Preparation And Drug Release Of Tumor Microenvironment Responsive Amphoteric Polymer

Chemotherapy currently is the main clinical treatment for human cancer.By means of nano-drug delivery system（nano drug delivery system,NDDS）,the dispersity of hydrophobic drugs can be improved,and the non-specific distribution of drugs and side effects in vivo can be effectively reduced,which has become an important development direction of cancer treatment.NDDS stability in the circulatory system and the release characteristics in tumor cells are the key factors for its therapeutic effect.Hydrophilic polymers,such as polyethylene glycol（PEG）and zwitterionic polymers,have excellent performance against nonspecific protein adsorption and high biocompatibility,which can effectively prolong the in vivo circulation time of NDDS and enrich the carrier level at the tumor site by EPR effect.In addition,the concentration of glutathione in tumor cells is higher than that in normal tissues,which can improve the release rate of drug carriers in cells by reducing responsiveness.Based on the discussion above,this work constructed polymer micelles with reduction responsiveness based on polyethylene glycol（PEG）and zwitterionic polymers,the structure of polymer micelles and drug release characteristics under tumor microenvironment were evaluated,and the anticancer efficiency of responsive and non-responsive carriers was compared.The main elements and conclusions are as follows:1、Construction of a reductive responsive amphoteric ion system.The amphiphilic triblock copolymer and polycarboxyl betaine methacrylate（PCBMA-SS-PCL-SS-PCBMA）with disulfide bond-linked poly-ε-caprolactone have many advantages in the preparation of polymeric micelles.The polymer micelles were obtained by self-assembly method.The DLS and TEM showed that the polymer micelles have a narrow and spherical distribution with a diameter of about 102±2 nm,indicating a stable structure.The micelles exhibit high dimensional stability after post-treatment such as centrifugation and freeze-drying.The polymeric drug-loaded micelles containing doxorubicin hydrochloride were prepared through the co-precipitation method.GSH triggered PCBMA shell shedding could lead to micelle recombination and accelerate intracellular drug release.Such kinds of micelles had low cytotoxicity and good biocompatibility.Their 48-hour drug release reached about61%and their IC₅₀ values on human hepatoma cells were 0.72 mg/L,twice as high as that of drug-loaded micelles without reduction responsiveness（30%DOX release and1.44 mg/L）.The fluorescence inversion microscopy and flow cytometry experiments showed that DOX had high fluorescence intensity in hepatoma cell Hep G2.Through the high GSH concentration and reduction response in cancer cells,the rapid release of drugs and a strong effect of inhibiting cell proliferation were obtained.2、Construction of a reduction responsive polyethylene glycol system.Three amphiphilic triblock copolymers including PEG₄₅-SS-PCL₁₇-SS-PEG₄₅、PEG₄₅-SS-PCL₃₁-SS-PEG₄₅ and PEG₄₅-SS-PCL₄₄-SS-PEG₄₅ were first synthesized by introducing cysteamine to PCL terminal groups with different chain lengths and by amide reaction of the terminal groups.The effect of hydrophobic polymer length on self-assembly behavior was investigated.The prepared polymer micelles with water and kinetic dimensions were 41 nm,56（±3）nm and 79（±5）nm,respectively.All three polymers exhibited low critical micelle concentrations（CMC）.The polymeric micelles exhibited significant reduction responsiveness and low cytotoxicity.Drug-loaded micelles with high adriamycin loading efficiency were prepared by co-precipitation method.PEG-SS-PCL-SS-PEG micelle carrier showed faster DOX release,increased from 40%to 80%,and higher cell inhibition in cell reduction environment compared with redox insensitive PEG-b-PCL micelles.These results preliminarily showed that the polymer micelles with hydrophilic polymer PEG or zwitterionic polymer polycarboxylic acid betaine as shell and biodegradable poly-caprolactone as core had high protein adsorption and biocompatibility.Between the polymer micellar core-shells,the introduction of disulfide bonds improved the intracellular release rate of those micellar drug carriers,thus providing a stronger inhibitory effect against cancer cells proliferation.It is expected to achieve better therapeutic effects on tumours in vivo.