Glycine Transporter Research Articles

Progressive Encephalomyelitis With Rigidity and Myoclonus With Glycine Receptor and GAD65 Antibodies: Case Report and Potential Mechanisms.

Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a severe form of stiff-person spectrum disorder that can be associated with antibodies against surface antigens (glycine receptor (GlyR), dipeptidyl-peptidase-like-protein-6) and intracellular antigens (glutamate decarboxylase (GAD65), amphiphysin). We report clinico-pathologic findings of a PERM patient with coexisting GlyR and GAD65 antibodies. A 75-year-old man presented with myoclonus and pain of the legs, subsequently developed severe motor symptoms, hyperekplexia, a pronounced startle reflex, hallucinations, dysautonomia, and died 10 months after onset despite extensive immunotherapy, symptomatic treatment, and continuous intensive care support. Immunotherapy comprised corticosteroids, IVIG, plasmapheresis, immunoadsorption, cyclophosphamide, and bortezomib. Intensive care treatment and permanent isoflurane sedation was required for more than 20 weeks. CNS tissue revealed neuronal loss, astrogliosis and microgliosis, representing a pallido-nigro-dentato-bulbar-spinal degeneration pattern, specifically along GlyR and GAD expression sites. Neurons showed pSTAT1, MHC class I, and GRP78 upregulation. Inflammation was moderate and characterized by CD8+ T cells and single CD20+/CD79a+ B/plasma cells. Focal tau-positive thread-like deposits were detected in gliotic brainstem areas. In the spinal cord, GlyR, glycine transporter-2, and GAD67 expression were strongly reduced. A possible potentiating effect of pathogenic GlyR antibodies together with T cells directed against neurons may have led to the severe and progressive clinical course.

Glycine Transporter 1 Inhibitors Minimize the Analgesic Tolerance to Morphine.

Opioid analgesic tolerance (OAT), among other central side effects, limits opioids' indispensable clinical use for managing chronic pain. Therefore, there is an existing unmet medical need to prevent OAT. Extrasynaptic N-methyl D-aspartate receptors (NMDARs) containing GluN2B subunit blockers delay OAT, indicating the involvement of glutamate in OAT. Glycine acts as a co-agonist on NMDARs, and glycine transporters (GlyTs), particularly GlyT-1 inhibitors, could affect the NMDAR pathways related to OAT. Chronic subcutaneous treatments with morphine and NFPS, a GlyT-1 inhibitor, reduced morphine antinociceptive tolerance (MAT) in the rat tail-flick assay, a thermal pain model. In spinal tissues of rats treated with a morphine-NFPS combination, NFPS alone, or vehicle-comparable changes in µ-opioid receptor activation, protein and mRNA expressions were seen. Yet, no changes were observed in GluN2B mRNA levels. An increase was observed in glycine and glutamate contents of cerebrospinal fluids from animals treated with a morphine-NFPS combination and morphine, respectively. Finally, GlyT-1 inhibitors are likely to delay MAT by mechanisms relying on NMDARs functioning rather than an increase in opioid efficacy. This study, to the best of our knowledge, shows for the first time the impact of GlyT-1 inhibitors on MAT. Nevertheless, future studies are required to decipher the exact mechanisms.

GlyT1 inhibition promotes neuroprotection in the middle cerebral artery occlusion model through the activation of GluN2A-containing NMDAR

Glycine Transporter Type 1 (GlyT1) inhibition confers neuroprotection against different forms of cerebral damage. This effect occurs through the elevation of synaptic glycine concentrations, which enhances N-methyl-d-aspartate receptor (NMDAR) activation by glutamate. To investigate the neuroprotective mechanism of GlyT1 inhibition, we used the Middle Cerebral Artery Occlusion (MCAO) model in male C57BL/6 mice, aged 10–12 weeks. We administered N-[3-(4′-fluorophenyl)-3-(4′-phenylphenoxy)propyl] sarcosine (NFPS), a GlyT1 inhibitor, 24 h prior to ischemia induction. NFPS pretreatment provided significant neuroprotection in the MCAO model, associated with modulation of pathways related to long-term potentiation. Specifically, GluN2A subunit expression was upregulated, while GluN2B subunit expression was downregulated in cortical areas, correlating with enhanced phosphorylation of CaMKIV and CREB proteins. Coadministration with the GluN2B antagonist Eliprodil or the CREB inhibitor C646 did not affect the neuroprotective effects of NFPS pretreatment, but TCN-201, a specific GluN2A antagonist, disrupted these effects. These findings suggest that GlyT1 inhibition mediates neuroprotection through activation of GluN2A-containing NMDARs and the GluN2A/CaMKIV/CREB signaling cascade, thereby modulating the balance between GluN2A and GluN2B subunits.

