|Phase I||Phase II||Phase III|
Much of the research MDA supports is what is termed “basic” research: research investigating the fundamental biological processes of nerves, muscles and what goes awry to cause disease. Much of this research is not aimed at one specific disease, but can apply to many neuromuscular diseases. Projects at this stage, for example, may initially seek answers about a muscular dystrophy, but ultimately lead to a therapy for ALS. This is how MDA’s broad coverage of diseases can be so powerful. Basic research that results in the identification of a therapeutic target might also be called “discovery research”.
As the scientific community has developed a better understanding of the biological processes leading toward neuromuscular disease, MDA has also broadened its funding strategy into “translational” research. Translational research covers the work necessary to develop a potential therapeutic from the point when a potential drug has been identified to the stage in which the candidate therapy must be tested in humans (clinical trials). This includes improving the compound, testing to see if it is safe and effective in animal disease models, determining appropriate doses, and other tests required by the Food and Drug Administration (FDA) before a drug can be tested in humans. Once the best, or “lead” compound is identified, this work is also called “preclinical research”.
The most important tests of a potential drug are to determine whether it is safe and effective in humans. This is done through a series of carefully controlled and monitored experiments called “clinical trials”. These are split into three stages, conducted consecutively, and are heavily regulated by the FDA. The FDA analyzes preclinical data to determine if an “Investigational New Drug (IND)” should be approved: this is the go-ahead to initiate clinical trials.
Phase I clinical trials are small safety trials, with the sole purpose of determining whether the therapy is safe in humans. These are usually (but not always) conducted in healthy volunteers, not in patients with the disease. Researchers may collect data to see if there is any suggestion that the drug has an effect, but the trials are designed to look for signals of toxicity and are generally too small (i.e. involve too few test participants) and too short to determine any significant effectiveness of the therapy. Phase I trials may test different doses of the drug, or increased doses over time.
Phase II trials are generally the first trials in patients. Like Phase I trials, Phase II trials usually involve a relatively small number of participants, but often include a placebo arm. That is, some of the participants are given the experimental drug, while the others receive a mock treatment (such as a sugar pill). Often, even the researchers don’t know which participants are receiving the drug. When neither the participants nor the researchers know who has received the therapy and who has received a placebo until the conclusion of the study, it is said to be a “double-blinded” trial. This is important for ensuring that any interpretations of the results are completely unbiased. Researchers will analyze a number of outcomes from these trials, both in terms of safety and evidence that the therapy is effective. Phase II trials usually last longer than Phase I trials, and may be followed by an “extension phase” in which participants may be asked to remain on the drug for longer periods of time.
Phase III trials are typically the final necessary hurdle for FDA approval of an experimental therapy. These are usually large trials, conducted over a lengthy time period, and involve a single dose of the drug and a placebo arm. These trials involve enough people for sufficient time to enable researchers to see a statistically significant difference in outcome between the drug and placebo arms if the drug has an effect. Longer term side effects are closely monitored as well. The FDA reviews the data from the trials, and if it deems the data to demonstrate safety and efficacy, it will approve the drug for use. It may still require post-marketing surveillance (study), phase IV studies, of patients taking the drug to look for long term safety issues, or studies in additional populations (e.g., children) if they were not included in the original studies.
Glucocorticoid medications (corticosteroids) such as prednisone and deflazacort, are an integral part of the standard of care for DMD, having been proven effective at prolonging walking and slowing the loss of strength. However, since corticosteroid treatment has many undesirable side effects, such as weight gain, increased appetite, loss of bone mass, cataracts and behavioral changes, steroids are not generally prescribed for BMD. Researchers are always looking for improved drugs, or alternate dosing regimens in an effort to maximize the beneficial effects while minimizing side effects as much as possible. Some MDA-supported researchers are working on developing modified corticosteroids that have fewer or less severe side effects than those currently in use. Reveragen Biopharma is the most advanced of these, currently planning a Phase I trial of its modified steroid. MDA has targeted over $4 million investigating the actions of corticosteroids in DMD.
