SNSP113 (PAAG) improves mucociliary transport and lung pathology in the Scnn1b-Tg murine model of CF lung disease.

BACKGROUND: Mucus stasis, a hallmark of muco-obstructive disease, results from impaired mucociliary transport and leads to lung function decline and chronic infection. Although therapeutics that target mucus stasis in the airway, such as hypertonic saline or rhDNAse, show some therapeutic benefit, they do not address the underlying electrostatic defect apparent in mucins in CF and related conditions. We have previously shown poly (acetyl, arginyl) glucosamine (PAAG, developed as SNSP113), a soluble, cationic polymer, significantly improves mucociliary transport in a rat model of CF by normalizing the charge defects of CF mucin. Here, we report efficacy in the CFTR-sufficient, ENaC hyperactive, Scnn1b-Tg mouse model that develops airway muco-obstruction due to sodium hyperabsorption and airway dehydration. METHODS: Scnn1b-Tg mice were treated with either 250 µg/mL SNSP113 or vehicle control (1.38% glycerol in PBS) via nebulization once daily for 7 days and then euthanized for analysis. Micro-Optical Coherence Tomography-based evaluation of excised mouse trachea was used to determine the effect on the functional microanatomy. Tissue analysis was performed by routine histopathology. RESULTS: Nebulized treatment of SNSP113 significantly improved mucociliary transport in the airways of Scnn1b-Tg mice, without altering the airway surface or periciliary liquid layer. In addition, SNSP113 significantly reversed epithelial hypertrophy and goblet cell metaplasia. Finally, SNSP113 significantly ameliorated eosinophilic crystalline pneumonia and lung consolidation in addition to inflammatory macrophage influx in this model. CONCLUSION: Overall, this study extends the efficacy of SNSP113 as a potential therapeutic to alleviate mucus stasis in muco-obstructive diseases in CF and potentially in related conditions.

Understanding and addressing the needs of people with cystic fibrosis in the era of CFTR modulator therapy.

Cystic fibrosis is a multiorgan disease caused by impaired function of the cystic fibrosis transmembrane conductance regulator (CFTR). Since the introduction of the CFTR modulator combination elexacaftor-tezacaftor-ivacaftor (ETI), which acts directly on mutant CFTR to enhance its activity, most people with cystic fibrosis (pwCF) have seen pronounced reductions in symptoms, and studies project marked increases in life expectancy for pwCF who are eligible for ETI. However, modulator therapy has not cured cystic fibrosis and the success of CFTR modulators has resulted in immediate questions about the new state of cystic fibrosis disease and clinical challenges in the care of pwCF. In this Series paper, we summarise key questions about cystic fibrosis disease in the era of modulator therapy, highlighting state-of-the-art research and clinical practices, knowledge gaps, new challenges faced by pwCF and the potential for future health-care challenges, and the pressing need for additional therapies to treat the underlying genetic or molecular causes of cystic fibrosis.

Repurposing sunscreen as an antibiotic: zinc-activated avobenzone inhibits methicillin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major healthcare concern with associated healthcare costs reaching over ${\$}$1 billion in a single year in the USA. Antibiotic resistance in S. aureus is now observed against last line of defense antibiotics, such as vancomycin, linezolid, and daptomycin. Unfortunately, high throughput drug discovery approaches to identify new antibiotics effective against MRSA have not resulted in much tangible success over the last decades. Previously, we demonstrated the feasibility of an alternative drug discovery approach, the identification of metallo-antibiotics, compounds that gain antibacterial activity only after binding to a transition metal ion and as such are unlikely to be detected in standard drug screens. We now report that avobenzone, the primary active ingredient of most sunscreens, can be activated by zinc to become a potent antibacterial compound against MRSA. Zinc-activated avobenzone (AVB-Zn) potently inhibited a series of clinical MRSA isolates [minimal inhibitory concentration (MIC): 0.62-2.5 µM], without pre-existing resistance and activity without zinc (MIC: >10 µM). AVB-Zn was also active against clinical MRSA isolates that were resistant against the commonly used zinc-salt antibiotic bacitracin. We found AVB-Zn exerted no cytotoxicity on human cell lines and primary cells. Last, we demonstrate AVB-Zn can be deployed therapeutically as lotion preparations, which showed efficacy in a mouse wound model of MRSA infection. AVB-Zn thus demonstrates Zn-activated metallo-antibiotics are a promising avenue for future drug discovery.

