Cyclodextrin encapsulated β-estradiol and progesterone were used for enhancement of gene delivery using the breast cancer cell line Sk-Br-3. A non-toxic concentration of cyclodextrin encapsulated sex steroids (50 μM) added to lipid or liposomal transfection led to a 12-fold increase of reporter gene expression (luciferase) with progesterone and an 8-fold increase with estradiol using Lipofectamine Plus mediated transfection. Using the lipid formulation Fugene-6 the results were a 5.5-fold and a 4.5-fold increase respectively. This enhancement could only be observed if the sex steroids were added to the cells before application of the DNA-Fugene complex supporting the evidence that intracellular processes are responsible for the activity of the steroids. The strong differences between progesterone and estradiol in modifying Lipofectamine Plus transfection in Sk-Br-3 cells may to be explained by differences in the distribution of these receptors in the cellular compartments. These results seem to add evidence on the possibility of using sex steroids to increase the efficiency of non-viral vectors for transfection, and may ultimately prove to be relevant to gene therapy in the treatment of breast cancer as well as other solid tumors.

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