Sulfonamidoacetamide small-molecule inducer of axon regeneration and neurite outgrowth
A synthetic sulfonamidoacetamide identified through phenotypic cell-based screening and structure-activity optimization as a potent inducer of neurite outgrowth in hippocampal, cortical, and retinal primary neurons, with demonstrated in vivo axon regeneration activity in an optic nerve crush injury model.
Abstract
Compound 7P (CAS 1890208-58-8) is a synthetic sulfonamidoacetamide with the systematic name 2-[(2-methoxyphenyl)[(4-methylphenyl)sulfonyl]amino]-N-(4-methoxy-3-pyridinyl)acetamide and molecular formula C22H23N3O5S (molecular weight 441.50 g/mol). The compound was identified at Hanyang University (Republic of Korea) through a phenotypic cell-based screening campaign of chemical libraries followed by iterative structure-activity-guided optimization, culminating in its characterization as the lead compound in a 2016 Journal of Medicinal Chemistry report by Ku, Park, Lee, and colleagues [1]. Compound 7P promotes neurite outgrowth in cultured primary neurons derived from the hippocampus, cerebral cortex, and retina, and in an in vivo rat model of optic nerve crush injury it induces the growth of GAP-43-positive regenerating axons at distances extending beyond 1500 micrometers distal to the crush epicenter, a finding that demonstrates translation of the in vitro neurite outgrowth phenotype into bona fide central nervous system axon regeneration.
The compound was selected as the optimization lead on the basis of three convergent improvements over the parent hit (compound 1): enhanced neurite outgrowth activity in the primary neuron phenotypic assay, improved aqueous solubility attributable to the introduction of a 4-methoxypyridinyl amide pharmacophore replacing a lipophilic aniline, and markedly improved metabolic stability (61.2 percent of parent compound remaining after microsomal incubation, compared to 0.7 percent for the original hit) driven by reduction of the calculated partition coefficient from 3.76 to 2.43 [1]. These properties rendered compound 7P suitable for the in vivo optic nerve injury study that constitutes the principal translational evidence for the compound class.
The molecular target or targets through which compound 7P stimulates axon regeneration have not been definitively identified. The phenotypic screening approach that generated the compound was target-agnostic, and the published literature does not report a defined receptor, enzyme, or signaling node as the primary binding partner. Contextual evidence from the broader axon regeneration field implicates pathways including the mammalian target of rapamycin (mTOR), the signal transducer and activator of transcription 3 (STAT3), and phosphatase and tensin homolog (PTEN) signaling as determinants of central nervous system axon growth competence, but the specific engagement of these pathways by compound 7P has not been demonstrated in pathway-deconvolution or target-identification studies.
Compound 7P has no clinical development history. No human pharmacokinetic, safety, or efficacy data have been generated. The compound is not approved by any regulatory authority for any indication. It has entered the research-chemical supply chain as a nootropic-marketed powder on the basis of the published preclinical neurite outgrowth and axon regeneration data, but no clinical evidence supports cognitive enhancement, neuroprotection, or any other therapeutic claim in humans. This monograph documents the chemistry, structure-activity optimization, published preclinical pharmacology, the limited mechanistic and pharmacokinetic characterization, sourcing and handling considerations, and a comparative assessment against five alternative axon-regeneration-promoting small molecules on five competency standards. Investigators should treat compound 7P as an early-stage preclinical research tool with a single peer-reviewed primary publication and no human translational data.
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A first-in-class dual PPARalpha/delta agonist developed by Genfit for hepatic steatoinflammatory and cholestatic liver diseases, granted FDA accelerated approval in June 2024 as Iqirvo for the treatment of primary biliary cholangitis in adults with inadequate response or intolerance to ursodeoxycholic acid.
