Molecular effects of CK2 blockage in MM cells. (A) Western blot shows the molecular consequences of CK2 inhibition in MM cells: cleavage of pro-caspases 8, 9, and 3 and of the downstream target PARP on treatment of OPM2 cells with increasing concentrations of K27 for 12 hours. (B) Western blot shows mitochondrial apoptotic mediators cytochrome c and SMAC/DIABLO release in the cytosol of OPM2 and RPMI 8226 cells treated with the indicated increasing concentrations of K27 for 12 hours. (C) CK2 blockage lowers the threshold of sensitivity to the cytotoxic effect of melphalan of MM cells. OPM2 cells were treated with the indicated increasing doses of melphalan in the absence (▪) or in the presence of subtoxic doses of the CK2 inhibitor K27 (0.3 μM, □;1 μM, ) and were subjected to MTT-based viability assay 48 hours later. Data are the mean ± SD. ^**P < .05; ^*P < .02.