Biological targets and mechanisms of action of natural products from marine cyanobacteria

Cephalotane diterpenoids: structural diversity, biological activity, biosynthetic proposal, and chemical synthesis

Covering: up to the end of 2023Cephalotane diterpenoids are a unique class of natural products exclusive to the genus Cephalotaxus, featuring a rigid 7,6,5,6-fused tetracyclic architecture. The study of cephalotanes dates back to the 1970s, when harringtonolide (1), a Cephalotaxus troponoid with a peculiar norditerpenoid carbon skeleton, was first discovered. In recent years, prototype C20 diterpenoids proposed as cephalotane were disclosed, which triggered intense studies on this diterpenoid family. To date, a cumulative total of 105 cephalotane diterpenoids with great structural diversity and biological importance have been isolated. In addition, significant advances have been made in the field of total synthesis and biosynthesis of cephalotanes in recent years. This review provides a complete overview of the chemical structures, bioactivities, biosynthetic aspects, and completed total synthesis of all the isolated cephalotane diterpenoids, which will help guide future research on this class of compounds.

Opportunities and challenges of RiPP-based therapeutics

Covering: up to 2024Ribosomally synthesised and post-translationally modified peptides (RiPPs) comprise a substantial group of peptide natural products exhibiting noteworthy bioactivities ranging from antiinfective to anticancer and analgesic effects. Furthermore, RiPP biosynthetic pathways represent promising production routes for complex peptide drugs, and the RiPP technology is well-suited for peptide engineering to produce derivatives with specific functions. Thus, RiPP natural products possess features that render them potentially ideal candidates for drug discovery and development. Nonetheless, only a small number of RiPP-derived compounds have successfully reached the market thus far. This review initially outlines the therapeutic opportunities that RiPP-based compounds can offer, whilst subsequently discussing the limitations that require resolution in order to fully exploit the potential of RiPPs towards the development of innovative drugs.

Modified peptides and organic metabolites of cyanobacterial origin with antiplasmodial properties

As etiological agents of malaria disease, Plasmodium spp. parasites are responsible for one of the most severe global health problems occurring in tropical regions of the world. This work involved compiling marine cyanobacteria metabolites reported in the scientific literature that exhibit antiplasmodial activity. Out of the 111 compounds mined and 106 tested, two showed antiplasmodial activity at very low concentrations, with IC50 at 0.1 and 1.5 nM (peptides: dolastatin 10 and lyngbyabellin A, 1.9% of total tested). Examples of chemical derivatives generated from natural cyanobacterial compounds to enhance antiplasmodial activity and Plasmodium selectivity can be found in successful findings from nostocarboline, eudistomin, and carmaphycin derivatives, while bastimolide derivatives have not yet been found. Overall, 57% of the reviewed compounds are peptides with modified residues producing interesting active moieties, such as α- and β-epoxyketone in camaphycins. The remaining compounds belong to diverse chemical groups such as alkaloids, macrolides, polycyclic compounds, and halogenated compounds. The Dolastatin 10 and lyngbyabellin A, compounds with antiplasmodial high activity, are cytoskeletal disruptors with different protein targets.

Plant-based compositions for the treatment of local and topical bacterial infections: a patent review

Aim: To examine recent patents related to plants with antimicrobial effects. Methods: Our investigation was carried out using the Espacenet database, searching patents related to International Patent Classification (IPC) codes A61P31/04, and A61K36/00 between 2008 and 2023. Results: The study began with 360 patents, of which 15 were found to be duplicates; 144 were not related to the research topic and six were not available. Then, 48 patents were related to other administration routes. The final selection was 47 patents related to local administration compositions. The potential for these herbal compositions to be marketed as over-the-counter medicines was evident. Conclusion: Developing new plant-origin anti-infective agents could provide promising solutions for combating resistant infections and offer accessible treatment options.

Widespread Peptide Surfactants with Post-translational C-methylations Promote Bacterial Development

Bacteria produce a variety of peptides to mediate nutrient acquisition, microbial interactions, and other physiological processes. Of special interest are surface-active peptides that aid in growth and development. Herein, we report the structure and characterization of clavusporins, unusual and hydrophobic ribosomal peptides with multiple C-methylations at unactivated carbon centers, which help drastically reduce the surface tension of water and thereby aid in Streptomyces development. The peptides are synthesized by a previously uncharacterized protein superfamily, termed DUF5825, in conjunction with a vitamin B12-dependent radical S-adenosylmethionine metalloenzyme. The operon encoding clavusporin is wide-spread among actinomycete bacteria, suggesting a prevalent role for clavusporins as morphogens in erecting aerial hyphae and thereby advancing sporulation and proliferation.

More than just an eagle killer: The freshwater cyanobacterium Aetokthonos hydrillicola produces highly toxic dolastatin derivatives

Cyanobacteria are infamous producers of toxins. While the toxic potential of planktonic cyanobacterial blooms is well documented, the ecosystem level effects of toxigenic benthic and epiphytic cyanobacteria are an understudied threat. The freshwater epiphytic cyanobacterium Aetokthonos hydrillicola has recently been shown to produce the "eagle killer" neurotoxin aetokthonotoxin (AETX) causing the fatal neurological disease vacuolar myelinopathy. The disease affects a wide array of wildlife in the southeastern United States, most notably waterfowl and birds of prey, including the bald eagle. In an assay for cytotoxicity, we found the crude extract of the cyanobacterium to be much more potent than pure AETX, prompting further investigation. Here, we describe the isolation and structure elucidation of the aetokthonostatins (AESTs), linear peptides belonging to the dolastatin compound family, featuring a unique modification of the C-terminal phenylalanine-derived moiety. Using immunofluorescence microscopy and molecular modeling, we confirmed that AEST potently impacts microtubule dynamics and can bind to tubulin in a similar matter as dolastatin 10. We also show that AEST inhibits reproduction of the nematode Caenorhabditis elegans. Bioinformatic analysis revealed the AEST biosynthetic gene cluster encoding a nonribosomal peptide synthetase/polyketide synthase accompanied by a unique tailoring machinery. The biosynthetic activity of a specific N-terminal methyltransferase was confirmed by in vitro biochemical studies, establishing a mechanistic link between the gene cluster and its product.

Identification, Heterologous Expression, and Characterization of the Tolypodiol Biosynthetic Gene Cluster through an Integrated Approach

Cyanobacteria are tremendous producers of biologically active natural products, including the potent anti-inflammatory compound tolypodiol. However, linking biosynthetic gene clusters with compound production in cyanobacteria has lagged behind that in other bacterial genera. Tolypodiol is a meroterpenoid originally isolated from the cyanobacterium HT-58-2. Here we describe the identification of the tolypodiol biosynthetic gene cluster through heterologous expression in Anabaena and in vitro protein assays of a methyltransferase found in the tolypodiol biosynthetic gene cluster. We have also identified similar biosynthetic gene clusters in cyanobacterial and actinobacterial genomes, suggesting that meroterpenoids with structural similarity to the tolypodiols may be synthesized by other microbes. We also report the identification of two new analogs of tolypodiol that we have identified in both the original and heterologous producer. This work further illustrates the usefulness of Anabaena as a heterologous expression host for cyanobacterial compounds and how integrated approaches can help to link natural product compounds with their producing biosynthetic gene clusters.

