Development and current applications of thrombin-specific inhibitors

Thrombin-specific inhibitors directly diminish thrombin-induced coagulation and cellular activities without the side effects of heparin. Hirudin is the most potent natural thrombin-specific inhibitor. Recombinant hirudins (such as desirudin) have been shown to be effective in the treatment of heparin-induced thrombocytopenia (HIT) and in the prevention of thrombotic complications after hip or knee surgery. The application of recombinant hirudin has been limited mainly by hemorrhagic complications. Synthetic thrombin-specific inhibitors, including oligopeptides, tripeptides and non-peptide low molecular weight (LMW) thrombin inhibitors, have been designed according to their interactions with the active sites of thrombin. Bivalirudin (an anti-thrombin oligopeptide) has been approved for preventing thrombosis in unstable angina patients following angioplasty in adjunct to aspirin. Argotroban (a tripeptide thrombin inhibitor) has been used for the treatment of HIT, peripheral and cerebral thrombotic diseases. The benefit of using thrombin-specific inhibitors alone in acute myocardial infarction or unstable angina remains uncertain. A number of LMW thrombin-specific inhibitors have been developed. Some of them can be administrated orally, and cause less increase in bleeding time than other thrombin inhibitors. The efficacy, safety, stability and oral bioavailability of the thrombin inhibitors may be considerably improved through structural optimization. Most of the LMW thrombin inhibitors are currently being tested in animal models or at early stages of clinical trials. In this review, we will present an overview of recent advances in thrombin-specific inhibitors.