Abstract
Elafibranor (GFT505) is a synthetic phenoxyalkanoic acid derivative and dual agonist of the peroxisome proliferator-activated receptor alpha (PPARalpha) and peroxisome proliferator-activated receptor delta (PPARdelta), with additional lower-potency agonist activity at the peroxisome proliferator-activated receptor gamma (PPARgamma). The compound activates PPARalpha with an EC50 of approximately 45 nanomolar and PPARdelta with an EC50 of approximately 175 nanomolar, producing a composite pharmacological profile that modulates hepatic fatty acid beta-oxidation, triglyceride metabolism, high-density lipoprotein cholesterol, bile acid synthesis and transport, glucose homeostasis, and macrophage-mediated hepatic inflammation through coordinated transcriptional regulation at both receptor subtypes. Elafibranor and its principal active metabolite GFT1007, formed by hydrolysis of the parent compound, both contribute to the pharmacological activity. The compound was discovered and initially developed by Genfit S.A. (Lille, France) for the treatment of nonalcoholic steatohepatitis (NASH), advancing through a Phase 2b trial (GOLDEN-505) in 274 patients that produced a post-hoc signal for NASH resolution without fibrosis worsening at the 120 mg daily dose, and into the Phase 3 RESOLVE-IT trial in over 1,000 patients, which was terminated in 2020 following an interim futility analysis that failed to demonstrate statistically significant separation from placebo on the primary endpoint. Development subsequently pivoted to primary biliary cholangitis (PBC), where elafibranor received FDA Breakthrough Therapy Designation in 2019 and demonstrated robust efficacy in the Phase 3 ELATIVE trial: 51 percent of patients receiving elafibranor 80 mg daily achieved a biochemical cholestasis response at week 52, compared to 4 percent on placebo, with alkaline phosphatase normalization in 15 percent of treated patients versus none on placebo. On June 10, 2024, the United States Food and Drug Administration granted accelerated approval to elafibranor (trade name Iqirvo, marketed by Ipsen) for the treatment of PBC in combination with ursodeoxycholic acid (UDCA) in adults with inadequate response to UDCA, or as monotherapy in patients unable to tolerate UDCA. European Union authorization followed in September 2024, and the United Kingdom National Institute for Health and Care Excellence (NICE) recommended elafibranor for National Health Service use in October 2024. Pharmacokinetics are characterized by high plasma protein binding (approximately 99.7 percent), a large apparent volume of distribution (approximately 4,731 liters), a long elimination half-life of the parent compound (approximately 60 to 70 hours), and metabolism of GFT1007 through CYP2C8, UGT1A3, and UGT2B7. The compound is generally well tolerated at the approved 80 mg daily dose; the principal adverse events in controlled trials were gastrointestinal (abdominal pain, diarrhea, nausea, and vomiting, each occurring in approximately 11 percent of treated patients versus 2 to 9 percent on placebo), weight gain, arthralgia, and musculoskeletal complaints including rare myopathy and rhabdomyolysis. Dose-dependent hepatotoxicity has been observed at supratherapeutic doses (exceeding 120 mg daily), with transaminase elevations above 5 times the upper limit of normal in approximately one-third of healthy volunteers at those exposures. The compound is contraindicated in decompensated cirrhosis and complete biliary obstruction and carries a warning for embryo-fetal toxicity. This monograph reviews the chemistry, synthesis, and structural class of elafibranor; the PPAR-mediated molecular pharmacology; the comprehensive pharmacokinetic profile including the GFT1007 active metabolite; the preclinical evidence in rodent models of steatohepatitis, fibrosis, and cholestasis; the clinical evidence base across NASH and PBC indications; sourcing and quality verification; reconstitution and handling; stack interactions and combinations; adverse events and safety signals; and a comparative assessment of five alternative agents (obeticholic acid, seladelpar, bezafibrate, fenofibrate, and saroglitazar) against elafibranor on five competency standards.
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Selective phosphodiesterase type 5 (PDE5) inhibitor of the pyrrolopyrimidinone structural class
A second-generation pyrrolopyrimidinone PDE5 inhibitor developed by SK Chemicals in South Korea for erectile dysfunction, distinguished from first-generation agents by approximately 10-fold higher PDE5 affinity, superior isoenzyme selectivity, and an emerging multimodal research profile in Alzheimer’s disease through cGMP/PKG/CREB signaling, autophagy enhancement, and neuroinflammatory modulation.
Abstract
Mirodenafil (SK3530) is a potent, selective, and reversible inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5) belonging to the pyrrolopyrimidinone structural class. Developed by SK Chemicals Life Science (Seongnam, South Korea) and approved in 2007 by the Korea Ministry of Food and Drug Safety for the treatment of erectile dysfunction, mirodenafil is marketed as Mvix in 50 mg and 100 mg oral tablet formulations and as a 50 mg orally dissolving film. The compound inhibits PDE5 with an IC50 of 0.34 nmol/L, approximately 10-fold more potent than sildenafil (IC50 3.5 nmol/L), and exhibits selectivity ratios of approximately 48,235-fold over PDE1, 254,000-fold over PDE3, and greater than 10,000-fold over PDE11. The PDE6 selectivity ratio is approximately 30-fold, intermediate between sildenafil and tadalafil but clinically associated with a low incidence of visual disturbance at therapeutic doses. Pharmacokinetically, mirodenafil is rapidly absorbed after oral administration with a time to maximum plasma concentration of 0.67 to 1.5 hours, an elimination half-life of 1.32 to 3.0 hours, oral bioavailability of 24 to 43 percent for the parent compound, and approximately 97 percent plasma protein binding. Metabolism is predominantly hepatic through CYP3A4-mediated N-dealkylation to the active metabolite SK-3541, which retains approximately one-tenth of the PDE5 inhibitory activity of the parent compound. Clinical efficacy in erectile dysfunction has been demonstrated in multiple randomized, double-blind, placebo-controlled trials totaling more than 700 patients across general, diabetic, and hypertensive populations, with improvements in the International Index of Erectile Function erectile function domain score of 7 to 12 points over placebo. Adverse events are predominantly mild to moderate, with flushing (3.3 to 24.1 percent) and headache (1.8 to 14.8 percent) as the most common; no visual disturbances or myalgia have been reported in published trials. Beyond erectile dysfunction, mirodenafil (designated AR1001 by licensee AriBio) has entered clinical development for Alzheimer’s disease on the basis of preclinical evidence demonstrating multimodal neuroprotective activity: activation of the cGMP/PKG/CREB signaling pathway, enhancement of autophagy-lysosome clearance of amyloid-beta and phosphorylated tau, suppression of neuroinflammation, and improvement of mitochondrial function. A Phase 2 randomized placebo-controlled trial in 210 patients with mild to moderate Alzheimer’s disease reported that AR1001 30 mg daily as monotherapy produced a statistically significant 4.019-point improvement on the ADAS-Cog 13 at 26 weeks (p = 0.012) with concurrent reductions in plasma phosphorylated tau-181 and tau-217 biomarkers. The global Phase 3 POLARIS-AD trial, enrolling approximately 1,150 participants with early Alzheimer’s disease across 200 sites under FDA, EMA, and MHRA authorization, is currently underway with a primary endpoint of change in Clinical Dementia Rating Sum of Boxes at 52 weeks. This monograph reviews the chemistry, pharmacology, pharmacokinetics, clinical evidence, sourcing, handling, stack interactions, safety profile, and comparative positioning of mirodenafil against five PDE5 inhibitor alternatives.
