequently small in size (less than 1.0 cm) and are difficult to find preoperatively. Tumor localization studies (▶CT, ▶MRI, and ▶octreotide scanning) are necessary for preoperative localization. Exploratory ▶laparotomy with intraoperative ultrasonography, transduodenal endoscopic illumination, duodenotomy, and surgical resection of the tumor is currently recommended for patients with sporadic ZES patients. The usefulness of surgery varies for patients with ZESMEN1 who usually have multiple tumors. Treatment of patients with ZES is also directed at reducing gastric acid hypersecretion. Total gastrectomy or vagotomy has been used. However, over the past 15 years a highly potent antisecretory proton pump inhibitor, ▶omeprazole, has been effective in suppression of gastric acid output and has significantly decreased the early mortality of patients due to complications of ulcer disease. With the increased ability to control hyperchlorhydria, the progression of gastrinoma and metastases are becoming the primary factor in long-term survival of patients with ZES. The clinical course of gastrinoma is indolent and the prognosis is directly related to the spread of the tumor. Patients with liver metastases have only a 20–30% chance of surviving for 5 years, whereas patients without liver metastases have an excellent long-term prognosis (>90% 5-year survival rate). Genetics The role of the MEN1 gene as an early event in gastrinoma tumorigenesis has been established in MEN1associated gastrinomas as well as in 33% of sporadic gastrinomas regardless of metastases. In both familial and sporadic gastrinomas the MEN1 gene, located on chromosome 11q13, is thought to act as a tumor suppressor based on the presence of inactivating mutations in the normal tissue/blood DNA, accompanied by the loss of the wild type allele in the tumor. Either ▶homozygous deletion or ▶hypermethylation at the 5′ region of the p16/MTS1 or ▶p16INK4a tumor suppressor gene on chromosome 9p21 was demonstrated exclusively in sporadic gastrinomas and not in other pancreatic neuroendocrine tumors. The finding suggests that p16/MTS1 or p 16INK4adefect is restricted to gastrinproducing tumors. Somatic genetic changes associated with the development of most sporadic gastrinomas and as well as with the progression to malignancy are currently unknown.

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References

Definition

1. Jensen RT, Fraker DL (1994) Zollinger-Ellison syndrome: advances in treatment of gastric hypersecretion and gastrinoma. JAMA 18:1429–1435 2. Norton JA, Fraker DL, Alexander HR et al. (1999) Surgery to cure the Zollinger-Ellison syndrome [see comments]. N Engl J Med 341:635–644 3. Debelenko L, Zhuang Z, Emmert-Buck MR et al. (1997) Allelic deletions on chromosome 11q13 in multiple endocrine neoplasia type 1-associated and sporadic gastrinomas and pancreatic endocrine tumors. Cancer Res 57:2238–2243 4. Zhuang Z, Vortmeyer A, Pack S et al. (1997) Somatic mutations of the MEN1 tumor suppressor gene in sporadic gastrinomas and insulinomas. Cancer Res 57:4682–4686 5. Muscarella P, Melvin WS, Fisher WE et al. (1998) Genetic alterations in gastrinomas and nonfunctioning pancreatic neuroendocrine tumors: an analysis of p16MTS1 tumor suppressor gene inactivation. Cancer Res 58:237–240

GastroIntestinal Stromal Tumor (GIST) is a type of sarcoma (i.e., a connective tissue neoplasia). GIST is a rare cancer affecting the digestive tract or nearby structures within the abdomen.

Gastroesophageal Reflux Disease Definition GERD; The reflux from acidic gastric content into the esophagus mostly due to a gastric hernia results in esophagitis, favoring cancer risk in the lower esophagus. ▶Alcohol Consumption ▶Esophageal Cancer

Gastrointestinal Hormones ▶Gut Peptides

Gastrointestinal Stromal Tumor C HI TARN , A NDREW K. G ODWIN Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, PA, USA

Synonyms GIST

Characteristics Epidemiology and Clinical-Pathological Features of GIST GISTs are believed to arise from the ▶Interstitial Cells of Cajal (ICCs), the pacemaker cells for the autonomous movement of the GI tract. Other studies have suggested that GISTs arise from interstitial mesenchymal precursor ▶stem cells; however, pinpointing the progenitor cell has been difficult. Although it is considered a rare tumor, nearly 4,500–6,000 new cases are diagnosed annually in the United States. The peak incidence of GIST occurs later in life with a median age of 58 years; however, there are also reports of pediatric GISTs. The most common sites of origin for GIST are the stomach (39–70%) and small intestine (31–45%). Other primary sites include the large bowel, rectum, appendix, and rarely the esophagus. A small percentage of GISTs arise outside the tubal gut, i.e., within the mesentery, gallbladder, and omentum. These tumors are known as extra-gastrointestinal GIST. The symptoms of GIST include bloating, gastrointestinal bleeding, or fatigue related to anemia. The common metastatic sites for GIST include the liver and omentum, and less frequently, the lung and bone. Diagnosis Approximately 95% of GISTs express the antigen CD117 (better known as ▶KIT) when examined by ▶immunohistochemistry (IHC) (Fig. 1). The c-KIT gene is the normal cellular homologue of a viral oncogene (v-Kit, Hardy Zuckerman 4 feline sarcoma viral oncogene homologue). There is a small subset of GISTs that lack KIT expression. Oncogenic Signaling Pathways in GIST KIT is a 145-kDa transmembrane glycoprotein and is a member of the tyrosine kinase family of receptors. Other members in this family include PDGFRα and β (Fig. 2a). KIT is normally expressed in hematopoietic stem cells, ▶mast cells, melanocytic cells, germ cells, and the ICC. The normal function of KIT is dependent on binding to its ligand, ▶Stem Cell Factor (SCF), and is essential in embryonic development. Acquired mutations in the c-KIT gene are referred to as “▶gain-offunction” or “activating” mutations, which lead to constitutive ligand-independent activation of the tyrosine kinase activity of the receptor. Molecular genetic studies have shown that the vast majority of GISTs (70– 80%) possess a c-KIT mutation in either exon 9, 11, 13,

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Gastrointestinal Stromal Tumor

Gastrointestinal Stromal Tumor. Figure 1 GIST. Left: Surgically resected gastric GIST; right: Immunohistochemical staining of a paraffin-embedded GIST tissue section for KIT protein expression.

or 17, and that a subset of GIST (10%) possesses a PDGFRα mutation in either exon 12, 14, or 18. Even though c-KIT or PDGFRα mutations are detected in GIST, approximately 10% of GISTs lack mutations in either of these genes. Therefore, other yet to be discovered genetic and potentially epigenetic mechanisms, independent of c-KIT and PDGFRα activation, may contribute to the pathogenesis of GIST. KIT gain-of-function mutations result in autoactivation of the receptor, and consequently transmit the KIT oncogenic signal to downstream targets such as phosphatidylinositol 3-Kinase (▶PI3K), ▶AKT (as known as protein kinase B), and mitogen-activated protein kinases (▶MAPK). These signaling proteins influence proliferation, ▶apoptosis, differentiation and/or cell ▶adhesion (Fig. 2b). Clinical observations and laboratory research have shown that different gain-offunction mutations within the same receptor can affect different down-stream pathways and clinical response to therapy. Cytogenetics and Molecular Cytogenetic Alterations Even though mutations in c-KIT or PDGFRα appear to be the primary driving force in the pathogenesis of GIST, several other genetic and genomic changes have been documented which contribute to the development of this disease. ▶Monosomy for chromosome 14 is one of the most frequent (>60%) genomic alterations detected in GISTs. Other common changes in metastatic GISTs include loss of chromosome arms 1p, 9p, 10, 14q, 15q, and 22, and gains involving 5p and 20q. Therapy ▶Cytoreductive surgery is the standard of care for patient with primary GIST. This surgery seeks to remove the entire gross tumor, and may require total or subtotal organ resection, depending on tumor location

and size. However, surgery has limited success for locally recurrent or metastatic GIST and clinical response of patients to systemic therapy using conventional chemotherapies is abysmal. ▶Chemotherapy response rates in patients with metastatic disease are less than 5% for all tested cytotoxic agents with a median survival of 10–20 months. ▶Imatinib mesylate (STI571 or Gleevec™), is an oral 2-phenylaminopyrimidine derivative that acts as a selective inhibitor against several ▶receptor tyrosine kinases including KIT, PDGFRα, and ▶BCR-ABL (which is the causative ▶chromosomal translocation in ▶chronic myelogenous leukemia). Based on a high percentage of metastatic GIST patients demonstrating clinical response to imatinib in phase I/II ▶clinical trials, the FDA granted Novartis approval of imatinib for the treatment of advanced GIST in 2001. Clinically, it has been reported that patients with metastatic or localized GIST possessing a mutation in exon 11 (i.e., involving the juxtamembrane domain of the receptor) of c-KIT mutations have a longer ▶progression free survival and overall survival when treated with imatinib as compared to patients with tumors with other types of c-KIT mutations. Likewise, mutations in exon 12 (juxtamembrane domain) of PDGFRα are more sensitive to imatinib treatment than patients with other types of mutations in PGDFRα. In summary, GISTs are the most common mesenchymal tumors of the digestive tract and possess mutations in either c-KIT or PDGFRα. For patients with localized resectable GIST, surgery remains the treatment of choice, whereas, for patients with metastatic disease, imatinib-based therapy is providing benefit for longterm disease control.

References 1. Hirota S, Isozaki K, Moriyama Y et al. (1998) Gain-offunction mutations of c-kit in human gastrointestinal stromal tumors. Science 279:577–580

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Gastrointestinal Stromal Tumor. Figure 2 Structure and signaling pathways of KIT and PDGFRα. (a) Schematic structure of KIT and PDGFRα. (b) Signaling pathways down-stream of KIT activated by stem cell factor or by oncogenic mutations. Shown are some of the most studied signaling events that are set in motion in response to KIT activation. Red circles with a “P” indicate phosphorylation of the protein. Phosphorylation of proteins by kinases is a means of controlling the activity of the recipient protein.

2. Hirota S, Isozaki K, Nishida T et al. (2000) Effects of lossof-function and gain-of-function mutations of c-kit on the gastrointestinal tract. J Gastroenterol 35(Suppl 12):75–79 3. Tarn C, Godwin AK (2005) Molecular research directions in the management of gastrointestinal stromal tumors. Curr Treat Options Oncol 6:473–486

4. Tarn C, Godwin AK (2006) The molecular pathogenesis of gastrointestinal stromal tumors. Clin Colorectal Cancer 6(Suppl 1):S7–S17 5. Demetri GD, von Mehren M, Blanke CD et al. (2002) Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors. N Engl J Med 347:472–480

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Gastrulation

Gastrulation Definition Is the formation of a gastrula from a blastula during embryogenesis. ▶Homeobox Genes

Gaucher Disease Definition

An inborn genetic disease due to a defective βglucosidase that normally hydrolyzes glucosylceramide. In another form of the disease, the protein (saposin C) that activates the glucosidase is absent. ▶Sphingolipid Metabolism

Gatekeeper Definition Type of tumor suppressor gene; Refers to a subgroup of gene products, whose major cellular function is in the control of cell division, death or lifespan. Inactivation of gatekeeper genes favors, through a variety of mechanisms, the unrestrained growth typical of cancer cells. Multiple gatekeeper mutations may be required for the neoplastic transformation of a cell. Gatekeeper gene products often participate in the control of ▶cell cycle (for example, the Rb gene product [▶retinoblastoma protein, cellular biochemistry]) or in the signals that regulate proliferation (for example, the ▶APC gene product). It is possible that large proteins with several functional domains (pleiotropic genes), such as ▶BRCA1 and ▶BRCA2 proteins originally described as gatekeepers may also have caretaker functions. ▶von Hippel-Lindau Tumor Suppressor Gene ▶Breast Cancer Genes BRCA1 and BRCA2 ▶Caretakers Genes

GBM ▶Glioblastoma Multiforme

GBP28 ▶Adiponectin

GCL Definition

Glutamate cysteine ligase, also known as γ-glutamylcysteine synthetase (GCS), comprises a catalytic subunit and a regulatory subunit. It is the rate-limiting enzyme in ▶glutathione biosynthesis. ▶Phase 2 Enzymes

Gatekeeper Position Definition Is a protein residue located at the back of the ATP binding site, whose properties (size, charge and hydrophobicity) regulate the binding of inhibitors. ▶Nilotinib

GC-MS Definition Gas chromatography-mass spectroscopy (GC-MS) has the advantage of unequivocally identifying the analytes in a mixture. It is used to identify ▶adducts to DNA or

GEF

altered DNA bases, which result for instance from ▶oxidative DNA damage.

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GDF Definition

GC/Post-GC Type B-Cell Tumors

Synonym growth differentiation factor-11; ▶BMP-11 and member of the ▶TGF-β superfamily.

Definition Since somatically mutated V genes (▶immunoglobulin genes) are a hallmark of ▶B cells that have left the ▶germinal center (GC), studies of V genes in B-cell tumors provide information on their stage of maturation; post-GC type tumors that carry mutated V genes include ▶DLBCL, ▶Burkitt lymphoma, ▶marginal zone lymphoma and classical ▶Hodgkin lymphoma. The pattern of mutations in ▶follicular lymphoma reveals intraclonal heterogeneity, indicating ongoing mutation (GCtype); ▶chronic lymphocytic leukemia and ▶mantle cell lymphoma cells harbor unmutated V genes (pre-GC type). ▶BCL6 Translocations in B-cell Tumors

GDF15 ▶MIC-1

GDP Definition Guanosine diphosphate. ▶RAS

GCSF GDP-Fucose Definition

▶Granulocyte Colony-Stimulating Factor

Definition A common donor substrate for fucosyltransferases. ▶Fucosylation

GCV Definition

▶Ganciclovir

GEF Definition

GDEPT ▶HSV-TK/Ganciclovir Mediated Toxicity

Guanine nucleotide exchange factors (GEFs) are proteins that stimulate the exchange (replacement) of guanine nucleoside diphosphates for guanine nucleoside triphosphates bound to ▶G proteins. ▶RAS Activation

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Gefitinib

Gefitinib Definition An orally available tyrosine kinase inhibitor that has the chemical structure of 4-(3-chloro-4-fluoroanilino)-7methoxy-6-(3-morpholinopropoxy)quinazoline and is capable of selectively inhibiting the epidermal growth factor receptor kinase. Gefitinib is used to treat patients with advanced ▶non-small cell lung carcer, and it is most effective for patients who have specific mutations within the catalytic domain of the epidermal growth factor receptor kinase drug target.

and subsequently degraded upon treatment with Geldanamycin or its clinically more relevant derivatives 17-AAG (17-allylamino-17-demethoxygeldanamycin) and 17-DMAG (17-(Dimethylaminoethylamino)-17demethoxygeldanamycin). ▶Ansamycin Class of Natural Product Hsp90 Inhibitors ▶B-Raf Signaling ▶Hsp90

▶Drug Design ▶Tyrosine Kinase Inhibitors

Gelsolin C HRISTINE C HAPONNIER 1 , H ELEN L. Y IN 2 1

Gelatin-Binding Protein 28 ▶Adiponectin

Gelatinase B

Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland 2 Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA

Definition

Is a widely expressed 82–84 kDa ▶actin-binding protein that is found inside the cells and also in a secreted form in extracellular fluid. Gelsolin severs actin filaments ▶actin filament severing by breaking the ionic interactions between actin molecules within the filament and it caps the fast growing (+) end of actin filaments. Filament severing and capping are regulated by Ca2+, the ▶phosphoinositide phosphatidylinositol 4,5 bisphosphate (PIP2) and pH.

▶Serum Biomarkers

Characteristics

Geldanamycin Definition GM; A benzoquinone ansamycin antibiotic from Streptomyces hygroscopicus var. Geldanus that binds to Heat Shock Protein 90 (▶Hsp90) and thereby blocks its function as an important (▶Ansamycin Class of Natural Product Hsp90 Inhibitors) chaperone. From a tumor biology perspective, the more than 50 ▶HSP90 client proteins include ▶TP53, the kinases ▶SRC, Raf-1, B-Raf, HER-2/neu/ErbB2 and ▶BcrAbl as well as several members of the ▶steroid hormone receptor family, which become de-stabilized

Cytoplasmic gelsolin was discovered in 1979 and named for its ability to activate gel–sol transformation of actin filaments in a Ca2+-dependant manner. Gelsolin is the founding member of a ▶gelsolin family of ▶actin filament severing and/or capping proteins. Other members include villin, scinderin, adseverin, CapG, and flightless I. Among these, gelsolin and CapG have been implicated as ▶tumor suppressor. The ▶actin cytoskeleton is remodeled dynamically during cell movements. Gelsolin contributes to dynamic remodeling by promoting the disassembly and subsequent reassembly of the actin cytoskeleton in response to changes in intracellular signals. Disassembly is mediated through filament severing and reassembly is mediated by filament uncapping. Gelsolin is activated by micromolar Ca2+ to bind to the side of actin filaments and to sever them. After severing, gelsolin remains attached to the (+) ends of these short filaments

Gelsolin

even as Ca2+ level decreases to submicromolar level. Gelsolin is detached from the (+) ends (uncapping) by PIP2. It is hypothesized that the combination of severing to generate large number of short capped actin filaments and subsequent uncapping can account for explosive actin filament growth. The importance of gelsolin for cell motility has been demonstrated by gelsolin overexpression and depletion by RNA interference in tissue culture cells and by gelsolin gene knockout. For example, although the gelsolin ▶knockout mice are viable, their ▶neutrophils and ▶fibroblasts have decreased motility. Gelsolin has also been implicated in ▶apoptosis, either as an enabler or a protector. Gelsolin is cleaved by ▶caspase-3 into two halves and the resulting amino terminal half severs actin filament in a Ca2+independent manner. This may contribute in part to the morphologic changes associated with apoptosis in some type of cells. However, a protective role of gelsolin has been suggested in Jurkat cells and in neuronal cells. Thus, blockage or enhancement of gelsolin cleavage might retard or enhance apoptosis depending on the cellular context. The relation between gelsolin, apoptosis and tumorigenesis probably reflects a complex balance between the multiple effector functions of gelsolin.

Gelsolin and Cancer The role of gelsolin in reorganizing the actin cytoskeleton suggests that it may be involved in promoting tumor cell ▶invasion and dissemination. The first study investigating the distribution of gelsolin in ▶breast cancer showed that, in ▶ductal carcinoma, it is notably downregulated in epithelial cells compared with normal breast tissue. However, gelsolin is expressed at a high level in stromal ▶myofibroblasts. Therefore, cytoplasmic gelsolin is expressed in normal epithelial cells, in some tumor cells and importantly in intratumoral and peritumoral stromal myofibroblasts, and in vessel smooth muscle cells. The function of gelsolin in these highly contractile cells is not yet understood. Since the initial study, there have been many other investigations to determine if gelsolin has a role in tumorigenesis. These studies suggest that depending on the type of tissue and the stage of cancer growth, gelsolin may act as a tumor suppressor or a tumor enhancer. In some cases, gelsolin is a reliable prognostic marker. In this general and short chapter, it is not possible to review of all reports in the field. We therefore took the liberty of selecting only studies that investigate both in vitro and in vivo conditions; these studies should be most relevant for understanding the role of gelsolin in tumor development.

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Gelsolin Considered as a Tumor Suppressor ▶Immunohistochemistry studies showed that gelsolin expression is downregulated in many types of cancer including breast, stomach, colon, bladder, prostate, lung, kidney, and ovary. For example, 78% of ▶bladder tumor tissues and six bladder cancer cell lines displayed low or undetectable gelsolin compared with their normal counterparts. Furthermore, transfection of exogeneous gelsolin cDNA into a bladder cancer cell line reduced colony-forming ability and tumorigenicity in vivo. Loss of gelsolin was also observed in human ▶ovarian cancer cell lines and in ovarian carcinoma compared with normal ovaries and benign adenoma. As in the case of bladder cancer cells, reexpression of gelsolin in ovarian tumor cell lines resulted in a reduction in colony formation. Knockdown of gelsolin using small interfering (si) RNA has given contradictory results. For example, gelsolin depletion in the human immortalized mammary epithelial cell line MCF10A unexpectedly increased cell motility and induced overexpression of the small ▶GTPase ▶Rac, which has been implicated in dynamic ▶lamellipodia formation. Gelsolin depletion also converted ▶cadherin from E- to N-type via the induction of the ▶transcription factor Snail, whose expression is inversely correlated with E-cadherin mRNA levels in several epithelial tumor cell lines. These unexpected results suggest how a decrease in gelsolin expression can nevertheless lead to enhanced tumor ▶cell motility. The molecular basis for the decrease in gelsolin expression in tumor cells is not known. There are suggestions that gelsolin mRNA level may decrease due to ▶epigenetic modifications resulting from DNA ▶methylation and ▶histone deacetylation, in ▶ovarian cancer and in ▶breast cancer cell lines. Paradoxically, although gelsolin can suppress tumor progression, it was also shown that overexpression of gelsolin in malignant tumors was associated with poor prognosis. Gelsolin has been suggested to be a motility marker for tumor cells, although its prognostic value has so far only been examined in a small number of malignant tumors. Furthermore, there is surprisingly little information about the possibility that other members of the ▶gelsolin family may substitute for the depleted gelsolin in cancer cells. Gelsolin Considered as a Tumor Enhancer Besides acting as a tumor suppressor, gelsolin has also been implicated as a tumor enhancer, particularly in lung and breast carcinomas. For example, ▶nonsmall cell lung carcinoma (NSCLC), which comprises 70–80% of all lung carcinomas and has a 5-year survival rate of about 15%, is usually associated with decreased gelsolin level in about 70% of the cases

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Gelsolin Family

examined. However, the decrease in gelsolin is not associated with adverse prognostics. Instead, the small percent of cells with high focal gelsolin expression was correlated with the highest risk of cancer recurrence compared with tumors that had no or low gelsolin expression. Likewise, the expression of gelsolin in breast cancer is variable and may involve only a few cells in the issue. Although gelsolin is absent in many breast cancers, about one third of cases have detectable gelsolin. In some cases, gelsolin expression was focally localized and accentuated in cell clusters or in single invasive cells that show transendothelial migration or are embedded in the stroma. Interestingly, an overexpression of gelsolin, when associated with ERBB2 and EGFR expression, resulted in a more agressive tumor phenotype. Altogether, these results suggest that although gelsolin can be extinguished during cell transformation, its focal high expression in a subpopulation of tumor cells can facilitate tumor dissemination and metastasis by promoting tumor cell locomotion. In summary, the current findings are consistent with the hypothesis that gelsolin functions in a complex manner in the development and progression of tumors.

References 1. Chaponnier C, Gabbiani G (1989) Gelsolin modulation in epithelial and stromal cells of mammary carcinoma. Am J Pathol 134:597–603 2. Noske A, Denkert C, Schober H et al. (2005) Loss of gelsolin expression in human ovarian carcinomas. Eur J Cancer 41:461–469 3. Silacci P, Mazzolai L, Gauci C et al. (2004) Gelsolin superfamily proteins: key regulators of cellular functions. Cell Mol Life Sci 61:2614–2623 4. Thor AD, Edgerton SM, Liu S et al. (2001) Gelsolin as a negative prognostic factor and effector of motility in erbB2-positive epidermal growth factor receptor-positive breast cancers. Clin Cancer Res 7:2415–2424 5. Yang J, Tan D, Asch HL et al. (2004) Prognostic significance of gelsolin expression level and variability in non-small cell lung cancer. Lung Cancer 46:29–42

Gelsolin Family Definition

A superfamily of ▶gelsolin-like proteins that has a conserved modular motif. Gelsolin is the founding member; other members include villin, scinderin, adseverin, supervillin, CapG, and flightless I. With

the exception of flightless I, all are shown to be Ca2+-activated ▶actin severing and/or binding proteins. Some of these proteins have also been implicated in transcriptional regulation.

Gemcitabine G RAZIELLA P RATESI Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy

Synonyms dFdC; 2′,2′-Difluoro-2′-deoxycytidine; GEMZAR

Definition Is an antitumor drug belonging to the class of antimetabolites. Antimetabolites are agents that interfere with normal metabolism due to their structural similarity to normal intermediates in the synthesis of RNA and DNA precursors. Due to differences in metabolism between normal and cancer cells, antimetabolites have the potential to act with a certain degree of specificity in cancer cells. Antimetabolites target the synthetic pathway of pyrimidines (uracil, cytosine, thymine) and purines (guanine, adenosine) nucleotides, where they can serve as substrates for enzymes, or can inhibit enzymes, or both. As a consequence of their interference, either by incorporation or inhibition, antimetabolites induce cell damage leading to apoptotic cell death. Several cytidine and deoxycytidine analogs have been synthesized in the past and tested for antitumor efficacy. The first successful agent in clinical practice was ara-C (1-β-D-arabinofuranosylcytosine) which is currently used as first-line treatment in acute myeloid leukemia and ▶non-Hodgkin lymphoma.

Characteristics Mechanism of Action and Resistance Is a potent and specific fluorine substituted ara-C analog with pronounced activity against solid tumors. Gemcitabine presents advantages in ▶pharmacokinetic and ▶pharmacodynamic properties over ara-C. Its mechanism of action is well characterized. Gemcitabine exhibits cell-phase specificity, primarily killing cells undergoing DNA synthesis (S-phase) and also blocking the progression of cells through the ▶G1/S transition. Membrane transport is mediated by facilitated diffusion catalyzed by human equilibrative nucleotide transporter 1, a carrier for physiologic nucleosides. The molecule itself is inactive and needs to be metabolized

Gemcitabine

intracellularly to its mononucleotide by deoxycytidine kinase, and then by nucleotide kinases to the active diphosphate (dFdCDP, gemcitabine-DP) and triphosphate (dFdCTP, gemcitabine-TP) nucleotides. The activity of gemcitabine is strongly correlated with the extent of gemcitabine-TP. Once incorporated into the DNA strand, an additional natural nucleotide is added, masking gemcitabine, preventing ▶DNA repair by base pair excision, and eventually resulting in chain termination. Such process is self-potentiated by the inhibitory effect of gemcitabine-DP on the reaction generating normal deoxycitidine-TP, thus favoring the incorporation of gemcitabine-TP into DNA. Gemcitabine is also incorporated into RNA and induces cell ▶apoptosis. Ribonucleotide reductase can be inhibited by gemcitabine-DP, resulting in depletion of deoxycitidine-TP and deoxiadenosine-TP. Deoxycitidine-TP is a feedback regulator of nucleotide kinase, thus favoring the activation of gemcitabine. The depletion of deoxiadenosine-TP will inhibit DNA repair. Collectively, the various effects of gemcitabine result in a unique pattern of self-potentiation. Inactivation of gemcitabine can occur by deamination into its inactive metabolite difluoro-deoxyuridine by cytidine deaminase (CDD) or dephosphorylation of nucleotide-MP by 5′-nucleotidase (5′-NU), which exerts the opposite function of deoxycitidine kinase. Three general mechanisms of resistance to nucleotide analogs have been described. The first one arises from insufficient intracellular concentration of nucleotidesTP, which may result from inefficient cellular uptake, reduced levels of activating enzymes, increased degradation by increased 5′-NU or CDD activity, or expansion of the natural deoxynucleotide-TP pool. The second mechanism may be due to inability to achieve sufficient alterations in DNA strands or deoxynucleotide-TP pool. The third mechanism may be a consequence of defective apoptotic pathways, which can impair the activity of antitumor drugs of various mechanistic classes. Clinical Profile For clinical use gemcitabine is administered intravenously. The standard administration of gemcitabine is a 30 min infusion of 1,000 mg/m2/week up to 7 weeks, followed by 1 week rest. Toxicity The dose limiting toxicity is ▶myelosuppression, with 25 and 5% of patients experiencing severe (G3-4) ▶neutropenia and ▶thrombocytopenia, respectively. At the standard regimen hematological toxicity is of short duration, and mild gastrointestinal toxicities (nausea, vomiting), alteration in liver and renal functions, diarrhea and stomatitis are also observed.

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Serious renal or liver toxicities are rare but not reversible. Other toxicities include edema, cutaneous toxicity associated to pruritus, fever, neurotoxicity and dyspnea (uncommon but severe). Indications Gemcitabine is approved for the treatment of several solid tumors such as pancreatic cancer, advanced ▶nonsmall cell lung carcinoma (NSCLC), ▶bladder cancer, ▶ovarian cancer and ▶breast cancer. NSCLC. Gemcitabine is approved for use in combination with ▶cisplatin for first-line treatment of patients with inoperable, locally advanced (Stage IIIA or IIIB) or metastatic (Stage IV) NSCLC. Two schedules have been investigated and the optimal schedule has not been determined. The combination with cisplatin was investigated on the basis of preclinical studies showing inhibition of repair of platinum-induced DNA damage, and of the results of Phase II studies with single agent gemcitabine in more than 400 patients producing response rates consistently above 20%. Promising results are reported in a Phase III study combining gemcitabine to carboplatin, a platinum-analog less myelotoxic than cisplatin. The combination produced better results, in terms of response rate and time to progression than gemcitabine alone. Several Phase II trials have investigated the combination with non-platinum derivatives such as ▶docetaxel, ▶paclitaxel or vinorelbine, but no one has proven advantages when compared to the standard platinum-based regimen. Due to the low toxicity profile gemcitabine is under investigation in elderly patients with advanced NSCLC, either as single-agent or in combination with other drugs. Pancreatic Cancer. Gemcitabine is approved for the treatment of patients with locally advanced (nonresectable Stage II or III) or metastatic (Stage IV) ▶adenocarcinoma of pancreas both for first-line treatment and for patients previously treated with a ▶5-fluorouracil-containing regimen. The approval for first-line treatment was based on the results of a randomized study showing improvement in median survival, 1-year survival and clinical benefits over weekly 5-fluorouracil. Several randomized trials have compared gemcitabine with a gemcitabine-based combination, none of which having shown any incremental benefit in terms of survival or quality of life. Improvement in survival might be achieved by prolonged infusion strategy of gemcitabine and is currently under evaluation. Breast Cancer. Gemcitabine is approved for use in combination with ▶paclitaxel for the first-line treatment of patients with metastatic breast cancer after failure of prior ▶anthracycline-containing adjuvant chemotherapy. The combination of gemcitabine and ▶taxanes (docetaxel or paclitaxel) was tested in clinical

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Gemtuzumab Ozogamicin

trials based on the good single-agent activity of each drug. In a Phase III study gemcitabine in combination with paclitaxel significantly improved response rate, time to progression and survival versus paclitaxel in metastatic breast cancer, with no significant increase in toxicity. The best schedule for administration of gemcitabine-taxane combination and the relevance of the combination in ▶Her-2/neu positive patients are currently under investigation. Bladder Cancer. Systemic chemotherapy has reached a plateau in the treatment of ▶transitional cell carcinoma of the bladder. Gemcitabine is approved for such disease in combination with cisplatin. Such regimen has equivalent response rate and survival, but improved toxicity profile, compared to the previous standard regimen including ▶methotrexate, ▶vinblastine, ▶adriamycin and ▶cisplatin. Promising results have been observed with intrabladder infusion of gemcitabine. Ovarian Cancer. Gemcitabine is approved in combination with ▶carboplatin in several European countries for the treatment of recurrent epithelial ovarian cancer. It has been recently approved also in the USA on the basis of a randomized trial comparing the combination against carboplatin alone in 356 women with recurrent ovarian cancer, whose tumors had previously responded to first-line therapy. The median progression-free survival was 8.6 months for patients taking carboplatin and gemcitabine, and 5.8 months for patients taking carboplatin alone. Quality-of-life was comparable in the two groups of patients. Multicenter Phase III trials are ongoing comparing paclitaxel plus carboplatin with gemcitabine plus carboplatin. The results of a single-institution Phase II study in 24 patients, indicate an acceptable toxicity (with bone marrow toxicity as dose-limiting) with high overall response rate (91%) for the combination gemcitabine plus carboplatin.

Clinical Pharmacology Pharmacokinetic studies indicate that the drug is eliminated in the urine. Gemcitabine is rapidly converted to the inactive uracil metabolite (recovered in the urine for more than 90%), which has a long half life. Gemcitabine pharmacokinetic is linear and described by a 2-compartment model. ▶Clearance and ▶volume of distribution vary with duration of infusion, age and gender. Gemcitabine plasma protein binding is negligible.

Future Perspective Due to its low bone marrow toxicity, gemcitabine might be a suitable drug to be combined with ▶immunotherapy, and preclinical studies support such expectation.

Gemcitabine can induce massive tumor-cell apoptosis both in in vitro and in vivo systems. Uptake of dead cells by ▶antigen presenting cells, still alive after gemcitabine treatment, will result in increase of cross presenting tumor antigens to T lymphocytes in tumor draining lymph nodes. Moreover gemcitabine, which is particularly toxic for B lymphocytes, by impairing the antitumor antibody response might favorite the generation of ▶cytotoxic T lymphocytes, which have to be generated for immunotherapy to be effective. Again, chemotherapy may upregulate cellular death receptors, which are used by T cells to kill targets. Gemcitabine followed by CpG-oligodeoxynucleotide, a modulator of the natural ▶immune response, results in a strong therapeutic synergism in a pancreatic tumor model. Thus, in addition to more combination studies with established or novel antitumor drugs, future clinical studies should address the role of gemcitabine in combination with various immunotherapies for the treatment of cancer.

References 1. Galmarini CM, Mackey JR, Dumontet C (2001) Nucleoside analogues: mechanisms of drug resistance and reversal strategies. Leukemia 15:875–890 2. Lake RA, Robinson BWS (2005) Immunotherapy and chemotherapy – a practical partnership. Nat Rev 5:397–405 3. Peters GJ, Jansen G (2002) Antimetabolites. In: Souhami RL, Tannock I, Hohenberger P, Hoiot J-C (eds) Oxford textbook of oncology, 2nd edn. Oxford University Press, New York pp 663–713 4. Smith IE (2006) Overview of gemcitabine activity in advanced breast cancer. Semin Oncol 33:19–23 5. Toschi L, Finocchiaro G, Bartolini S et al. (2005) Multistep Role of gemcitabine in cancer therapy. Future Oncol 1:7–17

Gemtuzumab Ozogamicin Definition Is a humanized IgG4κ anti-▶CD33 antibody linked to the anti-tumor antibiotic calicheamicin. Gemtuzumab ozogamicin is approved for treatment of relapsed ▶acute myeloic leukemia in patients older than 60 years. ▶Monoclonal Antibody Therapy

Gene Knockout

GEMZAR ▶Gemcitabine

Gene Amplification Definition Amplification of the numbers of copies of one or more genes; synthesis of additional copies of an original gene.

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Gene Expression Profile Definition Messenger-RNA from relevant cells is copied to labeled (with fluorescence dye or radioactive nucleotide) complementary cDNA probes. The probes are incubated on a DNA array containing spots of DNA from known genes being investigated. Hybridization of a given probe signifies the presence of the mRNA in question in the cell or tissue studied, i.e., the gene is active. The method allows estimation of activity genes in one assay. Firstarray many was developed in early 1980 as “Oncogip” for profilin of ▶oncogene expression. ▶Microarray (cDNA) Technology

▶Amplification ▶Neuroblastoma

Gene Expression Profiling Gene Battery

Definition

Definition

A microarray-based methodology to study gene expression (RNA) patterns. Parallel analysis of the expressed transcriptome of a given cell line or tissue sample, first developed in early 1980ies for ▶oncogene profiling.

Refers to a group of genes regulated by a particular transcription factor.

▶Microarray (cDNA) Technology

▶Dioxin

Gene Gun Gene Directed Enzyme-Prodrug Therapy ▶HSV-TK/Ganciclovir Mediated Toxicity

Definition Is a way for in vivo transformation of cells or organisms used for gene therapy and genetic immunization. This gun uses particle bombardment where DNA- (or RNA-) coated gold particles are loaded into the gun. A low pressure helium pulse delivers the coated gold particles into virtually any target cell or tissue. ▶DNA Vaccination

Gene Expression Cassette Definition Stretch of recombinant DNA typically comprising a ▶promoter, a gene and a polyadenylation signal; often used in ▶gene therapy.

Gene Knockout Definition Is a genetically engineered organism that carries one or more genes in its chromosomes that have been made

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Gene Profile

inoperative (have been “knocked out” of the organism). This is done for research purposes. Also known as knockout organisms (▶knock-out mice) or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function. Researchers draw inferences from the difference between the knockout organism and normal individuals.

Gene Profile Definition A extensive survey of genes leading to RNA encompassing known coding sequences in the genome. ▶Gene Expression Profile

Gene Therapy VALERIE B OSCH Forschungsschwerpunkt Infektion und Krebs, F020, German Cancer Research Center (DKFZ), Heidelberg, Germany

Definition Directed introduction and expression of new genetic information in cells of an organism for therapeutic purposes. Only somatic gene therapy is presently permitted, and the introduction of genetic material into germ-line cells is not allowed.

for the development of gene therapeutic intervention strategies. Transfer of Genes Very many different methods have been developed to transfer therapeutic genes to patient cells. A consideration which is central to the choice of gene transfer vehicle (▶vector) is whether stable or only transient gene expression is required. Stable gene expression is necessary for the treatment of hereditary genetic defects whereas transient gene expression is sufficient, and may even be desirable, when employing genes encoding toxic gene products e.g. in the treatment of cancer. Many gene transfer vehicles employ components of viruses (viral vector-mediated gene transfer) since viruses have evolved to efficiently transfer their own genes to cells and to express the respective gene products at high levels. Since it may not be possible to completely eliminate potential safety problems with viral vectors, non-viral gene transfer vehicles have been developed in parallel. These transfer vehicles are based on lipids/▶liposomes (lipoplexes), on polycations (polyplexes), on branched polymer structures (dendriplexes) or consist simply of naked DNA (▶Nonviral vectors for cancer therapy). In general, the transfer efficiencies and gene expression levels achieved with non-viral vectors are poorer than with viral vectors. The commonly used gene transfer vectors, their advantages and their disadvantages are summarized in Table 2. In many situations, in addition to high gene transfer efficiency, it is necessary that the transfer vector is selective i.e. mediates expression of the therapeutic gene exclusively in targeted diseased cells. Achieving selectivity is a major hurdle which is being approached in several ways. Gene vectors are being manipulated (on the surface of the gene vector particle) such that targeted cells are exclusively accessed. Selectivity can be achieved by ensuring that, even in the situation in which many cells have been accessed, expression of the therapeutic gene can only occur in specific targeted cells (e.g. by employing tissue-specific promoter/enhancer elements to control therapeutic gene expression).

Characteristics The science of gene therapy has its beginnings in the early 1980s, subsequent to the identification of several disease-related genes and the development of technologies for gene isolation, purification and transfer to cells in culture. Many different human diseases represent theoretical targets for gene therapeutic intervention and the strategies developed depend on the nature of the disease to be treated. Table 1 illustrates several classes of human disease and the respective treatment strategies currently being followed. It goes without saying that detailed knowledge of the molecular mechanisms of disease development and progression is a prerequisite

Clinical Relevance Therapeutic genes can be introduced into patient cells either ex vivo or in vivo (see Fig. 1). In the ex vivo application, a patient biopsy is genetically manipulated outside the body and subsequently reinjected or transplanted. This procedure has the advantage that only the cells in the biopsy come in contact with the transfer vector. Furthermore, the circumstances in cell culture generally allow more efficient gene transfer than on in vivo application. In addition, in some cases it is possible to expand the cells in the biopsy and create a pool of genetically modified cells which can be

Gene Therapy Gene Therapy. Table 1

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Examples of gene therapeutic strategies for different disease groups

Disease group

Genetic basis of disease

Strategy

Hereditary monogenic disease e.g. haemophilia, cystic fibrosis Multifactorial disease e.g. cardiac disease, diabetes

Defective gene which results in a single gene product being missing or non-functional Many genes and their gene products directly or indirectly involved

Cancer

Somatic mutation of cellular genes (several)

Introduction of wild-type gene (e.g. into liver or muscle for the production of a protein in the blood circulation, into lung in the case of cystic fibrosis) At present too complex. However, restenosis. (i.e. tissue proliferation after surgical dilation of a blood vessel) can be treated by locally expressing genes which inhibit cell proliferation 1. Induction of cell death employing genes encoding toxic gene products 2. Stimulation of the immune system to recognise and destroy cancer cells. (▶Cancer vaccines ▶DNA vaccination) 3. Inhibition of “cancer genes.” (▶Cell-cycle targets for cancer therapy) 4. Prevention of tumor ▶angiogenesis

Infectious diseases e.g. AIDS

Gene Therapy. Table 2

New genetic material from the infectious agent (e.g. virus) induces pathogenic processes

1. Inhibition of expression of genes encoded by the infectious agent employing e.g. antisense, ribozyme or small-interfering (si) RNA approaches. (▶Antisense DNA therapy) 2. Vaccination against viral gene products expressed from transferred heterologous viral vectors or from naked DNA i.e. infection prevented or eliminated by the patient’s immune system

Gene transfer vehicles, their advantages and disadvantages

Gene vehicle Retrovirus vectors including those based on lentiviruses

▶Adenovirus vectors

Advantages

Disadvantages

1. Integration of vector into host genome leading to stable gene expression 2. No cellular toxicity 3. Lentiviral vectors also infect (transduce) differentiated non-dividing cells 1. Very high titers (1013/ml) 2. Very high, but transient, gene expression

1. Titer not as high as e.g. adenoviral vectors 2. Vector integration into host genome is potentially mutagenic

Adeno-associated virus (▶AAV) 1. AAV is not pathogenic in humans vectors 2. Non-toxic

Lipoplexes, polyplexes and dendriplexes Naked DNA

3. Infects non-dividing cells No viral genes, no toxic effects No viral genes, no toxic effects

reapplied to the patient as required. The main disadvantage of the ex vivo procedure is that it is technically cumbersome, time-consuming and very expensive. The most straightforward and desirable situation would be to

1.Only transient gene expression 2. Immune response to vector and transgene 1. lower coding capacity than with retroviral and adenoviral vectors 2. Gene expression in proliferating tissue only transient Mostly lower and transient gene expression Mostly lower and transient gene expression

apply the gene transfer vehicle in vivo either directly into specific tissues or organs (e.g. directly into tumor tissue) or by injection into the blood circulation. In vivo application requires that the transfer vector efficiently

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Gene Transfection

Gene Transfection Definition Synonym Gene Transduction, Gene Transfer; Introduction of genes into cells. ▶Transfection

Gene Therapy. Figure 1 Application routes for gene therapy.

reaches the appropriate diseased cells and at present, this is very often not the case. In fact, major problems hampering gene therapeutic approaches today concern the efficiency and the selectivity of the transfer vectors when applied in vivo. Further problems are related to the induction of host immune reactions towards the (viral) vector and the transgene. Permission for the first clinical gene therapy study was granted in 1989 and since then numerous ▶clinical trials, for the most part with only relatively small numbers of patients, have been carried out. Lack of sufficient selectivity and efficiency of transfer as well as lack of stability of transgene expression, the results of most of these trials did not establish any statistically verified positive effects on disease progression or mortality. Recently, however, more favorable results have been obtained. Thus, as a result of a gene therapeutic intervention with a retroviral vector, several individuals were cured of severe X-linked combined immunodeficiency. Unfortunately, however, within this same trial, severe adverse side-effects were observed in three treated patients. In the meantime, the reasons for these adverse effects have been largely elucidated and subsequent protocols will be adjusted accordingly. At present, basic research is focussed on improving gene vector properties and on gaining a better understanding of the interactions between the gene vector, the transgene and the patient’s immune system. It is to be anticipated that the combined knowledge gained from these efforts will allow gene therapeutic protocols to be developed which will represent valid treatments for diseases which have been difficult or impossible to therapy up until now.

Gene-Environment Interaction Definition The combined effect of genetic susceptibility and exposure to non-genetic factors, broadly defined as “environmental.” ▶Cancer Epidemiology

Genetic Association Definition

Studies of genetic association test whether ▶allele or ▶genotype frequencies are different between groups of individuals (for example, subjects with and without cancer). ▶Linkage Disequilibrium

Genetic Association Study ▶Case Control Association Study

Genetic Epidemiology

Reference

Definition

1. Thomas CE, Ehrhardt A, Kay MA (2003) Progress and problems with the use of viral vectors for gene therapy. Nat Rev Genet 4:346–358

The branch of epidemiology which aims at elucidating and quantifying the genetic causes of cancer. Genetic epidemiology investigates the aggregation of cancers in

Genetic Instability

families (linkage studies), and the presence of high-risk genetic variants in sporadic cases (association studies). ▶Cancer Epidemiology ▶Epidemiology of Cancer

Genetic Haplotype Definition

Is a term used in the context of ▶case–control association study where instead of analyzing the association between trait and each genetic marker singly, multiple markers are analyzed simultaneously for a combined effect. These multiple markers when combined together are called a haplotype. There are two rationales for examining haplotypes. First, using haplotypes allows multiple potentially causal markers to be tested simultaneously for association. However, for haplotypes to be superior to individual markers, multiple functional markers must have a strong interaction when combined and yet have no detectable effect when considered individually. Second, haplotypes can be tested for association because they may be a proxy for untyped causal markers. Some have pointed out that the additional association tests entailed in haplotype-based analyses can actually result in a loss of power, and hence lower efficiency, once corrections for multiple testing are taken into account. ▶Case–Control Association Study ▶Haplotype

Genetic Immunization ▶DNA Vaccination

Genetic Instability Definition Synonym genomic instability, seems to be the hallmark of cancer cells, in contrast to the normal cells that, with few exceptions such as e.g. telomeres (▶telomerase) or ▶V(D)J-recombination, are genetically stable. The

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principal concept here is that when genes involved in the maintenance of genetic stability of the cellular genome undergo mutation, the repair of ▶DNA damage often will be incomplete, due to impaired DNA repair (▶repair of DNA) systems. As the consequence, during tumor ▶multistep development, tumor cells assume a ▶mutator phenotype and will accumulate mutations leading to the evolution, by Darwinian selection, of tumor cells that escape cellular growth signals and become more and more malignant. This process is not necessarily related, as often postulated, to very rapid tumor cell proliferation. Cells of many types of tumors actually multiply rather slowly and, in contrast, normal cells in various sites, like the epithelium of the intestine, multiply very rapidly but still remain normal. The ensuing genetic instability drives tumor ▶progression by generating mutations in ▶oncogenes and ▶tumorsuppressor genes. These mutant genes provide cancer cells with a selective growth advantage, thereby leading to the clonal outgrowth of a tumor. Genetic instability can be at the level of the chromosome (▶chromosomal instability; CIN) or can be expressed as ▶microsatellite instability (MIN; also referred to as MSI). Chromosomal instability (CIN) is a defining characteristic of most human cancers. Mutation of CIN genes increases the probability that whole chromosomes or large fractions of chromosomes are gained or lost during cell division. The consequence of CIN is an imbalance in the number of chromosomes per cell (▶aneuploidy) and an enhanced rate of ▶loss of heterozygosity. Microsatellite instability is a condition manifested by damaged DNA due to defects in the normal DNA repair process. MSI is a key factor in several cancers including ▶colon cancer, ▶endometrial cancer, ▶ovarian cancer and ▶gastric cancer. For colon cancer, a prominent form is hereditary non-polyposis colorectal cancer (HNPCC) or ▶Lynch Syndrome, where an inherited mutation in a ▶mismatch repair gene causes ▶microsatellite instability. The replication error results in a ▶frameshift mutation that inactivates or alters ▶tumor suppressor genes. Genetic changes in genetically unstable cells will occurs at random possibly affecting, in humans, any of the estimated 30,000 genes present in the genome. Because of this randomness, genomic instability eventually will lead to tumor cell populations that are genetically different, both within a given tumor in the individual patient and in the same tumor type of different patients. Because the biological behavior of tumor cells is dictated by the profile of genetic changes, the heterogenous populations of cells will respond differently to therapeutic treatments, such as ▶chemotherapy or any other form of therapy. Very often, large populations of tumor cells, due to the pattern of genetic changes, may disappear by therapy-induced ▶apoptosis. Still, minor populations, again because of their

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particular genetic pattern, may be inherently ▶drug resistant and may develop into a new tumor that now is fully resistant against therapeutic drugs. For the same reason, tumors in different patients may respond differently.

Definition

▶Chromosomal Instability

An inherited increase in the risk of developing a specific disease.

Genetic Susceptibility

▶Mutagen Sensitivity

Genetic Knock-out Definition A gene knockout is a genetically engineered organism that carries one or more genes in its chromosomes that have been made inoperative (have been “knocked out” of the organism). Also known as knockout organisms or simply knockouts (▶knock-out mice), they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function. Researchers draw inferences about gene function from the difference between the knockout organism and normal individuals.

Genetic Toxicology J OSEPH R. L ANDOLPH J R . Cancer Research Laboratory, USC/Norris Comprehensive Cancer Center, Keck School of Medicine/School of Pharmacy, University of Southern California, Los Angeles, CA, USA

Synonyms Chemical mutagenesis; Clastogenesis; Chemical carcinogenesis

▶Orphan Nuclear Receptors

Definition

Genetic Polymorphism Definition Genetic polymorphism is the presence of multiple inheritable forms of a gene within the population; a genetic trait where the least common ▶allele is found in approximately at least 1% of the population ▶Detoxification ▶Modifier Loci ▶Pharmacogenomics in Multidrug Resistance

The study of the processes and mechanisms by which chemicals or radiations cause damage, including ▶mutations, DNA single-strand breaks and doublestrand breaks, ▶gene rearrangements and gene ▶amplifications, and ▶chromosome damage in prokaryotes or eukaryotic cells. This includes aspects of mutagenesis, i.e., the process by which specific chemicals induce changes in the sequence of DNA bases in genomes. It includes also ▶chemical carcinogenesis, i.e., the molecular mechanisms by which chemicals carcinogens induce mutation in ▶tumor suppressor genes, inactivating them, and induce mutations, rearrangements, or amplifications of ▶oncogenes, deregulating them, causing fifteen such changes. These five to eight changes, consisting of inactivation of tumor suppressor genes and activation of oncogenes, leads to further derangements in the expression of ▶numerous genes, which results in the cell acquiring a tumorigenic phenotype and the eventual development of cancer.

Genetic Recombination Characteristics Definition Is the process whereby DNA from one chromosomal location is exchanged for, or replaces, another region of the genome.

Genetic Toxicology Genetic Toxicology, or the science of the study of chemicals and radiations (▶Radiation-induced cancer) that can cause damage to genes and the genome, is now a very advanced science. There are now many

Genetic Toxicology

assay systems, both in bacteria, yeast, Drosophila, mice, and in cultured murine and human cells, which can be used to detect ▶DNA damage. Such damage includes mutations induced by chemicals or radiation, gene rearrangements, gene amplification, chromosome damage (gaps, breaks, fragments, dicentrics, and satellites), single-strand breaks in DNA, and doublestrand breaks in DNA. Important assay detection systems include the ▶Ames assay that detect reversion of His − Salmonella back to His + Salmonella, and which also utilizes addition of exogenous ▶cytochrome P450 to metabolically activate premutagens, such as ▶polycyclic aromatic hydrocarbons to epoxides and diol epoxides. Mutation and recombination can also be studied in yeast. In addition, there are assays to study mutation in mice, using the “spot test.” Plasmids can also be added to mice and retrieved from mice treated with suspect chemical mutagens, and then analyzed to detect mutations in these plasmids. There is now an extensive body of data indicating that specific chemicals and radiations can be assayed in mammalian cells, both rodent cells (murine, rat, and hamster cells) and cultured human cells, for their ability to cause mutation. Examples of these assays include the assay for mutation to 6-thioguanine (or 8-agazguanine) resistance, which detects base substitution, frameshift, and deletion mutations caused by chemicals and radiations. There is an assay for mutation to ouabain resistance, which detects base substitution mutations in the (Na, K) adenosine triphosphatase (ATPase) in rodent and human cells. There is also an assay in L5178Y mouse lymphoma cells that detects large chromosomal mutations and also point mutations, in which the cells are assayed that are resistant to bromodeoxyuridine. These cells have mutations in or deletions of, the thymidine kinase gene. There is also a simple assay in which cells are exposed to chemical mutagens or radiations, and then the cells are lysed, and DNA damage is assayed in a gel electrophoretic assay (“▶COMET assay”). From results of these assays, we now know that we can easily detect chemicals that cause genetic toxicity, in the form of DNA damage, mutations, gene amplification, or breaks in the single- or double-strands of DNA, or damage to chromosomes (gaps, breaks, fragments, dicentrics, satellites) (▶Clastogenesis). In terms of correlations of genetic toxicity with cancercausing ability, it has also been established that 45% of all chemical carcinogens are mutagens. Hence, these assays detect mutagenesis/DNA damage, and will therefore detect mutagenic chemical carcinogens and radiations. Many chemical carcinogens are also clastogenic agents. The other classes of carcinogens involve those that cause ▶methylation of tumor suppressor genes, rendering them transcriptionally quiescent, or demethylation of oncogenes rendering them transcriptionally active at inappropriate times. Another group of

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carcinogens are certain hormones (▶Hormonal carcinogenesis), such as ▶diethylstilbestrol, estrogen, and ▶testosterone, which act by inducing cell division. Inappropriately high numbers of cell division can lead to spontaneous mutations in cells, or can drive cell division to replicate the DNA of cells that have been adducted by chemical mutagens or damaged by radiations, leading to fixation of chemical mutations. Chemical, Viral, and Radiation Carcinogens Broadly defined, a ▶carcinogen is any material, whether radiation, chemical, or virus, which can induce tumors in lower animals or in humans. ▶Tobacco contains 4,500 different chemicals, and over 20 different known strong human carcinogens, as well as ▶tumor promoters and ▶cocarcinogens. Exposure to tobacco and tobacco products is thought to account for 30% of all human cancers. These include ▶lung cancer, ▶bladder cancer, ▶oral cancer, ▶pharyngeal cancer, ▶laryngeal cancer, ▶nasopharyngeal cancer, ▶esophageal cancer, ▶kidney cancer, ▶liver cancer, and ▶pancreatic cancer, according to the latest US Surgeon General’s report. ▶Second-hand tobacco smoke, or environmental tobacco smoke, also causes cancer in exposed individuals. A second grouping of human cancers is thought to be due to exposure to excess levels of normal hormones, including ▶estrogens and ▶testosterone. Excess estrogen is believed to lead to ▶breast cancer by causing an excessive stimulation of cell division, leading to spontaneous mutations in the oncogenes and tumor suppressor genes of breast epithelial cells. An excessive level of cell division in the epithelial cells of the prostate, driven by testosterone and its metabolites, is thought to contribute to the induction of prostate cancer. Human ▶endometrial cancer is thought to be caused by estrogens without progestogens. ▶Ovarian cancer can be induced by ovulation and the accompanying hormonal changes. Exposure to excess levels of hormones is estimated to induce 30% of new human cancer cases. Dietary influences are very important in human cancer induction. Dietary influences are estimated to contribute to 15% of human cancers. Cancers influenced by diet include ▶stomach cancer, ▶colorectal cancer, and nasopharyngeal cancer. Consumption of an excess of animal fat and excess caloric intake predispose to cancer induction. Conversely, high consumption of green leafy and yellow vegetables and fresh fruits and a diet high in fiber inversely correlate with cancer induction. There are also a number of dietary mutagens formed by pyrolysis of foods. These include the tryptophan metabolites, TRP P1 and TRY P2, and other metabolites such as PhiP and MeIQX. ▶Colon cancer in particular is thought to be induced by an excess of animal fat and deficiency of dietary fiber. Caloric excess in the diet correlates with

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endometrial cancer induction. Excessive ▶alcohol consumption correlates with increased risk of induction of pharyngeal cancer, laryngeal cancer, liver cancer esophageal cancer, oral cancer, colon cancer, and breast cancer (▶Alcohal-rediated Cancer). Another specific example of a known human chemical carcinogen occurring during food consumption is ▶aflatoxin B1, a biocidal metabolite of the mold, Aspergillus flavus. A. flavus biosynthesizes and then utilizes aflatoxin B1 as a biocide against other microorganisms in order to establish its own ecological niche. Aflatoxin B1 is metabolized by cytochrome P450 in mammals to a mutagenic metabolite, aflatoxin B1 2,3-epoxide, which binds covalently to DNA and induces mutations in the ▶p53 tumor suppressor gene and in other genes. This process leads liver cancer in humans. Aflatoxin B1induced liver cancer is common in The People’s Republic of China, Taiwan, Africa, and Mozambique, where hot, wet climates favor the growth of A. flavus, and this fungus contaminates fruits and grains, which are ingested by humans, leading to liver cancer. Exposure to oncogenic viruses is estimated to induce 10% of all human cancers. Notable and well-studied viruses that are oncogenic include the ▶human papillomaviruses, including HPV16 and 18, which induce human ▶cervical cancer. ▶Hepatitis B virus and ▶hepatitis C virus induce human liver cancer in Taiwan, in The People’s Republic of China, and in Mozambique. The ▶human T cell leukemia virus (HTLV) induces human T cell leukemias in Japan and the Caribbean. Infection of humans with the human immunodeficiency virus (HIV) is known to lead to ▶lymphomas. Exposure to ▶Epstein-Barr Virus can lead to benign conditions such as mononucleosis, and also at lower incidences, to Burkitt Lymphoma in Africa and to ▶nasopharyngeal carcinoma in The People’s Republic of China. A fifth category of agents that induce human cancer are drugs, ▶x-rays, and ▶UV radiation. This combined category of carcinogens is estimated to induce 10% of all human cancers. Certain medically approved drugs, such as a fraction of cancer chemotherapeutic agents, including ▶alkylating agents, ▶adriamycin, and ▶tamifoxen, can induce secondary malignancies (▶secondary tumor). Certain analgesics, such as phenacetin, can induce renal pelvic cancer. Prominent examples of radiation carcinogens include ▶ultraviolet light associated with ▶skin cancer and ionizing radiations – gamma rays, x-rays, beta particles, alpha particles, and neutrons. Studies of the atomic bomb blasts in Hiroshima and Nagasaki during World War II have provided the best estimates of dose–response curves for radiation-induced carcinogenesis. UV light from the sun and in tanning salons can induce skin cancer. The sixth broad category of carcinogens that can induce human cancer occurs in the occupational

setting. Occupationally induced cancer is estimated to contribute 5% of all human cancers. In this context, exposure to ▶benzene has been linked in epidemiological studies to the induction of ▶acute myelogenous leukemia, ▶non-Hodgkin lymphoma, ▶chronic myelogenous leukemia, and many other types of leukemia in rubber workers and in workers in shoe factories in the past. Exposure of nickel refinery workers to mixtures of soluble and insoluble ▶nickel compounds as aerosols has been correlated with increased incidences of nasal sinus and respiratory cancers. Similarly, exposure of workers to hexavalent ▶chromium compounds in the chromate manufacturing industry and in the chrome plating industry correlates with induction of lung cancer. Vinyl chloride exposure has led to human lung, liver, and brain cancer, and to the immune-mediated disease, vinyl chloride disease, which is similar to scleroderma. Other examples of occupational carcinogens include bis-chloromethyl ether (lung cancer), ▶asbestos (lung cancer and ▶mesothelioma), and trichloroethylene (cancer at multiple sites) and perchloroethylene. ▶Dioxin (TCDD, or 2,3,7,8-tetrachloro-p-dibenzo-dioxin), a by-product of paper manufacturing, is a potent carcinogen and tumor promoter. ▶Arsenic, a by-product of copper smelting, is also found as an environmental carcinogen in drinking water contaminated by arsenate leached from iron sulfide-bearing rocks. Environmental carcinogenesis is thought to be important also. However, at the present time, no solid estimates of the amount of human cancer that environmental pollution with carcinogens causes can be made with confidence due to our lack of knowledge in this area. Chemical Carcinogenesis Chemical carcinogenesis is the process by which chemical carcinogens (and radiations) can induce tumors in lower animals or in humans. Broadly viewed, chemical carcinogenesis begins as the process in which the very complicated series of ▶signal transduction pathways mediating cellular growth and proliferation and their negative regulators are disrupted and deregulated. Chemical carcinogenesis is clearly a multistep process. Chemical carcinogenesis has been divided conceptually and experimentally in the l930s by Isaac Berenblum, of the Weizmann Institute in Israel, into two stages, initiation and promotion (▶Tumor promotion), when studying carcinogenesis on the backs of shaved mice. Berenblum used small doses of the ▶polycyclic aromatic hydrocarbon 7,12-dimethylbenza(a)anthracene (▶DMBA) as the initiator and the mixture croton oil, a biocide isolated from the plant, Euphorbia lathyris, as a promoter. Initiation is thought to be a mutation, likely in an oncogene such as the ▶RAS cellular oncogene. Stimulation of the initiated

Genetic Toxicology

cells bearing mutations in the RAS or other cellular oncogenes with croton oil stimulates the cells to grow. With repeated croton oil stimulation, the initiated cells form a benign tumor called a ▶papilloma. With further croton oil stimulation, the cells convert into a malignant tumor, called a ▶carcinoma. Further damage to the cells of this carcinoma can result in a metastatic carcinoma. For many decades, investigators have used tetradecanoyl-phorbol acetate (▶TPA), a chemical purified form croton oil, as the tumor promoter. TPA is one of the most potent tumor promoters known, and it binds to ▶protein kinase C to stimulate cell division of initiated cells. Studies of how tumor cells interact with fibroblasts and immune effector cells to enable them to continuously grow and break free of the homeostatic mechanisms of the host that mediate tissue integrity are subjects of intense current interest. Chemically Induced Morphological and Neoplastic Transformation and the Molecular Biology of Carcinogenesis/Cell Transformation and Human Cancer At the cellular level, chemical carcinogenesis first involves the conversion of a normal cell into a tumor cell. There are a number of in vitro cell culture systems in which this process can be studied in a systematic way. They involve studying the loss of contact inhibition of cell division, the loss of anchorage dependence of cell division, escape from calcium ion-induced terminal differentiation, and the eventual acquisition of the property of tumorigenicity. These include C3H/10T1/ 2 Cl 8 mouse embryo fibroblastic cells, Balb/c 3T3 cells, Syrian hamster cells, mouse epidermal keratinocytes, and rat tracheal hamster epithelial cells among the rodent cell systems. Additional human cell systems involve diploid human fibroblasts and human epidermal keratinocytes. This process of malignant cell transformation proceeds first through a series of mutations, rearrangements, or amplifications of oncogenes, or in epigenetic changes involving methylation status of oncogenes, leading to inappropriate expression of the normal oncogene product, or to expression of a mutated oncogene product. Such expression can lead to inappropriately high expression of various proteins involved in signal transduction pathways downstream of the oncogene product in the signal transduction pathway. A number of oncogenes contribute to cellular progression chemical carcinogenesis. Oncogenes are a set of genes controlling cellular growth and proliferation, and consist of a large number of gene families. Prominent members of these families include the ▶RAS gene family, the ▶MYC gene family, ▶ABL, ▶FOS, ▶JUN, ▶ERBB2, FMS, ▶KIT, RAF, SIS, ERBA, ETS, REL, ▶HER2/neu, ▶SRC, ▶BCL-2, BCL-3, BCL-6, HOX1, RHOM-1, RHOM-2, TAL-1, TAL-2, TAN-1, and many others.

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Secondly, this process involves the inactivation of a number of ▶tumor suppressor genes. Tumor suppressor genes are negative regulators of cell growth and proliferation. Prominent members of this large group of genes include the genes ▶RB1, ▶FHIT, ▶VHL, ▶APC, ▶WT1, ▶NF1, ▶NF2, ▶TP53, ▶MEN1, ▶PTEN, and many others. Inactivation of the RB1 tumor suppressor gene leads to release of the transcription factor EF-2 from the Rb–EF2 complex, which can cause cell cycle progression. Mutational inactivation or deletion of TP53 can lead to failure to stop cell cycle progression and allow DNA repair to proceed, leading to an accumulation of mutations in cells. Additionally, inactivation of TP53 can lead to a failure of cells bearing many mutations to undergo ▶apoptosis. This allows accumulation of cells bearing mutations, and allows these cells to progress toward malignancy. The accumulation of mutations, gene amplifications, gene rearrangements, or deletions is thought to lead to conversion of a normal cell into a malignant cell. These include events that activate a number of cellular oncogenes, and that inactivate tumor suppressor genes. Hence, a number of cellular oncogenes would be mutated and activated, or amplified, or rearranged and placed under the control of strong promoters. This would lead to expression of mutant oncogene product, or to higher steady-state levels of normal oncogene product. These protein products then would impact upon signal transduction pathways to stimulate these pathways. In the same manner, mutational inactivation of tumor suppressor genes, methylation of the promoters of these genes to transcriptionally inactivate them, and breakage and loss of part of the chromosome bearing these genes, or loss of the entire chromosome bearing these genes, can also contribute to carcinogenesis. It is thought that fifteen events, including activation of oncogenes and inactivation of tumor suppressor genes, lead to carcinogenesis. What has only recently become known is that fifteen such events can have far-reaching effects on global gene expression, leading to aberrant expression of 100–300 genes in cells, which results in the malignant phenotype. This is because mutation or overexpression of each oncogene can lead to increased expression of 10 additional genes in signal transduction pathways in which this gene participates. Similarly, each tumor suppressor gene may control expression of approximately an additional 10 genes. When this suppressor gene is inactivated, stimulation of its expression of these additional 10 genes is also lost. Hence, physiologically, tumor cells suffer global derangement of gene expression. Our knowledge of this complexity paradoxically provides many opportunities for therapeutic intervention to kill tumor cells, cause them to apoptose, or to cause them to differentiate into nontumorigenic cells.

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References 1. Hanahan D, Weinberg RA (2000) The hallmarks of cancer. Cell 100:57–70 2. Klaasen CD (ed) (2001) Casarett and Doull’s toxicology: the basic science of poisons, 6th edn. Mc-Graw-Hill, New York 3. Verma R, Ramnath J, Clemens F et al. (2004) Molecular biology of nickel carcinogenesis: identification of differentially expressed genes in morphologically transformed C3H/10T1/2 Cl8 mouse embry fibroblast cell lines induced by specific insoluble nickel compounds. Mol Cell Biochem 255:2013–2216 4. Warshawsky D, Landolph JR Jr (eds) (2006) Molecular carcinogenesis and the molecular biology of human cancer. CRC/Taylor and Francis Group, Boca Raton, Florida, New York and London, UK 5. Weinberg RA (2007) The biology of cancer. Garland Science, The Taylor and Francis Group, LLC, Boca Raton, Florida, New York

Genistein. Figure 1 The chemical structure of Genistein.

Definition

Genistein is an ▶isoflavone, derived principally from soybeans, that has cancer preventive and therapeutic effects (see Fig. 1).

Characteristics

Genetically Engineered Mice ▶Mouse Models

Genetically Engineered Model Definition Cancer models created by genetically altering an animal (usually a mouse) to make it more susceptible to cancer. The genetic alteration can cause the animal to overexpress a gene that promotes tumor development or inactivate a gene that suppresses tumor development. ▶Ultrasound Micro-Imaging ▶Gene Knockout ▶Transgenic ▶Knock-out mice

Genistein RUIWEN Z HANG University of Alabama at Birmingham, Birmingham, AL, USA

Synonyms 4′,5,7-Trihydroxyisoflavone; Soy phytoestrogen

Soy and Cancer Numerous epidemiological studies have indicated that a diet high in soy products can decrease the risk of developing cancers, including ▶breast cancer, ▶prostate cancer, ▶colon cancer, ▶lung cancer and ▶skin cancer. In countries where soy products are frequently consumed, there is a lower incidence of these and other cancers. A study of more than 600 women in Singapore (420 healthy controls and 200 women with confirmed breast cancer) demonstrated that ingestion of soy products correlated with a decrease in cancer risk. Moreover, a similar study with men showed that soy consumption decreased prostate cancer mortality. Two isoflavones, genistein and daidzein, appear to be the major mediators of the cancer preventive activity of soybeans. For genistein, which is probably the primary active component, a body of work related to its cancer preventive and therapeutic effects, as well as to its mechanisms of action, has emerged. Cancer Prevention by Genistein Studies of ▶chemical carcinogenesis and cancer development in transgenic animals have demonstrated that administration of genistein can decrease the incidence of cancer and decrease the multiplicity of tumors that develop. For example, treatment of transgenic adenocarcinoma of the mouse prostate (TRAMP) mice with 100–500 mg genistein/kg diet reduced the incidence of advanced-stage prostate tumors in a dose-dependent manner. A high-isoflavone diet also inhibited methylnitrosourea-induced prostate tumors in Lobund-Wistar rats. Treatment of mouse mammary tumor virus (MMTV)-neu mice with diets containing 250 mg/kg of genistein or daidzein increased the latency for spontaneous breast tumors but did not affect tumor size or multiplicity. Topically applied to ▶DMBA-initiated and ▶TPA-promoted Sencar mice,

Genomic Imbalance

genistein reduced the incidence and multiplicity of skin tumors by 20% and 50%, respectively. In addition to its chemopreventive effects, genistein can be used therapeutically. It increases the survival of animals bearing ▶xenograft, chemically induced and spontaneous (transgenic) tumors and improves the response to conventional therapies. Genistein can act additively or synergistically with chemotherapeutic agents, hormone therapy, ▶immunotherapy or ▶radiation therapy. Epidemiological studies with cancer patients suggest that increased soy consumption may increase survival. Moreover, while randomized trials are still ongoing (or have yet to be performed for many types of cancers), genistein appears to have little or no toxicity. Mechanisms of Action of Genistein Although the mechanisms of action for the anticancer effects of genistein have not been established, there are a number of candidate pathways. Reported in vitro and/or in vivo activities of genistein include estrogen agonism/antagonism; inhibition of protein tyrosine phosphorylation; ▶topoisomerase inhibition; suppression of ▶angiogenesis; scavenging of free radicals; and inhibition of ▶matrix metalloproteinases, ▶NF-κB and oncogenes, such as ▶MDM2. Any or all of these effects can decrease carcinogenesis and tumor progression, lead to the induction of apoptosis and cell differentiation, and suppress ▶metastasis.

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Other Indications Because of its estrogenic effects, genistein has been used to ameliorate the effects of menopause. Studies so far have been inconclusive, although some suggest that genistein can improve the symptoms. Future studies, especially those involving use of randomized placebo controls, will be needed to determine its efficacy. Based on its estrogenic, anti-oxidant and other properties, genistein has also been suggested to prevent osteoporosis, improve cognitive function, decrease cholesterol, and improve cardiovascular health.

References 1. Dixon RA, Ferreira D (2002) Genistein. Phytochemistry 60:205–211 2. Sarkar FH, Li Y (2004) The role of isoflavones in cancer chemoprevention. Front Biosci 9:2714–2724 3. Lambert JD, Hong J, Yang GY et al. (2005) Inhibition of carcinogenesis by polyphenols: evidence from laboratory investigations. Am J Clin Nutr 81:284S–291S 4. Ravindranath MH, Muthugounder S, Presser N et al. (2004) Anticancer therapeutic potential of soy isoflavone, genistein. Adv Exp Med Biol 546:121–165 5. Li M, Zhang Z, Hill DL et al. (2005) Genistein, a dietary isoflavone, down-regulates the MDM2 oncogene at both transcriptional and posttranslational levels. Cancer Res 65:8200–8208

Genomic Imbalance Bioavailability and Safety The ▶bioavailability of genistein appears to be greater than that of many other natural compounds. Plasma concentrations of genistein in tumor-bearing ▶nude mice fed a diet containing 1 mg/g genistein were 3.4 μmol/L; in humans, a single oral dose of 460 mg resulted in peak plasma concentrations of 20–25 μmol/L. In most commercially available products, isoflavones are present as glycosides, which may require hydrolysis by intestinal beta-glucosidases. After absorption, ▶phytoestrogens are primarily converted to glucuronic acid derivatives. Extensive metabolism, accomplished by bacteria in the gut, leads to the formation of equol and lignans. Although genistein is generally regarded as safe, and toxic effects of genistein do not occur when cells are exposed to physiologically relevant levels of the compound, there are some undesirable effects, most of which have been observed in animal models and are due to its hormone-like properties. Because there is evidence from in vitro and animal studies that it can stimulate the growth of hormone-dependent cancers (especially ▶estrogen receptor alpha positive breast cancers), use of genistein to treat these cancers is controversial.

R OBERTA VANNI Department of Biomedical Science & Technology, University of Cagliari, Monserrato (CA), Italy

Definition Refers to a genome showing any loss or gain of DNA sequences compared with the reference DNA whole sequence of the genome of interest. The term usually indicates extensive disequilibrium in the number of chromosomes or chromosome segments per cell.

Characteristics Genomic Imbalance Concept The relative dosage of genes governing cell physiology, is the product of evolution. Human somatic cells have evolved their “genome balance” as ▶diploid, and variation in the number of chromosome copies as compared to the euploidy which has evolved, leads to genomic imbalance. This affects gene dosage and, consequently, promotes imbalances in cellular pathways. Most cancer cells acquire genomic imbalance as a consequence of ▶aneuploidy, i.e. an abnormal copy number

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Genomic Imbalance

of genomic elements, identified as gain and/or loss of whole chromosome(s) (aneuploidy) or chromosome segment(s) (partial aneuploidy). Genomic imbalance reflects the ▶karyotype complexity of the cancer cells. Cancer as a Genetic Disease Cancer as a genetic diseasse involving genomic imbalance is a concept that has been explored since the end of the nineteenth century. In 1890 Paul von Hansemann (1858–1920), noticed that chromosomes in carcinomas segregate in unbalanced fashions, and at the beginning of the twentieth century, in 1914, Theodor Boveri (1862–1915) proposed his “chromosome theory of cancer,” according to which cancer results from abnormal chromosomal composition within cells. Nowadays, this concept is widely accepted, based on molecular evidence, according to which cancer is a biological process characterized not only by accumulation of chromosome changes, but also by gene mutations, all contributing to the cell transformation process. The loss of critical cellular checks and balances throws proliferation processes into disorder by means of sequential steps, broadly including ▶initiation, ▶progression, ▶invasion and ▶metastasis. Cause of Genomic Imbalance in Cancer Genomic imbalance is the product of a phenomenon called ▶chromosome instability (CIN), resulting in the increased probability that during cell division, whole chromosomes or chromosome segments will be acquired or lost. CIN is actually an ongoing process, responsible for variation in the rate of chromosome changes according to Darwinian selection, and may end with the production of stable aneuploid cells having proliferative advantages. A certain degree of cytogenetic heterogeneity within a tumor is maintained by CIN, and cytogenetically related or unrelated clones often persist alongside the favored one, contributing to intratumoral genomic imbalance. Many aggressive cancers, such those of the bladder, brain, breast, bone, cervix, colon, gallbladder, head and neck, liver, lung, ovary, pancreas, prostate, and testis show an accumulation of complex rearranged chromosome patterns, which may include, in addition to aneuploidy, ▶double-minutes and the formation of ▶homogeneously-staining regions. CIN, and the consequent genomic imbalance, calls for the interaction of various outcomes, including, abnormal mitotic segregation, abnormal shortening of ▶telomeres and ▶mitotic checkpoint deficiency. . Abnormal mitotic segregation. Chromosome segregational defects may be due to different mechanisms, such as ▶multipolar spindles formation, loss of ▶sister chromatid cohesion, ▶kinetochore defects during spindle attachment.

Multipolar spindles may develop in the presence of supernumerary ▶centrosomes. Centrosome amplification is frequently seen in almost all types of solid tumors, and to a lesser extent in leukemia and lymphoma. Its occurrence is strongly associated with a high degree of aneuploidy. Amplification of STK15/ aurora kinaseA gene, inactivation of tumor suppressor genes, such as TP53 (Tumor Protein 53), RB1 (Retinoblastoma), and BRCA1 (breast cancer1) as well as overexpression of cyclins D and E, play a prominent role in this process. Loss of sister chromatid cohesion is crucial in the metaphase-to-anaphase transition and the correct separation of genetic material in the cell. Cohesion is maintained by proteins called ▶cohesins, which have to be degraded to lead to sister chromatid separation. Cohesins are released through a number of catabolic steps driven by the anaphase-promoting complex (APC), a ▶ubiquitin ligase, targeting proteins for degradation. In yeast, APC acts on ▶securin proteins, which in turn prevent ▶separin (a cysteine protease, also called separase) from promoting sister chromatid separation. Human homologs of yeast separin and securin are respectively ESP1 (Extra Spindle Poles-like1) and ▶PTTG1 (Pituitary Tumor-Transforming Gene1) proteins, and their inactivation interferes with the correct distribution of genetic material at ▶anaphase. ▶Kinetochore defects during spindle attachment may also have a major impact on chromosome malsegregation. Kinetochore is a highly-complex proteinaceous structure located in centromeric DNA and providing dynamic attachments to spindle microtubules, mediating the chromosome bi-orientation necessary to facilitate accurate segregation. Disturbances in this process result in aneuploid cells. . Abnormal shortening of telomeres. This phenomenon is observed in both benign and malignant tumors. Shortening of ▶telomeres during normal cell development and aging is the rule; however, in somatic cells that have lost proliferation control, it gives rise to genome instability and abnormal cell proliferation. Such abnormal shortening causes telomeres to lose their ability to protect chromosome ends from fusion. The products of chromosome fusion contribute to CIN by the formation of anaphase bridges, leading to structural and numerical chromosome changes or, through cell division inhibition, to poliploydization and subsequent multipolar spindle formation. . Mutations at mitotic checkpoint. The regular mitotic phase of the ▶cell cycle involves an orderly set of events, subdivided into phases: the prophase, prometaphase, metaphase, anaphase and telophase. In a normal cell, anaphase can start only when all chromosomes have congressed to the metaphase plate and achieved bipolar attachment to the mitotic

Genomic Imprinting

spindle. This scenario requires a powerful ▶mitotic checkpoint, based on a dynamic balance of ▶ubiquitination (by APC) and deubiquitination (possibly by ▶USP44, Ubiquitin-Specific Protease44) of target proteins. Breakdown of mitotic checkpoint signaling brings on cell death, whereas its weakening, i.e. minor changes in checkpoint protein levels, does not compromise cell viability but promotes aneuploidy, since the mitotic checkpoint does not recognize a single or a few chromosomes lacking spindle attachment. Although the role of genomic imbalance in tumorigenesis is recognized, and for some tumors diverse genomic imbalances correlate with prognosis, whether or not it may actually initiate tumorigenesis is still being debated.

References 1. Von Hansemann D (1890) Ueber asymmetrische Zellteilung in Epithelkrebsen und deren biologische Bedeutung. Virschows Arch Pathol Anat 119:299–326 2. Boveri T (1914) Zur Frage der Entstehung Maligner Tumoren. Gustav Fischer Verlag, Jena 3. Stegmeier F, Rape M, Draviam VM et al. (2007) Anaphase initiation is regulated by antagonistic ubiquitination and deubiquitination activities. Nature 446:876–881 4. Duesberg P, Li R, Helmann R (2006) Aneuploidy and cancer: from correlation to causation. In: Dittmar T, Zaenker KS, Schmidt A (eds) Infection and inflammation: impacts on oncogenesis (Contributions to Microbiology), vol 13 Basel, Karger, pp 16–44 5. Michor F, Iwasa Y, Vogelstein B et al. (2006) Can chromosomal instability initiate tumorigenesis? Semin Cancer Biol 15:43–49

Genomic Imprinting A NDREW P. F EINBERG Department of Medicine and Center for Epigenetics, Institute for Basic Biomedical Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, USA

Definition

Is an ▶epigenetic alteration (i.e., not involving a change in base sequence) of a specific parental ▶allele of a gene, or the chromosome on which it resides, in the gamete or zygote, leading to differential expression of the two alleles of the gene in somatic cells of the offspring. Genomic imprinting challenges two

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assumptions of conventional Mendelian genetics applied to human disease: that the maternal and paternal alleles of a gene are equivalent, and that two functional copies of a gene always are associated with health (Table 1).

Characteristics Imprinted genes probably account for many examples of developmental malformations in humans, as uniparental disomy (UPD) of several chromosomes is associated with a variety of recognized defects, but UPD affecting most or all of a chromosome is rarely seen. Imprinting may have arisen in mammals as a result of an evolutionary conflict between maternal and paternal genomes. There is a strong and sometimes surprising relationship between imprinted genes and growth, including both prenatal growth and postnatal growth related to nurturing ability. Imprinting is also thought to underlie some quantitative trait loci for growth, with considerable potential commercial application in animal husbandry, and imprinting may be a potential barrier to stem cell transplantation. For all these reasons, genomic imprinting has generated intense interest. Imprinted Genes and their Regulation Despite this interest, the comprehensive identity of all imprinted genes remains unknown. At present over 80 imprinted genes are suspected in one or more species (see http://www.geneimprint.com). Imprinted genes appear to be organized within genomic domains. Evidence for this idea comes from studies of the region of 15q11-13 involved in Prader-Willi and Angelman syndromes, which cause mental retardation and neurological problems. This region harbors at least six imprinted genes and the region of the IGF2R gene contains at least three. Similarly, band 11p15 contains a domain of imprinted genes distributed over *1Mb. These genes play diverse roles including hormonemediated growth stimulation (insulin-like growth factor II, or IGF2), control of the cell cycle (p57KIP2) and ion trafficking (KVLQT1). Both cis-acting and trans-acting factors appear to be important in the regulation of genomic imprinting. It is believed that cis-acting sequences can regulate imprinting over large distances. Evidence for this idea comes from the identification of patients with microdeletions involving upstream exons of the small nuclear ribonucleoprotein N gene (SNRPN), in the Prader-Willi region of chromosome 15. These deletions lead to disrupted imprinting extending over several megabases. This deletion site has therefore been termed an “imprinting center” for this chromosomal region. However, the molecular basis for the function of the imprinting center is as yet unknown.

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Genomic Imprinting. Table 1

Key ideas of genomic imprinting and cancer

Genomic imprinting

An epigenetic alteration in the gamete leading to differential allele expression in the offspring

Examples of imprinting in disease

UPD with birth defects Specific disorders (PWS, AS) Human cancer Loss of imprinting (LOI) in childhood and adult tumors Both gene silencing and gene activation Link to cancer risk DNA methylation Conserved regulatory elements and genomic domains Modifier genes

Imprinting in cancer

Mechanisms

Imprinting and DNA Methylation Cytosine DNA ▶methylation also appears to be important in the regulation of genomic imprinting, as loss of the cytosine DNA methyltransferase I gene (Dnmt1) disrupts normal genomic imprinting in mice. DNA methylation is a covalent modification of DNA in which a methyl group is transferred from S-adenosyl methionine to the C-5 position of cytosine. DNA methylation occurs almost exclusively at CpG dinucleotides. CpG islands, which are sequences unusually rich in ▶CpG dinucleotides, are usually found in the vicinity of imprinted genes. Recently, one mediator of imprinting was discovered. It is the CCCTC-binding factor (▶CTCF), a transcription factor that binds to an unmethylated, GC-rich sequence *2kb upstream of the H19 gene. The latter has previously been shown to be necessary for normal imprinting of H19 and ▶IGF2. The same CTCF does not bind to methylated DNA. CTCF is known to be an insulator binding protein, and its binding prevents access by IGF2 to a shared enhancer 3′ to H19 (and about 200 kb telomeric to IGF2 itself). Loss of Imprinting (LOI) in Cancer In 1993, it was discovered that IGF2 can undergo loss of imprinting (LOI) in cancer, with abnormal expression of the normally silent maternal allele. LOI of IGF2 has been found in a wide variety of tumors, including embryonal tumors and adult malignancies. In the case of ▶colon cancer, LOI was found not only in the tumors but in the normal tissues of patients with colon cancer. Furthermore, multiple well-controlled studies have now shown an association of LOI with a positive family history and personal history of colorectal tumors, both benign and malignant. Studies of mouse models with LOI and a gene mutation causing intestinal tumors show that LOI increases tumor initiation, and acts by increasing and altering the tissue stem cell compartment. Thus, tests for LOI may eventually prove useful

for identifying patients at risk of cancer, thereby reducing overall cancer mortality (Fig. 1). In the case of embryonal tumors, this activation of the maternal allele of IGF2 is coupled to silencing of the maternal H19 allele and methylation of a normally unmethylated maternal H19 ▶CpG island. However, LOI of IGF2 occurs independently of H19 in adult tumors, such as ▶cervical cancer and ▶brain cancer. LOI of IGF2 is now recognized as one of the most common genetic alterations in human cancer. LOI of IGF2 is also found in about 15% of patients with ▶Beckwith-Wiedemann syndrome (BWS). BWS is a disorder of prenatal overgrowth, birth defects and cancer, which is transmitted as an ▶autosomal dominant trait, although most cases arise sporadically. In addition, LOI of the LIT1 gene, also on 11p15, is found in about 40% of BWS patients. This gene is particularly interesting, as it is an antisense transcript normally expressed from the paternal allele, that lies entirely within the maternally expressed KVLQT1 gene. A link between LOI and DNA methylation is also suggested by studies using the drug 5-aza-2′deoxycytidine, which inhibits DNA methylation. This drug can restore a normal pattern of imprinting to tumor cells with LOI, suggesting that this or other pharmacological agents might eventually be used to treat cancers specifically with LOI or as chemopreventive agents in patients with LOI in their normal tissues. Frequent loss of heterozygosity (▶LOH) of 11p15 has also been observed generally in embryonal tumors, including ▶Wilms tumor, ▶rhabdomyosarcoma and ▶hepatoblastoma. LOH of 11p15 is one of the most common genetic changes in cancer and is found in many adult malignancies, including those of the stomach bladder, ovary, breast and lung. Further strong support for the existence of an embryonal ▶tumor suppressor gene on 11p15 derives from genetic complementation experiments. ▶Microcell-mediated chromosome transfer of a human chromosome 11 suppresses the growth of rhabdomyosarcoma cells

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sequences is by comparative genomics, in which the mouse sequence is obtained and compared to human sequence, in order to identify species conserved orthologous elements. These elements can then be tested in functional assays and be analyzed for mutations or deletions in patients with cancer or ▶BWS. Proteins that interact with such sequences could include as yet unidentified modifiers of DNA methylation and/or genomic imprinting. Thus, one of the most important implications of the study of imprinting is that the lessons learned may be applicable to understanding the regulation of genomic domains generally, and their dysregulation may provide novel insights into the mechanism of cancer.

References

Genomic Imprinting. Figure 1 Upper panel shows a normally imprinted IGF2 and H19 gene, with IGF2 expressed (drawn large) from the paternal allele, and H19 from the maternal allele. A shared enhancer (green) cannot cross an unmethylated CpG island (small open circles) upstream of the maternal H19 allele, presumably because of binding of CTCF to this island. The lower panel shows loss of imprinting (LOI) in cancer, with a switch of the paternal chromosome to a maternal epigenotype. Here the H19 CpG island is also methylated on the maternal chromosome, allowing the enhancer to interact with IGF2, with activation of the maternal IGF2 allele and silencing of the maternal H19 allele.

in vitro. Furthermore, subchromosomal transferable fragments limited to 11p15 do suppress tumor cell growth. However, in the investigation of an 11p15 tumor suppressor gene it is puzzling that in virtually all cases of LOH of 11p15 in embryonal tumors it is the maternal allele that is lost, an observation made before the discovery of human imprinted genes or such genes on 11p15 in particular. To address this problem, Sapienza argued that a gene that is not normally imprinted might become so aberrantly. According to Sapienza, a specific parental allele (in this case the paternal) would become silenced in some individuals. One or more of the maternally expressed genes on 11p15 might fulfill this role. One of the most exciting frontiers in the study of genomic imprinting and its role in cancer is the identification of sequences that lie between genes, which might serve a regulatory role in the maintenance of normal imprinting of large genomic domains, such as on 11p15. One recent approach to identifying such

1. Moore T, Haig D (1991) Genomic imprinting in mammalian development: a parental tug-of war. Trends Genet 7:45–49 2. Nicholls RD, Saitoh S, Horsthemke B (1998) Imprinting in Prader-Willi and Angelman syndromes. Trends Genet 14:194–200 3. Feinberg AP (2001) Genomic imprinting and cancer. In: Scriver CR et al. (eds) The metabolic and molecular bases of inherited disease, 8th edn. McGraw-Hill, New York, pp 525–537 4. Cui H, Horon IL, Ohlsson R et al. (1998) Loss of imprinting in normal tissue of colorectal cancer patients with microsatellite instability. Nat Med 4:1276–1280 5. Sakatani T, Kaneda A, Iacobuzio-Donahue CA et al. (2005) Loss of imprinting of Igf2 alters intestinal maturation and tumorigenesis in mice. Science 307:1976–1978

Genomic Instability Definition

▶Genetic Instability

Genomics Definition Denotes the complete study of the hereditary material of living beings: both the coding and noncoding portions. Structural genomics involves creating “maps” of genomes, carrying out DNA sequencing, and determining the localization and the regulatory regions of genes on ▶chromosomes. Functional genomics is the branch of genomics that studies the biological function of the

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Genotoxic

genes and their products, the coded proteins, their expression and regulation, as well as the interactions between different genes.

Genotype Definition

Genotoxic Definition Causes damage to DNA. Examples of genotoxic agents are chemicals or radiations that cause mutation to cells, chromosome breakage in cells, gene ▶amplification in cells, or single-stranded or ▶DNA-double strand breaks. ▶Chemically Induced Cell Transformation ▶Chemical Carcinogenesis ▶DNA Damage

Catalog of individual’s two alleles at a particular DNA location. Refers to the complete genetic composition of a single cell or organism. It also can refer to the specific allelic composition of a particular gene or group of genes. ▶Arylamine N-Acetyltransferases (NAT) ▶Biomonitoring ▶Linkage Disequilibrium

Geranylgeranyl Definition

Genotoxic Carcinogen Definition

C20 isoprenoid lipid, an intermediate in the HMG-CoA reductase mevalonate biosynthetic pathway, used in the biosynthesis of geranylgeranylated proteins. ▶Rho Family Proteins

A carcinogen capable of causing a change to the structure of the genome. ▶Toxicological Carcinogenesis

Genotoxicity Tests Definition

Geranylgeranylation Definition Post-translational modification of proteins by the attachment of an isoprenoid to C-terminal cysteine residues.

These represent a range of standardized assays designed to test chemicals for interaction with DNA, i.e. genotoxicity or mutagenicity. These comprise a number of different tests both in vitro and in vivo. The most usual study conducted early in the development of a new drug is the ▶Ames Assay that utilizes mutants of Salmonella typhimurium. Various mammalian cell culture systems are also employed such as Chinese hamster ovary (CHO) cells. Clastogenic activity is assessed by exposing cells to chemicals and examining cells microscopically for chromosome damage. An in vivo study is also often performed examination of the bone marrow in treated rodents.

▶Statins

▶Preclinical Testing ▶Clastogen

▶Cowden Syndrome ▶Germ Cell Tumors

Germ Cell Layers Definition Collection of cells formed during embryogenesis into the mesoderm, endoderm and ectoderm that go on to form specific organs of the body.

Germ Cell Tumors

Germ Cell Tumors C RAIG KOVITZ 1 , P HILLIPPE E. S PIESS 2 , N IZAR M. TANNIR 3 1

Department of Medical Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA 2 Department of Urologic Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA 3 Department of Genitourinary Medical Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA

Synonyms Testicular tumors; Gonadal neoplasms; Dysgerminomas

Definition

▶Testicular cancer represents a group of histologically heterogeneous neoplasms typically arising in gonadal tissue and, uncommonly, arising in extragonadal sites such as the retroperitoneum or mediastinum. A disease of young men which, when metastatic was previously uniformly fatal, testicular cancer is now usually cured.

Characteristics Incidence Germ cell tumors represent the most common cancer in young men between the ages of 20 years and 40 years. These tumors have a bimodal age distribution being most common in men ages 15–25 with a second, smaller peak at about age 60. It is estimated that 8,000 new cases of testicular cancer were diagnosed in the United States in 2005. During the past century, the worldwide incidence of testicular neoplasms has nearly doubled, with the highest increases reported in the United States, Great Britain and Northern Europe. Risk Factors Numerous case-control and cohort studies have established cryptorchidism as the major identifiable risk factor, although only about 10% of cases are associated with this phenomenon. This increased risk is true for the contralateral testicle even if it is normally descended. Additional risk factors include a personal history of testicular cancer as well as the presence of a first degree relative with the disease. Scrotal trauma and toxic exposures have not clearly been associated with the occurrence of germ cell tumors. Histological Classification The main histological categories of germ cell tumors are seminomas (▶Seminomatous Germ Cell Tumor) and non-seminomas (▶Non-seminomatous Gene Cell

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Tumor). Non-seminomas are further subcategorized as embryonal carcinomas, endodermal sinus tumors (also known as yolk sac tumors), choriocarcinoma and ▶teratoma. Tumors that contain more than one histological subtype are termed mixed germ cell tumors. For classification and treatment purposes, any tumor not histologically a pure seminoma is classified as a non-seminoma. Clinical Presentation and Diagnosis The majority of patients with testicular cancer presents with a painless testicular swelling or a palpable mass. In many cases, testicular swelling can be accompanied by pain secondary to bleeding or infarction within the tumor. Systemic symptoms at presentation such as abdominal pain, decreased appetite with or without associated weight loss, night sweats, chest pain, shortness of breath or hemoptysis usually indicate either an advanced stage of disease or an extragonadal primary tumor. If the diagnosis of a germ cell tumor is suspected, a bilateral high-resolution testicular ultrasound should be performed. In addition, the tumor markers human chorionic ▶gonadotropin (hCG), ▶alpha-fetoprotein (AFP) and lactate dehydrogenase (LDH) have unique diagnostic and prognostic significance in germ cell tumors and levels should be obtained on all patients with suspected germ cell tumors. Though not specific for germ cell tumors, AFP is produced by tumors with endodermal sinus or embryonal components as well as by immature teratomas. HCG is a hormonal product of syncitiotrophoblasts and can be expressed by choriocarcinomas, mixed germ cell tumors and, sometimes, by seminomas. LDH is a cellular protein expressed in numerous tissues and can be produced by non-seminomas. These markers are important for ▶staging of tumors, monitoring therapy, deciding when to apply surgical consolidation as well as to sensitively detect residual or recurrent disease. Additional preoperative workup typically includes a chest radiograph and discussion of sperm banking with the patient. When a testicular mass is found on ultrasonography, a radical inguinal ▶orchiectomy should be performed, unless the patient is ill, and initiation of systemic therapy is deemed urgent. In this instance, it would be appropriate to proceed with ▶chemotherapy without tissue diagnosis, if the markers are elevated and the clinical picture is compatible with the diagnosis of germ cell tumor. Trans-scrotal biopsies should be avoided as they can disrupt regional lymphatics, potentially altering the typically predictable lymphatic spread of these tumors. Postoperatively (or preoperatively if this will not delay surgery) an abdominal and pelvic computed tomography (CT) scan should be obtained and, if clinically indicated, brain magnetic resonance imaging (MRI) and a bone scan. CT scans can reveal clinically significant adenopathy

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that will be important in clinical decision-making. The preferred sites of initial spread for right-sided tumors are typically the infra-renal paracaval, inter-aortocaval and possibly paraortic nodes. In contrast, left-sided tumors preferentially spread to the infra-renal paraortic nodes initially. Staging and Risk Stratification As with all staging systems, the purpose is to classify patients with respect to prognosis and to allow one to offer treatments having a toxicity profile commensurate with the burden of disease and risk of recurrence. Given the importance of tumor markers in the management of germ cell tumors, the staging for germ cell tumors takes these into account along with histology, site of origin and anatomic extent of disease. The standard risk stratification used for these tumors is that developed by the International Germ Cell Cancer Consensus Group (IGCCCG). Through a retrospective multivariate analysis of nearly 6,000 patients with germ cell tumors, this group identified the clinical features strongly associated with prognosis: primary site of disease, the presence of non-pulmonary visceral metastases and marker levels at the initiation of therapy. Using these features, they divided non-seminomatous germ cell tumors into good-, intermediate- and poor-risk categories and seminomas into good- and intermediate-risk categories (Table 1). This risk stratification system provided the basis for the

Germ Cell Tumors. Table 1

Good risk

Intermediate risk

Poor risk

most recent American Joint Commission on Cancer (AJCC) TNM staging system for germ cell tumors. In general, Stage I disease is confined to the testis, stage II disease is disease that does not spread beyond the retroperitoneum and stage III disease involves the nodal regions beyond the retroperitoneum or non-nodal metastatic disease. Elevated serum tumor markers can help to define higher stages of disease. Management As the biology and management of seminomas and non-seminomas are quite different, we will consider the management of these distinct histologies separately. Seminomas By IGCCCG risk stratification, all patients with seminomas without non-pulmonary visceral metastates are categorized as having good-risk disease. Amongst these patients are those with Stages I and II disease and some with Stage III disease. The majority of patients with Stage I disease will be cured with radical inguinal orchiectomy alone, however, ~15–20% of patients with Stage I seminoma will have recurrent disease. As a result, there exists a need to identify those features of Stage I disease that would indicate a higher risk of relapse so that such patients could be offered adjuvant therapy. It has been reported that there is a subset of patients with Stage I seminoma with a primary tumor

International germ cell cancer consensus group classification prognostic risk stratification Seminoma

Nonseminoma

Any primary site No non-pulmonary visceral metastases Normal AFP, any hCG, any LDH

Testis/retroperitoneal primary and No non-pulmonary visceral metastases and AFP < 1,000 ng/mL and hCG < 5,000 mIu/mL and LDH < 1.5 × upper limits of normal range (ULN) 86% 5-year PFS; 90% 5-year OS Testis/retroperitoneal primary and No non-pulmonary visceral metastases and AFP 1,000–10,000 ng/mL and hCG 5,000–50,000 mIu/mL and LDH 1.5–10 × ULN 75% 5-year PFS; 80% 5-year OS Mediastinal primary or Non-pulmonary visceral metastases or AFP > 10,000 ng/mL or HCG > 50,000 mIu/mL or LDH > 10 × ULN 41% 5-year PFS; 48% 5-year OS

82% 5-year PFS; 86% 5-year OS Any primary site Non-pulmonary visceral metastases Normal AFP, any hCG, any LDH

67% 5-year PFS; 72% 5-year OS –

Germ Cell Tumors

less than 4 cm in size and without rete testis involvement who have a relapse free survival of 88%, and thus may constitute a group of patients most appropriate for surveillance. At present, surveillance is considered a reasonable option for highly motivated patients with Stage I seminoma after orchiectomy, though given the fact that nearly one third of patients with recurrent disease will require systemic chemotherapy, this has not been the most commonly used approach. At present, the majority of patients with Stage I seminoma are treated with infra-diaphragmatic radiotherapy (20 Gy) to the para-aortics. Such treatment results in 5-year survival rates of 98–99%. Data exists to support the use of a single dose of ▶carboplatin as ▶adjuvant therapy in Stage I seminoma, but this practice has not been widely adopted at present. Recently published retrospective data from the Princess Margaret Hospital in Toronto, Canada, showed comparable long-term results for patients with stage I seminoma treated with radiation prophylactically versus those with stage I who elected to be followed with active surveillance with initiation of therapy at the time of recurrence. Patients with Stage II disease are divided into those with non-bulky disease (those with nodal metastases no larger than 5 cm) and those with bulky disease (those with nodal metastases greater than 5 cm). For patients with non-bulky disease (Stage IIA-B), infradiaphragmatic radiation therapy (20 Gy) to include the para-aortics and ipsilateral iliac nodes with a boost (6–10 Gy) to the involved site is the standard therapy. Residual abnormalities are sometimes encountered following radiation therapy, but observation is generally recommended. For patients with advanced seminoma, defined as having Stage IIC or Stage III disease, chemotherapy is the treatment modality of choice. For those patients with good-risk disease, chemotherapy with four cycles of ▶etoposide and ▶cisplatin (EP) is generally offered. ▶Bleomycin is generally excluded as the risk of pulmonary toxicity outweighs the small incremental benefit afforded by its use. In the same light, ▶carboplatin has been demonstrated to be inferior to cisplatin and is thus not substituted in this scenario. For those patients with intermediate-risk disease, chemotherapy is usually administered with four cycles of ▶bleomycin, ▶etoposide and ▶cisplatin (BEP). After completion of chemotherapy, patients with advanced seminoma are restaged with chest, abdominal and pelvic CT scans as well as serum tumor markers. If no residual mass is found, or the residual mass measures 3 cm in size, a ▶positron emission tomography (PET) scan is performed, if available, to assess for the presence of viable tumor. In the presence

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of a positive PET scan, salvage radiation therapy is offered at our institution. For those patients unable to undergo PET scan, the size of the residual mass guides post-chemotherapy management, with masses greater than 3 cm having a higher risk of relapse. In this case, a surgical biopsy or consolidative radiation therapy are the interventions of choice. Patients who are found to have progressive disease after initial therapy are generally treated with salvage chemotherapy. Non-Seminomatous Germ Cell Tumors (NSGCT) NSGCT are risk stratified according to the IGCCCG classification schema based on the location of the primary tumor, the presence of non-pulmonary visceral metastases and the level of tumor marker elevation. Treatment options vary by stage and can include observation, chemotherapy and/or retroperitoneal lymph node dissection (RPLND). Patients with Stage IA NSGCT (tumor limited to the testis and epididymis without lympho-vascular invasion and normal post-orchiectomy tumor markers) are generally managed with either surveillance (in reliable patients) or RPLND. The reason for surveillance as an option is that the majority of patients with Stage I NSGCT will not have recurrence and of those approximately 30% who do have recurrent disease, there is effective chemotherapy which can result in long-term survival for most patients. RPLND is often used because it usually leads to accurate staging and can be curative in the majority of patients. The presence of N1 or N2 disease found at RPLND can then be managed either with surveillance or two cycles of EP or BEP chemotherapy. Patients with N3 disease found at RPLND are typically managed as good-risk advanced stage patients and are treated with EP for four cycles or BEP for three cycles. Patients with Stage IB NSGCT are generally managed with RPLND, although either active surveillance (for T2 disease only) or chemotherapy with two cycles of BEP is also appropriate. PostRPLND management is as stated above for Stage IA disease. Patients with Stage IS disease (persistent marker elevation after orchiectomy) are managed with chemotherapy (either four cycles of EP or three cycles of BEP). Stage IIA NSGCT in the presence of negative postorchiectomy tumor markers are generally approached with either RPLND or primary chemotherapy with EP for four cycles or BEP for three cycles. Those patients with Stage IIA disease who have persistent tumor marker elevations are managed with chemotherapy alone. Patients with Stage IIB disease and negative markers may undergo RPLND as long as lymph node metastases are within lymphatic drainage sites. PostRPLND management is the same as for those patients who have RPLND for Stage I disease. If the patient

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Germinal Center

has multi-focal lymph node metastases, adjuvant chemotherapy is considered the management option of choice. For patients who have received chemotherapy and have a residual retroperitoneal mass posttreatment, RPLND is generally performed to look for viable tumor, or teratoma. Patients with advanced disease (Stage IIC and III) disease are risk stratified by the IGCCCG into three categories (good, intermediate and poor). Those with good-risk disease (testis or retroperitoneal primary; no non-pulmonary visceral metastases as well as AFP >f

Lung

1st–8th Dec.; peak 2nd/3rd Dec. Median 40y

Solitary, rarely multifocal 50% Multifocal

f>m

>50% Multifocal

Liver

2nd–9th Dec.

f>m

>50% Multifocal

Mortality (%)

35

The majority of primary epithelioid hemangioendothelioma arises from soft tissue, bone, lung, and liver. The worst outcome is seen in the lung and hepatic tumors. There is a difference in age and gender distribution of EH in various sites [1].

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Hepatic Epithelioid Hemangioendothelioma

Hepatic Epithelioid Hemangioendothelioma. Figure 1 Hepatic epithelioid ▶hemangioendothelioma. (a) Macroscopy: Multifocal growth pattern of nodules and coalescence of them to form confluent masses specifically in the periphery with extension to and retraction of liver capsule. (b) Hematoxylin–eosin stain: The tumor cells form intracytoplasmic lumina containing erythrocytes. (c) Tissue stain for factor VIII-related antigen: In addition to the intracytoplasmic lumens, the pleomorphic cells of tumor are immunoreactive for factor VIII related Ag in this tissue section.

imaging, ▶low uptake is the major finding, which can be useful for the follow-up of patients under therapy. Angiographic findings are nonspecific ranging from hypo- to hyperperfusion. It is noteworthy that imaging studies can only lead to a strong suspicion regarding the presence of HEH and its pattern. Histopathology. Definitive diagnosis requires a histopathological examination. Often, a laparoscopic wedge or core biopsy is sufficient to depict architectural features of the HEH such as the intravascular characteristics. The diagnosis is mostly confirmed with ▶immunohistochemical (Immunohistochemistry) evidence of endothelial differentiation (Fig. 1b and c). Differential Diagnosis. More than two thirds of HEH cases may be initially misdiagnosed. The most common misdiagnoses are ▶cholangiocarcinoma, angiosarcoma, ▶hepatocellular carcinoma (HCC), ▶metastatic carcinoma (▶Metastasis), and sclerosing hemangioma.

Hepatic Epithelioid Hemangioendothelioma. Figure 2 MRI sections of HEH T2-weighted hyperintense lesions and central necrosis showing a target appearance.

Hepatic Ethanol Metabolism

Some important features for differential diagnosis include the infiltrative growth pattern with preservation of the hepatic acinar (▶Hepatic acinus) landmarks such as portal areas, the characteristic vascular invasion with tufting of portal vein branches and terminal hepatic venules, the identification of epithelioid tumor cells especially with intracytoplasmic lumina, and the delay of staining for epithelial differentiation markers. Therapy There is no generally accepted strategy for the treatment of HEH due to its heterogeneous dignity and variable clinical outcome. Theoretically, ▶liver resection is the first choice for curative treatment of HEH, but in the majority of the cases an oncological resection is impossible due to multicentricity of the lesions or anatomical difficulties. ▶Liver transplantation is generally the most common treatment modality. According to the Pychlmayr classification of hepatic malignancies, HEH is placed among the favorable indications for liver transplantation. Life expectancy of the patients with HEH is potentially good. Long-term disease-free survival after liver transplantation is reported in patients with disseminated disease at the time of diagnosis; conversely some patients with disease confined to the liver developed rapid recurrence and metastases following liver transplantation. The experience with other therapeutic modalities such as systemic or regional chemotherapy, ▶transarterial chemoembolization (▶Chemotherapy), and ▶radiotherapy (▶Chemoradiotherapy) is limited and variable, therefore, generally these treatments are of limited value especially as the first line therapy. Considering only follow-up without any treatment as a management option is controversial. There are some cases with long-term survival or even complete spontaneous tumor regression without receiving any treatment but until now, it is impossible to reliably identify HEH patients with a nonaggressive tumor and to consider them for a “wait and see” strategy. The mode of hepatic involvement and presence or absence of extrahepatic involvement are the main factors in the decision of the treatment modality. When less than one lobe is involved and there is no extrahepatic involvement, liver resection could be done as the first choice in treatment of HEH. The therapeutic strategy in the presence of extrahepatic involvement is especially controversial. When extrahepatic involvement exists, independent of performing liver resection or not, ▶adjuvant chemotherapy (▶Adjuvant chemoendocrine therapy) may be considered. In the case of massive involvement of the liver, liver transplantation is the best therapeutic choice. Extrahepatic involvement by itself does not exclude liver transplantation. Although chemotherapy in this situation is questionable, it may control the growth of the extrahepatic tumor. It is noteworthy that the clinical course of HEH is variable, ranging from a

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favorable disease with prolonged survival, even without therapy, to a rapidly progressive disease with a grave outcome. Therefore, the decision of the treatment strategy has to be tailored for each case, and the individual rate of progression, severity of signs and symptoms, and response to other treatment modalities may be important determinants for decision making. Clinical Outcome Three main causes for tumor recurrence and treatment failure after liver transplantation are error in the pretransplant evaluation, enhanced tumor growth under immunosuppressive therapy, and lack of effective anticancer therapy following surgery. The 5-year survival in different reports varies from 45 to 70%. Generally, the surgical therapies such as liver resection or transplantation have the best survival rates and chemoradiotherapy or no treatment lead to the worst clinical outcome. The presence of tumor necrosis may be associated with poor outcome, while typical indicators of biologic aggression such as ▶nuclear atypia, capsule penetration, and number of ▶mitosis are found to be unrelated to clinical outcome. The unpredictable natural course and prognosis of HEH makes it difficult to give a correlation between the morphological grading or clinical staging and outcome.

References 1. Mehrabi A, Kashfi A, Fonouni H et al. (2006) Primary malignant hepatic epithelioid hemangioendothelioma: a comprehensive review of the literature with emphasis on the surgical therapy. Cancer 107(9):2108–2121 2. Ishak KG, Sesterhenn IA, Goodman ZD et al. (1984) Epithelioid hemangioendothelioma of the liver: a clinicopathologic and follow-up study of 32 cases. Hum Pathol 15:839–852 3. Makhlouf HR, Ishak KG, Goodman ZD (1999) Epithelioid hemangioendothelioma of the liver: a clinicopathologic study of 137 cases. Cancer 85:562–582 4. Lauffer JM, Zimmermann A, Krahenbuhl L et al. (1996) Epithelioid hemangioendothelioma of the liver. A rare hepatic tumor. Cancer 78:2318–2327

Hepatic Ethanol Metabolism I AIN H. M C K ILLOP, L AURA W. S CHRUM Department of Biology, The University of North Carolina at Charlotte, Charlotte, NC, USA

Definition

The majority of ▶ethanol metabolism occurs in the ▶liver following the ingestion of alcoholic beverages.

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The enzymatic reactions involved in ethanol metabolism can in turn lead to a variety of deleterious effects on cells both within the liver and at the systemic level which has led to chronic ethanol consumption being identified as a major risk factor in the development of ▶liver cancer and a significant risk factor for the development of non-hepatic tumors.

Characteristics

The liver demonstrates a “dual circulation” vasculature in which oxygenated blood is delivered via the hepatic artery and deoxygenated blood, containing substances that have been absorbed from the gastro-intestinal tract, via the hepatic portal vein. Following ingestion ethanol is rapidly absorbed and enters the hepatic portal vein where it is delivered to the functional subunits of the liver termed the hepatic lobules. As blood flows through the hepatic vasculature (sinusoids) specialized epithelial cells, termed ▶hepatocytes, that line the vasculature process materials absorbed in the GI tract to maintain normal physiological homeostasis. In addition to performing essential physiological functions such as protein, lipid and carbohydrate metabolism, bile production and regulation of vitamin A storage the liver also plays a central role in drug and hormone metabolism. Following ethanol consumption metabolism occurs in the hepatocyte via three main enzymatic pathways; ▶alcohol dehydrogenase (ADH), ▶cytochrome p450 2 E1 (CYP2E1) and catalase. The metabolism of ethanol is a two step process, the first involves the conversion of ethanol to ▶acetaldehyde (via ADH, CYP2E1 or catalase) and the second requires the

conversion of acetaldehyde to acetate by the ▶aldehyde dehydrogenase (ALDH) enzyme (Fig. 1). In both instances, these reactions lead to the production of the reduced form of nicotinamide dinucleotide (▶NADH). These metabolic pathways for ethanol directly contribute to many of the deleterious effects of ethanol intake on normal hepatic and systemic physiology. While the metabolism of acetaldehyde by ALDH is an efficient metabolic pathway, acetaldehyde is a highly reactive species that, if allowed to accumulate, can cause significant protein damage and formation of ▶adducts to DNA and ▶DNA damage. In addition to the damaging effects of acetaldehyde/NADH, once formed, must be recycled to the oxidized NAD+ form by the electron transport chain in the mitochondria of hepatocytes. This process requires increased oxygen demand and can in turn lead to the production of reactive oxygen species (▶ROS) and increase cellular ▶oxidative stress that can cause ▶oxidative DNA damage and protein/lipid peroxidation. In the instance of moderate ethanol consumption the ADH–ALDH system is sufficient to metabolize ethanol. However, following chronic, excessive ethanol intake the CYP2E1 enzyme becomes induced leading to increased acetaldehyde/NADH production and further elevating ROS synthesis and hepatic oxidative stress (Fig. 1). Although ethanol metabolism is localized primarily in the hepatocytes, the nonparenchymal cells of the liver including ▶hepatic stellate cells (HSCs) and ▶Kupffer cells (KCs) have also been shown to express ethanol metabolizing genes. Human HSCs express both ADH and ALDH, and CYP2E1 expression has been observed

Hepatic Ethanol Metabolism. Figure 1 Hepatic ethanol metabolism as it pertains to potential mechanisms of liver damage. Ethanol is metabolized by a two-step process to acetaldehyde that, in turn, is metabolized by acetaldehyde dehydrogenase (ALDH) to acetate.

Hepatic Ethanol Metabolism

in both HSCs and KCs, therefore further contributing to the detrimental effects of ethanol metabolism in the liver. Depending on the level and period of ethanol consumption normal hepatic function becomes increasingly compromised with complications ranging from moderate steatosis (fatty liver) to acute alcoholic hepatitis and eventually the development of fibrosis and cirrhosis. In addition, epidemiological data indicates that chronic ethanol consumption acts synergistically to accelerate the progression of ▶HCC in patients exposed to other common risk factors including exposure to ▶aflatoxins and ▶hepatitis virus associated HCC. The damage caused to the liver through acetaldehyde adduct formation and/or ROS generation/oxidative stress is thought to be a major risk factor for ethanol related liver cancer development. Greater than 80% of all primary tumors diagnosed in the liver arise as a result of hepatocyte cell transformation (▶hepatocellular carcinoma; HCC). Unlike other common malignancies HCC occurs most commonly in the absence of familial patterns and largely within the realms of known risk factors. Chronic ethanol consumption, metabolism and the cellular and genetic damage associated with these events thus represent a significant risk factor for hepatic damage, cell transformation and the development of HCC. In addition to the direct effects of ethanol metabolism on the hepatocyte integrity, such as impaired microtubule polymerization, several other direct and indirect factors can combine to augment the effects of ethanol consumption in the liver and the body as a whole. Glutathione (▶GSH) is an antioxidant important in reducing the oxidative stress caused by the synthesis and release of ROS. In the mitochondria, GSH is the only source of hydrogen peroxide metabolism and becomes significantly depleted following chronic ethanol ingestion due, at least in part, to decreased GSH transport into the mitochondria. While these detrimental effects on hepatocyte function directly increase the probability of cell transformation, increasing evidence suggests that the sequential nature of tumor formation and/or other systemic effects may play an increasing role in the effects of ethanol during the development and progression of HCC. Ethanol abuse accounts for the majority of liver fibrosis and cirrhosis cases in the western world; however, even though the clinical progression is well-described, the ▶molecular pathology is less well understood. Current models propose that alcoholic liver disease is initiated by an inflammatory response due to the activation of KCs as well as the infiltration of leukocytes including macrophages, neutrophils and lymphocytes. The activation of these inflammatory cells has been shown to be due to elevated gut-derived endotoxin plasma levels. Ethanol alters gut permeability to macromolecules, decreases gut motility and increases growth of Gram-negative bacteria in the intestinal microflora which ultimately leads to the introduction of endotoxin

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into the portal microcirculation. The activation and recruitment of inflammatory cells lead to the production of several profibrogenic cytokines. These cytokines likely induce and perpetuate the activation of HSCs leading to increased deposition of extracellular matrix (ECM) like type I collagen. The HSCs themselves can also exacerbate the inflammatory response through the secretion of chemoattractants and adhesion molecules necessary for leukocyte adhesion and infiltration. The presence and activation of KCs, other infiltrating inflammatory cells and damaged hepatocytes, lead to increased ROS resulting in the activation of quiescent HSCs. The quiescent HSCs reside in the perisinusoidal space of Disse, and one of their primary functions in the healthy liver is the storage and homeostasis of vitamin A, namely retinol, retinal and retinoic acid. Upon a fibrogenic stimulus, including ethanol, the HSC transdifferentiates from a quiescent, vitamin A storing cell to that of an activated myofibroblast-like cell which proliferates, migrates to the site of injury and is responsible for the excessive accumulation of ECM. This continued deposition of ECM leads to scarring of the liver and ultimately liver dysfunction. Reduced levels of serum and hepatic vitamin A have been reported in persons with alcoholic liver disease (▶ALD). Ethanol exposure to HSCs inhibits retinoic acid production and intracellular retinol levels. Possible mechanisms which interfere with retinoid metabolism in the cell may include reduced vitamin A uptake and enhanced degradation of vitamin A. In addition to oxidative damage incurred directly by the hepatocyte, liver damage also affects cell membrane integrity due to ethanol metabolism via a nonoxidative pathway leading to the generation of fatty acid ethyl esters (FAEE). Fatty acid ethyl esters accumulate in the cell plasma membrane as well as in the mitochondrial membrane leading to organelle dysfunction. Accumulation of FAEE, particularly linolenic acid ethyl ester (LAEE) has been reported to activate signaling pathways important in regulating collagen expression which may further contribute to ethanol-induced fibrosis and subsequently HCC progression. In addition to the effects of ethanol and ethanol metabolism on hepatocytes and other cell populations other factors must also be considered as to how ethanol can affect tumorigenesis. For example, the high incidence of cigarette smoking in ethanol dependent patients, regional differences in dietary intake, the type of beverage consumed and the socio-economic status and relative balance of diet in ethanol dependent patients can all affect the incidence and rate of hepatic tumor development and progression. Similarly, the induction of CYP2E1 (following chronic ethanol intake) has also been demonstrated to play a significant role in pro-carcinogen and ▶carcinogen metabolism, many of which are present in cigarette smoke and alcoholic beverages.

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Since oxidative stress has been linked to the development of ALD, the use of antioxidants as possible therapeutic strategies has been explored. The addition of antioxidants such as vitamin E, superoxide dismutase, GSH precursors such as S-adenosyl-L-methionine (SAMe) and the green tea extract, (–)-epigallocatechin3-gallate (EGCG), have been shown to prevent or ameliorate ethanol-induced liver injury in a variety of animal models of ALD and HCC. However, the use of antioxidants should be approached with caution due to the possible toxic properties of antioxidants under certain conditions. Similarly, the use of “over the counter” antioxidants raises the possibility of drug–drug interactions and altered endogenous and exogenous agent metabolism caused by antioxidant intake, many of which are currently poorly studied and reported.

References 1. McKillop IH, Moran DM, Jin X et al. (2006) Molecular pathogenesis of hepatocellular carcinoma. J Surg Res 136:125–135 2. McKillop IH, Schrum LW (2005) Alcohol and liver cancer. Alcohol 35:195–203

Hepatic (Liver) Fixed Macrophages ▶Kupffer Cells

Hepatic Stellate Cell Definition HSC; Pericytes located in the perisinusoidal space of the liver responsible for vitamin A storage. In the damaged liver activation of HSCs leads to depleted Vitamin A storage and synthesis of extracellular matrix proteins (scarring). ▶Hepatic Ethanol Metabolism

Hepatitis Definition

Hepatic Excretion Definition Is the excretion of a drug by the liver by way of the gall bladder emptying into the intestine and ultimately into the feces. ▶ADMET Screen

Is liver inflammation and necrosis of varying severity and etiologies, such as toxic (drugs, alcohol), metabolic, autoimmune or viral. ▶Hepatitis C Virus ▶Hepatic Ethanol Metabolism

Hepatitis B Virus Definition

Is a basic leucine zipper protein defined by a PAR domain that plays a critical role in hematopoietic specific expression of the LMO2 gene. A role for HLF in HSC self-renewal is supported by studies showing that ectopic expression of HLF enhanced HSC engraftment and inhibited apotosis.

HBV; is a member of the Hepadnaviridae family (hepatotropic DNA viruses). The HBV genome is a partially relaxed double-stranded circular DNA of 3,200 base pairs, and encodes four partly overlapping open reading frames (ORFs). Thirty to fifty percent of persons who acquire the infection before the age of 5 years develop chronic HBV infection. HBV is a high-risk factor for ▶hepatocellular carcinoma. ▶Hepatocellular Carcinoma – Clinical Oncology; Hepatocellular carcinoma – etiology, risk factors and prevention; ▶liver cancer – molecular biology.

▶NUP98-HOXA9 Fusion ▶E2A-PBX1

▶Hepatocellular Carcinoma ▶Hepatitis Virus Associated Heptocellular Carcinoma

Hepatic Leukemia Factor (HLF) Definition

Hepatitis B Virus x Antigen Associated Hepatocellular Carcinoma

Hepatitis B Virus x Antigen Associated Hepatocellular Carcinoma M ARK A. F EITELSON Department of Biology, Temple University, Philadelphia, PA

Synonyms Liver cancer; Hepatocellular carcinoma; HCC

Definition The term hepatitis B x antigen, or HBxAg, refers to the gene product of hepatitis B virus (HBV) that contributes importantly to virus replication, the pathogenesis of chronic liver disease, and to the development of HCC.

Characteristics There are an estimated 350 million people worldwide who are chronically infected with HBV and often replicate virus for many years or decades. These people are at high risk for the development of chronic hepatitis, which may progress onto cirrhosis (end stage liver disease) and then HCC. Although the pathogenesis of infection is immune mediated, this is characterized most often by responses that trigger hepatocellular damage and destruction but do not clear virus. An important characteristic of ▶chronic liver disease (CLD) is that ▶liver cell regeneration provides opportunities for integration of virus DNA into the replication forks of cellular DNA. It turns out that the region encoding HBxAg is the most frequently integrated region of HBV DNA into the host genome. This region often encodes HBxAg, which is a ▶transactivating protein that alters the expression of cellular genes in many chromosomes throughout the host genome. This is quite an accomplishment for a small protein of only 17 kDa, and is achieved by constitutively activating a number of signal transduction pathways in the cytoplasm (such as JAK/STAT [▶signal transducers and activators of transcription in oncogenesis], ▶NF-κB, ▶AP-1, AP-2, ▶ras, src, PI3K/Akt [▶PI3K signaling; ▶Akt signal transduction pathways in oncogenesis] and β-catenin [▶Wnt signaling], among others) and by binding to transcription factors in the nucleus (such as Oct-1, CREB, ATF-2, b-zip, TBP, and other basal transcription factors) or sequestering them in the cytoplasm (e.g., p53). HBxAg also alters gene expression at the post-transcriptional level by blocking the activity of the ▶proteasome, which normally degrades proteins, and by altering the integrity of translation. Some of these pathways have been shown to be operative in the mechanism(s) whereby HBxAg

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promotes cell growth in culture dishes and anchorage independent growth in soft agar (a property often associated with cancer cells). The findings that HBxAg is capable of conferring tumorigenicity upon nonmalignant liver cells, and that the sustained over-expression of HBxAg in transgenic mice gives rise to HCC, further underscores the centrality of HBxAg expression to the development of HCC. It is likely that inadequate immune responses permit the persistence of infected hepatocytes during chronic infection. However, there is increasing evidence that HBxAg inhibits a number of ▶apoptotic pathways (▶apoptosis signaling) (e.g., Fas and tumor necrosis factor alpha (TNFα), both of which trigger programmed cell death) during chronic infection, thereby promoting the persistence of infected cells during CLD. HBxAg is also promotes ▶fibrogenesis, in that it promotes the expression of extracellular matrix proteins such as ▶fibronectin, promotes the cross-linking of collagen, and potentiates ▶TGFβ1 signaling, in part, by inhibiting expression of the TGFβ1 binding partner, α-2macroglobulin. In this context, it is not surprising to find a strong direct correlation between intrahepatic HBxAg expression and CLD. This relationship would protect virus infected cells from immune destruction, but these same features also promote carcinogenesis, since tumor cells are also resistant to apoptosis and demonstrate constitutively active signaling pathways that had been previously altered in preneoplastic tissue by HBxAg. There are few natural effectors of HBxAg that are known to be responsible for these profound biological changes that ultimately result in cancer. HBxAg appears to stimulate ▶insulin-like growth factor 2 (IGF2), which promotes hepatocellular growth, activates wild type β-catenin (and its effector, c-myc), trans-activates several unique “oncogenes,” and promotes ▶angiogenesis. HBxAg also binds to and inactivates the ▶tumor suppressors, ▶p53 and ▶PTEN, down-regulates expression of the natural cell cycle inhibitor, ▶p21WAF1/SDI1/CIP1, and promotes phosphorylation (inactivation) of the Rb tumor suppressor protein (▶retinoblastoma protein), suggesting the molecular basis upon which HBxAg stimulates unchecked cell growth. HBxAg also binds to and inactivates a novel ▶senescence factor, p55sen, suggesting that HBxAg contributes to carcinogenesis, in part, by overcoming cellular senescence. The observation that HBxAg also down-regulates ▶E-cadherin expression, the latter of which is involved in cell adhesion, provides at least part of the explanation as to how HBxAg stimulates cell motility (metastasis) in carcinogenesis. ▶Oxidative stress is a common feature of CLD, resulting in the activation of HBxAg in CLD and HCC. Over-expression of HBV envelope associated polypeptides, cytokine signaling, and cell mediated immunity against HBV infected cells, all promote the development

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of oxidative stress. This was associated with decreased intrahepatic levels of superoxide dismutase (Cu/Zn), which normally protects cells from ▶reactive oxygen species. These conditions stimulate HBxAg, which compromises transcription coupled DNA repair and ▶nucleotide excision repair, resulting in increased chromosomal alterations (genetic instability) and micronuclei formation (where metaphase plates separate prior to complete DNA replication). In addition, HBxAg is associated with the outer mitochondrial membrane, where it binds to the voltage dependent anion channel (VDAC3), resulting in decreased mitochrondrial membrane potential and the further development of oxidative stress. In this way, oxidative stress augments HBxAg function in propagating chronic infection and in stepwise hepatocarcinogenesis.

References 1. Breuhahn K, Longerich T, Schirmacher P (2006) Dysregulation of growth factor signaling in human hepatocellular carcinoma. Oncogene 25:3787–3800 2. Arbuthnot P, Capovilla A, Kew M (2000) Putative role of hepatitis B virus X protein in hepatocarcinogenesis: effects on apoptosis, DNA repair, mitogen-activated protein kinase and JAK/STAT pathways. J Gastroenterol Hepatol 15:357–368 3. Waris G, Siddiqui A (2003) Regulatory mechanisms of viral hepatitis B and C. J Biosci 28:311–321 4. Jin YM, Yun C, Park C et al. (2001) Expression of hepatitis B virus X protein is closely correlated with the high periportal inflammatory activity of liver diseases. J Viral Hepatitis 8:322–330 5. Feitelson MA (2004) Molecular and genetic determinants of primary liver malignancy. In: Khatri VP, Schneider PD (eds) Surgical clinics of North America. Liver surgery: Modern concepts and techniques, vol. 84. WB Saunders, Philadelphia, pp. 339–354

Hepatitis C Virus WOLFGANG H. C ASELMANN Medizinische Klinik und Poliklinik I, Rheinische Friedrich-Wilhelms-Universität, Bonn, Germany

Synonyms HCV

Definition

▶Hepatitis C virus (HCV) belongs to the flaviviridae family (Hepaciviruses genus) and is a pathogenic human RNA virus, which causes chronic liver disease and

hepatocellular carcinoma (▶liver cancer, molecular biology) (HCC).

Characteristics

The size of this enveloped virus is 60 nm. Its nucleocapsid contains a single-stranded RNA genome of 9.6 kb genome (Fig. 1) of plus(+) strand polarity that carries a single open reading frame. At least six major genotypes (1–6) with up to three subtypes (a to c) exist, which differ not only in their nucleic acid sequence but also in their pathophysiological properties. All structural and non-structural viral proteins are processed from a polyprotein precursor of 3,010–3,033 amino acids in the cytoplasm or endoplasmic reticulum of the infected cell. Untranslated Regions The 5′- and 3′-untranslated regions (UTR) are highly conserved within the different genotypes. The 341–344 nucleotides 5′-UTR (Fig. 1) forms extensive stem-loop structures, which are important in translation initiation. It also harbors an internal ribosomal entry site. The 3′-UTR is composed of a poorly conserved variable region (28–42 nucleotides), a variable polypyrimidine stretch and conserved 98 nucleotides at the 3′ end (x region). Both UTRs seem to be crucial for regulation of HCV translation and possibly also for controlling HCV replication, and are therefore candidate targets for experimental antiviral strategies. Structural Proteins The core protein C (21 kD) polymerizes to an icosaedric capsid and binds RNA to form the nucleocapsid. The envelope proteins E1 (31 kD) and E2 (70 kD) form heterodimers whose formation is mediated by the chaperon calnexin. These dimers are embedded in a host-derived lipid bilayer. Within the E2 sequence there are two hot spots of mutations (hypervariable regions, HVR1 and HVR2). Mutations occurring during HCV infections are due to a selection driven by the host immune system and account for the regular existence of a variety of ▶quasispecies. The E2 protein is produced as two precursors, E2/NS2 and E2/p7 that differ in their C-terminus. The hydrophobic p7 is probably important for membrane anchoring of E2. The function of p7 or E2/p7 during the HCV life cycle is not known. All structural protein processing is performed by cellular signal peptidases. Non-structural Proteins The non-structural protein NS2 (23 kD) is released from the polyprotein precursor both by host signal peptidases at the C-terminus of p7 and by a NS2/3 proteinase at the NS2-NS3 junction. NS3 (68 kD) has

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Hepatitis C Virus. Figure 1 Genomic organization and designation of HCV RNA, and amino acid positions and function of HCV proteins.

three different functions: It is part of the NS2/3 proteinase, its N-terminal third contains a serine proteinase and at the C-terminus a RNA-dependent NTPase/ helicase was discovered. Together with NS4A (6 kD) as a stable complexed cofactor, the N-terminal NS3 serine proteinase catalyses the cleavage between NS3NS4A, followed by cleavage between NS5A-NS5B, NS4A-NS4B and NS4B-NS5A. The NS3 helicase can unwind double-stranded (ds)RNA, dsDNA and RNA/ DNA heteroduplex molecules. For this purpose any NTP or dNTP is used as source of energy. NS4B is a 26 kD membrane associated protein of unknown function. NS5A (56–58 kD) represents two cytoplasmatic proteins, p56 and p58, which are both phosporylated at serine residues. This process may be essential for the viral replication cycle, but the biological functions of these proteins are not understood. There is some evidence that NS5A mediates interferon-alpha resistance of HCV. The NS5B (65 kD) protein is responsible for HCV RNA replication; it represents an RNA-dependent RNA-polymerase that is not found in humans and may therefore be another attractive target for antiviral strategies. The RNA minus(−) strand is transcribed in the host cytoplasm into a plus(+) strand RNA. This serves as a template to produce new minus(−) strands for packaging into the envelope. Both steps are accomplished by the NS5B protein.

Cellular and Molecular Regulation Although the HCV genome does not harbor acutely transforming oncogenes, the HCV core as well as the NS3 gene are candidate genes whose products may mediate malignant hepatocyte transformation. Oncogene complementation assays using HCV core and H-▶ras or c-▶myc oncogenes showed that HCV core cooperates with these oncogenes and transforms primary rat embryo fibroblasts to the tumorgenic phenotype. Focus formation, soft agar growth and tumor development was also shown in nude mice using Rat-1 fibroblasts. Also in this model a loss of contact inhibition, morphological changes and anchorage- and serumindependent growth occurred when HCV core and v-H-ras were cooperatively expressed. The most striking evidence of an oncogenic potential of HCV comes from an HCV core-transgenic mouse model, in which hepatic tumors arose in up to 30% of animals of two different strains. Interestingly, all tumors occurred in male animals. However, other mice transgenic for HCV core or C-terminally truncated (amino acid 384–715) HCV core failed to develop histological or biochemical signs of liver disease. The postulated underlying molecular mechanisms of HCV core-induced hepatocyte transformation are manifold. They comprise sequestration of LZIP in the cytoplasm leading to a loss of CRE-dependent

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transcription and regulation of cell proliferation and subsequently to morphological transformation of NIH 3T3 cells. Other mechanisms may be interference with ▶apoptosis or ▶transactivation of cellular c-fos, c-myc, p53 or β-interferon promoters. Stable expression of the 5′-portion of the NS3 gene was able to induce focus formation and soft agar growth in NIH 3T3 cells. Only recently it was demonstrated that internal cleavage of the NS3 protein occurs at cleavage sites FCH(1395)//S(1396)KK and IPT(1428)// S(1429) GD within the HCV RNA helicase domain in presence of NS4A. These findings were confirmed in two different isolates of HCV of genotype 1b. The 5′-portion of NS3 was more oncogenic than the fulllength NS3 protein. Clinical Relevance An estimated 2% of the world’s population is chronically infected with HCV. It accounts for 20% of acute and 70% of chronic hepatitis cases. HCV is mainly transmitted by blood. Since screening and treatment of blood products for HCV has been routinely performed, post-transfusion hepatitis has become extremely rare. Intravenous drug addiction is today a major way of HCV transmission. Acute hepatitis is often clinically inapparent, and in chronic hepatitis symptoms occur mainly in later stages of disease. A high chronicity rate of up to 75% of acute infection and its silent course account for the pathogenic potential of this virus, which includes extrahepatic manifestations. Twenty percent of chronically infected patients develop ▶liver cirrhosis and 2–5% per year will progress to hepatocellular carcinoma (HCC). Therapy for HCV infection comprises the combined use of 3–6 MU of α-interferon administered subcutaneously three times a week and 800–1200 mg of the nucleoside analog ▶ribavirin p.o daily for 6–12 months dependent on the genotype and viral load. Roughly 40–45% of previously untreated or relapse patients benefit from the treatment, i.e. eliminate HCV and normalize liver enzymes. In addition, this treatment is capable of improving histological signs of liver damage. Its effect on HCC prevention can not clearly be judged at present. Recent therapeutic innovations comprise ▶pegylated interferons that allow single weekly dosing due to slow effector release from subcutaneous depots and a decrease of systemic side effects. Sustained response rates up to 70 % can be reached. A synthetic consensus interferon-alpha showed promising effects in monotherapeutic use in a preliminary trial and is presently being evaluated in combination with ribavirin. Major future achievements are expected from the development of inhibitors of HCV protease, helicase or RNA-dependent RNA polymerase, which may improve effectivity of antiviral treatment similarly to

the situation in HIV infection, but are not yet available for clinical use. Therapeutic nucleic acids such as antisense oligodeoxynucleotides, RNAs or ribozymes may be another experimental concept for the treatment of HCV infection in the future.

References 1. Moriya K, Fujie H, Fukuda K et al. (1998) The core protein of hepatitis C virus induces hepatocellular carcinoma in transgenic mice. Nat Med 4:1065–1067 2. Wedemeyer H, Caselmann WH, Manns MP (1998) Combination therapy of chronic hepatitis C – an important step but not the final goal. J Hepatol 29:1010–1014

Hepatoblastoma T ORSTEN P IETSCH 1 , D IETRICH 1

VON

S CHWEINITZ 2

Institut für Neuropathologie, Universitätskliniken Bonn, Bonn, Germany Kinderchirurgie 2 Universitäts-Kinderspital beider Basel (UKBB), Basel, Switzerland

Definition Heptoblastoma is a childhood malignant embryonal liver tumor consisting of immature epithelial cells with or without additional mesenchymal component.

Characteristics Hepatoblastomas are the most frequent malignant liver tumors of childhood. Their annual incidence is 0.5–1 cases per million children under 15 years of age in Western countries. The affected children are most frequently between 6 months and 3 years old. Hepatoblastoma has also been detected in utero by prenatal ultrasound examination. Since liver tumors lack early clinical symptoms, hepatoblastoma patients often present with locally extended tumors at diagnosis. However, distant metatases usually occur very late in the disease progression. The patients frequently have highly elevated ▶α-fetoprotein levels. In these cases this ▶oncofetal antigen can be useful as a sensitive diagnostic marker and also as a marker for the monitoring of treatment response. Pathological Classification Hepatoblastomas always consist of immature epithelial liver cells resembling fetal or embryonal liver cells. Approximately one third of the cases contain additional mesenchymal components and are then termed “mixed” hepatoblastomas. According to Weinberg and Finegold (1983) the epithelial component is further classified into

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Hepatoblastoma. Figure 1 Histopathology of an epithelial hepatoblastoma showing foci of hematopoietic cells.

well differentiated “fetal,” less differentiated “embryonal” and undifferentiated “small cell anaplastic” categories. The latter is rare, as are “macrotrabecular” or “teratoid” variants. Small cell anaplastic as well as macrotrabecular variants indicate a bad prognosis. A histopathological hallmark of hepatoblastomas, in particular of the fetal differentiated cases, is the occurrence of hematopoietic foci mainly consisting of erythropoietic or thrombopoietic progenitor cells mimicking fetal hematopoiesis in the liver (Fig. 1).

with prolonged preoperative chemotherapy (SIOP, USA) or with mega-therapy (Germany).

Staging In the last 30 years the treatment modalities and outcome of hepatoblastoma patients has significantly improved. It turned out that hepatoblastomas are responsive to chemotherapy. Today, most hepatoblastoma patients are enrolled in multicenter studies and receive a stage and risk adapted multimodal therapy. Different staging systems are used including the American and German fourgraded postoperative staging system, the Japanese TNM classification and the European SIOP PreTreatment Extent of Disease (PRETEXT) grouping system. The patients are stratified into standard and high risk patients, the latter often presenting with extended, multifocal or metastatic disease.

Predictive Factors Several histological, clinical as well as serological factors have been evaluated for their predictive value. In particular, the extension of the tumor in the liver, multifocality, vascular invasion and the presence of metastases have been of predictive importance in most studies. The decline of alpha-fetoprotein levels under chemotherapy predicts the clinical response. In contrast, the impact of distinct histological features such as mixed versus epithelial, or fetal versus embryonal differentiation and chromosome ▶ploidy of the tumors is still under discussion and the data is controversial. The etiology of hepatoblastomas is unknown. Environmental factors do not seem to play a major role in the pathogenesis of hepatoblastomas. Preterm infants may have an elevated risk for the development of hepatoblastomas. Although most hepatoblastomas occur sporadically, familial cases have been described. The incidence is highly elevated in families with ▶adenomatous polyposis coli (FAP [▶APC Gene in Familial Adenomatous Polyposis]) and ▶Beckwith-Wiedemann Syndrome.

