Facet Biotech Corp said on Tuesday it has rejected an unsolicited bid by Biogen Idec Inc to acquire Facet for $14.50 a share, saying the offer is inadequate and not in the best interests of shareholders.

Redwood City, California-based Facet and Biogen are co-developing daclizumab, a drug for multiple sclerosis, and volociximab, for solid tumors.

Facet said Biogen's offer, of about $355 million, values the company at roughly the value of its cash, marketable securities and restricted cash, which was $371.1 million as of June 30, or about $15.11 a share.

It thus places no value on the operating and other assets of the company, Facet said in a statement.

Biogen, which is based in Cambridge, Massachusetts, and makes the multiple sclerosis drugs Avonex and Tysabri, made its offer in a letter last week to Facet's board. Biogen's offer was lower than a previous offer it had made on August 17, of $15.00 a share.

Biogen said it reduced its offer to $14.50 a share after Facet announced a collaboration with Trubion Pharmaceuticals Inc. Biogen said the Trubion deal reduced the value of Facet in its eyes, noting Facet shares have fallen more than 20 percent since the Trubion deal was announced.

Geoffrey Meacham, an analyst at J.P. Morgan, said last week that given Facet's cash position, Biogen would seem to effectively be paying less than $50 million for Facet.

Still, investors expect Biogen will increase its offer. On Friday Facet's shares rose 74 percent to close at $15.38 on Nasdaq. They rose 0.78 percent to $15.50 in premarket electronic trading on Tuesday, after the Labor Day holiday.

(Reporting by Toni Clarke, editing by Gerald E. McCormick)