RESUMEN
The persistence of chronic pain and continuing overdose deaths from pain-relieving opioids targeting µ opioid receptor (µOR) have fueled the need for reliable long-term analgesics which use different targets and mechanisms. The δ opioid receptor (δOR) is a potential alternative target for non-addictive analgesics to alleviate chronic pain, made more attractive by its lack of respiratory depression associated with µOR agonists. However, early δOR full agonists were found to induce seizures, precluding clinical use. Partial δOR agonists may offer more controlled activation of the receptor compared to full agonists, but the development of such ligands has been hindered by uncertainty over the molecular mechanism mediating partial agonism. Using a structure-based approach, we explored the engagement of the sodium binding pocket in δOR and developed a bitopic ligand, C6-Quino, predicted to be a selective δOR partial agonist. Functional studies of C6-Quino revealed that it displayed δOR partial agonist activity at both G-protein and arrestin pathways. Its interaction with the sodium pocket was confirmed and analyzed using a single particle cryo-EM. Additionally, C6-Quino demonstrated favorable chemical and physiological properties like oral activity, and analgesic activity in multiple chronic pain models. Notably, µOR-related hyperlocomotion and respiratory depression, and δOR-related convulsions, were not observed at analgesic doses of C6-Quino. This fundamentally new approach to designing δOR ligands provides a blueprint for the development of partial agonists as safe analgesics and acts as a generic method to optimize signaling profiles of other Class A GPCRs.
RESUMEN
The µ-opioid receptor (µOR) is a well-established target for analgesia1, yet conventional opioid receptor agonists cause serious adverse effects, notably addiction and respiratory depression. These factors have contributed to the current opioid overdose epidemic driven by fentanyl2, a highly potent synthetic opioid. µOR negative allosteric modulators (NAMs) may serve as useful tools in preventing opioid overdose deaths, but promising chemical scaffolds remain elusive. Here we screened a large DNA-encoded chemical library against inactive µOR, counter-screening with active, G-protein and agonist-bound receptor to 'steer' hits towards conformationally selective modulators. We discovered a NAM compound with high and selective enrichment to inactive µOR that enhances the affinity of the key opioid overdose reversal molecule, naloxone. The NAM works cooperatively with naloxone to potently block opioid agonist signalling. Using cryogenic electron microscopy, we demonstrate that the NAM accomplishes this effect by binding a site on the extracellular vestibule in direct contact with naloxone while stabilizing a distinct inactive conformation of the extracellular portions of the second and seventh transmembrane helices. The NAM alters orthosteric ligand kinetics in therapeutically desirable ways and works cooperatively with low doses of naloxone to effectively inhibit various morphine-induced and fentanyl-induced behavioural effects in vivo while minimizing withdrawal behaviours. Our results provide detailed structural insights into the mechanism of negative allosteric modulation of the µOR and demonstrate how this can be exploited in vivo.
Asunto(s)
Analgésicos Opioides , Evaluación Preclínica de Medicamentos , Naloxona , Receptores Opioides mu , Bibliotecas de Moléculas Pequeñas , Animales , Humanos , Masculino , Ratones , Regulación Alostérica/efectos de los fármacos , Analgésicos Opioides/antagonistas & inhibidores , Analgésicos Opioides/farmacología , Sitios de Unión/efectos de los fármacos , Microscopía por Crioelectrón , Fentanilo/antagonistas & inhibidores , Fentanilo/farmacología , Cinética , Ligandos , Modelos Moleculares , Morfina/antagonistas & inhibidores , Morfina/farmacología , Naloxona/administración & dosificación , Naloxona/química , Naloxona/metabolismo , Naloxona/farmacología , Antagonistas de Narcóticos/administración & dosificación , Antagonistas de Narcóticos/química , Antagonistas de Narcóticos/metabolismo , Antagonistas de Narcóticos/farmacología , Sobredosis de Opiáceos/tratamiento farmacológico , Conformación Proteica/efectos de los fármacos , Estabilidad Proteica/efectos de los fármacos , Receptores Opioides mu/agonistas , Receptores Opioides mu/antagonistas & inhibidores , Receptores Opioides mu/química , Receptores Opioides mu/metabolismo , Células Sf9 , Transducción de Señal/efectos de los fármacos , Bibliotecas de Moléculas Pequeñas/química , Bibliotecas de Moléculas Pequeñas/farmacología , Ratones Endogámicos C57BLRESUMEN
