PSI’s Drug Delivery program is focused on creating polymers capable of extending the biological half-life of therapeutic proteins and maintaining their pharmacologic activity. Currently this stabilization is achieved by the covalent grafting of polyethylene glycol (PEG) moieties to specific amino acids along the protein sequence. This often results in a reduction in bioactivity and in certain cases undesired alterations in the protein properties. The process of protein PEGylation involves a series of expensive and laborious procedures that adds significant complexity to the development and manufacturing process.

Preliminary experiments suggest that PEG-mimicking polyphosphazenes can confer protective properties to proteins in aqueous solutions through the formation of water-soluble complexes. This eliminates the need for covalent modification and has the potential to radically simplify the development process while delivering desired improvements in the pharmacokinetics. Unlike PEG, polyphosphazenes can be designed to be biodegradable which presents additional advantages for the development of macromolecular delivery systems. PSI is currently evaluating a program specific library of 300 synthesized polymers, and the underlying technology may provide new delivery options for a variety of biological agents including peptides and small molecules. The PSI polymer system may open several attractive areas: the addition of targeting moieties, the modulation of release profiles, and high loading of therapeutic agents on the polymeric carriers.