Molecular Perspectives In Carcinogenesis
Dolores V. Viliran, MD
Department of Biochemistry & Nutrition FEU-NRMF,INSTITUTE OF MEDICINE
INTRODUCTION
CANCER
Cancer is an overgrowth of cells bearing cumulative genetic injuries that confer growth advantage over the normal cells [Nowell’s Law]
Cancer cells can be characterized as antisocial, fairly autonomous units that appear to be indifferent to the constraints and regulatory signals imposed on normal cells [Robbin’s]
CANCER CELLS AND NORMAL CELLS
CANCER CELLS AND NORMAL CELLS
CANCER CELLSCANCER CELLS NORMAL CELLSNORMAL CELLS
Loss of contact inhibitionLoss of contact inhibition
Increase in growth factor secretionIncrease in growth factor secretion
Increase in oncogene expressionIncrease in oncogene expression
Loss of tumor suppressor genesLoss of tumor suppressor genes
Oncogene expression is rareOncogene expression is rare
Intermittent or co-ordinatedIntermittent or co-ordinatedgrowth factor secretiongrowth factor secretion
Presence of tumor suppressorPresence of tumor suppressorgenesgenes
NormalNormalcellcell
FewFewmitosesmitoses
FrequentFrequentmitosesmitoses
NucleusNucleus
Blood vesselBlood vessel
AbnormalAbnormalheterogeneous cellsheterogeneous cells
CHARACTERISTICS OF CANCER
• Clonality
• Autonomy
• Anaplasia
• Metastasis
CHARACTERISTICS OF CANCERClonalityClonality
• Cancer is a genetic disease at the cellular level.• Genetic mutations play a critical role in
pathogenesis of cancer.• Consequences of genetic instability:
– Phenotypic heterogeneity– Tumor progression
• Proto-oncogenes and oncogenes• Dominant mutations = mutation resulting from
conversion of protooncogenes to oncogenes• Recessive mutations = mutation resulting from
damage or loss of tumor suppressor gene.
Cancer Genetics
• Tumors arise as clones from a single cell. At the cellular level, cancer is a genetic disease.
• The development of the malignant clone is due to mutations in DNA due to:– Random replication errors– Exposure to carcinogens– Faulty DNA repair process
Evidence that Mutations Cause Cancer
• Recurring sites of chromosome change are observed in cancers at sites of genes involved in cellular growth control.
• Most carcinogens are mutagens.• Defects in DNA repair systems increase
the possibility of cancer.
• Cancer cells are able to proliferate despite regulatory influences.
• Unrestricted proliferation results in tumor formation.
• Mechanisms:– Growth factor secretion– Increased number of cell receptors– Independent activation of key biochemical
process
• Proliferation depends on the cell cycle.
CHARACTERISTICS OF CANCERAutonomy
AUTONOMY
• Brought about by mutations in the cell’s genetic apparatus
• Most common in tissues with rapid turnover, especially:
- those exposed to environmental agents- those whose proliferation is hormone-
dependent
• Proliferation is dependent on the cell regeneration cycle
DEATH
DIFFERENTIATION
DNA DNA content = 2n = 2n
MitosisMitosis
MM
SSDNA synthesisDNA synthesis
GG22
GG11
G0
DNA DNA content = 4n = 4n
The Cell Cycle
G1/S checkpoint
G2/M checkpoint
CYCLIN, CDK,CDKI: PHOSPHORYLATION
Cell Cycle Regulation
• Process assures that cell accurately duplicates its contents.
• Important checkpoints are present at G1 and G2 and are regulated by protein kinases called cyclins (cdk).
• Checkpoints determine whether the cell proceeds to next phase of the cycle.
G2/M Checkpoint
• Regulated by the cyclin B/cdc2 (mitosis promoting factor or MPF).
• Activity of this cyclin with its substrate results in:– Chromosome condensation– Nuclear membrane breakdown– Spindle formation
G1/S Checkpoint
• Area most often disrupted in cancer.• Mechanism of regulation is complex
and involves the phosphorylation of the Rb gene. This results in:– Activation of several genes needed for
S phase progression.– Promotes differentiation through
association with transcription factors.