Despite the increasing number of GPCR structures and recent advances in peptide design, the development of efficient technologies allowing rational design of high-affinity peptide ligands for single GPCRs remains an unmet challenge. Here, we develop a computational approach for designing conjugates of lariat-shaped macrocyclized peptides and a small molecule opioid ligand. We demonstrate its feasibility by discovering chemical scaffolds for the kappa-opioid receptor (KOR) with desired pharmacological activities. The designed De Novo Cyclic Peptide (DNCP)-ß-naloxamine (NalA) exhibit in vitro potent mixed KOR agonism/mu-opioid receptor (MOR) antagonism, nanomolar binding affinity, selectivity, and efficacy bias at KOR. Proof-of-concept in vivo efficacy studies demonstrate that DNCP-ß-NalA(1) induces a potent KOR-mediated antinociception in male mice. The high-resolution cryo-EM structure (2.6 Å) of the DNCP-ß-NalA-KOR-Gi1 complex and molecular dynamics simulations are harnessed to validate the computational design model. This reveals a network of residues in ECL2/3 and TM6/7 controlling the intrinsic efficacy of KOR. In general, our computational de novo platform overcomes extensive lead optimization encountered in ultra-large library docking and virtual small molecule screening campaigns and offers innovation for GPCR ligand discovery. This may drive the development of next-generation therapeutics for medical applications such as pain conditions.
Asunto(s)
Analgésicos Opioides , Receptores Opioides kappa , Masculino , Ratones , Animales , Receptores Opioides kappa/metabolismo , Ligandos , Analgésicos Opioides/química , Receptores Opioides mu/metabolismo , Péptidos Cíclicos/químicaRESUMEN
Drugs acting at the opioid receptor family are clinically used to treat chronic and acute pain, though they represent the second line of treatment behind GABA analogs, antidepressants and SSRI's. Within the opioid family mu and kappa opioid receptor are commonly targeted. However, activation of the mu opioid receptor has side effects of constipation, tolerance, dependence, euphoria, and respiratory depression; activation of the kappa opioid receptor leads to dysphoria and sedation. The side effects of mu opioid receptor activation have led to mu receptor drugs being widely abused with great overdose risk. For these reasons, newer safer opioid analgesics are in high demand. For many years a focus within the opioid field was finding drugs that activated the G protein pathway at mu opioid receptor, without activating the ß-arrestin pathway, known as biased agonism. Recent advances have shown that this may not be the way forward to develop safer analgesics at mu opioid receptor, though there is still some promise at the kappa opioid receptor. Here we discuss recent novel approaches to develop safer opioid drugs including efficacy vs bias and fine-tuning receptor activation by targeting sub-pockets in the orthosteric site, we explore recent works on the structural basis of bias, and we put forward the suggestion that Gα subtype selectivity may be an exciting new area of interest.
Asunto(s)
Dolor Agudo , Analgésicos Opioides , Humanos , Analgésicos Opioides/efectos adversos , Receptores Opioides mu , Receptores Opioides kappa , Receptores OpioidesRESUMEN
The κ-opioid receptor (KOR) represents a highly desirable therapeutic target for treating not only pain but also addiction and affective disorders1. However, the development of KOR analgesics has been hindered by the associated hallucinogenic side effects2. The initiation of KOR signalling requires the Gi/o-family proteins including the conventional (Gi1, Gi2, Gi3, GoA and GoB) and nonconventional (Gz and Gg) subtypes. How hallucinogens exert their actions through KOR and how KOR determines G-protein subtype selectivity are not well understood. Here we determined the active-state structures of KOR in a complex with multiple G-protein heterotrimers-Gi1, GoA, Gz and Gg-using cryo-electron microscopy. The KOR-G-protein complexes are bound to hallucinogenic salvinorins or highly selective KOR agonists. Comparisons of these structures reveal molecular determinants critical for KOR-G-protein interactions as well as key elements governing Gi/o-family subtype selectivity and KOR ligand selectivity. Furthermore, the four G-protein subtypes display an intrinsically different binding affinity and allosteric activity on agonist binding at KOR. These results provide insights into the actions of opioids and G-protein-coupling specificity at KOR and establish a foundation to examine the therapeutic potential of pathway-selective agonists of KOR.
