Identification and pharmacological characterization of GV150526, a novel glycine antagonist as potent neuroprotective agent

Pharmacological approaches to acute ischaemic stroke: reperfusion certainly, neuroprotection possibly

Stroke is a major cause of both death and disability. However, there are no pharmacological treatments used in most countries other than recombinant tissue plasminogen activator, a thrombolytic, and this is only used in about 4% of patients presenting after an acute ischaemic stroke. One novel thrombolytic (desmoteplase) has just been reported to have failed in a Phase IIb/III trial, but other thrombolytics and reperfusion agents remain in development. The picture with neuroprotectant agents, that is compounds that act to preserve neurones following an acute cerebral ischaemic insult, is even more bleak. Despite the development of over 1,000 compounds, many proving effective in animal models of stroke, none has demonstrated efficacy in patients in the over 100 clinical trials conducted. This includes NXY-059, which was developed in accordance with the guidelines proposed by an academic-industry roundtable group (STAIR). This review examines the available data on compounds currently in development. It also proposes that the failure of translation between efficacy in preclinical models and patients is likely to terminate most current neuroprotective drug development. It is suggested that animal models must be made more representative of the patient condition (with other co-morbid conditions) and suggests that since stroke is primarily a cardiovascular disease with a neurological outcome, more research on the neurovascular unit would be valuable. New approaches on neuroinflammation, neurorestoration and neurorepair are also likely to gain prominence in the search for new drugs to treat this major clinical problem.

Chiral tetrahydroquinoline derivatives as potent anti-hyperalgesic agents in animal models of sustained inflammation and chronic neuropathic pain

Chiral tetrahydroquinoline derivatives have been prepared by an asymmetric Mannich-type condensation reaction using commercially available vinyloxyethylsilane and a N-arylimino R-(+)-t-butyl lactate ester, in the presence of a catalytic amount of metal triflates as Lewis acids. This synthetic approach gave rise to the target aldehyde intermediate in moderate facial diastereoselectivity and in high chemical yield. This efficient route enabled to scale up the synthesis of an orally bioavailable glycine antagonist showing outstanding in vivo anti-hyperalgesic activity in different animal models of sustained inflammation and chronic neuropathic pain.

Therapeutic strategies for the treatment of stroke

Acute ischaemic stroke is a major health problem with no effective treatments apart from the thrombolytic recombinant tissue plasminogen activator (rt-PA), which must be given within 3h of stroke onset. However, rt-PA increases the risk of symptomatic intracranial haemorrhage and is administered to <5% of stroke patients. New perfusion-enhancing compounds are in development but the risk:benefit ratio remains to be determined. Many neuroprotective drugs have been studied but all those that reached clinical development have failed to demonstrate efficacy. However, adherence to recently published guidelines on preclinical development has resulted in one novel compound (NXY-059) demonstrating efficacy in a Phase III trial, providing encouragement for the validity of the concept of neuroprotection. There are a variety of new neuroprotective compounds in the early stages of investigation and some could prove clinically effective, provided appropriate preclinical development guidelines are observed.

Benzoazepine derivative as potent antagonists of the glycine binding site associated to the NMDA receptor

A series of benzoazepine derivatives, bearing suitable substituents at the C-3 position, was designed and evaluated by superimposition with the pharmacophore model of the glycine binding site. To fully explore the SAR of this class of compounds and to allow the preparation of new different compounds at the C-3 position, appropriate synthetic routes were set up. The benzoazepines were evaluated in terms of in vitro affinity using [3H]glycine binding assay and in vivo potency by inhibition of convulsions induced by N-methyl-D-aspartate (NMDA) in mice. This further analysis confirmed the preliminary results previously reported and that compound 27 is the most promising compound (Ki=32 nM, ED(50)=0.09 mg/kg, i.v.) in this series. Significant neuroprotective effect was observed after both pre- and post-ischaemia administration in the MCAo model. In particular, after post-ischaemia administration, it was found to be still effective when the administration was delayed up to 6 h after occlusion of the middle cerebral artery.

Enantiomerically pure tetrahydroquinoline derivatives as in vivo potent antagonists of the glycine binding site associated to the NMDA receptor

To identify neuroprotective agents after stroke, new substituted tetrahydroquinoline derivatives were designed as antagonists of the glycine binding site associated to the NMDA receptor, satisfying the key pharmacophoric requirements. In particular, the racemate 3c exhibited outstanding in vivo activity in the MCAo model in rats, when given iv both pre- and post-ischemia. Pure enantiomers 3c-(+) and 3c-(-) have been prepared following an original synthetic route. Despite the significant difference of activity observed in vitro, they shown similar neuroprotective profile in the MCAo model in rats.

Antagonists and agonists at the glycine site of the NMDA receptor for therapeutic interventions

For decades neuroreceptor research has focused on the development of NMDA glycine-site antagonists, after Johnson and Ascher found out in 1987 about the co-agonistic character of this achiral amino acid at the NMDA receptor. Contrary to the inhibitory glycine receptor (glycine(A)) the glycine binding site on the NMDA receptor (glycine(B)) is strychnine-insensitive. A great diversity of diseases showing a disturbed glutamate neurotransmission have been linked to the NMDA receptor. Glycine site antagonists have been investigated for acute diseases like stroke and head trauma as well as chronic ones like dementia and chronic pain.

