1 CS-747 is a novel antiplatelet agent that generates an active metabolite, R-99224, in vivo. CS-747 itself was totally inactive in vitro. This study examined in vivo pharmacological pro®les of CS-747 after single oral administration to rats. ). 6 CS-747, clopidogrel, and ticlopidine prolonged the bleeding time. The order of potency of these agents in this activity was the same as that in antiaggregatory and antithrombotic activities. 7 These ®ndings indicate that CS-747 is an orally active and a potent antiplatelet and antithrombotic agent with a rapid onset and long duration of action, and warrants clinical evaluations of the agent.

The greater in vivo antiplatelet effects of prasugrel as compared to clopidogrel reflect more efficient generation of its active metabolite with similar antiplatelet activity to that of clopidogrelÕs active metabolite. J Thromb Haemost 2007; 5: 1545-51.Summary. Background and methods: Prasugrel is a novel orally active thienopyridine prodrug with potent and longlasting antiplatelet effects. Platelet inhibition reflects inhibition of P2Y 12 receptors by its active metabolite (AM). Previous studies have shown that the antiplatelet potency of prasugrel is at least 10 times higher than that of clopidogrel in rats and humans, but the mechanism of its higher potency has not yet been fully elucidated. Results: Oral administration of prasugrel to rats resulted in dose-related and time-related inhibition of ex vivo platelet aggregation, and its effect was about 10 times more potent than that of clopidogrel. The plasma concentration of prasugrel AM was higher than that of clopidogrel AM despite tenfold higher doses of clopidogrel, indicating more efficient in vivo production of prasugrel AM than of clopidogrel AM. In rat platelets, prasugrel AM inhibited in vitro platelet aggregation induced by adenosine 5¢-diphosphate (ADP) (10 lM) with an IC 50 value of 1.8 lM. Clopidogrel AM similarly inhibited platelet aggregation with an IC 50 value of 2.4 lM. Similar results were also observed for ADP-induced (10 lM) decreases in prostaglandin E 1 -stimulated rat platelet cAMP levels. These results indicate that both AMs have similar in vitro antiplatelet activities. Conclusions: The greater in vivo antiplatelet potency of prasugrel as compared to clopidogrel reflects more efficient in vivo generation of its AM, which demonstrates similar in vitro activity to clopidogrel AM.

1 CS-747 is a novel thienopyridine-type platelet ADP inhibitor which lacks in vitro activity. This study examined pharmacological pro®les of R-99224, a hepatic metabolite of CS-747. 2 R-99224 produced a concentration-dependent inhibition of in vitro platelet aggregation in washed human platelets (0.03 ± 1 mg ml 71 ), which was relatively speci®c to ADP compared to collagen and thrombin. ) also inhibited the ADP-induced decrease in cyclic AMP levels in PGE 1 -stimulated platelets, whereas the agent did not aect ADP (10 mM)-induced Ca 2+ mobilization. 7 These ®ndings suggest that R-99224 is a selective and irreversible antagonist of G i -linked P2T receptors and that R-99224 is a responsible molecule for in vivo actions of CS-747.

CS-747 (Prasugrel, LY640315) is a thienopyridine antiplatelet prodrug that is metabolized to the thiol-containing active metabolite R-138727,which binds to and irreversibly inhibits the platelet P2Y12ADP receptor. R-138727 is composed of 4 stereo-isomers, (R, S)-, (R, R)-, (S, S)-, and (S, R)-isomers (the first letter for the configuration of a chiral center at the sulfur-bearing position and the second for that at the benzylic position). In the present study, we determined the stereoselectivity of P2Y12 antagonist effects by assessing the antagonism of the [3H]-2-MeS-ADP that binds to human P2Y12 receptors expressed in Chinese hamster ovary cells as an affinity assay, and by the inhibition of ADP-induced aggregation of washed human platelets as a functional assay. R-138727 and its 2 components, R-99224, a mixture of (R, S)- and (S, R)-isomers and R-100364, a mixture of (R, R)- and (S, S)-isomers, inhibited [3H]-2-MeS-ADP binding and platelet aggregation. The rank order of potency of these compounds were identical in both assays: R-99224>R-138727>> R-100364. Inhibition of ADP-induced platelet aggregation by R-138727 and R-99224 was concentration- and time-related. In experiments using the 4 single stereo-isomers, all isomers inhibited ADP-induced platelet aggregation, but the (R, S)-isomer was found to be the most potent, followed by the (R, R)-isomer. These in vitro studies indicate that R- 138727 is an effective antagonist of P2Y12 and potent inhibitor of ADP-induced platelet aggregation, and that these antiplatelet activities of R-138727 are largely dependent on its (R, S)-isomer. This suggests that the (R)-configuration of the reactive thiol group of the active metabolite of CS-747 is critical for P2Y12 and platelet inhibitory activities.

