Figure 2

Ph⁺ALL samples are sensitive to YM155. (A) The Ph⁺ALL cell line SUPB15 was tested for sensitivity to dasatinib (top left) and YM155 (Top right) with increasing concentrations of drug (0 nM to 10 μM). The IC₅₀ for each drug was approximately 10 nM. Combination of YM155 and dasatinib on SUPB5 cells showed a decrease in IC₅₀ suggestive of synergy/additive by isobologram analysis [34]. Dose–response of SUPB15 cells with YM155 was carried out with increasing concentrations of dasatinib (bottom left). IC₅₀ of individual drug alone was used as the reference value of 1 and subsequent IC₅₀ of combination of drugs were compared (bottom right). Points on the red dotted line would be additive, while points left of the line would be synergistic and points on the right would be antagonistic. (B) Sensitivity to YM155 and dasatinib was further tested on primary Ph⁺ALL patient samples (10–668) and xenograft samples (10–668 xenograft, ICN1, SFO2, TXL3, LAX2, BLQ5, x10-378). Red samples signify dasatinib-resistant T315I mutants. (C) Knockdown of BCR-ABL1 expression. SUPB15 were treated with either non-specific (NS) or ABL1 siRNA. The cells were then incubated in increasing concentrations of YM155 (0 to 1 μM) for 4 days and then assayed for viability with MTS. Top panel describes the viability of the cells normalized to NS without YM155 exposure. Bottom panel describes the viability normalized to with NS or ABL1 without YM155 exposure. An aliquot of electroporated cells were used for immunoblot analysis of BCR-ABL1 knockdown 3 days after electroporation. (D) P53 Ser-15 phospho-flow after treatment with YM155. Each cell line (REH, RCH, HAL01, and SUPB15) and xenograft samples (SFO2, BLQ5) were treated with 100 nM YM155 for 24 h. (Red peak) Control signal for ser15-phospho-p53. (Blue peak) YM155 treatment. REH and RCH cells showed a distinctive increase in phosphorylation of p53. In contrast, the Ph⁺ALL cells showed minimal increase in p53 phosphorylation.