Inhibition of FLT3 and PIM Kinases by EC-70124 Exerts Potent Activity in Preclinical Models of Acute Myeloid Leukemia

Internal tandem duplication (ITD) or tyrosine kinase domain mutations of FLT3 is the most frequent genetic alteration in acute myelogenous leukemia (AML) and are associated with poor disease outcome. Despite considerable efforts to develop single-target FLT3 drugs, so far, the most promising clinical response has been achieved using the multikinase inhibitor midostaurin. Here, we explore the activity of the indolocarbazole EC-70124, from the same chemical space as midostaurin, in preclinical models of AML, focusing on those bearing FLT3-ITD mutations. EC-70124 potently inhibits wild-type and mutant FLT3, and also other important kinases such as PIM kinases. EC-70124 inhibits proliferation of AML cell lines, inducing cell-cycle arrest and apoptosis. EC-70124 is orally bioavailable and displays higher metabolic stability and lower human protein plasma binding compared with midostaurin. Both in vitro and in vivo pharmacodynamic analyses demonstrate inhibition of FLT3-STAT5, Akt-mTOR-S6, and PIM-BAD pathways. Oral administration of EC-70124 in FLT3-ITD xenograft models demonstrates high efficacy, reaching complete tumor regression. Ex vivo, EC-70124 impaired cell viability in leukemic blasts, especially from FLT3-ITD patients. Our results demonstrate the ability of EC-70124 to reduce proliferation and induce cell death in AML cell lines, patient-derived leukemic blast and xenograft animal models, reaching best results in FLT3 mutants that carry other molecular pathways' alterations. Thus, its unique inhibition profile warrants EC-70124 as a promising agent for AML treatment based on its ability to interfere the complex oncogenic events activated in AML at several levels. Mol Cancer Ther; 17(3); 614–24. ©2018 AACR.

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