Disruption of Wnt/β-Catenin Exerts Antileukemia Activity and Synergizes with FLT3 Inhibition in FLT3-Mutant Acute Myeloid Leukemia

Purpose: Wnt/beta-catenin signaling is required for leukemic stern cell function. FLT3 mutations are frequently observed in acute myeloid leukemia (AML). Anomalous FTL3 signaling increases beta-catenin nuclear localization and transcriptional activity. FLT3 tyrosine kinase inhibitors (TKI) are used clinically to treat FLT3-mutated AMI patients, but with limited efficacy. We investigated the antileukeinia activity of combined Wnt/beta-catenin and 11.13 inhibition in 1'1 7 3-mutant AML. Experimental Design: Wnt/beta-catenin signaling was inhibited by the beta-ratenin/CAP antagonist C-82/PRI-724 or siRNAs, and FED signaling by sorafenib or quizartinib. Treatments on apoptosis, cell growth, and cell signaling were assessed in cell lines, patient samples, and in vivo in immunodeficient mice by flow cytometty, Western blot, Kr-PCR, and CyTOF. Results: We found significantly higher beta-catenin expression in cytogenetically unfavorable and relapsed AML patient samples and in the bone marrow-resident leukemic cells compared with circulating blasts. Disrupting Wnt/beta-catenin signaling suppressed cell growth, induced apoptosis, abrogated stromal protection, and synergized with TKLs in FLT3-mutated AML cells and stem/progenitor cells in vitro. The aforementioned combinatorial treatment improved survival of AML-xenografted mice in two in vivo models and impaired leukemia cell engraftment. Mechanistically, the combined inhibition of Wnt/beta-catenin and TKT3 cooperatively decreased nuclear beta-catenin and the levels of c-Myc and other Wnt/beta-catenin and FLT3 signaling proteins. Importantly, beta-ratenin inhibition abrogated the microenvironmental protection afforded the leukemic stem/progenitor cells. Conclusions: Disrupting Wnt/beta-cateni n signaling exerts potent activities against AML stem/progenitor cells and synergizes with FLT3 inhibition in an-mutant AML. These findings provide a rationale for clinical development of this strategy for treating FLT3-mutated AM L patients. (C) 2018 AACR.