Pharmacological interruption of acute thrombus formation with minimal hemorrhagic complications by a small molecule tissue factor/factor VIIa inhibitor: comparison to factor Xa and thrombin inhibition in a nonhuman primate thrombosis model

Potential anticoagulant of traditional chinese medicine and novel targets for anticoagulant drugs

BACKGROUND

Anticoagulants are the main drugs used for the prevention and treatment of thrombosis. Currently, anticoagulant drugs are primarily multitarget heparin drugs, single-target FXa inhibitors and FIIa inhibitors. In addition, some traditional Chinese drugs also have anticoagulant effects, but they are not the main direction of treatment at present. But the anticoagulant drugs mentioned above, all have a common side effect is bleeding. Many other anticoagulation targets are under investigation. With further exploration of coagulation mechanism, how to further determine new anticoagulant targets and how to make traditional Chinese medicine play anticoagulant role have become a new field of exploration.

PURPOSE

The purpose of the study was to summarize the recent research progress on coagulation mechanisms, new anticoagulant targets and traditional Chinese medicine.

METHODS

A comprehensive literature search was conducted using four electronic databases, including PubMed, Embase, CNKI, Wanfang database and ClinicalTrials.gov, from the inception of the study to 28 Feb 2023. Key words used in the literature search were "anticoagulation", "anticoagulant targets", "new targets", "coagulation mechanisms", "potential anticoagulant", "herb medicine", "botanical medicine", "Chinese medicine", "traditional Chinese medicine", "blood coagulation factor", keywords are linked with AND/OR. Recent findings on coagulation mechanisms, potential anticoagulant targets and traditional Chinese medicine were studied.

RESULTS

The active components extracted from the Chinese medicinal herbs, Salvia miltiorrhiza, Chuanxiong rhizoma, safflower and Panax notoginseng have obvious anticoagulant effects and can be used as potential anticoagulant drugs, but the risk of bleeding is unclear. TF/FVIIa, FVIII, FIX, FXI, FXII, and FXIII have all been evaluated as targets in animal studies or clinical trials. FIX and FXI are the most studied anticoagulant targets, but FXI inhibitors have shown stronger advantages.

CONCLUSION

This review of potential anticoagulants provides a comprehensive resource. Literature analysis suggests that FXI inhibitors can be used as potential anticoagulant candidates. In addition, we should not ignore the anticoagulant effect of traditional Chinese medicine, and look forward to more research and the emergence of new drugs.

Screening of a Library for Factor VIIa Inhibitors

Background:

As an alternative to the anticoagulant’s strategy using direct or indirect anti-Xa drugs, considering other targets upstream in the coagulation cascade such as anti-Factor VIIa could represent an effective and safer strategy in coagulation and pathological angiogenesis.

Objective:

The objective of the study was to assess a high technology methodology composed of virtual screening, anticoagulant, and anti-angiogenesis assays to identify potent small-molecule FVIIa inhibitors.

Methods:

Chemical databanks were screened to select molecules bearing functional groups that could fit into the active site of FVIIa, which were then tested. Ligands assigned with the lowest scores were retained and then biologically assessed.

Results:

From the 500 molecules considered, 8 chemical structures revealed to be effective compounds in vitro and to inhibit angiogenesis in the chick chorioallantoic membrane (CAM) model.

Conclusion:

New potent small-molecule FVIIa inhibitors have been identified; further biochemical and chemical developments would be investigated directly from the selected scaffolds.

Immunothrombosis and the molecular control of tissue factor by pyroptosis: prospects for new anticoagulants

The interplay between innate immunity and coagulation after infection or injury, termed immunothrombosis, is the primary cause of disseminated intravascular coagulation (DIC), a condition that occurs in sepsis. Thrombosis associated with DIC is the leading cause of death worldwide. Interest in immunothrombosis has grown because of COVID-19, the respiratory disease caused by SARS-CoV-2, which has been termed a syndrome of dysregulated immunothrombosis. As the relatively new field of immunothrombosis expands at a rapid pace, the focus of academic and pharmacological research has shifted from generating treatments targeted at the traditional 'waterfall' model of coagulation to therapies better directed towards immune components that drive coagulopathies. Immunothrombosis can be initiated in macrophages by cleavage of the non-canonical inflammasome which contains caspase-11. This leads to release of tissue factor (TF), a membrane glycoprotein receptor that forms a high-affinity complex with coagulation factor VII/VIIa to proteolytically activate factors IX to IXa and X to Xa, generating thrombin and leading to fibrin formation and platelet activation. The mechanism involves the post-translational activation of TF, termed decryption, and release of decrypted TF via caspase-11-mediated pyroptosis. During aberrant immunothrombosis, decryption of TF leads to thromboinflammation, sepsis, and DIC. Therefore, developing therapies to target pyroptosis have emerged as an attractive concept to counteract dysregulated immunothrombosis. In this review, we detail the three mechanisms of TF control: concurrent induction of TF, caspase-11, and NLRP3 (signal 1); TF decryption, which increases its procoagulant activity (signal 2); and accelerated release of TF into the intravascular space via pyroptosis (signal 3). In this way, decryption of TF is analogous to the two signals of NLRP3 inflammasome activation, whereby induction of pro-IL-1β and NLRP3 (signal 1) is followed by activation of NLRP3 (signal 2). We describe in detail TF decryption, which involves pathogen-induced alterations in the composition of the plasma membrane and modification of key cysteines on TF, particularly at the location of the critical, allosterically regulated disulfide bond of TF in its 219-residue extracellular domain. In addition, we speculate towards the importance of identifying new therapeutics to block immunothrombotic triggering of TF, which can involve inhibition of pyroptosis to limit TF release, or the direct targeting of TF decryption using cysteine-modifying therapeutics.

