Target-specific gene silencing by siRNA plasmid DNA complexed with folate-modified poly(ethylenimine)

A target-specific delivery system of green fluorescent protein (GFP) small interfering RNA (siRNA) plasmid DNA was developed by using folate-modified cationic polyethylenimine (PEI). A GFP siRNA plasmid vector (pSUPER-siGFP), which inhibits the synthesis of GFP, was constructed and used for suppressing GFP expression in folate receptor over-expressing cells (KB cells) in a target-specific manner. A PEI-poly(ethylene glycol)-folate (PEI-PEG-FOL) conjugate was synthesized as a pSUPER-siGFP plasmid gene carrier. KB cells expressing GFP were treated with various formulations of pSUPER-siGFP/PEI-PEG-FOL complexes to inhibit expression of GFP. The formulated complexes were characterized under various conditions. Their GFP gene inhibition and cellular uptake behaviors were explored by confocal microscopy and flow cytometry analysis. pSUPER-siGFP/PEI-PEG-FOL complexes inhibited GFP expression of KB cells more effectively than pSUPER-siGFP/PEI complexes with no folate moieties and showed far reduced extent of inhibition for folate receptor deficient cells (A549 cells). The results indicated that folate receptor-mediated endocytosis was a major pathway in the process of cellular uptake, suggesting that targeted delivery of siRNA vector could be achieved to a specific cell.