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Aflatoxin,Tobacco, and the p53 Tumor Suppressor Gene: Cancer's Missing Link?

Kerry Scott Lane M.D. Copyright September 21, 2000

North Carolina State University

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Aflatoxin And Tobacco What is Aflatoxin Natural Production of Aflatoxin Evidence for Contamination of Tobacco p53 Mutation as Biomarker p53 Tumor Suppressor and All Cancers Aflatoxin and Immunosuppressive States Future Regulatory Framework (FDA-WHO-TART) Future Technology Solutions

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What is Aflatoxin ?Aflatoxin is a mycotoxin produced by

Aspergillus Flavus, Aspergilli and Penicillium fungi.

It is an complex aromatic heterocycle.It decomposes at 269 C.(Heat stable). AFB

likely survives combustion, especially in ETS.It has profound genetic mutational capabilities

due to its sterospecificity.

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Natural Production of Aflatoxin Aspergillus is found worldwide, described as a

storage fungus. Aflatoxin production is favored by heat and

humidity. Likely contamination of tobacco is episodic,

random, and even microscopic. Regulated by FDA on corn, grain, peanuts, since

late 1960s. Also regulated by EU countries. Max. permissible level for corn is 20ppb, milk- 0.5

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Evidence for Contamination of Tobacco Welty and Lucas, NC State 1968 Pattee, NC State 1969 Egypt 1994-El Magrahby India 2000-Guhtka Industry Internal Documents-WARF-1967 Combustion Studies- Kentucky 1970s Combustion Studies-Cincinnati-Lane 1978 Human experiments and p53 biomarkers and

adducts.

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p53 Mutations as Biomarker p53 is the “Guardian of the genome” which

instructs genetically damaged cells to repair or die. As a tumor suppressor gene it is a last ditch effort

to prevent cancer. p 53 is the most common mutation in all cancers. Most typically laboratory cancer experiments use

aflatoxin to mutate p53. Over 10,000 articles on Medline about aflatoxin

but none had made the aflatoxin-tobacco connection.

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p53 and most Cancers p53 mutations by aflatoxin at codon 249 AGG to AGT

thought to cause liver cancer. (G-T transversions). Guanines preferentially bound by aflatoxin covalently,

especially poly GG, GGG and GCs. Lung cancer “hotspot” is codon 249, AGG to ATG WHO-IARC database analysis show substantial mutations

in human cancers consistent with aflatoxin etiology. Dennisenko has shown aflatoxin mutates p53 often

consistent with WHO data. Breast cancer shows similar mutational profile. Most cancers show p53 mutations.

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Lung Cancer Mutational Spectra

0 10 20 30 40 50 60 70

Other

CCC, G-->C, Arg to Pro

CTC, G-->T, Arg to Leu

TGG, C-->T, Arg to Trp

CCG, G-->C, Arg to Pro

Other

AGC, G-->A, Gly to Ser

GTC, G-->T, Gly to Val

Other

AGT, G-->T, Arg to Ser

Other

CAT, G-->A, Arg to His

CCT, G-->C, Arg to Pro

Percentage of substitutions

Codon 249 (AGG)AFB1

Codon 273 (CGT)AFB1, BPDE

Codon 245 (GGC)AFB1

Codon 248 (CGG)AFB1, BPDE

Codon 158 (CGC)Probable AFB1

CpG sites

CpG sites

CpG site

nonCpG site

CpG site

273 n = 67249 n = 59245 n = 56248 n = 51158 n = 41

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p53, Lung Cancer and ETS

0 5 10 15 20 25 30 35

Other

T-->G

A-->C

nonCpG: G-->A

G-->T

P e rc e n ta g e o f mu ta tio n s

Nonsmoking (n = 136)

Smoking (n = 341)

Nonsmoking (n = 136) 3.68 5.15 8.08 2.94 5.15 0.74 2.94 10.29 6.62 9.56 9.56 4.41 24.26 6.62

Smoking (n = 341) 11.73 1.47 6.16 1.17 1.76 2.05 2.05 9.68 8.21 9.09 4.4 5.57 30.5 6.16

Other nonCpG: T-->C nonCpG: A-->G T-->G T-->A A-->T A-->C CpG: G-->A, C-->T nonCpG: C-->T nonCpG: G-->A C-->G C-->A G-->T G-->C

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Breast Cancer and AflatoxinPatterns of p53 Substitutions in Breast Cancer

0 5 10 15 20 25

Other

Deletions

nonCpG: T-->C

nonCpG: A-->G

CpG: A-->G

T-->G

T-->A

A-->T

A-->C

CpG: G-->A, C-->T

nonCpG: C-->T

nonCpG: G-->A

C-->G

C-->A

G-->T

G-->C

Percentage of mutations

A:T

bas

e p

airs

G:C

bas

e p

airs

n = 1,448

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Aflatoxin and Immunosuppression

AFB is a carcinogen, teratogen, mutagen, inhibitor of protein synthesis, and is immunosuppressive.

AFB has been shown to increase HIV levels 500% Smokers have increased HIV levels. Increased HIV levels correlate with increased

infectivity and poorer prognosis. Therefore, AFB contaminated tobacco is likely

contributing to the AIDS pandemic.

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Future Regulatory Framework (FDA-WHO-TART)

WHO FCTC seeks to regulate toxin levels on tobacco products worldwide by 2003.

TART-Tobacco-Aflatoxin Reduction Talks Aflatoxin and mycotoxin contamination of tobacco

are prime candidates for a Harm Reduction Strategy.

FDA will likely adopt similar guidelines soon. Industry Compliance may provide limited legal

immunity.

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Future Technology Solutions Multiple solutions available to limit aflatoxin and

mycotoxin production on tobacco products. Monitoring of AFB and mycotoxin contamination from

multiple curing practices will provide valuable data. Prevention, remediation and terminal testing will result in

a less harmful product with less liabilty. Aflatoxin bioinformatics will yield cancer therapies,

vaccines, diagnostic tests, and possibly cures for many human diseases.

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Aflatoxin and Tobacco

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