Inter- and intraindividual variability of riluzole serum concentrations in patients with ALS

Video-Based Kinematic Analysis of Movement Quality in a Phase 3 Clinical Trial of Troriluzole in Adults with Spinocerebellar Ataxia: A Post Hoc Analysis

INTRODUCTION

Traditional methods for assessing movement quality rely on subjective standardized scales and clinical expertise. This limitation creates challenges for assessing patients with spinocerebellar ataxia (SCA), in whom changes in mobility can be subtle and varied. We hypothesized that a machine learning analytic system might complement traditional clinician-rated measures of gait. Our objective was to use a video-based assessment of gait dispersion to compare the effects of troriluzole with placebo on gait quality in adults with SCA.

METHODS

Participants with SCA underwent gait assessment in a phase 3, double-blind, placebo-controlled trial of troriluzole (NCT03701399). Videos were processed through a deep learning pose extraction algorithm, followed by the estimation of a novel gait stability measure, the Pose Dispersion Index, quantifying the frame-by-frame symmetry, balance, and stability during natural and tandem walk tasks. The effects of troriluzole treatment were assessed in mixed linear models, participant-level grouping, and treatment group-by-visit week interaction adjusted for age, sex, baseline modified Functional Scale for the Assessment and Rating of Ataxia (f-SARA), and time since diagnosis.

RESULTS

From 218 randomized participants, 67 and 56 participants had interpretable videos of a tandem and natural walk attempt, respectively. At Week 48, individuals assigned to troriluzole exhibited significant (p = 0.010) improvement in tandem walk Pose Dispersion Index versus placebo {adjusted interaction coefficient: 0.584 [95% confidence interval (CI) 0.137 to 1.031]}. A similar, nonsignificant trend was observed in the natural walk assessment [coefficient: 1.198 (95% CI - 1.067 to 3.462)]. Further, lower baseline Pose Dispersion Index during the natural walk was significantly (p = 0.041) associated with a higher risk of subsequent falls [adjusted Poisson coefficient: - 0.356 [95% CI - 0.697 to - 0.014)].

CONCLUSION

Using this novel approach, troriluzole-treated subjects demonstrated improvement in gait as compared to placebo for the tandem walk. Machine learning applied to video-captured gait parameters can complement clinician-reported motor assessment in adults with SCA. The Pose Dispersion Index may enhance assessment in future research. TRIAL REGISTRATION-CLINICALTRIALS.

GOV IDENTIFIER

NCT03701399.

A phase I trial of riluzole and sorafenib in patients with advanced solid tumors: CTEP #8850

BACKGROUND

Overexpression of metabotropic glutamate receptor 1 (GRM1) has been implicated in the pathogenesis of multiple cancers. Riluzole, an inhibitor of glutamate release, showed synergistic antitumor activity in combination with the multi-kinase inhibitor sorafenib in preclinical models. This phase I trial identified the toxicity profile, dose-limiting toxicities, maximum tolerated dose (MTD), and pharmacokinetic and pharmacodynamic properties of riluzole combined with sorafenib in patients with advanced cancers.

PATIENTS AND METHODS

Patients with refractory solid tumors were enrolled utilizing a 3+3 dose-escalation design. Riluzole was given at 100 mg PO BID in combination with sorafenib, beginning at 200 mg PO daily and escalating in 200 mg increments per level in 28-day cycles. Restaging evaluations were performed every 2 cycles.

RESULTS

35 patients were enrolled over 4 dose levels. The MTD was declared at dose level 3 (riluzole: 100 mg PO BID; sorafenib: 400 mg AM/200 mg PM). Pharmacokinetic analyses did not reveal definitive evidence of drug-drug interactions. Consistent decreases in phospho-forms of ERK and AKT in tumor tissue analyses with accompanying decrease in GRM1 expression and increase in pro-apoptotic BIM suggest target engagement by the combination. Best responses included a partial response in 1 (2.9%) patient with pancreatic acinar cell carcinoma with a KANK4-RAF1 fusion, and stable disease in 11 (36%) patients.

