mavoglurant and Fragile-X-Syndrome

Fragile X syndrome (FXS) is the most common monogenic form of inherited mental retardation caused by a trinucleotid repeat expansion and transcriptional shutdown of the FMR1 gene. FXS patients present a complex and often severe neuropsychiatric phenotype yet have mild somatic symptoms, normal life expectancies, and no indications of neurodegeneration. The therapeutic potential of mGlu5 inhibitors was proposed in the 'mGluR theory of FXS' based on early insights into the molecular pathophysiology of FXS. Studies in Fragile X mental retardation 1 (Fmr1) knock-out mice, a widely used disease model, demonstrated that mGlu5 inhibitors can correct a broad range of disease-related phenotypes. Recent clinical trials, however, with two different mGlu5 inhibitors (basimglurant and mavoglurant) showed no therapeutic benefit in FXS patients for reasons as yet unclear.

Topics: Animals; Disease Models, Animal; Excitatory Amino Acid Antagonists; Fragile X Syndrome; Humans; Imidazoles; Indoles; Mice; Mice, Knockout; Molecular Targeted Therapy; Phenotype; Pyridines; Receptor, Metabotropic Glutamate 5

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. With no curative treatment available, current therapeutic approaches are aimed at symptom management. FXS is caused by silencing the FMR1 gene, which encodes FMRP; as loss of FMRP leads to the development of symptoms associated with FXS.. In this evaluation, the authors examine the role of the metabotropic glutamate receptor 5 (mGluR5) in the pathophysiology of FXS, and its suitability as a target for rescuing the disease state. Furthermore, the authors review the evidence from preclinical studies of pharmacological interventions targeting mGluR5 in FXS. Lastly, the authors assess the findings from clinical studies in FXS, in particular the use of the Aberrant Behavior Checklist-Community Edition (ABC-C) and the recently developed ABC-C for FXS scale, as clinical endpoints to assess disease modification in this patient population.. There is cautious optimism for the successful treatment of the core behavioral and cognitive symptoms of FXS based on preclinical data in animal models and early studies in humans. However, the association between mGluR5-heightened responsiveness and the clinical phenotype in humans remains to be demonstrated. Many questions regarding the optimal treatment and outcome measures of FXS remain unanswered.

Topics: Animals; Fragile X Syndrome; Humans; Indoles; Receptor, Metabotropic Glutamate 5

Numerous preclinical studies have supported the theory that enhanced activation of mGluR5 signaling, due to the absence or reduction of the FMR1 protein, contributes to cognitive and behavioral deficits in patients with fragile X syndrome (FXS). However multiple phase 2 controlled trials in patients with FXS have failed to demonstrate efficacy of compounds that negatively modulate mGluR5, including two phase 2b randomized controlled trials (RCT) of mavoglurant (AFQ056, Novartis Pharma AG), when the primary measures of interest were behavioral ratings. This has cast some doubt onto the translation of the mGluR5 theory from animal models to humans with the disorder.. We evaluated social gaze behavior-a key phenotypic feature of the disorder-and sympathetic nervous system influence on pupil size using a previously-validated eye tracking paradigm as a biobehavioral probe, in 57 adolescent or adult patients with FXS at baseline and following three months of blinded treatment with one of three doses of mavoglurant or placebo, within the context of the AFQ056 RCTs.. Patients with FXS treated with mavoglurant demonstrated increased total absolute looking time and number of fixations to the eye region while viewing human faces relative to baseline, and compared to those treated with placebo. In addition, patients had greater pupil reactivity to faces relative to baseline following mavoglurant treatment compared to placebo.. The study shows that negative modulation of mGluR5 activity improves eye gaze behavior and alters sympathetically-driven reactivity to faces in patients with FXS, providing preliminary evidence of this drug's impact on behavior in humans with the disorder.

