Protein kinase and HDAC inhibitors from the endophytic fungus Epicoccum nigrum

Discovery and Characterization of R/S-N-3-Cyanophenyl-N'-(6-tert-butoxycarbonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-4-yl)urea, a New Histone Deacetylase Class III Inhibitor Exerting Antiproliferative Activity against Cancer Cell Lines

A new series of N-aryl-N'-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-4-yl)ureas bearing an alkoxycarbonylamino group at the 6-position were synthesized and examined as putative anticancer agents targeting sirtuins in glioma cells. On the basis of computational docking combined to in vitro sirtuin 1/2 inhibition assays, we selected compound 18 [R/S-N-3-cyanophenyl-N'-(6-tert-butoxycarbonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-4-yl)urea] which displays a potent antiproliferative activity on various glioma cell types, assessed by quantitative videomicroscopy, eventually triggering senescence. The impact on normal glial cells was lower with a selectivity index of >10. Furthermore, human U373 and Hs683 glioblastoma cell lines served to demonstrate the inhibitory activity of 18 against histone deacetylase (HDAC) class III sirtuins 1 and 2 (SIRT1/2) by quantifying acetylation levels of histone and non-histone proteins. The translational potential of 18 was validated by an NCI-60 cell line screen and validation of growth inhibition of drug resistant cancer cell models. Eventually, the anticancer potential of 18 was validated in 3D glioblastoma spheroids and in vivo by zebrafish xenografts. In summary, compound 18 is the first representative of a new class of SIRT inhibitors opening new perspectives in the medicinal chemistry of HDAC inhibitors.

Construction of Nitrated Benzo[3.3.1]bicyclic Acetal/Ketal Core via Nitration of o-Carbonyl Allylbenzenes

Intramolecular annulation of o-carbonyl allylbenzenes was achieved to construct novel nitrated [6,6,6]tricycles having an acetal or ketal motif in good yields. The expeditious one-step nitration route provides 4 or 5 new bond formations, including 2 or 3 C-N bonds and 2 C-O bonds. The structural framework of benzobicycle [3.3.1] is confirmed by X-ray crystallographic analysis. A plausible mechanism is proposed.

Natural Compound Histone Deacetylase Inhibitors (HDACi): Synergy with Inflammatory Signaling Pathway Modulators and Clinical Applications in Cancer

The remarkable complexity of cancer involving multiple mechanisms of action and specific organs led researchers Hanahan and Weinberg to distinguish biological capabilities acquired by cancer cells during the multistep development of human tumors to simplify its understanding. These characteristic hallmarks include the abilities to sustain proliferative signaling, evade growth suppressors, resist cell death, enable replicative immortality, induce angiogenesis, activate invasion and metastasis, avoid immune destruction, and deregulate cellular energetics. Furthermore, two important characteristics of tumor cells that facilitate the acquisition of emerging hallmarks are tumor-promoting inflammation and genome instability. To treat a multifactorial disease such as cancer, a combination treatment strategy seems to be the best approach. Here we focus on natural histone deacetylase inhibitors (HDACi), their clinical uses as well as synergies with modulators of the pro-inflammatory transcription factor signaling pathways.

Cytotoxic 14-Membered Macrolides from a Mangrove-Derived Endophytic Fungus, Pestalotiopsis microspora

Seven new 14-membered macrolides, pestalotioprolides C (2), D-H (4-8), and 7-O-methylnigrosporolide (3), together with four known analogues, pestalotioprolide B (1), seiricuprolide (9), nigrosporolide (10), and 4,7-dihydroxy-13-tetradeca-2,5,8-trienolide (11), were isolated from the mangrove-derived endophytic fungus Pestalotiopsis microspora. Their structures were elucidated by analysis of NMR and MS data and by comparison with literature data. Single-crystal X-ray diffraction analysis was used to confirm the absolute configurations of 1, 2, and 10, while Mosher's method and the TDDFT-ECD approach were applied to determine the absolute configurations of 5 and 6. Compounds 3-6 showed significant cytotoxicity against the murine lymphoma cell line L5178Y with IC50 values of 0.7, 5.6, 3.4, and 3.9 μM, respectively, while compound 5 showed potent activity against the human ovarian cancer cell line A2780 with an IC50 value of 1.2 μM. Structure-activity relationships are discussed. Coculture of P. microspora with Streptomyces lividans caused a roughly 10-fold enhanced accumulation of compounds 5 and 6 compared to axenic fungal control.