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Substituted phenethylamine benzoate ester with hypermnesic (memory-enhancing) activity and mixed dopaminergic-cholinergic-serotonergic pharmacology
A synthetic amino ethyl meta-benzoic acid methyl ester developed at Creighton University in the 1970s as a novel psychotropic agent, distinguished by a single double-blind human study demonstrating statistically significant enhancement of verbal memory retention at a 5 mg oral dose, and by a nearly complete absence of follow-up clinical investigation despite favorable acute tolerability and a high therapeutic index in animal models.
Abstract
PRL-8-53 (methyl 3-[2-[benzyl(methyl)amino]ethyl]benzoate hydrochloride) is a synthetic substituted phenethylamine and benzoate ester first synthesized by Nikolaus R. Hansl at Creighton University in the early 1970s as part of a systematic exploration of amino ethyl meta-benzoic acid esters for spasmolytic and psychotropic activity. The compound is classified as a hypermnesic agent on the basis of a single published double-blind, placebo-controlled human study (Hansl and Mead, 1978) in which a 5 mg oral dose produced statistically significant improvement in the retention of serially presented verbal material in 47 healthy volunteers, with the most pronounced effects observed in subjects over 30 years of age who had below-average baseline recall performance. The magnitude of the retention enhancement was substantial: subjects in the over-30 subgroup demonstrated approximately 108 percent improvement in 24-hour recall and 152 percent improvement in one-week recall relative to their placebo performance, with most P values better than 0.01 and some better than 0.001. The compound did not significantly alter visual reaction time or motor control at the studied dose, suggesting a selective cognitive action rather than generalized central nervous system stimulation.
The molecular pharmacology of PRL-8-53 remains incompletely characterized. Preclinical evidence from Hansl’s laboratory and from the patent literature (US 3,870,715; granted March 11, 1975) indicates that the compound potentiates dopaminergic neurotransmission, partially inhibits serotonergic activity, and displays possible cholinergic properties. In animal models, PRL-8-53 reverses reserpine-induced catatonia and ptosis, improves avoidance learning in conditioned response paradigms, and exhibits spasmolytic activity against acetylcholine-, barium chloride-, and histamine-induced smooth muscle contraction. The compound does not exhibit stimulant properties at doses up to 200 mg/kg in rodents and does not potentiate the locomotor effects of dextroamphetamine at 20 mg/kg. The oral median lethal dose in mice is approximately 860 mg/kg, conferring a therapeutic index of approximately 170 relative to the projected human-equivalent dose, and chronic toxicology studies in rats, dogs, and monkeys through two offspring generations revealed no evidence of organ pathology or teratogenicity.
Despite these promising early findings, no additional controlled human studies have been published since the 1978 report. The compound’s development was interrupted by Hansl’s retirement from Creighton University and a 1985 institutional dispute that resulted in the loss of stored experimental materials. The patent expired in approximately 1992, placing the compound in the public domain. Formal pharmacokinetic characterization in humans has not been published; the plasma elimination half-life is estimated at 2 to 4 hours on the basis of the compound’s structural properties and the time course of cognitive effects observed in the Hansl study. The metabolic pathways, routes of elimination, plasma protein binding, and blood-brain barrier penetration characteristics remain uncharacterized. PRL-8-53 is not approved by any regulatory authority for any indication. It is available as a research-grade preparation from multiple chemical suppliers at greater than 98 percent purity; investigators should obtain independent analytical confirmation of identity and purity on every lot. This monograph reviews the chemistry, synthesis, and structural classification of PRL-8-53; the available preclinical pharmacology; the single published human study in detail; the limited pharmacokinetic information; sourcing and quality verification; reconstitution and handling; stack-interaction considerations; adverse-event and safety signal; and a structured comparative assessment of five nootropic memory-enhancing compounds against PRL-8-53 on five competency standards.
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Small-molecule Wnt/beta-catenin signaling pathway activator for topical dermatological application
A synthetic 1,4-diketone Wnt pathway activator developed by Samumed (Biosplice Therapeutics) as a topical treatment for androgenetic alopecia, distinguished by its mechanism of follicular Wnt/beta-catenin signaling restoration and hair follicle neogenesis capacity in preclinical models, advanced through Phase 3 clinical evaluation before discontinuation.
