ZymoGenetics Inc. filed a patent-infringement proceeding related to Enbrel against Immunex Corp. in the U.S. District Court for the Western District of Washington in Seattle.

The lawsuit alleges patent infringement by Immunex through its manufacture, importation and sale of Enbrel, its etanercept dimeric fusion protein for the treatment of rheumatoid arthritis and other conditions.

The lawsuit charges Seattle-based Immunex with infringing six patents. One patent was issued in 1998, a second in 2000 and the remaining four were issued last year.

“We’ve had discussions on and off for the past two years,” ZymoGenetics Chief Financial Officer James Johnson said. “This is not just an isolated action it’s part of a process that’s been ongoing for quite some time.”

Immunex’s reaction was swift.

“There’s no question that we will vigorously defend the company against this lawsuit,” said Josh Schroeter, Immunex’s senior manager of corporate communications. “We believe that ZymoGenetics’ allegations are without merit.”

Enbrel sold in excess of $750 million worldwide last year.

In the suit, ZymoGenetics said U.S. Patent Nos. 5,843,725, 6,018,026, 6,291,212 B1, 6,291,646 B1, 6,300,099 B1 and 6,323,323 B1 were infringed through the manufacture, importation and sale of Enbrel, the type of protein it said is covered by the patent claims.

“They all claim priority of invention, going back to 1988,” Johnson said.

ZymoGenetics, also of Seattle, called the move consistent with its business strategy to protect and commercialize its extensive patent portfolio. ZymoGenetics said it is seeking monetary damages based on Immunex’s infringement of ZymoGenetics’ patents.

“In terms of what we’re trying to get, it’s more of a big- picture statement,” Johnson said. “We want fair value for the right to practice our invention. There are several different ways of getting that value. We haven’t specified damages or specifically what we desire to recover in the suit. We believe the patents are being infringed, we believe that Immunex needs a license to it, and that’s the point of the suit.”

Early last month, ZymoGenetics sold 10 million shares at $12 apiece in a $120 million initial public offering. (See BioWorld Today, Feb. 4, 2002.)

ZymoGenetics had for 12 years been a unit of Novo Nordisk A/S, of Denmark, before being spun out as an independent, privately held company in 2000. The company has played a part in developing five protein products currently marketed, bringing ZymoGenetics about $10 million annually in royalty payments.

ZymoGenetics’ stock (NASDAQ:ZGEN) gained 43 cents Friday to close at $10.78. Immunex’s stock (NASDAQ:IMNX) fell 10 cents to close at $29.70.