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Activation of the μ-opioid receptor (μOR) is responsible for the efficacy of the most effective analgesics. To shed light on the structural basis for μOR activation, here we report a 2.1 Å X-ray crystal structure of the murine μOR bound to the morphinan agonist BU72 and a G protein mimetic camelid antibody fragment. The BU72-stabilized changes in the μOR binding pocket are subtle and differ from those observed for agonist-bound structures of the β 2 -adrenergic receptor (β 2 AR) and the M2 muscarinic receptor. Comparison with active β 2 AR reveals a common rearrangement in the packing of three conserved amino acids in the core of the μOR, and molecular dynamics simulations illustrate how the ligand-binding pocket is conformationally linked to this conserved triad. Additionally, an extensive polar network between the ligand-binding pocket and the cytoplasmic domains appears to play a similar role in signal propagation for all three G-protein-coupled receptors. X-ray crystallography and molecular dynamics simulations of the μ-opioid receptor reveal the conformational changes in the extracellular and intracellular domains of this G-protein-coupled receptor that are associated with its activation. Activation of the μ-opioid receptor The μ-opioid receptor is a G-protein-coupled receptor (GPCR) activated by various analgesics, endogenous endorphins and drugs of abuse such as heroin and opium. Our understanding of the mechanism by which agonist binding leads to recognition, coupling, and activation of a particular G protein subtype is incomplete. In two papers in this issue of Nature , the authors used X-ray crystallography, molecular dynamics simulations, and NMR spectroscopy to probe the structural basis for receptor activation. As well as revealing the conformational changes in the extracellular and intracellular domains of this GPCR associated with receptor activation, these studies help explain why the allosteric coupling between the agonist-binding pocket and the cytoplasmic G-protein-coupling interface of this receptor is relatively weak.

Opioids are the primary drugs used in Western medicine for pain management and palliative care. Farming of opium poppies remains the sole source of these essential medicines, despite diverse market demands and uncertainty in crop yields due to weather, climate change, and pests. We engineered yeast to produce the selected opioid compounds thebaine and hydrocodone starting from sugar. All work was conducted in a laboratory that is permitted and secured for work with controlled substances. We combined enzyme discovery, enzyme engineering, and pathway and strain optimization to realize full opiate biosynthesis in yeast. The resulting opioid biosynthesis strains required the expression of 21 (thebaine) and 23 (hydrocodone) enzyme activities from plants, mammals, bacteria, and yeast itself. This is a proof of principle, and major hurdles remain before optimization and scale-up could be achieved. Open discussions of options for governing this technology are also needed in order to responsibly realize alternative supplies for these medically relevant compounds.

Opium is one of the world's oldest drugs, and its derivatives morphine and codeine are among the most used clinical drugs to relieve severe pain. These prototypical opioids produce analgesia as well as many undesirable side effects (sedation, apnoea and dependence) by binding to and activating the G-protein-coupled µ-opioid receptor (µ-OR) in the central nervous system. Here we describe the 2.8 Å crystal structure of the mouse µ-OR in complex with an irreversible morphinan antagonist. Compared to the buried binding pocket observed in most G-protein-coupled receptors published so far, the morphinan ligand binds deeply within a large solvent-exposed pocket. Of particular interest, the µ-OR crystallizes as a two-fold symmetrical dimer through a four-helix bundle motif formed by transmembrane segments 5 and 6. These high-resolution insights into opioid receptor structure will enable the application of structure-based approaches to develop better drugs for the management of pain and addiction.

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 overdose 1 . Here, in an effort to design safer therapeutic agents, we report an approach targeting a conserved sodium ion-binding site 2 found in µOR 3 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 Asp 2.50 residue in the Na + site. Two bitopics (C5 and C6 guano) maintain nanomolar potency and high efficacy at G i subtypes and show strongly reduced arrestin recruitment—one (C6 guano) also shows the lowest G z 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 G i , G o and G z subtypes and arrestins, thus modulating their in vivo pharmacology. Bitopic functionalized ligands based on fentanyl can target the sodium ion-binding site of the mu-opioid receptor and selectively modulate downstream signalling pathways, potentially leading to safer analgesics.

