Glycine Transporter Inhibitors Research Articles

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

Molecular mechanisms underlying sex and treatment-dependent differences in an animal model of cue-exposure therapy for cocaine relapse prevention.

Environmental enrichment combined with the glycine transporter-1 inhibitor Org24598 (EE+ORG) during cocaine-cue extinction (EXT) inhibited reacquisition of 1.0 mg/kg cocaine self-administration in male but not female rats in a previous investigation. In this investigation, we determined if this treatment benefit in males required EXT training and ascertained the molecular basis for the observed sex difference in treatment efficacy. Nine groups of male rats trained to self-administer 1.0 mg/kg cocaine or receiving yoked-saline underwent EXT or NoEXT with or without EE and/or ORG. Next, they underwent reacquisition of cocaine self-administration or were sacrificed for molecular analysis of 9 protein targets indicative of neuroplasticity in four brain regions. Two groups of female rats trained to self-administer 1.0 mg/kg cocaine also underwent EXT with or without EE + ORG and were sacrificed for molecular analysis, as above. EE + ORG facilitated the rate of EXT learning in both sexes, and importantly, the therapeutic benefit of EE + ORG for inhibiting cocaine relapse required EXT training. Males were more sensitive than females to neuroplasticity-inducing effects of EE + ORG, which prevented reductions in total GluA1 and PSD95 proteins selectively in basolateral amygdala of male rats trained to self-administer cocaine and receiving EXT. Females were deficient in expression of multiple protein targets, especially after EE + ORG. These included total GluA1 and PSD95 proteins in basolateral amygdala, and total TrkB protein in basolateral amygdala, dorsal hippocampus, and ventromedial prefrontal cortex. Together, these results support the clinical view that sex-specific pharmacological and behavioral treatment approaches may be needed during cue exposure therapy to inhibit cocaine relapse.

A Phase I/II, Intra-Patient Dose-Escalation Study of Bitopertin, a Selective Inhibitor of GlyT1 and Heme Synthesis, for Steroid-Refractory Diamond-Blackfan Anemia

Background: Diamond-Blackfan anemia (DBA) is a heritable bone marrow failure disorder characterized by macrocytic anemia with reticulocytopenia and bone marrow erythroid hypoplasia, usually presenting within the first two years of life. Treatment consists of systemic corticosteroids. Treatment failure or steroid intolerance occurs in approximately half of all cases, necessitating chronic transfusions, which carry the risks of iron overload and infections. Hematopoietic cell transplant remains the sole curative therapy for DBA. In cases where a causative mutation can be identified, with rare exceptions, the affected genes encode ribosomal proteins (RPs), defining DBA as prototypic haploinsufficient ribosomopathy. Erythrocyte hemoglobinization requires balanced heme synthesis and globin translation. Various in vitro and animal models suggest that RP insufficiency results in reduced ribosomal biogenesis, disrupting this balance and leading to excess of heme, resulting in toxicity to developing erythroid cells and premature termination of erythroid differentiation. Bitopertin is an investigational, orally administered, inhibitor of the GlyT1 glycine transporter. Outside the central nervous system (CNS), GlyT1 is expressed almost exclusively on developing erythrocytes. By reducing intracellular glycine, a rate-limiting substrate for heme synthesis, bitopertin slows heme synthesis and thus we hypothesize rebalances hemoglobin synthesis. In preclinical DBA models, bitopertin rescues erythropoiesis. The drug was originally developed for CNS indications, and has been shown to exhibit a favorable safety profile in prior studies with cumulative enrollment of over 4,000 patients and healthy volunteers. It is currently under clinical investigation for the treatment of erythropoietic protoporphyria. Study Design and Methods: This is a phase I/II, intra-patient dose-escalation study of bitopertin for steroid-refractory DBA, conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, Maryland. Subjects visit the NIH for initial evaluation and eligibility assessment and at the primary endpoint, with interim follow-up conducted via telehealth and local laboratory assessments. Subjects must be 18 years of age or and older, diagnosed with DBA and with clinically significant anemia (hemoglobin < 9/dL and/or requiring 2 units PRBC per 8 weeks). They must have relapsed and/or steroid refractory disease or be intolerant of systemic steroids, and be without significant comorbidities. Ongoing transfusions and chelation therapy are allowed, but other DBA-directed therapy, most notably steroids and growth factors, are not. Each subject will take oral bitopertin daily, escalating the dose monthly (5 mg, 10 mg, 20 mg, 40mg, and 60 mg) until reaching either the study maximum dose of 60 mg, the minimum effective dose (MED), or the maximum tolerated dose (MTD). Subjects will be followed for 8 months (32 weeks), including a minimum of 4 months (16 weeks) at the final dose (MED, MTD or study maximum). Response will be assessed on an ongoing basis and will be defined as an increase in hemoglobin ≥by 1.5 g/dL and/or a reduction in the units of PRBC transfusions by ≥50% from baseline. Furthermore, a robust response will be defined as a hemoglobin ≥10 g/dL and transfusion independence for 8 weeks. Patients with response (robust or non) by the 8-month primary endpoint will be allowed to continue extended therapy for 3 additional years. The primary endpoint is erythroid response. Secondary endpoints include safety as defined by the toxicity profile over 8 months of therapy and on extended therapy, relapse, survival, clonal evolution, health-related quality of life, and ancillary laboratory studies including the impact of bitopertin upon erythroid cell dynamics. The study employs a minmax design. A minimum of 15 patients will be enrolled. If the minimum efficacy threshold is met or surpassed (≥13% response rate), an additional 10 patients will be enrolled. Status: This study has been granted an FDA IND (165778) and is open for enrollment. It is monitored under the NIH Institutional Review Board (001528-H) and is registered with the U.S. National Library of Medicine (NCT05828108). Funding: This study is supported by the NHLBI Division of Intramural Research and in part through a Cooperative Research and Development Agreement (CRADA) with Disc Medicine, Inc. (Watertown, MA).

