Nocathiacin, Thiazomycin, and Polar Analogs Are Highly Effective Agents against Toxigenic Clostridioides difficile

Clostridioides difficile is a commensal Gram-positive gut bacterium that causes C. difficile-associated diarrhea. Currently available antibacterial therapeutic treatment options are effective except for the repeated recurrences significantly burdening the health care system and causing mortality. The development of new therapeutic modalities including new effective antibiotics with a low rate of recurrence has been unpredictive and exceedingly challenging, requiring continued profiling of many new classes of antibiotics. Nocathiacins and thiazomycins are a class of thiazolyl peptides exhibiting potent and selective broad-spectrum Gram-positive activity including activity against the anaerobe C. difficile. These compounds showed MIC values of 0.015-0.06 μg/mL against C. difficile with more than 100-200-fold selectivity versus commensurate Gram-negative Bacteroides fragilis. Nocathiacin I and one of its analogs exhibited potent in vivo efficacy in the gold-standard hamster model of C. difficile infection, providing 100% protection in this lethal model at 6.25 mg/kg orally twice daily. The efficacy was corroborated by robust reduction of cecum C. difficile burden and proportionate exposure of the compounds in the cecum contents without any systemic absorption. In this paper, details of the results of in vitro, in vivo, pharmacodynamics, and pharmacokinetic studies have been described.

Isolation, structure elucidation, and biological activity of altersolanol P using Staphylococcus aureus fitness test based genome-wide screening

Bacteria continue to evade existing antibiotics by acquiring resistance by various mechanisms, leading to loss of antibiotic effectiveness. To avoid an epidemic from infections of incurable drug-resistant bacteria, new antibiotics with new modes of action are desperately needed. Using a genome-wide mechanism of action-guided whole cell screening approach based on antisense Staphylococcus aureus fitness test technology, we report herein the discovery of altersolanol P (1), a new tetrahydroanthraquinone from an unknown fungus from the Hypocreales isolated from forest litter collected in Puerto Rico. The structure was elucidated by high-resolution mass spectrometry and 2D NMR spectroscopy. Relative stereochemistry was established by NOESY correlations, and absolute configuration was deduced by the application of MPA ester-based methodology. Observed (1)H and (13)C NMR shifts were well aligned with the corresponding chemical shifts predicted by DFT calculations. Altersolanol P exhibited Gram-positive antibacterial activity (MIC range 1-8 μg/mL) and inhibited the growth of Gram-negative Haemophilus influenzae (MIC 2 μg/mL). The isolation, structure elucidation, and antibacterial activity of altersolanol P are described.

Isolation, structure elucidation, and antibacterial activity of methiosetin, a tetramic acid from a tropical sooty mold (Capnodium sp.)

Drug-resistant bacteria continue to make many existing antibiotic classes ineffective. In order to avoid a future epidemic from drug-resistant bacterial infections, new antibiotics with new modes of action are needed. In an antibiotic screening program for new drug leads with new modes of action using antisense Staphylococcus aureus Fitness Test screening, we discovered a new tetramic acid, methiosetin, from a tropical sooty mold, Capnodium sp. The fungus also produced epicorazine A, a known antibiotic. The structure and relative configuration of methiosetin was elucidated by 2D NMR and ESIMS techniques. Methiosetin and epicorazine A showed weak to modest antibacterial activity against S. aureus and Haemophilus influenzae. The isolation, structure elucidation, and antibacterial activity of both compounds are described.

Isolation, structure, and coccidiostat activity of coccidiostatin A

Coccidiosis is one of the more common and costly diseases in poultry that is caused by various Eimeria species. In our quest to discover coccidiostats from natural products, we discovered a microbial fermentation extract that exhibited in vivo anticoccidial activity. Fractionation of this extract led to the discovery of two potent antiprotozoals, emecorrugatin A (1) and coccidiostatin A (2). The former compound exhibited only in vitro activity, whereas the latter new compound exhibited in vivo activity against Eimeria species in chickens at 150 ppm dosed in chicken feed. The isolation, structure elucidation, relative configuration, and activity of coccidiostatin A (2) are described.

