CASP9 and acute myeloid leukemia: To characterize the mechanisms underlying apoptotic response to ouabain in AML cells, KG-1 cells were first treated with ouabain (30 nM) in the presence or absence of caspase-8 inhibitor zVAD-IETD (10 μM) and caspase-9 inhibitor zVAD-LEHD (10 μM), and apoptosis was evaluated by Annexin V/7-AAD and Hoechst 33342 assays at 48 h.