FMS-like tyrosine kinase 3–targeted (FLT3-targeted) therapies have shown initial promise for the treatment of acute myeloid leukemia (AML) expressing FLT3-activating mutations; however, resistance emerges rapidly. Furthermore, limited options exist for the treatment of FLT3-independent AML, demonstrating the need for novel therapies that reduce toxicity and improve survival. MERTK receptor tyrosine kinase is overexpressed in 80% to 90% of AMLs and contributes to leukemogenesis. Here, we describe MRX-2843, a type 1 small-molecule tyrosine kinase inhibitor that abrogates activation of both MERTK and FLT3 and their downstream effectors. MRX-2843 treatment induces apoptosis and inhibits colony formation in AML cell lines and primary patient samples expressing MERTK and/or FLT3-ITD, with a wide therapeutic window compared with that of normal human cord blood cells. In murine orthotopic xenograft models, once-daily oral therapy prolonged survival 2- to 3-fold over that of vehicle-treated controls. Additionally, MRX-2843 retained activity against quizartinib-resistant FLT3-ITD–mutant proteins with clinically relevant alterations at the D835 or F691 loci and prolonged survival in xenograft models of quizartinib-resistant AML. Together, these observations validate MRX-2843 as a translational agent and support its clinical development for the treatment of AML.
Katherine A. Minson, Catherine C. Smith, Deborah DeRyckere, Clara Libbrecht, Alisa B. Lee-Sherick, Madeline G. Huey, Elisabeth A. Lasater, Gregory D. Kirkpatrick, Michael A. Stashko, Weihe Zhang, Craig T. Jordan, Dmitri Kireev, Xiaodong Wang, Stephen V. Frye, H. Shelton Earp, Neil P. Shah, Douglas K. Graham
MRX-2843 mediates functional antitumor effects in quizartinib-resistant FLT3-ITD cell lines.