CONCLUSION

Combination therapy with riluzole and sorafenib was safe and tolerable in patients with advanced solid tumors. The partial response in a patient with a RAF1 fusion suggests that further exploration in a genomically selected cohort may be warranted.

Mixture effects of tetrodotoxin (TTX) and drugs targeting voltage-gated sodium channels on spontaneous neuronal activity in vitro

Tetrodotoxin (TTX) potently inhibits TTX-sensitive voltage-gated sodium (Na_V) channels in nerve and muscle cells, potentially resulting in depressed neurotransmission, paralysis and death from respiratory failure. Since a wide range of pharmaceutical drugs is known to also act on Na_V channels, the use of medicines could predispose individuals to a higher susceptibility towards TTX toxicity. We therefore first assessed the inhibitory effect of selected medicines that act on TTX-sensitive (Riluzole, Chloroquine, Fluoxetine, Valproic acid, Lamotrigine, Lidocaine) and TTX-resistant (Carbamazepine, Mexiletine, Flecainide) Na_V channels on spontaneous neuronal activity of rat primary cortical cultures grown on microelectrode arrays (MEA). After establishing concentration-effect curves, binary mixtures of the medicines with TTX at calculated NOEC, IC₂₀ and IC₅₀ values were used to determine if pharmacodynamic interactions occur between TTX and these drugs on spontaneous neuronal activity. At IC₂₀ and IC₅₀ values, all medicines significantly increased the inhibitory effect of TTX on spontaneous neuronal activity of rat cortical cells in vitro. Subsequent experiments using human iPSC-derived neuronal co-cultures grown on MEAs confirmed the ability of selected medicines (Carbamazepine, Flecainide, Riluzole, Lidocaine) to inhibit spontaneous neuronal activity. Despite the need for additional experiments using human iPSC-derived neuronal co-cultures, our combined data already highlight the importance of identifying and including vulnerable risk groups in the risk assessment of TTX.

Troriluzole inhibits methamphetamine place preference in rats and normalizes methamphetamine-evoked glutamate carboxypeptidase II (GCPII) protein levels in the mesolimbic pathway

Riluzole, approved to manage amyotrophic lateral sclerosis, is mechanistically unique among glutamate-based therapeutics because it reduces glutamate transmission through a dual mechanism (i.e., reduces glutamate release and enhances glutamate reuptake). The profile of riluzole is favorable for normalizing glutamatergic dysregulation that perpetuates methamphetamine (METH) dependence, but pharmacokinetic and metabolic liabilities hinder repurposing. To mitigate these limitations, we synthesized troriluzole (TRLZ), a third-generation prodrug of riluzole, and tested the hypothesis that TRLZ inhibits METH hyperlocomotion and conditioned place preference (CPP) and normalizes METH-induced changes in mesolimbic glutamate biomarkers. TRLZ (8, 16 mg/kg) reduced hyperlocomotion caused by METH (1 mg/kg) without affecting spontaneous activity. TRLZ (1, 4, 8, 16 mg/kg) administered during METH conditioning (0.5 mg/kg x 4 d) inhibited development of METH place preference, and TRLZ (16 mg/kg) administered after METH conditioning reduced expression of CPP. In rats with established METH place preference, TRLZ (16 mg/kg) accelerated extinction of CPP. In cellular studies, chronic METH enhanced mRNA levels of glutamate carboxypeptidase II (GCPII) in the ventral tegmental area (VTA) and prefrontal cortex (PFC). Repeated METH also caused enhancement of GCPII protein levels in the VTA that was prevented by TRLZ (16 mg/kg). TRLZ (16 mg/kg) administered during chronic METH did not affect brain or plasma levels of METH. These results indicate that TRLZ, already in clinical trials for cerebellar ataxia, reduces development, expression and maintenance of METH CPP. Moreover, normalization of METH-induced GCPII levels in mesolimbic substrates by TRLZ points toward studying GCPII as a therapeutic target of TRLZ.

