2‐Chloro N 6 ‐methyl‐(N)‐methanocarba‐2′‐deoxyadenosine‐3′,5′‐bisphosphate is a selective high affinity P2Y 1 receptor antagonist

We reported previously that bisphosphate derivatives of adenosine are antagonists of the P2Y 1 receptor and that modification of the ribose in these analogues is tolerated in the P2Y 1 receptor binding pharmacophore. Here we delineate the pharmacological activity of one such non‐nucleotide molecule, 2‐chloro N 6 ‐methyl‐(N)‐methanocarba‐2′‐deoxyadenosine‐3′,5′‐bisphosphate (MRS2279), in which the ribose is replaced by a cyclopentane ring constrained in the (N)‐conformation by a cyclopropane moiety. MRS2279 antagonized 2MeSADP‐stimulated inositol phosphate formation in turkey erythrocyte membranes with competitive kinetics (pK B =7.75). High affinity competitive antagonism by MRS2279 was also observed at the human P2Y 1 receptor (pK B =8.10) stably expressed in 1321N1 human astrocytoma cells. Antagonism was specific for the P2Y 1 receptor since MRS2279 had no effect on activation of the human P2Y 2 , P2Y 4 , P2Y 6 , or P2Y 11 receptors by their cognate agonists. MRS2279 also did not block the capacity of ADP to act through the Gi/adenylyl cyclase linked P2Y receptor of platelets to inhibit cyclic AMP accumulation. In contrast, the P2Y 1 receptor is known to be obligatory in the process of ADP‐induced platelet aggregation, and MRS2279 competitively inhibited ADP‐promoted platelet aggregation with an apparent affnity (pK B =8.05) similar to that observed at the human P2Y 1 receptor heterologously expressed in 1321N1 cells. Taken together these results illustrate selective high affinity antagonism of the P2Y 1 receptor by a non‐nucleotide molecule that should prove useful for pharmacological delineation of this receptor in various tissues. British Journal of Pharmacology (2002) 135 , 2004–2010; doi: 10.1038/sj.bjp.0704673