Bursatella leachii Purple Ink Secretion Concentrate Exerts Cytotoxic Properties against Human Hepatocarcinoma Cell Line (HepG2): In Vitro and In Silico Studies.

Liver cancer is a leading cause of cancer death globally. Marine mollusc-derived drugs have gained attention as potential natural-based anti-cancer agents to overcome the side effects caused by conventional chemotherapeutic drugs during cancer therapy. Using liquid chromatography-mass spectrometry, the main biomolecules in the purple ink secretion released by the sea hare, named Bursatella leachii (B. leachii), were identified as hectochlorin, malyngamide X, malyngolide S, bursatellin and lyngbyatoxin A. The cytotoxic effects of B. leachii ink concentrate against human hepatocarcinoma (HepG2) cells were determined to be dose- and time-dependent, and further exploration of the underlying mechanisms causing the programmed cell death (apoptosis) were performed. The expression of cleaved-caspase-8 and cleaved-caspase-3, key cysteine-aspartic proteases involved in the initiation and completion of the apoptosis process, appeared after HepG2 cell exposure to the B. leachii ink concentrate. The gene expression levels of pro-apoptotic BAX, TP53 and Cyclin D1 were increased after treatment with the B. leachii ink concentrate. Applying in silico approaches, the high scores predicted that bioactivities for the five compounds were protease and kinase inhibitors. The ADME and cytochrome profiles for the compounds were also predicted. Altogether, the B. leachii ink concentrate has high pro-apoptotic potentials, suggesting it as a promising safe natural product-based drug for the treatment of liver cancer.

Two New Neo-debromoaplysiatoxins-A Pair of Stereoisomers Exhibiting Potent Kv1.5 Ion Channel Inhibition Activities.

A pair of stereoisomers possessing novel structures with 6/6/5 fused-ring systems, neo-debromoaplysiatoxin E (1) and neo-debromoaplysiatoxin F (2), were isolated from the marine cyanobacterium Lyngbya sp. Their structures were elucidated using various spectroscopic techniques including high resolution electrospray ionization mass spectroscopy (HRESIMS) and nuclear magnetic resonance (NMR). The absolute stereochemistry was determined by calculated electronic circular dichroism (ECD) and gauge-independent atomic orbital (GIAO) NMR shift calculation followed by DP4+ analysis. Significantly, this is the first report on aplysiatoxin derivatives with different absolute configurations at C9-C12 (1: 9S, 10R, 11S, 12S; 2: 9R, 10S, 11R, 12R). Compounds 1 and 2 exhibited potent blocking activities against Kv1.5 with IC50 values of 1.22 ± 0.22 µM and 2.85 ± 0.29 µM, respectively.

Oscillatoxin I: A New Aplysiatoxin Derivative, from a Marine Cyanobacterium.

Cyanobacteria have been shown to produce a number of bioactive compounds, including toxins. Some bioactive compounds obtained from a marine cyanobacterium Moorea producens (formerly Lyngbya majuscula) have been recognized as drug leads; one of these compounds is aplysiatoxin. We have isolated various aplysiatoxin derivatives from a M. producens sample obtained from the Okinawan coastal area. The frozen sample was extracted with organic solvents. The ethyl acetate layer was obtained from the crude extracts via liquid-liquid partitioning, then separated by HPLC using a reversed-phase column. Finally, 1.1 mg of the compound was isolated. The chemical structure of the isolated compound was elucidated with spectroscopic methods, using HR-MS and 1D and 2D NMR techniques, and was revealed to be oscillatoxin I, a new member of the aplysiatoxin family. Oscillatoxin I showed cytotoxicity against the L1210 mouse lymphoma cell line and diatom growth-inhibition activity against the marine diatom Nitzschia amabilis.

MS/MS-Based Molecular Networking Approach for the Detection of Aplysiatoxin-Related Compounds in Environmental Marine Cyanobacteria.

Certain strains of cyanobacteria produce a wide array of cyanotoxins, such as microcystins, lyngbyatoxins and aplysiatoxins, that are associated with public health issues. In this pilot study, an approach combining LC-MS/MS and molecular networking was employed as a rapid analytical method to detect aplysiatoxins present in four environmental marine cyanobacterial samples collected from intertidal areas in Singapore. Based on 16S-ITS rRNA gene sequences, these filamentous cyanobacterial samples collected from Pulau Hantu were determined as Trichodesmium erythraeum, Oscillatoria sp. PAB-2 and Okeania sp. PNG05-4. Organic extracts were prepared and analyzed on LC-HRMS/MS and Global Natural Product Social Molecular Networking (GNPS) for the presence of aplysiatoxin-related molecules. From the molecular networking, six known compounds, debromoaplysiatoxin (1), anhydrodebromoaplysiatoxin (2), 3-methoxydebromoaplysiatoxin (3), aplysiatoxin (4), oscillatoxin A (5) and 31-noroscillatoxin B (6), as well as potential new analogues, were detected in these samples. In addition, differences and similarities in molecular networking clusters related to the aplysiatoxin molecular family were observed in extracts of Trichodesmium erythraeum collected from two different locations and from different cyanobacterial species found at Pulau Hantu, respectively.

