Reverse polymeric micelles for pharmaceutical applications

Star-shaped (4- to 8-arms) and linear poly(glycidyl methacrylate)s were synthesized by atom transfer radical polymerization as precursors of poly(glycerol methacrylate)s (PG(OH)MAs). The water-soluble PG(OH)MA backbones were modified through the esterification of pendant hydroxyl functions with acyl chlorides (12 to 18 carbons). Alkyated PG(OH)MAs were shown to self-assemble into reverse micelles (RMs) in organic solvents and/or oil. The resulting nanosized aggregates (20-60 nm) were able to reversibly extract anionic dyes from water and solubilise them in an organic phase. Furthermore, the encapsulation of vasopressin, a model peptide, in RMs significantly improved its solubility in an oily vehicle. This observation led to the development of water-free peptide formulations. In vitro release studies showed that the entrapped peptide slowly diffused out of an oily RM solution (<15% in 7 days). The release rate could be significantly increased upon emulsification of the oleaginous phase. In vivo, the subcutaneous administration of loaded RMs to rats significantly prolonged the pharmacological effect of vasopressin (>48 h vs. 8-10 h for an aqueous solution). These results highlight the ability of RMs to act as solubilizers for hydrophilic solutes in organic media, a property that may be exploited for applications in organic chemistry and pharmaceutical technology. (C) 2008 Elsevier B.V. All rights reserved.