Protease-Activated Receptor 4 (PAR4)-Tethered Ligand Antagonists Demonstrate Thrombin Liability.

The Hamm laboratory recently published a cohort of PAR4 antagonists that were effective against the tethered ligand activation of PAR4. These compounds were generated from an ultralarge virtual screen using a homology model of PAR4. Upon further investigation, it appears the protease-activated receptor antagonists highlighted in this work have some thrombin liability. The Hamm laboratory further characterized the activity of these compounds using various methods, including a fluorescent thrombin activity assay, a chromogenic thrombin activity assay, and flow cytometry assays. We conclude that they do indeed antagonize PAR4, but thrombin is an additional target.