S35972, a direct-acting thrombin inhibitor with high oral bioavailability and antithrombotic efficacy

OBJECTIVES

Dabigatran etexilate is the first oral thrombin inhibitor to demonstrate superior efficacy to warfarin for stroke prevention in patients with atrial fibrillation. This study describes the in vitro, ex vivo anticoagulant and in vivo antithrombotic effects of an oral thrombin inhibitor, S35972, in comparison with dabigatran etexilate.

METHODS

Enzyme assays with thrombin and related serine proteases were performed. Clotting times, including activated partial thromboplastin time (APTT) and thrombin time (TT), were measured in vitro in different species and ex vivo in dogs and rats to determine pharmacologic bioavailabilities. The formation of occlusive venous and arterial thrombi in the rat vena cava and aorta was induced with stasis plus thromboplastin or ferrous chloride, respectively.

RESULTS

 S35972 inhibited human thrombin with an IC(50) of 3.7 nm, and did not inhibit other serine proteases. The anticoagulant activities of S35972 in vitro were comparable in dog and human plasmas, and the sensitivity of the clotting times to S35972 was TT > APTT > prothrombin time. In the fasted dog, oral administration of 3 mg kg(-1) S35972 increased TT rapidly and for at least 8 h, and its pharmacologic bioavailability was 75.4% ± 0.1%. In the rat venous thrombosis model, 3 mg kg(-1) oral S35972 or dabigatran etexilate significantly decreased the thrombus weight. In the rat aortic thrombosis model, oral S35972 at 10mg kg(-1) significantly decreased thrombus weight, by approximately 50%, whereas, at this dose, no effect was obtained with dabigatran etexilate.

CONCLUSIONS

 S35972 is a non-prodrug thrombin inhibitor with high selectivity, oral bioavailability, and antithrombotic efficacy.

Psychotropic profile of S 17092, a prolyl endopeptidase inhibitor, using quantitative EEG in young healthy volunteers

The central activity of S 17092, a prolyl endopeptidase (PEP) inhibitor, was investigated by quantitative electroencephalography (qEEG) in 48 young healthy men participating in a double-blind, randomized, placebo-controlled, cross-over study. S 17092 (100, 200, 400 or 600 mg) and placebo were administered once daily for 10 days in a rising multiple-dose scheme. EEG recordings were performed before and repeatedly from 0.5 to 24 h after dose on day 1 and day 10. PEP activity in plasma was also measured for the same periods. S 17092 appeared as a potent inhibitor of PEP activity at all doses, after both single and repeated administrations. EEG changes after acute doses were slight and of short duration, mainly characterized by increased relative alpha 1 power, suggesting a vigilance-promoting EEG profile. After repeated doses and more strikingly after a superimposed dose, increases in relative alpha 1 power were still present with additional increase in relative delta power and decreases in absolute fast alpha, fast beta, theta powers and total power at all doses. These EEG findings suggest that S 17092 might possess some mood-stabilizing potential in addition to its cognition-enhancing properties.

S 18326: a thrombin inhibitor that shows potential for oral treatment of thromboembolic disorders

Antivitamin K agents are currently the only orally available anticoagulant compounds. During the past two decades, important research has focused on the discovery of a direct, orally active thrombin inhibitor. In 1991, DuP 714, a boro arginine derivative, was shown to possess anticoagulant activity in different animal species after oral administration. S 18326, structurally related to DuP 714, is a further potent thrombin inhibitor. Moreover, its improved selectivity profile, associated with potent anticoagulant and antithrombotic properties, favours potential development of this compound for venous, as well as arterial, thromboembolism.

Disease-modifying anti-osteoarthritic drugs: current therapies and new prospects around protease inhibition

Although osteoarthritis is commonly found in the elderly, the pathophysiological mechanisms of this degenerative disease are still poorly understood. Among the many factors leading to cartilage degradation, the proteolytic activity of a panel of enzymes seems to play a major role, leading to the cleavage of collagen and proteoglycans, the two main components of cartilagenous matrix. Aspartic, cysteine, serine and metalloproteases have been detected in or around the osteoarthritic articulation and their enzymatic activity is reviewed here. The cartilage-sparing properties of the respective inhibitors are listed, giving rise to the hypothesis that some of these compounds could be developed as chondroprotective agents.

