Combined NPI-0052 and bortezomib triggers synergistic antitumor activity in MM patient (CD138⁺) cells and other cancer cell types. (A) Purified patient MM cells (CD138⁺) were treated with the indicated concentrations of NPI-0052, bortezomib (3 nM), or combined NPI-0052 plus bortezomib and assessed for viability using MTT assays. Data represent means plus or minus SD of triplicate samples (P < .05 for all patient samples). A CI of less than 1 indicates synergy. PBMNCs from healthy donors were treated with indicated concentrations of NPI-0052, bortezomib, or NPI-0052 plus bortezomib and then analyzed for viability. Data are means plus or minus SD of 3 independent experiments (P = .25 from J-T test for trend). (B) MTT assays were performed after incubation of leukemia, lymphoma, pancreatic, and breast cancer cells with NPI-0052, bortezomib, or combined NPI-0052 plus bortezomib. The concentrations of agents for cell lines were as follows: Molm-14, SUDHL-4, and Panc-1 cells: 7 nM bortezomib, 7 nM NPI-0052, or NPI-0052 (7 nM) plus bortezomib (7 nM); MCF-7 cells: 10 nM bortezomib, 3 nM NPI-0052, or NPI-0052 (3 nM) plus bortezomib (10 nM). Data presented are means plus or minus SD (n = 2; P < .05 for all cell lines).