P.11.17 Optimization of preclinical antisense oligonucleotide development for Duchenne muscular dystrophy

In recent years, the field of antisense oligonucleotides (AONs) as RNA modulating therapeutics has made significant progress. Several antisense drug candidates are in (pre-) clinical development for Duchenne muscular dystrophy (DMD). Their length may vary between 15 and 40 nucleotides depending on chosen chemistry, and their mechanism of action is based on highly sequence-specific binding to a target exon such that splicing regulatory factors and/or structures are interfered with. The resulting exon skipping aims to correct the transcript’s open reading frame, which is disrupted by a mutation (in 70% of cases a deletion of one or more exons) in the DMD gene of DMD patients. This approach is mutation-dependent and, although applicable to subpopulations of DMD patients with grouped mutations in the area of the targeted exon, the development of multiple AONs will be needed to treat a majority of patients. In our preclinical programs, selection of AON candidates depends on multiple characteristics, including pharmacology, pharmacokinetics, physico-chemical properties, and safety effects both in vitro and in vivo. Through this extensive preclinical screening we have identified the safest and most efficient AONs for the skipping of DMD exons 45, 52, 53, or 55, which are currently in clinical development. We have also explored further optimization of the 2′-O-methyl phosphorothioate RNA oligochemistry to improve binding affinity and stability, activity, safety, and/or synthesis procedures. For instance, the effect of chemical base modifications has been tested. Here, we present an overview of results from our extensive preclinical AON candidate selection program, and from our studies on AONs with 5-substituted pyrimidines.