A VARIANT OF T-PA (T103N, KHRR-296-299 AAAA) THAT, BY BOLUS, HAS INCREASED POTENCY AND DECREASED SYSTEMIC ACTIVATION OF PLASMINOGEN

In the accompanying paper, we reported that the properties of decrease d plasma clearance rate, increased fibrin specificity, and resistance to inactivation by PAI-1 could be effectively combined in the t-PA var iant T103N, KHRR 296-299 AAAA. In the current study we.evaluated the i n vivo efficacy of this variant as well as variants containing the ind ividual mutations T103N and KHRR 296-299 AAAA. Plasma clearance and in vivo lysis of whole blood and platelet-rich clots were determined in a rabbit arterio-venous shunt model. The T103N containing variants wer e administered as an intravenous (i. v.) bolus. KHRR 296-299 AAAA and t-PA were infused i. v. over 90 min. The clearance rate of the KHRR 29 6-299 AAAA variant was similar to t-PA. However, the clearance of the T103N and T103N, KHRR 296-299 AAAA variants were 8 and 6-fold reduced, respectively. Potency of the variants relative to t-PA on whole blood clots ranged from 0.9 (T103N, KHRR 296-299 AAAA) to 1.7 (T103N). Rela tive potency on platelet-rich clots ranged from 2.4 (T103N) to 4.2 (T1 03N, KHRR 296-299 AAAA). Fibrinogen concentrations in rabbits 120 min after dosing with a 2.5 mg/kg bolus were: 24, 16, 82, and 77% of initi al for t-PA; T103N; KHRR 296-299 AAAA; and T103N, KHRR 296-299 AAAA tr eatment groups, respectively. These results suggest that the T103N, KH RR 296-299 AAAA variant of t-PA, given as a bolus, could result in gre ater efficacy, particularly on refractory platelet-rich clots, without inducing the severe systemic lytic state produced by a bolus of a les s fibrin specific variant.