Effects of CDDO-Im on normal lymphocytes, patient MM (CD138⁺), and bone marrow stromal cells (BMSCs). (A) Normal lymphocytes from 5 healthy donors were treated with CDDO-Im (0-600 nM) for 24 hours, and viability was assessed by an MTT assay. Results are the mean ± SD of 3 independent experiments, P = .25 from Jonchkeere-Tepstra (J-T) test for trend. (B) MM cells (CD138⁺) from 5 patients (patients a-e) were treated with either CDDO (0.9 μM) or CDDO-Im (0.2 μM) for 24 hours, followed by analysis of cell viability using an MTT assay. Values are the mean ± SD of triplicate samples, P = .05; experiments were repeated 3 times with similar results. (C) CDDO-Im triggers apoptosis in BMSCs. Patient MM-derived BMSCs (patients a-c) were treated with CDDO-Im (200 nM) for 24 hours and analyzed for apoptosis using DNA fragmentation assays. Results are mean ± SD from triplicate samples, P = .002. (D) Effect of CDDO-Im on MM cell adhesion–induced IL-6 secretion. IL-6 levels were measured using IL-6 ELISA on supernatants obtained from 24-hour cultures of MM cells, BMSCs, and BMSCs + MM cells in the presence or absence of either CDDO-Im (200 nM) or bortezomib/proteasome inhibitor PS-341 (4 nM). Results are mean ± SD of 3 independent experiments.