Abstract
SM-04554, also designated dalosirvat (International Nonproprietary Name), is a synthetic small-molecule activator of the canonical Wnt/beta-catenin signaling pathway developed by Samumed, LLC (subsequently renamed Biosplice Therapeutics, Inc.) as a topical treatment for androgenetic alopecia (AGA). The compound activates Wnt signaling with an EC50 of approximately 28 to 29 nanomolar in cell-based reporter assays, producing increases in total and nuclear beta-catenin, versican expression, and Ki-67 proliferation marker specifically in hair follicle compartments. The molecular formula is C18H16O4 with a molecular weight of 296.32 g/mol; the compound is a 1,4-diketone bearing a 2,3-dihydro-1,4-benzodioxin-6-yl moiety and a terminal phenyl group, conferring moderate lipophilicity (calculated XLogP 2.6) suitable for topical scalp formulation.
The mechanistic rationale for SM-04554 in androgenetic alopecia rests on the observation that Wnt/beta-catenin signaling is essential for the initiation and maintenance of the anagen (growth) phase of the hair cycle and that progressive reduction of Wnt pathway activity in the dermal papilla and hair bulge stem cell niche is a molecular correlate of follicular miniaturization in AGA. SM-04554 activates the pathway downstream of ligand-receptor interaction, increasing nuclear translocation of beta-catenin and transcription of Wnt target genes including those regulating dermal progenitor cell differentiation toward the hair follicle lineage. In preclinical models, topical SM-04554 induced hair follicle neogenesis in CD1 and C57BL/6 mice (2-fold increase in total follicle count after 4 days of treatment) and in Hanford mini-pigs (significant increase in vellus follicle number sustained through 112 days of observation following a 42-day treatment course).
Clinical development proceeded through Phase 1 (29 subjects, 14-day topical application at 0.05%, 0.15%, and 0.45% concentrations), Phase 2 (two studies: a 49-subject biopsy-endpoint trial and a 300-subject efficacy trial, both 90-day treatment), and Phase 3 (625-subject registration trial initiated November 2018 and completed January 2021). The Phase 1 trial demonstrated safety with only one drug-related adverse event (eye irritation at the 0.45% concentration). The Phase 2 program demonstrated statistically significant increases in non-vellus hair count and density at the 0.15% concentration relative to vehicle, with an inverted-U dose-response in which the 0.15% concentration outperformed the higher 0.25% concentration. Adverse events across the Phase 2 program were mild (scalp redness, burning, stinging) and comparable in frequency to vehicle. No serious adverse events were reported in any treated patient across the Phase 2 program. The Phase 3 trial results were not publicly disclosed; Biosplice Therapeutics removed SM-04554 from its development pipeline in 2021, and a 2023 literature review confirmed cancellation of development based on Phase 3 outcomes. The compound is not approved by any regulatory authority.
SM-04554 is one component of a broader Wnt-modulating therapeutic platform developed by Samumed/Biosplice, which includes lorecivivint (SM-04690, a CLK2/DYRK1A kinase inhibitor for knee osteoarthritis) and SM-04755 (a Wnt pathway inhibitor for tendinopathy). The compound is available from multiple research chemical suppliers as a white powder at greater than 99% purity. This monograph reviews the chemistry, Wnt pathway pharmacology, preclinical hair growth models, the complete clinical evidence base across all trial phases, pharmacokinetic considerations for topical delivery, sourcing and handling, stack-interaction considerations, adverse-event profile, and a comparative assessment of five alternative androgenetic alopecia candidates against SM-04554 on five competency standards.
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Synthetic bioregulatory tripeptide (Glu-Asp-Arg) with proposed epigenetic neuromodulatory activity
A synthetic tripeptide bioregulator derived from the pineal gland peptide fraction, investigated as a neuroepigenetic modulator of gene expression with reported neuroprotective, antioxidant, and geroprotective activity in preclinical oxidative stress, ischemia, and neurodegeneration models.
Abstract
Pinealon (EDR peptide; L-glutamyl-L-aspartyl-L-arginine) is a synthetic tripeptide bioregulator developed at the Saint Petersburg Institute of Bioregulation and Gerontology under the direction of Vladimir Khavinson as part of a multigenerational program to identify tissue-specific short-chain peptides capable of modulating gene expression through direct interaction with chromatin. The compound was identified as one of the shortest biologically active sequences within Cortexin, a complex peptide fraction extracted from bovine cerebral cortex tissue that has been used clinically in several post-Soviet jurisdictions for the treatment of traumatic brain injury, ischemic stroke, and cognitive impairment. Pinealon was subsequently synthesized as a standalone tripeptide and advanced through a series of in vitro and in vivo investigations spanning antioxidant activity, neuroprotection, serotonin biosynthesis regulation, dendritic spine preservation in Alzheimer’s disease models, and preliminary open-label clinical observations in elderly patients with cognitive decline and in patients recovering from craniocerebral trauma.
