Potential of marine natural products against drug-resistant fungal, viral, and parasitic infections

A reusable AuNPS with increased stability applied for fast screening of trace heavy metals in edible and medicinal marine products

Heavy metal pollution in marine environment poses a severe threat to the safety of marine products and is thus causing increasingly concerns in terms of their toxicity and potential health risks pose to human. Due to the complex matrix of marine products, a fast screening method for heavy metals at trace level with low price, reusability, high accuracy and long lifetime is of urgency and necessity for consumers and processing factories. This work described a simplified screening system through the preparation, characterization and particular application of Au nano particle sensor (AuNPS) in the complex marine matrix, the main aim is to significantly increase the stability, sensitivity and lifetime of detection system dedicated to Cu and Hg trace analysis in marine products. It is worth mentioning that, the proposed screening system was characterized through electrochemical experiments and theoretical calculations, which could be a new evidence for selecting the detection system in commercially complex samples. Importantly, the discipline of deposition and oxidative stripping process on AuNPS was explained based on the mechanism of Metal Ion Deficient Layer (MIDL), and illustrated with SEM changes during stripping process, as well as the dissolving-out rate of metals on AuNPS material. Moreover, to further improve the reusability and stability of AuNPS sensor, the complex marine matrix was purified by pre-plating interferences on indium tin oxide glass electrode. The screening system exhibited a liner response in the range of 0.02-0.10 μg mL^-1 for Hg, 0.01-0.10 μg mL^-1 and 0.001-0.01 μg mL^-1 for Cu with the detection limits of 0.138 mg kg^-1 and 1.51 mg kg^-1 in marine matrix, respectively. The sensitivity and lifetime was at least two times better as compared to similar works even after 20-times use. Finally, this proposed analysis system combined with purification procedure was successfully applied for the edible and medicinal marine products analysis, meanwhile, the accuracy and stability were confirmed with standard analytical methods.

Natural Products Repertoire of the Red Sea

Marine natural products have achieved great success as an important source of new lead compounds for drug discovery. The Red Sea provides enormous diversity on the biological scale in all domains of life including micro- and macro-organisms. In this review, which covers the literature to the end of 2019, we summarize the diversity of bioactive secondary metabolites derived from Red Sea micro- and macro-organisms, and discuss their biological potential whenever applicable. Moreover, the diversity of the Red Sea organisms is highlighted as well as their genomic potential. This review is a comprehensive study that compares the natural products recovered from the Red Sea in terms of ecological role and pharmacological activities.

Microbiome in Chronic Obstructive Pulmonary Disease: Role of Natural Products Against Microbial Pathogens

The "microbiome" is the operative term to refer to a collection of all taxa constituting microbial communities, such as bacteria, archaea, fungi and protists (originally microbiota). The microbiome consists of the indigenous microbial communities and of the host environment that they inhabit. Actually, it has been shown that there is a close relationship between the microbiome and human health and disease condition. Although, initially, the lung was considered sterile, actually, the existence of a healthy lung microbiome is usually accepted. Lung microbiome changes are reported in Chronic Obstructive Pulmonary Disease (COPD) and in its exacerbation. Viral and bacterial infections of the respiratory system are a major cause of COPD exacerbations (AECOPD) leading to increased local and systemic inflammation. Detection rates of virus in AECOPD are variable between 25-62% according to the detection method. The study of human airway and lung disease virome is quite recent and still very limited. The purpose of this review is to summarize recent findings on the lung microbiome composition with a special emphasis on virome in COPD and in AECOPD. Some drugs of natural origins active against resistant bacteria and virus are described.

Targeting Bacterial Antioxidant Systems for Antibiotics Development

The emergence of multidrug-resistant bacteria has become an urgent issue in modern medicine which requires novel strategies to develop antibiotics. Recent studies have supported the hypothesis that antibiotic-induced bacterial cell death is mediated by Reactive Oxygen Species (ROS). The hypothesis also highlighted the importance of antioxidant systems, the defense mechanism which contributes to antibiotic resistance. Thioredoxin and glutathione systems are the two major thiol-dependent systems which not only provide antioxidant capacity but also participate in various biological events in bacteria, such as DNA synthesis and protein folding. The biological importance makes them promising targets for novel antibiotics development. Based on the idea, ebselen and auranofin, two bacterial thioredoxin reductase inhibitors, have been found to inhibit the growth of bacteria lacking the GSH efficiently. A recent study combining ebselen and silver exhibited a strong synergistic effect against Multidrug-Resistant (MDR) Gram-negative bacteria which possess both thioredoxin and glutathione systems. These drug-repurposing studies are promising for quick clinical usage due to their well-known profile.

