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BACKGROUND: Cost of illness studies are important tools to summarise the burden of disease for individuals, the healthcare system and society. The lack of standardised methods for reporting costs for cystic fibrosis (CF) makes it difficult to quantify the total socioeconomic burden. In this study, we aimed to comprehensively report the socioeconomic burden of CF in Canada. METHODS: The total cost of CF in Canada was calculated by triangulating information from three sources (Canadian CF Registry, customised Burden of Disease survey and publicly available information). A prevalence-based, bottom-up, human capital approach was applied, and costs were categorised into four perspectives (ie, healthcare system, individual/caregiver, variable (ie, medicines) and society) and three domains (ie, direct, indirect and intangible). All costs were converted into 2021 Canadian dollars (CAD) and adjusted for inflation. The cost of cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies was excluded. RESULTS: The total socioeconomic burden of CF in Canada in 2021 across the four perspectives was $C414 million. Direct costs accounted for two-thirds of the total costs, with medications comprising half of all direct costs. Out-of-pocket costs to individuals and caregivers represented 18.7% of all direct costs. Indirect costs representing absenteeism accounted for one-third of the total cost. CONCLUSION: This comprehensive cost of illness study for CF represents a community-oriented approach describing the socioeconomic burden of living with CF and serves as a benchmark for future studies.
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Efeitos Psicossociais da Doença , Fibrose Cística , Custos de Cuidados de Saúde , Humanos , Fibrose Cística/economia , Fibrose Cística/terapia , Fibrose Cística/epidemiologia , Canadá/epidemiologia , Feminino , Masculino , Adulto , Custos de Cuidados de Saúde/estatística & dados numéricos , Adolescente , Adulto Jovem , Criança , Gastos em Saúde/estatística & dados numéricos , Pré-Escolar , Cuidadores/economia , Fatores Socioeconômicos , Lactente , Absenteísmo , Prevalência , Pessoa de Meia-Idade , Sistema de RegistrosRESUMO
BACKGROUND: Cystic Fibrosis causing mutations in the gene CFTR, reduce the activity of the CFTR channel protein, and leads to mucus aggregation, airway obstruction and poor lung function. A role for CFTR in the pathogenesis of other muco-obstructive airway diseases such as Chronic Obstructive Pulmonary Disease (COPD) has been well established. The CFTR modulatory compound, Ivacaftor (VX-770), potentiates channel activity of CFTR and certain CF-causing mutations and has been shown to ameliorate mucus obstruction and improve lung function in people harbouring these CF-causing mutations. A pilot trial of Ivacaftor supported its potential efficacy for the treatment of mucus obstruction in COPD. These findings prompted the search for CFTR potentiators that are more effective in ameliorating cigarette-smoke (CS) induced mucostasis. METHODS: Small molecule potentiators, previously identified in CFTR binding studies, were tested for activity in augmenting CFTR channel activity using patch clamp electrophysiology in HEK-293 cells, a fluorescence-based assay of membrane potential in Calu-3 cells and in Ussing chamber studies of primary bronchial epithelial cultures. Addition of cigarette smoke extract (CSE) to the solutions bathing the apical surface of Calu-3 cells and primary bronchial airway cultures was used to model COPD. Confocal studies of the velocity of fluorescent microsphere movement on the apical surface of CSE exposed airway epithelial cultures, were used to assess the effect of potentiators on CFTR-mediated mucociliary movement. RESULTS: We showed that SK-POT1, like VX-770, was effective in augmenting the cyclic AMP-dependent channel activity of CFTR. SK-POT-1 enhanced CFTR channel activity in airway epithelial cells previously exposed to CSE and ameliorated mucostasis on the surface of primary airway cultures. CONCLUSION: Together, this evidence supports the further development of SK-POT1 as an intervention in the treatment of COPD.
