SummaryThe effects of G4120, a cyclic Arg-Gly-Asp (RGD) containing peptide which inhibits fibrinogen binding to the platelet receptor GPIIb/IIIa, on thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) were investigated in a combined arterial and venous thrombosis model in heparinized dogs. The arterial thrombus model consisted of a 3 cm everted (inside-out) carotid arterial segment inserted into a transsected femoral artery which occludes within 30 min with platelet-rich material and which is resistant to recanalization with 0.5 mg/kg rt-PA. The venous thrombus was a 125I-fibrin labeled whole blood clot produced in the contralateral femoral vein.In 5 dogs given an intravenous bolus of 0.05 mg/kg G4120 followed by a continuous infusion of 0.05 mg/kg per hour for 3 h (group I), arterial occlusion persisted throughout a 4 h observation period and was still present at 24 h in all dogs; the extent of venous clot lysis after 120 min was 27 ± 7%. In 5 dogs given the same infusion of G4120 in combination with 0.5 mg/kg rt-PA over 60 min, recanalization of the arterial graft occurred in all dogs, within 13 ± 2 min and persisted throughout the observation period of 4 h (p = 0.01 versus G4120 or rt-PA alone); at 24 h, however, all grafts were occluded. Venous clot lysis in this group was 75 ± 8% (p = 0.002 versus G4120 alone andp NS versus rt-PA alone). Pathologic analysis revealed platelet-rich or mixed thrombus with platelet-rich and erythrocyte-rich zones. The last 6 dogs were given a reduced dose of G4120 consisting either of a 0.05 mg/kg bolus followed by an infusion of 0.05 mg/kg over 1 h in 3 dogs (group III) or of a single 0.05 mg/kg bolus in 3 dogs (group IV), both given in combination with 0.5 mg/kg rt-PA infused over 60 min. These protocols produced recanalization within 15 ± 2 and 34 ± 8 min, respectively, which was maintained throughout the 4 h observation period. Venous lysis in these groups was 63 ± 4 and 97 ± 1% respectively. Bleeding times prolonged from 1 to 2 min to >30 min with G4120, but returned towards baseline within 2 h after the end of the infusion. Platelet aggregation with ADP was completely inhibited with G4120 but partially recovered within 1 h after the end of the infusion. No fibrinogen breakdown was observed in association with the rt-PA infusion.Thus, G4120, a synthetic GPIIb/IIIa receptor antagonist, enhances and accelerates lysis of platelet-rich arterial thrombosis with rt-PA and prevents reocclusion during and within 3 h after the infusion. It may be useful for the conjunctive use with thrombolytic agents in patients with arterial thromboembolic disease.
