Construction Of Multifunctional Stimulus-responsive Drug Delivery Systems And Their Performance In Tumor Therapy

At present,chemotherapy has always been employed as the most common therapy to treat cancers,however,chemotherapeutic drugs couldn’t target cancer cells,which directly affects the therapeutic efficacy and even causes serious side effects.Recently,drug delivery systems have become a hot spot in the field of oncology research owing to their multiple advantages,such as improvement of the solubility and distribution of drugs in vivo,reduction of immunogenicity and extension of the half-life.However,the construction of the drug delivery system still faces some urgent problems:（a）The stability of drug delivery system is low,which could lead to serious toxic side effects and reduce the anti-cancer efficacy;（b）Some targeted recognition molecules have some defects,such as low specific selectivity,short half-life,and high cost,which is difficult to realize accurate localization of cancer cells;（c）After entering the tumor cells,some drug delivery systems could not thoroughly degrade and the drugs could not be completely released because of the tight structure,it would reduce the anti-cancer efficacy and even lead to the drug resistance.To solve the above problems,molecular imprinting technology,fluorescence imaging technology,nanotechnology,cell biology and other interdisciplinary,and cutting-edge technologies were combined to construct some new drug loading systems,including an intelligent drug delivery system based on MOF-dopamine and molecular imprinting,a GSH-responsive hydrogel drug delivery system based on lipoic acid,and a drug delivery system based on DNA nanospheres with controllable size and p H-responsive self-degradable property for efficient delivery and controlled release of drugs.The main research content is as follows:（1）Dopamine（DA）is a kind of neurotransmitter in the human body,and can be polymerized to form polydopamine（PDA）under mild conditions.Moreover,PDA has a good photothermal conversion performance,and it could realize photothermal treatment under near-infrared light（808 nm）.Furthermore,PDA can combine with DOX to form p H-responsive structures and could release the drug under acidic conditions.In this paper,DA acts as functional monomer and crosslinker,zeoliticimidazolate frame-8（ZIF-8）serves as the drug carrier and support material,epidermal growth factor receptor（EGFR）epitope works as template molecule,a capsule-like molecularly imprinted polymer（MIP）nanoparticle with simple structure was designed and constructed by combining surface molecular imprinting technology and epitope imprinting technology for the targeted chemotherapy-photothermal synergistic therapy.During the process of imprinting on the ZIF-8 surface,PDA can capture Zn²⁺in ZIF-8 through coupling effect,resulting in the disintegration of ZIF-8,and leaving only the PDA capsule-like imprinted polymer（MD）as the drug delivery system.The results showed that MD exhibited good p H-responsive drug release performance.The cumulative release rate of DOX from MD in acidic condition（p H=5.0）was 6 times than that in neutral condition（p H=7.4）.MD could target the EGFR-overexpressing cancer cells,and the DOX fluorescence intensity of A549 cells treated with MD was 5 times than that treated with ND.Furthermore,the DOX fluorescence intensity of A549 cells treated with MD was 7 times than that of 16HBE cells treated with MD.So MD nanoparticles have many advantages,including targeted identification for cancer cells,intelligent-responsive drug release,good biocompatibility,good stability and chemical-photothermal system therapy.This work solves the problems of poor stability,ineffective targeting and high cost of traditional drug delivery system,and provided a new method and pathway for developing a safe and efficient drug delivery system for controlled-responsive drug release and targeted therapy.（2）The concentration of glutathione（GSH）in tumor cells or tissues is at least 4 times higher than that in normal tissues.Therefore,to achieve the purpose of precision treatment,a GSH-responsive hydrogel based on natural small molecules（Lipoic acid,TA）was constructed for local precision treatment of tumors.TA is an antioxidant coenzyme in the human body,which has a dithiolane and can form polylipoic acid（PTA）through heating.However,TA-based delivery gels for cancer therapy have not yet been developed.In this paper,a novel polylipoic acid-polyethylene glycol（PEG-PTA）hydrogel was prepared through esterification and polyreaction.The prepared hydrogels enriched with disulfide bonds and can be degraded through sulfhydryl exchange with abundant GSH in the tumor microenvironment,and then released the drug.The results showed that the cumulative release rate of DOX@PEG600-PTA hydrogel in the GSH solution could reach about80%at 90 hours while the cumulative release rate of DOX@PEG600-PTA hydrogel in the PBS solution was still less than 3%.Therefore,the injectable GSH-responsive hydrogel prepared in this paper solves the problems of poor stability,incomplete drug release and high cost of traditional drug delivery system,and it is expected to serve as a smart drug delivery system for cancer treatment.（3）DNA nanocarriers are widely used in the field of drug delivery because of programmability,good biocompatibility,low immunogenicity,and easily predictable thermodynamic property.The i-motif sequence is cytosine-rich,it could form a double helix structure with the hybridization chain in a neutral environment,and in an acidic environment,i-motif strand can form a CC（+）base pair and be folded to a tetramer structure（duplex to-i-motif structure）,thus i-motif strand has a p H-responsive performance.In this paper,four simple U-shaped DNA short strands（containing two i-motif strands and a linker strand with aptamer AP-ZY11）were used to fabricate a size-controllable,p H-responsive self-degrading DNA nanosphere through the cyclic self-assembly of DNA strands.The DNA nanosphere drug delivery system can targeted kill cancer cells.It is worth noting that DNA nanospheres with different sizes（25-260 nm）can be obtained by regulating the sequence or number of DNA single-stranded linkers.The results showed that the appropriate size of nanocarriers can effectively promote the uptake of nanospheres by cells.DNA nanospheres exhibited good p H-responsive drug release performance owing to the existence of i-motif strands,and the released DOX fluorescence of DOX@AP-NSs2was triple at p H=5.0 than at p H=7.4.Moreover,the pathway for DNA nanospheres entering cells was also investigated.The results showed that the DNA nanospheres targeted cancer cells through aptamer and then were uptaken by cells through the caveolin-mediated endocytosis pathway.Therefore,this novel DNA nanosphere with controllable size and p H-responsive self-degradation performance solves the problems of poor stability and poor targeting of traditional drug delivery system and has the potential to target tumor cells and precision treatment for cancer.