No abstract

No abstract

to Glu mutation (factor XI-Glu555): a cross-reactive material positive variant defective in factor IX activation. J Thromb Haemost 2004; 2: 1782-9.Summary. During normal hemostasis, the coagulation protease factor (F)XIa activates FIX. Hereditary deficiency of the FXIa precursor, FXI, is usually associated with reduced FXI protein in plasma, and circulating dysfunctional FXI variants are rare. We identified a patient with < 1% normal plasma FXI activity and normal levels of FXI antigen, who is homozygous for a FXI Gly555 to Glu substitution. Gly555 is two amino acids N-terminal to the protease active site serine residue, and is highly conserved among serine proteases. Recombinant FXIGlu555 is activated normally by FXIIa and thrombin, and FXIa-Glu555 binds activated factor IX similarly to wild type FXIa (FXIa WT ). When compared with FXIa WT , FXIa-Glu555 activates factor IX at a greatly reduced rate (400-fold), and is resistant to inhibition by antithrombin. Interestingly, FXIa WT and FXIa-Glu555 cleave the small tripeptide substrate S-2366 with comparable k cat s. Modeling indicates that the side chain of Glu555 significantly alters the electrostatic charge around the active site, and would sterically interfere with the interaction between the FXIa S2¢ site and the P2¢ residues on factor IX and antithrombin. FXI-Glu555 is the first reported example of a naturally occurring FXI variant with a significant defect in FIX activation.

BACKGROUND AND PURPOSEPrasugrel is a third-generation thienopyridine prodrug and ticagrelor is a non-competitive P2Y12 receptor antagonist. In their phase 3 studies, both agents reduced rates of ischemic events relative to treatment with clopidogrel. EXPERIMENTAL APPROACHThe pharmacodynamic profile of anti-platelet effects of prasugrel was compared with that of ticagrelor in rats. KEY RESULTSThe active metabolite of prasugrel was less potent than ticagrelor and its active metabolite on platelet aggregation in vitro. In contrast, prasugrel was a more potent antiplatelet agent than ticagrelor on ex vivo platelet aggregation: their ED50 values at peak for ADP 20 mmol·L -1 were 1.9 and 8.0 mg·kg, respectively. Prasugrel's inhibition of platelet aggregation was maintained for up to 24 h after administration, but ticagrelor's duration of action was substantially shorter. Prasugrel and ticagrelor significantly inhibited thrombus formation with ED50 values of 1.8 and 7.7 mg·kg -1 , respectively. Both agents also prolonged bleeding times (ED200 values of 3.0 and 13 mg·kg -1 respectively) suggesting that at equivalent levels of inhibition of platelet aggregation, the agents would show comparable antithrombotic activity with similar bleeding risk. Platelet transfusion significantly increased blood platelet numbers similarly in prasugrel-and ticagrelor-treated rats. In the prasugrel-treated group, platelet transfusion caused significant shortening of bleeding time, while in the ticagrelor-treated group, platelet transfusion showed no influence on bleeding time under the experimental conditions employed. CONCLUSIONS AND IMPLICATIONSPrasugrel and ticagrelor showed several differences in their pharmacological profiles and these disparities may reflect their differing reversibility and/or pharmacokinetic profiles. AbbreviationsACS, acute coronary syndrome; PCI, percutaneous coronary intervention; PRP, platelet-rich plasma