Subsequent studies have elucidated several potential mechanisms key to the anti-CML effect of omacetaxine: (1) down-regulation of short-lived proteins, such as the myeloid cell leukemia-1 (MCL-1) protein, that regulate proliferation and cell growth; (2) a reduction in the expression of BCR-ABL thought to be due in part to effects on Hsp90; and (3) apoptotic effects on leukemic stem cells (Chen, Peng, Sullivan, Li, & Li, 2010; Klag et al., 2012; Tang et al., 2006). Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.