Biosynthesis of the teleocidin-type terpenoid indole alkaloids.

Teleocidin B is a terpenoid indole alkaloid with unique structures including indolactam and cyclic terpenoid, and is a strong protein kinase C activator. Its unique structure and bioactivity have drawn vast interest from chemists and biologists, and numerous isolation and bioactivity studies on this molecule have been performed. Recently, its biosynthetic enzymes were identified, and some of their crystal structures were reported. In this review, we describe the isolation of teleocidin derivatives, biosynthetic studies, and detailed analyses of biosynthetic enzymes, to clarify their biosynthetic reactions toward the enzymatic synthesis of bioactive teleocidin compounds.

Enantioselective total synthesis of (+)-lyngbyabellin M.

Lyngbyabellin M is a non-ribosomal peptide synthetase/polyketide synthase derived metabolite isolated from the cyanobacterium M. bouillonii displaying thiazole rings and a distinct chlorinated octanoic acid chain. Its absolute configuration was proposed based on the comparison of its spectroscopic data with those of other representatives of this family of marine natural products, as well as degradation and derivatization studies. Here the first total synthesis of (+)-lyngbyabellin M is described based on the coupling of three key intermediates: two chiral thiazole moieties and an anti hydroxycarboxylic acid prepared stereoselectively via a boron enolate mediated aldol reaction directed by Masamune's chiral auxiliary.

2,3-seco-2,3-dioxo-lyngbyatoxin A from a Red Sea strain of the marine cyanobacterium Moorea producens.

Chemical investigation of the organic extract of a Red Sea strain of the cyanobacterium Moorea producens has afforded 2,3-seco-2,3-dioxo-lyngbyatoxin A (1). Five known compounds including lyngbyatoxin A (2), majusculamides A and B (3 and 4), aplysiatoxin (5) and debromoaplysiatoxin (6) were also isolated. Their structures were elucidated by using HR-FAB-MS, 1D and 2D NMR analyses. The compounds were evaluated for antiproliferative activity against HeLa cancer cells. Lyngbyatoxin A (2) showed potent activity, with an IC50 of 9.2 nM, while 5 and 6 displayed modest activity with IC50 values of 13.3 and 3.03 µM, respectively. In contrast, compounds 1, 3 and 4 were inactive, with IC50 values greater than 50 µM. The lack of cytotoxicity for 2,3-seco-2,3-dioxo-lyngbyatoxin A (1) demonstrates that the indole moiety in lyngbyatoxin (2) is essential for its cytotoxicity, and suggests that detoxification of 2 may be carried out by biological oxidation of the indole moiety to yield 1.

Apratoxin H and apratoxin A sulfoxide from the Red Sea cyanobacterium Moorea producens.

Cultivation of the marine cyanobacterium Moorea producens, collected from the Nabq Mangroves in the Gulf of Aqaba (Red Sea), led to the isolation of new apratoxin analogues apratoxin H (1) and apratoxin A sulfoxide (2), together with the known apratoxins A-C, lyngbyabellin B, and hectochlorin. The absolute configuration of these new potent cytotoxins was determined by chemical degradation, MS, NMR, and CD spectroscopy. Apratoxin H (1) contains pipecolic acid in place of the proline residue present in apratoxin A, expanding the known suite of naturally occurring analogues that display amino acid substitutions within the final module of the apratoxin biosynthetic pathway. The oxidation site of apratoxin A sulfoxide (2) was deduced from MS fragmentation patterns and IR data, and 2 could not be generated experimentally by oxidation of apratoxin A. The cytotoxicity of 1 and 2 to human NCI-H460 lung cancer cells (IC50 = 3.4 and 89.9 nM, respectively) provides further insight into the structure-activity relationships in the apratoxin series. Phylogenetic analysis of the apratoxin-producing cyanobacterial strains belonging to the genus Moorea, coupled with the recently annotated apratoxin biosynthetic pathway, supports the notion that apratoxin production and structural diversity may be specific to their geographical niche.