Rb Gene Activation
Cyclin Regulators
• Regulated by cdk inhibitors (cdki).• May be induced by growth
inhibitors and inhibited by positive growth factors.
• Genetic alterations in cdki occur with high frequency in some cancers.
Cyclin Regulators
• p 21: inhibits cell cycle progression and permits DNA repair to take place.
• P53: “the guardian of the genome”– In the presence of DNA damage, influences
transcription to either:• Halt cell cycle progression to facilitate DNA repair.• In cases of severe DNA damage, activates
apoptosis.
– Mutations in p53 are the most common genetic alterations found in human cancer.
CHARACTERISTICS OF CANCER: Anaplasia
• Loss of differentiated function resulting to bizarre-looking cells
• Large nuclei, prominent nucleoli, increased chromatin
• Increased and/or abnormal mitosis• Aneuploidy• Partial or complete loss of normal
architecture
Invasion and Metastasis
• The defining characteristic of a malignancy.
• Invasion: active translocation of neoplastic cells across tissue barriers.
• Critical pathologic point: local invasion and neovascularization. These events may occur before clinical detection.
ATTRIBUTES OF CANCER
Metastasis
Two basic steps:Destruction of the BM
Attachment to the laminin of distant BM
Genes up-regulated among good metastasizers:
EDGF receptorBasic Fibroblast Growth FactorType IV Collagenase-Cathepsin (under-expressed)Cathepsin B (a lamininase)Heparanase
Angiogenesis
• Process of new blood vessel formation.• Clinical importance:
– Tumor vessel number correlates positively with risk and degree of dissemination.
– Several cytokines that stimulate endothelial cell proliferation also stimulate proliferation of malignant cells.
INVASION AND METASTASIS INVASION AND METASTASIS
Triad of Invasion• Adhesion with the basement
membrane
• Local proteolysis
• Mobility and ability to translocate through dents in body’s structural barriers
MOLECULAR CARCINOGENESIS
Mutation
the molecular hallmark of most forms of cancer
Gene Families in Cancer Development
1 - Oncogenes
2 - Tumor Suppressor genes
3 - Mutator genes
Cancer Genes
• Proto-oncogenes – normally promote normal cell growth; mutations convert them to oncogenes.
• Tumor suppressor genes – normally restrain cell growth; loss of function results in unregulated growth.
• Mutator or DNA repair genes – when faulty, result in an accumulated rate of mutations.
ONCOGENE FAMILY
+ oncogenes
Oncogenes promote cell proliferation
dominant & highly conserved
types: viral oncogenes [v-oncs]cellular oncogenes [c-oncs]
Proto-oncogene “Mutation” Oncogene
ONCOGENE FAMILY
Classification of Oncogenes
A. Secreted Growth Factors
B. Cell Surface Receptors
C. Intracellular Transducers
D. DNA-binding Nuclear Proteins
E. Regulators of the Cell Cycle
Components of signal transduction pathways
c-sis, hst
erb B, fms, ret, trk, fes, fms
c-src, c-abl, mst, ras
myc, jun, fos
bcl, bax, bad
SIGNAL TRANSDUCTION
ONCOGENE FAMILY
Mechanisms of Oncogene Activation
1. Point Mutation
H-ras [codon 12]
Normal CGC GlyBladder ca CTC Val
H-rasGTP
Perpetual cell division
2. Gene Amplification
Double minutes
HSRs
Homogenously
Staining regions Normal copy Multiple copies
ONCOGENE FAMILY
Mechanisms of Oncogene Activation
3. Gene Translocation
Ex. Burkitt’s Lymphoma
ONCOGENE FAMILY
Mechanisms of Oncogene Activation
3. Gene Translocation
Ex. Chronic Myelogenous Leukemia [CML]
ONCOGENE FAMILY
