Glucose-sensitive polypeptide micelles for self-regulated insulin release at physiological pH

Abstract

Three novel phenylboronic acid functionalized block copolymers, monomethoxy poly(ethylene glycol)-b-poly(L-glutamic acid-co-N-3-L-glutamylamidophenylboronic acid) (mPEG-b-P(GA-co-GPBA)), were synthesized by modifying mPEG-b-PGA with 3-aminophenylboronic acid (APBA). The resultant diblock copolymers self-assembled into micelles in phosphate buffer at physiological pH (pH 7.4). More interestingly, at pH 7.4, the hydrodynamic radii (R_h) of the micelles increased with an increase in glucose concentration by formation of hydrophilic PBA–glucose complex. Thus, insulin, a model drug, was loaded into the glucose-sensitive polypeptide micelles. The in vitro release profiles revealed that the release of insulin from the micelles could be triggered by glucose, i.e. less insulin was released under healthy blood glucose level (1 mg mL⁻¹ glucose), while quick release occurred under diabetic blood glucose level (above 2 mg mL⁻¹ glucose). Furthermore, in vitro methyl thiazolyl tetrazolium (MTT) assays and hemolysis tests suggested that the copolymers had good biocompatibility. Therefore, the phenylboronic acid functionalized block copolymers with high glucose-sensitivity and good biocompatibility may have potential as self-regulated insulin release systems.