Recent Insights on Glutamatergic Dysfunction in Alzheimer's Disease and Therapeutic Implications

Alzheimer's disease (AD) poses a critical public health challenge, and there is an urgent need for novel treatment options. Glutamate, the principal excitatory neurotransmitter in the human brain, plays a critical role in mediating cognitive and behavioral functions; and clinical symptoms in AD patients are highly correlated with the loss of glutamatergic synapses. In this review, we highlight how dysregulated glutamatergic mechanisms can underpin cognitive and behavioral impairments and contribute to the progression of AD via complex interactions with neuronal and neural network hyperactivity, Aβ, tau, glial dysfunction, and other disease-associated factors. We focus on the tripartite synapse, where glutamatergic neurotransmission occurs, and evidence elucidating how the tripartite synapse can be pathologically altered in AD. We also discuss promising therapeutic approaches that have the potential to rescue these deficits. These emerging data support the development of novel glutamatergic drug candidates as compelling approaches for treating AD.

Screening Platforms for Genetic Epilepsies-Zebrafish, iPSC-Derived Neurons, and Organoids

Recent advances in molecular and cellular engineering, such as human cell reprogramming, genome editing, and patient-specific organoids, have provided unprecedented opportunities for investigating human disorders in both animals and human-based models at an improved pace and precision. This progress will inevitably lead to the development of innovative drug-screening platforms and new patient-specific therapeutics. In this review, we discuss recent advances that have been made using zebrafish and human-induced pluripotent stem cell (iPSC)-derived neurons and organoids for modeling genetic epilepsies. We also provide our prospective on how these models can potentially be combined to build new screening platforms for antiseizure and antiepileptogenic drug discovery that harness the robustness and tractability of zebrafish models as well as the patient-specific genetics and biology of iPSC-derived neurons and organoids.

Variant-specific changes in persistent or resurgent sodium current in SCN8A-related epilepsy patient-derived neurons

Missense variants in the SCN8A voltage-gated sodium channel gene are linked to early-infantile epileptic encephalopathy type 13, also known as SCN8A-related epilepsy. These patients exhibit a wide spectrum of intractable seizure types, severe developmental delay, movement disorders, and elevated risk of sudden unexpected death in epilepsy. The mechanisms by which SCN8A variants lead to epilepsy are poorly understood, although heterologous expression systems and mouse models have demonstrated altered sodium current properties. To investigate these mechanisms using a patient-specific model, we generated induced pluripotent stem cells from three patients with missense variants in SCN8A: p.R1872>L (Patient 1); p.V1592>L (Patient 2); and p.N1759>S (Patient 3). Using small molecule differentiation into excitatory neurons, induced pluripotent stem cell-derived neurons from all three patients displayed altered sodium currents. Patients 1 and 2 had elevated persistent current, while Patient 3 had increased resurgent current compared to controls. Neurons from all three patients displayed shorter axon initial segment lengths compared to controls. Further analyses focused on one of the patients with increased persistent sodium current (Patient 1) and the patient with increased resurgent current (Patient 3). Excitatory cortical neurons from both patients had prolonged action potential repolarization. Using doxycycline-inducible expression of the neuronal transcription factors neurogenin 1 and 2 to synchronize differentiation of induced excitatory cortical-like neurons, we investigated network activity and response to pharmacotherapies. Both small molecule differentiated and induced patient neurons displayed similar abnormalities in action potential repolarization. Patient induced neurons showed increased burstiness that was sensitive to phenytoin, currently a standard treatment for SCN8A-related epilepsy patients, or riluzole, an FDA-approved drug used in amyotrophic lateral sclerosis and known to block persistent and resurgent sodium currents, at pharmacologically relevant concentrations. Patch-clamp recordings showed that riluzole suppressed spontaneous firing and increased the action potential firing threshold of patient-derived neurons to more depolarized potentials. Two of the patients in this study were prescribed riluzole off-label. Patient 1 had a 50% reduction in seizure frequency. Patient 3 experienced an immediate and dramatic seizure reduction with months of seizure freedom. An additional patient with a SCN8A variant in domain IV of Nav1.6 (p.V1757>I) had a dramatic reduction in seizure frequency for several months after starting riluzole treatment, but then seizures recurred. Our results indicate that patient-specific neurons are useful for modelling SCN8A-related epilepsy and demonstrate SCN8A variant-specific mechanisms. Moreover, these findings suggest that patient-specific neuronal disease modelling offers a useful platform for discovering precision epilepsy therapies.

