Endogenous neuropeptide agonist of galanin receptor type 2 (GALR2) and galanin receptor type 3 (GALR3)
A 14-amino-acid C-terminally amidated neuropeptide of the galanin/kisspeptin/spexin superfamily, identified by bioinformatic hidden Markov model screening of the human proteome in 2007 and subsequently characterized as a satiety factor, metabolic regulator, anxiolytic peptide, and antinociceptive agent operating through selective activation of galanin receptor subtypes 2 and 3.
Abstract
Spexin (SPX), also designated neuropeptide Q (NPQ), is a 14-amino-acid peptide hormone encoded by the C12orf39 gene on human chromosome 12 and processed from a 116-amino-acid prepropeptide by dibasic cleavage and C-terminal alpha-amidation [1, 2]. The mature human sequence (NWTPQAMLYLKGAQ-NH2) is perfectly conserved across all mammalian species examined and differs by only one to two residues from teleost orthologs, placing spexin among the most evolutionarily conserved vertebrate peptide hormones [3]. First identified in 2007 by Mirabeau and colleagues through a hidden Markov model algorithm designed to detect novel secreted peptide hormones in the human genome, and first confirmed biochemically in murine esophageal and gastric tissue [1], spexin was subsequently shown to activate galanin receptor type 2 (GALR2) and galanin receptor type 3 (GALR3) with nanomolar potency (EC50 values of approximately 45.7 and 112.2 nM respectively) while showing no measurable activity at galanin receptor type 1 (GALR1) [4, 5]. This receptor selectivity profile distinguishes spexin from galanin itself, which activates all three galanin receptor subtypes, and establishes spexin as a naturally occurring GALR2/GALR3-selective agonist. The peptide is expressed broadly across central and peripheral tissues including the hypothalamus, hippocampus, amygdala, adipose tissue, liver, gastrointestinal tract, pancreas, kidney, heart, ovary, and testis [6, 7]. Functionally, spexin has been characterized as a satiety factor that suppresses food intake in goldfish, zebrafish, and mice through hypothalamic regulation of orexigenic (neuropeptide Y, agouti-related protein) and anorexigenic (proopiomelanocortin, cocaine- and amphetamine-regulated transcript) neuropeptides [8, 9, 10]. In adipose tissue, spexin inhibits long-chain fatty acid uptake into adipocytes and promotes weight loss in diet-induced obese rodents [11]. Circulating spexin concentrations are significantly reduced in human obesity, type 1 diabetes, type 2 diabetes, metabolic syndrome, and polycystic ovary syndrome, establishing the peptide as a candidate biomarker for metabolic dysregulation [12, 13, 14]. Beyond metabolic regulation, spexin-based GALR2-selective agonists produce anxiolytic effects in murine behavioral models [5], and the metabolically stabilized analog LIT-01-144 produces potent non-opioid peripheral antinociception in persistent inflammatory pain through GALR2 activation [15]. In reproductive physiology, spexin inhibits gonadotropin (LH and FSH) synthesis and secretion in multiple vertebrate species and negatively regulates ovarian steroidogenesis [16, 17]. No human clinical trials of exogenous spexin administration have been reported; the compound remains in the preclinical and biomarker research phase. This monograph reviews the chemistry, gene structure, and peptide processing of spexin; the receptor pharmacology and signal transduction through GALR2 and GALR3; the preclinical pharmacology across metabolic, appetite, nociceptive, anxiolytic, reproductive, and cardiovascular domains; the human biomarker and associative clinical evidence; sourcing and handling considerations for research-grade material; analog development for metabolic stability; and a comparative assessment against five related peptide or receptor-targeted candidates on five competency standards.
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Methoxyflurane is an early halogenated ether that had a remarkable second life. As a general anesthetic (Penthrane, 1962) it was withdrawn in 1974 after dose-dependent nephrotoxicity was traced to intrarenal defluorination producing high plasma fluoride that blocks ascending-limb chloride transport. Forty years later it returned in a low-dose hand-held inhaler format (Penthrox, the green whistle) for procedural analgesia, approved in Australia and re-approved in the EU and UK in 2018. The 3 mL inhaler dose for fracture reduction or dressing changes delivers fluoride exposures orders of magnitude below the historical nephrotoxic threshold. Mechanism includes the standard volatile anesthetic profile plus pronounced TRPA1 modulation that contributes to the analgesia. A genuinely novel sub-anesthetic application of an old molecule. Not stocked by Kodiac. This monograph is provided for research and educational reference.
Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.
Halogenated ether volatile general anesthetic and analgesic
An early halogenated ether withdrawn for nephrotoxicity but reintroduced in low-dose hand-held inhaler format (Penthrox) for procedural analgesia.
Abstract
Methoxyflurane (2,2-dichloro-1,1-difluoroethyl methyl ether; CAS 76-38-0; molecular formula C3H4Cl2F2O; molecular weight 164.97) is a halogenated methyl ethyl ether developed by Ross Terrell in the 1950s and introduced clinically by Abbott in 1962 (Penthrane). The agent was widely used as a general anesthetic through the early 1970s before reports of dose-dependent nephrotoxicity led to withdrawal as a primary anesthetic in 1974 in the United States. The mechanism of methoxyflurane nephrotoxicity is intrarenal defluorination by CYP2E1 producing inorganic fluoride at concentrations sufficient to inhibit ascending limb chloride transport (high-output renal failure with vasopressin-resistant polyuria, the classical methoxyflurane nephropathy). The threshold for clinically apparent renal injury is approximately 50 micromolar plasma fluoride and is exceeded by general anesthetic doses (MAC 0.16 percent for many hours) but not by the brief, low-dose inhaler format reintroduced as Penthrox in Australia and re-approved in the EU and UK in 2018 for procedural analgesia. The Penthrox formulation delivers approximately 3 mL methoxyflurane through a hand-held disposable inhaler (the green whistle), producing analgesia for procedural pain (extremity injuries, dressing changes, fracture reduction) at exposure levels orders of magnitude below the historical nephrotoxic threshold. The blood-gas partition coefficient is 13, the highest in the class, corresponding to slow induction and prolonged emergence; the clinical Penthrox dose is sub-anesthetic and produces only analgesia and mild sedation. Mechanism includes the standard halogenated ether profile plus pronounced TRPA1 modulation contributing to the analgesic phenotype.
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A research-grade arginate salt formulation of the pentadecapeptide BPC-157 sequence, formulated for improved aqueous stability and shelf life relative to acetate-salt parent.
Abstract
Pentadeca Arginate (PDA; the pentadecapeptide Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val formulated as the arginate salt; the underlying peptide is identical to BPC-157, CAS 137525-51-0; molecular formula C62H98N16O22 free peptide; molecular weight 1419.55 free peptide; the arginate salt adds counterions and is formulated for improved stability) is a research-grade alternative formulation of the BPC-157 pentadecapeptide that has emerged in research-grade peptide vendor catalogs in 2023 to 2024 as a stabilized analog. The pharmacological argument is that the arginate counterion improves aqueous solubility and extends shelf life of the lyophilized solid relative to acetate-salt BPC-157, which is the standard formulation; the underlying peptide sequence and pharmacology are identical, and any differences between PDA and BPC-157 in vivo are attributable to formulation rather than to a different molecule. The published preclinical record on the BPC-157 sequence is summarized in the Kodiac BPC-157 monograph (KDC-MN-002): tendon and ligament healing, vascular reorganization, gastrointestinal mucosal protection, dopaminergic system modulation, broad rodent injury-recovery activity, with the limitation that the literature is dominated by the originating Sikiric group at the University of Zagreb. PDA has no independent published preclinical record beyond the parent BPC-157 work; vendor literature emphasizes formulation stability claims rather than novel pharmacology. Investigators should not assume that PDA differs pharmacologically from BPC-157 acetate; the choice between formulations should be made on stability and handling considerations. Reconstitution and dosing follow BPC-157: bacteriostatic water for injection, refrigerated storage of reconstituted solution, parenteral administration at 250 to 500 mcg per dose. The compound is research-grade and not approved by any regulatory authority for human or veterinary use.
