Amgen Inc. on Tuesday announced plans to acquire Rodeo Therapeutics Corp., a private biopharmaceutical company based in Seattle.

The Thousand Oaks pharma giant will buy all outstanding shares of Rodeo in exchange for an upfront payment of $55 million, plus future milestone payments worth up to an additional $666 million in cash.

Rodeo will be a “strategic fit” for Amgen’s inflammation portfolio with its 15-PGDH program, Amgen said in a statement. The program is developing small-molecule drugs for use in repairing diseased or damaged tissue in the body.

“The enzyme 15-PGDH plays a key role in many disease-relevant processes such as stem cell self-renewal and epithelial barrier repair,” Dr. Raymond Deshaies, vice president of global research at Amgen, said in a statement. “Given the encouraging preclinical data to date, we are excited about the opportunity to develop a novel therapy.”

Added Rodeo Chief Executive Thong Le: “With decades of experience in developing, manufacturing and commercializing innovative therapies for patients suffering from a broad range of immunologic diseases and conditions, Amgen is ideally positioned to rapidly advance our program into the clinic.”

Cooley LLP and Gunderson Dettmer LLP acted as legal advisors to Rodeo and Amgen, respectively.

Shares of Amgen Inc. (AMGN) closed down $5.21, or more than 2 percent, to $249.75 on the Nasdaq on Tuesday, a day when overall the Nasdaq was down a fraction of a percent.