Abstract 4337: SYS6051, a next-generation tissue factor-targeted antibody-drug conjugates for the treatment of TF-expressing malignancies

Abstract Tissue factor (TF) is an integral membrane protein, normally separated from the blood by the vascular endothelium, which plays a key role in the initiation of blood coagulation. However, TF is aberrantly expressed in solid tumors and its expression associated with poor prognosis. The first TF targeting antibody-drug conjugate (ADC) , a microtubule inhibitor based ADC(MTI-ADC), is approved for the treatment of cervical cancer. It had several prespecified adverse effects (AEs) including bleeding risks, ocular toxicity and perpheral neuropathy, the last two of which were known MMAE related AEs. In order to mitigate the safety concerns, we developed a novel ADC, SYS6051. It was composed of a humanized TF-targeting IgG1 antibody site-specifically conjugated to a topoisomerase I inhibitor (Exatecan) at a drug-to-antibody ratio (DAR) of 6 via a protease-cleavable linker. In addition, SYS6051 had improved resistance towards retro-Michael elimination reactions, resulting in improved stability compared to cysteine thiol-maleimide conjugated ADCs. The naked SYS6051-mAb did not interfere with the interaction among TF, Factor FVII and Factor X, and had no impact on coagulation cascade. SYS6051-mAb could quickly enter cells through endocytosis 3 hours after treatment, faster than the antibody of the MTI-ADC. Treatment with SYS6051 resulted in significant tumor growth inhibition in a panel of TF-positive cell line derived xenografts (CDXs), including pancreatic and cervical cancer xenografts. Furthermore, SYS6051 was well tolerated in a toxicity study in cynomolgus monkey at dosages ≤30 mg/kg. A stable PK profile of SYS6051 was also observed in NHP. Neither coagulation disorder nor skin rash was observed, superior to the historical toxicity data in NHP of the MTI-ADC. Taken together, SYS6051 has a wide therapeutic window because of promising efficacy, higher tolerability, stable PK profile, and could potentially provide benefits for the patients carrying TF positive malignancies. Citation Format: Xiaojuan Wu, Mingyue Shen, Mo Dan, Xiwu Hui, Bing Yao, Yanling Li, Wei Yang, Hanqian Xu, Can Yuan, Yufei Sun, Bin Kang, Yang Zhang, Linlin Xiao. SYS6051, a next-generation tissue factor-targeted antibody-drug conjugates for the treatment of TF-expressing malignancies [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 4337.