Abstract 3378: The rGel/BLyS fusion toxin can overcome chemoresistance in malignant B cells..

Abstract

Abstract Diffuse large B cell lymphoma (DLBCL) is an aggressive sub-type accounting for 30-40% of non-Hodgkin's lymphoma. Approximately 95% of B cell lymphoma expresses CD20 and 26% of relapsed B-cell lymphoma patients demonstrate reduced CD20 expression on tumor cells after treatment with the anti-CD-20 antibody rituxumab. This result suggests that novel agents that can overcome rituximab resistance may be an excellent candidate for the treatment of DLBCLs which are resistant to rituximab. MCL and ABC-DLBCL cell lines (SP53, Mino, OCI-Ly3, OCI-Ly10 and U2932) were resistant to rituximab whereas GC-DLBCL cell lines (SUDHL-4 and SUDHL-6) were very sensitive to rituximab. To understand the mechanism of rituximab resistance, we developed rituximab-resistant SUDHL-6 cell line. Compared with parental rituximab-sensitive cells (SUDHL-6-S, IC50=0.2 μg/ml), rituximab-resistant cells (SUDHL-6-R, IC50 > 1,000 μg/ml) demonstrated ∼5,000 fold resistance. The rituximab-sensitive cells formed single-cell suspensions whereas resistant cells demonstrated cell aggregates. We previously generated a highly cytotoxic fusion toxin designated rGel/BLyS for receptor-mediated delivery of the rGel toxin to malignant B cells. The rituximab-sensitive (SUDHL-6-S) and resistant (SUDHL-6-R) both cells showed similar IC50 values (150 nM) for rGel/BLyS. In contrast, intrinsically rituximab-resistant cell lines (SP53, Mino, OCI-Ly3, OCI-Ly10 and U2932) were also sensitive to rGel/BLyS. Treatment with rituximab specifically induced down-regulation of p-Akt (Ser473), Akt, and Syk and activation of caspase-9, caspase-3 and PARP in a dose-dependent manner in rituximab-sensitive cells (SUDHL-6-S) but not rituximab-resistant cell lines (SUDHL-6-R, OCI-Ly3, or OCI-Ly10). 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. Treatment with rGel/BLyS induced down-regulation of p-Akt, Akt, Syk, interleukin-6 receptor, Mcl-1, and c-Myc in rituximab-resistant DLBCL cells in both the absence and presence of MSCs. In addition, treatment of cells with rGel/BLyS induced apoptosis through caspase-9 activation, caspase-3 activation, and PARP cleavage. These results suggest that the Akt pathway is involved in rituximab resistance and 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 DLBCLs which are resistant to rituximab. This research was conducted, in part, by the Clayton Foundation for Research. Citation Format: Mi-Ae Lyu, Lawrence H. Cheung, John W. Marks, Michael G. Rosenblum. The rGel/BLyS fusion toxin can overcome chemoresistance in malignant B cells. [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 3378. doi:10.1158/1538-7445.AM2013-3378