Comparison of CGS15943, ZM241385 and SCH58261 as antagonists at human adenosine receptors

Three structurally related non-xanthine compounds, CGS 15943, ZM 241385 and SCH 58261, are potent A(2A) adenosine receptor antagonists and have been used as tools in many pharmacological studies. We have now characterized their affinity and selectivity profile on human adenosine receptors stably transfected into either CHO cells (A(1) and A(2B) receptors) or HEK-293 cells (A(2A) and A(3) receptors). In binding studies using [H-3]SCH 58261 as a radioligand, the three compounds were equally potent at A(2A) receptors, their K-i value being less than 1 nM. Affinity for A(1) and A(3) receptors was measured using [H-3]DPCPX and [I-125]AB-MECA as radioligands. Given the lack of selective ligands, interaction with A(2B) receptors was assessed using the cAMP accumulation assay following stimulation by the adenosine receptor agonist N-ethylcarboxamidoadenosine (NECA). CGS 15943 was almost as potent at A(1) receptors (K-i 3.5 nM) as at A(2A) receptors, showed moderate affinity for A(3) receptors (K-i 95 nM) and also interacted with A(2B) Peceptors (K-i 44 nM; pA(2) 7.5). ZM 241385 showed little affinity for A(1) receptors (K-i 255 nM), and did not interact with A(3) receptors (K-i >10 mu M); however, it displayed moderate affinity for A(2B) receptors (K-i 50 nM; pA(2) 7.3). SCH 58261 had weak affinity for A(1) receptors (K-i 287 nM), no interaction with A(3) receptors (K-i > 10 mu M), and showed negligible interaction with A(2B) receptors (K-i 5 mu M; pA(2) 6.0). These data indicate that SCH 58261 is the most selective A2A antagonist currently available. Moreover, the different receptor selectivity of these three chemically related compounds provides useful information to progress with structure-activity relationship studies.