GO-203 is effective in increasing sensitivity to FLT3 inhibitors. BaF3/FLT3(D835Y) cells were left untreated or treated with the indicated concentrations of GO-203 for 72 hours. Cell number (mean ± SD of 3 determinations) was determined by trypan blue staining (A). Percentage cell death (mean ± SD of 3 determinations) was determined by PI staining and flow cytometry (B). (C) MOLM-14 cells were treated with 25 nM PKC412, 2 nM AC220, or 2 μM GO-203 in the absence (−) and presence (+) of 50 nM FLT3 ligand (FL) for 72 hours. Cell number (mean ± SD of 3 determinations) was determined by trypan blue staining. MOLM-14 cells were treated with 10 nM PKC412 or 2.5 μM GO-203 alone and in combination for 96 hours (D). MOLM-14 cells were treated with 2.5 nM AC220 or 2.5 μM GO-203 alone and in combination for 72 hours (E). Cell number was determined by trypan blue exclusion. The results are expressed as the relative cell number (mean ± SD of 3 determinations) compared with that obtained for the untreated control. P values were determined by the Student’s t test.