Fermented Fish Collagen Attenuates Melanogenesis via Decreasing UV-Induced Oxidative Stress.

Excessive melanogenesis leads to hyperpigmentation-related cosmetic problems. UV exposure increases oxidative stress, which promotes melanogenesis-related signal pathways such as the PKA, microphthalmia-associated transcription factor (MITF), tyrosinase (TYR), tyrosinase-related protein-1 (TRP1), and tyrosinase-related protein-2 (TRP2) pathways. Glycine is a source of endogenous antioxidants, including glutathione. Fermented fish collagen (FC) contains glycine; thus, we evaluated the effect of FC on decreasing melanogenesis via decreasing oxidative stress. The glycine receptor (GlyR) and glycine transporter-1 (GlyT1) levels were decreased in UV-irradiated keratinocytes; however, the expression levels of these proteins increased upon treatment with FC. The FC decreased oxidative stress, as indicated by the decreasing expression of NOX1/2/4, increased expression of GSH/GSSG, increased SOD activity, and decreased 8-OHdG expression in UV-irradiated keratinocytes. Administration of conditioned media from FC-treated keratinocytes to melanocytes led to decreased p38, PKC, MITF, TRP1, and TRP2 expression. These changes induced by the FC were also observed in UV-irradiated animal skin. FC treatment increased the expression of GlyR and GlyT, which was accompanied by decreased oxidative stress in the UV-irradiated skin. Moreover, the FC negatively regulated the melanogenesis signaling pathways, leading to decreased melanin content in the UV-irradiated skin. In conclusion, FC decreased UV-induced oxidative stress and melanogenesis in melanocytes and animal skin. FC could be used in the treatment of UV-induced hyperpigmentation problems.

Role of palmitoylation on the neuronal glycine transporter GlyT2.

The neuronal glycine transporter GlyT2 removes glycine from the synaptic cleft through active Na+, Cl-, and glycine cotransport contributing to the termination of the glycinergic signal as well as supplying substrate to the presynaptic terminal for the maintenance of the neurotransmitter content in synaptic vesicles. Patients with mutations in the human GlyT2 gene (SLC6A5), develop hyperekplexia or startle disease (OMIM 149400), characterized by hypertonia and exaggerated startle responses to trivial stimuli that may have lethal consequences in the neonates as a result of apnea episodes. Post-translational modifications in cysteine residues of GlyT2 are an aspect of structural interest we analyzed. Our study is compatible with a reversible and short-lived S-acylation in spinal cord membranes, detectable by biochemical and proteomics methods (acyl-Rac binding and IP-ABE) confirmed with positive and negative controls (palmitoylated and non-palmitoylated proteins). According to a short-lived modification, direct labeling using click chemistry was faint but mostly consistent. We have analyzed the physiological properties of a GlyT2 mutant lacking the cysteines with high prediction of palmitoylation and the mutant is less prone to be included in lipid rafts, an effect also observed upon treatment with the palmitoylation inhibitor 2-bromopalmitate. This work demonstrates there are determinants of lipid raft inclusion associated with the GlyT2 mutated cysteines, which are presumably modified by palmitoylation.

In silico evidence of bitopertin's broad interactions within the SLC6 transporter family.

The Glycine Transporter Type 1 (GlyT1) significantly impacts central nervous system functions, influencing glycinergic and glutamatergic neurotransmission. Bitopertin, the first GlyT1 inhibitor in clinical trials, was developed for schizophrenia treatment but showed limited efficacy. Despite this, bitopertin's repositioning could advance treating various pathologies. This study aims to understand bitopertin's mechanism of action using computational methods, exploring off-target effects, and providing a comprehensive pharmacological profile. Similarity Ensemble Approach (SEA) and SwissTargetPrediction initially predicted targets, followed by molecular modeling on SWISS-MODEL and GalaxyWeb servers. Binding sites were identified using PrankWeb, and molecular docking was performed with DockThor and GOLD software. Molecular dynamics analyses were conducted on the Visual Dynamics platform. Reverse screening on SEA and SwissTargetPrediction identified GlyT1 (SLC6A9), GlyT2 (SLC6A5), PROT (SLC6A7), and DAT (SLC6A3) as potential bitopertin targets. Homology modeling on SwissModel generated high-resolution models, optimized further on GalaxyWeb. PrankWeb identified similar binding sites in GlyT1, GlyT2, PROT, and DAT, indicating potential interaction. Docking studies suggested bitopertin's interaction with GlyT1 and proximity to GlyT2 and PROT. Molecular dynamics confirmed docking results, highlighting bitopertin's target stability beyond GlyT1. The study concludes that bitopertin potentially interacts with multiple SLC6 family targets, indicating a broader pharmacological property.

