AZD6244 induces apoptotic signaling in MM cells adherent to BMSCs. (A) Dex-resistant MM1R cells were incubated for 2 days with serial dilutions of AZD6244 (0-10 μM), in the presence or absence of BMSCs, followed by caspase 3 activity assays. (B) CD138⁺ patient MM cells were incubated with AZD6244 (200 nM, ■) or control medium (□), in the presence or absence of BMSCs. Cytotoxicity was assayed by growth inhibition (left panel), and apoptosis was measured by caspase 3 activity assay (right panel). **P < .01 compared with control. (C) MM1S cells were cultured in BMSC-coated plates for 24 hours, in the presence or absence of AZD6244. MM1S cells were then harvested, lysed, electrophoresed, and immunoblotted for pERK, PARP, and caspase 3, with α-tubulin as loading control.