Lecture3 kensler

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Environmental Carcinogenesis

Thomas Kensler, PhD Bloomberg School of Public Health

3

Lecture OutlineCancer - What is it? What causes it?Epidemiological evidence for a role of environment/life-style factors as causes of cancerMechanisms of carcinogenesis– Carcinogenic agents– Carcinogen bioactivation, DNA damage/repair– Molecular targets: oncogenes, tumor suppressor

genes

Multistage nature of carcinogenesisPrevention of carcinogenesis

Section A

Cancer: What It Is and What Causes It

5

Cancer: The Endpoint

What is it?– Group of diseases– Uncontrolled growth– Spread (invasion, metastasis)

6

Carcinogenesis: The Process

What causes it?– Exogenous: Chemicals, radiation,

viruses– Endogenous: Hormones, immune

dysfunction,– Inherited mutations (susceptibilities)

7

CANCER ARISES FROMTHE ACCUMULATION OF GENETIC DAMAGE

(only 5-15 % of cancer is due to inherited cancer

genes)

Public Domain

8

SINGLE AND SUSCEPTIBILITY GENES IN CANCER CAUSE

Single Susceptibility GeneDefinition Necessary & sufficient Alters risk but is neither

for disease necessary nor sufficientfor disease causation

Example BRCA (breast/ovary) CYP1A1 (lung)APC (polyposis coli) CYP2D6 (lung)RB (retinoblastoma) GST-M1 (lung, bladder)

Gene prevelence Low Often highGene type Mutation Polymorphism or mutationStudy setting Family Gen. population/epi. studiesStrength of association Very high Low to moderateAbsolute risk High LowPopulation attributable risk Low High

Gene-environment interaction 2° and variable 1° and implicit

Role of environmentalexposure 2° and variable Crucial

9

Risk of Breast Cancer Among BRCA1 or BRAC2 Mutation Carriers

JHSPH OpenCourseWare has removed this image because license for its use could not be secured.

See Figure 1A. King MC, et al. Breast and ovarian cancer risks due to inherited mutations in BRCA1 and BRCA2.

Science. 2003;302:643-646. Free with registration.

http://dx.doi.org/10.1126/science.1088759



10

Influence of Birth Cohort on Risk of Breast Cancer in BRCA1 or BRCA2 Mutation Carriers


See Figure 1D. King MC, et al. Breast and ovarian cancer risks due to inherited mutations in BRCA1 and BRCA2.





11

Effect of Physical Activity on Risk of Breast Cancer in BRCA1 or BRCA2 Carriers


See Figure 1F. King MC, et al. Breast and ovarian cancer risks due to inherited mutations in BRCA1 and BRCA2.





12

SINGLE AND SUSCEPTIBILITY GENES IN CANCER CAUSE

Single Susceptibility GeneDefinition Necessary & sufficient Alters risk but is neither

for disease necessary nor sufficientfor disease causation

Example BRCA (breast/ovary) CYP1A1 (lung)APC (polyposis coli) CYP2D6 (lung)RB (retinoblastoma) GST-M1 (lung, bladder)

Gene prevelence Low Often highGene type Mutation Polymorphism or mutationStudy setting Family Gen. population/epi. studiesStrength of association Very high Low to moderateAbsolute risk High LowPopulation attributable risk Low High

Gene-environment interaction 2° and variable 1° and implicit

Role of environmentalexposure 2° and variable Crucial

13

Progression of Pre-Cancer to Cancer in Humans: A Multiyear Process

BreastBreast AtypicalHyperplasia

AtypicalHyperplasia DCISDCIS CancerCancer14-18 yrs14-18 yrs 6-10 yrs6-10 yrs

ColonColon AdenomaAdenoma5-20 yrs5-20 yrs

CervixCervix CIN ICIN I CIN III/CIS

CIN III/CIS9-13 yrs9-13 yrs 10-20 yrs10-20 yrs

ProstateProstate PINPIN LatentCarc.

LatentCarc.> 10 yrs> 10 yrs Clin.

