Mycenon, a new metabolite from a Mycena species TA 87202 (basidiomycetes) as an inhibitor of isocitrate lyase

The alkynyl-containing compounds from mushrooms and their biological activities

Mushrooms have been utilized by humans for thousands of years due to their medicinal and nutritional properties. They are a crucial natural source of bioactive secondary metabolites, and recent advancements have led to the isolation of several alkynyl-containing compounds with potential medicinal uses. Despite their relatively low abundance, naturally occurring alkynyl compounds have attracted considerable attention due to their high reactivity. Bioactivity studies have shown that alkynyl compounds exhibit significant biological and pharmacological activities, including antitumor, antibacterial, antifungal, insecticidal, phototoxic, HIV-inhibitory, and immunosuppressive properties. This review systematically compiles 213 alkynyl-containing bioactive compounds isolated from mushrooms since 1947 and summarizes their diverse biological activities, focusing mainly on cytotoxicity and anticancer effects. This review serves as a detailed and comprehensive reference for the chemical structures and bioactivity of alkynyl-containing secondary metabolites from mushrooms. Moreover, it provides theoretical support for the development of chemical constituents containing alkynyl compounds in mushrooms based on academic research and theory.

Inhibitory Effects of Nitrogenous Metabolites from a Marine-Derived Streptomyces bacillaris on Isocitrate Lyase of Candida albicans

Two nitrogenous metabolites, bacillimide (1) and bacillapyrrole (2), were isolated from the culture broth of the marine-derived actinomycete Streptomyces bacillaris. Based on the results of combined spectroscopic and chemical analyses, the structure of bacillimide (1) was determined to be a new cyclopenta[c]pyrrole-1,3-dione bearing a methylsulfide group, while the previously reported bacillapyrrole (2) was fully characterized for the first time as a pyrrole-carboxamide bearing an alkyl sulfoxide side chain. Bacillimide (1) and bacillapyrrole (2) exerted moderate (IC50 = 44.24 μM) and weak (IC50 = 190.45 μM) inhibitory effects on Candida albicans isocitrate lyase, respectively. Based on the growth phenotype using icl-deletion mutants and icl expression analyses, we determined that bacillimide (1) inhibits the transcriptional level of icl in C. albicans under C2-carbon-utilizing conditions.

Itaconate: an antimicrobial metabolite of macrophages

Itaconate is a conjugated 1,4-dicarboxylate produced by macrophages. This small molecule has recently received increasing attention due to its role in modulating the immune response of macrophages upon exposure to pathogens. Itaconate has also been proposed to play an antimicrobial function; however, this has not been explored as intensively. Consistent with the latter, itaconate is known to show antibacterial activity in vitro and was reported to inhibit isocitrate lyase, an enzyme required for survival of bacterial pathogens in mammalian systems. Recent studies have revealed bacterial growth inhibition under biologically relevant conditions. In addition, an antimicrobial role for itaconate is substantiated by the high concentration of itaconate found in bacteria-containing vacuoles, and by the production of itaconate-degrading enzymes in pathogens such as Salmonella enterica ser. Typhimurium, Pseudomonas aeruginosa, and Yersinia pestis. This review describes the current state of literature in understanding the role of itaconate as an antimicrobial agent in host–pathogen interactions.

D319 induced antifungal effects through ROS-mediated apoptosis and inhibited isocitrate lyase in Candida albicans

BACKGROUND

Candida albicans (C. albicans) is an opportunistic pathogen that can cause superficial and life-threatening systemic infections in immunocompromised patients. However, the available clinically antifungals are limited. Therefore, the development of effective antifungal agents and therapies is urgently needed. Quinoline type of compounds were reported to possess potent anti-fungal effect. A series of quinoline derivatives were synthesized. Moreover their inhibitory activities and mechanisms on C. albicans were evaluated in this study.

