Takeshi Shigenaga

Role of Hemocyte-Derived Granular Components in Invertebrate Defensea

Figure 2 illustrates an outline of the cellular and humoral defense systems in limulus. On the basis of the knowledge described above, it is suggested that granular components present in L and S granules in the hemocytes play a decisive role in the biological defense for this animal. The isolated L granules contain at least three clotting factors plus coagulogen as the major component. The known anti-LPS factor and a number of additional unknown protein components are also present in the L granules. On the other hand, the isolated S granules contain antimicrobial tachyplesins as the major component, in addition to six unidentified proteins. We speculate that the L-granule-derived protein components, which probably contain all the factors essential for the Limulus clotting system participate, in immobilizing invading microbes, and that the S-granule-derived tachyplesins contribute to a self-defense system against invaders. Although we have not mentioned hemolymph plasma components, there are many humoral factors, such as proteinase inhibitors, alpha 2-macroglobulin, various lectins, C-reactive protein, and polyphemin, all of which are important for antimicrobial defense. Furthermore, Liu and colleagues have reported several endotoxin-binding proteins and a cell-adhesion protein found in the Limulus hemocytes. Although the exact functions of these substances are unknown, they may act in concert with other components to provide biological defense for the animal. Nevertheless, compared to our knowledge of mammalian blood cells, much less remains to be learned of biological/physiological events in horseshoe crab hemocytes.

Pharmacological properties of YM-254890, a specific G α q/11 inhibitor, on thrombosis and neointima formation in mice

The pharmacological properties of YM-254890, a specific G(alpha)q/11 inhibitor, on acute thrombosis and chronic neointima formation after vascular injury have been investigated. FeCl3 was used to induce vascular injury in the carotid artery of mice. For the thrombosis studies, the test drug was either intravenously or orally administered before vascular injury. For the neointima studies, the test drug was orally administered 1 h before and twice daily for 1 week after vascular injury. Histological analysis was then performed 3 weeks later. YM-254890 significantly inhibited ex vivo platelet aggregation 5 min after intravenous bolus injection at 0.03 mg/kg or more, and 1 h after oral administration at 1 mg/kg. YM-254890 significantly inhibited thrombus formation after intravenous bolus injection at 0.03 mg/kg as well as after oral administration at 1 mg/kg, but tail transection bleeding time was significantly prolonged at 0.1 mg/kg for intravenous injection and 3 mg/kg for oral administration. Furthermore, oral administration of YM-254890 dose-dependently inhibited neointima formation 3 weeks after vascular injury with significant effects at 1 mg/kg twice daily for 1 week. Clopidogrel also significantly inhibited neointima formation at its antithrombotic dose, but its inhibitory potency was less than that of YM-254890. However, YM-254890 significantly reduced systemic blood pressure at doses 3 times higher than those that produced significant inhibitory effects on thrombosis and neointima formation. Though the systemic use of YM-254890 may be limited, owing to its narrow therapeutic window, this unique compound is a useful research tool for investigating the physiological roles of G(alpha)q/11 .

Discovery of N-[2-Hydroxy-6-(4-methoxybenzamido)phenyl]-4- (4-methyl-1,4-diazepan-1-yl)benzamide (Darexaban, YM150) as a Potent and Orally Available Factor Xa Inhibitor

Inhibitors of factor Xa (FXa), a crucial serine protease in the coagulation cascade, have attracted a great deal of attention as a target for developing antithrombotic agents. We previously reported findings from our optimization study of a high-throughput screening (HTS) derived lead compound 1a that resulted in the discovery of potent amidine-containing FXa inhibitors represented by compound 2. We also conducted an alternative optimization study of 1a without incorporating a strong basic amidine group, which generally has an adverse effect on the pharmacokinetic profile after oral administration. Replacement of 4-methoxybenzene with a 1,4-benzodiazepine structure and introduction of a hydroxy group at the central benzene led to the discovery of the potent and orally effective factor Xa inhibitor 14i (darexaban, YM150). Subsequent extensive study revealed a unique aspect to the pharmacokinetic profile of this compound, wherein the hydroxy moiety of 14i is rapidly transformed into its glucuronide conjugate 16 (YM-222714) as an active metabolite after oral administration and it plays a major role in expression of potent anticoagulant activity in plasma. The distinctive, potent activity of inhibitor 14i after oral dosing was explained by this unique pharmacokinetic profile and its favorable membrane permeability. Compound 14i is currently undergoing clinical development for prevention and treatment of thromboembolic diseases.