Structural Studies of the Taurine Transporter: A Potential Biological Target from the GABA Transporter Subfamily in Cancer Therapy.

The taurine transporter (TauT, SLC6A6) is a member of the solute carrier 6 (SLC6) family, which plays multiple physiological roles. The SLC6 family is divided into four subfamilies: GABA (γ-aminobutyric acid), monoamine, glycine and neutral amino acid transporters. Proteins from the GABA group, including the taurine transporter, are primarily considered therapeutic targets for treating central nervous system disorders. However, recent studies have suggested that inhibitors of SLC6A6 could also serve as anticancer agents. Overexpression of TauT has been associated with the progression of colon and gastric cancer. The pool of known ligands of this transporter is limited and the exact spatial structure of taurine transporter remains unsolved. Understanding its structure could aid in the development of novel inhibitors. Therefore, we utilized homology modelling techniques to create models of TauT. Docking studies and molecular dynamics simulations were conducted to describe protein-ligand interactions. We compared the obtained information for TauT with literature data on other members of the GABA transporter group. Our in silico analysis allowed us to characterize the transporter structure and point out amino acids crucial for ligand binding: Glu406, Gly62 and Tyr138. The significance of selected residues was confirmed through structural studies of mutants. These results will aid in the development of novel taurine transporter inhibitors, which can be explored as anticancer agents.

B-Glycine as a marker for β cell imaging and β cell mass evaluation.

β cell mass (BCM) and function are essential to the diagnosis and therapy of diabetes. Diabetic patients serve β cell loss is, and damage of β cells leads to severe insulin deficiency. Our understanding of the role of BCM in diabetes progression is extremely limited by lacking efficient methods to evaluate BCM in vivo. In vitro methods of labeling islets, including loading of contrast reagent or integration of exogenous biomarker, require artificial manipulation on islets, of which the clinical application is limited. Imaging methods targeting endogenous biomarkers may solve the above problems. However, traditional reagents targeting GLP-1R and VAMT2 result in a high background of adjacent tissues, complicating the identification of pancreatic signals. Here, we report a non-invasive and quantitative imaging technique by using radiolabeled glycine mimics ([18F]FBG, a boron-trifluoride derivative of glycine) to assay islet function and monitor BCM changes in living animals. Glycine derivatives, FBG, FBSa, 2Me-FBG, 3Me-FBG, were successfully synthesized and labeled with 18F. Specificity of glycine derivatives were characterized by in vitro experiment. PET imaging and biodistribution studies were performed in animal models carring GLYT over-expressed cells. In vivo evaluation of BCM with [18F]FBG were performed in STZ (streptozocin) induced T1D (type 1 diabetes) models. GLYT responds to excess blood glycine levels and transports glycine into islet cells to maintain the activity of the glycine receptor (GLYR). Best PET imaging condition was 80min after given a total of 240 ~ 250 nmol imaging reagent (a mixture of [18F]FBG and natural glycine) intravenously. [18F]FBG can detect both endogenous and exogenous islets clearly in vivo. When applied to STZ induced T1D mouse models, total uptake of [18F]FBG in the pancreas exhibited a linear correlation with survival BCM. [18F]FBG targeting the endogenous glycine transporter (GLYT), which is highly expressed on islet cells, avoiding extra modification on islet cells. Meanwhile the highly restricted expression pattern of GLYT excluded the background in adjacent tissues. This [18F]FBG-based imaging technique provides a non-invasive method to quantify BCM in vivo, implying a new evaluation index for diabetic assessment.

Dynamic role of GlyT1 as glycine sink or source: Pharmacological implications for the gain control of NMDA receptors

