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Approximately 5% of patients with cystic fibrosis express one allele with some retained CFTR function. In a prospective trial, tezacaftor–ivacaftor had a greater effect on increasing FEV 1 than ivacaftor alone, and both ivacaftor alone and the combination were more effective than placebo.

This preclinical, phase 2 report shows that VX-445, a CFTR potentiator when administered with tezacaftor and ivacaftor, improved lung function and reduced sweat chloride concentrations and symptoms in patients harboring one or two Phe508del alleles.

Leaf hydraulic conductance (K leaf) and mesophyll conductance (g m) both represent major constraints to photosynthetic rate (A), and previous studies have suggested that K leaf and g m is correlated in leaves. However, there is scarce empirical information about their correlation. In this study, K leaf, leaf hydraulic conductance inside xylem (K x), leaf hydraulic conductance outside xylem (K ox), A, stomatal conductance (g s), g m, and anatomical and structural leaf traits in 11 Oryza genotypes were investigated to elucidate the correlation of H2O and CO2 diffusion inside leaves. All of the leaf functional and anatomical traits varied significantly among genotypes. K leaf was not correlated with the maximum theoretical stomatal conductance calculated from stomatal dimensions (g smax), and neither g s nor g smax were correlated with K x. Moreover, K ox was linearly correlated with g m and both were closely related to mesophyll structural traits. These results suggest that K leaf and g m are related to leaf anatomical and structural features, which may explain the mechanism for correlation between g m and K leaf.

This companion article to the VX-445 report shows that VX-659, a new CFTR potentiator, when administered with tezacaftor and ivacaftor improved lung function, sweat chloride concentration, and symptoms in patients with cystic fibrosis who harbored one or two Phe508del alleles.

BackgroundVX-809, a cystic fibrosis transmembrane conductance regulator (CFTR) modulator, has been shown to increase the cell surface density of functional F508del-CFTR in vitro.MethodsA randomised, double-blind, placebo-controlled study evaluated the safety, tolerability and pharmacodynamics of VX-809 in adult patients with cystic fibrosis (n=89) who were homozygous for the F508del-CFTR mutation. Subjects were randomised to one of four VX-809 28 day dose groups (25, 50, 100 and 200 mg) or matching placebo.ResultsThe type and incidence of adverse events were similar among VX-809- and placebo-treated subjects. Respiratory events were the most commonly reported and led to discontinuation by one subject in each active treatment arm. Pharmacokinetic data supported a once-daily oral dosing regimen. Pharmacodynamic data suggested that VX-809 improved CFTR function in at least one organ (sweat gland). VX-809 reduced elevated sweat chloride values in a dose-dependent manner (p=0.0013) that was statistically significant in the 100 and 200 mg dose groups. There was no statistically significant improvement in CFTR function in the nasal epithelium as measured by nasal potential difference, nor were there statistically significant changes in lung function or patient-reported outcomes. No maturation of immature F508del-CFTR was detected in the subgroup that provided rectal biopsy specimens.ConclusionsIn this study, VX-809 had a similar adverse event profile to placebo for 28 days in F508del-CFTR homozygous patients, and demonstrated biological activity with positive impact on CFTR function in the sweat gland. Additional data are needed to determine how improvements detected in CFTR function secondary to VX-809 in the sweat gland relate to those measurable in the respiratory tract and to long-term measures of clinical benefit.Clinical trial numberNCT00865904

Ivacaftor, a potentiator of CFTR, was studied in patients with cystic fibrosis (CF) who had mutations that reduced the function of the CFTR protein. Ivacaftor significantly improved FEV 1 and reduced pulmonary exacerbations; it holds promise in the treatment of selected patients with CF. Cystic fibrosis, the most common lethal genetic disease in whites, affects approximately 70,000 people worldwide. 1 – 3 There is no cure for this disease, and the progressive lung disease associated with it is the leading cause of death. Current treatments for cystic fibrosis target the secondary effects of dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The CFTR protein is an epithelial ion channel contributing to the regulation of absorption and secretion of salt and water in various tissues, including the lung, sweat glands, pancreas, and gastrointestinal tract. 4 , 5 Cystic fibrosis is caused by mutations in CFTR that affect . . .

