Comparison between cationic polymers and lipids in mediating systemic genedelivery to the lungs

Airway inflammation frequently found in congenital and acquired lung diseas es may interfere with gene delivery by direct administration through either instillation or aerosol. Systemic delivery by the intravenous administrati on represents an alternative route of delivery that might bypass this barri er. A nonviral approach for transfecting various airway-derived cell lines in vitro showed that cationic polymers (PEI 22K and 25K) and lipids (DOTAP, GL-67/DOPE) are able to transfect with high efficiency the reporter genes firefly luciferase and E. coli lacZ. Notably, two properties predicted that cationic vectors would be useful for a systemic gene delivery approach to the lung: (I) transfection was not inhibited or increased when cells were i ncubated with cationic lipids or polymers in the presence of serum; and (2) cationic vectors protected plasmid DNA from DNase degradation. A single in jection of DNA complexed to the cationic polymer PEI 22K into the tail vein of adult mice efficiently transfected primarily the lungs and to a lesser extent, heart, spleen, kidney and liver. The other vectors mediated lower t o undetectable levels of luciferase expression in the lungs, with DOTAP > G L67/DOPE > PEI 25K > DOTMA/DOPE. A double injection protocol with a 15-min interval between the two doses of DOTAP/DNA complexes was investigated and showed a relevant role of the first injection in transfecting the lungs. A two log increase in luciferase expression was obtained either when the two doses were comprised of luciferase plasmid or when an irrelevant plasmid wa s used in the first injection. The double injection of luciferase/PEI 22K c omplexes determined higher transgene levels than a single dose, but a clear difference using an irrelevant plasmid as first dose was not observed Usin g lacZ as a reporter gene, it was shown that only cells in the alveolar reg ion, including type II penumocytes, stained positively for the transgene pr oduct.