Further assessment of durability of a gene editing therapy for Duchenne muscular dystrophy

Project Summary Gene editing offers an innovative approach for gene correction that can permanently edit the patient’s own DNA. To inform how permanent editing may translate to long-term clinical benefit, durability must be characterized in preclinical animal models. Here a gene editing therapy for Duchenne muscular dystrophy that targets deletion of DMD exons 45-55 to restore the reading frame for 50% of all patients will be assessed in a humanized mouse model. This approach is advantageous because it maintains the normal gene regulation and retains three times more of the protein coding sequence than mini/micro-dystrophin gene replacement approaches for Duchenne. This therapy uses systemic adeno-associated virus delivery of CRISPR/Cas9 to edit DNA in muscles throughout the body. In this study, functional efficacy (through non-invasive muscle function measures), restoration of molecular markers (including dystrophin, the dystrophin-glycoprotein complex, histopathology and blood biomarkers) and pilot toxicity readouts will be compared at 2 months versus 6 months post-dosing. Two different immune suppression regimens and three different dosing levels will be tested in juvenile hDMD del45 mdx mice. This work will clarify the long-term durability of gene editing efficacy and how it is influenced by dosing regimens. Learnings from this proposal will have wide applicability to other gene editing therapies which target post-mitotic tissues. As recommended in FDA Guidance, these data will be included in future IND filings and will help advance development of an innovative gene editing therapy for Duchenne muscular dystrophy to clinical studies and then commercialization.