Tag: NOVEL

  • LDN-193189

    Selective bone morphogenetic protein (BMP) type I receptor kinase inhibitor targeting ALK2 and ALK3

    A pyrazolopyrimidine-scaffold small molecule derived from dorsomorphin structure-activity optimization, selectively inhibiting BMP type I receptor kinases ALK2 and ALK3 at low-nanomolar potency with 200-fold selectivity over TGF-beta signaling, and widely adopted as a research tool for BMP pathway dissection, directed stem cell differentiation, and preclinical modeling of fibrodysplasia ossificans progressiva and diffuse intrinsic pontine glioma.

    Abstract

    LDN-193189 (DM-3189; CAS 1062368-24-4) is a cell-permeable, small-molecule inhibitor of bone morphogenetic protein (BMP) type I receptor serine/threonine kinases, developed through structure-activity relationship optimization of dorsomorphin at the Brigham and Women’s Hospital and Harvard Medical School laboratories of Paul B. Yu. The compound inhibits activin receptor-like kinase 2 (ALK2, also designated ACVR1) with an IC50 of approximately 5 nM and activin receptor-like kinase 3 (ALK3, also designated BMPR1A) with an IC50 of approximately 30 nM, while exhibiting approximately 200-fold selectivity for BMP receptors over the transforming growth factor-beta (TGF-beta) type I receptor ALK5 and negligible activity against ALK4 and ALK7 at concentrations below 500 nM. The mechanism of action involves competitive binding at the ATP-binding pocket of BMP type I receptor kinases, preventing receptor autophosphorylation and blocking downstream phosphorylation of the canonical signaling effectors Smad1, Smad5, and Smad8. In addition to canonical Smad pathway inhibition, LDN-193189 suppresses BMP-induced non-canonical signaling through the p38 mitogen-activated protein kinase (MAPK) and Akt (protein kinase B) pathways, providing broader coverage of BMP-dependent intracellular signaling than Smad-selective interventions alone.

    The compound originated from the 2008 Cuny, Yu, and colleagues structure-activity relationship study that optimized the pyrazolo[1,5-a]pyrimidine scaffold of dorsomorphin, a compound itself discovered in 2008 by Yu et al. through a phenotypic zebrafish embryo screen of approximately 7,500 bioactive compounds for agents that could dorsalize the developing embryo and thereby phenocopy loss-of-function mutations in the BMP signaling pathway. Dorsomorphin, while the first small-molecule BMP pathway inhibitor identified, exhibited substantial off-target activity against AMP-activated protein kinase (AMPK), vascular endothelial growth factor receptor 2 (VEGFR2), and platelet-derived growth factor receptor (PDGFR), limiting its utility as a selective BMP pathway probe. LDN-193189 retained the central pyrazolopyrimidine core but incorporated a quinoline moiety and a piperazinylphenyl substituent that conferred markedly improved potency and selectivity for BMP type I receptors over the off-target kinases that compromised dorsomorphin’s pharmacological profile.

    LDN-193189 has become one of the most widely used pharmacological tools for interrogating BMP signaling in developmental biology, stem cell biology, and disease modeling. In stem cell biology, the compound is a core component of the dual SMAD inhibition protocol (in combination with the TGF-beta/Activin/Nodal inhibitor SB431542) developed by Chambers et al. (2009) for the efficient directed differentiation of human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) toward neuroectodermal and neural progenitor fates, a protocol that has become the standard method for generating central nervous system neurons from human pluripotent stem cells. In disease modeling, the compound has been extensively characterized in preclinical models of fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder caused by gain-of-function mutations in the ACVR1/ALK2 gene that produce constitutive BMP pathway activation and progressive heterotopic ossification of soft tissues. Treatment of mice expressing constitutively active ALK2 with LDN-193189 reduced heterotopic bone formation in the landmark Yu et al. (2008) Nature Medicine study. The compound has also demonstrated preclinical efficacy in orthotopic xenograft models of diffuse intrinsic pontine glioma (DIPG) harboring ACVR1 mutations, extending survival in treated animals. Additional research applications span iron metabolism and hepcidin regulation (through BMP6-dependent Smad signaling in hepatocytes), pulmonary arterial hypertension modeling, chondrogenesis and osteogenesis research, and cancer biology.

    LDN-193189 has not entered human clinical trials and is not a registered medicine in any jurisdiction. The compound is classified as a research tool and is supplied by multiple commercial vendors (Selleck Chemicals, MedChemExpress, Cayman Chemical, Tocris, Sigma-Aldrich, Stemgent/REPROCELL, and others) as the free base or hydrochloride salt at greater than 98 percent purity. In vivo pharmacokinetic characterization in mice has demonstrated oral bioavailability and brain penetration sufficient for central nervous system target engagement, though metabolic liabilities including aldehyde oxidase-dependent metabolism and generation of reactive piperazinyl iminium intermediates have been identified as concerns for clinical translation and have motivated the development of next-generation analogs (LDN-212854, LDN-214117, ML347, DMH1, K02288) with improved selectivity or metabolic profiles. This monograph reviews the chemistry, synthesis, and structural pharmacology of LDN-193189; the molecular mechanism of BMP type I receptor kinase inhibition; the preclinical pharmacology across FOP, DIPG, stem cell, iron metabolism, and cancer applications; the pharmacokinetic and metabolic characterization; sourcing, reconstitution, and handling; stack interactions with other signaling pathway modulators; the adverse-event and safety signal from preclinical studies; and a comparative assessment of five alternative BMP pathway inhibitors against LDN-193189 on five competency standards.

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  • T3D-959

    Dual peroxisome proliferator-activated receptor delta/gamma (PPARd/g) agonist with primary PPARd selectivity and brain-penetrant insulin-sensitizing activity

    A non-thiazolidinedione dual nuclear receptor agonist originally developed for metabolic disease and repositioned as a first-in-class brain insulin-sensitizing therapy for Alzheimer’s disease, distinguished by concurrent PPARd and PPARg activation, high central nervous system penetrance, and Phase 2 evidence of disease-modifying effects on cognition and amyloid biomarkers.

