Second-generation fast skeletal muscle troponin activator (FSTA) selective for fast skeletal muscle fibers
A next-generation fast skeletal muscle troponin activator developed by Cytokinetics to amplify skeletal muscle force output through calcium sensitization of the sarcomere, evaluated in Phase 2 and Phase 3 clinical trials in amyotrophic lateral sclerosis and spinal muscular atrophy.
Abstract
Reldesemtiv (CK-2127107) is a small-molecule fast skeletal muscle troponin activator (FSTA) that selectively binds the regulatory troponin complex in fast skeletal muscle fibers, slows the rate of calcium release from troponin C, and thereby sensitizes the sarcomere to calcium at submaximal stimulation frequencies. The compound was discovered at Cytokinetics, Inc. through property-based optimization of a high-throughput screening hit, yielding improved free exposure, in vivo muscle activation potency, and tolerability relative to the first-generation FSTA tirasemtiv, which had failed the Phase 3 VITALITY-ALS trial primarily because of dose-limiting tolerability (dizziness, nausea, weight loss, insomnia) and a 34.2 percent treatment discontinuation rate. Reldesemtiv does not activate slow skeletal or cardiac troponin complexes, providing a selectivity basis for its intended use in conditions characterized by fast skeletal muscle weakness secondary to attenuated neuronal input, including amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and chronic obstructive pulmonary disease. In a Phase 1 pharmacodynamic study in 16 healthy volunteers, reldesemtiv amplified the tibialis anterior force-frequency response by approximately 60 percent at 10 Hz nerve stimulation at the highest plasma concentrations tested, confirming the mechanism of action in human skeletal muscle. Pharmacokinetics across five Phase 1 studies demonstrated dose-proportional exposure with a terminal half-life of approximately 5 to 14 hours depending on dose, a time to peak concentration of 2 to 3 hours, and similar pharmacokinetic profiles in young and elderly subjects. The Phase 2 FORTITUDE-ALS trial (n=458; 12 weeks; placebo, 150, 300, or 450 mg twice daily) did not reach statistical significance on its primary endpoint of slow vital capacity change (p=0.11), though trends favoring reldesemtiv were observed across all three endpoints and a post hoc analysis of the ALSFRS-R functional scale reached nominal significance (p=0.01). The Phase 2 SMA study (n=70; 8 weeks; 150 or 450 mg twice daily) reported statistically significant improvement in six-minute walk distance at week 4 (35.6 m, p=0.0037) and maximum expiratory pressure at week 8 (13.2 cmH2O, p=0.03) in the 450 mg group, with concentration-response relationships in the highest plasma concentration quartile reaching significance on both endpoints. The Phase 3 COURAGE-ALS trial (n=486; 24 weeks; 300 mg twice daily versus placebo; 83 centers in 16 countries) was terminated for futility at the second planned interim analysis when conditional power for the primary endpoint (ALSFRS-R score change at 24 weeks) was 8.4 percent. The primary analysis showed a mean difference of negative 1.1 points (95 percent CI, negative 2.17 to negative 0.08; p=0.04), numerically favoring placebo. No preplanned subgroup favored reldesemtiv. The compound is not approved by any regulatory authority for any indication. This monograph reviews the chemistry, discovery, molecular pharmacology, pharmacokinetics, preclinical and clinical evidence, sourcing, handling, adverse events, and a comparative assessment of reldesemtiv against tirasemtiv, tofersen, riluzole, edaravone, and risdiplam on five competency standards.
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Sigma-2 receptor antagonist and serotonin 5-HT2A receptor antagonist with alpha-1A adrenergic receptor antagonism
A cyclic amide derivative with equipotent nanomolar antagonism at sigma-2 and 5-HT2A receptors, developed by Minerva Neurosciences as monotherapy for the negative symptoms of schizophrenia and distinguished from conventional antipsychotics by the absence of dopaminergic receptor binding.
