Different sensitivity levels of triple-negative breast cancer (TNBC) cells to the co-administration of poly (ADP-ribose) polymerase (PARP) and histone deacetylase (HDAC) inhibitors. (A) The cells were exposed to increasing doses of olaparib with a fixed concentration of suberoylanilide hydroxamic acid (SAHA) for 5 d. Cell survival was measured and the results are presented in a graph. (B) Cells were treated with olaparib and SAHA alone or in combination at the indicated concentrations for 5 d. DNA contents of the cells were analyzed with fluorescence-activated cell sorting. The proportion of cells undergoing the G2/M phase and apoptosis is presented in bar graphs. Columns represent the mean of three independent experiments and are shown with error bars (± SE); *P <0.001.