    Abstract

    T3D-959 (DB-959, DB-959Na as the sodium salt) is an orally bioavailable, brain-penetrant, non-thiazolidinedione dual agonist of peroxisome proliferator-activated receptor delta (PPARd; human ED50 19 nM) and peroxisome proliferator-activated receptor gamma (PPARg; human ED50 297 nM), conferring approximately 15-fold selectivity for the delta isoform. The compound was originally synthesized by Bayer and advanced through Phase 1 clinical trials for dyslipidemia and type 2 diabetes by DARA BioSciences before being acquired in 2013 by T3D Therapeutics and repositioned as a disease-modifying candidate for Alzheimer’s disease (AD) on the basis of the “type 3 diabetes” hypothesis, which posits that sporadic AD is driven by progressive brain insulin resistance, deficient insulin and insulin-like growth factor signaling, and consequent neurometabolic dysfunction. T3D-959 is the first PPARd-activating compound to enter clinical development for AD and represents a mechanistically distinct approach from the anti-amyloid antibody and cholinesterase inhibitor classes that dominate the current AD therapeutic landscape. Preclinical characterization in the intracerebral streptozotocin (i.c. STZ) rat model of sporadic AD, conducted principally by the de la Monte laboratory at Brown University, demonstrated that oral T3D-959 at doses of 0.3 to 3.0 mg/kg/day preserved spatial learning and memory in the Morris water maze, prevented brain weight loss, normalized phosphorylated tau and amyloid precursor protein-amyloid beta 42 (AbPP-Ab42) levels, reduced markers of oxidative stress, and partially restored cholinergic enzyme expression and white matter integrity. Therapeutic effects were observed even when treatment was delayed seven days after the STZ insult, suggesting relevance to mild and moderate disease stages. A separate preclinical study demonstrated that T3D-959 at 1.0 mg/kg/day improved motor function and prevented cerebellar white matter atrophy in the same model. An exploratory Phase 2a clinical trial in 36 subjects with mild to moderate AD (Chamberlain et al. 2020) demonstrated safety and tolerability at oral doses of 3, 10, 30, and 90 mg daily for 14 days, with no serious adverse events. Pharmacokinetic analysis confirmed dose-dependent systemic exposure exceeding the PPARd ED50 at all doses tested. Plasma metabolomics showed dose-dependent reductions in branched-chain amino acids and ceramides and increases in acylcarnitines, consistent with improved insulin sensitivity and enhanced fatty acid beta-oxidation. FDG-PET neuroimaging demonstrated dose-dependent increases in regional cerebral glucose metabolism, with the strongest effects in the putamen, anterior cingulate, insula, and orbital frontal cortex. Cognitive assessments showed improvements on the ADAS-Cog11 at 30 mg and on the Digit Symbol Substitution Test at all doses, with a delayed improvement pattern consistent with a transcriptional regulatory mechanism of action and an apparent ApoE4 genotype interaction. The Phase 2 PIONEER trial, a 24-week multicenter randomized double-blind placebo-controlled study in 250 patients with mild to moderate AD, reported positive top-line results in November 2023 at the 16th Clinical Trials on Alzheimer’s Disease (CTAD) conference. In the modified intent-to-treat population (n=141), the 30 mg group showed improvement on ADAS-Cog11 (0.73 versus 2.70 on placebo; p=0.073), and the 15 mg group showed improvement on ADCS-CGIC (0.39 versus 0.86 on placebo; p=0.060). Plasma amyloid beta 42/40 ratio improved significantly in the 30 mg (p=0.011) and 45 mg (p=0.033) groups, and the neurodegeneration marker neurogranin improved significantly in the 30 mg group (p=0.035). The compound was well tolerated, with adverse event rates similar between active and placebo arms (37.3% versus 43.1%) and no treatment-related serious adverse events. A Phase 2b/3 trial (NCT06964230) at 30 mg daily for 78 weeks in approximately 376 patients with biomarker-validated mild to moderate AD is planned to initiate in 2026. T3D-959 is not approved for any indication in any jurisdiction. This monograph reviews the chemistry, dual-receptor pharmacology, preclinical evidence base, clinical development program, pharmacokinetics, sourcing, reconstitution, stack interactions, adverse-event signal, and a comparative assessment of five alternative PPAR-targeting and insulin-sensitizing candidates against T3D-959 on five competency standards.

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  • Olpasiran

    N-acetylgalactosamine-conjugated small interfering RNA (GalNAc-siRNA) targeting hepatic LPA messenger RNA for lipoprotein(a) reduction

    A synthetic, chemically modified, GalNAc-conjugated siRNA developed by Arrowhead Pharmaceuticals and licensed to Amgen that silences hepatic LPA gene expression through RNA interference, producing sustained and near-complete reduction of circulating lipoprotein(a) concentrations in patients with established atherosclerotic cardiovascular disease.

    Abstract

    Olpasiran (AMG 890; formerly ARO-LPA) is an investigational, first-in-class, synthetic double-stranded small interfering RNA (siRNA) conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand for selective hepatocyte delivery via the asialoglycoprotein receptor (ASGPR). The compound targets the messenger RNA transcribed from the LPA gene, which encodes apolipoprotein(a), the defining protein component of lipoprotein(a) [Lp(a)]. Elevated Lp(a) is a genetically determined, independent, and causal risk factor for atherosclerotic cardiovascular disease (ASCVD), aortic valve stenosis, and thrombotic events, affecting an estimated 20 to 30 percent of the global population at concentrations associated with increased cardiovascular risk. Prior to the development of RNA-targeted therapies, no pharmacologic intervention produced clinically meaningful reduction in Lp(a) concentration; niacin and PCSK9 inhibitors achieve modest decreases of 20 to 30 percent, insufficient to test the causal hypothesis relating Lp(a) lowering to cardiovascular event reduction.

