An Acid Sensitive Ketal-Based Polyethylene Glycol-Oligoethylenimine Copolymer Mediates Improved Transfection Efficiency at Reduced Toxicity

Abstract

Dynamic PEG-polycation copolymers that release PEG and degrade into small fragments after cell entry might present efficient and biocompatible gene carriers. PEG-OEI-MK was synthesized by copolymerization of 5 kDa polyethyleneglycol (PEG) and 800 Da oligoethylenimines through acid-degradable acetone-bis-(N-maleimidoethyl)ketal linkers (MK). To evaluate any benefit of the reversible over stable linkage, also the corresponding pH-stable analog, PEG-OEI-BM, was synthesized via ether linkages. Luciferase and GFP expression plasmids were used for transfections, in vivo biocompatibility was evaluated by intravenous application of polymers in Balb/c mice. PEG-OEI-MK showed efficient DNA binding as analyzed by ethidium bromide exclusion, resulting in formation of polyplexes with sizes around 100 nm and surface charges of below 5 mV zeta potential. This surface shielding of PEG-OEI-MK polyplexes remained stable at neutral pH 7.4, while polyplexes deshielded and aggregated at pH 5 within 15-30 min. Cell culture experiments demonstrated reduced polymer toxicity compared to the non-PEGylated OEI-MK. Transfection experiments demonstrated reduced gene expression of PEG-OEI-BM compared with the non-PEGylated analog OEI-BM, whereas the pH-reversible polymer PEG-OEI-MK mediated a significant increased transfection efficiency over the non-PEGylated OEI-MK. PEG-OEI-MK mediated the highest gene transfer at lowest cytotoxicity levels and also best in vivo biocompatibility.