Abstract 1657: HZ-S109, a potent and selective HPK1 degrader with enhanced T cell modulation efficacy and improved bioavailability

Abstract Background: Hematopoietic Progenitor Kinase 1 (HPK1/MAP4K1) has been demonstrated to restrain T cell activation through phosphorylating SLP-76 at Serine 376 during the T-cell activation process. Given its irreplaceable negative regulation role in TCR pathway, HPK1 is considered as a promising target in immuno-oncology. Recently, HPK1 has been shown to function as scaffolding protein and bind to adaptor proteins to promote JNK signaling and actin cytoskeleton rearrangement involved in lymphocyte adhesion. Additionally, the turnover rate of HPK1 is low. These evidences suggest that HPK1 is a suitable target to develop protein-degrader. Objective: Accordingly, we described our state-of-the-art work in discovery and identification of HPK1 degrader HZ-S109. We asked if this degrader could exhibit stronger engagement with the HPK1 target, leading to the restoration of suppressed T-cell function and inhibition of tumor growth. Methods: HZ-S109 was identified based on our in-house unique DaTProD® platform. CCK-8, ELISA and WB detection were performed by PEG2, NECA and TGF-β induced depleted cell model in vitro.PK/PD detection and tumor measurement were performed by oral gavage of CT-26 subcutaneously transplanted tumor models in C57BL/c mice. Results: HZ-S109 exhibits potent HPK1 degradation with DC50 values lower than 10 nM across various cell types, including Jurkat, Ramos, PBMC, and CAR-T cells. Importantly, HZ-S109 demonstrated no significant effect on other family members, such as GCK, GLK, HGK, or KHS. HZ-S109 can significantly enhance the activation of primary T cell at nanomolar level concentrations, with the maximum activation fold exceeding 15-fold. Furthermore, HZ-S109 restores T cell function in the presence of multiple immune-suppressed conditions including NECA/ PGE2/ TGF-β or their combination. Despite its higher molecular weight, HZ-S109 boasts superior oral bioavailability. In in-vivo anti-tumor efficacy evaluation, oral administration of HZ-S109, either as a single agent or in combination with PD-L1 antibody, robustly suppressed the tumor growth in CT26, A20 and MC38 syngenic mice model, achieving a tumor growth inhibition (TGI) of over 90%. These results suggest that HZ-S109 stands out as a potent and distinct HPK1 modulator, exhibiting enhanced potency and oral bioavailability. At present, HZ-S109 is in the IND-enabling study stage. Citation Format: Yizhe Wu, Jiangfeng Xie, Jinglai Huang, Mengchao Zheng, Xinglu Zhou. HZ-S109, a potent and selective HPK1 degrader with enhanced T cell modulation efficacy and improved bioavailability [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 1657.