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Selective alpha-7 nicotinic acetylcholine receptor full agonist
A quinuclidine benzofuran-2-carboxamide developed at Targacept as a selective alpha-7 nicotinic full agonist with a binding affinity of 1.4 nanomolar at the human alpha-7 receptor, advanced through Phase 2 development for cognitive impairment and negative symptoms of schizophrenia with a positive 12-week exploratory trial followed by a negative larger 24-week confirmatory trial, subsequently licensed to Anvylic Therapeutics for Tourette syndrome and other indications.
Abstract
Bradanicline (development codes TC-5619 and ATA-101) is a small-molecule, highly selective full agonist of the homopentameric alpha-7 subtype of the neuronal nicotinic acetylcholine receptor (alpha-7 nAChR), originated at Targacept Pharmaceuticals (Winston-Salem, North Carolina) from a quinuclidine benzofuran-2-carboxamide chemistry program in the mid-2000s and advanced through Phase 1 and Phase 2 clinical development for cognitive impairment associated with schizophrenia. The compound binds the human alpha-7 nicotinic receptor with a Ki of approximately 1.4 nanomolar, slightly higher affinity than encenicline (Ki approximately 4 nanomolar) and substantially higher affinity than tropisetron at the alpha-7 site, and exhibits functional intrinsic activity of approximately 80 to 90 percent of the acetylcholine maximum response in heterologous expression systems, placing it in the high-efficacy stratum of alpha-7 ligands as a full agonist rather than the partial-agonist class that encenicline and tropisetron occupy. The full-agonist intrinsic activity is the principal medicinal-chemistry differentiator of bradanicline within the broader quinuclidine-amide chemical class. Selectivity over alpha-4-beta-2, alpha-3-beta-4, alpha-3-beta-2, and other neuronal nicotinic subtypes is approximately 100-fold or greater. The compound was advanced through an exploratory Phase 2 trial in 185 schizophrenia patients (Lieberman et al. 2013) at 5 milligrams once daily for 12 weeks, with statistically significant improvement on the Groton Maze Learning Task and on the Scale for Assessment of Negative Symptoms compared to placebo, and a statistically significant drug effect on working memory in the tobacco-using subgroup. A larger confirmatory Phase 2 trial (Walling et al. 2016) in 477 schizophrenia outpatients across 64 sites at 5 or 50 milligrams once daily for 24 weeks did not support a benefit on negative or cognitive symptoms compared to placebo. Targacept terminated the cognitive impairment program in 2013 and the compound was subsequently licensed to Catalyst Biosciences and to Anvylic Therapeutics for Tourette syndrome and selected other neurological indications. The compound represents a useful research-clinical reference for the alpha-7 nicotinic full-agonist class and for the assessment of whether higher functional intrinsic activity at the receptor produces greater clinical benefit. Bradanicline did not produce the severe gastrointestinal toxicity that triggered the September 2015 FDA clinical hold on encenicline; the safety profile in Phase 2 was well-tolerated with no clinically noteworthy findings reported. The compound is supplied as a research-grade reagent (greater than 98 percent purity) by multiple chemical suppliers and continues to serve as a reference alpha-7 nicotinic full agonist for fundamental pharmacology research. This monograph reviews the chemistry, synthesis, and stereochemistry of bradanicline; the receptor pharmacology in detail; the human pharmacokinetic record; the indication-by-indication clinical evidence base; and a structured comparative assessment of five alpha-7 nicotinic acetylcholine receptor candidates against bradanicline on five competency standards.
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Cathelicidin-derived cationic antimicrobial and immunomodulatory peptide
The sole human cathelicidin-derived antimicrobial peptide, a 37-residue amphipathic alpha-helical cationic peptide released from the precursor protein hCAP-18 by proteinase 3 cleavage, possessing direct broad-spectrum antimicrobial activity through membrane disruption and pleiotropic immunomodulatory functions mediated by formyl peptide receptor 2, P2X7, and toll-like receptor signaling.
