Generation Strategies Of Free Radicals For Tumor Therapy

In recent decades,photodynamic therapy(PDT)has achieved great development.As a minimally invasive treatment,PDT can produce reactive oxygen species(ROS)under laser irradiation and induce apoptosis.As a kind of free radical therapy,PDT does not induce the emergence of drug resistance in tumor cells,which has great significance for clinical tumor treatment.However,there are still several limitations in PDT,including the non-effective accumulation of photosensitizers,hypoxic microenvironment of tumor,and the limited laser tissue penetration.These factors limited PDT application in clinical.Based on these considerations,we have explored some new free radical therapies,which are expected to be highly effective,low-toxic and tumor-specific.Based on this,this paper designed a series of free-radical generation strategies,and tried to treat tumor from different aspects.The details are as follows:In the first chapter,we outlined the generation strategies of free radical,including light(PDT),chemical reaction(Fenton reaction),heat(thermal initiator),drug(cisplatin,etc.chemotherapy drugs),radioactive ray(radiotherapy,RT)and ultrasound(sonodynamic therapy,SDT).In addition,we briefly summarized the synergistic treatment of free radicals,including PDT/chemotherapy,PDT/Photothermal therapy and PDT/immunotherapy.In the second chapter,we designed a multifunctional nanosystem for synergistic PDT/PTT,which was p H-responsive.This multifunctional nanosystem was consist of the two-dimensional Mo S₂,a p H-responsive charge-reversible peptide LA-K₁₁(DMA),and a photosensitizer toluidine blue(TBO).The LA-K₁₁(DMA)peptide was modified on the surface of Mo S₂ by thiol group.The TBO is then adsorbed on Mo S₂ through electrostatic interaction.Under normal conditions(p H 7.4),LA-K₁₁(DMA)peptide was negatively charged,and the TBO was adsorbed on the Mo S₂,fluorescence of TBO was quenched by Mo S₂.However,under tumor area(p H 6.8),the lysyl succinamide bond of LA-K₁₁(DMA)was hydrolyzed,and the peptide converted into positively charged,which can weaken The electrostatic interaction between TBO and Mo S₂,promoting TBO release.This multifunctional nanosystem performed combined PTT/PDT therapy to enhance the antitumor effect.In Chapter three,we developed a bioreactor that could target tumor effectively.The engineered bacteria could synthesize hydrogen peroxide(H₂O₂)in the tumor site,and produce therapeutic free radicals via Fenton reaction.In the bioreactor,the engineered bacteria were designed through synthetic biology.The non-pathogenic bacteria E.coli MG1655 was transfected with plasmid to overexpress the respiratory chain enzyme II(NDH-2)(name as Ec-p E).During bacterial respiration,NDH-2 received electrons from NADH and transfered them to oxygen molecules to form superoxide anions.By SOD catalysis,superoxide anions were catalysted to generate H₂O₂.Then,magnetic Fe₃O₄ nanoparticles were chemically linked to the surface of the engineered bacteria,and were carried to the tumor site by the bacteria.The Fenton reaction was catalyzed in tumor and a large amount of hydroxyl radical was produced for tumor treatment.At the same time,due to the eutrophication and immune evasion of tumor microenvironment of the tumor area,the bacteria possessed tropism toward the tumor area.In Chapter four,we verified that mitochondria have a higher temperature than cytoplasm,and mitochondrial heat was utilized to initiate free-radical generation in tumor cells.The mitochondria have been reported to have a temperature close to 50°C and can be used as an endogenous thermal stimulus for thermal initiators.Inspired by the thermal-sensitive property of initiators,initiator V044 was applied for mitochondrial free-radical generation.Firstly,it was necessary to verify the mitochondrial overheating.The free radical probe 2',7'-dichlorodihydrofluorescein diacetate(DCFH)proved that V044 would generate more free radicals in mitochondria,indicating high temperature of mitochondria.Then,based on the higher temperature of mitochondria and its sensitivity to free radicals,V044 was modified with the mitochondrial targeting group triphenylphosphine(TPP)to construct a mitochondria-targeting TPPV for tumor therapy.TPPV could be initiated by the endogenous mitochondrial heat,which could avoid the limitations of tumor hypoxia and laser tissue penetration.Furthermore,the mitochondrial temperature could also serve as a new target for mitochondrial targeted therapy.