pH-Sensitive ,Dimethylalkane-1-amine -Oxides in DNA Delivery: From Structure to Transfection Efficiency.

pH-sensitive liposomes composed of homologues of series of ,-dimethylalkane-1-amine -oxides (CNO, = 8-18, where is the number of carbon atoms in the alkyl substituent) and neutral phospholipid dioleoylphosphatidylethanolamine (DOPE) were prepared at two molar ratios (CNO/DOPE = 0.4:1 and 1:1) and tested for their transfection activity. Several techniques (SAXS/WAXS, UV-vis, zeta potential measurements, confocal microscopy) were applied to characterize the system in an effort to unravel the relationship among the transfection efficiency, structure, and composition of the lipoplexes. The transfection efficiency of CNO/DOPE for plasmid DNA in U2OS cells follows a quasi-parabolic dependence on CNO's alkyl substituent length with a maximum at = 16. The transfection efficiency of CNO/DOPE ( = 12-18) lipoplexes was found to be higher than that of commercially available Lipofectamine 2000. C16NO/DOPE also positively transfected HEK 293T and HeLa cells. Small-angle X-ray scattering (SAXS) shows large structural diversity depending on the complex's composition and pH. Transfection efficiencies mediated by two structures, either a condensed lamellar (L) or epitaxially connected L and a condensed inverted hexagonal (H) phase (L & H), were found to be very similar. The change in pH from acidic to neutral induces phase transition L & H → Q + L, with cubic phase Q of the 3 space group. Q detected in lipoplexes of most efficient composition CNO/DOPE ( = 16 and 18) facilitates DNA release and promotes its internalization in the cell.