Assuntos
Aminofenóis , Brônquios , Regulador de Condutância Transmembrana em Fibrose Cística , Células Epiteliais , Quinolonas , Humanos , Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Quinolonas/farmacologia , Aminofenóis/farmacologia , Células Epiteliais/efeitos dos fármacos , Células Epiteliais/metabolismo , Brônquios/efeitos dos fármacos , Brônquios/metabolismo , Fumaça/efeitos adversos , Células Cultivadas , Células HEK293 , Agonistas dos Canais de Cloreto/farmacologia , Agonistas dos Canais de Cloreto/uso terapêutico , Mucosa Respiratória/efeitos dos fármacos , Mucosa Respiratória/metabolismoRESUMO
Background: Cystic Fibrosis causing mutations in the gene CFTR , reduce the activity of the CFTR channel protein, and leads to mucus aggregation, airway obstruction and poor lung function. A role for CFTR in the pathogenesis of other muco-obstructive airway diseases such as Chronic Obstructive Pulmonary Disease (COPD) has been well established. The CFTR modulatory compound, Ivacaftor (VX-770), potentiates channel activity of CFTR and certain CF-causing mutations and has been shown to ameliorate mucus obstruction and improve lung function in people harbouring these CF-causing mutations. A pilot trial of Ivacaftor supported its potential efficacy for the treatment of mucus obstruction in COPD. These findings prompted the search for CFTR potentiators that are more effective in ameliorating cigarette-smoke (CS) induced mucostasis. Methods: A novel small molecule potentiator (SK-POT1), previously identified in CFTR binding studies, was tested for its activity in augmenting CFTR channel activity using patch clamp electrophysiology in HEK-293 cells, a fluorescence-based assay of membrane potential in Calu-3 cells and in Ussing chamber studies of primary bronchial epithelial cultures. Addition of cigarette smoke extract (CSE) to the solutions bathing the apical surface of Calu-3 cells and primary bronchial airway cultures was used to model COPD. Confocal studies of the velocity of fluorescent microsphere movement on the apical surface of CSE exposed airway epithelial cultures, were used to assess the effect of potentiators on CFTR-mediated mucociliary movement. Results: We showed that SK-POT1, like VX-770, was effective in augmenting the cyclic AMP-dependent channel activity of CFTR. SK-POT-1 enhanced CFTR channel activity in airway epithelial cells previously exposed to CSE and ameliorated mucostasis on the surface of primary airway cultures. Conclusion: Together, this evidence supports the further development of SK-POT1 as an intervention in the treatment of COPD.
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BACKGROUND: Elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) significantly improves health outcomes in people with cystic fibrosis (pwCF) carrying one or two F508del mutations. According to in vitro assays performed in FRT cells, 178 additional mutations respond to ELX/TEZ/IVA. The N1303K mutation is not included in this list of mutations. Recent in vitro data suggested that ELX/TEZ/IVA increases N1303K-CFTR activity. Based on the in vitro response, eight patients commenced treatment with ELX/TEZ/IVA. METHODS: Two homozygotes; and six compound heterozygotes N1303K/nonsense or frameshift mutation pwCF were treated off label with ELX/TEZ/IVA. Clinical data before and 8 weeks after starting treatment were prospectively collected. The response to ELX/TEZ/IVA was assessed in intestinal organoids derived from 5 study patients and an additional patient carrying N1303K that is not receiving treatment. RESULTS: Compared to the values before commencing treatment, mean forced expiratory volume in 1 second increased by 18.4 percentage points and 26.5% relative to baseline, mean BMI increased by 0.79 Kg/m2, and mean lung clearance index decreased by 3.6 points and 22.2%. There was no significant change in sweat chloride. Nasal potential difference normalized in four patients and remained abnormal in three. Results in 3D intestinal organoids and 2D nasal epithelial cultures showed a response in CFTR channel activity. CONCLUSIONS: This report supports the previously reported in vitro data, performed in human nasal and bronchial epithelial cells and intestinal organoids, that pwCF who carry the N1303K mutation have a significant clinical benefit by ELX/TEZ/IVA treatment.
