By Randall Osborne

A pivotal Phase III study by Immunex Corp. has found statistically significant evidence that the company's tumor necrosis factor (TNF) receptor, Enbrel, works against rheumatoid arthritis, a painful disease that afflicts an estimated 2.5 million Americans per year, most of them women.

Immunex, of Seattle, will release complete data from the study on Nov. 9 at a meeting of the American College of Rheumatology. A spokeswoman for the company, Valoree Dowell, said the results of the six-month Phase III trial duplicate the results of a three-month Phase II study, which were published in the July 17 issue of The New England Journal of Medicine (NEJM).

The drug "produced significant improvements in all measures of disease activity," the NEJM report said. Improvement of swollen and tender joints "was apparent by the end of week two and was most pronounced at the end of treatment."

Immunex's stock (NASDAQ: IMNX) closed Thursday at $55.875, up $12.375, a 28 percent surge.

TNF is like a ball that adheres to the surface of the immune system cell, causing the cell to create white blood cells and become inflamed, Dowell said. Enbrel, a soluble TNF receptor floating in the bloodstream, is the glove that catches the ball before it sticks to the cell.

In the Phase III study, 234 subjects were given a dose of Enbrel or a placebo twice a week for six months. All patients had shown little or no results from other drugs. "They are considered a serious segment," Dowell said. "It's a highly unsatisfied market at this point."

The patients' responses to Enbel were measured by scales established by the American College of Rheumatology (ACR) called ACR 20 and ACR 50, which include such factors as joint swelling, joint tenderness and blood chemistry.

"The results we had seen earlier were confirmed," Dowell said. Those who improved with the drug, as compared with those given the placebo, "were enough to be beyond chance," she added.

Immunex is testing Enbrel for safety in a long-term open-label study that will be completed sometime in February. Another study examines how the receptor works with methotrexate, a standard treatment for rheumatoid arthritis. A third study is testing Enbrel on 50 juveniles. The company expects to file a biologics license application with the FDA in the first half of next year.

Immunex's strategic partner in developing Enbrel outside the U.S. is American Home Products (AHP) Corp., of Madison, N.J., which is also Immunex's principal investor. Under a previous agreement, AHP paid $1 million quarterly to retain international rights to Enbrel; now, the companies are sharing costs of its development in North America and Europe.

In early 1998, Immunex expects to receive its final payment from AHP. Then, existing funds will be used to support operations, including — if the FDA approves Enbrel — the purchase of commercial inventory of Enbrel that year, the company said. *