Novel Phenylene Lipids That Are Positive Allosteric Modulators of Glycine Receptors and Inhibitors of Glycine Transporter 2.

Chronic pain is a complex condition that remains resistant to current therapeutics. We previously synthesized a series of N-acyl amino acids (NAAAs) that inhibit the glycine transporter, GlyT2, some of which are also positive allosteric modulators of glycine receptors (GlyRs). In this study, we have synthesized a library of NAAAs that contain a phenylene ring within the acyl tail with the objective of improving efficacy at both GlyT2 and GlyRs and also identifying compounds that are efficacious as dual-acting modulators to enhance glycine neurotransmission. The most efficacious positive allosteric modulator of GlyRs was 2-[8-(2-octylphenyl)octanoylamino]acetic acid (8-8 OPGly) which potentiates the EC5 for glycine activation of GlyRα1 by 1500% with an EC50 of 664 nM. Phenylene-containing NAAAs with a lysine headgroup were the most potent inhibitors of GlyT2 with (2S)-6-amino-2-[8-(3-octylphenyl)octanoylamino]hexanoic acid (8-8 MPLys) inhibiting GlyT2 with an IC50 of 32 nM. The optimal modulator across both proteins was (2S)-6-amino-2-[8-(2-octylphenyl)octanoylamino]hexanoic acid (8-8 OPLys), which inhibits GlyT2 with an IC50 of 192 nM and potentiates GlyRs by up to 335% at 1 μM. When tested in a dual GlyT2/GlyRα1 expression system, 8-8 OPLys caused the greatest reductions in the EC50 for glycine. This suggests that the synergistic effects of a dual-acting modulator cause greater enhancements in glycinergic activity compared to single-target modulators and may provide an alternate approach to the development of new non-opioid analgesics for the treatment of chronic pain.

