CFTR Function Research Articles

246 CFTR function is restored in cystic fibrosis rats treated with airway gene-addition therapy as neonates

246 CFTR function is restored in cystic fibrosis rats treated with airway gene-addition therapy as neonates

165 Assessing CFTR function and lung mechanics in Phe508del rats treated with modulators

165 Assessing CFTR function and lung mechanics in Phe508del rats treated with modulators

239 Organoid-guided synergistic treatment of minimal function CFTR mutations with CFTR modulators, roflumilast and simvastatin: A personalized approach

239 Organoid-guided synergistic treatment of minimal function CFTR mutations with CFTR modulators, roflumilast and simvastatin: A personalized approach

325 Corrector elexacaftor mimics potentiator action by increasing numbers of functional CFTR channels via recovery of rescued inactivated F508del

325 Corrector elexacaftor mimics potentiator action by increasing numbers of functional CFTR channels via recovery of rescued inactivated F508del

Use of adenine base editing and homology-independent targeted integration strategies to correct the cystic fibrosis causing variant, W1282X.

Small molecule drugs known as modulators can treat ~ 90% of people with cystic fibrosis (CF), but do not work for premature termination codon variants such as W1282X (c.3846G > A). Here we evaluated two gene editing strategies, Adenine Base Editing (ABE) to correct W1282X, and Homology-Independent Targeted Integration (HITI) of a CFTR superexon comprising exons 23-27 (SE23-27) to enable expression of a CFTR mRNA without W1282X. In Flp-In-293 cells stably expressing a CFTR expression minigene bearing W1282X, ABE corrected 24% of W1282X alleles, rescued CFTR mRNA from nonsense mediated decay and restored protein expression. However, bystander editing at the adjacent adenine (c.3847A > G), caused an amino acid change (R1283G) that affects CFTR maturation and ablates ion channel activity. In primary human nasal epithelial cells homozygous for W1282X, ABE corrected 27% of alleles, but with a notably lower level of bystander editing, and CFTR channel function was restored to 16% of wild-type levels. Using the HITI approach, correct integration of a SE23-27 in intron 22 of the CFTR locus in 16HBEge W1282X cells was detected in 5.8% of alleles, resulting in 7.8% of CFTR transcripts containing the SE23-27 sequence. Analysis of a clonal line homozygous for the HITI-SE23-27 produced full-length mature protein and restored CFTR anion channel activity to 10% of wild-type levels, which could be increased three-fold upon treatment with the triple combination of CF modulators. Overall, these data demonstrate two different editing strategies can successfully correct W1282X, the second most common class I variant, with a concomitant restoration of CFTR function.

Drug-induced eRF1 degradation promotes readthrough and reveals a new branch of ribosome quality control

Suppression of premature termination codons (PTCs) by translational readthrough is a promising strategy to treat a wide variety of severe genetic diseases caused by nonsense mutations. Here, we present two potent readthrough promoters-NVS1.1 and NVS2.1-that restore substantial levels of functional full-length CFTR and IDUA proteins in disease models for cystic fibrosis and Hurler syndrome, respectively. In contrast to other readthrough promoters that affect stop codon decoding, the NVS compounds stimulate PTC suppression by triggering rapid proteasomal degradation of the translation termination factor eRF1. Our results show that this occurs by trapping eRF1 in the terminating ribosome, causing ribosome stalls and subsequent ribosome collisions, and activating a branch of the ribosome-associated quality control network, which involves the translational stress sensor GCN1 and the catalytic activity of the E3 ubiquitin ligases RNF14 and RNF25.

Pathogenic Relationships in Cystic Fibrosis and Renal Diseases: CFTR, SLC26A9 and Anoctamins.

