The effect of silencing ARPC1B on cell migration was studied in a breast cancer cell line. A monolayer of cells was uniformly scraped, and the rate of cell migration to close the scrape (wound healing) was evaluated. Both unmodified and ON-TARGETplus siRNA reagents induced potent target knockdown. Inconsistent phenotypes due to off-target effects (red outline) were observed for cells transfected with unmodified individual siRNAs.
The unmodified SMARTpool improved the false phenotype considerably while the ON-TARGETplus SMARTpool significantly reduced off-target effects to produce a consistent phenotype. In collaboration with Kaylene Simpson, Laura Selfors, and Joan Brugge, Harvard Medical School.
Unmodified and sense strand-inactivated siRNAs were used to target five genes. In four cases, off-targets were increased due to enhanced RISC loading of the antisense strand when the sense strand was modified. The unmodified siRNAs have natural guide-strand loading characteristics. All siRNAs had comparable silencing potency. Data shown represents genes down-regulated by twofold or more. HEK293 cells were transfected with 100 nM siRNA using 0.2 μL of DharmaFECT 1. Data was analyzed at 24 hours by genomewide microarray analysis (Agilent).
Why not modify ALL siGENOME siRNAs to ensure proper strand loading? It has been demonstrated by Dharmacon scientists and others that forcing antisense (guide) strand entry into RISC may actually INCREASE off-targets due to increased loading of the guide strand and resulting off-target activity by its seed region. siGENOME siRNAs are designed with thermodynamic properties to naturally facilitate guide strand entry to RISC, which has been demonstrated to correlate with functionality. However, in cases where a high-scoring siGENOME siRNA does not possess ideal strand-loading characteristics, a sense (passenger) strand-inhibiting chemical modification (ON-TARGET) is utilized to promote guide strand entry. Approximately 20% of siGENOME siRNAs carry the ON-TARGET modification.