Bioactivity of the Murex Homeopathic Remedy and of Extracts from an Australian Muricid Mollusc against Human Cancer Cells

Molluscan Compounds Provide Drug Leads for the Treatment and Prevention of Respiratory Disease

Respiratory diseases place an immense burden on global health and there is a compelling need for the discovery of new compounds for therapeutic development. Here, we identify research priorities by critically reviewing pre-clinical and clinical studies using extracts and compounds derived from molluscs, as well as traditional molluscan medicines, used in the treatment of respiratory diseases. We reviewed 97 biomedical articles demonstrating the anti-inflammatory, antimicrobial, anticancer, and immunomodulatory properties of >320 molluscan extracts/compounds with direct relevance to respiratory disease, in addition to others with promising bioactivities yet to be tested in the respiratory context. Of pertinent interest are compounds demonstrating biofilm inhibition/disruption and antiviral activity, as well as synergism with approved antimicrobial and chemotherapeutic agents. At least 100 traditional medicines, incorporating over 300 different mollusc species, have been used to treat respiratory-related illness in cultures worldwide for thousands of years. These medicines provide useful clues for the discovery of bioactive components that likely underpin their continued use. There is particular incentive for investigations into anti-inflammatory compounds, given the extensive application of molluscan traditional medicines for symptoms of inflammation, and shells, which are the principal molluscan product used in these preparations. Overall, there is a need to target research toward specific respiratory disease-related hypotheses, purify bioactive compounds and elucidate their chemical structures, and develop an evidence base for the integration of quality-controlled traditional medicines.

In vitro attenuation of classic metastatic melanoma‑related features by highly diluted natural complexes: Molecular and functional analyses

Metastasis is responsible for the majority of deaths among patients with malignant melanoma. Despite recent advances, the majority of current and modern therapies are ineffective and/or financially unfeasible. Thus, in this study, we investigated two low‑cost highly‑diluted natural complexes (HDNCs) that have been shown to be effective against malignant melanoma in a murine model in vivo. The aim of this study was to determine the mechanisms through which these HDNCs directly affect melanoma cells, either alone or in an artificial tumor microenvironment, suppressing the metastatic phenotype, thus explaining previous in vivo effects. For this purpose, HDNC in vitro treatments of B16‑F10 melanoma cells, alone or in co‑culture with Balb/3T3 fibroblasts, were carried out. Molecular biology techniques and standard functional assays were used to assess the changes in molecule expression and in cell behaviors related to the metastatic phenotype. Melanoma progression features were found to be regulated by HDNCs. Molecules related to cell adhesion (N‑cadherin, β1‑integrin and CD44), and migration, extracellular matrix remodeling and angiogenesis were modulated. The cell migratory, invasive and clonogenic capacities were reduced by the HDNCs. No loss of cell proliferation or viability were observed. On the whole, the findings of this study indicate that HDNCs directly reprogram, molecularly and functionally, melanoma cells in vitro, modulating their metastatic phenotype. Such findings are likely to be responsible for the attenuation of tumor growth and lung colonization previously observed in vivo.

Bioactive Compounds Isolated from Neglected Predatory Marine Gastropods

A diverse range of predatory marine gastropods produce toxins, yet most of these molecules remain uncharacterized. Conus species have received the most attention from researchers, leading to several conopeptides reaching clinical trials. This review aims to summarize what is known about bioactive compounds isolated from species of neglected marine gastropods, especially in the Turridae, Terebridae, Babyloniidae, Muricidae, Buccinidae, Colubrariidae, Nassariidae, Cassidae, and Ranellidae families. Multiple species have been reported to contain bioactive compounds with potential toxic activity, but most of these compounds have not been characterized or even clearly identified. The bioactive properties and potential applications of echotoxins and related porins from the Ranellidae family are discussed in more detail. Finally, the review concludes with a call for research on understudied species.

