Biotechnology company Amgen Inc. said Friday it will buy privately held Avidia for $290 million in cash and additional milestone payments.

Avidia, a biopharmaceutical company, is developing a class of therapeutics called Avimer proteins. Specifically, the deal gives Amgen a lead product candidate for the treatment of inflammation and autoimmune diseases, currently in early-stage clinical trials.

Both companies' boards have approved the deal, which includes up to an additional $90 million in milestone payments. Amgen Ventures, the company's investment division, already owns a 4 percent stake in Avidia.

"The Avimer technology is among the most attractive protein-based technologies currently under development," said Dr. Roger M. Perlmutter, Amgen's executive vice president for research and development, in a statement. "Avimers may have several advantages as therapeutic products in terms of biological activity, tissue distribution, reduced immunogenicity and improved manufacturing efficiencies."

The deal is expected to close during the fourth quarter, at which point Mountain View, Calif.-based Avidia will become a wholly owned subsidiary of Amgen.

News of the acquisition comes at the end of a busy week for Amgen. It moved into the week after receiving a non-exclusive licensing agreement for a key patent to rival ImClone Systems Inc.'s Erbitux cancer drug. That was followed by Food and Drug Administration approval of its colon cancer drug Vectibix, which competes with Erbitux.

Shares of Amgen fell 2 cents to $71.53 on the Nasdaq in Friday's trading.