FASTER-ACTING AND MORE POTENT FORM OF TISSUE-PLASMINOGEN ACTIVATOR

Current treatment with tissue plasminogen activator (tPA) requires an intravenous infusion (1.5-3 h) because the clearance of tPA from the c irculation is rapid (t(1/2) approximate to 6 min). We have developed a tPA variant, T103N,N117Q, KHRR(296-299)AAAA (TNK-tPA) that has substa ntially slower in vivo clearance (1.9 vs. 16.1 ml per min per kg for t PA in rabbits) and near-normal fibrin binding and plasma clot lysis ac tivity (87% and 82% compared with wild-type tPA). TNK-tPA exhibits 80- fold higher resistance to plasminogen activator inhibitor 1 than tPA a nd 14-fold enhanced relative fibrin specificity. In vitro, TNK-tPA is 10-fold more effective at conserving fibrinogen in plasma compared to tPA. Arterial venous shunt models of fibrinolysis in rabbits indicate that TNK-tPA (by bolus) induces 50% lysis in one-third the time requir ed by tPA (by infusion). TNK-tPA is 8- and 13-fold more potent in rabb its than tPA toward whole blood clots and platelet-enriched clots, res pectively. TNK-tPA conserves fibrinogen and, because of ifs slower cle arance and normal clot lysis activity, is effective as a thrombolytic agent when given as a bolus at a relatively low dose.