Mutual Effects of Single and Combined CFTR Modulators and Bacterial Infection in Cystic Fibrosis

The impact of cystic fibrosis transmembrane conductance regulator (CFTR) modulators on the pulmonary microbiota

Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy has significantly changed the course of the disease in people with cystic fibrosis (CF) (pwCF). The approved triple therapy of elexacaftor, tezacaftor and ivacaftor (ETI), commercially known as Trikafta, increases CFTR channel function, leading to improvements in sweat chloride concentration, exercise capacity, body mass index, lung function and chronic respiratory symptoms. Because of this, the majority of pwCF are living longer and having fewer CF exacerbations. However, colonization with the common CF respiratory pathogens persists and remains a major cause of morbidity and mortality. Here, we review the current literature on the effect of ETI on the respiratory microbiota and discuss the challenges in addressing CF lung infections in the era of these new life-extending therapies.

The F508del-CFTR trafficking correctors elexacaftor and tezacaftor are CFTR-independent Ca2+-mobilizing agonists normalizing abnormal Ca2+ levels in human airway epithelial cells

BACKGROUND

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) channel. For people with CF (pwCF) affected by the most common pathogenic variant F508del, a tritherapy, named Trikafta/Kaftrio (ETI: elexacaftor (VX-445) /tezacaftor (VX-661) / ivacaftor (VX-770)) was successfully developed. However, in CF airway epithelial cells the calcium homeostasis is also disturbed; it is observed an increased calcium mobilization in CF cells compared to non-CF cells. Here, we studied the effects of ETI on intracellular calcium levels in F508del-CFTR airway epithelial cells to determine whether these compounds, individually or collectively, could normalize intracellular calcium levels.

METHODS

We measured intracellular calcium variations using human airway epithelial cells (hAEC) from pwCF, human bronchial epithelial CFBE41o- F508del-CFTR cells and Chinese Hamster Ovary (CHO) cells using the fluorescent probe Fluo4-AM, in the presence or absence of extracellular calcium. The rescue to the plasma membrane of F508del-CFTR protein by ETI was determined by western blot. The SarcoEndoplasmic Reticulum Calcium ATPase (SERCA), was also analysed by western blotting and by interference assay.

RESULTS

We show that ETI normalizes calcium homeostasis in our cellular models. However, we also found that (1) each ETI-corrector compound is capable of mobilizing calcium acutely in the absence of CFTR, and (2) tezacaftor mobilizes calcium from the endoplasmic reticulum (ER) probably via inhibition of the SERCA pump.

CONCLUSIONS

We show that ETI not only corrects the abnormal trafficking and function of F508del-CFTR but also normalizes calcium homeostasis in our cellular models. Finally, we identified SERCA as a potential intracellular target for tezacaftor.

Evaluating the effects of ivacaftor exposure on Staphylococcus aureus small colony variant development and antibiotic tolerance

Background

Ivacaftor exhibits anti-staphylococcal properties but does not clear Staphylococcus aureus from the lungs of people with cystic fibrosis (pwCF). We assessed whether exposure to therapeutic concentrations of ivacaftor could allow S. aureus to form small colony variants (SCVs), a phenotype commonly associated with bacterial persistence.

Methods

Humanized G551D-CFTR (hG551D) rats were treated with ivacaftor for 7 days. Concentrations in the plasma, epithelial lining fluid and lung tissue lysate were measured using LC-MS/MS. Survival of S. aureus during ivacaftor treatment was assessed in an hG551D rat model of lung infection. S. aureus adaptation to therapeutic concentrations of ivacaftor was investigated in vitro by serial passage in the presence of 10 µM ivacaftor. Bacterial survival in the presence of antimicrobials was evaluated using growth curves and density assays.

Results

Ivacaftor plasma concentrations of treated hG551D rats reached 3.488 ± 1.118 µM, with more variable concentrations in the epithelial lining fluid and lung tissue lysate. During S. aureus infection, ivacaftor-treated hG551D rats returned similar numbers of bacteria from the lung, compared with vehicle-treated controls. Exposure of S. aureus to ivacaftor in vitro led to the formation of ivacaftor-tolerant SCVs with an unstable phenotype and increased antibiotic tolerance.

Conclusions

Treatment with ivacaftor did not alter S. aureus burden in the cystic fibrosis rat and led to the formation of tolerant SCVs in vitro, suggesting that development of an SCV phenotype may allow S. aureus to persist in the cystic fibrosis lung during ivacaftor therapy.

Highly Effective Modulator Therapy: Implications for the Microbial Landscape in Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal recessive multisystem disorder caused by mutations in the cystic fibrosis conductance regulator (CFTR) anion channel. In the lungs specifically, CFTR mutations lead to changes in mucus viscosity and defective mucociliary clearance. Moreover, people with CF (pwCF) mount an insufficient immune response to invading pathogens, which predisposes individuals to chronic airway disease associated with chronic inflammation, colonization, and recurrent infections by mainly opportunistic pathogens. These chronic infections in the CF lung are typically polymicrobial and frequently harbour multidrug-resistant pathogens, making both treatment and eradication very challenging. During the last decade, the development of highly effective CFTR modulator therapy (HEMT) has led to a breakthrough in treatment options for pwCF. While the majority of pwCF now live longer and have fewer CF exacerbations, colonisation with common respiratory pathogens persists, thereby contributing to chronic inflammation and infection. Interestingly, there are limited reports examining the lung microbiome in the post-modulator era. Since ETI treatment is still quite novel and has only been used for about five years by now, this review will be one of the first discussing the current literature on the effect of ETI on CF pathogens. In addition, we will identify unanswered questions that remain from the effect of HEMT on the CF microbiome.

