AZD6244 induces MM-cell cytotoxicity in the presence of IL-6 or BMSCs. (A) CD138-purified patient MM cells were treated with AZD6244 (20 nM) in the presence or absence of IL-6 (10 ng/mL). Cytotoxicity (growth and viability) was measured by [³H]thymidine uptake and MTT assay. **P < .01 compared with control. (B) INA-6 MM cells were treated for 2 days with serial dilutions of AZD6244 (0-10 μM) in the presence or absence of BMSCs, followed by MTT assay (left panel) and caspase 3 activity assay (right panel). Data represent mean (+ SE) of triplicate cultures; au indicates arbitrary unit. (C) Freshly purified CD138⁺ tumor cells from 3 MM patients were cultured with AZD6244 (200 nM, ■) or control medium (□), alone or with BMSCs. Cytotoxicity was determined by [³H]thymidine incorporation assay (MM1 and MM3) or MTT assay (MM2). (D) MM1S cells were treated with AZD6244 (0.2-20 μM) for 2 days in the presence or absence of BMSCs, and supernatants were assayed for IL-6 by ELISA. (E) BMSCs derived from MM patients were incubated for 2 days with AZD6244 (0.5-500 μM) in triplicate and then subjected to MTT assay. Results represent mean (+ SE) of BMSCs from 3 patients.