Structure-based discovery of nonhallucinogenic psychedelic analogs

Identification of Psychoplastogenic Tropanes Lacking Muscarinic Activity

Tropane-containing small molecules like scopolamine are a promising class of psychoplastogens. However, their potent antagonism of all muscarinic receptor subtypes presents the potential for undesirable anticholinergic side effects. In an effort to decouple their neuroplasticity-promoting effects from their muscarinic activity, we performed phenotypic structure-activity relationship studies across a variety of structurally distinct subclasses of tropanes. We discovered several novel tropanes capable of significantly increasing cortical neuronal growth while exhibiting drastically reduced activity at all muscarinic receptor subtypes compared to scopolamine.

Uncovering the unique characteristics of different groups of 5-HT5AR ligands with reference to their interaction with the target protein

BACKGROUND

The serotonin 5-HT5A receptor has attracted much more research attention, due to the therapeutic potential of its ligands being increasingly recognized, and the possibilities that lie ahead of these findings. There is a growing body of evidence indicating that these ligands have procognitive, pro-social, and anti-depressant properties, which offers new avenues for the development of treatments that could address socially important conditions related to the malfunctioning of the central nervous system. The aim of our study was to unravel the molecular determinants for 5-HT5AR ligands that govern their activity towards the receptor.

METHODS

In response to the need for identification of molecular determinants for 5-HT5AR activity, we prepared a comprehensive collection of 5-HT5AR ligands, carefully gathering literature and patent data. Leveraging molecular modeling techniques, such as pharmacophore hypothesis development, docking, and molecular dynamics simulations enables to gain valuable insights into the specific interactions of 5-HT5AR ligand groups with the receptor.

RESULTS

The obtained comprehensive set of 2160 compounds was divided into dozens of subsets, and a pharmacophore model was developed for each group. The results from the docking and molecular dynamics simulations have enabled the identification of crucial ligand-protein interactions that are essential for the compound's activity towards 5-HT5AR.

CONCLUSIONS

The findings from the molecular modeling study provide valuable insights that can guide medicinal chemists in the development of new 5-HT5AR ligands. Considering the pharmacological significance of these compounds, they have the potential to become impactful treatments for individuals and communities in the future. Understanding how different crystal/cryo-EM structures of 5-HT5AR affect molecular modeling experiments could have major implications for future computational studies on this receptor.

PET brain imaging in neurological disorders

Brain disorders are a series of conditions with damage or loss of neurons, such as Parkinson's disease (PD), Alzheimer's disease (AD), or drug dependence. These individuals have gradual deterioration of cognitive, motor, and other central nervous system functions affected. This degenerative trajectory is intricately associated with dysregulations in neurotransmitter systems. Positron Emission Tomography (PET) imaging, employing radiopharmaceuticals and molecular imaging techniques, emerges as a crucial tool for detecting brain biomarkers. It offers invaluable insights for early diagnosis and distinguishing brain disorders. This article comprehensively reviews the application and progress of conventional and novel PET imaging agents in diagnosing brain disorders. Furthermore, it conducts a thorough analysis on merits and limitations. The article also provides a forward-looking perspective in the future development directions of PET imaging agents for diagnosing brain disorders and proposes potential innovative strategies. It aims to furnish clinicians and researchers with an all-encompassing overview of the latest advancements and forthcoming trends in the utilization of PET imaging for diagnosing brain disorders.

Pharmacological inhibition of Kir4.1 evokes rapid-onset antidepressant responses

Major depressive disorder, a prevalent and severe psychiatric condition, necessitates development of new and fast-acting antidepressants. Genetic suppression of astrocytic inwardly rectifying potassium channel 4.1 (Kir4.1) in the lateral habenula ameliorates depression-like phenotypes in mice. However, Kir4.1 remains an elusive drug target for depression. Here, we discovered a series of Kir4.1 inhibitors through high-throughput screening. Lys05, the most potent one thus far, effectively suppressed native Kir4.1 channels while displaying high selectivity against established targets for rapid-onset antidepressants. Cryogenic-electron microscopy structures combined with electrophysiological characterizations revealed Lys05 directly binds in the central cavity of Kir4.1. Notably, a single dose of Lys05 reversed the Kir4.1-driven depression-like phenotype and exerted rapid-onset (as early as 1 hour) antidepressant actions in multiple canonical depression rodent models with efficacy comparable to that of (S)-ketamine. Overall, we provided a proof of concept that Kir4.1 is a promising target for rapid-onset antidepressant effects.

AlphaFold2 structures guide prospective ligand discovery

AlphaFold2 (AF2) models have had wide impact but mixed success in retrospective ligand recognition. We prospectively docked large libraries against unrefined AF2 models of the σ2 and serotonin 2A (5-HT2A) receptors, testing hundreds of new molecules and comparing results with those obtained from docking against the experimental structures. Hit rates were high and similar for the experimental and AF2 structures, as were affinities. Success in docking against the AF2 models was achieved despite differences between orthosteric residue conformations in the AF2 models and the experimental structures. Determination of the cryo-electron microscopy structure for one of the more potent 5-HT2A ligands from the AF2 docking revealed residue accommodations that resembled the AF2 prediction. AF2 models may sample conformations that differ from experimental structures but remain low energy and relevant for ligand discovery, extending the domain of structure-based drug design.

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI): From an Obscure to Pivotal Member of the DOX Family of Serotonergic Psychedelic Agents - A Review

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI, or DOX where X = -I) was first synthesized in 1973 in a structure-activity study to explore the effect of various aryl substituents on the then newly identified, and subsequently controlled, hallucinogenic agent 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM, or DOX where X = -CH3). Over time, DOI was found to be a serotonin (5-HT) receptor agonist using various peripheral 5-HT receptor tissue assays and later, following the identification of multiple families of central 5-HT receptors, an agonist at 5-HT2 serotonin receptors in rat and, then, human brain. Today, classical hallucinogens, currently referred to as serotonergic psychedelic agents, are receiving considerable attention for their potential therapeutic application in various neuropsychiatric disorders including treatment-resistant depression. Here, we review, for the first time, the historical and current developments that led to DOI becoming a unique, perhaps a landmark, agent in 5-HT2 receptor research.

Unraveling the Mechanisms of Cannabidiol's Pharmacological Actions: A Comprehensive Research Overview

Cannabis sativa has long been used for neurological and psychological healing. Recently, cannabidiol (CBD) extracted from cannabis sativa has gained prominence in the medical field due to its non-psychotropic therapeutic effects on the central and peripheral nervous systems. CBD, also acting as a potent antioxidant, displays diverse clinical properties such as anticancer, antiinflammatory, antidepressant, antioxidant, antiemetic, anxiolytic, antiepileptic, and antipsychotic effects. In this review, we summarized the structural activity relationship of CBD with different receptors by both experimental and computational techniques and investigated the mechanism of interaction between related receptors and CBD. The discovery of structural activity relationship between CBD and target receptors would provide a direction to optimize the scaffold of CBD and its derivatives, which would give potential medical applications on CBD-based therapies in various illnesses.

Pharmacological and behavioural effects of tryptamines present in psilocybin-containing mushrooms

BACKGROUND AND PURPOSE

Demand for new antidepressants has resulted in a re-evaluation of the therapeutic potential of psychedelic drugs. Several tryptamines found in psilocybin-containing "magic" mushrooms share chemical similarities with psilocybin. Early work suggests they may share biological targets. However, few studies have explored their pharmacological and behavioural effects.

EXPERIMENTAL APPROACH

We compared baeocystin, norbaeocystin and aeruginascin with psilocybin to determine if they are metabolized by the same enzymes, similarly penetrate the blood-brain barrier, serve as ligands for similar receptors and modulate behaviour in rodents similarly. We also assessed the stability and optimal storage and handling conditions for each compound.

