Modulating Calcium Signals to Boost AON Exon Skipping for DMD
Abstract
Duchenne Muscular Dystrophy (DMD) is the most common fatal genetic disease of childhood, affecting approximately 1 in 5,000 boys. Progressive muscle degeneration typically leads to death in the early twenties. There are no highly effective therapies. DMD is often caused by frame-shifting mutations that abolish dystrophin expression. "Exon skipping" is a promising personalized genetic medicine aimed at repairing the genetic defect and rescuing functional dystrophin protein expression. Exon skipping is currently performed by designed short RNA sequence molecules called antisense oligonucleotide (AON), which are intended to disrupt the inclusion of a given exon in the mature RNA and thus "exon skip." Once optimized, it is predicted to enhance the quality of life through slowing of disease progression and extend life expectancy. Ongoing clinical trials using AON exon skipping drugs demonstrate restoration of dystrophin expression in muscle biopsies and stabilization of disease progression for up to 4 years in open label extension studies. Phase 3/confirmatory trials for exon 51 skipping have initiated in late 2014, while exon 45, 44, and 53 Phase 2/3 trials are planned for 2015. This timeline is based on Food and Drug Administration (FDA) guidelines recently provided to Sarepta and Prosensa, outlining a potential path toward accelerated approval of exon 51 AON as early as the end of 2015 (conventional approval as early as 2016). If proven effective, additional sequence designs are feasible to target many different exons, and then would hold the potential to repair up to 80% of DMD patient mutations. Presently, levels of rescued dystrophin produced in human trials are low, and more efficient exon skipping or stabilization of the protein product should lead to greater therapeutic efficacy. We have identified drugs, including FDA-approved Dantrolene, that boost AON directed exon 51 skipping in patient-derived myotube cell cultures containing a deletion of exons 45-50, but we have yet to determine if these drugs are applicable to all DMD gene mutations that are possible to be treated by exon 51 skipping, or if they are beneficial in combination with other exons being targeted by AON skipping that are currently in the clinical trial pipeline. These drugs all impinge on a common pathway, leading us to predict that second-generation drugs designed to more effectively modulate this pathway may have even greater skip boosting activity. Two of these drugs, Ryanodex and ARMGO RyCal, are proprietary formulations, which promise even greater efficacy, therapeutic window, and commercialization opportunities than Dantrolene. Here we explore the ability of Dantrolene, Ryanadex, and ARMGO RyCal to promote skipping in combination with AON directed to exons currently in the clinical trial pipeline (51, 45, 44, and 53). We will screen activity on multiple lines of patient-derived myotubes to determine which common mutations are amenable to Dantrolene AON combinations. We also will test whether RyR antags used without AON might be effective in promoting exon skipping of DMD mutations in those patients who exhibit some naturally occurring small amount of exon skipping. Finally, we will investigate the mechanism by which these skip boosting compounds function using state-of-the-art genomics, bioinformatics, and chemical genomics approaches. Together, these studies promise to identify (1) the patient population most likely to be benefited from planned future clinical trials involving RyR antags to boost exon skipping (alone or in combination with AON), (2) the best lead compounds to pursue in planned future clinical trials involving RyR antags to boost exon skipping, and (3) molecular mechanisms and novel targets for promoting more optimal exon skipping. Because Dantrolene and Ryanodex are already FDA approved, translation of our findings to clinical trials could be rapid and hold the potential to render this potentially life-cha
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 29, 2016
- Source ID
- W81XWH1510182
Entities
People
- M. Carrie Miceli
Organizations
- United States Army
- University of California, Los Angeles