MCL1 and acute myeloid leukemia: To evaluate the antitumor efficacy of 753b, we tested it in an acute myeloid leukemia (AML) cell line, Kasumi-1, which primarily depends on both BCL-xL and BCL-2 for survival because ABT263 (a BCL-xL/2 dual inhibitor) was more potent to kill the cells than A133187234 (a selective BCL-xL inhibitor), ABT19935 (a selective BCL-2 inhibitor) or S6384536 (a selective MCL-1 inhibitor) (Fig. 7a).