L19 Chemical Carcinogenesis PDF

L19 Chemical carcinogenesis Timo Hamers Set up  Cancer  Multistage process Initiation Promotion Progression  Mutagenic compounds Intercalating agents Reactive substances (direct/indirect) Smoking Oxidative stress  Risk assessment o...

L19 Chemical carcinogenesis Timo Hamers Set up  Cancer  Multistage process Initiation Promotion Progression  Mutagenic compounds Intercalating agents Reactive substances (direct/indirect) Smoking Oxidative stress  Risk assessment of carcinogenic compounds: See L21 2 Cancer  Collective name for diseases  Characterized by unlimited cell divisions (proliferation) Concentrated: tumor, neoplasm, mass Diffuse: leukemia 3 Cancer and tumors Tumors  Benign: Encapsulated Differentiated cells Slow growth  Malign Dedifferentiated cells Invasive Metastasis 4 Risk factors for cancer  Genetic factors (pre-disposition)  Environmental factors (migrant-studies) Food, e.g. fat (-), alcohol (-), anti-oxidants (+), vitamins (+) Radiation (UV, radioactivity) Compounds, other than in food (e.g. smoking, at work) Fibers (e.g. asbestos) Viruses  Hormonal and reproduction factors Pregnancy at later age Contraceptives? Number of sexual contacts  Consequence: variation between individuals AND populations  Check www.cancer.gov/cancertopics/prevention-genetics- causes/causes 5 Percival Pott, London 1775  Chimney sweeper as a child?  Then increased incidence of scrotum-cancer at later age!  Discovers relationship between Cancer and exposure to compounds (soot) Cancer at later age and exposure at younger age Occupational hygiene and cancer prevention 10 Set up  Cancer  Multistage process Initiation Promotion Progression  Indirect mutagenicity of PAHs  Mutagenic compounds Intercalating agents Reactive substances (direct/indirect) Smoking Oxidative stress  Risk assessment of carcinogenic compounds: See L21 11 Multistage process  Initiation Change in DNA (mutation)  Promotion Dedifferentiation of cells Increased proliferation  Progression Invasion Metastasis 12  Mutagenic compounds Carcinogenic compounds cause an inheritable can cause cancer change in the nucleotide order of the DNA Genotoxic Non-genotoxic carcinogens carcinogens are tumor promoting compounds damage DNA 13 Multistage process initiation (mutation promotio progressio metastasis ) n n invasion normal cells pre-neoplastic tumor cells Malignant cells tumor 14 Multistage process and compounds Each phase in the process of carcinogenesis can be influenced by Compounds (chemical carcinogenesis): Initiation: mutagens Promotion: tumor promotors Progression: tumor progressors (often mutagens) Other factors Initiation: e.g. viruses, radiation Promotion: e.g. endogenous hormones Progression: spontaneous mutations 15  initiation (mutation) Initiation and compounds normal cells pre-neoplastic  DNA damage cells  Change in the nucleotide order of the DNA strain  If not repaired before cell division?  Then inherited by daughter cells! (gene or point mutation)  Gene mutations can be classified according to: What happens at DNA level: base-pair substitution and frameshift mutation (deletion or insertion) What the consequence is at protein level: missense, nonsense or silent mutation 16  O O CH3 DNA damage O O O O S O O O H3C OMe A T G A A G T T T G G C T A A T A C T T C A A A C C G A T T 1. Electrophilic (reactive) compounds Bind to base (DNA-adduct) E.g. benzo[a]pyrene 2. Intercalating agents Fit between nucleotides E.g. acridine 17 Indirect vs direct mutagenicity bioactivation 18 Types of mutations: base-pair substitution wildtype A T G A A G T T T G G C T A A Met Lys Phe Gly STOP missense A T G A A G T T T A G C T A A base-pair substitution Met Lys Phe Ser STOP silent A T G A A G T T T G G T T A A base-pair substitution Met Lys Phe Gly STOP 19 Types of mutations: frame-shifts wildtype A T G A A G T T T G G C T A A Met Lys Phe Gly STOP T missense A T G A A G T T G G C T A A … frame-shift mutation Met Lys Leu Ala … nonsense A T G T A A G T T T G G C T A A frame-shift mutation Met STOP 20 Types of mutations  WT: The fat cat ate the hot dog  Base-pair substitution The fat car ate the hot dog (missense) The fat cet ate the hot dog (silent)  Frame shift mutation The fma