Mechanisms of Oncogene Activation
4. Viral Gene Integration
promoter
Viral promoter
TUMOR SUPPRESSOR GENE FAMILY
TS Genes inhibit growth and multiplication of mutated cells
prevent neoplastic transformation
recessive & highly conserved
Classification of TS genes
A. Cell Adhesion Molecules
B. Regulators of the Cell Cycle
APC, DCC
RB1, Tp53
TUMOR SUPPRESSOR GENE FAMILY
KNUDSON’S Two-Hit Hypothesis
1st Hit: TS mutation or Inherited mutation
2nd Hit: gross chromosomal loss
TUMOR SUPPRESSOR GENE FAMILY
Retinoblastoma gene [RB1 gene]
rare form of childhood malignancy
forms: hereditary & sporadic
pRb
105-KDa nuclear protein
inhibits E2F [prevents G1 S transition]
inhibited by: phosphorylation
viral oncoproteins [E1A, HPV E7]
TUMOR SUPPRESSOR GENE FAMILY
Tp53 gene
location: 17p13.1
product: p53 protein [53 KDa]
function: induces DNA repair or apoptosis
mutation: point mutation > deletion
results to: loss of function & extended lifespan of p53
Clinical conditions: carcinomas, Li Fraumeni Syndrome
p53 inhibited by: E1B, HPV E6, mdm2
TUMOR SUPPRESSOR GENE FAMILY
p53 protein
p53 in action
MUTATOR GENE FAMILY
Mutator Genes
involved in ensuring the fidelity of replication
function: checks for & corrects mismatched pairs
mutation inefficient repair & replication leading increased propensity of oncogenes and tumor suppressor genes to undergo mutation
first described in E coli [Mut-HSL system]
Fischel, et al = Human homologs
leads to the formation of Microsatellite Instability [MIN+]
In summary …..
ONCOGENES TS GENES
MUTATOR GENES
Re-cap of Molecular Carcinogenesis
Proto-oncogene Gain-of-function
TS gene Loss-of-function
Mutator gene Loss-of-function
CANCER
CARCINOGENS
• Occupation related causes• Lifestyle related causes
– Tobacco– Diet– Sexual practices
• Multifactorial causes• Viral carcinogens• Chemical carcinogens• Ionizing radiation
Sources of Free Radicals
Smoking 10 Quad Trillion free radicals per
cigarette!
X-rays Stress Toxins Sunlight Solvents Pollution Cigarette Pesticides Herbicides Medications Airline travel Radioactivity Food additives Polluted Foods High heat cooking Synthetic materials Household cleaners Environmental Chemicals
MENULots more…
R.I.P
They only said it was dangerous. They didn’t say
it could be
lethal.
Occupational Risk Factors
EtiologyArsenicAsbestosBenzeneBenzedineChromium cpdsRadiation (mining)Mustard gasPolycyclic hydrocarbonsVinyl Chloride
Site of MalignancyLung, skin, liverMesothelium, lungLeukemiaBladderLungNumerous locationsLungLung, skinAngiosarcoma of liver
Lifestyle Risk Factors
Tobacco-related:• Lung cancer• Pancreatic cancer• Bladder cancer• Renal cancer• Cervical cancer
Diet-Related Risk Factors
NitratesSaltLow vitamins A, C, ELow consumption of
yellow-green vegetables
Gastric Cancer
Esophageal Cancer
Diet-Related Risk FactorsHigh fatLow fiberLow calciumHigh fried
foods
Colon CancerPancreatic
CancerProstate CancerBreast CancerUterine Cancer
Mycotoxins
Liver Cancer
Sexual Practices Risk Factors
Cervical Cancer
Sexual promiscuityMultiple partnersUnsafe SexHuman
Papillomavirus
Multifactorial Factors
Tobacco + Alcohol Oral Cavity Cancer
Esophageal Cancer
Tobacco + Asbestos
Tobacco + miningTobacco + uranium
+ radium
Respiratory Tract Cancer
Lung Cancer
CARCINOGEN METABOLISM
Three Main Categories:
I. Chemical Carcinogens
II. Physical Carcinogens
III. Viral Agents
Carcinogens Mutations Cancer
Environmental factors
?
