Despite the fact that it has been tied to a deadly brain infection, and is being investigated for a possible link to melanoma, the makers of Tysabri are busy trying to find new uses for the drug. Last week, Biogen Idec and Elan said they have begun a clinical trial to see if Tysabri can be used to treat relapsed or refractory multiple myeloma. Eventually, the companies would like to see Tysabri used to treat other forms of cancer.
In the U.S. Tysabri was taken off the market in 2005 after three patients in clinical trials developed progressive multifocal leukoencephalopathy (PML). But the drug was reapproved in 2006, although it was subject to restrictions. Tysabri is now available only to patients with relapsing multiple sclerosis (MS) or Crohn’s disease (CD) who are enrolled in the risk minimization plan called the TOUCH Prescribing Program. Under the TOUCH Prescribing Program, every Tysabri-treated patient is closely monitored and followed for the occurrence of PML and other serious opportunistic infections.
PML attacks the brain and central nervous system and is usually fatal. It is caused by a polyomavirus, called the JC virus. The JC virus is often acquired during childhood. Most adults have been infected with the JC virus but do not develop PML. The virus appears to remain inactive until something (such as a weakened immune system) allows it to be reactivated and start to multiply. People with a weakened immune system or people taking drugs that suppress their immune system (immunosuppressants) are most likely to get the disease. Symptoms include vision problems, loss of coordination, and memory loss. Patients who survive the disease are often permanently disabled.
Just last month, Elan and Biogen Idec announced that Tysabri had been associated with two more cases of PML, this time among patients taking it in Europe. The most disturbing aspect of the latest PML cases, however, was that both patients had been taking Tysabri as monotherapy – with no other drugs. It had been theorized that patients contracting PML had done so because of exposure to multiple medications and that monotherapy with Tysabri was less risky.
The new European PML cases prompted the U.S. Food & Drug Administration (FDA) to announce that it was working with Elan and Biogen Idec to amend the product labeling to inform prescribers and patients that cases of PML have occurred in patients taking Tysabri as monotherapy.
PML is not the only safety issue faced by Tysabri. Late last week, the FDA released a list of 20 drugs currently under investigation for safety issues. Tysabri made the roster not just for PML, but for a possible association with melanoma as well. In February, the New England Journal of Medicine reported two MS patients developed the skin cancer shortly after starting treatment with Tysabri. But Biogen Idec said it found no increased risk of melanoma in clinical trials.