| Background:Malignant tumors are the diseases which have highest morbidity and mortality in the world.In recent years,the morbidity and mortality of malignant tumors are increasing continuously,and that influenced the human health seriously.Although the mortality rate of malignant tumors is abnormal high,however the five-year survival rate would be significantly improved if the early diagnosis of cancer.Therefore,early diagnosis and treatment of malignant tumors are particularly important for cancer patient.At present,X-ray,CT,MRI,ultrasound imaging and other medical imaging strategiesare commonly used in the diagnosis of cancer,but they still cannot meet the needs of early diagnosis of cancer because of the missed diagnosisoccured sometimes and delayed the treatment.At present,with the rapid development of the integration of diagnosis and treatment,it is one of the hot points and difficulties in clinical research to realize the early diagnosis,precise localization,in situ treatment,cooperative treatment and real-time monitoring and prognosis in the course of treatment simultaneously.Photoacoustic imaging is a promising biomedical imaging method,which perfectly combines the high contrast of optical imaging and the deep penetration of ultrasound imaging.Therefore,it has a good application prospect in the field of cancer early diagnosis.Photothermal therapy could utilize the photothermal effect of photothermal converter(PTAs)which can convert light energy into heat to induce the surrounding environment overheating for cancer cells death Gold nanorods(AuNR)have a good optical response and biocompatibility,and are widely used as PAI contrast agents and PTAs.However,the optical properties of gold nanorods areenhancedalong with the size of gold nanorods increased usually,and then it is unfavorable for the infiltration and imaging of tumors.The self-assembled AuNRs have plasma coupling because of they can generate strong electromagnetic fields for the enhancement of optical absorption ability.Therefore,the photoacoustic imaging performance of the composite nano-assembly is greatly improved,and which is beneficial for tumors early diagnosis.The nano-assembly composite maintains the size of about 70 nm at physiological level,thus guaranteeing a longer blood circulation time and a higher tumors cumulative efficiency.After reaching the tumor site,it is decomposed into penetrating AuNR monomers and DOX upon the acidic microenvironment of the tumor,and the synergistic effect of photothermalchemotherapy can be achieved under the external near infrared laser irradiation.This nano-loading strategy significantly reduces the side effects of mono-drug DOX chemotherapy on systemic drugand is a more ideal choice.Purpose:The aim of this study is to construct a nano-drug-loaded assembly which can respond step by step to the micro-environment of tumors.It has the characteristics of enhancing photoacoustic performance,targeting delivery,targeting release,and can realize the integration of diagnosis,photothermal and chemical therapy at the same time.Methods:(1)Preparing polymer-gold nanorod assembly with double response of pH and reduction reaction;(2)The morphological structure and particle size distribution of PEG-PCR VP/AuNR@PDOX were characterized by transmission electron microscopy and DLS,and spectral analysis was carried out.(3)To investigate the pH and GSH double-response decomposition performance of PEG-PCR VP/AuNR@PDOX.(4)The photothermal effect of nano-assembly was evaluated according to the photothermal heating performance of aqueous solution in vitro.The photoacoustic signal of nano-assembly with different water suspension and concentration was measured by photoacoustic imager,and the photoacoustic enhancement performance of nano-assembly was proved.(5)PEG-PCRVP/AuNR@PDOX dual-response drug release experiment;(6)Intracellular drug release experiments and in vitro imaging studies of PEG-PCR VP/AuNR@PDOX;(7)To construct the subcutaneous transplantation model of MG-435 cells in mice,and to evaluate the enhancement of photoacoustic imaging in vivo by nano-assembly and the effect of chemotherapeutics-photothermal therapy after treatment,and to further evaluate the safety of nano-assembly.Results:1.PEG-PCR VP/AuNR@PDOX nano-assembly was successfully prepared.TEM and DLS characterization showed that its size and distribution characteristics and the size and surface PEG modification could ensure its stable existence in the physiological environment,then prolong the circulation time in the blood and improve the penetration and retention effect(EPR effect)of the tumor site.2.The PEG-PCR VP shell can be removed by AuNR assembly in pH 6.0solution.When the VP shell is further treated with GSH,the AuNR@PDOX assembly dissociates into a single AuNR and releases DOX.The size of nanomaterials in tumors decreases due to gradual dissociation,which greatly increases the permeability of drugs.3.The temperature rise and photoacoustic signal of AuNR assemblies were significantly higher than those of AuNR clusters and PEG-PCR VPNP in vitro,which indicated that AuNR assemblies were beneficial to increase the contrast between tumor sites and surrounding normal tissues,and to improve the early diagnosis of tumors.PEG-PCR VP/AuNR@PDOX could improve the photothermal therapeutic effect of tumors by improving the photothermal conversion efficiency of PEG-PCR VP/AuNR@PDOX.4.The results of intracellular drug release experiment further showed that the rupture of the shell of AuNR assembly was caused by intracellular acidic environment,and the reduction environment of intracellular caused the release of DOX on the surface of AuNR.AuNR assembly can enhance SERS signal of MDA-MB-435 cells,and the combination of photothermal and chemical effects has stronger toxicity to MDA-MB-435 cells.5.AuNR assembly can significantly enhance the photoacoustic signal and SERS signal of tumor site in tumors bearing mice.Under laser irradiation,AuNR assembly significantly inhibited the growth of tumors in mice,suggesting that the combination of chemical-photothermal therapy can significantly inhibit the growth of tumors.Conclusions:1.The coupling of strong electrostatic magnetic field produced by AuNR assembly improves the photothermal conversion efficiency of shell PEG-PCR VP,and greatly enhances the photothermal and photoacoustic properties of nano-assembly.2.The diameter of PEG-modified nano-assembly is about 70 nm,which endows the assembly with good biological stability and longer blood circulation time,and improves the EPR effect of the tumor site.3.The nano-assembly was separated step by step in the weak acidic and high GSH tumour microenvironment,and the PEG-PCR VP shell was decomposed in the acidic environment.Then AuNR@PDOX was decomposed into a single AuNR in the high GSH environment.The size of the nano-assembly was reduced after dissociation,so that it could penetrate into deeper tumour areas to release DOX and improve the therapeutic effect.4.Nano-assemblers have enhanced SERS and photoacoustic signals in vivo.Nano-assemblers accumulate at the tumor site and undergo step-by-step response dissociation.This imaging-guided drug release therapy is of great significance for cancer treatment.5.AuNR and DOX achieve the goal of combining chemo-photothermal therapy.In vivo experiments show that they have good anti-tumor effect and no recurrence after treatment.and has good safety. |
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