Changing profile of bacterial infection and microbiome in cystic fibrosis: when to use antibiotics in the era of CFTR-modulator therapy

The advent of cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy, especially the triple therapy combining the drugs elexacaftor, tezacaftor, ivacaftor (ETI), has significantly changed the course of the disease in people with cystic fibrosis (pwCF). ETI, which is approved for the majority (80-90%) of pwCF, partially restores CFTR channel function, resulting in improved mucociliary clearance and, consequently, improved lung function, respiratory symptoms and pulmonary exacerbations. The bacterial burden of classical CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus is reduced without reaching eradication in the majority of infected patients. Limited data is available on less common or emerging bacterial pathogens. ETI has a positive effect on the lung microbiome but does not fully restore it to a healthy state. Due to the significant reduction in sputum production under ETI, respiratory samples such as deep-throat swabs are commonly taken, despite their inadequate representation of lower respiratory tract pathogens. Currently, there are still unanswered questions related to this new therapy, such as the clinical impact of infection with cystic fibrosis (CF) pathogens, the value of molecular diagnostic tests, the durability of the effects on respiratory infection and the role of fungal and viral infections. This article reviews the changes in bacterial lung infections and the microbiome in CF to provide evidence for the use of antibiotics in the era of ETI.

Effect of CFTR Modulators on Oxidative Stress and Autophagy in Non-CFTR-Expressing Cells

The triple combination therapy for cystic fibrosis (CF), including elexacaftor, tezacaftor and ivacaftor (ETI or Trikafta), has been shown to improve lung function and reduce pulmonary exacerbations, thereby enhancing the quality of life for most CF patients. Recent findings suggest that both the individual components and ETI may have potential off-target effects, highlighting the need to understand how these modulators impact cellular physiology, particularly in cells that do not express CF transmembrane conductance regulator (CFTR). We used HEK293 cells, as a cell model not expressing the CFTR protein, to evaluate the effect of ETI and each of its components on autophagic machinery and on the Rab5/7 components of the Rab pathway. We firstly demonstrate that the single modulators Teza and Iva, and the combinations ET and ETI, increased ROS production in the absence of their target while decreasing it in cells expressing the CFTR ∆F508del. This increase in cellular stress was followed by an increase in the total level of polyubiquitinated proteins as well as the p62 level and LC3II/LC3I ratio. Furthermore, we found that ETI had the opposite effect on Rabs by increasing Rab5 levels while decreasing Rab7. Interestingly, these changes were abolished by the expression of mutated CFTR. Overall, our data suggest that in the absence of their target, both the individual modulators and ETI increased ROS production and halted both autophagic flux and plasma membrane protein recycling.

Considerations for the use of inhaled antibiotics for Pseudomonas aeruginosa in people with cystic fibrosis receiving CFTR modulator therapy

The major cause of mortality in people with cystic fibrosis (pwCF) is progressive lung disease characterised by acute and chronic infections, the accumulation of mucus, airway inflammation, structural damage and pulmonary exacerbations. The prevalence of Pseudomonas aeruginosa rises rapidly in the teenage years, and this organism is the most common cause of chronic lung infection in adults with cystic fibrosis (CF). It is associated with an accelerated decline in lung function and premature death. New P. aeruginosa infections are treated with antibiotics to eradicate the organism, while chronic infections require long-term inhaled antibiotic therapy. The prevalence of P. aeruginosa infections has decreased in CF registries since the introduction of CF transmembrane conductance regulator modulators (CFTRm), but clinical observations suggest that chronic P. aeruginosa infections usually persist in patients receiving CFTRm. This indicates that pwCF may still need inhaled antibiotics in the CFTRm era to maintain long-term control of P. aeruginosa infections. Here, we provide an overview of the changing perceptions of P. aeruginosa infection management, including considerations on detection and treatment, the therapy burden associated with inhaled antibiotics and the potential effects of CFTRm on the lung microbiome. We conclude that updated guidance is required on the diagnosis and management of P. aeruginosa infection. In particular, we highlight a need for prospective studies to evaluate the consequences of stopping inhaled antibiotic therapy in pwCF who have chronic P. aeruginosa infection and are receiving CFTRm. This will help inform new guidelines on the use of antibiotics alongside CFTRm.