A novel in vitro model to study prolonged Pseudomonas aeruginosa infection in the cystic fibrosis bronchial epithelium.

Pseudomonas aeruginosa (PA) is known to chronically infect airways of people with cystic fibrosis (CF) by early adulthood. PA infections can lead to increased airway inflammation and lung tissue damage, ultimately contributing to decreased lung function and quality of life. Existing models of PA infection in vitro commonly utilize 1-6-hour time courses. However, these relatively early time points may not encompass downstream airway cell signaling in response to the chronic PA infections observed in people with cystic fibrosis. To fill this gap in knowledge, the aim of this study was to establish an in vitro model that allows for PA infection of CF bronchial epithelial cells, cultured at the air liquid interface, for 24 hours. Our model shows with an inoculum of 2 x 102 CFUs of PA for 24 hours pro-inflammatory markers such as interleukin 6 and interleukin 8 are upregulated with little decrease in CF bronchial epithelial cell survival or monolayer confluency. Additionally, immunoblotting for phosphorylated phospholipase C gamma, a well-known downstream protein of fibroblast growth factor receptor signaling, showed significantly elevated levels after 24 hours with PA infection that were not seen at earlier timepoints. Finally, inhibition of phospholipase C shows significant downregulation of interleukin 8. Our data suggest that this newly developed in vitro "prolonged PA infection model" recapitulates the elevated inflammatory markers observed in CF, without compromising cell survival. This extended period of PA growth on CF bronchial epithelial cells will have impact on further studies of cell signaling and microbiological studies that were not possible in previous models using shorter PA exposures.

Engineered tRNAs suppress nonsense mutations in cells and in vivo.

Nonsense mutations are the underlying cause of approximately 11% of all inherited genetic diseases1. Nonsense mutations convert a sense codon that is decoded by tRNA into a premature termination codon (PTC), resulting in an abrupt termination of translation. One strategy to suppress nonsense mutations is to use natural tRNAs with altered anticodons to base-pair to the newly emerged PTC and promote translation2-7. However, tRNA-based gene therapy has not yielded an optimal combination of clinical efficacy and safety and there is presently no treatment for individuals with nonsense mutations. Here we introduce a strategy based on altering native tRNAs into  efficient suppressor tRNAs (sup-tRNAs) by individually fine-tuning their sequence to the physico-chemical properties of the amino acid that they carry. Intravenous and intratracheal lipid nanoparticle (LNP) administration of sup-tRNA in mice restored the production of functional proteins with nonsense mutations. LNP-sup-tRNA formulations caused no discernible readthrough at endogenous native stop codons, as determined by ribosome profiling. At clinically important PTCs in the cystic fibrosis transmembrane conductance regulator gene (CFTR), the sup-tRNAs re-established expression and function in cell systems and patient-derived nasal epithelia and restored airway volume homeostasis. These results provide a framework for the development of tRNA-based therapies with a high molecular safety profile and high efficacy in targeted PTC suppression.

Acute Infection with a Tobramycin-Induced Small Colony Variant of Staphylococcus aureus Causes Increased Inflammation in the Cystic Fibrosis Rat Lung.

Cystic fibrosis (CF) disease is characterized by lifelong infections with pathogens such as Staphylococcus aureus, leading to eventual respiratory failure. Small colony variants (SCVs) of S. aureus have been linked to worse clinical outcomes for people with CF. Current studies of SCV pathology in vivo are limited, and it remains unclear whether SCVs directly impact patient outcomes or are a result of late-stage CF disease. To investigate this, we generated a stable menadione-auxotrophic SCV strain by serially passaging a CF isolate of S. aureus with tobramycin, an aminoglycoside antibiotic commonly administered for coinfecting Pseudomonas aeruginosa. This SCV was tobramycin resistant and showed increased tolerance to the anti-staphylococcal combination therapy sulfamethoxazole-trimethoprim. To better understand the dynamics of SCV infections in vivo, we infected CF rats with this strain compared with its normal colony variant (NCV). Analysis of bacterial burden at 3 days postinfection indicated that NCVs and SCVs persisted equally well in the lungs, but SCV infections ultimately led to increased weight loss and neutrophilic inflammation. Additionally, cellular and histopathological analyses showed that in CF rats, SCV infections yielded a lower macrophage response. Overall, these findings indicate that SCV infections may directly contribute to lung disease progression in people with CF.

