Toshiaki Aoki

The anti-platelet and anti-thrombotic effects of FK633, a peptide-mimetic GPIIB/IIIA antagonist

The anti-platelet and anti-thrombotic properties of FK633, a peptide mimetic GPIIb/IIIa antagonist were studied. In human platelet rich plasma, FK633 inhibited ADP-, collagen-, thrombin-, and PAF-induced platelet aggregation with IC50 values of 103, 87, 98, and 239 nM, respectively. RGDS acted similarly, but its potency was about 1,000 times weaker than FK633, FK633 inhibited 125I-fibrinogen binding to human washed platelet with an IC50 of 88 nM. FK633 did not inhibit alphavbeta3, alpha5beta1, and alphavbeta1 integrin-mediated cellular adhesion up to 1.0mM, while RGDS inhibited all these interactions. In dogs, bolus injection of FK633 at 0.1 mg/kg significantly suppressed ex vivo ADP-induced platelet aggregation (>40% inhibition) and thrombus formation at stenosed and injured coronary artery, but did not prolong template bleeding time. However, FK633 inhibited >90% ADP-induced aggregation at 0.32 mg/kg, causing significant prolongation of the bleeding time. Thus, FK633 is a specific GPIIb/IIIa antagonist with potent anti-thrombotic effect in vivo, but careful dosing study might be necessary to avoid the bleeding complications in the clinic.

Comparison of the Antithrombotic Effects of FK633, GPIIb/IIIa Antagonist, and Aspirin in a Guinea Pig Thrombosis Model

Antiplatelet and antithrombotic effects of FK633 (a GPIIb/IIIa antagonist) and aspirin were compared. FK633 at 0.32 mg/kg i.v. or aspirin at 10 mg/ kg i.v. inhibited ex vivo collagen-induced aggregation by >50% for 1 hour in guinea pigs. However, aspirin was very weak in inhibiting ADP-induced aggregation. In vivo antithrombotic effects of FK633 and aspirin were compared using a FeCl3-induced carotid artery thrombosis model in guinea pigs. Pretreatment with 0.32 mg/kg i.v. of FK633 significantly prevented occlusive thrombus formation, but aspirin at 10 mg/kg i.v. did not. In thrombolysis experiments, adjunctive use of FK633 (0.32 mg/kg i.v.) with rt-PA (0.3 mg/kg bolus+1.0 mg/kg/hr) achieved reperfusion in five of five animals without reocclusion. Aspirin (10O mg/kg i.v.) with rt-PA also achieved reperfusion in three of five animals with high incidence of reocclusion. These results suggest that FK633 may be a more effective antithrombotic agent than aspirin due to its agonist-independent antiplatelet effects.

Design, synthesis, and evaluation of orally active fibrinogen inhibitors

Abstract Low molecular weight and orally active fibrinogen inhibitors are described. The compounds studied in this work were rationally designed based on a metabolic study of a peptidic fibrinogen inhibitor, 4-(4-amidinophenoxy)butanoylaspartylvaline ( 1 , FK633), which led to the synthesis of a potent and orally active antiplatelet agent, 4-(4-amidinophenoxy)butanoylaspartylvalylthiomorpholine 1,1-dioxide ( 3f , FR158999).

Design, synthesis, and evaluation of fibrinogen inhibitors, ω-(p-amidinophenoxy) alkanoylaspartic acid derivatives

Abstract Low molecular weight inhibitors of platelet aggregation are described. Compounds studied in this work were derived from the presumed active conformation of the adhesion tripeptide, ArgGlyAsp, using computer simulations. These studies led to the synthesis of a potent anti-platelet agent, 4-(4-amidinophenoxy)-butanoylaspartylvaline (6, FK633).