CHEMICAL CARCINOGENESIS
Stages:
Initiation - primary exposure
Promotion - transformation
Progression - Cancer growth
Frank Cancer
CHEMICAL CARCINOGENESIS
Initiation normal cells are exposed to a carcinogen
not enough to cause malignant transformation
requires one round of cell division
normal cells are exposed to a carcinogen
1. Direct-acting carcinogens
2. Indirect-acting carcinogens
procarcinogen Cytochrome P450
Ultimate carcinogen
CHEMICAL CARCINOGENESIS
Promotion initiated cells are exposed to promoters
promoters are not carcinogens !
properties of promoters reversible
dose-dependent
time-dependentTypes of Carcinogens …...
1. Direct carcinogens
2. Procarcinogens Ultimate carcinogens
CHEMICAL CARCINOGENESIS
Direct-acting Carcinogens
cyclophosphamide
chlorambucil
busulfan
melphalan
Procarcinogens PAHs
Aromatic amines & Azo dyes
Aflatoxin B1
Nitrosamine & Amides
Asbestos
Vinyl chloride
Chromium, nickel, other metals
Arsenic
Promoters saccharine & cyclamates
Estrogen
Diesthystilbestrol [DES]
Physical Carcinogenesis
• Radiation-induced mutation in the host cell
• Transmits irreversible changes in gene expression to cell progeny
Sources of Potentially Carcinogenic Radiation
• Sunlight• Artificial sources of UV light• X-rays• Radio-chemicals• Nuclear fission
PHYSICAL CARCINOGENESIS
Ultraviolet Rays
UV-A = 320 - 400 nm
UV-B = 280 - 320 nm
UV-C = 200 - 280 nm
PHYSICAL CARCINOGENESIS
Ultraviolet Rays
UV-C filtered by ozone
UV-B
Inhibition of cell division inactivation of enzymes induction of mutations
cell death at high doses
Squamous cell cancer Basal cell cancer Melanocarcinoma
PHYSICAL CARCINOGENESIS
Ionizing Radiation includes electromagnetic rays & particulate matter
mechanism: free radicals & mutations
pathology: leukemias > thyroid ca > lung & breast ca
resistant tissues: bone, skin and the GIT
PRE-IRRADIATION POST-IRRADIATION
Viral Carcinogenesis• Viral carcinogens are classified into Viral carcinogens are classified into
RNA and DNA viruses.RNA and DNA viruses.
• Most RNA oncogenic viruses belong Most RNA oncogenic viruses belong to the family of retroviruses that to the family of retroviruses that contain contain reverse transcriptase mediates transfer of viral RNA into mediates transfer of viral RNA into virus specific DNA.virus specific DNA.
