Stabilized plasmid-lipid particles for regional gene therapy: formulation and transfection properties

Previous work (Wheeler et al, Gene Therapy 1999; 6: 271-281) has shown that plasmid DNA can be entrapped in 'stabilized plasmid-lipid particles' (SPLP ) containing the fusogenic lipid dioleoylphosphatidylethanolamine (DOPE), l ow levels (5-10 mol%) of cationic lipid, and stabilized by a polyethylenegl ycol (PEG) coating. The PEG moieties are attached to a ceramide anchor cont aining an arachidoyl acyl group (PEG-CerC(20)). These SPLP exhibit low tran sfection potencies in vitro, due in part to the long residence time pf the PEG-CerC(20) on the SPLP surface. In this work we employed SPLP stabilized by PEG attached to ceramide containing an octanoyl acyl group (PEG-CerC(B)) , which is able to quickly exchange out of the SPLP, to develop systems tha t give rise to optimized in vitro and in vivo (regional) transfection. A pa rticular objective was to achieve cationic lipid contents that give rise to maximum transfection levels. If is shown that-by performing the dialysis p rocedure in the presence of increasing concentrations of citrate, SPLP cont aining up to 30 mol% of the cationic lipid dioleoydimethylammonium chloride (DODAC) could be generated. The SPLP produced could be isolated from empty vesicles by sucrose density gradient centrifugation, and exhibited a narro w size distribution (62 +/- 8 nm, as determined by freeze-fracture electron microscopy) and a high plasmid-to-lipid ratio of 65 mu g/mu mol (correspon ding to one plasmid per particle) regardless of the DODAC content It was fo und that isolated SPLP containing 20-24 mol% DODAC resulted in optimum tran sfection of COS-7 and HepG2 cells in vitro, with luciferase expression leve ls comparable to those achieved for plasmid DNA-cationic lipid complexes. I n vivo studies employing an intraperitoneal B16 tumor model and intraperito neal administration of SPLP also demonstrated maximum luciferase expression for DODAC contents of 20-24 mol% and significantly improved gene expressio n in tumor tissue as compared with complexes. We conclude that SPLP stabili zed by PEG-CerC(8) and containing 20-24 mol% cationic lipid are attractive alternatives to plasmid DNA-cationic lipid complexes for regional gene ther apy applications.