Muc5b Contributes to Mucus Abnormality in Rat Models of Cystic Fibrosis.

Cystic fibrosis (CF) airway disease is characterized by excessive and accumulative mucus in the airways. Mucociliary clearance becomes defective as mucus secretions become hyperconcentrated and viscosity increases. The CFTR-knockout (KO) rat has been previously shown to progressively develop delayed mucociliary transport, secondary to increased viscoelasticity of airway secretions. The humanized-G551D CFTR rat model has demonstrated that abnormal mucociliary clearance and hyperviscosity is reversed by ivacaftor treatment. In this study, we sought to identify the components of mucus that changes as the rat ages to contribute to these abnormalities. We found that Muc5b concentrations, and to a lesser extent Muc5ac, in the airway were increased in the KO rat compared to WT, and that Muc5b concentration was directly related to the viscosity of the mucus. Additionally, we found that methacholine administration to the airway exacerbates these characteristics of disease in the KO, but not WT rat trachea. Lastly we determined that at 6 months of age, CF rats had mucus that was adherent to the airway epithelium, a process that is reversed by ivacaftor therapy in the hG551D rat. Overall, these data indicate that accumulation of Muc5b initiates the muco-obstructive process in the CF lung prior to infection.

Static mucus impairs bacterial clearance and allows chronic infection with Pseudomonas aeruginosa in the cystic fibrosis rat.

Cystic fibrosis (CF) airway disease is characterised by chronic Pseudomonas aeruginosa infection. Successful eradication strategies have been hampered by a poor understanding of the mechanisms underlying conversion to chronicity. The CFTR-knockout (KO) rat harbors a progressive defect in mucociliary transport and viscosity. KO rats were infected before and after the appearance of the mucus defect, using a clinical, mucoid-isolate of P. aeruginosa embedded in agarose beads. Young KO rats that were exposed to bacteria before the development of mucociliary transport defects resolved the infection and subsequent tissue damage. However, older KO rats that were infected in the presence of hyperviscous and static mucus were unable to eradicate bacteria, but instead had bacterial persistence through 28 days post-infection that was accompanied by airway mucus occlusion and lingering inflammation. Normal rats responded to infection with increased mucociliary transport to supernormal rates, which reduced the severity of a second bacterial exposure. We therefore conclude that the aberrant mucus present in the CF airway permits persistence of P. aeruginosa in the lung.

Poly (acetyl, arginyl) glucosamine disrupts Pseudomonas aeruginosa biofilms and enhances bacterial clearance in a rat lung infection model.

Pseudomonas aeruginosa is a common opportunistic pathogen that can cause chronic infections in multiple disease states, including respiratory infections in patients with cystic fibrosis (CF) and non-CF bronchiectasis. Like many opportunists, P. aeruginosa forms multicellular biofilm communities that are widely thought to be an important determinant of bacterial persistence and resistance to antimicrobials and host immune effectors during chronic/recurrent infections. Poly (acetyl, arginyl) glucosamine (PAAG) is a glycopolymer that has antimicrobial activity against a broad range of bacterial species, and also has mucolytic activity, which can normalize the rheological properties of cystic fibrosis mucus. In this study, we sought to evaluate the effect of PAAG on P. aeruginosa bacteria within biofilms in vitro, and in the context of experimental pulmonary infection in a rodent infection model. PAAG treatment caused significant bactericidal activity against P. aeruginosa biofilms, and a reduction in the total biomass of preformed P. aeruginosa biofilms on abiotic surfaces, as well as on the surface of immortalized cystic fibrosis human bronchial epithelial cells. Studies of membrane integrity indicated that PAAG causes changes to P. aeruginosa cell morphology and dysregulates membrane polarity. PAAG treatment reduced infection and consequent tissue inflammation in experimental P. aeruginosa rat infections. Based on these findings we conclude that PAAG represents a novel means to combat P. aeruginosa infection, and may warrant further evaluation as a therapeutic.

