Autophagy Targeting and Hematological Mobilization in FLT3-ITD Acute Myeloid Leukemia Decrease Repopulating Capacity and Relapse by Inducing Apoptosis of Committed Leukemic Cells

Simple Summary One of the most frequent molecular anomalies in acute myeloid leukemia (AML) is the mutation of the fms-like receptor tyrosine kinase 3 through internal tandem duplications, giving rise to a constitutive proliferative signaling. Even though clinical trials have shown that targeting this mutated kinase is of interest and well tolerated, there is still a high frequency of relapse. The emergence of AML cells upon treatment is linked to their maintenance through resistance and persistence mechanisms. Because FLT3-ITD AML cells require autophagy, we explored the consequence of autophagy inhibition by blocking the PI3-kinase class III, Vps34, when AML cells were committed. Results in vitro, ex vivo and in vivo suggest that remission with low minimal residual disease in FLT3-ITD AML offers a promising therapeutic window to target persistent leukemic cells. Targeting FLT3-ITD in AML using TKI against FLT3 cannot prevent relapse even in the presence of complete remission, suggesting the resistance and/or the persistence of leukemic-initiating cells in the hematopoietic niche. By mimicking the hematopoietic niche condition with cultures at low oxygen concentrations, we demonstrate in vitro that FLT3-ITD AML cells decrease their repopulating capacity when Vps34 is inhibited. Ex vivo, AML FLT3-ITD blasts treated with Vps34 inhibitors recovered proliferation more slowly due to an increase an apoptosis. In vivo, mice engrafted with FLT3-ITD AML MV4-11 cells have the invasion of the bone marrow and blood in 2 weeks. After 4 weeks of FLT3 TKI treatment with gilteritinib, the leukemic burden had strongly decreased and deep remission was observed. When treatment was discontinued, mice relapsed rapidly. In contrast, Vps34 inhibition strongly decreased the relapse rate, and even more so in association with mobilization by G-CSF and AMD3100. These results demonstrate that remission offers the therapeutic window for a regimen using Vps34 inhibition combined with mobilization to target persistent leukemic stem cells and thus decrease the relapse rate.