Vol. 30, Issue 6, 701-708, June 2002

Inhibition Kinetics of Monoclonal Antibodies against Cytochromes P450

Qin Mei, Cuyue Tang, Yuh Lin, Thomas H. Rushmore, and Magang Shou

Department of Drug Metabolism, Merck Research Laboratories, West Point, Pennsylvania

Monoclonal antibodies (MAbs) inhibitory to individual cytochromes P450 (P450s) are of tremendous utility in identification of P450s responsible for the metabolism of a given drug or drug candidate in pharmaceuticals. In the present study, two inhibitory MAbs against CYP2D6 (MAb_2D6-50, IgG_2b and MAb_2D6-184, IgG_2a) were developed by hybridoma technology to exhibit their high specificity and potency. The MAbs were further employed to assess the quantitative role (47-93%) of CYP2D6 to the metabolism of bufuralol in human liver microsomes from seven donors. Together with the MAb inhibitory to CYP3A4 as previously reported (Mei et al., 1999), the MAbs were used to study the inhibition kinetics of dextromethorphan O-demethylation (CYP2D6), testosterone 6-hydroxylation (CYP3A4) and aflatoxin B1 3-hydroxylation (CYP3A4), respectively, with an adequate size of sample measurement. A kinetic model was proposed to fit the experimental observations with three-dimensional nonlinear regression, thereby resulting in a solution of kinetic parameters, i.e., K_I, K_S, V_max, , and  (changes in K_I or K_S and V_max in the presence of the MAb). As a result, dissociation constants (K_I) of the MAbs for the enzymes and the maximal inhibition () values for the P450-catalyzed reactions were predicted to have 0.04 to 0.25 µM and 94%, respectively. The results have demonstrated that the model can accurately predict the kinetic parameters and provide some insights into the understanding of the mechanism of MAb interaction with P450 enzyme in nature and the applications of the MAbs in qualitative and quantitative identification of P450s involved in drug metabolism.