RETROVIRUSRETROVIRUS
OncogeneOncogene Viral RNAViral RNA
Viral DNAViral DNA
NUCLEUSNUCLEUS
DNADNA
OncogeneOncogene
REVERSE TRANSCRIPTASEREVERSE TRANSCRIPTASE
INSERTIONINSERTION
TRANSCRIPTIONTRANSCRIPTION
OncogeneOncogeneViral RNAViral RNA
CELLCELLMEMBRANEMEMBRANE CYTOPLASMCYTOPLASM
Viral genomeViral genome
RNA messengerRNA messenger TRANSCRIPTIONTRANSCRIPTION
OncogeneOncogeneproteinprotein
Viral Oncogenes
Viruses Associated With The Development Of Human
NeoplasiaVIRUSES NEOPLASMS
DNA VIRUSES
Human papilloma virus Cervical Ca, warts, ano-
genital carcinomaHerpes simplex virus II Cervical carcinomaEpstein-Barr virus NPCa, African Burkitt’sHerpes simplex virus 8 Kaposi’s sarcomaHepatitis B virus Hepatocellular CaHerpes simplex virus 6 Certain B cell (HBLV) lymphomas
VIRUSES NEOPLASMS
RNA VIRUSESHuman T-cell leukemia virus I Some T-cell Human T-cell leukemia virus I Some T-cell
leukemia, leukemia, lymphoma lymphoma Human T-cell leukemia virus II Some cases of Human T-cell leukemia virus II Some cases of
hairy hairy cell leukemia cell leukemia Human immunodeficiency virus I Lymphoma; Human immunodeficiency virus I Lymphoma;
Kaposi’s Kaposi’s sarcomasarcoma
Viruses Associated With The Development Of Human
Neoplasia
VIRAL AGENTS: DNA viruses
Human Papillomavirus [HPV types 16, 18, 31, 33 & 35]
Interruption of the E1/E2 ORF
E2 is not expressed
Over-expression of E6 & E7
VIRAL AGENTS: DNA viruses
Epstein-Barr Virus [EBV]
in Burkitt’s, B-cell & Hodgkin’s lymphomas + NP ca
tropism: CD21+ cells [e.g., B cells, epithelial cells]
mechanism: viral entry episomal existence latency (+) LMP-1, EBNA-1, EBNA-2 immortalization
Hepatitis B virus [HBV]
induction of chronic hepatocyte injury (+) HBx
HBx activates protein kinase c for transformation
VIRAL AGENTS: RNA viruses
Human T-cell Leukemia Virus [HTLV]
a retrovirus
tropism: CD4+ cells
mechanism: Tax protein
transcription c-fos, c-sis, IL-1 and IL-2
Viral replication T cell proliferation
Principal Pathways of Malignancy
1. Proliferation2. Cell-Cycle Progression
3. DNA Repair4. Immortalization
5. Apoptosis6. Angiogenesis
7. Metastasis and Invasion
SIGNAL TRANSDUCTION
PROLIFERATION(Growth Factor Signaling Pathway)
• Uncontrolled and uncoordinated proliferation
• Uncontrolled growth stimulated by:1. Increased secretion of Growth Factors
(PDGF,EGF,FGF,VEGF,NGF)2. Increased Growth Factor receptors3. Independent activation of certain
enzyme and protein production pathways
PROLIFERATION(Growth Factor Signaling
Pathway)• Receptor Tyrosine kinase
Pathway (RTK)-Main pathway• RTK ligands: NGF PDGF FGF EGF• Functions of RTK: 1. promotion of cell survival2. regulation of cell proliferation and
differentiation3. modulation of cellular metabolism
PROLIFERATION(Growth Factor Signaling
Pathway)
RTK SIGNALING PATHWAYS• Ras-MAP Kinase Pathway- most
prominent• PI3 kinase Pathway• Phospholipase C Pathway
PROLIFERATION
PROLIFERATION (Growth Factor Signaling
Pathway)Therapeutic implicationsBlocking of GF mitogenic signaling is
achieved by:• Preventing binding of GF to receptor or
receptor dimerization with specific agent• Preventing receptor activation with small
molecule inhibitors• Blocking cytoplasmic proteins
downstream of the activated receptor pathway
DEATH
DIFFERENTIATION
DNA DNA content = 2n = 2n
MitosisMitosis
MM
SSDNA synthesisDNA synthesis
GG22
GG11
G0
DNA DNA content = 4n = 4n
The Cell Cycle
G1/S checkpoint
G2/M checkpoint
Cell Cycle Regulation
• Process assures that cell accurately duplicates its contents.
• Important checkpoints are present at G1 and G2 and are regulated by proteins Cyclins and Cyclin-dependent Kinases (CDKs).
• Checkpoints determine whether the cell proceeds to next phase of the cycle.
Cyclins and Cyclin-dependent Kinases
(CDKs)• CYCLINS – activate protein kinases• CDKs – protein enzymes which
selectively phosphorylate specific serine/threonine residues in their substrates
• Dimeric complex withcatalytic subunit (CDK 1-9)regulatory subunit (Cyclin A-H,T)
G2/M Checkpoint
• Regulated by the cyclin B/cdc2 (mitosis promoting factor or MPF).