Response to Elexacaftor/Tezacaftor/Ivacaftor in people with cystic fibrosis with the N1303K mutation: Case report and review of the literature

Cystic fibrosis (CF) is caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Thousands of CFTR mutations have been identified, but only a fraction are known to cause CF, with the most common being the prototypical class II CFTR mutation F508del. Elexacaftor-Tezacaftor-Ivacaftor (ETI) is a CFTR modulator that significantly increases ppFEV1 and reduces exacerbation frequencies. It is indicated for people with CF (pwCF) 2 years or older with at least one copy of F508del or one copy of the other 177 CFTR mutations that are responsive to ETI based on clinical or in vitro data. N1303K is the second most common class II mutation in the U.S. but is not yet FDA-approved for CFTR modulator therapy. However, N1303K is very similar to the F508del mutation and reveals variable in vitro responses to ETI. Theratyping provides an opportunity to consider ETI therapy for pwCF with mutations currently not approved by the FDA. We describe the case of an adult CF patient with W1282X and N1303K CFTR mutations and advanced CF lung disease (ACFLD) and declining lung function in which ETI was started after theratyping of nasal cells showed a meaningful response to ETI (current enhanced to over 10% of WT CFTR). The patient experienced clinical improvement with a 5% improvement in ppFEV1 and 10% increase in weight. However, there was no change in sweat chloride and the increase in ppFEV1 was less than what has been described for ACFLD patients with more typical ETI-amenable mutations. However, the response was in line with a few other cases described in the literature. This suggests a partial functional CFTR rescue like first-generation modulators for F508del. Thus, pwCF with N1303K CFTR variant could be considered for ETI eligibility.

A Novel Co-Culture Model Reveals Enhanced CFTR Rescue in Primary Cystic Fibrosis Airway Epithelial Cultures with Persistent Pseudomonas aeruginosa Infection

People with cystic fibrosis (pwCF) suffer from chronic and recurring bacterial lung infections that begin very early in life and contribute to progressive lung failure. CF is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which encodes an ion channel important for maintaining the proper hydration of pulmonary surfaces. When CFTR function is ablated or impaired, airways develop thickened, adherent mucus that contributes to a vicious cycle of infection and inflammation. Therapeutics for pwCF, called CFTR modulators, target the CFTR defect directly, restoring airway surface hydration and mucociliary clearance. However, even with CFTR modulator therapy, bacterial infections persist. To develop a relevant model of diseased airway epithelium, we established a primary human airway epithelium culture system with persistent Pseudomonas aeruginosa infection. We used this model to examine the effects of CFTR modulators on CFTR maturation, CFTR function, and bacterial persistence. We found that the presence of P. aeruginosa increased CFTR mRNA, protein, and function. We also found that CFTR modulators caused a decrease in P. aeruginosa burden. These results demonstrate the importance of including live bacteria to accurately model the CF lung, and that understanding the effects of infection on CFTR rescue by CFTR modulators is critical to evaluating and optimizing drug therapies for all pwCF.

Antibiotic failure: Beyond antimicrobial resistance

Despite significant progress in antibiotic discovery, millions of lives are lost annually to infections. Surprisingly, the failure of antimicrobial treatments to effectively eliminate pathogens frequently cannot be attributed to genetically-encoded antibiotic resistance. This review aims to shed light on the fundamental mechanisms contributing to clinical scenarios where antimicrobial therapies are ineffective (i.e., antibiotic failure), emphasizing critical factors impacting this under-recognized issue. Explored aspects include biofilm formation and sepsis, as well as the underlying microbiome. Therapeutic strategies beyond antibiotics, are examined to address the dimensions and resolution of antibiotic failure, actively contributing to this persistent but escalating crisis. We discuss the clinical relevance of antibiotic failure beyond resistance, limited availability of therapies, potential of new antibiotics to be ineffective, and the urgent need for novel anti-infectives or host-directed therapies directly addressing antibiotic failure. Particularly noteworthy is multidrug adaptive resistance in biofilms that represent 65 % of infections, due to the lack of approved therapies. Sepsis, responsible for 19.7 % of all deaths (as well as severe COVID-19 deaths), is a further manifestation of this issue, since antibiotics are the primary frontline therapy, and yet 23 % of patients succumb to this condition.

Revisiting Host-Pathogen Interactions in Cystic Fibrosis Lungs in the Era of CFTR Modulators

Cystic fibrosis transmembrane conductance regulator (CFTR) modulators, a new series of therapeutics that correct and potentiate some classes of mutations of the CFTR, have provided a great therapeutic advantage to people with cystic fibrosis (pwCF). The main hindrances of the present CFTR modulators are related to their limitations in reducing chronic lung bacterial infection and inflammation, the main causes of pulmonary tissue damage and progressive respiratory insufficiency, particularly in adults with CF. Here, the most debated issues of the pulmonary bacterial infection and inflammatory processes in pwCF are revisited. Special attention is given to the mechanisms favoring the bacterial infection of pwCF, the progressive adaptation of Pseudomonas aeruginosa and its interplay with Staphylococcus aureus, the cross-talk among bacteria, the bronchial epithelial cells and the phagocytes of the host immune defenses. The most recent findings of the effect of CFTR modulators on bacterial infection and the inflammatory process are also presented to provide critical hints towards the identification of relevant therapeutic targets to overcome the respiratory pathology of pwCF.