Boerechalasins A-G, cytochalasans from the fungus Boeremia exigua with anti-inflammatory and cytotoxic activities.

Seven previously undescribed cytochalasans, namely, boerechalasins A-G, together with one analogue, were characterized from the solid culture of the fungus Boeremia exigua. Their structures and absolute configurations were elucidated on the basis of extensive spectroscopic analysis as well as electronic circular dichroism calculations. Remarkably, boerechalasin F possessed an unusual sulfoxide moiety that might be derived from methionine, while boerechalasin G had an unusual 5-methylcyclohexane-1,2,3-triol substituent at N-2 position. Boerechalasins A and E exhibited inhibitory activities against nitric oxide production in LPS-induced RAW264.7 macrophages with IC50 values of 21.9 and 5.7 µM, respectively. Boerechalasin F displayed cytotoxicity against human MCF‒7 cells with an IC50 value of 22.8 µM.

Cytochalasans and Their Impact on Actin Filament Remodeling.

The eukaryotic actin cytoskeleton comprises the protein itself in its monomeric and filamentous forms, G- and F-actin, as well as multiple interaction partners (actin-binding proteins, ABPs). This gives rise to a temporally and spatially controlled, dynamic network, eliciting a plethora of motility-associated processes. To interfere with the complex inter- and intracellular interactions the actin cytoskeleton confers, small molecular inhibitors have been used, foremost of all to study the relevance of actin filaments and their turnover for various cellular processes. The most prominent inhibitors act by, e.g., sequestering monomers or by interfering with the polymerization of new filaments and the elongation of existing filaments. Among these inhibitors used as tool compounds are the cytochalasans, fungal secondary metabolites known for decades and exploited for their F-actin polymerization inhibitory capabilities. In spite of their application as tool compounds for decades, comprehensive data are lacking that explain (i) how the structural deviances of the more than 400 cytochalasans described to date influence their bioactivity mechanistically and (ii) how the intricate network of ABPs reacts (or adapts) to cytochalasan binding. This review thus aims to summarize the information available concerning the structural features of cytochalasans and their influence on the described activities on cell morphology and actin cytoskeleton organization in eukaryotic cells.

Inhibition of cell cycle-dependent hyphal and biofilm formation by a novel cytochalasin 19,20­epoxycytochalasin Q in Candida albicans.

Biofilm-mediated drug resistance is a key virulence factor of pathogenic microbes that cause a serious global health threat especially in immunocompromised individuals. Here, we investigated the antihyphal and antibiofilm activity of 19,20­epoxycytochalasin Q (ECQ), a cytochalasin actin inhibitor isolated from medicinal mushroom Xylaria sp. BCC1067 against Candida albicans. Remarkably, 256 µg/ml of ECQ inhibited over 95% of C. albicans hyphal formation after 24 h-treatment. Combined ECQ and lipid-based biosurfactant effectively enhanced the antihyphal activity, lowering required ECQ concentrations. Hyphal fragmentation and reduction of biofilm biomass, shown by SEM and AFM visualization of ECQ-treated biofilms, were well corelated to the reduced metabolic activities of young and 24 h-preformed C. albicans biofilms. Induced intracellular accumulation of reactive oxygen species (ROS) also occurred in accompany with the leakage of shrunken cell membrane and defective cell wall at increasing ECQ concentrations. Transcriptomic analyses via RNA-sequencing revealed a massive change (> 1300 genes) in various biological pathways, following ECQ-treatment. Coordinated expression of genes, associated with cellular response to drugs, filamentous growth, cell adhesion, biofilm formation, cytoskeleton organization, cell division cycle, lipid and cell wall metabolisms was confirmed via qRT-PCR. Protein-protein association tool identified coupled expression between key regulators of cell division cyclin-dependent kinases (Cdc19/28) and a gamma-tubulin (Tub4). They coordinated ECQ-dependent hyphal specific gene targets of Ume6 and Tec1 during different phases of cell division. Thus, we first highlight the antihyphal and antibiofilm property of the novel antifungal agent ECQ against one of the most important life-threatening fungal pathogens by providing its key mechanistic detail in biofilm-related fungal infection.

Specialized metabolites of the fungal genus Phomopsis: Structures, bioactivities and biosynthesis.

Fungi are important resources of novel bioactive compounds which have a high potential to be drug leads or candidates for further pharmacological applications. Phomopsis, a genus widely distributed in the environment, can produce various types of compounds including polyketides, alkaloids, terpenoids, cytochalasins, steroids and flavonoids. The metabolites of Phomopsis sp. showed diverse bioactivities such as antibacterial, anti-inflammatory, antimalarial, and so on, many of which may influence the physiological behaviour of the host plants. In this review, we focus on the chemical structures and biological activities of 183 specialized metabolites isolated from Phomopsis sp. in the decade (2013-2022). Moreover, the biosynthetic pathways of some typical components are summarized.

