Peptide-mediated lipofection is governed by lipoplex physical properties and the density of surface-displayed amines

Peptides can potentiate lipid‐mediated gene delivery by modifying lipoplex physiochemical properties to overcome rate‐limiting steps to gene transfer. The objectives of this study were to determine the regimes over which cationic peptides enhance lipofection and to investigate the mechanism of action, such as increased cellular association resulting from changes in lipoplex physical properties. Short, cationic peptides were incorporated into lipoplexes by mixing peptide, lipid and DNA. Lipoplexes were characterized using gel retardation, dynamic light scattering, and fluorescent microscopy, and the amount of surface‐displayed amines was quantified by fluorescamine. Size, zeta potential, and surface amines for lipoplexes were dependent on peptide/DNA ratio. Inclusion of peptides in lipoplexes resulted in up to a 13‐fold increase in percentage of cells transfected, and up to a 76‐fold increase in protein expression. This transfection enhancement corresponded to a small particle diameter and positive zeta potential of lipoplexes, as well as increased amount of surface‐displayed amines. Relative to lipid alone, these properties of the peptide‐modified lipoplexes enhanced cellular association, which has been reported as a rate‐limiting step for transfection with lipoplexes. The addition of peptides is a simple method of lipofection enhancement, as direct chemical modification of lipids is not necessary for increased transfection. © 2008 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4794-4806, 2008