The proposed mechanism of action is unconventional relative to classical receptor-mediated peptide pharmacology. Due to its low molecular weight (418.41 g/mol) and cationic character, Pinealon is reported to penetrate lipid bilayers and nuclear membranes without requiring surface receptor engagement, gaining direct access to chromatin. Molecular modeling and in vitro binding studies from the Khavinson laboratory have identified complementary binding sites in the promoter regions of several genes relevant to neuroprotection and neurodegeneration, including TPH1 (tryptophan hydroxylase 1, the rate-limiting enzyme in serotonin biosynthesis), SOD2 (mitochondrial superoxide dismutase), GPX1 (glutathione peroxidase 1), PPARA and PPARG (peroxisome proliferator-activated receptor alpha and gamma), CASP3 (caspase-3), and APOE (apolipoprotein E). The proposed binding occurs at specific DNA sequences, principally d(CCTGCC)2 and d(CCAGC)2, through sequence-specific steric and electrostatic complementarity with the major groove of double-stranded DNA. The functional consequence is reported to be destabilization of local DNA secondary structure, alteration of histone modification patterns, and increased accessibility of regulatory regions to transcription factors, resulting in upregulation of neuroprotective gene products and downregulation of pro-apoptotic pathways.
Preclinical pharmacology studies, conducted predominantly by the Khavinson group and affiliated Russian laboratories, have reported that Pinealon produces dose-dependent suppression of reactive oxygen species accumulation in cerebellar granule cells, neutrophils, and pheochromocytoma (PC12) cells; increases cell viability under oxidative stress conditions; delays ERK1/2 activation in neurons exposed to homocysteine; reduces caspase-3 expression and p53 protein synthesis in brain tissue; increases serotonin synthesis in neuronal cultures of rat cerebral cortex; normalizes superoxide dismutase and glutathione peroxidase activity in the brains of hypoxia-sensitive rats; prevents the loss of mushroom-shaped dendritic spines in hippocampal neurons from 5xFAD transgenic mice (a model of familial Alzheimer’s disease); and protects rat offspring from prenatal hyperhomocysteinemia-induced cognitive deficits. In an open-label clinical observation in 72 patients with traumatic brain injury, addition of Pinealon to standard rehabilitation therapy improved memory function in approximately 59 percent of patients.
No completed, peer-reviewed randomized controlled trial of Pinealon has been published in English-language indexed journals as of the date of this monograph. No Phase 1 formal safety study, no Phase 2 efficacy trial, and no Phase 3 registration study exist in any population. The compound has no approved indication in any jurisdiction recognized by the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use. Virtually all published Pinealon research originates from the Khavinson laboratory and closely affiliated institutions; independent replication by Western academic laboratories is absent. The chromatin-interaction model, while supported by computational molecular modeling and fluorescence microscopy studies from the originating group, has not been independently validated by structural biology methods (X-ray crystallography, cryo-electron microscopy) at the resolution required to confirm the proposed binding geometry. This monograph documents the chemistry, proposed mechanism, preclinical pharmacology, clinical observations, sourcing and handling, and comparative assessment of the compound, and identifies the principal evidence gaps that currently limit its positioning in the research-clinical translation pipeline.
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A first-in-class triazinetrione pan-Trk positive allosteric modulator developed by AlzeCure Pharma that enhances BDNF and NGF signaling for the treatment of cognitive dysfunction in Alzheimer’s disease, with additional preclinical support for depression, traumatic brain injury, and sleep disorders.
Abstract
ACD856 is a novel, orally bioavailable triazinetrione compound functioning as a positive allosteric modulator (PAM) of the tropomyosin receptor kinases TrkA, TrkB, and TrkC, the principal signal-transducing receptors for the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3), respectively [1, 2]. The compound was identified through a high-throughput screening campaign of approximately 25,000 compounds and structurally optimized from the veterinary antiparasitic triazinetrione scaffold shared by toltrazuril and ponazuril (ACD855), with the critical improvement of a substantially shortened elimination half-life suitable for once-daily human dosing [3, 4]. ACD856 potentiates the tropomyosin receptor kinases with EC50 values of 382 nM (TrkA), 295 nM (TrkB), and approximately 330 nM (TrkC), and exhibits additional positive allosteric modulation of the insulin-like growth factor 1 receptor (IGF1R) and fibroblast growth factor receptor 1 (FGFR1) [1, 5]. The mechanism of action is distinct from orthosteric Trk agonism: ACD856 binds the intracellular kinase domain of Trk receptors and increases the maximal catalytic velocity (Vmax) of the kinase, thereby amplifying endogenous neurotrophin signaling rather than substituting for it [2, 6]. This allosteric mechanism preserves the spatiotemporal specificity of native neurotrophin activity, a property expected to confer a more favorable safety profile than direct agonist approaches that have historically been limited by pain, hyperalgesia, and off-target proliferative effects.
