Portland, Ore.Natalizumab, marketed as Tysabri, prevents flare-ups of brain disorder.
An Oregon Health & Science University neurologist is applauding the Food and Drug Administration's approval of a breakthrough drug that may be more effective than other available therapies in treating multiple sclerosis.
Natalizumab, marketed as Tysabri and formerly known as Antegren, is the first monoclonal antibody treatment for MS approved by the FDA, which handed down its license Nov. 23. According to the federal agency, it is given intravenously once a month in an outpatient clinic to reduce the frequency of MS symptom flare-ups or exacerbations among patients with relapsing forms of the disease.
Relapsing-remitting MS, in which acute symptoms or worsening of neurologic function occur intermittently, is the most common form of the disease affecting some 350,000 Americans.
Dennis Bourdette, M.D., professor and chairman of neurology in the OHSU School of Medicine, and director of the OHSU MS Center of Oregon, said Tysabri, which was bioengineered from part of a mouse antibody to closely resemble a human antibody, was at least two times more effective than current treatments, at least during the first year of treatment. OHSU was a study site for the drug.
"After one year of treatment, subjects receiving Tysabri had a 66 percent reduction in relapses of MS compared with those receiving placebo," he said. "Those receiving Tysabri also had a substantial decrease in the number of new MS lesions, or areas of MS damage in the brain, with 60 percent of those receiving Tysabri having no new MS lesions, while only 22 percent of those receiving placebo were free of new lesions after one year."
In contrast, Bourdette added, medications such as Avonex, Betaseron, Rebif and Copaxone typically reduced relapses by about one-third after one year of therapy compared with placebo, and by a similar amount after two years of therapy. Results of Tysabri's effectiveness after two years of therapy are not known, but results should be available in the next year, he said.
Tysabri also appears to be relatively safe, and it's generally well tolerated, with only 1 percent of study participants forced to stop taking it due to allergic reactions.
Carol Wilkerson, a Portland resident with MS, called the announcement "great news."
"I am always thrilled when another MS treatment is approved by the FDA," she said. The FDA approved the first MS drug, Betaseron, in 1993, the year Wilkerson was diagnosed, and she's marveled at the progress made toward treating MS since then. "I am very encouraged and hopeful about treatments such as Tysabri, which offer more and more options to those of us with MS," she said. "We are all unique with varied symptoms. More treatment options expand the possibilities of effectively treating more people."
Scientists believe a sub-population of T cells, the white blood cells produced by the human body to defend against infection, cause MS by attacking myelin, the fatty, insulating sheath that is wrapped around larger nerve fibers in the brain and spinal cord. Tysabri appears to work by binding to immune system cells and keeping them from migrating to the brain through the blood-brain barrier, the protective barrier composed of tightly knit endothelial cells that line the walls of the blood vessels in the brain.
"Tysabri represents a new approach to treating MS in two ways: First, it is a drug that specifically interferes with the ability of white blood cells to enter the brain and spinal cord. There are other treatments that can do the same things and I believe we will see this avenue of treatment actively investigated," he said. "Second, Tysabri is a monoclonal antibody and there are other monoclonal antibodies under study as treatments for MS. These other monoclonal antibodies work through other mechanisms."
Bourdette noted that the MS Center of Oregon has started a study of another monoclonal antibody called Rituxan, which suppresses the white blood cells that make antibodies that may be involved in causing damage in MS.
"This study is of particular importance because we are testing it in patients with another form of MS, primary progressive MS," he said "We currently have no treatments that are effective at controlling primary progressive MS, which affects 15 percent of people with MS, and we are hopeful that Rituxan will prove useful for this form of MS."
As for Tysabri, Bourdette said he likely won't recommend MS patients switch to Tysabri if they are on other medications, have their MS under control and aren't suffering significant side effects. But he will discuss switching to the drug, or even adding it to a therapy regimen, for those with inadequate control of their MS or side effects that interfere with their quality of life.
"For newly diagnosed patients, I will discuss the treatment options and Tysabri will be one of the treatments that we will consider," he said. "For some people, Tysabri will be the treatment of choice, and for others, one of the current therapies will be the treatment of choice. But for most patients with very active relapsing MS, I will definitely be recommending Tysabri as part of their treatment regimen."
Wilkerson said relapse is a concern for every person with MS. Her relapses typically involve extreme numbness somewhere on the left side of her body - a finger, her whole hand, her foot, her whole leg or her face. She also experiences double-vision.
"We never know what to expect," she said. "It could be a symptom we've never had before. MS is very unpredictable. Each new treatment provides a little more certainty that more of us will live a better, healthier life."
Tysabri is marketed by Biogen Idec Inc. of Cambridge, Mass., and Elan Pharmaceuticals Inc. of Dublin, Ireland.