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Fibrose Cística , Humanos , Fibrose Cística/tratamento farmacológico , Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Mutação , Benzodioxóis/uso terapêutico , Aminofenóis/uso terapêutico , Agonistas dos Canais de Cloreto/uso terapêuticoRESUMO
It has been suggested that in vitro studies of the rescue effect of CFTR modulator drugs in nasal epithelial cultures derived from people with cystic fibrosis have the potential to predict clinical responses to the same drugs. Hence, there is an interest in evaluating different methods for measuring in vitro modulator responses in patient-derived nasal cultures. Commonly, the functional response to CFTR modulator combinations in these cultures is assessed by bioelectric measurements, using the Ussing chamber. While this method is highly informative, it is time-consuming. A fluorescence-based, multi-transwell method for assaying regulated apical chloride conductance (Fl-ACC) promises to provide a complementary approach to theratyping in patient-derived nasal cultures. In the present work, we compared Ussing chamber measurements and fluorescence-based measurements of CFTR-mediated apical conductance in matching, fully differentiated nasal cultures derived from CF patients, homozygous for F508del (n = 31) or W1282X (n = 3), or heterozygous for Class III mutations G551D or G178R (n = 5). These cultures were obtained through a bioresource called the Cystic Fibrosis Canada-Sick Kids Program in Individual CF Therapy (CFIT). We found that the Fl-ACC method was effective in detecting positive responses to interventions for all genotypes. There was a correlation between patient-specific drug responses measured in cultures harbouring F508del, as measured using the Ussing chamber technique and the fluorescence-based assay (Fl-ACC). Finally, the fluorescence-based assay has the potential for greater sensitivity for detecting responses to pharmacological rescue strategies targeting W1282X.
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Fibrose Cística , Humanos , Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Fluorescência , Mutação , GenótipoRESUMO
BACKGROUND: Cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulator therapies show variable efficacy for patients with CF. Patient-derived predictive tools may identify individuals likely to respond to CFTRs, but are not in routine use. We aimed to determine the cost-utility of predictive tool-guided treatment with CFTRs as add-on to standard of care (SoC) for individuals with CF. METHODS: This economic evaluation compared two strategies using an individual level simulation: (i) Treat All, where all patients received CFTRs plus SoC and (ii) TestâTreat, where patients who tested positive on predictive tools received CFTRs plus SoC and those who tested negative received SoC only. We simulated 50,000 individuals over their lifetime, and estimated costs (2020 CAD) per quality-adjusted life year (QALY) from the healthcare payer's perspective, discounted at 1.5% annually. The model was populated using Canadian CF registry data and published literature. Probabilistic and deterministic sensitivity were conducted. RESULTS: The Treat All and TestâTreat and strategies yielded 22.41 and 21.36 QALYs, and cost $4.21 M and $3.15 M respectively. Results of probabilistic sensitivity analysis showed that TestâTreat was highly cost-effective compared to Treat All in 100% of simulations at cost-effectiveness thresholds as high as $500,000 per QALY. TestâTreat may save between $931 K to $1.1 M per QALY lost, depending on sensitivity and specificity of predictive tools. CONCLUSION: The use of predictive tools could optimize the health benefits of CFTR modulators while reducing costs. Our findings support the use of pre-treatment predictive testing and may help inform coverage and reimbursement policies for individuals with CF.
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Fibrose Cística , Humanos , Fibrose Cística/diagnóstico , Fibrose Cística/genética , Fibrose Cística/terapia , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Análise de Custo-Efetividade , Canadá , Análise Custo-BenefícioRESUMO
For those people with cystic fibrosis carrying rare CFTR mutations not responding to currently available therapies, there is an unmet need for relevant tissue models for therapy development. Here, we describe a new testing platform that employs patient-specific induced pluripotent stem cells (iPSCs) differentiated to lung progenitor cells that can be studied using a dynamic, high-throughput fluorescence-based assay of CFTR channel activity. Our proof-of-concept studies support the potential use of this platform, together with a Canadian bioresource that contains iPSC lines and matched nasal cultures from people with rare mutations, to advance patient-oriented therapy development. Interventions identified in the high-throughput, stem cell-based model and validated in primary nasal cultures from the same person have the potential to be advanced as therapies.
