vrt-532 and Cystic-Fibrosis

The enzyme Arylsulfatase B (ARSB; N-acetylgalactosamine 4-sulfatase), is required for degradation of sulfated glycosaminoglycans (GAGs) which accumulate in cystic fibrosis. ARSB is reduced in cystic fibrosis cells and increases when defective CFTR is repaired by insertion of the normal gene. This study was undertaken to determine if modification of CFTR by small molecule correctors or potentiators could also increase ARSB and reduce the accumulation of chondroitin 4-sulfate (C4S).. CF bronchial epithelial cells homozygous for the F508 deletion (ACD#14071) and normal human bronchial epithelial cells (BEC) were grown and differentiated following an established protocol. Cells were treated with either VRT-532, a CFTR potentiator, or VRT-534, a CFTR corrector, or vehicle control. The impact on ARSB activity, protein and mRNA expression, C4S and total sulfated glycosaminoglycan content, Interleukin-8 and Interleukin-6 secretion, and neutrophil chemotaxis was determined by specific assays.. The CFTR potentiator, but not the corrector, increased ARSB activity and expression to the level in the normal bronchial epithelial cells (BEC). Concomitantly, total sulfated glycosaminoglycans and C4S declined, secreted IL-8 increased, secreted IL-6 declined, and neutrophil chemotaxis to the spent media obtained from the potentiator-treated CF cells increased.. The CFTR potentiator increased ARSB activity and expression and associated effects. This suggests that a critical interaction between CFTR and ARSB is related to CFTR function in regulation of a ligand-gated anion channel at the cell membrane, rather than to CFTR processing and intracellular trafficking.

Topics: Bronchi; Cell Line; Chemotaxis, Leukocyte; Chondroitin Sulfates; Cresols; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Epithelial Cells; Glycosaminoglycans; Humans; Interleukin-6; Interleukin-8; N-Acetylgalactosamine-4-Sulfatase; Pyrazoles; Respiratory Mucosa

Cystic fibrosis (CF) is a lethal recessive genetic disease caused by mutations in the CFTR gene. The gene product is a PKA-regulated anion channel that is important for fluid and electrolyte transport in the epithelia of lung, gut, and ducts of the pancreas and sweat glands. The most common CFTR mutation, ΔF508, causes a severe, but correctable, folding defect and gating abnormality, resulting in negligible CFTR function and disease. There are also a large number of rare CF-related mutations where disease is caused by CFTR misfolding. Yet the extent to which defective biogenesis of these CFTR mutants can be corrected is not clear. CFTRV232D is one such mutant that exhibits defective folding and trafficking. CFTRΔF508 misfolding is difficult to correct, but defective biogenesis of CFTRV232D is corrected to near wild-type levels by small-molecule folding correctors in development as CF therapeutics. To determine if CFTRV232D protein is competent as a Cl(-) channel, we utilized single-channel recordings from transfected human embryonic kidney (HEK-293) cells. After PKA stimulation, CFTRV232D channels were detected in patches with a unitary Cl(-) conductance indistinguishable from that of CFTR. Yet the frequency of detecting CFTRV232D channels was reduced to ∼20% of patches compared with 60% for CFTR. The folding corrector Corr-4a increased the CFTRV232D channel detection rate and activity to levels similar to CFTR. CFTRV232D-corrected channels were inhibited with CFTR(inh-172) and stimulated fourfold by the CFTR channel potentiator VRT-532. These data suggest that CF patients with rare mutations that cause CFTR misfolding, such as CFTRV232D, may benefit from treatment with folding correctors and channel potentiators in development to restore CFTRΔF508 function.

Topics: Benzamides; Cresols; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; HEK293 Cells; Humans; Patch-Clamp Techniques; Protein Folding; Pyrazoles; Thiazoles

Modulator compounds intended to overcome disease-causing mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) show significant promise in clinical testing for cystic fibrosis. However, the mechanism(s) of action underlying these compounds are not fully understood. Activation of CFTR ion transport requires PKA-regulated phosphorylation of the regulatory domain (R-D) and dimerization of the nucleotide binding domains. Using a newly developed assay, we evaluated nine compounds including both CFTR potentatiators and activators discovered via various high-throughput screening strategies to acutely augment CFTR activity. We found considerable differences in the effects on R-D phosphorylation. Some (including UC(CF)-152) stimulated robust phosphorylation, and others had little effect (e.g., VRT-532 and VX-770). We then compared CFTR activation by UC(CF)-152 and VRT-532 in Ussing chamber studies using two epithelial models, CFBE41o(-) and Fischer rat thyroid cells, expressing various CFTR forms. UC(CF)-152 activated wild-type-, G551D-, and rescued F508del-CFTR currents but did not potentiate cAMP-mediated CFTR activation. In contrast, VRT-532 moderately activated CFTR short-circuit current and strongly potentiated forskolin-mediated current. Combined with the result that UC(CF)-152, but not VRT-532 or VX-770, acts by increasing CFTR R-D phosphorylation, these findings indicate that potentiation of endogenous cAMP-mediated activation of mutant CFTR is not due to a pathway involving augmented R-D phosphorylation. This study presents an assay useful to distinguish preclinical compounds by a crucial mechanism underlying CFTR activation, delineates two types of compound able to acutely augment CFTR activity (e.g., activators and potentiators), and demonstrates that a number of different mechanisms can be successfully employed to activate mutant CFTR.

