In previous studies, CuE (1–10 μM) inhibited the pSTAT3 and induced apoptosis in human breast cancer cell lines Bcap37 and MDA-MB-231 [6] and decreased the levels of the anti-apoptotic proteins XIAP, Survivin, and Mcl-1, and increased the level of Bax in human leukemia HL-60 cells [8]. Here, MCL1 is linked to leukemia.