Abstract 1033: Distinct response of chronic lymphocytic leukemia cells to PI-3Kδ inhibitor GS-1101 is related to MAPK signaling and likely associated with IGHV mutation.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background: PI3Kδ is expressed and regulates survival and proliferation of malignant B-cells. The PI-3Kδ inhibitor, GS-1101, has promising therapeutic efficacy in chronic lymphocytic leukemia (CLL) through inhibiting B-cell receptor signaling, PI3K signaling and chemokine networks. It is currently in clinical trials either as monotherapy or in combination with others therapies. Here we report the exploration of the signaling molecules which are related to distinct response of CLL cells to GS-1101. Methods: Cells isolated from peripheral blood of CLL patients were treated with GS-1101 and analyzed by flow cytometry based apoptotic assay. Human Phospho-Kinase Array (R&D Systems) was performed with CLL cells which had distinct response to GS-1101. RNA or genomic DNA was isolated and analyzed for IGHV somatic hypermutation (InVivoScribe Technologies). Sequences containing more than 2% deviation from the germline sequence were considered as somatically hypermutated. Results: To date, 20 CLL cases have been tested for their in vitro response to GS-1101. In comparison to the control group, GS1101-exposed CLL cells displayed a wide range of apoptotic cells (3 to 59%). 3 cases with high levels apoptosis in response to GS-1101 were subjected to Human Phospho-Kinase Array screening. These showed down regulation of p-ERK1/2(T202/Y204), p-P38α(T180/Y182), MEK1/2 (S218/S222), among tested 46 kinases’ phosphorylation sites, upon GS-1101 exposure. Two of the three cases also showed down-regulation of p-STAT5(Y699). In contrast, no alteration or minor up-regulation of the above 4 targets was observed in a GS-1101 non-responsive case. Currently we are performing immunoblotting assay to evaluate/confirm the alteration of above targets in multiple CLL cases and preliminary p-P38 expression data is consistent with that of array assay. 15 of the tested 20 CLL samples had high quality of IGHV sequence data from both directions which cover the entire variable region of IGH (FR1, CDR1, FR2, CDR2 and FR3). Nine cases were IGHV unmutated with a mean of GS1101 caused apoptotic induction of 25.3% (range 5-59%); while the mean of apoptotic induction of the 6 cases with somatic hypermutation was 12.5% (range 3 - 32%). The p value of the unmutated verse mutated group was 0.046 (T-test). Conclusion: Our preliminary studies suggest that GS-1101-induced apoptosis is associated with alterations in the MAPK signaling pathway. Combination of GS-1101 with MAPK inhibitor may be rational for further synergy study. GS-1101 may have differential activity against IGHV unmutated CLL cases compared to IGHV mutated ones. Ongoing studies with additional cases will further evaluate this observation. Profiling CLL cells for IGHV mutation status might be a strategy to predict CLL patients’ response to GS-1101 in clinical trials. Citation Format: Xiaoxian Zhao, Juraj Bodo, Eric D. Hsi. Distinct response of chronic lymphocytic leukemia cells to PI-3Kδ inhibitor GS-1101 is related to MAPK signaling and likely associated with IGHV mutation. [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 1033. doi:10.1158/1538-7445.AM2013-1033