Cytochalasans produced by Xylaria karyophthora and their biological activities.

The recent description of the putative fungal pathogen of greenheart trees, Xylaria karyophthora (Xylariaceae, Ascomycota), prompted a study of its secondary metabolism to access its ability to produce cytochalasans in culture. Solid-state fermentation of the ex-type strain on rice medium resulted in the isolation of a series of 19,20-epoxidated cytochalasins by means of preparative high-performance liquid chromatography (HPLC). Nine out of 10 compounds could be assigned to previously described structures, with one compound being new to science after structural assignment via nuclear magnetic resonance (NMR) assisted by high-resolution mass spectrometry (HRMS). We propose the trivial name "karyochalasin" for the unprecedented metabolite. The compounds were used in our ongoing screening campaign to study the structure-activity relationship of this family of compounds. This was done by examining their cytotoxicity against eukaryotic cells and impact on the organization of networks built by their main target, actin-a protein indispensable for processes mediating cellular shape changes and movement. Moreover, the cytochalasins' ability to inhibit the biofilm formation of Candida albicans and Staphylococcus aureus was examined.

Cytochalasans with Inhibitory Activity against NPC1L1 from the Endophytic Fungus Chaetomium nigricolor F5.

Mass spectrometry (MS)-based metabolic profiling of the endophytic fungus Chaetomium nigricolor F5 guided the isolation of five novel cytochalasans, chamisides B-F (1-5), and two known ones, chaetoconvosins C and D (6 and 7). Their structures including stereochemistry were unambiguously determined by MS, nuclear magnetic resonance, and single-crystal X-ray diffraction analyses. Compounds 1-3 share a new 5/6/5/5/7-fused pentacyclic skeleton in cytochalasans and are appropriately proposed to be the key biosynthetic precursors of co-isolated cytochalasans with a 6/6/5/7/5, 6/6/5/5/7, or 6/6/5 ring system. Remarkably, compound 5 with a relatively flexible side chain showed promising inhibition activity against the cholesterol transporter protein Niemann-Pick C1-like 1 (NPC1L1), expanding the function of cytochalasans.

Epigenetic Manipulation Induced Production of Immunosuppressive Chromones and Cytochalasins from the Mangrove Endophytic Fungus Phomopsis asparagi DHS-48.

A mangrove endophytic fungus Phomopsis asparagi DHS-48 was found to be particularly productive with regard to the accumulation of substantial new compounds in our previous study. In order to explore its potential to produce more unobserved secondary metabolites, epigenetic manipulation was used on this fungus to activate cryptic or silent genes by using the histone deacetylase (HDAC) inhibitor sodium butyrate and the DNA methyltransferase (DNMT) inhibitor 5-azacytidine (5-Aza). Based on colony growth, dry biomass, HPLC, and 1H NMR analyses, the fungal chemical diversity profile was significantly changed compared with the control. Two new compounds, named phaseolorin J (1) and phomoparagin D (5), along with three known chromones (2-4) and six known cytochalasins (6-11), were isolated from the culture treated with sodium butyrate. Their structures, including their absolute configurations, were elucidated using a combination of detailed HRESIMS, NMR, and ECD and 13C NMR calculations. The immunosuppressive and cytotoxic activities of all isolated compounds were evaluated. Compounds 1 and 8 moderately inhibited the proliferation of ConA (concanavalin A)-induced T and LPS (lipopolysaccharide)-induced B murine spleen lymphocytes. Compound 5 exhibited significant in vitro cytotoxicity against the tested human cancer cell lines Hela and HepG2, which was comparative to the positive control adriamycin and fluorouracil. Our finding demonstrated that epigenetic manipulation should be an efficient strategy for the induction of new metabolites from mangrove endophytic fungi.

Effect of mechanical properties of Jurkat cell on adhesion properties of Jurkat integrin and VCAM-1: An AFM study.

