Vorinostat induces apoptosis in cells expressing JAK2V617F. BA/F3-EpoR cells expressing JAK2WT, JAK2V617F, and human HEL, UKE-1, and K562 cells were treated with DMSO or various concentrations of vorinostat (0.25-1.0μM) for 24 hours. (A) Apoptosis was determined by staining with propidium iodide and annexin V, followed by flow cytometric analysis. Results shown are representative of 3 independent experiments. Note that vorinostat treatment significantly increased apoptosis in JAK2V617F⁺ cells. (B) Cell-cycle distribution of HEL and K562 cells after 24 hours of exposure to vorinostat (1.0μM). Cell-cycle analysis was performed by propidium iodide staining and analyzed by ModFit software. Results from 3 independent experiments are shown as means ± SEM. Asterisks indicate significant differences (P < .05) between vehicle and vorinostat-treated cells. Note that vorinostat-treated HEL cells were arrested at the G_0/G₁ phase and there was a significant decrease in the percentage of cells in the S phase.