Screening of a chemical library reveals novel PXR-activating pharmacologic compounds

The pregnane X receptor (PXR) is one of the master regulators of xenobiotic transformation. Interactions between pharmacologic compounds and PXR frequently result in drug-to-drug interactions, drug-induced hepatotoxicity, and the development of drug-resistant phenotypes in cancer cells. Potential PXR-mediated effects on drug metabolism can be predicted using high-throughput methods to detect PXR transactivation. We used the reporter cell line nhrtox-hepg2 to screen an 1120-compound library of pharmacologic substances. Using a three-stage screening process combined with a quantitative structure-activity relationships (QSAR) analysis, we detected 16 novel, previously unreported PXR activators capable of upregulating CYP450 expression. For some of these compounds such as mycophenolic acid, leflunomide, and trifluridine, the observed interactions with PXR occurred at clinically significant concentrations and could provide potential mechanistic explanations for observed drug-to-drug interactions and drug-induced toxicity. A parallel QSAR analysis revealed significant correlation between the experimentally measured PXR-dependent bioactivity and the calculated molecular descriptors of the PXR activators.