Chemical Chemical

Carcinogenesis:Carcinogenesis:Initiation, Promotion, ProgressionInitiation, Promotion, Progression

Ivan RusynLaboratory of Environmental Genomics

Department of Environmental Sciences & Engineering

iir@unc.edu 843-2596 0031 MHRC

ENVR 430

CANCER:CANCER:““A multicausal, multistage group of diseases the mechanisms of which are still only A multicausal, multistage group of diseases the mechanisms of which are still only partially knownpartially known” (IARC Scientific Publications, 1992)” (IARC Scientific Publications, 1992)

““Cancer is a group of diseases characterized by uncontrolled growth and spread of Cancer is a group of diseases characterized by uncontrolled growth and spread of abnormal cells […] that can result in death”abnormal cells […] that can result in death” (American Cancer Society, 2006) (American Cancer Society, 2006)

Age adjusted Cancer Death Rates, by Site, US, 1930-2002

• 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

WHAT MAY CAUSE CANCER ?WHAT MAY CAUSE CANCER ? Hereditary Hereditary disordersdisorders ChemicalsChemicals VirusesViruses Chronic inflammationChronic inflammation ??????

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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

• 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

History of Chemical Carcinogenesis

WORLD HEALTH ORGANIZATIONINTERNATIONAL AGENCY FOR RESEARCH ON CANCER

IARC Monograph Evaluations

LYON, FRANCE

Slide courtesy of V. Cogliano (IARC)

IARC:

Slide courtesy of V. Cogliano (IARC)

A tour of IARC’s classificationsPreamble, Part B, Section 6(d)

Slide courtesy of V. Cogliano (IARC)

Slide courtesy of V. Cogliano (IARC)

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

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%

IARC Group 1 – Carcinogenic to humans

Monographs Volumes 1-84 (1972-2002): 89 Agents and Exposures

Medical drugs and treatments 24Industrial processes 13Infectious agents or processes 10Physical agents 10Industrial chemicals 7Inhaled particulates 5Metals and inorganic salts 5Lifestyle factors (incl. herbal remedies) 7Other 8

Exposures to Chemicals in the Workplace

Modified from Cullen et al. (1990).

Carcinogenic Risks of Chemical Agents Associated with Medical Therapy and

Diagnosis

Carcinogenic Factors Associated with Lifestyle

Modified from Pitot (1986) and Vainio et al. (1991)

Chemical Carcinogenesis in the 21st Century

New perceptions of previously known carcinogens:

Combined effects of multiple exposures

Examples:oAlcohol drinking and aflatoxinsoAlcohol drinking and HBV/HBCoAlcohol drinking and tobacco smokingoAlcohol drinking and asbestos/arsenic/radon

Initiating

Event

Cell Proliferation

(clonal expansion)

Progression

Cell Proliferation

Cell Proliferation

Malignancy

Second Mutating

Event

"N" Mutating Event

Initiation

Promotion

Stages of CarcinogenesisStages of Carcinogenesis

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

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“Simple” genetic changes

SOURCES OF SOURCES OF MUTATIONSMUTATIONS

ENDOGENOUS DNA DAMAGEENDOGENOUS DNA DAMAGE EXOGENOUS DNA DAMAGEEXOGENOUS DNA DAMAGE

DepurinatioDepurinationn

DNA REPAIRDNA REPAIR

MUTATIONMUTATION

LifLifeeStyleStyless

EnvironmentaEnvironmentallAgentAgentss

FreFreee

RadicalsRadicals

PolymerasPolymerasee

ErrorsErrors

CELL REPLICATIONCELL REPLICATION

Chemical ExposureChemical Exposure (air, water, food, etc.) (air, water, food, etc.)

Internal ExposureInternal Exposure

Metabolic ActivationMetabolic Activation

Macromolecular BindingMacromolecular Binding DetoxicationDetoxication

DNADNA RNARNA ProteinProtein

Biologically Effective DoseBiologically Effective Dose

Efficiency of MispairingEfficiency of Mispairing

Cell ProliferationCell Proliferation

XX

XXInitiationInitiation

(Biomarker)(Biomarker)

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

Accumulation of mutations during tumor Accumulation of mutations during tumor progressionprogression

Loeb L.A. Cancer Res. 61:3230-9 (2001)

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

EPIGENETICS

SAM SAH

DNMT1DNMT3aDNMT3b

Methylation of DNA

Modifications of histones

RNA-mediated modifications

• RNA-directed DNA methylation

• RNA-mediated chromatin remodeling

• RNAi, siRNA, miRNA …

A

Me

P

U

- acetylation

- methylation

- phosphorylation

- ubiquitination

P UMe

A

GENETIC AND EPIGENETIC MODELS OF THE CANCER INITIATION

Epigenetically reprogrammed cells

Mutator phenotype cells

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ALTERATIONS IN CELLULAR EPIGENOME

Normal cells

Cancer cells

Clonal selection and expression of initiated cells

Mutator phenotype cells

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ACQUISITION OF ADDITIONAL RANDOM MUTATIONS

Normal cells

Cancer cells

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

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Role of Increased Cell Proliferation in Carcinogenesis

• Decreases time available for DNA repair

• Converts repairable DNA damage intononrepairable mutations (not DNA damage anymore!)

• Necessary for chromosomal aberrations, insertions, deletions and gene amplification

• Clonally expands existing cell populations with mutations

No Tumors

Tumors

No Tumors

No Tumors

Tumors

1.

2.

3.

4.

5.

X

X

X

X

Time

X = Application of Initiator = Application of Promoter

N Basophilic Focus Adenoma Carcinoma

M 1 MN

Promotion Regression Progression

Adapted from: Marsman and Popp. Carcinogenesis 15:111-117 (1994)

No Tumors

Tumors= Application of Promoter

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

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“Complex” genetic changes

• Immortalization

• Transformation

• Loss of contact growth inhibition

• Autonomy of proliferation

• Avoidance of apoptosis

• Aberrant differentiation

• Induction of angiogenesis

Phenotypic characteristics of cancer cells:

Human Tumors and Stages of Carcinogenesis

Hussain et al., Oncogene, 2007