tca tat eth eho tdo (insertie - missense) The ftc ata tet heh otd og (deletie - missense) 21 Measuring mutagenic potency: Ames assay Mutated: cannot synthesize histidine Agar: Contains NO histidine 22 Ames fluctuation assay 23  Ames assay on sediment extracts Spittelwasser Frameshift mutation Basepair substitution -S9 +S9 Reifferscheid et al. 2011 24 DNA repair  Not every DNA-binding ultimately leads to a mutation  Cell has several repair mechanisms Nucleotide excision Recombination Error prone repair 30 Summary initiation Excretable metabolites Normal cell detoxification DNA repair Indirect activation Direct DNA mutagen mutagen DNA adduct binding DNA replication Cell death Mutated cell 31 Set up  Cancer  Multistage process Initiation Promotion Progression  Mutagenic compounds Intercalating agents Reactive substances (direct/indirect) Smoking Oxidative stress  Risk assessment of carcinogenic compounds: See L21 32  promotion Tumor promotion and compounds pre- tumor cellen neoplastische cellen Not genotoxic Not reactive Threshold value Reversible Loss of differentiation Increased cell proliferation Decreased apoptosis Many “natural” compounds such as hormones 33 Tumor promotion and compounds 34 Tumor progression and compounds progression metastasis  Karyotypic instability invasion Chromosome-abberations Breaks tumor cells malign tumor Exchange Aneuploidy and polyploidy  Extra mutations Proto-oncogenes on Tumor-suppressor genes off  Irreversible 36 Oncogene and tumor-suppressor gene Oncogene: Tumor suppressor gene: Normal Proto-oncogene Active tumor suppressor gene Normal function in Activation Inactivation regulation and mutation, Mutation cell growth duplication, chromosomal exchange Cancer Oncogene Inactive tumor suppressor gene Uncontrolled cell growth 37 Set up  Cancer  Multistage process Initiation Promotion Progression  Mutagenic compounds Intercalating agents Reactive substances (direct/indirect) Smoking Oxidative stress  Risk assessment of carcinogenic compounds: See L21 40 Intercalating compounds: frameshift mutations mother daughter mother daughter mother daughter strain strain strain strain strain strain INSERTION DELETION acridine N 41 Dimethylsulfate: direct mutagenic - alkylating  Methylating substance  Application CH3 O Organic synthesis O O S Methylation O H3C  Production Plasticizers Pesticides Pharmaceuticals Paints Coatings 42 DNA methylation and mutations (type I) cytosine uracil G G C C C G guanine methyl- guanine 43 DNA methylation and mutations (type II) Empty base spot methyl- guanine 44 Benzo[a]pyrene  Polycyclic Aromatic Hydrocarbon (PAH)  Natural product Fossil fuels  Rest product incomplete combustion Soot (chimney sweepers) Traffic emissions Smoking (Burnt meat) 47 Benzo[a]pyrene and other PAHs O N bay region NH biotransformation DNA N N NH O DNA HO strain HO HO OH OH benzo[a]pyrene benzo[a]pyrene benzo[a]pyrene guanine diolepoxide adduct O O O O OH OH OH OH OH OH OH OH phenanthrene benzo[a]anthracene chrysene dibenzo[a,h]anthracene O OH OH benzo[e]pyrene 48 Oxidative stress: oxidation of hydroquinones H2Q S- Q Hydroquinon Semiquinon Quinon OH O O CYP OH O O O2  e O2 O2  H2O HO2  OH  HO2  e  H  H2O2 H2O2  e OH  OH 49 Oxidative stress leads to 8OH-G DNA adduct formation O O HN N HN N + OH OH Mutation H2N N N H2N N N : GT DNA DNA strain strain guanine 8OH-guanine 50 Oxidative stress (in general) ROS: reactive oxygen species 51 Nitrosoamines from tobacco smoke smoking metabolisation methylation 52 Types of mutagenic compounds  Compounds that fit exactly in DNA (intercalating)  Reactive compounds that bind to DNA (electrophilic) Direct mutagen versus indirect mutagen  Oxidative stress By redox cycling of the compound itself By inflammations 53 Goals: after this lecture, you are able to  Name the three different stages in carcinogenesis, each with their own characteristics  Explain the difference between a base-pair-substitution and a frameshift mutation  Explain the difference between silent, missense and nonsense mutations  Know the difference between direct and indirect mutagens  Explain what oncogenes and tumor suppressor genes are  Recognize how reactive compounds can bind to DNA  Understand how PAHs can be mutagenic 54