    Following uptake into hepatocytes through ASGPR-mediated endocytosis, the antisense strand of olpasiran incorporates into the RNA-induced silencing complex (RISC), which catalytically cleaves LPA mRNA and suppresses de novo synthesis of apolipoprotein(a). The resulting reduction in hepatic apolipoprotein(a) secretion produces a dose-dependent, sustained, and near-complete lowering of circulating Lp(a) particles. In the Phase 1 single ascending-dose trial (NCT03626662), olpasiran produced dose-dependent Lp(a) reductions of 71 to 97 percent that persisted for several months after a single subcutaneous injection, with effects lasting up to six months at higher doses [1]. In the pivotal Phase 2 OCEAN(a)-DOSE trial (NCT04270760), a randomized, double-blind, placebo-controlled study in 281 patients with established ASCVD and Lp(a) greater than 150 nmol/L, olpasiran at doses of 75 mg or higher administered every 12 weeks produced placebo-adjusted Lp(a) reductions exceeding 95 percent at 36 weeks, with the 225 mg every-12-week regimen achieving a placebo-adjusted reduction of 101.1 percent [2]. The off-treatment extension analysis demonstrated that participants who received doses of 75 mg or higher every 12 weeks sustained approximately 40 to 50 percent Lp(a) reduction close to one year after the last dose, reflecting the durability of RISC-mediated mRNA silencing in hepatocytes [3].

    The serum pharmacokinetics of olpasiran are characterized by rapid absorption after subcutaneous injection (time to maximum concentration approximately 3 to 9 hours) and rapid clearance from the systemic circulation (serum half-life approximately 3 to 8 hours), consistent with efficient hepatocyte uptake via the GalNAc-ASGPR pathway. The pharmacodynamic effect is dissociated from serum drug concentrations: the prolonged Lp(a) lowering reflects the intracellular persistence of the active RISC complex in hepatocytes rather than circulating drug exposure. The compound is well tolerated. In the OCEAN(a)-DOSE trial, the overall incidence of adverse events was similar in the olpasiran and placebo arms; the most frequently reported treatment-related adverse event was mild injection-site pain, which resolved without intervention [2]. No clinically significant changes in hepatic, renal, hematologic, or glycemic laboratory parameters were observed.

    Olpasiran is currently under evaluation in the Phase 3 OCEAN(a)-Outcomes trial (NCT05581303), a large cardiovascular outcomes study assessing the effect of olpasiran versus placebo on the composite endpoint of coronary heart disease death, myocardial infarction, or urgent coronary revascularization in participants with ASCVD and elevated Lp(a). An additional Phase 3 primary prevention trial, OCEAN(a)-PreEvent (NCT07136012), is evaluating olpasiran for prevention of first major cardiovascular events. The compound is not approved by any regulatory authority as of the date of this monograph. This document reviews the chemistry and structural class of olpasiran; the biology of lipoprotein(a) and the LPA gene target; the GalNAc-siRNA delivery mechanism; the preclinical pharmacology in transgenic mice and cynomolgus monkeys; the comprehensive human pharmacokinetic and pharmacodynamic record; the clinical evidence base from Phase 1 through Phase 3; sourcing and handling considerations for research applications; stack interactions; adverse events and safety signal; and a structured comparative assessment of five Lp(a)-lowering candidates against olpasiran on five competency standards.

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  • CHIR-99021

    Highly selective aminopyrimidine glycogen synthase kinase 3 (GSK-3) inhibitor and canonical Wnt/beta-catenin signaling pathway activator

    A potent, orally active aminopyrimidine developed at Chiron Corporation as a selective dual-isoform GSK-3 inhibitor, distinguished by sub-10-nanomolar potency against both GSK-3alpha and GSK-3beta with greater than 500-fold selectivity over closely related kinases, and now the most widely deployed small-molecule Wnt pathway activator in stem cell biology, directed differentiation, chemical reprogramming, and regenerative medicine research.

    Abstract

    CHIR-99021 (CT99021, laduviglusib) is a synthetic aminopyrimidine derivative and the most potent and selective small-molecule inhibitor of glycogen synthase kinase 3 (GSK-3) in current research and clinical use, with half-maximal inhibitory concentrations of approximately 10 nM against GSK-3alpha and 6.7 nM against GSK-3beta. The compound was developed at Chiron Corporation in the early 2000s as part of a medicinal chemistry program targeting GSK-3 for the treatment of type 2 diabetes mellitus, and was first characterized in the seminal Ring et al. (2003) publication demonstrating that selective GSK-3 inhibition potentiates insulin-stimulated glucose transport and utilization both in vitro and in vivo [1]. CHIR-99021 achieves its selectivity through an aminopyrimidine scaffold bearing a 2,4-dichlorophenyl substituent and a 5-methyl-1H-imidazol-2-yl group, producing greater than 500-fold selectivity for GSK-3 over 20 closely related protein kinases and greater than 800-fold selectivity across a broader panel of 23 additional enzymes and 22 receptors [1, 2].

    The principal pharmacological consequence of GSK-3 inhibition by CHIR-99021 is stabilization of cytoplasmic beta-catenin through prevention of its phosphorylation-dependent proteasomal degradation. Accumulated beta-catenin translocates to the nucleus and transactivates Wnt-responsive genes through interaction with T-cell factor/lymphoid enhancer factor (TCF/LEF) family transcription factors, producing a pharmacological activation of the canonical Wnt/beta-catenin signaling pathway that is functionally equivalent to Wnt ligand stimulation. This mechanism has made CHIR-99021 the standard small-molecule Wnt pathway activator in stem cell biology and regenerative medicine, where it is deployed in the “2i” naive pluripotency medium (in combination with the MEK inhibitor PD0325901) for maintenance of mouse embryonic stem cells, in directed differentiation protocols for the generation of cardiomyocytes, neural progenitor cells, pancreatic beta cells, and hematopoietic progenitors from human pluripotent stem cells, and in chemical reprogramming cocktails for the generation of induced pluripotent stem cells from somatic cells without genetic manipulation [3, 4, 5].

