HDACIs reduce platelet number in mice. Cohorts of C57BL/6 mice were treated with (A) alternate weekly daily IP panobinostat 10 mg/kg (Pan) or vehicle or (B) 4 days of romidepsin 1 mg/kg (Romi) or vehicle (treatment schedules indicated by arrows). At the indicated time points, platelet counts were taken from 3 mice in each group. Platelet number in each HDACI-treated group decreased with treatment, and on drug cessation a rebound thrombocytosis occurred. Error bars represent SEM. Results were compared using the 2-tailed unpaired t tests. Cohorts of C57BL/6 mice were treated with (C) continuous daily IP panobinostat 10 mg/kg or vehicle or (D) continuous daily IP romidepsin 1 mg/kg or vehicle (treatment schedules indicated by arrows). At the indicated time points, platelet counts were taken from 3 mice in each group. Platelet number in each HDACI-treated group decreased with treatment and with continued dosing remained in a plateau. Error bars represent standard error of the mean. Differences in groups were calculated using linear regression analysis.