Abstract
Roluperidone (MIN-101, formerly MT-210 and CYR-101) is a cyclic amide (isoindolinone) derivative that combines high-affinity antagonism at the sigma-2 receptor (TMEM97; Ki 8.19 nM) and the serotonin 5-HT2A receptor (Ki 7.53 nM) with lower-affinity antagonism at alpha-1A adrenergic receptors (Ki 4.17 nM), while exhibiting essentially no binding at dopamine D1 through D5 receptors, muscarinic, cholinergic, or histaminergic receptors. This receptor binding profile distinguishes roluperidone from all marketed antipsychotics and underwrites a pharmacological rationale for addressing the negative symptoms of schizophrenia through nondopaminergic mechanisms. The sigma-2 receptor, identified in 2017 as the transmembrane protein TMEM97, is expressed at high density in cortical and hippocampal neurons and is implicated in calcium signaling, cholesterol homeostasis, autophagy, and the modulation of dopaminergic and glutamatergic neurotransmission. The 5-HT2A antagonist component promotes slow-wave sleep normalization, a deficit that is consistently documented in schizophrenia and that correlates with negative symptom severity. Roluperidone was originally synthesized by Mitsubishi Tanabe Pharma Corporation (designated MT-210), licensed through Cyrenaic Pharmaceuticals (CYR-101), and advanced through clinical development by Minerva Neurosciences (MIN-101). In a Phase 2b randomized, double-blind, placebo-controlled trial of 244 patients with stable schizophrenia and moderate-to-severe negative symptoms (MIN-101C03), roluperidone monotherapy at 32 mg/day and 64 mg/day produced statistically significant improvement on the PANSS negative symptom factor score at 12 weeks (effect sizes 0.45 and 0.58, respectively; both p < 0.025). In the subsequent Phase 3 trial (EMERGENT-3, NCT03397134, 513 patients), the 64 mg/day dose reached nominal statistical significance on the primary negative symptom endpoint in the modified intent-to-treat analysis (p = 0.044, effect size 0.26), with statistically significant improvements in social functioning on the Personal and Social Performance scale (p = 0.021, effect size 0.27) and a negative symptom responder rate of 39% versus 23% on placebo (p = 0.006). Network intervention analysis of both trials identified avolition as the directly targeted symptom, with improvements cascading across the broader negative symptom constellation. Pharmacokinetics are characterized by oral bioavailability of 73% to 81%, peak plasma concentration at approximately 3.5 hours, and a plasma elimination half-life of approximately 7 hours after a 64 mg dose, supporting once-daily administration. CYP2D6 is involved in metabolism, and poor or intermediate CYP2D6 metabolizers were excluded from the Phase 3 trial. Tolerability across both trials was notable for the absence of clinically meaningful weight gain, metabolic changes, extrapyramidal symptoms, or prolactin elevation; the principal safety signal was QTc interval prolongation leading to discontinuation of three patients at the 64 mg dose in the Phase 3 trial. Minerva Neurosciences filed a New Drug Application with the U.S. Food and Drug Administration in April 2023. The FDA issued a Complete Response Letter in February 2024, citing insufficient evidence of effectiveness from a single adequate trial, absence of data on concomitant antipsychotic administration, and the need for additional evidence of clinical meaningfulness. The compound remains in development as of the monograph date. This monograph documents the chemistry, dual-receptor pharmacology, pharmacokinetics, preclinical and clinical evidence base, safety profile, and a comparative assessment of five compounds in the negative symptom treatment space against roluperidone on five competency standards. The compound is investigational and is not approved by any regulatory authority for any indication.
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First-in-class oxysterol-derived positive allosteric modulator of the N-methyl-D-aspartate receptor
A first-in-class synthetic analog of the endogenous cholesterol metabolite 24(S)-hydroxycholesterol, developed by Sage Therapeutics as an oral NMDA receptor positive allosteric modulator for cognitive impairment in Huntington’s disease, Alzheimer’s disease, and Parkinson’s disease, with development discontinued in late 2024 following negative Phase 2 efficacy readouts across all three indications.
Abstract
Dalzanemdor (development code SAGE-718) is a first-in-class, orally bioavailable, small-molecule positive allosteric modulator (PAM) of the N-methyl-D-aspartate receptor (NMDAR), structurally derived from the endogenous cholesterol metabolite 24(S)-hydroxycholesterol (24(S)-HC). The compound was designed by Sage Therapeutics to address cognitive impairment in neurodegenerative disorders associated with NMDAR hypofunction, including Huntington’s disease, Alzheimer’s disease, and Parkinson’s disease. Dalzanemdor potentiates NMDAR-mediated currents at all four GluN2 subunit-containing receptor assemblies (GluN1/GluN2A through GluN1/GluN2D) with equipotency, exhibiting EC50 values in the low-nanomolar range (approximately 79 to 86 nM) and high intrinsic activity. The modulation increases NMDAR channel open probability without directly gating the receptor in the absence of endogenous glutamate, a feature that preserves physiological patterns of synaptic transmission and mitigates the excitotoxicity risk associated with direct NMDAR agonism.
The compound emerged from a research program initiated by the foundational discovery of Paul et al. (2013) demonstrating that 24(S)-HC, the major brain-specific cholesterol metabolite synthesized by CYP46A1, is a potent and selective endogenous NMDAR PAM at submicromolar concentrations. Medicinal chemistry optimization at Sage Therapeutics yielded dalzanemdor (compound 5 in the Hill et al. 2022 disclosure), a trifluoromethylated oxysterol with an optimized pharmacokinetic profile for oral dosing. In preclinical models, dalzanemdor enhanced NMDAR-mediated long-term potentiation in hippocampal slices, increased excitatory postsynaptic potential amplitude in striatal medium spiny neurons, and reversed cognitive and behavioral deficits induced by NMDAR channel blockers and cholesterol depletion, without producing epileptiform activity or neurodegeneration on chronic dosing.
Phase 1 dose-finding studies (single-ascending dose, 0.35 to 3.0 mg; multiple-ascending dose, 0.5 to 1.0 mg for 14 days) in healthy participants and Huntington’s disease participants established a pharmacokinetic profile characterized by oral absorption with median Tmax of 4 to 7 hours, terminal half-life of approximately 28 to 40 hours after single doses extending to 99 to 125 hours after multiple doses, and dose-proportional exposures suitable for once-daily dosing. Exploratory cognitive assessments in Huntington’s disease participants during the Phase 1 multiple-ascending dose study showed statistically significant improvement on the Two-Back Learning Task (executive function). Open-label Phase 2 studies in Parkinson’s disease mild cognitive impairment (PARADIGM, n=18) and Alzheimer’s disease (LUMINARY, n=26) generated signals of improvement on measures of executive function and learning. However, three subsequent randomized, double-blind, placebo-controlled Phase 2 studies (PRECEDENT in Parkinson’s disease, LIGHTWAVE in Alzheimer’s disease, DIMENSION in Huntington’s disease) each failed to meet their primary cognitive endpoints. Sage Therapeutics discontinued all clinical development of dalzanemdor in November 2024.
