(688a) Characterization of Protein Stability and Release in Monodisperse Poly(lactide-co-glycolide) Microspheres

Poly(lactide-co-glycolide) (PLG) microspheres are a common choice for controlled release drug delivery of protein therapeutics. However, several properties of PLG microspheres may have detrimental effects on encapsulated protein, causing structural destabilization, potential immunogenicity, and a loss of biological activity. Researchers have successfully utilized a number of additives to counteract PLG's detrimental effects and protect encapsulated protein molecules, but it remains important to characterize the mechanisms that drive protein destabilization in PLG microspheres. In particular, microsphere size plays an important role in polymer degradation, microsphere erosion, and accumulation of acidic by-products, all of which may affect protein stability. It is our aim to elucidate relationships between microsphere size, PLG molecular weight, and protein destabilization by monitoring changes in protein aggregation state and bioactivity during in vitro release studies. Specifically, we have investigated the PLG-induced destabilization pathways of a model drug (bovine serum albumin) and a more therapeutically relevant drug (polyclonal human immunoglobulin G) using SDS-PAGE, laser-scanning confocal microscopy, and several assaying techniques such as BCA and ELISA. Our results show that rates of loss of protein structure and activity correlate with microsphere size. These results suggest that the rate and nature of protein destabilization correspond to autocatalytic PLG degradation, which in turn controls the relationship between microsphere diameter and protein release as previously demonstrated by our research group. A clear understanding of the important behaviors affecting protein stability and release will help us to better comprehend the capabilities of PLG microspheres and to optimize microsphere formulations for more precise controlled release protein delivery.