Identification of diverse microbial metabolites as potent inhibitors of HIV-1 Tat transactivation

HIV-1 Tat is one of six regulatory proteins that are required for viral replication and is an attractive target for the development of new anti-HIV agents. Screening of microbial extracts using a whole cell Tat-dependent transactivation assay, which guided the separation of the active broths, led to the identification of five structurally diverse classes (M(R) range 232-1126) of natural products. These include i) three sesquiterpenoids, namely, sporogen-AO1, petasol, and 6-dehydropetasol, ii) two resorcylic 14-membered lactones, namely monorden and monocillin IV, iii) a ten-membered lactone, iv) a quinoline and quinoxiline bicyclic octadepsipeptides, namely echinomycin and UK-63598, and v) a cyclic heptapeptide, ternatin. These compounds displayed varying degrees of potencies with IC50 values ranging from 0.0002 to 100 microM. The most active compound was the quinoxiline bicyclic octadepsipeptides, UK-63598, which inhibited Tat-dependent transactivation with an IC50 value of 0.2 nM and exhibited a 100-fold therapeutic window with respect to toxicity. In a single-cycle antiviral assay, UK-6358 inhibited viral replication with an IC50 value of 0.5 nM; however, it appeared to be equally toxic at that concentration. Monocillin IV was significantly less active (Tat transactivation inhibitory IC50 of 5 microM) but was not toxic at 100 microM in an equivalent cytotoxicity assay. The compound exhibited antiviral activity with an IC50 value of 6.2 microM in the single-cycle antiviral assay and a sixfold therapeutic window. Details of the isolation, fermentation, and biological activities of these structurally diverse natural products are described.

Isolation and structures of novel fungal metabolites as chemokine receptor (CCR2) antagonists

The chemokine receptor, CCR2, is predominantly expressed on monocytes/macrophages, and on a subset of memory T cells. It binds to several CC type chemokines of the monocyte chemoattractant protein (MCP) family of which MCP-1 exhibits the highest affinity. CCR2/MCP-1 expression/association in monocyte/macrophage/T cells has been associated with inflammatory processes such as rheumatoid arthritis, multiple sclerosis and atherosclerosis. Neutralization of CCR2 with either a peptide or receptor antagonist results in the prevention of joint swelling in rodent models of arthritis. In this paper, bioassay-guided discovery of CCR2 receptor antagonists derived from natural product extracts are reported. These antagonists belong to two main classes exemplified by bisthiodiketopiperazines and cytochalasins. Six compounds, including emestrin, two new emestrin analogs, and chaetomin represent the first group of compounds. These compounds inhibited the binding of MCP-1 to CCR2 (CHO membrane) with IC50 values of 0.8 to 9 microM and exhibited good activity in a whole cell assay using MCP-1 and human monocytes with IC50's ranging from 4-9 microM. Cytochalasins A and B represented the second group and inhibited the binding activity with IC50 values of 5 and 188 microM, respectively. This is the first report of natural product antagonists of the CCR2 receptor.

New fungal metabolite geranylgeranyltransferase inhibitors with antifungal activity

Geranylgeranyltransferase I (GGTase I) catalyzes the post-translational transfer of lyophilic diterpenoid geranylgeranyl to the cysteine residue of proteins terminating with a CaaX motif such as Rho1p and Cdc42p. It has been shown that GGTase I activity is essential for viability of Saccharomyces cerevisiae and hence its inhibition is a potential antifungal target. From natural product screening, a number of azaphilones including one novel analog were isolated as broad-spectrum inhibitors of GGTase I. Isolation, structure elucidation, GGTase I inhibitory activities and antifungal activities of these compounds are described.

Discovery of structurally diverse natural product antagonists of chemokine receptor CXCR3

The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC50 ranging 0.1-41 microM) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using 125I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC50 of 0.1 microM. Roselipins 2A, 2B and 1A showed IC50 values of 14.6, 23.5, and 41 microM, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC50 values of 2.1, 0.47 and 3 microM, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC50 of 0.67 microM.

Isolation and structure of antagonists of chemokine receptor (CCR5)

Human CCR5 is a G-coupled receptor that binds to the envelope protein gp120 and CD4 and mediates the HIV-1 viral entry into the cells. The blockade of this binding by a small molecule receptor antagonist could lead to a new mode of action agent for HIV-1 and AIDS. Screening of natural product extracts led to the identification of anibamine (1), a novel pyridine quaternary alkaloid as a TFA salt, from Aniba sp.; ophiobolin C from fermentation extracts of fungi Mollisia sp.; and 19,20-epoxycytochalasin Q from Xylaria sp. Formation of the TFA salt of anibamine is plausibly an artifact of the isolation. The identity of the natural counterion is unknown. Anibamine.TFA competed for the binding of 125I-gp120 to human CCR5 with an IC50 of 1 microM. Ophiobolin C and 19,20-epoxycytochalasin Q exhibited binding IC50) values of 40 and 60 microM, respectively.

