Bioactivities and Future Perspectives of Chaetoglobosins

Preliminary Evidence for the Role of Fungi, Specifically Chaetomium, in Gulf War Illness

INTRODUCTION

For veterans of the Persian Gulf War (1990-1991), dozens of possible causes for their illness have been proposed. We hypothesize that all may be correct. These may have weakened the immunity of the military personnel to fungal pathogens in the soil. These microbes, in turn, may have afflicted the veterans either directly by infection or indirectly by toxins.

MATERIALS AND METHODS

In 1990, the military (source confidential) provided the first author with soil samples from the Persian Gulf to determine if there were biothreats present. His team found that per gram of soil, there had few bacteria but many fungi. The National Centre for Human Mycotic Diseases (Edmonton) identified some of these fungi. They sent to the first author reference cultures of 12 pathogenic fungal species isolated from Canadian patients. Supernatant antigens of these fungi were used to assess if control and Gulf War Illness (GWI) patient sera had IgG antibodies against them.

RESULTS

Human sera were tested on pathogenic fungal supernatant antigens. Controls had low IgG titers against all 12 fungal sources. Gulf War Illness (GWI) patient sera had low IgG titers against 11 of the 12 fungal antigens. However, 12 of 28 GWI patient sera (43%, P ≤ .0002 compared to controls) had high IgG titers against one fungus, Chaetomium, supernatant antigen.

CONCLUSIONS

We suggest that the military personnel in the Persian Gulf War (1990-1991) may have had their immunity weakened from a variety of causes. The role of pathogenic fungi and/or their supernatant antigens or toxins as a contributing factor to GWI should be further investigated.

Chaetoglobosin E inhibits tumor growth and promotes the anti-tumor efficacy of cytotoxic drugs in esophageal squamous cell carcinoma by targeting PLK1

Background

Currently, there is no satisfactory treatment available for esophageal squamous cell carcinoma (ESCC), and thus, there is a pressing need to develop effective drugs. Chaetoglobosin E, a cytochalasan alkaloid derived from metabolites of Chaetomium madrasense 375, is a chaetoglobosin with intense anti-tumor activity. Therefore, revealing its anti-tumor mechanism for the application of cytochalasans is crucial.

Methods

The cytotoxic effect of chaetoglobosin E and cisplatin on esophageal cancer KYSE-30, KYSE-150, and TE-1 cells was detected using cell viability or colony formation assays. The cell cycle, apoptosis, autophagy, invasion, and metastasis were assayed by flow cytometry or western blot. The potential target of chaetoglobosin E was assayed by RNA sequencing (RNA-seq) and large loop prediction software analysis and was assessed by western blot and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The effect of its target on cell pyroptosis was assayed using overexpression and silence experiments.

Results

Chaetoglobosin E significantly inhibited the proliferation of KYSE-30, KYSE-150, and TE-1 cells, especially KYSE-30 cells. Our results showed that chaetoglobosin E induced the G2/M phase arrest of KYSE-30 cells, followed by the down-regulation of cyclinB1, CDC2, and p-CDC2, and up-regulation of p21. Moreover, chaetoglobosin E also decreased the anti-apoptotic protein expression of Bcl-2, increased apoptotic expression of Bax, increased autophagy protein expressions of beclin1 and LC3, decreased invasion and metastasis protein expression of E-cadherin, and increased expression of vimentin. The RNA-seq and large loop prediction software analysis results indicated that its potential target might be polo-like kinase 1 (PLK1). Moreover, results also showed that chaetoglobosin E can reverse the PLK1 overexpression plasmid-induced up-regulation of the PLK1 protein. Furthermore, we found that chaetoglobosin E induced pyroptosis via the activation of the gasdermin E (GSDME) protein. Further studies showed that the high expression of PLK1 inactivated the GSDME protein, while the knockdown of PLK1 expression activated the GSDME protein, indicating that chaetoglobosin E induced cell pyroptosis by inhibiting PLK1.

Conclusions

This study suggested that chaetoglobosin E may be a novel lead compound to the treatment of ESCC patients by targeting PLK1, and elucidated for the first time that PLK1 was involved in a new pyroptosis mechanism.

Diversified Chaetoglobosins from the Marine-Derived Fungus Emericellopsis sp. SCSIO41202

Two undescribed cytochalasins, emeriglobosins A (1) and B (2), together with nine previously reported analogues (3–11) and two known tetramic acid derivatives (12, 13) were isolated from the solid culture of Emericellopsis sp. SCSIO41202. Their structures, including the absolute configurations of their stereogenic carbons, were fully elucidated based on spectroscopic analysis and the calculated ECD. Some of the isolated compounds were evaluated for their cytotoxicity and enzyme inhibitory activity against acetylcholinesterase (AChE) in vitro. Among them, 8 showed potent AChE inhibitory activity, with an IC₅₀ value of 1.31 μM, and 5 showed significant cytotoxicity against PC-3 cells, with an IC₅₀ value of 2.32 μM.