The genus Micromonospora as a model microorganism for bioactive natural product discovery

This review covers the development of the genus Micromonospora as a model for natural product research and the timeline of discovery progress from the classical bioassay-guided approaches through the application of genome mining and genetic engineering techniques that target specific products. It focuses on the reported chemical structures along with their biological activities and the synthetic and biosynthetic studies they have inspired. This survey summarizes the extraordinary biosynthetic diversity that can emerge from a widely distributed actinomycete genus and supports future efforts to explore under-explored species in the search for novel natural products.

Hepatitis C Virus NS3 Protease and Helicase Inhibitors from Red Sea Sponge (Amphimedon) Species in Green Synthesized Silver Nanoparticles Assisted by in Silico Modeling and Metabolic Profiling

Background

Hepatitis C virus (HCV) infection is a major cause of hepatic diseases all over the world. This necessitates the need to discover novel anti-HCV drugs to overcome emerging drug resistance and liver complications.

Purpose

Total extract and petroleum ether fraction of the marine sponge (Amphimedon spp.) were used for silver nanoparticle (SNP) synthesis to explore their HCV NS3 helicase- and protease-inhibitory potential.

Methods

Characterization of the prepared SNPs was carried out with ultraviolet-visible spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The metabolomic profile of different Amphimedon fractions was assessed using liquid chromatography coupled with high-resolution mass spectrometry. Fourteen known compounds were isolated and their HCV helicase and protease activities assessed using in silico modeling of their interaction with both HCV protease and helicase enzymes to reveal their anti-HCV mechanism of action. In vitro anti-HCV activity against HCV NS3 helicase and protease was then conducted to validate the computation results and compared to that of the SNPs.

Results

Transmission electron–microscopy analysis of NPs prepared from Amphimedon total extract and petroleum ether revealed particle sizes of 8.22–14.30 nm and 8.22–9.97 nm, and absorption bands at λ_max of 450 and 415 nm, respectively. Metabolomic profiling revealed the richness of Amphimedon spp. with different phytochemical classes. Bioassay-guided isolation resulted in the isolation of 14 known compounds with anti-HCV activity, initially revealed by docking studies. In vitro anti–HCV NS3 helicase and protease assays of both isolated compounds and NPs further confirmed the computational results.

Conclusion

Our findings indicate that Amphimedon, total extract, petroleum ether fraction, and derived NPs are promising biosources for providing anti-HCV drug candidates, with nakinadine B and 3,4-dihydro-6-hydroxymanzamine A the most potent anti-HCV agents, possessing good oral bioavailability and penetration power.

Targeting antimicrobial drug resistance with marine natural products

The rise and spread of antimicrobial resistance represents one of the most pressing health issues of today. Antimicrobial resistance in micro-organisms can arise due to a multiplicity of factors, including permeability changes in the cell membrane, increase of drug efflux pumps, enzymatic modification or inactivation of the antibiotic, target site modification, alternative metabolic pathways and biofilm formation. The marine environment is a valuable source of diverse natural products with a huge variety of biological activities. Among them, antimicrobial compounds show promising biological activities against numerous drug-resistant bacteria and fungi, making marine natural products a very promising resource in the search for novel antimicrobial agents. This review summarises the state-of-art of marine natural products with antibacterial and antifungal properties against drug-resistant micro-organisms. These natural products were categorised based on their chemical structure, and their respective sources and activities are highlighted. The chemical diversity associated with these marine-derived molecules is enormous, including peptides, polyketides, alkaloids, sterols, terpenoids, lactones, halogenated compounds, nucleosides, etc., some of which have rare substructures. Some of the marine compounds mentioned do not have intrinsic antimicrobial activity but potentiate the antimicrobial effect of other antimicrobials via inhibition of efflux pumps. Although these agents are still in preclinical studies, evidence of their in vivo efficacy suggest research of new drugs from the ocean to overcome antimicrobial resistance in order to fulfil an unmet medical need.

New Cytotoxic Natural Products from the Red Sea Sponge Stylissa carteri

Bioactivity-guided isolation supported by LC-HRESIMS metabolic profiling led to the isolation of two new compounds, a ceramide, stylissamide A (1), and a cerebroside, stylissoside A (2), from the methanol extract of the Red Sea sponge Stylissa carteri. Structure elucidation was achieved using spectroscopic techniques, including 1D and 2D NMR and HRMS. The bioactive extract's metabolomic profiling showed the existence of various secondary metabolites, mainly oleanane-type saponins, phenolic diterpenes, and lupane triterpenes. The in vitro cytotoxic activity of the isolated compounds was tested against two human cancer cell lines, MCF-7 and HepG2. Both compounds, 1 and 2, displayed strong cytotoxicity against the MCF-7 cell line, with IC50 values at 21.1 ± 0.17 µM and 27.5 ± 0.18 µM, respectively. They likewise showed a promising activity against HepG2 with IC50 at 36.8 ± 0.16 µM for 1 and IC50 30.5 ± 0.23 µM for 2 compared to the standard drug cisplatin. Molecular docking experiments showed that 1 and 2 displayed high affinity to the SET protein and to inhibitor 2 of protein phosphatase 2A (I2PP2A), which could be a possible mechanism for their cytotoxic activity. This paper spreads light on the role of these metabolites in holding fouling organisms away from the outer surface of the sponge, and the potential use of these defensive molecules in the production of novel anticancer agents.

