Abstract 4501: Sensitivities of kinase inhibitors of BCR signaling are correlated with the BCR signaling pathway activities in DLBCL and CLL
Authors: Obidi Joyce O. , Burke Patricia , Richman Laura , Mendel Dirk , Bao Haifeng 
Published: May 2015

Abstract
B-cell malignancies are hematologic disorders for which new therapeutic agents and novel treatment strategies are evolving. B cell receptor (BCR) signaling plays an important pathogenic role in diffuse large b-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL). There is rapid clinical development of inhibitors targeting BCR-associated kinases such as Spleen tyrosine kinase (SYK), Bruton's tyrosine kinase (BTK), and phosphoinositide 3-kinase (PI3K)δ. Recent clinical studies using these agents have demonstrated effectiveness and low toxicity in CLL and DLBCL patients with relapsed/refractory disease. With a great response rate, there are still a group of patients that do not respond to these therapeutic agents. The goal of this study is to investigate potential resistance mechanism(s) of BCR pathway inhibitors based on signature-signaling profiles. 21 CLL and DLBCL cell lines with different molecular features were assessed in this study to establish relevant signaling features and their association with sensitivities to BCR signaling inhibitors. First, we evaluated response of cell lines to small molecule inhibitors targeting the BCR signaling pathways (PCI-32765, R406, CAL 101, and Dasatinib). 28% (6/21) of the cell lines were resistant to PCI-32765; we found that these cells lines were also non responsive to CAL 101 and Dasatinib. Then we used phosphoflow assays and phosphoprotein arrays to profile BCR signaling in both responsive and non-responsive cell lines. The BCR signaling activities were assessed at baseline, after stimulation with IgG-IgM, and following pretreatment with phosphatase inhibitors. Interrogating pathway activity in cell lines with pervanadate, a phosphatase inhibitor, was especially revealing. After treatment with pervanadate, we observed an increase in phosphorylation status of SYK, BTK, p38, and S6 in normal B cells. However, 24% of tumor cell lines do not exhibit phosphorylation of BCR related proteins, SYK and BTK, after pervanadate treatment. Moreover, 83% (5/6) of cell lines resistant to PCI 32765 (IC50 &gt; 20μM) did not respond to pervanadate, whereas only 12.5% (1/8) sensitive cell lines (IC50 &lt; 2.5uM) did not respond to pervanadate. The difference observed in these cell lines indicates tumor cell lines with an abnormal BCR signaling may not be dependent upon BCR signaling for survival. More studies are being conducted to confirm this observation in patient samples and to further explore the molecular causes of the abnormal BCR signaling. We also explore combination treatments of PCI-32765, CAL-101 and other target therapy agents, which may provide useful insights for the optimal therapeutic use of these BCR signaling inhibitors in CLL and DLBCL. Overall, our results suggest that profiling of signaling network activities represents a promising approach to molecularly classifying DLBCL and CLL subtypes for target therapies.
Citation Format: Joyce O. Obidi, Patricia Burke, Laura Richman, Dirk Mendel, Haifeng Bao. Sensitivities of kinase inhibitors of BCR signaling are correlated with the BCR signaling pathway activities in DLBCL and CLL. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4501. doi:10.1158/1538-7445.AM2014-4501