Ophiobolin A induces paraptosis-like cell death in human glioblastoma cells by decreasing BKCa channel activity

Glioblastoma multiforme (GBM) is the most lethal and common malignant human brain tumor. The intrinsic resistance of highly invasive GBM cells to radiation- and chemotherapy-induced apoptosis accounts for the generally dismal treatment outcomes. This study investigated ophiobolin A (OP-A), a fungal metabolite from Bipolaris species, for its promising anticancer activity against human GBM cells exhibiting varying degrees of resistance to proapoptotic stimuli. We found that OP-A induced marked changes in the dynamic organization of the F-actin cytoskeleton, and inhibited the proliferation and migration of GBM cells, likely by inhibiting big conductance Ca(2+)-activated K(+) channel (BKCa) channel activity. Moreover, our results indicated that OP-A induced paraptosis-like cell death in GBM cells, which correlated with the vacuolization, possibly brought about by the swelling and fusion of mitochondria and/or the endoplasmic reticulum (ER). In addition, the OP-A-induced cell death did not involve the activation of caspases. We also showed that the expression of BKCa channels colocalized with these two organelles (mitochondria and ER) was affected in this programmed cell death pathway. Thus, this study reveals a novel mechanism of action associated with the anticancer effects of OP-A, which involves the induction of paraptosis through the disruption of internal potassium ion homeostasis. Our findings offer a promising therapeutic strategy to overcome the intrinsic resistance of GBM cells to proapoptotic stimuli.

Bioactive sesterterpenes and triterpenes from marine sponges: occurrence and pharmacological significance

Marine ecosystems (>70% of the planet's surface) comprise a continuous resource of immeasurable biological activities and immense chemical entities. This diversity has provided a unique source of chemical compounds with potential bioactivities that could lead to potential new drug candidates. Many marine-living organisms are soft bodied and/or sessile. Consequently, they have developed toxic secondary metabolites or obtained them from microorganisms to defend themselves against predators [1]. For the last 30-40 years, marine invertebrates have been an attractive research topic for scientists all over the world. A relatively small number of marine plants, animals and microbes have yielded more than 15,000 natural products including numerous compounds with potential pharmaceutical potential. Some of these have already been launched on the pharmaceutical market such as Prialt (ziconotide; potent analgesic) and Yondelis (trabectedin or ET-743; antitumor) while others have entered clinical trials, e.g., alpidin and kahalalide F. Amongst the vast array of marine natural products, the terpenoids are one of the more commonly reported and discovered to date. Sesterterpenoids (C(25)) and triterpenoids (C(30)) are of frequent occurrence, particularly in marine sponges, and they show prominent bioactivities. In this review, we survey sesterterpenoids and triterpenoids obtained from marine sponges and highlight their bioactivities.

Free fatty acid receptor GPR120 is highly expressed in enteroendocrine K cells of the upper small intestine and has a critical role in GIP secretion after fat ingestion

Gastric inhibitory polypeptide (GIP) is an incretin secreted from enteroendocrine K cells in response to meal ingestion. Recently free fatty acid receptor G protein-coupled receptor (GPR) 120 was identified as a lipid sensor involved in glucagon-like peptide-1 secretion. However, Gpr 120 gene expression and its role in K cells remain unclear, partly due to difficulties in separation of K cells from other intestinal epithelial cells. In this study, we purified K cells using GIP-green fluorescent protein (GFP) knock-in mice, in which K cells can be visualized by GFP fluorescence. GFP-positive cells (K cells) were observed in the small intestine but not in the stomach and colon. K cell number and GIP content in K cells were significantly higher in the upper small intestine than those in the lower small intestine. We also examined the expression levels of several free fatty acid receptors in K cells. Among free fatty acid receptors, GPR120 was highly expressed in the K cells of the upper small intestine compared with the lower small intestine. To clarify the role of GPR120 on K cells in vivo, we used GPR120-deficient mice (GPR120(-/-)). GPR120(-/-) exhibited significantly lower GIP secretion (75% reduction, P < .01) after lard oil ingestion compared with that in wild-type mice. Consistently, pharmacological inhibition of GPR120 with grifolic acid methyl ether in wild-type mice significantly attenuated lard oil-induced GIP secretion. In conclusion, GPR120 is expressed abundantly in K cells of the upper small intestine and plays a critical role in lipid-induced GIP secretion.

