Elexacaftor-tezacaftor-ivacaftor Research Articles

P355 Long-term impact of elexacaftor/tezacaftor/ivacaftor (ETI) therapy on weight gain and body composition in adult cystic fibrosis patients: a retrospective analysis

P355 Long-term impact of elexacaftor/tezacaftor/ivacaftor (ETI) therapy on weight gain and body composition in adult cystic fibrosis patients: a retrospective analysis

WS12.03 Elexacaftor/tezacaftor/ivacaftor (ETI) therapy increases fat-soluble vitamin levels in children with cystic fibrosis

WS12.03 Elexacaftor/tezacaftor/ivacaftor (ETI) therapy increases fat-soluble vitamin levels in children with cystic fibrosis

EPS10.02 Gene expression profiles of intestinal organoids from patients with cystic fibrosis upon their exposure to elexacaftor/tezacaftor/ivacaftor (ETI)

EPS10.02 Gene expression profiles of intestinal organoids from patients with cystic fibrosis upon their exposure to elexacaftor/tezacaftor/ivacaftor (ETI)

P230 Real-life impact on elexacaftor/tezacaftor/ivacaftor (ETI) on sputum microbiology in a large adult cystic fibrosis (CF) unit

P230 Real-life impact on elexacaftor/tezacaftor/ivacaftor (ETI) on sputum microbiology in a large adult cystic fibrosis (CF) unit

EPS9.04 Lung epithelial 3D air-liquid-interface culture systems for high-resolution investigations of bacterial infection dynamics during treatment with elexacaftor/tezacaftor/ivacaftor (ETI)

EPS9.04 Lung epithelial 3D air-liquid-interface culture systems for high-resolution investigations of bacterial infection dynamics during treatment with elexacaftor/tezacaftor/ivacaftor (ETI)

Anti-inflammatory effects of elexacaftor/tezacaftor/ivacaftor in adults with cystic fibrosis heterozygous for F508del.

Inflammation is a key driver in the pathogenesis of cystic fibrosis (CF). We assessed the effectiveness of elexacaftor/tezacaftor/ivacaftor (ETI) therapy on downregulating systemic and immune cell-derived inflammatory cytokines. We also monitored the impact of ETI therapy on clinical outcome. Adults with CF, heterozygous for F508del (n = 19), were assessed at baseline, one month and three months following ETI therapy, and clinical outcomes were measured, including sweat chloride, lung function, weight, neutrophil count and C-reactive protein (CRP). Cytokine quantifications were measured in serum and following stimulation of peripheral blood mononuclear cells (PBMCs) with lipopolysaccharide (LPS) and adenosine triphosphate and analysed using LEGEND plex™ Human Inflammation Panel 1 by flow cytometry (n = 19). ASC specks were measured in serum and caspase-1 activity and mRNA levels determined from stimulated PBMCs were determined. Patients remained stable over the study period. ETI therapy resulted in decreased sweat chloride concentrations (p < 0.0001), CRP (p = 0.0112) and neutrophil count (p = 0.0216) and increased percent predicted forced expiratory volume (ppFEV1) (p = 0.0399) from baseline to three months, alongside a trend increase in weight. Three months of ETI significantly decreased IL-18 (p< 0.0011, p < 0.0001), IL-1β (p<0.0013, p = 0.0476), IL-6 (p = 0.0109, p = 0.0216) and TNF (p = 0.0028, p = 0.0033) levels in CF serum and following PBMCs stimulation respectively. The corresponding mRNA levels were also found to be reduced in stimulated PBMCs, as well as reduced ASC specks and caspase-1 levels, indicative of NLRP3-mediated production of pro-inflammatory cytokines, IL-1β and IL-18. While ETI therapy is highly effective at reducing sweat chloride and improving lung function, it also displays potent anti-inflammatory properties, which are likely to contribute to improved long-term clinical outcomes.

Extent of foetal exposure to maternal elexacaftor/tezacaftor/ivacaftor during pregnancy.