Combining Iclepertin (BI 425809) With Computerized Cognitive Training in Patients With Schizophrenia: Baseline Data From an Ongoing Phase II Trial

AbstractIntroductionThere are currently no approved pharmacotherapies to treat cognitive impairment associated with schizophrenia (CIAS). Iclepertin (BI 425809) is a novel glycine transporter-1 inhibitor under development for treatment of CIAS. A previous study demonstrated pro-cognitive effects of iclepertin in patients with schizophrenia; however, concurrent cognitive stimulation could in theory enhance any pro-cognitive pharmacological effects on neuroplasticity. We present preliminary demographics and baseline data from a trial exploring the efficacy of iclepertin together with at-home computerized cognitive training (CCT).MethodsThis is an ongoing Phase II, double-blind, placebo-controlled, parallel-group trial in patients with schizophrenia on stable antipsychotic therapy across ~58 centers in 6 countries. Patients aged 18–50 years, compliant with CCT during the run-in period (completing ≥2 hours/week for 2 weeks), were randomized (1:1) to receive once-daily iclepertin 10 mg or placebo together with CCT for 12 weeks. Thereafter, minimum compliance for at-home CCT is 1 hour/week, with a target of ~30 hours across 3–5 sessions totaling 2.5 hours/week. Patients have been stratified to balance potential effects of age (18–40; 41–50 years). Primary endpoint is change from baseline (CfB) in neurocognitive composite T-score of the MATRICS Consensus Cognitive Battery (MCCB) at Week 12. Secondary endpoints include CfB in the Schizophrenia Cognition Rating Scale (SCoRS) total score, MCCB overall composite T-score, and Positive and Negative Syndrome Scale (PANSS) total scores. Novel exploratory endpoints include the Virtual Reality Functional Capacity Assessment Tool to assess daily functioning and the Balloon Effort Task to assess motivation in cognitive performance.ResultsOf the planned sample of 200 randomized patients, the overall treated population currently includes 183: 67% (n=122) are male; mean (standard deviation [SD]) age and time since first diagnosis are 38.2 (7.9) years and 13.5 (8.5) years. Overall, 49% (n=89) are White and 43% (n=79) are Black or African American; 80% (n=147) are from North America, 15% (n=28) from Europe, and 4% (n=8) from Australia/New Zealand. Mean (SD) baseline MCCB neurocognitive composite and overall T-scores (n=178) are 33.7 (11.9) and 32.5 (12.6). Mean (SD) baseline SCoRS total score (n=167) is 35.2 (8.7). Mean (SD) baseline PANSS total and negative symptom scale scores (n=183) are 64.7 (14.6) and 17.3 (5.4). Median (Q1, Q3) CCT compliance over the on-treatment period for patients who have completed or discontinued early is 2.00 (1.21, 2.51) hours/week.ConclusionThis trial is, to our knowledge, the largest of its kind combining daily pharmacotherapy for CIAS with at-home CCT. It will indicate whether iclepertin together with concurrent cognitive stimulation provides enhanced cognitive benefit, and whether any improvements in neurocognition can translate into improved measures of daily functioning in patients.FundingBoehringer Ingelheim International GmbH (NCT03859973/1346-0038)

Efficacy and safety of the novel GlyT1 inhibitor BI 425809 in Alzheimer’s dementia: a randomized controlled trial

BackgroundThis phase II proof-of-concept study assessed the efficacy and safety of BI 425809, a novel selective glycine transporter-1 inhibitor, for the treatment of cognitive impairment associated with probable Alzheimer’s disease dementia.MethodsThis 12-week, multicenter, double-blind, placebo-controlled, parallel-group study randomized (1:1:1:1:1) patients with mild-to-moderate probable Alzheimer’s disease dementia to BI 425809 2, 5, 10, and 25 mg or placebo once daily. The primary efficacy endpoint was the change from baseline in Alzheimer’s Disease Assessment Scale-Cognitive Subscale 11-item total score after 12 weeks of treatment. Safety was also assessed.ResultsSix hundred and ten male and female patients were randomized to BI 425809 2 mg (n = 123), 5 mg (n = 122), 10 mg (n = 122), and 25 mg (n = 123) or placebo (n = 120). Approximately 47% (n = 286) were male; the mean (standard deviation) age was 72.9 (7.7) years. Treatment compliance was above 97% for all dose groups. The Mini-Mental State Examination category on the median score was < 22 in 47% (n = 287) of patients and ≥ 22 in 53% (n = 322) of patients. No significant, non-flat dose–response relationship was detected for the primary endpoint (adjusted p-value > 0.76 for all models). BI 425809 was generally well-tolerated. Overall, 47.9% (n = 292) of patients reported at least one adverse event during the trial; the frequency of patients with investigator-defined drug-related adverse events was similar in all treatment groups, ranging from 15.4 to 19.5% across the BI 425809 treatment groups and 15.8% for placebo.ConclusionsNo clinically meaningful changes from baseline were observed following treatment with BI 425809 in patients with mild-to-moderate probable Alzheimer’s disease dementia.Trial registrationClinicalTrials.gov NCT02788513 (1346-0023). Registered on June 2, 2016. EU Clinical Trials Register 2015-005438-24. Registered on May 6, 2016

