Multistep Carcinogenesis

Transcription

1 Multistep Carcinogenesis M.Rosemann, Institute for Radiation Biology Helmholtz Center Munich, Research Centre for Health and Environment

2 The Hallmarks of Cancer D.Hanahan, Cell 2011

3 The Hallmarks of Cancer Impairments of the normal cellular homeostasis in a multicellular organisms D.Hanahan, Cell 2011

4 Cancer Formation: Several cellular defence mechanisms have to be bypassed in one and the same cell These cellular alterations have to be persistent (i.e. stable inheritable from one cell to ist progeny D.Hanahan, Cell 2011

5 Chemical carcinogenesis in a mouse skin tumor model (Benz-Pyrene + TPA) B(a)P Hyperplasia, no malignant carcinoma B(a)P TPA Adenoma, Carcinoma TPA B(a)P Hyperplasia, no malignant carcinoma B(a)P TPA Adenoma, Carcinoma TPA: 12-O-Tetradodecanoyl-Phorbol-13-Acetat (Phorbolester) B(a)P: Benz(a)Pyren

6 Multistep-Model of Carcinogenesis Initiation Activation of Oncogenes Hyperplasia Progression Activation of genes that promote metastasis, invasion, angiogenesis immunological tolerance etc. malignant Tumor Promotion Mutation in Tumor- Suppressor-Genes Carcinoma in situ

7 Colorectal Cancer 11% of cancerrelated deaths Tumor progression may take years Adenomatous polyp develops into carcinoma

8 Stepwise Transformation of normal epithelial tissue giving rise to malignant carcinoma Multistep Carcinogenesis 2015 DoReMi Mol Mech Rad Carc

9 Adenoma-Carcinoma-Sequence (Colon carcinoma) transition from normal epithelium to adenoma and to carcinoma is associated with aquired molecular events, including: deletion activation deletion mutation APC=brake on Wnt-signaling, transcriptional activation of ß-catenin activation of oncogenes G-protein, signal transduction p53 mutation, no: DNA-repair, apoptosis, cell cycle arrest etc. stepwise pattern of mutational activation of oncogenes and inactivation of TS genes, resulting in cancer (Vogelstein et al. 1988)

10 Multistep Colorectal Carcinoma formation and the associated genetic alterations Loss or Mutation Of APC Gene K-Ras Mut. Activation DCC Loss P53 Mutation Fearon and Vogelstein, Cell 1990

11 metastasis processes metastases = new malignant tumor growing at different places/organs of the body; only malignant tumors build metastases steps in metastasis processes: cells have to penetrate several times extracellular matrix and basal layer, migrate through the body, attach to the new localisation, penetrate again the wall of vessels and basal membrans

12 Individual cancer risk is determined by : - NATURE : inherited, genetic factors (cancer predisposition) - NORTURE : exposure to carcinogenic noxae (dose, dose-rate, type of radiation) - CHANCE : random fluctuations in biochemical processes (errors in DNA replication/dna repair)

13 DNA the primary target of radiation damage A - dose of about 2 Gy deposits in the entire exposed human body about 150 Joule energy (less than the thermal energy of a cup of hot coffee). Why than has ionizing radiation such a sever biological effect? The energy of ionizing radiation is deposited in living matter in the form of discret ionisations. Their spatial pattern match the structure of the DNA double-helix. Ionizing radiation thus has a high efficiancy to produce DNA breaks. DNA is a single-copy molecule Chromosomal DNA with a M r > 6x10 4 kda is several hundred times larger than the largest protein and has thus the biggest target size.

14 Initial radiation effect causes DNA fragmentation by double-strand breaks) Living cells can repair most of these damages Dose [Gy] intact, chromosomale DNA fragmented DNA Repair h 3h 5h following 20Gy

15 Incomplete or miss-repair can result in fixed genetic alterations such as Chromosomal translocation or deletions/losses of DNA (micronuclei) V79 cells (Chin. Hamsters ovary cells) 2 Gy gamma-irradiation, 6 h ROS17/2.8 cells (Osteoblasten, Ratte) 4 Gy gamma-irradiation, 12 h

16 Chromosomal Aberrations might contribute to tumor-development If an essential gene is lost, cell dies. Chromatid type Aberration Chromosome type Aberration Deletion S-Phase Mitosis Deletion If no essential gene is lost, cell might survive (but might have lost Tumor-Suppressor-Genes) Loss of acentric fragments Translocation If a stable translocation is generated, cell survives (but might acquire an activated Oncogens )

17 Ionizing Radiation causes stochastic damage to the genome..

18 Ionizing Radiation causes stochastic damage to the genome... Is the process of malignant transformation after irradiation a manifestation of genetic disorder?

