W0453

Structure-Based Design of Selective Tissue Factor-VIIa Inhibitors. Ravi G Kurumbail, Anna M Stevens, Roderick A Stegeman, Gennadiy I Poda, Michael Clare^*, John J Parlow, Michael S South, Rhonda M LaChance, Thomas J Girard, William C Stallings, Pfizer Global Research & Development, Departments of Medicinal Chemistry & Cardiovascular Research, Chesterfield, Missouri & ^*Skokie, IL.

The formation of a thrombus via the extrinsic coagulation pathway is initiated by plaque rupture that exposes tissue factor (TF) to factor VIIa (VIIa), a serine protease circulating in the blood. Formation of the TF-VIIa complex is the first step in a cascade of biochemical activation events that generates downstream serine proteases factor Xa and thrombin. This ultimately leads to the formation of a life threatening fibrin clot and thrombus. Serine proteases of the coagulation pathway have long been recognized as potential targets for the development of antithrombotic drugs. However, the challenge so far has been to balance the therapeutic efficacy vs. bleeding side effects. Animal studies have indicated that TF-VIIa might be a safer target for an anti-thrombotic drug compared to factor Xa and thrombin.

The first crystal structure of TF-VIIa complexed with a peptidomimetic inhibitor was reported several years ago by Banner and co-workers at Roche. Using synchrotron X-ray radiation, we have determined crystal structures of ketothiazole tripeptide inhibitors complexed with TF-VIIa. This class of inhibitors forms a tight complex with factor VIIa by forming a reversible covalent bond to the active site serine of factor VIIa. Docking and iterative structure-based design cycles were then used to generate a novel series of pyrazinone-based VIIa inhibitors, which are potent, selective, reversible and non-covalent. One of these inhibitors was used in pre-clinical proof of concept studies in animals to demonstrate separation between anti-thrombotic efficacy and bleeding side effects The study showed that at efficacious doses, the VIIa inhibitor caused minimal bleeding while specific inhibition of downstream targets resulted in excessive blood loss. The presentation will highlight the contributions of crystallography and molecular modeling that have been integral to the discovery of specific TF-VIIa inhibitors.