Apoptogenic Metabolites in Fractions of the Benthic Diatom Cocconeis scutellum parva

Benthic diatoms of the genus Cocconeis contain a specific apoptogenic activity. It triggers a fast destruction of the androgenic gland in the early post-larval life of the marine shrimp Hippolyte inermis, leading to the generation of small females. Previous in vitro investigations demonstrated that crude extracts of these diatoms specifically activate a dose-dependent apoptotic process in human cancer cells (BT20 breast carcinoma) but not in human normal lymphocytes. Here, a bioassay-guided fractionation has been performed to detect the apoptogenic compound(s). Various HPLC separation systems were needed to isolate the active fractions, since the apoptogenic metabolite is highly active, present in low amounts and is masked by abundant but non-active cellular compounds. The activity is due to at least two compounds characterized by different polarities, a hydrophilic and a lipophilic fraction. We purified the lipophilic fraction, which led to the characterization of an active sub-fraction containing a highly lipophilic compound, whose molecular structure has not yet been identified, but is under investigation. The results point to the possible medical uses of the active compound. Once the molecular structure has been identified, the study and modulation of apoptotic processes in various types of cells will be possible.     

Echinohalimane A, a Bioactive Halimane-Type Diterpenoid from a Formosan Gorgonian Echinomuricea sp. (Plexauridae)

A new halimane-type diterpenoid, echinohalimane A (1), was isolated from a gorgonian, identified as Echinomuricea sp. The structure of 1 was determined by spectroscopic methods and this compound was found to exhibit cytotoxicity toward various tumor cells and display an inhibitory effect on the release of elastase by human neutrophils. Echinohalimane A (1) is the first halimane analogue from the marine organisms belonging to phylum Cnidaria.     

Deep-Sea Coral Garden Invertebrates and Their Associated Fungi Are Genetic Resources for Chronic Disease Drug Discovery

Chronic diseases characterized by bone and cartilage loss are associated with a reduced ability of progenitor cells to regenerate new tissues in an inflammatory environment. A promising strategy to treat such diseases is based on tissue repair mediated by human mesenchymal stem cells (hMSCs), but therapeutic outcomes are hindered by the absence of small molecules to efficiently modulate cell behaviour. Here, we applied a high-throughput drug screening technology to bioprospect a large library of extracts from Irish deep-sea organisms to induce hMSC differentiation toward musculoskeletal lineages and reduce inflammation of activated macrophages. The library included extracts from deep-sea corals, sponges and filamentous fungi representing a novel source of compounds for the targeted bioactivity. A validated hit rate of 3.4% was recorded from the invertebrate library, with cold water sea pens (octocoral order Pennatulacea), such as Kophobelemnon sp. and Anthoptilum sp., showing the most promising results in influencing stem cell differentiation toward osteogenic and chondrogenic lineages. Extracts obtained from deep-sea fungi showed no effects on stem cell differentiation, but a 6.8% hit rate in reducing the inflammation of activated macrophages. Our results demonstrate the potential of deep-sea organisms to synthetize pro-differentiation and immunomodulatory compounds that may represent potential drug development candidates to treat chronic musculoskeletal diseases.     

Identification of Renieramycin A as an Antileishmanial Substance in a Marine Sponge Neopetrosia sp.

The newly developed assay system using recombinant Leishmania amazonensis expressing enhanced green fluorescent protein (La/egfp) has been applied to the screening of Japanese marine sponges for antileishmanial activity. Bioassay-guided fractionation of an active sponge Neopetrosia sp. afforded an active compound which was identified as renieramycin A by spectroscopic analysis. It inhibited La/egfp with an IC₅₀ value of 0.2 μg/mL.     

Dysidenin from the Marine Sponge Citronia sp. Affects the Motility and Morphology of Haemonchus contortus Larvae In Vitro

High-throughput screening of the NatureBank marine extract library (n = 7616) using a phenotypic assay for the parasitic nematode Haemonchus contortus identified an active extract derived from the Australian marine sponge Citronia sp. Bioassay-guided fractionation of the CH₂Cl₂/MeOH extract from Citronia sp. resulted in the purification of two known hexachlorinated peptides, dysidenin (1) and dysideathiazole (2). Compound 1 inhibited the growth/development of H. contortus larvae and induced multiple phenotypic changes, including a lethal evisceration (Evi) phenotype and/or somatic cell and tissue destruction. This is the first report of anthelmintic activity for these rare and unique polychlorinated peptides.     

Potent Cytotoxic Peptides from the Australian Marine Sponge Pipestela candelabra

Two consecutive prefractionated fractions of the Australian marine sponge extract, Pipestela candelabra, were identified to be selectively active on the human prostate cancer cells (PC3) compared to the human neonatal foreskin fibroblast non-cancer cells (NFF). Twelve secondary metabolites were isolated in which four compounds are new small peptides. Their structures were characterized by spectroscopic and chemical analysis. These compounds inhibited selectively the growth of prostate cancer cells with IC₅₀ values in the picomolar to sub-micromolar range. Structure-activity relationship of these compounds is discussed.     

