Synergistic antileukemia effects of vorinostat and dexamethasone in vitro and in vivo. (A) ALL-2 and (B) ALL-19 xenograft cells were treated with vorinostat (green), dexamethasone (blue), or both (red) in vitro at a fixed ratio of concentrations as described in “In vitro cytotoxicity assays” and mitochondrial activity was assessed by MTT assay. Data represent the mean ± SEM of 3 independent experiments. (C-F) The in vivo antileukemia effects of dexamethasone (C, blue; 5 mg/kg Monday through Friday for 4 weeks; n = 9) and vorinostat (D, green; 200 mg/kg for 7 days then 100 mg/kg for 21 days; n = 9) individually and in combination (E, red; n = 9) were evaluated against ALL-2 inoculated in NOD/SCID mice in vivo. Colored lines indicate the %huCD45⁺ in each mouse within the drug-treated groups, while black lines show the progression in vehicle-treated controls (n = 9). (F) Kaplan-Meier graphs indicate the EFS of each cohort in the weeks post treatment initiation. Solid bars in panels C-F represent treatment periods.