Design and evaluation of potent peptide-mimetic PAR1 antagonists

The serine protease alpha-thrombin is a powerful mediator of cellular responses, not only playing a key regulatory role in the maintenance of normal hemostasis, but also contributing more broadly to a range of physiological and potentially pathological conditions. Most of the cellular actions attributed to alpha-thrombin have been linked to the activation of a family of seven-transmembrane G-protein-coupled protease-activated receptors, termed PARs. Of the four family members identified, PAR(1) has received recognition as the most significant receptor for mediating thrombin's cellular actions. Thus, the development of a potent, selective antagonist of PAR(1) would be an important and essential tool to probe the physiological and potential pathological roles of PAR(1). In this review, we provide a synopsis of our de novo design approach to the discovery of selective PAR(1) antagonists, exemplified by RWJ-58259, along with the in vitro and in vivo studies performed to demonstrate the important role of this receptor in thrombosis and vascular injury. RWJ-58259 demonstrated antithrombotic activity in a model of vascular injury-induced thrombosis in cynomolgus monkeys and prevented neointimal proliferation in a rat balloon angioplasty model. These seminal studies clearly lay the groundwork for more detailed preclinical in vivo studies and ultimately, advancing PAR, antagonists into human clinical studies. Expanded chemical synthetic efforts and other novel technologies targeted to PAR, and its intracellular signaling pathways are already on the horizon in an effort to further modulate thrombin's biological actions. (C) 2003 Wiley-Liss, Inc.