This monograph documents the chemistry, structural pharmacology, oxysterol-site mechanism, human pharmacokinetics, the complete clinical trial inventory including both positive open-label signals and negative controlled results, sourcing and handling considerations for research-grade material, adverse-event profile, and a comparative assessment of five NMDAR-targeting compounds against dalzanemdor on five competency standards. The compound is not approved by any regulatory authority. Research-grade dalzanemdor is available from chemical suppliers for in vitro and in vivo investigation of NMDAR positive allosteric modulation; investigators should obtain analytical confirmation of identity and purity on every lot.
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Selective transthyretin tetramer kinetic stabilizer designed to mimic the naturally occurring T119M protective variant
A fluorinated benzoic acid derivative engineered to replicate the enthalpy-driven transthyretin stabilization of the protective T119M genetic variant, approved for transthyretin amyloid cardiomyopathy following a positive Phase 3 trial demonstrating reductions in all-cause mortality and cardiovascular hospitalization.
Abstract
Acoramidis (AG10) is a potent, selective, orally bioavailable small-molecule kinetic stabilizer of the transthyretin (TTR) tetramer, approved in the United States, European Union, United Kingdom, and Japan for the treatment of cardiomyopathy caused by wild-type or hereditary transthyretin-mediated amyloidosis (ATTR-CM). The compound was rationally designed to replicate the molecular mechanism of the naturally occurring T119M variant of TTR, a protective mutation that stabilizes the tetramer against the rate-limiting dissociation step that initiates amyloid fibril formation. Structurally, acoramidis is a 3,5-dimethylpyrazole linked through a propyloxy tether to a 4-fluorobenzoic acid; the pyrazole ring forms two hydrogen bonds with serine 117 and serine 117 prime residues at the floor of the thyroxine binding pocket, replicating the inter-dimer contact created by the threonine-to-methionine substitution in T119M carriers. This enthalpy-driven binding mechanism (binding enthalpy of negative 13.6 kilocalories per mole, compared to negative 5.0 kilocalories per mole for tafamidis) underpins the high selectivity of acoramidis for TTR over albumin and its capacity to achieve greater than 90 percent tetramer stabilization across the entire dosing interval at steady state. The clinical development program for acoramidis established pharmacokinetic parameters favorable for twice-daily oral dosing: rapid absorption (time to peak concentration less than one hour), terminal elimination half-life of approximately 25 hours, metabolism principally by UGT-mediated glucuronidation rather than cytochrome P450 enzymes, and renal elimination of conjugated metabolites. The pivotal Phase 3 ATTRibute-CM trial randomized 632 patients with wild-type or hereditary ATTR-CM to acoramidis 800 milligrams (as the hydrochloride salt) twice daily or placebo for 30 months. On the primary hierarchical endpoint (a four-component analysis of all-cause mortality, cardiovascular-related hospitalization, NT-proBNP change, and six-minute walk distance), acoramidis demonstrated a win ratio of 1.8 (95 percent confidence interval 1.4 to 2.2; P less than 0.001). The time-to-event composite of all-cause mortality or first cardiovascular hospitalization favored acoramidis with a hazard ratio of 0.64 (95 percent confidence interval 0.50 to 0.83; P equals 0.0008), with Kaplan-Meier curves separating at three months and benefit sustained through 42 months of follow-up in the open-label extension. A cardiac magnetic resonance substudy demonstrated stabilization of left ventricular mass and improvement of ejection fraction in the acoramidis arm relative to progressive deterioration in placebo recipients. The adverse event profile was similar to placebo; diarrhea (11.6 versus 7.6 percent) and gout (10.9 versus 8.1 percent) were the most frequent treatment-emergent events occurring at higher rates with acoramidis. This monograph reviews the chemistry, synthesis, and rational design of acoramidis; the enthalpy-driven TTR stabilization mechanism characterized through isothermal titration calorimetry and X-ray crystallography; the complete human pharmacokinetic profile; preclinical pharmacology in rodent and canine models; the clinical evidence base from Phase 1 through Phase 3 and the open-label extension; sourcing and quality considerations for research applications; reconstitution and handling; metabolic and pharmacodynamic interactions; the adverse event and safety profile; and a comparative assessment of five transthyretin-directed therapies (tafamidis, diflunisal, patisiran, vutrisiran, and eplontersen) against acoramidis on five competency standards. Acoramidis is a prescription medicine in its approved jurisdictions and is available as a research-grade preparation for investigational applications outside the approved indication. Investigators should obtain analytical confirmation of identity and purity on every research-grade lot.
