The realization of a long-awaited hope arrived this past month for many families in the form of a new treatment for cystic fibrosis. Cystic fibrosis (CF) is one of the most common recessively inherited diseases, affecting about 30,000 people in the United States. There are at least 500 mutations in a gene called CFTR that cause CF, but about 4% of patients carry a particular mutation targeted by this new therapy. For these individuals, hope for a longer and fuller life is now a tangible reality.
Individuals with cystic fibrosis produce thick mucus in their lungs in which bacteria thrive leading to constant lung infections. Treatments, until now, have targeted the symptoms: loosening and thinning the mucus, treating infections, and widening the airways. Because of these treatments, many people with CF now live into their thirties or even forties. Nevertheless, anyone affected by CF will tell you that these treatments and the resulting additional few decades of life are no substitute for a cure.
Last month the FDA approved the drug ivacaftor (Kalydeco ®) as the first treatment to address one of the underlying causes of CF, as opposed to just the resulting symptoms. Ivacaftor targets a particular mutation called G551D. G551D is an example of a CFTR “gating” mutation; it prevents the CFTR protein from opening and closing as it normally would on the cell surface.
In November, 2011, Dr. Ramsey from the Seattle Children’s Hospital and University of Washington School of Medicine Seattle published a study in the New England Journal of Medicine showing that ivacaftor is effective in treating individuals with the G551D mutation. The study showed that the ivacaftor-treated individuals fared far better than their placebo counterparts over the 48-week study: they gained more weight, suffered fewer serious adverse events, showed improvements in lung function, and reported a better quality of life. This study, and those like it, motivated the FDA to approve ivacaftor for CF-affected individuals over six years of age with at least one G551D mutation.
The approval of this new treatment is an exciting development for individuals carrying the G551D mutation. What impact ivacaftor will have on the other 96% of CF patients, however, is yet to be seen. It may be possible that ivacaftor can treat patients with other CFTR gating mutations, such as S549N or S549R, as suggested by the recent investigation led by Dr. Yu at Vertex Pharmaceuticals, the company that developed ivacaftor. It is unlikely, however, that ivacaftor could be used in isolation to treat most other types of mutations. For instance, ivacaftor would likely not benefit patients whose CF is caused by the most common deltaF508 mutation, which affects the shape of the CFTR protein and prevents it from reaching the cell surface in the first place. It may be possible, however, to use ivacaftor in conjunction with other drugs to treat CF patients with mutations other than G551D.
Many are recognizing ivacaftor’s impact on the perception of personalized medicine in general. FDA Commissioner Dr. Margaret Hamburg called ivacaftor (Kalydeco ®) “an excellent example of the promise of personalized medicine – targeted drugs that treat patients with a specific genetic makeup.” President and CEO of the Cystic Fibrosis Foundation, Dr. Robert Beall, hails the drug “an amazing proof of concept” and foresees it as the next “poster child of personalized medicine.” Ivacaftor, thus, is the fruition of hopes held by pharmacogeneticists as well as CF patients. This powerful little pill represents a great step forward, both for personalized medicine and for CF treatment.