Pharmacological characterization of DPTN and other selective A adenosine receptor antagonists.

The A adenosine receptor (AR) is emerging as an attractive drug target. Antagonists are proposed for the potential treatment of glaucoma and asthma. However, currently available AAR 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 AAR antagonist, DPTN, and evaluated its affinity and selectivity at human, mouse, and rat ARs. We showed that DPTN, indeed, is a potent AAR antagonist for all three species tested, albeit a little less selective for mouse and rat AAR in comparison to the human AAR. DPTN's K values at respective A, A, A, and A 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 AARs was confirmed in a cyclic AMP functional assay. Considering controversial use of currently commercially available AAR antagonists in rats and mice, we also re-examined other commonly used and selective AAR antagonists under the same experimental conditions. The K values of MRS1523 were shown to be 43.9, 349, and 216 nM at human, mouse, and rat AARs, respectively. MRS1191 and MRS1334 showed incomplete inhibition of [I]I-AB-MECA binding to mouse and rat AARs, while potent human AAR antagonists, MRS1220, MRE3008F20, PSB10, PSB-11, and VUF5574 were largely inactive. Thus, we demonstrated that DPTN and MRS1523 are among the only validated AAR antagonists that can be possibly used (at an appropriate concentration) in mouse or rat to confirm an AAR-related mechanism or function.