OSU-2S induces maturation and prolongs survival in a Tet2^−/−Flt3^ITD mutated murine AML model. (A) Workflow diagram depicting coinjection of CD45.2 expressing AML cells from Tet2^−/−Flt3^ITD donor and normal support marrow from CD45.1 donor in lethally irradiated CD45.1 mice to generate an immunocompetent AML model. BMT-only control mice received normal support marrow only. (B) OSU-2S (10 mg/kg, thrice a week, until the end of the study) treatment (IP) significantly prolonged survival of leukemic mice (n = 10 [Veh] and 11 [OSU-2S]; P = .022). (C) Mac1 (Mac1-APC) median fluorescence intensity (MFI) in CD45.2 BM of Veh (n = 3) and OSU-2S–treated mice (n = 5). OSU-2S treatment in vivo induced Mac1 expression (P = .0326). (D) Expression of maturation markers Mac1 and Ly6G (Ly6G-AF700) in BM and spleen of Veh and OSU-2S–treated mice, representative flow cytometry plots and graphs (E) showing quantification. OSU-2S treatment significantly increased the Mac1⁺ and Ly6G⁺ mature population in vivo. Representative flow cytometric plots (F) and quantification of progenitor marker cKit (cKit-PE Cy7) (G), and maturation marker Mac1 (Mac1-APC) in BM of Veh- and OSU-2S–treated mice (n = 3). OSU-2S treatment significantly lowered the immature cKit⁺/Mac1⁻ (P = .021) and increased the mature cKit⁻/Mac1⁺ population (P = .0002) in the BM. Representative flow cytometric plots (I) and quantification of progenitor marker cKit (cKit-PE Cy7) and maturation marker Mac1 (Mac1-APC) (J) in the spleen of Veh- and OSU-2S–treated mice (n = 3). OSU-2S treatment significantly lowered the immature cKit⁺/Mac1⁻ and increased the mature cKit⁻/Mac1⁺ population in the spleen. *P < .05; **P < .01; ***P < .001.