Combination of a PIM inhibitor with tyrosine kinase inhibitors achieves synergistic effect on cancer cell growth and biomarker suppression. (A) Modulation of MYC protein expression by a PIM inhibitor in high CD25 subpopulation. KG1 cells were sorted according to the level of CD25 functional expression. The MYC protein level of the top 1% of CD25-positive cells was compared with that of CD25-negative cells in the presence of DMSO or compound C. (B) Comparison of growth suppression by depleting MYC, STAT5, or both, with siRNAs. Sustained knockdown of endogenous STAT5, MYC, or both was achieved by daily exposure of cells to Accell siRNAs (see supplemental Methods) over the course of experiments. Culture volume was diluted 1:1 every day to avoid overconfluency and to ensure the optimal growth of cells. (C) Assessment of synergistic cell growth inhibition. HNT34 (i) and KG1 (ii,iii) cell lines were treated with a combination of compound C/imatinib or compound C/pan-FGFR inhibitors. Combination index (CI) value less than 0.5 denotes significant synergism of combinatorial compound treatment. (D) Effect of compound C/imatinib or compound C/pan-FGFR inhibitor combination on MYC protein expression. (E) Effect of compound C/imatinib or compound C/pan-FGFR inhibitor combination on CD25 mRNA levels.