Oxidative Stress-Generating Antimicrobials, a Novel Strategy to Overcome Antibacterial Resistance

Antimicrobial resistance is becoming one of the most important human health issues. Accordingly, the research focused on finding new antibiotherapeutic strategies is again becoming a priority for governments and major funding bodies. The development of treatments based on the generation of oxidative stress with the aim to disrupt the redox defenses of bacterial pathogens is an important strategy that has gained interest in recent years. This approach is allowing the identification of antimicrobials with repurposing potential that could be part of combinatorial chemotherapies designed to treat infections caused by recalcitrant bacterial pathogens. In addition, there have been important advances in the identification of novel plant and bacterial secondary metabolites that may generate oxidative stress as part of their antibacterial mechanism of action. Here, we revised the current status of this emerging field, focusing in particular on novel oxidative stress-generating compounds with the potential to treat infections caused by intracellular bacterial pathogens.

Antibiotics Development and the Potentials of Marine-Derived Compounds to Stem the Tide of Multidrug-Resistant Pathogenic Bacteria, Fungi, and Protozoa

As the search for new antibiotics continues, the resistance to known antimicrobial compounds continues to increase. Many researchers around the world, in response to antibiotics resistance, have continued to search for new antimicrobial compounds in different ecological niches such as the marine environment. Marine habitats are one of the known and promising sources for bioactive compounds with antimicrobial potentials against currently drug-resistant strains of pathogenic microorganisms. For more than a decade, numerous antimicrobial compounds have been discovered from marine environments, with many more antimicrobials still being discovered every year. So far, only very few compounds are in preclinical and clinical trials. Research in marine natural products has resulted in the isolation and identification of numerous diverse and novel chemical compounds with potency against even drug-resistant pathogens. Some of these compounds, which mainly came from marine bacteria and fungi, have been classified into alkaloids, lactones, phenols, quinones, tannins, terpenes, glycosides, halogenated, polyketides, xanthones, macrocycles, peptides, and fatty acids. All these are geared towards discovering and isolating unique compounds with therapeutic potential, especially against multidrug-resistant pathogenic microorganisms. In this review, we tried to summarize published articles from 2015 to 2019 on antimicrobial compounds isolated from marine sources, including some of their chemical structures and tests performed against drug-resistant pathogens.

Chemical and Bioactive Marine Natural Products of Coral-Derived Microorganisms (2015-2017)

Coral-derived microorganisms are known for their inherent ability to produce novel products of pharmaceutical importance. Nearly 260 marine natural products (MNPs) have been isolated from coral-derived microorganisms till 2014. In the last three years, 118 MNPs have been isolated from coral-associated microorganisms including 46 new compounds, two with a novel skeleton, and four new natural products. Most of them exhibited in vitro or in vivo activities against tumor cell lines, parasites, pathogenic bacteria, fungi and virus. We reviewed the natural products reported from 2015 to 2017 that have a wide range of bioactivities against different biological targets.

Photeroids A and B, unique phenol–sesquiterpene meroterpenoids from the deep-sea-derived fungus Phomopsis tersa

Photeroids A (1) and B (2), two structurally fascinating meroterpenoids, were isolated from the deep-sea-derived fungus Phomopsis tersa FS441.

Characterization of the Noncanonical Regulatory and Transporter Genes in Atratumycin Biosynthesis and Production in a Heterologous Host

Atratumycin is a cyclodepsipeptide with activity against Mycobacteria tuberculosis isolated from deep-sea derived Streptomyces atratus SCSIO ZH16NS-80S. Analysis of the atratumycin biosynthetic gene cluster (atr) revealed that its biosynthesis is regulated by multiple factors, including two LuxR regulatory genes (atr1 and atr2), two ABC transporter genes (atr29 and atr30) and one Streptomyces antibiotic regulatory gene (atr32). In this work, three regulatory and two transporter genes were unambiguously determined to provide positive, negative and self-protective roles during biosynthesis of atratumycin through bioinformatic analyses, gene inactivations and trans-complementation studies. Notably, an unusual Streptomyces antibiotic regulatory protein Atr32 was characterized as a negative regulator; the function of Atr32 is distinct from previous studies. Five over-expression mutant strains were constructed by rational application of the regulatory and transporter genes; the resulting strains produced significantly improved titers of atratumycin that were ca. 1.7-2.3 fold greater than wild-type (WT) producer. Furthermore, the atratumycin gene cluster was successfully expressed in Streptomyces coelicolor M1154, thus paving the way for the transfer and recombination of large DNA fragments. Overall, this finding sets the stage for understanding the unique biosynthesis of pharmaceutically important atratumycin and lays the foundation for generating anti-tuberculosis lead compounds possessing novel structures.