Therapy and Outsome In current protocols most patients receive a ▶neoadjuvant chemotherapy with ▶cisplatin and ▶doxorubicin, in some studies combined with ifosphamid, 5-fluorouracil or carboplatin. The combination carboplatin and etoposide has also been effective. The overall survival after chemotherapy and resection is 70–80%. Unfortunately, approximately one quarter of the patients still die from the disease, so that predictive factors are important to early recognize these high risk patients and to offer them an intensified therapy. High risk patients have been treated

Genetic and Molecular Characteristics Cytogenetic analyses have revealed several recurrent numerical aberrations as well as structural alterations. Most frequently trisomies of chromosomes 1, 2, 8 and 20 have been described as well as a recurrent translocation t(1;4)(q12;q34) in 15% of hepatoblastomas. Approximately 50% of cases show gain of material of chromosome 2q. A few cases have an ▶amplification of material from chromosomal band 2q24, indicating the location of a hepatoblastoma related oncogene. ▶Microsatellite analyses have uncovered

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frequent allelic losses of chromosomal regions of chromosome arms 1p and 11p. The losses of chromosomal region 11p15.5 are always of maternal origin indicating the existence of one or more imprinted hepatoblastoma associated gene(s) expressed from the maternal ▶allele. Studies on the mutational status of the ▶TP53 gene resulted in conflicting data. Whereas TP53 mutations were described in a small Japanese tumor collection, these were absent in other studies. Similarly, somatic missense mutations were described in one study but not confirmed by others. The activation of the ▶WNT signaling pathway by activating mutations in the ▶β-catenin gene is a frequent event in hepatoblastomas. Approximately 50% of the hepatoblastomas save point mutations or deletions of exon 3 encoding the protein degradation targeting site of the β-catenin protein, resulting in a destruction of N-terminal phosphorylation sites that are necessary for protein degradation. This leads to the accumulation of a mutated protein, which transfers oncogenetic signals to the nucleus and increases transcription of specific target genes of the ▶TCF/LEF family of transcriptions factors such as ▶cyclin D1 and ▶c-myc. Similar mutations have been described in other tumor entities including colorectal cancer. However, hepatoblastoma represents the malignant tumor with the highest incidence for β-catenin mutations. Cellular Characteristics Hepatoblastoma cells resemble liver progenitor cells during embryonic and fetal development suggesting that hepatoblastomas are derived from such progenitors. Hepatoblastoma cells are still dependent on growth factors and use specific growth factor signaling systems. The important fetal mitogen, insulin-like growth factor-II, has been demonstrated to be highly over-expressed in hepatoblastomas. The encoding ▶IGF2 gene maps to chromosome 11p15.5, a region frequently altered in hepatoblastomas and related embryonal tumors. They also produce several hematopoietic ▶cytokines such as ▶interleukin-1, ▶stem cell factor, ▶erythropoietin and ▶thrombopoietin that induce hematopoietic foci in hepatoblastomas. Hepatoblastoma cells over-express the receptor ▶Met for hepatocyte growth factor (HGF; ▶scatter factor) and proliferate in response to HGF in vitro. Concentrations needed for this effect are usually found in the serum of patients after liver surgery. This may explain why hepatoblastomas often show rapid regrowth after partial resection. Therefore it is now common sense that the tumors should undergo primary resection, only when they can be removed without residual tumor cells.

References 1. Weinberg AG, Finegold MJ (1983) Primary hepatic tumors of childhood. Hum Pathol 14:512–537

2. Brown J, Perilongo G, Shafford E et al. (2000) Pretreatment prognostic factors for children with hepatoblastoma – results from the International Society of Paediatric Oncology (SIOP) study SIOPEL 1. Eur J Cancer 36: 1418–1425 3. Mann JR, Kasthuri N, Raafat F et al. (1990) Malignant hepatic tumours in children: incidence, clinical features and aetiology. Paediatr Perinat Epidemiol 4:276–289 4. Von Schweinitz D, Hecker H, Schmidt-von-Arndt G et al. (1997) Prognostic factors and staging systems in childhood hepatoblastoma. Int J Cancer 74:593–599 5. Von Schweinitz D, Byrd DJ, Hecker H et al. (1997) Efficiency and toxicity of ifosfamide, cisplatin and doxorubicin in the treatment of childhood hepatoblastoma. Study Committee of the Cooperative Paediatric Liver Tumour Study HB89 of the German Society for Paediatric Oncology and Haematology. Eur J Cancer 33:1243–1249

Hepatocellular Carcinoma T OSHIHIKO M IZUTA Department of Internal Medicine, Saga Medical School, Saga, Japan

Synonyms Liver cancer; Hepatoma; Hepatic carcinoma; Hepatitis B Virus x Antigen Associated Hepatocellular Carcinoma; Primary liver cancer; Primary hepatic carcinoma; Liver cell carcinoma

Definition Hepatocellular carcinoma (HCC) is a primary cancer that arises from hepatocytes, the major cell type of the liver. Most cases of HCC are secondary to either hepatitis virus (usually type B or C) infection or cirrhosis.

Characteristics Epidemiology HCC is the fifth most common cancer in men and the eighth most common cancer in women worldwide. An estimated more than half a million new cases are diagnosed annually, while there are major geographical differences in incidence. The annual incidence rates in Eastern Asia and sub-Saharan Africa exceed 15/10,000 inhabitants, while the figures are intermediate (between 5/10,000 and 15/10,000) in the Mediterranean Basin and Southern Europe, and very low (50% chance of surviving 3 years, even without treatment. In contrast, a patient with multiple tumors involving both lobes of the liver with decompensated cirrhosis is unlikely to survive more than 6 months, even with treatment. AFP levels have been shown to be prognostically important, with the median survival of AFP-negative patients significantly longer than that of AFP-positive patients. Other prognostic variables include performance status (measure of general wellbeing), liver functions, and the presence or absence of cirrhosis and its severity in relation to the ▶Child-Pugh classification. Prognostic Staging System A clinical staging system provides guidance for patient assessment and appropriate therapy. It is useful for the decision to treat certain patients aggressively while avoiding the overtreatment of other patients who would not tolerate therapy or whose life expectancy rules out any chance of success. Clinical staging is also an essential tool for comparison between groups in therapeutic trials and between different studies. The current classifications most commonly used for HCC are the ▶Okuda staging system, the ▶Child-Pugh staging system, tumor node metastasis (TNM) staging, and Cancer of the Liver Italian Program (CLIP) score (Table 1). Among these, the CLIP score is currently the most commonly used integrated staging score, for both tumor and liver disease stages. The Japan Integrated Staging (JIS) system, a new system that is based on a combination of the Child-Pugh system and the Liver Cancer Study Group of Japan (LCSGJ) system – the LCSGJ system is also concordant with TNM classification for HCC by the International Hepato-Pancreato-Biliary Association and the International Union Against Cancer (UICC) – has recently been proposed in Japan (Table 2). The stratification ability of the JIS scoring system is much better than that of the CLIP scoring system. The JIS scoring system also performed better than the CLIP scoring system in selecting the best prognostic patient group. Treatment There is no worldwide agreement on a common treatment strategy for patients with HCC, and several proposals have been published (Fig. 1).

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Hepatocellular Carcinoma. Table 1

Definitions of the CLIP score Score

Variables Child-Turcotte-Pugh stage Tumor morphology AFP (ng/ml) Portal vein thrombosis

0

1

2

A

B

C

Unilobular and extension ≤50% 50% − −

Hepatocellular Carcinoma. Table 2

Japan Integrated staging (JIS) scoring system Score

Variables

0

1

2

3

Child-Pugh grade TNM stage by LCSGJ

A I

B II

C III

IV

Definition of TNM stage by the Liver Cancer Study Group of Japan (LCSGJ)

T factor T1 T2 T3 T4 Stage I Stage II Stage III

I. Single

II. 20%, and chromosome arms 6q, 9p, 13q, 16p, and 17p LOH have been linked to inactivation of the tumorsuppressor insulin-like growth factor 2 receptor (IGF2R), p16, retinoblastoma (RB1), axin 1, and p53. The genetic changes involved in hepatocarcinogenesis can be divided into at least five pathways: the p53 pathway, which is involved in the response to DNA damage or genomic instability; the p16/p27/RB1 pathway, which is involved in cell-cycle control; the transforming growth factor-β (TGF-β) pathway, which is involved in growth inhibition and apoptosis of hepatocytes; the Wnt/β-catenin/APC pathway, which is involved in intercellular interactions; and the E-cadherin/ integrin and extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways, which are involved in cancer cell migration and metastasis.

Hepatocellular Carcinoma – Etiology, Risk Factors and Prevention

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H Hepatocellular Carcinoma – Etiology, Risk Factors and Prevention. Figure 1 Possible mechanisms of hepatocarcinogenesis. Cell-cycle regulators involved in hepatocarcinogenesis.

Among the different signaling pathways involved in hepatocarcinogenesis, deregulation of the cell-cycle machinery is thought to be closely involved in the progression of HCC. Cell-cycle progression in mammalian cells is mainly governed by cyclin A, cyclin D, and cyclin E, along with cyclin-dependent kinase 2 (CDK2) and CDK4. The kinase activities of these proteins are negatively regulated by the CDK inhibitors (CDKIs) p16 and p27. RB1, which is phosphorylated by CDKs and activates the E2F family of transcription factors, is mutated in 15% of HCCs. The cyclin D1 gene, which is involved in the G1 progression and G1/S transition phases of the cell cycle, has been shown to be amplified in 10–20% of HCCs. By contrast, both p16 and p27 are frequently inactivated in HCCs. P16 is inactivated in 50% of HCCs, mainly due to the de novo methylation of the DNA-promoter region. Somatic mutation of the p16 gene has also been described in some cases of HCC. Recently, p16 DNA methylation was identified in preneoplastic liver tissues of individuals with chronic hepatitis virus infections. P27 is a member of the KIP family of CDKIs, and its expression is reduced in 40– 60% of HCCs. Decreased p27 expression is closely associated with poor prognoses of individuals with HCCs, indicating that it is an adverse prognostic factor. In some cases of HCC, increased cell proliferation has been noted despite relatively high levels of p27 expression, suggesting the inactivation of p27 by sequestration into cyclin D1–CDK4-containing complexes. Although many genes appear to be altered in HCC, the frequencies of individual mutations are low, and the patterns of genetic alteration differ among patients. Connections between different pathways might thus be plausible mechanisms underlying hepatocarcinogenesis.

Diagnosis Serum alpha-fetoprotein (AFP) and des-γ-carboxy prothrombin, which is also known as protein induced by vitamin K antagonist (PIVKA II), are useful serological markers of HCC. Although AFP exists in normal human tissues (both fetal and adult), serum levels are sensitive to the presence of HCC. The overall diagnostic accuracy of AFP is 80%. By contrast, PIVKA II is only present in HCC tissues, so its specificity is relatively high, and its overall diagnostic accuracy is 55%. The simultaneous measurement of AFP and PIVKA II could therefore be useful for the detection of HCC. However, as elevated AFP levels can be the result of liver cirrhosis, it is important to determine whether they are caused by active liver cirrhosis or by HCC that has arisen from liver cirrhosis. The elevation of serum AFP reflected as regeneration of hepatocytes. The levels of carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) are also often elevated in the serum of patients with HCC. However, the specificities of these markers are lower than those of AFP and PIVKAII. Total imaging is important for detecting small HCCs. The majority of HCCs arise from chronic hepatitis and liver cirrhosis; periodical checking using ultrasound scanning and computed tomography (CT) is therefore crucial to detect the early stages of HCCs. Recent advances in the use of imaging tools, such as CT scanning with contrast medium and magnetic resonance imaging (MRI), have enabled the precise detection of HCCs. Accuracy levels have reached >90% using enhanced CT and MRI techniques, and the current limit of detection for HCCs is 10 mm diameter.

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HCCS can develop from small nodules into large nodules when given access to an arterial blood supply rather than a portal blood supply. Small HCCs with poor arterial blood supplies are difficult to distinguish from adenomatous hyperplasia, large regenerative nodules, or angiomyolipoma. Direct tumor biopsy guided by ultrasound with a fine needle is therefore useful for making a final diagnosis in such cases. Treatment There are several treatment modalities for HCC. Surgical treatment is divided into two categories: hepatic resection and liver transplantation. The former is based upon the hepatic functional reserve, tumor location, and tumor numbers, and includes many procedures ranging from partial resection to extended right or left hepatic lobectomy. The latter is based on the tumor size and tumor numbers alone. The Milan criteria (that is, the presence of one nodule 10% during the previous six months, documented fever, and night sweats. There is a slight male

Hodgkin and Reed/Sternberg Cell

predominance and a bimodal age distribution in Western populations, with peaks of incidence in young adulthood and old age. Among economically disadvantaged populations, the first peak of incidence occurs earlier in childhood, particularly for males. There is a relatively low incidence of Hodgkin disease among Asian populations. Hodgkin disease usually starts at a single site and progresses in an orderly manner through the lymphatic system to local lymph nodes before disseminating hematogenously to distant sites, particularly the bone marrow, spleen, or liver. Hodgkin disease is typically staged from I to IV. Stage I represents involvement of a single lymph node structure, stage II is involvement of two or more lymph node regions on the same side of the diaphragm, stage III is involvement of lymph node regions or structures on both sides of the diaphragm, and stage IV is involvement of extranodal sites. Prognosis is directly related to stage. Hodgkin disease is typically treated by multidrug chemotherapy and/or radiotherapy, with an overall 5-year survival of greater than 80%. Patients who relapse usually do so within the first three years after treatment, and have a significantly worse prognosis. High-dose chemotherapy with ▶autologous bone marrow transplantation or peripheral blood stem-cell transplantation has become a standard therapy for patients who fail conventional chemotherapy regimens. Novel immunotherapies have been proposed, including treatment with interleukin-2, bi-specific antibodies, immunotoxins, and radioimmunoconjugates. Patients with the nodular lymphocyte predominance subtype may behave differently than the classical forms of Hodgkin disease, with a better overall survival, but a greater number of recurrences, which are independent of time after treatment.

References 1. Hansmann M-L, Kuppers R (2005) The Hodgkin and Reed/Sternberg cell. Int J Biochem Cell Biol 37:511–517 2. Hoppe RT, Advani RH, Bierman PJ et al. (2006) National Comprehensive Cancer Network. Hodgkin disease/lymphoma. Clinical practice guidlelines in oncology. J Natl Compr Canc Netw 4:210–230 3. Hoppe RT, Mauch PM, Armitage JO et al. (2007) Hodgkin Disease Lippincott Williams & Wilkins, Baltimore

Hodgkin Lymphoma Definition

▶Hodgkin disease ▶Hodgkin Disease, Clinical Oncology

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Hodgkin and Non-Hodgkin Lymphomas ▶B-cell Tumors

Hodgkin and Reed/Sternberg Cell R ALF K U¨ PPERS Institute for Cell Biology (Tumor Research), University of Duisburg-Essen, Medical School, Essen, Germany

Definition Hodgkin and Reed/Sternberg (HRS) cells are large cells with a peculiar morphology and immunophenotype that does not resemble any other normal cell in the body. The cells are called Hodgkin cells when they are mononucleated and Reed/Sternberg cells when they are multinucleated. HRS cells in nearly all instances derive from B lymphocytes, but in rare cases they originate from T cells. HRS cells are the hallmark cells of Hodgkin lymphoma, in which they represent the tumor cell clone.

Characteristics Associated Pathologies The first cases of Hodgkin lymphoma (HL) were described by Thomas Hodgkin in 1832. A peculiar type of cells that is a hallmark of HL was first characterized in detail about 100 years ago by Dorothy Reed and Carl Sternberg. These cells are called Hodgkin cells when they are mononucleated and Reed/Sternberg cells when they are bi- or multinucleated. HRS cells are large cells ten times or more of the size of small lymphocytes with prominent nucleoli. Reed/Sternberg cells most likely derive from Hodgkin cells by endomitosis, i.e., nuclear division without cell division. In HL, the HRS cells usually represent less than 1% of cells in the tumor tissue (Fig. 1). They are surrounded by a mixture of various types of cells, including T cells, B cells, plasma cells, macrophages, eosinophils, and others. In about 40% of cases of HL in the Western world, the HRS cells are latently infected by the ▶Epstein–Barr virus (EBV). HL is one of the most frequent malignant lymphomas in the Western world, with an incidence of about 2.5–3 new cases per 100,000 people per year. Nowadays, about 90% of the patients can be cured by chemo- and/or radiation therapy. Based on differences in the histological picture and the cellular

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morphology and to some extend the immunophenotype of HRS cells. As HRS cells have most extensively been analyzed in HL, the following discussion of HRS cells refers to HRS cells in HL.

Hodgkin and Reed/Sternberg Cell. Figure 1 HRS cells in Hodgkin lymphoma tissue. CD30 immunostaining (red) of a HL lymph node tissue section with CD30-positive HRS cells. Nuclei of the cells are stained in blue with haemalaun.

composition of the lymphoma, HL is subdivided in four types of classical HL (nodular sclerosis, mixed cellularity, lymphocyte depletion, and lymphocyte-rich classical) and lymphocyte-predominant HL. This latter type represents about 5% of cases. In lymphocytepredominant HL, the tumor cells have a distinct morphology and immunophenotype and are normally not multinucleated. These cells are not called HRS cells but lymphocytic and histiocytic ▶(L&H) cells. It is very difficult to grow HRS cells in culture, and only a few cell lines could be established from HL biopsies. Nevertheless, these cell lines are valuable models for the functional analysis of HRS cells. The cell lines still available and considered as HRS cellderived include the B cell lineage lines L428, L1236, KMH2, L591 (the latter is the only EBV-positive line) and the T cell lineage HL lines HDLM2 and L540. Although HRS cells are the pathognomonic cells in HL, HRS or HRS-like cells are also occasionally observed in other lymphomas. These include some ▶diffuse large B cell lymphomas and ▶B cell chronic lymphocytic leukemia (B-CLL). In B-CLL, the HRSlike cells can either be clonally related to the B-CLL lymphoma clone, or they can represent an independent cell clone. HRS cells are also regularly found in an infectious disease, i.e., ▶infectious mononucleosis. This disease is caused by EBV and can occur if the primary infection of an individual by EBV does not occur in young children (when it is usually asymptomatic) but is delayed into adolescence or adulthood. In infectious mononucleosis many B cells are infected by EBV and can expand to large clones. Some of the EBV-infected B cells for unknown reasons acquire the

Cellular Origin As the HRS cells usually represent only a small fraction of the cells in the HL tissue and as they have an unusual immunophenotype that does not resemble any normal hematopoietic cell type (see later) the cellular origin of these cells was unclear for a long time. However, about 10 years ago, the molecular analysis of isolated HRS cells revealed that these cells derive from B lymphocytes in nearly all cases. HRS cells carry rearranged immunoglobulin (Ig) genes which is specific for B cells. These rearranged Ig genes carry with few exceptions a high load of somatic mutations. The acquisition of such mutations through the process of ▶somatic hypermutation takes place in antigenactivated B cells in the course of T cell-dependent immune responses in specific histological structures of lymph nodes and other lymphoid organs – the ▶germinal centres. Therefore, it is very likely that HRS cells derive from such mature germinal centre B cells. Curiously, HRS cells frequently carry destructive somatic mutations that prevent expression of a functional B cell antigen receptor. As normal germinal centre B cells acquiring such mutations undergo ▶apoptosis, HRS cells may represent transformed preapoptotic germinal centre B cells. The detection of rearranged T cell receptor genes in a few cases of HL indicates that in rare instances (less than 2% of cases), HRS cells may also derive from T cells. Immunophenotype HRS cells show an unusual immunophenotype with coexpression of markers of distinct hematopoietic cell lineages. B cell antigens (e.g., CD19, CD20) or T cell antigens (e.g., CD3, CD4) are detectable on variable proportions of HRS cells in about 10–20% of cases. Several markers of dendritic cells are regularly expressed (e.g., thymus and activation regulated chemokine (TARC), fascin, and restin), but also markers of myeloid cells are found (CD15). As HRS cells are in nearly all cases derived from B cells, it is evident that many of these markers are aberrantly expressed by HRS cells. It also became clear that HRS cells lost expression of most typical B cell markers. For the diagnosis of HL, it is important that HRS cells in all cases of classical HL express CD30, an activation marker and member of the tumor necrosis factor receptor family. Cell Differentiation and Function HRS cells can be considered as hyperactivated cells, as a multitude of signaling pathways is chronically

Hoechst-33342 Dye

activated in these cells. HRS cells show constitutive activity of the transcription factor NFκB, which regulates the expression of many genes, including important antiapoptotic factors. Indeed, inhibition of NFκB in HRS cell lines induced apoptosis of the cells. Also the PI3 kinase/AKT signaling pathway and the activator protein 1 (AP-1) are active in HRS cells and contribute to cell survival and/or proliferation. Remarkable is Notch-1 activity in HRS cells, as this transcription factor is normally active only in T cells and suppresses expression of B cell-specific genes. Thus, the deregulated activity of Notch-1 in HRS cells may contribute to the downregulation of B cell genes, as discussed earlier. In HL tissues, many cytokines are produced by HRS cells and surrounding cells. On this basis, it is perhaps not surprising that HRS cells have an active Jak/STAT pathway, as many cytokines signal through this pathway. There appears to be even an autocrine interleukin stimulation in HRS cells, as they express interleukin 13 and the interleukin 13 receptor. Three of the STAT transcription factors have been identified as constitutively active in HRS cells, STAT3, 5 and 6. Another important family of signaling molecules is receptor tyrosine kinases. In several cancers, specific members of this family show deregulated activity that contributes to pathogenesis. In HL, multiple receptor tyrosine kinases are expressed and active, which is in its extent unique among human tumors. Transforming Mechanisms of HRS Cells As mentioned earlier, in about 40% of cases of HL in the Western world, HRS cells are infected by EBV. In some instances (e.g., in childhood cases in Central America) the association can be even up to 90%. In EBV-positive cases, three latent viral proteins are expressed, the EBV nuclear antigen EBNA1, and the latent membrane proteins LMP1 and LMP2A. EBNA1 is essential for the replication of the viral genome in proliferating cells. Interestingly, LMP1 and LMP2A functionally mimic two main survival signals for germinal centre B cells, i.e., CD40 signaling and B cell receptor signaling. In this way, EBV can rescue the HRS cell precursors from apoptosis and contributes to the malignant transformation. HRS cells usually show multiple numerical and structural chromosomal abnormalities. Some of these are shared by all HRS cells, while others are found only in fractions of cells of a tumor clone, indicating a significant genomic instability. Due to the multitude of genomic aberrations, it has been difficult to identify events causally involved in the transformation of HRS cells. However, some genomic imbalances occur recurrent and are therefore candidates for pathogenetic events. These include, for example, amplification of the genomic region including the c-Rel gene, a member

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of the NFκB family. HRS cells frequently also harbor translocations involving the immunoglobulin loci, but the partner genes involved in these translocations have not yet been identified. Isolated HRS cells were also analyzed for mutations in proto-oncogenes and tumor suppressor genes. Mutations in the tumor suppressor genes p53 and CD95 were found in less than 10% of cases investigated. Inactivating mutations in a main inhibitor of the NFκB transcription factor, IκBα, are present in about 20% of cases. Rare cases may also carry mutations in IκBε, another inhibitor of NFκB. Mutations in these NFκB inhibitors contribute to the constitutive activity of this factor, which has an important role as an antiapoptotic factor in HRS cells (see earlier). Mutations were recently also found in the SOCS1 gene, which is an inhibitor of STAT transcription factors. Thus, these mutations likely contribute to the constitutive activity of STATs in HRS cells. In summary, the transforming events involved in the generation of the malignant HRS cells in classical HL have only partly been revealed, and it appears so far that multiple different combinations of genetic aberrations can cause the pathogenesis of HL.

References 1. Pileri SA, Ascani S, Leoncini L et al. (2001) Hodgkin’s lymphoma: the pathologist’s viewpoint. J Clin Pathol 55:162–176 2. Re D, Thomas RK, Behringer K et al. (2005) From Hodgkin disease to Hodgkin lymphoma: biologic insights and therapeutic potential. Blood 105:4553–4560 3. Küppers R, Re D (2007) Nature of Reed-Sternberg and L&H cells, and their molecular biology in Hodgkin lymphoma. In: Hoppe RT, Armitage JO, Diehl V, Mauch PM, Weiss LM (eds) Hodgkin lymphoma. Lippincott Williams & Wilkins, Philadelphia 4. Küppers R (2002) Molecular biology of Hodgkin's lymphoma. Adv Cancer Res 84:277–312

Hoechst-33342 Dye Definition Is a UV-excitable nucleic acid stain that is readily taken up by all cells, except those cells that express the transporterABCG2. Hoechst-dim cells can be detected by flow cytometry or by fluorescence microscopy. ▶Stem Cell Markers ▶FISH

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Hollow Fiber Assay

Hollow Fiber Assay I RENE V. B IJNSDORP, G ODEFRIDUS J. P ETERS Department of Medical Oncology, VU University Medical Center, Amsterdam, The Netherlands

Definition The hollow fiber assay (▶HFA) is a fast in vivo assay to determine the cytotoxic effect of drugs, as well as their pharmacodynamic (▶Pharmacodynamics) effects on human tumor cell lines grown in hollow fibers that are implanted subcutaneously or intraperitoneally in mice or rats.

Characteristics Various in vivo models exist to asses the efficacy of potential anticancer agents, including subcutaneously implanted ▶xenografts, ▶orthotopic models, and the HFA. The HFA has been optimized at the National Cancer Institute (▶NCI) and is a unique in vivo model for ▶drug discovery. It permits the simultaneous evaluation of the efficacy of anticancer agents against multiple tumor cell lines in two physiological compartments of one animal. In this assay, semipermeable biocompatible fibers are used, which can be filled with cancer cells. These cancer cells can be derived from different tissue origins and can have different cellular characteristics. The fibers are made of polyvinylidene fluoride (PVDF) and have an internal diameter of 0.5–1 mm and are 2 cm long. The fiber has a molecular weight exclusion of 500,000 Da. Therefore soluble bioactive agents (e.g., proteins, such as growth factors produced by tumor cells or host) can bypass the fiber, but tumor cell to host cell contact is not possible. The fibers are mostly implanted in mice, but it is also possible to implant the fibers in rats and other animals for ▶preclinical testing of anticancer agents. One mouse can support the growth of up to six cancer cell lines, and therefore enables to test more than one cell line simultaneously in one animal. The fibers can be transplanted in both immunocompromized and in immunocompetent mouse strains, since the immune cells of the host can not infiltrate into the hollow fiber and therefore can not activate an immune response or impede the growth of the tumor cells. The fiber can be implanted either intraperitoneally (▶i.p.) or subcutaneously (▶s.c.), therefore differences of intravenous (▶i.v.), oral, i.p., and s.c. administration of drugs can aid in assessing the effects of hepatic pass through, thus providing information for dose estimations and administration routes for more extensive in vivo testing of both cytotoxic and antiangiogenic ▶chemotherapy. After treatment, active cell proliferation and cellular

characteristics, including ▶cell cycle distribution, ▶DNA damage induction, cell death induction (▶Apoptosis), protein expression levels and cell morphology can easily be studied (Fig. 1). Besides this, in vivo pharmacokinetic (▶Pharmacokinetics) parameters, including drug transport, pH and pO2 can be analyzed. The NCI currently uses a panel of 12 tumor cell lines for routine hollow fiber screening of anticancer drug activities. It is used as the initial in vivo assessment to determine potential activity of agents that have reproducible activity in the in vitro anticancer drug screen. The HFA prioritizes compounds for secondary ▶xenograft screening and helps to reduce the large number of active compounds generated by the in vitro ▶NCI 60 cell line screen that were forming a bottleneck for entry into secondary xenograft testing. The NCI HFA requires 24 mice for testing of one compound against a panel of 12 cancer cell lines in contrast to the NCI xenograft model, where three xenograft models are used to test one agent with each xenograft model, which requires about 50 mice. The use of the HFA in early ▶preclinical drug screens fits excellently with the philosophy of replacement, refinement and reduction (3Rs) of animals in research, controlling the use of laboratory animals.

Hollow Fiber Assay. Figure 1 Schematic overview of the HFA procedure for preclinical testing the anticancer activity of a compound using cancer cell lines transplanted subcutaneously (s.c.) or intraperitoneally (i.p.) in mice. Method is described according to NCI guidelines, http:// dtp.nci.nih.gov/branches/btb/hfa.html.

Hollow Fiber Assay

Since the development of the HFA for ▶drug screening, other groups have used this assay to independently demonstrate drug activity. Compound efficacy has been demonstrated using the HFA, using both primary human tumor cells and characterized tumor cell lines. Although the NCI uses the HFA successfully to quantitatively define anticancer activity, the role of this in vivo assay could be extended. The HFA has already been adapted for evaluation of antiviral agents and it may also be adapted to use it in other medical fields. The in vivo HFA has demonstrated a good predictivity of xenograft activity. Anticancer activity in xenograft models is defined by a reduction in relative tumor volume. In the HFA the activity is defined as a reduction of the number of viable cells, measured with an ▶MTT assay. Any compound found to be active in xenograft models is often also active in the HFA. A xenograft model does not easily permit elucidation of the mechanism of action of a compound in a tumor. Retrieval of tumor cells from xenograft models for pharmacodynamic analysis is complicated by host cell contamination. Cells grown in a hollow fiber can easily be harvested for mechanistic studies as a single cell suspension without contamination of host cells. When the HFA is used for preclinical pharmacodynamic investigations, compounds may progress to the clinic much faster. On the other hand, more information is required on tumor cell–stroma interaction. The development of such a model using the HFA is a new challenge in its application. The HFA has several advantages over standard animal efficacy models. First, the assay has demonstrated the ability to provide quantitative indices of drug efficacy with minimum expenditures of time (procedure takes less than 2 weeks) and materials (e.g., test compounds). It is not limited by the high costs that are associated with large-scale animal testing using xenograft tumor models. Second, conducting studies in animal models requires substantial amounts of time and resources for the testing procedure. Even when it is possible to conduct such studies, it is possible that the experimental agents will exhibit only minimal antitumor activity. Thus, the HFA will prevent to test inactive compounds in a xenograft model. Third, cancer treatments that appear promising in tissue culture are often less effective in solid tumors. This can be partially because of the proliferative and microenvironmental heterogeneity that develops in these tumors during their growth in a ▶three-dimensional structure; cells in a hollow fiber also grow in a three-dimensional structure. Fourth, this procedure of testing takes the pharmacokinetic behavior of the drug into account, as well as potential biotransformation. Fifth, the HFA is excellently suited to perform initial in vivo experiments to study combinations, because the compounds will have a

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dynamic in vivo interaction. Sixth, the HFA prevents that the mouse suffers from the tumor induced cachexia. The HFA was not developed to replace the classic xenograft model. Complex interactions which occur when the transplanted tumor cells are growing in and interacting with the host’s tissue can not be analyzed. Cells can not metastasize to secondary organs of the animal, since the fiber prevents cellular ▶migration. Although ▶angiogenesis in the tumor will not be induced when these fibers are used, neovascularization occurs to supply the fiber with nutrients. This is possibly induced by growth factors that are released by the tumor cells in the fiber. The hollow fiber can be used perfectly as a preliminary tool to asses the capacity of a compound to reach tumor cells growing in two distinct physiologic compartments (s.c. or i.p.) and to asses whether the drug can reach pharmacologically active concentrations in the tumor cells. Using modern ▶bioluminescent techniques, it will be possible to perform dynamic growth of the cells in the fibers.

Methodology The HFA procedure is as follows (Fig. 1): tumor cells are harvested at the desired cell density from a log phase growing in vitro culture. The cell suspension is flushed into the hollow fibers, which are subsequently heatsealed so that the cells can not escape from the fiber. The density is dependent on the cell line and may vary from 1 to 100 × 105 cells/fiber. Prior to transplantation into the host, fibers are placed into tissue culture medium and incubated at 37°C in 5% CO2 atmosphere for 24–48 h. On the day of implantation, samples of each tumor cell line preparation can be quantified for viable cell mass by a stable endpoint MTT assay. Mice can then be treated with anticancer agents starting few days after fiber implantation and for a maximum of 2 weeks. Following treatment, the fibers are collected from the host and subjected to the stable endpoint MTT assay. The percent net growth for each cell line is calculated and compared to the percent net growth in the vehicle treated controls. Furthermore, at the treatment endpoint, various other cellular analyses can be performed.

References 1. Hollingshead MG, Alley MC, Camalier RF et al. (1995) In vivo cultivation of tumor cells in hollow fibers. Life Sci 57:131–141 2. Suggitt M, Bibby MC (2005) 50 years of preclinical anticancer drug screening: empirical to target-driven approaches. Clin Cancer Res 11:971–981 3. Decker S, Hollingshead M, Bonomi CA et al. (2004) The hollow fibre model in cancer drug screening: the NCI experience. Eur J Cancer 40:821–826

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4. Temmink OH, Prins HJ, van Gelderop E et al. (2007) The hollow fibre assay as a model for in vivo pharmacodynamics of fluoropyrimidines in colon cancer cells. Br J Cancer 96:61–66 5. Suggitt M, Cooper PA, Shnyder SD et al. (2006) The hollow fibre model – facilitating anti-cancer pre-clinical pharmacodynamics and improving animal welfare. Int J Oncol 29:1493–1499

Homeobox Definition A short usually highly conserved DNA sequence found within genes that are involved in the regulation of development (morphogenesis) of animals, fungi and plants. Genes that have a homeobox are called homeobox genes and form the homeobox gene family. ▶Nucleoporin

Homeobox Genes S TACEY S TEIN , C ORY A BATE -S HEN Center for Advanced Biotechnology and Medicine, UMDMJ – Robert Wood Johnson Medical School, Piscataway, NJ, USA

Definition Homeobox genes are a class of developmental regulatory genes that encode homeoproteins. Homeoproteins function as transcription factors to regulate downstream targets, turning on (activating) or turning off (repressing) other genes that in turn regulate developmental processes. Aberrant expression of homeobox genes has been implicated as causal factors in leukemia and solid tumors.

Characteristics Homeobox genes are often referred to as master control genes. They are active during embryonic development and regulate important processes such as ▶morphogenesis and cellular ▶differentiation. They were first identified in Drosophila as the homeotic cluster (HOM-C) genes and were later found to have homologs in many species. They are now known to be highly evolutionarily conserved and are present in animals, plants and fungi.

Homeobox genes share a common sequence motif (the homeobox), which is 180 nucleotides in length and encodes a 60 amino acid region (the homeodomain). The homeodomain mediates DNA binding to sites containing a ▶TAAT sequence that are found in the transcriptional regulatory elements of target genes. Upon DNA binding, homeoproteins are thought to act as transcription factors to regulate downstream targets. There are two major subclasses of vertebrate homeobox genes: . The clustered genes, or HOX genes . The non-clustered genes The non-clustered genes are sub-divided into many subfamilies, which are classified on the basis of sequence similarities within their homeobox regions. The HOX family of homeobox genes, as well as most other families of homeobox genes, is thought to control cellular proliferation and differentiation during development. The HOX genes are expressed beginning in ▶gastrulation and are involved in patterning the body axis from the branchial arches to the tail. What is most notable about HOX genes is their positioning on four chromosome clusters. Not only are the sequences of the individual genes highly conserved across species, the order of the genes on the chromosomes is conserved as well. Moreover, the physical order of the genes on the chromosome correlates with their spatial and temporal expression patterns along the anteroposterior axis of the embryo. Many studies have reported a link between deregulated homeobox gene expression and abnormal cellular proliferation, which implicates homeobox genes not only as development regulators, but also as potential protooncogenes and tumor suppressor genes. The downstream targets of homeobox genes are postulated to include extracellular matrix proteins, adhesion molecules and growth factors. Because these target genes are likely to be important for tumorigenesis as well as development, their misexpression may upset the delicate balance of cell proliferation, differentiation and apoptosis, thereby contributing to carcinogenesis. Hox Genes and Leukemia In addition to their functions during development, homeobox genes also play important roles in adult tissues. For instance, the HOX genes are expressed in specific patterns during lineage determination in ▶hematopoiesis. HOX genes have been demonstrated to be important for normal blood cell formation; in addition, abnormal expression of HOX and other homeobox genes contributes to the development of leukemia and lymphoma. A common mechanism by which abnormal gene expression contributes to leukemia is through translocation of two chromosomal regions, which may

Homeostasis

produce fusion proteins with novel properties or impaired activities. For example, in human acute myeloid leukemia (AML) a translocation between chromosomes 7 and 11 fuses the nucleophorine gene NUP98 in frame with HOXA9. It is thought that the resulting chimeric protein is no longer able to interact with HOXA9 target genes. Another example of a homeobox translocation in leukemia is the fusion of PBX1 homeobox gene and the E2A gene. Normally, PBX1 forms transcriptionally active protein complexes with HOX proteins; its fusion with E2A alters such interactions, which is thought to direct homeoproteins to different targets, thereby inducing leukemogenesis. Like PBX, other divergent homeoproteins interact with specific HOX proteins to potentiate or modulate their effects, and their genes are potential targets for deregulation in carcinoma. For example, it now appears that the MEIS1 homeobox gene is co-activated with HOXA9 in human myeloid leukemia. In addition, translocation of the MLL gene is a common event having been found to be fused to more than 25 other genes in leukemia. While MLL is not a homeobox gene, it is homologous to a Drosophila protein that is an important regulator of HOM-C genes. The leukemogenic MLL fusion proteins are thought to disrupt HOX gene expression in hematopoietic progenitor cells, thereby contributing to myeloid or lymphoid acute leukemias. Homeobox Genes and Solid Tumors A common feature of HOX gene expression in certain adult organs, such as kidney, lungs and colon, are the significant differences in expression pattern between normal and cancer tissue. For example, in the kidney HOXC11 is present in tumors but not in normal tissue. Conversely, HOXB5 and HOXB9 are normally expressed in the kidney but expression is often lost in tumors. Other HOX genes, such as HOXD4, are expressed in both normal kidney and in kidney tumors, although they express a different-sized transcript in the tumors versus the normal tissue. In each of these cases the significance of these differential gene expression patterns remains undetermined. Similar observations have been made in the colon. Misexpression of some HOX genes (HOXA9, HOXB7 and HOXD11) is found in primary colon cancer and metastatic lesions originating from colorectal tumors. In addition, HOXB6, HOXB8, HOXC8 and HOXC9 are misexpressed at specific stages of colon cancer progression. And, while HOXB7 and HOXD4 are both expressed in normal and neoplastic colon, the size of the transcripts differ. Again, the significance of these observations for disease initiation or progression is unclear. CDX1 and CDX2 homeobox genes are expressed in normal colon, while their expression is reduced in colon

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tumors. Interestingly, there appears to be an inverse correlation between the levels of protein expression and the severity of the dysplasia. This correlation, in conjunction with other data, suggests that expression of CDX1 and CDX2 is important for maintaining normal colon differentiation and that their loss of expression may promote a cancer phenotype. These observations have been supported by mutant mouse models in which loss of CDX genes results in colon tumors. Misexpression of certain homeobox genes has also been implicated in prostate cancer. For example, the GBX2 homeobox gene is overexpressed in several metastatic prostate cell lines, suggesting a possible role in cancer progression. Conversely, loss of function of the NKX3.1 homeobox genes has been implicated in prostate cancer initiation. Notably, NKX3.1 maps to a hotspot that is frequently deleted in many prostate cancer samples, and mutant mice lacking NKX3.1 display prostatic epithelial dysplasia. Like, the CDX genes, these mutant mouse models provide excellent support for a functional role of these homeobox genes in cancer. At this point much of the data is rather circumstantial and based on altered expression patterns. Nonetheless, the available evidence suggests that homeobox genes may provide an important link in understanding the delicate balance of development, cell-cycle control and cancer. The specific molecular events that occur between the misexpression of homeobox genes and the progression to cancer remains a topic of active investigation.

References 1. Cillo C, Faiella A, Cantile M et al. (1999) Homeobox genes and cancer. Exp Cell Res 248:1–9 2. Cristina M, Largman C, Lawrence J (1997) Effects of HOX homeobox genes in blood cell differentiation. J Cell Physiol 173:168–177 3. Look A (1997) Oncogenic transcription factors in the human acute leukemias. Science 278:1059–1064 4. Mark M, Rijli F, Chambon P (1997) Homeobox genes in embryogenesis and pathogenesis. Pediatr Res 42:421–429

Homeostasis Definition Is one of the fundamental characteristics of living things. It is the maintenance of the internal environment within tolerable limits. Homeostasis is maintained by

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means of multiple dynamic equilibrium adjustments, controlled by interrelated regulatory mechanisms, resulting in a stable, constant condition. ▶Apoptosis-Induction for Cancer Therapy

Homeotic Genes Definition Genes involved in developmental patterns and sequences. ▶Polycomb Group

Homer Wright Rosette Definition Is a circular or spherical grouping of dark tumor cells around a pale, eosinophilic, central area that contains neurofibrils but lacks a lumen; seen in some cases of ▶medulloblastoma, ▶neuroblastoma, and ▶retinoblastoma. A rosette structure is also an important morphologic finding in the diagnosis ▶Ewing sarcoma/ ▶pPNET.

target tissues through the circulation. The resultant peptides bind to endothelial (and possibly pericyte) surface proteins that are selectively expressed in the vasculature of individual tissues (Fig. 1). Homing peptides have been obtained for the vasculature in a large number of individual normal tissues that reveal a previously unsuspected degree of endothelial specialization. Screening for tumor homing has produced a collection of peptides that home to tumor vasculature. Atherosclerotic lesions have also been targeted in this manner. The vessels of some normal organs have been known to express specific marker molecules, but in vivo phage has revealed an unprecedented degree of diversification in endothelia. The tissues for which vascular homing peptides have been described in the literature include brain, kidney, lung, heart, skin, pancreas, retina, intestine, muscle, uterus, prostate, fat tissue, and the adrenal gland. Success with so many tissues indicates that many, perhaps all, organs modify the endothelium of the vasculature, and that it is justified to refer to this heterogeneity as “vascular zip codes.” The vasculature of tumors is also specialized. Tumors depend on ▶angiogenesis to grow and undergo ▶metastasis. The actively growing tumor vessels are biochemically and structurally different from normal resting blood vessels. Integrins αvβ3, αvβ3, and α5β1as well as receptors for various vascular endothelial growth factors, are examples of molecules expressed at elevated levels in tumor blood vessels. Significantly, each of these receptors plays a critical role in angiogenesis. Other markers of tumor vasculature include an alternatively

Homing Peptides and Vascular Zip Codes E RKKI R UOSLAHTI Vascular Mapping Center, Burnham Institute for Medical Research at University of California, Santa Barbara, CA, USA

Definition Vascular Zip Codes refers to tissue- and disease-specific molecular differences in vessels.

Characteristics Peptide libraries displayed on phage can be screened in vivo to derive peptides capable of homing to selected

Homing Peptides and Vascular Zip Codes. Figure 1 Homing peptides direct phage binding to specific sites in the vasculature.

Homogeneously Staining Region

spliced form of fibronectin, endosialin, certain aminopeptidases, an anthrax toxin receptor, and intracellular proteins aberrantly expressed at the cell surface (nucleolin, annexin A1). Melanoma-associated proteoglycan NG2 is a marker of pericytes in tumor vessels. Phage library screening in vivo has resulted in the identification of several peptide motifs that selectively direct phage into tumors. One of these motifs contains the sequence RGD (arginine-glycine-aspartic acid) embedded in a peptide motif previously shown to bind selectively to αv integrins. A number of additional tumor-homing peptides and receptors for some of them have been identified. Examples include peptides that recognize aminopeptidase N, cell surface nucleolin and clotted plasma proteins in tumor vessels. Homing peptides have also been used to show that the blood vessels of pre-malignant lesions differ from those of the corresponding normal tissue and from the vessels of fully developed tumors in that tissue. Further, lymphatic vessels in tumors differ molecularly from the lymphatics of normal tissues. Biological Significance Vascular zip code molecules are functionally important in the vessels that express them. A prime example is various angiogenesis markers, many of which are involved in the angiogenesis process. One known function of zip code molecules in the vessels of normal tissues is to serve cell trafficking. Tumor cells appear to make use of such molecules in homing to preferred sites of metastasis. Clinical Significance Coupling of drugs, ▶apoptosis-inducing peptides, protein therapeutics, or imaging agents to tumor-homing peptides enhances the activity of these compounds in mice and lowers their toxicity. The homing peptides are also useful for the targeting of nanoparticles and potentially also cells to tumors. Delivery strategies similar to the tumor targeting should be applicable to targeting of pathological conditions other than tumors.

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Homing receptor ▶CD44

Homo Sapiens Mitotic Arrest Deficient-like 1 Protein ▶Mitotic Arrest-Deficient Protein?

H Homodimer Definition A type of protein interaction in which two of the same protein bind together to form a complex, often necessary for the normal function of receptors. ▶Prostate-Specific Membrane Antigen

Homo- or Heterodimers Definition A protein complex consisting of two identical (homo) or different (hetero) subunits. ▶Early B-cell Factors

References 1. Ruoslahti E (2002) Specialization of tumour vasculature. Nat Rev Cancer 2:83–90 2. Laakkonen P, Porkka K, Hoffman JA et al. (2002) A tumor-homing peptide with a lymphatic vessel-related targeting specificity. Nat Med 8:743–751 3. Brown D, Ruoslahti E (2004) Metadherin, a cell-surface protein in breast tumors that mediates lung metastasis. Cancer Cell 5:365–374 4. Ruoslahti E, (2004) Vascular zipcodes in angiogenesis and metastasis. Biochem Soc Transact 32:397–402 5. Simberg D, Duza T, Park JH et al. (2007) Biomimetic amplification of nanoparticle homing to tumors. Proc Natl Acad Sci USA 104:932–936

Homogeneously Staining Region Definition HSR; is a region within a chromosome lacking the typical banding pattern after staining with Giemsa, indicative of DNA amplification. In tumor cells indicating oncogene amplification, in some cases also amplification of genes encoding proteins for drug metabolism. ▶Amplification

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Homogenous Assays

Homogenous Assays ▶Time-Resolved Fluorescence Resonance Energy Transfer Technology in Drug Discovery

Homogenous Time Resolved Fluorescence ▶Time-Resolved Fluorescence Resonance Energy Transfer Technology in Drug Discovery

Homolog Definition Genes that share a high degree of sequence identity or similarity, indicating their common ancestor or function.

Homologous Recombination Repair J OHN T HACKER Medical Research Council, Radiation and Genome Stability Unit, Harwell, Oxfordshire, UK

Definition Homologous recombination repair is a DNA repair process that includes the invasion of an undamaged DNA molecule by a damaged molecule of identical or very similar sequence. Resynthesis of the damaged region is accomplished using the undamaged molecule as a template.

Characteristics Homologous recombination repair has been found in all organisms examined from bacteria to man. It has an important role in repairing DNA damage with high fidelity by correcting damage with the use of information copied from an homologous undamaged molecule. Sister chromatids (duplicated chromosomes following DNA replication) or the paternal and maternal copies of

chromosomes provide the required homology (sequence identity or near-identity over a few hundred DNA base pairs). In somatic cells, if the homologues have some sequence differences the copying process may alter the sequence of the damaged chromosome to the same as that of the undamaged chromosome, potentially revealing mutations (▶loss of heterozygosity). Additionally, recombination between repeat sequences may lead to high frequencies of sequence variation as seen in certain ▶minisatellite sequences. In germ cells, homologous recombination is vital for the reassortment of chromosomes during meiosis to create genetic diversity in organisms. Cellular Regulation The proteins that mediate homologous recombination repair have functions and often structures that have been conserved in evolution. These proteins have to seek out homologous regions of chromosomes, exchange DNA strands, copy sequence from the undamaged strand and finally resolve the DNA structures arising from exchange. This complex series of events is best understood in bacteria but recently many of the components and functions of homologous recombination repair have been identified in mammalian cells. Evidence suggests that DNA double-strand breaks commonly trigger repair by homologous recombination; these breaks may be caused by the interaction of DNA with chemical radicals, produced as a consequence of cellular metabolism, or by external damaging agents such as ionizing radiations. Meiotic recombination is also driven by DNA double-strand breaks, but these are formed enzymatically at specific sites in DNA. In bacteria, the ▶RecA protein is central to homologous recombination through its ability to search for homologous regions of DNA and promote strand exchange. RecA forms a polymer on DNA to give a nucleoprotein filament, acting as a DNA-dependent ATPase. Filament formation occurs very rapidly on single-stranded DNA; in purified solutions the rate can approach 1,000 RecA monomers assembled per minute. RecA will also polymerize on double-stranded DNA but needs a short single-stranded gap to start the process, potentially targeting the protein to sites needing repair. On binding RecA and in the presence of homologous double-stranded DNA, strand exchange occurs to form junctions between the two DNA molecules. A number of other proteins are involved in the early stages of homologous recombination repair in bacteria; to generate the single-stranded DNA required for RecA-mediated strand exchange different proteins (RecBCD, RecJ, RecQ, or RecE) may be used depending on the initial state of the DNA. For example, during bacterial conjugation the RecBCD protein will unwind DNA from a break and cut the unwound DNA at a specific sequence-recognition site,

Homologous Recombination Repair

forming a long 3′ single-stranded region suitable for invading homologous double-stranded DNA. Other proteins assist in the loading of RecA onto singlestranded DNA and/or strand-invasion activities (RecF, RecO, RecR and single-stranded DNA binding protein). During recombination the junctions formed at sites of exchange migrate along the DNA molecules to complete gap repair, and finally the junctions must be cut to free the participating DNA molecules. Again some of these functions are supplied by different proteins, in this case either RuvABC or RecG, indicating the presence of more than one pathway for homologous recombination. While much of the mechanistic detail of homologous recombination repair has been described in bacteria, it is clear that the principles of this mechanism have been retained by all organisms. RecA-like proteins have been found in eukaryotes; in particular the ▶Rad51 protein from the yeast Saccharomyces cerevisiae (Rad51p) has both structural and functional similarities to RecA. Rad51p leads to the formation of nucleoprotein filaments on DNA and the promotion of homologous pairing and strand exchange reactions in vitro. However, in addition to Rad51p there are three other ▶RecA/Rad51-like proteins in yeast; Rad55p, Rad57p and Dmc1p. Biochemical studies suggest that these RecA/Rad51-like proteins do not have redundant functions but rather have distinct roles to play in the early stages of repair. The Dmc1 protein functions exclusively in meiosis, with loss of its function leading to sterility, while the other RecA-like proteins operate in both mitosis and meiosis. Rad55p and Rad57p exist as a dimer and appear to act as a cofactor for the assembly of Rad51p onto single-stranded DNA. A three-protein complex (▶Rad50p/▶Mre11p/Xrs2p) has been found that promotes the early stages of homologous recombination but is also involved in a number of other repair and DNA maintenance functions; the Mre11 protein in particular has nuclease activities that may process double-strand breaks to form single-stranded regions associated with strand invasion. Other yeast recombination proteins, such as ▶Rad52p and ▶Rad54p, interact with Rad51p and promote Rad51-mediated strand exchange. Rad52p interacts with single-stranded DNA binding protein (Rpa) and facilitates the loading of Rad51p onto single-stranded DNA lacking secondary structure. Rad54p is structurally related to a family of putative DNA helicases but its precise function is unknown. Rad51 also occurs in human cells. Despite millions of years of evolutionary divergence, the human protein is remarkably similar in structure and function to the yeast Rad51 protein. Additionally, six further RecA/ Rad51-like proteins have recently been identified in humans. Two of these, Xrcc2 and Xrcc3, were found through their ability to complement the sensitivity of

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certain mammalian cell mutants to DNA-damaging agents. The remainder, including a protein closely similar to the yeast Dmc1, were found by searching for RecA/Rad51-like proteins in the human protein sequence databases. These proteins are presently the subject of intensive study but there is already evidence that some may function like the yeast Rad55 and Rad57 proteins in forming dimers that help Rad51 to function efficiently. The increase in the numbers of RecA/ Rad51-like proteins in higher organisms also suggests that certain specialized functions may have evolved to deal with specific types of DNA damage or with tissuespecific recombination events. The yeast Rad50 and Mre11 proteins are also conserved in mammalian cells, but a structural homologue of the yeast Xrs2 protein has not been found in humans. Instead the Nbs1 (▶Nijmegen breakage syndrome) protein (also known as p95 or nibrin), defective in the radiosensitive and cancer-prone human disorder Nijmegen breakage syndrome, appears to be a functional analogue of Xrs2. The features of Nbs1-deficient cells are very similar to those of ataxiatelangiectasia cells, and recently the human Mre11 protein has been shown to be mutated in individuals with an ataxia-telangiectasia-like disorder. Proteins similar to the yeast Rad52 and Rad54 have also been found in humans, and in the case of Rad54 it has been shown that the human protein is able to function in place of the yeast protein. The Rad52 protein is not so well conserved in structure between yeast and humans, although it is possible that another Rad52-like protein remains to be discovered in humans. In biochemical experiments, however, the human Rad52 protein has been shown to stimulate Rad51-mediated DNA-strand transfer reactions, probably at an early stage of Rad51 filament formation. Proteins involved in the later stages of recombination repair have yet to be identified in yeast or mammalian cells. The interactions of these proteins in the early stages of repair of a DNA doublestrand break by homologous recombination are illustrated in the Fig. 1. To study the effects of loss of recombination genes in mammals, several of the genes have been disrupted in mice (“knockout mice”). Surprisingly, disruption of Rad51 in mice is lethal for embryonic development and cells could not be cultured from tissue derived from the knockout animal. This finding suggests that the mammalian Rad51 gene has an important role in essential aspects of DNA metabolism or in development. It also suggests that the other Rad51-like genes cannot replace the function of Rad51 itself. Disruption of some of the Rad51-like genes in mice also leads to embryonic lethality, showing that these similarly have important functions in the organism. In contrast, knocking-out other recombination genes in mice is not necessarily lethal. Disruption of the meiosisspecific Dmc1 gene, as well as similar knockout

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Homologous Recombination Repair

Homologous Recombination Repair. Figure 1 A model for the repair of a DNA double-strand break by homologous recombination in human cells. The main steps are noted to the left, and the proteins involved (where known) to the right. The Rad51-like proteins include Xrcc2 and Xrcc3. The broken DNA molecule (black) is processed to give long 3′ single stranded regions; these invade an undamaged homologous molecule (red). The branched-out undamaged strand acts as a template to repair the break. Repair synthesis is accompanied by branch migration. Resolution involves cutting the junctions between the two molecules; here it is shown without crossing-over, potentially leading to gene conversion where the homologous molecules differ in sequence.

experiments with the mouse Rad52 and Rad54 genes, yielded viable progeny. With the possible exception of the Rad52 knockout mouse, each has severe defects in aspects of mitotic and/or meiotic processes, consistent with roles in homologous recombination repair. The potential importance of homologous recombination repair genes in genetic stability and in development has been highlighted by several recent discoveries. Firstly, it has been found that the human Rad51 protein interacts physically with the tumor-suppressor protein p53, which has a central role in the control of the cell cycle and apoptosis. Additionally, Rad51 knockout embryos survived longer in a p53-deficient background, suggesting at least part of the growth problems experienced by Rad51 knockouts arises from unrepaired damage triggering ▶cell-cycle checkpoints leading to growth arrest. Equally important, Rad51 interacts with the breast cancer-susceptibility gene products ▶Brca1 and ▶Brca2. Disruption of the Brca1 or Brca2 genes in

mice gives embryonic lethality and shows a similar elevation of chromosomal aberrations as that found in Rad51-disrupted cells. The link between the Brca proteins and homologous recombination repair has been extended by showing that Brca1 and Brca2-deficient cells have a large reduction in ability to repair doublestrand breaks in homologous substrates integrated into the genome. Brca1 is phosphorylated in response to DNA damage and this event is dependent on the protein kinase mutated in the cancer-prone disorder ataxia-telangiectasia (Atm). Atm may act as a sensor of DNA damage, especially double-strand breaks, and there is evidence supporting a model in which Brca1 phosphorylation triggers the activity of Rad51 and Brca2 to initiate homologous recombination repair. However, Brca1 also associates with the human Rad50 protein and has a role in the ▶transcription-coupled repair pathway, so its action is likely to be broader than this model suggests.

Homophilic and Heterophilic Adhesion

The role of recombination proteins in influencing development in multicellular organisms has been illustrated by recent findings in the fruit fly, Drosophila melanogaster. Mutations in the spindle class of genes lead to patterning defects in the oocyte and embryo, apparently due to mis-localization and/or failure to accumulate normal levels of oocyte signaling molecules. The cloning and sequencing of these genes showed that they are homologues of RAD51 or RAD54. Mutation in these genes leads to the accumulation of DNA damage, which triggers a meiotic recombination checkpoint that down-regulates some of the genes essential for embryonic development. Interestingly, oocytes that are mutant for both spindle-class genes and the Drosophila homologue of ATM (mei-41) can bypass this meiotic arrest and show normal developmental patterning, suggesting that loss of ability to signal damage fails to trigger this checkpoint. The downside of this checkpoint loss is that DNA damage may be carried through into later cell divisions, resulting in genomic instability. The mechanisms of homologous recombination repair are still being investigated, but it is clear that this repair pathway is of considerable significance in all organisms. Other pathways can repair certain types of DNA damage; for example, in mammalian cells, ▶non-homologous end joining is an alternative way to repair DNA double-strand breaks. However, simple end joining of broken DNA is prone to loss of sequence (DNA deletion) at the damage site, while homologous recombination repair can rejoin breaks with high fidelity. In bacteria it is clear that a major role of homologous recombination repair is to sort out problems arising during DNA replication, in particular where a replication fork stalls due to damage in its path. In yeast and mammals there is also evidence that homologous recombination proteins are particularly active during DNA replication. Additionally, certain types of DNA damage such as ▶DNA interstrand cross-links formed by agents such as mitomycin-C may be resolved only by the homologous recombination repair pathway. In support of this idea, cell lines lacking homologous recombination repair genes are very sensitive to mitomycin-C and other DNA cross-linking agents. Clinical Relevance Loss of homologous recombination repair leads to unrepaired damage in the genome, which in turn can give rise to genomic instability. Both Mre11 and Nbs1 have been found to be associated with rare human disorders with complex phenotypes, including radiation sensitivity and cancer-proneness (ataxia-telangiectasia and Nijmegen breakage syndrome, respectively). The association of homologous recombination repair

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proteins with p53 and the Brca proteins also suggests that this repair pathway has potentially important connections with predisposition to cancer. The links are strongest with breast cancer, through the Brca proteins and possibly the Atm protein. Additionally, loss of one of the human Rad51-like proteins (Rad51L1) has been associated with uterine leiomyomas.

References 1. Li X, Heyer W-D (2008) Homologous recombination in DNA repair and DNA damage tolerance. Cell Research 18:99–113 2. Thorslund T, West SC (2007) BRCA2: a universal recombinase regulator. Oncogene 26, 7720–7730 3. Helleday T, Lo J, van Gent DC, Engelward BP (2007) DNA double-strand break repair: from mechanistic understanding to cancer treatment. DNA Repair 6:923–935 4. Thacker J (2005) The RAD51 gene family, genetic instability and cancer. Cancer Letters 219:125–135

Homologue of Synaptopodin ▶Myopodin

Homomeric Complex Definition Complex composed of two or more identical subunits. ▶Hamartin

Homophilic and Heterophilic Adhesion Definition Adhesion between two undefined cell types can be mediated by either identical (homophilic) or different (heterophilic) adhesion molecules. ▶Cell Adhesion Molecules

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Homoplasmy

Homoplasmy

Hormonal Carcinogenesis

Definition

S USHANTA K. B ANERJEE

In normal conditions all copies of mtDNA are identical within coding region.

Cancer Research Unit, Research Division, VA Medical Center, Kansas City, MO Division of Hematology and Oncology, School of Medicine, Kansas University of Medical Center, Kansas City, KS, USA

▶Mitochondrial DNA

Definition

Homotypic and Heterotypic Adhesion Definition Adhesion mediated by undefined adhesion molecules between identical cell types (homotypic) or two different cell types (heterotypic). ▶Cell Adhesion Molecules

Homozygous Deletion Definition In a diploid organism, loss of both alleles or portion of both alleles from the genome of a cell, tumor or organism. Physical loss of both copies of the same gene or of the same chromosomal segment of a pair of homologous chromosomes. ▶Fragile Histidine Triad

Horizontal Gene Transfer (HGT) Definition In this process, an organism transfers its genetic material to another cell that is not its offspring. The horizontal transfer of genetic material was originally detected in prokaryotes, but recent data show that it occurs not only in unicellular, but also in multicellular eukaryotes and might be an important evolutionary mechanism. ▶Circulating Nucleic Acids

The process by which a normal cell is transformed into a cancer cell is called “Carcinogenesis”. When the carcinogenic event is either potentiated or promoted by hormones (i.e., natural or synthetic) (▶diethylstilbestrol, estradiol) is considered as “Hormonal Carcinogenesis” (▶Estrogenic hormone and cancer) (▶Hormones and Cancer).

Characteristics There are three major classes of hormones based upon their chemical structures. These are (i) peptide/protein hormones (e.g., leptin, angiotensin II, interleukins, ACTH, gastrin and others), (ii) amino acid or fatty acidderived hormones (e.g., epinephrine, acetylcholine, prostaglandins and others, and (iii) steroid hormones (e.g., estrogen, progesterone, testosterone and others). Each hormone has its unique features and plays specific role under normal physiological conditions. Normally, it requires very minute amounts to exert its biological function through its receptor or other signaling pathways. However, excess or alter form of a hormone or its receptor sometimes exhibits carcinogenic behavior and distort the regulated state of the cells, which ultimately activate the carcinogenic switch or growth of the tumor or aggressive properties of a tumor or all the above events. The ideal example of carcinogenic hormone is natural or synthetic estrogens such as 17β-estradiol (E2) and diethylstilbestrol (DES). In animal system (i.e., mice, rats and hamsters), these two estrogenic compounds induces tumors in various estrogen-depended organs or tissues and the incidence rate is 100%. Moreover, a strong links between estrogens and the development cancer in human have been evident over 300 years ago that showed a protective effect of pregnancy on the development of breast cancer and also underscored that the higher rates of breast cancer among catholic nuns. This finding was reconfirmed by several epidemiological studies that showed a single full-term pregnancy reduces the risk of development of breast cancer by 50% or more. Subsequent births, especially at an early age, further reduce the risk. Moreover, breast cancer risk in the presence of estrogen can be determined by several factors including early menarche, late menopause and obesity in postmenopausal women.

Hormonal Carcinogenesis

Several cancers have been found to relate with the status of carcinogenic hormones in the body. For instance, breast or prostate cancer development may depend on the supply of estrogen or androgen, respectively, or their cognate receptors in the tumor cells. Therefore, the removal of the source glands (ovary, testis or pituitary) or targeting the receptors by antagonists (i.e., tamoxifen) of the hormones is used to prevent the growth of these tumors. Mechanisms Cancer is a mixed tissue of abnormal cells, and the etiology of this disease remains uncertain. After decades of studies it has been apparent that cancer begins with multiple genetic and epigenetic insults that included mutations of regulatory genes, activation of oncogenes or inactivation of tumor suppressor genes. These molecular insults facilitate the cells to grow abnormally, gain motile behavior and other features needed to grow the cancer cells and invade to distant parts of the body. These fatal abnormalities are probably built up in the normal cells through endogenous or exogenous carcinogens. Estrogens have been used for last several decades to explore the molecular mechanisms of hormonal carcinogenesis by several investigators. These studies found chronic exposure of estrogens involve interplay and cross-talk between genotoxic and epigenetic

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changes that eventually lead to an uncontrolled cell proliferation and cellular transformation (Fig. 1). The genetic alterations are accomplished by estrogens through the formation of DNA adducts and chromosomal abnormalities including chromosome breaks, aneuploidy and telomeric association, while epigenetic alterations are potentiated through DNA methylation/ demethylation or through the alterations in cell signaling molecules such as WISP-2/CCN5 and others. These epigenetic changes through the molecular crosstalk may precede genetic changes in normal or premalignant cells and foster the accumulation of additional genetic and epigenetic hits. How estrogens induce genetic and epigenetic abuses in some cells? Despite decades of investigations, an absolute answer of this question is elusive. Because estrogeninduced carcinogenesis can be blocked by estrogen antagonists (i.e., Tamoxifen or ICI 182,780) or estrogen withdrawal, the estrogen receptors (nuclear or cytoplasmic) may be involved in estrogen-induced carcinogenic switch (Fig. 2). The normal physiological effects of estrogen are usually mediated through two classical estrogen receptors, estrogen receptor-alpha (ER-α) and estrogen receptor-beta (ER-β). These receptors are encoded by two separate genes though they have some common domains and have similar binding affinity with the ligands. Nevertheless, these two receptors play redundant roles in estrogen signaling. In cells where both

Hormonal Carcinogenesis. Figure 1 Putative Pathways involved in hormonal carcinogenesis. Carcinogenic estrogens-induced neoplastic transformation is mediated through genetic and epigenetic abuses in the target tissues or cells. Presumably genetic and epigenetic changes by carcinogenic hormones are interdependent and cross-talk or side-talk with each other to enhance uncontrolled proliferation and genomic instability which are the hallmarks of carcinogenic switch.

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Hormonal Carcinogenesis

Hormonal Carcinogenesis. Figure 2 The role of nuclear and cytoplasmic receptors in hormonal carcinogenesis. The endogenous or exogenous estrogen binds with either cytoplasmic estrogen receptor or nuclear receptor and subsequently activates estrogen-response genes associated with cellular proliferation and transformation events.

receptors are expressed, the estrogen responsiveness is determined by the ER-α: ER-β ratio. The studies shown that isoforms of ER-β heterodimerize and inhibit the activity of ER-α, which suggest a modulatory role of ER-β. In hormonal carcinogenesis, participations of these two receptors are considered to be crucial. However, some investigators believe that non-receptor pathways are also involved in hormonal carcinogenesis. Like estrogens, other hormones which are having carcinogenic potential exhibit identical effect on the cells for the induction of transformation. The formation of new blood vessels surrounding the tumors from preexisting blood vessel, which is also known as tumor angiogenesis, is the hallmark of cancers. It is necessary for increased nutrient and oxygen supply to the tumor cells. This process is controlled by several positive and negative angiogenic factors including vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and transforming growth factoralpha (TGF-α), TGD-β, thrombospondin-1 (TSP-1) and statin (▶Antiangiogenesis). Some of these angiogenic factors such as PDGF and TGFs are proteins/peptide hormones. Normally, angiogenesis is a highly controlled

Hormonal Carcinogenesis. Figure 3 Angiogenic switch during hormonal carcinogenesis. Estrogen plays dual roles in tumor angiogenic switch. It activates positive regulator of angiogenesis and simultaneously silenced the expression of negative regulator.

process. Uncontrolled and persistent changes in angiogenic process are occurred at different stages of tumor progression. This phenomenon is occurred by imbalance expression of positive and negative angiogenic

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regulators. Multiple studies have shown that tumor angiogenic switch can be regulated by steroid hormones including estrogen and progesterone. These hormones modulate both positive and negative angiogenic regulators for angiogenic switch (Fig. 3).

Definition

References

HRPC; Synonym androgen-independent prostate cancer (AIPC); Prostate cancer that has become refractory, that is, it no longer responds to hormone therapy.

1. Banerjee SK, Islam A, Banerjee S (2005) The regulatory roles of estrogen in carcinogenesis. In: Bagchi D, Preuss HG (eds) Phytopharmaceuticals in cancer chemoprevention. CRC Press, Washington, DC, pp 105–121 2. Norman AW, Litwack G (1997) Hormones, 2nd edn. Academic Press, UK 3. Cavalieri EL, Stack DE, Devanesan PD et al. (1997) Molecular origin of cancer: Catechol estrogen-3,4-quinones as endogenous tumor initiators. Proc Natl Acad Sci USA 94:10937–10942

Hormonal Therapy Definition

▶Endocrine Therapy

Hormonal Treatments Definition Treatment that adds, blocks, or removes hormones. To slow or stop the growth of certain cancers (such as prostate cancer and breast cancer), synthetic hormones or other drugs may be given to block the body’s natural hormones.

Hormone-Refractory Prostate Cancer

Hormone-related Cancers ▶Endocrine-Related Cancers

Hormone Replacement Therapy Definition HRT; Is a medical treatment for menopausal, perimenopausal, and postmenopausal men and women, based on the assumption that it may prevent discomfort and health problems caused by diminished circulating estrogen and progesterone hormones in the female. The treatment involves a series of drugs designed to artificially boost hormone levels. The main types of hormones involved are estrogens, progesterone or progestins, and sometimes testosterone in the case of men. ▶Estrogenic Hormones ▶Estradiol ▶Progestin

▶Temsirolimus ▶Hormones

Hormone-Responsive Element Hormone-induced Cancers ▶Endocrine-Related Cancers

Definition A specific cis-regulatory DNA sequence for a certain hormone that acts by binding to a receptor. This hormone–receptor complex can act as a transcription factor by binding to the hormone responsive element.

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Hormones

Hormones R EKHA M EHTA , J AYADEV R AJU Toxicology Research Division, Bureau of Chemical Safety, Food Directorate, HPFB, Health Canada, Ottawa, ONT, Canada

Definition Hormones are complex chemical messengers that bind with high affinity to specific cellular receptors to activate single or multiple ▶signal transduction pathway(s) leading to growth, ▶differentiation, embryogenesis or other biological processes. More than one hormone may work in concert to fulfill a physiological function. Hormones, through their capacity to influence cell growth and differentiation, may further modify the response of the body to carcinogens, the biological behavior of established tumors, and overall ▶cancer risk. Hormones, therefore, play an important role in both the genesis and treatment of cancer.

Characteristics Hormone-dependent malignancy has been most extensively studied in steroid hormone responsive organs. The steroid hormones, androgens, estrogens (▶Estradiol; estrogenic hormones and cancer) and progestins (▶Progestins and cancer), are implicated as key regulators in the development and the cancer process in the breast (▶Breast cancer), prostate (▶Prostate cancer, clinical oncology), ovary (▶Ovarian cancer) and endometrium (▶Endometrial cancer). More recently, however, hormonal influences in cancer are also becoming apparent in steroid hormone independent organs such as the colon. Likewise, non-steroid hormones participate, directly or indirectly, as modifiers of cancer, not only in endocrine system responsive organs, but also at other sites. Mechanisms The precise mechanisms of hormonal influences on cancer are being elucidated. In the context of the multistage theory of ▶carcinogenesis (▶Multistep development), it has been generally recognized that the principal effects of a given hormone are during the ▶cancer promotion stage, occurring predominantly in tissues where normal cellular growth and function are regulated by the specific hormone. Single or multiple hormones may interact to modify carcinogenesis. The tumor promoting effects of hormone(s) may be a result of indirect interaction of the hormone with the genome, culminating in epigenetic (▶Epigenetics) consequences. Recent evidence, however, implicates hormonal modulation during the ▶cancer initiation stage as well by direct

interaction of certain hormonal metabolites with the genetic material.

The Receptor Concept A receptor-mediated mechanism for hormone action during normal physiological functions is now widely accepted (Fig. 1). Hormones play a role as ligands that interact with specific receptors: the protein type binds to trans-membrane receptors, while the steroidal type binds to intracellular receptors. In the case of a protein hormone, a cascade of receptor-ligand mediated cytoplasmic responses is triggered leading to activation of post-receptor secondary messengers. On the other hand, a steroid hormone on entry into the cell forms cytoplasmic – receptor complexes that bind to DNA as a dimer. In both cases, recruitment of other co-factors ultimately regulate the activities of the cell’s general transcription apparatus assembled at the gene’s promoter. The mRNA produced is eventually translated into proteins which elicit and achieve a complex array of cellular responses such as alterations in growth and differentiation of the target tissue. An interplay of a variety of factors can interfere with the normal development and function of the ▶hormone receptors in target tissues, culminating in pathological conditions such as cancers. Thus, hormone receptors may be activated non-specifically by hormone-like endogenous metabolites or xenobiotic (▶Xenobiotics) ligands found as dietary constituents (e.g. ▶phytoestrogens), environmental pollutants, or food contaminating chemical or veterinary drug residues. Inherited genetic polymorphisms or mutations in hormone receptors and/ or hormone metabolizing enzymes may further affect normal hormonal function. In the case of steroid hormones, estrogens function as growth promoters through the nuclear receptors, estrogen receptor-α (ER-α) (▶Estrogen receptor) or ER-β by signal transduction-mediated increase in cellular proliferation, decrease in ▶apoptosis and regulation of growth factor production. ER-α and ER-β are products of two different genes, and ER-α may predominate in breast tumors. Likewise, androgen action on physiological processes such as cellular differentiation, secretory function, metabolism, morphology, proliferation and survival, is exerted in target tissues via binding to another nuclear receptor transcription factor, the ▶androgen receptor (AR). Testosterone, produced mainly in the testis, is able to directly bind to and activate the AR. However, the androgens produced in the adrenal glands, androstenedione and dehydroepiandrosterone, are converted to testosterone in peripheral tissues prior to their interaction with the AR. Similarly, in the prostate, testosterone is first metabolized to a more potent ligand dihydrotestosterone, before its interaction with the AR. The effects of progestins as

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Hormones. Figure 1 Schematic presentation of two types of receptor mediated hormonal action. Hormone binding to a trans-membrane or an intracellular receptor activates a cascade of events which eventually regulate the cell’s transcription and translation machinery to elicit a complex array of functional responses by the cell.

well are mediated through two isoforms of progesterone receptor in a tissue-specific manner. Prolactin exhibits dual characteristics of a circulating hormone and a ▶cytokine, both of which utilize receptor-mediated mechanisms. In its role as a cytokine, prolactin is secreted and regulated in extrapituitary sites where its binding to cytokine superfamily receptors not only can promote cell proliferation and survival, but also increase cell motility, suppress apoptosis, upregulate BRCA1 (▶Breast cancer genes BRCA1/ BRCA2), induce both ER-positive and ER-negative tumors, increase tumor growth rates (▶Prolactin and cancer), support tumor vascularization and enhance tumor metastases. Insulin and ▶insulin-like growth factors (IGF-I) likewise act through a receptor (▶Insulin receptor) -mediated mechanism to regulate energy metabolism. The bioactivity of IGF-I is increased through its enhanced synthesis and by a decrease in several of its binding proteins (IGFBP; IGFBP-1 and -2). Insulin and IGF-I both stimulate ▶anabolism based on the amount of available energy and the necessary substrates such as amino acids. The anabolic signals by insulin or IGF-I can promote tumor development by inhibiting

apoptosis, and by stimulating cell proliferation. Furthermore, both insulin and IGF-I stimulate the synthesis of sex steroids, and inhibit the synthesis of sex hormone-binding globulin, a binding protein that regulates the bioavailability of circulating sex steroids to tissues. Receptor-mediated mechanisms also intercede the action of thyroid hormone, and the gastrointestinal hormones gastrin, cholecystokinin, neurotensin and ▶gastrin-releasing peptide. Hence, the receptor concept provides one common mechanism whereby a steroid or a non-steroid hormone may potentially mediate or modulate cancer under the conditions that an aberration in its receptor-mediated signal transduction system favors an enhancement or prevention of neoplasia. Endogenous Metabolic Activation of Steroids A second mechanism of action implicated in hormonal modification of carcinogenesis involves endogenous metabolism of the steroid hormones, estrogen and androgens by tissue-specific enzymes (Fig. 2). A similar mechanism for non-steroid hormones has not been described so far. Estrogen is biotransformed by several ▶cytochrome P450 isoforms and various peroxidases

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Hormones

Hormones. Figure 2 Metabolic activation of steroid hormones. Aromatase-mediated metabolism of androgens to estrogens, and further oxidative metabolism of estrogens lead to genotoxic effects that may contribute to cancer induction.

to produce estrogenic metabolites that may be protective through their antioxidant properties or growth and ▶angiogenesis inhibitory activities. On the contrary, the more reactive quinone metabolites of estrogen may directly form ▶adducts with DNA and/or cause oxidative damage to lipids and DNA (▶Oxidative DNA damage) through redox cycling processes that produce ▶reactive oxygen species (ROS). Increased production of ROS may further alter regulation of gene expression through effects on transcription factor function. The androgens testosterone, androstenedione and dehydroepiandrosterone may act as additional cancer modifiers in situ in their respective target organs when they are metabolized first to estrogens by aromatase, another cytochrome P-450 enzyme, followed by their metabolic activation to quinones. Epidemiology and Animal Studies Steroid Hormones Breast cancer risk is associated with prolonged exposure to predominantly estrogens. Thus, increased in utero exposure to estrogens, early onset of ▶menarche, late ▶menopause, hormone replacement therapy and postmenopausal obesity enhance breast cancer incidence. Androgens, through their metabolism to estradiol by the aromatase enzyme expressed in epithelial cells of both normal and neoplastic breast, act synergistically with estrogens to directly stimulate tumor growth and increase breast cancer risk in postmenopausal women.

Androgens are further implicated as a causative factor in prostate cancer induction, though with limited epidemiological evidence (▶Epidemiology of cancer). Human plasma levels of androgens do not always correlate with prostate cancer susceptibility. Animal studies, however, support a strong tumor promoting role for androgens acting via androgen receptor-mediated mechanisms, and following a tumor-initiating stimulus. Exposure of the fetus to higher androgen concentrations is a potential ▶risk factor for prostate cancer in later life. However, as in the breast, malignant changes to the prostate gland depend upon both androgenic and estrogenic responses that are accomplished through aromatase mediated conversion of testosterone to estradiol and via estrogen receptors found in both human and rat prostate. Similar synergistic links between androgens and estrogens have been reported in uterine cancer in experimental animals, and clinically, in ovarian and endometrial cancers. Estrogen receptors are likewise expressed in several ▶gastrointestinal cancers such as those of the esophagus, gallbladder, stomach and colon (▶Colon cancer). Estrogens may further interact with additional growth factors and polyamines to modulate growth and progression (▶Cancer progression) of colorectal tumors. However, the epidemiological evidence for a role for estrogens in colorectal cancers is currently inconsistent. Loss or down-regulation of progesterone receptor observed in ovarian carcinoma, and antiproliferative

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and apoptotic effects of progesterone in the ovary, suggest that progestins protect against ovarian cancer. On the contrary, synthetic progestins, globally used as contraceptive agents, are implicated as tumor promoters or ▶cocarcinogens in rodent liver, pituitary and mammary gland.

specific G-protein-coupled receptors through which the gastrointestinal hormones stimulate cancer cell growth. Gastrointestinal hormone receptors have also been noted in breast, lung and prostate cancers where they may modify neoplastic growth and aggressive behavior of the lesions.

Prolactin The neuroendocrine hormone prolactin may play a role in several types of cancers in reproductive and nonreproductive tissues. Its possible role in breast cancer has been widely considered because of its physiological action in the stimulation of mammary gland development and differentiation during puberty, pregnancy, and lactation. While experimental data support a relationship between increased prolactin levels and breast cancer, epidemiological data is discrepant.

Thyroid Hormones An association between thyroid hormones and cancer has been considered extensively with conflicting results. In experimental models, perturbations in thyroid hormones affect estrogen and prolactin secretion, and cause pathological alterations in the ovary, endometrium and breast that are consistent with precancer. However, clinical evidence for the role of thyroid hormones in cancers in these organs is not definitive due to difficulties in differentiating thyroid hormoneinduced cellular alterations from neoplasia-induced cellular atypia.

Insulin Physiologically, the growth hormone insulin-like growth factor-I (IGF-I)-axis is an important modulator of growth and development, as well as a regulator of a wide range of biological functions. Their potent mitogenic and anti-apoptotic effects, for example, play a critical role in the development of the breast, and in regulation of rapidly renewing epithelial cell populations such as those in the colon. In cancer patients, increased insulin production is commonly observed during cancer development. Some types of tumors produce constituents that stimulate insulin secretion by the pancreas, while other more aggressive tumor types produce insulin ectopically. Global variations in cancer incidence rates provide evidence for diet and associated factors such as nutritional energy balance, macronutrient composition of the diet, physical activity and body size (▶Obesity and cancer risk) as among the most important lifestyle factors that influence cancer risk (▶Nutritional status and cancer). Recent studies further suggest that these dietary and related factors may influence the risk of cancers of the colon, pancreas, endometrium, breast, ovary and prostate by affecting the levels of circulating serum insulin and increasing the bioavailability of IGF-I. IGF-I has been positively associated with the risk of colorectal cancer in human studies. In vitro, IGF-I elicits mitogenic and anti-apoptotic actions on colorectal cancer cells. Gastrointestinal Hormones The gastrointestinal hormones (▶GI hormones), gastrin, cholecystokinin, neurotensin and gastrin-releasing peptide (▶Gut peptides), are localized mainly in the pancreas and in the mucosa of the gastrointestinal tract from the stomach to the rectum. Certain gastric (▶Gastric cancer), pancreatic (▶Pancreas cancer, basic and clinical parameters) and colorectal cancers possess

Hormonal Management of Cancer Recognition of the role of estrogens in the stimulation of breast tumor growth has led to the development of several therapeutic endocrine agents. In premenopausal women ▶gonadotrophin-releasing hormone (GnRH) agonists suppress ovarian oestrogen synthesis and reduce estradiol close to postmenopausal levels. Inhibition of aromatase, the terminal step in estrogen biosynthesis, provides another way of treating hormone-dependent breast cancer in older patients. Currently available ▶aromatase inhibitors are effective in the management of hormone-dependent breast cancer in post-menopausal women failing antiestrogen or tamoxifen therapy (▶Tamoxifen) in locally advanced or metastatic disease. GnRH agonists used in combination with an aromatase inhibitor suppress estrogen levels even further. Similarly, hormone therapy for prostate cancer has evolved from the use of estrogens to GnRH agonists. Recently, investigational GnRH antagonists have been discovered that cause the inhibition of luteinizing hormone production, eventually leading to a suppression of testosterone and dihydrotestosterone on which continued growth of prostate cancer cells is dependant. Steroid hormone receptors are another well established therapeutic target in cancer, and drug development has continued to focus on agents that either block steroid hormone production or bind to and modulate their receptors. The implication of insulin and IGF-I as additional factors in cancer modulation may further advance development of newer cancer prevention drugs that restore sensitivity to insulin and reduce hyperinsulinemia. ▶Celecoxib ▶Estrogenic Hormones ▶Hormonal Carcinogenesis

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Hornstein–Knickenberg syndrome

References 1. Argiles JM, Lopez Soriano FJ (2001) Insulin and cancer. Int J Oncol 18:683–687 2. Ben Jonathan N, Liby K, McFarland M et al. (2002) Prolactin as an autocrine/paracrine growth factor in human cancer. Trends Endocrinol Metab 3:245–250 3. Bernstein L (2002) Epidemiology of endocrine-related risk factors for breast cancer. J Mammary Gland Biol Neoplasia 7:3–15 4. Bosland MC (2000) The role of steroid hormones in prostate carcinogenesis. J Natl Cancer Inst Monogr 27:39–66 5. Yager JD, Davidson NE (2006) Estrogen carcinogenesis in breast cancer. N Engl J Med 354:270–282

may regulate gene expression, morphogenesis, and differentiation. ▶Methylation of this gene may result in the loss of its expression and, since the encoded protein up-regulates the tumor suppressor p53, this protein may play an important role in tumorigenesis. ▶Pleiotrophin ▶P53 Family

HOXA9 Hornstein–Knickenberg syndrome ▶Birt–Hogg–Dubé Syndrome

Definition Is a member of the abdominal-B subclass of HOX genes and plays important roles in normal hematopoiesis as well as in leukemia development. ▶NUP98-HOXA9 Fusion

HOX Definition The HOX homeodomain (HD) proteins are DNAbinding transcription factors that are key regulators of development and hematopoiesis. In vertebrates, there are 39 HOX genes that are organized into four chromosomal clusters (HOXA, B, C and D), which can be classified into 13 paralogous groups based on their extensive sequence homology within the HD and their relative chromosomal locations within a cluster. HOX genes are expressed at various stages during hematopoietic development. Perturbation of orderly HOX gene activation and inactivation results in hematological abnormalities. Increased expression of HOXA and B genes has been documented in human acute myeloid malignancies. ▶NUP98-HOXA9 Fusion

HOXA5 gene

HpaII Tiny Fragments (HTF) Islands ▶CpG Islands

HPAEC Definition

Human pulmonary artery ▶endothelial cells.

HPD

Definition Is part of the A cluster of HOX genes on chromosome 7 and encodes a DNA-binding transcription factor that

Definition

▶Hematoporphyrin derivative

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HPRT

HSC

Definition

Definition

Hypoxanthine phosphoribosyl transferase.

Hematopoietic stem cell. HSCs are multipotent stem cells found in the bone marrow and give rise to all the cell types of both the myeloid and lymphoid lineages.

▶Microcell-Mediated Chromosome Transfer

▶Adult Stem Cells

hPTTG1 HSD18 ▶Securin ▶Methylation-Controlled J Protein

HPV ▶Human Papillomaviruses

HRPC Definition

HSF ▶Interleukin-6

HSF-III ▶Leukemia Inhibitory Factor

▶Hormone refractory prostate cancer

hSNF5 HS1

▶hSNF5/INI1/SMARCB1 Tumor Suppressor Gene

Definition Hematopoietic Specific protein 1 is a protein found exclusively in leukocytes that is functionally similar to cortactin. It is a component of the ZAP 70 and Syk tyrosine kinase signaling pathways activated during the immune response. ▶Cortactin

HSNF5/INI1 Definition

▶Tumor Suppressor hSNF5/INI1.

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hSNF5/INI1/SMARCB1 Tumor Suppressor Gene

hSNF5/INI1/SMARCB1 Tumor Suppressor Gene F RANCK B OURDEAUT 1 , PAUL F RE´ NEAUX 2 1

Département de pédiatrie, INSERM 830, Biologie et génétique des tumeurs, Institut Curie, Paris, France 2 Département de Pathologie, Institut Curie, Paris, France

Synonyms hSNF5; Human non sucrose fermenting 5; SMARCB1; SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin subfamily b, member1; BAF47; BRG- and BRM-associated factor, 47 kDa

Definition hSNF5/INI1 is a member of the highly conserved ▶SWI/SNF complex, involved in the ATP-dependent ▶chromatin remodeling. hSNF5/INI1 acts as a ▶tumor suppressor gene.

Characteristics The Chromatin Remodeling and the SWI/SNF Complex In the nucleus of eukaryotic cells, DNA is wrapped around histones, constituting a dense histone–DNA complex referred to as nucleosomes. The closed conformation of DNA in nucleosomes precludes the binding of transcription factors to their target promoters. By regulating the compaction degree of nucleosomes, cells can allow interactions between promoters and transcription factors. This regulation relies on two main mechanisms: (i) stable covalent modifications of histones, including actelyation, methylation, ubiquitination, etc. (ii) ATP-hydrolysis-dependent chromatin remodeling, capable to affect the spatial organization of the

chromatin and the stability of nucleosomes in a dynamic way. The SWI/SNF complex, first described in Saccharomyces cerevisia, is the prototype of ATP-dependent chromatin remodeling complex. Approximately 5% of the genome is affected by the SWI/SNF-dependent regulation of the transcription, either by induction or by repression (Fig. 1). The SWI/SNF complexes are conserved throughout the evolution. In humans, chromatography has lead to identify two fractions of SWI/SNF complexes, PBAF or SWI/SNF-B, characterized by the presence of polybromo protein, and BAF or SWI/SNF-A, which may be the actual homolog of yeast SWI/SNF. The BAF complexes are variably composed of approximately ten subunits, in a cell-type-specific manner. However, all BAF complexes contain one of the two ySnf2 human homologs, hBRM or hBRG1 (Fig. 2). Either of them brings the ATPase activity of the complex. In vitro, hBRG1 and hBRM are sufficient to induce a chromatin remodeling. Nevertheless, the addition of other members of the core complex increases the efficiency of the remodeling. Furthermore, the integrity of the entire complex seems to be indispensable in vivo. Among the BAF proteins, at least three are ubiquitously expressed, demonstrating a critical role in the function of the complex: BAF155, BAF 170 and BAF47. Altogether, these indispensable subunits constitute the core complex of SWI/SNF. The latter, BAF47, maintains the stability of the whole complex in yeasts but might not play such a role in mammals. Since its interaction with the HIV1 integrase IN was its first role identified, it has been called “INI1.” hSNF5/INI1 Gene and Protein Structures In human, hSNF5/INI1 gene is located in 22q11.2. It is composed of nine exons and spreads over 50 kb (Fig. 3a). An alternative splicing in exon 2 produces two

hSNF5/INI1/SMARCB1 Tumor Suppressor Gene. Figure 1 Chromatin remodeling and regulation of transcription. The chromatin is wrapped around histones. Acetyl or methyl radicals are added or removed by histone acetyltransferases (HAT) or histone deacetylases (HDAC) and histone methyl transferases (HMT) and histone demethylases (HDMT) respectively. ATP hydrolysis (ATP = ADP + Pi) also participates to a direct chromatin remodeling through the ATPase activity of remodeling complexes such as SWI/SNF, regulating the accessibility of the chromatin to transcriptions factors (TF).

hSNF5/INI1/SMARCB1 Tumor Suppressor Gene

different transcripts of 1155 and 1128 nucleotides. hSNF5 protein has strong homologies with other SWI/ SNF proteins in various species (yeast Snf5, Drosophila dSNR1, Caenorhabditis elegans CeSnf5). The homology domain encompasses 193 amino acids and two highly conserved repeated sequences, Rpt1 and Rpt2 (Fig. 3b). This repeated domain brings a nuclear export signal, consistent with the subcellular localization of the protein. Rpt1 directly interacts with several partners, such as HIV IN, c-MYC, hBRM or ALL1. A coiled-coil domain at the C-terminal extremity plays a role in the binding to interaction partners. Biological Roles of hSNF5/INI1 Studies of Snf5 inactivation in cell and mouse models have brought numerous insights on Snf5 biological

hSNF5/INI1/SMARCB1 Tumor Suppressor Gene. Figure 2 The SWI/SNF complex. SWI/SNF complexes are composed of up to 12 proteins. Alternatively hBRM or hBRG1 carries the ATPase activity. The other proteins of the core complex are BAF155, BAF170, and BAF47.

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functions. First, there are some strong evidences of Snf5 being involved in cell survival. Indeed, complete inactivation of Snf5 leads to early embryonic lethality and decreases cell survival in vitro. In MEFs, loss of Snf5 also impairs the cell cycle progression and, consistently, alters the expression of various Rb-E2fresponsive genes. Furthermore, the defect of Snf5 enhances sensitivity to DNA damage and subsequent apoptosis through a p53-dependent manner. These paradoxical roles in survival and apoptosis might be time-, cell-type- and stress-dependent. However, the most relevant observation is that conditional inactivation of Snf5 leads to the development of a tumor in 100% of the mice. Moreover, the short median delay of 11 weeks before tumor development is rarely observed with the inactivation of a single gene, and indicates a tremendously potent tumor suppressor role for SNF5. To which extent the tumor suppressor function of SNF5 depends on SWI/SNF remains unclear. However, reexpression of hSNF5/INI1 in rhabdoid cells has demonstrated its critical role in the control of the ▶G1– S transition. This effect could rely either on a repressive effect upon ▶Cyclin D1 expression, or on a strong induction of ▶p16/INK4a. Interestingly, a functional RB protein is required for INI1-dependent cycle control, whereas INI1 is dispensable for normal RBmediated growth arrest (Fig. 4). Hence, INI1 definitely acts upstream RB. However, the control of the G1–S transition may not fully explain the antioncogenic role of hSNF5/INI. Indeed, missense mutations do not affect the replication checkpoint, but might rather lead to polyploidy by promoting chromosomal instability and compromising the mitotic checkpoint. Furthermore, there has been evidence for the involvement of hSNF5/INI1 in

hSNF5/INI1/SMARCB1 Tumor Suppressor Gene. Figure 3 hSNF5/INI1 gene and protein structure. Interacting proteins are indicated in front of the Rpt2 domain. a. Structure of the gene: 9 exons encompassing ~50 kb. b. Structure of the protein with the highly conserved hemology domain.

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hSNF5/INI1/SMARCB1 Tumor Suppressor Gene

hSNF5/INI1/SMARCB1 Tumor Suppressor Gene. Figure 4 hSNF5/INI1 and the G1–S transition. Arrows in green and red indicate respectively a positive and negative regulation. Dot lines indicate not fully consensual links. SWI/SNF has a physical interaction with RB and directly coregulates E2F1 transcription. hSNF5/INI1 on its own represses the G1 to S transition. This effect can be due either to CCND1 downregulation or to p16/INK4a over expression. hSNF5/INI1 acts upstream RB.

dynamic regulation of the cytoskeleton. The restoration of the hSNF5/INI1 gene in rhabdoid cells alters the expression of Rho-family genes, likely to modulate the cytoskeleton, and obviously modifies the organization of actin stress fibers. hSNF5/INI1 might therefore play a role in cellular adhesion and migration properties. Finally, taking into consideration the critical role of chromatin remodeling in the activation of celltype-specific genetic programs, the role of hSNF5/INI1 in driving cell differentiation has also been investigated. INI1-dependent differentiating effect has been observed in hepatocytes. Conversely, reexpression of hSNF5/INI1 in rhabdoid cell lines drives distinct differentiation phenotypes according to the cell anatomic origin. A critical impairment of INI1-dependent differentiation programs may account for the highly undifferentiated phenotype of hSNF5/INI1-deficient tumors. Genetic Alterations of hSNF5/INI1 in Human Malignancies Deletions encompassing the hSNF5/INI1 locus are encountered in many tumor types, including ▶rhabdoid tumors (RTs), ▶proximal epitheliod sarcomas (PES), meningiomas, schwannomas. Biological effects of hemizygous INI1 deletions are questionable, since loss of one allele results only in a 15–20% reduction in total INI1 mRNA levels due to transcriptional compensation by the remaining allele. Hence, “two-hit” events only are likely to drive transformation. Strikingly, biallelic inactivation is encountered in about 80% of rhabdoid

tumors. Karyotypic analyses in RTs usually show no or few other alterations than deletions or translocations of 22q11. Altogether, this indicates a very strong association between hSNF5/INI1 extinction and RTs. Both homozygous deletions and hemizygous deletions with point mutations are encountered. In RTs cell lines, mitotic recombinations of chromosome 22q and nondisjunction/duplication, lead to partial or complete uniparental disomy. This mechanism may account for most homozygous changes and result in the total or partial loss of one chromosome associated with the duplication of the remaining chromosome carrying the deleted or mutated allele. The association of a point mutation with a whole gene deletion is less frequently encountered, but seems to be preponderant in ▶brain tumors. Point mutations, consisting in nucleotides replacement, deletion or insertion and leading to truncating nonsense codons, are spread all over the nine exons with no obvious hotspot. Missense mutations are much rarely reported. Studies using immunohistochemistry with antiSMARCB1 antibody have confirmed the total loss of protein expression in a high proportion of RTs as a direct consequence of the genetic alterations. Whether hSNF5/INI1 inactivation is specific for RT or could be involved in miscellaneous other tumors remains not fully consensual (see next section). Congenital multifocal rhabdoid tumors and familial cases strongly supported the existence of constitutional mutations in a predisposing syndrome. Indeed, about 40

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hSNF5/INI1/SMARCB1 Tumor Suppressor Gene. Figure 5 pathological aspects of hSNF5/INI-deficient ▶rhabdoid tumor. (a) “Rhabdoid” cells: discohesive polygonal or round cells with abundant cytoplasm, juxtanuclear globular eosinophilic cytoplasmic inclusion, large nucleus with one prominent nucleolus. (b) negative staining of rhabdoid cells with anti-hSNF5/INI1 antibody, resulting from a complete loss of the protein and the biallelic inactivation of hSNF5/INI1 gene. Positive staining is retained in normal stromal cells.

germline mutations have been reported so far, associated to the development of a tumor during early childhood in almost all patients. Hence, the penetrance is very high, though not full. Nucleotides or whole gene deletions, point mutations and splice site changes have all been observed at the constitutional level. Pathological and Clinical Aspects of hSNF5/ INI-Deficient Tumors RTs were initially described as highly aggressive variants of Wilm tumors occurring in infants (▶Nephroblastoma). “Rhabdoid” cells were defined by key morphologic histological and immunophenotypical features: polygonal or round shape with abundant cytoplasm, juxtanuclear globular eosinophilic cytoplasmic inclusion, large nucleus with one prominent nucleolus (Fig. 5a), coexpression of vimentin and epithelial markers such as epithelial membrane antigen and/or cytokeratins. Such features were then observed in other pediatric malignancies, in brain (Atypical Teratoid/Rhabdoid Tumors) (Brain tumors) and miscellaneous soft-tissues. Presently, the cell origin of RTs remains unknown. The actual incidence of RTs may still be underestimated since those rare tumors are frequently misdiagnosed. However, immunohistochemistry with a monoclonal anti-hSNF5/INI1 antibody is very sensitive and highly specific for the detection of hSNF5/INI1 loss-of-function (Fig. 5b), and should now facilitate the diagnosis of most RTs. hSNF5/INI1 biallelic genetic inactivation has also been reported in other types of ▶childhood cancers such as central PNET (▶Medulloblastoma, deleted in malignant brain tumors), choroid plexus carcinomas, and in a small subset of undifferentiated malignant tumors without evidence of “rhabdoid” morphological features. In adults

interestingly, in which RTs are thought to be much rarer, hSNF5/INI1 complete defect has also been observed in some “proximal-type” of epithelioid sarcomas (▶Proximal-type epithelioid sarcomas), and, marginally, in composite tumors with “rhabdoid” component. hSNF5/ INI1 deficiency might therefore account for a wider spectrum of tumors. Nevertheless, it still remains unclear whether these different malignancies should be considered as phenotypical variants of a same biological entity. In accordance with this hypothesis, they usually share with typical RTs a highly aggressive clinical behavior. Conclusion There are increasing evidences of chromatin remodeling being a critical process in oncogenesis. hSNF5/INI1 offers a convincing example as a tremendously potent tumor suppressor gene. In humans, hSNF5/INI1 inactivation is strongly associated with rhabdoid tumors, but may not be as restricted to these children malignancies as previously thought. Identification of hSNF5/INI1 involvement in human cancers has given helpful diagnostic tools, based on molecular screening and specific anti-hSNF5/INI1 immunohistochemistry. Better knowledge on hSNF5/INI1 roles in oncogenesis should lead to more efficient targeted therapies, and improve the dramatically poor prognosis of hSNF5/ INI1-deficient tumors.

References 1. Roberts CW, Orskin SH (2004) The SWI/SNF complexchromatin and cancer. Nat Rev Cancer 4:133–142 2. Robert CW, Leroux MM, Fleming MD et al. (2002) Highly penetrant, rapid tumorigenesis through conditional inversion of the tumor suppressor gene Snf5. Cancer Cell 2:415–425

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3. Imbalanzo AN, Jones SN (2005) Snf5 tumor suppressor couples chromatin remodelling, checkpoint control, and chromosomal stability. Cancer Cell 7:294–295 4. Versteeg I, Sevenet N, Lange J et al. (1998) Truncating mutations of hSNF5/INI1 in aggressive paediatric cancer. Nature 394:203–206 5. Sevenet N, Lellouch-Tubiana A, Schofield D et al. (1999) Spectrum of hSNF5/INI1 somatic mutations in human cancer and genotype-phenotype correlations. Hum Mol Genet 8:2359–2358

HSP Definition Heat shock protein. HSP89α, HSP90β; the HSP89α and HSP90β genes are composed of 11 and 12 exons, respectively. The regulation of HSP gene expression in eukaryotes is mediated by the conserved heat shock transcription factor (HSF). HSF acts through heat shock elements (HSEs) composed of three contiguous inverted repeats of a 5 bp sequence, nGAAnnTTCn; upon heat stress, HSF binds to HSEs as a trimer. ▶Hsp 90

Hsp60 Definition Heat shock proteins that acts as molecular chaperones in complex in bacteria and eukaryotes; the Hsp60/ Hsp10 complex is important for import and folding of key proteins into mitochondria. ▶Molecular Chaperones

Hsp90 P HILIP J. T OFILON Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA

Synonyms Heat shock protein 90

Definition

Hsp90, the 90-kDa heat shock protein, is a ▶molecular chaperone that regulates the degradation, folding and/or transport of a diverse set of critical cellular regulatory proteins. Most Hsp90 clients, i.e. those proteins that require its “chaperoning” activity for appropriate function, participate in some aspect of signal transduction including a wide variety of protein kinases, hormone receptors, and transcription factors. Moreover, Hsp90 can stabilize mutated proteins allowing them to maintain normal function despite genetic abnormalities. This ability to buffer genetic changes and serve as a capacitor of phenotypic variation has implicated Hsp90 in evolutionary and oncogenic processes.

Characteristics Hsp90 is an ATP-dependent molecular chaperone and is one of the most highly expressed proteins in eukaryotic cells. There are two major isoforms of Hsp90, the major form Hsp90α and the minor form Hsp90β. The two hsp90 genes differ primarily in their non-coding and regulatory regions. Both the α and β proteins consist of four basic structural domains. The N-terminal domain is the site of ATP binding and is essential for its chaperone function. Inhibitory agents, at least those developed to date, specifically target this site preventing ATP binding and consequently Hsp90 function. The N-terminal domain is connected to the middle domain by a small highly charged linker region that is thought to be the site for co-chaperone binding. The larger middle domain contains the site for client protein binding and the C-terminal domain provides the dimerization site, which is essential for Hsp90 activity. The Hsp90 proteins function as homodimers of α/α and β/β. Whereas there does appear to be functional differences between the isoforms with β being associated with development, there is also considerable overlap. Although the majority of Hsp90 is located in the cytoplasm, this molecular chaperone can also be found in the nucleus, albeit at considerably lower levels, where it has been associated with the regulation of gene expression and the ▶DNA damage response to radiation. In addition, Hsp90 is located on the cell surface where it plays a role in antigen processing and the immune response. Finally, recent studies have shown that Hsp90 can be secreted into the extracellular space. Although the specific function has not been clearly defined, in this location Hsp90 has been suggested to play a role in blood clotting, cell migration and tumor metastatic processes. Mechanism Hsp90 chaperone function is mediated by an ATPdependent cycling between two conformations, which regulates its interactions with specific co-chaperones

Hsp90

and co-factors and drives the loading and off loading of client proteins. The Hsp90 dimer typically exists in a multi-protein chaperone complex that includes the co-chaperones Hsp70 (70-kDa heat-shock protein) and Hsp40 (40-kDa heat-shock protein), the adaptor protein HOP (hsp co-chaperone organizing protein) and the cofactor p23. In addition, there are specific immunophilins and other co-chaperones that regulate substrate binding. For example, the co-chaperone ▶Cdc37 is involved in Hsp90-mediated stabilization of protein kinases. A client protein initially binds to the Hsp70/Hsp40 complex, which links via HOP to an ADP-bound Hsp90. Exchanging ADP with ATP alters Hsp90 confirmation such that HOP and Hsp70/Hsp40 are released and p23 and other co-chaperones such as Cdc37 are recruited to the complex. In the ATP-bound confirmation and associated with these co-chaperones Hsp90 folds and stabilizes a client protein maintaining it in a responsive conformation. Although the specific processes have not been completely defined, in the absence of the appropriate stimulus or ligand binding to the client protein, Hsp90 through its ATPase activity cycles back to its ADP-bound conformation recruiting the initial set of co-chaperones, which ultimately leads to client protein degradation. Considerable insight into the mechanism of Hsp90 chaperone activity has been generated through the use of the inhibitor ▶geldanamycin. This benzoquinone ansamycin binds to the nucleotide binding site of Hsp90 resulting in a conformation that resembles the ADP-bound conformation. The inability of Hsp90 to cycle to its ATP-bound conformation then maintains the chaperone complex in a state that favors client protein degradation. Studies to date indicate that in cells treated with geldanamycin or one of its analogs the half lives of the Hsp90 client proteins are uniformly and significantly reduced. Clinical Aspects As a Single Modality Hsp90 has received considerable attention as a potential target for cancer therapy. Because of an increased understanding of the mechanisms and molecules that mediate malignant transformation, recent strategies in cancer therapy have begun to focus on a target-based approach. The putative advantages of this strategy include tumor selectivity sparing normal cells and the availability of markers indicative of tumor susceptibility. Most attempts to apply target based therapy have entailed the use of agents that target a single molecule. For tumors in which their phenotype is driven by a single oncogenic molecule, such as the targeting of Bcr-Abl by ▶STI571 in chronic myelogenous leukemia and ▶Her2/neu by ▶Herceptin is certain breast tumors, this approach has demonstrated clinical activity. However, most tumors, especially solid neoplasms, contain multiple genetic abnormalities and are subject to a high degree of genomic

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instability. The result is that their malignancy/survival is driven by variety of molecules existing in a number of different survival pathways. Under these circumstances, targeting a single molecule is likely to be of limited consequence. As an alternative to targeting a single molecule, inhibiting Hsp90 provides a multi-target approach to cancer treatment. Hsp90 client proteins include a large number kinases, receptors and transcription factors that have been implicated in transformation and maintenance of the malignant phenotype. Examples of such proteins dependent on Hsp90 include ErbB2 (▶Her2/Neu), Src, ▶Akt, ▶c-Raf-1, cyclin dependent kinases Cdk4 and Cdk6, HIF1-α, estrogen and androgen receptors and hTERT. Thus, Hsp90 inhibition provides a means of simultaneously targeting multiple proteins critical to a malignant cell. In addition, Hsp90 can stabilize mutant proteins (e.g. ▶p53) allowing for at least some functional activity. Given the level of genomic abnormalities and instability of tumor cells, the ability to buffer against such genetic variation suggests another avenue through which Hsp90 contributes to tumor cell survival. In laboratory studies exposure of tumor cells to Hsp90 inhibitors such as geldanamycin and its analogs 17-allylaminogeldanamycin (17-AAG) and 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) results in the combinatorial decrease in its client proteins mentioned above as well as additional client proteins, although there is some cell type specificity. With respect to a potential cancer therapy, inhibition of Hsp90 induces tumor cell death or significantly slows their proliferation in a number of in vitro and in vivo experimental systems, although the critical target or targets (i.e., client proteins) for the most part have not been defined. An additional characteristic that supports the application of Hsp90 inhibitors in cancer treatment is their relative selectivity for tumor cells over normal cells. The molecular basis for this selectivity has not been clearly defined. However, Hsp90 is typically expressed at higher levels in tumor cells than normal cells suggesting that tumors may be more dependent on its chaperoning activity. Regardless of the specific mechanisms involved, the ability of Hsp90 inhibitors to preferentially kill tumor cells over normal has led to the ongoing evaluation of 17AAG and 17DMAG in clinical trials as single modality agents. In Combination with Radiotherapy Hsp90 has also been identified as a determinant of tumor cell ▶radiosensitivity. Among Hsp90 clients are included a number of proteins (e.g. Raf-1, Akt and ErbB2/Her2/ Neu) that have been associated with protection against radiation-induced cell death; a reduction in their individual activities has been shown to result in radiosensitization in some, but not all tumor cell lines. Tumor cell radiosensitivity is regulated by a wide variety of signaling

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molecules with their specific contributions often determined by cell type. Because Hsp90 inhibitors induce the simultaneous loss of a number of these molecules that can potentially affect radiosensitivity, the use of these agents allows for implementing a multi-target approach to ▶radiosensitization. The putative advantages of such a multi-target strategy are increases in the degree and probability of radiosensitization. Indeed, inhibitors of Hsp90 such as geldanamycin, 17AAG, 17DMAG and radicicol have been shown to significantly enhance the radiosensitivity of a number of tumor cell lines derived from a variety of histologies. As for Hsp90 inhibitor treatment alone, the inhibitors have little to no effect on the radiosensitivity of normal cells evaluated in vitro. This lack of normal cell radiosensitization occurs despite a similar reduction in client proteins suggesting that it is not the difference between Hsp90 per se in tumor and normal cells, but the actions of its client proteins. Mechanistic studies of the tumor cell radiosensitization induced by 17DMAG have implicated Hsp90 in two components of the DNA damage response – DNA double strand break repair and ▶cell cycle checkpoint activation. The inhibition of double strand break repair could be traced to the loss of ErbB2 (Her2/neu) in 17DMAG treated cells and the consequent reduction in ErbB1 (EGFR) activity, which leads to a reduction in the ErbB1 interaction with DNA-PKcs and the subsequent attenuation of ▶DNA-PK activation after irradiation. The abrogation of cell cycle checkpoint activation by 17DMAG was associated with a reduction in radiation-induced activation of ▶ATM, which was the result of a reduced interaction between ▶NBS1 and ATM. Whereas most studies regarding Hsp90 as a target for cancer treatment have focused on its cytoplasmic activities, these radiation studies indicate that this chaperone has a critical role within the nucleus. The contribution of Hsp90 to double strand break repair and cell cycle checkpoint activation in tumor cells suggests that its inhibition may also be of benefit in combination with chemotherapeutic agents that kill tumor cells through DNA damage.

References 1. Dote H, Burgan WJ, Camphausen K et al. (2006) Inhibition of Hsp90 compromises the DNA damage response to radiation. Cancer 66:9211–9220 2. Eustace BK, Jay DG (2004) Extracellular roles for the molecular chaperone, hsp90. Cell Cycle 3:1098–1100 3. Sangster TA, Lindquist S, Queitsch C (2004) Undercover: causes, effects and implications of Hsp90-mediated genetic capacitance. BioEssays 26:348–362 4. Sharp S, Workman P (2006) Inhibitors of the Hsp90 molecular chaperone: current status. Adv Cancer Res 95:323–348 5. Sreedhar AS, Kalmar E, Csermely P et al. (2004) Hsp90 isoforms: functions, expression and clinical importance. FEBS 562:11–15

HSPG Definition Heparan sulfate proteoglycan; extracellular matrix protein containing heparan-sulfate polysaccharide chains. ▶Wnt Signaling ▶Proteoglycans

HSR Definition Homogeneously staining region. ▶Amplification

HSV-TK/Ganciclovir Mediated Toxicity D ONNA S HEWACH Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, USA

Synonyms Suicide gene therapy; Gene directed enzyme-prodrug therapy; GDEPT

Definition

A form of ▶suicide gene therapy in which the cDNA for a viral enzyme, the herpes simplex virus thymidine kinase (HSV-TK), is transferred to tumor cells followed by treatment with the antiviral drug ganciclovir (GCV). Expression of HSV-TK enables cells to phosphorylate GCV to a monophosphate derivative. Cellular enzymes convert the monophosphate to GCV triphosphate, which elicits toxicity through incorporation into DNA.

Characteristics HSV-TK/GCV mediated killing of tumor cells, and indeed suicide gene therapy in general, has been developed as a mechanism to improve the selectivity of cancer chemotherapy. Since traditional antitumor drugs target rapidly dividing tissues, such as tumor cells, they also can destroy normal dividing host tissue

HSV-TK/Ganciclovir Mediated Toxicity

such as cells in the bone marrow, gastrointestinal tract, or hair follicles. Normal tissue toxicity is the major impediment to traditional chemotherapy. With HSVTK/GCV therapy, a foreign gene (encoding HSV-TK) which can activate a normally innocuous ▶prodrug (GCV) to a toxic product is transferred selectively to the tumor. When the patient is treated with the prodrug, only the tumor cells expressing the foreign gene will be affected (thus the designation of “suicide” gene therapy); since normal host tissues cannot activate the prodrug, they are spared from toxicity. Toxicity to HSV-TK-Expressing Cells GCV is an acyclic analog of 2′-deoxyguanosine that requires phosphorylation for biologic activity (Fig. 1). It was originally discovered as an antiherpesvirus agent, and it is used clinically in the treatment of cytomegalovirus infection. When herpes simplex virus infects human cells, a number of proteins are expressed from the viral genome to facilitate virus replication and spread. One of these proteins, HSV-TK, contrasts with mammalian thymidine kinase in that it can phosphorylate purine as well as pyrimidine nucleoside substrates and their analogs. GCV serves as a substrate for HSV-TK with a Km value of 50 μM, but it is not an efficient substrate for any of the mammalian nucleoside kinases thus accounting for its selectivity in herpesvirus-infected cells. Following subsequent phosphorylation by mammalian kinases to its triphosphate metabolite, the drug is incorporated into the viral DNA leading to cessation of replication. Based on this mechanism of selectivity, it was proposed that tumor cells genetically engineered to express HSV-TK would be killed when treated with GCV. Proof of this principle was first shown in murine sarcoma cells, and since then numerous reports have demonstrated similar results in many different cell types. At the triphosphate level, GCV can compete with the endogenous 2′-deoxyguanosine 5′-triphosphate (dGTP)

HSV-TK/Ganciclovir Mediated Toxicity. Figure 1 Structure of GCV.

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for incorporation into DNA by mammalian DNA polymerases. Since GCV has the equivalent of both the 5′ and 3′ hydroxyls of deoxyguanosine, it can be incorporated into DNA and allow further extension of the DNA strand (internucleotide addition). In contrast, the structurally related ▶acyclovir lacks the equivalent of a 3′ hydroxyl group, and thus is an obligate DNA chain terminator. GCV and its metabolites do not interfere with RNA or protein synthesis. The incorporation of GCV monophosphate into DNA is the primary lesion that results in cell death. For some cell types, GCV induces cell death through ▶apoptosis (Fig. 2). Compared to other substrates for HSV-TK, such as acyclovir, GCV is significantly more toxic and more mutagenic to cells that express HSV-TK. The action of acyclovir is primarily ▶cytostatic, whereas GCV induces cell killing at low, clinically achievable concentrations. Although GCV triphosphate accumulates in cells to a relatively low level of 10–20 μM, this is sufficient to produce several logs of cell death. This high toxicity may be attributable to the avid incorporation and lengthy retention of GCV into DNA. GCV triphosphate and its incorporation into the nascent DNA strand do not produce strong inhibition of DNA synthesis, so cells incorporate high levels of this drug, complete DNA replication and go on to divide. Daughter cells become irreversibly blocked when they enter S-phase, suggesting that GCV monophosphate cannot serve as a template for DNA replication. A

HSV-TK/Ganciclovir Mediated Toxicity. Figure 2 Mechanism of Cytotoxicity for GCV in HSV-TKExpressing Cells and Bystander Cells. GCV is selectively phosphorylated to the monophosphate in HSV-TK expressing cells. Further phosphorylation can be accomplished by cellular enzymes. GCV triphosphate competes with the endogenous dGTP for incorporation into DNA, leading to cell death. GCV at the mono-, di- or triphosphate level can be transferred directly to bystander (non-HSV-TK-expressing) cells via GJIC channels, resulting in its incorporation into DNA of bystander cells with subsequent cytotoxicity.

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strong G2/M block has also been observed in some cell types after GCV treatment. The cell cycle position in which cells become blocked may depend on the concentration of GCV. Toxicity to Non-HSV-TK-Expressing Cells (▶Bystander Effect) With current gene transfer technologies, only a small percentage of tumor cells will express the foreign gene. For this approach to be successful in cancer treatment in patients, there must be a mechanism by which cells that do not express the ▶transgene (bystander cells) can be killed. It was noted early on that when only a fraction of the cell population expressed HSV-TK, treatment with GCV resulted in killing of both the HSV-TK-expressing and HSV-TK-nonexpressing bystander cells. The strong cell killing ability of GCV in HSV-TK-expressing and neighboring bystander cells has resulted in complete regressions of experimental tumors in animals, spurring clinical interest in this approach. In suicide gene therapy, bystander cell killing generally occurs through the transfer of a toxic metabolite, produced in the transgene-expressing cell, to bystander cells. The bystander cell killing with HSVTK/GCV was an unexpected finding since the toxic metabolite, GCV triphosphate, is negatively charged and therefore would not readily pass through cell membranes to kill bystander cells. However, GCV mono, di- and triphosphate accumulate in bystander cells when co-cultured with HSV-TK-expressing cells and GCV. The primary mechanism that appears to account for transfer of GCV phosphates is ▶gap junctional intercellular communication (GJIC). GJIC allows the direct exchange of small molecules (90% accuracy in detecting bladder cancer. Furthermore, HYAL-1 mRNA levels measured in exfoliated cells are elevated in patients with invasive and poorly differentiated carcinoma. These studies show that HAase is a highly accurate marker for detecting high-grade bladder cancer, and when it is combined with HA, it detects both low-grade and high-grade bladder cancer with 90% accuracy. The prognostic potential of HYAL-1 has been explored in prostate cancer. By performing immunohistochemistry on radical prostatectomy specimens, on whom there was a minimum 5-year follow-up, Posey et al. and Ekici et al. found that HYAL-1 staining in radical prostatectomy tissues is an independent predictor of prostate cancer progression (local recurrence or distant metastasis). Furthermore, HA-HYAL-1 staining has an 87% accuracy in predicting disease progression. It is noteworthy that in prostate cancer specimens, while HYAL-1 is exclusively expressed by tumor cells, HA expression mainly results from the tumor-associated stroma. In a limited number of studies, HAase expression has also been studied in other carcinomas. For example, there is some evidence that HYAL-1 may be a marker for head and neck squamous cell carcinomas, as salivary HAase levels are elevated in head and neck cancer patients. PH20 mRNA levels are elevated in primary and lymph node metastatic lesions of laryngeal carcinoma when compared to normal laryngeal tissues. In contrast to the observations in many carcinomas, increased HYAL-2 expression inversely correlates with invasion in B-cell lymphomas and may serve as a prognostic indicator (▶Chemotherapy of cancer; Progression and perspectives). HAase and Cancer Therapeutics. Testicular HAase has been added in cancer chemotherapy regimens to improve drug penetration. Tumor cells growing in threedimensional multicellular masses, such as spheroids

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in vitro and solid tumors in vivo acquire resistance to chemotherapeutic drugs (i.e., multicellular resistance). But this acquired chemoresistance can be abolished by the addition of testicular HAase. In limited clinical studies, HAase has been used to enhance the efficacy of vinblastin in the treatment of malignant melanoma and Kaposi’s sarcoma, boron neutron therapy of glioma, intravesical mitomycin treatment for bladder cancer and chemotherapy involving cisplatin and vindesine in the treatment of head and neck squamous cell carcinoma. It is noteworthy that the HAase concentrations (1 × 105– 2 × 105 IU) used in these clinical studies far exceed the amount of HAase present in tumor tissues, and therefore, it is unlikely that at these concentrations the infused HAase will act as a tumor promoter. Summary HAase appears to be an important molecular determinant of tumor growth, infiltration and angiogenesis. At concentrations that are present in tumor tissues, HAase acts as a tumor promoter. HAases either alone, or together with HA are potentially accurate diagnostic and prognostic indicators for cancer detection and tumor metastasis. We are only beginning to understand the complex role that this enzyme plays in cancer. Nonetheless, it is already proving to be a useful target for developing novel cancer therapeutics and diagnostics. ▶Hyaluronidases ▶Early Detection

References 1. Stern R (2005) Hyaluronan metabolism: a major paradox in cancer biology. Pathol Biol (Paris) 53(7):372–382 2. Stern R, Jedrzejas MJ (2006) Hyaluronidases: their genomics, structures, and mechanisms of action. Chem Rev 106:818–839 3. Lokeshwar VB, Schroeder GL, Carey RI et al. (2002) Regulation of hyaluronidase activity by alternative mRNA splicing. J Biol Chem 277:33654–33663 4. Lokeshwar VB, Cerwinka WH, Isoyama T et al. (2005) HYAL1 hyaluronidase in prostate cancer: a tumor promoter and suppressor. Cancer Res 65:7782–7789 5. Lokeshwar VB, Cerwinka WH, Lokeshwar BL (2005) HYAL1 hyaluronidase: a molecular determinant of bladder tumor growth and invasion. Cancer Res 65:2243–2250

Hybrid Genes ▶Fusion Genes

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Hybrid Positron Emission Tomography/Computed Tomography

Hydrogen Peroxide M IGUEL LOPEZ -L AZARO

▶Positron Emission Tomography

Department of Pharmacology, Faculty of Pharmacy, University of Seville, Seville, Spain

Synonyms Dihydrogen dioxide; Hydrogen dioxide

Definition

Hybridomas Definition Are fusion cells consisting of antibody-producing B cells and non-secreting cultured myeloma cells. After isolation of antibody-producing B cells from the spleen of immunized animals these polyclonal B cells are fused with myeloma tumor cells by permeabilization of the cell membranes. Hybridoma cells grow and multiply rapidly and produce large amounts of the desired antibodies. ▶Monoclonal Antibody Therapy ▶Bispecific Antibodies

Hydrogen Dioxide ▶Hydrogen Peroxide

Hydrogen Nuclei Definition Contain a single proton with a net charge and spin. They therefore possess a magnetic moment. They are abundant in the human body in water and fat and are the Magnetic Resonance Imaging (MRI) active nuclei used in all clinical and most research MRI. ▶Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Hydrogen peroxide (H2O2) is a ▶reactive oxygen species (ROS) generated from molecular oxygen (O2). Although the controlled cellular production of H2O2 plays an important physiological role, high cellular levels of H2O2 can produce carcinogenic effects and induce cell death.

Characteristics H2O2 is a pale-blue liquid first isolated in 1818 by Louis Jacques Thénard. H2O2 has industrial and domestic uses (e.g. paper bleaching, chemical synthesis, laundry detergents, antiseptic for wound cleaning, etc.) and it is manufactured today through an autoxidation reaction using O2 from the air. Cells of aerobic organisms also generate H2O2 from O2. Most of the energy (ATP) that aerobic cells need to live is obtained through a process called ▶oxidative phosphorylation (oxphos). In this process, ATP generation is coupled with a reaction in which O2 is reduced [▶reduction/oxidation] to water (H2O) by a mitochondrial protein complex called cytochrome oxidase. In this reaction, four electrons and four protons are added to O2 to form two molecules of H2O. But when a molecule of O2 gains only one electron to form superoxide anion (O2•−), this highly reactive oxygen species tends to gain three more electrons and four protons to form H2O; this process involves several reactions and results in the production of other ROS such as H2O2 (Fig. 1). ROS are generated in multiple compartments within the cell (e.g. mitochondria, cytosol, plasma membrane, peroxisomes, endoplasmic reticulum, etc.) and by numerous enzymes (e.g. cytochrome oxidases, NADPH oxidases, cyclooxygenases, cytochromes P450, xanthine oxidase, etc.). ROS can be eliminated by endogenous antioxidant systems. For instance, glutathione and thioredoxin systems decrease the cellular levels of H2O2 by catalyzing a reaction in which H2O2 is reduced to H2O. Likewise, the enzyme catalase eliminates H2O2 by transforming two molecules of H2O2 into two molecules of H2O and one molecule of O2. Antioxidant agents can reduce the cellular levels of ROS by preventing their generation or by favoring their elimination. For instance, some polyphenols (e.g. ▶flavonoids) can prevent the generation

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Hydrogen Peroxide. Figure 1 Aerobic cells generally use O2 to generate energy (ATP) through a process called oxidative phosphorylation (oxphos), but they can also use O2 to generate reactive oxygen species such as hydrogen peroxide (H2O2).

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Hydrogen Peroxide. Figure 2 While the controlled generation of H2O2 has an important physiological role, a sustained increase in the cellular levels of H2O2 can produce carcinogenic effects, and an excessive increase in the levels of H2O2 can induce cell death. Antioxidant agents can reduce the cellular levels of H2O2 and prevent the carcinogenic effects induced by H2O2; these agents may therefore exert a cancer-preventive activity. Prooxidant agents can increase the cellular levels of H2O2 and may induce carcinogenic effects. A sufficient increase in the cellular levels of H2O2 induced by prooxidant agents may trigger cell death and be therapeutically useful.

of H2O2 by scavenging O2•−; and selenium compounds can favor the elimination of H2O2 by providing selenium atoms, which are essential components of the H2O2detoxifying enzyme glutathione peroxidase. Prooxidant agents, on the contrary, can increase the cellular levels of ROS by increasing their generation or by reducing their elimination. For instance, arsenic can increase ROS generation by activating the enzyme NADPH oxidase, and buthionine sulfoximine (an inhibitor of γ-glutamylcysteine synthetase, the rate-limiting enzyme of glutathione synthesis) can reduce ROS elimination by decreasing glutathione-mediated H2O2 decomposition. The controlled generation of ROS plays an important role in the physiological control of cell function. For instance, cells under hypoxic conditions generate H2O2 and use it to activate hypoxia-inducible factor 1 (HIF-1) [▶hypoxia and tumor physiology], a transcription factor that codes for many proteins that help cells adapt to low oxygen levels. An uncontrolled or excessive cellular production of H2O2, however, can produce carcinogenic effects and cell death (Fig. 2).

Carcinogenic Effects Cancer cells from different tissues have been observed to produce high amounts of H2O2. High cellular levels of H2O2 have been associated with DNA alterations, including DNA damage, mutations, and genetic instability. For instance, transition metals such as iron or copper can react with H2O2 to produce hydroxyl radical (OH•) via the Fenton reaction; OH• is a highly reactive species known to produce ▶oxidative DNA damage. The production of DNA alterations by H2O2 may play an important role in ▶carcinogenesis, as cancer is considered to be a genetic disease caused by DNA alterations. Cell proliferation, ▶apoptosis resistance, ▶angiogenesis, invasion and ▶metastasis are key events of the carcinogenesis process. It is well known that, in order for cancer to develop, tumor cells must proliferate. Accumulating data have shown that H2O2 stimulates cell proliferation; in fact, the cell proliferation induced by different stimuli can be decreased by H2O2-detoxifying enzymes (e.g. catalase). Under

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physiological conditions, cells with irreparable damages usually commit suicide by triggering a programmed process called apoptosis. Since tumor cells have important damages in many of their components, the formation of a cancer requires that tumor cells develop apoptosis resistance. Interestingly, it has been found that non-cytotoxic concentrations of H2O2 can produce apoptosis resistance in cancer cells. Angiogenesis – the generation of new blood vessels – is also necessary for the formation of a solid tumor; without vascular growth, the tumor mass is restricted to within a tissue-diffusion distance of approximately 0.2 mm. Recent results support that H2O2 has an important function in angiogenesis. For instance, angiopoietin-1 plays an important role in angiogenesis and it has been found that its angiogenic effect is mediated by H2O2. It is recognized that the metastatic spread of primary tumors accounts for approximately 90% of all cancer deaths. The process by which cells from a localized tumor invade adjacent tissues and metastasize to distant organs is therefore the most clinically relevant processes involved in carcinogenesis. H2O2 has been found to modulate the activity of several processes (e.g. cell ▶motility, migration, adhesion) and molecules (e.g. ▶MET, ▶matrix metalloproteinases) involved in tumor invasion and metastasis. Indeed, studies carried out in animal models have revealed that the targeted delivery of catalase can inhibit tumor metastasis. Although the transcription factor HIF-1 plays an important role in the physiological control of cell function, HIF-1 overexpression is commonly observed in most human cancers and has been associated with increased patient mortality in several cancer types. HIF-1 increases the transcription of a variety of genes that code for proteins involved in processes intimately related to cancer, including apoptosis resistance, angiogenesis or invasion and metastasis. H2O2 can both activate HIF-1 and mediate the activation of HIF-1 caused by different stimuli; in fact, the presence of enzymes that reduce the cellular levels of H2O2 prevents the activation of HIF-1 caused by different triggers (e.g. hypoxia, TNF-alpha). The key role of H2O2 in carcinogenesis is also supported by experimental data that have demonstrated that H2O2 can cause and mediate cell malignant transformation. For instance, it has been reported that the expression of Nox1 (a homologue of gp91phox, the catalytic moiety of the O2•−-generating NADPH oxidase of phagocytes) in normal NIH3T3 fibroblasts resulted in cells with malignant characteristics that produced tumors in athymic mice. These transformed cells showed a 10-fold increase in H2O2 levels. When catalase was overproduced in these transformed cells, H2O2 concentration decreased, and the cells reverted to a normal appearance, the growth rate normalized, and cells no longer produced tumors in athymic mice.

Clinical Relevance Despite some important advances in cancer therapy, the number of cancer deaths has not decreased in the last three decades. New strategies to control this disease are required. It is recognized that cancer chemoprevention (the use of chemicals to prevent, stop or reverse the process of carcinogenesis) is an essential approach to controlling cancer. Since H2O2 seems to have an important role in carcinogenesis, a chemical capable of preventing or decreasing excessive cellular levels of H2O2 might be useful in cancer chemoprevention. Some complementary and alternative medicine practitioners have used H2O2 and other “hyperoxygenation” therapies for the treatment of cancer. In 1993, the American Cancer Society studied the available literature and found no evidence that treatment with H2O2 and other “hyperoxygenation” therapies was safe or resulted in objective benefit in the treatment of cancer. Today it is accepted that the direct administration of H2O2 is not an appropriate strategy for the treatment of cancer, as H2O2 can produce toxicity by oxidizing macromolecules such as DNA, proteins or lipids. Indeed, as discussed above and represented in Fig. 2, a large body of research strongly supports that H2O2 can produce carcinogenic effects. However, an increasing number of reports indicate that a sufficient increase in the cellular levels of H2O2 may be an effective therapeutic strategy. For instance, it is recognized that many anticancer drugs currently used in the clinic produce their antitumor activity by inducing apoptosis in cancer cells, and H2O2 is an effective inductor of apoptosis in cancer cells. In addition, some studies have shown that specific concentrations of H2O2 can kill cancer but not normal cells; it has been proposed that the increased levels of H2O2 found in tumor cells may account for their increased susceptibility to H2O2. This selectivity for cancer cells is in accordance with animal experiments that have shown that the use of H2O2generating systems can deliver H2O2 to sites of malignancy and produce anticancer effects with little toxicity to the host. The therapeutic potential of H2O2 is also supported by the fact that the anticancer activity of several drugs commonly used in the clinic (e.g. paclitaxel [▶taxol], arsenic trioxide) is mediated, at least in part, by an increase in the cellular levels of H2O2. Recent data have also shown that high concentrations of vitamin C (only achievable through the i.v. route) can produce selective killing of cancer cells through a H2O2-dependent mechanism. Therefore, although the direct administration of H2O2 does not seem an appropriate anticancer approach, any strategy capable of increasing the levels of H2O2 in cancer cells might be therapeutically useful. Accumulating evidence suggests that the modulation of the cellular levels of H2O2 may be an important

5-HydroxyIndoleacetic Acid (5-HIAA)

approach for the development of cancer chemopreventive and therapeutic strategies. Chemicals with antioxidant properties may reduce the cellular levels of this oxidant and produce cancer chemopreventive effects; indeed, most cancer chemopreventive agents have antioxidant properties. Chemicals with prooxidant properties may induce a sufficient increase in the cellular levels of H2O2 and produce cell death in cancer cells; these drugs may produce a chemotherapeutic effect. Many chemicals (e.g. vitamin C, vitamin E, β-carotene, ▶curcumin, ▶sulforaphane, ▶epigallocatechin, etc) induce either an antioxidant or prooxidant effect mostly depending on the concentration at which they reach the cells. Low concentrations of these agents would therefore produce chemopreventive effects, while high concentrations would produce chemotherapeutic effects. However, these agents may produce carcinogenic effects when used at concentrations that increase the cellular levels of H2O2, but not sufficiently to induce cell death (Fig. 2). Antioxidant/prooxidant drugs may act as cancer preventive, therapeutic or carcinogenic agents mostly depending on their dose and route of administration. ▶Oxidative Stress

References 1. Burdon RH (1995) Superoxide and hydrogen peroxide in relation to mammalian cell proliferation. Free Radic Biol Med 18:775–794 2. Szatrowski TP, Nathan CF (1991) Production of large amounts of hydrogen peroxide by human tumor cells. Cancer Res 51:794–798 3. Arnold RS, Shi J, Murad E et al. (2001) Hydrogen peroxide mediates the cell growth and transformation caused by the mitogenic oxidase Nox1. Proc Natl Acad Sci USA 98:5550–5555 4. American Cancer Society (1993) Questionable methods of cancer management: hydrogen peroxide and other ‘hyperoxygenation’ therapies. CA Cancer J Clin 43:47–56 5. Lopez-Lazaro M (2007) Dual role of hydrogen peroxide in cancer: possible relevance to cancer chemoprevention and therapy. Cancer Lett 252:1–8

Hydrophilic

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Hydroquinone Definition Product of two-electron (C6H4(OH)2).

reduction

of

quinone

▶Mitomycin C

Hydroxyapatite Definition Hydroxyapatite crystals constitute the major and essential component of normal bone and teeth. Hydroxyapatite crystals represent the mineral matrix of bone and teeth and give rigidity to bones and teeth. The chemical formula of basic hydroxyapatite is Ca10(PO4)2OH6 and these crystals can be physiologically substituted with magnesium, fluor, or carbonate. ▶Zoledronic Acid ▶Bisphosphonates

Hydroxybutyrate Dehydrogenase ▶Serum Biomarkers

5-HydroxyIndoleacetic Acid (5-HIAA) Definition

Definition Literally means water loving. These are drugs that much prefer to dissolve in water than in fat.

A breakdown product of serotonin that is eliminated in the urine. Urinary levels of 5-HIIA are used as a diagnostic and monitoring tool in carcinoid tumors.

▶ADMET Screen

▶Neuroendocrine Carcinoma

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Hydroxyl Group

Hydroxyl Group Definition Functional group consisting in an atom of oxygen joined to a hydrogen atom by a single bond. ▶Bisphosphonates

2-Hydroxyoleic Acid Definition

Synonym α-hydroxyoleic acid and 2-hydroxy-9-cisoctadecenoic acid. Synthetic derivative of oleic acid with anticancer activity against a wide variety of cancer types, oral administration and negligible side effects. ▶Membrane-Lipid Therapy

Hydroxylapatite 7-Hydroxystaurosporine Definition

Synonym ▶hydroxyapatite Ca5(PO4)3(OH).

14-Hydroxyldaunorubicin ▶Adriamycin

▶UCN-01 Anticancer Drug

7-Hydroxystaurosporine, NSC 638850 Definition

▶UCN-01 Anticancer drug

4-Hydroxynonenal Hydroxysteroid Dehydrogenases Definition An unsaturated hydroxyalkenal that is generated by the breakdown of arachidonic acid during stress in cells.

▶Reductases

▶Glutathione Conjugate Transporter RLIP76

Hyperalgesia 13-Hydroxyoctadecadienoic Acid (13-HODE) Definition A primarily growth stimulatory signaling molecule resulting from the metabolism of LA by 15-lipoxygenase-1 in cancer cells. ▶Melatonin

Definition Type of pain that is frequently associated to cancer chemotherapy or cancer itself. Hyperalgesia is an increased sensitivity and lowered threshold to a stimulus – such as burn of the skin – that is normally painful. Allodynia is caused by a stimulus – such as touch, pressure and warmth – that does not normally provoke pain. ▶Cannabinoids and Cancer ▶Allodynia

Hypericin

Hypercalcemia

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Hyperglycemia

Definition

Definition

An excess of calcium in the blood (normal range: 9– 10.5 mg/dL or 2.2–2.6 mmol/L). Can be due to excessive skeletal calcium release, increased intestinal calcium absorption, or decreased renal calcium excretion. Symptoms of hypercalcemia include fatigue, vomiting, depression, confusion, anorexia. Severe hypercalcemia (range above 15–16 mg/dl) may lead to coma and cardiac arrest.

Is a condition of elevated glucose levels in the bloodstream. It is a hallmark of metabolic syndrome and diabetes.

▶Vitamin D ▶Bone Loss, Cancer Mediated

▶Adiponectin

Hypericin C ONSTANCE L. L. S AW, PAUL W. S. H ENG Department of Pharmacy, National University of Singapore, Singapore, Singapore

Hyperchlorhydria

Synonyms Hypericum extract; Hypericum red

Definition Is the increased gastric acid secretion. ▶Gastrinoma

Hyperdiploidy Definition Having a chromosome number that is more than the normal diploid number. ▶Acute Lymphoblastic Leukemia

Hypergastrinemia Definition Is increased serum gastrin. ▶Gastrinoma

Definition

Hypericin is a natural ▶photosensitizer present in the plant, Hypericum perforatum, commonly known as St John’s wort. It belongs to the class of phenanthroperylenequinones and napthodianthrone, has a molecular weight of 504.45. St John’s wort has been used for centuries to treat mental disorders and nerve pain. In ancient times, herbalists wrote about its use as a sedative and a treatment for malaria, as well as a balm for wounds, burns, and insect bites. Today, St John’s wort is used by some for depression, anxiety, and/or sleep disorders. Hypericin is used in photodynamic diagnosis (▶PDD) and photodynamic therapy (▶PDT) for diagnosis and treatment of cancers.

Characteristics Physical Properties Hypericin yields red fluorescence when excited with a specific wavelength of light by lasers such as 442 nm (He-Cd), 488 nm (Ar), or 543 nm (He–Ne), and light by xenon-arc lamp with a band-pass filter of 380–450 nm or 375–400 nm. It has a high extinction coefficient near 600 nm. The two main maximum absorption and ▶photoactivation peaks of hypericin occur near 550 and 600 nm. The two fluorescence peaks of hypericin are near 600 and 650 nm. Hypericin has very low water solubility. The aggregated hypericin is not fluorescent. It generates a high quantum yield of singlet oxygen and superoxides.

