The pipeline for targeted cystic fibrosis drugs is flowing faster than the rate of this journal’s print cycle. Just a few weeks back, I did some reporting on the growing number of experimental compounds in clinical development that aim to directly overcome the genetic detects seen in people with this disease. Yet by the time my story came out last week, it was already somewhat out of date, it seems, because in the two weeks after Nature Medicine’s April issue went to press even more good news about mutation-specific agents has emerged.

I wrote my news story off the back of a February announcement of phase 3 trial results showing that a cystic fibrosis drug called VX-770 could improve measures such as lung capacity in people aged 12 or older who carry a particular mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which codes for a chloride channel associated with the disease. The so-called G551D mutation is seen in around 4% of people with cystic fibrosis.

Later, on 29 March, the drug’s manufacturer, Cambridge, Massachusetts-based Vertex Pharmaceuticals, reported that VX-770 met its primary clinical endpoint in a small phase 3 trial involving six- to 11-year-olds with the same G551D mutation. “Children with [cystic fibrosis] treated with VX-770 showed the same profound improvements in lung function,” Vertex’s chief medical officer Robert Kauffman said in a statement.

VX-770 works by propping open the defective CFTR protein to help chloride ions flow across the cell membrane. But this adjustment alone is not enough to fully correct the genetic defect found in the majority of people with cystic fibrosis, who harbor a mutation in CFTR called F508del, which leads to abnormal ion pumping as well as incorrect protein folding and localization. To treat people with this more common mutation, over the past few years Vertex has advanced a second compound known as VX-809 that helps CFTR fold properly and land correctly nestled in the cell membrane. However, this molecule on its own did not significantly improve people’s lung function in a phase 2 trial reported last year. So now, in a financing deal announced last week with the Cystic Fibrosis Foundation (CFF), the company is moving into clinical development with a third drug called VX-661, which works in much the same way as VX-809.

Sam Moskowitz, director of the cystic fibrosis basic science program at MassGeneral Hospital for Children in Boston, speculates that both Vertex and the CFF remained pretty tight-lipped about VX-661 — not even mentioning it when I queried them in March for my story — because they “are worried about the potency of VX-809.” By moving simultaneously forward with a similar agent, VX-661, they are therefore “increasing the odds of success," he says.

Eric Olson, head of Vertex’s cystic fibrosis project, appears confident that one of these so-called ‘corrector’ molecules will work in the clinic. “We think it’s certainly a viable path, and we want to continue down that path,” he told the Boston Herald. Backed by up to $75 million from the Cystic Fibrosis Foundation Therapeutics, the drug development affiliate of the CFF, Vertex plans to begin the first human clinical trials of VX-661 by the end of the year in people with the F508del mutation.