Carc.Clin.Carc.3-15 yrs3-15 yrs20 yrs20 yrs

5-15 yrs5-15 yrs

14

Epidemiological Evidence

For a role of environmental-life factorsas causes of cancer– Epidemiology provides important

inferences and helps build hypotheses about the role of environmental factors in human carcinogenesis

15

Role of Environmental Agents in Human Cancer

Although overall cancer incidence is reasonably constant between countries, incidences of specific tumor types can vary up to several hundred-foldThere are large differences in tumor incidences within populations of a single country

Continued

16

Role of Environmental Agents in Human Cancer

Migrant populations assume the cancer incidence of their new environment within one to two generationsCancer rates within a population can change rapidly

17

TypeHigh

IncidenceLow

IncidenceRatio

(35-64 yrs)Breast USA Uganda 5Colon USA Nigeria 10Cervix Columbia Israeli Jews 15Rectum Denmark Nigeria 20Stomach Japan Uganda 25

Geographic Variation in the Incidence of Some Common Cancers

18

TypeHigh

IncidenceLow

IncidenceRatio

(35-64 yrs)Prostate US Blacks Norway 30Liver Mozambique Norway 70Skin Australia India >200Penis Uganda Israeli Jews 300

Geographic Variation in the Incidence of Some Common Cancers

19

Cancer Around the World Age Adjusted Mortality per 100,000

Population 46 Countries (1974–1975)

Stomach

0

10

20

30

40

50

60

Japan (1) USA (44)

Male Female

Breast

0

10

20

30

40

50

60

Japan(43)

USA (13) England(1)

20

Mortality from Stomach Cancer (Japan and California)

0

10

20

30

40

50

60

Age

Sta

ndar

dize

d M

orta

lity/

100,

000/

year

In Japan Immigrantsto CA

Born in CA

CaucasiansIn CA

M

F

Japanese

21

0

10

20

30

40

50

60

Age

Stan

dard

ized

M

orta

lity/

100,

000/

year


Bornin CA

Caucasiansin CA

Japanese

M F

Mortality From Colon Cancer (Japan and California)

22

0

10

20

30

40

50

60

Age

Sta

ndar

dize

d M

orta

lity/

100,

000/

yr


Born in CA

Caucasiansin CA

Japanese

M F

Mortality From Rectal Cancer (Japan and California)

23

Lung Cancer MortalityMale

1950 - 1969

1970 - 1994

Public Domain

24

Lung Cancer MortalityFemale

1950 - 1969

1970 - 1994

Public Domain

25

1970 - 1994

1950 - 1969

Colon Cancer Mortality Male

Public Domain

26Public Domain

27

Age-Adjusted Cancer Death Rates/100,000, US Males by Site, 1930–94

*

28

Per Capita Consumption of Different Forms of Tobaccoin the United States: 1880 -

1995

29

Age-Adjusted Cancer Death Rates/100,000, US Females by Site, 1930–94*

30

State Name Death Count Population Age Adjusted

Rate

District of Columbia 31,365 12,114,011 272.0

Delaware 28,898 13,174,117 241.1

Louisiana 169,699 86,260,188 236.6

Maryland 187,723 93,374,200 236.1

Kentucky 161,990 74,851,849 230.7

Maine 55,404 23,893,173 230.2

New Jersey 351,681 154,248,561 230.2

Nevada 44,249 23,522,411 226.6

Rhode Island 47,715 19,625,760 225.8

New Hampshire 42,737 21,176,058 225.8

Cumulative Cancer Mortality In the Worst 10 States and DC (1979-1998)

31

Maryland Cancer Mortality 1997

COLON ANDRECTUM

11.7%

LEUKEMIAS3.3%

PANCREAS4.7%

OVARY2.2%

BLADDER2.0%

ESOPHAGUS2.5%

STOMACH2.6%

PROSTATE6.4%

OTHER19.5%

LUNG ANDBRONCHUS

28.7%

BREAST8.5%

PHARYNX1.4%

MELANOMA1.2%

LIVER1.8%

NHL3.3%

Presenter

Presentation Notes

While the task force has been inundated with cancer statistics, I wanted to show the impact of various cancers on the mortality rates in Maryland. Emphasize common cancers

32

Cancer Mortality Rates in Maryland by County, 1983–1987

s

So

152 184 161

191

168

185

185 184

163174

194

205

206

192

176

180214

201198

190203

176

195236

Rates are age-adjusted to US 1970 population; rates per 100,000 population

Data source: Maryland Center for Health Studies

Significantly higher than US Rate (171)

33

Breast Cancer Incidence, 1996-1997

88.9-91.2

91.2-107.7

107.7-116.1

116.1-132.7

132.7-143.8

SEER Incidence Rate: 113.9/100,000; Average 96-97

34

Breast Cancer Mortality, 1993-1997

Regions with rates that are statistically significantly higher than the US average

35

Prostate Cancer Incidence, 1996-1997

89-102.7

102.7-116

116-147.5

147.5-169.4

169.4-200

SEER Incidence Rate: 137.4; Average 96-97

36

Prostate Cancer Mortality, 1993-1997

Regions with rates that are statistically significantly higher than the US average

