Melphalan-resistant myeloma cells have less drug-induced growth inhibition and apoptosis compared with melphalan-sensitive cells. (A) MTT assay. Median inhibitory concentration (IC50) values are the mean of 3 independent experiments and SD. Student t test was used for statistical analysis. ^*P < .05. (B) Apoptosis assay. Melphalan treatment causes less apoptosis in drug-resistant 8226/LR5 and U266/LR6 cells compared with drug-sensitive 8226/S and U266/S cells. The mean values and standard deviations from a representative experiment performed in triplicate are shown. Student t test was used for statistical analysis. ^*P < .05.