Study On Enzyme-responsive Linear-dendaritic Block Copolymers Based On Dendritic Phenylalanyl-lysine Dipeptides

Enzyme-responsive micelles or vesicles are highly promising carriers for targeted drug delivery because they are capable of controlling drug release rates based on overexpression and expression levels of the enzyme at specific sites.Linear-dendritic block copolymers（LDBCs）combine the easy synthesis,availability,and processability of linear polymeric chains with the regular and well-defined structure of dendrons,which have an exact number of peripheral groups that can be modified for the introduction of functionality in a controlled manner.These make them potentially useful in drug delivery systems.However,studies on enzyme-responsive drug-loaded micelles or vesicles from LDBCs have rarely been reported.In this thesis,two novel series of enzyme-responsive LDBCs were synthesized and used to prepare drug-loaded micelles or vesicles.Their enzyme responsiveness was investigated.Three generations of linear-dendritic diblock copolymer PNVP-b-dendr（Phe-Lys）_n（n=1-3）and triblock copolymer dendr（Phe-Lys）_nb-PNVP-b-dendr（Phe-Lys）_n（n=1-3）based onlinear poly（N-vinylpyrrolidone）（PNVP）and dendritic phenylalanyl-lysine（Phe-Lys）dipeptides via a combination of reversible addition-fragmentation chain transfer（RAFT）/xanthates（MADIX）polymerization of N-vinylpyrrolidone and stepwise peptide chemistry.Their structures were characterized by ¹H-NMR and GPC.The self-assembly behavior and enzyme response properties of these block copolymers in aqueous solution were investigated by ¹H-NMR,TEM and fluorescence spectroscopy.The results showed that the diblock copolymers PNVP-b-dendr（Phe-Lys）₂ and PNVP-b-dendr（Phe-Lys）₃ can self-assemble into spherical micelles in aqueous solution.The micelles are able to disassemble and release the encapsulated anticancer drug doxorubicin or hydrophobic dye Nile red upon trypsin treatment.Moreover,when the generation of LDBCs increases,the stability and size of the micelles increase,but disassembly rate of the micelles decreases.The result of in vitro drug release experiments showed that PNVP-b-dendr（Phe-Lys）₃ has a higher encapsulation efficiency for DOX than PNVP-b-dendr（Phe-Lys）₂.However,PNVP-b-dendr（Phe-Lys）₂ released DOX faster than PNVP-b-dendr（Phe-Lys）₃ at the same concentration of trypsin.In vitro cytotoxicity experiments showed that these LDBCs have good biocompatibility with human lung epithelial cells（BEAS-2B）and human liver cancer cells（SMMC-7721）.Thetriblockcopolymerdendr（Phe-Lys）_n-b-PNVP-b-dendr（Phe-Lys）_n（n=1-3）self-assembles into vesicle aggregates in aqueous solution.These vesicles can disassemble and release the encapsulated hydrophobic model drug under the action of trypsin.In addition,as the generation of these triblock copolymer increases,the vesicle aggregates formed in the aqueous solution are more stable and disassembly rate of the micelles is slower,but the sizes of the aggregates were smaller.A dendritic–linear–dendritic triblock copolymer based on linear PNVP and dendritic phenylalanyl-lysine（Phe-Lys）dipeptides decorated at the periphery with amino cation groups was obtained via removing the amino protecting groups（Fmoc）from dendr（Phe-Lys）₃-b-PNVP-b-dendr（Phe-Lys）₃ by 4-methylpiperidine.The triblock copolymer and a plurality of negatively charged adenosine triphosphates（ATP）can form a polymeric superamphiphile in aqueous solution as a result of electrostatic interaction.The self-assembly behavior and enzyme response property of the superamphiphile were studied by ¹H-NMR,TEM and fluorescence spectroscopy.The results show that the superamphiphile can self-assemble into spherical micelles in aqueous solution.The micelles disassemble and release loaded hydrophilic small molecule HPTS after treatment with trypsin or alkaline phosphatase（CIAP）.The release rate of the solution treated with trypsin and CIAP was significantly greater than that in the absence of trypsin or CIAP,indicating that the superamphiphile has dual enzyme responsiveness.