Review of Marine Cyanobacteria and the Aspects Related to Their Roles: Chemical, Biological Properties, Nitrogen Fixation and Climate Change

Marine cyanobacteria are an ancient group of photosynthetic microbes dating back to 3.5 million years ago. They are prolific producers of bioactive secondary metabolites. Over millions of years, natural selection has optimized their metabolites to possess activities impacting various biological targets. This paper discusses the historical and existential records of cyanobacteria, and their role in understanding the evolution of marine cyanobacteria through the ages. Recent advancements have focused on isolating and screening bioactive compounds and their respective medicinal properties, and we also discuss chemical property space and clinical trials, where compounds with potential pharmacological effects, such as cytotoxicity, anticancer, and antiparasitic properties, are highlighted. The data have shown that about 43% of the compounds investigated have cytotoxic effects, and around 8% have anti-trypanosome activity. We discussed the role of different marine cyanobacteria groups in fixing nitrogen percentages on Earth and their outcomes in fish productivity by entering food webs and enhancing productivity in different agricultural and ecological fields. The role of marine cyanobacteria in the carbon cycle and their outcomes in improving the efficiency of photosynthetic CO2 fixation in the chloroplasts of crop plants, thus enhancing the crop plant's yield, was highlighted. Ultimately, climate changes have a significant impact on marine cyanobacteria where the temperature rises, and CO2 improves the cyanobacterial nitrogen fixation.

Recent Advances in Nanoplatform Construction Strategy for Alleviating Tumor Hypoxia

Hypoxia is a typical feature of most solid tumors and has important effects on tumor cells' proliferation, invasion, and metastasis. This is the key factor that leads to poor efficacy of different kinds of therapy including chemotherapy, radiotherapy, photodynamic therapy, etc. In recent years, the construction of hypoxia-relieving functional nanoplatforms through nanotechnology has become a new strategy to reverse the current situation of tumor microenvironment hypoxia and improve the effectiveness of tumor treatment. Here, the main strategies and recent progress in constructing nanoplatforms are focused on to directly carry oxygen, generate oxygen in situ, inhibit mitochondrial respiration, and enhance blood perfusion to alleviate tumor hypoxia. The advantages and disadvantages of these nanoplatforms are compared. Meanwhile, nanoplatforms based on organic and inorganic substances are also summarized and classified. Through the comprehensive overview, it is hoped that the summary of these nanoplatforms for alleviating hypoxia could provide new enlightenment and prospects for the construction of nanomaterials in this field.

Isolation and Biological Activity of Iezoside and Iezoside B, SERCA Inhibitors from Floridian Marine Cyanobacteria

Marine cyanobacteria are a rich source of bioactive natural products. Here, we report the isolation and structure elucidation of the previously reported iezoside (1) and its C-31 O-demethyl analogue, iezoside B (2), from a cyanobacterial assemblage collected at Loggerhead Key in the Dry Tortugas, Florida. The two compounds have a unique skeleton comprised of a peptide, a polyketide and a modified sugar unit. The compounds were tested for cytotoxicity and effects on intracellular calcium. Both compounds exhibited cytotoxic activity with an IC₅₀ of 1.5 and 3.0 μΜ, respectively, against A549 lung carcinoma epithelial cells and 1.0 and 2.4 μΜ against HeLa cervical cancer cells, respectively. In the same cell lines, compounds 1 and 2 show an increase in cytosolic calcium with approximate EC₅₀ values of 0.3 and 0.6 μΜ in A549 cells and 0.1 and 0.5 μΜ, respectively, in HeLa cells, near the IC₅₀ for cell viability, suggesting that the increase in cytosolic calcium is functionally related to the cytotoxicity of the compounds and consistent with their activity as SERCA (sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase) inhibitors. The structure-activity relationship provides evidence that structural changes in the sugar unit may be tolerated, and the activity is tunable. This finding has implications for future analogue synthesis and target interaction studies.

New Nostocyclophanes from Nostoc linckia

Six new nostocyclophanes and four known compounds have been isolated from Nostoc linckia (Nostocaceae) cyanobacterial strain UTEX B1932. The new compounds, nostocyclophanes E-J (1-6), were characterized by NMR and MS techniques. The known compounds were nostocyclophanes B-D, previously isolated from this strain, and dedichloronostocyclophane D. Structural modifications on the new [7.7]paracyclophane analogs 1-5, isolated from the 80% methanol fraction, range from simple changes such as the lack of methylation or halogenation to more unusual modifications such as those seen in nostocyclophane H (4), in which the exocyclic alkyl chains are of different length; this is the first time this modification has been observed in this family of natural products. In addition, nostocyclophane J (6) is a linear analog in which C-20 is chlorinated in preparation for the presumed enzymatic Friedel-Craft cyclization needed to form the final ring structure, analogous to the biosynthesis of the related cylindrocyclophanes. Nostocyclophane D, dedichloronostocyclophane D, and nostocyclophanes E-J demonstrated moderate to weak growth inhibition against MDA-MB-231 breast cancer cells.

From model organism to application: Bacteria-induced growth and development of the green seaweed Ulva and the potential of microbe leveraging in algal aquaculture

The marine green macroalga Ulva (Chlorophyta, Ulvales), also known as sea lettuce, coexists with a diverse microbiome. Many Ulva species proliferate in nature and form green algal blooms ("green tides"), which can occur when nutrient-rich wastewater from agricultural or densely populated areas is flushed into the sea. Bacteria are necessary for the adhesion of Ulva to its substrate, its growth, and the development of its blade morphology. In the absence of certain bacteria, Ulva mutabilis develops into a callus-like morphotype. However, with the addition of the necessary marine bacteria, the entire morphogenesis can be restored. Surprisingly, just two bacteria isolated from U. mutabilis are sufficient for inducing morphogenesis and establishing the reductionist system of a tripartite community. While one bacterial strain causes algal blade cell division, another causes the differentiation of basal cells into a rhizoid and supports cell wall formation because of a low concentration of the morphogen thallusin (below 10^-10 mol/L). This review focuses on the research conducted on this topic since 2015, discusses how U. mutabilis has developed into a model organism in chemical ecology, and explores the questions that have already been addressed and the perspectives that a reductionist model system allows. In particular, the field of systems biology will achieve a comprehensive, quantitative understanding of the dynamic interactions between Ulva and its associated bacteria to better predict the behavior of the system as a whole. The reductionist approach has enabled the study of the bacteria-induced morphogenesis of Ulva. Specific questions regarding the optimization of cultivation conditions as well as the yield of raw materials for the food and animal feed industries can be answered in the laboratory and through applied science. Genome sequencing, the improvement of genetic engineering tools, and the first promising attempts to leverage macroalgae-microbe interactions in aquaculture make this model organism, which has a comparatively short parthenogenetic life cycle, attractive for both fundamental and applied research. The reviewed research paves the way for the synthetic biology of macroalgae-associated microbiomes in sustainable aquacultures.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Metabolomics Applied to Cyanobacterial Toxins and Natural Products

The biological and chemical diversity of Cyanobacteria is remarkable. These ancient prokaryotes are widespread in nature and can be found in virtually every habitat on Earth where there is light and water. They are producers of an array of secondary metabolites with important ecological roles, toxic effects, and biotechnological applications. The investigation of cyanobacterial metabolites has benefited from advances in analytical tools and bioinformatics that are employed in metabolomic analyses. In this chapter, we review selected articles highlighting the use of targeted and untargeted metabolomics in the analyses of secondary metabolites produced by cyanobacteria. Here, cyanobacterial secondary metabolites have been didactically divided into toxins and natural products according to their relevance to toxicological studies and drug discovery, respectively. This review illustrates how metabolomics has improved the chemical analysis of cyanobacteria in terms of speed, sensitivity, selectivity, and/or coverage, allowing for broader and more complex scientific questions.

