Use of poly(ethylene glycol)-lipid conjugates to regulate the surface attributes and transfection activity of lipid-DNA particles

We evaluated the use of poly(ethylene glycol) (PEG)-modified lipids to cont rol the surface properties of a lipid-based gene transfer system. The lipid -DNA. particles (LDPs) used form spontaneously when plasmid DNA is added to mixed detergent lipid micelles consisting of the non-ionic detergent n-oct yl-D-glucopyranoside, the cationic lipid dioleyldimethylammonium chloride ( DODAC), the zwitterionic lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamin e (DOPE), and selected PEG-modified phosphatidylethanolamines. The inclusio n of DODAC is required to form the hydrophobic lipid-DNA complex. DOPE is i ncluded to facilitate dissociation of DNA from the cationic lipid and the P EG-modified lipids are added in an effort to stabilize the surface attribut es of the resulting lipid-DNA particles. We used PEG-lipids that varied in acyl chain composition because of recent results demonstrating acyl chain d ependent transfer of PEG-lipids from lipid vesicles, providing the potentia l to allow a transformation of the surface properties due to loss of surfac e grafted PEG. The addition of PEG-modified lipids does not interfere in LD P formation and its presence favors formation of smaller particles (75 nm i n contrast to 130 nm in the absence of the PEG-modified lipid). PEG-lipid i ncorporation causes a concentration dependent reduction in LDP-mediated tra nsfection of B16/BL6 melanoma cells, a result that can be partially attribu ted to a reduction in particle binding to cells. However, significant LDP b inding to B16/BL6 cells was still observed under conditions where LDP trans fection activity was reduced by more than 85%. The potential for PEG to int erfere with LDP processing following cell binding is discussed. (C) 2000 Wi ley-Liss, Inc.