The novel suramin analogue NF864 selectively blocks P2X1 receptors in human platelets with potency in the low nanomolar range

The role of ATP-stimulated P2X(1) receptors in human platelets is still unclear. They may act alone or in synergy with other pathways, such as P2Y(1) or P2Y(12) receptors, to accelerate and enhance calcium mobilisation, shape change and aggregation. To date very few pharmacological means of selectively inhibiting platelet P2X(1) receptors have been described, although recent work has shown that suramin is a useful lead compound for the development of high-affinity P2X(1) antagonists. We therefore investigated the effects of a series of bivalent and tetravalent suramin analogues on alpha beta meATP (P2X(1) receptors)-induced or ADP (P2Y(1) receptors)-induced intracellular calcium increases and shape change, as well as on ADP-induced aggregation (P2Y(1) & P2Y(12) receptors) in human platelets. Changes in intracellular calcium were measured using standard fluorescence techniques, while shape change and aggregation were determined by turbidimetry. The novel tetravalent compound NF864 (8,8',8",8"-(carbonylbis(imino-5,1,3-benzenetriyl- bis(carbonylimino)))tetrakis-naphthalene-1,3,5-trisulfonic acid-dodecasodium salt) proved to be the most potent platelet P2X(1) antagonist reported to date, blocking alpha beta meATP-induced Ca2+ stop increases and shape change in a concentration-dependent manner, with a pA(2) of 8.17 and 8.49, respectively. The ability to inhibit the platelet P2X(1) receptor displayed the following order : NF864 > NF449 >= NNF110 > NF023=MK-HU1=suramin. A different antagonistic profile was observed for ADP-induced Ca2+ stop increases, shape change and aggregation; however, overall four compounds showed sufficient ability to selectively inhibit P2X(1) responses, with the order NF110 > NF449 >= NNF864 >= NMK-HU1. Therefore, these compounds should prove useful tools for investigating the functional significance of platelet P2X(1) receptors in thrombosis and haemostasis, NF864 being the most promising compound.