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How does cigarette smoke induce cancer?

Institution: Beckman Research Institute of the City of Hope
Investigator(s): Gerd Pfeifer, Ph.D.
Award Cycle: 1997 (Cycle 6) Grant #: 6RT-0361 Award: $811,518
Subject Area: Cancer
Award Type: Research Project Awards
Abstracts

Initial Award Abstract
Lung cancers are strongly associated with cigarette smoking and cigarette smoke contains a number of proven and suspected carcinogens (cancer-causing agents). In order to understand how cigarette smoke components cause lung cancer and other smoking-related cancers, it is necessary to understand the sequence of events that leads from smoke inhalation to formation of a tumor many years or decades later. One of the initial crucial events is most likely damage of the genetic material (DNA) by a cigarette smoke carcinogen. This damage can, under certain circumstances, be repaired by cellular DNA repair mechanisms. However, if not repaired, cells will attempt to duplicate their DNA during normal cell division, but are impeded by the damage and will carry out an error-prone duplication process leading to gene mutations (changes in the gene). Such gene mutations are then found many years later in the DNA of lung tumors. Gene mutations are particularly harmful if they occur in genes that control cell division rates or genetic stability. According to current thinking, a number of genes need to be mutated or functionally disabled before a normal cell loses all normal growth control mechanisms and is brought onto a path of uncontrolled cell division eventually leading to a tumor. Gene mutations have been found in genes such as p53, ras, and pl6 at a relatively high frequency in human lung cancer.

One of the cigarette smoke carcinogens that is implicated in the development of lung cancers is benzo[a]pyrene. In our previous work, we have mapped the distribution of benzo[a]pyrene lesions along the p53 gene in normal human lung cells exposed to the carcinogen. Strong and selective damage formation occurred at the same positions that are the major mutational hotspots in human lung cancers. These results provided a direct link between a defined cigarette smoke carcinogen and human lung cancer (the smoking gun hypothesis).

Since benzo[a]pyrene is not the only carcinogen found in cigarette smoke and p53 is not the only gene that gets damaged by these compounds, much additional research is needed to understand how cigarette smoking causes cancer. The theme of our proposed work is to investigate what specific kind of DNA damage is caused by a number of cigarette smoke carcinogens, which genes and which positions within genes are targeted, with what efficiency the damage is repaired, and how this damage and repair relates to specific gene mutations found in tobacco-associated cancers. This study should increase our understanding of the mechanisms of cancer initiation by defined cigarette smoke carcinogens.

Final Report
Lung cancers are strongly associated with cigarette smoking. In order to understand how cigarette smoke causes lung cancer, it is necessary to- understand the molecular mechanisms of DNA damage caused by cigarette smoke components. If this damage is not repaired efficiently it can eventually cause gene mutations. The same mutations are then found years later in the DNA of lung tumor cells. Mutations are particularly harmful if they occur in genes that control cell division or genetic stability. Mutations occur frequently in genes such as p53, ras, and p16 in human lung cancers. The Specific Aims of this grant were to measure DNA adducts induced in these genes by the cigarette smoke carcinogens benzo[a]pyrene diol epoxide, chrysene diol epoxide, and 5-methylchrysene diol epoxide.

We have used six cigarette smoke components of the polycyclic aromatic hydrocarbon (PAH) class to induce DNA damage in the p53 gene in human lung epithelial cells. PAH diol epoxides of benzo[a]pyrene (BPDE), chrysene (CDE), 5-methylchrysene (5MCDE), 6-methylchrysene (6MCDE), benzo[c]phenanthrene (B[c]PDE), and benzo[g]chrysene (B[g]CDE) were investigated. In the p53 gene, 5MCDE, 6MCDE, B[g]CDE and B[c]PDE efficiently induced adducts within codons 156, 157, and 158 of exon 5 and codons 248 and 273 of exons 7 and 8, respectively. B[g]CDE and B[c]PDE induced damage at codons 157, 158, 248 and 273 more selectively than the three methyl-chrysene diol epoxides. The combined DNA damage distribution patterns of these PAH compounds matched well with the occurrences of mutational hotspots in the p53 gene from smokers, but not nonsmokers. In another study, partially supported by this grant, we have identified a new putative lung tumor suppressor gene from the chromosomal area 3p21.3.

The work should increase our understanding of the mechanisms of cancer causation by cigarette smoke. If the causes of tobacco-associated cancers are better understood at the molecular level, then legislation will be provided with better scientific arguments for further tobacco control efforts. Our findings have been employed in science-based tobacco use prevention efforts by the governments of Australia (see http://www q-uitnow.info.au/damage.html#anchgM53).
Publications

DNA damage and repair in human genes: relation to cancer mutations
Periodical: Toxicologist Index Medicus:
Authors: Denissenko MF, Tommasi S, Pfeifer GP ART
Yr: 1998 Vol: 42 Nbr: Abs: Pg: 297

Formation and repair of DNA lesions in the p53 gene: relation to cancer mutations?
Periodical: Environmental Molecular Mutagenesis Index Medicus:
Authors: Pfeifer GP, Denissenko MF ART
Yr: 1998 Vol: 31 Nbr: Abs: Pg: 197-205

An apolipoprotein E synthetic peptide targets to lipoproteins in plasma and mediates both cellular lipoprotein interactions in vitro and acute clearance of cholesterol-rich lipoproteins in vivo
Periodical: Journal of Clinical Investigation Index Medicus:
Authors: Nikoulin IR, Curtiss LK ART
Yr: 1998 Vol: 101 Nbr: Abs: Pg: 223-234

Biologic activity of an apoE synthetic peptide in apoE deficient mice
Periodical: Circulation Index Medicus:
Authors: Curtiss LK, Nikoulin I ART
Yr: 1997 Vol: 96 Nbr: 8 Abs: Pg: 1-347

PCR-based approaches to adduct analysis
Periodical: Toxicology Letters Index Medicus:
Authors: Pfeifer GP, Denissenko MF, Tang M-S ART
Yr: 1998 Vol: Nbr: Abs: Pg: 102-103,447-451

p53 mutational spectra and the role of methylated CpG sequences
Periodical: Mutation Research Index Medicus:
Authors: Pfeifer GP ART
Yr: 2000 Vol: 450 Nbr: Abs: Pg: 155-166

Targeting of lung cancer mutational hotspots by polyvcyclic aromatic hydrocarbons
Periodical: Journal of the National Cancer Institute Index Medicus:
Authors: Smith LE, Denissenko MF, Bennett WP, et al ART
Yr: 2000 Vol: 92 Nbr: Abs: Pg: 803-811

Epigenetic inactivation of a Ras effector homologue from the lung tumor suppressor locus 3p21.3
Periodical: Nature Genetics Index Medicus:
Authors: Dammann R, Li C, Yoon J-H, Chin PL, Bates S, Pfeifer GP ART
Yr: 2000 Vol: 25 Nbr: Abs: Pg: 315-319

Patterns of p53 G to T transversions in lung cancers reflect the primary mutagenic signature of DNA-damage by tobacco smoke
Periodical: Carcinogenesis Index Medicus:
Authors: Hainaut P, Pfeifer GP ART
Yr: 2001 Vol: 22 Nbr: Abs: Pg: 367-374