Cotreatment with ABT-737 and panobinostat synergistically induces apoptosis of CTCL cells. (A) HH and MJ cells were treated with panobinostat and/or ABT-737 (1000 nM) for 24 hours. Total cell lysates were prepared and immunoblot analysis was done for cleaved PARP. The levels of β-actin in the lysates served as the loading control. (B) HH and primary normal CD34⁺ cells were treated with the indicated concentrations of panobinostat and/or ABT-737 for 48 hours. Then, the percentages of nonviable cells were determined by trypan blue dye uptake in a hemocytometer. Values represent the percentage of nonviable cells from each condition compared with untreated cells. Columns represent mean of 3 experiments; bars, standard error of the mean. (C) MJ cells were treated with the indicated concentrations of ABT-737 and panobinostat for 48 hours. Following this, the percentage of apoptotic cells was determined by flow cytometry. Columns represent mean of 3 experiments; bars, standard error of the mean. (D) HH and MJ cells were treated with panobinostat and/or ABT-737 at a fixed ratio of 1 to 10 (with concentrations ranging from 10-100 nM panobinostat) for 48 hours. Then, the percentage of apoptotic cells was determined by flow cytometry. Using Calcusyn software (Biosoft), the analysis of the dose-effect relationship for panobinostat and ABT-737–induced apoptosis of HH or MJ cells was performed according to the median effect equation of Chou and Talalay. The combination index (CI) values were calculated for 3 independent experiments. CI less than 1, CI = 1, and CI more than 1 represent synergism, additivity, and antagonism of the 2 agents, respectively.