Sesquiterpene dimer (DSF-52) from Artemisia argyi inhibits microglia-mediated neuroinflammation via suppression of NF-κB, JNK/p38 MAPKs and Jak2/Stat3 signaling pathways

Microglia-involved neuroinflammation is thought to promote brain damage in various neurodegenerative disorders. Therefore, novel therapeutics suppressing microglia over-activation could prove useful for neuroprotection in inflammation-mediated neurodegenerative diseases. DSF-52 is a novel sesquiterpene dimer compound isolated from medical plant Artemisia argyi by our group. In this study, we investigated whether DSF-52 inhibited the neuroinflammatory responses in lipopolysaccharide (LPS)-activated microglia. Our findings showed that DSF-52 inhibited the production of nitric oxide (NO), prostaglandin E2 (PGE2), tumor necrosis factor-α (TNF-α), as well as mRNA expression of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), interleukin-1β (IL-1β), granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage inflammatory protein-1α (MIP-1α) in LPS-activated BV-2 microglia. Moreover, DSF-52 markedly up-regulated mRNA levels of anti-inflammatory cytokine IL-10. Mechanism study indicated that DSF-52 suppressed Akt/IκB/NF-κB inflammation pathway against LPS treatment. Also, DSF-52 down-regulated the phosphorylation levels of JNK and p38 MAPKs, but not ERK. Furthermore, DSF-52 blocked Jak2/Stat3 dependent inflammation pathway through inhibiting Jak2 and Stat3 phosphorylation, as well as Stat3 nuclear translocation. We concluded that the inhibitory ability of DSF-52 on microglia-mediated neuroinflammation may offer a novel neuroprotective modality and could be potentially useful in inflammation-mediated neurodegenerative diseases.

Novel bacterial metabolite merochlorin A demonstrates in vitro activity against multi-drug resistant methicillin-resistant Staphylococcus aureus

Background

We evaluated the in vitro activity of a merochlorin A, a novel compound with a unique carbon skeleton, against a spectrum of clinically relevant bacterial pathogens and against previously characterized clinical and laboratory Staphylococcus aureus isolates with resistance to numerous antibiotics.

Methods

Merochlorin A was isolated and purified from a marine-derived actinomycete strain CNH189. Susceptibility testing for merochlorin A was performed against previously characterized human pathogens using broth microdilution and agar dilution methods. Cytotoxicity was assayed in tissue culture assays at 24 and 72 hours against human HeLa and mouse sarcoma L929 cell lines.

Results

The structure of as new antibiotic, merochlorin A, was assigned by comprehensive spectroscopic analysis. Merochlorin A demonstrated in vitro activity against Gram-positive bacteria, including Clostridium dificile, but not against Gram negative bacteria. In S. aureus, susceptibility was not affected by ribosomal mutations conferring linezolid resistance, mutations in dlt or mprF conferring resistance to daptomycin, accessory gene regulator knockout mutations, or the development of the vancomycin-intermediate resistant phenotype. Merochlorin A demonstrated rapid bactericidal activity against MRSA. Activity was lost in the presence of 20% serum.

Conclusions

The unique meroterpenoid, merochlorin A demonstrated excellent in vitro activity against S. aureus and C. dificile and did not show cross-resistance to contemporary antibiotics against Gram positive organisms. The activity was, however, markedly reduced in 20% human serum. Future directions for this compound may include evaluation for topical use, coating biomedical devices, or the pursuit of chemically modified derivatives of this compound that retain activity in the presence of serum.

