Phenolic compounds from cultivated Glycyrrhiza uralensis and their PD-1/PD-L1 inhibitory activities

Total synthesis of isoflavonoids

Covering: 2012 to 2024Isoflavonoids are phenolic compounds with wide structural diversity and a plethora of biological activities. Owing to their structural variation and potential health-promoting and other benefits, they have been targeted for synthesis. Herein, we review the synthesis of natural isoflavonoids belonging to different classes that include isoflavones, isoflavanones, isoflavans, isoflavenes, pterocarpans, rotenoids, coumaronochromones, and coumestans. The synthetic methodologies employed and advancements in synthetic strategies are highlighted.

Exploring the Therapeutic Potential of Flavonoids in the Management of Cancer

Flavonoids are a class of polyphenolic compounds that can be classified into six distinct categories, namely isoflavonoids, flavanones, flavanols, flavonols, flavones, and anthocyanidins. These compounds are naturally occurring and can be found in a diverse range of plant species. Flavonoids, a class of bioactive compounds, are mostly obtained through the consumption of vegetables, fruits and plant-derived beverages such as wine, cocoa-based products and green tea. Flavonoids have been demonstrated to exhibit a diverse range of anticancer properties. These include the modulation of activities of enzymes involved in scavenging reactive oxygen species, involvement in cell cycle arrest, induction of apoptosis and autophagy, as well as suppression of cancer cell proliferation and invasiveness. Flavonoids exhibit a dual role in maintaining reactive oxygen species balance. They function as antioxidants in regular physiological conditions, while also demonstrating significant pro-oxidant properties in cancer cells. This prooxidant activity induces apoptotic pathways and downregulates pro-inflammatory signalling pathways. The paper explores the biochemical characteristics, bioavailability, anticancer efficacy, and modes of action of flavonoids.

Effects of licorice root (Glycyrrhiza glabra) extract on the livers of obese rats

We have investigated anti-obesity effects of the extract of licorice (Glycyrrhiza glabra) root in rats with diet-induced obesity and hyperlipidemia by using histopathological and biochemical methods. Thirty-two Wistar albino rats were divided to four groups of eight: normal control (C), high fat diet (HFD), high fat Diet + Glycyrrhiza glabra (HFD+M), and normal diet with Glycyrrhiza glabra (M). The high fat diet contained 300 g/kg fat (4000 kcal/kg); the daily dosage of Glycyrrhiza glabra extract was 1g/kg body weight by orogastric gavage. Supplementation of Glycyrrhiza glabra extract dramatically reduced increases in body weight caused by the induction of obesity. A hepatoprotective effect of Glycyrrhiza glabra extract was supported by the almost normal histology in the livers of the HFD+M rats, in contrast to the degenerative changes in the HFD rats, which included macrovesicular and microvesicular fat deposits, hydropic degeneration, dilatation of sinusoids and coagulation necrosis of some hepatocytes. Serum levels of alanine transaminase (ALT), aspartic transaminase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), cholesterol (HDL and LDL) and triglycerides, were ameliorated by Glycyrrhiza glabra extract treatment. We conclude that Glycyrrhiza glabra extract given together with HFD could prevent obesity and reduce liver damage in rats.

Enrichment and qualitative analysis of flavonoid glycosides from the aerial parts of Glycyrrhiza uralensis Fisch

Our previous study found that the aerial parts of Chinese liquorice (Glycyrrhiza uralensis Fisch.) had pharmacological effects against chronic non-bacterial prostatitis in rats, however the pharmacologically active compounds remain unclear. Here, a method based on UPLC-Q-Exactive Orbitrap-MS was established to qualitatively analyse the flavonoid glycosides rich fraction extracted from the aerial part of G. uralensis Fisch., after pretreatment with n-butanol and enrichment using AB-8 macroporous resin. Using both positive and negative ion modes, 52 compounds were identified or tentatively characterised by comparison with standards and the literature: 40 flavonoids, 8 organic acids, 2 chromones, 1 coumarin, and 1 phenylethanoid glycoside. This study provides not only an approach to enrich flavonoid glycosides but also a methodology for quickly determining the relevant bioactive components in the aerial parts of G. uralensis Fisch.