Glycine transporter 1 (GlyT1) mediates the termination of inhibitory glycinergic receptor signaling in the spinal cord and brainstem, and is also present diffusely in the forebrain. Here, it regulates the ambient glycine concentration and influences the ‘glycine’ site occupancy of N-methyl-d-aspartate receptors (NMDARs). GlyT1 is a reversible transporter with a substantial, but not excessive, sodium-motive force for uphill transport. This study investigates its role as a potential source of glycine supply, either by reverse uptake or heteroexchange. Indeed, glutamate alone does not induce NMDAR current in “naive” oocytes co-expressing GluN1/GluN2A and GlyT1, a previously characterized cellular model. However, after substantial intracellular glycine accumulation, GlyT1 reverses its transport mode, and begins to release glycine into the external compartment, allowing NMDAR activation by glutamate alone. These uptake-dependent glutamate currents were blocked by ALX-5407 and potentiated by sarcosine, a specific inhibitor and substrate of GlyT1, respectively, suggesting a higher occupancy of the co-agonist site when GlyT1 functions as a glycine source either by reversed-uptake or by heteroexchange. These two glycine release mechanisms can be distinguished by their voltage dependence, as the reversed-uptake cycle decreases at hyperpolarized potentials, whereas heteroexchange electroneutrality preserves glycine efflux and NMDAR activation at these potentials. These results establish GlyT1-mediated efflux as a positive regulator of NMDAR coagonist site occupancy, and demonstrate the efficacy of sarcosine heteroexchange in enhancing coagonist site occupancy. Because NMDAR facilitation by GlyT1-inhibitors and sarcosine relies on different transport mechanisms, their actions may be a source of variability in reversing NMDAR hypofunction in schizophrenia.

The iAAA-mitochondrial protease YME1L1 regulates the degradation of the short-lived mitochondrial transporter SLC25A38.

Mitochondrial transporters facilitate the exchange of diverse metabolic intermediates across the inner mitochondrial membrane, ensuring an adequate supply of substrates and cofactors to support redox and biosynthetic reactions within the mitochondrial matrix. However, the regulatory mechanisms governing the abundance of these transporters, crucial for maintaining metabolic compartmentalization and mitochondrial functions, remain poorly defined. Through analysis of protein half-life data and mRNA-protein correlations, we identified SLC25A38, a mitochondrial glycine transporter, as a short- lived protein with a half-life of 4 hours under steady-state conditions. Pharmacological inhibition and genetic depletion of various cellular proteolytic systems revealed that SLC25A38 is rapidly degraded by the iAAA-mitochondrial protease YME1L1. Depolarization of the mitochondrial membrane potential induced by the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrozone prevented the degradation of SLC25A38. This dual regulation of SLC25A38 abundance by YME1L1 and mitochondrial membrane potential suggests a link between SLC25A38 turnover, the integrity of the inner mitochondrial membrane, and electron transport chain function. These findings open avenues for investigating whether mitochondrial glycine import coordinates with mitochondrial bioenergetics.

GlyT1 Inhibition by NFPS Promotes Neuroprotection in Amyloid-β-Induced Alzheimer's Disease Animal Model.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-β, leading to N-methyl-D-aspartate (NMDA) receptor-dependent synaptic depression, spine elimination, and memory deficits. Glycine transporter type 1 (GlyT1) modulates glutamatergic neurotransmission via NMDA receptors (NMDAR), presenting a potential alternative therapeutic approach for AD. This study investigates the neuroprotective potential of GlyT1 inhibition in an amyloid-β-induced AD mouse model. C57BL/6 mice were treated with N-[3-([1,1-Biphenyl]-4-yloxy)-3-(4-fluorophenyl)propyl]-N-methylglycine (NFPS), a GlyT1 inhibitor, 24h prior to intrahippocampal injection of amyloid-β. NFPS pretreatment prevented amyloid-β-induced cognitive deficits in short-term and long-term memory, evidenced by novel object recognition and spatial memory tasks. Moreover, NFPS pretreatment curbed microglial activation, astrocytic reactivity, and subsequent neuronal damage from amyloid-β injection. An extensive label-free quantitative UPLC-MSE proteomic analysis was performed on the hippocampi of mice treated with NFPS. In proteomics, KEGG enrichment analysis revealed increased in dopaminergic synapse, purine-containing compound biosynthetic process and long-term potentiation, and a reduction in Glucose catabolic process and glycolytic process pathways. The western blot analysis confirmed that NFPS treatment elevated BDNF levels, correlating with enhanced TRKB phosphorylation and mTOR activation. Moreover, NFPS treatment reduced the GluN2B expression after 6h, which was associated with an increase on CaMKIV and CREB phosphorylation. Collectively, these findings demonstrate that GlyT1 inhibition by NFPS activates diverse neuroprotective pathways, enhancing long-term potentiation signaling and countering amyloid-β-induced hippocampal damage.

The SLC6A18 Transporter Is Most Likely a Na-Dependent Glycine/Urea Antiporter Responsible for Urea Secretion in the Proximal Straight Tubule: Influence of This Urea Secretion on Glomerular Filtration Rate.

