Attenuating pregnane X receptor (PXR) activation: A molecular modelling approach

Recent studies have demonstrated that the pregnane X receptor (PXR) is a key regulator of cytochromes P450 3A (e.g. CYP3A4 in human) gene expression. As a result, activation of PXR may lead to CYP3A4 protein over-expression. Because induction of CYP3A4 could result in clinically important drug-drug interactions, there has been a great interest in reducing the possibility of PXR activation by drug candidates in drug-discovery programmes. In order to provide structural insight for attenuating drug candidate-mediated PXR activation, we used a docking approach to study the structure-activity relationship for PXR activators. Based on our docking models, it is proposed that introducing polar groups to the end of an activator should reduce its human PXR (hPXR) activity via destabilizing interactions in the hydrophobic areas of the PXR ligand-binding pocket. A number of analogues that incorporate these structural features then were designed and synthesized, and they exhibited significantly lower hPXR activation in a transactivation assay and decreased CYP3A4 induction in a human hepatocytes-based assay. In addition, an example in which attenuating hPXR activation was achieved by sterically destabilizing the helices 11 and 12 of the receptor is presented.