Preparation And Characterization Of PH-responsive Spherical Nucleic Acids

In recent years,with the development of modern molecular biology technology,gene therapy using nucleic acid molecules as drugs is a therapeutic strategy at the genetic molecular level,and has become one of the key and hot research directions in the field of tumor therapy.Compared with traditional drug treatment methods,it has the advantages of specificity,safety,efficacy,high selectivity,non-toxicity or low toxicity to tissues.However,naked nucleic acid molecules are easily degraded by nucleases in the serum environment in vivo,are unstable,have strong hydrophilicity and are negatively charged,are not easily absorbed by tissues,and cannot enter the nucleus.Disadvantages such as low dyeing efficiency.The study found that spherical nucleic acid is easy to be taken up by cells,inhibits nuclease degradation,has low immunogenicity,and is unique in non-toxicity.We modified PEG to introduce acetal bonds into spherical nucleic acid system.The amphiphilic polymer is prepared to realize the protection of PEG to nucleic acid when circulating in the body.When the nanoparticle enters the tumor microenvironment,PEG can fall off and expose the spherical nucleic acid so that it can enter the cell smoothly.In the second chapter of this paper,we first modified m PEG to have a p H-responsive acetal bond.Then,the modified acetal m PEG is used for ring-opening polymerization of lactide,and the amphiphilic polymer acetal m PEG-b-PLA with different hydrophobic chain lengths is obtained by different feeding ratios.Polylactide is modified to have N3 group,and then it is bonded with a nucleic acid chain with a cycloalkyne bond to obtain a PEG-protected spherical nucleic acid polymer.We first conducted an acid response study on the p H-responsive gene carrier to determine the good acid response of the acetal bond,and then performed a series of characterizations on spherical nucleic acids with different hydrophobic chain lengths to obtain the most suitable gene carrier for binding nucleic acid chains.Avoid amphiphilic polymers circulating in the human body because the hydrophilic chains are too long to form nanoparticles,or because the hydrophobic chains are too long,the nanoparticles formed by the amphiphilic polymers are too large to pass through the tumor tissue.The walls of the blood vessels enter the cells.Considering the instability of spherical nucleic acid circulating in vivo,we introduced a cross-linking group into the spherical nucleic acid system to avoid premature dissociation of the formed spherical nucleic acid during in vivo circulation and exposing the nucleic acid strand to be degraded by nucleases.In the third chapter of this paper,we synthesized an amphiphilic comb polymer acetal m PEG-b-P（LA-g-N₃）-b-P（LA-g-Py）,pyridine disulfide（PDS）enabled the polymer to have core cross-linking sites.At the same time,as shown in Chapter 2,the length of the hydrophobic chain is controlled to obtain a gene vector with the most suitable length of the hydrophobic chain,and then the nucleic acid chain with a cycloalkyne bond is bonded to obtain a spherical nucleic acid polymer containing a cross-linking group,and then add a catalytic amount of dithiothreitol（DTT）into the system to form a core cross-linked spherical nucleic acid polymer,which makes the spherical nucleic acid have better stability,so as to realize that the spherical nucleic acid can not only be circulated in the body PEG protection can greatly improve the stability of spherical nucleic acid micelles.