• Regulated mainly by intracellular signal (Completion of DNA Synthesis)
• MPF is activated by dephosphorylation by cdc25
• Cyclin B is degraded by Anaphase Promoting Complex (APC)
• Role of G2/M checkpoint: to prevent mitosis when DNA is damaged and not yet repaired
CYCLIN, CDK,CDKI: PHOSPHORYLATION
G1/S Checkpoint
• Area most often disrupted in cancer.• Mechanism of regulation is complex and
involves the phosphorylation of the Rb gene.
• Regulated by extracellular signals (e.g. GF)
• “R” point (restriction)- point late in G1 beyond which cell cycle progression becomes independent from external GF
• Regulated mainly by CDK4/cyclin D
Rb Gene Activation
Cyclin Regulators- CDK Inhibitors
• CDK inhibitors – inhibit the activity of CDK-cyclin complex
• Two Groups:1) INK4 family – p15 16 18 192) CIP-KIP family – p21 p27
Actions:P15- change response to anti-mitogenic agentsP16- inhibits CDK4/cyclin DP19- induces p53 stabilizationP21-induces cell cycle arrest via activation by p53P27- inhibits CDK2/cyclin E
Cyclin Regulators
• p 21: activated by p53 inhibiting cell cycle progression and permitting DNA repair to take place.
• P53: “the guardian of the genome”– In the presence of DNA damage, influences
transcription to either:• Halt cell cycle progression to facilitate DNA repair.• In cases of severe DNA damage, activates apoptosis.
– Mutations in p53 are the most common genetic alterations found in human cancer.
p53 in action
CELL-CYCLE PROGRESSION
Clinical Significance
Oncogenic alterations in cell cycle regulators:• Loss of p53 and pRB function as tumor
suppressors• Increased expression of Cyclin D1(Mantle Cell
Lymphoma)• CDK4 amplification in sarcomas, glioma• Mutations in p16-binding domain of
CDK4(Familial Melanoma)• Inactivation of INK4• Alterations in Cyclin D1,p16• Decreased levels of p27 (Breast Ca)• Over expression of cdc25
Therapeutic Implications
Approaches using Inhibitors of CDKs as therapeutic agents
• Small molecules • Protein therapy• Antisense• Gene therapyMost cytotoxic agents block the
cell cycle in the S/G2/M phases
DNA REPAIR PATHWAYS
• Cancer as “Malady of Genes”• Defects in the maintenance of genome
stability• Repair Mechanisms:1. Mismatch excision repair2. Base excision repair3. Nucleotide excision repair4. Double strand base repair
DNA REPAIR PATHWAYS
Clinical SignificanceHNPCC – mutations in genes involved in
DNA repair pathways (MSH1 MSH2)• Somatic defects in repeated DNA
elements leading to Microsatellite instability (MSI)
• Inactivation of TGF-β (tumor suppressor)• Inactivation of BAX gene
IMMORTALIZATION
Telomeres and Telomerase
Telomeres- specialized structures at chromosome ends generated and maintained by telomerase
Telomerase- ribonucleoprotein enzyme which preserves the integrity of telomeres* key component in immortalization of cancer cells
Telomere length- represents a molecular clock that determines the life span of the cell
Telomeres and Telomerase
Clinical Significance• Most normal adult tissues have NO telomerase
activity• Telomerase activity is present in 90% of
tumorsTherapeutic ImplicationhTERT- protein identified to be catalytic subunit
of telomerase • limiting component of telomerase activity• can be a target for small molecule inhibitor
APOPTOSIS
• APOPTOSIS – programmed cell death• Important in: 1. Steady-state kinetics of normal tissues2. Focal deletion of cells during normal
embryonic development3. Seen after chemotherapy and radiation* Balance between proliferation and
apoptosis is critical in determining growth or regression
Components of Apoptotic Pathway