Six Trikentrin-like Cyclopentanoindoles from Trikentrion flabelliforme. Absolute Structural Assignment by NMR and ECD

Six new cyclopenta[g]indoles were isolated from a West Australian sponge, Trikentrion flabelliforme Hentschel, 1912, and their structures elucidated by integrated spectroscopic analysis. The compounds are analogues of previously described trikentrins, herbindoles, and trikentramides from related Axinellid sponges. The assignment of absolute configuration of the new compounds was carried out largely by comparative analysis of specific rotation, calculated and measured ECD, and exploiting van't Hoff's principle of optical superposition. Five of the new compounds were chemically interconverted to establish their stereochemical relationships, leading to a simple chiroptical mnemonic for assignment of the this family of chiral indoles. The first biosynthetic hypothesis is advanced to explain the origin of the trikentrin-herbinole family and proposes a pyrrole-carboxylic thioester-initiated polyketide synthase mechanism.

An Updated Review on Marine Anticancer Compounds: The Use of Virtual Screening for the Discovery of Small-Molecule Cancer Drugs

Marine secondary metabolites are a promising source of unexploited drugs that have a wide structural diversity and have shown a variety of biological activities. These compounds are produced in response to the harsh and competitive conditions that occur in the marine environment. Invertebrates are considered to be among the groups with the richest biodiversity. To date, a significant number of marine natural products (MNPs) have been established as antineoplastic drugs. This review gives an overview of MNPs, both in research or clinical stages, from diverse organisms that were reported as being active or potentially active in cancer treatment in the past seventeen years (from January 2000 until April 2017) and describes their putative mechanisms of action. The structural diversity of MNPs is also highlighted and compared with the small-molecule anticancer drugs in clinical use. In addition, this review examines the use of virtual screening for MNP-based drug discovery and reveals that classical approaches for the selection of drug candidates based on ADMET (absorption, distribution, metabolism, excretion, and toxicity) filtering may miss potential anticancer lead compounds. Finally, we introduce a novel and publically accessible chemical library of MNPs for virtual screening purposes.

Anti-Inflammatory Activity and Structure-Activity Relationships of Brominated Indoles from a Marine Mollusc

Marine molluscs are rich in biologically active natural products that provide new potential sources of anti-inflammatory agents. Here we used bioassay guided fractionation of extracts from the muricid Dicathais orbita to identify brominated indoles with anti-inflammatory activity, based on the inhibition of nitric oxide (NO) and tumour necrosis factor α (TNFα) in lipopolysaccharide (LPS) stimulated RAW264.7 macrophages and prostaglandin E2 (PGE2) in calcium ionophore-stimulated 3T3 ccl-92 fibroblasts. Muricid brominated indoles were then compared to a range of synthetic indoles to determine structure-activity relationships. Both hypobranchial gland and egg extracts inhibited the production of NO significantly with IC₅₀ of 30.8 and 40 μg/mL, respectively. The hypobranchial gland extract also inhibited the production of TNFα and PGE2 with IC₅₀ of 43.03 µg/mL and 34.24 µg/mL, respectively. The purified mono-brominated indole and isatin compounds showed significant inhibitory activity against NO, TNFα, and PGE2, and were more active than dimer indoles and non-brominated isatin. The position of the bromine atom on the isatin benzene ring significantly affected the activity, with 5Br > 6Br > 7Br. The mode of action for the active hypobranchial gland extract, 6-bromoindole, and 6-bromoisatin was further tested by the assessment of the translocation of nuclear factor kappa B (NFκB) in LPS-stimulated RAW264.7 mouse macrophage. The extract (40 µg/mL) significantly inhibited the translocation of NFκB in the LPS-stimulated RAW264.7 macrophages by 48.2%, whereas 40 µg/mL of 6-bromoindole and 6-bromoistain caused a 60.7% and 63.7% reduction in NFκB, respectively. These results identify simple brominated indoles as useful anti-inflammatory drug leads and support the development of extracts from the Australian muricid D. orbita, as a new potential natural remedy for the treatment of inflammation.

