Molecular switch for CLC-K Cl ⁻ channel block/activation: Optimal pharmacophoric requirements towards high-affinity ligands

Abstract

ClC-Ka and ClC-Kb Cl ؊ channels are pivotal for renal salt reabsorption and water balance. There is growing interest in identifying ligands that allow pharmacological interventions aimed to modulate their activity. Starting from available ligands, we followed a rational chemical strategy, accompanied by computational modeling and electrophysiological techniques, to identify the molecular requisites for binding to a blocking or to an activating binding site on ClC-Ka. The major molecular determinant that distinguishes activators from blockers is the level of planarity of the aromatic portions of the molecules: only molecules with perfectly coplanar aromatic groups display potentiating activity. Combining several molecular features of various CLC-K ligands, we discovered that phenyl-benzofuran carboxylic acid derivatives yield the most potent ClC-Ka inhibitors so far described (affinity <10 M). The increase in affinity compared with 3-phenyl-2-p-chlorophenoxypropionic acid (3-phenyl-CPP) stems primarily from the conformational constraint provided by the phenyl-benzofuran ring. Several other key structural elements for high blocking potency were identified through a detailed structure-activity relationship study. Surprisingly, some benzofuran-based drugs inhibit ClC-Kb with a similar affinity of <10 M, thus representing the first inhibitors for this CLC-K isoform identified so far. Based on our data, we established a pharmacophore model that will be useful for the development of drugs targeting CLC-K channels.kidney ͉ molecular modeling ͉ pharmacology

Structure-Activity Relationship of Fenamates as Slo2.1 Channel Activators

“…The dual action of fenamates has been reported previously for kidney CLC-K Cl Ϫ channels (Liantonio et al, 2006(Liantonio et al, , 2008. In our study, the activation effect of NSAIDs was rapid in onset and completely and quickly reversible on washout, sug- NFA.…”

Novel diuretic targets

“…Toward this end, a residue near the extracellular vestibule of the channel has been identified as a major determinant of inhibitor selectivity (83,93). In parallel studies, Pusch and colleagues (82,83,107) also characterized the interactions of another class of compounds, the fenamates, with the ClC-K channels. The fenamates are NSAID that are also known to inhibit and/or activate a wide variety of ion channels (14,19,44,77,117,153).…”

“…The excellent bioavailability of MT-189 motivates further development of this scaffold to improve specificity. The in vitro threefold selectivity of MT-189 for ClC-Ka over ClC-Kb (which is 90% identical to ClC-Ka) (83) arouses hope that it may be feasible to engineer more stringent specificity through molecular docking and rational design. Toward this end, a residue near the extracellular vestibule of the channel has been identified as a major determinant of inhibitor selectivity (83,93).…”

“…The in vitro threefold selectivity of MT-189 for ClC-Ka over ClC-Kb (which is 90% identical to ClC-Ka) (83) arouses hope that it may be feasible to engineer more stringent specificity through molecular docking and rational design. Toward this end, a residue near the extracellular vestibule of the channel has been identified as a major determinant of inhibitor selectivity (83,93). In parallel studies, Pusch and colleagues (82,83,107) also characterized the interactions of another class of compounds, the fenamates, with the ClC-K channels.…”

“…Of relevance to the kidney, Pusch and colleagues (48) have systematically characterized and developed small-molecule inhibitors and activators of the ClC-K channels. In a series of elegant studies, they evolved the low-affinity (mM) ClC-1 inhibitor p-chlorophenoxy-propionic acid (CPP) (5, 112) into a low-micromolar inhibitor of ClC-Ka, MT-189 (80,83,84,108) (Fig. 3; see below).…”