Résumé :
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Duchenne Muscular Dystrophy (DMD) is a chromosome X-inherited disorder, characterised by the absence of the protein dystrophin which plays a role in the protection of muscle fibers against damage. Patients display progressive degeneration of skeletal muscles leading to functional impairment and premature death. One of the most promising therapeutic approaches for DMD involves the restoration of the disrupted reading frame through exon skipping with antisense oligonucleotides (AON). In cultured cells from patients and in the mdx mouse model AON treatment resulted in the generation of dystrophin proteins similar to those seen in Becker Muscular Dystrophy patients, who generally display a milder phenotype than Duchenne patients. Recently, we showed local restoration of dystrophin expression after intramuscular injection of an exon 51 specific 2’-O-methyl phosphorothioate AON in four Duchenne patients in a first-in-man clinical trial. For future clinical studies on full body treatment we are currently optimizing systemic AON delivery. We here compared different doses (25 mg/kg to 100 mg/kg) and treatment periods (4 to 8 weeks) with murine exon 23 specific AONs in mdx mice applying subcutaneous administration. The exon skip levels varied between specific muscle groups from 8% in the diaphragm to 26% in the extensor muscles of the lower forelimb and up to 2% in the heart, after twice weekly repeated injections with a 100 mg/kg AON dose during 8 weeks treatment. Dystrophin expression was observed in all samples analysed. This was accompanied by trends of decreased CK and improved rota-rod running times of treated mice compared to saline injected control mice. Markers for kidney and liver function remained unaffected, indicating that repeated AON treatment was well tolerated even when performed over longer time periods. Our results show that systemic injections of 2’-O-methyl phosphorothioate AON lead to restoration of dystrophin and an improved functionality without apparent toxicity.
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