Mechanical properties play key roles in the immune system, especially the activation, transformation and subsequent effector responses of immune cells. As transmembrane adhesion receptors, integrins mediate the adhesion events of both cells and cell-extracellular matrix (ECM). Integrin affinity would influence the crosslinking of cytoskeleton, leading to the change of elastic properties of cells. In this study, the cells were treated with F-actin destabilizing agent Cytochalasin-D (Cyt-D), fixed by Glutaraldehyde, and cultivated in hypotonic solution respectively. We used Atomic force microscopy (AFM) to quantitatively measure the elasticity of Jurkat cells and adhesion properties between integrins and vascular cell adhesion molecule-1 (VCAM-1), and immunofluorescence to study the alteration of cytoskeleton. Glutaraldehyde had a positive effect on the adhesion force and Young's modulus. However, these mechanical properties decreased in a hypotonic environment, confirming the findings of cellular physiological structure. There was no significant difference in the bond strength and elasticity of Jurkat cells treated with Cytochalasin-D, probably because of lower importance of actin in suspension cells. All the treatments in this study pose a negative effect on the adhesion probability between integrins and VCAM-1, which demonstrates the effect of structural alteration of the cytoskeleton on the conformation of integrin. Clear consistency between adhesion force of integrin/VCAM-1 bond and Young's modulus of Jurkat cells was shown. Our results further demonstrated the relationship between cytoskeleton and integrin-ligand by mechanical characteristics.

Immunosuppressive Cytochalasins from the Mangrove Endophytic Fungus Phomopsis asparagi DHS-48.

Three new cytochalasins, phomoparagins A-C (1-3), along with five known analogs (4-8), were isolated from Phomopsis asparagi DHS-48, a mangrove-derived endophytic fungus. Their structures, including their absolute configurations, were elucidated using a combination of detailed HRESIMS, NMR, and ECD techniques. Notably, 1 possessed an unprecedented 5/6/5/8/5-fused pentacyclic skeleton. These compounds were tested for their inhibitory activity against concanavalin A (ConA)/lipopolysaccharide (LPS)-induced spleen lymphocyte proliferation and calcineurin (CN) enzyme. Several metabolites (2 and 4-6) exhibited fascinating inhibitory activities with a relatively low toxicity. Furthermore, 2 was demonstrated to inhibit ConA-stimulated activation of NFAT1 dephosphorylation and block NFAT1 translocation in vitro, subsequently inhibiting the transcription of interleukin-2 (IL-2). Our results provide evidence that 2 may, at least partially, suppress the activation of spleen lymphocytes via the CN/NFAT signaling pathway, highlighting that it could serve as an effective immunosuppressant that is noncytotoxic and natural.

Binding of phenochalasin A, an inhibitor of lipid droplet formation in mouse macrophages, on G-actin.

Phenochalasin A, a unique phenol-containing cytochalasin produced by the marine-derived fungus Phomopsis sp. FT-0211, was originally discovered in a cell morphological assay of observing the inhibition of lipid droplet formation in mouse peritoneal macrophages. To investigate the mode of action and binding proteins, phenochalasin A was radio-labeled by 125I. Iodinated phenochalasin A exhibited the same biological activity as phenochalasin A. [125I]Phenochalasin A was found to be associated with an approximately 40 kDa protein, which was identified as G-actin. Furthermore, detail analyses of F-actin formation in Chinese hamster ovary cells (CHO-K1 cells) indicated that phenochalasin A (2 µM) caused elimination of F-actin formation on the apical site of the cells, suggesting that actin-oriented specific function(s) in cytoskeletal processes are affected by phenochalasin A.

New Cytochalasin Derivatives from Deep-Sea Cold Seep-Derived Endozoic Fungus Curvularia verruculosa CS-129.

Two new antimicrobial cytochalasin derivatives, 6ß,7ß-epoxydeoxaphomin C (1) and 12-hydroxydeoxaphomin C (2), a new natural occurring product 24-nor-cytochalasin B (3), together with two related known analogs (4-5) were isolated and identified from an endozoic fungus Curvularia verruculosa CS-129, isolated from the deep-sea squat lobster Shinkaia crosnieri which was collected in cold seep region of south China sea. The structures of new compounds were elucidated on the basis of detailed spectroscopic analysis and ECD calculation. The spectroscopic data of 24-nor-cytochalasin B (3) were reported for the first time. All compounds were tested for their antibacterial activities against human and aquatic pathogenic bacteria.

TRAIL-sensitizing Cytochalasins from the Endophytic Fungus Phoma multirostrata.