KEY RESULTS

In vitro enzyme kinetics assays found that all compounds had nearly identical rates of dephosphorylation via alkaline phosphatase and metabolism by monoamine oxidase. Further, we found that only the dephosphorylated products of baeocystin and norbaeocystin crossed a blood-brain barrier mimetic to a similar degree as the dephosphorylated form of psilocybin, psilocin. The dephosphorylated form of norbaeocystin was found to activate the 5-HT2A receptor with similar efficacy to psilocin and norpsilocin in in vitro cell imaging assays. Behaviourally, only psilocybin induced head twitch responses in rats, a marker of 5-HT2A-mediated psychedelic effects and hallucinogenic potential. However, like psilocybin, norbaeocystin improved outcomes in the forced swim test. All compounds caused minimal changes to metrics of renal and hepatic health, suggesting innocuous safety profiles.

CONCLUSIONS AND IMPLICATIONS

Collectively, this work suggests that other naturally occurring tryptamines, especially norbaeocystin, may share overlapping therapeutic potential with psilocybin, but without causing hallucinations.

Mind shift I: Fructus Aurantii - Rhizoma Chuanxiong synergistically anchors stress-induced depression-like behaviours and gastrointestinal dysmotility cluster by regulating psycho-immune-neuroendocrine network

BACKGROUND

Researchers have not studied the integrity, orderly correlation, and dynamic openness of complex organisms and explored the laws of systems from a global perspective. In the context of reductionism, antidepressant development formerly focused on advanced technology and molecular details, clear targets and mechanisms, but the clinical results were often unsatisfactory.

PURPOSE

MDD represents an aggregate of different and highly diverse disease subtypes. The co-occurrence of stress-induced nonrandom multimorbidity is widespread, whereas only a fraction of the potential clusters are well known, such as the MDD-FGID cluster. Mapping these clusters, and determining which are nonrandom, is vital for discovering new mechanisms, developing treatments, and reconfiguring services to better meet patient needs.

STUDY DESIGN

Acute stress 15-minute forced swimming (AFS) or CUMS protocols can induce the nonrandom MDD-FGID cluster. Multiple biological processes of rats with depression-like behaviours and gastrointestinal dysmobility will be captured under conditions of stress, and the Fructus Aurantii-Rhizoma Chuanxiong (ZQCX) decoction will be utilized to dock the MDD-FGID cluster.

METHODS/RESULTS

Here, Rhizoma Chuanxiong, one of the seven components of Chaihu-shugan-San, elicited the best antidepressant effect on CUMS rats, followed by Fructus Aurantii. ZQCX reversed AFS-induced depression-like behaviours and gastrointestinal dysmobility by regulating the glutamatergic system, AMPAR/BDNF/mTOR/synapsin I pathway, ghrelin signalling and gastrointestinal nitric oxide synthase. Based on the bioethnopharmacological analysis strategy, the determined meranzin hydrate (MH) and senkyunolide I (SI) by UPLC-PDA, simultaneously absorbed by the jejunum and hippocampus of rats, have been considered major absorbed bioactive compounds acting on behalf of ZQCX. Cotreatment with MH and SI at an equivalent dose in ZQCX synergistically replicated over 50.33 % efficacy of the parent formula in terms of antidepressant and prokinetic actions by modulating neuroinflammation and ghrelin signalling.

CONCLUSION

Brain-centric mind shifts require the integration of multiple central and peripheral systems and the elucidation of the underlying neurobiological mechanisms that ultimately contribute to novel therapeutic options. Ghrelin signalling and the immune system may partially underlie multimorbidity vulnerability, and ZQCX anchors stress-induced MDD-FGID clusters by docking them. Combining the results of micro details with the laws of the macro world may be more effective in finding treatments for MDD.

Psilocybin reduces heroin seeking behavior and modulates inflammatory gene expression in the nucleus accumbens and prefrontal cortex of male rats

Preclinical and human studies indicate psilocybin may reduce perseverant maladaptive behaviors, including nicotine and alcohol seeking. Such studies in the opioid field are lacking, though opioids are involved in more >50% of overdose deaths. Psilocybin is an agonist at the serotonin 2A receptor (5-HT2AR), a well-documented target for modulation of drug seeking, and evidence suggests 5-HT2AR agonists may dampen motivation for opioids. We sought to investigate the therapeutic efficacy of psilocybin in mediating cessation of opioid use and maintenance of long-lasting abstinence from opioid seeking behavior in a rat model of heroin self-administration (SA). Psilocybin or 5-HT2AR antagonists ketanserin and volinanserin were administered systemically to rats prior to SA of 0.075 mg/kg/infusion of heroin, or relapse following forced abstinence. Psilocybin did not alter heroin taking, but a single exposure to 3.0 mg/kg psilocybin 4-24 hours prior to a relapse test blunted cue-induced heroin seeking. Conversely, 5-HT2AR antagonists exacerbated heroin relapse. To begin to elucidate mechanisms of psilocybin, drug-naïve rats received psilocybin and/or ketanserin, and tissue was collected from the prefrontal cortex (PFC), a region critical for drug seeking and responsive to psilocybin, 24 hours later for RNA-sequencing. 3.0 mg/kg psilocybin regulated ~2-fold more genes in the PFC than 1.0 mg/kg, including genes involved in the cytoskeleton and cytokine signaling. Ketanserin blocked >90% of psilocybin-regulated genes, including the IL-17a cytokine receptor, Il17ra. Psychedelic compounds have reported anti-inflammatory properties, and therefore we performed a gene expression array to measure chemokine/cytokine molecules in the PFC of animals that displayed psilocybin-mediated inhibition of heroin seeking. Psilocybin regulated 4 genes, including Il17a, and a subset of genes correlated with relapse behavior. Selective inhibition of PFC IL-17a was sufficient to reduce heroin relapse. We conclude that psilocybin reduces heroin relapse and highlight IL-17a signaling as a potential downstream pathway of psilocybin that also reduces heroin seeking.

Intranasal Delivery of Near-Infrared and Magnetic Dual-Response Nanospheres to Rapidly Produce Antidepressant-Like and Cognitive Enhancement Effects

Restricted by synaptic plasticity, dopamine receptor (DR) upregulation takes a long time to work. Moreover, the impact of the blood-brain barrier (BBB) on delivery efficiency restricts the development of drugs. Taking inspiration from snuff bottles, a convenient, fast-acting, and nonaddictive nasal drug delivery system has been developed to rapidly reshape the balance of synaptic transmitters. This optical and magnetic response system called CFs@DP, comprised of carbonized MIL-100 (Fe) frameworks (CFs) and domperidone (DP), which can enter the brain via nasal administration. Under dual stimulation of near-infrared (NIR) irradiation and catecholamine-induced complexation, CFs@DP disintegrates to release iron ions and DP, causing upregulation of the dopamine type 1 (D1), type 2 (D2) receptors, and brain-derived neurotrophic factor (BDNF) to achieve a therapeutic effect. In vivo experiments demonstrate that the DR density of mice (postnatal day 50-60) increased in the prefrontal cortex (PFC) and the hippocampus (HPC) after 10 days of therapy, resulting in antidepressant-like and cognitive enhancement effects. Interestingly, the cognitive enhancement effect of CFs@DP is even working in noniron deficiency (normal fed) mice, making it a promising candidate for application in enhancing learning ability.

Disentangling the acute subjective effects of classic psychedelics from their enduring therapeutic properties

Recent research with classic psychedelics suggests significant therapeutic potential, particularly for neuropsychiatric disorders. A mediating influence behind symptom resolution is thought to be the personal insight - at times, bordering on the mystical - one acquires during the acute phase of a psychedelic session. Indeed, current clinical trials have found strong correlations between the acute subjective effects (ASE) under the influence of psychedelics and their enduring therapeutic properties. However, with potential barriers to widespread clinical implementation, including the healthcare resource-intensive nature of psychedelic sessions and the exclusion of certain at-risk patient groups, there is an active search to determine whether ASE elimination can be accompanied by the retention of persisting therapeutic benefits of these class of compounds. Recognizing the aberrant underlying neural circuitry that characterizes a range of neuropsychiatric disorders, and that classic psychedelics promote neuroplastic changes that may correct abnormal circuitry, investigators are rushing to design and discover compounds with psychoplastogenic, but not hallucinogenic (i.e., ASE), therapeutic potential. These efforts have paved the discovery of 'non-psychedelic/subjective psychedelics', or compounds that lack hallucinogenic activity but with therapeutic efficacy in preclinical models. This review aims to distill the current evidence - both clinical and preclinical - surrounding the question: can the ASE of classic psychedelics be dissociated from their sustained therapeutic properties? Several plausible clinical scenarios are then proposed to offer clarity on and potentially answer this question.

