Abstract 183: A novel bispecific antibody macrophage engager (BiME) designed for the treatment of solid tumors

Abstract Background: Anti-CD3-based bispecific T cell engagers (BiTE) showed limited clinical efficacy in solid tumors and caused significant cytokine storm. Similar to BiTE where T cells are activated by CD3 antibody, we constructed a novel bi-specific macrophage engager (BiME) platform where macrophage is activated by anti-SIRPa that is directed to a particular tumor via the targeting of the tumor-associated antigen (TAA), resulting in phagocytosis of the tumor cells. This BiME does not lead to cytokine storm and is particularly applicable for the treatment of solid tumors whose microenvironment contains plenty of macrophages. Tumor-associated macrophages are major component of immune cells in the tumor micro-environment (TME) that express an array of effector molecules leading to the inhibition of anti-tumor immune responses. Signal regulatory protein α (SIRPα) is a myeloid-lineage inhibitory receptor that restricts phagocytosis through engagement of its ligand CD47 expressed on tumors and normal tissues. Compared to anti-CD47 therapeutics, targeting myeloid-restricted SIRPα provides a differential pharmacokinetic, safety, and efficacy profile. Here, we report the construction of a SIRPα antagonist-based bispecific macrophage engager (BiME) platform, a potent tumor-killing bi-specific antibody platform. Methods: We have generated a panel of single domain antibody (sdAb), scFv or Fab antibodies targeting different TAAs and SIRPa. We constructed BiME antibodies using different orientations, ratios, and IgG isotypes of anti-TAA arm and anti-SIRPα arm. These bispecific antibodies were evaluated for homologue binding, and CD47-SIRPα blocking properties by ELISA and FACS. In vitro function activity was determined by phagocytosis assay using human monocyte derived macrophage and mouse bone marrow derived macrophage. In vivo anti-tumor efficacy was tested in a syngeneic tumor model with hSIRPα knock-in mice. The pharmacokinetic (PK) and safety profile were assessed in hSIRPα knock-in mice or cynomolgus monkeys. Results: Through Elpiscience proprietary BiME platform, we have generated a panel of TAA/SIRPα bispecific antibodies with TAA being Claudin18.2, EGFR, PDL1 and DLL-3. The BiME treatment demonstrated strong anti-tumor efficacy in multiple mouse syngeneic tumor models. Mechanistically, both myeloid and T cells were activated and contributed to antitumor activity of BiME bispecific antibody. the BiME bispecific antibodies were well tolerated in non-human primates (NHPs) and there is no hematotoxicity or cytokine release syndrome (CRS) observed after treatment of BiME antibodies. Conclusions: These findings provide novel mechanistic insights into how myeloid and T cells can be uniquely modulated by the bispecific macrophage engagers (BiMEs) and demonstrate the potential and advantage of BiME in future clinical development for solid tumor treatment as compared to BiTE approach. Citation Format: Dawei Sun, Haixia Jiang, Yanan Geng, Yue Wu, Rui Gao, Yefeng Lu, Quan Qiu, Yanfen Hu, Yingchao Liu, Xiaoli Guo, Xiaofeng Niu, Hongtao Lu. A novel bispecific antibody macrophage engager (BiME) designed for the treatment of solid tumors [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 183.