Urea is the major end-product of protein metabolism in mammals. In carnivores and omnivores, a large load of urea is excreted daily in urine, with a concentration that is 30-100 times above that in plasma. This is important for the sake of water economy. Too little attention has been given to the existence of energy-dependent urea transport that plays an important role in this concentrating activity. This review first presents functional evidence for an energy-dependent urea secretion that occurs exclusively in the straight part of the proximal tubule (PST). Second, it proposes a candidate transmembrane transporter responsible for this urea secretion in the PST. SLC6A18 is expressed exclusively in the PST and has been identified as a glycine transporter, based on findings in SLC6A18 knockout mice. We propose that it is actually a glycine/urea antiport, secreting urea into the lumen in exchange for glycine and Na. Glycine is most likely recycled back into the cell via a transporter located in the brush border. Urea secretion in the PST modifies the composition of the tubular fluid in the thick ascending limb and, thus, contributes, indirectly, to influence the "signal" at the macula densa that plays a crucial role in the regulation of the glomerular filtration rate (GFR) by the tubulo-glomerular feedback. Taking into account this secondary active secretion of urea in the mammalian kidney provides a new understanding of the influence of protein intake on GFR, of the regulation of urea excretion, and of the urine-concentrating mechanism.

Inhibition of astrocytic glycine transporter-1: friend or foe for ameliorating NMDA receptor hypofunction?

Inhibition of astrocytic glycine transporter-1: friend or foe for ameliorating NMDA receptor hypofunction?

Decreased inhibition of ventral brainstem liver-related neurons in high-fat diet fed mice

Pre-sympathetic liver-related neurons in the ventrolateral and ventromedial medulla (VLM/VMM) participate in the regulation of hepatic carbohydrate and lipid metabolism. Increased sympathetic activity observed in diet-induced obese mice likely contributes to excessive hepatic glucose production, and thus to the development, and/or progression of type 2 diabetes mellitus. At the cellular level, change in neuronal activity and/or synaptic balance is one of the underlying mechanisms that can lead to increased sympathetic outflow. In this study, we tested the hypothesis that high-fat diet (HFD) diminishes glycinergic inhibition of liver-related neurons in the VLM/VMM. We crossed heterozygous glycine transporter 2 Cre (GlyT2Cre) mice with floxed channelrhodopsin 2 (ChR2-EYFP) mice to generate GlyT2-ChR2 expressing mice (GlyT2ChR2/EYFP). Liver-related neurons were identified in the VLM/VMM with a retrograde viral tracer and patch-clamp recordings were conducted. Whole-cell recordings from pre-sympathetic, liver-related neurons revealed that spontaneous inhibitory postsynaptic currents (sIPSCs) are mediated by GABA and glycine. Our data showed that increasing the activity of inhibitory inputs leads to increased glycine release. Next, light stimulation was used to trigger glycine release in GlyT2ChR2/EYFP mice. Light stimulation of ChR2-expressing glycinergic fibers triggered evoked IPSCs (eIPSCs) generated by co-release of GABA and glycine with identical time courses for the two neurotransmitters. Intriguingly, in HFD-fed mice we found that the amplitude of light evoked IPSCs was significantly decreased. These data suggest that liver-related neurons in the VLM/VMM are co-inhibited by GABA and glycine and in HFD-fed mice inhibition of liver-related neurons is reduced. This reduced inhibition of ventral brainstem neurons may contribute to increased sympathetic activity in diet-induced obesity. Supported by: NIDDK122842 and Tulane Brain Institute Marko Spark Innovation Research Fund. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Deciphering the role of brainstem glycinergic neurons during startle and prepulse inhibition

Prepulse inhibition (PPI) of the auditory startle response, a key measure of sensorimotor gating, diminishes with age and is impaired in various neurological conditions. While PPI deficits are often associated with cognitive impairments, their reversal is routinely used in experimental systems for antipsychotic drug screening. Yet, the cellular and circuit-level mechanisms of PPI remain unclear, even under non-pathological conditions. We recently showed that brainstem neurons located in the caudal pontine reticular nucleus (PnC) expressing the glycine transporter type 2 (GlyT2±) receive inputs from the central nucleus of the amygdala (CeA) and contribute to PPI but via an uncharted pathway. Here, using tract-tracing, immunohistochemistry and in vitro optogenetic manipulations coupled to field electrophysiological recordings, we reveal the neuroanatomical distribution of GlyT2± PnC neurons and PnC-projecting CeA glutamatergic neurons and we provide mechanistic insights on how these glutamatergic inputs suppress auditory neurotransmission in PnC sections. Additionally, in vivo experiments using GlyT2-Cre mice confirm that optogenetic activation of GlyT2± PnC neurons enhances PPI and is sufficient to induce PPI in young mice, emphasizing their role. However, in older mice, PPI decline is not further influenced by inhibiting GlyT2± neurons. This study highlights the importance of GlyT2± PnC neurons in PPI and underscores their diminished activity in age-related PPI decline.

