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 u sed as tools in many pharmacological studies. We have now characterized the ir affinity and selectivity profile on human adenosine receptors stably tra nsfected 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 ra dioligand, the three compounds were equally potent at A(2A) receptors, thei r 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 lac k of selective ligands, interaction with A(2B) receptors was assessed using the cAMP accumulation assay following stimulation by the adenosine recepto r agonist N-ethylcarboxamidoadenosine (NECA). CGS 15943 was almost as poten t at A(1) receptors (K-i 3.5 nM) as at A(2A) receptors, showed moderate aff inity for A(3) receptors (K-i 95 nM) and also interacted with A(2B) Pecepto rs (K-i 44 nM; pA(2) 7.5). ZM 241385 showed little affinity for A(1) recept ors (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 in teraction with A(3) receptors (K-i > 10 mu M), and showed negligible intera ction with A(2B) receptors (K-i 5 mu M; pA(2) 6.0). These data indicate tha t SCH 58261 is the most selective A2A antagonist currently available. Moreo ver, the different receptor selectivity of these three chemically related c ompounds provides useful information to progress with structure-activity re lationship studies.