Discovery of highly efficient CRBN-recruiting HPK1-PROTAC as a potential chemical tool for investigation of scaffolding roles in TCR signaling

Hematopoietic progenitor kinase 1 (HPK1, MAP4K1) is a promising target for immune-oncology therapy. It has been recently demonstrated that loss of HPK1 kinase activity can enhance T cell receptor (TCR) signaling. However, many essential functions mediated by the HPK1 scaffolding role are still beyond the reach of any kinase inhibitor. Proteolysis targeting chimera (PROTAC) has emerged as a promising strategy for pathogenic proteins degradation with the characteristics of rapid, reversible, and low-cost versus RNA interference or DNA knock-out technology. Herein we first disclosed the design, synthesis, and evaluation of a series of thalidomide-based PROTAC molecules and identified B1 as a highly efficient HPK1 degrader with DC50 value of 1.8 nM. Further mechanism investigation demonstrated that compound B1 inhibits phosphorylation of the SLP76 protein with IC50 value of 496.1 nM, and confirmed that B1 is a bona fide HPK1-PROTAC degrader. Thus, this study provides a basis for HPK1 degraders development and the candidate could be used as a potential chemical tool for further investigation of the kinase-independent signaling of HPK1 in TCR.