Asunto(s)
Microscopía por Crioelectrón , Proteínas de Unión al GTP Heterotriméricas , Ligandos , Receptores Opioides kappa , Analgésicos Opioides/metabolismo , Analgésicos Opioides/farmacología , Receptores Opioides kappa/química , Receptores Opioides kappa/metabolismo , Receptores Opioides kappa/ultraestructura , Transducción de Señal , Proteínas de Unión al GTP Heterotriméricas/química , Proteínas de Unión al GTP Heterotriméricas/metabolismo , Proteínas de Unión al GTP Heterotriméricas/ultraestructura , Especificidad por Sustrato , Regulación Alostérica/efectos de los fármacos , Alucinógenos/metabolismo , Alucinógenos/farmacologíaRESUMEN
Clinical treatment of acute to severe pain relies on the use of opioids. While their potency is significant, there are considerable side effects that can negatively affect patients. Their rise in usage has correlated with the current opioid epidemic in the United States, which has led to more than 70,000 deaths per year (Volkow and Blanco, 2021). Opioid-related drug development aims to make target compounds that show strong potency but with diminished side effects. Research into pharmaceuticals that could act as potential alternatives to current pains medications has relied on mechanistic insights of opioid receptors, a class of G-protein coupled receptors (GPCRs), and biased agonism, a common phenomenon among pharmaceutical compounds where downstream effects can be altered at the same receptor via different agonists. Opioids function typically by binding to an active site on the extracellular portion of opioid receptors. Once activated, the opioid receptor initiates a G-protein signaling pathway and/or the ß-arrestin2 pathway. The proposed concept for the development of safe analgesics around mu and kappa opioid receptor subtypes has focused on not recruiting ß-arrestin2 (biased agonism) and/or having low efficacy at the receptor (partial agonism). By altering chemical motifs on a common scaffold, chemists can take advantage of biased agonism as well as create compounds with low intrinsic efficacy for the desired treatments. This review will focus on ligands with bias profile, signaling aspects of the receptor and probe into the structural basis of receptor that leads to bias and/or partial agonism.
Asunto(s)
Analgésicos Opioides , Receptores Opioides mu , Humanos , Analgésicos Opioides/efectos adversos , Receptores Opioides mu/agonistas , Receptores Opioides mu/metabolismo , Analgésicos/farmacología , Transducción de Señal , Receptores OpioidesRESUMEN
Drugs targeting the µ-opioid receptor (µOR) are the most effective analgesics available but are also associated with fatal respiratory depression through a pathway that remains unclear. Here we investigated the mechanistic basis of action of lofentanil (LFT) and mitragynine pseudoindoxyl (MP), two µOR agonists with different safety profiles. LFT, one of the most lethal opioids, and MP, a kratom plant derivative with reduced respiratory depression in animal studies, exhibited markedly different efficacy profiles for G protein subtype activation and ß-arrestin recruitment. Cryo-EM structures of µOR-Gi1 complex with MP (2.5 Å) and LFT (3.2 Å) revealed that the two ligands engage distinct subpockets, and molecular dynamics simulations showed additional differences in the binding site that promote distinct active-state conformations on the intracellular side of the receptor where G proteins and ß-arrestins bind. These observations highlight how drugs engaging different parts of the µOR orthosteric pocket can lead to distinct signaling outcomes.
