Antiplatelet effects of the novel thromboxane A2 receptor antagonist sodium (E)-11-[2-(5,6-dimethyl-1-benzimidazolyl)-ethylidene]-6,11- dihydrodibenz[b,e] oxepine-2-carboxylate monohydrate.

The effects of KW-3635 (sodium (E)-11-[2-(5,6-dimethyl-1-benzimidazolyl)- ethylidene]-6,11-dihydrodibenz[b,e] oxepine-2-carboxylate monohydrate, CAS 127166-41-0) on platelet aggregation were examined. In human washed platelets, KW-3635 shifted the concentration-aggregation curves for U-46619, a thromboxane A2 (TxA2) mimetic, to the right. The pA2 value for KW-3635 was 8.8 +/- 0.10, while those for sulotroban and daltroban were 6.31 +/- 0.18 and 7.75 +/- 0.07, respectively. In human platelet rich plasma (PRP), KW-3635 at 10(-8) mol/l to 10(-6) mol/l inhibited the aggregations induced by U-46619 (1 mumol/l) or collagen (1.5 micrograms/ml). However, KW-3635 at up to 10(-5) mol/l did not affect the primary phase of platelet aggregation induced by adenosine diphosphate or epinephrine. KW-3635 at 10(-5) mol/l did not affect the antiaggregatory effects of the prostaglandins PGI2, PGE1 and PGD2. These results indicate that KW-3635 is a potent and selective TxA2 receptor antagonist. The TxA2 antagonistic effects of KW-3635 were compared with that of daltroban in PRP from various animals species. The effects of KW-3635 on platelet aggregation were species-dependent and KW-3635 exhibited the most prominent activity in human platelets. The activities of KW-3635 in mouse and rabbit PRP were much less potent. In PRP from guinea-pigs, dogs, cats and rats, KW-3635 exhibited moderate anti-aggregatory effects. In the guinea-pig PRP, KW-3635 at 10(-7) mol/l to 3 x 10(-6) mol/l inhibited both the platelet aggregation and the concomitant adenosine triphosphate secretion in a concentration-dependent manner, the effect being more potent than those of sulotroban and daltroban. In the experiments on the platelet aggregation ex vivo in guinea-pigs, KW-3635 at oral doses of 3 and 10 mg/kg inhibited the aggregations induced by U-46619 (1, 3 mumol/l), collagen (3, 6, 9 micrograms/ml) and arachidonate (50, 100 mumol/l). The effects lasted for longer than 7 h following oral administration. These results indicate that KW-3635 is a specific and orally active TxA2 receptor antagonist. KW-3635 is expected to be a drug useful for the treatment of patients with thrombotic disorders.