Sarcosine (glycine transporter inhibitor) attenuates behavioural and biochemical changes induced by ketamine, in the rat model of schizophrenia

Schizophrenia is a neurological disorder that alters the behavior and affects the quality of life of a patient. It is characterized by hallucinations, disorganized behavior, cognitive dysfunction, hyperlocomotion, and loss of the reward system. Schizophrenia constitutes three symptoms' domains, viz. positive, negative and cognitive. Typical and atypical antipsychotics do not fully resolve all the symptoms' domains thus paving the way to the genesis of the glutamatergic hypothesis, i.e. N-methyl-D-aspartate (NMDA) receptor hypofunction in the pathophysiology of schizophrenia. Positive modulation of NMDA receptors by enhancing co-agonist, glycine effect is proposed to produce a therapeutic effect in schizophrenia. Hence, sarcosine (N-methyl glycine), natural amino acid, and a glycine transporter inhibitor (GlyT-1) which also acts on NMDA receptors were used in the present study. The present study unravels the role of sarcosine in the attenuation of ketamine-induced three symptom domains in a rat model through modulation of oxidative stress, mitochondrial dysfunction, and neuroinflammatory pathways. The animal model of schizophrenia was established by injecting ketamine intraperitoneal (ip) at a 30mg/kg dose for 10 consecutive days, after which sarcosine (300, 600mg/kg, ip) as a treatment was given for 7days followed by behavioral, biochemical, molecular, and histopathological analysis. It was revealed that sarcosine reversed ketamine-induced behavioral impairments. Moreover, sarcosine ameliorated oxidative and nitrosative stress, mitochondrial dysfunction, and neuroinflammation and showed protective effects in histopathological examination by hematoxylin and eosin staining. Hence, conclusively, sarcosine was regarded to attenuate the behavioural symptoms of schizophrenia by alleviating oxidative stress, neuroinflammation, and mitochondrial dysfunction established by the ketamine.

Phase 2, Randomized, Open-Label Trial of Bitopertin in Erythropoietic Protoporphyria: Beacon Trial Design

Background: Erythropoietic protoporphyria (EPP) caused by FECH and ALAS2 mutations results in toxic accumulation of photoreactive protoporphyrin IX (PPIX). High levels of PPIX result in excruciating phototoxic reactions and hepatopathy caused by biliary stasis. Reduction of PPIX is associated with amelioration of disease in the settings of hematopoietic stem cell transplant, pregnancy and extracorporeal photoinactivation. Bitopertin is a small molecule inhibitor of glycine transporter 1 (GlyT1), which imports large amounts of extracellular glycine into erythropoietic precursors. GlyT1 is needed to supply adequate amounts of substrate for the heme synthesis pathway to enable the large amounts of hemoglobin needed for normal red blood cell production. Treatment of EPP mouse models with FECH and ALAS2 mutations resulted in 45-73% reduction in PPIX, as compared to controls (Hong et al. 2021). These data, combined with a well-defined safety profile that has previously been established in over 4,000 patients and healthy volunteers motivates the current study to evaluate this potentially disease-modifying treatment. Study Design and Methods: This is a Phase 2, randomized, open-label, parallel arm trial of 20 and 60 mg bitopertin daily for 24 weeks in EPP patients. The trial is being conducted at 2 sites in Australia. The primary endpoint is percent change in metal-free PPIX. Secondary endpoints include patient reported outcomes of light tolerance, safety and tolerability, and PK parameters. Eligibility criteria include: age ≥18 years with EPP by FECH/ALAS2 genotyping or porphyrin analysis, AST/ALT <2x upper limit of normal, normal bilirubin, and hemoglobin ≥10 g/dL. Up to 22 participants will be randomized and stratified by baseline daily light tolerance (< or ≥ 30 minutes) and study site. Study sample size calculations were not performed for this first in EPP study. Endpoints will be summarized using descriptive statistics. Results: Subject enrollment began July 2022. Initial data will be presented at the meeting. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Quantitative electroencephalography parameters as neurophysiological biomarkers of schizophrenia-related deficits: A Phase II substudy of patients treated with iclepertin (BI 425809)

