Clinical and experimental experience with factor Xa inhibitors

Factor XI/XIa Inhibition: The Arsenal in Development for a New Therapeutic Target in Cardio- and Cerebrovascular Disease

Despite major advancements in the development of safer and more effective anticoagulant agents, bleeding complications remain a significant concern in the treatment of thromboembolic diseases. Improvements in our understanding of the coagulation pathways highlights the notion that the contact pathway-specifically factor XI (FXI)-has a greater role in the etiopathogenesis of thrombosis than in physiological hemostasis. As a result, a number of drugs targeting FXI are currently in different stages of testing and development. This article aims to review the different strategies directed towards FXI-inhibition with a brief summation of the agents in clinical development, and to comment on the therapeutic areas that could be explored for potential indications. Therapeutics targeting FXI/FXIa inhibition have the potential to usher in a new era of anticoagulation therapy.

The impact of factor Xa inhibition on axial dependent arterial thrombus formation triggered by a tissue factor rich surface

This study was designed to assess the effect of Factor Xa antagonists on thrombus formation at various axial positions on a tissue factor rich surface under arterial blood flow conditions. Non-anticoagulated, flowing human blood, drawn directly from an antecubital vein, was perfused over a tissue factor coated cover slip in a parallel-plate perfusion chamber. Thrombus surface coverage, thrombus mean height and fibrin surface coverage were measured at six different axial positions by confocal microscopy. Both thrombus surface coverage and mean height decreased along the cover slip axis whereas the fibrin surface coverage increased. Pre-chamber treatment of blood with the direct Factor Xa inhibitors Razaxaban and 813893 resulted in significantly reduced thrombus and fibrin formation at all axial positions investigated (P < 0.05). Thrombus and fibrin deposition in a laminar flow chamber changed with axial position with surface coverage measurements being more reproducible than thrombus mean height. Data were more reproducible towards the centre of the flow chamber than at the extremities. Razaxaban and 813893 inhibited thrombus and fibrin formation at the highest concentrations tested. No difference in drug effect was apparent at different axial positions. In conclusion, axial position influences the degree of thrombus and fibrin deposition with measurements being less reproducible at the extremities of the flow chamber. This technique may prove useful for analysing anti-thrombotic drug effects before progression to clinical trials.

Preparation of 1-(3-aminobenzo[d]isoxazol-5-yl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-ones as potent, selective, and efficacious inhibitors of coagulation factor Xa

Previously, potent factor Xa inhibitors were described based on the 1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one bicyclic core and a 4-methoxyphenyl P1 moiety. This manuscript describes 1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one and related bicyclic cores with the 3-aminobenzisoxazole P1 moiety. Many of these compounds are potent, selective, and efficacious inhibitors of coagulation factor Xa.

Structure- and property-based design of factor Xa inhibitors: pyrrolidin-2-ones with acyclic alanyl amides as P4 motifs

Structure-based drug design was exploited in the synthesis of 3-(6-chloronaphth-2-ylsulfonyl)aminopyrrolidin-2-one-based factor Xa (fXa) inhibitors, incorporating an alanylamide P4 group with acyclic tertiary amide termini. Optimized hydrophobic contacts of one amide substituent in P4 were complemented by hydrophobicity-modulating features in the second, producing potent fXa inhibitors including examples with excellent anticoagulant properties.

Preparation of 1-(4-methoxyphenyl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-ones as potent, selective and bioavailable inhibitors of coagulation factor Xa

Previously, potent factor Xa inhibitors were described based on a pyrazole core. Modifications of the pyrazole core have provided additional novel, highly potent factor Xa inhibitors. This manuscript will describe the synthesis and biological activity of factor Xa inhibitors containing the 1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one and related bicyclic cores. Many of these compounds are potent, selective, and orally bioavailable inhibitors of coagulation factor Xa.

Aminobenzisoxazoles with biaryl P4 moieties as potent, selective, and orally bioavailable factor Xa inhibitors

We have previously reported on a series of aminobenzisoxazoles as potent, selective, and orally bioavailable factor Xa inhibitors, which culminated in the discovery of razaxaban. Herein, we describe another approach to improve factor Xa inhibitory potency and pharmacokinetic profile by incorporating basic and water soluble functionalities on the terminal ring of the P4 biaryl group found in our earlier Xa inhibitors. This approach resulted in a series of potent, selective, and orally bioavailable factor Xa inhibitors.

Heparin chain-length dependence of factor Xa inhibition by antithrombin in plasma

Heparin anticoagulants function by enhancing the inhibition of coagulation proteases by the serpin antithrombin (AT). A direct evaluation of the specific anti-factor Xa (fXa) activity of therapeutic heparins in the physiologically relevant plasma-based clotting assays has not been feasible since thrombin, the final protease of the cascade, is the primary target for inhibition by AT in the presence of heparin. To circumvent this problem, we developed an assay in which the native AT in plasma was replaced with an AT mutant which exhibits identical affinity for heparin and near normal reactivity for fXa, but does not react with thrombin and other coagulation proteases in either the absence or presence of heparin. This assay was used to distinguish the anti-fXa activity of different molecular weight heparins from their anti-thrombin activity in clotting assays which were initiated by the triggers of either the extrinsic or intrinsic coagulation pathway. The results suggest that the acceleration of fXa inhibition by AT exhibits a marked heparin chain-length dependence, with fondaparinux (a pentasaccharide) having the lowest and unfractionated heparin having the highest effect. Interestingly, comparative studies revealed that the fondaparinux-catalyzed acceleration of thrombin inhibition by AT also contributes to the prolongation of the clotting time, possibly suggesting that the anticoagulant function of the therapeutic pentasaccharide is mediated though the inhibition of both fXa and thrombin.