Mutation-Specific Potency and Efficacy of Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel Potentiators

Abstract

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) ClϪ channel. The mutations G551D and G1349D, which affect the nucleotidebinding domains (NBDs) of CFTR protein, reduce channel activity. This defect can be corrected pharmacologically by small molecules called potentiators. CF mutations residing in the intracellular loops (ICLs), connecting the transmembrane segments of CFTR, may also reduce channel activity. We have investigated the extent of loss of function caused by ICL mutations and the sensitivity to pharmacological stimulation. We found that E193K and G970R (in ICL1 and ICL3, respectively) cause a severe loss of CFTR channel activity that can be rescued by the same potentiators that are effective on NBD mutations. We compared potency and efficacy of three different potentiators for E193K, G970R, and G551D. The 1,4-dihydropyridine felodipine and the phenylglycine PG-01 [2-[(2-1H-indol-3-yl-acetyl)-methylamino]-N-(4-isopropylphenyl)-2-phenylacetamide] were strongly effective on the three CFTR mutants. The efficacy of sulfonamide SF-01 [6-(ethylphenylsulfamoyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid cycloheptylamide], another CFTR potentiator, was instead significantly lower than felodipine and PG-01 for the E193K and G970R mutations, and almost abolished for G551D. Furthermore, SF-01 modified the response of G551D and G970R to the other two potentiators, an effect that may be explained by an allosteric antagonistic effect. Our results indicate that CFTR potentiators correct the basic defect caused by CF mutations residing in different CFTR domains. However, there are differences among potentiators, with felodipine and PG-01 having a wider pharmacological activity, and SF-01 being more mutation specific. Our observations are useful in the prioritization and development of drugs targeting the CF basic defect.

Stimulation of Murine Intestinal Secretion by Daily Genistein Injections: Gender-dependent Differences

“…Small molecule correctors (aminoarylthiozoles, quinazolinylaminopyrimidinones and bisaminomethylbithiazoles) have been shown to have varying effects on CF epithelia dependent upon the mutation [50]. The idea of mutation specific correctors was verified by Caputo et al [51] whose results suggested that felodipine and the phenyglycine PG-01, exerted a wider pharmacological effect (acting on CFTR mutations E193K, G970R and G551D) compared to the lesser potentiative sulfonamide SF-01. More recently, the newest CFTR corrector, VX-770, has been described in vitro to increase CFTR channel open probability in recombinant cells expressing mutated CFTR ( F508 and G551D) and to increase chloride secretion in human CF bronchial epithelia [52].…”

Ivacaftor potentiation of multiple CFTR channels with gating mutations

“…These included derivatives of 1,4-dihydropyridine and phenylglycine which potentiated G551D-, G970R-, and G1349D-CFTR to a similar extent as ivacaftor [23,[25][26]. In contrast, sulfamoyl-4-oxoquinoline-3-carboxamides were weakly effective on G551D-, G970R-, and G1349D-CFTR [26] and phloxine B strongly potentiated G551D-CFTR, but not G1349D-CFTR [22].…”

“…These included derivatives of 1,4-dihydropyridine and phenylglycine which potentiated G551D-, G970R-, and G1349D-CFTR to a similar extent as ivacaftor [23,[25][26]. In contrast, sulfamoyl-4-oxoquinoline-3-carboxamides were weakly effective on G551D-, G970R-, and G1349D-CFTR [26] and phloxine B strongly potentiated G551D-CFTR, but not G1349D-CFTR [22]. Previous studies have speculated that these differences may be due to distinct binding sites which may be differentially altered by CFTR mutations or which may modulate CFTR channel gating through different mechanisms [22][23]26].…”

Emergent Properties of Proteostasis in Managing Cystic Fibrosis

“…CF potentiators promote surface channel activity but do not promote folding and/or trafficking of the nascent polypeptide. Importantly, the potentiator drug Vertex 770 (http://www.cff.org/research/ClinicalResearch/ FAQs/VX-770/) (Caputo et al 2009;Van Goor et al 2009;Wellhauser et al 2009;Moran 2010) has recently completed a Phase II clinical trial with the G551D mutant (Fig. 3A), which is trafficked from the ER normally, cell surface localized but lacks channel activity.…”