In preclinical pharmacology, ACD856 has demonstrated reversal of scopolamine-induced and dizocilpine (MK-801)-induced memory impairment in passive avoidance and novel object recognition tasks in mice, restoration of age-related memory deficits in 21-month-old mice to the performance level of young animals following single-dose administration, neuroprotection against amyloid-beta(1-42)-induced synaptotoxicity in primary cortical neurons, enhancement of NGF-stimulated neurite outgrowth in PC12 cells, elevation of BDNF protein levels in the brains of aged mice following repeated dosing, and sustained antidepressant-like effects in the forced swim test persisting up to seven days after the last dose [5, 7, 8]. The compound also enhanced mitochondrial ATP production under energy-deprived conditions, increased phosphorylation of TrkB and ERK1/2 in cortical neurons, elevated hippocampal concentrations of serotonin, noradrenaline, and dopamine by in vivo microdialysis, and increased expression of the presynaptic protein SNAP25, collectively indicating a broad neuroprotective and neuroplasticity-promoting pharmacological profile [5, 7].
ACD856 has completed two Phase 1 clinical studies in healthy volunteers. The single ascending dose (SAD) study (1 to 150 mg oral, n = 56) demonstrated rapid absorption (median tmax 0.33 to 1.0 hours), linear dose-proportional pharmacokinetics, near-complete oral bioavailability (approximately 93 percent relative bioavailability), a terminal elimination half-life of approximately 20 hours supporting once-daily dosing, and an acceptable safety profile with no serious adverse events and no dose-related safety signals [9]. The multiple ascending dose (MAD) study (10, 30, and 90 mg daily for seven days, n = 24) confirmed dose-dependent increases in cerebrospinal fluid concentrations (geometric mean 3.98 to 100 ng/mL), CSF-to-unbound-plasma ratios of 0.37 to 1.20 indicating substantial blood-brain barrier penetration, dose-dependent changes on quantitative electroencephalography (increased theta power and theta/beta ratio) consistent with central target engagement, and continued safety and tolerability with no serious adverse events [10, 11]. AlzeCure Pharma has received a EUR 2.5 million grant from the European Innovation Council to conduct a Phase IIa clinical study of ACD856 in Alzheimer’s disease, with higher doses to be evaluated based on the favorable Phase 1 safety profile [12]. Additional indications under preclinical investigation include depressive disorders, traumatic brain injury, sleep disorders, and postoperative cognitive dysfunction.
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Orally active pyrazolinone-piperidine dipeptide growth hormone secretagogue receptor type 1a (GHS-R1a) agonist
A non-peptide ghrelin receptor agonist developed at Pfizer as a peptidomimetic growth hormone secretagogue for age-related functional decline, subsequently approved in veterinary medicine for appetite stimulation in dogs and weight management in cats with chronic kidney disease.
Abstract
Capromorelin (CP-424,391) is an orally active, non-peptide agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a, the ghrelin receptor) belonging to the pyrazolinone-piperidine dipeptide structural class. The compound was discovered at Pfizer Global Research and Development through systematic structure-activity optimization of peptidomimetic scaffolds and was selected as a clinical development candidate on the basis of high receptor affinity (Ki = 7 nM at human GHS-R1a), potent functional activity (EC50 = 3 nM in rat pituicyte growth hormone release assay), oral bioavailability, and robust in vivo growth hormone secretion in rodent and canine models [1, 2]. Capromorelin mimics the endogenous acylated peptide hormone ghrelin by binding the GHS-R1a receptor on somatotroph cells of the anterior pituitary gland and on hypothalamic neurons, activating Gq/11-coupled phospholipase C signaling, intracellular calcium mobilization, and consequent pulsatile growth hormone release through a pathway mechanistically distinct from and synergistic with the growth hormone releasing hormone (GHRH) receptor pathway. Secondary pharmacological activities include appetite stimulation through hypothalamic orexigenic circuits, transient elevation of circulating cortisol and prolactin, and sustained elevation of insulin-like growth factor 1 (IGF-1) on chronic dosing. In human clinical development, capromorelin advanced through Phase I single ascending dose studies in healthy volunteers and spinal cord injured patients (Ellis et al. 2015), demonstrating safety, tolerability, and dose-proportional pharmacokinetics at oral doses of 20 to 100 mg, and through a Phase II multicenter randomized placebo-controlled trial in 395 older adults aged 65 to 84 years with mild functional limitation (White et al. 2009), in which 12 months of daily oral capromorelin produced statistically significant increases in lean body mass (1.4 kg at 6 months, 1.6 kg at 12 months), growth hormone secretion, IGF-1 concentrations, and tandem stair climbing power compared to placebo [5, 6]. Human clinical development was subsequently discontinued; the compound did not advance to Phase III registration trials for age-related sarcopenia or functional decline. In veterinary medicine, capromorelin oral solution received United States Food and Drug Administration approval in 2016 as Entyce (Aratana Therapeutics, subsequently Elanco Animal Health) for appetite stimulation in dogs at an oral dose of 3 mg/kg once daily, and in October 2020 as Elura for the management of weight loss in cats with chronic kidney disease [7, 8, 9]. These veterinary approvals represent the only registered therapeutic applications of capromorelin as of the most recent monograph revision. The compound is the first and only FDA-approved ghrelin receptor agonist for appetite stimulation in companion animals and demonstrates the translational validity of the GHS-R1a mechanism for orexigenic and anabolic applications. Pharmacokinetics in dogs are characterized by rapid oral absorption (Tmax approximately 0.83 hours), moderate oral bioavailability (44 percent), hepatic metabolism predominantly through CYP3A4 and CYP3A5 mediated N-dealkylation and O-debenzylation, and a short terminal elimination half-life (approximately 1.2 hours in dogs, 2.4 hours in rats) [2, 15, 16]. In humans, single ascending oral doses of 20 to 100 mg produced dose-proportional increases in plasma concentration with broadly similar pharmacokinetic behavior between able-bodied and spinal cord injured participants [5]. The compound is well tolerated at studied doses; the principal adverse events across species are transient hypersalivation, mild emesis, loose stools, and transient increases in serum cortisol and glucose concentrations that normalize within hours of dosing. This monograph reviews the chemistry, synthesis, and structure-activity relationships of capromorelin; the GHS-R1a receptor pharmacology and downstream signaling; the comprehensive pharmacokinetic record across species; the preclinical pharmacology in rodent and canine models; the human clinical evidence base including Phase I and Phase II trials; the veterinary clinical evidence and regulatory approvals; sourcing and quality verification; reconstitution and handling; stack-interaction considerations for research applications; the adverse-event and safety profile; and a comparative assessment of five growth hormone secretagogue candidates (ibutamoren, anamorelin, macimorelin, ipamorelin, tabimorelin) against capromorelin on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation).