Cystic fibrosis (CF) patients are living longer and healthier due to improved treatments, e.g. cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy elexacaftor/tezacaftor/ivacaftor (ETI), with treatment possibly occurring in pregnancy. The risk of ETI to foetuses remain unknown. Thus the effect of maternally administered ETI on foetal genetic and structural development was investigated. Pregnant Sprague Dawley rats were orally treated with ETI (6.7mg·kg-1·day-1 elexacaftor + 3.5mg·kg-1·day-1 tezacaftor + 25 mg·kg-1·day-1 ivacaftor) for 7days from E12 to E19. Tissue samples collected at E19 were analysed using histology and RNA sequencing. Histological changes and differentially expressed genes (DEG) were assessed. No overt structural abnormalities were found in foetal pancreas, liver, lung and small intestine after 7-day ETI exposure. Very few non-functionally associated DEG in foetal liver, lung and small intestine were identified using RNA-seq. 29 DEG were identified in thymus (27 up-regulated and two down-regulated) and most were functionally linked to each other. Gene ontology enrichment analysis revealed that multiple muscle-related terms were significantly enriched. Many more DEG were identified in cortex (44 up-regulated and four down-regulated) and a group of these were involved in central nervous system and brain development. Sub-chronic ETI treatment in late pregnancy does not appear to pose a significant risk to the genetic and structural development of many foetal tissues. However, significant gene changes in foetal thymic myoid cells and cortical neuronal development requires future follow-up studies to assess the risk to these organs.

Tezacaftor is a direct inhibitor of sphingolipid delta-4 desaturase enzyme (DEGS)

BackgroundWe recently demonstrated that 48 h exposure of primary human bronchial epithelial (hBE) cells, obtained from both CF (F508del homozygous) and non-CF subjects, to the triple drug combination Elexacaftor/Tezacaftor/Ivacaftor (ETI) results in a CFTR genotype-independent modulation of the de novo synthethic pathway of sphingolipids, with an accumulation of dihydroceramides (dHCer). Since dHCer are converted into ceramides (Cer) by the action of a delta-4 sphingolipid desaturase (DEGS) enzyme, we aimed to better understand this off-target effect of ETI (i.e., not related to CFTR rescue) MethodshBE cells, both F508del and wild-type, were cultured to create fully differentiated bronchial epithelia. We analyzed Cer and dHCer using an LC-MS based method previously developed by our lab. DEGS expression levels in differentiated hBE cells lysates were quantified by western blot analysis. ResultsWe demonstrated that 1) dHCer accumulate in hBE with time following prolonged ETI exposure, that 2) similar inhibition occurs in wild-type primary human hepatocytes and that 3) this does not result in an alteration of DEGS expression. We then proved that 4) ETI is a direct inhibitor of DEGS, that 5) Tezacaftor is the molecule responsible for this effect, that 6) the inhibition is concentration dependent. Finally, after repeated oral administration of ETI to naïve, non-CF, mice, we observed a slight accumulation of dHCer in the brain. ConclusionsWe believe that further investigations on Tezacaftor should be envisaged, particularly for the use of ETI during pregnancy, breastfeeding and in the early stages of development. DEGS dysfunction and dHCer accumulation causes impairment in the development of the nervous system, due to a derangement in myelin formation and maintenance.

Changes in exercise capacity in people with Cystic Fibrosis after one year of Elexacaftor/Tezacaftor/Ivacaftor treatment – A Danish prospective cohort

BackgroundCystic Fibrosis (CF) is an inherited multiorgan disease that causes lung damage and early death. People with CF (pwCF) experience diminished exercise capacity compared to the general population. This is due to an accelerated decline in lung function resulting from recurrent lung infections, declining lung function and nutritional challenges. Since 2020 the CFTR-modulator Elexacaftor/Tezacaftor/Ivacaftor (ETI) has been approved for pwCF aged 12 and above in Denmark. Initial experiences with the medication have shown promising results, including improved lung function and disease stability. To date a limited number of studies have evaluated the impact of CFTR-modulators on exercise capacity in pwCF. ObjectiveThe study aims to assess the impact of one year of ETI treatment, without any further intervention, on exercise capacity measured through cardiopulmonary exercise test (CPET) in pwCF aged 12 years and above. MethodsA Danish prospective registry cohort study including pwCF from CF-Center Copenhagen, Copenhagen University Hospital and CF-Center Aarhus, Aarhus University Hospital. Participants underwent CPET before initiating ETI and at follow up one year later. Primary outcomes were VO₂ peak (ml/kg/min), secondary outcomes were VO2 peak (ml/min), VO2 peak (% pred), watt-max, HR-max and saturation at max. The difference between baseline and follow-up was assessed using a paired-sample t-test and regression analyses were applied to relevant outcomes. ResultsWe included 229 pwCF in the analyses. An increase in oxygen uptake, VO₂ peak (ml/kg/min) from baseline to follow-up was observed; 0.6, 95% CI [0.06; 1.09] p = 0.03. Moreover, significant increase was noted for all other CPET outcomes. Regression analysis showed that changes in FEV₁% pred and BMI could explain some of the differences, 0.05 ml/kg/min, 95% CI [0.01, 0.1] p = 0.02 and -0.5 ml/kg/min, 95% CI [-0.8, -0.2] p = 0.002 respectively. ConclusionAmong Danish pwCF we found a significant, but not clinically relevant, increase in oxygen uptake, after one year of ETI treatment.

