SSR182289A, a Novel, Orally Active Thrombin Inhibitor: In Vitro Profile and ex Vivo Anticoagulant Activity

Abstract

SSR182289A competitively inhibits human thrombin (K i ϭ 0.031 Ϯ 0.002 M) and shows good selectivity with respect to other human proteases, e.g., trypsin (K i ϭ 54 Ϯ 2 M), factor Xa (K i ϭ 167 Ϯ 9 M), and factor VIIa, factor IXa, plasmin, urokinase, tPA, kallikrein, and activated protein C (all K i values Ͼ250 M). In human plasma, SSR182289A demonstrated anticoagulant activity in vitro as measured by standard clotting parameters (EC 100 thrombin time 96 Ϯ 7 nM) and inhibited tissue factor-induced thrombin generation (IC 50 of 0.15 Ϯ 0.02 M). SSR182289A inhibited thrombin-induced aggregation of human platelets with an IC 50 value of 32 Ϯ 9 nM, but had no effect on aggregation induced by other platelet agonists. The anticoagulant effects of SSR182289A were studied by measuring changes in coagulation markers ex vivo after i.v. or oral administration in several species. In dogs, SSR182289A (0.1-1 mg/kg i.v. and 1-5 mg/kg p.o.) produced dose-related increases in clotting times. After oral dosing, maximum anticoagulant effects were observed 2 h after administration with increases in thrombin time, 2496 Ϯ 356%; ecarin clotting time (ECT), 1134 Ϯ 204%; and activated partial thromboplastin time (aPTT), 91 Ϯ 20% for the dose of 3 mg/kg p.o., and thrombin time, 3194 Ϯ 425%; ECT, 2017 Ϯ 341%; and aPTT, 113 Ϯ 9% after 5 mg/kg p.o. Eight hours after administration of 3 or 5 mg/kg SSR182289A, clotting times were still elevated. SSR182289A also showed oral anticoagulant activity in rat, rabbit, and macaque. Hence, SSR182289A is a potent, selective, and orally active thrombin inhibitor.

Antithrombotic Properties of SSR182289A, a New, Orally Active Thrombin Inhibitor

“…For example, comparison of the direct thrombin inhibitors SSR182289A and melagatran shows that melagatran possesses higher i.v. antithrombotic potency than SSR182289A but is also a more potent thrombin inhibitor in vitro (Berry et al, 2002), although this factor alone appears not to fully explain the difference in antithrombotic potency. Argatroban, which has a K i value against thrombin (Bush, 1991) similar to that reported for SSR182289A (Berry et al, 2002), shows comparable i.v.…”

“…We have previously shown that i.v. or oral administration of SSR182289A produces dose-related increases in coagulation parameters (thrombin time, ecarin clotting time, and activated partial thromboplastin time) in several animal species (rat, rabbit, dog, and macaque) (Berry et al, 2002). In this context, the ecarin clotting time has been reported to be a good predictor of antithrombotic effects for direct thrombin inhibitors in rat venous and arterial thrombosis models (Berry et al, 1998).…”

“…routes in several animal thrombosis models. We have previously reported (Berry et al, 2002) that SSR182289A is a potent and highly selective thrombin inhibitor (K i 31 nM). In particular, SSR182289A has little or no affinity for other serine proteases involved in the blood coagulation cascade (i.e., factor Xa, factor VIIa/tissue factor, factor IXa).…”

“…or oral administration (Berry et al, 2002). In this article, we report the antithrombotic effects of SSR182289A in different animal models of thrombosis including those representative of venous, arterial, and "mixed" thrombus formation.…”

“…Comparative studies have been performed with several reference antithrombotic agents and, notably, in the case of the oral route with the thrombin inhibitor ximelagatran (Gustafsson et al, 2001). Unlike ximelagatran (which is a double prodrug), SSR182289A does not require metabolism to an active form to achieve oral activity (Berry et al, 2002).…”