Novel Therapeutic Strategy to Achieve Upregulation of Dystrophin Isoforms
Abstract
Duchenne Muscular Dystrophy (DMD) and its milder version, Becker Muscular Dystrophy (BMD), are muscle-wasting disorders caused by genetic changes in the dystrophin gene. These changes result in either absent or severely reduced levels of dystrophin, an essential protein that acts as a shock absorber to protect muscle from damage. Current therapies in clinical trials do not capture the entire DMD/BMD patient population and thus, novel approaches are needed to address the remaining genetic causes of the disease. For example, there exists a subset of patients with DMD mutations who express reduced levels of near full-length dystrophin. These patients would benefit more from increasing their own levels of near full-length dystrophin than treatment with micro-dystrophin gene replacement therapy that introduces a severely truncated protein. With the emergence of CRISPR gene-editing technology, we now have the means of increasing the expression of a specific gene. In this project, we propose to design a CRISPR gene-editing construct to boost dystrophin levels in patients whose genetic mutation allows them to express residual, albeit low levels of dystrophin at baseline. These are typically older patients on the milder end of the DMD spectrum who are not associated with early adult morbidity, as they do not completely lack dystrophin. Our approach is novel and differs from existing therapies currently in development, such as micro-dystrophin gene replacement and other CRISPR-based gene-editing of dystrophin. Firstly, unlike micro-dystrophin approaches that aim to restore functional domains, we aim to boost a patient’s own ability to produce near full-length dystrophin protein. Secondly, unlike traditional CRISPR gene-editing approaches employed to correct specific mutations and require customization for each mutation type, our approach relies on a single construct with a broad design to encapsulate a wider patient population. Moreover, our CRISPR platform employs a no-cut enzyme that removes the potential to create off-target edits in the genome, thus resulting in a more clinically translatable strategy that is safer for patients. We have already developed similar CRISPR-based gene activation constructs in our lab to boost a non-muscle version of dystrophin – a strategy which benefits DMD patients with exon 1 mutations. This approach, which when combined with adeno-associated virus delivery, has the capacity to boost target gene levels, in affected skeletal and cardiac muscles in a robust and safe manner. Using a similar framework, we can rapidly generate a similar construct to boost muscle dystrophin levels for therapeutic testing in a disease-relevant model based on a candidate DMD mutation. The clinical benefit of boosting dystrophin expression in patients who are severely lacking its expression is expected to be significant and target approximately 8% of the dystrophinopathy patient population (according to mutation databases), who would otherwise not benefit from existing therapies. A previous study that employed a similar strategy of increasing the expression of a truncated dystrophin in a DMD mouse model resulted in a milder phenotype. Given these findings, we would anticipate our proposed treatment to halt disease progression in the often neglected subgroup of older DMD/BMD patients.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 05, 2021
- Source ID
- W81XWH2110956
Entities
People
- Monkol Lek
Organizations
- United States Army
- Yale University