Uridine Triphosphate Thio-analogues Inhibit Platelet P2Y12 Receptors and Aggregation Condensed title: UTP Thio-analogues and Platelet Aggregation

Platelet P2Y12 is an important ADP receptor that is involved in agonists-induced platelet aggregation and is an important target for the development of anti-platelet aggregation drugs. Here the effects of thio-analogues of uridine triphosphate (UTP) on ADP-induced platelet aggregation are characterised. Using human platelet rich plasma we demonstrate that UTP inhibits P2Y12 but not P2Y1 receptors and antagonises ADP-induced platelet aggregation in a conc.-dependent manner with an IC50 value of ~250 μM against ADP (10 μM). An 8-fold increase in the platelet inhibitory activity was observed with 2-thio analogue of UTP (2S-UTP) with an IC50 value of 30 μM. A 33-fold increase in anti-platelet aggregation activity was observed with 4-thio analogue (4S-UTP) with an IC50 value of 7.5 μM. However, a 3-fold decrease in activity was observed by introducing an isobutyl group at the 4Sposition. A complete loss in anti-platelet aggregation activity was observed with thio-modification of gamma phosphate of the sugar moiety which yields an enzymatically stable analogue. The interaction of UTP analogues with P2Y12 receptors was further verified by P2Y12 receptor binding assay and cAMP assay. The novel data demonstrate for the first time that 2and 4-thio analogues of UTP are potent P2Y12 receptor antagonists that can be useful candidates for therapeutic intervention.