Cytotoxic metabolites from an Indonesian sponge Lendenfeldia sp

The lipid extract of an Indonesian Lendenfeldia sp. sponge inhibited hypoxia-induced hypoxia-inducible factor-1 (HIF-1) activation in T47D breast tumor cells. Chromatographic separation yielded the new substituted naphthalene dimer 1, the new furanolipid 2, and three known homoscalarane sesterterpenes, 3-5. Compounds 1 and 3-5 inhibited hypoxia-induced HIF-1 activation (IC50 values: 0.64-6.9 microM), but also reduced the viability of T47D and MDA-MB-231 breast tumor cells. Compound 4 was the most potent and showed a unique tumor cell line selectivity in the NCI 60-cell line panel. The general cytotoxicity of these compounds precluded their further consideration as HIF-1 inhibitors.

The Biological Activities of Sesterterpenoid-Type Ophiobolins

Ophiobolins (Ophs) are a group of tricarbocyclic sesterterpenoids whose structures contain a tricyclic 5-8-5 carbotricyclic skeleton. Thus far, 49 natural Ophs have been reported and assigned into A-W subgroups in order of discovery. While these sesterterpenoids were first characterized as highly effective phytotoxins, later investigations demonstrated that they display a broad spectrum of biological and pharmacological characteristics such as phytotoxic, antimicrobial, nematocidal, cytotoxic, anti-influenza and inflammation-promoting activities. These bioactive molecules are promising drug candidates due to the developments of their anti-proliferative activities against a vast number of cancer cell lines, multidrug resistance (MDR) cells and cancer stem cells (CSCs). Despite numerous studies on the biological functions of Ophs, their pharmacological mechanism still requires further research. This review summarizes the chemical structures, sources, and biological activities of the oph family and discusses its mechanisms and structure-activity relationship to lay the foundation for the future developments and applications of these promising molecules.

Ophiobolins from the Mangrove Fungus Aspergillus ustus

Seven new ophiobolins (1-5, 12, and 14) along with the 11 known analogues (6-11, 13, 15-18) were isolated from the ethyl acetate extracts of the liquid and solid cultures of the mangrove fungus Aspergillus ustus 094102. The structures including the absolute configurations of the seven new compounds were elucidated by spectroscopic analysis, chemical methods, and quantum ECD calculations. Compounds 4-8 and 11-15 showed cytotoxicities against the G3K, MCF-7, MD-MBA-231, MCF/Adr, A549, and HL-60 human cancer cell lines with the IC₅₀ values ranging from 0.6 to 9.5 μM.

Defense sesterterpenoid lactones from Leucosceptrum canum

Ten sesterterpenoids, leucosceptroids E-N (1-10), possessing an α,β-unsaturated γ-lactone moiety, were isolated from the leaves and flowers of a woody Labiatae, Leucosceptrum canum. Their structures including relative stereochemistry were determined by comprehensive 1D and 2D NMR, MS, and in the case of 1 and 10, by single crystal X-ray diffraction analyses. This class of unique plant terpenoids was designated as leucosceptrane sesterterpenoids (=leucosceptroids). The potent antifeedant activity of the most abundant compound, leucosceptroid G (3), and a representative compound, leucosceptroid N (10), against the generalist plant-feeding insect Helicoverpa armigera suggested that they might also be defense compounds of L. canum against insects.

Hippolides A-H, acyclic manoalide derivatives from the marine sponge Hippospongia lachne

Eight new acyclic manoalide-related sesterterpenes, hippolides A-H (1-8), together with two known manoalide derivatives, (6E)-neomanoalide (9) and (6Z)-neomanoalide (10), were isolated from the South China Sea sponge Hippospongia lachne. The absolute configurations of 1-8 were established by the modified Mosher's method and CD data. Compound 1 exhibited cytotoxicity against A549, HeLa, and HCT-116 cell lines with IC50 values of 5.22×10(-2), 4.80×10(-2), and 9.78 μM, respectively. Compound 1 also showed moderate PTP1B inhibitory activitiy with an IC50 value of 23.81 μM, and compound 2 showed moderate cytotoxicity against the HCT-116 cell line and PTP1B inhibitory activity with IC50 values of 35.13 and 39.67 μM, respectively. In addition, compounds 1 and 5 showed weak anti-inflammatory activity, with IC50 values of 61.97 and 40.35 μM for PKCγ and PKCα, respectively.