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Hypericin

Clinical Applications PDD of Cancers The initial presentations of bladder cancer in 70–80% of the cases are superficial and limited to the urothelial lining of the bladder mucosa and submucosa. Visual differentiation between normal tissue and transitional cell carcinoma is relatively easy but not for carcinoma in situ or nonmalignant diseases such as cystitis due to radiotherapy, chemical or bacterial origins. They are often invisible to the naked eye. ▶Fluorescence cystoscopy is a form of PDD of cancer and has significantly improved the diagnosis and early detection of cancer. In bladder cancer detection, hypericin has several advantages over conventional photosensitizer, ▶5-aminolevulinic acid (▶5-ALA, a prodrug) (Table 1). A human clinical trial had found that the use of hypericin showed higher sensitivity (82%) than just white-light cystoscopy (62%). This report justifies the use of hypericin-PDD for bladder cancer in clinical settings. Hypericin was also shown to accumulate in patients with stomach cancer, and detected stomach cancer with 85% specificity. ▶PDT of Cancers ▶Basal cell carcinoma and ▶squamous cell carcinoma are the most common cancers among the Caucasians. The effect of hypericin-PDT had been investigated in these skin cancers. It was found that 1 mg or more of hypericin was acceptable as an alternative treatment for basal cell carcinoma with clinical remission achieved in 2 out of 11 patients. One out of eight patients with squamous cell carcinoma achieved clinical remission without sign of recurrence observed after 5 months of treatment with 1.5–3 mg of hypericin. Mild to transient erythema and edema at the tumor lesions were observed when the cancers were treated with hypericin and there appeared to be a correlation between the degree of tumor reduction and occurrence of erythema and edema at the tumor lesions. As this is the first reported clinical trial on the use of hypericin-PDT in the reported skin

Hypericin. Table 1

cancers, the PDT treatment protocol and dosage were transposed from results with animal models and the trial was restricted to 4–6 weeks because of ethical reasons. Thus, long-term remission rates are needed to further evaluate the clinical usefulness of hypericin with additional trials. Another hypericin-PDT use in cancer treatment was for local application of hypericin in a patient with recurrent malignant mesothelioma. The patient had previously been treated with radiotherapy, chemoimmunotherapy and subsequently PDT using hematoporphyrin derivatives (Photosan III). Topical hypericin was applied to the patient and a month later, the combination of hypericin and Photosan III was applied. It was found that complete remission was achieved histologically with a light dose at 90 J/cm2 together with PDT using combined systemic Photosan III and topical application of hypericin. Preclinical Investigations The chemical groups reported to cause the photodynamic activities of hypericin are semiquinone, singlet oxygen, and superoxide anion radicals. Light triggers the photosensitization (photoactivation) of hypericin for photodynamic reactions. Hypericin-PDT effect is a function of drug, light, and oxygen present. There are three PDT effects of the photosensitizers on biological systems. Firstly, it can damage the vasculature, causing thrombosis and blood flow stasis. Secondly, PDT kills tumor cells via generation of free radicals that damage mitochondria, plasma membrane, and other organelles, hence inducing apoptosis or necrosis of the tumor. Thirdly, PDT modulates the immune system against cancer cells. Successful cancer treatment is usually a result of the combination of all these effects. With the appropriate use of light and adjuvant therapy such as heat or ▶antiangiogenesis agents, better therapeutic outcomes can be expected. Table 2 shows the reported methods to improve the efficiency of hypericin for PDD and PDT in preclinical investigations. As

Comparison of 5-ALA and hypericin for detecting human superficial bladder carcinoma

Characteristics Form

5-ALA

Stability

Prodrug, need to be converted to the active form 75–100% Very low specificity, 43–68.5% (with many false-positives) Easily photobleached during process

Permeability across biological membrane

Charged molecule – difficult to cross biomembranes

Sensitivity Specificity

Hypericin Active form 82–94% High, 91–98.5% Greater stability, no significant photobleaching Hydrophobic – good permeability

Hypericin Hypericin. Table 2

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Methods for enhancement of hypericin-PDD/PDT efficacy

Concept Chemical modifications Physical methods Pharmaceutical formulations Combination with adjuvant therapy

Methods Improve physicochemical properties of hypericin. Analogs with better water solubility, absorption and fluorescence properties, and singlet oxygen quantum yield Optimize light conditions (fractionated light dose), oxygen perfusion, hyperthermia Prepare liposomes, nanoparticles, topical applications Add oxygen carrier, antiangiogenesis agents, drugs that are able to synergize with hypericin for cancer treatment

administration of hypericin to patients remains a challenging task due to its poor aqueous solubility and lipophilic nature, the most popular approach is by a formulation approach to enhance the efficacy of hypericin-PDT. There is a trend to develop formulations of hypericin without plasma proteins. Despite the use of cutting-edge technology approaches, such as preparing transferrin-mediated targeted delivery liposomes and nanoparticles of hypericin, such preparations did not always confer the desired enhanced treatment effects. It appeared that the use of an adjunct with hypericin, especially those prepared without using plasma proteins, was more successful in enhancing the delivery of hypericin with both in vivo and in vitro systems. Using a pharmaceutical solvent and penetration enhancer, N-methyl pyrrolidone, delivery of hypericin was shown to be better than the conventional formulation of hypericin with albumin. Using chick chorioallantoic membrane implanted with human bladder cancer cells, N-methyl pyrrolidone was demonstrated to be an excellent alternative to plasma proteins as adjuvant with hypericin. The improved N-methyl pyrrolidone–hypericin formulation enabled more efficient delivery and uptake of hypericin at the target site. This will not only allow a lower drug dose to be used potentially but will also significantly reduce patients’ waiting time. The exact mechanism for the tumor selectivity uptake of hypericin has not been fully understood. The uptake/ transport/delivery of hypericin is dependent on several competing or interrelated factors, which include the type of incubation medium (with or without serum proteins), cell type, delivery system, and biological testing method. It is likely that both active and passive transport mechanisms contribute to the overall uptake of hypericin but passive diffusion is likely to be the more dominant mechanism. Apart from its photosensitizing properties, hypericin was found to be a ▶protein kinase C inhibitor. It was also reported to involve in the modulation of immune system such as expression of cytokines. Hypericin-PDT triggered the expression of angiogenic factors, ▶matrix metalloproteinases, and various signaling pathways.

The rapid advancement in genetic research had shown that the effects of hypericin-PDT could be independent of the status of ▶p53, the tumor suppressor gene. Many reports have attributed the failure of conventional chemotherapy and radiotherapy to the mutated ▶p53, due to apoptosis failure caused by the nonfunctional p53. Therefore, hypericin-PDT provides an alternative pathway in treating cancers. In the absence of light, toxicity of hypericin was found to be very low. Apart from its potent photosensitizing properties that are light-dependent, hypericin shows unique activities even in the dark. In complete darkness, hypericin has cytostatic activities that were able to prolong the survival of mice with high-grade squamous carcinoma tumors. This is attributed to hypericin inhibiting several key steps of the angiogenesis. Many different types of cancers including leukemia, glioblastoma, and childhood rhabdomyosarcoma have been treated with hypericin-PDT and in vitro results were promising in many of the cases. Continual effort in basic and translational research will lead to a better understanding of the contributing factors responsible for effective hypericin-PDT applications. ▶Photodynamic Therapy

References 1. Kiesslich T, Krammer B, Plaetzer K (2006) Cellular mechanisms and prospective applications of hypericin in photodynamic therapy. Curr Med Chem 13:2189–2204 2. Saw CL, Olivo M, Soo KC et al. (2006) Delivery of hypericin for photodynamic applications. Cancer Lett 241:23–30 3. Saw CL, Olivo M, Chin WW et al. (2007) Superiority of N-methyl pyrrolidone over albumin with hypericin for fluorescence diagnosis of human bladder cancer cells implanted in the chick chorioallantoic membrane model. J Photochem Photobiol B 86:207–218 4. Dets SM, Buryi AN, Melnik IS et al. (1996) Laser-induced fluorescence detection of stomach cancer using hypericin. Proc Soc Photo Opt Instrum Eng 2926:51–56 5. Koren H, Schenk GM, Jindra RH et al. (1996) Hypericin in phototherapy. J Photochem Photobiol B 36:113–119

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Hyperlipidemia

Hyperlipidemia

Hypersensitivity Reaction

Definition

Definition

Refers to an elevation of lipids (fats) in the bloodstream.

A serious and sometimes life-threatening reaction to a drug or other chemical or venom.

▶Cachexia

▶Paclitaxel

Hypermethylation Hyperthermia Definition

Increased ▶methylation of cytosine residues in cytosine-guanine pairs in regulatory regions of DNA of specific genes or of global DNA within a cell or tissue. ▶Fragile Histidine Triad ▶Methylation-Controlled J Protein (MCJ)

A SHLEY A. M ANZOOR , M ARK W. D EWHIRST Department of Radiation Oncology, Duke University, Durham, NC, USA

Definition Hyperthermia refers to the elevation of temperature above physiological levels, typically to values of 40–45°C.

Characteristics

Hyperplasia Definition Consists of an increase in the number of tissue cells, without changes in their volume. This alteration, generally secondary to prolonged growth stimuli, is reversible and does not evolve to malignancy.

Hyperthermia utilizes elevated tissue temperatures, typically between 40°C and 45°C, to alter the tumor and normal tissue environment. The goal of hyperthermia in cancer treatment is to create an environment that will aid in eradicating tumor while sparing normal tissue. Hyperthermia accomplishes this by causing direct cytotoxic effects and a variety of physiologic effects, including the alteration of blood flow and oxygenation status. Clinically, hyperthermia can work synergistically with both radiation and chemotherapy.

▶Preneoplastic lesions

Hyperplastic growth Definition Tissue overgrowths that still retain their normal characters and ability to differentiate.

Hypersensitivity ▶Allergy

Cytotoxic Effects Hyperthermia elicits cytotoxic effects in tissue through a variety of mechanisms, inducing both ▶apoptosis and ▶necrosis. Above 40°C, protein is a dominant molecular target, with protein denaturation exhibiting a similar heat of inactivation as thermal cell kill and damage (130–170 kcal/mole). Other cellular targets include the cytoskeleton, which controls many signal transduction pathways, cellular respiration enzymes, and DNA repair processes. These components of the cell are particularly heat sensitive and lead to increased cytotoxic effects. Physiologic Effects Hyperthermia also has an intricate relationship with tumor physiology, as the degree of physiologic response varies with temperature. An initial temperature increase to 41–41.5°C will result in elevated blood flow and increased vascular permeability.

Hyperthermia

Generally, muscle and skin perfusion increase by at least tenfold, while tumor perfusion increases only 1.5to 2-fold. This difference in response between normal and cancerous tissue is one of the most exploited benefits of hyperthermia in cancer treatment. At these initial hyperthermia temperatures, edema may result from the increase in vascular permeability, and as higher temperatures are reached, vascular stasis and hemorrhage may develop. Additionally, higher temperatures may result in vascular damage, although typically these temperatures are neither utilized nor often achievable in the clinic. With respect to normal tissue, thermal damage from hyperthermia exhibits varying degrees of severity depending on temperature and tissue type. Some normal tissues are more heat sensitive than others, yet the sensitivity is not easily predicted by classical cytotoxicity or radiotherapy principles. While these principles correlate proliferative potential with radiation or chemo-sensitivities, this is not predictive of thermal sensitivity. For example, the brain and testes both exhibit high thermal sensitivities, yet the brain has almost no proliferative potential and the testes are highly proliferating. Furthermore, in addition to showing no correlation between thermal sensitivity and proliferative potential, there is also no tissue-specificity. For instance, the spinal cord, peripheral nerves, and brain all demonstrate varying sensitivity to heat, yet these are all nervous tissue. In addition to physiologic changes in blood flow and vascular permeability, ▶tumor metabolism and oxygenation can also be altered substantially with hyperthermia. As mentioned earlier, certain enzymes may be highly heat sensitive. Along metabolic pathways, enzymes involved in aerobic tumor metabolism exhibit much greater heat sensitivity than those involved in anaerobic metabolism. This lends itself to a theory that hyperthermia treatment may cause reductions in tumor metabolism and respiration. Reported effects in support of this theory have been decreased ATP production and increased lactate concentration following hyperthermia. Furthermore, alteration in tumor metabolism has additional downstream effects, particularly with respect to tumor oxygenation status. As a tumor shifts from aerobic to anaerobic metabolism following hyperthermia, the tumor may experience decreased oxygen consumption rates; this decrease in oxygen consumption may consequently lead to significant improvement in the tumor oxygenation status. Studies have shown oxygenation increases following hyperthermia in rodent and canine tumors, as well as human tumors. However, this oxygenation effect is most pronounced at temperatures between 41°C and 43°C, decreasing at higher temperatures where vascular damage occurs.

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Immunological Effects Hyperthermia can augment the body’s innate immunity as well as increase immune activity specifically towards tumors. In general, the body increases in temperature as a response to infection; many bacterial or viral pathogens are heat sensitive and thus an elevation in body temperature serves as a primary method of defense against invading agents. Furthermore, as body temperature rises, cellular metabolism does as well, which can aid in accelerating immunologic responses. With regards to immune response towards tumor, hyperthermia can induce maturation of ▶dendritic cells, cause increased lymphocyte trafficking, and engage in ▶heat shock protein 70 (HSP70) mediated immune response, which in turn increases T-cell specific antitumor activity and further stimulates dendritic cells. These physiologic responses augment the body’s natural immune response against tumors. Hyperthermia Physics Delivery Modalities Hyperthermia may be delivered using either invasive or non-invasive sources. Non-invasive techniques are generally preferred, and consist of two main methods of delivering heat to tissues: ▶electromagnetic (EM) heating or ▶ultrasound. While the underlying physics principles of heat deposition differ between EM and ultrasound modalities, they are similar in a variety of ways. Both are sensitive to tissue heterogeneity as well as blood flow geometry, and are susceptible to difficulties of energy coupling into tumor tissue. Materials with finite electrical conductivity experience energy dissipation with the flow of electric current; this is the principle behind ohmic, or resistance electromagnetic heating. Delivery of EM heating is dependent on both frequency and wavelength. As EM frequency increases over the radio frequency (RF) and microwave (MW) range, electrical conductivity also increases. Since energy deposition in tissue is proportional to the local tissue conductivity and the magnitude of the electric field, these higher frequencies result in greater energy deposition and shorter penetration depths. Additionally, in the design of antennae or electrodes to deliver the EM field, there is a general constraint that limits the ability to localize heating at depths greater than 2–5 cm. This arises from the relation between EM frequency and wavelength to the physical size of the antenna or electrode source. Longer wavelengths will penetrate deeper into tissue, but require physically larger heating antennae, thus preventing localization of the EM field. This tradeoff between localization and penetration yields a critical limitation in electromagnetic heating: localized heating is limited to depths less than 2–5 cm. At depths greater than 2–5 cm EM heating will result in regional energy deposition, potentially involving large volumes of normal tissue.

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Hyperthermia

In accordance with these depth limitations, electromagnetic heating devices are typically divided into two categories: superficial applicators which provide focused heating at depths less than 2–5 cm and deep heating devices which distribute heat to a deeper penetration but over a broader range. Superficial devices consist of waveguides and microstrip or patch antennas which operate in typical microwave band frequencies (433, 915, or 2,450 MHz) and usually require a water bolus to couple energy into the tissue. The deep heating devices typically used are magnetic induction, capacitive coupling, and phased array fields. These devices operate at lower frequencies, between 5 MHz and 200 MHz. A schematic illustration of a phased array device for deep heating is shown in Fig. 1. Similarly to electromagnetic heating, ultrasound also experiences decreased penetration with increasing frequency. As an advantage over EM, however, ultrasound operates with much lower wavelengths and consequently avoids the severity of problems associated with focusing at greater depths. Unfortunately, ultrasound is limited by resolution, since it is particularly sensitive to the reflective and absorptive effects of air and bone, respectively. This imposes severe limitations of ultrasound heating in regions of tissue heterogeneity and changing geometry. Ultrasound devices are also separated into categories of superficial and deep heating. Single and multiple transducer plane wave devices operating with frequencies between 1 MHz and 3 MHz have been designed for superficial tumors, while at depths greater than 2–5 cm scanned focused transducers, phased arrays, or multiple scanned focused transducers in the 0.5–2 MHz

range are used. Ultrasound devices require a temperature controlled water bolus for energy coupling. Thermometry One of the greatest challenges facing clinical hyperthermia is the difficulty in obtaining accurate and noninvasive thermometry. Currently, most thermometry is performed through placement of ▶catheters into the tumor via ultrasound or CT guidance; thermometers are then placed within the catheters. Temperature readings are attained statically with multipoint thermometers or dynamically by moving a single point thermometer through the catheter during heating. There are many disadvantages to the common method of invasive thermometry. For one, there is a greater risk to the patient. Invasive methods are uncomfortable and present a risk for infection and hemorrhage. Additionally, the procedure is lengthy, requiring image registration and extra time of the physician. Perhaps most crucially, the data obtained from invasive methods is limited and often does not provide much spatial data, which in turn limits the control and uniformity of the hyperthermic treatment. In an attempt to gain better uniformity of treatment, noninvasive thermometry methods have been developed; these methods rely mostly on ▶Magnetic Resonance Imaging (MRI) techniques, although a variety of technologies are being pursued. MR imaging has many temperature sensitive parameters that can be exploited for thermometry purposes, including relaxation times T1 and T2, bulk magnetization, and proton resonance frequency. Of these four parameters, the proton resonance frequency is the most commonly

Hyperthermia. Figure 1 Illustration of an annular phased microwave array for heating deep situated tumors.

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normalizing thermal data between different patients or treatments. This is expressed as Cumulative Equivalent Minutes at 43°C (CEM 43°C) and is given by the equation: CEM 43 C ¼ tRð43TÞ Hyperthermia. Figure 2 Example of noninvasive thermometry data acquired with phase difference (chemical shift) MRI in a sarcoma of the lower leg. This method can yield temperature data with a resolution of 1.0°C.

used, and has demonstrated superior temperature sensitivity and resolution. Clinical studies have illustrated resolutions of 0.5–1°C with MRI thermometry. Figure 2 shows a temperature distribution image obtained from an MRI of a sarcoma in the lower leg. Despite the many advantages hyperthermia affords, clinical implementation has proved challenging. As mentioned above, hyperthermia heating regimens can be difficult to reproduce, utilizing invasive thermometry methods that have limited spatial coverage. Additionally, the definition and calculation of thermal dose used in hyperthermia is not well defined, making clinical trial comparisons between institutions difficult. However, the technology associated with clinical hyperthermia continues to improve, and many of these challenges are being addressed in ongoing research. Thermal Dosimetry The Arrhenius relationship is used to describe the rate of cell kill for a given temperature over time, and provides the basis for thermal dosimetry. Hyperthermia cell survival curves decrease exponentially, with higher rates of cell kill at increased temperatures. Arrhenius plots can be determined from in vitro data by taking the log of the slope of cell survival curves as a function of temperature. A typical graph of surviving fraction with temperature and its resulting Arrhenius plot is given in Fig. 3. Arrhenius plots are characterized by their biphasic nature, with the temperature at which the slope changes commonly referred to as the “breakpoint;” this phenomenon is derived from tissues developing thermal tolerance. For human tissue, the “breakpoint” occurs at 43.5°C. Below the breakpoint, the rate of cell kill decreases twofold to fourfold for each 1.0°C decline in temperature. Above the breakpoint, the rate of cell kill doubles for each 1.0°C elevation of temperature. Achieving constant temperatures over time is difficult in tumor tissue, leading to non-uniformity in hyperthermia delivery between patients. Since the in vivo slopes of the Arrhenius plots are practically identical to the in vitro slopes, and they provide a correlation between rate of cell kill and temperature, the Arrhenius relationship is used as a method for

Where t = time of treatment in minutes, T = average temperature in Celsius during treatment, and R is a constant, equal to 0.5 above the breakpoint and 0.25 below. In more complex situations with large temperature variations, the thermal data may be broken into shorter time intervals of 1–2 min where the temperature remains relatively constant. In these instances the total CEM 43°C for the treatment is attained through summation of CEM 43°Cs for each interval period. Also referred to as the thermal isoeffect dose, the CEM 43°C has been a valuable predictor of treatment efficacy and standardization of heat treatment in clinical trials. Clinical Hyperthermia Hyperthermia has been used to treat superficial tumors as a lone method of treatment. However, while the occasional response is observed, in general heat treatment alone is not associated with long term tumor control. While the practice of using solely hyperthermia is still performed in some clinics, this use is not supported by peer-reviewed published scientific data. Instead, hyperthermia is best utilized as a synergistic adjunct modality to oncology treatments, including radiation and chemotherapy. Figure 4 underscores the important physiological processes of hyperthermia in augmenting radiation and chemotherapy efficacy. Radiation Therapy and Hyperthermia The rationale for combining hyperthermia with radiation therapy is based on a variety of synergistic effects. For one, the areas of radiation resistivity and heat sensitivity are complimentary. While cells in ▶S-phase are typically radioresistant, this is the most heat sensitive phase of the cell cycle. Also, hypoxic cells are typically three times more resistant to radiation than normoxic cells, whereas there is no difference in thermal sensitivity based on cellular oxygenation status. Furthermore, hyperthermia can augment radiation response by causing reoxygenation of tumor tissue and inhibiting sublethal repair through inactivation of critical DNA repair pathways. Clinically, the therapeutic gain of combining radiation therapy and hyperthermia is determined by the Thermal Enhancement Ratio, or TER. The TER is defined as the ratio of radiation dose to achieve an isoeffect for radiation divided by the radiation dose to achieve the same effect with combined radiation and hyperthermia. Typical TER values for local tumor control are greater than one, and are typically smaller

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Hyperthermia

Hyperthermia. Figure 3 Example of thermal cell survival curves (on the left), plotted as surviving fraction over time at a specific temperature. On the right, the Arrhenius plot is shown for the data. The breakpoint is observed at 43°C.

Hyperthermia. Figure 4 Physiologic benefits of low temperature (40–43°C) hyperthermia and the rationale behind synergistic radiation and chemotherapy uses.

for normal tissue damage, suggesting therapeutic gain for a combined hyperthermia and radiation course over radiation alone. Chemotherapy and Hyperthermia Hyperthermia also exhibits synergism with some chemotherapeutic agents, through increasing cellular uptake, oxygen radical production, and DNA damage, while inhibiting DNA repair. Chemotherapeutic drugs that have been shown to have heightened efficacy when combined with hyperthermia include ▶cisplatin, ▶nitrogen mustards, doxorubicin (▶Adriamycin), ▶nitrosoureas, ▶bleomycin, ▶mitomycin C, and hypoxic cell sensitizers. While this list of drugs that are synergistic

with hyperthermia are many, there are also those that have not shown interaction when combined with heat, such as ▶etoposide and the ▶vinca alkaloids. In addition to showing additive effects with traditional chemotherapeutic agents, hyperthermia also offers an avenue for exploitation of innovative drug delivery strategies. Liposomes (▶Liposomal Chemotherapy) are nanoparticle lipid vesicles that can be loaded with a variety of high concentration chemotherapeutics. These liposomes show enhanced extravasation following hyperthermia due to increased permeability of the vasculature. Furthermore, this enhanced accumulation is tumor specific, due to the discrepancy in degree of permeability increase between

Hypertrophy of Male Breast

Hyperthermia. Figure 5 Illustration of the principles underlying thermosensitive liposome efficacy. Thermosensitive liposomes release their contents upon heating to a desired temperature, and release drug both within the tumor vasculature and after extravasation into tumor tissue.

tumor and normal blood vessels. Not only does hyperthermia increase overall liposomal extravasation, but novel thermosensitive liposomes have been developed with lipid bilayers that degrade upon reaching a thermal transition temperature, typically designed to release in a range of 40–43°C. This allows for both targeted and triggered drug release into tumor tissue. Figure 5 shows an illustration of thermosensitive liposomes extravasating into tumor tissue and releasing their contents upon heating. There are a variety of factors that should be considered when combining hyperthermia and chemotherapy. For one, response may vary based on the hypoxic and pH parameters of the tumor. Additionally, a very notable effect of hyperthermia is its influence on tumor resistivity to certain drugs; hyperthermia can induce at least partial reversal of drug resistance with a variety of drugs, most notably cisplatin, ▶melphalan, nitrosoureas, and doxorubicin. Finally, sequencing of hyperthermia and drug delivery may greatly influence efficacy of treatment. Most drugs exhibit optimal results when heat and drug are delivered concomitantly, or when drug is given immediately prior to heating; some exceptions include 5-FU (▶Fluorouracil) and a few other antimetabolites. Clinical Trials Phase III clinical trials, particularly those comparing radiotherapy (RT) alone to RT + HT, have yielded significant positive results for a variety of cancers. Both superficial and deep tumor sites have been investigated, as well as both palliative and curative treatment goals. Statistically significant improvement in complete response (CR) rates with HT + RT versus RT alone have

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been demonstrated with many cancers, most notably chest wall recurrences of breast cancer, stage III and IV head and neck, metastatic melanoma, bladder, and cervical carcinoma. Most importantly, improvements in survival have also been shown in cervix, head and neck, glioblastoma, esophageal cancers. While many trials have been performed validating the use of hyperthermia with radiotherapy, fewer exist for chemotherapy (CT) and hyperthermia. However, phase II trials have illustrated improved treatment efficacy of CT + HT in sarcomas and breast carcinomas, compared with historical controls. Additionally, the use of tri-modality (CT, RT, and HT) treatments are being investigated, with encouraging results in phase II trials of locally advanced rectal and cervical cancers and a phase III trial for esophageal cancer.

References 1. Dewhirst MW, Jones E, Samulski T et al. (2006) Hyperthermia. In: Kufe DW, Bast RC Jr, Hait WN, Hong WK, Pollock RE, Weichselbaum RR, Holland JF, Frei III E (eds) Cancer medicine. BC Decker, Hamilton, pp 549–561 2. Jones EL, Samulski TV, Vujaskovic Z et al. (2004) Hyperthermia. In: Perez CA, Brady LW, Halperin EC, Schmidt-Ullrich RK (eds) Principles and practice of radiation oncology. Lippincott Williams and Wilkins, Philadelphia, PA, pp 699–735 3. Horsman MR, Overgaard J (2007) Hyperthermia: a potent enhancer of radiotherapy. Clin Oncol 19(6):418–426 4. Ponce AM, Vujaskovic Z, Yuan F et al. (2006) Hyperthermia mediated liposomal drug delivery. Int J Hyperthermia 22(3):205–213 5. Van der Zee J (2002) Heating the patient: a promising approach. Ann Oncol 13:1173–1184

Hypertrophy Definition Increase in size of an organ or tissue due to an increase in the size of cells while the number stays the same. ▶Peroxisome Proliferator-Activated Receptor

Hypertrophy of Male Breast ▶Gynecomastia

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Hypervariable Region

Hypervariable Region Definition

Regions of the heavy or light chains of ▶immunoglobulins in which there is considerable sequence diversity within that set of immunoglobulins in a single individual. These regions specify the antigen affinity of each antibody.

Hypomethylation of DNA M IGUEL A. P EINADO Institute of Predictive and Personalized Medicine of Cancer (IMPPC), Badalona, Barcelona, Spain

Synonyms DNA demethylation; DNA undermethylation

Definition

Hypodiploidy Definition Having a chromosome number that is less than the normal diploid number. ▶Acute Lymphoblastic Leukemia

DNA hypomethylation refers to the loss of the methyl group in the 5-methylcytosine nucleotide. Methylation is a natural modification of DNA, and mainly affects the cytosine base (C) when it is followed by a guanosine (G) in mammals ▶(Methylation). The term hypomethylation can be applied to describe the unmethylated state of most CpG sites in a specific sequence that is normally methylated, or as a general phenomenon affecting the bulk of the genome; this is a decrease in the proportion of methylated versus unmethylated cytosines.

Characteristics

Hypoechoic Definition The echo of the tissue is low compared to the adjacent area. ▶Hepatic Epithelioid Hemangioendothelioma

Hypogammaglobulinemia Definition Abnormally low levels of immunoglobulins.

Hypomethylation Definition

A reduced level of CpG island ▶methylation relative to the normal tissue specific pattern. ▶Methylation-Controlled J Protein (MCJ) ▶CpG Islands

In human, DNA methylation mainly occurs at CpG sites. Up to 80% of all CpG sites in human DNA are methylated. However, this methylation occurs primarily in areas where CpG density is low, or at repeat DNA sites, such as Alu elements. CpG islands are regions where CpG density is high and most of them are unmethylated. Patterns of DNA methylation have been linked to control of gene expression, maintenance of chromosomal integrity, and in regulation of DNA recombination in mammals. Methylation in a gene promoter region is generally associated with gene silencing. Heavily methylated DNA replicates later than nonmethylated DNA, and late replication is associated with the formation of inactive chromatin, which facilitates transcriptional silencing of noncoding regions. Global hypomethylation is typical in aging cells, as well as in neoplasia, where it is an early event. Early studies in the eighties already identified a depletion of the methyl-cytosine content as a landmark in colorectal cancer and other types of tumors. DNA hypomethylation has been shown to promote tumorigenesis in murine colon and liver and was included as an early event in a genetic model for colorectal tumorigenesis. Different investigations sustain a causal link between DNA hypomethylation and genetic instability, reporting an association between defects in DNA methylation and aneuploidy in human colorectal cancer cell lines, increased chromosomal rearrangements in hypomethylated centromeric regions in mitogen-stimulated cells from individuals affected with immunodeficiency, centromere instability and facial anomalies (ICF

Hypoxia

syndrome), and an increased mutation rate owing to DNMT1 deficiency in murine embryonic stem cells and in murine somatic cells. Moreover, DNMT1 deficiency also results in constitutive chromosomal instability in a human colon cancer cell line. Decreased methylation levels in LINE sequences correlate with losses of heterozygosity on discrete chromosomal loci in colorectal carcinomas and other studies have demonstrated that DNA hypomethylation precedes genomic damage in human gastrointestinal cancer.

References 1. Ehrlich M (2002) DNA methylation in cancer: too much, but also too little. Oncogene 21:5400–5413 2. Feinberg AP, Tycko B (2004) The history of cancer epigenetics. Nat Rev Cancer 4:143–153

Hypospadias Definition A congenital defect of the ventral surface of the penis which causes abnormal urethral opening proximal to its normal location. ▶Nephroblastoma

Hypothalamus Definition A region of the brain below the cortex and the cerebrum that regulates numerous important body functions and makes hormones that impact pituitary function. ▶Prolactin

Hypoxia L AWRENCE B. G ARDNER The NYU Cancer Institute, New York University School of Medicine, New York, NY, USA

Synonyms Anoxic; Anaerobic

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Definition Being oxygen deprived.

Characteristics Cellular hypoxia is a common stress in normal development and numerous pathological conditions, including cancer. By the time a tumor has grown to a detectable size, poor and disordered ▶angiogenesis, leaky vessels, and high interstitial tumor pressure all result in significant tumor hypoxia. Studies in human tumor ▶xenografts reveal a mean pO2 of T mutations at codon 249 in ▶hepatocellular carcinoma of ▶HBV chronic carriers; ▶ultraviolet radiation and CC to TT tandem mutations in nonmelanoma skin cancer; and cigarette smoke and G>T transversions in ▶lung cancer of smokers (▶tobaccorelated lung cancer). Specific mutation patterns in TP53 may thus help identify environmental exposures that may be involved in ▶carcinogenesis.

Database Structure and Content The IARC TP53 Database contains data that are extracted from peer-reviewed publications or bioinformatics databases and curated manually. The core database is a relational database that integrates data on somatic mutations in sporadic cancers, on germline mutations in familial cancers, on TP53 gene status of cell-lines, on polymorphisms in human population and on functional assessment of mutations. It is organized around a “gene variation module” to which five modules are connected: a “somatic module,” a “germline module,” a “function module,” a “polymorphism module” and a “cell-line module” (Fig. 1). The database is a relational database in which different sets of data are integrated in a single scheme. The structure and content presented corresponds to the R11 (October 2006) release of the database that is maintained in SQL sever. This database design and content allow, for every single gene variation, to retrieve data on its functional and structural impact, and data related to its expression in a somatic, cell-line or germline context. Details on database contents and annotations are available at http://www-p53.iarc.fr/ Help.html. The “gene variation module” contains all possible single nucleotide substitutions in the coding sequence and splice sites of TP53, plus all other sequence alterations that have been reported in human cancers, each alteration being a unique entry. Gene variation are described at the DNA and protein levels and are annotated with structural and functional information related to the position of the mutation in the protein sequence (functional domain, residue function, structural motif, solvent accessibility of residue). For missense mutations, classifications based on the predicted or experimentally assessed functional impacts are also available. The “▶polymorphism” includes common gene variations reported in publications or extracted from ▶SNP databases, with links to databases that provide information on population frequency or disease associations. The “somatic and germline modules” contain data related to the somatic or germline expression of mutations respectively, with common set of dictionaries used to annotate pathological, clinical and patient information. The “cell-line module” contains TP53 gene status of human cell-lines with links to the ATCC catalog (cell-line provider). The “Function module” contains experimental data obtained on the activities and properties of p53 mutant proteins when transfected and over-expressed in human or yeast cells. Each entry in this module corresponds to the results of a set of experiments performed with one mutant in a specific cell-type. Experimental assays that have been included were performed in yeast or human cells and were designed to (i) measure the transactivation activities of mutant proteins on reporter genes placed

IARC TP53 Database

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IARC TP53 Database. Figure 1 Structure and contents of the IARC TP53 database (R11, 2006).

under the control of various p53 response-elements, (ii) test the capacity of mutant proteins to induce cell-cycle arrest or apoptosis, (iii) exert dominant-negative effect over the wild-type protein, be temperature sensitive, or display various activities that are independent and unrelated to the wild-type protein (gain of function). A specific vocabulary has been implemented to describe experimental results in a standard format. The detailed annotation system used in all modules is described in the online user guide at http://www-p53. iarc.fr/Help.html. Web Site and New Search Tools The IARC TP53 web site (http://www-p53.iarc.fr/) provides a search interface for the core database and includes a comprehensive user guide, a slide-show on TP53 mutations in human cancer, protocols and references for sequencing TP53 gene, and links to relevant publications and entries to bioinformatics and cancer databases. The database interface allows the download of all modules and propose various tools for the selection, analysis and downloads of specific sets of data according to user’s query (Fig. 2). Mutations reported in specific types of cancers and/or population groups can be analyzed with graphs that display their type by base substitutions (mutation patterns), codon distribution,

position within the 3D structure of p53 DNA-binding domain, and predicted or observed effect on protein (function patterns). Other graphs can be drawn to display the types of tumor associated with specific mutations expressed in a somatic or germline context, and to display the prevalence of mutations found in specific tumor types and/or population groups. Other tools include: a mutation validation tools that allows the retrieval of all data available in the database for a specific DNA variation (frequency as a somatic or germline mutation, predicted and observed functional impact); a search option to retrieve experimental data on functional properties of mutant proteins; a search option to retrieve cell-lines for which TP53 gene status is known. Several options and tools are available to retrieve and analyze specific sets of data from the core database according to user defined queries. Different types of graphs are implemented to analyze data and raw data can be downloaded as tables. All datasets can be entirely downloaded as tab-delimited text files. The search page is available at http://www-p53.iarc.fr/ P53main.html. Recommendation to Users The IARC TP53 database is exclusively based on peer-reviewed publications. Trends in reporting and

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IARC TP53 Database

IARC TP53 Database. Figure 2 Search system for the analysis of the IARC TP53 database.

publishing mutations have thus a strong influence on the data included in the database. Studies from which data are extracted have diverse designs and diverse way of reporting mutations and related information. This diversity requires an effort of standardization of

annotations and affect database analysis. It thus important that users are aware of the limitations and possible biases that may affect their analysis of the database. These bias are described in details at http:// www-p53.iarc.fr/Help.html#Recommendations.

Id Proteins

The IARC TP53 database is a free service to the scientific community, and contributions from researchers and journal editors are most welcome to help us develop this important resource for cancer research.

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IC50 Definition

References 1. Hainaut P Hollstein M (2000) p53 and human cancer: the first ten thousand mutations. Adv Cancer Res 77:81–137 2. Hernandez-Boussard T, Montesano R, Hainaut P (1999) Sources of bias in the detection and reporting of p53 mutations in human cancer: analysis of the IARC p53 mutation database. Genet Anal 14:229–233 3. Petitjean A, Mathe E, Kato S, Ishioka C, Tavtigian SV, Hainaut P, Olivier M (2007) Impact of mutant p53 functional properties on TP53 mutation patterns and tumor phenotype: lessons from recent developments in the IARC TP53 database. Hum Mutat 28:622–629 4. Vogelstein B, Lane D, Levine AJ (2000) Surfing the p53 network. Nature 408:307–310

50% inhibitory concentration; Refers to the concentration of a drug that reduces a biochemical activity (e.g. an enzymatic activity) or cellular parameter (such as cell multiplication) to 50% of its normal value in the absence of the inhibitor. ▶Small Molecule Screens

ICAMs I Definition

IkB Definition Are initially described as proteins that inhibit the function of transcription factor ▶NF-κB (inhibitor of κB). Meanwhile, IκBs extended to a protein family of seven members primarily structural related by the presence of several ▶ankyrin repeats in their central domain. Through these motifs, they interact with and regulate NF-κB function in various ways.

Intercellular ▶adhesion molecules are cell-surface ligands for the ▶leukocyte integrins and are crucial in the binding of lymphocytes and other leukocytes to certain cells, including ▶antigen-presenting cells and ▶endothelial cells. They are members of the immunoglobulin superfamily. ICAM-1 is the most prominent ligand for the integrin CD11a:CD18 or LFA-1. It is rapidly inducible on endothelial cells by infection, and plays a major role in local ▶inflammatory response. ICAM-2 is constitutively expressed at relatively low levels by endothelium. ICAM-3 is expressed only on leukocytes and is thought to play an important part in adhesion between T cells and antigen-presenting cells, particularly ▶dendritic cells. ▶Integrin Signaling

▶BCL3 ▶Nuclear Factor kappa-B

Id1 IkBa

Definition

Member of the group of ▶Id Proteins.

Definition MAD-3, pp40, RL/IF-1 and ECI6; Is one of a family of proteins that are the natural inhibitors of ▶NF-κB. It acts by complexing to NF-κB in the cytoplasm of unstimulated cells. When IκBα is inactivated, NF-κB is allowed to enter the nucleus. ▶Hodgkin Disease, Clinical Oncology ▶Nuclear Factor kappa-B

Id Proteins Definition Inhibitor of DNA (Id) binding proteins are a family of related nuclear ▶helix-loop-helix-proteins implicated

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Idarubicin

in the control of differentiation and cell cycle progression. Id nuclear proteins interact with ▶transcription factors and prevent them from binding to DNA. The primary targets of Id proteins are the basic helix-loophelix (bHLH) transcription factors, which regulate celltype-specific gene expression and expression of ▶cell cycle regulatory genes. Generally, they act as positive regulators of cell growth and as negative regulators of differentiation. Id proteins lack a basic DNA-binding domain; therefore, heterodimers between Id and bHLH proteins cannot bind to DNA. This mode of regulation is referred to as dominant-negative. Id proteins act as dominant-negative antagonists of other helix-loop-helix transcription factors; Id1, Id2, Id3, Id4, E-box. . Id1, inhibitor of DNA binding 1, is a protein of 154 amino acids and 16 kD. The gene maps to chromosome 20 band q11. . Id2, inhibitor of DNA binding 2, is a protein of 134 amino acids and 14 kD. It is expressed in most early fetal tissues but not in the corresponding mature tissues. The gene maps to 2p25. . Id3, inhibitor of DNA binding 3, also known as Heir1 is a protein of 119 amino acids and 12 kD. It is expressed abundantly in lung, kidney, and adrenal gland, but lacking in adult brain. The gene maps to 1p36, a region frequently deleted in human cancers including neuroblastoma. . Id4, inhibitor of DNA binding 4, is a protein of 161 amino acids and 16 kD. The gene maps to 6p22-21. ▶E-box ▶Helix-Loop-Helix Domain

Idiopathic Myelofibrosis ▶Primary Myelofibrosis

Idiotype Definition Is the collection of all antigenic determinants (idiotopes) contained within the variable regions of both heavy and light chain of an antibody molecule. The sum of the antigenic determinants of epitopes that are encoded in the variable regions of the ▶immunoglobulins heavy and light chain. ▶Idiotype Vaccination ▶B-cell Tumors

Idiotype Vaccination M AURIZIO B ENDANDI University Clinic and Center for Applied Medical Research, University of Navarra, Pamplona, Spain

Synonyms Anti-idiotype vaccination; Idiotypic vaccination

Idarubicin Definition

Is a semisynthetic ▶anthracycline antibiotic derived from ▶daunorubicin. ▶Adriamycin

Idiopathic Bone Infarction

Definition

▶Idiotype vaccination is an ▶immunotherapy procedure based on the fact that save for its very early stage of differentiation, each clone of B lymphocytes features a specific antibody on the cell surface. The most variable portion of this antibody is a unique feature of the corresponding clone. Its natural function is that of specifically recognizing an antigen, but it can also be used as an antigen (idiotype) itself, that is as a potential vaccine target and tool. The most relevant context in which this second function is exploited is idiotype vaccination as a treatment for human ▶B-cell lymphoma.

Definition

Characteristics

▶Bone Tumors

Field of Application The vast majority of B-cell lymphomas consist of the clonal expansion of neoplastic B-cells, all featuring the same surface antibody and consequently the same

Localized bone ▶necrosis and its associated bone marrow for unknown reasons.

Idiotype Vaccination

idiotype. However, each patient’s tumor presents with a different, patient- and tumor-specific idiotype. Therefore, an individualized, custom-made idiotype vaccine must be produced for each patient. Most of what we know about idiotype vaccination in human B-cell lymphoma derives from studies conducted in an indolent subset called ▶follicular lymphoma. Far less has been instead concluded so far as to whether or not the same approach could be successful in other B-cell malignancies, such as ▶mantle cell lymphoma, ▶multiple myeloma, and ▶chronic lymphocytic leukemia, or even in certain solid tumors, whenever an anti-idiotype ▶monoclonal antibody structurally mimics tumor-associated antigens other than antibodies. Nevertheless, idiotype vaccination stands out as the most successful human cancer vaccine, since over the last 20 years has provided the first formal proofs of principle concerning biological efficacy, clinical efficacy, and clinical benefit of such a procedure. Formulation Although idiotypic vaccination has been tested in humans with different formulations, such as soluble protein idiotype associated with an immunogenic carrier and an immunologic adjuvant, ▶dendritic cells pulsed with the soluble protein idiotype, or idiotype ▶DNA vaccine, most clinical results and all proofs of principle have been obtained using the first of these three options. In particular, the most successful idiotype vaccine formulation consists of soluble protein idiotype, that is the patient- and tumor-specific antigen, which is conjugated with keyhole limpet hemocyanin (KLH), the immunogenic carrier, and administered together with granulocyte-macrophage colony-stimulating factor (GM-CSF), the immunologic adjuvant. Production While KLH and GM-CSF are commercially available, soluble protein idiotype needs to be produced one patient at the time through either hybridoma or ▶recombinant technology. In the former case, each patient’s tumor cells, which are capable of producing the idiotype, but not to release it, are fused with a cell line that vice versa can release an idiotype, but is unable to produce it. The ▶hybridoma resulting from the fusion process features both functions, can be cultivated in vitro, and releases therapeutic amounts of the patient- and tumor-specific, soluble protein idiotype. In the latter scenario, the genetic information encoding for the idiotype is introduced by means of a vector inside mammalian, insect, plant, or bacteria cells, which will ultimately replace the hybridoma as a factory for soluble protein idiotype production. Clinical Aspects Idiotype vaccination has provided the first formal proof of biological efficacy in 1992, when scientists at Stanford University showed that patients with follicular lymphoma were capable of developing a specific, anti-idiotype

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immune response after receiving idiotype vaccination. Seven years later, researchers at the National Cancer Institute proved clinical efficacy of idiotype vaccination by showing that in most follicular lymphoma patients who had received it, the immune system had become capable of killing in vivo tumor cells that had survived prevaccine ▶chemotherapy. Finally, in 2006 clinical efficacy of idiotype vaccination was proved by showing that all follicular lymphoma patients who respond to the vaccine from an immunologic standpoint experience a significant prolongation of their disease-free survival. Idiotype vaccination’s procedure typically consists of a monthly, subcutaneous injection of 0.5 mg of idiotype conjugated with 0.5 mg of KLH, administered together with 125 mcg of GM-CSF. The same dose of GM-CSF alone is then given daily over the following 3 days at the same site of the complete vaccine formulation delivery. After 5 or 6 monthly doses, further boosts every 2–3 months are becoming increasingly popular and recommended. Idiotype vaccination’s side effects are mild and mostly local, if at all present. Flu-like symptoms are rare and self-limiting. Open Questions To date, a number of questions remain open with respect to idiotype vaccination. For instance, from a clinical standpoint, we do not know whether this form of active ▶immunotherapy has the potential to cure or just to control the disease in lymphoma patients who respond to it. Nor do we know whether patients with B-cell malignancies other than follicular lymphoma may benefit from it. The former question implies that it remains currently impossible to determine whether the administration of boosts should or could be stopped in patients who have responded to the vaccine from an immunologic point of view, irrespective of whether that immune response persists detectable, and remain free of disease. The latter question implies instead that only through welldesigned ▶clinical trials it might be possible to test idiotype vaccination in settings other than follicular lymphoma. In particular, it has to be reminded that typical randomized studies may fail to serve the purpose of proving the clinical benefit of a customized form of immunotherapy. In this respect, surrogate endpoints such as those defining minimal residual disease also need to be used with caution. For instance, in the very case of follicular lymphoma, both ▶bcl-2 rearrangement assessed by molecular fingerprinting through qualitative and quantitative polymerase chain reaction and tumor cell phenotype assessed through ▶flow cytometry not always correlate with immune responses and clinical outcome. All in all, it is possible that the currently ongoing randomized clinical trials will be at least able to shed some light on whether it may be possible to match the financial concerns of pharmaceutical companies

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with the peculiar logistic requirements of a customized treatment like idiotype vaccine. As for the adequate timing for treating patients with this immunotherapeutic approach, it seems to have become ever clearer that the best clinical setting to use idiotype vaccination is a good quality clinical complete response. This prevaccine result can be achieved nowadays through a variety of old and new therapeutic approaches such as standard or high-dose chemotherapy, cold or passive immunotherapy using ▶radioimmunoconjugates. However, it is likely that in lymphoma patients selected to later undergo idiotype vaccination, prevaccine treatment should privilege agents and procedures with the lowest immune suppressive potential. At the opposite side of the widening spectrum of possible applications of idiotype vaccination stand the anecdotal attempts conducted with healthy donors undergoing this totally safe procedure with the myeloma-specific soluble protein idiotype obtained from their sibling recipient before ▶hematopoietic stem cell allotransplant. Clinical and biological results remain incompletely understood, though extremely appealing from a purely scientific point of view. Another crucial context in which idiotype vaccination specialists still struggle is that of defining the relevance of idiotype vaccine-induced humoral and cellular responses. In fact, it is not yet clear whether, though both desirable, just either of them is required for patients to experience clinical benefit. The question is of no little importance, considering that in nearly half of the patients with any vaccine-induced, idiotype-specific immune response, either type of immune response is not detectable. Currently, humoral responses, that is those featuring vaccine-induced anti-idiotype antibodies, are assessed and monitored in the lab by a single, relatively standardized method, whereas at least half a dozen of nonstandardized techniques are used in different labs worldwide to assess and monitor vaccine-induced cellular responses

Idiotypic Vaccination ▶Idiotype Vaccination

IDO ▶Indoleamine 2,3-Dioxygenase

I-FLICE ▶FLICE Inhibitory Protein

IFN Definition

▶Interferon are ▶cytokines that can induce cells to resist viral replication. Interferon-α (IFN-α) and interferon-β (IFN-β) are produced by ▶leukocytes and ▶fibroblasts, respectively, as well as by other cells, whereas interferon-γ (IFN-γ) is a product of CD4 TH1 cells, ▶CD8 T cells, and ▶NK cells. IFN-γ has its primary action the activation of ▶macrophages.

References 1. Kwak LW, Campbell MJ, Czerwinski DK et al. (1992) Induction of immune responses in patients with B-cell lymphoma against the surface-immunoglobulin idiotype expressed by their tumors. N Engl J Med 327:1209–1215 2. Bendandi M, Gocke CD, Kobrin CB et al. (1999) Complete molecular remissions induced by patientspecific vaccination plus granulocyte-monocyte colonystimulating factor against lymphoma. Nat Med 5: 1171–1177 3. Inogés S, Rodríguez-Calvillo M, Zabalegui N et al. (2006) Clinical benefit associated with idiotypic vaccination in follicular lymphoma. J Natl Cancer Inst 98:1292–1301 4. Bendandi M (2006) Clinical benefit of idiotype vaccines: too many trials for a clever demonstration? Rev Recent Clin Trials 1:67–74

iFOBT ▶Fecal Immunochemical Test

IgE-Mediated Hypersensitivity ▶Allergy

Illegitimate Recombination

IGF Definition

▶Insulin- Like Growth Factors. ▶Insulin Receptor

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IISRE Definition

A type IIS “stretch” restriction endonuclease (IISRE) is a restriction enzyme that binds double-stranded DNA at a particular sequence and then cleaves double-stranded DNA at a fixed distance and direction from its binding site without regard to sequence specificity. Examples include BsgI, BpmI, Eco57I, FokI, and HphI. ▶Combinatorial Selection Methods

IGF-2 Definition Insulin-like growth factor 2. ▶Insulin Receptor ▶Insulin-Like Growth Factors

IL-1 Definition

▶Interleukin-1 ▶Photodynamic Therapy

IGF-I Definition Insulin-like growth factor-1. ▶Insulin Receptor-1 ▶Insulin-Like Growth Factors

IGs Definition

IL-12 Definition

▶Interleukin-12 is the product of ▶monocytes such as ▶macrophages, ▶neutrophils and ▶dendritic cells. It is an early component of the innate immune response and serves to activate ▶natural killer cells and assist in the differentiation of Th cells to the Th1 phenotype. Since both these cells are a source of ▶IFN-γ, IL-12 is a key regulator of IFN-γ production by the immune system. ▶Immunoediting

▶Immunoglobulin Genes.

Illegitimate Recombination IHC ▶Immunohistochemistry

Definition Recombination with nonhomologous regions of DNA, each of the polynucleotide strands of dsDNA being

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Image Cytometry

religated with DNA from different regions of the same or different chromosomes. ▶Chromosomal Translocation ▶Fusion Genes

Characteristics

Image Cytometry Definition Involves measurement of the shape and density of cellular structures to assess anatomic pathology of a given cell. Modern approaches to image ▶cytometry incorporate computational analysis to infer disease state based on hundreds of measurements from each individual cell. ▶Malignancy-Associated Changes

Imaginal Discs Definition Monolayer sac-like epithelial tissues in Drosophila larvae that later give rise to adult structures. ▶Lats in Growth Regulation and Tumorigenesis

Imatinib B RIAN J. D RUKER Oregon Health & Science University Cancer Institute, Portland, OR, USA

Synonyms Imatinib mesylate; Gleevec; ▶STI-571; CGP57148

(▶Platelet-derived growth factor receptor). It has significant anti-tumor activity in chronic myeloid leukemia and ▶gastrointestinal stromal tumors.

Glivec;

STI571;

Definition Is a small molecular weight compound that inhibits ▶tyrosine kinases including ▶ABL, ▶KIT (▶Kit/stem cell factor receptor in oncogenesis) and PDGFR

Imatinib (Gleevec, Glivec, formerly STI571 or CGP57148) is a tyrosine kinase inhibitor with activity against all of the ABL tyrosine kinases including ▶BCR-ABL, ABL, v-ABL, and ARG (Abelson-related gene). Besides the ABL tyrosine kinase, other kinases inhibited by imatinib are the platelet-derived growth factor receptor alpha (PDGFRA) and beta (PDGFRB) and KIT. Given the critical role of tyrosine kinases in the regulation of cellular growth and known activating mutations that cause several cancers, it was hypothesized that specific inhibitors of these protein kinases might be effective anticancer agents. Beginning in the late 1980s, scientists at Ciba Geigy (now Novartis), under the direction of N. Lydon and A. Matter, performed high throughput screens of chemical libraries searching for compounds with kinase inhibitory activity. From this time-consuming approach, a lead compound was identified. Its inhibitory activity against the PDGFR was optimized by synthesizing a series of chemically related compounds and analyzing their relationship between structure and activity (▶Drug design). The most potent molecules in the series were dual inhibitors of the PDGFR and ABL kinases. Of the several compounds generated from this program, imatinib emerged as the lead compound for clinical development based on its superior in vitro selectivity against ▶CML cells and its drug-like properties, including pharmacokinetic and formulation properties (▶Pharmacokinetics; ▶pharmacodynamics). BCR-ABL and CML as a Target for Imatinib CML is characterized by the presence of the BCR-ABL ▶fusion gene and protein. It arises from a ▶reciprocal translocation between the long arms of chromosomes 9 and 22 (▶Chromosome translocations) that generates a shortened chromosome 22 termed the ▶Philadelphia chromosome. This was the first consistent chromosome abnormality associated with a human cancer. The (9;22) translocation results in fusion of the ABL ▶oncogene from chromosome 9 with sequences from chromosome 22, the breakpoint cluster region (BCR), giving rise to a chimeric BCR-ABL gene. This fusion gene is transcribed and translated into a protein that functions as a constitutively activated tyrosine kinase. BCR-ABL induces a CML-like syndrome when introduced into bone marrow cells of mice (▶Mouse models), confirming its causative role in the human disease. All of the transforming activities of BCR-ABL are dependent on its tyrosine kinase activity, thus a specific inhibitor of

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counts, ▶Myelosuppression, fluid retention, diarrhea, nausea, muscle and joint aches, and skin rashes.

Imatinib. Figure 1 Schematic representation of the mechanism of action of the BCR-ABL tyrosine kinase and its inhibition by STI571 (imatinib).

this kinase would be predicted to be an effective and selective therapeutic agent for CML (Fig. 1). In a pivotal set of ▶preclinical testing, imatinib was shown to suppress the proliferation of BCR-ABLexpressing cells in vitro and in vivo. In colony-forming assays of peripheral blood or bone marrow from patients with CML, imatinib caused a 92–98% decrease in the number of BCR-ABL colonies formed, with minimal inhibition of normal colony formation. Activity of Imatinib in CML Given the central role of the BCR-ABL tyrosine kinase in causing CML and the favorable preclinical profile of imatinib, CML was selected as the initial disease in which to test imatinib. In a standard dose-escalation Phase I study (▶Clinical trial) conducted in patients with CML, imatinib was well tolerated. Significant clinical benefits were observed at doses of 300 mg per day and above. In patients with chronic-phase disease who were interferon resistant or intolerant, 53 of 54 (98%) had their previously abnormal blood counts return to normal, typically within 4–6 weeks after beginning imatinib. Ninety percent of these responses lasted beyond 1 year. In patients with myeloid ▶blast crisis, the most advanced phase of the disease, 21 of 38 (55%) patients responded, with 18% having responses lasting beyond 1 year. Imatinib rapidly advanced through Phase II and III testing for patients with CML and was FDA-approved in May 2001. It is now the standard initial therapy for patients with CML. A 5-year update of imatinib as initial therapy for patients with CML demonstrates an overall survival of 89%. At 5 years, an estimated 93% of patients remain free from disease ▶progression to advanced phases of the disease: accelerated phase or blast crisis. Most of the side effects of imatinib are classified as mild to moderate and include low blood

Mechanisms of Relapse/Resistance to Imatinib Response rates to imatinib in CML patients with chronic-phase disease are quite high and, thus far, have been durable. Response rates are also quite high in patients with advanced-phase disease, but relapses, despite continued therapy with imatinib, are common. In the largest studies of resistance or relapse, several consistent themes have emerged. In the majority of patients who respond to imatinib but subsequently relapse while remaining on therapy, the BCR-ABL kinase has been reactivated. BCR-ABL kinase activity was analyzed by assessing tyrosine phosphorylation of CRKL, a direct substrate of the BCR-ABL kinase, and the major tyrosine phosphorylated protein in samples from patients with CML. In these studies, between 50 and 90% of relapsed patients have a BCR-ABL point mutation located in one of over 40 different amino acids scattered throughout the ABL kinase domain. Some other patients have amplification of BCR-ABL at the genomic or transcript level. In contrast, in patients with primary resistance – that is, patients who do not respond to imatinib therapy – BCR-ABL-independent mechanisms are most common. In patients who relapse as a consequence of reactivation of the BCR-ABL kinase, the BCR-ABL kinase remains a good target. Alternate ABL kinase inhibitors are already in clinical trials (▶Nilotinib, ▶dasatinib) and dasatinib is FDA-approved for patients with CML with imatinib resistance. There remains at least one imatinib-resistant mutation, T315I, that is not inhibited by either drug. Activity of Imatinib in Other Diseases Given the success of imatinib in CML, it was logical to try imatinib in other diseases where activated tyrosine kinases targeted by imatinib have causative roles. Thus, imatinib also has significant activity in patients with ▶acute lymphoblastic leukemia who are BCR-ABLpositive. Another tumor in which imatinib has shown activity is ▶gastrointestinal stromal tumor (GIST). GISTs are mesenchymal neoplasms that can arise in any organ in the gastrointestinal tract or from the mesentery or omentum. The majority of GISTs express KIT, and in 90% of cases, KIT activation is linked to mutations, usually involving exons 9 or 11. Published data suggest that the response rate of GISTs to single- or multi-agent ▶chemotherapy is less than 5%. In contrast, the response rate to imatinib as a single agent in patients with advanced GIST was 53–65% with another 19–36% of patients having disease stabilization. Mutational status helps predict response to imatinib in GIST patients. Patients whose tumors contain the most common activating KIT mutation exon 11 have a significantly higher partial response rate (83.5%) to imatinib therapy

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than did patients whose tumors had no detectable mutations in KIT. Patients whose tumor harbored a KIT exon 9 mutation did less well than those with an exon 11 mutation but responded better (response rate of 48.7%) and had a longer time-to-treatment failure than those with no detectable mutation. Similar to the situation in CML, many imatinibresistant tumors have acquired kinase mutations in the kinase domain of KIT. However, resistance mechanisms in GISTs are more heterogeneous than those seen in chronic-phase CML as some tumors actually lose KIT expression and other tumors become imatinib-resistant without acquisition of secondary kinase mutations. Again, similar to the situation with CML, novel KIT kinase inhibitors are being tested in patient with imatinib-resistant GIST and one of them, sunitinib, has been FDA-approved for this indication. Imatinib also has activity in neoplasms that are caused by oncogenic activation of PDGFRs (Plateletderived growth factor receptor). This includes the subset of patients with chronic myelomonocytic leukemia that results from fusion of the ▶EVT6 (TEL) and PDGFRB genes. Similarly, dermatofibrosarcoma protuberans, a low-grade sarcoma of the dermis, is characterized by a (17;22) translocation involving the COL1A1 and PDGF-B genes, which results in overproduction of fusion COL1A1-PDGF-BB ligand and consequent hyperactivation of PDGFRB. Patients with this tumor also respond to imatinib. Hypereosinophilic syndrome is another example of an imatinib-sensitive disease. In this case a PDGFRA fusion gene product (FIP1L1-PDGFRA) is the activated target. Conclusion The development of imatinib and its clinical application demonstrate an emerging paradigm in cancer therapy where the tumor is defined by molecular genetic abnormalities instead of the tissue of origin. It further demonstrates that effectiveness of cancer therapy when treatments target events critical to the growth and survival of specific tumors. (▶Molecular therapy).

References 1. Druker BJ, Tamura S, Buchdunger E et al. (1996) Effects of a selective inhibitor of the Abl tyrosine kinase on the growth of Bcr-Abl positive cells. Nat Med 2:561–566 2. Druker BJ, Talpaz M, Resta DJ et al. (2001) Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia. N Engl J Med 344:1031–1037 3. Heinrich MC, Corless CL, Demetri GD et al. (2003) Kinase mutations and imatinib response in patients with metastatic gastrointestinal stromal tumor. J Clin Oncol 21:4342–4349

4. Druker BJ, Guilhot F, O’Brien SG et al. (2006) Five-year follow- up of patients receiving imatinib for chronic myeloid leukemia. N Engl J Med 355:2408–2417 5. Druker BJ (2006) Circumventing resistance to kinaseinhibitor therapy. N Engl J Med 354:2594–2596

Imatinib Mesylate ▶Imatinib

Imiquimod Definition A small molecular drug that activates TLR7 and/or TLR8 agonist that is used as a prescription medication to treat ▶skin cancer (▶basal cell carcinoma, ▶Bowen disease, superficial squamous cell carcinoma, some superficial malignant melanomas and actinic keratosis) as well as genital warts.

Immature B Cells Definition

Are ▶B cells that have rearranged a heavy- and a lightchain V-region gene and express surface IgM, but have not yet matured sufficiently to express surface IgD as well.

Immediate Early Genes Definition IEGs; A class of approximately 100 structurally and functionally unrelated genes, whose transcription is induced through the phosphorylation and activation of pre-existing transcription factors such as ▶ELK-1 by intracellular signaling pathways like ▶MAP kinase. A hallmark of immediate early genes (IEGs) is that their transcription is independent from de novo protein

Immune Escape

synthesis, which distinguishes them from delayed early genes. Examples for IEG products include ▶FOS, a component of the ▶AP-1 transcription factor complex, and several members of dual specificity phosphatases, which act as negative feedback regulators of MAP kinases. ▶B-Raf Signaling

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Immune Adjuvants Definition Substances that are typically added to vaccines to enhance their immunogenicity. ▶Peptide Vaccines for Cancer ▶Adjuvant

Immediate Early Stress Response ▶Stress Response

Immune Complex Definition

Immortalization Definition Describes the acquisition by a eukaryotic cell line of the ability to grow through an indefinite number of divisions in culture. Cells are capable of indefinite proliferation (or unlimited lifespan) without any other changes in the phenotype necessarily occurring. In long lived multicellular organisms, immortality may be thought of as an abnormal escape from cellular ▶senescence. ▶Telomerase ▶Senescence and Immortalization

The binding of antibody to a soluble antigen forms an immune complex. Large immune complexes form when sufficient antibody is available to cross-link the antigen; these are readily cleared by the reticuloendothelial system of cells bearing Fc and complement receptors. Small, soluble immune complexes that form when antigen is in excess can be deposited in and damage small blood vessels.

Immune Deviation Definition

Immortalized

Is the deliberate polarization of an immune response from one dominated by TH1 to one dominated by TH2, or vice versa.

Definition

Refers to the status of ▶immortalisation of cells.

Immune Escape Immortalized Cells Definition Transformed cells that can grow and divide indefinitely in vitro. ▶Adult Stem Cells ▶Immortalization

J IAHUA Q IAN , TAMARA F LOYD, Y UFEI J IANG , A NAT O HALI , R AED S AMARA , H ONG YANG , S AMIR N. K HLEIF Cancer Vaccine Section, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA

Definition Is one of the hallmarks of cancer development and ▶metastasis. It is characterized by the lack of ability of

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the immune system to eliminate transformed cells prior to and after tumor development.

Characteristics Several mechanisms have been proposed and tested to explain cancer immune escape. It is now evident that both the host as well as the tumor play important roles in this phenomenon. The host’s contribution is manifested by the host’s ability to recognize to antigens expressed by tumor cells, a phenomenon known as “Host Ignorance”. It happens because of defects in both the innate and adaptive arms of the immune system. The tumor’s contribution is manifested by the adaptation of tumor cells to evade the immune systems or developing a ▶microenvironment that suppresses the immune system. Host Ignorance The innate arm of the immune system forms a first line of defense against cancers. ▶Macrophages, ▶dendritic cells, and ▶monocytes are essential in eliminating cancers. Another type of cell involved in the elimination of cancers is ▶NK cells. These cells are capable of recognizing and attacking cells that have down-regulated ▶MHC class I expression. This phenomenon is known as “missing self-recognition.” NK cells can effectively eliminate cells that have been altered due to cellular transformation, infection, or other carcinogens and cannot present new antigens. If these players involved in the ▶innate immune system are defective, cancer cells may escape tumor ▶immunosurveillance from not only innate immunity but also ▶adaptive immunity as NK cells, macrophages, NKT cells, play a role in the induction and enhancement of ▶adaptive immune responses. The adaptive arm of the immune system has also been shown to play a crucial role in recognizing and eliminating cancer cells. However, several defects have been shown to hamper the ability of this arm to combat tumor cells. 1. Defects in ▶antigen-presenting cell (APC). To elicit an effective immune response, antigens must be processed first by the APCs and presented to the immune system. Dendritic cells (DCs) are professional APCs and play an important role in regulation of adaptive immune response. Many tumor patients have shown defects in the DC compartment in terms of cell number and/or altered function. Tumor infiltrating DCs have defective surface expression of HLA and B7 costimulatory molecules, thus are likely to induce anergy rather than to stimulate tumor-specific T cells. Additionally, the immunosuppressive enzyme indoleamine-2,3-dioxygenase (IDO), which has been implicated as one mechanism that helps to maintain maternal ▶tolerance toward the fetus during pregnancy, was recently recognized

as a potential mechanism of tolerance in malignancies. Expression of ▶IDO on APCs was observed in tumor draining lymph nodes, which may be indicative of the creation of a tolerogenic microenvironment. The molecular mechanism by which ▶IDO suppresses T cells is still being elucidated. It was suggested to be mediated by depletion of the essential amino acid tryptophan and by the generation of pro-apoptotic metabolites. 2. Negative immune regulation by suppressive cells. There are several types of suppressive cells in the immune system, including ▶regulatory T cells, ▶myeloid suppressor cells (MSCs) and NKT cells. They exist to keep the immune response under control and prevent autoimmunity. In addition, these cells have been shown to inhibit immune responses against tumor cells. (i) Regulatory T (Treg) cells are a subpopulation of CD4+ ▶T cells. Tregs are crucial for controlling autoreactive ▶T cell responses. At least two distinct subsets of Tregs have been identified: natural and inducible Tregs. Natural Tregs are T cells that arise in the thymus. They require direct cell contact with their target cells in order to exert their regulatory functions. Inducible Tregs arise in the periphery and exert their regulatory functions by the soluble cytokines IL-10 and TGF-β. The exact mechanisms by which Tregs exert their regulatory functions remain largely unknown. However, there is sufficient evidence, both in humans as well as in rodents, demonstrating that Tregs play crucial roles in suppressing anti-tumor responses. (ii) Myeloid suppressor cells were first identified by the expression of surface marker CD11b and Gr-1. Their suppressive activity was shown by inhibiting lymphocyte proliferation and inducing apoptosis in CD8 T cells. (iii) NKT cells are a unique sub-lineage of T cells. However, in contrast to conventional and regulatory T cells that recognize peptides in the context of MHC class I and II molecules, NKT cells recognize glycolipids presented by CD1d, a non-classical antigen presenting molecule. This difference in recognition means that NKT cells can recognize a class of antigens that conventional T cells cannot recognize. NKT cells have been shown to promote as well suppress immune responses to cancer. Currently, it is still unclear what factors determine their function. 3. Defective anti-tumor T cells. Another factor that leads to a failed immune response to tumor is cells dysfunction in ▶tumor-infiltrating lymphocytes (TILs). In a number of studies, TILs have been shown to have defective anti-tumor killing effect. This dysfunction may result from the ineffective granule exocytosis. TILs also have been reported to have defective cytokine production and low expression of B7.1 and B7.2 costimulatory molecules, suggesting anergy could occur.

Immune Escape of Tumors

Tumor Cell Adaptation To escape immune surveillance, tumor cells deploy several strategies. 1. Downregulation of MHC class I expression on cell surface. The presentation of antigen by ▶MHC class I is crucial for immune responses. By downregulating MHC class I molecules on the surface, tumor cells may become elusive targets for T cells thereby escape the destruction by ▶cytotoxic T lymphocytes (CTLs). 2. Suppression of the Immune System. Tumor cells have several “counterattack” methods to fight the immune system. This include: (i) Secretion of immunosuppressive cytokines such as IL-10, TGFβ, IL-13, etc. IL-10 interferes with the induction of anti tumor responses. It has been shown to block dendritic cell-mediated priming of T cells into CTL effectors in vitro, and its expression in serum appears to be associated with negative prognosis in certain cancers. ▶TGF-β is another cytokine that inhibits activation, proliferation, and activity of T lymphocytes. This ▶cytokine is often found at high levels in malignancies and is associated with a poor prognosis as well as lack of response to tumor immunotherapy. Both cytokines can be produced by the tumor cells themselves or by infiltrating stroma cells. Interestingly, TGF-β has also been shown to drive expansion of regulatory T cells, thus bringing together two evasion mechanisms. (ii) Up-regulation of tumor cells of Fas ligand on the surface to induce apoptosis of tumor killing effector cells. The deathinducing ▶FAS/APO-1/CD95 ligand (FasL/ CD95L) has been reported to be expressed on many human tumors of various origins. Expression of FasL in tumors implies that cancer cells are resistant to Fas-induced cell death, which preserves them from extermination by cytotoxic T cells and actively induces death of effector T cells. In addition to local defense, accumulating evidence suggests that the FasL expression may also be relevant for tumor progression and formation of metastasis. It was further described that tumor cells are able to release membrane vesicles (MV) or exosomes containing FasL which induce ▶apoptosis of activated T cells. This apoptosis-inducing pathway, via the release of FasL-positive MV, may indeed play a significant role in eliminating the most effective component of the anti tumor T cell response, and provides an explanation for the observed spontaneous T cell apoptosis in the peripheral circulation of cancer patients. (iii) Inhibition of effector cells by inhibitory ligands including PD-L1, CTLA-4 and LAG-3. Evidence suggests that tumor cells may evade T and NK cell recognition by receptor ligand interaction. CTLA-4 is a receptor predominantly

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found on T lymphocytes interacting with CD86 ligand. CTLA-4 is related to CD28 on T lymphocytes, but plays an opposite role. CTLA-4 may act at the level of TCR or CD28 signaling to inhibit T cell activation. Several studies provide evidence that CTLA-4 can up-regulate TGF-β expression and can attenuate CD28 signals on Treg expansion and survival. The precise mechanism of T cell inactivation by CTLA-4/CD86 signaling, however, remains uncertain. The PD-1 – PD-L pathway has been postulated to regulate the immune response in both lymphoid and non-lymphoid organs. PD-Ls are expressed in many tumors such as ▶ovarian cancer, ▶esophageal cancer, ▶kidney cancer and ▶brain cancer. It is suggested that tumor associated PD-Ls may promote T cell apoptosis and thus affect immune responses. Another inhibitory ligand associated with ▶MHC class II interactions is LAG-3 (lymphocyte activation gene-3). LAG-3-MHC class II could enhance the cross-talk between T cell and DC. In human cells, LAG-3 serves as a negative regulator of activated T cells. A comprehensive understanding of these inhibitory pathways will facilitate the design of effective ▶immunotherapy in the future.

References 1. Lang K, Entschladen F, Weidt C et al. (2006) Tumor immune escape mechanisms: impact of the neuroendocrine system. Cancer Immunol Immunother 55:749–760 2. Munn DH (2006) Indoleamine 2,3-dioxygenase, tumorinduced tolerance and counter regulation. Curr Opin Immunol 18:220–225 3. Rivoltini L, Canese P, Huber V et al. (2005) Escape strategies and reasons for failure in the interaction between tumour cells and the immune system: how can we tilt the balance towards immune-mediated cancer control? Expert Opin Biol Ther 5:463–476 4. Gajewski TF, Meng Y, Harlin H (2006) Immune suppression in the tumor microenvironment. J Immunother 29:233–240 5. Diefenbach A, Raulet D (2002) The innate immune response to tumors and its role in the induction of T-cell immunity. Immunol Rev 188:9–21

Immune Escape of Tumors Definition Many tumors grow progressively despite an ongoing tumor-specific immune response. It has been experimentally shown that tumor cells adopt a variety of

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strategies to “escape” both ▶innate immunity as well as ▶adaptive immunity. For example, tumor cells downregulate or loose tumor antigens or important components of the antigen-processing machinery so that ▶T cells are no longer able to recognize peptides bound to major histocompatibility complex molecules on the cell surface. Tumor cells may also express ▶cytokines (such as IL-10 or ▶TGFβ) or cell surface molecules (such as ▶FAS or PD-1) which actively inhibit cellular anti-tumor immunity including the induction of T cell ▶apoptosis, T cell anergy and regulatory T cells. ▶Melanoma Vaccines ▶T-Regulatory Cells

(iii) the escape phase, in which tumors actively disable immune recognition by co-opting immune cells for growth, ▶angiogenesis and ▶invasion. ▶Melanoma Vaccines ▶Immunoprevention ▶Allergy

Immune System Definition

Immune Response

Refers to the tissues, cells, and molecules involved in ▶adaptive immunity, or sometimes the totality of host defense mechanisms.

Definition Is the response made by the host to defend itself against a pathogen.

Immunoassay Definition

Immune Responses to Autoantigens

A test using antibodies to identify and quantify substances. Often the ▶antibody is linked to a marker such as a fluorescent molecule, a radioactive molecule, or an enzyme.

▶Autoimmunity and Prognosis

Immunoblotting Immune Surveillance of Tumors Definition Definition The concept that the immune system is able to recognize and eliminate cancerous or pre-cancerous cells was first postulated in 1909 by Paul Ehrlich and was further propagated by McFarlane Burnet in the 1950s. Studies in genetically modified, immunodeficient mice have led to a refinement of this theory by Robert Schreiber and co-workers and has been called “cancer ▶immunoediting.” It describes three phases: (i) The elimination phase in which nascent tumor cells are destroyed by elements of the ▶innate immunity and ▶adaptive immunity; (ii) the equilibrium phase, in which tumor cells persists but are “equilibrated” by the immune system which prevents tumor progression; and

Is a common technique in which proteins separated by gel electrophoresis are blotted onto a nitrocellulose membrane and revealed by the binding of specific labeled antibodies.

Immunochemical Fecal Occult Blood Test ▶Fecal Immunochemical Test

Immunoediting

Immunocompetent Definition

Capable of developing an ▶immune response.

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Immunoediting Y VONNE PATERSON Professor of Microbiology, University of Pennsylvania, Philadelphia, PA, USA

Definition

Immunocytochemistry Definition

synonym: ▶Immunohistochemistry; Is a method of identifying cell types based on the demonstration of a specific cytoplasmic or nuclear protein or antigen in situ. It does this by detecting specific antibodyantigen interactions where the antibody has been tagged with a visible label, most commonly an enzyme. It is very useful for differentiating and subclassifying ▶carcinomas, ▶sarcomas, ▶melanomas and ▶lymphomas. ▶Fine Needle Aspiration ▶Pathology

Immunodeficient Nude Mice Definition Are athymic hairless mice without T-cells, that are unable to generate an effective ▶immune response. This makes possible the transplantation of human cancer cells without rejection. ▶MIC-1 ▶T cell

Immunodiffusion Definition Is the detection of antigen or antibody by the formation of an antigen:antibody precipitate in a clear agar gel.

Changes in the immunogenicity of tumors due to the anti-tumor response of the immune system that result in the emergence of immune-resistant variants.

Characteristics History The concept of immunoediting is predicated on the insight that the immune system can recognize tumor cells. The notion that the immune system monitors the host, not only for pathogen invasion but also for neoplastic changes, arose early in the history of Immunology, was first proposed by Paul Ehrlich in 1909 and then resurrected 50 years later by Burnet and Thomas. These early immunologists proposed that the immune system recognizes cells that have undergone neoplastic changes and eliminates them before they can form tumors, a concept known as immune surveillance. However, although this notion has been around for nearly a century it was only quite recently unequivocally demonstrated in murine models when Schreiber and colleagues, in 2001, examined the incidence of adenomas and carcinomas in aging wild type mice compared to mice lacking the ▶recombinase activating gene-2 (RAG2). The RAG2 gene controls the ▶V(D)J recombination of genes required to generate ▶B cell and ▶T cell antigen-specific receptors. In its absence, or the absence of its partner in this process, RAG1, the development of lymphocytes that bear these receptors is aborted. Thus in mice that lack RAG1 or RAG2, T cells, B cells and NKT cells fail to develop and the mouse has no adaptive immune response. The Schreiber lab showed that these immunodeficient mice had a higher incidence of spontaneous cancer and were more susceptible to carcinogen induced sarcomas. These tendencies were increased in mice lacking not only the RAG2 gene but in addition the ▶STAT-1 gene, which controls the ▶interferon– gamma ▶signal transduction pathway. Thus both adaptive immune effector cells and the multifunctional lymphokine IFN-γ were shown to play a clear role in immunosurveillance. However, in the process of studying ▶immunosurveillance the Schreiber group made the interesting observation that a high proportion of tumors that emerged in carcinogen treated RAG2 deficient mice failed to grow in wild type mice indicating that within the population of tumor cells that

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arose in the immunodeficient mice were cells that could be recognized and eliminated by an intact immune system. In contrast tumors that arose in wild type mice were less immunogenic and would grow when transplanted into either wild type or RAG2 deficient mice. Schreiber termed this process by which the immunological environment alters the immunogenicity of tumors “immunoediting.” The Role of Interferons and Other Immune Components A large body of work provides evidence that both ▶adaptive immunity and ▶innate immunity play a role in controlling the immunogenicity of tumors that develop in the mouse. Most of these studies have focused on the formation of carcinogen induced sarcomas in mice genetically manipulated to lack the expression of genes required for the generation of lymphocytes and cytokines. Thus in terms of innate immune cells, ▶γδ (gamma delta) T cells, ▶Natural Killer cells and NKT cells have been shown to be involved in controlling tumor growth as have conventional αβ (alpha beta) ▶T cells, the hallmark of the adaptive cellular immune response. The importance of cytotoxic lymphocytes, such as T cells and ▶NK cells, is highlighted by the inability of mice that lack the specific toxic molecules ▶perforin and ▶Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL), expressed by cytotoxic cells, to control both carcinogen induced and spontaneous tumors. That at least a subset of the lymphocytes that recognize and control tumor growth are ▶MHC class I restricted, tumor-specific, ▶cytotoxic T cells (CTLs) is evidenced by the fact that mice lacking the ▶LMP2 (Low Molecular Mass Protein 2) ▶proteasome subunit, involved in processing antigen for recognition by CTL, develop spontaneous ▶uterine tumors. The adaptive immune response has evolved to ignore its own tissues, by eliminating self-reactive lymphocytes during their development, in order to avoid ▶autoimmunity or “horror autoxicus” as Paul Ehrlich termed it. Thus the participation of CTLs in tumor immunoediting implies that tumors must express ▶tumor-associated antigens. The original observation of immune editing identified a key role for the type II interferon, IFN-γ, in the process. This pleiotropic cytokine is the product of lymphocytes of both the innate (γδ T cells, NK and NKT cells) and adaptive (CD4+, MHC class II restricted ▶helper T (Th) cells and CD8+ MHC class I restricted CTLs). It seems likely that both innate and adaptive lymphocytes are the source of the IFN-γ that shapes the immune response to tumors. The effects of IFN-γ on the immunogenicity of tumors could occur though multiple processes since it is known as a key regulator of adaptive and innate immune responses. There is a

great deal of evidence that some of its effects are mediated through host cells in addition to tumor cells. However, given that many tumor cells express IFN-γ receptors, it can directly interact with tumor cells and there is evidence that it stimulates tumor cells to increase MHC class I expression, downregulate ▶angiogenesis and promote the infiltration of CTLs into the tumor mass. Another cytokine, ▶IL-12, has also been shown to promote tumor immunoediting. IL-12 is intimately involved in the regulation of IFN-γ production early in the immune response and probably mediates its effects through its influence on IFN-γ expression. In addition to IFN-γ, the ▶type I interferons have a profound influence on tumor growth. Early studies in mice using type I interferons for tumor ▶immunotherapy have been translated into several clinical applications for these cytokines in the therapy of ▶melanoma, ▶CML, ▶follicular lymphoma, ▶hair cell leukemia and ▶Kaposi sarcoma. There are several important differences in mice and humans between the type I interferon, IFN-γ, which is the sole molecular species, and the type II interferons, IFN-α for which there are at least 12 variants, and IFN-β, which is unique. Unlike IFN-γ, which is the product only of cells of the lymphocytic lineage, type I interferons can be produced by all nucleated cells when stimulated by products of viral infection and also by infection with some bacteria. As such they are a first line of defense against pathogen invasion of the host. In addition, although tumor cells can express receptors for type I interferons, it appears, that unlike IFN-γ, the type I interferons do not act directly on tumor cells and mediate their anti-tumor effects though host cell responses. Exactly which cells are involved requires further study but they appear to be cells of the hematopoietic lineage. Similar to IFN-γ, there are several points at which type I interferons might influence the immune response to tumors since they can activate ▶dendritic cells, ▶macrophages and ▶NK cells and are involved in the priming and survival of T cells. In addition, similarly to IFN-γ they can act on stromal cells within and surrounding tumors to down regulate angiogenic factors. Finally, there is evidence that type I interferons may inhibit the transformation of normal cells by upregulating the expression of the tumor-suppressor molecule, ▶p53. The importance of this class of cytokines in shaping the immune response to tumors was confirmed recently by studies in mice lacking the IFN-α receptor. Carcinogen induced sarcomas were found to arise more frequently in these mice and were also shown to be more immunogenic when transplanted into wild type mice. The Role of Induced Immune Pressure The editing of tumors in response to immune pressure is exacerbated when the immune system has been specifically primed to a ▶tumor-associated antigen.

Immunoglobulin

In a ▶mouse model for ▶breast cancer in which ▶HER-2/neu, a member of the ▶epidermal growth factor receptor family, is overexpressed on breast tissue, resulting in the emergence of breast tumors, it was shown that mice immunized with ▶cancer vaccines expressing fragments of HER-2/neu could control tumor outgrowth for a significant length of time but eventually succumbed. When HER-2/neu was isolated from the emerging tumors they were found to have accumulated a significant number of mutations in the precise region of the molecule the particular vaccine targeted. In addition, it was verified for one of the fragments that each mutation occurred in a region recognized by CTLs and that this mutation abrogated CTL recognition. This is a clear demonstration of how the host immune system can sculpt a tumor-associated antigen to evade the immune system. Transplanted, syngeneic mouse tumors have also been shown to mutate in a region of an antigen expressed by the tumor and recognized by CTLs after adoptive transfer of T cells that recognize that region. Evidence of Immunoediting in Human Cancer Although there is an abundance of evidence for immunoediting in murine models of cancer, the evidence that this occurs in human cancer is largely circumstantial. It has long been known that cancer patients develop immune responses to their own tumors. Indeed, both tumor-specific Tcells and antibodies isolated from cancer patients have been harnessed to identify tumor-associated antigens by methods such as ▶SEREX. In addition the ability of a patient to mount a response to their tumors, particularly if there is evidence of tumor infiltration of immune effector cells, is a strong predictor of a favorable prognosis. That the immune system sculpts tumor immunogenicity in tumors that arise in cancer patients is supported by the emergence of tumors in patients undergoing antigen-specific immunotherapy that have down regulated the tumor antigen to which the therapy is directed, or components of the cellular machinery that generates the cell surface complex of ▶HLA I and antigen recognized by CTLs. These include LMP proteasome subunits and transporter molecules that chaperone antigen peptides from the cytosol to the Golgi apparatus for loading onto HLA class I molecules. Sometimes the HLA I molecule itself is lost, usually by mutation of the beta2 microglobulin subunit, common to all HLA class I molecular complexes. In some cases, however, lack of HLA class I on the surface of a tumor is due not to mutational events in the HLA class I genes themselves but to down regulation of expression of the protein. This can often be reversed by cytokines, such as IFN-γ but it is interesting to note that human tumors have been shown to arise that lack the IFN-γ receptor. The phenomenon of HLA class I loss from the surface of tumor cells has been documented in numerous clinical

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cancer vaccine trials for ▶melanoma, ▶prostate carcinoma and for HER-2/neu positive tumors. In addition, even in the absence of immunotherapy, HLA class I expression has been shown to be lost or down regulated in all types of tumors especially in patients with advanced disease. Indeed, the frequency of deletion or down regulation of these cell surface molecules has been found to be as high as 15% in primary melanoma lesions and 50% in primary ▶prostate carcinoma lesions. A final piece of evidence for immunoediting in human cancer is that patients that are seriously immunosuppressed, for example post organ transplant, have a higher incidence of cancer than healthy individuals.

References 1. Bui JD, Schreiber RD (2007) Cancer immunosurveillance, immunoediting and inflammation: independent or interdependent processes? Curr Opin Immunol 19:203–208 2. Dunn GP, Koebel CM, Schreiber RD (2006) Interferons, immunity and cancer immunoediting. Nat Rev Immunol 6:836–848 3. Neeson P, Paterson Y (2006) Effects of the tumor microenvironment on the efficacy of tumor immunotherapy. Immunol Invest 35:359–394 4. Singh R, Paterson Y (2007) Immunoediting sculpts tumor epitopes during immunotherapy. Cancer Res 67:1887– 1892 5. Chang CC, Campoli M, Ferrone S (2005) Classical and nonclassical HLA class I antigen and NK Cell-activating ligand changes in malignant cells: current challenges and future directions. Adv Cancer Res 93:189–234

Immunogenicity Definition The ability of a foreign substance to confer a certain level of immunity to the host. ▶T-Cell Response

Immunoglobulin Definition Ig; The immunoglobulin molecule, composed of two light and two heavy protein chains, comprising the antibody. ▶Immunoglobulin Genes

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Immunoglobulin E (IgE)

Immunoglobulin E (IgE)

Immunoglobulins

Definition

Definition

An antibody characteristic of the atopic allergic immune response.

Immunoglobulins (Ig): All antibody molecules belong to a family of plasma proteins called immunoglobulins (Ig). Membrane-bound immunoglobulin serves as the specific antigen receptor on B lymphocytes. Different immunoglobulin isotypes are called IgM, IgD, IgG, IgA, and IgE. Immunoglobulin A (IgA): Immunoglobulin A is the class of immunoglobulin characterized by α heavy chains. IgA antibodies are secreted mainly by mucosal lymphoid tissues. Immunoglobulin D (IgD): Immunoglobulin D is the class of immunoglobulin characterized by δ heavy chains. It appears as surface immunoglobulin on mature naïve B cells but its function is unknown. Immunoglobulin E (IgE): Immunoglobulin E is the class of immunoglobulin characterized by ε heavy chains. It is involved in allergic reactions. Immunoglobulin G (IgG): Immunoglobulin G is the class of immunoglobulin characterized by γ heavy chains. It is the most abundant class of immunoglobulin found in the plasma. Immunoglobulin M (IgM): Immunoglobulin M is the class of immunoglobulin characterized by μ heavy chains. It is the first immunoglobulin to appear on the surface of B cells and the first to be secreted.

▶Allergy ▶Immunoglobulin Genes

Immunoglobulin Genes Definition Cluster in multimember gene families and are located on chromosome 14 (heavy chain gene segments), 2 (κ light chain) and 22 (λ light chain): V genes (variable region genes), D genes (diversity region genes) and J genes ( joining region genes) for the heavy Ig heavy chains, V and J region genes for κ and λ light chains. Ig gene rearrangement brings together one representative of these gene families (V, D and J for the heavy chain, V and J for κ and λ light chains). ▶V(D)J recombination is a remarkable process since it entails double strand DNA breaks, loss or DNA and re-ligation of DNA strands. Joining of the V-D-J segments is imprecise and involves insertion of non-template nucleotides (N-additions) and trimming back of the beginning/ends of the gene segments. Ultimately, the rearrangement leads to a unique sequence of VH-N-DN-JH, which generates diversity for antigen recognition, and which acts a marker for each individual B-cell and its progeny. ▶B-Cell Tumors

Immunohistochemistry M ARC B IRKHAHN , C LIVE R. TAYLOR , R ICHARD J. C OTE Departments of Urology and Pathology, University of Southern California Keck School of Medicine, Los Angeles, CA, USA

Synonyms

Immunoglobulin Libraries Definition Recombinant nucleic acid libraries of natural or synthetic origin that encode antiBody binding sites (Fab or scFv) for which the products (and corresponding genes) can be selected against an antigen of interest and subsequently modified to improve their affinity. Applications: Fast selection of new antiBody binding sites from different species. Modification of pre-existing binding site affinity.

IHC; Immunohistology; Immunocytochemistry; Molecular Morphology

Definition Immunohistochemistry (IHC) is a technique to detect and localize specific proteins in tissue sections by labeled antibodies that bind specifically to the investigated antigen.

Characteristics History Since the introduction of microscopy into the diagnosis of diseases by Bennett in 1842 and Virchow in 1858,

Immunohistochemistry

pathologists have searched for better and more specific stains. In 1934, Marrack was the first to employ modified antibodies to visualize cholera and typhoid agents. Nearly a decade later, Coons (1941) used a primary antibody that was labeled with a fluorescent dye, fluorescein isothiocyanate, and utilized it on human tissue. However, as a specialized dark-field microscope and use of frozen sections were needed for the fluorescent dyes, the technique remained mainly a research tool until other labels were developed. In 1974, Taylor and Burns demonstrated that IHC could be performed on routinely processed tissue using immunoperoxidase techniques with chromogenic dyes. This step enabled the use of IHC in routine clinical laboratories.

Techniques Immunohistochemistry combines the principles of immunology with histochemistry, and involves two basic steps: first, an ▶antibody binds to its specific target antigen at the cellular location in the tissue sample. The antigen-antibody binding is then detected by labeling techniques. IHC therefore not only enables pathologists to detect whether or not particular antigens are present within a given tissue, but also allows marking its cellular location. There are two major types of antibodies in use: polyclonal antibodies or antisera and monoclonal antibodies. Polyclonal antibodies are produced by an injection of an antigen or antigen fragments into a host animal. The most common host animals are rabbit, horse, mouse and goat. If a small antigenic molecule or antigen fragment (hapten) is used as immunogen, immunogenicity is typically enhanced by coupling the hapten with a compound such as keyhole limpet hemocyanin. In the resulting immunologic reaction, host lymphocytes are activated and ultimately plasma cells initiate production of antibodies. As antigens contain various immunogenic determinants, the resulting antiserum will be a heterogeneous mix that recognizes several epitopes. Such potentially crossreacting specificities are unwanted for use in IHC and must be removed by further purification. Monoclonal antibodies are developed by the hybridoma technique or through molecular engineering using bacteriophages. In the hybridoma technique, activated (antibody-secreting) B-lymphocytes are isolated from the immunized animal (in the past usually mouse, now increasingly common rabbit) and fused with cultured myeloma cells which have limitless proliferative potential. Each of the resulting hybrid cells (hybridoma) produces a single type of antibody, thus being ‘monoclonal’ in nature. The detection methods include the ‘direct’ and the ‘indirect’ alternatives. In the direct conjugate-labeledantibody method, the label (such as a fluorescent agent

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or an enzyme) is chemically attached to the primary antibody. The localization of this fluorescent label is detected by ▶immunofluorescence microscopy or if the label is an enzyme (typically, horseradish peroxidase) coupled to antibody, it is detected by its action on a chromogenic substrate. The indirect method uses an unlabeled primary antibody and a labeled secondary antibody (second layer) directed against the primary antibody. Several secondary antibody molecules bind to each primary antibody molecule resulting in signal enhancement, thus in increased sensitivity. Furthermore, methods involving a third layer for signal amplification can be employed. These include the PAP (peroxidase-antiperoxidase) method, the biotin-avidin mediated procedures (such as those employing the avidin-biotin conjugate or ABC procedure, biotin-streptavidin systems), immunogold or polymer based labels, catalyzed signal amplification and alkaline phosphatase-based methods. Several efforts have been made to improve the sensitivity, the reliability and the standardization of IHC. A major step was the development of antigen retrieval. The antigen retrieval process breaks protein cross linkages formed during formaldehyde fixation of a tissue and enables these proteins to be accessible for antibodies. Antigen retrieval is performed by exposing tissue to heat for various lengths of time in retrieval buffer solutions with specific pH. Several protocols are available but these often have to be adjusted for optimal results which can be done standardized for various temperatures and durations in a ‘test battery’ approach. Several automated immunostaining systems are commercially available. While they significantly increase the reproducibility and standardization, they certainly do not guarantee optimal results. Quality control issues as well as the need for the validation of the results apply for staining carried out with both the automated systems and manual IHC. Interpretation of IHC staining results necessitates a highly trained pathologist and even among experts is subject to inter-observer discrepancies. The development of automated image analysis systems addresses this problem. The currently available systems can both assess the intensity as well as the percentage positivity of antigenic markers. The limitations of the human eye to differentiate colors restrict the use of multiple markers on the same slide. The spectral imaging technology allows to differentiate different chromogens reporting on multiple markers by serially, digitally “erasing” a given chromogen image from the microscope image by a specially designed software. Uses IHC plays an essential role in modern pathology. Its most common use is the identification of tumor origin

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and tumor type by tissue-specific markers. By IHC a pathologist can specify tumor entities and evaluate tumors of unknown origin as well as stage lymph nodes and bone marrow for the presence of metastatic disease. More recently, several markers have been identified that can predict disease prognosis, treatment response and serve as therapeutic target. Use in Research In a research setting, the expression of relevant markers is investigated. This demands studies on well-defined samples across various tumor stages and clinical outcome. The tissue microarray technique allows an acceleration of such studies in a high-throughput manner. Tissue microarrays (TMA) consist of compendia of 0.6 mm cylindrical biopsy cores from paraffin-embedded tissue that are transferred to defined array coordinates in a recipient block. These multi-tissue-core blocks can then be processed similar to a routine single-tissue block. A difference from the conventional IHC is the high level of standardization since all slides in one TMA experiment are incubated together, ensuring identical reagent concentrations and incubation temperatures.

Clinical Uses Diagnosis Intermediate Filaments The presence of intermediate filaments, which function as cytoskeletal components in both normal and malignant cells, is useful in the initial classification and diagnosis of neoplasms. Five major classes of intermediate filaments exist: ▶Cytokeratin (CK), vimentin, desmin, neurofilament and glial fibrillary acidic protein (GFAP). Most neoplasms show a predominant expression of one or more of these intermediate filaments. Based on their molecular weight and isoelectric point, the cytokeratins are subdivided into more than 20 types. Carcinomas are typically CK positive, whereas sarcomas, melanomas, and lymphomas are generally vimentin positive. Tumors of myogenic origin characteristically express desmin and/or muscle actins and vimentin. Glial tumors are predominantly positive for GFAP. Nuclear Transcription Factors Transcription factors are proteins involved in the regulation of gene expression. By binding to promoter elements upstream of genes they either facilitate or inhibit transcription. Though not exclusively found in a specific tumor type, transcription factors are highly tissue specific and can be useful in determining the primary site of a tumor.

Carcinoma Essentially all cells of epithelial origin express cytokeratins, which are therefore highly sensitive markers for carcinomas. However, other tumors such as mesotheliomas and non-seminomateous germ cell tumors also stain positive for CK. More specific markers and sub-typing of keratins have to be applied to further differentiate CKpositive cells and to assess the site of origin of the carcinoma. The profile of cytokeratin sub-types is useful to determine the tumor type. As for example, hepatocellular carcinomas are positive for CK antigens that can be detected by antibodies AE3 and CAM5.2 but are negative for antibody AE1, which is directed against a different set of CK. Recently, the use of CK7 and CK20 profile has proven a useful tool in distinguishing cellular origin. Nuclear transcription factors are useful in the detection of carcinomas. Thyroid transcription factor-1 (TTF-1) is found in the thyroid and lung. CDX-2 is specific for colorectal epithelium. For some tissue types, tissue-specific tumor markers (e.g. prostate specific antigen (PSA) for prostate, or thyroglobulin for thyroid) or tissue-associated markers (e.g. gross cystic disease fluid protein 15 (GCDFP-15) and mammaglobin in breast, uroplakins for transitional urothelial cells, OC 125 for ovarian cells, synaptophysin for neuroendocrine lesions, etc.) are available. It is important to remember that these markers are often not uniquely found in the specific tissue. For instance, the detection of PSA has also been described for samples of salivary glands and breast. Melanoma For melanomas, which usually are cytokeratin-negative and vimentin-positive, a sensitive tissue marker, S-100, is available. HMB-45, Melan A and tyrosinase are used to confirm the diagnosis. Sarcoma The common IHC pattern for all forms of sarcoma includes vimentin positivity. Generally speaking, sarcomas are CK-negative, but some may yield positive reactions especially for low molecular CKs following antigen retrieval and highly sensitive labelling techniques. Additional stains are then employed to identify the tumor type. Rhabdomyosarcoma and Leiomyosarcoma express markers that are typical for muscular tissue such as desmin and muscle specific actin. Lymphoma Lymphomas show a wide variety of morphologic appearances, making IHC especially important in their diagnosis. Membranous staining for ▶CD45 can typically be seen in lymphoid tissue. CD3 and ▶CD20 are more specific markers and are used to

Immunohistochemistry

further confirm lymphomas. ▶CD antigens are essential in subclassifying lymphoid tissue. Infectious Agents Since the early days of its development, IHC has been used for the detection of infectious agents. Nowadays, microbiologic cultures are the gold standard but for pathogens that are difficult to culture such as cytomegalovirus, mycobacteria, toxoplasmosis, pneumocystis carinii, histoplasma capsulatum, ▶Helicobacter pylori and ▶human papillomavirus IHC methods are at least as effective. Tumor Stage and Occult Metastases The most important factor determining outcome of patients with cancer is the presence of regional and/or systemic dissemination (metastases). While routine pathologic work-up cannot detect small metastatic deposits in many instances, IHC is a highly sensitive way to detect such occult metastases in blood, lymph nodes and bone marrow. This technique is based on the fact that monoclonal antibodies can reveal cells of different histogenesis in the investigated tissue. As normal lymph nodes, bone marrow or blood do not contain cells with epithelial antigens, the finding of CKpositive cells suggests metastases of a carcinoma. The presence of occult metastases has been shown to influence clinical outcome for several cancer types such as breast, lung and prostate cancer. In breast cancer, IHC is able to show the presence of occult metastases in bone marrow in 10–40% of patients with low-stage disease. Lymph node metastases occult to routine pathologic work-up have been described for several tumors including breast cancer in up to 20% of patients and in more than 10% of patients with prostate cancer. The reported sensitivity of this technique ranges from the detection of 1 epithelial cell in 10,000 to 2–5 epithelial cells in a million hematopoietic cells. Prognosis Mutations and overexpression of oncogenes and tumor suppressor genes play a vital role in tumorigenesis. The presence or absence of their protein products may predict the biological behavior of tumors more accurately than clinical and pathologic criteria. Since antibodies are available for many of these gene products, tumors with different prognosis can be differentiated by means of IHC. The best investigated proteins include ▶p53, the protein product of the ▶Retinoblastoma gene (pRb), p27, ▶p21 and ▶p16. RB gene alterations resulting in reduced expression are known to characterize tumors with a higher risk for metastatic disease. p21, p16 and p27 are the three major cyclin-dependent kinase

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inhibitors which negatively regulate pRb activity and are normally required for cell cycle suppression. The loss of p27 expression is associated with colon, breast, prostate, and gastric cancer progression. Changes in protein expression of p21 have been associated with higher tumor grade and worse prognosis in patients with bladder cancer. p53 plays an important role in cell cycle progression, and apoptosis in response to DNA damage, and is expressed by all human cells. Normal (wild-type) p53 protein has a short half-life of only 6 to 30 minutes because of its ubiquitin action-mediated degredation dictated by its binding with another regulatory protein, ▶MDM2. Therefore p53 does not accumulate in normal cells. Overexpression of p53 (by altered p53 gene or because of ineffective MDM2 protein) in the nuclear compartment therefore indicates a dysfunctional p53 pathway, a characteristic of tumors. Alterations in p53, p21 and pRb act in cooperative or synergistic ways to promote cancer progression and simultaneous overexpression has been linked to worse prognosis. Treatment Response An increasingly important application of IHC is to identify specific targets for therapy. Consequently, this will allow better selection of patients who will benefit from certain treatment modalities. In several tumor types, treatment decisions already are influenced or determined by molecular findings. An early example is hormonal therapy for breast cancer patients depending on estrogen and progesterone expression of the tumor. Because of its vital role in the apoptotic pathway ▶p53 alterations are likely to influence response to chemotherapy. p53 alterations confer increased chemosensitivity on tumors such that combining agents with different actions may have synergistic effects on tumor cell killing. Targeted Therapy In breast cancer Her-2/neu overexpression was linked to resistance to tamoxifen therapy and commonly used adjuvant chemotherapy. However, it has been shown that the HER2/neu receptor tyrosine kinase can serve as a therapeutic target. Treatment with the monoclonal antibody ▶trastuzumab (brandname: Herceptin) which is directed against this protein is effective only for patients whose tumors show overexpression of Her2/ neu. In invasive ▶bladder cancer there is evidence to suggest that patients who harbor p53 alterations respond to adjuvant chemotherapy that contains DNA-damaging agents such as cisplatinum. Immunohistochemistry has allowed for identification of tumor origin, tumor prognosis, and likelihood of response to therapy for an increasing array of tumors. The ability to determine which tumors are most likely

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to progress (and thus need further therapy), coupled with the ability to predict specifically the response of individual tumors to chemotherapeutic agents and the ability to identify specific targets of therapy will have a profound effect on the way treatment decisions for patients with cancer are made. It is not difficult to envision the day when drug selection is based on the presence of specific targets and on the resistance patterns of individual tumors to specific agents. Treatment decisions will become less organ based and will reflect the biology of the tumors. This has already helped us to approach patient-specific (as opposed to disease specific) management of care. ▶Gastrointestinal Stromal Tumor

References 1. Mitra AP, Lin H, Cote RJ et al. (2005) Biomarker profiling for cancer diagnosis, prognosis and therapeutic management. Natl Med J India 18(6):304–12 2. Shi SR, Cote RJ, Taylor CR (2001) Antigen retrieval immunohistochemistry and molecular morphology in the year 2001. Appl Immunohistochem Mol Morphol 9(2):107–116 3. Taylor CR, Cote RJ (2006) Immunomicroscopy: a diagnostic tool for the surgical pathologist, 3rd edn. Saunders, Philadelphia, PA 4. Hawes D, Taylor CR, Cote R (2003) Immunohistochemistry. In: Weidner N, Cote R, Suster S, Weiss L (eds) Modern surgical pathology, 1st edn. Saunders, Philadelphia, PA, pp 57–80

Immunohistology ▶Immunohistochemistry

Immunoliposomes R OLAND E. KONTERMANN Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany

Definition

Are ▶liposomal drug formulations possessing antibody molecules conjugated to the liposomal surface. This allows for a ▶targeted drug delivery to tumor cells or other tumor-associated structures (active targeting).

Characteristics

▶Liposomes are vesicular particles composed of a lipid bilayer enclosing a hydrophilic inner phase. Liposomes can be used as carrier systems for cancer drugs (▶Drug delivery systems) by encapsulating hydrophilic drugs into the interior or by incorporating lipophilic drugs into the lipid bilayer. Liposomes have normally a size (diameter) of 100–200 nm. Several liposomal formulations of therapeutic drugs are approved for cancer therapy, e.g., liposomal doxorubicin (Doxil/Caelyx, Myocet) (▶Liposomal chemotherapy). Delivery of these drugs to tumors is a passive process and efficacy depends on long circulation and enhanced permeability and retention in the tumor tissue (EPR effect). New formulations of liposomal drugs (e.g., Doxil/Caelyx) have polyethylene glycol (PEG) chains incorporated into the lipid bilayer to further increase stability and pharmacokinetic properties and to decrease elimination of the liposomes by phagocytic cells. The coupling of antibody molecules to the lipid surface allows for an active targeting by recognition of antigenic structures expressed by the tumor. Thus, immunoliposomes are designed to increase selectivity and efficacy of liposomal drugs. Immunoliposome Types and Antibody Formats Immunoliposomes are generated by chemically coupling antibodies or antibody fragments to the liposomal surface. Besides whole ▶antibody molecules (e.g., IgG molecules), antibody fragments such as Fab′ fragments or ▶single-chain Fv fragments can be utilized for the generation of immunoliposomes. The use of whole antibodies is less favorable since these immunoliposomes are recognized by phagocytic cells via Fc receptors. Consequently, Fab′ or scFv′ fragments are the formats of choice to generate immunoliposomes. Immunoliposomes can be classified depending on the position of coupled antibodies and the liposomal composition. In type I immunoliposomes, the antibodies are coupled directly to the lipid bilayer either in the absence (type Ia) or presence of PEG chains (type Ib). Coupling of the antibodies to the distal end of incorporated PEG chains results in type II immunoliposomes (Fig. 1a). Coupling of antibodies is facilitated by the use of functionalized lipids, e.g., lipids possessing an aminoreactive succinimidyl moiety or a sulfhydryl-reactive maleimide group. Antibody or antibody fragments can be generated by established ▶hybridoma technology and biochemical means or by genetic engineering as recombinant molecules. For example, Fab′ fragments can be produced by enzymatic cleavage of IgG molecules with pepsin resulting in F(ab′)2 fragments, which after reduction are separated in Fab’ fragments exposing a free sulfhydryl group at the end of the molecule (Fig. 1b). Furthermore, the implementation of antibody engineering allows for the generation of

Immunoliposomes

small antibody molecules with desired properties, e.g., scFv molecules exposing a genetically introduced cysteine residue at the C-terminus used for site-directed coupling (Fig. 1b).

Immunoliposomes. Figure 1 Classification of immunoliposomes and antibody formats. (a) Three types of immunoliposomes can be distinguished. Type I immunoliposomes have the antibody molecules coupled directly to the lipid bilayer, either in the absence (type Ia) or presence (type Ib) of polyethylene glycol (PEG) chains. In type II immunoliposomes, the antibodies are coupled to the distal end of PEG chains. (b) Antibodies formats used for the generation of immunoliposomes. The two variable domains (VH, VL) forming the antigen-binding site are shown in dark and light gray.

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Drugs and Targets Immunoliposomes can be combined with a wide variety of different drugs. Besides small compounds and chemotherapeutic drugs, immunoliposomes can also be used for the delivery of nucleic acids (e.g., ▶siRNA) or therapeutically useful peptides and proteins (Fig. 2). Encapsulation of drugs into liposomes alters their pharmacokinetic properties, e.g., reduces rapid renal elimination of small molecular weight drugs. In addition, drug encapsulation has been shown to reduce side effects and to increase stability of the drug within the body. Several modes of action have been described for immunoliposomes. Delivery to extracellular structures may lead to increased accumulation of liposomes in the tumor tissue and slow release of drug, which then can enter the target cell. Alternatively, binding of immunoliposomes to cell surface receptors results in internalization of immunoliposomes (▶Endocytosis) and intracellular release of the drug. Several studies have shown that internalization of immunoliposomes leads to increased cytotoxicity and may also bypass drug resistance mechanisms. Main targets of immunoliposomes are molecules expressed by tumor cells. Thus, various immunoliposomal formulations of chemotherapeutic drugs (e.g., ▶doxorubicin, ▶vincristine) have been generated using antibodies against tumor-associated antigens including CD19, ▶CD20, Her2/neu, ▶epidermal growth factor receptor (EGFR), and disialoganglioside GD2 for therapy of lymphoma and solid tumors. In addition, research has been focused on targeting of tumor blood vessels (▶vascular-targeting adjents) as well as targeting of extracellular tumor stroma components or tumor stroma fibroblasts, which are more easily accessible for circulating liposomes. Efficacy of immunoliposomes is influenced by several factors. Besides lipid composition, which has an influence on stability and release of drug, and the antibody format used, efficacy depends also on the kind of target molecule as well as its density on the cell surface and sensitivity of target cells for the encapsulated drug.

Immunoliposomes. Figure 2 Active compounds combined with immunoliposomes. Immunoliposomes allow for a targeted delivery of various kinds of active molecules, including small compounds, chemotherapeutic drugs, nucleic acids, and peptides and proteins.

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Immunologic Tolerance

References 1. Kontermann RE (2006) Immunoliposomes for cancer therapy. Curr Opin Mol Ther 8:39–45 2. Park JW, Benz CC, Martin FJ (2004) Future directions of liposome- and immunoliposome-based cancer therapeutics. Semin Oncol 31:196–205 3. Allen TM, Cullis PR (2004) Drug delivery systems: entering the mainstream. Science 303:1818–1822 4. Drummond DC, Meyer O, Hong K, et al. (1999) Optimizing liposomes for delivery of chemotherapeutic agents to solid tumors. Pharmacol Rev 51:691–743 5. Sapra P, Tyagi P, Allen TM (2005) Ligand-targeted liposomes for cancer treatment. Curr Drug Deliv 2:369–381

Immunophenotyping Definition Determining the expression of antigens on or in cells. ▶Flow Cytometry ▶Leukemia Diagnostics

Immunophilins Immunologic Tolerance Definition

The lack of an ▶immune response.

Immunological Fecal Occult Blood Test ▶Fecal Immunochemical Test

Definition Are a group of intracellular proteins that bind to the anti-inflammatory agents ▶cyclosporine A and FK506. The complexes interfere with calcineurin-mediated transcriptional activation and inhibit the transcription of genes encoding several proinflammatory molecules. Proteins that bind immunosuppressant drugs.

Immunoprevention P IER-LUIGI L OLLINI , PATRIZIA N ANNI Section of Cancer Research, Department of Experimental Pathology, University of Bologna, Bologna, Italy

Immunophenotype

Synonyms Immunoprophylaxis of cancer

Definition The overall expression of proteins that identify a specific cell type as determined by using specific antibodies reacting against surface proteins on cell membrane. The collective repertoire of proteins expressed on the outer surface of a particular type of cell.

Definition

▶CD Antigens

Characteristics

Immunophenotypic Determinants ▶CD Antigens

Prevention of cancer onset or of early cancer development and ▶progression by means of immunological treatments, such as vaccines, antibodies or cytokines.

Immunoprevention of cancer can be applied to tumors caused by viruses (and other infectious agents) or to tumors unrelated to infectious agents. In both cases the aim is the same, however the underlying concepts and the advancement of clinical development are different. Prevention of viral tumors is based on vaccines against viral antigens, whereas immunoprevention of tumors unrelated to infectious agents targets antigens expressed by early neoplastic cells.

Immunoprevention

Immunoprevention of Viral Tumors About 18% of all human tumors are directly caused by infectious agents or indirectly by persisting inflammation accompanying chronic infection. In such cases the application of immunological strategies to prevent infection is a type of ▶primary cancer prevention because it aims at removing a risk factor that can cause cancer. The first success in this direction was the demonstration that vaccination programs implemented in the 1980s against ▶hepatitis B virus (HBV) significantly reduce the incidence of hepatitis virus associated ▶hepatocellular carcinoma. Current vaccines are highly effective (90–95%) in preventing chronic HBV infection. Studies in countries where HBV infection is frequent demonstrated that vaccination reduced by half infantile hepatocellular carcinoma incidence and mortality. HBV is responsible for one third (developed countries) to two thirds (less developed countries) of all cases of hepatocellular carcinoma, and ▶hepatitis C virus (HCV) causes about one fourth. HCV vaccines under development are expected to contribute a further substantial decrease in the worldwide incidence of hepatocellular carcinoma. ▶Human papillomaviruses (HPV) are the most prevalent carcinogenic viruses in humans; various types of HPV cause more than half a million new cases of ▶cervical cancer and other tumors worldwide. The first human vaccine against HPV was approved in 2006 in the US, EU, and various other countries. It is a quadrivalent vaccine against HPV types 6, 11, 16 and 18. A divalent vaccine against HPV 6 and 18 is undergoing approval in 2007. Both vaccines are made of ▶virus-like particles (VLP). Clinical trials of both vaccines demonstrated 89–100% protection of vaccinated women from persistent HPV infection, 100% protection from histologic evidence of cervical cancer, and no serious adverse events. These vaccines are thus expected to have a major impact on the incidence and mortality of HPV-related cancers. Four critical issues are (i) current vaccines do not include HPV types causing one third of cervical cancers worldwide, hence screening programs should not be abandoned until cross-protection by current vaccines has been demonstrated or novel multivalent vaccines have been developed; (ii) vaccines are currently very expensive, and only a few national or regional health systems are prepared to subsidize the costs; (iii) the matter is further complicated by the need to vaccinate prepuberal (9–12-year-old) girls against a sexually-transmitted virus, an issue that is causing considerable ethical debate in some countries; (iv) the follow-up of vaccinated persons is still too short to estimate the long-term duration of immunity and the need for periodic boosts. Attempts toward the development of vaccines against ▶Helicobacter pylori, the third major infectious risk

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factor of human cancer, until now did not produce a credible candidate for mass vaccination. On the whole it can be estimated that a full-scale deployment of the approaches described above for HBV, HCV and HPV could lead to the immunoprevention of two thirds of infectious human cancers, or more than 10% of all human cancers. This is a very important result which however leaves open the question of what immunoprevention can do for the majority of human cancer not caused by infectious agents. Immunoprevention of Tumors Unrelated to Infectious Agents Immunoprevention of non-infectious tumors is a relatively recent development and is currently at the level of ▶preclinical testing. This type of immunoprevention targets early neoplastic cells, hence it can be classified as a kind of ▶secondary cancer prevention because it aims at preventing the evolution of incipient tumors into clinically-evident, symptomatic masses. The ▶immune surveillance theory posits prevention of tumor onset as a fundamental function of the immune system, on a par with prevention of infection. In fact cancer incidence in knockout mice lacking ▶adaptive immunity and ▶non-adaptive immunity is much higher that in immunocompetent mice. However the very existence of progressive, malignant tumors demonstrates that the efficiency of spontaneous immune surveillance is lower than 100%. Thus the aim of cancer immunoprevention is to enhance immune surveillance of tumors by means of treatments that elicit protective antitumor immune responses and/or decrease immunosuppressive components. Immune targeting of ▶preneoplastic lesions or of early neoplastic cells has several advantages with respect to conventional cancer ▶immunotherapy, which instead must necessarily target advanced tumors. The efficacy of immune defenses is higher against smaller tumor deposits, a property shared by most antitumor approaches, including chemotherapy. Nascent neoplastic lesions are less protected from immune effectors by ▶stromagenesis and ▶angiogenesis, tumor progression caused by the accumulation of multiple genetic alterations is still at an early stage, and genomic instability has not yet generated a wide array of heterogeneous tumor variants, eventually leading to the selection of immunoresistant phenotypes. Demonstrations of cancer immunoprevention were mainly obtained in ▶cancer-prone genetically modified mouse models and in some ▶chemical carcinogenesis systems. Three different strategies were effective in inhibiting and/or delaying tumor onset in mice: (i) monoclonal antibodies directed against membrane tumor antigens; (ii) immunostimulants, such as recombinant ▶cytokines (▶interleukin-12), plasmids containing CpG sequences (▶CpG islands), or bacterial

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derivatives (α-galactosylceramide); (iii) vaccines containing whole cells, recombinant proteins, synthetic peptides or plasmids encoding the target antigen. Using standard categories borrowed from immunotherapeutic jargon, the first approach can be classified as passive immunoprevention, because it is based on the administration of a preformed immunological “drug” directly acting on tumor cells, the second as active, antigen nonspecific immunoprevention and the third as active, antigen specific immunoprevention. Early attempts provided proof-of-principle demonstrations that stimulation of the immune system in healthy, cancer-prone hosts can effectively delay or reduce tumor incidence later in life. Second generation studies aimed at increasing preventive efficacy through the combination of different strategies, much as it happened in chemotherapy (▶Chemotherapy of cancer, progress and perspectives). Various combinations of antigen specific vaccines and powerful immunostimulants completely prevented tumor onset in very aggressive mouse models of cancer development, thus demonstrating that cancer immunoprevention can effectively halt a genetic predisposition to cancer. Microscopic analysis of tumor-free aged mice showed that tumor progression is blocked at the stage reached when vaccination begins. For effective immunoprevention of tumor onset vaccination must start before tumor progression reaches specific critical stages, such as in situ carcinoma. Immune Mechanisms of Cancer Prevention Highly active vaccines like those used for complete cancer immunoprevention elicit simultaneously many overlapping immune responses in immunocompetent mice, hence vaccination of mice with selective immunodepressions is the only way to dissect protective mechanisms from less important immune components. The most important immune mechanisms at work in cancer immunoprevention comprised both ▶T cell responses, including the release of cytokines (interferon-γ, IFN-γ) and, less frequently, ▶cytotoxic T lymphocytes (CTL), along with antibodies whenever the target antigen was expressed on the cell surface. The importance of antibody responses clearly distinguishes cancer immunoprevention from cancer immunotherapy, the latter being mainly based on CTL rather than antibodies. The largely different time scales involved justifies this discrepancy, because cancer immunoprevention requires a long-term protection from tumor onset, ideally extending for the entire life of the host, whereas a rapid destruction of tumors or metastases is the goal of cancer immunotherapy. CTL activity must be of short duration to avoid severe toxicity for the host, whereas protective antibodies persisting for a long time are harmless. The same dualism applies to viral

immunity in which acute infection is mostly resolved by CTL, whereas long term immunity from reinfection and protection elicited by vaccination are provided by neutralizing antibodies. The direct interaction of cytokines like IFN-γ and of antibodies with early neoplastic cells results in multiple molecular blocks of cell growth and tumor progression combining cytostatic and cytotoxic mechanisms. Inhibition of cell proliferation is a logical part of the set of antiviral activities of IFN-γ that can directly block tumor cell growth, moreover it inhibits the release of ▶matrix metalloproteinases involved in tumor cell invasiveness (▶Invasion) and induces the production of chemokines with antiangiogenic activity. Antibodies binding to surface tumor antigens mediate tumor cell killing via ▶complement-mediated cytotoxicity and ▶antibody-dependent cell-mediated cytotoxicity (ADCC). Whenever the target antigen is involved in mitogenic signaling, antibodies can directly inhibit tumor cell proliferation without the need of further molecules or cells of the immune system, in practice by acting as “receptor antagonists.” In the case of the ▶HER-2/neu oncogene, specific antibodies induced by preventive cancer vaccines inhibit dimerization of surface HER-2/neu proteins (a key step required for the initiation of signal transduction) and induce HER-2/ neu internalization and recycling, eventually leading to a complete depletion of HER-2/neu surface expression. In HER-2/neu-addicted cells (▶Oncogene addiction) a prolonged loss of HER-2/neu expression and signaling blocks cell proliferation and can trigger ▶apoptosis. Target Antigens of Cancer Immunoprevention The inhibitory mechanisms targeting HER-2/neu can be ineffective against most other tumor antigens, either because the target is not a surface molecule and antibodies cannot bind tumor cells, or because tumor progression leads to a loss of antigen processing machinery (including major histocompatibility complex molecules), required for antigen recognition by T cells. The latter is a very frequent event affecting 80–90% of all human tumors. For cancer immunoprevention it was proposed that the immune recognition of ideal target antigens should persist even if defects in antigen processing impede T cell recognition, hence the antigen should be expressed on the cell surface and recognized by antibodies. A second desirable property is a direct involvement of the target antigen in oncogene addiction or in the maintenance of tumorigenicity, as is the case of HER-2/neu, because this prevents tumor escape from immune defenses through loss of antigen expression, again a frequent phenomenon for most other tumor antigens. Tumor antigens fulfilling both requirements were named ▶oncoantigens. Members of this new class of tumor antigens ideally suit the

Immunoreceptor

concepts of cancer immunoprevention, in particular for what concerns the need of persistent, lifelong antitumor responses, however oncoantigens make also attractive new targets for cancer immunotherapy because they are not prone to relevant mechanisms of immunoresistance and therapeutic failure. Clinical Developments The mass of preclinical data demonstrating the efficacy of cancer immunoprevention in mouse models warrants the translation of this approach to humans, however this will require a precise definition of the subjects who can benefit from this type of intervention and consequently of the design of clinical trials. The analysis of these issues reveals key scientific issues to be investigated and suggests possible developments. Immunoprevention of hereditary cancer syndromes would be a straightforward translation from preclinical models, however the definition of suitable target antigens in most hereditary tumors is currently lacking and will require adequate immunological studies. Analogous problems face the application of cancer immunoprevention to other human groups at increased risk of cancer due to exposure to carcinogens and/or presence of preneoplastic lesions, moreover the lower level of risk (as compared to hereditary cancer) implies the recruitment of a large number of subjects. Lessons for the clinical deployment of cancer immunoprevention might come from the development of ▶tamoxifen, which was first used for therapy of advanced ▶breast cancer patients, followed by ▶adjuvant therapy i.e. for prevention of tumor relapse and ▶metastasis; the finding that tamoxifen also prevented the appearance of additional primary tumors eventually led to large prevention trials that demonstrated its efficacy in preventing breast cancer. Early clinical testing of preventive vaccines in advanced cancer patients will also provide much needed data concerning safety and risks of adverse effects. The Risks of Cancer Immunoprevention The lack of severe adverse effect registered in the clinical trials leading to the approval of HPV vaccines, along with similar results from worldwide HBV vaccination programs, indicates that the immunoprevention of virus-related cancers will share with other vaccines for infectious diseases an intrinsic high level of biosafety. The main reason is that the target antigens are not expressed by normal tissues of the host, hence the risk of triggering autoimmune reactions is very low. On the contrary, virtually all tumor antigens unrelated to infectious agents are also expressed by some normal cells during life. In some cases normal cells express a cross-reacting molecule with minor aminoacidic differences from the tumor version, but more frequently the

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antigens are structurally identical, and the only differences are either quantitative or topographical. The implication is that some autoimmune responses will frequently accompany successful prophylactic or therapeutic vaccination, even though development of autoimmune diseases is not an automatic consequence. A major difference between cancer therapy and prevention is that both physicians and patients accept inherently high risks of serious adverse effects when dealing with an existing life-threatening disease, whereas preventive treatments to be administered for long periods to healthy individuals need to minimize not only severe, but also mild adverse reactions. Preclinical studies of cancer immunoprevention did not reveal major risks of ▶autoimmunity, however the use of transgenic mouse models implies that in most instances protective immune responses were actually directed against transgenic products rather than against endogenous molecules, thus minimizing “real” autoimmunity. Therefore early clinical trials of cancer immunoprevention in humans will require intensive analyses to discover early signs of autoreactive immune responses and a special attention to the long-term risks of triggering autoimmunity.

References 1. Lollini PL, Cavallo F, Nanni P et al. (2006) Vaccines for tumour prevention. Nat Rev Cancer 6:204–216 2. Wheeler CM (2007) Advances in primary and secondary interventions for cervical cancer: human papillomavirus prophylactic vaccines and testing. Nat Clin Pract Oncol 4:224–235 3. Stewart BW, Kleihues P (eds) (2003) World cancer report. Lyon, IARC, pp 144–150 4. Lollini PL, Forni G (2003) Cancer immunoprevention: tracking down persistent tumor antigens. Trends Immunol 24:62–66

Immunoprophylaxis ▶Immunoprevention

Immunoreceptor ▶Chimeric T Cell Receptors

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Immunoreceptor Tyrosine-based Activation Motif

Immunoreceptor Tyrosine-based Activation Motif

Immunostimulatory Molecules Definition

Definition ITAM; A common cytoplasmic motif, YxxL/I-6-8YxxL/I, that activates signaling pathways; it is found for example in adapter molecules (DAP12) that associate with NK activation receptors that lack cytoplasmic domains (for example NKp44), which is recognized by downstream signaling molecules of the tyrosine kinase family. This conserved amino acid sequence was originally discovered in receptors found in immune cells, but has also been found in other types of non-hematopoietic, non-receptor proteins. Phosphorylation of two tyrosine amino acids within this motif creates a binding site for other proteins and activates complex signaling pathways. ▶Natural Killer Cell Activation

Are molecules that provide signals for antigenic specificity and immune response of T cells. Examples include ▶T cell receptor (TCR), CD28, CD40, B7-1 and ▶cytokines. ▶T-Cell Response

Immunosuppressed Definition A state of reduced immune function. ▶Immunosuppression ▶Allergy

Immunoregulatory Aberrations ▶Autoimmunity and Prognosis

Immunosuppression Definition

Immunoscreening cDNA Expression Libraries

Is a state in which the ability of the body’s immune system to fight infections or disease is decreased. A process or act that leads to a reduced activation or efficacy of the immune system.

Definition This method utilizes the exquisite specificity of antibodies to recognize a given antigen in the midst of thousands of antigens in a cDNA library. It lends itself to study structure and function of the expressed autoantigen in cDNA expression libraries of the desired cancer, built into a virus such as λgt11, T7, or other virus which are grown in bacteria. The viral coat displays the universe of potential autoantigens selected by autoantibodies in sera which can be arrayed forming a library. The microarray can be probed with multiple sera from patients and controls and finally, associations are sought between positive phages, diagnosis, or other clinical parameters ▶Autoantibodies

Immunosuppressive Drugs Definition Compounds that inhibit adaptive immune responses are called immunosuppressive drugs. They are used mainly in the treatment of graft rejection and severe autoimmune disease. ▶Adaptive Immunity ▶Allograft Rejection ▶Graft Acceptance and Rejection

Immunotherapy

Immunotherapy M EHMET K EMAL T UR 1 , S TEFAN B ARTH 1,2 1

Department of Experimental Medicine and Immunotherapy, Helmholtz Institute for Biomedical Engineering, University Hospital RWTH Aachen, Aachen, Germany 2 Department of Pharmaceutical Product Development, Fraunhofer Institute for Molecular Biology and Applied Ecology, Aachen, Germany

Synonyms Biological therapy

Definition Immunotherapy is the treatment of cancer or inflammatory/autoimmune disease by inducing, enhancing or suppressing an immune response. Immunotherapy can be nonspecific or (antigen)-specific. Nonspecific immunotherapy aims to enhance the overall host immune response, whereas specific immunotherapy targets the immune system against a particular tumor or increases tolerance towards a specific allergen. There are four main categories of specific immunotherapy: ▶adoptive immunotherapy, antibody-based immunotherapy, cancer ▶vaccine therapy and ▶allergen-specific immunotherapy. From these, adoptive and antibody-based immunotherapies are passive approaches, whereas cancer vaccine therapy and allergen-specific immunotherapy are active approaches.

Characteristics Despite advances in oncological research, cancer remains a leading cause of death throughout the developed world. Nonspecific approaches to cancer treatment, such as surgery, radiotherapy and generalized chemotherapy, have been successful in the management of a distinct group of leukemias and slow-growing solid cancers. However, many solid tumors show considerable resistance to such approaches, and the prognosis in these cases is correspondingly poor. Immunotherapy is an emerging alternative area of cancer treatment. Cancer immunotherapy includes both passive and active strategies. Passive immunotherapy involves the ex vivo creation of established tumor-immune elements (antibodies, immune cells) that are administered to patients to mediate anti-tumor activity directly or indirectly, and which do not stimulate the host immune system. In contrast, active immunotherapy induces a tumorspecific immune response in the patient, leading to the production of specific immune effectors (antibodies and T-cells). Historically, cancer immunotherapy has

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focused on nonspecific immune stimulants. Pioneer work began more than 140 years ago, when Wilhelm Busch observed that tumors show temporary regression during an infection. Two decades later, Sir William Coley developed and improved this therapeutic concept by vaccinating a large number of sarcoma patients with attenuated mixed bacterial extracts (▶Coley toxin). Nonspecific Immunotherapy 1. ▶Bacillus Calmette-Guerin (BCG) is the most effective intravesical nonspecific immunotherapeutic agent, and is used for the prevention and treatment of superficial ▶bladder cancer. The proposed anti-tumor mechanism of BCG involves activation of the immune system and the promotion of a local acute nonspecific ▶inflammation in the bladder lumen. Immune cell activation in response to BCG is mediated by a family of transmembrane recognition receptors called ▶Toll-like receptors (TLRs). Intravesical, BCG-induced inflammation facilitates the infiltration of a broad range of immune cells (▶macrophages, ▶lymphocytes and ▶natural killer cells) and the activation of pro-inflammatory cytokines such as ▶interleukin-1 (IL-1), ▶interleukin-6 and ▶tumor necrosis factor-alpha (TNF-α). 2. ▶Cytokines are low-molecular-weight, soluble proteins that regulate the innate and adaptive immune systems. The anti-tumor activity of cytokines is mediated by one of two general mechanisms: first, a direct anti-tumor effect, and second, indirect enhancement of the anti-tumor ▶immune response. It has been hypothesized that both the cytokineactivated lymphocytes and their secretory products such as interferon-gamma and tumor necrosis factorbeta (TNF-β) may contribute to the lysis of tumor cells in vivo. The exogenous administration of ▶interleukin-2 (IL-2) is efficient in a broad spectrum of experimental tumors, including sarcomas, carcinomas, hemoblastoses, melanomas and hepatomas. In humans, IL-2 and interferon-α2b are approved for the treatment of advanced melanoma and for use with ▶adjuvant therapy. Specific Immunotherapy 1. Adoptive Immunotherapy involves the infusion of immunologically-competent, ex vivo-expanded, donor-derived lymphocytes (DLI), which specifically destroy tumor cells by ▶graft-versus-leukemia (GvL) or ▶graft-versus-tumor (GvT) effects. In addition, peripheral blood-derived ▶lymphokine-activated killer (LAK) cells and ▶tumor-infiltrating lymphocytes (TILs) derived from tumor sections have proven to be effective anti-tumor agents. To address MHC and exogenous cytokine-independent activation of anti-tumor effector functions, T cells can be engineered to express ▶chimeric T-cell receptors.

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Immunotoxin

Chimeric receptors are composed of a recognition unit (antibody fragment) and an intracytoplasmic signaling molecule. Such receptors can be used to target various types of effector cells including cytotoxic T-cells towards any tumor-associated antigen for which there is a suitable antibody. 2. Antibody-based immunotherapy exploits the highly specific binding between antibodies and their corresponding ▶tumor-associated antigens (TAAs), resulting in some significant clinical responses. Tumor-associated antigens are structures presented predominantly by tumor cells, thereby allowing antibodies to distinguish tumors from non-malignant tissue. Therapeutic ▶monoclonal antibodies can destroy tumor cells directly by inducing ▶apoptosis or indirectly through immunologic mechanisms such as ▶antibody-dependent cell-mediated cytotoxicity (ADCC) and/or ▶complement-dependent cytotoxicity (CDC). In addition, the natural function of antibodies can be enhanced by conjugating them to toxins (▶immunotoxins), radionucleotides (radioimmunoconjugates), liposomes (▶immunoliposomes) and cytotoxic drugs. Host immune responses can be enhanced through the induction of ▶anti-idiotypic antibodies or through the use of ▶bispecific antibodies containing arms with different specificities. Monoclonal antibodies are the largest class of biotechnology-derived proteins, with 19 monoclonal antibodies already approved for human use by the United States Food and Drug Administration (FDA). 3. ▶Cancer vaccine therapy represents an active, systemic, tumor-specific immune response of host origin. It is used either to treat existing cancers (▶therapeutic vaccines) or to prevent cancer development (▶prophylactic vaccines). There are several types of cancer vaccine: isolated whole cell cancer vaccines or tumor cell lysates, protein- or peptidecontaining vaccines, viral vector vaccines and antiidiotype vaccines. Following the administration of a vaccine-antigen that resembles a specific target, the patient’s humoral and T-cell-specific immune response induces defense mechanisms to combat the target in vivo. ▶Cytokine Receptor as the Target for Immunotherapy and Immunotoxin Therapy

Immunotoxin Definition A toxic substance that is attached to a cell binding ligand and used to destroy a specific target cell. ▶Cytokine Receptor as the Target for Immunotherapy and Immunotoxin Therapy ▶Monoclonal Antibody Therapy

Importin-Alpha-3 Definition Is a nuclear localization signal receptor subtype that helps in translocation of certain proteins from cytosolic compartment to the nuclear compartment. ▶Transglutaminase-2

Importins Definition A group of proteins involved in transporting molecules from the cytoplasm through the nuclear pores of the nuclear envelope into the cell nucleus. ▶Modular Transporters

Imprinted Gene Definition

References 1. Schuster M, Nechansky A, Kircheis R (2006) Cancer Immunotherapy. Biotechnol J 1(2):138–147 2. Waldmann TA (2003) Immunotherapy: past, present and future. Nat Med 9(3):269–277

A gene that is marked in the germline; this denotes its maternal or paternal origin and influences its expression in the developing embryo. Refers to the parent-oforigin-specific monoallelic expression of a gene. ▶Imprinting

Imprinting

Imprinting C HRISTOPH P LASS German Cancer Research Center, Toricology and Cancer Risk Factors, Heidelberg, Germany

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of imprinted genes encode for RNAs but do not have an open reading frame and are not translated. It is believed that these RNAs play a role in the regulation of the imprinting process. Interestingly, short GC-rich repeat sequences were identified in the vicinity of many imprinted genes usually located in or near so called differentially methylated sites, ▶CpG island-like sequences that are methylated on only one allele.

Definition

▶Genomic imprinting; Describes a phenomenon in which a gene is expressed either from the paternal or form the maternal ▶allele and thus discriminates these genes from the majority of genes that are expressed from both alleles.

Characteristics Normally genes are expressed from both the maternal and the paternal allele. Genomic imprinting results in allele specific expression of certain genes from either the paternal or the maternal allele. These genes are marked before fertilization in a way that either the maternal or the paternal allele is transcriptionally silenced in the offspring. One of the first indications that certain autosomal regions are subject to genomic imprinting came from mouse genetic studies using Robertsonian and ▶reciprocal translocations. In these studies, uniparental duplications or deficiencies for certain chromosomal regions were analyzed. The failure of a disomy or duplication from one parent to complement a corresponding nullisomy or deficiency from the other parent constituted the genetic evidence for the occurrence of imprinting effects. In addition, embryos that contain either two copies of the maternal or the paternal genomes fail to survive in early development indicating the complementary need for both the maternal and paternal genome. More than 25 imprinted genes have been identified in mice and humans and there are estimates for about 100 imprinted genes in the mammalian genome. Certain characteristic features have been identified for imprinted genes. Most of the imprinted genes have important roles in early development. Interestingly, imprinted genes tend to occur in clusters suggesting a common regulatory mechanism. One of the best studied cluster of imprinted genes is located on mouse distal chromosome 7 (human 11p15.5), encompassing 1.5 Mbp and including the maternally expressed genes p57KIP2, Kvlqt1, Mash2 and H19 as well as the paternally expressed genes Ins2 and Igf2. It is now well accepted that imprinting could be regulated in a tissue specific manner in a way that only some tissues express the gene from one allele while others show biallelic expression. Here, unknown mechanisms exist that allow to by-pass the regulation of imprinting. It is interesting to note that a number

Cellular and Molecular Aspects Regulatory mechanisms underlying genomic imprinting are under intense investigations in many laboratories but only incompletely understood. The features of the imprinting signal and the mechanism are unknown, but strong evidence suggests the involvement of DNA ▶methylation. Several requirements for the underlying mechanisms can be postulated. First, the imprinting signal, or imprint mark, in the imprinted region must be established before fertilization. Second, the imprint mark must be an ▶epigenetic modification and must directly or indirectly affect the transcription of a gene by silencing one allele and leaving the other active. Third, the imprint mark must be stable in ▶mitosis and must be transmitted during cell division. Finally, the imprint mark must be reversible in a passage through the opposite germline. At present, DNA methylation is the only mechanism that conforms with the above requirements. Several lines of experimental data support the assumption that DNA methylation plays an important role in imprinted regulation. In mammals, ▶DNA methylation occurs only at the cytosine residue of ▶CpG dinucleotides. It was shown that DNA methylation in promoter regions can turn off the transcription of a gene. Most genes are subject to a process of demethylation directly after fertilization with most of the CpG sites unmethylated at the 16 cell stage. However imprinted genes are exceptions in this demethylation process by maintaining small regions that show allele specific methylation. DNA methyltransferase generates methylation patterns that are transmitted correctly following DNA replication and cell divisions. Studies of the expression of imprinted genes in DNA methyltransferase-deficient mutant mice indicated that normal level of DNA methylation are required for the control of allele specific expression. Studies with transgenic mice suggested that methylation is the epigenetic modification underlying genomic imprinting. A direct correlation between paternal inheritance, ▶transgene, ▶hypomethylation and tissue specific expression of the transgene was shown, while the maternally derived copy is methylated and not expressed. Clinical Relevance Imprinted genes are involved in critical steps during normal embryonic development. A growing body of

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In Situ Breast Cancer

evidence implicates genomic imprinting in the pathogenesis of certain human disorders, inherited tumor syndromes and sporadic tumors. At least ten genetic disorders have been found to be associated with genomic imprinting effects. In some cases, the trait is transmitted exclusively (or mainly) from one parent (either father or mother) or the disease is particularly severe when transmitted from one parent. In other cases the disease is associated with uniparental disomies or parent-of-origin specific aberrations. The best studied examples of imprinted genetic diseases are the Prader–Willi-Syndrome (PWS) and Angelman syndrome (AS). PWS is characterized by mild to moderate mental retardation, individuals are slow moving and overweight due to severe hyperphangia. Patients with AS show severe mental retardation are thin, hyperactive and show disorders of movement and uncontrolled laughter. Both syndromes are linked to abnormalities on human chromosome 15q11–13. The first hint for a possible imprinting effect in these syndromes came from the finding that the deleted fragments in both syndromes are from opposite parental origins. In PWS the deletion occurred in the paternal copy and in cases of AS the maternal copy was deleted. Additional evidence came from the finding of maternal disomy of chromosome 15 in PWS patients and paternal disomies of chromosome 15 in AS. These data suggest that the PWS gene(s) is transcribed from the paternal allele only and the AS gene(s) is expressed from the maternal allele. Several imprinted genes were identified in the critical region for PWS/AS including paternally expressed SNRPN and maternally expressed UBE3A. There is also evidence that some of the imprinted genes have oncogenic or tumor suppressor function. Loss of tumor suppressor function of an imprinted gene could be achieved by ▶loss of heterozygosity (LOH) involving the usually active copy, as shown for the cyclin dependent kinase inhibitor, p57KIP2, in lung cancers, H19 in ▶Wilms tumor and NOEY2, a member of the ▶RAS superfamily, in breast and ovarian cancers. Alternatively, uniparental disomy including the normally silent allele could lead to inactivation of an imprinted tumor suppressor gene. Activation of a growth supporting gene such as IGF2 (▶Insulin-like Growth Factors) could occur by uniparental disomy involving the normally active copy. In addition, relaxation of imprinting control, also called loss of imprinting (LOI), could lead to biallelic expression and thus overexpression of an imprinted oncogene, as shown for IGF2 in Wilms tumor. The first evidence for the involvement of DNA methylation in LOI came from the finding of complete methylation of the CpG island located immediately upstream of H19 transcription start site. Usually this ▶CpG island shows allele specific methylation on the maternal allele. This epigenetic change correlated with LOI in IGF2 and silencing of H19.

Another human disease is the ▶Beckwith–Wiedemann Syndrome (BWS) that is characterized by a number of growth abnormalities including gigantism. Between 5% and 10% of BWS patients are prone to Wilms tumor, adrenocortical carcinoma, hepatoblastoma or embryonal rhabdomyosarcoma. Wilms tumors have been shown to exhibit preferential loss of maternal alleles at chromosome 11p. A cluster of at least seven imprinted genes was identified in 11p15.5 including the paternally expressed IGF2 and the maternally expressed H19. The most common abnormality in BWS patients is LOI of IGF2 without any detectable chromosomal abnormalities.

