Efficacy and safety of ataluren in patients with nonsense-mutation cystic fibrosis not receiving chronic inhaled aminoglycosides: The international, randomized, double-blind, placebo-controlled Ataluren Confirmatory Trial in Cystic Fibrosis (ACT CF)

BACKGROUND

Ataluren was developed for potential treatment of nonsense-mutation cystic fibrosis (CF). A previous phase 3 ataluren study failed to meet its primary efficacy endpoint, but post-hoc analyses suggested that aminoglycosides may have interfered with ataluren's action. Thus, this subsequent trial (NCT02139306) was designed to assess the efficacy and safety of ataluren in patients with nonsense-mutation CF not receiving aminoglycosides.

METHODS

Eligible subjects with nonsense-mutation CF (aged ≥6 years; percent predicted (pp) FEV1 ≥40 and ≤90) from 75 sites in 16 countries were randomly assigned in double-blinded fashion to receive oral ataluren or matching placebo thrice daily for 48 weeks. The primary endpoint was absolute change in average ppFEV1 from baseline to the average of Weeks 40 and 48.

FINDINGS

279 subjects were enrolled; 138 subjects in the ataluren arm and 136 in the placebo arm were evaluable for efficacy. Absolute ppFEV1 change from baseline did not differ significantly between the ataluren and placebo groups at Week 40 (-0.8 vs -1.8) or Week 48 (-1.7 vs -2.4). Average ppFEV1 treatment difference from baseline to Weeks 40 and 48 was 0.6 (95% CI -1.3, 2.5; p = 0.54). Pulmonary exacerbation rate per 48 weeks was not significantly different (ataluren 0.95 vs placebo 1.13; rate ratio p = 0.40). Safety was similar between groups. No life-threatening adverse events or deaths were reported.

INTERPRETATION

Neither ppFEV1 change nor pulmonary exacerbation rate over 48 weeks were statistically different between ataluren and placebo groups. Development of a nonsense-mutation CF therapy remains elusive.

The effects of aerosolized dextran in a mouse model of Pseudomonas aeruginosa pulmonary infection

Airway infections initiated by the interaction of bacterial adhesins with carbohydrate receptors can be potentially prevented by nontoxic carbohydrate inhibitors. Intranasal inoculation of neonatal mice with Pseudomonas aeruginosa PAO1 caused pneumonia in 55% of control mice but in only 13% of mice inoculated 2 h after dextran inhalation (P<.001) and in 28% inoculated 4 h after dextran inhalation (P=.02). PAO1 adherence to epithelial cells was inhibited by 50% in the presence of dextran. Dextran was well distributed throughout the airways and stimulated tumor necrosis factor-alpha production in murine lungs but not interleukin-8 production by human epithelial cell lines. Phagocytosis of PAO1 was not affected by dextran nor was killing by human neutrophils diminished. Administration of dextran by aerosol may prevent murine pneumonia by impeding bacterial access to epithelial receptors and by stimulation of the immune functions of the epithelium.

Activation of NF-kappaB by adherent Pseudomonas aeruginosa in normal and cystic fibrosis respiratory epithelial cells

PMN-dominated airway inflammation is a major component of cystic fibrosis (CF) lung disease. Epithelial cells respond to organisms such as Pseudomonas aeruginosa, the major pathogen in CF, by expressing the leukocyte chemokine IL-8. Experiments were performed using several different types of respiratory epithelial cells that demonstrate that ligation of ceramide-associated receptors on epithelial surfaces by P. aeruginosa pili is a major stimulus for the translocation of transcription factor nuclear factor (NF)-kappaB and initiation of IL-8 expression by epithelial cells. Using electrophoretic mobility shift assays and Western hybridizations, nuclear NF-kappaB was found shortly after epithelial cells were stimulated by either whole organisms, isolated pili, or antibody to the pilin receptor asialoGM1. IB3 cells, which express mutations in cystic fibrosis transmembrane conductance regulator (CFTR) (DeltaF508/W1282X), were noted to have significantly greater amounts of endogenous nuclear NF-kappaB, but not the transcription factor C/EBP, than CF cells corrected by episomal copies of normal CFTR (C-38) or IB3 cells grown at a permissive temperature (25 degreesC). Activation of NF-kappaB and subsequent IL-8 expression in epithelial cells can result from activation of at least two pathways: an exogenous signaling cascade that is activated by ligation of ceramide-associated adhesins such as P. aeruginosa pilin, or endogenous stimulation, suggested to be a consequence of cell stress caused by the accumulation of mutant CFTR in the endoplasmic reticulum.

Contribution of specific Pseudomonas aeruginosa virulence factors to pathogenesis of pneumonia in a neonatal mouse model of infection

We sought to identify which Pseudomonas aeruginosa products are involved initiating respiratory tract infection. Defined mutants derived from strain PAO i.e., PAOR1 (lasR),PAO-pmm (algC) (an LPS mutant), and AK1152 (which is Fla- and lacks functional pili), were significantly less virulent than PAO1 in a BALBc/ByJ neonatal mouse model of infection as measured by their abilities to cause acute pneumonia, bacteremia, and death. All three mutants were also less adherent to epithelial cells in an in vitro binding assay. PAOR1 and AK1152 were less able to elicit epithelial production of interleukin-8 than PAO1. LasR was found to be required for the optimal expression of neuraminidase under conditions of increased osmolarity, as might be present in certain pathological conditions. PAO-exsA::omega,, which lacks exoenzyme S expression, was fully virulent, causing at least as much pathology as PAO1. The expression of several P. aeruginosa virulence factors appears to be required to establish pulmonary infection in the neonatal mouse.

Diverse Pseudomonas aeruginosa gene products stimulate respiratory epithelial cells to produce interleukin-8

Respiratory epithelial cells play a crucial role in the inflammatory response during Pseudomonas aeruginosa infection in the lungs of patients with cystic fibrosis. In this study, we determined whether the binding of specific Pseudomonas gene products (pilin, flagellin) to their receptors on respiratory epithelial cells would result in production of the neutrophil chemoattractant IL-8. Piliated wild-type organisms, purified pili, or antibody to the pilin receptor (asialoGM1) evoked significant production of IL-8 by immortalized airway epithelial cells, whereas nonpiliated organisms were less able to bind to respiratory epithelial cells and stimulated much less IL-8 secretion (P < 0.01). A piliated, nonflagellated strain was also associated with decreased binding and a diminished level of IL-8 production when compared to wild-type organisms. Isogenic, nonadherent rpoN mutants, lacking pilin and flagellin, did not bind or elicit an IL-8 response. In addition, the IL-8 response was four-fold higher in a cystic fibrosis cell line compared with its corrected cell line. The Pseudomonas autoinducer, an exoproduct secreted during chronic infection, was found to stimulate IL-8 in a dose-dependent manner. P. aeruginosa adhesins, which are necessary for initial infection, directly stimulate IL-8 production by respiratory epithelial cells and therefore play a major role in the pathogenesis of Pseudomonas infection in patients with cystic fibrosis. The inflammatory response is subsequently perpetuated by Pseudomonas autoinducer which is secreted during chronic infection.