Cytotoxicity of ABT-737 plus vincristine, dexamethasone, or L-ASP in PMBCs. (A) Dose-response curves of PBMCs to ABT-737 (●), L-ASP (△), vincristine (VCR; ○), dexamethasone (DEX; □), and the combinations (gray symbols). The concentrations of ASP used for PBMCs were increased to 1 to 10 IU/mL to assure examination of cytotoxicity in clinically achievable concentrations. Each condition had 12 replicates, and error bars represent standard deviation. (B) Cells (COG-LL-317 and PBMCs) were incubated with ABT-737 (2.5 μM), ASP (1 IU/mL), or the combination for 6 hours. Then, apoptosis assessed with annexin V and PI staining measured by flow cytometry. COG-LL-317 cells were used as positive controls. For PBMCs, apoptosis was assessed only in lymphocytes that fell within a standard forward- and side-scatter lymphocyte gate. Cells that were annexin V–FITC⁺, PI⁻ were defined as apoptotic. The bar graph shows the percentage of cells in apoptosis, and the values represent means (± SD) of 3 samples, and the experiments were repeated twice. Apoptosis in COG-LL-317 for ABT-737 + L-ASP was significantly higher than control (P < .001), while neither single agents nor ABT-737 + L-ASP induced significant apoptosis in lymphocytes.