Rapid Interruption Of Occlusive Thrombus Formation By The Protein C Activator Enzyme EWE Thrombin (ProCase) In Primates

A hemostatically safe antithrombotic treatment with rapid onset could significantly improve the chances for survival during acute thrombotic events such as heart attack and ischemic stroke. Current thrombolytic treatment with tissue plasminogen activator (tPA) is effective at halting and reversing the progression of arterial thrombi, but bleeding side-effects significantly limit its usefulness. EWE thrombin (ProCase) is an investigational selective protein C activator thrombin analog under development for treating acute thrombotic emergencies. We therefore tested the ability of EWE thrombin to interrupt arterial-type thrombus formation in baboons compared to a standard interventional dose of tPA (1mg/kg, iv). Thrombosis was initiated by interposing 2mm or 4mm internal diameter (ID) collagen coated ePTFE vascular grafts within an arterio/venous shunt. Platelet thrombus formation was monitored by gamma camera imaging of autologous ¹¹¹In-labelled platelets for a total of 90 min in the 4mm grafts, or until occlusion time in the 2mm grafts. Fibrin deposition was determined by direct measurement of ¹²⁵I-labelled fibrinogen. All interventions were given systemically, starting 30 min or 15 min after thrombus initiation for the 4mm grafts and 2mm grafts, respectively. In the 4mm devices, treatment with tPA reduced graft-associated platelet accumulation by 17% and fibrin deposition by 61% compared with controls (n=6 each). A negative platelet accumulation rate, which is an indication of thrombolysis, occurred between 40-50 min after initiating tPA treatment. EWE thrombin, at doses ranging from 2-10µg/kg iv bolus rapidly interrupted thrombus development and reduced platelet deposition by 43-65% (n=4). Fibrin deposition was also reduced by 36-49% compared with controls. A negative platelet accumulation rate occurred between 10-15 min after EWE thrombin treatment, compared with continuous platelet accumulation in all control experiments. In the 2mm ID grafts, 0/6 control group devices remained patent with an average occlusion time of 25±2 min. By comparison, EWE thrombin (10µg/kg iv bolus given at 15 min) successfully interrupted occlusive thrombus formation in 40% of the devices (2/5) during the 60 min study, and significantly prolonged the occlusion time to an average of 43±8 min. These data suggest that EWE thrombin can effectively interrupt occlusive arterial-type thrombus development at very low doses, and appears to be more effective and act more rapidly than tPA at limiting experimental platelet-rich thrombus accumulation. We conclude that EWE thrombin may be a more effective and safer alternative to tPA for treating acute thrombotic emergencies.