Applications Of Multifunctional Silver Nanotriangles In Chemotherapy,Photothermal Therapy And Ct Imaging Of Tumors

Background: Malignant tumors are one of the leading causes of death in humans and seriously threaten human life and health.The clinical treatment strategies for tumors mainly include surgical resection,chemotherapy and radiotherapy.However,some tumors are difficult to be completely resected by surgery,and thus have a high recurrence rate.In addition,treatment outcomes for many patients are limited by resistance of tumor cells to chemotherapy and radiotherapy,and the emergence of various adverse effects.Therefore,it has always been an urgent clinical problem to enhance the therapeutic effect of tumors,inhibit their recurrence and metastasis,and reduce side effects.Computed tomography(CT)is an important method for tumor diagnosis,while clinical commonly used CT contrast agents have some drawbacks,such as short blood circulation time and risk of inducing anaphylaxis.In recent years,the development of nanotechnology in medical field has provided novel strategies for the diagnosis and treatment of various diseases.Some studies have shown that the combination of nanomaterials and chemotherapy drugs can produce synergistic effects,thereby exerting better anti-tumor effects than single-agent treatment.Silver nanotriangles(AgNTs)have good photothermal conversion properties,and the application of targeted modified AgNTs in photothermal therapy of tumors is expected to minimize adverse effects and achieve excellent therapeutic effects.In addition,silver-based nanomaterials also possess strong X-ray attenuation capabilities.The use of AgNTs with targeted modification as CT contrast agents is a promising strategy to overcome the defects of commonly used contrast agents and exert a good imaging effect.Therefore,this study performed a series of researches on the applications of multifunctional AgNTs in chemotherapy,photothermal therapy and CT imaging of tumors.The main contents are shown as the following aspects.Part Ⅰ Synergistic effect and mechanism of silver nanotriangles combined with chemotherapeutics against gliomaPurpose: The research aimed to assess the anti-glioma effect of chitosan-coated silver nanotriangles(AgNTs)combined with cyclophosphamide(CTX),5-fluorouracil(5-FU),oxaliplatin(OXA),doxorubicin(DOX)or gemcitabine(GEM)in different glioma cell lines(U87,U251 and C6),and to screen out a drug with the most broad-spectrum and strongest synergistic anti-glioma activity.The possible underlying mechanisms of the synergy were also investigated.Methods: Chitosan-coated AgNTs were prepared,followed by characterization using transmission electron microscopy and ultraviolet-visible absorption spectroscopy.The anti-tumor effects of diffrent drugs combined with AgNTs in diffrent glioma cell lines were studied with MTT assay.The intracellular reactive oxygen species(ROS)level,mitochondrial membrane potential(MMP)and cell apoptosis were detected by flow cytometry.The possible underlying mechanisms of the synergy were further investigated with ROS scavenger and specific inhibitors of p38,extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase(JNK)pathways.Results: The synthesized AgNTs were mainly triangular with an average edge length of 125 nm.A synergistic anti-glioma effect of AgNTs combined with CTX was not observed,and the synergism between AgNTs and 5-FU was cell type-specific.AgNTs combined with OXA,DOX or GEM displayed synergistic effects in three glioma cell lines,and the combination of AgNTs and GEM showed the strongest synergistic activity.Their synergy induced ROS production,decreased cell viability,reduced MMP and promoted cell apoptosis,while pretreatment with ROS scavenger N-acetylcysteine or JNK inhibitor SP600125 significantly reversed changes in cell viability,MMP and apoptosis rate.Conclusion: The combination of AgNTs and GEM possessed a broad-spectrum and potent synergistic anti-glioma activity,resulting from cell apoptosis mediated by a ROS-dependent mitochondrial pathway,in which JNK might be involved.Our study might provide an important theoretical basis for the development of highly efficacious therapy of glioma.Part Ⅱ AS1411 and EpDT3 conjugated silver nanotriangle-mediated photothermal therapy for breast cancer cells and cancer stem cellsPurpose: This study aimed to construct AS1411 and EpDT3 conjugated PEGylated silver nanotriangles(AENTs),and assess their targeting abilities to breast cancer cells and cancer stem cells(CSCs),as well as the anti-tumor and anti-metastatic effects of AENTs-mediated photothermal therapy(PTT)by in vitro and in vivo experiments.Methods: AENTs were constructed and then characterized by transmission electron microscopy,X-ray diffraction,Fourier transform infrared spectroscopy,ultraviolet-visible absorption spectroscopy and dynamic light scattering.Infrared thermal camera was utilized to detect the photothermal conversion effect of the prepared nanomaterials under near-infrared laser irradiation.Inductively coupled plasma mass spectrometry,confocal microscopy and in vivo imaging were applied to evaluate the tumor targeting property of AENTs.Wound healing assay,transwell invasion assay and a mouse model of breast cancer were used to investigate the anti-metastatic and anti-tumor effects of AENTs-mediated PTT.Results: The characterization results showed that the prepared nanomaterials were mainly triangles with a mean edge length of 123 nm,and AS1411 and EpDT3 were successfully conjugated to them.The photothermal conversion effect and photothermal stability of the nanomaterials were proved to be excellent.Dual-aptamer modification could significantly increase the uptake of nanomaterials by breast cancer cells and CSCs,and AENTs injected through the tail vein was able to efficiently target the tumor site of the mice.Moreover,AENTs-mediated PTT significantly inhibited the viability,migration and invasion of breast cancer cells,and greatly suppressed tumor growth and lung metastasis in breast cancer-bearing mice.Conclusion: AENTs were able to efficiently target breast cancer cells and CSCs,and AENTs-mediated PTT could exert excellent anti-tumor and anti-metastatic effects.Our study might provide novel perspectives for development of highly effective breast cancer targeted therapy strategies.Part Ⅲ Application of silver nanotriangles as a novel contrast agent in computed tomography imaging of breast cancerPurpose: The research aimed to prepare chitosan-coated AgNTs,evaluate their X-ray attenuation capabilities,and assess their CT contrast properties in breast cancer cells and breast cancer-bearing mice.Methods: AgNTs with a range of sizes were synthesized and subsequently characterized by transmission electron microscopy,atomic force microscopy,ultraviolet-visible absorption spectroscopy and dynamic light scattering.The X-ray attenuation properties of all prepared AgNTs were evaluated using micro CT.The AgNTs with the highest X-ray attenuation coefficient were selected for targeted modification with AS1411 and their CT imaging effect at the cellular level was detected.In addition,the CT imaging effect after intratumoral injection of AgNTs was observed in a mouse model of breast cancer.Results: All synthesized AgNTs were mainly triangular in shape and their mean edge lengths were 60 nm,88 nm,120 nm and 149 nm,respectively.At the same mass concentration of the active elements,all AgNTs tested exhibited stronger X-ray attenuation capability than iohexol,a clinical commonly used CT contrast agent.AgNTs with the largest size were selected for further research,due to their strongest X-ray attenuation capability and best biocompatibility.The attenuation coefficient of breast cancer cells treated with PEGylated AgNTs or AS1411 conjugated PEGylated AgNTs increased in a particle concentration-dependent manner.At the same mass concentration,AS1411 modified AgNTs showed better CT contrast effect than PEGylated AgNTs.In vivo CT imaging showed that the density of the tumor injected with AgNTs was significantly increased.Conclusion: AgNTs might be a promising CT contrast agent,and targeted modification with AS1411 could further improve the CT imaging effect.This study might provide an important theoretical and experimental basis for the development of highly efficient tumor CT contrast agents.