CpdA overcomes drug resistance and induces chemosensitization. (A) Multiple myeloma cell lines RPMI 8226, RPMI 8226/LR5, RPMI 8226/Dox40, U266, U266/LR6, ANBL-6, ANBL-6/B7R, MM1.S, and MM1.R were cultured with CpdA for 3 days, and cell viability was determined as described previously. Data represent the mean IC50 plus or minus SD of triplicate cultures. (B) RPMI 8226 cells were treated with the indicated concentrations of bortezomib alone or together with 10 or 15 μM of CpdA for 24 hours, and then analyzed for viability using the WST-1 assay (top panel). CI values are shown in the table (bottom panel), with values of 0.9 or less indicating synergy. (C) IL-6–dependent KAS-6/1 myeloma cells were treated with bortezomib or CpdA alone or together for 24 hours, and then analyzed for staining with annexin V–FITC and TO-PRO-3 by flow cytometry. The proportion of cells present in the respective quadrants is indicated inside each of the panels, including viable cells (FITC−/To Pro3−), early apoptotic cells (FITC+/To Pro3−), and late apoptotic or necrotic cells (FITC+/To Pro3+). (D) MM.1S myeloma cells were plated either in the absence or presence of HS-5/GFP stromal cells, and then exposed to the indicated concentrations of CpdA or bortezomib for 18 hours or dexamethasone for 48 hours. The proportion of viable cells was then evaluated by flow cytometry. Specific cell death is represented as the mean plus or minus SD of triplicate experiments.
