Sestrin modulator NV-5138 produces rapid antidepressant effects via direct mTORC1 activation

Preclinical studies demonstrate that rapid acting antidepressants, including ketamine require stimulation of mTORC1 signaling. This pathway is regulated by neuronal activity, endocrine and metabolic signals, notably the amino acid leucine, which activates mTORC1 signaling via binding to the upstream regulator sestrin. Here, we examined the antidepressant actions of NV-5138, a novel highly selective small molecule modulator of sestrin that penetrates the blood brain barrier. The results demonstrate that a single dose of NV-5138 produced rapid and long-lasting antidepressant effects, and rapidly reversed anhedonia caused by chronic stress exposure. The antidepressant actions of NV-5138 required BDNF release as the behavioral responses are blocked by infusion of a BDNF neutralizing antibody into the medial prefrontal cortex (mPFC) or in mice with a knock-in of a BDNF polymorphism that blocks activity dependent BDNF release. NV-5138 administration also rapidly increased synapse number and function in the mPFC, and reversed the synaptic deficits caused by chronic stress. Together, the results demonstrate that NV-5138 produced rapid synaptic and antidepressant behavioral responses via activation of the mTORC1 pathway and BDNF signaling, indicating that pharmacological modulation of sestrin is a novel approach for development of rapid acting antidepressants.

Thioester Chromogenic Substrates for Human Factor VIIa: Substituted Isocoumarins Are Inhibitors of Factor VIIa and In Vitro Anticoagulants

Arginine thiobenzyl esters are convenient chromogenic substrates of factor Vila (Z-Arg-SBzl, kcat/KM = 1,600 M−1 s−1) and were used to study the kinetics of inhibition of factor Vila by several mechanism-based isocoumarin inhibitors of trypsin-like enzymes. Isocoumarin derivatives substituted with a 7-guanidino or 3-isothiureidopropoxy group were good inhibitors of factor Vila and acted as anticoagulants in human and rabbit plasma. With normal citrated human plasma, 4-chloro-3-ethoxy-7-guanidinoisocoumarin (3) and 7-amino-4-chloro-3-(3-isothiurei-dopropoxy) isocoumarin (ACITIC, 6) prolonged the prothrombin time (PT) ca. two-fold and prolonged the activated partial thromboplastin time (APTT) more than 4.5-fold at 20-30 pM. Both compounds had smaller effects in rabbit plasma. The short half-life of ACITIC and related isocoumarins in plasma should make these compounds uniquely useful as anticoagulants in therapeutic situations where it is desirable to have anticoagulant effects for a short defined time period.

Primary Prevention of Coronary Arterial Thrombosis with the Factor Xa Inhibitor rTAP in a Canine Electrolytic Injury Model

The antithrombotic efficacies of the coagulation factor Xa inhibitor recombinant tick anticoagulant peptide (rTAP) and heparin were compared in a canine model of left circumflex (LCX) coronary artery electrolytic lesion. Intravenous infusions of saline (controls), rTAP (50 μg/kg/min continuous infusion) or heparin (200 U/kg bolus followed by 2 U/kg/min continuous infusion) were started 60 min prior to the initiation of LCX coronary artery electrolytic injury (150 μA continuous anodal current). All 6/6 saline-treated control animals developed occlusive thrombi at 49.8 ± 13.6 min after the initiation of vessel injury, and possessed a residual thrombus mass of 20.7 ± 3.3 mg. In the rTAP treatment group, 4/6 preparations developed occlusive thrombi, but with times to thrombosis delayed significantly compared to both the saline control as well as to the heparin treatment group (202.7 ± 28.9 min; p <0.01 to both saline and heparin groups). The remaining 2 rTAP-treated preparations remained patent despite the continued electrical stimulation of the coronary vessel for 5 h. Residual thrombus mass in the rTAP treatment group was reduced markedly compared to the saline control group (4.4 ± 1.0 mg; p <0.01). Heparin infusion resulted in a modest but statistically insignificant delay in occlusive LCX coronary artery thrombosis compared to saline controls, with all 6/6 heparin-treated preparations occluding at 79.7 ± 16.5 min after the initiation of vessel injury. Residual thrombus mass in heparin-treated animals, however, was reduced compared to saline controls (9.4 ± 1.4 mg; p <0.01). These results support a pivotal role for fXa in the process of arterial thrombosis, as well as the feasibility of inhibiting fXa as an effective strategy for the primary prevention of arterial thrombosis.

Anticoagulant Efficacy and Immunogenicity of the Selective Factor Xa Inhibitor Antistasin Following Subcutaneous Administration in the Rhesus Monkey

The antithrombotic efficacy and duration of action of a single subcutaneous administration of the selective factor Xa inhibitor recombinant antistasin (rATS) was evaluated in a rhesus monkey model of mild disseminated intravascular coagulation. rATS (1 mg/kg) was shown to be fully effective and comparable to standard heparin (1,000 U/kg) in the suppression of thromboplastin-induced fibrinopeptide A generation for at least 5 h following a single subcutaneous administration. The absorption rate of rATS, as measured by ex vivo activated partial thromboplastin times (aPTT), mirrored that of standard heparin exhibiting peak anticoagulant activity between 1 and 2 h post administration. The anticoagulant effects of a single rATS dose lasted for longer than 30 h maintaining an aPTT value at least 2-fold higher than baseline. Repeated subcutaneous administrations of rATS resulted in the generation of fully neutralizing antibodies. These results suggest that specific factor Xa inhibition may be as effective as standard heparin in the treatment of venous thrombosis. Due to its antigenicity however, rATS is probably not suitable for chronic subcutaneous anticoagulant therapy.

A small molecule inhibitor of Rheb selectively targets mTORC1 signaling

The small G-protein Rheb activates the mechanistic target of rapamycin complex 1 (mTORC1) in response to growth factor signals. mTORC1 is a master regulator of cellular growth and metabolism; aberrant mTORC1 signaling is associated with fibrotic, metabolic, and neurodegenerative diseases, cancers, and rare disorders. Point mutations in the Rheb switch II domain impair its ability to activate mTORC1. Here, we report the discovery of a small molecule (NR1) that binds Rheb in the switch II domain and selectively blocks mTORC1 signaling. NR1 potently inhibits mTORC1 driven phosphorylation of ribosomal protein S6 kinase beta-1 (S6K1) but does not inhibit phosphorylation of AKT or ERK. In contrast to rapamycin, NR1 does not cause inhibition of mTORC2 upon prolonged treatment. Furthermore, NR1 potently and selectively inhibits mTORC1 in mouse kidney and muscle in vivo. The data presented herein suggest that pharmacological inhibition of Rheb is an effective approach for selective inhibition of mTORC1 with therapeutic potential.