Patients with homozygous Phe508del cystic fibrosis were assigned to receive combination tezacaftor–ivacaftor or placebo for 24 weeks. The combination resulted in an FEV 1 that was 4 percentage points higher and a pulmonary-exacerbation rate that was 35% lower than with placebo.

Gliomas are morbid brain tumors that are extremely resistant to available chemotherapy and radiology treatments. Some studies have suggested that calcium-activated potassium channels contribute to the high proliferative potential of tumor cells, including gliomas. However, other publications demonstrated no role for these channels or even assigned them antitumorogenic properties. In this work we characterized the expression and functional contribution to proliferation of Ca(2+)-activated K(+) channels in human glioblastoma cells. Quantitative RT-PCR detected transcripts for the big conductance (BK), intermediate conductance (IK1), and small conductance (SK2) K(+) channels in two glioblastoma-derived cell lines and a surgical sample of glioblastoma multiforme. Functional expression of BK and IK1 in U251 and U87 glioma cell lines and primary glioma cultures was verified using whole-cell electrophysiological recordings. Inhibitors of BK (paxilline and penitrem A) and IK1 channels (clotrimazole and TRAM-34) reduced U251 and U87 proliferation in an additive fashion, while the selective blocker of SK channels UCL1848 had no effect. However, the antiproliferative properties of BK and IK1 inhibitors were seen at concentrations that were higher than those necessary to inhibit channel activity. To verify specificity of pharmacological agents, we downregulated BK and IK1 channels in U251 cells using gene-specific siRNAs. Although siRNA knockdowns caused strong reductions in the BK and IK1 current densities, neither single nor double gene silencing significantly affected rates of proliferation. Taken together, these results suggest that Ca(2+)-activated K(+) channels do not play a critical role in proliferation of glioma cells and that the effects of pharmacological inhibitors occur through their off-target actions.

Ivacaftor (VX-770), a cystic fibrosis transmembrane conductance regulator (CFTR) potentiator, has been shown to improve lung function, pulmonary exacerbation rate, respiratory symptoms, and weight gain compared with placebo in patients with cystic fibrosis aged 12 years or older with a G551D-CFTR mutation. This randomized, double-blind, placebo-controlled trial evaluated ivacaftor in patients with cystic fibrosis aged 6-11 years with a G551D-CFTR mutation on at least one allele. Patients were randomly assigned to receive ivacaftor administered orally at 150 mg (n = 26) or placebo (n = 26) every 12 hours for 48 weeks in addition to existing prescribed cystic fibrosis therapies. Despite near-normal mean baseline values in FEV1, patients receiving ivacaftor had a significant increase in percent predicted FEV1 from baseline through Week 24 versus placebo group (treatment effect, 12.5 percentage points; P < 0.001). Effects on pulmonary function were evident by 2 weeks, and a significant treatment effect was maintained through Week 48. Patients treated with ivacaftor gained, on average, 2.8 kg more than those receiving placebo at Week 48 (P < 0.001). The change from baseline through Week 48 in the concentration of sweat chloride, a measure of CFTR activity, with ivacaftor was -53.5 mmol/L (P < 0.001) versus placebo. The incidence of adverse events was similar in the two groups. In patients who are younger and healthier than those in previously studied populations, ivacaftor demonstrated a significant improvement in pulmonary function, weight, and CFTR activity compared with placebo. Clinical trial registered with www.clinicaltrials.gov (NCT00909727).

Summary When the rate of photosynthesis is greatly diminished, such as during severe drought, extreme temperature or low light, it seems advantageous for plants to close stomata and completely halt water loss. However, water loss continues through the cuticle and incompletely closed stomata, together constituting the leaf minimum conductance (gmin). In this review, we critically evaluate the sources of variation in gmin, quantitatively compare various methods for its estimation, and illustrate the role of gmin in models of leaf gas exchange. A literature compilation of gmin as measured by the weight loss of detached leaves is presented, which shows much variation in this trait, which is not clearly related to species groups, climate of origin or leaf type. Much evidence points to the idea that gmin is highly responsive to the growing conditions of the plant, including soil water availability, temperature and air humidity – as we further demonstrate with two case studies. We pay special attention to the role of the minimum conductance in the Ball–Berry model of stomatal conductance, and caution against the usual regression-based method for its estimation. The synthesis presented here provides guidelines for the use of gmin in ecosystem models, and points to clear research gaps for this drought tolerance trait.