Abstract 2670: Development of novel anti-SIRPα/β dual antibody with single-agent phagocytosis activity

Abstract Signal-regulatory protein alpha (SIRPα) is an inhibitory receptor expressed on macrophages that interacts with CD47, resulting a "don't eat me" signal on cancer cells. This interaction suppresses macrophage dependent phagocytosis and contributes to the evasion of host immune system. Consequently, the SIRPα-CD47 axis has become a well sought after and established therapeutic angle to treat cancer. While CD47-targeting agents have shown promise in clinical trials, the ubiquitous expression of CD47 raises the concerns about hematologic toxicity, including anaemia and thrombocytopenia, hindering the development of CD47-targeting therapies. This has prompted exploration of another end of the axis i.e., targeting SIRPα. Moreover, targeting SIRPβ protein, expressed on myleoid cells, via agonistic approach would generate ITAM-mediated activating signal through DAP12 protein contributing to cancer cell death. Considering the limited expression of SIRPα and β, a dual antibody capable of blocking the CD47-SIRPα pathway and activating SIRPβ downstream signaling may result in a desirable efficacy and safety profile. In this study, we present novel anti-SIRP α/β dual antibody clones discovered from a proprietary human antibody discovery platform consisting of a large human antibody library, along with in vitro and in silico screening technologies. The platform was explored against native SIRPα/β antigens to identify novel human antibody clones based on affinity-based epitope coverage. Subsequently, antibody clones were produced and evaluated for preclinical functional relevance. Novel full-length SIRPα/β dual antibody clones demonstrated high affinity binding to soluble human SIRPα and SIRPβ proteins as well as these receptors expressed on CHO-K1 cells and macrophages. The antibody clones effectively disrupted CD47-SIRPα interaction in biochemical assays and significantly enhanced activation of macrophages as observed by increased cytokine release. Most importantly, the dual antibody clones demonstrated potent in vitro single-agent phagocytosis activity against tumor cells. In summary, the novel SIRPα/β dual antibodies activating macrophage mediated phagocytosis of tumor cells without the need for tumor opsonizing antibodies or agents capable of inducing “eat-me-signals” highlight their potential as a single-agent therapy. These findings prompt us to continue the development of the anti-SIRP α/β dual antibody for use in cancer therapy. Citation Format: Subhra Prakash Chakrabarty, Sandeep Sadashiv Patil, Sunaina Singh Rajput, Amrita Mukerji, Sandhya Aurumugam, Pooja Balu Gade, Sidhesha S, Anup Kumar Patra, Shivaranjini C, Vaishnavi Shivaji Khamkar, Lavanya P, Lakshmeesha K N, Ujjwal Kapoor, Jagadeesh R, Jwala Nagaraj, Vijaya Shankar Nataraj, Kavitha Nellore, Thomas Antony, Susanta Samajdar, Murali Ramachandra. Development of novel anti-SIRPα/β dual antibody with single-agent phagocytosis activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2670.