Summary
Tissue-type plasminogen activator (t-PA) is a fibrin-specific agent which has been
used to treat acute myocardial infarction. In an attempt to clarify the determinants
for its rapid clearance in vivo and high affinity for fibrin clots, we produced five
variants containing amino acid substitutions in the finger domain, at amino acid residues
7–9, 10–14, 15–19, 28–33, and 37–42. All the variants had a prolonged half-life and
a decreased affinity for fibrin of various degrees. The 37–42 variant demonstrated
about a 6-fold longer half-life with a lower affinity for fibrin. Human plasma clot
lysis assay estimated the fibrinolytic activity of the 37–42 variant to be 1.4-fold
less effective than that of the wild-type rt-PA. In a rabbit jugular vein clot lysis
model, doses of 1.0 and 0.15 mg/kg were required for about 70% lysis in the wild-type
and 37–42 variant, respectively. Fibrinogen was degraded only when the wild-type rt-PA
was administered at a dose of 1.0 mg/kg. These findings suggest that the 37–42 variant
can be employed at a lower dosage and that it is a more fibrin-specific thrombolytic
agent than the wild-type rt-PA.
