Melphalan-induced HR activity in MM cells is reversed by nilotinib. (A) MM.1S cells were treated with different concentrations of melphalan and evaluated for RAD51 expression by western blotting (top panel) and HR activity (bottom panel). (B) HR activity assessed in MM.1S cells treated with nilotinib (2.5 μM), melphalan (5 μM), and a combination of both drugs for 48 hours. Error bars indicate SDs of experiments conducted in triplicate and 2-tailed P values are derived by t test (∗P < .05-.001; ∗∗P < .001). SD, standard deviation. D, DMSO; M, melphalan; M+N, melphalan and nilotinib; N, nilotinib.