Four New Cytotoxic Arborinane-Type Triterpenes from the Endolichenic Fungus Myrothecium inundatum

Endolichenic Fungi: A Promising Medicinal Microbial Resource to Discover Bioactive Natural Molecules-An Update

Lichens are some of the most unique fungi and are naturally encountered as symbiotic biological organisms that usually consist of fungal partners (mycobionts) and photosynthetic organisms (green algae and cyanobacteria). Due to their distinctive growth environments, including hot deserts, rocky coasts, Arctic tundra, toxic slag piles, etc., they produce a variety of biologically meaningful and structurally novel secondary metabolites to resist external environmental stresses. The endofungi that live in and coevolve with lichens can also generate abundant secondary metabolites with novel structures, diverse skeletons, and intriguing bioactivities due to their mutualistic symbiosis with hosts, and they have been considered as strategically significant medicinal microresources for the discovery of pharmaceutical lead compounds in the medicinal industry. They are also of great importance in the fundamental research field of natural product chemistry. In this work, we conducted a comprehensive review and systematic evaluation of the secondary metabolites of endolichenic fungi regarding their origin, distribution, structural characteristics, and biological activity, as well as recent advances in their medicinal applications, by summarizing research achievements since 2015. Moreover, the current research status and future research trends regarding their chemical components are discussed and predicted. A systematic review covering the fundamental chemical research advances and pharmaceutical potential of the secondary metabolites from endolichenic fungi is urgently required to facilitate our better understanding, and this review could also serve as a critical reference to provide valuable insights for the future research and promotion of natural products from endolichenic fungi.

Rubiarbonol B induces RIPK1-dependent necroptosis via NOX1-derived ROS production

The activation of receptor-interacting protein kinase 1 (RIPK1) by death-inducing signaling complex (DISC) formation is essential for triggering the necroptotic mode of cell death under apoptosis-deficient conditions. Thus, targeting the induction of necroptosis by modulating RIPK1 activity could be an effective strategy to bypass apoptosis resistance in certain types of cancer. In this study, we screened a series of arborinane triterpenoids purified from Rubia philippinesis and identified rubiarbonol B (Ru-B) as a potent caspase-8 activator that induces DISC-mediated apoptosis in multiple types of cancer cells. However, in RIPK3-expressing human colorectal cancer (CRC) cells, the pharmacological or genetic inhibition of caspase-8 shifted the mode of cell death by Ru-B from apoptosis to necroptosis though upregulation of RIPK1 phosphorylation. Conversely, Ru-B-induced cell death was almost completely abrogated by RIPK1 deficiency. The enhanced RIPK1 phosphorylation and necroptosis triggered by Ru-B treatment occurred independently of tumor necrosis factor receptor signaling and was mediated by the production of reactive oxygen species via NADPH oxidase 1 in CRC cells. Thus, we propose Ru-B as a novel anticancer agent that activates RIPK1-dependent cell death via ROS production, and suggest its potential as a novel necroptosis-targeting compound in apoptosis-resistant CRC.

Metabolomics-Guided Discovery, Isolation, Structure Elucidation, and Bioactivity of Myropeptins C-E from Myrothecium inundatum

The saprotrophic filamentous fungus Myrothecium inundatum represents a chemically underexplored ascomycete with a high number of putative biosynthetic gene clusters in its genome. Here, we present new linear lipopeptides from nongenetic gene activation experiments using nutrient and salt variations. Metabolomics studies revealed four myropeptins, and structural analyses by NMR, HRMS, Marfey's analysis, and ECD assessment for their helical properties established their absolute configuration. A myropeptin biosynthetic gene cluster in the genome was identified. The myropeptins exhibit general nonspecific toxicity against all cancer cell lines in the NCI-60 panel, larval zebrafish with EC50 concentrations of 5-30 μM, and pathogenic bacteria and fungi (MICs of 4-32 μg/mL against multidrug-resistant S. aureus and C. auris). In vitro hemolysis, cell viability, and ionophore assays indicate that the myropeptins target mitochondrial and cellular membranes, inducing cell depolarization and cell death. The toxic activity is modulated by the length of the lipid side chain, which provides valuable insight into their structure-activity relationships.