Extraction and Quantification of Bioactive Tyrian Purple Precursors: A Comparative and Validation Study from the Hypobranchial Gland of a Muricid Dicathais orbita

Muricidae are marine molluscs known for the production of Tyrian purple and bioactive precursor compounds. A validation study for the extraction and analysis of secondary metabolites found in the hypobranchial gland of the muricid Dicathais orbita is reported, using high performance liquid chromatography–mass spectrometry (HPLC-MS) with diode array detector (DAD). Quantification of the dominant secondary metabolites from D. orbita is described, followed by a comparison of solvent extraction procedures and stability studies. The intra- and inter-day relative standard deviation (RSD) for tyrindoxyl sulphate was 0.46% and 0.17%, respectively. The quantification was linear for standards murexine, 6-bromoisatin, and tyrindoxyl sulphate. The limits of detection were 0.03, 0.004, and 0.07 mg/mL, respectively, and the limits of quantification were 0.09, 0.01, and 0.22 mg/mL, respectively. The results showed that alcoholic solvents were better for extracting choline ester and indoxyl sulphate ultimate precursors, while chloroform was more suitable for the extraction of the intermediate precursors. Multivariate analysis revealed significant differences in extract composition according to the solvent used. Stability testing showed an increase of the oxidative compounds 6-bromoisatin and putative tyrindoxyl S-oxide sulphate in the ethanol extracts while more degradation products were seen in the chloroform extracts after months of cold storage. The validated method was found to be simple, reproducible, precise, and suitable for quantification of the secondary metabolites of muricid molluscs for dye precursor and nutraceutical quality control, as well as applications in marine chemical ecology.

Are the Traditional Medical Uses of Muricidae Molluscs Substantiated by Their Pharmacological Properties and Bioactive Compounds?

Marine molluscs from the family Muricidae hold great potential for development as a source of therapeutically useful compounds. Traditionally known for the production of the ancient dye Tyrian purple, these molluscs also form the basis of some rare traditional medicines that have been used for thousands of years. Whilst these traditional and alternative medicines have not been chemically analysed or tested for efficacy in controlled clinical trials, a significant amount of independent research has documented the biological activity of extracts and compounds from these snails. In particular, Muricidae produce a suite of brominated indoles with anti-inflammatory, anti-cancer and steroidogenic activity, as well as choline esters with muscle-relaxing and pain relieving properties. These compounds could explain some of the traditional uses in wound healing, stomach pain and menstrual problems. However, the principle source of bioactive compounds is from the hypobranchial gland, whilst the shell and operculum are the main source used in most traditional remedies. Thus further research is required to understand this discrepancy and to optimise a quality controlled natural medicine from Muricidae.

Combined Effects of Muricid Extract and 5-Fluorouracil on Intestinal Toxicity in Rats

Chemotherapy drugs, such as 5-fluorouracil (5FU), are the standard approach for cancer and are associated with several peripheral toxicities. We previously demonstrated that Muricidae marine molluscs exhibit chemopreventive properties. This study investigated the combined effect of muricid extract derived from Dicathais orbita, with 5FU, on intestinal toxicity in rats. Groups of rats were orally gavaged water, muricid extract, or sunflower oil, with or without 5FU (150 mg/kg). Metabolic data was collected daily and small intestinal brush border enzyme activity was measured by sucrose breath test (SBT). Blood was collected by cardiac puncture for whole blood analysis. Intestinal biopsies were taken for histopathology. Neutrophil activity was measured by myeloperoxidase activity. No additional toxicity effects were observed in rats receiving the combination of 5FU and muricid extract compared to 5FU alone, as indicated by SBT, histopathology, and myeloperoxidase activity. Intestinal integrity was protected from 5FU-induced damage in the sunflower oil vehicle group, compared to controls, as measured by SBT, villus height, and crypt depth. We concluded that combination of muricid extract and 5FU did not confer any additional intestinal toxicity, further supporting its potential as a chemopreventive food product. In this model system, sunflower oil partially protected against 5FU-induced intestinal toxicity.

