Molecular OncogenesIs

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


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


3. Gene Translocation

Ex. Burkitt’s Lymphoma

ONCOGENE FAMILY


3. Gene Translocation

Ex. Chronic Myelogenous Leukemia [CML]

ONCOGENE FAMILY


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


KNUDSON’S Two-Hit Hypothesis

1st Hit: TS mutation or Inherited mutation

2nd Hit: gross chromosomal loss


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]


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


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


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


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


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


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


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


MitosisMitosis

MM

SSDNA synthesisDNA synthesis

GG22

GG11

G0


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


• 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


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


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)


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


• 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 ?

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Molecular OncogenesIs