| Cancer is still a huge challenge for modern medicine.Photodynamic therapy(PDT,a light-triggered tumor therapeutic approach)is considered to be a promising treatment modality with the advantages of spatio-temporal controllability,noninvasiveness,no cellular resistance,reproducible treatment,and rapid therapeutic efficacy.However,oxygen is an integral part of PDT and the hypoxic tumor microenvironment limits its further applications.Recently,responsive nanodrugs have been developed,and they can specifically reach the tumor microenvironment and release drugs in a responsive manner.In this thesis,we constructed the tumor microenvironment-responsive liposomes(Met/Ce6@PEOz-Liposome,termed MCPL),in which the three lipid components cholesterol,hydrogenated soy phosphatidylcholine(HSPC),1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(2-ethyl-2-oxazoline)(DSPE-PEOz)constitute the liposomal carrier,and the internally encapsulated chlorin e6(Ce6,a photosensitiser molecule)and metformin(Met,a molecule with respiratory inhibitory effect)constitute the loaded drugs.The synthesized liposomes displayed excellent tumor targeting ability and selective drug release property.The liposomes could inhibit aerobic respiration of tumor cells and reduce intracellular oxygen consumption,thus increasing the oxygen concentration.The transformation of tumor hypoxia allowed the photosensitizer Ce6 to produce more reactive oxygen species,eventually causing apoptosis or necrosis of tumor cells.The main content of this thesis is as follows:(1)Preparation and characterization of the acid-responsive liposomes: The liposomes(hydrodynamic diameter: 57.5 nm;zeta potential: –4.16 m V)with acid-responsive and long-circulating properties were prepared by a thin-film dispersion method(using organic solvent to dissolve the lipid mixtures and ultrasonication to disperse the hydrated vesicles).The liposomes were characterized by ultraviolet–visible(UV–vis)spectrophotometer,spectrofluorophotometer,and transmission electron microscopy.The results revealed that the liposomes had excellent acid-responsive property and outstanding singlet oxygen production capacity(2)In vitro anticancer treatment: Using 4T1 mouse breast cancer cells(4T1 cells)as model cells,we evaluated the cytotoxicity,endocytic process,endocytosis pathways,lysosomal escape ability,4T1 tumor spheroid penetration,and apoptotic effect of the liposomes.The experiment results of cytotoxicity assays indicated that the acid-responsive liposomes were more toxic to tumor cells than normal cells,further demonstrating the tumor-targeting property of the liposomes.The liposomes entered tumor cells mainly through ATP-and caveolae-dependent endocytosis.The liposomes escaped from lysosomes and released drugs rapidly after being internalized by tumor cells.The experiment results of 4T1 tumor spheroid indicated that the liposomes had good tumor penetration capability.The results of ATP assay revealed that the liposomes successfully reduced ATP production,which is achieved by the function of Met.We also found that the hypoxia of 4T1 tumor spheres was converted after incubation with the liposomes.Under the laser treatment,the liposomes group produced the most reactive oxygen species among all groups,and had the most excellent therapeutic effect of tumor.(3)In vivo fluorescence imaging and antitumor therapy: The 4T1 tumor-bearing mouse models were used to evaluate the tumor targeting ability and antitumor efficacy of the liposomes.The mice were monitored using an in vivo animal imager after intravenous injection of different drugs and the results demonstrated that the liposomes had good tumor targeting ability and long-circulating effect.The changes in the tumor size of the tumor-bearing mice were recorded within 14 days after drug injection,and it was found that the liposomes had significant therapeutic effect.The results of body weight monitoring,hematoxylin and eosin(H&E)staining,and hematology analysis had no significant differences,demonstrating the good biosafety of the liposomes. |
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