Polymeric Micelles Using Pseudo-Amphiphilic Block Copolymers

PS-b-PMA block copolymers carrying terminal anionic groups have been studied. Their synthesis is achieved by mean of 3-(benzylsulfanyl thiocarbonylsulfanyl) propionic acid and 3-(1-phenylethylsulfanyl thiocarbonylsulfanyl) propanesulfonic acid sodium salt as RAFT agents. These block copolymers, when dispersed in methanol, display a pseudo-amphiphilic behaviour and provide micelles that can be suspended in water by osmosis. During the self-assembling process, the anionic terminations lead to the formation of nanosized monodispersed particles and confer stability to the micelles in aqueous media. The core of the micelles is loaded with Nile Red to achieve the intracellular delivery of a lipophilic substance; this has been demonstrated by Confocal Laser Scanning Microscopy. The particles, when loaded with Doxorubicin, are able to overcome the intrinsic resistance of LoVo-MDR cancer cells. A further stabilization is given to the micelles by covalent shell crosslinking provided by triethylene glycol diacrylate. The increased intracellular stability of the crosslinked micelles makes them stain, when loaded with Nile Red, the aqueous cytosol instead of the lipophilic cellular compartments. The unimers constituting the micelles have been covalently labelled with fluorescein to follow their fate once incorporated into the cells.