Structurally modified polyethylenimines and their interpolyelectrolyte complexes with DNA as non-viral gene delivery systems

A variety of different block copolymers containing polyethylenimine (PEI) and poly(ethylene glycol) (PEG) blocks, as well as biodegradable PEI derivatives were synthesized, and their potential as gene delivery vehicles were investigated with regard to DNA condensation, transfection efficiency and biocompatibility. Since this first study revealed that with increasing degree of PEGylation DNA condensation is impaired, a synthesis route was developed that exclusively led to PEG-block- PEI diblock copolymers where the degree of PEGylation did not exceed one. The new synthesis concept involved the ring-opening-polymerization of ethylenimine in the presence of a so called 'macrostopper', a PEG with a primary amine as end group allowing to terminate the polymerization reaction. Compact spherical and stable polymer/DNA complexes of about 100 nm size were obtained with these diblock copolymers. The DNA condensation potential of low MW PEIs was significantly enhanced when they were coupled to a larger unit by multi-star-PEGs using HMDI as linker. The resulting 4- and 8-star-(PEG-block-PEI) copolymers yielded small (100 nm) and stable polymer/DNA complexes. EtBr could no longer intercalate into the DNA within these complexes, thus, the DNA was properly condensed by these star-block copolymers. Biodegradable PEIs was synthesized by connecting several low MW PEIs to larger units using oligo(L-lactic acid-co-succinic acid)s. As a result, the PEI macromolecules were conjugated by succinamide units to the copolymer poly(ethylenimine-co-L-lactamide-cosuccinamid) [P(EI-co-LSA)]. The hydrolytic degradation of these amide bonds was found to be pH dependent. The characterization of the synthetic polycations, mainly PEI and its derivatives, was successfully performed by size exclusion chromatography in combination with static and dynamic laser light scattering. Using these methods the MW, the polydispersity and the hydrodynamic radii of the polycations was determined. The degree of branching of the hyperbranched PEIs was measured using 13C-NNE-NMR spectroscopy. Further, estimations of the degree of branching were also achieved by the evaluation of viscosity data in combination with the absolute data of the static light scattering experiments (Mark-Houwink parameters).SIGLEAvailable from: http://deposit.ddb.de/cgi-bin/dokserv?idn=972777083 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman