Activation mechanism and novel binding sites of the BKCa channel activator CTIBD.

The large-conductance calcium-activated potassium (BKCa) channel, which is crucial for urinary bladder smooth muscle relaxation, is a potential target for overactive bladder treatment. Our prior work unveiled CTIBD as a promising BKCa channel activator, altering V 1/2 and G max This study investigates CTIBD's activation mechanism, revealing its independence from the Ca2+ and membrane voltage sensing of the BKCa channel. Cryo-electron microscopy disclosed that two CTIBD molecules bind to hydrophobic regions on the extracellular side of the lipid bilayer. Key residues (W22, W203, and F266) are important for CTIBD binding, and their replacement with alanine reduces CTIBD-mediated channel activation. The triple-mutant (W22A/W203A/F266A) channel showed the smallest V 1/2 shift with a minimal impact on activation and deactivation kinetics by CTIBD. At the single-channel level, CTIBD treatment was much less effective at increasing P o in the triple mutant, mainly because of a drastically increased dissociation rate compared with the WT. These findings highlight CTIBD's mechanism, offering crucial insights for developing small-molecule treatments for BKCa-related pathophysiological conditions.

Medication adherence to CFTR modulators in patients with cystic fibrosis: a systematic review.

BACKGROUND: In the last decade, a fundamental shift in the treatment of cystic fibrosis (CF) took place due to the introduction of CF transmembrane conductance regulator (CFTR) modulators. Adequate medication adherence is a prerequisite for their effectiveness, but little is known about adherence to CFTR modulators. We aimed to assess the extent of medication adherence to CFTR modulators in patients with CF and assess which characteristics are associated with adherence. METHODS: A systematic review following PRISMA guidelines was performed. Studies needed to report adherence to CFTR modulators. Main outcomes were: 1) level of medication adherence and 2) associations of demographic and/or clinical characteristics with adherence. RESULTS: In total, 4082 articles were screened and 21 full-text papers were assessed for eligibility. Ultimately, seven studies were included. Most studies were retrospective and focused on adherence to ivacaftor or lumacaftor-ivacaftor with only one focusing on elexacaftor-tezacaftor-ivacaftor. The majority used pharmacy refill data with adherence determined with the proportion of days covered (PDC) or the medication possession ratio (MPR). One study additionally used electronic monitoring and patient self-reported adherence. Adherence was 0.62-0.99 based on pharmacy data (PDC or MPR), 61% via electronic monitoring and 100% via self-report. Age <18 years appeared to be associated with good adherence, as was a higher lung function. CONCLUSIONS: Despite the wide variety of adherence methods used, adherence to CFTR modulators is suboptimal, based on objective measures such as pharmacy refill data or electronic monitoring. CFTR modulator adherence measurement and definitions requires more standardisation with a preference for objective and granular methods.

Real-world impact of ivacaftor in people with cystic fibrosis and select ivacaftor-responsive mutations.

BACKGROUND: Ivacaftor approval was extended to people with cystic fibrosis (CF) with ≥1 of 28 additional ivacaftor-responsive mutations in the USA in 2017 based on preclinical in vitro data. This retrospective, observational study assessed real-world clinical response to ivacaftor in people with CF with ≥1 of these mutations, using data from the US Cystic Fibrosis Foundation Patient Registry. METHODS: Participants aged ≥2 years with ≥1 of 28 eligible mutations initiating ivacaftor between May 2017 and December 2018 were included. Clinical outcomes data were evaluated for ≤1 year before and ≤2 years after ivacaftor initiation. Participants initiating ivacaftor between May and December 2017 (2017 cohort) were used for the primary analysis because up to 2 years of post-ivacaftor-initiation data were available. Analyses were descriptive; key outcomes included percent predicted forced expiratory volume in 1 s (ppFEV1), body mass index (BMI) and BMI z-score, pulmonary exacerbations (PEx) and hospitalisations. RESULTS: The study included 1004 eligible participants. In the 2017 cohort (n=613), mean absolute change in ppFEV1 from pre-ivacaftor initiation was 1.9 (95% CI 1.4, 2.4) and 1.8 (95% CI 1.0, 2.7) percentage points in years 1 and 2 post-ivacaftor initiation, respectively; mean absolute change in BMI was 0.6 (95% CI 0.5, 0.7) and 1.0 (95% CI 0.8, 1.2) kg/m2 in years 1 and 2, respectively; BMI z-score was unchanged. Annualised event rates of PEx and hospitalisations per patient-year were lower with ivacaftor (0.24 (95% CI 0.21, 0.26) and 0.28 (95% CI 0.25, 0.31), respectively) compared with pre-ivacaftor initiation (0.41 (95% CI 0.37, 0.46) and 0.45 (95% CI 0.41, 0.49), respectively). CONCLUSIONS: These real-world observational study findings support the effectiveness of ivacaftor in people with CF aged ≥2 years with selected CFTR mutations.