Inhaled gene therapy of preclinical muco-obstructive lung diseases by nanoparticles capable of breaching the airway mucus barrier.

INTRODUCTION: Inhaled gene therapy of muco-obstructive lung diseases requires a strategy to achieve therapeutically relevant gene transfer to airway epithelium covered by particularly dehydrated and condensed mucus gel layer. Here, we introduce a synthetic DNA-loaded mucus-penetrating particle (DNA-MPP) capable of providing safe, widespread and robust transgene expression in in vivo and in vitro models of muco-obstructive lung diseases. METHODS: We investigated the ability of DNA-MPP to mediate reporter and/or therapeutic transgene expression in lung airways of a transgenic mouse model of muco-obstructive lung diseases (ie, Scnn1b-Tg) and in air-liquid interface cultures of primary human bronchial epithelial cells harvested from an individual with cystic fibrosis. A plasmid designed to silence epithelial sodium channel (ENaC) hyperactivity, which causes airway surface dehydration and mucus stasis, was intratracheally administered via DNA-MPP to evaluate therapeutic effects in vivo with or without pretreatment with hypertonic saline, a clinically used mucus-rehydrating agent. RESULTS: DNA-MPP exhibited marked greater reporter transgene expression compared with a mucus-impermeable formulation in in vivo and in vitro models of muco-obstructive lung diseases. DNA-MPP carrying ENaC-silencing plasmids provided efficient downregulation of ENaC and reduction of mucus burden in the lungs of Scnn1b-Tg mice, and synergistic impacts on both gene transfer efficacy and therapeutic effects were achieved when DNA-MPP was adjuvanted with hypertonic saline. DISCUSSION: DNA-MPP constitutes one of the rare gene delivery systems providing therapeutically meaningful gene transfer efficacy in highly relevant in vivo and in vitro models of muco-obstructive lung diseases due to its unique ability to efficiently penetrate airway mucus.

Ivacaftor partially corrects airway inflammation in a humanized G551D rat.

Animal models have been highly informative for understanding the pathogenesis and progression of cystic fibrosis (CF) lung disease. In particular, the CF rat models recently developed have addressed mechanistic causes of the airway mucus defect characteristic of CF, and how these may change when cystic fibrosis transmembrane conductance regulator (CFTR) activity is restored using new modulator therapies. We hypothesized that inflammatory changes to the airway would develop spontaneously and progressively, and that these changes would be resolved with modulator therapy. To test this, we used a humanized-CFTR rat expressing the G551D variant that responds to the CFTR modulator ivacaftor. Markers typically found in the CF lung were assessed, including neutrophil influx, small airway histopathology, and inflammatory cytokine concentration. Young hG551D rats did not express inflammatory cytokines at baseline but did upregulate these in response to inflammatory trigger. As the hG551D rats aged, histopathology worsened, accompanied by neutrophil influx into the airway and increasing concentrations of TNF-α, IL-1α, and IL-6 in the airways. Ivacaftor administration reduced concentrations of these cytokines when administered to the rats at baseline but was less effective in the rats that had also received inflammatory stimulus. Therefore, we conclude that administration of ivacaftor resulted in an incomplete resolution of inflammation when rats received an external trigger, suggesting that CFTR activation may not be enough to resolve inflammation in the lungs of patients with CF.

Development of a Broadly Protective, Self-Adjuvanting Subunit Vaccine to Prevent Infections by Pseudomonas aeruginosa.