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Diferenciação Celular/genética , Fibrose Cística/genética , Células-Tronco Pluripotentes Induzidas/metabolismo , Pulmão/metabolismo , Células-Tronco/metabolismo , Células Cultivadas , Fibrose Cística/metabolismo , Fibrose Cística/patologia , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Perfilação da Expressão Gênica/métodos , Humanos , Pulmão/citologia , Mutação , RNA-Seq/métodos , Células-Tronco/citologiaRESUMO
Positive results in pre-clinical studies of the triple combination of elexacaftor, tezacaftor and ivacaftor, performed in airway epithelial cell cultures obtained from patients harbouring the class II cystic fibrosis transmembrane conductance regulator (CFTR) mutation F508del-CFTR, translated to impressive clinical outcomes for subjects carrying this mutation in clinical trials and approval of Trikafta.Encouraged by this correlation, we were prompted to evaluate the effect of the elexacaftor, tezacaftor and ivacaftor triple combination on primary nasal epithelial cultures obtained from individuals with rare class II CF-causing mutations (G85E, M1101K and N1303K) for which Trikafta is not approved.Cultures from individuals homozygous for M1101K responded better than cultures harbouring G85E and N1303K after treatment with the triple combination with respect to improvement in regulated channel function and protein processing. A similar genotype-specific effect of the triple combination was observed when the different mutations were expressed in HEK293 cells, supporting the hypothesis that these modulators may act directly on the mutant proteins. Detailed studies in nasal cultures and HEK293 cells showed that the corrector, elexacaftor, exhibited dual activity as both corrector and potentiator, and suggested that the potentiator activity contributes to its pharmacological activity.These pre-clinical studies using nasal epithelial cultures identified mutation genotypes for which elexacaftor, tezacaftor and ivacaftor may produce clinical responses that are comparable to, or inferior to, those observed for F508del-CFTR.
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Regulador de Condutância Transmembrana em Fibrose Cística , Fibrose Cística , Aminofenóis , Benzodioxóis , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Combinação de Medicamentos , Células HEK293 , Humanos , Indóis , Mutação , Pirazóis , Piridinas , Pirrolidinas , Quinolinas , QuinolonasRESUMO
The combination therapies ORKAMBITM and TRIKAFTATM are approved for people who have the F508del mutation on at least one allele. In this study we examine the effects of potentiator and corrector combinations on the rare mutation c.3700A>G. This mutation produces a cryptic splice site that deletes six amino acids in NBD2 (I1234-R1239del). Like F508del it causes protein misprocessing and reduced chloride channel function. We show that a novel cystic fibrosis transmembrane conductance regulator CFTR modulator triple combination (AC1, corrector, AC2-2, co-potentiator and AP2, potentiator), rescued I1234-R1239del-CFTR activity to WT-CFTR level in HEK293 cells. Moreover, we show that although the response to ORKAMBI was modest in nasal epithelial cells from two individuals homozygous for I1234-R1239del-CFTR, a substantial functional rescue was achieved with the novel triple combination. Interestingly, while both the novel CFTR triple combination and TRIKAFTATM treatment showed functional rescue in gene-edited I1234-R1239del-CFTR-expressing HBE cells and in nasal cells from two CF patients heterozygous for I1234-R1239del/W1282X, nasal cells homozygous for I1234-R1239del-CFTR showed no significant response to the TRIKAFTATM combination. These data suggest a potential benefit of CFTR modulators on the functional rescue of I1234-R1239del -CFTR, which arises from the rare CF-causing mutation c.3700A>G, and highlight that patient tissues are crucial to our full understanding of functional rescue in rare CFTR mutations.
RESUMO
BACKGROUND: Therapies targeting certain CFTR mutants have been approved, yet variations in clinical response highlight the need for in-vitro and genetic tools that predict patient-specific clinical outcomes. Toward this goal, the CF Canada-Sick Kids Program in Individual CF Therapy (CFIT) is generating a "first of its kind", comprehensive resource containing patient-specific cell cultures and data from 100 CF individuals that will enable modeling of therapeutic responses. METHODS: The CFIT program is generating: 1) nasal cells from drug naïve patients suitable for culture and the study of drug responses in vitro, 2) matched gene expression data obtained by sequencing the RNA from the primary nasal tissue, 3) whole genome sequencing of blood derived DNA from each of the 100 participants, 4) induced pluripotent stem cells (iPSCs) generated from each participant's blood sample, 5) CRISPR-edited isogenic control iPSC lines and 6) prospective clinical data from patients treated with CF modulators. RESULTS: To date, we have recruited 57 of 100 individuals to CFIT, most of whom are homozygous for F508del (to assess in-vitro: in-vivo correlations with respect to ORKAMBI response) or heterozygous for F508del and a minimal function mutation. In addition, several donors are homozygous for rare nonsense and missense mutations. Nasal epithelial cell cultures and matched iPSC lines are available for many of these donors. CONCLUSIONS: This accessible resource will enable development of tools that predict individual outcomes to current and emerging modulators targeting F508del-CFTR and facilitate therapy discovery for rare CF causing mutations.
