Abstract 613: AL009 is a multi-Siglec inhibitor engineered to bind myeloid cells that enhances innate and adaptive immunity to cancer

Abstract

Abstract Background - Inhibitory sialic acid-binding immunoglobulin-type lectins (Siglecs) are a subset of the Siglec family of cell surface receptors that potentiate immune tolerance. A multitude of inhibitory Siglecs on myeloid cells become engaged in sialic acid-rich tumor microenvironments, suggesting that disrupting Siglec-sialic acid signaling could confer therapeutic benefit in cancer. To accomplish this, we designed AL009, an engineered Siglec-9 extracellular domain-Fc fusion molecule that acts as a sialic acid trap and a multi-Siglec inhibitor, repolarizing suppressive myeloid cells and activating an anti-cancer response. Methods - Cooperative binding of AL009 was analyzed by flow cytometry using cultured human tumor cell lines and myeloid-derived suppressor cells (MDSCs) differentiated from primary human monocytes. Monocytes, MDSCs, and macrophages differentiated from primary human monocytes were assessed for AL009 binding by flow cytometry. AL009m (AL009 with a mouse Fc) was fluorophore-labeled and intravenously injected into B6 mice to analyze biodistribution via ex vivo tissue imaging over time. Initial toxicology screening was conducted in cynomolgus monkeys in a non-terminal study. Results - AL009 displays cooperative binding with sialic acid and Fc gamma receptors on myeloid cells. When comparing binding among myeloid cell subsets, AL009 preferentially binds MDSCs. Analysis of the biodistribution of labeled AL009m in mice showed the greatest accumulation in the spleen, consistent with immune cell targeting in vivo. Further, Fc engineering of AL009 improved the pharmacodynamic profile compared to a non-engineered Fc. In cynomolgus monkeys, single doses of 80 mg/kg appeared safe and without clinically significant findings. Conclusions - The engineered structure of AL009 leads to preferential binding to an immunosuppressive subset of myeloid cells. This targeting leads to repolarization of myeloid cells and activates an innate and adaptive anti-cancer response. Pharmacologically relevant doses of AL009 appear well-tolerated in initial studies in non-human primates, supporting further development for entry into clinical studies. Citation Format: Sam Nalle, Helen Lam, Cheryl Barner, Hua Long, Spencer Liang, Arnon Rosenthal, Daniel Maslyar. AL009 is a multi-Siglec inhibitor engineered to bind myeloid cells that enhances innate and adaptive immunity to cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 613.