The Cl--transporting proteins CFTR, SLC26A9, and anoctamin (ANO1; ANO6) appear to have more in common than initially suspected, as they all participate in the pathogenic process and clinical outcomes of airway and renal diseases. In the present review, we will therefore concentrate on recent findings concerning electrolyte transport in the airways and kidneys, and the role of CFTR, SLC26A9, and the anoctamins ANO1 and ANO6. Special emphasis will be placed on cystic fibrosis and asthma, as well as renal alkalosis and polycystic kidney disease. In essence, we will summarize recent evidence indicating that CFTR is the only relevant secretory Cl- channel in airways under basal (nonstimulated) conditions and after stimulation by secretagogues. Information is provided on the expressions of ANO1 and ANO6, which are important for the correct expression and function of CFTR. In addition, there is evidence that the Cl- transporter SLC26A9 expressed in the airways may have a reabsorptive rather than a Cl--secretory function. In the renal collecting ducts, bicarbonate secretion occurs through a synergistic action of CFTR and the Cl-/HCO3- transporter SLC26A4 (pendrin), which is probably supported by ANO1. Finally, in autosomal dominant polycystic kidney disease (ADPKD), the secretory function of CFTR in renal cyst formation may have been overestimated, whereas ANO1 and ANO6 have now been shown to be crucial in ADPKD and therefore represent new pharmacological targets for the treatment of polycystic kidney disease.

Pancreatic duct organoid swelling is chloride-dependent

Pancreatic secretions become viscous and acidic in Cystic fibrosis (CF), highlighting the role of CFTR in pancreatic fluid and bicarbonate secretion. Forskolin-induced swelling (FIS) assay developed in intestinal organoids measures residual CFTR function. It is not known whether FIS reflects bicarbonate secretion in pancreas, an organ that secretes near-isotonic NaHCO3 levels. To investigate this, we generated pancreatic duct organoids from CF and non-CF pigs. Epithelial and ductal origin was confirmed with epithelial markers, ion transporters and lack of acinar, islet cell markers. CF organoids were small with no identifiable lumen; CFTR was expressed only in non-CF organoids. Utilizing FIS, organoid size increased only in response to chloride, not bicarbonate. This report highlights pancreatic duct organoids isolated for the first time from CF pigs and evidence for chloride and not bicarbonate driving pancreatic organoid swelling. These organoids would be useful to test chloride permeability of CFTR mutations that cause CF pancreatic disease.

CFTR dysfunction in smooth muscle drives TGFβ dependent airway hyperreactivity

BackgroundThe primary underlying defect in cystic fibrosis (CF) is disrupted ion transport in epithelia throughout the body. It is unclear if symptoms such as airway hyperreactivity (AHR) and increased airway smooth muscle (ASM) volume in people with CF are due to inherent abnormalities in smooth muscle or are secondary to epithelial dysfunction. Transforming Growth Factor beta 1 (TGFβ) is an established genetic modifier of CF lung disease and a known driver of abnormal ASM function. Prior studies have demonstrated that CF mice develop greater AHR, goblet cell hyperplasia, and ASM hypertrophy after pulmonary TGFβ exposure. However, the mechanism driving these abnormalities in CF lung disease, specifically the contribution of CFTR loss in ASM, was unknown.MethodsIn this study, mice with smooth muscle-specific loss of CFTR function (Cftrfl/fl; SM-Cre mice) were exposed to pulmonary TGFβ. The impact on lung pathology and physiology was investigated through examination of lung mechanics, Western blot analysis, and pulmonary histology.ResultsCftrfl/fl; SM-Cre mice treated with TGFβ demonstrated greater methacholine-induced AHR than control mice. However, Cftrfl/fl; SM-Cre mice did not develop increased inflammation, ASM area, or goblet cell hyperplasia relative to controls following TGFβ exposure.ConclusionsThese results demonstrate a direct smooth muscle contribution to CF airway obstruction mediated by TGFβ. Dysfunction in non-epithelial tissues should be considered in the development of CF therapeutics, including potential genetic therapies.

Identification of α-Tocopherol succinate as an RFFL-substrate interaction inhibitor inducing peripheral CFTR stabilization and apoptosis

