Upregulation of Bim by SBHA potentiates ABT-737 lethality in bortezomib-resistant MM cells. (A-D) Bortezomib-resistant PS-R or 8226/VR cells were treated with ABT-737 (PS-R, 500 nM; 8226/VR, 300 nM) with or without the indicated concentrations (μM) of SBHA for 48 hours or 24 hours, respectively. After drug treatment, immunoblotting analysis and flow cytometry were performed to determine (A,B) levels of Bim and cleavage of caspases and PARP or (C,D) percentage of apoptosis. (E) Primary CD138⁺ cells were isolated from a bone marrow sample from a patient with relapsed MM. Cells were then treated with the indicated concentrations of ABT-737 (nM) with or without SBHA (μM) for 24 hours, after which flow cytometry was conducted to monitor percentage of early (annexin V⁺/PI^–) and late (annexin V⁺/PI⁺) apoptosis. Values indicate the percentage of total annexin V⁺ cells. Parallel experiments were performed in additional primary samples derived from newly diagnosed MM patients or relapsed patients after treatment with bortezomib (arrowhead) (n = 6; 3 each for diagnosis and R patients). P < .05 for combination treatment vs each single agent. A+S, ABT-737 + SBHA; PI, propidium iodide.