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Small-molecule filamin A conformation modulator proposed to disrupt amyloid beta-driven tau hyperphosphorylation and neuroinflammation in Alzheimer’s disease
A spirocyclic triazaspirodecanone developed by Cassava Sciences to target an altered conformation of the scaffolding protein filamin A in Alzheimer’s disease, discontinued in November 2024 after two large Phase 3 randomized controlled trials failed to demonstrate cognitive or functional benefit over placebo.
Abstract
Simufilam (PTI-125) is an oral small-molecule drug candidate of the triazaspirodecanone structural class, developed by Cassava Sciences, Inc. for the treatment of mild-to-moderate Alzheimer’s disease (AD). The compound’s proposed mechanism centers on binding an altered conformation of the intracellular scaffolding protein filamin A (FLNA) that is reportedly induced by amyloid beta 1-42 (Abeta42) in AD brain tissue. According to the published preclinical literature, simufilam binds altered FLNA with femtomolar affinity and restores its native conformation, thereby disrupting two pathogenic signaling cascades: Abeta42 signaling via the alpha-7 nicotinic acetylcholine receptor (alpha7nAChR) that hyperphosphorylates tau protein, and persistent activation of toll-like receptor 4 (TLR4) that drives neuroinflammation. The proposed mechanism, if validated, would represent a first-in-class approach targeting a protein conformational change rather than a conventional receptor or enzyme.
The preclinical and early clinical pharmacology of simufilam was developed almost entirely within the laboratory of Hoau-Yan Wang at the City University of New York (CUNY), in collaboration with Lindsay Burns, then chief science officer of Cassava Sciences. Published reports from this laboratory described femtomolar binding affinity for altered FLNA, picomolar efficacy in postmortem human brain tissue, and reduction of tau hyperphosphorylation, amyloid aggregation, and inflammatory cytokine release in intracerebroventricular Abeta42-infusion and triple-transgenic mouse models. A Phase 2a open-label study in 13 AD patients (100 mg twice daily for 28 days) reported significant reductions in cerebrospinal fluid biomarkers of neurodegeneration and neuroinflammation. These results, published in the Journal of Prevention of Alzheimer’s Disease in 2020, provided the basis for Phase 3 advancement. However, the Wang laboratory subsequently became the subject of data integrity investigations: a CUNY panel initially cited Wang for “egregious misconduct” across 20 papers (later reversed under a different evidentiary standard), a federal grand jury indicted Wang for fraud involving approximately 16 million dollars in NIH grants (charges later dropped), seven Wang papers have been retracted, and the Journal of Neuroscience issued expressions of concern for two foundational simufilam papers. In September 2024, the U.S. Securities and Exchange Commission charged Cassava Sciences with securities fraud, resulting in a 40 million dollar settlement and the resignation and barring of the chief executive officer and chief science officer. Independent replication of the proposed FLNA conformation-modulation mechanism has not been published by laboratories outside the Wang group.
Two large Phase 3 randomized, double-blind, placebo-controlled trials evaluated simufilam in mild-to-moderate AD. The ReThink-ALZ trial (n = 804, simufilam 100 mg twice daily versus placebo for 52 weeks) found no significant difference on either co-primary endpoint: ADAS-Cog12 (least-squares mean difference negative 0.39, p = 0.431) or ADCS-ADL (difference 0.51, p = 0.403). The ReFocus-ALZ trial (n = 1,125, simufilam 50 mg or 100 mg twice daily versus placebo for 76 weeks) similarly failed all co-primary, secondary, and exploratory biomarker endpoints. No significant changes in plasma p-tau217, neurofilament light chain, or glial fibrillary acidic protein were observed. Simufilam was well tolerated in both trials, with an adverse event profile similar to placebo. Cassava Sciences discontinued the AD program in November 2024. An independent cell-culture assessment published in 2026 found that simufilam produced no beneficial effects on amyloid processing, neurotrophic factors, or mitochondrial function in differentiated human neuronal cells, aligning with the clinical outcomes.
This monograph documents the chemistry, proposed molecular pharmacology, pharmacokinetics, preclinical pharmacology, the complete clinical evidence base including Phase 3 trial results, the data integrity controversies that accompanied development, sourcing and handling considerations, adverse event profile, and a comparative assessment of five Alzheimer’s disease therapeutic candidates against simufilam. The compound is not approved by any regulatory authority for any indication. Investigators considering simufilam for research applications should weigh the absence of independent mechanism validation, the complete Phase 3 clinical failure, and the unresolved questions regarding the integrity of the foundational preclinical data.
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A spirocyclic thiadiazine-piperidine compound developed at the Israel Institute for Biological Research as a dual allosteric M1 muscarinic and sigma-1 receptor agonist, distinguished by sub-nanomolar allosteric potency at M1, disease-modifying preclinical efficacy in transgenic Alzheimer’s disease models, and active clinical development across schizophrenia, frontotemporal dementia, and Alzheimer’s disease indications.