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Selective beta-3 adrenergic receptor agonist with secondary CYP2D6 inhibitory activity
A selective beta-3 adrenoceptor agonist developed by Astellas Pharma as the first non-antimuscarinic oral treatment for overactive bladder, distinguished from the antimuscarinic drug class by its distinct receptor mechanism, favorable dry mouth and cognitive side-effect profile, moderate CYP2D6 inhibitory activity, and emerging research interest in brown adipose tissue thermogenesis, metabolic disease, and oncology.
Abstract
Mirabegron (YM-178) is a selective beta-3 adrenergic receptor (beta-3-AR) agonist approved in over 40 countries for the treatment of overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and urinary frequency. Developed by Astellas Pharma and first approved in Japan in 2011 and by the United States Food and Drug Administration in June 2012, mirabegron represented a paradigm shift in OAB pharmacotherapy as the first non-antimuscarinic agent approved for the indication, offering clinically meaningful efficacy with a substantially lower incidence of the dry mouth, constipation, and cognitive impairment that limit long-term adherence to antimuscarinic agents such as oxybutynin, tolterodine, solifenacin, darifenacin, and fesoterodine. The compound activates beta-3 adrenergic receptors on detrusor smooth muscle cells, producing cyclic adenosine monophosphate (cAMP)-mediated relaxation of the bladder wall during the storage phase and thereby increasing functional bladder capacity without impairing voiding contractility. At clinically approved doses (25 mg and 50 mg extended-release tablets administered once daily), mirabegron demonstrates high selectivity for the beta-3-AR over beta-1 and beta-2 adrenergic receptor subtypes, although modest beta-1-AR activity at supratherapeutic concentrations has been characterized and contributes to the dose-dependent cardiovascular signal (small increases in heart rate and blood pressure) that is the principal safety consideration in clinical use. The compound is also a moderate inhibitor of cytochrome P450 2D6 (CYP2D6), producing clinically relevant increases in systemic exposure to CYP2D6 substrates including metoprolol, desipramine, and thioridazine, a property that requires attention in polypharmacy contexts. Four pivotal Phase 3 randomized controlled trials (SCORPIO, ARIES, CAPRICORN, and DRAGON) enrolling over 4,500 patients established the efficacy and tolerability of mirabegron at 25 mg and 50 mg doses, demonstrating statistically significant reductions in mean daily micturition frequency and incontinence episodes compared to placebo over 12-week treatment periods, with efficacy sustained through 12-month extension studies. The safety profile in pooled clinical trial data and in extensive postmarketing surveillance confirms a low incidence of dry mouth (comparable to placebo), with the principal treatment-emergent adverse events being hypertension (7 to 11 percent), nasopharyngitis, urinary tract infection, and headache. Cardiovascular safety analyses, including a multinational non-interventional cohort study, have not identified increased risk of major adverse cardiovascular events relative to antimuscarinic comparators. Beyond the established OAB indication, mirabegron has attracted substantial research interest as a pharmacological activator of brown adipose tissue (BAT) thermogenesis through beta-3-AR-mediated stimulation of uncoupling protein 1 (UCP1) expression. Chronic mirabegron treatment in human subjects has been shown to increase BAT metabolic activity, resting energy expenditure, high-density lipoprotein cholesterol, adiponectin, and insulin sensitivity, positioning the compound as a research tool for metabolic disease and obesity pharmacology. Additional preclinical research has demonstrated antitumor activity through adipose tissue browning and modulation of the tumor microenvironment. This monograph reviews the chemistry, synthesis, and receptor pharmacology of mirabegron; the comprehensive human pharmacokinetic record including CYP2D6 inhibition; the clinical evidence base across OAB and emerging metabolic indications; the reconstitution, sourcing, and stack-interaction considerations for laboratory work; and a comparative assessment of five OAB pharmacotherapies against mirabegron on five competency standards.
