Abstract 993: Upregulation of B-cell activation genes and negative regulators of apoptosis determines resistance to bendamustine in chronic lymphocytic leukemia cells.

Abstract

Chronic lymphocytic leukemia (CLL), the most common leukemia in Western countries, is characterized by the accumulation of monoclonal CD5+ B cells in the blood, bone marrow, lymph nodes, spleen and other lymphoid organs. Bendamustine hydrochloride, a cytotoxic agent comprising structural features of both an alkylating drug and a purine nucleoside analog, was recently approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of CLL and indolent B cell non-Hodgkin's lymphoma (NHL). Although several recent clinical trials have documented the activity of bendamustine in CLL, the mechanisms of bendamustine resistance in CLL cells have not been yet elucidated. We analyzed the ex vivo cytotoxicity of bendamustine in cells from 48 CLL cases by incubating them with bendamustine 25 μM for 24 hours. Cell death was assessed by annexinV-PI labeling and cases were classified as bendamustine-resistant (cytotoxicity below 30%) or bendamustine-sensitive (cytotoxicity over 30%) cases. We found that sensitivity of CLL primary cells correlated with the mutational status of IGHV gene, being the IGHV-unmutated cases significantly more resistant to bendamustine (p<0.015) than those cases with mutated IGHV. Although the number of cases analyzed was low, no correlation with the mutational status of NOTCH1 or SF3B1 was observed. We compared the gene expression profiling of bendamustine-resistant and bendamustine-sensitive groups by performing a high-throughput analysis of basal gene expression in CLL cells with the U219 Affymetrix array. After a supervised analysis using the Rank Products method and a FDR below 0.001, we observed 393 up-regulated genes and 415 down-regulated genes in the bendamustine-resistant group. Annotation of the differentially expressed genes identified some well-known markers of prognosis in CLL, together with genes related to apoptosis regulation and B cell activation. One of the genes with a highest positive fold-change and most relevant according to its role in cell cycle progression, apoptosis and transformation was C-MYC. These results suggest that overexpression of genes related to proliferation and B-cell activation could be involved in CLL resistance to bendamustine therapy, which is known to be clinically more effective in indolent than in aggressive lymphomas. Further studies will assess whether this set of overexpressed genes might be useful as biomarkers to predict the sensitivity to bendamustine and open the door to new combinatorial strategies that might overcome resistance to bendamustine in CLL patients within the context of tailored medicine Citation Format: Eriong Lee-Verges, Arnau Montraveta, Magda Pinyol, Pedro Jares, Cristina Arimany-Nardi, Marta Aymerich, Neus Villamor, Marçal Pastor-Anglada, Armando Lopez-Guillermo, Patricia Perez-Galan, Gael Roue, Elias Campo, Dolors Colomer. Upregulation of B-cell activation genes and negative regulators of apoptosis determines resistance to bendamustine in chronic lymphocytic leukemia 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 993. doi:10.1158/1538-7445.AM2013-993