Bioactive Usual and Unusual Triterpenoids Derived from Natural Sources Used in Traditional Medicine

Triterpenoids are accessible in several terrestrial plants as well as marine organisms, including sponges, algae, fungi, and sea cucumbers are examples of marine creatures. So far, more than 20,000 natural triterpenoids have exhibited several varied bioactivities, including anticancer, antimalarial, anti-HIV, inhibit HIF-1 activation, antibacterial, chemopreventive, anti-inflammatory, antioxidant, cardioprotective, antiviral, neuroprotective, hepatoprotective, insecticidal, antidiabetic, cytotoxic. Several plants are used in folklore medicine to treat numerous ailments, and the preparation or uses of traditional practices have been scientifically validated. Although various structural diversity has been observed in the triterpenoids, this review presents the sources and uses of those triterpenoids that showed significant biological activities which could be accessible and promoted to familiar people in the form of traditional medicine or for industrial, or pharmaceutical applications.

Identification and Pathogenicity of Paramyrothecium Species Associated with Leaf Spot Disease in Northern Thailand

Species of Paramyrothecium that are reported as plant pathogens and cause leaf spot or leaf blight have been reported on many commercial crops worldwide. In 2019, during a survey of fungi causing leaf spots on plants in Chiang Mai and Mae Hong Son provinces, northern Thailand, 16 isolates from 14 host species across nine plant families were collected. A new species Paramyrothecium vignicola sp. nov. was identified based on morphology and concatenated (ITS, cmdA, rpb2, and tub2) phylogeny. Further, P. breviseta and P. foliicola represented novel geographic records to Thailand, while P. eichhorniae represented a novel host record (Psophocarpus sp., Centrosema sp., Aristolochia sp.). These species were confirmed to be the causal agents of the leaf spot disease through pathogenicity assay. Furthermore, cross pathogenicity tests on Coffea arabica L., Commelina benghalensis L., Glycine max (L.) Merr., and Dieffenbachia seguine (Jacq.) Schott revealed multiple host ranges for these pathogens. Further research is required into the host-pathogen relationship of Paramyrothecium species that cause leaf spot and their management. Biotic and abiotic stresses caused by climate change may affect plant health and disease susceptibility. Hence, proper identification and monitoring of fungal communities in the environment are important to understand emerging diseases and for implementation of disease management strategies.

Isolation, Crystal Structure, and In Silico Aromatase Inhibition Activity of Ergosta-5, 22-dien-3β-ol from the Fungus Gyromitra esculenta

Ergosterol derivatives exhibited copious promising biological activities. The fungus Gyromitra esculenta is widely distributed in Europe and North America. In order to examine the chemical properties of Gyromitra esculenta, a phytochemical study has been preceded and resulted in the isolation of the steroid, ergosta-5, 22-dien-3β-ol (brassicasterol), from its methanol extract. The complete identification and absolute configuration of the isolated compound have been established by X-ray structural analysis to be (22E, 24R)-24-methylcholesta-5, 22-dien-3beta-ol. The reported cytotoxicity and the great structural similarity of the isolated compound with the cocrystallized ligand of the aromatase enzyme inspired us to run molecular docking studies against that protein. Ergosta-5, 22-dien-3β-ol occupied the target protein with a binding mode almost the same as the cocrystallized ligand and a binding affinity of −33.55 kcal/mol, which was better than that of the cocrystallized ligand (−22.61 kcal/mol). This promising result encouraged us to conduct in silico ADMET and toxicity studies of ergosta-5, 22-dien-3β-ol against 6 models, and the results expected the likeness of the isolated compound to be a drug. In conclusion, ergosta-5, 22-dien-3β-ol has been isolated from Gyromitra esculenta, identified by X-ray structural analysis, and exhibited promising in silico activities against aromatase enzyme.

