Immunex Corp. said Tuesday that it is beginning Phase Iclinical trials of soluble interleukin-1 receptor to inhibitallergic reactions to skin allergens.

IL-1 is an immune system protein that mediates inflammation.Soluble IL-1 receptor binds to IL-1 before it can bind to thecell and trigger an inflammatory response.

Later this year, Immunex plans clinical trials of IL-1 receptorto treat rheumatoid arthritis. Trials of another solublereceptor, tumor necrosis factor (TNF) receptor, are scheduledto begin in 1992 to treat sepsis and septic shock and cachexia,a wasting syndrome that affects cancer patients.

Immunex believes that TNF is a more important mediator ofseptic shock than IL-1. Nevertheless, spokesman Jason Rubinsaid, the company is considering combination trials of IL-1receptor and TNF receptor for a variety of indications,including septic shock.

According to Immunex, preclinical studies of soluble IL-1receptor have shown that it inhibits IL-1 activity to the samedegree as Synergen Inc.'s IL-1 receptor antagonist, but at one-hundredth to one-thousandth the dose.

This may be because laboratory studies of Immunex's drug haveshown that it has a much longer serum half-life thanSynergen's product, said Rubin.

The number of binding sites each drug needs to target may alsobe a factor, Rubin said. Theoretically, if IL-1 must occupy 10of 100 cellular receptor sites to trigger an inflammatoryresponse, IL-1ra would have to block 91 sites to preventinflammation. But only one molecule of soluble IL-1 receptorwould be needed to bind to and block IL-1.

Rubin emphasized that the binding theory is based onpreliminary studies and that there is disagreement on itsvalidity.

Immunex licensed U.S. rights for its receptor products fromReceptech Corp. (NASDAQ:RECP), which Immunex created in1989 to fund receptor development. Receptech shares closed up$3.13 at $20.13 on Tuesday. Immunex stock (NASDAQ:IMNX)climbed $1.25 to $47.25.

-- Karen Bernstein BioWorld Staff

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