Environmental Health Carcinogenesis

1. Environmental Health Carcinogenesis Week 7

2. Genotoxicity: toxic effects on genetic material • Cancer • Developmental (gestational timing crucial) • Somatic diseases

3. The nature of “life information”… • DNA structure • Base-sugar-triphosphate • Purines: A, G; Pyrimidines: C, T(U) • Double helix; A-T; C-G pairs • Chromosomes (with chromatin) • Humans: 23 autos. pairs + sex pair (XY, XX) • DNA (code) --> protein: 3nucleic acids /1 aminoacid • Universal code - the same principles and molecules in every organism (amoebas to humans) • Genes (units of information) are the same in every cell of an organism, but expression of genes varies by cell/tissue • Conserved and variable regions of code

4. Types of Genotoxic effects • Chromosomal aberrations • Deletions • Duplications • Inversions • Translocations • Sister chromatid exchanges • Gene mutations • Point mutations (base replacement) • Frameshift mutations (insertion/deletion of part of gene)

5. Mutagens:agents that cause a mutation • Mutation: Alteration in the genetic code (DNA sequence of nucleotides), that may result in altered population of cells or organisms (nucleic DNA most important) • Mutations • Adaptation/survival and speciation • Disease and death

6. Effects of mutations • Silent - no effect • Change in gene expression • protein amount, location, timing • Change in structure of protein • Single aminoacid change (especially hydrophilic-phobic) • Multiple aminoacids/Trancation • Change or loss of activity • Inefficient or improper biochemical process • Altered cell function • Disease; cancer; birth defects; hereditary diseases

7. Genotoxic factors • UV light (200-300nm)(>10-10m) • Thymine dimerization (T-T) • Cytosine hydration (C + H2O) • Ionizing radiation (x/  -rays, <10-10m; ,  particles) • Single strand, double strand breaks, base changes • Biotoxins (aflatoxin-B1) • Viruses (HPV)

8. More genotoxic factors • Chemicals • Alkylating (diethylnitrosamine) • Mispairing (G-T vs G-C) • Depurination (transition, transversion) • Backbone break • Arylating (forming DNA adducts) • Intercalating (planar aromatic hydrocarbons) • Base analogues (5-Br-uracil; 5-F-uracil) • Metaphase blockers • Deamination agents • Enzyme inhibitors • Metals (As, Be, Cd, Cr(IV, V), Ni, Pb)

9. Types of DNA damage

10. Reactive oxygen species

11. Post genetic-damage events • Repair • Apoptosis • Permanent change • Cell level • Tissue level • Organism level • Species level See also p. 64 and 262 of Casarett and Doull’s “Toxicology”

12. Extensive DNA repair system

13. Cancer, a.k.a. malignant neoplasm • Uncontrolled growth and spread of abnormal cells • Solid tumors: liver, lung, intestine, breast, etc • Blood and lymphatic system, incl. bone marrow • Reasons for increased cancer incidence: • increased age • increased number of carcinogens present • other?

14. Causes of Death All causes Unintentional injuries Cancer Heart disease Suicide, homicide Congenital anomalies Years of Life Lost* 11,761,000 2,306,000 1,803,000 1,563,000 1,247,000 584,000 Cancer is the leading disease-related cause of years of life lost in the US. * Estimated years of life lost before the age of 65

15. Carcinogenesis Terms • Chemical Carcinogenesis is the chemically-induced generation of cancerous growths in living organisms. Cancerous growths are often called neoplasms. • A neoplasm is an abnormal tissue mass, the growth of which exceeds and is uncoordinated with that of normal tissue and persists in a similar manner following cessation of stimulus. Unique feature is the continuous replication of a cell population.

16. Cancer is therefore the malignant uncontrolled proliferation of neoplastic cells. Also a description of a multitude of different disease states (~200)

17. Benign Usually encapsulated Usually non-invasive Highly differentiated Rare mitoses Slow growth Little or no anaplasia No metastases Malignant Encapsulated Invasive Poorly differentiated Mitoses relatively common Rapid growth Anaplastic to varying degrees Metastases Malignant vs. Benign Neoplasms

18. The many faces of cancer Malignant neoplasms are usually called carcinomas (endo- or ectoderm) or sarcomas (mesoderm). Exceptions are hematopoietic malignancies, melanoma, neuroblastoma, thymoma.

19. Carcinogens Genotoxic Non-genotoxic

20. Many different chemical structures are carcinogenic

21. Natural/endogenous molecules with carcinogenic properties

22. Synthetic hormone-like structures

25. Millers showed that metabolic activation is key to carcinogenicity (1950’s)

26. …metabolic activation, continued

27. Activation can occur also following Phase II reactions

28. Reactive metabolites bind covalently to DNA and form adducts which can generate mutations

29. …adducts, continued

30. …adducts, continued

31. Effective elimination of carcinogens is a means of protection

32. Carcinogenesis • Initiation • Dose related • Dividing cells in site are targets • Genetic damage on expressed genes • Can be repaired • Promotion • Activation of initiated cell • First cell of tumor • Progression • Rapid (relatively) expansion of abnormal cells See also p. 267, 271, 275 of Casarett and Doull’s “Toxicology”

33. Initiation and promotion

34. Polyaromatic hydrocarbons (PAHs) are initiating agents in tumor development

35. Tumor promoters TPA is the experimental skin tumor promoter found in croton oil

37. Liver tumor incidence after daily doses of 2-acetylaminofluorene

38. Tumor response on mice initiated with 0.2mol of dimethylbenzanthracene and promoted with 12-O-tetradecanoylphorbol-13-acetate

39. Potency of carcinogens • Defined as the slope of the dose-response curve for induction of neoplasms • Iball index (% animals with tumors) • TD50 (used in comparative list) • T25 (dose rate that gives 25% of neoplasms at specific site) See also p. 301 of Casarett and Doull’s “Toxicology”

40. Clonal Selection Model of Neoplastic Progression

41. The multistep pathway to colorectal cancer By B. Vogelstein