Smart Nanoparticles Based On Photothermal-enhanced Intracellular Oxidative Stress In Tumor Therapy

In recent decades,the rapid development of nanotechnology has brought many opportunities for tumor treatment.Some nano-based anti-tumor drugs have completed clinical transformation,such as liposomes containing chemotherapeutic drugs.However,in the systemic circulation,nanocarriers would inevitably leak highly toxic small molecule chemotherapeutic drugs,which will cause serious side effects on normal tissues.This side effect severely limited the clinical administration dose,thereby weakening the therapeutic effect.Therefore,finding safe and efficient treatment strategies is an important direction for the development of anti-tumor nanomedicine.Because it avoids damage to normal tissues,the emerging Fenton reaction-based chemodynamic therapy has been considered a promising strategy,which converts low-toxic H₂O₂ into highly-toxic hydroxyl radicals（·OH）in situ catalyzed by transition metal（Fe,Cu,Mn,etc.）ions,causing tumor cell redox imbalance and then leading to cell death.In addition,the high concentration of reduced glutathione（GSH）in tumor cells will eliminate reactive oxygen species（ROS）.Thus,reducing the level of GSH in cells is another direction to promote tumor cell redox imbalance.In addition,combined treatment with hyperthermia can further enhance intracellular oxidative stress,thereby enhancing the effect of tumor treatment.Through rational design,this paper constructs three combined treatment strategies of photothermal and chemodynamic therapy to enhance the oxidative stress in tumor cells,thereby inhibiting tumor growth.The main contents are as follows:（1）In response to the obstacles encountered by Fenton reaction in chemodynamic therapy,we enhanced the generation of ROS by increasing the efficiency of Fenton reaction and increasing the concentration of H₂O₂ at the tumor site,thereby enhancing intracellular oxidative stress.Firstly,the Fe（Ⅲ）-gallic acid（GA）coordination polymer（Fe（III）-GA）was successfully prepared and co-loaded with the glucose oxidase（GOx）in the zeolite imidazole ester framework（ZIF-8）,and then surface modified with azobenzene-bovine serum albumin conjugate（Azo-BSA）,realizing positive feedback cell uptake activated by hypoxia and photothermal enhancement of intracellular oxidative stress.Among them,there are three ways to improve the efficiency of the Fenton reaction specifically as followed:（ⅰ）GA converts Fe³⁺to Fe²⁺under acidic conditions;（ⅱ）Fe（III）-GA has photothermal conversion performance to improve the efficiency of Fenton reaction;（ⅲ）The GOx catalysis reaction can produce gluconic acid to lower the local p H and meet the requirements of the Fenton reaction.In addition,hyperthermia can increase GOx enzyme activity,produce a large amount of H₂O₂,and realize the self-supply of H₂O₂.Moreover,the continuous consumption of oxygen by GOx will cause the tumor to be hypoxic.Azo can break responsive to hypoxia,so that FGGZA can be reversed from negative to positive,and they are more easily absorbed by cells,thereby realizing hypoxia-activated positive feedback cellular uptake.In vitro and in vivo experiments have shown that FGGZA can achieve positive feedback cellular uptake activated by hypoxia and intracellular oxidative stress enhanced by photothermal,and the combined treatment of photothermal and chemodynamic therapy can effectively inhibit tumor growth.（2）In addition to Fe,Cu is also a potential Fenton catalyst,which avoids the strict requirements on p H,having a reaction activity 160 times higher than Fe-mediated Fenton reaction,and having the ability to consume GSH.Firstly,polydopamine nanoparticles（PDA）was prepared,and used as a template to grow Cu-doped ZIF-8 in situ on the surface to realize a new type of photothermal and chemodynamic combined therapy.Among them,Cu²⁺in Cu/ZIF-8 can be reduced by GSH to Cu⁺,which not only consumes GSH,but also produces Cu⁺for Fenton-like reaction,which could catalyze H₂O₂ to·OH and increase the level of ROS.Importantly,after catalyzing the Fenton reaction,Cu⁺is converted to Cu²⁺.And Cu²⁺can continue to consume GSH,forming a cyclic cascade reaction,continuously consuming GSH and generating ROS.Moreover,PDA has photothermal conversion properties,which can make local temperature elevated,not only promoting the consumption of GSH,but also promoting the generation of ROS.In vitro and in vivo experiments have shown that PDA@Cu/ZIF-8 can achieve simultaneously photothermal-enhanced ROS production and GSH consumption,and greatly enhance intracellular oxidative stress.It is worth mentioning that this work first discovered the promoting effect of photothermal on Cu²⁺depletion of GSH,and opened up a new synergistic mechanism for the combined treatment of photothermal and chemodynamic therapy.（3）Based on the above work,this work used Cu as Fenton catalyst,and solved the problem of insufficient H₂O₂ levels in the tumor site.GOx is a highly efficient H₂O₂-generating enzyme,but the hypoxic environment in tumor sites cannot meet its continuous oxygen consumption,thereby limiting the amount of H₂O₂ production.This work used perfluoropentane（PFP）as the oxygen carrier to deliver oxygen to the tumor site,realizing intelligent hyperthermia-responsive release and then light-unlocked H₂O₂ generation.Firstly,mesoporous copper sulfide nanoparticles（HMC）were prepared,surface-modified with GOx（HMCG）,and then loaded with PFP and oxygen（PO@HMCG）to achieve photo-unlocked photothermal and chemodynamic combined therapy.Among them,HMC has photothermal conversion performance.Under near-infrared irradiation,Cu²⁺/Cu⁺could be released,realizing simultaneously hyperthermia-enhanced ROS generation and GSH consumption,thereby enhancing intracellular oxidative stress.At the same time,when the local temperature rised above the boiling point of PFP,PFP could realize the conversion from liquid to gas,thereby releasing oxygen,providing raw materials for the catalytic process of GOx,and activating the synthesis of H₂O₂.In vitro and in vivo experiments have shown that PO@HMCG can achieve light-unlocked photothermal and chemodynamic combined therapy,which not only achieved excellent tumor suppression effects,but also avoided damage to normal tissues.