Optimization of peptide-based inhibitors targeting the HtrA serine protease in Chlamydia: Design, synthesis and biological evaluation of pyridone-based and N-Capping group-modified analogues

The obligate intracellular bacterium Chlamydia trachomatis (C. trachomatis) is responsible for the most common bacterial sexually transmitted infection and is the leading cause of preventable blindness, representing a major global health burden. While C. trachomatis infection is currently treatable with broad-spectrum antibiotics, there would be many benefits of a chlamydia-specific therapy. Previously, we have identified a small-molecule lead compound JO146 [Boc-Val-Pro-Val^P(OPh)₂] targeting the bacterial serine protease HtrA, which is essential in bacterial replication, virulence and survival, particularly under stress conditions. JO146 is highly efficacious in attenuating infectivity of both human (C. trachomatis) as well as koala (C. pecorum) species in vitro and in vivo, without host cell toxicity. Herein, we present our continuing efforts on optimizing JO146 by modifying the N-capping group as well as replacing the parent peptide structure with the 2-pyridone scaffold at P3/P2. The drug optimization process was guided by molecular modelling, enzyme and cell-based assays. Compound 18b from the pyridone series showed improved inhibitory activity against CtHtrA by 5-fold and selectivity over human neutrophil elastase (HNE) by 109-fold compared to JO146, indicating that 2-pyridone is a suitable bioisostere of the P3/P2 amide/proline for developing CtHtrA inhibitors. Most pyridone-based inhibitors showed superior anti-chlamydial potency to JO146 especially at lower doses (25 and 50 μM) in C. trachomatis and C. pecorum cell culture assays. Modifications of the N-capping group of the peptidyl inhibitors did not have much influence on the anti-chlamydial activities, providing opportunities for more versatile alterations and future optimization. In summary, we present 2-pyridone based analogues as a new generation of non-peptidic CtHtrA inhibitors, which hold better promise as anti-chlamydial drug candidates.

Tissue factor in atherosclerosis and atherothrombosis

Atherosclerosis is a chronic inflammatory disease that is characterized by the formation of lipid rich plaques in the wall of medium to large sized arteries. Atherothrombosis represents the terminal manifestation of this pathology in which atherosclerotic plaque rupture or erosion triggers the formation of occlusive thrombi. Occlusion of arteries and resultant tissue ischemia in the heart and brain causes myocardial infarction and stroke, respectively. Tissue factor (TF) is the receptor for the coagulation protease factor VIIa, and formation of the TF:factor VIIa complex triggers blood coagulation. TF is expressed at high levels in atherosclerotic plaques by both macrophage-derived foam cells and vascular smooth muscle cells, as well as extracellular vesicles derived from these cells. Importantly, TF mediated activation of coagulation is critically important for arterial thrombosis in the setting of atherosclerotic disease. The major endogenous inhibitor of the TF:factor VIIa complex is TF pathway inhibitor 1 (TFPI-1), which is also present in atherosclerotic plaques. In mouse models, increased or decreased expression of TFPI-1 has been found to alter atherosclerosis. This review highlights the contribution of TF-dependent activation of coagulation to atherthrombotic disease.

Tissue factor: newer concepts in thrombosis and its role beyond thrombosis and hemostasis

For many years, the attention on tissue factor (TF) in human pathophysiology has been limited to its role as initiator of extrinsic coagulation pathway. Moreover, it was described as a glycoprotein located in several tissue including vascular wall and atherosclerotic plaque. However, in the last two decades, the discovery that TF circulates in the blood as cell-associated protein, microparticles (MPs) bound and as soluble form, is changing this old vessel-wall TF dogma. Moreover, it has been reported that TF is expressed by different cell types, even T lymphocytes and platelets, and different pathological conditions, such as acute and chronic inflammatory status, and cancer, may enhance its expression and activity. Thus, recent advances in the biology of TF have clearly indicated that beyond its known effects on blood coagulation, it is a "true surface receptor" involved in many intracellular signaling, cell-survival, gene and protein expression, proliferation, angiogenesis and tumor metastasis. Finally, therapeutic modulation of TF expression and/or activity has been tested with controversial results. This report, starting from the old point of view about TF as initiator of extrinsic coagulation pathway, briefly illustrates the more recent concepts about TF and thrombosis and finally gives an overview about its role beyond thrombosis and haemostasis focusing on the different intracellular mechanisms triggered by its activation and potentially involved in atherosclerosis.

