Figure 2. HO-1 inhibition enhances myeloma cell sensitivity to bortezomib. (A, B) Effects of bortezomib on the viability and apoptosis of U266 cell. Cells were treated with the indicated doses of bortezomib for 24 h and the percentage of cell viability was assessed by the CCK8 assay relative to an untreated control. (C, D) Effects of bortezomib on the viability and apoptosis of RPMI8226 cell. (E, F) Effects of ZnPPIX on the viability and apoptosis of myeloma cells in the presence of bortezomib. Cells were treated with the indicated doses of ZnPPIX plus bortezomib for 24 h. Data are presented as mean ± SD (n = 4). *P < 0.05 vs. control group (0 nM). (G–I) CCK8 showing the cell viability of human primary CD138+ cells treated with bortezomib alone (control group) or bortezomib plus ZnPPIX. n=5, *P<0.05. (J) Cell apoptosis (Q2+Q3) of human primary CD138+ cells assessed by flow cytometry after treatment with or without ZnPPIX for 24 h.