Mutagenic activation of 2-amino-3-methylimidazo[4,5-f]quinoline by complementary DNA-expressed human liver P-450.

Eight forms of human liver microsomal P-450 were individually expressed in human hepatoma Hep G2 cells with a vaccinia virus cDNA expression system. Using the Ames test, each expressed P-450 was examined for its ability to activate to mutagenic products the compounds, 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline, respectively. Three forms of human P-450 significantly activated 2-amino-3-methylimidazo[4,5-f]quinoline when the latter was at high substrate concentrations, but only a single form, P-450IA2, showed very high activation of all promutagens at lower substrate concentrations. Human IA2 had extraordinarily high affinity towards four promutagens tested and is likely the predominant P-450 enzyme responsible for their mutagenic activation in human liver.