8-Benzamidochromen-4-one-2-carboxylic Acids: Potent and Selective Agonists for the Orphan G Protein-Coupled Receptor GPR35

Abstract

8-Amido-chromen-4-one-2-carboxylic acid derivatives were identified as novel agonists at the G protein-coupled orphan receptor GPR35. They were characterized by a β-arrestin recruitment assay and optimized to obtain agonists with nanomolar potency for the human GPR35. The compounds were found to exhibit high selectivity versus the related GPR55. The most potent agonists were 6-bromo-8-(4-methoxybenzamido)-4-oxo-4H-chromene-2-carboxylic acid (85, EC50 12.1 nM) and 6-bromo-8-(2-chloro-4-methoxybenzamido)-4-oxo-4H-chromene-2-carboxylic acid (90, EC50 11.1 nM), both of which were >1700-fold selective versus GPR55. Most compounds were considerably less potent at rat and mouse than at human GPR35. 6-Bromo-8-(2-methoxybenzamido)-4-oxo-4H-chromene-2-carboxylic acid (87) was the only derivative that activated GPR35 of all three species at similar, low micromolar concentration. Compounds 85 and 90 are the most potent agonists at the human GPR35 known to date and might thus serve as powerful pharmacological tools to further elucidate the receptor's (patho)physiological role and its potential as a future drug target.

The Antiallergic Mast Cell Stabilizers Lodoxamide and Bufrolin as the First High and Equipotent Agonists of Human and Rat GPR35

“…These ligands, although also active at GPR35, displayed marked differences in potency between the rat and human orthologs, a feature previously noted for zaprinast (Taniguchi et al, 2006;Jenkins et al, 2010). The published literature indicates that certain GPR35 agonists such as pamoate (Jenkins et al, 2010), 4-{(Z)-[(2Z)-2-(2-fluorobenzylidene)-4-oxo-1,3-thiazolidin-5-ylidene]methyl}benzoic acid , and various 8-benzamidochromen-4-one-2-carboxylic acids (Funke et al, 2013) are highly selective for the human ortholog, whereas others such as pemirolast and amlexanox are highly selective for the rat ortholog. Although it is clearly speculative, it may be interesting to consider whether the inability to progress various antiallergics in the clinic may have a basis in this species selectivity.…”

“…4B). We and others have reported that many compounds first identified as ligands at human GPR35, including zaprinast, display markedly different potency and/or activity at rodent orthologs (Taniguchi et al, 2006;Jenkins et al, 2010Jenkins et al, , 2012Funke et al, 2013;Neetoo-Isseljee et al, 2013). We next examined the activity of a variety of mast cell stabilizers at the rat ortholog of GPR35 in the BRET-based b-arrestin-2 interaction assay.…”

“…Although GPR35 is indicated to be a receptor responsive to the endogenously produced tryptophan metabolite kynurenic acid (Wang et al, 2006), lack of convergence on this issue has resulted in a number of efforts to identify surrogate agonist ligands that might be used to help further define the roles of this receptor. Although a number of such ligands have been identified (Taniguchi et al, 2006;Jenkins et al, 2010;Zhao et al, 2010;Deng et al, 2012;Funke et al, 2013;Neetoo-Isseljee et al, 2013), many of these are either of modest potency and/or display markedly different potency at human and rodent orthologs of GPR35 (Jenkins et al, 2010;Funke et al, 2013;Neetoo-Isseljee et al, 2013). This has posed challenges both in efforts to define the orthosteric binding pocket of the receptor and to use rodents and cell lines derived from such animals to further explore the function of GPR35.…”

Functional G-protein-coupled receptor 35 is expressed by neurons in the CA1 field of the hippocampus

“…In high-throughput systems, expression of a chimeric G protein a subunit switches the preference of GPR35 from G i/o or G s to G q , and, consequently, evokes a rise in the level of inositol phosphate and intracellular Ca 2+ , each serving as a readout for receptor activation [2,7,20,21]. These assays, which are efficient, convenient, and allow rapid screening of large numbers of molecules led to the identification of a battery of pharmacological tools essential for identification of functional GPR35s [12,13,21,22].…”

On the 6- and 7-substituted chromone system. A computational study

“…Chromone-based drugs exhibit anticancer, anti-HIV, antioxidant, antiinflammatory, analgesic, antimicrobial, antimalarial, anti-diabetic, anticonvulsant, antiplatelet, gastroprotective, antihistaminic, antihypertensive, and insecticidal activity [4,5]. The chromen-4-one core has recently been identified as a potent and selective orphan G proteincoupled receptor (GPR35) agonist [6] in which, according to 3D-QSAR studies [7], steric, electrostatic, and hydrophobic substituents play a significant role. The substitution of a chemical system by a group is the most important fundamental modification in the search for new molecular properties.…”