Sinomenine (SIN) is a promising candidate for the treatment of rheumatoid arthritis (RA). Although it possesses the advantage of being non-addictive, its poor aqueous solubility and low oral bioavailability have limited its clinical application. To address these issues, SIN was encapsulated into lipid cubic liquid crystal nanoparticles (LCNPs) and systematically characterized. Molecular dynamics (MD) simulations were first employed to screen suitable excipients for formulation development. Combined with single-factor optimization and Box-Behnken response surface design, the optimal composition and preparation process were determined. The resulting SIN-LCNPs exhibited a particle size of 149.7 ± 0.9 nm, a polydispersity index (PDI) of 0.223 ± 0.01, a zeta potential of -18.9 mV, and an encapsulation efficiency (EE%) of 92.2%. Spectroscopic analyses confirmed successful incorporation of SIN into the lipid matrix. Pharmacodynamic studies revealed that SIN-LCNPs enhanced targeted drug delivery to inflamed joints, significantly alleviating inflammation and suppressing disease progression in rats. In vivo single-pass intestinal perfusion (SPIP) experiments further demonstrated that SIN was primarily absorbed through the small intestine and that the LCNP carrier effectively improved its intestinal permeability. Collectively, this study provides a novel strategy and theoretical foundation for developing efficient formulations of poorly water-soluble drugs, highlighting the potential clinical application of SIN-LCNPs in RA therapy.

Sinomenine (SIN), as a potential therapeutic agent for rheumatoid arthritis (RA), exhibits advantages such as non-addictiveness. However, its low aqueous solubility and poor membrane permeability result in limited bioavailability, which compromises its therapeutic efficacy in conventional formulations. To address these limitations, this study developed nanostructured lipid carriers (NLCs) with optimized formulations and evaluated their pharmacodynamic performance. Molecular dynamics (MD) simulations were employed to screen excipients and analyze the blending system. SIN-loaded NLCs (SIN-NLCs) were prepared using high-pressure homogenization. Single-factor experiments were performed to optimize the processing conditions of SIN-NLCs. A three-factor, three-level experimental design was established using Design Expert 13 software and further refined through Box-Behnken design (BBD) response surface methodology. This approach enabled cross-validation between molecular dynamics simulations and conventional experiments. Additionally, transmission electron microscopy (TEM) was used to examine morphology, while X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FT-IR) were employed to characterize the physicochemical state of SIN in NLCs. Pharmacodynamic evaluation was performed in a RA model, supplemented by single-pass intestinal perfusion study (SPIP). Initially, MD simulations were employed to evaluate drug-excipient compatibility, thereby identifying suitable formulation excipients: stearic acid and oleic acid as lipid components, and Poloxamer 188 as the surfactant. Subsequently, single-factor experiments combined with the BBD response surface methodology were employed to optimize preparation parameters, establishing the ideal process conditions: drug-to-lipid ratio of 1:42, solid-to-liquid lipid ratio of 5.58:4.42, and Poloxamer 188 concentration of 1.20%. The optimized SIN-NLCs exhibited spherical particles with uniform dispersion and no agglomeration. The average particle size was 173.90 ± 1.97 nm, with a polydispersity index (PDI) of 0.18 ± 0.01, a zeta potential of -22.65 ± 0.60 mV, and an encapsulation efficiency (EE%) of 91.27% ± 0.01. Spectroscopic analysis confirmed that SIN existed in an amorphous state and was successfully encapsulated within the lipid matrix. In vivo, SIN-NLCs significantly reduced paw swelling and arthritis scores in model rats, promoted synovial cell proliferation, and suppressed inflammatory cell infiltration. The intestinal perfusion study demonstrated that SIN-NLCs were primarily absorbed in the small intestine and markedly enhanced drug permeability. SIN-NLCs represent an effective delivery system to enhance the solubility and permeability of SIN. This study provides a novel strategy and methodology for the formulation of hydrophobic drugs, offering valuable insights for future pharmaceutical development.

The word opium derives from the ancient Greek word ὄπιον (ópion) for the juice of any plant, but today means the air-dried seed capsule latex of Papaver somniferum. Alkaloid chemistry began with the isolation of morphine from crude opium by Friedrich Wilhelm Adam Sertürner in 1804. More than a century later, Hungarian pharmacist János Kabay opened new perspectives for the direct isolation of morphine from dry poppy heads and straw without the labor-intensive harvesting of opium. In 2015, Kabay’s life and achievements obtained official recognition as constituting a «Hungarikum», thereby entering the national repository of matters of unique cultural value. To this day, the study of Papaver alkaloids is a focus of medicinal chemistry, the (perhaps unstated) aspiration of which is to obtain an opioid with lesser abuse potential and side effects, while retaining good analgesic properties. We begin this review with a brief account of opiate biosynthesis, followed by a detailed presentation of semisynthetic opioids, emphasizing the efforts of the Alkaloida Chemical Company, founded in 1927 by János Kabay, and the morphine alkaloid group of the University of Debrecen.