1,5-Diazacyclohenicosane,a New Cytotoxic Metabolite from the Marine Sponge Mycale sp

A new cyclic diamine, 1,5-diazacyclohenicosane (1), was isolated from samples of the marine sponge Mycale sp. collected at Lamu Island (Kenya). Its structure was determined by a combination of spectroscopic techniques, including (+)-HRESIMS and 1D and 2D NMR spectroscopy. The compound displayed cytotoxicity at the μM level against three human tumor cell lines.     

Synthesis and Antitumor Activities of Derivatives of the Marine Mangrove Fungal Metabolite Deoxybostrycin

Deoxybostrycin (1) is an anthraquinone compound derived from the marine mangrove fungus Nigrospora sp. No. 1403 and has potential to be a lead for new drugs because of its various biological properties. A series of new derivatives (2–22) of deoxybostrycin were synthesized. The in vitro cytotoxicity of all the new compounds was tested against MDA-MB-435, HepG2 and HCT-116 cancer cell lines. Most of the compounds exhibit strong cytotoxicity with IC₅₀ values ranging from 0.62 to 10 μM. Compounds 19, 21 display comparable cytotoxicity against MDA-MB-435 to epirubicin, the positive control. The primary screening results indicate that the deoxybostrycin derivatives might be a valuable source of new potent anticancer drug candidates.     

Long-Chain Acetylenic Ketones from the Micronesian Sponge Haliclona sp. Importance of the 1-yn-3-ol Group for Antitumor Activity

Two new long-chain C₃₃ polyacetylenic compounds, halicynones A and B were isolated from the marine sponge Haliclona sp. along with known analogs. The known compound pellynol A possessing a 1-yn-3-ol terminus, exhibited strong antitumor activity against the human colon tumor cell line HCT-116 (IC₅₀ 0.026 μg/mL), however, the corresponding 1-yn-3-one, halicynone A, was inactive, which suggests an important role for the terminal 1-yn-3-ol functional group in mediating cytotoxic activity.     

Identification and Bioactivity of Compounds from the Fungus Penicillium sp. CYE-87 Isolated from a Marine Tunicate

In the course of our continuous interest in identifying bioactive compounds from marine microbes, we have investigated a tunicate-derived fungus, Penicillium sp. CYE-87. A new compound with the 1,4-diazepane skeleton, terretrione D (2), together with the known compounds, methyl-2-([2-(1H-indol-3-yl)ethyl]carbamoyl)acetate (1), tryptamine (3), indole-3-carbaldehyde (4), 3,6-diisobutylpyrazin-2(1H)-one (5) and terretrione C (6), were isolated from Penicillium sp. CYE-87. The structures of the isolated compounds were established by spectral analysis, including 1D (¹H, ¹³C) and 2D (COSY, multiplicity edited-HSQC and HMBC) NMR and HRESIMS, as well as comparison of their NMR data with those in the literature. The compounds were evaluated for their antimigratory activity against the human breast cancer cell line (MDA-MB-231) and their antiproliferation activity against HeLa cells. Compounds 2 and 6 showed significant antimigratory activity against MDA-MB-231, as well as antifungal activity against C. albicans.     

Extract from the Zooxanthellate Jellyfish Cotylorhiza tuberculata Modulates Gap Junction Intercellular Communication in Human Cell Cultures

On a global scale, jellyfish populations in coastal marine ecosystems exhibit increasing trends of abundance. High-density outbreaks may directly or indirectly affect human economical and recreational activities, as well as public health. As the interest in biology of marine jellyfish grows, a number of jellyfish metabolites with healthy potential, such as anticancer or antioxidant activities, is increasingly reported. In this study, the Mediterranean “fried egg jellyfish” Cotylorhiza tuberculata (Macri, 1778) has been targeted in the search forputative valuable bioactive compounds. A medusa extract was obtained, fractionated, characterized by HPLC, GC-MS and SDS-PAGE and assayed for its biological activity on breast cancer cells (MCF-7) and human epidermal keratinocytes (HEKa). The composition of the jellyfish extract included photosynthetic pigments, valuable ω-3 and ω-6 fatty acids, and polypeptides derived either from jellyfish tissues and their algal symbionts. Extract fractions showed antioxidant activity and the ability to affect cell viability and intercellular communication mediated by gap junctions (GJIC) differentially in MCF-7and HEKa cells. A significantly higher cytotoxicity and GJIC enhancement in MCF-7 compared to HEKa cells was recorded. A putative action mechanism for the anticancer bioactivity through the modulation of GJIC has been hypothesized and its nutraceutical and pharmaceutical potential was discussed.     

