Cotreatment with LBH589 and AMN107 inhibits more colony growth than either agent alone and induces synergistic apoptotic effects. (A) K562 cells were treated with the indicated concentrations of LBH589 and/or AMN107 for 48 hours. Following this, colony growth in semisolid medium was assessed after 7 days. The bar graphs represent the mean percentage values ± SEM of untreated control colony growth. K562 cells (B) and LAMA-84 cells (C) were treated with LBH589 and AMN107 at a fixed ratio of 1 to 2, respectively, with concentrations ranging between 10 and 100 nM, for 48 hours. Following this, the percentage of annexin V–stained apoptotic cells was determined by flow cytometry. Using Calcusyn software (Biosoft), the analysis of the dose-effect relationship for LBH589 and AMN107-induced apoptosis of K562 or LAMA-84 cells was performed according to the median effect method of Chou and Talalay.39 The combination index (CI) values were calculated for 3 independent experiments. CI < 1, CI = 1, and CI > 1 represent synergism, additivity, and antagonism of the 2 agents, respectively.
