Preparation And Properties Of Chondroitin Sulfate Based Polymeric Micelles

The studies toward to polymeric micelles (PMs) as drug delivery systems have been conducted for several decades. Among various PMs systems, polysaccharides-based PMs have received growing attention over years for their unique properties, such as high structural stability and solubilization capacity, tumor passive localization by permeability and retention effect, good biocompatibility and biodegradability. As a consequence, they have promising application in preclinical and clinical. In this paper, chondroitin sulfate was selected as raw polysaccharide, and modified by hydrophobic molecules to form stimuli-responsive "smart’polymeric micelles. These micelles were further studied in terms of self-assemble behavior, stimuli-responsive behavior, drug release behavior and biological property. The specific contents were summarized as follows:(1) Reduction-responsive shell-sheddable micelles based on disulfide-linked chondroitin sulfate-cholesterol conjugates (CS-ss-Chol) were developed for efficient encapsulation and triggered intracellular release of hydrophobic drug. CS-ss-Chol conjugates with different cholesterol content were synthesized and self-assembled into spherical micelles in aqueous medium with tunable sizes (124～237nm) and desirable critical micelle concentration (5.8～3.6×10-2mg/L). These micelles were highly sensitive to intracellular reductive environments, which resulted in fast formation of large aggregates due to shedding of the CS shells through reductive cleavage of the intermediate disulfide bonds. Quercetin, a model hydrophobic drug, was efficiently loaded into the core of these micelles, with a drug loading efficiency of23.4%. The in vitro release studies showed that quercetin release was minimal (<20%in24h) at low concentrations of dithiothreitol (DTT,10μM) mimicking the extracellular environment, but significantly enhanced (>50%in24h) under tumor-relevant reductive condition (DTT,20mM). MTT assays against HeLa cells and HSF cells indicated that these CS-ss-Chol micelles had negligible toxicity up to a conjugate concentration of200μg/mL. These reduction-responsive shell-sheddable micelles offer a promising means to intracellularly delivery hydrophobic payloads, and therefore, they possess high clinical values.(2) A series of novel chondroitin sulfate-histamine conjugates were synthesized using amine coupling reaction. The obtained CS-his conjugates possess amphiphilic structure with hydrophilic CS backbone and hydrophobic histamine branches. These conjugates could self-assemble to form various morphologies of aggregates in aqueous solution, such as spherical, necklace-like, vesicle, rod, film and so on. The transformations of the CS-his conjugates micelles depended on a number of parameters, including the relative hydrophobic block contents, their concentrations, the ionic strength and pH values. The FTIR results found that the hydrogen-bonding formed by the hydroxyl and amino groups remained on the CS-his backbone played an important role during the aggregation process. These morphology controlled micelles based on CS-his had the proposal ability for controlling anticancer drug release.(3) The CS-his micelles with desirable size (133nm) and low critical micelle concentration (0.05mg/L) were used as drug carrier. Owning to the pH-sensitive structure of imidazole, the nanoparticles show pH-responsive behavior upon reducing the pH value of surrounding media, accompany with formation of large aggregates and increase of ζ potential. When the nanoparticles were utilized to deliver the model drug DOX, they exhibited a specific on-off switch drug release behavior, triggering DOX release in acidic surroundings (intracellular endosomes) and sealing DOX in neutral surroundings (blood circulation or extracellular matrix). CCK-8assays and con-focal laser scanning microscopy against HepG2cells indicated that the nanoparticles themselves had no associated cytotoxicity, while drug-loaded nanoparticles possessed high cytotoxicity to model cells and presented high efficiency of cellular uptake. These flexible micelles with an on-off switched drug release may offer a promising pattern to accurately deliver a wide variety of hydrophobic payloads to tumor cells for cancer therapy.