    Beyond stem cell research, CHIR-99021 has demonstrated preclinical efficacy in rodent models of type 2 diabetes (enhanced glucose disposal at 30 mg/kg oral dosing), neurodegenerative disease (enhanced spatial learning and memory through GSK-3beta inhibition and reduction of tau hyperphosphorylation), bone regeneration (promotion of osteogenesis through canonical and autophagy-mediated Wnt signaling), and cochlear hair cell regeneration (in combination with valproic acid as the proprietary formulation FX-322, which has advanced to Phase 2b clinical trials for sensorineural hearing loss) [1, 6, 7, 8]. The compound has also been identified as a component of chemical cocktails for direct reprogramming of fibroblasts to cardiomyocytes and to chemically induced pluripotent stem cells (CiPSCs) [9, 10].

    Pharmacokinetic characterization in rodents demonstrates oral bioavailability sufficient for in vivo efficacy studies, though the compound is used predominantly as an in vitro research tool and has not been independently advanced through human pharmacokinetic characterization outside the FX-322 combination formulation. Safety considerations include the potential for off-target effects on dopaminergic neurotransmission, with ex vivo studies demonstrating that CHIR-99021 causes inactivation of tyrosine hydroxylase and depletion of dopamine in rat brain striatum, a finding that warrants consideration in the design of in vivo studies and in the interpretation of central nervous system effects [11]. The compound is supplied as a research-grade preparation by multiple chemical suppliers at greater than 98 percent purity; investigators should confirm identity and purity on every lot and should prepare stock solutions in dimethyl sulfoxide owing to the limited aqueous solubility of the free base form.

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  • AAZ-A-154

    Non-hallucinogenic psychoplastogen; isotryptamine-derived 5-HT2A receptor partial agonist with neuroplasticity-promoting activity

    A non-hallucinogenic isotryptamine psychoplastogen discovered via engineered 5-HT2A biosensor screening at UC Davis, producing rapid and sustained antidepressant-like effects through serotonin receptor-mediated structural neuroplasticity without psychedelic, dissociative, or psychotomimetic activity.

    Abstract

    AAZ-A-154, subsequently designated DLX-001 and assigned the international nonproprietary name zalsupindole, is a substituted isotryptamine derivative that acts as a low-potency, low-efficacy partial agonist of the serotonin 5-HT2A receptor (EC50 approximately 8,200 nM; Emax approximately 17 percent of serotonin maximum) and a moderate-efficacy partial agonist of the 5-HT2C receptor (EC50 approximately 3,300 nM; Emax approximately 70 percent), with silent antagonism at the 5-HT2B receptor and selectivity for serotonergic over dopaminergic, adrenergic, and opioid targets. The compound was first synthesized in 2019 in the laboratory of David E. Olson at the University of California, Davis, and was identified from a library screen using psychLight, a genetically encoded fluorescent biosensor constructed from the human 5-HT2A receptor with a circularly permuted green fluorescent protein inserted into the third intracellular loop [1]. PsychLight discriminated hallucinogenic from non-hallucinogenic 5-HT2A ligands on the basis of differential conformational activation signatures, and AAZ-A-154 was selected as a lead compound on the basis of its favorable ligand score, a metric that predicted non-hallucinogenic character despite retention of 5-HT2A-dependent psychoplastogenic activity.

    The compound is structurally related to 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) but is an isotryptamine (the aminoalkyl side chain is attached to the indole nitrogen at position 1 rather than at position 3), a modification that repositions the compound in chemical space outside classical psychedelic tryptamines. The (R)-enantiomer is the active form; the alpha-methyl substituent on the aminoalkyl chain confers metabolic stability and enantioselective receptor engagement. In rodent models, AAZ-A-154 at doses of 15 to 20 mg/kg intraperitoneally produced rapid-onset (30 minutes) and sustained (7 to 14 days) antidepressant-like behavioral effects in the forced swim test and in the sucrose preference test in VMAT2 heterozygous mice, a genetic model of depressive phenotype [1]. The compound increased dendritic arbor complexity in cultured embryonic rat cortical neurons to a degree comparable to ketamine, and the neuroplastogenic effect was abolished by the 5-HT2 receptor antagonist ketanserin, confirming receptor dependence [1]. Critically, AAZ-A-154 failed to produce the head-twitch response in mice at doses up to 100 mg/kg, the standard behavioral proxy for hallucinogenic activity in the 5-HT2A agonist class [1].

    A comprehensive preclinical characterization published by Agrawal et al. (2025) in ACS Chemical Neuroscience demonstrated that zalsupindole promoted cortical neuritogenesis in vitro, increased dendritic spine density in the prefrontal cortex in vivo, and enhanced measures of functional plasticity to a degree comparable to or greater than ketamine, psilocybin, and N,N-dimethyltryptamine, despite lacking any of the acute cellular and behavioral characteristics of hallucinogenic or dissociative compounds [2]. Pharmacokinetic studies revealed high brain penetrance, rapid distribution, and rapid clearance. In Phase 1 clinical trials enrolling 106 healthy volunteers, oral zalsupindole was well tolerated across a dose range of 2 to 360 mg, with no reports of psychotomimetic, hallucinogenic, or dissociative effects, and with quantitative electroencephalography demonstrating measurable changes in cortical activity consistent with target engagement [3, 4]. A Phase 1b study in 18 adults with major depressive disorder reported clinically meaningful reductions in Montgomery-Asberg Depression Rating Scale scores of approximately 12 points (approximately 50 percent improvement) by Day 8, with effects maintained through Day 36, and comparable efficacy between a seven-day once-daily regimen and a two-dose regimen [5]. No serious adverse events were reported across more than 120 individuals studied. Dose-dependent nausea, headache, and dizziness were the principal mild adverse events. In October 2025, the United States Food and Drug Administration cleared the Investigational New Drug application for a Phase 2, multi-site, randomized, double-blind, placebo-controlled trial in major depressive disorder featuring at-home self-administration [5]. This monograph reviews the chemistry, biosensor-guided discovery, receptor pharmacology, neuroplasticity mechanisms, pharmacokinetics, preclinical and clinical evidence, sourcing and handling, stack interactions, adverse-event signal, and a comparative assessment of five psychoplastogen and rapid-acting antidepressant candidates against AAZ-A-154.