A Comprehensive Review of Licorice: The Preparation, Chemical Composition, Bioactivities and Its Applications

Licorice (Glycyrrhiza) is a medicinal and food homologue of perennial plants derived from the dried roots and rhizomes of the genus Glycyrrhiza in the legume family. In recent years, the comprehensive utilization of licorice resources has attracted people's attention. It is widely utilized to treat diseases, health food products, food production, and other industrial applications. Furthermore, numerous bioactive components of licorice are found using advanced extraction processes, which mainly include polyphenols (flavonoids, dihydrostilbenes, benzofurans, and coumarin), triterpenoids, polysaccharides, alkaloids, and volatile oils, all of which have been reported to possess a variety of pharmacological characteristics, including anti-oxidant, anti-inflammatory, antibacterial, antiviral, anticancer, neuroprotective, antidepressive, antidiabetic, antiparasitic, antisex hormone, skin effects, anticariogenic, antitussive, and expectorant activities. Thereby, all of these compounds promote the development of novel and more effective licorice-derived products. This paper reviews the progress of research on extraction techniques, chemical composition, bioactivities, and applications of licorice to provide a reference for further development and application of licorice in different areas.

Small-molecule modulators of tumor immune microenvironment

In recent years, tumor immunotherapy, aimed at increasing the activity of immune cells and reducing immunosuppressive effects, has attracted wide attention. Among them, immune checkpoint blocking (ICB) is the most commonly explored therapeutic approach. All approved immune checkpoint inhibitors (ICIs) are clinically effective monoclonal antibodies (mAbs). Compared with biological agents, small-molecule drugs have many unique advantages in tumor immunotherapy. Therefore, they also play an important role. Immunosuppressive signals such as PD-L1, IDO1, and TGF-β, etc. overexpressed in tumor cells form the tumor immunosuppressive microenvironment. In addition, the efficacy of multi-pathway combined immunotherapy has also been reported and verified. Here, we mainly reviewed the mechanism of tumor immunotherapy, analyzed the research status of small-molecule modulators, and discussed drug candidates' structure-activity relationship (SAR). It provides more opportunities for further research to design more immune small-molecule modulators with novel structures.

Micropyrones A and B, two new α-pyrones from the actinomycete Microbacterium sp. GJ312 isolated from Glycyrrhiza uralensis Fisch

Two new α-pyrones, micropyrones A (1) and B (2), along with four known γ-pyrones, nocapyrone D (3), nocapyrone A (4), marinactinone A (5), and nocapyrone H (6), were isolated from the culture extract of actinomycete Microbacterium sp. GJ312, which was isolated from Glycyrrhiza uralensis. The structures of these compounds were identified by analysis of spectral data. They are the first α- and γ-pyrones reported from the genus Microbacterium. The antibacterial activity of all compounds against Staphylococcus aureus and methicillin resistant S. aureus was evaluated. However, none of them showed significant activity. This study represents the first phytochemical example of a Glycyrrhiza-derived actinomycete.

Natural Blockers of PD-1/PD-L1 Interaction for the Immunotherapy of Triple-Negative Breast Cancer-Brain Metastasis

The limited treatment options for triple-negative breast cancer with brain metastasis (TNBC-BM) have left the door of further drug development for these patients wide open. Although immunotherapy via monoclonal antibodies has shown some promising results in several cancers including TNBC, it cannot be considered the most effective treatment for brain metastasis. This is due to the protective role of the blood-brain barrier (BBB) which limits the entrance of most drugs, especially the bulky ones such as antibodies, to the brain. For a drug to traverse the BBB via passive diffusion, various physicochemical properties should be considered. Since natural medicine has been a key inspiration for the development of the majority of current medicines, in this paper, we review several naturally-derived molecules which have the potential for immunotherapy via blocking the interaction of programmed cell death protein-1 (PD-1) and its ligand, PD-L1. The mechanism of action, physicochemical properties and pharmacokinetics of these molecules and their theoretical potential to be used for the treatment of TNBC-BM are discussed.

