A Fluorescent Probe to Unravel Functional Features of Cannabinoid Receptor CB1 in Human Blood and Tonsil Immune System Cells

Highly Selective Drug-Derived Fluorescent Probes for the Cannabinoid Receptor Type 1 (CB1R)

The cannabinoid receptor type 1 (CB1R) is pivotal within the endocannabinoid system regulating various signaling cascades with effects in appetite regulation, pain perception, memory formation, and thermoregulation. Still, understanding of CB1R's cellular signaling, distribution, and expression dynamics is very fragmentary. Real-time visualization of CB1R is crucial for addressing these questions. Selective drug-like CB1R ligands with a defined pharmacological profile were investigated for the construction of CB1R fluorescent probes using a reverse design-approach. A modular design concept with a diethyl glycine-based building block as the centerpiece allowed for the straightforward synthesis of novel probe candidates. Validated by computational docking studies, radioligand binding, and cAMP assay, this systematic approach allowed for the identification of novel pyrrole-based CB1R fluorescent probes. Application in fluorescence-based target-engagement studies and live cell imaging exemplify the great versatility of the tailored CB1R probes for investigating CB1R localization, trafficking, pharmacology, and its pathological implications.

A new fluorescent probe for the visualization of progerin

Hutchinson-Gilford progeria syndrome (HGPS) or progeria is a rare genetic disease that causes premature aging, leading to a drastic reduction in the life expectancy of patients. Progeria is mainly caused by the intracellular accumulation of a defective protein called progerin, generated from a mutation in the LMNA gene. Currently, there is only one approved drug for the treatment of progeria, which has limited efficacy. It is believed that progerin levels are the most important biomarker related to the severity of the disease. However, there is a lack of effective tools to directly visualize progerin in the native cellular models, since the commercially available antibodies are not well suited for the direct visualization of progerin in cells from the mouse model of the disease. In this context, an alternative option for the visualization of a protein relies on the use of fluorescent chemical probes, molecules with affinity and specificity towards a protein. In this work we report the synthesis and characterization of a new fluorescent probe (UCM-23079) that allows for the direct visualization of progerin in cells from the most widely used progeroid mouse model. Thus, UCM-23079 is a new tool compound that could help prioritize potential preclinical therapies towards the final goal of finding a definitive cure for progeria.

A Robust and Efficient FRET-Based Assay for Cannabinoid Receptor Ligands Discovery

The identification of new modulators for Cannabinoid Receptors (CBRs) has garnered significant attention in drug discovery over recent years, owing to their manifold pathophysiological implications. In the context of hit identification, the availability of robust and sensitive high-throughput screening assays is essential to enhance the likelihood of success. In this study, we present the development and validation of a Tag-lite® binding assay designed for screening hCB1/hCB2 binding, employing a dual fluorescent ligand, CELT-335. Representative ligands for CBRs, exhibiting diverse affinity and functional profiles, were utilized as reference compounds to validate the robustness and efficiency of the newly developed Tag-lite® binding assay protocol. The homogeneous format, coupled with the sensitivity and optimal performance of the fluorescent ligand CELT-335, establishes this assay as a viable and reliable method for screening in hit and lead identification campaigns.

Cannabinoid WIN55,212-2 reprograms monocytes and macrophages to inhibit LPS-induced inflammation

Introduction

Chronic or uncontrolled activation of myeloid cells including monocytes, macrophages and dendritic cells (DCs) is a hallmark of immune-mediated inflammatory disorders. There is an urgent need for the development of novel drugs with the capacity to impair innate immune cell overactivation under inflammatory conditions. Compelling evidence pointed out cannabinoids as potential therapeutic tools with anti-inflammatory and immunomodulatory capacity. WIN55,212-2, a non-selective synthetic cannabinoid agonist, displays protective effects in several inflammatory conditions by mechanisms partially depending on the generation of tolerogenic DCs able to induce functional regulatory T cells (Tregs). However, its immunomodulatory capacity on other myeloid cells such as monocytes and macrophages remains incompletely understood.