References 1. Bartolomei MS, Tilghman SM (1997) Genomic imprinting in mammals. Annu Rev Genet 31:493–525 2. Cattanach BM, Kirk M (1985) Differential activity of maternally and paternally derived chromosome regions in mice. Nature 315:496–498 3. Falls JG, Pulford DJ, Wylie AA, et al. (1999) Genomic imprinting: implications for human disease. Am J Pathol 154:635–647 4. Nicholls RD, Saitoh S, Horsthemke B (1998) Imprinting in Prader–Willi and Angelman syndromes. Trends Genet 14:194–200 5. Reik W, Maher ER 1997 Imprinting in clusters: lessons from Beckwith–Wiedemann syndrome. Trends Genet 13:330–334

In Situ Breast Cancer ▶Ductal Carcinoma In Situ

In Situ Cancer or Carcinoma ▶Dormancy

In Situ Carcinoma ▶Dormancy

Indian

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Incidence

Definition

Definition

Describes experiments undertaken outside of a living organism (e.g. in Petri dish).

The number of new cases of a disease or condition occurring in a specific population during a given period of time.

▶Malignancy-Associated Changes

▶Incidence Rate

In Vitro Genetics Definition Is an umbrella term encompassing a variety of ▶combinatorial selection methods that involve large pools of nucleic acid sequence variants, a selectable function (e.g. protein binding or ribozyme-catalyzed chemical transformation), and ▶PCR amplification.

Incidence Rate I Definition Is the number of new disease cases per population at risk measured over a given time interval (high incidence rate implies high disease occurrence). ▶Epidemiology of Cancer ▶Cancer Epidemiology

In Vivo Definition Inside of a living organism.

Independent Prognostic Factor Definition

Inbred Lines ▶Mouse Models

An indicator used to estimate the risk of disease recurrence and death in an individual patient. Multivariate statistical analysis determines whether a prognostic factor exhibits a new, independent value as compared to established prognostic factors. ▶Prognosis ▶Prognostic Biomaker

Inbred Strain Definition A strain of animal that has no genetic differences (▶polymorphisms) with other animals of the same strain. ▶Mouse Models

Indian Definition

Gene in ▶Hedgehog Signaling.

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Indirubin and Indirubin Derivatives

Indirubin and Indirubin Derivatives G ERHARD E ISENBRAND, K ARL -H EINZ M ERZ Department of Chemistry, Division of Food Chemistry and Toxicology, University of Kaiserslautern, Kaiserslautern, Germany

Synonyms 3-(1,3-Dihydro-3-oxo-2H-indol-2-ylidene)-1,3-dihydro2H-indol-2-one; 2′,3-Biindolinylidene-2,3′-dione: 3-(3Indolinone-2-ylidene)-indolin-2-one

Definition Indirubin is the parent compound of a spectrum of 2′,3-bisindoles synthesized to improve the biological activity of this natural 2′,3-bisindole lead structure. Indirubin and its isomers indigo and isoindigo are composed of two indolinone ring systems, linked through a double bond to make up 2,2′-(indigo), 3,2′(indirubin) and 3,3′-(isoindigo) bisindoles, respectively (Fig. 1).

Characteristics History While indigo is one of the oldest dyes known, with a history of use dating back to bronze age, the two other isomers, especially indirubin, have gained reputation as components of traditional medications used against a variety of human diseases. The discovery of the anticancer activity of indirubin can be traced back to a traditional Chinese medication, consisting of 11 ingredients, mostly of herbal origin, with the name of Danggui Longhui Wan. The preparation is used traditionally for a variety of chronic and acute diseases including chronic myelocytic leukemia (▶CML). Chinese scientists achieved the identification of the active ingredient of this medication, Quing Dai, which corresponds to natural indigo, prepared from the leaves of indigo-producing plants. Furthermore, the Chinese scientists discovered that not only the blue dye indigo, but a minor byproduct, the red colored trace constituent indirubin was the active antileukemic principle. In a clinical trial, synthetic indirubin was given orally to CML patients at dosages of 150–450 mg/day. A total of 314 patients participated in the study. Complete remissions were observed in 26%, partial remission in 33%, and some beneficial response in 28% of patients. Treatment was well-tolerated, without major side effects. Studies exploring the mechanism of action reported a spectrum of relatively unspecific biological effects, not really convincing to fully explain the respectable anti-CML activity of the compound.

Indirubin and Indirubin Derivatives. Figure 1 Structures and numeration of indigoid bisindoles. (a) Indigo, (b) Indirubin (E211), (c) Isoindigo.

Mechanism Research on indirubins gained momentum, when in 1999 it was discovered that such 3,2′-bisindoles act as potent inhibitors of serine/threonine kinases, especially of ▶cyclin-dependent kinases (CDKs) and of glycogensynthase kinase 3β (GSK3β). Later it was found that indirubins also inhibit ▶receptor tyrosine kinases, such as ▶vascular endothelial growth factor receptor (VEGFR) or ▶Src kinase and block Stat-3 signaling. Moreover, indirubins have also been discovered to activate the ▶aryl hydrocarbon receptor transduction pathway. Thus indirubins exert, in addition to their multimodal kinase inhibitory activity, further bimolecular effects contributing to anticancer activity. The relative kinase inhibitory profile of individual representatives of these 3,2′-bisindoles, as well as their pharmacokinetic properties is markedly influenced by the type and pattern of substituents attached to the 3,2′bisindole basic scaffold. Within cancer targets, VEGFR2 and c-Src, as well as specific CDKs are of prime interest, since their respective partner proteins, activators or inhibitors, are aberrantly expressed in many human malignancies.

Indirubin and Indirubin Derivatives

Structure/Activity Chemical improvement of the parent molecule initially was driven by the aim to improve solubility and bioavailability without compromising anticancer activity.

Indirubin and Indirubin Derivatives. Figure 2 Superposition of crystal structures of CDK2–E226 (yellow) and CDK2–AMPPNP (white). Green arrows point to 5- and 3′-position of indirubin scaffold. (Reprinted from Davies et al (2001), Structure 9:389; with permission from Elsevier).

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Indirubins act as ATP-competitive inhibitors of ATP-dependent kinases. Crystal structures of CDK2–indirubin complexes have been described in detail. It was shown that the flat disk shape of the 3,2′-bisindole molecule slides easily into the binding pocket and is tightly bound, mainly by virtue of hydrogen bonding and lipophilic interactions with the ATP-binding cleft, situated in the hinge region connecting the amino terminal with the carboxy terminal part of the kinase. The strong binding affinity of indirubin derivatives to the ATP site is practically not affected by additional binding of the activating partner cyclin A to CDK2. A superposition of the structures of the binding complexes of the indirubin derivative, E 226, and of a nonhydrolyzable ATP mimic, AMPPNP, with CDK2, unraveled molecular positions of the indirubin scaffold preferably to be exploited for chemical improvement of the molecule. Thus, positions 5 and 3′ (arrows in Fig. 2) were identified as those of first choice for molecular modifications by attaching appropriate substituents. The chemistry to achieve the synthesis of such derivatives has been described in detail. A selection of results from comprehensive structure/activity studies is summarized in Tables 1 and 2. The results show that the inhibitory activity of the parent molecule, indirubin (E211) on isolated

Indirubin and Indirubin Derivatives. Table 1 Inhibition of CDK/cyclin complexes (IC50-Werte, μM) by indirubins in comparison with roscovitine Substance

E-Nr E211 E226 E231

1

O O NOH

2

R

H So3− H

CDK1/Cyclin B a

CDK2/Cyclin A

CDK6/Cyclin D

7.5 0.15a 0.33 ± 0.05b 0.25a 0.09 ± 0.01b

– – 0.08 ± 0.03b

a

E729

OCH3

E804

H

1.7 ± 0.4b

0.5 ± 0.1b

0.2 ± 0.04b

0.06 ± 0.01b

7.9 ± 0.4b 0.65a

3.5 ± 1.3b 0.7a

1.0 ± 0.4b 0.7a

>10b

Method: Meijer et al. (1997). Method: Jakobs et al. (2005) Glc: β-D-glucopyranosyl –: not determined.

b

CDK2/Cyclin E

2.2 0.035a 2.2 ± 0.2b 0.44a 0.8 ± 0.1b

a

10 0.055a 5.1 ± 2.9b 0.18a 5.6 ± 1.3b

Roscovitine a

R

0.4 ± 0.1b

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Individual Susceptibility

Indirubin and Indirubin Derivatives. Table 2 derivatives a

Substance E211 E226 E231 E729 E804

Solubility in water and human tumor cell growth inhibition of indirubin

Solubility in water (mg/L) >100 0.12 42 1.6

LXFL-529L 9.9 ≥100 3.0 0.5 0.9

MCF-7 4.0 ≥100 3.3 1.2 0.1

HCT116 – – – 0.5 8 years) and anatomical extent of colitis [standardized incidence ratio (SIR): 1.7, 95% confidence interval (CI): 0.8–8.2 for proctitis; SIR: 2.8, 95% CI: 1.6–4.4 for left-sided colitis; SIR: 14.8, 95% CI: 11.4–19.9 for pancolitis], appear as the most important and reproducible from one study to another. Other factors like family history of sporadic CRC (twofold higher risk), young age of IBD onset, backwash ileitis, and more recently degree of inflammation in the involved colon, are also considered as risk factors. Finally, association to primary sclerosing cholangitis (PSC), although rare (approximately 2–7.5% of IBD patients, more frequently in UC patients), appears as a very important risk factor and has conducted to a specific surveillance strategy in these particular patients since the cumulative incidence of patients presenting both UC and PSC was 33% at 20 years in a population-based Swedish study. By contrast, a few other factors have been suggested to be protective, such as folate, ursodeoxycholic acid, and with the highest degree of evidence, treatment by 5-aminosalicylates (5-ASA). The goal of surveillance strategies (i.e., surveillance ▶colonoscopy) is to detect by using a safe and effective intervention, neoplasia at a curable stage (ideally as ▶dysplasia). Dysplasia is defined as an unequivocally

Inflammatory Bowel Disease-associated Cancer

but noninvasive (intraepithelial) neoplasia. Despite the theory proposing that IBD-associated colon carcinogenesis progresses from no dysplasia to indefinite dysplasia, and then to low grade dysplasia (LGD), high grade dysplasia (HGD), and finally invasive cancer, in reality, this conceptually useful model is by no means absolute. This uncertainty thrives on much of the controversy regarding treatment of LGD. Except in the case of dysplasia in DALM which usually is not too difficult to detect for experienced practitioners, macroscopic identification of flat dysplastic lesions (either of low or high grade) appears particularly difficult during conventional colonoscopic surveillance. Nevertheless, this early identification represents a major challenge, as the presence of HGD in the colonic epithelium is associated with concurrent, macroscopically-undetectable CRC in 42–67% of patients (in case of colectomy performed shortly after HGD diagnosis at colonoscopy), and to the finding of a synchronous CRC in up to 19% of patients in case of LGD diagnosis at colonoscopy. Considering these facts, recommendations for colonoscopic surveillance have been established. Screening ▶colonoscopy should be initiated after 8–10 years of disease, including biopsies of each macroscopic lesion (with additional biopsies in the flat mucosa surrounding the DALM) and random biopsies of the macroscopically normal appearing mucosa (four-quadrant biopsies every 10 cm, some authors considering sampling every 5 cm in the rectosigmoid). In patients with PSC, colonoscopic surveillance should begin at the time of diagnosis of PSC and IBD. At each surveillance examination, the whole colon should be examined, and biopsies processed in separate clearly identified specimen containers. Recently, new endoscopic technologies have been suggested to improve the diagnosis yield of early malignancy, especially dysplasia detection in flat mucosa. This is the case for high-resolution and magnifying endoscopy, chromo (or dye) endoscopy based on vital staining with methylene blue or contrast staining with indigo carmine, magnifying chromoendoscopy, narrow-band imaging, and confocal laser endoscopy. These techniques open a new world of endoscopic imaging, but their usefulness for improving dysplasia detection in IBD needs to be carefully assessed before they will be recommended in routine screening. Nevertheless, the most recent data indicate that dye endoscopy with indigo carmine or methylene blue have to be seriously considered in daily practice. If no dysplasia is identified, surveillance examination is recommended every 1–3 years (some authors proposing a subsequent screening at 3 years between 8 and 20 years of disease, every 2 years between 20 and 30 years, and each year after 30 years of IBD diagnosis), except for IBD patients with concurrent PSC (surveillance colonoscopy recommended each

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year regardless of IBD duration). In case of LGD detection in flat mucosa, sample analysis by a second pathologist is recommended, and if LGD is confirmed, a surveillance colonoscopy should be performed 6 months later, although some authors propose to perform colectomy. Detection of HGD in flat mucosa indicates colectomy. Decision after LGD or HGD diagnosis in a polypoid lesion should integrate additional information: (i) if the polypoid lesion has been completely removed and no dysplasia has been detected elsewhere in the colon, a control colonoscopy with multiple random biopsies is recommended 6 months later; (ii) if this is not the case (incomplete removal and/or dysplasia detected in other biopsies), colectomy is indicated. A number of studies have examined the chemopreventive potential of several medications. Until now, 5-ASA have been the most thoroughly studied as potential IBD-associated CRC preventing agents. In fact, at least in vitro but also in some in vivo studies, 5-ASA have been shown to inhibit cell proliferation, to induce apoptosis, to act as potent RONS scavengers, and to enhance DNA repair. Although the optimal dose and duration of 5-ASA treatment to prevent IBDassociated CRC are unclear, data suggest that chronic systemic administration of 5-ASA at a dose of at least 1.2 g/day is the most likely to prevent IBD-associated CRC development. Small Bowel Adenocarcinoma in Crohn Disease The incidence of small bowel adenocarcinoma (SBA) is very low. In CD, its relative risk has been reported to be up to 50 times higher than in the general population. In a recent study, its cumulative risk in patients with ileal CD has been estimated to be 0.2% after 10 years of disease, and 2.2% after 20 years, with a median age at diagnosis of 47 years compared with 68 years for patients with SBA de novo. It occurs in a median time of 15 years after CD diagnosis arising from long-standing inflammation. CD-associated SBA is difficult to diagnose and causes premature mortality in early-onset CD patients. Cancer risk Associated to Immunosuppressive Therapy in IBD In the recent years, the efficacy of “classical” immunosuppressive drugs [azathioprine, 6-mercaptopurine (6-MP), or methotrexate], as well as that of biological agents (i.e., in current practice, anti-TNFα antibodies such as infliximab) led to their increased use in IBD. This emphasizes the question of their potential carcinogenic effects, in particular considering the risk of lymphoma which has been previously reported in patients treated by azathioprine or 6-MP after renal or hepatic transplantation (although used at doses even higher than in IBD). This question is not definitively resolved, probably due to the heterogeneity

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Inflammatory Cytokines

of the different studies, in particular when considering population-based cohorts on one hand and hospitalbased cohorts on the other hand. Discrepancies may result from varying factors such as cohort sizes, duration and dosage of treatment, and/or duration of follow-up. Nevertheless, some general statements based on the most relevant studies in the field can be suggested: (i) the absolute risk of ▶lymphoma in the general IBD population appears extremely low, (ii) lymphoma risk in IBD patients treated by azathioprine or 6-MP is probably not more than two- to fourfold increased, although the respective responsibility of treatment and underlying disease has to be more accurately investigated, (iii) particular attention needs to be brought to the ▶Epstein–Barr virus positive lymphoma risk in azathioprine or 6-MP treated IBD patients, and finally, (iv) the issue of lymphoma risk is likely to become more relevant in the future with the growing number of immunosuppressive and/or biological agents being used (or tested) in IBD, sometimes concurrently. This has been emphasized by the report of hepatosplenic T-cell lymphomas in young petients treated both with purine analogs and infliximab.

manner. ▶Interleukins, ▶lymphokines, and ▶interferons are all cytokines. ▶Aging and Cancer ▶Inflammation

Inflammatory Response Definition Refers to the ability of the innate component of the immune system to react to an infection or irritation. An orchestrated cellular and biochemical response of the body to injury or infection. Can be classified into acute and chronic. The response consists of cellular and exudative components. These involve the movement of white cells and fluid containing proteins and antibodies into the tissue to repair damage and inactivate a foreign agent. ▶Inflammation ▶Inflammatory Response and Immunity

References 1. Farraye FA (ed) (2006) Dysplasia and cancer in inflammatory bowel disease. Gastroenterol Clin North Am 35:517–734 2. Itzkowitz SH, Yio X (2004) Inflammation and cancer IV. Colorectal cancer in inflammatory bowel disease: the role of inflammation. Am J Physiol Gastrointest Liver Physiol 287:G7–G17 3. Kwon JH, Farrell RJ (2005) The risk of lymphoma in the treatment of inflammatory bowel disease with immunosuppressive agents. Crit Rev Oncol Hematol 56:169–178 4. Li HC, Stoicov C, Rogers AB et al. (2006) Stem cells and cancer: evidence for bone marrow stem cells in epithelial cancers. World J Gastroenterol 12:363–371 5. Palascak-Juif V, Bouvier AM, Cosnes J et al. (2005) Small bowel adenocarcinoma in patients with Crohn’s disease compared with small bowel adenocarcinoma de novo. Inflamm Bowel Dis 11:828–832

Infratentorial Primitive Neuroectodermal Tumor ▶Medulloblastoma

Inherited Human Polycystic Kidney Disease ▶Polycystic Kidney Disease

Inflammatory Cytokines Definition Small proteins that are released primarily by activated immune cells. Inflammatory ▶cytokines act by binding to specific cell membrane receptors that are involved in amplification of inflammatory reactions. Cytokines can act in an ▶autocrine, ▶paracrine, or ▶endocrine

Inhibin Definition Dimeric peptide hormones (designated inhibin A and inhibin B) secreted by the follicular cells of the ovary

Initiation and Promotion

and the Sertoli cells of the testis. Inhibits production and secretion of ▶follicle stimulating hormone (FSH) by the pituitary. ▶Granulosa Cell Tumors

Inhibitor of Apoptosis Family Definition IAPs are a family of proteins that are important regulators of ▶apoptosis. IAPs function by binding to and inhibition of activated ▶caspases. IAPS are characterized by having one or more protein domains of 70 amino-acids called baculovirus IAP repeat (▶BIR domain). ▶Apoptosis-Induction for Cancer Therapy

Inhibitor of Cyclin-Dependent Kinase Definition:

Protein that inhibits the kinase activity of ▶CDK. ▶Early B-cell Factors ▶Cyclic Dependent Kinases

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which require administration to cells and tissues by various routes. ▶Cystatins

Initial Area Under the Gadolinium Contrast Agent Concentration–Time Curve Definition IAUGC; A model-free biomarker derived from contrast agent concentration data that is used as a biomarker in clinical trials of angiogenesis inhibitors. ▶Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Initiation Definition In carcinogenesis, the first step in skin carcinogenesis is initiation, which is a reversible process during genetic mutations, gene activation or inactivation occur. Examples of initiation are mutations in the ▶RAS oncogene or inactivation of the p53 tumor suppressor gene ▶Skin Carcinogenesis

Inhibitor of FLICE ▶FLICE Inhibitory Protein

Initiation and Promotion Inhibitors

Definition

Definition

In carcinogenesis, the process in which an animal is treated with a low dose of a carcinogen, then this is followed once per week with a tumor promoter, and leads to a synergistic induction of tumors.

Proteins or chemicals capable of blocking the activity of an enzyme. Endogenous inhibitors are natural products of cells and tissues as opposed to exogenous inhibitors,

▶Chemical Carcinogenesis ▶Tumor Promotion

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Initiation Codon

Initiation Codon Definition The mRNA sequence AUG, which specifies methionine, the first amino acid used in the ▶translation process.

p18INK4c, and p19INK4d) contain four tandemly repeated ▶ankyrin motifs and have similar biochemical phenotypes. The p16INK4a is an alternative reading frame product (▶ARF) of p16INK4a and p15INK4b, which are coded at the human chromosome 9p21 region. The significance of the p16INK4a, ARF, and p15INK4b in tumorigenesis are confirmed by the high frequency of the genetic and epigenetic modifications of these genes in tumor samples.

Characteristics

Initiation Factors Definition

Initiation of ▶translation involves the small subunit of the ribosome binding to 5′ end of mRNA with the help of initiation factors.

Initiator Caspases Definition Are activated independent of cleavage by dimerization of the monomeric zymogen at multiprotein complexes, to which the ▶caspase zymogens are recruited by virtue of their N-terminal recruitment domain. In the extrinsinc pathway, ▶caspase-8 and -10 are activated at the death-inducing signaling complex (▶DISC), whereas in the intrinsinc pathway, the site of activation of caspase-9 is the ▶apoptosome.

INK4a TAKEHIKO K AMIJO Division of Biochemistry, Chiba Cancer Center Research Institute, Chuoh-ku, Chiba, Japan

Definition

Inhibitor of ▶cyclin-dependent kinase 4; proteins are cyclin-dependent kinase inhibitors that block the action of cyclin-dependent kinase to induce cell cycle arrest. The four INK4 family proteins (p16INK4a, p15INK4b,

Structure of INK4b/ARF/INK4a Locus and Molecular Functions of INK4s/ARF The INK4b/ARF/INK4a gene locus is located at the human chromosome 9p21 region. Chromosome region 9p21 is involved in chromosomal ▶inversions, ▶translocations, and ▶deletions in a variety of malignant cell lines and primary tumor samples, including those from ▶melanoma, pancreatic adenocarcinoma, ▶non-small cell lung cancer, ▶leukemia, and ▶glioma. These findings indicate that 9p21 contains a tumor suppressor locus that may be involved in the tumorigenesis of several tumor types. In a region of less than 40 kb of the human genome, three related genes, p15INK4b, ARF, and p16IN4a are encoded (Fig. 1). The INK4 class of ▶cell cycle inhibitors, p15INK4b and p16IN4a are homologous inhibitors of the cyclindependent kinases, CDK4 and CDK6, which inactivate the tumor suppressor RB1 protein via phosphorylation of its c-terminal region. The association of the INK4 proteins to CDK4/CDK6 induces an allosteric modification that abrogates the binding of these kinases to ▶cyclin D, resulting in inhibition of CDK4/6-mediated phosphorylation of retinoblastoma family member proteins. Hence, the existence of p15INK4b and p16INK4a maintains retinoblastoma family member proteins in a hypophosphorylation state, which facilitates binding of ▶E2F to induce a cell cycle arrest in the G1 phase (Fig. 2). ARF and INK4a have different first exons, exon 1 beta and exon 1 alpha, respectively. These first exons are spliced to a common second exon and third exon. Although exons 2 and 3 are shared by p16INK4a and ARF, these proteins are encoded in alternative reading frames. The predicted 132-amino acid p14 (ARF) is shorter than the corresponding mouse protein, p19(ARF), and the 2 proteins share only 50% identity. However, both proteins have the ability to elicit a p53 response, manifest in the increased expression of both p21Cip1/Waf1 and several p53-downstream proapoptotic molecules, resulting in a distinctive cell cycle arrest in the G1/G2M phases and apoptotic cell death, respectively. Previous reports showed that ARF binds to ▶MDM2 and promotes the segregation of MDM2 in the nucleolus. This interaction is mediated by the exon

INK4a

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INK4a. Figure 1 Genomic stucture of INK4b/ARF/INK4a locus. Residing on chromosome 9p21 in humans and chromosome 4 in mice, the INK4b/ARF/INK4a locus includes 2 different genes. INK4b and INK4a/ARF. INF4a and ARF, which have the independent exon1 alpha and exon1 beta, respectively, and common exon2/exon3, encode different proteins via an alternative splicing mechanism. In this commentary, p14ARF (murine p19ARF) will be referred to as ARF.

I

INK4a. Figure 2 Physiological roles of INK4s/ARF. Mitogenic signals activated cyclin D-dependent kinases, which phosphorylate RB and RB family proteins to facilitate entry into S phase. Consititutive oncogenic signals can activate the INK4a/ARF locus. By antagonizing the activity of cyclin D-dependent kinases, p16INK4a and p15INK4b prevent entry into S phase. MDM2 is a p53-inducible gene that normally acts to terminate the p53 response. The ARF protein inhibits MDM2 to induce p53, leading either to p53-dependent apotosis or to induction of the CDK inhibitor p21Cip1, inhibition of cyclinE/Cdk2, and RB-dependent cell cycle arrest.

1-beta-encoded N-terminal domain of ARF and a C-terminal region of MDM2. Roles in Tumorigenesis Human cancers frequently harbor ▶homozygous deletions of the INK4b/ARF/INK4a locus that abrogate expression of all p15INK4b/ARF/p16IN4a. In a large number of human cancers, specific somatic loss of p16INK4a, through ▶point mutation or small deletion, has been reported. Furthermore, silencing of p16INK4a through promoter methylation is reported at high frequency in numerous types of human malignancies.

Therefore, p16INK4a is an important tumor suppressor in human malignancies. In the case of p15INK4b, specific ▶epigenetic gene silencing by ▶hypermethylation of the p15INK4b promoter has been described in ▶hematological malignancies including ▶leukemia and ▶myelodysplastic syndrome and rare cases of glial tumors. In myelodysplastic syndrome, hypermethylation of p15INK4b has been reported in the absence of p16INK4a hypermethylation. p15INK4b seems to be an important tumor suppressor in specific lineages of human malignancies, e.g., hematological malignancies.

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INK4a

Selective inactivation of ARF, in the absence of additive loss of p16INK4a and p15INK4b, has only been reported in a small number of human malignancies, e.g., familial melanoma/astrocytoma patients and somatic ARF-specific mutations and promoter methylations in colon carcinoma patients. Therefore, it seems that ARF cooperates with p16INK4a and p15INK4b in tumorigenesis of human malignancies and their relative and combinational importance in any given tumor types remains to be elucidated. Roles in Senescence Cellular ▶senescence is a fundamental cellular program that is activated in various situations of stress and acts to prevent further cell proliferation. Senescence induced by extrinsic stress, such as DNA damage or oncogene activation, occurs relatively rapidly, in a matter of days. As a population of cells is propagated in culture, cells are exposed to various extrinsic and intrinsic stresses and the population gradually stops dividing. These findings have led to a distinction between “stressinduced premature senescence,” a term referring to rapid senescence triggered by extrinsic stress, and “replicative senescence,” a term referring to senescence that occurs following extended proliferation, presumably triggered by various stresses. Cellular senescence is thought to play an important role in tumor suppression and contribute to organismal aging. In fact, the two definitive tumor suppressor pathways, ARF/MDM2/p53 and p16INK4a/Rb, have been shown to play critical roles in the induction of cellular senescence. In tissue culture of primary cells, the accumulation of one or more INK4b/ARF/INK4a locus genes can eventually lead to cell cycle arrest through the mechanisms presented in Fig. 2. The cellular senescence is cancelled by downregulation of expression caused by gene deletion or epigenetic regulation, by inactivation of the gene products by mutation, or by cellular resistance to those cell cycle inhibitors. Considering the significance of the INK4b/ARF/INK4a locus genes in the cellular life span, p16INK4a plays a central role in senescence in human cells, whereas ARF assumes a prominent role in mouse cells. For mice, p19ARF and p16INK4a both accumulate significantly after passage, but spontaneous escape from senescence occurs through deletion of INK4/ARF or p53 mutation in wild type MEFs. Consistent with this, ARF-null MEFs do not have proliferation failure, but p16INK4anull and p15INK4b-null MEFs indicate limited proliferation. Whereas senescence generally occurs in the setting of increased expression of p16INK4a, but not ARF, and enforced Ras–Raf pathway activation also appears to induce only p16INK4a, along with senescence in cultured human cells. Furthermore, only p16INK4a induction has been reported with human

aging, although ARF expression studies in human aging have not been reported. Activators of the p15INK4b/ARF/p16INK4a Ras–Raf–p38MAPK Pathway Involvement of the Ras signaling pathway into the regulation of the INK4b/ARF/INK4a locus-encoded genes has been reported in detail. Expression of oncogenic Ras in primary human or rodent cells results in a permanent G1 arrest of the cell cycle. The arrest induced by ▶Ras is accompanied by accumulation of ▶p53 and ▶p16, and is phenotypically indistinguishable from cellular senescence. Constitutive activation of MAPKK induces both p53 and p16, and is required for Ras-induced senescence of normal human fibroblasts. Ras signaling pathway activation can result in phosphorylation and enhance binding of ▶Ets transcription factor to the p16INK4a promoter. These results imply that premature senescence via INK4b/ARF/INK4a locus activation acts as a fail-safe mechanism to limit the transforming potential of excessive Ras mitogenic signaling. Whereas oncogenic Ras induces ARF transcription in MEFs, similar effects have not been detected in human cells. One of the key molecules activated by Ras signaling pathway is DMP1, which binds directly to the p19ARF promoter region. Although there are putative binding sites in the human ARF promoter region, the effects of DMP1 have not been demonstrated in human cells. E2F The ▶E2F transcriptional factors are divided into two groups; (i) transcriptional activating E2F1, E2F2, and E2F3; (ii) transcriptional repressing E2F4, E2F5, and E2F6. Several E2Fs have been detected at the endogeneous ARF promoter by chromatin immunoprecipitation assay and directly activate ARF transcription without association with DP-1. Since ARF transcription is not regulated by a cell cycle-dependent manner, the unphysiological level of E2F seems to be required to induce ARF. Some studies described the inverse correlation between pRb status and p16INK4a expression in tumor cells. However, the physiological relation remains to be elucidated in terms of the relationship between the pRb/E2Fs and INK4 pathway. Myc Oncogene ▶Myc Oncogene has the ability to control p16INK4a transcription in human cells. Myc protein binds to the promoter and first intron of human p16INK4a, which is in line with the reports that Myc upregulates p16INK4a transcription in human cells. However, Myc has little effect on p16INK4a expression in mouse cells. In mouse cells, establishment of MEFs as continuously growing cell lines is normally accompanied

INK4a

by loss of the p53 or p19ARF, which act in a common biochemical pathway. Myc rapidly activates ARF and p53 transcription in MEFs and triggers replicative crisis by inducing apoptosis. MEFs that survive Myc overexpression sustain p53 mutation or ARF loss during the process of establishment and become immortal. These observations are consistent with the cooperation of -Myc and Bmi1 in mouse lymphomagenesis, suggesting that the ARF/p53 pathway is a physiological safeguard system against Myc-induced oncogenic stresses. Suppressors of p15INK4b/ARF/p16INK4a AML1/ETO ▶AML1/ETO chimeric protein results from the t(8;21) translocation in human ▶acute myelogenous leukemia. AML1/ETO can bind directly to the ARF promoter regions as well as the POZ/BTB domain protein, ZBT7B. The translocation seems to convert the wildtype AML1 from being an inducer of ARF to a repressor. p53 One of the most important tumor suppressors, p53 seems to have a significant role in ARF transcriptional suppression because ARF is generally transcriptionally upregulated in ▶p53-inactivated cells. However, the mechanism of the transcriptional repression of ARF by reintroduction of wild-type p53 into p53-null cells remains to be elucidated. ▶Polycomb Proteins Traditionally, cancer has been viewed as a genetic disease that is driven by the sequential acquisition of mutations, leading to the constitutive activation of proto-oncogenes and loss of function of tumor suppressor genes. However, it has become increasingly evident that tumor development also involves “▶epigenetic changes” patterns of altered gene expression that are mediated by mechanisms that do not affect the primary DNA sequences. The INK4b/ARF/INK4a region is known to be regulated by not only the genetic alteration but also by epigenetic modifications. ▶Polycomb group (PcG) genes were first identified in Drosophila as a group of genes required for maintenance of stable repression of Hox cluster genes during development. There are increasing lines of evidence that PcG proteins themselves affect cellular proliferation and replicative senescence. Targeted disruption of Bmi1, Mel18, rae28, and M33, which are members of the class II PcG complex, leads to proliferation defects in hematopoietic stem cells and mouse embryo fibroblasts, indicating that inactivation of these PcGs results in cell proliferation failure.

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Replicative senescence of MEFs derived from Bmi1-, M33-, and Phc2-null mice has been shown to be mediated by derepression of the central mediators of senescence signals, p19ARF and p16INK4a, which are encoded by the INK4b/ARF/INK4a region. The molecular mechanism underlying the transcriptional regulation of these genes by mammalian PcG complexes, however, has not yet been appropriately addressed except for physical interactions of Bmi1 and Phc2 gene products to ARF and INK4a genomic regions. Future Directions The significant role of the INK4b/ARF/INK4a region and its products, p15INK4b/p14(p19)ARF/p16INK4a, in suppression of tumor development is well-established. However, regulatory mechanisms controlling these genes remain to be elucidated. The entire genomic region, which covers the genomic region from p15INK4b to p16INK4a (Fig. 1), is frequently deleted in a wide spectrum of tumors as described previously. However, the precise molecular mechanism of the biallelic gene deletion has not been addressed previously. In mouse MEFs, c-Myc induces the accumulation of p19ARF/p53 at the transcriptional level and has a significant proportion of the cells undergo apoptosis, whereas Myc-induced cell cycle accelerators, e.g., cyclin E, cyclin A, and CDC25A, are upregulated. In the face of Myc overexpression, there was a strong selective advantage for cells that sustained p53 mutations or the INK4b/ARF/INK4a deletion, and once such variants emerged, these soon predominated and were able to continuously proliferate. These results suggest that genes encoded by the INK4b/ARF/INK4a region are deleted by oncogene-derived stress-induced unknown molecular mechanisms and the safe guard machineries-broken cells continuously proliferate by oncogene-derived stimulations. The precise mechanisms of the locus deletion should be addressed to understand the immortalization and malignant transformation of normal cells. A particularly important recent finding with regard to the INK4b/ARF/INK4a regulation was a coordination of transcription at the locus and DNA replication. The coordination between silencing of the locus and DNA replication was reported. In detail, a DNA replication origin in close proximity to the locus appears to transcriptionally repress p15INK4b/ARF/ p16INK4a expression in a CDC6-dependent manner. Obviously, these findings suggest a novel molecular connection between DNA replication and p15INK4b/ ARF/p16INK4a transcription. Further analysis of the cooperation between this CDC6-dependent regulation and other known regulatory mechanisms of this locus, both of genetic and epigenetic regulations, seems to be worthwhile.

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Innate Immune System

References 1. Ruas M, Peters G (1998) The p16INK4a/CDKN2A tumor suppressor and its relatives. Biochim Biophys Acta 1378: F115–F177 2. Lowe SW, Sherr CJ (2003) Tumor suppression by Ink4aARF: progress and puzzles. Curr Opin Genet Dev 13:77–83 3. Sherr CJ (2001) The INK4a/ARF network in tumour suppression. Nat Rev Mol Cell Biol 2:731–737 4. Sparmann A, van Lohuizen M (2006) Polycomb silencers control cell fate, development and cancer. Nat Rev Cancer 6:846–856 5. Gil J, Peters G (2006) Regulation of the INK4b-ARFINK4a tumour suppressor locus: all for one or one for all. Nat Rev Mol Cell Biol 7:667–677

Innate Immune System Definition Comprises the cells and mechanisms that defend the host from infection by other organisms or tumor growth, in an immediate and non-specific manner. The recognition of tumor cells by ▶natural killer cells is part of an innate immune response and does not depend upon the adaptive immune system; it does not confer long-lasting or protective immunity to the host. ▶Toll-Like Receptors ▶Adaptive Immunity

system. Innate immune cells recognize common molecular patterns on infectious agents, cells infected with viruses, and transformed cells. Cells of the innate immune response include ▶macrophages, ▶dendritic cells, mast cells, neutrophils, eosinophils, natural killer (NK) cells, natural killer T (NKT) cells and γδ cells, and the cytokines they secrete on activation, as well as antimicrobicides that are made by specialized cells and tissues. ▶Immunoediting ▶Bacillus Calmette-Guérin ▶DNA Vaccination

Innexins Definition Are the invertebrate gap junction proteins. ▶Pannexins ▶Gap-Junctions

iNOS Definition

Inducible ▶nitric oxide synthase.

Innate Immunity

▶Nitric Oxide ▶Nitric Oxide Synthase

Definition

Used together with the term ▶adaptive immunity to describe the two functional parts of the immune system. The original strict separation of the two parts of the immune system is currently reconsidered because a deep and intimate interconnection and cross-talk between the humoral and cellular parts of innate and adaptive immunity does exist. Nevertheless, innate immunity describes the immediate (within hours to a few days) reaction of the immune system in response to a given challenge. Typically involves, but is not limited to, (antimicrobial) phagocytes and substances, natural killer cells, certain cytokines and the complement

Inosine Definition A nucleoside; the breakdown product of adenosine through the enzyme adenosine deaminase (ADA). ▶Adenosine and Tumor Microenvironment

Inositol Lipids

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Among different inositol lipids, the importance in ▶transmembrane signaling and regulation of cell functions are best documented for PtdIns (4,5)P2 and PtdIns (3,4,5)P3. There are several ways in which these low abundance inositol lipids (less that 1% of membrane phospholipids) could provide a signaling link or fulfill other roles in different cellular processes.

trisphosphate (Ins(1,4,5)P3) and diacylglycerol (DAG) molecules. The reaction is catalyzed by phosphoinositide-specific ▶phospholipase C (PI-PLC) (Fig. 1). There are several ▶isoforms of this enzymes (PLCβ, PLCγ, PLCδ, and PLCε) linked to and activated by different cellular receptors. For example, PLCγ is regulated through tyrosine kinase receptors such as receptors for ▶epidermal growth factor, ▶fibroblast growth factor, and ▶platelet-derived growth factor, while PLCε could be a novel target for ▶RAS proteins. The second messengers generated from PtdIns(4,5)P2 interact with specific intracellular targets and, in turn, cause their activation. Ins(1,4,5)P3 binds to specific receptors in the endoplasmic reticulum causing a release of calcium from this intracellular store into the cytoplasm. Membrane resident diacylglycerol (DAG) is required for activation of several isoforms of ▶protein kinase C (PKC). These second messengers act as a common component in different signaling pathways, contributing to diverse cellular responses. Specificity of the pathways is provided at the level of a receptor and downstream components (e.g., calcium-regulated proteins and PKC substrates) present in a specific cell type or state.

Hydrolysis of PtdIns(4,5)P2 to Generate Second Messenger Molecules Hydrolysis of PtdIns(4,5)P2 occurs in response to a large number of extracellular signals and generates two ▶second messenger molecules, inositol (1,4,5)

Binding of PtdIns(4,5)P2 to Specific Proteins In addition to its role as a precursor of Ins(1,4,5)P3 and DAG, PtdIns(4,5)P2 has emerged as a highly versatile signaling molecule in its own right. These other functions are mediated through direct binding of PtdIns(4,5)P2

Inositol Lipids M ATILDA K ATAN CRC Centre for Cell and Molecular Biology, Institute of Cancer Research, London, UK

Definition

Are a class of ▶phospholipids where inositol is the polar headgroup. The simplest inositol phospholipid is ▶phosphatidylinositol (ptdlus). The inositol moiety can be phosphorylated at several different positions giving rise to a number of other molecular species.

Characteristics

Inositol Lipids. Figure 1 Structure of phosphatidylinositol (4,5) bisphosphate (PtdIns (4,5)P2) shows a typical phospholipid containing an inositol ring as a headgroup. The positions on the inositol ring are designated 1–6 and two phosphate groups are present at positions 4 and 5. Phosphatidylinositol (3,4,5) trisphosphate (PtdIns(3,4,5)P3) is generated in a phosphorylation reaction; the third phosphate group is added at position 3 of the inositol ring. Hydrolysis of PtdIns (4,5)P2 at the C-bond separates the hydrophobic part that contains two lipid chains, from watersoluble inositol that contains phosphates at the positions 1, 4, and 5.

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to specific protein targets, and include fundamental processes in membrane trafficking and plasma membranecytoskeleton linkages. Many proteins that regulate actin cytoskeleton (e.g., gelsolin and profilin) and proteins involved in ▶endocytosis (e.g., dynamin and AP-2 adaptor) bind PtdIns(4,5)P2. The binding involves different positively charged protein surfaces that in some proteins are present within the modular ▶pleckstrin homology domain (PH-domain). The result of the binding could be a direct change in the protein function or a regulated membrane targeting. For example, the PH domain of phospholipase Cδ1 associates with membranes of many cell types, but after PLC stimulation and the reduction in PtdIns (4,5)P2 concentrations, it translocates to the cytoplasm. Concentration of PtdIns(4,5)P2 is not only regulated at the level of hydrolysis by PLC but also through regulation of several types of inositol lipid kinases and phosphatases. Generation of PtdIns(3,4,5)P3 and Other 3-Phosphorylated Inositol Lipids and Their Binding to Specific Intracellular Targets Inositol lipids phosphorylated at the 3-position of the inositol ring (PtdIns(3)P, PtdIns(3,4)P2, PtdIns (3,5)P2, and PtdIns(3,4,5)P3) are generated by ▶phosphoinositide 3-kinase (▶PI3-K). PI3-Ks are grouped into three classes on the bases of their structure and according to the inositol lipid they preferentially utilize as a substrate. For example, the class I PI3-Ks are receptor-regulated ▶signal-transducer proteins that preferentially phosphorylate PtdIns(4,5)P2 in vivo and generate PtdIns(3,4,5)P3 (Fig. 1). Several target proteins for PtdIns(3,4,5)P3 and PtdIns(3,4)P2 have been described and they include protein kinases such as PKB/Akt, PDK1, and Btk. In the case of PKB/Akt, the direct binding to the PH domain (with high affinity and specificity toward 3-phosphorylated inositol lipids compared with more abundant PtdIns(4,5)P2) results in both membrane targeting and conformational changes that lead to phosphorylation and activation of this protein kinase. Activated kinases, in turn, phosphorylate and regulate downstream targets and thus propagate the signal. The 3-phosphorylated inositol lipids also participate in diverse cellular functions including cell survival, proliferation, migration, and vesicle budding. In addition to regulation of PI3-K, the levels of PtdIns (3,4,5)P3 are also controlled by a 3-phosphatase. Clinical Relevance There is considerable experimental evidence that the key enzymes involved in the control of inositol lipids, ▶PIPLC and ▶PI3-K, play an important role in processes critical for tumor development and spreading, including cell proliferation, survival, and ▶migration. However, oncogenic or constitutively active mutants of either

PI-PLC or PI3-K have not yet been isolated from human tumors. In the case of PI3-K, an oncogenic form (v-p3k) of the class I PI3-K has been isolated from a chicken ▶retrovirus that causes ▶hemangiosarcomas. Another oncogenic form of class I PI3-K (mutation in the regulatory subunit) has been isolated from transformed murine lymphoid cells. Nonetheless, the importance of the control of inositol lipid levels in human cancers have been emphasized by the findings that the tumor suppressor protein ▶PTEN is a 3-phosphatase that dephosphorylates PtdIns(3,4,5)P3. The PTEN gene is deleted or mutated in a wide variety of human cancers. Many human tumors have also been found to express increased levels of PI-PLC or PI3-K. The role of a signaling protein in generation and spreading of a malignant tumor is not limited to its function as an oncogene or a tumor suppressor gene. For example, it has been documented that the activation of PLCγ is a rate limiting step in breast and prostate tumors that overexpress growth factor receptors. This type of tumor is associated with a poor prognosis. PLCγ seems to be required for cell migration but not for proliferation, and the motility and invasiveness of cancer cells are strongly inhibited either after treatment with a chemical PLC inhibitor (U73 122) or in the presence of molecular inhibitors. ▶Polyphosphoinositides

References 1. Katan M (1998) Families of phosphoinositide-specific phospholipase C: structure and function. Biochim Biophys Acta 1436:5–17 2. Katan M, Allen VL (1999) Modular PH and C2 domains in membrane attachment and other functions. FEBS Lett 452:36–40 3. Czech MP (2000) PIP2 and PIP3: complex roles at the cell surface. Cell 100:603–606 4. Rameh LE, Cantly LC (1999) The role of phosphoinositide 3-kinase lipid products in cell function. J Biol Chem 274:8347–8350 5. Wells A (2000) Tumor invasion: role of growth factorinduced cell motility. Adv Cancer Res 78:31–101

Inositol Polyphosphates Definition IPs; Inositol derivatives with various numbers of inorganic phosphate groups attached at each of the carbon atoms. ▶Pentakisphosphate

Insulin Receptor

Inositol Tetrakisphosphate

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Insulator

Definition

Definition

Inositol Polyphosphate (IP) containing four phosphate groups within the inositol ring.

Is a DNA sequence that acts as a barrier to the influence of neighboring genes.

▶Pentakisphosphate

▶CCCTC-Binding Factor

Inositol 1,4,5-trisphosphate Definition Natural compound containing three phosphate groups at the 1, 4 and 5 positions within the inositol ring. Its production is a common step seen in cell signaling. ▶Pentakisphosphate

Insulin Definition Is a natural hormone produced in the pancreas by the beta cells of the ▶islets of Langerhans; controls the level of the sugar glucose in the blood. Insulin permits cells to use glucose for energy. Cells cannot utilize glucose without insulin. People who are Type 1 ▶Diabetes mellitus must use manufactured insulin, usually in an injectable form, to replace the natural insulin that is no longer produced by their body (for instance as the result of beta-cell degeneration). People with Type 2 sometimes need to use insulin when their cells become too resistant to the insulin that they produce naturally and when oral medications are no longer working.

Inositoltrisphosphate Definition

IP3; is generated by ▶phospholipase C from phosphatidylinositol and is instrumental in Ca2+ mobilization required in signal transduction. ▶Lipid Mediators

Insulin Receptor A NTONIO B RUNETTI Department of Experimental and Clinical Medicine “G. Salvatore”, University of Catanzaro “Magna Græcia”, Catanzaro, Italy

Definition

Insertional Mutagenesis Definition Is the alteration of a gene by integration of a foreign, often exogenous, DNA sequence. For instance, a virus DNA can integrate into a gene or in the vicinity of a gene. ▶Retroviral Insertional Mutagenesis

IR; Is a phylogenetically ancient ▶receptor tyrosine kinase protein embedded in the ▶plasma membrane of virtually all cells. When the peptide hormone ▶insulin binds to the IR, the receptor becomes activated and induces a cascade of intracellular events that will lead to several metabolic and growth promoting effects.

Characteristics The IR belongs to the tyrosine kinase growth factor receptor family and functions as an enzyme that transfers phosphate groups from ▶ATP to tyrosine

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residues on intracellular target proteins. The IR consists of two identical extracellular alpha subunits (130 kDa) that house insulin binding domains, and two transmembrane beta subunits (95 kDa) that contain ligandactivated tyrosine kinase activity in their intracellular domains (Fig. 1). When insulin binds to the alpha subunits, the receptor is first activated by tyrosine autophosphorylation, and then the IR tyrosine kinase phosphorylates various intracellular effector molecules (e.g. ▶IRS proteins and ▶Shc) which in turn alters their activity, thereby generating a biological response. The IR exists as two splice variant isoforms: the IR-B isoform that is responsible for signaling metabolic responses involved mainly in the regulation of glucose uptake and metabolism by increasing glucose transporter (▶Glut4) molecules on the plasma membrane of the insulin-responsive tissues muscle, liver, and fat, and the IR-A isoform that is capable of binding ▶IGF-2 with high affinity and signals predominantly mitogenic responses. As a consequence of these cellular activities, abnormalities of IR expression and/ or function can facilitate the development of several metabolic and neoplastic disorders in humans as well as in animal models. Regulation Gene expression in eukaryotic cells is controlled by nuclear regulatory proteins (trans-acting factors) that modulate the transcription of genes by binding to specific cis-acting transcriptional elements in the promoter of target genes. The IR gene promoter extends over 1,800 bases 5′ upstream from the IR gene ATG codon, contains a series of GGGCGG repeats that are putative binding sites for the mammalian transcription factor Sp1, and has neither a ▶TATA box nor a CAAT box, reflecting the common features for the promoters of constitutively expressed genes (so-called housekeeping genes). Like other housekeeping promoters, the IR gene promoter confers a basal level of transcriptional activity common to all cells, whereas significantly higher transcriptional activity is induced in the muscle, liver, and fat, at which levels the IR has been shown to be under the regulation of hormones, metabolites, and differentiation. Promoters of genes that are activated in a tissue specific manner are often regulated by a combination of tissue specific and ubiquitous transcription factors, where the ubiquitous element facilitates or enhances the action of one or more tissue-specific transcription factors. The molecular mechanisms regulating IR gene expression are being elucidated and evidence has been provided showing that the architectural transcription factor ▶HMGA1 is required for proper transcription of the IR gene in cells expressing IRs. HMGA1 acts on the IR gene promoter as an element necessary for the formation of a transcriptionally active multiprotein–DNA complex involving, in addition to

the HMGA1 protein, the ubiquitously expressed transcription factor Sp1 and the CCAAT-enhancer binding protein beta (C/EBP-beta). By potentiating the recruitment and binding of Sp1 and C/EBP-beta to the IR promoter, HMGA1 greatly enhances the transcriptional activities of these factors in the context of the IR gene. Conversely, repression of HMGA1 function in cells and tissues adversely affects transactivation of the IR gene promoter by Sp1 and C/EBP-beta, and considerably reduces IR protein expression. Clinical Relevance The IR is of major importance in certain states of ▶insulin resistance in humans, in which abnormalities of the receptor may lead to defective transmembrane signaling. In this respect, dysfunctional IR signaling is implicated in certain common dysmetabolic disorders, including ▶obesity, type 1 and type 2 ▶diabetes, the dysmetabolic syndrome X, and the polycystic ovary syndrome (PCOS). Also, clinical syndromes due to mutations in the IR gene have been identified in patients with genetic forms of severe insulin resistance (i.e. leprechaunism, type A insulin resistance, and the Rabson–Mendenhall syndrome). Many of these patients have point mutations in the coding sequence of the IR gene, leading to reduced or absent IR expression in target tissues. Recently, defects in IR gene regulation have been reported in individuals with insulin resistance and type 2 diabetes, in which the generation of IR mRNA was considerably impaired, although the IR genes were normal. In these individuals, cellsurface IRs were decreased and the expression of HMGA1 was markedly reduced. Even though it is an open question whether IR plays a critical role in aging and longevity in mammals, disturbance of the neuronal IR seems to be of pathogenetic relevance in human Alzheimer’s disease and depressive disorders, suggesting a neurotrophic role of IR in the brain. According to recent studies, IR in the brain begins to disappear early in Alzheimer’s and continue to decline as the disease progresses. It has been shown that stimulation in the brain of a receptor that mediates insulin responses can halt or diminish the neurodegeneration of Alzheimer’s disease. Also, a high prevalence of insulin resistance has been reported in patients with depression, and an increased risk of cognitive decline has been found in women with insulin-resistant PCOS. A relation between IR and cancer has been established following the observation that overexpression of functional IRs can occur in human ▶breast cancer and other epithelial tumors including ovarian and colon cancer, in which the IR may exert its oncogenic potential via abnormal stimulation of multiple cellular signaling cascades, enhancing growth factor-dependent proliferation and/or by directly affecting cell metabolism.

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Insulin Receptor. Figure 1 In the absence of insulin, most of the IRs in the plasma membrane are in a non-tyrosine phosphorylated inactive state, and only a very small proportion of receptors are lightly phosphorylated and subjected to constitutive ▶endocytosis and recycling. Upon binding of insulin, the IR undergoes autophosphorylation which enables the receptor to have a kinase activity and phosphorylates various cytoplasmic substrates, such as IRSs. From this point, signaling proceeds via a variety of signaling pathways (i.e. PI3K signaling pathway, Ras and MAP kinase cascade) that are responsible for the metabolic, growth-promoting and mitogenic effects of insulin.

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An explanation for increased IR expression in epithelial tumors has been recently provided for several human breast cancers, in which overexpression of the transcription factor ▶AP2-alpha accounts for increased IR expression in neoplastic breast tissue. In these cases, it has been demonstrated that transactivation of the IR gene by AP-2 alpha needs direct physical association of AP2 with HMGA1 and Sp1, which represents a fundamental prerequisite for AP-2 alpha to activate IR gene transcription in neoplastic breast tissue. Epidemiological and clinical evidence points to a link between insulin resistant syndromes such as obesity and type 2 diabetes and cancer of the colon, liver, pancreas, breast and endometrium. The mechanistic link between insulin resistance and cancer is unknown, but constitutive activation of the tyrosine kinase activity of IR and related downstream signaling pathways by chronic sustained hyperinsulinemia (a hallmark of insulin resistance) in these clinical syndromes appears to have a role in the neoplastic transformation process. Thus, the IR plays a major role in the pathophysiology of a wide range of metabolic, neurodegenerative and proliferative disorders in humans. Selective modulation of IR expression and/or function may represent a useful therapeutic strategy for these diseases. Also, measures to decrease insulin resistance in insulin resistant patients may offer a general approach to prevention of cancer in these predisposed individuals.

References 1. Goldfine ID (1987) The insulin receptor: molecular biology and transmembrane signalling. Endocr Rev 8:235–255 2. White MF, Khan CR (1994) The insulin signaling system. J Biol Chem 261:1–4 3. Yarden Y, Ullrich A (1998) Growth factor receptor tyrosine kinases. Annu Rev Biochem 57:443–478 4. Foti D, Chiefari E, Fedele M et al. (2005) Lack of the architectural factor HMGA1 causes insulin resistance and diabetes in humans and mice. Nat Med 11:765–773 5. Paonessa F, Foti D, Costa Vet al. (2006) Activator protein2 overexpression accounts for increased insulin receptor expression in human breast cancer. Cancer Res 66:5085–5093

Src-homology 2 (SH2) domain containing proteins to bind and transmit signals downstream. ▶Receptor Cross-Talk ▶Insulin Receptor ▶SH2/SH3 Domains

Insulin Resistance Definition Occurs when the body does not respond properly to ▶insulin, a hormone made by the pancreas. It is characterized by the diminished ability of cells to respond to the action of insulin in transporting glucose from the bloodstream into muscle and other tissues. ▶Adiponectin ▶Diabetes

Insulin-like Growth Factor Binding Proteins Definition IGFBPs are a family of secreted proteins that bind the ▶insulin-like growth factors, IGF-I and IGF-II, with affinities comparable to their respective receptors. To date, six insulin-like growth-factor-binding proteins (IGFBP-1 to IGFBP-6) have been identified. ▶Kallikreins ▶Diabetes

Insulin-like Growth Factors Insulin Receptor Substrate Proteins

RUSLAN N OVOSYADLYY, D EREK L E R OITH Division of Endocrinology, Diabetes and Bone Diseases, Departmant of Medicine, Mount Sinai School of Medicine, New York, NY, USA

Definition

IRS proteins; Large intracellular ▶docking proteins through which the ▶insulin receptor and IGF-1Recepror propagate their signals. Receptor tyrosine phosphorylation of IRS proteins yields sites for

Definition The insulin-like growth factors (IGF-I and IGF-II) are structurally related molecules that play essential roles in the regulation of cell survival, growth, proliferation,

Insulin-like Growth Factors

differentiation and metabolism. The IGF family is comprised of (i) ligands (IGF-I, IGF-II and insulin), (ii) six well characterized high affinity binding proteins (IGFBP-1 through -6), (iii) IGFBP proteases and (iv) cell surface receptors that mediate the biological functions of IGFs. These transmembrane receptors include the IGF-I receptor (IGF-IR), IGF-II/mannose 6-phosphate receptor (IGF-II/M6PR), ▶insulin receptor (IR) and insulin receptor-related receptor (IRR). In many tumor cells the IGF-IR is often upregulated and/or hyperactivated. Furthermore, increased circulating IGF-I levels are considered a significant risk factor for the development of various types of cancers. Although the oncogenic role of IGFs (i.e. their ability to initiate ▶carcinogenesis) is still under the debate, numerous lines of evidence suggest that these powerful growth factors enhance tumor growth and ▶progression.

Characteristics IGFs The insulin-like growth factors (IGF-I and IGF-II) are ubiquitously expressed growth factors that are structurally related to insulin. However, in contrast to insulin and other peptide hormones, they are not stored within cells of a specific tissue but are produced by numerous cell types in the body and circulate in approximately 1,000-fold higher concentrations than most other known peptide hormones. These properties suggest more universal functions of the IGFs in the body compared to the more specific metabolic role of insulin. The IGFs are critical in a broad range of functions during pre- and postnatal life. In adult tissues, IGFs are important trophic factors that support normal differentiated functions of various tissues and prevent programmed cell death (▶apoptosis). IGF-I is known as a major regulator of postnatal growth. Most of the circulating IGF-I is produced by the liver, although other tissues are capable of synthesizing this peptide locally. Thus, IGF-I has characteristics of both a circulating hormone and a tissue growth factor. In contrast to IGF-I, IGF-II plays a fundamental role in embryonic and fetal growth, whereas due to ▶imprinting of the Igf 2 gene, its role in postnatal period of life is less important, especially in rodents.

IGF Receptors Most of the actions of both IGF-I and IGF-II are mediated via the IGF-IR, which is expressed by virtually all cell types except adult hepatocytes. The IGF-IR and IR belong to the large family of ▶receptor tyrosine kinases. The two receptors are structurally related and are composed of two α-subunits localized entirely extracellularly and two β-subunits spanning the membrane

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and localized primarily intracellularly. Both subunits are linked together by disulfide bonds. They assemble a α2β2-configuration with ligand binding primarily mediated by the α-subunits, which form a binding pocket. Binding of the ligand to the α-subunit leads to conformational changes resulting in stimulation of the β-subunit intrinsic tyrosine kinase activity with subsequent multisite phosphorylation of the β-subunit. The current concept is that insulin and the IGFs act as bivalent ligands, both IGF-IR and IR are capable of binding insulin and IGF-I or -II, though each receptor binds its own ligand with a 100–1,000-fold higher affinity than the heterologous peptide. In cells expressing both receptor genes, hybrid insulin/IGF-I receptors can form. The hybrid receptors have ligand specificity profiles more comparable to the IGF-IR than to the IR since they bind IGF-I with an affinity similar to the IGF-IR, but insulin with a much lower affinity. Moreover, the IR is also responsible for some of the mitogenic actions of IGF-II. IGF-II is an agonist of the A isoform of the IR. This splice variant of the IR is expressed at high levels in fetal and neoplastic tissues. IRR and hybrid IR/IRR have not yet been extensively studied, and their ability to bind all the different insulin-like peptides as well as their biological significance remains unclear. The IGF-II/M6PR is structurally distinct from the IGF-IR and is actually identical to the cationindependent mannose 6-phosphate receptor, which lacks tyrosine kinase activity and is not considered to have any role in IGF ▶signal transduction. The IGF-II/ M6PR functions as a scavenger receptor and is involved in uptake and degradation of IGF-II. The IGF-II/M6PR is strongly expressed during tissue differentiation and organogenesis, and high levels of the IGF-II/ M6PR were found in fetal tissue, which decline in late gestation and in the early postnatal period due to genomic imprinting. IGFBPs Unlike insulin, the IGFs are present in the circulation and throughout the extracellular compartments almost entirely bound to a family of multifunctional, structurally related, high affinity IGF-binding proteins (IGFBPs), which can modulate biological effects of the IGFs. To date, six IGFBPs with high affinity have been cloned and sequenced. All share structural homology with each other and specifically bind the IGFs. They differ in molecular mass, binding affinities for the IGFs, posttranslational modifications such as phosphorylation and glycosylation as well as susceptibility to proteolysis. The IGFBPs act as carrier proteins in plasma, control the efflux of the IGFs from the vascular space, and prolong half-lives of the IGFs. They regulate metabolic clearance and tissue- and cellspecific localization of the IGFs thereby modulating

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their biological actions in a negative or a positive manner. Finally, some IGFBPs also have intrinsic bioactivities that are independent of the IGFs (Fig. 1). Mechanisms The biological effects of IGFs are mainly mediated by the IGF-IR and two principal signaling pathways including ▶mitogen-activated protein kinase (MAPK) pathway that plays a pivotal role in cell growth and proliferation, and ▶phosphatidylinositol-triphosphate kinase (PI3K) pathway, which is mainly involved in mediating the metabolic, antiapoptotic and other more differentiated effects of IGF-I. Upon ligand binding and receptor autophosphorylation, the IGF-IR recruits and phosphorylates several adaptor proteins including ▶Shc and members of the insulin receptor substrate (IRS) family of proteins. They bring together and coordinate the activity of other signaling intermediates, finally resulting in activation of the ▶MAPK and PI3K pathways. Typically, the MAPK pathway is initiated by the recruitment of growth factor receptor bound 2 protein (Grb2) that via the guanine nucleotide exchange factor Son of Sevenless (SOS) stimulate the activity of the GTPases ▶Ras and Rac, which, in turn, through the sequential phosphorylation of certain kinases finally lead to activation of terminal MAP kinases ERK1/2, ▶JNK and p38 kinase. Although JNK and p38 kinase are primarily activated by environmental stressors, several lines of evidence suggest that they can also be activated in response to IGFs. The activated MAP kinases phosphorylate several important cytoplasmic substrates and also translocate to the nucleus where they phosphorylate transcription factors leading to immediate-early gene induction followed by progression of the cell cycle. Alternatively, signal transduction through the PI3K pathway results in the activation of protein kinase B also known as ▶Akt, which is known to block apoptosis by phosphorylating numerous cellular substrates such as Bad, GSK3, Foxo, Mdm2, CREB, IKK, caspase-9, p21 and p27. The PI3K pathway also activates p70S6 kinase involved in regulation of ribosome biogenesis as well as some isoforms of ▶protein kinase C, which are capable of potentiating signal transduction through the MAPK pathway. Thus, IGFs induce cell proliferation both by enhancing cell cycle progression and by inhibiting apoptosis. Furthermore, evidence for both direct and indirect interaction between the IGFIR and other growth regulatory signals has been demonstrated, thereby expanding the traditional view of highly specific IGF-IR/IGF interactions and rendering the IGF-IR central in cellular response. For instance, in many cell types IGF-IR and ▶epidermal growth factor receptor family members physically interact and transphosphorylate each other. ▶Estrogen receptor activation augments the IGF-I response in estrogen

receptor-positive MCF-7 mammary carcinoma cells at multiple levels. Moreover, estrogens enhance the tyrosine phosphorylation of the IGF-IR and IRS-1 and eventually increase expression of cyclins and reduce the level of cdk inhibitors (Fig. 2). Altered Expression of the IGF System Components in Tumor Cells The expression of the components of the IGF system is often altered in malignant cells. In certain tumors, the ▶imprinting of the Igf 2 gene is lost, and this results in increased IGF-II gene expression. In general, IGF-II is more commonly expressed by tumors than IGF-I, although increased IGF-I expression has been found in numerous tumors as well. The IGF-IR is often upregulated or hyperactivated in tumor cells. Expression of the IGF-IR is regulated by tumor suppressors and growth factors in a negative and positive manner, respectively. Tumor suppressors such as ▶Wilms Tumor-1 (WT1) and ▶p53 bind to the Igf1r gene promoter and inhibit receptor gene expression. Mutations of these genes occur in various tumors and paradoxically enhance the activity of the Igf1r gene promoter. This explains the upregulation of the IGF-IR gene expression in Wilms tumor (a pediatric kidney tumor) and ▶colon cancer, which is often accompanied by p53 mutations. Both WT1 and p53 also inhibit IGF-II gene expression. By analogy with the IGF-I receptor, IGF-II gene expression is increased when WT1 and p53 genes are mutated. Thus, the autocrine IGF-IR/IGF-II loop is turned on under these circumstances. Basic ▶fibroblast growth factor and ▶platelet-derived growth factor are capable of enhancing the IGF-IR gene expression. Since tumors often express these and other growth factors, this could also upregulate the IGF-IR gene expression. Certain ▶oncogenes can also regulate the IGF-IR at posttranslational level. For instance, ▶Src augments the phosphorylation state of the IGF-IR, thereby increasing its kinase activity. Neoplastic growth can be also enhanced by injections of recombinant human IGF-I into mice. In this case, the latency period is shortened and tumor growth is accelerated. This response is particularly enhanced in tumors with higher levels of IGF-IR expression. In contrast to the IGF-IR, the IGF-II/M6PR expression is often decreased or lost in tumor cells. The IGF-II/M6PR possesses properties of a ▶tumor suppressor gene. Tumor cell growth is inhibited when the IGF-II/M6PR expression is restored and is increased when its expression is reduced. In addition to the IGFs and their receptors, the IGFBP expression is also altered in tumor cells. Various IGFBPs are expressed by numerous tumors and often in different combinations. For example, estrogen receptor-positive breast cancer cells release IGFBP-2, whereas estrogen receptor-negative breast tumors

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Insulin-like Growth Factors. Figure 1 The IGF family is comprised of (i) ligands (IGF-I, IGF-II and insulin), (ii) IGF-binding proteins (IGFBPs), (iii) IGFBP proteases and (iv) cell surface receptors. IGFBPs act as carrier proteins in plasma, control the efflux of the IGFs from the vascular space, prolong half-lives of the IGFs, regulate their metabolic clearance, provide tissue- and cell-specific localization of the IGFs, modulate biological actions of the IGFs, and some also have intrinsic bioactivities that are IGF-independent. The IGFs can be released from the IGF/IGFBP complexes by the action of IGFBP proteases. The insulin receptor (IR), insulin-like growth factor I receptor (IGF-IR) and insulin receptor-related receptor (IRR) are heterotetrameric complexes composed of extracellular α-subunits that bind the ligands, and β-subunits that anchor the receptor in the membrane and contain tyrosine kinase activity in their cytoplasmic domains. Hybrids consist of a hemireceptor from both IR and IGF-IR. The IGF-II/M6PR is not structurally related to the IGF-IR and IR or the IRR, having a short cytoplasmic tail and no tyrosine kinase activity. IR is responsible for metabolic effects, whereas IGF-IR and hybrid IR/IGF-IR for cell survival, growth, proliferation and differentiation. The insulin-like growth factor II/mannose 6-phosphate receptor (IGF-II/M6PR) functions as scavenger receptor and is responsible for uptake and degradation of the IGFs. This receptor is not considered to have any role in IGF signaling.

release IGFBP-1 and -3. The IGFBP production can be altered by growth factors, steroid hormones, cytokines, and these changes in IGFBP levels may alter biological effects of the IGFs on tumor growth and progression. Interestingly, wild type p53 induces the expression of IGFBP-3 that seems to be critical for the inhibitory function of p53 on cell growth. Furthermore, enhanced IGFBP proteolysis is thought to contribute to carcinogenesis. Numerous IGFBP proteases produced by tumor cells mediate release of the IGFs from the IGFBP/IGF complexes that eventually leads to

increased IGF-IR stimulation. For instance, prostate cancer cells secrete ▶prostate-specific antigen (PSA), which exerts IGFBP-3 proteolytic activity thereby enhancing the local bioavailability of free IGFs. Syndrome of Hypoglycemia An emerging clinical syndrome is tumor-induced hypoglycemia. This phenomenon is often seen in terminally-ill, poorly nourished patients. In addition, it can be also observed in patients with large mesenchymal tumors in the abdomen or thorax that

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Insulin-like Growth Factors

Insulin-like Growth Factors. Figure 2 Signal transduction cascades initiated by the IGF-IR. Activation of the IGF-IR kinase results in receptor autophosphorylation and tyrosine phosphorylation of several docking proteins such as Shc and insulin receptor substrate (IRS) proteins. Once activated, IRS molecules recruit Src homology 2 (SH2)-domain containing molecules such as Grb2 and the p85 subunit of phosphatidylinositol-3′-kinase (PI3-K). Grb2 via SOS stimulates the activity of the GTPases Ras and Rac, which through the phosphorylation of numerous kinases finally lead to activation of terminal MAP kinases ERK, JNK and p38 kinase. Activated MAP kinases are translocated to the nucleus where they activate a variety of transcription factors. Alternatively, the binding of the p85 and p110 subunit of PI3-K to IRS proteins generates phospholipids that participate in the activation of 3-phosphoinositide-dependent kinase (PDK) 1 and 2. In turn, they phosphorylate several targets involved in the regulation of different biological processes including glucose transport, protein synthesis, glycogen synthesis, cell proliferation and cell survival.

secrete large quantities of IGF-II. In these patients, IGF-II is not fully processed, and therefore it is poorly bound to the circulating IGFBPs. This allows IGF-II to interact more readily with insulin receptors thereby causing hypoglycemia. Clinically, tumor-induced hypoglycemia can be diagnosed in cancer patients that have normal or elevated circulating IGF-II levels, whereas their insulin, growth hormone (GH), IGF-I and IGFBP-3 levels are suppressed. These patients usually have a poor prognosis. Surgical excision and ▶chemotherapy or ▶radiation therapy-induced reduction of tumor size is ▶palliative, and GH and corticosteroid therapy provides symptomatic relief. Clinical Aspects An increasing body of evidence suggests that the IGF system is a promising target for adjuvant anticancer therapy. If chemotherapy inadequately ablates tumor

cells, then blockade of the proliferative and antiapoptotic effects of the IGFs may be helpful. The IGF system could potentially be targeted at various levels. Reduction of circulating IGF-I levels can be achieved by GHRH antagonists or somatostatins as well as GH receptor antagonists. Application of inactive IGF molecules, small-molecule competitive binding antagonists or soluble IGF-I receptors may inhibit binding of endogenous IGFs to the receptor thereby abrogating their tumor-promoting effects. The IGF-IR represents another attractive therapeutic target. Approaches that are currently being tested in preclinical and clinical studies include the use of blocking ▶monoclonal antibodies directed against the extracellular portion of the IGF-IR and ▶small molecule drugs that inhibit the tyrosine kinase activity of the IGF-IR. Application of ▶RNA interference and ▶antisense therapy to reduce the IGF-IR expression, as well as overexpression of altered or

Insulinoma

truncated IGF-IR that acts in a ▶dominant-negative manner, represent additional approaches that have been effective in laboratory studies.

References 1. Khandwala HM, McCutcheon IE, Flyvbjerg A, et al. (2000) The effects of insulin-like growth factors on tumorigenesis and neoplastic growth. Endocrine Rev 21:215–244 2. LeRoith D, Werner H, Beitner-Johnson D, et al. (1995) Molecular and cellular aspects of the insulin-like growth factor I receptor. Endocrine Rev 16:143–163 3. Pollak MN, Schernhammer ES, Hankinson SE (2004) Insulin-like growth factors and neoplasia. Nat Rev Cancer 4:505–518 4. Rubin R, Baserga R (1995) Insulin-like growth factor-I receptor. Its role in cell proliferation, apoptosis, and tumorigenicity. Lab Invest 73:311–331 5. Samani AA, Yakar S, LeRoith D, et al. (2007) The role of the IGF system in cancer growth and metastasis; overview and recent insights. Endocrine Rev 28:20–47

Insulinoma B OAZ H IRSHBERG Cardiovascular and Metabolic Diseases, Pfizer Inc, Groton, CT, USA

Synonyms

β-Cell tumor of the islets

Definition

Insulinomas are functioning ▶insulin producing tumors of the pancreatic ▶islets of Langerhans, resulting in hypoglycemia.

Characteristics

Insulinomas arise from the β-Cell of the pancreatic islets. The nonregulated secretion of insulin from these tumor cells into the blood stream results in fasting hypoglycemia. Insulinomas are relatively rare, with approximately four cases per million person-years. However, they are the most common tumor of the pancreatic islets. Insulinomas may appear at any age, but the majority appears in the fifth decade. Insulinomas are evenly distributed along the pancreas. Insulinomas, associated with ▶multiple endocrine neoplasia type 1 (MEN1), tend to appear one decade earlier. Insulinomas are usually solitary and their localization is even along the pancreas, exceptions are those associated with MEN1, where multiple tumors are the rule.

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Diagnosis The presence of ▶Whipple Triad (hypoglycemia and neuroglycopenic symptoms that are corrected by the administration of carbohydrate) is the hallmark of the diagnosis of insulinoma. Fasting, therefore, is the major maneuver used in the diagnosis of insulinoma and has two important purposes. The first goal is to document hypoglycemia and its relationship to the patient’s symptoms, and the second is to demonstrate inappropriate insulin concentrations in the face of hypoglycemia. The prolonged (48–72 h) fast is the gold standard for the diagnosis of hypoglycemia. This study should be conducted under supervised conditions (i.e., while hospitalized). Diagnosis of insulinoma has been centered on the 72-h fast that was introduced long before to measure insulin or insulin-related components. Now the insulin and proinsulin measurements are widely available, all of the necessary information from a fast can be derived in the first 48 h. Thus, the 48-h fast has become the new standard. The diagnosis is based on detectable insulin levels (≥6 μU/ml), detectable C-peptide, and elevated proinsulin levels, when the patient has symptoms of hypoglycemia and glucose levels tÞ

Kaplan–Meier Product Limit Estimator ▶Kaplan-Meier Survival Analysis

¼ Pðsurviving past time tÞ and is called the survival function. Note that although t measures the time-until-failure, it also represents the disease-free survival time. Fig. 1 illustrates a typical Kaplan–Meier survival function estimate.

Kaplan-Meier Survival Analysis

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Kaplan-Meier Survival Analysis. Figure 1 Kaplan–Meier survival curve.

Censoring If all individuals in the study fail, we can precisely describe the survival distribution, SðtÞ ¼ 1  FðtÞ Suppose we have decided to follow patients in a clinical trial for 5 years and that our outcome is recurrence at a specific tumor site. For those who are diagnosed with recurring tumor during the study period, exact failure times are recorded. Those who complete the 5-year follow-up but do not have a recurrence are said to be right censored. By focusing on survival instead of failure, we are able to conclude that the survival time was at least 5 years for the censored individuals without knowing the exact time of failure beyond that 5-year study period. In other words, we may not know the exact time of failure for individuals that survived longer than 5 years, but we do know they lived without recurrence for at least 5 years. In addition to ▶censoring by the limits of the study design, individuals may also be censored due to factors beyond the investigators control, such as death from other causes. Although the analysis itself does not distinguish between these types of censoring, one caveat in generalizing results is that intermittent censoring must be non-informative so that the reason for censoring should not be related to the either the time of failure or the treatment choice. In other words, this type of censoring should be random. Parametric, Semi-Parametric and Nonparametric Survival Three major divisions are made in the types of survival analyses; ▶parametric, semi-parametric and

▶nonparametric. If survival times are assumed to follow a specific mathematical distribution, the parameters of that distribution can be estimated from the sample. Perhaps the simplest parametric assumption in survival analysis is one of a constant hazard rate, λ, leading to the failure distribution, FðtÞ ¼ 1  elt , and the complementary survival distribution, SðtÞ ¼ elt that we recognize as exponential decay. Metabolism studies, for example, may exhibit exponential decay. ^l ¼ r=T The parameter, λ, is estimated from the data asP where r is the total number of events and T ¼ t is the total of all survival times. Other useful parametric survival distributions are the Weibull, lognormal and gamma distributions. Another common approach introduced; by D. R. Cox in 1972 and called ▶Cox proportional hazards modeling has become one of the most common methods of survival analysis and is based on semi-parametric estimation where the background hazard rate is not estimated. Cox P assumed the survival distribution, expð bxÞ where S ðtÞ is a baseline hazard SðtÞ ¼ ½S ðtÞ 0

0

rate that is typically treated as a nuisance, x is some covariate of interest and β is the slope parameter associated with that covariate. In this type of analysis, we are usually interested in comparing covariate parameters so that S(t) itself is not estimated fully. Finally, nonparametric methods including actuarial and life table methods are useful for summarizing survival distributions. Perhaps one of the nonparametric approaches to survival analysis that is most often used in the medical literature is that introduced by E. L Kaplan and P. Meier in 1958. Useful in visualizing

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Kaplan-Meier Survival Analysis

survival data, the Kaplan–Meier curve is plotted as a starting point in most survival analyses. Unlike the parametric and semi-parametric approaches to quantifying a survival distribution, the nonparametric Kaplan– Meier method requires few assumptions other than independence of failure time observations. Kaplan–Meier Product Limit Estimator Many of the survival analysis methods, such as Cox proportional hazards models and parametric models, require iterative solutions and specialized software. The Kaplan–Meier Product Limit Estimator, on the other hand, is easily calculated. The r event times are ordered from smallest to largest so that t1 < t2 < t3 <    < tr . For example, assume the relapse times (in months) for ten cancer patients are recorded as (2, 3, 5, 7, 9, 11, 12, 12, 12, 12). If there is no censoring, the Kaplan–Meier estimator at any event time, j, is simply the proportion with event times greater than tj. For example, at t = 7 months four have relapsed and six have not so that the probability of surviving more than seven months is ^ Sð7Þ ¼ 6=10 . In the case of single right censoring at the end of the study, the calculations are similar. If the relapse times are (2, 3, 5, 7, 9, 11, 12+, 12+, 12+, 12+) ^ where “+” indicates censoring, Sð7Þ ¼ 6=10 is the proportion surviving longer than 7 months as before. In addition to the plot of these data in Fig. 1, we might choose to report summary statistics in the form of quantiles, medians or means. For these data, the median ^ is 9 months since Sð9Þ ¼ 0:5 . The mean is related to the area under the survival curve and, for data sets in which the largest observation is censored, the mean is based on the truncated failure times so that the estimate of the mean is too low. In this case, the mean is 8.5 months. The probability of surviving can be found using simple counting rules and the multiplication rule for joint conditional probabilities. At each distinct event time, there are nj individuals at risk of whom dj relapse and nj  dj do not relapse. Assume the event times are recorded as follows: (2, 3, 5, 7, 9, 11, 12+, 12+, 12+, 12+). At 7 months, we find nj ¼ 7 individuals still at risk of relapse of whom dj ¼ 1 relapses and nj  dj ¼ 6 do not. Applying the multiplication rule to the conditional probabilities for each distinct event time, the probability of surviving past 7 months is      9 8 7 6 6 ^ Sð7Þ ¼ ¼ 10 9 8 7 10 as we found previously. If any censored times are less than any event times, we must alter the formula slightly. In essence, the Kaplan–Meier product limit estimator is still an application of counting rules and conditional probabilities but the numbers at risk at some event times are altered due to censoring. Suppose we find that one

observation is censored prior to seven months and the event times are recorded as (2, 3, 5+, 7, 9, 11, 12+, 12+, 12+, 12+). In terms of an event, all we know of the individual who was censored at five months is that they at least survived longer than the previous event time of 3 months. The product of the conditional probabilities using only event times is     9 8 6 ^ ¼ 0:6857 Sð7Þ ¼ 10 9 7 and is slightly different from the estimate when no censoring prior to seven months was observed. The censored observation provides additional information for the first two periods by increasing the overall sample size. The median survival time for these data is 11 months, illustrating the effect of censoring on the estimates. The mean is 9.1 months but, again, may be too low due to the censoring of all observations at 12 months. In general, the Kaplan–Meier estimator is defined as Y nj  dj  ^ ¼ SðtÞ nj tj 40 years of age with an even sex distribution. Interestingly, >60% of GISTs are associated with exon 11 mutations in Kit/ SCF-R, but none with mutations in exon 17, including of D816. Kit exon 11 GOF mutations occur mainly in malignant GISTs, which tend to be larger, with necrosis, hemorrhage, intra-abdominal spread and liver metastases and frequent recurrences. Hence, the exon 11 mutations portend poor prognosis with a 3 year survival 65% for exon 11 mutation negative tumors, and it has been reported that Kit exon 11 mutations are an independent prognostic factor for GIST survival. The Kit/SCF-R (CD117) expression is diagnostic for GI stromal tumors versus ▶leiomyomasa and gastric Schwannomas. Most cases examined are also CD34-positive, and ultrastructurally cells look like ▶interstitial cells of Cajal (ICC), which is why it has been proposed that the ICC is the cell of origin for most GISTs. However, tumors phenotypically identical to GISTs (CD117+, most CD34+) occur as primary tumors in the omentum and mesentery as well, which indicates that GISTs might not all originate

Kit/Stem Cell Factor Receptor in Oncogenesis

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Kit/Stem Cell Factor Receptor in Oncogenesis. Figure 2 Schematic representation of mutations in Kit/SCF-R, associated with human malignancies and dysplasias. Amino acid residues are denoted with single letters, numbers indicate the residue number in the human Kit protein sequence. Point-mutated amino acid residues are shown in outline, amino acid deletions with a dash and amino acid additions are underlined. The D52N mutation has been associated with myelodysplastic syndromes that include myelofibrosis and chronic myeloid leukemia. The AY duplication, the juxtamembrane mutations and the K642E mutations have mainly been associated with gastro-intestinal stromal tumors, but also with mast cell leukemias. The D816V and E839K mutations have been connected with mast cell leukemias. The D816H mutation has been connected with seminomas and dysgerminomas. Mutations, found in the hydrophilic region between the N- and C-terminal region of the kinase domain result -due to alternative promoter usage- in truncated versions of Kit. These isoforms have been identified in various cell lines which derived from colon carcinomas and hematopoietic malignancies.

from ICCs, but rather from a multi-potential precursor cell. A characteristic of GISTs is mitochondrionrich ICCs, and some GISTs are gastro-intestinal autonomic nerve tumor (GANT)-like stromal tumors. An immunohistochemical and histological re-evaluation

of archived paraffin-embedded esophageal tumor samples disclosed that 25% of these were indeed Kit-positive GISTs with exon 11 mutations rather than leiomyomas or leiomyosarcomas, which was the original classification. This is important, since

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Kit/Stem Cell Factor Receptor in Oncogenesis

esophageal GISTs are malignant, while leiomyomas, which are Kit-negative, are benign. Analysis of eight GISTs devoid of exon 11 mutations in Kit/SCF-R revealed exon 9 mutations in 6 and an exon 13 mutation (K642E) in 2, the latter causing constitutive tyrosine autophosphorylation of Kit/SCF-R. Finally, in colon carcinoma cell lines certain intron 15 alternative promoter splice variants, causing either a 78 bp deletion or a truncated Kit/SCFR with 25 unique amino acids fused to the C-terminal 257 amino acids, have been reported sporadically. The functional consequences are unknown. However, a potential autocrine loop of Kit/ SCF-R and SCF might exist in colon cancer, since colonic mucosal cells usually express SCF, but areKit/ SCF-R-negative. In conclusion, a majority of GISTs harbor GOF mutations in exon 11 of Kit/SCFR and there is overwhelming evidence that these are involved in the oncogenesis. Kit expression and exon 11 mutations are both of significant diagnostic and prognostic value for GISTs, the prognosis being significantly more severe if both are present.

Acute and Chronic Myeloid Leukemias A vast number of publications have attempted to address the putative role of Kit/SCF-R in myeloid leukemias. While it is still unclear whether Kit/SCF-R is causally involved in these diseases, it does have an important diagnostic and prognostic value. While only 1–3% of normal mononuclear marrow blasts express Kit/SCF-R, a big European multi-center study concluded that 67% of all ▶acute myeloid leukemia (AML) cases, 30% of all biphenotypic acute leukemias and all undifferentiated acute leukemias express Kit/SCF-R. Kit/SCF-R is expressed mainly in M4 and M5 AML subclasses, but the highest expression levels are found on blasts in M1 and M2 subclass AML cases. A high proportion of megakaryocytic and erythroid leukemic cells are also positive for Kit expression, as is most blasts in chronic myeloid leukemia (CML). In general, Kit/SCF-R expression is useful in the differential diagnosis between AML (mostly positive) and acute lymphocytic leukemia (ALL; all negative). Negative expression for Kit/SCFR in AML also identifies with some certainty two M5b subgroups. AML blasts express between 600 and 29,000 Kit molecules/cell, but there is no correlation between expression level and prognosis. Despite conflicting reports, it seems to be the consensus from the literature that there is no correlation between Kit expression and prognosis for AML in general, but that expression of Kit/SCF-R in the M1 subclass indicates a worse prognosis. This might be due to a strong correlation between expression of a non-P-glycoprotein multidrug resistance protein and Kit/SCF-R. Mutations in exon 8 of c-kit have been identified in

a high proportion of AML cases, and all had the inv. 16 re-arrangement. Conversely, 20% of inv. 16 AMLs had c-kit exon 8 mutations. All exon 8 mutations involved either deletion or replacement of the codon for D419. The functional consequences of these mutations for the kinase activity of Kit/SCF-R are unknown at present. However, retroviral transduction of murine hematopoietic precursors with D816V-Kit and transplantation of these cells into syngeneic hosts resulted in myeloid leukemias in a significant proportion of cases, showing that GOF mutations in Kit is sufficient for leukemic progression in mice. It has been suggested that constitutive association of ▶BCR-ABL1 with activated Kit/SCF-R is responsible for the basophilia and myeloid growth in the chronic phase of ▶CML. However, the ability of SCF to stimulate blast growth has also been utilized to mobilize peripheral CD34+/CD38– and other committed progenitors in patients about to undergo bone marrow transplantation for subsequent autologous transplantation. Addition of SCF together with GCSF and with standard chemotherapy is superior to GCSF and chemotherapy for this purpose.

Germ Cell Tumors All carcinoma-in-situ (▶CIS) testis, 90% of seminomas and dysgerminomas, but only 5% of nonseminomas express Kit/SCF-R. Isochrome 12p is a marker of ▶germ cell tumors, and ▶loss of heterozygosity on the long arm of chromosome 12 implicates SCF as a tumor suppressor. Furthermore, intersex gonads (45X/46XY and other cases with additional Y chromosome material) have delayed Kit expression and increased testicular cancer risk. This could indicate an anti-oncogenic role of Kit/SCF-R and its ligand for germ cell tumor development under some circumstances. However, other results might indicate that SCF and Kit/SCF-R can drive tumor progression. Hence, ectopic expression of Kit and SCF has been found in cervical and ovarian carcinomas and ovarian teratomas. Furthermore, there is an association between mediastinal germ cell tumors (MGCT) and hematological malignancies (e.g. acute leukemia and malignant histiocytosis), and often Kit-positive areas are found in these mediastinal tumors. This and other results have made it clear that Kit/SCF-R expression is a diagnostic aid for extragonadal seminomas. All classical seminomas are Kit-positive, aneuploid and positive for placental alkaline phosphatase, while 40% of spermatocytic seminomas are Kit-positive, and all are diploid or polyploid and negative for placental alkaline phosphatase. This indicates that some spermatocytic seminomas might originate from primordial germ cells. In line with this, experimental testicular teratomas can be generated by transplanting E12 male genital ridges to

Kit/Stem Cell Factor Receptor in Oncogenesis

testes of adult mice. Importantly, it was recently found that tumors of seminoma/dysgerminoma type had a D816H mutation in Kit/SCF-R causing its constitutive activation. In conclusion, Kit/SCF-R expression is of diagnostic help for seminomas/dysgerminomas, and GOF mutations in Kit/SCF-R might be oncogenic and involved in the generation of such tumors. Malignant Melanoma Normal melanocytes depend on ▶bFGF, ▶HGF and SCF in vitro. ▶Melanoma cells become independent of these growth factors, in part through autocrine bFGF stimulation. Interestingly, Kit mRNA and protein are down-regulated in human and murine ▶melanoma cell lines. This correlates with in vivo findings: While Kit/ SCF-R is expressed in normal melanocytes, benign and dysplastic naevi and nontumorigenic melanomas, expression is lost in dysplastic naevi, tumorigenic primary melanomas and metastases. In addition, transfection of Kit/SCF-R into highly metastatic melanoma cell lines, induced slowed growth rate and fewer lung metastases in nude mice. The transcription factor AP-2 controls expression of c-kit and the gene for MCAM/MUC18 positively and negatively, respectively. AP-2 is downregulated in melanomas and this is thought to be the reason for loss of Kit expression, allowing the malignant cells to escape SCF-induced apoptosis. Conversely, enforced AP-2 expression suppresses tumorigenicity and metastatic potential, possibly through c-kit transactivation and subsequent SCF-induced apoptosis. It has been proposed that AP-2 loss is a crucial event in malignant melanoma development. Other Neoplastic/Malignant Lesions Kit/SCF-R and its ligand have been found co-expressed in cells from ▶small cell lung cancer and ▶neuroblastoma, and it was reported that it might be involved in malignant progression in these cases. In ▶neurofibromatosis 1 (NF-1) there is infiltration with Kit-positive mast cells in the neurofibroma tissue, which is composed mainly of Schwann cells with an increased SCF mRNA expression compared to normal skin. The mast cells produce collagen VIII, which might contribute to the fibrosis in this disease. There is an abnormally high expression level of Kit in NF-1derived Schwann cell lines and decreased neurofibromin expression (Ras-GTPase). The proliferation is Kitdependent. In myelodysplastic lesions, Kit mutations might be involved in the pathogenesis. A recurrent D52N-Kit/SCFR mutation has been reported in these cases. Finally, down-regulation of Kit/SCF-R has been reported in breast cancer and in ▶thyroid carcinoma, despite expression by normal mammary duct epithelial cells and thyroid cells. It has been proposed that the Kit/ SCF-R downregulation enables de-differentiation of the cells in these tumor types.

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Gene Transfer, Immunotherapy, Vaccination SCF might be useful in expansion of peripheral blood leukocytes and of hematopoietic progenitors in culture before retroviral transduction or re-introduction in conjuction with autologous bone marrow transplantation. Phase II and III trials are currently being conducted on advanced stages of breast cancer and certain leukemias for this purpose. SCF might also be useful in conjuction with immuno-therapy. For instance, following high-dose ▶cyclophosphamide and IL-3, ▶dendritic cells can be mobilized and expanded ex vivo from CD34+ cells in the presence of GM-CSF, TNFα, Flt3 ligand and SCF. Dendritic cells are competent antigen-presenting cells for CD8+ cytotoxic T cells, so they can be used to stimulate the host immune defense against undesirable antigens, including tumor antigens. Ongoing phase II trials are examining the use of such expanded dendritic cells for immunotherapy or vaccination. Finally, in the past five years several small molecule protein kinase inhibitors have been approved as drugs for the treatment of specific types of cancer. Among these are two that act as inhibitors of Kit tyrosine kinase activity. ▶Imatinib (STI571/GleevecTM), an Abl, PDGFR and Kit inhibitor, was originally approved by the FDA for the treatment of chronic myelogenous leukemia (▶CML) in 2001. Shortly thereafter, imatinib was shown to be efficacious for treatment of gastrointestinal sarcomas (GIST), which are caused by mutant forms of Kit and PDGFRalpha, and was approved by the FDA for treatment of GIST in 2002. In 2006, a second tyrosine kinase inhibitor (TKI), ▶sunitinib (SU11248/ SutentTM), was approved for the treatment of imatinib-resistant GIST. Several additional TKIs have either approved or are in clinical trials for the treatment of cancer and other diseases caused by mutant Kit and other activated tyrosine kinases, and the number of approved TKI drugs is likely to grow significantly in the next ten years.

References 1. Hanks SK, Hunter T (1995) Protein kinases 6. The eukaryotic protein kinase superfamily: kinase (catalytic) domain structure and classification. FASEB J 9:576–596 2. Hubbard SR, Till JH (2000) Protein tyrosine kinase structure and function. Annu Rev Biochem 69:373–389 3. Blume-Jensen P, Hunter T (2001) Receptor tyrosine kinase-initiated signal transduction: mechanisms and specifity. In: Bertino JR (ed) Encyclopedia of cancer, 2nd edn. (Academic Press). 2:213–234 4. Besmer P et al. (1993) The kit-ligand (steel factor) and its receptor c-kit/W: pleiotropic roles in gametogenesis and melanogenesis. Dev Suppl 125–137 5. Galli SJ, Zsebo KM, Geissler EN (1994) The kit ligand, stem cell factor. Adv Immunol 55:1–96

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Klatskin Tumors

Klatskin Tumors TANIA M. W ELZEL , K ATHERINE A. M C G LYNN Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA

Synonyms (Peri-) Hilar Cholangiocarcinoma; Extrahepatic; cholangiocarcinoma; Cholangiocellular carcinoma; Bile duct carcinoma

Definition Klatskin tumors are anatomically defined as extrahepatic ▶cholangiocarcinomas that occur at the confluence of the left and right hepatic duct (Fig. 1a). Morphologically, most Klatskin tumors (hilar cholangiocarcinomas) exhibit a nodular-sclerosing growth pattern. Few are papillary tumors and mass-forming hilar lesions are rare. Histologically, the vast majority of these tumors are adenocarcinomas.

Characteristics History and Classification Hilar cholangiocarcinomas were first described by Klatskin and were further classified by Bismuth and Corlette (Fig. 1b): Bismuth type I tumors involve the common hepatic duct below the confluence of the right and left hepatic ducts; Bismuth type II tumors involve the confluence of the left and right hepatic duct; Bismuth type III tumors involve the common hepatic duct and the right (type IIIa) or left hepatic duct (type IIIb). Bismuth type IV tumors involve either the confluence of the hepatic ducts and the right and left hepatic duct, or are multicentric. Epidemiology Over the last decades, the incidence of intrahepatic cholangiocarcinoma increased in the United States, as it did worldwide. In contrast, the incidence of extrahepatic cholangiocarcinoma remained constant (Fig. 2). A recent study showed, that extrahepatic cholangiocarcinomas (including Klatskin tumors and distal extrahepatic lesions) represent 50% of all cholangiocarcinomas in the Surveillance Epidemiology and End Results (SEER) cancer registries of the United States. A frequently cited study reported that 67% of cholangiocarcinomas were hilar tumors. However, the study was a retrospective examination of cholangiocarcinoma patients who underwent surgical exploration at a tertiary medical center. Due to the study design, the patients were unlikely to be representative of all cholangiocarcinoma patients in the United

Klatskin Tumors. Figure 1 (a) Anatomical location of Klatskin tumors. (b) Bismuth Corlette classification of Klatskin tumors (hilar cholangiocarcinoma).

States. In addition, the International Classification of Diseases for Oncology (ICD-O) assigned Klatskin tumors a histology code rather than a topography code, and the histology code was cross-referenced to the topography code for intrahepatic rather than extrahepatic tumors. This misclassification has introduced error into the reporting of cholangiocarcinoma rates in the U.S. SEER cancer registries, making it impossible to define Klatskin tumor incidence on a populationbased level.

Klatskin Tumors

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Klatskin Tumors. Figure 2 Age-adjusted incidence rates for intrahepatic CC (ICC), extrahepatic CC (including Klatskin’s tumors under 8162/3; ECC) diagnosed in SEER9 registries, 1973–2002. The dashed line represents the incidence of tumors reported in SEER to histology code 8162 (Klatskin). It must be noted that these tumors are unlikely to comprise all Klatskin tumors, since according to the ICD-O coding (1992–to date) could also be coded as ECC using other histology codes.

Etiology and Risk Factors There is recent evidence that the molecular pathogenesis of Klatskin tumors/extrahepatic cholangiocarcinoma and intrahepatic cholangiocarcinoma may differ. Conditions that are associated with biliary inflammation increase the risk for cholangiocarcinogenesis. Well defined risk factors for Klatskin tumors and other extrahepatic cholangiocarcinomas include primary sclerosing cholangitis, infection with liver flukes (Opisthorchis viverrini, Clonorchis sinensis), choledochal cysts, ▶Caroli Syndrome, biliary stones, smoking and ▶Thorotrast exposure. Hepatitis C virus has been reported to be associated with intrahepatic cholangiocarcinoma and, in some reports, with hilar cholangiocarcinoma. Many patients do not exhibit any of the known risk factors, highlighting the need for further studies on etiopathogenesis of these tumors. Biology Diagnosis Clinical Symptoms. Patients present with obstructive jaundice (icterus, dark urine, pale stools, pruritus) and weight loss, and frequently signs of bacterial cholangitis. Abdominal pain and ascites may be present in patients with advanced disease. Biochemical Investigations. Parameters indicating obstructive cholestasis such as increased alkaline phosphatase, gamma glutamyltranspeptidase, serum bilirubin, and sometimes transaminase concentrations, may be found in patients with Klatskin tumors. ▶Tumor markers such as ▶CA 19-9 and ▶CEA, may

be elevated. These tumor markers, however, are not specific for Klatskin tumors/cholangiocarcinoma and CA19-9 may also be elevated in conditions with benign cholestatic disease. Imaging Methods. Accurate diagnosis is key to delineate benign from malignant biliary strictures and to determine the resectability of Klatskin tumors. Ultrasound is the initial diagnostic test to evaluate hilar cholangiocarcinoma and may show intrahepatic duct dilatation and caliber changes of bile ducts, but may fail to show liver infiltration of smaller tumors. On ▶computed tomography (CT), the primary obstructing hilar lesion may be invisible. On contrast enhanced CT, (infiltrative) lesions may show as thickening of the duct. Further signs include dilatation of the intrahepatic bile ducts or the atrophy-hypertrophy complex. Used to assess resectability, the accuracy of CT ranges from 60 to 75%. On ▶magnetic resonance imaging, Klatskin tumors appear hypointense on T1and hyperintense on T2-weighted images. Compared to the liver parenchyma, most Klatskin tumors are hypovascular. Gadolinium chelates and ferumoxide contrast agents can be used to assess liver invasion because of a good liver-tumor contrast. Magnetic resonance cholangiopancreatography (MRCP) can be used to visualize the obstructing lesion and intrahepatic bile duct dilatation and, in a small study, was shown to have an accuracy of 84% to assess the level of bile duct involvement. Endoscopic retrograde cholangiopancreatography (ERCP) can be used to endoscopically determine the

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location and extent of biliary tract obstruction. ERCP also allows palliative stent implantation for biliary drainage, and to obtain tumor cytology or biopsy. However, according to the specific growth pattern of Klatskin tumors, the sensitivity of brush cytology is 30%, and the combination of brush cytology/biopsy only ranges up to 70%.

Treatment To date, the only curative approach to hilar cholangiocarcinomas is surgery with resection of the bile ducts and hepatojejunostomy, and/or partial hepatectomy to achieve tumor free margins. However, at the time of diagnosis, only few/a small proportion of patients have resectable disease. Resection is contraindicated for Bismuth Type IV tumors or in the presence of any of the following: vascular encasement, occlusion or invasion of the main portal vein or hepatic artery, distant or lymph node metastases, liver invasion, or invasion of extrahepatic organs. Surgery for hilar cholangiocarcinoma with curative intent is associated with 5-year survival rates of 40%. Recently, there has been some evidence that liver transplantation, together with neoadjuvant chemoradiation may improve survival in selected patients with unresectable hilar cholangiocarcinoma. ▶Palliative approaches include the endoscopic placement of biliary stents or percutaneous biliary drainage to improve the symptoms of cholestasis. ▶Photodynamic therapy with hematoprophyrin based photosensitizers, in addition to bilateral endoprosthesis insertion, has been shown to prolong survival by several months and improve quality of life in several randomized controlled trials. So far, ▶radiation, as well as systemic ▶chemotherapy has not led to a significant improvement of survival rates, however, several new protocols are currently under investigation.

4. Nakeeb A, Pitt HA, Sohn TA et al. (1996) Cholangiocarcinoma: a spectrum of intrahepatic, perihilar, and distal tumors. Ann Surg 224:463–473 5. Slattery JM, Sahani DV (2006) What is the current state-of the-art imaging for detection and staging of cholangiocarcinoma? Oncologist 11:913–922

KLK3 ▶PSA

KLRK1 ▶NKG2D Receptor and Cancer

Knobloch Syndrome Definition Is an autosomal recessive disease that is characterized by ocular defects leading to retinal detachment, macular degeneration and blindness.

Knock-Down Survival The prognosis of hilar cholangiocarcinoma is poor, with 5 year survival rates ranging between 5 and 10%.

Definition

▶Knockdown

References 1. Klatskin G (1965) Adenocarcinoma of the hepatic duct at its bifurcation within the porta hepatis. An unusual tumor with distinctive clinical and pathological features. Am J Med 38:241–256 2. Bismuth H, Corlette MG (1975) Intrahepatic cholangioenteric anastomosis in carcinoma of the hilus of the liver. Surg Gynecol Obstet 140:170–176 3. Welzel TM, McGlynn KA, Hsing AW et al. (2006) Impact of classification of hilar cholangiocarcinomas (Klatskin tumors) on the incidence of intra- and extrahepatic cholangiocarcinoma in the United States. J Natl Cancer Inst 98(12):873–875

Knock-in Definition A genetically engineered mouse that has a different version of a gene inserted into its genome. ▶Mouse Models

Koch’s Postulates

Knock-Out

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Knudson Hypothesis

Definition

Definition

Gene invalidation resulting in the absence of expression of the corresponding protein. A commonly used model is the ▶Knock-out mouse.

Originally described as a model where in retinoblastoma two genetic “hits” result in cancer; subsequently, the two “hits” were identified as occurring as inactivating mutations in the two alleles of a gene today known as the ▶retinoblastoma gene (RB1). The two mutations can occur somatically in an individual. More often, one mutation inactivates one allele in a germ cell, the developing embryo then has one inactivated and one normal allele. Because of the ▶recessive nature of the RB1 gene, there will be no phenotype in the child, it does have however an increased risk. In most cases, the remaining normal allele will mutate in the retina during early childhood resulting in cells with both RB1 alleles inactivated. As the consequence, the child will develop retinoblastoma. This two-hit hypothesis has been generalized to entertain the idea that most cancers develop following this model. Accordingly, numerous ▶loss-of-heterozygosity studies have been done on virtually every tumor entity to identify genomic regions deleted on one tumor cell chromosome with co-existing gene mutation on the other chromosome. Only in few models the two-hit model could be convincingly verified, and today the Knudson hypothesis more or less appears to be restricted to few cancer types. Instead, there are convincing data now to support the idea that cellular effects supporting the process of malignant cellular conversion can result from the inactivation of one of the alleles. The basic concept here is ▶haploinsufficiency.

▶Gene Knockout ▶Mouse Models

Knock-out Mice ▶Knock-out Mouse

Knock-Out Mouse Definition Knock-out mouse is a genetically engineered mouse carrying one or more of its genes made inoperable through a ▶gene knockout (usually an inactivating mutation). Knockout is a technical approach to functionally characterize a gene that has been sequenced but has an unknown or incompletely known function. Because genes between mouse and humans are evolutionary conserved and, a priori, are assumed to have similar functions, the phenotype that a knock-out gene has in the mouse may be used to extrapolate its function in humans. For many genes, however, disease-associations in humans did not identify a similar phenotype in a knock-out mouse. Different strains of the mouse also may develop different phenotypes upon knock-out of a particular gene.

Koch’s Postulates R OY J. D UHE´ Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, MS, USA

Knockdown

Synonyms Henle–Koch postulates

Definition

Definition

Gene knockdown refers to the experimental reduction of expression of a gene. This is commonly achieved by introducing small interfering RNAs (▶SiRNAs) or other anti-sense oligonucleotides into cells.

Characteristics

▶Antisense Nucleic Acid

A set of criteria used to identify the specific pathogen that causes an infectious disease.

Koch’s postulates are attributed to Robert Koch, who received the 1905 Nobel Prize in Medicine or

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Koch’s Postulates

Physiology “for his investigations and discoveries in relation to tuberculosis.” Jakob Henle was a professor at the University of Göttingen when Koch enrolled as a student there in 1862, and Henle was one of the early proponents of the idea that contagious diseases were caused by microorganisms. In the early days of bacteriology there were numerous heated arguments over the identity of pathogenic agents. The presence of commensal microorganisms alongside pathogenic microorganisms often resulted in the misidentification of the real disease-causing organism. At that time there was also a school of thought which held that there were no true bacterial species, but rather that a bacterium could adopt nearly limitless morphologies and physiologies, which would allow it to cause tuberculosis, anthrax, food spoilage, or other problems depending on the particular form adopted by the bacterium. It was against this backdrop that Koch proposed the following three criteria (as translated by Thomas M. Rivers) for identifying a microbiological cause of disease. 1. “The parasite occurs in every case of the disease in question, and under circumstances which can account for the pathological changes and clinical course of the disease.” 2. “It occurs in no other disease as a fortuitous and nonpathogenic parasite.” 3. “It, after being fully isolated from the body and repeatedly grown in pure culture, can induce the disease anew.” Koch famously applied these principles as he isolated Bacillus anthracis and Mycobacterium tuberculosis and identified them as the causes of anthrax and tuberculosis, respectively. By establishing a theoretical framework for determining cause and effect, Koch’s postulates had a profound effect on infectious disease research. Within a few decades, the identities of dozens of new pathogens were revealed. Yet these precepts had obvious limitations arising from the simple fact that not all pathogens can be propagated in pure form as autonomous living organisms. Viruses were the first such examples to be considered by the scientific community, and it was soon apparent that Koch’s postulates had to be revised to accommodate the scientific discoveries of the twentieth century. Over the years since Koch’s postulates were first postulated, many investigators have articulated a revised set of criteria to permit the systematic evaluation of viruses, prions, serum cholesterol, tobacco smoke, chromosomal translocations (▶chromosomal translocation) and other factors as the underlying cause of a disease, contagious or otherwise. In 1976, Alfred S. Evans proposed the following ten criteria as a “unified concept” for disease causality, which could be applied to either chronic or acute diseases.

1. Prevalence of the disease should be significantly higher in those exposed to the putative cause than in case controls not so exposed. 2. Exposure to the putative cause should be present more commonly in those with the disease than in controls without the disease when all risk factors are held constant. 3. Incidence of the disease should be significantly higher in those exposed to the putative cause than in those not so exposed as shown in prospective studies. 4. Temporally, the disease should follow exposure to the putative agent with a distribution of incubation periods on a bell shaped curve. 5. A spectrum of host responses should follow exposure to the putative agent along a logical biologic spectrum from mild to severe. 6. A measurable host response following exposure to the putative cause should regularly appear in those lacking this before exposure (i.e. antibody, cancer cells) or should increase in magnitude if present before exposure; this pattern should not occur in persons so exposed. 7. Experimental reproduction of the disease should occur in higher incidence in animals or man appropriately exposed to the putative cause than in those not so exposed; this exposure may be deliberate in volunteers, experimentally induced in the laboratory, or demonstrated in a controlled regulation of natural exposure. 8. Elimination or modification of the putative cause or of the vector carrying it should decrease the incidence of the disease (control of polluted water or smoke or removal of the specific agent). 9. Prevention or modification of the host’s response on exposure to the putative cause should decrease or eliminate the disease (immunization, drug to lower cholesterol, specific lymphocyte transfer factor in cancer). 10. The whole thing should make biologic and epidemiologic sense. The correct identification of the cause of a cancer is essential, because the cause can either be avoided, thereby preventing cancer, or the cause can be targeted through drug design, thereby curing the cancer. It is also clear that if one invests preventive or drug design efforts into the wrong cause, then one will have accomplished naught. Obvious limitations of Koch’s postulates arise when one attempts to apply them to noncontagious diseases, when suitable animal models for reproducing the disease do not exist, or when there is an inordinately long latent period between initial exposure to the causal agent and the disease’s manifestation. These circumstances often apply to the development of cancer. The ability of a pathogenic agent to cause cancer is also dependent upon the presence or absence of various tumor

KSP Mitotic Spindle Motor Protein

suppressors, which causes some individuals to be more susceptible to developing cancer than others. For these and other technical reasons, it is often unwise to dogmatically invoke Koch’s postulates in an effort to disprove a particular agent as a cause of disease. An infamous controversy arose in the late 1980s and early 1990s when Koch’s postulates were invoked in an attempt to disprove that HIV-1 caused AIDS, although that pathogenic link is now universally accepted. Koch’s postulates are of great historical significance because they marked the application of logic and reason to the field of pathology. As many scholars have noted, it is unwise to insist upon the application of the original postulates when we now know that there are pathogenic mechanisms that do not conform to the lifestyles of protozoa, fungi, or bacteria. It is the rigorous application of logic and reason to the elucidation of the cause of disease which remains as the lasting legacy of Koch’s postulates.

References 1. Rivers TM (1937) Viruses and Koch’s postulates. J Bacteriol 33:1–12 2. Evans AS (1976) Causation and disease: The Henle–Koch postulates revisited. Yale J Biol Med 49:175–195

Kostmann Syndrome Definition Synonym: Severe Congenital neutropenia; Is an inherited disorder of the bone marrow. Children born with this condition lack ▶neutrophils (a type of white blood cell that is important in fighting infection, also called granulocytes). These children suffer frequent infections from bacteria which in the past led to death in three-quarters of cases before 3 years of age. Children with hostmann syndrome have an increased risk of developing ▶acute myeloid leukemia (CML) or ▶myelodysplasia. ▶myelodyplastic syndromes

Kringle Domain Definition

Is a triple-disulfide-loop structure spanning 80 amino acids and playing a role in protein-protein

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interactions. This domain was first found in bovine prothrombin. ▶Macrophage-stimulating Protein ▶Scatter Factor

KSA ▶EpCAM

KSP ▶KSP Mitotic Spindle Motor Protein

KSP Mitotic Spindle Motor Protein W EIKANG TAO Department of Cancer Research, Merck Research Laboratories, West Point, PA, USA

Synonyms Eg5; Kinesin spindle protein; KSP; Kinesin-5; Kinesinlike protein KIF11

Definition KSP mitotic spindle motor protein is a microtubuleassociated molecular motor belonging to the ▶kinesin superfamily, which plays an essential role in the separation of centrosomes, the assembly of bipolar spindles, and the faithful segregation of chromosomes into daughter cells during ▶mitosis.

Characteristics

KSP is a plus-end-directed ▶microtubule motor protein, well conserved from yeast to mammals. It can generate directed mechanical force by hydrolyzing ATP and move along microtubule filaments from the minus end (oriented towards the nucleus) to the

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KSP Mitotic Spindle Motor Protein

plus end (oriented towards the cell periphery). The KSP protein contains a highly conserved N-terminal motor domain encompassing the head and neck motifs, a coiled-coil stalk domain, and a tail region containing a characteristic BimC box close to the C-terminus. Based on the N-terminal motor domain sequence, the vertebrate KSP belongs to the BimC subfamily of ▶kinesins, a large family of ▶microtubule-based motor proteins. More recently, KSP was classified to the kinesin-5 subgroup according to a new nomenclature system. The globular motor domain of KSP is responsible for catalyzing hydrolysis of ATP, interacting with microtubules and nucleotides, and driving the movement along microtubules empowered by ATP hydrolysis, whereas the stalk domain mediates protein–protein interactions to form homotetramers. Active KSP is a homotetramer in which two polypeptides first dimerize to form a parallel coiled-coil and then two dimers form an antiparallel tetramer containing four motor domains with a dimeric motor unit at each end (Fig. 1). As a tetramer, KSP is able to crosslink and translocate along two adjacent microtubules with each dimeric motor unit interacting with a single microtubule fiber. Fluorescence studies suggest that when binding to two antiparallel microtubules, KSP can slide them apart, thereby pushing spindle poles apart. If binding to two parallel microtubules, KSP can mediate bundling of parallel microtubules, contributing to the assembly and integrity of mitotic spindles (Fig. 2). Like other ▶kinesins of the BimC subfamily, human KSP is required early in prometaphase for the separation of duplicated centrosomes and the formation of bipolar mitotic spindles. Inhibition of KSP with neutralizing antibodies, small molecule inhibitors, or small interfering RNAs (siRNAs) causes formation of the characteristic monopolar mitotic spindle (also termed monoaster), a radial array of microtubules surrounded by a ring of chromosomes, and cell cycle arrest at prometaphase. Further studies indicate that suppression of KSP activates the ▶spindle assembly checkpoint, thereby preventing

the onset of anaphase and causing mitotic arrest. Prolonged mitotic arrest induces apoptosis. Inhibition of KSP does not affect postmitotic cells, indicating that KSP is only required for cell proliferation and that it functions exclusively in mitosis. Consistent with its exclusive role in cell division, KSP is preferentially expressed in proliferating tissues, such as thymus, bone marrow ,and intestine epithelium, with minimal or no expression in nonproliferating tissues such as the central nervous system. In addition, it displays much more abundant expression in actively proliferating tumor tissues than in normal adjacent tissues. Regulation The ATPase activity of KSP is essential for its function and it is stimulated by the interaction with microtubules. The control of ATPase activity by interactions with microtubules is thought to prevent futile hydrolysis of ATP. It has been shown that there is an evolutionarily conserved p34cdc2 phosphorylation site (Thr-927 in human KSP) located in the BimC box of KSP, and that p34cdc2-mediated phosphorylation of this site controls the association of KSP with the microtubule spindles. Moreover, KSP can be phosphorylated by ▶Aurora kinase, a mitotic kinase, but the functional importance of this phosphorylation remains to be determined. Relevance to Cancer The mitotic spindle is a protein complex consisting of multiple components including microtubules and motor proteins and it is a pharmaceutically validated target for cancer therapeutics. ▶Vinca alkaloids and ▶taxanes that interfere with the dynamics of microtubules by binding to β-tubulin perturb mitosis and have been used in the clinic for decades for the treatment of many human malignancies. However, since microtubules have essential functions beyond mitosis in nonproliferating cells, including intracellular transport

KSP Mitotic Spindle Motor Protein. Figure 1 Schematic representation of the structures of KSP dimmer and tetramer.

KSP Mitotic Spindle Motor Protein

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K KSP Mitotic Spindle Motor Protein. Figure 2 Schematic illustration of KSP functions.

and organelle positioning, drugs that target microtubules cause microtubule-dependent side effects, such as peripheral neuropathy. In addition, an increasing number of tumors have acquired resistance to these antimicrotubule drugs via various mechanisms including acquired mutations on β-tubulin, altered expression of tubulin isoforms, changed microtubule dynamics as well as elevated expression of membrane drug efflux pumps like ▶P-glycoproteins (P-gp). Thus, agents that are able to selectively disrupt the mitotic spindle via a novel mechanism of action and without P-gp liability are greatly desired for cancer therapy. There are several important traits that make KSP an attractive target for cancer treatment: (i) KSP is a crucial component of the mitotic spindle and is essential for spindle bipolarity and proper segregation of chromosomes during mitosis. (ii) KSP functions exclusively in dividing cells and there is no evidence that inhibition of KSP affects nonproliferating cells. (iii) KSP is overexpressed in tumor tissues relative to adjacent normal tissues. (iv) Since KSP is an ATPase and the ATPase activity is required for its function, KSP is a druggable target. Indeed, a number of small molecule inhibitors of KSP ATPase with distinct chemical structures have been generated and currently at different stages of development. Some specific inhibitors of KSP have exhibited broad antiproliferative activity in tumor cell lines and significant antitumor efficacy in various murine tumor models. A few KSP inhibitors

have entered clinical trials. Among them ispinesib demonstrated some activity in taxane-treated patients with metastatic breast cancer in a phase II study. As expected, the clinical trial data indicate that KSP inhibitors could not exhibit neurotoxicity because of their lack of effect on microtubule dynamics. Although KSP inhibitors hold great promise for cancer treatment, their clinical antitumor activity remains to be determined. The clinical development of these novel antimitotic agents holds many challenges. A critical issue is how to identify the responders in the clinic, or what ▶biomarkers could predict clinical response of tumors to KSP inhibitors. Preclinical studies suggest that tumor cells with a competent spindle assembly checkpoint are more sensitive to KSP inhibitor-mediated cell death than those with a deficient spindle checkpoint. This awaits confirmation in the clinic. Additionally, a better understanding of the mechanism that mediates the lethality of these agents or the link between KSP inhibition and induction of cell death is required to guide the selection of dosing schedules and the identification of determinants of drug sensitivity. Finally, since antimicrotubule drugs and KSP inhibitors may kill cancer cells through a partially overlapping pathway, elucidation of the mechanisms that cause resistance to microtubule inhibitors in the clinical setting would tell whether KSP inhibitors should be used for the treatment of antimicrotubule agent-resistant tumors.

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Ku70

References 1. Wood KW, Cornwell WD, Jackson JR (2001) Past and future of the mitotic spindle as an oncology target. Curr Opin Pharmacol 1:370–377 2. Bergnes G, Brejc K, Belmont (2005) Mitotic kinesins: prospects for antimitotic drug discovery. Curr Topics Med Chem 5:127–145 3. Miki H, Okada Y, Hirokawa N (2005) Analysis of the kinesin superfamily: insights into structure and function. Trends Cell Biol 15:467–476 4. Tao W, South V, Zhang Y et al. (2005) Induction of apoptosis by an inhibitor of the mitotic kinesin KSP requires both activation of the spindle assembly checkpoint and mitotic slippage. Cancer Cell 8:49–59 5. Valentine MT, Fordyce PM, Block SM (2006) Eg5 steps it up! Cell Div 1:31

Kupffer Cells P ETER T HOMAS Departments of Surgery and Biomedical Sciences, Creighton University, Omaha, NE, USA

Synonyms Hepatic (Liver) fixed macrophages

Definition

Kupffer cells are ▶macrophages that are fixed within the sinusoids of the liver. They are the body’s most abundant source of fixed macrophages.

Characteristics

Ku70 Definition The protein of 70-kDa molecular weight is a DNAhelicase involved in the DNA double-strand break repair system (▶Double-strand break DNA repair), more precisely the nonhomologous end joining. ▶Ku Antigen, 70-kDa Subunit ▶Lupus Autoantigen p70 ▶Thyroid-Lupus Autoantigen (TLAA) ▶Thyroid Autoantigen, 70-kDa (G22P1) ▶Securin

Kulchitsky Cell Carcinoma ▶Extrapulmonary Small Cell Cancer

Kunitz Trypsin Inhibitor Definition KTI; Antinutritional/allergen protein found in soybean that KTI acts as a inhibitor of pancreatin and chymotrypsin. ▶Lunasin

Kupffer cells were first described in 1876 and are named for, the German pathologist Karl Wilhelm von Kupffer who called them the star cells (sternzellen) of the liver. Kupffer cells are tissue macrophages that are located in the hepatic sinusoidal blood flow attached to the endothelial cell lining. They represent 10% of all liver cells and are the body’s largest population (approximately 80%) of fixed macrophages. They are the first macrophage population to contact bacteria, bacterial debris and ▶endotoxins arising in the gastrointestinal tract. Kupffer cells are both highly endocytic and phagocytic and a major function is to remove particulate matter from the circulation. They are also an important component of innate immunity which is the most rapid response to dangerous stimuli and can modulate immune responses by antigen presentation and suppression of T-cell activation. Thus, the main role of Kupffer cells is to protect the body by removing potentially harmful substances from the blood. In addition Kupffer cells function to remove and destroy old red blood cells. Kupffer cells have also been implicated in cancer cell surveillance (see below). Kuppfer cells originate in the bone marrow. These bone marrow monocytes enter the circulation and become implanted in the liver where they differentiate into fixed tissue macrophages. Kupffer cells are considered terminally differentiated and the cells no longer divide (Fig. 1). Kupffer Cells and Liver Disease Kupffer cells are involved in the development of alcoholic liver disease. Kupffer cells become activated when they are exposed to the bacterial cell wall component endotoxin (Lipopolysaccharide, LPS). This results in the secretion of signaling molecules including ▶cytokines and ▶reactive oxygen species (ROS), which can be damaging to liver cells especially those that have been affected by alcohol ingestion and contain a large amount

Kupffer Cells

Kupffer Cells. Figure 1 Section of mouse liver showing stellate shaped Kupffer cells (arrows). The cells are stained by the immunoperoxidase method for the presence of a breast cancer associated antigen, the gross cystic disease fluid protein (GCDFP-15), 15 min after intravenous injection of the purified protein.

of fat (alcoholic steatosis). Endotoxin is produced by gram negative bacteria in the large intestine and ingestion of alcohol alters the permeability of the intestine (leaky gut) to endotoxin causing an increased level in the portal blood entering the liver. To activate Kupffer cells and other macrophages endotoxins combine with a serum protein, lipopolysaccharide binding protein (LBP). This complex reacts with a cell surface receptor, ▶CD14 which in turn interacts with the Toll like receptor ▶TLR4 and the intracellular signaling protein ▶MyD88. This causes a cascade of intra-cellular signals that activate transcription factors such as ▶NFκB and result in the synthesis and secretion of cytokines and ROS. Relationship of Kupffer Cells to Primary and Secondary Liver Cancers The liver is a favored site for the secondary spread of many cancers including those of the large intestine and breast. The role of Kupffer cells in the development of cancers in the liver is controversial. There is no doubt that they play an important part in both the development of primary liver cancer (▶hepatocellular carcinoma or hepatoma) and in the formation of ▶metastasis from a distant site including cancers of the lungs, breast, colon and other gastrointestinal cancers. Some experimental studies have shown that elimination of Kupffer cells from the liver results in enhanced metastatic disease. Other studies have implicated Kupffer cells as agents that interact with the tumor cells entering the liver and their pro-inflammatory responses can induce tumor cell implantation and growth allowing increased metastatic disease. In primary liver cancer recent evidence has shown a role for Kupffer cell activation in carcinogenesis and progression of the

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cancer. Some liver carcinogens are able to activate Kupffer cells and induce cytokines and other factors that promote hepatocyte growth. These factors can also effect growth of pre-neoplastic cells and lead to the development of hepatoma. Evidence has accumulated that the pro-inflammatory cytokine IL-6 plays an important role in promoting hepatoma cell survival and proliferation. This tumor cell related increase in IL-6 is mediated through the MyD88/NFκB signaling cascade in Kupffer cells. In the case of colorectal cancer metastasis to the liver cytokines produced by Kupffer cells play a part in both tumor cell implantation and their subsequent survival and growth. During the development of colorectal cancer metastasis to the liver, Kupffer cells respond to the glycoprotein carcinoembryonic antigen (▶CEA). The cells bind CEA via a pentapeptide that reacts with a surface protein that is identical to the RNA binding protein hnRNP M4. This results in Kupffer cell activation and a cytokine cascade that includes IL-1, IL-6, IL-10 and TNF-α. The high local concentration of cytokines produced within the hepatic sinusoids has multiple effects that influence cancer cell implantation, survival and proliferation. The initial effect of the Kupffer cell produced cytokines seems to be on the sinusoidal endothelial cells. They become activated and produce adhesion molecules such as ▶E-selectin and ▶ICAM-1 on their cell surfaces. This allows the cancer cells to attach to the endothelial cell layer and arrest in the liver sinusoids. When this happens the tumor cells can break through the endothelial cell layer and invade the parenchyma Cytokines, in particular IL-10 are also protective against the effects of ischemia/reperfusion (IR) injury caused by blockage of the blood supply by tumor cell infiltrates into the small sinusoids. IR causes oxidative stress and cell death. Secretion of anti-inflammatory cytokines such as IL-10 counteracts these effects and aids the initial survival of the cancer cells following implantation in the sinusoids. These studies were largely carried out using human colorectal cancer cells in culture or in metastasis models in immuno-suppressed mice and imply that Kupffer cells are important participants in metastasis development. However, other experiments using syngeneic animal tumors have shown a role for Kupffer cells in preventing liver metastasis. Experiments where Kupffer cells have been depleted prior to injection of tumor cells have often resulted in extensive tumor growth in the liver. Similarly when Kupffer cells have been activated prior to tumor cell injection reduced tumor growth in the liver is seen. Kupffer Cell Cancers Cancer originating in Kupffer cells is very rare and few cases have been reported in the literature. They are described as Kupffer cell ▶sarcomas or hemangioendotheliosarcomas of the liver. The tumors contain

K

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Kuzbanian

phagocytic giant cells and numerous other cells with morphology similar to Kupffer cells. These hemorrhagic tumors tend to be quickly fatal with abdominal discomfort, ascites and jaundice as symptoms. Kupffer cell cancers will metastasize to distant sites including the pancreas and lung. Similar tumors to those found in humans can be induced in rats by exposure to low doses of carcinogens during liver regeneration.

Kuzbanian Definition

▶ADAM10

References 1. Von Kupffer C, Uber Sternzellen der Leber (1876) Arch Mikr Anat 12:353–358 2. Bilzer M, Roggel F, Gerbes AL (2006) Role of Kupffer cells in host defense and liver disease. Liver Inter 26:1175–1186 3. Burston J (1958) Kupffer Cell sarcoma. Cancer 11:798–802

Kv10.1 ▶Ether à-go-go Potassium Channels

L

L-PAM Definition

▶Melphalan

Lactate Definition A 3-carbon carboxylic acid also known as 2-hydroxypropanoic acid. ▶Warburg Effect

L&H Definition Lymphocytic and/or histiocytic. ▶Hodgkin Disease, Clinical Oncology

L&H Cells Definition Lymphocytic and Histiocytic Cells.

Lactate Dehydrogenase Definition LDH is a ubiquitously expressed enzyme. Serum levels of LDH can be used to monitor treatment of testicular cancer, ▶Ewing sarcoma, non Hodgkin lymphoma and some types of leukemia. Elevated levels of LDH can also be caused by a number of non-cancerous conditions, including heart failure, hypothyroidism, anemia, as well as lung and liver diseases. ▶Serum Biomarkers ▶Testis Cancer ▶Hodgkin Disease

Label-Free Analysis Definition A biochemical analysis employing detection method without the need of label such as fluorescence or radioactive tag. ▶Surface Plasmon Resonance

Labile Factor Definition

▶Factor V.

Lactoferricin Antiangiogenesis Inhibitor DAVID W. H OSKIN Departments of Pathology, and Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada

Definition Lactoferricin is a cationic peptide that is generated by the acid-pepsin hydrolysis of mammalian ▶lactoferrin present in the secretory granules of neutrophils (polymorphonuclear leukocytes), as well as in exocrine

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Lactoferricin Antiangiogenesis Inhibitor

secretions, including milk, tears, and saliva. Interestingly, substantial quantities of lactoferricin are generated in the stomach following the ingestion of lactoferrin-containing milk. Lactoferricin possesses potent antimicrobial, antiviral, immunomodulatory, and antitumor activities. In terms of anticancer activity, the best studied of the lactoferricins is bovine lactoferricin, which consists of amino acid residues 17–41 from the NH2-terminal region of bovine lactoferrin (Fig. 1). A disulfide bond that forms between cysteine residues located at each end of the peptide creates a looped or hairpin structure. In an aqueous environment, bovine lactoferricin assumes an ▶amphipathic, twisted β-sheet configuration with clear positively charged and hydrophobic faces. The relatively high proportion of asymmetrically clustered basic amino acid residues (arginine and lysine) and the hydrophobic tryptophan residues that in part comprise bovine lactoferricin are believed to be important for the peptide’s biological activity.

Characteristics The in vitro and in vivo anticancer activity of bovine lactoferricin has been attributed to the selective cytotoxic effect (either by membrane lysis or ▶apoptosis induction) exerted by this cationic peptide on a broad range of cancer cell types, including leukemias, lymphomas, fibrosarcomas, and various carcinomas. However, recent studies indicate that bovine lactoferricin is also able to inhibit ▶angiogenesis. A similar, but less potent, antiangiogenic activity has also been reported for bovine lactoferrin. Although ▶neovascularization is normally tightly regulated by the opposing effects of proangiogenic and antiangiogenic factors, this

process becomes dysregulated during tumor growth. The action of proangiogenic factors, in combination with basement membrane degradation by proteolytic enzymes, results in the proliferation, migration, and differentiation of tumor-associated endothelial cells. Neovascularization is an essential step in ▶tumorigenesis since the new blood vessels provide oxygen and nutrients to rapidly dividing cancer cells and remove metabolic wastes from the tumor ▶microenvironment. This allows solid tumors to grow in size, as well as promoting the development of metastatic disease. Diffusible, tumor-associated growth factors that stimulate angiogenesis include ▶vascular endothelial growth factor165, ▶platelet-derived growth factor, ▶heparin-binding epidermal growth factor-like growth factor, and basic ▶fibroblast growth factor (also known as fibroblast growth factor 2). Bovine lactoferricin is a potent in vivo inhibitor of vascular endothelial growth factor165- and basic fibroblast growth factor-induced angiogenesis in the mouse ▶Matrigel-plug assay. This finding is consistent with the observation that administration of bovine lactoferricin by subcutaneous injection reduces the number of tumor-associated blood vessels in B16-BL6 melanoma-bearing mice. In addition, bovine lactoferricin exhibits a dose-dependent inhibitory effect on the in vitro proliferation of human umbilical vein endothelial cells in response to vascular endothelial growth factor165 or basic fibroblast growth factor, as well as inhibiting the in vitro migration of human umbilical vein endothelial cells across transwell membranes in response to vascular endothelial growth factor165 or basic fibroblast growth factor. Bovine lactoferricin therefore inhibits endothelial cell proliferation and

Lactoferricin Antiangiogenesis Inhibitor. Figure 1 Primary structure of bovine lactoferricin. The amino acid sequence of bovine lactoferricin is indicated by single-letter code (see the accompanying key). Basic and hydrophobic amino acid residues are important for peptide function and are colored red and blue, respectively. The disulfide bond, indicated by the solid bar between cysteine residues at opposite ends of the peptide, forms a loop consisting of 18 amino acids. Numbers indicate the sequence position in bovine lactoferrin.

Lactoferricin Antiangiogenesis Inhibitor

migration, which are essential steps in neovascularization. Importantly, bovine lactoferricin does not affect the viability of human umbilical vein endothelial cells, suggesting that the antiangiogenic activity of bovine lactoferricin is independent of its membranelytic and apoptosis-inducing activity. Vascular endothelial growth factor165 and basic fibroblast growth factor must first interact with ▶heparan sulfate proteoglycans on the surface of endothelial cells in order for these proangiogenic factors to bind to and trigger signal transduction through their respective cellsurface receptors. Other heparan sulfate proteoglycandependent proangiogenic factors that have been linked to tumor progression include platelet-derived growth factor and ▶heparin-binding epidermal growth factorlike growth factor. Positively charged bovine lactoferricin mediates its inhibitory effect on basic fibroblast growth factor- and vascular endothelial growth factor165-induced angiogenesis by interacting with negatively-charged heparin-like structures on the surface of human umbilical vein endothelial cells, thereby competing with basic fibroblast growth factor and vascular endothelial growth

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factor165 for the heparan sulfate proteoglycans that are required for these proangiogenic factors to bind to and signal through their specific cell-surface receptors (Fig. 2). Although not yet formally proven, it is likely that bovine lactoferricin will have a similar inhibitory effect on angiogenesis induced by other heparin-binding tumorassociated proangiogenic factors. However, ▶electrostatic interactions alone do not govern the binding of bovine lactoferricin to the heparan sulfate proteoglycans that are involved in cell-surface receptor signaling caused by heparin-binding proangiogenic factors. Thus, a scrambled form of bovine lactoferricin that retains the net positive charge of the native peptide is unable to inhibit the binding of vascular endothelial growth factor165 or basic fibroblast growth factor to human umbilical vein endothelial cells. The primary and secondary structure that is conferred on bovine lactoferricin by its amino acid sequence is therefore an important factor in the selectivity of bovine lactoferricin for heparin-like structures that are involved in basic fibroblast growth factor and vascular endothelial growth factor165 interactions with their respective receptors on human endothelial cells.

L

Lactoferricin Antiangiogenesis Inhibitor. Figure 2 Model of bovine lactoferricin-mediated blockade of heparin-binding growth factor-induced angiogenesis. (a) Heparin-binding proangiogenic growth factors such as vascular endothelial growth factor165 (VEGF) must interact with heparin-like binding sites on heparan sulfate proteoglycans in order to bind to and signal through receptors on the surface of endothelial cells. (b) Bovine lactoferricin (Lfcin) complexes with heparin-like binding sites on cell-surface heparan sulfate proteoglycans, thereby competing with heparan sulfate proteoglycan-dependent proangiogenic growth factors for heparin-like binding sites and preventing proangiogenic growth factor receptor signaling from taking place.

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Lactoferrin

Clinical Perspectives Starving a solid tumor of its blood supply by preventing or interfering with tumor-induced neovascularization has generated considerable interest as an alternative to conventional chemotherapy for the prevention of tumor growth and metastasis. Indeed, several different inhibitors of angiogenesis are currently being used in the treatment of human cancers. However, the results obtained to date in clinical practice have been less than was hoped for on the basis of preclinical studies, most likely because the current generation of antiangiogenic agents only target a single proangiogenic growth factor receptor, whereas multiple proangiogenic factors are typically associated with tumor-induced angiogenesis. In this regard, the ability of bovine lactoferricin to inhibit neovascularization in response to multiple heparin-binding growth factors may allow bovine lactoferricin to be more effective than current antibody-based antiangiogenic agents for the blockade of tumor-induced angiogenesis. However, the susceptibility of bovine lactoferricin to enzymatic degradation and inactivation through interactions with anionic serum components remains a major obstacle to any future use of this host defense peptide as an antiangiogenic agent. One possible solution is to synthesize an all-▶D amino acid analogue of bovine lactoferricin since cationic peptides that consist of all-D amino acids exhibit dramatically increased stability in serum. Alternatively, tumor-targeted ▶liposomes might be used to encapsulate and deliver bovine lactoferricin directly to tumor sites while retaining the peptide’s ability to mediate antiangiogenic activity. Although preclinical studies have revealed that bovine lactoferricin is a potent inhibitor of angiogenesis, additional research will be needed in order to realize the potential of bovine lactoferricin as a novel antiangiogenic agent for the treatment of human cancers.

5. Yoo Y-C, Watanabe S, Watanabe R et al. (1997) Bovine lactoferrin and lactoferricin, a peptide derived from bovine lactoferrin, inhibit tumor metastasis in mice. Jpn J Cancer Res 88:184–190

Lactoferrin Definition Is an 80-kDa iron-binding glycoprotein belonging to the transferrin family. Lactoferrin has important multifunctional roles in host defense. ▶Lactoferricin Antiangiogeneis Inhibitor

LAIR1 Definition Leukocyte-associated immunoglobulin-like receptor 1.

LAK ▶Activated Natural Killer Cells

LAMB References 1. Gifford JL, Hunter HN, Vogel HJ (2005) Lactoferricin: a lactoferrin-derived peptide with antimicrobial, antiviral, antitumor and immunological properties. Cell Mol Life Sci 62:2588–2598 2. Mader JS, Hoskin DW (2006) Cationic antimicrobial peptides as novel cytotoxic agents for cancer treatment. Expert Opin Investig Drugs 15:933–946 3. Mader JS, Smyth D, Marshall JS et al. (2006) Bovine lactoferricin inhibits basic fibroblast growth factor- and vascular endothelial growth factor165-induced angiogenesis by competing for heparin-like binding sites on endothelial cells. Am J Pathol 169:1753–1766 4. Vogel HJ, Schibli DJ, Jing W et al. (2002) Towards a structure-function analysis of bovine lactoferricin and related tryptophan- and arginine-containing peptides. Biochem. Cell Biol 80:49–63

▶Carney Complex

Lamellar Phase Definition The most common lipid secondary structure, also called the lipid bilayer, which defines most phospholipid membranes found. ▶Membrane-Lipid Therapy

Laminin Signaling

Lamellipodia

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Laminin Signaling

Definition

R EUVEN R EICH

Areas at the edge of adherent cells that extend away from the cell body by the pushing of internal actin filaments as they polymerize. Flattened sheet-like structures composed of a crosslinked F-actin meshwork that project from the cell membrane. Often associated with the leading edge of migrating cells.

Department of Pharmacology, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel 2 Reuven Reich is affiliated with the David R. Bloom Center of Pharmacy at the Hebrew University

▶Cortactin ▶Migration

Laminin Definition LM are large, heterotrimeric, cruciform matrix glycoproteins composed of highly homologous α, β, and γ subunits. Five α (α1–5), four β (β1–4), and three γ (γ1–3) chains variably assemble to create 14 known isoforms that convey a variety of important biological functions. Specific LM isoform expression and posttranslational processing can directly influence cellular response to growth factors, intracellular signaling, cell proliferation, susceptibility to apoptosis and migratory capacity. Changes in LM isoform expression in vessel walls have been shown to foster angiogenesis as well as leakage in vessels, rendering them attractive to tumor cells and susceptible to metastatic invasion. Laminins are expressed in both normal and malignant tissue, but different specific isoforms predominate in each case. ▶Aging and Cancer ▶Laminin Signaling ▶Tissue Inhibitors Of Metalloproteinases

Laminin-Receptor Definition

Are proteins that bind ▶laminin and transduce a certain signal into the cell bearing the receptor. ▶Laminin Signaling

1

Definition

▶Laminins are a family of glycoproteins with an apparent molecular weight between 400 and 900 kDa. They are heterotrimers of three subunits, α, β, and γ held together by disulphide bonds to form triple helical coiled coil in a shape of a cross. Five α chains, three β chains, and three γ chains have been identified and by combination they assemble to form over 14 laminin isoforms that have different tissue distributions and functions. Laminins are essential for basement membrane assembly, promote cell attachment and ▶angiogenesis, induce neurite outgrowth, affect gene expression and are involved in cell proliferation, migration, and differentiation. Biochemical dissection related some of the laminin functions to specific parts of the glycoproteins. It appears that different parts in the molecules have different effects on cells. Some of these parts are cryptic and interact with cells only after proteolytic cleavage of the laminin molecules. In vitro, most structural and functional studies have been performed on laminin-1 (α1β1γ1).

