Digoxin and its derivatives suppress Th17 cell differentiation by antagonizing RORγt activity

Thus, the pathway towards differentiation of Th17 cells and, perhaps, of related innate lymphoid cells with similar effector functions4, 5, is an attractive target for therapeutic applications. Mouse and human Th17 cells are distinguished by expression of the retinoic acid receptor-related orphan nuclear receptor RORγt, which is required for induction of IL-17 transcription and for the manifestation of Th17-dependent autoimmune disease in mice6. By performing a chemical screen with an insect cell-based reporter system, we identified the cardiac glycoside digoxin as a specific inhibitor of RORγt transcriptional activity. Digoxin inhibited murine Th17 cell differentiation without affecting differentiation of other T cell lineages and was effective in delaying the onset and reducing the severity of autoimmune disease in mice. At high concentrations, digoxin is toxic for human cells, but non-toxic synthetic derivatives, 20,22-dihydrodigoxin-21,23-diol (Dig(dhd)) and digoxin-21-salicylidene (Dig(sal)), specifically inhibited induction of IL-17 in human CD4+ T cells. Using these small molecule compounds, we demonstrated that RORγt is imporant for the maintenance of IL-17 expression in mouse and human effector T cells. These data suggest that derivatives of digoxin can be used as chemical probes for development of RORγt-targeted therapeutic agents that attenuate inflammatory lymphocyte function and autoimmune disease.