Preclinical development of DMD exon 44 skipping using AAV.U7snRNA: a versatile tool that can help 6-12% of DMD patient

Research Inst Nationwide Children'S Hosp, Columbus OH

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT Duchenne Muscular Dystrophy (DMD) typically results from mutations in the DMD gene that disrupt the open reading frame, resulting in no dystrophin protein production. In contrast, the milder Becker Muscular Dystrophy (BMD) typically results from mutations that allow expression of a partially functional dystrophin protein. Current therapeutic approaches in trials are directed toward expressing shorter, “micro-dystrophin” proteins, likely ameliorating DMD into a BMD-like phenotype. An alternative approach is to use exon skipping. This strategy uses antisense oligonucleotide sequences (AONs) to modulate pre-mRNA splicing of DMD transcripts to restore the reading frame and to express a truncated but functional dystrophin. An alternative approach is to use a small virus, such as Adeno-Associated Virus, containing a small promoter expressing the AON (also referred as vectorized exon skipping [VES]), alleviating the need to reinject the AONs as they get degraded over time. Based on our published studies in mice and our publicly presented data in infant Dup2 patients, VES for DMD exon 2 demonstrate a more robust exon skipping and protein expression than the alternative exon skipping approach using AONs. Exon 44 is among the mutational hotspots of the DMD gene, and its skipping would benefit around 6-12% of DMD patients. Our long-term goal is to develop a vector that maximizes exon 44 skipping to provide the best potential outcome for this patient subpopulation. Our central hypothesis is that VES will provide a robust exon-skipping response, leading to therapies with significant efficacy. We have already generated promising preclinical data for this program, but a new vector design is required for the next phase, especially if this vector becomes commercially available. In Aim 1 (R61 phase, year 1), we will compare our current VES with a newly designed one that will have manufacturing advantages compared to our current vector both in vitro and in vivo. In Aim 2 (R61 phase, year 1-2), we will check if the designed vectors have splicing off-targets by RNA seq analyses. In Aim 3 (R33 phase, years 2-3), we will test a minimal efficacious dose of our lead candidate to generate data for a pre-Investigational New Drug (pre-IND). Our rationale for this project is that evaluation of potential therapeutic vectors, assessing their efficiency and confirming absence of off-targets, measuring minimal efficacious dosage, and early engagement with the FDA will lead to a streamlined path toward vector development. The immediate impact of our work will be data to support our ongoing interaction with the FDA in developing rapid VES personalized gene therapies.