Recent Updates on Corals from Nephtheidae

Marine natural products display a wide range of biological activities, which play a vital role in the innovation of lead compounds for the drug development. Soft corals have been ranked at the top in regard to the discovery of bioactive metabolites with potential pharmaceutical applications. Many of the isolated cembranoids revealed diverse biological activities, such as anticancer, antidiabetic and anti-osteoporosis. Likewise, sterols from soft corals exhibited interesting biological potential as anti-inflammatory, antituberculosis and anticancer. Consequently, investigating marine soft corals will definitely lead to the discovery of a large number of chemically varied secondary metabolites with countless bioactivities for possible applications in medicine and pharmaceutical industry. This review provides a complete survey of all metabolites isolated from the family Nephtheidae, from 2011 until November 2018, along with their natural sources and biological potential whenever possible.

Potential of marine natural products against drug-resistant bacterial infections

Natural products have been a rich source of compounds with structural and chemical diversity for drug discovery. However, antibiotic resistance in bacteria has been reported for nearly every antibiotic once it is used in clinical practice. In the past decade, pharmaceutical companies have reduced their natural product discovery projects because of challenges, such as high costs, low return rates, and high rediscovery rates. The largely unexplored marine environment harbours substantial diversity and is a large resource to discover novel compounds with novel modes of action, which is essential for the treatment of drug-resistant bacterial infections. In this Review, we report compounds derived from marine sources that have shown in-vivo and in-vitro efficacy against drug-resistant bacteria. Analysis of the physicochemical properties of these marine natural products with activity against drug-resistant bacteria showed that 60% of the compounds have oral bioavailability potential. Their overall distribution pattern of drug characteristics agrees with the observation that marketed antibacterial drugs have a polar distribution, with a lower median calculated logP. The aim of this Review is to summarise the diversity of these marine natural products, with a special focus on analysis of drug bioavailability. Such biologically active compounds, with high degrees of bioavailability, have the potential to be developed as effective drugs against infectious diseases.

Marine Macrolides with Antibacterial and/or Antifungal Activity

Currently, the increasing resistance of microorganisms to antibiotics is a serious problem. Marine organisms are the source of thousands of substances, which also have antibacterial and antifungal effects. Among them, marine macrolides are significant. In this review, the antibacterial and/or antifungal activities of 34 groups of marine macrolides are presented. Exemplary groups are chalcomycins, curvulides, halichondramides, lobophorins, macrolactins, modiolides, scytophycins, spongistatins, or zearalanones. In the paper, 74 antibiotics or their analog sets, among which 29 with antifungal activity, 25 that are antibacterial, and 20 that are both antifungal and antibacterial are summarized. Also, 36 macrolides or their sets are produced by bacteria, 18 by fungi, ten by sponges, seven by algae, two by porifera, and one by nudibranch. Moreover, the chemical structures of representatives from each of the 34 groups of these antibiotics are presented. To summarize, marine organisms are rich in natural macrolides. Some of these may be used in the future in the treatment of bacterial and fungal infections. Marine macrolides can also be potential drugs applicable against pathogens resistant to currently known antibiotics.

Genome- and MS-based mining of antibacterial chlorinated chromones and xanthones from the phytopathogenic fungus Bipolaris sorokiniana strain 11134

Halogen substituents are important for biological activity in many compounds. Genome-based mining of halogenase along with its biosynthetic gene cluster provided an efficient approach for the discovery of naturally occurring organohalogen compounds. Analysis of the genome sequence of a phytopathogenic fungus Bipolaris sorokiniana 11134 revealed a polyketide gene cluster adjacent to a flavin-dependent halogenase capable of encoding halogenated polyketides, which are rarely reported in phytopathogenic fungi. Furthermore, MS- and UV-guided isolation and purification led to the identification of five chlorine-containing natural products together with seven other chromones and xanthones. Two of the chlorinated compounds and four chromones are new compounds. Their structures were elucidated by NMR spectroscopic analysis and HRESIMS data. The biosynthetic gene clusters of isolated compounds and their putative biosynthetic pathway are also proposed. One new chlorinated compound showed activity against Staphylococcus aureus, methicillin-resistant S. aureus, and three clinical-resistant S. aureus strains with a shared minimum inhibitory concentration (MIC) of 12.5 μg/mL. Genome-based mining of halogenases combined with high-resolution MS- and UV-guided identification provides an efficient approach to discover new halogenated natural products from microorganisms.