Tricyclic indole-2-carboxylic acids: highly in vivo active and selective antagonists for the glycine binding site of the NMDA receptor

A series of tricyclic indole-2-carboxylic acid derivatives were synthesized and evaluated by the radioligand binding assay and the anticonvulsant effects in the mouse NMDA-induced seizure model. Among them, derivatives of 3S-(-)-4 such as 3a, 3f, and 3g which had certain zwitterionic anilides showed high affinity to the NMDA-glycine binding site. The absolute configuration of 3S-(-)-4 was confirmed by X-ray crystallographic analysis. In particular, 3g (SM-31900) was found to be a highly active glycine antagonist for both in vitro and in vivo assays (K(i) = 1.0 +/- 0.1 nM, ED(50) = 2.3 mg/kg, iv) and also showed high selectivity for the glycine site. In addition, 3g was soluble enough in aqueous media (>10 mg/mL at pH 7.4) to use for medications by intravenous injection.

Neuroprotection for ischaemic stroke: an unattainable goal?

Neuroprotective therapies for acute ischaemic stroke have yet to be realised despite the determined efforts of basic science and clinical investigators. Progressive elucidation of the complex pathophysiology involved in the ischaemic cascade has led to the development of numerous candidate interventions. Preliminary efficacy in animal models has repeatedly resulted in frustration after extensive clinical testing. Failure in the translation of results from animal models to humans implicates potential limitations of the current drug development process. Reflection on prior studies suggests possible flaws at several stages. Incorporation of standardised guidelines for preclinical testing of putative neuroprotective therapies and modification of clinical trial design, methodology and reporting may improve chances for success. The future of neuroprotection for stroke remains bright in spite of previous disappointments.

Synthesis and pharmacological characterisation of a conformationally restrained series of indole-2-carboxylates as in vivo potent glycine antagonists

After the identification of GV150526, the indole-2-carboxylate template was further explored in order to identify novel potential anti-stroke agents. In particular, the SAR of the side chain present at the C-3 position of the indole nucleus was widely studied. In this paper, the synthesis and the pharmacological profile of a further class of conformationally restricted analogues of GV150526 as in vitro and in vivo potent glycine antagonists is reported. In particular, a pyrazolidinone derivative was identified as a potent neuroprotective agent in animal models of cerebral ischaemia.

Indeno[1,2-b]pyrazin-2,3-diones: a new class of antagonists at the glycine site of the NMDA receptor with potent in vivo activity

Indeno¿1,2-bpyrazin-2,3-diones have been identified as a novel series of potent ligands on the glycine site of the NMDA receptor. To improve their in vivo activities, an acetic acid-type side chain was introduced to the 5-position, giving water-soluble compounds when formulated as the sodium salt (>10 mg/mL). Introduction of a chlorine atom in the 8-position led to a dramatic improvement of anticonvulsant activity and this was surprising since this change did not improve binding affinity. A plausible explanation is a reduced recognition by a Na(+),K(+)-ATPase active transport system responsible for the excretion of these compounds from the brain and kidney. This promising new chemical series led to the optically active isomer (-)-10i (RPR 118723), a glycine/NMDA antagonist with nanomolar binding affinity and in vivo activity in animal model of convulsions and electrophysiology at doses in the range of 2-3 mg/kg following iv administration.

Glycine antagonist (gavestinel) in neuroprotection (GAIN International) in patients with acute stroke: a randomised controlled trial. GAIN International Investigators

BACKGROUND

Early treatment may improve acute ischaemic stroke outcome. Gavestinel is a selective antagonist at the glycine site of the N-methyl-D-aspartate (NMDA) receptor, and is neuroprotective in animal models of ischaemic stroke.

METHODS

We did a randomised, double-blind, placebo-controlled trial to test whether gavestinel could improve functional outcome after acute stroke in human beings. Conscious patients with stroke involving limb weakness received either gavestinel at an intravenous loading dose of 800 mg followed by 200 mg every 12 h for five doses, or matching placebo, within 6 h of stroke onset. Stratification variables were age and stroke severity. A computed tomography brain scan within 18 h of stroke onset identified the primary efficacy population with ischaemic stroke. Outcome was assessed by an independent observer with the Barthel index at 3 months. Three outcome categories were applied: good (Barthel index 95-100), moderate (60-90), and poor (0-55 or dead). Analysis was by intention to treat.

