Fig. 1.

Biophysical characterization of cationic liposome (CL)–DNA complexes with and without PEGylation. (A-C) Schematic drawings of CL–DNA complexes prepared without PEG-lipid (A), with PEG2K-lipid (B), and with RGD-PEG2K-lipid (C). The drawings depict complexes in the prevalent lamellar phase (with an onion-like internal structure). (D, E) Hydrodynamic diameter of DOTAP-based CL–DNA complexes as a function of ρ (the lipid/DNA charge ratio), determined by dynamic light scattering. Measurements were performed 20 min and 24 h after complexes were formed in cell culture medium (DMEM). (D) Data for complexes at low σ_M (membrane charge density) containing varied amounts of PEG2K-lipid or RGD-PEG2K-lipid (i.e., with a lipid composition of 30/70–x/x, mol/mol/mol, DOTAP/DOPC/PEG-lipid; x=0, 5, and 10). (E) Data for complexes at high σ_M (i.e., at 80/20–x/x, mol/mol/mol, DOTAP/DOPC/PEG-lipid; x=0, 5, and 10). (F) Zeta potential of complexes prepared with 0 or 10 mol% PEG-lipid (see above) as a function of ρ. (G) Cryo-EM micrograph of a CL–DNA complex without PEG-lipid (DOTAP/DOPC=80/20, mol/mol) at ρ=10 in 50 mM aqueous NaCl. The multilamellar internal structure of the complex is clearly visible. (H) Cryo-EM micrograph showing PEGylated CL– DNA complexes (DOTAP/DOPC/PEG2K-lipid=80/15/5, mol/mol/mol) at ρ=10 in 50 mM NaCl. Although the sample underwent extensive centrifugation, the complex particles maintain well defined shapes and sub-100 nm sizes. Oligolamellar complexes (solid arrow) and unilamellar liposomes (dashed arrow) coexist. All scale bars represent 100 nm.