Effects of CK2 blockage on MM cell viability. (A) Top panels: MM cell lines (legend indicated at the far right) were grown for 48 hours in the absence or presence of increasing concentrations (as indicated) of the selective CK2 inhibitors. Viability was measured by the MTT method and is expressed as a percentage of vehicle-treated control. Bottom panels: Level of CK2 enzymatic activity was measured in MM cell (OPM2) lysates treated with the indicated concentration of inhibitors. For each inhibitor, results of 1 of 6 different experiments is shown; data are the mean ± SD. (B) Apoptosis of MM cell lines by CK2 blockage as measured by FACS analysis of annexin V/propidium iodide (AV/PI)-stained MM cells. Graph shows the survival (as AV-negative cells) of OPM2 and RPMI 8226 cells treated for 24 hours with 2 different doses of the CK2 inhibitor K27 (2.5 and 5 μM); data are the mean ± SD. (C) CK2α knock-down by RNA interference is associated with MM cell apoptosis. Left: Histogram shows the amount of AV-positive U266 MM cells after 96 hours from mock transfection or transfection with control (ctr) siRNAs or CK2α-specific siRNAs. Right: Western blot analysis of CK2α levels in mock, control (ctr) siRNA-, and CK2α-directed siRNA-transfected U266 MM cells. (D) Apoptosis of freshly isolated MM cells from patients on CK2 blockage. Top: Results of representative FACS experiment of AV/CD138 staining of freshly isolated BM cells from an MM patient (MM7) treated with K27 (5 μM); FACS analysis of apoptotic cells in the CD138⁺ and CD138^- fractions is shown. Bottom: Graph shows the percentage of apoptotic cells (in the malignant CD138⁺ and nonmalignant CD138^- populations) in freshly isolated PB or BM cells from 4 MM patients (MM1, MM2, MM4, MM7). Cells were treated with vehicle or K27, and apoptosis was assessed 8 hours later.