Referenced in: none

Automatically associated channels: ClC1 , ClC4 , Kir2.3

Title: Structural requisites of 2-(p-chlorophenoxy)propionic acid analogues for activity on native rat skeletal muscle chloride conductance and on heterologously expressed CLC-1.

Authors: Antonella Liantonio, Annamaria De Luca, Sabata Pierno, Maria Paola Didonna, Fulvio Loiodice, Giuseppe Fracchiolla, Paolo Tortorella, Laghezza Antonio, Elisabetta Bonerba, Sonia Traverso, Laura Elia, Alessandra Picollo, Michael Pusch, Diana Conte Camerino

Journal, date & volume: Br. J. Pharmacol., 2003 Aug , 139, 1255-64

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/12890704

Abstract
(1) The 2-(p-chlorophenoxy)propionic acid (CPP) modulates in a stereoselective manner the macroscopic chloride conductance (gCl), the electrical parameter sustained by the CLC-1 channel, of skeletal muscle. In order to determine the structural requirements for modulating native gCl and to identify high-affinity ligands, the effects of newly synthesised CPP analogues have been evaluated on gCl of rat EDL muscle fibres by means of the two-microelectrode current-clamp technique. (2) Each type of the following independent modification of CPP structure led to a three- to 10-fold decrease or to a complete lack of gCl-blocking activity: replacement of the electron-attractive chlorine atom of the aromatic ring, substitution of the oxygen atom of the phenoxy group, modification at the chiral centre and substitution of the carboxylic function with a phosphonate one. (3) The analogues bearing a second chlorophenoxy group on the asymmetric carbon atom showed a significant gCl-blocking activity. Similar to racemate CPP, the analogue with this group, spaced by an alkyl chain formed by three methylenic groups, blocked gCl by 45% at 100 micro M. (4) These latter derivatives were tested on heterelogously expressed CLC-1 performing inside-out patch-clamp recordings to further define how interaction between drug and channel protein could take place. Depending on the exact chemical nature of modification, these derivatives strongly blocked CLC-1 with K(D) values at -140 mV ranging from about 4 to 180 micro M. (5) In conclusion, we identified four molecular determinants pivotal for the interaction with the binding site on muscle CLC-1 channels: (a) the carboxylic group that confers the optimal acidity and the negative charge; (b) the chlorophenoxy moiety that might interact with a hydrophobic pocket; (c) the chiral centre that allows the proper spatial disposition of the molecule; (d) an additional phenoxy group that remarkably stabilises the binding by interacting with a second hydrophobic pocket.