Abstract
LL-37, the carboxy-terminal 37-residue peptide of human cationic antimicrobial protein 18 (hCAP-18), is the only cathelicidin-derived antimicrobial peptide identified in the human genome and is a central effector of innate immune defense across epithelial surfaces, wound repair, and inflammatory regulation. The peptide was first identified as FALL-39 by Gudmundsson, Agerberth, and colleagues at the Karolinska Institutet in 1996 through screening of a human bone marrow cDNA library [1], and the mature processed form was subsequently designated LL-37 on the basis of its amino-terminal leucine-leucine sequence and 37-residue length [2]. hCAP-18, the 18-kilodalton holoprotein precursor, is constitutively stored in the specific granules of neutrophils and is released and proteolytically processed by neutrophil-derived proteinase 3 at sites of infection and inflammation to yield the biologically active LL-37 fragment [3]. The peptide adopts an amphipathic alpha-helical conformation in membrane-mimetic environments and exerts direct antimicrobial activity against gram-positive and gram-negative bacteria, enveloped viruses, and fungi through electrostatic interaction with anionic microbial membranes followed by membrane permeabilization and disruption [4, 5]. Beyond direct microbicidal activity, LL-37 functions as a multifunctional immunomodulatory mediator: it signals through formyl peptide receptor 2 (FPR2/ALX) to recruit neutrophils, monocytes, and T cells [6]; it neutralizes bacterial lipopolysaccharide and prevents endotoxin-driven inflammatory cascades [7]; it promotes angiogenesis and wound re-epithelialization through epidermal growth factor receptor transactivation [8]; and it modulates adaptive immune responses through effects on dendritic cell maturation and T helper cell polarization [9]. Expression of hCAP-18/LL-37 is transcriptionally regulated by 1,25-dihydroxyvitamin D3 through a vitamin D response element in the CAMP gene promoter, a mechanism first characterized by Liu et al. (2006) in a landmark demonstration that toll-like receptor activation of human macrophages by Mycobacterium tuberculosis triggers CYP27B1-mediated conversion of 25-hydroxyvitamin D to the active 1,25-dihydroxy form, which then induces cathelicidin expression and intracellular killing of the mycobacterium [10]. This vitamin D-cathelicidin axis has become a major research focus in tuberculosis, respiratory infection, and immunodeficiency. Clinical translation of LL-37 has advanced through Phase I and Phase II trials in chronic wound healing, where topical application of synthetic LL-37 at 0.5 and 1.6 mg/mL produced healing rate constants approximately three- to six-fold greater than placebo in hard-to-heal venous leg ulcers [11], and through a Phase IIb multicenter trial of 148 patients that identified a subgroup benefit in ulcers exceeding 10 cm2 [12]. A randomized trial of recombinant LL-37 delivered via Lactococcus lactis as oral therapy against SARS-CoV-2 Omicron BA.5.1.3 demonstrated significant shortening of viral RNA negative conversion time with early intervention and acceptable safety [13]. The peptide is also implicated in the pathogenesis of rosacea, where aberrant processing of cathelicidin by kallikrein 5 serine protease generates proinflammatory LL-37 fragments in facial skin [14]; in psoriasis, where LL-37 complexed with self-DNA activates plasmacytoid dendritic cells through toll-like receptor 9 [15]; and in cancer biology, where context-dependent pro-tumorigenic and anti-tumorigenic effects have been reported across colorectal, breast, ovarian, and lung malignancies [16, 17]. Pharmacokinetically, the peptide is susceptible to rapid proteolytic degradation in serum with a half-life of minutes to hours depending on protease milieu, limiting systemic bioavailability and driving research toward local and topical delivery, protease-resistant analogs, d-amino acid substitutions, and nanoparticle encapsulation strategies [18, 19]. The compound is commercially available as a synthetic peptide at greater than 95 percent purity from multiple peptide synthesis suppliers. This monograph reviews the chemistry, structure, and processing of LL-37; the molecular pharmacology including direct antimicrobial mechanisms and immunomodulatory receptor signaling; the vitamin D transcriptional axis; preclinical pharmacology across infection, inflammation, and wound healing models; the clinical evidence base in chronic wounds, infectious disease, and dermatologic conditions; reconstitution and handling; stack interactions; adverse events and safety signals including the rosacea and psoriasis pathogenic associations; and a comparative assessment of five alternative antimicrobial and immunomodulatory peptide candidates against LL-37 on five competency standards.
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PEGylated recombinant human growth hormone receptor antagonist
A protein-engineered, PEGylated analog of human growth hormone carrying nine amino acid substitutions that confer high-affinity binding at growth hormone receptor site 1 and functional antagonism at site 2, developed as the first and only growth hormone receptor antagonist approved for the treatment of acromegaly refractory to surgery and radiation.