Methods

Human monocyte-derived DCs (hmoDCs) were differentiated in the absence (conventional hmoDCs) or presence of WIN55,212-2 (WIN-hmoDCs). Cells were stimulated with LPS, cocultured with naive T lymphocytes and their cytokine production and ability to induce T cell responses were analysed by ELISA or flow cytometry. To evaluate the effect of WIN55,212-2 in macrophage polarization, human and murine macrophages were activated with LPS or LPS/IFNγ, in the presence or absence of the cannabinoid. Cytokine, costimulatory molecules and inflammasome markers were assayed. Metabolic and chromatin immunoprecipitation assays were also performed. Finally, the protective capacity of WIN55,212-2 was studied in vivo in BALB/c mice after intraperitoneal injection with LPS.

Results

We show for the first time that the differentiation of hmoDCs in the presence of WIN55,212-2 generates tolerogenic WIN-hmoDCs that are less responsive to LPS stimulation and able to prime Tregs. WIN55,212-2 also impairs the pro-inflammatory polarization of human macrophages by inhibiting cytokine production, inflammasome activation and rescuing macrophages from pyroptotic cell death. Mechanistically, WIN55,212-2 induced a metabolic and epigenetic shift in macrophages by decreasing LPS-induced mTORC1 signaling, commitment to glycolysis and active histone marks in pro-inflammatory cytokine promoters. We confirmed these data in ex vivo LPS-stimulated peritoneal macrophages (PMΦs), which were also supported by the in vivo anti-inflammatory capacity of WIN55,212-2 in a LPS-induced sepsis mouse model.

Conclusion

Overall, we shed light into the molecular mechanisms by which cannabinoids exert anti-inflammatory properties in myeloid cells, which might well contribute to the future rational design of novel therapeutic strategies for inflammatory disorders.

The cannabinoid WIN55212-2 impairs peanut allergic sensitization and promotes the generation of allergen-specific regulatory T cells

BACKGROUND

Cannabinoids are lipid-derived mediators with anti-inflammatory properties in different diseases. WIN55212-2, a non-selective synthetic cannabinoid, reduces immediate anaphylactic reactions in a mouse model of peanut allergy, but its capacity to prevent peanut allergic sensitization and the underlying mechanisms remains largely unknown.

OBJECTIVE

To investigate the capacity of WIN55212-2 to immunomodulate peanut-stimulated human dendritic cells (DCs) and peanut allergic sensitization in mice.

METHODS

Surface markers and cytokines were quantified by flow cytometry, ELISA and qPCR in human monocyte-derived DCs (hmoDCs) and T cell cocultures after stimulation with peanut alone or in the presence of WIN55212-2. Mice were epicutaneously sensitized with peanut alone or peanut/WIN55212-2. After peanut challenge, drop in body temperature, hematocrit, clinical symptoms, peanut-specific antibodies in serum and FOXP3⁺ regulatory (Treg) cells in spleen and lymph nodes were quantified. Splenocytes were stimulated in vitro with peanut to analyse allergen-specific T cell responses.

RESULTS

WIN55212-2 reduced peanut-induced hmoDC activation and promoted the generation of CD4⁺ CD127^- CD25⁺ FOXP3⁺ Treg cells, while reducing the induction of IL-5-producing T cells. In vivo, WIN55212-2 impaired the peanut-induced migration of DCs to lymph nodes and their maturation. WIN55212-2 significantly reduced the induction of peanut-specific IgE and IgG₁ antibodies in serum during epicutaneous peanut sensitization, reduced the clinical symptoms score upon peanut challenge and promoted the generation of allergen-specific FOXP3⁺ Treg cells.

CONCLUSIONS

The synthetic cannabinoid WIN55212-2 interferes with peanut sensitization and promotes tolerogenic responses, which might well pave the way for the development of novel prophylactic and therapeutic strategies for peanut allergy.