Cryo-EM structure of the human Asc-1 transporter complex

The Alanine-Serine-Cysteine transporter 1 (Asc-1 or SLC7A10) forms a crucial heterodimeric transporter complex with 4F2hc (SLC3A2) through a covalent disulfide bridge. This complex enables the sodium-independent transport of small neutral amino acids, including L-Alanine (L-Ala), Glycine (Gly), and D-Serine (D-Ser), within the central nervous system (CNS). D-Ser and Gly are two key endogenous glutamate co-agonists that activate N-methyl-d-aspartate (NMDA) receptors by binding to the allosteric site. Mice deficient in Asc-1 display severe symptoms such as tremors, ataxia, and seizures, leading to early postnatal death. Despite its physiological importance, the functional mechanism of the Asc-1-4F2hc complex has remained elusive. Here, we present cryo-electron microscopy (cryo-EM) structures of the human Asc-1-4F2hc complex in its apo state, D-Ser bound state, and L-Ala bound state, resolved at 3.6 Å, 3.5 Å, and 3.4 Å, respectively. Through detailed structural analysis and transport assays, we uncover a comprehensive alternating access mechanism that underlies conformational changes in the complex. In summary, our findings reveal the architecture of the Asc-1 and 4F2hc complex and provide valuable insights into substrate recognition and the functional cycle of this essential transporter complex.

Preliminary data from the CONNEX-X extension trial examining the long-term safety of iclepertin in patients with schizophrenia who completed Phase III CONNEX trials

IntroductionCognitive impairment associated with schizophrenia (CIAS) is an important unmet need as there are no effective treatments available. Iclepertin (BI 425809), a glycine transporter-1 inhibitor, has been shown to improve CIAS in Phase II trials, and Phase III trials are underway.ObjectivesThe ongoing CONNEX-X extension study aims to collect additional safety data relating to iclepertin treatment in patients with CIAS.MethodsCONNEX-X (NCT05211947/1346-0014) is a multinational, multicentre, open-label, single-arm extension study in patients with CIAS who completed 26 weeks of treatment (iclepertin 10 mg or placebo) in one of 3 Phase III CONNEX parent trials (NCT04846868/1346-0011, NCT04846881/1346-0012, NCT04860830/1346-0013). An estimated 1400 clinically stable outpatients will be treated (iclepertin 10 mg daily) for 1 year, irrespective of previous treatment (iclepertin/placebo). Patients are excluded if any of the following circumstances occur during the parent study and up to Visit 1 of CONNEX-X: suicidal behaviour or ideation (type 5 on the Columbia-Suicide Severity Rating Scale), diagnosis with moderate/severe substance use disorder, diagnosis other than schizophrenia (according to Diagnostic and Statistical Manual of Mental Disorders – Fifth Edition), development of any condition preventing participation, a haemoglobin level decrease (>25% or <100g/L from baseline in parent trial) or haemoglobinopathies. The primary endpoint is the occurrence of treatment-emergent adverse events. The secondary endpoints include change from baseline (CfB) in Clinical Global Impressions-Severity (CGI-S) and CfB in haemoglobin. Further efficacy endpoints include CfB in MATRICS Consensus Cognitive Battery (MCCB) overall composite T-score, CfB in Schizophrenia Cognition Rating Scale total score and CfB in Virtual Reality Functional Capacity Assessment Tool (VRFCAT) total times.ResultsCurrently, 460 patients have been enrolled and randomised from the parent trials with 0% screening failures (-80% roll-over rate, 30 August 2023). Current study status, including recruitment, screening failures and data collection experiences, are presented.ConclusionsPatient enrolment rates from the CONNEX trials to the CONNEX-X open-label extension study are stable. CONNEX-X will allow the exploration of long-term safety, as well as descriptive analyses of cognitive and functional endpoints of iclepertin in the treatment of CIAS.FundingBoehringer IngelheimDisclosure of InterestC. Reuteman-Fowler Employee of: Boehringer Ingelheim Pharmaceuticals, Inc., Z. Blahova Employee of: Boehringer Ingelheim RCV GmbH & Co. KG, S. Marder Consultant of: Boehringer Ingelheim Pharma GmbH, Merck, Biogen and Sunovion, S. Ikezawa Consultant of: Boehringer Ingelheim Pharma GmbH, Lundbeck, Takeda Pharma, Sumitomo Dainippon Pharma, Employee of: International University of Health and Welfare, Mita Hospital, Tokyo, Japan, P. Falkai Consultant of: Boehringer Ingelheim Pharma GmbH, Boehringer Ingelheim Pharma advisory board

