Preparation Of Cationic Multi-responsive Polymers And Application In Gene Vector

Despite the great potential of non-viral delivery systems in gene therapy, their application has been impaired by various impediments. Hence, these smart polymers are expected to target tumor cells more specifically, and thereby reducing the side toxicity of gene delivery systems. By changing the functional monomer, multi-responsive polymers can make it have the advantages of large capacity, low toxicity, no immunogenicity, etc. In this thesis, we aimed to design two multi-responsive block and core cross linked star polymer vectors via reversible addition-fragmentation chain transfer（RAFT） polymerization for targeted gene delivery.PH-responsive poly(2-（dimethylamino）ethyl acrylate（PDMAEA） was synthesized via RAFT polymerization using BSPA and AIBN as chain transfer agent and initiator. Then water-soluble thermosensitive copoly（oligoethylene oxide） acrylates（POD） were synthesized by the copolymerization of oligo（ethylene oxide） acrylate（OEGA） and di（ethylene oxide） ethyl ether acrylate（DEGA） using BSPA as chain transfer agent and AIBN as initiator, by RAFT polymerization. Linear block POD-b-PDMAEA was synthesized using POD as macro RAFT agent, Then the POD and PDMAEA arms were cross-linked by the disulfide crosslinker of N,N’-double acryloyl cystamine（BAC） to produce a degradable multi-responsive CCS polymers whose core can be cleaved by a reducing agent.The chemical structure and composition were characterrized by FT-IR and 1H-NMR spectroscopy, the molecule weight and molecular weight distribution of the copolymers were obtained by GPC. The phase aggregation and muti-responsive behavior of polymers were evaluated in solution using UV-vis spectroscopy and dynamic light scattering（DLS）. The buffering capacity and p Ka were tested by automatic potentiometric titrator. In addition, agarose gel electrophoresis, z-average size and Zeta potential measurements demonstrate that such block and CCS can effectively condense DNA, potential applications for the gene delivery.The results show that well-defined linear block and core cross linked star polymers were synthesized successfully（PDI< 1.3） by RAFT polymerization. The molar ratio of POD and PDMAEA in block and star polymer were about 1:1, the LCST of star polymer was lower then that of linears, and their LCST were nearly human temperature. Both block and star polymers were temperature, p H/CO₂, salt responsive, in addition, they could self-catalyzed hydrolysis. The star polymer has slower hydrolysis rate, stronger proton buffering capacity and lower p Ka, and the unique positive-to-negative charge-reversal induced by self-catalyzed hydrolysis may efficiently promote the subsequent DNA release. Furthermore, CCS50:50 polymer could effectively condense and protect DNA at an N/P ratio of 1, forming nanocomplexes with favorable particle size（200 nm）. However, POD-b-PDMAEA could condense and protect DNA to form nanocomplexes with favorable particle size（180 nm）, at low N/P ratio, the particle size increases gradually. According to the results, CCS50:50 polymer can ondense and protect DNA better than POD-b-PDMAEA, provide better stable spatial structure for DNA and not easy to form aggregation at high N/P. In brief, star polymers could offer more effective protection of DNA than linear counter part because of the greater buffering capability conferred by unique molecular architecture.