Antibody-Mediated Targeting of siRNA via the Human Insulin Receptor Using Avidin−Biotin Technology

Delivery of short interfering RNA (siRNA) to cells in culture, and in vivo, is possible with combined use of a receptor-specific monoclonal antibody (mAb) and avidin-biotin technology. In the present studies, the luciferase gene is transiently expressed in human 293 epithelial cells. The siRNA delivery system is composed of the siRNA, monobiotinylated on the 3'-terminus of the sense strand, and a conjugate of streptavidin (SA) and a mAb to the human insulin receptor (HIR). Exposure of cells to 3'-biotinyl-siRNA bound to the HIRMAb/SA conjugate, but not to unconjugated SA, avidin, or the HIRMAb, causes a >90% reduction in luciferase gene expression. The receptor-targeted siRNA effect is maximal at 48 h after delivery of the siRNA to the cells, and the effect is lost by 7 days after a single application of the targeted siRNA in culture. The KI of the receptor-targeted siRNA inhibition of gene expression is 30.5 +/- 11.7 nM, and significant inhibition is observed with siRNA concentrations as low as 3 nM. In conclusion, the combination of a receptor-specific targeting ligand, such as the HIRMAb, and avidin-biotin technology allows for high affinity capture of the monobiotinylated siRNA by the targeting mAb. The siRNA is effectively delivered to the cytosol of cells, and knockdown of gene expression with the HIRMAb/SA delivery system is comparable to RNA interference effects obtained with cationic polyplexes. Whereas the use of cationic polyplexes in vivo is problematic, the bond between the targeting mAb and the siRNA is stable with avidin-biotin technology, and RNAi effects at distant sites such as brain are observed in vivo following an intravenous administration of the targeted siRNA.