Patients with schizophrenia experience cognitive impairment related to neural network dysfunction and deficits in sensory processing. These deficits are thought to be caused by N-methyl-D-aspartate receptor hypofunction and can be assessed in patient populations using electroencephalography (EEG). This substudy from a Phase II, randomized, double-blind, placebo-controlled, parallel-group study investigating the safety and efficacy of the novel glycine transporter-1 inhibitor, iclepertin (BI 425809), assessed the potential of EEG parameters as clinically relevant biomarkers of schizophrenia and response to iclepertin treatment. Eligible patients were randomized to once-daily add-on iclepertin (2, 5, 10, or 25 mg), or placebo (1:1:1:1:2 ratio) for 12 weeks. EEG data were recorded from a subgroup of patients (n = 79) at baseline and end of treatment (EoT). EEG parameters of interest were mismatch negativity (MMN), auditory steady-state response (ASSR), and resting state gamma power, and their correlations with clinical assessments. At baseline, MMN and ASSR exhibited consistent correlations with clinical assessments, indicating their potential value as neurophysiological biomarkers of schizophrenia-related deficits. ASSR measures were positively correlated to the MATRICS Consensus Cognitive Battery overall and neurocognitive composite scores; MMN amplitude was positively correlated with Positive and Negative Syndrome Scale scores. However, correlations between change from baseline (CfB) at EoT in clinical assessments, and baseline or CfB at EoT for EEG parameters were modest and inconsistent between dose groups, which might indicate low potential of these EEG parameters as predictive and treatment response biomarkers. Further methodological refinement is needed to establish EEG parameters as useful drug development tools for schizophrenia.

Analysis of Binding Determinants for Different Classes of Competitive and Noncompetitive Inhibitors of Glycine Transporters.

Glycine transporters are interesting therapeutic targets as they play significant roles in glycinergic and glutamatergic systems. The search for new selective inhibitors of particular types of glycine transporters (GlyT-1 and GlyT-2) with beneficial kinetics is hampered by limited knowledge about the spatial structure of these proteins. In this study, a pool of homology models of GlyT-1 and GlyT-2 in different conformational states was constructed using the crystal structures of related transporters from the SLC6 family and the recently revealed structure of GlyT-1 in the inward-open state, in order to investigate their binding sites. The binding mode of the known GlyT-1 and GlyT-2 inhibitors was determined using molecular docking studies, molecular dynamics simulations, and MM-GBSA free energy calculations. The results of this study indicate that two amino acids, Gly373 and Leu476 in GlyT-1 and the corresponding Ser479 and Thr582 in GlyT-2, are mainly responsible for the selective binding of ligands within the S1 site. Apart from these, one pocket of the S2 site, which lies between TM3 and TM10, may also be important. Moreover, selective binding of noncompetitive GlyT-1 inhibitors in the intracellular release pathway is affected by hydrophobic interactions with Ile399, Met382, and Leu158. These results can be useful in the rational design of new glycine transporter inhibitors with desired selectivity and properties in the future.

Abstract 1803: Lethal synthesis: Potent anticancer activity of a glycine uptake inhibitor in tumor cells with mitochondrial methylenetetrahydrofolate dehydrogenase (MTHFD2) knocked down

