Synthesis, characterization, and gene transfer application of poly(ethylene glycol-b-ethylenimine) with high molar mass polyamine block.

The study of ethyloxazoline/methyloxazoline (EtOXZ/MeOXZ) copolymerization, initiated by methyl tosylate (MeOTs), showed that (i) incorporation of MeOXZ units into random copolymer becomes effective over DP = 100 and (ii) propagation process proceeds with negligible transfer to monomer up to a DP of 400 despite the presence of MeOXZ in the polymerization medium. These results produced random poly(EtOXZ-co-MeOXZ) copolymers with various molar composition ratios in alkyloxazoline units. The close values found for the comonomer reactivity ratios in acetonitrile (r(1MeOXZ) = 1.18; r(2EtOXZ) = 0.34) implied a random chain organization in short sequences of each repeating unit, which was an important parameter in view of the optimization of their subsequent modification: the alkaline hydrolysis was successfully achieved when the MeOXZ unit content of the polyoxazoline chains reached 75%. Using these results, the diblock copolymer poly(ethylene glycol-b-(ethyloxazoline-co-methyloxazoline)) (poly(EG-b-(EtOXZ-co-MeOXZ))) with high DP was synthesized by cationic copolymerization of EtOXZ/MeOXZ comonomers using CH(3)-PEG(2kDa)-Ts as macroinitiator. The comonomer composition of this new compound was adjusted in order to optimize the hydrolysis step and obtain finally the diblock copolymer poly(ethylene glycol-b-ethylenimine) (poly(EG-b-EI)). The high molar mass of this copolymer was confirmed both by (1)H NMR and SANS measurements. Gene delivery experiments showed that the copolymer has significant DNA transfection capacities.

Linear topology confers in vivo gene transfer activity to polyethylenimines.

Although polyethylenimines (PEIs) are frequently used transfection agents, it is still unclear which of their properties are required for efficient gene delivery. This is even more striking when working in vivo since some PEIs are able to generate significant gene expression, whereas others are not. To facilitate a rational development of compounds with improved transfection activities, studies aimed at identifying the properties involved in the transfection process seem indispensable. In the present work, we investigated how transfection with linear PEI of 22 kDa allows for high reporter gene expression in lungs after intravenous injection, whereas the branched PEI of 25 kDa does not. To this end, we synthesized L-PEI derivatives that are intermediates between linear and branched PEIs. Our results show that the topology plays a crucial role in obtaining in vivo reporter gene expression, whereas the content of primary, secondary, and tertiary amines is only of minor importance.