We typically have a great knockdown efficiency with antisense oligos (ASOs) in which the phosphodiester bonds are substituted with phosphorothioate bonds to make them nuclease-resistant. Also, I gather that adding 2′-O-Methyl groups to these oligos in a "gapmer" fashion will reduce the toxicity of the ASOs. Although we haven't had much of toxicity without it.

My question is if one uses an ASO without any of the two mentioned modifications, would you still expect an RNAseH-mediated knockdown? I can imagine the ASO will eventually be digested by nucleases, but wouldn't you expect to achieve a lower level of knockdown?

I appreciate your thoughts/experiences.