Targeted and intracellular delivery of paclitaxel using multi-functional polymeric micelles

Natural paclitaxel (Taxol (R)) is an effective anti-cancer drug, although a critical disadvantage is its non-targeting nature. To address this issue, cholesterol-grafted poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide-co-undecenoic acid) was synthesized with different starting monomer ratios via a free radical copolymerization route. Folate was subsequently attached to the hydrophilic segment of the polymer in order to target folate receptors-overexpressing cancer cells. The success of synthesis was confirmed with H-1-NMR carried out in CDCl3/D2O. Using a membrane dialysis method, the polymer was then self-assembled into micelles whose hydrophobic cores could be utilized to encapsulate paclitaxel, an extremely hydrophobic compound. The polymer had a low CMC of similar to 20 mg/L in water. Dynamic light scattering further showed that the sizes of blank micelles formed from the polymer were below 180 nm at different pH values tested and similar to 220 nm upon drug incorporation. More importantly, it was demonstrated that the micelles exhibited a useful pH-induced thermo-sensitivity, such that drug was released more rapidly at pH 5.0 (acidic endosomal/lysosomal environment) than at pH 7.4 (normal extracellular pH). In vitro cytotoxicity assays performed against KB cells then provided concluding evidences that the cellular uptake of micelles surface-functionalised with folate was indeed enhanced due to a receptor-assisted endocytosis process'. This novel polymeric design thus has the potential to be a useful paclitaxel vehicle for the treatment of folate-receptor positive cancers. (c) 2006 Elsevier Ltd. All rights reserved.