Metabolomic Profiling and Genomic Study of a Marine Sponge-Associated Streptomyces sp

Metabolomics and genomics are two complementary platforms for analyzing an organism as they provide information on the phenotype and genotype, respectively. These two techniques were applied in the dereplication and identification of bioactive compounds from a Streptomyces sp. (SM8) isolated from the sponge Haliclona simulans from Irish waters. Streptomyces strain SM8 extracts showed antibacterial and antifungal activity. NMR analysis of the active fractions proved that hydroxylated saturated fatty acids were the major components present in the antibacterial fractions. Antimycin compounds were initially putatively identified in the antifungal fractions using LC-Orbitrap. Their presence was later confirmed by comparison to a standard. Genomic analysis of Streptomyces sp. SM8 revealed the presence of multiple secondary metabolism gene clusters, including a gene cluster for the biosynthesis of the antifungal antimycin family of compounds. The antimycin gene cluster of Streptomyces sp. SM8 was inactivated by disruption of the antimycin biosynthesis gene antC. Extracts from this mutant strain showed loss of antimycin production and significantly less antifungal activity than the wild-type strain. Three butenolides, 4,10-dihydroxy-10-methyl-dodec-2-en-1,4-olide (1), 4,11-dihydroxy-10-methyl-dodec-2-en-1,4-olide (2), and 4-hydroxy-10-methyl-11-oxo-dodec-2-en-1,4-olide (3) that had previously been reported from marine Streptomyces species were also isolated from SM8. Comparison of the extracts of Streptomyces strain SM8 and its host sponge, H. simulans, using LC-Orbitrap revealed the presence of metabolites common to both extracts, providing direct evidence linking sponge metabolites to a specific microbial symbiont.     

Structure Elucidation of Calyxoside B,a Bipolar Sphingolipid from a Marine Sponge Cladocroce sp. through the Use of Beckmann Rearrangement

Marine sponges are an excellent source of biologically active secondary metabolites. We focus on deep-sea sponges for our discovery study. A marine sponge Cladocroce sp. exhibited cytotoxic activity in the bioactivity screening. From this sponge a previously unreported cytotoxic glycosphingolipid, calyxoside B, was isolated and the structure of this compound was elucidated by analyses of MS and NMR spectra and chemical derivatization. We converted the ketone in the middle of a long aliphatic chain into an oxime to which was applied Beckmann rearrangement to afford two positional isomers of amides. The products were subjected to acidic hydrolysis followed by LC-MS analysis, permitting us to assign unequivocally the position of the ketone. Calyxoside B shows cytotoxicity against HeLa cells with an IC₅₀ value of 31 µM and also weakly stimulated the production of cytokines in mice.     

Inhibition of Lipopolysaccharide-Induced Inflammatory Signaling by Soft Coral-Derived Prostaglandin A2 in RAW264.7 Cells

Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria and causes inflammatory diseases. We searched MeOH extracts of collected marine organisms for inhibitors of LPS-induced nitric oxide (NO) production in RAW264.7 cells and identified prostaglandin A₂ (PGA₂) as an active compound from the MeOH extract of the soft coral Lobophytum sp. PGA₂ inhibited the production of NO and reduced the expression of inducible NO synthase (iNOS) in LPS-stimulated RAW264.7 cells. Although short preincubation with PGA₂ did not inhibit LPS-induced degradation and resynthesis of IκBα, the suppressive effect of PGA₂ was observed only after a prolonged incubation period prior to LPS treatment. In addition, PGA₂-inhibited NO production was negated by the addition of the EP4 antagonist L161982. Thus, PGA₂ was identified as an inhibitor of LPS-induced inflammatory signaling in RAW264.7 cells.     

Can Some Marine-Derived Fungal Metabolites Become Actual Anticancer Agents?

Marine fungi are known to produce structurally unique secondary metabolites, and more than 1000 marine fungal-derived metabolites have already been reported. Despite the absence of marine fungal-derived metabolites in the current clinical pipeline, dozens of them have been classified as potential chemotherapy candidates because of their anticancer activity. Over the last decade, several comprehensive reviews have covered the potential anticancer activity of marine fungal-derived metabolites. However, these reviews consider the term “cytotoxicity” to be synonymous with “anticancer agent”, which is not actually true. Indeed, a cytotoxic compound is by definition a poisonous compound. To become a potential anticancer agent, a cytotoxic compound must at least display (i) selectivity between normal and cancer cells (ii) activity against multidrug-resistant (MDR) cancer cells; and (iii) a preferentially non-apoptotic cell death mechanism, as it is now well known that a high proportion of cancer cells that resist chemotherapy are in fact apoptosis-resistant cancer cells against which pro-apoptotic drugs have more than limited efficacy. The present review thus focuses on the cytotoxic marine fungal-derived metabolites whose ability to kill cancer cells has been reported in the literature. Particular attention is paid to the compounds that kill cancer cells through non-apoptotic cell death mechanisms.     

