Post on 20-Jan-2016
Chemical Chemical
Carcinogenesis:Carcinogenesis:GENOTOXIC and NON-GENOTOXICGENOTOXIC and NON-GENOTOXIC
carcinogenscarcinogens
Initiating
Event
Cell Proliferation
(clonal expansion)
Progression
Cell Proliferation
Cell Proliferation
Malignancy
Second Mutating
Event
Third Mutating
Event
Initiation
Promotion
Stages of CarcinogenesisStages of Carcinogenesis
Initiating
Event
Cell Proliferation
(clonal expansion)
Progression
Cell Proliferation
Cell Proliferation
Malignancy
Second Mutating
Event
Third Mutating
Event
Initiation
Promotion
Stages of CarcinogenesisStages of Carcinogenesis
Classification of Carcinogens Classification of Carcinogens According to the Mode of ActionAccording to the Mode of Action
GENOTOXIC NON-GENOTOXIC NON-GENOTOXICGENOTOXIC
Classification of Carcinogens Classification of Carcinogens According to the Mode of ActionAccording to the Mode of Action
GENOTOXICGENOTOXIC:: DNA-reactive or DNA-reactive metabolitesDNA-reactive or DNA-reactive metabolites Direct interaction to alter chromosomal Direct interaction to alter chromosomal
number/integritynumber/integrity May be mutagenic or cytotoxicMay be mutagenic or cytotoxic Usually cause mutations in simple systemsUsually cause mutations in simple systems
DNA AdductDNA Adduct MutationMutation CancerCancer
Mechanism of Carcinogenesis:Mechanism of Carcinogenesis:GenotoxicGenotoxic Carcinogens Carcinogens
1. Carcinogen activation1. Carcinogen activation 2. DNA binding2. DNA binding 4. Gene4. Gene mutationmutation
Chemical "Activated“carcinogen
3. Cell proliferation3. Cell proliferation(fix mutation)(fix mutation)
“inactivated“carcinogen
CYP450s
DNA Repair APOPTOSIS
Interaction of the exo-epoxide of Interaction of the exo-epoxide of aflatoxin Baflatoxin B11 with DNA with DNA
Smela et al., Carcinogenesis 22:535-45 (2001)Smela et al., Carcinogenesis 22:535-45 (2001)
Classification of Carcinogens Classification of Carcinogens According to the Mode of ActionAccording to the Mode of Action
NON-GENOTOXICNON-GENOTOXIC:: Do not directly cause DNA mutation Mechanism of action is not completely
understood Difficult to detect - requires rodent carcinogen
bioassay
?? MutationMutation CancerCancer
Non-Genotoxic Carcinogens
1)1) Mitogens: Mitogens: • stimulation of proliferationstimulation of proliferation
• mutations may occur secondarily to cell proliferationmutations may occur secondarily to cell proliferation
• may cause preferential growth of preneoplastic cellsmay cause preferential growth of preneoplastic cells
2) 2) Cytotoxicants: Cytotoxicants: • cytolethalcytolethal• induce regenerative growthinduce regenerative growth• mutations may occur secondarily to cell proliferationmutations may occur secondarily to cell proliferation
Tissue Changes with Mitogenic Tissue Changes with Mitogenic and Cytotoxic Agentsand Cytotoxic Agents
Proliferation
Cell Death Proliferation
Cytotoxic Agent
MitogenicAgent
Tissue
Mechanism of Carcinogenesis:Non-Genotoxic carcinogens
Cell proliferation (to fix “spontaneous” mutation)Cell proliferation (to fix “spontaneous” mutation)
APOPTOSIS
CANCER
X
Mechanisms of Non-Genotoxic Mechanisms of Non-Genotoxic CarcinogenesisCarcinogenesis
(what’s in a “black box” ?)(what’s in a “black box” ?)
Increased cell proliferationIncreased cell proliferation
Decreased apoptosisDecreased apoptosis
Changes in gene expression Changes in gene expression
Induction of metabolizing enzymesInduction of metabolizing enzymes
Activation of receptors (signaling)Activation of receptors (signaling)
Oxidative stressOxidative stress
??????
