Cytochromes P450 (CYP) are a superfamily of enzymes responsible for the activation and metabolism of carcinogens, drugs, as well as endogenous compounds. Studies are conducted to characterize the metabolism of the most potent carcinogen dibenzo[a,l]pyrene (DBP), and the endogenous carcinogenic estrogens, as well as the promising antitumor agent taxotere and the worldwide used drug diazepam (DZ). The specificity of individual CYPs is confirmed by activity comparisons, monoclonal antibody inhibition, enzyme kinetics and correlation studies, to show that CYP1A1 primarily activates DBP (5 to 23 fold higher activity than the other CYPs) and followed by 2C9, 1A2, 2B6 and 3A4; CYP1A2 catalyzes exclusively estrone 2-hydroxylation and 3A4 mediates mainly 16alpha-hydroxylation, both of which are known to contribute to estrogen carcinogenesis; CYP3A4 and 3A5 mainly catalyze the metabolism of taxotere, a mitotic spindle poison, to the primary metabolite RPR104952 which is subsequently oxidized to the RPR111059 and RPR111026 diastereomers; and in the metabolism of DZ, CYP3A is the primary enzyme for C3-hydroxylation, and 2B6 and 2C are for N1-demethylation. The oxidation of these drugs is believed to be an inactivation and detoxification pathway and suggests that care must be taken when administering these drugs with other drugs that are also substrates for these enzymes. The model for the monoclonal antibody (MAb)-linked P450 inhibition was generated to show that the MAbs specific for CYP3A4, 2E1 and 2B6 exhibit the mix-type inhibition. Kinetic parameters (alpha, beta, Ki, Ks, Vmax, etc.) related to the model were determined to compare the inhibitory potency of the MAbs for individual P450s and to estimate the contribution of each simple type inhibition to the inhibition complex. These findings are of great importance in understanding the property of biological inhibitors for CYP-catalyzed drug metabolism.
