Experimental Treatments for Muscular Dystrophy
There is no cure for muscular dystrophy (MD) yet, but several treatments and therapies are under development to help manage the symptoms, improve patients’ quality of life, and even treat the underlying cause of the disease.
Small Molecule Therapy
Small molecules are compounds with low molecular weights that can easily enter cells and directly affect the target, which may be a protein or other molecules within the cell. More than 90% of the therapeutics made today are small molecules.
Givinostat is a molecule being developed to treat Duchenne and Becker muscular dystrophies. It inhibits enzymes called histone deacetylases that turn off gene expression and can reduce a muscle’s ability to regenerate. Givinostat is currently being evaluated in a Phase 3 trial in Duchenne patients and a Phase 2 trial in Becker.
Rimeporide is an investigational treatment for Duchenne MD. The muscle cells of Duchenne patients have an overload of calcium, which is thought to be caused by dysfunctional NHE-1. Over time, high calcium concentrations contribute to the muscle damage that is seen in patients. Rimeporide inhibits NHE-1, thereby correcting calcium levels in the cell. A Phase 1b trial has been completed.
Signaling Pathway Inhibition
In signaling pathway inhibition, small molecules called signal transduction inhibitors block the communication between different molecules of the pathway. These signals control many cellular processes, including growth, cell division, and death. Several small molecules can block the function of specific proteins in signaling pathways, which can mitigate symptoms of muscular dystrophy.
Signaling Pathway Upregulation
Signaling pathway upregulation is a process by which the availability of molecules involved in the signaling pathway — such as proteins, mRNA, or even energy — is increased in the cell. There are several small molecules that can upregulate signaling pathways to promote the availability of energy, and synthesis of proteins required for proper muscle growth and function.
Several experimental therapies that may treat the underlying cause of different types of muscular dystrophy are being investigated. These treatments are called disease-modifying therapies, and they could one day even offer the possibility of a cure for MD. These investigational treatments include exon-skipping therapies, stop codon readthrough, RNA interference, and CRISPR/Cas9.
The CRISPR/Cas9 method for genome editing is a powerful new technology with many applications in biomedical research, including the potential to treat human genetic diseases, such as muscular dystrophy. Preclinical studies are being conducted to assess the potential of the CRISPR/Cas9 system in treating some types of MD.
BB-301 is being developed as a potential treatment for oculopharyngeal muscular dystrophy. BB-301’s therapeutic approach is called DNA-directed RNA interference, or ddRNAi. It combines gene therapy with an RNA interference, or RNAi, strategy. It is in the preclinical stages of development.
Translarna (ataluren) is designed to treat only patients who have Duchenne or Becker muscular dystrophies caused by a particular type of defect in the DMD gene called a nonsense mutation. It is aimed at enabling the production of a full-length, functional dystrophin protein. A Phase 3 trial in Duchenne patients is underway.
Exon skipping is a treatment approach for people whose Duchenne muscular dystrophy is due to certain mutations in its causative gene. Exon skipping works like a molecular patch, so that the DMD gene can produce a shorter version of the dystrophin protein to help protect and maintain the strength of muscle fibers.
AAV-mediated Gene Therapy
Gene therapy is a promising treatment option for genetic conditions such as muscular dystrophy. It involves correcting the genetic defect by introducing a normal copy of the affected gene into the patient’s cell or by silencing a faulty gene. Harmless modified viruses are commonly used for the targeted delivery of healthy genes into the body. The adeno-associated virus (AAV) is one such delivery vector, and several AAV-mediated gene therapy candidates are currently being evaluated as potential treatments for muscular dystrophy.
GALGT2 is a potential gene therapy being developed for Duchenne MD. It uses AAVs to deliver the GALGT2 gene to the body. The GALGT2 gene provides instructions to build a protein that increases the production of other proteins essential for muscle function. A Phase 1/2 trial assessing the safety and efficacy of the experimental gene therapy is ongoing.
PF-06939926 uses an adeno-associated virus serotype 9 (AAV9) capsid to deliver a shortened version of the human DMD gene that provides instructions for making a so-called mini-dystrophin protein. Because the DMD gene is too long to fit into the adenoviral vector, a shorter but still functional version of the gene is used for the therapy. A Phase 3 trial is now enrolling boys with Duchenne.
rhLAM-111 is being explored to potentially treat Duchenne and congenital muscular dystrophy type 1A (MDC1A). In MDC1A, rhLAM-111 can replace laminin, a structural protein that is normally present in embryonic muscle tissue, but absent in adult muscles and in the disease. rhLAM-111 also can increase the production of alpha-7 beta-1 integrin and utrophin to potentially treat Duchenne. It is also thought to stimulate muscle healing pathways. The potential therapy is currently in preclinical studies.
SGT-001 is an experimental gene therapy being developed for Duchenne MD. It uses a harmless virus to transmit a piece of DNA into muscle cells. This DNA encodes for a small synthetic dystrophin that has the key components of normal dystrophin. Once the gene is within cells, it is hoped that it will be expressed normally and hopefully slow or reverse disease progression. A Phase 1/2 trial is ongoing and still recruiting Duchenne patients.
SRP-9001 micro-dystrophin is a gene therapy candidate that is designed to deliver the microdystrophin-encoding gene directly to the muscle tissue for the targeted production of the microdystrophin protein. It uses a harmless modified virus (AAVrh74) that has a high affinity for muscle tissue, allowing for targeted delivery. A two-part Phase 2 trial is currently underway.
SRP-9003 is a gene therapy candidate for the treatment of limb-girdle muscular dystrophy type 2E. It is aimed at restoring the levels of beta-sarcoglycan in muscle tissues by delivering a functional copy of the human SGCB gene to skeletal, heart, and diaphragm muscles. AAVrh74 is used for the targeted delivery of the healthy gene. The therapy is being evaluated in a Phase 1/2 trial.
SRP-9004 is a gene therapy being developed to possibly treat limb-girdle muscular dystrophy type 2D. It that consists of a modified and safe virus that carries a healthy, working copy of the SGCA gene. Once inserted into the cell, the gene should be able to produce the alpha-sarcoglycan protein. A Phase 1/2 trial has been completed.
Other Experimental Treatments
CAP-1002 is an investigational cardiac cell therapy being developed for treating heart conditions, including cardiomyopathy linked to Duchenne muscular dystrophy. This treatment is directly administered by infusion into one or more coronary arteries using regular cardiac catheterization methods. A Phase 2 trial has been completed with positive results.
Vamorolone is a dissociative steroid that works in a similar way to other corticosteroids by activating certain pathways within the cell and inhibiting others. It also binds to and helps stabilize the membranes around cells without causing transactivation. Vamorolone also may help preserve heart function in Duchenne patients. A Phase 2 trial has been completed.