METHODS

The structure of D319 was identified by extensive spectroscopic analysis. The antifungal activity of D319 on C. albicans was evaluated using conventional methods, including the inhibition zone diameters with filter paper, Clinical Laboratory Standard Institute (CLSI) broth microdilution method in vitro, and in a murine model in vivo. Flow cytometry, fluorescence microscopy, western blot, knockout mutant and revertant strain techniques, and molecular modeling were applied to explore the mechanism of action of D319 in anti-Candida.

RESULTS

D319 exhibited potent anti-Candida activity with Minimum Inhibitory Concentration value of 2.5 μg/mL in vitro. D319 significantly improved survival rate and reduced fungal burden compared to vehicle control in a murine model in vivo. The treatment of C. albicans with D319 resulted in fungal apoptosis through reactive oxygen species (ROS) accumulation in C. albicans. Furthermore, D319 inhibited the glyoxylate enzyme isocitrate lyase (ICL) of C. albicans, which was also confirmed by docking analysis.

CONCLUSIONS

Quinoline compound D319 exhibited strong anti-Candida activities in vitro and in vivo models through inhibiting ICL activity and ROS accumulation in C. albicans.

GENERAL SIGNIFICANCE

This study showed that compound D319 as a novel isocitrate lyase inhibitor, would be a promising anti-Candida lead compound, which provided a potential application of this type of compounds in fighting clinical fungal infections. Furthermore, this study also supported ICL as a potential target for anti-Candida drug discovery.

Inhibitory Effects of Epipolythiodioxopiperazine Fungal Metabolites on Isocitrate Lyase in the Glyoxylate Cycle of Candida albicans

Four epipolythiodioxopiperazine fungal metabolites (1-4) isolated from the sponge-derived Aspergillus quadrilineatus FJJ093 were evaluated for their capacity to inhibit isocitrate lyase (ICL) in the glyoxylate cycle of Candida albicans. The structures of these compounds were elucidated using spectroscopic techniques and comparisons with previously reported data. We found secoemestrin C (1) (an epitetrathiodioxopiperazine derivative) to be a potent ICL inhibitor, with an inhibitory concentration of 4.77 ± 0.08 μM. Phenotypic analyses of ICL-deletion mutants via growth assays with acetate as the sole carbon source demonstrated that secoemestrin C (1) inhibited C. albicans ICL. Semi-quantitative reverse-transcription polymerase chain reaction analyses indicated that secoemestrin C (1) inhibits ICL mRNA expression in C. albicans under C₂-assimilating conditions.

Inhibitory Effects of Diketopiperazines from Marine-Derived Streptomyces puniceus on the Isocitrate Lyase of Candida albicans

The glyoxylate cycle is a sequence of anaplerotic reactions catalyzed by the key enzymes isocitrate lyase (ICL) and malate synthase, and plays an important role in the pathogenesis of microorganisms during infection. An icl-deletion mutant of Candida albicans exhibited reduced virulence in mice compared with the wild type. Five diketopiperazines, which are small and stable cyclic peptides, isolated from the marine-derived Streptomyces puniceus Act1085, were evaluated for their inhibitory effects on C. albicans ICL. The structures of these compounds were elucidated based on spectroscopic data and comparisons with previously reported data. Cyclo(L-Phe-L-Val) was identified as a potent ICL inhibitor, with a half maximal inhibitory concentration of 27 μg/mL. Based on the growth phenotype of the icl-deletion mutants and icl expression analyses, we demonstrated that cyclo(L-Phe-L-Val) inhibits the gene transcription of ICL in C. albicans under C₂-carbon-utilizing conditions.

Acetylenic Terrestrial Anticancer Agents

Acetylenic metabolites belong to a class of molecules containing triple bond(s). They are found in plants, fungi, microorganisms, and marine invertebrates. This review presents 139 active acetylenic molecules of plant, fungal, and soil bacterial origin that reveal cytotoxic and/or anticancer activities. Although many compounds of this group possess encouraging characteristics, they have never been evaluated as potential anticancer agents. They are of great interest, especially for the medicine and/or pharmaceutical industries. Here we describe structures and biological activities of acetylenic metabolites.

