Mutagenicity of IQ and MeIQx at the hypoxanthine-guanine phosphori

In order to Investigate the metabolic activation pathway of food-derived heterocyclic amities, 2-amino-3-metbylimldazo[4,5-fjquinoline (IQ) and 2-amino-3,8-dlmethyllmidaw[4,5-fjquinoxallne (MeIQx), cultured cell lines which stably expressed human cytochrome P4501A2 (CYP1A2) and N-acetyltransferases (NATs) were developed by the method of comple mentary DNA (cDNA) transfection. First, a cell line expressing CYP1A2, designated A2R-5, was established from the cell line CR-68, which was previously established by introducing NADPH-cytochrome P.450 reduc tam cDNA Into Chinese hamster CHL cells. The expression ofCYP1A2 in the transfected cells was confirmed by determining sensitivity to aflatoxin B1. As the next step, the AIR-S as well as CR-68 cells were further transfected with human monomorphic NAT (NAT1) or polymorphic NAT (NAT2) cDNAs. The expression of NAT In the transfected cells was confirmed using p-aminobenzoic acid and sulfamethazine as substrates, while no activity was seen in parental CR-68 and A2R-5 cells. The cell line, ANP-25, which expressed both CYPIA2 and NAT2, was approximately 370and 100-foldmore sensitiveto IQ and MeIQx, respectively, than parental CR-68 cells In cytotoxicity assays. There were no clear differ cures in sensitivity to both compounds among CR-68, A2R-5, and the cell lines which expressed NAT1 alone, NAT2 alone, and CYP1A2 plus NAT!. Mutagenicity of IQ and MeIQx at the hypoxanthine-guanine phosphori bosyltransferase locus was also detectable only in ANP-25 cells but not in AIR-S or the cell line expressing CYP1A2 plus NAT!. From these results, it is proposed that both CYP1A2 and NAT2 (but not NAT!) are required for mutagenic activation of these compounds, implying that acetylator polymorphism may be an important risk factor in the carcinogenicfty of these compounds.