Abstract 3389: Nuclear accumulation of c-Rel transcription factor is correlated with the proteasome inhibitor resistance in mantle cell lymphoma.

Abstract

Abstract Purpose: Nuclear factor kB (NF-kB) plays essential roles in survival and drug resistance of multiple malignancies including mantle cell lymphoma (MCL) and multiple myeloma (MM). Proteasome inhibitors have been shown to block constitutively active NF-kB and clinical data indicates a high overall response of MCL and MM patients to this treatment. The 2nd generation proteasome inhibitor, carfilzomib (CFZ), has a therapeutic effect on relapsed or refractory disease and low toxicity to normal lymphocytes. However, there are increasing numbers of proteasome inhibitor-resistant cases. Thus, this study was designed to identify the molecular mechanism that leads to CFZ-resistance. Experimental design: In this study we have determined the cytotoxic effect of CFZ in a panel of MM and MCL cell lines, as well as primary tumor cells. The cell growth inhibition was assessed by the thymidine intake and MTT assay. NF-kB activity was examined by electrophoretic mobility shift assay (EMSA) using nuclear extracts from CFZ-treated and control cells. Nuclear pattern of NF-kB family members, such as RelA/p50, cRel/p50 and RelB/p52 complexes, was analyzed by supershift and western blot. Results: CFZ-induced NF-kB inhibition was not observed in two (out of eight) examined cell lines, even with the highest doses (100 nM). Consistently, cell growth was suppressed only in cells with a CFZ-sensitive NF-kB activity (IC50<20 nM), as shown by EMSA and MTT assay. In contrast, the treatment with proteasome inhibitor increased the nuclear accumulation and DNA binding of NF-kB in CFZ-resistant cells. Furthermore, we have found that only these cells had upregulated c-Rel/p50 member of NF-kB family. Supershift analysis revealed that all examined cell lines and primary cells had constitutively active classical (RelA/p50 dimer) and/or non-classical (RelB/p52 dimer) NF-kB, excluding CFZ-resistant cells with prominent nuclear accumulation of c-Rel. This data suggests that activated c-Rel may trigger resistance to CFZ. Enhanced nuclear accumulation of c-Rel is also an unwanted molecular consequence of exposure to CFZ. Conclusion: Our work indicates the need for new treatment strategies in c-Rel-positive cases. A strategic combination targeting different signaling mediators, especially upstream of c-Rel, would enhance the ultimate anticancer effect. Citation Format: Marzenna Blonska, Deng Pan, Zhishuo Ou, Liang Zhang, Xin Lin, Michael Wang. Nuclear accumulation of c-Rel transcription factor is correlated with the proteasome inhibitor resistance in mantle cell lymphoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3389. doi:10.1158/1538-7445.AM2013-3389