Fabrication Of Reduction-sensitive Polymeric Nanomicelles Based On Disulfide Bond And Its Properties As Drug Carrier

In the past few decades nanoparticle and its application in drug delivery system had attracted great attention and became a hot topic, because their ability to enhance the solubility of insoluble drug, prolong the retention time of drug in the body circulation and release drug by sustained-release or controlled-release property. And the nanoparticle were widely used in the anti-tumor drugs deliver system, because they have passive targeting ability in tumor tissue which has the enhanced permeation and retention effect (EPR effect). The disulfide bond is reduction-sensitive and is prone to rapid cleavage at a time scale from minutes to hours under a reductive environment. Since intracellular environment is much reducing compared with body circulation and extracellular milieus, micelle based on polymer which contain the disulfide bond have great potential to be used as the drug carriers to achieve the controlled-release of the drug.The major works of this paper are:biodegradable micelles were fabricated based on poly(ethylene glycol)-block-poly(y-benzyl L-glutamate)(mPEG-SS-PBLG) diblock copolymer which have the reduction-sensitive disulfide linkage in between. The polymeric micelle were used as the carrier of anti-tumor drug7-ethyl-10-hydroxy-camptothecin (SN-38) to enhance its solubility and stability and also control its release behavior. The size, size distribution, morphology and critical micelle concentration (CMC) of the mPEG-SS-PBLG polymeric micelle were studied in this work. And also the encapsulation efficiency (EE), drug loading (DL), the protection effect on lactone ring of SN-38, controlled release behavior and the Cell viability assays of the drug loaded micelle were carried out in this study Chapter1:IntroductionThis chapter will focus on the introduction of four aspect:1) nanoparticle systems used in drug delivery and their classification, their advantages over other systems,2) the reduction-sensitive polymeric nonomicelle system in drug delivery and their advantages over other system,3) the anti-cancer mechanism of the camptothecin and it's derivatives, and their limitation in cancer therapy in term of their poor solubility and stability,4) The introduction of nanotechnology in cancer therapy.Chapter2:Synthesis and characterization of mPEG-SS-PBLG copolymerBLG-NCA was opened by mPEG-SS-NH2to obtain the target product mPEG-SS-PBLG with three different component ratio of mPEG and PBLG,the reaction condition in each step was optimized. And the control polymer without the disulfide bond was synthesized. The products were characterized by1H NMR spectra.Chapter3:Micellization study of mPEG-SS-PBLGThe aqueous nanomicelle solutions were prepared by dialysis method. The polymer was able to form the micelles of nano-scale in aqueous media, suggesting their passive targeting potential to tumor tissue. And the stability of the polymeric micelle with different component ratio of mPEG and PBLG was studied. The particle sizes and size distributions of mPEG-SS-PBLG micelles were measured by dynamic light scattering (DLS). Transmission electron microscope (TEM) image was used to further observe the morphology of the micelles. The CMC research was carried out using pyrene as a probe to prove the formation of the mPEG-SS-PBLG nanomicelles in aqueous media, it revealed that the CMC of mPEG-SS-PBLG was at about5.0×10-2mg/mL in aqueous solutions. Chapter4:Study of the SN-38incorporated mPEG-SS-PBLG polymeric nanomicellesWater-insoluble antitumor drug, SN-38, was easily encapsulated into mPEG-SS-PBLG nanomicelles by lyophilization method with a high Drug loading. And the Encapsulation efficiency (EE%) and Drug loading (DL%) was found to be related with component ratio of mPEG and PBLG. The mPEG-SS-PBLG micelles effectively protected the active lactone ring of SN-38from hydrolysis under physiological condition. Owing to the disulfide bond in mPEG-SS-PBLG, intense release of SN-38occurred in the presence of dithiothreitol (DTT) at the concentration of simulating the intracellular condition, however, micelles showed gradual release of SN-38in the absence of DTT. In vitro cytotoxicity of mPEG-SS-PBLG nanomicelles was showed almost non-toxicity. Compared with free SN-38, SN-38-loaded nanomicelles showed essentially decreased cytotoxicity, the gradual drug release profile was thought to contribute to the decreased cytotoxicity of SN-38-loaded nanomicelle. The cytotoxicity of SN38-SS-PM was significantly greater than that of SN38-PM, which may be explained by the rapid release of SN-38from biodegradable micelles by cleavage of the disulfide bond in reducing environment.