Terminal antisense oligonucleotide modifications can enhance induced exon skipping

Induction of specific exon skipping during the processing of the dystrophin gene transcript is being pursued as a potential therapy for Duchenne muscular dystrophy. Antisense oligonucleotides directed at motifs involved in pre-mRNA processing can manipulate dystrophin exon incorporation in the mature gene transcript. We have compared the exon skipping ability of oligodeoxyribonucleotides with compounds of the identical sequence incorporating 2′-O-methyl modified bases. Antisense oligonucleotides composed entirely of 2′-O-methyl modified bases on a phosphorothioate backbone were consistently more efficient at inducing exon skipping than comparable oligodeoxyribonucleotides. Chimeric antisense oligonucleotides, mixtures of unmodified and 2′-O-methyl modified bases, induced intermediate levels of exon skipping. In addition, we describe terminal modifications that may be incorporated into the 2′-O-methyl antisense oligonucleotides to further enhance efficiency of exon skipping. Our findings suggest that 2′-O-methyl antisense oligonucleotides should be considered for human clinical trials involving targeted exon skipping in dystrophin gene expression in preference to oligodeoxyribonucleotides.