Site-Specific Insulin-Trehalose Glycopolymer Conjugate by Grafting from Strategy Improves Bioactivity

Insulin is an important therapeutic protein for the treatment of diabetes, but it is unstable and aggregates upon exposure to environmental stressors encountered during storage and transport. To prevent degradation of the protein in this manner and retain as much in vivo bioactivity as possible, a well-defined insulin trehalose glycopolymer conjugate was synthesized. To accomplish this, a strategy was employed to site specifically modify insulin with a polymerization initiator at a particular conjugation site; this also facilitated purification and characterization. Lysine of the B chain was preferentially modified by conducting the reaction at high pH, taking advantage of its higher nucleophilicity than the N-terminal amines. Trehalose monomer was polymerized directly from this macroinitiator to form a well-defined conjugate. Bioactivity of the site specific conjugate was shown to be higher compared to the nonspecific conjugate and the same as the analogous site-specific poly(ethylene glycol) (PEG) conjugate, as confirmed by the insulin tolerance test (ITT) in mice. The conjugated trehalose glycopolymer also stabilized insulin to heat as measured by high-performance liquid chromatography (HPLC).