Pharmacological characterisation of novel adenosine A₃ receptor antagonists.

ABSTRACT: The adenosine A₃ receptor (A₃R) belongs to a family of four adenosine receptor (AR) subtypes which all play distinct roles throughout the body. A₃R antagonists have been described as potential treatments for numerous diseases including asthma. Given the similarity between (adenosine receptors) orthosteric binding sites, obtaining highly selective antagonists is a challenging but critical task. Here we screen 39 potential A₃R, antagonists using agonist-induced inhibition of cAMP. Positive hits were assessed for AR subtype selectivity through cAMP accumulation assays. The antagonist affinity was determined using Schild analysis (pA₂ values) and fluorescent ligand binding. Structure-activity relationship investigations revealed that loss of the 3-(dichlorophenyl)-isoxazolyl moiety or the aromatic nitrogen heterocycle with nitrogen at ?-position to the carbon of carboximidamide group significantly attenuated K18 antagonistic potency. Mutagenic studies supported by molecular dynamic simulations combined with Molecular Mechanics-Poisson Boltzmann Surface Area calculations identified the residues important for binding in the A₃R orthosteric site. We demonstrate that K18, which contains a 3-(dichlorophenyl)-isoxazole group connected through carbonyloxycarboximidamide fragment with a 1,3-thiazole ring, is a specific A₃R (3R antagonist and the description of its orthosteric binding mode. Our findings may provide new insights for drug discovery.

SUBMITTER: Barkan K 

PROVIDER: S-EPMC7695835 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature