HPK1 inhibitors (Hongyun)

Hematopoietic progenitor kinase 1 (HPK1), a negative regulator of T cell receptor signaling, plays a crucial role in multiple cellular immune responses. Emerging researches have demonstrated that inhibiting HPK1 kinase function enhances T cells' ability to recognize tumor antigens and boosts anti-tumor immune responses. As a result, HPK1 has become a promising target for tumor immunotherapy. Herein, we report the design, synthesis, and biological evaluation of a series of novel HPK1 inhibitors featuring a 3-cyano-quinoline scaffold. Among these, compound 3a was identified as the most potent HPK1 inhibitor (HPK1 IC₅₀ = 48 nM). It effectively inhibited SLP76 phosphorylation, enhanced IL-2 cytokine secretion, and reversed PGE2-induced immunosuppression in Jurkat cells. In addition, compound 3a exhibited favorable metabolic stability in mouse liver microsomes and plasma. Overall, this work provides a structurally novel lead compound for the development of HPK1 inhibitors.

Hematopoietic progenitor kinase 1 (HPK1) serves a key immunosuppressive role as a negative regulator of T-cell receptor (TCR) signaling. HPK1 loss-of-function is associated with augmentation of immune function and has demonstrated synergy with immune checkpoint inhibitors in syngeneic mouse cancer models. These data offer compelling evidence for the use of selective small molecule inhibitors of HPK1 in cancer immunotherapy. We identified a novel series of isoquinoline HPK1 inhibitors through fragment-based screening that displayed promising levels of biochemical potency and activity in functional cell-based assays. We used structure-based drug design to introduce key selectivity elements while simultaneously addressing pharmacokinetic liabilities. These efforts culminated in a molecule demonstrating subnanomolar biochemical inhibition of HPK1 and strong in vitro augmentation of TCR signaling in primary human T-cells. Further profiling of this molecule revealed excellent kinase selectivity (347/356 kinases <50% inhibition @ 0.1 μM), a favorable in vitro safety profile, and good projected human pharmacokinetics.