Disulfide crosslinked PEGylated starch micelles as efficient intracellular drug delivery platforms† Aiping Zhang, a Zhe Zhang, a Fenghua Shi, a Jianxun Ding, b Chunsheng Xiao, b Xiuli Zhuang, * b Chaoliang He, b Li Chen * a and Xuesi Chen b Novel reduction-responsive disulfide core-crosslinked micelles based on amphiphilic starch-graft- poly(ethylene glycol) (starch-g-PEG) were prepared and used for efficient intracellular drug delivery. The starch-g-PEG copolymers can be conveniently prepared by grafting starch with carboxyl group terminated PEG, and subsequently conjugated with lipoic acid for disulfide crosslinking. The self- assembled starch-g-PEG micelles and the corresponding disulfide core-crosslinked micelles were then characterized by transmission electron microscopy, dynamic laser scattering and fluorescence techniques. It is interesting to observe that the hydrodynamic radii of disulfide core-crosslinked micelles would increase gradually in phosphate buffered saline (PBS) due to the cleavage of the disulfide bond in the micellar core, caused by the presence of reductive glutathione (GSH). The glutathione-responsive behaviors of the disulfide core-crosslinked micelles should be attractive for intracellular drug delivery. Thus, a model anticancer drug doxorubicin (DOX) was loaded into micelles and the in vitro drug release in response to GSH was also studied. The results showed that only a small amount of loaded DOX was released from the core-crosslinked starch-g-PEG micelles in PBS solution without GSH, while quick release occurred in the presence of 10.0 mM GSH. Confocal laser scanning microscopy and flow cytometry analyses further demonstrate that the disulfide crosslinked micelles exhibited a faster drug release behavior in glutathione monoester (GSH-OEt) pretreated HeLa cells than that in the nonpretreated and buthionine sulfoximine (BSO) pretreated cells. In addition, the DOX-loaded crosslinked micelles show higher cellular proliferation inhibition against GSH-OEt pretreated HeLa and HepG2 than against the nonpretreated and BSO pretreated ones. These results suggest that such disulfide crosslinked starch-g-PEG micelles, which can efficiently release the loading drug in response to intracellular GSH concentration, may provide favorable platforms for cancer therapy. 1 Introduction Nowadays, there is a continuously growing interest in drug delivery, especially for the treatment of cancer, which is one of the major causes of morbidity and mortality in the world. 1 Conventional chemotherapy has proved partially successful in treatment and prolonging the lives of patients. The limited clinical success is mostly due to the lack of tumor-selectivity of anticancer drugs, which results in severe side effects to normal tissues and low efficacy against multi-drug resistant cancer cells. 2 Aiming to improve chemotherapy, tremendous effort has been centered on the development of various nanocarriers that are capable of targeted controlled delivery of anticancer drugs, including polymeric micelles, 3 vesicles, 4 liposomes 5 and nano- gels 6 etc. These nanocarriers can not only enhance the aqueous solubility and bioavailability of the drug but also improved pharmacokinetics and biodistribution proles via the enhanced permeability and retention (EPR) effect. Polymeric micelles, as one kind of antitumor drug nano- carrier based on amphiphilic block/gra copolymers, have received considerable attention. 7,8 The hydrophobic inner core acts as a depot for drugs and the hydrophilic outer shell as a protective interface between the hydrophobic core and the external aqueous milieu. 9,10 Polymeric micelles offer several distinct advantages for anticancer drug delivery, such as improved solubility, prolonged in vivo circulation time and preferential accumulation at the tumor site via the EPR effect. However, one practical challenge is their low stability in vivo, because of the large dilution volume and/or interactions with cells and biomolecules presented in the blood, which oen lead to premature drug release, aggregation, and a diminished ability of the drug to reach its target. In order to overcome this a Department of Chemistry, Northeast Normal University, Changchun 130024, P. R. China. E-mail: chenl686@nenu.edu.cn b Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China. E-mail: zhuangxl@ ciac.jl.cn † Electronic supplementary information (ESI) available. See DOI: 10.1039/c2sm27189c Cite this: Soft Matter, 2013, 9, 2224 Received 23rd September 2012 Accepted 5th December 2012 DOI: 10.1039/c2sm27189c www.rsc.org/softmatter 2224 | Soft Matter , 2013, 9, 2224–2233 This journal is ª The Royal Society of Chemistry 2013 Soft Matter PAPER Downloaded by Changchun Institute of Applied Chemistry, CAS on 25 January 2013 Published on 07 January 2013 on http://pubs.rsc.org | doi:10.1039/C2SM27189C View Article Online View Journal | View Issue