Molecular Analysis of Neuromuscular Diseases
Current Research Programmes
Development of an effective therapy for duchenne muscular dystophy (DMD)
Duchenne muscular dystrophy is the most common genetic form of muscular dystrophy affecting 1 in 5000 boys. Although the disease is known to be caused by the absence of the cytoskeletal protein, dystrophin; no effective treatment is yet approved.
Dystrophin-associated protein complex:
Dystrophin forms a vital link between the extracellular matrix and the internal actin cytoskeleton (see figure above) and it is absent, or present in very small amounts, in DMD patients. Any effective therapy has to replace the dystrophin-associated protein complex to reconstruct the vital link. Therapy for DMD is a challenge since the protein is large (427kD) and needs to be delivered to many muscle cells in the body for therapeutic effect. However, the field has reached an exciting phase where there are several strategies for therapy in clinical trials. Drugs for stop codon read through and exon skipping have been approved but their efficacy needs to be improved and is dependent on the mutation in the particular patient being treated (for review see Babbs et al, 2020). Gene therapy is showing great promise but this cannot be used if patients have antibodies against AAV and there is some toxicity associated with the high titres of virus used. We are taking an alternative approach to treatment through increasing the levels of a protein closely related to dystrophin, called utrophin, which can replace the missing dystrophin. The strategy will be applicable to all patients independent of their particular mutation.
We have demonstrated that over expression of utrophin in the mdx animal model of the disease prevents the muscle pathology in both skeletal and cardiac muscle. Our data suggest that up-regulation of utrophin would be an effective treatment. Furthermore, utrophin may only need to be increased 2-3 fold over the mdx mouse for therapeutic effect. We have set up mdx and human cell line screens for small molecules that increase utrophin and have shown that administration of these compounds systemically to the mdx mouse can prevent the pathology (for review see Babbs et al, 2020). An example of one of these compounds, SMT022357, is shown below where the imbalance of calcium homeostasis is corrected and staining of utrophin is increased and expressed along the entire length of the sarcolemma. This work was carried out in collaboration with Summit Therapeutics and our colleagues in the Department of Chemistry, Professors Steve Davies and Angela Russell. We developed non-invasive biomarkers for the disease so that we can monitor the effects of utrophin modulation therapy in both preclinical and clinical studies. We have recently demonstrated that developmental myosin is an excellent biomarker in muscle biopsies both for human trials and in preclinical studies in the mdx mouse.
One of the lead compounds we developed with Summit Therapeutics which modulates the expression of utrophin is called ezutromid (SMT C1100). Summit Therapeutics successfully completed Phase I trials. In a Phase 2 trial initial data at 24 weeks looked promising with reduction in regenerating fibres in patient muscle biopsies as assessed by developmental myosin staining, but the data at 48 weeks showed this clinical benefit was no longer maintained. The trial was therefore terminated. Since then, we have investigated the reason why we initially observed positive effects which were not maintained. Our hypothesis was that ezutromid is rapidly metabolised thus preventing a sustainable effect. We have demonstrated that this is indeed the case. Furthermore, we have shown that ezutromid is an Aryl hydrocarbon receptor (AhR) antagonist which prevents AhR translocating into the nucleus (Wilkinson et al, 2020). In collaboration with Professor Russell’s group we have shown that other AhR antagonists increase utrophin levels in vitro and we are currently screening these molecules for utrophin modulation effects in vivo.