Investigation On "switched" Photodynamic Therapy Nano-system Based On The Conformational Change Of Nucleic Acid Aptamer

Malignant tumor is one of the major diseases which threaten mankind's health.While,Photodynamic therapy(PDT)is a kind of treatment which transfer the energy of photosensitizer to oxygen efficiently under the corresponding wavelength excitation,and then produce ROS to kill cancer cells.Due to its advantages of mild,non-invasive and low side effects,photodynamic therapy has become an international research hotspot among the researchers.However,due to the poor solubility of most photosensitizers in water and the difficulty in crossing the multiple biological barriers in vivo,it is difficult to achieve the goal of accurate delivery to tumor tissues.In addition,photosensitizers which detained in normal tissues still have phototoxicity,so the reduction of phototoxicity and the improvement of photodynamic efficiency are the key issues to be solved.Presently,researches on tumor PDT mainly focus on the targeted delivery of PS,and the mechanism of photodynamic therapy on tumor and the synergistic effect with other treatment methods.Based on this,this project intends to construct a tumor cell membrane protein-triggered PDT system which based on the conformational change of aptamer nucleic acid.While improving the efficiency of tumor PDT,the concept of "switch photodynamic therapy" is adopted to reduce the phototoxicity of PDT.In this research,gold nanorods of uniform size were prepared by seed medicated growth,the size and aspect ratio of which are 50 nm and 3:1 respectively,and the nucleic acid aptamers which can specifically bind to MUC1 protein high expressed on the surface of tumor cell membrane were modified on the surface of gold nanorods.The hydroxy of the hairpin aptamer was modified with photosensitizer Ce6.When MUC1 protein was absent,the photosensitizer was pulled close to the gold nanorods,and its photodynamic therapeutic activity was quenched.When the aptamer binds with MUC1 protein,the aptamer's structure changes conformably,Ce6 is far away from the surface of the gold nanorod,and the photodynamic treatment activity is restored,forming a "switch" type nano-level photodynamic treatment system.In this study,the preparation was systematically characterized,and its morphology,particle size,zeta potential,the ability of reactive oxygen production,fluorescence quenching,and the conformational changing efficiency of aptamer,as well as its feasibility as a "switching" material were investigated.In addition,MCF-7 human breast cancer cells and Hs578 bst normal breast cells were selected as the subjects in this study,and the "on-off" photodynamic treatment nano-system constructed was used to investigate the anti-tumor activity in vitro and in vivo.It is proved that the PDT system has the ability of selectively inducing the apoptosis of tumor cells and the application for the treatment of malignant tumors.As for in vivo anti-tumor activity experiments,MCF-7 cell line was used to construct tumor-bearing nude mice as model animals,and investigated the therapeutic effect of the preparation.By analyzing the distribution of the preparation in tumor-bearing nude mice,the results showed that the preparation modified with aptamer had a stronger targeting ability,and Ce6 could be highly concentrated at the tumor site.The production of reactive oxygen species in tumor tissues was significantly higher than that of other groups,and the preparation could effectively inhibit the growth of tumor,besides,the effect was observably higher than that of Ce6 group.The relative tumor volume ratio was 1.21,while the saline group and Ce6 group were 10.74 and 9.40,respectively.The tumor inhibition effect was significantly higher than that of the Ce6 group(***,P<0.001).The TUNEL results demonstrated that the drug delivery system can effectively inhibit tumor growth and promote the apoptosis of tumor tissue further(which the apoptotic area was about 55.1%,analyzed through tumor slides).The results of H&E also indicated that the preparation had unconspicuous damage to the organs except tumor tissue in nude mice.This paper systematically investigated the "on-off" photodynamic system based on the conformation change of aptamer,achieved the specific photodynamic treatment in tumor tissues,while reducing the photosensitive toxicity.The constructed drug delivery system produces ROS efficiently in tumor and kill tumor cells specifically under laser irradiation,which is expected to be used in tumor treatment.