N'-Nitrosonornicotine (1, NNN) has been evaluated extensively as a strong carcinogen in multiple animal models and is classified, together with the related compound 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), as a Group 1 human carcinogen by IARC. Upon metabolic activation by cytochrome P450s, NNN is oxidized to reactive electrophiles, such as a diazonium ion from 2'-hydroxylation or a diazonium ion and an oxonium ion (2) from 5'-hydroxylation, which alkylate DNA to form phosphate adducts and base adducts. A previous study from our laboratory quantified the formation of an NNN-specific base adduct, 2-(2-(3-pyridyl)-N-pyrrolidinyl)-2'-deoxyinosine (py-py-dI), in rat tissues after NaBH3CN reduction, which proceeded through the diazonium ion pathway of 5'-hydroxylation. However, this adduct was not detected in the human lung tissue. To further investigate new NNN-specific DNA adducts that have potential as biomarkers, a comprehensive study was performed using a highly sensitive and selective LC-NSI-HRMS/MS method. After confirming the existence of previously observed DNA base adducts formed by NNN in vitro and in vivo, a new adduct N6-((5-(3-pyridyl)tetrahydrofuran-2-yl)-2'-deoxyadenosine (3, Py-THF-dAdo) was detected for the first time in vivo at relatively high level when compared with py-py-dI. Its structure was further confirmed by comparison with a synthetic standard. To the best of our knowledge, this is the first DNA adduct identified in rat liver tissues that forms directly through the oxonium ion pathway of NNN metabolism. The relative stability and high abundance of Py-THF-dAdo suggest it could be a promising activation biomarker of NNN. Mass spectrometric quantitation of Py-THF-dAdo by stable isotope dilution in the rat tissues is currently in progress.

Identification of a new N'-nitrosonornicotine (NNN)-specific DNA adduct N6-((5-(3-pyridyl)tetrahydrofuran-2-yl)-2'-deoxyadenosine in rat liver

2019 Fall National Meeting

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