Comparison of a novel potentiator of CFTR channel activity to ivacaftor in ameliorating mucostasis caused by cigarette smoke in primary human bronchial airway epithelial cells.

BACKGROUND: Cystic Fibrosis causing mutations in the gene CFTR, reduce the activity of the CFTR channel protein, and leads to mucus aggregation, airway obstruction and poor lung function. A role for CFTR in the pathogenesis of other muco-obstructive airway diseases such as Chronic Obstructive Pulmonary Disease (COPD) has been well established. The CFTR modulatory compound, Ivacaftor (VX-770), potentiates channel activity of CFTR and certain CF-causing mutations and has been shown to ameliorate mucus obstruction and improve lung function in people harbouring these CF-causing mutations. A pilot trial of Ivacaftor supported its potential efficacy for the treatment of mucus obstruction in COPD. These findings prompted the search for CFTR potentiators that are more effective in ameliorating cigarette-smoke (CS) induced mucostasis. METHODS: Small molecule potentiators, previously identified in CFTR binding studies, were tested for activity in augmenting CFTR channel activity using patch clamp electrophysiology in HEK-293 cells, a fluorescence-based assay of membrane potential in Calu-3 cells and in Ussing chamber studies of primary bronchial epithelial cultures. Addition of cigarette smoke extract (CSE) to the solutions bathing the apical surface of Calu-3 cells and primary bronchial airway cultures was used to model COPD. Confocal studies of the velocity of fluorescent microsphere movement on the apical surface of CSE exposed airway epithelial cultures, were used to assess the effect of potentiators on CFTR-mediated mucociliary movement. RESULTS: We showed that SK-POT1, like VX-770, was effective in augmenting the cyclic AMP-dependent channel activity of CFTR. SK-POT-1 enhanced CFTR channel activity in airway epithelial cells previously exposed to CSE and ameliorated mucostasis on the surface of primary airway cultures. CONCLUSION: Together, this evidence supports the further development of SK-POT1 as an intervention in the treatment of COPD.

Impact of lumacaftor/ivacaftor on nutrition and growth in modulator-naïve children over 24 weeks.

BACKGROUND: Cystic fibrosis transmembrane conductance regulator (CFTR) modulators improve nutritional status and are of importance in achieving normal growth among younger children with CF. The study was designed to examine CFTR modulator-associated changes in nutrition status, including bile acids and fatty acids after lumacaftor/ivacaftor therapy for 24 weeks. METHODS: Children 2 to 5.9 years were recruited from US and Canadian CF Centers. Eligible children were lumacaftor/ivacaftor naïve and approved to initiate therapy. Anthropometrics, diet, energy expenditure, nutrition biomarkers, pancreatic status, serum and fecal calprotectin, serum bile acids and plasma fatty acids were measured. Changes from baseline at 12 and 24 weeks were examined using mixed effects linear regression modeling. RESULTS: Weight-for-age z-score (WAZ) increased at 12 (0.15 ± 0.1, p = 0.01) and 24 weeks (0.23 ± 0.1, p = 0.001) from baseline following modulator therapy. Head circumference-for-age (HCZ) increased at 12 weeks compared to baseline (0.22 ± 0.1, p = 0.03) and subscapular Z score increased from baseline at 24 weeks following therapy (0.33 ± 0.1, p = 0.02). There were no changes in energy expenditure. Serum total bile acids (6.7 ± 2.0, p = 0.001), chenodeoxycholic acid (CDCA) (2.4 ± 1.1, p = 0.001), and cholic acid (CA) (3.5 ± 0.8, p < 0.0001) increased at 24 weeks compared to baseline. Fecal calprotectin decreased at 12 and 24 weeks compared to baseline (-463 ± 310, p = 0.03 and 566 ± 347, p = 0.047). A number of plasma fatty acids changed over the course of 24 weeks of therapy. Noteably, alpha-linolenic acid (ALA) decreased at 12 and 24 weeks (-24 ± 10,p = 0.03 and -18 ± 10, p = 0.02, respectively). CONCLUSIONS: Overall, young children experienced favorable changes in nutritional and growth, with the exception of plasma ALA status in the first 24 weeks of lumacaftor/ivacaftor therapy.

Impact of lumacaftor/ivacaftor on the bacterial and fungal respiratory pathogens in cystic fibrosis: a prospective multicenter cohort study in Sweden.