Topics: Adolescent; Adult; Attention; Female; Fixation, Ocular; Fragile X Syndrome; Humans; Indoles; Male; Middle Aged; Pupil; Receptor, Metabotropic Glutamate 5; Social Behavior; Young Adult

Fragile X syndrome (FXS) is the most common monogenic cause of inherited intellectual and developmental disabilities. Mavoglurant, a selective metabotropic glutamate receptor subtype-5 antagonist, has shown positive neuronal and behavioral effects in preclinical studies, but failed to demonstrate any behavioral benefits in two 12-week, randomized, placebo-controlled, double-blind, phase IIb studies in adults and adolescents with FXS. Here we report the long-term safety (primary endpoint) and efficacy (secondary endpoint) results of the open-label extensions. Adolescent (n = 119, aged 12-19 years) and adult (n = 148, aged 18-45 years) participants received up to 100 mg bid mavoglurant for up to 34 months. Both extension studies were terminated prematurely due to lack of proven efficacy in the core studies. Mavoglurant was well tolerated with no new safety signal. Five percent of adults and 16.9 percent of adolescents discontinued treatment due to adverse events. Gradual and consistent behavioral improvements as measured by the ABC-C

Topics: Adolescent; Adult; Child; Dose-Response Relationship, Drug; Double-Blind Method; Excitatory Amino Acid Antagonists; Female; Fragile X Syndrome; Humans; Indoles; Male; Mental Disorders; Middle Aged; Placebos; Receptor, Metabotropic Glutamate 5; Young Adult

Fragile X syndrome (FXS), the most common cause of inherited intellectual disability and autistic spectrum disorder, is typically caused by transcriptional silencing of the X-linked FMR1 gene. Work in animal models has described altered synaptic plasticity, a result of the up-regulation of metabotropic glutamate receptor 5 (mGluR5)-mediated signaling, as a putative downstream effect. Post hoc analysis of a randomized, placebo-controlled, crossover phase 2 trial suggested that the selective mGluR5 antagonist mavoglurant improved behavioral symptoms in FXS patients with completely methylated FMR1 genes. We present the results of two phase 2b, multicenter, randomized, double-blind, placebo-controlled, parallel-group studies of mavoglurant in FXS, designed to confirm this result in adults (n = 175, aged 18 to 45 years) and adolescents (n = 139, aged 12 to 17 years). In both trials, participants were stratified by methylation status and randomized to receive mavoglurant (25, 50, or 100 mg twice daily) or placebo over 12 weeks. Neither of the studies achieved the primary efficacy end point of improvement on behavioral symptoms measured by the Aberrant Behavior Checklist-Community Edition using the FXS-specific algorithm (ABC-C(FX)) after 12 weeks of treatment with mavoglurant. The safety and tolerability profile of mavoglurant was as previously described, with few adverse events. Therefore, under the conditions of our study, we could not confirm the mGluR theory of FXS nor the ability of the methylation state of the FMR1 promoter to predict mavoglurant efficacy. Preclinical results suggest that future clinical trials might profitably explore initiating treatment in a younger population with longer treatment duration and longer placebo run-ins and identifying new markers to better assess behavioral and cognitive benefits.

Topics: Adolescent; Adult; Age Factors; Behavior; Cognition; Demography; DNA Methylation; Double-Blind Method; Female; Fragile X Syndrome; Humans; Indoles; Least-Squares Analysis; Male; Placebos; Treatment Outcome

Metabotropic glutamate receptor 5 (mGluR

Topics: Animals; Cells, Cultured; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Female; Fragile X Mental Retardation Protein; Fragile X Syndrome; Indoles; Isoquinolines; Mice; Mice, Inbred C57BL; Mice, Knockout; Phenotype; Pregnancy; Pyrazoles; Pyrimidines; Random Allocation; Receptor, Metabotropic Glutamate 5