The selectivity and bioavailability improvement of novel oral anticoagulants: An overview

Anticoagulants have exhibited a critical role in the prevention and/or treatment of thrombotic diseases. Up to now, kinds of novel oral anticoagulants, inhibiting plasma serine proteases in the coagulation cascade, have been developed to overcome the clinical limitations of classical anticoagulants (like warfarin and heparins). Some of them, such as Apixaban, Rivaroxaban, Edoxaban, and Dabigatran, have been approved by FDA in recent years. This review summarizes the discovery and optimization of representative novel oral anticoagulants with the aim to improve selectivity and bioavailability of compounds. The impact of different targets in the cascade on bleeding risk also is discussed. We hope some more effective, selective, and safer anticoagulants can be developed in the future on the basis of these design experiences.

Design and Synthesis of Novel Meta-Linked Phenylglycine Macrocyclic FVIIa Inhibitors

Two novel series of meta-linked phenylglycine-based macrocyclic FVIIa inhibitors have been designed to improve the rodent metabolic stability and PK observed with the precursor para-linked phenylglycine macrocycles. Through iterative structure-based design and optimization, the TF/FVIIa K_i was improved to subnanomolar levels with good clotting activity, metabolic stability, and permeability.

Microbial hydroxylation and glycosylation of pentacyclic triterpenes as inhibitors on tissue factor procoagulant activity

To discover new inhibitors on tissue factor procoagulant activity, 20 pentacyclic triterpenes were semi-synthetized through microbial transformation and assayed on the model of human THP-1 cells stimulated by lipopolysaccharide. In the biotransformation two types of reactions were observed, regio-selective hydroxylation and glycosylation. The bioassay results showed that most of tested compounds were significant effective on this model and two of the biotransformation products 23-hydroxy-28-O-β-d-glucopyranosyl betulinic acid (3d) and 28-O-β-d-glucopyranosyl oleanic acid (1a) exhibited most potential activities with the IC₅₀ values of 0.028, 0.035nM respectively. The preliminary structure and activity relationship analysis revealed that the aglycones with single free hydroxyl group on the skeleton (1, 1j) were less effective than that with more free hydroxyl groups (1d, 1f, 2), mono-glycosylation can significantly enhance their inhibitory effects. Our findings also provide some potential leading compounds for tissue factor-related diseases, such as cancer and cardiovascular diseases.

Factor XIa inhibitors: A review of the patent literature

INTRODUCTION

Anticoagulants are the mainstay for prevention and/or treatment of thrombotic disorders. Each clinically used anticoagulant is associated with significant adverse consequences, especially bleeding. Factor XIa (FXIa), a key factor involved in the amplification of procoagulation signal, has been suggested as a major target for anticoagulant drug discovery because of reduced risk of bleeding.

AREAS COVERED

Our literature search uncovered dozens of industrial and academic patents on the discovery of novel FXIa/FXI inhibitors. Small peptidomimetics, sulfated glycosaminoglycan mimetics, polypeptides, antisense oligonucleotides, and monoclonal antibodies have been developed as inhibitors of FXIa. Although many agents are in early discovery/development phases, the activity and safety of a few have been evaluated in various animal models and in humans.

EXPERT OPINION

FXIa is a promising drug target for development of effective anticoagulants with limited bleeding complications. Literature reveals a major trend in the number of patent applications over the last three years. These inhibitors exploit different approaches for target inhibition. Allosteric modulation of FXIa and biosynthetic inhibition of FXI are mechanistically unique. Despite initial results in patients undergoing knee anthroplasty as with antisense oligonucleotides, major advances should be realized, particularly with respect to pharmacokinetics, for FXI/FXIa inhibitors to enter the clinic.

Discovery of a Highly Potent, Selective, and Orally Bioavailable Macrocyclic Inhibitor of Blood Coagulation Factor VIIa-Tissue Factor Complex

Inhibitors of the tissue factor (TF)/factor VIIa complex (TF-FVIIa) are promising novel anticoagulants which show excellent efficacy and minimal bleeding in preclinical models. Starting with an aminoisoquinoline P1-based macrocyclic inhibitor, optimization of the P' groups led to a series of highly potent and selective TF-FVIIa inhibitors which displayed poor permeability. Fluorination of the aminoisoquinoline reduced the basicity of the P1 group and significantly improved permeability. The resulting lead compound was highly potent, selective, and achieved good pharmacokinetics in dogs with oral dosing. Moreover, it demonstrated robust antithrombotic activity in a rabbit model of arterial thrombosis.

Structure-Based Design of Macrocyclic Coagulation Factor VIIa Inhibitors

On the basis of a crystal structure of a phenylpyrrolidine lead and subsequent molecular modeling results, we designed and synthesized a novel series of macrocyclic FVIIa inhibitors. The optimal 16-membered macrocycle was 60-fold more potent than an acyclic analog. Further potency optimization by incorporation of P1' alkyl sulfone and P2 methyl groups provided a macrocycle with TF/FVIIa Ki = 1.6 nM, excellent selectivity against a panel of seven serine proteases, and FVII-deficient prothrombin time EC2x = 1.2 μM. Discovery of this potent, selective macrocyclic scaffold opens new possibilities for the development of orally bioavailable FVIIa inhibitors.