Abstract
ANAVEX 3-71 (development code AF710B; CAS 1235733-73-9) is a synthetic spirocyclic thiadiazine-piperidine compound and a dual allosteric agonist at the M1 subtype of the muscarinic acetylcholine receptor and the sigma-1 receptor (SIGMAR1). The compound was invented by Abraham Fisher at the Israel Institute for Biological Research (IIBR) in Ness Ziona, Israel, as the fourth generation of a series of cholinergic agonists (AF102B, AF267B, AF292, AF710B) with progressively greater selectivity and allosteric character at the M1 muscarinic receptor. ANAVEX 3-71 emerged from high-throughput receptogram profiling as a compound with sub-nanomolar allosteric binding affinity at M1 muscarinic receptors (approximately 0.05 nM) and nanomolar affinity at the sigma-1 receptor (Ki approximately 1.3 nM), with no agonistic activity at M2 through M5 muscarinic subtypes, no significant binding at alpha-4-beta-2 or alpha-7 nicotinic receptors, and a clean off-target profile across 83 additional G-protein-coupled receptors, ion channels, and transporters screened at 10 micromolar. The preclinical pharmacology of ANAVEX 3-71 has been characterized principally in three studies using transgenic rodent models of Alzheimer’s disease. Fisher et al. (2016) reported that AF710B at 10 micrograms per kilogram per day intraperitoneally for two months in 3xTg-AD mice reversed cognitive deficits in the Morris water maze, decreased BACE1, GSK3-beta activity, and tau phosphorylation at multiple epitopes (AT180, AT270, PHF-1), reduced soluble and insoluble amyloid-beta 40 and 42, and rescued mushroom dendritic spine loss in hippocampal neuronal cultures at 30 nanomolar. Hall et al. (2018) extended these findings to McGill-R-Thy1-APP transgenic rats, demonstrating that oral treatment at 10 micrograms per kilogram per day for 4.5 months at 13 months of age (postplaque) reverted cognitive deficits, reduced amyloid pathology and neuroinflammation, and increased cerebrospinal fluid amyloid clearance, with effects maintained following a 5-week treatment interruption consistent with disease-modifying rather than symptomatic activity. Orciani et al. (2023) demonstrated that early (preplaque, 7 months of age) treatment at the same dose for 7 months prevented cognitive impairment, reduced hippocampal plaque burden and cortical amyloid-beta peptides, attenuated microglial and astrocytic neuroinflammation, and rescued pro-BDNF to mature BDNF conversion, with effects persisting through a 4-week washout. Human pharmacokinetics characterized in a Phase 1 single ascending dose study (NCT04442945; 36 healthy volunteers; 5 to 200 mg) demonstrate linear, dose-proportional, and time-invariant pharmacokinetics with a mean apparent terminal elimination half-life of 3.56 hours for the parent compound and 6.59 hours for the M8 metabolite. No clinically relevant effects on QTc or other electrocardiographic parameters were observed across the full studied dose range. Food had no effect on the pharmacokinetics of ANAVEX 3-71 or its M8 metabolite. Clinical development is ongoing across multiple indications. A Phase 2 study in schizophrenia (NCT06245213; 71 subjects) reported dose-dependent improvements in electroencephalographic biomarkers and favorable safety and tolerability with no serious treatment-emergent adverse events. A modified-release oral tablet enabling once-daily dosing was successfully developed in a Phase 1b study completed in October 2025. ANAVEX 3-71 is not approved by any regulatory authority and is supplied as a research-grade preparation. This monograph reviews the chemistry, dual-receptor pharmacology, preclinical pharmacology in transgenic Alzheimer’s models, human pharmacokinetics, the clinical evidence base, sourcing and quality verification, handling considerations, interaction profile, adverse event signal, and a comparative assessment of five mechanistically related compounds against ANAVEX 3-71 on five competency standards.
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Antisense oligonucleotide targeting SOD1 mRNA via RNase H-dependent degradation for SOD1-associated amyotrophic lateral sclerosis
A 2′-O-methoxyethyl gapmer antisense oligonucleotide developed by Ionis Pharmaceuticals and Biogen for intrathecal reduction of SOD1 protein in genetically defined SOD1-associated amyotrophic lateral sclerosis, the first gene-targeted therapy approved for any form of ALS.
