This article is related to the effects of the headgroups and spacer length of cationic lipids on transfection efficiency. To develop highly potent cationic lipids, a series of divalent lysine-diamine conjugated cholesterol-based cationic lipids with three different headgroups (ammonium, trimethyl ammonium, and guanidinium) were synthesized. The newly synthesized cationic lipids (1-6)A formed cationic liposomes in the presence and absence of a zwitterionic helper lipid, DOPE (dioleoylphosphatidylethanolamine). A gel retardation assay showed that most of the prepared lipoplexes could retard DNA migration in the presence of DOPE. We attempted to modify the diverse cationic headgroups to improve the transfection efficiency. However, the lysine-1,3-diaminopropane-conjugated cholesterol-based lipid 4A, having divalent ammonium of unmodified lysine headgroup, exhibited high relative transfection efficiency in HEK293. When the transfection efficiency of 4A was formulated with DOPE (1 : 1 weight ratio), it produced the same range in comparison with that of a commercially available transfection agent, Lipofectamine™ 2000 (L2k). The lipid 4A was studied to optimize the conditions with respect to the lipid/DOPE and DNA/lipid ratios and the amount of DNA. The transfection efficiency of the highly potent lipid 4A was also studied to determine the transfection efficiency of HeLa, PC3, and HC-04 cell lines. This lipid also protected the DNA from a serum and had low toxicity. Lipoplexes 4A with DOPE had the particle size of around 300-600 nm and the zeta potential of around 0-45 mV. In summary, cationic liposomes 4A demonstrated a high performance as DNA carriers.
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