Identification of Small-Molecule Regulators of Testicular Receptor 4 via a Drug Repurposing Screening

[Image: see text] The testicular receptor 4 (TR4) is a nuclear receptor implicated in multiple pathological processes, including cancer development, chemotherapy, and radiotherapy resistance. However, no effective TR4 small-molecule regulator is available to date. Here, we assessed a physical-interaction-based surface plasmon resonance imaging assay for discovery of TR4 regulators. We screened 1018 FDA-approved drugs and obtained 126 drugs with K(D) values below 10(–6) M. The dual-luciferase-based biological assay verified four activatory compounds and two inhibitory compounds against TR4. Among them, nilotinib exhibited the most potent inhibitor, with an EC(50) of 1.05 μM, while genistein represented the most potent activator, with an EC(50) of 2.42 μM. Both drugs were predicted to bind in the ligand binding pocket of TR4. The circular dichroism spectroscopic assay revealed differed conformation changes upon nilotinib or genistein binding. These results established our combined physical and biological approaches as a highly effective way to identify and develop new TR4 regulators.