Indole Alkaloids from Tropical Sponge Hyrtios sp. as Isocitrate Lyase Inhibitors

A new β-carboline alkaloid, 3,4-dihydrohyrtiosulawesine (8), and fifteen known alkaloids were isolated from the tropical marine sponge Hyrtios sp. Among these known compounds, β-ketoserotonin (10) has been isolated for the first time from a natural source. The structures of the isolated compounds were determined by spectroscopic analyses and comparison with literature values. Compound 8 displayed potent inhibitory activities against isocitrate lyase (IC50: 92.9 μM) from Candida albicans.

Potential inhibitors for isocitrate lyase of Mycobacterium tuberculosis and non-M. tuberculosis: a summary

Isocitrate lyase (ICL) is the first enzyme involved in glyoxylate cycle. Many plants and microorganisms are relying on glyoxylate cycle enzymes to survive upon downregulation of tricarboxylic acid cycle (TCA cycle), especially Mycobacterium tuberculosis (MTB). In fact, ICL is a potential drug target for MTB in dormancy. With the urge for new antitubercular drug to overcome tuberculosis treat such as multidrug resistant strain and HIV-coinfection, the pace of drug discovery has to be increased. There are many approaches to discovering potential inhibitor for MTB ICL and we hereby review the updated list of them. The potential inhibitors can be either a natural compound or synthetic compound. Moreover, these compounds are not necessary to be discovered only from MTB ICL, as it can also be discovered by a non-MTB ICL. Our review is categorized into four sections, namely, (a) MTB ICL with natural compounds; (b) MTB ICL with synthetic compounds; (c) non-MTB ICL with natural compounds; and (d) non-MTB ICL with synthetic compounds. Each of the approaches is capable of overcoming different challenges of inhibitor discovery. We hope that this paper will benefit the discovery of better inhibitor for ICL.

Suvanine sesterterpenes from a tropical sponge Coscinoderma sp. inhibit isocitrate lyase in the glyoxylate cycle

The glyoxylate cycle is a sequence of anaplerotic reactions catalyzed by the key enzymes isocitrate lyase (ICL) and malate synthase (MLS). Mutants of Candida albicans lacking ICL are markedly less virulent in mice than the wild-type. Suvanine sesterterpenes (1−9) isolated from a tropical sponge Coscinoderma sp. were evaluated for their inhibitory activities toward recombinant ICL from C. albicans. These studies led to the identification of a potent ICL inhibitor, suvanine salt (2), which possesses a sodium counterion and displays an inhibitory concentration value (IC₅₀) of 6.35 μM. The growth phenotype of ICL deletion mutants and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated that compound 2 inhibits the ICL mRNA expression in C. albicans under C₂-carbon-utilizing conditions. The present data highlight the potential for suvanine sesterterpenes treatment of C. albicans infections via inhibition of ICL activity.

Lajollamycins, nitro group-bearing spiro-β-lactone-γ-lactams obtained from a marine-derived Streptomyces sp

Lajollamycins (1-4), each of which bears a spiro-β-lactone-γ-lactam ring and a nitro-tetraene moiety, were obtained from a marine-derived Streptomyces strain isolated from the southern area of Jeju Island, Republic of Korea. The planar structures of the lajollamycins were elucidated on the basis of spectroscopic analyses by NMR, UV, IR, and MS. The absolute configuration of lajollamycin (1), the planar structure of which has been previously reported, was determined using J-based configuration analysis based on (1)H-(1)H and (1)H-(13)C coupling constants, as well as ROESY correlations, followed by the modified Mosher's method. The absolute configurations of lajollamycins B-D (2-4) were established by comparing their CD spectra with that of 1. The lajollamycins exhibited moderate inhibitory activity toward Candida albicans isocitrate lyase.

Bahamaolide A from the marine-derived Streptomyces sp. CNQ343 inhibits isocitrate lyase in Candida albicans

Bahamaolide A, a new macrocyclic lactone isolated from the culture of marine actinomycete Streptomyces sp. CNQ343, was evaluated for its inhibitory activity toward isocitrate lyase (ICL) from Candida albicans. These studies led to the identification of bahamaolide A as a potent ICL inhibitor with IC50 value of 11.82 μM. The growth phenotype of ICL deletion mutants and quantitative RT-PCR analyses indicated that this compound inhibits the ICL mRNA expression in C. albicans under C2-carbon-utilizing conditions. The present data highlight the potential for bahamaolide A treatment of C. albicans infections via inhibition of ICL activity.