Pharmacologic inhibition of platelet vWF-GPIbα interaction prevents coronary artery thrombosis

Under high shear arterial blood flow von Willebrand Factor (vWF) binds the platelet receptor glycoprotein (GP) Ibα, leading to platelet adhesion, activation and thrombosis. Blockade of vWF-GPIbα interactions by GPG-290 was investigated in a canine model of coronary artery thrombosis alone and in combination with clopidogrel. GPG-290 (100 µg/kg, n=6; 500 µg/kg, n=6) prolonged time to thrombotic occlusion (TTO) to 105±34 and 156±23 (p<0.05) min, respectively compared to the saline treated control group (32±6min, n=6). Patency of the injured vessel was sustained in 1/6 (100µg/kg) and 3/6 vessels (500 µg/kg) 4 hours after injury, in contrast to 0/6 in the control group. There was an increase in bleeding after the 500 µg/kg dose, but only at the 1 hr time point. Clopidogrel was studied in two dosing regimens representing either a clinical pretreatment regimen (PTR) of 4.3 mg/kg on day –2 followed by 1.1 mg/kg daily for2 days prior to the procedure or pre-procedural loading dose regimen (LDR) of 4.3 mg/kg 3 hr pre-procedure. The PTR and LDR clopidogrel treatments prolonged TTO to 98.2±30.0 min and 136.1±39.5 min (p<0.05), and sustained patency in 1/6 and 4/8 vessels, respectively. However, template bleeding time in the LDR clopidogrel group was sustained higher than the control group. The combination of PTR clopidogrel and GPG-290 (100 µg/kg) prolonged TTO equivalent to LDR clopidogrel alone (141.4±35.1 min) and sustained patency in 3/7 dogs, without increased bleeding while LDR clopidogrel combined with 100 µg/kg GPG-290 prevented occlusion in 5/8 dogs and further prolonged TTO (173.5±32.6 min) but was associated with increased bleeding compared to control. GPG-290 is an antithrombotic agent that may be combined with lower doses of clopidogrel to yield similar antithrombotic efficacy as higher loading doses.

A Randomized, Placebo-Controlled Study of SRT2104, a SIRT1 Activator, in Patients with Moderate to Severe Psoriasis

Activation of Sirtuin (silent mating type information regulation 2 homolog) 1, or SIRT1, is an unexplored therapeutic approach for treatment of inflammatory diseases. We randomized 40 patients with moderate-to-severe psoriasis (4:1) to three escalating doses of SRT2104, a selective activator of SIRT1, or placebo. Across all SRT2104 groups, 35% of patients (p<0.0001) achieved good to excellent histological improvement based on skin biopsies taken at baseline and day 84 but was not consistently in agreement with PASI. Improvement in histology was associated with modulation of IL-17 and TNF-α signaling pathways and keratinocyte differentiation target genes. 27 subjects (69%) across all treatment groups, including placebo, experienced at least one treatment emergent adverse event. The majority of AEs were either mild or moderate. Most common were headache (8%), dizziness (8%), upper respiratory tract infection (8%), and psoriatic arthropathy (8%). Average drug exposure increased in a dose-dependent manner for escalating doses of SRT2104 and had high intra-subject variability in exposure (AUC %CV: 51–89%). Given the interesting signals of clinical activity, impact on gene expression and the generally favorable safety profile seen in this study, further investigation of SIRT1 activators for the treatment of psoriasis is warranted.

A phase II, randomized, placebo-controlled, double-blind, multi-dose study of SRT2104, a SIRT1 activator, in subjects with type 2 diabetes

AIM

SRT2104 is a selective activator of SIRT1. In animal models, SRT2104 improves glucose homeostasis and increases insulin sensitivity. We evaluated the tolerability and pharmacokinetics of SRT2104, and its effects on glycaemic control, in adults with type 2 diabetes mellitus.

METHOD

Type 2 diabetics with glycosylated haemoglobin (HbA1c) ≥ 7.5% and ≤10.5%, fasting glucose ≥160 and ≤240 mg dl(-1) , and on stable doses of metformin were evenly randomized to placebo or SRT2104 0.25 g, 0.5 g, 1.0 g or 2.0 g, administered orally once daily for 28 days. Changes in fasting and post-prandial glucose and insulin were analyzed.

RESULTS

Safety evaluation found no major differences between groups in the frequency of adverse events. SRT2104 concentrations did not increase in a dose-proportional fashion. Significant variability in exposure was observed. Treatment with SRT2104 did not lead to any consistent, dose-related changes in glucose or insulin. Day 28 change from baseline (mean (SD)): fasting glucose (mmol l(-1) ) = -1.17 (2.42), -1.11 (3.45), -0.52 (2.60), -0.97 (2.83) and -0.15 (2.38) for placebo, 0.25 g, 0.5 g, 1.0 g and 2.0 g, respectively. Day 28 change from baseline (mean (SD)): fasting insulin (mmol l(-1) ) = 1.0 (51.66), 8.9 (95.04), -6.9 (41.45), 4.1 (57.16) and 15.2 (138.79) for placebo, 0.25 g, 0.5 g, 1.0 g and 2.0 g, respectively) Treatment with SRT2104 was associated with improvement in lipid profiles.

CONCLUSION

Treatment with SRT2104 for 28 days did not result in improved glucose or insulin control which is likely due to the observed pharmacokinetics which were not dose proportional and had large between subject variability.

Crystallographic structure of a small molecule SIRT1 activator-enzyme complex

SIRT1, the founding member of the mammalian family of seven NAD⁺-dependent sirtuins, is composed of 747 amino acids forming a catalytic domain and extended N- and C-terminal regions. We report the design and characterization of an engineered human SIRT1 construct (mini-hSIRT1) containing the minimal structural elements required for lysine deacetylation and catalytic activation by small molecule sirtuin-activating compounds (STACs). Using this construct, we solved the crystal structure of a mini-hSIRT1-STAC complex, which revealed the STAC-binding site within the N-terminal domain of hSIRT1. Together with hydrogen-deuterium exchange mass spectrometry (HDX-MS) and site-directed mutagenesis using full-length hSIRT1, these data establish a specific STAC-binding site and identify key intermolecular interactions with hSIRT1. The determination of the interface governing the binding of STACs with human SIRT1 facilitates greater understanding of STAC activation of this enzyme, which holds significant promise as a therapeutic target for multiple human diseases.

Sirtuins are NAD⁺-dependent deacylases implicated in the regulation of stress responses, bioenergetics and epigenetic control. Here the authors describe the crystal structure of a sirtuin-activating compounds (STAC)-sirtuin complex and begin to elucidate the mechanism of sirtuins activation by STACs.

Sirtuin 1 activator SRT2104 protects Huntington's disease mice

Sirtuin 1 is a nicotinamide adenine dinucleotide-dependent protein deacetylase which regulates longevity and improves metabolism. Activation of Sirtuin 1 confers beneficial effects in models of neurodegenerative diseases. We and others have provided convincing evidence that overexpression of Sirtuin 1 plays a neuroprotective role in mouse models of Huntington's disease. In this study, we report that SRT2104, a small molecule Sirtuin 1 activator, penetrated the blood–brain barrier, attenuated brain atrophy, improved motor function, and extended survival in a mouse model of Huntington's disease. These findings imply a novel therapeutic strategy for Huntington's disease by targeting Sirtuin 1.