Assuntos
Aminofenóis/uso terapêutico , Aminopiridinas/uso terapêutico , Benzodioxóis/uso terapêutico , Fibrose Cística/terapia , Terapia Genética/métodos , Medicina de Precisão/métodos , Desenvolvimento de Programas/métodos , Quinolonas/uso terapêutico , Canadá/epidemiologia , Criança , Fibrose Cística/epidemiologia , Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Combinação de Medicamentos , Humanos , Incidência , Mutação de Sentido Incorreto , RNA/genéticaRESUMO
Cystic fibrosis transmembrane conductance regulator (CFTR) is a multidomain membrane protein that functions as a phosphorylation-regulated anion channel. The interface between its two cytosolic nucleotide binding domains and coupling helices conferred by intracellular loops extending from the channel pore domains has been referred to as a transmission interface and is thought to be critical for the regulated channel activity of CFTR. Phosphorylation of the regulatory domain of CFTR by protein kinase A (PKA) is required for its channel activity. However, it was unclear if phosphorylation modifies the transmission interface. Here, we studied purified full-length CFTR protein using spectroscopic techniques to determine the consequences of PKA-mediated phosphorylation. Synchrotron radiation circular dichroism spectroscopy confirmed that purified full-length wild-type CFTR is folded and structurally responsive to phosphorylation. Intrinsic tryptophan fluorescence studies of CFTR showed that phosphorylation reduced iodide-mediated quenching, consistent with an effect of phosphorylation in burying tryptophans at the transmission interface. Importantly, the rate of phosphorylation-dependent channel activation was compromised by the introduction of disease-causing mutations in either of the two coupling helices predicted to interact with nucleotide binding domain 1 at the interface. Together, these results suggest that phosphorylation modifies the interface between the catalytic and pore domains of CFTR and that this modification facilitates CFTR channel activation.
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Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Fibrose Cística/metabolismo , Mutação de Sentido Incorreto , Substituição de Aminoácidos , Proteínas Quinases Dependentes de AMP Cíclico/genética , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Células HEK293 , Humanos , Fosforilação/genética , Domínios ProteicosRESUMO
The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a unique channel-forming member of the ATP Binding Cassette (ABC) superfamily of transporters. The phosphorylation and nucleotide dependent chloride channel activity of CFTR has been frequently studied in whole cell systems and as single channels in excised membrane patches. Many Cystic Fibrosis-causing mutations have been shown to alter this activity. While a small number of purification protocols have been published, a fast reconstitution method that retains channel activity and a suitable method for studying population channel activity in a purified system have been lacking. Here rapid methods are described for purification and functional reconstitution of the full-length CFTR protein into proteoliposomes of defined lipid composition that retains activity as a regulated halide channel. This reconstitution method together with a novel flux-based assay of channel activity is a suitable system for studying the population channel properties of wild type CFTR and the disease-causing mutants F508del- and G551D-CFTR. Specifically, the method has utility in studying the direct effects of phosphorylation, nucleotides and small molecules such as potentiators and inhibitors on CFTR channel activity. The methods are also amenable to the study of other membrane channels/transporters for anionic substrates.
