BNA^NC Gapmers Revert Splicing and Reduce RNA Foci with Low Toxicity in Myotonic Dystrophy Cells

Myotonic dystrophy type 1 (DM1) is a multisystemic disease caused by an expanded CTG repeat in the 3′ UTR of the <i>dystrophia myotonica protein kinase</i> (<i>DMPK</i>) gene. Short, DNA-based antisense oligonucleotides termed gapmers are a promising strategy to degrade toxic CUG expanded repeat (CUG_exp) RNA. Nucleoside analogs are incorporated to increase gapmer affinity and stability; however, some analogs also exhibit toxicity. In this study, we demonstrate that the 2′,4′-BNA^NC[NMe] (BNA^NC) modification is a promising nucleoside analog with high potency similar to 2′,4′-LNA (LNA). BNA^NC gapmers targeting a nonrepetitive region of the DMPK 3′ UTR show allele-specific knockdown of CUG_exp RNA and revert characteristic DM1 molecular defects including mis-splicing and accumulation of RNA foci. Notably, the BNA^NC gapmers tested in this study did not induce caspase activation, in contrast to a sequence matched LNA gapmer. This study indicates that BNA^NC gapmers warrant further study as a promising RNA targeting therapeutic