Characteristics Laminin Signaling Laminins activate various ▶signal transduction pathways. It was shown that ▶chemotaxis induced by laminin-1 is pertussis toxin sensitive, indicating on the involvement of a pertussis toxin-sensitive G protein in the process, while ▶haptotaxis seems to involve a different mechanism. It was shown that human osteoclast-like cells selectively recognize laminin isoforms. The cells adhered to laminin-2 but not to laminin-1, and a sharp increase in intracellular Ca2+ was detected upon addition of soluble laminin-2 to the cells. Another study showed that laminin-1 induced a rapid and transient mRNA expression of c-fos and c-Jun in PC12 cells, and stimulated the DNA binding activity of the complex of these proteins to the ▶AP-1 site. In tumor cells, addition of laminin-1 resulted in a time- and dose-dependent activation of phospholipase D (PLD) followed by generation of ▶phosphatidic acid that is involved in signal transduction events leading to the induction of ▶MMP-2 and enhanced invasiveness of metastatic tumor cells. This effect of laminin-1 was not seen in normal cells in vitro. Laminins’ signaling has

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been shown to involve kinase/phosphatase cascades since bound laminin-1 and laminin-5 induce protein ▶dephosphorylation in neural cells during process formation. A recent study performed in our laboratory showed that mitogen activated protein kinases (▶MAPK) are involved in laminin signaling. Addition of exogenous soluble laminin-1 resulted in a significant decrease in the ▶phosphorylation (activation) of ERK, JNK, and p38 after 30 min of incubation. This laminin-induced dephosphorylation of all MAPK was dose-dependent and transient. Another study demonstrated that incubation of macrophages with a peptide from the laminin-α1 chain, but not intact laminin-1, triggered protein kinase C-dependent activation of ERK1/2, leading to upregulation of proteinase expression. Several recent studies using laminin-5 have shown activation of ERK1/2 via focal ▶adhesion kinase (FAK), while other studies have shown activation of Rac1 via phosphoinositide 3 kinase (PI3K). Although some functions may be common to all laminin variants, other may be unique and isoform-specific, depending on the tissue or organ in which they are expressed. In addition, various signal transduction pathways may be activated by different ▶laminin receptors. Laminin Receptors The biological effects of laminins are mediated by numerous laminin receptors that are divided into two major groups: ▶integrin and nonintegrin receptors (Table 1). Integrins Integrins are a large family of cell-membrane receptors for extracellular matrix proteins (Table 1). Integrins are heterodimeric combination of various α-subunits with various β-subunits. The ligand specificity for different integrins can be altered depending on the type of divalent cation present, the surrounding lipid environment, and various cell-specific factors. Inside

the cell, the short cytoplasmic domains of integrins associate with various cytoskeletal proteins that mediate integrin signal transduction. At least eight integrins bind laminin; some of them bind additional extracellular matrix components as well. Integrins recognize mainly laminin-α chains and hence determine cell adhesion and response to laminin isoforms. Two possible integrin-related signal transduction pathways have been identified. First is direct signaling, where binding to integrins by extracellular proteins triggers intracellular signaling events. The second is integrin modulation of mitogen-initiated signaling; in this case, integrin-mediated cell anchorage influences signaling pathways activated by growth factors. In general, integrin direct signaling activates FAK, small GTPases of the ▶Rho family, and MAPK, resulting in accumulation of highly ▶phosphorylated proteins and cytoskeletal molecules at the adhesion sites. Binding to integrins is followed by receptor clustering that initiates activation and autophosphorylation of FAK. Tyrosinephosphorylated FAK can recruit Src family kinases to focal contact sites. This sets up additional tyrosine phosphorylation of proteins such as cytoskeletal proteins and adaptor proteins such as Grb2. Small GTPases of the Rho family (Rho, Rac, and Cdc42) are involved in ▶integrin signal transduction and affect cytoskeleton arrangement. Rho contributes to cell adhesion to extracellular matrix. Rac and Cdc42, via PI3K, mediate the increase in cell motility and invasiveness induced by the integrin. Some integrins activate MAPK cascades. For example, laminin binding to the integrin α6β4 results in activation of an associated kinase and consequently tyrosine phosphorylation of the β4-subunit cytoplasmic domain, followed by association of the adaptor protein Shc with tyrosine-phosphorylated β4 integrin subunit. Shc is then phosphorylated on tyrosine residues, presumably by an integrin-associated kinase, and combines with the adaptor protein Grb2 which exists in a complex with the ras GTP exchange factor

Laminin Signaling. Table 1 Laminin receptors and their additional ligands Receptor Integrins α1β1 Integrins α2β1 Integrins α3β1 Integrins α6β1 Integrins α6β4 Integrins α7β1 67 kDa laminin receptor Dystroglycan Heparan sulfate

Ligands Collagen (I,II,IV), laminin (1, 2) Collagen (I,II,IV), laminin (1, 2), chondroadherin ▶Fibronectin, collagen (I), laminin (2, 5, 8, 10, 11), nidogen, epiligrin, perlecan Laminin (1, 2, 5, 8, 10, 11) Laminin (1, 2, 5, 10) Laminin (1, 2, 8, 10) Laminina Laminin (1, 2), agrin, perlecan Laminin (1, 2), collagen XVIII

Laminin-4 receptor interactions presumed to be similar to those of laminin-2. a Most studies on laminin-1.

Laminin Signaling

SOS. This leads to Ras activation followed by activation of a kinase cascade consisting of Raf, MEK (MAPK/ ERK kinase), and ERK, resulting in increased cell motility and proliferation. In addition, integrin α6β4 activates the JNK cascade, via Rac1, resulting in jun protein expression. Jun associates with fos, whose expression is induced by ERK cascade, to form the AP-1 transcription factor. In human hepatocellular carcinoma cells, laminin-binding integrin α6β1 stimulation resulted in FAK tyrosine phosphorylation, leading to FAK–GRB2 association and ERK cascade activation, which promotes tumor cell migration. Interestingly, aggregation of integrin receptors, even in the absence of ligand occupancy, is sufficient to induce a prompt transmembrane accumulation of at least 20 signal transduction molecules, including Src, Rho, Rac1, Ras, ERK1/2, and JNK. Nonintegrin Receptors The 67kDa laminin receptor is a nonintegrin receptor. A highly conserved 37 kDa protein is the precursor of the receptor, but the exact manner by which it configures its mature form is not clear. The amino acid sequence of the 37 kDa precursor is extremely well conserved through evolution, however, it corresponds to that of additional proteins, suggesting a multifunctional protein. The cDNA of the 37 kDa precursor is virtually identical to a cDNA encoding the ribosomal protein p40. In addition, the 37 kDa precursor acts as a receptor for cellular prion protein and is involved in the life cycle of prions. It has also been found that the 37 kDa precursor is identical to the oncofetal antigen protein that is expressed by tumors. The 67 kDa laminin receptor mediates cell attachment to laminin. Colocalization of the 67 kDa laminin receptor with the cytoskeleton constituents α-actinin and vinculin, and the focal adhesion plaque was found. The receptor is involved in several physiological processes such as implantation [56], invasive phenotype of trophoblastic tissue, angiogenesis, T-cell biology, and shear stress-dependent endothelial nitric oxide synthase expression. Increased expression of the 67 kDa laminin receptor correlates with cell proliferation, migration, and ▶invasion capacity. Clinical data suggest a correlation between 67 kDa laminin receptor expression in tumor cells and tumor progression. Expression of the receptor has been shown to be upregulated in neoplastic cells compared to their normal counterparts and directly correlates with an enhanced invasive and metastatic potential in numerous malignancies. Malignant ▶mesothelioma is one of the most aggressive human cancers, however, no tumor is less susceptible to distant ▶metastasis and still associated with such high mortality rates. In a recent study, we wound frequent expression of 67 kDa mRNA but very rare expression of the protein in clinical malignant

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mesothelioma samples in contrast to metastatic breast or lung carcinomas. These findings suggest that the differences between malignant mesothelioma and carcinomas regarding expression of the 67 kDa laminin receptor may account at least in part for the reduced ability of MM to metastasize to distant organs, due to lack of the signaling mediated by the receptor. By stable transfection of A375SM melanoma cells, we established lines expressing reduced or elevated 67 kDa laminin receptor. We found that stable antisensetransfected cells that expressed reduced 67 kDa laminin receptor demonstrated significantly less aggressive tumor phenotype, as reflected by their reduced invasiveness through Matrigel, diminished attachment to laminin, and decreased MMP-2 expression and activity. Further, the basal phosphorylation extent (activity) of ERK, JNK, and p38 was significantly higher in cell lines expressing reduced 67 kDa laminin receptor, compared to parental cells. The increase in MAPK phosphorylation in cells expressing reduced 67 kDa laminin receptor was accompanied by a significant reduction in MKP-1 mRNA level and a significant increase in PAC-1 mRNA level. It seems that the 67 kDa laminin receptor induces downregulation of MKP-1 expression that may contribute to the reduced activity (dephosphorylation) of MAPK induced by the receptor, which is followed by an upregulation of PAC-1 expression, possibly as a negative feedback. 67 kDa Laminin Receptor and Integrins There are studies that indicate an association between the 67 kDa laminin receptor and the α6 integrin subunit that is a part of the laminin-binding integrins α6β4 and α6β1. Biochemical analyses indicate on coimmunoprecipitation of the 67 kDa laminin receptor with the α6 integrin subunit. Specific reduction of the α6 integrin subunit by an antisense was accompanied by a proportional decrease in the cell surface expression of the 67 kDa laminin receptor. Other studies targeting the 67 kDa laminin receptor, showed a significant reduction in one of the α6 integrin subunit isoforms. Analysis of α6 integrin subunit and of the 67 kDa laminin receptor in ▶ovarian carcinoma samples showed no statistical correlation between the two. ▶Dystroglycan Dystroglycan consists of two subunits, which are translated from a single mRNA as a propeptide that is proteolytically cleaved into two noncovalently associated proteins. Dystroglycan was originally isolated from skeletal muscle as an integral membrane component of the dystrophin–glycoprotein complex (DGC). The exact function of the entire DGC is not completely determined but evidence indicates that it confers structural stability to the sarcolemma during contraction. In fact, mutations in components of this complex

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lead to various types of muscle disorder such as Duchenne muscular dystrophy and limb-girdle muscular dystrophies. Dystroglycan is also expressed in many other cell types and it plays important roles outside skeletal muscle. It has been implicated in early mouse development, structure and function of the central nervous system, myelination and nodal architecture of peripheral nerves, epithelial morphogenesis, cell adhesion, synaptogenesis, and signaling. In addition, several extra- and intracellular proteins are less tightly associated with the DGC, such as nitric oxide synthase [nNOS], dystrobrevin, and laminin-2. Molecules that bind to the cytoplasmic tail of β-dystroglycan include the signaling molecule Grb2, components of the ERK– MAP kinase cascade including MEK and ERK, and rapsyn. Binding of laminin-2 to dystroglycan induces phosphorylation of Grb2 followed by Sos binding. This phosphorylation initiates activation of Rac1 pathway that is further followed by MAPK activation.

References 1. Aumailley M, Smyth N (1998) The role of laminins in basement membrane function. J Anat 193:1–21 2. Barresi R, Campbell KP (2006) Dystroglycan: from biosynthesis to pathogenesis of human disease. J Cell Sci 119:199–207 3. Ekblom P, Lonai P, Talts JF (2003) Expression and biological role of laminin-1. Matrix Biol 22:35–47 4. Givant-Horwitz V, Davidson B, Reich R (2005) Laminininduced signaling in tumor cells. Cancer Lett 233:1–10 5. Schneider H, Muhle C, Pacho F (2006) Biological function of laminin-5 and pathogenic impact of its deficiency. Eur J Cell Biol doi:10.1016/j.ejcb.2006.07.004

Langerhans Cell Definition

Langerhans’ cells are immature ▶dendritic cells found in skin containing Birbeck granules and expressing CD1a. They are the most efficient antigen processing and presenting cells of dendritic cell family. ▶Langerhans Cell Histiocytosis ▶Birbeck Granules

Langerhans Cell Histiocytosis A KIRA M ORIMOTO Department of Pediatrics, Kyoto Prefectural University of Medicine, Kyoto, Japan

Synonyms Histiocytosis X

Definition

▶Langerhans Cell Histiocytosis (LCH), previously referred to as Histiocytosis X, is a rare clonal disorder of Langerhans cell proliferation, involving the skin, bone and other organs. The disease family consists of the syndromes originally described as ▶eosinophilic granuloma, ▶Hand–Schüller–Christian disease, and ▶Letterer–Siwe disease. Modern classification of LCH consists of single-system versus multisystem and unifocal versus multifocal.

Langerhans, Islets of Characteristics Definition Are groups of specialized cells in the pancreas that produce and secrete hormones. Named after the German pathologist Paul Langerhans (1847–1888), who discovered them in 1869, these cells are arranged in groups that Langerhans likened to little islands in the pancreas. There are five types of cells in an islet: alpha cells that produce ▶glucagon, which raises the level of glucose (sugar) in the blood; beta cells that produce ▶insulin; delta cells that produce ▶somatostatin which inhibits the release of numerous other hormones in the body; and PP cells and D1 cells, about which little is known. Degeneration of the insulin-producing beta cells is the main cause of type I (insulin-dependent) diabetes mellitus.

Epidemiology Most patients diagnosed with LCH are children with a peak percentage of diagnoses occurring between 1 and 3 years of age. The incidence of LCH has been estimated to be five cases per million per year in children. It appears to be more common in boys than in girls (1.2–2:1). The incidence of LCH in adults is thought to be one-half of that in children. Development of the disease is usually sporadic; however, the fact that about 1% of patients have relatives with LCH and monozygotic twin pairs are concordant for LCH suggests a genetic predisposition. A higher frequency of malignant disorders has been reported in patients with LCH than in the normal population. Acute lymphoblastic leukemia is the most common malignancy preceding or co-occurring with LCH.

Langerhans Cell Histiocytosis

Etiology Whether LCH is a neoplasm or is reactive in nature has been a controversial issue. Pathological Langerhans cells (LCH cells) are monoclonal, and sometimes show chromosomal deletion or gain, suggesting a neoplastic etiology. While LCH lesions often regress spontaneously, there is no evidence that LCH cells are immortalized, supporting the possibility of a reactive nature. Although infection may play a role in the development or reactivation of LCH, no well-accepted environmental risk factors are associated with the disease, except for cigarette smoking in adult pulmonary LCH. It has been demonstrated that 77% of adult patients with LCH pulmonary lesions are smokers.

Pathophysiology LCH lesions not only contain LCH cells but also various inflammatory participants, including T lymphocytes, macrophages, plasma cells, eosinophils, osteoclast-like multinucleated giant cells and neutrophils. These cells stimulate each other to produce abundant cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-1, IL-2, IL-4, IL-5, IL-7, IL-10, transforming growth factor (TGF)-ß, ▶RANKL and ▶osteoprotegerin. This cytokine storm plays a role in the proliferation of LCH cells and of other infiltrating cells, and is responsible for the various clinical features of LCH. LCH cells in the bone, lymph node and some skin lesions contain immature ▶dendritic cells. These cells do not express CD83 or CD86, but do express intracellular the major histocompatibility complex (MHC) class II antigen. They also express the immature dendritic cell marker ▶CCR6 and produce the ligand for CCR6 (▶CCL20/MIP-3α) as well as ▶CCL5/ RANTES and ▶CXCL11/I-TAC. These ligands may play a role in recruiting eosinophils and CD4 positive T cells into the lesions, respectively. LCH cells show a greater proliferative capacity and a lower antigen presenting capability, suggesting maturation is arrested at an activated state. It is hypothesized that IL-10 as well as TGF-ß could be key factors in the inhibition of maturation of these cells.

Clinical Manifestations LCH affects a number of different organs, so clinical signs and symptoms may be extremely variable. Patients can present with either single-system or multisystem involvement. Single-system presentations most often occur in the bone with single-site or multifocal involvement, but can also occur in the skin. Most commonly, the initial manifestations include the occurrence of soft tissue mass, bone pain, skin rash and fever. Laboratory findings include normochromic and normocytic

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anemia and an elevated erythrocyte sedimentation rate. Elevations in IgM are also common. The bone is involved in about 80% of patients with LCH. The skull is most often affected followed by the extremities, ribs, spine, and mandible and maxilla. Osteolytic “punched out” lesions with sharp margins are typically seen on X-ray. Bone lesions may be asymptomatic or accompanied with pain and soft tissue swelling, which may cause compression of adjacent structures such as the optic nerve or the spinal cord. The clinical course of LCH when localized solely to the bone is generally benign and it sometimes resolves spontaneously over a period of months to years. However, it may result in permanent sequelae including the collapse of vertebral bodies, orthopedic deformities and growth impairment. Skin involvement is seen in approximately half of patients. Patients present with lesions that are seborrhea-like eruptions on the scalp or an erytematous rash on the trunk, abdomen and inguinal areas. Ulcerative lesions in the genital or inguinal region may also be present. There may be bleeding into the lesions, even in the absence of thrombocytopenia. Lymph nodes in the cervical, axillary and inguinal areas are most commonly affected. Rarely, the nodes can become massive and cause upper airway obstruction. Earinvolvement usually appears as an aural discharge caused by external otitis, which is often associated with the destruction of mastoid. Ossicle or vestibular damage of the middle ear may cause a loss of hearing. Hepatosplenomegaly occurs in 20% of patients with the infiltration of histiocytes into hepatic sinuses. Various degrees of liver dysfunction may appear, including hyperbilirubinemia, hypoproteinemia, hypoalbuminemia, elevation of γ-GTP, alkaline phosphatase and/or transaminases, ascites and edema. Histological examination of the liver shows portal infiltrates which can cause bile duct destruction and periportal fibrosis (sclerosing cholangitis) leading to biliary cirrhosis with portal hypertension and ultimately secondary hypersplenism. Pulmonary involvement in children is usually part of multisystem disease, but in adults the lung involvement may be solitary and frequently regresses after the cessation of smoking. The lung pathology is associated with tachypnea, dyspnea, cyanosis, cough, pleural effusion and recurring pneumothorax. High resolution computed tomography may reveal reticular or micronodular opacities as well as large nodules and honeycombing. Typical histological findings are alveolar destruction and diffuse interstitial infiltration of histiocytes. Pulmonary fibrosis develops in 10% of patients and can lead to respiratory failure. Hematopoietic involvement is seen in disseminated LCH and defined by anemia (hemoglobin < 10 g/dl in the absence of iron deficiency), leukopenia (leukocytes < 4.0 × 109/l) or thrombocytopenia (platelets < 100 × 109/l)

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with or without bone marrow involvement. In severe cases, serious anemia and thrombocytopenia may develop, often associated with a secondary hemophagocytic syndrome. Oral mucosa infiltration may appear as ulcerations or swelling of gingiva resulting in the loss of teeth. Infiltration of the small bowel may occur and cause malabsorption of nutrients. Diarrhea with blood and/or mucus suggests involvement of the colon. Occasionally the pancreas is also involved. In the central nervous system (CNS), infiltration and dysfunction of the pituitary gland and/or adjacent hypothalamus occurs in about 20% of cases in those with multisystem involvement. The most frequent manifestation is diabetes insipidus (DI), which may precede, co-occur, or follow other symptoms and signs of the disease. DI occurs more often among patients with skull involvement (known as “CNS risk lesions”). Infiltration of the anterior pituitary is less common and may cause growth retardation and panhypopituitarism. These pathologies usually develop in those with DI after a disease course of 10 years. Magnetic resonance imaging (MRI) findings of LCH involvement of the pituitary gland and the hypothalamus are demonstrated by the loss of the physiologic high intensity signal of the posterior pituitary lobe on T1-weighted images. There can also be thickening of the pituitary stalk or a hypothalamic mass. Progressive, degenerative CNS disease may develop over the years after onset of disease, often when the disease is considered quiescent. CNS involvement causes ataxia, tremor, dysarthria, dysphagia and hyperreflexia. Changes in personal behavior, judgment and cognitive function may also develop. In this case, MRI studies using T2-weighted or FLAIR images may reveal bilateral symmetric lesions in the cerebellar white matter and basal ganglia. Histologically, the neurodegenerative LCH is characterized by the presence of CD8 positive T lymphocyte infiltration, microglia activation, gliosis, neuronal and axonal destruction with secondary demyelination. There may be a lack of ▶CD1a positive LCH cells, as is seen in autoimmune encephalitis. Currently there is no established therapy for LCH-CNS disease. Pathology and Diagnosis A pathological examination is indispensable in the diagnosis of LCH. With hematoxylin-eosin staining, LCH cells have a distinctive homogeneously stained pink cytoplasm. The nuclei appear twisted with a longitudinal groove and a small nucleolus, often with a “coffee bean” appearance. Immuno-histochemical staining of ▶S-100 protein and ▶langerin (CD207) is helpful for detection of LCH cells. In active lesions of the disease, LCH lesions show granulomas caused by the aggregation of LCH cells as well as a number of

various inflammatory cells. A definitive diagnosis can be made by either positive staining for CD1a or electron microscopic demonstration of ▶Birbeck granules in the granulomatous lesional cells. In the later stages of LCH, macrophages are more predominant than LCH cells in the lesions, and xanthomatous and fibrotic changes are characteristic. It is not uncommon that lesions at different stages of disease may be mixed in the same organ simultaneously. Prognosis The clinical course of LCH varies quite widely depending on the extent of organ involvement. Multisystem disease can be separated into two categories based on whether or not “risk organs” are involved. Risk organs are defined as the liver/spleen, lung or the hematopoietic system. LCH may resolve spontaneously in patients with localized, unifocal disease. Patients with single-system disease or without risk of organ involvement have a mortality of less than 5%. Prognosis is worse in children with multisystem and risk organ involvement who often have fatal outcomes despite intensive treatment Mortality rates of 10–50% have been reported. Infants younger than 2 years at diagnosis tend to have risk organ involvement, more often than older children; however, a recent study revealed onset age itself is not a prognostic factor. A major, positive prognostic factor appears to be a favorable response to the first 6 weeks of systemic multi-agent chemotherapy. Patients without an initial response tend to have an extremely high mortality rate with reports of 15–70%. This is in contrast to that of less than 5% in patients with a good initial response. In adults, lung disease may be a life threatening complication; it has been reported to contribute to a mortality rate of approximately 25%. Reactivation can occur unpredictably in more than half of patients, even those treated with multi-agent chemotherapy. Reactivated lesions may sometimes resolve spontaneously but there is an increased risk of permanent sequelae. Treatment Treatment of LCH should be planned according to the clinical presentation and the extent of organ involvement. In single-system LCH, the major aims of treatment are to lessen symptoms and to reduce the chance of permanent sequelae. In the case of a single bone lesion without symptoms, a wait-and-see approach or diagnostic curettage is the standard method of care. Steroids may be used for symptomatic bone lesions. Systemic chemotherapy with vinca alkaloids and corticosteroids for 6 or 12 months could be applied for patients with CNS-risk lesions or multifocal symptomatic bone disease. Radical operation of jaw lesions is discouraged as this often results in disfigurement and loss of

Laparoscopy

teeth. Radiation is rarely used because of the reported increased risk of secondary tumors. When there is skin involvement only a wait-and-see approach is considered optimal. Alternatively, patients can be provided therapies such as topical corticosteroids or thalidomide. In patients with isolated pulmonary LCH with functional impairment, systemic chemotherapy is indicated to reduce further parenchymal destruction. In multisystem LCH, the major aims of treatment are to increase survival and to reduce the incidence of late sequelae. Systemic chemotherapy with vinca alkaloids and corticosteroids for 12 months is the most commonly used regimen. In cases with risk-organ disease, more aggressive chemotherapy combined with agents such as cytarabine (Ara-C), 6-mercaptopurine and methotrexate may be considered. Etoposide (VP-16) is no longer considered a reasonable therapeutic agent because there is no reported significant efficacy and it has been shown to cause therapy-related acute myeloid leukemia (t-AML). In patients with refractory progressive disease, myeloablative therapy with a combination of high dose Ara-C and cladribine (2-CdA) is currently being tested. Immuno-suppressive therapy with cyclosporin A, anti-thymocyte globulin or anti-TNF agent, and immuno-modulation agents like thalidomide, IFN-α or bisphosphonate are also used on an investigational basis. Allogeneic hematopoietic stem cell transplantation has proved to be efficacious in some cases. Additionally, liver or heart and lung transplants have been performed successfully in patients with end-stage organ involvement. Late Sequelae Permanent sequelae are common events in many LCH patients. They are most often the result of the infiltrative nature of the disease itself which causes tissue destruction and granulomatous fibrosis or gliosis of various tissues. Seventy percent of patients with multisystem disease and 25% of single-system disease patients suffer one or more life-long sequelae, including DI (24%), orthopedic problems (20%), hearing loss (13%), neurologic problems (11%), growth hormone deficiency, loss of teeth, pulmonary fibrosis and biliary cirrhosis with portal hypertension. t-AML may develop as a consequence of LCH treatment with chemotherapy, especially following the use of topoisomerase II inhibitors, such as VP-16. The cumulative incidence of t-AML in patients treated with VP-16 for LCH has been estimated to be around 1%. In addition, secondary solid tumors, particularly sarcomas and brain tumors may develop in irradiated areas.

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2. McClain KL (2005) Drug therapy for the treatment of Langerhans cell histiocytosis. Expert Opin Pharmacother 6(14):2435–2441 3. Savasan S (2006) An enigmatic disease: childhood Langerhans cell histiocytosis in 2005. Int J Dermatol 45 (3):182–188 4. Morimoto A, Ikushima S, Kinugawa N et al. (2006) Improved outcome in the treatment of pediatric multifocal Langerhans cell histiocytosis: results from the Japan Langerhans cell Histiocytosis Study Group-96 protocol study. Cancer 107(3):613–619 5. Donadieu J, Egeler RM, Pritchard J (2005) Langerhans cell histiocytosis: a clinical update. In: Weitzman S, Egeler RM (eds) Histiocytic disorders of children and adults; basic science, clinical features and therapy. Cambridge University Press, Cambridge, pp 95–129

Langerin Definition Is a cell surface receptor that induces the formation of the ▶Birbeck granule. ▶Langerhans Cell Histiocytosis

LAP Definition Latency-Associated Peptide. ▶Transforming Growth Factor Beta

Laparoscopy Definition

References

Examination of the abdominal and pelvic structures within the peritoneum using an illuminated tubular instrument, which is passed through the abdominal wall via a small incision. It can be used for diagnosis and for certain operations.

1. Henter JI, Tondini C, Pritchard J (2004) Histiocyte disorders. Crit Rev Oncol Hematol 50(2):157–174

▶Endometriosis

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Lapatinib

Lapatinib Definition

Is an anti-cancer drug, a ▶tyrosine kinase inhibitor of human ▶epidermal growth factor receptor type 2 (HER2, (synonym ▶HER2/neu, also epidermal growth factor receptor (EGFR). Lapatinib is active in combination with capecitabine in women with HER2positive metastatic breast cancer that has progressed after ▶trastuzumab-based therapy.

is just in the lung or has spread to other places), tumor size, the type of lung cancer, whether there are symptoms, and the patient’s general health. Patients unsuitable for surgery may be offered curative intent radiotherapy. ▶Adjuvant therapy may be given to more advanced resected cases. For late stage cases, chemotherapy with or without palliative radiotherapy are the conventional options, although the long term survival rates are very low.

Large Granular Lymphocyte Large Cell Calcifying Sertoli Cell Tumor

▶Activated Natural Killer Cells

Definition

LCCST; Is a rare type of ▶testis cancer.

Large Tumor Suppressor Gene ▶Lats in Growth Regulation and Tumorigenesis

Large Cell Medulloblastoma Definition Variant of medulloblastoma accounting ~5% of cases. Characterized by more abundant cytoplasm than seen in classic medulloblastoma and large areas of necrosis. ▶Medulloblastoma

Laryngeal Carcinoma C HARLOTTE J IN Departments of Clinical Genetics, University Hospital, Lund, Sweden

Definition

Large-Cell Undifferentiated Carcinoma Definition

About 10–15% of ▶lung cancer are this type. It can start in any part of the lung. It tends to grow and spread quickly. Non-small cell lung cancer is a common disease. It is usually treated by surgery (taking out the cancer in an operation) or radiation therapy (using high-dose x-rays to kill cancer cells). However, chemotherapy may be used in some patients. The prognosis (chance of recovery) and choice of treatment depend on the stage of the cancer (whether it

The vast majority of malignant neoplasms of the larynx arises from the surface epithelium and therefore classified as keratinizing or nonkeratinizing ▶squamous cell carcinomas (SCC). The other rare malignant forms include verrucous carcinoma, adenocarcinoma, fibrosarcoma, and chondrosarcoma. Histopathologically, laryngeal SCC can further be classified into: well differentiated (more than 75% keratinization), moderately differentiated (25–75% keratinization), poorly differentiated (1 cm in size) and they can be associated with symptoms related to the hypersecretion of the hormones originating from the tumor as well as symptoms of the intracranial mass and its extensions, such as headaches, visual field disturbance (from extension superiorly to the optic chiasm), and extraocular movement dysfunction (from extension laterally into the cavernous sinuses and impingement on the cranial nerves governing eye movement). In addition to these effects, growth hormone-secreting tumors may themselves cosecrete prolactin, suggesting somatotrophs (growth hormone-secreting cells) and lactotrophs may share common origins. Lactotrophic tumors (prolactinomas) themselves account for the majority of pituitary tumors (roughly 40% of all pituitary adenomas) and have an estimated prevalence of 100/million population. The vast majority of prolactinomas are adenomas. Prior to the sixth decade of life, prolactinomas are much more common in women (roughly 10:1 female:male), but the distribution between the sexes is roughly equal thereafter. Most prolactinomas in women (therefore most prolactinomas in general) are microadenomas (10 and Gleason score >7 are correlated with increased risk of extra-prostatic spread and are considered to be the key factors in determining the need for staging work-up. PSA levels 10 with high grade histology or DRE findings suggesting stage T3 disease should undergo staging CT scan and bone scan (Fig. 5). MRI is superior

1. Early localized disease (T1-2N0M0): A multitude of treatment modalities are available that include active surveillance, watchful waiting, radiation therapy, and surgery. (a) Active surveillance is a program of regular examinations and PSA and DRE monitoring to distinguish clinically insignificant cancers from life-threatening cancers with intent to administer curative therapy. Watchful waiting is defined as delaying active treatment until patient develops symptomatic disease progression in order to limit morbidity from the disease and therapy without the goal to administer curative treatment.

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Advanced age, significant comorbidities are indications for watchful waiting. A prospective, randomized clinical trial reported that patients with clinically localized prostate cancer managed with watchful waiting have significantly higher rates of local cancer progression, metastases, and death from prostate cancer than do those treated initially with radical prostatectomy. (b) External beam radiation treatment used with curative intent. Modalities include conventional external beam, conformal/IMRT external beam and ▶brachytherapy (Fig. 4). Randomized trials have found total androgen ablation should be combined with radiation for improved disease specific survival and increased time to recurrence in locally advanced cases. Complications from radiation include cystitis, proctitis, enteritis, impotence and urinary incontinence. Prostate cancer specific mortality can be estimated on the basis of pretreatment serum PSA, biopsy Gleason score, and clinical T category. The percentage of positive biopsies is an independent predictor of time to postoperative PSA failure after external beam radiotherapy. Nomograms have been developed that have excellent predictors for PSA failure after radiotherapy. (c) Radical prostatectomy is removal of the prostate and seminal vesicles and pelvic lymphadenectomy. For low stage, low PSA, well-differentiated tumors the lymph node dissection may be omitted. There are currently three approaches used to remove the prostate gland: the retropubic, perineal and laparoscopic or robotic assisted retropubic approach. Laparoscopic and roboticassisted prostatectomy are generally associated with decreased blood loss compared to the open technique. The following patient criteria are commonly used guidelines for patients to be candidates for radical prostatectomy regardless of the approach; age less than 70 years, few comorbidities, life expectancy >10 years, Gleason score ≤7 and PSA ≤10. Complications include impotence, incontinence and urethral stricture. Modifications to the classic technique to spare the neurovascular bundles has allowed improved potency and continence outcomes. Most recently, a study found that men whose PSA level increases by more than 2.0 ng/mL/year before the diagnosis of prostate cancer have an increased risk for death from prostate cancer despite undergoing radical prostatectomy. Important pathologic criteria that predict prognosis after radical prostatectomy are tumor grade, surgical margin status, presence of extracapsular disease, seminal vesicle invasion, and pelvic lymph node involvement. Nomograms have been developed that have

Prostate Cancer, Clinical Oncology. Figure 4 Prostate brachytherapy.

Prostate Cancer, Clinical Oncology. Figure 5 Staging bone scan.

excellent predictors for PSA failure after prostatectomy as well as adverse pathological outcomes if these tools are used pre-operatively. 2. Locally advanced disease (T3-4N0M0): Active surveillance is an option in highly selected patients but failures usually result due to relative aggressive nature of these tumors. Radiation options as for early disease. The most common approach is external beam radiotherapy combined with androgen deprivation. If brachytherapy is used, it is often combined with external beam and androgen deprivation and

Prostate Cancer, Clinical Oncology Prostate Cancer, Clinical Oncology. Table 1

The 1997 UICC/AJC TNM staging system

UICC/AJC 1997 T1a T1b T1c T2a T2b T3a T3b T3c T4a T4b N(+) M(+)

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Description Tumor incidental histologic finding in 5% or less of tissue resected and Gleason < 7 Tumor incidental histologic finding in more than 5% of tissue resected or Gleason ≥ 7 Tumor identified by needle biopsy due to elevation of PSA; tumors found in one or both lobes by needle biopsy, but not palpable or visible by imaging Tumor involves 1 lobe or less Tumor involves more than 1 lobe Unilateral extracapsular extension Bilateral extracapsular extension Tumor invades seminal vesicle(s) Tumor invades bladder neck, external sphincter, and/or rectum Tumor invades levator muscle and/or fixed to pelvic wall Involvement of regional lymph nodes Distant metastatic spread

patients receiving such multimodality radiation therapy display superior biochemical relapse free survival compared with those receiving surgery or brachytherapy alone. Surgery is usually not an option outside clinical trials and ▶neoadjuvent androgen deprivation therapy before radical prostatectomy does not appear to improve cancer-specific (PSA free) or overall survival. 3. Hormonally naïve metastatic disease: Radiation therapy as described above for patients with nodal only disease. When this is accompanied by long term androgen deprivation, up to 30% of patients may have a long terms disease free interval. In patients with metastatic disease to bone, medical (▶LHRH agonists ± anti-androgens) or surgical (bilateral orchiectomy) androgen ablation is the treatment of choice. Androgen ablation is associated with sexual dysfunction, osteoporosis, hot flashes, and cognitive function alterations. Serious liver toxicity is a possible side effect of all anti-androgens. Radiation therapy is used to palliate symptoms such as bone pain from metastatic deposits and neurologic symptoms secondary brain metastases or emergently in the setting of spinal cord compression (Fig. 5). Laminectomy or other orthopedic procedures can be used for pathologic fractures in the setting of bone metastases. 4. Hormonally refractory metastatic disease: Androgen ablation therapy can induce a prolonged response (several years) in most men with metastatic disease. However, in most patients the disease becomes ‘androgen independent’ and begins to grow despite androgen withdrawal. At this time, hormonerefractory prostate cancer is not curable. All the available forms of therapy are palliative, which means that they can be used only to slow the progression of the disease and to relieve symptoms.

Generally, for the patient who begins to fail hormonal therapy and has received combined hormonal therapy with an LHRH agonist and an antiandrogen or with an orchiectomy and an antiandrogen, antiandrogen withdrawal (stopping the antiandrogen) is undertaken. In many patients this will result in a short term decrease in serum PSA level. For patients who received LHRH agonist alone or orchiectomy alone, secondary forms of hormonal therapy may be considered, such as the addition of an antiandrogen or suppression of adrenal androgen synthesis. However, these clinical therapies are generally of limited benefit. Radiation therapy is used to help manage pain associated with the growth of bone metastases and this can be delivered via external beam therapy or osteomimetic radioisotopes (strontium-89 radionuclide) which tend to be absorbed into areas of bone remodeling such as is found in bone metastases. ▶Docetaxel (Taxotere) is a cytotoxic agent and induces apoptosis of cancer cells and has become the standard treatment for hormone refractory prostate cancer. Large phase III randomized trials have demonstrated docetaxel prolongs progression free and overall survival, improves pain, and improves quality of life. Newer experimental approaches such as ▶bisphosphonates, immunotherapeutics/vaccines, differentiation therapies, induction of ▶apoptosis and inhibition of angiogenesis are currently in clinical trials.

References 1. D’Amico AV, Chen MH, Roehl KA et al. (2004) Preoperative PSA velocity and the risk of death from prostate cancer after radical prostatectomy. N Engl J Med 351:125–135

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2. Fletcher SG, Mills SE, Smolkin ME et al. (2006) Casematched comparison of contemporary radiation therapy to surgery in patients with locally advanced prostate cancer. Int J Radiat Oncol Biol Phys 66:1092–1099 3. Gleason DF (1992) Histologic grading of prostate cancer: a perspective. Hum Pathol 23:273–279 4. Johansson JE, Andren O, Andersson SO et al. (2004) Natural history of early, localized prostate cancer. JAMA 291:2713–2719 5. Petrylak DP, Tangen CM, Hussain MHA et al. (2004) Docetaxel and Estramustine compared with Mitoxantrone and Prednisone for advanced refractory prostate cancer. N Engl J Med 351:1513–1520

Prostate-Specific Membrane Antigen Synonyms Glutamate carboxypeptidase II; NAALADase; folate hydrolase; PSMA

Definition Prostate-specific membrane antigen (EC 3.4.17.21), is a 750 amino acid, 100 kDa type II transmembrane glycoprotein that is highly expressed by normal prostate and ▶prostate cancer cells and by the neovasculature of many epithelial cancers. Due to this relative cancer restricted expression, PSMA-based imaging agents and PSMA-targeted therapies are under development.

Characteristics PSMA Expression PSMA is a type II transmembrane protein consisting of a small intracellular segment of 18 amino acids, a transmembrane domain, and an extensive extracellular domain that contains the catalytic site (Fig. 1). The extracellular domain of PSMA is highly glycosylated and ▶glycosylation is required for enzymatic activity. Human PSMA was originally isolated by the laboratory of Dr. Warren Heston from a cDNA library from the androgen responsive LNCaP human prostate cancer cell line and was later found to be located on chromosome 11p11–12. The entire sequence of PSMA contains 19 exons and has a modest degree of homology to at least four other human proteins: NLDL, NLD2, transferrin receptor (TfR) 1 and 2. Both TfR1 and PSMA are internalized into endosomes via cytoplasmic YXRF and MXXXL motifs, respectively. Whereas TfR1 delivers iron-loaded transferrin cells, it is currently not known whether PSMA may internalize ligands such as polyglutamated folate (a PSMA substrate). Immunohistochemical studies using monoclonal antibodies have demonstrated that PSMA is expressed by normal prostate epithelium and is even more highly

expressed by a large proportion of prostate cancers, including metastatic prostate cancers. Low-level detection of the PSMA protein has also been seen in the duodenal mucosa and in a subset of proximal renal tubules. PSMA enzymatic activity is also present in the brain. In all other human tissues, including normal vascular endothelium, PSMA expression was not detectable by ▶immunohistochemistry. The number of PSMA molecules per 10,000 actin molecules in prostate tissue is approximately 170, which is approximately 10–15-fold higher than expression in liver, kidney, and brain. As a comparison, the ratio of PSA per 10,000 actin molecules is 18,000. PSMA expression was also undetectable in other nonprostatic primary tumors. In multiple studies, however, PSMA expression has been detected in the neovasculature of a large number of different tumor types including breast, renal, colon, and transitional cell carcinomas. In contrast, PSMA expression was not observed in nontumor induced neovascularization associated with choroidal neovascular membrane development. Two regulatory elements controlling PSMA expression have been characterized: the proximal 1.2 kb PSMA promoter and a PSMA enhancer located within the third intron. This PSMA enhancer is activated in a prostate specific manner and is negatively regulated by the ▶androgen receptor. This negatively regulated enhancer seems to underlie findings from preclinical and clinical studies demonstrating that PSMA mRNA is upregulated upon androgen withdrawal. The PSMA structure revealed a twofold symmetric homodimer with overall structural similarity to the transferrin receptor. Unlike the transferrin receptor, PSMA possesses an enzymatically active protease domain containing a binuclear zinc site, catalytic residues, and a proposed substrate-binding arginine patch. Enzymatic Functions of PSMA In addition to its role as a tumor marker and imaging target, PSMA contains a binuclear zinc site and functions as a glutamate carboxypeptidase II possessing two discrete enzymatic functions. Initially, PSMA was demonstrated to possess the hydrolytic properties of an N-acetylated α-linked acidic dipeptidase (NAALADase). NAALADase is a membrane hydrolase activity that is able to hydrolyze the neuropeptide N-acetyl-l-aspartyll-glutamate (NAAG) to yield the neurotransmitter glutamate and N-acetyl-aspartate. In addition to the NAALADase activity, PSMA also functions as a pteroyl poly-γ-glutamyl carboxypeptidase (folate hydrolase). It is able to progressively hydrolyze γ-glutamyl linkages of both poly-γ-glutamated folates and methotrexate analogs with varying length glutamate chains. Mhaka et al. demonstrated that PSMA could also hydrolyze peptides containing both α- and γ-linked acidic amino

Prostate-Specific Membrane Antigen

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Prostate-Specific Membrane Antigen. Figure 1 Structure of PSMA with Filamin A (FLNa), J591, and Capromab monoclonal antibody binding sites indicated.

acids. This finding has implications for exploiting the enzymatic activity of PSMA for the design of prodrugs, in which an inactive aspartyl/glutamyl peptide is selectively cleaved from the prodrug by PSMA thereby activating the drug within the vicinity of PSMA expressing cells. The role that PSMA’s NAAG or folate hydrolase activity plays in the physiology of prostate cells is presently unknown. NAAG is an inhibitor of the NMDA ionotropic receptor and an agonist of the type II metabotropic glutamate receptor subtype 3. A breakdown of the regulation of glutamatergic neurotransmission by NAAG is implicated in schizophrenia, seizure disorders, Alzheimer’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. Thus, inhibition of PSMA potentially confers neuroprotection both by reducing glutamate and increasing –NAAG and has been shown to provide neuroprotection in cell culture and/or animal models of ischemia, diabetic neuropathy, drug abuse, chronic pain, and amyotrophic lateral sclerosis. Does PSMA have a Signaling Function? PSMA’s structural similarities with the transferrin receptor, its homodimeric membrane form, and its selective expression on tumor endothelial cells have raised questions whether PSMA may have a ▶signal transduction functionality in addition to its carboxypeptidase activity. Inhibition of PSMA activity in cell culture or in subcutaneously implanted PSMA expressing xenografts does not lead to inhibition of growth. However, Ghosh et al. demonstrated that ectopic expression of PSMA in human prostate cancer cells reduced the invasiveness of these cells while knockdown of PSMA expression or expression of mutant PSMA lacking carboxypeptidase function increased invasiveness. Thus, this study suggested that the

enzymatic activity of PSMA is somehow associated with pathways involved in promoting invasiveness. The cytoplasmic tail of PSMA interacts with the actin binding anchor protein Filamin a (FLNa) and this association appears necessary for PSMA localization to the recycling endosomal compartment. PSMA also binds to ▶caveolin-1 in human microvascular endothelial cells and undergoes internalization via a caveolae-dependent mechanism. These associations suggest a link between PSMA at the cell surface, internalization, and downstream signaling processes. ▶Angiogenesis is severely impaired in PSMA-null animals and this angiogenic defect occurs at the level of endothelial cell invasion through the extracellular matrix barrier. PSMA is a principal component of a regulatory loop that modulates ▶laminin-specific integrin signaling and GTPase-dependent, p21-activated kinase 1 (PAK-1) activity. PSMA inhibition, knockdown, or deficiency decreased endothelial cell invasion in vitro via ▶integrin and PAK whereas inactivation of PAK increased PSMA activity. This negative regulation appeared to be mediated by the cytoskeleton as the disruption of interactions between the PSMA cytoplasmic tail and FLNa decreased PSMA activity, integrin function, and PAK activation, while the inhibition of PAK activation enhances the PSMA–FLNa interaction and increased PSMA activity. These data suggest a model whereby PSMA participates in an autoregulatory loop, in which active PSMA facilitates integrin signaling and PAK activation, leading to both productive invasion and downregulation of integrin beta(1) signaling via reduced PSMA activity. While enzymatically active PSMA appeared necessary for this signaling, the role of PSMA hydrolysis of its putative ligands was not addressed in this study.

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PSMA and Imaging In contrast to other prostate-related antigens such as PSA, prostatic acid phosphatase, and prostate secretory protein, PSMA is a type II integral membrane cell surface protein that is not secreted and, therefore, is an excellent target for monoclonal antibody (mAb)-based imaging and therapy. PSMA is constitutively internalized, but internalization is also induced by antibody binding (). Initial validation of PSMA as an in vivo mAb target has been demonstrated by imaging trials with mAb 7E11/CYT-356 (marketed as ProstaScint, Cytogen, Princeton, New Jersey) an FDA approved imaging agent. 7 However, molecular mapping indicates that mAb 7E11/CYT-356 targets an intracellular portion of the PSMA molecule not exposed on the outer cell surface. Since the 7E11/CYT-356 epitope is within the cell, the mAb does not bind viable cells. ProstaScint has met with limited success in the clinic. ProstaScint scans are considerably less sensitive than bone scans at detecting bone disease. Since >80% of prostate cancer patients have metastatic disease in the bone, ProstaScint is not used routinely in the clinical evaluation of these patients. Thus, the only patients in whom clinically useful information is derived from a ProstaScint scan may be those in whom regional and/or systemic disease is demonstrated, and where a biopsy or other modality could confirm the findings were not a false-positive result. Given these limitations, the ProstaScint scan has not been used to any significant degree by clinicians in the work up of patients with suspected recurrent prostate cancer outside of the prostatic fossa. The recognition that ProstaScint recognizes an internal epitope of PSMA led to the development of a series of monoclonal antibodies to extracellular epitopes of PSMA that could bind to both intact and permeabilized cells. Researchers at Cornell University, led by Dr. Neil Bander, developed four IgG mAbs (J591, J415, J533 and E99) to the extracellular domain of PSMA. These antibodies demonstrated high affinity binding to prostate cancer cells in tissue culture, on tissue sections and in animal models in vivo 9,11. Moreover, once bound, PSMA antibody complexes were shown to be rapidly internalized with intracellular accumulation of Ab, resulting in the potential internalization of toxins or isotopes conjugated to the mAb. Clinical studies using humanized antibody (HuJ591) labeled with 111In, 90Y and 177Lu confirmed that mAb HuJ591 targeted and could image PSMA expressing human prostate cancer xenografts. Subsequently, several clinical studies have been performed evaluating efficacy of labeled humanized mAb to PSMA. 111 In-DOTA-huJ591 was tested in phase I trial with tumor visualization seen in both soft tissue and bone metastases. Additional phase I trials have been performed with 90Y and 177Lu DOTA-huJ591 conjugate and

demonstrated excellent imaging capabilities with detection of >95% of bone metastases. A few PSA responses were observed in these trials. With all three radiolabeled approaches, significant nonspecific accumulation of antibody uptake was observed in the liver and kidney in all studies. In each study, the doselimiting toxicity has been myelosuppression, particularly thrombocytopenia, which was most likely due to the long plasma half-lives of these antibodies. However, despite the theoretical advantage of targeting an extracellular PSMA epitope, a report describing initial experience with a technetium-99m-labeled J591 antibody found decidedly inferior prostate cancer imaging relative to ProstaScint. Encouraging results were reported using 11C or 125 I radiolabeled urea derivatives that have high affinity for PSMA to image in experimental models of prostate cancer in vivo. These low molecular weight compounds offer potential advantages over antibody-based imaging that include better tissue penetration, higher specificity, and shorter half-life. PSMA as a Therapeutic Target The demonstration of PSMA expression by tumor vasculature, high expression in prostate cancer, and upregulation in androgen ablated patients have made PSMA an attractive therapeutic target. Current targeting strategies include ▶immunotoxin conjugates, ▶cancer vaccines, PSMA inhibitor–drug conjugates, and PSMAactivated prodrugs/protoxins. As described, ▶radioimmunotherapy using the antiPSMA mAb coupled to radionuclides like 90Y and 177Lu has been tested in clinical trials. PSMA-based ▶monoclonal antibody therapy using the J591 antibody coupled to maytansinoid, a highly potent microtubule depolymerizing natural product (MLN2704) has been tested clinically. This agent showed antitumor response against PSMA producing human prostate cancer xenografts and has been evaluated in a phase I trial in 23 patients. Overall, MLN2704 was well tolerated in the majority of patients and two patients had a >50% decline in PSA from baseline. Further studies with this antibody–toxin conjugate are anticipated. In addition, a number of groups have described PSMA-based vaccine strategies that range from PSMA-primed dendritic cells to injection of naked human and mouse DNA. Since PSMA is a carboxypeptidase, a large number of PSMA inhibitors have been generated. While these inhibitors show some promise in neurologic diseases, to date no antitumor effect from direct inhibition of PSMA has been reported. However, strategies involving coupling of PSMA inhibitors or PSMA-binding moieties such as ▶aptamer bioconjugates or peptides to cytotoxic agents are under exploration. Prodrug and protoxin strategies attempt to take advantage of the unique enzymatic activities of PSMA to selectively

Protease Activated Receptor Family

activate cytotoxic agents within the peritumoral extracellular fluid surrounding PSMA producing cells. Unlike antibody and other PSMA-binding strategies, an advantaged of this ▶targeted drug delivery approach is that drug/toxin release in the extracellular fluid is amplified by PSMA’s activity. In addition, since every cell does not need to produce PSMA to be killed this approach overcomes potential resistance based on heterogeneous expression of PSMA while, at the same time, producing a substantial bystander effect. Finally, PSMA targeted cytotoxins may also function as ▶vascular disrupting agents and have therapeutic potential against a variety of solid tumor types expressing PSMA in the neovasculature.

References 1. Ghosh A, Heston WD (2004) Tumor target prostate specific membrane antigen (PSMA) and its regulation in prostate cancer. J Cell Biochem 91:528–539 2. Davis MI, Bennett MJ, Thomas LM et al. (2005) Crystal structure of prostate-specific membrane antigen, a tumor marker and peptidase. Proc Natl Acad Sci USA 102:5981– 5986 3. Heston WDW (1997) Characterization and glutamyl preferring carboxypeptidase function of prostate specific membrane antigen: A novel folate hydrolase. Urology 49 (Suppl 3A):104–112 4. Rajasekaran AK, Anilkumar G, Christiansen JJ (2005) Is prostate-specific membrane antigen a multifunctional protein? Am J Physiol Cell Physiol 288:C975– C981 5. Bander NH (2006) Technology Insight: monoclonal antibody imaging of prostate cancer. Nature Clin Practice Urol 3:216–225

Protease Activated Receptor Family V ILLARES GJ, Z IGLER M, B AR-E LI M ENASHE Department of Cancer Biology, The University of Texas, M.D. Anderson Cancer Center, Houston, TX, USA

Definition The Protease Activated Receptors (PARs) are a group of seven transmembrane ▶G protein-coupled receptors with a unique mechanism of activation. Most receptors are activated when the ligand binds to the ligand binding domain of that receptor. However, the different ▶serine protease ligands that activate PAR will cleave the N-terminus of the receptor. This results in the formation of a new N-terminus peptide which acts as a tethered ligand that will now bind to the activation site of the receptor and cause irreversible activation of PAR (Fig. 1).

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Characteristics To date, there are four members of the PAR family that have been identified. PAR-1, PAR-3 and PAR-4 are activated by thrombin although other proteases can cleave these receptors. PAR-2 is activated by trypsin like proteases including trypsin and tryptase. Studies on PARs have been performed most extensively with PAR-1 and to a lesser degree with PAR-2. However, the role and importance of PAR-3 and PAR-4 have yet to be fully understood in cancer. Therefore, only the role of PAR-1 and PAR-2 in cancer will be discussed. PAR-1: PAR-1, also known as the thrombin receptor, was the first family member to be discovered. It is expressed on a wide variety of cells including endothelial, epithelial, T-cells, astrocytes, neurons and platelets. It can be activated by thrombin as well as coagulation factor Xa, ▶granzyme A, trypsin and ▶matrix metalloprotease 1 (MMP-1) although thrombin is the most potent activator. The role of PAR-1 in platelet aggregation and degranulation has been extensively studied. In cancer, studies have shown that activation of coagulation factors, including thrombin, ▶tissue factor and ▶fibrinogen, is a common occurrence. In fact, activation of PAR-1 leads to induction of G proteins that trigger various downstream molecules and signal transduction pathways such as Rho kinase, phosphoinositol-3-kinase (PI3-K) and ▶mitogen-activated protein kinases (MAPK), which have been shown to be involved in cell growth, tumor promotion and carcinogenesis. Activation of PAR-1 has also been implicated in secretion of many factors involved in angiogenesis and tumor cell invasion such as interleukin 8 (IL-8), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), urokinase plasminogen activator (uPA), and MMP-2 (Fig. 2). Therefore the thrombin receptor has been implicated in tumorigenesis and metastasis of several human cancers including melanoma, breast, prostate, pancreatic, lung and colon carcinomas among others. PAR-2 is the second member of the PAR family to be discovered. Similar to other PAR family members, activation of PAR-2 occurs through the cleavage of the extracellular domain which forms a tethered ligand followed by downstream signaling. In contrast to other PAR family members, PAR-2 is activated mostly by trypsin which is the most potent protease, as well as by other trypsin-like proteases such as tryptase and factor Xa. PAR-2 can also be activated by PAR-1 and therefore, indirectly by thrombin. Data also suggests that the tethered ligand domain from activated PAR-1 can trans-activate PAR-2 when both receptors are present on cells in close proximity to one another as occurs on endothelial cells. This trans-activation of PAR-2 might enhance the response of cells to thrombin. In addition, tissue factor (TF) which has been found to be activated in cancer, can indirectly activate PAR-2

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Protease Activated Receptor Family. Figure 1 PAR-1 is cleaved by proteases such as thrombin at Ser 41 resulting in formation of a new N-terminus pepide. This tethered ligand binds to the activation site of PAR-1 causing its activation and downstream signaling.

Protease Activated Receptor Family. Figure 2 Schematic of cell invasion and angiogenic molecules involved in tumor progression via activation of PAR-1 in melanoma cells. The tumor-promoting signals transduced by PAR-1 through G proteins upregulate molecules involved in invasion and angiogenesis, including uPA, IL-8, VEGF, PDGF, MMP-2, and integrins.

Protease Activated Receptor Family

through components of the coagulation cascade. TF binds factor VIIa which can either directly activate PAR-2 or cause activation of factor X thereby mediating cleavage of PAR-2. Another manner of activation of this receptor is mediated through membrane type serine protease-1(MT-SP1), an enzyme which has been found on tissues that also express PAR-2. MT-SP1 can directly cleave PAR-2 thereby causing its activation. PAR-2 activation induces the release of IL-6 and IL-8, granulocyte macrophage-colony stimulating factor, prostaglandins and intracellular calcium mobilization. In fact, it has been suggested that trypsin and PAR-2 act in an autocrine loop to activate signal transduction pathways, promoting cell proliferation invasion and metastasis. In-vitro studies have shown that activation of PAR-2 causes an induction of different signaling pathways that induce proliferation, migration, invasion and metastasis. PAR-2 also contributes to reorganization of the cytoskeleton in a different manner than PAR-1 thereby elucidating different functions of these two receptors in cell migration. PAR-2 is also involved in integrin activation by promoting integrin α5β1 dependent cell adhesion. PAR-2 is highly expressed in different tissues such as colon, liver, pancreas, stomach and small intestine. It is also expressed in a wide variety of cells such as endothelial cells, T cells, smooth muscle cells and surface epithelial cells. Both PAR-1 and PAR-2 are expressed in tumor cells and in the tumor microenvironment and contribute to tumorigenisis and metastasis. PAR-2 is expressed in tumors such as lung, colon, pancreas, stomach and melanoma. However, the role of PAR-2 in cancer has not been completely elucidated. Melanoma In human melanoma cells, thrombin acts as a growth factor and is ▶mitogenic, suggesting that signaling by PAR-1 is involved in the biological response of these cells. Thrombin sources not only include systemic activation of coagulation factors seen in many cancer types but also several studies have shown that tissue factor can be expressed independent of the coagulation pathway in malignant melanoma cells thereby activating thrombin. Furthermore, fibrin deposits are formed from the cleavage of fibrinogen by thrombin. These fibrin deposits in the stromal microenvironment surrounding tumor cells may store active thrombin that is released when the clots undergo degradation. PAR-1 has been found to be differentially expressed within human melanoma cell lines. Highly metastatic melanoma cells have over-expression of PAR-1 mRNA, while non-metastatic melanoma cells have lower levels. Over-expression of the thrombin receptor has also recently been found in clinical specimens of invasive melanoma and metastases as compared to levels found in ▶common melanocytic nevi and normal

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skin. In-vitro studies have shown that when PAR-1 expression is induced in non-metastatic melanoma cells that normally have low levels of PAR-1, they acquire a more invasive and aggressive phenotype. Furthermore, there is evidence that demonstrates a physiological role for PAR-1 in the melanoma metastatic cascade where PAR-1 was the rate limiting factor in an experimental murine lung metastasis assay. It has been recently proposed that in highly metastatic melanoma cell lines, cell migration requires activation of PAR-Z, in addition to PAR-1, and results in enhanced metastasis by promoting cell motility. In-vivo experiments demonstrated that PAR-2 activation by trypsin or by agonist peptide in highly metastatic melanoma cell lines have more lung metastasis as compared to those cells not exposed to these agonists. Breast Cancer The levels of PAR-1 expression on tumor cells directly correlates with the degree of invasiveness and therefore metastatic potential in both primary breast carcinomas and established breast cancer cell lines. The more metastatic breast cancer cell lines expressed very high levels of PAR-1, while the minimally invasive lines showed minimal expression of PAR-1. In human specimens, high grade ductal carcinoma in-situ (DCIS) showed expression of the thrombin receptor while the highest levels of PAR-1 were found in infiltrating ductal carcinoma. In contrast, undetectable levels of PAR-1 were found in low grade DCIS and normal breast tissue. In-vitro studies revealed increased levels of migration and invasion in a null PAR-1 breast cancer cell line transfected with PAR-1. These cells expressing PAR-1 were examined in a mouse ▶xenograft model for human breast cancer which showed increased tumor growth and invasion in nude mice. Recent findings have demonstrated that MMP-1, a collagenase of the MMP family, which is found in the stromal tumor microenvironment, is an additional proteolytic activator of PAR-1 promoting invasion and tumorigenesis of breast cancer cells. A new study on breast cancer suggests that PAR2 has a significant role in induction of migration and invasion. In this study, an invasive breast cancer cell line transfected with PAR-2 siRNA showed a decrease in both migration and invasion comparable to cells that were transfected with PAR-1 siRNA. Prostate Cancer PAR-1 expression has been found in prostate cancer cell lines. Over-expression in highly invasive prostate cancer cell lines correlates with increased metastatic potential. Recently clinical specimens were analyzed for expression of PAR-1. Advanced stage prostate cancer tissue specimens had significantly higher expression of PAR-1 as compared with tissue from early stage patients. PAR-1 expression of the activated

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receptor in the vasculature from benign prostatic hyperplasia (BPH) tissue was also compared with early stage and advanced stage prostate cancer specimens. BPH tissue showed very low expression of PAR-1 with the most expression being found in advanced stage prostate cancer specimens. Early stage cancer also showed positive expression of the thrombin receptor but less than advanced stage cancer. Furthermore, prostate cells from bone metastases have higher expression of PAR-1 than those from soft tissue metastasis. Bone metastasis from prostate cancer is a common feature of prostate cancer and a significant cause of morbidity. These data suggest that PAR-1 plays a pivotal role in the progression of prostate cancer. Pancreatic Cancer In-vitro studies have shown that pancreatic cancer cell lines express PAR-1 while no expression is seen in normal pancreatic epithelial cells. Higher levels of PAR-1 mRNA were seen in pancreatic cancer tissue samples as compared to healthy pancreas which suggests that PAR-1 could play a key role in the pathogenesis of pancreatic cancer. PAR-2 might play a unique role in pancreatic cancer since the pancreas is a major site of production of the trypsin ▶zymogen (trypsinogen) by the ▶acinar cells. Studies have also proposed that it is produced by pancreatic cancer cells. It has been shown that PAR-2 is highly expressed in the pancreas and in pancreatic ductal carcinoma. In vitro studies suggest that trypsin might act as a stimulating growth factor in pancreatic cancer cells expressing PAR-2 thereby inducing proliferation and invasion. Examination of pancreatic cancer tissues, have shown that in tissues with infiltrative growth patterns, PAR-2 expression was higher than in tissues with expansive growth patterns. Moreover, a correlation between fibrosis, which is one of the characteristics of human pancreatic tumors that is linked to poor prognosis and high expression of PAR-2, exists in pancreatic tumors. Therefore, PAR-2 might also be involved in induction of fibrosis. Lung Cancer PAR-1 is highly expressed in the lung alveolar wall tissue of patients with lung adenocarcinoma when compared to those tissues without neoplastic cells. In a recent study, more than half of all specimens of nonsmall-cell lung cancer (NSCLC) patients also showed over expression of PAR-1. A higher and more uniform expression of the receptor was detected in aggressive tumors as compared to those with a more favorable outcome. In fact, the 3 year survival for patients expressing PAR-1 was significantly shorter than those with no expression of PAR-1. These data suggest that PAR-1 might represent a new prognostic factor in NSCLC patients.

Colon Cancer PAR-1 has also been found to be expressed in human colon cancer cell lines and clinical specimens but is absent in epithelial cells from normal human colon. It is present in dysplastic mucosa and cancer mucosal tissues but not in the adjacent normal mucosa. In-vitro studies revealed that thrombin can act as a growth factor for colon cancer cells. Thrombin induces cell migration and proliferation of human colon cancer cells through PAR-1 in a similar manner seen with a PAR-1 agonist. This effect in part is due to the activation of the MAPK pathway by thrombin and its receptor. In colorectal cancers (CRC), PAR-2 has been shown to be over expressed and its activation may promote both tumor progression and metastasis. It has been shown that in a colon carcinoma cell line, PAR-2 activation results in cell proliferation. Upon proteolysis of PAR-2 by trypsin, a signal transduction pathway is activated by the phosphorylation of MEK1/2 and ERK1/2 leading to proliferative response. This might indicate a significant role of MAPK pathway activation through PAR-2 in CRC. Furthermore, activation of PAR-2 can lead to activation of MMPs which promotes invasion and metastasis. MMP activation causes release of TGF-α which triggers activation and phosphorylation of EGFR, promoting proliferation.

References 1. Boire A, Covic L, Agarwal A et al. (2005) PAR1 is a matrix metalloprotease-1 receptor that promotes invasion and tumorigenesis of breast cancer cells. Cell 120(3):303–313 2. Ikeda O, Egami H, Ishiko T et al. (2003) Expression of proteinase-activated receptor-2 in human pancreatic cancer: a possible relation to cancer invasion and induction of fibrosis. Int J Oncol 22(2):295–300 3. Kaushal V, Kohli M, Dennis RA et al. (2006) Thrombin receptor expression is upregulated in prostate cancer. Prostate 66(3):273–282 4. Macfarlane SR, Seatter MJ, Kanke T et al. (2001) Proteinaseactivated receptors. Pharmacol Rev 53(2):245–282 5. Tellez C, Bar-Eli M (2003) Role and regulation of the thrombin receptor (PAR-1) in human melanoma. Oncogene 22(20):3130–3137

Protease Activated Receptors B AR-S HAVIT, R ACHEL Department of Oncology, Hadassah-University Hospital, Jerusalem, Israel

Synonyms PAR1; Thrombin-receptor

Protease Activated Receptors

Definition

▶Protease Activated Receptors (PARs) form a family of seven transmembrane ▶G- protein coupled receptors consisting of 4 gene members. PAR1, 3 and 4 respond to the serine protease thrombin while PAR2 is activated by trypsin, tryptase and the coagulation factors VIIa and Xa, but not by thrombin. All members are uniquely activated via proteolytic cleavage that exposes an otherwise hindered ligand at their N-terminus extra cellular portion. PARs can be viewed as receptors that carry their own ligands. In addition to thrombin, PARs convey cellular responses to a wide spectrum of serine proteases as also the ▶matrix metallo protease 1, MMP1. PARs1-4 are similarly organized, all encoded by two exons and separated by an intron of variable size. Exon 1 encodes a signal peptide, and exon 2 encodes the mature receptor protein. In humans, PARs1-3 are localized on chromosome 5q13.

Characteristics Protease Activated Receptors (PARs) belong to the large group of ▶G-protein coupled receptors (GPCRs) of seven transmembrane domain proteins, uniquely activated by proteolytic cleavage. While originally established as thrombin receptors, they serve nonetheless as cell surface sensors that convey signaling to an array of serine-proteases and a matrix metallo protease, MMP-1. In addition to their critical roles in thrombosis, hemostasis, inflammation and vascular biology, PAR1 emerges with considerable assignments in tumor biology (▶Epithelial tumors) and ▶angiogenesis. PARs possess an unusual mode of activation. These receptors carry their own ligand/s, hindered in the non-activated state and exposed after proteolytic cleavage at their N-terminal, extra cellular portion. Once exposed, the ligand remains tethered and interacting with loop number two and initiates cell signaling. Alternatively, proteolytic cleavage can be bypassed by ectopic application of a synthetic peptide representing the internal ligand sequence that directly associates with loop number two for cellular signaling. The mechanism of PAR1 activation is striking also because of its shut-off mechanism. PARs are irreversibly activated and their desensitization and cell trafficking control, in part, the magnitude and duration of PARs signaling. Human PAR1, PAR3, and PAR4 are all activated by thrombin. In contrast, PAR2 is activated by trypsin and tryptase as well as by coagulation factors VIIa and Xa, but not by thrombin. PAR1 is the first and prototype member of the family, originally discovered in a search for a functional receptor that confers thrombin signaling in human platelets. PAR2 was next identified in a screen of a mouse genomic library using probes homologous to the transmembrane regions of substance K receptor. Studies in PAR1 knock-out mice showed fifty percent

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lethality with no effect on thrombin signaling in mice platelet, but abrogated thrombin signaling in fibroblasts. These unexpected findings initiated the exploration and identification of PAR3 and PAR4. The latest family members revealed a selective expression pattern in human and mice platelets. While PAR1 and PAR4 are the functional receptors of thrombin in human platelets, PAR3 and PAR4 are responsible for thrombin signaling in the mice platelets. The notion that hPar1 is one of a series of genes that are part of an invasive program stems from studies showing that hPar1 expression correlates directly with the invasion properties of breast carcinoma (Fig. 1) and of trophoblast placenta physiological invasion into the uterine decidua. In fact, hPar1 plays an active role in breast carcinoma invasion because antisense silencing of the gene abrogates efficiently metastatic breast carcinoma cells (▶Breast cancer) from invading Matrigelcoated filters, in vitro. PAR1 expression is found high in a wide spectrum of ▶epithelia malignancies (e.g., colon, breast, prostate, ovary, esophagus, pancreas, etc) as compared to no expression in normal epithelia shown both in a collection of tissue biopsy specimens and differentially metastatic cell lines. In prostate cancer (▶Prostate cancer clinical oncology) PAR1 has been implicated in bone metastasis and the over expression of PAR1 in murine and human melanoma have yielded enhanced experimental lung metastasis in mice. In colon cancer PAR1 has been demonstrated to cross talk with EGFR, thereby promoting cell proliferation. In parallel, a cDNA expression library screen based on the loss of anchorage-dependent growth and focus-forming activity in NIH3T3 cells have identified PAR1 as a novel ▶oncogene. With these observations, PAR1 joins other GPCRs, encoded by mas and g2a, that behave as oncogene. The oncogenic properties of PAR1 accompany a collection of data showing that hPar1 is over expressed in a wide range of epithelial tumors, pointing altogether to the central role of PAR1 in carcinoma invasion. PAR1 has been shown to promote tumor progression through several mechanisms on different levels. PAR1 has been shown to promote cell growth, invasion, and metastasis, and also contribute to tumor cell survival by preventing the apoptotic pathway. In a xenograft nude mice model, it was demonstrated that the expression of PAR1 in non invasive MCF7 breast carcinoma is sufficient to promote growth and invasion. In contrast, when a truncated form of hPar1, devoid of the entire cytoplasmic tail, is introduced to MCF7 cells and injected to the mice mammary fat pads, tumor development was markedly attenuated (Cohen I and Bar-Shavit R manuscript in preparation). This outcome underscores the significance of PAR1 signaling in tumor progression and invasion.

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Protease Activated Receptors. Figure 1 Schematic illustration of PAR1 pattern of expression, along the progression of epithelia malignancy. While no PAR1 is seen in either normal or dysplastic tissues, PAR1 expression is high in DCIS (ductal carcinoma in situ) IDC (invasive ductal carcinoma).

Since PARs are irreversibly activated, signaling must be tightly regulated. Part of this regulation is the extent and mode of cell surface receptor internalization targeted to lysosomal degradation. Cellular trafficking of the proteolytically activated PARs leads to its desensitization, thereby controlling the magnitude, duration and spatial aspects of receptor signaling. In breast carcinoma, in addition to PAR1 over expression, these cells display aberrant PAR1 trafficking, which causes persistent signaling and cellular invasion. Tissue factor is also up regulated in many tumor cells and supports FVIIa and FXa activity. TF bound to FVIIa can activate PAR2, whereas FXa can signal through either PAR1 or PAR2. There is increasing evidence that PAR2 is also an important mediator of tumor progression. Trypsin, a potent and physiological activator of PAR2, is elevated in gastric, colon, ovarian and lung tumors. To gain further insight into the causal relationship between hPar1 expression, breast tumor formation and mammary gland development, a line of mice carrying MMTV-driven hPar1 designated to over express in the mammary glands was established. These mammary

glands exhibited hyperplasia characterized by a dense network of ductal side branching and accelerated proliferation. In addition, these glands showed increased levels of wnt-4 and wnt-7b and the striking stabilization of β-catenin. The canonical wnt/wingless signaling pathway directs cell fate in many cell types and plays a central role in development and in tumor progression. The core event of the Wnt pathway (▶Wnt signaling) is the stability of β-catenin. Nuclear localization of β-catenin is observed in hPar1 transgenic mice tissue sections but not in the wild-type age-matched counterparts (Fig. 2). PAR1 also induces β-catenin nuclear localization in established epithelial tumor cell lines. Once localized in the nuclei, β-catenin forms functional complexes with the lymphoid enhancer factor (Lef)/ T-cell factor (Tcf) transcription factors. Introducing hPar1 SiRNA constructs depleting efficiently hPar1 levels efficiently inhibited wnt-4 expression. Therefore, it is proposed that PAR1 induced ▶β-catenin stabilization is mediated in part via the generation of Wnt/s. The novel link between PAR1, β-catenin and Wnt may impinge significantly on both development and tumor progression processes.

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Protease Activated Receptors. Figure 2 hPar1- tg mammary glands show hyperplasia and increased β-catenin expression in the nuclei. A. Whole mount hematoxylin staining of wt and hPar1-tg mammary glands at different developmental stages. The epithelial tissue derived from the hPar1-tg mammary glands displays increased lateral branching and pervasive intraductal hyperplasia in virgin (V-13w) and pregnant mammary glands (days 8 and 12 of pregnancy, respectively. B. Western blot analysis of β-catenin expression in hPar1-tg mammary glands at different developmental stages compared with age matched wt mammary glands. C. Immunohistochemical staining shows β-catenin localization in the mammary glands of hPar1-tg and wt mice. At 8 & 10 days of pregnancy, nuclear β-catenin is observed in hPar1-tg mice but not in wt mice (×40). At 10d of pregnancy a higher magnification is shown (×100).

References 1. Coughlin SR (2000) Thrombin signaling and proteaseactivated receptors. Nature 407:258–264 2. Rasmussen UB, Vouret-Craviari V, Jallat S et al. (1991) cDNA cloning and expression of a hamster alphathrombin receptor coupled to Ca2 + mobilization. FEBS Lett 288(1–2):123–128 3. Nystedt S, Emilsson K, Wahlestedt C, Sundelin J (1994) Molecular cloning of a potential proteinase activated receptor. Proc Natl Acad Sci USA 91 (20):9208–92012 4. Even-Ram S, Uziely S, Cohen P et al. (1998) Thrombin receptor overexpression in malignant and physiological invasion processes. Nat Med 4(8):909–914 5. Yin YJ, Katz V, Salah Z et al. (2006) Mammary gland tissue targeted overexpression of human protease-activated receptor 1 reveals a novel link to beta-catenin stabilization. Cancer Res 66(10):5224–5233

Protease Signaling Definition For example the protease-activated receptors (PARs) convey protease cellular signaling.

Proteases Definition Proteins with enzymatic function (or enzymes) capable of catalyzing the hydrolysis of peptide bonds in

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Proteasomal Cleavage

proteins. Synonyms: proteolytic enzymes; exopeptidases (amino- or carboxypeptidases); endopeptidases (or proteinases). Depending on the amino acid or chemical group involved in the enzymatic catalysis, proteases are divided into different classes: . . . . .

serine-proteases (serine residue) cysteine-proteases (cysteine residue) aspartyl-proteases (aspartic acid residue) metallo-proteases (bivalent cation, e.g. Zn2+ or Mg2+) threonin-proteases (threonin residue)

the proteasome, whereupon the tagged protein is degraded. ▶Apoptosis-Induction for Cancer Therapy ▶Ubiquitination ▶Proteasome Inhibitors

Proteasome Inhibitors ▶Cystatins

D HARMINDER C HAUHAN , K ENNETH C. A NDERSON

Proteasomal Cleavage Definition

▶Proteasomes are large protein complexes that degrade unneeded or damaged proteins by proteolysis. This process is initiated by the addition of an ubiquitine tag to these proteins. The ubiquinated proteins are subsequently cleaved into seven to eight amino acids long peptides, which can be degraded further into single amino acids. ▶Proteasome Inhibitors

Department of Medical Oncology, The Jerome Lipper Multiple Myeloma Center, Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, USA

Definition

▶Proteasomes are multi-subunit ▶protease complexes that selectively degrade ▶ubiquitinated intracellular proteins. ▶Proteolysis is essential for normal cell cycle progression, inflammation, transcription, DNA replication, and spontaneous ▶apoptosis. The ▶UbiquitinProteasome System (UPS) mediates normal intracellular protein degradation; conversely, blockade of UPS with proteasome inhibitors trigger apoptosis in tumor cells. Bortezomib (VelcadeTM), the first in class of proteasome inhibitors, has become a standard therapy for treatment of refractory ▶multiple myeloma (MM).

Characteristics

Proteasome Definition Synonym prosome or macropain; Is a large protein complex that functions mainly to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Proteasomes are a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. Proteasomal degradation yields peptides of about seven to eight amino acids long. Those peptides can be further degraded into amino acids that can subsequently be used for the synthesis of new proteins. Proteins are marked for proteasomal degradation by a small protein called ubiquitin, which is attached to the target protein by enzymes called ubiquitin ligases. Once a protein is tagged with a single ubiquitin molecule, this is a signal to other ligases to attach additional ubiquitin molecules. The result is a polyubiquitin chain that is recognized by

Rationale for Therapeutic Utility of Targeting Proteasome. Many cellular proteins, such as those regulating metabolism, cell cycle, growth, survival, stress and immune responses, are substrates of proteasomes. The UPS pathway is responsible for elimination of most of the misfolded, short or long-lived, proteins in the cell; conversely, blockade of proteasome-mediated protein degradation results in intracellular accumulation of unwanted/toxic proteins, induction of heat-shock response, and apoptosis. Because protein breakdown is a component of normal cellular functioning, the notion of targeting proteasomes as an anti-cancer therapy was initially viewed with cynicism, due to potential apoptotic activity against normal cells. Inhibition of proteasome activity is more cytotoxic to malignant than normal cells, thereby providing an acceptable therapeutic index. Additionally, proteasome inhibition abrogates pro-survival signaling pathways. For example, nuclear factor-kappa B (NF-κB) mediates growth and drugresistance in cancer cells; conversely, proteasome inhibitors downregulate NF-κB, thereby enhancing

Proteasome Inhibitors

the cytotoxic effects of chemotherapy. Together, these findings support the notion of targeting proteasomes in novel therapeutics. Proteasome and Its Functional Inhibitors. The 26S proteasome complex consists of 19S units flanking a barrel-shaped 20S proteasome core; the 19S units regulate entry of proteins marked for degradation into the 20S core chamber. Protein breakdown via UPS is a multi-step process: protein is first labeled with ubiquitin molecules; E1 ubiquitin enzyme then activates ubiquitin and links it to the ubiquitin-conjugating enzyme E2; E3 ubiquitin ligase then links the ubiquitin molecule to the protein; a long polypeptide chain of ubiquitin moieties is formed; and finally, proteasomes degrade the protein into small fragments and free ubiquitin for recycling. The three primary proteolytic activities of the proteasome are chymotrypsin-like (CT-L) (beta-5), trypsinlike (beta-1) and caspase-like (beta-2) proteolytic activities; all reside within the 20S proteasome core. Natural and synthetic inhibitors of the UPS pathway include peptide epoxyketones, peptide aldehydes, nonpeptide inhibitors, peptide boronates, and peptide vinyl sulfones. Peptide aldehydes (e.g. MG-132, ALLN) potently, but reversibly, block the CT-L activity; they also inhibit lysosomal cysteine and serine proteases as well as calpains, thereby limiting their clinical utility. Lactacystin is a natural, irreversible, nonpeptide inhibitor; the clasto-lactacystin beta-lactone, an analog of its active metabolite, is currently in phase-I clinical trails. The dipeptidyl boronic acid Bortezomib/PS-341 is a reversible inhibitor of CT-L activity and exhibited remarkable anti-tumor activity against 60 NCI tumor cell lines. Preclinical studies showed that Bortezomib induces MM cell apoptosis, downregulates adhesion molecules, inhibits constitutive and MM cell-adhesioninduced cytokine secretion, and blocks angiogenesis in the BM milieu. These laboratory studies translated into Phase-I trials, which showed safety and acceptable toxicity. Phase II clinical trials showed durable responses, with associated clinical benefits, and these results led to the FDA approval of Bortezomib for the treatment of patients with MM. A randomized Phase-III trial showed higher responses as well as prolonged time to progression and survival in patients treated with Bortezomib versus Dexamethasone, providing the basis for extension of FDA approval to include relapsed MM. While Bortezomib therapy is a major advance in the treatment of MM, it is associated with toxicity and the development of drug-resistance. Ongoing studies are delineating the mechanisms mediating Bortezomibtriggered cytotoxicity and drug resistance in order to design novel therapeutic strategies to both enhance anti-MM activity of Bortezomib and overcome drug resistance.

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Mechanisms Mediating Bortezomib-Induced Apoptosis in MM Cells Blockade of Pro-Survival Signaling. Treatment of MM cells with Bortezomib is associated with inhibition of a major survival signaling pathway mediated via NF-κB. Specifically, adhesion of MM cells to bone marrow stromal cells (BMSCs) triggers NF-κB-mediated transcription and secretion of IL-6 and insulin like growth factor-I (IGF-I), both of which promote survival and conventional drug resistance in MM cells in the BM milieu; conversely, treatment of MM cells with Bortezomib inhibits not only NF-κB activation, but also its downstream targets and related cytokine production, thereby overcoming the survival advantage for MM cells conferred by BMSCs. Importantly, NF-κB inhibition alone does not account for the overall anti-MM activity of Bortezomib. Besides NF-κB, Bortezomib downregulates MAPK/JAK-STAT growth/survival signaling pathway, and disables DNA-repair machinery via inactivation of DNA-PK. Treatment of MM cells with Bortezomib is not always associated with the inhibition of pro-survival signaling, as in the case of NF-κB, but can also induce pro-survival signaling, such as Akt phosphorylation or heat shock proteins (hsp-27/70/90). These in vitro findings have already led to phase-I clinical trials of combined Bortezomib therapy with agents that specifically block Akt or hsp’s in an attempt to enhance the anti-MM activity of Bortezomib. Induction of Pro-Apoptotic Signaling. Gene profiling and proteomic studies show that Bortezomib-induced apoptosis is associated with induction of apoptotic signaling pathways: (i) upregulation of pro-apoptotic c-Jun-NH2-terminal kinase (JNK); (ii) induction of ER-stress response via GADD153, CHOP, or PERK; (iii) change of mitochondrial membrane potential and production of reactive oxygen species (ROS); (iv) the release of mitochondrial proteins cytochrome-c/Smac into cytosol, resulting in activation of caspase-9 > caspase-3 cascade; and (v) activation of the extrinsic apoptotic cascade via caspase-8 cleavage. Studies using dominant negative strategies and knockout cell line models have established a direct role for JNK and Bax/Bak during Bortezomib-inducedapoptosis.Additionally,Bortezomib also affects signaling events upstream of mitochondria; i. e. Ca2+ influx into mitochondria triggers cyto-c release and caspase-9-mediated apoptosis, whereas treatment of MM cells with mitochondrial Ca2+ uptake inhibitor abrogates Bortezomib-triggered apoptosis. Bortezomibinduced apoptosis involves activation of ER-related stress pathways, including activation of caspase-12. Clinical Relevance The multiple signaling pathways associated with Bortezomib-induced cytotoxicity or the development of resistance suggest that combinations of Bortezomib with other conventional and novel agents may both

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Proteasome (prosome, macropain) 26S subunit, non-ATPase, 10

enhance its anti-tumor activity and overcome drugresistance. Combined Bortezomib and irinotecan treatment triggers apoptosis in pancreatic tumor xenografts and enhances chemosensitivity in colorectal cancer xenograft models. Studies to date in MM show that combining Bortezomib with Dex, Doxorubicin, or Melphalan, induces additive or synergistic anti-MM activity. Treatment of MM cells with Bortezomib and novel agents Lenalidomide or triterpenoids CDDOImidazolide induces synergistic anti-MM activity and overcomes Bortezomib-resistance by activating both intrinsic (via caspase-9) and extrinsic (via caspase-8) apoptotic signaling, thus providing the rationale for clinical protocols using combination regimens. Microarray analysis of Bortezomib-treated MM cells shows robust induction of hsp-90 in MM cells; conversely, blockade of hsp-90 with 17-AAG enhances sensitivity and even overcomes Bortezomib-resistance. Ongoing phase-1 clinical trials show promise of combined therapy in Bortezomib refractory MM. An alternative aggresome cascade for protein catabolism in MM cells may be significant: histone deacetylase-6 (HDAC-6) is required for the chaperoning of ubiquitinated proteins for aggresomal degradation; and conversely, blockade of HDAC triggers modest anti-MM activity. However, simultaneous blockade of proteasomes and aggresomes with Bortezomib and HDAC inhibitor, respectively, triggers additive/ synergistic cytotoxicity, providing the framework for clinical translation of this new class of cancer therapeutics. New Proteasome Inhibitor NPI-0052 The novel proteasome inhibitor NPI-0052 can overcome Bortezomib-resistance in MM cells. NPI-0052 is a small molecule derived from fermentation of Salinospora, a new marine gram-positive actinomycete. NPI-0052 is a nonpeptide proteasome inhibitor with structural similarity to Omuralide, a beta-lactone derived from naturally occurring lactacystin. NPI-0052, in contrast to Omuralide, possess a uniquely methylated C3 ring juncture, chlorinated alkyl group at C2, and cyclohexene ring at C5, which accounts for its higher anti-tumor activity than omuralide. Initial screening of NPI-0052 against the NCI panel of 60 tumor cell lines showed GI50 of 50%) proteolysis. Therefore NPI-0052 may block more protein breakdown than Bortezomib in MM cells. Moreover, mechanisms conferring Bortezomibresistance may not be effective against NPI-0052. NPI-0052 is a potent inducer of apoptosis in tumor cells obtained from Bortezomib-refractory MM patients. Examination of signal transduction pathways further showed that (i) NPI-0052 is a more potent inhibitor of NF-κB and related cytokine transcription and secretion than Bortezomib; (ii) NPI-0052-induced MM cell-death is predominantly mediated by caspase8; and (iii) Bortezomib-induced apoptosis requires both caspase-8 and caspase-9 activation. These findings confirm differential actions of NPI-0052 versus Bortezomib in MM cells. Animal studies using a human plasmacytoma xenograft mouse model showed that NPI-0052 inhibited MM tumor growth and prolonged survival of mice at concentrations which were well tolerated and without either significant weight loss or any neurological behavioral changes. Analysis at day 300 showed no recurrence of tumor in 57% of NPI0052-treated mice. Together, these data provide the preclinical framework for the ongoing multi-center phase-I clinical trial of NPI-0052 in MM patients.

References 1. Adams J (2004) The proteasome: a suitable antineoplastic target. Nat Rev Cancer 4:349–360 2. Ciechanover A (2003) The ubiquitin proteolytic system and pathogenesis of human diseases: a novel platform for mechanism-based drug targeting. Biochem Soc Trans 31:474–481 3. Chauhan D, Hideshima T, Anderson KC (2005) Proteasome inhibition in multiple myeloma: therapeutic implication. Annu Rev Pharmacol Toxicol 45:465–476 4. Kisselev AF, Callard A, Goldberg AL (2006) Importance of the different proteolytic sites of the proteasome and the efficacy of inhibitors varies with the protein substrate. J Biol Chem 281:8582–8590 5 Chauhan D, Catley L, Li G et al. (2005) A novel orally active proteasome inhibitor induces apoptosis in multiple myeloma cells with mechanisms distinct from Bortezomib. Cancer Cell 8:407–419

Proteasome (prosome, macropain) 26S subunit, non-ATPase, 10 ▶Gankyrin

Protein Kinase

26S Proteasome Definition A multicomponent complex within the cell responsible for processing and degrading ubiquitinated proteins that are target for degradation via the ubiquitin signal. A multicatalytic proteinase complex composed of a 20S core and a 19S regulator. The 19S regulator is composed of a base, which contains six ATPase subunits and two non-ATP subunits, and a lid, which contains up to 10 non-ATPase subunits. ▶Gankyrin ▶Herpesvirus-Associated Ubiquitin-Specific Protease ▶(HAUSP) De-Ubiquitinase ▶Ubiquitination

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Protein Disulfide Reductase ▶Thioredoxin System

Protein Disulphide Isomerase Definition PDI; An enzyme belonging to the thiol-disulphide oxidoreductases family of proteins that catalyzes the oxidation, isomeration and reduction of disulphide bonds. ▶Endoplasmic Reticulum Stress

26S Proteasome Regulatory Subunit p28 ▶Gankyrin

Protein-fragment Complementation Assays Definition

Protein Array ▶Proteinchip

PCAs are designed to measure the physical interaction of two cellular components through the reconstitution of the enzymatic activity of a reporter gene. Each of the components (typically proteins) are genetically or chemically fused with a fragment of the reporter, and their binding reconstitutes enzymatic activity to produce a detectable signal. Most common reporter genes can be used in PCAs, with the two most common being β-lactamase and luciferase. ▶Luciferase Reporter Gene Assays

Protein DATA Bank Definition An organization that maintains a database of experimentally determined three-dimensional structures of macromolecules (http://www.pdb.org). Tools for visualizing and manipulating these structures are also available.

Definition

▶Structural Biology

Enzyme that moves phosphate groups from ATP to serine, threonine or tyrosine residues in another protein.

Protein Kinase

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Protein Kinase B

Protein Kinase B Definition

PKB synonym Akt; Is an important “effector” enzyme lying downstream of ▶PI3K turnover of PIP2 to PIP3. Active PKB acts on many target proteins the majority of which inhibit ▶apoptosis (cell-death). Its hyper-activation therefore can lead to carcinogenesis. ▶Akt Signal Transduction Pathway ▶Pentakisphosphate

domain resembles the phosphorylation motifs in PKC substrates but contains an alanine instead of the serine or threonine, which act as phosphate acceptors in PKC substrates. The C1 region of cPKCs and nPKC contains two cysteine-rich domains in tandem orientation, which serve as DAG- or phorbol ester binding sites. Only one copy of this cysteine-rich domain is found in DAG- and phorbol ester- non-responsive aPKCs. 2. The C2 region of the cPKCs has been identified as the Ca2+-binding site. A homologous region is also found in nPKCs but the absence of a critical aspartate residue renders this C2-domain incapable of Ca2+-binding. Atypical PKCs lack a C2 domain. The C3- and C4-domains are parts of the catalytic region. ATP is bound to the C3 region, whereas the C4 domain contains binding sites for substrates.

Protein Kinase C H ANS H. G RUNICKE Biocenter, Division of Medical Biochemistry, Medical University of Innsbruck, Innsbruck, Austria

Definition Protein kinase C (PKC) represents a family of serine/ threonine protein kinases comprising at least 11 structurally related enzymes. PKC isozymes have been grouped into three subfamilies. The conventional or classical PKCs (cPKCs) can be activated by Ca2+, diacylglycerol (DAG) or phorbol esters and include the isotypes α, β I, β II and γ. Novel PKCs (nPKCs), comprising the isoforms ó, ε, δ, η and θ are also activated by DAG or phorbol esters but are Ca2+independent. The more recently discovered “atypical” PKCs (aPKCs) ι (the mouse homologue of ι has been termed λ) and ζ are Ca2+- and DAG-independent and do not respond to phorbol esters. Each PKC isozyme is encoded by a separate gene with the exception of PKC β I and β II, which represent alternative spliced variants.

Characteristics Each PKC isozyme consists of a single polypeptide containing an amino-terminal regulatory domain and a carboxy-terminal catalytic domain connected by a hinge region that is highly sensitive to proteolytic cleavage by cellular proteases (Fig. 1). The enzymes possess regions that are highly conserved between different PKC isoforms (termed C1–C4) and five variable regions (V1–V5). 1. The C1 region, which is present in all PKC isozymes, contains an autoinhibitory pseudosubstrate domain. The amino acid sequence of the pseudosubstrate

Mechanism of Activation Activation of PKC requires an unmasking of the catalytic domain by the removal of the pseudosubstrate. The necessary conformational change is mediated by the binding of DAG or phorbol ester in the presence of a lipid cofactor, especially phosphatidyl-serine. Other lipids, like free fatty acids, phosphatidyl-choline, lysophosphatidic acid and phosphatidyl inositol 3,4,5trisphosphate, can also act as co-factors for some PKC isotypes. There is evidence that the pseudosubstrate sequence, once removed from its binding site, may contribute to membrane binding through its basic residues; a process that is also controlled by proteinprotein interaction. Membrane association or translocation to membrane compartments is often considered as a hallmark of PKC activation. Ca2+ has been shown to increase the affinity of cPKCs to acidic phospholipids. In addition to allosteric regulation by Ca2+ and lipid co-factor, phosphorylation of PKC is essential for enzyme activation. The enzyme phosphoinositide dependent kinase 1 (PDK1) has been identified as a major upstream kinase catalyzing phosphorylation probably of all PKC isotypes within the activation loop of the C4 domain of the catalytic region. In cPKCs, the PDK1-mediated phosphorylation is followed by phosphorylation on two additional sites within the V5region of the carboxy-terminal sequence, probably due to autophosphorylation. Autophosphorylation of one site, Thr-641, is essential for the catalytic activity of nPKC δ. Novel PKC δ is the only PKC isoform that is subject to phosphorylation on tyrosine residues. However, the biological significance of the tyrosine phosphorylation of PKC δ remains controversial. Protein-protein interaction appears of particular relevance for the regulation of atypical PKCs. LIP (λ/ι interacting protein) has been identified as a PKC λ/ι

Protein Kinase C

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Protein Kinase C. Figure 1 Structure of PKC isozymes: C1–C4, constant regions; V1–V5, variable regions; PS, pseudosubstrate domain; CR, cysteine-rich region; ATP, ATP-binding domain; Ca2+-binding domain (note that the C2 region in nPKCs is uncapable of Ca2+-binding as outlined in the text).

specific activator. Binding of par-4 to aPKC λ/ι or a PKC ζ inactivates the enzyme. PKC-Binding Proteins PKC-interacting proteins can be classified into different subgroups according to their function: 1. PKC substrates (also termed STICKS) 2. Regulatory proteins like LIP, par-4, or syndecan-4 3. Docking proteins like RACKS, AKAPS or caveolin that may be involved in regulating the intracellular localization of PKCs 4. Scaffolding signaling proteins that cluster specific PKC isoforms together with other signaling elements in order to regulate a particular signal transduction pathway Putative PKC scaffolds include ZIP and proteins of the 14-3-3 family. This list of PKC-binding proteins is incomplete and grows continuously. The techniques employed to detect PKC-interacting proteins, e.g. the yeast two-hybrid system or overlay assays, do not always prove that these interactions occur in vivo and do not indicate the biological significance of this interaction. Therefore, these data should be interpreted with caution. Bioactivity Enzymes of the PKC family are important elements of intracellular signal transduction. They are differentially involved in the regulation of a broad variety of cellular functions: These include proliferation; differentiation; ▶apoptosis; immune response; release of messengers from endocrine, exocrine and neuronal tissues; modulation of ion channels, receptors, transporters; organization of the cytoskeleton; contraction and basal tone of smooth muscles. In many cases, however, the implication of PKC is based on effects obtained with phorbol esters or PKC-inhibitors. Since none of them are PKC-specific, the role of PKC in several systems needs to be re-examined. More

specific techniques that are now available include depletion of defined PKC-isozymes by siRNA, antisense techniques, expression of dominant negative or constitutively active mutants of particular isoforms, and generation of “knock-out” mice lacking functional alleles for a defined PKC isoform. PKC in Cancer PKC first attracted the attention of oncologists when it was found that PKC acts as a highly specific receptor for the classical tumor promoting phorbol esters like ▶TPA. The mechanism by which TPA exerts its tumor promoting activity is still unclear. Elucidation of the mechanism of action of phorbol esters is hampered by the fact that they act in a bimodal fashion; after an initial activation of phorbolester-responsive PKC isozymes, they cause a depletion of these proteins. Thus, it is unclear whether the phorbol ester effect is due to an activation or an inhibition of a PKC-mediated reaction. Furthermore, in addition to PKC, other highly specific non-kinase receptors for phorbol esters have been described, including the chimerins, Munc13/1 and RasGRP. Binding to these receptors is activated by the same co-factors activating c- and nPKCs and inhibited by classical PKC inhibitors. Interestingly, chimerins act as Rac-GAPs, thereby regulating the duration of the active state of the Ras-homology protein Rac. Ras-GRP functions as an guanylate nucleotide exchange factor for Ras and activates Ras by promoting the GTPcharged form of Ras. Thus, the chimerins as well as Ras-GRP should be considered as perhaps equally important as PKC in tumor promotion. The implication of a role of the enzymes of the PKC family in the regulation of cellular proliferation is documented by a vast number of studies. However, when the effects are analyzed with respect to individual PKC isotypes, the observations are frequently contradictory and generally confusing. For instance, PKC α has been described as activated and overexpressed in several tumors, like hepatomas and breast cancer, and

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to transform MCF7 cells following ectopic overexpression. However, in B16 melanoma cells or K562 cells ectopic expression of PKC α was found to inhibit cellular proliferation or to induce differentiation. Similar controversial findings have been reported for PKCs β, γ and ζ. Thus, the function of PKC isozymes is to a great extent cell type dependent. A more general picture has emerged with regard to nPKC ε, which was found to act as a growth-promoting enzyme in most systems, except in neuronal cells. Overexpression of PKC ε leads to transformation in fibroblasts and epithelial cells. Based on these findings, the PKC ε encoding gene is considered to represent an oncogene. Expression of dominant negative aPKC λ/ι reverses transformation by Ras. These and other findings (see below) suggest that PKC λ/ι acts as a positive regulator of cell growth. More uniform effects have also been observed with PKC δ, which appears to act as a general suppressor of tumor growth. A better understanding of the biological role of PKC requires elucidation of their function at the molecular level. Information describing the biochemical function of individual PKC isoforms in mitogenic signal transduction is accumulating. An implication for the role of PKC isoforms in the regulation of the Ras > Raf > MEK > ERK pathway is well documented. This pathway, also known as the MAP kinase cascade, is a major route for the transmission of mitogenic signals from growth factor receptors or oncogenic Ras. PKCs α and η activate cRaf and PKC ζ stimulates MEK. Evidence for a co-ordinate function of aPKC λ, nPKC ε and aPKC ζ for the Ras-mediated induction of c-Fos by the Ras > Raf > ERK pathway and the transcriptional activation of cyclin D, a critical step for the progression of cells through the G1-phase of the cell cycle, has been published. Other PKC isoforms including α, δ and η have been shown to arrest cells in G1 by enhancing the cell cycle inhibitory proteins p21waf/cip and p27kip. Several PKC isozymes, notably λ/ι and ζ, are implicated in cytoskeletal functions, thereby linking cell shape alterations to the cell cycle. Activation of survival pathways by an inhibition of apoptosis is of utmost importance for malignant transformation and maintenance of the transformed phenotype. PKC isotypes α, δ and ζ are frequently associated with these mechanisms. The function of PKC α has been reported to act pro- and anti-apoptotic, dependent on cell type. The anti-apoptotic activity of α has been correlated to a PKC α-mediated activation of Akt, an inhibitor of programmed cell death. PKC δ is involved in the execution phase of apoptosis; its function is at least in part explained by a caspase 3-mediated activation of this PKC isoform. A clear picture has emerged with regard to PKC ζ; atypical PKC ζ stimulates cell survival by activating NfκB either by mediating the release from the inhibitor I-κB or by

phosphorylating the RelA subunit of NFκB. Similar effects have been reported for the structurally related aPKC λ/ι. Furthermore, par-4, a prominent mediator of apoptosis binds and inactivates PKC ζ. Resistance to anti-tumor agents has been correlated to overexpression or activation of several PKC isotypes. This also applies to multidrug resistance mediated by an overexpression of the MDR1 gene encoded P-glycoprotein. However, the biochemical basis of this correlation remains obscure. A PKC-mediated phosphorylation of the P-glycoprotein could be excluded, as deletion of all PKC phosphorylation sites did not affect the pumping activity of the P-glycoprotein. The correlation is in part based on observations indicating a reversion of the resistant phenotype by PKC inhibitors. In some cases, however, these PKC inhibitors were found to interact directly with the P-glycoprotein and to inhibit its activity by a PKCindependent mechanism. It is intriguing to speculate that the observed correlation between intracellular PKC activity and drug resistance is due to a PKC-mediated activation of anti-apoptotic survival pathways described above. This may also explain the observed synergistic effects of combinations of PKC inhibitors with established anti-tumor agents. Clinical Relevance The implication of PKC isozymes in tumor cell proliferation, invasion and metastasis, apoptosis and drug resistance has led to the development of PKC inhibitors that can be used for the chemotherapy of cancer. Several of these agents have entered clinical trials. Bryostatin-1, a macrocyclic lactone derived from Bugula neritina, occupies the same binding site as phorbol esters but is not a tumor promoter and leads to a depletion of c- and n-type PKCs. Phase II trials with bryostatin including a wide range of tumor types have so far been disappointing. Phase II studies on combinations of bryostatin I with other cytotoxic agents are ongoing. Phase II studies with an antisense construct targeted against PKC α (aprinocarsen, ISIS 3521) are in progress. These studies include patients with brain tumors, breast, colon, ovarian and prostate cancer. Phase II studies in breast cancer patients and patients with high grade astrocytomas did not reveal any activity. A phase III study in NSCLC failed to show any clinical benefit from a combination of aprinocarsen with gemcitabine and cisplatin or paclitaxel and carboplatin. Safingol, a dihydrosphingosine analogue, has been employed in clinical trials as a sensitizing agent in order to potentiate chemotherapy. Many other compounds are now in pre-clinical and early clinical development. The majority of these PKC inhibitors interact with the ATP binding site of the catalytic region. Most of them are bisindolylmaleimides or indolocarbazoles and are structurally related to the

Protein Kinase C Family

biological compound staurosporine, a product of Streptomyces staurosporeus. Clinical phase I/II trials with the indolocarbazoles midostaurin and enzastaurin (LY317615) revealed some sensitizing effects in combination with doxorubicin or vinblastine (midostaurin) or gemcitabine, 5FU, cisplatin or radiotherapy (enzastaurin). More recently, a series of very potent PKC inhibitors was described that represent derivatives of balanol, an azepine natural product. Balanol analogues also interact with the ATP binding site of c- and nPKCs. However, PKC inhibitors are not only of interest as potential anti-tumor agents. Other areas in which PKC inhibitors are presently investigated include diabetes, cardiovascular diseases, inflammation and immunological disorders and diseases of the central nervous system. ▶Toxicological Carcinogenesis

References 1. Ron D, Kazanietz MG (1999) New insights into the regulation of protein kinase C and novel phorbol ester receptors. FASEB J 13:1658–1676 2. Mackay HJ, Twelves CJ (2007) Targeting the protein kinase C family: are we there yet? Nat Rev Cancer 7:554–562 3. Buchner K (2000) The role of protein kinase C in the regulation of cell growth and in signalling to the cell nucleus. J Cancer Res Clin Oncol 126:1–11 4. Goekjian PG, Jirousek MR (1999) Protein kinase C in the treatment of disease: signal transduction pathways, inhibitors, and agents in development. Curr Med Chem 6:877–903 5. Hofmann J (2001) Modulation of protein kinase C in antitumor treatment. Rev Physiol Biochem Pharmacol 142:1–96

Protein Kinase C Family J UHA P ELTONEN , V ESA A ALTONEN Department of Anatomy, Institute of Biomedicine, University of Turku, Turku, Finland

Synonyms

Ca2+-activated phospholipid dependent protein kinase; PKC

Definition Protein kinase C was found originally in 1977 by Nishizuka and co-workers. The group named this

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▶serine/threonine kinase as Ca2+-activated, phospholipid dependent protein kinase, or protein kinase C in short, since the kinase activity was found to be increased in the presence of phospholipids and calcium. Today, human protein kinase C (PKC) family is known to consist of at least 11 serine/threonine kinases which are classified into three major groups based on their structure and biochemical properties: classical (α, βI, βII, γ), novel (δ, ε, η, and θ), and atypical (ζ and ι). PKCμ differs structurally from all three major groups. The genes of different PKC isoenzymes are dispersed throughout the genome. Different PKCs play a role in multiple cellular processes, which are important in cancer cell behavior. PKCs exert their functions by phosphorylating their target proteins, which are numerous and largely unknown. Originally, relevance of PKC to cancer development was discovered when PKC was identified as a primary target of tumor-promoting phorbol esters.

Characteristics Regulation Activation of classical PKC isoenzymes (cPKC) depends on calcium, ▶diacylglycerol, and acidic phospholipids, such as ▶phosphatidylserine. Novel isoenzymes (nPKC) are activated by diacylglycerol and acidic phospholipids, and atypical isoenzyme (aPKC) activation takes place independent of calcium and diacylglycerol. Activation of aPKCs takes place by acidic phospholipids, ▶ceramides, and protein–protein interactions, such as interaction with other PKCs. Growth factor-mediated ▶phospholipase C activation plays a central role in the activation of cPKC and nPKC. On ligand binding, growth factor receptor activates and induces phospholipase C translocation from cytosol to the plasma membrane. Activated phospholipase C then generates diacylglycerol and ▶inositol trisphosphate (IP3) from plasma membrane phospholipids. Subsequently, diacylglycerol activates both cPKC and nPKC, and IP3 releases calcium from intracellular stores. Calcium enhances the activation of cPKC. PKC activation also depends on complex series of phosphorylations which make PKC catalytically competent. Following ligand binding on the plasma membrane, PKC acts as a target for different kinases. These kinases phosphorylate PKC at activation loop sites and hydrophobic sites. PKC is stabile and phosphatase-resistant after autophosphorylation. However, PKC activity is not determined by these phosphorylations only. If the ligand dissociates, PKC can diffuse away from plasma membrane but remain phosphorylated. In this case, PKC can be reactivated by diacylglycerol binding alone. PKC Expression in Cancer Members of PKC family are normally ubiquitously expressed in a wide range of tissues, isoenzymes α, β,

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and δ being the most abundant. However, PKC isoenzymes have been shown to display altered expression in cancer when compared with normal tissues. The most common isoenzymes displaying alterations in expression during cancer progression are α, β, and δ, but change in expression of other isoenzymes may also take place. Immunohistochemical studies on human tumors have shown PKCα overexpression in urinary bladder, prostate, and endometrial cancers, whereas low grade tumors and normal epithelia of the respective organs show significantly lower expression. In contrast, breast, colon, hepatocellular, and basal cell cancers display downregulation of PKCα expression. PKCβ expression has been shown to be high in colon and prostate cancers, and low in high grade urinary bladder cancers. Furthermore, the expression profile of PKCs within a single tumor can be variable, as exemplified by the fact that increased PKCα- and βI expression and activity have been shown to associate with high proliferation areas of urinary bladder tumors. Even single neighboring cells may display manifold difference in the expression of these enzymes. This suggests that PKC expression level is under control even in carcinoma tissue. Similarly to cPKC expression, PKCδ can be either upregulated or downregulated. For instance, hepatocellular cancer displays increased PKCδ expression, while in urinary bladder cancer the isoenzyme is downregulated. Studies have mainly focused on cPKC and PKCδ, while the expression of other PKC isoenzymes in cancers is less well known. The expression of PKCλ, ι, and ε is decreased in pancreatic cancers, PKCη is increased in renal cancers, and PKCλ is increased in ovarian cancer. It is unclear, whether PKC isoenzyme expression in cancer can be associated with patient survival. Expression of PKCι has been suggested to be a negative prognostic factor in ovarian carcinoma and PKCγ as positive prognostic factor in B-cell lymphoma. Based on the variability of expression of different PKC isoenzymes in different cancers, it can be stated that no general conclusions can be drawn from the expression patterns with respect to carcinogenesis in general. In addition, the levels of isoenzyme proteins do not directly correlate with the overall enzyme activity, making conclusions difficult. PKC Activation in Carcinogenesis Evolution of a malignant tumor is a multistep process, which includes mutations in several genes as well as other molecular changes in cellular proteins. First, initiating agents mutate proto-oncogenes and thus initiate the malignant transformation. Second, a prolonged exposure to ▶tumor promoters induces the clonal outgrowth of the mutagen-initiated cell population and increase genetic instability. The primary target

of the tumor promoters, such as ▶phorbol 12-myristate acetate (PMA, TPA), aplysiatoxin, and teleocidin seems to be PKC. One mechanism of expressional changes seen in human cancers may result from the tumor promoter action. Tumor promoters, such as PMA, bind to the diacylglycerol binding site of PKC and promote chronic activation of PKC. Prolonged activation of PKC leads to degradation of the enzyme by ubiquitin– proteasome pathway. In fact, changes in expression and activity of PKC are apparently not due to genetic chances, since mutations in PKC genes are found very rarely in human cancers. However, evidence has been provided for loss-of-function mutation of PKCα gene in thyroid and pituitary cancers. Furthermore, a deletion has been reported in PKCα gene in melanoma. Significance of this mutation is unknown, but several melanoma cell lines display decreased PKCα expression. The role of PKCs in cancer seems to result from their action as targets of tumor promoters or from their action as downstream effectors of growth factor receptors. Tobacco smoke contains a number of substances considered as tumor promoters which activate PKCs, such as catechol and hydroquine. Furthermore, high consumption of dietary lipids is carcinogenic. Carcinogenicity of dietary lipids may, at least in part, be exerted through direct or indirect PKC activation, which have also been shown in animal models. PKC expression and activity seems to be modulated by a wide variety of genetic and epigenetic factors. Chemical carcinogens such as nitrosamines which are present in tobacco smoke are known to induce increased expression and activation of PKCα and β, while PKCδ is downregulated. Furthermore, oncogenic ▶Ras increases PKCα, ▶c-myc oncogene increases PKCβ expression, and wild type ▶p53 tumor suppressor decreases PKCα expression. Targets of PKC and its Cancer-Related Functions PKCs are involved in multiple physiological processes of cells. Short-term activation of PKC is often associated with short-term events such as secretion and ion influx. In contrast, sustained activation has been shown to induce cellular proliferation, differentiation, ▶apoptosis, ▶migration, ▶adhesion, tumorigenesis, and epithelial barrier function. The role of PKC in the control, or rather in the loss of control of cancer cell growth is well established. However, different isoenzymes function differently and have variable effects on cell growth which may also vary depending on the cell type. Thus, general conclusions with respect to PKC function in cell growth may be difficult to make. PKCα has been linked to decreased and increased cellular proliferation, and to induction or inhibition of apoptotic cell death of cancer cells. However, most of the studies consider PKCα as an inducer of proliferation and suppressor of apoptosis.

Protein Kinase C Family

Also PKCβ has been associated with increased proliferation rate of cancer cells. Of novel isoenzymes, PKCδ has been strongly associated with control of apoptosis. PKCδ activity results in many proapoptotic signals, such as increased mitochondrial ▶cytochrome c release and ▶c-Abl activation. In malignancies, downregulation of PKCδ activity has been shown to lead to inhibition of apoptosis and resistance to DNAdamaging agents. ▶Telomerase activity is associated with immortalization and malignant phenotype of a cell. PKCα, βI, δ, and ζ isoenzymes phosphorylate and activate telomerase, and PKC inhibitors inhibit its activity. The target of PKC appears to be telomerase reverse transcriptase, hTERT, one of telomerase subunits. There is strong evidence that PKCα activity is associated with increased motility and invasion of cancer cells. This has been suggested to occur through inhibition of ▶adherens junctions and ▶desmosomes, inhibition of hemidesmosomes, and changes in focal adhesions. Also, ε, βII, and ζ isoenzymes have been associated with cellular motility. Other cancer-related associations for PKC include ▶multidrug-resistance (mdr), since PKCα activity has been shown to phosphorylate, and PKCα and θ to increase expression of ▶P-glycoprotein. Furthermore, simultaneous loss of P-glycoprotein and PKCα expression is associated with reversion of mdr, while inhibition of PKCα attenuates resistance to cytotoxic agent. PKCs may also regulate tumor vascularization, since PKCβ has been shown to act as a mediator of vascular endothelial growth factor (VEGF) signaling and its inhibition leads to decreased endothelial cell proliferation and reduction of neovascularization of a malignant tumor. Furthermore, PKCα- and ζ isoenzymes regulate VEGF expression through posttranscriptional mechanisms. A high number of different potentially cancer-related direct or indirect targets have been reported. Some of the most important include, in addition to the targets mentioned above, the following: PKCα, βI, and γ have been shown to phosphorylate and inactivate ▶glycogen synthase kinase-3 beta (GSK-3β), leading to increased c-Jun DNA binding activity. C-Jun is an important controller of cell growth and apoptosis. PKC can directly activate ▶Raf-1/MEK/MAPK pathway by phosphorylating Raf-1. Raf-1/MEK/MAPK pathway affects several targets related to cell growth. Transcription factor ▶nuclear factor kappa beta (Nf-κB), which is a central regulator of several apoptosis-related genes, is also activated by PKC. PKC also regulates intercellular communication through gap junctions and PKC has been shown to be directly phosphorylate ▶gap junction protein, connexin 43. Recently, it was shown that PKCα directly phosphorylates ▶neurofibromin, a Ras

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GTPase-activating tumor suppressor, and increases its association to actin cytoskeleton. PKC as a Target in Cancer Therapy Since many tumor promoters act as PKC activators and as PKCs play an important role in diverse cellular functions, PKCs are potential therapeutic targets. Multiple PKC modulating approaches have been developed during the last decades. PKC inhibitors may be divided to isoenzyme selective and broad spectrum inhibitors. However, PKC agonists, such as bryostatin-1, may also be used to inactivate PKC, since long-term activation of PKC leads to its downregulation. Many PKC inhibitors have been tested in vitro and in vivo animal models, with promising results. The most tested PKC inhibitors are bryostatin-1, PKC412 (broad spectrum inhibitor, N-benzoyl staurosporine, also named CGP41251 and midostaurin), UCN-01 (cPKC pointed broad spectrum inhibitor, 7-hydroxy-staurosporine), aprinocarsen (PKCα antisense oligodeoxynucleotide, also named ISIS3521, LY900003, CGP 64128A, or affinitak), enzastaurin (PKCβ inhibitor, also named LY317615), safingol (PKCα inhibitor), and Go6976 (PKCα/βI inhibitor, also named Gö6976). PKC412, aprinocarsen, and Go6976 have shown impressive antiinvasive properties. Furthermore, reduced growth of cancer cells has been shown with UCN-01, PKC412, aprinocarsen, Go6976, and enzastaurin. The antiproliferative mechanism of these agents has been suggested to be cell cycle arrest and increased apoptosis. Also bryostatin-1 inhibits proliferation, induces differentiation, and apoptosis. In addition to its direct effects on cancer cell growth, enzastaurin has been shown to reduce plasma ▶VEGF levels and inhibit angiogenesis in a tumor model. Combining different PKC inhibitors with classical ▶chemotherapeutic agents or radiotherapy has resulted in additive growth inhibiting effects. It has been speculated that these additive effects result from inhibition of ▶mdr or modulation of apoptosis. An interesting mechanism for PKC inhibitors in increasing cancer cell death is ▶cell cycle checkpoint abrogation. When a cell faces DNA damage induced by chemotherapy or ionizing radiation, it activates its cell cycle checkpoints, resulting in cell cycle arrest. It has been demonstrated that many PKC inhibitors inhibit, either directly or through PKC, kinases that control especially G2 checkpoint of the cell cycle. Therefore, cancer cells that are arrested to G2 by chemotherapy can be forced from G2 to mitosis by using selected PKC inhibitors. This treatment kills the cancer cells very effectively by ▶mitotic catastrophe or apoptosis. Bryostatin, aprinocarsen, UCN-01, PKC412, enzastaurin, and safingol have been tested in clinical trials as single agents and in combination with various chemothrerapeutic drugs. Go6976 has not been studied in

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clinical trials. The clinical responses for the substances have varied considerably. For instance, aprinocarsen displayed some promising effects, but phase III studies showed that the substance did not improve response or survival when used in combination with chemotherapy in advanced non-small cell lung cancers. Additionally, major thrombocytopenia was observed. The clinical efficiency of UCN-01 and PKC412 has been poor as well. UCN-01 has shown unusually prolonged half-life and low clearance, which results from high binding to plasma proteins. Several human studies are ongoing with these substances and results are eagerly awaited. www.gancer.gov/clinicaltrials.

References 1. Aaltonen V, Koivunen J, Laato M et al. (2006) Heterogeneity of cellular proliferation within transitional cell carcinoma: correlation of protein kinase C α/βI expression and activity. J Histochem Cytochem 54(7):795–806 2. Inoue M, Kishimoto A, Takai Y et al. (1977) Studies on a cyclic nucleotide-independent protein kinase and its proenzyme in mammalian tissues. II. Proenzyme and its activation by calcium-dependent protease from rat brain. J Biol Chem 252(21):7610–7616 3. Koivunen J, Aaltonen V, Peltonen J (2006) Protein kinase C (PKC) family in cancer progression. Cancer Lett 235:1–10 4. Koivunen J, Aaltonen V, Koskela S et al. (2004) Protein kinase C alpha/beta inhibitor Go6976 promotes formation of cell junctions and inhibits invasion of urinary bladder carcinoma cells. Cancer Res, 64(16):5693–5701 5. Parekh DB, Ziegler W, Parker PJ (2000) Multiple pathways control protein kinase C phosphorylation. EMBO J 19(4):496–503

Protein Microarray Definition Protein microarray is composed of array containing full-length functional proteins or protein domains. It is fabricated by depositing a library of proteins or antibodies immobilized in a 2-D addressable grid on a chip coated with a chemically or physically functional layer for covalent or noncovalent immobilization of proteins or other capture reagents. Quantification of microarray-based assay is achieved by capturing array images with an optical device and using compatible image analysis software to determine fluorescent, chemilluminescent, or colorimetric intensity of each spot on array images. Protein microarray is used to study the biochemical activities of an entire proteome in a single experiment, such as protein–protein, protein– DNA, protein–RNA, protein–phospholipid, and protein–small molecule interactions.

Protein Stabilization Definition A generalized term that represents the process of preventing protein degradation, either through deubiquitination or some other type of cellular process. ▶Herpesvirus-Associated Ubiquitin-Specific Protease (HAUSP) De-Ubiquitinase

Protein-tyrosine Kinase Inhibitors ▶Tyrosine Kinase Inhibitors

Proteinase Definition Synonym protease; An enzyme which catalyses hydrolysis of peptide bonds. Endopeptidase refers to proteinase activity within an intact protein. ▶Proteasome Inhibitors

Proteinase-Activated Receptor-1 A NKE R ATTENHOLL , T OBIAS G O¨ RGE , S TEFAN W. S CHNEIDER , M ARTIN S TEINHOFF Department of Dermatology, University of Münster, Münster, Germany

Synonyms Thrombin receptor; Coagulation factor II receptor; PAR1

Definition

▶PAR1 is a ▶G protein-coupled receptor which can be activated preferentially by ▶thrombin, ▶trypsin, ▶factor Xa, activated ▶protein C, ▶plasmin and ▶matrix metalloproteinase-1 (MMP-1). It consists of 425 amino acids (47 kDa) including the amino-terminal signal sequence, and is widely expressed in different tissues and overexpressed in numerous cancers. The gene maps to 5q13.3 (gene name: F2R).

Proteinase-Activated Receptor 2

Characteristics

PAR1 is stimulated by specific cleavage at the site LDPR41 ↓ S42FLLRN to expose the tethered ligand SFLLRN which binds to the second extracellular loop, thus activating the receptor, resulting in ▶signal transduction. A synthetic peptide (“activating peptide”) that mimics the tethered ligand domain (TFLLRN-NH2) directly binds to and activates PAR1 in vitro without proteolytic cleavage. Thrombin can activate PAR1 by a two-step mechanism. First the proteinase binds to a ▶hirudin-like site distal to the cleavage site, subsequently cleaving the receptor. This mechanism allows efficient activation of the receptor. Hence, PAR1 is a high-affinity receptor for thrombin, mediating rapid and transient cellular responses. Moreover, evidence exists that uncleaved PAR1 can also be activated intermolecularly by another activated PAR1 receptor molecule (transactivation). Overexpression of PAR1 in breast cancer cells correlates with tumor progression. Activation of PAR1 in these cells induces reorganization of the cytoskeleton and the formation of focal contact complexes. These complexes are important for cell migration and invasion. Moreover, overexpression in murine mammary glands results in accelerated cell proliferation due to persistent activation of ▶β-catenin. In contrast, experimental downregulation of PAR1 in an aggressively metastatic breast cancer cell line reduces invasion. In prostate cancer, PAR1 has been implicated in bone metastasis. Metastatic human melanoma cell lines express PAR1, and overexpression of PAR1 in melanoma cells leads to enhanced invasion and metastasis. Deregulation of PAR1 expression was found to be associated with a loss of the transcription factor activator protein-2α. PAR1 activation also contributes to tumor growth by enhancing tumor cell proliferation, as has been shown for melanoma and colon carcinoma cell lines. Moreover, the ability of tumor cells to activate the coagulation system and to generate thrombin has been shown to enhance metastasis, while anticoagulant therapies can interfere metastasis formation. Thrombin and potentially other coagulation proteinases can modify tumor cell behavior directly through the activation of PAR1 or other thrombin receptors. PAR1 is present on ▶platelets, where it mediates platelet aggregation, a central event in ▶thrombus formation. Thrombus formation is a crucial step during metastasis: cancer cells circulating in the blood stream produce thrombin which promotes ▶fibrin (Factor Ia) and platelet deposition. This enables tumor cells to adhere to the blood clot, facilitating penetration through the vessel wall. Interestingly, factor Xa (FXa), apart from its role in the extrinsic and intrinsic ▶coagulation pathways to activate ▶zymogens, can directly cleave PAR1. However, optimum cleavage capacity is only achieved when the factor is immobilized on the cell membrane via ▶tissue factor (TF) as a complex together with ▶factor VIIa (FVIIa). Both TF and FVIIa can be produced by the cancer cells themselves.

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PAR1 is able to couple to ▶epidermal growth factor receptor (EGFR) signaling. This receptor ▶transactivation was found to promote migration of renal carcinoma cells. Metastasis requires adhesion of tumor cells to endothelial cells of the vessel wall. Melanoma cells secrete MMP-1 which is able to activate PAR1 on endothelial cells. This leads to secretion of ▶von Willebrand factor (vWF) and proangiogenic ▶interleukin-8. ▶Angiogenesis has also shown to be stimulated in the presence of the PAR1 agonists thrombin and activated protein C. Tumors induce the formation of new blood vessels. These provide nutrition for the tumor cells which have a high metabolical turnover. In addition, MMP-1 that was secreted by stromal cells of the tumor microenvironment was shown to activate PAR1 on breast cancer cells, increasing tumor cell migration and invasion. In addition to the hypercoagulable state which is associated with advanced cancer, activation of the fibrinolytic system has also been linked to poor prognosis: plasmin can activate PAR1 to induce the angiogenic cytokine Cyr61. In turn, Cyr61 expressed by the tumor cells induced MMP-1 secretion by the stromal host cells. Together, the role of PAR1 in tumor progression involves not only the tumor cells themselves but also a close interaction between the cancer cells and the surrounding tumor microenvironment.

References 1. Boire A, Covic L, Agarwal A et al. (2005) PAR1 is a matrix metalloproteinase-1 receptor that promotes invasion and tumorigenesis of breast cancer cells. Cell 120:303–313 2. Koizume S, Jin MS, Miyagi E et al. (2006) Activation of cancer cell migration and invasion by ectopic synthesis of coagulation factor VII. Cancer Research 66:9453–9460 3. Ahamed J, Versteeg HH, Kerver M et al. (2006) Disulfide isomerization switches tissue factor from coagulation to cell signaling. Proc Natl Acad Sci USA 103:13932–13937 4. Ruf W, Mueller BM (2006) Thrombin generation and the pathogenesis of cancer. Semin Thromb Hemost 32 (Suppl 1):61–68

Proteinase-Activated Receptor 2 A NKE R ATTENHOLL , T OBIAS G O¨ RGE , S TEFAN W. S CHNEIDER , M ARTIN S TEINHOFF Department of Dermatology, University of Münster, Münster, Germany

Synonyms Thrombin receptor-like 1; Coagulation factor II receptorlike 1; G-protein coupled receptor 11; PAR2

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Proteinase-Activated Receptor-3 (PAR3)

Definition

▶PAR2 is a ▶G protein-coupled receptor which can be activated by ▶trypsin, ▶tryptase, ▶factor VIIa, ▶factor Xa, ▶matriptase (MT-SP1), and ▶proteinase 3. It consists of 397 amino acids (44 kDa) including the amino-terminal signal sequence, and is widely expressed in different tissues and upregulated in numerous cancers. The gene maps to 5q13.3 (gene name: F2RL1).

Characteristics PAR2 is activated by specific proteolysis at the site SKGR36 ↓ S37LIGKV to expose the tethered ligand SLIGKV which binds to the second extracellular loop, thus activating the receptor, resulting in ▶signal transduction. A synthetic peptide (“activating peptide”) that mimics the tethered ligand domain (SLIGKV-NH2) directly binds to and activates PAR2 in vitro without proteolytic cleavage. In vivo, PAR2 can also be stimulated by ▶transactivation through PAR1: the tethered ligand domain of PAR1 is able to bind to and activate uncleaved PAR2. Hence, the peptide sequence SFLLRN, derived from the tethered ligand domain of PAR1, can stimulate both PAR1 and PAR2 in vitro. In addition, it was observed that thrombin is able to activate PAR2 on melanoma cells indirectly and independent of receptor cleavage. The underlying mechanism, however, is yet unclear. PAR2 activation in cancer cells induces cytoskeletal reorganization. This results in enhanced ▶migration, ▶invasion and ▶metastasis. Moreover, PAR2 is able to promote proliferation of various tumor cells. This is achieved at least partly by ▶transactivation of the epidermal growth factor receptor (EGFR). In ▶pancreatic cancer, PAR2 was reported to induce fibrosis. As observed with PAR1, the complex TF-FVIIaFXa can also activate PAR2. In breast cancer cells, PAR2 is able to promote migration and invasion via TF-FVIIa-FXa and TF-FVIIa. Activation of PAR2 in these cells leads to release of the angiogenic factor ▶vascular endothelial growth factor (VEGF). PAR2 promotes proliferation of most cells. An exception are epidermal keratinocytes of the upper skin layer, where activation of PAR2 inhibits cell growth. Although PAR2 is overexpressed in several tumor cell lines, the receptor is downregulated in poorly differentiated ▶squamous cell carcinomas of the skin and esophagus, which are derived from keratinocytes, and in certain ▶gastric carcinomas. These findings point to a tumor-suppressing role of PAR2 in certain tissues. However, the underlying mechanisms are not elucidated yet. Another serine proteinase with trypsin-like activity is ▶matriptase (MT-SP1), a transmembrane proteinase. PAR2 can be cleaved by this enzyme,

and matriptase is overexpressed in numerous cancers and has been implicated in tumor progression and ▶metastasis.

Proteinase-Activated Receptor-3 (PAR3) A NKE R ATTENHOLL , T OBIAS G O¨ RGE , S TEFAN W. S CHNEIDER , M ARTIN S TEINHOFF Department of Dermatology, University of Münster, Münster, Germany

Synonyms Thrombin receptor-like 2; Coagulation factor II receptor-like 2; PAR3

Definition

▶PAR3 is a G protein-coupled receptor which can be activated by ▶thrombin (Factor IIa). It consists of 374 amino acids (42 kDa) including the amino-terminal signal sequence, and is highly expressed in ▶megakaryocytes of the bone marrow. A lower expression is found in mature ▶megakayrocytes, platelets, heart and gut. The gene maps to 5q13.3 (gene name: F2RL2).

Characteristics PAR3 is activated by specific proteolysis at the site LPIK38 ↓ T39FRGAP to expose the tethered ligand LPIK which binds to the second extracellular loop, thus activating the receptor. No synthetic peptides exist which are able to stimulate PAR3 in vitro, as observed with the other members of this receptor family. Distal to the thrombin cleavage site, there is a ▶hirudin-like binding site located. This enables binding and concentration of thrombin at the cell surface, rendering PAR3 a high-affinity receptor for thrombin. However, it seems that PAR3 needs the interaction with other PARs for ▶signal transduction, since it was found that mouse PAR3 is unable to signal when expressed in the absence of other PAR receptors. PAR3 is well expressed in mouse platelets, which are deficient in PAR1. Here, PAR3 is a cofactor for PAR4. Thus in mouse platelets, PAR3 adopts the role played by PAR1 in the human system. PAR3 does not seem to play a major role in tumorigenesis. However, it was reported to be expressed in ▶renal cell carcinomas together with PAR1.

Proteinchip

Proteinase-Activated Receptor-4 A NKE R ATTENHOLL , T OBIAS G O¨ RGE , S TEFAN W. S CHNEIDER , M ARTIN S TEINHOFF Department of Dermatology, University of Münster, Münster, Germany

Synonyms Thrombin receptor-like 3; Coagulation factor II receptor-like 3; PAR4

Definition

▶PAR4 is a ▶G protein-coupled receptor which can be activated by ▶thrombin (Factor IIa), ▶plasmin, ▶trypsin and ▶cathepsin G. It consists of 385 amino acids (41 kDa), including the amino-terminal signal sequence, and is widely expressed in various tissues. It is not expressed in brain, kidney, spinal cord and peripheral blood leukocytes. The gene maps to 19p2 (gene name: F2RL3).

Characteristics PAR4 is activated by specific proteolysis at the site PAPR47 ↓ G48YPGQV to expose the tethered ligand GYPGKV which binds to the second extracellular loop, thus activating the receptor. A synthetic peptide (“activating peptide”) that mimics the tethered ligand domain (GYPGQV-NH2) directly binds to and activates PAR4 in vitro without proteolytic cleavage. PAR4 does not carry a ▶hirudin-like binding site for thrombin as observed in PAR1 and PAR3. Thus, PAR4 is a low-affinity receptor for thrombin. Despite this fact, cellular responses mediated by PAR4 are sustained, and the receptor desensitizes only slowly in contrast to the high-affinity thrombin receptor PAR1, leading to a prolonged signal. PAR4 is involved in ▶invasion and ▶angiogenesis, and it was reported to be overexpressed in adenocarcinomas and ▶squamous cell carcinomas of the lung.

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seven transmembrane domains. So far, four different PARs are known. They are stimulated by specific proteolytic cleavage of the extracellular N-terminus (see Fig. 1). The newly formed N-terminus, the socalled “tethered ligand,” is then able to bind intramolecularly to the receptor to initiate multiple signaling cascades. There is no known function of the removed N-terminal peptide fragment. Despite the irreversible activation mechanism, PAR signaling is efficiently terminated by desensitization (phosphorylation and uncoupling from ▶G proteins) and degradation. A wide range of proteinases, most of them serine proteinases, cleave and activate PARs. They include proteinases from the ▶coagulation cascade, inflammatory cells, the digestive tract, and the tumor microenvironment as well as the malignant cells themselves. PARs are ubiquitously expressed but are often found to be overexpressed in many different tumor types. In certain tumor types, downregulation of PARs has also been described.

References 1. Steinhoff M, Buddenkotte J, Shpacovitch V et al. (2005) Proteinase-activated receptors: transducers of proteinasemediated signaling in inflammation and immune response. Endocr Rev 26:1–43

Proteinchip W ILLIAM C HI -S HING C HO Department of Clinical Oncology, Queen Elizabeth Hospital, Kowloon, Hong Kong

Synonyms Protein array; Biochip

Proteinase-Activated Receptors A NKE R ATTENHOLL , T OBIAS G O¨ RGE , S TEFAN W. S CHNEIDER , M ARTIN S TEINHOFF Department of Dermatology, University of Münster, Münster, Germany

Definition

▶Proteinase-activated receptors (PARs) belong to the protein family of ▶G protein-coupled receptors with

Definition The functional proteinchip is a small size planar analytical ▶protein microarray with probes arranged in high density on which different molecules of protein are affixed at separate locations in an ordered manner to form a microscopic array. The recent development of protein microarray offers the possibility to simultaneously analyze the expression of several hundred proteins. It is used to identify protein–protein interactions, the substrates of protein kinases, or the targets of biologically active small molecules. The innovative reverse-phase protein microarray has the potential to

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Proteinchip

Proteinase-Activated Receptors. Figure 1 Schematic presentation depicting the mechanism of PAR activation. The particular proteinase cleaves the PAR receptor at a specific site (scissors), unmasking a previously hidden peptide sequence, termed “tethered ligand” (blue box). The newly formed N-terminus then binds to the conserved second extracellular loop (dotted arrow). This interaction leads to conformational changes and subsequent receptor activation (a detailed description of PAR1 and PAR2 signal transduction pathways is given by Steinhoff et al. [1]). The human sequences of the “tethered ligand” domains and the second extracellular loops (both printed in blue) are presented in the boxes. The hirudin-like binding domain sequences of PAR1 and PAR3 are depicted in purple color.

provide information about the state of cellular circuitry from minute samples. Nevertheless, the most common functional proteinchip is the ▶antibody microarray, where antibodies are spotted onto the proteinchip and are used as capture molecules to detect proteins from biological samples. The analytical proteinchip is used in conjunction with a ▶time-of-flight (TOF) ▶mass spectrometry (MS) detector to enable protocols of protein capture and detection from complex samples without additional labels. Based on chromatographic interactions, protein– protein interactions, DNA–protein interactions, or receptor–ligand interactions, the analytical proteinchip is designed with a wide variety of capture affinities. The techniques include reverse-phase, cation exchange, and anion exchange. The most common analytical proteinchip is the ▶surface-enhanced laser desorption/ ionization (SELDI)-TOF MS array, where proteins are captured and enriched on a chemically or bioaffinity

active solid phase surface to detect proteins in tissue, blood, urine, or other clinical samples.

Characteristics Technologies There are three main types of proteinchip formats. The glass slide chips are relatively inexpensive and they are usually compatible with standard microarray equipment, however, the samples are prone to evaporate and there may be cross-contamination between spots. Using well chips or 3-D matrix gels these problems can be reduced, but they are more expensive and can not be used with DNA microarray spotting equipment. To prepare the proteinchip, coating with a substance should be bound to the slide without denaturing the proteins. There are several types of binding methods, which include the absorption, cross-linking, and hybridization. With the absorption method, the noise level of

Proteinchip

the attachment layer is high due to nonspecific medium, such as sugary gel. In contrast, the cross-linking or hybridization methods allow the binding of specific groups of proteins covalently. However, the conformation or activity of the proteins may be affected. Many proteinchips are spotted using automated technology, with spot densities greater than 30,000 spots per chip. Besides, synthesis of peptides can be performed on the chip by ▶photolithography. Analytical Approaches The labeled analytical approaches involve fluorescence or radioisotope labeling techniques. The label is directly attached to the protein or capture agent and detected straight away. It is then attached to a different molecule (such as antibody, antigen, or substrate) with subsequent washing of the proteinchip to avoid altering the conformation of proteins. The most common labeled detection methods include the enzyme-linked immunosorbent assay, sandwich immunoassay, isotopic labeling, planar waveguide, and electrochemical. However, although the approaches try to prevent label from altering protein conformation, interference with protein interactions may still exist. As label influence on binding properties, along with a knack for having a lack of reproducibility, some studies thus shift to use the label-free approaches. There are three main types of label-free analytical approaches. With the MS, proteinchips are coupled to a ▶matrix-assisted laser desorption/ionization-TOF MS detector. Improved resolution can be obtained using SELDI-TOF MS. Following the sample fractionation and subsequent processed with a proteinchip reader, protein profiles are generated and analyzed by specific software. Unlike MS, ▶surface plasmon resonance is an optical effect produced when polarized light is shone on a specially designed proteinchip. It can be coupled to MS for protein identification using microrecovery from the chip surface. A third method is the atomic force microscopy, which uses changes in surface topology to detect protein interactions. It is a high resolution technique and the data is collected in the form of topographical maps. Applications in Cancer Research The main applications of proteinchip profiling in ▶cancer research include identifying cancer ▶biomarkers, investigating protein–protein and protein–drug interactions, study of ▶posttranslational modifications, cancer profiling, determining the amount of protein in a sample, detection of microorganisms and toxins in cancer fluid, as well as testing for the presence of antibodies in a cancer cell. Proteinchip profiling has been used successfully to discover biomarkers with potential clinical usefulness

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in some cancer types, several examples are illustrated underneath. There was a development of integrated antibody microarray for simultaneous detection of multiple antigens and antibodies of five human ▶hepatitis viruses (HBV, HCV, HDV, HEV, and HGV). This integrated antibody microarray can be used for clinical diagnosis and epidemiological screening of ▶hepatitis virusassociated hepatocellular carcinoma. Serum samples from the patients with malignant or benign prostatic disease and control subjects were analyzed on antibody microarray targeting multiple candidate prostate cancer biomarkers to distinguish malignant from benign prostatic diseases. With the several detected disease-associated protein alterations, thrombospondin-1 was found to be the most significantly altered protein. It was decreased in the patients with prostate cancer, but increased in the patients with benign prostatic disease. To explore the use of combined measurements for serum sample classification, antibody microarray was also used to examine the associated proteins of pancreatic cancer. The antibodies that had reproducibly different binding levels between the patients with malignant and benign pancreatic diseases revealed different types of alterations, reflecting ▶inflammation (high C-reactive protein, alpha-1-antitrypsin, and serum amyloid A (SAA)), immune response (high IgA), leakage of cell breakdown products (low plasma gelsolin), and possibly altered vitamin K usage or glucose regulation (high protein-induced vitamin K antagonist-II). Using SELDI-TOF MS, two isoforms of SAA protein that were useful in the diagnosis of relapse in ▶nasopharyngeal carcinoma were identified. Monitoring the patients longitudinally for SAA level both by proteinchip and immunoassay showed a dramatic increase in SAA correlated with relapse, and a drastic fall in SAA correlated with response to salvage chemotherapy. Subsequent tandem MS sequencing and immunoaffinity capture assay identified platelet factor-4 as a treatment-associated serum biomarker that might serve for the triage of patients with nasopharyngeal carcinoma to appropriate chemotherapy treatment. The SELDI-TOF MS was also used to identify differentially cytosolic expressed proteins with a prognostic impact in node-negative ▶breast cancer patients with no relapse versus patients with metastatic relapse. The proteinchip laser desorption ionizationtandem quadrupole-TOF MS was used for biomarkers identification. Results showed that a high level of cytosolic ubiquitin and/or a low level of ferritin light chain were associated with a good prognosis in breast cancer.

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Proteins

Challenges and Perspectives There are many challenges when developing a protein microarray, such as creating an expression clone library, actual protein production that includes isolation and purification, adaptation of microarray technology, stabilizing the proteins on the array, as well as keeping the concentrations of the protein constant between slides and spots on the same slide. The analysis of proteinchips also comes with many challenges. Protein concentration is dynamic within a cell and there is trillion fold of difference between the low abundant proteins and the high abundant proteins. Unfortunately, the proteins that are usually of interest are normally in low concentration. Although purification and enrichment of proteins can address this problem, it is quite laborious and time-consuming. Besides, the application of protein microarray is limited by various fundamental problems, such as its multiplexing ability is limited by the cross-reactivity in parallel sandwich immunoassays. Therefore to determine a specific probe for each protein constitute another challenge. In addition, to integrate the proteomic profiling data with genomics and metabolomics, as well as translated them from bench to bedside applications is also a major challenge. Nevertheless, protein microarray is among the novel classes of rapidly evolving proteomic technologies that holds great promise in biomedicine. Out of a large background of immunoglobulins including natural antibodies, patients with cancer produce a minute amount of specific ▶autoantibodies against protein antigens. The ability to identify the fingerprintings of antibody signatures in malignancies can be useful in cancer diagnosis and prognosis. The great power of multiplex antibody microarray lies in its potential for rapid identification of antibody biomarkers found in blood and other biological fluids, which is sorely needed in the clinic to improve diagnosis, prediction of prognosis, and selection of ▶targeted therapy. With the development of advanced technologies, such as improved quantitative ▶proteomics methods, MS of ultra resolution, speed, and sensitivity, the development of functional protein assays, as well as sophisticated ▶bioinformatics, further advancement of the high-throughput proteinchip technology will be achieved. After confirmation in independent proteinchip profiling studies, promising potential cancer biomarkers should be submitted to higherthroughput methods practical for large-scale multiinstitutional validation studies and, ultimately, for clinical and epidemiological applications.

3. Cho WC, Yip TT, Ngan RK et al. (2007) ProteinChip array profiling for identification of disease- and chemotherapyassociated biomarkers of nasopharyngeal carcinoma. Clin Chem 53:241–250 4. Cho WC, Yip TT, Yip C et al. (2004) Identification of serum amyloid A protein as a potentially useful biomarker to monitor relapse of nasopharyngeal cancer by serum proteomic profiling. Clin Cancer Res 10:43–52 5. MacBeath G, Schreiber S (2000) Printing proteins as microarrays for high-throughput function determination. Science 289:1760–1764

Proteins Definition Are relatively large organic compounds made of amino acids arranged in a linear chain and joined together between the carboxyl atom of one amino acid and the amine nitrogen of another. This bond is called a peptide bond. The sequence of amino acids in a protein is defined by a gene and encoded in the genetic code.

14-3-3 Proteins Definition

References

Are abundant, highly conserved adaptor proteins of 30 kDa found in all eukaryotes. Similar to the binding of ▶SH2 domains to phosphorylated tyrosine residues, 14-3-3 proteins usually bind to their client protein via a phosphorylated Ser- or Thr-residue in a sequencespecific context (mode I: RSXpS/TP; mode II: RXXXpS/TXP with p indicating the phosphorylated residue and X any amino acid). 14-3-3 proteins assist in the stabilization of the client protein in either an active or inactive conformation. 14-3-3 proteins regulate a multitude of biological processes ranging from metabolic control to the regulation of apoptosis, cell cycle progression and mitogenic signaling. One of the seven of human 14-3-3 genes, 14-3-3σ/Stratifin, is frequently epigenetically silenced in breast, lung and prostate cancer and is discussed as a ▶tumor suppressor gene.