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Regulador de Condutância Transmembrana em Fibrose Cística/química , Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Animais , Transporte Biológico , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/isolamento & purificação , Humanos , Proteolipídeos/química , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Células Sf9RESUMO
The most common mutation causing cystic fibrosis (CF), F508del, impairs conformational maturation of CF transmembrane conductance regulator (CFTR), thereby reducing its functional expression on the surface of epithelia. Corrector compounds including C18 (VRT-534) and VX-809 have been shown to partially rescue misfolding of F508del-CFTR and to enhance its maturation and forward trafficking to the cell surface. Now, we show that there is an additional action conferred by these compounds beyond their role in improving the biosynthetic assembly. In vitro studies show that these compounds bind directly to the metastable, full-length F508del-CFTR channel. Cell culture and patient tissue-based assays confirm that in addition to their cotranslational effect on folding, certain corrector compounds bind to the full-length F508del-CFTR after its partial rescue to the cell surface to enhance its function. These findings may inform the development of alternative compounds with improved therapeutic efficacy.
Assuntos
Aminopiridinas/farmacologia , Benzodioxóis/farmacologia , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Regulador de Condutância Transmembrana em Fibrose Cística/química , Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Fibrose Cística/tratamento farmacológico , Animais , Células Cultivadas , Cricetinae , Fibrose Cística/metabolismo , Fibrose Cística/patologia , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Relação Dose-Resposta a Droga , Células HEK293 , Humanos , Estabilidade Proteica/efeitos dos fármacos , Relação Estrutura-Atividade , Propriedades de SuperfícieRESUMO
Wzx flippases are crucial for bacterial cell surface polysaccharide assembly as they transport undecaprenyl pyrophosphate-linked sugar repeat units from the cytoplasmic to the periplasmic leaflets of the inner membrane (IM) for final assembly. Our recently reported three-dimensional (3D) model structure of Wzx from Pseudomonas aeruginosa PAO1 (WzxPa) displayed a cationic internal vestibule and functionally essential acidic amino acids within transmembrane segment bundles. Herein, we examined the intrinsic transport function of WzxPa following its purification and reconstitution in phospholipid liposomes. WzxPa was capable of mediating anion flux, consistent with its cationic interior. This flux was electrogenic and modified by extraliposomal pH. Mutation of the above-mentioned acidic residues (E61, D269, and D359) reduced proton (H(+))-modified anion flux, showing the role of these amino acid side chains in H(+)-dependent transport. Wzx also mediated acidification of the proteoliposome interior in the presence of an outward anion gradient. These results indicate H(+)-dependent gating and H(+) uptake by WzxPa and allow for the first H(+)-dependent antiport mechanism to be proposed for lipid-linked oligosaccharide translocation across the bacterial IM. IMPORTANCE Many bacterial cell surface polysaccharides that are important for survival and virulence are synthesized at the periplasmic leaflet of the inner membrane (IM) using precursors produced in the cytoplasm. Wzx flippases are responsible for translocation of lipid-linked sugar repeat units across the IM and had been previously suggested to simply facilitate passive substrate diffusion. Through our characterization of purified Wzx in a reconstitution system described herein, we have observed protein-dependent intrinsic transport producing a change in the electrical potential of the system, with H(+) identified as the coupling ion. These results provide the first evidence for coupled (i.e., secondary active) transport by these proteins and, in conjunction with structural data, allow for an antiport mechanism to be proposed for the directed transport of lipid-linked sugar substrates across the IM. These findings bring our understanding of lipid-linked polysaccharide transporter proteins more in line with the efflux pumps to which they are evolutionarily related.
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Ânions/metabolismo , Proteínas de Bactérias/metabolismo , Membrana Celular/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Pseudomonas aeruginosa/metabolismo , Motivos de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Membrana Celular/química , Membrana Celular/genética , Proteínas de Membrana Transportadoras/química , Proteínas de Membrana Transportadoras/genética , Antígenos O/metabolismo , Prótons , Pseudomonas aeruginosa/química , Pseudomonas aeruginosa/genéticaRESUMO
High-throughput screens for small molecules that are effective in "correcting" the functional expression of F508del-CFTR have yielded several promising hits. Two such compounds are currently in clinical trial. Despite this success, it is clear that further advances will be required in order to restore 50% or greater of wild-type CFTR function to the airways of patients harboring the F508del-CFTR protein. Progress will be enhanced by our better understanding of the molecular and cellular defects caused by the F508del mutation, present in 90% of CF patients. The goal of this chapter is to review the current understanding of defects caused by F508del in the CFTR protein and in CFTR-mediated interactions important for its biosynthesis, trafficking, channel function, and stability at the cell surface. Finally, we will discuss the gaps in our knowledge regarding the mechanism of action of existing correctors, the unmet need to discover compounds which restore proper CFTR structure and function in CF affected tissues and new strategies for therapy development.
