8:30am - 8:50amPreclinical evaluation of antiepileptic drugs in the Grin2aS/S murine model
Ilaria Bertocchi
Università di Torino, Italy
GRIN-related disorders are neurodevelopmental disorders caused by mutations in the N-methyl-D-aspartate receptor (NMDAR) subunit receptor GRIN genes. A large fraction of these mutations leads to gain of function of the NMDAR. Patients present with a combination of symptoms that includes epilepsy, intellectual disability, behavioural and motor symptoms. Controlling seizures is a significant medical need in most of GRIN-related disorders patients.
The aim of this study was to assess the therapeutic efficacy of radiprodil, a selective negative allosteric modulator of the GluN2B-containing NMDARs, in counteracting audiogenic seizures (AGS) in a murine model carrying the human analogous GRIN2A(N615S) mutation in homozygosity (Grin2aS/S mice).
Radiprodil was acutely administered before the presentation of a high-frequency acoustic stimulus commonly used for AGS induction. Radiprodil significantly reduced dose-dependently the onset and severity of AGS in Grin2aS/S mice.
Our data clearly indicates that radiprodil has the potential to control seizures in patients with GRIN2A gain of function mutations targeting the underlying pathophysiology of the disorder.
8:50am - 9:10amRadiprodil, a NR2B-NMDA negative allosteric modulator in clinical development for GRIN related disorders caused by gain of function mutations
Pierandrea Muglia
GRIN Therapeutics, Belgium
Radiprodil is an investigational, clinical stage, orally active potent and selective negative allosteric modulator of the N methyl-D-aspartate receptor subtype 2B (NR2B) containing the N-methyl-D-aspartate (NMDA) receptors. The inhibitory effect of radiprodil on NMDA glutamate currents is fully retained in receptors containing NR2B subunits coded by GRIN2B gene with gain-of-function (GoF) mutations, which are known to cause GRIN2B-related disorder. GRIN2B mutations cause GRIN2B related disorder that is part of a group of recently described syndromes (Lemke et al., 2014) characterized by delayed childhood development, learning disabilities, behavioural symptoms and often drug resistant seizures (Benke et al., 2021). Radiprodil showed anticonvulsant effects in a variety of preclinical models both in acute and after sub-chronic dosing and in a transgenic mice carrying GRIN2A GoF mutations. Radiprodil has also been administered in a phase 1B clinical study in three infantile spasms patients with drug resistant seizures. In this study radiprodil showed to be well tolerated for up to a month of treatment and to reduce spasm seizures (Auvin et al 2020). By selectively inhibiting the NR2B-NMDA receptors, radiprodil has the potential to treat seizures and neurology symptoms in GRIN-related disorder patients caused by GoF mutations in the genes coding for the NMDA subunits. A clinical study in GRIN related disorder patients with established GoF mutations in the GRIN gene is currently ongoing in several EU countries.
9:10am - 9:25amMissense variants in RPH3A cause defects in excitatory synaptic function and are associated with a clinically variable neurodevelopmental disorder
Marta Barzasi1, Lisa Pavinato2, Jennifer Stanic1, Antonia Gurgone3, Gisueppe Chiantia3, Valentina Cipriani4, Ivano Eberini1, Luca Palazzolo1, Monica Di Luca1, Alex Costa5, Andrea Marcantoni6, Elisa Biamino7, Marco Spada7, Susan M. Hiatt8, Whitley V. Kelley8, Letizia Vestito4, Sanjay Sisodiya9, Stephanie Efhtymiou10, Alessandro Bruselles11, Simona Cardaropoli12, Marco Tartaglia13, Silvia De Rubeis14, Joseph D. Buxbaum14, Damian Smedley4, Giovanni Battista Ferrero15, Maurizio Giustetto3, Fabrizio Gardoni1, Alfredo Brusco2
1Department of Pharmacological and Biomolecular Sciences, DiSFeB, University of the Studies of Milan, 20122, Milan, Italy; 2Department of Medical Sciences, University of Turin, 10126, Turin, Italy; 3Department of Neuroscience, University of Turin, 10126, Turin, Italy; 4William Harvey Research Institute, Clinical Pharmacology Precision Medicine, Queen Mary University of London, Charterhouse Square, London E1 4NS, United Kingdom; 5Department of Biosciences, University of the Studies of Milan, 20122, Milan, Italy; 6Department of Drug Science and Technology, University of Turin, 10126, Turin, Italy; 7Department of Pediatrics, Regina Margherita Children Hospital, 10126, Turin, Italy; 8HudsonAlpha Institute for Biotechnology, Huntsville, AL 35806, USA; 9Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London WC1E 6BT, United Kingdom; 10Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, UK.; 11Department of Oncology and Molecular Medicine, Istituto Superiore di Sanità, 00161, Rome, Italy; 12Department of Public Health and Pediatric Sciences, University of Torino, 10126, Torino, Italy; 13Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, IRCCS, 00146, Rome, Italy; 14Seaver Autism Center for Research and Treatment, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; 15Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Rabphilin 3A (RPH3A) encodes for a protein involved in the regulation of exo- and endocytosis processes at presynaptic terminals and dendritic spines. The protein is also involved in the stabilization of the NMDA-type glutamate receptors (NMDARs) at the cell surface, forming a ternary complex with the PSD-95 and GluN2A subunit of the receptor, essential for synaptic plasticity and cognition.
By trio-based exome sequencing, GeneMatcher and screening of 100,000 Genomes Project data, we identified six heterozygous variants in RPH3A. Four cases had a neurodevelopmental disorder (NDD) with untreatable epileptic seizures [p.(Gln73His)dn; p.(Thr450Ser)dn; p.(Arg209Lys); p.(Gln508His)], and two cases [p.(Asn618Ser)dn; p.(Arg235Ser)] showed high functioning autism spectrum disorder (ASD). Using primary hippocampal neuronal cultures, we demonstrated that p.(Arg209Lys), p.(Thr450Ser), p.(Gln508His) and p.(Asn618Ser) reduce the co-localization of PSD-95 and GluN2A; Rph3A variants p.(Arg209Lys), p.(Thr450Ser) and p.(Gln508His) also increased the surface levels of GluN2A. These results indicate that RPH3A mutants induce GluN2A-containing NMDARs to localize prevalently at the extrasynaptic sites, suggesting that their stimulation can promote a detrimental effect. This reduced synaptic localization of GluN2A was confirmed in neurons overexpressing Rph3AThr450Ser by the impaired activation of the CREB intracellular pathway, known to be correlated to activation of synaptic NMDARs. Electrophysiological recordings showed increased GluN2A-dependent NMDAR currents for Rph3AThr450Ser and Rph3AAsn618Ser and an alteration of NMDAR-dependent postsynaptic calcium levels at resting state. Finally, expression of the Rph3AThr450Ser mutant in neurons affected dendritic spine morphology.
Overall, we provide evidence that missense gain-of-function variants in RPH3A increase GluN2A-containing NMDARs at extrasynaptic sites and alter synaptic function leading to a clinically variable neurodevelopmental presentation, ranging from untreatable epilepsy to ASD.
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