LAUSR

Background The ubiquitin-proteasome pathway (UPP) plays a key role in the intracellular degradation of abnormal and misfolded proteins in eukaryotic cells. Multiple myeloma (MM) is a common hematologic malignancy caused by clonal expansion of malignant plasma cells. Proteasome-targeted drugs such as carfilzomib, which is a selective proteasome inhibitor (PI), could play an important role in the treatment of diseases such as MM. Methods MM cells were treated with different concentrations of carfilzomib and apoptosis as well as the viability of MM cells were measured by flow cytometry analysis and MTT assay. We also measured the effect of carfilzomib on the proliferation of myeloma cells by DNA incorporation of the pyrimidine analog BrdU. The effect of carfilzomib on apoptosis was detected by immunofluorescence TUNEL staining and western blot. We also verified its effect on the STAT1/COX-2/iNOS pathway by western blot. Results Carfilzomib inhibited the growth of MM cells in a concentration-dependent manner, with the strongest inhibitory activity on RPMI-8226 cells. Carfilzomib also induced apoptosis of MM cells in a concentration-dependent manner, with the strongest effect on RPMI-8226. BrdU assay was then performed with RPMI-8226 cells, and the results showed that carfilzomib inhibited cell proliferation in a concentration-dependent manner. Immunofluorescence TUNEL staining and western blot assays showed that carfilzomib induced apoptosis in a dose-dependent manner, and promoted the expression of apoptosis-related proteins such as cleaved-caspase-3, cleaved-caspase-3, Bax and Bcl2. Western blot also verified that carfilzomib promoted STAT1 inhibition and subsequently inhibited COX-2 and iNOS. Conclusions Inhibition of the STAT1/COX-2/iNOS signaling pathway by carfilzomib not only inhibited MM cell proliferation, but was also an important mechanism of inducing MM cell apoptosis.