Chemical Carcinogenesis: Initiation, Promotion, Progression

1. ENVR 430 Chemical Carcinogenesis:Initiation, Promotion, Progression Ivan Rusyn Laboratory of Environmental Genomics Department of Environmental Sciences & Engineering iir@unc.edu 843-2596 0031 MHRC

2. CANCER: “A multicausal, multistage group of diseases the mechanisms of which are still only partially known” (IARC Scientific Publications, 1992) “Cancer is a group of diseases characterized by uncontrolled growth and spread of abnormal cells […] that can result in death” (American Cancer Society, 2006) Age adjusted Cancer Death Rates, by Site, US, 1930-2002

3. Benign tissue is not cancer. Although the cell growth is moderately increased, the cells do not invade nearby tissue or spread to other parts of the body • Malignant tissue is cancer. The cancer cells divide out of control. They can invade and destroy nearby healthy tissue. Also, cancer cells can break away from the tumor they form and enter the bloodstream and lymphatic system • Metastasis: the spread of cancer beyond the organ of origin

4. WHAT MAY CAUSE CANCER ? • Hereditary disorders • Chemicals • Viruses • Chronic inflammation • ??? From http://www.cancersupportivecare.com/riskintro.html

5. History of Chemical Carcinogenesis • Chemical carcinogenesis was first suggested by clinicians 200 years ago • Scrotal cancer in chimney sweeps - Potts • Nasal cancer and snuff dipping - Hill • Today, >50 chemicals are recognized as human carcinogens • First experimental studies in animals were done ~80 years ago

6. History of Chemical Carcinogenesis • Large numbers of chemicals were tested for carcinogenic potential in the 1970-1990s • Maximum Tolerated Doses (MTD) were used. • 60% of rodent carcinogens were genotoxic • 40% of rodent carcinogens were nongenotoxic • Some chemicals were single site, single species carcinogens • Others were multisite, multispecies carcinogens • Dose-response varies from <1/2 MTD to <1/1000 MTD • Most regulations use straight mathematical extrapolation of high dose rodent data to predict risks

7. WORLD HEALTH ORGANIZATION INTERNATIONAL AGENCY FOR RESEARCH ON CANCER IARC Monograph Evaluations LYON, FRANCE Slide courtesy of V. Cogliano (IARC)

8. IARC: Slide courtesy of V. Cogliano (IARC)

9. A tour of IARC’s classificationsPreamble, Part B, Section 6(d) Slide courtesy of V. Cogliano (IARC)

10. Slide courtesy of V. Cogliano (IARC)

11. IARC (2007) - monographs.iarc.fr • Carcinogenic to humans (group 1) – 100 agents to date • Probably carcinogenic to humans (group 2A) – 68 • Possibly carcinogenic to humans (group 2B) – 246 • Not classifiable as to its carcinogenicity to humans (group 3) – 516 • Probably not carcinogenic to humans (group 4) – 1 • U.S. EPA (2003) • Carcinogenic to humans • Likely to be carcinogenic to humans • Suggestive evidence of carcinogenic potential • Inadequate information to assess carcinogenic potential • Not likely to be carcinogenic to humans • U.S. NTP (2002)(see NTP levels of evidence.pdf) • Known to be a human carcinogen • Reasonably anticipated to be a human carcinogen • Cal/EPA (2004) • Known to the state to cause cancer

13. Cancer Cases Attributable to Environmental Carcinogens (Worldwide, 1990) Infections (viruses, parasites, H. pylori) 16% Tobacco (smoked and smokeless) 14% Occupation 4% Alcohol drinking 3% 37% Diet and dietary components including contaminants 25% Pollution 2% Reproductive factors 2% 29%

14. IARC Group 1 – Carcinogenic to humansMonographs Volumes 1-84 (1972-2002): 89 Agents and Exposures Medical drugs and treatments 24 Industrial processes 13 Infectious agents or processes 10 Physical agents 10 Industrial chemicals 7 Inhaled particulates 5 Metals and inorganic salts 5 Lifestyle factors (incl. herbal remedies) 7 Other 8

