BIOCHEMICAL AND BIOLOGICAL PROPERTIES OF A RECOMBINANT CHIMERA CONSISTING OF AMINO-ACIDS ASN-1 TO LYS-12 OF ALPHA-2-ANTIPLASMIN (FIBRIN CROSS-LINKING SITE) AND AMINO-ACIDS LEU-4 TO LEU-411 OF SINGLE CHAIN UROKINASE-TYPE PLASMINOGEN-ACTIVATOR
Fibrinolysis: An International Journal of Fibrinolysis and Thrombolysis vol:6 issue:2 pages:87-98
date:NIPPON SODA CO LTD,ODAWARA RES CTR,ODAWARA 25002,JAPAN
A recombinant chimeric plasminogen activator (APUK) consisting of amino acids Asn1 to Lys12 of alpha-2-antiplasmin (fibrin cross-linking site) and amino acids Leu4 to Leu411 of single chain urokinase-type plasminogen activator (scu-PA) was expressed in E. coli and purified to homogeneity. APUK was obtained as a single chain molecule which was quantitatively converted to a two chain moiety by treatment with plasmin; this was associated with an increase in specific amidolytic activity from less-than-or-equal-to 300 IU/mg to 95000IU/mg. Its specific activity on fibrin plates was approximately 120 000 IU/mg. Activation of plasminogen by two chain APUK obeyed Michaelis-Menten kinetics with K(m) = 3.7-mu-M and k2 = 3.4s-1. APUK induced dose-dependent lysis of a 0.12 ml I-125-fibrin labelled human plasma clot submersed in 0.5 ml citrated human plasma; 50% clot lysis in 2 h was obtained with 0.80 or 1.0-mu-g/ml single chain or two chain APUK and was associated with respectively 0 or 52% fibrinogen degradation. None of these properties of APUK was significantly different from those of recombinant scu-PA (rscu-PA) obtained in the same expression system. In the presence of Ca2+, however, significant binding of APUK, but not of rscu-PA, to forming fibrin clots was observed. The thrombolytic properties of APUK were compared with those of rscu-PA following a 1 h intravenous infusion in a combined femoral arterial whole blood clot and femoral venous blood clot model in the dog. At the arterial side, similar recanalisation rates were obtained with APUK at doses of 0.30-1.20 mg/kg (8 of 11 dogs) and with rscu-PA at doses of 0.25-1.0 mg/kg (5 of 9 dogs). Persistence of recanalisation was also similar, with patency at 2 h occurring in 6 of 11 dogs with APUK and in 4 of 9 dogs with rscu-PA. At the venous side, the thrombolytic potency of APUK was 84 +/- 33 % lysis per mg compound administered per kg body weight, versus 140 +/- 51% lysis per mg/kg for rscu-PA (p = 0.3). APUK disappeared from plasma after the end of the infusion with an initial half-life of 1.8-2.7 min, corresponding to a plasma clearance of 210-240 ml/min; corresponding values for rscu-PA were 2.5-3.0 min and 200-270 ml/min. These findings indicate that APUK, a chimera comprising the fibrin cross-linking site Of alpha-2-antiplasmin in addition to scu-PA, has the potential to bind to forming fibrin. However, this does not result in an increased thrombolytic potency in a combined arterial and venous thrombosis model in the dog.