Light-triggered Aggregation Of Gold Nanoparticles For Tumor Theranostics In Vivo

Background:With the continuous development of nanotechnology,a lot of new nanomaterials are emerging in the diagnosis and therapy of tumors.Among them,gold nanoparticles?AuNPs?,as promising nanomaterials for theranostics,are widely used in photothermal therapy?PTT?,radiosensitization therapy?RT?,photoacoustic?PA?imaging,computed tomography?CT?imaging,etc.Recent studies revealed that small AuNPs had the ability to penetrate deep into the tumor tissue,but were easy to being backflow to the blood or cleared into surrounding tissues,reducing the accumulation of the nanoparticles in tumor sites.However,large aggregate of AuNPs did not overflow beyond the blood vessels and could be trapped in the extracellular matrix between cells,resulting in large accumulation of AuNPs within tumor tissues.For AuNPs,only those with size larger than 50 nm have strong absorption in near-infrared region?NIR?,which can be used for PAI and PTT of the tumor.In addition,the retention time of AuNPs at the tumor site can be further prolonged after aggregation,which would greatly enhance the CT imaging and radiosensitization therapy of tumor.Thus far,there are numerous techniques have been developed for AuNPs aggregation in vivo,such as tumor microenvironment triggered?pH-sensitive,enzyme-sensitive AuNPs?and DNA-mediated AuNPs aggregation.However,the endogenous stimuli-induced AuNPs aggregation has some shortcomings.For example,it easily leads to unwanted particle aggregate due to the sophisticated biological environment.In addition,due to susceptibility to nucleases in blood,it is technically challenging to apply the DNA-mediated AuNPs aggregation approach in vivo.Therefore,it is highly meaningful to develop new strategies for spatiotemporally manipulating the aggregation of AuNPs in order to achieve Au NPs aggregate for the diagnosis and therapy of tumors in vivo.Objective:To develop a new approach to spatiotemporally manipulate the aggregation of AuNPs in vivo and explore its application in tumor imaging and treatment in vivo.Methods:In the first part of this research,the photolabile gold nanoparticles?dAuNPs?were prepared by modifying the NH₂ terminal group of PEG5000 ligands on the surface of AuNPs?²0.5 nm?with NHS-diazirine?DA-NHS?.Upon 405 nm irradiation,dAuNPs can covalently crosslink together to aggregate in tumor,which generates strong absorption in NIR region.The strong surface plasmon resonance appearing in NIR thus makes the AuNPs potentially useful for PTT and PAI of tumors.In the second part of the research,in order to improve the accumulation of dAuNPs in tumor,folate with tumor targeting function was conjugated to the surface of dAuNPs to get the folate-modified photolabile gold nanoparticles?dAuNP-FA?.The small dAuNP-FA can reach to the tumor site through the EPR effect and folate receptor-mediated endocytosis.Upon 405 nm laser irradiation,dAu NP-FA can covalently crosslink together to aggregate within tumor,thus greatly prolonging the retention time of dAuNP-FA in tumor site and subsequently enhancing the CT imaging and radiotherapy of tumors in vivo.Results:Firstly,the results show that the dAuNPs have different levels of aggregation with different irradiation time of 405 nm laser in vitro,the longer the time,the more seriously aggregate of dAuNPs.Once the dAuNPs were injected into mice via tail vein,they could be triggered to form covalently crosslinking aggregate upon405 nm laser irradiation in vivo,which can be effectively applied for PAI and PTT of tumors.It was found that the thermal ablation of PTT could completely kill the tumor cells and prevent the tumor recurrence and metastasis.In addition,we also successfully synthesized the dAuNP-FA nanoparticles with folate group on the surface of dAuNPs for active tumor targeting.The in vitro studies show that the cellular uptake of dAuNP-FA is apparently higher than dAuNPs due to the presence of folate.And the in vivo results indicate that dAuNP-FA can covalently crosslink to aggregate under the405 nm laser irradiation,which prolongs the retention time of dAuNP-FA in the tumor,resulting in enhanced CT imaging as well as effective radiotherapy treatment for tumor.Conclusion:We have successfully developed an innovative strategy of light-triggered aggregation of AuNPs.It can be not only used for enhanced photoacoustic and CT imaging,but also for effective PTT and radiotherapy treatment of malignant tumors.