Psilocybin promotes neuroplasticity and induces rapid and sustained antidepressant-like effects in mice

BACKGROUND

Psilocybin offers new hope for treating mood disorders due to its rapid and sustained antidepressant effects, as standard medications require weeks or months to exert their effects. However, the mechanisms underlying this action of psilocybin have not been identified.

AIMS

To investigate whether psilocybin has rapid and sustained antidepressant-like effects in mice and investigate whether its potential mechanisms of action are related to promoted neuroplasticity.

METHODS

We first examined the antidepressant-like effects of psilocybin in normal mice by the forced swimming test and in chronic corticosterone (CORT)-exposed mice by the sucrose preference test and novelty-suppressed feeding test. Furthermore, to explore the role of neuroplasticity in mediating the antidepressant-like effects of psilocybin, we measured structural neuroplasticity and neuroplasticity-associated protein levels in the prefrontal cortex (PFC) and hippocampus.

RESULTS

We observed that a single dose of psilocybin had rapid and sustained antidepressant-like effects in both healthy mice and chronic CORT-exposed mice. Moreover, psilocybin ameliorated chronic CORT exposure-induced inhibition of neuroplasticity in the PFC and hippocampus, including by increasing neuroplasticity (total number of dendritic branches and dendritic spine density), synaptic protein (p-GluA1, PSD95 and synapsin-1) levels, BDNF-mTOR signalling pathway activation (BDNF, TrkB and mTOR levels), and promoting neurogenesis (number of DCX-positive cells).

CONCLUSIONS

Our results demonstrate that psilocybin elicits robust, rapid and sustained antidepressant-like effects which is accompanied by the promotion of neuroplasticity in the PFC and hippocampus.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic- and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice 24 h post-treatment. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than anxiolytic effects.

Flexible scaffold-based cheminformatics approach for polypharmacological drug design

Effective treatments for complex central nervous system (CNS) disorders require drugs with polypharmacology and multifunctionality, yet designing such drugs remains a challenge. Here, we present a flexible scaffold-based cheminformatics approach (FSCA) for the rational design of polypharmacological drugs. FSCA involves fitting a flexible scaffold to different receptors using different binding poses, as exemplified by IHCH-7179, which adopted a "bending-down" binding pose at 5-HT2AR to act as an antagonist and a "stretching-up" binding pose at 5-HT1AR to function as an agonist. IHCH-7179 demonstrated promising results in alleviating cognitive deficits and psychoactive symptoms in mice by blocking 5-HT2AR for psychoactive symptoms and activating 5-HT1AR to alleviate cognitive deficits. By analyzing aminergic receptor structures, we identified two featured motifs, the "agonist filter" and "conformation shaper," which determine ligand binding pose and predict activity at aminergic receptors. With these motifs, FSCA can be applied to the design of polypharmacological ligands at other receptors.

Ligand bias and inverse agonism on 5-HT2A receptor-mediated modulation of G protein activity in post-mortem human brain

BACKGROUND AND PURPOSE

Whereas biased agonism on the 5-HT2A receptor has been ascribed to hallucinogenic properties of psychedelics, no information about biased inverse agonism on this receptor is available. In schizophrenia, increased 5-HT2A receptor constitutive activity has been suggested, highlighting the therapeutic relevance of inverse agonism. This study characterized the modulation of G protein activity promoted by different drugs, commonly considered as 5-HT2A receptor antagonists, in post-mortem human brain cortex.

EXPERIMENTAL APPROACH

Modulation of [35S]GTPγS binding to different subtypes of Gα proteins exerted by different 5-HT2A receptor drugs was determined by scintillation proximity assays in brain from human, WT and 5-HT2A receptor KO mice.

KEY RESULTS

MDL-11,939 was the only drug having no effect on the basal activity of 5-HT2A receptor. Altanserin and pimavanserin decreased basal activation of Gi1, but not Gq/11 proteins. This effect was blocked by MDL-11,939 and absent in 5-HT2A receptor KO mice. Volinanserin showed 5-HT2A receptor-mediated inverse agonism both on Gi1 and Gq/11 proteins. Ketanserin exhibited 5-HT2A receptor partial agonism exclusively on Gq/11 proteins. On the other hand, eplivanserin and nelotanserin displayed inverse agonism on Gq/11 and/or Gi1 proteins, which was insensitive to MDL-11,939 and was present in KO mice suggesting a role for another receptor.

CONCLUSION AND IMPLICATIONS

The results reveal the existence of constitutively active 5-HT2A receptors in human pre-frontal cortex and demonstrate different pharmacological profiles of various 5-HT2A receptor drugs previously considered antagonists. These findings indicate that altanserin and pimavanserin possess biased inverse agonist profile towards 5-HT2A receptor activation of Gi1 proteins.

Therapeutic potential of psychedelics: History, advancements, and unexplored frontiers

Psychedelics (serotonergic hallucinogens) are psychoactive substances that can alter perception and mood, and affect cognitive functions. These substances activate 5-HT2A receptors and may exert therapeutic effects. Some of the disorders for which psychedelic-assisted therapy have been studied include depression, addiction, anxiety and post-traumatic stress disorder. Despite the increasing number of studies reporting clinical effectiveness, with fewer negative symptoms and, additionally, minimal side effects, questions remain to be explored in the field of psychedelic medicine. Although progress has been achieved, there is still little understanding of the relationship among human brain and the modulation induced by these drugs. The present article aimed to describe, review and highlight the most promising findings in the literature regarding the (putative) therapeutic effects of psychedelics.

Discovery and in vitro Evaluation of Novel Serotonin 5-HT2A Receptor Ligands Identified Through Virtual Screening

The 5-HT2A receptor is a molecular target of high pharmacological importance. Ligands of this protein, particularly atypical antipsychotics, are useful in the treatment of numerous mental disorders, including schizophrenia and major depressive disorder. Structure-based virtual screening using a 5-HT2A receptor complex was performed to identify novel ligands for the 5-HT2A receptor, serving as potential antidepressants. From the Enamine screening library, containing over 4 million compounds, 48 molecules were selected for subsequent experimental validation. These compounds were tested against the 5-HT2A receptor in radioligand binding assays. From the tested batch, six molecules were identified as ligands of the main molecular target and were forwarded to a more detailed in vitro profiling. This included radioligand binding assays at 5-HT1A, 5-HT7, and D2 receptors and functional studies at 5-HT2A receptors. These compounds were confirmed to show a binding affinity for at least one of the targets tested in vitro. The success rate for the inactive template-based screening reached 17 %, while it was 9 % for the active template-based screening. Similarity and fragment analysis indicated the structural novelty of the identified compounds. Pharmacokinetics for these molecules was determined using in silico approaches.

A unified analysis of evolutionary and population constraint in protein domains highlights structural features and pathogenic sites

Protein evolution is constrained by structure and function, creating patterns in residue conservation that are routinely exploited to predict structure and other features. Similar constraints should affect variation across individuals, but it is only with the growth of human population sequencing that this has been tested at scale. Now, human population constraint has established applications in pathogenicity prediction, but it has not yet been explored for structural inference. Here, we map 2.4 million population variants to 5885 protein families and quantify residue-level constraint with a new Missense Enrichment Score (MES). Analysis of 61,214 structures from the PDB spanning 3661 families shows that missense depleted sites are enriched in buried residues or those involved in small-molecule or protein binding. MES is complementary to evolutionary conservation and a combined analysis allows a new classification of residues according to a conservation plane. This approach finds functional residues that are evolutionarily diverse, which can be related to specificity, as well as family-wide conserved sites that are critical for folding or function. We also find a possible contrast between lethal and non-lethal pathogenic sites, and a surprising clinical variant hot spot at a subset of missense enriched positions.

