Dual Redox-responsive Nanogels Crosslinked By Diselenide Bonds For Tumor Therapy

Nanogels are three-dimensional hydrogels in the nanoscale,simultaneously having the good biocompatibility and biodegradability of hydrogels,but also having the outstanding drug loading properties of nanoparticles.They are widely applied in the design of drug delivery and controlled drug release system.Hyaluronic acid,a component of extracellular matrix,is a commonly used nontoxic medical material.In addition,it is also a nature ligand of CD44/CD168 protein which is highly expressed on the surface of tumor cells.Besides,the carboxyl group and hydroxyl group of hyaluronic acid provided active reactive site for various compounds.All these properties indicate hyaluronic acid is a befitting carrier material for targeted drug delivery to tumor cells.Tumor has a special physicochemical microenvironment,such as slight acidity,high level active oxygen and high level glutathione,etc.The well-designed responsive nanocarriers can realize site-specific drug release,enhanced drug toxicityand reduced damage to normal cells.The diselenide bond has dual-redox responsiveness and can be cleaved under oxidation and/or reduction conditions in tumor microenvironment.By cross-linking the diselenide bond to the long chain of hyaluronic acid,we can obtain a dual redox-responsive nanogel.As designed,the constructed nanogel can positively target to tumor tissue by hyaluronic acid and CD44/CD168interaction.Furthermore,due to the response of the diselenide bond,the drug can be specially released in tumor tissues,achieving the enhanced tumor killing efficacy without obvious side effect and controlled drug release.In this paper,the responsive nanogel Se-NG were prepared by chemical-crosslinking hyaluronic acid with selenocystamine dihydrochloride,the ratio of COOH（from hyaluronic acid）:NH₂（from selenocystamine dihydrochloride）is 1:1.The DLS results showed that the particle size was uniform.The average particle size was157.53±1.24nm and the surface charge was-9.6±0.18mV.The morphology of the nanogel was regular spherical by TEM observation.The infrared spectrum of Se-NG shows a characteristic Se-Se peak at750cm^-1.Subsequently,the chemotherapeutic drug oxaliplatin（OXA）was encapsulated into Se-NG to form Se-NG-OXA.The drug encapsulation efficiency was（46.58±2.54）%and the drug loading efficiency was（8.42±0.43）%.Compared with S-NG which contains disulfide bonds,Se-NG releases drug more quickly and efficiently under 100?M H₂O₂ and 5mM GSH conditions,indicating it is a good responsive nanogel.In the tumor cell viability assay,compared with free oxaliplatin treated group(IC₅₀=23.34?M),Se-NG-OXA(IC₅₀=15.42?M)shows an enhanced tumor cell killing efficiency.At the same time,considering the characteristic that oxaliplatin can induce immunogenic cell death（ICD）,a molecular level study was carried out in vitro.The results showed that Se-NG-OXA treatment can enhance the exposure of calreticulin（CRT）in colon cancer CT26 cells,increasing the release of internal ATP and high mobility group protein B1（HMGB1）.All these results revealed oxaliplatin-induced ICD was strengthened.In summary,this article prepared a diselenide bond crosslinked and oxaliplatin-loaded hyaluronic acid nanogel.We also performed antitumor studies in vitro.The results proved that Se-NG showed a great potential to be used in tumor therapy and provided an option for the design and application of tumor responsive nanogels.