SRT2104 extends survival of male mice on a standard diet and preserves bone and muscle mass

Increased expression of SIRT1 extends the lifespan of lower organisms and delays the onset of age-related diseases in mammals. Here, we show that SRT2104, a synthetic small molecule activator of SIRT1, extends both mean and maximal lifespan of mice fed a standard diet. This is accompanied by improvements in health, including enhanced motor coordination, performance, bone mineral density, and insulin sensitivity associated with higher mitochondrial content and decreased inflammation. Short-term SRT2104 treatment preserves bone and muscle mass in an experimental model of atrophy. These results demonstrate it is possible to design a small molecule that can slow aging and delay multiple age-related diseases in mammals, supporting the therapeutic potential of SIRT1 activators in humans.

Carboxamide SIRT1 inhibitors block DBC1 binding via an acetylation-independent mechanism

SIRT1 is an NAD (+) -dependent deacetylase that counteracts multiple disease states associated with aging and may underlie some of the health benefits of calorie restriction. Understanding how SIRT1 is regulated in vivo could therefore lead to new strategies to treat age-related diseases. SIRT1 forms a stable complex with DBC1, an endogenous inhibitor. Little is known regarding the biochemical nature of SIRT1-DBC1 complex formation, how it is regulated and whether or not it is possible to block this interaction pharmacologically. In this study, we show that critical residues within the catalytic core of SIRT1 mediate binding to DBC1 via its N-terminal region, and that several carboxamide SIRT1 inhibitors, including EX-527, can completely block this interaction. We identify two acetylation sites on DBC1 that regulate its ability to bind SIRT1 and suppress its activity. Furthermore, we show that DBC1 itself is a substrate for SIRT1. Surprisingly, the effect of EX-527 on SIRT1-DBC1 binding is independent of DBC1 acetylation. Together, these data show that protein acetylation serves as an endogenous regulatory mechanism for SIRT1-DBC1 binding and illuminate a new path to developing small-molecule modulators of SIRT1.

The SIRT1 activator SRT1720 extends lifespan and improves health of mice fed a standard diet

The prevention or delay of the onset of age-related diseases prolongs survival and improves quality of life while reducing the burden on the health care system. Activation of sirtuin 1 (SIRT1), an NAD(+)-dependent deacetylase, improves metabolism and confers protection against physiological and cognitive disturbances in old age. SRT1720 is a specific SIRT1 activator that has health and lifespan benefits in adult mice fed a high-fat diet. We found extension in lifespan, delayed onset of age-related metabolic diseases, and improved general health in mice fed a standard diet after SRT1720 supplementation. Inhibition of proinflammatory gene expression in both liver and muscle of SRT1720-treated animals was noted. SRT1720 lowered the phosphorylation of NF-κB pathway regulators in vitro only when SIRT1 was functionally present. Combined with our previous work, the current study further supports the beneficial effects of SRT1720 on health across the lifespan in mice.

Cardiovascular effects of a novel SIRT1 activator, SRT2104, in otherwise healthy cigarette smokers

BACKGROUND

We examined the effect of the oral SIRT1 activator SRT2104 on cardiovascular function in otherwise healthy cigarette smokers.

METHODS AND RESULTS

Twenty-four otherwise healthy cigarette smokers participated in a randomized double-blind, placebo-controlled crossover trial and received 28 days of oral SRT2104 (2.0 g/day) or matched placebo. Plasma SRT2104 concentrations, serum lipid profile, plasma fibrinolytic factors, and markers of platelet and monocyte activation were measured at baseline and at the end of each treatment period together with an assessment of forearm blood flow during intra-arterial bradykinin, acetylcholine, and sodium nitroprusside infusions. Three hours postdose, mean plasma SRT2104 concentration was 1328 ± 748 ng/mL after 28 days of active treatment. Compared with placebo, serum lipid profile improved during SRT2104 administration, with reductions in serum total cholesterol (-11.6 ± 20 versus 6 ± 21 mg/dL), low-density lipoprotein cholesterol (-10 ± 17 versus 3 ± 21 mg/dL), and triglyceride (-39.8 ± 77 versus 13.3 ± 57 mg/dL) concentrations (P<0.05 for all). All vasodilators produced a dose-dependent increase in blood flow (P<0.0001) that was similar during each treatment period (P>0.05 for all). No significant differences in fibrinolytic or blood flow parameters were observed between placebo and SRT2014.

CONCLUSIONS

SRT2104 appears to be safe and well tolerated and associated with an improved lipid profile without demonstrable differences in vascular or platelet function in otherwise healthy cigarette smokers.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov. Unique identifier: NCT01031108.

Discovery of thieno[3,2-d]pyrimidine-6-carboxamides as potent inhibitors of SIRT1, SIRT2, and SIRT3

The sirtuins SIRT1, SIRT2, and SIRT3 are NAD(+) dependent deacetylases that are considered potential targets for metabolic, inflammatory, oncologic, and neurodegenerative disorders. Encoded library technology (ELT) was used to affinity screen a 1.2 million heterocycle enriched library of DNA encoded small molecules, which identified pan-inhibitors of SIRT1/2/3 with nanomolar potency (e.g., 11c: IC50 = 3.6, 2.7, and 4.0 nM for SIRT1, SIRT2, and SIRT3, respectively). Subsequent SAR studies to improve physiochemical properties identified the potent drug like analogues 28 and 31. Crystallographic studies of 11c, 28, and 31 bound in the SIRT3 active site revealed that the common carboxamide binds in the nicotinamide C-pocket and the aliphatic portions of the inhibitors extend through the substrate channel, explaining the observable SAR. These pan SIRT1/2/3 inhibitors, representing a novel chemotype, are significantly more potent than currently available inhibitors, which makes them valuable tools for sirtuin research.

Evidence for a common mechanism of SIRT1 regulation by allosteric activators

A molecule that treats multiple age-related diseases would have a major impact on global health and economics. The SIRT1 deacetylase has drawn attention in this regard as a target for drug design. Yet controversy exists around the mechanism of sirtuin-activating compounds (STACs). We found that specific hydrophobic motifs found in SIRT1 substrates such as PGC-1α and FOXO3a facilitate SIRT1 activation by STACs. A single amino acid in SIRT1, Glu(230), located in a structured N-terminal domain, was critical for activation by all previously reported STAC scaffolds and a new class of chemically distinct activators. In primary cells reconstituted with activation-defective SIRT1, the metabolic effects of STACs were blocked. Thus, SIRT1 can be directly activated through an allosteric mechanism common to chemically diverse STACs.

A pilot randomized, placebo controlled, double blind phase I trial of the novel SIRT1 activator SRT2104 in elderly volunteers

BACKGROUND

SRT2104 has been developed as a selective small molecule activator of SIRT1, a NAD(+)-dependent deacetylase involved in the regulation of energy homeostasis and the modulation of various metabolic pathways, including glucose metabolism, oxidative stress and lipid metabolism. SIRT1 has been suggested as putative therapeutic target in multiple age-related diseases including type 2 diabetes and dyslipidemias. We report the first clinical trial of SRT2104 in elderly volunteers.