Introducing urea into tirapazamine derivatives to enhance anticancer therapy

Tirapazamine (TPZ) has been approved for multiple clinical trials relying on its excellent anticancer potential. However, as a typical hypoxia-activated prodrug (HAP), TPZ did not exhibit survival advantages in Phase III clinical trials when used in combination therapy due to the insufficient hypoxia levels in patients' tumors. In this study, to improve the therapeutic effects of TPZ, we first introduced urea to synthesize a series of urea-containing derivatives of TPZ. All urea-containing TPZ derivatives showed increased hypoxic cytotoxicity (9.51-30.85-fold) compared with TPZ, while maintaining hypoxic selectivity. TPZP, one of these derivatives, showed 20-fold higher cytotoxicity than TPZ while maintaining a similar hypoxic cytotoxicity ratio. To highly efficiently deliver TPZP to the tumors and reduce its side effects on healthy tissues, we further prepared TPZP into a nanodrug with fibrin-targeting ability: FT11-TPZP-NPs. CA4-NPs, a vascular disrupting agent, was used to increase the fibrin level within tumors and exacerbate tumor hypoxia. By being combined with CA4-NPs, FT11-TPZP-NPs can accumulate in the hypoxia-aggravated tumors and activate sufficiently to kill tumor cells. After a single-dose treatment, FT11-TPZP-NPs + CA4-NPs showed a high inhibition rate of 98.1% against CT26 tumor models with an initial volume of ∼480 mm3 and four out of six tumors were completely eliminated; it thereby exerted a significant antitumor effect. This study provides a new strategy for improving the therapeutic effect of TPZ and other HAPs in anticancer therapy.

High-resolution tracking of unconfined zebrafish behavior reveals stimulatory and anxiolytic effects of psilocybin

Serotonergic psychedelics are emerging therapeutics for psychiatric disorders, yet their underlying mechanisms of action in the brain remain largely elusive. Here, we developed a wide-field behavioral tracking system for larval zebrafish and investigated the effects of psilocybin, a psychedelic serotonin receptor agonist. Machine learning analyses of precise body kinematics identified latent behavioral states reflecting spontaneous exploration, visually-driven rapid swimming, and irregular swim patterns following stress exposure. Using this method, we found that acute psilocybin treatment has two behavioral effects: [i] facilitation of spontaneous exploration ("stimulatory") and [ii] prevention of irregular swim patterns following stress exposure ("anxiolytic"). These effects differed from the effect of acute SSRI treatment and were rather similar to the effect of ketamine treatment. Neural activity imaging in the dorsal raphe nucleus suggested that psilocybin inhibits serotonergic neurons by activating local GABAergic neurons, consistent with psychedelic-induced suppression of serotonergic neurons in mammals. These findings pave the way for using larval zebrafish to elucidate neural mechanisms underlying the behavioral effects of serotonergic psychedelics.

Synthesis and bioactivity of psilocybin analogues containing a stable carbon-phosphorus bond

Psilocybin analogues have been synthesized comprising a non-hydrolysable P-C bond to evaluate the biological activity and the selectivity towards 5-HT2AR, 5-HT2BR and the TNAP receptor. No activity was observed towards the phosphatase, however all compounds showed good binding affinity for 5-HT2AR and 5-HT2BR and one compound showed a higher selectivity towards 5-HT2AR than psilocin.

Structure-based design of non-hypertrophic apelin receptor modulator

Apelin is a key hormone in cardiovascular homeostasis that activates the apelin receptor (APLNR), which is regarded as a promising therapeutic target for cardiovascular disease. However, adverse effects through the β-arrestin pathway limit its pharmacological use. Here, we report cryoelectron microscopy (cryo-EM) structures of APLNR-Gi1 complexes bound to three agonists with divergent signaling profiles. Combined with functional assays, we have identified "twin hotspots" in APLNR as key determinants for signaling bias, guiding the rational design of two exclusive G-protein-biased agonists WN353 and WN561. Cryo-EM structures of WN353- and WN561-stimulated APLNR-G protein complexes further confirm that the designed ligands adopt the desired poses. Pathophysiological experiments have provided evidence that WN561 demonstrates superior therapeutic effects against cardiac hypertrophy and reduced adverse effects compared with the established APLNR agonists. In summary, our designed APLNR modulator may facilitate the development of next-generation cardiovascular medications.

AlphaFold2 structures template ligand discovery

AlphaFold2 (AF2) and RosettaFold have greatly expanded the number of structures available for structure-based ligand discovery, even though retrospective studies have cast doubt on their direct usefulness for that goal. Here, we tested unrefined AF2 models prospectively, comparing experimental hit-rates and affinities from large library docking against AF2 models vs the same screens targeting experimental structures of the same receptors. In retrospective docking screens against the σ2 and the 5-HT2A receptors, the AF2 structures struggled to recapitulate ligands that we had previously found docking against the receptors' experimental structures, consistent with published results. Prospective large library docking against the AF2 models, however, yielded similar hit rates for both receptors versus docking against experimentally-derived structures; hundreds of molecules were prioritized and tested against each model and each structure of each receptor. The success of the AF2 models was achieved despite differences in orthosteric pocket residue conformations for both targets versus the experimental structures. Intriguingly, against the 5-HT2A receptor the most potent, subtype-selective agonists were discovered via docking against the AF2 model, not the experimental structure. To understand this from a molecular perspective, a cryoEM structure was determined for one of the more potent and selective ligands to emerge from docking against the AF2 model of the 5-HT2A receptor. Our findings suggest that AF2 models may sample conformations that are relevant for ligand discovery, much extending the domain of applicability of structure-based ligand discovery.

The novel non-hallucinogenic compound DM506 (3-methyl-1,2,3,4,5,6-hexahydroazepino[4,5-b]indole) induces sedative- and anxiolytic-like activity in mice by a mechanism involving 5-HT2A receptor activation

The anxiolytic and sedative-like effects of 3-methyl-1,2,3,4,5,6-hexahydroazepino[4,5-b]indole (DM506), a non-hallucinogenic compound derived from ibogamine, were studied in mice. The behavioral effects were examined using Elevated O-maze and novelty suppressed feeding (NSFT) tests, open field test, and loss of righting reflex (LORR) test. The results showed that 15 mg/kg DM506 induced acute and long-lasting anxiolytic-like activity in naive and stressed/anxious mice, respectively. Repeated administration of 5 mg/kg DM506 did not cause cumulative anxiolytic activity or any side effects. Higher doses of DM506 (40 mg/kg) induced sedative-like activity, which was inhibited by a selective 5-HT2A receptor antagonist, volinanserin. Electroencephalography results showed that 15 mg/kg DM506 fumarate increased the transition from a highly alert state (fast γ wavelength) to a more synchronized deep-sleeping activity (δ wavelength), which is reflected in the sedative/anxiolytic activity in mice but without the head-twitch response observed in hallucinogens. The functional, radioligand binding, and molecular docking results showed that DM506 binds to the agonist sites of human 5-HT2A (Ki = 24 nM) and 5-HT2B (Ki = 16 nM) receptors and activates them with a potency (EC50) of 9 nM and 3 nM, respectively. DM506 was relatively less potent and behaved as a partial agonist (efficacy <80%) for both receptor subtypes compared to the full agonist DOI (2,5-dimethoxy-4-iodoamphetamine). Our study showed for the first time that the non-hallucinogenic compound DM506 induces anxiolytic- and sedative-like activities in naïve and stressed/anxious mice in a dose-, time-, and volinanserin-sensitive manner, likely through mechanisms involving 5-HT2A receptor activation.

Antidepressant-like effects of psychedelics in a chronic despair mouse model: is the 5-HT2A receptor the unique player?

