Inhibition of platelet-mediated clot retraction by integrin antagonists

The effects of the platelet alphaIIb beta3 integrin (GPIIb/IIIa) antagonists XV459 (non-peptide), c7E3 (Fab monoclonal antibody) and DMP728 (cyclic peptide) as well as the alpha(v)beta3 integrin antagonists, LM609 (monoclonal antibody) and XT199 (non-peptide) on clotting and platelet-mediated clot retraction were examined. While 30 nM of XV459 had no significant effect on the kinetics of coagulation, platelet-mediated clot retraction was nearly fully inhibited at this concentration (Relative Retraction Rate = 0.09). XV459 resulted in a concentration related-response curve. Other experiments demonstrated that platelet aggregation was maximally inhibited at XV459 concentrations ranging from 30-50 nM. Similarly, c7E3 demonstrated comparable inhibitory efficacy in inhibiting either clot retraction or platelet aggregation. In contrast, DMP728, an equally potent anti-aggregatory agent with an IC50 of 20-50 nM in inhibiting platelet aggregation induced by various agonists, was found to be a less potent inhibitor of platelet-mediated clot retraction with a half-maximal inhibition of clot retraction at approximately 0.7 microM, and maximum effects at concentrations of 10 microM. The alpha(v)beta3 integrin antagonists, LM609 or XT199 were without any significant effects on either platelet-mediated clot retraction or platelet aggregation. In conclusion, these data suggest a differential efficacy among different GPIIb/IIIa antagonists in inhibiting platelet-mediated clot retraction in spite of the equivalent anti-aggregatory potency. Additionally, the alpha(v)beta3 integrin antagonists do not affect platelet-mediated clot retraction or aggregation. Further studies with the previously described alphaIIb beta3 integrin antagonists as well as others revealed a distinct correlation between the Kd to resting and activated platelets and the efficacy in inhibiting platelet-mediated clot retraction.