Liposomal lipid and plasmid DNA delivery to B16/BL6 tumors after intraperitoneal administration of cationic liposome DNA aggregates

The transfer of plasmid expression vectors to cells is essential for transf ection after administration of lipid-based DNA formulations (lipoplexes). A murine i.p. B16/BL6 tumor model was used to characterize DNA delivery, lip osomal lipid delivery, and gene transfer after regional (i.p.) administrati on of free plasmid DNA and DNA lipoplexes. DNA lipoplexes were prepared usi ng cationic dioleoyldimethylammonium chloride/dioleoylphosphatidylethanolam ine (50:50 mol ratio) liposomes mixed with plasmid DNA (1 mu g DNA/10 nmol lipid). The plasmid used contained the chloramphenicol acetyltransferase ge ne and chloramphenicol acetyltransferase expression (mU/g tumor) was measur ed to estimate transfection efficiency. Tumor-associated DNA and liposomal lipid levels were measured to estimate the efficiency of lipid-mediated DNA delivery to tumors. Plasmid DNA delivery was estimated using [3H]-labeled plasmid as a tracer, dot blot analysis, and/or Southern analysis. Liposomal lipid delivery was estimated using [C-14]-dioleoylphosphatidylethanolamine as a liposomal lipid marker. Gene expression in the B16/BL6 tumors was hig hly variable, with values ranging from greater than 2,000 mU/g tumor to les s than 100 mU/g tumor. There was a tendency to observe enhanced transfectio n in small (<250 mg) tumors. Approximately 18% of the injected dose of DNA was associated with these small tumors 2 h after i.p. administration. South ern analysis of extracted tumor DNA indicated that plasmid DNA associated w ith tumors was intact 24 h after administration. DNA and associated liposom al lipid are efficiently bound to tumors after regional administration; how ever, it is unclear whether delivery is sufficient to abet internalization and appropriate subcellular localization of the expression vector.