Pharmacological Activities and Pharmacokinetics of Glycycoumarin

Glycycoumarin is a representative coumarin compound with significant pharmacological activities isolated from Glycyrrhiza uralensis Fisch., Fabaceae. Studies have shown that glycycoumarin has many biological activities, such as anti-tumor, liver protection, antispasmodic, antibacterial, and antivirus. However, the poor solubility of glycycoumarin in water and the accompanying reactions of the phase I (hydroxylation) and II (glucuronidation) metabolism limit its druggability, which manifests as low absorption in the body after oral administration and low free drug concentration, ultimately leading to low bioavailability. Therefore, a comprehensive review of the pharmacological effects and pharmacokinetics of glycycoumarin is presented to provide a reference for further research and application as a therapeutic agent.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43450-022-00342-x.

Chemical basis of pregnane X receptor activators in the herbal supplement Gancao (licorice)

Background and aims

The herbal supplement Gancao, also known as licorice, belongs to the genus Glycyrrhiza and has been used worldwide for its hepatoprotective effect. Recent studies have raised concerns about potential herb-drug interactions associated with Gancao via pregnane X receptor (PXR)-mediated induction of hepatic cytochrome P450 3A4 (CYP3A4). The current work aimed to determine the phytochemicals in Gancao that activate PXR and induce CYP3A4.

Methods

DPX2 cells were used for cell-based PXR reporter assays. The phytochemicals in Gancao extract were identified using a metabolomics approach. The effects of PXR activators identified from in vitro studies were further investigated in PXR- and CYP3A4-humanized mouse models.

Results

Gancao was verified to be a PXR-activating herb. Two major phytochemicals in Gancao, glycyrrhizin (GZ) and glycyrrhetinic acid (GA), did not activate PXR in the cell-based reporter assays. However, glabridin was shown to activate PXR in a dose-dependent manner. In vivo studies confirmed that GZ is not a PXR activator and glabridin is a weak PXR activator. Although GA did not active PXR in vitro, it induced CYP3A4 expression in a PXR-dependent manner in the PXR- and CYP3A4-humanized mice.

Conclusions

GZ is not a PXR activator. GA could not activate PXR in cell-based reporter assays but it could activate PXR in vivo. Glabridin is a weak PXR activator. This work provides novel insights into the underlying mechanisms of Gancao-related herb-drug interactions via PXR.

Glycyrrhiza glabra (Licorice): A Comprehensive Review on Its Phytochemistry, Biological Activities, Clinical Evidence and Toxicology

There are more than 30 species of Glycyrrhiza genus extensively spread worldwide. It was the most prescribed herb in Ancient Egyptian, Roman, Greek, East China, and the West from the Former Han era. There are various beneficial effects of licorice root extracts, such as treating throat infections, tuberculosis, respiratory, liver diseases, antibacterial, anti-inflammatory, and immunodeficiency. On the other hand, traditional medicines are getting the attraction to treat many diseases. Therefore, it is vital to screen the medicinal plants to find the potential of new compounds to treat chronic diseases such as respiratory, cardiovascular, anticancer, hepatoprotective, etc. This work comprehensively reviews ethnopharmacological uses, phytochemistry, biological activities, clinical evidence, and the toxicology of licorice, which will serve as a resource for future clinical and fundamental studies. An attempt has been made to establish the pharmacological effect of licorice in different diseases. In addition, the focus of this review article is on the molecular mechanism of licorice extracts and their four flavonoids (isoliquiritigenin, liquiritigenin, lichalocone, and glabridin) pharmacologic activities. Licorice could be a natural alternative for current therapy to exterminate new emerging disorders with mild side effects. This review will provide systematic insights into this ancient drug for further development and clinical use.