Selective blockade of neurokinin (NK)(1) receptors facilitates the activity of adrenergic pathways projecting to frontal cortex and dorsal hippocampus in rats

The selective NK(1) receptor antagonist, GR205,171 (2.5-40.0 mg/kg, i.p.), dose-dependently elevated dialysate levels of noradrenaline (NA), but not serotonin (5-HT), in the frontal cortex of freely moving rats. This action was exerted stereospecifically inasmuch as its less active isomer, GR226,206, was ineffective. In the dorsal hippocampus, GR205,171 (but not GR226,206) also significantly increased dialysate levels of NA, whereas levels of 5-HT were unaffected. Further, in anaesthetized rats, GR205,171 dose-dependently (1.0-4.0 mg/kg, i.v.) increased the firing rate of adrenergic perikarya in the locus coeruleus. In contrast, their activity was not modified by GR226,206. These findings indicate that selective blockade of NK(1) receptors enhances the activity of ascending adrenergic pathways in rats. Adrenergic mechanisms may, thus, be involved in the potential antidepressant and other functional properties of NK(1) receptor antagonists.

Pharmacodynamic and pharmacokinetic profile of S 17092, a new orally active prolyl endopeptidase inhibitor, in elderly healthy volunteers. A phase I study

AIMS

The aim of this study was to characterize the pharmacodynamics and the pharmacokinetics of S 17092, a new orally active prolyl endopeptidase inhibitor following single and repeated administration in elderly healthy volunteers.

METHODS

This was a double-blind, randomized, placebo-controlled, single and multiple dose study in elderly healthy male and female volunteers (n = 36). Four doses were investigated in sequential order: 100, 400, 800 and 1200 mg. Each dose was administered orally once a day in single administration and then, after a 1 week washout period, during 7 days. Pharmacodynamics were assessed by measurement of plasmatic prolyl endopeptidase (PEP) activity, quantitative electroencephalogram (EEG) and psychometric tests. S 17092 concentrations in plasma were quantified by high performance liquid chromatography with tandem mass spectrometric detection.

RESULTS

PEP activity in plasma was dose-dependently inhibited both after administration of a single dose and after repeated doses of S 17092. The mean maximal inhibition was obtained within 0.5-2 h after dosing, while inhibition lasted at least 12 h after dose administration. S 17092 appeared to be a centrally active substance as it induced statistically significant modifications in EEG compared with placebo. S 17092 at 100 mg exerted an acute increase in alpha band following single administration at 4 h and 8 h postdosing. When administered repeatedly over 7 days S 17092 did not appear to induce significant lasting central nervous system (CNS) effects. In psychometric tests, response times in the numeric working memory were significantly reduced compared with placebo, following the 800 mg dose. There were some beneficial residual effects of the 1200 mg dose on day 13: delayed word recall and word recognition sensitivity improved compared with the declines noted under placebo. Maximum measured concentration (Cmax) and area under the curve (AUC) parameters increased in proportion to the dose. The terminal half-life (t(1/2)) values ranged between 9 and 31 h on day 1 and between 7 and 18 h on day 14. A high interindividual variability was observed at all dose levels. S 17092 was well tolerated with no clinically significant changes in laboratory or physical parameters observed at any dose.

CONCLUSIONS

S 17092 had a potent, dose-dependent inhibitory effect on plasmatic PEP, increased alpha band EEG at the 100 mg dose and improved performance in two verbal memory tests at the 1200 mg dose while there were disruption to the vigilance task. The results obtained in elderly healthy subjects indicated that S 17092 is suitable for once-daily dosing without any serious adverse events.

Further evidence for a dissociation between different forms of mnemonic expressions in a mouse model of age-related cognitive decline: effects of tacrine and S 17092, a novel prolyl endopeptidase inhibitor

