Abstract 6301: Post-translational modifications regulate sensitivity to Polatuzumab Vedotin in DLBCL

Abstract

Abstract Diffuse Large B-Cell Lymphoma (DLBCL) is an aggressive malignancy of which one-third of diagnosed patients ultimately relapse and die. New treatment paradigms for relapsed-refractory patients are needed. Most DLBCL tumors are reliant on signaling through their cell surface B-cell receptor (BCR) mediated by ITAMs on CD79A and CD79B to drive anti-apoptotic NF-kB and PI3 kinase signaling. In order to understand how surface BCR is regulated, we performed whole genome CRISPR screens in 9 DLBCL cell lines in which we sorted for high and low surface CD79B or added the CD79B targeted antibody-drug conjugate Polatuzumab-Vedotin (POLA-V). Strikingly, independent of genetic or cell of origin subtype, sgRNAs encoding the entire N-linked glycosylation pathway and specific sugar modification by addition of galactose and sialic acid were found to be enriched in high CD79B fractions and depleted in POLA-V treated samples compared to control. Further testing showed that removing sialic acid by treating with a small molecule inhibitor of sialic acid, genetic perturbation of golgi sugar transporters SLC35A1 and SLC35A2, or the a2,6 sialyltransferase ST6GAL1 resulted in more surface CD79B antibody binding with no significant change in CD79B protein abundance. The specificity of the effect of sialic acid loss on POLA antibody binding was confirmed by removing cell surface sialic acid with exogenous sialidase and observing increased binding of POLA, but not other therapeutic antibodies like Rituximab or CD19 FMC-63. Loss of SLC35A1, SLC35A2, and ST6GAL1 synergized with POLA-V but not the drug conjugate MMAE alone, showing a BCR dependent mechanism of sialic acid loss on POLA-V sensitization. In a further cell of origin subtype analysis of the germinal center B-cell (GCB) DLBCL cell lines, loss of the E3 ligase KLHL6 was found to synergize with POLA-V. Importantly, KLHL6 is heavily mutated across all germinal center derived malignancies, is more highly expressed in germinal center B-cells than other members of the B-cell lineage, and plays an unknown role in the development of autoimmune diseases. Further work will give evidence for the target of KLHL6 mediated ubiquitination and will show how this gene can drive lymphoma and autoimmune disease development in the germinal center. Citation Format: Sean R. Corcoran, Louis M. Staudt, Daniel Hodson. Post-translational modifications regulate sensitivity to Polatuzumab Vedotin in DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6301.