The E3 ubiquitin ligase RFFL is an apoptotic inhibitor highly expressed in cancers and its knockdown suppresses cancer cell growth and sensitizes to chemotherapy. RFFL also participates in peripheral protein quality control which removes the functional cell surface ΔF508-CFTR channel and reduces the efficacy of pharmaceutical therapy for cystic fibrosis (CF). Although RFFL inhibitors have therapeutic potential for both cancer and CF, they remain undiscovered. Here, a chemical array screening has identified α-tocopherol succinate (αTOS) as an RFFL ligand. NMR analysis revealed that αTOS directly binds to RFFL’s substrate-binding region without affecting the E3 enzymatic activity. Consequently, αTOS inhibits the RFFL-substrate interaction, ΔF508-CFTR ubiquitination and elimination from the plasma membrane of epithelial cells, resulting in the increased functional CFTR channel. Among the α-tocopherol (αTOL) analogs we tested, only αTOS inhibited the RFFL-substrate interaction and increased the cell surface ΔF508-CFTR, depending on RFFL expression. Similarly, the unique proapoptotic effect of αTOS was dependent on RFFL expression. Thus, unlike other αTOL analogs, αTOS acts as an RFFL protein-protein interaction inhibitor which may explain its unique biological properties among αTOL analogs. Moreover, αTOS may act as a CFTR stabilizer, a novel class of drugs that extend cell surface ΔF508-CFTR lifetime.

Personalized CFTR Modulator Therapy for G85E and N1303K Homozygous Patients with Cystic Fibrosis.

CFTR modulator therapy with elexacaftor/tezacaftor/ivacaftor (ETI) has been approved for people with CF and at least one F508del allele in Europe. In the US, the ETI label has been expanded to 177 rare CFTR mutations responsive in Fischer rat thyroid cells, including G85E, but not N1303K. However, knowledge on the effect of ETI on G85E or N1303K CFTR function remains limited. In vitro effects of ETI were measured in primary human nasal epithelial cultures (pHNECs) of a G85E homozygous patient and an N1303K homozygous patient. Effects of ETI therapy in vivo in these patients were assessed using clinical outcomes, including multiple breath washout and lung MRI, and the CFTR biomarkers sweat chloride concentration (SCC), nasal potential difference (NPD) and intestinal current measurement (ICM), before and after initiation of ETI. ETI increased CFTR-mediated chloride transport in G85E/G85E and N1303K/N1303K pHNECs. In the G85E/G85E and the N1303K/N1303K patient, we observed an improvement in lung function, SCC, and CFTR function in the respiratory and rectal epithelium after initiation of ETI. The approach of combining preclinical in vitro testing with subsequent in vivo verification can facilitate access to CFTR modulator therapy and enhance precision medicine for patients carrying rare CFTR mutations.

Olive Leaf Extract (OLE) as a Novel Antioxidant That Ameliorates the Inflammatory Response in Cystic Fibrosis.

The deletion of phenylalanine at position 508 (F508del) produces a misfolded CFTR protein that is retained in the ER and degraded. The lack of normal CFTR channel activity is associated with chronic infection and inflammation which are the primary causes of declining lung function in Cystic Fibrosis (CF) patients. Moreover, LPS-dependent oxidative stress downregulates CFTR function in airway epithelial cells. Olive leaf extract (OLE) is used in traditional medicine for its effects, including anti-oxidant and anti-inflammatory ones. We found that OLE decreased the intracellular ROS levels in a dose-response manner in CFBE cells. Moreover, OLE attenuates the inflammatory response to LPS or IL-1β/TNFα stimulation, mimicking the infection and inflammatory status of CF patients, in CFBE and primary nasal epithelial (HNE) cells. Furthermore, we demonstrated that OLE restored the LPS-mediated decrease of TrikfaftaTM-dependent F508del-CFTR function in CFBE and HNE cultures. These findings provide strong evidence of OLE to prevent redox imbalance and inflammation that can cause chronic lung damage by enhancing the antioxidant activity and attenuating inflammation in CF airway epithelial cells. Additionally, OLE might be used in combination with CFTR modulators therapy to improve their efficacy in CF patients.

The revolution of personalized pharmacotherapies for cystic fibrosis: what does the future hold?

ABSTRACT Introduction Cystic fibrosis (CF), a potentially fatal genetic disease, is caused by loss-of-function mutations in the gene encoding for the CFTR chloride/bicarbonate channel. Modulator drugs rescuing mutant CFTR traffic and function are now in the clinic, providing unprecedented breakthrough therapies for people with CF (PwCF) carrying specific genotypes. However, several CFTR variants are unresponsive to these therapies. Area covered We discussed several therapeutic approaches that are under development to tackle the fundamental cause of CF, including strategies targeting defective CFTR mRNA and/or protein expression and function. Alternatively, defective chloride secretion and dehydration in CF epithelia could be restored by exploiting pharmacological modulation of alternative targets, i.e., ion channels/transporters that concur with CFTR to maintain the airway surface liquid homeostasis (e.g., ENaC, TMEM16A, SLC26A4, SLC26A9, and ATP12A). Finally, we assessed progress and challenges in the development of gene-based therapies to replace or correct the mutant CFTR gene. Expert opinion CFTR modulators are benefiting many PwCF responsive to these drugs, yielding substantial improvements in various clinical outcomes. Meanwhile, the CF therapy development pipeline continues to expand with the development of novel CFTR modulators and alternative therapeutic strategies with the ultimate goal of providing effective therapies for all PwCF in the foreseeable future.