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  • Cogitum

    Acetylated amino acid derivative; synthetic N-acetylaspartate analog with neurometabolic and adaptogenic activity

    A potassium salt of N-acetyl-DL-aminosuccinic acid developed in France as an oral neurometabolic tonic for asthenic syndrome, cognitive fatigue, and pediatric neurodevelopmental delay, distinguished by its structural relationship to endogenous N-acetylaspartate and downstream modulation of glutamatergic and myelinogenic pathways.

    Abstract

    Cogitum is the proprietary pharmaceutical preparation of potassium N-acetyl-DL-aminosuccinate (bipotassium acetylaminosuccinate), a synthetic analog of N-acetylaspartate (NAA), the most concentrated free amino acid derivative in the mammalian central nervous system. The compound was developed in France and patented in the United States in 1969 (US 3,433,875) for the improvement of mental performance in adults experiencing intellectual overwork, memory disorders, and cognitive decline associated with senescence. The active substance provides an exogenous source of the acetylated aspartate moiety that participates in neuronal energy metabolism through the tricarboxylic acid cycle, serves as the obligate precursor for myelin lipid synthesis via oligodendrocytic aspartoacylase-mediated deacetylation, functions as an osmolyte maintaining neuronal volume homeostasis, and is the direct biosynthetic precursor of N-acetylaspartylglutamate (NAAG), the most abundant neuropeptide in the human brain and an endogenous agonist at the presynaptic metabotropic glutamate receptor type 3 (mGluR3). Cogitum is classified pharmacologically as a tonic agent and adaptogen; it is registered and marketed as a drinkable oral solution (250 mg per 10 mL ampoule) in France, Portugal, and several other jurisdictions, and is used extensively in Russian neuropediatric practice for the treatment of asthenic syndrome, attention deficit hyperactivity disorder with subclinical epileptiform activity, speech and language delay, and neurodevelopmental disorders in children aged seven years and older.

    The clinical evidence base includes a 2023 double-blind, randomized, placebo-controlled trial demonstrating that potassium N-acetylaminosuccinate at 750 mg daily for 21 days significantly reduced fatigue scores and improved complex cognitive functions in adults with asthenic syndrome compared to placebo, with no reported adverse events (Esin et al., 2023). Pediatric evidence comprises a 249-patient study in children with ADHD and subclinical epileptiform electroencephalographic activity demonstrating significant improvements in attention, memory, and speech without aggravation of epileptiform discharges or provocation of seizures; additional cohort studies in children with speech delay, traumatic brain injury sequelae, mental retardation, and schizotypal spectrum disorders have reported efficacy in improving cognitive and linguistic performance. The pharmacological rationale rests on the established neurobiology of endogenous N-acetylaspartate: NAA concentrations in the brain reach 10 millimolar or greater, are confined almost exclusively to neurons, and serve as the principal magnetic resonance spectroscopy marker of neuronal viability; reduced NAA is a consistent finding in neurodegenerative disease, traumatic brain injury, multiple sclerosis, and neurodevelopmental disorders. The exogenous provision of the acetylaminosuccinate moiety is hypothesized to support neuronal mitochondrial energy production, to provide acetate substrate for oligodendrocytic myelin lipid synthesis, and to augment NAAG-mediated glutamatergic neuromodulation.

    Safety data across pediatric and adult populations demonstrate excellent tolerability. The compound has no reported cases of overdose toxicity, produces no clinically significant drug interactions at registered doses, and is contraindicated only in cases of known hypersensitivity to the active substance or excipients. The principal limitation of the evidence base is the concentration of clinical research in Russian-language journals with limited replication in Western multicenter trial frameworks. This monograph documents the chemistry, synthesis, mechanism, pharmacokinetics, clinical evidence, sourcing, reconstitution, stack interactions, adverse events, and comparative assessment of Cogitum against five neurometabolic and nootropic alternatives on five competency standards.

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  • Zelquistinel

    Novel positive allosteric modulator of the N-methyl-D-aspartate receptor acting at a unique extracellular binding site independent of the glycine co-agonist site

    A third-generation, orally bioavailable spirocyclic beta-lactam NMDA receptor modulator developed from the rapastinel peptidomimetic platform, distinguished by nanomolar positive allosteric modulation of NR2A-, NR2B-, and NR2C-containing NMDA receptors through reduction of calcium-dependent inactivation, producing rapid and sustained antidepressant-like effects without psychotomimetic liability.

    Abstract

    Zelquistinel (GATE-251, formerly AGN-241751) is a novel, orally bioavailable, small-molecule positive allosteric modulator of the N-methyl-D-aspartate (NMDA) glutamate receptor, currently in Phase 2b clinical development for major depressive disorder (MDD) under the sponsorship of Syndeio Biosciences (operating as Gate Neurosciences). The compound is the third-generation successor to the tetrapeptide rapastinel (GLYX-13) and the dipeptide apimostinel (NRX-1074), sharing a common mechanism of NMDA receptor positive modulation but replacing the peptide scaffold with a spirocyclic 2,5-diazaspiro[3.4]octane (beta-lactam) core that confers oral bioavailability approaching 100 percent in preclinical species, a plasma half-life of approximately 1.2 to 2.1 hours, and approximately 1000-fold greater potency than rapastinel on a weight basis.