Abstract
Tofersen (BIIB067, marketed as Qalsody) is a 20-base 2′-O-methoxyethyl (MOE) gapmer antisense oligonucleotide that binds to and mediates RNase H-dependent degradation of superoxide dismutase 1 (SOD1) messenger RNA, reducing synthesis of both mutant and wild-type SOD1 protein in the central nervous system. Developed by Ionis Pharmaceuticals and licensed to Biogen, tofersen received accelerated approval from the United States Food and Drug Administration on April 25, 2023, for the treatment of amyotrophic lateral sclerosis (ALS) in adults with a confirmed SOD1 gene mutation, making it the first gene-targeted therapy approved for any form of ALS. Subsequent approvals followed from the European Medicines Agency (May 30, 2024), the Therapeutic Goods Administration of Australia (January 5, 2025), and Health Canada (March 3, 2025). SOD1 mutations, first identified in familial ALS by Rosen et al. in 1993, account for approximately 13 to 20 percent of familial ALS cases and 1 to 2 percent of sporadic ALS cases. Over 200 pathogenic SOD1 variants have been reported, producing a spectrum of disease phenotypes from rapidly progressive (p.A5V, median survival approximately 1 year from onset) to slowly progressive (p.D91A homozygous, median survival exceeding 10 years). The pathogenic mechanism is a toxic gain of function in which mutant SOD1 protein undergoes misfolding, aggregation, and formation of cytoplasmic inclusions in motor neurons and astrocytes, driving neurodegeneration through oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, and impaired protein degradation. Tofersen addresses this mechanism directly by reducing the concentration of the causative toxic protein. The clinical development program comprises a Phase 1-2 ascending-dose trial (50 participants) establishing dose-dependent CSF SOD1 reduction of up to 36 percent at the 100 mg intrathecal dose; the Phase 3 VALOR trial (108 participants) that did not meet its primary efficacy endpoint of change in the ALS Functional Rating Scale-Revised (ALSFRS-R) at 28 weeks (difference 1.2 points, p = 0.97) but demonstrated robust reductions in CSF SOD1 protein (29 percent) and plasma neurofilament light chain (60 percent); and an open-label extension demonstrating that participants who initiated tofersen early had a statistically significant 3.5-point advantage on ALSFRS-R decline compared with those whose treatment was delayed (p = 0.03 at 52 weeks). Accelerated approval was based on the reduction in plasma neurofilament light chain as a surrogate endpoint reasonably likely to predict clinical benefit. The ongoing ATLAS trial (NCT04856982) evaluates tofersen initiation in presymptomatic SOD1 variant carriers using plasma neurofilament light chain as a biomarker trigger for randomization. Tofersen is administered intrathecally at a dose of 100 mg in 15 mL, with three loading doses at 14-day intervals followed by maintenance doses every 28 days. The estimated CSF half-life is approximately four weeks, and elimination occurs through exonuclease-mediated hydrolysis without cytochrome P450 involvement. The principal adverse events are procedure-related (pain, headache) and drug-related (CSF pleocytosis in 42 percent of treated participants, fatigue, arthralgia, myalgia). Serious neurologic adverse events including myelitis, radiculitis, papilledema with elevated intracranial pressure, and aseptic meningitis have been reported in approximately 7 percent of tofersen-treated participants. This monograph reviews the chemistry, development history, molecular mechanism, pharmacokinetics, preclinical and clinical evidence, sourcing and handling, adverse event profile, and a comparative assessment of five alternative ALS therapeutic agents against tofersen.
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Trifluoroacetyl hydrazone geroneuroprotector with AMPK-mediated neuroprotective and neurogenic activity
A synthetic trifluoroacetyl hydrazone derived from the curcumin scaffold via four generations of phenotypic optimization at the Salk Institute, selected for combined neuroprotective and neurogenic activity in human neural precursor cells, with preclinical efficacy in transgenic Alzheimer’s disease and accelerated-aging mouse models through AMPK-dependent modulation of fatty acid metabolism, inflammation, and acetyl-CoA homeostasis.
Abstract
CAD-31 (CAD-031; CAS 2071209-49-7) is a synthetic trifluoroacetyl hydrazone (molecular weight 404.31, C18H14F6N2O2) derived from the curcumin scaffold through four generations of phenotypic optimization at the Cellular Neurobiology Laboratory of the Salk Institute for Biological Studies. The compound was selected from a library of more than 200 derivatives of the parent compound J147 on the basis of superior potency in a human embryonic stem cell-derived neural precursor cell (hNPC) neurogenesis assay and retention of broad neuroprotective activity across six cell culture models of age-associated brain toxicity [1, 2]. In assays for trophic factor withdrawal, oxidative stress (oxytosis), in vitro ischemia, extracellular and intracellular amyloid-beta toxicity, and BDNF-like neurotrophic activity, CAD-31 demonstrates EC50 values in the range of 12 to 95 nanomolar, comparable to J147 in most assays and superior in the trophic factor withdrawal model [1]. Neurogenesis markers in human neural precursor cells (nestin, Pax6, doublecortin, Ki67) are elevated 2.6- to 5.2-fold relative to J147 at matched concentrations, representing the distinctive pharmacological advance of CAD-31 within the compound series [2]. The molecular mechanism of CAD-31 converges on the AMP-activated protein kinase (AMPK) signaling cascade. CAD-31 activates AMPK by phosphorylation at threonine 172 and inhibits the downstream target acetyl-CoA carboxylase 1 (ACC1) by phosphorylation at serine 79, resulting in elevated acetyl-CoA levels, reduced free fatty acid synthesis, and increased ketone body availability in the brain [1, 6]. This metabolic reprogramming is accompanied by reductions in inflammatory markers (vascular cell adhesion molecule, receptor for advanced glycation endproducts, clusterin) and increases in synaptic proteins (drebrin, activity-regulated cytoskeleton-associated protein) in hippocampal tissue of transgenic Alzheimer’s disease mice [1]. In the therapeutic APPswe/PS1deltaE9 transgenic mouse model of Alzheimer’s disease, CAD-31 administered orally at approximately 10 mg/kg/day to symptomatic 10-month-old mice for three months rescued hippocampus-dependent memory deficits in fear conditioning, Morris water maze, and elevated plus maze paradigms to wild-type control levels [1]. In rapidly aging SAMP8 mice, CAD-31 extended median lifespan by approximately 30 percent when administered in the final quarter of life, with corresponding preservation of youthful gene, protein, and metabolite expression profiles in the brain [6]. Pharmacokinetic characterization in rats demonstrates brain penetrance with a brain-to-plasma ratio of 2.8 at eight hours after oral gavage at 20 mg/kg, and maximum brain concentrations approximately tenfold higher than the in vitro EC50 values [1]. Preclinical safety screening shows no acute toxicity at 2 g/kg, no activity in hERG, Ames, or micronucleus assays, and no inhibition of five major cytochrome P450 enzymes at concentrations more than tenfold above the effective range [1]. No formal molecular target has been identified for CAD-31; the parent compound J147 binds the alpha-F1 subunit of mitochondrial ATP synthase (ATP5A), and CAD-31 likely engages the same or a closely related target given the shared downstream AMPK activation and neuroprotective phenotype [7, 8]. CAD-31 has not entered human clinical trials. The parent compound J147 completed a Phase 1 safety study (NCT03838185), and the related compound CMS121 has received National Institutes of Health funding for Investigational New Drug studies [5]. This monograph reviews the chemistry and synthesis lineage, molecular pharmacology, preclinical pharmacokinetics, in vivo efficacy in transgenic Alzheimer’s disease and accelerated-aging models, the safety profile, and a comparative assessment of five compounds in the geroneuroprotector and Alzheimer’s disease therapeutic landscape against CAD-31. The compound is available as a research-grade preparation from multiple chemical suppliers; it has no approved medical indication in any jurisdiction.