Discovery of novel P1 groups for coagulation factor VIIa inhibition using fragment-based screening

A multidisciplinary, fragment-based screening approach involving protein ensemble docking and biochemical and NMR assays is described. This approach led to the discovery of several structurally diverse, neutral surrogates for cationic factor VIIa P1 groups, which are generally associated with poor pharmacokinetic (PK) properties. Among the novel factor VIIa inhibitory fragments identified were aryl halides, lactams, and heterocycles. Crystallographic structures for several bound fragments were obtained, leading to the successful design of a potent factor VIIa inhibitor with a neutral lactam P1 and improved permeability.

Discovery methodology for the development of direct factor VIIa inhibitors

INTRODUCTION

Heparin and warfarin have historically been the only antithrombotics available. Recently, however, newer anticoagulants have been developed. Factor VIIa (fVIIa) inhibitors represent one of the new and potentially exciting classes of anticoagulants currently under development. Indeed, several methodologies have been used to develop fVIIa inhibitors.

AREAS COVERED

The authors highlight some of the methologies applied for the discovery of fVIIa inhibitors including phage display, isolation of endogenous peptides from hematophagous animals and the use of the 1,5-benzothiazepine molecular scaffolds and screens of large chemical libraries previously used to identify other serine protease inhibitors. Although these screens were intended to identify thrombin and factor Xa inhibitors, the compounds often had concomitant fVIIa activity. The authors also discuss the utilization of medical chemistry techniques for the discovery of these compounds.

EXPERT OPINION

FVIIa inhibitors represent a viable option for the development of new anticoagulants. There are theoretical advantages that fVIIa inhibitors may possess over existing anticoagulants and highly specific inhibitors that possess oral bioavailability and low bleeding risk may succeed.

Tissue factor-fVIIa inhibition: update on an unfinished quest for a novel oral antithrombotic

The tissue factor-coagulation factor VIIa complex (TF-fVIIa) is a well-validated biological target and has been the focus of extensive research directed toward the discovery of novel oral antithrombotics. This review briefly summarizes the key antithrombotic target validation data and provides an update on recent advances in small molecule TF-fVIIa inhibitors.

Berberine inhibits LPS-induced TF procoagulant activity and expression through NF-κB/p65, Akt and MAPK pathway in THP-1 cells

BACKGROUND

Considering the key role of TF in coagulation of sepsis or acute lung injury (ALI), we investigated whether berberine (BBR) could inhibit TF expression and procoagulant activity and explored its possible mechanism.

METHODS

The effects of berberine on the expression, procoagulant activity of TF and related signal pathways induced by lipopolysaccharide (LPS) were observed in THP-1 cells.

RESULTS

Our results showed that berberine could inhibit LPS-induced TF activity and expression, and down-regulate NF-κB, Akt and MAPK/JNK/p38/ERK pathways.

CONCLUSION

Berberine inhibits TF expression and related pathway, which provides some new insights on its mechanism for sepsis treatment.

Design and Synthesis of Phenylpyrrolidine Phenylglycinamides As Highly Potent and Selective TF-FVIIa Inhibitors

Inhibitors of the Tissue Factor/Factor VIIa (TF-FVIIa) complex are promising novel anticoagulants that show excellent efficacy and minimal bleeding in preclinical models. On the basis of a zwitterionic phenylglycine acylsulfonamide 1, a phenylglycine benzylamide 2 was shown to possess improved permeability and oral bioavailability. Optimization of the benzylamide, guided by X-ray crystallography, led to a potent TF-FVIIa inhibitor 18i with promising oral bioavailability, but promiscuous activity in an in vitro safety panel of receptors and enzymes. Introducing an acid on the pyrrolidine ring, guided by molecular modeling, resulted in highly potent, selective, and efficacious TF-FVIIa inhibitors with clean in vitro safety profile. The pyrrolidine acid 20 showed a moderate clearance, low volume of distribution, and a short t 1/2 in dog PK studies.

Selective tissue factor/factor VIIa Inhibitor, ER-410660, and its prodrug, E5539, have anti-venous and anti-arterial thrombotic effects with a low risk of bleeding

INTRODUCTION

Many anticoagulant drugs target factors common to both the intrinsic and extrinsic coagulation pathways, which may lead to bleeding complications. Since the tissue factor (TF)/factor VIIa complex is associated with thrombosis onset and specifically activates the extrinsic coagulation pathway, compounds that inhibit this complex may provide therapeutic and/or prophylactic benefits with a decreased risk of bleeding.

MATERIALS AND METHODS

The in vitro enzyme profile and anticoagulation selectivity of the TF/VIIa complex inhibitor, ER-410660, and its prodrug E5539 were assessed using enzyme inhibitory and plasma clotting assays. In vivo effects of ER-410660 and E5539 were determined using a TF-induced, thrombin generation rhesus monkey model; a stasis-induced, venous thrombosis rat model; a photochemically induced, arterial thrombosis rat model; and a rat tail-cut bleeding model.