Ophiobolin-Type Sesterterpenoids from the Mangrove Endophytic Fungus Aspergillus sp. ZJ-68

Eleven new ophiobolin-type sesterterpenoids, asperophiobolins A-K (1-11), along with 12 known analogues (12-23) were isolated from the cultures of the mangrove endophytic fungus Aspergillus sp. ZJ-68. The structures of the new compounds were elucidated through spectroscopic analyses, and their absolute configurations were assigned by a combination of Mo₂(AcO)₄-induced electronic circular dichroism spectra and quantum chemical calculations. Asperophiobolins A-D (1-4) represent the first examples possessing a five-membered lactam unit between C-5 and C-21 in ophiobolin derivatives. In the bioactivity assays, compounds 8-10 and 14-17 exhibited inhibitory effects on lipopolysaccharide-induced nitric oxide production in RAW 264.7 macrophage cells with IC₅₀ values ranging from 9.6 to 25 μM, and compound 8 was found to show comparable inhibition of Mycobacterium tuberculosis protein tyrosine phosphatase B with an IC₅₀ value of 19 μM.

An antimicrobial guanidine-bearing sesterterpene from the cultured cyanobacterium Scytonema sp

Scytoscalarol (1), a antimicrobial sesterterpene bearing a guanidino group, was isolated from the cultured cyanobacterium Scytonema sp. (UTEX 1163) by bioassay-guided fractionation. The chemical structure was determined by spectroscopic analysis including MS and 1D and 2D NMR. Scytoscalarol (1) showed antimicrobial activities against Bacillus anthracis, Staphylococcus aureus, Escherichia coli, Candida albicans, and Mycobacterium tuberculosis with MIC values in the range from 2 to 110 microM.

Fungal metabolite ophiobolin A as a promising anti-glioma agent: In vivo evaluation, structure-activity relationship and unique pyrrolylation of primary amines

Glioblastoma, the most common form of malignant primary brain tumor, is characterized by resistance to apoptosis, which is largely responsible for the low effectiveness of the classical chemotherapeutic approaches based on apoptosis induction in cancer cells. Previously, a fungal secondary metabolite ophiobolin A was found to have significant activity against apoptosis-resistant glioblastoma cells through the induction of a non-apoptotic cell death, thus, offering an innovative strategy to combat this type of cancer. The current work describes the results of a preliminary evaluation of ophiobolin A in an in vivo glioblastoma model and its chemical derivatization to establish first synthetically generated structure-activity relationship. The synthetic work has also led to the discovery of a unique reaction of ophiobolin A with primary amines suggesting the possibility of pyrrolylation of lysine residues on its intracellular target protein(s).

Bio-activity and dereplication-based discovery of ophiobolins and other fungal secondary metabolites targeting leukemia cells

The purpose of this study was to identify and characterize fungal natural products (NPs) with in vitro bioactivity towards leukemia cells. We based our screening on a combined analytical and bio-guided approach of LC-DAD-HRMS dereplication, explorative solid-phase extraction (E-SPE), and a co-culture platform of CLL and stromal cells. A total of 289 fungal extracts were screened and we tracked the activity to single compounds in seven of the most active extracts. The novel ophiobolin U was isolated together with the known ophiobolins C, H, K as well as 6-epiophiobolins G, K and N from three fungal strains in the Aspergillus section Usti. Ophiobolins A, B, C and K displayed bioactivity towards leukemia cells with induction of apoptosis at nanomolar concentrations. The remaining ophiobolins were mainly inactive or only slightly active at micromolar concentrations. Dereplication of those ophiobolin derivatives possessing different activity in combination with structural analysis allowed a correlation of the chemical structure and conformation with the extent of bioactivity, identifying the hydroxy group at C3 and an aldehyde at C21, as well as the A/B-cis ring structure, as indispensible for the strong activity of the ophiobolins. The known compounds penicillic acid, viridicatumtoxin, calbistrin A, brefeldin A, emestrin A, and neosolaniol monoacetate were identified from the extracts and also found generally cytotoxic.

