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

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 KD 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 EC50 of 1.05 μM, while genistein represented
the most potent activator, with an EC50 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.