RGD Modified Protein–Polymer Conjugates for pH-Triggered Targeted Thrombolysis

It holds great promise to develop thrombolytic agent delivery systems with prolonged circulation time, minimized adverse effect, and preferential thrombolytic activity at the thrombus site. In this work, a pH-triggered delivery system for the thrombolytic agent was synthesized. Fluorescein isothiocyanate-labeled urokinase-type plasminogen activator (uPA) was conjugated to oxidized dextran (Oxd) via the pH-sensitive imine linkage, and then the conjugation was modified with RGD peptide. The uPA-Oxd conjugates displayed enhanced stability to resist enzymatic hydrolysis in comparison with the native uPA. Meanwhile, the bioactivity of uPA in the uPA-Oxd conjugates was masked at physiological pH and regenerated under weak acidic condition due to the release of uPA via the hydrolysis of imine bond in the conjugates. RGD modification endowed the conjugates with targeting ability to the thrombus site due to the specific peptide-GP IIb/IIIa binding and enhanced the thrombolysis efficacy via an endogenous low-pH triggered uPA release at the thrombus site, reducing the risk of acute hemorrhage complication. Thus, the RGD modified pH-sensitive uPA-Oxd conjugates provide a promising potential of the system in local thrombolysis therapy.