Abstract
Pegvisomant (B2036-PEG; trade name Somavert; CAS 218620-50-9) is a PEGylated recombinant human growth hormone (hGH) analogue engineered to function as a selective competitive antagonist of the growth hormone receptor (GHR), approved by the United States Food and Drug Administration in 2003 for the treatment of acromegaly in patients who have had an inadequate response to surgery, radiation therapy, or other medical therapies, or for whom these therapies are not appropriate. The compound consists of a 191-amino-acid polypeptide backbone (designated B2036) carrying nine amino acid substitutions relative to wild-type hGH: eight substitutions in the site 1 binding interface (His18Asp, His21Asn, Arg167Asn, Lys168Ala, Asp171Ser, Lys172Arg, Glu174Ser, Ile179Thr) that increase binding affinity for the first GHR molecule, and one substitution in the site 2 binding interface (Gly120Lys) that introduces a bulky lysine side chain preventing the conformational change required for functional receptor dimerization and activation of the JAK2-STAT5 signaling cascade [1, 2]. The B2036 protein is covalently conjugated with four to six polyethylene glycol (PEG) polymers of approximately 5 kDa each at lysine residues and the N-terminus, yielding a final molecular mass of approximately 42 to 52 kDa depending on PEGylation stoichiometry. PEGylation extends the plasma elimination half-life from approximately 15 minutes (unpegylated B2036) to 60 to 138 hours, reduces immunogenicity, and permits once-daily subcutaneous dosing [3, 4]. Pegvisomant was discovered in 1987 by John Kopchick and Wen Chen at the Edison Biotechnology Institute at Ohio University through transgenic mouse studies demonstrating that substitution of glycine 120 in the third alpha-helix of growth hormone with bulky amino acids abolished growth-promoting activity and created a functional antagonist of endogenous growth hormone action [1]. Sensus Drug Development Corporation licensed the technology and advanced the compound through clinical development with PEGylation applied to extend the pharmacokinetic profile. Pharmacia Corporation acquired Sensus in 2001 and was subsequently acquired by Pfizer. The FDA approved pegvisomant (Somavert) on March 26, 2003; the European Medicines Agency granted marketing authorization in November 2002 [5]. The mechanism of action is fundamentally distinct from the other medical therapies for acromegaly. Somatostatin receptor ligands (octreotide, lanreotide, pasireotide) and dopamine agonists (cabergoline) act at the pituitary level to suppress growth hormone secretion. Pegvisomant acts at the peripheral target organ level by competitively blocking GHR activation, thereby reducing hepatic production of insulin-like growth factor I (IGF-I), the principal mediator of the somatic and metabolic consequences of growth hormone excess. This peripheral mechanism renders pegvisomant effective regardless of pituitary tumor somatostatin receptor expression, GH secretory dynamics, or tumor histological subtype [2, 6]. In the pivotal Phase 3 randomized, double-blind, placebo-controlled trial reported by Trainer et al. (2000) in the New England Journal of Medicine, pegvisomant at 10, 15, and 20 mg daily subcutaneously for 12 weeks normalized serum IGF-I concentrations in 54, 81, and 89 percent of patients with acromegaly, respectively, compared to 10 percent on placebo [6]. Long-term surveillance data from the ACROSTUDY international observational registry, encompassing 2,221 patients followed for a median of 7.4 years, confirmed a favorable safety profile with IGF-I normalization rates reaching 75.4 percent at 10 years of treatment, pituitary tumor size increase in 7.1 percent by local reading, liver function abnormalities in 3.2 percent, and treatment-related adverse events leading to drug withdrawal in only 1.3 percent [7, 8]. Pharmacokinetics are characterized by slow subcutaneous absorption (time to peak concentration 33 to 77 hours), limited volume of distribution (approximately 7 liters), low renal clearance (less than 1 percent excreted unchanged in urine), and a long elimination half-life of 60 to 138 hours supporting once-daily dosing [3]. Bioavailability after subcutaneous injection is approximately 57 percent relative to intravenous administration. The compound does not cross the blood-brain barrier [9]. Approximately 17 percent of treated patients develop low-titer, non-neutralizing anti-growth hormone antibodies without apparent impact on efficacy [3]. The compound improves glucose metabolism and insulin sensitivity in acromegaly patients, an advantage over somatostatin analogues that may suppress insulin secretion and worsen glucose homeostasis [10, 11]. This monograph reviews the protein engineering, PEGylation chemistry, and structural pharmacology of pegvisomant; the molecular mechanism of growth hormone receptor antagonism; the comprehensive human pharmacokinetic record; preclinical pharmacology in transgenic and xenograft models; the clinical evidence base across the pivotal registration trial, long-term observational studies, and combination therapy investigations; sourcing and quality verification; reconstitution and handling; stack interactions with somatostatin receptor ligands, dopamine agonists, insulin, and other endocrine agents; the adverse-event and safety signal; and a structured comparative assessment of five alternative acromegaly pharmacotherapies (octreotide, lanreotide, pasireotide, cabergoline, and paltusotine) against pegvisomant on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation).
