Human platelet alphaIIbeta3 integrin binding affinity and specificity of SJ874: antiplatelet efficacy versus aspirin

OBJECTIVE: To define the affinity and specificity of SJ874, a nonpeptide antiplatelet agent for platelet glycoprotein Ilb/IIIa integrin, and to determine the antiplatelet efficacy of SJ874 relative to those of glycoprotein IIbIIIa antagonists and aspirin. METHODS: Binding affinity and specificity of SJ874 for platelet glycoprotein IIb/IIIa integrin were determined using integrin-mediated binding and adhesion assays with human cells. Additionally, the antiplatelet efficacy of SJ874 was determined and compared with those of other glycoprotein IIb/IIIa antagonists and aspirin using light-transmittance and laser-scattering aggregometry. RESULTS: SJ874 inhibited aggregation of human platelets induced by 10 micromol/l adenosine diphosphate (ADP) with a concentration for half-maximal effect of 0.046 +/- 0.005 micromol/l using light-transmittance aggregometry. Using laser-scattering aggregometry, SJ874 was found to totally inhibit formation both of micro-aggregates and of macro-aggregates induced either by ADP or by epinephrine. In contrast, administration of 325 mg aspirin to normal healthy volunteers attenuated formation of macro-aggregates but not micro-aggregates. SJ874 inhibited binding of [125I]-fibrinogen to activated (by ADP, epinephrine, and arachidonic acid at concentrations of 100 micromol/l each) gel-filtered human platelets with a concentration for half-maximal effect of 0.0012 +/- 0.0005 micromol/l. SJ874 was demonstrated to associate more tightly with resting human platelets than did DMP754 [1] and slightly less tightly than did DMP802 [2]. SJ874 was demonstrated to exhibit a high degree of specificity for platelet glycoprotein IIb/IIIa (alphaIIb/beta3) integrin compared with other known integrins, including alphavbeta3, alphavbeta5, and alpha5beta1 (concentration for half-maximal effect > 100 micromol/l). CONCLUSION: SJ874 is a potent and specific platelet glycoprotein IIb/IIIa antagonist with high affinity for and tight association with human platelets. These data suggest that SJ874 might have good antiplatelet utility for inhibiting formation both of platelet micro-aggregates and of macro-aggregates of platelets and a long duration of action in humans due to its slow dissociation from human platelets.