RESULTS

ER-410660 selectively prolonged prothrombin time, but had a less potent anticoagulant effect on the intrinsic pathway. It also exhibited a dose-dependent inhibitory effect on thrombin generation caused by TF-injection in the rhesus monkey model. ER-410660 also reduced venous thrombus weights in the TF-administered, stasis-induced, venous thrombosis rat model and prolonged the occlusion time induced by arterial thrombus formation after vascular injury. The compound was capable of doubling the total bleeding time in the rat tail-cut model, albeit with a considerably higher dose compared to the effective dose in the venous and arterial thrombosis models. Moreover, E5539, an orally available ER-410660 prodrug, reduced the thrombin-anti-thrombin complex levels, induced by TF-injection, in a dose-dependent manner.

CONCLUSION

Selective TF/VIIa inhibitors have potential as novel anticoagulants with a lower propensity for enhancing bleeding.

Chemical and microbial semi-synthesis of tetrahydroprotoberberines as inhibitors on tissue factor procoagulant activity

To discover new inhibitors on tissue factor procoagulant activity, 21 tetrahydroprotoberberines were screened on the model of human THP-1 cells stimulated by lipopolysaccharide. Among these tetrahydroprotoberberines, several unique compounds were synthesized through microbial transformation: compound 6 (l-corydalmine) was obtained through regio-selective demethylation by Streptomyces griseus ATCC 13273, whereas compounds 4a, 4b, 5h, and 5i were microbial glycosylation products by Gliocladium deliquescens NRRL1086. The bioassay results showed that compounds 3 (tetrahydroberberine), 10 (tetrahydroberberrubine), and 5f (cinnamyl ester of 5) and 5i (glycosidic product of 5), exhibited the most potential effects, with IC(50) values of 8.35, 6.75, 3.75, and 8.79 nM, respectively. The preliminary structure and activity relationship analysis revealed that the 2,3-methylenedioxy group of the A ring was essential for the strong inhibitory effects, and the R configuration of the chiral center C-14 showed higher activity than S-form products. The formation of fatty acid or aromatic acid esters of compound 5, except the cinnamyl esters, would weaken its effects. It is also interesting to note that the glycosylation of tetrahydroprotoberberines will maintain and even enhance the inhibitory effects. Because of the importance of glycochemistry in new drug discovery and development, this deserves further exploration and may provide some guide on the semi-synthesis of tetrahydroprotoberberines as tissue factor pathway inhibitors. Our findings also provide some potential leading compounds for tissue factor-related diseases, such as cancer and cardiovascular diseases.

Inhibitors of the initiation of coagulation

Initiation of blood coagulation occurs mainly through tissue factor (TF) that becomes exposed to blood following vascular injury. Cell-associated TF binds to the serine protease FVIIa and initiates a cascade of amplified zymogen activation reactions leading to thrombus formation. As TF-FVIIa directed inhibitors might achieve anticoagulant efficacy without significantly interfering with normal haemostasis, the TF-FVIIa complex is an interesting target in thrombosis-related disease. Various approaches have been used to inhibit the TF-FVIIa complex including active site-inhibited FVIIa, TF antibodies, tissue factor pathway inhibitor (TFPI), naturally occurring inhibitors, peptide exosite inhibitors and active site inhibitors. Several experimental studies using these inhibitors have displayed promise. However, none of these TF/FVIIa inhibitors has reached clinical testing. Further studies are required to evaluate the clinical efficacy of these novel inhibitors.

A Simplified and High-Throughput Chromogenic Assay for Testing Tissue Factor–Dependent Procoagulant Activity

Tissue factor (TF), the primary initiator of the coagulation cascade, plays a critical role in hemostasis and thrombosis, and inhibition of TF activity appears to be an attractive target for the treatment of cardiovascular diseases. However, few selective small-molecule inhibitors of TF are available, and the present assays for measuring TF activity are relatively expensive and complex. The authors present a simple and high-throughput chromogenic assay for screening TF inhibitors based on using commercial human prothrombin complex instead of purified coagulation factors, reducing the dosage, and performing with a one-stage procedure. In the optimized assay, <45 µL cell lysates was incubated with Tris-CaCl2 buffer (pH 7.3) containing human prothrombin complex at 37°C for 15 min in 96-well or 384-well plates. Tris-EDTA buffer (pH 8.4) containing chromogenic substrate Xa was then added and the absorbance measured at 405 nm. This simplified assay was more sensitive or precise than some reported methods for TF procoagulant activities. Two known active compounds (curcumin and simvastatin) inhibiting TF activity were tested by the simplified assay to validate the screening method. Furthermore, berberine and cryptotanshinone suppressed TF activity induced by lipopolysaccharides in human monocytes by this assay and might be promising new TF inhibitors.

