Biomacromolecules 2010, 11, 3007–3013
3007
Synthesis of Statistical Copolymers Containing Multiple Functional Peptides for Nucleic Acid Delivery Russell N. Johnson, Rob S. Burke, Anthony J. Convertine, Allan S. Hoffman, Patrick S. Stayton, and Suzie H. Pun* Department of Bioengineering, University of Washington, Seattle, Washington 98195, United States Received July 16, 2010; Revised Manuscript Received September 13, 2010
Our report describes RAFT copolymerization of multiple species of active peptide monomers with N-(2hydroxypropyl(methacrylamide) (HPMA) under aqueous conditions. Resulting statistical copolymers are narrowly disperse with highly controlled molecular weight and composition. Side-chain peptide copolymers were synthesized using a DNA condensing peptide (K12), and an endosomal escape peptide (K6H5) that had been modified with an aminohexanoic linker and capped with methacrylamide vinyl on the NH2-terminus. Copolymers of HMPA-coK12 and HPMA-co-K12-co-K6H5 efficiently condensed DNA into small particles that maintain size stability even in 150 mM salt solutions. With increasing peptide content, the peptide-based polymers demonstrated gene delivery efficiencies to HeLa cells that were comparable to branched polyethylenimine.
Introduction Biomimetic copolymers containing peptide motifs combine the highly specific functions of peptides with the scalable synthesis of synthetic polymers. Recently, these hybrid materials have received increased interest because of their applications in drug and gene delivery, tissue engineering, and biosensors, to name a few.1 The architecture of these materials includes peptides incorporated as backbone segments in block copolymers or as pendant side chains. The latter offers a significantly higher concentration of peptides incorporated per polymer and also facile incorporation of multiple peptide sequences. Side-chain peptide-polymer bioconjugates can be synthesized by covalent coupling of peptides to polymer precursors or by direct polymerization of peptide monomers. Disadvantages of peptide coupling include unfunctionalized polymer side chains and generally lower peptide concentrations in the final polymer. Alternatively, synthetic copolymers with pendant peptides have been synthesized by free radical polymerization; however, resulting polymers were broadly disperse and poorly controlled.2-4 Living polymerization of peptide monomers has been demonstrated by atom transfer radical polymerization (ATRP), reverse addition-fragmentation polymerization (RAFT), and ringopening metathesis polymerization (ROMP) techniques with peptides including elastin-based pentapeptides, integrin-binding sequences, and the antibiotic gramicidin.5-9 Limitations of these approaches included (a) restriction to short peptides (typically
