Switzerland's Actelion said yesterday that a strong case is building to continue testing its endothelin antagonist Tracleer in idiopathic pulmonary fibrosis.

Data presented from the BUILD programme (Bosentan Use in Interstitial Lung Disease) at the American Thoracic Society (ATS) conference in San Diego, has encouraged it to go forward with a new morbidity/mortality-driven Phase III study to further evaluate the safety and efficacy of Tracleer (bosentan) in IPF, a chronic disease characterised by progressive scarring of the lungs.

Preliminary results announced last year showed that bosentan missed its primary endpoint (improvement in the six-minute walk test) in BUILD-1, but showed a positive trend for pre-defined morbidity/mortality endpoints.

Further analyses presented at the ATS confirm that bosentan delayed time to disease progression in patients with lung biopsy proven IPF. The combined incidence of disease progression or death up to 12 months was 38% in the placebo group versus 12% in the bosentan group – a relative risk reduction of 68% (p=0.005).

Presenting the data yesterday, Professor Talmadge King, of the University of California at San Francisco, the principal investigator of the BUILD-1 study, said that the response to treatment in this sub group had been dramatic.

“These patients have less end stage scarring, with more lung that potentially could recover. The take-home message is that patients with milder disease appear to have a positive response to bosentan. Now we have to prove this.”

Actelion say that the company is currently in advanced discussion with regulatory authorities to finalise the design and scope of a Phase III study in this sub-group of biopsy proven IPF. Enrollment is expected to start by the end of the year.

“About half of all patients with IPF die within two to three years of diagnosis. No current therapy improves the disease or survival so researchers are anxiously truing to find an answer,” said Professor King. His data, presented for the first time at the ATS will be submitted for publication.

Analysts have suggested that an effective drug to treat the disease could garner sales of $500 million or more. Tracleer is already approved for the treatment of pulmonary arterial hypertension, and brought in nearly $500 million in sales in 2005, although the drug is expected to come under pressure in PAH as more therapies, including Pfizer’s Revatio (sildenafil), have entered the marketplace.