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The cystic fibrosis transmembrane conductance regulator (CFTR) acts as a channel on the apical membrane of epithelia. Disease-causing mutations in the cystic fibrosis gene can lead to CFTR protein misfolding as in the case of the F508del mutation and/or channel dysfunction. Recently, a small molecule, VX-770 (ivacaftor), has shown efficacy in restoring lung function in patients bearing the G551D mutation, and this has been linked to repair of its channel gating defect. However, these studies did not reveal the mechanism of action of VX-770 in detail. Normally, CFTR channel activity is regulated by phosphorylation, ATP binding, and hydrolysis. Hence, it has been hypothesized that VX-770 modifies one or more of these metabolic events. In this study, we examined VX-770 activity using a reconstitution system for purified CFTR protein, a system that enables control of known regulatory factors. We studied the consequences of VX-770 interaction with CFTR incorporated in planar lipid bilayers and in proteoliposomes, using a novel flux-based assay. We found that purified and phosphorylated CFTR was potentiated in the presence of Mg-ATP, suggesting that VX-770 bound directly to the CFTR protein, rather than associated kinases or phosphatases. Interestingly, we also found that VX-770 enhanced the channel activity of purified and mutant CFTR in the nominal absence of Mg-ATP. These findings suggest that VX-770 can cause CFTR channel opening through a nonconventional ATP-independent mechanism. This work sets the stage for future studies of the structural properties that mediate CFTR gating using VX-770 as a probe.
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Trifosfato de Adenosina/química , Aminofenóis/química , Regulador de Condutância Transmembrana em Fibrose Cística/química , Ativação do Canal Iônico/efeitos dos fármacos , Proteínas Mutantes/química , Quinolonas/química , Animais , Caprilatos/química , Linhagem Celular , Cromatografia de Afinidade , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/isolamento & purificação , Detergentes/química , Fluorocarbonos/química , Humanos , Lipossomos , Mutação de Sentido Incorreto , Fosforilação , Ligação Proteica , Conformação Proteica/efeitos dos fármacos , Processamento de Proteína Pós-Traducional , Deleção de Sequência , Transdução de Sinais/efeitos dos fármacos , SpodopteraRESUMO
These are exciting times with the appearance of small molecule compounds in clinical trials which target the basic defects caused by mutation in the CFTR gene. This progress was enabled by years of basic research probing the molecular and cellular consequences caused by mutation and the development of methods by which to study the primary anion transport defect in a high-throughput manner by robotics. Future progress with the development of new, more effective corrector compounds is needed. Such discovery will require further progress in defining the molecular targets for effective intervention using a multidisciplinary approach, merging computational, molecular, proteomic and cell biological methods. There is also an urgent need to develop means to link the right therapeutic compound to the right patients given the heterogeneity of the CF patient population. We envision a time when mid to high-throughput methods will be married with stem cell biology to enable testing a compendium of compounds on cells derived from each individual patient. Given the rate of progress in this field- this scenario may exist in the not too distant future.
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Regulador de Condutância Transmembrana em Fibrose Cística/efeitos dos fármacos , Fibrose Cística/tratamento farmacológico , Desenho de Fármacos , Descoberta de Drogas , Ensaios de Triagem em Larga Escala , Bibliotecas de Moléculas Pequenas/uso terapêutico , Animais , Regulador de Condutância Transmembrana em Fibrose Cística/genética , HumanosRESUMO
Cystic fibrosis is a genetic disease caused by mutations in the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. In vitro experiments have demonstrated that 4-methyl-2-(5-phenyl-1H-pyrazol-3-yl)phenol (VRT-532, 1) is able to partially restore the function of mutant CFTR proteins. To help elucidate the nature of the interactions between 1 and mutant CFTR, molecular probes based on the structure of 1 have been prepared. These include a photoreactive aryl azide derivative 11 and a fluorescent dansyl sulfonamide 15. Additionally, a method for hydrogen isotope exchange on 1 has been developed, which could be used for the incorporation of radioactive tritium. Using iodide efflux assays, the probe molecules have been demonstrated to modulate the activity of mutant CFTR in the same manner as 1. These probe molecules enable a number of biochemical experiments aimed at understanding how 1 rescues the function of mutant CFTR. This understanding can in turn aid in the design and development of more efficacious compounds which may serve as therapeutic agents in the treatment of cystic fibrosis.
