Numero stimato delle varie forme di tumore nel 1997 (US)

Transcription

1 chi la fa l aspetti

2 Numero stimato delle varie forme di tumore nel 1997 (US)

3 Mortality-cancer type Mortality and incidence-time National cancer institute US

4 Una base genetica per il cancro Stato canceroso nella cellula - clonale Geni portati da virus Cancro indotto da agenti mutageni In alcuni casi ereditato in famiglie Alcuni tumori associati con aberrazioni cromosomiche

5 Non una sola malattia, non un solo gene mutato 25 years of research More than 100 types of cancer, plus subtypes Common pathways? Weinberg RA: Cell 2000 suggests 6 alterations in cell physiology virus Oncogeni e oncosoppressori Malattia a base genetica (ereditaria e acquisita) Fenotipo e genotipo eterogenei

6 Ciclo cellulare

7 Processes needed for cancer

8 1. Self sufficiency in growth signals Cells move from quiescent (G0 state) to active proliferative state in response to : -growth factors, -extracellular matrix components -cell-to-cell adhesion/interaction molecules Possible alterations of ligands, receptors, or signalling molecules.

9 Examples of mutated genes that insure self efficiency in growth: Over-exp. Over-exp. or constitutive activation switch Over-exp. or constitutive activation IL6 and multiple myeloma PDGF and TGFalpha in glioblastomas and sarcomas EGF-R/erbB in stomach, brain and breast tumors HER2/neu in stomach and mammary carcinomas Integrin Alterations of Ras pathway (25% of human tumors, 50% of human colon carcinomas)

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11 Ras wild type Weinberg

12 Ras nella cellula tumorale-oncogene Mutated in 25% of tumors (posizioni 12,59,61)

13 Processes needed for cancer

14 2. Insensitivity to antigrowth signals: soluble and cell to cell 2 types of growth block in normal tissue: -temporary G0 - irreversible post-mitotic differentiated state

15 Genes implicated in temporary G0, citostatic control - oncosoppressori Crucial role of prb and of related p107 and p130: In the cancer cell the circuit can be altered:mut of prb, TGFbeta, Smad,p15, CDK4 sequestration of Rb by oncoproteins (E7 papilloma, E1A adeno)

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17 Retinoblastoma: raro tumore infantile dell occhio Incidenza 5/ % mutazione ereditaria 60% sporadico Mappatura nel locus 13q14.2 Clonaggio posizionale e caratterizzazione del gene Rb

18 prb proteina nucleare di 105 kd coinvolta nel controllo del ciclo cellulare Omologhi di prb: p107 e p130 prb tumorale perde la capacita di legare E2F, ciclo sbloccato

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20 Post-mitotic differentiation control Role of c-myc Overexpression of c-myc avoids terminal differentiation in cancer cell

21 Traslocazione nel linfoma di Burkitt che coinvolge il gene c-myc (che viene iper-espresso; effetto di posizione)

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23 Se beta-catenina lega APC questa viene degradata e non funziona se manca APC, c e attivazione costitutiva da parte di betacatenina => tumori benigni, polipi e adenomi

24 Processes needed for cancer

25 3. Evading apoptosis Apoptosis: cellular membranes are disrupted, cytoplasmic and nuclear skeletons broken down, cyotsol extruded, chromosomes degraded, nucleus fragmented, in min. within 24 hrs shriveled cell corpse is engulfed by nearby cells in a tissue and disappears

26 Apoptotic genes Apoptotic sensors: -extracellular (Fas, TNFalpha receptors). FAS decoy high fraction of lung and colon carcinoma lines -intracellular (detect DNA damage, signalling imbalance, survival factor insufficiency, hypoxia) mut p53, 50% of human cancers -cell-to-cell Apoptotic mediators: Bcl2 family, cytocrome C Apoptotic effectors: caspases

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28 Come funziona p53

29 Piu del 50% dei tumori sono mutati nella p53

30 Domini principali di p53 (fattore di trascrizione, il guardiano del genoma) TAD attivazione trascrizionale DBD legame al DNA OD oligomerizzazione

31 Processes needed for cancer

32 4. Limitless replicative potential: telomers telomers: several thousands of repeats of a short 6bp sequence element i) Cells have a finite replicative potential (60-70 times) (erosion of telomers, bp loss of telomeric end during each cell cycle) ii) If mut. p53 and prb cells continue to replicate up to crisis (telomeric erosion, end-to-end chromosomal fusions) iii) 1/10 7 immortalizes (most types of tumor cells) Up regulation of Telomerase enzyme or of ALT(telomerase independent recombination-based reconstitution of telomers)

33 Processes needed for cancer

34 5. Sustained angiogenesis A growing cell must reside within 100um of a capillary blood vessel Pro-angiogenic signals Growth factors (VEGF up-regulation induced by Ras mutation) Cell-to-cell Matrix binders (integrin switch) Proteases (protein maturation) Anti-angiogenic signals Growth factors (thrombospondin, transcription inhibited by p53) Cell-to-cell Matrix binders (integrin switch) Proteases Angiogenesis: early to mid-stage event in human cancer (shared in most common cancers) Good therapeutic target (Folkman)

35 Processes needed for cancer

36 6. Tissue invasion and metastasis Invasion and travelling to distant sites, eventual colonization Importance of: CAM (cell-to-cell adhesion molecules) Ig(N-CAM) in neuroblastoma, Wilm s tumor, small cell lung cancer, pancreatic and colorectal cancer) CAM calcium-dependent cadherins (E-cadherin lost in most epithelial cancers) integrins (carcinoma switch to alpha3beta1 and alphavbeta3 subtypes) extracellular proteases

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38 Ubiquitinylation and cancer? The UPS regulates an enormous range of biological processes, including cell cycle, apoptosis, protein trafficking, signaling, DNA replication and repair, and angiogenesis. Consistently, defects in the UPS have already been directly implicated with many diseases. Deregulated protein ubiquitylation represents a major contributing factor for cancer development. These E3 ligases or their components are over-expressed in many human cancers and their inhibition leads to growth suppression or apoptosis. Proteina =>proteina-u => cascata (proteina polyu) => proteasoma Velcade: inibitore del proteasoma contro mieloma (US FDA approved may 2003)

39 Overall capability: Genome instability Malfunctions of maintenance care-takers: chromosome numbers and genome sequence Central role of p53, repair enzymes At which moment does the mutator phenotype occur?

40 Mechanisms Chronology Mutation in p53

41 Gene targets for cancer therapy A recombinant bcl-x s adenovirus selectively induces apoptosis in cancer cells but not in normal bone marrow cells. Clarke MF, Apel IJ, Benedict MA, Eipers PG, Sumantran V, Gonzalez-Garcia M, Doedens M, Fukunaga N, Davidson B, Dick JE, et al. PNAS 1995

42 bcl-2: inhibits apoptosis => protects tumor cell bcl-x: inhibits bcl2, Adbclx should help to kill tumor cells selectively

43 Gene targets for cancer therapy Growth retardation and tumour inhibition by BRCA1. Holt JT, Thompson ME, Szabo C, Robinson- Benion C, Arteaga CL, King MC, Jensen RA. Nat Gen 1996

44 BRCA: tumor suppressor (DNA repair?)-> loss of function = cancer In vitro: Breast cancer cells, cell number upon infection with wt or mutant BRCA-retro wt

45 In vivo: Breast cancer model (intraperitoneal tumours). Mice survival after injection with wt or mutant BRCA retro

46 Bibliografia Snustad The Hallmarks of cancer. Cell, January 2000 Approfondimenti: Ciclo cellulare Telomeri