Heterogeneity in response to Elexacaftor/Tezacaftor/Ivacaftor in people with cystic fibrosis

BackgroundHighly effective modulators of the CFTR channel have been demonstrated to dramatically impact disease progression and outcome. However, real-world data indicates that the magnitude of the clinical benefit is not equal among all patients receiving the treatment. We aimed to assess the variability in treatment response (as defined by the 6-month change in sweat chloride concentration, forced expiratory volume in one second [ppFEV1], body mass index [BMI], and CF Questionnaire-Revised [CFQ-R] respiratory domain score) and identify potential predictors in a group of patients receiving Elexacaftor-Tezacaftor-Ivacaftor (ETI) triple combination therapy. MethodsThis was a single-center, prospective cohort study enrolling adults with CF at a major center in Italy. We used linear regression models to identify a set of potential predictors (including CFTR genotype, sex, age, and baseline clinical characteristics) and estimate the variability in treatment response. ResultsThe study included 211 patients (median age: 29 years, range: 12–58). Median changes (10–90th percentile) from baseline were: - 56 mEq/L (–76; –27) for sweat chloride concentration, +14.5 points (2.5; 32.0) for ppFEV1, +0.33 standard deviation scores (–0.13; 1.05) for BMI and +17 points (0; 39) for the CFQ-R respiratory domain score. The selected predictors explained 23 % of the variability in sweat chloride concentration changes, 18 % of the variability in ppFEV1 changes, 39 % of the variability in BMI changes, and 65 % of the variability in CFQ-R changes. ConclusionsThis study highlights a high level of heterogeneity in treatment response to ETI, which can only be partially explained by the baseline characteristics of the disease.

Elexacaftor/tezacaftor/ivacaftor influences body composition in adults with cystic fibrosis: a fully automated CT-based analysis

A poor nutritional status is associated with worse pulmonary function and survival in people with cystic fibrosis (pwCF). CF transmembrane conductance regulator modulators can improve pulmonary function and body weight, but more data is needed to evaluate its effects on body composition. In this retrospective study, a pre-trained deep-learning network was used to perform a fully automated body composition analysis on chest CTs from 66 adult pwCF before and after receiving elexacaftor/tezacaftor/ivacaftor (ETI) therapy. Muscle and adipose tissues were quantified and divided by bone volume to obtain body size-adjusted ratios. After receiving ETI therapy, marked increases were observed in all adipose tissue ratios among pwCF, including the total adipose tissue ratio (+ 46.21%, p < 0.001). In contrast, only small, but statistically significant increases of the muscle ratio were measured in the overall study population (+ 1.63%, p = 0.008). Study participants who were initially categorized as underweight experienced more pronounced effects on total adipose tissue ratio (p = 0.002), while gains in muscle ratio were equally distributed across BMI categories (p = 0.832). Our findings suggest that ETI therapy primarily affects adipose tissues, not muscle tissue, in adults with CF. These effects are primarily observed among pwCF who were initially underweight. Our findings may have implications for the future nutritional management of pwCF.

Concentrations of dehydroepiandrosterone-sulphate (DHEA-S) in people with cystic fibrosis on and off elexacaftor-tezacaftor-ivacaftor

BackgroundLevels of sulfated Dehydroepiandrosterone (DHEA-S) are unknown in people with Cystic Fibrosis (pwCF). DHEA-S is reported to have an inverse association with inflammation and warrants evaluation in pwCF. MethodsWe compared differences in DHEA-S and other hormones between pwCF (n = 180) and without CF (n = 180) and DHEA-S association with percent predicted forced expiratory volume in one second (ppFEV1). We also evaluated DHEA-S levels in people with CF on elexacaftor-tezacaftor-ivacaftor (ETI) (n = 145). ResultsPwCF (not on ETI) had lower DHEA-S levels compared to healthy non-CF controls. DHEA-S levels in individuals with CF on ETI were similar to those without CF. Lower DHEA-S levels were associated with lower ppFEV1. ConclusionsPwCF (not on ETI) have lower levels of DHEA-S than people without CF or people with CF on ETI. Additional studies are needed to investigate the impact of DHEA-S on the health of pwCF and mechanisms involved.