New bioactive metabolites from the elicited marine sponge-derived bacterium Actinokineospora spheciospongiae sp. nov

Several approaches have been dedicated to activate the cryptic gene clusters in the genomes of actinomycetes for the targeted discovery of new fascinating biomedical lead structures. In the current study, N-acetylglucosamine was used to maximize the chemical diversity of sponge-derived actinomycete Actinokineospora spheciospongiae sp. nov. HR-ESI-MS was employed for dereplication study and orthogonal partial least square-discriminant analysis was applied to evaluate the HR-ESI-MS data of the different fractions. As a result, two new fridamycins H (1) and I (2), along with three known compounds actinosporin C (3), D (4), and G (5) were isolated from the solid culture of sponge-associated actinomycete Actinokineospora spheciospongiae sp. nov., elicited with N-acetylglucosamine. Characterization of the isolated compounds was pursued using mass spectrometry and NMR spectral data. Fridamycin H (1) exhibited significant growth inhibitory activity towards Trypanosoma brucei strain TC221. These results highlight the potential of elicitation in sponge-associated actinomycetes as an effective strategy for the discovery of new anti-infective natural products.

Marine natural products as potential anti-tubercular agents

Tuberculosis has been one of the greatest global health challenges of all time. Although the current first-line anti-tuberculosis (anti-TB) medicines used in the clinic have reduced mortality, multidrug-resistance and extensively drug-resistance forms of the disease have now spread worldwide and become a global problem. Even so, few new clinically approved drugs have emerged during the past 30 years. Highly biodiverse marine organisms have received considerable attention for drug discovery in the past couple of decades, and emerging TB drug resistance has motivated interest in assessing marine natural products (MNPs) in the treatment of this disease. So far, more than 170 compounds have been isolated from marine organisms with anti-TB properties, ten of which exhibit potent activity and have the potential for further development. This review systematically surveys MNPs with anti-TB activity and illustrates the impact of these compounds on drug discovery research against tuberculosis.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Detection and Inhibition of Bacteria on a Dual-Functional Silver Platform

Detection and inhibition of bacteria are universally required in clinics and daily life for health care. Developing a dual-functional material is challenging and in demand, engaging advanced applications for both defined bioanalysis and targeted biotoxicity. Herein, magnetic silver nanoshells are designed as a multifunctional platform for the detection and inhibition of bacteria. The optimized magnetic silver nanoshells enable direct laser desorption/ionization mass spectrometry based metabolic analysis of bacteria (≈10 µL^-1 ), in complex biofluids. The serum infection process (0-10 h) is monitored by statistics toward clinical classification. Moreover, magnetic silver nanoshells facilitate surface adhesion on bacteria due to nanoscale surface roughness and thus display long-term antibacterial effects. Bacteria metabolism is studied with metabolic biomarkers (e.g., malate and lysine) identified during inhibition, showing cell membrane destruction and dysfunctional protein synthesis mechanisms. This work not only guides the design of material-based approaches for bioanalysis and biotoxicity, but contributes to bacteria-related diagnosis by using specific metabolic biomarkers for sensitive detection and new insights by monitoring metabolomic change of bacteria for antibacterial applications.

Total synthesis of spiromastilactone A

Spiromastilactone A is synthesized for the first time in 44% overall yield in eight synthetic steps, among which six are quantitative, and the 89 : 11 enantiomeric ratio (78% ee value) is in favour of the right enantiomer (R configuration).

Investigational drugs for the treatment of Zika virus infection: a preclinical and clinical update

INTRODUCTION

The Zika virus (ZIKV) infection results in severe neurological complications and has emerged as a threat to public health worldwide. No drugs or vaccines are available for use in the clinic and the need for novel and effective therapeutic agents is urgent.

AREAS COVERED

This review describes the latest progress of antiviral development for the treatment of ZIKV infection; it primarily focuses on the literature describing 20 potential anti-ZIKV drugs/agents currently being tested in vivo or in clinical trials. The paper also discusses the need for novel ZIKV inhibitors and the critical issues for successful antiviral drug development.

EXPERT OPINION

So far, 20 compounds have been tested in vivo and three in the clinical trials; progressing these compounds to the clinic is a challenge. Novel ZIKV inhibitors that target virus or host factors are urgently needed. Knowledge-driven drug repurposing, structure-based discovery, RNA interference, long noncoding RNAs, miRNAs, and peptide inhibitors may pave the way for the discovery of such novel agents.

