Effects of vorinostat or VPA in combination with idarubicin on cell viability. Cell lines were treated with increasing doses of VPA (0.25-3 mM) or vorinostat (0.075-1 μM) concomitantly with idarubicin at 0.5 nM in MOLT4 or 1.5 nM in HL60 cells daily for 3 days. Numbers on the y-axis represent the percentage of viable cells. (A) MOLT4 cells. (B) HL60 cells. IDA indicates idarubicin; VPA, valproic acid; and Vor, vorinostat. Error bars indicate standard deviation.