ED01.02 Tobacco Carcinogens and Lung Cancer Susceptibility

Abstract

While cigarette smoking is clearly the major cause of lung cancer, only 11% of female and 24% of male lifetime smokers will get lung cancer by age 85 or greater, and this relatively small percentage is not due to competing causes of death from smoking 1 The major goal of the research approach discussed in this presentation is to identify individuals who are highly susceptible to the carcinogenic effects of cigarette smoke. These individuals would be candidates for intensive lung cancer surveillance and screening, increasing the probability of detection of a tumor at an early stage. We are not proposing methods for early detection of tumors such as the identification of metabolites or proteins characteristic of lung tumors, but rather early identification of susceptible individuals. While there are already algorithms relating various parameters to lung cancer susceptibility , they are mostly retrospective in nature, with pack-years of cigarette smoking being a major prog-nostic factor. 2,3 Thus, these algorithms are typically applied to subjects who are older, when the process may be more advanced. Our ultimate goal is to develop a risk model that is prospective in nature. Overall, there would be a greater probability of success if one could identify high risk individuals early in the carcinogenic process. Even if this were effective in only 10% of tobacco users, the outcome could be prevention of more than 15,000 lung cancer deaths per year in the U.S. alone and massive financial savings. Among the more than 7,000 identified chemical compounds in cigarette smoke, there are 72 fully characterized carcinogens among which at least 20 are known to cause lung tumors in laboratory animals. 4,5 Important among the lung carcinogens are polycyclic aromatic hydrocarbons (PAH) such as benzo [a]pyrene, tobacco-specific nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and volatiles such as 1,3-butadiene. Other related volatile compounds that may contribute to the carcinogenic process include acrolein, crotonaldehyde, and benzene. Perhaps the most important compound in tobacco smoke is nicotine e while not a carcinogen, it is the addictive constituent of smoke that causes people to continue to inhale this incredibly unhealthy mixture. In pursuit of our goal of identifying smokers susceptible to lung cancer, we have focused on several tobacco smoke toxicant and carcinogen parent substances and metabo-lites in urine. 6 Thus, we and others have developed and applied analytically validated mass spectrometric methods for total nicotine equivalents (the sum of nicotine and six metabolites: nicotine glucuronide, co-tinine, cotinine glucuronide, 3 0-hydroxycotinine and its glucuronide, and nicotine-N-oxide); total 4-(methylni-trosamino)-1-(3-pyridyl)-1-butanol (NNAL), a metabo-lite of NNK; phenanthrene tetraol (PheT) and 3-hydroxyphenanthrene (3-PheOH), metabolites of a representative PAH; S-phenylmercapturic acid (SPMA), a metabolite of the carcinogen benzene; 3-hydrox-ypropylmercapturic acid (HPMA), a metabolite of acro-lein; and 3-hydroxy-1-methylpropylmercapturic acid (HMPMA), a metabolite of crotonaldehyde. We have collaborated with epidemiologists to evaluate the relationship of these urinary metabolites to cancer, as determined in prospective cohort studies. These studies collect and store bio-samples from large numbers of healthy subjects, then follow the subjects until sufficient numbers of cancer cases occur for statistical analysis. Samples from the cases and matched controls without cancer are retrieved from biorepositories and analyzed for specific biomarkers. The results of these studies have been reviewed. 7,8 In summary, statistically significant relationships of urinary total cotinine (cotinine plus its glucuronide, the major metabolite of nicotine), total NNAL, and PheT with lung cancer risk were observed among male smokers in Shanghai. Urinary total cotinine and total NNAL were related to lung cancer risk in a study of male and female smokers in Singapore, and total NNAL in serum was related to lung cancer risk in a study of male and female smokers in the U.S. 7,8 Levels of urinary SPMA, HPMA, and HMPMA were not independently related to lung cancer in the Shanghai study. These results indicate that total cotinine, total NNAL, and PheT are possible biomarkers of lung cancer risk. We are also collaborating with scientists from the Multiethnic