Decreases time available for DNA repairDecreases time available for DNA repair Converts repairable DNA damage into non-repairable Converts repairable DNA damage into non-repairable
mutationsmutations Necessary for chromosomal aberrations, insertions, Necessary for chromosomal aberrations, insertions,
deletions and gene amplificationdeletions and gene amplification Clonally expands existing cell populationsClonally expands existing cell populations
Cell Replication is Essential for Cell Replication is Essential for Multistage CarcinogenesisMultistage Carcinogenesis
Mitogenic Cytokines andMitogenic Cytokines andInduction of Cell Proliferation Induction of Cell Proliferation
Complete Mitogens:Complete Mitogens:
EEpidermal pidermal GGrowth rowth FFactor, actor, TTumor umor NNecrosis ecrosis FFactor actor , ,
HHepatocyte epatocyte GGrowth rowth FFactor, etc.actor, etc.
Co-Mitogens:Co-Mitogens:
Insulin, glucagon, norepinephrin, estrogensInsulin, glucagon, norepinephrin, estrogens
Growth Inhibitors:Growth Inhibitors:
TTransforming ransforming GGrowth rowth FFactor actor , , IInternterLLeukin 1eukin 1
Reasons That Not All Agents That Increase Reasons That Not All Agents That Increase Cell Proliferation are CarcinogensCell Proliferation are Carcinogens
Quality of the dataQuality of the data Temporal association of the increase in cell Temporal association of the increase in cell
proliferationproliferation Selective cytotoxicity for initiated cellsSelective cytotoxicity for initiated cells Terminal differentiation of proliferating cellsTerminal differentiation of proliferating cells
Mutagenesis Mutagenesis Carcinogenesis Carcinogenesis
Cell Proliferation Cell Proliferation Carcinogenesis Carcinogenesis
Toxicity Toxicity Cell Proliferation Cell Proliferation
ApoptosisApoptosis
Programmed Cell Death (Apoptosis): Active, orderly and cell-Programmed Cell Death (Apoptosis): Active, orderly and cell-type-specific death distinguishable from necrotic cell death type-specific death distinguishable from necrotic cell death (passive process):(passive process):
Induced in normal and cancer cells Induced in normal and cancer cells Non-random eventNon-random event Result of activation of a cascade of biochemical, gene Result of activation of a cascade of biochemical, gene
expression and morphological eventsexpression and morphological events tissue and cell specifictissue and cell specific Growth factors and mitogens inhibit apoptosisGrowth factors and mitogens inhibit apoptosis
Alteration of Gene ExpressionAlteration of Gene Expression
Nuclear (hormone-like) receptors Nuclear (hormone-like) receptors
Kinase cascadesKinase cascades
Calcium-, nitric oxide-mediated signalingCalcium-, nitric oxide-mediated signaling
Transcription factorsTranscription factors
Gene methylation status (hypo -> enhanced gene Gene methylation status (hypo -> enhanced gene
expression; hyper -> gene silencing)expression; hyper -> gene silencing)
Induction of Metabolizing EnzymesInduction of Metabolizing Enzymes
May be a reason for tissue-, and/or species-May be a reason for tissue-, and/or species-
selectivity of carcinogensselectivity of carcinogens
Metabolites may be ligands for receptorsMetabolites may be ligands for receptors
Production of reactive oxygen speciesProduction of reactive oxygen species
Nature 407, 920 - 923 (2000) ©Nature 407, 920 - 923 (2000) ©
The nuclear receptor CAR mediates specific The nuclear receptor CAR mediates specific xenobiotic induction of drug metabolismxenobiotic induction of drug metabolism
ATCGGTTA……
XB
CAR
CYP 2b10
Oxidative StressOxidative Stress
Indirect DNA damageIndirect DNA damage
Induction of cell proliferation/apoptosis signaling Induction of cell proliferation/apoptosis signaling
cascadescascades
Peroxisome ProliferatorsPeroxisome Proliferators
