Abstract 3509: ATG-110, a novel “2+1” LY6G6D-targeted T-cell engager (TCE) for the treatment of MSS colorectal cancer

Abstract Background: Colorectal cancer (CRC) is one of the most common cancers worldwide and requires more effective and safer therapies to improve its poor survival outcome. LY6G6D is a GPI-anchored cell surface protein with expression that is particularly specific to colorectal cancer (CRC). LY6G6D exhibits significantly elevated expression levels in colorectal cancer (CRC) tissue comparing to normal tissue, particularly in pMMR/MSS CRC, which demonstrates primary resistance to immune checkpoint inhibitor (ICI) therapy. T cell engagers have shown encouraging efficacy in treating hematological malignancies, while exhibiting suboptimal performance in solid tumors. The potential of cytokine release syndrome (CRS) remains significant issues. We present a novel 2+1 LY6G6DxCD3 T cell engager, ATG-110, which demonstrated LY6G6D-dependent CD3 binding and significant anti-tumor activity with reduced cytokine release. Methods: ATG-110 was constructed by introducing a novel conformational epitope-targeted anti-CD3 single chain fragment variable (scFv) to the hinge region of one of the heavy chains of a LY6G6D monoclonal antibody. It was evaluated in a series of preclinical in vitro studies for binding affinity, T cell activation and cytokine release, T cell dependent cytotoxicity (TDCC), and drug developability. The in vivo anti-tumor efficacy was evaluated in PBMC-humanized immunodeficient NDG mice engrafted with LY6G6Dmedium-expression HT55 or LY6G6Dvery low-expression SW480 MSS CRC cells. Results: ATG-110 bound to LY6G6D-positive cell lines, LY6G6D-overexpression 293T, HT55, LS1034, with the nanomolar grade EC50. The CD3 binding site of ATG-110 is concealed by the LY6G6D Fab arm before binding to LY6G6D, due to the steric hindrance. Therefore, ATG-110 demonstrated limited binding capability to CD3+ cells before LY6G6D crosslinking. It activated T cells and induces cytokine release only in the presence of LY6G6D+ cells. In vitro, ATG-110 resulted in potent T cell dependent cytotoxicity with single-digit pM IC50 values on HT55 and SW480 cells. ATG-110 also showed potent anti-tumor activity in PBMC-humanized SW480 xenograft model and exhibited complete response (CR) in PBMC-humanized HT55 xenograft model. ATG-110 demonstrated good drug developability. Conclusion: ATG-110 demonstrated LY6G6D-dependent CD3 binding and activation with low risk of CRS. It showed powerful in vitro and in vivo anti-tumor efficacy against colorectal cancer, which warrants further clinical evaluation. Citation Format: Gang Bian, Jiahui Hua, Ge Lin, Xueli Chen, Huiling Liu, Peng Chen, Jay Mei, Bing Hou. ATG-110, a novel “2+1” LY6G6D-targeted T-cell engager (TCE) for the treatment of MSS colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3509.