Preparation Of Reduction-response Polymeric Micelles Based On Starch For Drug Delivery

Polymeric micelles(PMs), an important nanocarrier focused on enhancing pharmaceutical bioavailability, may be used for solubilization, stabilization, and delivery of challenging agents. However, because of the diffusion-controlled Mechanism, the drug release of traditional PMs is usually too slow and deficient after a period of days, which limits its effect in the treatment of cancer. Compared to traditional micelle systems, intelligent nanomicelles are actively chosen that can stably encapsulate therapeutics and release them at a desired site in response to external stimuli such as pH, redox, glucose and enzyme conditions. At present, diselenide bonds have been considered as a novel dual redox-sensitive linkage. Diselenide bonds are more easily cleaved than disulfide bonds in reductive environment because of their lower bond energy. Because of the excellent biocompatibility and biodegradability, starch always is a potentially good candidate in the drug delivery system. Based on the above considerations, in this thesis we selected soluble starch and 3, 3’-Diselanediyldipropanoic acid(DSeDPA) as main materials, and prepared a series of amphiphilic polymeric micelles based on starch. And we studied their properties as drug nanocarriers. The three main parts of this thesis are as described below:1. A new kind of amphiphilic mPEG-SeSe-St micelles was successfully synthesized by efficiently introducing mPEG grafted onto starch bones via functionalized diselenide bonds. Above the CMC, 0.049 mg/mL, the mPEG-SeSe-St self-assembled to form spherical micellar aggregates(136 nm)having diselenide bonds at the mPEG/starch interface. Meanwhile, mPEG-SeSe-St micelles were bestowed with superb redox-sensitivity by size and morphology changes under low concentration of H2O2(0.1%(v/v)) or GSH(1 mM). Furthermore, the micelles can readily encapsulate DOX and in vitro drug release profiles revealed that only 45% of the loaded DOX from mPEG-SS-St micelles was released at 22 h with 10 mM GSH, while up to about 70% of the loaded DOX from mPEG-SeSe-St micelles could be rapidly released in the same period. These results, combined with intracellular release of DOX into TC1 Lung cancer cells confirmed by CLSM and MTT viability, suggested that the novel kind of amphiphilic mPEG-SeSe-St micelles had an excellent application potential in drug delivery.2. We fabricated a novel kind of core-crosslinked copolymers(mPEG-St-SeSex) based on mPEGylated starch using 3, 3’-Diselanediyldipropanoic acid as crosslinker. The corresponding corecrosslinked analogs mPEG-St-SSx and mPEG-St-CCx copolymers with 3, 3’-dithiodipropionic acid and octanedioic acid as crosslinker separately were synthesized and compared. Above the CMC, all core-crosslinked copolymers self-assembled to form micelles with spherical structures around 120~160 nm in size and exhibited impressive stability compared to non-crosslinked micelles(mPEG-St) in physiologically related and ultra micelle destabilization conditions. The stimulisensitive ability studies testified that mPEG-St-SeSex micelles showed more rapid and sensitive reduction-responsive compared with mPEG-St-SSx micelles under a low concentration of DTT(1 mM). The in vitro drug release assay revealed that only 20% of DOX and 60% of DOX were released from DOX-loaded mPEG-St-CCx micelles and DOX-loaded mPEG-St-SSx micelles respectively with 10 mM GSH at 120 h, while up to about 85% of DOX from DOX-loaded mPEG-St-SeSex micelles could be more completely released in the same conditions. Intracellular drug release studies using confocal laser scanning microscopy(CLSM) confirmed the higher anti-tumor activity of DOX-loaded mPEG-St-SeSex micelles. Cell cytotoxicity studies demonstrated that the mPEG-StSeSex micelles displayed lower cell cytotoxicity and better biocompatibility.3. Based on mPEG-St-SeSex copolymers in the system 2, a new kind of actively targeted, corecrosslinked copolymers(FA-St-SeSex) was prepared by successfully introducing folic acid grafted onto starch bones. FA-St-SeSex copolymers could self-assemble to form spherical micellar aggregates about 155 nm diameter in the aqueous solution. FA-St-SeSex micelles still maintained outstanding stability in physiologically related conditions. FA-St-SeSex micelles also showed good reduction-responsive in 1mM DTT. Cellular uptake studies using confocal laser scanning microscopy(CLSM) exhibited the higher cellular uptake efficiency of DOX-loaded FA-St-SeSex micelles than DOX-loaded mPEG-St-SeSex micelles in MCF-7 cells. MTT viability studies confirmed the good biocompatibility of FA-St-SeSex micelles, which had potential to develop controlled drug-delivery systems for cancer therapy. Remarkable extracellular stability, actively targeting, sensitive reduction-responsive and excellent biocompatibility make the FA-St-SeSex micelles an admirable application potential for drug delivery.