Fragile X syndrome is the most common monogenetic form of intellectual disability and autism. Although the Fmr1 knockout mouse model recapitulates many aspects of the human FXS condition, the establishment of robust social behavioural phenotypes suitable for drug screening has been difficult. Here, we describe a novel social behavioural paradigm, the Automated Tube Test (ATT), for which Fmr1 knockout mice demonstrate a highly reliable and robust phenotype. Fmr1 KO mice show highly dominant behaviour over wild-type littermates in the ATT. Consistent with previous findings, we observed a highly significant, albeit partial, rescue of the altered social behaviour of Fmr1 knockout mice in the ATT, using genetic (mGluR5 deletion) or pharmacological inhibition (mGluR5 antagonist) of mGluR5 signalling independently. Together, our results validate the Automated Tube Test as a robust outcome measure for social behaviour in preclinical research for FXS, and confirm the pathophysiological relevance of mGluR5 signalling. Moreover, our findings highlight the strategy of initiating pharmacological intervention in adulthood as holding significant clinical potential.

Topics: Animals; Disease Models, Animal; Excitatory Amino Acid Antagonists; Fragile X Mental Retardation Protein; Fragile X Syndrome; Indoles; Male; MAP Kinase Signaling System; Mice, Inbred C57BL; Mice, Knockout; Phenotype; Phosphorylation; Psychological Tests; Psychotropic Drugs; Receptor, Metabotropic Glutamate 5; Social Behavior; Synapses

Fragile X syndrome (FXS) is the leading monogenic cause of intellectual disability and autism. The disease is a result of lack of expression of the fragile X mental retardation protein. Brain tissues of patients with FXS and mice with FMRP deficiency have shown an abnormal dendritic spine phenotype. We investigated the dendritic spine length and density of hippocampal CA1 pyramidal neurons in 2-, 10-, and 25-week-old Fmr1 knockout (KO). Next, we studied the effects of long-term treatment with an mGluR5 antagonist, AFQ056/Mavoglurant, on the spine phenotype in adult Fmr1 KO mice. We observed alterations in the spine phenotype during development, with a decreased spine length in 2-week-old Fmr1 KO mice compared with age-match wild-type littermates, but with increased spine length in Fmr1 KO mice compared with 10- and 25-week-old wild-type controls. No difference was found in spine density at any age. We report a rescue of the abnormal spine length in adult Fmr1 KO mice after a long-term treatment with AFQ056/Mavoglurant. This finding suggests that long-term treatment at later stage is sufficient to reverse the structural spine abnormalities and represents a starting point for future studies aimed at improving treatments for FXS.

Topics: Animals; CA1 Region, Hippocampal; Dendritic Spines; Disease Models, Animal; Excitatory Amino Acid Antagonists; Fragile X Mental Retardation Protein; Fragile X Syndrome; Indoles; Male; Mice; Mice, Knockout; Microscopy, Confocal; Phenotype; Pyramidal Cells; Receptor, Metabotropic Glutamate 5

Fragile X syndrome is caused by lack of FMR1 protein (FMRP) leading to severe symptoms, including intellectual disability, hyperactivity and autistic-like behaviour. FMRP is an RNA binding protein involved in the regulation of translation of specific target mRNAs upon stimulation of metabotropic glutamate receptor 5 (mGluR5) at the synapse. The absence of FMRP leads to enhanced activity of mGluR5 signal transduction pathways. Many conflicting results have been reported regarding social behaviour deficits in Fmr1 knockout mice, and little is known about the involvement of mGluR5 pathways on social behaviour. In this study, a three-chambered task was used to determine sociability and preference for social novelty in Fmr1 knockout mice. Disruption of Fmr1 functioning resulted in enhanced interaction with stranger mouse during sociability while no significant changes were observed during preference for social novelty assay. Chronic administration of a specific mGluR5 antagonist, AFQ056/Mavoglurant, was able to restore sociability behaviour of Fmr1 knockout mice to levels of wild type littermates. These results support the importance of mGluR5 signalling pathways on social interaction behaviour and that AFQ056/Mavoglurant might be useful as potential therapeutic intervention to rescue various behavioural aspects of the fragile X phenotype.

Topics: Animals; Disease Models, Animal; Excitatory Amino Acid Antagonists; Fragile X Mental Retardation Protein; Fragile X Syndrome; Indoles; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Social Behavior; Time Factors