15. Exposures to Chemicals in the Workplace Modified from Cullen et al. (1990).

16. Carcinogenic Risks of Chemical Agents Associated with Medical Therapy and Diagnosis

17. Carcinogenic Factors Associated with Lifestyle Modified from Pitot (1986) and Vainio et al. (1991)

18. Chemical Carcinogenesis in the 21st Century New perceptions of previously known carcinogens: Combined effects of multiple exposures Examples: • Alcohol drinking and aflatoxins • Alcohol drinking and HBV/HBC • Alcohol drinking and tobacco smoking • Alcohol drinking and asbestos/arsenic/radon

19. Stages of Carcinogenesis Initiation Initiating Event Cell Proliferation (clonal expansion) Second Mutating Event Promotion Cell Proliferation Progression "N" Mutating Event Cell Proliferation Malignancy

20. Cellular and Molecular Mechanisms in Multistage Carcinogenesis: INITIATION Initiating event involves cellular genome – MUTATIONS Target genes: - oncogenes/tumor suppressor genes - signal transduction - cell cycle/apoptosis regulators “Simple” genetic changes From http://newscenter.cancer.gov/sciencebehind/

21. SOURCES OF MUTATIONS EXOGENOUS DNA DAMAGE ENDOGENOUS DNA DAMAGE Free Polymerase Environmental Life Radicals Errors Depurination Agents Styles DNA REPAIR CELL REPLICATION MUTATION

22. Chemical Exposure (air, water, food, etc.) Internal Exposure Metabolic Activation Macromolecular Binding Detoxication Protein DNA RNA (Biomarker) Biologically Effective Dose X Efficiency of Mispairing Initiation X Cell Proliferation

23. Williams J.A., Carcinogenesis 22:209-14 (2001)

24. Accumulation of mutations during tumor progression Loeb L.A. Cancer Res. 61:3230-9 (2001)

25. RNA-directed DNA methylation • RNA-mediated chromatin remodeling • RNAi, siRNA, miRNA … DNMT1 P P DNMT3a U U DNMT3b Me Me SAM SAH A A EPIGENETICS Epigenetic alterations – changes induced in cells that alter the expression of the information on transcriptional, translational, or post-translational levels without changes in DNA sequence Methylation of DNA Modifications of histones RNA-mediated modifications - acetylation - methylation - phosphorylation - ubiquitination

26. GENETIC AND EPIGENETIC MODELS OF THE CANCER INITIATION Normal cells Normal cells Environmental Environmental Endogenous Endogenous ACQUISITION OF ADDITIONAL RANDOM MUTATIONS ALTERATIONS IN CELLULAR EPIGENOME Clonal selection and expression of initiated cells Epigenetically reprogrammed cells Mutator phenotype cells Mutator phenotype cells Cancer cells Cancer cells

27. Cellular and Molecular Mechanisms in Multistage Carcinogenesis: PROMOTION Reversible enhancement/repression of gene expression: - increased cell proliferation - inhibition of apoptosis No direct structural alteration in DNA by agent or its metabolites From http://newscenter.cancer.gov/sciencebehind/

28. Role of Increased Cell Proliferation in Carcinogenesis • Decreases time available for DNA repair • Converts repairable DNA damage into nonrepairable mutations (not DNA damage anymore!) • Necessary for chromosomal aberrations, insertions, deletions and gene amplification • Clonally expands existing cell populations with mutations

29. X 1. No Tumors X 2. Tumors X 3. Tumors X 4. No Tumors No Tumors 5. Time = Application of Initiator = Application of Promoter X

30. Basophilic Focus N Adenoma Carcinoma M M 1 N Promotion Regression Progression No Tumors Tumors = Application of Promoter Adapted from: Marsman and Popp. Carcinogenesis 15:111-117 (1994)

31. Cellular and Molecular Mechanisms in Multistage Carcinogenesis: PROGRESSION • Irreversible enhancement/repression of gene expression • Complex genetic alterations (chromosomal translocations, deletions, gene amplifications, recombinations, etc.) • Selection of neoplastic cells for optimal growth genotype/ phenotype in response to the cellular environment From http://newscenter.cancer.gov/sciencebehind/ “Complex” genetic changes

32. Phenotypic characteristics of cancer cells: • Immortalization • Transformation • Loss of contact growth inhibition • Autonomy of proliferation • Avoidance of apoptosis • Aberrant differentiation • Induction of angiogenesis

33. Human Tumors and Stages of Carcinogenesis Hussainet al., Oncogene, 2007