308 (PB088) - Develop selective inhibitors of drug-metabolizing enzymes CYP3A4/5 to improve cancer drug efficacy and reduce drug toxicity and resistance

Abstract

Background: The human cytochrome P450 (CYP) CYP3A4 and CYP3A5 enzymes metabolize more than half of marketed drugs. They share high structural and substrate similarity and are often studied together as CYP3A4/ 5. However, they preferentially metabolize different clinically prescribed drugs. Moreover, the differential distribution and expression levels of CYP3A4 and CYP3A5 in both normal and diseased tissues can aggravate toxicity and induce resistance during treatment. Therefore, selective inhibitors of CYP3A4 and CYP3A5 are needed to distinguish their roles and serve as starting points for potential therapeutic development. Materials and methods: We used biochemical and cell-based assays and high-throughput screening to discover and characterize selective inhibitors. We used X-ray crystallography to unravel the structural basis of selective inhibition. Results: We discovered clobetasol propionate as the first selective inhibitor of CYP3A5 and reported the crystal structure of CYP3A5 in complex with clobetasol propionate. Supported by structure-guided mutagenesis analyses, the CYP3A5-clobetasol propionate structure showed that a unique conformation of the F–F′ loop in CYP3A5 enables selective binding of clobetasol propionate to CYP3A5, thus proving the structural basis for the selective inhibition. Based on these results we performed large-scale high-throughput screening to identify additional selective inhibitors of both CYP3A4 and CYP3A5 that are suitable for chemical optimization. Conclusions: It is feasible to selectively inhibit the highly homologous CYP3A4 and CYP3A5 enzymes, thus chemically validating CYP3A4 and CYP3A5 as targets for development of therapeutics to improve drug efficacy while reducing drug toxicity and resistance during treatment. No conflict of interest.