Novel anticoagulant therapy: principle and practice

Currently, there are several lines of evidence supporting the interplay between coagulation and inflammation in the propagation of various disease processes, including venous thromboembolism (VTE) and inflammatory diseases. Major advances in the development of oral anticoagulants have resulted in considerable progress toward the goal of safe and effective oral anticoagulants that do not require frequent monitoring or dose adjustment and have minimal food/drug interactions. Indirect inhibitors such as low-molecular-weight heparin (LMWH) and the pentasaccharide fondaparinux represent improvements over traditional drugs such as unfractionated heparin for acute treatment of VTE, constituting a more targeted anticoagulant approach with predictable pharmacokinetic profiles and no requirement for monitoring. Vitamin K antagonist, with its inherent limitations in terms of multiple food and drug interactions and frequent need for monitoring, remains the only oral anticoagulant approved for long-term secondary thromboprophylaxis in VTE. The oral-direct thrombin inhibitor ximelagatran was withdrawn from the world market due to safety concerns. Newer anticoagulant drugs such as parenteral pentasaccharides (idraparinux, SSR126517E), novel oral-direct thrombin inhibitors (dabigatran), oral-direct factor Xa inhibitors (rivaroxaban, apixaban, YM-150, DU-176b), and tissue factor/factor VIIa complex inhibitors have been "tailor-made" to target specific procoagulant complexes and have the potential to greatly expand oral antithrombotic targets for both acute and long-term treatment of VTE, acute coronary syndromes, and for the prevention of stroke in atrial fibrillation patients.

Tissue factor and thrombosis: The clot starts here

Thrombosis, or complications from thrombosis, currently occupies the top three positions in the cardiovascular causes of morbidity and mortality in the developed world. There are a limited number of safe and effective drugs to prevent and treat thrombosis. Animal models of thrombosis are necessary to better understand the complex components and interactions involved in the formation of a clot. Tissue factor (TF) is required for the initiation of blood coagulation and likely plays a key role in both arterial and venous thrombosis. Understanding the role of TF in thrombosis may permit the development of new antithrombotic drugs. This review will focus on the role of TF in in vivo models of thrombosis.

Design and synthesis of peptidomimetic factor VIIa inhibitors

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is regarded as a promising target for developing new anticoagulant drugs. In previous reports, we described a S3 subsite found in the X-ray crystal structure of compound 2 that bound to FVIIa/soluble tissue factor (sTF). Based on the X-ray crystal structure information and with the aim of improving the inhibition activity for FVIIa/TF and selectivity against other serine proteases, we synthesized derivatives by introducing substituents at position 5 of the indole ring of compound 2. Among them, compound 16 showed high selectivity against other serine proteases. Contrary to our expectations, compound 16 did not occupy the S3-subsite; X-ray structure analysis revealed that compound 16 improved selectivity by forming hydrogen bonds with Gln217, Thr99 and Asn100.

Inhibition of acute vascular thrombosis in chimpanzees by an anti-human tissue factor antibody targeting the factor X binding site

Tissue factor (TF) antagonists targeting the factor VII (FVII) binding domain have been shown to interrupt acute vascular thrombus formation without impairing haemostasis in non-human primates. In this study, we evaluate whether a human/mouse chimeric monoclonal antibody (ALT-836, formerly known as Sunol-cH36) blocking the factor X/factor IX (FX/FIX) binding site of tissue factor could achieve similar clinical benefits in an arterial thrombosis model induced by surgical endarterectomy in chimpanzees. In this model, sequential surgical endarterectomies on right and left superficial femoral arteries were performed 30 days apart in five chimpanzees. A bolus (1 mg/kg) of ALT-836 was injected intravenously immediately preceding the restoration of flow in the endarterectomised femoral artery. Pre-surgical labelling of autologous platelets using (111)In-Oxine and post-surgical gamma camera imaging of (111)In-platelet deposition at endarterectomy sites was performed. The manipulated arterial segments were harvested for patency analysis 30 days following surgery. The results indicate that ALT-836 was highly effective at reducing acute vascular thrombosis, with no significant variations in surgical blood loss and template-bleeding time in the treated group compared to the control animals. These data suggest that ALT-836 is an effective and safe antithrombotic agent in preventing TF-initiated vascular thrombogenesis without compromising haemostasis.

Natural occurring polyphenols as template for drug design. Focus on serine proteases

Several major physio-pathological processes, including cancer, inflammatory states and thrombosis, are all strongly dependent upon the fine regulation of proteolytic enzyme activities, and dramatic are the consequences of unbalanced equilibria between enzymes and their cognate inhibitors. In this perspective, the discovery of small-molecule ligands able to modulate catalytic activities has a massive therapeutic potential and is a stimulating goal. Numerous recent experimental evidences revealed that proteolytic enzymes can be opportunely targeted, reporting on small ligands capable of binding to these biological macromolecules with drug-like potencies, and primarily with comparable (or even higher) efficiency with respect to their endogenous binding partner. In particular, natural occurring polyphenols and their derivatives recently disclosed these intriguing abilities, making them promising templates for drug design and development. In this review, we compared the inhibitory capacities of a set of monomeric polyphenols toward serine proteases activity, and finally summarized the data with an emphasis on the derivation of a pharmacophore model.

