Abstract 7009: Discovery of UBX-306 as a potent, selective, and orally bioavailable HPK1 degrader

Abstract Background: Hematopoietic progenitor kinase 1 (HPK1), part of the MAP4K family, is a serine/threonine kinase critical for modulating immune cell signaling and function. HPK1 is predominantly expressed in hematopoietic cells, where it acts as a negative regulator of T-cell receptor (TCR) signaling and other immune pathways. Upon activation, HPK1 dampens immune responses by phosphorylating key adapter proteins, such as SLP-76, and promoting their degradation, ultimately inhibiting T-cell activation, proliferation, and cytokine production. Given the critical role of T-cells in anti-tumor immunity, HPK1 has emerged as an attractive target in immuno-oncology for enhancing immune responses. Results: UBX-306;NT2020 demonstrated robust HPK1 protein degradation, achieving single-digit nanomolar DC50 levels in the Jurkat cell line in a dose-dependent manner. The degradation effect of UBX-306-1 is strongly dependent on the ubiquitin-proteasome system (UPS). Both UBX-306-1 and UBX-306-3 significantly enhanced IL-2 secretion in Jurkat cells, demonstrating superior EC50 values compared to the warhead of UBX-306, AZ1, or reference HPK1 degrader. Treatment with UBX-306-1 increased IL-2 production in a concentration-dependent manner, even in the presence of immunosuppressive molecules such as PGE2 and NECA. UBX-306-2 effectively degrades HPK1 protein in Ramos, Raw264.7, THP-1, and KG-1 cell lines. In vivo pharmacodynamic (PD) data demonstrated that UBX-306-1 efficiently degraded the HPK1 protein in the mouse blood. UBX-306-1 induced peak degradation of HPK1 at 6 hours after oral administration, with the degradation activity sustained for up to 24 hours. The antitumor efficacy of UBX-306-1 was evaluated in the CT-26 (Colorectal cancer) syngeneic tumor mouse model. Daily oral administration of UBX-306-1 at doses of 10 mg/kg and 30 mg/kg resulted in robust tumor growth inhibition. Conclusion: We demonstrate that potent HPK1 degraders, effectively activate immune cells and inhibit tumor growth in mouse syngeneic tumor models as single agents. These degraders enhance IL-2 and IFNγ production while overcoming immunosuppressive factors. Further, in vivo studies will deepen our understanding of HPK1 degradation as a promising immunomodulatory strategy for enhancing anti-tumor immunity. Citation Format: Ae-Ran Choi, Na-rae Jeong, Sun-Mi Yoo, Han Wool Kim, So Hyuk Kim, Hyun-Hwi Kim, Sun-Kyoung Im, Miyoung Jang, Hohyun Lee, Jungmin Ahn, Je Ho Ryu, Song Hee Lee. Discovery of UBX-306 as a potent, selective, and orally bioavailable HPK1 degrader [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 7009.