Major depressive disorder (MDD) is one of the most disabling psychiatric disorders in the world. First-line treatments such as selective serotonin reuptake inhibitors (SSRIs) still have many limitations, including a resistance to treatment in 30% of patients and a delayed clinical benefit that is observed only after several weeks of treatment. Increasing clinical evidence indicates that the acute administration of psychedelic agonists of the serotonin 5-HT2A receptor (5-HT2AR), such as psilocybin, to patients with MDD induce fast antidepressant effects, which persist up to five weeks after the treatment. However, the involvement of the 5-HT2AR in these antidepressant effects remains controversial. Furthermore, whether the hallucinogenic properties of 5-HT2AR agonists are mandatory to their antidepressant activity is still an open question. Here, we addressed these issues by investigating the effect of two psychedelics of different chemical families, DOI and psilocybin, and a non-hallucinogenic 5-HT2AR agonist, lisuride, in a chronic despair mouse model exhibiting a robust depressive-like phenotype. We show that a single injection of each drug to wild type mice induces anxiolytic- and antidepressant-like effects in the novelty-suppressed feeding, sucrose preference and forced swim tests, which last up to 15 days. DOI and lisuride administration did not produce antidepressant-like effects in 5-HT2A-/- mice, whereas psilocybin was still effective. Moreover, neither 5-HT1AR blockade nor dopamine D1 or D2 receptor blockade affected the antidepressant-like effects of psilocybin in 5-HT2A-/- mice. Collectively, these findings indicate that 5-HT2AR agonists can produce antidepressant-like effects independently of hallucinogenic properties through mechanisms involving or not involving the receptor.

Psychedelics for acquired brain injury: a review of molecular mechanisms and therapeutic potential

Acquired brain injury (ABI), such as traumatic brain injury and stroke, is a leading cause of disability worldwide, resulting in debilitating acute and chronic symptoms, as well as an increased risk of developing neurological and neurodegenerative disorders. These symptoms can stem from various neurophysiological insults, including neuroinflammation, oxidative stress, imbalances in neurotransmission, and impaired neuroplasticity. Despite advancements in medical technology and treatment interventions, managing ABI remains a significant challenge. Emerging evidence suggests that psychedelics may rapidly improve neurobehavioral outcomes in patients with various disorders that share physiological similarities with ABI. However, research specifically focussed on psychedelics for ABI is limited. This narrative literature review explores the neurochemical properties of psychedelics as a therapeutic intervention for ABI, with a focus on serotonin receptors, sigma-1 receptors, and neurotrophic signalling associated with neuroprotection, neuroplasticity, and neuroinflammation. The promotion of neuronal growth, cell survival, and anti-inflammatory properties exhibited by psychedelics strongly supports their potential benefit in managing ABI. Further research and translational efforts are required to elucidate their therapeutic mechanisms of action and to evaluate their effectiveness in treating the acute and chronic phases of ABI.

Are "mystical experiences" essential for antidepressant actions of ketamine and the classic psychedelics?

The growing interest in the rapid and sustained antidepressant effects of the dissociative anesthetic ketamine and classic psychedelics, such as psilocybin, is remarkable. However, both ketamine and psychedelics are known to induce acute mystical experiences; ketamine can cause dissociative symptoms such as out-of-body experience, while psychedelics typically bring about hallucinogenic experiences, like a profound sense of unity with the universe or nature. The role of these mystical experiences in enhancing the antidepressant outcomes for patients with depression is currently an area of ongoing investigation and debate. Clinical studies have shown that the dissociative symptoms following the administration of ketamine or (S)-ketamine (esketamine) are not directly linked to their antidepressant properties. In contrast, the antidepressant potential of (R)-ketamine (arketamine), thought to lack dissociative side effects, has yet to be conclusively proven in large-scale clinical trials. Moreover, although the activation of the serotonin 5-HT2A receptor is crucial for the hallucinogenic effects of psychedelics in humans, its precise role in their antidepressant action is still under discussion. This article explores the importance of mystical experiences in enhancing the antidepressant efficacy of both ketamine and classic psychedelics.

Exploring Novel Antidepressants Targeting G Protein-Coupled Receptors and Key Membrane Receptors Based on Molecular Structures

Major Depressive Disorder (MDD) is a complex mental disorder that involves alterations in signal transmission across multiple scales and structural abnormalities. The development of effective antidepressants (ADs) has been hindered by the dominance of monoamine hypothesis, resulting in slow progress. Traditional ADs have undesirable traits like delayed onset of action, limited efficacy, and severe side effects. Recently, two categories of fast-acting antidepressant compounds have surfaced, dissociative anesthetics S-ketamine and its metabolites, as well as psychedelics such as lysergic acid diethylamide (LSD). This has led to structural research and drug development of the receptors that they target. This review provides breakthroughs and achievements in the structure of depression-related receptors and novel ADs based on these. Cryo-electron microscopy (cryo-EM) has enabled researchers to identify the structures of membrane receptors, including the N-methyl-D-aspartate receptor (NMDAR) and the 5-hydroxytryptamine 2A (5-HT2A) receptor. These high-resolution structures can be used for the development of novel ADs using virtual drug screening (VDS). Moreover, the unique antidepressant effects of 5-HT1A receptors in various brain regions, and the pivotal roles of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and tyrosine kinase receptor 2 (TrkB) in regulating synaptic plasticity, emphasize their potential as therapeutic targets. Using structural information, a series of highly selective ADs were designed based on the different role of receptors in MDD. These molecules have the favorable characteristics of rapid onset and low adverse drug reactions. This review offers researchers guidance and a methodological framework for the structure-based design of ADs.

Advances in structure-based drug design: The potential for precision therapeutics in psychiatric disorders

Over the years, the field of GPCR drug design has undergone a remarkable evolution, fueled by advancements in science and technology. This evolution has given rise to a diverse range of ideas and approaches in structure-based drug design, bolstering the versatility and strength of the GPCR drug design toolbox. This review encapsulates the iterative development process, navigating challenges and opportunities in structure-based drug design within GPCRs. With a focused emphasis on its impact on psychiatric disorders, the review accentuates recent advancements and delves into the potentials unlocked by emerging technologies. The review explores the intricate interplay between scientific progress and iterative refinement, offering profound insights into the potential pathways that lie ahead for GPCR drug design.

Effect of chemically synthesized psilocybin and psychedelic mushroom extract on molecular and metabolic profiles in mouse brain

Psilocybin, a naturally occurring, tryptamine alkaloid prodrug, is currently being investigated for the treatment of a range of psychiatric disorders. Preclinical reports suggest that the biological effects of psilocybin-containing mushroom extract or "full spectrum" (psychedelic) mushroom extract (PME), may differ from those of chemically synthesized psilocybin (PSIL). We compared the effects of PME to those of PSIL on the head twitch response (HTR), neuroplasticity-related synaptic proteins and frontal cortex metabolomic profiles in male C57Bl/6j mice. HTR measurement showed similar effects of PSIL and PME over 20 min. Brain specimens (frontal cortex, hippocampus, amygdala, striatum) were assayed for the synaptic proteins, GAP43, PSD95, synaptophysin and SV2A, using western blots. These proteins may serve as indicators of synaptic plasticity. Three days after treatment, there was minimal increase in synaptic proteins. After 11 days, PSIL and PME significantly increased GAP43 in the frontal cortex (p = 0.019; p = 0.039 respectively) and hippocampus (p = 0.015; p = 0.027) and synaptophysin in the hippocampus (p = 0.041; p = 0.05) and amygdala (p = 0.035; p = 0.004). PSIL increased SV2A in the amygdala (p = 0.036) and PME did so in the hippocampus (p = 0.014). In the striatum, synaptophysin was increased by PME only (p = 0.023). There were no significant effects of PSIL or PME on PSD95 in any brain area when these were analyzed separately. Nested analysis of variance (ANOVA) showed a significant increase in each of the 4 proteins over all brain areas for PME versus vehicle control, while significant PSIL effects were observed only in the hippocampus and amygdala and were limited to PSD95 and SV2A. Metabolomic analyses of the pre-frontal cortex were performed by untargeted polar metabolomics utilizing capillary electrophoresis - Fourier transform mass spectrometry (CE-FTMS) and showed a differential metabolic separation between PME and vehicle groups. The purines guanosine, hypoxanthine and inosine, associated with oxidative stress and energy production pathways, showed a progressive decline from VEH to PSIL to PME. In conclusion, our synaptic protein findings suggest that PME has a more potent and prolonged effect on synaptic plasticity than PSIL. Our metabolomics data support a gradient of effects from inert vehicle via chemical psilocybin to PME further supporting differential effects. Further studies are needed to confirm and extend these findings and to identify the molecules that may be responsible for the enhanced effects of PME as compared to psilocybin alone.