The Phase III CONNEX programme assessing the efficacy and safety of iclepertin in patients with schizophrenia: Trial design and recruitment update

IntroductionIn a 12-week, Phase II (NCT02832037) trial, iclepertin (BI 425809), an inhibitor of glycine transporter-1, was generally well tolerated and significantly improved cognition in 509 patients with schizophrenia.ObjectivesThe Phase III CONNEX programme aims to confirm the efficacy, safety and tolerability of iclepertin in improving cognition and functioning across a larger cohort of patients with schizophrenia.MethodsThe CONNEX programme includes 3 randomised, double-blind, placebo-controlled parallel group trials in patients with schizophrenia (NCT04846868, NCT04846881, NCT04860830) receiving stable antipsychotic treatment. Each trial aims to recruit ˜586 patients, 18–50 years old, treated with 1–2 antipsychotic medications (≥12 weeks on current drug and ≥35 days on current dose before treatment) who have functional impairment in day-to-day activities and interact ≥1 hour per week with a designated study partner. Patients with cognitive impairment due to developmental, neurological or other disorders, with a current DSM-5 diagnosis other than schizophrenia or receiving cognitive remediation therapy within 12 weeks prior to screening, will be excluded. Patients will be recruited from multiple centres across 41 countries in Asia, North and South America, Europe and the Asia-Pacific Region, and randomised 1:1 to receive either iclepertin 10 mg (oral administration; n=293), or placebo (n=293) once daily for 26 weeks. The primary endpoint is change from baseline in overall composite T-score of the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery. The key secondary endpoints are change from baseline in total score on the Schizophrenia Cognition Rating Scale and change from baseline in the adjusted total time T-score in the Virtual Reality Functional Capacity Assessment Tool.ResultsThe CONNEX programme is currently recruiting (Table); the first patients were enrolled in Aug–Sept 2021 and completion is expected in Q1 2025. The presentation will describe the current study status, information relating to screening failures, and the experience of collecting these data as part of a large multi-country, multicentre study.Table.The number of patients recruited by 31 August 2023CONNEX 1CONNEX 2CONNEX 3Screened565521493Randomised409360350Completed trial medication202184191ConclusionsIclepertin may represent the first efficacious medication for cognitive impairment associated with schizophrenia.FundingBoehringer IngelheimDisclosure of InterestC. Reuteman-Fowler Employee of: Boehringer Ingelheim, Z. Blahova Employee of: Boehringer Ingelheim, S. Ikezawa Consultant of: Boehringer Ingelheim Pharma GmbH, Lundbeck, Takeda Pharma, Sumitomo Dainippon Pharma, Employee of: International University of Health and Welfare, Mita Hospital, Tokyo, Japan, S. Marder Consultant of: Boehringer Ingelheim Pharma GmbH, Merck, Biogen and Sunovion, P. Falkai Consultant of: Boehringer Ingelheim Pharma GmbH, Boehringer Ingelheim Pharma Advisory Board, J. H. Krystal Shareolder of: Freedom Biosciences, Inc., Biohaven Pharmaceuticals, Sage Pharmaceuticals, Spring Care, Biohaven Pharmaceuticals Medical Sciences, EpiVario, RBNC Therapeutics, Terran Biosciences and Tempero Bio, Consultant of: Aptinyx, Atai Life Sciences, AstraZeneca Pharmaceuticals, Biogen, Biomedisyn Corporation, Bionomics, Boehringer Ingelheim International, Cadent Therapeutics, Clexio Bioscience, COMPASS Pathways, Concert Pharmaceuticals, Epiodyne, EpiVario, Greenwich Biosciences, Heptares Therapeutics, Janssen, Jazz Pharmaceuticals, Otsuka America Pharmaceutical, Perception Neuroscience Holdings, Spring Care, Sunovion Pharmaceuticals, Takeda Industries, Taisho Pharmaceutical Co.; Biohaven Pharmaceuticals, BioXcel Therapeutics, Cadent Therapeutics, Cerevel Therapeutics, Delix Therapeutics, EpiVario, Eisai, Jazz Pharmaceuticals, Novartis, PsychoGenics, RBNC Therapeutics, Tempero Bio and Terran Biosciences Advisory Boards

3H]-NFPS binding to the glycine transporter 1 in the hemi-parkinsonian rat brain.

