Monosaccharide-Responsive Polymers of Boronic acid Derivatives and Their Medical Applications

NanochemistryWe synthesized the boroxole-containing styrenic monomer that can be polymerized by radical addition-fragmentation and chain transfer (RAFT) method. Polystyreneboroxole (PBOx) and its block copolymers with a poly(ethylene glycol) (PEG) as a hydrophilic block showed monosaccharide binding in phosphate buffer at neutral pH, which was quantified by Wang's competitive binding experiments. Amphiphilic block copolymers having a monosaccharide-responsive PBOx block self-assembled to polymersomes of which the average diameter was readily controllable by adjusting the number of boroxole units in the PBOx block via a controlled radical polymerization. These polymersomes also exhibited glucose-responsive disassembly at neutral pH. We demonstrated the possibility of using these polymersomes as glucose-responsive delivery vehicles for insulin at physiologically relevant pH medium. Polymers containing organoboronic acids have recently gained interest as sugar-responsive materials owing to the reversible binding of saccharides to boronic acids, which triggers a change in the physical and chemical properties of these polymers, such as their water solubility. In particular, the ability of these polymers to bind glucose has attracted considerable attention because of the promise of these materials for the development of sensors and drug delivery systems for glucose-related human diseases, such as diabetes. We report here a new class of sugar-responsive polymers that are based on a sequence-specific copolymer of styreneboroxole and N-functionalized maleimide. The reversible addition-fragmentation and chain transfer (RAFT) polymerization of this pair of monomers ensured that a glucose-receptor alternates with a non-responsive solubilizing group throughout the sugar-responsive polymer chain. Due to the presence of hydrophilic solubilizing groups beween the solubility-switching boroxole moieties in the membrane-forming block, the polymersomes of the block copolymers responded to a lower level of glucose in the medium, resulting in diassembly of the bilayer membrane under a physiologically relevant pH and glucose-level.ope