Mechanism of Action of Ribosomally Synthesized and Post-Translationally Modified Peptides

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a natural product class that has undergone significant expansion due to the rapid growth in genome sequencing data and recognition that they are made by biosynthetic pathways that share many characteristic features. Their mode of actions cover a wide range of biological processes and include binding to membranes, receptors, enzymes, lipids, RNA, and metals as well as use as cofactors and signaling molecules. This review covers the currently known modes of action (MOA) of RiPPs. In turn, the mechanisms by which these molecules interact with their natural targets provide a rich set of molecular paradigms that can be used for the design or evolution of new or improved activities given the relative ease of engineering RiPPs. In this review, coverage is limited to RiPPs originating from bacteria.

Marine Cyanobacteria as Sources of Lead Anticancer Compounds: A Review of Families of Metabolites with Cytotoxic, Antiproliferative, and Antineoplastic Effects

The marine environment is highly diverse, each living creature fighting to establish and proliferate. Among marine organisms, cyanobacteria are astounding secondary metabolite producers representing a wonderful source of biologically active molecules aimed to communicate, defend from predators, or compete. Studies on these molecules’ origins and activities have been systematic, although much is still to be discovered. Their broad chemical diversity results from integrating peptide and polyketide synthetases and synthases, along with cascades of biosynthetic transformations resulting in new chemical structures. Cyanobacteria are glycolipid, macrolide, peptide, and polyketide producers, and to date, hundreds of these molecules have been isolated and tested. Many of these compounds have demonstrated important bioactivities such as cytotoxicity, antineoplastic, and antiproliferative activity with potential pharmacological uses. Some are currently under clinical investigation. Additionally, conventional chemotherapeutic treatments include drugs with a well-known range of side effects, making anticancer drug research from new sources, such as marine cyanobacteria, necessary. This review is focused on the anticancer bioactivities of metabolites produced by marine cyanobacteria, emphasizing the identification of each variant of the metabolite family, their chemical structures, and the mechanisms of action underlying their biological and pharmacological activities.

Genome Mining as an Alternative Way for Screening the Marine Organisms for Their Potential to Produce UV-Absorbing Mycosporine-like Amino Acid

Mycosporine-like amino acids (MAAs) are small molecules with robust ultraviolet (UV)-absorbing capacities and a huge potential to be used as an environmentally friendly natural sunscreen. MAAs, temperature, and light-stable compounds demonstrate powerful photoprotective capacities and the ability to capture light in the UV-A and UV-B ranges without the production of damaging free radicals. The biotechnological uses of these secondary metabolites have been often limited by the small quantities restored from natural resources, variation in MAA expression profiles, and limited success in heterologous expression systems. Overcoming these obstacles requires a better understanding of MAA biosynthesis and its regulatory processes. MAAs are produced to a certain extent via a four-enzyme pathway, including genes encoding enzymes dehydroquinate synthase, enzyme O-methyltransferase, adenosine triphosphate grasp, and a nonribosomal peptide synthetase. However, there are substantial genetic discrepancies in the MAA genetic pathway in different species, suggesting further complexity of this pathway that is yet to be fully explored. In recent years, the application of genome-mining approaches allowed the identification of biosynthetic gene clusters (BGCs) that resulted in the discovery of many new compounds from unconventional sources. This review explores the use of novel genomics tools for linking BGCs and secondary metabolites based on the available omics data, including MAAs, and evaluates the potential of using novel genome-mining tools to reveal a cryptic potential for new bioproduct screening approaches and unrevealing new MAA producers.

Isolation of Caldorazole, a Thiazole-Containing Polyketide with Selective Cytotoxicity under Glucose-Restricted Conditions

Caldorazole (1) was isolated from the marine cyanobacterium Caldora sp. collected on Ishigaki Island, Okinawa, Japan. Its structure was determined to be a new polyketide that contained two thiazole rings and an O-methylenolpyruvamide moiety. Caldorazole (1) showed strong cytotoxicity toward tumor cells that had been seeded at a high density. Cell death induced by 1 in HeLa and A431 cells was also observed only in the presence of the glycolysis blocker 2-deoxy-d-glucose (2DG). Co-treatment with 1 and 2DG remarkably decreased ATP levels in these cells. Furthermore, 1 selectively inhibited complex I in the mitochondrial respiratory chain. Thus, 1 was demonstrated to exert cytotoxicity toward human tumor cells by blocking mitochondrial respiration.

Pseudanabaena galeata CCNP1313—Biological Activity and Peptides Production

Even cyanobacteria from ecosystems of low biodiversity, such as the Baltic Sea, can constitute a rich source of bioactive metabolites. Potent toxins, enzyme inhibitors, and anticancer and antifungal agents were detected in both bloom-forming species and less commonly occurring cyanobacteria. In previous work on the Baltic Pseudanabaena galeata CCNP1313, the induction of apoptosis in the breast cancer cell line MCF-7 was documented. Here, the activity of the strain was further explored using human dermal fibroblasts, African green monkey kidney, cancer cell lines (T47D, HCT-8, and A549ACE2/TMPRSS2) and viruses (SARS-CoV-2, HCoV-OC43, and WNV). In the tests, extracts, chromatographic fractions, and the main components of the P. galeata CCNP1313 fractions were used. The LC-MS/MS analyses of the tested samples led to the detection of forty-five peptides. For fourteen of the new peptides, putative structures were proposed based on MS/MS spectra. Although the complex samples (i.e., extracts and chromatographic fractions) showed potent cytotoxic and antiviral activities, the effects of the isolated compounds were minor. The study confirmed the significance of P. galeata CCNP1313 as a source of metabolites with potent activity. It also illustrated the difficulties in assigning the observed biological effects to specific metabolites, especially when they are produced in minute amounts.

