Formation of formaldehyde adducts in the reactions of DNA and deoxyribonucleosides with α-acetates of 4-(methylnitrosamino)-1-(3- pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and N-nitrosodimethylamine (NDMA)

The cytochrome P450-mediated α-hydroxylation of the carcinogenic nitrosamines N-nitrosodimethylamine (NDMA, 1), 4-(methylnitrosamino)-1-(3- pyridyl)-1-butanone (NNK, 6a), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, 6b) produces diazonium ions and formaldehyde. The DNA-binding properties of the diazonium ions have been thoroughly characterized, and there is no doubt that they are critical in cancer induction by these nitrosamines. However, the possibility of additional DNA damage via released formaldehyde has not been reported. In this study, we used acetoxymethylmethylnitrosamine (5), 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (10a), and 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanol (10b) as stable precursors to the α-hydroxymethylnitrosamines that would be formed in the metabolism of NDMA, NNK, and NNAL. These α-acetates were incubated with calf thymus DNA in the presence of esterase at pH 7.0 and 37°C. The DNA was isolated and enzymatically hydrolyzed to deoxyribonucleosides, and the hydrolysates were analyzed by liquid chromatography-electrospray ionization-mass spectrometry-selected ion monitoring for formaldehyde DNA adducts. Convincing evidence for the formation of the formaldehyde adducts N⁶- hydroxymethyl-dAdo (11), N⁴-hydroxymethyl-dCyd (12), N ²-hydroxymethyl-dGuo (13), and the cross-links di-(N ⁶-deoxyadenosyl)-methane (14), (N⁶-deoxyadenosyl-N ²-deoxyguanosyl)methane (15), and di-(N²-deoxyguanosyl) methane (16) was obtained in these reactions. These results demonstrate that NDMA, NNK, and NNAL have the potential to be bident carcinogens, damaging DNA through the metabolic formation of both diazonium ions and formaldehyde.