Combined entinostat and lapatinib at clinically relevant doses inhibited the cell cycle and induced apoptosis. a Cells (2×105) were placed on a 6-well plate overnight and then treated with or without the drugs (entinostat, 1.0 μM for all cell lines; lapatinib, 1.0 μM for SUM190 and 0.1 μM for BT474) for 48 hours. After the cells were collected, a PI staining assay was performed for cell-cycle analysis using flow cytometry. b Cells (2×105) were placed on a 6-well plate overnight, and then treated with or without the drugs (entinostat, 1.0 μM for all cell lines; lapatinib, 1.0 μM for SUM190 and 0.1 μM for BT474) for 48 hours. An Annexin V/7AAD staining assay was performed for detection of apoptosis using flow cytometry. * p <0.05 combination compared with lapatinib. ** p <0.01 combination compared with either control or entinostat. Data shown are representative of 3 experiments with similar results.