Inhibitors of Factor VIIa/tissue factor

The formation of the proteolytic complex composed of the serine protease Factor VIIa and the cell-associated glycoprotein tissue factor (FVIIa/TF) initiates a cascade of amplified zymogen activation reactions leading to thrombus formation. The critical role of the coagulation cascade in pathological thrombosis has been the basis for significant efforts to design selective inhibitors of the protease components as new anticoagulant alternatives for the treatment of thrombotic diseases. However, for the new generation of anticoagulant drugs in development that primarily target protease complexes distal from FVIIa/TF, the differential between efficacy and safety as defined by bleeding is unresolved. Targeting the FVIIa/TF complex has several theoretical advantages that exploit the amplified nature of the coagulation cascade. However, progress on the development of clinical-stage FVIIa/TF-based anticoagulants has not been as successful to date. This review summarizes recent efforts in the discovery of synthetic inhibitors of FVIIa/TF.

Role of the extrinsic pathway of blood coagulation in hemostasis and thrombosis

Hemostasis requires both platelets and the coagulation system. At sites of vessel injury, bleeding is minimized by the formation of a hemostatic plug consisting of platelets and fibrin. The traditional view of the regulation of blood coagulation is that the initiation phase is triggered by the extrinsic pathway, whereas amplification requires the intrinsic pathway. The extrinsic pathway consists of the transmembrane receptor tissue factor (TF) and plasma factor VII/VIIa (FVII/FVIIa), and the intrinsic pathway consists of plasma FXI, FIX, and FVIII. Under physiological conditions, TF is constitutively expressed by adventitial cells surrounding blood vessels and initiates clotting. In addition so-called blood-borne TF in the form of cell-derived microparticles (MPs) and TF expression within platelets suggests that TF may play a role in the amplification phase of the coagulation cascade. Under pathologic conditions, TF is expressed by monocytes, neutrophils, endothelial cells, and platelets, which results in an elevation of the levels of circulating TF-positive MPs. TF expression within the vasculature likely contributes to thrombosis in a variety of diseases. Understanding how the extrinsic pathway of blood coagulation contributes to hemostasis and thrombosis may lead to the development of safe and effective hemostatic agents and antithrombotic drugs.

Potent 4-amino-5-azaindole factor VIIa inhibitors

The 4-amino-5-azaindole as an amidino-benzimidazole replacement is described. A series of potent and selective analogs were discovered and showed desirable ex vivo efficacy as measured by PT.

The antithrombotic and anti-inflammatory effects of BCX-3607, a small molecule tissue factor/factor VIIa inhibitor

Tissue factor (TF) is a transmembrane glycoprotein that binds its zymogen cofactor, Factor VIIa (FVIIa) on the cell surface. Together (TF/FVIIa) they activate Factor X (FX) and Factor IX (FIX) and start the extrinsic pathway of blood coagulation. As such, the TF/FVIIa complex plays an important role in normal physiology as well as in thrombotic diseases such as unstable angina (UA), disseminated intravascular coagulation (DIC), and deep vein thrombosis (DVT). In addition to its function as an initiator of coagulation, TF/FVIIa plays an important role in inflammation. Expression of TF on the cell surface and its appearance as a soluble molecule are characteristic features of acute and chronic inflammation in conditions such as sepsis and atherosclerosis. Here we demonstrate that BCX-3607, a small molecule potent inhibitor of TF/FVIIa, reduces thrombus weight in an animal model of DVT. BCX-3607 also decreases the level of interleukin-6 (IL-6) in a LPS-stimulated mouse model of endotoxemia. Additionally, in vitro studies indicate that BCX-3607 blocks the generation of TF/FVIIa-induced IL-8 mRNA in human keratinocytes and reduces the TF/FVIIa-mediated generation of IL-6 and IL-8 in human umbilical vein endothelial cells (HUVEC). Therefore, BCX-3607 might block the TF/FVIIa-mediated coagulation and inflammation associated with pathological conditions.

Novel 5-azaindole factor VIIa inhibitors

The discovery and development of 5-azaindole factor VIIa inhibitors will be described.

Tissue factor upregulation drives a thrombosis-inflammation circuit in relation to cardiovascular complications

The extrinsic coagulation is recognized as an 'inducible' signalling cascade resulting from tissue factor (TF) upregulation by exposure to clotting zymogen FVII upon inflammation or tissue injury. Following the substantial initiation, an array of proteolytic activation generates mediating signals (active serine proteases: FVIIa, FXa and FIIa) that lead to hypercoagulation with fibrin overproduction manifesting thrombosis. In addition, TF upregulation plays a central role in driving a thrombosis-inflammation circuit. Coagulant mediators (FVIIa, FXa and FIIa) and endproduct (fibrin) are proinflammatory, eliciting tissue necrosis factor, interleukins, adhesion molecules and many other intracellular signals in different cell types. Such resulting inflammation could ensure 'fibrin' thrombosis via feedback upregulation of TF. Alternatively, the resulting inflammation triggers platelet/leukocyte/polymononuclear cell activation thus contributing to 'cellular' thrombosis. TF is very vulnerable to upregulation resulting in hypercoagulability and subsequent thrombosis and inflammation, either of which presents cardiovascular risks. The prevention and intervention of TF hypercoagulability are of importance in cardioprotection. Blockade of inflammation reception and its intracellular signalling prevents TF expression from upregulation. Natural (activated protein C, tissue factor pathway inhibitor, or antithrombin III) or pharmacological anticoagulants readily offset the extrinsic hypercoagulation mainly through FVIIa, FXa or FIIa inhibition. Therefore, anticoagulants turn off the thrombosis-inflammation circuit, offering not only antithrombotic but anti-inflammatory significance in the prevention of cardiovascular complications.

