title: Surface functionalized cationic lipid-DNA complexes for gene delivery: PEGylated lamellar complexes exhibit distinct DNA-DNA interaction regimes.
abstract: Cationic lipid-DNA (CL-DNA) complexes are abundantly used in nonviral gene therapy clinical applications. Surface functionality is the next step in developing these complexes as competent, target-specific gene carriers. Poly(ethylene glycol) (PEG) is the natural choice to serve as a protective coat or act as a tether for a specific ligand on the surface of these complexes due to its biocompatibility and ability to convey stealth-like properties. Understanding the effect of PEG on the internal structure and surface properties of CL-DNA complexes is essential in developing vectors with more complex derivatives of PEG, such as Arg-Gly-Asp (RGD)-based peptide-PEG-lipids. We report on x-ray diffraction studies to probe the internal structure of CL-DNA complexes consisting of a ternary mixture of cationic lipids, neutral lipids, and PEG-lipids. The PEG-coated complexes are found to exhibit a structure consistent with the lamellar phase. In addition, three distinct DNA interchain interaction regimes were found to exist, due to a), repulsive long-range electrostatic forces; b), short-range repulsive hydration forces; and c), novel polymer-induced depletion attraction forces in two dimensions. Optical microscopy and reporter gene assays further demonstrate the incorporation of the PEG-lipids into the lamellar CL-DNA complexes under biologically relevant conditions, revealing surface modification. Both techniques show that PEG-lipids with a polymer chain of molecular weight 400 do not provide adequate shielding of the PEGylated CL-DNA complexes, whereas PEG-lipids with a polymer chain of molecular weight 2000 confer stealth-like properties. This surface functionalization is a crucial initial step in the development of competent vectors for in vivo systemic gene delivery and suggests that a second type of surface functionality can be added specifically for targeting by the incorporation of peptide-PEG-lipids.
authors.affiliation: Materials Department, Biomolecular Science and Engineering Program, University of California, Santa Barbara, California 93106, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Martin-Herranz
authors.forename: Ayesha
authors.initials: A
authors.lastname: Ahmad
authors.forename: Heather M
authors.initials: HM
authors.lastname: Evans
authors.forename: Kai
authors.initials: K
authors.lastname: Ewert
authors.forename: Uwe
authors.initials: U
authors.lastname: Schulze
authors.forename: Cyrus R
authors.initials: CR
authors.lastname: Safinya
mesh_terms: D000818:Animals; D002412:Cations / Q000737:chemistry; D002478:Cells, Cultured; D020099:Coated Materials, Biocompatible / Q000138:chemical synthesis; D004247:DNA / Q000008:administration & dosage* / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D016503:Drug Delivery Systems / Q000379:methods*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D018014:Gene Transfer Techniques; D008055:Lipids / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances; D051379:Mice; D011092:Polyethylene Glycols / Q000737:chemistry*; D013499:Surface Properties; D014162:Transfection / Q000379:methods
chemical_list: D002412:Cations; D020099:Coated Materials, Biocompatible; D008055:Lipids; D008081:Liposomes; D046911:Macromolecular Substances; D011092:Polyethylene Glycols; D004247:DNA