2‐amino‐1‐methyl‐6‐phenylimidazo [4,5‐b] pyridine‐induced DNA adducts and genotoxicity in chinese hamster ovary (CHO) cells expressing human CYP1A2 and rapid or slow acetylator N‐acetyltransferase 2

Heterocyclic amine carcinogens such as 2‐amino‐1‐methyl‐6‐phenylimidazo [4,5‐b] pyridine (PhIP) are present in diet and cigarette smoke. Bioactivation in humans includes N‐hydroxylation catalyzed by cytochrome P4501A2 possibly followed by O‐acetylation catalyzed by N‐acetyltransferase 2 (NAT2). Nucleotide excision repair‐deficient Chinese hamster ovary (CHO) cells were stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles. CYP1A2 and NAT2 catalytic activities were undetectable in untransfected CHO cell lines. CYP1A2 catalytic activity levels did not differ significantly ( P  > 0.05) among the CYP1A2 ‐transfected cell lines. Cells transfected with NAT2*4 had significantly higher levels of N‐acetyltransferase ( P  = 0.0001) and N‐hydroxy‐PhIP O‐acetyltransferase ( P  = 0.0170) catalytic activity than cells transfected with NAT2*5B . PhIP caused dose‐dependent decreases in cell survival and significant ( P  < 0.001) increases in mutagenesis measured at the hypoxanthine phosphoribosyl transferase ( hprt ) locus in all the CYP1A2 ‐transfected cell lines. Transfection with NAT2*4 or NAT2*5B did not further increase hprt mutagenesis. PhIP‐induced hprt mutant cDNAs were sequenced, and 80% of the mutations were single base substitutions at G:C base pairs. dG‐C8‐PhIP DNA adduct levels were dose‐dependent in the order: untransfected < transfected with CYP1A2  < transfected with CYP1A2 and NAT2*5B  < transfected with CYP1A2 and NAT2*4 . Following incubation with 1.2 µM PhIP, DNA adduct levels were significantly ( P  < 0.05) higher in CHO cells transfected with CYP1A2 / NAT2*4 versus CYP1A2 / NAT2*5B . These results strongly support an activation role for CYP1A2 in PhIP‐induced mutagenesis and DNA damage and suggest a modest effect of human NAT2 and its genetic polymorphism on PhIP DNA adduct levels. © 2007 Wiley‐Liss, Inc.