Increased intestinal permeability and downregulation of absorptive ion transporters Nhe3, Dra, and Sglt1 contribute to diarrhea during Clostridioides difficile infection

ABSTRACT Background & Aim Clostridioides difficile infection (CDI) is the leading cause of hospital-acquired diarrhea and pseudomembranous colitis. Two protein toxins, TcdA and TcdB, produced by C. difficile are the major determinants of disease. However, the pathophysiological causes of diarrhea during CDI are not well understood. Here, we investigated the effects of C. difficile toxins on paracellular permeability and apical ion transporters in the context of an acute physiological infection. Methods We studied intestinal permeability and apical membrane transporters in female C57BL/6J mice. Üssing chambers were used to measure paracellular permeability and ion transporter function across the intestinal tract. Infected intestinal tissues were analyzed by immunofluorescence microscopy and RNA-sequencing to uncover mechanisms of transporter dysregulation. Results Intestinal permeability was increased through the size-selective leak pathway in vivo during acute CDI in a 2-day-post infection model. Chloride secretory activity was reduced in the cecum and distal colon during infection by decreased CaCC and CFTR function, respectively. SGLT1 activity was significantly reduced in the cecum and colon, accompanied by ablated SGLT1 expression in colonocytes and increased luminal glucose concentrations. SGLT1 and DRA expression was ablated by either TcdA or TcdB during acute infection, but NHE3 was decreased in a TcdB-dependent manner. The localization of key proteins that link filamentous actin to the ion transporters in the apical plasma membrane was unchanged. However, Sglt1, Nhe3, and Dra were drastically reduced at the transcript level, implicating downregulation of ion transporters in the mechanism of diarrhea during CDI. Conclusions CDI increases intestinal permeability and decreases apical abundance of NHE3, SGLT1, and DRA. This combination likely leads to dysfunctional water and solute absorption in the large bowel, causing osmotic diarrhea. These findings provide insights into the pathophysiological mechanisms underlying diarrhea and may open novel avenues for attenuating CDI-associated diarrhea.

Structural changes in lung morphology detected by MRI after modulating therapy with elexacaftor/tezacaftor/ivacaftor in adolescent and adult patients with cystic fibrosis

IntroductionElexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) improves CFTR function in cystic fibrosis (CF) patients homozygous or heterozygous for F508del mutation. The aim of the study was to evaluate the response to ELX/TEZ/IVA treatment both clinically and morphologically in terms of bronchiectasis, bronchial wall thickening, mucus plugging, abscess and consolidations. MethodsWe retrospectively collected data from CF patients followed at Parma CF Centre (Italy) treated by ELX/TEZ/IVA between March and November 2021. Post-treatment changes in respiratory function, quality of life, sweat chloride concentration, body mass index, pulmonary exacerbations and lung structure by chest magnetic resonance imaging (MRI) were assessed. T2-and T1-weighted sequences were acquired with a 20 min-long scanning protocol on a 1.5T MRI scanner (Philips Ingenia) without administration of intravenous contrast media. Results19 patients (32.5 ± 10.2 years) were included in the study. After 6 months of treatment with ELX/TEZ/IVA, MRI showed significant improvements in the morphological score (p < 0.001), with a reduction in bronchial wall thickening (p < 0.001) and mucus plugging (p 0.01). Respiratory function showed significant improvement in predicted FEV1% (58.5 ± 17.5 vs 71.4 ± 20.1, p < 0.001), FVC% (79.0 ± 11.1 vs 88.3 ± 14.4, p < 0.001), FEV1/FVC (0.61 ± 0.16 vs 0.67 ± 0.15, <0.001) and LCI2.5% (17.8 ± 4.3 vs 15.8 ± 4.1 p < 0.005). Significant improvement was found in body mass index (20.6 ± 2.7 vs 21.9 ± 2.4, p < 0.001), pulmonary exacerbations (2.3 ± 1.3 vs 1.4 ± 1.3 p 0.018) and sweat chloride concentration (96.5 ± 36.6 vs 41.1 ± 16.9, p < 0.001). ConclusionsOur study confirms the efficacy of ELX/TEZ/IVA in CF patients not only from a clinical point of view but also in terms of morphological changes of the lungs.

