Synthesis Of Zwitterionic Polymer Prodrugs And Their Controlled Drug Release

The practical application of anticancer drugs is often seriously hindered by the disadvantages of poor water solubility,large toxic side effects and rapid release,which is also a common problem faced by most anticancer drugs.Anticancer drugs will be cleared by the kidneys in a short period in the human body,so that the concentration of the drug in the blood will decrease rapidly,resulting in a low drug concentration in the tumor.To ensure the therapeutic effect,the injection dose is generally increased,and the increase of the dose will cause serious side effects and drug resistance,thereby making it extremely necessary to modify the drug to minimize the side effects.2-Methacryloyloxyethylphosphorylcholine is provided with super hydrophilicity,and the phosphorylcholine group contained is widely present on the cell membrane,features good biocompatibility,and is also easy to polymerize.To this end,two polymer conjugates with sustained release and low toxicity were hereby synthesized based on2-methacryloyloxyethylphosphorylcholine（MPC）,and their structures and properties were characterized respectively.The slow-release effect and esterase responsiveness during release provide new ideas and an experimental basis for the development of prodrug carriers.（1）Preparation and application of MPC-modified SN38 drug micelles7-Ethyl-10-Hydroxycamptothecin（SN38）was modified with small molecules,a SN38 prodrug containing an ester bond was synthesized,and 2-methacryloyloxyeth-ylphosphorylcholine（MPC）was polymerized into macromolecular chain transfer agent PMPC.Synthesis of zwitterionic prodrug PMPC-b-PSN38 was carried out by RAFT polymerization,with poly-2-methacryloyloxyethylphosphorylcholine（PMPC）taken as the chain transfer agent.The structures of the ¹H NMR were characterized by UV,FT-IR,MS,and GPC.PMPC-b-PSN38 micelles were prepared using the ultrasonic method,and the stability,sustained release,esterase responsiveness,drug release char-acteristics,and in vivo and in vitro toxicity of the micelles were evaluated by DLS,Zeta potential,as well as in vivo and in vitro toxicity methods.The results show that the critical micelle concentration（CMC）of PMPC-b-PSN38micelles is lower than 0.05 mg/m L,and that PMPC₂₂-b-PSN38_9.6 micelle can self-as-semble in water to form spherical gels with a particle size of about 50 nm and high negative charge（Zeta potential>-20 m V）.Besides,free SN38 can reach the peak re-lease of 41%after 6 h,while the PMPC₂₂-b-PSN38_9.6 micelles only release 13%of the drug after 6 h in PBS solution,and then slowly release 268 h to reach the maximum release amount of 68%.The micelles exhibit a good slow-release effect.The micelles can ensure the slow release of the drug,maintain the drug concentration in the blood,have a longer blood circulation period,and reduce the frequency of administration after entering the human blood.The release amount of PMPC₂₂-b-PSN38_DM9.6micelles can reach 69%in 72 h under the action of 60U/m L esterase,which has esterase responsive-ness.After entering the tumor cells,the micelles can be released more easily under the action of intracellular esterase come out.In the cytotoxicity experiment,under the ac-tion of free SN38,only 43%of colon cancer cell viability is left at 5ug/m L at 48 hours,close to the minimum value.However,under the action of PMPC₂₂-b-PSN38_9.6 mi-celles,When the content of SN38 is 5 ug/m L,the cancer cell viability is still 90%and remains 75%even at 20 ug/m L,indicating that the drug is slowly released,limiting the cytotoxicity.In the in vivo toxicity test,the mouse feces evaluation chart shows that mice in the micelles group present less toxicity,indicating the lower toxicity of the micelles.Additionally,the liver and intestinal pathological sections of mice also sug-gest lower toxicity of the micelles than CPT-11.（2）Preparation and application of MPC-modified MTX drug micellesMethotrexate（MTX）was modified to synthesize a MTX prodrug containing an ester bond,the zwitterionic conjugate PMPC was then synthesized with poly 2-meth-acryloyloxyethyl phosphorylcholine（PMPC）-b-MTX,and their structures were char-acterized by ¹H NMR,UV,FT-IR,and MS.Besides,PMPC-b-PMTX micelles were prepared using the ultrasonic method,and the stability,sustained release,esterase re-sponsiveness,drug release characteristics and cytotoxicity of the micelles were evalu-ated by DLS,Zeta potential,and cck-8 methods.The experimental results show that the PMPC-b-PMTX micelles have a small particle size（<50 nm）,the PMPC₂₂-b-PMTX₄ micelles release 41%of the drug under the condition of no enzyme for 12 h,and 48%of the drug is released under the condition of 60U/m L enzyme,53%of the drug is released under the condition of no enzyme at 120h,and 77%of the drug is released under the condition of 60 U/m L esterase,reflecting the esterase responsiveness and sustained release of micelles.In addition,PMPC₂₂-b-PMTX_9.5micelles release 74%of the drug at 120 h under the condition of PBS,and 97%of the drug is released after216 h.The drug release rate will be faster in the case of a higher drug loading.Cyto-toxicity assessment was also performed on PMPC₂₂-b-PMTX_9.5 micelles.After 24 h of incubation in the cytotoxicity experiment,free MTX becomes more toxic to cells.After72 h of incubation,the cell activity under free MTX drops from 85%to 65%,while the cell viability response of PMPC₂₂-b-PMTX_9.5micelles increases slightly,reflecting the good low toxicity of micelles.