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    Home > Active Ingredient News > Study of Nervous System > Expert Review: Cell Xu Huaqiang/Xie Xin/Wang Mingwei/Zhuang Youwen collaborated to reveal the mechanism of action of the powerful analgesics fentanyl and morphine

    Expert Review: Cell Xu Huaqiang/Xie Xin/Wang Mingwei/Zhuang Youwen collaborated to reveal the mechanism of action of the powerful analgesics fentanyl and morphine

    • Last Update: 2023-01-06
    • Source: Internet
    • Author: User
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    Reviews | Zhang Xu (Academician of the Chinese Academy of Sciences), Pei Gang (Academician of the Chinese Academy of Sciences)
    Pain, especially chronic pain, is a common class of neurological diseases
    .
    According to statistics, nearly 20% of adults worldwide suffer from chronic pain, and nearly 40%
    in some economically backward countries.
    Common chronic pains include low back pain, arthritis pain, migraine and cancer pain, which not only lead to the weakening or loss of behavioral ability, but also bring adverse effects such as depression, sleep disorders and suicidal tendencies, seriously affecting people's physical and mental health, and bringing a huge economic burden
    to society.

    Figure 1.
    Opioids of opium poppy (
    https://unsplash.
    com/

    ) are currently the most widely used and highly effective analgesics
    .
    Human use of opioids can be traced back thousands of years to the use of plant poppy for analgesic and sedative and recreational
    purposes (pleasure, euphoria occurs), and subsequent studies have found that the opioid morphine is the main substance
    that exerts activity in opium poppy.
    Common opioids include natural opioid alkaloids such as morphine, cocaine, and synthetic opioids such as demeraldine and fentanyl, and synthetic opioids produce morphine-like effects
    in the human body.
    Opioids mainly
    activate downstream inhibitory G I/O proteins to exert physiological activities such as analgesia by acting on opioid receptors in the G protein-coupled receptor family in the human body, especially μ μ opioid receptors (μOR).

    。 The development of opioid receptor drugs has long been a hot spot in analgesic drug research, and most of the opioids that have been marketed are agonists of μOR, as representative classical opioid analgesics, morphine and fentanyl have shown high selectivity
    for μOR.
    However, the use of opioid analgesics has many toxic side effects, including addiction, respiratory depression, constipation, etc.
    , which greatly limits the clinical application of opioid analgesics and makes the development of safe and effective analgesics targeting opioid receptors a major
    difficulty.
    Respiratory depression deaths caused by opioid addiction have also directly contributed to the widespread "opioid crisis", mainly in North America and Canada, causing more than 100,000 deaths per year, mainly due to the abuse of fentanyl and its derivatives
    .
    As the main factor of the "opioid crisis" and a powerful analgesic drug still in clinical use, the molecular mechanism of fentanyl and its receptor μOR interaction has been unknown for a long time, and the analysis of the relevant molecular mechanism is of great
    significance for us to rationally design safer and more efficient fentanyl-derived analgesics.

    Figure 2.
    Drug addiction (
    www.
    shutterstock.
    com)

    Previous studies have shown that the analgesic effects of opioids are responsible for the G protein signaling pathway of μOR, while side effects are caused
    by the arrestin signaling pathway 。 However, several recent studies have questioned this hypothesis, arguing that neurotoxic side effects such as respiratory depression are not related to arrestin
    signaling [1].

    Despite the doubts, a large number of studies have been invested in the development of G protein-biased μOR agonist drugs to discover highly effective and low-toxicity targeted μOR analgesics
    [2].

    In 2020, the US FDA approved the first and so far only μOR analgesic designed based on the concept of G protein bias, Olisteridine
    (TRV130), for the treatment of moderate to severe pain, which exhibits lower toxic side effects
    than morphine 。 Due to the lack of understanding of the molecular mechanism of G protein preference of μOR, the discovery of G protein biased agonists of μOR has been obtained through large-scale high-throughput blind screening for nearly 20 years since the above hypothesis was proposed, which greatly hinders the rational design and discovery
    of novel G protein-biased analgesic drugs targeting μOR.

