Deamidation, acylation and proteolysis of a model peptide in PLGA films.

The relative rates of deamidation, acylation and proteolysis (i.e. amide bond cleavage) were determined for a model peptide (VYPNGA) in poly (dl-lactide-co-glycolide) films. Films were stored at 70 degrees C and either 95%, 75%, 60%, 45%, 28%, or approximately 0% relative humidity and at 37 degrees C and 95% relative humidity. Peptide degradation products were identified by ESI+MS/MS and quantitated by LC/MS/MS. Extensive overlap of degradation mechanisms occurred, producing a complex mixture of products. Acylation was the dominant peptide degradation reaction (10-20% of total peptide) at early stages of PLGA hydrolysis and at intermediate relative humidity (60-45% RH). Deamidation and proteolysis were dominant (25-50% and 20-40% of total peptide, respectively) at later stages and at high relative humidity (95-75% RH). Understanding the relative rates of each peptide degradation reaction will allow for improved design of PLGA formulations that preserve the stability of peptide and protein drugs.