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

## TL;DR

This paper shows that certain PAR4 antagonists also affect thrombin, a key blood-clotting enzyme.

## Contribution

The study reveals that previously developed PAR4 antagonists have unintended thrombin liability.

## Key findings

- PAR4 antagonists effectively block PAR4 activation.
- The same compounds inhibit thrombin activity.
- Multiple assays confirmed the dual targeting of PAR4 and thrombin.

## Abstract

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.