The gut microbiome: a key player in the complexity of amyotrophic lateral sclerosis (ALS)

BACKGROUND

Much progress has been made in mapping genetic abnormalities linked to amyotrophic lateral sclerosis (ALS), but the majority of cases still present with no known underlying cause. Furthermore, even in families with a shared genetic abnormality there is significant phenotypic variability, suggesting that non-genetic elements may modify pathogenesis. Identification of such disease-modifiers is important as they might represent new therapeutic targets. A growing body of research has begun to shed light on the role played by the gut microbiome in health and disease with a number of studies linking abnormalities to ALS.

MAIN BODY

The microbiome refers to the genes belonging to the myriad different microorganisms that live within and upon us, collectively known as the microbiota. Most of these microbes are found in the intestines, where they play important roles in digestion and the generation of key metabolites including neurotransmitters. The gut microbiota is an important aspect of the environment in which our bodies operate and inter-individual differences may be key to explaining the different disease outcomes seen in ALS. Work has begun to investigate animal models of the disease, and the gut microbiomes of people living with ALS, revealing changes in the microbial communities of these groups. The current body of knowledge will be summarised in this review. Advances in microbiome sequencing methods will be highlighted, as their improved resolution now enables researchers to further explore differences at a functional level. Proposed mechanisms connecting the gut microbiome to neurodegeneration will also be considered, including direct effects via metabolites released into the host circulation and indirect effects on bioavailability of nutrients and even medications.

CONCLUSION

Profiling of the gut microbiome has the potential to add an environmental component to rapidly advancing studies of ALS genetics and move research a step further towards personalised medicine for this disease. Moreover, should compelling evidence of upstream neurotoxicity or neuroprotection initiated by gut microbiota emerge, modification of the microbiome will represent a potential new avenue for disease modifying therapies. For an intractable condition with few current therapeutic options, further research into the ALS microbiome is of crucial importance.

[Liver Injury Risk Factors in Amyotrophic Lateral Sclerosis Patients Treated with Riluzole]

Riluzole, a drug used in the management of amyotrophic lateral sclerosis (ALS), is associated with a high incidence of liver failure. It is imperative to determine risk factors and severity of liver injury in patients taking riluzole to devise an appropriate treatment regimen. We, therefore, studied risk factors for liver injury in ALS patients who were prescribed riluzole at Kitasato University East Hospital from 1999 to 2015. Of the 222 patients enrolled in this study, 113 and 109 patients were diagnosed with mild to moderate (grade 1 or 2) and without (grade 0) liver injury, respectively. Prediction of risk factors was determined using binary logistical regression analyses. The results showed that 50.9% (n=113) of ALS patients developed mild to moderate liver injury; 71.7% and 53.1% of patients were concurrently using CYP1A2 inhibitors (p=0.005) and diclofenac (p=0.032), respectively; 55.8% of patients with liver injury had a history of smoking (p=0.011). Multivariate analyses revealed that the concurrent use of CYP1A2 inhibitors [odds ratio (OR) 2.152, 95% confidence interval (CI) 1.225-3.780, p=0.008] and history of smoking (OR 1.938, 95% CI 1.125-3.340, p=0.017) were independent risk factors for liver injury in patients receiving riluzole. In conclusion, treatment of ALS patients with riluzole, smoking habits, and concurrent use of CYP1A2 inhibitors are independent liver injury risk factors. Further studies on liver injury are warranted in ALS patients treated with riluzole to comprehensively understand the underlying mechanisms of riluzole-associated liver toxicity.