BACKGROUND: A significant decline in pulmonary exacerbation rates has been reported in CF patients homozygous for F508del treated with lumacaftor/ivacaftor. However, it is still unclear whether this reduction reflects a diminished microbiological burden. OBJECTIVES: The aim of this study was to determine the impact of lumacaftor/ivacaftor on the bacterial and fungal burden. DESIGN: The study is a prospective multicenter cohort study including 132 CF patients homozygous for F508del treated with lumacaftor/ivacaftor. METHODS: Clinical parameters as well as bacterial and fungal outcomes 1 year after initiation of lumacaftor/ivacaftor were compared to data from 2 years prior to initiation of the treatment. Changes in the slope of the outcomes before and after the onset of treatment were assessed. RESULTS: Lung function measured as ppFEV1 (p < 0.001), body mass index (BMI) in adults (p < 0.001), and BMI z-score in children (p = 0.007) were improved after initiation of lumacaftor/ivacaftor. In addition, the slope of the prevalence of Streptococcus pneumoniae (p = 0.007) and Stenotrophomonas maltophilia (p < 0.001) shifted from positive to negative, that is, became less prevalent, 1 year after treatment, while the slope for Candida albicans (p = 0.009), Penicillium spp (p = 0.026), and Scedosporium apiospermum (p < 0.001) shifted from negative to positive. CONCLUSION: The current study showed a significant improvement in clinical parameters and a reduction of some of CF respiratory microorganisms 1 year after starting with lumacaftor/ivacaftor. However, no significant changes were observed for Pseudomonas aeruginosa, Staphylococcus aureus, or Aspergillus fumigatus, key pathogens in the CF context.

Safety and efficacy of ivacaftor in infants aged 1 to less than 4 months with cystic fibrosis.

BACKGROUND: Ivacaftor (IVA) has been shown to be safe and efficacious in children aged ≥4 months with cystic fibrosis (CF) and CFTR gating variants. We evaluated safety, pharmacokinetics (PK), and efficacy of IVA in a small cohort of infants aged 1 to <4 months with CF. METHODS: In this phase 3, open-label study, infants 1 to <4 months with CF and an IVA-responsive CFTR variant received an initial low dose of IVA based on age and weight. Because IVA is a sensitive CYP3A substrate and CYP3A maturation is uncertain in infants, doses were adjusted at day 15 to better match median adult exposures based on individual PK measurements taken on day 4. Primary endpoints were safety and PK measurements. RESULTS: Seven infants (residual function CFTR variants [n=5]; minimal function CFTR variants [n=2]) received ≥1 dose of IVA. Six infants had doses adjusted at day 15 and one infant did not require dose adjustment; subsequent PK analyses showed mean trough concentrations for IVA and metabolites were within range of prior clinical experience. Four infants (57.1%) had adverse events (AEs); no serious AEs were noted. One infant discontinued study drug due to a non-serious AE of elevated alanine aminotransferase >8x the upper limit of normal. Mean sweat chloride concentration decreased (-40.3 mmol/L [SD: 29.2]) through week 24. Improvements in biomarkers of pancreatic function and intestinal inflammation, as well as growth parameters, were observed. CONCLUSIONS: In this small, open-label study, IVA dosing in infants achieved exposures previously shown to be safe and efficacious. Because PK was predictable, a dosing regimen based on age and weight is proposed. IVA was generally safe and well tolerated, and led to improvements in CFTR function, markers of pancreatic function and intestinal inflammation, and growth parameters, supporting use in infants as young as 1 month of age.

Multisystemic Effects of Elexacaftor-Tezacaftor-Ivacaftor in Adults with Cystic Fibrosis and Advanced Lung Disease.

Rationale: Limited data exist on the safety and effectiveness of elexacaftor-tezacaftor-ivacaftor (ETI) in people with cystic fibrosis (pwCF) and advanced lung disease. Objectives: To evaluate the effects of ETI in an unselected population of pwCF and advanced lung disease. Methods: A prospective observational study, including all adults aged 18 years and older with percentage predicted forced expiratory volume in 1 second (ppFEV1) ⩽ 40 who initiated ETI from December 2019 to June 2021 in France, was conducted. PwCF were followed until August 8, 2022. Results: ETI was initiated in 434 pwCF with a median ppFEV1 of 30 (interquartile range, 25-35), including 27 with severe cystic fibrosis liver disease and 183 with diabetes. PwCF were followed for a median of 587 (interquartile range, 396-728) days after ETI initiation. Discontinuation of ETI occurred in 12 (2.8%) pwCF and was due mostly to lung transplantation (n = 5) or death (n = 4). Absolute increase in ppFEV1 by a mean of +14.2% (95% confidence interval, 13.1-15.4%) occurred at 1 month and persisted throughout the study. Increase in ppFEV1 in the youngest age quartile was almost twice that of the oldest quartile (P < 0.001); body mass index < 18.5 kg/m2 was found in 38.6% at initiation versus 11.3% at 12 months (P = 0.0001). Increases in serum concentrations of vitamins A and E, but not 25-hydroxy vitamin D3, were observed. Significant reductions in the percentages of pwCF using oxygen therapy, noninvasive ventilation, nutritional support, and inhaled and systemic therapies (including antibiotics) were observed; insulin was discontinued in 12% of patients with diabetes. Conclusions: ETI is safe in pwCF and advanced lung disease, with multisystem pulmonary and extrapulmonary benefits.

