Combination of bendamustine and entinostat enhances DNA damage response. MM cells were cultured with RPMI1640 (0.5% FBS) in the absence or presence of entinostat (Ent), bendamustine (Benda) alone or the combinations of entinostat and bendamustine for 24 h. Cells were collected and subjected to western blot analyses with specific antibody directed against P-H2AX, H2AX, P-CHK1, CHK1, P-CHK2, CHK2 or β-actin. (A) U266; (B) MM1.S; (C) MM1.R.