Targeted Drug Delivery And Imaging Studies Based On Nucleic Acid Aptamers

With the continuous acceleration of industrialization and urbanization,the deterioration of the natural environment has become more and more serious,and the number of cancer patients has increased year by year,which has become one of the major diseases that threaten human life and health.Therefore,it is very important for the treatment and diagnosis of cancer.Nucleic acid aptamers have a wide range of applications in the precise imaging and treatment of major diseases,but they are easily affected by complex environments,resulting in poor stability and off-target effects.Therefore,developing the modification technology of nucleic acid aptamer conjugates to improve their stability and circulation time in vivo,and then improve their application effect in cancer targeted therapy and imaging is a key scientific bottleneck that needs to be broken through.In this paper,a recognition molecule with better stability was obtained through the design of circular bivalent nucleic acid aptamer.The maytansine drug modification can successfully construct a circular bivalent nucleic acid aptamer-maytansine drug conjugate（cb-Ap DC）for targeted drug delivery in HER2-positive breast cancer.In addition,in this thesis,the fluorescently modified aptamer was coupled with EG₃Glu polymer to form a nucleic acid aptamer-polymer conjugate,which can effectively attenuate the degradation issue of aptamers in serum.The specific research contents are as follows:（1）cb-Ap DC for targeted drug delivery to HER2-positive breast cancer.cb-Heraptamer and cb-Ap DC were efficiently constructed by T4 DNA ligase.The differences between circular bivalent aptamers and single-stranded aptamers were explored.The experimental results implied that cb-Heraptamer and Herapptamer have similar binding ability against HER2-positive SKBR3 cells,but cb-Heraptamer has stronger endocytosis efficiency and stability.The results of cytotoxicity experiments revealed that among cb-Heraptamer-1DM1 has a stronger targeted toxicity over cb-Heraptamer-DM1,cb-Heraptamer-2DM1,and cb-Heraptamer-3DM1,and the IC₅₀value against SKBR3 cells is 5.62 n M.（2）FAM-Sgc8-EG₃Glu for imaging studies of acute lymphoblastic leukemia.The nucleic acid aptamer（Sgc8）was reacted with the polymer to synthesize FAM-Sgc8-EG₃Glu,and its successful coupling was proved by agarose gel electrophoresis.The results of flow cytometry and confocal imaging experiments showed that FAM-Sgc8-EG₃Glu had similar binding and endocytosis to FAM-Sgc8.Compared with FAM-Sgc8,FAM-Sgc8-EG₃Glu is less affected by serum and has higher stability.