1. Cho WC (2007) Contribution of oncoproteomics to cancer biomarker discovery. Mol Cancer 6:25 2. Cho WC, Cheng CH (2007) Oncoproteomics technologies– current trends and future perspectives. Expert Rev Proteomics 4(3):401–410

▶B-Raf Signaling ▶Mitogen-Inducible Gene 6 (MIG-6) in Cancer ▶G2/M Transition ▶Kit/Stem Cell Factor Receptor in Oncogenesis

Proteomic Techniques

Proteoglycan

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Proteolysis

Definition

Definition

Glycosaminoglycans that are covalently linked to a core protein. Proteoglycans are complex macromolecules present primarily at the cell surface, in the extracellular matrix that surrounds most mammalian cell types, and also in body fluids. By virtue of the multiplicity of their protein binding partners (e.g., growth factors, chemokines, enzymes, and other extracellular matrix proteins), they have been shown to play major roles in regulating normal cellular processes, such as ▶adhesion, proliferation, remodeling, ▶migration, or ▶angiogenesis, which can become dysregulated in ▶inflammation and during cancer progression. Structurally, PGs consist of a core protein, of variable size and structure, and one or more associated glycosaminoglycan (GAG) chains. These GAGs can be of five types: chondroitin sulfate (CS), dermatan sulfate (DS), heparan sulfate (HS), heparin or keratan sulfate (KS). Growing evidence suggests that DS, like the better studied heparin and HS, is an important cofactor in a variety of cell behaviors.

Protein breakdown (degradation), which occurs generally as a result of hydrolysis at one or more peptide bonds. ▶Proteasome Inhibitors

Proteolytic Processing Definition Cleavage of proteins yielding peptides with biological functions distinct from the uncleaved form. ▶GLI Proteins

▶Endocan ▶Adhesion ▶Cell Adhesion Molecules ▶Hyaluronan Synthases

Proteome P Proteoglycanase ▶Stromelysin-1

Definition Is the complete profile of proteins expressed in a given tissue, cell or biological system at a given time. ▶Chromophore-Assisted Laser Inactivation

Proteoglycans Definition Proteoglycans are large glycoproteins, consisting of long polysaccharide chains (glycosaminoglycans) attached to a relatively small protein core. They are mainly found in the extracellular matrix or attached to the cell surface by a membrane spanning region or a glycosylphosphotidylinositol anchor. ▶Cell Adhesion Molecules

Proteomic Techniques Definition Methods for analysis of the large repertoire of proteins in a human cell, procedures for analysis of membrane proteins are highly specialized. ▶CD Antigens ▶Protein Microarray

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Proteomics

Proteomics WON -A J OO, DAVID W. S PEICHER The Wistar Institute, Philadelphia, PA, USA

Definition Proteomics is any systematic large scale study of a proteome or sub-proteome. The term proteome was coined in the mid-1990s as a linguistic equivalent to the concept of the genome. It refers to the complete set of proteins present in a biological specimen such as a single cell organism, a cell line, tissue, or biological fluid (serum, urine, saliva etc.). The proteomes of complex organisms are far more complex than the set of expressed genes because genes are usually alternatively spliced and expressed proteins are often extensively and heterogeneously posttranslationally modified. Unlike a genome that is largely static over the lifetime of a cell or organism, proteomes are constantly changing in response to changes in the environment of the cell, tissue or organism. Hence terms such as the “human proteome” or even the proteome of a cell line in tissue culture are meaningless because there are an essentially infinite number of proteomes.

Characteristics Because many proteomics studies are discovery-based rather than hypothesis driven, they are not constrained by prior knowledge. Proteomics, therefore, provides opportunities for unprecedented progress in biomedical and biological research. These discovery based studies are highly complementary to hypothesis driven research, and they are quite often appropriately referred to as “hypothesis generating.” Three major types of proteome analyses are: (i) protein profile comparisons, where quantitative changes in proteins between two or more experimental conditions are compared; (ii) compositional analyses, where the goal is to identify all proteins present in a single biological sample; and (iii) analysis of protein–protein interactions. Another way of phrasing proteome studies is as an attempt to define: who, when, where and with whom. Protein profiling and compositional analyses often utilize similar separation and analysis tools, with the latter type of study simply lacking a requirement for quantitation. The successive steps and associated critical issues for most types of proteome studies are: (i) experimental design – this includes selection of the organism and biological sample, conditions to be studied, goals of the study, and methods that will be utilized; (ii) sample preparation – method should be reproducible and care must be taken to avoid introducing artifacts that may be

difficult to segregate from biologically important features; (iii) analytical separations – how will the proteins in the targeted proteome or sub-proteome be separated and how many tandem separation methods will be used; (iv) protein identification – while tandem mass spectrometry (MS/MS) is used to identify proteins in most proteomics studies, important considerations include the type of mass spectrometer to be utilized and whether intact proteins or proteolytic fragments will be analyzed in the mass spectrometer; and (v) proteome informatics – issues include the sequence database that will be searched, the computer program(s) used to compare the MS/MS data to the database, and the software tools used to manage, view and data mine search results. Subproteomes and their Advantages The complexity of most proteomes from multi-cellular organisms is usually much greater than the capacity of most current analytical methods both in terms of the number of unique protein forms present and the wide range of protein abundance. As a result, when one attempts to analyze entire complex proteomes, only a small portion of the total proteins present in the biological specimen are analyzed. Hence, where feasible, it is advantageous to focus on a sub-proteome that can address the biological question of interest. Key factors are to select the appropriate sub-proteome and to ensure that isolation of this sub-proteome is highly reproducible as variations in sample preparation could be misinterpreted as experimentally important changes. Sub-proteomic approaches rely on enrichment techniques for isolation of proteins with similar biochemical characteristics, with similar function or within a specific cellular compartment. In many cases, widely used methods are used for sample isolation, such as sucrose gradient centrifugation for isolating organelles or cellular machines. Affinity purification using antibodies, the tandem affinity tag system or similar methods are typically used to isolate large multi-protein complexes. Common Protein Profiling Methods The most common type of proteomics analysis involves the quantitative comparison of protein changes under two or more experimental conditions. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) is the oldest and most commonly used method for comparative proteomics, despite several well known limitations. A newer version of 2D gels is 2D differential in gel electrophoresis (DIGE) where two to three different samples can be compared in a single gel after fluorescently tagging each sample with a different cyanine dye (Cy2, Cy3 or Cy5). Even though 2D-PAGE and 2D-DIGE can provide high resolution separation of proteins with detection of many single charge changes,

Proteomics

some groups of proteins are poorly recovered and detected, including very basic or acidic proteins, large proteins and membrane proteins. Quantitative changes are detected on 2D gels using either the cyanine dyes or conventional protein stains. Protein spots that are observed to change in intensity in the biological samples being compared are identified by excising the spot, digesting it with trypsin and analyzing it by LC–MS/MS An alternative strategy for quantifying protein changes in complex biological samples is to digest the entire sample with a protease, usually trypsin, and then separate the extremely complex mixture by ion exchange chromatography prior to capillary scale reverse phase chromatography interfaced directly with a mass spectrometer. This LC/LC–MS/MS approach is often referred to as “bottom up” or shotgun proteomics. It is better than 2D gels at detecting low abundance, acidic, basic, and membrane proteins but it provides very little information about changes in protein splicoforms, closely homologous proteins or posttranslational modifications because most protein identifications are inferred from identification of a few tryptic peptides. Quantitative comparisons are usually achieved in shotgun proteomics analyses by tagging two samples to be compared with a reagent that is chemically identical where one form is heavier than normal because it contains heavy stable isotopes of one or more atoms. Where feasible, the best method of introducing a heavy label is achieved by growing cells or simple organisms in media enriched in stable isotopecontaining metabolites such as 13C labeled essential amino acids. This stable isotope labeling in culture (SILAC) approach has the advantage that labeling occurs before any sample processing occurs, thereby avoiding the potential to interpret variable recovery of specific proteins during sample processing as biologically important changes. The alternative methods for introducing mass tags including modifying reactive groups on the proteins or chemical end labeling of peptides after proteolysis by a variety of different chemistries. An alternative method of quantitating proteins that is gaining in popularity is “label-free” quantitation, which compares the intensity of the ion current for a given peptide in a tandem MS experiment on an instrument with an electrospray interface (ESI). Labelfree methods have somewhat larger errors and lower reproducibility than stable isotope tagging methods, but they may prove adequate for detecting most biologically meaningful changes. Ion currents from ESI MS analysis are substantially more reproducible than signals from matrix assisted laser desorption/ionization (MALDI) MS measurements and the related surface enhanced laser desorption/ionization (SELDI) method. Other methods of comparing protein changes include using antibody arrays, reverse arrays where biological lysates are immobilized and probed with specific

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antibodies or other ligands of interest, and “top down” proteomics. Top down proteomics uses one or more modes of protein separation prior to introducing the intact protein into a mass spectrometer where the intact mass is measured prior to fragmenting the protein in the mass spectrometer in an attempt to identify the protein from the fragment information. Each method has its strengths and weaknesses and most of these methods are likely to continue to be useful for the foreseeable future. Proteome Informatics Computational analysis of the complex data resulting from most proteomics studies is often quite challenging. The importance of having good informatics tools for data interpretation and management has continued to increase as sequence databases become more complex, proteomes are divided into more fractions in attempts to dig more deeply into biological samples, and mass spectrometer become faster and more sensitive, thereby producing far larger datasets than older models. There is a need for standard methods to: describe proteomics experiments; store, manage and analyze MS data; and exchange data within the scientific community. The Proteome Standards Initiative of the Human Proteome Organization (HUPO), leading proteomics journals, and others are developing standards for data management, interpretation and dissemination in proteomic research across instrumentation and software platforms. Clinical Aspects Most diseases are expected to substantially alter the composition of the proteomes of affected cells and tissues. Such changes can include differences in protein levels, post-translational modifications, proteolytic processing, and sub-cellular location. Invariably when diseased and normal cells or tissues are compared, many protein changes are seen. The major challenge is to discern those changes that are most critical from incidental or nonspecific changes. Direct analysis of proteome changes in disease studies has great potential to identify novel diagnostic and therapeutic targets because protein activities are directly responsible for observed phenotype and most known drug targets are proteins. Logically, one focus of disease related proteomics studies is to compare diseased tissue with normal tissue, ▶Biomarkers. An alternative promising approach is to analyze changes in the blood or other biological fluids that are proximal to the affected tissue, ▶Serum Biomarkers. In general, potential disease biomarkers should be easiest to detect in the most proximal biological fluid but ultimately a blood test would be preferred since collection of blood is routine and minimally invasive. While proteomics has great potential for discovery of new disease diagnostic

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Prothrombotic, Proinflammatory, and Proadhesive Endothelium

and therapeutic targets, progress has been slowed by: the high complexity of human proteomes, especially blood; the substantial biological variability among the human population, the polygenetic and often heterogeneous nature of many diseases, and the limited detection and throughput capacity of current proteomics technologies. The discovery of cancer serum biomarkers is particularly challenging because the most specific markers are likely to be shed by only the tumor and not by other tissues. Hence, these proteins will be very low abundance in blood and very hard to detect, especially for early stage, small tumors, ▶Early Detection. However, proteomics technologies continue to evolve steadily and promising advances are being made in investigation of cancer and other diseases using proteomics approaches.

Proton Beam Therapy M ASAHARU H ATA Department of Radiology, Yokohama City University, Graduate School of Medicine, Yokohama, Kanagawa, Japan

Synonyms Proton therapy; Proton radiation therapy; Charged particle therapy

Definition

▶Proteomic Techniques

Proton beam therapy is a form of advanced radiation therapy that uses charged particles; it is used principally for the treatment of malignant tumors and occasionally for benign diseases.

References

Characteristics

1. Feng J, Shang S, Beretta L (2006) Proteomics for the early detection and treatment of hepatocellular carcinoma. Oncogene 25:3810–3817 2. Garcia-Foncillas J, Bandres E, Zarate R et al. (2006) Proteomic analysis in cancer research: potential application in clinical use. Clin Transl Oncol 8(4):250–260 3. Abbott A (1999) Proteomics, transcriptomics: what’s in a name? Nature 402:715–720 4. Speicher D, Lee K, Tang H et al. (2004) Current challenges in proteomics; mining low abundance proteins and expanding protein profiling capacities. In: Ashcroft A, Brenton G, Monaghan J (eds) Advances in mass spectrometry, vol. 16. Elsevier B.V., Amsterdam, pp 37–57

Prothrombotic, Proinflammatory, and Proadhesive Endothelium Definition Upon stimulation, the physiologically quiescent endothelium shifts into an activated state that promotes the adhesion of leukocytes, platelets, and tumor cells. ▶Tumor-Endothelial Cross-talk

Protoadjuvant Therapy ▶Neoadjuvant Therapy

Advanced radiation techniques that use photons (X-rays), such as ▶three-dimensional conformal radiation therapy (3D CRT) and ▶intensity-modulated radiation therapy (IMRT), have seen rapid recent development. The common goal of these treatments is to deliver a high dose to the target while minimizing the dose given to normal tissues. This is essential to achieve better local control and lower toxicity in the treatment of malignant tumors. Although advanced radiation therapies such as these enable higher-dose irradiation to a target, they produce a larger low-dose irradiated volume of normal tissues around the target due to the dispersion of radiation; this will increase the risk of radiationinduced secondary malignancies, especially for children, or unexpected late adverse events. In contrast, proton beams can theoretically produce excellent dose localization to a target compared with photons because of the sharp distal fall-off of the Bragg peak, which gives no dose to normal tissues beyond the target. This physical characteristic is extremely useful for dose escalation to malignant tumors and is expected to yield enhanced treatment efficacy and reduced toxicity, especially in the treatment of tumors adjacent to critical organs. Physical Properties A proton is a positively charged elementary particle and is the nucleus of the hydrogen atom. It is 1,836 times more massive than an electron, which is the other constituent particle of a hydrogen atom. When a proton obtained by stripping a hydrogen atom of an electron is accelerated to high energy in electric fields using a particle accelerator such as a cyclotron or synchrotron, it becomes a type of ionizing radiation and can penetrate a deep area of the tissue. The charged proton decelerates

Proton Beam Therapy

as its energy is lost due to interactions with electrons in atoms of the tissue; eventually it stops. Just before the proton stops, the interaction rapidly augments and abruptly increases ▶excitation and ▶ionization of the atoms. This sharp increase in dose absorption is called the “Bragg peak.” Once the proton stops, the interactions no longer arise, and no dose is given beyond the Bragg peak. The penetration depth of the Bragg peak depends on the initial energy of the charged proton. Accordingly, the Bragg peak can be precisely placed according to the depth of the target; however, pristine and unmodulated monoenergetic protons are unsuitable for clinical use because the dimensions of most targets are far greater than that of the narrow Bragg peak. To overcome this problem, the Bragg peak is modulated in practical treatment, the so-called “spread-out Bragg peak (SOBP),” to cover the targets effectively (Fig. 1). Biological Properties Excitation and ionization occur in tissues along a proton path, producing chemically active ▶radicals that impair DNA in the chromosome of a cell. Although cells usually have the ability to self-recover from such impairment, they cannot divide normally or proliferate when the impairment exceeds a certain level. Proton beams are used for cancer treatment utilizing these actions in the same way as photons. Relative biological effectiveness (RBE) is defined as the ratio of the physical dose required to produce a specified effect using reference photons (usually 60Co) relative to that of a specific radiation required to produce the same

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effect. RBE values in the mid-SOBP of proton beams obtained from outcomes of various experiments in vitro and in vivo range from 0.7 to 2.1. It is known that different accelerators of protons or instruments for beam delivery used at each institution have different RBE values. Furthermore, different RBE values occur even in different measured points of the SOBP, e.g., in the proximal, middle, or distal SOBP. An RBE value of 1.0 or 1.1 is usually adopted for clinical use, and a physical dose of protons multiplied by the RBE value is indicated using the unit of Gray Equivalent (GyE). An RBE value of 1.0 or 1.1 signifies that there is no great difference between protons and photons in terms of the physical doses required to produce a certain specified effect. Thus, the abundant medical data available concerning treatment efficacies for tumors and toxicities of normal tissues using photon irradiation are directly applicable to proton beam therapy. Clinical Aspects Compared with conventional photon irradiation, proton beam irradiation is expected to yield enhanced treatment efficacy and reduced toxicity in radiation therapy for a wide range of malignancies. Representative diseases that are widely treated with proton beam therapy are described in the following section. Uveal (choroidal) Melanoma ▶Uveal melanoma is one of the most common primary ocular tumors; it was formerly treated with enucleation of the eye. ▶Brachytherapy with radioactive plaques

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Proton Beam Therapy. Figure 1 Depth-dose curves for 10 MV X-rays, 15 MeV electrons, pristine protons, and the spread-out Bragg peak (SOBP) produced by a composition of variously modulated protons. For pristine protons, the dose suddenly increases and the Bragg peak is formed before the dose abruptly decreases to zero due to sharp distal fall-off; X-rays penetrate a deeper area, while electrons do not penetrate deeply.

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has been used as an eye-preserving therapy in place of enucleation over the past few decades. This approach provides local control of more than 80% at 5 years. Proton beam therapy has recently been applied as a less invasive treatment, and total doses of 50–70 GyE in 4–5 fractions achieves an excellent 5-year local control rate of approximately 95%. Sarcomas of the Skull Base and Spine ▶Chondrosarcoma and chordoma are common tumors of the skull base and spine. Surgical resection is performed for these tumors with curative intent, but they are frequently resected incompletely because of their proximity to critical organs such as the brain and spinal cord. Although conventional photon irradiation is used for unresectable tumors, it is very difficult to give a sufficient tumoricidal dose due to the limited tolerable doses of the adjacent critical organs. Proton beam irradiation allows the delivery of higher doses over 70 GyE and provides 5-year local control of almost 100% for chondrosarcoma and 50–60% for chordoma. Head and Neck Cancers Radiation therapy alone or in combination with chemotherapy is widely used for head and neck cancers for the purpose of preserving the function and configuration of organs. Proton beams facilitate the prevention of brain and bone necrosis and the conservation of salivary function while delivering high doses to tumors. The advantages of proton beams are of particular benefit in irradiation of paranasal sinus and ▶nasopharyngeal carcinomas located adjacent to the central nervous system. Although few reports describe the use of proton beams for head and neck cancers, this group is among the most suitable subjects for proton beam therapy. Lung Cancer Surgical resection remains the most standard and curative treatment for early stage ▶non-small cell lung cancer (NSCLC); however, radiation therapy is a feasible treatment option for patients who are inoperable because of comorbidities or who refuse surgical procedures. The irradiated volume and dose given to a pulmonary tumor are frequently restricted due to the low tolerable dose of the lung, and irradiation with large radiation fields and high doses causes severe and occasionally mortal ▶radiation pneumonitis. The use of proton beams for lung cancer may reduce the incidence of radiation pneumonitis and enable the safe delivery of high doses to tumors adjacent to the heart, esophagus, and spinal cord. Hypofractionated high-dose proton beam therapy, e.g., with a total dose of 60 GyE in ten fractions, provides local control of approximately 95% for Stage I NSCLC.

Hepatocellular Carcinoma The most reliable curative treatment for ▶hepatocellular carcinoma (HCC) remains surgical resection; however, approximately 80% of HCCs are unresectable due to advanced tumors and coexisting cirrhosis at diagnosis. Although nonsurgical treatments such as transcatheter arterial chemoembolization (TACE), percutaneous ethanol injection (PEI), and radiofrequency ablation (RFA) are usually applied to inoperable HCC patients, local failures are common following TACE, and PEI and RFA are unsuitable for patients with bleeding tendency due to cirrhosis, large-sized tumors, or unfavorable tumor location. Therefore, there are numerous patients who have limited treatment options and are unable to undergo effective treatments. Proton beam therapy is widely available for such patients, and provides local control of approximately 90% at 5 years. Furthermore, almost all unresectable HCCs with portal vein tumor thrombus are locally controlled with proton beam therapy. HCC patients commonly develop new intrahepatic lesions remote from the initial tumor after irradiation. In these cases, proton beams enable reirradiation of the new lesions because the irradiated volume and dose given to the normal liver was minimized at the time of previous irradiation. The difference in isodose distributions between protons and photons is shown in Fig. 2. Prostate Cancer ▶Prostate cancer is one of the diseases that are most commonly treated with proton beam therapy worldwide. Radiation therapy can almost match the treatment results of surgery in patients with localized prostate cancer. Prostate cancer is more likely to arise in the elderly; the number of prostate cancer patients is expected to increase because the average life span has been prolonged in many countries. As a less invasive treatment is generally more favorable for aged patients, the proportion of prostate cancer patients receiving radiation therapy will probably increase in the future. Because the prostate is located adjacent to the urinary bladder and rectum, high-dose irradiation to the prostate causes an increase in the incidence of radiation-induced urinary and rectal complications. Proton beam irradiation is used with the aim of decreasing these toxicities. Proton beam therapy alone or in combination with photon irradiation with total doses of 74 GyE or more in conventional fractions provides a biochemical diseasefree (▶prostate-specific antigen failure-free) rate of approximately 80% at 5 years for patients with earlystage prostate cancer. Childhood Cancers Proton beams are used for the treatment of ▶childhood cancers, e.g., brain tumors such as ▶medulloblastoma and optic pathway glioma, ▶retinoblastoma, ▶malignant

Proton Radiation Therapy

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Proton Beam Therapy. Figure 2 Treatment planning with CT for a hepatocellular carcinoma patient with tumor thrombus in the left main portal vein. (a) Isodose distribution of proton beams delivered through three ports (one anterior and two oblique) to a tumor, including portal vein tumor thrombus. The entire target (contoured by the white line) is homogeneously encompassed by the 100% dose level (red color). Critical organs such as the spinal cord and digestive tract are located entirely outside the irradiated volume, due to the sharp distal fall-off of the Bragg peak of proton beams. (b) Isodose distribution shaped by 10 MV X-rays delivered through the same ports. The irradiated volume increases considerably, meaning that normal structures, including the above-mentioned critical organs and normal liver, are exposed to radiation.

lymphoma, and soft-tissue sarcomas including ▶rhabdomyosarcoma. As proton beam therapy is useful in reducing the risk of radiation-induced secondary malignancies, growth failure, and neurological deficits, it is a treatment of great significance for this group. Miscellaneous Proton beam therapy is also attempted for other various malignant tumors such as ▶glioblastoma multiforme, ▶breast cancer, ▶esophageal cancer, ▶bladder cancer, and ▶cervical cancer, as well as benign diseases such as pituitary adenoma and arteriovenous malformation. Facilities and Costs for Proton Beam Therapy There are more than 20 facilities for proton beam therapy in operation worldwide; more than 48,000 patients have received proton beam therapy as of January 2007. Although several new facilities are being built internationally, the number remains insufficient to meet the needs of cancer patients. The large area and great expense involved in building a new facility hamper the spread of proton beam therapy; however, construction of a new facility is becoming easier because miniaturization of the particle accelerator has reduced the size requirement of the site, and construction costs have fallen with the rationalization of production procedures. This reduction in cost will reduce the cost disparity per treatment between radiation therapies using protons and photons. Furthermore, the greater the number of patients that receive proton beam therapy, the lower the cost per treatment. The relative cost of proton beam therapy compared to

IMRT with photons is currently estimated at approximately 2.4, but is predicted to decrease to 1.7–2.1 over the next few years. There is a need for a future environment in which more patients can undergo proton beam therapy at lower cost.

References 1. Goitein M, Jermann M (2003) The relative costs of proton and X-ray radiation therapy. Clin Oncol 15:S37–S50 2. Hata M, Tokuuye K, Kagei K et al. (2007) Hypofractionated high-dose proton beam therapy for stage I nonsmall-cell lung cancer: preliminary results of a phase I/II clinical study. Int J Radiat Oncol Biol Phys 68:786–793 3. Hata M, Tokuuye K, Sugahara S et al. (2006) Proton beam therapy for hepatocellular carcinoma with limited treatment options. Cancer 107:591–598 4. Paganetti H, Niemierko A, Ancukiewicz M et al. (2002) Relative biological effectiveness (RBE) values for proton beam therapy. Int J Radiat Oncol Biol Phys 53:407–421 5. Suit H, Goldberg S, Niemierko A et al. (2003) Proton beams to replace photon beams in radical dose treatments. Acta Oncol 42:800–808

Proton Radiation Therapy ▶Proton Beam Therapy

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Proton Therapy ▶Proton Beam Therapy

Proto-oncogene Definition A proto-oncogene is a normal cellular gene that, when activated by mutations, acquires oncogenic function. The activating mutations can include intragenic point mutation, translocation (creating a fusion transcript or resulting in transcriptional up-regulation) or amplification with the consequence of enhanced expression; oncogene. Also referred to as cellulor Oncogene (conc). ▶Transduction of Oncogenes

Protoporphyrin IX

Prox-1 Definition A transcription factor expressed in lymphatic endothelial cells but not vascular endothelial cells that is required for development of the lymphatic system. This factor regulates expression of a number of lymphatic endothelial cell genes and suppresses vascular endothelial cell specific gene expression. ▶Lymphangiogenesis

Proximal-type Epithelioid Sarcomas Definition Highly aggressive soft-tissue tumors of young adults, characterized by both epithelial and mesenchymal phenotype; they harbor a variable amount of rhabdoid cells and occasional hSNF5/INI1 inactivation. ▶Tumor Suppressor hSNF5/INI1

Definition PpIX; Is the precursor of heme, which is the prosthetic group of hemoglobin, myoglobin, cytochromes, and metalloproteins. PpIX is a potent fluorescent dye and photosensitizer. Its induced accumulation in malignant cells is used for fluorescence-guided resection or fluorescence diagnosis and photodynamic therapy of malignant and nonmalignant diseases. ▶Photodynamic Therapy

Proximate Carcinogen Definition A metabolite of a carcinogen intermediate in the conversion to an ultimate carcinogen. ▶Toxicological Carcinogenesis

Provirus Definition

Prozac

The double-stranded DNA form of a retroviral genome. ▶Transduction of Oncogenes

▶Fluoxetine

Prune

Prune M ASSIMO Z OLLO Department of Genetics, Faculty of Biotechnological Sciences Federico II, Naples, CEINGE, Biotecnologie Avanzate, Naples, Italy

Definition Prune stands for the human homologue of the Drosophila prune gene. Prune protein was initially identified in Drosophila, in which its mutation caused a brownishpurple “prune” eye color due to significant loss of drosopterins “red pigments,” compared to the bright red eye of the wild-type fly, thus explaining its mutant name.

Characteristics Prune is appertaining to the DHH family phosphoesterase proteins including RecJ DNA repair Exonucleases, Pyrophosphatases (PPASEs) and Exopolyphospatases (PPX). The DHH super-family can be divided into two main groups on the basis of a C-terminal motif that is very well conserved within each group, but not across

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the groups. All the members of this super-family possess four other motifs that contain highly conserved charged residues predicted to be responsible for binding ions and catalyzing the phosphoesterase reaction. The most characteristic of these is the third motif, with the signature DHH (Asp-His-His), after which this superfamily was named. Prune is a cyclic nucleotides phosphodiesterase. Due to its protein similarities, Prune might possess other biochemical functionalities within the DHH family of proteins. Human prune, a 62 kDa protein, acting as a cytoplasmic cyclic nucleotides phosphodiesterases (cNMP-PDE) is involved in both promoting cellular mobility and stimulating expression of genes involved in metastatic pathways. In breast cancer, metastatic spread is responsible for virtually all cancer deaths. ▶Metastasis is a highly complex molecular and cellular process. To become invasive, tumor cells need to change their adhesive properties, to lose contact with other cells in the primary tumor, and make new contacts with the extracellular matrix of host cells they encounter as they invade. They also need to be able to penetrate into the surrounding host tissue, and here the modulation of protease activity in the vicinity of the tumor cells plays a critical role.

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Prune. Figure 1 Ribbon structure of the h-prune protein based on the crystal structure of PPASE and the RecJ protein. Red balls indicate potential cofactor ions (Mg2+ and/or Mn2+) and the region of binding to motif III. Arrows indicate the aspartic acids (D). Aspartic acids of the four DHH motifs are represented, indicating the potential catalytic site of DHH protein family [1].

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To migrate away from the primary tumor, tumor cells also need to gain motility functions. These same properties are also thought to be important when circulating tumor cells exit the circulatory system and start metastatic colonization in secondary organs. Prune possesses a cAMP phosphodiesterase activity, which is responsible for increasing cell motility in breast carcinoma cell lines. Within the breast cancer cellular model, using gene expression analyses, several key players were identified acting as signals of cytoskeleton remodeling and cell motility, thus influencing the malignancy of Prune overexpressing breast cancer cells. The physical interaction between Prune and nm23H1, a suppressor of metastasis protein, enhances Prune cAMP-PDE activity, thus the interaction causes the subtraction of unbound nm23-H1 proteins into the cell. The major component of the nm23-H1 anti-metastases function is its capability to induce “low motility cellular processes” if overexpressed in aggressive breast cancer cells, although this activity was found in other solid tumors such as prostate, colon, lung, head and neck. Amplification of Prune copy numbers induces cell proliferation and high levels of Prune expression compared to the moderate or lower nm23-H1 level of expression that is correlated to aggressiveness of sarcoma and breast carcinoma, colon and gastric carcinoma, thus postulating an inhibitory role of Prune versus the antimetastasis nm23 function “in vivo.”

The region of the nm23–h-prune interaction lies between S120 and S125 of nm23, where missense mutants show impaired binding; this region can undergo serine phosphorylation by casein kinase I. Thus, the casein kinase I δ-ε specific inhibitor IC261 impairs the formation of the nm23–h-prune complex, which translates “in vitro” into inhibition of cellular motility in a breast cancer cellular mode. Regulation Prune participates in the complex network of interactions with proteins involved in cell cycle and cell motility. It is known that: (i) Prune together with glycogen synthase kinase-3 (GSK3β), a kinase involved in ▶WNT signaling pathway, cooperatively regulates the disassembly of focal adhesions to promote cell migration, and (ii) Prune via interaction with Gelsolin, an ATP severing protein acting in focal adhesions, leads to invasion properties of cancer cells. Both of these pathways promote cancer metastasis. Interestingly, Prune has also been shown to be highly expressed in brain development together with nm23-H1, expression was observed in cortex, hippocampus, midbrain and during cerebellum development. Clinical Relevance Prune has a role in the metastatic processes through specific inhibition of the anti-metastasis function of

Prune. Figure 2 (a) Expression and cytogenetic analysis of h-prune in breast carcinomas. (b) FISH analyses on the same samples using h-prune/ PAC279-H19 (red) and control pUC177 (green) as probes [4]. (c) Expression and cytogenetic analysis of h-prune in colon cancer. (d) Expression and cytogenetic analysis of h-prune in a metastasis site in lung from primary colon cancer (see c) (data unpublished).

PSA

▶nm23-H1 in vivo. Overexpression of Prune is involved in cancer progression and tumor aggressiveness, particularly by defining the lymphnode positive status and correlated to breast cancer advanced disease status. This condition is enhanced in colon carcinoma where Prune positive tumors have a bad sign of malignancy and prognosis. Significant statistical analyses of Prune immunostaining positive colon carcinoma associates the level of expression to tumor grade (T1-T2/T3-T4) (▶grading of tumors), lymphnode status (N0/N1-N2) and metastases grade (M0/M1), while only to tumor grade (T1-T2/T3-T4) and lymphnode status (N0/N1), in pancreatic cancer. Two reports described h-prune involvement with tumor progression in gastric cancer and in esophageal squamous cell carcinoma as an independent prognostic marker. Inhibition Four ways of inhibition of Prune pro-motility activity in cancer cells (in breast, colon and pancreas) are postulated at this time. Firstly the use of Dipyridamole, which alters its cAMP-PDE function in breast cancer cells, and thus negatively influencing its pro-motility effect. Secondly, the strategy of using the inhibition of Prune-GSK3β functional interaction in focal adhesion using SB216763 (a specific GSK3β inhibitor) or a combination of dipyridamole and SB216763. Thirdly, by using a peptide mimicking the region of interaction between Prune and GSK3β including the amino-acid region position 333–443 of Prune protein. Fourthly, by using IC261, a drug that impairs the CKI function thus inhibiting nm23-H1 S125 phosphorylation and consequently impairing the binding with Prune.

References 1. D’Angelo A, Garzia L, Andre A et al. (2004) Prune cAMP phosphodiesterase binds nm23-H1 and promotes cancer metastasis. Cancer Cell 5:137–149 2. D’Angelo A, Zollo M (2004) Unraveling genes and pathways influenced by H-prune PDE overexpression: a model to study cellular motility. Cell Cycle 3:758–761 3. Garzia L, D’Angelo A, Amoresano A et al. (2007) Phosphorylation of nm23-H1 by CKI induces its complex formation with h-prune and promotes cell motility. Oncogene doi:10.1038/sj.onc.1210822 4. Zollo M, Andre A, Cossu A, et al. (2005) Overexpression of h-prune in breast cancer is correlated with advanced disease status. Clin Cancer Res 11:199–205

PS 341 ▶Bortezomib

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PSA C ARSTEN S TEPHAN Department of Urology, Charité Universitätsmedizin, Campus Charité Mitte, Berlin, Germany

Synonyms Human kallikrein 3; KLK3

Definition Prostate-specific antigen (PSA) is a serine protease (33 kD) secreted mainly by prostatic epithelium. It is important for its role in the liquefaction of seminal coagulum.

Characteristics After a tissue specific antigen was identified in the human prostate in 1970 and the discovery of prostatic antigens in seminal plasma, PSA was subsequently isolated and characterized in 1979. PSA was cloned in 1987. PSA mRNA encodes for (261) 244 amino acid (pre)proforms of the protein, although the mature, catalytically active, single-chain form of the protein contains 237 amino acid residues. As member of the human ▶kallikrein family, PSA shares considerable structural and functional homology with all other 14 human kallikreins, together with a gene location on the long arm of chromosome 19 (19q13.2-q13.4). Kallikreins are proteases that cleave vasoactive kinin peptides from kininogen. PSA, however, functions as a chymotrypsin-like serine protease cleaving substrates such as seminogelin I, seminogelin II, fibronectin, and insulin-like growth factor/binding protein in the seminal plasma which helps maintain sperm motility. PSA is made primarily by prostatic epithelium and periurethral glands in males, but it has also been detected in endometrium, breast tissue, breast cancer, breast milk, and female serum. In normal prostate, the epithelium secretes PSA into the seminal fluid, where it reaches concentrations of 0.4–5 g/L. In the normal male, PSA is detected in the circulation at low concentrations of 0–1 (2) μg/L. Approximately 75% of PSA found in serum is irreversibly bound to the protease inhibitor alpha-1antichymotrypsin (ACT). Serum PSA also binds to alpha2-macroglobulin (A2M). Measured PSA in serum comprises 5–50% unbound or free (fPSA). PSA has five immunoreactive sites. Two of these epitopes are hidden in ACT-PSA, allowing commercial immunoassays to differentiate bound from free PSA. All five epitopes are hidden in A2M-PSA. Therefore, total PSA (tPSA) measured by commercial assays corresponds to f PSA plus PSA bound to proteins other than A2M-PSA.

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A small part of tPSA (0.9–1.6%) is also bound to alpha1protease inhibitor (API-PSA). Complexed PSA (cPSA), defined on the basis of an assay utilizing a blocking antibody to fPSA, detects ACT-PSA and API-PSA, but not the A2M-PSA complex. Several uses of the cPSA test have been proposed. Free PSA has recently been shown to exist in at least three molecular forms; “benign” PSA (bPSA), inactive “intact” PSA (iPSA), and proPSA. An overview of all PSA forms is given in the figure. The bPSA is a specifically clipped subform of fPSA, which is highly associated with the transition zone containing benign prostatic hyperplasia (BPH) nodules in prostate tissue. BPSA represents 0–60% of fPSA but it cannot discriminate between BPH and ▶prostate cancer (PCa). Based on the development of novel anti-PSA antibodies that do not recognize internally cleaved PSA at Lys145-Lys146 and thus are specific for intact, unclipped PSA, an assay has been developed for “intact” PSA (iPSA). The iPSA assay detects both proPSA and other inactive non-clipped fPSA entities and can discriminate between BPH and PCa. Recently, proPSA forms were isolated in serum and tissue from PCa patients. The proPSA in serum and prostate tissue exists as a mixture of differently designated forms including the (–7), (–5), (–4) forms and, partially, the (–2) and (–1) forms. Whereas the (–5, –7) proPSA have limited validity to improve PCa detection, the (–2) proPSA seems to better discriminate BPH and PCa and may further detect more aggressive PCa, as indicated by Gleason score 7 or greater. The ratio of free to total PSA used in literature as f/tPSA ratio (percent free PSA, %fPSA) tends to be increased in benign disease compared to PCa. The reason for this difference is not completely understood. It is assumed that due to the loss of tissue architecture in PCa the intracellular active PSA gains quicker access to the circulation and protease inhibitors, like ACT and A2M, can bind PSA easily. If PSA reaches the circulation from normal or BPH cells, it first has to leak into the extracellular space, where it is susceptible to proteolytic degradation. After degradation, the inactive PSA can still form complexes with A2M but only to a very small degree with ACT. This may explain the decreased capability of PSA to form complexes with ACT and the higher concentration of PSA-A2M in BPH patients. Clinical Aspects PSA is organ-specific, but not cancer-specific, since it can by produced by normal, hyperplastic, and neoplastic prostate epithelial cells. PSA synthesis is influenced by testosterone levels. It has limited sensitivity and specificity in appropriately detecting the earlier stages of abnormal prostate growth. The elevated circulating PSA levels can be due

to PSA leakage into the bloodstream from abnormal prostate growth or inflammation, such as prostatitis.

PSA as Diagnostic Marker Measurement of serum PSA is commonly used to aid the diagnosis of PCa. The introduction of routine PSA-based screening, together with digital rectal examination (DRE), over the past 20 years has led to a dramatic increase in the rate of disease detection and a subsequent stage shift at the time of diagnosis. For many years, a PSA value of 4 μg/L has been used as the cutoff for prostate biopsy. However, in 2004, an analysis of 2950 men, who never had a PSA level >4.0 μg/L or an abnormal DRE, PSA levels of 0–4 μg/L were associated with a positive predictive value (PPV) for PCa of 6.6% (PSA 0–0.5 μg/L) to 26.9% (PSA 3.1– 4 μg/L). Overall, 15% of men with PCa had high-grade disease, with this rate reaching 25% among men with a PSA level of 3.1–4 μg/L. Thus, there is no PSA level, where PCa or even aggressive PCa can be excluded. A further problem is evidence that PSA screening can reduce PCa mortality in large randomized prospective studies and therefore population screening is debated. In 2008/2009, results of two large randomized studies in Europe and USA will provide sufficient information whether PSA screening can reduce PCa mortality. Despite these controversies, PSA has revolutionized the management of PCa especially for the early disease detection, which has improved curative treatment. To date, the most commonly used and easy available PCa screening tool is the combined use of DRE and PSA as each can identify cancers not detected by the other. It has been shown, that screening intervals can be extended to 5–8 years for men with an initial serum PSA level of 90% of nasopharyngeal carcinomas in Hong Kong, 50% of those in Guangzhou and >60% of those in Chinese people in Malaysia are due to childhood consumption of salted fish. Animal data have further strengthened the evidence for Cantonese-style salted fish as a nasopharyngeal carcinogen. For example, rats fed this human food developed cancer of the nasal cavity in a dose-dependent manner, though this cancer rarely occurs in this species. Based on these evidences, the relationship between Chinese-style salted fish and nasopharyngeal carcinoma was determined to be “convincing” by the WHO/FAO (World Health Organization/Food and Agriculture Organization) Expert Consultation on Diet. However, it may be that salted fish has an oncogenic action not shared by salt alone. Experimental studies have shown that low levels of several nitrosamines/ precursors and ▶Epstein–Barr virus-activating substances exist in preserved salted fish. Some epidemiological studies have also indicated that nitrosamines and nitrates included in preserved food play a role in the development of nasopharyngeal carcinoma if such foods are consumed during childhood. On the other hand, the antibody of Epstein–Barr virus has been found in the sera of nasopharyngeal carcinoma patients, suggesting that this virus is associated with nasopharyngeal carcinoma as well as with Burkitt’s lymphoma. The consumption of salted fish may lead to

the activation of Epstein–Barr virus in the sera. Further investigations are needed to examine the mechanisms through which Chinese-style salted fish increases the incidence of nasopharyngeal carcinoma. Gastric Cancer The incidence of gastric cancer also differs by geographic location and ethnicity. In 2002, the agestandardized incidence rates (per 100,000) of gastric cancer in Japan were 62.0 in men and 26.1 in women, and these rates as well as those in Korea (69.7 in men and 26.8 in women) were among the highest in the world. In contrast, among the white population in western countries, the incidence rate was 7.4–12.8 in men and 3.4–6.6 in women, which is clearly far lower than that in Asian countries. In the INTERSALT study, median sodium levels were analyzed in relation to national gastric cancer mortality rates. For the 24 countries studied, the Pearson’s correlation coefficient for gastric cancer mortality with sodium was 0.70 in men and 0.74 in women (both P3 months. ▶Menopausal Symptoms After Breast Cancer Therapy

Secondary Cancer Prevention Definition

Secondary Lymphedema Definition A condition in which the lymphatic system is physically damaged by surgery (such as to remove lymph nodes) or injury, resulting in interrupted flow of lymph and blocked drainage of fluid from tissues, skin thickening and adipose tissue accumulation. ▶Lymphangiogenesis

Prevention of tumor progression through early diagnosis of asymptomatic tumors and/or treatments against preneoplastic or early neoplastic lesions. ▶Immunoprevention of Cancer

Secondary Cancer Site Definition The discontinuous end location where a metastatic cancer cell grows after it spreads from its primary site. For metastatic breast cancer to the bones, the secondary site is the bones. ▶Metastatic Colonization

Secondary Lymphoid Organs Definition

Secondary (or “peripheral”) lymphoid organs include the lymph nodes, spleen and mucosa-associated lymphoid tissue (MALT). The secondary lymphoid structures function to survey all entering or circulating antigen and to mobilize an immune response against antigen upon its discovery. This is in contrast to the primary (or “central”) lymphoid organs. These are the sites where the cells of the immune system are produced including the bone marrow and the thymus required for T cell maturation. ▶DNA Vaccination

Secondary Dissemination Definition

Secondary Metabolites

Dissemination following initial treatment. ▶Leptomeningeal Dissemination

▶Natural Products

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Secondary Structure

Secondary Structure Definition

The linear arrangement or topology of α-helices and β-sheets with respect to the amino acid sequence. ▶Structural Biology

g-Secretase Definition A protease that is responsible for the processing of the cytoplasmic domains of several type I membrane proteins, such as the amyloid beta-protein precursor (in Alzheimer disease), Notch, and CD44. The cytoplasmic regions are translocated to the nucleus where they function as transcription factors. ▶CD44

Secondary Tumor ▶Metastasis

Secreted Phosphoprotein 1 ▶Osteopontin

Secondhand Tobacco Smoke Definition

Secreted Protein Acidic and Rich in Cysteine

A composite of sidestream smoke and the smoke exhaled by a smoker. Sidestream smoke is the material released into the air from the burning tip of the cigarette plus the material which diffuses through the paper.

A LEXANDRE C HLENSKI , S USAN L. C OHN

▶Tobacco Carcinogenesis

Department of Pediatrics, Section of Hematology/ Oncology, University of Chicago, Chicago, IL, USA

Synonyms Osteonectin; BM-40; SPARC

Secosteroid Definition Steroid molecule with a broken B-ring (C9 and C10). ▶Vitamin D

Definition Secreted Protein Acidic and Rich in Cysteine (SPARC) belongs to a group of non-structural proteins of the extracellular matrix (ECM), termed ▶matricellular proteins, which modulate interactions between cells and their environment. It is expressed in developing and remodeling tissues, and regulates cell attachment, deposition of ECM, matrix mineralization, and ▶angiogenesis.

Characteristics

Secretagogues ▶Gut Peptides

SPARC is a counter-adhesive protein that induces cell rounding, inhibits cell spreading and mediates focal adhesion disassembly and the reorganization of actin stress fibers. In several cell types, it delays cell cycle in G1 phase. It is the main non-collagenous component of bone, where binding of SPARC to

Secreted Protein Acidic and Rich in Cysteine

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collagen can induce deposition of calcium. However, inhibition of ▶hydroxylapatite crystallization suggests that SPARC prevents matrix mineralization rather than inducing it. SPARC also regulates the production, assembly, and organization of ECM, and accordingly, it is expressed at high levels in developing tissues during embryogenesis and in remodeling adult tissues, such as gut, ovary, testis, mammary gland, bone and in healing wounds. SPARC is predominantly secreted by non-epithelial cells including endothelial and smooth muscle cells, osteoblasts and platelets. Fibroblasts and ▶macrophages express SPARC in healing wounds, where it is also released by platelet degranulation.

expression by ▶retinoic acid and dexamethasone. Histone acetylation is essential for the activation of transcription by ▶retinoid receptors. Sodium butyrate, an inhibitor of ▶histone deacetylase, has been shown to stimulate SPARC expression. The activation of SPARC transcription by cAMP is consistent with several cAMP consensus sequences found in the promoter region and in the first intron. The presence of a heat shock element correlates with heat- and stressinduction of SPARC expression. Jun and ATF family members repress SPARC transcription in fibroblasts, but stimulate expression in epithelial cells, although this regulation appears to be indirect.

Gene Organization The SPARC gene spans 25.9 kb on human chromosome 5q31.3-q32. Its first non-coding exon is separated from the following coding exons by a large 10.6 kb intron. Exon 10 contains the entire 3′ non-translated region. This gene organization and the transcription start site are highly conserved in vertebrates. The major human 2.2 kb transcript contains an open reading frame from nucleotides 84 to 992, followed by 1,137 bp of 3′ non-translated region. The less abundant 3.0 kb transcript has an identical coding region, but utilizes a downstream polyadenylation signal. The SPARC promoter lacks TATA and CAAT boxes, but contains a GGA box 1 between nucleotides −51 and −120 which drives transcription. A GGA box 2 is located between nucleotides −131 and −165. Both boxes are mainly composed of a repetitive GGA motif. They are positive regulators of promoter activity, while a 10 bp spacer of low purine content has a negative impact. Three ▶Retinoid X/▶Vitamin D receptor binding sites, immediately followed by an ▶E-box in GGA box 1, may be responsible for stimulation of SPARC

Protein Structure The structure of SPARC is highly conserved among different species. All cysteine residues are found at identical positions from human to nematode, indicating that protein folding is critical for function. After the 17 amino acid signaling peptide is removed, the human protein is secreted as a polypeptide of 286 residues with a calculated mass of 32 kDa, which migrates at 40–43 kDa on SDS-PAGE due to ▶glycosylation and possibly other posttranslational modifications. The protein is divided into three distinct domains (Fig. 1). The loosely structured N-terminal acidic domain (Ala1-Glu52) has an α-helical character, which depends on binding several Ca2+ molecules with low affinity. Clusters of glutamic acid in this region resemble the γ-carboxyglutamic acid (Gla) domain of vitamin K-dependent proteins of the blood clotting system. Gln3 and Gln4 are the amine acceptor residues for tissue ▶transglutaminase-catalyzed crosslinking, of which SPARC is the major substrate in maturing cartilage. This domain also mediates the interaction with hydroxylapatite, indicating that it may play role in

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Secreted Protein Acidic and Rich in Cysteine. Figure 1 Domain organization of SPARC. Schematic representation of the structure of each SPARC domain. All domains and modules are shown in individual colors. Ca2+ ions bound with high and low affinity are respectively in black and grey. The numbers in the circles represent cysteines and TG denotes transglutaminase cross-linking acceptor residues. The N-glycosylation site is located immediately after cysteine 7.

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Secreted Protein Acidic and Rich in Cysteine

stabilization of connective tissue. A peptide from this domain inhibits endothelial cell spreading. The follistatin-like (FS) domain (Asn53-Pro137) consists of two loosely linked modules. The N-terminal epidermal growth factor-like (EGF) module is a highly twisted β-hairpin with two disulfide bonds. Peptides from the EGF module have anti-▶angiogenic properties. They inhibit endothelial cell ▶migration and proliferation, and promote the disassembly of focal adhesions of endothelial cells. An adjacent small hydrophobic core of mixed α/β structures stabilized by three disulfide bonds has high structural homology to the serine proteases of the Kazal family. A peptide from the Kazal module, which contains the copper-binding sequence KGHK, can stimulate angiogenesis. This module carries an N-linked carbohydrate at Asn99, which causes a 2 kDa shift in electrophoretic mobility. SPARC glycosylation is tissue-specific and has functional significance. Bone SPARC, which carries high-mannose and biantennary glycans, binds collagens with high affinity. Platelet and recombinant SPARC have bi- and triantennary structures and bind collagens with low affinity. SPARC glycosylation is apparently sensitive to neoplastic transformation, as tumor-produced SPARC has a unique hybrid pattern of glycosylation. The C-terminal extracellular ▶calcium-binding (EC) domain (Cys138-Ile286) folds into a compact globular and predominantly α-helical structure. It carries a canonical pair of ▶EF-hand motifs, which bind Ca2+ with high affinity. A peptide corresponding to the second EF-hand motif inhibits endothelial cell proliferation. A long α-helix at the N-terminus of the EC domain and a short loop, which connects two EF-hand motifs, form a collagen-binding site. This domain organization is shared by a family of proteins that have common FS/EC domain pairs, but different acidic N-termini and sometimes C-termini. Other members of the family include hevin, tsc36, testicans and SMOCs. Functional Properties SPARC binds and modulates the activities of structural and soluble components of the ECM, often in a Ca2+dependent manner. Ca2+ enhances binding to collagens, but inhibits interaction with multimeric vitronectin. In the α-granules, the major storage organelle for platelet-secreted proteins, SPARC binds to ▶thrombospondin with high affinity in the presence of Ca2+. The action of various growth factors is modulated by SPARC. SPARC co-localizes with PDGF in platelet α-granules and binds with high affinity to PDGF-AB and PDGF-BB, but not PDGF-AA. This interaction results in interference of PDGF binding to its receptor on fibroblasts and inhibition of PDGF-stimulated proliferation of human vascular smooth muscle and mesangial cells. SPARC has also been shown to bind

▶VEGF and antagonize its pro-angiogenic effect on endothelial cells. Although SPARC does not directly bind ▶bFGF, it antagonizes its effect on the proliferation and migration of endothelial cells. SPARC can also suppress ligand-induced autophosphorylation of the bFGF receptor and inhibit both bFGF- and VEGF-induced ERK activation in endothelial cells. ▶TGFβ and SPARC induce one another’s expression in a reciprocal manner. In mesangial cells, SPARC binds the TGFβ/TGFβRII complex. Accordingly, in these cells, treatment with SPARC has no effect, but in combination with TGFβ it causes stimulation of ▶SMAD phosphorylation, ▶JNK activation, and an increase in total and phosphorylated c-jun. Treatment with SPARC stimulates SMAD phosphorylation in TGFβ-responsive epithelial and endothelial cells, but inhibits TGFβ-induced activation in fibroblasts. Integrin-linked kinase (ILK) was identified as a SPARC binding partner. SPARC can induce Ser473 phosphorylation of ▶AKT through ILK and ▶focal adhesion kinase (FAK) in glioma cells. In contrast, in ▶ovarian cancer, SPARC significantly suppresses activation of AKT and ERK signaling. A scavenger receptor, stabilin-1, was identified as another SPARC binding partner. Binding results in receptor-mediated ▶endocytosis of SPARC, followed by its targeting for degradation in macrophages. Animal Models In the nematode C. elegans, SPARC is expressed in muscle cells along the body wall and in the sex muscle, with no evidence of expression in other cell types. SPARC overexpression leads to the Unc phenotype consisting of a lack of coordinated movement or paralysis, accompanied by frequent disorganization of gonad and vulval protrusions. The offspring embryos are deformed and not viable. During Xenopus laevis development, SPARC is expressed in the notochord and mesoderm prior to appearance of the first somites, and later in the neural tube. Disruption of normal SPARC function causes a broad spectrum of developmental abnormalities including embryonic axes deformities associated with disorganized myotomes, lack of intersomitic boundaries, and defects in eye development. SPARC knockout mice do not have significant developmental abnormalities, but display multiple defects associated with abnormal ECM deposition. Animals develop early-onset cataracts accompanied by abnormal collagen IV deposition in the lens capsule. A reduced number of osteoblasts and osteoclasts leads to decreased bone remodeling and profound osteopenia. Animals have an enlargement of fat pads due to an increase in the number and diameter of adipocytes. The accumulation of adipose tissue compensates for

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the body weight loss caused by osteopenia. The skin of adult transgenic mice has decreased tensile strength and reduced collagen content with smaller diameter collagen fibrils compared to wild-type mice. SPARC-null mice also show significant acceleration of wound healing in vivo. SPARC in Cancer The role of SPARC in tumorigenesis is complex and appears to be cell-type specific due to its diverse function in a given ▶microenvironment. In some types of cancer, high levels of SPARC expression have been shown to correlate with disease progression and poor prognosis. In ▶melanoma cells, high levels of SPARC expression induce ▶epithelial to mesenchymal transition (EMT), and increase ▶invasion and tumor progression. High levels of SPARC are also associated with invasive meningioma and ▶osteosarcoma. In glioma, SPARC promotes invasion, but delays tumor growth. In other types of cancer SPARC functions as a tumor suppressor. It inhibits the proliferation of ▶breast cancer cells and induces apoptosis in ovarian cancer cells. In the majority of primary ▶lung adenocarcinomas, SPARC is silenced by ▶methylation, and this epigenetic aberration is associated with poor outcome. In ▶non-small cell lung cancer, SPARC is not ▶methylated, but its expression is frequently downregulated due to methylation of the recently identified ▶tumor suppressor gene RASSF1A. Similarly, in breast and ▶prostate cancers and ▶neuroblastoma, the majority of neoplastic cells do not express SPARC. In neuroblastoma, high levels of SPARC are expressed in Schwannian stromal cells, which is associated with a favorable outcome. Stroma-associated fibroblasts are commonly SPARC-positive, which in some types of cancer correlates with poor prognosis. However, other studies indicate that SPARC plays a role in creating a microenvironment that is inhibitory to tumor progression. SPARC has been characterized as a potent inhibitor of angiogenesis. It also induces the formation of tumor stroma and prevents the activation of fibroblasts. Enhanced growth of Lewis lung carcinoma and ▶pancreatic cancer xenografts in SPARC-null mice is associated with altered production and organization of ECM within and surrounding the implanted tumors. SPARC has also been found to have tumor suppressive activity in a number of animal studies. Significantly lower numbers of ▶metastases are seen following injection of ▶adenoviral SPARCinfected breast cancer cells compared to controls. In SPARC-null mice, enhanced tumor growth and extensive dissemination has been reported following inoculation of ovarian cancer cells. Continuous infusion of SPARC into nude mice has also been shown to potently

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inhibit the growth of neuroblastoma xenografts. Recent studies have demonstrated that SPARC sensitizes ▶colon carcinoma cells to ▶radiotherapy and ▶chemotherapy. In nude mice with xenografted colon carcinoma tumors, SPARC enhances the anti-tumor effects of cytotoxic agents, resulting in improved survival.

References 1. Lane TF, Sage EH (1994) The biology of SPARC, a protein that modulates cell-matrix interactions. FASEB J 8:163–173 2. Framson PE, Sage EH (2004) SPARC and tumor growth: where the seed meets the soil? J Cell Biochem 92:679–690 3. Chlenski A, Guerrero LJ, Yang Q et al. (2007) SPARC enhances tumor stroma formation and prevents fibroblast activation. Oncogene 26:4513–4522

Secretor Enzyme Definition A product of the Secretor gene, also named fucosyltransferase2 (FUT2), that catalyzes addition of fucose in α1,2 position onto type 1 chains. The name of the gene and enzyme stem from the presence of the gene product in secretions, namely in saliva. ▶Lewis Antigens

Securin FALK H LUBEK Department of Pathology, Ludwig-MaximiliansUniversity of Munich, Munich, Germany

Synonyms Human pituitary tumor-transforming gene 1; hPTTG1; Human ESP1-associated protein 1; EAP1; Tumortransforming 1; TUTR1; Pituitary tumor-transforming gene 1; PTTG1

Definition Securin is a 22 kDa protein that is crucial for the stability of the cells’ genome. By preventing premature

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▶sister-chromatid separation during mitosis, securin is involved in the regulation of accurate cell cycle progression.

Characteristics The protooncogene PTTG was first isolated from rat pituitary tumor cells. The human homolog of PTTG, securin (hPTTG1), was found to be overexpressed in Jurkat T cells (human lymphoma T cell line) and in leukocytes from patients with different types of hematopoietic neoplasms or myelodysplastic syndromes. High levels of securin protein expression have been reported for various other tumors, including tumors of the pituitary gland, adrenal gland, kidney, endometrium, uterus, and ovary as well as esophageal and colorectal cancer. Hence securin has been implicated in cell transformation and tumor development. In contrast, most normal adult tissues express little securin with the exception of tissues with highly proliferating cells, e.g., testis and thymus. Thus the level of securin expression correlates with cell proliferation in normal tissue. In fact, the securin protein is expressed in a cell cycle-dependent manner. Securin Function The cell division cycle (▶Cell cycle targets for cancer therapy) is a tightly regulated process to ensure the correct division of the genome into the daughter cells. Low securin expression is characteristic for noncycling cells and for cells at the beginning of the cell cycle (G1-phase). As the cell cycle proceeds, the securin level rises continuously, peaking in mitosis (M-phase). During M-phase the ▶sister-chromatids are connected by cohesin proteins and aligned at the metaphase plate while being attached to the mitotic spindle. In this phase of the cell cycle, securin acts as sister-chromatid separation inhibitor by binding to separin (human ESP1), which is responsible for the destruction of the cohesin complexes (Fig. 1). In late M-phase, the metaphase–anaphase transition, securin is ubiquitylated (▶Ubiquitination) by the activated ▶anaphase-promoting complex or cyclosome (APC/C). This triggers securin destruction by the proteolysis machinery enabling separin activation and sisterchromatid separation, followed by cell division. In addition to regulating cell cycle progression, securin is involved in processes like DNA repair, ▶apoptosis, angiogenesis, and tumor development. The multifunctional protein securin consists of 202 amino acids and contains, like many APC/C substrates (e.g., cyclins), a destruction box motif (D-box) within the N-terminus. The D-box is recognized by the APC/C complex at the end of metaphase leading to securin ubiquitylation and subsequent proteolysis. Furthermore, a central ▶transactivation domain, a DNAbinding domain and proline-rich motifs representing potential Src homology 3 domain (SH3)-binding sites

Securin. Figure 1 During M-phase of the cell cycle, chromosomes are aligned at the metaphase plate with the centromers linked to the mitotic spindle. The sister-chromatids are connected in the centromeric region by cohesin proteins. Securin binds to separin, thereby inhibiting the cohesin degradation activity of the protein. In late M-phase when all chromosomes are accurately aligned, the activated anaphase-promoting complex induces securin degradation by ubiquitylation (Ub). Activated separin cleaves the cohesin proteins enabling an even distribution of the sister-chromatids to the daughter cells (Adapted from Malumbres M, Barbacid M (2001) Nat Rev Cancer 1:222–231 with permission).

(▶SH2/SH3 domains) have been identified in securin. Securin (hPTTG1) is the only member of the PTTG protein family that has been studied in detail. The protein family consists of at least three members that have no significant homology to other known proteins. The different expression pattern of the hPTTG1, hPTTG2, and hPTTG3 genes in normal and tumor tissue may suggest a tissue-specific expression and diverse functions of the encoded proteins. Securin Function in Tumor Development Overexpression of securin can transform mouse and human cells (NIH3T3, HEK293), enabling them to form tumors in ▶nude mice, thus specifying securin as an oncoprotein. Mutation of the proline-residues of the SH3-binding sites abrogates the transforming (in vitro) and tumor inducing (in vivo) activity. However, securin seems to be involved in tumor development in several ways, although the precise mechanisms remain unknown. First, as securin is essential for sister-chromatid separation during mitosis, it regulates cell proliferation and chromosome stability. Loss of securin function in tumor cells increases abnormal mitosis resulting in ▶aneuploidy and apoptosis. The antiapoptotic function of securin is partly mediated by the interaction with the tumor suppressor protein p53 (▶p53 Protein),

“Seed and Soil” Theory of Metastasis

blocking its DNA-binding and transactivating activity. Despite this effect, overexpression of securin can also cause aneuploidy by failure of the cells to divide the chromosomes evenly between the daughter cells. The induction of chromosomal instability in combination with the inhibition of apoptosis possibly accounts in part for the oncogenic activity of securin. Consequently securin overexpression results, depending on the degree of expression, in elevated cell proliferation and nontumor cell transformation, which may also be mediated by the induction of c-Myc oncogene expression (▶Myc oncogene). Recently an additional mechanism for the induction of genetic instability by securin in tumor cells has been suggested. Securin binds to DNA repair proteins (p53 and ▶Ku70) and, when overexpressed, inhibits ▶double-strand break DNA repair activity in colorectal cancer cells. Second, high securin expression levels induce angiogenesis in vitro and in vivo possibly by activating the expression of basic fibroblast growth factor (▶bFGF) and ▶vascular endothelial growth factor (VEGF), both potent mitogenic and angiogenic factors. This activity of securin is dependent on the proline-rich domain of the protein suggesting that securin may function through SH3-signal transduction pathways. Third, securin expression correlates with tumor cell ▶invasion and has been implicated to serve as prognostic marker for poor prognosis of pituitary, thyroid, colorectal, breast, esophageal cancers, and squamous cell carcinoma of the head and neck. The proinvasive and angiogenic effect of securin may be facilitated by its induction of ▶matrix metalloproteinase 2 (MMP-2) expression. Taken together, securin appears to contribute to at least three important hallmark features of cancer: cell transformation, angiogenesis, and cell invasion. However, the regulation of securin expression in tumors is largely unknown. The growth factors ▶HGF, TGFα (▶Transforming growth factor), ▶EGF, IGF-1 (▶Insulin-like growth factors), and the hormone insulin have been implicated in securin regulation. Recently, in colorectal cancer and esophageal squamous cell carcinoma, the β-catenin/TCF-signaling pathway (▶APC/beta-catenin pathway) has been found to control securin expression. In the process of tumor development, this crucial signaling pathway is deregulated, leading to the accumulation of the oncogenic protein β-catenin, which acts as transcriptional activator in the β-catenin/TCF4 protein complex. The constitutive activity of β-catenin causes at least in part the overexpression of securin and other target genes with the potential to contribute to tumor initiation and progression. Although the molecular mechanisms of securin participation in tumor development are currently poorly understood, further research will reveal whether it is relevant as potential diagnostic or therapeutic target.

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References 1. Bradshaw C, Kakar SS (2007) Pituitary tumor transforming gene: an important gene in normal cellular functions and tumorigenesis. Histol Histopathol 22:219–226 2. Hlubek F, Pfeiffer S, Budczies J et al. (2006) Securin (hPTTG1) expression is regulated by beta-catenin/TCF in human colorectal carcinoma. Br J Cancer 94:1672–1677 3. Tfelt-Hansen J, Kanuparthi D, Chattopadhyay N (2006) The emerging role of pituitary tumor transforming gene in tumorigenesis. Clin Med Res 4:130–137 4. Zhou C, Liu S, Zhou X et al. (2005) Overexpression of human pituitary tumor transforming gene (hPTTG), is regulated by beta-catenin/TCF pathway in human esophageal squamous cell carcinoma. Int J Cancer 113:891–898

“Seed and Soil” Theory of Metastasis C HAO -N AN Q IAN , B IN T EAN T EH Laboratory of Cancer Genetics, Van Andel Research Institute, Grand Rapids, MI, USA

Definition A theory proposed to explain the metastatic preference of ▶cancer cells for specific organs is called the “seed and soil” theory, the cancer cells being the “seeds” and the specific organ ▶microenvironments being the “soil.” Interaction between the “seeds” and the “soil” determines the formation of a secondary tumor.

Characteristics Historical Development of the “Seed and Soil” Theory ▶Metastasis is the spread of a cancer from its primary location to distant sites in the body, forming the secondary tumors. When cancer cells metastasize, they usually do so to preferential organs, depending on the type of cancer. For example, breast cancer cells usually metastasize to the lymph nodes, bones, lungs, liver, and brain; colon cancer cells often metastasize to the lymph nodes and liver. The propensity of certain organs to harbor metastatic tumors was noticed in the middle of nineteenth century. When Fuchs studied the metastasis pattern of uveal melanoma in 1882, he found that a favorable site for secondary tumor development should be taken into account. Paget, a surgeon, reported the autopsy results of 735 cases of breast cancer and summarized the studies of others, and clearly proposed the “seed-andsoil” theory in 1889, pointing out that metastasis depends on interaction between cancer cells and specific organ microenvironments. The theory has had a great influence on the field of cancer research.

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Recent Evidence Shows that the “Seeds” Can Even Prepare the “Soils” A primary tumor can induce reorganization of the vasculature and lymph channels in the ▶sentinel lymph node before metastasis, that is, before the cancer cells arrive. The dramatically remodeled vasculature of the sentinel lymph node can then integrate into the tumor vascular system after metastasis and nurture the fast growing metastatic tumor. The molecular basis for this pre-metastatic remodeling is not yet known. The preparation of a pre-metastatic “niche” in bone marrow before the arrival of cancer cells has also been reported. The bone marrow-derived hematopoietic progenitor cells that express ▶vascular endothelial growth factor receptor 1 are responsible for creating a favorable niche for incoming tumor cells.

Selectins Definition A family of cell-adhesion molecules mediating inflammatory cell arrest. E-selectin is found on activated endothelium. P-selectin (CD62-P) is expressed by endothelium and platelets upon stimulation with, e.g., thrombin. L-selectin is expressed on leukocytes. Adhesion molecules that contain a lectin-like domain that recognizes and binds carbohydrates. Relevant examples for adhesion mediated by sialyl-Lewis antigens are E(endothelial)-selectin and P(platelet)-selectin. ▶Lewis Antigens ▶Tumor-Endothelial Cross-talk

References 1. Paget S (1889) The distribution of secondary growths in cancer of the breast. Lancet 133:571–573 2. Weiss L (2000) Metastasis of cancer: a conceptual history from antiquity to the 1990s. Cancer Metastasis Rev 19: I–XI, 193–383 3. Fuchs E (1882) Das Sarkom des Uvealtractus. Graefe’s Arch Ophthalmol XII:233 4. Qian CN, Berghuis B, Tsarfaty G et al. (2006) Preparing the “soil”: the primary tumor induces vasculature reorganization in the sentinel lymph node before the arrival of metastatic cancer cells. Cancer Res 66:10365– 10376 5. Kaplan RN, Riba RD, Zacharoulis S et al. (2005) VEGFR1-positive haematopoietic bone marrow progenitors initiate the pre-metastatic niche. Nature 438:820–827

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Selection Template Definition An oligonucleotide, typically double-stranded DNA, that is used either directly or through a derivative (e.g. RNA transcript) in a combinatorial selection method. Selection templates usually contain a region of selectable randomized sequence flanked by defined sequences used minimally in ▶PCR amplification but also containing additional information for use in the selection process (e.g. bacteriophage promoter for RNA transcript production in ▶SELEX, IISRE binding sites for IISRE cleavage in REPSA). ▶Combinatorial Selection Methods

Definition Surveillance epidemiology and end results. ▶Childhood Cancer

Selective Estrogen Receptor Modulator Definition

SELDI-TOF MS Definition

▶Surface-enhanced laser desorption/ionization time-of flight mass spectrometry.

SERM; Is a designer estrogen that possesses some, but not all, of the actions of prototypical estrogen. Some prevent bone loss and lower serum cholesterol but (unlike estrogen) do not stimulate the endometrial lining of the uterus. Therefore, they are considered more safe. ▶Isoflavones ▶Estrogenic Hormones

Selenium

Selective Serotonin Reuptake Inhibitors SSRIs ▶Fluoxetine

Selenium A NNA B ATISTATOU, KONSTANTINOS C HARALABOPOULOS Ioannina University Medical School, Ioannina, Greece

Definition Selenium (Se) is an essential trace element having multiple effects in many functions of the normal human organism and inducing disturbances when deficient. Thus, it has an important role in health maintenance, being furthermore implicated, when in low levels, in various chronic pathological conditions such as rheumatoid arthritis, diabetes mellitus, cardiovascular diseases, renal insufficiency, and cancer.

Characteristics More than 10 million new cancer cases each year are recorded worldwide, with cancer being one of the leading causes of death. Much progress has been made in the quest of the etiology and pathogenesis of cancer in humans, however there are still a lot of issues to be elucidated. Identifying cancer risk factors is critical both in prevention and treatment. Epidemiological and genetic studies suggest that factors such as smoking, bioactive food components and hormones can influence the incidence and mortality of this disease. Among them a lot of attention has been drawn in those that indicate a strong relationship between low Se concentration in the serum and increased risk of various types of cancer in humans. Trace elements such as Se, zinc, arsenic, cadmium, and nickel, found naturally in the environment, are delivered to humans from a variety of sources including air, drinking water and food. In the human body Se is absorbed by the gastrointestinal tract, skin, and respiratory system. Concentrations of this trace element in the air are low. Thus, diet and drinking water supplies are the primary sources of Se intake. Se enters the food chain through plants, which uptake it from the soil. Notably, there is a wide geographic distribution of Se in the soils varying from high concentrations in the former USSR. and USA. to low concentrations in

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China, and some other parts of Asia, as well as in many European countries. Se is present in a wide range of foods such as grains, meat, fish, eggs, as well as in some vegetables. Average selenium consumption from foods ranges from 71 to 152 μg daily. The suggested daily Se uptake in adults varies between scientists groups, ranging from 60–120 μg to 200–300 μg daily. Se intake from dietary sources is assessed by 24-h and weekly dietary recalls, diet histories and food frequency questionnaires. The latter is the least preferred method, since potential differences in Se absorption from the intestinal lumen, various food preparations methods and variations depending on geographical Se distribution, impair the results. In humans, high Se concentrations are detected in the thyroid gland, kidneys, genitals and liver, whilst the lowest Se concentrations are detected in pancreas and lymph nodes. Organic Se is present in foods mainly in the form of selenomethionine, selenocysteine and seleniummethylselenocysteine, whilst inorganic Se either in the form of selenite or selenate is found infrequently and in very low amounts. Both organic and inorganic Se are utilized with similar efficacy in the human body, producing selenoproteins (SPs), although, Se enters at different points in the metabolism processes depending on the chemical form. Twenty-five SPs have been identified until now, out of a possible 50 thought to exist. Glutathione (GSH) reduces the inorganic forms (selenate and selenite) of Se. The originally discovered cytosolic glutathione peroxidase GSH-Px or GPx-1, the phospholipid hydroperoxide GSH-Px, and the secretory GSH-Px represent three isoenzymes of glutathione peroxidase. The latter, ubiquitously expressed, is the first and best characterized SP in mammals. Other selenoproteins such as thioredoxin reductase (TrxR) and selenoprotein P (SeP) also contain molecular Se in their active center and act in a similar fashion. Through all of them Se regulates the cellular antioxidant defence system, DNA damage and protein function. Se also controls cell-mediated immunity and B-cell function. TrxR is considered to be a key enzyme in Se metabolism, reducing Se compounds and controlling the intracellular redox state and SeP appears to protect endothelial cells against damage from free radicals. The varying degree of anti-carcinogenic activity of different forms of selenium, may be attributed to their metabolism in vivo. High Se concentration can lead to either cytotoxic effects or possibly to carcinogenesis, due to DNA strand breaks. Thus, in the first half of the twentieth century Se was considered an undesirable element for higher organisms. In the second half of the twentieth century the role of Se in human nutrition and biology was appreciated, since there was growing evidence that Se has multiple roles in many biological systems. Among them, Se controls cell-mediated immunity and B-cell function. Se role as an antioxidant,

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as well as a cancer-preventing factor nowadays is well established by accumulating evidence. A bulk of studies strongly supports the issue that Se supplementation is effective in the reduction of cancer incidence when non-toxic doses of the element are provided with the diet, possessing thus, anticancer properties. Experimental data have shown that the chemopreventive effect of Se is due, at least partly, to its inhibitory effect on cell growth, DNA, RNA, and protein synthesis in transformed cells. Furthermore, changes in stressrelated cellular proteins are widely implicated in explaining the protective role of Se. Several reports have described the inhibitory effect of Se on kinase enzyme activity. Cell cycle cyclin-dependent-kinase 2 (cdk2) and/or cell signaling protein kinases and/or some redox regulated proteins with critical transcription factors, have been proposed as targets against which Se exerts its chemopreventive actions. An increase in cyclin B expression as well as phosphorylation of the cdk2 coincidentally with the cell cycle arrest has been demonstrated. In addition, Se exerts an antiproliferative effect by modulating cellular proliferation in G1 phase in both normal and neoplastic cells and possibly impairing the expression of c-fos and c-myc oncogenes. Furthermore, human defense mechanisms against reactive oxygen species (ROS), which induce oxidative damage are amplified by Se. Cellular oxidative damage is a general mechanism for cell and tissue injury. Selenocystein reduces the levels of hydrogen peroxide and a number of organic hydroperoxides, thereby, acting as antioxidant. Oxidative stress in the target tissue has been suggested to play an important role in carcinogenic process. Thus, Se may act as an antitumoral agent although more studies are needed to investigate the actual role of antioxidants and their possible relationships with trace elements alterations, and Se in particular, in the pathogenesis of various cancer types. It has also been shown that in colorectal cancer cells Se supplementation decreases the COX-2 protein and PGE-2 levels. Se plasma and tissue concentration is regulated by incompletely understood homeostatic mechanisms. For estimation of the body Se amount levels, whole blood, serum, plasma, erythrocytes, urine, hair, and nails represent biological specimens suitable for sampling. Each of these differs in terms of the exposure period represented. Plasma and serum measures tend to reflect short term exposure, whilst Se levels in erythrocytes represent a long term exposure. Longer term exposure is measured by toenails samples. Early epidemiological studies 40 years ago suggested an inverse association between Se levels and risk of cancer. Studies from about 30 countries showed a significant inverse correlation with age-adjusted mortality for colorectal (CRC), prostate, breast, ovary and

lung cancer as well as for some hematological malignancies, whilst only a weak association was found for pancreatic and skin cancer. Low Se is associated with risk of lung, colorectum, oesophagus, stomach, liver, breast, prostate, and urinary bladder cancer. Results from many chemoprevention trials strongly suggest that Se supplementation may have some protective effects against the above mentioned cancer types in populations where average dietary Se levels are low. There are a few data regarding the association between Se and CRC or adenomas. These results depending mainly on small studies are inconclusive and probably new prospective studies with large series of individuals are needed. However, epidemiological studies have reported an inverse association between Se and CRC, cancer stage and survival, whilst some others failed to detect this association reporting null results. A pooled analysis reported by Jacobs et al. indicates that individuals with high blood Se concentration (median value 150 ng/ml) had 34% lower odds ratios (OR 0.66, 95% CI 0.50–0.87, Ptrend 0.006) for developing a new adenoma throughout the follow up time period, in comparison with those individuals with lower plasma Se levels (median value 113 ng/ml). Thus, new prospective studies regarding Se alone or in combination with other trace elements must be designed in the near future. In breast, contradictory studies have been reported. Although there is some evidence indicating the chemopreventive role of Se in breast cancer, rigorous retrospective and prospective studies are needed to confirm this issue. The urinary bladder mucosa differs from other tissues, being exposed to Se directly, via the urine, and indirectly, via the blood. An inverse association between serum Se levels and bladder cancer has been reported in the literature. Serum Se levels and glutathione peroxidase activity in patients suffering from transitional cell carcinoma were inversely correlated with tumor grade. Similarly, this strong inverse association has also been detected in prostate cancer. In recent reports, individuals taking Se supplementation exhibited a significant reduction in the risk of prostate cancer. Regarding the other cancer types the usual reverse association between serum Se levels and neoplastic development has been observed, although this phenomenon is not universally accepted, since there are also not confirmatory studies. By several studies it has been indicated that the process of the underlying tumor development can lead to an uptake of trace elements by neoplastic cells explaining, thus, the increased levels of Se in tumor mass. The same phenomenon is also observed with some other trace elements such as Zn, Fe, Cu in neoplastic tissue. It is not clear whether the increased Se concentration in the cancerous tissues is responsible for the decreased serum Se levels found in these patients

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or if the decreased serum Se levels precede the development of cancer. In conclusion, Se is found naturally in the environment and is uptaken by humans through a variety of sources, including food, drinking water and air. Intake and plasma levels differ depending on geographical distribution and genetic factors. Se chemopreventive action has been demonstrated in some types of human cancers. More clinical trials are needed to investigate the role of Se supplementation in reducing cancer incidence in humans.

References 1. Charalabopoulos K, Kotsalos A, Batistatou A et al. (2006) Selenium in serum and neoplastic tissue in breast cancer: correlation with CEA. Br J Cancer 95(6):674–676 2. Charalabopoulos K, Kotsalos A, Karkabounas S et al. (2006) Low selenium levels in serum and increased concentration in neoplastic tissues in patients with colorectal cancer. Correlation with serum carcinoembryonic antigen. Scand J Gastroenterol 41:359–360 3. Charalabopoulos K, Karkabounas S, Charalabopoulos A et al. (2003) Inhibition of benzo(a)pyrene induced carcinogenesis by vitamin C alone, and by pairs of vitamin C/vitamin E and selenium/glutathione. Biol Trace Elem Res 93(1–3):201–211 4. Rayman MP (2000) The importance of selenium to human health. Lancet 356:233–241

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SELEX Definition Systematic evolution of ligands by exponential enrichment (SELEX) is a combinatorial selection method that identifies oligonucleotide aptamers exhibiting high affinity and binding specificity to a variety of ligands, including proteins and small molecules. ▶Combinatorial Selection Methods ▶Aptamer Bioconjugates for Cancer Therapy

Self-Renewal Definition Is the ability to undergo multiple rounds of cell division while maintaining an undifferentiated state. ▶Stem Cell Markers

Self-Sufficiency in Growth Signals Selenocysteine Definition

A ▶selenium analog of cysteine, where a selenium atom in selenocysteine has taken the place of sulfur in cysteine. Selenocysteine is naturally present in 25 known human proteins, of which thioredoxin receptor (TrxR) isoenzymes constitute three. ▶Thioredoxin System

Selenoenzyme

Definition Capacity of tumoral cells, which refers to the ability that they have to proliferate in the absence of stimulatory growth signals. Normal cells require growth signals in order to actively proliferate. However, tumor cells are characterized by a greatly reduced dependence on exogenous growth stimulation. The explanation is that tumor cells generate many of their own growth signals, inducing a growth signal autonomy. ▶Funnel Factors

Sella Turcica

Definition

Definition

An enzyme containing selenocysteine as one of the amino acids of the protein.

The bony cavity in the skull that houses the pituitary gland.

▶Thioredoxin System

▶Prolactin

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SEMA

SEMA ▶Semaphorin

SEMA Domain Definition

Is commonly found in ▶semaphorins – a large family of secreted and transmembrane proteins. Some semaphorins function as repellent signals during axon guidance.

Semanova´ II syndrome ▶Nijmegen Breakage Syndrome

Semaphorin C LAUS C HRISTENSEN Department of Cancer Genetics, Danish Cancer Society, Copenhagen, Denmark

Synonyms SEMA; Collapsin; Growth guidance cue; Neuropilin ligand; Plexin ligand

Definition The semaphorins (abbreviated SEMA) constitute a family of genes encoding secreted and membrane associated proteins which share a common domain called the sema domain. The name semaphorin is derived from the greek words “sema” meaning “signal” and “phor,” which means “to carry.” This name was given to semaphorins owing to the function of the first semaphorins in ▶axon guidance.

Characteristics Subclasses To date, the semaphorin family comprises at least 18 different members in vertebrates and at least three

different members in invertebrates. All semaphorins contain an approximately 500 amino acid extracellular sema domain and a class specific carboxy terminus that may encompass additional sequence motifs. At present the known semaphorins are divided amongst eight subclasses on the basis of these structural features and phylogenetic analysis. Other protein families including ▶plexins and the ▶receptor tyrosine kinases MET and ▶RON contain sema domains, but on the basis of phylogenetic analysis these proteins are only distantly evolutionary related to semaphorins. Structure and Processing With respect to cellular localization semaphorins fall into three categories: secreted (subclass 2, 3, and V), transmembrane (subclass 1, 4, 5, and 6) and ▶GPIlinked (subclass 7) (Fig. 1). Class 3 semaphorins require posttranslational modifications to gain activity. During maturation these proteins are proteolytically processed by ▶furin or related serine endoproteases, possibly glycosylated (see ▶Glycosylation) and they undergo dimerization. Their activity is further regulated by proteolytic cleavage of an internal RXK/RR site which separates the sema domain from the rest of the dimer. This was shown to cause a loss of the repellent activity of these semaphorins in neurobiology. However, such processing may positively add to semaphorin activity during tumor ▶progression as recently shown in the case of Sema3E. In the case of membrane-associated semaphorins, proteolytic processing may cause shedding of the extracellular domains from the cell surface, as shown for the class 4 semaphorin Sema4D. Brief History of the Semaphorin Family The first discoveries of semaphorins were made in 1992 and 1993 by Alex Kolodkin and co-workers in Corey Goodman´s lab at the Howard Hughes Medical Institute, Berkeley, University of California. They were attempting to identify molecules involved in the fasciculation of nerve axons in Grasshoppers and this led to the isolation of a transmembrane protein, which they first called Fasciclin IV. This protein turned out to possess a repelling activity which guided nerves in developing insect limp buds. The sequence was unique and used in the cloning of related sequences from other species including human SEMA3A. Meanwhile, in 1993, Yuling Luo and co-workers working in Jonathan Raper´s lab at the University of Pennsylvania isolated a protein from chicken brain extracts responsible for the growth cone collapsing activity observed when such extracts were added to sensory ganglion neurites in vitro. This protein was named Collapsin-1 and subsequently realized as the chick counterpart to human SEMA3A. Based on these sequences the

Semaphorin

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Semaphorin. Figure 1 The structure of vertebrate and viral semaphorin proteins. Semaphorins are secreted, transmembrane or linked to the surface by GPI anchor. They are found as dimers which may undergo proteolytic processing. This processing may cause shedding of the extracellular part of transmembrane semaphorins.

semaphorin/collapsin family was defined. The common family trait was a 500 amino acid region, named the sema domain, constituting the better part of these proteins and containing a number of unique and highly conserved motifs (see characteristics). In the following years a number of new semaphorin members were isolated from different species. Semaphorins isolated from chick continued to be named collapsins until the nomenclature of semaphorins was changed by initiative of the Semaphorin Nomenclature Committee [1]. Evidence was rapidly mounting to suggest that the semaphorins were acting within the nervous system as ▶guidance cues that guided migrating ▶axonal growth cones as the complex wiring of the nervous system was established. Semaphorins were typically expressed by neighboring cells and at first considered to act primarily as repelling factors. This notion was changed in 1999 when a semaphorin was for the first time shown to be able to act as an attractive guidance cue. Today, semaphorins are considered to be bidirectional guidance factors, exerting repelling or attractive guidance depending on the composition of receptor complexes on the responding cells. Today, semaphorins are furthermore known to take part in different aspects of biology outside the nervous system including ▶angiogenesis, immunobiology, and ▶cancer. In cancer biology semaphorins appear to be bifunctional acting either as suppressors (see ▶Tumor Suppressor Genes and ▶Tumor Suppression) or promoters of tumor progression.

Semaphorins and the Composition of their Receptors

Although many different types of receptors and ▶adhesion molecules are today implicated in semaphorin receptor complexes, two distinct types of receptors form the core of most of these complexes: the neuropilins and the plexins (Fig. 2). Members of the membrane-anchored class 1, 4 or 7 semaphorins bind plexins independent of neuropilins. Hence, Plexin-B1 and Plexin-C1 function as receptors for the transmembrane Sema4D and the GPI-linked Sema7A, respectively. On the contrary, the secreted class 3 semaphorins have for long been considered to require a complex of neuropilin and plexin. Hence, the earliest studies addressing this question showed that plexin-A1 combined with NP-1 and NP-2 constituted functional receptor complexes for Sema3A and Sema3F, respectively. But, this concept was challenged in 2004, when Sema3E and plexin-D1 were shown to control vascular development together independently of neuropilins. The reason for this discrepancy is currently unknown. Neuropilins The neuropilin family consists of neuropilin-1 (NP-1) and neuropilin-2 (NP-2), the latter existing in different splice variants. Neuropilins are transmembrane proteins that extracellularly possess two CUB (complement-binding) domains, two domains of homology

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Semaphorin

Semaphorin. Figure 2 Semaphorin receptor complexes. The core of semaphorin receptor complexes is made of plexins or plexins in combination with neuropilins (NP). Plexins bind semaphorins directly. In the case of class 3 semaphorins, it is generally so that a neuropilin is required in order to bind this class of semaphorins. Neuropilins also act as co-receptors for vascular endothelial growth factors (VEGFs). Other proteins may be involved in semaphorin receptor complexes including vascular endothelial growth factor receptors (VEGFRs), the off-track kinase (OTK), the cell adhesion molecule L1-CAM or the receptor tyrosine kinase Met. Hepatocyte growth factor (HGF) is the ligand for Met.

to coagulation factors V and VII, and an oligomerization domain, abbreviated MAM (short for meprin, A5,μ). The CUB domain is involved in the binding to class 3 semaphorins. NP-1 binds Sema3A but not Sema3F; whereas NP-2 binds Sema3F but not Sema3A. The other class 3 semaphorins Sema3C, Sema3D and Sema3E bind both neuropilins. The intracellular domains of NP proteins are very short and devoid of classical signaling motifs. Yet, they are highly conserved and bind possible adapter molecules with a ▶PDZ domain. Neuropilins may facilitate clustering of neuropilinplexin receptor complexes but neuropilins also serve as bridges to other families of adhesion- and receptor molecules. Notably, neuropilins bind members of the ▶vascular-endothelial-growth-factor-receptor (VEGFR) family. In addition, NP-1 binds to L1-CAM, which is a member of the immunoglobulin (Ig) superfamily of ▶cell adhesion molecules (Fig. 2). Plexins Nine plexins have been identified and they are grouped into four subclasses (plexin-A, -D). There are four A-type, three B-type, one C-type and one D-type plexin. Like semaphorins, sema domains are a characteristic of

the extracellular part of plexins. In addition, plexins have two to three ▶Met related sequences (PSI domains), and three IPT domains. Intracellularly plexins have two highly conserved stretches, separated by a variable linker region. The conserved domains include motifs distantly related to ▶GTPase-activating proteins (▶GAPs). In type-B plexins the carboxy terminus contains PDZ-domain binding motifs. Plexin Signaling At least some plexins may be locked in an autoinhibited configuration when not binding semaphorins. As shown for Plexin-A1 this involves the binding of the plexin sema domain to the rest of the extracellular part. It is believed that the plexins upon binding to semaphorins change configuration in a manner that allows phosphorylation of tyrosine residues in the intracellular domain as well as binding to various ▶small GTPases and ▶GTPase exchange factors (▶GEFs). The phosphorylation of the tyrosine residues in the intracellular part of the plexins is not because of autokinase activity inherent to the plexins but occurs because plexins are coupled to tyrosine kinases. Upon the binding of the semaphorin ligand, the plexins become phosphorylated by the tyrosine kinases with which they

Semaphorin

interact. Hence, Plexin-B1 binds the receptor tyrosine kinase Met, and when Plexin-B1 is stimulated by Sema4D, Met causes phosphorylation of Plexin-B1. A similar interaction has been reported between PlexinB1 and the tyrosine kinase receptor ErbB-2. Other examples of plexins interacting with tyrosine kinases are Plexin-A1 and Plexin-A2, which bind the intracellular tyrosine kinases Fes and Fyn, respectively. Plexin-A1 also interacts with the Off-track receptor, which possesses a kinase domain yet no kinase activity, as well as the VEGF receptor KDR/VEGFR-2. The binding of these two receptors to Plexin-A1 appears to have opposing effects on heart morphogenesis (Fig. 2). The GAP-related domains in the cytoplasmic part of plexins have been shown to serve as docking sites for small GTPases such as Rac1 and Rnd1 (see ▶GTPase and ▶Rho family proteins). Furthermore the activation of RhoA is implicated in the axonal collapse mediated by B-type plexins. However, Plexin-B1 does not bind RhoA directly. Instead it binds to leukemia-associated Rho-GEF (LARG) and PDZ-Rho-GEF (PRG) through the PDZ-domain-binding motifs that are specific to Btype plexins. Despite the presence of a segmented GAP domain in plexins, at first plexins were considered not to have any intrinsic GAP activity. However, Plexin-B1 does exert GAP-activity when Sema4D binds to the extracellular domain and Rnd1 at the same time binds to the linker region. Under such circumstances Plexin-B1 exerts a GTPase activation activity on R-Ras (see ▶RAS). R-Ras appears to function mainly in the regulation of ▶integrins (see ▶Integrin Signaling and Cancer). The small GTPases Rho, Rac, and Rnd are known for their regulatory function with respect to the actin filament assembly and actin-myosin contraction, which constitute the basis for cellular structure and locomotion. Integrins couple this machinery to the extracellular matrix and provide much of the stability during ▶migration (see also ▶Motility). By recruiting activated forms of small GTPases or affecting integrin function plexins may influence the shape and migratory behavior of cells and axonal growth cones. Brief History of Semaphorins in Cancer Research The first discoveries of semaphorins in cancer biology were made in 1996 when SEMA3B and SEMA3F were located at the chromosomal region 3p21.3, which is deleted in small cell lung cancers. Today these semaphorins are thought to act as tumor suppressors through their ability to compete with ▶vascular endothelial growth factors for the binding to neuropilin coreceptors. An alternative model predicts that SEMA3F acts by reducing expression of β1 integrin in cancer cells. Whereas SEMA3F and SEMA3B are located together on chromosome 3, the other subclass 3 semaphorins, SEMA3A, SEMA3C and SEMA3E are

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located on chromosome 7. The present studies of SEMA3C and SEMA3E suggest functions of these genes that promote tumor progression. In 1997 SEMA3C was identified in cis-diaminedichloroplatinum (CDDP) (see ▶cisplatin and ▶platinum drugs) resistant ovarian TYKnuR cells as a gene capable of conferring chemoresistance to other cells upon ectopic expression. The underlying mechanism is presently unknown. Later SEMA3C has been shown to be upregulated in metastatic human lung adenocarcinoma cells and in malignant glioma cells. In 1998 Sema3E was identified in murine mammary adenocarcinoma cells (see ▶Breast Cancer) and reported to be expressed in a manner correlating with the metastatic potential of such cells. It was later shown to stimulate experimental lung ▶metastasis when overexpressed in a nonmetastatic cell line of the same origin. The exact mechanism is currently unknown but seems to deviate from existing models since it requires proteolytic processing of Sema3E. So far human SEMA3E has also been associated with mammary adenocarcinoma, where it seems to be overexpressed in a subset of clinical samples and cell lines as seen in the case of murine Sema3E. In 2002 Sema4D was shown to stimulate invasive growth in vitro through a receptor complex consisting of Plexin-B1 and Met. Later Sema4D has been shown to promote angiogenesis in vitro and in vivo in a manner that likewise requires a coupling between Plexin-B1 and Met. Experimental evidence for a role of Sema4D in tumor angiogenesis has been reported in the context of head and neck squamous cell carcinoma. Sema4D is also expressed in activated B and T lymphocytes and at a high level in lymphoid and myeloid leukemia cell lines as well as in some T-cell and B-cell non-Hodgkin lymphomas (see ▶Hematological Malignancies; Hodgkin Disease and ▶Malignant Lymphoma, Hallmarks and Concepts). Whether Sema4D contributes to the progression of these cancers is not known, and if so it might involve a plexin-independent mechanism since the major Sema4D receptor within the immune system appears to be CD72 rather than Plexin-B1. In 2003, Sema5C was identified in a genetic screen for genes that would suppress a tumor phenotype in Drosophila that arises from inactivation of the lethal giant larvae l(2)gl gene. This work showed that inactivation of Sema5C blocked tumor growth in such flies and pointed to a mechanism involving a TGF-betalike signal pathway. Other class 5 semaphorins (SEMA5A, -5B and -5D) as well as the class 6 semaphorins SEMA6A and SEMA6B have also been associated with different human cancer cells, but the significance of these findings is unknown. Table 1 summarizes the expression and alleged functions of semaphorins in cancer according to published material.

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Semaphorin

Semaphorin. Table 1 The expression and possible functions of semaphorins in cancer. Whenever the semaphorin has been implicated with human cancer it is listed by its human name Semaphorin SEMA3A SEMA3B

SEMA3C

SEMA3E SEMA3F

SEMA4D

Type of aberrant expression Down-regulated Expressed Maps to 3p21.3 deleted in lung cancer Down-regulated Over-expression Differentially expressed (only seen in metastatic cell line) Differentially expressed (only seen in metastatic cell lines) Maps to 3p21.3 deleted in lung cancer Down-regulated Expressed Differentially expressed

SEMA5A SEMA5B Sema5C SEMA5D SEMA6A SEMA6B

Expressed Over-expressed Differentially expressed Inactivation (experimentally by P element insertion) Expressed

Tumor type(s) Mesothelioma Breast carcinoma cell lines Lung cancer Lung, ovarian and breast cancer cell lines Ovarian, lung, glioma cancer cell lines Lung adenocarcinoma cell lines

Function(s) Inhibition of angiogenesis and migration Inhibition of angiogenesis

Promotes cancer cell survival (chemo resistance)

Breast carcinoma cell lines

Promotes metastasis

Lung cancer

Inhibition of angiogenesis

Malignant melanoma

Inhibition of adhesion and migration Promotes angiogenesis and invasive growth Unknown

Head and neck squamous cell carcinoma Lymphoid and leukemia cell lines non-Hodgkin lymphoma Malignant Melanoma cell line Uterine leiomyomata Renal cell carcinoma Drosophila l(2)gl tumor model Malignant melanoma cell line Ovarian cancer cells Lung cancer

Maps to 5q21-22 deleted in lung cancer Down-regulated when cells treated Glioblastoma with retinoids

Different Mechanisms may Account for Semaphorin Functions in Cancer Biology Model I: Semaphorins may act as antagonists of Vascular Endothelial Growth Factor (VEGF) signaling. Both class 3 semaphorins and vascular-endothelial growth factors are known ligands of the neuropilin receptors, meanwhile neuropilins exist in complexes with either plexins and VEGF receptors (VEGFR). This creates the basis for a mutually antagonistic relationship between class 3 semaphorins and VEGF ligands (see Fig. 3). Hence, NP-1 is a coreceptor of VEGFR-2 (also known as KDR) mediating the activity of certain VEGF-A isoforms in angiogenesis. However SEMA3A binding to NP-1 blocks this activity in endothelial cells. Likewise, NP-2 is a coreceptor for VEGFR-1 and VEGFR-2, and binding of NP-2 to SEMA3F or SEMA3B may influence signaling through these two

Unknown Unknown Necessary for tumor growth Unknown Unknown Unknown

receptors. Recently, NP-2 was also shown to act as a coreceptor for VEGFR-3 mediating the activity of VEGF-C and VEGF-D during ▶lymphangiogenesis. Initially, class 3 semaphorins were considered to be tumor-suppressors due to their antagonistic activity on VEGF signaling in endothelial cells (see ▶Antiangiogenic and ▶Antiangiogenesis). Today, the picture is made complicated by the fact that both endothelial cells and many cancer cells express class 3 semaphorins and VEGF ligands, and both cell types may express any combination of neuropilins, plexins and VEGF-receptors dependent on tumor type and localization. The effect these expressions have on the overall migratory, adhesive and proliferative capabilities of the EC and cancer cells within a given tumor may depend upon the ratio between the different receptors and between ligands. One updated model

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Semaphorin. Figure 3 Model for how semaphorins may suppress tumorigenesis by blocking VEGF signaling. Neuropilins (NP) are co-receptors for both class 3 semaphorins and vascular endothelial growth factors (VEGFs). When class 3 semaphorins bind neuropilins they prevent the binding and activation of VEGF-receptors (VEGF-R) thereby blocking the pro-angiogenic signaling of VEGF.

depicts that down-regulated expression of class 3 semaphorins such as SEMA3F and SEMA3B shifts the balance in favor of VEGF ligands and their promigratory activity in cancer cells or pro-angiogenic activity in EC. Model II: Semaphorins may act through complexes of receptor tyrosine kinases and plexins. The reason for both tumor-suppressive and tumor promoting activities of semaphorins may originate from the interaction between different plexins and tyrosine kinases. The most prominent example of a potential tumor growth promoting mechanism is the interaction between Plexin-B1 and Met (see Fig. 4). The Met receptor is a known ▶oncogene, and both Met and its ligand hepatocyte growth factor (HGF; see ▶Scatter Factor) contribute to increased invasiveness and angiogenic activity in tumors. Sema4D and HGF have been shown to act in synergy to cause activation of Plexin-B1 and Met and facilitate invasive growth in vitro and angiogenesis in vivo. Although it remains to be shown, other semaphorins may contribute to cancer progression through similar interactions between plexins and receptor-tyrosine kinases. Model III: Semaphorins may act through signaling to integrins. Integrins constitute a family of adhesion molecules of major importance to the migration of cells through the extracellular matrix. At the same time migration is a

crucial aspect of the behavior of endothelial cells during angiogenesis as well as the behavior of cancer cells during ▶invasion and metastasis. By affecting the function of integrins semaphorins may therefore affect the ability of a tumor to invade or stimulate angiogenesis. Today, compelling evidence suggests that semaphorin signaling as well as plexin activation inhibit integrin-dependent adhesion and migration of different cell types (see Fig. 5). Notably, in 2004 it was shown that SEMA3F expression in melanoma cells induces a poorly vascularized, non-metastatic phenotype, which was partly attributed to a decrease in β1-integrin mediated migration of the cancer cells. This highlights an alternative way by which class 3 semaphorins may act as tumor suppressors. Model IV: Semaphorins may act as suppressors of the immune system. Semaphorins are part of the viral genomes of different ▶pox viruses and the alcelaphine herpes virus. This has sponsored ideas concerning possible immunosuppressive functions of semaphorins. In accordance, the Vaccinia virus encoded semaphorin called A39R have been shown to negatively affect the migration of monocytes and phagocytosis by dendritic cells. Furthermore, the closest ancestor to the viral semaphorins is Sema7A, which seems to play a role endogenous to the immune system although its exact function is unknown.

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Semaphorin

Semaphorin. Figure 4 Semaphorins may promote tumorigenesis because of the synergistic interaction between Plexins and receptor tyrosine kinases. A prominent example of this is the interaction between Plexin-B1 (the receptor of Sema4D) and Met (the receptor of hepatocyte growth factor (HGF) Met causes phosphorylation of Plexin-B1, when Sema4D binds Plexin-B1.

Semaphorin. Figure 5 Model for how semaphorin signaling may influence the adhesion and migration of tumor cells. When semaphorins do not bind plexins, R-Ras is active (binding GTP), resulting in integrin-mediated binding to the extracellular matrix leading to higher adhesive and migratory behavior of the tumor cells. When semaphorins bind and activate plexin receptors, the GAP (GTPase activating protein) activity of plexins causes the conversion of R-Ras from a GTP-bound state (active) to a GDP-bound state (inactive). This leads to a decrease in integrin-mediated attachment and hence diminished cellular adhesion and migration. The activation of the plexin GAP activity requires the intracellular binding of the small GTPase RND1 to the plexins (not shown).

Senescence and Immortalization

These findings make it likely that certain semaphorins expressed by cancer cells add to the ways by which the cancer cells evade the immune system.

References 1. Semaphorin Nomenclature Committee (1999) Unified nomenclature for the semaphorin/collapsins. Cell 97:551–552 2. Kruger RP, Aurandt J, Guan K-L (2005) Semaphorins command cells to move. Nat Rev Mol Cell Biol 6:789–800 3. Chédotal A, Kerjan G, Moreau-Fauvarque C (2004) The brain within the tumor: new roles for axon guidance molecules in cancers. Cell Death Differ 12:1044–1056 4. Tamagnone L, Comoglio PM (2004) To move or not to move. Semaphorin signaling in cell migration. EMBO Rep 5:356–361

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the number of cell divisions and is generally brought about through the gradual shortening of the telomeres (repeat sequences at the ends of chromosomes) with each successive population doubling. Senescence is a permanent growth arrest that occurs after cells have exhausted their proliferative capacity. In normal human fibroblast, senescence takes place after approximately 60 population doublings in culture. ▶Telomerase ▶Senescence and Immortalization ▶Aging

Senescence Accelerated Semaphorin Receptors ▶Plexins

Seminomatous Germ Cell Tumor ▶Testicular Cancer

Sendai Virus Definition

▶Hemagglutinating Virus of Japan.

Definition Accelerated senescence, the process of rapid terminal growth arrest, is accompanied by phenotypic features of cell senescence (enlarged and flattened morphology, increased granularity, expression of specific biochemical and enzymatic markers such as senescenceassociated β-galactosidase activity). It can be induced in normal cells by DNA damage or introduction of mutant RAS and is also induced in tumor cells by different anticancer drugs or ionizing radiation. ▶Mitotic Catastrophe ▶Senescence and Immortalization

Senescence and Immortalization S R OGER R EDDEL Children’s Medical Research Institute, Westmead, The University of Sydney NSW, Australia

Definition

Senescence

Senescence is the permanent exit of a cell from the cell division cycle, accompanied by morphological and biochemical changes characteristic of ageing. Immortalization is the ability of cell populations to undergo an unlimited number of cell divisions.

Definition Is the limited capacity of cells to divide, an irreversible growth arrest state that depends on the age or cell doublings of a cell, a stage in the life cycle of a cell at which it can no longer divide. This state is dependent on

Characteristics Senescence Normal mammalian somatic cells can proliferate only a limited number of times in vitro, and the maximum

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number is often referred to as the “Hayflick limit.” When this limit is reached, the cells undergo various morphological and biochemical changes suggestive of ageing, so the process is referred to as senescence. Senescent cells can remain metabolically active for a long period of time, even though they have permanently exited from the cell cycle. Senescence is thus distinct from cell death (including ▶apoptosis and ▶autophagy). It is also distinct from terminal differentiation, where cells also exit permanently from the cell cycle and undergo changes that allow them to perform specialized normal functions. Senescent cells have been extensively studied as an in vitro model of ageing. In humans, cellular senescence appears to be a major barrier to the development of cancer. Immortalization It is not practicable to test whether cells are truly capable of continuing to divide forever, so cells are usually regarded as being immortalized if they have undergone many cell divisions (typically 100) beyond the Hayflick limit. Many cancers contain immortalized cells and some cancer-derived cell lines have been proliferating in vitro for many decades. Relevance of Senescence and Immortalization to Cancer Although the Hayflick number may be quite large (fibroblasts from an adult, for example, may divide up to 40 times before they become senescent), in most situations it is not large enough to permit tumor formation. A tumor containing 240 cells would be big enough to be lethal, but there are two major reasons why 40 cell divisions does not result in a tumor of this size. The first is that cell death occurs at a very substantial rate within tumors, for reasons that include genetic instability (see chapters on ▶chromosomal instability and ▶microsatellite instability) and difficulties with blood supply (see chapter on ▶angiogenesis) that result in cell death. The second is that the genesis of a fully malignant tumor cell requires the accumulation of a number of critically important genetic changes. Most of these changes occur at random and provide a growth advantage to the nascent tumor cell. This process consumes many more cell divisions than a normal cell is able to undergo before it becomes senescent. Consequently, senescence forms a major barrier to carcinogenesis in humans. A cell containing some of the genetic changes required for carcinogenesis will not usually be able to proliferate sufficiently to form a clinically significant tumor while the senescence barrier is intact. Human cells become immortalized at a very low frequency (so low, that no clear example has yet been found of a normal human cell undergoing immortalization spontaneously in cell culture), so immortalization is a rate-limiting step in human carcinogenesis. In contrast,

mouse cells become immortalized spontaneously at a measurable frequency and, correspondingly, the probability of a mouse cell becoming malignant is many orders of magnitude higher than for human cells. The ability to suppress tumor formation is a major selective advantage for a long lived species such as H. sapiens. A Cell Division Counting Mechanism The existence of a limit to the number of times a cell can divide implies that there must be a cell division counting mechanism. According to the telomere hypothesis of senescence, the counting mechanism is based on the progressive shortening of the ends of chromosomes (▶telomeres) that occurs with cell division. Telomeres form protective caps that prevent the cell recognizing the ends of chromosomes as double strand breaks and repairing them, for example by fusing the ends to each other. They contain repetitive DNA (in all vertebrates the repeat unit is a hexanucleotide, TTAGGG), which ends in a single-stranded G-rich tail. Telomeres are able to fold back on themselves and form a loop structure (referred to as a “t-loop”) when the single-stranded telomere invades duplex telomeric DNA and anneals to the complementary strand, thus hiding the free single-stranded telomere end. Telomeric DNA is recognized by specific binding proteins, including TRF1 and TRF2 which bind to doublestranded telomeric DNA and POT1 which binds to single-stranded telomeric DNA. The reasons for telomere shortening include the following. First, DNA replication depends on small RNA primers, which get degraded and replaced by DNA. However, there is no mechanism for replacing the terminal RNA primer required for lagging strand DNA synthesis, which results in the template for the next round of DNA synthesis being shorter. This is known as the “▶end replication problem.” Second, there appears to be a 5′-3′ exonuclease that shortens the C-rich strand, which creates or increases the length of a single-stranded G-rich telomeric tail. Regardless of the exact mechanism of telomere shortening, eventually telomeres become so short that they trigger the cell to exit permanently from the cell cycle. In order for a cell to become immortalized, it must somehow prevent telomere shortening. In most cancers this is achieved by the activity of an enzyme, ▶telomerase, and in a minority it is achieved by another mechanism referred to as ▶alternative lengthening of telomeres (ALT). Every immortalized cell line examined to date has either telomerase or ALT activity. Telomerase The telomerase holoenzyme complex is normally expressed in cells of the germ-line. It is also found in some normal somatic cells, especially those that are

Senescence-associated Chronic Inflammation

required to undergo extensive proliferation, but at levels that are insufficient to prevent telomere shortening. Telomerase synthesizes telomeric DNA to replace the DNA lost during cell division. The essential subunits include an RNA molecule (TElomerase RNA; TER; encoded by a gene designated TERC, which is an abbreviation of TElomerase RNA Component) that acts as the template for synthesis of telomeric DNA, the reverse transcriptase catalytic subunit (TElomerase Reverse Transcriptase; TERT) that carries out the synthesis, and dyskerin (encoded by the DKC1 gene), a protein that binds to TER. Telomerase activity can be detected in some normal human somatic cells, especially cells in highly proliferative tissue compartments such as the bone marrow, skin, mucous membranes and epithelia of the gastrointestinal tract (GIT), but not at sufficient levels to completely prevent telomere shortening. Telomerase has an important role in these tissues, because inherited mutations in any of the genes that encode one of the three telomerase components (TERT, TERC or DKC1), result in a condition called Dyskeratosis Congenita which is characterized by premature failure of proliferative capacity in tissues such as the bone marrow, skin and GIT. In contrast, at least 85% of all cancers contain sufficient levels of telomerase to prevent telomere shortening and the percentage is even higher in most types of carcinomas. The factors controlling hTERT expression are not well understood but it is known that hTERT can be upregulated by ▶MYC. If TERT expression is artificially switched on by genetic manipulation in normal cells, it is usually able to induce telomerase enzyme activity, because there is usually expression of the other telomerase subunits. This prevents telomere shortening and in some types of human cells this results in immortalization. Inhibiting telomerase activity in cancer cells may cause cellular senescence or cell death, so telomerase is an attractive target for the development of new anticancer treatments. Alternative Lengthening of Telomeres (ALT) Some immortalized cell lines and cancers have no detectable telomerase activity and maintain their telomeres by an alternative mechanism, referred to as Alternative Lengthening of Telomeres (ALT). Overall, about 8–10% of human tumors utilize ALT to prevent telomere shortening. Although the details are not fully understood, ALT is likely to be a recombinational mechanism in which one telomere uses another telomere (or itself via looping back) as a template for synthesis of new telomeric DNA. The ALT mechanism depends on the activity of the ▶MRN complex which is known to be involved in ▶homologous recombination. Cells that maintain their telomeres by ALT characteristically have very heterogeneous telomere lengths, ranging from undetectably short to extremely long. They also have

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substantial quantities of extrachromosomal telomeric repeat DNA, that may be either linear or circular, some of which is sequestered within ▶PML nuclear bodies. The presence of telomeric DNA and telomere binding proteins within PML bodies is highly characteristic of ALT-positive cells, and may be used to determine whether a tumor utilizes the ALT mechanism. Types of tumors where ALT is common include ▶glioblastoma multiforme (the most common primary brain tumor in adults), ▶osteosarcomas, and some types of ▶soft tissue sarcomas such as ▶malignant fibrous histiocytomas and ▶liposarcomas. Tumor Suppressor Genes Immortalization is facilitated by loss-of-function of the ▶p16INK4a or ▶RB1 genes, and the ▶p53 gene. Loss of the normal function of these genes results in a significant, but finite, increase in cellular proliferative potential. This permits the accumulation of additional genetic changes and increases the probably that activation of a telomere maintenance mechanism will occur. Cells containing an inherited p53 mutation from individuals with ▶Li-Fraumeni syndrome are the only type of human cells known to undergo immortalization spontaneously. Clinical Relevance Treatments that reverse the immortal phenotype may be a useful form of cancer therapy. An attractive target is telomerase, but inhibitors of telomerase may need to be combined with inhibitors of ALT to prevent the emergence of drug resistance.

References 1. Campisi J (2005) Suppressing cancer: the importance of being senescent. Science 309:886–887 2. Reddel RR (2000) The role of senescence and immortalization in carcinogenesis. Carcinogenesis 21:477–484 3. Reddel RR (2003) ALT, telomerase and cancer. Cancer Lett 194:155–162 4. Shay JW, Wright WE (2006) Telomerase therapeutics for cancer: challenges and new directions. Nat Rev Drug Discov 5:577–584 5. Stewart SA, Weinberg RA (2006) Telomeres: cancer to human aging. Annu Rev Cell Dev Biol 22:531–557

Senescence-associated Chronic Inflammation ▶Aging-Associated Inflammation

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Senile Involution

Senile Involution ▶Lobular Involution

Sensorineural Definition Associated with the inner ear or nerves involved in hearing. ▶Connexins

Sentinel Lymph Nodes I RIS M. C. VAN DER P LOEG , M AARTJE C. VAN R IJK , O MGO E. N IEWEG , B IN B. R. K ROON Department of Surgery, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands

the efferent lymphatic vessel that joins the artery and vein in the hilum. Direct drainage of the marginal sinus into the efferent vessel also exists (Fig. 1). The Sentinel Node The ▶sentinel node is the lymph node upon which the primary tumor drains directly. Lymph fluid moves subsequently to ▶second-tier and ▶third-tier lymph nodes. Lymph from the primary tumor region does not necessarily travel to the nearest node. Two lymphatic channels originating in the primary tumor can run to two different sentinel lymph nodes (Fig. 2). The sentinel node hypothesis implies orderly progression of ▶metastases from a primary lesion through the ▶lymphatic system. The concept is only relevant in tumors (▶cancer) with pre-dominant lymphatic dissemination, such as melanoma and cancer of the breast, penis or colon. If the first node contains a metastasis, there is a chance of tumor spreading downstream. In case of a tumor-negative sentinel node, second-tier and third-tier nodes are generally without metastases. Lymphatic Mapping The lymphatic drainage pattern can be visualized by ▶lymphoscintigraphy after injection of a ▶radiolabeled tracer in or near the site of the tumor. The radio-labeled tracer is cleared from the lymphatic channels and accumulated by the phagocytic cells in the lymph node. ▶Lymphoscintigraphic images depict

Synonyms First-tier node; First-echelon node

Definition

▶A sentinel lymph node is a lymph node upon which the primary tumor drains directly.

Characteristics General anatomy and physiology of the lymphatic system Lymphatic capillaries are 10–50 μm in diameter, consist of a single endothelial layer with a discontinuous membrane and are supported by collagen filaments. They are filled with lymph fluid originating from the interstitial space due to an osmotic pressure gradient and fluctuating intraluminal pressures. These intraluminal pressures are caused by lymphatic flow that is generated by lymph formation, contractions of the vessel wall and external pressure. Lymph fluid absorbed by lymphatic capillaries drains into larger collecting ▶lymphatic vessels. Such lymphatic vessels drain into marginal and medullar sinuses located between germinal centers within a lymph node. These centers contain large numbers of phagocytic cells that accumulate protein colloids. Then, a plexus within the lymph node drains to

Sentinel Lymph Nodes. Figure 1 The different relations between lymphatic vessels and lymph nodes. Afferent lymphatic ducts on the left discharge their contents into the marginal sinus. One lymphatic duct runs through the node on the right and another over its surface, bypassing the germinal centers. (Illustration made by Tanis PJ; Reprinted from Tanis et al. (2001) Anatomy and physiology of lymphatic drainage of the breast from the perspective of sentinel node biopsy. J Am Coll Surg 192(3):399–409, with permission from “The American College of Surgeons”).

Sentinel Lymph Nodes

Sentinel Lymph Nodes. Figure 2 A sentinel lymph node (SN) is the lymph node upon which the primary tumor drains directly. Two lymphatic channels originating in the primary tumor can run to two different sentinel lymph nodes. Lymph fluid moves subsequently to second-tier (*) and third-tier nodes. The SN is not always the node nearest to the primary tumor (Non-SN).

the lymph channels and the lymph node or nodes that contain the injected tracer. Dynamic scintigraphy and intraoperative ▶blue dye mapping give insight in the lymphatic drainage pattern, which enables the surgeon to find the sentinel node(s). The earliest sentinel lymph node identification techniques involved the injection of a vital blue dye, usually isosulfan blue. It was a key point in the general acceptance of ▶sentinel node biopsy. The blue dye was injected intradermally at the primary tumor site in melanoma patients. An incision was made over the expected lymph node region and the lymphatic channel was visually identified. This channel was dissected and followed to the first draining lymph node. Subsequent reports described the use of radio-labeled tracers, such as technetium-99m-bound colloids. Colloids with a small particle size can rapidly pass the openings of interendothelial junctions and allow visualization of the lymphatic channels leading directly to the sentinel node. A disadvantage of small sized particles is that some of the tracer moves on to nodes further downstream because phagocytic cells in the first node cannot trap them all. Larger colloid particles enter lymphatic channels more slowly. The tracer almost never moves on to subsequent nodes, but the channels are visualized less often. Nowadays, the ▶lymphatic mapping technique mostly used involves administration of a radio-labeled tracer into or near the primary lesion in combination with blue dye. During surgery, the sentinel node is found with the assistance of both blue dye and a ▶gamma-ray detection probe. Preoperative lymphoscintigraphy is added for better specification of the location and number of sentinel nodes. Different methodologies based on these lymphatic mapping techniques are nowadays applied all over the world.

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Sentinel Node Biopsy A sentinel node biopsy is a minimally invasive technique that was initially developed as an alternative to complete lymph node dissection in patients with a melanoma. The majority of patients are spared a more complex surgical procedure with a higher morbidity rate while the same staging information is obtained. All nodes of a complete node dissection used to be bisected and evaluated by haematoxylin-eosin staining. This way, metastases larger than 2 mm were usually identified. With the selective sentinel node biopsy, the pathologist can focus on the one or few nodes that are most likely to contain metastatic disease. The sentinel nodes are evaluated by both haematoxylin-eosin and immunohistochemistry staining, which occasionally distinguish metastases with a size of one tumor cell. The combined procedure of lymphatic mapping and sentinel node biopsy provides prognostic information, identifies patients who may benefit from early regional therapy (▶locoregional therapy) and, depending on the situation, from adjuvant systemic treatment (▶adjuvant therapy). This way optimal survival rates may be realized. Breast Cancer The predominant lymphatic drainage pathway from the breast is towards the axilla. Metastases initially remain localized in the lower axilla and then may travel higher up the chain to the subclavicular and the supraclavicular basins (Figs. 3 and 4). Axillary lymph node dissection used to be performed in almost every breast cancer patient. This operation has several side effects, such as lymph oedema, pain and decreased mobility of the arm, and often no metastases were found. With the introduction of sentinel node biopsy, axillary lymph node dissection is only indicated if this node is involved. As a result, many patients are spared an unnecessary operation. Whether the omission of routine axillary node dissection jeopardizes regional tumor control and survival is still subject of research. Large observational studies revealed excellent results in patients who did not receive axillary node dissection because of a tumornegative sentinel node. Recurrence rates vary between 0.12% and 0.6% and these numbers do not exceed the known recurrence rates after routine axillary clearance. Melanoma There is consensus on the way lymphatic mapping should be carried out in melanoma patients. Preoperative lymphoscintigraphy and intraoperative use of blue dye and a gamma-ray detection probe are standard. The first large studies on sentinel node biopsy in melanoma showed a 95% sensitivity. Recent studies show falsenegative rates of around 10%. False-negative means that

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Sentinel Node

Concluding Remarks The development of the sentinel node concept is a milestone in the understanding of dissemination of solid malignancies. The introduction of lymphatic mapping in 1989 initiated the widespread use and general acceptance of this approach. Now that the technique has been validated, many patients are spared unnecessary surgery without compromising regional control and the accuracy of staging. Lymphatic mapping with ▶sentinel lymph node biopsy has become a standard component in the management of patients with breast cancer or melanoma. This suggests potential in other tumors that spread primarily through lymphatic channels. In the future, studies need to focus on more peripheral issues such as the prognostic significance of ▶micrometastases and techniques such as molecular assays or markers. These may provide more information to optimize the staging of tumor dissemination and will enable the fine-tuning of therapy. Sentinel Lymph Nodes. Figure 3 A tumor (black area) with lymphatic channels to nodes in the axilla (a) and to lymph nodes below (b) and above (c) the clavicula. A metastasis may be found along this lymphatic pathway.

References 1. Nieweg OE, Tanis PJ, Kroon BBR (2001) The definition of a sentinel node. Ann Surg Oncol 8(6):538–541 2. Tanis PJ, Nieweg OE, Valdés Olmos RA et al. (2001) Anatomy and physiology of lymphatic drainage of the breast from the perspective of sentinel node biopsy. J Am Coll Surg 192(3):399–409 3. Tanis PJ, Nieweg OE, Valdés Olmos RA et al. (2001) History of sentinel node and validation of the technique. Breast Cancer Res 3(2):109–112 4. Nieweg OE, Van Rijk MC, Valdés Olmos RA et al. (2005) Sentinel node biopsy and selective lymph node clearance – impact on regional control and survival in breast cancer and melanoma. Eur J Nucl Med Mol Imaging 32(6):631–634 5. Morton DL, Thompson JF, Cochran AJ et al. (2006) Sentinel-node biopsy or nodal observation in melanoma. N Engl J Med 355(13):1307–1317

Sentinel Lymph Nodes. Figure 4 Anterior and lateral lymphoscintigrapic images of a woman with left-sided breast cancer. A sentinel node and several second-tier nodes are visualized in the axilla.

the sentinel node is disease-free, while there are metastases in the lymph node basin. Patients with an involved sentinel node have a 5-year survival rate of around 65% and in patients with a tumor-negative sentinel node this is 90%. A large randomized study showed that early regional node dissection based on a positive sentinel node improves survival in patients with an intermediate-thickness melanoma.

Sentinel Node O LA W INQVIST 1 , M AGNUS T HO¨ RN 2 1

Department of Medicine (OW), Karolinska Institutet, Stockholm, Sweden 2 Department of Surgery (MT), Karolinska Institutet, Stockholm, Sweden

Synonyms Draining lymph node

Sentinel Node

Definition Sentinel means a lookout, and the sentinel node is defined as the first ▶lymph node or nodes that are located on the direct draining lymphatic route from the area of a primary tumor.

Characteristics

The ▶lymphatic system was first described in the seventeenth century by Olof Rudbeck who systematically studied the lymphatic vessels collecting extra cellular fluids from tissues emptying into ▶lymph nodes. The lymphatic system is more variable then the blood system and is anatomically less well defined. The drainage from tumors seems to vary considerably, making prediction of the draining lymph node difficult without guidance. Tumor cells become metastatic either by invasive growth through basal membranes or by entering into capillaries. The endothelial cells comprising the lymph capillaries are widely fenestrated (▶Fenestration) making easy access to the lymph vessel. There is also an active transport of primarily white blood cells into the lymphatic vessels but tumor cells may also use this mechanism. After entering into the capillaries of the lymphatic vessel, the metastatic cell may then enter into the draining lymph node. Thus, the tumor draining lymph node is the primary location to find lymph node metastases. If tumor cells are present in the sentinel node, the risk of systemic dissemination of the disease is high since about half of the lymphatic fluid entering a lymph node continues directly to the blood circulation via ▶lymphovenous shunts. In 1960 Gould first described a sentinel node draining a cancer of the parotid gland. Cabanas introduced the technique in 1977 for guidance of the surgical procedure for inguinofemoroiliac lymph node dissection of patients with penile carcinoma. This first study demonstrated two important principles regarding sentinel node investigations; (i) the sentinel node is the first site of metastases and may be the only lymph node involved containing metastatic cells (ii) sentinel nodes negative for metastatic cells suggest that no spreading of the disease has occurred and this finding is coupled to increased survival. Studies of prognostic factors in colorectal cancer point out the histological status of the regional lymph nodes as the most important predictor of survival and the presence of regional lymph node metastases implies a 50% reduction in 5-year survival rates. Similar observations have been reported in most solid tumors. However, the quality of the staging process of lymph node investigations are dependent on the total number of locoregional lymph nodes identified and the extent of the following histopathology investigation. Malignant tumor often induce a peritumoral upregulation of lymphatic vessels and blood vessels by producing ▶angiogenic factors such as the vascular

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endothelial growth factor (▶VEGF), making the pathways for lymphatic drainage difficult to predict. Studies have shown that elevated levels of the cytokine cascade of VEGF-C and VEGF-D promote tumoral ▶lymphangiogenesis and that inhibition of their joint receptor, VEGFR-3, suppresses the effects. Further, elevated levels of VEGF-C and VEGFR-3 correlate with presence of lymph node metastases and lymphatic invasion in human colorectal cancer. A large study of patients with breast cancer demonstrated an increased presence of lymphatic vessels in metastatic axillary lymph nodes (85%) compared to nonmetastatic lymph nodes (25%) and that intra- and perinodal lymphatic endothelial cell proliferation fractions were higher in metastatically involved lymph nodes. These discoveries underline the association of lymphangiogenesis with lymph node metastases. Sentinel Node Procedure The sentinel node is either located before surgery through lymphoscintigraphy or during surgery by the superficial injection of a tracer substance around the tumor (Fig. 1). When the tumor is located in the skin, the injection is usually placed around it in four places subcutaneously or intradermally. In visceral tumors (colorectal and gastric tumors) the injections should be superficial, precisely beneath the serosa whereas in parenchymatous organs (liver) the injections are preferably placed under the capsula into the parenchyma around the lesion. When approaching the tumor from the mucosal side, the injections are made through the mucosa and into the muscular wall (urinary bladder tumors). Within a few minutes the tracer has entered the ▶fenestrated lymph capillaries. The tracer is then transported inside lymph vessels and accumulates through phagocytosis by ▶dendritic cells in the sentinel node(s). Coal particles, dyes such as patent blue, isosulfan blue, and/or radioactive 99Technetium colloid markers have been used as tracers for intraoperative ocular identification or detection using a hand held γ-counter respectively. A preoperative lymphoscintigraphy can facilitate the location of the regional lymph node basin draining the tumor and may be combined with computerized tomography for precise anatomical information in certain cases. The procedure is dependent on the surgeon’s experience with the method and initial procedures are more likely to give rise to false negative sentinel lymph node, i.e., sentinel node does not contain metastatic cells whereas other regional lymph nodes are positive for tumor cells. The false negative rates in large series performed by experienced surgeons are usually as low as 3–5%. Clinical Relevance During recent years the importance of correct staging (▶Staging of tumors) regarding lymph node metastases including presence of micro metastases has become evident for most types of human solid tumors. However,

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Sentinel Node

Sentinel Node. Figure 1 The sentinel node concept. Identification of the tumor draining (sentinel) node is accomplished by peritumoral injections of Patent blue dye and/or a radioactive tracer 99Technetium. The tracers enter into the lymph capillaries, which follows the lymphatic drainage and accumulation in a lymph node. During surgery the area of drainage is explored after the guidance of a γ-counter and the sentinel node is visualized by dissection. Since the tumor is in contact with the sentinel node, the sentinel node is the preferred site for metastases. When the sentinel node is investigated microscopically, it can be considered diagnostic for the whole lymph node region, guiding prognosis and therapy. In a progressively growing tumor, there is a rapid turnover of cells and disruption of normal tissue architecture, causing release of inflammatory mediators and attraction of macrophages and dendritic cells. Tumor cell debris is phagocytosed by these antigen presenting cells, which after the encounter migrate to the sentinel node, presenting peptides derived from tumor antigens to naïve T lymphocytes. Sentinel node lymphocytes mount proliferative responses and become clonally expanded against tumor antigen in an attempt to fight cancer.

the search for metastases or micro metastases among a large number of lymph nodes in a pathology specimen is time-consuming, labor-intensive, and expensive. Therefore the use of the sentinel node technique has received increasing interest since it entails detailed investigation of (in most cases) only one to three lymph nodes. Thus an increased awareness regarding an extended histopathological investigation of lymph nodes for staging and guidance for therapy has become apparent. The sentinel node concept entails the possibility of

multiple drainage pathways from different parts of the primary tumor, thus a patient may have more than one sentinel node. The tumor status of this node reflects the status of the regional lymphatic field and has a strong impact on prognosis. Thus, the sentinel node procedure is increasingly used in malignant melanoma and breast cancer where it has become part of the standard staging (Staging of tumors) procedure and an important factor to consider when deciding about postoperative adjuvant therapy. In fact even insurance companies have taken the status of the sentinel node into account when determining life insurances. In a large randomized study of patients with malignant melanoma, sentinel node biopsy was compared with nodal observation demonstrating that sentinel node biopsy-guided staging provides important prognostic information and furthermore identifies patients that may benefit from immediate lymphadenectomy. In breast cancer, the introduction of sentinel node biopsy has limited the number of axillary lymph node dissections. Thus, the removal of the tumor draining sentinel node permits a smaller surgical axillary procedure and decreases the risk for different side effects including lymphoedema and nerve damage. The 5-year survival rate in patients with negative sentinel node biopsies is not different from women with breast cancer having undergone axillary lymph node dissection without the presence of metastases. Thus, sentinel node biopsy is a safe and accurate metastases screening method for patients with breast cancer. The sentinel node procedure has recently been shown to be applicable in many solid tumors including colorectal cancer, urinary bladder cancer, vulvae cancer, and gastric cancer, and the procedure may be valid for staging the majority of solid tumors. Immunology of the Sentinel Node According to the immune surveillance hypothesis, the immune system is continuously sensitized against developing tumors, most of which are eliminated at an early stage. Not only metastatic cells from the tumor enter into the lymphatic vessels but also antigen presenting cells, dendritic cells, which have endocytosed dying tumor cells, or debris from tumor cells containing ▶tumor antigens, accumulate in the sentinel node. Since experimental evidence indicates that activation of naïve T cells (▶T-cell response) occurs within the highly specialized microenvironment of secondary lymphoid organs, i.e., lymph nodes, the sentinel node may be regarded as the primary site for the immune system to encounter tumor antigens. Thus sentinel node acquired lymphocytes are clonally expanded (▶Clonal expansion) T cells recognizing tumor antigens and may therefore serve as a useful source for immunotherapy. ▶Adoptive Immunotherapy ▶Immunotherapy ▶Sentinel Lymph Node

Ser/Thr-Phosphorylation

References 1. Cabanas RM (1977) An approach for the treatment of penile carcinoma. Cancer 39:456–466 2. Marits P, Karlsson M, Dahl K et al. (2006) Sentinel node acquired lymphocytes – tumour reactive lymphocytes identified preoperatively for the use in immunotherapy of colon cancer. Br J Cancer 94:1478–1484 3. Morton DL, Thompson JF, Cochran AJ et al. (2006) Sentinel-node biopsy or nodal observation in melanoma. N Engl J Med 355:1307–1317 4. Swanson RS, Compton CC, Stewart AK et al. (2003) The prognosis of T3N0 colon cancer is dependent on the number of lymph nodes examined. Ann Surg Oncol 10:65–71 5. Veronesi U, Paganelli G, Viale G et al. (2003) A randomized comparison of sentinel-node biopsy with axillary dissection in breast cancer. N Engl J Med 349:546–553

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Separin Definition A protease, also called separase, that cleaves the cohesin subunit Scc1/Mcd1 to induce sister-chromatid segregation. Its C-terminus is conserved, it.is inhibited by association with securin at the non conserved N-terminus.

Sequence Identification Definition Determination of the primary structure of a biomolecule (e.g. amino acids; DNA).

Sentinel Node Biopsy

▶Oncopeptidomics

Definition A minimally invasive technique to remove the first node in the draining lymphatic basin. The sentinel node is examined by the pathologist for cancer cells. ▶Sentinel Lymph Nodes

Sentinel Vessels

Sequestered Definition In biochemistry a term, e.g., for a protein, synonymous to covered up, shielded, locked away resulting in biologically not available orphan receptor. The collective term for receptors with unidentified ligands/ without known ligands. ▶Arachidonic Acid Pathway

S

Definition Dilated episcleral vessels that provide nourishment to an underlying ciliary body tumor. ▶Uveal Melanoma

Ser/Thr-Phosphorylation Definition

Solitary extraosseous or extramedullary plasmacytoma.

Protein phosphorylation is a post-translational modification carried out by enzymatic transfer of a phosphate group from a donor-molecule to a polypeptide backbone. The enzymes that catalyze this type of reactions are known as kinases. They transfer phosphate groups either to tyrosine residues (Tyr-kinases) or to serine or threonine residues (Ser/Thr-kinases) according to defined motifs within the polypeptide.

▶Plasmacytoma

▶Cystatins

SEP Definition

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SERCA

SERCA Definition A pump situated in the membrane of the sarcoplasmic/ endoplasmic reticulum that couples ATP hydrolysis to the import of Ca2+ from the cytosol to the endoplasmic reticulum lumen. ▶Endoplasmic Reticulum Stress

Serex C ARSTEN Z WICK , M ICHAEL P FREUNDSCHUH Klinik für Innere Medizin I, Universität des Saarlandes, Homburg, Germany

Definition A method for identification and molecular analysis of antigens by recombinant expression cloning; Acronym for serological analysis of antigens by recombinant expression cloning.

Characteristics For SEREX, a cDNA library is constructed from fresh tumor specimens, cloned into λ phage expression vectors and phages are used to transfect E. coli. Recombinant proteins which are expressed during the lytic infection of the bacteria are transferred onto a nitrocellulose membrane. These membranes are incubated with the diluted serum of the autologous patients and screened for clones reactive with high-titered IgG antibodies. Positive clones are visualized by staining after incubation with an enzyme-conjugated secondary antibody specific for human IgG. Positive clones are subcloned to monoclonality, and the nucleotide sequence of the inserted cDNA is then determined. The SEREX approach is technically characterized by several features: . The use of fresh tissue obviates the need for culturing cells in vitro and therefore circumvents in vitro artifacts. . The analysis is restricted to genes that are expressed by the tissue in vivo. . The use of high-titered IgG antibodies in the initial screening procedure limits the analysis to such antigens which elicit a strong immune response in the host and imply a cognate T-cell help. . The serological analysis covers the whole repertoire of proteins expressed by the respective tissue.

. SEREX uses polyspecific sera to scrutinize monoclonal antigens which are highly enriched in lytic plaques. This allows for a direct molecular definition of antigens, since the cDNA sequence of the antigen can be determined instantaneously. . The specificity of the antigen, i.e. its expression spectrum is determined by the analysis of the mRNA expression pattern by Northern blots and RT PCR. . If defined types of antigens are to be preselected for, the original SEREX approach can be modified appropriately by using biased cDNA libraries (e.g.normal testis) or modified detection systems (e.g. for IgA, IgM). To overcome the problem of incorrect folding and the lack of posttranslational modifications, which are both inherent problems of bacterial expression systems, a eukaryotic expression system in yeast, designated as “recombinant antigen expression on yeast surface” (RAYS) has been established. For RAYS, a cDNAlibrary is cloned for expression as Aga2 fusion proteins on the yeast surface. After incubation with patient’s sera, FACS-sorted positive clones are spotted onto 96-well-plates, re-analyzed for specific detection and the nucleotide sequence for the cDNA insert is then determined. Cellular and Molecular Regulation High-titered IgG responses imply a cognate T-cell help. Therefore, in an approach of “reverse T-cell immunology” antigens detected by SEREX can be used for the definition of epitopes that are presented in the context of MHC I and MHC II. Preferably, specific T-cell reactivities are looked for in patients with high serum antibody reactivity to the respective antigen, and for many SEREX antigens both CD4 and CD8 stimulating epitopes have been identified. Clinical Relevance SEREX allows for an unbiased search and the direct molecular definition of immunogenic proteins based on their reactivity with autologous and allogeneic patient sera. Hence, while SEREX was originally developed for the serological analysis of human ▶tumor antigens, it can be used whenever antibody reactivities against tissue antigens are suspected and neither the antibody nor the antigen is known, e.g. for the identification and molecular characterization of ▶autoantigens in ▶autoimmune diseases. Using the RAYS approach might enable us to identify antigens that have escaped detection to date, because they elicit immune responses against post-translational modified or conformational epitopes not detectable by conventional SEREX. An international effort led by the Ludwig Institute for Cancer Research aims at defining the entire spectrum of antigens expressed by human tumors. All SEREX data are entered into the Cancer Immunome Database,

Serine Proteases (Type II) Spanning the Plasma Membrane

which is accessible to the public (http://www2.licr.org/ CancerImmunomeDB/.) ▶Autoantibodies

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proteases share a common reaction mechanism based on the formation of an acyl–enzyme intermediate on a specific active serine residue. ▶Class II Tumor Suppressor Genes

References 1. Sahin U, Türeci Ö, Schmitt H et al. (1995) Human neoplasms elicit multiple immune responses in the autologous host. Proc Natl Acad Sci USA 92:11810–11813 2. Türeci Ö, Sahin U, Pfreundschuh M (1997) Serological analysis of human tumor antigens: molecular definition and implications. Mol Med Today 3:342–349 3. Preuss KD, Zwick C, Bormann C et al. (2002) Analysis of the B-cell repertoire against antigens expressed by human neoplasms. Immunol Rev 188:43–50 4. Neumann F, Wagner C, Kubuschok B et al. (2004) Identification of an antigenic peptide derived from the cancer-testis antigen NY-ESO-1 binding to a broad range of HLA-DR subtypes. Cancer Immunol Immunother 53:589–599 5. Mischo A, Wadle A, Wätzig K et al. (2003) Recombinant antigen expression on yeast surface (RAYS) for the detection of serological immune responses in cancer patients. Cancer Immun 3:5–16

Serine Protease Inhibitor-like Domain ▶RECK Glycoprotein

Serine Proteases (Type II) Spanning the Plasma Membrane B EATRICE K NUDSEN , P ETER N ELSON , J ARED LUCAS

Serine Elastase

Divisions of Public Health Sciences, Human Biology and Clinical Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA

Synonyms ▶Neutrophil Elastase

Serine Protease

Matriptase: Epithin, MT-SP1, suppression of tumorigenicity 14 Transmembrane protease serine 1–13: hepsin (TMPRSS 1); Epitheliasin (TMPRSS 2); TMPRSS2 = TMPRSS4; Spinesin (TMPRSS5), matriptase-2 (TMPRSS6), matriptase-3 (TMPRSS7), distal intestinal serine protease (mouse only, TMPRSS8), polyserase (TMPRSS9), Corin (TMPRSS10), TMPRSS11–13 (human genes)

S

Definition A class of enzymes that cleave peptide bonds in proteins that contain a serine residue in the active site of the enzyme. They play an important role in digestion, blood clotting, and the complement system. ▶Protease Activated Receptor Family

Serine Protease Inhibitor

Definition The family of type II transmembrane serine proteases consists of 14 members identified to date. They share a transmembrane orientation with an intracellular N-terminus and a basic, multidomain structure, which contains several individually folded protein modules in the extracellular domain (Fig. 1). Members of the family possess specific tissue and cell type distributions. For example ▶Matriptase and ▶Hepsin are epithelial, while ▶Corin (TMPRSS10) is expressed in cardiac muscle cells. Matriptase, TMPRSS2 and Hepsin are associated with cancer development or progression.

