Dr. Todd M. Przybycien
Carnegie Mellon University
Departments of Chemical Engineering and Biomedical Engineering
Friday-February 22, 2013
MUB- Alumni Lounge
Unconventional Applications of Poly(ethylene glycol)-modified Proteins in BioProcessing and Drug Delivery
The covalent attachment of poly(ethylene glycol) (PEG) polymer chains, or “PEGylation,” improves the efficacy of protein drugs by extending their half-lives in the circulation without adversely affecting biological binding activity: the PEG chains are thought to hinder recognition by proteases, inhibitors and antibodies through steric interactions and to retard renal clearance through increased molecular size. We used a more complete understanding of the solution and interfacial adsorption behavior of PEG-protein conjugates to explore new applications of protein PEGylation in bioprocessing and drug delivery.
We have developed new, high selectivity protein affinity chromatography media by PEGylating immobilized protein affinity ligands outside of the target binding site. This discourages the non-specific binding of contaminant species without decreasing target binding. We find selectivity enhancements for IgG-class antibodies of 2x to 3x for Protein A affinity chromatography media modified with 5 kDa and 20 kDa PEG chains relative to the un-modified media, without loss of antibody binding affinity. Increased contaminant rejection by Protein A media has important implications for simplifying downstream processing operations for monoclonal antibody production and for extending the operating lifetime of this expensive class of bioseparations media.
We have exploited PEGylation to reduce denaturing adsorptive interactions between proteins and interfaces that limit the successful delivery of protein drugs from poly(lactide-co-glycolide) (PLG) microsphere delivery systems. Oil/water interfaces are present during the generation of protein-loaded PLG microspheres by the double emulsion technique and solid/water interfaces are present as the microspheres erode during delivery. The depressed adsorption isotherms of conjugates reduce the extent of adsorption at denaturing interfaces and the attached PEG random coils serve as steric diluents at interfaces. While PEGylation with 20 kDa PEG has little effect on protein behavior at ethyl acetate/water interfaces, at PLG/water interfaces we find decreased extents of adsorption, increased reversibility of adsorption and decreased tendency to aggregate. These results have translated to ~50% and ~100% improvements in active protein release for monoPEGylated and diPEGylated ribonuclease A, respectively.