Some drugs can allow cells to read past one type of mutation, called a nonsense mutation, which acts as a molecular stop sign. The result is that muscle fibers with this type of mutation can be coaxed into making dystrophin. In a clinical trial of the antibiotic gentamicin, six of twelve boys with DMD showed measurable amounts of dystrophin in their muscle, although no clinical benefit was seen. PTC Therapeutics, in collaboration with the pharmaceutical company Genzyme, tested the nonsense mutation suppressing drug PTC 124 or ataluren in a Phase IIb human clinical trial. This drug looked promising in an early phase II trial funded in part by MDA, but the later trial did not meet its primary endpoint. However, the data suggest that the drug may be effective at lower doses, and PTC Therapeutics is continuing developing the drug. As of August 2013, it is recruiting patients for a Phase III trial.
Other drugs that work through the same mechanism are also in early development for DMD, and MDA has awarded nearly $500,000 to Carmen Bertoni at UCLA to develop drugs that may work better than ataluren. To date, these compounds, called RTC13 and RTC14, have succeeded in the DMD mouse model at increasing dystrophin production as much or more than ataluren. To date MDA has invested almost $4 million on the development of nonsense suppression compounds for DMD.
Exon skipping is a strategy currently being developed for DMD, in which sections of genetic code (exons) are “skipped,” allowing the reading frame to be restored and leading to creation of a shorter, partially functional dystrophin. MDA has invested over $4.5 million into exon skipping research. Exon skipping is not a cure for DMD, but potentially could lessen the severe muscle weakness and atrophy that is the hallmark of this disease, making it more like Becker muscular dystrophy (BMD). Exon skipping may also have application to other genetic diseases down the line.
Exon skipping drugs are currently under development by the biopharmaceutical companies Prosensa, in conjunction with GlaxoSmithKline, and Sarepta Therapeutics (formerly AVI Biopharma). These drugs have shown encouraging results in Phase I trials and Phase II, and are now starting Phase III testing for patients with certain dystrophin mutations (those in the vicinity of exon 51 and exon 44), with therapies targeting other areas of the dystrophin gene planned for future development. These treatments can only be developed for specific groups of dystrophin mutations at one time, so several different therapies need to be developed to cover all of the DMD population that could potentially benefit from exon skipping strategies.
In July of 2013, Sarepta Therapeutics announced that weekly infusion of eteplirsen stabilized walking ability on the 6-Minute Walk Test, a measure of the distance walked in the 6 minutes. While patients in both the active-treatment and placebo groups declined in their walking distance over the course of the year and a half-long study, those receiving active treatment declined less. Muscle biopsy confirmed the production of dystrophin in those receiving treatment. A Phase III trial is planned to begin in 2014. The company is also expanding its development program to include exons 45, 50, and 53. Targeting of exon 44 is being tested in Europe.
The pharmaceutical company GlaxoSmithKline in collaboration with Prosensa began testing its exon-skipping drug drisapersen (GSK2402968) in nonwalking boys with DMD in 2010. Disappointing results of a phase III trial in ambulatory patients came out in late 2013, but the companies are still analyzing the data. Prosensa has indicated that it will continue its commitment to DMD, and is reviewing the data from this trial to determine what the next steps should be. Prosensa also has drugs targeting a number of different groups of mutations in early stage trials.
Both eteplirsen and drisapersen target the same set of mutations, which together account for about 13% of all cases of DMD. Different drugs will be needed to target other mutations. It is likely that many of these can be developed based on the existing technology, but it is unclear whether the same level of prolonged safety testing will be required to bring them forward. The expense of that testing program, and the relative rarity of some of the other mutations, may determine whether companies will go forward with development.
TG003, an experimental drug being studied by Japanese researchers, has been shown to cause skipping of mutant exon 31 in patient cells.
Gene transfer therapy refers to the delivery of genes as therapeutic agents. Since genes carry the instructions for protein synthesis, they can lead to production of proteins that are directly or indirectly therapeutic in neuromuscular diseases. Because transferred genes potentially can continue to produce protein for some time, gene therapy may offer a more permanent fix than other therapies. But gene therapy faces many technical challenges, as well as a high bar set by regulatory agencies like the U.S. Food and Drug Administration (FDA).
The key challenges are delivering the genes to the targeted tissue while avoiding off-target tissues, and avoiding unwanted immune response to the proteins made from the new genes, or to the delivery vehicles in which the new genes are delivered. A special challenge arises with the dystrophin gene, because its very large size excludes it from the smallest and safest delivery vehicles.