Small molecule inhibitors against PD-1/PD-L1 immune checkpoints and current methodologies for their development: a review

Programmed death-1/programmed death ligand-1 (PD-1/PD-L1) based immunotherapy is a revolutionary cancer therapy with great clinical success. The majority of clinically used PD-1/PD-L1 inhibitors are monoclonal antibodies but their applications are limited due to their poor oral bioavailability and immune-related adverse effects (irAEs). In contrast, several small molecule inhibitors against PD-1/PD-L1 immune checkpoints show promising blockage effects on PD-1/PD-L1 interactions without irAEs. However, proper analytical methods and bioassays are required to effectively screen small molecule derived PD-1/PD-L1 inhibitors. Herein, we summarize the biophysical and biochemical assays currently employed for the measurements of binding capacities, molecular interactions, and blocking effects of small molecule inhibitors on PD-1/PD-L1. In addition, the discovery of natural products based PD-1/PD-L1 antagonists utilizing these screening assays are reviewed. Potential pitfalls for obtaining false leading compounds as PD-1/PD-L1 inhibitors by using certain binding bioassays are also discussed in this review.

Naturally occurring coumestans from plants, their biological activities and therapeutic effects on human diseases

Naturally occurring coumestans are known as a collection of plant-derived polycyclic aromatic secondary metabolites which are characterized by the presence of an oxygen heterocyclic four-ring system comprising a coumarin moiety and a benzofuran moiety sharing a C˭C bond. Recently, there is an increasing attention in excavating the medicinal potential of coumestans, particularly coumestrol, wedelolactone, psoralidin and glycyrol, in a variety of diseases. This review is a comprehensive inventory of the chemical structures of coumestans isolated from various plant sources during the period of 1956-2020, together with their reported biological activities. 120 molecules were collected and further classified as coumestans containing core skeleton, dimethylpyranocoumestans, furanocoumestans, O-glycosylated coumestans and others, which showed a wide range of pharmacological activities including estrogenic, anti-cancer, anti-inflammatory, anti-osteoporotic, organ protective, neuroprotective, anti-diabetic and anti-obesity, antimicrobial, immunosuppressive, antioxidant and skin-protective activities. Furthermore, this review focuses on the counteraction of coumestans against bone diseases and organ damages, and the involved molecular mechanisms, which could provide important information to better understand the medicinal values of these compounds. This review is intended to be instructive for the rational design and development of less toxic and more effective drugs with a coumestan scaffold.

Phenoxychromone and 4-hydroxyisoflavans from the roots of Glycyrrhiza uralensis

In an attempt to find species specific markers, a phenoxychromone (1) and eight isoflavonoids including six isoflavans (2-7) and two isoflavanones (8 and 9) were isolated from the root of Glycyrrhiza uralensis. Among the isolated phenolic compounds, glycyurelone (1), glycyurelvanins A and B (2 and 3) were found to be undescribed while others, (-)-vestitol (4), conferol A (5), glyasperin C (6), glyasperin D (7), (-)-licoisoflavanone (8), and (-)-3'-(γ,γ-dimethylallyl)kievitone (9) were previously reported. All compounds except 4 and 5 were prenylated and majority of these possess isoflavan scaffold with highly conserved stereo specificity at C-3 center. Structure elucidation was mainly based on extensive NMR, ECD and mass spectral data analysis.

Identification wild and cultivated licorice by multidimensional analysis

Licorice is known as a botanical source in medicine and a sweetening agent in food products. Commercial licorice is from the source of wild and cultivated G. uralensis. It was recognized that the material basis of wild and cultivated licorice is different. This study systematically investigated the difference between them by multidimensional analysis technology. The results showed that the content of starch grain, total dietary fibre (TDF), and 11 secondary metabolite components was significantly different in wild and cultivated licorice. principal component analysis (PCA) and orthogonal partial least square (OPLS-DA) analyses showed that the wild and cultivated licorice samples could be clearly separated based on the acquired data of microscopic, macromolecular substance and secondary metabolite analysis. The main markers were starch grain, isoliquiritin apioside, liquirtin apioside and TDF. Additionally, NIR spectroscpy combined with PLS-DA has demonstrated a suitable, fast and nondestructive methodology for authentication of wild and cultivated licorice.

