Levels of Exon-Skipping Are Not Artificially Overestimated Because of the Increased Affinity of Tricyclo-DNA-Modified Antisense Oligonucleotides to the Target DMD Exon

Antisense oligonucleotides (ASO) are very promising drugs for numerous diseases including neuromuscular disorders such as Duchenne muscular dystrophy (DMD). Several ASO drugs have already been approved by the US Food and Drug Administration for DMD and global efforts are still ongoing to improve further their potency, notably by developing new delivery systems or alternative chemistries. In this context, a recent study investigated the potential of different chemically modified ASO to induce exon-skipping in mouse models of DMD. Importantly, the authors reported a strong discrepancy between exon-skipping and protein restoration levels, which was mainly owing to the high affinity of locked nucleic acid (LNA) modifications to the target RNA, thereby interfering with the amplification of the unskipped product and resulting in artificial overamplification of the exon-skipped product. These findings urged us to verify whether a similar phenomenon could occur with tricyclo-DNA (tcDNA)-ASO that also display high-affinity properties to the target RNA. We thus ran a series of control experiments and demonstrate here that exon-skipping levels are not overestimated owing to an interference of tcDNA-ASO with the unskipped product in contrast to what was observed with LNA-containing ASO.