CHARACTERIZATION OF A NOVEL SERIES OF APROTININ-DERIVED ANTICOAGULANTS .1. IN-VITRO AND PHARMACOLOGICAL PROPERTIES

Previous investigations have indicated that interference with the init ial level of the blood coagulation may lead to effective antithromboti c therapy. Recently a series of potential coagulation inhibitors deriv ed from bovine pancreatic trypsin inhibitor (BPTI, aprotinin) was desc ribed. We have determined their inhibition constants, effects on coagu lation assays, effects in an in vitro human thrombosis model and pharm acological profiles in hamsters. The aprotinin-derived analogues (4C2, 7L22, 5L15, 6L15, 5L84) showed significantly increased inhibitory act ivity towards factor Xa, factor VIIa-tissue factor (TF) complex, facto r XIa and plasma kallikrein or a combination of them, and a significan tly decreased plasmin inhibition as compared to aprotinin. In the coag ulation assays, 4C2 and 7L22 mainly inhibited factor Xa, 5L15 and 6L15 inhibited factor VIIa-TF complex and 5L84 inhibited factor Xa, factor VIIa-TF complex and the contact activation. In flow chamber experimen ts with human blood 7L22, 5L15, 6L15, 5L84 and rTAP significantly inhi bited fibrin formation and platelet deposition on extracellular matrix from phorbol ester stimulated human endothelial cells both under high and low shear stress and in the presence of low molecular weight hepa rin. The pharmacological profiles of the aprotinin analogues and rTAP with a mean residence time of 64 to 140 min were not significantly dif ferent. Modification of an aprotinin analogue with PEG (5L15-PEG) resu lted in a 10-fold decrease of the inhibition constant for the factor V IIa-TF complex and in a significant prolongation of the secondary half -life, while the initial half-life was unchanged. Thus the investigate d aprotinin-derived coagulation inhibitors resulted in a series of com bined coagulation inhibitors with a pharmacological behaviour, which j ustifies in vivo testing of their potential antithrombotic action, as reported in the accompanying paper.