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HR Lu, HR Lijnen, JM Stassen and D Collen
Center for Thrombosis and Vascular Research, K.U. Leuven, Belgium.
The recombinant chimeric plasminogen activator, rt-PA-delta FE/scu-PA- e,
consisting of amino acids 1 to 3 and 87 to 274 of tissue-type plasminogen
activator (t-PA) and amino acids 138 to 411 of single-chain urokinase-type
plasminogen activator (scu-PA), has a markedly increased thrombolytic
potency following its continuous intravenous infusion in animal models of
venous thrombosis (Collen et al, Circulation, in press). In the present
study, the thrombolytic potencies of intravenous bolus injections of
rt-PA-delta FE/scu-PA-e, of recombinant t-PA (rt- PA), and of recombinant
scu-PA (rscu-PA), given alone or in combination, were compared with those
of intravenous infusions in a hamster pulmonary embolism model.
Dose-dependent clot lysis was obtained in the absence of systemic
activation of the fibrinolytic system and fibrinogen breakdown. In bolus
injection experiments, the maximal rate of clot lysis, expressed in percent
clot lysis per milligrams per kilogram compound administered, was 120 +/-
10 for rt- PA, 54 +/- 8 for rscu-PA, and 2,100 +/- 500 for rt-PA-delta
FE/scu-PA-e (P less than .01 v rt-PA or rscu-PA). Comparative results with
continuous infusion over 1 hour were 270 +/- 64, 99 +/- 18, and 1,500 +/-
250 (P less than .01 v rt-PA or rscu-PA) percent lysis per mg/kg compound
infused for rt-PA, rscu-PA, and rt-PA-delta FE/scu-PA-e, respectively.
Thus, rt-PA and rscu-PA are more potent when administered as an infusion
than as a bolus, whereas rt-PA-delta FE/scu-PA-e is at least as potent when
administered as a bolus. Combined bolus injections of rt-PA and rscu-PA had
a 2.2-fold synergistic effect on clot lysis, but no synergism was observed
with combined bolus injections or with combined infusions of rt-PA and
rt-PA-delta FE/scu-PA-e, or of rscu-PA and rt-PA-delta FE/scu-PA-e. The
present study thus shows that rt-PA- delta FE/scu-PA-e is much more potent
for clot lysis than rt-PA or rscu- PA when administered as a bolus
injection, but no synergistic interaction is observed between the chimera
and either rt-PA or rscu-PA.
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