37

The Causes of Cancer Quantitative Estimates

of Avoidable Risks of Cancer in the United States

By comparison of cancer incidence in the U.S. and the lowest incidence areas of the world, Doll and Peto concluded that:– 80% of male cancers and 77% of

female cancers are potentially avoidable

38

Proportion of Cancer Deaths Attributed to Environmental Influences

38

Diet 35%

Tobacco 30%

Infection 10%

Reproductive and sexual behavior 7%

Occupation 4%

Geophysical factors 3%

Alcohol 3%

Pollution 2%

Medicines & medicinal procedures 1%

Industrial products <1%

Food additives <1%

Data Source: Doll and Peto

39

Historical Perspective

1713: Ramazzini– Noted that nuns exhibited a higher

frequency of breast cancer than other women; attributed it to celibate life

1761: Hill– Associated the use of tobacco snuff with

cancer of the nasal passages

Continued

40


1775: Pott– Noted the occurrence of soot-related

cancer in chimney sweeps1894: Unna– Associated sunlight exposure with skin

cancer

Continued

41


1895: Rehn– Associated occupational exposure to

aromatic amine dyes with bladder cancer

1915: Ichikawa– First experimental production of tumors

in animals (application of coal tar to ears of rabbit)

Continued

Section B

Mechanisms of Carcinogenesis

43

The Causes of Cancer

BreathingEatingDrinkingRadiationSexDoctorsParents

44

Carcinogenic Agents

Physical agents– X-rays: breast, leukemias– Ultraviolet light: skin: non-melanoma

and melanoma– Asbestos: lung

Continued

45Continued

Carcinogenic Agents

Biological agents– Viruses

• RNA tumor viruses (ex.: Human T-cell leukemia virus—HIV/HTLV)

• DNA tumor viruses (ex.: Hepatitis B and C: liver cancer; papilloma viruses: cervical cancer; Epstein-Barr virus: Burkitt’s lymphoma)

46Continued

Carcinogenic Agents

Biological agents– Bacteria

• Helicobacter pylori (Ex.: Stomach cancer)

47

Carcinogenic Agents

Chemicals– Inorganic: Arsenic, cadmium,

chromium, nickel, etc.– Organic: Polycyclic aromatic

hydrocarbons, heterocyclic amines, aflatoxin, nitrosamines, etc.

– Hormones: DES, ethinyl estradiol, estradiol, tamoxifen, etc.

48

Selected Human CarcinogensOccupational Medicinal Environmental

Aflatoxins ×4-Aminobiphenyl ×Arsenic compounds × × ×Asbestos × ×Benzene × ×Benzidine ×Bis-2-chloroethylsulfide (mustard gas) ×Bis-chloromethyl methyl ether ×Chromium compounds ×Cyclophosphamide ×Diethylstilbestrol ×Melphalan ×b-Napthylamine ×N,N-bis-2-chlorotheyl 2-naphthyl amine ×Vinyl chloride ×

49

Naturally Occurring Carcinogens

Microorganisms– Alfatoxins– Sterigmatocytin– Ochratoxin A– T-2 toxin– Luteoskyrin– Islanditoxin– Griseofulving– Actinomycins– Daunomycin– Azaserine– Streptozotocin

Plants– Pyrrolizidine– Mushroom toxins

(hydrazines)– Safrole– Bracken fern– Betel nut– Cycasin– Tannins– Goitrogen (thiourea)– Tobacco, snuff– Coffee (?)

Section C

Multistage Nature of Carcinogenesis I

51

Multistage Carcinogenesis

51

52

Mechanisms of Chemical Carcinogenesis

Activation of carcinogens by biotransformation– Molecular targets: DNA

• Types of DNA damage• DNA repair processes• Gene targets: cellular and proto-

oncogenes, and tumor suppressor genes

Multistage carcinogenesis

53

Enzymatic Activation/Inactivation of BP

54

Reactive Groups Added During Bioactivation

55

Sites for Carcinogen-DNA Adducts

O

H2 N N

HNN

N

DNA

2

1

4

3

6

5

8

7

9

III

I

II

I. Alkylating Agents, MycotoxinsII. Aromatic AminesIII. Polycyclic Aromatic Hydrocarbons, Alkenylbenzenes

56

Examples of Carcinogen-DNA Adducts

57

Examples of DNA Damage

Break– single strand– double Strand

Crosslink– DNA-protein– intra-protein– intra-strand

Specific bindingBase alterationBase detachmentIntercolation

58

DNA Repair Processes

Direct damage reversal– Ex.: AlkyltransferasesBase excision repair– Ex.: Glycosylases and