Asklepios Biopharmaceuticals, which has previously received extensive MDA support, is using a “miniaturized” dystrophin gene, delivered to muscle cells via a viral “vector” for its gene therapy trials, which are the most advanced trials for DMD at this time. A phase 1 human clinical trial of gene therapy into a single muscle for DMD did not show prolonged dystrophin expression, and patients displayed signs of an immune response to the therapy. Researchers continue to refine gene therapy strategies as well as develop methods for delivery of the therapy to multiple muscles simultaneously, which will be necessary for a clinical benefit.
For well more than a decade, MDA has been a leader in supporting the development of gene therapies for neuromuscular diseases, with DMD being in the forefront of such research. MDA has devoted almost $27 million to gene therapy development.
In addition to therapies targeting the root cause of the disease, a number of therapies in development act indirectly to alleviate symptoms, such as loss of strength. Many of these therapies may be applicable to multiple muscular dystrophies, not just DMD, and possibly other neuromuscular disorders. For example inhibitors of myostatin have received much attention from the neuromuscular disease research community ever since it was found several years ago that people and animals with a genetic deficiency of myostatin appear to have large muscles and good strength without apparent ill effects. In 2010, a study showed that mice lacking dystrophin and showing a DMD-like disease benefited from treatment with a "decoy" that lured myostatin away from their muscles.
The biotechnology company Acceleron Pharma then developed a drug based on this decoy and began testing it, with MDA support, in boys with DMD. Unfortunately, unexpected safety issues arose during that trial, causing Acceleron to terminate it in 2011; the development program has now been halted permanently. Other strategies to inhibit myostatin, such as injecting genes for the myostatin-blocking follistatin, also are under consideration, as are strategies to accelerate muscle growth with insulin-like growth factor 1 (IGF-1), which is inhibited by myostatin. Several companies have projects investigating these pathways, some of which are close to clinical trials. MDA has devoted over $5.5 million on muscle strengthening approaches.
Utrophin is a muscle protein that is similar to dystrophin, but normally found in a restricted area of the muscle, rather than along the entire muscle surface, like dystrophin. Researchers have found if it is produced at sufficient levels, utrophin can substitute for dystrophin in muscles. Several companies are developing methods to express utrophin throughout the muscle. This can either be achieved using small molecule drug therapy that “turns up” expression of the utrophin gene in the muscle (the approach used by MDA funded Summit Plc), or indirectly, by activating other biochemical pathways in muscle. A young company, Tivorsan Plc (also MDA supported), has shown that modulating levels of another protein, called biglycan, can also lead to increased levels of utrophin. The company is currently investigating this strategy as a potential DMD therapy. This is at an early pre-clinical stage. Other proteins discovered by MDA-sponsored researchers that increase utrophin levels include sarcospan, osteopontin and laminin-111. The most advanced potential therapy using this strategy is Summit Plc’s SMT-C1100, which appears safe and well-tolerated in healthy volunteers at all doses tested, and reaches levels in the bloodstream believed to be adequate for a therapeutic benefit. MDA has invested almost $10M on utrophin up-regulation strategies.
If cells that produce dystrophin can be introduced into the muscle, it is hoped that they will supply enough dystrophin to improve muscle function and health. A number of researchers are investigating the possibility of using stem cells to supply dystrophin to muscles. There were high expectations for such strategies, particularly myoblast transfer, in the 1990s, and considerable effort was devoted to such therapies. Despite major technological hurdles research on this therapeutic approach continues to advance.
The most advanced stem cell project to date is being conducted by Guilio Cossu, of the San Raffeale Scientific Institute in Milan, Italy, who is using a special kind of stem cell, termed a “mesoangioblast,” that can be isolated from muscle biopsies of living donors. Other stem cell technologies being tested include cells derived from bone marrow, and cells derived from umbilical cord. MDA has funded almost $12 million toward such strategies.
One serious consequence of DMD (and several other muscular dystrophies) is cardiomyopathy, or heart muscle weakness. The MDA DMD Clinical Research Network has made studying the natural history and treatment of this condition a primary focus. In addition, MDA sponsored a meeting of more than 40 leading clinicians and researchers from the United States and Europe in January 2011 to discuss optimal clinical care of the DMD/BMD-affected heart.
