Many myasthenia gravis patients do not benefit from already existing therapies, such as steroids, acetylcholinesterase inhibitors, or immunosuppressants. It is this fact that has pushed many biotechnology companies to start work on FcRn inhibitors. In fact, argenx has recently released the data from the study of their treatment, efgartigimod.
About Myasthenia Gravis
Myasthenia gravis (MG) is the most common autoimmune neuromuscular disorder. Those affected experience weakness in the voluntarily controlled muscles. Physical activity worsens the symptoms, whereas periods of rest can improve them. Throughout the world, about 20 of every 100,000 people have MG. It is an autoimmune condition, meaning the body attacks itself, specifically the proteins that are necessary for communication between the brain and muscles. This causes symptoms like drooping eyelids, issues with chewing and swallowing, fatigue and weakness in the skeletal muscles, slurred speech, double vision, and a changed gait. For a small percentage of those with MG, weakness in the chest could lead to life-threatening respiratory issues.
Doctors diagnose this condition through a physical exam, evaluation of patient history, blood tests, and EMGs. Like many rare disorders, a diagnosis is not always easy to obtain. The similarity of symptoms to other conditions often results in a misdiagnosis. After doctors have confirmed that one has MG, treatment consists of steroids, plasmapheresis, or surgery to remove the thymus gland. While there is no cure, some medications can greatly improve symptoms or even induce remission.
About the Study
Before delving into the data from argenx’s study, it is necessary to understand what an FcRn inhibitor is. FcRn stands for neonatal Fc receptor, and this inhibitor stops IgG antibodies from degrading. It does so by moving the antibodies away from lysosomes. With less degradation, more of the antibody is available.
Now that we understand the treatment, we can talk about the study. This trial was placebo-controlled, enrolled 167 adult participants, and lasted 26 weeks. The primary endpoint was to reach a percentage of responders on a daily living, measured with an MG scale. 67.7% of those receiving efgartigimod achieved the primary endpoint, compared to only 29.7% of the placebo group.
Secondary endpoints were also met. These included a response on the Quantitative Myasthenia Gravis (QMG) scale, fast onset of response, and time to reach a clinically meaningful improvement. For the first of these endpoints, 63.1% of those treated with efgartigimod responded, while only 14.1% of the placebo group did. The only secondary endpoint that was not met was the time to qualify for retreatment. Along with this positive data, there were no “red flags on the safety side.”
These positive results have pushed argenx to turn in their marketing application by the end of this year. Upon approval, which will most likely happen in 2021, they will be able to market the IV form of this drug.
Other companies are working on FcRn inhibitors as well, including UCB, Momenta Pharmaceuticals, Immunovant, and Alexion. Hopefully these companies will be able to offer a treatment that is viable for myasthenia gravis patients.
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