The Impact of NAT2 Acetylator Genotype on Mutagenesis and DNA Adducts from 2-Amino-9H-pyrido[2,3-b]indole

2-Amino-9H-pyrido[2,3-b]indole (A alpha C) is a carcinogenic heterocyclic aromatic amine (HAA) that is produced in high quantities in tobacco smoke and that also forms in charred meats. The bioactivation of A alpha C occurs by cytochrome P450-mediated (P450 1A2) N-oxidation of the exocyclic amine group, to form 2-hydroxyamino-9H-pyrido[2,3-b]indole (HONH-A alpha C). The HONH-A alpha C metabolite can then undergo further activation by phase II enzymes to form the penultimate ester species, which bind to DNA. Some epidemiological studies suggest a role for NAT2 genetic polymorphisms in human susceptibilities to various cancers from tobacco smoke and from consumption of well-done meats, where the exposures to A alpha C can be substantial. In this investigation, we have measured the genotoxicity of A alpha C in nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human P450 1A2 and either the NAT2*4 (rapid, wild-type acetylator) or the NAT2*5B (the most common slow acetylator) allele, to determine the role of NAT2 phenotype in the biological effects of A alpha C. Mutations at the hypoxanthine phosphoribosyl transferase (hprt) locus were induced in a dose-dependent manner by A alpha C and were found to be highest in cells transfected with P450 1A2 and NA72*4, followed by cells transfected with P450 1A2 and NAT2*5B. The level of formation of the deoxyguanosine (dG) adduct N-(deoxyguanosin-8-yl)-2-amino-9H-pyrido[2,3-b]indole (dG-C8-A alpha C) paralleled the mutagenic potency in these cell lines. However, A alpha C did not form DNA adducts or induce mutations in untransfected CHO cells or in cells only expressing P450 1A2. These findings clearly demonstrate that NAT2 genetic polymorphism plays a major role in the genotoxic potency of A alpha C.