The chimeric molecule
K1K2Pu, comprising the two kringle domains (K1 and K2) of
tissue-type plasminogen activator (t-PA) and the COOH-terminal region with the
serine protease domain (Pu) of
urokinase-type plasminogen activator (
u-PA), was previously shown to have a 5- to 10-fold reduced clearance rate with maintained specific thrombolytic activity, resulting in an increased thrombolytic potency in animal models of venous and arterial
thrombosis. To document the thrombolytic potential of
K1K2Pu, the thrombolytic potency and
fibrin specificity were studied in a combined platelet-rich arterial eversion graft
thrombosis and venous whole
blood clot model in heparinized dogs (100 U/kg bolus and 50 U/kg per h infusion). Dose-response effects of bolus
injections of
K1K2Pu (0.032 to 0.25 mg/kg) were compared with those of recombinant t-PA (rt-PA) and of recombinant single chain
u-PA (rscu-PA) (0.25 to 1.0 mg/kg each) in groups of five or six dogs, each given
heparin with or without the
thromboxane synthase inhibitor/prostaglandin endoperoxide receptor antagonist
ridogrel.
Heparin and
ridogrel in the absence of a
thrombolytic agent did not produce arterial reflow or venous clot lysis in five dogs. Addition of
K1K2Pu, rt-PA or rscu-PA resulted in a dose-dependent induction of arterial reflow and of venous clot lysis in the absence of systemic fibrinolytic activation and
fibrinogen breakdown. Consistent arterial reflow required 0.063 mg/kg of
K1K2Pu and 0.5 mg/kg of rt-PA or of rscu-PA. The thrombolytic potency for venous clot lysis, expressed as percent lysis per mg compound administered per kg
body weight, was (mean +/- SEM) 750 +/- 160 for
K1K2Pu, 68 +/- 17 for rscu-PA (p less than 0.001 vs.
K1K2Pu) and 110 +/- 29 for rt-PA (p less than 0.001 vs.
K1K2Pu). The plasma clearance rates were significantly lower for
K1K2Pu than for rscu-PA and rt-PA. In the absence of
ridogrel, arterial reflow was significantly slower and was followed by cyclic reocclusion and reflow; however, venous clot lysis was unaffected. Template bleeding times were not significantly altered in the absence but were markedly prolonged in the presence of
ridogrel. These results confirm and establish that, when given as a bolus injection,
K1K2Pu has an approximately 10-fold higher thrombolytic potency for arterial and venous thrombolysis than does rt-PA or rscu-PA. Thrombolysis with
K1K2Pu is obtained in the absence of systemic fibrinolytic activation and
fibrinogen breakdown. These properties suggest that
K1K2Pu offers potential for
thrombolytic therapy by bolus administration in patients with thromboembolic disease.