Identification of farnesoid X receptor modulators by a fluorescence polarization-based interaction assay

Farnesoid X receptor (FXR) serves as a receptor for chenodeoxycholic acid (CDCA) and other bile acids, and it coordinates cholesterol and lipid metabolism. Because targeting the FXR–CDCA interaction might provide a way to regulate lipid homeostasis, we developed an FXR binding assay based on fluorescence polarization. Employing a fluorescently labeled CDCA (CDCA-F), we showed that CDCA-F selectively bound to the ligand binding domain of FXR (FXR–LBD) among nuclear receptors. The assay was then used for screening inhibitors against the FXR–CDCA interaction, thereby discovering four relatively potent inhibitors. The selected inhibitors were further studied for changes in intrinsic tryptophan fluorescence of FXR–LBD to gain structural insights into the interaction. Furthermore, transactivation effects of the inhibitors on the human bile salt excretory pump (BSEP) promoter were examined to reveal their cellular activities in the FXR-mediated pathway. Therefore, we demonstrated that the developed assay would offer an efficient primary screening tool for identifying FXR modulators.