Abstract 5632: HDM2006, A novel and potent HPK1 PROTAC, enhances immune cell activation and induces robust tumor growth inhibition

Abstract Background: HPK1 (Hematopoietic Progenitor Kinase 1) is a member of the MAP4K family, which is a group of kinases that catalyze the phosphorylation of serine or threonine residues in proteins. HPK1 is mainly expressed in hematopoietic and immune cells. Loss of HPK1 kinase function increases cytokine secretion, enhances T cell signaling, viral clearance, and tumor growth inhibition. Therefore, HPK1 is considered as a promising target for tumor immunotherapy. Currently, there are several small molecule inhibitors targeting HPK1 in clinical trials, which only inhibit the kinase activity of HPK1, and cannot completely block its downstream signal transduction, and have low selectivity and poor safety. Therefore, we developed a proteolysis targeting chimera (PROTAC) drug, HDM2006, that specifically targets HPK1 while inhibiting HPK1 kinase activity and deleting its skeletal function, and has better efficacy and safety than small molecule inhibitors. The robust monotherapy and combined with anti-mPD-1 efficacy of HDM2006 makes it a IO drug and also a new option for patients with advanced tumors. Methods: TR-FRET assay were utilized to assess the target binding activity and ternary complex formation activity. Western blot was utilized to investigate the degradation activity of HDM2006 in human T lymphoma Jurkat cells. The effect of HDM2006 on the secretion of IL-2 and IFN-γ by human Pan-T cells was detected by ELISA. In vivo anti-tumor efficacy of HDM2006 monotherapy and combined with anti-mPD-1 was evaluated in murine colorectal cancer MC38 cell allograft models. Oral-bioavailability and repeat-dose GLP toxicity studies were profiled in rats and cynomolgus monkeys. Results: HDM2006 bound to human HPK1 and E3 ubiquitin ligase CRBN, and formed a ternary complex. Meanwhile, HDM2006 targeted and degraded HPK1 in Jurkat cells, with a DC50 of 20.68 nM and a Dmax of 96.36% (24 h). HDM2006 did not degrade other CRBN substrates, avoiding IMiDs off-target effect. HDM2006 can stimulate hPBMCs to secrete IL-2 and IFN-γ, the maximum activation fold can be more than 9.3-41.6 folds. Furthermore, immune activation upon HPK1 degradation was observed even in immune-suppressed environments (PGE2, adenosine, and T cell exhaustion). In vivo, HDM2006 showed efficacy in mouse colorectal cancer model in mono and in combination with anti-mPD-1, and TGI was similar to the small-molecule inhibitor at very low dose. In addition, the results of GLP toxicity studies in rats and cynomolgus monkeys indicated that HDM2006 has a large safety margin, and the NOAEL dose exposure was approximately 435.9-fold and 21.4-fold of the optimal effective dose exposure. Conclusions: HDM2006 is a novel, potent, highly selective and orally active PROTAC targeting HPK1. Preclinical studies have confirmed that HDM2006 has excellent profile for druggability, safety, and efficacy. HDM2006 has entered the clinical Phase 1 trial. Citation Format: Liubin Guo, Zhimin Zhang, Xi Yang, Rongyao Zhu, Zhiping Zhang, Sirui Liu, Hao Pan, Zhao Dong, Chunhua Jiang, Dongzhou Liu. HDM2006, A novel and potent HPK1 PROTAC, enhances immune cell activation and induces robust tumor growth inhibition [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 5632.