1) CASPASES (Cysteine-containing aspartate-specific proteases)
• Initiator Caspases – activated in response to cell death signal
• Executioner or Effector Caspases- progress the death signal activating cascade resulting to DNA fragmentation and cell death
Caspase prodomains – DED CARDDeath ligands – TNF-α , Fas , TRAILSurvival Signals – NFκβ
Components of Apoptotic Pathway
2) CYTOCHROME C – component of mitochondria released in response to apoptotic signals
3) BCL-2 Family of Proteins- located upstream in the pathway
• Provides pivotal decisional checkpoint in the fate of the cell after a death stimulus
• Contains BH1-BH4 domains necessary for interaction
• Anti-apoptotic – BCL-2 BCL-xL• Pro-apoptotic – BAX BAD BAK BID
APOPTOTIC PATHWAYS
1) FAS-mediated apoptosis• FAS – cell surface receptor of TNF family
which binds to FAS-L• Eliminates unwanted activated T cells• Pathway for cytotoxic-mediated signaling2) P53-mediated apoptosis • important after chemotherapy and radiation• Induction of BAX and downregulation of BCL-2• Induced expression of FAS and DR5
Clinical Significance
• Over expression of BCL-2 as a prognostic indicator
• Mutations of BAX in GI Ca and leukemias
• P53 provides a link between cell proliferation and apoptosis
• Cell survival signals: NFκβ BCL-2• P53 mutations confer chemoresistance
EVADING APOPTOSIS
Therapeutic Implications
• Antisense oligonucleotide against BCL-2 in the treatment of lymphoma
• BCL-2 antisense as chemosensitizing agent in solid tumors
• TRAIL ( TNF-related apoptosis inducing ligand) to induce apoptosis
ANGIOGENESIS
• Formation of new blood vessels from existing vascular bed
• Carried out by endothelial cells (EC) and extra cellular matrix (ECM)
• Regulated by angiogenic factors (inducers and inhibitors)
* A tumor is unable to grow larger than 1 mm3 w/o developing a new blood supply
Components of Angiogenesis
1) ENDOTHELIAL CELLS• Fenestrated• Increased cell adhesion molecules
( E-selectin)• Increased integrins αγβ3 essential
for viability during growth• Activated ECs release: bFGF PDGF
IGF-1
Components of Angiogenesis
2) INDUCERS OF ANGIOGENESIS• VEGF – main inducer• TGF- β• TNF-α low concentration - inducer high concentration - inhibitor• PDGF/thymidine phosphorylase• TGF-α• EGF• IL-8
Components of Angiogenesis
3) CELL ADHESION MOLECULES (CAM)• Mediate cell-cell adhesion processes• Selectins• IG Supergene family- ICAM VCAM• Cadherins• Integrins- vitronectin receptor4) PROTEASES• Degrade ECM to provide suitable
environment for EC migration thru adjacent stroma Ex: Metalloproteinases (MMP)
Components of Angiogenesis
5) ANGIOGENESIS INHIBITORS• Interferon• TSP-1• Angiostatin• Endostatin• VasostatinCLINICAL SIGNIFICANCE:Tumor angiogenesis switch is triggered
as a result of shift in the balance of stimulators to inhibitors
ANGIOGENESIS
Therapeutic Implications
• Metalloproteinase inhibitors (MMPI) – block the degradation of basement membrane
• Inhibitors of endothelial function- thalidomide, TNP 470,endostatin
• Anti-angiogenic factors – tyrosine kinase inhibitors of VEGF bFGF PDGF
• Interferon – angiogenic inhibitor• COX-2 inhibitor – thromboxane A2 as
critical intermediary of angiogenesis
INVASION AND METASTASIS INVASION AND METASTASIS
Invasion and Metastasis
• The defining characteristic of a malignancy.
• Invasion: active translocation of neoplastic cells across tissue barriers.
• Critical pathologic point: local invasion and neovascularization. These events may occur before clinical detection.
PROCESS OF METASTASIS
Triad of Invasion
• Adhesion with the basement membrane.
