The bioavailability and clearance of most therapeutic drugs are primarily mediated by cytochrome P450 enzymes, and adverse drug-drug interactions frequently occur because of altered P450 activities. In this article, we describe cytochrome P450 assays that can predict both P450 induction-based and P450 inhibition-based drug-drug interactions at the earliest stages of drug discovery. We focus on assays for the CYP3A4 enzyme, which accounts for about 30% of the P450 in human liver and oxidizes about half of all drugs that are eliminated after prior metabolism. We have developed three luminogenic P450-Glo™ CYP3A4 substrates: Luciferin-BE, Luciferin-PFBE and Luciferin-PPXE. Each substrate is used as a probe for in vitro biochemical assays of recombinant CYP3A4 to detect P450 inhibition by test compounds. Additionally, Luciferin-PFBE is ideal for cell-based measurements of CYP3A gene inductions by drugs. The cell-based assay is rapid and simple and can be performed in a nonlytic mode that leaves cells intact for additional analysis.
Promega Notes 96, 15–18.