siRNA-Lipoplex-Mediated Bcl-2 and Bcl-xL Gene Silencing Induces Apoptosis in MCF-7 Human Breast Carcinoma Cells

Abstract

Bcl-2 family genes play a central role in cell apoptosis and cell proliferation, and are implicated in the pathol- ogy of many malignancies. We explored different ways of introducing siRNA duplexes into cells, comparing "naked" with lipoplex- and polyplex-based formulations in order to decrease the level of the Bcl-2 and Bcl-xL proteins. Our results show that siRNA binds efficiently to all cationic liposomes used. Upon binding, siRNA reduces the zeta potential of the particles, although in most cases they remain positively charged. 70% of MCF-7 cells took up fluorescently-labeled siRNA after 24 h. All siRNA sequences caused growth inhibition of cells, with variable efficiency in a dose-dependent manner. Significant decreases in Bcl-2 and Bcl-xL proteins were caused by two siRNA sequences. Both caused signifi- cant growth inhibition in concentrations as low as 100 nM. These two siRNAs caused the greatest increase in caspase-7 activity and DNA fragmentation level. Addition of CaCl 2 as a transfection enhancer resulted in marked increase of growth inhibition and Bcl-2 gene suppression by siRNA. Our lipoplexes containing siRNA showed equal or superior efficacy in comparison with commercial siRNA transfection kits. Efficiency of cell growth inhibition per RNA molecule using siRNA was found to be twenty fold higher than by a well-established Bcl-2 antisense oligonucleotide (ODN) molecule af- ter optimization of ODN delivery to cells in culture. This study indicates the potential for efficient delivery of siRNA for treatment of various malignancies.