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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.
Dimethylxanthine adenosine receptor antagonist and selective cGMP-preferring phosphodiesterase (PDE9) inhibitor
The principal dimethylxanthine metabolite of caffeine in humans, distinguished from the parent compound and from other methylxanthines by selective inhibition of cGMP-preferring phosphodiesterase 9, potentiation of nitric oxide signaling, ryanodine receptor channel activation, and a favorable safety profile relative to caffeine.
Abstract
Paraxanthine (1,7-dimethylxanthine) is the primary metabolite of caffeine in humans, accounting for approximately 80 percent of caffeine biotransformation through hepatic cytochrome P450 1A2 (CYP1A2) catalyzed N3-demethylation. Although structurally an isomer of the naturally occurring dimethylxanthines theophylline (1,3-dimethylxanthine) and theobromine (3,7-dimethylxanthine), paraxanthine is not produced by plants and is encountered in human plasma exclusively as a product of caffeine metabolism. The compound has received escalating research attention since the mid-2000s as a pharmacologically distinct entity rather than a mere intermediate metabolite, with a mechanism of action profile that diverges meaningfully from caffeine at several molecular targets.
The principal pharmacological activities of paraxanthine are competitive antagonism at adenosine A1 and A2A receptors (with binding affinities comparable to or modestly greater than caffeine), selective inhibition of the cGMP-preferring phosphodiesterase PDE9 (an activity not shared by caffeine, theophylline, or theobromine), potentiation of nitric oxide neurotransmission (a unique property among the naturally occurring methylxanthines), and activation of ryanodine receptor calcium release channels (the mechanism underlying its neuroprotective activity in dopaminergic cell models). The composite pharmacology produces psychostimulant, procognitive, neuroprotective, lipolytic, and ergogenic effects that are quantitatively and qualitatively distinguishable from those of caffeine in both preclinical and clinical studies.
Pharmacokinetically, paraxanthine is generated in the liver from caffeine with a formation half-life determined by CYP1A2 activity and reaches plasma concentrations that exceed those of the parent compound approximately 8 to 10 hours after caffeine ingestion. When administered exogenously as pure paraxanthine, the compound exhibits an elimination half-life of approximately 3.1 hours (shorter than caffeine at 4.1 hours, theophylline at 6.2 hours, and theobromine at 7.2 hours), rapid oral absorption, and dose-proportional pharmacokinetics across the studied range of 100 to 400 mg. The shorter half-life contributes to a cleaner offset of stimulant effects and reduced sleep disruption relative to caffeine at equimolar doses.
Clinical evidence from double-blind, placebo-controlled crossover trials demonstrates that acute oral paraxanthine at 100 to 200 mg improves sustained attention, working memory, executive function, reaction time, and psychomotor vigilance in healthy adults, with effects comparable to or exceeding those of caffeine on several cognitive endpoints and with fewer reported adverse events. A 2024 study demonstrated superior cognitive maintenance after a 10-kilometer run compared to caffeine, with caffeine-treated subjects committing 31 percent more errors while paraxanthine-treated subjects improved correct responses by approximately 6.8 percent. Preclinical studies in rodents have demonstrated that paraxanthine supplementation increases muscle mass by 14 to 41 percent, forelimb grip strength by 17 percent, and treadmill endurance by 39 percent relative to control. Paraxanthine has also been shown to enhance brain-derived neurotrophic factor (BDNF) levels, elevate hippocampal acetylcholine and dopamine, and provide neuroprotection against MPTP-induced dopaminergic cell death through ryanodine receptor channel activation.
The safety profile of paraxanthine is favorable relative to caffeine. In 90-day repeat-dose oral toxicity studies in rats, the no-observed-adverse-effect level (NOAEL) for paraxanthine was established at 185 mg/kg body weight compared to 150 mg/kg for caffeine; mortality was observed in two rats receiving caffeine at 185 mg/kg but in none receiving paraxanthine at the same dose. The acute oral LD50 in rats is 829.20 mg/kg. In vitro genotoxicity and mutagenicity studies are negative. In human clinical studies, acute and 7-day daily ingestion of paraxanthine at doses up to 300 mg has not been associated with clinically significant adverse events, changes in blood pressure, or anxiogenic effects at the magnitude observed with equivalent caffeine doses. The ingredient has achieved self-affirmed Generally Recognized as Safe (GRAS) status for use in food and beverages in the United States at levels up to 300 mg per serving. This monograph reviews the chemistry, synthesis, and structural relationships of paraxanthine; the multi-target mechanism of action; the comprehensive pharmacokinetic record; preclinical pharmacology across cognitive, neuroprotective, ergogenic, and metabolic endpoints; the clinical evidence base; sourcing and quality verification; reconstitution and handling; stack interactions and combinations; adverse events and safety; and a comparative assessment of five methylxanthine and stimulant alternatives against paraxanthine on five competency standards.
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The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, sourcing and quality verification, and a curated reference list. Embedded inline below; download for offline reading.
FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.
