Romidepsin-resistant HuT78 cells are resistant to multiple HDIs. (A) HuT78, DpVp35, DpVp50, and DpP75 cells were incubated with 1, 10, or 100 ng/mL romidepsin (Dp) for 48 hours, after which cells were incubated with anti-annexin V antibody and propidium iodide (PI) as outlined in “Materials and methods.” The percentage of live cells is shown in the lower left quadrant. The percentage of annexin-positive cells was derived from the upper and lower right quadrants. (B) HuT78, DpVp35, DpVp50, and DpP75 cells were treated with the noted concentrations of romidepsin, apicidin, entinostat, vorinostat, belinostat, or panobinostat for 48 hours, and percent annexin-positive cells are presented. Results from at least 3 independent experiments are shown.