721. Antisense Oligonucleotide Therapy for Duchenne Muscular Dystrophy: From Cell Culture to Clinical Trial

Duchenne muscular dystrophy (DMD) results from non-sense or frame-shifting mutations in the dystrophin gene. The majority of these mutations can be corrected by removal of one extra exon to create shortened, but in-frame transcripts and produce at least partially functional proteins. Earlier studies showed that antisense oligonucleotide (AON)-mediated splicing alteration can achieve specific skipping of targeted exon, providing the potential for the treatment of DMD. This promise was firmly established when we demonstrated that AON can specifically remove the mouse dystrophin exon 23 containing a nonsense point mutation and restore the functional levels of dystrophin protein in muscle via intramuscular administration. More recently, we further demonstrated that systemic delivery of AON can effectively restore dystrophin expression in body-wide muscles. These data have prompted much of the current enthusiasm for clinical trials with AONs. We also demonstrated that modifications of AON chemistry are critical for achieving therapeutical effect by antisense therapy. Morpholinos is one of the most effective chemistry for inducing functional levels of dystrophin in bodywide skeletal muscles with improved force generation. We have been examining several chemistries with various delivery systems using mdx mouse as an in vivo model system to search for more effective chemistry and clinically applicable delivery approaches to achieve long-term restoration of dystrophin expression. Individual human dystrophin exon has been selected for systematic screening of AON sequences to maximize the potential of antisense effect as a preparation for clinical trials. We are also developing animal models to select AON sequences for targeting individual human dystrophin exon and to examine the therapeutic capacity of exon skipping in vivo. In conclusion, our results have provides realistic hope for the treatment of a majority of DMD patients.