Disclosing the antitumour potential of the marine bromoditerpene sphaerococcenol A on distinct cancer cellular models

Nature has revealed to be a key source of innovative anticancer drugs. This study evaluated the antitumour potential of the marine bromoditerpene sphaerococcenol A on different cancer cellular models. Dose-response analyses (0.1-100 µM; 24 h) were accomplished in eight different tumour cell lines (A549, CACO-2, HCT-15, MCF-7, NCI-H226, PC-3, SH-SY5Y, SK-MEL-28). Deeper studies were conducted on MFC-7 cells, namely, determination of hydrogen peroxide (H₂O₂) levels and evaluation of apoptosis biomarkers (phosphatidylserine membrane translocation, mitochondrial dysfunction, Caspase-9 activity, and DNA changes). The ability of the compound to induce genotoxicity was verified in L929 fibroblasts. Sphaerococcenol A capacity to impact colorectal-cancer stem cells (CSCs) tumourspheres (HT29, HCT116, SW620) was evaluated by determining tumourspheres viability, number, and area, as well as the proteasome inhibitory activity. Sphaerococcenol A hepatoxicity was studied in AML12 hepatocytes. The compound exhibited cytotoxicity in all malignant cell lines (IC₅₀ ranging from 4.5 to 16.6 µM). MCF-7 cells viability loss was accompanied by H₂O₂ generation, mitochondrial dysfunction, Caspase-9 activation and DNA nuclear morphology changes. Furthermore, the compound displayed the lowest IC₅₀ on HT29-derived tumourspheres (0.70 µM), followed by HCT116 (1.77 µM) and SW620 (2.74 µM), impacting the HT29 tumoursphere formation by reducing their number and area. Finally, the compound displayed low cytotoxicity on AML12 hepatocytes without genotoxicity. Overall, sphaerococcenol A exhibits broad cytotoxic effects on different tumour cells, increasing H₂O₂ production and apoptosis. It also affects colorectal CSCs-enriched tumoursphere development. These data highlight the relevance to include sphaerococcenol A in further pharmacological studies aiming cancer treatments.

Discovery of Anticancer Agents of Diverse Natural Origin

Research progress from mainly over the last five years is described for a multidisciplinary collaborative program project directed toward the discovery of potential anticancer agents from a broad range of taxonomically defined organisms. Selected lead compounds with potential as new antitumor agents that are representative of considerable structural diversity have continued to be obtained from each of tropical plants, terrestrial and aquatic cyanobacteria, and filamentous fungi. Recently, a new focus has been on the investigation of the constituents of U.S. lichens and their fungal mycobionts. A medicinal chemistry and pharmacokinetics component of the project has optimized structurally selected lead natural products, leading to enhanced cytotoxic potencies against selected cancer cell lines. Biological testing has shown several compounds to have in vivo activity, and relevant preliminary structure-activity relationship and mechanism of action studies have been performed. Several promising lead compounds worthy of further investigation have been identified from the most recent collaborative work performed.

Targeted Discovery of Amantamide B, an Ion Channel Modulating Nonapeptide from a South China Sea Oscillatoria Cyanobacterium

Amantamide B (1) is a new linear nonapeptide analogue of the cyanobacterial natural product amantamide A (2), and both have methyl ester and butanamide termini. These compounds were discovered in this study from the organic extract of a tropical marine filamentous cyanobacterium, Oscillatoria sp., collected around the Paracel Islands in the South China Sea. The use of LC-MS/MS molecular networking for sample prioritization and as an analytical dereplication tool facilitated the targeted isolation of 1 and 2. These molecules were characterized by spectroscopy and spectrometry, and configurational assignments were determined using chemical degradation and chiral-phase HPLC analysis. Compounds 1 and 2 modulated spontaneous calcium oscillations without notable cytotoxicity at 10 μM in short duration in vitro testing on primary cultured neocortical neurons, a model system that evaluates neuronal excitability and/or the potential activity on Ca²⁺ signaling. Both molecules were also found to be moderately cytotoxic in longer duration bioassays, with in vitro IC₅₀ values of 1-10 μM against CCRF-CEM human T lymphoblastoid cells and U937 human histiocytic lymphoma cells. These formerly undiscovered bioactivities of known compound 2 expand upon its previously reported function as a selective CXCR7 agonist among 168 GPCR targets.

Photoaffinity Probe Reveals the Potential Target of Harringtonolide for Cancer Cell Migration Inhibition

Harringtonolide (HO, 1) is a bioactive diterpenoid tropone isolated from Cephalotaxus harringtonia with antiproliferation activity. Until now there have been no reports to elucidate its anticancer mechanism. Herein we report the synthesis of HO-derived probes (10, 11, and 12) to identify the possible target of HO. As a result, the application of a novel photoaffinity alkyne-tagged probe from HO (compound 12) showed direct engagement between HO and receptor for activated C kinase 1 (RACK1). Furthermore, HO could suppress the epithelial-mesenchymal transition (EMT) process and inhibit activation of the FAK/Src/STAT3 signaling pathway in A375 cells. This study provides a groundwork for HO as an effective antitumor agent that targets RACK1 to suppress cancer cell migration.

Possible Functional Roles of Patellamides in the Ascidian-Prochloron Symbiosis

Patellamides are highly bioactive compounds found along with other cyanobactins in the symbiosis between didemnid ascidians and the enigmatic cyanobacterium Prochloron. The biosynthetic pathway of patellamide synthesis is well understood, the relevant operons have been identified in the Prochloron genome and genes involved in patellamide synthesis are among the most highly transcribed cyanobacterial genes in hospite. However, a more detailed study of the in vivo dynamics of patellamides and their function in the ascidian-Prochloron symbiosis is complicated by the fact that Prochloron remains uncultivated despite numerous attempts since its discovery in 1975. A major challenge is to account for the highly dynamic microenvironmental conditions experienced by Prochloron in hospite, where light-dark cycles drive rapid shifts between hyperoxia and anoxia as well as pH variations from pH ~6 to ~10. Recently, work on patellamide analogues has pointed out a range of different catalytic functions of patellamide that could prove essential for the ascidian-Prochloron symbiosis and could be modulated by the strong microenvironmental dynamics. Here, we review fundamental properties of patellamides and their occurrence and dynamics in vitro and in vivo. We discuss possible functions of patellamides in the ascidian-Prochloron symbiosis and identify important knowledge gaps and needs for further experimental studies.

Photosynthetic Oxygenation-Augmented Sonodynamic Nanotherapy of Hypoxic Tumors

Reactive oxygen species (ROS) has been employed as a powerful therapeutic agent for eradicating tumor via oxidative stress. As an emerging ROS-involving noninvasive anticancer therapeutic modality, sonodynamic therapy (SDT) with high tissue penetration depth and benign remote spatiotemporal selectivity has been progressively utilized as the distinct alternative for ROS-based tumor treatment. However, the hypoxic tumor microenvironment substantially restricts the sonodynamic effect. In this work, an oxygen self-sufficient hybrid sonosensitizer on the basis of photosynthetic microorganisms cyanobacteria (Cyan) integrated with ultrasmall oxygen-deficient bimetallic oxide Mn_1.4 WO_x nanosonosensitizers, termed as M@C, is designed and engineered to overcome the critical issue of hypoxia-induced tumor resistance and strengthen the SDT effect. The sustained photosynthetic oxygen production by Cyan under light illumination can promote Mn_1.4 WO_x nanosonosensitizers to produce more ROS against cancer cells both in vitro and in vivo under ultrasound (US) irradiation. Especially, the sustained oxygen evolution for suppressing the gene expression of hypoxia-inducible factor 1alpha (HIF-1α) further boosts and augments the SDT efficiency. Thus, this work provides the paradigm that the rationally engineered biohybrid microorganism-based multifunctional sonosensitizers can serve as an effective bioplatform for augmenting the therapeutic efficiency of SDT, particularly for the treatment of hypoxic tumors.

