| A new type of acid-labile cationic copolymer consisting of a hydrophilic poly (ethyleneglycol)(PEG) block and a polymethacrylamide block bearing tertiary amines linked byacid-labile ortho ester rings in the chains (PAOE), with defined chain length (22,48, and66repeating units), had been synthesized via reversible addition-fragmentation chain transfer(RAFT) polymerization.The copolymers could efficiently bind and condense plasmid DNA at neutral pH intonarrowly dispersed nano-scale polyplexes. With increased N/P ratio, polymer/DNApolyplexes had smaller average particle size and showed higher stability against electrostaticdestabilization by heparin. The surface of PEGylated/DNA complexes retained positivecharges at N/P ratio of2:1. The hydrolysis of ortho ester group in the side-chains of PAOEfollowed a distinct exocyclic mechanism and the rate of hydrolysis was much accelerated atmildly acidic pH, resulting in the accelerated disruption of polyplexes and the release of intactDNA plasmid.The polymers were not toxic to COS7cells and293cells by MTT, and only displayedchain-length-dependent toxicity at a high concentration (1mg/mL). The gene transfectionefficiency was detected by flow instrument, which provides a basis for the relationshipbetween diblock copolymer structures and gene transfection efficiency. In vitro genetransfection efficiency was also found to correlate with chain-length of the PAOE block withthe longer polymer chain favoring transfection. The transfection efficiency of293cells wasmuch higher than Cos-7cells. Both in COS-7cells and293cells, PEG-b-PAOE66copolymerturned out to display the highest gene transfection efficiency at the N/P ratio of8:1. All of theabove results showed that diblock copolymer possessed excellent stability, low cytotoxicity,and stong ability of combining with DNA, which indicated that the PEG-b-PAOE have greatpotential to be a novel acid-sensitive non-viral gene delivery vector. |
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