The preparation of cationic amphiphiles that induce minor cytotoxic response during polynucleotide delivery into mammalian cells has been limited by the conventional use of ester, amide, or carbamate linkages to tether either the polar or the hydrophobic domains. The deleterious effects of ammonium-based lipidic salts on cellular processes have been well-established. The present report is the first example of a linchpin tetraester construct that utilizes ester linkages to tether both the polar and hydrophobic domains. Dimyristoyl and dioleoyl analogues were prepared from pentaerythritol, N,N-dimethylglycine, and their corresponding fatty acyl groups via successive diesterifications followed by amine quaternization. The resultant cationic tetraesters were examined in transfection (luciferase) and cell proliferation (MTS) assays using NIH 3T3 and 16HBE14(o)- cells. The tetraesters exhibited transfection activity comparable to the well-studied lipids DOTAP and DC- cholesterol (DC-chol) in both cell lines. The tetraester construct afforded no cytotoxicity in NIH3T3 cells and provided a significant lowering of cytotoxicity relative to DC-chol in the 16HBE14(o-) cells. The expression of green fluorescent protein (GFP) in both cell lines also was examined using the lipid panel. Comparison of fluorescent and corresponding phase-contrast images confirmed the chemical cytotoxicity results and revealed that the cytotoxic response was not dependent on transgene expression. Phase-contrast micrographs of cells treated with the cationic lipid panel in the absence of GFP plasmid showed identical morphology to the GFP- transfected cells, suggesting that the onset of a lipid-mediated cytotoxic response might occur at a stage prior to endosomal encapsulation.
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