Allosteric Inhibition of Endothelin ETA Receptors by 3,5-Dibromosalicylic Acid

Abstract

Derivatives of salicylic acid (SA) and benzoic acid prevent endothelin-1 (ET-1) binding to ETA receptors. This study analyzed actions of 30 derivatives of benzoic acid and salicylic acid on 125 I-ET-1 binding to recombinant rat ETA receptors. The most active compounds were 3,5-dibromosalicylic acid (Br2SA, K i ϭ 0.5 mM) and 3,5-diiodosalicylic acid (K i ϭ 0.3 mM). They were about 50 times more potent than SA and aspirin. Br2SA inhibited equilibrium 125 I-ET-1 binding in an apparently competitive manner. It accelerated 8-fold the dissociation of 125 I-ET-1 receptor complexes and did not modify the second order rate constant of association of 125 I-ET-1 to its receptors. Br2SA also decreased the affinity of ETA receptors for receptor antagonists BQ-123 and bosentan. Br2SA accelerated dissociation of 125 I-ET-1-solubilized ETA receptor complexes and decreased the apparent molecular size of solubilized receptors. Br2SA and 3,5-diiodosalicylic acid inhibited two cellular actions of ET-1: the mobilization of intracellular Ca 2ϩ stores in isolated cells and contractions of rat aortic rings. They accelerated the relaxing action of BQ-123 and bosentan in ET-1-treated aortic rings. The results suggest the existence of an allosteric modifier site on ETA receptors that recognizes selected derivatives of SA. SA derivatives might be of therapeutic interest to relieve tight ET-1 binding and to favor actions of receptor antagonists.

Allosteric Inhibition of [125I] ET-1 Binding to ETA Receptors by Aldoxime and Hydroxamic Acid Derivatives

“…As shown in Table 1, the benzohydroxamic acid derivatives 1a-3a, which present in their structure an amino group at position 2, are the best of the series because showed an appreciable inhibitory activity of one order of magnitude higher than that of 3, 5-disubstitutedsalicylic acids reported in the literature [40]. In fact, our compounds are active within the micromolare range of concentrations ( Table 1, 2, 3) while those reported in literature show activity between high micromolare and millimolar ranges [40]. Many competitive antagonists reported in literature are active in nM concentration while all allosteric inhibitors reported are active in mM concentration but even at this concentration it has great advantage that can generate new form of selectivity beside it can potentiate the competitive antagonist effects and might be of therapeutic interest to relieve tight ET-1 binding and to favor actions of receptor antagonist, this might solve the simple fact the usefulness of ET receptor antagonists against endogenous ET-1.…”

“…These compounds (1a-3a, 1b-3b, 1c-5c, 1d-3d, 1e-4e, 1f-2f and 1h-3h) were designed as analogues of previously studied 3, 5-disubstitutedsalicylic acids [39,40] with the aim to obtain potent allosteric inhibitors of ET A receptors. As shown in Table 1, the benzohydroxamic acid derivatives 1a-3a, which present in their structure an amino group at position 2, are the best of the series because showed an appreciable inhibitory activity of one order of magnitude higher than that of 3, 5-disubstitutedsalicylic acids reported in the literature [40]. In fact, our compounds are active within the micromolare range of concentrations ( Table 1, 2, 3) while those reported in literature show activity between high micromolare and millimolar ranges [40].…”

“…Like peptide [1,[33][34][35][36], and non peptide antagonist, the non peptides could be classified to sulfonamides and nonsulfonamides [1,33,35,37,38]. Recently allosteric modulation inhibition of endothelin *Address correspondence to this author at the Department of Pharmaceutical Chemistry, Garyounis University, Benghazi, Libya; Fax: 00218-61-2231520; E-mail: mabuajila@yahoo.ca receptors ET A has been described in literature [39,40]. The allosteric effect is an alternative approach in principle is to target the drug to a second site that is different from the Orthosteric site, but which is conformationally linked to the Orthosteric site (i.e.…”

“…This procedure led to the identification of dihalogenated derivatives of salicylic acid that are about 50 times more potent than aspirin. Results showed that the hydroxyl group of salicylate contributes little to the effect for related molecules in the benzoic acid, and salicylic acid series are equally potent [40]. Substitution of the aromatic hydrogen ring with halogens dramatically improves activity.…”

“…3, 5-Diisopropylsalicylic acid is almost as potent as dihalogenated derivatives. These indicate that bulky groups at positions 3 and 5 of the aromatic ring of benzoic acid or of salicylic acid favour activity of these compounds [40].…”