Specific Inhibitors of Activated Protein C

Factors V and VIII are procofactors which are essential components of the blood coagulationprocess. Deficiency in either of these proteins is associated with severe bleeding disorders, hemophiliaand para-hemophilia. Deficiency states of these proteins can be caused by their proteolytic inactivationby Activated Protein C (APC), a natural anticoagulant enzyme. Therapeutic intervention in hemophilia-Athrough the use of replacement plasma factor VIII is a standard measure to control bleeding. It is logicalto expect that selective inhibitors of APC might improve the efficacy of factor VIII replacement therapyby reducing the losses of Factor VIlla to APC cleavage. Inhibitors of APC which express reasonableaffinity and high specificity have not been reported. Recent identification of the cleavage sites of FactorsVa and VIlla by APC have led-to the development of synthetic peptide inhibitors with affinity for APC.These inhibitors did not inhibit thrombin and showed very low affinity for Factor Xa, raising thepossibility that such inhibitors might selectively neutralize the anticoagulant effect of APc. Factor VIIIreplacement therapy is a 300 million dollar per year business in the United States alone. It is conceivablethat by improving the prophylactic effect of this replacement therapy and/or alleviating the need for suchtherapy in border-line cases, as much as 100 million dollars per year could be saved in health care costswithin the United States. This proposal has the following specific aims: l) further design and synthesisof specific APC inhibitors; 2) evaluation of the influence of these inhibitors on Thrombin and Factor Xageneration 3) evaluation of synthesized compounds in blood clotting assays.