Pharmacological characterization of DPTN and other selective A

The A(3) adenosine receptor (AR) is emerging as an attractive drug target. Antagonists are proposed for the potential treatment of glaucoma and asthma. However, currently available A(3)AR antagonists are potent in human and some large animals, but weak or inactive in mouse and rat. In this study, we re-synthesized a previously reported A(3)AR antagonist, DPTN, and evaluated its affinity and selectivity at human, mouse, and rat ARs. We showed that DPTN, indeed, is a potent A(3)AR antagonist for all three species tested, albeit a little less selective for mouse and rat A(3)AR in comparison to the human A(3)AR. DPTN’s K(i) values at respective A(1), A(2A), A(2B), and A(3) receptors were (nM) 162, 121, 230, and 1.65 (human); 411, 830, 189, and 9.61 (mouse); and 333, 1147, 163, and 8.53 (rat). Its antagonist activity at both human and mouse A(3)ARs was confirmed in a cyclic AMP functional assay. Considering controversial use of currently commercially available A(3)AR antagonists in rats and mice, we also re-examined other commonly used and selective A(3)AR antagonists under the same experimental conditions. The K(i) values of MRS1523 were shown to be 43.9, 349, and 216 nM at human, mouse, and rat A(3)ARs, respectively. MRS1191 and MRS1334 showed incomplete inhibition of [(125)I]I-AB-MECA binding to mouse and rat A(3)ARs, while potent human A(3)AR antagonists, MRS1220, MRE3008F20, PSB10, PSB-11, and VUF5574 were largely inactive. Thus, we demonstrated that DPTN and MRS1523 are among the only validated A(3)AR antagonists that can be possibly used (at an appropriate concentration) in mouse or rat to confirm an A(3)AR-related mechanism or function. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11302-021-09823-5.