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Synthetic pentapeptide ghrelin receptor (GHSR-1a) agonist with gastrocolokinetic and growth hormone secretagogue activity
A synthetic pentapeptide ghrelin analog developed as a selective growth hormone secretagogue receptor agonist with approximately sixfold greater potency than native ghrelin, advanced through Phase 2 and Phase 3 clinical trials for diabetic gastroparesis, chronic idiopathic constipation, and anorexia nervosa.
Abstract
Relamorelin (RM-131, BIM-28131) is a synthetic pentapeptide analog of ghrelin that activates the growth hormone secretagogue receptor type 1a (GHSR-1a) with approximately three- to sixfold greater binding affinity and functional potency than native human ghrelin, and with substantially enhanced plasma stability and a terminal elimination half-life of approximately 4.5 to 19.4 hours depending on dose and measurement interval. The compound was originally synthesized by Ipsen as BIM-28131 and subsequently developed by Rhythm Pharmaceuticals (as RM-131), Motus Therapeutics, Allergan, and AbbVie for gastrointestinal motility disorders, principally diabetic gastroparesis, chronic idiopathic constipation, and anorexia nervosa. Relamorelin accelerates gastric emptying through activation of ghrelin receptors expressed on enteric neurons, interstitial cells of Cajal, and gastric smooth muscle, producing dose-dependent increases in antral contractile frequency and propagated colonic contractions without inhibition of gastric accommodation or induction of early satiation. In nonclinical studies, the compound reversed morphine-induced gastroparesis in Sprague-Dawley rats at potencies approximately 100-fold greater than native ghrelin and stimulated gastrointestinal transit throughout the small and large intestine. In clinical trials, relamorelin administered subcutaneously at 10 to 100 micrograms once or twice daily significantly accelerated gastric emptying half-time (mean difference of approximately 8 to 11 minutes versus placebo), reduced vomiting frequency by approximately 60 to 75 percent in diabetic gastroparesis populations with documented delayed gastric emptying, and improved composite symptom scores for nausea, bloating, abdominal pain, and early satiety. A Phase 2 trial in chronic idiopathic constipation demonstrated significant acceleration of colonic transit at 32 and 48 hours and increased spontaneous bowel movement frequency over 14 days of treatment. A proof-of-concept randomized trial in outpatient women with anorexia nervosa demonstrated significant reduction in gastric emptying time (median 58 versus 85 minutes) and a trend toward weight gain after four weeks of treatment. The principal adverse events observed across clinical programs were hyperglycemia (reflecting accelerated nutrient delivery to the small intestine in diabetic populations), diarrhea, headache, and dizziness, with no clinically significant injection site reactions. Growth hormone, prolactin, and cortisol elevations were observed as expected pharmacodynamic consequences of GHSR-1a activation. Allergan initiated a Phase 3 program (PLEDGE) comprising two pivotal 12-week randomized controlled trials in diabetic gastroparesis beginning in 2018; however, in September 2020, the program was terminated following the AbbVie acquisition of Allergan, and the compound is not currently in active clinical development. Relamorelin is not approved by any regulatory authority. It remains available as a research-grade compound from multiple chemical suppliers and is the subject of ongoing academic interest as both a pharmacological tool for ghrelin receptor biology and a potential therapeutic candidate for gastrointestinal dysmotility syndromes. This monograph reviews the chemistry, structure, and synthesis of relamorelin; the molecular pharmacology at the GHSR-1a receptor; comprehensive pharmacokinetics; preclinical gastrointestinal pharmacology; the clinical evidence base across diabetic gastroparesis, chronic constipation, and anorexia nervosa indications; sourcing and quality verification; reconstitution and handling; stack interactions; adverse events and safety signals; and a comparative assessment of five gastroparesis therapeutic candidates against relamorelin on five competency standards.