Seven undescribed cytochalasins, multirostratins K - Q (2: -8: ), together with one known analogue, cytochalasin Z3 (1: ), were isolated from the culture of Phoma multirostrata XJ-2-1, an endophytic fungus obtained from the root of Parasenecio albus. Their structures with absolute configurations were determined by 1D and 2D NMR, high-resolution electrospray ionization mass spectrometry (HRESIMS), electronic circular dichroism (ECD), single-crystal X-ray crystallography, and chemical methods. The structure of ascochalasin was revised from Δ 13 to Δ 21 by detailed analysis of the NMR data and by comparison with the data for 7: . In a TRAIL (tumor necrosis factor related apoptosis inducing ligand)-resistance-overcoming experiment, co-treatment of 2: or 6: with TRAIL reduced the cell viability of A549 cells by 30.3% and 27.5% at 10 µM, respectively.

Cytochalasan Alkaloids as TRAIL Sensitizers from an Endophytic Fungus Chaetomium sp.

Two new cytochalasans with a rare 6/6/5/5/7 pentacyclic ring system, named chaetoconvosins C-D (1: -2: ), together with two known congeners (3: -4: ), were isolated from the fermentation of an endophytic fungus, Chaetomium sp. SG-01, harbored in the fibrous roots of Schisandra glaucescens Diels. Their structures including the absolute configuration were elucidated by extensive spectroscopic (HRESIMS, NMR, and ECD) and X-ray crystallographic analyses. The TRAIL-resistance-overcoming activity of 1: -4: in a TRAIL-resistant HT29 colorectal cancer cell line was evaluated, which revealed that co-treatment of 1: -4: at 50 µM with TRAIL (150 ng/mL) reduced the HT29 cell viability by 19.0%, 24.1%, 17.9%, and 15.5%, respectively, compared to treatment with 1: -4: alone.

Influencing the Actin Dynamics in Plant Cells by Jasplakinolide, Chondramides, Phalloidin, Cytochalasins, and Latrunculins.

This chapter presents an overview of the most common F-actin influencing substances, used to study actin dynamics in living plant cells for studies on morphogenesis, motility, organelle movement, apoptosis, or abiotic stress. These substances can be divided into two major subclasses-F-actin-stabilizing and F-actin-polymerizing substances like jasplakinolide and chondramides and F-actin-severing compounds like cytochalasins and latrunculins. Jasplakinolide, which may have anti-cancer activities, was originally isolated from a marine sponge and can now be synthesized and has become commercially available, which is responsible for its wide distribution as membrane-permeable F-actin-stabilizing and F-actin-polymerizing agent. Recently an acyclic derivate of jasplakinolide was isolated. Cytochalasins, derived from fungi, show an F-actin-severing function, and many derivatives are commercially available (A, B, C, D, E, H, J), also making it a widely used compound for F-actin disruption. The same can be stated for latrunculins (A, B), derived from Red Sea sponges; however the mode of action is different by binding to G-actin and inhibiting incorporation into the filament. In the case of swinholide, isolated from red algae or the cyanobacterium Nostoc, a stable complex with actin dimers is formed, resulting in severing F-actin.For influencing F-actin dynamics in plant cells, only membrane permeable drugs are useful in a broad range. We, however, introduce also the phallotoxins and synthetic derivatives thereof, as they are widely used to visualize F-actin in fixed cells. A particular uptake mechanism has been shown for hepatocytes but has also been described in siphonal giant algae. The focus is set on F-actin dynamics in plant cells where alterations in cytoplasmic streaming can be particularly well studied; moreover fluorescence methods for phalloidin- and antibody staining as well as techniques for immunoelectron microscopy are explained.

Cytochalasin Derivatives from the Endozoic Curvularia verruculosa CS-129, a Fungus Isolated from the Deep-Sea Squat Lobster Shinkaia crosnieri Living in the Cold Seep Environment.

A new cytochalasin dimer, verruculoid A (1), three new cytochalasin derivatives, including 12-nor-cytochalasin F (2), 22-methoxycytochalasin B6 (3), and 19-hydroxycytochalasin B (4), and 20-deoxycytochalasin B (5), a synthetic product obtained as a natural product for the first time, together with four known analogues (6-9), were isolated and identified from the culture extract of Curvularia verruculosa CS-129, an endozoic fungus obtained from the inner fresh tissue of the deep-sea squat lobster Shinkaia crosnieri, which was collected from the cold seep area of the South China Sea. Structurally, verruculoid A (1) represents the first cytochalasin homodimer containing a thioether bridge, while 12-nor-cytochalasin F (2) is the first 12-nor-cytochalasin derivative. Their structures were elucidated by detailed interpretation of the NMR spectroscopic and mass spectrometric data. X-ray crystallographic analysis and ECD calculations confirmed their structures and absolute configurations. Compound 1 displayed activity against the human pathogenic bacterium Escherichia coli (MIC = 2 µg/mL), while compounds 4, 8, and 9 showed cytotoxicity against three tumor cell lines (HCT-116, HepG-2, and MCF-7) with IC50 values from 5.2 to 12 µM. The structure-activity relationship was briefly discussed.

