Study On The Preparation Of Stimuli-Responsive Nanogels Based On Hyaluronic Acid And Its Application In Targeting Drug Delivery

Polysaccharides are widely distributed in organism. They constitute a living system together with proteins, nucleic acids and other substances, and participate in various life activities of the organism. Due to their favorable biocompatibility and specific interactions with membrane proteins, polysaccharides have been frequently used in biomedical field. In recent years, nanoparticles have become hot research topics in the field of cancer therapy, because they can overcome a serious of biological barriers in vivo, improve drug accumulation in tumors and reduce side effect. However, the passive tumor targeting effect of nanoparticles, resulting from the enhanced permeability and retention (EPR) effect of tumors, cannot fully meet the requirement of targeted therapy to different types and stages of cancer. Thus, we systematically studied the interactions between polysaccharides and different tumor cells expressing different receptors and the cell endocytosis mechanism, and we found that these interactions are useful in cancer metastasis therapy. According, we prepared a kind of intelligent nano carriers to transport antitumor agent, doxorubicin (DOX), where we used the highly specific affinity between polysaccharide and certain receptors on tumor cells, and stimuli-responsive groups to enhance the delivery efficiency. As an important composite targeting system, they can accumulate in tumors and not be assimilated by normal somatic cells. The stimuli-responsive properties to pH, redox conditions, specific enzymes, temperature, light, and so on, can improve the cell endocytosis and drug release behaviors and thus improve the therapeutic effect. Meanwhile, such nanoparticles are stable in blood circulation, which is helpful for improving the drug loading efficiency and reducing side effects. By integrating the polysaccharide with tumor-targeting function and stimuli-responsive groups into a drug carrier, we can improve the targeting efficiency, cell uptake, drug release behavior of the carrier, and intelligently control the biodistributions of carrier and drug payload in different types and stages of tumors. Ultimately, we can improve the therapeutic effect.In this dissertation, we prepared kinds of stimuli-responsive nanogels with hyaluronic acid as the key component, where the affinity between hyaluronic acid and CD44 or RHAMM receptors overexpressed in tumor cells was used to enhance the tumor-targeting ability of the carriers. We studied their physical and chemical properties, the response to various stimuli, the targeting effects, the delivery behavior in vitro and in vivo and anti-tumor effect in solid tumor and lymphatic metastasis. The main contents are described as follows:(1) Hyaluronic acid (HA) was functionalized by methyl acrylic acid and co-polymerized with diethylene glycol acrylate (DEGDA) in aqueous solution to prepare the enzymatic degradable tumor-targeting nanogels. We explored their degradation kinetics in vitro and the corresponding morphological variation. By using the electrostatic interaction between the negative charged hyaluronic acid and DOX, we loaded DOX into the nanogels, and investigated the uptake of nanogel in different cells and three-dimensional (3D) cell clusters, the drug distribution and penetration in vivo, anti-tumor performance in vivo and so on.(2) We intensively studied the interaction between hyaluronic acid and a specific receptor RHAMM (CD 168), and used this interaction to enhance the tumor-targeting ability of nano carriers for the first time. The hyaluronic acid with functional groups was co-polymerized with N, N'-bis(acryloyl) cystamine (CBA) in aqueous solution to prepare a redox-responsive nanogel. After drug loading, we examined the targeting effects and antitumor effects in variety of tumor models. Meanwhile, we explored the effect of inhibiting tumor lymphatic metastasis using this carrier.(3) We conjugated polyethylene glycol (PEG) with different molecular weight to the branched polyethyleneimine (PEI) through schiff base linkages to provide a pH-sensitive PEI-b-PEG polymer. Then the PEI-b-PEG polymer was coated onto the surface of HA nanogel containing disulfide linkages. We investigated the related cellular uptake, biodistribution and anti-tumor effect of the PEG coating nanogel. The PEG-coated nanogels are stable in blood circulation (pH=7.4). Once entering tumors which provide a slightly acidic environment, the PEG chains fall off, and the particle surface converts to positively charged, which promotes the cell uptake and accumulation of particles in tumor. The rate of disintegration and release of loaded DOX under the reductive environmental are also increased.