Cannabinoids induce functional Tregs by promoting tolerogenic DCs via autophagy and metabolic reprograming

The generation of functional regulatory T cells (Tregs) is essential to keep tissue homeostasis and restore healthy immune responses in many biological and inflammatory contexts. Cannabinoids have been pointed out as potential therapeutic tools for several diseases. Dendritic cells (DCs) express the endocannabinoid system, including the cannabinoid receptors CB1 and CB2. However, how cannabinoids might regulate functional properties of DCs is not completely understood. We uncover that the triggering of cannabinoid receptors promote human tolerogenic DCs that are able to prime functional FOXP3⁺ Tregs in the context of different inflammatory diseases. Mechanistically, cannabinoids imprint tolerogenicity in human DCs by inhibiting NF-κB, MAPK and mTOR signalling pathways while inducing AMPK and functional autophagy flux via CB1- and PPARα-mediated activation, which drives metabolic rewiring towards increased mitochondrial activity and oxidative phosphorylation. Cannabinoids exhibit in vivo protective and anti-inflammatory effects in LPS-induced sepsis and also promote the generation of FOXP3⁺ Tregs. In addition, immediate anaphylactic reactions are decreased in peanut allergic mice and the generation of allergen-specific FOXP3⁺ Tregs are promoted, demonstrating that these immunomodulatory effects take place in both type 1- and type 2-mediated inflammatory diseases. Our findings might open new avenues for novel cannabinoid-based interventions in different inflammatory and immune-mediated diseases.

Lighting Up the Plasma Membrane: Development and Applications of Fluorescent Ligands for Transmembrane Proteins

Despite the fact that transmembrane proteins represent the main therapeutic targets for decades, complete and in-depth knowledge about their biochemical and pharmacological profiling is not fully available. In this regard, target-tailored small-molecule fluorescent ligands are a viable approach to fill in the missing pieces of the puzzle. Such tools, coupled with the ability of high-precision optical techniques to image with an unprecedented resolution at a single-molecule level, helped unraveling many of the conundrums related to plasma proteins' life-cycle and druggability. Herein, we review the recent progress made during the last two decades in fluorescent ligand design and potential applications in fluorescence microscopy of voltage-gated ion channels, ligand-gated ion channels and G-coupled protein receptors.

Therapeutic Attributes of Endocannabinoid System against Neuro-Inflammatory Autoimmune Disorders

In humans, various sites like cannabinoid receptors (CBR) having a binding affinity with cannabinoids are distributed on the surface of different cell types, where endocannabinoids (ECs) and derivatives of fatty acid can bind. The binding of these substance(s) triggers the activation of specific receptors required for various physiological functions, including pain sensation, memory, and appetite. The ECs and CBR perform multiple functions via the cannabinoid receptor 1 (CB1); cannabinoid receptor 2 (CB2), having a key effect in restraining neurotransmitters and the arrangement of cytokines. The role of cannabinoids in the immune system is illustrated because of their immunosuppressive characteristics. These characteristics include inhibition of leucocyte proliferation, T cells apoptosis, and induction of macrophages along with reduced pro-inflammatory cytokines secretion. The review seeks to discuss the functional relationship between the endocannabinoid system (ECS) and anti-tumor characteristics of cannabinoids in various cancers. The therapeutic potential of cannabinoids for cancer-both in vivo and in vitro clinical trials-has also been highlighted and reported to be effective in mice models in arthritis for the inflammation reduction, neuropathic pain, positive effect in multiple sclerosis and type-1 diabetes mellitus, and found beneficial for treating in various cancers. In human models, such studies are limited; thereby, further research is indispensable in this field to get a conclusive outcome. Therefore, in autoimmune disorders, therapeutic cannabinoids can serve as promising immunosuppressive and anti-fibrotic agents.

Design and Application of Receptor-Targeted Fluorescent Probes Based on Small Molecular Fluorescent Dyes

In recent years, a variety of receptor-targeted fluorescent probes have been developed and widely used to realize the visualization of certain receptors, which facilitates the early diagnosis and treatment of diseases. In this Review, we focus on the recent achievements in design, chemical structure, imaging characterization, and potential applications of receptor-targeted fluorescent probes from the past 10 years. The development and application of receptor-targeted fluorescent probes will expand our knowledge of the distribution and function of disease-related receptors, shed light on the drug discovery for clinical diseases where receptors are implicated, and feed into the diagnosis and treatment of a plethora of diseases, including tumors.