• Local proteolysis• Mobility and ability to translocate
through rents in body’s structural barriers.
ADHESION• De-regulated function of CAM (E-
cadherin)• Changes in catenin expression leads to
loss of cadherin function• Integrin over expression in naturally
occurring cancers• Downregulation of integrin in more
advanced stages of cancer• Upregulation of ICAM-1 which enhances
extravasation• Adhesion molecules on EC: E-selectin,VCAM
ICAM
LOCAL PROTEOLYSIS• Degradation of basement
membrane to traverse barriers• Carried out by:1. Serine proteases -uPA elastase
plasmin cathepsin G2. Cysteine proteases- cathepsin B L3. Aspartate proteases – cathepsin D4. Matrix metalloproteinases-
gelatinases interstitial collagenases stromelysins matrilysins
MOTILITY• Tumor cells can move randomly or
directionally toward attractants• Modulators of motility
GF, hyaluronases, components of ECM, tumor-secreted factors, host-derived factors
THERAPEUTIC IMPLICATIONS:MMPI and monoclonal antibodies
against integrin
METASTASIS AND INVASION
Which of the following is TRUE of carcinogenesis?
A. Carcinogenesis occurs as a result of genetic mutation secondary to physical and chemical agents only
B. The ultimate carcinogens are usually electrophiles which can readily attack NA
C. The most common base involved in mutagenesis is adenine
D. Tumor suppressor gene is transformed to oncogene
Which of the following is TRUE of carcinogenesis?
A. Carcinogenesis occurs as a result of genetic mutation secondary to physical and chemical agents only
B. The ultimate carcinogens are usually electrophiles which can readily attack NA
C. The most common base involved in mutagenesis is adenine
D. Tumor suppressor gene is transformed to oncogene
Tumor p53 suppressor protein is reffered to as guardian of the genome bec. it:
A. Enhances the survival of tissues
B. Allows apoptosis to occur on seriously damaged cells
C. Plays a key role in G2 checkpoint control
D. Arrests the cell cycle at Go phase
Tumor p53 suppressor protein is reffered to as guardian of the genome bec. it:
A. Enhances the survival of tissues
B. Allows apoptosis to occur on seriously damaged cells
C. Plays a key role in G2 checkpoint control
D. Arrests the cell cycle at Go phase
TRUE statements about oncogenes, EXCEPT:
A. They positively affect cell proliferation
B. Single mutant allele is enough to cause phenotypic
C. They are mutant protooncegenes
D. Mutation involves a loss in function
TRUE statements about oncogenes, EXCEPT:
A. They positively affect cell proliferation
B. Single mutant allele is enough to cause phenotypic
C. They are mutant protooncegenes
D. Mutation involves a loss in function
This is not a characteristics of cancer
A. Loss of contact inhibition
B. Uncontrolled proliferation
C. Gain in function of mutator gene
D. Loss of differentiated function
This is not a characteristics of cancer
A. Loss of contact inhibition
B. Uncontrolled proliferation
C. Gain in function of mutator gene
D. Loss of differentiated function
TRUE statements about RAS oncogene activation except:
A. It involves a point mutation in codon 12
B. The mutated RAS results to increased GTPase activity
C. The mutated gene codes for valine instead of glycine
D. It is over-expressed in bladder cancer
TRUE statements about RAS oncogene activation except:
A. It involves a point mutation in codon 12
B. The mutated RAS results to increased GTPase activity
C. The mutated gene codes for valine instead of glycine
D. It is over-expressed in bladder cancer
A biochemical change found in fast growing tumor cells:
A. Increased catabolism of nucleobases and nucleotides
B. Inappropriate synthesis of certain growth factors and hormones
C. An adult pattern of isozymes
D. Markedly decreased glycolysis
A biochemical change found in fast growing tumor cells:
A. Increased catabolism of nucleobases and nucleotides
B. Inappropriate synthesis of certain growth factors and hormones
C. An adult pattern of isozymes
D. Markedly decreased glycolysis
Any Questions ?