Dramatic influence of the hydroxy functionality of azasugar moiety in the head group region of tocopherol-based cationic lipids on in vitro gene transfection efficacies

Cationic lipids have been effectively used as nonviral vectors for the delivery of polynucleic acids into the cytosol. In particular, lipids having hydroxy groups in the head group region facilitate the strong binding of polynucleic acids with the negatively charged phosphate groups of DNA via hydrogen bonding and electrostatic interactions and, thus regulate the transfection efficiency. In this regard, we designed and synthesised two cationic lipids, namely, aza sugar head group-based cationic lipids (Toc-Aza) and non-aza sugar-based cationic lipids (Toc-Pyr) as the control lipid. A well-known co-lipid, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) was used to formulate liposomes and lipoplexes, which were biophysically characterised for hydrodynamic diameters, global surface charges, and DNA binding. Three cell lines, namely, HEK-293, CHO, and HepG2 were used for cell viability assays and in vitro transfection studies. In vitro transfection studies revealed that the aza sugar head group-based cationic lipid (Toc-Aza) and the cationic lipid without hydroxyl groups on the aza sugar head group (pyrrolidine group) (Toc-Pyr) showed contrast transfection efficacies at a 2 : 1 charge ratio in all the three cell lines studied. Toc-Aza showed almost 10-fold better activities than Toc-Pyr at the 2 : 1 charge ratio in all the three cell lines studied. More importantly, the aza sugar head group-based cationic lipid (Toc-Aza) showed 1.5-fold transfection activity in HepG2 and HEK-293 cells and a similar pattern of transfection efficiency in CHO cell lines when compared with commercially available Lipofectamine 2000. These findings improve the knowledge of cationic liposomes and their effects on the variation in the hydroxyl functional group.