Tobacco use is responsible for 90% of all lung cancers. Yet, the risk of lung cancer for individual smokers and members of different ethnic/racial groups varies significantly. Differences in carcinogen exposure, activation and detoxification contribute to this variable risk. In this proposal we will characterize the metabolic pathways of the tobacco-specific lung carcinogen, NNK, in Japanese American (JA), Native Hawaiians (NH) and White smokers. The rationale for focusing on NNK metabolism in these three groups is: 1) CYP2A6 activity and genotype is associated with lung cancer, 2) the prevalence of CYP2A6 copy number variants and other loss of function alleles is relatively high in JA and NH. 3) CYP2A6 is a catalyst of NNK bioactivation and 4) the ?- hydroxymethyl NNK glucuronide (?-OHNNK Gluc) identified in smokers (prior grant period) is a potential biomarker of NNK activation. The association of CYP2A6 activity and genotype with the risk of lung cancer is in part due to the influence of CYP2A6-mediated nicotine metabolism on tobacco dose. CYP2A6 also catalyzes the metabolism NNK. Therefore, individuals deficient in P450 2A6 activity may not only smoke less but may also be protected from NNK carcinogenesis. In this project we will test the hypothesis that carcinogen activation varies by ethnicity and that this variation is in part due to variable P450 2A6 activity. NNK is activated by ?-hydroxylation, in addition it is reduced to NNAL, which is also a carcinogen: activated by ?-hydroxylation. The final products of NNK and NNAL ?-hydroxylation are minor metabolites of nicotine. Therefore, it is not possible to quantify the NNK bioactivation in smokers by metabolite analysis. The administration of D4-NNK to smokers eliminates the complication with nicotine metabolites; however, it is still not possible to distinguish the metabolites of NNAL and NNK ?-hydroxylation. The ?-OH-NNK Gluc is a unique product of NNK ?-hydroxylation and its level in smokers should be dependent on CYP2A6 activity. The goals of the below aims are: to characterize the ?-OH-NNK Gluc as a measure of NNK-activation, to develop an NNK metabolite profiling method and to determine the contribution of CYP2A6 to NNK bioactivation.
Aim 1 will determine the effect of CYP2A6 genotype on the level of NNK ??hydroxylation in JA smokers administered D4 NNK, Aim 2 will quantify ?-OH NNK Gluc in JA, NH and White smokers, Aim 3 will develop a high resolution mass spectrometry based metabolic profiling method to measure NNK bioactivation in smokers. The method will be validated in urine from rats administered NNK and D4-NNK and smokers of D4-NNK spiked cigarettes.
Aim 4 will characterize the NNK metabolic profile in smokers receiving D4-NNK (Aim 1) and in JA, NH and White smokers.
Smoking is the cause of 90% of all lung cancer, but only 11-24% of smokers develop the disease. The risk of lung cancer varies by individual and by ethnic/racial group. In this project we will explore how individual differences in the metabolism of a tobacco-specific lung carcinogen may contribute to the variable risk of lung cancer between ethnic/racial groups
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