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Mitochondria-targeted cardiolipin-binding tetrapeptide without intrinsic radical-scavenging activity
A synthetic Szeto-Schiller tetrapeptide (Phe-D-Arg-Phe-Lys-NH2) that selectively concentrates on the inner mitochondrial membrane through electrostatic and hydrophobic interactions with cardiolipin, restoring electron transport chain coupling efficiency and ATP synthesis under ischemic, oxidative, and age-related stress without direct free-radical scavenging, thereby dissociating mitochondrial protection from antioxidant chemistry and establishing cardiolipin modulation as the operative therapeutic mechanism of the SS peptide class.
Abstract
SS-20 (SBT-20; H-Phe-D-Arg-Phe-Lys-NH2; CAS 736992-19-1; molecular weight 595.75; molecular formula C30H45N9O4) is a cell-permeable, mitochondria-targeted synthetic tetrapeptide of the Szeto-Schiller (SS) class, developed at the Department of Pharmacology at Weill Cornell Medical College by Hazel H. Szeto and colleagues as a structural analog of SS-31 (elamipretide) that retains mitochondrial targeting and cardiolipin binding but lacks the 2′,6′-dimethyltyrosine (Dmt) residue responsible for intrinsic reactive oxygen species scavenging in SS-31 [1, 2]. The deliberate substitution of phenylalanine for Dmt at position 1 eliminates the phenolic hydroxyl group that confers direct radical-scavenging capacity, making SS-20 an indispensable mechanistic control compound that has proven essential for establishing that cardiolipin interaction, rather than antioxidant chemistry, is the operative therapeutic mechanism of the SS peptide class [3, 4]. SS-20 carries a net 3+ charge at physiological pH and concentrates approximately 1000-fold on the inner mitochondrial membrane (IMM), where it binds the tetra-acyl dianion cardiolipin through electrostatic interactions between its basic residues (D-Arg, Lys) and the cardiolipin phosphate head groups, with its aromatic phenylalanine residues inserting into the hydrophobic acyl chain region [5, 6]. This binding modulates the interaction between cardiolipin and cytochrome c, promoting the electron carrier function of cytochrome c over its peroxidase activity, thereby improving mitochondrial electron transport chain coupling efficiency, increasing ATP synthesis per unit oxygen consumed, and reducing mitochondrial reactive oxygen species generation as a downstream consequence of improved coupling rather than through direct scavenging [3, 4]. In preclinical models, SS-20 has demonstrated efficacy comparable to SS-31 in protecting against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity in mice at 4 mg/kg intraperitoneal, with complete preservation of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta and 40 percent attenuation of striatal dopamine depletion [7]. In renal ischemia-reperfusion models, pretreatment with SS-20 extended warm ischemia tolerance in rat kidneys from 30 to 45 minutes, preserved cristae architecture on electron microscopy, restored tissue ATP levels, and reduced apoptosis, cytoskeletal breakdown, and interstitial fibrosis [8]. In cardiac ischemia-reperfusion, intravenous SS-20 (SBT-20) at 0.3 and 3.0 mg/kg/hour reduced myocardial infarct size by 20 percent relative to saline control in a rat coronary occlusion model, outperforming the reported 11 percent reduction achieved by elamipretide (MTP-131) in comparable protocols [9]. In pressure-overload heart failure induced by transverse aortic constriction (TAC) in mice, SS-20 produced partial but significant attenuation of cardiac hypertrophy and improvement in fractional shortening, with preferential protection of actin cytoskeletal pathways over mitochondrial and metabolic pathways in global proteomic analysis, a pattern distinct from the broader mitochondrial proteomic protection provided by SS-31 [10]. In chronic renal failure induced by 5/6 nephrectomy in mice, SBT-20 at 5 mg/kg intraperitoneal reduced inflammatory cytokines (interleukin-1-beta, interleukin-6, tumor necrosis factor alpha), normalized NF-kappaB signaling, restored mitochondrial membrane potential, and improved serum creatinine, blood urea nitrogen, and creatinine clearance [11]. The compound has not entered human clinical trials; all pharmacological characterization is preclinical. SS-20 is not approved by any regulatory authority for any indication. It is supplied as a research-grade synthetic peptide by multiple chemical suppliers at greater than 98 percent purity by high-performance liquid chromatography and is used principally as a mechanistic tool to dissect the relative contributions of cardiolipin binding and antioxidant activity within the SS peptide class, and as a candidate therapeutic lead for ischemia-reperfusion injury, neurodegenerative disease, and chronic kidney disease in settings where direct radical scavenging may not be the desired pharmacological intervention.
