Polymer-protein conjugation is attractive for a large number of therapeutic and diagnostic applications. Controlled radical polymerization offers a unique tool to design well defined polymers with functional end-groups that could be used for protein conjugation. Here we compare head-to-head different RAFT based approaches to design polymers with a protein-reactive end-group. For this purpose, a series of functional chain transfer agents were synthesized. 2-propionic acidyl butyl trithiocarbonate was modified with either a NHS (N-hydroxysuccinimide) or a PFP (pentafluorophenyl) ester as lysine-reactive moiety, and either a furan-protected MAL (maleimide) or PDS (pyridyl disulfide) as cysteine-reactive moiety. These functional CTAs were used for RAFT polymerization of 2-hydroxyethylacrylate. Polymerization with NHS, PFP and PDS CTAs provided well defined polymers with low dispersity. The maleimide CTA however, was prone to side-reaction above 50% conversion. This is probably due to early deprotection of the maleimide during polymerization. Additionally, further side-reactions were observed upon final deprotection of the maleimide, even after end-capping of the trithiocatbonate group. Protein conjugation was performed in aqueous buffer using bovine serum albumin and ovalbumin as model proteins, and evaluated by SDS-PAGE. PFP-functionalized polymers were found to outperform NHS-polymers, likely owing to the higher hydrolytic stability of the PFP group. PDS-functionalized polymers outperformed the MAL-polymers, likely due to the higher end-group fidelity obtained via the PDS route. Additionally, the disulfide bond between formed with the PDS-strategy can be cleaved in reductive medium, which could offer particular advantages.  

Protein-reactive RAFT agents for the design of polymer-protein conjugates

248th National Meeting (2014)

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