Abstract Methylene tetrahydrofolate dehydrogenase 2 (MTHFD2) is a mitochondrial bifunctional enzyme with dehydrogenase and cyclohydrolase activity. MTHFD2 is expressed in embryonic tissues and not in adult tissues, and by generating formate for purine biosynthesis, enhances proliferation. It is over expressed in many cancers, including breast cancer, and has become an important cancer drug target. Knockdown (KD) of MTHFD2 in breast cancer cell lines MCF7 and T47D, slowed proliferation and resulted in an increase in early apoptosis and a S-phase block. Lack of MTHFD2 causes a dependence on glycine, and in the absence of glycine, proliferation of the MCF-7 cell line with MTHFD2 knocked down was inhibited even further. A known specific glycine transporter type-I (GlyT1) inhibitor, ORG 25935 potently inhibited growth of MCF7 cell with MTHFD2 KD, while it had less of an effect on T47D cells with MTHFD2 KD. Furthermore, both cell lines with MTHFD2 KD showed increase in expression of GlyT1 (SLC6A9) at both mRNA and protein level, using the qPCR and western blotting, respectively. The metabolomics studies showed that intracellular glycine, and NAD+ pools are more reduced in control cells compared to MTHFD2 KD cells on treatment with GlyT1 inhibitor, suggesting that this inhibitor causes glycine depletion in the cells. These data encourage the development of inhibitors of MTHFD2 for use in combination with glycine transport inhibitors. Citation Format: Gulam Mohmad Rather, Joseph R. Bertino. Lethal synthesis: Potent anticancer activity of a glycine uptake inhibitor in tumor cells with mitochondrial methylenetetrahydrofolate dehydrogenase (MTHFD2) knocked down [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1803.

Effects of the Glycine Transporter-1 Inhibitor Iclepertin (BI 425809) on Sensory Processing, Neural Network Function, and Cognition in Animal Models Related to Schizophrenia.

N-methyl-D-aspartate (NMDA) receptor hypofunction leading to neural network dysfunction is thought to play an important role in the pathophysiology of cognitive impairment associated with schizophrenia (CIAS). Increasing extracellular concentrations of the NMDA receptor co-agonist glycine through inhibition of glycine transporter-1 (GlyT1) has the potential to treat CIAS by improving cortical network function through enhanced glutamatergic signaling. Indeed, the novel GlyT1 inhibitor iclepertin (BI 425809) improved cognition in a recent clinical study in patients with schizophrenia. The present study tested the ability of iclepertin to reverse deficits in auditory sensory processing and cortical network function induced by the uncompetetive NMDA receptor antagonist, MK-801, using electroencephalography (EEG) to measure auditory event-related potentials (AERPs) and 40 Hz auditory steady-state response (ASSR). In addition, improvements in memory performance with iclepertin were evaluated using the T-maze spontaneous alternation test in MK-801-treated mice and the social recognition test in naïve rats. Iclepertin reversed MK-801-induced deficits in the AERP readouts N1 amplitude and N1 gating, as well as reversing deficits in 40 Hz ASSR power and intertrial coherence. Additionally, iclepertin significantly attenuated an MK-801-induced increase in basal gamma power. Furthermore, iclepertin reversed MK-801-induced working memory deficits in mice and improved social recognition memory performance in rats. Overall, this study demonstrates that inhibition of GlyT1 is sufficient to attenuate MK-801-induced deficits in translatable EEG parameters relevant to schizophrenia. Moreover, iclepertin showed memory-enhancing effects in rodent cognition tasks, further demonstrating the potential for GlyT1 inhibition to treat CIAS. SIGNIFICANCE STATEMENT: Despite the significant patient burden caused by cognitive impairment associated with schizophrenia, there are currently no approved pharmacotherapies. In this preclinical study, the novel glycine transporter inhibitor iclepertin (BI 425809) reversed sensory processing deficits and neural network dysfunction evoked by inhibition of N-methyl-D-aspartate receptors and enhanced working memory performance and social recognition in rodents. These findings support previous clinical evidence for the procognitive effects of iclepertin.

P.0526 Effects of the novel glycine transporter-1 inhibitor bi 425809 on mouse electroencephalography and auditory event-related potential biomarkers related to schizophrenia

P.0526 Effects of the novel glycine transporter-1 inhibitor bi 425809 on mouse electroencephalography and auditory event-related potential biomarkers related to schizophrenia

Screening for New Inhibitors of Glycine Transporter 1 and 2 by Means of MS Binding Assays.

