NEW YORK (AP) ¿ Biogen Idec Inc. said Friday it offered to buy its partner Facet Biotech Corp. for $356 million, and at the same time criticized Facet for entering a partnership with Trubion Pharmaceuticals Inc. last week.

Biogen Idec said it would pay $14.50 per share for Redwood City, Calif.-based Facet. Biogen said the companies have been working together since 2005 to develop the cancer drug candidate volociximab and the multiple sclerosis drug daclizumab.

In going public with its offer, Biogen was sharply critical of Facet, saying it stated its interest in August and offered to buy the company for $15 per share on Aug. 21. A week after that, Facet announced a collaboration with Trubion on a leukemia drug. Facet acquired the marketing rights to a potential leukemia treatment in return for a $10 million investment, $20 million upfront, and potential payments of as much as $176.5 million.

In a letter to Facet CEO Faheem Hasnain, Biogen said the Trubion deal reduces Facet's value, noting that Facet shares are down 18.8 percent since the partnership was announced. Facet did not immediately return calls seeking comment.

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