Identification of Novel HPK1 Hit Inhibitors: From In Silico Design to In Vitro Validation

Hematopoietic progenitor kinase 1 (HPK1), a negative regulator of T-cells, B-cells, and dendritic cells, has gained attention in antitumor immunotherapy research over the past decade. No HPK1 inhibitor has yet reached clinical approval, largely due to selectivity and drug-like limitations. Leveraging the available structural insights into HPK1, we conducted a rational hit identification using a structure-based virtual screening of over 600,000 drug-like molecules from ASINEX and OTAVA databases. A series of molecular docking studies, in vitro kinase assays, and molecular dynamics simulations were conducted to identify viable HPK1 inhibitor hits. This approach resulted in two promising novel hit scaffolds, 4H-Pyrido[1,2-a] thieno[2,3-d] pyrimidin-4-one (ISR-05) and quinolin-2(1H)-one (ISR-03), neither of which has previously been reported as an HPK1 inhibitor. ISR-05 and ISR-03 exhibited IC₅₀ values of 24.2 ± 5.07 and 43.9 ± 0.134 µM, respectively, in kinase inhibition assays. These hits constitute tractable starting points for future hit-to-lead optimization aimed at developing more effective HPK1 inhibitors for cancer therapy.