Definition

Characteristics

Large group of proteins that inhibit or antagonize the biosynthesis or actions of serine-type proteases. Serine

The serine protease domain, which is located at the C-terminal end of all family members, encodes

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Serine Proteases (Type II) Spanning the Plasma Membrane

Serine Proteases (Type II) Spanning the Plasma Membrane. Figure 1 Domain structures of the known type II transmembrane serine proteases. All are oriented with their amino terminal in the cytoplasm, a single transmembrane spanning domain and their carboxy terminal exposed extracellularlly. They are not drawn to scale but the total amino acid residues for each are indicated in parentheses. TMPRSS11 has known isoforms (a, b, d, e, and f) with similar domain structures and vary by only a few amino acids in length. Domains are abbreviated as; SEA: sea urchin sperm protein, enterokinase and agrin; CUB: complement C1r/C1s, Uegf and BMP-1; LDLa: low density lipoprotein receptor class A; SPD: trypsin like serine protease; SR: scavenger receptor cysteine-rich; FRI: frizzled.

the central function of the extracellular domain. The mechanism of activation, substrate specificity and physiological function of the serine protease domain are best understood for Matriptase and are described below. Hepsin is functionally related to matriptase in its ability to autoactivate, digest epithelial basement membrane proteins and activate hepatocyte growth factor/▶scatter factor. Hepsin was discovered in liver and reported as overexpressed in metastatic prostate cancer cells. TMPRSS2 is preferentially expressed in the prostate under the regulation of androgen and the fusion of its promoter with genes from the family of ▶ETS transcription factor plays an important role in prostate

cancer development and progression (▶TMPRSS2/ERG Fusions). TMPRSS2 is, itself, over-expressed in the majority of advanced prostate cancers where it often becomes mis-localized away from the plasma membrane. Regulation of Activity The activity of matriptase is regulated through autoactivation and is facilitated by lysophospholipids, steroid hormones and the polyanionic compound, ▶suramin. For complete activation, matriptase requires glycosylation and serine protease domains to increase protein stability, an intact ▶LDL receptor domain and an initial cleavage at Gly149 in the juxtamembrane

Serine Proteases (Type II) Spanning the Plasma Membrane

▶SEA domain. In addition, the interaction of the LDL receptor domain with the serine protease inhibitor, hepatocyte activator inhibitor-1 (HAI-1) is critical for autoactivation. Active matriptase has a limited range of known substrates. These are ▶HGF, urokinase plasminogen activator (▶Plasminogen Activating System), ▶stromelysin (Matrix Metalloproteinases), ▶protease activated receptor (PAR-2) and ▶extracellular matrix and cell ▶adhesion proteins. The enzymatic activities of matriptase and hepsin are inhibited by HAI-1, a membrane-associated Kunitz type-1 serine protease inhibitor. HAI-1 shares amino acid sequence homology and a similar domain structure with HAI-2 and consists of two Kunitz domains (Nterminal KD-1 and C-terminal KD-2) intersected by a low-density lipoprotein receptor (LDLR)-like domain. HAI-1 has a remarkable and unique specificity for a serine protease inhibitor and only inhibits the serine proteases matriptase, hepsin, prostasin, hepatocyte growth factor activator (HGFA) and a phosphatidylinositol (GPI)-anchored epithelial serine protease. Through regulation of matriptase, hepsin or HGFA activity, HAI-1 controls the amount of biologically active two-chain HGF on the cell surface and the activation of the Met receptor (▶MET). Biological Responses Matriptase and hepsin have been shown to facilitate the invasion and metastasis of cancer cells through proteolysis of extracellular matrix, activation of uPA and MMP-3 and increasing in ▶angiogenesis. Transgenic mice overexpressing hepsin show a defect in the epithelial basement membrane, characterized by loss and disorganization of collagen-IV and laminin-5 (▶Adhesion; ▶laminin signaling). Several proteases and proteolytic cascades mediate the activation of HGF (▶Scatter factor). Matriptase and hepsin are central proteases for HGF activation, since pro-HGF is their direct substrate. In addition, matriptase also activates uPA, and thereby magnifies the activity for HGF activation on the cell surface. Studies in genetic mouse models reveal that matriptase is required for post-natal survival by maintaining the barrier function of the epidermis. Matriptase deficiency phenocopies the loss of its proteolytic target, the serine protease, prostasin/CAP1/ Prss8. Matriptase also plays an important role in hair follicle development, thymic homeostasis and keratinocyte differentiation. In humans, matriptase is shed from the cell surface and is found complexed with HAI-1 in human milk. Expression in Cancer Matriptase is expressed on cancer cells, that originate from a variety of epithelial origins and has been implicated in cancer development, progression and

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▶angiogenesis. Matriptase translocates from a perinuclear reservoir to activation foci in cell-cell junctions and later moves to membrane protrusions in response to growth factor stimulation. On the cell surface, the balance between matriptase and hepatocyte activator inhibitor-1 (HAI-1) and HAI-2 regulates matriptase activity. The ratio of matriptase to HAI-1/ HAI-2 expression increased with tumor grade and progression in ovarian, cervical, prostate and colon cancer. The resulting increase in active matriptase on the cell surface facilitates invasion and metastasis of cancer cells. Matriptase and HAI-1 are indirectly regulated by ▶androgens. In a ▶prostate cancer cell line, treatment with ▶testosterone transiently increased matriptase expression and activity and increased shedding of proteolytically cleaved HAI-1. As a result an increase in HAI-1–matriptase complexes occurred in the extracellular space. In normal human prostate glands, HAI-1 protein expression decreased after androgen suppressive therapy, however, in cancerous glands, intracellular protein expression was not affected by androgen. Clinical Relevance Pathologic deregulation of matriptase, hepsin or TMPRSS2 can result from increased expression, activation and from an imbalance relative to their cognate inhibitors, e.g. HAI-1. Elevated expression of matriptase and HAI-1 are associated with poor outcome in several human cancers, including node-negative breast, prostate and ovarian cancers. In a transgenic mouse model modest expression of matriptase in epidermis is sufficient to cause ▶squamous cell carcinoma, and matriptase expression enhances ▶gastric cancer metastasis in ▶nude mice. Forced expression of Hepsin in prostate cancer stimulates metastasis while inhibiting local growth. Consistent with matriptase’s role in cancer, inhibition of matriptase expression or activity by matriptase-specific small molecular inhibitors, matriptase ▶anti-sense, or ▶siRNA, suppresses cancer growth in cell culture and ▶xenograft models.

References 1. List K, Bugge TH, Szabo R (2006) Matriptase: potent proteolysis on the cell surface. Mol Med 12:1–7 2. Wu Q (2003) Type II transmembrane serine proteases. Curr Top Dev Biol 54:167–206 3. Wu Q, Kuo HC, Deng GG (2005) Serine proteases and cardiac function. Biochim Biophys Acta 1751:82x–94 4. Kataoka H, Miyata S, Uchinokura S et al. (2003) Roles of hepatocyte growth factor (HGF) activator and HGF activator inhibitor in the pericellular activation of HGF/ scatter factor. Cancer Metastasis Rev 22:223–236 5. Planes C, Caughey GH (2007) Regulation of the epithelial Na+ channel by peptidases, Curr Top Dev Biol 78:23–46

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Serine/Threonine Kinase

Serine/Threonine Kinase Definition Enzyme that adds phosphate group to serine or threonine amino acid residue in substrate protein. ▶Herceptin ▶Protein Kinase C Family

Serine-Threonine Kinase Receptor-Associated Protein N ILESH D. K ASHIKAR , P RAN K. DATTA Departments of Surgery and Cancer Biology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA

Synonyms hMAWD: Human MAPK activator with WD repeats; Unrip: unr-interacting protein; STRAP

Definition STRAP is a 39 kDa protein of WD-40 family involved in probable chaperoning function during the formation of multiprotein complexes shown to be active in the ▶Transforming growth factor-β (TGF-β) receptor signaling network and U-rich small nuclear ribonucleoprotein (U snRNP) assembly. ▶Oncogenic STRAP is up-regulated in human cancers and may be involved in tumor progression.

Characteristics STRAP was first cloned from mouse embryonic cDNA library while searching for novel proteins that bind the cytoplasmic region of TGF-β type I receptor (TβRI) using yeast two-hybrid screening. Later it was found that STRAP could associate with both type I and type II (TβRII) serine-threonine kinase receptors. Southern blot analyses demonstrate that STRAP is evolutionarily conserved from yeast to mammals. The importance of this conservation was revealed when STRAP knockout mice were generated using the gene-trap mutagenesis technology coupled with ▶microarray in the process to identify the probable targets of ▶platelet-derived growth factor (PDGF) signaling. STRAP was found to be a PDGF-BB-inducible gene. The gene trap insertion results in embryonic lethality between embryonic day (E) 10.5 and E12.5. Homozygous mutant embryos had

defects in ▶angiogenesis, cardiogenesis, somitogenesis, neural tube closure and embryonic turning. This highlights an indispensable function for STRAP during early development. Later STRAP was also identified in humans as an interacting protein with upstream of N-ras (unr) that is involved in the internal initiation of translation of human rhinovirus RNA and is implicated in cap-independent translation. STRAP belongs to the family of WD repeat proteins that are known to have four or more repeating units containing a conserved core of approximately 40 amino acids that mostly end with tryptophan-aspartic acid (WD). Most of them are thought to form a circularized β propeller structure. Though the underlying common function is coordinating multiprotein complex assemblies, these proteins are also involved in various cellular processes like signal transduction, transcriptional regulation, programmed cell death, RNA synthesis/processing, chromatin assembly, cell cycle progression and vesicular trafficking. Other common examples of WD repeat proteins are the β subunit of the ▶G proteins, TATA box binding protein associated factor II (TAFII), ▶apoptotic protease-activating factor 1 (APAF-1), retinoblastoma-binding protein p48 (RbAp-48), receptor activated protein kinase C 1 (RACK1), and phospholipase A2-activating protein (PLAP) or TGF-beta receptorinteracting protein 1 (TRIP-1), which is also known to interact with TβRII. The human STRAP gene is placed in chromosome 12p12.3 near the marker D12S1593. Northern blot analysis, using different tissues in mice, indicated a major transcript of 1.8 kb, though in some tissues a larger transcript was detectable. This may suggest alternative splicing of the STRAP RNA at least in some tissues. It is ubiquitously expressed in all mouse tissues with highest levels in liver and testes and less abundantly in spleen. In humans, STRAP expression has also been shown to be ubiquitous and it forms a 2 kb transcript. Both human and mouse STRAP genes contain 10 exons, which finally form a 350 amino acid protein migrating with an apparent mass of 39 kD on SDS-PAGE. Murine STRAP has more than 97% amino acid identity over the entire sequence with its human version. Sequence analysis indicates that STRAP contains six WD40 repeats. STRAP shows a 55% similarity in base pairs and a 19% similarity in amino acid sequence to another known WD40 protein, TRIP-1. Some of these similarities are among the conserved amino acid residues within the WD repeats. STRAP is localized predominantly in the cytoplasm but a good level is also present in the nucleus. It forms homo-oligomers probably through the WD repeats and this may be important for the multi-protein complex assembly. The physical interaction of STRAP with the TGF-β receptor complex raises the possibility that STRAP is a substrate of the receptors. Our findings showed that an increase in the phosphorylation of STRAP

Serine-Threonine Kinase Receptor-Associated Protein

requires the kinase activity of receptors in vivo, but STRAP does not appear to be a direct substrate of the receptors during in vitro kinase assays. The C-terminal 57 amino acids are important for this phosphorylation. Eukaryotic Linear Motif resource (ELM) search indicates the presence of putative phosphorylation sites in the Cterminal region for the casein kinases I and II. Multiple phosphorylation sites also seem to be present inside the different WD repeat domains for different kinases and may serve to modify the function of STRAP. Apart from TβRI and TβRII, STRAP also binds with ▶Smad2, ▶Smad3, ▶Smad6, ▶Smad7, 3phosphoinositide-dependent protein kinase 1 (PDK1), Ewing’s sarcoma protein (EWS), hMAWD binding protein (MAWBP), unr, microtubule associated protein 1B (MAP1B), nuclear export factor (NXF) proteins, Gemin6, Gemin7, and 3 small nuclear ribonucleoproteins (SmB), SmD2, SmD3. Additionally, using ELM motif search, it also shows putative binding sites for other proteins like C-terminal Binding Protein (CtBP), protein phosphatase 1, retinoblastoma protein (pRb), TNF receptor-associated factor 2 (TRAF-2), and glycosaminoglycans and also has binding sites for domains like class II PDZ domain, ▶SH2 domain and class IV WW domain. STRAP also shows the presence of multiple potential membrane targeting N-myristoylation sites, at least one of which is outside the WD repeat domains in the C-terminal region. Structural analysis of the WD repeat proteins in general shows that they act as a very rigid platform or scaffold, irrespective of the proteins with which they interact. Mechanisms STRAP binds with both TβRI and TβRII in a ligand independent manner. It synergizes specifically with Smad7, but not with another inhibitor Smad6, in the inhibition of TGF-β signaling. STRAP stabilizes the association between Smad7 and activated receptor complex, thus assisting Smad7 in preventing phosphorylation and activation of Smad2 and Smad3 by the receptor complex. Though Smad6 is also shown to interact with STRAP, this association does not seem to interfere with bone morphogenic protein (BMP) signaling in which Smad6 acts as an inhibitor. STRAP inhibits TGF-β-induced nuclear translocation of Smad2/3 and Smad4 and as a result, activation of TGF-β responsive reporter genes including plasminogen activator inhibitor 1 (PAI-1) and ▶p21Cip1 is abrogated. Downregulation of p21Cip1 by STRAP leads to hyperphosphorylation of ▶retinoblastoma protein (pRb). In vitro kinase assay demonstrated that overexpression of STRAP can induce extracellular signal-regulated kinase (MEK/ERK) activity in a TGF-β-independent manner. Activation of MEK/ERK pathway by endogenous STRAP was further confirmed by knocking it down using ▶small interfering RNA (siRNA).

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Although STRAP is not a kinase, it may facilitate the activation of MAPK pathway by functioning as a chaperone for upstream kinases. Therefore, STRAP may inhibit activation and nuclear translocation of Smad2 and Smad3 by interacting with receptors and Smad7 and/or by activating MAPK/ERK pathway (Figs. 1 and 2). 3-phosphoinositide-dependent protein kinase-1 (PDK1) has been shown to phosphorylate and activate many members of the protein kinase A, G, and C subfamily that include protein kinase B (PKB), p70 S6 kinase, protein kinase A and serum/glucocorticoid regulated kinase (SGK). STRAP interacts with the catalytic domain of PDK1 and this interaction is important for the modulation of PDK1 activity. The interaction of STRAP and PDK1 is inhibited by TGF-β and induced by insulin. This induction in binding by insulin is abrogated by wortmannin, a PI3K inhibitor. The mechanism behind PDK1 activation by STRAP is thought to be due to displacement of the 14-3-3 protein from PDK1 complex, which negatively regulates it (Fig. 1). The binding of PDK1 with STRAP also potentiates negative regulation of TGF-β mediated transcription by STRAP. This repression occurs through increased association of Smad7 with both STRAP and TβRI. Cell survival is induced by this interaction between STRAP and PDK1 probably through phosphorylation of Bad and attenuation of ▶tumor necrosis factor-alpha (TNF-α) induced ▶apoptosis. STRAP is localized in both cytoplasm and nucleus. It colocalizes and associates with the oncogenic EWS protein in the nucleus through its NH2 and COOH termini. STRAP inhibits the interaction between EWS and p300, a protein that is a transcriptional coactivator of EWS. This results in downregulation of EWS target genes like ApoCIII and c-fos. Although TGF-β has no effect on the interaction between STRAP and EWS, TGF-β-dependent transcription is inhibited by EWS. Unr is an RNA binding protein that plays an important role in the initiation of HRV-IRES dependent translation of the animal picornavirus RNA, like the rhinoviral RNA. STRAP interacts with unr and is thought to be important during the translation stimulation activity. The macromolecular survival motor neuron (SMN) complex that helps in the assembly of spliceosomal Uridine-rich small ribonucleoprotein (U snRNP), contains the SMN protein and six additional proteins, named Gemin2-7, according to their localization (Fig. 1). STRAP seems to be involved in this assembly through its interaction with Gemin6 and Gemin7 as well as SmB, SmD2 and SmD3 components of the SMN complex. Although STRAP is localized in both cytoplasm and nucleus, it is present predominantly in the cytoplasm and may help the nuclear-cytoplasmic distribution of the SMN complex. The presence of STRAP in the SMN complexes was shown to be

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Serine-Threonine Kinase Receptor-Associated Protein

Serine-Threonine Kinase Receptor-Associated Protein. Figure 1 STRAP in diverse biological functions through a role in protein complex assemblies in different signaling pathways.

Serine-Threonine Kinase Receptor-Associated Protein. Figure 2 STRAP may be involved in the progression of human cancers by activating multiple oncogenic pathways.

essential for U snRNP assembly. In contrast, STRAP was also shown not to be essential for this assembly by other groups. STRAP along with EWS was shown to be present in the kinesin driven mRNA transport granules in the dendrites of murine neurons. In eukaryotes, the nuclear export of mRNA is mediated by nuclear export factor 1 (NXF1)

receptors. As shown in mouse neuroblastoma N2a cells, NXF proteins bind to brain-specific microtubule associated proteins (MAP) such as MAP1B and also STRAP. Additionally, MAP1B also binds with STRAP. This assembly helps in the nuclear export of mRNA. In an independent setting, NXF-7 binds with MAP1B and STRAP only in the cytoplasm and colocalizes with

Seropositive

Staufen1 containing mRNA transport granules in the neurites of these cells (Fig. 1). As in other cases, STRAP seems to play a role in the multiprotein complex assembly required for both nuclear export of mRNA and the cytoplasmic transport of mRNA containing granules along microtubules. STRAP is a substrate for SUMO4 (a novel member of the SUMO gene family) sumoylation. Although the significance of this is not yet known, SUMO4 sumoylation is predicted to have a role in the regulation of intracellular stress. It will be interesting to determine whether sumoylation of STRAP has any effect on its biological functions. Clinical Aspects Although STRAP seems to be involved in mutually independent biological functions, there is increasing clinical and experimental evidence suggesting that STRAP acts as an oncogene. The level of STRAP is found to be altered in different ▶cancers. The protein level is elevated in 60% of ▶colorectal, 78% of ▶lung and 46% of ▶breast carcinomas. Several lines of evidence suggest that carcinoma cells frequently lose the tumor suppressor function of TGF-β. Upregulation of TGF-β signaling inhibitors like STRAP and Smad7 and their synergistic function present a novel intracellular mechanism by which a portion of human tumors become refractory to antitumor effects of TGF-β. STRAP also exerts several other biological functions in a TGF-β independent manner that contribute to cell proliferation and inhibition of apoptosis (Fig. 2). Ectopic expression of STRAP in different cell lines promotes cellular proliferation, induces anchorageindependent growth and increases tumorigenicity during in vitro and in vivo experiments. Downregulation of p21Cip1, which results in hyperphosphorylation of pRb as well as activation of MAPK/ERK pathway, may contribute to the tumorigenic effects of STRAP during tumor formation and progression (Fig. 2). As noted earlier, STRAP also has an anti-apoptotic role probably through Bad phosphorylation and inhibition of TNF-α induced apoptosis. STRAP interacts with Ewing Sarcoma protein (EWS), an oncoprotein known to be involved in 80% of Ewing tumors after chromosomal translocations. Normal EWS protein is also upregulated in human cancers, which correlates with the upregulation of STRAP in 71% of colorectal cancers and 54% of lung cancers, suggesting a cooperative role of these two proteins in human cancers. In an attempt to determine whether STRAP is of prognostic value or predictive of ▶chemotherapy benefit, STRAP gene was found to be amplified in 23% of colorectal tumors and amplification of STRAP in patients without adjuvant chemotherapy was found to exhibit better prognosis. These patients had a worse survival when treated with ▶adjuvant therapy when compared with patients without chemotherapy. In

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contrast, patients carrying tumors with diploidy or deletion of STRAP benefited from the treatment. These results suggest that STRAP is an unfavorable prognostic marker for 5-FU-based adjuvant chemotherapy. Taken together, STRAP appears to facilitate multiple steps in the process of tumorigenesis and possibly during ▶metastasis, and it could be a potentially important drug target for therapeutic intervention in human cancers.

References 1. Buess M, Terracciano L, Reuter J et al. (2004) STRAP is a strong predictive marker of adjuvant chemotherapy benefit in colorectal cancer. Neoplasia 6(6):813–820 2. Datta P, Chytil A, Gorska A et al. (1998) Identification of STRAP, a novel WD domain protein in transforming growth factor-beta signaling. J Biol Chem 273(52):34671–34674 3. Datta P, Moses H (2000) STRAP and Smad7 synergize in the inhibition of transforming growth factor beta signaling. Mol Cell Biol 20(9):3157–3167 4. Halder S, Anumanthan G, Maddula R et al. (2006) Oncogenic function of a novel WD-domain protein, STRAP, in human carcinogenesis. Cancer Res 66(12):6156–6166 5. Seong H, Jung H, Choi H et al. (2005) Regulation of transforming growth factor-beta signaling and PDK1 kinase activity by physical interaction between PDK1 and serine-threonine kinase receptor-associated protein. J Biol Chem 280(52):42897–42908

Serological Analysis of cDNA Expression Libraries Definition SEREX; A method to identify cancer-specific antigens based on screening of cDNA expression libraries with serum from cancer patients. ▶Cancer-Germline (CG) Antigens

Seropositive Definition Indicative of the presence of an antibody to a particular antigen in a patient’s blood.

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Serotonin

Serotonin

Sertoli-Leydig Cell Tumor

Definition

Definition

5-hydroxytryptamine, 5-HT; Is a neurotransmitter synthesized in specific nerve cells (serotonergic) in the central nervous system (CNS) and is believed to play an important role in the regulation of mood, sleep, emesis (vomiting), sexuality and appetite.

Synonym Arrhenoblastoma; Is a rare cancer of the ovaries. The cancer cells produce and release high level of the a male sex hormone testosterone, which may cause the women to develop male physical characteristics, including facial hair and a deep voice. While the tumor can occur at any age, it develops most often in young adults.

▶Fluoxetine

Serotypes Definition A taxonomic subgroup of a microorganism or virus determined by the antigens expressed.

▶Ovarian Tumors During Childhood and Adolescence

Serum Definition The clear liquid that separates from the blood when it is allowed to clot. This fluid retains any ▶antibodies that were present in the whole blood.

▶Oncolytic Adenovirus

Serpin Definition

Serine protease inhibitor – a group of structurally related proteins, many of which inhibit proteases. ▶Maspin

Serum-Ascites Albumin Concentration Gradient Definition Is a parameter of pressure reflecting presence or absence of portal hypertension. It is calculated by subtracting the albumin concentration of the ascitic fluid from the albumin concentration of a serum specimen obtained on the same day. If the gradient is less than 1.1 g/dL, portal hypertension can be ruled out. ▶Acites

Sertoli Cell Serum Biomarkers Definition Tall columnar cells found in the mammalian testis closely associated with developing spermatocytes and spermatids. Probably provide appropriate microenvironment for sperm differentiation. Its main function is to nurture the developing sperm cells through the stages of spermatogenesis. Because of this, it has also been called the “mother cell.” It provides both secretory and structural support.

A NDREAS F. H OTTINGER , A DI´ LIA H ORMIGO Department of Neurology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA

Synonyms BR 27-29; CYFRA 21-1; Hydroxybutyrate dehydrogenase; Gelatinase B; Breast regressing protein 39 Kd;

Serum Biomarkers

brp-39; Chitinase-3-like-1; CHI3L1; Chondrex; Human cartilage glycoprotein-39; HC gp39; 8-kDa heparinbinding glycoprotein; Gp38k; 40 kDa mammary gland protein; MGP-40

Definition

Cancer ▶biomarkers are usually proteins detected in the blood, urine or other body fluids that are either produced by the tumor itself or in response to the presence of cancer. Ideally, biomarkers should allow at least one of the following: (i) early cancer detection by screening a healthy or high-risk population, (ii) help confirm the diagnosis of cancer or of a specific type of cancer, (iii) predict prognosis, (iv) monitor treatment response or (v) detect early recurrence.

Characteristics Most biomarkers are not specific for tumors or organs and their levels may rise in other diseases. The diagnostic value of a tumor marker will depend on the prevalence of a disease in a population group and on its specificity (percentage of normal individuals without disease for whom a negative result is obtained) and sensitivity (percentage of tests which are correctly positive in the presence of a tumor). A cancer biomarker should be measured at a low cost, by a widely available assay with reproducible results in a specimen that is easy to access. We are interested in developing biomarkers for ▶brain tumors. Response to treatment of a ▶brain tumor is evaluated by noninvasive imaging. This may be unreliable when assessing novel cytocidal drugs, distinguishing between disease ▶progression or radionecrosis and predicting malignant transformation from low to high-grade glioma. ▶YKL-40, MMP-9 and ▶lactate dehydrogenase (LDH) are potential ▶biomarker candidates. Monitoring circulating endothelial and progenitor cells as well as markers of this process including basic fibroblast growth factor and stromal cell-derived factor 1α may help determine treatment effect. As recent methods such as proteomics are utilized, new candidate proteins will be screened as potential biomarkers for a variety of cancers. Alpha-Fetoprotein (AFP) ▶Alpha-fetoprotein (AFP) is a fetal serum protein that shares sequence homology with albumin. It is normally synthesized during gestation by liver, yolk sac, and gastrointestinal tract. Following birth, AFP rapidly clears from the circulation. It may be elevated in patients with cirrhosis, viral hepatitis, drug or alcohol abuse as well as pregnancy, and may be used for screening of fetal spinal cord defects and placental disease. Serum levels of AFP are elevated in up to 80% of patients with ▶hepatocellular carcinoma (HCC). Changes in serum AFP levels reflect the course of

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disease. In patients with cirrhosis, elevation of serum AFP may be increased for up to 18 months before symptoms of HCC manifest and may be used to assist in the diagnosis. An elevation of AFP greater than 400 ng/ mL is predictive for HCC with a specificity >95%. In the setting of cirrhosis and a growing liver mass, many centers use a level greater than 1,000 ng/mL as presumptive evidence of HCC and do not require a biopsy. In men with nonseminomatous germ cell tumors (NSGCT), AFP is produced by yolk sac (endodermal sinus) tumors and, less often, embryonal carcinomas. In addition, up to 80% of mediastinal NSGCTs are associated with elevated serum AFP, regardless of histologic subtype. Whereas only 10–20% of stage I tumors express elevated levels of AFP, 40–60% of disseminated NSGCT express abnormal levels of AFP. Although these markers may be helpful for the initial diagnosis of a testicular cancer and for prognostication, their main utility is for follow-up of disease status (Table 1). Beta Subunit of Human Chorionic Gonadotropin (b-hCG) ▶Beta subunit of human chorionic gonadotropin (β-hCG) is normally produced by the placenta and human fetal tissue. Elevated serum β-hCG is most commonly associated with pregnancy, gestational trophoblastic disease and germ cell tumors. It can also be found in hypogonadal states and with marijuana use. β-hCG and AFP are elevated in up to 85% of patients with germ cell tumors, but only in about 20% of those with stage I disease. In patients with extragonadal or metastatic disease, highly elevated serum levels of β-hCG or AFP can establish a diagnosis of nonseminomatous germ cell tumor instead of biopsy. Serial measurements of β-hCG every 2–3 months for 1 year following treatment is important as elevation is often the first sign of recurrence, indicating the need to restart treatment. β-hCG is also used to diagnose and monitor response to treatment of gestational trophoblastic disease (Table 1). Cancer Antigen 15-3 (CA 15-3) Elevated ▶cancer antigen 15-3 (CA 15-3) levels may be found in patients with ▶breast cancers, and with much less specificity and sensitivity in patients with ▶ovarian, ▶lung, or ▶prostate cancers. Increased levels may be associated with pregnancy and lactation, benign breast or ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis. Because of a lack of sensitivity for early disease detection and lack of specificity, It has not been approved for screening of early breast cancer. However, high preoperative serum levels of CA 15-3 are associated with adverse patient outcome. CA 15-3, like

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Serum Biomarkers

Serum Biomarkers. Table 1 Tumor marker

Tumor markers

Primary tumor and other cancers

Other conditions with elevated levels

Use of tumor marker Diagnosis

AFP

Hepatocellular carcinoma, Cirrhosis, viral hepatitis, nonseminomatous germ cell pregnancy tumor, gastric, biliary and pancreatic cancer

β-hCG

Nonseminomatous germ cell Hypogonadal states, tumors, gestational marijuana trophoblastic disease, gastrointestinal cancer (rare)

CA 15-3

Breast, ovarian, lung, or prostate cancer

CA 19-9

Pancreatic and biliary tract, colon, eosophagal and pancreatic cancer Breast, stomach, ovary, lung, Benign breast or ovarian or prostate cancer disease, endometriosis, pelvic inflammatory disease, and hepatitis

Yes (selected pancreatic masses)

CA 125

Ovarian, endometrium, fallopian tubes, pancreas, breast, colon and lung cancer

Yes

No (except in selected situations, i.e. follow-up by conventional clinical procedures not possible) Yes

CEA

Colorectal, breast, lung, stomach, pancreas, bladder, medullary thyroid, head and neck and liver cancer, lymphoma melanoma Prostate cancer

No

Yes

Yes

Yes

No

No

CA 27-29

PSA

YKL-40

Glioblastoma multiforme, ovarian and endometrial cancer

Benign breast disease, benign ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis Pancreatitis, biliary disease, cirrhosis

Menstruation, pregnancy, endometriosis, pelvic inflammatory disease, liver disease, pancreatitis, peritonitis and inflammation of the pleura Tobacco, peptic ulcer, inflammatory bowel disease, pancreatitis, hypothyroidism, cirrhosis, biliary obstruction Prostatitis, benign prostate hypertrophy, prostate trauma, after ejaculation Inflammatory disease

▶carcinoembryonic antigen (CEA) and ▶cancer associated antigen 27-29 (CA 27-29), are most useful for monitoring treatment response in women with breast cancer, especially in advanced disease. Serial

Yes (poorly differentiated cancer of unknown origin, patients with cirrhosis and a liver mass) Yes (poorly differentiated cancer of unknown origin, gestational trophoblastic disease) No

Monitoring of treatment response

No

Yes

Yes (nonseminomatous germ cell tumor and gestational trophoblastic disease) No (except in selected situations, i.e. follow-up by conventional clinical procedures not possible) No

determinations of tumor markers after primary treatment can detect recurrent/metastatic disease with lead times of 2–9 months over clinical symptoms. However the clinical value of this lead-time remains to be determined.

Serum Biomarkers

The ASCO guidelines do not recommend serial monitoring of CEA, CA 27-29 or CA 15-3 after primary therapy, except in selected situations, where patients cannot be followed by conventional diagnostic techniques. Cancer Associated Antigen 19-9 (CA 19-9) ▶Cancer associated antigen 19-9 (CA 19-9), an intercellular adhesion molecule, is an epitope of sialyated Lewis A blood group antigen. Elevated serum levels of CA 19-9 are found typically in patients with ▶pancreatic and biliary tract cancers, and less often in ▶gastric, ovarian, ▶colorectal, lung, breast and ▶uterine cancer. Elevated levels of CA 19-9 are also found in acute cholangitis, cirrhosis or other cholestatic diseases. Five percent of the population is genotypically Lewis-null blood type and will never produce CA 19-9 antigen, even in the presence of tumoral disease. The sensitivity and specificity for pancreatic cancer has been estimated to be 80–90%. These values correlate with tumor size so that CA 19-9 has limited value in identifying patients with small surgically resectable cancers (Table 1). CA 27-29 Cancer antigen 27-29 (synonym: BR 27-29) is a normal epithelial cell mucin-1 (MUC1) apical surface glycoprotein. Elevated serum levels are highly associated with breast cancer. However they can also be found in cancers of ▶colon, ▶stomach, ▶kidney, ▶lung, ▶ovary, ▶pancreas, ▶uterus and ▶liver and in a number of noncancerous conditions, including first trimester pregnancy, endometriosis, ovarian cyst, benign kidney, liver and breast disease. Therefore, it has no role in breast cancer screening. Serum CA 27-29 levels are elevated in approximately one third of women with early-stage breast cancer (stage I or II) and in two thirds of women with stages III or IV. There is no agreement regarding the ability of CA 27-29 to detect asymptomatic recurrence after curative treatment. Serial monitoring is currently not recommended by the ASCO guidelines (Table 1). CA-125 ▶CA-125 is a glycoprotein that is expressed by celomic epithelium of ovaries, fallopian tubes, endometrium and uterine cervix. Up to 90% of ovarian cancers are celomic epithelial carcinomas and overexpress CA 125. This glycoprotein can be detected in most endometroid, serous and clear cell ovarian carcinomas. Mucinous tumors however express this antigen less frequently. Serum levels of CA 125 may also be elevated in cancers of endometrium, fallopian tubes, pancreas, breast, colon and lung. Non-cancerous conditions with elevated CA 125 levels include menstruation, pregnancy, endometriosis, pelvic inflammatory disease, liver disease,

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pancreatitis, peritonitis and inflammation of the pleura. CA-125 is an important tumor marker for the diagnosis of epithelial ovarian cancer although it is not perfectly sensitive or specific for ovarian cancer. CA 125 can be used clinically to determine response to treatment and predict relapse and survival (Table 1).

Carcinoembryonic Antigen (CEA) CEA is a normal mucosal cell oncofetal glycoprotein involved in cell adhesion. It is overexpressed in gastric, ▶pulmonary, breast, pancreatic and predominantly ▶colorectal adenocarcinomas. It may also be elevated in the serum of heavy smokers and patients with ulcerative colitis, pancreatitis and cirrhosis. Its role as a screening tool remains uncertain because of poor sensitivity and specificity. In patients with established disease, the absolute serum level of CEA correlates with disease burden and has prognostic value. After complete resection, elevated preoperative levels of CEA return to baseline and persistently elevated levels should warrant a search for residual tumor. CEA serum levels should be checked every 3 months for at least 3 years in patients with stage II or III colon cancer if the patient is a candidate for re-resection because elevated levels give a 1.5–6 months lead-time for detection of recurrence detection in comparison to other methods such as imaging. Early detection of asymptomatic recurrence increases the likelihood of a subsequent complete resection (Table 1).

Cytokeratin 19 Fragments CYFRA 21-1 is a soluble fragment of cytokeratin 19 expressed in normal squamous cells. Elevated serum concentrations are found in tumors of squamous origin, including lung and are associated with short patient survival. The sensitivity of ▶cytokeratin 19 fragments (CYFRA 21-1) depends on the histological type, being lowest for small cell lung cancer (about 16–40%). It is not used in early detection or monitoring of disease and has not been incorporated in the ASCO guidelines for patients with lung cancer.

Lactate Dehydrogenase (LDH) Lactate dehydrogenase (LDH) is an ubiquitous enzyme that catalyses the conversion of pyruvate and lactate with concomitant interconversion of NADH and NAD+. Increased serum levels of LDH have been shown in a number of cancers, including ▶melanoma, ▶lymphoma, ▶germ cell tumors and ▶small cell lung cancer. Elevated levels of LDH can also be caused by a number of noncancerous conditions, including heart failure, hypothyroidism, anemia, as well as lung and liver diseases.

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Matrix Metalloproteinase-9 (MMP-9) ▶Matrix metalloproteinase-9 (MMP-9) is a member of the zinc-dependent homologous proteinase family that degrades extracellular matrix proteins, such as cell adhesion receptors, chemokines, growth factors and their receptors and protease inhibitors. They are implicated in proliferation of endothelial and hematopoietic stem cells by inducing the release of kit ligand. MMP-9 expression is elevated in most tumor tissues, including ovarian, thyroid, hepatocellular and gastrointestinal carcinoma. Expression of MMP-9 has been detected in both glioma and its endothelial cells. Increasing levels of MMP-9 as measured by in situ hybridization and immunohistochemistry correlate with higher grade gliomas. In GBM patients, serum levels of MMP-9 are significantly higher in patients with radiologic evidence of disease compared to patients whose disease is inactive. It is a potential future biomarker. Placental Alkaline Phosphatase (PLAP) Placental isoenzyme of PLAP is increased in 30% of ovarian cancer (especially serous cystadenocarcinoma), as well as cancers of endometrium, lung, breast and 40% of seminomas (75% in metastatic seminoma). Smokers may also have elevated PLAP levels.

cancer cells, stimulating angiogenesis, and inducing proliferation of fibroblasts surrounding the tumor and remodeling of the extracellular matrix. Elevated serum values of YKL-40 have been reported in a variety of cancers, including breast, colon/▶rectum, ovary, lung, kidney, glioblastoma, and melanoma. YKL-40 levels may also be increased in other diseases with an inflammatory component. In a microarray analysis of brain tumors, YKL-40 was found to be highly overexpressed in a subset of patients with glioblastoma multiforme (GBM) in comparison to low-grade gliomas and detected in serum by ELISA. In a prospective study of 143 patients with high-grade gliomas, we found that serum levels of YKL-40 were increased in patients with active disease compared to those with absence of radiographic disease. Elevated levels of YKL-40 also correlated with shorter survival in GBM patients. In patients with endometrial or ovarian cancer, elevated preoperative levels of YKL-40 may identify a subset of high-risk patients with worse clinical outcome. Studies in a larger sample population are underway to further evaluate its potential role as a biomarker YKL-40.

References Prostate-Specific Antigen (PSA) ▶Prostate-specific antigen (PSA) is a glycoprotein that is expressed by normal prostate tissue and is overexpressed in prostate cancer. It is a sensitive and specific marker for this cancer. Levels of PSA depend upon the age and race of the patient. The predictive value for cancer is 20–30% if serum levels are greater than 4 ng/mL and 50% for values exceeding 10 ng/mL. However 20–30% of patients with prostate cancer have levels within the normal range. The American Urological Association recommends that serial PSA measurements be obtained routinely to detect early recurrence in men who have undergone primary therapy for localized disease. PSA levels should decrease and remain undetectable after radical prostatectomy or at low levels following radiation therapy and cryotherapy. The nadir serum PSA and percent PSA decline at 3 and 6 months predict progression-free survival in men with metastatic prostate cancer treated with androgen deprivation. The degree of PSA decline following second-line treatment of metastatic disease correlates with disease survival (Table 1). YKL-40 YKL-40 is a member of the mammalian chitinase-like proteins that is highly conserved among different species. It has no enzymatic activity due to amino acid substitutions at the catalytic site. In vitro studies suggest that YKL-40 plays a role in proliferation and differentiation of malignant cells, by decreasing apoptosis of

1. American Urological Association (2000) Prostate-specific antigen (PSA) best practice policy. Oncology (Williston Park) 14:267–272, 2. Bast RCJ, Ravdin P, Hayes DF et al. (2001) 2000 update of recommendations for the use of tumor markers in breast and colorectal cancer: clinical practice guidelines of the American Society of Clinical Oncology. J Clin Oncol 19:1865–1878 3. Hormigo A, Gu B, Karimi S et al. (2006) YKL-40 and matrix metalloproteinase-9 as potential serum biomarkers for patients with high-grade gliomas. Clin Cancer Res 12:5698–5704 4. Khatcheressian JL, Wolff AC, Smith TJ et al. (2006) American Society of Clinical Oncology 2006 update of the breast cancer follow-up and management guidelines in the adjuvant setting. J Clin Oncol 24:5091–5097 5. Locker GY, Hamilton S, Harris J et al. (2006) ASCO 2006 update of recommendations for the use of tumor markers in gastrointestinal cancer. J Clin Oncol 24:5313–5327

Severe Combined Immunodeficiency Disease Definition

▶SCID; ▶Severe Combined Immunodeficient Mice represent a model for the human disease.

Sezary Syndrome

Severe Combined Immunodeficient Mice

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organism. Like many other kinds of hormones, sex hormones may also be artificially synthesized. ▶Androgens ▶Estrogens

Definition Scid mice; Spontaneous mutant mice that lack B- and T-cells. As a consequence, scid-mice are severely immunocompromised. Scid-mice do not reject implanted human cells as would normal mice. Hence, these mice allow investigators to study the growth and progression of human tumors in an in vivo model. ▶Cystatins

Severe Hypoxia ▶Anoxia

Sex Hormone Dependent Cancers Definition Prostate cancer is first dependent on androgens (e.g., testosterone) for growth and may become later hormone-independent. Breast cancer is mainly sex hormone-dependent (estrogen and progesterone), but some breast tumors are hormone-independent and are more difficult to treat. ▶Gonadotropin-Releasing Hormone

Sezary Syndrome

Sex Cord Stromal Tumors Definition SCST; Primary ovarian neoplasms derived from the stromal component of the ovary. During childhood and adolescence, SCSTs most frequently present as juvenile ▶granulosa cell tumors or Sertoli-Leydig cell tumors (synonym gynandroblastoma). Less frequent types include sclerosing stromal cell tumor, sex cord stromal tumor with annular tubules, steroid tumors and Brenner tumors. ▶Brenner tumor ▶Sex cord stromal tumors ▶Gynandroblastoma ▶Sertoli-Leydig cell tumor ▶Ovarian Tumors During Childhood and Adolescence

Sex Hormone Definition A chemical substance produced by a sex gland or other organ that has an effect on the sexual features of an

E LIZABETH K NOBLER 1 , R OBERT K NOBLER 2 1

Department of Dermatology, Columbia College of Physicians and Surgeons, New York, NY, USA 2 Department of Dermatology, Medical University of Vienna, Vienna, Austria

Definition Sezary syndrome (SS), named after the French dermatologist Albert Sezary (1880–1956), is a variant of cutaneous T cell lymphoma (CTCL), a malignancy of mature T-helper cells involving the skin and blood. It is defined by the presence of an ▶exfoliative erythroderma, lymphadenopathy, and evidence of neoplastic cells in the skin and blood. “Sezary” cells refer to enlarged mature CD4+ lymphocytes with hyperconvoluted nuclei. Historically, the presence of Sezary cells in the peripheral blood was a defining criteria for SS. However, an increased number of these cells can be found in several benign dermatologic conditions and is no longer the agreed upon standard. The presence of a clonally expanded population of CD4+ cells resulting in an increased CD4/CD8 >10 in the blood is considered a more accurate measure. Immunophenotypic abnormalities which support a diagnosis of SS include decreased/absent expression of T-cell antigens CD2, CD3, CD5, and CD7. The

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characteristic histologic features of involved skin seen in other forms of CTCL are often not present in SS and thus may not be a useful tool in its diagnosis. The etiology of SS is unknown.

CRD; in most cases inhibit Wnt signals by binding to Wnt proteins; often downregulated in cancer. ▶Wnt Signaling

Characteristics SS is a rare disease making up less than 5% of all CTCLs. It occurs primarily in adults over the age of 60 with predominance in males. Clinical features of SS include intractable, debilitating pruritus with an exfoliative erythroderma, edema, ▶lichenification, thickening and fissuring of the palms and soles, nail dystrophy, hair loss, and ectropion. Malignant cell infiltrates of the skin can often lead to disfiguring features in the face (known as “leonine faces”) and body.

SH2/SH3 Domains J OSEPH H. M C C ARTY M. D. Anderson Cancer Center, Houston, TX, USA

Synonyms Src homology 2; SH2/src homology 3; SH3 domains

Staging and Treatment Staging of SS as CTCL stage III or IV depends on the degree of lymph node involvement and evidence of solid organ spread. With SS representing an advanced stage of the disease, the prognosis is usually poor with a median survival of 2–4 years. Immune compromise in these patients leads to increased bacterial infection and often to the demise of the patient. Since SS involves both the skin and blood, systemic treatment is necessary to control the disease. The most common therapeutic tools used singly or in combination include: ▶extracorporeal photochemotherapy (photopheresis), interferon alpha, bexarotene, denileukin diftitox, radiation with total skin electron beam therapy, leukeran, and gemcitabine.

References 1. Willemze R, Jaffe ES, Burg G et al. (2005) WHOEORTC classification for cutaneous lymphomas. Blood 105: 3768–3785 2. Trautinger F, Knobler R, Willemze R et al. (2006) EORTC consensus recommendations for the treatment of mycosis fungoides/Sezary syndrome. Eur J Cancer 42:1014–1030 3. Willemze R (2003) Cutaneous T-cell lymphoma. In: Bologna J, Jorizzo J, Rapini R (eds) Dermatology. Elsevier, Amsterdam, pp 1921–1961

sFRP Definition Secreted frizzled related protein; family of proteins with a cysteine-rich domain (CRD) related to the Fz receptor

Definition Proteins containing SH2/SH3 domains play critical roles in regulating the formation of intracellular signal transduction complexes. SH2 and SH3 domains recognize amino acid motifs containing phosphotyrosine and polyproline, respectively. Signaling pathways activated by SH2/SH3 domains subsequently lead to cellular responses including differentiation, proliferation and migration.

Characteristics SH2/SH3 domains were originally identified as conserved sequences found in the Src tyrosine kinase and a variety of other proteins. These domains are now known to reside in hundreds of functionally diverse signaling molecules, ranging from tyrosine kinases and phosphatases to phospholipases and transcription factors. . SH2 domains are composed of 100 amino acids organized into a modular structure that recognize phosphotyrosine-containingsequences onprotein tyrosine kinases and their substrates. The specificity of interaction is generally determined by the 3–4 amino acids C-terminal to the phosphorylated tyrosine position on the target protein. SH2 domain-mediated signaling events lead to cellular responses ranging from DNA synthesis to transcriptional activation. . SH3 domains are about 50 amino acids in size and bind to target proteins containing the proline-rich consensus sequence PXXP (where P is proline and X is any amino acid). Unlike SH2 domains, SH3 domains generally remain constitutively associated with their cognate ligands, making their function less dependent on tyrosine phosphorylation. Protein interactions mediated by SH3 domains have been implicated in cytoskeletal alterations necessary for changes in cell morphology and motility.

SH2/SH3 Domains

In response to extracellular cues, SH2/SH3 domains act both intramolecularly and intermolecularly to regulate signal transduction. Their functions are well illustrated by two classical signaling cascades exemplified by the Src protein tyrosine kinase pathway and the Ras GTPase pathway. Src is a membrane bound intracellular tyrosine kinase that contains one SH2 and one SH3 domain (the kinase domain was originally termed the SH1 domain). The post-translational phosphorylation of Src on tyrosine 527

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negatively regulates kinase activity. This inhibition is the result of complex intramolecular interactions between phosphotyrosine 527 and the SH2 domain, as well the SH3 domain and a proline-rich central region (see Fig. 1). Concomitant dephosphorylation of tyrosine 527 and phosphorylation of tyrosine 416 relieves this steric block. This allows for the association of the SH2 and SH3 domains with target proteins and enhancement of Src catalytic activity. Thus, Src SH2/SH3 domains both positively and negatively regulate protein tyrosine kinase

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SH2/SH3 Domains. Figure 1 Pathways exemplifying SH2/SH3 domain functions. (a) Activation of the Src tyrosine kinase domain serves as an example of both intermolecular and intramolecular functions for SH2/SH3 domains. The Src SH2/SH3 domains serve to inhibit the kinase activity. Dephosphorylation of phosphotyrosine 527 and phosphorylation of tyrosine 416 results in a Src conformational change. The tyrosine kinase is activated and the protein associates with downstream substrates via its SH2 and SH3 domains. (b) The activation of the Ras GTPase by various receptor tyrosine kinases is a classic example of SH2/SH3 domains providing an intermolecular link between critical signal transduction components. Receptor autophosphorylation leads to re-localization of constitutively associated Grb2-Sos, leading to GTP exchange and Ras activation.

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activity. Various protein tyrosine kinases utilize a similar mechanism to regulate their function. The Ras GTPase is a membrane associated growth regulator, and mutated forms are found in many human tumors. When in its GTP-bound state, Ras is considered “on” and activates multiple downstream signaling pathways. In many cases growth factor stimulation of the Ras pathway occurs via the Grb2 SH2/SH3 protein (see Fig. 1). Grb2 is an SH2/SH3 “adaptor” protein, consisting of two SH3 domains flanking a central SH2 domain. The Grb2 SH3 domains constitutively associate with various proteins, including the son-ofsevenless (Sos) GTP exchange factor. Following growth factor stimulation, phosphotyrosine motifs on the activated receptors recruit the Grb2 SH2 domain. This event in part serves to re-localize the Grb2-Sos complex from the cytoplasm to the membrane, placing Sos in proximity to membrane-bound Ras and allowing the exchange of Ras-GDP for -GTP. Based on similar observations made for other SH2/SH3 adaptor proteins, intracellular re-localization may be a common mechanism used to activate a variety of enzymatic pathways. These examples illustrate important aspects of SH2/ SH3 domain function in response to a specific stimulus. It is clear, however, that most signal transduction pathways are interconnected, and that a single extracellular cue can elicit a response involving hundreds of effector proteins. Identifying how various extracellular cues individually and combinatorally affect signaling pathways will be an important challenge for fully understanding SH2/SH3 domain functions. Clinical Relevance Many tumor cells possess amplifications and/or mutations in genes encoding components of the tyrosine kinase machinery. Therefore, it follows that proteins regulating cell proliferation have become central targets for drug discovery. The crystallographic structures of many SH2 and SH3 domains in complex with their various ligands has allowed for the rational design of highly specific peptidomimetic molecules. The challenge is to utilize drugs that affect only the pathological action of the specific targeted molecule, while enabling normal signal events to proceed unperturbed. For example, one can envision using SH2 and/or SH3 domain antagonists to inhibit the proliferative capacity of cells transformed due to hyperactivated or aberrantly expressed protein tyrosine kinases. Importantly, ongoing genomic analyses will undoubtedly identify new SH2/SH3 domain-containing proteins. Characterizing the functions of these newly identified effectors and linking them to the pathogenesis of specific cancers and other disease states will be a worthwhile goal. The use of novel proteomic techniques in combination with classical cell biology will greatly aid this process.

References 1. Hunter T (2000) Signaling- 2000 and beyond. Cell 100:113–127 2. Pawson T (1995) Protein modules and signaling networks. Nature 373:573–580 3. Sudol M (1999) From src homology domains to other signaling modules: the proposal of the protein recognition code. Oncogene 17:1469–1474 4. Hanahan D, Weinberg RA (2000) The hallmarks of cancer. Cell 100:57–70

SH2/src Homology 3 ▶SH2/SH3 Domains

SH2 Domain Definition

Src homology (SH) 2 domain; Is comprised of 100 amino acid residues capable of binding specifically to a phosphorylated tyrosine residue in a signaling protein. Its binding specificity is determined through interactions between an SH2 sequence and a target sequence of a phosphorylated tyrosine and additional amino acid residues mainly from −1 to + 3 positions surrounding the phosphotyrosine. ▶SH2/SH3 Domains

SH3 Domain Definition Src-homology domain 3 is a protein domain of about 50 amino acid residues that binds to specific proline-rich sequences; Modular protein interaction domain commonly found in signal transduction proteins. Binds amino acid recognition sequences that include prolineX-X-proline in target proteins. Seen often in adapter proteins that coordinate the function of macromolecular complexes with the actin cytoskeleton. ▶SH2/SH3 domains

Shark Cartilage

SHANK Definition Refers to large adaptor proteins that can self-associate and bind a variety of different proteins. Best characterized in neurons where they serve to organize receptor proteins at the synapse, shank proteins are also found in epithelia cells where their function is currently unclear. ▶Cortactin

Shark Cartilage A DITYA B ARDIA 1 , C HARLES L. LOPRINZI 2 1

Department of Internal Medicine, Mayo Clinic, Rochester, MN, USA 2 Department of Oncology, Mayo Clinic, Rochester, MN, USA

Definition A dietary supplement derived from cartilage obtained from sharks, commonly hammerhead (Sphyrna lewini) and dogfish (Squalus acanthias) sharks.

Characteristics Shark cartilage is a popular dietary supplement that traditionally has been proclaimed to be able to prevent and/or treat established cancer. In the early part of the twenty-first century, it has been one of the ten most common dietary supplements used among cancer patients. It has been suggested that the widespread popularity of this product has partly contributed to an increase in shark fishing, with a resultant sharp, ≥75%, decline in the world shark population in the past 15 years. Shark cartilage is available as a capsule (taken orally), powder (for oral use when mixed with juice or as an enema), and also as an intravenous preparation. The recommended doses can vary from 500 mg to several grams per day. The adverse effects are predominantly gastrointestinal, such as nausea, abdominal pain, and diarrhea, and even hepatitis. Given its potential anti-angiogenesis properties, it has been advised that pregnant females should not consume the product. The popularity of shark cartilage soared in the early 1990s after a book (Sharks Don’t Get Cancer) by William Lane postulated that sharks do not get cancer due to the high proportion of cartilage in their body,

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suggesting that shark cartilage has chemopreventive properties. The authors predicted that “As events and research continue to unfold, shark cartilage may prove to be the first momentous step towards preventing and conquering cancer.” However, subsequent research has not substantiated this prediction. Moreover, sharks do develop cancers, although the rate of cancer incidence among sharks is unclear. A number of studies have been conducted to evaluate the potential cancer treatment properties of shark cartilage. One of the first reports of a human trial was featured on the TV show “60 Minutes” wherein results from two trials were reported, receiving considerable media coverage. In one trial, researchers from Cuba claimed that 16 weeks of shark cartilage was effective in treating cancer in 3 of the 15 patients that received the treatment. In the other trial, researchers at Simone Protective Cancer Center (NJ) claimed 4 of the 20 cancer patients consuming shark cartilage showed partial or complete response with use of the product. However, these studies had serious methodological flaws (9), the results suggested only a small response rate (20%), and the results were never reported completely in a peer reviewed PubMed indexed journal. In a well designed phase II study, involving 60 patients with advanced cancer, 1 g/kg/day of shark cartilage was reported to be ineffective in reducing the progression of disease, to have no beneficial effect on quality of life, and to have substantial gastrointestinal toxicity in about 25% of the patients. Two other phase II studies reported similar negative results with the use of shark cartilage among cancer patients. Likewise, no suggestion of efficacy of shark cartilage was seen in a relatively small randomized placebocontrolled, double-blinded clinical trial. Among the 83 patients involved in this trial (42 receiving shark cartilage and 41 receiving placebo), there was no difference in overall survival or quality of life among the two groups. The shark cartilage and its identical smelling, tasting, and appearing placebo were not well tolerated by the study patients, with 50% of subjects stopping the study medication within a month of initiation. Given the presently available evidence, shark cartilage has generally been considered to be an ineffective agent for cancer and promotion of its use as an anti-cancer agent has been widely criticized. While shark cartilage supplementation has been found to be ineffective as a chemoprevention or anti-cancer agent in clinical trials, laboratory research has identified a few compounds isolated from shark cartilage that could potentially have anti-angiogenesis properties. In the late 1970s, Langer et al. first isolated a factor from shark cartilage that was found to strongly inhibit the growth of new blood vessels toward tumors and thereby restricted tumor growth. Similar findings have been reported independently by other authors. One

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of the standardized extract shark cartilage products obtained from dogfish (AE-941, or Neovastat) has been reported to be a promising agent. In a phase II trial among 80 patients with lung cancer, those receiving higher doses (>2.6 ml/kg/day) of AE-941 were reported to have better survival, compared to patients receiving lower doses (median, 6.1 months vs. 4.6 months; P = 0.026). Neovastat is postulated to exert its anti-angiogenesis effects by multiple effects, including inhibition of tissue metalloproteinases, modulation of VEGF (vascular endothelial growth factor), and enhancement of endothelial cell apoptosis. This product was tested in a large phase III lung cancer clinical trial funded by the United States National Cancer Institute. However, the early results of this trial did not support that this agent had any benefit. Thus, in total, currently available study data do not support the efficacy of shark cartilage as a chemopreventive or anti-cancer agent. Given the lack of established efficacy, its toxicity, and the environmental impact related to harvesting sharks, the use of shark cartilage among patients with cancer should be discouraged.

Shedding of Cells ▶Exfoliation of Cells

Shimada System Definition Is the clinical classification of neuroblastoma.

Short Hairpin RNA ▶RNA Interference

References 1. Loprinzi CL, Levitt R, Barton DL et al. (2005) North Central Cancer Treatment Group. Evaluation of shark cartilage in patients with advanced cancer: a North Central Cancer Treatment Group trial. Cancer 104(1):176–182 2. Lane IW, Comac L (1992) Sharks don’t get cancer: how shark cartilage could save your life. Avery Publishing Group Garden City Park, NY 3. Miller DR, Anderson GT, Stark JJ et al. (1998) Phase I/II trial of the safety and efficacy of shark cartilage in the treatment of advanced cancer. J Clin Oncol 16:3649–3655 4. Lee A, Langer R (1983) Shark cartilage contains inhibitors of tumor angiogenesis. Science 221:1185–1187 5. Latreille J, Batist G, Laberge F et al. (2003) Phase I/II trial of the safety and efficacy of AE-941 (Neovastat) in the treatment of non-small-cell lung cancer. Clin Lung Cancer 4(4):231–236

SHP-1 Definition Src homology 2 domain-containing tyrosine phosphatase, non-receptor type 6, PTPN6. ▶Erythropoietin ▶SH2 Domain

SHP-2 Shc Definition An adaptor protein that contains both phosphotyrosinebinding and Src homology 2 ▶SH2 domain. It is a prominent effector of protein–tyrosine kinase signaling. ▶Insulin Receptor

Definition The Src homology 2 (SH2) domain-containing tyrosine phosphatase which plays a positive role in transducing signals from receptor protein tyrosine kinases down to the MAPKs, Ras, ▶PI3K or the Src family kinases. ▶Major Vault Protein ▶SH2 Domain

Signal Sequence

SH3P9 ▶Bin1

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Sicca Complex Definition Refers to dryness of the eyes and mouth; Is a chronic, inflammatory disease that affects the exocrine glands. The primary targets appear to be the lacrimal and salivary gland duct epithelium.

shRNA

▶Sjögren Syndrome

▶RNA Interference

Sicca Syndrome Sialoglycoconjugates

▶Sjögren Syndrome

Definition Are sugar chains terminally modified by an acidic sugar (sialic acid). ▶Adhesion

Signal Sequence Definition

Sialyl Lewis-a/x Determinants Definition Are blood group antigens that comprise type 1 (Lewis a) and type 2 (Lewis X) carbohydrates. Lewis a and Lewis x are regarded as tumor-associated markers, and these antigens and their derivatives interact with E-selectin, mediating cancer cell-to-endothelial cell adhesion. ▶E-selectin-Mediated Adhesion in Cancer

Sialyltransferases Definition Enzymes that catalyze addition of sialic acid (neuraminic acid). ▶Lewis Antigens

Synonym signal peptide; Is a N-terminal, short (18–26) amino acid sequence that acts like a zip code in nascent polypeptides and determines their subcellular targeting. A signal sequence is a protein region with which a protein can be directed to the appropriate cellular compartment within a cell, they initiate co-translational transfer through the membrane of the endoplasmic reticulum (ER). Proteins are often synthesized in an immature version (pre-protein) that is larger than the mature functional form. This is due to the presence of N-terminal amino acid stretches, referred to as leader sequences. The pre-protein is a transient precursor, since the leader sequence is cleaved off during protein processing. This signal sequence is a short stretch of 15–30 amino acids that mediates the transfer of any attached polypeptide to the endoplasmic reticulum. it provides the means for the ribosomes to attach to the ER membrane (ER regions with associated ribosomes are called “rough ER.” As soon as the first few amino acids of the protein have been synthesized, the nascent protein chain can be co-translationally transferred to the membrane. The signal hypothesis proposes that the N-terminus of a secreted protein has a signal sequence whose presence marks it for membrane insertion. Once the protein chain is well inserted into the membrane, the signal sequence is cleaved off by a protease within

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the membrane and the protein can then enter or even pass through the membrane. This principle does not hold for nuclear proteins, which are synthesized in their mature form.

Signal Transducer and Activator of Transcription ▶Signal Transducers and Activators of Transcription in Oncogenesis

Signal-Transducer Proteins Definition Proteins function as units in signaling pathways are described as signal-transducers. They have at least two “working parts,” one involved in recognition of an input signal (receptor part) and the other in generation of an output signal (generator) recognized by the downstream components. Some signal transducer molecules can respond to additional input signals that modulate their function (modulator) or could, after a short period, terminate generation of the output signal (timer). ▶Inositol Lipids ▶Signal Transduction

Signal Transducers and Activators of Transcription in Oncogenesis R ALF B UETTNER , R OY G ARCIA , R ICHARD J OVE City of Hope National Medical Center and Beckman Research Institute, Duarte, CA, USA

Synonyms STAT; signal transducer and activator of transcription

Definition Signal transducer and activator of transcription (STAT) proteins comprise a family of latent ▶transcription

factors that reside in the cytoplasm and have been shown to control normal ▶cytokine and ▶growth factor-induced responses. In response to extracellular signals, such as cytokines or growth factors, STATs are activated through ▶phosphorylation by ▶tyrosine kinases. Subsequently, these activated dimers translocate (▶translocation) into the nucleus where they bind to specific DNA sequences and regulate the transcription of cellular genes. Thus, STATs perform dual roles in transmitting receptor-generated signals from the cytoplasm to the nucleus and regulating cellular genes necessary for ▶ligand-induced biological responses.

Characteristics All multicellular organisms possess complex networks of molecular messengers that coordinate vital organ functions. Among the most common mechanisms used by multicellular organisms to ensure appropriate timing and duration of essential biological processes are production and secretion of cytokines and growth factors. Cytokines and growth factors control a wide variety of fundamental biological processes in diverse cell types, including immune responses, cellular differentiation, proliferation and programmed cell death (▶Apoptosis; ▶Apoptosis Signaling). Although differences exist between the biological processes and cell types regulated by cytokines and growth factors, these ligands possess some overlapping functions and share remarkably similar mechanisms of signal transmission. Cytokines and growth factors generally elicit a biological response by binding to receptor proteins located on the outer cell surface. Binding of these ligands to their specific receptors induces a change in the ability of the receptor to recruit and activate cytoplasmic signaling molecules that participate in signal transmission. Modulation of the activity of these cytoplasmic signaling proteins by the receptors initiates a cascade of biochemical signaling events, which ultimately lead to changes in nuclear gene expression that mediate the biological responses (▶Signal Transduction). Cytokine and growth factor-induced processes are normally tightly controlled to ensure proper functioning. Aberrant functioning of these pathways results in deregulated signaling and is associated with development of a variety of pathological conditions including ▶cancer. STATs in Cytokine and Growth Factor Induced Signaling In response to cytokine or growth factor-induced activation of signaling, cytoplasmic STATs become phosphorylated on specific tyrosine residues by receptors or receptor-associated proteins possessing tyrosine kinase activity (see Fig. 1) (▶Receptor Tyrosine Kinases). Tyrosine phosphorylation of STAT proteins

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Signal Transducers and Activators of Transcription in Oncogenesis. Figure 1 Constitutive activation of STATs by tyrosine kinases. Growth factors (e.g. EGF) and cytokines (e.g. IL-6) stimulate activation of receptor-intrinsic (RTK) or receptor-associated (JAK, Src) tyrosine kinases. Activated tyrosine kinases phosphorylate receptors to provide docking sites for unphosphorylated STATs. Once recruited, STATs themselves become tyrosine phosphorylated. Oncogenic tyrosine kinases such as SRC and ABL can also phosphorylate STATs independently of receptor engagement. Phosphorylated STAT dimers translocate to the nucleus, bind to specific DNA elements and regulate gene expression. In normal cells, STAT activation is transient and tightly regulated by inhibitory proteins, including PTPase, SOCS and PIAS. In cancer cells, constitutive activation of STATs, in particular Stat3 and Stat5, is associated with changes in the expression of genes that control fundamental cellular processes subverted in oncogenesis. RTK, receptor tyrosine kinase; R, receptor. See text for details. (Buettner et al. (2002) Clin Cancer Res 8(4):945–954 [2].)

allows STAT dimers to rapidly translocate into the nucleus. Once in the nucleus, STAT dimers bind to DNA and control the transcription of specific cellular genes. Under normal circumstances, the biological responses elicited by cytokines and growth factors are transient, and transmission of signaling is terminated through several inhibitory mechanisms, including (i) protein tyrosine phosphatases (▶PTPase) that dephosphorylate and inactivate STATs, (ii) ▶suppressor of cytokine signaling (▶SOCS) family of proteins that prevent STAT activation by tyrosine phosphorylation, or (iii) protein inhibitors of activated STATs (▶PIAS), a group of proteins that decrease transcription by binding to and thereby inhibiting STATs. While tyrosine phosphorylation of STAT proteins has been shown to be essential for cytokine-induced signals, activated

cytokine receptors generally do not possess kinase activity and are not capable of directly phosphorylating STAT proteins on tyrosine. Cytokines induce activation of STATs indirectly through activation of receptor-associated tyrosine kinases of the Janus kinase (▶JAK) family. After cytokine binding, STATs are phosphorylated by the receptor-associated JAKs, allowing signal transmission to proceed. Activation of STAT proteins has also been shown to be required for growth factor-induced cellular responses. However, the majority of growth factors that induce STAT activation bind to receptors that possess intrinsic tyrosine kinase activity, and tyrosine phosphorylation of STATs can be directly mediated by the activated receptor protein, receptorassociated JAK proteins or by additional non-receptor tyrosine kinases such as Src.

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Bioactivity Significantly, constitutive tyrosine phosphorylation and activation of STATs has been detected in cells that have undergone malignant ▶transformation in response to expression of a variety of viral oncoproteins, which are often themselves constitutively activated tyrosine kinases (▶Cell Transformation; ▶Oncogene). Consistent with a role for STATs in oncogenesis, regulation of gene expression by one STAT family member, Stat3, has been shown to be required for induction of malignant transformation by the oncogenic Src tyrosine kinase. Furthermore, expression of a constitutively activated mutant of Stat3 can induce malignant transformation of specific cell types. These results demonstrate that, in addition to signals important to normal cellular functions, activated STATs can also transmit signals critical to oncogenic transformation. STAT Activation During Progression of Human Cancer Constitutive tyrosine phosphorylation and activation of STATs, in particular Stat3 and to a lesser extent Stat5, has been shown to occur frequently in a variety of human tumor types including leukemias, lymphomas, multiple myeloma, head and neck cancer, lung cancer, prostate cancer, renal cell carcinoma, colon carcinoma, melanoma and breast cancer. Frequent activation of specific tyrosine kinase signaling pathways, including activation of growth factor receptor tyrosine kinases, has also been detected in many of these tumor types. These findings suggest that constitutive activation of STAT proteins results from the constitutive activation of tyrosine kinases. Moreover, because STAT proteins control the transcription of nuclear genes involved in growth control, constitutive activation of STATs may transmit signals essential for oncogenic signaling and contribute to ▶tumor progression. Among the genes that are regulated by STATs are genes involved in controlling cell cycle progression and programmed cell death (including ▶Cyclins D1/D2, ▶c-Myc, ▶Mcl-1, ▶BCL-x, and ▶Survivin) (▶Cyclin D; Myc Oncogene; Mcl Family; Survivin), genes that are involved in immunosuppression (interleukins-6, -10, -12, TNF, and ▶MHC class II) (MHC), and genes that also participate in the regulation of angiogenesis (such as ▶VEGF, MMPs 2 and 9, HGF, bFGF and HIF1α) (▶Vascular Endothelial Growth Factor; Matrix Metalloproteinases; Fibroblast Growth Factors; Hypoxia Inducible Factor-1). Thus, constitutive activation of STATs – in particular Stat3 and Stat5 – in human tumors may contribute to progression of cancer by multiple mechanisms, including proliferation and survival of the tumor cell itself, induction of angiogenesis and suppression of immune cells in the tumor ▶microenvironment (immunosuppression).

Targeting STATs for Cancer Therapy Inhibition of STAT signaling has repeatedly been demonstrated to result in growth inhibition and induction of apoptosis in tumor cells harboring constitutive activation of Stat3 or Stat5. The observed dependence of certain tumors on constitutive STAT activation for survival has wide implications for cancer therapy, offering the potential for preferential tumor cell killing. Targeting the Tumor Cell Persistent Stat3 and Stat5 signaling within tumor cells directly participates in the development and progression of human cancers by either preventing apoptosis, inducing cell proliferation, or both. Targeting of tyrosine kinase activity upstream of STAT pathways has drawn special attention because of the recent development of tyrosine kinase-selective inhibitors. However, one potential draw-back of tyrosine kinase inhibitors is that they block multiple downstream signaling pathways in addition to STAT proteins, increasing the likelihood of undesirable toxicity. Since STAT activation is a point of convergence for many different tyrosine kinases, STATs themselves represent promising targets for the development of cancer drugs. One of the attractive features of STAT proteins for cancer therapy is that there are only two molecular targets, Stat3 and Stat5, as opposed to a multitude of tyrosine kinases. Antisense oligonucleotides and small-interfering RNA (▶siRNA) that target STATs are just two of the many possibilities to interfere with aberrant STAT signaling (▶Antisense DNA Therapy). Alternatively, small-molecule inhibitors are being developed to directly interfere with STAT proteins (▶Drug Design). Recent progress has been made in design of short peptides, ▶peptidomimetics and other non-peptide compounds that effectively block Stat3 dimerization and DNA-binding activity both in vitro and in vivo. Importantly, these compounds inhibit cell transformation mediated by activated Stat3 and provide the basis for development of novel drugs for potential cancer therapy. Targeting the Tumor Microenvironment Recent evidence suggests that Stat3-positive cancer cells can crosstalk with adjacent “normal” immune cells for the purpose of modifying the tumor microenvironment in favor of the cancer cell. Stat3-positive cancer cells can suppress the production and secretion of pro-inflammatory factors that otherwise would stimulate an anti-tumor immune response (▶Inflammation; ▶Inflammation in Cancer). At the same time, cancer cells can secrete immune-suppressive factors that act on immune cells. Some of the factors secreted by tumor cells, such as IL-6, IL-10 and VEGF, act on both tumor cells and adjacent immune cells by maintaining Stat3 activation in the tumor cell and simultaneously inducing Stat3 activation in immune cells. It has been shown

Signal Transduction

for many immune cells in the tumor microenvironment that Stat3 acts as a negative regulator of immunestimulating molecules. Stat3 activation in immune cells has been found to inhibit the anti-tumor function of natural killer cells (NK), ▶dendritic cells (DC), T-cells and ▶macrophages, among other cell types (▶Natural Killer Cells; Dendritic Cells; ▶T Regulatory Cells; Macrophages). In the case of macrophages, for example, it has been demonstrated that ablation of both Stat3 alleles leads to increased levels of several proinflammatory cytokines similar to those found in cancer cells in which Stat3 signaling is inhibited. Moreover, simultaneous inhibition of Stat3 signaling in immune cells and tumor cells induces a more pronounced antitumor effect, demonstrating the additive nature of blocking Stat3 signaling in both tumor cells and normal cells of the tumor microenvironment. In addition to negatively regulating immune cell function, some of the factors secreted by Stat3-positive cancer cells, such as VEGF, bFGF, HGF and MMPs, are pro-angiogenic and facilitate tumor growth by increasing blood supply (tumor angiogenesis). Summary Because STATs play essential roles in regulation of cell proliferation and survival, the frequent activation of these proteins in human tumors suggests that they have essential roles in the malignant progression of human cancers. Furthermore, recent studies indicate that STATs also propagate signals between tumor and normal cells in the tumor microenvironment, thereby promoting tumor immune evasion and tumor angiogenesis Detection of constitutively activated STATs could provide an important marker for activation of oncogenic tyrosine kinase signaling pathways during tumor progression. Currently, characterization of the full complement of STAT-regulated genes that participate in growth regulation and tumorigenesis remains a very active and important area of investigation (▶Microarray (cDNA) Technology). These studies have the potential to provide new information critical to understanding how fundamental cellular processes are subverted in tumor cells. Finally, activated STATs in human tumors provide promising targets for the design of novel therapeutics that block STAT functions involved in stimulation of proliferation, prevention of cell death, and induction of immune evasion and tumor angiogenesis. Early results in this area suggest that targeted inactivation of STAT proteins may be an effective approach to halting the growth of various types of human tumor cells. Inhibition of STAT signaling in tumors is predicted to impart therapeutic benefit by inducing growth arrest and apoptosis as well as suppressing tumor angiogenesis and immune evasion. However, targeting STAT proteins for therapeutic intervention in cancer remains to be fully explored.

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References 1. Bowman T, Garcia R, Turkson J et al. (2000) STATs in oncogenesis. Oncogene 19:2474–2488 2. Buettner R, Mora LB, Jove R (2002) Activated STAT signaling in human tumors provides novel molecular targets for therapeutic intervention. Clin Cancer Res 8:945–954 3. Levy DE, Darnell JE Jr (2002) Stats: transcriptional control and biological impact. Nat Rev Mol Cell Biol 3:651–662 4. Yu H, Jove R (2004) The STATs of cancer – new molecular targets come of age. Nat Rev Cancer 4:97–105 5. Yu H, Kortylewski M, Pardoll D (2007) Crosstalk between cancer and immune cells: role of STAT3 in the tumour microenvironment. Nat Rev Immunol 7:41–51

Signal Transduction DAVID A. F RANK Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, USA

Definition Signal transduction is the process by which information from extracellular stimuli is propagated within a cell to alter cellular function. These signals frequently modulate gene expression, but they may also directly regulate processes such as cellular survival, metabolism, and macromolecular synthesis.

Characteristics Starting shortly after fertilization, the phenotype of a cell becomes regulated largely by extracellular cues. Soluble factors such as cytokines and hormones, direct contact between cells, and interactions with the extracellular matrix all provide critical information affecting cellular morphology, proliferation, differentiation, and survival. A central question in cellular physiology is how these extracellular processes are converted into signals that can modulate the phenotype of a cell. A number of mechanisms have evolved by which such stimuli arising outside of a cell can regulate the expression of genes in the nucleus and other critical cellular processes. Several processes are used in a variety of ways by mammalian cells to transmit these signals. Each of these processes is also balanced by feedback mechanisms to modulate the cellular response. In essentially every kind of cancer, an abnormality in one or more signal transduction pathways provides a cell with signals for survival, proliferation, or self-renewal in the absence of the normal physiologic cues. Thus, elucidating signal transduction pathways is critical to understanding tumor

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Signal Transduction

pathogenesis and tumor biology. Furthermore, among the most important advances in cancer therapy in recent years has been the introduction of signal transduction inhibitors that specifically target these molecular defects. These agents hold the potential to have much greater efficacy and much less toxicity than conventional cytotoxic agents. Receptors The ability to respond to the extracellular environment is mediated by receptors (Fig. 1). Although dozens of receptor molecules have been described in mammalian cells, from a functional perspective they can be grouped into three categories. First are receptors that are coupled to kinases. Activation of these receptors initiates the transfer of the terminal phosphate of ATP (or GTP) to an amino acid residue in a protein. Most receptorassociated protein kinases have specificity for phosphorylating tyrosine residues. This often leads to the subsequent activation of protein kinases that can phosphorylate serine or threonine residues, or lipid kinases. Thus, the interaction of a soluble ligand with an extracellular receptor can lead to the amplification of the signal through kinase cascades that can modulate cellular function through a number of mechanisms.

Receptors may contain intrinsic tyrosine kinase activity, as is the case for polypeptide growth factor receptors such as the receptors for insulin, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and others (▶receptor tyrosine kinases). Receptors may lack tyrosine kinase activity of their own, but associate with cytoplasmic tyrosine kinases which become activated by the binding of a ligand. Cytokine receptors, such as receptors for interferons, interleukins, oncostatin M, and leukemia inhibitory factor (LIF) associate with tyrosine kinases of the Janus kinase family whose activation propagates the signal. Activation of receptor-associated tyrosine kinases leads to two major effects. First, it allows the tyrosine phosphorylation of specific substrates whose activity is regulated by this modification. For example, transcription factors of the ▶signal transducers and activators of transcription (STAT) family are found inactive in the cytoplasm under basal conditions. Once phosphorylated by a tyrosine kinase, STATs form dimers, which allows them to translocate to the nucleus, bind to specific DNA regions, and regulate the transcription of target genes. The second effect of tyrosine kinase activation results from the phosphorylation of the receptor itself and associated proteins. These phosphotyrosine

Signal Transduction. Figure 1 Through signal transduction, extracellular stimuli are converted into biochemical processes that control cellular function. Steroid hormones bind to intracellular receptors which then directly control gene expression. Cytokines, growth factors, and peptide hormones interact with cell surface receptors which then initiate cascades of protein phosphorylation, lipid phosphorylation, and second messenger generation. These mediators then regulate gene expression or directly alter processes such as cellular metabolism, protein translation, and apoptosis.

Signal Transduction

residues form potential docking sites for proteins that have structural domains, such as the ▶Src homology 2 (SH2) domain, that allow them to specifically bind to phosphorylated tyrosine residues. This can trigger a series of interactions with other proteins in which tyrosine phosphorylation of proteins performs a “scaffolding” function, allowing other proteins to associate, which then activates their function. In addition to the phosphorylation of proteins, kinases that can phosphorylate lipids play a key role in signal transduction. For example, ▶phosphatidyl inositol 3-kinase (PI3 kinase), which is activated downstream of many receptors, leads to the phosphorylation of lipids in the cell membrane which can serve as a docking site for proteins with the lipid-binding ▶pleckstrin homology domain. The recruitment of proteins such as ▶Akt to these sites then leads to their activation. The second family of receptors do not directly modify other proteins, but rather trigger the production of small molecule mediators that diffuse through a cell and modulate cellular function. Such “▶second messengers” include molecules like cyclic AMP (cAMP), cGMP, calcium ions, and lipids released from cellular membranes (such as diacylglycerol). Thus, for example, the binding of glucagon to the glucagon receptor leads to the generation of cAMP by ▶adenylyl cyclase associated with the glucagon receptor. cAMP can then activate cAMP-dependent protein kinase, also known as protein kinase A, which phosphorylates a variety of substrates on serine and threonine residues. Among these is the transcription factor ▶cAMP response element binding protein (CREB), which becomes activated by this phosphorylation, and mediates the expression of a cohort of target genes. The third functional group of receptors for extracellular signals are not located on the cell surface, but rather are intracellular. The steroid hormone family of receptors makes use of the fact that the ligands with which it interacts are small lipophilic molecules that are cell permeable. For example, hydrocortisone is secreted by the adrenal glands, circulates in the bloodstream, and then directly enters cells where it binds to the glucocorticoid receptor. The receptor and its associated ligand then binds to specific regulatory sequences in the genome and activates or represses the expression of specific target genes. Targets of Signaling Pathways While the modulation of gene expression is a key endpoint of signaling pathways and plays a major role in the modulation of cellular behavior triggered by extracellular stimuli, other important targets of signaling pathways are present in a cell. For example, among the serine, threonine kinases activated downstream

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of cell surface receptors are kinases that can phosphorylate ribosomal proteins. The ribosomal protein S6 can be phosphorylated by members of the p70S6 kinase family or the ribosomal S6 kinase (RSK) family. Phosphorylation of S6 increases the rate of translation of a subset of mRNAs, which may be important for increasing cellular growth and proliferation. Kinases such as the “mammalian target of rapamycin” (mTOR) can directly phosphorylate and affect the function of proteins involved in both translation initiation and elongation. Signaling pathways can also directly regulate cellular metabolic function. for example, the serine, threonine kinase ▶Akt, which is activated by a variety of receptors, can phosphorylate the glucose transporter Glut4, which promotes its localization to the cell surface, and enhances glucose uptake in ▶adipocytes. For humans and other mammals to develop and function normally, the ability of cells to die through the process of ▶apoptosis is a critical step. The development of organs such as the brain and the function of the immune system is dependent on the programmed death of large numbers of cells. While there are several mechanisms by which a cell can die, one central process involves families of proteins that regulate mitochondrial permeability. These proteins may serve to promote survival or apoptosis, and their relative levels and activity are a major determinant of whether or not a cell survives. A number of signaling pathways directly regulate these proteins. For example, the serine, threonine kinase Akt can phosphorylate the pro-apoptotic protein BAD (a member of the ▶BCL-2 family of proteins), which blocks its ability to trigger apoptosis, and thereby promotes the survival of a cell. Signal Transduction in Cancer Pathogenesis Given the importance of signal transduction in a range of critical cellular processes, it is not surprising that inappropriate activation of signaling pathways can contribute directly to the development of cancer. Signaling pathways may be activated by a variety of mechanisms. Among the most common mutations in human cancer, and the first identified in a human tumor, are activating point mutations of ▶Ras family proteins. These mutations lead to the activation of a number of downstream kinases that promote cellular survival and proliferation. Cell surface tyrosine kinases can become activated by overexpression resulting from gene amplification. This mechanism leads to enhanced production of the ▶Her2 (ErbB2) protein in 30% of breast cancers, with the consequent activation of downstream signaling pathways. Receptor tyrosine kinases can also be activated by point mutations, deletions, or internal tandem repeats, all of which can lead to enhanced

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tyrosine kinase activity in the absence or presence of ligand. Another common mechanism by which tyrosine kinases are activated in cancer is through ▶chromosomal translocations that lead to the formation of a chimeric gene that encodes a tyrosine kinase with enhanced activity. The prototype for this is ▶Bcr-Abl, a tyrosine kinase resulting from a translocation between chromosomes 9 and 22 (forming the so-called ▶Philadelphia chromosome). The tyrosine kinase c-abl is a relatively weak tyrosine kinase that localizes primarily in the nucleus and is involved in responding to DNA damage. By contrast, Bcr-Abl is a highly active kinase which is found in the cytoplasm and phosphorylates and activates a number of key signaling molecules. Bcr-Abl is found in essentially all patients with chronic myeloid leukemia (CML), and a subset of patients with acute lymphoblastic leukemia (ALL). Most signal transduction pathways have negative feedback systems that limit their effect. However, signaling pathways can become activated during tumorigenesis by the loss of such a negative feedback component. For example, ▶PTEN is a lipid phosphatase that dephosphorylates inositol phosphates, thereby countering the effect of PI3 kinase. The PTEN gene is frequently deleted in cancers which leads to unrestrained activity of the ▶PI3 kinase cascade.

Signal Transduction in Cancer Therapy Current cytotoxic cancer therapies kill cells in a largely indiscriminate manner, and thus have limited efficacy and considerable toxicities. However, increased understanding of how signaling pathways are activated in cancer has presented an opportunity to develop targeted agents which are more effective at inhibiting tumor cells while causing few side effects. Current signal transduction inhibitors generally target activated tyrosine kinases by blocking the ability of ATP to bind to the kinase. Drugs such as imatinib mesylate, which inhibits the abl kinase, have been enormously successful in treating CML, and cause few serious side effects. While much effort is going into the development of kinase inhibitors, there is also an interest in developing inhibitors for signaling proteins without catalytic function. For example, drugs that inhibit the post-translational lipid modifications of Ras might be able to overcome the effects of an activating point mutation in this protein.

References 1. Frank DA (2006) STAT inhibition in the treatment of cancer: transcription factors as targets for molecular therapy. Curr Cancer Ther Rev 2:57–65 2. Paez J, Sellers WR (2003) PI3K/PTEN/Akt pathway: a critical mediator of oncogenic signaling. Cancer Treat Res 115:145–167

3. McKenna N, O’Malley B (2002) Combinatorial control of gene expression by nuclear receptors and coregulators. 108:165–474 4. Pawson T (2002) Regulation and targets of receptor tyrosine kinases. Eur J Cancer 38(Suppl 5):S3–S10 5. Shawver LK, Slamon D, Ullrich A (2002) Smart drugs: tyrosine kinase inhibitors in cancer therapy. Cancer Cell 1:117–123

Signal Transduction Cross-Talk Definition Is the mechanism by which activated signaling molecules in a primary ▶signal transduction pathway can regulate signaling molecules in another primary signal transduction pathway. ▶Kit/Stem Cell Factor Receptor in Oncogenesis

Signal Transduction Inhibitor-571 ▶STI-571

Signaling Cascades Definition Cascades involving enzymes that act one on another to relay molecular signals (hormone, growth factor) or physical signals (sensory stimuli) from a cell’s exterior to its intracellular response mechanisms. ▶Signal Transduction

Signalosome Definition Functional definition of a multi-protein complex of various signaling elements, whose association and activities is regulated by scaffold proteins. The

Single-Chain Fv Fragment

assembly of the signalosome is modulated in a complex spatio-temporal manner and ensures the specificity and speed of intracellular signal ▶transduction.

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Single Cell Gel Electrophoresis Assay (SCGE) ▶Comet Assay

Silencing Mediator of Retinoid and Thyroid Hormone Receptor Definition

▶SMRT co-repressor.

Single Cell Invasion Definition

Simian Virus 40 Definition

▶SV40; A virus of the genus Polyomavirus of the family Papovaviridae, originally isolated from kidney cells of the rhesus monkey. SV40 nucleotide sequences have been identified in certain human cancers, such as ▶osteosarcomas and ▶mesothelioma. ▶SV40

Simulation

Cell-cell adherence is lost and the cells migrate solitarily. This invasion pattern is usually seen in the presence of ▶epithelial-mesenchymal-transition or amoeboid transition (change to a leukocyte-like migration pattern) and requires the expression of β1-integrin. ▶Podoplanin

Single Cell Microgel Electrophoresis Assay ▶Comet Assay

Definition Allows precise radiation dose distribution within the prescribed treatment volume by integrating data from the computed tomography scanner or magnetic resonance imager to the three dimensional treatment planning computer system. ▶Radiation Oncology

Single-chain Fv Dimer ▶Diabody

SIN3A Single-Chain Fv Fragment Definition

Transcriptional repressor protein interacting with ▶histone deacetylases.

Definition

▶Chromosomal Translocation t(8;21)

Single-chain Fv fragment recombinant antibody molecule composed of the variable light chain domain (VL)

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Single Dose Toxicity Studies

and variable heavy chain domain (VH) of an antibody linked by a short and flexible peptide linker.

strands of a specific amplified region. Detection is performed after ▶PCR within non denaturating gels.

▶Bispecific Antibodies

▶Leukemia Diagnostics

Single Dose Toxicity Studies Definition Synonyms acute toxicity studies; Are standardized protocols whereby small groups of animals are given a single dose of a chemical usually at several doses to define a dose-response. The top dose is usually expected to be at about the maximum tolerated dose in the particular animal species under study. After euthanasia the animals are subjected to a full autopsy examination and most tissues are examined microscopically for any adverse effects. They are conducted according to Good Laboratory Practice. The so called LD50 (lethal dose 50) study is no longer performed. ▶Preclinical Testing

Siomycin A Definition Is a thiazole antibiotic compound that was identified from the culture broth of Actinomycetes, that inhibits FoxM1 activity. ▶Forkhead Box M1

SIOP Definition The Societe Internationale Oncologie Pediatrique (International Society of Paediatric Oncology) is an international organization of clinicians involved in the treatment of childhood cancer.

Single Nucleotide Polymorphism Definition Refer to SNP; single nucleotide changes (A, T, C or G) in the genome sequence. Such changes can sometimes modify the function of a protein and an understanding of these changes can enhance our understanding and treatment of disease. ▶MIC-1

Single Stranded Conformation Analysis Definition SSCP; Method applied for mutation screening that is based on the identification of secondary structure differences between mutated und unmutated single

Sipa-1 (Spa-1) Definition Signal-induced proliferation associated protein 1; is a GTPase-activating protein specific for Rap1 and is encoded by Sipa-1 gene. There are several proteins with a homologous structure and function, including human E6TP1 (▶human papillomavirus E6-targeted protein 1, also called Spa-L1 in mouse and SPAR in rat), Spa-L2, and Spa-L3. ▶Rap1/Sipa-1

Sipple Syndrome ▶Multiple Endocrine Neoplasia Type 2

siRNA

Sir2-like Proteins ▶Sirtuins

siRNA Definition Short Interfering RNA; Refers to short double-stranded RNA molecules that can be incorporated into ▶RISC. They are very similar to ▶microRNAs but they are usually synthesised in vitro and not by the cells. If siRNAs are produced in cells (in lower animals or plants) they are produced from long double-stranded RNA and many siRNAs are produced from one such RNA in contrast to microRNAs that are produced from imperfect stem-loop structure precursors and only one from each precursor. SiRNAs are used to knock down the expression of genes using ▶RNA interference. ▶MicroRNA ▶RNA Interference

siRNA T ETSUYA N AKATSURA Section for Frontier Medicine, Investigative Treatment Division, Research Center for Innovative Oncology, National Cancer Center Hospital East, Kashiwa City, Chiba Prefecture, Japan

Definition The small interfering RNA (siRNA) transcripts are 21–25 bp long, double-stranded transcripts as a defense response to nonendogenous double-stranded RNA (dsRNA), leading to sequence-specific mRNA cleavage. This double-stranded induced cleavage was named ▶RNA interference (RNAi).

Characteristics siRNA transcripts are 21–25 bp long, double-stranded transcripts that were found in Caenorhabditis elegans in 1998 as a defense response to nonendogenous dsRNA, leading to sequence-specific mRNA cleavage. This double-stranded induced cleavage was named

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RNAi and was soon to be found in other organisms, for example, Drosophila melanogaster, and in vertebrates. The main function of the mechanism is believed to a defense system against introduced viral double-stranded sequences, cutting them to pieces and thereby rendering them unable to infect the cell. The gene regulation part was not discovered until recently. RNAi was also quickly adapted for use in the laboratory as a gene-silencing tool for the silencing of specific genes by introducing the specific double-stranded sequence, and has become a common tool today for the study of gene expression and regulation due to its specificity. siRNA is generated by Dicer cleavage of long dsRNA sequences. After cleavage, the double-stranded siRNA is loaded into the RNA-induced silencing complex (RISC). During the loading process one strand is peeled off, leaving a single-stranded siRNA lodged inside RISC. This strand is then used by RISC as a template to recognize the cleavage target in the target mRNA transcript. A full match induces a cleavage in Drosophila RISC complexes, Argonaute2 (AGO2) has been identified as carrying the slicing action, but several other proteins are also involved in the RISC complex (Fig. 1). Clinical Aspects There are still unknown details regarding the biogenesis and function of siRNA, especially in mammals. The siRNA technique of using siRNA transcripts to knock down gene expression of specific genes has quickly become a popular method that is used for gene function analysis in molecular biology. The method is still being developed to improve the siRNA vectors, both the specificity and the usability of the technique, but already it exhibits a high specificity. The hope of the future is to be able to use siRNA knock down techniques to treat both genetic disorders, viral infections and, in extension, to be able to use siRNA as a cancer treatment. The advantage of RNAi technology is that it can be used to target a large number of different genes involving a number of distinct cellular pathways. This is particularly important for a disease as complex as cancer. Most of the RNAi candidate cancer gene targets are involved in pathways that contribute to net tumor growth (either through increased tumor-cell proliferation or reduced tumor-cell death, or both). While mRNAs expressed from mutated cancer ▶oncogenes can be directly targeted for RNAi intervention, RNAi can also be used to target and silence gene products that negatively regulate the function of endogenous ▶tumor suppressor genes. Other gene products that can be targeted by RNAi include proteins involved in cellular ▶senescence, or protein stability and degradation. Although these additional targets are not directly involved in the oncogenesis pathway, they can indirectly

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siRNA

siRNA. Figure 1 Schematic representation of RNA interference (RNAi). siRNA is generated by Dicer cleavage of long double-stranded RNA sequences. After cleavage, the double-stranded siRNA is loaded into the RNA-induced silencing complex (RISC). Synthetic siRNA is directly incorporated in the RISC. During the loading process one strand is peeled off by Argonaute2 (AGO2) leaving a single-stranded siRNA lodged inside RISC. This strand is then used by RISC as a template to recognize the cleavage target in the target mRNA transcript. A full match induces a cleavage.

contribute to net tumor growth, and therefore represent potential candidates for RNAi intervention. Delivery RNAi-mediated gene silencing in mammalian cells can be achieved by transfection, for example, using liposomes or electroporation of synthetic siRNA molecules, or by gene transfer using plasmid- or virus-based expression cassettes with RNA polymerase III promoter encoding dsRNA molecules. The easiest way to induce RNAi is the use of chemically synthesized siRNAs. However, in addition to siRNAs produced by chemical synthesis, siRNAs may be generated by from long dsRNAs in vitro via recombinant Dicer, by in vitro transcription using T7 RNA polymerase, or siRNAs can be isolated from Drosophila embryo extracts. Classic transfection of siRNA molecules using different physical methods such as liposome-mediated transfection, electroporation, or

single-cell microinjection has been successfully applied. Treatment of mammalian cells with siRNAs typically results in a transient downregulation of the target mRNA after 1–2 days for a duration of 3–5 days. In vivo delivery of chemically synthesized siRNAs to mice was reported by injection into the tail veins. By this approach, a downregulation of 90% of endogenous mRNA transcripts in the majority of liver cells after a single siRNA injection could be achieved. In the liver, the RNAi effect persists for several days. Although siRNAs are readily taken up into worm and fly cells, most mammalian cells do not efficiently internalize these small molecules. This is even true of cells, such as dendritic cells and ▶macrophages, which are actively sampling their environment. Therefore, the major obstacle for using small RNAs as drugs is to deliver them into the cytoplasm of cells. An exception may be mucosal tissues. In the lung and vagina, siRNA uptake is extremely efficient and occurs even in the absence of transfection reagents. For clinical indications where siRNAs only need to be delivered to a localized region, such as the eye, pulmonary or vaginal mucosa, or superficial tumors, efficient siRNA delivery and silencing can be achieved by mixing siRNAs with cationic lipid transfection reagents used for in vitro transfection and directly injecting the siRNA–lipid complexes into the relevant tissue or instilling it into the body cavity. A similar approach is certain to apply to the skin. Mixing siRNAs with other molecules known to carry nucleic acids into cells, such as certain cationic peptides, might also be used effectively for local delivery. However, some cell types, such as lymphocytes, dendritic cells, and hematopoietic stem cells, are refractory to transfection using cationic lipids. Therefore, even when these targets might be localized, alternate delivery strategies may be needed. The first demonstrations of the therapeutic potential of siRNAs for silencing disease-related genes delivered siRNAs systemically by rapid high-pressure intravenous injection. This method leads to transient rightsided heart failure, where elevated venous pressures somehow enable siRNAs to get into cells in highly vascularized organs like the liver, pancreas and lungs. Nonetheless, this strategy is too risky for human use. It is, however, possible to deliver siRNAs into an organ, such as the kidney, by rapid retrograde injection via catheter into the draining vein. It may be possible to use hydrodynamic injection into a peripheral vein to treat skeletal muscle by blocking venous outflow using a tourniquet. Elevated venous pressures are generated only in the targeted tissue without inducing potentially fatal heart failure. However, a minimally invasive method for delivering siRNAs requires alternate approaches. A variety of strategies that involve complexing siRNAs to cationic polymers or peptides or incorporating siRNAs into nanoparticles or liposomes have

SIRTs

been proposed. Alternately, siRNAs can be covalently or noncovalently linked to antibody fragments or ligands to cell surface receptors to limit the delivery of the siRNAs to cells that bear the specific receptor. These strategies probably deliver siRNAs via receptormediated endocytosis, although the trafficking of siRNAs into and within cells has not been well studied. The directed delivery of siRNAs into specific cells will decrease the amount of siRNAs needed for the efficient silencing of gene expression in the target organ or tissue and will reduce potential toxicity by preventing targeting of unintended cells and tissues. The optimal delivery strategy may differ between different therapeutic indications and will depend on efficiency and duration of delivery and silencing, lack of systemic toxicity, and lack of immunoreactivity, which would interfere with repetitive treatments. The first examples of effective systemic delivery have only recently been described. Nonspecific Immune Stimulation While there is a high degree of specificity associated with RNAi, some effects have been observed that are independent of the specific gene targeted for silencing. In general, 21 bp or longer dsRNAs can lead to a sequence-independent ▶interferon response. Interferon can also activate the dsRNA-dependent protein kinase (PKR), which phosphorylates and subsequently inactivates the translation factor eIF2, leading to a global inhibition of mRNA translation. The length of the initiating siRNA clearly has some role in triggering the interferon response, with more recent data suggesting that sequences shorter than 19 nucleotides are more likely to escape the interferon antiviral response. It is anticipated that the judicious selection of siRNA sequences together with a greater understanding of their interactions with any given target gene will resolve this issue. Similarly, evidence exists that siRNAs can activate dendritic cells and other cells of the immune system through a much more specific and restricted class of receptors, the toll-like receptors, which can recognize foreign nucleic acids including dsRNAs and when activated can send a danger signal to trigger a proinflammatory response. These findings raise the possibility that RNAi reagents may trigger unforeseen immune responses, including autoimmune diseases, in vivo. Off-Target Interference Nucleic acid-based gene-silencing molecules may also have effects on genes that are not considered targets, the so-called off-target effects, due to similarities in nucleic acid sequences. The degree of the off-target effect is dependent upon the mode of silencing and the stability of the nucleic acid hybrid. If siRNAs are not carefully selected, siRNAs having partial complementarity to an mRNA target can repress translation or subject

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unintended mRNAs to degradation. A study that compared the gene-expression profiles created by different siRNAs targeted against the same transcript revealed that in extreme cases, as little as seven nucleotide complementarity between the 5′ end of either siRNA strand to an mRNA can cause a reproducible reduction in transcript levels. Interestingly, it has been found from studies in primitive organisms that off-target effects are not observed when complete dsRNAs are introduced instead of synthetic siRNAs. This may be explained by the fact that the siRNAs derived endogenously from the cleavage of dsRNAs are generated and selected by Dicer and the RISC complex, which may have a proofreading mechanism that protects against the generation of siRNA sequences that might result in the silencing of endogenous genes. Therefore, it is possible that mammalian siRNAs generated from dsRNA precursors through the action of Dicer and the RISC complex may be less prone to induce off-target effects than synthetically designed siRNAs. Several algorithms and software are available to select siRNA target sequences with reduced off-target effects, and it will be important to select siRNA targets with relatively sophisticated sequence comparison tools to minimize potential off-target effects.

References 1. Tomaru Y, Hayashizaki Y (2006) Cancer research with non-coding RNA. Cancer Sci 97:1285–1290 2. Pai SI, Lin YY, Macaes B et al. (2006) Prospects of RNA interference therapy for cancer. Gene Ther 13:464–477 3. Dykxhoorn DM, Palliser D, Lieberman J (2006) The silent treatment: siRNAs as small molecule drugs. Gene Ther 13:541–552 4. Vogelstein B, Kinzler KW (2004) Cancer genes and pathways they control. Nat Med 10:789–799

S SIRS Definition

▶Systemic Inflammatory Response Syndrome.

SIRTs ▶Sirtuins

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Sirtuins

Sirtuins O LAF W ITT CCU Pediatric Oncology, German Cancer Research Center, Heidelberg, Germany

Synonyms SIRTs; Class III histone deacetylases; Sir2-like proteins

Definition Sirtuins are a family of protein deacetylases (▶Histone deacetylases) and ADP ribosyltransferases requiring NAD+ for their enzymatic activity.

Characteristics Biochemical Features of Sirtuins Sirtuins are protein deacetylases and ADP ribosyltransferases that target a wide range of cellular proteins in the nucleus, cytoplasm, and mitochondria. Among the substrates are histone proteins, and therefore sirtuins are also referred to as class III ▶histone deacetylases. Seven human sirtuins (SIRT1–7, see Table 1) have been identified and share a catalytic domain of 275 amino acids. As opposed to ▶histone deacetylases, sirtuins require ▶NAD± as a cofactor for their enzymatic activity. Therefore, NAD+/NADH ratio and metabolic status of the cell influences the activity of sirtuins. Nicotinamide is a physiological intracellular inhibitor of sirtuins. Cellular Functions of Sirtuins Human sirtuins (SIRTs) are structurally related to the silent information regulator 2 (Sir2) family, which are conserved from bacteria to humans and regulate lifespan in lower organisms. Sirtuins are involved in regulation of the cellular stress response, cell cycle Sirtuins. Table 1

progression, chromosomal stability and aging. SIRT1 knock-out mice show multiple developmental defects and die around birth and is thus required for normal embryonal development. Mammals have seven sirtuins (Table 1). In addition to the intranuclear SIRT1, there is the cytoplasmic SIRT2, the three mitochondrial sirtuins SIRT3, 4, 5, and also within the nucleus the ▶heterochromatinassociated SIRT6 and the nucleolar SIRT7. Based on sequence homology, the sirtuins can be grouped into four classes. SIRT1, 2, 3 comprise class I, SIRT4 is in class II, SIRT5 is in class III, and SIRT6, 7 are class IV sirtuins. Table 1 summarizes the cellular localization and functions of the 7 human sirtuins. Among the 7 sirtuins, SIRT1 has been most intensively studied, whereas the functions and target proteins of SIRT2–6 are less well understood. SIRT1 regulates the acetylation status of histone proteins and is thereby involved in the control of ▶chromatin structure and regulation of transcriptional activity. For example, SIRT1 directly deacetylates lysine 16 of histone H4, which is a mark for transcriptional inactive heterochromatin, whereas acetylated lysine 16 is found in transcriptionally active ▶euchromatin. SIRT1 is a component of the polycomb group repressor complex, a multiprotein complex which controls differentiation and developmental programs in embryonic cells. In addition to its function in regulating chromatin structure, SIRT1 regulates the activity of several cellular proteins via modulating their acetylation status. For example, deacetylation of the ▶tumor suppressor protein ▶p53 by SIRT1 results in downregulation of its transcriptional and ▶apoptosis-inducing as well as ▶senescence-inducing activity. Other proteins known to be targets of SIRT1 are MyoD (a transcriptional regulator of muscle gene expression and differentiation), FOXO proteins (family of transcription factors that regulate oxidative stress response, cell cycle arrest, DNA repair, and apoptosis),

Cellular localization and functions of sirtuins

Localization SIRT1 Nucleus

SIRT2 Cytoplasm Shuttles into nucleus SIRT3 Mitochondria SIRT4 Mitochondria SIRT5 Mitochondria SIRT6 Nucleus SIRT7 Nucleolus

Function Deacetylation of histone and non-histone proteins Regulation of chromatin structure Regulation of activity of p53 and several other transcription factors (see text) Involved in cellular stress response, survival, senescence, cellular life span, differentiation Deacetylation of α-tubulin Mitotic checkpoint regulation Acetyl-CoA production ADP-ribosylation, suppression of insulin signaling not known Guards genomic instability, target unknown Promotes rRNA transcription

Site-Directed Mutagenesis

Ku70 (a protein involved in nonhomologous repair of DNA double-strand breaks), PPAR-y (a member of the nuclear receptor superfamily that integrates energy control, lipid metabolism, and glucose homeostasis), and NF-kB (transcription factor that regulates immune response, inflammation, cell proliferation, and cell death). As a result of modulating the function of these proteins, SIRT1 is involved in cell survival, muscle differentiation, and fat metabolism and is upregulated during caloric restriction. SIRT1 plays a role in regulation replicative senescence and limit of proliferation of normal cells. SIRT1 ensures that damaged DNA is not propagated and that mutations do not accumulate in cells. In recent years, much attention has been paid to the function of SIRT1 in controlling lifespan and longevity. Sirtuins and Cancer SIRT1 limits proliferation capacity and induces senescence in normal, non-transformed cells exposed to chronic stress stimuli and genomic insults. Therefore, sirtuins are thought to protect against the development of cancer. Sirtuins are considered as targets for chemoprevention of age-related cancers by promoting their function in guarding genomic stability and senescence. However, SIRT1 is also found to be overexpressed in a number of cancers such as acute myeloid leukemia (AML), skin, breast, and colon cancer, and is upregulated in chemotherapy-resistant cancer cells. High levels of SIRT1 protects malignant cells from apoptosis via deacetylation and subsequent reduction of the activity of proteins involved in programmed cell death. Among the cancer-relevant substrates of SIRT1 is the tumor suppressor protein p53. SIRT1 deacetylates p53 resulting in repression of its functional activity. Another substrate of SIRT1 is the critical B-cell lymphoma protein 6 (BCL6). Various tumor cell lines cease growth and undergo apoptosis after SIRT1 ▶knockdown. SIRT1 ▶overexpression blocks ▶oncogene-induced senescence. At the ▶epigenetic level, SIRT1 deacetylates ▶histone H4 at lysine 16, a modification which is a common hallmark of human cancer. Thus, inhibition of sirtuins appear to be a promising target for certain cancers which are dependent on high levels of sirtuin activity. Sirtuin Inhibitors and Activators The biological activity of sirtuins can be modulated by small molecule inhibitors and activators. Nicotinamide, a natural byproduct of the sirtuin deacetylase reaction, is a general inhibitor of all sirtuin family members. Other small molecule inhibitors are sirtinol, M15, and splitomycin. The observation that calorie restriction increases life span through increase of the activity of sirtuins in animal models lead to the screening of compounds with sirtuin stimulating activity. Among the

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substances identified were the polyphenols quercetin and piceatannol, and resveratrol, a polyphenol found in the skin of red grapes.

Acknowledgments The work of the author is supported by a grant from the National Genome Research Network 2 (NGFN2) of the Federal Ministry of Education and Research (BMBF), Germany.

References 1. Schwer B, North BJ, Ahuja N et al. (2006) The class III protein deacetylases. In: Verdin E (ed) Histone deacetylases. Humana Press, Totowa, NJ, pp 237–268 2. Minucci S, Pelicci PG (2006) Histone deacetylase inhibitors and the promise of epigenetic (and more) treatments for cancer. Nat Rev Cancer 6:38–51 3. Saunders LR, Verdin E (2007) Sirtuins: critical regulators at the crossroads between cancer and aging. Oncogene 26:5489–5504

Sister Chromatid Exchange Definition SCE; Is the mitotic recombination between the two newly replicated sister chromatids, leading to exchange of genetic information.

Sister-Chromatids Definition Chromatids of the same chromosome, which are connected by a centromer. Nonsister-chromatids are the chromatides of homologous chromosomes ▶Anaphase-promoting complex. ▶Securin

Site-Directed Mutagenesis Definition Is a mutation created at a defined site of known sequence in a DNA molecule of a wild-type, by a molecular biology technique.

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Site-specific Drug Delivery

Site-specific Drug Delivery ▶Targeted Drug Delivery

Sivelestat K AZUHIRO YOSHIDA Department of Surgical Oncology, Gifu University School of Medicine, Gifu, Japan

Definition Sivelestate is a low molecular weight synthetic inhibitor of human ▶neutrophil elastase (NE) (▶Netrophile elastase and cancer), which was produced by Ono Pharmaceutical Company Co., Ltd., in 1991 as ONO-5046, N-[2-{4-(2,2-Dimethylpropionyloxy) phenylsulfonylamino}-benzonyl] aminoacetic acid (MW. 434.47). The structure is illustrated in Fig. 1. This is a potent, specific and intravenously active NE inhibitor and it is widely used to treat patients with lung injury diagnosed as ▶SIRS (systemic inflammatory response syndrome), in Japan at a dose of 0.2 mg/kg/h for 14 days.

Characteristics Mechanisms of Action Sivelestat inhibits the action of NE which is a member of serine proteases produced by polymorphonuclear neutrophils and monocytes/macrophages. NE degrades a broad spectrum of extracellular matrix (ECM) (▶Extracellular remodeling) and cell surface proteins, such as elastin, interstitial collagens, proteoglycans, fibronectin, laminin, and type IV collagens. Under normal physiological conditions, the proteolytic activity of elastase released by recruited neutrophils is strictly regulated by antiproteases, such as alpha-1-protease inhibitor and secretary leukoprotease inhibitor. However,

Sivelestat. Figure 1 Structure of sivelestat, ONO-5046, N-[2-{4-(2,2-dimethylpropionyloxy) phenylsulfonylamino}-benzonyl] aminoacetic acid (MW. 434.47).

under conditions of physiological disturbance, such as the presence of neoplasms, surgical stress, or inflammation, the balance between elastase and antiprotease is disrupted, and the predominant elastolytic activity causes the destruction of peripheral ECM of the lung. NE also cleaves pro-▶transforming growth factoralpha (TGF-α) (▶Epidermal growth factor receptor ligands) on the surface of human airway epithelial cells via its proteolytic activity and releases mature, soluble TGF-α on human airway epithelial cells. Release of TGF-α activates the ▶epidermal growth factor receptor (EGFR) (Epidermal growth factor receptor ligands) signaling cascade (▶Transduction of oncogene), resulting in mucinous secretion in the peripheral airways that might cause severe respiratory complications after major surgical stress or severe inflammatory response. Clinical Aspects Clinical Application in Practice Sivelestat is prescribed clinically for the treatment of various inflammatory diseases in Japan. The antiinflammatory effects of sivelestat are applied for the alleviation of surgical stress, and can reduce morbidity and organ dysfunction, including ▶acute respiratory distress syndrome (ARDS). Considerable amount of NE is released from activated neutrophils which are induced by systemic cytokines including ▶TNF-α, ▶IL-8 and ▶IL-6 produced by ▶macrophages in the lung. SIRS is often observed after surgical injury, which influences on the function of leukocytes and endothelial cells leading to the ARDS or ▶acute lung injury (ALI) with the destruction of the alveolar construction of the lung.

Application to Cancer Treatment as Molecular Targeting Therapy Rapid recurrence or regrowth of tumors are often observed after major cancer surgery, or perioperative surgical complications with SIRS that involve the release of NE by neutrophils and also by cancer cells. On the other hand, cancer cells have multi▶autocrine growth factor and receptor loops including EGFR- TGF-α system for the development of growth and metastatic potential. The growth and invasion activity of cancer cells are stimulated by NE and the growth stimulation occurs via the cleaved TGF-α from the cell membrane, which activates the EGFR and then activates the subsequent intracellular signal transduction. Moreover, NE stimulates the release of several growth factors including ▶PDGF (platelet derived growth factor) and ▶VEGF (vascular endotherial growth factor) that are closely

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Sivelestat. Figure 2 Action mechanism of sivelestat. NE released from activated neutrophils by SIRS cleaves the pro-TGF-α on the cell surface of the cancer cells, which stimulate the growth of the cell via EGFR. Sivelstat blocks the cleaveage of the TGF-α.

related to the growth and angiogenesis of tumor cells. As mentioned above, sivelestat inhibits the NE-induced release of TGF-α from cell membrane of not only neutrophils but also cancer cells (Fig. 2). Therefore, sivelestat might be a new therapeutic tool for the treatment of anti-inflammatory response and also for molecular targeting therapy (▶Molecular therapy) of postoperative cancer patients by inhibiting the rapid cancer cell growth after resection of tumors accompanied with SIRS.

References 1. DiCamillo SJ, Carreras I, Panchenko MV et al. (2002) Elastase-released epidermal growth factor recruits epidermal growth factor receptor and extracellular signal-regulated kinases to down-regulate tropoelastin mRNA in lung fibroblasts. J Biol Chem 277:18938– 18946 2. Kawabata K, Suzuki M, Sugitani M et al. (1991) ONO5046, a novel inhibitor of human neutrophil elastase. Biochem Biophys Res Commun 177:814–820 3. Matsuzaki K, Hiramatsu Y, Homma S et al. (2005) Sivelestat reduces inflammatory mediators and preserves neutrophil deformability during simulated extracorporeal circulation. Ann Thorac Surg 80:611–617 4. Tamakuma S, Ogawa M, Aikawa N et al. (2004) Relationship between neutrophil elastase and acute lung injury in humans. Pulm Pharmacol Ther 17:271–279 5. Wada Y, Yoshida K, Hihara J et al. (2006) Sivelestat, a specific neutrophil elastase inhibitor, suppresses the growth of gastric carcinoma cells by preventing the release of transforming growth factor-alpha. Cancer Sci 97:1037–1043

Sjo¨gren Syndrome P EI -LUN C HOU 1,2 , G REGORY J. T SAY 3 1

Division of Allergy-Immunology-Rheumatology, Department of Internal Medicine, Lin Shin Hospital, Taichung, Taiwan 2 Central Clinic Hospital, Division of Allergy-Immunology-Rheumatology Department of Internal Medicine, Taipei, Taiwan 3 Department of Medicine, Institute of Immunology, Chung Shan Medical University, Taichung, Taiwan

Synonyms Sicca syndrome; Sicca complex; Dry mouth syndrome; Dry eyes syndrome; Keratoconjunctivitis sicca; KCS; Xerostomia; Xerophthalmia

Definition Sjögren syndrome is a chronic, progressive autoimmune disorder that primarily affects the exocrine glands. The classic signs and symptoms include enlargement of the parotid and lacrimal glands, with mucosal dryness manifested by dry mouth (▶Xerostomia) and dry eyes (▶Xerophthalmia) (▶Keratoconjunctivitis sicca). Lymphocytic infiltrates replace functional epithelium, which results in decreased exocrine secretions (exocrinopathy). Numerous features suggest an immunologic etiology. Patients demonstrate hypergammaglobulinemia and have several types of ▶autoantibodies, such as the

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Sjo¨gren Syndrome

rheumatoid factor (RF), antinuclear antibodies (ANA), Ro/SS-A and/or La/SS-B, and antibodies to salivary duct epithelium.

Characteristics Sjögren syndrome is named after the Swedish ophthalmologist Henrik Sjögren. However, the disease was addressed during the nineteenth century in a number of case reports, between the years of 1882 and 1924, describing various combinations of dry mouth, dry eyes, and chronic arthritis. Mikulicz reported in 1892 a man with bilateral parotid and lacrimal gland enlargement associated with massive round cell infiltration. Later on, the link between Sjögren syndrome and ▶malignant lymphoma was described in a classic paper in 1964. More recently, a set of preliminary classification criteria was identified by a European Concerted Action in 1993 and they have been widely accepted. The triad of dry mouth (xerostomia), dry eyes (keratoconjunctivitis sicca), and a connective tissue disease, usually ▶rheumatoid arthritis (▶RA) or ▶systemic lupus erythematosus (SLE), is termed secondary Sjögren syndrome. In the absence of a connective tissue disease, the designation primary Sjögren syndrome (or sicca syndrome) is used. Incidence Sjögren syndrome is the most common form of autoimmunity disorder and is seen mostly in women (female:male ratio 9:1) in the fourth and fifth decades of life. Its frequency in RA is 20% and therefore Sjögren syndrome is most commonly seen in this context. Etiology The etiology of Sjögren syndrome is unknown but may involve genetic and immunological factors. 1. Genetic Factors. ▶A prominent feature of Sjögren syndrome is its genetic predisposition. The polymorphic ▶major histocompatibility complex (MHC) genes are well-documented genetic risk factors for the development of ▶autoimmune diseases overall. With regard to Sjögren syndrome, the most relevant MHC complex genes are the class II genes, more specifically the ▶HLA-DR and ▶DQ alleles. In whites of northern and western European background, including North American whites, Sjögren syndrome is one of several autoimmune diseases associated with the ▶haplotypes HLA-B8, DRw52, and DR3. An association with DR2 has been reported in Scandinavians and DR5 in Greeks. 2. Immunological Factors. ▶Immunological abnormalities include a marked hyperactivity of B lymphocytes with hyperglobulinemia and serum autoantibodies, some organ-specific such as antibodies to salivary duct epithelium, and others nonspecific such as ANA

and rheumatoid factor. Impaired cellular immunity with defective suppressor T cell (▶Regulatory or suppressor T cells) function has been reported in some patients but not in others. Both ▶T lymphocytes and B lymphocytes have been identified in the tissue lesions and local synthesis of ▶immunoglobulins has been demonstrated. Since the ▶lymphocyte infiltration has been demonstrated to be initially periductular in local lymphocyte cytotoxicity directed against ▶antigens on salivary gland duct cells has been postulated. 3. Environment. Among the possible etiologic and triggering factors involved in Sjögren syndrome, the discussion about a relationship between viral infections causing development of autoimmune reactions began some decades ago. The putative role of different ▶viruses in Sjögren syndrome can be viewed in the light that salivary glands are a site of latent viral infections. Potential viral triggers include a number of viruses. Among these, ▶Epstein-Barr virus (EBV) has been widely studied in relation to Sjögren syndrome. A higher prevalence of serum human herpesvirus-6 (HHV-6)-specific antibodies has also been detected in patients with Sjögren syndrome than in normal individuals (36% vs. 10%). Retroviruses are known to infect cells of the ▶immune system and cause abnormalities in immune regulation. High serum titers of antihuman T lymphotropic virus type I (HTLV-1) antibodies and a high prevalence of salivary ▶immunoglobulin A (IgA) class anti-HTLV-1 antibodies in patients with Sjögren syndrome were reported endemically in Japan. Hepatitis C virus (HCV) infection in some populations has been frequently (14%) detected in patients with primary Sjögren syndrome. Analysis of the association between ▶chronic lymphocytic sialadenitis and ▶chronic HCV liver disease showed that histologic features of Sjögren syndrome were significantly more common in HCV-infected patients (57%) compared with controls (5%). ▶Lymphotropic viruses have the potential to trigger the autoimmune process. Some of the immunoreactive regions within the La/SS-B protein have been found to have sequence similarities with proteins of EBV, HHV-6, and human immunodeficiency virus (▶HIV)-1. It seems reasonable that these viruses can promote autoantibody (particularly anti-La/SS-B) production through ▶molecular mimicry or exposure of La/SSB homolog sequences on cellular surfaces after translocation of cryptic self-determinants. Clinical Manifestations Presentation The typical case is of a middle-aged woman who developed sicca symptoms insidiously. Less commonly it presents with parotid swelling or with constitutional

Sjo¨gren Syndrome

symptoms such as malaise and arthralgias. Rarely the presenting feature is cutaneous ▶vasculitis, a cranial neuropathy usually involving the trigeminal nerve, a peripheral neuropathy, or the hyperviscosity syndrome. Sicca symptoms tend to develop more rapidly in primary Sjögren syndrome, when episodic parotitis and involvement of other organs is more common. Involvement of Exocrine Glands Ocular symptoms due to reduced lacrimal secretion and dessication of the cornea and conjunctiva (keratoconjunctivitis sicca) include a gritty or sandy sensation, reduced tearing, photophobia and the presence of a ropey discharge, particularly at the inner canthus. Recurrent infections are also common. In advanced cases, the cornea may be severely damaged and complications include corneal ulceration and occasionally perforation. Decreased saliva results in dryness of the mouth (xerostomia) that leads to dysphagia, abnormalities of taste, and adherence of food to the buccal surface. Widespread involvement of mucosal glands elsewhere may result in dryness of the nose, posterior pharynx, trachea, bronchial tree, skin, and vagina. Involvement of the respiratory tract leads to an increased frequency of upper and lower respiratory tract infections and otitis media. There is parotid gland enlargement in 50% of cases (80% in primary Sjögren syndrome) sometimes accompanied by pain and fever. Extraglandular Involvement Extraglandular lymphoproliferation occurs in 25% of primary Sjögren syndrome, and involves the ▶reticuloendothelial system, kidney, muscle, and lungs. Systemic manifestations are varied and include diffuse interstitial pneumonitis, renal tubular abnormalities, peripheral and cranial neuropathy, nonthrombocytopenic purpura, and the development of pseudomalignant and malignant lymphoid proliferation. Malignant lymphoma occurs more often than can be explained by chance alone, and Sjögren syndrome has often been considered to be a link in the spectrum between autoimmune disorders and lymphoproliferative disorders (Malignant lymphoma, Antonino Carbone and concepts). Diagnosis The most commonly used tests for the detection of dry eyes are the Schirmer I and the rose bengal (alternatively Lissamine green dye) and subsequent scoring according to van Bijsterveld. Schirmer I is performed using standardized tear tests strips. In the European classification criteria, ▶Schirmer I test is positive ▶when the wetting is less than 5 mm in 5 min. The scoring according to van Bijsterveld detects destroyed conjunctival epithelium induced by dryness. Saliva production tests are simple screening tests for salivary

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gland involvement in Sjögren syndrome. Saliva, which is produced by the three major and numerous minor submucosal salivary glands, exhibits great flow variations among healthy individuals and in the same individual under diverse conditions. The test should therefore be standardized; the unstimulated whole saliva collection test is performed for 15 min, and the test is considered positive when 1.5 ml or less whole saliva is collected, being well below the normal mean range. Other tests used to evaluate salivary gland involvement include parotid sialography and salivary gland scintigraphy. The sialography typically shows sialectasis in contrast to the fine arborization seen in normal parotid ductules. In the scintigraphic test, 99m technetium-pertechnate is given intravenously, and in Sjögren syndrome patients, the typical finding is decreased uptake in response stimulation of the parotid and submandibular salivary glands. This test is a sensitive and valid method to measure abnormalities in salivary gland function in the hands of skilled personnel. SS is Diagnosed on the Basis of Either European Classification European Classification. (Preliminary criteria for the classification of Sjögren syndrome, Vitali C et al.) 1. Ocular symptoms – Positive response to 1 of 3 questions pertaining to dry eyes 2. Ocular signs – Positive Schirmer test ( Snail2). The precise mechanism for Snail1-mediated E-cadherin repression requires the recruitment of specific corepressor complexes containing the mSin3 corepressor and histone deacetylase (HDAC1) and HDAC2. In addition, histone and DNA methylases can be recruited by Snail1 to the repressor complexes to mediate epigenetic silencing of the E-cadherin gene, and potentially of

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other target genes. The possibility of Snail factors acting as transcriptional activators should be also considered, since Snail2 seems to positively regulate its own promoter during embryonic development in Xenopus and at least human Snail2 and Drosophila snail contain a transcriptional activation domain as assayed by transfection. Regulation of Expression and Functional Activity Expression of Snail1/Snail2 factors is regulated by a plethora of signals, most of them actively participating in induction of developmental EMT. Among them, growth factors activating ▶receptor tyrosine kinases (RTK) and ▶MAPK pathways (like fibroblast growth factor (FGF), epidermal growth factor (EGF), ▶hepatocyte growth factor/scatter factor (HGF/SF), or oncogenic ▶Ras), ▶TGF-β/BMP signals and ▶Wnt/ β-catenin pathways are major inducers of vertebrate Snail1/Snail2 expression. Significantly, crosstalking between distinct signaling pathways are important for Snail1 induction in different systems, particularly those involving TGFβ, Ras/RTKs, ▶Notch, and/or Wnt/βcatenin pathways. Additional transcriptional regulatory mechanisms can be exerted through steroid receptors in some particular cellular systems, like in breast mammary carcinoma cells in which ligated ▶oestrogen

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Snail Transcription Factors. Figure 2 Snail targets. Snail induces a full EMT through the downregulation of epithelial markers, the upregulation of mesenchymal markers and the acquisition of invasive properties. In addition, Snail regulates cell division and survival. Decreased cell division favors invasion versus tumor growth. Altogether, the ability to move, invade and survive confers Snail-expressing cells a selective advantage to delaminate from the primary tumor and to form distant metastasis. Direct targets are shown in bold.

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Snail Transcription Factors

receptors downregulate expression of Snail1 gene through activation of the specific ▶MTA3-NuRD correpressor complex. Significantly, Snail factors can exert an autoregulatory control, underlining the necessity of tight regulation of Snail levels. Besides transcriptional regulation, functional activity of Snail factors can be modulated at posttanscriptional levels. Phosphorylation of Snail1 by GSK3β (▶Wnt signaling) in Ser residues located at the central DB and NES domain induces Snail1 nuclear export and cytoplasmic degradation, while potential modification of neighboring Lys residues, phosphorylation by Pak1 and/or interaction with specific ▶zinc transporters (like LIV1) positively control Snail1 nuclear localization, protein stability and repressor activity. Much less is known on posttranscriptional regulatory mechanisms of Snail2, except for the induction of proteasome degradation mediated by Ppa2. Additional Snail Functions Apart from their implication in EMT, Snail factors can regulate other cellular processes, related to cell proliferation and cell survival with important implications during embryonic development, tumor progression and other pathologies. In some particular cell/ tissue contexts, Snail1 expressing cells have a low proliferative potential, exhibiting a partial G1/S cell cycle arrest, a property that may ease migration of cancer cells during tumor progression. For Snail targets related to cell proliferation see Fig. 2. Snail factors also participate in protection against cell death induced by different external cues, thus acting as survival mediators. Significantly, the prosurvival action of Snail1/Snail2 factors has been demonstrated during embryonic development and in human carcinoma cells under genotoxic stress induced by chemotherapeutic agents and in radioresistance of hematological precursor cells. Snail1/Snail2 negatively regulate p53 (▶p53 protein) -dependent (like ▶Puma) and p53-independent genes (for additional targets see Fig. 2). Thus, Snail factor expression can contribute to the acquired resistance to ▶apoptosis of tumor cells, a characteristic that might be crucial for the metastatic (▶metastasis) process. It is very likely that the Snailmediated pro-survival/resistance function is associated with EMT, as observed in hepatocytes in culture. Nevertheless, the different functions of Snail factors such as induction of EMT, reduced proliferation and survival can be dissociated in some cellular contexts, at least during embryonic development. Clinical Significance SNAIL1 expression was originally detected in several carcinoma cells associated to E-cadherin downregulation

and invasiveness. Importantly, SNAIL1 expression was also detected at the E-cadherin negative invasive regions of mouse skin carcinomas (▶skin carcinogenesis), human breast carcinomas and hepatocarcinomas (▶hepatocellular carcinoma), supporting its in vivo implication in induction of tumor invasion. Further studies in different tumor series indicate SNAIL1 expression associated to lymph-node status and/or distant metastasis in breast and ovarian carcinomas (▶ovarian cancer), colorectal tumors (▶colon cancer) and squamous cell carcinomas, while SNAIL2 has been implicated in ▶melanoma metastasis. SNAIL1/2 expression in different tumor series correlates with E-cadherin downregulation and/or induction of several ▶matrix metalloproteinases (MMPs). The expression of specific MMPs (i.e., MMP2, MMP9) has been found to be transcriptionally upregulated by Snail1/2 in different cell model systems, further supporting the implication of Snail factors as active invasion inducers through the coordinated regulation of the molecular players of the process. The recent identification of SNAIL1 at the tumor-stroma interface of restricted tumor areas strongly support the implication of SNAIL1 at focally restricted invasion areas where the EMT processes are most likely to occur. Interestingly, SNAIL1 expression has been associated to tumor recurrence in breast carcinoma and to poor prognosis in hepatocarcinomas, while SNAIL2 has been recently associated to poor prognosis or overall patient survival in several tumor types (i.e., colon carcinomas and squamous cell carcinomas). It should be important to analyze in the near future whether the implication of SNAIL1/SNAIL2 in tumor recurrence might be related to the prosurvival function of Snail factors, or perhaps to a potential contribution of Snail factors to cell stemness. Further studies in large tumor series using highly specific anti-SNAIL1 antibodies, recently developed, (and hopefully anti-SNAIL2 in the near future) are certainly required. This, together with additional functional studies in cellular models and, most importantly, in defined mouse model systems of tumor progression, will contribute to get a complete understanding of the clinical relevance of Snail factors in human tumors.

References 1. Thiery JP (2002) Epithelial-mesenchymal transitions in tumour progression. Nat Rev Cancer 2:442–454 2. Nieto MA (2002) The snail superfamily of zinc-finger transcription factors. Nat Rev Mol Cell Biol 3:155–166 3. Barrallo-Gimeno A, Nieto MA (2005) The snail genes as inducers of cell movement and survival: implications in development and cancer. Development 132: 3151–3161

snRNP

SNAILH (Human) ▶Snail Transcription Factors

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formation. More then 300 different ones have been described in humans. ▶Cajal Bodies

SNP SNCA Definition

A gene on human chromosome 4 that encodes the α▶synuclein protein. Synonym NACP, PARK1 or PARK4.

Definition

Single nucleotide ▶polymorphism: single base variation in the DNA, with a population frequency of >1%. ▶Metabolic Polymorphisms and Cancer Susceptibility

SNP Array SNCB Definition A gene on human chromosome 5 that encodes the ▶synuclein β protein.

Definition High-density arrays containing thousands of single nucleotide ▶polymorphisms (SNPs). ▶Modifier Loci

snRNA SNCg Definition A gene on human chromosome 10 that encodes the ▶synuclein γ protein. Also known as ▶BCSG1.

Definition Small nuclear RNA, the RNA components of the snRNPs involved as part of snRNPs in mRNA splicing. ▶pre-mRNA Splicing ▶Cajal Bodies

snRNP snoRNA Definition Definition Small Nucleolar RNAs, are small RNAs (between 60 and 300 nucleotides long) found in the nucleolus. They function as guides for site specific modifications of ribosomal RNA, 2’-O-methylation and pseudouridine

Small nuclear ribonucleoprotein; A complex composed of small nuclear RNAs (snRNA) and proteins. snRNPs are important for splice site recognition and catalysis of the splicing reaction. ▶pre-mRNA Splicing

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SOCS

SOCS Definition

The ▶suppressors of cytokine signaling (SOCS) family of proteins are key physiological regulators of cytokine responses. Several SOCS proteins have been implicated in the negative regulation of cytokine signaling pathways including STATs. ▶Signal Transducers and Activators of Transcription in Oncogenesis ▶Suppressors of Cytokine Signaling

SOD Definition

▶Superoxide dismutase. ▶Photodynamic Therapy

Sodium Chloride ▶Salt Intake

Solar Light Induced Cancer ▶Photocarcinogenesis

Solar Ultraviolet Light T HOMAS M. R U¨ NGER Department of Dermatology, Boston University School of Medicine, Boston, MA, USA

Definition Solar ultraviolet light is ultraviolet light emitted by the sun.

Characteristics The sun emits ultraviolet radiation as part of the electromagnetic spectrum. It is usually subdivided, rather arbitrarily, into UVA (400–315 nm), UVB (315– 290 nm), and UVC (200–290 nm). UVA has been further subdivided into UVA1 (400–340 nm) and UVA2 (340–315 nm). More than 95% of the sun’s UV radiation reaching the earth’s surface is UVA. Practically all of the UVC, and much of the UVB, is absorbed by the oxygen and ozone in the earth’s atmosphere, so that ultraviolet radiation below 290 nm is virtually undetectable at ground level. Nevertheless, the remaining UV radiation can still be absorbed by biological molecules (DNA, proteins, lipids) and elicit photochemical and photobiological responses. A light-absorbing molecule is called a chromophore. Upon absorption of the radiation’s energy, this chromophore is elevated to an excited state. Ensuing photochemical reactions may either change the chromophore directly, or, through energy transfer in a so-called photosensitized reaction, indirectly change a molecule other than the chromophore. Effects of Exposure to Solar Ultraviolet Light on Skin Exposure of skin to solar ultraviolet light has both short-term and long-term effects. Visible short-term effects are sunburning and/or tanning. Long-term effects are photoaging and induction of skin cancers (▶skin carcinogenesis). Skin cancers clearly linked to sunlight exposure are ▶basal cell carcinomas and ▶squamous cell carcinomas, and ▶malignant melanomas. An individual’s tendency to develop sunburn and tanning after sun exposure correlates with the individual’s susceptibility to long-term effects as well. Therefore, those individuals with higher acute sun sensitivity are generally also more at risk for developing skin cancers after chronic UV exposure. Within the skin, the depth of penetration of UV light is wavelength-dependent – i.e. the longer the wavelength, the deeper the penetration. While UVA readily reaches the dermis, including its deeper portions, most of the UVB is absorbed in the epidermis, and only a small proportion reaches the upper dermis. UVC, if it reached the earth’s surface, would be absorbed or reflected predominantly in the stratum corneum and in upper layers of the epidermis. Both short-term and longterm effects of exposure to UV light are wavelengthdependent. Previously, it was .thought that only UVB is carcinogenic, and only UVA causes photoaging. Today, however, we know that both UVA and UVB cause skin cancer and photoaging. The relative contribution of each, however, continues to be a matter of controversy. Photocarcinogenesis involves a stepwise accumulation of specific genetic changes in a single cell, with

Solar Ultraviolet Light

Solar Ultraviolet Light. Figure 1 Photocarcinogenesis chain of events.

subsequent clonal expansion. Usually, it takes decades until a tumor arises. It is commonly accepted that UV-induced skin cancers develop along a photocarcinogenesis chain of events that involves (Fig. 1): . DNA damage formation after exposure to solar ultraviolet light . mutation formation following DNA damage formation . malignant transformation following mutation formation. DNA Damage Induced by Solar Ultraviolet Light Different wavelengths of UV light induce different types of DNA damage. UVC and UVB are capable of exciting the DNA molecule directly and subsequently generating ▶DNA photoproducts. DNA photoproducts are dimers, formed by covalently binding two adjacent pyrimidines in the same polynucleotide chain. The two major types of pyrimidine dimers are ▶cyclobutane pyrimidine dimers and ▶6,4-photoproducts. ▶Cyclobutane-pyrimidine dimers (CPDs) are the most common DNA photoproducts formed with solar ultraviolet irradiation of the skin. They are generated upon saturation of the 5,6 double bonds and formation of a four-membered cyclobutyl ring. Cyclobutane-pyrimidine dimers are observed at all possible di-pyrimidine sites, with the thymine–thymine dimer (T–T) being the most common, followed by C–T and T–C dimers. C–C dimers are the least common. The formation of CPDs is not a random phenomenon: it is influenced by the sequence and conformational context of the affected DNA sequence. The 6,4-photoproduct is a non-cyclobutane dipyrimidine photoproduct, which is formed upon covalent linkage between the C-6 position of one pyrimidine and the C-4 position of the 3′ adjacent pyrimidine. The T–C (6–4) dimer is the most common dimer of this type, but C–C and T–T dimers are also observed after UV irradiation. Upon further irradiation with UV wavelengths between 280 and 360 nm, the normal isomers of

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6,4-photoproducts can be converted to their Dewar valence isomers, which are less mutagenic than the normal isomers but may still contribute to solar mutagenesis. A few other rare DNA photoproducts have been described, such as complex purine lesions and pyrimidine hydrates, but their physiological significance in the photobiology of human skin is unknown. The absorption maximum of DNA is at 260 nm. This makes UVC the most effective wavelength for the induction of DNA photoproducts in naked DNA. However, in vivo, due to the absorption of shorter wavelengths in upper layers of the epidermis, 300 nm (UVB) is the most effective wavelength for inducing DNA photoproducts in the basal layer of the epidermis, the anatomical location from which most skin cancers arise. While UVA is much less effective in generating DNA photoproducts, UVA-induced DNA photoproducts may still have a significant contribution to sunlight-induced mutation formation, because of the much higher abundance of UVA in sunlight, as compared to UVB. UV radiation can also damage DNA indirectly. After absorption of photons by chromophores other than DNA, energy can be transferred either to DNA (type I photosensitized reaction), or to molecular oxygen, with ▶reactive oxygen species in turn being able to damage DNA (type II photosensitized reaction). UV-induced reactive oxygen species include singlet oxygen, and probably other non-radical and radical reactive oxygen species, such as hydrogen peroxide and the superoxide radical. Even the highly reactive hydroxyl radical may be formed by a reaction of hydrogen peroxide with nuclear metals through a Fenton reaction. This oxidative stress not only affects DNA, but also membranes and proteins. The relative contribution of each (oxidative membrane damage, oxidative protein damage, ▶oxidative DNA damage) to the different biologic effects of UV irradiation has not been well established. Singlet oxygen and the other reactive oxygen species react predominantly with guanine and generate several DNA changes including the mutagenic and well studied 7,8-dihydro-8oxyguanine (8-oxoG). It remains a matter of debate, whether the mutagenic properties of UVA (in particular UVA1: 340–400 nm) are mediated by ▶oxidative DNA damage or by the weak ability of UVA to form a few pyrimidine dimers. Mutations Induced by Solar Ultraviolet Light Cancer development requires the accumulation of numerous genetic changes in a single cell. Solar ultraviolet light induces mutations in several key genes involved in skin cancer development, e.g. ▶ras oncogenes, p53 (▶p53 protein, histological and clinical aspects), and PTCH tumor suppressor genes. The p53 tumor suppressor gene encodes a 53 kDa transcription factor that plays a critical role in cellular DNA damage responses.

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Solar Ultraviolet Light

Mutations in this gene can be found in most cutaneous squamous cell carcinomas and their precursors (actinic keratoses). In addition, chronically sun-exposed skin harbors many keratinocyte clones with p53 mutations, which are undetectable by light microscopy. This indicates that p53 mutations are an early event in the pathogenesis of UV-induced cutaneous squamous cell carcinomas. It is well established that different types of UVinduced DNA damage can lead to the formation of a variety of different mutations, either during attempts by the cell to repair (▶repair of DNA) or to replicate these lesions. Most of the p53 mutations in cutaneous squamous cell carcinomas and its precursors are C → T single and CC → TT tandem transition mutations at dipyrimidine sites. This spectrum of p53 mutations is very different from p53 mutations found in malignancies of internal organs; the latter do not have the preponderance of C → T or CC → TT mutations. This, together with the fact that pyrimidine dimers most commonly cause C → T and some CC → TT mutations, provides convincing evidence for a crucial role of pyrimidine dimers in cutaneous photocarcinogenesis. Therefore, C → T, and especially CC → TT mutations have been termed “▶UV-signature mutations.” They are, in fact, “signature mutations” for DNA photoproducts. Protection Against Photocarcinogenesis To ensure that most of the damage inflicted by sun exposure will not lead to the formation of skin cancer, UV-exposed cells have several lines of defense against the photocarcinogenesis cascade Fig. 2. First line of defense – to avoid formation of DNA damage: In order to prevent DNA damage as a consequence of UV exposure, the human epidermis is protected by melanin, the expression of which can be increased in response to ultraviolet light (tanning

response) to better protect against subsequent UV exposures. Melanin is a mixture of different polymerized pigments that absorb UV radiation. It is produced by melanocytes and transferred to keratinocytes, where it covers the upper pole of the nucleus in a microparasol to protect the nuclear DNA from the damaging effects of ultraviolet light. Skin can also increase its thickness, which reduces UV exposure of the basal layer, and it contains antioxidative enzymes, which quench reactive oxygen species and reduce the formation of oxidative DNA damage. Second line of defense – to avoid mutation formation at sites of DNA damage: To counteract potentially mutagenic effects, UV-induced DNA damage requires excision and replacement of damaged nucleotides by DNA repair pathways. No correction procedure is absolutely exact and error-free. If it were, UV-induced skin cancers would not occur in DNA repair-proficient individuals. DNA photoproducts (pyrimidine dimers) are mutagenic, but they can be repaired by the nucleotide excision repair (NER) pathway. As exemplified by the hereditary disorder ▶xeroderma pigmentosum, a defect in this repair pathway increases UV sensitivity and UV mutagenesis in cells, and non-melanoma and melanoma skin cancers in vivo. The NER pathway has become well understood, in part through the identification and characterization of the different xeroderma pigmentosum genes. Individual cancer and skin cancer risks are determined not just by a pronounced NER deficiency, as in xeroderma pigmentosum, but also by more subtle variations in DNA repair efficiency, e.g. as a consequence of polymorphism in DNA repair genes. Likewise, a decline in DNA repair efficiency with age has been linked to the increasing risk of skin cancer with advancing age.

Solar Ultraviolet Light. Figure 2 Inherent cellular defense mechanisms against the photocarcinogenesis chain of events.