Predicting weight gain in patients with cystic fibrosis on triple combination modulator.

Cystic fibrosis (CF) is caused by CF transmembrane conductance regulator (CFTR) gene mutations producing dysfunctional CFTR proteins leading to progressive clinical disease. Elexacaftor-tezacaftor-ivacaftor (ETI) remarkably improves lung disease but is associated with substantial weight gain. We performed a single-center longitudinal study predicting 6-month weight gain after ETI initiation. We used linear mixed effects modeling (LME) to determine association of ETI treatment with changing body mass index (BMI). Using linear regression, we examined BMI prediction models with distinct combinations of main effects to identify a model useful for patient counseling. We used up to eight commonly observed clinical characteristics as input variables (age, sex, percent predicted FEV1 [FEV1%], F508del homozygous state, pancreatic sufficiency, HgbA1c, prior modulator use and prior year number of pulmonary exacerbations). We evaluated 154 patients (19-73 years old, 54% female, FEV1% = 19-121, 0-6 prior year pulmonary exacerbations). LME demonstrated an association between ETI use and weight increases. Exhaustive testing suggested a parsimonious linear regression model well-fitted to data that is potentially useful for counseling. The two variable model shows that on average, BMI decreases by 0.045 (95% Confidence Interval [CI] = -0.069 to -0.021, p < 0.001) for every year of age and increases by 0.322 (CI = 0.142 to 0.502, p = 0.001) for each additional prior year exacerbation at the time of ETI initiation. Young patients with many prior year pulmonary exacerbations likely have the largest 6 month weight gain after starting ETI.

Improved Nutritional Outcomes and Gastrointestinal Symptoms in Adult Cystic Fibrosis Patients Treated with Elexacaftor/Tezacaftor/Ivacaftor

Introduction: Cystic fibrosis transmembrane conductance regulator modulator therapy improves nutritional status and quality of life. Clinical trials have shown pancreatic insufficiency conversion, mostly in pediatric patients treated with ivacaftor. Studies with elexacaftor/tezacaftor/ivacaftor (ETI) in older patients have not suggested restoration of exocrine pancreas function, but quality data in adults are lacking. Our aim was to show the effect of ETI in adults with cystic fibrosis (CF) on nutritional status and digestive function. We hypothesized improvement of nutritional parameters and gastrointestinal symptoms, reduction of pancreatic enzyme replacement therapy, but uncertain improvement in exocrine pancreatic function. Methods: We prospectively enrolled adults with CF treated with ETI from August 2021 to June 2022. We measured anthropometric parameters, laboratory nutritional markers, change of fecal elastase, pancreatic enzymes replacement therapy needs, and gastrointestinal symptoms. Results: In the cohort of 29 patients (mean age 29.1 years), 82.8% suffered exocrine pancreatic insufficiency. After ETI, mean BMI increased by 1.20 kg/m2 (p < 0.001), mean body weight by 3.51 kg (p < 0.001), albumin by 2.81 g/L, and prealbumin by 0.06 (both p < 0.001). Only 1 patient, initially pancreatic insufficient (4.5%, p < 0.001), developed pancreatic sufficiency, indicated by increased fecal elastase from 45 μg/g to 442.1 μg/g. Mean change in lipase substitution decreased by 1,969 units/kg/day (p < 0.001) and stools frequency by 1.18 per day (p < 0.001). Conclusion: Our data suggest increased nutritional parameters, lower pancreatic substitution requirements, and improved defecation in adult CF patients on ETI. Improvement in exocrine pancreatic function might be mutation-specific and needs further study.

Elexacaftor/Tezacaftor/Ivacaftor use in Pediatric Cystic Fibrosis Patients with Advanced Liver Disease

BackgroundCystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy extends the life expectancy of people with cystic fibrosis (PwCF). However, CFTR modulators have not been well studied in patients with cystic fibrosis liver disease (CFLD), specifically those with advanced liver disease with portal hypertension. The purpose of this report is to describe the use of elexacaftor/tezacaftor/ivacaftor (ETI) in pediatric CF patients with advanced CFLD. MethodsThis retrospective case series included PwCF < 18 years old with baseline advanced CFLD initiated on ETI. ResultsEleven PwCF and advanced CFLD were treated with ETI; six started a reduced dose regimen. No patient required treatment interruption and four patients received dose changes related to increase in transaminase and/or bilirubin elevations. Mean (SD) change in ppFEV1 from prior to ETI to highest value during therapy was 14.27 % (4.25) (p = 0.007). When evaluating the group as whole, AST decreased from baseline to last reported –15.18 (23.23) units/L (p = 0.054) and ALT slightly increased 0.73 (39.13) units/L (p = 0.96). Bilirubin increased minimally overall for patients with mean change from baseline of 0.83 (1.33) mg/dL [range –0.5–3] (p = 0.17). A model for time on ETI showed a significant decrease in AST over time of 0.955 per month of ETI but no other liver biochemistries were significant. No patient experienced decompensation of CFLD. ConclusionETI therapy in pediatric CF patients with advanced CFLD can be beneficial in improving pulmonary and nutritional outcomes without negative impact on liver biochemistries or hepatic outcomes. Close monitoring is recommended to ensure safety and tolerability.

International disparities in diagnosis and treatment access for cystic fibrosis.

Elexacaftor/tezacaftor/ivacaftor (ETI) has revolutionized cystic fibrosis (CF) treatment. However, previous research has demonstrated profound global disparities in diagnosis and treatment access. If unaddressed, these threaten to widen existing health inequities. Therefore, in this analysis we aimed to reappraise gaps and evaluate progress in diagnosis and treatment equity in high-income (HIC) versus low- and middle-income countries (LMICs). Estimates of the global CF population were made in 158 countries using patient registries, systematic literature searches, and an international survey of 14 CF experts. Estimates of the global burden of undiagnosed CF were made using epidemiological studies identified in literature searches and registry coverage data. The proportion of people receiving ETI was estimated using publicly available revenue data and a survey of 23 national drug pricing databases. 188,336 (163,421-209,204) people are estimated to have CF in 96 countries. Of these, 111,767 (59%) were diagnosed and 51,322 (27%) received ETI. The undiagnosed patient burden is estimated to be 76,569 people, with 82% in LMICs. ETI is reimbursed in 35 HICs, but only one LMIC. Four years after approval, there are 13,723 people diagnosed with CF who live in a country where ETI is inaccessible. This increases to 76,199 when including the estimated undiagnosed population. Equitable access to CFTR modulators must become a top priority for the international CF community. ETI costs up to $322,000 per year but could be manufactured for $5000 to allow access under a voluntary license. Given the extent of disparities, other mechanisms to improve access that circumvent the manufacturer should also be considered.

Effect of Elexacaftor/Tezacaftor/Ivacaftor on Pseudomonas aeruginosa Acquisition and Chronic Infection at a Single Pediatric Cystic Fibrosis Care Center

OBJECTIVES As cystic fibrosis (CF) lung disease progresses, the airways become infected with opportunistic pathogens, such as Pseudomonas aeruginosa (PA). In October 2019, the US Food and Drug Administration approved elexacaftor/tezacaftor/ivacaftor (ETI), a highly effective modulator therapy (HEMT), for individuals 12 years and older with 1 copy of the F508del cystic fibrosis transmembrane conductance regulator (CFTR) mutation. ETI increases the amount of and function of CFTR in the respiratory epithelium, improving mucociliary clearance and reducing static airway mucus, a major trigger for chronic infection and inflammation. METHODS A retrospective analysis of inhaled tobramycin (iTOB) prescriptions between January 1, 2016, and December 31, 2021, was performed. This captured data before and after ETI approval at Children’s Mercy Kansas City (CMKC). The number of individuals with new PA acquisition and individuals considered ­chronically infected was analyzed. RESULTS The number of eradication prescriptions declined in 2020 and 2021, with 15 (7%) and 12 (5%) ­individuals prescribed therapy for those years, respectively. A similar pattern was observed for ­prescriptions for chronic infection. A reduction was seen in 2020 and 2021, with 28 (13%) and 20 (9%) individuals ­prescribed therapy for the respective years. CONCLUSIONS The CMKC experienced a decrease in the number of courses of iTOB prescribed during the last 6 years. The reasons for this are likely multifactorial and may include the implementation of standardized PA surveillance and eradication protocols, the effect of HEMT on mucociliary clearance and airway microbiology, and the poorly understood effects of the SARS-CoV-2 pandemic on the epidemiology of respiratory infections.