Imaging Cannabinoid Receptors: A Brief Collection of Covalent and Fluorescent Probes for CB1 and CB2 Receptors

There has been an expanding public interest towards the notion that modulation of the sophisticated endocannabinoid system can lead to various therapeutic benefits that are yet to be fully explored. In recent years, the drug discovery paradigm in this field has been largely based on the development of selective CB2 receptor agonists, avoiding the unwanted CB1 receptor-mediated psychoactive side effects. Mechanistically, target engagement studies are crucial for confirming the ligand–receptor interaction and the subsequent biological cascades that lead to the observed therapeutic effects. Concurrently, imaging techniques for visualisation of cannabinoid receptors are increasingly reported in the literature. Small molecule imaging tools ranging from phytocannabinoids such as tetrahydrocannabinol (THC) and cannabidiol (CBD) to the endocannabinoids as well as the purely synthetic cannabimimetics, have been explored to date with varying degrees of success. This Review will cover currently known photoactivatable, electrophilic, and fluorescent ligands for both the CB1 and CB2 receptors. Structural insights from techniques such as ligand-assisted protein structure (LAPS) and the discovery of novel allosteric modulators are significant additions for better understanding of the endocannabinoid system. There has also been a plethora of fluorescent conjugates that have been assessed for their binding to cannabinoid receptors as well as their potential for cellular imaging. More recently, bifunctional probes containing either fluorophores or electrophilic tags are becoming more prevalent in the literature. Collectively, these molecular tools are invaluable in demonstrating target engagement within the human endocannabinoid system.

New small molecule fluorescent probes for G protein-coupled receptors: valuable tools for drug discovery

G protein-coupled receptors (GPCRs) are essential signaling proteins and tractable therapeutic targets. To develop new drug candidates, GPCR drug discovery programs require versatile, sensitive pharmacological tools for ligand binding and compound screening. With the availability of new imaging modalities and proximity-based ligand binding technologies, fluorescent ligands offer many advantages and are increasingly being used, yet labeling small molecules remains considerably more challenging relative to peptides. Focusing on recent fluorescent small molecule studies for family A GPCRs, this review addresses some of the key challenges, synthesis approaches and structure-activity relationship considerations, and discusses advantages of using high-resolution GPCR structures to inform conjugation strategies. While no single approach guarantees successful labeling without loss of affinity or selectivity, the choice of fluorophore, linker type and site of attachment have proved to be critical factors that can significantly affect their utility in drug discovery programs, and as discussed, can sometimes lead to very unexpected results.

Can Natural Polyphenols Help in Reducing Cytokine Storm in COVID-19 Patients?

SARS-CoV-2 first emerged in China during late 2019 and rapidly spread all over the world. Alterations in the inflammatory cytokines pathway represent a strong signature during SARS-COV-2 infection and correlate with poor prognosis and severity of the illness. The hyper-activation of the immune system results in an acute severe systemic inflammatory response named cytokine release syndrome (CRS). No effective prophylactic or post-exposure treatments are available, although some anti-inflammatory compounds are currently in clinical trials. Studies of plant extracts and natural compounds show that polyphenols can play a beneficial role in the prevention and the progress of chronic diseases related to inflammation. The aim of this manuscript is to review the published background on the possible effectiveness of polyphenols to fight SARS-COV-2 infection, contributing to the reduction of inflammation. Here, some of the anti-inflammatory therapies are discussed and although great progress has been made though this year, there is no proven cytokine blocking agents for COVID currently used in clinical practice. In this regard, bioactive phytochemicals such as polyphenols may become promising tools to be used as adjuvants in the treatment of SARS-CoV-2 infection. Such nutrients, with anti-inflammatory and antioxidant properties, associated to classical anti-inflammatory drugs, could help in reducing the inflammation in patients with COVID-19.