19 Flt3 internal tandem duplications in Radiation-induced Acute Myeloid Leukaemia wt Flt3 Flt3 ITD FL O M ITD O M O M Flt3 genomic PCR Exon13/Intron13/Exon14 internal tandem duplications: 15, 31 (liquidator AML) 13 (victim AML) 20,30 (unexposed AML) Flt3 ITD in about 25% of all AML (spontaneous + radiation-induced)

20 Structure of Flt3 ITDs in spontaneous and radiation-associated Acute Myeloid Leukaemia AMLcase / Duplication Exposure duplicated AA Allele [bp] Group Victim SQLQMVQ VTGSSDNEYF YVDFREYEYD LKWEFPRENL EFG Victim YF YVDFREYEYD LKWE 15-1 ~ 24 Liquid. n.d Liquid. VTGSSDNEYF YVDFREYEYD LKWEFPRENL EF Liquid. GSSDNEYF YVDFREYE Contr. VDFREYE Contr. EYF YVDFREYEYD LK Liquid REYEYD LKWEFPRENL EFG consensus All Flt3 ITDs are in-frame and affect the juxtamembrane domain of the protein

21 Bone Tumors induced in mice following α-particle Th227 incorporation 227 Th

22 P53 Mutations radiation-induced osteosarcoma in mice spont (2) Transak- spez. DNA Bindung Protein-WW tivierung E5 E6 E7 E8 E9 viral (7) ACC-->ACT (18) 6 Fälle: keine p53 cdna amplifizierbar C.Dalke, PhD 2000

23 Stochastics and Specifity Ionizing Radiation causes a genome-wide stochastic damage to the DNA. During the carcinogenic process, out of this pool of random genetic changes specific gene-alterations are selected that confer a growth advantage to the tumor cells. Persistent genetic alterations in Radiation Carcinogenesis can be activated Oncogenes or inactivated Tumor- Suppressor Genes

24 The selection of a few specific gene-alterations out of a large pool of random genetic damages is a very inefficient mechanism.

25 The selection of a few specific gene-alterations out of a large pool of random genetic damages is a very inefficient mechanism. Therefore, you need several billions irradiated cells in a person, several thousands of exposed person and several years or decades after exposure to find a single radiation-associated tumor.

26 In the context of cancer as a multifactorial disease - NATURE : inherited, genetic factors (cancer predisposition) - NORTURE : exposure to carcinogenic noxae (dose, dose-rate, type of radiation) - CHANCE : random fluctuations in biochemical processes (errors in DNA replication/dna repair)

27 Inherited cancer syndroms (showing increased cancer risk after radiation exposure): Rb1 : Ercc1 Ercc5: Patched: familial bilateral Retinoblastom patients develop Bone sarcoma following RT Xeroderma Pigmentosum Basalioma and squamous cell carcinoma of skin following UV-B Gorlin-Syndrome (NBCC) Basalioma following RT P53: Li-Fraumeni-Syndrome Lymphoma, Soft-tissue sarcoma following X-ray (P53+/- mouse) ATM: Ataxia Telangiectasia (Lymphoma, Breast carcinoma..., severe acute radiation effects following RT)

28 NBCCS (Gorlin-Syndrome) Ataxia Telangiectasia

29 Occurence of secondary tumors (mainly Osteosarcoma) following RT in Retinoblastoma-Patients Rb families congenital predisposition sporadic cases Rb familie patients carry a heterozygote germline defect in a tumor-suppressor gene. Tumor formation following RT in these patients require inactivation of the wt allele (second hit)

30 Multistep-Model of Carcinogenesis Germline Mutation in Repair-Genes Hyperplasia Adenoma Progression Activation of genes that promote metastasis, invasion, angiogenesis immunological tolerance etc. malignant Tumor Initiation Activation of Oncogenes Promotion Mutation in Tumor- Suppressor-Genes

31 Multistep Carcinogenesis with induced or inherited genomic instability Germline Predisposition (Mutation in a repair- Gene) Accelerated Initiation (2nd Hit) Accelerated Promotion Progression (Transformation)

32 S U M M A R Y - The malignant transformation of a cell and the formation of a tumor requires several cellular and molecular functions to be altered. - These alterations have to be irreversible. - Depending on the degree of these alterations, tumors with different stage of malignancy can be found. - The process of malignant transformation is a time-dependent process. - Ionizing radiation can contribute to this process, but not in a deterministic manner. - The stepwise carcinogenic process can be dramatically accelerated in patients carrying germline mutations in cancer-predisposing genes.