Novel nonpeptide antiplatelet glycoprotein llb/llla receptor antagonist, DMP754: receptor binding affinity and specificity

Objective To define the antiplatelet efficacy and specificity of the glycoprotein llb/llla complex (GPIIb/llla) antagonist prodrug DMP754 and its free acid form, XV459. Methods and materials DMP754 has an IC50 > 1 μmol/l, and, upon its conversion with esterases to its free acid form, demonstrated high potency (IC50 20–45 nmol/l) in inhibiting human platelet aggregation induced by 10 μmol/l adenosine diphosphate, 20 μg/ml collagen, 1 mmol/l epinephrine, 10 μmol/l platelet activating factor or 0.5 lU/ml thrombin. The in-vitro rate of hydrolysis of DMP754 or XV459 is much faster with human or canine liver esterases (t1/2 = 2.4–23 min) than with plasma esterases (t1,2 = 5.5–7.6 h). Platelet Gpllb/llla integrin binding affinity and specificity for XV459 were determined using cell binding/adhesion assays. Results The range of IC50 values of XV459 in inhibiting platelet aggregation in platelet-rich plasma obtained from 12 subjects was 0.035–0.069 μmol/l with a mean IC50 of 0.050 ± 0.003 μmol/l. Additionally, XV459 inhibited platelets obtained from mongrel dogs, baboons, sheep, guinea pigs, and mice with IC50 in the range 0.024–0.06 μmol/l, and IC50 in the range 0.16–5.8 μmol/l in pigs, rabbits, and rats. XV459 inhibited [125l]-fibrinogen binding to activated human platelets with an IC50 of 0.011 ± 0.003 μmol/l. XV459 demonstrated a high degree of selectivity in specifically inhibiting fibrinogen binding to the platelet integrin, GPIIb/llla (IC50 = 0.00025 ± 0.00005 μmol/l) compared with inhibiting other integrins (αvβ3, IC50 > 10 μmol/l; or αvβ5, α5β1, or α5β1, for which the IC50 exceeded 100 μmol/l). Conclusion DMP754 is a potent antiplatelet agent in inhibiting platelet aggregation, and has a high specificity and affinity for human platelet GPIIb/llla receptors.