WS17.05 LUNAR ®-CF mRNA replacement therapy restores CFTR expression and function in human bronchial epithelial cells

Objectives: To evaluate LUNAR®-CF-mediated restoration of CFTR expression and function in fully differentiated human bronchial epithelial cells (HBEC) derived from Cystic Fibrosis (CF) patients.

P071 Evaluation of CFTR modulator efficacy by rectal organoid morphology analysis (ROMA) indexes

Objectives: In patient-derived rectal organoids (PDRO), CFTR modulator efficacy can be evaluated in the forskolin-induced swelling (FIS) assay. In this assay, PDRO swelling in response to acute stimulation with forskolin (Fsk) and potentiator(s) is quantified as a measure of restoration of CFTR function after incubation with corrector(s). However, with high residual CFTR function and/or modulator efficacy (eg. potentiator effect of elexacaftor), PDRO may swell already during the incubation step, before any FIS measurements. The magnitude of modulator efficacy is underestimated in these cases. Comparison with non-CF organoids is therefore also not informative. Rectal organoid morphology analysis (ROMA) indexes have been shown previously (Cuyx Thorax 2021) to discriminate between PDRO from subjects with and without CF.

EPS3.10 Novel CFTR modulator combinations directly address the ΔF508-CFTR NBD1 stability defect and enable full CFTR correction

Objectives: CFTR mutations cause Cystic Fibrosis (CF). CFTR modulating drugs have improved CF outcomes, however, current drugs do not restore normal CFTR function to most patients. ΔF508, the most prevalent CF mutation, causes a loss of F508 within CFTR’s first Nucleotide Binding Domain (NBD1). This destabilizes NBD1 and impairs CFTR folding and function. ΔF508 also impairs CFTR domain-domain assembly, weakening the interface of NBD1 with CFTR’s fourth intracellular loop (ICL4) and transmembrane domain 1 (TMD1). Combining CFTR suppressor mutations that stabilize NBD1 with others that improve CFTR assembly can correct ΔF508 to wild-type (WT) levels. Without NBD1 stabilization, correction is significantly reduced. Drugs that stabilize NBD1 thus have the potential to improve treatment, but no current drugs fully address this defect. To restore WT function to ΔF508-CFTR, Sionna aims to discover and develop small molecule NBD1 stabilizers and CFTR assembly correctors for use in combination.

WS09.04 Enhancement of channel activity of the CFTR protein delivered via gene therapy vectors

Objectives: The advancements in developing CFTR-targeted drugs offer effective treatments for most cystic fibrosis patients. However, there is still a small portion of patients who do not respond to the new drugs. In addition, it is still unclear whether the drugs can maintain the lung function of the patients in long term. Thus, other novel therapeutic strategies should be investigated. Using gene therapy to express a copy of functional CFTR gene in CF cells is an attractive strategy. Currently, one of the major challenges is how to deliver enough functional CFTR protein to CF lungs to achieve therapeutic effects. Our group has been using a gene expression cassette based on the human cytokeratin 18 (K18) gene promoter to express the CFTR gene. Since K18 gene expression has been reported to be enhanced by sodium butyrate, here we are examining whether CFTR expression can be further enhanced following vector delivery to CF cells.

WS04.05 Alternative targets for the treatment of cystic fibrosis basic defect

Correction of CF lung abnormalities may be obtained by restoring the function of CFTR with mutation-specific treatments. A potentially alternative approach is to modulate the activity of other targets to stimulate CFTR-independent anion secretion or inhibit acidification. Despite the increasing interest towards possible alternative targets such as TMEM16A, SLC26A9, SLC26A4 and ATP12A, their precise function and expression in the airways is largely unknown or controversial, and specific modulators are still lacking.