Biological Activity and Stability of Aeruginosamides from Cyanobacteria

Aeruginosamides (AEGs) are classified as cyanobactins, ribosomally synthesized peptides with post-translational modifications. They have been identified in cyanobacteria of genera Microcystis, Oscillatoria, and Limnoraphis. In this work, the new data on the in vitro activities of three AEG variants, AEG A, AEG625 and AEG657, and their interactions with metabolic enzymes are reported. Two aeruginosamides, AEG625 and AEG657, decreased the viability of human breast cancer cell line T47D, but neither of the peptides was active against human liver cancer cell line Huh7. AEGs also did not change the expression of MIR92b-3p, but for AEG625, the induction of oxidative stress was observed. In the presence of a liver S9 fraction containing microsomal and cytosolic enzymes, AEG625 and AEG657 showed high stability. In the same assays, quick removal of AEG A was recorded. The peptides had mild activity against three cytochrome P450 enzymes, CYP2C9, CYP2D6 and CYP3A4, but only at the highest concentration used in the study (60 µM). The properties of AEGs, i.e., cytotoxic activity and in vitro interactions with important metabolic enzymes, form a good basis for further studies on their pharmacological potential.

Luquilloamides, Cytotoxic Lipopeptides from a Puerto Rican Collection of the Filamentous Marine Cyanobacterium Oscillatoria sp

Luquilloamides A-G (1-7) were isolated from a small environmental collection of a marine cyanobacterium found growing on eelgrass (Zostera sp.) near Luquillo, Puerto Rico. Structure elucidation of the luquilloamides was accomplished via detailed NMR and MS analyses, and absolute configurations were determined using a combination of advanced Mosher's method, J-based configuration analysis, semisynthetic fragment analysis derived from ozonolysis, methylation, Baeyer-Villiger oxidation, Mosher's esterification, specific rotations, and ECD data. Except for 2, the luquilloamides share a characteristic tert-butyl-containing polyketide fragment, β-alanine, and a proposed highly modified polyketide extension. While compound 1 is a linear lipopeptide with two α-methyl branches and a vinyl chloride functionality in the polyketide portion, compounds 4, 6, and 7 possess a cyclohexanone structure with methylation on the α- or β-positions of the polyketide as well as an acetyl group. Interestingly, the absolute configuration at C-5 and C-6 on the cyclohexanone unit in 7 is opposite to that of 4-6. Compound 3 was revealed to have a tert-butyl-containing polyketide, β-alanine, and a PKS/NRPS-derived γ-isopropyl pyrrolinone. Compound 2 may be a hydrolysis product of 3. Of the seven new compounds, 1 showed the most potent cytotoxicity to human H-460 lung cancer cells.

Development of an agar-plug cultivation system for bioactivity assays of actinomycete strain collections

Natural products are an important source of lead compounds for the development of drug substances. Actinomycetes have been valuable especially for the discovery of antibiotics. Increasing occurrence of antibiotic resistance among bacterial pathogens has revived the interest in actinomycete natural product research. Actinobacteria produce a different set of natural products when cultivated on solid growth media compared with submersed culture. Bioactivity assays involving solid media (e.g. agar-plug assays) require manual manipulation of the strains and agar plugs. This is less convenient for the screening of larger strain collections of several hundred or thousand strains. Thus, the aim of this study was to develop a 96-well microplate-based system suitable for the screening of actinomycete strain collections in agar-plug assays. We developed a medium-throughput cultivation and agar-plug assay workflow that allows the convenient inoculation of solid agar plugs with actinomycete spore suspensions from a strain collection, and the transfer of the agar plugs to petri dishes to conduct agar-plug bioactivity assays. The development steps as well as the challenges that were overcome during the development (e.g. system sterility, handling of the agar plugs) are described. We present the results from one exemplary screening campaign targeted to identify compounds inhibiting Agr-based quorum sensing where the workflow was used successfully. We present a novel and convenient workflow to combine agar diffusion assays with microtiter-plate-based cultivation systems in which strains can grow on a solid surface. This workflow facilitates and speeds up the initial medium throughput screening of natural product-producing actinomycete strain collections against monitor strains in agar-plug assays.

First Total Synthesis and Structure-Activity Relationship of Iheyamide A, an Antitrypanosomal Linear Peptide Isolated from a Dapis sp. Marine Cyanobacterium

Iheyamide A (1) is an antitrypanosomal linear peptide isolated from a Dapis sp. marine cyanobacterium by our group in 2020, and based on structure-activity relationships of its natural analogues, the C-terminal pyrrolinone moiety has been identified as the phamacophore for its antiparasitic activity. Further, we isolated this pyrrolinone moiety by itself as a new natural product from the marine cyanobacterium and named it iheyanone (2). As expected, iheyanone (2) showed antitrypanosomal activity, but its potency was weaker than iheyamide A (1). To clarify more detailed structure-activity relationships, we completed a total synthesis of iheyamide A (1) along with iheyanone (2) and evaluated the antitrypanosomal activities of several synthetic intermediates. As a result, we found that the longer the peptide chain, the stronger the antitrypanosomal activity. As iheyamide A (1) showed selective toxicity against Trypanosoma brucei rhodesiense, these findings can provide design guidelines for antitrypanosomal drugs.

Portobelamides A and B and Caciqueamide, Cytotoxic Peptidic Natural Products from a Caldora sp. Marine Cyanobacterium

Three new compounds, portobelamides A and B (1 and 2), 3-amino-2-methyl-7-octynoic acid (AMOYA) and hydroxyisovaleric acid (Hiva) containing cyclic depsipeptides, and one long chain lipopeptide caciqueamide (3), were isolated from a field-collection of a Caldora sp. marine cyanobacterium obtained from Panama as part of the Panama International Cooperative Biodiversity Group Program. Their planar structures were elucidated through analysis of 2D NMR and MS data, especially high resolution (HR) MS²/MS³ fragmentation methods. The absolute configurations of compounds 1 and 2 were deduced by traditional hydrolysis, derivative formation, and chromatographic analyses compared with standards. Portobelamide A (1) showed good cytotoxicity against H-460 human lung cancer cells (33% survival at 0.9 μM).