Kaempferol and Its Glycoside, Kaempferol 7-O-Rhamnoside, Inhibit PD-1/PD-L1 Interaction In Vitro

Kaempferol (KO) and kaempferol 7-O-rhamnoside (KR) are natural products from various oriental herbs such as Geranii Herba. Previous studies have reported some biological activities of KO and KR; however, their effects on PD-1/PD-L1 interaction have not been reported yet. To elucidate their inhibitory activities on PD-1/PD-L1 protein–protein interaction (PPI), biochemical assays including competitive ELISA and biolayer interferometry (BLI) systems were performed. Cellular PD-1/PD-L1 blocking activity was measured in a co-culture system with PD-1 Jurkat and PD-L1/aAPC CHO-K1 cells by T-cell receptor (TCR) activation-induced nuclear factor of activated T cells (NFAT)-luciferase reporter assay. The detailed binding mode of action was simulated by an in silico docking study and pharmacophore analysis. Competitive ELISA revealed that KO and its glycoside KR significantly inhibited PD-1/PD-L1 interaction. Cellular PD-1/PD-L1 blocking activity was monitored by KO and KR at non-cytotoxic concentration. Surface plasmon resonance (SPR) and biolayer interferometry (BLI) analysis suggested the binding affinity and direct inhibition of KR against PD-1/PD-L1. An in silico docking simulation determined the detailed mode of binding of KR to PD-1/PD-L1. Collectively, these results suggest that KR could be developed as a potent small molecule inhibitor for PD-1/PD-L1 blockade.

Flavonoids as Anticancer Agents

Flavonoids are polyphenolic compounds subdivided into 6 groups: isoflavonoids, flavanones, flavanols, flavonols, flavones and anthocyanidins found in a variety of plants. Fruits, vegetables, plant-derived beverages such as green tea, wine and cocoa-based products are the main dietary sources of flavonoids. Flavonoids have been shown to possess a wide variety of anticancer effects: they modulate reactive oxygen species (ROS)-scavenging enzyme activities, participate in arresting the cell cycle, induce apoptosis, autophagy, and suppress cancer cell proliferation and invasiveness. Flavonoids have dual action regarding ROS homeostasis—they act as antioxidants under normal conditions and are potent pro-oxidants in cancer cells triggering the apoptotic pathways and downregulating pro-inflammatory signaling pathways. This article reviews the biochemical properties and bioavailability of flavonoids, their anticancer activity and its mechanisms of action.

Constituents Isolated from the Leaves of Glycyrrhiza uralansis and Their Anti-Inflammatory Activities on LPS-Induced RAW264.7 Cells

Licorice, the root and rhizome of Glycyrrhiza uralansis Fisch, is one of the most frequently used Traditional Chinese Medicines in rigorous clinical trials to remove toxins and sputum, and to relieve coughing. However, the aerial parts are not used so widely at present. It has been reported that the aerial parts have many bioactivities such as anti-microbial and anti-HIV activities. In this study, we aimed to discover the bioactive compounds from the leaves of G. uralensis. Four new compounds, licostilbene A-B (1-2) and licofuranol A-B (3-4), together with eight known flavonoids (5-12), were isolated and identified from the leaves of G. uralensis. Their structures were elucidated mainly by the interpretation of high-resolution electrospray mass spectrometry (HR-ESI-MS) and nuclear magnetic resonance (NMR) spectroscopic data. Compared with quercetin, which showed a 50% inhibitory concentration (IC₅₀) value of 4.08 μg/mL, compounds 1-9 showed significant anti-inflammatory activities by inhibiting lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC₅₀ values of 2.60, 2.15, 3.21, 3.25, 2.00, 3.45, 2.53, 3.13 and 3.17 μg/mL, respectively. The discovery of these active compounds is important for the prevention and treatment of inflammation.