Potency of siRNA versus shRNA mediated knockdown in vivo

The intracellular delivery of small interfering RNA (siRNA) is a therapeutic strategy to transiently block gene expression. Two silencing RNA strategies utilize either synthetic double stranded RNA or plasmid DNA encoding a short hairpin RNA (shRNA). In the present study, we have quantitatively compared the potency of siRNA (siLuc1) and shRNA (pShagLuc) mediated knockdown of luciferase expression in vivo using hydrodynamic dosing and bioluminescence imaging (BLI). Following hydrodynamic coadministration of siLuc1 or pShagLuc with a plasmid encoding luciferase (pGL3), mice were analyzed for transgene expression by BLI. The knockdown of luciferase expression by siLuc1 or pShagLuc was observed at 3 h and persisted for 3 days. The potency of siLuc1 and pShagLuc was equivalent with maximal effect at 10 µg coadministered with 1 µg of pGL3 resulting in >80% knockdown. Combined dosing of siLuc1 and pShagluc (5 µg each) with 1 µg of pGL3 resulted in >99% knockdown. Analysis of the data established that shRNA was significantly more potent than siRNA at mediating knockdown when compared on a mole basis. The combination of hydrodynamic dosing and BLI to measure siRNA or shRNA mediated knockdown of luciferase provide an attractive in vivo quantitative method to test formulations that target the liver. © 2007 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 2922–2930, 2007