METHODS

Oral doses of 0.5 or 2.0 g SRT2104 or matching placebo were administered once daily for 28 days. Pharmacokinetic samples were collected through 24 hours post-dose on days 1 and 28. Multiple pharmacodynamic endpoints were explored with oral glucose tolerance tests (OGTT), serum lipid profiles, magnetic resonance imaging (MRI) for assessment of whole body visceral and subcutaneous fat, maximal aerobic capacity test and muscle 31P magnetic resonance spectroscopy (MRS) for estimation of mitochondrial oxidative capacity.

RESULTS

SRT2104 was generally safe and well tolerated. Pharmacokinetic exposure increased less than dose-proportionally. Mean Tmax was 2-4 hours with elimination half-life of 15-20 hours. Serum cholesterol, LDL levels and triglycerides decreased with treatment. No significant changes in OGTT responses were observed. 31P MRS showed trends for more rapid calculated adenosine diphosphate (ADP) and phosphocreatine (PCr) recoveries after exercise, consistent with increased mitochondrial oxidative phosphorylation.

CONCLUSIONS

SRT2104 can be safely administered in elderly individuals and has biological effects in humans that are consistent with SIRT1 activation. The results of this study support further development of SRT2104 and may be useful in dose selection for future clinical trials in patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00964340.

SIRT1 activation by small molecules: kinetic and biophysical evidence for direct interaction of enzyme and activator

SIRT1 is a protein deacetylase that has emerged as a therapeutic target for the development of activators to treat diseases of aging. SIRT1-activating compounds (STACs) have been developed that produce biological effects consistent with direct SIRT1 activation. At the molecular level, the mechanism by which STACs activate SIRT1 remains elusive. In the studies reported herein, the mechanism of SIRT1 activation is examined using representative compounds chosen from a collection of STACs. These studies reveal that activation of SIRT1 by STACs is strongly dependent on structural features of the peptide substrate. Significantly, and in contrast to studies reporting that peptides must bear a fluorophore for their deacetylation to be accelerated, we find that some STACs can accelerate the SIRT1-catalyzed deacetylation of specific unlabeled peptides composed only of natural amino acids. These results, together with others of this study, are at odds with a recent claim that complex formation between STACs and fluorophore-labeled peptides plays a role in the activation of SIRT1 (Pacholec, M., Chrunyk, B., Cunningham, D., Flynn, D., Griffith, D., Griffor, M., Loulakis, P., Pabst, B., Qiu, X., Stockman, B., Thanabal, V., Varghese, A., Ward, J., Withka, J., and Ahn, K. (2010) J. Biol. Chem. 285, 8340-8351). Rather, the data suggest that STACs interact directly with SIRT1 and activate SIRT1-catalyzed deacetylation through an allosteric mechanism.

Estrogen receptor beta agonism increases survival in experimentally induced sepsis and ameliorates the genomic sepsis signature: a pharmacogenomic study

BACKGROUND

Nonsteroidal agonists have been developed that selectively bind to and activate estrogen receptor beta (ERbeta) rather than estrogen receptor alpha (ERalpha). ERbeta is expressed equally in both male and female mammals in multiple extragonadal tissues. Work reported elsewhere has demonstrated that ERbeta agonists have beneficial effects in multiple (but not all) models of inflammatory diseases and also increase survival in experimentally induced sepsis.

METHODS

In these experiments, ERbeta agonists (ERB-041 or WAY-202196) were compared with vehicle control in the murine cecal ligation and puncture (CLP) model and in the pneumococcal pneumonia model of sepsis. The effect of WAY-202196 on the gene expression profile in the CLP model was further studied by transcriptome analysis of lung and small intestine tissue samples.

RESULTS

ERbeta agonists provided a significant survival benefit in both experimental models of bacterial sepsis. This survival advantage was accompanied by reduced histologic evidence of tissue damage, reduced transcription of multiple proinflammatory proteins by transcriptome analysis and was not associated with increased bacterial outgrowth.

CONCLUSIONS

ERbeta agonist administration provided a survival advantage in septic animals and appears to be a promising therapeutic modality in sepsis.

Modulation of nutrient sensing nuclear hormone receptors promotes weight loss through appetite suppression in mice

AIM

Peroxisome proliferator activated receptors (PPARs) are nuclear receptors involved in glucose and lipid metabolism. Three isoforms of PPARs have been identified with different tissue distribution and biological functions. Although the pharmacology of each receptor is well studied, the physiological effect of simultaneous activation of PPARalpha, gamma and delta is only starting to emerge. We sought to determine the biological effects of a novel PPAR pan activator and elucidate the physiological mechanisms involved.

METHODS

Ob/ob, diet-induced obese (DIO) or PPARalpha knockout mice were administered a novel agonist that activates all PPARs to various degrees to determine the effect on body weight, body composition, food intake and energy expenditure. In addition, serum parameters including glucose, insulin, triglycerides and ketone bodies as well as tissue acylcarnitine were evaluated. The effect of the novel agonist on liver and skeletal muscle histopathology was also studied.

RESULTS

We report that simultaneous activation of all PPARs resulted in substantial weight loss in ob/ob and DIO mice. Consistent with known PPAR pharmacology, we observed that agonist treatment increased lipid oxidation, although appetite suppression was mainly responsible for the weight loss. Agonist-induced weight loss was completely absent in PPARalpha knockout mice suggesting that PPARalpha pharmacology was the major contributor to weight regulation in mice.

CONCLUSIONS

Our work provides evidence that simultaneous activation of PPARalpha, gamma and delta decreases body weight by regulating appetite. These effects of the pan agonist were completely absent in PPARalpha knockout mice, suggesting that PPARalpha pharmacology was the major contributor to weight loss.

LXR ligand lowers LDL cholesterol in primates, is lipid neutral in hamster, and reduces atherosclerosis in mouse

Liver X receptors (LXRs) are ligand-activated transcription factors that coordinate regulation of gene expression involved in several cellular functions but most notably cholesterol homeostasis encompassing cholesterol transport, catabolism, and absorption. WAY-252623 (LXR-623) is a highly selective and orally bioavailable synthetic modulator of LXR, which demonstrated efficacy for reducing lesion progression in the murine LDLR(-/-) atherosclerosis model with no associated increase in hepatic lipogenesis either in this model or Syrian hamsters. In nonhuman primates with normal lipid levels, WAY-252623 significantly reduced total (50-55%) and LDL-cholesterol (LDLc) (70-77%) in a time- and dose-dependent manner as well as increased expression of the target genes ABCA1/G1 in peripheral blood cells. Statistically significant decreases in LDLc were noted as early as day 7, reached a maximum by day 28, and exceeded reductions observed for simvastatin alone (20 mg/kg). Transient increases in circulating triglycerides and liver enzymes reverted to baseline levels over the course of the study. Complementary microarray analysis of duodenum and liver gene expression revealed differential activation of LXR target genes and suggested no direct activation of hepatic lipogenesis. WAY-252623 displays a unique and favorable pharmacological profile suggesting synthetic LXR ligands with these characteristics may be suitable for evaluation in patients with atherosclerotic dyslipidemia.