Isolation, structure, absolute stereochemistry, and HIV-1 integrase inhibitory activity of integrasone, a novel fungal polyketide

HIV-1 integrase is a critical enzyme for replication of HIV, and its inhibition is one of the most promising new drug targets for anti-retroviral therapy with potentially significant advantages over existing therapies. In this Note, the isolation, structure elucidation, and absolute stereochemistry of integrasone, a novel polyketide, derived from an unidentified sterile mycelium have been described. This bicyclic dihydroxy epoxide lactone inhibited the strand transfer reaction of HIV-1 integrase with an IC(50) of 41 microM.

Citrafungins A and B, Two New Fungal Metabolite Inhibitors of GGTase I with Antifungal Activity

[structure: see text] Screening of natural products extracts led to the discovery of citrafungins A and B, two new fungal metabolites of the alkylcitrate family that are inhibitors of GGTase I of various pathogenic fungal species with IC(50) values of 2.5-15 microM. These compounds exhibited antifungal activities with MIC values of 0.40-55 microM. The isolation, structure elucidation, relative and absolute stereochemistry, and biological activities of citrafungins are described.

Isolation, structure, and HIV-1-integrase inhibitory activity of structurally diverse fungal metabolites

HIV-1 integrase is a critical enzyme for replication of HIV, and its inhibition is one of the most promising new drug strategies for anti-retroviral therapy, with potentially significant advantages over existing therapies. In this report, a series of HIV-1 inhibitors isolated from the organic extract of fermentations from terrestrial fungi is described. These fungal species, belonging to a variety of genera, were collected from throughout the world following the strict guidelines of Rio Convention on Biodiversity. The polyketide- and terpenoid-derived inhibitors are represented by two naphthoquinones, a biphenyl and two triphenyls, a benzophenone, four aromatics with or without catechol units, a linear aliphatic terpenoid, a diterpenoid, and a sesterterpenoid. These compounds inhibited the coupled and strand-transfer reaction of HIV-1 integrase with an IC(50) value of 0.5-120 micro M. The bioassay-directed isolation, structure elucidation, and HIV-1 inhibitory activity of these compounds are described.

Integracides: tetracyclic triterpenoid inhibitors of HIV-1 integrase produced by Fusarium sp

HIV-1 integrase is a critical enzyme in the replication of HIV-1. It is absent in the host cells and therefore is a good target for treatment of HIV-1 infections. Integracides are members of the tetracyclic triterpenoids family that were isolated from the fermentation broth of a Fusarium sp. Integracide A, a sulfated ester, exhibited significant inhibitory activity against strand transfer reaction of HIV-1 integrase. The discovery, structure elucidation including single crystal X-ray structure and HIV-1 inhibitory activity of these compounds are described.

Isolation, structure, and HIV-1 integrase inhibitory activity of Cytosporic acid, a fungal metabolite produced by a Cytospora sp

HIV-1 integrase is a critical enzyme for replication of HIV, and its inhibition has the potential to lead to an anti-retroviral therapy that has advantages over existing therapies. Cytosporic acid (1) is a polyketide-derived novel natural product that was isolated from a fermentation broth of the filamentous fungus Cytospora sp. collected from Puerto Rico. It inhibited strand transfer reaction of HIV-1 integrase with an IC(50) of 20 microM. The isolation, structure elucidation, relative stereochemistry, and activity of 1 are described.

Isolation, Structure and HIV-1 Integrase Inhibitory Activity of Exophillic Acid, a Novel Fungal Metabolite from Exophiala pisciphila

HIV-1 integrase is one of the three enzymes that are critical for replication and spread of HIV and its inhibition is one of the most promising new drug targets for anti-retroviral therapy with potential advantage over existing therapies. This paper describes the isolation and structure elucidation of exophillic acid, a novel dimeric 2,4-dihydroxy alkyl benzoic acid, derived from Exophiala pisciphila, a fungus isolated from a soil sample collected in Georgia, USA. Exophillic acid (1) and aquastatin A (2), a related compound, inhibited the strand transfer reaction of HIV-1 integrase with IC50 values of 68 and 50 microM, respectively.

Integramides A and B, two novel non-ribosomal linear peptides containing nine C(alpha)-methyl amino acids produced by fungal fermentations that are inhibitors of HIV-1 integrase

[structure: see text]. Integramides A and B are two novel 16-mer linear peptides rich in C(alpha)-methyl amino acids that were isolated from fungal extracts of Dendrodochium sp. by employing a bioassay-guided isolation procedure using recombinant HIV-1 integrase. The structure and stereochemistry were elucidated by a combination of 2D NMR and ESI- and FAB-MS including MS/MS studies and by Marfey's method. Integramides A and B inhibited the coupled reaction of HIV-1 integrase with IC50 values of 17 and 10 microM, respectively.

