Supramolecular architectures constructed through a self-assembly of block copolymers are attracting much interest due to their various morphologies. In particular, polymersomes have emerged as a key area of focus because of interest in the study of their formation mechanisms, morphology tuningand their potential as delivery carriers. Among various interactions utilized in constructing polymersomes, we focused on metal coordination bond because the membrane properties of polymersomes can be changed within water by a ligand exchange reaction, allowing controlled release of loaded materials in the polymersomes. Spontaneous polymersome formation with uniform size (~100 nm) triggered by metal coordination bond, namely metallosomes, were found to occur in aqueous medium through the reaction of an anticancer agent, DACHPt, with a Y-shaped block copolymer of omega-cholesteroyl-poly(L-glutamic acid) and two-armed poly(ethylene glycol) (PEGasus-PLGA-Chole)   . Circular dichroism spectrum measurements revealed that the PLGA segment forms an alfa-helix structure within the metallosomes, suggesting that secondary-structure formation of metallo-complexed PLGA segment may drive the self-assembly of the system into vesicular structure. These metallosomes can encapsulate water-soluble fluorescent macromolecules into their inner aqueous phase, and eventually deliver them selectively into tumor tissues in mice owing to the prolonged blood circulation. Accordingly, fluorescent imaging of the tumor was successfully demonstrated along with an appreciable antitumor activity by DACHPt retained in the vesicular wall of the metallosomes, indicating the potential of metallosomes as multifunctional drug carriers.

Metallosomes as bioactive polymersomes formed by supramolecular assembly of block copolymer-metal complexation

248th National Meeting (2014)

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