Safety and efficacy of elexacaftor/tezacaftor/ivacaftor in people with Cystic Fibrosis following liver transplantation: A systematic review.

BACKGROUND & AIMS: Cystic Fibrosis (CF) liver disease progresses to liver failure requiring transplantation in about 3 % of patients, 0.7 % of CF patients are post liver transplant. The prognosis of CF has improved with the introduction of elexacaftor/tezacaftor/ivacaftor (ETI). Due to the paucity of data and concerns regarding interactions with immunosuppressive drug regimens, there is no general consensus on use of ETI post liver transplantation. The aim of this review is to report the safety and efficacy of ETI in CF patients who underwent liver transplantation. METHODS: A systematic review was conducted through MEDLINE/Pubmed and EMBASE databases. English-written articles reporting clinical data on liver transplanted CF patients treated with ETI were included. Article quality was evaluated using the Critical Appraisal Checklist for Case Reports. RESULTS: Twenty cases were retrieved from 6 reports. Temporary discontinuation and/or dose reduction due to elevated transaminases was required in 5 cases. ETI restarted on a reduced dose was tolerated in 3 out of 5 patients, 1 patient tolerated full dose. Tacrolimus dose change was required in 14 cases, in 1 case ETI was discontinued due to tacrolimus toxicity. Improvement in percentage predicted FEV1 was noted in 15/19 patients (median +17 %, range 8 %-38 %). CONCLUSIONS: In the majority of liver transplanted patients ETI is well tolerated, although adverse events and liver function abnormalities may occur. Close monitoring of liver function and tacrolimus level is warranted. Significant improvement in lung function after ETI initiation is confirmed, highlighting the importance of accessing this medication for this group of patients.

In utero and postnatal ivacaftor/lumacaftor therapy rescues multiorgan disease in CFTR-F508del ferrets.

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, with F508del being the most prevalent mutation. The combination of CFTR modulators (potentiator and correctors) has provided benefit to CF patients carrying the F508del mutation; however, the safety and effectiveness of in utero combination modulator therapy remains unclear. We created a F508del ferret model to test whether ivacaftor/lumacaftor (VX-770/VX-809) therapy can rescue in utero and postnatal pathologies associated with CF. Using primary intestinal organoids and air-liquid interface cultures of airway epithelia, we demonstrate that the F508del mutation in ferret CFTR results in a severe folding and trafficking defect, which can be partially restored by treatment with CFTR modulators. In utero treatment of pregnant jills with ivacaftor/lumacaftor prevented meconium ileus at birth in F508del kits and sustained postnatal treatment of CF offspring improved survival and partially protected from pancreatic insufficiency. Withdrawal of ivacaftor/lumacaftor treatment from juvenile CF ferrets reestablished pancreatic and lung diseases, with altered pulmonary mechanics. These findings suggest that in utero intervention with a combination of CFTR modulators may provide therapeutic benefits to individuals with F508del. This CFTR-F508del ferret model may be useful for testing therapies using clinically translatable endpoints.

Predicting lung function decline in cystic fibrosis: the impact of initiating ivacaftor therapy.