A synthetic farnesoid X receptor (FXR) agonist promotes cholesterol lowering in models of dyslipidemia

The nuclear hormone receptor farnesoid X receptor (FXR) plays a critical role in the regulation of bile acid, triglyceride (TG), and cholesterol homeostasis. WAY-362450 (FXR-450/XL335) is a potent synthetic FXR agonist as characterized in luciferase reporter assays and in mediating FXR target gene regulation in primary human and immortalized mouse hepatocytes. In vivo, WAY-362450 dose dependently decreased serum TG levels after 7 days of oral dosing in western diet-fed low-density lipoprotein receptor-/- mice and in the diabetic mouse strains KK-Ay and db/db comparable to that achieved with the peroxisome proliferator activated receptor-alpha agonist, fenofibrate. WAY-362450 treatment also reduced serum cholesterol levels via reductions in LDLc, VLDLc, and HDLc lipoprotein fractions that were not accompanied by hepatic cholesterol accumulation. This cholesterol lowering was dependent on FXR as demonstrated in a hypothyroid-induced hypercholesterolemia setting in FXR-/- mice. In fructose-fed models, WAY-362450 also decreased TG and VLDLc levels in rats and hamsters but significantly increased HDLc levels in rats while reducing HDLc levels in hamsters. The differential effect of WAY-362450 on HDLc is likely due to a murine-specific induction of endothelial lipase and scavenger receptor-BI that does not occur in rats. These studies demonstrate a consistent ability of WAY-362450 to lower both serum TG and cholesterol levels and suggest that synthetic FXR agonists may have clinical utility in the treatment of mixed dyslipidemia.

Effect of tiplaxtinin (PAI-039), an orally bioavailable PAI-1 antagonist, in a rat model of thrombosis

OBJECTIVE

To assess the antithrombotic and profibrinolytic effects of tiplaxtinin (PAI-039), an orally bioavailable antagonist of PAI-1, in rat models of thrombosis.

METHODS AND RESULTS

Carotid artery and vena cava vascular injury was produced by application of FeCl3 and blood flow was monitored using ultrasonic technology. To assess efficacy in a thrombosis prevention paradigm, PAI-039 was administered orally 90 min before injury (1-30 mg kg(-1)). To assess efficacy in a thrombosis treatment paradigm, vascular injury and stable thrombus formation were followed 4 h later by recovery and PAI-039 administration. PAI-039 prevented carotid artery occlusion in 20, 68 and 60% of animals pretreated with 0.3, 1.0 and 3.0 mg kg(-1), respectively. Time to occlusive thrombosis was increased from 18.2 +/- 4.6 min in controls to 32.5 +/- 8.7 (P = ns), 46.1 +/- 7.0 (P < 0.05), and 41.6 +/- 11.3 min (P < 0.05) in the respective PAI-039 treatment groups. In the vena cava protocol, PAI-039 pretreatment significantly reduced thrombus weight at PAI-039 doses of 3, 10 and 30 mg kg(-1). When PAI-039 was dosed in a treatment paradigm 4 h after stable arterial and venous thrombosis, a significant reduction in thrombus weight was observed 24 h later at PAI-039 doses of 3, 10 and 30 mg kg(-1). PAI-039 (10, 30 and 100 mg kg(-1)) had no effect on platelet aggregation in response to ADP or collagen and was not associated with increased bleeding or prolonged prothrombin time. In animals bearing no vascular injury, PAI-039 had no effect on circulating, low-levels of PAI-1 activity. In contrast, circulating PAI-1 activity increased 5-fold following the induction of vascular injury, which was completely neutralized by PAI-039.

CONCLUSIONS

PAI-039 exerts antithrombotic efficacy in rat models of arterial and venous vascular injury without effecting platelet aggregation.

Prophylactic P-selectin inhibition with PSI-421 promotes resolution of venous thrombosis without anticoagulation

P-selectin inhibition has been evaluated as a therapeutic for prevention and treatment of venous thrombosis. In this study, a novel oral small-molecule inhibitor of P-selectin, PSI-421, was evaluated in a baboon model of stasis induced deep vein thrombosis (DVT). Experimental groups included i) primates receiving a single oral dose of 1 mg/kg PSI-421 two days prior and continued six days after thrombosis (n = 3); ii) primates receiving a single daily subcutaneous dose of 0.57 mg/kg enoxaparin sodium two days prior and continued six days post thrombosis (n = 3); and iii) primates receiving no treatment (n = 3). PSI-421 treated primates had greater percent vein reopening and less vein wall inflammation than the enoxaparin and controls at day 6. Microparticle tissue factor activity (MPTFA) was significantly lower in the animals receiving PSI-421 immediately after thrombosis (T+6 hours day 0) suggesting lower potential for thrombogenesis in these animals. PSI-421 also reduced soluble P-selectin levels versus controls at T+6 hours day 0, day 2 and 6. Experimental animals in any group showed no adverse effects on coagulation. This study is the first to demonstrate a reduction in MPTFA associated with vein reopening and reduced vein inflammation due to oral P-selectin inhibition in a baboon model of DVT.

Neutralization of Plasminogen Activator Inhibitor I (PAI-1) by the Synthetic Antagonist PAI-749 via a Dual Mechanism of Action

PAI-749 is a potent and selective synthetic antagonist of plasminogen activator inhibitor 1 (PAI-1) that preserved tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) activities in the presence of PAI-1 (IC(50) values, 157 and 87 nM, respectively). The fluorescence (Fl) of fluorophore-tagged PAI-1 (PAI-NBD119) was quenched by PAI-749; the apparent K(d) (254 nM) was similar to the IC(50) (140 nM) for PAI-NBD119 inactivation. PAI-749 analogs displayed the same potency rank order for neutralizing PAI-1 activity and perturbing PAI-NBD119 Fl; hence, binding of PAI-749 to PAI-1 and inactivation of PAI-1 activity are tightly linked. Exposure of PAI-1 to PAI-749 for 5 min (sufficient for full inactivation) followed by PAI-749 sequestration with Tween 80 micelles yielded active PAI-1; thus, PAI-749 did not irreversibly inactivate PAI-1, a known metastable protein. Treatment of PAI-1 with a PAI-749 homolog (producing less assay interference) blocked the ability of PAI-1 to displace p-aminobenzamidine from the uPA active site. Consistent with this observation, PAI-749 abolished formation of the SDS-stable tPA/PAI-1 complex. PAI-749-mediated neutralization of PAI-1 was associated with induction of PAI-1 polymerization as assessed by native gel electrophoresis. PAI-749 did not turn PAI-1 into a substrate for tPA; however, PAI-749 promoted plasmin-mediated degradation of PAI-1. In conclusion, PAI-1 inactivation by PAI-749 using purified components can result from a dual mechanism of action. First, PAI-749 binds directly to PAI-1, blocks PAI-1 from accessing the active site of tPA, and abrogates formation of the SDS-stable tPA/PAI-1 complex. Second, binding of PAI-749 to PAI-1 renders PAI-1 vulnerable to plasmin-mediated proteolytic degradation.