Natural product structure and fragment-based compound development inspire pseudo-natural product design through different combinations of a given natural product fragment set to compound classes expected to be chemically and biologically diverse. We describe the synthetic combination of the fragment-sized natural products quinine, quinidine, sinomenine, and griseofulvin with chromanone or indole-containing fragments to provide a 244-member pseudo-natural product collection. Cheminformatic analyses reveal that the resulting eight pseudo-natural product classes are chemically diverse and share both drug- and natural product-like properties. Unbiased biological evaluation by cell painting demonstrates that bioactivity of pseudo-natural products, guiding natural products, and fragments differ and that combination of different fragments dominates establishment of unique bioactivity. Identification of phenotypic fragment dominance enables design of compound classes with correctly predicted bioactivity. The results demonstrate that fusion of natural product fragments in different combinations and arrangements can provide chemically and biologically diverse pseudo-natural product classes for wider exploration of biologically relevant chemical space. Natural products inspire the development of pseudo-natural products through combinations of fragments of compound classes that are chemically and biologically distinct. Here, the authors report a library of 244 pseudo-natural products, evaluate them in the cell painting essays and identify the phenotypic role of individual fragments.

Sinomenine has long been known as an anti-inflammatory drug, while poor efficiency and large-dose treatment had limited its further application. Five novel sinomenine 1-Br-4-cinnamic acid esters derivatives 2a–2e were designed and synthesized to improve its analgesic and anti-inflammatory activity. All synthesized sinomenine derivatives were structurally confirmed by NMR and ESI-MS. Molecular docking results showed that compounds 2a–2e had stable binding to the GBP5 protein. The compounds 2a–2e showed stable binding to the GBP5 protein by molecular docking Pre-preparing the druggability of compounds 2a–2e by ADEMT 3.0 showed that each derivative had similar druggability to sinomenine. The analgesic activity of compounds 2a–2e was preliminarily determined by hot plate and acetic acid writhing experiments, while anti-neuroinflammatory effects were evaluated by a xylene-induced mouse ear edema model. The results of the hot plate method showed that the synthesized sinomenine derivatives 2a–2e had some analgesic effects. The results of the acetic acid writhing test showed that the analgesic effects of 2a, 2c, 2e were better than that of sinomenine, and the other derivatives were equivalent to sinomenine. Compound 2b showed excellent anti-inflammatory properties in mouse ear edema.

Opioid receptors mediate the actions of endogenous and exogenous opioids on many physiological processes, including the regulation of pain, respiratory drive, mood, and—in the case of κ-opioid receptor (κ-OR)—dysphoria and psychotomimesis. Here we report the crystal structure of the human κ-OR in complex with the selective antagonist JDTic, arranged in parallel dimers, at 2.9 Å resolution. The structure reveals important features of the ligand-binding pocket that contribute to the high affinity and subtype selectivity of JDTic for the human κ-OR. Modelling of other important κ-OR-selective ligands, including the morphinan-derived antagonists norbinaltorphimine and 5′-guanidinonaltrindole, and the diterpene agonist salvinorin A analogue RB-64, reveals both common and distinct features for binding these diverse chemotypes. Analysis of site-directed mutagenesis and ligand structure–activity relationships confirms the interactions observed in the crystal structure, thereby providing a molecular explanation for κ-OR subtype selectivity, and essential insights for the design of compounds with new pharmacological properties targeting the human κ-OR. The crystal structure of the human κ-opioid receptor in complex with an antagonist, JDTic, is determined, with potential importance for the design of new therapeutic agents. Where opiates hit home Four papers in this issue of Nature present the long-awaited high-resolution crystal structures of the four known opioid receptors in ligand-bound conformations. These G-protein-coupled receptors are the targets of a broad range of drugs, including painkillers, antidepressants, anti-anxiety agents and anti-addiction medications. Brian Kobilka’s group reports the crystal structure of the µ-opioid receptor bound to a morphinan antagonist and the δ-opioid receptor bound to naltrindole. Raymond Stevens’ group reports on the κ-opioid receptor bound to the selective antagonist JDTic, and the nociceptin/orphanin FQ receptor bound to a peptide mimetic. In an associated News and Views, Marta Filizola and Lakshmi Devi discuss the implications of these landmark papers for research on the mechanisms underlying receptor function and drug development.