Purified brominated indole derivatives from Dicathais orbita induce apoptosis and cell cycle arrest in colorectal cancer cell lines

Dicathais orbita is a large Australian marine gastropod known to produce bioactive compounds with anticancer properties. In this research, we used bioassay guided fractionation from the egg mass extract of D. orbita using flash column chromatography and identified fractions containing tyrindoleninone and 6-bromoisatin as the most active against colon cancer cells HT29 and Caco-2. Liquid chromatography coupled with mass spectrometry (LCMS) and 1H NMR were used to characterize the purity and chemical composition of the isolated compounds. An MTT assay was used to determine effects on cell viability. Necrosis and apoptosis induction using caspase/LDH assay and flow cytometry (PI/Annexin-V) and cell cycle analysis were also investigated. Our results show that semi-purified 6-bromoisatin had the highest anti-cancer activity by inhibiting cell viability (IC50 = ~100 µM) and increasing caspase 3/7 activity in both of the cell lines at low concentration. The fraction containing 6-bromoisatin induced 77.6% apoptosis and arrested 25.7% of the cells in G2/M phase of cell cycle in HT29 cells. Tyrindoleninone was less potent but significantly decreased the viability of HT29 cells at IC50 = 390 µM and induced apoptosis at 195 µM by increasing caspase 3/7 activity in these cells. This research will facilitate the development of these molluscan natural products as novel complementary medicines for colorectal cancer.

Natural product research in the Australian marine invertebrate Dicathais orbita

The predatory marine gastropod Dicathais orbita has been the subject of a significant amount of biological and chemical research over the past five decades. Natural products research on D. orbita includes the isolation and identification of brominated indoles and choline esters as precursors of Tyrian purple, as well as the synthesis of structural analogues, bioactivity testing, biodistributional and biosynthetic studies. Here I also report on how well these compounds conform to Lipinski’s rule of five for druglikeness and their predicted receptor binding and enzyme inhibitor activity. The composition of mycosporine-like amino acids, fatty acids and sterols has also been described in the egg masses of D. orbita. The combination of bioactive compounds produced by D. orbita is of interest for further studies in chemical ecology, as well as for future nutraceutical development. Biological insights into the life history of this species, as well as ongoing research on the gene expression, microbial symbionts and biosynthetic capabilities, should facilitate sustainable production of the bioactive compounds. Knowledge of the phylogeny of D. orbita provides an excellent platform for novel research into the evolution of brominated secondary metabolites in marine molluscs. The range of polarities in the brominated indoles produced by D. orbita has also provided an effective model system used to develop a new method for biodistributional studies. The well characterized suite of chemical reactions that generate Tyrian purple, coupled with an in depth knowledge of the ecology, anatomy and genetics of D. orbita provide a good foundation for ongoing natural products research.

Gastrointestinal and hepatotoxicity assessment of an anticancer extract from muricid molluscs

Marine molluscs from the family Muricidae are under development as a potential medicinal food for the prevention of colon cancer and treatment of gynaecological cancers. Here we report the outcome of the first in vivo toxicity assessment on an anticancer extract from a muricid mollusc containing brominated indole derivatives. Mice received the concentrated lipophilic extract by daily oral gavage over a two-week period. Mortality or clinical toxicity symptoms resulting from the extract were not detected during the trial, and there was no difference in the body weight of treated and control mice at the end of the trial. Histological analysis revealed some evidence for mild, idiosyncratic effects on the gastrointestinal tract and liver, including necrosis, fatty change, and inflammation in a small proportion (<40%) of mice. This is likely to result from first-pass hepatic metabolism of tyrindoxyl sulphate combined with second-pass metabolism of indoles. Overall however, oral administration of muricid extract containing brominated indoles does not result in severe clinical toxicity.

