Rationale for a Combination Therapy Consisting of MCL1- and MEK-Inhibitors in Acute Myeloid Leukemia

Amplification and overexpression of the myeloid cell leukemia differentiation protein MCL1 and the murine double minute protein MDM2 have been reported in various human tumors as well as hematological malignancies including acute myeloid leukemia (AML). While MCL1 is an anti-apoptotic member of the BCL-2 family proteins, MDM2 is an important cellular inhibitor of the p53 tumor suppressor. The key oncogene in AML is the FLT3 growth factor receptor gene. FLT3 signaling pathways including the MAPK cascade (RAS-RAF-MEK-ERK) are highly active in AML cells, leading to induced protein translation and cell proliferation as well as reduced apoptosis. Consequently, combined administration of MCL1-, MDM2-, and MEK-inhibitors may present a promising anti-leukemic treatment strategy. Here, we assessed the MCL1-antagonist S63845, the MDM2-inhibitor HDM201, and the MEK1/2-inhibitor trametinib as single agents and in combination in a variety of AML cell lines and mononuclear cells isolated from patients with hematological malignancies centered on myeloid leukemia, some lymphatic leukemia, as well as some lymphomas, for their ability to induce apoptosis and cell death. We observed a considerably varying anti-leukemic efficacy of the MCL1-inhibitor S63845 and the MEK1/2-inhibitor trametinib. Hematological cells with susceptibility to the single compounds as well as to the combined treatment were defined by elevated MCL1- and MEK-protein levels, independent of the mutational status of FLT3 and TP53. Our data indicate that hematological cells with elevated MCL1- and MEK-protein levels are most sensitive to the combined treatment with S63845 and trametinib. MCL1- and MEK1/2-protein expression may be valid biomarkers for treatment response to S63845 and trametinib, respectively.