ATO sensitizes resistant T-ALL cell lines to dexamethasone treatment. (A) Response to increasing concentrations of dexamethasone (DEX) after 72-hour incubation with or without 0.25 μM ATO. Cell viability was assessed using the MTT assay. (B) Apoptosis rates were determined using annexin-V/propidium iodide stainings. Cells were incubated for 48 hours (CEM-C1, CEM-C7, and MOLT-4) or 72 hours (Jurkat) with control, 0.25 μM ATO, 7.6 μM Dex (or 0.1 μM for CEM-C7), and the appropriate combination and analyzed by flow cytometry. (C) Induction of caspase-3 activity was assessed by flow cytometry. For panel A, the measurements were normalized to untreated controls, and for all experiments, values of 3 experiments are shown as mean plus or minus SD; **P < .05 (Student t test).