Preparation And Anti-Tumor Effect Of Multiple Sensitive Au Nanoclusters@Biopolymer Composite Gel

The global mortality rate associated with cancer is increasing,which has seriously threatened human life and health,reflecting that the current treatment methods are not sufficient to achieve satisfactory therapeutic effects.In recent years,phototherapy,including photothermal therapy（PTT）and photodynamic therapy（PDT）,has attracted attention as an effective cancer treatment strategy due to its minimally invasive,temporal controllability and low systemic toxicity.Local administration to the tumor site is a very promising method,because it can target the tumor site to release the drug at a specific point,thereby minimizing the damage to normal tissues.How to simplify the synthesis and drug delivery process,alleviate the problem of hypoxia in the tumor environment,and ensure excellent biocompatibility and biodegradability is the key to promoting the clinical application of photochemotherapy.However,current phototherapeutics have great difficulties in meeting the requirements of clinical drugs from synthesis to administration.In recent years,the advantages of water-soluble gold nanoclusters（Au NCs）,such as small size（<3nm）,good targeting of specific surface ligands and low toxicity,have been extensively studied in the field of medical diagnosis.However,it is well known that water-soluble nanoclusters have shortcomings such as poor stability and single performance.How to prepare nanoclusters with excellent phototherapy performance and low toxicity is a problem that needs to be solved immediately.Therefore,it is necessary to design a new multifunctional nano-diagnosis and treatment platform,which helps to enhance and combine other treatment methods to achieve the effect of synergistic killing of tumors.This article focuses on the characteristics of hypoxia and weak acidity in the tumor microenvironment,with the goal of constructing an anti-tumor nano-integrated system with high efficiency,low side effects and a combination of diagnosis and treatment,and has prepared a tumor diagnosis and treatment that integrates targeting,imaging and PDT/PTT（/Chemotherapy）.The nano-platform can not only overcome the shortcomings of the low efficiency of single therapy,but also improve the microenvironment within the tumor that is not conducive to treatment,and greatly enhance the anti-tumor effect.The specific results are summarized as follows:1.Firstly,Au NCs/PM mixed sol was prepared in situ by using the natural green tofu extract（PM）as reducing agent.Then,reusing the constant concentration of Ca²⁺/Mg²⁺existing in the organism as a gelling agent,a"bullet-carrying"envelope containing Au NCs@PM/Ca²⁺/Mg²⁺gel was constructed in situ on the surface of tumor cells.The research results show that both Au NCs and PM in the enveloping layer can be used as photosensitizers to induce toxic singlet oxygen to kill tumor cells under the irradiation of 808nm laser;at the same time,because PM is rich in peroxidase,it can catalyze the over-expressed hydrogen peroxide（H₂O₂）in the tumor cell,thus alleviating the tumor’s hypoxic microenvironment and greatly enhancing the effect of photodynamic therapy.The Au NCs in the gel also have good photothermal conversion properties,which exhibit excellent PTT effects.The experiments in vitro have shown that Au NCs@PM/Ca²⁺/Mg²⁺gel has good biocompatibility and strong Au NCs fixation ability,so that the effective anti-tumor ingredients can be concentrated on the tumor site,which enhances the therapeutic effect.The results of in vitro experiments showed that when the concentration of the Au NCs@PM/Ca²⁺/Mg²⁺gel envelope was 1.2 mg/m L,the survival rate of tumor cells was only 23.7%under near-infrared laser irradiation.The experiments of animals showed that the tumors in ICR mice nearly disappeared after 10 days of administration,verifying that the synthesized Au NCs@PM/Ca²⁺gel has an outstanding PTT/PDT synergistic anti-tumor effect.In addition,the composite gel layer also exhibits near-infrared thermal imaging capabilities,which can monitor the location of solid tumors.Therefore,such a natural green treatment method that integrates a variety of treatment methods provides a new idea for tumor treatment.2.The potassium borohydride（KBH₄）and carrageenan extracted from red algae（Carr）were used as raw material for forming temperature/p H-sensitive Au NCs@Carr hydrogel nanoparticles by a one-step method.KBH₄ can reduce the chloroauric acid aqueous solution in situ to form gold nanoclusters（Au NCs）,which are uniformly coated inside the natural hydrogel three-dimensional network.The temperature-sensitive drug 5-FU was loaded with the targeting molecule lactobionic acid（LA）to form such a small temperature/p H-sensitive hydrogel particle of Au NCs/5-FU@Carr-LA.The TEM image shows that the Au NCs are 3 nm in diameter and are evenly dispersed in the natural Carr hydrogel three-dimensional network.The composite gel particles are spherical with a size of 60 nm.In this system,the sulfate group contained in the carrageenan is reduced to sulfhydryl（-SH）,which can stabilize the water-soluble Au NCs,and the carrageenan enhances the biocompatibility of the complex.The Au NCs in the gel particles can be used as a photothermal treatment agent or a photodynamic agent,and it has the ability to catalyze the decomposition of H₂O₂ to produce oxygen for improving the effect of PDT.When nanogel particles reach the tumor site,Au NCs produces PDT and PTT effects under near-infrared laser irradiation to increase the temperature of the system and lead to the occurrence of Carr hydrogel for releasing 5-FU.The experiments in vitro showed that when the concentration of Au NCs/5-FU@Carr-LA was 1.0 mg/m L,the survival rate of tumor cells was only 31.5%under near-infrared laser irradiation.The results of animal experiments show that the prepared samples have photothermal imaging capabilities and have a strong inhibitory effect on tumor growth in ICR mice.Such a treatment platform with high biocompatibility and excellent anti-tumor effects is worthy of our further development and exploration.