Synthesis Of PH-responsive Y-shaped Amphiphilic Polymers,Study On Their Drug Encapsulation And Antitumor Activity In Vitro

In recent years,amphiphilic polymer micelles as anticaner drug delivery system is one of the research hotspots in cancer therapy.Based on high permeability and retention effect(EPR)of tumor location,which not only can improve the drug’s therapeutic efficacy,but also reduce the side effects.A large number of pH responsive polymer micelles were prepared and applied to the drug delivery system due to the weak acidity of the tumor stroma or intracellular endo/lysosomes.At present,the linear amphiphilic polymer micelles were most widely studied,recent studies showed that non-linear amphiphilic polymers have special properties in drug delivery due to their structural specificity,such as assembly morphology,drug loading and release kinetics,in vivo and in vitro treatment efficiency.In this paper,two types of pH-responsive Y-shaped amphiphilic polymers were synthesized,which containing methoxy polyethylene glycol(mPEG)as hydrophilic unit,poly ethoxy ethyl glycidyl ether(PEEGE)and poly caprolactone(PCL)as hydrophobic unit,respectively.The weak acid cleavable ketal as the branching point was introduced in the copolymer to obtain the pH-sensitivity.The relationship between the structure,composition and the drug delivery performance was investigated.In addition,the growth inhibition effect of drug loaded micelles on tumor cells was also investigated.The details are as follows:1、mPEG-DMX was synthesized via etherification reaction of mPEG with an excess of α,α’-dichloro-m-xylene.Then a pH-sensitive ketal bond was introduced into mPEG through etherification reaction with mPEG-DMX,The terminal allyl group was followly oxidized by osmium tetroxide and NMO,and mPEG-Ketal-20H was obtained.A pH-responsive Y-shaped amphiphilic polymer mPEG-Ketal-(PEEGE)2 was obtained by the anion ring opening polymerization(AROP)of ethoxyethyl glycidyl ether(EEGE)with diphenyl potassium(DPMK)as a initiator.In contrast,a non-pH-sensitive Y-shaped amphiphilic polymer mPEG-b-(PEEGE)2 was synthesized.In order to compare the effects of different aggregation units on drug loading performance,two types of Y-shaped polymer mPEG-Ketal-(PCL)2 and mPEG-b-(PCL)2 were synthesized by the ring opening polymerization of ε-caprolactone(ε-CL)with mPEG-Ketal-20H and APEG-20H as macromolecular initiators and stannous octoate as catalyzer.The amphiphilic polymers with different hydrophilic and hydrophobic block ratios were obtained by adjusting the feeding ratio of initiator and polymer monomer.The structure and molecular weight of the polymer were characterized by nuclear magnetic hydrogen spectrum(1H-NMR),fourier infrared spectroscopy(FT-IR)and gel permeation chromatography(GPC).The crystallization behavior and melting properties of the polymers were characterized by differential scanning calorimeter(DSC).2.The polymer micelles were prepared by the evaporation method.The size and morphology were characterized by dynamic light scattering(DLS)and transmission electron microscopy(TEM).The critical micelle concentration(CMC)was determined by pyrene fluorescence probe method.The mPEG-Ketal-(PEEGE25)2 and mPEG-Ketal-(PCL25)2 were hydrolyzed under different pH conditions.The degradation of polymers and pH responsiveness were studied by observing the size variation trend of micelles.The drug loading performance of various polymer micelles was investigated by using doxorubicin as a drug model.The drug release of the DOX-loaded micelles was performed in vitro under different pH,and the results showed that mPEG-Ketal-(PCL25)2 had a good pH responsiveness.The cytotoxicity of mPEG-Ketal-(PCL25)2 and mPEG-b-(PCL25)2 was investigated by using MTT assay.The results showed that both polymer micelles had nontoxicity and good biocompatibility.The drug-loaded micelles had significant anticancer effect on tumor cells,and the survival rate of cells decreased with the increase of doxorubicin dose,and mPEG-Ketal-(PCL25)2 had better anticancer properties.The drug uptake and intracellular distribution of cells were studied by laser confocal microscope and flow cytometry.The results showed that the cells incubating by mPEG-Ketal-(PCL25)2/DOX have a higher fluorescence intensity than that of mPEG-b-(PCL25)2/DOX.It is shown that the drug-loaded micelles can effectively enter into tumor cells and rapidly release drug in acid endo/lysosomes enviroment,which can effectively improve their anticancer efficiency.