It has been demonstrated previously on the radial maze that the emergence of an age-related mnemonic impairment is critically dependent on the form which the discrimination problems took. Hence, when the arms were presented one by one (i.e., successive go-no-go discrimination), both adult and aged mice learned to distinguish between positive (baited) and negative (unbaited) arms readily, as evidenced by their increased readiness to enter positive relative to negative arms (i.e., by a differential in arm-entry latencies). A selective impairment in the aged mice was seen when these arms were presented subsequently as pairs, such that the mice were confronted with an explicit choice (i.e., simultaneous 2-choice discrimination). When discriminative performance was measured by the differential run speed between positive and negative arms, aged mice were also impaired. This was particularly pronounced in the 2-choice discrimination condition. We examined the effects of tacrine (3mg/kg, subcutaneously) or S 17092 (10mg/kg, orally) in aged mice on the three behavioral indices of this 2-stage spatial discrimination paradigm. The results indicated that: (1) Tacrine, but not S 17092, enhanced the acquisition of go-no-go discrimination as reflected in arm-entry latencies; (2) both drugs improved choice accuracy in simultaneous discrimination, although the effect of tacrine was less striking and, in particular, far from statistical significance in the very first 2-choice responses; and (3) neither drugs significantly affected run-speed performance. We conclude further that the specific patterns of drug effects on the three indices of discriminative performance might suggest that each index is associated with a distinct form of mnemonic expression relying on separate neural systems.

S 17092-1, a highly potent, specific and cell permeant inhibitor of human proline endopeptidase

Several lines of evidence indicate that proline endopeptidase (PE) could participate to the symptomatology and/or etiology of Alzheimer's disease. Thus, proline endopeptidase appears to contribute to the degradation of neuropeptides involved in learning and memory and could also control the production of the amyloidogenic peptide Abeta. Therefore the design of potent, selective and permeant inhibitors of human PE should lead to potential probes to assess the genuine contribution of this enzyme in Alzheimer's pathology. A novel perhydroindol carboxylic derivative, S17092-1 inhibits the hydrolysis of Z-Gly-Pro-7AMC-hydrolysing activity present in human brain nuclei with a high affinity (Ki = 1 nM) and behaves as a highly potent (Ki = 1.5 nM) inhibitor of partially purified human PE. By contrast, S17092-1 is unable to affect a series of other peptidases including aminopeptidases B and M, dipeptidylaminopeptidase IV, endopeptidases 3.4.24.11, 3.4.24.15, 3.4.24.16, calpains and angiotensin-converting enzyme. Furthermore, we show that the embryonic human kidney 293 cell line displays an intracellular PE-like activity that is blocked after preincubating cells with S17092-1, indicating that this inhibitor penetrates in HEK293 cells and could affect intracellular human PE. Altogether, we establish that S17092-1 behaves as a highly potent, specific and cell permeant inhibitor of human proline endopeptidase and can be seen as a probe to examine PE contribution in Alzheimer's disease.

Dual inhibition of human leukocyte elastase and lipid peroxidation: in vitro and in vivo activities of azabicyclo[2.2.2]octane and perhydroindole derivatives

A series of potent and selective human leukocyte elastase (HLE) inhibitors of the Val-Pro-Val type has been developed. Initially, the central proline residue was replaced by nonnatural amino acids Phi ((2S,3aS,7aS)-perhydroindole-2-carboxylic acid) and Abo ((3S)-2-azabicyclo-[2.2.2]octane-3-carboxylic acid), and secondly several groups able to confer antioxidant properties to the molecule were introduced at the lipophilic N-terminal side chain. When compared to reference inhibitors, in vitro HLE inhibitory potency was maintained (10-100 nM) both with compounds containing the antioxidant moiety at the end of the N-terminal side chain and with compounds in which the N-terminal valine of the tripeptidic sequence had been replaced by a epsilon-substituted lysine. The lipidic peroxidation inhibitory potency of this series of inhibitors was found to be similar to that of the reference antioxidant compounds (around 1 microM). Moreover, HLE-induced hemorrhage in the hamster lung was effectively prevented (40-60% at 15 micrograms/kg) by most of the inhibitors tested when administered intratracheally 3 h before instillation of elastase. Among the most active analogs, compounds 11a,c,g were still active when administered 18 h before elastase. Interestingly, compound 14a was able to prevent HLE-mediated lung damage when administered 72 h prior to enzymatic challenge, indicating exceptional stability and retention in the lung. Finally, in a 14-day chronic model of emphysema in the hamster, 14a significantly conserved alveolar spaces, a marker of lung tissue destruction, and was more potent than reference inhibitor ICI 200 880. This indicates that addition of peroxidation inhibitory properties to an HLE inhibitor can provide a powerful in vivo inhibitor of pulmonary tissue destruction.

