Effect of NF-κB inhibition on apoptosis in MM cells.

NF-κB inhibition induces apoptosis in MM cells. (A) (B) Dose-response survival curves based on MTT colorimetric assay were generated for MM cells and healthy donor B cells cultured for 18 hours with SN50 (0 to 25 μM). Data shown (absorbance at 570 nm, mean ± SD) are representative of 3 experiments. Panel A shows dexamethasone-sensitive MM.1S (▴) and dexamethasone-resistant MM.1R (●) cells; RPMI-8226/S (▪) and its cytotoxic drug–resistant subline Dox40 (filled diamond) cells; and OCI-My5 (▵) and MM-AS (■) cells. Panel B shows EBV-transformed ARH-77 (▵) cells, HS Sultan (▴) cells, and IM-9 (■) cells; freshly isolated patient MM cells (▪); and healthy donor peripheral blood B cells (filled diamond). SN50 induced concentration-dependent cell death in 7 of 9 cell lines, including MM cell lines resistant to dexamethasone or doxorubicin, as well as in freshly isolated patient MM cells. In contrast, normal peripheral B cells were resistant to SN50-induced cell death. (C) (D) Annexin–PI staining of MM.1S cells cultured without (panel C) or with (panel D) SN50 (20 μM) for 4 hours revealed early externalization of phosphatidylserine in MM.1S cells treated with SN50 for 5 hours, confirming that SN50 induced apoptosis. (E) The proapoptotic activity of the NF-κB inhibitor SN50 (▴) was compared with its mutant (2 amino-acid residue difference), inactive analog SN50M (▪) in MM.1S cells. Data shown (absorbance at 570 nm, mean ± SD) are representative of 3 experiments. Loss of NF-κB inhibitory activity abolishes anti-MM activity.