apurinic/apyrimidinic– Endonucleases

Source Pitot & Dragan. In Casarett & Doull, 1996 Continued

59

DNA Repair Processes

Nucleotide excision repair– Ex.: repair of pyrimidine dimers– Repair of “bulky” adductsRecombination: Postreplication repairMismatch repair– Ex.: Repair of deaminated 5-

methylcytosine

Source Pitot & Dragan. In Casarett & Doull, 1996

6060

61

62

Genotoxicity

Mutagenesis– Occurrence of “point” or “gene-locus”

mutation (base pairs), substitution, and small deletions or additions

Clastogenesis– Occurrence of chromosomal breaks

resulting in gain, loss, or rearrangement of pieces of chromosome

Continued

63

Genotoxicity

Aneuplodization– Gain or loss of one or more

chromosomes

64

Genetic Damage and Cancer

Gain of function: (proto-oncogenes and oncogenes)– Point mutation– Translocation– AmplificationLoss of function: (tumor suppressor genes)– Deletion– Translocation– Mutation

65

Ways By Which Different Oncogene Products May Disrupt Normal Regulation of Cell Growth

Growth Factors

Receptors

2nd Messengers

DNA Synthesis

Oncogenes

66

A. Oncogenes

Functions of Gene Product Genes Cell Localization

Growth Factors sis, fgf ExtracellularReceptor/protein tyrosine kinases met, neu Extra cell/cell membraneProtein tyrosine kinases src, ret Cell membrane/cytoplasmicMembrane-associated G proteins ras, gip-2 Cell membrane/cytoplasmicCytoplasmic protein serine kinases raf, pim-1 CytoplasmicNuclear transcription factors myc, fos, jun NuclearUnknown, undetermined bcl-2, crk Mitochondrial, cytoplasmic

Functions of Representative Oncogenes and Tumor

Suppressor Genes

Continued

67

B. Tumor Suppressor genes

Functions of Gene Product Genes Cell Localization

GTPase activation NF1 Cell membrane/cytoplasmicCell cycle-regulated nucleartranscriptional repressor RB-1 Nuclear

Cell cycle-regulated nucleartranscription factor p53 Nuclear

Zinc finger transcription factor WT1 NuclearMismatch DNA repair hMLH1 NuclearZinc finger transcription factor (?) BRCA1 Nuclear

Functions of Representative Oncogenes and Tumor

Suppressor Genes

68

Role of Estrogen in Mammary Carcinogenesis

Section D

Multistage Nature of Carcinogenesis II

70


70

71

Mechanisms of Chemical Carcinogenesis

Activation of carcinogens by biotransformationMultistage carcinogenesis– Initiation: somatic cell mutation– Promotion: clonal expansion of initiated

cells– Progression: evolution of neoplastic

phenotype (angiogenesis, invasiveness, metastasis)

72

Initiation and Promotion Operational Definitions

Many Tumors

No Tumors

Initiator

Promotor

73

Mechanisms for Selection and Clonal Expansion by

Tumor Promoters

74

Chemical Structures of Some Tumor Promoters

75

Promoters Can Determine the Target Site for Tumors

Initiator Tumor Promoter Target Organ

2-AAF or BBN phenobarbitalsaccharin

liverbladder

N-methylnitroso- urea

phenobarbitalsaccharin

liver & thyroidbladder

76

Neoplasms Associated with Prolonged Contact With Promoting Agents in the Environment

Agent Resulting NeoplasmDietary fat Mammary adenocarcinomaHigh caloric intake Increased cancer incidence in generalCigarette smoke Bronchogenic carcinoma (esophageal and

bladder cancer)Asbestos Bronchogenic carcinoma & mesotheliomaHalogenated hydrocarbons Liver

(dioxin, PCBs)Phorbol esters Esophageal cancer (?)Saccharin Bladder cancer*Phenobarbital Liver*Prolactin Mammary adenocarcinomaSynthetic estrogens Liver adenomasAlcoholic beverages Liver and esophageal cancer

* Promotion demonstrated in experimental animals, but not in humans

77

Lung Cancer

Since 1987, more women have died of lung cancer than breast cancerRisk factors: SMOKING, industrial exposures, radiation exposureEarly detection: DifficultPrevention: STOP SMOKING!