Solar Ultraviolet Light

Cells from patients with xeroderma pigmentosum variant have an intact NER, yet a phenotype that is indistinguishable from the other xeroderma pigmentosum complementation groups. Cells from these patients do not have a deficit in repairing DNA photoproducts, but a deficiency in what they do with unrepaired DNA photoproducts during replication in the S-phase of the cell cycle. Replicative DNA polymerases usually stall at unrepaired DNA lesions and detach from the DNA strand. For this situation, cells have a number of specialized DNA polymerases that are able to bypass different kinds of DNA damage and extend replication forks through damaged sites. Different polymerases perform this “translesional DNA synthesis” (▶translesion DNA polymerases and cancer) with variable fidelity. Due to a mutation in the pol-η gene, cells from patients with XP variant lack the particular ability of DNA polymerase-η to bypass thymine–thymine dimers with correct insertion of two A residues. This indicates that NER does not always repair all DNA lesions and that the function of a high-fidelity translesional DNA polymerase is crucial for maintaining genomic stability if cells enter S-phase with unrepaired DNA damage. In cells from patients with xeroderma pigmentosum variant, NER can remove most of the thymine–thymine dimers, but, because polymerase-η is missing, any remaining dimers are more likely to be bypassed by polymerases that insert incorrect residues. This causes a UV-▶mutator phenotype. If DNA polymerase-η or any other specialized translesional DNA polymerase fails to bypass DNA damage during S-phase, the cell is faced with a stalled replication fork. In these cases, DNA recombination repair, which utilized strand invasion from the sister chromatid, can resolve the stalled replication forks. Following formation of DNA damage by solar ultraviolet light, cells undergo significant changes. The transcription factor p53 (▶p53 protein; biological and clinical aspects), which is both upregulated and activated following exposure to solar ultraviolet light, plays a pivotal role in these DNA damage responses. Genome-protecting effects of p53 in response to UVexposure are manifold: . it mediates a cell cycle arrest that allows for more time to repair DNA damage and prevents replication of damaged DNA; . with overwhelming DNA damage it may induce apoptosis (an affect often seen as sunburn cells, which are apoptotic keratinocytes formed after high dose sun exposure) and thereby prevent survival of damaged cells; . and it augments DNA repair capacity. Loss of these protective responses with acquired inactivating p53 mutations results in a UV-mutator phenotype. This explains why p53 plays such a prominent role early in photocarcinogenesis.

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Third line of defense – to prevent that cells with mutations expand clonally and form skin cancers: Even after mutations have fixed the inflicted damage for the lifetime of the affected cells, the organism still removes most of these cells, for example, through immune surveillance. However, solar ultraviolet light has several immuno-suppressive effects, which contribute to the carcinogenic properties of solar ultraviolet light. Ultraviolet light is therefore a double-edge sword with regard to photocarcinogenesis: Not only does it generate DNA damage that entails mutation formation and malignant transformation, its immunosuppressive properties and the induction of specific tolerance to UV-induced skin tumors also reduces the ability of the host immunedefense to recognize and remove malignant cells. The latter also impairs the immune-surveillance of cells infected with oncogenic viruses (such as certain HPV types commonly found in squamous cell carcinomas of transplant patients) and may thereby further promote skin cancer formation. In addition to the intrinsic protective mechanisms against the chain of events leading to the formation of skin cancer, there are extrinsic protective agents and behaviors that can help individuals to reduce their individual skin cancer risk. In order to prevent or reduce UV irradiation of the skin, one can avoid the sun, especially around noontime, stay in the shade, wear protective clothing, and/or wear sunscreens. Sunscreens are topical preparations which attenuate UV radiation before it enters the skin by reflection, absorption, or both. Sunscreens not only protect against the acute skin injury of sunburn, but also against UV-induced immune suppression, photoaging, and skin cancer. The sun protection factors (SPF) of sunscreens, however, which indicate by what factor sunburn is prevented by sunscreen use, do not correlate well with protection factors for other non-erythema endpoints. Therefore, the SPF cannot be regarded as a reliable guide to non-erythema and chronic endpoints. Topical application of DNA repair enzymes has been shown to increase DNA repair in skin cells and to accelerate removal of DNA photoproducts. In patients with xeroderma pigmentosum, such applications have been reported to reduce the occurrence of actinic keratoses. This indicates that it may be possible to prevent the formation of mutations after the introduction of DNA photoproducts with the use of such “enzymatic sunscreens.” Hereditary Disorders with Increased Photocarcinogenesis Many disorders with an increased skin cancer risk after exposure to solar ultraviolet light are characterized by a deficiency in the intrinsic protective mechanisms discussed above. For example, men with androgenetic alopecia have a much higher risk of developing

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Solitary Bone Plasmacytoma

skin cancers on the scalp than men who have retained their UV-protective hair cover. Lack of protective melanin, as in oculo-cutaneous albinism, increases the amount of DNA damage in the basal layer of the epidermis after UV irradiation and, subsequently, the risk of skin cancer. The different DNA repair defects of xeroderma pigmentosum and the DNA damage-processing defect of xeroderma pigmentosum variant (see above) generate a UV-mutator phenotype, with an increased chance that DNA damage will result in the formation of a mutation. Some cases of familial melanoma are caused by a germ-line mutation in the CDKN2A locus, which encodes two gene products, p16INK4a and p14ARF. Intact p16 induces a G1 cell cycle arrest by inhibiting ▶cyclin-dependent kinases 4 and 6, which in turn inhibit the phosphorylation of the ▶retinoblastoma protein. Loss of p16INK4a function, therefore, entails a loss of the G1 checkpoint, leading to abnormal proliferation, unrestricted progression into S-phase, and, importantly, no cell cycle arrest after UV irradiation. P14ARF is an upstream regulator of p53, another important factor mediating UV-induced growth arrest. The disruption of cell cycle control with loss of CDKN2A does not, however, explain why loss of p16/ p14 function predisposes mostly to malignant melanoma, and only to a much lesser degree to internal neoplasias, namely pancreatic cancer. A recent finding that loss of p16INK4A- or p19ARF-function also impairs the ability of affected cells to repair DNA photoproducts, leading to a UV-mutator phenotype, might be the missing link, explaining why alteration in CDKN2a predisposes mainly to UV-induced tumors. Similarly, p53 protects against UV mutagenesis by inducing a cell cycle arrest after UV-induced damage, by inducing apoptosis in cells with overwhelming UV-induced DNA damage, and by stimulating DNA repair by directly binding to DNA repair enzymes. Consequently, loss of p53 function has been shown to result in a UV-mutator phenotype and reduced repair of UV-induced DNA damage. Li–Fraumeni syndrome is characterized by a germ-line mutation of the p53 gene, and predisposes to malignancies of various internal organs and cutaneous melanoma. Patients with the nevoid basal cell carcinoma syndrome, who develop multiple basal cell carcinomas, especially in UV-exposed areas, harbor germline mutations in the PTCH gene. PTCH belongs to the ▶hedgehog signal transduction pathway that transmits extracellular growth and differentiation signals to the nucleus. While many of the PTCH mutations in sporadic basal cell carcinomas are UV signature mutations (C → T and CC → TT), their frequency is lower than in p53, and it is unclear whether sporadic PTCH mutagenesis is purely UV induced.

References 1. Rünger TM (2008) Ultraviolet light. In. Bolognia JL, Jorizzo JL, Rapini RP (eds) Dermatology. Mosby, Elsevier, London, pp. 1321–1331 2. Rünger TM, Kappes UP (2008) Mechanisms of mutation formation with long-wave ultraviolet light (UVA). Photodermatol Photoimmunol Photomed 24:2–10 3. Friedberg EC, Walker GC, Siede W (eds) et al. (2005) DNA repair and mutagenesis. ASM Press, Washington 4. Wikonkal NM, Brash DE (1999) Ultraviolet radiation induced signature mutations in photocarcinogenesis. J Invest Dermatol Symp Proc 4:6–10 5. Rünger TM, Vergilis I, Sarkar-Agrawal P et al. (2005) How disruption of cell cycle regulating genes might predispose to sun-induced skin cancer. Cell Cycle 4: 643–645

Solitary Bone Plasmacytoma ▶Plasmacytoma

Solitary Extramedullary/Extraosseous Plasmacytoma ▶Plasmacytoma

Solitary Plasma Cell Myeloma ▶Plasmacytoma

Solute Carrier Transporters Definition SLC Transporters; Are a large group of membrane transporters that function as secondary-active or passive transporters in the translocation of ions and small molecules, including drugs, across biological

Somatostatin

membranes. The group comprises more than 360 members in 46 families. ▶Membrane Transporters

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Somatic Recombination of V, D and J Segments ▶V(D)J Recombination

Somatic Cells Definition

Somatic Stem Cells

Cells other than those of the gamete-forming germ line. ▶Adult Stem Cells ▶Somatic Tissue

Somatic Cross-Over Point Mapping Definition Is a method exploiting the fact that certain genetically unstable cells, e.g. in ▶Bloom syndrome, show excessive DNA cross-overs within the BLM gene itself. This leads to restoration of BLM function in cells inheriting two different mutations in BLM.

▶Adult Stem Cells

Somatic Tissue Definition Most tissues in a multicellular organism. Cells in these tissues do not contribute to the production of gametes and thus mutations in these tissues are not heritable. In humans, many somatic tissues contain cells that are dividing or capable of dividing and thus are capable of renewal, repair, and sometimes regeneration. ▶Aging

Somatic Hypermutation Definition Somatic hypermutation is a process by which somatic mutations are introduced at a high rate into the variable region parts of immunoglobulin genes. This process is specifically activated in germinal centre B cells. As a result of somatic hypermutation, antibody variants are generated that differ by a few aminoacids from the original antibody. In the germinal centre reaction, B cells expressing antibodies with increased affinity due to favorable mutations can be selected. Somatic hypermutation may be involved in the generation of B cell lymphomas when non-Ig genes are targeted or when chromosomal translocations happen as mistakes of the process. ▶Hodgkin and Reed/Sternberg Cell ▶Diffuse Large B-Cell Lymphoma

Somatostatin M ICHAEL C. F RU¨ HWALD Department of Pediatric Hematology and Oncology, University Children’s Hospital Muenster, Muenster, Germany

Synonyms Somatotropin release inhibiting factor; SRIF

Definition Somatostatin is a bioactive peptide that exists in the two isoforms SST-14 and SST-28, of 14 and 28 amino acids, (SST-14) and SST-28, respectively. It acts as a ▶neuropeptide, (neurotransmitter), is produced by neurons and endocrine-like cells and is distributed

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Somatostatin

throughout the central and peripheral nervous system, endocrine pancreas, gut, thyroid, adrenals, submandibular glands, kidneys, prostate and placenta. Many tumor cells, immune cells and inflammatory cells produce somatostatin.

Characteristics Somatostatin was initially isolated as an inhibitor of growth hormone (GH) release, but is now best described as a multifunctional peptide, capable of inhibiting secretory processes and cell proliferation. Hypothalamic somatostatin inhibits the release of pituitary growth hormone (GH), thyroid-stimulating hormone (TSH) and corticotropin releasing hormone (CRH). As a neurotransmitter it affects several functions such as autonomous, sensory, locomotive and cognitive. Locally produced somatostatin generally inhibits gut exocrine secretion (e.g. on insulin, glucagon, gastrin), suppresses stomach, small intestine and gall bladder motility, and mediates vasoconstriction, especially of splanchnic vessels. In the adrenals somatostatin inhibits angiotensin II stimulated aldosterone secretion and in the kidneys hypovolemia stimulated renin release. In the immune system it blocks the release of cytokines, including IFN-γ and IL-6, and limits the proliferation of lymphocytes, intestinal mucosar and inflammatory precursor cells. Furthermore, it blocks the action of growth factors such as ▶IGF1, ▶EGF and ▶PDGF. The plasma half life of somatostatin is less than 3 min. Somatostatin Secretion and Gene Expression The human somatostatin gene is encoded on chromosome 3q28 in a prehormone form (▶preprosomatostatin) with a mRNA of 351bp. The two bioactive forms SST-14 and the N-terminally extended SST-28 are produced by proteolytic cleavage of prosomatostatin. SST-14 is the peptide that is found predominantly. However, up to 30% of immunoreactive SST in the brain is SST-28. Somatostatin secretion is triggered by membrane depolarization, certain ions, nutrients and neurohormones/neuropeptides. Potent stimulators are glucagon, growth hormone releasing hormone (GHRH), neurotensin, corticotropin releasing hormone (CRH), calcitonin gene related peptide (CGRP) and bombesin. Somatostatin gene expression is stimulated by multiple cytokines and growth factors including IGF1 and 2, GH, IL-1, -6,-10, TNF-α, IFN-γ, NMDA receptor ligands and by steroid hormones such as testosterone, glucocorticoids and estradiol. Insulin, leptin, ▶TGF-β and some glucocorticoids inhibit somatostatin expression. Transcription of the somatostatin gene is regulated by the intracellular second messengers cAMP, cGMP, NO and Ca2+ and the associated pathways involving

▶CREB and ▶CBP (cyclic AMP response element binding protein and CREB binding protein). Somatostatin Receptors (sst) Somatostatin binds to five currently known G-protein coupled seven transmembrane receptor subtypes (sst1–5) that were initially classified according to their differential binding of somatostatin analogues. The genes for sst1,3,4,5 lack introns, while sst2 contains at least three potential transcriptional start sites, one of which is located in exon 1, 50 kb upstream of the start site in exon 3. All cloned receptor subtypes contain recognition motifs for glycosylation and phosphorylation. Homo- and heterodimerization of the receptors as well as receptor internalization have been described. Upon ligand binding sst induce a multitude of intracellular effects mediated by varying G-proteins coupled to second messengers. All receptors block the formation of cAMP by inhibiting ▶adenylyl cyclase and activate tyrosine phosphatases (Table 1). Molecular Basis of Somatostatins Antiproliferative Effects Somatostatin limits the proliferation of tumor cells in vitro and in vivo directly and indirectly. Direct regulation is by somatostatin receptors (ssts) that are localized on neoplastic cells; indirect regulation is exerted via ssts on non-neoplastic cells. Mechanistically, this is done by inhibiting the secretion of growth promoting hormones and growth factors (e.g. IGF-1), by promoting vasoconstriction (which leads to a reduced blood flow to tumor tissue), by inhibiting angiogenesis and by influencing the function of immune cells. Theblock of secretion is due to inhibition of the second messengers cAMP and Ca2+ and the inhibition of exocytosis in a G-protein dependent manner. The direct antiproliferative effects of somatostatin appear to be largely due to the activation of protein phosphatases. Somatostatin induced protein tyrosine phosphatases (PTP) dephosphorylate tyrosine kinases of receptors for growth promoters such as insulin and possibly EGF and IGF-1. Furthermore, somatostatin inactivates MAPK activity via PTP dependent dephosphorylation (sst2), PTP-dependent Raf-1 inactivation (sst3) and inhibitionof cGMP formation (sst5). Activation of PTP is also involved in somatostatin induced apoptosis. While in CHO-K1 cells transfected with each individual sst, sst3 appears to induce apoptosis by activation of TP53, independent of G1 arrest, all other ssts prompt G1 arrest and induction of Rb. A base pair change in the sst2 gene, found in a lung cancer cell line (COR-L103), lead some authors to the assumption of a tumor suppressor role for somatostatin receptors.

Somatostatin Somatostatin. Table 1

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The somatostatin receptor family (sst) (modified after Patel) sst1

Chromosome 14q13 mRNA (kb) 4.8 Amino acids 391 Molecular weight (kD) 53–72 Ligand affinity (IC50 nM) SST-14 0.1–2.26 SST-28 0.1–2.2 Octreotide 290–1,140 RC-160 >1,000 Seglitide >1,000 CH275 3.2–4.3 L-797,591 1.4 L-779,976 2,760 L-796,778 1,255 L-803,087 199 L-817,818 3.3 Signal transduction Adenylyl cyclase ↓ Tyrosine phosphatase ↑ MAP kinase ↑ Ca2+ -influx ↓ Na+/H+ exchange ↑ Phospholipase C activity Phospholipase A2 activity Tumor expression Gastro- enteropancreatic tumors

sst2A

sst3

sst4

sst5

17q24 8.5 (?) 369 71–95

22q13.1 5.0 418 65–85

20p11.2 4.0 388 45

16p13.3 4.0 363 52–66

0.3–1.3 0.2–4.1 0.4–2.1 5.4 0.1–1.5 >1,000 1,875 0.05 >10,000 4,720 52

0.3–1.6 0.3–6.1 4.4–34.5 31 27–36 >1,000 2,240 729 24 1,280 64

0.3–1.8 0.3–7.9 >1,000 45 127-> 1,000 4.3–874 170 310 8,650 0.7 82

0.2–0.9 0.05–0.4 5.6–32 0.7 2–23 >1,000 3,600 4,260 1,200 3,880 0.4

↓ ↑ ↓ ↓

↓ ↑ ↑↓

↓ ↑ ↑

↓ ↑ ↓



↑↓ ↑

Gastro- entero-pancreatic Gastro- enteroMeningioma tumors pancreatic tulipoma mors Medullary thyroid Growth hormone (GH) Medullary thyroid carcinoma and thyroid stimulating carcinoma hormone (TSH) producing pituitary adenomas Ovarian cancer Breast carcinoma Ovarian cancer Prostate cancer Neuroblastoma Pheochromocytoma Pheochromocytoma Medulloblastoma Meningioma Small cell lung cancer (SCLC) Hodgkin lymphoma Peritumoral vessels

Pituitary adenoma Not in nonfunctioning pituitary adenoma

Characteristics of the five cloned human ssts and information about their distribution in human cancer. Methods that rely on tissue homogenates are unreliable since ssts are found in immune cells and veins surrounding the tumor tissue. Subtype selectivity of ligands is indicated by bold italics for IC50. Subtype expression has only been studied in a limited number of tumor types.

Clinical Relevance Somatostatin Analogue Therapy The demonstration of receptor subtype expression in malignancies has paralleled the creation of subtype

selective receptor ligands. While the best characterized and oldest analogue, the octapeptide octreotide (plasma half life 2 h), exhibits a preference for sst2 with lower affinities for sst5 and sst3, highly specific nonpeptide

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Somatostatin Receptor Scintigraphy

agonists for each of the five subtypes have been developed. The longest clinical experience exists for the treatment of hormone secreting tumors with octreotide and its microencapsulated longacting release form (LAR). The classic indication for somatostatin analogue therapy is a growth hormone secreting pituitary adenoma in ▶acromegaly. Furthermore octreotide and other somatostatin analogues have been used in the treatment of carcinoids, insulinomas, gastrinomas, ▶VIPomas, glucagonomas and somatostatinomas, producing symptomatic or subjective responses in 30–75%, and significant reduction in tumor size in 10–15% of patients. In clinical studies octreotide and other analogues have been used as single agents or in combination with conventional cytostatic drugs with varying results in carcinomas of the breast, prostate, pancreas, colorectum, thyroid and lung, inmeningiomas, ▶neuroblastomas and Non-Hodgkinlymphomas.

Somatostatin Receptor Imaging and Radiotherapy The in vitro detection of somatostatin receptors on a multitude of tumor tissues has led to the development of ▶somatostatin receptor scintigraphy (SRS). Apart from neuroendocrine tumors expressing ssts, SRS has successfully been used in the imaging of pheochromocytomas, non small cell lung cancers (NSCLC), meningiomas, ▶breast cancer, ▶gliomas, ▶medulloblastomas, Non-Hodgkin and Hodgkin lymphomas (▶Hodgkin disease), granulomatous disease, Sjögren syndrome and rheumatoid arthritis. Binding of radioactive somatostatin analogues has been used in radioreceptor-guided surgery as an asset in the surgery of neuroendocrine gastroenteropancreatic tumors and neuroblastomas with occult metastases. After ligand binding a fraction of receptors are internalized. This phenomenon has been used for clinical studies of in situ radiotherapy using 111Indium or 90Yttrium labeled somatostatin analogues in terminally ill patients with neuroendocrine tumors.

General Clinical Applications In carcinoids and neuroblastomas the level of somatostatin or somatostatin receptor expression (e.g. by SRS) has been reported to correlate with tumor differentiation and therapeutic outcome of the disease. As a therapeutic adjuvant octreotide has been used in the treatment of infectious and secretory diarrhea, L-asparaginase induced pancreatitis, symptomatic treatment of fistulas and in the management of severe pain due to neoplasia.

References 1. Patel YC (1999) Somatostatin and its receptor family. Front Neuroendocrinol 20:157–198 2. Lamberts SW, Krenning EP, Reubi JC (1991) The role of somatostatin and its analogs in the diagnosis and treatment of tumors. Endocr Rev 12:450–482 3. Woltering EA, O’Dorisio MS, O’Dorisio TM (1995) The role of radiolabelled somatostatin analogs in the management of cancer patients. In: DeVita VT, Hellman S, Rosenberg SA (eds) Principles and progress in oncology: updates, vol 9. JB Lippincott, Philadelphia, PA, pp 1–15 4. Reubi JC, Laissue JA (1995) Multiple actions of somatostatin in neoplastic disease. Trends Pharmacol Sci 16:110–115 5. Frühwald MC, O’Dorisio MS, Pietsch T et al. (1999) High expression of somatostatin receptor subtype 2 (sst2) in medulloblastoma: implications for diagnosis and therapy. Pediatr Res 45:697–708

Somatostatin Receptor Scintigraphy Definition SRS; Is a type of scan used for the diagnosis of neuroendocrine carcinomas. A radioactive form of octreotide (an analog of ▶somatostatin) is injected into the patient; this will bind to the tumor cells with somatostatin receptors. A radioactivity-measuring device will detect radioactivity and make a picture showing where the tumor cells are localized. ▶Neuroendocrine Carcinoma

Somatostatinoma Definition Is a functioning neuroendocrine tumor of the pancreas that produces high amounts of the hormone ▶somatostatin that can result in the so-called somatostatinoma syndrome. ▶Neuroendocrine Carcinoma

Somatostatinoma Syndrome Definition Is a clinical pentad of diabetes mellitus, cholelithiasis, weight loss, diarrhea, and hypochlorhydria/achlorhydria

Soy Proteins

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observed in association with tumors that overproduce the gastrointestinal hormone ▶somatostatin.

the RAF serine/threonine kinase. Sorafenib is used to treat patients with ▶renal carcinoma.

▶Neuroendocrine Carcinoma ▶Somastatinoma

▶Drug Design ▶RAF Kinase

Somatotropin Release Inhibiting Factor

SOX18 Definition

▶Somatostatin

Sonic

A transcription factor in the SOX family, which regulates lymphatic vessel development. Missense mutations or deletions of this gene lead to primary ▶lymphedema. ▶Lymphangiogenesis

Definition Gene in hedgehog signaling.

Soy Isoflavonoids

▶Hedgehog Signaling

Definition

Sonic Hedgehog Definition

A group of ▶phytoestrogens found in soybean which possess potent antioxidant and antiangiogenic properties. ▶Isoflavones interact with animal and human estrogen receptors, causing effects in the body similar to hormone ▶estrogen. ▶Chemoprotectants

One of three proteins in the mammalian hedgehog family that plays a key role in regulating vertebrate organogenesis, such as in the growth of digits on limbs and organization of the brain. ▶Hedgehog signaling

Soy Phytoestrogen ▶Genistein

Sorafenib Definition An orally available multi-kinase inhibitor that has the chemical structure of N-(3-trifluoromethyl-4-chlorophenyl)-NΥ-(4-(2-methylcarbamoylpyridin-4-yl)oxyphenyl)urea and is capable of simultaneously inhibiting ▶VEGFR and ▶PDGFRβ tyrosine kinases as well as

Soy Proteins Definition

Are a mixture of proteins (α-, β-, and γ-conglycinins, β-amylase, lectin, the Kunitz inhibitor of trypsin, the

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Sp

Bowman-Birk inhibitor of chymotrypsin and trypsin, among others) differing in physicochemical and other properties. They are used in human foods in a variety of forms and their consumption is increasing because of reported beneficial effects on nutrition and health. These effects include lowering of plasma cholesterol, prevention of cancer, diabetes, obesity, and protection against bowel and kidney disease. ▶Nutraceuticals

Sp

SPC1 ▶Furin

Specific Immunotherapy for Melanoma ▶Melanoma Vaccines

Definition Specificity protein transcription factor.

Specificity

▶Betulinic Acid

Definition

Sp-Like Proteins

The specificity of a test indicates the proportion of patients without the target condition who have a negative result with the test. ▶Molecular Pathology

Definition Proteins related to Sp-1 (specific protein-1), the first transcription factor identified. Sp-like proteins contain a C2H2-type zinc finger that binds to GC/GT-rich DNA elements. Sp1–Sp4 are four different full length members of the Sp-like protein family, while Sp5-Sp8 seem to be truncated forms of Sp1–Sp4. ▶Parathyroid Hormone-Related Protein

Spectral Karyotyping LUBA T RAKHTENBROT Head of Molecular Cytogenetics Laboratory, Institute of Hematology, The Chaim Sheba Medical Center, Tel Hashomer, Israel

Definition

SPARC ▶Secreted Protein Acidic and Rich in Cysteine

SPB, in Yeast ▶Centrosome

Spectral karyotyping (SKY) is a multi-fluorochrome ▶fluorescence in situ hybridization technique (FISH) in which all the chromosome pairs are simultaneously visualized in different colors in a single hybridization. SKY determines the unique spectral profile of each chromosome generated by specific combinations of different ▶fluorochromes. At the present time, SKY can be used to analyze human, mouse and rat chromosomes.

Characteristics

Structural and numerical ▶chromosomal alterations (aberrations) are the hallmarks of malignant diseases.

Spectral Karyotyping

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Routine cytogenetic analysis based on ▶G-banding techniques provides important information of diagnostic and prognostic relevance both in hematological malignancies and solid tumors. However, detection of chromosomal alterations by this method is complicated by the difficulty in routinely preparing metaphase spreads of sufficient quality and quantity, the clonal heterogeneity of the tumors and the complexity of the many ▶chromosomal aberrations. In addition, homogeneously staining regions or double minute chromosomes, results of ▶oncogene amplification, are impossible to characterize using G-banding analysis alone. As a result a large number of chromosomal abnormalities are described as so-called marker and derivative chromosomes instead of being precisely defined. Fluorescence in situ hybridization, a highly sensitive and specific tool for the detection of chromosomal aberrations, provides additional information to G-banding analysis clarifying particular problems. However, the ▶FISH technique is unable to screen the whole ▶karyotype in one experiment and therefore analysis of complex unknown chromosomal alterations requires a large panel of painting probes and several hybridizations. The fantastic advantage of Spectral Karyotyping (SKY) is the ability to visualize simultaneously all the chromosome pairs in different colors in one hybridization. In this way, karyotype rearrangements are easily detected as a transition from one color to another at the chromosomal breakpoint region. The SKY method involves several steps: 1. A probe cocktail (Applied Spectral Imaging Ltd, Migdal, Ha’Emek Israel) consisting of fluorescently labeled probes for each chromosome is made by labeling chromosome specific libraries generated by PCR from flow-sorted chromosomes with specific combinations of one or more of the five spectrally distinct fluorochromes (FITC, Rhodamine, Texas Red, Cy5 and Cy5.5). 2. Metaphase preparations are hybridized with this probe cocktail and then stained with 4,6-diamidino2 phenylindole (DAPI) in antifade medium. 3. The SpectraCube® Imaging system (Applied Spectral Imaging Ltd, Migdal Ha’Emek, Israel) is used to discriminate between the different spectral characteristics of chromosomes. The system measures chromosome-specific emission spectra generated by the combinatorially labeled chromosome-specific painting probes. 4. The spectral signature of the fluorochrome combinations is analyzed using SKYView™ software. It classifies the chromosomes by comparing the acquired spectral characteristics to the combinatorial library containing the fluorochrome combinations for each chromosome. In the classified image the

Spectral Karyotyping. Figure 1 Schematic presentation of chromosome identification according to the spectral characteristics. Each graph consists of a fluorescence emission spectra and a RGB display of the chromosome. The horizontal axis shows wavelength, the vertical axis shows relative intensity of fluorescence. (a–d) Chromosomes 8, 20, 2 and X, labeled with FITC, Rhodamine, Cy5.5 and a combination of Rhodamine and Cy5.5, respectively.

chromosomes appear in a Red-Green-Blue (RGB) display in which FITC is seen as blue, Rhodamine and Texas Red are seen as different shades of green and the infrared dyes not visible to the human eye, Cy5 and Cy5.5, are assigned different shades of red.

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Figure 1 schematically presents the principle of the chromosome classification according to the spectra characteristics. Each graph consist of fluorescence emission spectra of the distinct fluorochromes (or combination of fluorochromes) and a Red-Green-Blue (RGB) display of the appropriate chromosome. Emission maximums for presented fluorochromes are: FITS – 525 nm, Rhodamine – 570 nm, Cy5.5 – 703 nm. Figure 1(a) shows chromosome 8 labeled with FITC, in the RGB display it’s seen as blue color; Fig. 1(b) chromosome 20 labeled with Rhodamine, in the RGB display it’s seen as green color; Fig. 1(c) chromosome 2 labeled with Cy5.5, in the RGB display it’s seen as red color

and Fig. 1(d) chromosome 2 labeled with combination of Rhodamine and Cy5.5, in the RGB display it’s seen as specific color. 5. The chromosomes are then automatically sorted into a karyotype table according to the nomenclature rules for G-bands. Rearrangements, ▶translocations between different chromosomes and components of marker chromosomes are all easily identified because of a change in color at the point of transition (Fig. 2a and b). Finally, the software assigns a specific classification pseudocolor to each chromosome allowing chromosomal aberrations to be even more easily visualized (Fig. 2b).

Spectral Karyotyping. Figure 2 Spectral karyotyping of metaphase of a neuroblastoma tumor (a) Red-Green-Blue (RGB) display after hybridization with the SKY kit; (b) Karyotype table of spectrally classified chromosomes. Chromosomal aberrations are detected by the combination of two or more colors on the same chromosome (marked by arrows). (c) DAPI-stained separately and inverted to give a G-banding like pattern. (D. R. Betts, Department of Oncology, University Children’s Hospital, Zürich, Switzerland; L.Trakhtenbrot, Institute of Hematology, Tel Hashomer, Israel).

Spectral Karyotyping

6. The DAPI image is captured separately and inverted to give a G-banding like pattern. This image may be used to compliment the SKY analysis with chromosome banding information (Fig. 2c).

Advantages of SKY SKY analysis has revealed numerous marker and derivate chromosomes (Fig. 3a, b, d), hidden translocations (Fig. 3a, c), chromosomal ▶insertions, homogeneous staining regions and double minutes unidentified or incorrectly identified by G-banding. The combination of SKY with FISH increases the accuracy of karyotype interpretation, permitting precise breakpoint mapping and the detection of small interstitial ▶deletions and cryptic translocations. SKY is particularly useful in cancer cytogenetics and provides a much more detailed description of the highly abnormal karyotypes that characterize advanced tumors and cancer cell lines. The precise definition of markers by the SKY technique leads to the determination of an increased number of aberrations per tumor, identification of more chromosomal regions involved in the karyotype evolution and the analysis of more metaphases, especially polyploid. SKY enables the discovery of a larger number of subclones and the revelation of different clonal evolution pathways of karyotype alterations. In general, SKY provides an opportunity to assess the level of tumor

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instability that is usually associated with advanced or aggressive disease. The flexibility of SKY permits it to be used with any genome, provided the effective flow sorting of chromosomes can be accomplished. Recently SKY has been developed for murine and rat chromosomes, the most popular species used as model systems for the investigation of tumorgenesis. Disadvantages Due to the nature of painting probes, SKY alone can not detect intrachromosomal rearrangements, such as paracentric or pericentric ▶inversions, small ▶duplications and deletions. The resolution of SKY (1–3 Mb) depends on the level of chromosomal condensation and on the combination of the fluorochromes involved in structural rearrangements. Thus, SKY should be seen as a complement, and not as a replacement, of conventional G-banding analysis. To overcome these limitations and to elevate the accuracy of cytogenetic analysis a new method named “spectral color banding (SCAN)” was developed on the basis of the conventional SKYanalysis. SCAN analyzes a single chromosome, allowing simultaneous visualization of all the chromosome bands in different colors in a single hybridization since each band is labeled with a unique combination of fluorochromes (similar to the SKY technique) with a specific spectral pattern. In this

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Spectral Karyotyping. Figure 3 SKY detection of chromosomal aberrations incorrectly identified by G-banding. (a) SKY showing translocations t(12;21), t(2;16) and der(6)t(X;6), displayed in classification colors. (b) G-banding failed to recognized the cryptic translocation t(12;21), and the origin of the additional segments on chromosomes 2 and 6. (c) Translocation t(7;8)(q32;q34) is detected by SKY (RGB display), but not by G-banding. (d) SKY demonstrates a complex translocation involving three chromosomes – 1, 8 and 22. G-banding identifies this rearrangement only as a marker of chromosome 1 origin. (D. R. Betts, Department of Oncology, University Children’s Hospital, Zürich, Switzerland; L.Trakhtenbrot, Institute of Hematology, Tel Hashomer, Israel).

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way different bands can be distinguished from each other by different colors. SCAN analysis employs a detection system and algorithm for spectral pattern recognition identical to that used in SKY analysis. The drawback of SCAN is its inability to detect aberrations in the other chromosomes. To overcome this shortcoming, a combination of SKY and SCAN was developed based on a probe cocktail composed of the SCAN banding probes for an individual chromosome and the SKY probe kit without the painting probe for this particular chromosome. Clinical Significance Since its introduction in 1996, SKY has been extensively used to elucidate chromosomal aberrations in hematological malignancies as well as solid tumors, including sarcomas, carcinomas and brain tumors. The highly important input of SKY analysis to clinical research of malignant diseases is the identification of novel recurrent aberrations with pathogenic potential and the prediction of a specific phenotype or modified response to treatment or outcome. The results of SKY analyses contribute to diagnosis, therapy decisions, and follow-up studies.

differently colored fluorescent probes or genetic reporters following their simultaneous detection. ▶Bioluminescence Imaging

Spermatocytes Definition Spermatocytes are the male germ cells before meiosis I. ▶BORIS

Spheroids Definition

▶Multicellular Spheroids.

References 1. Bayani J, Squire JA (2001) Advances in the detection of chromosomal aberrations using spectral karyotyping. Clin Genet 59:65–75 2. Cohen N, Betts DR, Tavori U et al. (2004) Karyotypic evolution pathways in medulloblastoma/primitive neuroectodermal tumor determined with a combination of spectral karyotyping, G-banding, and fluorescence in situ hybridization. Cancer Genet Cytogenet 149:44–52 3. Garini Y. Macville M, du Manoir S et al. (1996) Spectral karyotyping. Bioimaging 4:65–72 4. Kakazu N, Abe T (2006) Multicolor banding technique, spectral color banding (SCAN): new development and applications. Cytogenet Genome Res 114:250–256 5. Saez B, Martin-Subero JI, Largo C et al. (2006) Identification of recurrent chromosomal breakpoints in multiple myeloma with complex karyotypes by combined G-banding, spectral karyotyping and fluorescence in situ hybridization analysis. Cancer Genet Cytogenet 169:143–149

Sphinganine Definition Dihydrosphingosine, the basis of the minor dihydrosphingolipids, generally inactive in cell processes. ▶Sphingolipid Metabolism

Sphingolipid Metabolism N ORMAN S. R ADIN Department of Psychiatry, University of Michigan, Ann Arbor, MI, USA

Spectral Unmixing Definition Mathematical algorithm based technique, used in optical image analysis, to distinguish and quantitatively measure the light emission produced by multiple,

Definition

▶Sphingolipids (▶SLDs) contain ▶sphingosine (▶Sph) or a similar moiety. Sphingosine (Fig. 1a) is D-erythro-trans-4-octadecene-2-amino-1,3-diol; R1 is typically a C13 alkyl chain. ▶Ceramide (Fig. 1b) is a fatty acid amide of sphingosine that plays a pivotal role

Sphingolipid Metabolism

Sphingolipid Metabolism. Figure 1 Sketch (a) shows sphinogosine and (b) shows aramide R1 represents a tridecyl alkyl chain of a saturated or monounsat urated fatty acid

in cell growth and death, in which R2 symbolizes a saturated or monoenoic fatty acid containing 16–32 or more carbon atoms. Some fatty acids have an OH at carbon-2. Some ceramides contain phytosphingosine instead of Sph; here the double bond is replaced by an OH at C-4. Hundreds of SLD species occur. The C-1 OH can be phosphorylated to form Sph phosphate or ▶Cer phosphate, or esterified by a phosphocholine group to form ▶sphingomyelin (▶SM), the most common SLD. The OH can also be coupled to a sugar, usually galactose or glucose, to form GalCer or β-glucosylceramide (▶GlcCer). GalCer is a major component of human brain; a portion of the lipid has a sulfate group attached to the sugar (▶sulfatide). GlcCer, the primary ▶glucosphingolipid (▶GSL), can add other sugar moieties to the glucose, particularly galactose, NAc-galactosamine, and N-▶acetylneuraminic acid (a characteristic moiety of the ganglioside series of GSLs).

Characteristics Sphingolipids control the properties of cell membranes, the rate of cell growth-proliferation-destruction, apoptotic processes, the phosphorylation and dephosphorylation of proteins, the formation of reactive oxygen species (ROS), the hydrolysis of some proteins, the acetylation of nuclear histones, the binding of microbial pathogens and toxins to human cells, ▶angiogenesis, telomerase, matrix metalloproteinase, cytosolic and mitochondrial ▶glutathione level, and other cancerrelevant factors. Cancer cells appear to synthesize SLDs somewhat faster than normal cells and are more sensitive to SLD manipulation, even in multi-drug resistant cells. This difference in sensitivity bodes well for the design of a drug with a good therapeutic index.

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Some SLDs (Cer, ▶gangliosides GM3 and GD3) induce ▶apoptosis – especially in cancer cells – while other SLDs (Sph phosphate, Cer phosphate, GlcCer, GalGlcCer) promote growth and proliferation and prevent apoptosis. Since these two types of lipids can be interconverted by the enzymes that make and hydrolyze them, it is evident that cells must maintain a balance in their concentrations and activities. One or more controlling factors are missing from cancer cells, resulting in unrestrained growth and a high rate of DNA change. Cancer cells contain unusual assortments of SLDs, with dominance of the proliferative lipids. The essence of cancer chemotheraphy appears from this viewpoint – to be the targeting of these lipids, their enzymes, and the factors that control their levels in tumors. While SLDs occur almost everywhere in cells, there are special aggregates in plasma cell membranes, called ▶rafts (GSL- and cholesterol-enriched lipoid/protein ▶microdomains). The rafts function as signaling platforms for important cytokines and modification of their compositions can affect many of their functions. Depletion or augmentation of cellular SLDs leads to a remarkable number of important phenomena. ▶Poly-Drug Chemotherapy and Multi-Drug Resistance Because of the unusual sphingolipid Yin/Yang, Janusfaced metabolism, which promotes and blocks cell death, cancer therapy calls for the use of a poly-drug cocktail that stimulates the formation of Cer, ganglioside GM3, and GD3, while simultaneously inhibiting synthesis of the proliferative SLDs. The simultaneity is important because manipulation of just one of these lipid clusters leads the cancer cell to induce changes in the other cluster and proliferative factors. This response eventually leads to renewed tumor growth and resistance to the drugs that were used initially. A similar selection occurs when the initially attacked cancer cells mutate to form cells with a more resistant imbalance in SLD composition. Thus, treating tumors with a single, first-line drug can lead to clones that are resistant to the drug and the apparent cure turns out to be illusory. Evidently a cocktail is needed to cover all or most phases of SLD metabolism in an all-out attack, to kill all the cancer clones present in each individual patient. Preliminary trials of the poly-drug approach have indicated that the dose size of each component can be lower than the single-drug approach (i.e., synergistic), so side effects can be expected to be minimized.

Chemotherapy via Ceramide Control Cer levels can be elevated by the following approaches. Some of the drugs listed are not – or need not be – approved by the FDA.

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1. Stimulate the first step in de novo synthesis of Cer from serine and palmitic acid, formation of 3-keto ▶sphinganine, via pyridoxal phosphate as cofactor. Exogenous palmitate and serine are effective and supplementary pyridoxine may also help. Dietary carnitine, which helps mitochondria destroy the fatty acid, should be avoided. The apoptogenic effect of palmitate is augmented by etomoxir, which inhibits transport of fatty acid by carnitine. Several anticancer drugs (fenretinide, camptothecin, etoposide, paclitaxel, retinoic acid, tetrahydrocannabinol, and valspodar stimulate the de novo synthesis of Cer. The next steps in Cer synthesis are reduction of the carbonyl oxygen, forming sphinganine, and acylation of the amine group, forming dihydroCer. This somewhat inert analog of Cer is next dehydrogenated to form Cer, producing a double bond between carbons 4 and 5. The crucial segment of Cer is the ▶allylic structure, with the C-3 OH and the Δ4 double bond. Fumonisin, a fungal toxin commonly found in significant concentrations in some foods, inhibits the acylation step and should be avoided via good food handling practices. It also inhibits acylation of free Sph (see below). 2. Minimize the conversion of Cer to SM (sphingomyelin), an exchange of the C-1 OH for the phosphocholine moiety of phosphatidylcholine (lecithin) with formation of diacylglycerol. A similar reaction utilizes phosphatidylethanolamine, followed by N-methylation. The enzyme, SM synthase, as well as lecithin, has been found in high concentrations in some tumors, suggesting that they protect themselves against Cer toxicity this way. It is possible to lower the body content of lecithin by restricting the intake of fatty foods. The anticancer phospholipid analog, hexadecylphosphocholine, which inhibits lecithin synthesis, also slows SM synthesis and speeds Cer synthesis. Thus, the various anticancer phospholipid analogs may owe some of their effectiveness to this mechanism. It follows from this also that drugs emulsified with the aid of lecithin should be reformulated. Tamoxifen, which inhibits diversion of Cer by glucosylation, also stimulates phospholipases C and D, thus also lowers tumor lecithin. 3. Stimulate SM hydrolysis, which forms Cer + phosphocholine. The major SMases, Mg2+-requiring neutral SMase and an acidic SMase, are normally somewhat inhibited by mitochondrial glutathione (GSH). Thus an agent that lowers GSH levels will greatly elevate Cer level. Radiation, oxidation by ROS, condensation catalysis by glutathionyl S-transferase, inhibition of GSH biosynthesis (buthionine sulfoximine), and Michael reaction of GSH with anticancer drugs that contain allylic ketone moieties (doxorubicin, camptothecin, tetracycline, a keto metabolite of fenretinide, manumycin,

actinomycin D, curcumin, quercetin, 15-deoxy-Δ12,14prostaglandin J2, illudin, gossypolone, ciprofloxacin, 17AAG (a geldanomycin analog), and others) act this way to produce much of their anticancer activity. Other agents lower GSH levels in tumors. Cisplatin and dietary thiocyanates (sulforaphane in broccoli) react chemically with GSH. Sulforaphane also induces glutathione S-transferase activity. Cer and many antineoplastic drugs generate ROS in cells, thus raise the sulfur atom to more oxidized states. Even modest oxidation of GSH to form disulfides and mixed disulfides with the cysteine moieties of proteins unmasks the power of SM to form Cer. Many metabolites and nutrients generate ROS in mitochondria in the normal course of oxidative metabolism. Normally the ROS are kept under control by antioxidants. GSH is needed for important enzyme reactions, so its level should not be reduced too far. The hydrolysis of SM is stimulated by arachidonic acid, a common dietary fatty acid that is converted to prostaglandins. Thus its use would have to be controlled by the use of COX inhibitors. Thalidomide inhibits angiogenesis by stimulating the synthesis of Cer from SM. 4. Inhibit diversion of Cer to formation of GlcCer by treatment with D-threo-1-phenyl-2-decanoylamino3-morpholino-1-propanol (▶PDMP), ▶N-butyldeoxynojirimycin, dietary glucose deprivation, chlorpromazine, tamoxifen, mifepristone, antiandrogens, ketoconazole, irinotecan, doxorubicin, dihydroxy vitamin D3, mitoxanthrone, dexamethasone, arabinofuranosylcytosine, and others. PDMP and its analogs PPMP and PPPP produce Cer in more than one way. GlcCer and its anabolite, GalGlcCer, are growth stimulators and promoters of ▶P-gp (MDR1), a major cause of ▶multi-drug resistance; thus inhibiting Cer glucosylation is important in several ways. It is possible that food intake reduction, which prolongs life, owes some of its effectiveness to depletion of glucose and UDPglucose, the co-substrate in GlcCer synthesis. In addition, GlcCer and GalGlcCer are the precursors of the gangliosides, which prevent the normal action of ▶dendritic cells, the major first defense in immunological attack on cancer cells. Tumors shed a significant portion of their rapidly synthesized gangliosides into the extracellular fluid around the cancer cells. The mechanism by which these lipids inhibit dendritic cell development is not clear, possibly by inhibiting Cer glucosylation. The ▶ganglioside secretion or shedding also promotes angiogenesis, a vital tool of growing tumors. Thus it seems essential to prevent GSL synthesis so that the patient’s immune system can make a final clearing of cancer cells. The accumulated Cer prevents angiogenesis.

Sphingolipid Metabolism

A further advantage of inhibiting GlcCer synthesis is that it depletes cell surfaces of the GSLs that act as binding sites for many microbial organisms, including viruses. Alternatively, mimics of the surface GSLs can be used to compete with the cells for binding to infective agents. Thus the complication of ▶infection in cancer patients would be minimized. Patients with ▶Gaucher disease, who have a genetic deficiency in the amount of GlcCer hydrolase, are currently being treated by injection of a modified form of the human glucosidase. The enzyme lowers tissue GlcCer levels, forming Cer and glucose, thus should be helpful in cancer patients. A similar effect can be expected by injection of a small peptide that is needed for the glucosidase’s activity, ▶saposin C. 5. Inhibit Cer hydrolysis, which forms Sph + fatty acid, with D-erythro-2-(N-myristoylamino)-1-phenyl-1propanol (▶D-MAPP), N-oleoyl ethanolamine, and N-octadecylSph. Blocking ▶ceramidase seems to be an effective way of elevating Cer and inducing apoptosis. Reacylation of the Sph to regenerate Cer is performed by an acyltransferase produced from the ▶longevity assurance gene. 6. Inhibit the kinase that converts free Sph to its 1-phosphate ester (▶S1P). This ester competes with Cer in controlling a cell’s fate, so the ratio of the two lipids is critical for rebalancing the SLDs. N,Ndimethyl sphingosine, trimethylSph, and glabridin (an allylic ether in licorice) are suitable inhibitors. DimethylSph is a normal metabolite of sphingosine, but its concentration seems to be too low in tumors. 7. Chemotherapy with dietary Cer has shown beneficial effects in intestinal cancer. However it has to be included as part of the total poly-drug approach in order to prevent conversion of the extra Cer to proproliferative SLDs. Dietary SM is converted to Cer in the intestine and also has a beneficial effect; it can be considered a pro-drug. Since both lipids and GSLs occur in food, it is likely that they constitute a natural cancer-preventing mixture. SM has been used as part of a liposomal cocktail for dispersing water-insoluble anticancer drugs. A solubilizing chain of poly(ethyleneglycol), attached to Cer by a dicarboxy acid bridge, may solve the problem of administering so insoluble a lipid. It may also be useful for forming a liposomal suspension with SM. In recent years, analogs of Cer have been synthesized that are more active than Cer in the induction of apoptosis. Adding an additional double bond, conjugated with the ▶allylic double bond of Cer, improved the lipid considerably. It is significant that some antineoplastic drugs also have an allylic alcohol group that is part of a chain of conjugated bonds. A Cer analog with a pyridinium group in the fatty acid moiety was found to concentrate in tumors and prevent their growth

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in vivo. Its effectiveness was greatly enhanced by including gemcitabine, an antineoplastic drug that produces Cer elevation. Immunological Attack Against Cancer Cells Some, perhaps many, tumors consist of cells with an unusually high concentration of rare GSLs. Indeed, the ratio of Cer to GSLs decreases as the tumor malignancy increases. Unfortunately, SLDs are not potent inducers of Ab induction (see dendritic cells above) and special techniques had to be developed. Tumors of neuroectodermal origin (e.g.: melanoma and neuroblastoma) are being tested with a mouse/human chimeric ▶mAb against ganglioside GD2, a prominent GSL in these cells. Promising results have also been found by active immunization with ▶idiotypic peptides that mimic gangliosides. Pathogens containing idiotypes that resemble GSLs sometimes evoke neuropathological autoantibodies, as in Guillain-Barré syndrome. α-Linked galactose in GalCer (not the usual β-GalCer) is a potent stimulator of NKT cells and a killer of cancer cells. This finding is under active study. Mechanisms of Sphingolipid Antineoplastic Action 1. Since addition of Cer to whole cells or mitochondria produces ROS and apoptosis, the proposal has been made that the allylic OH of Cer is oxidized to an allylic ketone (keto Cer). Presumably the latter is the therapeutically active form of Cer, since it can undergo adduct formation with GSH, other thiols, and active amines. Antineoplastic drugs that contain an allylic alcohol, ester, or ether moiety may mimic Cer, forming ROS, allylic ketones, and Michael adducts. Cer – and several anticancer drugs – interfere with the mitochondrial electron-transporting oxido/ reduction cycle of ▶ubiquinone/ubiquinol that normally generates ATP. Ubiquinone is an allylic ketone, thus is likely to oxidize allylic alcohols. 2. Cer can generate pores in mitochondrial membranes, allowing cytochrome c and other components to escape into the cytoplasm where they activate the ▶caspases and initiate the apoptogenic death sequence. The pores, called barrels, seem to consist of assembled Cer molecules, lined up with their polar (OH) end facing the inside. A certain minimum amount of Cer must be accumulated in the mitochondria to generate one pore. DihydroCer (lacking the double bond) is inert. 3. Cer and Sph activate kinases that act on important proteins (e.g.: PKC ζ involved in the control of apoptosis and many other phenomena. Cer also activates ▶phosphatases (e.g.: PP1 and PP2A) that remove phosphate groups from many proteins (e.g.: ▶Akt). These effects are seen with synthetic anticancer drugs too. Generally, sphinganine-based SLDs are inactive in these activations so the

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presence of the allylic polar moiety seems to be essential. The mechanism of activation could be ascribed to binding of the active lipid to an allosteric region of the enzymes. However there is also the recently proposed idea that the SLD binds to the active site of the phosphate-transferring region, with the allylic alcohol moiety forming a transitional phosphate ester, functioning as an ▶anion-transferring coenzyme for the catalytic processes. These kinases and phosphatases control the activity of many phosphoproteins that control apoptosis and many other processes. For example, the Cer-activated phosphatase, PP2A, dephosphorylates and thereby inactivates µ- and m-calpains, leading to suppression of the migration and invasion properties of human lung cancer cells.

sphingomyelins, and glycosphingolipids, which differ in the substituents on their head group. Ceramides are the simplest type of sphingolipid. They consist of a fatty acid chain attached through an amide linkage to sphingosine. Sphingomyelins have a phosphorylcholine or phosphoroethanolamine molecule esterified to the 1-hydroxy group of a ceramide. Glycosphingolipids are ceramides with one or more sugar residues and are called gangliosides when they carry three sugars, however one of which must be sialic acid. Phosphorylated forms of sphingosine and ▶ceramide, namely sphingosine-1-phosphate (S1P) and ceramide1-phosphate (C1P) are involved in cell survival, angiogenesis and tumorigenesis. ▶Lipid Mediators ▶Sphingolipid metabolism

4. Cer is involved in other anion-transferring reactions of great importance to cancer therapy. It reduces N-acetylation of protein-linked lysine and is involved in ▶histone acetylation. It binds to and activates ▶cathepsin D, the acid aspartate protease that triggers the apoptotic program by activating Bid. The aspartate COOH in the enzyme’s substrate may form a transient ester link with Cer during the peptide cleavage.

Definition

References

Sphingomyelin-phosphodiesterase 1 (gene symbol: Smpd1) hydrolyses sphingomyelin to ▶ceramide. The maximum of the enzyme activity is at an acidic pH.

1. Merrill AH Jr, Hannun YA (eds) Sphingolipid metabolism and cell signaling, Part A (2000) Methods Enzymol 311: 3–748 2. Radin NS (2004) Sphingolipids as coenzymes in anion transfer and tumor death. Bioorg Med Chem 12:6029–6037 3. Ogretmen B, Hannun YA (2004) Biologically active sphingolipids in cancer pathogenesis and treatment. Nat Rev Cancer4:604–616 4. Ruvolo PP (2003) Intracellular signal transduction pathways activated by ceramide and its metabolites. Pharmacol Res 47:383–392

Sphingomyelinase

Sphingomyelins Definition Are sphingolipids that possess a phosphorylcholine or phosphoroethanolamine molecule esterified to the 1-hydroxy group of a ▶ceramide. ▶Lipid Mediators

Sphingolipids Definition Are a class of lipids derived from the aliphatic amino alcohol sphingosine. The sphingosine backbone is O-linked to a (usually) charged head group such as ethanolamine, serine, or choline. The backbone is also amide-linked to a fatty acid. Sphingolipids are often found in neural tissue, and play an important role in both signal transmission and cell recognition. There are three main types of sphingolipids: ceramides,

Sphingosine Definition Is an aliphatic amino alcohol that composes sphingolipids. ▶Lipid Mediators

Spinophilin

Sphingosine-1-Phosphate Definition S1P; Is a phosphorylated form of sphingosine and possesses tumorigenic properties. ▶Lipid Mediators

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chromosomes align and attach themselves along the metaphase plate and are then pulled apart from one another by motors that push and pull the separated chromosomes towards opposite poles of the cell. Formation of a spindle pole apparatus requires a change in microtubule dynamics. This is brought about by changes in the phosphorylation states of structural and motor microtubule associated proteins (MAPs); (not to be confused with mitogen activated protein kinase, MAP kinase!). Cyclin-dependent kinase 1 (CDK1) is known to phosphorylate many MAPs. ▶G2/M Transition

Spinal and Bulber Muscular Atrophy (SBMA) ▶Androgen Receptor

Spindle Pole Body ▶Centrosome

Spindle Assembly Checkpoint Definition SAC; Regulates metaphase-to-anaphase transition of the ▶cell cycle in order to ensure that chromosomes do not segregate until each is properly attached by microtubules to bilateral spindle poles during mitosis and meiosis. ▶Mitotic Arrest-Deficient Protein 1 (MAD1) ▶Checkpoint

Spinocerebellar Ataxia Type 1 Definition SCA1; Is an autosomal dominant progressive neurodegenerative disorder characterized by ataxia, dysarthria, ophthalmoparesis, and variable degrees of amyotrophy and neuropathy. The disease causing mutation is an expansion of a CAG trinucleotide repeat which lies within the coding region of ataxin-1. ▶Cajal Bodies

S Spindle Pole Apparatus Definition

Develops during the ▶cell cycle. Is a highly organized structure that consists of kinetochore microtubules attached to segregating chromatids, and polar microtubules moving apart the spindle poles immediately prior to cell division. Independent changes during G2/ M culminate in the formation of the spindle pole apparatus (▶G2/M transition). It consists of two opposed poles each arising from one of the two duplicated centrosomes. The bisecting line at which microtubules emanating from each pole of the spindle meet is known as the metaphase plate. Pairs of

Spinophilin Definition synonym neurabin II; Is ubiquitously expressed and interacts with protein phosphatase 1 (PP1), an alternate reading frame (p14ARF, a 14 kDa polypeptide in humans, 19 kDa in mouse), doublecortin and actin, and synergistically suppress osteosarcoma tumor growth with p14ARF. ▶Doublecortin

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Spirometry

Spirometry

mRNA from the same gene, allowing for different forms of the final protein produced.

Definition A physiologic test that measures inhaled and exhaled volumes of air independently and as a function of time. ▶Chronic Obstructive Pulmonary Disease and Lung Cancer

Spliceosome Definition A large multi-protein and snRNA complex that mediates the catalytic steps of the splicing reaction.

Spleen

▶pre-mRNA Splicing

Definition A lymphoid organ in the abdominal cavity that is an important center for immune system activities.

Splicing Definition

Spleen Tyrosine Kinase ▶Syk Tyrosine Kinase

Splenic Marginal Zone Lymphoma

The process by which introns are removed from an RNA transcript. ▶Pre-mRNA splicing

Spontaneous Bacterial Peritonitis

Definition

Definition

Indolent B-cell neoplasm, composed of small lymphocytes, that is marked by massive splenomegaly and peripheral blood and bone marrow involvement, usually without adenopathy.

Is characterized by the spontaneous infection of ascitic fluid in the absence of an intraabdominal source of infection involving the translocation from bacteria from the intestinal lumen to the lymph nodes with subsequent bacteremia and infection of ascitic fluid.

▶Rituximab ▶B-cell Tumors

▶Acites

Splice Variant Definition

Alternative ▶splicing of introns and exons on premessenger RNA (mRNA) creates variants of mature

Sporadic Definition Referring to gene mutation, a term frequently used as synonym for non-hereditary.

Sprouty

Sprouty T ING L ING LO, G RAEME R. G UY Signal Transduction Laboratory, Institute of Molecular and Cell Biology, Singapore

Synonyms Spry

Definition Sprouty (Spry) proteins are a family of endogenous proteins that negatively regulate the ▶ERK/MAP kinase (ERK/MAPK) signaling pathway (Fig. 1) that is activated by ▶Receptor Tyrosine Kinases (RTKs).

Characteristics Sprouty was initially discovered as an inhibitor of ▶fibroblast growth factor (FGF) signaling during tracheal development. It was involved in modulating branching in tracheal formation in the fly (Drosophila) and its absence led to excessive “sprouting” of tracheal tubules. As in the fly, mammalian Spry proteins work as feedback inhibitors of RTK signaling during ▶branching morphogenesis of the lung, vascular system, kidney tubules and breast ducts. To date, four mammalian Sprys (Spry1–4) have been identified with sequence similarity to the Drosophila protein (Fig. 2). These are expressed in the brain, heart, lung, kidney, limbs and skeletal muscle. The Spry proteins have a highly conserved cysteine-rich C-terminus. The N-terminal half of the Spry proteins are more divergent, however, except for the presence of an invariant tyrosine residue (Y) located in a short, conserved NxYxxxP motif. Many of the inhibitory functions of the Spry proteins are dependent on this residue. Of note, Spry1, 2 and 4 are tyrosine ▶phosphorylated/phosphorylation in response to RTK stimulation while the ability of growth factors to induce tyrosine phosphorylation of Spry3 is unknown. Mechanisms of Action Various studies conducted in the mammalian system confirm Spry proteins as negative regulators of the ERK/MAPK pathway; they differ in their conclusions as to the specific point in the ERK/MAPK pathway at which Spry acts. Spry has been found to interact with regulators of MAP kinase or mainstream components of MAP kinase (Fig. 1) (a comprehensive description can be found in the review by Mason et al. (2006)). Regulation of the Activity of Sproutys As a negative regulator, Spry is subject to tight control through post-translational modifications and through

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regulation of the protein levels in the cell. The activity of Spry proteins is regulated by post-translational modifications such as serine and tyrosine phosphorylation, palmitoylation and ▶ubiquitination. In their N-terminal domain, Spry proteins contain a conserved tyrosine residue (Tyr55 in Spry2) that undergoes phosphorylation in response to growth factor (FGF) and ▶epidermal growth factor (EGF) stimulation. This tyrosine residue is necessary for Spry proteins to function as inhibitors of FGF signaling. While tyrosine phosphorylation on the conserved tyrosine on Spry is important for its functional activity, it also promotes the binding of the E3 ubiquitin ligase c-Cbl to Spry2. Tyrosine phosphorylation of Y55 on Spry2, or Y53 on Spry1, creates a consensus binding motif [NxY(S/T)xxP] which serves as a binding site for c-Cbl. The interaction of Spry proteins with c-Cbl promotes the ubiquitination and ▶proteasome degradation of Sprys. This pathway has been postulated to serve as a mechanism to control the duration of Spry activity. In addition, several studies have found that serine phosphorylation of Sprys affect the activity of Sprys via influencing the stability and tertiary conformation of Spry proteins. The activity of Spry proteins is also regulated by controlling the expression of Spry proteins in the cell. Spry proteins are induced by the same RTK signaling pathways they negatively regulate. During vertebrate development, Spry genes are often expressed at sites associated with FGF signaling activity. Sprys were also observed to be up-regulated upon activation of RTK signaling in in vitro cell culture. Deregulation of Spry Expression in Cancer The central ERK/MAP kinase pathway is deregulated in many cancers. As Spry proteins are functional inhibitors of this pathway their own regulation is likely highly relevant to the status of some cancers. There is emerging evidence that the expression of the Sprouty family of proteins is deregulated in various cancers including breast, liver, prostate, ▶melanoma, ▶gastrointestinal stromal tumors (GISTs) and ▶lung tumors. Spry genes have been shown to be down-regulated in breast, liver and prostate cancers and up-regulated in melanoma, gastrointestinal stromal tumors and Rasinduced lung tumors. The up-regulation of Spry expression in certain tumors (gastrointestinal tumors, melanoma, lung tumors) is often induced by the presence of ▶oncogenic lesions (mutation of ▶c-Kit, ▶Raf kinase, ▶Ras) which cause the constitutive activation of the MAP kinase pathways in these tumors. Although numerous oncogenes are also activated in breast, liver and prostate cancers, the same phenomenon of up-regulation of Spry genes was not observed. Instead, down-regulation of Spry genes was observed. The mechanisms of down-regulation of Spry genes has not been completely elucidated in these

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Sprouty. Figure 1 The ERK/MAP kinase pathway. The ERK/MAPK cascade is known for its crucial role in mediating the transduction of signals from Receptor Tyrosine Kinases (RTKs). Following ligand binding, growth factor RTKs such as ▶VEGFR and ▶FGFR become activated. This induces the binding of adapter proteins such as growth-factor-receptor bound-2 (GrB2) that bind to the activated receptors. In cooperation with Grb2, the guanine-nucleotide exchange factor, son-of-sevenless (SOS) activates ▶Ras. This initiates membrane recruitment and activation of ▶MAP kinase ▶Raf, which leads to the activation of the ▶MAP kinase kinase (MEK) and subsequently, ▶MAP kinase ERK. ERK phosphorylates several cytoplasmic targets or migrates to the nucleus, where it phosphorylates and activates transcription factors that control the expression of genes that are required for cell growth, differentiation and survival. Various studies conducted in the mammalian system confirm Spry proteins as negative regulators of the ERK/MAPK pathways. Spry proteins are induced by the same RTK signaling pathways they negatively regulate and are observed to be up-regulated upon activation of RTK signaling.

cancers but at least for prostate cancers, some genetic (loss of parts of chromosomes) and ▶epigenetic gene silencing by ▶methylation mechanisms have been identified to be responsible for silencing of Spry genes. As the up-regulation of Sprys in cancers is a reflection of an over-active MAP kinase signaling pathway in cancers, Sprys have the potential to be used as ▶biomarkers to aid in cancer diagnosis and treatment. Up-regulation of Spry genes can be used concurrently with other molecular markers to distinguish between different types of tumors. When gene expression patterns of different soft tissue tumors were analyzed, Spry genes were found to be specifically expressed in gastrointestinal stromal tumors (GISTs) but not in synovial sarcomas, neural tumors and leiomyosarcomas. Similarly, Spry2 expression was found to be up-regulated in melanoma cells with BRaf (V599E) or N-Ras (Q61R) mutations but not melanoma cells with wild-type B-Raf. Increased MAP kinase activity in these cells was found to contribute to the higher levels of Spry2.

Up-regulation of Spry genes could also be potentially used concurrently with other biomarkers to aid ▶prognosis or monitor the response of patients to drug treatment. However, depending on the particular type of cancer, up-regulation of Spry genes can either be a marker for good or bad clinical prognosis. Spry4 is shown to be induced by aberrant c-Kit activation in GISTs. Aberrant c-Kit activity derived from activating c-Kit mutations have been shown to be important for development of GISTs. In a study that involved treating GIST cells with an inhibitor of c-Kit, ▶Imatinib (Gleevec, STI-571), Spry4 was identified and confirmed as one of the most significant Imantinibresponsive genes that were consistently down-regulated upon treatment with Imantinib. Imatinib has been shown to be an in vitro inhibitor of c-Kit phosphorylation and tumor cell ▶proliferation while inducing ▶apoptosis in a human GIST cell line. Treatment of GISTs cells with Imantinib resulted in a parallel loss of phosphorylated c-Kit, MAP kinase activation and Spry4 levels. Spry4 was found to be a reliable marker

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Sprouty. Figure 2 Structure of Sprouty proteins. Four mammalian Sprys (mSpry1–4) have been identified with sequence similarity to the fly (Drosophila) protein (dSpry). Spry proteins have highly conserved cysteine-rich C-termini and invariant tyrosine (Y) residues located in a short, conserved motif. Many of the inhibitory functions of Spry proteins are dependent on this residue.

with respect to the clinical response of the patients to Imatinib treatment. In patients responsive to the drug, Spry4 levels were dramatically decreased. However, in non-responsive patients, Spry4 levels did not decrease. In patients who initially responded but subsequently relapsed, Spry4 levels decreased dramatically in the tumor biopsy taken during clinical response but returned to pretreatment levels upon clinical relapse. Spry2 was also found to be up-regulated in mouse lung tumors which are induced by oncogenic K-Ras. Individual lung tumors were isolated from the mice and examined for Spry expression. The degree of Spry2 upregulation correlated with the histological grade of the tumor. While Sprouty is a potential marker of aberrant MAPK signaling in the above-mentioned cancers, in other cancers it is surprisingly a marker for good clinical prognosis. In a study of the gene expression profiles of ▶renal carcinoma (clear cell Renal Cell Carcinoma), 51 genes that effectively discriminate between patients with good and poor outcome were isolated. Spry1 was found to be up-regulated exclusively in the good outcome group.

Ability of Sprys to Inhibit Cancer Numerous in vitro cell-based assays demonstrated that Sprys inhibit cell proliferation, ▶migration, and ▶invasion as well as ▶anchorage-independent cell growth by repressing RTK-induced MAP kinase activation. Evidence from in vivo animal studies indicates that Spry proteins can act to suppress the tumorigenesis process. The first evidence detailing Sprys’ ability to interfere with the tumorigenic process was a study where over-expression of Spry2 in an osteosarcoma cell line was found to inhibit tumor growth and metastasis, possibly via the inhibition of MAP kinase activation and cell migration. In a subsequent animal study, Spry2 was shown to inhibit K-Ras-induced lung tumors in mice. In K-Ras-induced lung tumorigenesis, mice develop lung tumors due to the presence of activated K-Ras in their lung tissue. Spry2 was found to be upregulated in the lung tissue and was found to inhibit the tumor development. Mice with the presence of activated K-Ras in their lung tissue developed greater amount of tumors when the Spry2 expression is abrogated (deletion of Spry2 gene; Spry2 null mice). Analysis of the tumors demonstrated mild increase of

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MAP kinase activation in tumors in K-Ras; Spry null mice compared to K-Ras;and Spry2 wild type control mice. This evidence indicates that Spry2 functions to inhibit K-Ras-induced tumor development and that the mechanism may involve antagonism of MAP kinase signaling.

References 1. Kim HJ, Bar-Sagi D (2004) Modulation of signaling by Sprouty: a developing story. Nat Rev Mol Cell Biol 5:441–450 2. Lo TL, Fong CW, Yusoff P et al. (2006) Sprouty and cancer: the first terms report. Cancer Lett 242:141–150 3. Mason JM, Morrison DJ, Basson MA et al. (2006) Sprouty proteins: multifaceted negative-feedback regulators of receptor tyrosine kinase signaling. Trends Cell Biol 16:45–54 4. Shaw AT, Meissner A, Dowdle JA et al. (2007) Sprouty2 regulates oncogenic K-ras in lung development and tumorigenesis. Genes Dev 21:694–707

Spry ▶Sprouty

Sputum Cytology Definition Microscopic examination of a mucus sample to determine if abnormal cells are present. ▶Malignancy-Associated Changes

Squamous Cell Carcinoma W. A NDREW Y EUDALL Philips Institute of Oral and Craniofacial Molecular Biology, Virginia Commonwealth University, Richmond, VA, USA

Synonyms Epidermoid carcinoma

Definition Squamous cell carcinoma is a malignant tumor arising from non-glandular lining or covering epithelia.

Characteristics Squamous cell carcinoma (SCC) is an invasive tumor which may present at numerous body sites, including skin, ocular epithelium, ▶oral cavity, alimentary tract, anogenital region, larynx and bronchial epithelium. Thus, the incidence of SCC lesions varies with site. Estimates from the National Cancer Institute indicate that over one million new cases of skin SCC (▶Skin carcinogenesis) will be diagnosed in the USA in 2007, representing 16% of all types of skin cancer. Similarly, 40,000 new cases of head and neck SCC (comprising oral cavity, pharynx, larynx) occur each year. Squamous cell carcinoma is also one variety of ▶non-small cell lung cancer, the annual incidence of which is 170,000. Anogenital SCC, comprising lesions of cervix, vulva, vagina, penis and anus, are less frequent. Approximately 23,600 new cases are predicted to occur in the USA each year, of which the majority (12,000) will be ▶cervical cancers. Etiology As squamous cell carcinomas can occur at several body sites, multiple etiological factors have been implicated in development of these lesions. Skin cancer is largely associated with exposure to ultraviolet light, with the disease affecting those areas of the body exposed to sunlight. Additionally, persons with fair skin susceptible to sunburn are at higher risk. Immunosuppressed individuals, such as transplant recipients, patients suffering from ▶epidermodysplasia verruciformis (EV), or those infected with human immunodeficiency virus (HIV) are prone to develop SCC of skin, which is related to infection with ▶human papillomavirus (▶HPV). For ▶lung cancer, the major etiological agents are carcinogens present in ▶tobacco smoke (around 90% of male cancer deaths and 80% of those in females are associated with smoking); additional factors include a family history of the disease, or exposure to radon gas. Similarly, head and neck SCC is primarily related to tobacco use, particularly lesions of the oral cavity (▶Tongue cancer), oropharynx and larynx. In addition to cigarette smoking, intraoral lesions may also arise in users of chewing tobacco, as well as those who use pan (a combination of areca nut and slaked lime, rolled in a betel leaf to form a quid), with or without tobacco. This practice is popular in southern Asian cultures, and in immigrant populations from this region, resulting in large, exophytic tumors. Further etiological factors for head and neck cancer include alcohol use (also important for ▶esophageal SCC) and HPV infection. Anogenital SCCs are primarily caused by infection with “high-risk”

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HPV (Human Papilloma Virus) types. Additional etiology includes tobacco usage and HIV infection. Diagnosis and Clinical Features Diagnosis of squamous cell carcinoma is based on a combination of clinical examination and histopathological assessment of a biopsy specimen. In some cases, such as ▶lung and other internal tumors, clinical examination may be assisted by the use of imaging techniques, such as standard radiography or magnetic resonance imaging. SCCs of skin, oral or genital mucosa may present as exophytic, verrucous (warty) lesions (verrucous carcinoma), or as persistent ulcers that fail to heal. Typically, such ulcers have a raised, rolled border, and larger lesions may show signs of necrosis in the center. By definition, squamous cell carcinomas arise from squamous epithelium. Histopathologically, therefore, SCCs show signs of ▶invasion through the basement membrane into the underlying stromal tissue – the hallmark of carcinomas. Lesions may show varying degrees of differentiation: well-differentiated tumors will be more recognizable as squamous epithelium, forming nests of tumor cells within the stroma and may express an abundance of keratin, forming so-called “keratin pearls.” Some tumors can show fewer (or no) signs of squamous differentiation, and may be graded (▶Tumor grading) as moderately or poorly differentiated, or anaplastic. Highly aggressive lesions may invade adjacent muscle and bone, and enter into ▶lymphatic vessels or blood vessels, thus aiding their spread to secondary sites of growth (▶metastasis). Squamous cell carcinomas may develop through a series of well-defined premalignant stages, during which the epithelium shows increased disruption of normal growth and differentiation and loss of tissue architecture. The epithelium progresses through ever more advanced stages of ▶dysplasia, in which some (or all, depending of the degree of dysplasia) of the following ▶cellular atypia may be observed: . . . . . . . . .

Hyperchromatic nuclei More frequent mitoses Aberrant mitotic figures Mitoses in suprabasal cell layers (in stratified epithelia) Pleomorphic nuclei, altered nucleus/cytoplasmic ratio Loss of cellular polarity Dyskeratosis – keratinization deep within the epithelium Loss of ▶adhesion De-differentiation and loss of tissue architecture

Typically, premalignant lesions are described as mildly, moderately, or severely dysplastic depending on the number of cellular atypia observed upon

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histopathological examination. The most severe cases (but where invasion has not yet occurred) may be referred to as carcinoma-in-situ (CIS). Cervical dysplasias are generally graded as cervical intraepithelial neoplasia (CIN) grade I, II or III, or as CIS, representing increasing severity. Clinically, potential premalignant lesions may also be noted. ▶Actinic keratosis is a well-recognized condition seen on areas of sun-exposed skin which presents as scaly, erythematous patches. Similar lesions on the lip are known as actinic cheilitis. These lesions may range from mild to severe, depending on the degree of cellular atypia present histologically. Fullthickness cellular atypia (CIS) is known as ▶Bowen disease. Pre-neoplastic lesions are also recognized at other body sites. In the oral cavity, white patches (▶leukoplakia) may be dysplastic, although the majority does not progress to invasive cancer. Red, atrophic areas of ▶erythroplakia should be regarded with much more suspicion, as they have a greater propensity for malignant change. A combination of these two lesions – “speckled leukoplakia” or leuko-erythroplakia – are also more likely to undergo malignant transformation. Less frequently, lichen planus (particularly the erosive form) may develop into squamous cell carcinoma. In cervical epithelia, suspicious areas are identified by application of a dilute solution of acetic acid to the area under investigation, producing acetowhite lesions, the histological condition of which is then determined by biopsy. In the development of lung SCC, one of the intermediate histological events is the onset of squamous metaplasia, where the normal respiratory epithelium assumes squamous characteristics. This change may be reversible if exposure to the initiating agent (most commonly tobacco smoke) ceases. Disease Management Therapeutic modalities for squamous cell carcinomas include one of (or more commonly a combination of) surgical excision, chemotherapy or radiotherapy. Typically, smaller well-localized lesions are excised with a wide surgical margin of normal tissue. The “normality” of the margin is generally based on clinical and histological assessment. However, this is complicated by the phenomenon known as ▶field cancerization. This hypothesis proposes that histologically normal fields or patches of cells are present which have developed from genetically altered stem cells and, thus, are predisposed to undergo malignant ▶progression. This underlies the propensity of squamous cell carcinomas to recur following excision or for patients to develop multiple second primary lesions. The likelihood of future tumor occurrence makes preventive strategies appealing. In this regard, the use of ▶retinoids has been explored in several clinical trials. However, the success of this is still under debate as,

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in some trials, provision of beta-carotene actually increased the incidence of lung cancer. Novel chemotherapeutic drugs that target mutant epidermal growth factor receptors present on the tumor cells are being used for treatment of some ▶lung cancers and head and neck SCC. The central role for HPV in cervical ▶carcinogenesis has led to the development of a vaccine to prevent viral infection. Molecular Aspects A considerable body of research has documented the molecular genetics and biochemical features associated with squamous carcinogenesis. While distinct differences have been noted between tumors arising at specific body sites, there are many common genetic aberrations that are shared amongst SCCs. ▶Loss of heterozygosity (LOH), indicative of inactivation of ▶tumor suppressor genes, has been reported to occur at multiple chromosomal locations including chromosomes 1, 3p, 4, 5q, 6, 8, 9, 11q, 13q, 14q, 17p and 19q. Two of the most actively studied are the ▶CDKN2A gene on 9p21 and ▶TP53 on chromosome 17p13 which, respectively, encode p16/▶INK4A, an inhibitor of ▶cyclin D-dependent kinases, and ▶p53, a multi-faceted regulator of cell cycle progression, genomic damage and programmed cell death (apoptosis). Loss of p16/INK4A has been shown to occur through chromosomal loss or deletion, as a result of promoter hypermethylation and, less commonly, through intragenic mutation. The net effect of such a loss is to deregulate the activity of ▶cyclin dependent kinases (CDKs) 4 and 6, which are normally active in the G1 phase of the cell cycle. This leads to the hyperphosphorylation of pocket proteins, such as the ▶retinoblastoma protein pRB, and more rapid progression through the cell cycle, thus contributing to the enhanced proliferation seen in cancer cells. Loss or mutation of RB1 is observed less frequently in SCC which may be ascribed, at least in part, to the loss of p16/INK4A, increased expression of cyclin D1 as a result of gene amplification of a locus on chromosome 11p, and the action of the HPV E7 (▶Early Genes of Human Papilloma Viruses) oncoprotein. Loss of expression of a functional ▶p53 protein is a common feature of SCC, in some cases through chromosomal loss or deletion. More commonly, however, intragenic mutations result in expression of ▶p53 proteins harboring amino acid substitutions that disrupt normal function, or in expression of truncated proteins. The biological consequences of p53 loss can be wideranging, given the many functions of this protein, and include failure to activate cell cycle checkpoints in the event of genotoxic stress and failure to execute programmed cell death. C-to-T transition mutations are found commonly in skin cancer, with CC-to-TT changes present at high frequency. These are indicative of

ultraviolet irradiation-induced damage, consistent with the known etiology of SCC at this site. Similarly, mutations found in head and neck and lung SCCs are frequently ascribable to the actions of carcinogens present in tobacco smoke, such as the occurrence of Gto-T transversions. The presence of mutation in the TP53 gene may also be useful to identify clones of genetically altered cells that have arisen during the process of field cancerization. Deregulation of cell growth by human papillomavirus contributes to the genesis of the majority of cervical cancers. Additionally, HPV has been linked with other anogenital tumors as well as head and neck (primarily pharyngeal), skin and lung cancers. The E6 and E7 (▶Early Genes of Human Papilloma Viruses) oncoproteins encoded by “high-risk” HPV types deregulate cell cycle progression by targeting p53- and pRBdependent pathways. E6 (▶Early genes of human papilloma viruses) targets p53 for degradation by the ubiquitin-proteasome pathway (▶Ubiquitination). Additionally, E6 (▶Early Genes of Human Papilloma Viruses) targets PDZ-motif-containing target proteins such as Dlg, MAGI-1 and MUPP1, each of which has also been shown to suppress cell growth. The E7 (▶Early Genes of Human Papilloma Viruses) protein is well-recognized for its ability to bind the retinoblastoma protein and the related p107 and p130 pocket proteins, targeting them for degradation and, hence, also deregulating proliferation. E7 (▶Early Genes of Human Papilloma Viruses) also inhibits the function of the transcriptional coactivator FLH2 which may further enhance cellular transformation, while E6 and E7 (▶Early Genes of Human Papilloma Viruses) also upregulate expression of the cellular inhibitor of apoptosis protein cIAP2, leading to apoptosis resistance. Inactivation of the fragile histidine triad gene, ▶FHIT, located at chromosome 3p14 is another important ▶tumor suppressor gene loss that is observed in squamous cell carcinomas. Studies have documented reduced expression in ▶oral SCC and in oral premalignant lesions, as well as in esophageal, lung and ▶cervical carcinomas. In addition to gene loss, ▶epigenetic gene silencing by promoter hypermethylation contributes to reduced transcript levels, and may be attributable to exposure to tobacco smoke. Decreased expression is also reported to be an early event in tumor progression and may be associated with a worse prognosis. Conversely, studies of skin SCCs (nontobacco etiology) do not provide evidence of altered FHIT expression. Mutations in the ▶HRAS gene are reported in only 10–20% of skin tumors, in contrast to initial studies. However, NRAS mutations are found with higher prevalence in patients with xeroderma pigmentosum, an inherited condition in which there is a defect in DNA

Src

repair processes. Mutations in KRAS are reported in up to 30% of lung cancers. Genes encoding ▶Ras proteins are infrequently mutated in head and neck cancers, except for lesions associated with a pan or betel quid chewing habit. Disruption of growth factor signaling pathways is also common in many squamous cell carcinomas. Overexpression or mutation of the epidermal growth factor receptor (▶Epidermal growth factor receptor inhibitors/ligands) is seen with high frequency in head and neck, lung, alimentary and anogenital tumors, and helps to drive proliferation as well as ▶motility and ▶metastatic spread of tumor cells. Loss of the negative regulatory effects of transforming growth factor beta also contributes to deregulated cell growth, as well as the transition from an epithelial to a mesenchymal (▶Epithelial to mesenchymal transition) phenotype that is seen in some advanced cancers. Additionally, the role of ▶inflammation is becoming increasingly recognized in squamous cell carcinogenesis, as well as in other tumor types. Notable players in this area include members of the ▶chemokine network which can modulate immune function, induce tumor neovascularization (▶angiogenesis) and stimulate proliferation and metastasis of tumor cells. ▶Epithelial Tumors ▶Lung cancer

References 1. Boukamp P (2005) Non-melanoma skin cancer: what drives tumor development and progression? Carcinogenesis 26:1657–1667 2. Ha PK, Califano JA (2003) The molecular biology of mucosal field cancerization of the head and neck. Crit Rev Oral Biol Med 14:363–369 3. zur Hausen H (2002) Papillomaviruses and cancer: from basic studies to clinical application. Nat Rev Cancer 2:342–350 4. Schottenfeld D, Fraumeni JF Jr (2006) Cancer epidemiology and prevention, 3rd edn. New York Oxford University Press,

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Individual members of the SR family of proteins are able to complement non-splicing competent cytoplasmic extracts to gain splicing function. SR proteins are important for constitutive ▶splicing and have also been found to be important for regulation of alternative splicing. SR proteins facilitate alternative splicing by binding to elements within the pre-mRNA called splicing enhancers and recruiting other components of the ▶spliceosome

Src S ARAH J. PARSONS University of Virginia, Charlotteville, VA, USA

Synonyms

c-Src; v-Src; pp60c-Src; pp60v-Src

Definition v-Src (or viral Src) is a 60 kDa protein encoded by the oncogenic retrovirus, Rous sarcoma virus. The protein derives its name from its ability to induce sarcomas in experimental animals and malignantly transform cells in tissue culture. c-Src, or cellular Src, is the normal cellular progenitor of v-Src. c-Src is non- or weakly transforming when overexpressed in tissue culture cells. Both v- and c-Src are cytoplasmic tyrosine kinases that transfer phosphate from ATP to tyrosine residues within specific protein substrates. The resulting phosphotyrosine either conformationally activates the enzymatic activity of the recipient molecule or functions as a docking site for other molecules that transmit growth signals to the nucleus in a chain of events involving multiple phosphorylation and binding reactions. c-Src contains a carboxy-terminal region that maintains the molecule in a mostly inactive state. In v-Src, this 12 amino acid region is deleted, rendering the molecule constitutively active.

Characteristics

SR Proteins Definition A family of RNA binding proteins that are characterized by one or more amino-terminal RNA-recognition motifs (RRM), a glycine rich region, and a carboxyl terminal region that is rich in the amino acids arginine and serine which are largely arranged as dipeptides.

Domain Structure Each molecule of Src contains seven domains that are involved in targeting the protein to cellular membranes (the myristylation domain), in binding other proteins (the Unique, ▶SH3 and SH2 domains) and in regulating the catalytic activity (Fig. 1). Src is one of a family of at least nine proteins that have a similar overall structure, including Fyn, Yes, Fgr, Hck, Lck, Blk, Yrk, and Lyn. Some of the family members are present only in certain cell types, such as cells of the hematopoetic

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Src. Figure 1 Structure of c-Src. As a linear molecule, c-Src consists of an N-terminal membrane association domain that contains the site of myrisylation, a Unique domain that exhibits the widest sequence divergence among family members, an SH3 domain, an SH2 domain, an SH2/kinase linker, the catalytic domain, and a negative regulatory domain that contains Tyr 527 (531 in human c-Src). When c-Src is activated, Tyr 416 (Tyr 419 in human c-Src) in the kinase domain becomes phosphorylated. How all the domains of c-Src relate to one another in a three-dimensional context to generate the inactive and active states of the enzyme is also shown and explained in the text.

lineage, while others are ubiquitously expressed. c-Src is one of the latter family members. Subcellular Localization The myristate fatty acid modification on the amino terminus of Src targets it to intracellular membranes, including the plasma membrane and membranes of intracellular organelles, especially those of the endocytic pathway. c-Src has also been found to associate with ▶centrosomes in interphase cells. Interacting Proteins Src forms complexes with a variety of intracellular signaling molecules via its Unique SH2 and SH3 domains (Fig. 2). These proteins include, but are not limited to, polypeptide growth factor receptors such as the ▶epidermal growth factor (EGF) receptor, intercellular ▶adhesion molecules such as PECAM and ▶E cadherin, gap junction proteins such as connexin 43, and several proteins found in focal adhesions such as focal adhesion kinase (▶FAK) and p130CAS. While most of these binding proteins are also substrates of Src, Src can phosphorylate proteins that do not form complexes stable enough to extract from the cell, such as the cortical actin binding protein, ▶cortactin, p190RhoGAP (a GTPase activating protein for ▶Rho family GTPases) and clathrin, a component of endocytic vesicles.

Cellular and Molecular Aspects The extreme C-terminal domain of c-Src contains a tyrosine residue (Tyr 527 in chicken c-Src and Tyr 531 in human c-Src) that when phosphorylated binds its own SH2 domain in an intramolecular fashion (Fig. 1). This binding, together with the coupling of the SH3 domain to a pseudo-polyproline sequence in the SH2 kinase linker, renders the protein inactive. c-Src becomes activated when these intramolecular interactions are disrupted by competition with other signaling molecules that contain either phosphotyrosine or polyproline regions that bind the SH2 and SH3 domains, respectively, of c-Src. Such events occur, for example, when the c-Src SH2 domain binds phosphotyrosine 397 of FAK or phosphotyrosines of activated and tyrosine phosphorylated polypeptide growth factor receptors. Full activity is achieved upon dephosphorylation of Tyr 527/531 and autophosphorylation of Tyr 416/419 in the activation loop of the catalytic domain. Antibodies specific for phosphorylated Tyr 416/419 are frequently used to assess the activation state of c-Src in human tumors. c-Src activity has been reported to increase following integrin engagement of extracellular matrix (and subsequent activation of FAK) or upon stimulation of cells with growth factors, such as EGF, PDGF and FGF. v-Src is constitutively activated by deletion of the C-terminal phosphotyrosine 527/531 and mutations within the SH3 domain that reduce interactions with the pseudo-polyproline region.

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Src. Figure 2 Examples of c-Src targets and their potential roles in transformation.

Clinical Relevance c-Src is overexpressed or activated in multiple human tumors, particularly in ▶glioblastomas and ▶carcinomas of the breast, lung, colon, prostate, cervix, stomach and ▶ovary. In ▶breast cancers, the frequency of tumors overexpressing c-Src approaches 70%. Although analyses of other tumor types are not as extensive as those of breast cancers, existing data suggest the frequency of c-Src overexpression in lung and colon tumors may be similar to that in breast malignancies. Members of the EGF receptor family are also overexpressed in many of the same types of tumors that overexpress c-Src. Recent studies indicate that cSrc and EGFR synergistically promote tumor growth. This enhanced growth is accompanied by an EGFinduced association between c-Src and the EGFR,

phosphorylation of EGFR by c-Src on several novel sites, and activation of signaling pathways that are required for EGF-induced mitogenesis and cell survival following genotoxic stress. These findings are providing the impetus for discovering novel therapeutics that disrupt both the physical and functional interactions between c-Src and EGFR family members. c-Src’s involvement in the formation and turnover of focal adhesions and cell-cell contacts also suggests a role for this protein in cell ▶migration and ▶metastases. Regulation of ▶vascular endothelial growth factor (VEGF) expression in response to hypoxia implicates c-Src as a modulator of angiogenesis, further underscoring its potential importance as a target for anti-tumor therapy. To that end, numerous pharmaceutical companies have developed inhibitor compounds

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that target c-Src kinase activity, and several of these are being tested for treatment of solid tumors in clinical trials, including AZD0530 (AstraZeneca), BMS3554825 (Bristol Myers Squibb), and SKI-606 (Wyeth Research).

Src Homology 2 ▶SH2/SH3 Domains

References 1. Thomas SM, Brugge JS (1997) Cellular functions regulated by Src family kinases. Annu Rev Cell Dev Biol 13:513–609 2. Abram CL, Courtneidge SA (2000). Src family tyrosine kinases and growth factor signaling. Exp Cell Res 254:1–13 3. Ishizawar R, Parsons SJ (2004). c-Src and cooperating partners in human cancer. Cancer Cell 6:209–214 4. Belsches-Jablonski AP, Demory ML, Parsons JT et al. (2005). The Src pathway as a therapeutic strategy. Drug Discov Today: Ther Strateg 2:313–321

Src Homology Domain Definition SH; A region of a protein whose tertiary structure allows it to specifically bind to phosphorylated tyrosine residues. ▶SH2/SH3 Domains

SRC-3 ▶Amplified in Breast Cancer 1

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Src Kinase Definition

▶Src was the first discovered tyrosine kinase. v-Src (viral sarcoma) was the first discovered oncogene, isolated from Rous sarcoma virus and is constitutively activated. Src comprises ▶src homology domains, which recruit proteins, expressing these domains to Src. ▶Focal Adhesion Kinase

▶Cortactin

SRC-Homology Domains Src Family Tyrosine Kinase

Definition

▶SH2 Domain.

Definition

The ▶src gene is the first discovered viral oncogene carried by the ▶retrovirus Rous sarcoma virus and also is the first identified proto-oncogene. The Src family consists of nine family members encoding tyrosine kinases, which are anchored to the inner surface of cytoplasmic membrane with their N-terminal myristylation. Some members such as Src and Fyn are also located within nuclei as well as within mitochondria. ▶Membrane-Linked Docking Protein ▶Transduction of Oncogenes

▶SH3 Domain

SRCR Superfamily Definition The scavenger receptor cysteine-rich (SRCR) superfamily is a group of glycoproteins comprising cell

Staging of Tumors

surface molecules as well as secreted proteins that are characterized by the presence of at least one highly conserved SRCR-domain.

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St. John’s Wort Definition

Sterol regulatory element-binding protein (SREBP): A transcription factor for the transcription of genes that encode the low-density lipoprotein receptors and enzymes in cholesterol synthesis.

Synonym hypericum, goatweed. The flowering tops of St. John’s Wort are used to treas and tablets with concentrated extracts. Although St. John’s wort is not a proven therapy for depression, there is some evidence that St. John’s wort is useful for treating mild to moderate depression. It is also used for anxiety and/or sleep disorders. St. John’s wort can influence the clearance of specific drugs known to be metabolized by CYP3A (▶Cytochrome P450) or excreted via ▶ABC drug-transporters.

▶Fatty Acid Synthase

▶Irinotecan

SREBP Definition

SRF Definition Serum response factor (SRF) is a transcription factor that recognizes the CArG box (CC-ATrich-GG) in cellular genes, such as immediate-early-genes. SRF interacts either with an ▶Ras-regulated B-box containing ▶Ets protein (Elk-1, Sap, Net or FLI-1) or with β-actin/ Rho-GTPase (▶Rho Family Proteins) -regulated Mal to mediate responses to a variety of extracellular stimuli. ▶ETS Transcription Factors

Stage Definition Referring to tumors, is an internationally agreed index which objectively measures the extent of tumour growth and progression. Common criteria include tumour size, extent of local spread, and presence of lymph node or visceral metastasis. Each tumour-type has its own staging system, with variations in the common criteria, which correlates with prognosis. ▶Transcoelomic Metastasis

srGAPs Staging of Tumors Definition

Family of ▶GTPase activating proteins, srGAPs that facilitate hydrolysis of Cdc42 that ultimately leads to actin depolymerization and contributes to the repulsive effect of Slit in neurons. ▶Slit

SRIF ▶Somatostatin

FANG FAN Department of Pathology, University of Kansas School of Medicine, Kansas City, KS, USA

Synonyms Determination of tumor extent and spread; Tumor staging

Definition Tumor staging is a clinical procedure aimed at documenting the anatomic extent of a malignant tumor at a specific site, and the extent of its spread locally, regionally, or to distant sites. Upon completion of

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the clinical staging procedures, the tumor under consideration is assigned to a particular stage (stadium in Latin), i.e. given a semiquantitative designation summarizing the data about the size of the tumor and the extent of its spread.

absence of distant metastasis (M). For the sake of uniformity and consistency the following standardized definitions are used:

Characteristics

Primary tumor (T)

Purpose The staging of cancer is used to document the extent of the neoplastic disease in a standardized and consistent manner that will allow clinicians to compare the features of a particular tumor with other similar tumors. The main reasons for staging of tumors have been summarized by the American Joint Committee on Cancer as follows:

TX T0 Tis

. Selection of the most appropriate therapy for each individual patient . Formulation of prognosis for each cancer patient, i.e., prediction of the natural course of the neoplastic disease and its outcome with or without treatment . Objective and measurable assessment of the effects of therapy . Objective performance of clinical cancer studies within a single institution or geographically distant institutions Clinical staging of tumors is of paramount importance for the proper selection of treatment of each particular cancer patient. Many univariate and multivariate studies have shown that the tumor stage at the time of diagnosis is in most instances the most powerful predictor of outcome of a neoplastic disease and cancer patients’ survival with or without treatment. It is also essential for organizing multi-institutional cancer treatment studies and other forms of clinical cancer research. Methods Tumor staging is typically based on a multidisciplinary effort including oncologists, surgeons, radiologists, pathologist and even other clinicians. The data may be collected by biopsy, during surgical exploration, during definitive cancer surgery, laparoscopic surgery, and radiologic examination of the patient. The material collected during these procedures is usually submitted for macroscopic and microscopic pathologic examination. Additional studies, such as molecular biologic analysis of the tumor material may be undertaken in research institutions, but it is not routinely included in the staging of most tumors. The most widely used tumor staging system is called the TNM system. The TNM system is based on analysis of three parameters: the size or extent of the untreated primary tumor (T), the absence or presence of spread to the regional lymph nodes (N), and the presence or

Primary tumor cannot be evaluated No evidence of primary tumor Carcinoma in-situ (early cancer that has not invaded into the surrounding stroma)

Regional lymph nodes (N) NX N0

Regional lymph nodes cannot be evaluated No regional lymph node involvement

Distant metastasis (M) MX Distant metastasis cannot be evaluated M0 No distant metastasis (cancer has not spread to other parts of the body)

The staging based on the TNM data typically includes five categories, corresponding to stages 0 and stages I– IV. Each of these stages may be subdivided into subcategories labeled a, b, or c. Stage 0 denotes carcinoma in situ. Stage I, II and III tumors are localized to the organ of their origin or have spread regionally. Stage IV tumors have metastasized to distant sites. The criteria for T, N, and M and for stages 0–IV vary from one anatomic site to another. For example, bladder cancer T3N0M0 is stage III, while colon cancer T3N0M0 is stage II. For specific staging of tumors in various anatomic sites one must refer to specific staging manuals. Figure 1 illustrates the definition of T classifications for bladder cancer. Perspectives Staging of tumors has been standardized to a great extent but still many problems remain to be solved. The older staging systems such as the staging of colonic carcinoma according to Dukes are not used any more and are thus only of historical interest. New staging classifications are constantly being proposed and the merits of new approaches are discussed in medical literature. The same holds true for the new studies on the molecular biology techniques or new imaging techniques, which are used in

Standardization

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Staging of Tumors. Figure 1 Tumor staging. Extent of primary bladder cancer (T classification).

experimental protocols in many leading research centers. Overall, one can predict with confidence that the current protocols for staging of tumors will be improved by the introduction of newer technology, but all these modifications will require extensive independent confirmation and validation before they become widely accepted.

Ta Tis T1 T2 pT2a pT2b T3 pT3a pT3b T4 T4a T4b

Non-invasive papillary carcinoma Carcinoma in-situ: “flat tumor” Tumor invades subepithelial connective tissue Tumor invades muscle – Superficial muscle (inner half) – Deep muscle (outer half) Tumor invades perivesical tissue – Microscopically – Macroscopically (extravesical mass) Tumor invades any of the following: prostate, uterus, vagina, pelvic wall, abdominal wall – Prostate, uterus, vagina – Pelvic wall, abdominal wall

(Reproduced from Greene FL, Page DL, Fleming ID, Fritz AG, Balch

References 1. Greene FL, Page DL, Fleming ID, Fritz AG, Balch CM, Haller DG, Morrow M (eds) (2002) AJCC cancer staging manual, 6th edn. Springer-Verlag, New York 2. Wittekind Ch, Greene FL, Hutter RVP, Klimpfinger M, Sobin LH (eds) (2005) TNM atlas. Illustrated guide to the TNM classification of malignant tumours. Wiley-Liss, Hoboken, New Jersey

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Standardization Definition A consistent set of procedures for designing, administering, and scoring an assessment. The purpose of standardization is to ensure that all individuals are assessed under the same conditions. ▶Biomonitoring

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STAT

STAT Definition Signal transducer and activator of transcription, proteins activated in response to interleukins and other cytokines that regulate function of immune system and proliferation, apoptosis, and angiogenesis in various cell lines. ▶Suppressors of Cytokine Signaling ▶Signal Transducers and Activators of Transcription in Oncogenesis

Stathmin Definition Op 18; Is a ubiquitous cytosolic phosphoprotein with various regulatory functions in cell proliferation, differentiation signaling, and activation. In particular, stathmin is involved in the regulation of tubulin dynamics through inhibition of microtubule formation and/or microtubule depolymerization. ▶Microtubule-Associated Proteins. ▶Oncoprotein 18

Statins L EONIDAS C. P LATANIAS Robert H. Lurie Comprehensive Cancer Center and Division of Hematology-Oncology, Department of Medicine, Northwestern University Medical School, Chicago, IL, USA

Definition Statins are synthetic agents that inhibit HMG-CoA reductase, the rate-limiting enzyme that controls cholesterol biosynthesis. Currently, there are several statins in use for the treatment of hypercholesterolemia in humans. It is well established that these agents induce their therapeutic effects by decreasing low density lipoproteins (LDL). Such effects have been associated with a decrease in the rate of progression of atherosclerotic lesions in patients with coronary artery

disease, and it is now well established that the use of statins has changed the natural history of coronary artery disease in humans. Beyond their ability to lower cholesterol, statins have important additional biological effects in vitro and in vivo, including anti-inflammatory and antitumor properties.

Characteristics There has been substantial experimental evidence establishing that statins inhibit the growth of malignant cells and induce programmed cell death in vitro. Moreover, statins exhibit chemopreventive effects towards certain types of tumors in vivo when administered to humans. The ability of statins to generate such responses in vitro and in vivo is of high interest and may prove to be of clinical value in the future. Cellular Effects of Statins in Vitro Statins induce apoptosis of different types of malignant cells in vitro. These include cells of leukemia origin as well as cells originating from a variety of solid tumors, including colon, prostate, breast, thyroid, pancreatic, small and non-small cell lung cancers, as well as malignant melanoma, osteosarcoma, glioma and medulloblastoma. Although the mechanisms by which statins induce apoptosis have not been fully elucidated, there is evidence that distinct cellular events are involved in the induction of statin-dependent proapoptotic responses. Blocking protein ▶geranylgeranylation correlates with ▶lovastatin-induced apoptosis of human leukemia cell lines. In addition, statins activate the pro-apoptotic JNK ▶MAP kinase pathway in malignant cells, and the activation of this pathway is essential for statin-dependent programmed cell death. Beyond activation of the JNK pathway, statins inhibit the MEK/ERK signaling cascade, which is associated with increased cell proliferation, and this constitutes another major mechanism contributing to their antineoplastic properties. ▶Atorvastatin and ▶fluvastatin also induce differentiation of NB4 leukemic cells that are of acute promyelocytic leukemia (APL) origin. Such effects also occur in cell variants that are refractory to the differentiating effects of all-trans-retinoic acid (ATRA). Atorvastatin and fluvastatin exhibit also similar in vitro effects on primary leukemic blasts that have developed resistance to the differentiating effects of ATRA and appear to reverse such ATRA-resistance. Statins in the Prevention and Treatment of Cancer There is accumulating evidence from epidemiological studies indicating that statins exhibit chemopreventive effects against certain solid tumor types, including colorectal cancer, lung cancer, prostate cancer, and pancreatic cancer. On the other hand, statins do not seem to exert such chemopreventive effects against

Staurosporine

breast cancer. Extensive preclinical evidence has also suggested that statins may have therapeutic effects against certain malignancies. This has led to the recent initiation of clinical trials to examine the clinical activity of statins in certain malignancies. A recent phase I study assessed the combination of high doses of pravastatin with chemotherapy in the treatment of acute myelogenous leukemia patients. Such combination was found to be safe and well tolerated, while a high number of complete responses was seen. Altogether, there is a substantial amount of evidence raising the possibility that statins may eventually find a role in the prevention and/or treatment of certain tumors and hematologic malignancies. Several epidemiological and clinical studies are currently ongoing to address this issue.

References 1. Chan KK, Oza MM, Siu LL (2003) The statins as anticancer agents. Clin Cancer Res 9:10–19 2. Demierre MF, Higgins PD et al. (2005) Statins and cancer prevention. Nat Rev Cancer 5:930–942 3. Greenwood J, Mason JC (2007) Statins and the vascular endothelial inflammatory response. Trends Immunol 28:88–98 4. Schönbeck U, Libby P (2004) Inflammation, immunity, and HMG-CoA reductase inhibitors: statins as antiinflammatory agents? Circulation 109:18–26 5. Sassano A, Platanias LC (2008) Statins in tumor suppression. Cancer Lett 260:11–19

Staurosporine

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Characteristics The initial studies on AM-2282 focused on the taxonomy of the producing strain, fermentation, isolation, and physico-chemical and biological properties of this new alkaloid. Besides being identified as a new species, they also discovered that AM-2282 had antimicrobial activity. The term antimicrobial is given to any type of chemical compound that can suppress the growth of, or aid in the death of microorganisms, such as bacteria, yeast and mycoplasma. AM-2282 had antimicrobial activity against fungi and yeast, but no significant effects on bacteria. The structure of AM-2282, which herein will be referred to as staurosporine, is shown in Fig. 1. Staurosporine was the first of over 50 alkaloids to be isolated with this type of chemical structure, which was elucidated through X-ray analysis. In Fig. 1, the portion of the structure above the arrow, is known as an indole carbazole sub-unit, while the lower part of the structure is a sugar molecule. Although staurosporine was isolated in 1977 and, its X-ray crystal structure was determined in 1978, it was not until 1996 that the first total chemical synthesis was achieved. Part of the challenge to the synthesis of staurosporine was the joining together of the sugar and indole carbazole groups and establishing the sugar stereochemistry. In 1992, the indole carbazole group known as staurosporine aglycon was isolated. Aglycon is the non-sugar compound remaining after replacement of the glycosyl group with a hydrogen atom. Kinase Inhibition The anti-microbial activities of staurosporine were initially thought to be via its role as a potent inhibitor

M OLLIANE M CGAHREN -M URRAY, K HANDAN K EYOMARSI

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Department of Experimental Radiation Oncology, Department of Surgical Oncology, Unit 66, University of Texas, MD Anderson Cancer Center, Houston, TX, USA

Definition Staurosporine is a natural product originally isolated from the bacterium Streptomyces staurosporeus from a soil sample obtained in Japan (Iwate Prefecture) in 1977 during a search for new alkaloids present in actinomycetes and given the name AM-2282. The term alkaloid refers to a naturally occurring amine produced either by a plant, animal or fungus. Actinomycetes are a group of Gram-positive bacteria that had previously been shown to produce the alkaloids pyrindicin, NA-337A and TM-64.

Staurosporine. Figure 1 Structure of staurosporine (AM – 2282).

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of protein kinase C (PKC). These initial studies revealed that staurosporine was able to inhibit PKC from rat brain. Using other inhibitors such as triflouperazine, chloropromazine, and polymixin B, staurosporine was a more potent inhibitor of PKC than other known inhibitors. Furthermore, PKC inhibitors triflouperazine, chloropromazine, and polymixin B appeared to compete with phospholipids, whereas, the inhibition by staurosporine was not released by increasing the concentration of phosphatidylserine. Studies with cultured cells showed that staurosporine has very potent growth inhibitory activity. In addition to being an inhibitor of PKC, staurosporine also inhibits several other kinases, such as tyrosine kinases. The in vitro activity of staurosporine was analyzed by investigating the autophosphorylation of p60v-src in chicken embryo fibroblasts (CEF) that were infected with the rous sarcoma virus (RSV), revealing staurosporine was able to inhibit the autophosphorylation. This was evidence as staurosporine could inhibit tyrosine specific protein kinases similarly to serine and threonine specific kinases such as PKC. Together, staurosporine is a more potent inhibitor of protein-tyrosine kinase than other known inhibitors. Staurosporine can also inhibit the myosin light chain kinase. Myosin light chain kinase plays a critical role in smooth muscle contraction as well as in the activation of non-muscle cells, by catalyzing the transfer of the γ-phosphate from ATP to the myosin light chain, which is dependent upon Ca2+/calmodulin. The phosphorylation of the light chain is necessary for the activation of actomyosin ATPase, which is a prerequisite for tension development in both smooth and non-muscle cells. Inhibition of the myosin light chain kinase is ATPdependent. Other kinases that can be inhibited by staurosporine include the insulin receptor tyrosine kinase activity noncompetitive with ATP and the platelet-derived growth factor (PDGF) receptor tyrosine kinase. Besides having inhibitory activity on these kinases involved in signal transduction pathways, staurosporine was also shown to block cells in different phases of the cell cycle. Staurosporine can block the G1 to S transition at low concentration (1–10 ng/ml) and block cells in late G2 phase at higher concentrations (100–200 ng/ml). There have been several reports showing that the retinoblastoma protein is important in the ability of staurosporine to arrest cells in the G1 phase of the cell cycle. For example, staurosporine can be used to protect normal cells from the toxic effects of chemotherapy at subnanomolar concentrations, to allow for a reversible G1 arrest through inhibition of the retinoblastoma protein, followed by treatment with camptothecin. Such sequential treatment (with staurosporine first) results in a protection of cells against the toxic affects of chemotherapy. Tumor cells, however, appear unaffected by

staurosporine, and are sensitive to low amounts of camptothecin. The cell cycle associated kinase that is inhibited by staurosporine is Cdc2 (also known as CDK1) which is important in the G2/M transition of the cell cycle. Staurosporine also inhibits the cdk2 and cdk4 kinases which are involved in G1 and S phases. Collectively, these findings suggest that staurosporine is a non-specific kinase inhibitor because it can inhibit kinases of several different functions with similar efficiencies. This is due to the fact that the serine/theronine kinases conserve the amino acid sequence and 3-D structure of the ATP binding domain. Additionally, staurosporine inhibits the activity of both the insulin receptor tyrosine kinase and of Ca+/ calmodulin-dependent protein (CaM) kinase II in a non-competitive manner with ATP. This suggests that staurosporine can interact with other catalytic domains distinct from the ATP binding site. Staurosporine in Apoptosis Staurosporine has been a useful tool in analyzing apoptosis because it has been able to induce apoptotic cell death in cell lines that are normally resistant to chemotherapeutic drugs and death-inducing ligands. One of the death-inducing ligands, TRAIL ((TNF)related apoptosis-inducing ligand), can normally induce apoptosis in two-thirds of melanoma cell lines examined. Staurosporine, however, is able to induce apoptosis in all melanoma cell lines tested, including those resistant to TRAIL. Although staurosporine was shown to have a strong cytotoxic effect on the growth of several mammalian cell lines, it did not show anti-tumor activity in any in vivo models tested. However, a naturally occurring analog of staurosporine, UCN-01 showed anti-tumor activity in vivo. UCN-01 was also isolated from the same culture broth Streptomyces sp. No. 126 that produced staurosporine. UCN-01 differs structurally from staurosporine with a hydoxyl group at the C-7 carbon. Adding this hydroxyl group causes UCN-01 to be specific for PKC inhibition. UCN-01 also shows apoptotic effects in vitro on the cell lines HeLa S3 and MCF-7 similar to what was observed with staurosporine. Similar to staurosporine, UCN-01 can also inhibit cell proliferation by arresting cells in different phases of the cell cycle. The growth inhibitory affect of UCN01 is often used to modulate the affects of radiation and chemotherapy. When cells are treated with radiation, which arrests cells in the G2 phase of the cell cycle, in the presence of UCN-01, the cells are no longer able to accumulate in G2 leading to early mitosis and subsequent apoptosis. UCN-01 also abrogates the S phase of the cell cycle. For example, in p53 mutant cells, treatment with chemotherapeutic drugs such as camptothecin results in S and G2 arrest of

Stefins

the cells. When cells are subsequently treated with UCN-01, it leads to an abrogation of the camptothecinmediated arrest resulting in mitotic catastrophe and cell death.

Anti-tumor Activity Since UCN-01 shows anti-tumor activity in vivo with much less cytotoxicity than staurosporine, UCN-01 was used for further pre-clinical studies. Using a xenograft model system with several tumor cell lines (breast and renal carcinoma, and leukemia cells) and with either intravenous or intraperitoneal injections, UCN-01 was shown to have an anti-tumor effect. The first case of using UCN-01 to treat patients was in 1996 with a 72 h infusion in the United States (Bethesda, MD) and in Japan as a 3 h infusion. These initial studies showed an unusual pharmacological effect that was not observed in the animal models. The concentrations of UCN-01 in the human plasma were considered abnormally high compared to animal models. Furthermore, the half-life in humans was over 500 h, which was 100 times longer than in the animal models. Eventually it was discovered that in humans, UCN-01 binds strongly to the plasma α1-acidic glycoprotein resulting in its lack of plasma clearance. Although the initial schedule called for 72-h continuous infusion every 2 weeks, based on the low clearance and prolonged half-life of UCN-01, this was modified to 36-h continuous infusion every 4 weeks. This study has lead to several follow-up studies in which UCN-01 is given as 1–3 h infusions every 4 weeks along with several combinatorial trials. For example, a phase I/II trial of gemcitabine followed by UCN-01 for a 72-h infusion was recently initiated at the National Cancer Institute. Among some of the other agents that are being examined in combination with UCN-01 are cisplatin and 5-fluorouracil. Other ongoing studies with UCN-01 are to use this agent to protect normal cells against the toxic affects of chemotherapy. Since the concentration of UCN-01 required to reversibly arrest normal cells in the G1 phase of the cell cycle is much lower than those required to mediate a toxic affect in tumor cells, this rationale provides a promising alternative to chemotherapy alone. These pre-clinical and ongoing clinical studies provide a novel and potent target that can be used to biologically modify the mechanisms of deregulation of cancer cells and as such provide a novel class of anticancer agents.

References 1. Link JT, Raghavan S, Gallant M et al. (1996) Staurosporine and ent-staurosporine: the first total syntheses, prospects for a regioselective approach, and activity profiles. J Am Chem Soc 118:2825–2842

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2. Furusaki A, Hahiba H, Matsumoto T et al. (1978) X-ray crystal structure of staurosporine: a new alkaloid from a Streptomyces strain. J Chem Soc Chem Commun 18:800– 801 3. Tamaoki T et al. (1986) Staurosporine, a potent inhibitor of phospholipid/Ca++ dependent protein kinase. Biochem Biophys Res Commun 135(2):397–402 4. Zhang XD, Gillespie SK, Hersey P (2004) Staurosporine induces apoptosis of melanoma by both caspase-dependent and -independent apoptotic pathways. Mol Cancer Ther 3 (2):187–197 5. Sausville EA et al. (2001) Phase I trial of 72-hour continuous infusion UCN-01 in patients with refractory neoplasms. J Clin Oncol 19(8):2319–2333

Stefins J ANKO KOS Faculty to Pharmacy, University of Ljubljana, Ljubljana, Slovenia

Synonyms Type I cystatins; Cystatins A, B

Definition

▶Stefins are members of the ▶cystatin superfamily of cysteine proteinase inhibitors localized in the cytosol and thought to protect cytoskeletal proteins from degradation by ▶cysteine proteases released from lysosomes.

Characteristics Type-1 or Family-1 of the cystatin superfamily of cysteine protease inhibitors includes human stefins A and B and their homologues in other species such as ▶cystatins α and β in rat, bovine thymus stefin C, porcine thymus stefins D1 and D2, mouse stefins A (1–4) and others (see MEROPS subfamily I25A). The genes for human stefins A and B have been mapped to chromosomes 3q21 and 21q22.3, respectively. The lack of a signal sequence and disulfide bonds makes stefins distinct from other members of the cystatin superfamily. Stefins are single chain proteins consisting of 98–103 amino acid residues, with a molecular mass of 11–12 kDa. Human stefin A is an acidic protein with pI values between 4.5 and 5.0, whereas stefin B is neutral, having pI values in the range of 5.9–6.5. Their tissue and cellular distribution are different, stefin A being localized mainly to epithelial and lymphoid tissue, while stefin B is evenly distributed in various cells and tissues. Like other members of the cystatin superfamily, stefins are reversible and competitive inhibitors of cysteine proteases. The structural basis of the inhibition

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has been elucidated from the X-ray crystal structure of ▶papain-stefin B complex and NMR structure of stefin A. Stefins are potent inhibitors of ▶cathepsins L and S with Ki values in the picomolar range, whereas cathepsin B inhibition is weaker (Ki 10–8 M for stefin A and 10–7 M for stefin B). Physiological and Pathological Roles Besides protection of cytosolyc and cytoskeleton proteins from degradation by cysteine proteases accidentally released from lysosomes, several other functions have been suggested for stefins. For example, stefin A may be important in the control of normal ▶keratynocyte proliferation and differentiation. Also, it has been proposed that it plays a role in ▶apoptosis, since apoptotic bodies consistently stain for inhibitor, which also correlates with p53 activation. Stefin A should also protect epithelial and lymphoid tissues from cysteine proteases produced by pathogens invading the body. Increased levels of stefin A were found in inflammatory skin samples, psoriatic epidermis, and in inflamed gingival tissue homogenates from patients with periodontal inflammatory diseases. Decreased levels of stefin B mRNA were detected in patients with ▶progressive myoclonus epilepsy (PME) and associated with excessive activity of cathepsin B. Besides protease inactivation, stefin B could bind other proteins in a multiprotein complex that has a specific cerebellar function, which might contribute to the disease in patients with progressive myoclonus epilepsy. Recent genetic studies have also identified mouse stefin A to be involved in a control of ▶ovarian follicular growth and maturation. Stefins in Cancer Cysteine proteases, the targets for stefin’s inhibitory activity, have been implicated in multiple steps of tumor ▶progression, including processes of cell transformation and differentiation, ▶motility, ▶adhesion, ▶invasion, ▶angiogenesis, and ▶metastasis. In most tumor types their levels of expression, protein concentrations and enzymatic activities, in particular of cathepsins B and L, have been demonstrated to be significantly higher than in their control tissue counterparts. The increased levels of cathepsins are usually not accompanied by an equal increase of the cystatins, which was suggested as the main cause of harmful cysteine, cathepsins-dependent proteolytic activity in tumor tissue. However, the balance is selectively altered for type II cystatins, which are in most cases downregulated in tumors, whereas type I cystatins, i.e. stefins A and B, have been found up-regulated in a majority of cases when compared to control tissue counterparts. Higher levels of stefins A and B in tumors have been determined in lung, ▶breast, head and neck and ▶prostate cancer, as well as in murine lymphosarcomas, ▶hepatomas and Lewis lung carcinomas (Fig. 1). These

Stefins. Figure 1 Stefin A immunostaining in lung adenocarcinoma (Kindly provided by B. Werle).

higher levels, up to a certain level, may counter-balance the excessive activity of cysteine cathepsins, associated with matrix remodeling, resulting in the progression of the disease. On the other hand, high cytosolic levels of stefins may be relevant for regulation of apoptosis, when initiated via lysosomal cell death pathway inhibiting cathepsin B, which was proposed as a dominant execution protease in the lysosomal apoptotic pathways, induced in a variety of tumor cells by tumor necrosis factor alpha (▶TNF-α). In some studies lower levels of stefins in tumors have been reported. For example, stefin A immunoreactivity was lower in lymphomas and in tumors of squamous epithelial cell origin, as well as in prostate and ▶brain tumors. Lower mRNA levels of stefin A or B have been reported in breast and ▶esophagus tumors as compared to adjacent control tissues. Although stefins are cytosolic proteins, they have also been detected in body fluids of cancer patients. Stefin A and stefin B have been detected in ascitic fluid from patients with ovarian carcinoma and in bronhoalveolar fluid of lung cancer patients. Increased serum levels of stefin A in patients with ▶hepatocellular carcinoma and liver cirrhosis have been correlated with tumor size and with a number of neoplastic lesions. Stefin A, but not stefin B, levels were moderately increased also in patients with ▶colorectal or lung cancer. Increased levels of cysteine protease activity, not being balanced by a corresponding increase of cysteine protease inhibitors, are associated with the progression of malignant disease and patients’ poor prognosis. Enhanced expression of stefins is expected to diminish the tumor-associated proteolytic activity and indeed, there is evidence of a suppressive role of stefins in various cancer types. Moreover, higher levels of stefin A and stefin B in tumor tissues have been shown to correlate with a favorable prognosis for cancer patients. A significant prognostic value of stefin A and stefin B was determined in patients with lung and head and neck cancer. In the latter, high stefin A tumor levels were found as a strong factor for prediction of prognosis also in multivariant analysis when correlated with

Stem Cell Hypothesis in Cancer

established clinical parameters. In prostate tumors higher cathepsin B/stefin A ratios were associated with a more aggressive behavior of prostate cancer. Animal models with excluded expression of particular cystatin did not support a suppressive function for cysteine protease inhibitors in cancer. In stefin B as well as cystatin C ▶knock-out mouse, a significantly lower metastatic spread was detected than in wild-type animals. Similarly, higher levels of stefin A and stefin B in body fluids have been associated with a poor prognosis in cancer patients. Alterations in secretion may result in higher extracellular and lower intracellular levels of stefins and, therefore, a reverse correlation with patient survival is to be expected. However, cysteine proteases, and consequently their inhibitors, are involved in various physiological processes, including those which may act in a manner opposing tumor progression, such as apoptosis, activation of T-cell immune response, cell ▶migration, seeding, and drug resistance processes. Thus, besides their concentration, cell and tissue localization of stefins, and a number of extrinsic and intrinsic factors, could make a critical switch between harmless and harmful.

References 1. Keppler D (2006) Towards novel anti-cancer strategies based on cystatin function. Cancer Lett 235:159–176 2. Kos J, Lah T (2006) Role of cystatins and stefins in cancer. In: Zerovnik E, Kopitar-Jerala N, Uversky V (eds) Human stefins and cystatins. Nova Science Publisher, New York, pp 153–165 3. Kos J, Krasovec M, Cimerman N et al. (2000) Cysteine proteinase inhibitors stefin A, stefin B and cystatin C in sera from patients with colorectal cancer: relation to prognosis. Clin Cancer Res 6:505–511 4. Strojan P, Budihna M, Smid L et al. (2000) Prognostic significance of cysteine proteinases cathepsins B and L and their endogenous inhibitors stefins A and B in patients with squamous cell carcinoma of the head and neck. Clin Cancer Res 6:1052–1062 5. Turk V, Kos J, Turk B (2004) Cysteine cathepsins (proteases) – on the main stage of cancer? Cancer Cell 5:409–410

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stem cells, germinal stem cells, and adults stem cells that have different developmental potentials: totipotent, pluripotent, multipotent, or unipotent. ▶Adult Stem Cells ▶Stem Cell Markers ▶Stem Cells

Stem Cell Factor Definition SCF; Is a glycoprotein that acts as both a positive and negative regulator of hematopoiesis. The cell surface receptor for SCF is KIT, a cancer stem cell marker. SCF is also involved in mast cell development, gametogenesis, and melanogenesis. ▶Stem Cell Markers ▶Kit/Stem Cell Factor Receptor in Oncogenesis ▶Mastocytosis

Stem-Cell Harvest and Purging Definition Following stimulation with growth factors, chemotherapy or both, CD34+ stem cells can be mobilized to the blood and harvested via a central vein catheter. In case of malignant bone marrow involvement, tumor cells may be mobilized as well. By in vitro ▶purging the stem cells may be selected (e.g., CD34+ cell selection) or the tumor-cells depleted. By in vivo purging of the patient with monoclonal antibodies (e.g., CD20 antibodies in B-cell lymophomas), the amount of tumor cells in the stem cell product may be reduced to undetectable (by ▶PCR) levels. ▶Mantle Cell Lymphoma

Definition Is a founder cell that exists in all multicellular organisms and shows self-renewal ability through mitotic cell division and can differentiate into a wide range of lineage-committed cells. Upon division, each new cell has the potential to either remain as a stem cell or become another type of cell with a more specialized function. There are three kinds of stem cells: embryonic

Stem Cell Hypothesis in Cancer Definition

Tumors arise from cells termed cancer ▶stem cells that have properties of ▶adult stem cells, particularly the

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abilities to self-renew and differentiate into multiple cell types, and that these cells persist in tumors as a distinct population that likely causes disease relapse and metastasis. They are the only cells capable of, by themselves, giving rise to new tumors. ▶Pancreatic Cancer Stem Cells

Stem Cell Markers G AIL M. S EIGEL Department of Ophthalmology, University at Buffalo, Buffalo, NY, USA

Definition Stem cell markers are molecules used for the identification of unspecialized, undifferentiated cells, and in the case of malignancy, presumptive ▶cancer stem cells.

Characteristics There is increasing evidence that subpopulations of neoplastic cells demonstrate heterogeneity with respect to proliferation, differentiation, and expression of cellular proteins characteristic of ▶stem cells. Subpopulations of cells that express stem cell markers that can also be shown to contribute to tumor progression and resistance to chemotherapy are termed cancer stem cells. Cancer stem cells are found in very small subpopulations within tumors, in the range of 0.1-1% of the total cell number. Microscopically, cancer stem cells outwardly appear the same as any other tumor cell. Therefore, in order to identify these rare subpopulations, a number of stem cell markers have been identified and developed as a means of distinguishing stem-like cells from other cells within a cancer population. Unique expression patterns of stem cell markers provide a means for scientists to identify as well as isolate stem-like cells from heterogeneous tumor populations. Stem cell markers are generally cell surface proteins with the ability to selectively bind to, or activate other signaling molecules. In some cases, stem cell markers are transcription factors that maintain stem cell properties of ▶pluripotency and/or ▶self-renewal. Stem cell markers are often designated by short-hand terms, based on their cellular function and/or the molecules to which they bind. As yet, there is no unanimously agreed-upon universal stem cell marker. Therefore, multiple markers are used in combination for verification of stem cell identity.

Stem cell markers have been assigned to embryonic, hematopoietic, and neural categories based upon the original location(s) in which they were discovered. These categories work fairly well for embryonic and adult stem cells; distinctions blur in cancer, where, for example, embryonic and/or hematopoietic stem cell markers can be found in tumors of neural origin. Some examples of commonly used stem cell markers with applications in cancer biology include: ABCG2 (72,300 kDa) (also known as ATP-binding cassette superfamily G member 2, BCRP, BCRP1, BMDP, MXR, MXR1) defines a ▶Hoechst-33342negative phenotype of ▶side population (SP) cells. ABCG2 is expressed in cancers of the blood, ▶breast, ▶prostate, ▶lung, germ cell, and retina. ABCG2 may be a potential marker for positive selection of cancer stem cells from a wide variety of tissues. Bmi-1 (44–46 kDa, murine viral ▶oncogene homolog) is a ▶polycomb group gene. In addition to its role in development, Bmi is also a tumor-associated antigen, expressed in cancers of the blood, ▶brain, lung, oral mucosa and gastrointestinal tract. CD44 (80–95 kDa) is a ▶cluster of differentiation (CD) molecule that functions as a receptor for hyaluronic acid. It is involved in cell/cell and cell/ matrix interactions. Overexpression of CD44 has been associated with the development and spread of a range of different types of malignancies. CD44 is found in cancers of the blood, breast, prostate, germ cell and lung. CD133 (120 kDa), also a cluster of differentiation molecule, was first identified as a hematopoietic stem cell marker. It is a glycosylated protein which recognizes a CD34 + subset of human hematopoietic stem cells. CD133 expression has been demonstrated in human leukemias, prostate cancer, germ cell tumors as well as in ▶brain tumors. CD164 (80–90 kDa), also known as ▶sialomucin, is a cluster of differentiation molecule expressed on CD34 + hematopoietic progenitor cells. CD164 has been detected in prostate cancer. ▶c-kit (145 kDa, CD117) is the membrane receptor for ▶stem cell factor (SCF). It is an oncogene expressed in cancers of the blood, prostate, germ cell, lung and gastrointestinal tract. Musashi-1, 2 (39 kDa) are RNA binding proteins associated with ▶asymmetric cell division (asymmetric cytokinesis) in neural stem cells. Musashi-1 has been detected in cancers of the breast, brain and retina, while Musashi-2 is rearranged in chronic myeloid leukemia. Nanog (34 kDa) is a human embryonic stem cell marker and transcription factor also found in osteosarcomas, breast cancers, ▶retinoblastomas and germ cell tumors. Nestin (177kDa) is categorized as a neural stem cell marker. It is a class VI intermediate filament protein

Stem Cell Markers

primarily expressed in stem cells of the central nervous system, including brain tumors. Oct-4 (also termed Oct-3 or Oct3/4) is an embryonic stem cell marker. It is a ▶POU transcription factor that confers self-renewal and pluripotency to embryonic stem cells. Oct 4 is expressed in both embryonic stem and germ cells, as well as in germ cell neoplasias, ▶bone tumors and retinoblastoma. Sca-1 (18 kDa) is a mouse-specific stem cell marker (stem cell antigen 1, Ly-6A/E), and a member of the ▶Ly6 antigen family. Sca-1 is expressed in cancers of the blood, prostate, lung, breast, and retina. Sox2 (34 kDa) is a transcription factor important in maintaining self-renewal properties of neural progenitor cells. Sox2 is an acronym for “SRY-related HMG-box gene 2.” SRY refers to “sex-determining region Y,” as the first Sox gene was found to be important in sex determination of developing gametes. HMG refers to ▶“high mobility group (HMG group),” which is the DNA binding domain of Sox2. Sox2 has been localized to cancers of the brain, lung and gastrointestinal tract. A summary of stem cell markers with applications in cancer biology is shown in Table 1. Note that the field is changing rapidly, as new markers and tissue locations are added constantly. Therefore, this is not an exhaustive list, but rather a representative list of the most common stem cell markers to date that are applicable to cancer. Methods Used to Detect Stem Cell Markers in Cancer Biology Antibodies directed against stem cell markers can be used to identify and isolate stem cells. Fluorescentlylabeled secondary antibodies directed against primary

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antibodies bound to stem cell proteins identify specific populations of stem-like cells. Fluorescence-activated cell sorting can isolate rare stem cells from a heterogeneous tumor population. In this technique, a suspension of labeled cells passes by a laser, one at a time, and then through an electric field. The fluorescent cells become negatively charged and can be directed, based on charge, to a separate collecting tube for further analysis. In this way, a very small population of cells expressing stem cell markers can be isolated from a heterogeneous tumor population. Magnetic beads linked to secondary antibodies also allow for the isolation of rare cell populations based on expression of stem cell markers on the cell surface. Magnetically-beaded cells expressing stem cell markers can be separated based on magnetic attraction while the non-expressing cells are washed away. Once the beaded cells are isolated, the cells of interest can be freed from the magnetic beads for further analysis. Fluorescent antibodies can also be used to visually assess cells as they exist within the tissue of origin or within mixed cell cultures. Fluorescently-labeled stemlike cells will emit light at specific wavelengths that can be visualized by fluorescence microscopy. Polymerase chain reaction (PCR) can be used to detect the presence of genes coding for stem cell markers that are expressed in putative stem cells. This method is not as useful for isolating stem cells, but can be used to screen populations for stem cell markers and test isolated cell populations for expression of stem cell genes. Clinical Applications The hypothesis that a subpopulation of cancer stem cells drives tumorigenesis and chemo-resistance may

Stem Cell Markers. Table 1 Stem cell markers with applications in cancer biology for each marker, an “X” indicates localization to cancers of various tissues Marker

Blood

Breast

BCRP/ABCG2 CD133 CD34 CD44 CD164 Bmi-1 Sca-1 (mouse) Nestin Musashi-1,2 Sox2 Oct3/4 Nanog ▶c-kit

X X X X X X X

X

X

Brain

Prostate

Retina

Germ Cell

Lung

X

X X

X X

X X X X

X X

X

X X X

X X

X

X X X

X X X X X

X X

X

X

X X X

X

S

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Stem Cell Niche

lead to new approaches for cancer prognosis and therapy. Expression patterns of stem cell markers may indicate the differentiated or undifferentiated state of a tumor, and may correlate with a favorable or an unfavorable prognosis in the clinical setting. Once cancer stem cells are identified and characterized using stem cell markers, they can be targeted, using specific stem cell markers for immunologically-based therapies. New stem cell markers will continue to be discovered and are certain to play an important role in the rapidly emerging field of cancer stem cell biology.

References 1. Burkert J, Wright NA, Alison MR (2006) Stem cells and cancer: an intimate relationship. J Pathol 209:287–297 2. Behbod F, Rosen JM (2004) Will cancer stem cells provide new therapeutic targets? Carcinogenesis 26(4):703–711 3. Iczkowski KA, Butler SL (2006) New immunohistochemical markers in testicular tumors. Anal Quant Cytol Histol 28(4):181–187 4. Nicolis SK (2007) Cancer stem cells and “stemness” genes in neuro-oncology. Neurobiol Dis 25(2):217–229 5. Ichim CV, Wells RA (2006) First among equals: the cancer cell hierarchy. Leuk Lymphoma 47(10):2017–2027

Definition

Stem cell plasticity refers to the ability of some ▶stem cells to give rise to cell types, formerly considered outside their normal repertoire of differentiation for the location where they are found. Included under this umbrella title is often the process of “transdifferentiation” – the conversion of one differentiated cell type into another, and ▶metaplasia – the conversion of one tissue type into another. From the point of view of this essay, some metaplasias have a clinical significance because they predispose individuals to the development of cancer. Circulating bone marrow-derived cells (BMDCs) that usually generate all blood cell lineages, can switch cell lineage commitment and contribute to the regeneration of several damaged non-hematopoietic tissues, and some carcinomas may even have their origins in BMDCs. The bone marrow origin of some tumor stromal cells and vasculature is now widely acknowledged, but since this pathway was not formerly recognized, it too can be considered a further example of plasticity, which, importantly, has significant biological and therapeutic implications for cancer.

Characteristics

Stem Cell Niche Definition

The local ▶microenvironment that houses the stem cell population in a tissue or organ. Made up of cells, blood vessels and extracellular matrix, ▶stem cells adhere to the niche through ▶cell adhesion molecules and receive signals e.g. Wnt glycoproteins, that regulate their behavior. ▶Stem Cell Plasticity

Stem Cell Plasticity M ALCOLM R. A LISON Centre for Diabetes and Metabolic Medicine, Queen Barts and the London School of Medicine and Dentistry, Institute of Cell and Molecular Science, London E1 2AT, UK

Synonyms Transdifferentiation; Metaplasia

Most adult tissues have multipotential stem cells (▶Adult stem cells), cells capable of producing a limited range of differentiated cell lineages appropriate to their location, e.g. small intestinal stem cells can produce all four indigenous lineages (lysozyme-secreting Paneth cells, mucin-producing goblet cells, absorptive columnar cells and enteroendocrine cells). However, tissue-based stem cells may be more versatile than previously thought, particularly those of bone marrow, and these cells may generate unexpected cell types when engrafted in a damaged non-hematopoietic tissue or organ. This so-called plasticity is being exploited in the field of regenerative medicine where it is hoped to produce new cell therapies for currently intractable diseases such as diabetes and congestive heart failure. Other sources of malleable stem cells include ▶umbilical cord blood, ▶mesenchymal stem cells (MSCs) from many sources including liposuction waste (fat), skin fibroblasts and spermatogonia. Stem cell plasticity has been questioned by some investigators who have been unable to reproduce some of the claims: “blood to brain,” “brain to blood,” “bone marrow to oocytes,” “bone marrow to cardiomyocytes.” Other instances of plasticity have now been attributed to cell fusion between bone marrow cells (or their macrophage descendants) and cells of the recipient organ. Cell fusion may have implications for tumorigenesis. Such a process could endow differentiated cells with stem cell properties such as infinite selfrenewal, while at the same time result in genetic instability with obvious tumorigenic potential.

Stem Cell Plasticity

From the viewpoint of cancer, we should note that while a scattering of engrafted cells of hematopoietic origin (but with a phenotype appropriate to their new location) is often observed in damaged parenchymal organs, these cells appear to have engrafted not as stem cells but either as ▶transit amplifying cells or ▶terminally differentiated cells, thus their long-term significance for cancer development is highly questionable. If BMDCs did engraft as stem cells in a new location, it is not inconceivable that they could be the founder cells of tumors at these sites. Indeed in a murine model of gastric cancer, BMDCs repopulate the gastric mucosa and over time contribute to metaplasia, dysplasia and cancer in response to chronic infection with Helicobacterfelis (▶Gastric cancer, ▶Helicobacter pylori). BM-derived gastric glands are seen after 20 weeks of chronic infection, leading to a final replacement of 90% of the gastric mucosa with BMDCs after 1 year. Upon progression to epithelial dysplasia and gastric adenocarcinoma, the majority of the dysplastic glands were of BM-origin, most likely from MSCs. Chronic inflammation led to atrophic gastritis, probably ablating the ▶stem cell niche of numerous indigenous gastric glands, and the vacant niches were then occupied by BMDCs that subsequently behaved as gastric gland stem cells (Fig. 1) (▶Stem cells and cancer). An origin of carcinoma from BMDCs has also been suggested for one case of skin basal cell carcinoma arising in a female recipient of a male kidney transplant. In this case, most of the cytokeratin-positive tumor cells were male, and since BCC rarely if ever metastasizes (so no occult metastasis in the transplanted organ), it is likely that donor BMCs in the graft had migrated to the skin, either fusing with or differentiating into keratinocytes, before undergoing malignant transformation. On a cautionary note, it has been observed that in some

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murine and human cancers there are occasions when BMDCs incorporate into the tumors, phenotypically mimicking the cancer cells, but of course not actually initiating them. Metaplasia Metaplasias are major switches in tissue phenotype, invariably they occur in tissues subjected to chronic trauma, and are likely to represent epigenetic reprogramming of tissue stem cells – in-situ stem cell plasticity. Cancers can arise in areas of metaplasia, and we often have a metaplasia – dysplasia – carcinoma sequence. For example, the esophagus is normally lined by squamous epithelia, but due to acid reflux it can become lined by glandular tissue (Barrett’s esophagus) and adenocarcinomas usually arise in areas of dysplastic Barrett’s esophagus. In the airways of the lung, chronic irritation by tobacco smoke can lead to a switch from columnar to squamous epithelia, and squamous carcinoma of the lung usually arises from patches of squamous epithelia. Metaplasias may well be caused by misexpression of homeotic genes, a good example being intestinal metaplasia in the stomach caused by overexpression of the intestine-specifying CDX genes; here too, metaplasia predisposes to gastric cancer. The Bone Marrow and Tumor Stroma: Clinical Relevance BMDCs may indirectly influence tumor behavior by contributing to the ▶desmoplastic response and to the tumor vasculature, lineages not formerly considered to have arisen from bone marrow (▶Desmoplasia, ▶angiogenesis). ▶Myofibroblasts are a distinguishing feature of pathological fibrosis, normally regarded as having originated by activation of local organ

S

Stem Cell Plasticity. Figure 1 Stem cell plasticity could provide an alternative pathway for cancer development as seen in experimental gastric carcinogenesis. Continued inflammation and tissue damage leads to eradication of the indigenous stem cell compartment and its replacement by bone marrow derived cells (BMDCs), whose progeny subsequently repopulate the whole gland. Mutation in a BMDC engrafted as a stem cell can then lead to a dysplastic gland and subsequent gastric cancer. Key: indigenous normal epithelial cells are brown, indigenous stem cells are green, BMDCs are red and mutated BMDCs are blue.

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Stem Cell Telomeres

fibroblasts, but there is clear evidence that many are generated from bone marrow cells. These BMDCs can contribute to organ fibrosis, including the fibrosis surrounding many cancers – the desmoplastic response. Thus, BMDCs may be useful for the local delivery of anticancer agents such as interferon. ▶Endothelial progenitor cells (EPCs) are mobilized endogenously in response to tissue ischaemia or exogenously by cytokine therapy to augment neovascularization. The development of a vascular supply to a tumor is a prerequisite for tumor survival – allowing for the provision of oxygen and nutrients as well as the disposal of waste products. New vessel formation is also required for tumor metastasis. Previously, tumor vasculature was thought to develop exclusively via endothelial cell migration and proliferation – angiogenesis. However, the creation of new blood vessels by EPCs is known as vasculogenesis, and such a process is a significant event in tumorigenesis. This opens the possibility of using bone marrow cells as a vehicle for transporting antiangiogenesis molecules directly to the tumor vascular bed, in effect using BMDCs as Trojan horses.

References 1. Alison MR, Poulsom R, Otto WR et al. (2003) Plastic adult stem cells: will they graduate from the school of hard knocks? J Cell Sci 116:599–603 2. Alison MR, Lovell MJ, Direkze NC et al. (2006) Stem cell plasticity and tumour formation. European J Cancer 42:1247–1256 3. Burkert J, Wright NA, Alison MR (2006) Stem cells and cancer: an intimate relationship. J Pathol 209:287–297 4. Houghton J, Wang TC (2005) Helicobacter pylori and gastric cancer: a new paradigm for inflammationassociated epithelial cancers. Gastroenterology 128:1567– 1578 5. Slack JMW (2007) Metaplasia and transdifferentiation: from pure biology to the clinic. Nat Rev Mol Cell Biol 8:369–378

Stem Cell Telomeres E ISO H IYAMA Natural Science Center for Basic Research and Development, Department of Pediatric Surgery, Hiroshima University Hospital, Hiroshima University, Hiroshima, Japan

Synonyms Telomeric repeats of stem cells; Guanine-rich tandem DNA repeats of chromosomal ends

Definition

▶Telomeres are guanine-rich tandem DNA repeats that cap the ends of eukaryotic chromosomes. Their primary function is to prevent chromosomal degradation, fusions and instability. During cell division, telomeres shorten as a result of the incomplete replication of linear chromosomes. The slow rate of cell turnover in stem cell compartments means a longer period of ▶telomere length stability in stem cells versus somatic cells. Nevertheless, stem cell telomeres do gradually shorten with age.

Characteristics

Human ▶telomeres consist of tandem repetitive arrays of the hexameric sequence TTAGGG, with overall telomere sizes ranging from 15 kb at birth down to 5 kb of its length to form the t-loop. When the length shortens to