Relationship Between Lung Volumes and Heterogeneity in the Response to Elexacaftor/Tezacaftor/Ivacaftor in Patients With Cystic Fibrosis and Advanced Lung Disease

The effects of elexacaftor/tezacaftor/ivacaftor (ETI) on respiratory outcomes for people with cystic fibrosis (CF) were demonstrated by several clinical trials, mainly based on simple spirometry. However, gains in lung function may vary greatly between patients, and predictors of FEV1 change after treatment have yet to be defined. Which ventilatory parameters are involved in the heterogeneity of FEV1 change after 12-month ETI treatment in people with CF and advanced lung disease? This was a multicenter, observational, prospective cohort study at two major CF centers in Italy. We enrolled 47 adults with CF and advanced lung disease (FEV1< 40%or actively listed for lung transplant) who started ETI treatment between December 2019 and December 2021. At treatment initiation and after 12months, patients underwent body plethysmography. Values were compared at the two time points. To assess the relationship between baseline plethysmography measurements and treatment-induced changes in FEV1, we used the Spearman rank correlation coefficient (rs) and median quantile regressions. After 12months of ETI treatment, there was a significant increase in FEV1 %predicted from a median value of 36.0 (25th-75th percentile, 33-39) to 52 (25th-75th percentile, 43-61) (P< .001). Inspiratory capacity/total lung capacity (TLC) ratio also increased from 32.0 (25th-75th percentile, 28.6-36.9) to 36.3 (25th-75th percentile, 33.4-41.3) (P< .001). Specific airway resistance decreased from 263 (25th-75th percentile, 182-405) to 207 (25th-75th percentile, 120-258) (P< .001). Functional residual capacity/TLC ratio decreased from 68.2 (25th-75th percentile, 63.3-71.9) to 63.9 (25th-75th percentile, 58.8-67.1) (P< .001), and residual volume/TLC ratio decreased from 53.1 (25th-75th percentile, 48.3-59.4) to 45.6 (25th-75th percentile, 39.4-49.8) (P< .001). Changes in FEV1 %predicted negatively correlated with baseline functional residual capacity/TLC ratio (rs=-0.38, P= .009) and residual volume/TLC ratio (rs =-0.42, P= .004). After adjustment for age at treatment initiation and cystic fibrosis transmembrane conductance regulator genotype, we estimated that for each 10-unit increase in baseline residual volume/TLC ratio, the expected median change in FEV1 decreased by 2.3 (95%CI,-5.8 to-0.8). ETI was associated with improvements in both static and dynamic volumes in people with CF and advanced lung disease. Heterogeneity in FEV1 %predicted change after 12months of treatment may be predicted by the severity of hyperinflation at baseline.

Correlation between trough concentration and AUC for elexacaftor, tezacaftor and ivacaftor

Therapeutic drug monitoring (TDM) of elexacaftor, tezacaftor, ivacaftor (ETI) could be a useful tool to increase efficacy and decrease the risk of adverse effects in people with Cystic Fibrosis (pwCF). It is however unclear whether drug exposure should be monitored by assessment of trough (Cmin) levels or determination of the area under the curve (AUC). Hence, in this study the correlation between measured Cmin concentration and AUC was evaluated. Serial plasma samples, including Cmin, were drawn after administration of ETI in order to calculate the AUC and assess the correlation between the two parameters. A linear correlation between Cmin and AUC0–24h was found, with Pearson's r correlation coefficients of 0.963, 0.908 and 0.860 for elexacaftor, tezacaftor and ivacaftor, respectively. Exposure of ETI may be monitored by assessment of Cmin levels.

Effect of elexacaftor-tezacaftor-ivacaftor on nasal potential difference and lung function in Phe508del rats.

Introduction: Phe508del is the most common cystic fibrosis transmembrane conductance regulator (CFTR) gene variant that results in the recessive genetic disorder cystic fibrosis (CF). The recent development of highly effective CFTR modulator therapies has led to significant health improvements in individuals with this mutation. While numerous animal models of CF exist, few have a CFTR mutation that is amenable to the triple combination therapy elexacaftor-tezacaftor-ivacaftor (ETI). Methods: To determine the responsiveness of Phe508del rats to ETI, a baseline nasal potential difference was measured. Subsequently, they received ETI daily for 14days, after which post-treatment nasal potential difference, lung mechanics (via flexiVent) and lung ventilation (via X-ray Velocimetry) were assessed. Results: Chloride ion transport in nasal airways was restored in Phe508del rats treated with ETI, but neither lung mechanics nor ventilation were significantly altered. Discussion: These findings validate the usefulness of this rat model for future investigations of modulator therapy in CF.