NMI Linkage Modification Increases Potency and Stability of H-RAS Antisense Oligonucleotides

Abstract

Phosphorothioate antisense oligodeoxyribonucleotides (PS-ASOs) have proven to be useful first generation antisense tools for in vitro and in vivo uses and now show great promise as human therapeutic agents. However, there are two characteristics of PS-ASOs that make it desirable to continue to attempt to improve their biophysical characteristics through chemical modification. First, PS-ASOs have been reported, at very high concentrations, to have some nonspecific activities, both in vitro and in vivo, usually attributed to their protein binding properties. Second, while significantly more stable than their phosphodiester analogues, the in vivo stability of phosphorothioate oligonucleotides can still be improved. This instability is primarily due to 3′ exonucleases, 5′ exonucleases, and to a lesser degree, endonucleases. There is a strong rationale for exploring backbone modifications that can reduce the P=S content and maintain or increase nuclease resistance of antisense oligonucleotides. One such modification, methylene(methyl)imino (MMI), allows for complete substitution of the phosphate backbone while maintaining high affinity for the target RNA and enhanced nuclease resistance.^1,2 This modification is incorporated into the oligonucleotide as MMI-dimers.