A wide range of classes of chemicals: A wide range of classes of chemicals: lipid lipid lowering drugs, plasticizers, lowering drugs, plasticizers,
food flavors, industrial solvents, herbicides food flavors, industrial solvents, herbicides Cause marked increases in size and number of Cause marked increases in size and number of
peroxisomes peroxisomes Potent rodent liver carcinogensPotent rodent liver carcinogens Human exposure is from therapeutic, Human exposure is from therapeutic,
environmental, industrial and other sourcesenvironmental, industrial and other sources No clear epidemiological evidence for or against No clear epidemiological evidence for or against
carcinogenicity in humans carcinogenicity in humans
PEROXISOMEPEROXISOME
Fatty Acid
Acyl-CoA
Enoyl-CoA
Hydroxyacyl-CoA
Ketoacyl-CoA
Acetyl-CoA Acyl-CoA shortened by two carbons
Fatty acyl-CoA synthetase
Acyl-CoA oxidase
Enoyl-CoA hydrolase
Hydroxyacyl-CoAdehydrogenase
Thiolase
H2O2
• -oxidation of fatty acids• bile acid synthesis• purine and polyamine
catabolism• amino acid catabolism• oxygen metabolism
Peroxisome proliferation
• Liver growth– hypertrophy– hyperplasia
• Induction of liver enzymes– peroxisomal enzymes (peroxisome proliferation)– P450 - the CYP4 genes
• Proliferation of the endoplasmic reticulum and peroxisomes
• Hypolipidaemia
Adipocyte DifferentiationGlucose HomeostasisMacrophage Function
Peroxisome ProliferationLipid Homeostasis
Liver Carcinogenesis
Lipid HomeostasisSkin proliferation
Peroxisome Proliferator - Activated Peroxisome Proliferator - Activated ReceptorsReceptors
FA
FABP
DietFat Stores
FA StorageFA Metabolism
FA
PPRE
FA
PP
PPRE
??PPRE
LTP
G
PPAR agonist-induced hepatocarcinogenesis mode of action
Peters& Gonzalez, J. Mol. Med., 2005
Klaunig et al., Crit. Rev. Tox., 2003
Klaunig et al., Crit. Rev. Tox., 2003
Peters et al., Carcinogenesis, 1997
PPARPPAR (+/+) (+/+)
+ WY-14,643 (11 months)+ WY-14,643 (11 months)PPARPPAR (-/-) (-/-)
+ WY-14,643 (11 months)+ WY-14,643 (11 months)
Peroxisome Proliferators: Species Differences
• Mouse and rat: highly responsive• Marmoset: does not respond• Guinea Pig: no peroxisome proliferation, but have hypolipidaemia• Humans: believed to be unresponsive, but have hypolipidaemia
• PPAR exists in mouse, rat, guinea pig and human
• In humans: Lower hepatic levels of PPARa Lower ligand binding activityDifferent structure (polymorphisms)Different PP Response Elements in DNAPresence of competing proteins for PPREExpression of dominant-negative form of PPAR
So, we have a chemical that So, we have a chemical that is a non-genotoxic RODENT is a non-genotoxic RODENT
carcinogen!carcinogen!
If we would regulate this chemical, If we would regulate this chemical,
would it help to improve the quality would it help to improve the quality
of HUMAN life?of HUMAN life?
Proportion Percentage
Chemicals tested in both rats and mice 350/590 59%
Naturally occurring chemicals 79/139 57%
Synthetic chemicals 271/451 60%
Chemicals tested in rats and/or mice
Chem. in Carcinogen. Potency Database 702/1348 52%
Natural pesticides 37/71 52%
Mold toxins 14/23 61%
Chemicals in roasted coffee 21/30 70%
Innes negative chemicals retested 17/34 50%
Physician’s desk reference PDR
Drugs with reported cancer tests 117/241 49%
FDA database of drug submissions 125/282 44%
Proportion of chemicals evaluated as Proportion of chemicals evaluated as carcinogeniccarcinogenic
Ames and Gold Ames and Gold Mutat ResMutat Res 447:3-13, 2000 447:3-13, 2000
What do we do now?What do we do now?
Look at the “larger picture”Look at the “larger picture”
Probe human relevance of animal dataProbe human relevance of animal data
Continue research on the mechanismsContinue research on the mechanisms
Change/improve current test used for detection of Change/improve current test used for detection of
carcinogenicitycarcinogenicity