Abstract 1823: Overcoming siglec-9-mediated immunosuppression by using glycomimetics that block the binding of this receptor with its natural ligands

Abstract MUC16, a 3-5 million Da mucin overexpressed by ovarian cancer cells binds to Siglec-9, an inhibitory receptor on immune cells. Upon binding to Siglec-9, MUC16 triggers inhibitory signaling in the immune cells that allows ovarian cancer cells to evade cytolytic immune responses. Ovarian and other tumors express a plethora of cell surface as well as secreted glycoproteins with glycans that are terminated with the Siglec-9 ligand, α-2,3-linked sialic acid. Therefore, targeting the sialic acid-Siglec-9 axis has been of major interest to augment antitumor immunity. Here, we demonstrate that synthetic glycomimetic Siglec-9 ligands have the potential to enhance the immune recognition of ovarian cancer cells. We first demonstrate, using siglec-9 chimeras, that the glycomimetics developed by our group inhibit the binding of Siglec-9 to its natural ligands. Our data showed that 50-fold excess of the glycomimetics over Siglec-9 chimera prevented the Siglec-9 chimera from binding to the OVCAR-3 cell line (P.value, 0.039). Additionally, we demonstrate that glycomimetics (#153 and 157) developed by our group, enhance the recognition of ovarian cancer cell targets by human NK cells. In healthy donor 1, CD107a expression was increased (21, 17, 19 %) when 0.01, 0.025, 0.05 mM concentration of glycomimetic 153 was used, respectively. A statistically significant increase (5%) in CD107a expression was observed when the NK cells were treated with 0.05 mM concentration of glycomimetic 157. At higher concentrations of glycomimetic 153 and 157, inhibition of CD107a was repeatedly observed. These experiments, therefore, suggest that there is likely a certain concentration range of the glycomimetic that can be used to overcome NK cell suppression occurring via Siglec-9. To our knowledge, these data are among the first to demonstrate that specially designed glycomimetics can be used to overcome the suppression of NK cells against ovarian cancer cells. Future studies will employ murine and humanized models to demonstrate the therapeutic potential of the Siglec-9-targeting glycopeptides in enhancing immune responses against epithelial ovarian cancer. Citation Format: Lojain I. AlJohani, Manish Patankar, Weiping Tang, Christopher Stevens, Peng Teng. Overcoming siglec-9-mediated immunosuppression by using glycomimetics that block the binding of this receptor with its natural ligands [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 1823.