Tysabri (natalizumab), formerly known as Antegren, is the first humanised monoclonal antibody to be approved for MS and could achieve peak annual sales of $3 billion, according to analysts at CIBC WorldMarkets. It is the first alpha-4 integrin antagonist in the new selective adhesion molecule inhibitor class.
At present, there are only two approved treatment options for patients with MS: interferon beta (from Biogen Idec, Serono or Schering) or Copaxone (glatiramer acetate), developed and sold by Israel's Teva Pharmaceutical.
Tysabri has been tipped to shift the focus of MS therapy because the data from Phase III trials has been so strong.
Earlier this month, the results of the AFFIRM (Antegren safety and efficacy in relapsing-remitting MS) trial, a two-year study involving 942 patients, showed that Tysabri reduced the rate of relapse by 66 per cent compared to placebo. In contrast, currently available therapies reduce relapse rates 30 to 40 per cent, although it should be emphasised that Tysabri was not directly compared to them in a head-to-head trial.
However, in the Sentinel study in which Tysabri was added to a regime of Biogen Idec's own interferon beta drug Avonex, already approved for the treatment of MS, clinical relapses were reduced by 54 per cent versus patients who took Avonex alone. This data was revealed for the first time in the FDA's approved label for the drug.
There have been suggestions that Tysabri's success could come partially at the expense of Avonex through sales cannibalisation, although combination use with Avonex has also been approved by the Food and Drug Administration..
Lester Crawford, acting FDA commissioner, said in a statement: "While we eagerly await long-term results from ongoing clinical trials, we have reason to believe that Tysabri will significantly reduce relapses in MS."
In Europe, Biogen Idec and Elan filed for approval of the antibody with the European Medicines Agency (EMEA) in the summer.