Delivery of oligonucleotides into mammalian cells by anionic peptides: comparison between monomeric and dimeric peptides

The use of antisense oligonucleotides as putative therapeutic agents is limited by their poor delivery into the cytosol and/or the nucleus because they are not able to efficiently cross lipid bilayers. To circumvent this pitfall, anionic amphipathic peptides derived from the influenza virus fusogenic peptide have been used to destabilize membranes in an acidic environment. In this paper, we compare the ability of a monomeric and a dimeric peptide to introduce oligonucleotides into the cytosol and nuclei of several types of cultured cells. Cells incubated at pH 6.2 or at a slightly lower pH in the presence of the monomeric peptide but not the dimeric peptide were efficiently permeabilized. The location of fluorescent derivatives of peptides and of oligonucleotides was assessed by confocal microscopy. Both the peptides and oligonucleotides remained entrapped in vesicular compartments at neutral pH; at acidic pH, oligonucleotides in the presence of the monomeric peptide were mainly in the nucleus, while in the presence of the dimeric peptide they co-localized with the peptide into vesicles. The data are interpreted on the basis of the spectroscopic behaviour of monomeric and dimeric peptides in relation to the environmental pH.