In 2009, scientists found that dystrophin gene mutations that cause cardiomyopathy in BMD affect specific regions of the dystrophin protein, not necessarily the same regions associated with skeletal muscle loss. The study will allow better prediction of cardiomyopathy in BMD and earlier consideration of cardioprotective treatments in this disease, as well as giving researchers insight into which parts of the dystrophin protein are essential to preserve when shortened dystrophin molecules are being considered as therapeutic strategies.
The drug sildenafil (Viagra) has been found to impart cardioprotective effects in mice with both an early- and late-stage DMD-like disease. Sildenafil, which is used to treat erectile-dysfunction, belongs to a class of drugs called phosphodiesterase 5 (PDE5) inhibitors, which relax the smooth muscles lining blood vessels, increasing blood flow to muscles and the heart. Tadalafil, another drug in this class, is also being looked at in both DMD and BMD.
Phrixus Pharmaceuticals is developing a compound called Poloxamer-188 which is designed to seal leaks in the membranes of the dystrophic heart, reducing the risk of heart failure. Phrixus is in discussions with the US Food and Drug Administration about conducting a trial in DMD. This therapy would likely be used in combination with other therapies to treat associated cardiac problems. MDA has funded over $4 million on projects aimed at developing novel heart therapies for DMD.
As muscles degenerate in a person with DMD, the muscle fibers are replaced by fat and connective tissue in a process called “fibrosis.” Many researchers believe that muscles might be protected by medications, termed “anti-fibrotics,” that reduce this fibrotic process. Reducing fibrosis may also help increase the efficacy of other potential therapies. The most advanced drug in this class has just started a Phase II trial – Halo Therapeutics’ HT-100. MDA has invested almost $4 million into investigating the potential of such therapies.
Inflammation has been shown to be present in, and particularly harmful to, muscles affected by DMD. Scientists are working on understanding and interfering with inflammation in and around muscle fibers that may contribute to the DMD disease course. One of the main reasons why corticosteroids are thought to be effective for DMD may be through their ability to reduce inflammation. Unfortunately, these medications carry significant side effects.
Companies such as Reveragen Biopharma and Catabasis Pharmaceuticals are working to develop effective inhibitors of the anti-inflammatory pathways that will have fewer side effects than corticosteroids. Early stage trials are being planned for both compounds. Givinostat, from Italfarmco, is currently in a Phase II study of its potential to reduce inflammation and fibrosis. MDA has targeted more than $4.2 million on novel anti-inflammatory compounds, and more than $4 million on corticosteroids and improved versions of corticosteroids.
Nitric oxide is a gas that occurs in minute quantities in cells, but which has been found to be extremely important for cellular communications. Muscle strength and stamina are regulated by nitric oxide. Experiments have shown that, when dystrophin is missing from the muscle-fiber membrane, it causes another protein, known as nitric oxide synthase (nNOS), to be missing as well, and that this results in an inability of blood vessels supplying muscles to adequately dilate during exercise. When nNOS-deficient mice were treated with a phosphodiesterase inhibitor, which dilates blood vessels, their exaggerated fatigue response to exercise was eliminated. Phosphodiesterase inhibitors are a class of drugs that include sildenafil (Viagra) and tadalafil (Cialis), both used to treat erectile dysfunction.
Calcium is critical for muscle contraction, and one effect of defective dystrophin is that a muscle protein that pumps calcium back out of the muscle stops working properly, contributing to muscle degeneration. MDA is supporting ARMGO Pharma, which is developing a drug that alters the movement of calcium into and out of cell compartments. This is still in preclinical development, but looks exciting. A protein called Hsp72 helps that calcium pump, called SERCA1, to function properly. An experimental diabetes drug, called BGP-15, increases Hsp72 in mice, and improves muscle strength, structure, and function in a DMD mouse model. MDA has committed over $1.5M to this approach.
So-called “gene editing” strategies use new tools to target and correct mutations in specific genes. These strategies are currently in the preclinical stage, but show promise in cells taken from DMD patients. As this strategy is developed, it will be necessary to either perfect ways to implant cells containing the corrected gene in muscles of patients, or to correct the gene in place, by delivering the gene-editing molecules to the target muscle cells.