KF26777 (2-(4-bromophenyl)-7,8-dihydro-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one dihydrochloride), a new potent and selective adenosine A3 receptor antagonist

We investigated the biochemical and pharmacological properties of a new adenosine A(3) receptor antagonist, KF26777 (2-(4bromophenyl)-7,8-dihydro-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one dihydrochloride). This compound was characterized using N-6-(4-amino-3-iodobenzyl)adenosine-5'-N-methyluronamide (I-125]AB-MECA) or [S-35]guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding to membranes from human embryonic kidney 293 (HEK293) cells expressing human adenosine A, receptors, KF26777 showed a K-i value of 0.20 +/- 0.038 n.M for human adenosine A., receptors labeled with [I-125]AB-MECA and possessed 9000-, 2350- and 3100-fold selectivity vs. human adenosine A(1), A(2A) and A(2B) receptors, respectively. The inhibitory mode of binding was competitive. KF26777 inhibited the binding of [S-35]GTPgammaS stimulated by 1 muM 2-chloro-N-6-(3-iodobenzyl)adenosine-5'-N-methyluronamide (Cl-IB-MECA), The IC50 value was 270 +/- 85 nM; the compound had no effect on basal activity, Dexamethasone treatment for HL-60 cells, human promyelocytic leukemia, upregulated functional adenosine A3 receptors expression, and resulted in the enhanced elevation of intracellular Ca2+ concentration ([Ca2+](i)) via the adenosine A(3) receptor. KF26777 antagonized this [Ca2+](i) mobilization induced by Cl-IB-MECA, with a K-B value of 0.42 +/- 0.14 nM. These results indicate that KF26777 is a highly potent and selective antagonist of the human adenosine A(3) receptor. (C) 2002 Elsevier Science B.V All rights reserved.