A young Hispanic with c.1646G>A mutation exhibits severe cystic fibrosis lung disease: is ivacaftor an option for therapy?

Left behind: The potential impact of CFTR modulators on racial and ethnic disparities in cystic fibrosis

The advent of CFTR modulators, a genomic specific medication, revolutionized the treatment of CF for many patients. However, given that these therapeutics were only developed for specific CFTR mutations, not all people with CF have access to such disease-modifying drugs. Racial and ethnic minority groups are less likely to have CFTR mutations that are approved for CFTR modulators. This exclusion has the potential to widen existing health disparities.

Lumacaftor/ivacaftor combination for cystic fibrosis patients homozygous for Phe508del-CFTR

Cystic fibrosis (CF) is a life-shortening inherited disease caused by the loss or dysfunction of the CF transmembrane conductance regulator (CFTR) channel activity resulting from mutations in the CFTR gene. Phe508del is the most prevalent mutation, with approximately 90% of all CF patients carrying it on at least one allele. Over the past two or three decades, significant progress has been made in understanding the pathogenesis of CF, and in the development of effective CF therapies. The approval of Orkambi® (lumacaftor/ivacaftor) marks another milestone in CF therapeutics development, which, with the advent of personalized medicine, could potentially revolutionize CF care and management. This article reviews the rationale, progress and future direction in the development of lumacaftor/ivacaftor combination to treat CF patients homozygous for the Phe508del-CFTR mutation.

c.3623G > A mutation encodes a CFTR protein with impaired channel function

BACKGROUND

The aims of this study were to characterize clinical features of a pediatric African-American cystic fibrosis (CF) patient heterozygous for F508del and a novel c.3623G > A mutation, and to identify the molecular defect(s) associated with c.3623G > A mutation.

METHODS

The medical record of this patient was analyzed retrospectively. Western blotting and iodide efflux assay were used to study mutant CFTR protein expression level, maturation status, channel function, and the effects of CFTR modulation on these characteristics.

RESULTS

The encoding protein of c.3623G > A mutation, G1208D-CFTR, has a moderate processing defect and exhibits impaired channel function, which were partially rescued by using VX-809 or exposed to low temperature (28 °C). The patient has mild CF disease manifestations.

CONCLUSIONS

Our biochemical findings correlate with the clinical phenotype and suggest that c.3623G > A is a CF-causing mutation. The study helps expand our knowledge of rare CFTR mutations in a minority population and may have important clinical implications for personalized therapeutic intervention.

Capturing the Direct Binding of CFTR Correctors to CFTR by Using Click Chemistry

Cystic fibrosis (CF) is a lethal genetic disease caused by the loss or dysfunction of the CF transmembrane conductance regulator (CFTR) channel. F508del is the most prevalent mutation of the CFTR gene and encodes a protein defective in folding and processing. VX-809 has been reported to facilitate the folding and trafficking of F508del-CFTR and augment its channel function. The mechanism of action of VX-809 has been poorly understood. In this study, we sought to answer a fundamental question underlying the mechanism of VX-809: does it bind CFTR directly in order to exert its action? We synthesized two VX-809 derivatives, ALK-809 and SUL-809, that possess an alkyne group and retain the rescue capacity of VX-809. By using Cu(I) -catalyzed click chemistry, we provide evidence that the VX-809 derivatives bind CFTR directly in vitro and in cells. Our findings will contribute to the elucidation of the mechanism of action of CFTR correctors and the design of more potent therapeutics to combat CF.

Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for ivacaftor therapy in the context of CFTR genotype

Cystic fibrosis (CF) is a life-shortening disease arising as a consequence of mutations within the CFTR gene. Novel therapeutics for CF are emerging that target CF transmembrane conductance regulator protein (CFTR) defects resulting from specific CFTR variants. Ivacaftor is a drug that potentiates CFTR gating function and is specifically indicated for CF patients with a particular CFTR variant, G551D-CFTR (rs75527207). Here, we provide therapeutic recommendations for ivacaftor based on preemptive CFTR genotype results.

Normalization of sweat chloride concentration and clinical improvement with ivacaftor in a patient with cystic fibrosis with mutation S549N

The cystic fibrosis (CF) protein forms an anion channel in epithelial cells, and the absence or defective function of this channel results in the clinical manifestations of CF. CF is an autosomal recessive disorder, and its many disease-causing mutations divide into five or six classes. There are 10 known class 3 gating mutations, the most common of which is G551D. Ivacaftor is a drug that in vitro increases open time and transepithelial chloride transport in all 10 gating mutations, but it is approved for use only in patients with the G551D mutation. We report complete normalization of sweat chloride concentration and rapid clinical improvement over 6 weeks of treatment with ivacaftor in a patient with CF with the gating mutation S549N. The findings suggest that ivacaftor should be considered for use in patients with any of the known gating mutations.