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.

Endotoxaemia induces resistance to activated protein C in healthy humans

Systemic inflammation activates the tissue factor/factor VIIa complex (TF/FVIIa), leading to a procoagulant state, which may be enhanced by impairment of physiological anticoagulant pathways, such as the protein C system. Besides impaired protein C activation, resistance to activated protein C (APC) may occur. We studied the effect of endotoxemia on APC resistance, analysed its determinants and evaluated the effect of TF/FVIIa inhibition on endotoxin-induced APC resistance. Sixteen healthy male volunteers participated in the study, eight receiving endotoxin alone and eight receiving the combination of endotoxin and recombinant Nematode Anticoagulant Protein c2 (rNAPc2), a potent inhibitor of TF/FVIIa. Parameters of coagulation were subsequently studied. The sensitivity to APC was determined by two tests: a test based on the endogenous thrombin potential and a test based on the activated partial thromboplastin time. In response to endotoxemia, both tests detected a transient APC resistance that was predominantly mediated by an increase in factor VIII and was not influenced by TF/FVIIa inhibition. In vitro tests confirmed that an increase in factor VIII induced APC resistance, as measured by both tests. This finding suggests that APC resistance might play a role in the procoagulant state occurring during human endotoxemia.

Local activation of the tissue factor-factor VIIa pathway in patients with pneumonia and the effect of inhibition of this pathway in murine pneumococcal pneumonia

OBJECTIVE

The tissue factor (TF)-factor VIIa (FVIIa) complex not only is essential for activation of blood coagulation but also affect the inflammatory response during sepsis. The objective of this study was to determine the role of TF-FVIIa in pneumonia caused by Streptococcus pneumoniae, the most important causative organism in community-acquired pneumonia and a major cause of sepsis.

DESIGN

A controlled, in vivo laboratory study.

SETTING

Research laboratory of a health sciences university.

PATIENTS AND SUBJECTS

Patients with unilateral community-acquired pneumonia and female BALB/c mice.

INTERVENTIONS

Bilateral bronchoalveolar lavage was performed in patients with community-acquired pneumonia. In mice, pneumonia was induced by intranasal inoculation with S. pneumoniae with or without concurrent inhibition of TF-FVIIa by subcutaneous injections of recombinant nematode anticoagulant protein (rNAPc2).

MEASUREMENTS AND MAIN RESULTS

Patients with unilateral community-acquired pneumonia demonstrated elevated concentrations of FVIIa, soluble TF, and thrombin-antithrombin complexes in bronchoalveolar lavage fluid obtained from the infected site compared with the uninfected site. Mice with S. pneumoniae pneumonia displayed increased TF expression and fibrin deposits in lungs together with elevated thrombin-antithrombin complex levels in bronchoalveolar lavage fluid; inhibition of TF-FVIIa by rNAPc2 attenuated the procoagulant response in the lung but did not affect host defense, as reflected by an unaltered outgrowth of pneumococci and an unchanged survival.

CONCLUSIONS

These data suggest that TF-FVIIa activity contributes to activation of coagulation in the lung during pneumococcal pneumonia but does not play an important role in the antibacterial host defense in this murine model.

Pharmacokinetics and anticoagulant properties of the factor VIIa-tissue factor inhibitor recombinant Nematode Anticoagulant Protein c2 following subcutaneous administration in man. Dependence on the stoichiometric binding to circulating factor X

Recombinant Nematode Anticoagulant Protein c2 (rNAPc2) is a potent (K(i) =10 pM), inhibitor of the factor VIIa/tissue factor (fVIIa/TF) complex that requires the prerequisite binding to zymogen or activated factor X (fX). In two double blind, place-bo-controlled, sequential dose-escalation phase I studies, rNAPc2 was found to be safe and well tolerated following single and repeat subcutaneous administrations in healthy human male volunteers at doses ranging from 0.3 to 5 micro g/kg. There was a dose-dependent elevation of the prothrombin time reaching almost 4-fold above the baseline value in the highest dose group that directly correlated with rNAPc2 plasma concentration. In contrast, there was little or no effect on the activated partial thromboplastin time, thrombin time or template bleeding time. The pharmacokinetic behavior of rNAPc2 revealed a dose-independent and prolonged elimination half-life (t(1/2)beta) with a mean of >50 hours. A high affinity interaction between rNAPc2 and plasma fX was shown to be essential for the prolonged t(1/2)beta in man using crossed immunoelectrophoresis and was confirmed by exploiting the considerably weaker interaction between rNAPc2 and bovine fX which resulted in an attenuated t(1/2)beta of approximately 1.5 hours in calves. The accumulated data suggests that rNAPc2 is safe and well tolerated following repeat subcutaneous administrations at doses up to 5 micro g/kg in healthy volunteers. In addition, the in vivo fate of rNAPc2 in man appears to be governed by its high affinity interaction with circulating fX. This data supports the continued development of this novel anticoagulant for the prevention and treatment of acute thrombotic disorders.

Inhibition of the Tissue Factor/Factor VIIa Pathway Does Not Influence the Inflammatory or Antibacterial Response to Abdominal Sepsis Induced byEscherichia coliin Mice

BACKGROUND

Anticoagulants have gained increasing attention for the treatment of sepsis. Inhibition of the tissue factor (TF)/factor (F) VIIa pathway has been shown to attenuate the activation of coagulation and to prevent death in a primate model of sepsis caused by gram-negative bacteria.

METHODS

To determine the role of the TF/FVIIa complex in the host response to peritonitis, mice received an intraperitoneal injection of live Escherichia coli with or without concurrent treatment with recombinant nematode anticoagulant protein c2 (rNAPc2), a selective inhibitor of the TF/FVIIa pathway.

RESULTS

Peritonitis was associated with an increase in the expression of TF at the tissue level and activation of coagulation, as reflected by elevated levels of thrombin-antithrombin complexes and by increased fibrin(ogen) deposition in the liver and lungs. rNAPc2 strongly attenuated this procoagulant response but did not influence the inflammatory response (histopathology, leukocyte recruitment to the peritoneal cavity, and cytokine and chemokine levels). Moreover, rNAPc2 did not alter bacterial outgrowth locally or dissemination of the infection, and survival was not different between rNAPc2-treated mice and control mice.

CONCLUSIONS

These data suggest that TF/FVIIa activity contributes to the activation of coagulation during E. coli peritonitis but does not play a role in the inflammatory response or antibacterial host defense.

