Amgen has launched a pre-emptive strike against Ariad Pharmaceuticals in a move designed to defend two of its products from the treat of patent infringement proceedings.

In the suit, Amgen is seeking to have one of Ariad’s patents declared invalid, as well as a judgement that its rheumatoid arthritis drugs Enbrel (etanercept) and Kineret (anakinra) do not infringe the patent, which was awarded in 2002 and covers the cell signaling activity of a nuclear factor called NF-(kappa)B.

Ariad said hit had not filed a patent infringement against Amgen but would defend the validity of its patent, No 6,410,516, in the courts.

Last week, Amgen reported that first quarter sales of Enbrel reached $658 million, up 11%. The company does not publish details of Kineret sales.

The patent also lies at the heart of a lawsuit between Ariad and Eli Lilly, which got underway in Masachusetts earlier this month. In that case, Ariad is claiming that Lilly’s sepsis drug Xigris (drotrecogin alfa) and Evista (raloxifene) for osteoporosis infringe its intellectual property, and that it should be entitled to royalties. It is fighting the case alongside the Massachusetts Institute of Technology, Harvard University and the Whitehead Institute for Biomedical Research

In that case, Lilly is arguing that the NF-kB signaling pathway is naturally occurring so cannot be patented.