The Effects of Psychedelics on Neuronal Physiology

Psychedelics are quite unique among drugs that impact the central nervous system, as a single administration of a psychedelic can both rapidly alter subjective experience in profound ways and produce sustained effects on circuits relevant to mood, fear, reward, and cognitive flexibility. These remarkable properties are a direct result of psychedelics interacting with several key neuroreceptors distributed across the brain. Stimulation of these receptors activates a variety of signaling cascades that ultimately culminate in changes in neuronal structure and function. Here, we describe the effects of psychedelics on neuronal physiology, highlighting their acute effects on serotonergic and glutamatergic neurotransmission as well as their long-lasting effects on structural and functional neuroplasticity in the cortex. We propose that the neurobiological changes leading to the acute and sustained effects of psychedelics might be distinct, which could provide opportunities for engineering compounds with optimized safety and efficacy profiles.

Major depressive disorder: hypothesis, mechanism, prevention and treatment

Worldwide, the incidence of major depressive disorder (MDD) is increasing annually, resulting in greater economic and social burdens. Moreover, the pathological mechanisms of MDD and the mechanisms underlying the effects of pharmacological treatments for MDD are complex and unclear, and additional diagnostic and therapeutic strategies for MDD still are needed. The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis, but these hypothesis cannot completely explain the pathological mechanism of MDD. Even it is still hard to adopt only one hypothesis to completely reveal the pathogenesis of MDD, thus in recent years, great progress has been made in elucidating the roles of multiple organ interactions in the pathogenesis MDD and identifying novel therapeutic approaches and multitarget modulatory strategies, further revealing the disease features of MDD. Furthermore, some newly discovered potential pharmacological targets and newly studied antidepressants have attracted widespread attention, some reagents have even been approved for clinical treatment and some novel therapeutic methods such as phototherapy and acupuncture have been discovered to have effective improvement for the depressive symptoms. In this work, we comprehensively summarize the latest research on the pathogenesis and diagnosis of MDD, preventive approaches and therapeutic medicines, as well as the related clinical trials.

Membrane Permeation of Psychedelic Tryptamines by Dynamic Simulations

Renewed scientific interest in psychedelic compounds represents one of the most promising avenues for addressing the current burden of mental health disorders. Classic psychedelics are a group of compounds that exhibit structural similarities to the naturally occurring neurotransmitter serotonin (5-HT). Acting on the 5-HT type 2A receptors (HT2ARs), psychedelics induce enduring neurophysiological changes that parallel their therapeutic psychological and behavioral effects. Recent preclinical evidence suggests that the ability of psychedelics to exert their action is determined by their ability to permeate the neuronal membrane to target a pool of intracellular 5-HT2ARs. In this computational study, we employ classical molecular dynamics simulations and umbrella sampling techniques to investigate the permeation behavior of 12 selected tryptamines and to characterize the interactions that drive the process. We aim at elucidating the impact of N-alkylation, indole ring substitution and positional modifications, and protonation on their membrane permeability. Dimethylation of the primary amine group and the introduction of a methoxy group at position 5 exhibited an increase in permeability. Moreover, there is a significant influence of positional substitutions on the indole groups, and the protonation of the molecules substantially increases the energy barrier at the center of the bilayer, making the compounds highly impermeable. All the information extracted from the trends predicted by the simulations can be applied in future drug design projects to develop psychedelics with enhanced activity.

Effect of Bulky N-Dibenzofuranylmethyl Substitution on the 5-HT2 Receptor Affinity and Efficacy of a Psychedelic Phenethylamine

The introduction of arylmethyl substituents on the amine nitrogen atom of phenethylamines and tryptamines often results in profound increases in their affinity and functional activity at 5-HT2 serotonin receptors. To probe the sensitivity of this effect to substantially larger N-substituents, ten derivatives of the well-characterized psychedelic phenethylamine 2C-B were prepared by appending different dibenzo[b,d]furylmethyl (DBFM) moieties to the basic nitrogen. The DBFM group attached to the amino group through its 1-, -2-, or 3-position decreased affinity and agonist activity at the 5-HT2A/2C receptors. Substitution through the 4-position usually favored affinity for all three 5-HT2 receptor subtypes with compound 5 exhibiting 10- and 40-fold higher affinities at the 5-HT2A and 5-HT2C receptors, respectively, but less than fourfold selectivity among the three receptor subtypes. Nevertheless, all were relatively weak partial 5-HT2AR agonists, mostly in the low micromolar range, but full or nearly full agonists at the 5-HT2C subtype as determined in a calcium mobilization assay. Molecular docking simulations suggested that the dibenzofuryl portion dives more deeply into the orthosteric binding site of the 5-HT2A than the 5-HT2C receptor, interacting with the Trp3366.48 toggle switch associated with its activation, while the phenylamine moiety lies close to the extracellular side of the receptor. In conclusion, a very bulky N-substituent on a phenethylamine 5-HT2 receptor agonist is tolerated and may increase affinity if its orientation is appropriate. However, the Gq protein-mediated potencies are generally low, with low efficacy (relative to 5-HT) at the 5-HT2A receptor, somewhat higher efficacy at the 5-HT2B subtype, and full or nearly full efficacy at the 5-HT2C subtype.

Synthetic surprise as the foundation of the psychedelic experience

Psychedelic agents, such as LSD and psilocybin, induce marked alterations in consciousness via activation of the 5-HT2A receptor (5-HT2ARs). We hypothesize that psychedelics enforce a state of synthetic surprise through the biased activation of the 5-HTRs system. This idea is informed by recent insights into the role of 5-HT in signaling surprise. The effects on consciousness, explained by the cognitive penetrability of perception, can be described within the predictive coding framework where surprise corresponds to prediction error, the mismatch between predictions and actual sensory input. Crucially, the precision afforded to the prediction error determines its effect on priors, enabling a dynamic interaction between top-down expectations and incoming sensory data. By integrating recent findings on predictive coding circuitry and 5-HT2ARs transcriptomic data, we propose a biological implementation with emphasis on the role of inhibitory interneurons. Implications arise for the clinical use of psychedelics, which may rely primarily on their inherent capacity to induce surprise in order to disrupt maladaptive patterns.

Making Sense of Psychedelics in the CNS

For centuries, ancient lineages have consumed psychedelic compounds from natural sources. In the modern era, scientists have since harnessed the power of computational tools, cellular assays, and behavioral metrics to study how these compounds instigate changes on molecular, cellular, circuit-wide, and system levels. Here, we provide a brief history of psychedelics and their use in science, medicine, and culture. We then outline current techniques for studying psychedelics from a pharmacological perspective. Finally, we address known gaps in the field and potential avenues of further research to broaden our collective understanding of physiological changes induced by psychedelics, the limits of their therapeutic capabilities, and how researchers can improve and inform treatments that are rapidly becoming accessible worldwide.

Discovery of a peripheral 5HT2A antagonist as a clinical candidate for metabolic dysfunction-associated steatohepatitis

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is currently the leading cause of chronic liver disease worldwide. Metabolic Dysfunction-Associated Steatohepatitis (MASH), an advanced form of MASLD, can progress to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Based on recent findings by our team that liver 5HT2A knockout male mice suppressed steatosis and reduced fibrosis-related gene expression, we developed a peripheral 5HT2A antagonist, compound 11c for MASH. It shows good in vitro activity, stability, and in vivo pharmacokinetics (PK) in rats and dogs. Compound 11c also shows good in vivo efficacy in a diet-induced obesity (DIO) male mice model and in a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) male mice model, effectively improving histologic features of MASH and fibrosis. According to the tissue distribution study using [14C]-labeled 11c, the compound was determined to be a peripheral 5HT2A antagonist. Collectively, first-in-class compound 11c shows promise as a therapeutic agent for the treatment of MASLD and MASH.

