Down-regulation of Bad using siRNA decreases the sensitivity of the cells to the combination treatment of ATO and dexamethasone. (A) CEM-C1 cells were transfected with 2 distinct siRNAs directed against Bad. Down-regulation of Bad was assessed after 48 hours by Western blot. (B) Signal quantification by densitometry. (C) siBad treatment of CEM cells decreased the cytotoxic effect of 1 μM ATO as single agent and (D) of the combination of low-dose ATO (0.25 μM) with DEX. A scrambled siRNA was used for control. Triplicate results of the MTT assay are shown as mean plus or minus SD; **P < .05 (Student t test).