The US food and Drug Administration has halted clinical trials of GlaxoSmithKline and Tanabe Seiyaku’s 683699, a drug for multiple sclerosis in the same class as Tysabri (natalizumab), which was pulled from the market by Biogen Idec last month [[01/03/05a]], according to Industry reports.

Tysabri is a monoclonal antibody that binds to a protein called alpha-4-integrin, and was developed by Biogen Idec and Irish pharmaceutical company, Elan Corporation. It was withdrawn after a patient taking the drug died from a rare disease of the central nervous system, known as progressive multifocal leukoencephalopathy [[04/03/05a]]. Integrins are found primarily on the surface of white blood cells, and play a role in immune system activity and, while GSK points out that ‘699 has the same target as Tysabri, according to Reuters, it says it is a very different molecule. Tysabri is an antibody given by injection, while ‘699 is a small molecule delivered in an oral dose. The compound had reached Phase IIb testing with filing expected in 2008.

At the time of going to press, it was unclear whether other drugs affecting the alpha4 integrin target are included in the clinical hold, and the FDA would not comment on the issue.

A spokeswoman for Millennium Pharmaceuticals, which has a similar product – known as MLN02 – that has completed Phase II testing in MS, said that no trials were ongoing for this drug, so it was not affected. It was formerly partnered with Genentech, which returned the rights after the Phase II trial missed its primary endpoint. Millennium said it was still planning to move ahead with Phase III testing of another partner could be found.

Meanwhile, another company that has been developing drugs targeting alpha-4-integrin for MS is Celltech, now acquired by Belgium’s UCB [[09/07/04c]], [[18/05/04a]]. The company had not responded to enquiries about the status of this project as this article went to press.