Evidence of anti-proliferative activities in blue mussel (Mytilus edulis) by-products

Shellfish waste components contain significant levels of high quality protein and are therefore a potential source for biofunctional high-value peptides. The feasibility of applying a pilot scale enzymatic hydrolysis process to whole Mytilus edulis and, by fractionation, recover hydrolysates presenting a biological activity of interest, was evaluated. Fractions were tested on four immortalized cancerous cell lines: A549, BT549, HCT15 and PC3. The 50 kDa fraction, enriched in peptides, presented anti-proliferative activity with all cell lines and results suggest a bioactive molecule synergy within the fraction. At a protein concentration of 44 µg/mL, the 50 kDa fraction induced a mortality of 90% for PC3, 89% for A549, 85% for HCT15 and of 81% for BT549 cell lines. At the low protein concentration of only 11 µg/mL the 50 kDa fraction still entails a cell mortality of 76% for A549 and 87% for PC3 cell lines. The 50 kDa fraction contains 56% of proteins, 3% of lipids and 6% of minerals on a dry weight basis and the lowest levels detected of taurine and methionine and highest levels of threonine, proline and glycine amino acids. The enzymatic hydrolysis process suggests that Mytilus edulis by-products should be viewed as high-valued products with strong potential as anti-proliferative agent and promising active ingredients in functional foods.

Global phylogeny and new classification of the Rapaninae (Gastropoda: Muricidae), dominant molluscan predators on tropical rocky seashores

The monophyly of the muricid subfamily Rapaninae has recently been confirmed with molecular techniques, but its composition and the relationships among its constituent genera remain unclear. We use four genes (28S rRNA, 12S rRNA, 16S rRNA and cytochrome c oxidase subunit I, COI) to construct a Bayesian phylogeny of 80 rapanine species (73% of the approximately 109 currently accepted), representing 27 of the 31 nominal genera. This is the most complete phylogeny of this taxonomically confusing subfamily yet produced. We propose a revised phylogenetic classification of the Rapaninae, assigning the recognized species to 28 genera. Most of the morphologically-defined rapanine genera are considered valid, including Purpura, Drupa, Thais and Nassa, but many of them are here restricted or redefined so that they are monophyletic. In particular the familiar genus Thais is narrowly restricted to a single species. Many groups previously accepted as subgenera, including Mancinella, Vasula, Thalessa and Thaisella, are here accorded full generic rank. We describe one new genus, Indothais. While we do not formally alter species-level taxonomy, we show molecular evidence for two cryptic species and several instances of probable species synonymy. We estimate the age of diversification of the Rapaninae as Late Cretaceous (75.9 Ma) and of many of its genera as Miocene.

Marine compounds selectively induce apoptosis in female reproductive cancer cells but not in primary-derived human reproductive granulosa cells

Anticancer properties of tyrindoleninone and 6-bromoisatin from Dicathais orbita were tested against physiologically normal primary human granulosa cells (HGC) and reproductive cancer cell lines. Tyrindoleninone reduced cancer cell viability with IC₅₀ values of 39 µM (KGN; a tumour-derived granulosa cell line), 39 μM (JAr), and 156 μM (OVCAR-3), compared to 3516 μM in HGC. Apoptosis in HGC's occurred after 4 h at 391 µM tyrindoleninone compared to 20 µM in KGN cells. Differences in apoptosis between HGC and KGN cells were confirmed by TUNEL, with 66 and 31% apoptotic nuclei at 4 h in KGN and HGC, respectively. These marine compounds therefore have potential for development as treatments for female reproductive cancers.

Expression of Pigment Cell-Specific Genes in the Ontogenesis of the Sea Urchin Strongylocentrotus intermedius

One of the polyketide compounds, the naphthoquinone pigment echinochrome, is synthesized in sea urchin pigment cells. We analyzed polyketide synthase (pks) and sulfotransferase (sult) gene expression in embryos and larvae of the sea urchin Strongylocentrotus intermedius from various stages of development and in specific tissues of the adults. We observed the highest level of expression of the pks and sult genes at the gastrula stage. In unfertilized eggs, only trace amounts of the pks and sult transcripts were detected, whereas no transcripts of these genes were observed in spermatozoids. The addition of shikimic acid, a precursor of naphthoquinone pigments, to zygotes and embryos increased the expression of the pks and sult genes. Our findings, including the development of specific conditions to promote pigment cell differentiation of embryonic sea urchin cells in culture, represent a definitive study on the molecular signaling pathways that are involved in the biosynthesis of pigments during sea urchin development.