Actelion lung drug shows promise in small study

* Pulmonary vascular resistance reduced 30 pct vs placebo

* Trend toward walking distance improvement seen

* Phase III morbidity and mortality program under way

NEW YORK, May 17 (Reuters) - An experimental drug being developed by Actelion Ltd ATLN.VX for a serious lung disorder significantly eased resistance to blood pumping through arteries around the lungs, according to data from a small, mid-stage clinical trial presented on Monday.

The Swiss drugmaker is developing selexipag to treat pulmonary arterial hypertension, or PAH, a life-threatening condition in which abnormally high blood pressure in the arteries between the heart and lungs severely compromises the function of both organs.

Patients in the 43-subject trial who received selexipag on top of other treatments had a 30.3 percent reduction in pulmonary vascular resistance (PVR) after 17 weeks -- the main goal of the trial -- compared with those who received a placebo in addition to their regular medicine, researchers said.

The result was deemed to be highly statistically significant, researchers said.

PVR is a measure of the resistance to blood flow that must be overcome for the heart to push blood through the circulatory system around the lungs. Reduction in such resistance is seen as a potential indication of clinical effectiveness as PVR tends to become more pronounced as PAH worsens.

“These Phase II results are very encouraging, particularly considering that the efficacy observed is on top of (other) oral therapy,” Dr. Gerald Simonneau, the study’s lead investigator, who presented the data at the American Thoracic Society conference in New Orleans, said in a statement.

Actelion previously reported the drug met the primary goal of the Phase II trial, but full details of the data were presented for the first time at the ATS meeting.

In addition to the primary goal, the study looked at the drug’s ability to improve six-minute walking distance -- a standard goal in PAH studies because the disease can severely limit exercise capacity.

The drug led to what Simonneau called “an encouraging numerical improvement” in six-minute walk distance. But the study was too small to achieve statistical significance on that measure, the company said.

Selexipag is a new type of oral PAH treatment and works by inducing vasodilation, or widening of the blood vessels through relaxation of the muscle cells of the vessel walls. Similar drugs are given intravenously or by inhalation and have proven difficult to tolerate in high doses, the company said.

The patients in the study were initially given 200 micrograms of selexipag twice a day, with the dose gradually raised in those who could tolerate it to 800 mcg by day 21 of the trial.

If side effects, such as jaw pain, pain in the extremities, or uncomfortable flushing occurred, the dose was reduced to the highest tolerated.

The drug was generally well tolerated, researchers said.

Both selexipag and placebo patients in the study were also taking other oral PAH treatments, such as Actelion's Tracleer or Pfizer Inc's PFE.N Ravatio, a different type of drug that has the same active ingredient as Viagra.

A Phase III program that will study the ability of selexipag to reduce the risk of morbidity and mortality in PAH patients is underway, Actelion said.

Phase III is typically the final stage of human testing before a new drug is submitted to regulators for an approval decision.

Actelion has worldwide rights to the medicine outside Japan. If approved, it will be co-marketed in Japan with Nippon Shinyaku Co Ltd 4516.T, which discovered the drug. (Reporting by Bill Berkrot; editing by Andre Grenon)