    Zelquistinel binds to a unique extracellular site on the NMDA receptor that is distinct from the glutamate agonist site, the glycine co-agonist site, the phencyclidine channel-blocking site, and the polyamine modulatory site. The compound does not displace radioligands at any of these four canonical sites and shows no significant activity across a panel of 80 receptors, ion channels, and monoamine transporters. Mechanistically, zelquistinel acts through a long-distance allosteric pathway: extracellular binding reduces intracellular calcium-dependent inactivation (CDI) of the NMDA receptor channel, thereby enhancing NMDA receptor current in an activity-dependent manner. This mechanism has been demonstrated through experiments showing that replacement of the intracellular calcium chelator EGTA with the fast chelator BAPTA abolishes zelquistinel potentiation, and that removal of the NR1 C-terminal intracellular domain or infusion of calmodulin-blocking peptide similarly eliminates the modulatory effect. Subtype selectivity studies reveal potent enhancement at NR2A-containing (EC50 approximately 9.9 nM) and NR2C-containing (EC50 approximately 9.7 nM) receptors, with a larger ceiling enhancement at NR2B-containing receptors (EC50 approximately 35.0 nM) and no effect at NR2D-containing receptors.

    The pharmacological profile produces a characteristic biphasic, inverted-U dose-response relationship: potentiation of NMDA receptor-mediated calcium influx at concentrations of 0.3 to 60 nM and mild inhibition at concentrations exceeding 100 nM. In preclinical behavioral models, single oral doses of zelquistinel at 30 micrograms per kilogram produce rapid antidepressant-like effects in the forced swim test (onset within one hour) that are sustained for more than seven days, and rescue social approach behavior in the chronic social defeat model at efficacy comparable to ketamine at 10 mg/kg subcutaneous. The compound enhances long-term potentiation (LTP) in both medial prefrontal cortex and hippocampal Schaffer collateral-CA1 pathways, with metaplastic enhancement persisting for at least two weeks after a single dose. Critically, zelquistinel produces no motor impairment on the rotarod test at doses 100-fold above the antidepressant-effective dose and no psychotomimetic symptoms as measured by validated clinical scales in human subjects.

    In Phase 1 clinical evaluation, single ascending oral doses from 100 micrograms to 50 mg were well tolerated in 60 healthy volunteers, with dose-proportional pharmacokinetics, rapid absorption, significant cerebrospinal fluid penetration, and no clinically significant adverse events, vital sign changes, electrocardiographic abnormalities, or psychotomimetic symptoms. A Phase 2a exploratory trial in 251 patients with major depressive disorder demonstrated statistically significant reductions in Montgomery-Asberg Depression Rating Scale (MADRS) scores at the two highest once-weekly oral doses (reductions of 9.5 and 10.6 points versus 7.7 points with placebo at week three). The U.S. Food and Drug Administration granted Fast Track designation for zelquistinel in MDD in July 2018. As of the date of this monograph, a Phase 2b confirmatory trial is actively recruiting under Syndeio Biosciences sponsorship. Additional preclinical research has demonstrated durable relief of core behavioral deficits in three mouse models of autism spectrum disorder, and dose-dependent reversal of phencyclidine-induced hyperlocomotion, expanding the potential therapeutic scope beyond depression.

    This monograph reviews the chemistry, structural class, and synthesis of zelquistinel; the dual extracellular-intracellular allosteric mechanism in molecular and electrophysiological detail; the comprehensive preclinical and human pharmacokinetic record; the clinical evidence base in major depressive disorder; sourcing and quality verification considerations for research applications; reconstitution and handling; stack-interaction implications; adverse-event signal; and a comparative assessment of five NMDA receptor-targeting antidepressant candidates (rapastinel, apimostinel, esketamine, REL-1017, and AV-101) against zelquistinel on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation). The compound is not approved by any regulatory authority for any indication. It is available as a research-grade preparation from chemical suppliers; investigators should obtain analytical confirmation of identity and purity on every lot.

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  • CT1812

    Selective sigma-2 receptor (TMEM97) complex antagonist with anti-amyloid-beta oligomer synaptoproctective activity

    A first-in-class, orally bioavailable isoindoline sigma-2 receptor antagonist developed by Cognition Therapeutics to displace amyloid-beta oligomers from neuronal synapses, with Phase 2 clinical evidence of cognitive benefit in Alzheimer’s disease and dementia with Lewy bodies.

    Abstract

    CT1812 (zervimesine; CAS 1802632-22-9) is a first-in-class, orally bioavailable small-molecule antagonist of the sigma-2 receptor complex (also designated TMEM97, transmembrane protein 97) developed by Cognition Therapeutics for the treatment of Alzheimer’s disease (AD), dementia with Lewy bodies (DLB), and geographic atrophy secondary to dry age-related macular degeneration. The compound was identified through a phenotypic neuronal screening assay designed to detect reversal of amyloid-beta oligomer (ABO) induced synaptotoxicity and was chemically optimized from a series of isoindoline scaffolds selected for central nervous system penetration, metabolic stability, and selectivity against cardiac ion channel (hERG) liability. CT1812 binds the sigma-2 receptor with a Ki of 8.5 nM and demonstrates greater than 100-fold selectivity over a broad receptor panel, with approximately 10-fold selectivity over the sigma-1 receptor. The mechanism of action is allosteric antagonism of the sigma-2 receptor complex, which includes TMEM97, progesterone receptor membrane component 1 (PGRMC1), and low-density lipoprotein receptor (LDLR) at the neuronal surface. Engagement of this complex by CT1812 induces a conformational change that displaces prebound amyloid-beta oligomers from synaptic receptors without affecting oligomer assembly or dissociation, thereby restoring synaptic trafficking, reducing synaptotoxicity, and facilitating clearance of oligomers into the cerebrospinal fluid.