Heterologous production of cyanobacterial compounds

Cyanobacteria produce a plethora of compounds with unique chemical structures and diverse biological activities. Importantly, the increasing availability of cyanobacterial genome sequences and the rapid development of bioinformatics tools have unraveled the tremendous potential of cyanobacteria in producing new natural products. However, the discovery of these compounds based on cyanobacterial genomes has progressed slowly as the majority of their corresponding biosynthetic gene clusters (BGCs) are silent. In addition, cyanobacterial strains are often slow-growing, difficult for genetic engineering, or cannot be cultivated yet, limiting the use of host genetic engineering approaches for discovery. On the other hand, genetically tractable hosts such as Escherichia coli, Actinobacteria, and yeast have been developed for the heterologous expression of cyanobacterial BGCs. More recently, there have been increased interests in developing model cyanobacterial strains as heterologous production platforms. Herein, we present recent advances in the heterologous production of cyanobacterial compounds in both cyanobacterial and noncyanobacterial hosts. Emerging strategies for BGC assembly, host engineering, and optimization of BGC expression are included for fostering the broader applications of synthetic biology tools in the discovery of new cyanobacterial natural products.

Metabolomic Characterization of a cf. Neolyngbya Cyanobacterium from the South China Sea Reveals Wenchangamide A, a Lipopeptide with In Vitro Apoptotic Potential in Colon Cancer Cells

Metabolomics can be used to study complex mixtures of natural products, or secondary metabolites, for many different purposes. One productive application of metabolomics that has emerged in recent years is the guiding direction for isolating molecules with structural novelty through analysis of untargeted LC-MS/MS data. The metabolomics-driven investigation and bioassay-guided fractionation of a biomass assemblage from the South China Sea dominated by a marine filamentous cyanobacteria, cf. Neolyngbya sp., has led to the discovery of a natural product in this study, wenchangamide A (1). Wenchangamide A was found to concentration-dependently cause fast-onset apoptosis in HCT116 human colon cancer cells in vitro (24 h IC₅₀ = 38 μM). Untargeted metabolomics, by way of MS/MS molecular networking, was used further to generate a structural proposal for a new natural product analogue of 1, here coined wenchangamide B, which was present in the organic extract and bioactive sub-fractions of the biomass examined. The wenchangamides are of interest for anticancer drug discovery, and the characterization of these molecules will facilitate the future discovery of related natural products and development of synthetic analogues.

Promising Activities of Marine Natural Products against Hematopoietic Malignancies

According to the WHO classification of tumors, more than 150 typologies of hematopoietic and lymphoid tumors exist, and most of them remain incurable diseases that require innovative approaches to improve therapeutic outcome and avoid side effects. Marine organisms represent a reservoir of novel bioactive metabolites, but they are still less studied compared to their terrestrial counterparts. This review is focused on marine natural products with anticancer activity against hematological tumors, highlighting recent advances and possible perspectives. Until now, there are five commercially available marine-derived compounds for the treatment of various hematopoietic cancers (e.g., leukemia and lymphoma), two molecules in clinical trials, and series of compounds and/or extracts from marine micro- and macroorganisms which have shown promising properties. In addition, the mechanisms of action of several active compounds and extracts are still unknown and require further study. The continuous upgrading of omics technologies has also allowed identifying enzymes with possible bioactivity (e.g., l-asparaginase is currently used for the treatment of leukemia) or the enzymes involved in the synthesis of bioactive secondary metabolites which can be the target of heterologous expression and genetic engineering.

Phytotherapy of Hypertension: An Updated Overview

BACKGROUND

Cardiovascular disorders are the leading cause of morbidity and mortality throughout the globe. Hypertension is the main risk factor that contributes to the development of many diseases. The use of herbal therapies, medicinal plants and their derivatives for the remedy and management of hypertension is well-recognized and popular among a wide part of the world population.

METHODS

The aim of the current review was to collect, treat, and critically analyze the published research studies relative to experimental and clinical investigations which have studied the blood pressure lowering abilities of medicinal plant derivatives in the last decade. This review was organized into three principal axes; the first axis was attributed to the in vivo and in vitro experimental studies; the second treated the clinical trials; while, the last one is devoted to analyze the mechanisms of action underlying the therapeutic antihypertensive effectiveness of phytochemicals.

RESULTS

Different types of extracts and isolated molecules obtained from a large variety of species demonstrated their efficiency in improving the increase of blood pressure either experimentally or clinically. Medicinal species such as garlic (Allium sativum), celery (Apium graveolens), Black Cumin (Nigella sativa) and Ginseng (Panax) are among the most common and therapeutically used plant derivatives for controlling hypertension while Asteraceae, Apiaceae and Rosaceae are among the botanical families which were frequently studied in the last decade. Isolated compounds such as allicin and apigenin have received more interest in this field. Recent evidence from clinical trials suggests that a wide variety of herbal preparations and plant extracts or natural isolated compounds have a favorable therapeutic impact on blood flow. Interestingly, phytochemicals can either act directly on blood vessels via a vasorelaxant effect involving a variety of signaling cascades or indirectly through inhibiting or stimulating diversity of systems such as angiotensin-converting enzyme (ACE), renin-angiotensin system (RAS) or the diuretic activity. Hence, based on the findings of the present review medicinal plant derivatives could be used as preventive and curative agents in the case of cardiovascular disorders, particularly hypertension and could play a promoting function for the discovery of new antihypertensive agents.

CONCLUSION

The analysis of the published data shows that a great effort remains to be done to investigate the medicinal plants cited as antihypertensive through published ethnopharmacological surveys. The analysis of the literature in this field shows the lack of standardization at the level of experimental study methods as well as the need to study purified molecules. Moreover, the mechanistic studies when they exist remain in the whole partial. On the other hand, few advanced clinical studies have been conducted. Finally, the determination of the efficacy/safety ratio remains absent in almost all studies.

Inhibition of Intestinal Lipid Absorption by Cyanobacterial Strains in Zebrafish Larvae

Obesity is a complex metabolic disease, which is increasing worldwide. The reduction of dietary lipid intake is considered an interesting pathway to reduce fat absorption and to affect the chronic energy imbalance. In this study, zebrafish larvae were used to analyze effects of cyanobacteria on intestinal lipid absorption in vivo. In total, 263 fractions of a cyanobacterial library were screened for PED6 activity, a fluorescent reporter of intestinal lipases, and 11 fractions reduced PED6 activity > 30%. Toxicity was not observed for those fractions, considering mortality, malformations or digestive physiology (protease inhibition). Intestinal long-chain fatty acid uptake (C16) was reduced, but not short-chain fatty acid uptake (C5). Alteration of lipid classes by high-performance thin-layer chromatography (HPTLC) or lipid processing by fluorescent HPTLC was analyzed, and 2 fractions significantly reduced the whole-body triglyceride level. Bioactivity-guided feature-based molecular networking of LC-MS/MS data identified 14 significant bioactive mass peaks (p < 0.01, correlation > 0.95), which consisted of 3 known putative and 11 unknown compounds. All putatively identified compounds were known to be involved in lipid metabolism and obesity. Summarizing, some cyanobacterial strains repressed intestinal lipid absorption without any signs of toxicity and could be developed in the future as nutraceuticals to combat obesity.