Serotonin 2A Receptor (5-HT2AR) Agonists: Psychedelics and Non-Hallucinogenic Analogues as Emerging Antidepressants

Psychedelics make up a group of psychoactive compounds that induce hallucinogenic effects by activating the serotonin 2A receptor (5-HT2AR). Clinical trials have demonstrated the traditional psychedelic substances like psilocybin as a class of rapid-acting and long-lasting antidepressants. However, there is a pressing need for rationally designed 5-HT2AR agonists that possess optimal pharmacological profiles in order to fully reveal the therapeutic potential of these agonists and identify safer drug candidates devoid of hallucinogenic effects. This Perspective provides an overview of the structure-activity relationships of existing 5-HT2AR agonists based on their chemical classifications and discusses recent advancements in understanding their molecular pharmacology at a structural level. The encouraging clinical outcomes of psychedelics in depression treatment have sparked drug discovery endeavors aimed at developing novel 5-HT2AR agonists with improved subtype selectivity and signaling bias properties, which could serve as safer and potentially nonhallucinogenic antidepressants. These efforts can be significantly expedited through the utilization of structure-based methods and functional selectivity-directed screening.

Therapeutic mechanisms of psychedelics and entactogens

Recent clinical and preclinical evidence suggests that psychedelics and entactogens may produce both rapid and sustained therapeutic effects across several indications. Currently, there is a disconnect between how these compounds are used in the clinic and how they are studied in preclinical species, which has led to a gap in our mechanistic understanding of how these compounds might positively impact mental health. Human studies have emphasized extra-pharmacological factors that could modulate psychedelic-induced therapeutic responses including set, setting, and integration-factors that are poorly modelled in current animal experiments. In contrast, animal studies have focused on changes in neuronal activation and structural plasticity-outcomes that are challenging to measure in humans. Here, we describe several hypotheses that might explain how psychedelics rescue neuropsychiatric disease symptoms, and we propose ways to bridge the gap between human and rodent studies. Given the diverse pharmacological profiles of psychedelics and entactogens, we suggest that their rapid and sustained therapeutic mechanisms of action might best be described by the collection of circuits that they modulate rather than their actions at any single molecular target. Thus, approaches focusing on selective circuit modulation of behavioral phenotypes might prove more fruitful than target-based methods for identifying novel compounds with rapid and sustained therapeutic effects similar to psychedelics and entactogens.

Psychedelics: preclinical insights provide directions for future research

Recently, psychedelics have emerged as promising therapeutics for numerous neuropsychiatric disorders. While their potential in the clinic has yet to be fully elucidated, understanding their molecular and biological mechanisms is imperative as these compounds are becoming widely used both in therapeutic and recreational contexts. This review examines the current understanding of basic biology, pharmacology, and structural biology in an attempt to reveal both the knowns and unknowns within the field.

Snapshot of the cannabinoid receptor 1-arrestin complex unravels the biased signaling mechanism

Cannabis activates the cannabinoid receptor 1 (CB1), which elicits analgesic and emotion regulation benefits, along with adverse effects, via Gi and β-arrestin signaling pathways. However, the lack of understanding of the mechanism of β-arrestin-1 (βarr1) coupling and signaling bias has hindered drug development targeting CB1. Here, we present the high-resolution cryo-electron microscopy structure of CB1-βarr1 complex bound to the synthetic cannabinoid MDMB-Fubinaca (FUB), revealing notable differences in the transducer pocket and ligand-binding site compared with the Gi protein complex. βarr1 occupies a wider transducer pocket promoting substantial outward movement of the TM6 and distinctive twin toggle switch rearrangements, whereas FUB adopts a different pose, inserting more deeply than the Gi-coupled state, suggesting the allosteric correlation between the orthosteric binding pocket and the partner protein site. Taken together, our findings unravel the molecular mechanism of signaling bias toward CB1, facilitating the development of CB1 agonists.

Psilocybin and Eugenol Reduce Inflammation in Human 3D EpiIntestinal Tissue

Inflammation plays a pivotal role in the development and progression of inflammatory bowel disease (IBD), by contributing to tissue damage and exacerbating the immune response. The investigation of serotonin receptor 2A (5-HT2A) ligands and transient receptor potential (TRP) channel ligands is of significant interest due to their potential to modulate key inflammatory pathways, mitigate the pathological effects of inflammation, and offer new avenues for therapeutic interventions in IBD. This study investigates the anti-inflammatory effects of 5-HT2A ligands, including psilocybin, 4-AcO-DMT, and ketanserin, in combination with TRP channel ligands, including capsaicin, curcumin, and eugenol, on the inflammatory response induced by tumor necrosis factor (TNF)-α and interferon (IFN)-γ in human 3D EpiIntestinal tissue. Enzyme-linked immunosorbent assay was used to assess the expression of pro-inflammatory markers TNF-α, IFN-γ, IL-6, IL-8, MCP-1, and GM-CSF. Our results show that psilocybin, 4-AcO-DMT, and eugenol significantly reduce TNF-α and IFN-γ levels, while capsaicin and curcumin decrease these markers to a lesser extent. Psilocybin effectively lowers IL-6 and IL-8 levels, but curcumin, capsaicin, and 4-AcO-DMT have limited effects on these markers. In addition, psilocybin can significantly decrease MCP-1 and GM-CSF levels. While ketanserin lowers IL-6 and GM-CSF levels, there are no effects seen on TNF-α, IFN-γ, IL-8, or MCP-1. Although synergistic effects between 5-HT2A and TRP channel ligands are minimal in this study, the results provide further evidence of the anti-inflammatory effects of psilocybin and eugenol. Further research is needed to understand the mechanisms of action and the feasibility of using these compounds as anti-inflammatory therapies for conditions like IBD.

The possible place for psychedelics in pharmacotherapy of mental disorders

Since its emergence in the 1960s, the serotonergic theory of depression bore fruit in the discovery of a plethora of antidepressant drugs affecting the lives of millions of patients. While crucial in the history of drug development, recent studies undermine the effectiveness of currently used antidepressant drugs in comparison to placebo, emphasizing the long time it takes to initiate the therapeutic response and numerous adverse effects. Thus, the scope of contemporary pharmacological research shifts from drugs affecting the serotonin system to rapid-acting antidepressant drugs. The prototypical representative of the aforementioned class is ketamine, an NMDA receptor antagonist capable of alleviating the symptoms of depression shortly after the drug administration. This discovery led to a paradigm shift, focusing on amino-acidic neurotransmitters and growth factors. Alas, the drug is not perfect, as its therapeutic effect diminishes circa 2 weeks after administration. Furthermore, it is not devoid of some severe side effects. However, there seems to be another, more efficient, and safer way to target the glutamatergic system. Hallucinogenic agonists of the 5-HT2A receptor, commonly known as psychedelics, are nowadays being reconsidered in clinical practice, shedding their infamous 1970s stigma. More and more clinical studies prove their clinical efficacy and rapid onset after a single administration while bearing fewer side effects. This review focuses on the current state-of-the-art literature and most recent clinical studies concerning the use of psychedelic drugs in the treatment of mental disorders. Specifically, the antidepressant potential of LSD, psilocybin, DMT, and 5-MeO-DMT will be discussed, together with a brief summary of other possible applications.

