PEPTIDE DEGRADATION IN POLYMER MATRICES

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DESCRIPTION (Adapted from Investigator's Abstract): Peptide and polypeptide drugs such as interferons, immunoconjugates, tissue plasminogen activator, human growth hormone, and erythropoietin, made available by the biotechnological revolution, are now entering the marketplace and presenting pharmaceutical science with challenges in drug stability and delivery that range from basic science to developmental technology. This proposal links the practical problem of peptide formulation in polymer matrices for controlled-release applications (and will lead to later work on proteins in similar environments) to the basic mechanistic science involved in degradation of proteins and peptides in these unusual media. This group will study the chemical systematics of peptide and protein degradation in polymeric matrices used for controlled-release formulations and the influence of representative media on the rates and mechanisms of degradation at Asn and Asp "hot spots," one of the most common of the practically important routes of degradation of peptide and protein pharmaceuticals. The kinetics and product composition in the degradation of a model Asn-hexapeptide, VYPNGA, derived from a sequence in ACTH, will be studied in hydrogels and xerogels derived from polyvinyl alcohol (PVA) and in lyophilized preparations of polyvinyl pyrrolidone (PVP). For matrices that exhibit either stabilizing or accelerating effects, quantitative relationships will be developed between degradation rates and water content, and the matrices will be characterized by their glass transition temperatures, activity of water, differential scanning calorimetry, and nuclear magnetic resonance. Small-molecule models of the cyclic-imide intermediate that mediates intermediates (by 18O exchange), and product ratios in ring opening as a function of pH, buffer identity and concentration, and temperature. Transition states for ring formation will be approached through the microscopic reverse, the attack of amines on the cyclic imide. Steric, electronic and intramolecular catalytic effects will be examined by structural variation of the model compounds. The model compounds will also be examined in polymeric matrices found to be of interest with the Asn hexapeptide. The principal investigator's experience in the field of quantitative mechanistic bioorganic chemistry will be supplemented by collaborators and co-investigators with expertise in the degradation of peptides and proteins in solution and solid phases, in polymeric controlled-release formulations, in the characterization of polymeric matrices by polymer-science approaches, and in theoretical approaches to the glassy state.