Discovery of novel and potent 2-aminopyrazine-based HPK1 inhibitors enhancing T-cell immunity against cancer.

Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of immune signaling and a target of high interest for immuno-oncology. Although numerous campaigns have been conducted to identify potent and selective HPK1 inhibitors, few encouraging clinical outcomes have been reported. Herein, we present the optimization of 2E, an HPK1 inhibitor with a new 2-aminopyrazine scaffold. It was identified through a fragment-based deconstruction-reconstruction (FBDR) strategy. This process led to the discovery of a novel and highly potent HPK1 inhibitor 39, possessing nanomolar potency in biochemical and cellular assays. Mechanistic studies revealed that 39 effectively enhanced IL-2 cytokine production and counteracted prostaglandin E2 (PGE2)-mediated immunosuppression in Jurkat cells. Crucially, compound 39 showed T-cell-dependent antitumor efficacy in the CT26-Balb/c syngeneic tumor model and exhibited significant synergistic effects when combined with anti-PD-1 in vivo. Moreover, compound 39 enhanced infiltration of CD3/CD8 T cells into tumor tissues, verifying its immune-mediated antitumor mechanisms. These findings highlight compound 39 as a promising candidate for cancer immunotherapy, deserving further optimization and preclinical research.