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A precise understanding of the role of miR-223 in human hematopoiesis and in the pathogenesis of acute myeloid leukemia (AML) is still lacking. By measuring miR-223 expression in blasts from 115 AML patients, we found significantly higher miR-223 levels in patients with favorable prognosis, whereas patients with low miR-223 expression levels were associated with worse outcome. Furthermore, miR-223 was hierarchically expressed in AML subpopulations, with lower expression in leukemic stem cell-containing fractions. Genetic depletion of miR-223 decreased the leukemia initiating cell (LIC) frequency in a myelomonocytic AML mouse model, but it was not mandatory for rapid-onset AML. To relate these observations to physiologic myeloid differentiation, we knocked down or ectopically expressed miR-223 in cord-blood CD34⁺ cells using lentiviral vectors. Although miR-223 knockdown delayed myeloerythroid precursor differentiation in vitro, it increased myeloid progenitors in vivo following serial xenotransplantation. Ectopic miR-223 expression increased erythropoiesis, T lymphopoiesis, and early B lymphopoiesis in vivo. These findings broaden the role of miR-223 as a regulator of the expansion/differentiation equilibrium in hematopoietic stem and progenitor cells where its impact is dose- and differentiation-stage-dependent. This also explains the complex yet minor role of miR-223 in AML, a heterogeneous disease with variable degree of myeloid differentiation., (Copyright © 2015 ISEH - International Society for Experimental Hematology. Published by Elsevier Inc. All rights reserved.)

Objective: Dysregulation of signaling pathways leading to enhanced cell proliferation and resistance to apoptosis is frequent in acute myeloid leukemia (AML). The effectiveness of inhibiting two such pathways, the phosphatidylinosityl-3-kinase pathway via the intermediate integrin-linked kinase (ILK), and FMS-like tyrosine kinase-3 (FLT-3) signaling pathway in killing AML cells was studied., Materials and Methods: AML colony-forming cell (CFC) assays were used to determine the effects of a small molecule inhibitor of both ILK and FLT-3 (QLT0267) on poor prognosis primary AML sample viability. Kinase assays and Western blots were used to analyze effects of the compound on target molecules., Results: In 31/36 AML blast samples p-Akt was detected indicating phosphatidylinosityl-3-kinase activation. ILK was ubiquitously and FLT-3 abundantly expressed. Downregulation of ILK in the AML cell line TF-1 using small interfering RNA caused >or= 50% CFC death, suggesting ILK inhibition might also be toxic to primary AML cells. In vitro kinase assays on three AML samples showed inhibition of both ILK and FLT-3 by QLT0267. Treatment of AML patient blast cells (n=27) with QLT0267, caused a dose- and time-dependent downregulation of p-Akt and kill of AML-CFC with AML samples containing FLT-3 mutations being more sensitive to QLT0267 than those without. AML samples were more sensitive to QLT0267 killing than normal bone marrow (IC(50)=3 microM, vs 10 microM for AML-CFC and normal CFC, respectively, n=5)., Conclusion: Combined inhibition of ILK and FLT-3 with a small molecule kinase inhibitor can achieve selective targeting of AML rather than normal hematopoietic progenitors.