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Document<br />

10<br />

<strong>Structure</strong>-Based <strong>Design</strong> of Thrombin Inhibitors<br />

Patricia C. Weber and Michael Czarniecki<br />

Schering-Plough Research Institute, Kenilworth, New Jersey<br />

I. Roles of Thrombin in Hemostasis and the Therapeutic Utility of Thrombin Inhibitors<br />

Page 247<br />

Thrombin is a serine protease that plays critical roles in both blood clot formation and anticoagulation.<br />

In the penultimate step of the coagulation cascade, thrombin cleaves soluble fibrinogen to form<br />

insoluble fibrin. Thrombin also activates other coagulation factors including Factor XIII, the enzyme<br />

responsible for crosslinking fibrin to further stabilize the thrombus. Additional clot-promoting functions<br />

include stimulation of platelet aggregation <strong>by</strong> cleavage of the thrombin receptor. In contrast to its roles<br />

in clot formation, thrombin participates in anticoagulant functions. For example, thrombin-mediated<br />

activation of protein C, a protease involved in anticoagulation, is enhanced when thrombin is complexed<br />

with thrombomodulin, and in this complex, thrombin can neither cleave fibrinogen nor activate platelets.<br />

The interrelationship among thrombin's many roles in hemostasis is complex and presents several<br />

mechanisms for inhibition of thrombus formation. For recent reviews see References 1 through 5.<br />

Most drug discovery efforts focus on thrombin inhibition as a means to prevent the serious<br />

consequences of thrombus formation in myocardial infarction and stroke. Thrombin inhibitors may also<br />

prevent clot formation in patients prone to deep vein thrombosis or repeat heart attack. In combination<br />

with thrombus dissolution therapies, thrombin inhibitors may decrease the incidence of reocclusion due,<br />

in part, to the release of active clot-bound thrombin.<br />

In this article, recent examples of small molecule inhibitors interacting at the fibrinogen primary<br />

specificity pocket and with residues of the catalytic triad<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_247.html [4/5/2004 5:10:09 PM]

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