Thromboxane A2/prostaglandin endoperoxide (TXA2/PG-END) receptor binding properties in human platelets of ridogrel, a combined TXA2 synthase inhibitor--TXA2/PG-END receptor antagonist.
Ridogrel, a potent thromboxane A2 (TXA2) synthase inhibitor, also has thromboxane A2 prostaglandin endoperoxide (TXA2/PG-END) receptor antagonistic properties as documented in functional studies of human platelets. In the present study, the binding affinities of the TXA2 synthase inhibitors, ridogrel, dazoxiben, dazmegrel and pirmagrel, and the TXA2/PG-END receptor antagonists, GR32191, L670596, SQ29548, ICI159995, AH69212 and sulotroban, for the TXA2/PG-END receptor labelled with [3H]SQ29548 on intact human platelets were assessed. The potencies of the TXA2/PG-END receptor antagonists to inhibit specific [3H]SQ29548 binding to intact human platelets ranged between 1.2 nM and 6,200 nM and corresponded to the ability of the drugs to suppress human platelet aggregation induced by TXA2/PG-END receptor stimulation with U46619 and collagen. The TXA2 synthase inhibitors dazoxiben, dazmegrel and pirmagrel could not inhibit specific [3H]SQ29548 binding to intact human platelets, tested up to 10(-5) M, nor suppress human platelet aggregation, indicating lack of any receptor antagonistic properties. Ridogrel, however, directly bound to the TXA2/PG-END receptor with micromolar affinity (IC50 = 5.2 microM) and inhibited U46619-27, or collagen-induced platelet aggregation, with ED50-values of 27 microM and 4.7 microM respectively. The present study thus demonstrates that antagonism by ridogrel of TXA2/PG-END receptor activation on platelets as defined in functional tests, coincides with inhibition of specific ligand binding to the receptors.
Heylen
L
L
Department of Biochemical Pharmacology, Janssen Research Foundation, Beerse, Belgium.
De Clerck
F
F
Somers
Y
Y
Leysen
J E
JE
D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D010421:Pentanoic Acids / Q000097:blood*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000097:blood; D011725:Pyridines / Q000097:blood*; D011869:Radioligand Assay; D011982:Receptors, Prostaglandin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017482:Receptors, Thromboxane; D013930:Thromboxane-A Synthase / Q000037:antagonists & inhibitors*; D013931:Thromboxanes / Q000378:metabolism*
D010421:Pentanoic Acids; D010975:Platelet Aggregation Inhibitors; D011725:Pyridines; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D013931:Thromboxanes; D013930:Thromboxane-A Synthase; C060219:ridogrel