78

Smoking and Lung Cancer

79

Relative Risk for Developing Lung Cancer Compared with the Risk of Dying from Lung Cancer for a

Nonsmoker not Exposed to Asbestos

87

53

11

5

0 20 40 60 80 100

Asbestos workers smoking 1pack/day

Smoking asbestos workers

Smokers not exposed to asbestos

Nonsmoking asbestos worker

Times Higher

Source: Report of the Surgeon General, 1985

80Duration of Cessation (years)

MO

RTA

LITY

RA

TE R

ATI

O(fo

rmer

sm

oker

/nev

er s

mok

er)

0

5

10

15

20

25

30

5 10 15 20 25

1-9

10-19

2021-39

40+ # cigarettes per day

EFFECT OF SMOKING CESSATION ON MORTALITYFROM LUNG CANCER

81


81

82

Tumor Progression

Conversion of benign tumor to malignancyDNA-damaging agents are good progressors– Alkylating agents (mutagens)– H2 02 and organic peroxides– Radiation

83

Malignant Conversion by Benzoyl Peroxide

84Continued

Morphological and Biological Characteristics of Initiation, Promotion, and Progression

INITIATION PROMOTION PROGRESSIONIrreversible Operationally reversible

both at the level of gene expression and at the cellular level

Irreversible

Initiated “stem cell” not morphologically identifiable

Promoted cell population dependent on continued administration of promoting agent

Morphologically discernible alteration in cellular structure resulting from karyotypic instability

Efficiency sensitive to xenobiotic and other chemical factors

Efficiency sensitive to aging and dietary and hormonal factors

Growth of altered cells sensitive to environ mental factors during early phase of this stage

Spontaneous (endogenous) occurrence of initiated cells

Endogenous promoting agents may effect “spontaneous” promotion

85

Morphological and Biological Characteristics of Initiation, Promotion, and Progression

INITIATION PROMOTION PROGRESSION

Requirement for cell division for “fixation”

Dose-response not exhibiting a readily measurable threshold

Dose response exhibits measurable threshold and maximal effect

Benign or malignant neoplasms observed in this stage

Relative potency of initiators dependent on quantitation of preneoplastic lesions after defined period of promotion

Relative potency of promoters measured by their effectiveness in causing an expansion of the initiated cell population

“Progressor” agents advance promoted cells into this stage

86

Some Cellular and Molecular Mechanisms in Multistage Carcinogenesis


Simple mutations (transitions transversions, small deletions, etc.) involving the cellular genome

Reversible enhancement or repression of gene expression mediated via receptors specific for the individual promoting agent

Complex genetic alterations (chromosomal translocations, deletions, gene amplification, recombination, etc.) resulting from evolving karyotypic instability

In some species and tissues point mutations in protooncogenes and/or oncogenes

Inhibition of apoptosis by promoting agent; selective cytotoxicity to non-initiated cells

Irreversible changes in gene expression, including fetal gene expression, altered major histocompatibility complex (MHC) gene expression, and ectopic hormone production

Continued

87

Some Cellular and Molecular Mechanisms in Multistage Carcinogenesis


Mutations in genes of signal transduction pathways that may result in an altered phenotype

No direct structural alteration in DNA from action or metabolism of promoting agent

Selection of neoplastic cells for optimal growth genotype phenotype in response to the cellular environment and including the evolution of karyotypic instability

88

Classification of Chemical Carcinogens In Relation to Their Action on One or More

Stages of Carcinogenesis

Initiating agent (incomplete carcinogen): A chemical capable only of initiating cellsPromoting agent: A chemical capable of causing the expansion of initiated cell clones

Continued

89

Progressor agent: A chemical capable of converting an initiated cell or a cell in the stage of promotion to a potentially malignant cell

Continued



90

Complete carcinogen: A chemical possessing the ability to induce cancer from normal cells, usually with properties of initiating, promoting, and progressor agents



91

Prevention of Carcinogenesis

Affordable cancer = Prevention + Protection

92

Prevention

Elimination of carcinogenic influences(e.g., industrial carcinogens, cigarette smoking, radiation– Knowledge of identity of carcinogen is

essential

93

Protection

Measures designed to interrupt the carcinogenic process without specific efforts to identify or eliminate carcinogenic influences (e.g., dietary measures)– Knowledge of identity of carcinogen is

desirable

94

Key Points

Environmental factors may contribute to 3/4 of all human cancersChemicals, viruses, and radiation can be carcinogenicDNA is a major target for carcinogens– With damage leading to gain or loss of

function of key genes

Continued

95

Key Points

Carcinogenesis is a long, multistage process yielding a heterogeneous family of diseases: CancerMost cancer is, in theory, preventable

Education

Lecture3 kensler