Two Decades-Long Journey from Riluzole to Edaravone: Revisiting the Clinical Pharmacokinetics of the Only Two Amyotrophic Lateral Sclerosis Therapeutics

The recent approval of edaravone has provided an intravenous option to treat amyotrophic lateral sclerosis (ALS) in addition to the existing oral agent, riluzole. The present work was primarily undertaken to provide a comprehensive clinical pharmacokinetic summary of the two approved ALS therapeutics. The key objectives of the review were to (i) tabulate the clinical pharmacokinetics of riluzole and edaravone with emphasis on absorption, distribution, metabolism and excretion (ADME) properties; (ii) provide a comparative scenario of the pharmacokinetics of the two drugs wherever possible; and (iii) provide perspectives and introspection on the gathered clinical pharmacokinetic data of the two drugs with appropriate conjectures to quench scientific curiosity. Based on this review, the following key highlights were deduced: (i) as a result of both presystemic metabolism and polymorphic hepatic cytochrome P450 (CYP) metabolism, the oral drug riluzole exhibited more inter-subject variability than that of intravenous edaravone; (ii) using various parameters for comparison, including the published intravenous data for riluzole, it was apparent that edaravone was achieving the desired systemic concentrations to possibly drive the local brain concentrations for its efficacy in ALS patients with lesser variability than riluzole; (iii) using scientific conjectures, it was deduced that the availability of intravenous riluzole may not be beneficial in therapy due to its fast systemic clearance; (iv) on the contrary, however, there appeared to be an opportunity for the development of an oral dosage form of edaravone, which may potentially benefit the therapy option for ALS patients by avoiding hospitalization costs; and (v) because of the existence of pharmaco-resistance for the brain entry in ALS patients, it appeared prudent to consider combination strategies of edaravone and/or riluzole with suitable P-glycoprotein efflux-blocking drugs to gain more favorable outcomes in ALS patients.

A phase II trial of riluzole, an antagonist of metabotropic glutamate receptor 1 (GRM1) signaling, in patients with advanced melanoma

Studies demonstrate that GRM, expressed by >60% of human melanomas, may be a therapeutic target. We performed a phase II trial of 100 mg PO bid of riluzole, an inhibitor of GRM1 signaling, in patients with advanced melanoma with the primary endpoint of response rate. Thirteen patients with GRM1-positive tumors were enrolled. No objective responses were observed, and accrual was stopped. Stable disease was noted in six (46%) patients, with one patient on study for 42 weeks. Riluzole was well tolerated, with fatigue (62%) as the most common adverse event. Downregulation of MAPK and PI3K/AKT was noted in 33% of paired tumor biopsies. Hypothesis-generating correlative studies suggested that downregulation of angiogenic markers and increased leukocytes at the active edge of tumor correlate with clinical benefit. Pharmacokinetic analysis showed interpatient variability consistent with prior riluzole studies. Future investigations should interrogate mechanisms of biologic activity and advance the development of agents with improved bioavailability.

Riluzole Serum Concentration in Pediatric Patients Treated for Obsessive-Compulsive Disorder

PURPOSE/BACKGROUND

The goals of this study were to determine whether pediatric serum concentration of riluzole is similar to that observed in adults and to determine whether riluzole serum concentration is associated with adverse effects or efficacy in children and adolescents with treatment-refractory obsessive-compulsive disorder.

METHODS/PROCEDURES

Data were drawn from previously published studies: 1 open-label trial and 1 randomized controlled trial with an open-label extension phase. Serum was drawn at 24, 36, and 52 weeks in 37 patients who were taking approximately 100 mg riluzole daily (mean dose at 24 weeks, 99 ± 28 mg).

FINDINGS/RESULTS

Across all samples, serum riluzole concentration ranged from 7 to 963 ng/mL. At week 24 (n = 37), the median concentration was 76 ng/mL (interquartile range, 53-172 ng/mL). Within-patient concentration was relatively stable. One subject who had the highest serum concentration levels during the study developed pancreatitis after exiting the study. The patient had recently added fluvoxamine to the riluzole regimen. Controlling for concomitant fluvoxamine (in 6 participants) and time of draw, serum riluzole concentration was not associated with obsessive-compulsive disorder symptom severity, nor was it associated with adverse effect profile.

