Cyclodextrin based unimolecular micelles with targeting and biocleavable abilities as chemotherapeutic carrier to overcome drug resistance

An amphiphilic star-shaped copolymer beta-CD-g-PCL-SS-PEG-FA, consisting of a beta-cyclodextrin (beta-CD) core as well as grafted with bioreducible disulfide linkage in PCL-SS-PEG multiarms and targeting folic acid (FA) as end moiety, is designed with unimolecular micelles formation ability for targeted transport of chemotherapeutics to drug resistant tumor cells. Firstly, beta-CD was utilized as core to growth PCL arms by ring-opening polymerization (ROP) of epsilon-CL, before disulfide terminal group transformation to render beta-CD-g-PCL-SS-COOH. Secondly, alpha-hydroxy-omega-amine protected PEG (HO-PEG-NHBoc) was connected to beta-CD-g-PCL-SS-COOH to obtain amphiphilic beta-CD-g-PCL-SS-PEG, where PCL and PEG were connected via bioreducible disulfide bond. After deprotection of -Boc group, FA was introduced onto the distal end of block arms to obtain the desired beta-CD-g-PCL-SS-PEG-FA copolymer. Because of highly branched core-shell amphiphilic structures, beta-CD-g-PCL-SS-PEG-FA could act as unimolecular micelles. Interestingly, this unimolecular micelle could release the encapsulated drug in a glutathione (GSH) dependent manner due to disulfide linkage. More importantly, this unimolecular micelle could load doxorubicin (DOX) to promote its cellular uptake in multidrug resistance (MDR) protein overexpression tumor cells, by taking the advantage of FA targeting group and intracellular high GSH level in cancer cells. Together with satisfactory biocompatibility, this novel star-like beta-CD-g-PCL-SS-PEG-FA unimolecular micelle could potentially be utilized as targeting nanocarriers in drug resistant cancer therapy.