In Vitro and In Silico Cytotoxic and Antibacterial Activities of a Diterpene from Cousinia alata Schrenk

A biologically guided isolation of secondary metabolites from Cousinia alata Schrenk wild plant growing in Akmola region, Kazakhstan, led to the isolation of the bioactive diterpene grindelic acid (1). Six flavonoids were also isolated and identified as retusine (2), pachipodol (3), jaranol (4), penduletin (5), casticin (6), and 5, 7, 3′-trihydroxy-3, 4′-dimethoxyflavone (7). Penduletin (5) showed moderate cytotoxic activity assay. Grindelic acid exhibited promising cytotoxic activity against the Artemia salina nauplii and antibacterial activity against Staphylococcus aureus, Bacillus cereus, and Salmonella enteritidis. The presence of the essential pharmacophoric features of histone deacetylase (HDAC) inhibitors in the structure of grindelic acid encouraged us to run a molecular docking study against the HDAC enzyme to understand its mechanism of action on a molecular level. Grindelic acid showed a binding mode of interaction similar to that of the cocrystallized ligand and exhibited good binding affinity against HDAC with the binding free energy of −18.70 kcal/mol. The structures of isolated compounds were determined by MS, 1D, and 2D NMR spectroscopy methods. Compounds (1–7) were isolated for the first time from Cousinia genus.

Antioxidant and anti-tumour activity of triterpenoid compounds isolated from Morchella mycelium

Triterpenoid compounds are important bioactivity materials. Morchella is an abundant medicinal fungi found worldwide. In this study, we optimised the isolation and purification of triterpenoid compounds from Morchella mycelium fermentation. The results showed that the triterpenoid compounds yield was 35.22 mg/g, and we also identified two triterpenoid compounds using high-performance liquid chromatography. In addition, we evaluated the anti-tumour and antioxidant activity of the products, and the results showed that triterpenoid compounds from Morchella mycelium fermentation showed good bioactivity. The IC₅₀ values of four cancer cell lines treated with the triterpenoid compounds for 48 h were 7.20, 14.96, 4.41, and 13.43 mg/mL, respectively. Morphological changes associated with the apoptosis of PC-3 cells were observed using confocal scanning laser microscopy after treatment with triterpenoid compounds for 48 and 72 h. The triterpenoid compounds also exhibited DPPH radical, hydroxyl, and ABTS-free radical scavenging activities in vitro. These results suggest that triterpenoid compounds from Morchella mycelium fermentation, which are found in functional foods and used in the field of pharmacology, might be excellent products for the treatment of cancer and age-related illnesses.

Siderophores from the Entomopathogenic Fungus Beauveria bassiana

We report NMR- and MS-based structural characterizations of siderophores and related compounds from Beauveria bassiana (Balsamo-Crivelli) Vuillemin, including ten new chemical entities (2-4, 6-9, 11-12, and 15) and five known compounds, (1, 5, 10, 13, and 14). The siderophore mixture from ARSEF strain #2680 included two compounds in which N⁵-mevalonyl-N⁵-hydroxyornithine replaces both (2) or one (3) of the N⁵-anhydromevalonyl-N⁵-hydroxyornithine units of dimerumic acid (1). Mevalonolactone (14) was present as a degradation product of 2 and 3. ARSEF #2860 also produced compounds that have mannopyranose (5, 6) or 4-O-methyl-mannopyranose units (4, 7), two compounds (8, 9) that can be rationalized as 4-O-methyl-mannopyranosyl analogues of the esterifying acid moieties of metachelins A and B, respectively, and two probable decomposition products of 1, a nitro compound (11) and a formate (12). Beauverichelin A (15), a coprogen-type siderophore that represents the di-4-O-methyl-mannopyranosyl analogue of metachelin A, was detected in crude extracts of ARSEF #2860, but only in trace amounts. ARSEF strains #252 and #1955 yielded beauverichelin A in quantities that were sufficient for NMR analysis. Only the di- (1-7) and trihydroxamate (15) siderophores showed iron-binding activity in the CAS assay and, when ferrated, showed strong ESIMS signals consistent with 1:1 ligand/iron complexes.