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A second-generation phenylethanol amine ifenprodil derivative developed at Pfizer as a forebrain-selective neuroprotectant, distinguished from first-generation NR2B antagonists by absence of alpha-1 adrenergic receptor activity and clinically evaluated in traumatic brain injury, treatment-resistant major depression, and levodopa-induced dyskinesia in Parkinson’s disease.
Abstract
Traxoprodil (CP-101,606) is a potent and selective antagonist of N-methyl-D-aspartate (NMDA) receptors containing the NR2B (GluN2B) subunit, originally synthesized at the Central Research Division of Pfizer Inc. in Groton, Connecticut, and first disclosed by Chenard et al. in 1995 as a neuroprotectant with high selectivity for forebrain neurons. Structurally a substituted 4-phenylpiperidine and single-isomer phenylethanol amine derivative of the first-generation NR2B antagonist ifenprodil, traxoprodil retains the high-affinity NR2B binding (KD of 4.2 nanomolar in adult rodent forebrain) while eliminating the alpha-1 adrenergic receptor activity that limited the clinical utility of its predecessor. The compound binds at the amino-terminal domain interface of the NR1/NR2B heterodimer and inhibits channel opening by enhancing tonic proton inhibition, a mechanism formally characterized by Mott et al. (1998) that distinguishes the phenylethanol amine class from channel-blocking NMDA antagonists such as ketamine and memantine. Pharmacokinetics in humans are dominated by hepatic cytochrome P450 2D6 (CYP2D6) metabolism, producing a striking polymorphic phenotype: in CYP2D6 extensive metabolizers, the oral bioavailability at a 100 mg dose is approximately 39.5 percent with a plasma elimination half-life of 2 to 4 hours, whereas in poor metabolizers the bioavailability approaches 80 percent with a half-life of approximately 20 hours. The nonlinear, dose-dependent oral pharmacokinetics in extensive metabolizers reflect saturation of hepatic first-pass CYP2D6 metabolism; at high oral doses the impact of CYP2D6 polymorphism on exposure diminishes as the enzyme saturates. The compound was advanced through three principal clinical programs. In traumatic brain injury, an open-label study of 30 patients with severe head injury or spontaneous intracerebral hemorrhage demonstrated safety, tolerability, and 80 percent good recovery at 3 months; a subsequent randomized, double-blind, placebo-controlled Phase 2/3 trial of 404 severe TBI patients showed trends toward improved functional outcome (7.5 percent improvement on the dichotomized Glasgow Outcome Scale, p = 0.07) and reduced mortality (7 percent difference, p = 0.08) but did not reach conventional statistical significance. In treatment-resistant major depression, a randomized, double-blind, placebo-controlled proof-of-concept trial of 30 paroxetine-nonresponders demonstrated a 60 percent response rate on the Hamilton Depression Rating Scale after a single intravenous infusion of CP-101,606 versus 20 percent on placebo, with 78 percent of responders maintaining response for at least one week, and without dissociative side effects. In Parkinson’s disease, a double-blind crossover trial in 12 patients showed approximately 30 percent reduction in levodopa-induced dyskinesia but dose-dependent dissociative and amnestic adverse events. Clinical development was ultimately discontinued due to cardiovascular safety concerns, specifically QTc interval prolongation attributed to inhibition of the human ether-a-go-go-related gene (hERG) potassium channel, a liability that Pfizer determined precluded further advancement. This monograph reviews the chemistry and stereochemistry of traxoprodil; the NR2B-selective pharmacology including the proton-enhancing mechanism and the two-class distinction among NR2B antagonists; the comprehensive CYP2D6-dependent human pharmacokinetics; the preclinical neuroprotection, antinociception, antiparkinsonian, and antidepressant pharmacology; the clinical evidence across traumatic brain injury, treatment-resistant depression, and Parkinson’s disease; and a comparative assessment of five NR2B-selective or NMDA-targeting compounds (rislenemdaz, ifenprodil, Ro 25-6981, radiprodil, and ketamine) against traxoprodil on five competency standards. The compound is not approved by any regulatory authority for any indication. It is available as a research-grade preparation; investigators should obtain analytical confirmation of identity and purity on every lot.