Infections caused by the opportunistic pathogen Pseudomonas aeruginosa can be difficult to treat due to innate and acquired antibiotic resistance and this is exacerbated by the emergence of multi-drug resistant strains. Unfortunately, no licensed vaccine yet exists to prevent Pseudomonas infections. Here we describe a novel subunit vaccine that targets the P. aeruginosa type III secretion system (T3SS). This vaccine is based on the novel antigen PaF (Pa Fusion), a fusion of the T3SS needle tip protein, PcrV, and the first of two translocator proteins, PopB. Additionally, PaF is made self-adjuvanting by the N-terminal fusion of the A1 subunit of the mucosal adjuvant double-mutant heat-labile enterotoxin (dmLT). Here we show that this triple fusion, designated L-PaF, can activate dendritic cells in vitro and elicits strong IgG and IgA titers in mice when administered intranasally. This self-adjuvanting vaccine expedites the clearance of P. aeruginosa from the lungs of challenged mice while stimulating host expression of IL-17A, which may be important for generating a protective immune response in humans. L-PaF's protective capacity was recapitulated in a rat pneumonia model, further supporting the efficacy of this novel fusion vaccine.

Ivacaftor Reverses Airway Mucus Abnormalities in a Rat Model Harboring a Humanized G551D-CFTR.

Rationale: Animal models have been highly informative for understanding the characteristics, onset, and progression of cystic fibrosis (CF) lung disease. In particular, the CFTR-/- rat has revealed insights into the airway mucus defect characteristic of CF but does not replicate a human-relevant CFTR (cystic fibrosis transmembrane conductance regulator) variant.Objectives: We hypothesized that a rat expressing a humanized version of CFTR and harboring the ivacaftor-sensitive variant G551D could be used to test the impact of CFTR modulators on pathophysiologic development and correction.Methods: In this study, we describe a humanized-CFTR rat expressing the G551D variant obtained by zinc finger nuclease editing of a human complementary DNA superexon, spanning exon 2-27, with a 5' insertion site into the rat gene just beyond intron 1. This targeted insertion takes advantage of the endogenous rat promoter, resulting in appropriate expression compared with wild-type animals.Measurements and Main Results: The bioelectric phenotype of the epithelia recapitulates the expected absence of CFTR activity, which was restored with ivacaftor. Large airway defects, including depleted airway surface liquid and periciliary layers, delayed mucus transport rates, and increased mucus viscosity, were normalized after the administration of ivacaftor.Conclusions: This model is useful to understand the mechanisms of disease and the extent of pathology reversal with CFTR modulators.

Novel Therapy of Bicarbonate, Glutathione, and Ascorbic Acid Improves Cystic Fibrosis Mucus Transport.

Defective airway mucus clearance is a defining characteristic of cystic fibrosis lung disease, and improvements to current mucolytic strategies are needed. Novel approaches targeting a range of contributing mechanisms are in various stages of preclinical and clinical development. ARINA-1 is a new nebulized product comprised of ascorbic acid, glutathione, and bicarbonate. Using microoptical coherence tomography, we tested the effect of ARINA-1 on central features of mucociliary clearance in F508del/F508del primary human bronchial epithelial cells to assess its potential as a mucoactive therapy in cystic fibrosis. We found that ARINA-1 significantly augmented mucociliary transport rates, both alone and with CFTR (cystic fibrosis transmembrane conductance regulator) modulator therapy, whereas airway hydration and ciliary beating were largely unchanged compared with PBS vehicle control. Analysis of mucus reflectivity and particle-tracking microrheology indicated that ARINA-1 restores mucus clearance by principally reducing mucus layer viscosity. The combination of bicarbonate and glutathione elicited increases in mucociliary transport rate comparable to those seen with ARINA-1, indicating the importance of this interaction to the impact of ARINA-1 on mucus transport; this effect was not recapitulated with bicarbonate alone or bicarbonate combined with ascorbic acid. Assessment of CFTR chloride transport revealed an increase in CFTR-mediated chloride secretion in response to ARINA-1 in CFBE41o- cells expressing wild-type CFTR, driven by CFTR activity stimulation by ascorbate. This response was absent in CFBE41o- F508del cells treated with VX-809 and primary human bronchial epithelial cells, implicating CFTR-independent mechanisms for the effect of ARINA-1 on cystic fibrosis mucus. Together, these studies indicate that ARINA-1 is a novel potential therapy for the treatment of impaired mucus clearance in cystic fibrosis.

A Novel G542X CFTR Rat Model of Cystic Fibrosis Is Sensitive to Nonsense Mediated Decay.

