Polymeric micelles using pseudo-amphiphilic block copolymers and their cellular uptake

A PS-b-PMA block copolymer bearing a terminal carboxylic group has been synthesized using 3-(benzylsulfanyl thiocarbonylsulfanyl) propionic acid as RAFT agent. When dispersed in methanol, this block copolymer displays pseudo-amphiphilic behaviour providing micelles which can be suspended in water by osmosis. The carboxylic terminations are fundamental during the self-assembling process contributing to the formation of nanosized monodispersed particles. Furthermore, the anionic corona confers the to micelles stability in aqueous media. The core of the micelles was loaded with Nile Red to achieve the intracellular delivery of a lipophilic substance; this was demonstrated by Confocal Laser Scanning Microscopy. The particles, when loaded with doxorubicin, are able to overcome the intrinsic resistance of LoVo-MDR cancer cells. Further stabilization is given to the micelles by covalent shell crosslinking using triethylene glycol diacrylate. Because of the increased intracellular stability of the crosslinked micelles, they stain, when loaded with Nile Red, the aqueous cytosol instead of the lipophilic compartments. The unimers constituting the micelles were covalently labeled with fluorescein to follow their fate once incorporated into the cells.