Lagunamide C, a cytotoxic cyclodepsipeptide from the marine cyanobacterium Lyngbya majuscula.

Lagunamide C (1) is a cytotoxic cyclodepsipeptide isolated from the marine cyanobacterium, Lyngbya majuscula, from the western lagoon of Pulau Hantu Besar, Singapore. The complete structural characterization of the molecule was achieved by extensive NMR spectroscopic analysis as well as chemical manipulations. Several methods, including the advanced Marfey's method, a modified method based on derivatization with Mosher's reagents and analysis using LC-MS, and the use of (3)J(H-H) coupling constant values, were utilized for the determination of its absolute configuration. Compound 1 is related to the aurilide-class of molecules and it differs mainly in the macrocyclic structure by having a 27 membered ring system due to additional methylene carbon in the polyketide moiety. Lagunamide C displayed potent cytotoxic activity against a panel of cancer cell lines, such as P388, A549, PC3, HCT8, and SK-OV3 cell lines, with IC(50) values ranging from 2.1 nM to 24.4 nM. Compound 1 also displayed significant antimalarial activity with IC(50) value of 0.29 µM when tested against Plasmodium falciparum. In addition, lagunamide C exhibited weak anti-swarming activity when tested at 100 ppm against the Gram-negative bacterial strain, Pseudomonas aeruginosa PA01.

New peptides isolated from Lyngbya species: a review.

Cyanobacteria of the genus Lyngbya have proven to be prodigious producers of secondary metabolites. Many of these compounds are bioactive and show potential for therapeutic use. This review covers peptides and hybrid polyketide-non-ribosomal peptides isolated from Lyngbya species. The structures and bioactivities of 50 Lyngbya peptides which were reported since 2007 are presented.

Nhatrangins A and B, aplysiatoxin-related metabolites from the marine cyanobacterium Lyngbya majuscula from Vietnam.

Two polyketide metabolites, nhatrangins A (1) and B (2), were isolated from a Vietnamese collection of Lyngbya majuscula. These compounds are related to the aplysiatoxin series of metabolites, which have also been isolated from this species of marine cyanobacterium. The use of 900 MHz cryoprobe NMR allowed the elucidation of the 2D structure of 1 from approximately 0.3 mg of compound. LC-MS analysis was utilized to direct the isolation of additional material as well as the isolation of 2. Conformational analysis was completed using J-based coupling constant analysis and selective NOE experiments.

Cyanolide A, a glycosidic macrolide with potent Molluscicidal activity from the Papua New Guinea cyanobacterium Lyngbya bouillonii.

Over the last 50 years, molluscicides have played a critical role in the control of schistosomiasis transmission. Cyanolide A (2), isolated from extracts of a Papua New Guinea collection of Lyngbya bouillonii, is a new and highly potent molluscicidal agent against the snail vector Biomphalaria glabrata (LC(50) = 1.2 microM). The structure of cyanolide A (2) was elucidated through extensive NMR spectroscopic analyses, yielding a symmetrical dimer that represents the newest addition to the family of glycosidic macrolides from cyanobacteria.

Malyngolide dimer, a bioactive symmetric cyclodepside from the panamanian marine cyanobacterium Lyngbya majuscula.

Fractionation of the extract of the marine cyanobacterium Lyngbya majuscula collected from Panama led to the isolation of malyngolide dimer (1). The planar structure of 1 was determined using 1D and 2D NMR spectroscopy and HRESI-TOFMS. The absolute configuration was established by chemical degradation followed by chiral GC-MS analyses and comparisons with an authentic sample of malyngolide seco-acid (4). Compound 1 showed moderate in vitro antimalarial activity against chloroquine-resistant Plasmodium falciparum (W2) (IC(50) = 19 microM) but roughly equivalent toxicity against H-460 human lung cell lines. Furthermore, because the closely related cyanobacterial natural product tanikolide dimer (5) was a potent SIRT2 inhibitor, compound 1 was evaluated in this assay but found to be essentially inactive.

Enzymatic production of (-)-indolactam V by LtxB, a cytochrome P450 monooxygenase.

