Drug Rediscovery: Glybenclamide Exhibits Thromboxane Receptor-Dependent Antithrombotic Activity.

Abstract 2994

Poster Board II-971

While proper platelet function is a vital component of hemostasis, inappropriate activation of platelets contributes to occlusive disorders such as myocardial infarction, and stroke. One pathway for platelet activation involves the synthesis of the lipid mediator thromboxane A₂ (TXA₂), which acts by binding to its seven-transmembrane receptor (abbreviated as TPR). Although this signaling pathway participates in the genesis of thrombosis, currently, there are no TPR antagonists that are available for clinical use; and aspirin remains the sole agent targeting this pathway. However, since aspirin is associated with multiple adverse effects, there is still considerable interest in developing TPR antagonists. To this end, we took the “drug rediscovery” approach to identify TPR antagonists. Since the sulfonylurea glybenclamide appeared to possess most of the pharmacophores known to exist in the TPR antagonist SQ29,548, we predicted it would interact with TPRs (and exhibit antiplatelet/antithrombotic activity). It was found that glybenclamide: 1) inhibited human platelet aggregation induced by the TPR agonist U46619 (1μM) and the TXA₂ precursor arachidonic acid (0.5mM), concentration-dependently (1-10μM); 2) displaced SQ29,548 from its binding sites; 3) lacked any detectable effects on aggregation stimulated by 15μM ADP, or the thrombin receptor activating-peptide 4 (40μM); 4) failed to raise cAMP levels; 5) selectively (at 10mg/kg) blocked mouse TPR-mediated aggregation, under ex vivo settings; 6) prolonged (at 10mg/kg) the tail bleeding time in mice; and 6) prolonged (at 10mg/kg) the time for occlusion in a mouse carotid artery thrombosis model. Taken together, these findings indicate that glybenclamide exerts inhibitory effects on platelet function by interacting with TPR, and exhibits antithrombotic activity. Thus glybenclamide, or a rationally designed derivative, has the potential to be applied in the management of thrombotic disorders.