Studies On Bionic Ultra-pH-sensitive Nanoparticles With Small Size Based On Hydrogen Bonds Of Nucleobase Pairing

Chemotherapy is the mainstream for cancer therapy in clinic.However,regardless of the method of administration,chemotherapy drugs always will be distributed to the whole body of various tissues,organs.What's more,drug-loaded nanoparticles cannot quickly release drugs in the tumor cells.In order to enrichment the drug-loaded nanoparticles in the tumor site,rapidly disintegrate,we herein used adenine(A)and thymine(T)to synthesize hydrophobic copolymer PA-b-(PCL-g-P(HEA-A)(PCL-A)?PA-b-(PCL-g-P(HEA-A/VB7)(PCL-A/VB7)and hydrophilic copolymer mPEG-b-P(AGE-SH-T)(mPEG-T).Then small particle size nanoparticles with shield-unshield effect were prepared by self-assemble based on the complementary hydrogen bonds of nucleobase pairing,that were m PEG-T@A-PCL and m PEG-T@A/VB7-PCL.The effects of hydrogen bonds on the particle size,in vitro release of drugs and cell uptake were evaluated.Firstly,using benzyl alcohol(PA)as initiator,the polycaprolactone(PCL)was synthesizedbyring-openingpolymerization,andhydrophobiccopolymer PA-b-(PCL-g-P(HEA-A)(PCL-A)was prepared via reversible addition fragmentation chain transfer(RAFT)polymerization.mPEG-b-PAGE was synthesized via sequential living anionic ring-opening polymerization,and hydrophilic copolymer m PEG-T was prepared via the radical-mediated thiol-ene reaction.The m PEG-T@A-PCL nanoparticles and drug-loaded mPEG-T@A-PCL nanoparticles were prepared by dialysis.Under physiological condition(pH=7.4),the nanoparticles showed impaction structure with partical size around 40 nm.The results of variable-temperature ~1HNMR successfully demonstrated the existence of hydrogen bonds.The results of in vitro release showed that compared with the cumulative release of DOX under pH 7.4,it had been doubled in the condition of pH 6.0 and three times in the condition of pH 5.0,indicating that the nanoparticles have pH-sensitivity.The in vitro cytotoxicity of mPEG-T@A-PCL nanoparticles were evaluated using MCF7 cells,and indicating that these nanoparticles have excellent biocompatibility.PCL-A/VB7 was also prepared by esterification reaction between PCL-A and VB7,and self-assembled m PEG-T@A/VB7-PCL nanoparticles.Firstly,the results of variable-temperature ~1HNMR successfully demonstrated the existence of hydrogen bonds,and proved the introduction of VB7 do not affect the formation of hydrogen bonds.The particle size of PEG-T@A/VB7-PCL nanoparticles changed from 45 nm to 25 nm while the nanoparticles aqueous dispersion adjusted from 7.4 to 6.8,which proved the ultra-pH-sensitive to the micro-acid environment of our nanoparticles.The results of in vitro release showed that under pH 6.8 the cumulative release of DOX was about 40%.Under the condition of pH 6.8,the results of the cell uptake showed that the fluorescence intensity of DOX was significantly increased,which indicated that VB7 was unshielded and promoted the target ability of VB7.The above experiment proved that the hydrogen bonds were destroyed under the condition of pH6.8,some of mPEG-T was removed,so VB7 was unshielded and developed the function of target,which effectively verified the feasibility of using shield-unshield effect to build nanoparticles.