Conjugation to hyperbranched polyglycerols improves RGD-mediated inhibition of platelet function in vitro

RGD (arginine-glycine-aspartic acid) is a known peptide sequence that binds platelet integrin GPIIbIIIa and disrupts platelet-fibrinogen binding and platelet cross-linking during thrombosis. RGD peptides are unsuitable for clinical applications due to their high 50% inhibitory concentration (IC50) and low in vivo residence times. We addressed these issues by conjugating RGD peptides to biocompatible macromolecular carriers: hyperbranched polyglycerols (HPG) via divinyl sulfone. The GPIIbIIIa binding activity of RGD was maintained after conjugation and the effectiveness of the HPG-RGD conjugate was dependent upon molecular weight and the number of RGD peptides attached to each HPG molecule. These polyvalent inhibitors of platelet aggregation decreased the IC50 of RGD in an inverse linear manner based on the number of RGD peptides per HPG. Since HPG-RGD conjugates do not cause platelet activation by degranulation and certain substitution ratios do not increase fibrinogen binding to resting platelets, HPG-RGD may serve as a model for a novel class of antithrombotics.