Metabolomic profiling and biological investigation of the marine sponge-derived bacterium Rhodococcus sp. UA13

INTRODUCTION

Marine sponge-associated actinomycetes are potent sources of bioactive natural products of pharmaceutical significance. They also contributed to the discovery of several clinically relevant antimicrobials.

OBJECTIVE

To apply the non-targeted metabolomics approach in chemical profiling of the sponge-derived bacterium Rhodococcus sp. UA13, formerly recovered from the Red Sea sponge Callyspongia aff. Implexa, along with testing for the anti-infective potential of its different fractions.

METHODOLOGY

Metabolomic analysis of the crude extract was carried out using liquid chromatography with high resolution electrospray ionisation mass spectrometry (LC-HR-ESI-MS) for dereplication purposes. Besides, the three major fractions (ethyl acetate, methanol, and n-butanol) obtained by chromatographic fractionation of the crude extract were evaluated for their anti-infective properties.

RESULTS

A variety of metabolites, mostly peptides, were characterised herein for the first time from the genus Rhodococcus. Among the tested samples, the n-butanol fraction showed potent inhibitory activities against Staphylococcus aureus, Candida albicans, and Trypanosoma brucei brucei with IC₅₀ values of 9.3, 6.7, and 8.7 μg/mL, respectively, whereas only the ethyl acetate fraction was active against Chlamydia trachomatis (IC₅₀  = 18.9 μg/mL). In contrast, both fractions did not exert anti-infective actions against Enterococcus faecalis and Leishmania major, whereas the methanol fraction was totally inactive against all the tested organisms.

CONCLUSION

This study showed the helpfulness of the established procedure in metabolic profiling of marine actinomycetes using liquid chromatography mass spectrometry (LC-MS) data, which aids in reducing the complex isolation steps during their chemical characterisation. The anti-infective spectrum of their metabolites is also interestingly relevant to future drug development.

Marine Natural Products in Medicinal Chemistry

An overview of the marine natural products (MNPs) field is shown, including an update of FDA-approved drugs and those in clinical trials that can be considered derivatives of MNPs. The importance of marine microorganisms in present studies and the application of emerging techniques and technologies to this field are highlighted.

Natural molecules induce and synergize to boost expression of the human antimicrobial peptide β-defensin-3

Antimicrobial peptides (AMPs) are mucosal defense effectors of the human innate immune response. In the intestine, AMPs are produced and secreted by epithelial cells to protect the host against pathogens and to support homeostasis with commensals. The inducible nature of AMPs suggests that potent inducers could be used to increase their endogenous expression for the prevention or treatment of diseases. Here we aimed at identifying molecules from the natural pharmacopoeia that induce expression of human β-defensin-3 (HBD3), one of the most efficient AMPs, without modifying the production of proinflammatory cytokines. By screening, we identified three molecules isolated from medicinal plants, andrographolide, oridonin, and isoliquiritigenin, which induced HBD3 production in human colonic epithelial cells. This effect was observed without activation of the NF-κB pathway or the expression of associated proinflammatory cytokines. We identified the EGF receptor as the target of these compounds and characterized the downstream-activated MAPK pathways. At the chromatin level, molecules increased phosphorylation of histone H3 on serine S10 and recruitment of the c-Fos, c-Jun, and Elk1 or c-Myc transcription factors at the HBD3 promoter. Interestingly, stimulating cells with a combination of andrographolide and isoliquiritigenin synergistically enhanced HBD3 induction 10-fold more than observed with each molecule alone. Finally, we investigated the molecular basis governing the synergistic effect, confirmed our findings in human colonic primary cells, and demonstrated that synergism increased cellular antimicrobial activity. This work shows the capability of small molecules to achieve induction of epithelial antimicrobial defenses while simultaneously avoiding the deleterious risks of an inflammatory response.

New Cytotoxic Cyclic Peptide from the Marine Sponge-Associated Nocardiopsis sp. UR67

A new cyclic hexapeptide, nocardiotide A (1), together with three known compounds—tryptophan (2), kynurenic acid (3), and 4-amino-3-methoxy benzoic acid (4)—were isolated and identified from the broth culture of Nocardiopsis sp. UR67 strain associated with the marine sponge Callyspongia sp. from the Red Sea. The structure elucidation of the isolated compounds were determined based on detailed spectroscopic data including ¹D and ²D nuclear magnetic resonance (NMR) experimental analyses in combination with high resolution electrospray ionization mass spectrometry (HR-ESI-MS), while the absolute stereochemistry of all amino acids components of nocardiotide A (1) was deduced using Marfey’s method. Additionally, ten known metabolites were dereplicated using HR-ESI-MS analysis. Nocardiotide A (1) displayed significant cytotoxic effects towards the murine CT26 colon carcinoma, human HeLa cervix carcinoma, and human MM.1S multiple myeloma cell lines. The results obtained revealed sponge-associated Nocardiopsis as a substantial source of lead natural products with pronounced pharmacological activities.