    In preclinical studies, CT1812 demonstrated robust brain penetration (brain-to-plasma ratio of 5.7 at 24 hours; unbound brain-to-plasma partition coefficient Kp,uu of 6.75), achieved greater than 84 percent sigma-2 receptor occupancy at therapeutically relevant doses, and improved cognitive performance in transgenic Alzheimer’s mouse models across Y-maze, Morris water maze, and fear conditioning paradigms. The compound is not a P-glycoprotein substrate, exhibits favorable oral absorption with time to peak plasma concentration of 1 to 2 hours and a plasma elimination half-life of approximately 12 hours in humans, and is metabolized primarily by CYP3A4 with secondary contributions from CYP2D6 and CYP2C19.

    A Phase 1 trial in 80 healthy volunteers established safety and tolerability at single doses up to 1120 mg and multiple doses up to 840 mg daily for 14 days, with dose-proportional pharmacokinetics and cerebrospinal fluid penetration achieving estimated receptor occupancy of 97 to 98 percent. A Phase 1b/2 trial (COG0102) in 19 patients with mild to moderate AD demonstrated reductions in cerebrospinal fluid synaptic damage markers (neurogranin and synaptotagmin-1) and decreases of 30 percent or more in six tau phosphorylation sites after 28 days of treatment. The Phase 2 SHINE trial (COG0201) enrolled 153 patients with mild to moderate AD randomized to 100 mg, 300 mg, or placebo for 182 days; the 100 mg dose produced a 39 percent reduction in ADAS-Cog 11 decline relative to placebo, with a 95 percent slowing of cognitive decline in the subpopulation with baseline plasma p-tau217 below the median. The Phase 2 SHIMMER trial (COG1201) enrolled 130 patients with mild to moderate DLB and met its primary safety endpoint; secondary analyses showed 82 percent of treated patients demonstrated slowing on the total Neuropsychiatric Inventory, with a 91 percent reduction in decline of attentional fluctuation measures. CT1812 has also been evaluated in the Phase 2 MAGNIFY trial for geographic atrophy, where treated patients showed 28.6 percent slower lesion growth over 18 months compared to placebo. The compound is generally well tolerated; the principal adverse events are headache, gastrointestinal symptoms (nausea, diarrhea, constipation), and, at the 300 mg dose in SHINE, transient elevations in liver function tests that resolved upon drug discontinuation. CT1812 is positioned for Phase 3 development in Alzheimer’s disease. This monograph reviews the compound identification, discovery and development history, molecular pharmacology, pharmacokinetics, preclinical and clinical evidence, sourcing, reconstitution, stack interactions, safety profile, and a comparative assessment of five alternative approaches to amyloid-beta oligomer or sigma-2 receptor pharmacology.

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  • Cytoflavin

    Fixed-dose combination metabolic cytoprotectant comprising succinic acid, inosine, nicotinamide, and riboflavin for mitochondrial energy rescue and antihypoxant neuroprotection

    A four-component metabolic combination drug developed by POLYSAN Ltd. that supplies Krebs cycle substrate, purine nucleoside, NAD+ precursor, and FAD cofactor to restore aerobic energy production in ischemic, hypoxic, and neurodegenerative tissue.

    Abstract

    Cytoflavin is a fixed-dose combination metabolic agent comprising succinic acid (the principal mass component and Krebs cycle substrate), inosine (a purine nucleoside and precursor to adenine nucleotides), nicotinamide (the amide form of vitamin B3 and precursor to nicotinamide adenine dinucleotide), and riboflavin (vitamin B2, the precursor to flavin adenine dinucleotide and flavin mononucleotide). Developed and manufactured by POLYSAN Scientific and Technological Pharmaceutical Company (Saint Petersburg, Russia), the product is formulated as enteric-coated tablets (300 mg succinic acid, 50 mg inosine, 25 mg nicotinamide, 5 mg riboflavin per tablet) and as a concentrate for intravenous infusion (1000 mg succinic acid, 200 mg inosine, 100 mg nicotinamide, 20 mg riboflavin sodium phosphate per 10 mL ampoule, with meglumine and sodium hydroxide as excipients). The pharmacological rationale is the simultaneous provision of four complementary metabolic substrates and cofactors whose intracellular availability becomes rate-limiting during ischemia, hypoxia, and oxidative stress: succinic acid feeds directly into mitochondrial Complex II (succinate dehydrogenase), bypassing the NAD-dependent steps of the Krebs cycle that fail under hypoxic conditions; inosine supports purine salvage and ATP resynthesis; nicotinamide replenishes the NAD+ pool consumed by poly(ADP-ribose) polymerase activation during ischemic injury; and riboflavin provides the FAD prosthetic group required for succinate dehydrogenase function and for multiple flavoprotein-dependent antioxidant enzymes including glutathione reductase.

    The clinical evidence base for Cytoflavin spans ischemic stroke (acute and chronic cerebral ischemia), traumatic brain injury, diabetic polyneuropathy, postoperative cognitive decline in elderly surgical patients, post-COVID-19 asthenic syndrome, and organic asthenic disorder. The largest and most rigorous published trial is the CYLINDER study, a multicenter, double-blind, placebo-controlled, randomized trial in 216 patients with type 2 diabetes mellitus and symptomatic distal sensorimotor diabetic polyneuropathy conducted across 10 Russian clinical centers, which reported a statistically significant reduction in Total Symptom Score (TSS change of negative 2.65 points in the experimental group versus negative 1.73 points in the placebo group, p less than 0.001) after a sequential intravenous-then-oral treatment regimen. In acute ischemic stroke, multicenter studies have demonstrated marked reduction in neurological deficit severity by day 10 and higher probability of favorable functional outcome compared to standard-of-care controls. The CITADEL prospective randomized study demonstrated a pronounced anti-asthenic effect and correction of cognitive impairments in post-COVID-19 rehabilitation. An international, multicenter, randomized, single-blind, placebo-controlled trial (NCT04631484) evaluating Cytoflavin in moderate traumatic brain injury in adults was completed in 2024, with results published in Frontiers in Neurology in 2025, representing the first large-scale international trial of the compound outside the Russian Federation and Commonwealth of Independent States.

