Abstract 6510: BPI-511966,a potent and selective HPK1 inhibitor with robust single-agent efficacy for cancer immunotherapy

Abstract Although immune checkpoint inhibitors (ICIs) have become the standard treatment for many types of cancers, a large proportion of patients fail to respond to ICIs. Hematopoietic progenitor kinase 1 (HPK1) has been validated as a negative intracellular immune checkpoint that constrains T-cell activation. Genetic or pharmacological ablation of HPK1 induces a robust anti-cancer immune response in vivo, highlighting the potential of HPK1 as a next-generation target for cancer immunotherapy. Herein, we reported the discovery of BPI-511966, a highly potent ATP-competitive HPK1 inhibitor. The compound strongly inhibited HPK1 kinase with an IC50 of 2. 3 nM at physiologically relevant ATP concentration (1 mM) and reduced phosphorylation of SLP-76, a substrate adaptor of HPK1, in Jurkat T cells in vitro, with an IC50 value of 11 nM. Development of an optimal HPK1 inhibitor requires not only high potency for target engagement but also high selectivity to spare other kinases that are essential for T cell activation. BPI-511966 showed 100-fold higher IC50 (364 nM) against MAP4K3/GLK, an HPK1 homology kinase promoting T-cell activation, and also demonstrated weak inhibition in a panel of other immune-related kinases. The remarkable potency and selectivity of BPI-511966 translate into robust T cell-enhancing efficacy in vitro. Treatment with BPI-511966 promoted both IL-2 and IFN-γ production by Jurkat T cell and human PBMC in a dose-dependent manner. The on-target action of BPI-511966 was validated in HPK1-KO Jurkat T cells, in which no significant impacts on SLP-76 phosphorylation and IL-2 secretion were observed. In vivo, single dose escalation of BPI-511966 in mice leads to dose-proportional increases in drug exposure, accompanied by inhibition of SLP-76 phosphorylation in peripheral CD3+ T cells. Furthermore, repeated oral administration of BPI-511966 as a single agent significantly suppressed CT-26 tumor growth in immune-competent mice (92% TGI), correlating with increased infiltration of CD45+ CD8+ cells and enhanced cytokine production in tumor. Notably, the efficacy of BPI-511966 is abrogated in immune-compromised mice, suggesting its vital role in promoting anti-cancer immunity. In summary, this study presents a novel, highly potent, and selective HPK1 inhibitor BPI-511966. The robust single-agent activity of BPI-511966 makes it a promising small molecule I/O agent to address ICI resistance as monotherapy or in combination. Citation Format: Yong Zhang, Xiaoguan Zhu, Wenmao Wu, Zhifang Xia, Zhengyao Zou, Han Han, Cheng Yang, Haibo Chen, Tianyi Ma, Xiaoyun Liu, Jing Guo, Hao Wu, Hong Lan, Lieming Ding, Jiabing Wang, Quan Zhou. BPI-511966, a potent and selective HPK1 inhibitor with robust single-agent efficacy for cancer immunotherapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6510.