Asunto(s)
Analgésicos Opioides , Transducción de Señal , Animales , beta-Arrestinas/metabolismo , Analgésicos Opioides/química , Analgésicos Opioides/farmacología , Proteínas de Unión al GTP/metabolismo , Sitios de UniónRESUMEN
Mu-opioid receptor (µOR) agonists such as fentanyl have long been used for pain management, but are considered a major public health concern owing to their adverse side effects, including lethal overdose1. Here, in an effort to design safer therapeutic agents, we report an approach targeting a conserved sodium ion-binding site2 found in µOR3 and many other class A G-protein-coupled receptors with bitopic fentanyl derivatives that are functionalized via a linker with a positively charged guanidino group. Cryo-electron microscopy structures of the most potent bitopic ligands in complex with µOR highlight the key interactions between the guanidine of the ligands and the key Asp2.50 residue in the Na+ site. Two bitopics (C5 and C6 guano) maintain nanomolar potency and high efficacy at Gi subtypes and show strongly reduced arrestin recruitment-one (C6 guano) also shows the lowest Gz efficacy among the panel of µOR agonists, including partial and biased morphinan and fentanyl analogues. In mice, C6 guano displayed µOR-dependent antinociception with attenuated adverse effects, supporting the µOR sodium ion-binding site as a potential target for the design of safer analgesics. In general, our study suggests that bitopic ligands that engage the sodium ion-binding pocket in class A G-protein-coupled receptors can be designed to control their efficacy and functional selectivity profiles for Gi, Go and Gz subtypes and arrestins, thus modulating their in vivo pharmacology.
Asunto(s)
Diseño de Fármacos , Fentanilo , Morfinanos , Receptores Opioides mu , Animales , Ratones , Analgésicos Opioides/química , Analgésicos Opioides/metabolismo , Arrestinas/metabolismo , Microscopía por Crioelectrón , Fentanilo/análogos & derivados , Fentanilo/química , Fentanilo/metabolismo , Ligandos , Morfinanos/química , Morfinanos/metabolismo , Receptores Opioides mu/agonistas , Receptores Opioides mu/química , Receptores Opioides mu/metabolismo , Receptores Opioides mu/ultraestructura , Sitios de Unión , NocicepciónRESUMEN
Opioids continue to be of use for the treatment of pain. Most clinically used analgesics target the µ opioid receptor whose activation results in adverse effects like respiratory depression, addiction and abuse liability. Various approaches have been used by the field to separate receptor-mediated analgesic actions from adverse effects. These include biased agonism, opioids targeting multiple receptors, allosteric modulators, heteromers and splice variants of the µ receptor. This review will focus on the current status of the field and some upcoming targets of interest that may lead to a safer next generation of analgesics. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.
Asunto(s)
Efectos Colaterales y Reacciones Adversas Relacionados con Medicamentos , Insuficiencia Respiratoria , Humanos , Analgésicos Opioides/efectos adversos , Receptores Opioides mu , Dolor/tratamiento farmacológico , Dolor/inducido químicamente , Insuficiencia Respiratoria/inducido químicamenteRESUMEN
Background and Purpose: Mitragyna speciosa extract and kratom alkaloids decrease alcohol consumption in mice at least in part through actions at the δ-opioid receptor (δOR). However, the most potent opioidergic kratom alkaloid, 7-hydroxymitragynine, exhibits rewarding properties and hyperlocomotion presumably due to preferred affinity for the mu opioid receptor (µOR). We hypothesized that opioidergic kratom alkaloids like paynantheine and speciogynine with reduced µOR potency could provide a starting point for developing opioids with an improved therapeutic window to treat alcohol use disorder. Experimental Approach: We characterized paynantheine, speciociliatine, and four novel kratom-derived analogs for their ability to bind and activate δOR, µOR, and κOR. Select opioids were assessed in behavioral assays in male C57BL/6N WT and δOR knockout mice. Key Results: Paynantheine (10 mgâkg-1, i.p.) produced aversion in a limited conditioned place preference (CPP) paradigm but did not produce CPP with additional conditioning sessions. Paynantheine did not produce robust antinociception but did block morphine-induced antinociception and hyperlocomotion. Yet, at 10 and 30 mgâkg-1 doses (i.p.), paynantheine did not counteract morphine CPP. 7-hydroxypaynantheine and 7-hydroxyspeciogynine displayed potency at δOR but limited µOR potency relative to 7-hydroxymitragynine in vitro, and dose-dependently decreased voluntary alcohol consumption in WT but not δOR in KO mice. 7-hydroxyspeciogynine has a maximally tolerated dose of at least 10 mgâkg-1 (s.c.) at which it did not produce significant CPP neither alter general locomotion nor induce noticeable seizures. Conclusion and Implications: Derivatizing kratom alkaloids with the goal of enhancing δOR potency and reducing off-target effects could provide a pathway to develop novel lead compounds to treat alcohol use disorder with an improved therapeutic window.
