a, Chemical structure of digoxin. b, Digoxin demonstrates dose-dependent inhibition of RORγ transcriptional activity in the Drosophila S2 cell luciferase reporter system. Ratio of firefly to Renilla luciferase activity is shown as relative luciferase unit (RLU) on the y-axis. c, Digoxin (10 μM) selectively inhibits RORγ dependent transcriptional activity without affecting that of RORα, DHR3, or VP16. Percentages of relative luciferase units compared to DMSO-treated reporter cells are shown on the y-axis. Error bars indicate standard deviation. d, In vitro competition assay. Recombinant human RORγ LBD was loaded with fluorescently-labeled 25-hydroxycholesterol in the presence of the indicated concentrations of digoxin, and fluorescence polarization was measured.