FINDINGS

Of 1804 patients randomised, 16 received no treatment, and 333 had primary intracranial haemorrhage. 891 patients received gavestinel and 897 received placebo. Outcome in 721 patients who received gavestinel and were analysed for the primary endpoint at 3 months was good in 246 (34.1%), moderate in 136 (18.8%), and poor in 339 (47.0%), compared with 256 (34.9%), 133 (18.1%), and 345 (47.0%), respectively, of 734 patients who received placebo (p=0.8). Mortality at 3 months was 147 (20.4%) in the gavestinel group and 138 (18.8%) in the placebo group. Outcomes within preplanned subgroup and secondary analyses were also neutral. There were no significant differences in serious side-effects between the groups.

INTERPRETATION

Treatment with gavestinel within 6 h of acute ischaemic stroke did not improve outcome.

Synthesis and pharmacological properties of novel glycine antagonists

The NMDA receptor is an ionotropic receptor complex widely distributed in the central nervous system and its activation, particularly in hypoxic conditions such as stroke, traumatic head injury and hypoglycemia, results in a massive influx of calcium ions into the post-synaptic neurones, leading to cell death through the activation of several neurotoxic cascades. The NMDA receptor is a unique ionotropic receptor complex because its activation requires the simultaneous binding of glutamate and glycine and selective antagonists at the glycine binding site are endowed with a better side-effect profile than competitive NMDA antagonists. Then, considerable efforts have been devoted to find potent and selective ligands, resulting in the identification of several classes of glycine antagonists. The research at Glaxo Wellcome has been aimed at the identification of novel in vivo active glycine antagonists, and led to the synthesis and pharmacological characterization of a number of novel, potent and systemically active compounds belonging to different chemical classes.

Substituted analogues of GV150526 as potent glycine binding site antagonists in animal models of cerebral ischemia

A series of analogues of the indole-2-carboxylate GV150526, currently in clinical trials as a potential neuroprotective agent for the control of the cerebral damage after stroke onset, was designed based on previous studies dealing with the electronic features of the north-east region of the glycine binding site associated with the NMDA receptor. In particular, the substitution of the para position of the terminal phenyl ring of GV150526 with suitable hydrophilic groups resulted in the identification of a new class of glycine antagonists. These compounds exhibited nanomolar in vitro affinity to the glycine binding site, high receptor selectivity, and outstanding in vivo potency. In particular, 3-[(E)-2-[(4-ureidomethylphenyl)aminocarbonyl]ethenyl]-4, 6-dichloroindole-2-carboxylic acid was found to be highly effective in the middle cerebral artery occlusion (MCAo) model in the rat, an animal model of focal ischemia, when given both prior to and after the occlusion of the middle cerebral artery. Notably, a significant neuroprotective effect was seen in this model postischaemia, when the administration of this compound was delayed up to 6 h from the occlusion of the middle cerebral artery, further confirming the wide therapeutic window seen for GV150526A.

Safety and tolerability of GV150526 (a glycine site antagonist at the N-methyl-D-aspartate receptor) in patients with acute stroke

BACKGROUND AND PURPOSE

GV150526 is a novel glycine site antagonist at the N-methyl-D-aspartate receptor complex. It is a potent neuroprotective agent in animal models of stroke, including permanent middle cerebral artery occlusion in the rat. Unlike antagonists at the glutamate ligand binding site, GV150526 appears to be free of hemodynamic and central nervous system adverse effects. The purpose of this study was to assess the safety, tolerability, and pharmacokinetics of loading and maintenance infusions of GV150526 in patients with acute stroke.

METHODS

This was a randomized, placebo-controlled, parallel-group, ascending-dose study conducted in 2 phases. In part A of the study, loading doses of 50, 100, 200, 400, or 800 mg were administered. In part B, the maximum loading dose from part A was followed by maintenance infusions (5 infusions at 12-hour intervals), aiming to maintain neuroprotective levels. Safety data were collected throughout. The study was not designed to test efficacy, but outcome data (Barthel Index and National Institutes of Health Stroke Scale) were collected.

RESULTS

Sixty-six patients were recruited to the study over 11 months; 18 patients received placebo. GV150526 was well tolerated by the 48 patients who received it. There was no excess of central nervous system or hemodynamic adverse events compared with placebo. Minor abnormalities in liver function tests were observed in association with the higher maintenance doses tested. Four of 7 patients receiving the 800-mg loading dose followed by 400 mg BID and 1 of 6 patients who received the 200-mg BID maintenance dose showed a small rise in bilirubin, and 3 patients had increases in transaminases; the mean values at 72 hours remained under twice the upper limit of normal. These changes were asymptomatic and resolved within 10 days.

CONCLUSIONS

GV150526 is an emerging neuroprotective agent, with no apparent significant central nervous system or hemodynamic effects. Dose-limiting effects appear to be restricted to mild transient and asymptomatic rises in bilirubin and/or transaminases, primarily observed at high maintenance doses, and there were no findings that should preclude further clinical development.

Unusual synthesis of new glycine antagonists via sequential aldol condensation-lactonization-elimination reaction

Compounds 2 and 3 were designed in order to probe the North-East region of the strichnine-insensitive glycine binding site of the NMDA receptor. The two products were obtained readily by a tandem aldol condensation-lactonization-elimination step which affords the desired E isomer with complete regioselection.