Dynamic Measurements of Membrane Insertion Potential of Synthetic Cell Penetrating Peptide/pDNA/Ca2+ Complexes

Abstract

Noncovalent complexation of plasmid DNA (pDNA) using cell penetrating peptides (CPPs) has been less explored due to the relatively large complex size formed and the low-level gene expression. Here, condensing synthetic CPP polyplexes using CaCl2 produced small and stable complexes, which show higher level of in vitro gene expression. Anionic (i.e., POPS and POPG) or zwitterion (i.e., POPC) phospholipid monolayers at the air-water interface are used as model cell membranes to monitor the membrane insertion potential of synthetic CPPs. The insertion potential of complexes having different cationic (dTAT, H9, K9, R9, and RH9) and amphiphilic (RA9, RL9, and RW9) peptides were recorded using a Langmuir monolayer approach that records complexes adsorption to model membranes. Further, to mimic the pH of early endosome and late endosome and lysosome, phospholipid complex interactions were recorded at normal (pH 7.4) and low (pH 4.4) pH. All the complexes studied induced disruptions in phospholipid packing, which were most pronounced for the complexes having amphiphilic CPPs (i.e., RW9 and RL9). Particularly, the surface pressure of the complexes was significantly lower at normal pH when compared to acidic pH in the presence of POPC and POPS monolayers, except for RL9 and RW9 complexes. In contrast, the surface pressure of the complexes was significantly higher at normal pH when compared to acidic pH in the presence of POPG monolayer. Since the late endosomes contain an abundance of PC lipids and low pH, these results may be highly relevant to understand the efficiency of endosomal escape of these complexes.