RESUMEN
The leaves of Mitragyna speciosa (kratom), a plant native to Southeast Asia, are increasingly used as a pain reliever and for attenuation of opioid withdrawal symptoms. Using the tools of natural products chemistry, chemical synthesis, and pharmacology, we provide a detailed in vitro and in vivo pharmacological characterization of the alkaloids in kratom. We report that metabolism of kratom's major alkaloid, mitragynine, in mice leads to formation of (a) a potent mu opioid receptor agonist antinociceptive agent, 7-hydroxymitragynine, through a CYP3A-mediated pathway, which exhibits reinforcing properties, inhibition of gastrointestinal (GI) transit and reduced hyperlocomotion, (b) a multifunctional mu agonist/delta-kappa antagonist, mitragynine pseudoindoxyl, through a CYP3A-mediated skeletal rearrangement, displaying reduced hyperlocomotion, inhibition of GI transit and reinforcing properties, and (c) a potentially toxic metabolite, 3-dehydromitragynine, through a non-CYP oxidation pathway. Our results indicate that the oxidative metabolism of the mitragynine template beyond 7-hydroxymitragynine may have implications in its overall pharmacology in vivo.
Asunto(s)
Alcaloides de Triptamina Secologanina/farmacología , Animales , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Oxidación-Reducción , Receptores Opioides muRESUMEN
Most opioid analgesics used clinically, including morphine and fentanyl, as well as the recreational drug heroin, act primarily through the mu opioid receptor, a class A Rhodopsin-like G protein-coupled receptor (GPCR). The single-copy mu opioid receptor gene, OPRM1, undergoes extensive alternative splicing, creating multiple splice variants or isoforms via a variety of alternative splicing events. These OPRM1 splice variants can be categorized into three major types based on the receptor structure: (1) full-length 7 transmembrane (TM) C-terminal variants; (2) truncated 6TM variants; and (3) single TM variants. Increasing evidence suggests that these OPRM1 splice variants are pharmacologically important in mediating the distinct actions of various mu opioids. More importantly, the OPRM1 variants can be targeted for development of novel opioid analgesics that are potent against multiple types of pain, but devoid of many side-effects associated with traditional opiates. In this review, we provide an overview of OPRM1 alternative splicing and its functional relevance in opioid pharmacology.
Asunto(s)
Empalme Alternativo/genética , Dolor/genética , Precursores del ARN/genética , Receptores Opioides mu/genética , Analgésicos Opioides/química , Analgésicos Opioides/uso terapéutico , Humanos , Morfina/química , Morfina/uso terapéutico , Dolor/tratamiento farmacológico , Dolor/patología , Isoformas de Proteínas/genética , Empalme del ARN/genéticaRESUMEN
Mitragynine and 7-hydroxymitragynine (7OH) are the major alkaloids mediating the biological actions of the psychoactive plant kratom. To investigate the structure-activity relationships of mitragynine/7OH templates, we diversified the aromatic ring of the indole at the C9, C10, and C12 positions and investigated their G-protein and arrestin signaling mediated by mu opioid receptors (MOR). Three synthesized lead C9 analogs replacing the 9-OCH3 group with phenyl (4), methyl (5), or 3'-furanyl [6 (SC13)] substituents demonstrated partial agonism with a lower efficacy than DAMGO or morphine in heterologous G-protein assays and synaptic physiology. In assays limiting MOR reserve, the G-protein efficacy of all three was comparable to buprenorphine. 6 (SC13) showed MOR-dependent analgesia with potency similar to morphine without respiratory depression, hyperlocomotion, constipation, or place conditioning in mice. These results suggest the possibility of activating MOR minimally (G-protein Emax ≈ 10%) in cell lines while yet attaining maximal antinociception in vivo with reduced opioid liabilities.
