Cationic glycolipids with cyclic and open galactose head groups for the selective targeting of genes to mouse liver

Toward probing an hitherto unexplored structure-activity issue namely, the relative in vitro and in vivo efficacies of cationic glycolipids with cyclic and acyclic sugar heads for targeting of genes to liver, we have designed and synthesized two novel series of cationic glycolipids with cyclic (lipids 1-5) and open d-galactose heads (lipids 6-10) containing varying spacer arm lengths in between the sugar and positively charged nitrogen atoms. Among the cyclic glycolipids, lipid 3 with six methylene units spacer in between the quaternary nitrogen atom and among the glycolipids with the open-sugar heads, lipid 6 with only two methylene units spacer were found to be the most efficacious in targeting genes to cultured HepG2 (human hepatocarcinoma cells) and primary hepatocytes. Findings in the fluorescence resonance energy transfer (FRET) studies revealed biomembrane fusibilities as important physico-chemical parameters behind the varying spacer arm dependencies in the two series. Importantly, both the serum compatible glycolipids 3 &6 were found to be equally efficacious in selectively targeting genes to mouse livers under systemic settings. The significantly reduced efficiencies of the glycolipids 3 &6 in transfecting primary hepatocytes as well as mice pretreated with asialofetuin (the ligands of asialoglycoprotein receptors) support the notion that the cellular uptake of the lipoplexes prepared from both the open and the cyclic sugar-head series is mediated via asialoglycoprotein receptor. In summary, our present findings demonstrate for the first time that cationic glycolipids with cyclic sugar-head require longer spacer arms than their acyclic sugar-head counterparts for efficient gene transfection and both the series hold equal promise for selective gene targeting to liver under systemic settings.