Scalarane sesterterpenoids: semisynthesis and biological activity

Aiming to improve the potency and selectivity of scalarane sesterterpenoids, a series of natural and semisynthetic analogues, derived from the cytotoxic naturally abundant sesterterpene heteronemin (1), were evaluated for their in vitro antimicrobial and cytotoxic properties. The new sesterterpenes 16-O-methylsesterstatin 4 (6c), 17, 24-dihydroheteronemin (7a), 16, 25-deacetoxy-17, 24-dihydroheteronemin (7b), and 16-deacetoxy-25-methoxy-17, 24-dihydroheteronemin (7c) were structurally defined via physical data analyses. Scalarane sesterterpenes possessing an unsaturated 1,4-dialdehyde moiety showed potent inhibitory activity against methicillin-resistant Staphylococcus aureus at concentrations that are not significantly cytotoxic to mammalian cells. The structural features for the cytotoxicity of scalarane sesterterpenoids are discussed.

Bioactive scalaranes from the Thai sponge Hyrtios gumminae

Chemical investigation of the Thai sponge Hyrtios gumminae collected from Similan Island in the Andaman Sea, Thailand, yielded four new sesterterpenoids, similan A (1), 12beta,20-dihydroxy-16beta-acetoxy-17-scalaren-19,20-olide (2), 12beta-acetoxy-20-hydroxy-17-scalaren-19,20-olide (3), and 12beta,16alpha,20-trihydroxy-17-scalaren-19,20-olide (4), together with seven known compounds. The structures of these new compounds were elucidated on the basis of their spectroscopic data and chemical transformations. Some of the isolated compounds were tested for their cytotoxic activity.

Bioactive Natural Products of Marine Sponges from the Genus Hyrtios

Marine sponges are known as a rich source for novel bioactive compounds with valuable pharmacological potential. One of the most predominant sponge genera is Hyrtios, reported to have various species such as Hyrtios erectus, Hyrtios reticulatus, Hyrtios gumminae, Hyrtios communis, and Hyrtios tubulatus and a number of undescribed species. Members of the genus Hyrtios are a rich source of natural products with diverse and valuable biological activities, represented by different chemical classes including alkaloids, sesterterpenes and sesquiterpenes. This review covers the literature until June 2016, providing a complete survey of all compounds isolated from the genus Hyrtios with their corresponding biological activities whenever applicable.

Bioactive terpenes from Spongia officinalis

The terpene metabolite pattern of Mediterranean Spongia officinalis was chemically investigated. This study resulted in the isolation of a series of sesterterpenes and C21 furanoterpenes, according to the literature data on this sponge. Four new oxidized minor metabolites (compounds 1, 2, 3, and 4) were isolated along with six known compounds of the furospongin series (compounds 5-8, 9, and 10) and three scalarane sesterterpenes (compounds 11-13). Interestingly, tetrahydrofurospongin-2 (6) and dihydrofurospongin-2 (7), which were among the main metabolites, induced biofilm formation by Escherichia coli. All compounds isolated were also assayed for antibacterial and antifungal properties.