Covalent Modification of Proteins by Plant-Derived Natural Products: Proteomic Approaches and Biological Impacts

Plant-derived natural products (NPs) with electrophilic functional groups engage various subsets of the proteome via covalent modification of nucleophilic cysteine residues. This electrophile-nucleophile interaction can change protein conformation, alter protein function, and modulate their biological action. The biological significance of these covalent protein modifications in health and disease is increasingly recognized. One way to understand covalent NP-protein interactions is to utilize traditional proteomics and modern mass spectrometry (MS)-based proteomic strategies. These strategies have proven effective in uncovering specific NP protein targets and are critical first steps that allow for a much deeper understanding of the ability of NPs to modulate cellular processes. Here, plant-derived NPs that covalently modify proteins are reviewed, the biological significance of these covalent modifications, and the different proteomic strategies that have been employed to study these NP-protein interactions.

Therapeutic roles of natural remedies in combating hereditary ataxia: A systematic review

Background

Hereditary ataxia (HA) represents a group of genetically heterogeneous neurodegenerative diseases caused by dysfunction of the cerebellum or disruption of the connection between the cerebellum and other areas of the central nervous system. Phenotypic manifestation of HA includes unsteadiness of stance and gait, dysarthria, nystagmus, dysmetria and complaints of clumsiness. There are no specific treatments for HA. Management strategies provide supportive treatment to reduce symptoms.

Objectives

This systematic review aimed to identify, evaluate and summarise the published literature on the therapeutic roles of natural remedies in the treatment of HA to provide evidence for clinical practice.

Methods

A systematic literature search was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Web of Science, PubMed and Science Direct Scopus were thoroughly searched for relevant published articles from June 2007 to July 2020.

Results

Ten pre-clinical and two clinical studies were eligible for inclusion in this systematic review. We identified the therapeutic roles of medicinal plants Brassica napus, Gardenia jasminoides, Gastrodia elata, Ginkgo biloba, Glycyrrhiza inflata, Paeonia lactiflora, Pueraria lobata and Rehmannia glutinosa; herbal formulations Shaoyao Gancao Tang and Zhengan Xifeng Tang; and medicinal mushroom Hericium erinaceus in the treatment of HA. In this review, we evaluated the mode of actions contributing to their therapeutic effects, including activation of the ubiquitin–proteasome system, activation of antioxidant pathways, maintenance of intracellular calcium homeostasis and regulation of chaperones. We also briefly highlighted the integral cellular signalling pathways responsible for orchestrating the mode of actions.

Conclusion

We reviewed the therapeutic roles of natural remedies in improving or halting the progression of HA, which warrant further study for applications into clinical practice.

Editorial to Special Issue-"Structure-Activity Relationships (SAR) of Natural Products"

The topic of structure-activity-relationships (SAR) has recently drawn a lot of attention, and there is increasing interest in natural products (NPs) as a "source of inspiration" for the discovery of new lead compounds [...].

Cyanobacteria as Natural Therapeutics and Pharmaceutical Potential: Role in Antitumor Activity and as Nanovectors

Cyanobacteria (blue-green microalgae) are ubiquitous, Gram-negative photoautotrophic prokaryotes. They are considered as one of the most efficient sources of bioactive secondary metabolites. More than 50% of cyanobacteria are cultivated on commercial platforms to extract bioactive compounds, which have bene shown to possess anticancer activity. The chemically diverse natural compounds or their analogues induce cytotoxicity and potentially kill a variety of cancer cells via the induction of apoptosis, or altering the activation of cell signaling, involving especially the protein kinase-C family members, cell cycle arrest, mitochondrial dysfunctions and oxidative damage. These therapeutic properties enable their use in the pharma and healthcare sectors for the betterment of future generations. This review provides a baseline overview of the anti-cancerous cyanobacterial bioactive compounds, along with recently introduced nanomaterials that could be used for the development of new anticancer drugs to build a healthy future for mankind.

Phytochemical delivery through nanocarriers: a review

In recent times, phytochemicals encapsulated or conjugated with nanocarriers for delivery to the specific sites have gained considerable research interest. Phytochemicals are mostly plant secondary metabolites which reported to be beneficial for human health and in disease theraphy. However, these compound are large size and polar nature of these compounds, make it difficult to cross the blood-brain barrier (BBB), endothelial lining of blood vessels, gastrointestinal tract and mucosa. Moreover, they are enzymatically degraded in the gastrointestinal tract. Therefore, encapsulation or conjugation of these compounds with nanocrriers could be an alternate way to enhance their bioefficacy by influencing their gastrointestinal stability, rate of absorption and dispersion. This review presents an overview of nanocarriers alternatives which improves therapeutic value and avoid toxicity, by releasing bioactive compounds specifically at target tissues with enhanced stability and bioavailability. Future investigations may emphasize on deciphering the structural changes in nanocarriers during digestion and absorption, the difference between in-vitro and in-vivo digestion simulations, and impact of nanocarriers on the metabolism of phytochemicals.

Anti-Inflammatory, Antioxidant, and Wound-Healing Properties of Cyanobacteria from Thermal Mud of Balaruc-Les-Bains, France: A Multi-Approach Study

Background: The Balaruc-les-Bains' thermal mud was found to be colonized predominantly by microorganisms, with cyanobacteria constituting the primary organism in the microbial biofilm observed on the mud surface. The success of cyanobacteria in colonizing this specific ecological niche can be explained in part by their taxa-specific adaptation capacities, and also the diversity of bioactive natural products that they synthesize. This array of components has physiological and ecological properties that may be exploited for various applications. Methods: Nine cyanobacterial strains were isolated from Balaruc thermal mud and maintained in the Paris Museum Collection (PMC). Full genome sequencing was performed coupled with targeted and untargeted metabolomic analyses (HPLC-DAD and LC-MS/MS). Bioassays were performed to determine antioxidant, anti-inflammatory, and wound-healing properties. Results: Biosynthetic pathways for phycobiliproteins, scytonemin, and carotenoid pigments and 124 metabolite biosynthetic gene clusters (BGCs) were characterized. Several compounds with known antioxidant or anti-inflammatory properties, such as carotenoids, phycobilins, mycosporine-like amino acids, and aeruginosins, and other bioactive metabolites like microginins, microviridins, and anabaenolysins were identified. Secretion of the proinflammatory cytokines TNF-α, IL-1β, IL-6, and IL-8 appeared to be inhibited by crude extracts of Planktothricoides raciborskii PMC 877.14, Nostoc sp. PMC 881.14, and Pseudo-chroococcus couteii PMC 885.14. The extract of the Aliinostoc sp. PMC 882.14 strain was able to slightly enhance migration of HaCat cells that may be helpful in wound healing. Several antioxidant compounds were detected, but no significant effects on nitric oxide secretion were observed. There was no cytotoxicity on the three cell types tested, indicating that cyanobacterial extracts may have anti-inflammatory therapeutic potential without harming body cells. These data open up promising uses for these extracts and their respective molecules in drugs or thermal therapies.

