Design, synthesis, and transfection biology of novel cationic glycolipids for use in liposomal gene delivery

The molecular structure of the cationic lipids used in gene transfection st rongly influences their transfection efficiency. High transfection efficien cies of non-glycerol-based simple monocationic transfection lipids with hyd roxyethyl headgroups recently reported by us (Banerjee et al. J. Med. Chem. 1999, 42, 4292-4299) are consistent with the earlier observations that the presence of hydroxyl functionalities in the headgroup region of a cationic lipid contributes favorably in liposomal gene delivery. Using simple sugar molecules as the source of multiple hydroxyl functionalities in the headgr oup region of the transfection lipids, we have synthesized four novel simpl e monocationic transfection lipids, namely, 1-deoxy-1-[dihexadecyl(methyl)a mmonio]-D-xylitol (1), 1-deoxy-1-[methyl(ditetradecyl)ammonio]-D-arabinitol (2), 1-deoxy-1-[dihexadecyl(methyl)ammonio]-D-arabinitol (3) and 1-deoxy-1 -[methyl(dioctadecyl)ammonio]-D-arabinitol (4), containing hydrophobic alip hatic tails and the hydrophilic arabinosyl or xylose sugar groups linked di rectly to the positively charged nitrogen atom. Syntheses, chemical charact erizations, and the transfection biology of these novel transfection lipids 1-4 are described in this paper. Lipid 1, the xylosyl derivative, showed m aximum transfection on COS-1 cells. All the lipids showed transfection with cholesterol as colipid and not with dioleoylphosphatidylethanolamine (DOPE ). Radioactive quantitation of free and complexed DNA combined with ethidiu m bromide exclusion measurements suggest that though nearly 70% of the DNA exists as complexed DNA, the DNA may not have condensed as was observed wit h other cationic lipids. Presence of additional (more than two) hydroxyl fu nctionalities in the headgroup of the cationic lipids appears to have impro ved the transfection efficiency and made these lipids less cytotoxic compar ed to two-hydroxyl derivatives.