Construction Of Multifunctional Nucleic Acid Nanomachines Based On Gold Nanoparticles For Multimodal Cancer Diagnosis And Treatment

As an endogenous biomaterial,DNAs have been widely applied for construction of novel biocarriers due to their programmability,predictability and excellent biocompatibility.To date,using DNA nanotechnology,a variety of stimuli-responsive DNA nanomachines with controllable size and shape have been established,which have been further used in bioimaging,biosensing and precise drug delivery.Based on functional nucleic acids(e.g.aptamers and DNAzymes),this thesis constructed a multifunctional DNA-Au nanomachine,in which glutathione(GSH)in the tumor microenvironment can trigger controllable drug release and aggregation of gold nanoparticles(Au NPs),achieving multimodal photodynamic/photothermal/chemo combinational therapy of breast cancer at cellular and in vivo levels.This work provides novel ideas and strategies for the development of DNA nanotechnology and nanomedicine.This thesis mainly carried out the following two works:1.Construction of GSH-responsive multifunctional DNA-Au nanomachine based on functional nucleic acidsFirst,the G-quadruplex structures are used to specifically load catalytic molecule(hemin)and photosensitizer(Ce6),followed by hybridization with a GSH-responsive sequence modified with disulfide bond to form the double-stranded DNA(ds DNA).Subsequently,the obtained ds DNAs are immobilized on the Au NPs through Au-S bonds and further load anticancer drug Dox,generating GSH-responsive DNA-Au nanomachine.In the absence of GSH,the DNA-Au nanomachine can exist stably,while the introduction of GSH can activate the operation of DNA-Au nanomachine,resulting in the dissociation of nanomachines along with the release of drugs and aggregation of Au NPs.The proposed DNA-Au nanomachine exhibits the merits of easy preparation,high stability and multifunctionality,which can be applied in targeted drug delivery and cancer therapy.2.GSH-responsive DNA-Au nanomachine for photodynamic/photothermal/chemo combinational therapy of breast cancerDue to its high loading capacity and excellent targeting ability,the GSH-responsive DNA-Au nanomachine has been utilized as a multifunctional nanocarrier for co-delivery of Ce6,hemin and Dox.Notably,hemin can intercalate into the G-quadruplex to form the catalase-mimicking DNAzyme,which can catalyze the decomposition of excessive H₂O₂in cancer cells for in situ generation of O₂ to relieve hypoxia.Meanwhile,the formed O₂promotes the generation of ¹O₂ from Ce6 under near-infrared(NIR)laser irradiation,thus achieving the enhanced PDT.Moreover,combining with the chemotherapeutic effect of Dox as well as the photothermal conversion capacity of Au NPs,the multifunctional DNA-Au nanomachine can achieve photodynamic/photothermal/chemo combinational therapy.The in vitro and in vivo assays validate that the GSH-responsive DNA-Au nanomachine has highly targeted damage effect on murine breast cancer cells,which further inhibits the tumor growth.Therefore,this work exhibits a promising development prospect in biomedicine.