Peptide drug carrier: studies on incorporation of vasopressin into nano-associates comprising poly(ethylene glycol)-poly( -aspartic acid) block copolymer

To fabricate peptide delivery systems using polymeric drug carriers, an oligopeptide model drug, Arg⁸]-vasopressin(AVP), was incorporated into nano-associates comprising poly(ethylene glycol)-( -aspartic acid block copolymer (PEG-P(Asp)). Incorporation of the AVP was accomplished using a dialysis method. Static light scattering measurements revealed that the acid-type and mixture-type PEG-P(Asp)s formed nano-associates independently without AVP, while the salt form PEG-P(Asp) did not. High loading of AVP into acid-type PEG-P(Asp) was observed with loading levels controlled by changing the molar ratio of drug and block copolymer. Mixture-type PEG-P(Asp) did not show high loading and the salt-type PEG-P(Asp) form did not at all. Acid-type P(Asp) homopolymer formed associates including AVP, however, it was insoluble in aqueous medium. Dynamic light scattering measurements showed that the acid-type PEG-P(Asp) associates sizes narrowly clustered around 150 nm. This finding suggests that associates of acid-type PEG-P(Asp) effectively incorporates peptides possibly via a hydrogen bonding interaction between the block copolymer and the peptide.