Abstract 2366: Targeting PI3 pathway in ibrutinib resistant diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma (NHL) and approximately 30% of patients with DLBCL develop relapsed/refractory disease that becomes a major cause of mortality and morbidity. The Bruton kinase (BTK) inhibitor ibrutinib successfully blocks B-cell receptor signaling and shows clinical benefit in leukemia and lymphomas, including mantle cell lymphoma (MCL) and DLBCL. Ibrutinib elicits overall desirable response rate with relapsed/refractory MCL and ABC DLBCL. However, in spite of these encouraging results, responses are variable and generally incomplete, acquired resistance is common, and recurrence and persistence of lymphoma is a problem. We undertook a study of factors underlying acquired ibrutinib resistance (IR) in initially ibrutinib-sensitive DLBCL cell lines. In this study, IR DLBCL cell lines were generated by continuous culturing of parental (PT) cell lines in increasing concentrations of ibrutinib. Once established, IR cell lines were removed from ibrutinib, expanded, and cultured under the same conditions as the PT cell lines for further experiments. Of 5 ABC DLBCL cell lines tested, two (OCI-LY3, U2932) were initially resistant to ibrutinib (IC50>10µM).Three (TMD8, OCI-LY10, HBL1) were sensitive (IC50 < 10 nM). In comparison to PT versions of these cell lines, IR cells did not form clumps in suspension cultures, displayed irregular cell morphology, showed elevated colony formation ability in methylcellulose matrix, and had a higher proliferation rate. Western blots and gene expression profile analysis showed increased expression by IR cell lines of inhibitors of apoptosis (IAP) family members, survivin, cIAP2, and oncogenic BCL2 and BCL6. The DNA damage repair pathway was found to be elevated with enhanced expression of CHK1 kinase. IR cell lines had reduced BTK expression without acquiring mutations, and downstream enhanced PI3K-Akt signaling. Analysis of PI3K isoforms revealed up-regulation of PI3Kα and PI3Kβ with decreased expression of PI3Kδ and PTEN (PI3K negative regulator). Given the enhanced PI3K isoform expression with IR, we treated IR cell lines with the PI3Kβ/δ isoform-targeting drug KA2237 and observed reduced metabolic activity (survival) of PT cell lines and further reduction of surviving IR cell lines. In conclusion, this study highlights how changes in a regulator (PTEN) and mediator (p110β) of PI3K/AKT signaling have important roles in the development of ibrutinib resistance in DLBCL. Treatment with KA2237 may provide a better outcome for ibrutinib-resistant DLBCL. Note: This abstract was not presented at the meeting. Citation Format: Neeraj Jain, Lalit Sehgal, Stephen Joseph Shuttleworth, Felipe Samaniego. Targeting PI3 pathway in ibrutinib resistant diffuse large B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2366. doi:10.1158/1538-7445.AM2017-2366