WEDNESDAY, Nov. 2 (HealthDay News) -- A new drug that targets a faulty protein that causes cystic fibrosis led to improved lung function and fewer symptoms in people with the lung disease, researchers report.

The drug -- ivacaftor -- is the first to halt the underlying processes that cause the inherited disease, which causes thick, sticky mucus to build up in the lungs and the pancreas and can lead to life-threatening infections, experts said.

"It has a huge significance for the whole cystic fibrosis community," said study author Dr. Bonnie Ramsey, director of the Center for Clinical and Translational Research at Seattle Children's Hospital and a professor at the University of Washington School of Medicine. "It's the first time we have developed a therapy directed at the abnormal proteins and showing that it can be corrected."

Only 4 percent to 5 percent of cystic fibrosis patients have the particular genetic variant that the drug is being studied to treat, but for them, the results could mean a significant improvement in their health, said Robert Beall, president and CEO of the Cystic Fibrosis Foundation.

"We're talking about adding decades to these people's lives, that's how profound this drug is," Beall said.

But Beall and other experts say the drug may end up helping people with other cystic fibrosis genetic variants, including the most common one, D508, one copy of which is present in more than 90 percent of people with cystic fibrosis.

Though ivacaftor (previously known as VX-770) on its own didn't work all that well in these patients, a trial looking at using ivacaftor in conjunction with another drug is currently under way. Results of that trial are expected in the fall of 2012, said Beall, whose organization has provided funding for VX-770 research.

In the study reported in the Nov. 3 issue of the New England Journal of Medicine, 161 patients aged 12 and older were randomly divided into two groups. One received the drug every 12 hours and the other received a placebo. All patients had at least one copy of the G551D mutation.

Researchers could tell the drug was working two weeks after people started taking it and the concentration of chloride in their sweat dropped, for some to levels seen in people without the disease. Very salty sweat is a telltale sign of the disease.

Patients also showed improved lung function, as measured by FEV1, or how much air they could blow out in one second.

"It's not surprising you would see an effect in two weeks. By changing the hydration of the mucus, you can clear it out better and open up the airways," Ramsey said. "We saw the improvement across all illness severities ... That was very encouraging. We had been very worried once you had the lung damage or the infections you wouldn't be able to reverse it. That's not saying the lungs would return to normal, but there was more reversibility than we thought there would be."

Patients also experienced an average relative change in their lung function of 17 percent. Relative change means relative to where they started. The absolute change was about a 10 percent improvement.

At 48 weeks, patients on the drug were 55 percent less likely to have experienced an exacerbation, or an infection that left them ill and unable to work or hospitalized.

Patients on the drug also gained an average of 7 pounds, a huge feat for someone with cystic fibrosis, experts said. The weight gain brought people who were nutritionally deficient and underweight closer to a normal body weight, Ramsey said.

The results stayed consistent through 48 weeks, and there were few side effects, according to the study.

Best of all, patients reported feeling better, Beall said. "We had a lot of people call us and say it was incredible how much better they feel."

Cystic fibrosis is a progressive, inherited disease caused by a defect in the CF gene, which produces the CFTR (cystic fibrosis transmembrane conductance regulator) protein, which is important in the transport of salt and fluids in the cells of the lungs and digestive tract.

In healthy cells, when chloride moves out of cells, water follows, keeping the mucus around the cell hydrated.

In people with the faulty CFTR protein, the chloride channels don't work properly. Chloride and water in the cells of the lungs stay trapped inside the cell, causing the mucus to become thick, sticky and dehydrated.

Overtime, the abnormal mucus builds up in the lungs and in the pancreas, which helps to break down and absorb food. Patients with cystic fibrosis have both breathing problems and problems with maintaining weight.

In the lungs, the accumulation of the mucus leaves people prone to serious, hard-to-treat and recurrent infections. Overtime, the repeated infections destroy the lungs.

Though improving with inhaled antibiotics and other treatments, the average life expectancy for a person with cystic fibrosis is about 39, according to the Cystic Fibrosis Foundation.

Ivacaftor is believed to work by opening up the chloride channels, allowing the water to exit the cell and the mucus to become better hydrated. For people with the more common variant, D508, ivacaftor will likely open the channels, but only if the protein is properly transported to the surface of the cell. That's where a second drug would come in, experts explained.

Vertex Pharmaceuticals, the company developing the drug, has applied for expedited U.S. Food and Drug Administration approval. If the FDA grants the company's request, that would shorten the review time to six months from the usual 10, and would mean the FDA would make a decision by April, according to Dawn Kalmar, director of product communications for Vertex.

The drug will be marketed under the brand name Kalydeco.

Dr. Pamela Davis, dean of Case Western Reserve University School of Medicine, in Cleveland, said the drug holds great promise for cystic fibrosis sufferers.

"The exciting thing about this is a drug that interacts directly with the defective protein and changes its function," Davis said. "Admittedly this protein is only found in about 5 percent of the patients with CF but it does appear to restore normal function."

Though more testing is needed, it might be possible to give the drug to babies to head off the disease before it begins to damage the lungs, she added.

Millions of Americans carry a defective CF gene, but do not have any symptoms. To be symptomatic, a person with CF must inherit two defective CF genes -- one from each parent. About 30,000 people have CF, according to the Cystic Fibrosis Foundation.

More information

The Cystic Fibrosis Foundation has more on the disease.