Abstract 1021: Bortezomib-mediated inhibition of NF- κB activity leads to induction of apoptosis in activated B-cell like diffuse large B-cell lymphoma

Abstract

Abstract Diffuse large B-cell lymphoma (DLBCL) is considered to be the most common type of lymphoma in adults, accounting for 30-40% of cases of non-Hodgkin lymphoma, and classified as three distinct subtypes: germinal center B cell-like (GCB)-, activated B cell-like (ABC)-, and primary mediastinal B-cell lymphoma (PMBL). ABC DLBCL has a worse survival after upfront chemotherapy and is characterized by constitutive activation of the antiapoptotic nuclear factor-kappa B (NF-κB) pathway. Yet the implication of NF-κB inhibition in ABC DLBCL need to be further elucidated. Therefore, a panel of ABC DLBCL cell lines was used to examine the effect of bortezomib, a proteasome inhibitor which blocks degradation of phosphorylated IκBα and consequently inhibits NF-κB activity, and small interfering RNA (siRNA) on cell viability, apoptosis and downstream signaling pathway. Our data showed that bortezomib caused a dose-dependent growth inhibition in all cell lines studied. The IC 50 was 3.33 ± 0.29 nM, 2.73 ± 0.32nM, 2.60 ± 0.87nM and 4.35 ± 0.65nM for HBL-1, Riva, Sudhl-2 and OCI-LY3 respectively. Cell cycle assay showed a dose-dependent increase of sub-G1 population of all four cell lines studied after 48 hours treatment, and this increase in sub-G1 population was accompanied by a dose-dependent decrease in the percentage of cells in the G2-M phase indicating the feature of apoptosis. Further experiment using FITC-conjugated Annexin V and PI assay confirmed that apoptotic cell increased in a dose-dependent manner in all cell lines after 48 hour treatment. Moreover, the electrophoretic mobility shift assay showed that bortezomib treatment inhibited constitutive nuclear NF-κB in ABC cell lines. Furthermore, treatment of ABC cell lines with bortezomib or expression of small interfering RNA of NF-κB also down-regulated expression of NF-κB-regulated gene products, such as IκBα, Bcl-2, Bcl-Xl, XIAP and Survivin leading to apoptosis via the mitochondrial apoptotic pathway. Altogether, these results suggest that NF-κB may be a potential target for therapeutic intervention in DLBCL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1021. doi:10.1158/1538-7445.AM2011-1021