Nonsense mutations that lead to the insertion of a premature termination codon (PTC) in the cystic fibrosis transmembrane conductance regulator (CFTR) transcript affect 11% of patients with cystic fibrosis (CF) worldwide and are associated with severe disease phenotype. While CF rat models have contributed significantly to our understanding of CF disease pathogenesis, there are currently no rat models available for studying CF nonsense mutations. Here we created and characterized the first homozygous CF rat model that bears the CFTR G542X nonsense mutation in the endogenous locus using CRISPR/Cas9 gene editing. In addition to displaying severe CF manifestations and developmental defects such as reduced growth, abnormal tooth enamel, and intestinal obstruction, CFTR G542X knockin rats demonstrated an absence of CFTR function in tracheal and intestinal sections as assessed by nasal potential difference and transepithelial short-circuit current measurements. Reduced CFTR mRNA levels in the model further suggested sensitivity to nonsense-mediated decay, a pathway elicited by the presence of PTCs that degrades the PTC-bearing transcripts and thus further diminishes the level of CFTR protein. Although functional restoration of CFTR was observed in G542X rat tracheal epithelial cells in response to single readthrough agent therapy, therapeutic efficacy was not observed in G542X knockin rats in vivo. The G542X rat model provides an invaluable tool for the identification and in vivo validation of potential therapies for CFTR nonsense mutations.

Excess mucus viscosity and airway dehydration impact COPD airway clearance.

The mechanisms by which cigarette smoking impairs airway mucus clearance are not well understood. We recently established a ferret model of cigarette smoke-induced chronic obstructive pulmonary disease (COPD) exhibiting chronic bronchitis. We investigated the effects of cigarette smoke on mucociliary transport (MCT).Adult ferrets were exposed to cigarette smoke for 6 months, with in vivo mucociliary clearance measured by technetium-labelled DTPA retention. Excised tracheae were imaged with micro-optical coherence tomography. Mucus changes in primary human airway epithelial cells and ex vivo ferret airways were assessed by histology and particle tracking microrheology. Linear mixed models for repeated measures identified key determinants of MCT.Compared to air controls, cigarette smoke-exposed ferrets exhibited mucus hypersecretion, delayed mucociliary clearance (-89.0%, p<0.01) and impaired tracheal MCT (-29.4%, p<0.05). Cholinergic stimulus augmented airway surface liquid (ASL) depth (5.8±0.3 to 7.3±0.6 µm, p<0.0001) and restored MCT (6.8±0.8 to 12.9±1.2 mm·min-1, p<0.0001). Mixed model analysis controlling for covariates indicated smoking exposure, mucus hydration (ASL) and ciliary beat frequency were important predictors of MCT. Ferret mucus was hyperviscous following smoke exposure in vivo or in vitro, and contributed to diminished MCT. Primary cells from smokers with and without COPD recapitulated these findings, which persisted despite the absence of continued smoke exposure.Cigarette smoke impairs MCT by inducing airway dehydration and increased mucus viscosity, and can be partially abrogated by cholinergic secretion of fluid secretion. These data elucidate the detrimental effects of cigarette smoke exposure on mucus clearance and suggest additional avenues for therapeutic intervention.

Revealing the molecular signaling pathways of mucus stasis in cystic fibrosis.

Mucus obstruction is a hallmark of cystic fibrosis (CF) airway disease, leading to chronic infection, dysregulated inflammation, and progressive lung disease. As mucus hyperexpression is a key component in the initiation and perpetuation of airway obstruction, the triggers underlying mucin release must be identified and understood. In this issue of the JCI, Chen et al. sought to delineate the mechanisms that allow IL-1α/IL-1ß to perpetuate the mucoinflammatory environment characteristic of the CF airway. The authors demonstrated that IL-1α and IL-1ß stimulated non-CF human bronchial epithelial (HBE) cells to upregulate and secrete both MUC5B and MUC5AC in a dose-dependent manner, an effect that was neutralized by the inhibition of the IL-1α/IL-1ß receptor (IL-1R1). Further experiments using mouse models and excised lung tissue identified contributors that drive a vicious feedback cycle of hyperconcentrated mucus secretions and persistent inflammation in the CF airway, factors that are likely at the nidus of progressive lung disease.