(A) Combined effect of bor and BP determined by MTT assay. Mouse breast cancer 4T1 cells were treated with 0.5 µM BP, 5 µM BP, 1 nM bor, 10 nM bor alone or 0.5 µM BP + 1 nM bor 0.5 µM BP + 10 nM bor, 5 µM BP + 1 nM bor or 5 µM BP + 10 nM bor for 24 h. The number of viable cells was determined by MTT assay (n=3). (B) Combined effect of bor and BP determined by WST-1 assay. Cells were treated with 5 µM BP, 1 nM bor or 10 nM bor alone or 5 µM BP + 1 nM bor and 5 µM BP + 10 nM bor for 24 h. The number of viable cells was determined by WST-1 assay (n=8–9). Results are presented as the mean ± standard error of the mean. Mean values that do not share a letter in common are significantly different (P<0.05). BP, BAPTA-AM; bor, bortezomib; MTT, 3-(4,5-dimethylthylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide.