Glycosylation improves α-chymotrypsin stability upon encapsulation in poly(lactic-co-glycolic)acid microspheres

Enhancing protein stability upon encapsulation and release from polymers is a key issue in sustained release applications. In addition, optimum drug dispersion in the polymer particles is critical for achieving release profiles with low unwanted initial "burst" release. Herein, we address both issues by formulating the model enzyme α-chymotrypsin (α-CT) as nanoparticles to improve drug dispersion and by covalently modifying it with glycans to afford improved stability during encapsulation in poly(lactic-co-glycolic) acid (PLGA) microspheres. α-CT was chemically modified with activated lactose (500 Da) to achieve molar ratios of 4.5 and 7.1 lactose-to-protein. The bioconjugates were co-lyophilized with methyl-β-cyclodextrin followed by suspension in ethyl acetate to afford nanoparticles. Nanoparticle formation did not significantly impact protein stability: less than 5% of the protein was aggregated and the residual activity remained above 90% for all formulations. Using a solid-in-oil-in-water (s/o/w) methodology developed in our laboratory for nanoparticles, we obtained a maximum encapsulation efficiency of 61%. Glycosylation completely prevented otherwise substantial protein aggregation and activity loss during encapsulation of the non-modified enzyme. Moreover, in vitro protein release was improved for glycosylated formulations. These results highlight the potential of chemical glycosylation to improve the stability of pharmaceutical proteins in sustained release applications.