Design and characterization of polymeric micelles with entrapped peptides

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A variety of poly (ethylene glycol) (PEG) /polyamino acid block copolymers was synthesized by initiating the ring opening polymerization of alpha-amino acid N-carboxyanhydride (NCA) from primary amino group settled on the chain end of alpha-methoxy-omega-amino-poly (ethylene glycol). After the removal of protecting group, hydrophobic moieties were introduced into the side chain of poly (amino acid) segments of the block copolymer to control the hydrophilic/hydrophobic balance, allowing to form stable and monodispersive polymeric micelle. Micelles were prepared by solvent-substituting technique in the presence of peptide models to obtain peptide-loaded polymeric micelles. A fluorescent dye, pyrene, was used as a model compound for peptides. Dynamic light scattering measurements revealed a formation of micelles with relatively narrow distribution from block copolymers with considerably high substitution degree of side chain. These micelles had a very low critical micelle concentration (-30mg/l), indicating that they are thermodynamically stable. Of interest, in the case of block copolymers of PEG with poly (L-lysine) substituted with hydrocynnamic acid (HCA), secondary structure of poly (L-lysine) segments changed from random to beta-sheet upon micellization, indicating a close relationship between micelle formation and secondary structure of poly (amino acid) segments forming the core. Pyrene in the micelle was shown to be stably entrapped in the core, suggesting a promising feature of these micelles as novel peptide carriers.