    On November 10, 2022, the team of Xu Huaqiang/Zhuang Youwen, Xie Xin's team and Wang Mingwei's team from the Shanghai Institute of Materia Medica, Chinese Academy of Sciences published a long article entitled Molecular recognition of morphine and fentanyl by the human μ-opioid online Research paper
    by Receptor.
    This study solved and reported the high-resolution three-dimensional structure of opioid analgesics such as
    fentanyl, morphine and oliceridine to activate μOR, respectively, revealing for the first time the mechanism of action of
    fentanyl and morphine to recognize and activate μOR.
    This study further combines a variety of cellular-level functional analysis and molecular dynamics simulation methods to clarify the structure-activity relationship between fentanyl series derivatives and the target μOR and the key structural determinants of μOR-mediated arrestin signaling Opioid painkillers point the way
    .


    In this study, the researchers first analyzed human μOR-bound equilibrium agonists such as fentanyl, morphine and DAMGO (exhibiting bidirectional signaling activity of G protein and repressin) by cryo-EM and the three-dimensional structure of G protein-biased agonists such as TRV130, SR17018, PZM21, etc.
    , and the signaling characteristics of μOR under the activation of different signaling active agonists were characterized by molecular dynamics simulation and cellular-level functional analysis
    .
    The study found that fentanyl occupies an additional binding pocket at the TM2 to TM3 proximal outer end of μOR compared to morphine, and in addition, fentanyl's aniline ring side chain forms a direct π-π hydrophobic interaction with amino acid residues W295 and Y328, which confers it with receptor-activating activity
    up to 50-100 times higher than morphine 。 Through molecular docking and point-mutation function verification of different fentanyl derivatives, the researchers further explored the structure-activity relationship between fentanyl and its derivatives and μOR, and revealed the key role of different degrees of interaction between drug molecules and amino acid residues such as D149, Y150, W135 and W320 in determining the different activities of fentanyl and its derivatives
    (carfentanil, sufentanyl, oxymethamfentanil, etc.
    ).

    。 The analysis of the analyzed series of structures and molecular dynamics simulation showed that G protein biased agonist PZM21 and others were more inclined to bind to the TM2/3 side of the μOR ligand binding pocket, while the equilibrium agonist fentanyl showed a broader and more balanced interaction with the μOR transmembrane region, and made the intracellular domain of μOR more compacted, which was conducive to the binding of μOR to repressin, and also explained the molecular mechanism
    of equilibrium agonist manifestation of inhibitor activity 。 Based on these findings, the researchers also designed novel G protein-biased fentanyl derivatives FBD1 and FBD3
    with different activities based on the fentanyl molecular backbone.

    Figure 3: Structure
    of opioids with different chemical structures bound to human μOR.
    Top left: Different binding patterns of fentanyl and morphine; Bottom left: Structure-activity analysis of fentanyl and its derivatives with μOR; Top right: In molecular dynamics simulations, the equilibrium agonist of μOR mediates a more compact intracellular lumen conformation than the G protein biased agonist; Bottom right: Novel G protein-biased fentanyl derivatives FBD1 and FBD3
    with different activities based on structural design.
    Intermediate: TM6/7 interaction of attenuated ligand and μOR causes μOR signal bias
    .

    This study was completed by the team of Xu Huaqiang/Zhuang Youwen, Xie Xin and Wang Mingwei of Shanghai Institute of Materia Medica
    .
    Youwen Zhuang, associate researcher at the Shanghai Institute of Materia Medica, Chinese Academy of Sciences, and Yue Wang, Bingqing He and Xinheng He, doctoral students, are co-first authors
    of the paper.
    Prof.
    Huaqiang Xu, Prof.
    Xin Xie, Prof.
    Mingwei Wang and Prof.
    Youwen Zhuang are co-corresponding authors
    .


