Intracellular kinetics of non-viral gene delivery using polyethylenimine carriers

Polymeric nucleic acid carriers are designed to overcome one or more barriers to delivery. High molecular weight polyethylenimine (PEI) shows high transfection efficiency but exhibits high cytotoxicity (Fischer et al. Biomaterials, 24:1121-1131 (2003); Peterson et al. Bioconjug. Chem., 13:845-854 (2002)). Nontoxic water-soluble lipopolymer (WSLP) was previously developed using branched poly(ethylenimine) (PEI, mw 1,800) and cholesteryl chloroformate (Han, Mahato, and Kim. Bioconjug. Chem., 12:337-345 (2001)) and is an effective non-viral gene carrier with transfection levels equal or above high molecular weight PEI with a lower cytotoxicity profile. To understand how differences in these polymeric carriers influence transfection, we studied the pharmacokinetics of polymer gene carriers at the cellular level.

Cells were exposed in vitro to different polymeric carriers and the transport of the carriers into different cellular compartments was determined using cellular fractionation and real-time quantitative PCR. A multi-compartment mathematical model was applied to time series measurements of the trafficking of plasmids across each cellular barrier.

Our result indicates that the chemical modification of WSLP increased the rate parameter for endosomal escape significantly compared to conventional PEI carriers thereby increasing the overall transfection efficiency.

These results are consistent with the goal of endosomal destabilization of the carrier design. This method provides a quantitative means for assessing different polymer construct designs for gene delivery.