Kampanols: novel Ras farnesyl-protein transferase inhibitors from Stachybotrys kampalensis

Farnesyl-protein transferase (FPTase) is a critical enzyme that participates in the post-translational modification of the Ras protein. Inhibitors of this enzyme have the potential of being novel anticancer agents for tumors in which the ras oncogene is found mutated and contributes to cell transformation. Continued screening of natural product extracts led to the isolation of kampanols, which are novel and specific inhibitors of FPTase. The most active kampanols exhibited IC50 values between 7 to 13 microM against human recombinant FPTase. The isolation, structure determination, and biological activity of these compounds are described.

Apicidin: a novel antiprotozoal agent that inhibits parasite histone deacetylase

A novel fungal metabolite, apicidin [cyclo(N-O-methyl-L-tryptophanyl-L -isoleucinyl-D-pipecolinyl-L-2-amino-8-oxodecanoyl)], that exhibits potent, broad spectrum antiprotozoal activity in vitro against Apicomplexan parasites has been identified. It is also orally and parenterally active in vivo against Plasmodium berghei malaria in mice. Many Apicomplexan parasites cause serious, life-threatening human and animal diseases, such as malaria, cryptosporidiosis, toxoplasmosis, and coccidiosis, and new therapeutic agents are urgently needed. Apicidin's antiparasitic activity appears to be due to low nanomolar inhibition of Apicomplexan histone deacetylase (HDA), which induces hyperacetylation of histones in treated parasites. The acetylation-deacetylation of histones is a thought to play a central role in transcriptional control in eukaryotic cells. Other known HDA inhibitors were also evaluated and found to possess antiparasitic activity, suggesting that HDA is an attractive target for the development of novel antiparasitic agents.

Discovery of novel secondary metabolites from fungi—is it really a random walk through a random forest?

Twenty-nine Nodulisporium strains isolated from material obtained worldwide were found to produce secondary metabolites as measured by HPLC. Analysis of incubation conditions resulted in the clustering of three solid fermentation conditions and the clustering of five liquid fermentation conditions. Coverage of 69% of the products produced under eight fermentation conditions could be accomplished if one medium from each cluster was used. Subdivision of the Nodulisporium strains into groups based upon morphological similarity allows for a minimization of the rediscovery of common metabolites. Rare metabolites (HPLC peaks) appeared to occur as random events. However, within the set of cultures that produced the mean or greater than the mean number of metabolites, were found all of the producers of rarer metabolites. Key words: Nodulisporium, fermentation screening, endophytes.

Zaragozic acids D and D2: potent inhibitors of squalene synthase and of Ras farnesyl-protein transferase

Two new zaragozic acids, D and D2, have been isolated from the keratinophilic fungus Amauroascus niger. Zaragozic acids D [4] and D2 [5] are related to the previously described zaragozic acids A [1], B [2], and C [3] and are potent inhibitors of squalene synthase. Furthermore, all the zaragozic acids (A, B, C, D, and D2) are also active against farnesyl transferase. Zaragozic acids D and D2 inhibit farnesyl transferase with IC50 values of 100 nM, while zaragozic acids A and B are less potent.

Microfungi from Carpinus caroliniana

The microfungal flora and community structure of the bark of Carpinus caroliniana is described as perceived by a direct isolation method. Twenty-four bark discs were removed from 10 trees at five different sites in New Jersey and West Virginia and applied to three different isolation media. From 1200 bark discs from 50 trees, 155 species of fungi were isolated. The overall recovery rate was 11.5 species/tree. A medium with cycloheximide gave the highest species recovery rates and isolated the highest percentage of all the species recovered. A medium of malt–yeast extract gave the most isolates but lowest species recovery rate. Eleven of the 12 dominant species were preferentially isolated on one of the three isolation media. The community structure of the fungi recovered from Carpinus bark exhibited the typical dominance–diversity curve that has been reported for other saprobic fungal communities. Generally, the floristic composition was similar to the bark of other tree species previously studied in temperate deciduous forests. The total number of isolates was dominated by a few species of ubiquitous epiphytic taxa, but a large percentage of the species recovered appeared either at a single site or on a single tree. Sterile isolates accounted for 39% of the species and Coelomycetes for 13% of the species. The sites from West Virginia had a significantly higher recovery rate of species per tree than the New Jersey sites. In a search for fungi for potential biotechnological applications, bark is an easily utilized and rich resource. Simple isolation methods yield several ecological groups of fungi, including terrestrial epiphytes, soil decomposers, endophytes, entomopathogenic fungi, Ingoldian Hyphomycetes, and decomposer Basidomycetes. Key words: bark, ironwood, isolation methods, microbial diversity.