Pharmacological characterisation and inhibitory effects of (2R,3R,4S,5R)-2-(6-amino-2-{[(1S)-2-hydroxy-1-(phenylmethyl)ethyl]amino}-9H-purin-9-yl)-5-(2-ethyl-2H-tetrazol-5-yl)tetrahydro-3,4-furandiol, a novel ligand that demonstrates both adenosine A2A receptor agonist and adenosine A3 receptor antagonist activity

Abstract

The pharmacological properties of the novel ligand, (2R,3R,4S,5R)-2-(6-amino-2-{[(1S)-2-hydroxy-1-(phenylmethyl)ethyl]amino}-9H-purin-9-yl)-5-(2-ethyl-2H-tetrazol-5-yl)tetrahydro-3,4-furandiol (I), at the human adenosine receptors were investigated using Chinese hamster ovary cell lines recombinantly expressing these receptors. Functional studies were performed using a cyclic AMP-coupled reporter gene system. Binding studies were performed using membranes from these cells. The effects of ligand (I) were also determined on functional responses of human neutrophils and eosinophils. Ligand (I) had a high affinity for the adenosine A2A receptor (pKi 7.8±0.2) and was a potent agonist at this receptor (pEC50 9.0±0.2). Ligand (I) had a similar affinity for the adenosine A3 receptor (pKi 7.8±0.1) but displayed no agonist activity, acting instead as a competitive antagonist (pA2 8.3±0.04). Ligand (I) had lower affinity for adenosine A1 and A2B receptors (pKi≤6) and showed relatively weak agonist activity at these receptors (pEC50 7.1 at both receptors). Ligand (I) was a potent inhibitor of the generation of reactive oxygen species from human neutrophils and eosinophils (pEC50 9.7±0.1 and 9.4±0.2 respectively). The inhibitory effect of ligand (I) on the release of reactive oxygen species from neutrophils was antagonised competitively by the adenosine A2A receptor antagonist 9-chloro-2-(2-furanyl)-[1,2,4]triazolo[1,5-c]quinazolin-5-amine (CGS15943) with a pA2 value (10.03±0.44) consistent with an effect on adenosine A2A receptors. Ligand (I) also inhibited the release of granule proteins from neutrophils and eosinophils (pEC50 8.7 and 8.9 respectively), albeit less potently than as an inhibitor of reactive oxygen species generation. In summary, ligand (I) is a potent and selective agonist for the adenosine A2A receptor and a competitive antagonist at the adenosine A3 receptor. Ligand (I) has potent anti-inflammatory effects on human granulocytes in vitro.