    Article Links:

    https://doi.
    org/10.
    1016/j.
    cell.
    2022.
    09.
    041


    According to the 2020 China Pain Medicine Development Report, nearly 10%-20% of the population in China is plagued by chronic pain including cancer pain, postoperative pain, nerve damage and muscle fiber pain.
    The population of people with chronic pain has exceeded 300 million and growing
    .
    Pain has developed into the third major health problem in the current society after cancer and cardiovascular and cerebrovascular diseases, which has caused a huge impact and burden on people's lives and social and economic development, and the development of efficient and safe analgesics is a major demand
    for current medical and health care.

    Opioids are currently the most widely used and effective analgesic drugs
    .
    The earliest human use of opioids was reflected in the discovery
    of the value of the plant opium poppy.
    As an ancient medicinal plant, the poppy was mentioned as early as the Sumerian text around 4000 BC and was called Hul Gil
    (the delightful plant).

    Opium is a class of alkaloid active substances extracted from the opium poppy, and its application in human history dates back thousands of years, mainly for pain relief treatment and recreational use
    .
    The core active substance in opium is morphine, named after the Greek god of dreams
    , Morpheus, first isolated from opium in 1805 by the German pharmacist Friedrich Sertürner
    .
    Morphine has a potent analgesic effect, but it is also accompanied by toxic side effects
    such as high addiction and respiratory depression.
    In the pursuit of powerful, low-addiction analgesics, a series of opioids with different structures producing morphine-like physiological effects have been synthesized, including heroin discovered in 1874 and fentanyl synthesized in 1959
    .
    Although these synthetic opioids exhibit stronger analgesic effects than natural opioid alkaloid morphine, they are also associated with more intense toxic side effects
    .
    The design and development of new opioid analgesics and even non-opioid analgesics that are highly effective in analgesia and avoid neurotoxic side effects has always been the unremitting pursuit
    of scientists.

    Opioids exert analgesic effects
    by mimicking the antinociceptive physiological effects of endogenous opioid peptides, such as endorphins and dynorphins, and activating opioid receptors in the G protein-coupled receptor family.
    Among them, morphine and fentanyl, as representatives of classical opioid analgesics, mainly play a role by activating
    μ opioid receptor (μ μOR), and are still used as clinical analgesics
    .
    For a long time, a large amount of research has focused on the scientific question of how the two can be combined with μOR, in order to design safer opioid analgesics based on structural information, especially
    after
    the first μOR (inactive) structure was resolved in 2012.
    However, agonist binding models based on molecular docking and kinetic simulations are complex and cannot reflect the binding patterns
    of real agonists.
    This study is the first to resolve a series of near-atomic-resolution structures of agonist morphine and fentanyl binding μOR, clarifies the understanding of the confusion of fentanyl binding patterns, gives us the first understanding of how it interacts with μOR, and provides a precise template
    for the design of future painkillers.
    The μOR-mediated arrestin signaling pathway is considered to be an important factor in the occurrence of opioid toxicity, which also led to the discovery of the G protein-biased ligand TRV130 and its approval
    by the FDA in 2020 。 This study is also based on structural and multiple pharmacological function experiments and found that weakening the interaction of opioid molecules with the sixth and seventh transmembrane regions of μOR can weaken or even eliminate arrestin signaling, thereby triggering G protein biased signal transduction, which provides new ideas for subsequent design and discovery of opioids with pathway bias, which will promote the discovery
    of highly effective and low-addictive analgesics.

