Simultaneous expression of human CYP3A7 and N-acetyltransferase in Chinese hamster CHL cells results in high cytotoxicity for carcinogenic heterocyclic amines.

To investigate whether several food-derived heterocyclic amines are activated to genotoxic products in human fetal livers, cell lines stably expressing CYP3A7, a human fetus-specific form of cytochrome P450, NADPH-cytochrome P450 reductase, and human monomorphic or polymorphic N-acetyltransferase (NAT1 or NAT2) were established. The expression of CYP3A7 mRNAs and proteins was determined by RNA blot and immunoblot analyses, respectively. The introduction of CYP3A7 cDNA to CR-68 cells which had been transfected with guinea pig NADPH-cytochrome P450 reductase, NAT1, or NAT2 cDNA resulted in increased sensitivity of the cells to aflatoxin B1 compared to parental cells. The cytotoxicity assay for 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) showed that 7P-145 cells, which expressed the reductase, CYP3A7, and NAT2, were approximately 4-, 30-, and 14-fold more sensitive to respective IQ, MeIQ, and MeIQx than parental CR-68 cells. There were no clear differences in sensitivity to these compounds among CHL, CR-68, and the cells which expressed the reductase and CYP3A7 (7R-54), the reductase and NAT1 (CNM-4), the reductase and NAT2 (CNP-40), and the reductase, NAT1, and CYP3A7 (7M-124). From these results, it was suggested that both CYP3A7 and polymorphic NAT2 are required for mutagenic activation of several heterocyclic amines in human fetal livers.