BACKGROUND: Modulator therapies that seek to correct the underlying defect in cystic fibrosis (CF) have revolutionized the clinical landscape. Given the heterogeneous nature of lung disease progression in the post-modulator era, there is a need to develop prediction models that are robust to modulator uptake. METHODS: We conducted a retrospective longitudinal cohort study of the CF Foundation Patient Registry (N = 867 patients carrying the G551D mutation who were treated with ivacaftor from 2003 to 2018). The primary outcome was lung function (percent predicted forced expiratory volume in 1 s or FEV1pp). To characterize the association between ivacaftor initiation and lung function, we developed a dynamic prediction model through covariate selection of demographic and clinical characteristics. The ability of the selected model to predict a decline in lung function, clinically known as an FEV1-indicated exacerbation signal (FIES), was evaluated both at the population level and individual level. RESULTS: Based on the final model, the estimated improvement in FEV1pp after ivacaftor initiation was 4.89% predicted (95% confidence interval [CI]: 3.90 to 5.89). The rate of decline was reduced with ivacaftor initiation by 0.14% predicted/year (95% CI: 0.01 to 0.27). More frequent outpatient visits prior to study entry and being male corresponded to a higher overall FEV1pp. Pancreatic insufficiency, older age at study entry, a history of more frequent pulmonary exacerbations, lung infections, CF-related diabetes, and use of Medicaid insurance corresponded to lower FEV1pp. The model had excellent predictive accuracy for FIES events with an area under the receiver operating characteristic curve of 0.83 (95% CI: 0.83 to 0.84) for the independent testing cohort and 0.90 (95% CI: 0.89 to 0.90) for 6-month forecasting with the masked cohort. The root-mean-square errors of the FEV1pp predictions for these cohorts were 7.31% and 6.78% predicted, respectively, with standard deviations of 0.29 and 0.20. The predictive accuracy was robust across different covariate specifications. CONCLUSIONS: The methods and applications of dynamic prediction models developed using data prior to modulator uptake have the potential to inform post-modulator projections of lung function and enhance clinical surveillance in the new era of CF care.

Dual and triple modulator therapy for chronic rhinosinusitis in cystic fibrosis patients.

BACKGROUND: The introduction of CFTR modulators has changed the landscape in the treatment of cystic fibrosis (CF) and early case series have shown improvements in sinonasal outcomes in this patient population. METHODOLOGY: A real-word data study was performed to evaluate the impact of dual therapy with tezacaftor/ivacaftor (TEZ/IVA) and triple therapy with elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) on CF-related chronic rhinosinusitis (CRS), by comparing subjective and objective outcome measures at baseline, 12 months after treatment with TEZ/IVA and six months after treatment with ELX/TEZ/IVA. RESULTS: In total, 43 CF patients, with a mean age of 32 years, were included. After triple therapy, significant improvements in overall visual analogue scale, SNOT-22, Lund Kennedy, nasal polyps, and Lund-Mackay scores were observed, whereas no beneficial effect could be seen in patients treated with dual therapy. Bacterial upper airway colonization did not differ pre- and postmodulator therapy in the present study. The number of responders to dual and triple therapy is 23.8% and 63.2% of the patients, respectively. CONCLUSIONS: Triple therapy with ELX/TEZ/IVA is superior to dual therapy with TEZ/IVA in the treatment of CF-CRS, as significantly reduced sinonasal complaints, nasal endoscopy and CT scores were observed after triple therapy, whereas this was not the case for dual therapy.

Alterations in the fecal microbiota in patients with advanced cystic fibrosis liver disease after 6 months of elexacaftor/tezacaftor/ivacaftor.

BACKGROUND: Cystic fibrosis associated liver disease (CFLD) carries a significant disease burden with no effective preventive therapies. According to the gut-liver axis hypothesis for CFLD pathogenesis, dysbiosis and increased intestinal inflammation and permeability permit pathogenic bacterial translocation into the portal circulation, leading to hepatic inflammation and fibrosis. Evaluating the effect of CFTR (cystic fibrosis transmembrane conductance regulator) modulation with elexacaftor/tezacaftor/ivacaftor (ETI) may help determine the role of CFTR in CFLD and increase understanding of CFLD pathogenesis, which is critical for developing therapies. We aimed to characterize the fecal microbiota in participants with CF with and without advanced CFLD (aCFLD) before and after ETI. METHODS: This is an ancillary analysis of stool samples from participants ages ≥12 y/o enrolled in PROMISE (NCT04038047). Included participants had aCFLD (cirrhosis with or without portal hypertension, or non-cirrhotic portal hypertension) or CF without liver disease (CFnoLD). Fecal microbiota were defined by shotgun metagenomic sequencing at baseline and 1 and 6 months post-ETI. RESULTS: We analyzed 93 samples from 34 participants (11 aCFLD and 23 CFnoLD). Compared to CFnoLD, aCFLD had significantly higher baseline relative abundances of potential pathogens Streptococcus salivarius and Veillonella parvula. Four of 11 aCFLD participants had an initially abnormal fecal calprotectin that normalized 6 months post-ETI, correlating with a significant decrease in S. salivarius and a trend towards decreasing V. parvula. CONCLUSIONS: These results support an association between dysbiosis and intestinal inflammation in CFLD with improvements in both post-ETI, lending further support to the gut-liver axis in aCFLD.