Comparative Thrombolytic Properties of Tissue-Type Plasminogen Activator and of a Plasminogen Activator Inhibitor-1 -Resistant Glycosylation Variant, in a Combined Arterial and Venous Thrombosis Model in the Dog

Abstract

Summaryrt-PA-K, a variant of recombinant tissue-type plasminogen activator (rt-PA) with substitution of amino acids 296 to 299 with alanine (KHRR296-299AAAA) has increased fibrin-specificity and reduced sensitivity to plasminogen activator inhibitor-1; rt-PA-T, with threonine 103 replaced by asparagine has an additional glycosylation site and a reduced clearance; and rt-PA-N, with asparagine 117 mutagen-ized to glutamine lacks the high mannose carbohydrate side chain. We have investigated whether combination of these properties in a single molecule might yield an improved thrombolytic agent.The thrombolytic potency and fibrin-specificity of the combination mutant rt-PA-TNK was compared with that of rt-PA in a combined venous whole blood clot model and platelet-rich arterial eversion graft thrombosis model in dogs given intravenous heparin and aspirin. Infusion of 0.125 to 1.0 mg/kg over 60 min in groups of 4 to 5 dogs produced dose-dependent fibrin-specific venous clot lysis. The thrombolytic potency (percent lysis per mg compound administered per kg body weight) of rt-PA-TNK was significantly higher than that of rt-PA as evidenced by a higher maximal rate of lysis of 480 ± 100% versus 140 ± 40% within the 2 h observation period per mg of compound administered per kg body weight (mean ± SEM, p = 0.004) and a significantly lower dose of 0.08 ± 0.01 versus 0.21 ± 0.04 mg/kg body weight at which the maximal rate of lysis was obtained (p = 0.004). This higher thrombolytic potency was the result of a significantly reduced clearance (240 ± 32 versus 540 ± 49 ml/min, p = 0.002) and a similar specific thrombolytic activity (percent lysis per |ig/ml plasma antigen level). Arterial reflow was obtained with 1 mg/kg rt-PA and with 0.5 mg/kg rt-PA-TNK, but with each agent recanalization was consistently associated with cyclic reocclusion and reflow. The frequency of arterial recanalization was somewhat higher with rt-PA-TNK (10/12) than with rt-PA (4/12) (p = 0.07) but the total patency times during a 2 h observation period were similar.