Masaki Kawamura

Discovery of piperazinylimidazo[1,2-a]pyridines as novel S4 binding elements for orally active Factor Xa inhibitors

We have recently reported the discovery of orally active sulfonylalkylamide Factor Xa (FXa) inhibitors, as typified by compound 1 (FXa IC(50)=0.061 microM). Since the pyridylpiperidine moiety was not investigated in our previous study, we conducted detailed structure-activity relationship studies on this S4 binding element. This investigation led to the discovery of piperazinylimidazo[1,2-a]pyridine 2b as a novel and potent FXa inhibitor (FXa IC(50)=0.021 microM). Further modification resulted in the discovery of 2-hydroxymethylimidazo[1,2-a]pyridine 2e (FXa IC(50)=0.0090 microM), which was found to be a selective and orally bioavailable FXa inhibitor with reduced CYP3A4 inhibition.

Inhibitory effect of TCV-309, a novel platelet activating factor (PAF) antagonist, on endotoxin-induced disseminated intravascular coagulation in rats: possible role of PAF in tissue factor generation.

The possible involvement of platelet activating factor (PAF) in the pathogenesis of endotoxin-induced disseminated intravascular coagulation (DIC) was investigated in rats using a novel potent PAF antagonist, TCV-309. TCV-309 (> 1 mg/kg, i.v.) showed beneficial effects in rats with experimental DIC induced by a 4-hour sustained infusion of endotoxin (1 mg/kg) in a dose-dependent manner. TCV-309 (1 mg/kg) significantly ameliorated the decrease in platelet count and plasma fibrinogen, the prolongation of prothrombin time (PT) and activated partial thromboplastin time (APTT) and the increase in fibrin and fibrinogen degradation products (FDP) and inhibited glomerular fibrin deposition. Furthermore, plasma tissue factor (TF) activity was greatly increased in the DIC rats, and this was also significantly decreased by TCV-309 (1 mg/kg). TCV-309 (1 mg/kg) did not affect these parameters in normal rats. A 4-hour sustained infusion of PAF (60 micrograms/kg) caused mild but significant changes in some DIC parameters such as PT, fibrinogen and FDP concentration and increased the plasma TF activity. TCV-309 (1 mg/kg) inhibited all these PAF-induced changes. TCV-309 (0.1 mM) itself had no direct in vitro effects on the blood coagulation system including TF activity. These results strongly suggest that PAF plays a role in the pathogenesis of endotoxin-induced DIC via the generation of TF. Prophylactic use of PAF antagonists may therefore be useful for the treatment of DIC with sepsis.

Synergistic effect of a factor Xa inhibitor, TAK-442, and antiplatelet agents on whole blood coagulation and arterial thrombosis in rats

INTRODUCTIONnActivated platelets facilitate blood coagulation by providing factor V and a procoagulant surface for prothrombinase. Here, we investigated the potential synergy of a potent factor Xa/prothrombinase inhibitor, TAK-442, plus aspirin or clopidogrel in preventing arterial thrombosis and whole blood coagulation.nnnMETHODSnThrombus formation was initiated by FeCl(3)-induced rat carotid injury. Bleeding time was evaluated with the rat tail transection model. Whole blood coagulation was assessed by thromboelastographic examination (TEG) for which blood obtained from control, aspirin-, or clopidogrel-treated rats was transferred to a TEG analyzer containing, collagen or adenosine diphosphate (ADP), and TAK-442 or vehicle.nnnRESULTSnTAK-442 (3mg/kg, po), aspirin (100mg/kg, po) or clopidogrel (3mg/kg, po) alone had no significant effect on thrombus formation, whereas the combination of TAK-442 with aspirin and clopidogrel remarkably prolonged the time to thrombus formation without additional significant prolongation of bleeding time. TEG demonstrated that the onset of collagen-induced blood coagulation were slightly longer in aspirin-treated rats than control; however, when the blood from aspirin-treated rats was subsequently treated in vitro with 100 nM TAK-442, the onset of clotting was significantly prolonged. In contrast, only marginal prolongation was observed with TAK-442 treatment of blood from control animals. The onset time of ADP-induced blood coagulation was slightly longer in clopidogrel-treated rats compared with control, and it was further extended by TAK-442 treatment.nnnCONCLUSIONnThese results demonstrate that blood coagulation can be markedly delayed by the addition of TAK-442 to antiplatelets treatment which could contribute to synergistic antithrombotic efficacy in these settings.

Synthesis and biological evaluation of the metabolites of 2-(1-{3-[(6-chloronaphthalen-2-yl)sulfonyl]propanoyl}piperidin-4-yl)-5-methyl-1,2-dihydro-3H-imidazo[1,5-c]imidazol-3-one

We have recently discovered imidazo[1,5-c]imidazol-3-one derivative 1 as a potent, selective, and orally bioavailable factor Xa (FXa) inhibitor. In this study, we have synthesized metabolites of 1 and evaluated their biological activities. As a result, we identified the active metabolites S-5 and 6 with a potent FXa inhibitory activity comparable to 1 and a favorable pharmacokinetic profile in monkeys.

Effects of TAK-029, a novel GPIIb/IIIa antagonist, on arterial thrombosis in guinea pigs, dogs and monkeys.

The antithrombotic and bleeding time (BT) prolonging effects of TAK-029, a novel GPIIb/IIIa antagonist, were examined in three arterial thrombosis models. In guinea pigs, TAK-029 at 30 micrograms/kg (i.v.) inhibited ADP-induced ex vivo platelet aggregation completely and prolonged BT to 4.5 times the control value 5 min after administration, and it prevented thrombotic occlusion in 2 out of 5 animals in a photochemically-induced basilar thrombosis model. TAK-029 at 100 micrograms/kg (i.v.) prolonged BT more than 9 times 5 min after administration, and it prevented thrombus formation for over 60 min. In dogs, TAK-029 at 30 micrograms/kg (i.v.) inhibited ADP-induced ex vivo platelet aggregation by 87% 5 min after administration, and it prevented thrombotic occlusion in injured and stenosed coronary arteries for 22 min without prolonging the BT. TAK-029 at 100 micrograms/ kg (i.v.) inhibited platelet aggregation completely and prolonged BT 3.6 times 5 min after administration, and it prevented thrombus formation for over 45 min. In monkeys, TAK-029 at 10 micrograms/kg (i.v.) inhibited ADP-induced ex vivo platelet aggregation by 84% and prolonged BT 4.6 times 5 min after the administration, and it prevented thrombotic occlusion in injured and stenosed carotid arteries for 24 min. TAK-029 at 30 micrograms/kg (i.v.) completely inhibited platelet aggregation and thrombus formation for over 60 min, and it prolonged BT more than 7.3 times 60 min after administration. In conclusion, TAK-029 exerted potent antithrombotic effects with BT prolongation in three different arterial thrombosis models. TAK-029 may be effective for the treatment of various arterial thrombotic diseases.

POSSIBLE INVOLVEMENT OF PLATELET ACTIVATING FACTOR (PAF) IN TISSUE FACTOR GENERATION AND THE PATHOGENESIS OF DISSEMINATED INTRAVASCULAR COAGULATION (DIC)

PAF is a highly potent lipid mediator with diverse biological actions such as activation of platelets and leukocytes, induction of hypotension and bronchoconstriction (1). In earlier papers, we reported that PAF may play important roles in the pathogenesis of anaphylactic shock in mice and endotoxin shock and DIC in rats using the first PAF antagonist, CV-3988 (2–5).