GX015-070 is active against dexamethasone or melphalan-resistant HMCLs and has an additive effect with antimyeloma drugs, dexamethasone, melphalan, or velcade. HMCLs were treated with bortezomib (Btz), melphalan (Mel), dexamethasone, and/or GX015-070 (Gx) at the indicated concentrations. To determine cell viability, MTT assays were performed after 48 hours of treatment and the data were normalized as percent of untreated control. (A) Dexamethasone-sensitive MM1.S or -resistant MM.1R cells were cultured with dexamethasone (▵), GX015-070 (♦), or dexamethasone + GX015-070 (■). (B) Similarly, melphalan-sensitive (8226s) or melphalan-resistant (8226 LR5) cell lines were treated with melphalan (▵), GX070-015 (♦), or melphalan + GX015-070 (■). (C) Finally, 8226 cells were cultured in the presence of bortezomib (▵), GX015-070 (♦), or bortezomib + GX015-070 (■). For these experiments, bortezomib and GX015-070 were added simultaneously (left panel), GX015-070 was added after overnight incubation with Btz (center panel), or Btz was added after overnight incubation with GX015-070 (right panel). Values represent means of triplicate cultures ± SD.