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

Abstract

<b>Purpose:</b> Wnt/β-catenin signaling is required for leukemic stem cell function. <i>FLT3</i> mutations are frequently observed in acute myeloid leukemia (AML). Anomalous FLT3 signaling increases β-catenin nuclear localization and transcriptional activity. FLT3 tyrosine kinase inhibitors (TKI) are used clinically to treat <i>FLT3</i>-mutated AML patients, but with limited efficacy. We investigated the antileukemia activity of combined Wnt/β-catenin and FLT3 inhibition in <i>FLT3</i>-mutant AML.<b>Experimental Design:</b> Wnt/β-catenin signaling was inhibited by the β-catenin/CBP antagonist C-82/PRI-724 or siRNAs, and FLT3 signaling by sorafenib or quizartinib. Treatments on apoptosis, cell growth, and cell signaling were assessed in cell lines, patient samples, and <i>in vivo</i> in immunodeficient mice by flow cytometry, Western blot, RT-PCR, and CyTOF.<b>Results:</b> We found significantly higher β-catenin expression in cytogenetically unfavorable and relapsed AML patient samples and in the bone marrow-resident leukemic cells compared with circulating blasts. Disrupting Wnt/β-catenin signaling suppressed AML cell growth, induced apoptosis, abrogated stromal protection, and synergized with TKIs in <i>FLT3</i>-mutated AML cells and stem/progenitor cells <i>in vitro</i> The aforementioned combinatorial treatment improved survival of AML-xenografted mice in two <i>in vivo</i> models and impaired leukemia cell engraftment. Mechanistically, the combined inhibition of Wnt/β-catenin and FLT3 cooperatively decreased nuclear β-catenin and the levels of c-Myc and other Wnt/β-catenin and FLT3 signaling proteins. Importantly, β-catenin inhibition abrogated the microenvironmental protection afforded the leukemic stem/progenitor cells.<b>Conclusions:</b> Disrupting Wnt/β-catenin signaling exerts potent activities against AML stem/progenitor cells and synergizes with FLT3 inhibition in <i>FLT3</i>-mutant AML. These findings provide a rationale for clinical development of this strategy for treating <i>FLT3</i>-mutated AML patients. <i>Clin Cancer Res; 24(10); 2417-29. ©2018 AACR</i>.