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Armodafinil, sold as Nuvigil, is the active half of modafinil purified out as a single enantiomer. It produces longer-lasting wakefulness than racemic modafinil because it lacks the rapidly cleared inactive enantiomer. It is FDA-approved for the same indications as modafinil. Not stocked by Kodiac. This monograph is provided for research and educational reference.
Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.
The (R)-enantiomer of modafinil with extended duration of action and greater wakefulness-promoting potency per milligram.
Abstract
Armodafinil (CAS 112111-43-0; molecular formula C15H15NO2S; molecular weight 273.35) is the (R)-enantiomer of modafinil, marketed under the trade name Nuvigil and approved by the FDA in 2007 for the same indications as racemic modafinil. The (R)-enantiomer carries the majority of the wakefulness-promoting activity of the racemate; the (S)-enantiomer contributes a smaller fraction of the eugeroic effect and metabolizes more rapidly. Pharmacokinetics differ from racemic modafinil principally in elimination: the plasma half-life of armodafinil is 12 to 15 hours, similar to the (R)-enantiomer in racemic modafinil dosing, but absent the early peak from rapid (S)-enantiomer clearance. The result is a flatter plasma concentration curve, with sustained alertness later into the day at lower per-milligram doses. Approved doses are 150 or 250 mg once daily in the morning. Mechanism of action mirrors that of modafinil: weak dopamine transporter binding with downstream orexinergic, histaminergic, and glutamatergic effects. The cognitive enhancement evidence base in healthy individuals overlaps with that of modafinil; the effect sizes are modest and most consistent in sleep-deprived subjects. Schedule IV in the United States. Adverse events parallel those of modafinil; rare DRESS and Stevens-Johnson syndrome cases are documented. Drug interactions through CYP3A4 induction are clinically relevant for hormonal contraception and immunosuppressants.
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Rivastigmine, sold as Exelon, is an acetylcholinesterase and butyrylcholinesterase inhibitor approved for Alzheimer and Parkinson disease dementia. Available as oral capsule and transdermal patch. Not stocked by Kodiac. This monograph is provided for research and educational reference.
Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.
A pseudo-irreversible carbamate dual cholinesterase inhibitor approved for Alzheimer disease and Parkinson disease dementia, available as oral and transdermal formulations.
Abstract
Rivastigmine (Exelon; CAS 123441-03-2; molecular formula C14H22N2O2; molecular weight 250.34) is a pseudo-irreversible carbamate cholinesterase inhibitor approved by the FDA in 2000 for mild-to-moderate Alzheimer disease and subsequently expanded to Parkinson disease dementia. The compound is distinctive among the marketed AChE inhibitors in showing dual inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE); BChE may play a more prominent role in advanced Alzheimer disease as AChE expression declines, providing a theoretical advantage for rivastigmine in later disease stages. The pseudo-irreversible mechanism involves carbamoylation of the AChE serine residue, with slow regeneration over hours. Pharmacokinetics: short plasma half-life of the parent compound (1 to 2 hours) but the carbamoylation produces extended pharmacological effect (8 to 10 hours functional duration). Available as oral capsules and a transdermal patch (Exelon Patch); the patch produces smoother plasma exposure with reduced gastrointestinal adverse events. Approved doses are 6 to 12 mg per day oral or 4.6 to 13.3 mg/24 hr patch.
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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.