Antimalarial activities of novel synthetic cysteine protease inhibitors

Among promising new targets for antimalarial chemotherapy are the cysteine protease hemoglobinases falcipain-2 and falcipain-3. We evaluated the activities of synthetic peptidyl aldehyde and alpha-ketoamide cysteine protease inhibitors against these proteases, against cultured Plasmodium falciparum parasites, and in a murine malaria model. Optimized compounds inhibited falcipain-2 and falcipain-3, blocked hemoglobin hydrolysis, and prevented the development of P. falciparum at nanomolar concentrations. The compounds were equally active against multiple strains of P. falciparum with varied sensitivities to standard antimalarial agents. The peptidyl inhibitors were consistently less active against vinckepain-2, the putative falcipain-2 and falcipain-3 ortholog of the rodent malaria parasite Plasmodium vinckei. The lead compound morpholinocarbonyl-leucine-homophenylalanine aldehyde, which blocked P. falciparum development at low nanomolar concentrations, was tested in a murine P. vinckei model. When infused continuously at a rate of 30 mg/kg of body weight/day, the compound delayed the progression of malaria but did not eradicate infections. Our data demonstrate the potent antimalarial activities of novel cysteine protease inhibitors. Additionally, they highlight the importance of consideration of the specific enzyme targets of animal model parasites. In the case of falcipains, differences between P. falciparum and rodent parasites complicate the use of the rodent malaria model in the drug discovery process.

Recombinant nematode anticoagulant protein c2, an inhibitor of tissue factor/factor VIIa, attenuates coagulation and the interleukin-10 response in human endotoxemia

The tissue factor-factor (F)VIIa complex (TF/FVIIa) is responsible for the initiation of blood coagulation under both physiological and pathological conditions. Recombinant nematode anticoagulant protein c2 (rNAPc2) is a potent inhibitor of TF/FVIIa, mechanistically distinct from tissue factor pathway inhibitor. The first aim of this study was to elucidate the pharmacokinetics and pharmacodynamics of a single intravenous (i.v.) dose of rNAPc2. The second aim was to study its effect on endotoxin-induced coagulation and inflammation. Initially, rNAPc2 was administered to healthy volunteers in three different doses. There were no safety concerns and the pharmacokinetics were consistent with previous studies, in which rNAPc2 was administered subcutaneously. rNAPc2 elicited a dose-dependent reduction of the endogenous thrombin potential and a selective prolongation of prothrombin time. Subsequently, the effect on endotoxin-induced coagulation and inflammation was studied. The administration of rNAPc2 completely blocked the endotoxin-induced thrombin generation, as measured by plasma prothrombin fragment F1+2. The endotoxin-induced effect on fibrinolytic parameters such as plasmin-antiplasmin complexes and plasminogen activator inhibitor type 1 was not affected by rNAPc2. The administration of rNAPc2 attenuated the endotoxin-induced rise in interleukin (IL)-10, without affecting the rise in other cytokines. In conclusion, rNAPc2 is a potent inhibitor of TF/FVIIa, which was well tolerated and could safely be used intravenously in this Phase I study in healthy male volunteers. A single i.v. dose rNAPc2 completely blocked endotoxin-induced thrombin generation without affecting the fibrinolytic response. In addition, rNAPc2 attenuated the endotoxin-induced rise in IL-10, without affecting the rises in other cytokines.

Treatment of Ebola virus infection with a recombinant inhibitor of factor VIIa/tissue factor: a study in rhesus monkeys

BACKGROUND

Infection with the Ebola virus induces overexpression of the procoagulant tissue factor in primate monocytes and macrophages, suggesting that inhibition of the tissue-factor pathway could ameliorate the effects of Ebola haemorrhagic fever. Here, we tested the notion that blockade of fVIIa/tissue factor is beneficial after infection with Ebola virus.

METHODS

We used a rhesus macaque model of Ebola haemorrhagic fever, which produces near 100% mortality. We administered recombinant nematode anticoagulant protein c2 (rNAPc2), a potent inhibitor of tissue factor-initiated blood coagulation, to the macaques either 10 min (n=6) or 24 h (n=3) after a high-dose lethal injection of Ebola virus. Three animals served as untreated Ebola virus-positive controls. Historical controls were also used in some analyses.

FINDINGS

Both treatment regimens prolonged survival time, with a 33% survival rate in each treatment group. Survivors are still alive and healthy after 9 months. All but one of the 17 controls died. The mean survival for the six rNAPc2-treated macaques that died was 11.7 days compared with 8.3 days for untreated controls (p=0.0184). rNAPc2 attenuated the coagulation response as evidenced by modulation of various important coagulation factors, including plasma D dimers, which were reduced in nearly all treated animals; less prominent fibrin deposits and intravascular thromboemboli were observed in tissues of some animals that succumbed to Ebola virus. Furthermore, rNAPc2 attenuated the proinflammatory response with lower plasma concentrations of interleukin 6 and monocyte chemoattractant protein-1 (MCP-1) noted in the treated than in the untreated macaques.

INTERPRETATION

Post-exposure protection with rNAPc2 against Ebola virus in primates provides a new foundation for therapeutic regimens that target the disease process rather than viral replication.

Recombinant nematode anticoagulant protein c2 and other inhibitors targeting blood coagulation factor VIIa/tissue factor

Originally isolated from a haematophagous hookworm, recombinant nematode anticoagulant protein c2 (rNAPc2) is an 85-amino acid protein with potent anticoagulant properties. Unlike conventional anticoagulants that attenuate blood coagulation via inhibition of thrombin or activated factor X (FXa) at the downstream portion of the cascade, rNAPc2 is a potent inhibitor of the activated factor VII/tissue factor complex (FVIIa/TF), the key physiological initiator of blood coagulation. Its mechanism of action requires prerequisite binding to circulating FXa or zymogen factor X (FX) to form a binary complex prior to its interaction and inhibition of membrane-bound FVIIa/TF. The binding of rNAPc2 to FX results in an elimination half-life of longer than 50 h following either subcutaneous or intravenous administration. Recombinant NAPc2, like other inhibitors of FVIIa/TF including tissue factor pathway inhibitor (TFPI) and active site-blocked FVIIa (ASIS, FFR-rFVIIa or FVIIai), may have a promising role in the prevention and treatment of venous and arterial thrombosis, as well as potential efficacy in the management of disseminated intravascular coagulopathies because of their potent and selective inhibition of FVIIa/TF.

Recombinant nematode anticoagulant protein c2, an inhibitor of the tissue factor/factor VIIa complex, in patients undergoing elective coronary angioplasty

OBJECTIVES

We investigated the safety and pharmacodynamics of escalating doses of recombinant nematode anticoagulant protein c2 (rNAPc2) in patients undergoing elective coronary angioplasty.

BACKGROUND

Recombinant NAPc2 is a potent inhibitor of the tissue factor/factor VIIa complex, which has the potential to reduce the risk of thrombotic complications in coronary artery disease.

METHODS

In a randomized, double-blinded, dose-escalation, multicenter trial, 154 patients received placebo or rNAPc2 at doses of 3.5, 5.0, 7.5, and 10.0 microg/kg body weight as a single subcutaneous administration 2 to 6 h before angioplasty. All patients received aspirin, unfractionated heparin during angioplasty, and clopidogrel in case of stent implantation.