Natural Products Targeting the Mitochondria in Cancers

There are abundant sources of anticancer drugs in nature that have a broad prospect in anticancer drug discovery. Natural compounds, with biological activities extracted from plants and marine and microbial metabolites, have significant antitumor effects, but their mechanisms are various. In addition to providing energy to cells, mitochondria are involved in processes, such as cell differentiation, cell signaling, and cell apoptosis, and they have the ability to regulate cell growth and cell cycle. Summing up recent data on how natural products regulate mitochondria is valuable for the development of anticancer drugs. This review focuses on natural products that have shown antitumor effects via regulating mitochondria. The search was done in PubMed, Web of Science, and Google Scholar databases, over a 5-year period, between 2015 and 2020, with a keyword search that focused on natural products, natural compounds, phytomedicine, Chinese medicine, antitumor, and mitochondria. Many natural products have been studied to have antitumor effects on different cells and can be further processed into useful drugs to treat cancer. In the process of searching for valuable new drugs, natural products such as terpenoids, flavonoids, saponins, alkaloids, coumarins, and quinones cover the broad space.

Bioactive Compounds from Marine Heterobranchs

The natural products of heterobranch molluscs display a huge variability both in structure and in their bioactivity. Despite the considerable lack of information, it can be observed from the recent literature that this group of animals possesses an astonishing arsenal of molecules from different origins that provide the molluscs with potent chemicals that are ecologically and pharmacologically relevant. In this review, we analyze the bioactivity of more than 450 compounds from ca. 400 species of heterobranch molluscs that are useful for the snails to protect themselves in different ways and/or that may be useful to us because of their pharmacological activities. Their ecological activities include predator avoidance, toxicity, antimicrobials, antifouling, trail-following and alarm pheromones, sunscreens and UV protection, tissue regeneration, and others. The most studied ecological activity is predation avoidance, followed by toxicity. Their pharmacological activities consist of cytotoxicity and antitumoral activity; antibiotic, antiparasitic, antiviral, and anti-inflammatory activity; and activity against neurodegenerative diseases and others. The most studied pharmacological activities are cytotoxicity and anticancer activities, followed by antibiotic activity. Overall, it can be observed that heterobranch molluscs are extremely interesting in regard to the study of marine natural products in terms of both chemical ecology and biotechnology studies, providing many leads for further detailed research in these fields in the near future.

Targeting Notch in oncology: the path forward

Notch signalling is involved in many aspects of cancer biology, including angiogenesis, tumour immunity and the maintenance of cancer stem-like cells. In addition, Notch can function as an oncogene and a tumour suppressor in different cancers and in different cell populations within the same tumour. Despite promising preclinical results and early-phase clinical trials, the goal of developing safe, effective, tumour-selective Notch-targeting agents for clinical use remains elusive. However, our continually improving understanding of Notch signalling in specific cancers, individual cancer cases and different cell populations, as well as crosstalk between pathways, is aiding the discovery and development of novel investigational Notch-targeted therapeutics.

Ambigols from the Cyanobacterium Fischerella ambigua Increase Prodigiosin Production in Serratia spp

When a library of 573 cyanobacteria extracts was screened for inhibition of the quorum sensing regulated prodigiosin production of Serratia marcescens, an extract of the cyanobacterium Fischerella ambigua (Näg.) Gomont 108b was found to drastically increase prodigiosin production. Bioactivity-guided isolation of the active compounds resulted in the two new natural products ambigol D and E along with the known ambigols A and C. Ambigol C treatment increased prodiginine production of Serratia sp. ATCC 39006 (S39006) by a factor of 10, while ambigols A and D were found to have antibiotic activity against this strain. The RNA-Seq of S39006 treated with ambigol C and subsequent differential gene expression and functional enrichment analyses indicated a significant downregulation of genes associated with the translation machinery and fatty acid biosynthesis in Serratia, as well as increased expression of genes related to the uptake of l-proline. These results suggest that the ambigols increase prodiginine production in S39006 not by activating the SmaIR quorum sensing system but possibly by increasing the precursor supply of l-proline and malonyl-CoA.

Assessment of the Chemical Diversity and Potential Toxicity of Benthic Cyanobacterial Blooms in the Lagoon of Moorea Island (French Polynesia)

In the last decades, an apparent increase in the frequency of benthic cyanobacterial blooms has occurred in coral reefs and tropical lagoons, possibly in part because of global change and anthropogenic activities. In the frame of the survey of marine benthic cyanobacteria proliferating in the lagoon of Moorea Island (French Polynesia), 15 blooms were collected, mainly involving three species—Anabaena sp.1, Lyngbya majuscula and Hydrocoleum majus-B. Their chemical fingerprints, obtained through high performance liquid chromatography combined with UV detection and mass spectrometry (HPLC-UV-MS) analyses, revealed a high extent of species-specificity. The chemical profile of Anabaena sp.1 was characterized by three major cyclic lipopeptides of the laxaphycin family, whereas the one of L. majuscula was characterized by a complex mixture including tiahuramides, trungapeptins and serinol-derived malyngamides. Toxicity screening analyses conducted on these cyanobacterial samples using Artemia salina and mouse neuroblastoma cell-based (CBA-N2a) cytotoxic assays failed to show any toxicity to a degree that would merit risk assessment with regard to public health. However, the apparently increasing presence of blooms of Lyngbya, Hydrocoleum, Anabaena or other benthic cyanobacteria on coral reefs in French Polynesia encourages the implementation of ad hoc monitoring programs for the surveillance of their proliferation and potential assessment of associated hazards.

Discovery, Total Synthesis, and SAR of Anaenamides A and B: Anticancer Cyanobacterial Depsipeptides with a Chlorinated Pharmacophore

New modified depsipeptides and geometric isomers, termed anaenamides A (1a) and B (1b), along with the presumptive biosynthetic intermediate, anaenoic acid (2), were discovered from a marine cyanobacterium from Guam. Structures were confirmed by total synthesis. The alkylsalicylic acid fragment and the C-terminal α-chlorinated α,β-unsaturated ester are novelties in cyanobacterial natural products. Cancer cell viability assays indicated that the C-terminal unit serves as the pharmacophore and that the double-bond geometry impacts the cytotoxicity.

Marine Cyanobacteria: A Source of Lead Compounds and their Clinically-Relevant Molecular Targets

The prokaryotic filamentous marine cyanobacteria are photosynthetic microbes that are found in diverse marine habitats, ranging from epiphytic to endolithic communities. Their successful colonization in nature is largely attributed to genetic diversity as well as the production of ecologically important natural products. These cyanobacterial natural products are also a source of potential drug leads for the development of therapeutic agents used in the treatment of diseases, such as cancer, parasitic infections and inflammation. Major sources of these biomedically important natural compounds are found predominately from marine cyanobacterial orders Oscillatoriales, Nostocales, Chroococcales and Synechococcales. Moreover, technological advances in genomic and metabolomics approaches, such as mass spectrometry and NMR spectroscopy, revealed that marine cyanobacteria are a treasure trove of structurally unique natural products. The high potency of a number of natural products are due to their specific interference with validated drug targets, such as proteasomes, proteases, histone deacetylases, microtubules, actin filaments and membrane receptors/channels. In this review, the chemistry and biology of selected potent cyanobacterial compounds as well as their synthetic analogues are presented based on their molecular targets. These molecules are discussed to reflect current research trends in drug discovery from marine cyanobacterial natural products.