Abstract
Variation in pharmacology and function of ligands at species orthologs can be a confounding feature in understanding the biology and role of poorly characterized receptors. Substantial selectivity in potency of a number of GPR35 agonists has previously been demonstrated between human and rat orthologs of this G protein-coupled receptor. Via a bioluminescence resonance energy transfer-based assay of induced interactions between GPR35 and β-arrestin-2, addition of the mouse ortholog to such studies indicated that, as for the rat ortholog, murine GPR35 displayed very low potency for pamoate whilst potency for the reference GPR35 agonist zaprinast was intermediate between the rat and human orthologs. This pattern was replicated in receptor internalization and G protein activation assays. The effectiveness and mode of action of two recently reported GPR35 antagonists methyl-5-[(tert-butylcarbamothioylhydrazinylidene)methyl]-1-(2,4-difluorophenyl)pyrazole-4-carboxylate (CID-2745687) and 2-hydroxy-4-[4-(5Z)-5-[(E)-2-methyl-3-phenylprop-2-enylidene]-4-oxo-2-sulfanylidene-1,3-thiazolidin-3-yl]butanoylamino]benzoic acid (ML-145, CID-2286812) was investigated. Both CID-2745687 and ML-145 competitively inhibited effects of cromolyn disodium and zaprinast at human GPR35, two agonists that share an overlapping binding site. By contrast, although ML-145 also competitively antagonized effects of pamoate, CID-2745687 acted in a non-competitive fashion. Neither ML-145 nor CID-2745687 was able to effectively antagonize agonist effects of either zaprinast or cromolyn disodium at either rodent ortholog of GPR35. These studies demonstrate that marked species selectivity of ligands at GPR35 is not restricted to agonists and that considerable care is required to select appropriate ligands to explore the function of GPR35 in non-human cells and tissues.
- Received July 31, 2012.
- Revision received September 10, 2012.
- Accepted September 10, 2012.
- The American Society for Pharmacology and Experimental Therapeutics