Evaluation of Cytochrome P450 Inhibition in Human Liver Microsomes

Evaluation of lead compounds for P450 inhibition in human liver microsomes has been widely accepted as an in vitro approach to assess drug interaction potential. This chapter describes a detailed traditional CYP inhibition protocol for six major isoforms: 1A2, 2C9, 2C19, 2D6, 2E1, and 3A4. Microsomal incubation conditions were optimized and kinetic parameters determined to initially establish the inhibition assay. In CYP inhibition assay, separated incubations were performed for individual CYPs, and resulting samples were pooled and analyzed by liquid chromatography/tandem mass spectrometry (LC-MS/MS). It is without doubt that results from this in vitro experiment are of great value in lead optimization in drug discovery and development. It is obvious that more efforts are still needed to establish the relevance between in vitro CYP inhibition and drug interactions in the clinic.