Oral antiplatelet efficacy and specificity of a novel nonpeptide platelet GPIIb/IIIa receptor antagonist, DMP 802

This study was undertaken to define the platelet glycoprotein alpha IIb beta 3 integrin (GPII/IIIa) affinity, specificity, and oral antiplatelet efficacy of DMP 802, a small-molecule nonpeptide antiplatelet agent. Platelet GPIIb/IIIa integrin binding affinity and specificity for DMP 802 were determined by using binding and adhesion assays with cells from various species, including human. DMP 802 demonstrated a potent antiplatelet efficacy [median inhibitory concentration (IC50), 0.029 +/- 0.0042 mu M] in inhibiting human platelet aggregation induced by 10 mu M adenosine diphosphate (ADP), as assessed by light-transmittance aggregometry. DMP 802 inhibited I-125-fibrinogen binding to activated (ADP, epinephrine, and arachidonic acid at 100 mu M each) gel purified human platelets with an IC50 of 0.012 +/- 0.003 mu M. DMP 802 demonstrated tight association with unactivated human, baboon, or canine platelets (t(1/2) of dissociation, 32 +/- 2, 32 +/- 13, and 11 +/- 1 min, respectively). DMP 802 binds with high affinity to both unactivated and activated human platelets (Kd = 0.61 +/- 0.17, 0.57 +/- 0.21 nM, respectively). DMP 802 demonstrated species specificity in inhibiting platelet aggregation with IC,, values ranging from 0.025 to 0.092 mu M (human, guinea pig, dog, swine, hamster) and 0.88-1.0 mu M (rabbit and rat) in platelets obtained from these various species. DMP 802 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alpha IIb/beta 3) as compared with other integrins including alpha v beta 3 (IC50, >10 mu M); alpha v beta 5 (IC50, >100 mu M), alpha 4 beta 1 (IC50, >100 mu M), and alpha 5 beta 1 (IC50, >10 mu M). Oral antiplatelet efficacy of DMP 802 was examined after single oral (0.05-0.20 mg/kg) and after repeated oral dosing at 0.05 mg/kg daily for 5 days in mongrel dogs. Dose-dependent antiplatelet efficacy with an extended duration of antiplatelet efficacy was demonstrated based on ex vivo inhibition of platelet aggregation induced by 100 mu M ADP. DMP 802 has an oral bioavailability of 14.9% in dogs. In conclusion, the a sulfonamide isoxazoline analog, DMP 802, is a novel oral antiplatelet agent with high affinity, relatively slow dissociation rate and specificity for human platelet GPIIb/IIIa receptors.