New Ophiobolin Derivatives from the Marine Fungus Aspergillus flocculosus and Their Cytotoxicities against Cancer Cells

Five new sesterterpenes, 14,15-dehydro-6-epi-ophiobolin K (1), 14,15-dehydro- ophiobolin K (2), 14,15-dehydro-6-epi-ophiobolin G (3), 14,15-dehydro-ophiobolin G (4) and 14,15-dehydro-(Z)-14-ophiobolin G (5), together with four known ophiobolins (6–9) were isolated from the marine fungus Aspergillus flocculosus derived from the seaweed Padina sp. collected in Vietnam. The five new ophiobolins were first isolated as ophiobolin derivatives consisting of a fully unsaturated side chain. Their structures were elucidated via spectroscopic methods including 1D, 2D NMR and HR-ESIMS. The absolute configurations were determined by the comparison of chemical shifts and optical rotation values with those of known ophiobolins. All compounds (1–9) were then evaluated for their cytotoxicity against six cancer cell lines, HCT-15, NUGC-3, NCI-H23, ACHN, PC-3 and MDA-MB-231. All the compounds showed potent cytotoxicity with GI₅₀ values ranging from 0.14 to 2.01 μM.

Phorbaketal A, Isolated from the Marine Sponge Phorbas sp., Exerts Its Anti-Inflammatory Effects via NF-κB Inhibition and Heme Oxygenase-1 Activation in Lipopolysaccharide-Stimulated Macrophages

Marine sponges harbor a range of biologically active compounds. Phorbaketal A is a tricyclic sesterterpenoid isolated from the marine sponge Phorbas sp.; however, little is known about its biological activities and associated molecular mechanisms. In this study, we examined the anti-inflammatory effects and underlying molecular mechanism of phorbaketal A in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. We found that phorbaketal A significantly inhibited the LPS-induced production of nitric oxide (NO), but not prostaglandin E₂, in RAW 264.7 cells. Further, phorbaketal A suppressed the expression of inducible NO synthase at both the mRNA and protein levels. In addition, phorbaketal A reduced the LPS-induced production of inflammatory cytokines such as tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and monocyte chemotactic protein-1. Treatment with phorbaketal A inhibited the transcriptional activity of nuclear factor-kappaB (NF-κB), a crucial signaling molecule in inflammation. Moreover, phorbaketal A up-regulated the expression of heme oxygenase-1 (HO-1) in LPS-stimulated RAW 264.7 cells. These data suggest that phorbaketal A, isolated from the marine sponge Phorbas sp., inhibits the production of inflammatory mediators via down-regulation of the NF-κB pathway and up-regulation of the HO-1 pathway.

Ophiobolin A, a sesterterpenoid fungal phytotoxin, displays higher in vitro growth-inhibitory effects in mammalian than in plant cells and displays in vivo antitumor activity

Ophiobolin A, a sesterterpenoid produced by plant pathogenic fungi, was purified from the culture extract of Drechslera gigantea and tested for its growth-inhibitory activity in both plant and mammalian cells. Ophiobolin A induced cell death in Nicotiana tabacum L. cv. Bright Yellow 2 (TBY-2) cells at concentrations ≥10 µM, with the TBY-2 cells showing typical features of apoptosis-like cell death. At a concentration of 5 µM, ophiobolin A did not affect plant cell viability but prevented cell proliferation. When tested on eight cancer cell lines, concentrations <1 µM of ophiobolin A inhibited growth by 50% after 3 days of culture irrespective of their multidrug resistance (MDR) phenotypes and their resistance levels to pro-apoptotic stimuli. It is, thus, unlikely that ophiobolin A exerts these in vitro growth-inhibitory effects in cancer cells by activating pro-apoptotic processes. Highly proliferative human keratinocytes appeared more sensitive to the growth-inhibitory effects of ophiobolin A than slowly proliferating ones. Ophiobolin A also displayed significant antitumor activity at the level of mouse survival when assayed at 10 mg/kg in the B16F10 mouse melanoma model with lung pseudometastases. Ophiobolin A could, thus, represent a novel scaffold to combat cancer types that display various levels of resistance to pro-apoptotic stimuli and/or various MDR phenotypes.