RESULTS

Minor bleeding rates for the doses 3.5 to 7.5 microg/kg were comparable to that with placebo (6.7%), whereas an incidence of 26.9% was observed at the 10.0 microg/kg dose level (p < 0.01). Major bleedings occurred in the 5.0 microg/kg (n = 3) and 7.5 microg/kg (n = 1) dose groups. The three patients in the 5.0 microg/kg dose group also received a glycoprotein IIb/IIIa receptor inhibitor at the moment of major bleeding. Systemic thrombin generation, as measured by prothrombin fragment 1+2 (F(1+2)), was suppressed in all rNAPc2 dose groups to levels below pretreatment values for at least 36 h. In the placebo group, a distinct increase of F(1+2) levels was observed following cessation of heparin.

CONCLUSIONS

Inhibition of the tissue factor/factor VIIa complex with rNAPc2, at doses up to 7.5 microg/kg, in combination with aspirin, clopidogrel, and unfractionated heparin appears to be a safe and effective strategy to prevent thrombin generation during coronary angioplasty.

Tissue factor/factor VIIa inhibitors block angiogenesis and tumor growth through a nonhemostatic mechanism

An association between cancer and thrombosis has been recognized for more than a century. However, the manner by which tumor growth is regulated by coagulation in vivo remains unclear. To assess the role of coagulation on tumor growth, in vivo, we tested coagulation inhibitors specific for either tissue factor (TF)/factor VIIa (fVIIa) complexes or factor Xa (fXa) for antitumor activity. Here, we show that two inhibitors of TF/fVIIa, TF pathway inhibitor (TFPI) and the nematode anticoagulant protein rNAPc2, inhibit both primary and metastatic tumor growth in mice. In addition, we show that rNAPc2 is also a potent inhibitor of angiogenesis. In contrast, rNAP5, a second nematode anticoagulant protein that specifically inhibits fXa, does not exhibit antitumor activity. Because the hemostatic activity of TF/fVIIa is mediated through activation of fXa, these data suggest that proteolytic activity of TF/fVIIa promotes tumor growth and angiogenesis through a novel proangiogenic mechanism and independently of hemostasis.

Activation of coagulation by administration of recombinant factor VIIa elicits interleukin 6 (IL-6) and IL-8 release in healthy human subjects

The activation of coagulation has been shown to contribute to proinflammatory responses in animal and in vitro experiments. Here we report that the activation of coagulation in healthy human subjects by the administration of recombinant factor VIIa also elicits a small but significant increase in the concentrations of interleukin 6 (IL-6) and IL-8 in plasma. This increase was absent when the subjects were pretreated with recombinant nematode anticoagulant protein c2, the inhibitor of tissue factor-factor VIIa.

Inhibition of factor VIIa/tissue factor with nematode anticoagulant protein c2: from unique mechanism to a promising new clinical anticoagulant

Recombinant nematode anticoagulant protein c2 (rNAPc2) is a potent (K(i) = 10 pM) inhibitor of the factor VIIa/tissue factor complex (fVIIa/TF) that involves the pre-requisite binding to either zymogen or activated factor X (fX) prior to the formation of the final quaternary complex with fVIIa/TF. The formation of the binary complex with circulating fX governs the pharmacokinetic profile of rNAPc2 in humans, resulting in a prolonged elimination half-life of >50 h. The clinical antithrombotic potential of rNAPc2 has been evaluated in a phase-II trial in which the incidence of deep-vein thrombosis was reduced over 50% compared to historic controls with low-molecular-weight heparin in patients undergoing knee replacement surgery. A second phase-IIa trial demonstrated the safety of rNAPc2 and the significant suppression of thrombin generation in patients undergoing elective percutaneous coronary intervention treated with standard anticoagulant and antiplatelet therapies. Overall, rNAPc2 is a unique inhibitor of the fVIIa/TF complex and a promising new clinical anticoagulant.

Recombinant nematode anticoagulant protein c2, a novel inhibitor of tissue factor-factor VIIa activity, abrogates endotoxin-induced coagulation in chimpanzees

Systemic activation of coagulation leading to disseminated intra-vascular coagulation (DIC) is an important feature in patients with severe sepsis. Tissue factor has been shown to play a primary role in this pathological response, as revealed by the use of specific inhibitors and antagonists of the tissue factor/factor VIIa pathway. This class of agents has been demonstrated to attenuate the coagulation response in human volunteers with induced low-grade endotoxemia and to reduce mortality in primate models of Gram-negative sepsis. The efficacy of these agents in attenuating the activation of coagulation and formation of microvascular thrombosis in sepsis may depend on the mechanism of inhibition. Here we demonstrate the efficacy of recombinant nematode anticoagulant protein c2 (rNAPc2) that specifically inhibits the tissue factor/factor VIIa complex by a novel mechanism, in a model of endotoxin-induced coagulation activation in chimpanzees. Administration of a low dose of Gram-negative endotoxin induced marked increases of thrombin generation as measured by plasma levels of prothrombin activation fragment F(1+2) and thrombin-antithrombin complexes, which were completely blocked by rNAPc2. In chimpanzees receiving rNAPc2 alone, there was a significant reduction in the activation of factor X but not factor IX, compared to animals receiving placebo. In contrast to the effect of rNAPc2 on thrombin generation, there was no effect of this inhibitor on the well known enhanced systemic fibrinolytic response induced by endotoxin. In conclusion, the recombinant peptide rNAPc2 is an effective inhibitor of tissue factor-driven thrombin generation during low grade endotoxemia. These results suggest that rNAPc2 may be a promising therapeutic option to inhibit coagulation activation in patients with sepsis.

Nematode anticoagulant protein c2 reveals a site on factor Xa that is important for macromolecular substrate binding to human prothrombinase

The binding of recombinant nematode anticoagulant protein c2 (NAPc2) to either factor X or Xa is a requisite step in the pathway for the potent inhibition of VIIa tissue factor. We have used NAPc2 as a tight binding probe of human Xa to investigate protein substrate recognition by the human prothrombinase complex. NAPc2 binds with high affinity (K(d) approximately 1 nm) to both X and Xa in a way that does not require or occlude the active site of the enzyme. In contrast, NAPc2 is a tight binding, competitive inhibitor of protein substrate cleavage by human Xa incorporated into prothrombinase with saturating concentrations of membranes and Va. By fluorescence binding studies we show that NAPc2 does not interfere with the assembly of human prothrombinase. These are properties expected of an inhibitor that blocks protein substrate recognition by targeting extended macromolecular recognition sites (exosites) on the enzyme complex. A weaker interaction (K(d) = 260-500 nm) observed between NAPc2 and bovine X was restored to a high affinity one in a recombinant chimeric bovine X derivative containing 25 residues from the COOH terminus of the proteinase domain of human X. This region implicated in binding NAPc2 is spatially adjacent to a site previously identified as a potential exosite. Despite the weaker interaction with bovine Xa, NAPc2 was a tight binding competitive inhibitor of protein substrate cleavage by bovine prothrombinase as well. Extended enzymic surfaces elucidated with exosite-directed probes, such as NAPc2, may define a unique region of factor Xa that is modulated following its assembly into prothrombinase and in turn determines the binding specificity of the enzyme complex for its protein substrate.