Combination of HNK with bortezomib enhances cytotoxicity against MM.1S cells. (A) MM.1S cells were treated with HNK and bortezomib for 48 hours and cell growth was determined by colorimetric assay. Values represent the mean plus or minus SD of triplicate cultures (^*P < .05). (B) MM.1S cells were treated with HNK and bortezomib for 48 hours and induction of apoptosis was determined by APO2.7. Values represent the mean plus or minus SD of 2 independent cultures (^*P < .05). (C) MM.1S cells were treated with HNK and bortezomib for 8 hours. Whole-cell lysates were subjected to Western blotting to assess phosphorylation and protein expression of Hsp27, Hsp70, and Mcl-1.