Reversible acylation of factor Xa as a potential therapy for hemophilia

Current therapies for treatment of hemophilia A involve infusion of factor VIII, but are ineffective for patients who develop inhibitory antibodies. We have previously proposed that bypassing the intrinsic pathway (VIIIa/IXa) with reversibly acylated factor Xa offers an improvement on existing therapies as it provides a time-dependent release of procoagulant activity without the addition of factors VIII or IX. The present study was designed to determine the effect of substituted 4-amidinophenyl benzoates on the acylation of factor Xa, as well as the subsequent deacylation rates of the resulting acyl Xa. A subset of this series of acyl Xa's were incorporated into the prothrombinase complex and recovery of catalytic activity was measured by activation of prothrombin to thrombin. Similarly, some acyl Xa's were also evaluated for their capacity to enhance clotting times of human plasma. Our study indicates that by choosing the appropriate acyl Xa, the time course of factor Xa regeneration can be modulated extensively. Animal studies will be required to show that the use of acyl Xa as a procoagulant agent is feasible in an in vivo system.