Mining of Egypt's Red Sea invertebrates for potential bioactive producers

OBJECTIVE

The objective of this work was to isolate bacteria from Red Sea invertebrates, determine their antimicrobial activity, and screen for the biosynthetic gene clusters [polyketides (PKs) and nonribosomal peptides (NRPs)] which could be involved in the production of bioactive secondary metabolites.

RESULT

Eleven different samples of marine invertebrates' were collected from Egypt's Red Sea (El-Tor-Sharm El-Sheikh and Hurghada) by scuba diving, and a total 80 isolates of the associated microorganisms were obtained from the cultivation on six different cultural medium. Seven isolates of them showed an antimicrobial activity against five pathogenic reference strains, while the most active antimicrobial agent was isolate number HFF-8 which was 99% identical to Bacillus amyloliquefaciens. HFF-8's extract showed positive results against Gram negative bacteria, Gram positive bacteria and yeast. Moreover, the isolates gave positive bands when screened for the presence of PK synthase (PKS) I and II and NRP synthetase (NRPS) I and II biosynthetic genes, those biosynthetic fragments when cloned and sequenced were primitively predicted as biosynthetic fragments for kirromycin and leinamycin production by NaPDoS program with 56 and 55%, respectively.

CONCLUSION

The Red Sea can provide a sustainable solution to combat bacterial resistance. The contribution of this work is that B. amyloliquefaciens was isolated from Heteroxenia fuscescens, Red Sea, Egypt. Moreover, the bacterial extract showed a broad spectrum with a potent antimicrobial activity.

Microbial-derived products as potential new antimicrobials

Due to the continuing global concerns involving antibiotic resistance, there is a need for scientific forums to assess advancements in the development of antimicrobials and their alternatives that might reduce development and spread of antibiotic resistance among bacterial pathogens. The objectives of the 2nd International Symposium on Alternatives to Antibiotics were to highlight promising research results and novel technologies that can provide alternatives to antibiotics for use in animal health and production, assess challenges associated with their authorization and commercialization for use, and provide actionable strategies to support their development. The session on microbial-derived products was directed at presenting novel technologies that included exploiting CRISPR-Cas nucleases to produce sequence-specific antimicrobials, probiotics development via fecal microbiome transplants among monogastric production animals such as chickens and mining microbial sources such as bacteria or yeast to identify new antimicrobial compounds. Other research has included continuing development of antimicrobial peptides such as newly discovered bacteriocins as alternatives to antibiotics, use of bacteriophages accompanied by development of unique lytic proteins with specific cell-wall binding domains and novel approaches such as microbial-ecology guided discovery of anti-biofilm compounds discovered in marine environments. The symposium was held at the Headquarters of the World Organisation for Animal Health (OIE) in Paris, France during 12-15 December 2016.

A New Bioactive Compound From the Marine Sponge-Derived Streptomyces sp. SBT348 Inhibits Staphylococcal Growth and Biofilm Formation

Staphylococcus epidermidis, the common inhabitant of human skin and mucosal surfaces has emerged as an important pathogen in patients carrying surgical implants and medical devices. Entering the body via surgical sites and colonizing the medical devices through formation of multi-layered biofilms leads to refractory and persistent device-related infections (DRIs). Staphylococci organized in biofilms are more tolerant to antibiotics and immune responses, and thus are difficult-to-treat. The consequent morbidity and mortality, and economic losses in health care systems has strongly necessitated the need for development of new anti-bacterial and anti-biofilm-based therapeutics. In this study, we describe the biological activity of a marine sponge-derived Streptomyces sp. SBT348 extract in restraining staphylococcal growth and biofilm formation on polystyrene, glass, medically relevant titan metal, and silicone surfaces. A bioassay-guided fractionation was performed to isolate the active compound (SKC3) from the crude SBT348 extract. Our results demonstrated that SKC3 effectively inhibits the growth (MIC: 31.25 μg/ml) and biofilm formation (sub-MIC range: 1.95–<31.25 μg/ml) of S. epidermidis RP62A in vitro. Chemical characterization of SKC3 by heat and enzyme treatments, and mass spectrometry (HRMS) revealed its heat-stable and non-proteinaceous nature, and high molecular weight (1258.3 Da). Cytotoxicity profiling of SKC3 in vitro on mouse fibroblast (NIH/3T3) and macrophage (J774.1) cell lines, and in vivo on the greater wax moth larvae Galleria mellonella revealed its non-toxic nature at the effective dose. Transcriptome analysis of SKC3 treated S. epidermidis RP62A has further unmasked its negative effect on central metabolism such as carbon flux as well as, amino acid, lipid, and energy metabolism. Taken together, these findings suggest a potential of SKC3 as a putative drug to prevent staphylococcal DRIs.

