Pharmacokinetics and Coronary Thrombolytic Properties of Two Human Tissue-Type Plasminogen Activator Variants Lacking the Finger-Like, Growth Factor-Like, and First Kringle Domains (Amino Acids 6–173) in a Canine Model

Abstract

The pharmacokinetics and thrombolytic properties of two variants of recombinant human tissue-type plasminogen activator (rt-PA) were studied in dogs with a copper coil induced thrombosis of the left anterior descending coronary artery. The first variant, rt-PA-ΔFEK₁-Gln¹⁸⁴, lacked amino acids 6 to 173 [comprising the fibronectin finger-like (F), the epidermal growth factor-like (E), and the first kringle (K₁) domains] and had the glycosylated Asn¹⁸⁴ mutagenized to Gln. The second variant, rt-PA-ΔFEK₁-Gln¹⁸⁴,Val²⁷⁷, had in addition Lys²⁷⁷ mutagenized to Val. Injection of 0.25, 0.50, or 1.0 mg/kg of rt-PA in groups of three dogs caused reflow in six of nine dogs, within 18 ± 15 min (mean ± SD), but was associated with reocclusion within 2 h in all animals. Injection of 0.125, 0.25, or 0.50 mg/kg of rt-PA-ΔFEK₁-Gln¹⁸⁴ caused reflow in all of nine dogs, within 17 ± 23 min, with persistent patency in four animals (p = 0.02 vs. rt-PA). Bolus injection of 4:1 mixtures of rt-PA-ΔFEK₁-Gln¹⁸⁴ and rt-PA in total amounts of 0.125, 0.25, or 0.50 mg/kg resulted in reflow in eight of nine dogs within 25 ± 21 min with persistent patency in seven (p = 0.003 vs. rt-PA, p = 0.25 vs. rt-PA-ΔFEK₁-Gln¹⁸⁴ alone). Injection of 0.25, 0.50, or 1.0 mg/kg of rt-PA-ΔFEK₁-Gln¹⁸⁴,Val²⁷⁷ produced reperfusion in six of nine dogs, within 27 ± 26 min, with persistent patency in three (p = 0.59 vs. rt-PA and p = 0.23 vs. rt-PA-ΔFEK₁-Gln¹⁸⁴). Fibrinogen breakdown was negligible with rt-PA, moderate (30 to 60%) with rt-PA-ΔFEK₁-Gln¹⁸⁴, and extensive (>90%) with rt-PA-ΔFEK₁-Gln¹⁸⁴,Val²⁷⁷. Plasma clearance was 27–39 ml/min for rt-PA-ΔFEK₁-Gln¹⁸⁴; 16–32 ml/min for rt-PA-ΔFEK₁-Gln¹⁸⁴,Val²⁷⁷; and 320–540 ml/min for rt-PA.