Gymnopalynes A and B, chloropropynyl-isocoumarin antibiotics from cultures of the basidiomycete Gymnopus sp

A chlorinated isocoumarin with an acetylenyl side chain and its 3,4-dihydro derivative, named gymnopalynes A (1) and B (2), were isolated from cultures of a basidiomycete originating from the rain forest of Northern Thailand. The producing organism was identified as a species of Gymnopus (Marasmiaceae). Their structures were elucidated by spectroscopic methods including UV/vis and NMR spectroscopy as well as high-resolution mass spectrometry as 3-(3-chloroprop-1-yn-1-yl)-1H-isochromen-1-one (1) and 3-(3-chloroprop-1-yn-1-yl)-3,4-dihydro-1H-isochromen-1-one (2). The absolute stereochemistry of 2 was assigned as S by CD spectroscopy. Both compounds showed weak to moderate antimicrobial and pronounced cytotoxic activities.

Bioactive acetylenic metabolites

This article focuses on anticancer, and other biological activities of acetylenic metabolites obtained from plants and fungi. Acetylenic compounds belong to a class of molecules containing triple bond(s). Naturally occurring acetylenics are of particular interest since many of them display important biological activities and possess antitumor, antibacterial, antimicrobial, antifungal, and immunosuppressive properties. There are of great interest for medicine, pharmacology, medicinal chemistry, and pharmaceutical industries. This review presents structures and describes cytotoxic activities of more than 100 acetylenic metabolites, including fatty alcohols, ketones, and acids, acetylenic cyclohexanoids, spiroketal enol ethers, and carotenoids isolated from fungi and plants.

Bahamaolides A and B, antifungal polyene polyol macrolides from the marine actinomycete Streptomyces sp

Bahamaolides A and B (1 and 2), two new 36-membered macrocyclic lactones, were isolated from the culture of the marine actinomycete Streptomyces sp. derived from a sediment sample collected at North Cat Cay in the Bahamas. The planar structures of 1 and 2, bearing a hexaenone and nine consecutive skipped hydroxy groups, were determined by 1D and 2D NMR, mass, IR, and UV spectra. The absolute configurations of the bahamaolides were established by combined multistep chemical reactions and spectroscopic analysis. Bahamaolide A displayed significant inhibitory activity against Candida albicans isocitrate lyase and antifungal activity against various pathogenic fungi.

Bromophenols as Candida albicans isocitrate lyase inhibitors

A new series of bromophenols was synthesized by reactions of corresponding phenol analogs with bromine. The synthesized compounds were tested for inhibitory activity against isocitrate lyase (ICL) of Candida albicans and antimicrobial activity against gram-positive and, gram-negative bacteria and fungi. Among the synthesized bromophenols, bis(3-bromo-4,5-dihydroxyphenyl)methanone (11) and (3-bromo-4,5-dihydroxyphenyl)(2,3-dibromo-4,5-dihydroxyphenyl)methanone (12) displayed potent inhibitory activities against ICL, showing a stronger inhibitory effects than were found with natural bromophenol 1. The preliminary structure-activity relationships were investigated in order to determine the essential structural requirements for the inhibitory activities of these compounds against ICL of C. albicans.

5-Hydroxyindole-type alkaloids, as Candida albicans isocitrate lyase inhibitors, from the tropical sponge Hyrtios sp

Chemical investigations of the tropical marine sponge Hyrtios sp. have resulted in the isolation of a new alkaloid, 1-carboxy-6-hydroxy-3,4-dihydro-beta-carboline (1) together with the known metabolites, 6-hydroxy-3,4-dihydro-1-oxo-beta-carboline (2), 5-hydroxy-1H-indole-3-carboxylic acid methyl ester (3), serotonin (4), hyrtiosin A (5), 5-hydroxyindole-3-carbaldehyde (6), and hyrtiosin B (7). Their structures were elucidated on the basis of mass spectrometry and detailed 2D NMR spectroscopic data. Hyrtiosin B (7) displayed a potent inhibitory activity against isocitrate lyase (ICL) of Candida albicans with an IC(50) value of 89.0 microM.

