Non-viral pH-sensitive Gene Carriers based on Poly((2-ethyl-2oxazoline)- co-ethylenimine)-block-Poly(2-ethyl-2-oxazoline): A Study of Gene Release Behavior

The non-viral and pH-sensitive gene carrier poly((2-ethyl-2-oxazoline)-co-ethylenimine)-block-poly(2-ethyl-2-oxazoline) (P(EOz/EI)-b-PEOz-NH2) is synthesized. This gene carrier contains both cationic poly((2-ethyl-2-oxazoline)-co-ethylenimine) (P(EOz/EI)) segments and charge-neutral poly(2-ethyl-2-oxazoline) (PEOz) segments. PEOz is used as a biocompatible shell and core source. A technique in which methanesulfonyl poly((2-ethyl-2-oxazoline)-co-ethylenimine (P(EOz/EI)-OMs) is used as a macroinitiator is utilized to modify the outer shell of a PEOz segment, providing an amino group at the chain terminus. P(EOz/EI)-b-PEOz-NH2 is coordinated with plasmid DNA, and the resulting complexes are characterized by gel permeation chromatography and H-1 NMR spectroscopy. The P(EOz/EI)-b-PEOz-NH2 polyplexes show a suitable mean particle size, low cytotoxicity, and acceptable transfection as a result of the shielding of PEI by the PEOz outer shell. Transmission electron microscopy is used to examine morphology. Results show that the stable core-shell structure of ternary polyplexes collapses at pH 7.4 and releases plasmids at pH 5. Observations of cell uptake of the B-PEI/DNA polyplex and P(EOz/EI)-b-PEOz-NH2/DNA polyplexes using a confocal laser scanning microscope reveal that P(EOz/EI)-b-PEOz-NH2 polyplexes start to accumulate after 6 h of incubation and significantly accumulate after 12 h. The results indicate that the hydrophilic, charge-neutral PEOz shell stabilizes polyplex formation and enhances polyplex cell viability. Polyplex transfection efficiencies are as high as those of commercially available transfection reagents. The results suggest that this gene carrier, based on the diblock copolymer P(EOz/EI)-b-PEOz-NH2, has potential for in non-viral gene therapy applications.