Topics: Aminophenols; Animals; Blotting, Western; Cell Line; Chlorocebus aethiops; Colforsin; Cresols; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Diffusion Chambers, Culture; Dimerization; Enzyme-Linked Immunosorbent Assay; Gene Expression; High-Throughput Screening Assays; Humans; Ion Channel Gating; Ion Transport; Lentivirus; Membrane Transport Modulators; Mice; Mutation; Phosphorylation; Protein Structure, Tertiary; Pyrazoles; Quinolones; Retroviridae; Transduction, Genetic

CF (cystic fibrosis) is caused by mutations in CFTR (CF transmembrane conductance regulator), which cause its mistrafficking and/or dysfunction as a regulated chloride channel on the apical surface of epithelia. CFTR is a member of the ABC (ATP-binding-cassette) superfamily of membrane proteins and a disease-causing missense mutation within the ABC signature sequence; G551D-CFTR exhibits defective phosphorylation and ATP-dependent channel gating. Studies of the purified and reconstituted G551D-CFTR protein revealed that faulty gating is associated with defective ATP binding and ATPase activity, reflecting the key role of G551 in these functions. Recently, high-throughput screens of chemical libraries led to identification of modulators that enhance channel activity of G551D-CFTR. However, the molecular target(s) for these modulators and their mechanism of action remain unclear. In the present study, we evaluated the mechanism of action of one small-molecule modulator, VRT-532, identified as a specific modulator of CF-causing mutants. First, we confirmed that VRT-532 causes a significant increase in channel activity of G551D-CFTR using a novel assay of CFTR function in inside-out membrane vesicles. Biochemical studies of purified and reconstituted G551D-CFTR revealed that potentiation of the ATPase activity of VRT-532 is mediated by enhancing the affinity of the mutant for ATP. Interestingly, VRT-532 did not affect the ATPase activity of the Wt (wild-type) CFTR, supporting the idea that this compound corrects the specific molecular defect in this mutant. To summarize, these studies provide direct evidence that this compound binds to G551D-CFTR to rescue its specific defect in ATP binding and hydrolysis.

Topics: Adenosine Triphosphatases; Adenosine Triphosphate; Animals; Cell Line; Cresols; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Enzyme Activation; Glycine; Iodides; Kinetics; Mutation; Pyrazoles; Spodoptera

Cystic fibrosis (CF) is a fatal genetic disease caused by mutations in cftr, a gene encoding a PKA-regulated Cl(-) channel. The most common mutation results in a deletion of phenylalanine at position 508 (DeltaF508-CFTR) that impairs protein folding, trafficking, and channel gating in epithelial cells. In the airway, these defects alter salt and fluid transport, leading to chronic infection, inflammation, and loss of lung function. There are no drugs that specifically target mutant CFTR, and optimal treatment of CF may require repair of both the folding and gating defects. Here, we describe two classes of novel, potent small molecules identified from screening compound libraries that restore the function of DeltaF508-CFTR in both recombinant cells and cultures of human bronchial epithelia isolated from CF patients. The first class partially corrects the trafficking defect by facilitating exit from the endoplasmic reticulum and restores DeltaF508-CFTR-mediated Cl(-) transport to more than 10% of that observed in non-CF human bronchial epithelial cultures, a level expected to result in a clinical benefit in CF patients. The second class of compounds potentiates cAMP-mediated gating of DeltaF508-CFTR and achieves single-channel activity similar to wild-type CFTR. The CFTR-activating effects of the two mechanisms are additive and support the rationale of a drug discovery strategy based on rescue of the basic genetic defect responsible for CF.

Topics: 3T3 Cells; Animals; Biotinylation; Cell Line; Cells, Cultured; Chlorides; Cresols; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Humans; Ion Channel Gating; Mice; Pyrazoles; Rats; Recombinant Proteins; Sequence Deletion; Thyroid Gland