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Next Generation ASOs for Muscular Dystrophy
Discover how a next-generation ASO screening study has revealed a powerful and precise investigative technique
Duchenne muscular dystrophy (DMD) is an X-linked severe and progressive neuromuscular disease caused by lack of functional dystrophin, primarily in muscle and heart, causing weakness and atrophy in skeletal and heart muscle. While DMD is the most common form of muscular dystrophy, it is classified as a rare disease, affecting around 1 in 3500 live male births.
Currently there are four anti-sense oligonucleotide (ASO) therapies approved by the FDA for treating DMD, all of which induce exon skipping during pre-mRNA splicing to increase production of functional dystrophin. However, the extent to which these ASOs induce exon skipping and increase dystrophin protein levels is relatively low and there is still unmet clinical need for new, effective therapies for DMD. A recent paper from VICO therapeutics describes a funnel-like ASO screening study, aimed at identifying new ASOs that targeted novel stretches of dystrophin exon 51, using a combination of chemical modification screening, in vitro models, and in vivo studies.
Initially, a series of ASOs were screened for efficacy in DMD patient myotube cultures with digital droplet PCR (ddPCR) and immunoassays used to identify ASO candidates that induced the highest levels of exon 51 skipping and dystrophin expression in vitro. This process identified a new ASO (AON-C19 in the publication) that was 10-fold more effect at exon 51 skipping than drisapersen, an ASO for DMD formally under development at BioMarin.
Following in vitro testing, the effect of AON-C19 was examined in the hDMDdel52/mdx mouse model. This model has mutated human and mouse dystrophin so lacks any functional dystrophin and displays associated biomarkers and motor deficits, meaning it allows for the screening of candidates at a molecular and functional level. Tissue profiling showed that AON-C19 penetrated quadricep and heart muscle in the mdx mouse model, inducing a high % of exon skipping and reduction in dystrophin levels. Levels of serum biomarkers that are generally elevated in DMD patients (CK and LDH) were decreased in AON-C19 treated mdx mice.
To examine the effects of AON-C19 on gait and motor activity in the mdx mouse model, VICO therapeutics worked with Charles River’s site in Finland to perform a fine kinematic motor analysis. This high precision kinematic assay uses the MotoRater system with Charles River Laboratories’ proprietary algorithms for data analysis of multiple markers to assess gait, whole body movements, and movements of individual limbs. This results in output of over 100 paraments used to investigate the effects of therapeutics on movement, gait, and posture changes. Compared to traditional motor assays, fine kinematic motor analysis is more sensitive to the effects of therapeutics. Mdx mice display changes in stride distance, limb swing speed, hip, knee, and ankle angles, and ileac crest height compared to wild type controls. Following 20-week treatment with AON-C19, mdx mice showed improvement in motor and gait functions compared to vehicle treated mdx mice.
Webinar: Using Fine Motor Kinematic and Gait Analysis in In Vivo Pharmacology Studies
Learn about the application of motor and gait analysis in different disease models, and how this technique can be used to investigate the effect of pharmacological agents on motor performance.
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