Culturable Microorganisms Associated with Sea Cucumbers and Microbial Natural Products

Sea cucumbers are a class of marine invertebrates and a source of food and drug. Numerous microorganisms are associated with sea cucumbers. Seventy-eight genera of bacteria belonging to 47 families in four phyla, and 29 genera of fungi belonging to 24 families in the phylum Ascomycota have been cultured from sea cucumbers. Sea-cucumber-associated microorganisms produce diverse secondary metabolites with various biological activities, including cytotoxic, antimicrobial, enzyme-inhibiting, and antiangiogenic activities. In this review, we present the current list of the 145 natural products from microorganisms associated with sea cucumbers, which include primarily polyketides, as well as alkaloids and terpenoids. These results indicate the potential of the microorganisms associated with sea cucumbers as sources of bioactive natural products.

Pchaeglobolactone A, Spiropchaeglobosin A, and Pchaeglobosals A and B: Four Rearranged Cytochalasans from Chaetomium globosum P2-2-2

Four novel rearranged cytochalasans (1-4) were isolated from an endophytic fungus Chaetomium globosum P2-2-2. Pchaeglobolactone A (1) possessed an unprecedented 13-aza-21-oxa-tetracyclo-[10.6.1.2^17,19.0^15,19]henicosane core. Spiropchaeglobosin A (2) was the first example of cytochalasans featuring a novel spiro[5.10]hexadecane unit. Pchaeglobosals A (3) and B (4) featured a unique 5/5/13 fused tricyclic ring system. Compounds 1-4 were tested for their antiproliferative, apoptosis, cell cycle arrest, and TRAIL-resistance-overcoming activities on cancer cell lines.

The brlA Gene Deletion Reveals That Patulin Biosynthesis Is Not Related to Conidiation in Penicillium expansum

Dissemination and survival of ascomycetes is through asexual spores. The brlA gene encodes a C2H2-type zinc-finger transcription factor, which is essential for asexual development. Penicillium expansum causes blue mold disease and is the main source of patulin, a mycotoxin that contaminates apple-based food. A P. expansum PeΔbrlA deficient strain was generated by homologous recombination. In vivo, suppression of brlA completely blocked the development of conidiophores that takes place after the formation of coremia/synnemata, a required step for the perforation of the apple epicarp. Metabolome analysis displayed that patulin production was enhanced by brlA suppression, explaining a higher in vivo aggressiveness compared to the wild type (WT) strain. No patulin was detected in the synnemata, suggesting that patulin biosynthesis stopped when the fungus exited the apple. In vitro transcriptome analysis of PeΔbrlA unveiled an up-regulated biosynthetic gene cluster (PEXP_073960-PEXP_074060) that shares high similarity with the chaetoglobosin gene cluster of Chaetomium globosum. Metabolome analysis of PeΔbrlA confirmed these observations by unveiling a greater diversity of chaetoglobosin derivatives. We observed that chaetoglobosins A and C were found only in the synnemata, located outside of the apple, whereas other chaetoglobosins were detected in apple flesh, suggesting a spatial-temporal organization of the chaetoglobosin biosynthesis pathway.

Identification of the Antifungal Metabolite Chaetoglobosin P From Discosia rubi Using a Cryptococcus neoformans Inhibition Assay: Insights Into Mode of Action and Biosynthesis

Cryptococcus neoformans is an important human pathogen with limited options for treatments. We have interrogated extracts from fungal fermentations to find Cryptococcus-inhibiting natural products using assays for growth inhibition, differential thermosensitivity, and synergy with existing antifungal drugs. Extracts from fermentations of strains of Discosia rubi from eastern Texas showed anticryptococcal bioactivity with preferential activity in agar zone of inhibition assays against C. neoformans at 37°C versus 25°C. Assay-guided fractionation led to the purification and identification of chaetoglobosin P as the active component of these extracts. Genome sequencing of these strains revealed a biosynthetic gene cluster consistent with chaetoglobosin biosynthesis and β-methylation of the tryptophan residue. Proximity of genes of the actin-binding protein twinfilin-1 to the chaetoglobosin P and K gene clusters suggested a possible self-resistance mechanism involving twinfilin-1 which is consistent with the predicted mechanism of action involving interference with the polymerization of the capping process of filamentous actin. A C. neoformans mutant lacking twinfilin-1 was hypersensitive to chaetoglobosin P. Chaetoglobosins also potentiated the effects of amphotericin B and caspofungin on C. neoformans.