A straightforward screening of a compound library comprising 2439 substances for the identification of new inhibitors for the neurotransmitter transporters GlyT1 and GlyT2 is described. Screening and full‐scale competition experiments were performed using recently developed GlyT1 and GlyT2 MS Binding Assays. That way for both targets, GlyT1 and GlyT2, ligands were identified, which exhibited affinities (pK i values) in the low micromolar to sub‐micromolar range. The majority of these binders exhibit new chemical scaffolds in the class of GlyT1 and GlyT2 inhibitors, which could be of interest for the development of new ligands with improved affinities for the target proteins. Additionally, compounds with excellent fluorescent properties were found for GlyT2, which renders them promising compounds for future fluorescence‐based techniques. All in all, this study demonstrates that MS Binding Assays represent a powerful technology platform also well suited for the screening of compound libraries in a highly reliable and effective manner.

Med Check: FDA Breakthrough Status for Schizophrenia Drug, Review of Oral Film for Agitation, and More

Med Check: FDA Breakthrough Status for Schizophrenia Drug, Review of Oral Film for Agitation, and More

Glycine transporter inhibitor promising for cognition in schizophrenia patients

Patients with schizophrenia who were randomized to the novel glycine transporter inhibitor BI 425809 saw significant improvement in cognition compared with placebo in a 12‐week Phase 2 study. The most promising results were reported for daily doses of 10 and 25 mg. Study results were published in the March 2021 issue of Lancet Psychiatry.

Repurposing of glycine transport inhibitors for the treatment of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is a rare disease in which patients experience severe light sensitivity. It is caused by a deficiency of ferrochelatase (FECH), the last enzyme in heme biosynthesis (HBS). The lack of FECH causes accumulation of its photoreactive substrate protoporphyrin IX (PPIX) in patients' erythrocytes. Here, we explored an approach for the treatment of EPP by decreasing PPIX synthesis using small-molecule inhibitors directed to factors in the HBS pathway. We generated a FECH-knockout clone from K562 erythroleukemia cells, which accumulates PPIX and undergoes oxidative stress upon light exposure. We used these matched cell lines to screen a set of publicly available inhibitors of factors in the HBS pathway. Inhibitors of the glycine transporters GlyT1 and GlyT2 lowered levels of PPIX and markers of oxidative stress selectively in K56211B4 cells, and in primary erythroid cultures from an EPP patient. Our findings open the door to investigation of glycine transport inhibitors for HBS disorders.

Pharmacological Evidence on Augmented Antiallodynia Following Systemic Co-Treatment with GlyT-1 and GlyT-2 Inhibitors in Rat Neuropathic Pain Model.

The limited effect of current medications on neuropathic pain (NP) has initiated large efforts to develop effective treatments. Animal studies showed that glycine transporter (GlyT) inhibitors are promising analgesics in NP, though concerns regarding adverse effects were raised. We aimed to study NFPS and Org-25543, GlyT-1 and GlyT-2 inhibitors, respectively and their combination in rat mononeuropathic pain evoked by partial sciatic nerve ligation. Cerebrospinal fluid (CSF) glycine content was also determined by capillary electrophoresis. Subcutaneous (s.c.) 4 mg/kg NFPS or Org-25543 showed analgesia following acute administration (30–60 min). Small doses of each compound failed to produce antiallodynia up to 180 min after the acute administration. However, NFPS (1 mg/kg) produced antiallodynia after four days of treatment. Co-treatment with subanalgesic doses of NFPS (1 mg/kg) and Org-25543 (2 mg/kg) produced analgesia at 60 min and thereafter meanwhile increased significantly the CSF glycine content. This combination alleviated NP without affecting motor function. Test compounds failed to activate G-proteins in spinal cord. To the best of our knowledge for the first time we demonstrated augmented analgesia by combining GlyT-1 and 2 inhibitors. Increased CSF glycine content supports involvement of glycinergic system. Combining selective GlyT inhibitors or developing non-selective GlyT inhibitors might have therapeutic value in NP.

