Today, findings from a phase 3 trial evaluating the efficacy and safety of tezacaftor in combination with ivacaftor in patients with cystic fibrosis (CF) who were homozygous for the Phe508del mutation were published in the New England Journal of Medicine
The Phe508del mutation has been known to result in greatly reduced conductance regulator (CFTR) protein activity and a loss of chloride secretion, which can lead to impaction of mucus in the airways, gastrointestinal tract, and exocrine organs, with the potential for severe clinical consequences including gradual loss of lung function, nutritional deficits, pulmonary exacerbations, and respiratory failure. It is the most prevalent CFTR mutation worldwide, and affects approximately 46% of American CF patients.
Previous data has shown Ivacaftor’s association with a rate of progressive decline in lung function that is lower than that in untreated patients. In a phase 2 clinical trial involving patients who were homozygous for the Phe508del mutation or heterozygous for the Phe508del and G551D mutations, when combined with the investigational CFTR corrector tezacaftor, it has exhibited enhanced CFTR function and improved lung function.
In August, just one month removed from Vertex’s announcement of positive data
from Phase 1 and Phase 2 studies, Rare Disease Report
covered the acceptance of applications
for the use of the tezacaftor/ivacaftor combination treatment in this patient population by the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA).
The phase 3 trial enrolled a total of 510 patients 12 years and older with CF who were homozygous for the Phe508del CFTR mutation at 91 sites in the U.S., Canada, and Europe from January 30, 2015 to January 20, 2017. Patients were randomly assigned to be administered either tezacaftor and ivacaftor (administered as a fixed-dose combination tablet containing 100 mg of tezacaftor and 150 mg of ivacaftor in the morning and a tablet containing 150 mg of ivacaftor in the evening) combination therapy or placebo for 24 weeks.
In total, 475 patients completed the full 24 weeks of the trial, with 93.6% (n
=235) in the tezzacaftor-ivacaftor group and 93% (n
=240) in the placebo group. While no significant difference in the body mass index (BMI) was experienced between the groups at week 24, the use of the combination therapy led to a significantly greater absolute change from baseline in the predicted forced expiratory volume in 1 second (FEV1
) than placebo. Despite advances in standard-of-care therapy, patients with CF continue to lose lung function at a rate of an estimated 1% to 3% per year. This trial exhibited a significant effect of the combination therapy compared to the placebo, as the mean absolute change from baseline in FEV1
through week 24 was 3.4 percentage points in the former, compared to 0.6 in the latter.
The most common adverse events (AEs) among the enrolled patients included infective pulmonary exacerbation, cough, headache, nasopharyngitis, increased sputum production, pyrecia, hemoptysis, oropharyngeal pain, and fatigue. The incidence of AEs was similar in both the group for combination therapy and the placebo group, however, those treated with lumacaftor-ivacaftor in the phase 3 did not experience an increased incidence of respiratory events (33 patients [13.1%] vs. 41 patients [15.9%]).
This improved safety profile of the tezacaftor-ivacaftor combination supports its use in a broad range of patients with CF, and, if approved, the therapy will be the third of Vertex’s drugs approved for CF patients, and the second intended specifically to treat patients with F508del mutations (Orkami [lumacaftor/ivacaftor]).
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Taylor-Cousar JL, Munck A, McKone EF, et al. Tezacaftor-Ivacaftor in Patients with Cystic Fibrosis Homozygous for Phe508del. New England Journal of Medicine. 2017. doi: 10.1056/NEJMoa1709846.