A LONG-HALF-LIFE AND FIBRIN-SPECIFIC FORM OF TISSUE-PLASMINOGEN ACTIVATOR IN RABBIT MODELS OF EMBOLIC STROKE AND PERIPHERAL BLEEDING

Background and Purpose We compared the activity of a new long-half-lif e, fibrin-specific tissue-type plasminogen activator (TPA) variant wit h that of wild-type TPA in rabbit models of embolic stroke and periphe ral bleeding. Methods In the embolic stroke model, TPA-induced clot ly sis is followed by continuous monitoring of a radiolabeled clot lodged in the middle cerebral artery. Twenty-four hours after embolization a nd treatment with either thrombolytic agent or excipient, the brains a re removed, fixed, and evaluated for cerebral hemorrhage. In a paralle l template bleeding time experiment, the effects of equipotent doses o f the two TPA molecules were measured. Results Infusion of wild-type T PA or bolus administration of the TPA variant resulted in dose-depende nt clot lysis. The TPA variant was found to be an order of magnitude m ore potent than wild-type TPA on a milligram-per-kilogram basis. Unlik e wild-type TPA, the variant caused less systemic activation of plasmi nogen (P<.05) and fewer hemorrhagic transformations in this model (P<. 05). The TPA variant did not extend template bleeding times. Conclusio ns These findings show that by combining increased fibrin specificity with decreased plasma clearance, it is possible to produce a thromboly tic agent that is more convenient and more potent than wild-type TPA. At the same time the significant reduction in hemorrhagic conversions may be attributable to the conservation of systemic plasminogen seen w ith this molecule.