    The Shanghai Institute of Chinese Academy of Sciences has a long history in the mechanism of action of analgesic drugs and the discovery of new drugs, and has made a series of important discoveries and contributions
    .
    Mr.
    Zhao Chengga and Mr.
    Jin Guozhang, the first directors of the Institute of Medicine, respectively carried out purification and systematic pharmacological studies on the analgesic tetrahydrobarmatine in traditional Chinese medicine fumaso
    .
    Mr.
    Zou Gang of the Institute of Medicine has conducted in-depth and meticulous research on the mechanism of morphine action and neuropeptide pharmacology, and confirmed that the effective site of morphine analgesia is the third ventricle and the central gray matter around the brain aqueduct, which is known as a "milestone" in the study of the mechanism of morphine action
    .
    Mr.
    Chi Chi of the Institute of Pharmaceuticals has long been engaged in research on the neuropharmacology and analgesics of opioid receptors, and led the discovery of the highly potent analgesic oxymetfentanyl

    .
    This research is also a good inheritance
    of the research direction of opioid receptor analgesics where the drug is located.

    Experts commented that Pei Gang (academician of the Chinese Academy of Sciences) Opioid receptor is the most important target molecule of clinical analgesic drugs, and its related research is very necessary
    。 Recently, researchers Xu Huaqiang, Xie Xin, Wang Mingwei and Zhuang Youwen of Shanghai Institute of Materia Medica, together with multiple teams, have made important progress in the study of the mechanism of μ opioid receptor recognition of fentanyl, morphine and other drug molecules, and related work has been published in Cell
    .
    After the opioid receptor is activated by the ligand, it mainly mediates two downstream signaling pathways, namely G protein and β-arrestin signaling pathway, to achieve analgesic effects, but it is also accompanied by side effects
    such as addiction, respiratory depression, and constipation.
    There are many studies in the field suggesting that analgesia is mainly mediated by the G protein signaling pathway, while side effects are mediated by the β-arrestin pathway
    .
    Although there are many experiments that do not support the above observations, many scientists are still committed to the research of G protein pathway preference drugs, of which the G protein pathway preference ligand TRV130 was approved by the US FDA in 2020 for the treatment of moderate to severe acute pain in adults, but it still emphasizes its remaining side effects in the form of a "black box warning", which is "known, not known"
    .

    In this paper, we systematically elucidate the mode of opioid receptor binding to preferred and non-preferred drugs, and breakthrough has found the key binding characteristics
    that mediate the two signaling pathways.
    Both ligands have stronger interactions with the anterior transmembrane helix, while preference ligands interact weakly
    with the posterior transmembrane helix compared to non-preference ligands such as fentanyl and morphine.
    These results have not only been verified at the cellular level and molecular dynamics simulations, but the authors have also accurately modified fentanyl based on the mechanism provided by structural biology to synthesize FBD1 and FBD3, two derivatives with G protein pathway preference, further confirming the concept
    of preference key sites.
    These structures allow us to "know and why"
    the pathway selection mechanisms of opioid receptors.
    But the biological laws of nature are very complex and diverse, and I look forward to further validation
    of this mechanism of preference and the efficacy of potential opioid receptor modulators at the animal level.

    With the development of structural biology, Chinese researchers not only analyze the structure of biological macromolecules through multidisciplinary means such as biochemistry combined with computer, but also further explore and solve major problems and urgent needs
    in the frontier field of life science and biomedicine from these structures.
    The work, published in Cell, is a good example of translational research that not only advances the understanding of the molecular mechanisms of opioids, but also lays the foundation
    for structure-based drug design and development.


    Platemaker: Eleven



    References


    1 Azevedo Neto, J.
    et al.
    Biased versus Partial Agonism in the Search for Safer Opioid Analgesics.
    Molecules 25, 3870, doi:10.
    3390/molecules25173870 (2020).
    2 Che, T.
    , Dwivedi-Agnihotri, H.
    , Shukla, A.
    K.
    & Roth, B.
    L.
    Biased ligands at opioid receptors: Current status and future directions.
    Sci Signal 14, doi:10.
    1126/scisignal.
    aav0320 (2021).

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