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Dual orexin receptor antagonist (DORA) with balanced OX1R and OX2R competitive antagonism
A benzimidazole-triazole dual orexin receptor antagonist developed at Actelion and Idorsia Pharmaceuticals for the treatment of insomnia disorder, distinguished from earlier DORAs by an optimized pharmacokinetic profile yielding full-night sleep promotion with minimal next-morning residual impairment.
Abstract
Daridorexant (ACT-541468, marketed as Quviviq) is an orally administered, competitive dual orexin receptor antagonist (DORA) approved by the United States Food and Drug Administration in January 2022 and by the European Medicines Agency in April 2022 for the treatment of insomnia disorder in adults. The compound binds both the orexin type 1 receptor (OX1R) and orexin type 2 receptor (OX2R) at sub-nanomolar affinities (Ki 0.47 nM at OX1R, 0.93 nM at OX2R), producing competitive, reversible blockade of the wake-promoting orexin A and orexin B neuropeptides without direct engagement of GABAergic, histaminergic, monoaminergic, or opioid receptor systems. In a selectivity panel of more than 130 central and peripheral pharmacological targets, daridorexant demonstrated no significant off-target binding, a profile that distinguishes it from the benzodiazepines and the Z-drugs (zolpidem, zaleplon, eszopiclone) and that underpins a mechanism-based rationale for preservation of physiological sleep architecture, absence of rebound insomnia on discontinuation, and low liability for tolerance and physical dependence.
The compound was discovered at Actelion Pharmaceuticals Ltd in Allschwil, Switzerland, under the leadership of Jean-Paul and Martine Clozel, and was selected from a large series of benzimidazole-containing dual orexin receptor antagonists on the basis of an optimized pharmacokinetic profile: a terminal elimination half-life of approximately 8 hours, oral bioavailability of 62 percent, rapid absorption (time to peak plasma concentration 1 to 2 hours), and a plasma clearance rate designed to provide full-night sleep coverage at a dose of 25 to 50 mg while minimizing next-morning residual sedation at efficacious doses. When Actelion was acquired by Johnson and Johnson in June 2017, the drug discovery operations (including daridorexant) were spun off into the newly created Idorsia Pharmaceuticals Ltd, which advanced the compound through Phase 2 and Phase 3 clinical development and secured regulatory approval.
Two pivotal Phase 3 randomized, double-blind, placebo-controlled trials (Study 1, N=930; Study 2, N=924) conducted at 156 sites in 18 countries demonstrated statistically significant improvements in the co-primary endpoints of wake time after sleep onset (WASO) and latency to persistent sleep (LPS) measured by polysomnography at months 1 and 3. The 50 mg dose additionally improved patient-reported daytime functioning as measured by the Insomnia Daytime Symptoms and Impacts Questionnaire (IDSIQ), making daridorexant the first insomnia pharmacotherapy to demonstrate improvement on both nighttime sleep parameters and a validated daytime functioning instrument in a registration program. Sleep architecture analysis demonstrated preservation of rapid eye movement (REM) and non-REM sleep stage distributions, with no alteration of electroencephalographic spectral bands in N2, N3, or REM stages and no disruption of sleep spindle activity.
Pharmacokinetics are dominated by hepatic CYP3A4-mediated metabolism, which accounts for approximately 89 percent of metabolic clearance. Protein binding is exceptionally high at 99.7 percent; volume of distribution at steady state is 31 liters; and systemic clearance is 5.0 liters per hour. Concomitant administration with strong CYP3A4 inhibitors (itraconazole, clarithromycin, ritonavir) is contraindicated owing to a greater than 400 percent increase in daridorexant exposure; moderate CYP3A4 inhibitors (diltiazem, erythromycin, fluconazole) require dose reduction to 25 mg. The compound is classified as a Schedule IV controlled substance in the United States on the basis of human abuse potential data demonstrating dose-dependent drug-liking effects in recreational sedative drug users, consistent with the scheduling of the other approved DORAs suvorexant and lemborexant.
The safety profile in pivotal trials and in a 40-week extension study (total treatment duration up to 12 months) demonstrated favorable tolerability. The most common adverse events were nasopharyngitis, headache, somnolence, and fatigue, occurring at low incidence. Adverse events of special interest (sleep paralysis, hypnagogic and hypnopompic hallucinations, cataplexy-like symptoms, suicidal ideation) were rare. No evidence of withdrawal symptoms, rebound insomnia, or tolerance was observed on abrupt discontinuation after up to 12 months of treatment. This monograph reviews the chemistry, synthesis, and structural pharmacology of daridorexant; the dual-receptor antagonist mechanism in molecular and functional detail; the comprehensive human pharmacokinetic record; the preclinical pharmacology in rodent and canine models; the clinical evidence base from Phase 1 through Phase 3 and long-term extension; sourcing and quality verification considerations; reconstitution and handling; stack-interaction considerations; adverse-event and safety signal analysis; and a comparative assessment of five alternative insomnia pharmacotherapies against daridorexant on five competency standards.
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