UNC2025, a MERTK Small-Molecule Inhibitor, Is Therapeutically Effective Alone and in Combination with Methotrexate in Leukemia Models

Abstract

<b>Purpose:</b> MERTK tyrosine kinase is ectopically expressed in 30% to 50% of acute lymphoblastic leukemias (ALL) and more than 80% of acute myeloid leukemias (AML) and is a potential therapeutic target. Here, we evaluated the utility of UNC2025, a MERTK tyrosine kinase inhibitor, for treatment of acute leukemia.<b>Experimental Design:</b> Preclinical <i>in vitro</i> and <i>in vivo</i> assays using cell lines and primary leukemia patient samples were used to evaluate antileukemic effects of UNC2025.<b>Results:</b> UNC2025 potently inhibited prosurvival signaling, induced apoptosis, and reduced proliferation and colony formation in MERTK-expressing ALL and AML cell lines and patient samples. Approximately 30% of primary leukemia patient samples (78 of 261 total) were sensitive to UNC2025. Sensitive samples were most prevalent in the AML, T-ALL, and minimally differentiated (M0) AML subsets. UNC2025 inhibited MERTK in bone marrow leukemia cells and had significant therapeutic effects in xenograft models, with dose-dependent decreases in tumor burden and consistent two-fold increases in median survival, irrespective of starting disease burden. In a patient-derived AML xenograft model, treatment with UNC2025 induced disease regression. In addition, UNC2025 increased sensitivity to methotrexate <i>in vivo</i>, suggesting that addition of MERTK-targeted therapy to current cytotoxic regimens may be particularly effective and/or allow for chemotherapy dose reduction.<b>Conclusions:</b> The broad-spectrum activity mediated by UNC2025 in leukemia patient samples and xenograft models, alone or in combination with cytotoxic chemotherapy, supports continued development of MERTK inhibitors for treatment of leukemia. <i>Clin Cancer Res; 23(6); 1481-92. ©2016 AACR</i>.