Biocompatible Polymer Vesicles

POLYMER CHEMISTRY

A new class of pH-sensitive polymer vesicles formed from diblock copolymers could potentially be used as nanosized drug- and protein-delivery vehicles, according to the researchers in England who synthesized the materials (J. Am. Chem. Soc., published online Dec. 1, http://dx.doi.org/10.1021/ja056514l).

Unlike many literature examples of block copolymer vesicles, our diblock copolymers can be readily synthesized in high yields from commercially available monomers by atom transfer radical polymerization in methanol at room temperature without using protecting group chemistry, says University of Sheffield chemistry professor Steven P. Armes. He carried out the work with Andrew L. Lewis, research & technology director of Biocompatibles, based in Farnham, U.K., and coworkers.

The vesicles are composed of an AB diblock copolymer in which the A block is based on a highly biocompatible zwitterionic monomer that contains the biomimetic phosphorylcholine motif. The B block is based on a pH-responsive tertiary amine methacrylate monomer. The copolymer dissolves in aqueous acidic solution and self-assembles into well-defined vesicles above pH 7. The vesicles dissociate completely below pH 6.

The phosphorylcholine motif makes the polymers the most authentic polymeric analogs of conventional liposomes that have been reported to date, Armes notes. The vesicles can be easily prepared without recourse to organic solvents simply by switching the solution pH. They are also stable under physiologically relevant conditions.

The team also showed that the water-soluble anticancer drug doxorubicin can be encapsulated in the vesicles and released slowly over a period of several hours.

This cleverly designed system is readily prepared through the powerful technique of copper-catalyzed, controlled radical polymerization, comments Ian Manners, chemistry professor at the University of Toronto. The results on the anticancer drug release demonstrate proof of concept, and, bearing in mind the ease of synthesis, the materials look very promising with respect to further development for controlled-release applications.