A Series of Cinchona-Derived N-Oxide Phase-Transfer Catalysts: Application to the Photo-Organocatalytic Enantioselective α-Hydroxylation of β-Dicarbonyl Compounds

A series of cinchona-derived N-oxide asymmetric phase-transfer catalysts were synthesized and applied in the enantioselective photo-organocatalytic α-hydroxylation of β-keto esters and β-keto amides (23 examples) using molecular oxygen in excellent yields (up to 98%) and high enantioselectivities (up to 83% ee). These new catalysts could be recycled and reused six times for such a reaction with almost the original reactivity and enantioselectivity.

Non-canonical programmed cell death mechanisms triggered by natural compounds

Natural compounds are the fundament of pharmacological treatments and more than 50% of all anticancer drugs are of natural origins or at least derived from scaffolds present in Nature. Over the last 25 years, molecular mechanisms triggered by natural anticancer compounds were investigated. Emerging research showed that molecules of natural origins are useful for both preventive and therapeutic purposes by targeting essential hallmarks and enabling characteristics described by Hanahan and Weinberg. Moreover, natural compounds were able to change the differentiation status of selected cell types. One of the earliest response of cells treated by pharmacologically active compounds is the change of its morphology leading to ultra-structural perturbations: changes in membrane composition, cytoskeleton integrity, alterations of the endoplasmic reticulum, mitochondria and of the nucleus lead to formation of morphological alterations that are a characteristic of both compound and cancer type preceding cell death. Apoptosis and autophagy were traditionally considered as the most prominent cell death or cell death-related mechanisms. By now multiple other cell death modalities were described and most likely involved in response to chemotherapeutic treatment. It can be hypothesized that especially necrosis-related phenotypes triggered by various treatments or evolving from apoptotic or autophagic mechanisms, provide a more efficient therapeutic outcome depending on cancer type and genetic phenotype of the patient. In fact, the recent discovery of multiple regulated forms of necrosis and the initial elucidation of the corresponding cell signaling pathways appear nowadays as important tools to clarify the immunogenic potential of non-canonical forms of cell death induction.

New Fusaric Acid Derivatives from the Endophytic Fungus Fusarium oxysporum and Their Phytotoxicity to Barley Leaves

Chemical investigation of the endophytic fungus Fusarium oxysporum isolated from fruits of Drepanocarpus lunatus afforded eight new fusaric acid derivatives, fusaricates A-G, 1-7, and 10-hydroxy-11-chlorofusaric acid, 8, along with four known compounds. Their structures were elucidated by one- and two-dimensional NMR as well as MS data and by comparison with the literature. The absolute configurations of fusaricates C-E, 3-5, were determined using chiral GC-MS. Fusaricates A-G, 1-7, represent the first examples of fusaric acid linked to a polyalcohol moiety via an ester bond. All isolated fusaric acid derivatives 1-8 showed significant phytotoxicity to leaves of barley.

Epicochalasines A and B: Two Bioactive Merocytochalasans Bearing Caged Epicoccine Dimer Units from Aspergillus flavipes

Two bioactive merocytochalasans, epicochalasines A (1) and B (2), a new class of cytochalasans bearing unexpected scaffolds consisting of fused aspochalasin and epicoccine dimer moieties, were isolated from the liquid culture broth of Aspergillus flavipes. Both 1 and 2 possess a hendecacyclic 5/6/11/5/6/5/6/5/6/6/5 ring system containing an adamantyl cage and as many as 19 stereogenic centers; however, the fusion patterns of 1 and 2 differ greatly, thus resulting in different carbon skeletons. The absolute configurations of 1 and 2 were determined by X-ray diffraction and calculated ECD, respectively. The biogenetic pathways of 1 and 2 are proposed to involve Diels-Alder and nucleophilic addition reactions. Both 1 and 2 induced significant G2/M-phase cell-cycle arrest. Furthermore, we found that merocytochalasans induce apoptosis in leukemia cells through the activation of caspase-3 and the degradation of PARP.

Highly oxygenated chromones from mangrove-derived endophytic fungus Rhytidhysteron rufulum

Five highly oxygenated chromones, rhytidchromones A-E, were isolated from the culture broth of a mangrove-derived endophytic fungus, Rhytidhysteron rufulum, isolated from Thai Bruguiera gymnorrhiza. Their structures were determined by analysis of 1D and 2D NMR spectroscopic data. The structure of rhytidchromone A was further confirmed by single-crystal X-ray diffraction analysis. These compounds were evaluated for cytotoxicity against four cancer cell lines (MCF-7, Hep-G2, Kato-3 and CaSki). All compounds, except for rhytidchromone D, displayed cytotoxicity against Kato-3 cell lines with IC50 values ranging from 16.0 to 23.3μM, while rhytidchromones A and C were active against MCF-7 cells with IC50 values of 19.3 and 17.7μM, respectively.

