Abstract 1758: Influence of stromal microenvironment on rGel/BLyS-induced cytotoxicity in diffuse large B-cell lymphoma cells

Abstract

Abstract Diffuse large B cell lymphoma (DLBCL) is an aggressive sub-type accounting for 30-40% of non-Hodgkin's lymphoma. Despite recent advances in the understanding of the molecular and cellular basis for their pathogenesis, these tumors are still associated with poor response to treatment and a fatal outcome. The interactions of marrow stromal cells (MSCs) with tumor cells appear to be important in the development of tumor drug resistance through complex cytokine and adhesion-mediated mechanisms. We previously generated a highly cytotoxic growth factor fusion toxin designated rGel/BLyS for receptor-mediated delivery of the rGel toxin to malignant B cells. This fusion toxin specifically targets malignant B cells expressing the BLyS receptors BAFF-R, TACI, and BCMA. In this study, we examined the impact of marrow stromal cells (MSCs) on rGel/BLyS-induced cytotoxicity in DLBCL cells. Treatment of tumor cell lines with dexamethasone and doxorubicine in the presence of MSCs was found to suppress the cytotoxic effect. In contrast, in vitro treatment with rGel/BLyS showed specific cytotoxic effects to DLBCL cell lines (IC50 ∼ 1-10 nM) in absence of MSCs or in presence of MSCs. At these doses, we found no cytotoxicity to MSCs. Treatment with rGel/BLyS induced down-regulation of Mcl-1, c-Myc, Bcl-xL, X-IAP, and Bcl-2 in DLBCL cells in absence of MSCs or in presence of MSCs. We also found that rGel/BLyS induced down-regulation of interleukin-6 receptor in DLBCL cells in absence of MSCs or in presence of MSCs. In addition, treatment of cells with rGel/BLyS induced apoptosis through caspase-9 activation, caspase-3 activation, and PARP cleavage. Our results demonstrate that rGel/BLyS can overcome stromal cell-mediated drug resistance which is a factor reducing the effectiveness of other conventionally-used agents for the treatment of this disease. This suggests that rGel/BLyS may be an excellent candidate for the treatment of DLBCLs which are resistant to conventional chemotherapeutic regimens. This research was conducted, in part, by the Clayton Foundation for Research and by Translational Research Award (LLS 6234-07) from the Leukemia and Lymphoma Society. 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 1758. doi:10.1158/1538-7445.AM2011-1758