Background: Effective gene transfection without serum deprivation is a prerequisite for successful stem cell-based gene therapy. Polyethylenimine (PEI) is an efficient nonviral gene vector, but its application has been hindered by serum sensitivity and severe cytotoxicity.
Methods: To solve this problem, a new family of lipopolyplexes was developed by coating PEI/DNA polyplexes with three serum-resistant cationic lipids, namely, lysinylated, histidylated, and arginylated cholesterol. The physical properties, transfection efficiency, cellular uptake, subcellular distribution, and cytotoxicity of the lipopolyplexes was investigated.
Results: The outer coat composed of lysinylated or histidylated cholesterol remarkably improved the transfection efficiency of the polyplex with a low PEI/DNA ratio of 2 in the presence of serum. The resulting lysinylated and histidylated cholesterol lipopolyplexes were even more efficient than the best performing polyplex with a high PEI/DNA ratio of 10. Results from cellular uptake and subcellular distribution studies suggest that their higher transfection efficiency may result from accelerated DNA nuclear localization. The superiority of the lipopolyplexes over the best performing polyplex was also confirmed by delivering the therapeutic gene, hVEGF(165). Equally importantly, the lipid coating removed the necessity of introducing excess free PEI chains into the transfection solution for higher efficiency, generating lipopolyplexes with no signs of cytotoxicity.
Conclusion: Noncovalent modification of polyplexes with lysinylated and histidylated cholesterol lipids can simultaneously improve efficiency and reduce the toxicity of gene delivery under serum conditions, showing great promise for genetic modification of bone marrow stem cells.
Keywords: bone marrow stem cells; cationic lipids; gene delivery; lipopolyplex; nonviral vectors; polyethylenimine.