Drug combination effects on MV4-11 cell viability and FLT3 signaling. (A) MV4-11 and MOLM-13 cells were treated with DMSO or increasing concentrations of crenolanib (CRE), sorafenib (SOR), or both at a fixed concentration ratio for 72 hours and cell viability was measured. Calcusyn combination index (CI) values were generated for drug combination effects on cell viability. Cell viability experiments were performed in triplicate with 6 replicates each (n = 18; CI value > 1.0: antagonism; CI value = 1.0: additivity; CI value < 1.0: synergism). (B) MV4-11 cells were treated for 1 hour with DMSO or the indicated concentration of crenolanib (CRE), sorafenib (SOR), or both (combo) and lysed. Western blot analysis was performed on whole-cell lysate by use of the indicated antibodies. Densitometry measurements were normalized to total protein amount.