Chromenopyrazole-based High Affinity, Selective Fluorescent Ligands for Cannabinoid Type 2 Receptor

Cannabinoid type 2 receptor (CB₂R) is an attractive target for the treatment of pain and inflammatory disorders. Availability of a selective CB₂R fluorescent ligand to study CB₂R expression and localization in healthy and disease conditions would greatly contribute to improving our understanding of this receptor. Herein, we report a series of chromenopyrazole-based CB₂R fluorescent ligands. The highest affinity fluorescent ligand was Cy5-containing 24 (hCB₂R pK _i = 7.38 ± 0.05), which had 131-fold selectivity over CB₁R. In a cAMP BRET assay, 24 behaved as a potent CB₂R inverse agonist. Widefield imaging experiments showed that 24 binds to CB₂R in live cells with good selectivity and low levels of nonspecific fluorescence. The high affinity, selectivity, and suitable imaging properties of fluorescent ligand 24 make it a valuable tool for studying CB₂R.

Monoacylglycerol lipase (MAGL) as a promising therapeutic target

Monoacylglycerol lipase (MAGL) has been characterized as the main enzyme responsible for the inactivation of the most abundant brain endocannabinoid, 2-arachidonoylglycerol (2-AG). Besides this role, MAGL has progressively acquired a growing importance as an integrative metabolic hub that controls not only the in vivo levels of 2-AG but also of other monoacylglycerides and, indirectly, the levels of free fatty acids derived from their hydrolysis as well as other lipids with pro-inflammatory or pro-tumorigenic effects, coming from the further metabolism of fatty acids. All these functions have only started to be elucidated in the last years due to the progress made in the knowledge of the structure of MAGL and in the development of genetic and chemical tools. In this review we report the advances made in the field with a special focus on the last decade and how MAGL has become a promising therapeutic target for the treatment of several diseases that currently lack appropriate therapies.

Novel vaccines targeting dendritic cells by coupling allergoids to mannan

Allergen-specific immunotherapy (AIT) is the single disease-modifying treatment for allergy. Clinical trials show AIT to be safe and effective for many patients; however, it still faces problems related to efficacy, safety, long treatment duration and low patient adherence. There has been intensive research to develop alternative strategies, including novel administration routes, adjuvants or hypoallergenic molecules. Promising results are reported for some of them, but clinical progress is still moderate. Allergoids conjugated to nonoxidized mannan from Saccharomyces cerevisiae have emerged as a novel concept of vaccine targeting dendritic cells (DCs). Preclinical human and animal models demonstrated that allergoids conjugated to mannan enhance allergen uptake, promote healthy responses to allergens by inducing Th1 and T regulatory (Treg) cells, and show clinical efficacy in veterinary medicine. Dose-finding phase II clinical trials in humans are currently ongoing. We review the current stage of allergoids conjugated to mannan as next generation vaccines for AIT.

Development of a Fluorescent Bodipy Probe for Visualization of the Serotonin 5-HT1A Receptor in Native Cells of the Immune System

Serotonin (5-HT) modulates key aspects of the immune system. However, its precise function and the receptors involved in the observed effects have remained elusive. Among the different serotonin receptors, 5-HT_1A plays an important role in the immune system given its presence in cells involved in both the innate and adaptive immune responses, but its actual levels of expression under different conditions have not been comprehensively studied due to the lack of suitable tools. To further clarify the role of 5-HT_1A receptor in the immune system, we have developed a fluorescent small molecule probe that enables the direct study of the receptor levels in native cells. This probe allows direct profiling of the receptor expression in immune cells using flow cytometry. Our results show that important subsets of immune cells including human monocytes and dendritic cells express functional 5-HT_1A and that its activation is associated with anti-inflammatory signaling. Furthermore, application of the probe to the experimental autoimmune encephalomyelitis model of multiple sclerosis demonstrates its potential to detect the specific overexpression of the 5-HT_1A receptor in CD4+ T cells. Accordingly, the probe reported herein represents a useful tool whose use can be extended to study the levels of 5-HT_1A receptor in ex vivo samples of different immune system conditions.