Hellebrin is a cardiac glycoside that potently inhibits the Na+/K+-ATPase by binding to it and blocking its non-canonical function as a receptor for cardiac glycosides. Hellebrin has a higher affinity for the α1β1 subunit of the Na+/K+-ATPase than the α2β1 or α3β1 complexes, in contrast to other cardiac glycosides. This affinity for the α1β1 complex correlates with its cancer cell growth inhibition (GI50 = 6-58 nM in various human cancer cell lines). Hellebrin also induces caspase-dependent apoptosis in Jurkat T cells.