Shares in Vertex Pharmaceuticals have soared 54% on data from a mid-stage trial of its investigational cystic fibrosis drug VX-661, in combination with its already-approved treatment Kalydeco.

Results from a Phase II study of VX-661 and Kalydeco (ivacaftor) showed that the combo resulted in statistically significant improvements in lung function among adults with CF who have two copies of the most common mutation in the F508del gene, the most common genetic abnormality that causes the disorder.

Specifically, patients in the 100 and 150 mg combination dose groups showed statistically significant mean relative improvements in lung function, versus placebo, of 9.0% and 7.5%, respectively, at day 28. In contrast, patients who received placebo showed a 0.03% change.

VX-661 was generally well-tolerated, both as monotherapy and in combination with Kalydeco. Vertex said that it plans to conduct additional studies of the drug to further evaluate its potential for late-stage development, pending regulatory discussions.

Peter Mueller, Vertex chief scientific officer, said the study "provides further validation of the strategy of combining a corrector  [VX-661] and potentiator to improve lung function in people with the most common type of CF. He added that "with these data and the recent initiation of a Phase III programme for a combination of our lead cystic fibrosis transmembrane conductance regulator (CFTR) corrector VX-809 with ivacaftor, we are making significant progress toward our goal to help many more people with CF."

Kalydeco is currently approved use in patients aged six and over who have the G551D mutation in the CFTR gene. There are estimated to be around 2,000 such patients worldwide, out of 70,000 sufferers worldwide, while about half of all CF patients have two faulty copies of the F508del gene.