Efficacy and safety of the novel glycine transporter inhibitor BI 425809 once daily in patients with schizophrenia: a double-blind, randomised, placebo-controlled phase 2 study

Cognitive impairment associated with schizophrenia predicts poor functional outcomes, but currently no approved pharmacotherapy is available. This study investigated whether the glycine transporter-1 inhibitor BI 425809 improves cognition in patients with schizophrenia. This phase 2, randomised, double-blind, placebo-controlled, parallel-group trial (81 centres, 11 countries), randomly assigned outpatients (aged 18-50 years) with schizophrenia on stable treatment to add-on once-daily oral BI 425809 2 mg, 5 mg, 10 mg, or 25 mg or placebo (1:1:1:1:2) for 12 weeks. Treatment was assigned in blocks using interactive response technology; patients, investigators, and all trial personnel were masked to group assignment. The primary endpoint was change from baseline in MATRICS Consensus Cognitive Battery (MCCB) overall composite T-score at week 12. Six predefined dose-response models were evaluated using a multiple comparison procedure and modelling approach with mixed model repeated measures to assess evidence for a non-flat dose-response relationship for cognitive improvements with BI 425809. Adverse events were monitored. Safety analyses included all randomly allocated patients who received one or more doses of trial medication; efficacy analyses included patients from this set who also had available baseline data and at least one post-baseline on-treatment measurement for the primary or secondary endpoint. This study is registered with ClinicalTrials.gov, number NCT02832037. 509 patients were randomly assigned between April 25, 2018, and Oct 4, 2019 (BI 425809 2 mg, n=85; 5 mg, n=84; 10 mg, n=85; 25 mg, n=85; placebo, n=170 444 (87%) completed the 12-week treatment. Five of six dose-response models showed a statistically significant benefit of BI 425809 over placebo (linear [t=2·55, p=0·015], linear in log [t=2·56, p=0·015]; Emax [t=2·75, p=0·0089], sigmoid Emax [t=2·98, p=0·0038], logistic [t=2·77, p=0·0085]). Pairwise comparisons showed greater mean improvement from baseline in MCCB overall composite T-score at week 12 with BI 425809 10 mg and 25 mg versus placebo (adjusted mean difference 1·98 [95% CI 0·43-3·53] for 10 mg and 1·73 [0·18-3·28] for 25 mg; standardised effect size 0·34 for 10 mg and 0·30 for 25 mg). Adverse events were balanced across groups, reported in 50 (59%) of 85 patients on BI 425809 2 mg, 44 (52%) of 84 on 5 mg, 35 (41%) of 85 on 10 mg, 36 (42%) of 85 on 25 mg, and 74 (44%) of 170 on placebo. BI 425809 improved cognition after 12 weeks in patients with schizophrenia; doses of 10 mg and 25 mg showed the largest separation from placebo. If these encouraging results are confirmed in phase 3 trials, BI 425809 could provide an effective treatment for cognitive impairment associated with schizophrenia. Boehringer Ingelheim.

Sex differences in the effects of a combined behavioral and pharmacological treatment strategy for cocaine relapse prevention in an animal model of cue exposure therapy

Brief interventions of environmental enrichment (EE) or the glycine transporter-1 inhibitor Org24598 administered with cocaine-cue extinction training were shown previously to inhibit reacquisition of cocaine self-administration in male rats trained to self-administer a moderate 0.3 mg/kg dose of cocaine. Determining how EE and Org24598 synergize in combination in an animal model of cue exposure therapy is novel. Important changes made in this investigation were increasing the cocaine training dose to 1.0 mg/kg and determining sex differences. Adult male and female rats self-administering 1.0 mg/kg cocaine for 35–40 daily sessions exhibited an addiction-like phenotype under a second-order schedule of cocaine delivery and cue presentation. Rats next underwent 6 weekly extinction training sessions for which treatments consisted of EE or NoEE and Vehicle or Org24598 (3.0 mg/kg in males; 3.0 or 7.5 mg/kg in females). Rats then were tested for reacquisition of cocaine self-administration for 15 daily sessions. In males, the combined EE +3.0 mg/kg Org24598 treatment facilitated extinction learning and inhibited reacquisition of cocaine self-administration to a greater extent than no treatment and to individual EE or 3.0 mg/kg Org24598 treatments. In females, EE +7.5 mg/kg Org24598 facilitated extinction learning, but did not inhibit reacquisition of cocaine self-administration. Thus, there were sex differences in the ability of EE + Org24598 administered in conjunction with extinction training to inhibit cocaine relapse in rats exhibiting an addiction-like phenotype. These findings suggest that this multimodal treatment approach might be a feasible option during cue exposure therapy in cocaine-dependent men, but not women.