Asunto(s)
Analgésicos Opioides/farmacología , Receptores Opioides mu/agonistas , Alcaloides de Triptamina Secologanina/farmacología , Analgésicos Opioides/efectos adversos , Analgésicos Opioides/síntesis química , Analgésicos Opioides/metabolismo , Animales , Masculino , Ratones Endogámicos C57BL , Simulación del Acoplamiento Molecular , Simulación de Dinámica Molecular , Estructura Molecular , Ratas Sprague-Dawley , Receptores Opioides mu/metabolismo , Alcaloides de Triptamina Secologanina/efectos adversos , Alcaloides de Triptamina Secologanina/síntesis química , Alcaloides de Triptamina Secologanina/metabolismo , Relación Estructura-ActividadRESUMEN
Dry leaves of kratom (mitragyna speciosa) are anecdotally consumed as pain relievers and antidotes against opioid withdrawal and alcohol use disorders. There are at least 54 alkaloids in kratom; however, investigations to date have focused around mitragynine, 7-hydroxy mitragynine (7OH), and mitragynine pseudoindoxyl (MP). Herein, we probe a few minor indole and oxindole based alkaloids, reporting the receptor affinity, G-protein activity, and ßarrestin-2 signaling of corynantheidine, corynoxine, corynoxine B, mitraciliatine, and isopaynantheine at mouse and human opioid receptors. We identify corynantheidine as a mu opioid receptor (MOR) partial agonist, whereas its oxindole derivative corynoxine was an MOR full agonist. Similarly, another alkaloid mitraciliatine was found to be an MOR partial agonist, while isopaynantheine was a KOR agonist which showed reduced ßarrestin-2 recruitment. Corynantheidine, corynoxine, and mitraciliatine showed MOR dependent antinociception in mice, but mitraciliatine and corynoxine displayed attenuated respiratory depression and hyperlocomotion compared to the prototypic MOR agonist morphine in vivo when administered supraspinally. Isopaynantheine on the other hand was identified as the first kratom derived KOR agonist in vivo. While these minor alkaloids are unlikely to play the majority role in the biological actions of kratom, they represent excellent starting points for further diversification as well as distinct efficacy and signaling profiles with which to probe opioid actions in vivo.
Asunto(s)
Alcoholismo , Mitragyna , Analgésicos Opioides/farmacología , Animales , Indoles/farmacología , Ratones , Oxindoles/farmacología , Receptores Opioides , Alcaloides de Triptamina SecologaninaRESUMEN
Mitragynine (MG) is the most abundant alkaloid component of the psychoactive plant material "kratom", which according to numerous anecdotal reports shows efficacy in self-medication for pain syndromes, depression, anxiety, and substance use disorders. We have developed a synthetic method for selective functionalization of the unexplored C11 position of the MG scaffold (C6 position in indole numbering) via the use of an indole-ethylene glycol adduct and subsequent iridium-catalyzed borylation. Through this work we discover that C11 represents a key locant for fine-tuning opioid receptor signaling efficacy. 7-Hydroxymitragynine (7OH), the parent compound with low efficacy on par with buprenorphine, is transformed to an even lower efficacy agonist by introducing a fluorine substituent in this position (11-F-7OH), as demonstrated in vitro at both mouse and human mu opioid receptors (mMOR/hMOR) and in vivo in mouse analgesia tests. Low efficacy opioid agonists are of high interest as candidates for generating safer opioid medications with mitigated adverse effects.
Asunto(s)
Mitragyna/química , Extractos Vegetales/farmacología , Receptores Opioides mu/agonistas , Alcaloides de Triptamina Secologanina/farmacología , Analgésicos/química , Analgésicos/farmacología , Animales , Glicol de Etileno/química , Humanos , Ratones Noqueados , Modelos Químicos , Estructura Molecular , Extractos Vegetales/química , Unión Proteica , Receptores Opioides mu/genética , Receptores Opioides mu/metabolismo , Alcaloides de Triptamina Secologanina/químicaRESUMEN
Controlling receptor functional selectivity profiles for opioid receptors is a promising approach for discovering safer analgesics; however, the structural determinants conferring functional selectivity are not well understood. Here, we used crystal structures of opioid receptors, including the recently solved active state kappa opioid complex with MP1104, to rationally design novel mixed mu (MOR) and kappa (KOR) opioid receptor agonists with reduced arrestin signaling. Analysis of structure-activity relationships for new MP1104 analogs points to a region between transmembrane 5 (TM5) and extracellular loop (ECL2) as key for modulation of arrestin recruitment to both MOR and KOR. The lead compounds, MP1207 and MP1208, displayed MOR/KOR Gi-partial agonism with diminished arrestin signaling, showed efficient analgesia with attenuated liabilities, including respiratory depression and conditioned place preference and aversion in mice. The findings validate a novel structure-inspired paradigm for achieving beneficial in vivo profiles for analgesia through different mechanisms that include bias, partial agonism, and dual MOR/KOR agonism.
Asunto(s)
Morfinanos/química , Receptores Opioides kappa/química , Receptores Opioides mu/química , Secuencias de Aminoácidos , Analgésicos/química , Analgésicos/metabolismo , Animales , Sitios de Unión , Ligandos , Masculino , Ratones , Ratones Endogámicos C57BL , Simulación del Acoplamiento Molecular , Receptores Opioides kappa/metabolismo , Receptores Opioides mu/metabolismo , Relación Estructura-ActividadRESUMEN
Chronic administration of opioids produces physical dependence and opioid-induced hyperalgesia. Users claim the Thai traditional tea "kratom" and component alkaloid mitragynine ameliorate opioid withdrawal without increased sensitivity to pain. Testing these claims, we assessed the combined kratom alkaloid extract (KAE) and two individual alkaloids, mitragynine (MG) and the analog mitragynine pseudoindoxyl (MP), evaluating their ability to produce physical dependence and induce hyperalgesia after chronic administration, and as treatments for withdrawal in morphine-dependent subjects. C57BL/6J mice (n = 10/drug) were administered repeated saline, or graded, escalating doses of morphine (intraperitoneal; i.p.), kratom alkaloid extract (orally, p.o.), mitragynine (p.o.), or MP (subcutaneously, s.c.) for 5 days. Mice treated chronically with morphine, KAE, or mitragynine demonstrated significant drug-induced hyperalgesia by day 5 in a 48 °C warm-water tail-withdrawal test. Mice were then administered naloxone (10 mg/kg, s.c.) and tested for opioid withdrawal signs. Kratom alkaloid extract and the two individual alkaloids demonstrated significantly fewer naloxone-precipitated withdrawal signs than morphine-treated mice. Additional C57BL/6J mice made physically dependent on morphine were then used to test the therapeutic potential of combined KAE, mitragynine, or MP given twice daily over the next 3 days at either a fixed dose or in graded, tapering descending doses. When administered naloxone, mice treated with KAE, mitragynine, or MP under either regimen demonstrated significantly fewer signs of precipitated withdrawal than control mice that continued to receive morphine. In conclusion, while retaining some liabilities, kratom, mitragynine, and mitragynine pseudoindoxyl produced significantly less physical dependence and ameliorated precipitated withdrawal in morphine-dependent animals, suggesting some clinical value.
Asunto(s)
Analgésicos Opioides/efectos adversos , Mitragyna , Dependencia de Morfina/prevención & control , Alcaloides de Triptamina Secologanina/administración & dosificación , Alcaloides de Triptamina Secologanina/síntesis química , Síndrome de Abstinencia a Sustancias/prevención & control , Analgésicos Opioides/administración & dosificación , Animales , Masculino , Ratones , Ratones Endogámicos C57BL , Dependencia de Morfina/metabolismo , Dependencia de Morfina/psicología , Dimensión del Dolor/efectos de los fármacos , Dimensión del Dolor/métodos , Receptores Opioides delta/agonistas , Receptores Opioides delta/metabolismo , Receptores Opioides mu/agonistas , Receptores Opioides mu/metabolismo , Alcaloides de Triptamina Secologanina/efectos adversos , Alcaloides de Triptamina Secologanina/aislamiento & purificación , Síndrome de Abstinencia a Sustancias/metabolismo , Síndrome de Abstinencia a Sustancias/psicologíaRESUMEN
Mu opioid receptors (MOR-1) mediate the biological actions of clinically used opioids such as morphine, oxycodone, and fentanyl. The mu opioid receptor gene, OPRM1, undergoes extensive alternative splicing, generating multiple splice variants. One type of splice variants are truncated variants containing only six transmembrane domains (6TM) that mediate the analgesic action of novel opioid drugs such as 3'-iodobenzoylnaltrexamide (IBNtxA). Previously, we have shown that IBNtxA is a potent analgesic effective in a spectrum of pain models but lacks many side-effects associated with traditional opiates. In order to investigate the targets labeled by IBNtxA, we synthesized two arylazido analogs of IBNtxA that allow photolabeling of mouse mu opioid receptors (mMOR-1) in transfected cell lines and mMOR-1 protein complexes that may comprise the 6TM sites in mouse brain. We demonstrate that both allyl and alkyne arylazido derivatives of IBNtxA efficiently radio-photolabeled mMOR-1 in cell lines and MOR-1 protein complexes expressed either exogenously or endogenously, as well as found in mouse brain. In future, design and application of such radio-photolabeling ligands with a conjugated handle will provide useful tools for further isolating or purifying MOR-1 to investigate site specific ligand-protein contacts and its signaling complexes.