Dose-dependent antithrombotic activity of an orally active tissue factor/factor VIIa inhibitor without concomitant enhancement of bleeding propensity

The discovery of a highly potent and selective tissue factor/factor VIIa inhibitor is described. Upon oral administration of its double prodrug in the guinea pig, a dose-dependent antithrombotic effect is observed in an established model of arterial thrombosis without prolonging bleeding time. The pharmacodynamic properties of this selective inhibitor are compared to the behaviour of a mixed factor VIIa/factor Xa inhibitor.

Factor VIIa inhibitors: Improved pharmacokinetic parameters

Efforts to improve the potency and pharmacokinetic properties of small molecule factor VIIa inhibitors are described. Small structural modifications to existing leads allow the modulation of half-life and clearance, potentially making these compounds suitable candidates for drug development.

Factor VIIa inhibitors: A prodrug strategy to improve oral bioavailability

We have developed a series of potent and selective factor VIIa inhibitors based on the 2-[5-(5-carbamimidoyl-1H-benzoimidazol-2-yl)-6-hydroxy-biphenyl-3-yl]-succinic acid scaffold. These amidine-containing compounds have low oral bioavailability. Herein, we describe our efforts to improve the oral bioavailability of the parent amidine via a prodrug strategy where the amidine basicity and polarity were reduced with either an alkoxy-amidine or a carbamate prodrug.

The discovery of fluoropyridine-based inhibitors of the factor VIIa/TF complex—Part 2

The activated factor VII/tissue factor complex (FVIIa/TF) is known to play a key role in the formation of blood clots. Inhibition of this complex may lead to new antithrombotic drugs. A fluoropyridine-based series of FVIIa/TF inhibitors was discovered which utilized a diisopropylamino group for binding in the S2 and S3 binding pockets of the active site of the enzyme complex. In this series, an enhancement in binding affinity was observed by substitution at the 5-position of the hydroxybenzoic acid sidechain. An X-ray crystal structure indicates that amides at this position may increase inhibitor binding affinity through interactions with the S1'/S2' pocket.

Factor VIIa inhibitors: chemical optimization, preclinical pharmacokinetics, pharmacodynamics, and efficacy in an arterial baboon thrombosis model

Highly selective and potent factor VIIa-tissue factor (fVIIa.TF) complex inhibitors were generated through structure-based design. The pharmacokinetic properties of an optimized analog (9) were characterized in several preclinical species, demonstrating pharmacokinetic characteristics suitable for once-a-day dosing in humans. Analog 9 inhibited platelet and fibrin deposition in a dose-dependent manner after intravenous administration in a baboon thrombosis model, and a pharmacodynamic concentration-response model was developed to describe the platelet deposition data. Results for heparin and enoxaparin (Lovenox) in the baboon model are also presented.

Factor VIIa inhibitors: gaining selectivity within the trypsin family

Within the trypsin family of coagulation proteases, obtaining highly selective inhibitors of factor VIIa has been challenging. We report a series of factor VIIa (fVIIa) inhibitors based on the 5-amidino-2-(2-hydroxy-biphenyl-3-yl)-benzimidazole (1) scaffold with potency for fVIIa and high selectivity against factors IIa, Xa, and trypsin. With this scaffold class, we propose that a unique hydrogen bond interaction between a hydroxyl on the distal ring of the biaryl system and the backbone carbonyl of fVIIa lysine-192 provides a basis for enhanced selectivity and potency for fVIIa.

Selective and orally bioavailable phenylglycine tissue factor/factor VIIa inhibitors

We describe the structure-based design and synthesis of highly potent, orally bioavailable tissue factor/factor VIIa inhibitors which interfere with the coagulation cascade by selective inhibition of the extrinsic pathway.

Tissue factor: (patho)physiology and cellular biology

The transmembrane glycoprotein tissue factor (TF) is the initiator of the coagulation cascade in vivo. When TF is exposed to blood, it forms a high-affinity complex with the coagulation factors factor VII/activated factor VIIa (FVII/VIIa), activating factor IX and factor X, and ultimately leading to the formation of an insoluble fibrin clot. TF plays an essential role in hemostasis by restraining hemorrhage after vessel wall injury. An overview of biological and physiological aspects of TF, covering aspects consequential for thrombosis and hemostasis such as TF cell biology and biochemistry, blood-borne (circulating) TF, TF associated with microparticles, TF encryption-decryption, and regulation of TF activity and expression is presented. However, the emerging role of TF in the pathogenesis of diseases such as sepsis, atherosclerosis, certain cancers and diseases characterized by pathological fibrin deposition such as disseminated intravascular coagulation and thrombosis, has directed attention to the development of novel inhibitors of tissue factor for use as antithrombotic drugs. The main advantage of inhibitors of the TF*FVIIa pathway is that such inhibitors have the potential of inhibiting the coagulation cascade at its earliest stage. Thus, such therapeutics exert minimal disturbance of systemic hemostasis since they act locally at the site of vascular injury.