By Mary Welch

Immunex Corp. filed a biologics license application (BLA) with the FDA to market Enbrel, its treatment for active rheumatoid arthritis, triggering a $20 million milestone payment from American Home Products (AHP).

Designated a Fast Track Product by the FDA in March, Enbrel could get the marketing go-ahead within six months, said Tim Warner, spokesman for Seattle-based Immunex. The FDA has 45 days to decide whether Enbrel will receive priority review.

"We're confident of getting [that], since we've had a good working relationship with the FDA," Warner said. "It's great news." If all goes well, Enbrel could be on the market by late 1998 or early 1999.

The milestone payment will be made by Wyeth-Ayerst Laboratories, a division of Madison, N.J.-based AHP, which owns 54 percent of Immunex and sought to buy the company in 1995.

Under the marketing agreement with Immunex, Wyeth-Ayerst will promote Enbrel for all indications other than oncology, for which Immunex holds exclusive promotional rights. In the deal, Immunex got $15 million up front, $20 million for filing the NDA and $30 million upon approval. (See BioWorld Today, Sept. 29, 1997, p. 1.)

Enbrel is a tumor necrosis factor (TNF) receptor that regulates inflammation by blocking the interaction of the proinflammatory cytokine TNF with the cells that respond to its signal. The drug is believed to interfere specifically with the inflammatory process in rheumatoid arthritis, which may be driven by TNF.

"It's never been done before," Warner said.

Rheumatoid arthritis afflicts about 2.5 million Americans per year, most of them women. Kevin Tang, an analyst with BT Alex. Brown, of New York, in a written report said Enbrel has "truly blockbuster potential."

In Phase III trials, Enbrel significantly improved all measures of disease activity, as measured by scales established by the American College of Rheumatology. (See BioWorld Today, Sept. 12, 1997, p. 1.)

Immunex's stock (NASDAQ:IMNX) closed Friday at $68.125, down $0.937. *