    Cytoflavin is registered as a medicinal product in the Russian Federation and in Vietnam. The manufacturing facility holds GMP EU certification. The compound is not approved by the United States Food and Drug Administration, by the European Medicines Agency, or by other major Western regulatory authorities. The clinical literature is predominantly in Russian-language journals, with an expanding body of English-language publications in international peer-reviewed venues. The safety profile across published clinical studies is favorable; the principal adverse events are transient epigastric discomfort, headache, hyperuricemia (attributable to inosine-derived purine catabolism), and rare hypersensitivity reactions. No serious adverse events attributable to the drug have been reported in published controlled trials.

    This monograph reviews the composition, identification, and formulation chemistry of Cytoflavin; the individual and composite pharmacology of its four active components; the pharmacokinetic considerations for each component; the preclinical pharmacology; the clinical evidence base across all studied indications; sourcing and quality verification; reconstitution and handling; stack interactions and combinations; adverse events and safety signals; and a comparative assessment of five alternative neuroprotective metabolic agents (Mexidol, Actovegin, Cerebrolysin, citicoline, and Reamberin) against Cytoflavin on five competency standards.

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  • Esmethadone

    Uncompetitive N-methyl-D-aspartate receptor antagonist with residual low-affinity opioid receptor activity

    The (S)-enantiomer of racemic methadone, developed by Relmada Therapeutics as REL-1017 for major depressive disorder on the basis of low-potency, voltage-dependent uncompetitive NMDA receptor channel blockade with preferential tonic inhibition of GluN2D-containing receptors, negligible clinically relevant opioid agonist activity, and rapid mTORC1- and BDNF-dependent antidepressant-like effects in preclinical models.

    Abstract

    Esmethadone (REL-1017, d-methadone, dextromethadone) is the (S)-enantiomer of the synthetic opioid methadone and a low-potency, voltage-dependent, uncompetitive antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor that was advanced through Phase 3 clinical development by Relmada Therapeutics for the adjunctive and monotherapy treatment of major depressive disorder (MDD). Unlike the (R)-enantiomer levomethadone, which carries the analgesic opioid activity of the racemate, esmethadone exhibits approximately 10-fold lower affinity at mu-opioid receptors and lacks clinically meaningful opioid agonist effects, respiratory depression, reinforcing properties, or physical dependence liability at the doses studied for antidepressant activity. The compound blocks NMDA receptor ion channels with IC50 values in the low micromolar range (approximately 13 to 68 micromolar across GluN2A through GluN2D subunit combinations), with functional selectivity for tonically active GluN2D-containing receptors under physiological magnesium concentrations. This tonic blockade is proposed to disinhibit downstream alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated glutamatergic transmission, activate mammalian target of rapamycin complex 1 (mTORC1) signaling, and increase brain-derived neurotrophic factor (BDNF) expression, producing rapid-onset antidepressant effects comparable in mechanism (though not in potency or dissociative liability) to ketamine and esketamine. Preclinical studies in rodent models of depressive-like behavior (forced swimming test, novelty-suppressed feeding test, female urine sniffing test, chronic unpredictable stress) demonstrated that oral esmethadone produced antidepressant effects comparable to injectable ketamine in magnitude and duration, mediated by mTORC1 signaling in the medial prefrontal cortex and blocked by the selective mTORC1 inhibitor rapamycin. A Phase 1 study in healthy volunteers demonstrated that esmethadone increased circulating BDNF levels, providing translational biomarker support for the preclinical mechanism. Pharmacokinetics are characterized by approximately 70 to 80 percent oral bioavailability, a long elimination half-life exceeding 30 hours that supports once-daily dosing, and hepatic metabolism principally through CYP3A4/5 and CYP2B6 to the inactive metabolite EDDP, with approximately half the dose recovered in urine and 40 percent in feces. The compound is a CYP2D6 inhibitor in vitro, producing clinically relevant increases in exposure of CYP2D6 substrates such as dextromethorphan. The Phase 2a randomized, double-blind, placebo-controlled adjunctive trial in MDD patients with inadequate response to standard antidepressants (Fava et al., American Journal of Psychiatry, 2022) demonstrated rapid and sustained improvement on the Montgomery-Asberg Depression Rating Scale (MADRS) at 25 mg and 50 mg daily doses, with effect sizes of 0.7 to 1.0 and day-14 remission rates of 31 percent and 39 percent versus 5 percent on placebo. No dissociative or psychotomimetic effects were observed. The Phase 3 Reliance I trial (published 2024) did not meet its primary efficacy endpoint, attributed in part to an elevated placebo response during the COVID-19 pandemic enrollment period. A second Phase 3 trial (Reliance II) was initiated, but interim analysis in late 2024 indicated that the study was unlikely to meet its primary efficacy endpoint, and Relmada Therapeutics paused further development of REL-1017. A 12-month open-label extension study in 624 MDD patients confirmed long-term safety and tolerability, with the most common treatment-related adverse events being headache (4.6 percent), nausea (4.2 percent), and dizziness (2.6 percent), no signal for cardiovascular, metabolic, neurological, or sexual adverse events, no suicides or suicide attempts, and no withdrawal syndrome on discontinuation. A dedicated abuse-potential study in recreational drug users demonstrated no meaningful abuse potential. The compound is not approved by any regulatory authority. This monograph reviews the chemistry, stereochemistry, and synthesis of esmethadone; the NMDA receptor pharmacology including subunit selectivity and downstream signaling; the opioid receptor binding profile; comprehensive pharmacokinetics including drug-drug interactions; the preclinical and clinical evidence base across Phase 1, Phase 2, and Phase 3 programs; sourcing and quality considerations; reconstitution and handling; stack interactions; the adverse-event and safety profile; and a comparative assessment of five alternative NMDA receptor-targeting antidepressant candidates against esmethadone on five competency standards.

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