NPI-0052–induced cytotoxicity is enhanced in combination with bortezomib. (A) BCWM.1 cells were cultured with NPI-0052 (2.5, 5, and 10 nM) for 48 hours, in the presence or absence of bortezomib (5 and 10 nM). Cytotoxicity was assessed by MTT assay. (B) Representative isobologram of NPI-0052 associated to bortezomib with the CalcuSyn software demonstrating synergy for the combination. (C) Combination indexes (CIs) and fractions affected (FAs) of the combinations of NPI-0052 and bortezomib. All experiments were repeated in triplicate. (D) CD19+ primary WM cells were cultured with NPI-0052 (2.5, 5, and 10 nM) for 48 hours, in the presence or absence of bortezomib (5 and 10 nM). Cytotoxicity was assessed by MTT assay. (E) Representative isobologram of NPI-0052 associated to bortezomib with the CalcuSyn software demonstrating synergy for the combination. (F) Combination indexes (CIs) and fractions affected (FAs) of the combinations of NPI-0052 and bortezomib. All experiments were repeated in triplicate. (G) BCWM.1 cells were cultured with NPI-0052 (10 nM) in the presence or absence of bortezomib (10 nM) for 12 hours. Whole cell lysates were subjected to Western blotting using anti–caspase-8, –caspase-9, –caspase-3, -PARP, -Smac/DIABLO, -cIAP1, -XIAP, -survivin, -AIF, –p-eIF2α, -CHOP, –p-HSP27, -HSP27, -HSP70, -HSP90 and –α-tubulin antibodies.