PROCOAGULANT ACTIVITY OF REVERSIBLY ACYLATED HUMAN FACTOR XA

The plasma clotting factors used to treat hemophiliacs who have develo ped inhibitory antibodies have a shared history of limited clinical sa fety and utility. To improve on existing bypass factors, we have devel oped a reversibly acylated form of human plasma factor Xa capable of p roviding a time-dependent release of procoagulant activity. Factor Xa was treated with p-amidinophenyl p'-anisate to generate anisoyl Xa. Th e chemical modification of the protein involves acylation of the activ e site serine residue of factor Xa. Anisoyl Xa deacylated in a time, p H, and temperature-dependent manner. Active factor Xa generated on dea cylation of anisoyl Xa exhibited amidolytic and prothrombinase complex activities in in vitro assays, the level being comparable to those of untreated factor Xa. When Anisoyl Xa was infused into rabbits, active factor Xa was generated on deacylation of the acylated enzyme, which shortened the activated partial thromboplastin time (APTT) in a dose-d ependent manner. The duration of effect on rabbit APTT could be direct ly correlated to the level of human plasma factor Xa. Because anisoyl Xa bypasses the ''tenase'' complex that is compromised in hemophilia A and B and is unaffected by inhibitory antibodies, it has the potentia l to be used as an effective bypass therapy. (C) 1995 by The American Society of Hematology.