Stability and evaluation of siRNAs labeled at the sense strand with a 3'-azobenzene unit.

siRNAs bearing a 3'-azobenzene derivative on the sense strand were evaluated for their gene silencing ability in mammalian cell culture and nuclease stability in nuclease-rich media. Azobenzene can be isomerized between cis and trans isomers through the incubation of UV (cis isomer) and visible light (trans isomer). It was demonstrated that subtle differences in nuclease stability and activity were observed. These small changes can be used to photochemically fine-tune the activity of an siRNA for gene-silencing applications.