MK-2206 induces apoptosis of AML cells and enhances the cytotoxicity of cytarabine

Genetic alterations in the PI3K/AKT cascade have been linked to various human cancers including acute myeloid leukemia (AML) and have emerged to be promising targets for treatment. In this study, we explored the molecular mechanism and clinical implication of a specific allosteric AKT inhibitor, MK-2206, in the treat- ment of AML. Four leukemia cell lines, MV-4-11, MOLM- 13, OCI/AML3, and U937, were used. Apoptosis and cell cycle distribution were determined by flow cytometry analysis. Expression of anti-apoptotic protein family and glycogen synthase kinase 3b (GSK3b) signaling was determined by western blotting. Drug combination effects of MK-2206 with cytarabine were evaluated by cell pro- liferation assay, and the combination index values were calculated by CompuSyn software. MK-2206 had no effect on normal peripheral blood mononuclear cells, but induced G1-phase arrest and apoptosis in leukemia cells. Among anti-apoptotic Bcl-2 family members, only myeloid cell leukemia-1 (Mcl-1) was significantly suppressed. Mcl-1 suppression by MK-2206 was closely associated with decreased GSK3b phosphorylation at Ser9, an event leads to GSK3b activation. Furthermore, the effect of MK-2206 on Mcl-1 downregulation was abolished by GSK3b inhi- bitor, lithium chloride and proteasome inhibitor, MG-132, suggesting that MK-2206 acted through a GSK3b-medi- ated, proteasome-dependent protein degradation. In addi- tion, co-administration of MK-2206 with cytarabine could enhance the cytotoxic efficacy of cytarabine in leukemia cell lines. In conclusion, we have demonstrated that MK- 2206 is an active agent in AML and its efficacy as in combination with cytarabine is implicated.