HDACIs increase megakaryocyte numbers but reduce proplatelet extensions. (A) Representative images of hematoxylin- and eosin-stained bone marrow from mice after treatment with daily IP panobinostat 10 mg/kg or vehicle for 4 days, demonstrating megakaryocytic hyperplasia in panobinostat-treated mice. (B) C57BL/6 mice were treated with daily IP panobinostat 10 mg/kg (Pan) or vehicle for 4 days. Bone marrow was harvested for histology, and the number of megakaryocytes seen in at least 10 × 40 high-powered microscopy fields were counted and plotted. Error bars represent SEM. Results were compared using the 2-tailed unpaired t test. (C) C57BL/6 mice were treated with daily IP romidepsin 1 mg/kg (Romi) or vehicle for 4 days, daily IP ABT-737 75 mg/kg for 4 days, or a carboplatin 100 mg/kg single dose IP on day 2. Shown are bone marrow megakaryocyte numbers in mice treated with daily IP romidepsin 1 mg/kg or vehicle, a carboplatin 100 mg/kg single dose, or daily IP ABT-737 75 mg/kg. Bone marrow was harvested for histology and the number of megakaryocytes seen in at least 10 × 40 high-powered microscopy fields were counted and plotted. Error bars represent standard error of the mean. Results were compared using the 2-tailed unpaired t test. (D) Murine fetal liver cells were cultured with 100 ng/mL of TPO for 3 days, after which time large megakaryocytes were collected using a 3%/1.5% BSA gradient. Megakaryocytes were plated out with 100 ng/mL of TPO alone or in the presence of 10nM panobinostat, 1nM romidepsin, or dimethyl sulfoxide in triplicate. The proportion of megakaryocytes elaborating proplatelets after treatment was counted for the next 3 days, with at least 500 cells counted for each sample. Error bars represent SEM. Results were compared using the 2-tailed unpaired t test.