Pentacyclic Cytochalasins and Their Derivatives from the Endophytic Fungus Phomopsis sp. xz-18.

Eight new cytochalasins 1-8 and ten known analogs 9-18 were isolated from the endophytic fungus Phomopsis sp. xz-18. The planar structures of the cytochalasins were determined by HR-ESI-MS and NMR analysis. Compounds 1, 2, 9 and 10 were 5/6/6/7/5-fused pentacyclic cytochalasins; compounds 3 and 4 had conjugated diene structures in the macrocycle; and compound 6 had a ß,γ-unsaturated ketone. The absolute configuration of 6 was confirmed for the first time by the octant rule. The acid-free purification process proved that the pentacyclic system was a natural biosynthetic product and not an acid-mediated intramolecular cyclized artifact. The new compounds did not exhibit activities against human cancer cell lines in cytotoxicity bioassays or antipathogenic fungal activity, but compounds 1, 3 and 4 showed moderate antibacterial activity in disk diffusion assays.

Zopfiellasins A-D, Two Pairs of Epimeric Cytochalasins from Kiwi-Associated Fungus Zopfiella sp. and Their Antibacterial Assessment.

In our continuous search for antibacterial agents against Pseudomonas syringae pv. actinidiae (Psa) from kiwi-associated fungi, two pairs of epimeric cytochalasins, zopfiellasins A-D (1-4), were characterized from the fungus Zopfiella sp. The structures were established on the basis of spectroscopic data analysis, while the absolute configurations were determined by single-crystal X-ray diffraction. Compounds 1 and 3 exhibited antibacterial activity against Psa with MIC values of 25 and 50 µg/mL, respectively. This is the first report of anti-Psa activity of cytochalasin derivatives.

New Cytotoxic Cytochalasans from a Plant-Associated Fungus Chaetomium globosum kz-19.

Four new cytochalasans, phychaetoglobins A-D (1-4), together with twelve known cytochalasans (5-16), were isolated from a mangrove-associated fungus Chaetomium globosum kz-19. The new structures were elucidated on the basis of extensive 1D and 2D NMR, HR ESIMS spectroscopic analyses, and electronic circular dichroism (ECD) calculations. The absolute configuration of 2 was established by application of Mosher's method. Compounds 4-8 exhibited moderate cytotoxicities against A549 and HeLa cell lines with the IC50 values less than 20 µM.

Aspochalasin H1: A New Cyclic Aspochalasin from Hawaiian Plant-Associated Endophytic Fungus Aspergillus sp. FT1307.

Aspergillus is one of the most diverse genera, and it is chemically profound and known to produce many biologically active secondary metabolites. In the present study, a new aspochalasin H1 (1), together with nine known compounds (2-10), were isolated from a Hawaiian plant-associated endophytic fungus Aspergillus sp. FT1307. The structures were elucidated using nuclear magnetic resonance (NMR) (1H, 1H-1H COSY, HSQC, HMBC, ROESY and 1D NOE), high-resolution electrospray ionization mass spectroscopy (HRESIMS), and comparisons with the reported literature. The absolute configuration of the new compound was established by electronic circular dichroism (ECD) in combination with NMR calculations. The new compound contains an epoxide moiety and an adjacent trans-diol, which has not been reported before in the aspochalasin family. The antibacterial screening of the isolated compounds was carried out against pathogenic bacteria (Staphylococcus aureus, Methicillin-resistant S. aureus and Bacillus subtilis). The antiproliferative activity of compounds 1-10 was evaluated against human breast cancer cell lines (MCF-7 and T46D) and ovarian cancer cell lines (A2780).

Alternariasin A, new pentacyclic cytochalasin from the fungus Alternaria alternate.

Alternariasin A (1), one new cytochalasin possessing the benzo[4,5]indeno[2,1-d]isoindole-1,3,13(2H,3aH)-trione skeleton, and five known compounds 2-6 were isolated from the solid cultures of the Midui Glacier-derived fungus Alternaria alternata. Their structures were elucidated by NMR and MS spectroscopic analyses and by a comparison with data from the literature. The absolute configuration of 1 was assigned by combination of experimental and calculated electronic circular dichroism (ECD) spectra. Compound 1 displayed antibacterial activity against the S. aureus, B. subtilis and E. coli with MIC values of 16.7, 16.7 and 33.3 µΜ, respectively. While compound 3 showed potent cytotoxicity against a small panel of human tumour cell lines.