Inhibition of Candida albicans isocitrate lyase activity by sesterterpene sulfates from the tropical sponge Dysidea sp

Seven sesterterpene sulfates (1-7) were isolated from the tropical sponge Dysidea sp. and their inhibitory activities against isocitrate lyase (ICL) from Candida albicans were evaluated. Among the isolated natural products compound 6 and 7 were found to be strong ICL inhibitors. The isolated compounds (1-7) also showed potent antibacterial effect against Bacillus subtilis and Proteus vulgaris, but did not display antifungal activity.

Biosynthesis and function of polyacetylenes and allied natural products

Polyacetylenic natural products are a substantial class of often unstable compounds containing a unique carbon-carbon triple bond functionality, that are intriguing for their wide variety of biochemical and ecological functions, economic potential, and surprising mode of biosynthesis. Isotopic tracer experiments between 1960 and 1990 demonstrated that the majority of these compounds are derived from fatty acid and polyketide precursors. During the past decade, research into the metabolism of polyacetylenes has swiftly advanced, driven by the cloning of the first genes responsible for polyacetylene biosynthesis in plants, moss, fungi, and actinomycetes and the initial characterization of the gene products. The current state of knowledge of the biochemistry and molecular genetics of polyacetylenic secondary metabolic pathways will be presented together with an up-to-date survey of new terrestrial and marine natural products, their known biological activities, and a discussion of their likely metabolic origins.

Synthesis and evaluation of hydroquinone derivatives as inhibitors of isocitrate lyase

Isocitrate lyase (ICL) is envisaged as an attractive drug target for the development of antimicrobial agents. We have prepared a series of hydroquinone derivatives on the basis of the structure of halisulfates, a naturally occurring inhibitor of ICL. The obtained derivatives were evaluated against ICL of C. albicans. The preliminary structure-activity relationships and the minimal structural requirements for potency were established through structural modifications.

Inhibition of the pathogenicity of Magnaporthe grisea by bromophenols, isocitrate lyase inhibitors, from the red alga Odonthalia corymbifera

Magnaporthe grisea is a fungal pathogen of rice that forms appressoria that penetrate the outer cuticle of the rice plant. Data from recent studies indicate that M. grisea isocitrate lyase (ICL), a key enzyme in the glyoxylate cycle, is highly expressed during appressorium-mediated plant infection. Bromophenols isolated from the red alga Odonthalia corymbifera exhibited potent ICL inhibitory activity and blocked appressoria formation by M. grisea in a concentration-dependent manner. In addition, these compounds protected the rice plants from infection by M. grisea. Rice plants infected with wild-type M. grisea Guy 11 exhibited significantly lower disease severity with bromophenol treatment than without, and the treatment effect was comparable to the behavior of the Deltaicl knockout mutant I-10. The protective effect of bromophenols and their strong inhibition of appressorium formation on rice plants suggest that ICL inhibitors may be promising candidates for crop protection, particularly to protect rice plants against M. grisea.

Anticancer activity of natural and synthetic acetylenic lipids

This review is a comprehensive survey of acetylenic lipids and their derivatives, obtained from living organisms, that have anticancer activity. Acetylenic metabolites belong to a class of molecules containing triple bond(s). They are found in plants, fungi, microorganisms, and marine invertebrates. Although acetylenes are common as components of terrestrial plants, fungi, and bacteria, it is only within the last 30 years that biologically active polyacetylenes having unusual structural features have been reported from plants, cyanobacteria, algae, invertebrates, and other sources. Naturally occurring aquatic acetylenes are of particular interest since many of them display important biological activities and possess antitumor, antibacterial, antimicrobial, antifouling, antifungal, pesticidal, phototoxic, HIV-inhibitory, and immunosuppressive properties. There is no doubt that they are of great interest, especially for the medicinal and/or pharmaceutical industries. This review presents structures and describes cytotoxic and anticancer activities only for more than 300 acetylenic lipids and their derivatives isolated from living organisms.