The Brown Alga Stypopodium zonale (Dictyotaceae): A Potential Source of Anti-Leishmania Drugs

This study evaluated the anti-Leishmania amazonensis activity of a lipophilic extract from the brown alga Stypopodium zonale and atomaric acid, its major compound. Our initial results revealed high inhibitory activity for intracellular amastigotes in a dose-dependent manner and an IC₅₀ of 0.27 μg/mL. Due to its high anti-Leishmania activity and low toxicity toward host cells, we fractionated the lipophilic extract. A major meroditerpene in this extract, atomaric acid, and its methyl ester derivative, which was obtained by a methylation procedure, were identified by nuclear magnetic resonance (NMR) spectroscopy. Both compounds inhibited intracellular amastigotes, with IC₅₀ values of 20.2 μM (9 μg/mL) and 22.9 μM (10 μg/mL), and selectivity indexes of 8.4 μM and 11.5 μM. The leishmanicidal activity of both meroditerpenes was independent of nitric oxide (NO) production, but the generation of reactive oxygen species (ROS) may be at least partially responsible for the amastigote killing. Our results suggest that the lipophilic extract of S. zonale may represent an important source of compounds for the development of anti-Leishmania drugs.     

Dithiolopyrrolone Natural Products: Isolation,Synthesis and Biosynthesis

Dithiolopyrrolones are a class of antibiotics that possess the unique pyrrolinonodithiole (4H-[1,2] dithiolo [4,3-b] pyrrol-5-one) skeleton linked to two variable acyl groups. To date, there are approximately 30 naturally occurring dithiolopyrrolone compounds, including holomycin, thiolutin, and aureothricin, and more recently thiomarinols, a unique class of hybrid marine bacterial natural products containing a dithiolopyrrolone framework linked by an amide bridge with an 8-hydroxyoctanoyl chain linked to a monic acid. Generally, dithiolopyrrolone antibiotics have broad-spectrum antibacterial activity against various microorganisms, including Gram-positive and Gram-negative bacteria, and even parasites. Holomycin appeared to be active against rifamycin-resistant bacteria and also inhibit the growth of the clinical pathogen methicillin-resistant Staphylococcus aureus N315. Its mode of action is believed to inhibit RNA synthesis although the exact mechanism has yet to be established in vitro. A recent work demonstrated that the fish pathogen Yersinia ruckeri employs an RNA methyltransferase for self-resistance during the holomycin production. Moreover, some dithiolopyrrolone derivatives have demonstrated promising antitumor activities. The biosynthetic gene clusters of holomycin have recently been identified in S. clavuligerus and characterized biochemically and genetically. The biosynthetic gene cluster of thiomarinol was also identified from the marine bacterium Pseudoalteromonas sp. SANK 73390, which was uniquely encoded by two independent pathways for pseudomonic acid and pyrrothine in a novel plasmid. The aim of this review is to give an overview about the isolations, characterizations, synthesis, biosynthesis, bioactivities and mode of action of this unique family of dithiolopyrrolone natural products, focusing on the period from 1940s until now.     

Unravelling the Anti-Inflammatory and Antioxidant Potential of the Marine Sponge Cliona celata from the Portuguese Coastline

Inflammation is a double-edged sword, as it can have both protective effects and harmful consequences, which, combined with oxidative stress (OS), can lead to the development of deathly chronic inflammatory conditions. Over the years, research has evidenced the potential of marine sponges as a source of effective anti-inflammatory therapeutic agents. Within this framework, the purpose of this study was to evaluate the antioxidant and the anti-inflammatory potential of the marine sponge Cliona celata. For this purpose, their organic extracts (C1–C5) and fractions were evaluated concerning their radical scavenging activity through 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), and anti-inflammatory activity through a (lipopolysaccharides (LPS)-induced inflammation on RAW 264.7 cells) model. Compounds present in the two most active fractions (F5 and F13) of C4 were tentatively identified by gas chromatography coupled to mass spectrometry (GC-MS). Even though samples displayed low antioxidant activity, they presented a high anti-inflammatory capacity in the studied cellular inflammatory model when compared to the anti-inflammatory standard, dexamethasone. GC-MS analysis led to the identification of n-hexadecanoic acid, cis-9-hexadecenal, and 13-octadecenal in fraction F5, while two major compounds, octadecanoic acid and cholesterol, were identified in fraction F13. The developed studies demonstrated the high anti-inflammatory activity of the marine sponge C. celata extracts and fractions, highlighting its potential for further therapeutic applications.