IMPLICATIONS/CONCLUSIONS

The dose of riluzole used in these pediatric subjects seems to have achieved serum concentration levels similar to those observed in adults. However, as previously reported in adults, the serum concentration had no discernable relationship to efficacy or adverse effects.

Recent progress in the discovery of small molecules for the treatment of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with few therapeutic options. While several gene mutations have been implicated in ALS, the exact cause of neuronal dysfunction is unknown and motor neurons of affected individuals display numerous cellular abnormalities. Ongoing efforts to develop novel ALS treatments involve the identification of small molecules targeting specific mechanisms of neuronal pathology, including glutamate excitotoxicity, mutant protein aggregation, endoplasmic reticulum (ER) stress, loss of trophic factors, oxidative stress, or neuroinflammation. Herein, we review recent advances in the discovery and preclinical characterization of lead compounds that may ultimately provide novel drugs to treat patients suffering from ALS.

A review of the neural mechanisms of action and clinical efficiency of riluzole in treating amyotrophic lateral sclerosis: what have we learned in the last decade?

Amyotrophic lateral sclerosis (ALS) is a devastating and fatal neurodegenerative disease of adults which preferentially attacks the neuromotor system. Riluzole has been used as the only approved treatment for amyotrophic lateral sclerosis since 1995, but its mechanism(s) of action in slowing the progression of this disease remain obscure. Searching PubMed for "riluzole" found 705 articles published between January 1996 and June 2009. A systematic review of this literature found that riluzole had a wide range of effects on factors influencing neural activity in general, and the neuromotor system in particular. These effects occurred over a large dose range (<1 μM to >1 mM). Reported neural effects of riluzole included (in approximate ascending order of dose range): inhibition of persistent Na(+) current = inhibition of repetitive firing < potentiation of calcium-dependent K(+) current < inhibition of neurotransmitter release < inhibition of fast Na(+) current < inhibition of voltage-gated Ca(2+) current = promotion of neuronal survival or growth factors < inhibition of voltage-gated K(+) current = modulation of two-pore K(+) current = modulation of ligand-gated neurotransmitter receptors = potentiation of glutamate transporters. Only the first four of these effects commonly occurred at clinically relevant concentrations of riluzole (plasma levels of 1-2 μM with three- to four-fold higher concentrations in brain tissue). Treatment of human ALS patients or transgenic rodent models of ALS with riluzole most commonly produced a modest but significant extension of lifespan. Riluzole treatment was well tolerated in humans and animals. In animals, despite in vitro evidence that riluzole may inhibit rhythmic motor behaviors, in vivo administration of riluzole produced relatively minor effects on normal respiration parameters, but inhibited hypoxia-induced gasping. This effect may have implications for the management of hypoventilation and sleep-disordered breathing during end-stage ALS in humans.

Review of the use of the glutamate antagonist riluzole in psychiatric disorders and a description of recent use in childhood obsessive-compulsive disorder

The antiglutamatergic drug riluzole (Rilutek) is presently being used off label in the treatment of psychiatric conditions in adult patients and, increasingly, in children. This article briefly reviews the pharmacology of this drug and its current investigative and clinical uses and adverse effects. It also reports on our experience to date in the study of the drug in children, with emphasis on adverse effects noted so far in these younger patients.