Guignardones P-S, New Meroterpenoids from the Endophytic Fungus Guignardia mangiferae A348 Derived from the Medicinal Plant Smilax glabra

Four new meroterpenoids, guignardones P-S (1-4), and three known analogues (5-7) were isolated from the endophytic fungal strain Guignardia mangiferae A348. Their structures were elucidated on the basis of spectroscopic analysis and single crystal X-ray diffraction. All the isolated compounds were evaluated for their inhibitory effects on SF-268, MCF-7, and NCI-H460 human cancer cell lines. Compounds 2 and 4 exhibited weak inhibitions of cell proliferation against MCF-7 cell line.

4-Hydroxybenzoic acid derivatives as HDAC6-specific inhibitors modulating microtubular structure and HSP90α chaperone activity against prostate cancer

Histone deacetylase (HDAC)6 is a unique isoenzyme targeting specific substrates including α-tubulin and heat shock protein (HSP)90. HDAC6 is involved in protein trafficking and degradation, cell shape and migration. Deregulation of HDAC6 activity is associated with a variety of diseases including cancer leading to a growing interest for developing HDAC6 inhibitors. Here, we identified two new structurally related 4-hydroxybenzoic acids as selective HDAC6 inhibitors reducing proliferation, colony and spheroid formation as well as viability of prostate cancer cells. Both compounds strongly enhanced α-tubulin acetylation leading to remodeling of microtubular organization. Furthermore, 4-hydroxybenzoic acids decreased HSP90α regulation of the human androgen receptor in prostate cancer cells by increasing HSP90α acetylation levels. Collectively, our data support the potential of 4-hydroxybenzoic acid derivatives as HDAC6-specific inhibitors with anti-cancer properties.

Metabolites from Combretum dolichopetalum and its associated endophytic fungus Nigrospora oryzae--Evidence for a metabolic partnership

A new altersolanol derivative, 4-dehydroxyaltersolanol A (9), along with two known sesquiterpenoids, (S)-7'-hydroxyabscisic acid (7) and (S)-abscisic acid (8) were obtained from the endophytic fungus, Nigrospora oryzae, isolated from leaves of Combretum dolichopetalum. The host plant yielded six known compounds including ellagic acid (1), 3, 3', 4-tri-O-methylellagic acid (2), arjunolic acid (3), 4'-dihydrophaseic acid (4), echinulin (5) and arestrictin B (6). Close structural similarities with regard to compounds 4, 7 and 8 were observed between the metabolites from the host plant and those of the endophytic fungus. Furthermore compounds 5 and 6 are related to alkaloids isolated from N. oryzae previously thus stressing the notion that some of the isolated plant metabolites may actually be of fungal origin. The structures of the isolated compounds were established by spectroscopic methods including 1D, 2D NMR, MS, and by comparison with the literature. 4-Dehydroxyaltersolanol A (9) and 3, 3', 4-tri-O-methylellagic acid (2) showed cytotoxicity against L5178Y mouse lymphoma cells with IC50 values of 9.4 and 29.0 μM, respectively.

Pictet-Spengler reaction-based biosynthetic machinery in fungi

The Pictet-Spengler (PS) reaction constructs plant alkaloids such as morphine and camptothecin, but it has not yet been noticed in the fungal kingdom. Here, a silent fungal Pictet-Spenglerase (FPS) gene of Chaetomium globosum 1C51 residing in Epinephelus drummondhayi guts is described and ascertained to be activable by 1-methyl-L-tryptophan (1-MT). The activated FPS expression enables the PS reaction between 1-MT and flavipin (fungal aldehyde) to form "unnatural" natural products with unprecedented skeletons, of which chaetoglines B and F are potently antibacterial with the latter inhibiting acetylcholinesterase. A gene-implied enzyme inhibition (GIEI) strategy has been introduced to address the key steps for PS product diversifications. In aggregation, the work designs and validates an innovative approach that can activate the PS reaction-based fungal biosynthetic machinery to produce unpredictable compounds of unusual and novel structure valuable for new biology and biomedicine.

Eleganketal A, a highly oxygenated dibenzospiroketal from the marine-derived fungus Spicaria elegans KLA03

Eleganketal A (1), a naturally occurring aromatic polyketide possessing a rare highly oxygenated spiro[isobenzofuran-1,3'-isochroman] ring system, was isolated from the fungus Spicaria elegans KLA03 by culturing it in a modified mannitol-based medium. The structure of 1 including the absolute configuration was determined by combining spectroscopic analysis, synthesis of the racemic permethylated analogue, chiral-phase HPLC separation, and TDDFT-ECD analysis.