By Brady Huggett

Immunex Corp.¿s Enbrel, already approved and generating rising revenues, is taking aim at the psoriasis market, one that could add as many as 500,000 patients to the list of those taking the tumor necrosis factor-inhibiting drug.

Seattle-based Immunex released positive preliminary results from its first clinical study of Enbrel ¿ partnered with Wyeth-Ayerst, a division of American Home Products Corp., of Madison, N.J. ¿ in psoriasis patients. Full results are on the way, said Leslie Garrison, senior vice president of clinical research and development at Immunex.

¿We expect to have all the data analyzed in the next few months, and present at a dermatology meeting in March,¿ she told BioWorld Today. ¿In the meantime, we will work on the manuscript and have that published as soon as possible.¿

One hundred and twelve patients with moderate-to-severe plaque psoriasis participated in the trial and were randomized to receive 25 mg of Enbrel or placebo twice a week for six months. The primary endpoint was the proportion of patients achieving a 75 percent improvement in the Psoriasis Area and Severity Index (PASI) after 12 weeks. At the 12-week point, 30 percent of patients on Enbrel achieved PASI 75, compared to 2 percent of patients receiving placebo. Nice figures, Garrison said, made even more impressive when compared to Immunex¿s psoriatic rivals.

¿We were really looking for a statistical difference between placebo and Enbrel,¿ she said. ¿We were looking for PASI 75 at three months ¿ that is the endpoint in all the recent dermatology studies. We knew that the competitors ahead of us had shown they were in the 20 percent to 30 percent range of PASI 75. When looking at Amevive [Biogen Inc., of Cambridge, Mass.] and Xanelim [Genentech Inc., of South San Francisco and Xoma Ltd., of Berkeley, Calif.], we wanted to know how we were going to stack up with those therapeutics and we did very nicely.¿

Biogen filed for regulatory approval for Amevive in both the United States and the European Union earlier this month. Xoma and Genentech anticipate filing for approval of Xanelim in the United States by the end of 2001 or in the first quarter of 2002, if data analysis proves positive. (See BioWorld Today, Aug. 7, 2001, and June 27, 2001.)

Also notable, said Garrison, is what the drug did beyond the 12-week checkpoint.

¿Even though the primary endpoint was at three months, we were very pleased with the PASI scores at six months,¿ Garrison said. ¿Over half of the patients [receiving Enbrel] had a PASI score of 75 or more.¿ Only 5 percent of patients receiving placebo reached that mark. Also, about 20 percent of patients administered placebo improved by 90 percent or more at six months; none of the placebo patients fared as well.

In other indications for Enbrel, positive results have been achieved quicker at increased doses, something Immunex now wants to investigate with psoriasis before diving into Phase III trials.

¿The next step for us is trying to leverage what we know from our other trials,¿ Garrison said. ¿When we looked at 50-mg doses twice weekly in our [rheumatoid arthritis] trials, we found that we were able to get the maximum response more quickly. We are going to do a higher-dose arm to see if we can get those six-month results earlier.¿

Garrison called the dose-ranging study ¿key for our filing package¿ and said that, following that trial, Immunex would turn its attention to Phase III.

Critics have questioned Immunex¿s ability to produce enough Enbrel to meet demand, a concern exacerbated by each additional indication Immunex seeks. There are about 500,000 patients in the United States suffering from severe psoriasis, Garrison said, the first group that would most likely use Enbrel if approved for that indication. She brushed the manufacturing criticism aside.

¿Efi Cohen-Arazi, our senior vice president and head of manufacturing, has told us, We will have the drug,¿¿ she said. She pointed to four new manufacturing facilities ¿ two in Rhode Island, AHP¿s Grange Castle in Ireland, and Ingleheim, Germany-based Boehringer Ingleheim GmbH¿s second plant ¿ and said the foursome ¿will increase our ability to produce product multiplefold.¿

As Enbrel¿s potential uses continue to swell like an arthritic¿s knuckles, so have its revenues. Net sales for the product in the second quarter were $186.2 million, up 18 percent from 2000¿s second quarter. For the first half of the year, it brought Immunex $347.5 million, a 21 percent increase from the same period one year ago. In 2000, it provided Immunex with $652.4 million. Each indication potentially ratchets that year-end figure up. Garrison said Immunex¿s senior vice president of commercial operations and general manager estimates Enbrel sales could reach up to $4 billion in 2005.

Immunex sees no reason to slow down. It has filed for psoriatic arthritis and expects to see an approval there by the beginning of 2002. It is planning a Phase III study for ankylosing spondylitis and has a pivotal program under way for Wegener¿s granulomatosis. It is gathering pilot information in idiopathic pulmonary fibrosis, asthma and chronic obstructive pulmonary disease. Immunex also is investigating Enbrel¿s use in oncology and graft-vs.-host disease.

¿TNF is a key mediator in a lot of different diseases,¿ Garrison said. ¿The list is endless. Name a disease and we¿ve been evaluating it.¿

Immunex¿s stock (NASDAQ:IMNX) rose 64 cents Tuesday to close at $16.86, after trading as high as $17.59.