Riluzole metabolism and CYP1A1/2 polymorphisms in patients with ALS

Riluzole is the only FDA approved drug for the treatment of amyotrophic lateral sclerosis. Riluzole is assumed to be mainly metabolized by the liver cytochrome CYP1A2 and by the extra-hepatic cytochrome CYP1A1. CYP1A2 and CYP1A1 genetic polymorphisms are known, but their relationship to riluzole metabolism in ALS patients has not been investigated. The aim of this study was to determine whether the polymorphisms of the CYP1A2 and the CYP1A1 genes in ALS patients are associated with riluzole metabolic profiles. Thirty-two patients with a diagnosis of probable or definite ALS and who were on riluzole, participated in the study. Trough and peak plasma riluzole levels were measured using analytical chromatography-mass spectrometry methods. Association of the genotypes of the SNPs spanning the CYP1A1 and CYP1A2 genes (including one SNP in the intergenic region) with mean riluzole peak and trough levels was studied using ANOVA and Tukey's HSD. The mean peak riluzole level was 202+/-111 ng/ml and mean trough level 54.3+/-37.5 ng/ml. Our data do not support any association of the four CYP1A1 and CYP1A2 polymorphisms with the riluzole metabolic profile. In conclusion, genetic variations in CYP1A1 and CYP1A2 genes do not seem to influence riluzole levels. Further work is needed to better understand the genetic regulation of CYP1A enzymes and their role in riluzole metabolism.

Riluzole in the treatment of mood and anxiety disorders

Recent advances implicate amino acid neurotransmission in the pathophysiology and treatment of mood and anxiety disorders. Riluzole, which is approved and marketed for the treatment of amyotrophic lateral sclerosis, is thought to be neuroprotective through its modulation of glutamatergic neurotransmission. Riluzole has multiple molecular actions in vitro; the two that have been documented to occur at physiologically realistic drug concentrations and are therefore most likely to be clinically relevant are inhibition of certain voltage-gated sodium channels, which can lead to reduced neurotransmitter release, and enhanced astrocytic uptake of extracellular glutamate.Although double-blind, placebo-controlled trials are lacking, several open-label trials have suggested that riluzole, either as monotherapy or as augmentation of standard therapy, reduces symptoms of obsessive-compulsive disorder, unipolar and bipolar depression, and generalized anxiety disorder. In studies of psychiatrically ill patients conducted to date, the drug has been quite well tolerated; common adverse effects include nausea and sedation. Elevation of liver function tests is common and necessitates periodic monitoring, but has been without clinical consequence in studies conducted to date in psychiatric populations. Case reports suggest utility in other conditions, including trichotillomania and self-injurious behaviour associated with borderline personality disorder. Riluzole may hold promise for the treatment of several psychiatric conditions, possibly through its ability to modulate pathologically dysregulated glutamate levels, and merits further investigation.

Riluzole in psychiatry: a systematic review of the literature

BACKGROUND

The glutamate system seems to be an important contributor to the pathophysiology of mood and anxiety disorders. Thus, glutamatergic modulators are reasonable candidate drugs to test in patients with mood and anxiety disorders. Riluzole, a neuroprotective agent with anticonvulsant properties approved for the treatment of amyotrophic lateral sclerosis (ALS) is one such agent.

OBJECTIVE

To assess the potential risks and benefits of riluzole treatment in psychiatric patients.

METHODS

A PubMed search was performed using the keywords 'riluzole', 'inhibitor of glutamate release' and 'glutamatergic modulator' to identify all clinical studies and case reports involving riluzole in psychiatric patients.

RESULTS/CONCLUSION

Riluzole's side effect profile is favorable and preliminary results regarding riluzole for the treatment of severe mood, anxiety and impulsive disorders are encouraging.

Pharmacokinetics of riluzole: evidence for glucuronidation as a major metabolic pathway not associated with UGT1A1 genotype

Pharmacokinetic studies of riluzole show a large inter-individual variability of the drug's clearance and serum concentrations. Optimizing the individual dosage of riluzole may have the potential to improve the effect of riluzole treatment on survival of patients with amyotrophic lateral sclerosis (ALS). Limited data are available on the in vivo metabolic elimination of riluzole. From in vitro experiments, CYP1A2 seems to be mainly involved in riluzole clearance. However, in vitro studies suggest that formation of riluzole-glucuronide plays a role and may determine the drug's pharmacokinetic variability in patients to some extent. In the current study the formation of riluzole-glucuronide was examined in amyotrophic lateral sclerosis (ALS) patients. It also aimed at relating glucuronidation of riluzole to differential UGT1A1*28 genotypes. The formation of riluzole-glucuronide was confirmed in serum from a group of 14 ALS patients taking riluzole. Riluzole-glucuronide concentrations were positively associated with those of riluzole. In a separate group of 131 ALS patients taking riluzole, the UGT1A1*28 genotype was not associated with trough or peak serum concentrations of riluzole. This study provides evidence that the in vivo metabolic elimination of riluzole in ALS patients involves glucuronidation. The results do not indicate that glucuronidation of riluzole highly contributes to the drug's inter-individual pharmacokinetic variability.

