4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent lung
carcinogen present in tobacco products, and exposure to it is likely one of the factors contributing to the development of
lung cancer in cigarette smokers. To exert its carcinogenic effects, NNK must be metabolically activated into highly reactive species generating a wide spectrum of DNA damage. We have identified a new class of
DNA adducts,
DNA-
RNA cross-links found for the first time in NNK-treated mice lung
DNA using our improved high-resolution accurate mass segmented full scan data-dependent neutral loss MS3 screening strategy. The levels of these
DNA-
RNA cross-links were found to be significantly higher in NNK-treated mice compared to the corresponding controls, which is consistent with higher levels of
formaldehyde due to NNK metabolism as compared to endogenous levels. We hypothesize that this
DNA-
RNA cross-linking occurs through reaction with NNK-generated
formaldehyde and speculate that this phenomenon has broad implications for NNK-induced
carcinogenesis. The structures of these cross-links were characterized using high-resolution LC-MS2 and LC-MS3 accurate mass spectral analysis and comparison to a newly synthesized standard. Taken together, our data demonstrate a previously unknown link between
DNA-
RNA cross-link adducts and NNK and provide a unique opportunity to further investigate how these novel NNK-derived
DNA-
RNA cross-links contribute to
carcinogenesis in the future.