Chloro- and bromophenols from cultures of Mycena alcalina

Three new chlorinated phenols have been isolated from mycelial cultures of the mushroom Mycena alcalina. Their structures were determined by mass spectrometry and 1D and 2D NMR experiments. Addition of bromide to the medium resulted in the production of the corresponding brominated phenols. In addition, small amounts of the nonhalogenated precursor were also isolated, indicating that the halogenated metabolites are generated by a regioselectively operating halogenase.

Relationship of the glyoxylate pathway to the pathogenesis of Cryptococcus neoformans

Functional genomics has become a major focus in the study of microbial pathogenesis. This study used a functional genomic tool, differential display reverse transcription-PCR, to identify a transcriptional profile of Cryptococcus neoformans cells as they produced meningitis in an immunosuppressed host. This serial global gene expression during infection allowed for the identification of up- and down-regulated genes during infection. During this profiling, a single gene for the enzyme isocitrate lyase (ICL1) was found to be up regulated at 1 week of infection in a rabbit meningitis model and during a time of maximum host cellular response. The finding suggested that this enzyme and the glyoxylate shunt pathway are important to this yeast's energy production during infection. However, site-directed icl1 mutants had no apparent virulence defect in two animal models and no growth defect within macrophages. These observations suggest that although the yeast responded to a certain environmental cue(s) by an increase in ICL1 expression during infection, this gene was not necessary for progression of a C. neoformans infection. Compounds that specifically target only ICL1 are unlikely to cripple C. neoformans growth in vivo.

Sulfur tuft and turkey tail: biosynthesis and biodegradation of organohalogens by Basidiomycetes

Chlorinated aliphatic and aromatic compounds are generally considered to be undesirable xenobiotic pollutants. However, the higher fungi, Basidiomycetes, have a widespread capacity for organohalogen biosynthesis. Adsorbable organic halogens (AOX) and/or low-molecular-weight halogenated compounds are produced by Basidiomycetes of 68 genera from 20 different families. Most of the 81 halogenated metabolites identified from Basidiomycetes to date are chlorinated, although brominated and iodated metabolites have also been described. Two broad categories of Basidiomycete organohalogen metabolites are the halogenated aromatic compounds and the haloaliphatic compounds. Some of these organohalogen metabolites have demonstrable physiological roles as antibiotics and as metabolites involved in lignin degradation. Basidiomycetes produce large amounts of low-molecular-weight organohalogens or adsorbable organic halogens (AOX) when grown on lignocellulosic substrates. In our view, Basidiomycetes, as decomposers of forest litter, are a major source of natural organohalogens in terrestrial environments. Basidiomycetes are also potent degraders of a wide range of chlorinated pollutants, such as bleachery effluent from kraft mills and pentachlorophenol, polychlorinated dioxins, and polychlorinated biphenyls. The extracellular, lignin-degrading enzymes of the Basidiomycetes are involved in the oxidative degradation of chlorophenols and dioxin and can cause reductive dechlorination of halomethanes. There is no clear-cut separation between "polluters" and "clean-uppers" within the Basidiomycetes. Several genera, e.g. Bjerkandera, Hericium, Phlebia, and Trametes, produce significant amounts of chlorinated compounds but are also highly effective in metabolizing or biotransforming chlorinated pollutants.

Significant Biogenesis of Chlorinated Aromatics by Fungi in Natural Environments

Common wood- and forest litter-degrading fungi produce chlorinated anisyl metabolites. These compounds, which are structurally related to xenobiotic chloroaromatics, occur at high concentrations of approximately 75 mg of chlorinated anisyl metabolites kg of wood -1 or litter -1 in the environment. The widespread ability among common fungi to produce large amounts of chlorinated aromatic compounds in the environment makes us conclude that these kinds of compounds can no longer be considered to originate mainly from anthropogenic sources.