Polyethylenimine-mediated gene delivery: a mechanistic study

Background Ethylenimine polymers (PEIs) belong to one of the most efficient family of cationic compounds for delivery of plasmid DNA into mammalian ce lls. The high transfection efficiencies are obtained even in the absence of endosomolytic agents such as fusogenic peptides or chloroquine, which is i n contrast to most of the other cationic polymers. It has been hypothesized that the efficiency of PEI is due to its capacity to buffer the endosomes. Methods To investigate the importance of the acidification of endosomes dur ing PEI-mediated DNA transfer we used proton pump inhibitors such as bafilo mycin Al and concanamycin A. Moreover, we tested whether PEI is able to des tabilize natural membranes per se at neutral or acidic pH by performing ery throcyte lysis assays. Results PEI-mediated transfection in the presence of bafilomycin Al resulte d in a 7-74-fold decrease in reporter gene expression depending on the cell line used. In contrast, the efficiency of the monocationic lipid, DOTAP, w as not importantly altered in the presence of the drug. Furthermore, the pr esent data show that PEI cannot destabilize erythrocyte membranes, even at acidic pH, and that PEI, complexed or not to DNA, can increase the transfec tion efficiency of the cationic polymer, polylysine, when added at the same time to the cells. Conclusions The transfection efficiency of PEIs partially relies on their a bility to capture the protons which are transferred into the endosomes duri ng their acidification. In addition, PEI is able to deliver significant amo unts of DNA into cells and the DNA complexes involved in the expression of the transgene escape within 4 h from the endosomes. Copyright (C) 2001 John Wiley & Sons, Ltd.