Pyridinium cationic lipids in gene delivery: an in vitro and in vivo comparison of transfection efficiency versus a tetraalkylammonium congener

Cationic lipids provide a promising alternative to the use of viruses for delivering genes therapeutically. Among the several classes of lipidic vectors, those bearing a heterocyclic cationic head have shown important advantages, such as low cytotoxicity and improved efficiency across different cell lines. We recently reported a simple and efficient strategy for obtaining pyridinium cationic lipids, starting from pyrylium salts and primary amines. The present study is aimed to compare the cellular toxicity and transfection efficiency generated by the pyridinium polar head versus the tetramethylammonium one on several tumor cell lines and also in experimental animals, delivered via intratumor injections. Thus, the lead compound 1-(2,3-dioleoyloxypropyl)-2,4,6-trimethylpyridinium lipid (2Oc), coformulated with different helper lipids in various molar ratios, was tested against its ammonium congener DOTAP-a standard transfection reagent. The results revealed that when formulated with cholesterol at 1:1 molar ratio, the pyridinium lipid 2Oc was able to transfect several cancer cell lines with similar or better efficiency than its tetraalkylammonium congener DOTAP, while producing lower cytotoxicity. The NCI-H23 lung cancer cell line was found to be the most susceptible to be transfected. Therefore, we designed an in vivo assay based on this type of carcinoma in nude mice, which were injected intratumoral with 2Oc- and DOTAP-based lipoplexes. The red fluorescent protein reporter revealed that the pyridinium cationic lipid was superior to its tetraalkylammonium congener, transfecting the tissue on a higher area and with higher efficiency. These encouraging findings, together with the simple and efficient synthetic strategy, lay the foundation for further development of pyridinium lipids for gene therapy with improved transfection efficiency in vivo and even further reduced cytotoxicity.