An association study of riluzole serum concentration and survival and disease progression in patients with ALS

Patients with amyotrophic lateral sclerosis (ALS) who are treated with the antiglutamatergic drug riluzole receive a fixed-dose regimen of 50 mg b.i.d. The drug has been shown to increase tracheostomy-free survival by 3-6 months. The pharmacokinetics of riluzole show a high interindividual variability. Riluzole serum concentrations are associated with side effects and ALS symptoms, but the effect of the actual blood level of riluzole on disease progression and survival is unknown. We measured trough and peak serum concentrations of riluzole in 160 patients with ALS, and estimated the area under the curve for one dosage interval (AUCi) using a Bayesian method. We then determined the association between riluzole AUCi and survival over a 5-year period, and between riluzole AUCi and disease progression, defined by the rates of decline of arm strength and vital lung capacity. No significant association was found between riluzole AUCi and survival or disease progression.

Riluzole promotes cell survival and neurite outgrowth in rat sensory neurones in vitro

This study explored the effects of riluzole administration on cell survival and neurite growth in adult and neonatal rat dorsal root ganglion (DRG) neurones in vitro. Neuronal survival was assessed by comparing numbers of remaining neurones in vehicle- and riluzole-treated cultures. A single dose of 0.1 microm riluzole was sufficient to promote neuronal survival in neonatal DRG cultures, whereas repeated riluzole administration was necessary in adult cultures. However, a single administration of riluzole was sufficient to induce neuritogenesis, promote neurite branching and enhance neurite outgrowth in both neonatal and adult DRG cultures. The effects of a single dose of riluzole on adult DRG neurones after peripheral nerve or dorsal root injury were also studied in vitro at 48 h. For both types of injury, riluzole enhanced neurite outgrowth in terms of number, length and branch pattern significantly more on the injured side as compared with the contralateral side. No effect was seen on cell survival. The results suggest that, in addition to its cell survival effects, riluzole has novel growth-promoting effects on sensory neurones in vitro and that riluzole may offer a new way to promote sensory afferent regeneration following peripheral injury.

Association between CYP1A2 activity and riluzole clearance in patients with amyotrophic lateral sclerosis

AIMS

Riluzole is used in a fixed dosing schedule of 50 mg twice daily to treat patients with amyotropic lateral sclerosis (ALS), one form of motor neurone disease. The large variability in the pharmacokinetics of riluzole may be a factor contributing to its limited therapeutic benefit. Riluzole is assumed to be mainly metabolized by the cytochrome P450 enzyme 1A2 (CYP1A2). The aim of the study was to investigate the relationship between CYP1A2 activity and riluzole clearance with a view to optimize drug treatment.

METHODS

A group of 30 ALS patients participated in the study. In each patient the CYP1A2 activity was determined using caffeine as a metabolic probe. Riluzole clearance was estimated from serum drug concentration measurements followed by Bayesian fitting.

RESULTS

Riluzole clearance and the serum paraxanthine : caffeine (P/C) ratio showed a positive correlation (r = 0.693; P = 0.0002). Linear regression analysis identified the P/C ratio (beta: 1.16) and height (beta: 0.027) as independent predictors of riluzole clearance (adjusted r2 = 0.369).

CONCLUSIONS

The P/C ratio, used as measure of CYP1A2 activity, significantly correlated with the riluzole clearance, although only 37% of the observed variability could be explained.