A cardiotonic steroid that inhibits theNa+/K+-ATPase transporter (Kds = 42, 45, and 40 nM for the α1, α2, and α3 subunits, respectively); inhibits SRC-1 and SRC-3 at doses as low as 5 nM, promotes the degradation of SRC-3 protein, and inhibits cancer cell growth both in vitro and in vivo