L-3,4-dihydroxyphenylalanine (L-DOPA) is the main treatment for Parkinson's disease (PD) but with long term administration, motor complications such as dyskinesia are induced. Glycine transporter 1 (GlyT1) inhibition was shown to produce an anti-dyskinetic effect in parkinsonian rats and primates, coupled with an improvement in the anti-parkinsonian action of L-DOPA. The expression of GlyT1 in the brain in the dyskinetic state remains to be investigated. Here, we quantified the levels of GlyT1 across different brain regions using [3H]-NFPS in the presence of Org-25,935. Brain sections were chosen from sham-lesioned rats, L-DOPA-naïve 6-hydroxydopamine (6-OHDA)-lesioned rats and 6-OHDA-lesioned rats exhibiting mild or severe abnormal involuntary movements (AIMs). [3H]-NFPS binding decreased in the ipsilateral and contralateral thalamus, by 28% and 41%, in 6-OHDA-lesioned rats with severe AIMs compared to sham-lesioned animals (P < 0.01 and 0.001). [3H]-NFPS binding increased by 21% in the ipsilateral substantia nigra of 6-OHDA-lesioned rats with severe AIMs compared to 6-OHDA-lesioned rats with mild AIMs (P < 0.05). [3H]-NFPS binding was lower by 19% in the contralateral primary motor cortex and by 20% in the contralateral subthalamic nucleus of 6-OHDA-lesioned rats with mild AIMs animals compared to rats with severe AIMs (both P < 0.05). The severity of AIMs scores positively correlated with [3H]-NFPS binding in the ipsilateral substantia nigra (P < 0.05), ipsilateral entopeduncular nucleus (P < 0.05) and contralateral primary motor cortex (P < 0.05). These data provide an anatomical basis to explain the efficacy of GlyT1 inhibitors in dyskinesia in PD.

Abstract 1792: Synthetic lethal vulnerabilities stemming from inhibition of one carbon metabolism in anaplastic thyroid cancer

Abstract Reprogramming of metabolic processes by tumor cells is essential to cope with their increased proliferative activity, and with the challenges of the unique microenvironment they inhabit. These metabolic alterations are attractive targets to design novel therapeutic approaches.The most aggressive subtype of thyroid cancer, Anaplastic Thyroid Cancer (ATC), is often unresectable at presentation, highly resistant to therapy and usually lethal. We have recently discovered that ATCs overexpress several genes encoding enzymes involved in one-carbon metabolism (1C-Met), which utilizes serine and dietary folates to produce glycine and tetrahydrofolate-bound one-carbon units, required for nucleotide biosynthesis and for NADPH and glutathione (GSH) production. We have shown that i) the increased activity of the 1C-Met pathway supports the high purine demand of ATC; ii) inhibition of 1C-Met impairs tumor growth in vitro and in vivo, leading to growth arrest; iii) inhibition of 1C-Met renders thyroid cancer cells glycine-auxotroph.We now demonstrate that the profound addiction of ATC cells to 1C-Met creates a series of targetable vulnerabilities that can be harnessed to induce massive ATC cell death.Our new data demonstrate that:1- The purine depletion consequent impaired 1C-Met induces replicative stress and triggers the DNA Damage Response (DDR). Activation of DDR, coupled with the absence of functional TP53 in the vast majority of ATCs, leads to synthetic lethality between inhibition of 1C-Met and G2/M checkpoint kinases.2- Inhibition of 1C-Met in ATC cells generates an absolute dependence on extracellular glycine uptake. We have identified and validated the main glycine transporter(s) in ATC cells and show that inhibition of 1C-Met is synthetic lethal with inhibition of glycine uptake.3- Impaired 1C-Met leads to increased oxidative stress and decrease of NADPH and glutathione levels. These alterations create a synthetic lethality relationship with the glutathione-depleting activity of PRIMA-1 (APR246), a small molecule originally identified as a compound restoring mutant p53 conformation and function, but later shown to be converted within cells into the reactive electrophile methylene quinuclidinone, which acts in a p53-independent manner through a variety of mechanisms, including reduction of cellular GSH levels.Our data shed light on the molecular consequences of 1C-Met upregulation in ATC and support the efficacy of novel rationally designed therapeutic approaches with curative intent not only for ATC, but also for other aggressive, dedifferentiated solid tumors. Citation Format: Alexander Forrest, Anil Ahsan, Antonio Di Cristofano. Synthetic lethal vulnerabilities stemming from inhibition of one carbon metabolism in anaplastic thyroid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1792.