PHARMACOLOGICAL CHARACTERIZATION OF NOVEL A(3) ADENOSINE RECEPTOR-SELECTIVE ANTAGONISTS

The effects of putative A(3) adenosine receptor antagonists of three d iverse chemical classes (the flavonoid MRS 1067, the 6-phenyl-1,4-dihy dropyridines MRS 1097 and MRS 1191, and the triazoloquinazoline MRS 12 20) were characterized in receptor binding and functional assays. MRS 1067, MRS 1191 and MRS 1220 were found to be competitive in saturation binding studies using the agonist radioligand [I-125]AB-MECA amino-3- iodobenzyl)adenosine-5'-N-methyluronamide) at cloned human brain A(3) receptors expressed in HEK-293 cells. Antagonism was demonstrated in f unctional assays consisting of agonist-induced inhibition of adenylate cyclase and the stimulation of binding of [S-35]guanosine 5'-O-(3-thi otriphosphate) ([S-35]GTP-gamma-S) to the associated G-proteins. MRS 1 220 and MRS 1191, with K-B values of 1.7 and 92 nM, respectively, prov ed to be highly selective for human A(3) receptor vs human A(1) recept or-mediated effects on adenylate cyclase. In addition, MRS 1220 revers ed the effect of A(3) agonist-elicited inhibition of tumor necrosis fa ctor-alpha formation in the human macrophage U-937 cell line, with an IC50 value of 0.3 mu M. Published by Elsevier Science Ltd.