Construction Of Au@Copper-Based Core-Shell Nanostructures And Their Application In Photothermal/Oxidation Synergistic Tumour Therapy

Increasing the intracellular oxidative stress induced by the accumulation of reactive oxygen species(ROS)is an emerging approach to cancer treatment.Due to the high specificity and non-invasive nature of tumor microenvironmental response,it has aroused extensive research interest.In fact,many well-designed nanomaterials with enzyme-like properties,such as iron-based nanomaterials,carbon-based nanomaterials,metal-organic frameworks(MOFs)materials and noble metal nanoparticles,are often used as ROS generators for nano catalytic tumor therapy,especially based on the catalytic decomposition of H₂O₂ overexpressed in tumor cells to generate cytotoxic hydroxyl radical(·OH)to kill cancer cells by the peroxide mimics enzyme of nanomaterial.However,due to the weak acidity and insufficient endogenous H₂O₂ concentration(100 ?m)in the tumor microenvironment,some nanomaterials cannot effectively initiate the catalytic reaction and generate sufficient ROS.In addition,ROS has a very short diffusion distance and only produces a limited kill distance to neighboring cells.Furthermore,the generated ROS may be cleared by over-expressed glutathione(GSH)in the tumor microenvironment,thereby inhibiting oxidative damage of tumor cells.Thus,ROS-mediated tumor therapy is severely hampered.Therefore,the design of more effective nanocatcatalysts and downregulation of intracellular glutathione levels could improve the efficacy of ROS-mediated tumor therapy.Photothermal therapy(PTT)is an effective and least invasive treatment that relies on near-infrared(NIR)laser irradiation of photothermal reagents to generate hyperthermia(>42°C)for irreversible tumor ablation.Increasing temperature can not only kill cancer cells,but also significantly accelerate the production and diffusion distance of ROS so as to achieve the photothermal/oxidation synergistic therapy.Combining PTT technology with nanocatalytic therapy has the potential to improve the therapeutic efficiency.Firstly,Au@TACu NSs was successfully prepared and characterized.A core-shell nanostructure(Au@TACu NSs)was formed by coating TA-Cu²⁺chelate on the surface of gold nanoparticles by tannic acid(TA)assisted method.The core-shell structure of Au@TACu NSs was directly observed by transmission electron microscopy(TEM).In particular,the elemental composition of the core-shell was proved by qualitative and quantitative analysis of the photoelectron spectroscopy.Fourier transform infrared spectroscopy(FTIR)was used to characterize the chelation of tannic acid with Cu²⁺.The results showed that the C-OH and O-H vibrations of tannic acid were destroyed,which proved the coordination reaction with copper ion.The particle size and charge distribution of Au@TACu NSs were measured by dynamic light scattering.The results showed that negatively charged Au@TACu NSs had good colloidal stability.After incubation in different physiological solutions for 7 days,the hydration particle size and Zeta potential of Au@TACu NSs were almost unchanged.This proves the potential application of Au@TACu NSs in biomedical field.Secondly,the biological characteristics of Au@TACu NSs were systematically studied in vitro.The photothermal properties of Au@TACu NSs were evaluated by in vitro photothermal experiments.The results show that Au@TACu NSs has excellent photothermal effect.Under the condition of controlling sample concentration and laser power density,the temperature is precisely adjustable in the range of 26.8⁶6°C.The Au@TACu NSs core-shell structure has good photothermal stability and can be used as photothermal reagent for PTT.The simulation experiment was carried out in vitro under the simulated microacidic environment of tumor.The results showed that Au@TACu NSs showed strong peroxide-like enzyme properties,which could catalyze the conversion of H₂O₂ to highly toxic ·OH.At the same time,under the weak acid condition,the degradation of TACu complex resulted in the release of copper ions which could consume GSH so as to further enhance the production of ROS.It has been proved that photothermal can accelerate the production of ROS and realize the purpose of thermally enhanced oxidation therapy(PTT/OT).In vitro cytotoxicity test,hemolysis test was used to study the toxicity of Au@TACu NSs.The results showed that it had high biocompatibility.Even at the concentration of material up to 500 ?g/m L,the hemolysis rate was only about 4%,which proved the good safety of Au@TACu NSs.Finally,drug metabolism behavior and antitumor efficacy were evaluated in animals.Firstly,the blood circulation behavior of Au@TACu NSs was studied,showing that the blood circulation half-life(t1/2)of Au@TACu NSs could reach3.35±0.17 h,which proved that a long blood circulation time was conducive to the accumulation of Au@TACu NSs in tumor sites,which could reach 12.2% ID/g.As a potential delivery system.In the anti-tumor experimental study of Au@TACu NSs in tumor-bearing mice in vivo,the results showed that the tumor growth was almost completely suppressed after NIR irradiation of Au@TACu NSs,which can be attributed to the photothermal synergistic treatment of reactive oxygen species,namely the synergistic effect of PTT /OT.Pure Au NPs only slightly inhibited tumor growth due to their low reactive oxygen ·OH production and low photothermal effect of pure gold nanoparticles.The results of tumor H&E staining showed that Au@TACu/ Laser could induce obvious tumor cell necrosis,such as cell contraction and nuclear compression,while normal organ damage was negligible,further confirming the feasibility of the use of Au@TACu NSs in tumor treatment.In summary,Ta-Cu²⁺chelate was prepared by one-step method to form core-shell nanostructures(Au@TACu NSs)wrapped on the surface of gold nanoparticles.The obtained Au@TACu NSs has a strong near-infrared absorption ability,which can convert light into heat to ablate tumors.At the same time,the Au@TACu NSs has a good peroxidase activity,which can be oxidized by the decomposition of H₂O₂ to produce toxic hydroxyl radical(·OH).The thermal efficacy of Au@TACu NSs and the ability to consume GSH can further enhance the production of ·OH to achieve photothermal enhanced oxidation therapy(PTT/OT).In addition,this synergistic treatment strategy has demonstrated a highly effective inhibition of tumor growth in vivo,with no significant damage to normal tissue.The above research results provide a new method for Au based nanomaterials as PTT/OT synergistic tumor therapy.