Structures and potential antitumor activity of sesterterpenes from the marine sponge Hyrtios communis

The extract of marine sponge Hyrtios communis was found to inhibit activation of the transcription factor hypoxia-inducible factor-1 (HIF-1) in T47D human breast tumor cells. Bioassay-guided isolation led to the identification of six new (1-6) and five previously reported (7-11) sesterterpene analogues and two unrelated sesterterpenes. Two new sesterterpenes, thorectidaeolide A (1) and 4-acetoxythorectidaeolide A (2), and luffariellolide (11) were among the most potent inhibitors of hypoxia (1% O₂)-induced HIF-1 activation (IC₅₀ values of 3.2, 3.5, and 3.6 μM, respectively). Luffariellolide (11) exhibited a significant level of cytotoxicity that mirrored its HIF-1 inhibitory activity. Neither compound 1, compound 2, nor any of the other less active sesterterpenes suppressed breast tumor T47D or MDA-MB-231 cell viability.

Sesterterpenes from the tropical sponge Coscinoderma sp

Eight new sesterterpenes (2, 5, and 10-15), including structurally related pentaprenyl hydroquinones (2 and 5), and seven known ones of the same structural classes were isolated from the sponge Coscinoderma sp., collected from Chuuk Island, Micronesia. On the basis of the results of combined spectroscopic analyses, the new compounds were determined to be derivatives of the halisulfates and suvanine. These compounds exhibited moderate cytotoxicity against the K562 cell line and inhibitory activities against isocitrate lyase, sortase A, and Na+/K+-ATPase; significant structure-activity relationships were evident.

Secoemestrin D, a cytotoxic epitetrathiodioxopiperizine, and emericellenes A-E, five sesterterpenoids from Emericella sp. AST0036, a fungal endophyte of Astragalus lentiginosus1

A new epitetrathiodioxopiperizine, secoemestrin D (1), and five sesterterpenoids bearing a new carbon skeleton, emericellenes A-E (2-6), together with previously known fungal metabolites, sterigmatocystin (7), arugosin C (8), and epiisoshamixanthone (9), were obtained from the endophytic fungal strain Emericella sp. AST0036 isolated from a healthy leaf tissue of Astragalus lentiginosus. The planar structures and relative configurations of the new metabolites 1-6 were elucidated using MS and 1D and 2D NMR spectroscopic data. All compounds were evaluated for their potential anticancer activity using a panel of six tumor cell lines and normal human fibroblast cells. Only metabolites 1 and 7 showed cytotoxic activity. More importantly, secoemestrin D (1) exhibited significant cytotoxicity with IC50 values ranging from 0.06 to 0.24 μM and moderate selectivity to human glioma (SF-268) and metastatic breast adenocarcinoma (MDA-MB-231) cell lines.

Breaking down Leukemia Walls: Heteronemin, a Sesterterpene Derivative, Induces Apoptosis in Leukemia Molt4 Cells through Oxidative Stress, Mitochondrial Dysfunction and Induction of Talin Expression

Heteronemin, the most abundant secondary metabolite in the sponge Hippospongia sp., exhibited potent cytotoxic activity against several cancer cell lines. It increased the percentage of apoptotic cells and reactive oxygen species (ROS) in Molt4 cells. The use of ROS scavenger, N-acetyl cysteine (NAC), suppressed both the production of ROS from mitochondria and cell apoptosis that were induced by heteronemin treatment. Heteronemin upregulated talin and phosphorylated talin expression in Molt4 cells but it only upregulated the expression of phosphorylated talin in HEK293 cells. However, pretreatment with NAC reversed these effects. Talin siRNA reversed the activation of pro-apoptotic cleaved caspases 3 and 9. On the other hand, the downstream proteins including FAK and NF-κB (p65) were not affected. In addition, we confirmed that heteronemin directly modulated phosphorylated talin expression through ROS generation resulting in cell apoptosis, but it did not affect talin/FAK complex. Furthermore, heteronemin interfered with actin microfilament and caused morphology changes. Taken together, these findings suggest that the cytotoxic effect of heteronemin is associated with oxidative stress and induction of phosphorylated talin expression. Our results suggest that heteronemin represents an interesting candidate which can be further developed as a drug lead against leukemia.