New prolyl endopeptidase inhibitors: in vitro and in vivo activities of azabicyclo[2.2.2]octane, azabicyclo[2.2.1]heptane, and perhydroindole derivatives

A series of potent and selective prolylendopeptidase (PEP) inhibitors of the alpha-keto heterocyclic type has been obtained by replacing the classical central proline of 1-[1-(4-phenylbutanoyl)-L-prolyl]pyrrolidine (SUAM 1221,3) by non-natural amino acids PHI, ABO, and ABH. These 4-phenylbutanoyl side-chain-containing inhibitors exhibited potent in vitro inhibitory potencies with IC50 around 30 nM (compounds 24 and 25). Modulation of the side chain by replacement of the terminal phenyl ring by the dicyclopropyl moiety afforded derivatives 30 and 32 with improved potencies (IC50 between 10 and 20 nM). Furthermore, replacing the linear 4-phenylbutanoyl side chain by the (2-phenylcyclopropyl)carbonyl entity provided potent inhibitors with IC50 culminating at 0.9 nM on a rat cortex enzymatic preparation (compound 70). The configuration of the cyclopropyl ring had to be R,R in order to obtain not only a strong PEP inhibition in vitro but also a good activity in vivo, exemplified by inhibitor 68, which gave ID50 ip and po of 0.3 and 1 mg/kg, respectively. Finally, demonstration of the cognition-enhancing properties of compound 54 was given in the passive avoidance test using scopolamine-induced amnesia in the rat, where it dose dependently inhibited the scopolamine-induced decrease in avoidance response.

New tripeptidic thrombin inhibitors. Influence of P2 and P3 residues on activity and selectivity

Structural variations of P2 and P3 residues in tripeptidic boroarginine thrombin inhibitors led to compounds with similar potency than reference compound DuP 714, but with enhanced selectivity for thrombin compared to plasmin.

Biguanide derivatives: agonist pharmacology at 5-hydroxytryptamine type 3 receptors in vitro

The effects of 24 biguanide and four guanidine derivatives on 5-hydroxytryptamine (5-HT)3 receptors in N1E-115 neuroblastoma cells were examined using radioligand binding and whole-cell voltage-clamp techniques. Displacement of the selective 5-HT3 receptor antagonist [3H]BRL 43694 by phenylbiguanide (PBG) derivatives revealed Ki values ranging from 3.4 x 10(-4) to 4.4 x 10(-10) M. The rank order of potency of agonists was 2,3,5-trichloro-PBG > 2,3-dichloro-PBG = 2,5-dichloro-PBG = 3,5-dichloro-PBG > 3,4-dichloro-PBG = 3-chloro-PBG > 2-chloro-PBG = 4-chloro-PBG = 2-methyl-PBG = 2,4-difluoro-PBG > PBG = 2-trifluoro-5-chloro-PBG > 4-fluoro-PBG = 3-trifluoromethyl-PBG > 4-nitro-PBG = 1,5-bis-4-chloro-PBG = 3,5-ditrifluoromethyl-PBG > 4-ethoxy-PBG >> 4-sulfonic acid-PBG. All of the benzylbiguanides and indanylbiguanide were inactive on [3H]BRL 43694 binding or displaced it only weakly. The four guanidine derivatives were quite inactive. In the PBG series, all antagonist competition curves were steep (pseudo-Hill coefficients ranging from 1.05 to 1.58), monophasic, and best fit with a one-site model. Among PBG derivatives, the chlorinated compounds exhibited a good degree of selectivity for 5-HT3 receptors versus other 5-HT receptor subtypes and other neurotransmitter binding sites. Electrophysiological studies showed that the PBG derivatives tested produced rapid inward currents, at a holding potential of -65 mV, that showed rapid desensitization. The current induced by the 2,3,5-trichloro-PBG derivative was inhibited by the specific 5-HT3 receptor antagonist ICS 205-930 but was unaffected by the 5-HT2 receptor antagonist ketanserin. Analysis of concentration-response curves for the PBG derivatives gave EC50 values ranging from 2.2 x 10(-5) to 2.7 x 10(-8) M and Hill slopes ranging from 1.02 to 2.10. The rank order of potency was similar to that obtained from the binding data, and a good correlation was found between Ki and EC50 values. It is concluded that the triple-chloro substitution yielded a compound that is 30-fold more potent than 3-chloro-PBG and approximately 10-fold more potent than dichloro-PBG derivatives, making 2,3,5-trichloro-PBG the most potent 5-HT3 agonist described thus far.