Functionalized and Protein-Reactive Polymers Synthesized Using Controlled Polymerization Techniques
Attachment of poly(ethylene glycol) (PEG) to proteins or PEGylation has the ability to improve the pharmacokinetics and stability of protein-based drugs. In vivo circulation lifetimes can be increased and as a result, dosages may be decreased, resulting in improved patient quality of life. Polymers, including PEG, may be attached to proteins using a variety of different chemoselective reactions. Selectivity remains important as site-specific attachment of the polymer to the protein is essential for maintaining the activity of the conjugate.
Various procedures for the synthesis of site-selective polymers via reversible addition-fragmentation chain transfer polymerization (RAFT), a controlled radical polymerization (CRP) technique, are described. A previously explored and developed method for site-specific attachment to free cysteines (sulfhydryls) via Michael addition was applied to the previously un-explored copolymerization of poly(ethylene glycol) ethyl ether acrylate (PEGA) and unprotected sodium 4-styrene sulfonate (4SS) via RAFT. A two solvent system was utilized to solubilize the chain transfer agent (CTA) along with the two monomers. In addition, disulfide-containing biotin CTAs were also synthesized along with a two step synthesis of an aldehyde-containing monomer. This aldehyde-containing monomer was copolymerized via RAFT with PEGA to synthesize dual reversible avidin- and aminooxy-reactive polymers.
In addition, progress towards the synthesis of protein-polymer conjugates via ring opening metathesis polymerization (ROMP) is described. The exchange of the alkylidene unit of Grubbs catalyst with functionalized styrenes was explored, as well as the polymerization of a tetraethylene glycol (TEG) containing norbornenyl TEG ester monomer in organic solvent and under aqueous conditions in the presence of native and modified lysozyme. An activity study was performed to determine the effect of ROMP on unmodified lysozyme activity.