Prophylactic effects of arketamine, but not hallucinogenic psychedelic DOI nor non-hallucinogenic psychedelic analog lisuride, in lipopolysaccharide-treated mice and mice exposed to chronic restrain stress

Anesthetic ketamine and classical psychedelics that act as 5-hydroxytryptamine-2A receptor (5-HT2AR) agonists demonstrated rapid and sustained antidepressant actions in patients with treatment-resistant depression. The new antidepressant arketamine is reported to cause long-lasting prophylactic effects in lipopolysaccharide (LPS)-treated mice and mice exposed to chronic restrain stress (CRS). However, no study has compared the prophylactic effects of DOI (2,5-dimethoxy-4-iodoamphetamine: a hallucinogenic psychedelic drug with potent 5-HT2AR agonism), lisuride (non-hallucinogenic psychedelic analog with 5-HT2AR and 5-HT1AR agonism), and arketamine on depression-like behaviors in mice. Saline (10 ml/kg), DOI (2.0 or 4.0 mg/kg), lisuride (1.0 or 2.0 mg/kg), or arketamine (10 mg/kg) was administered intraperitoneally (i.p.) to male mice 6 days before administration of LPS (1.0 mg/kg). Pretreatment with aketamine, but not DOI and lisuride, significantly ameliorated body weight loss, splenomegaly, the increased immobility time of forced swimming test (FST), and the decreased expression of PSD-95 in the prefrontal cortex (PFC) of LPS-treated mice. In another test, male mice received the same treatment one day before CRS (7 days). Pretreatment with aketamine, but not DOI and lisuride, significantly ameliorated the increased FST immobility time, the reduced sucrose preference in the sucrose preference test, and the decreased expression of PSD-95 in the PFC of CRS-exposed mice. These findings suggest that, unlike to arketamine, both DOI and lisuride did not exhibit long-lasting prophylactic effects in mouse models of depression.

Psychedelics action and schizophrenia

Psychedelics are compounds acting by serotonin 5-hydroxytryptamine (5-HT)2A receptor activation and induce several behavioral responses. They are of special interest because of their positive effects on neuropsychiatric disorders (depression and posttraumatic stress disorder). However, several findings revealed that some psychedelic actions are similar to symptoms observed in schizophrenia (psychosis, sensorimotor gating impairments, attention, and working memory deficits) which might limit their clinical applications. Psychedelics activate some neurotransmitters, i.e., serotonergic, and glutamatergic, that are also impaired in schizophrenia. Therefore, the neurobiological background of psychedelics and schizophrenia is partially similar. Another important aspect to discuss is the perspective of using psychedelics in schizophrenia therapy. Postmortem studies showed a loss of synapses in schizophrenia, and the positive effects of psychedelics on neuroplasticity (synaptogenesis, neurogenesis, and neuritogenesis) might be essential in the context of schizophrenia therapy. However, because of psychedelics' psychotic action, the recommended doses of psychedelics in schizophrenia treatment are not established, and subpsychedelic dosing or microdosing are considered. Exploratory studies are needed to determine the tolerability of treatment and appropriate dosing regimen. Another therapeutic option is using non-hallucinogenic psychedelic analogs that also induce neuroplastic outcomes but do not have psychotogenic effects. Further preclinical and clinical studies are needed to recognize the potential effectiveness of 5-HT2A agonists in schizophrenia therapy.

Interaction of hallucinogenic rapid-acting antidepressants with mGlu2/3 receptor ligands as a window for more effective therapies

The desire to find a gold-standard therapy for depression is still ongoing. Developing one universal and effective pharmacotherapy remains troublesome due to the high complexity and variety of symptoms. Over the last decades, the understanding of the mechanism of pathophysiology of depression and its key consequences for brain functioning have undergone significant changes, referring to the monoaminergic theory of the disease. After the breakthrough discovery of ketamine, research began to focus on the modulation of glutamatergic transmission as a new pharmacological target. Glutamate is a crucial player in mechanisms of a novel class of antidepressants, including hallucinogens such as ketamine. The role of glutamatergic transmission is also suggested in the antidepressant (AD) action of scopolamine and psilocybin. Despite fast, robust, and sustained AD action hallucinogens belonging to a group of rapid-acting antidepressants (RAA) exert significant undesired effects, which hamper their use in the clinic. Thus, the synergistic action of more than one substance in lower doses instead of monotherapy may alleviate the likelihood of adverse effects while improving therapeutic outcomes. In this review, we explore AD-like behavioral, synaptic, and molecular action of RAAs such as ketamine, scopolamine, and psilocybin, in combination with mGlu2/3 receptor antagonists.

Ligand selectivity hotspots in serotonin GPCRs

Serotonin is a neurotransmitter regulating numerous physiological processes also modulated by drugs, for example, schizophrenia, depression, migraine, and obesity. However, these drugs typically have adverse effects caused by promiscuous binding across 12 serotonin and more than 20 homologous receptors. Recently, structures of the entire serotonin receptor family uncovered molecular ligand recognition. Here, we present a map of 19 'selectivity hotspots', that is, nonconserved binding site residues governing selectivity via favorable target interactions or repulsive 'off-target' contacts. Furthermore, we review functional rationale from observed ligand-binding affinities and mutagenesis effects. Unifying knowledge underlying specific probes and drugs is critical toward the functional characterization of different receptors and alleviation of adverse effects.

[Interest and mechanisms of action of ketamine in alcohol addiction- A review of clinical and preclinical studies]

Alcohol Use Disorder (AUD) is a psychiatric condition characterized by chronic and excessive drinking despite negative consequences on overall health and social or occupational functioning. There are currently limited treatment options available for AUD, and the effects size and the response rates to these treatments are often low to moderate. The World Health Organization has identified the development of medications to treat AUD as one of its 24 priorities. This past decade was marked by a renewed interest in psychedelic use in psychiatry. At the centre of this renaissance, ketamine, an atypical psychedelic already used in the treatment of major depression, is an NMDA receptor antagonist that exists as a racemic compound made of two enantiomers, S-ketamine, and R-ketamine. Each form can be metabolized into different metabolites, some of which having antidepressant properties. In this article, we review both clinical and preclinical studies on ketamine and its metabolites in the treatment of AUD. Preclinical as well as clinical studies have revealed that ketamine is effective in reducing withdrawal symptoms and alcohol craving. Convergent data showed that antidepressant properties of ketamine largely contribute to the decreased likelihood of alcohol relapse, especially in patients undergoing ketamine-assisted psychotherapies. Its effectiveness is believed to be linked with its ability to regulate the glutamatergic pathway, enhance neuroplasticity, rewire brain resting state network functional connectivity and decrease depressive-like states. However, it remains to further investigate (i) why strong differences exist between male and female responses in preclinical studies and (ii) the respective roles of each of the metabolites in the ketamine effects in both genders. Interestingly, current studies are also focusing on ketamine addiction and the comorbidity between alcohol addiction and depression occurring more frequently in females.

Psilocybin as a lead candidate molecule in preclinical therapeutic studies of psychiatric disorders: A systematic review

Psilocybin is the main psychoactive compound found in hallucinogenic/magic mushrooms and can bind to both serotonergic and tropomyosin receptor kinase b (TrkB) receptors. Psilocybin has begun to show efficacy for a range of neuropsychiatric conditions, including treatment-resistant depression and anxiety disorders; however, neurobiological mechanisms are still being elucidated. Clinical research has found that psilocybin can alter functional connectivity patterns in human brains, which is often associated with therapeutic outcomes. However, preclinical research affords the opportunity to assess the potential cellular mechanisms by which psilocybin may exert its therapeutic effects. Preclinical rodent models can also facilitate a more tightly controlled experimental context and minimise placebo effects. Furthermore, where there is a rationale, preclinical researchers can investigate psilocybin administration in neuropsychiatric conditions that have not yet been researched clinically. As a result, we have systematically reviewed the knowledge base, identifying 82 preclinical studies which were screened based on specific criteria. This resulted in the exclusion of 44 articles, with 34 articles being included in the main review and another 2 articles included as Supporting Information materials. We found that psilocybin shows promise as a lead candidate molecule for treating a variety of neuropsychiatric conditions, albeit showing the most efficacy for depression. We discuss the experimental findings, and identify possible mechanisms whereby psilocybin could invoke therapeutic changes. Furthermore, we critically evaluate the between-study heterogeneity and possible future research avenues. Our review suggests that preclinical rodent models can provide valid and translatable tools for researching novel psilocybin-induced molecular and cellular mechanisms, and therapeutic outcomes.