Combination of Second-Generation Proteasome Inhibitor Carfilzomib with Bortezomib in Four Different Breast Cancer Cell Lines

Abstract

Background: Proteasome inhibitors target different pathways in cells and therefore are promising drugs in cancer therapy. The use of these inhibitors is approved mainly in hematological cancers, and recently many clinical trials and preclinical studies are running for efficacy in solid tumors. Carfilzomib is a second generation inhibitor and developed to decrease the side effects of bortezomib. Although there are many valid therapies in breast cancer, resistance and recurrence are inevitable in many cases and the proteasomal system plays an important roles in related pathways. Objective: This study is a preliminary work to evaluate the combination effects of bortezomib and carfilzomib in four different breast cancer cells. Methods: MDA-MB-231, MCF-7, UACC-2087, and SKBR-3 cell lines were used. Cell viability was determined by using bortezomib and carfilzomib alone and in combination. Combination effect values were determined using the Chou-Talalay method. Apoptosis, proteasome activity, cleaved PARP, and HSP70 expressions were analyzed in the determined doses. Results: The response to the combination of the two inhibitors was different in four cell lines. Apoptosis was significantly higher in combination groups compared to carfilzomib in three cell lines except SKBR-3, and higher in combination group compared to bortezomib only in UACC-2087. Combination decreased cleaved PARP levels in MDA-MB-231 and MCF-7 and increased in SKBR-3 compared to bortezomib. HSP70 levels decreased in combination with UACC-2087 and SKBR-3 compared to carfilzomib. Conclusion: Taken together, the combination of the two inhibitors was more apoptotic compared to carfilzomib and apoptosis was higher only in UACC-2087 compared to bortezomib. This apoptosis data can not be directly correlated to degree of proteaasome inhibiton, PARP cleavage and HSP70 response.