Serum as a modulator of lipoplex-mediated gene transfection: dependence of amphiphile, cell type and complex stability

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Abstract
Background Cationic liposomes belong to the family of non-viral vectors for gene delivery. Despite several drawbacks, such as low efficiency compared to viruses and inactivation by serum, cationic liposomes remain a promising tool for gene therapy. Therefore further investigation of the mechanism of transfection and improvement of formulations are warranted. Method In a comparative study, we investigated the effect of serum on the ability of SAINT, a novel synthetic amphiphile, and Lipofectin to mediate transfection in vitro, employing a variety of cell lines. Results In all cell types, SAINT-mediated transfection was not significantly affected by the presence of serum, in contrast to Lipofectin-mediated transfection. Intriguingly, the extent of complex association was enhanced in the presence of serum, while cell association of the Lipofectin complex was approximately two-fold higher than that of SAINT. These data imply that transfection efficiency and the amount of cell-associated complex are not related. However, when the helper lipid dioleoylphosphatidylethanolamine (DOPE) was substituted for cholesterol, SAINT-mediated transfection was reduced in the presence of serum. This indicates that lipoplex composition rather than the cationic lipid per se codetermines the effect of serum. Also, the presence of serum decreased cytotoxicity, while no correlation could be demonstrated between toxicity and transfection efficiency. The binding of serum proteins to either complex was identical, both in terms of protein identity and relative amounts. Conclusion We propose that serum, in conjunction with cell-specific factors and lipoplex composition, determines complex (in)stability, which is crucial for effective gene delivery and expression. Copyright © 2000 John Wiley & Sons, Ltd.