An exon skipping PPMO has demonstrated dramatic effects in the prevention and treatment of severely affected, dystrophin and utrophin-deficient mice, preventing severe deterioration of the treated animals and extending their lifespan. These findings were published online today in the journal Molecular Therapy and support the promise of this therapeutic approach for the treatment of Duchenne muscular dystrophy (DMD). These results were published by researchers at University of Oxford, AVI BioPharma, Inc. (Nasdaq: AVII) and the University of Western Australia, Perth.
DMD is an incurable muscle-wasting disease associated with errors in the gene that makes dystrophin. Studies and research have shown that the ability to skip certain exons in dystrophin pre-mRNA could circumvent these dystrophin gene errors and provide a potential treatment for DMD patients. The paper "Prevention of Dystrophic Pathology in Severely Affected Dystrophin/Utrophin-deficient Mice by Morpholino-oligomer-mediated Exon-skipping" details the successful exon skipping and treatment of utrophin/dystrophin double knockout (dKO) mice with a cell-penetrating peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) targeting exon 23 in dystrophin pre-mRNA.
Videos accompanying the online publication show visual evidence of pronounced curving of the spine and dramatically reduced mobility as a result of deficiency of both dystrophin and utrophin proteins (Hyperlink to: Mouse Pretreatment/Supplementary Video S1, http://www.avibio.com/videos03.php). Treatment of affected mice from 10 days of age for six week with the mouse-specific PPMO at a dosage of 25 mg/kg/week resulted in a nearly complete skipping of exon 23 in all of the muscles examined except the heart. Skipping of exon 23 restored the reading frame of dystrophin mRNA and led to widespread continued translation of dystrophin protein. Treated dKO mice showed near normal measures for most of the examined parameters, including striking prevention of kyphosis and maintaining of near normal mobility. The publication also featured a video illustrating the impact of the treatment on the dKO mice (Hyperlink to: Mouse Post-Treatment with PPMO/Supplementary Video S2, http://www.avibio.com/videos03.php).
"This research demonstrates remarkable prevention of dystrophic pathology and retained near normal muscle function in severely affected dKO mice following treatment with a PPMO," said Dame Kay Davies, Ph.D, Director of the MRC Functional Genomics Unit and Head of the Department of Physiology, Anatomy and Genetics at University of Oxford and senior author on the paper. "Notably, this study demonstrates for the first time the efficiency of such an exon-skipping approach in the dKO mouse, which is a much more severe and progressive mouse model of DMD. These findings, should they prove to be replicated in human studies, suggest great potential for the treatment of DMD patients with a PPMO."
"Antisense-mediated exon-skipping represents one of the most promising approaches for the treatment of DMD because of its capacity to correct the reading frame and restore dystrophin expression," said Steve Wilton, Ph.D. Professor at the Center for Neuromuscular and Neurological Disorders, University of Western Australia, Perth, Western Australia, Australia and co-author of the study.