This is our final update from the 2015 World Muscle Society meeting in Brighton, United Kingdom (click here for updates from previous days). Before providing summaries of some presentations on the last two days, we must share that this was an exciting meeting for Duchenne. There were four major symposia, all of which included information about Duchenne (with the BioMarin, PTC Therapeutics, and Sarepta symposia very much dominated by Duchenne) and at least five Duchenne-intensive poster sessions that included preclinical studies, mechanistic research, therapy development, and patient care topics.
Throughout the week, several presenters mentioned specific PPMD activities, including our efforts in newborn screening, developing the FDA guidance, benefit risk, and the certified Duchenne care centers. Total attendance at the meeting was said to be 750 and there were many opportunities for us to interact with company representatives and academic researchers to emphasize the PPMD mission and strategies to end Duchenne.
Skeletal Muscle Stem Cells and Muscular Dystrophies
Jennifer Morgan (University College London) gave a platform presentation where she overviewed a large body of work from her lab and others on role of skeletal muscle satellite cells in regeneration of dystrophic muscles and where the barriers lie to effective regeneration. Specifically, she asked whether the condition of the satellite cells themselves or their surrounding environment (connective tissue, extracellular matrix) that satellite cells reside in is more important in determining how effective muscle regeneration is. Dr. Morgan used a transplantation model where she could transplant satellite cells from normal or mdx mice into skeletal muscles of normal or mdx mice. By using different combinations, she was able to show that the environment is critical for satellite cells to successfully drive muscle regeneration. For example, transplant of normal satellite cells into muscles of older mdx mice did not yield successful regeneration (so normal satellite cells but the fibrotic and inflammatory environment of old mdx mice blocked regeneration). Conversely, transfer of mdx satellite cells into a normal mouse muscle environment facilitated regeneration.
What does this tell us about treating Duchenne? It says that the environmental niche that best facilitates regeneration is one where the connective tissue/inflammatory response is as close to normal as possible. Satellite cells, whether from dystrophic or normal muscle, do better in a “good” extracellular matrix environment. The message for Duchenne is that we’ll likely need anti-fibrotic and anti-inflammatory drugs as important components of the cocktail that we use to treat Duchenne, and we’ll need to use those drugs as early as possible. This approach to addressing the extracellular environment will give other drugs that facilitate survival of existing muscle fibers or promote the formation of new muscle fibers, the best chance to succeed.
Signaling Pathways and Modifiers in Cardiac Function in Muscular Dystrophy
Beth McNally (Northwestern University) summarized her approach to identifying and validating modifier genes that has evolved over the last several years. She previously identified variants in LTBP4 as a very important genetic modifier of the progression of Duchenne. The IAAM variant of LTBP4 is associated with reduced signaling by the pro-inflammatory and pro-fibrotic TGF beta, and Duchenne boys carrying this variant go considerably longer before losing ambulation. McNally carefully described her approach of identifying LTBP4 in a mouse model, where she could better control the genetics and do studies in the larger number of animals required to identify genetic modifiers. After identifying LTBP4 in the mouse, she then moved on to the collaboration with Kevin Flanigan where they validated the important role of the IAAM variant in prolonging ambulation.
Using the same mouse-then-Duchenne patients approach, McNally has identified an important genetic modifier of the stability/permeability of the muscle fiber membrane in respiratory muscles and of right ventricular function. These studies identified a variant in annexin a6 (Anxa6), a calcium binding protein, in causing the respiratory and cardiac muscle defects. She is pursuing the same strategy as with LTBP4 to see if Anxa6 variants are linked to the same muscle changes in Duchenne.
Overall, understanding the factors behind the phenotypic variation in Duchenne will be critical for both identification of new treatment strategies and design of better clinical trials. Identifying and understanding modifier genes, such as LTBP4 and ANXA6, will play a crucial role in reaching the goals of the Duchenne Regulatory Science Consortium, the new collaboration between PPMD and the Critical Path Institute.
Short Talks on Sunday
Serum and Urine Proteomic Profiling Reveals Biomarkers Suitable for Monitoring the Outcome of Therapeutic Interventions in Muscular Dystrophies. Using mass spectroscopic analysis of proteins in serum and urine from Duchenne boys, Genethon investigators identified proteins that changed in both (muscle creatine kinase, myosin 7, myomesin 2, myomesin 3, beta enolase, glucose-6-phsophate isomerase, carbonic anhydrase, and filamin c). Myomesin 3, a protein that links together the thick (myosin) filaments in the muscle sarcomere, was also increased in mouse models of Duchenne and these levels were reduced when and exon skipping oligonucleotide was given to the mouse. These data suggested that myomesin 3 may be a biomarker, not only of the progression of Duchenne, but also a pharmacodynamics biomarker indicating early activity of an oligonucleotide drug. Validation of myomesin 3 as a biomarker in Duchenne then would be an important tool for facilitating clinical trials.
Epicatechin Enhances Mitochondrial Biogenesis, Increases Dystrophin and Utrophin, Increases Follistatin While Decreasing Myostatin and Improves Skeletal Muscle Exercise Response in Adults with Becker Muscular Dystrophy (BMD). Craig McDonald reviewed the data on his (-)-epicatechin clinical trial in Becker patients, that was presented at the 2015 PPMD Connect Conference. He indicated that the next steps were to conduct a one-year extension of the (-)-epicatechin trial in Becker and a phase 2 clinical trial of (+)-epicatechin in Duchenne.
Simvastatin Improves Physiological Function and Protects Against Muscle Degeneration in mdx Mice: A Novel Therapeutic Approach for Duchenne Muscular Dystrophy. Simvastatin is a HMG-CoA reductase inhibitor, more commonly known as an FDA approved statin that lowers cholesterol levels. Several studies show that statins are also anti-inflammatory, anti-fibrotic, and reduce oxidative stress, and have already proven safe in a pediatric population with hypercholesterolemia. Nick Whitehead (University of Washington; Stan Froehner’s lab) presented data from oral dosing of mdx mice with simvastatin, working under the rationale of exploiting the anti-fibrotic/anti-inflammatory properties would be valuable for Duchenne. Taken together, these investigators demonstrated a dramatic effect in reducing mdx muscle damage, inflammation, oxidative stress, and fibrosis, while improving both muscle specific force and fatigue resistance. Whitehead suggested that the mice efficacy, with substantial level of effect, and the pediatric safety profile supported conduct of clinical trials in Duchenne.