The P450 cytochrome monooxygenase gene, ltxB, was cloned and overexpressed in Escherichia coli as a 6xHis-tagged protein. The resulting recombinant LtxB was purified by Ni-NTA affinity chromatography and characterized biochemically. Purified LtxB demonstrated typical cytochrome P450 spectroscopic properties including substrate-induced transition from a low-spin (lambdamax=414 nm) to high-spin state (lambdamax=386 nm) upon incubation with N-methyl-L-valyl-L-tryptophanol. The catalytic activity of LtxB was verified by demonstrating the oxidation/cyclization of N-methyl-L-valyl-L-tryptophanol to (-)-indolactam V. LtxB shows a relaxed specificity for analogue substrates in which the valyl group is substituted for other aliphatic groups. The relaxed substrate specificity of LtxB, along with the relaxed specificity of the prenyltransferase, LtxC, allowed for the enzymatic production of a series of (-)-indolactam V and lyngbyatoxin analogues.

Dragonamide E, a modified linear lipopeptide from Lyngbya majuscula with antileishmanial activity.

Tropical parasitic and infectious diseases, such as leishmaniasis, pose enormous global health threats, but are largely neglected in commercial drug discovery programs. However, the Panama International Cooperative Biodiversity Group (ICBG) has been working to identify novel treatments for malaria, Chagas' disease, and leishmaniasis through an investigation of plants and microorganisms from Panama. We have pursued activity-guided isolation from an extract of Lyngbya majuscula that was found to be active against leishmaniasis. A new modified linear peptide from the dragonamide series was isolated, dragonamide E (1), along with two known modified linear peptides, dragonamide A (2) and herbamide B (3). Dragonamides A and E and herbamide B exhibited antileishmanial activity with IC50 values of 6.5, 5.1, and 5.9 microM, respectively. Spectroscopic and stereochemical data for dragonamide E (1) and herbamide B (3; the spectroscopic and stereochemical data for this substance is incomplete in the literature) are presented as well as comparisons of biological activity within the dragonamide compound family. Biosynthetic differences among marine compounds with a terminal free amide are also discussed.

Activity of mangosteen xanthones and teleocidin a-2 in death receptor expression enhancement and tumor necrosis factor related apoptosis-inducing ligand assays.

A screening study using a luciferase assay to identify natural products that enhance death receptor 5 (DR5) expression was carried out, and bioassay-guided fractionation of two organisms, the pericarp of Garcinia mangostana (mangosteen) and actinomycete CKK609 strain, led to the isolation of eight xanthone derivatives (1-8) and teleocidin A-2 (9). Among them, compounds 1, 2, and 5, isolated from G. mangostana, and 9, from the actinomycete, showed potent DR5 promoter activity. Furthermore, we revealed that combined treatment with gartanin (5) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) showed a potentiation effect in sensitizing TRAIL-resistant human gastric adenocarcinoma (AGS) cells. Thus, the present results suggested that 5 has the ability to overcome TRAIL resistance via the up-regulation of DR5 and may be an effective sensitizer of TRAIL-resistant cells.

Bisebromoamide, a potent cytotoxic peptide from the marine cyanobacterium Lyngbya sp.: isolation, stereostructure, and biological activity.

A novel cytotoxic peptide, termed bisebromoamide (1), has been isolated from the marine cyanobacterium Lyngbya sp. Its planar structure was determined by 1D and 2D NMR spectroscopy. The absolute stereostructure of 1 was determined by chemical degradation followed by chiral HPLC analysis. Bisebromoamide (1) exhibited potent protein kinase inhibition: the phosphorylation of ERK in NRK cells by PDGF-stimulation was selectively inhibited by treatment with 10-0.1 microM of 1.

Biselyngbyaside, a macrolide glycoside from the marine cyanobacterium Lyngbya sp.

Bioassay-guided fractionation of the cytotoxic constituents of the marine cyanobacterium Lyngbya sp. led to the isolation of biselyngbyaside (1), a new 18-membered macrolide glycoside. The structure of 1 was established by spectroscopic analysis including 2D-NMR techniques and by synthetic studies. Biselyngbyaside (1) exhibits broad-spectrum cytotoxicity in a human tumor cell line panel.

Bioassay-guided isolation and identification of desacetylmicrocolin B from Lyngbya cf. polychroa.

Bioassay-guided fractionation of a non-polar extract of Lyngbya cf. polychroa resulted in the isolation of the cytotoxic desacetylmicrocolin B (1) as well as the known compounds microcolins A (2) and B (3). Compound 1 was found to inhibit the growth of HT-29 colorectal adenocarcinoma and IMR-32 neuroblastoma cells with half maximal inhibitory concentration (IC(50)) values of 14 nM for both cancer cell types. Microcolins A and B were found to have little activity against two strains of the marine fungus Dendryphiella salina with LD(50) values above 200 microg/mL. Compounds 1, 2, and 3 were obtained by reverse-phase chromatography and their structures were determined by NMR and MS. In this paper we report the isolation, identification, and biological activity of 1.