Asunto(s)
Analgésicos Opioides/metabolismo , Azidas/metabolismo , Encéfalo/metabolismo , Naltrexona/análogos & derivados , Etiquetas de Fotoafinidad/metabolismo , Receptores Opioides/metabolismo , Analgésicos Opioides/síntesis química , Animales , Azidas/síntesis química , Encéfalo/efectos de los fármacos , Células CHO , Línea Celular , Cricetinae , Cricetulus , Relación Dosis-Respuesta a Droga , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Naltrexona/síntesis química , Naltrexona/metabolismo , Etiquetas de Fotoafinidad/síntesis química , Unión Proteica/fisiología , Ensayo de Unión Radioligante/métodosRESUMEN
Pain remains a very pervasive problem throughout medicine. Classical pain management is achieved through the use of opiates belonging to the mu opioid receptor (MOR) class, which have significant side effects that hinder their utility. Pharmacologists have been trying to develop opioids devoid of side effects since the isolation of morphine from papaver somniferum, more commonly known as opium by Sertürner in 1804. The natural products salvinorin A, mitragynine, and collybolide represent three nonmorphinan natural product-based targets, which are potent selective agonists of opioid receptors, and emerging next-generation analgesics. In this work, we review the phytochemistry and medicinal chemistry efforts on these templates and their effects on affinity, selectivity, analgesic actions, and a myriad of other opioid-receptor-related behavioral effects.
Asunto(s)
Productos Biológicos/farmacología , Diterpenos de Tipo Clerodano/farmacología , Dolor/tratamiento farmacológico , Alcaloides de Triptamina Secologanina/farmacología , Animales , Productos Biológicos/química , Productos Biológicos/uso terapéutico , Diterpenos de Tipo Clerodano/química , Diterpenos de Tipo Clerodano/uso terapéutico , Humanos , Fitoterapia , Alcaloides de Triptamina Secologanina/química , Alcaloides de Triptamina Secologanina/uso terapéuticoRESUMEN
Effective treatments for chronic pain without abuse liability are urgently needed. One in 5 adults suffer chronic pain and half of these patients report inefficient treatment. Mu opioid receptor agonists (MOP), including oxycodone, tramadol and morphine, are often prescribed to treat chronic pain, however, use of drugs targeting MOP can lead to drug dependency, tolerance and overdose deaths. Kappa opioid receptor (KOP) agonists have antinociceptive effects without abuse potential; however, they have not been utilised clinically due to dysphoria and sedation. We hypothesise that mixed opioid receptor agonists targeting the KOP and delta opioid receptor (DOP) would have a wider therapeutic index, with the rewarding effects of DOP negating the negative effects of KOP. MP1104, an analogue of 3-Iodobenzoyl naltrexamine, is a novel mixed opioid receptor agonist with potent antinociceptive effects mediated via KOP and DOP in mice without rewarding or aversive effects. In this study, we show MP1104 has potent, long-acting antinociceptive effects in the warm-water tail-withdrawal assay in male and female mice and rats; and is longer acting than morphine. In the paclitaxel-induced neuropathic pain model in mice, MP1104 reduced both mechanical and cold allodynia and unlike morphine, did not produce tolerance when administered daily for 23 days. Moreover, MP1104 did not induce sedative effects in the open-field locomotor activity test, respiratory depression in mice using whole-body plethysmography, or have cross-tolerance with morphine. This data supports the therapeutic development of mixed opioid receptor agonists, particularly mixed KOP/DOP agonists, as non-addictive pain medications with reduced tolerance.