Direct evidence for the formation of deoxyribonucleotide adducts from carcinogenic N-nitroso-N-methylaniline revealed by the 32P-postlabeling technique

N-Nitroso-N-methylaniline (NMA) is an esophageal carcinogen in the rat. NMA forms a benzenediazonium ion (BDI) during microsomal cytochrome P-450 2B1 (CYP2B1) catalyzed metabolism. Using the nuclease P1-enhanced version of the 32P-postlabeling assay we investigated the formation of adducts by NMA with deoxyadenosine 3′-monophosphate (dAp) and deoxyguanosine 3′-monophosphate (dGp). 32P-postlabeling analysis of dAp and dGp, which were modified by NMA activated with microsomes of rats pretreated with phenobarbital (PB), and directly labeled resulted in each case in the appearance of one single adduct spot. Quantitative analysis of adducts revealed that the extent of dGp modification by activated NMA was more than 23 times greater than the extent of modification of dAp. The results suggest strongly that BDI, derived from NMA by CYP2B1 present in PB microsomes, participates in the formation of dAp and dGp adducts.