Assuntos
Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Corantes Fluorescentes/síntese química , Sondas Moleculares/síntese química , Marcadores de Fotoafinidade/síntese química , Animais , Azidas/síntese química , Azidas/química , Azidas/farmacologia , Linhagem Celular , Cresóis/farmacologia , Cricetinae , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Compostos de Dansil/síntese química , Compostos de Dansil/química , Compostos de Dansil/farmacologia , Corantes Fluorescentes/química , Corantes Fluorescentes/farmacologia , Marcação por Isótopo , Sondas Moleculares/química , Sondas Moleculares/farmacologia , Mutação , Marcadores de Fotoafinidade/química , Marcadores de Fotoafinidade/farmacologia , Pirazóis/síntese química , Pirazóis/química , Pirazóis/farmacologia , Relação Estrutura-Atividade , TrítioRESUMO
Mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) cause CF (cystic fibrosis), a fatal genetic disease commonly leading to airway obstruction with recurrent airway inflammation and infection. Pulmonary obstruction in CF has been linked to the loss of CFTR function as a regulated Cl- channel on the lumen-facing membrane of the epithelium lining the airways. We have learned much about the molecular basis for nucleotide- and phosphorylation-dependent regulation of channel activity of the normal (wild-type) version of the CFTR protein through electrophysiological studies. The major CF-causing mutation, F508del-CFTR, causes the protein to misfold and be retained in the ER (endoplasmic reticulum). Importantly, recent studies in cell culture have shown that retention in the ER can be 'corrected' through the application of certain small-molecule modulators and, once at the surface, the altered channel function of the major mutant can be 'potentiated', pharmacologically. Importantly, two such small molecules, a 'corrector' (VX-809) and a 'potentiator' (VX-770) compound are undergoing clinical trial for the treatment of CF. In this chapter, we describe recent discoveries regarding the wild-type CFTR and F508del-CFTR protein, in the context of molecular models based on X-ray structures of prokaryotic ABC (ATP-binding cassette) proteins. Finally, we discuss the promise of small-molecule modulators to probe the relationship between structure and function in the wild-type protein, the molecular defects caused by the most common mutation and the structural changes required to correct these defects.
Assuntos
Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Fibrose Cística/tratamento farmacológico , Regulador de Condutância Transmembrana em Fibrose Cística/química , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/fisiologia , Humanos , Ativação do Canal Iônico , Modelos Moleculares , Mutação , Fosforilação , Conformação ProteicaRESUMO
Pseudomonas aeruginosa is the predominant pathogen associated with chronic lung infection among cystic fibrosis patients. During colonization of the lung, P. aeruginosa converts to a mucoid phenotype characterized by the overproduction of the exopolysaccharide alginate. Secretion of newly synthesized alginate across the outer membrane is believed to occur through the outer membrane protein AlgE. Here we report the 2.3 Å crystal structure of AlgE, which reveals a monomeric 18-stranded ß-barrel characterized by a highly electropositive pore constriction formed by an arginine-rich conduit that likely acts as a selectivity filter for the negatively charged alginate polymer. Interestingly, the pore constriction is occluded on either side by extracellular loop L2 and an unusually long periplasmic loop, T8. In halide efflux assays, deletion of loop T8 (ΔT8-AlgE) resulted in a threefold increase in anion flux compared to the wild-type or ΔL2-AlgE supporting the idea that AlgE forms a transport pathway through the membrane and suggesting that transport is regulated by T8. This model is further supported by in vivo experiments showing that complementation of an algE deletion mutant with ΔT8-AlgE impairs alginate production. Taken together, these studies support a mechanism for exopolysaccharide export across the outer membrane that is distinct from the Wza-mediated translocation observed in canonical capsular polysaccharide export systems.