Biopharmaceutical company

Gilead Sciences

(GILD) - Get Report

has invested $25 million in privately held respiratory-drug developer Corus.

As a result, Gilead will become the second-largest Corus shareholder and will have an exclusive option to buy the remaining shares at a prespecified price.

Corus is starting phase III trials for its inhaled antibiotic drug Cayston, which is meant for infections related to cystic fibrosis. In 2002, the Food and Drug Administration granted Cayston orphan drug status, a designation given to drugs proposed to treat rare diseases. Phase III is the final stage of clinical trials just before a drug is submitted to the FDA for marketing approval.

"This investment will provide Corus with the resources to continue the important clinical trials of

Cayston. There is no known cure for cystic fibrosis, and treatment of the disease and of related infections represents an area of tremendous unmet medical need," Gilead's CEO John Milligan said in a press release. "Through this alliance between Corus and Gilead, patients with cystic fibrosis may gain more rapid access to an important new treatment option."

Flu-vaccine maker

Chiron

(CHIR) - Get Report

, which is being acquired by Switzerland's

Novartis

(NVS) - Get Report

, has alleged that Corus and two of its officers misappropriated trade secrets related to the drug, but Corus is disputing the accusation.

Cystic fibrosis is a disease in which a gene defect causes the body to produce a thick mucus that clogs the lungs, leading to life-threatening infections. The secretions also interfere with the pancreas. Digestive enzymes are prevented from reaching the body's intestines where they would break down and absorb food.

According to the Cystic Fibrosis Foundation, about 30,000 people in the U.S. have the disease. The median life span for a person with cystic fibrosis is in the mid-30s.