Golodirsen restores DMD transcript imbalance in Duchenne Muscular Dystrophy patient muscle cells

Background: Antisense oligonucleotides (AON) represent a promising treatment for Duchenne muscular dystrophy (DMD) carrying out-of-frame deletions, but also show limitations. In a completed clinical trial golodirsen, approved by FDA to induce skipping of DMD gene exon 53 in eligible patients, we demonstrated increase in DMD expression and protein production, albeit with inter-patient variability. Methods: Here, we investigate further the golodirsen mechanism of action using myotubes derived from MyoD transfected fibroblasts isolated from DMD patients at the baseline of the clinical trial SRP-4053. Results: We confirm golodirsen's selectivity and efficiency in removing only exon 53. For the first time in human cells, we revealed a significant reduction in the so called DMD "transcript imbalance", in golodirsen-treated DMD muscle cultures. The transcript imbalance is a unique DMD phenomenon characterized by non-homogeneous transcript expression along its entire length and responsible for the reduced stability of the transcript. Our in-vivo study also showed that the efficiency of exon skipping did not always correspond to a proportional restoration of the dystrophin protein. Predominant nuclear localization of the DMD transcript, observed in patients and animal models, persists even after exon skipping. Conclusion: All these findings suggest challenges other than AON delivery for high level of protein restoration in DMD, highlighting the importance of investigating the biological mechanisms upstream of protein production to further enhance the efficiency of any AON treatment in this condition.