Isolation and Identification of an Anthracimycin Analogue from Nocardiopsis kunsanensis, a Halophile from a Saltern, by Genomic Mining Strategy

Modern medicine is unthinkable without antibiotics; yet, growing issues with microbial drug resistance require intensified search for new active compounds. Natural products generated by Actinobacteria have been a rich source of candidate antibiotics, for example anthracimycin that, so far, is only known to be produced by Streptomyces species. Based on sequence similarity with the respective biosynthetic cluster, we sifted through available microbial genome data with the goal to find alternative anthracimycin-producing organisms. In this work, we report about the prediction and experimental verification of the production of anthracimycin derivatives by Nocardiopsis kunsanensis, a non-Streptomyces actinobacterial microorganism. We discovered N. kunsanensis to predominantly produce a new anthracimycin derivative with methyl group at C-8 and none at C-2, labeled anthracimycin BII-2619, besides a minor amount of anthracimycin. It displays activity against Gram-positive bacteria with similar low level of mammalian cytotoxicity as that of anthracimycin.

Natural Product Potential of the Genus Nocardiopsis

Actinomycetes are a relevant source of novel bioactive compounds. One of the pharmaceutically and biotechnologically important genera that attract natural products research is the genus Nocardiopsis, mainly for its ability to produce a wide variety of secondary metabolites accounting for its wide range of biological activities. This review covers the literature from January 2015 until February 2018 making a complete survey of all the compounds that were isolated from the genus Nocardiopsis, their biological activities, and natural sources, whenever applicable.

Identification of Inhibitory Compounds Against Singapore Grouper Iridovirus Infection by Cell Viability-Based Screening Assay and Droplet Digital PCR

Singapore grouper iridovirus (SGIV) is one of the major causative agents of fish diseases and has caused significant economic losses in the aquaculture industry. There is currently no commercial vaccine or effective antiviral treatment against SGIV infection. Annually, an increasing number of small molecule compounds from various sources have been produced, and many are proved to be potential inhibitors against viruses. Here, a high-throughput in vitro cell viability-based screening assay was developed to identify antiviral compounds against SGIV using the luminescent-based CellTiter-Glo reagent in cultured grouper spleen cells by quantificational measurement of the cytopathic effects induced by SGIV infection. This assay was utilized to screen for potential SGIV inhibitors from five customized compounds which had been reported to be capable of inhibiting other viruses and 30 compounds isolated from various marine organisms, and three of them [ribavirin, harringtonine, and 2-hydroxytetradecanoic acid (2-HOM)] were identified to be effective on inhibiting SGIV infection, which was further confirmed with droplet digital PCR (ddPCR). In addition, the ddPCR results revealed that ribavirin and 2-HOM inhibited SGIV replication and entry in a dose-dependent manner, and harringtonine could reduce SGIV replication rather than entry at the working concentration without significant toxicity. These findings provided an easy and reliable cell viability-based screening assay to identify compounds with anti-SGIV effect and a way of studying the anti-SGIV mechanism of compounds.

Recent updates of marine antimicrobial peptides

Antimicrobial peptides are group of proteins showing broad-spectrum antimicrobial activity that have been known to be powerful agents against a variety of pathogens. This class of compounds contributed to solving the microbial resistance dilemma that limited the use of many potent antimicrobial agents. The marine environment is known to be one of the richest sources for antimicrobial peptides, yet this environment is not fully explored. Hence, the scientific research attention should be directed toward the marine ecosystem as enormous amount of useful discoveries could be brought to the forefront. In the current article, the marine antimicrobial peptides reported from mid 2012 to 2017 have been reviewed.

An ethanol extract of Lysimachia mauritiana exhibits inhibitory activity against hepatitis E virus genotype 3 replication

Hepatitis E virus (HEV) is an etiological agent of acute hepatitis E, a self-limiting disease prevalent in developing countries. HEV can cause fulminant hepatic failure with high mortality rates in pregnant women, and genotype 3 is reported to trigger chronic hepatitis in immunocompromised individuals worldwide. Screening of plant extracts for compounds with potential anti-HEV effects led to the identification of a 70% ethanol extract of Lysimachia mauritiana (LME) that interferes with replication of the swine HEV genotype 3 replicon. Furthermore, LME significantly inhibited replication of HEV genotype 3 and expression of HEV ORF2 in infected cells without exerting cytotoxic effects. Collectively, our findings demonstrate the potential utility of LME in the development of novel antiviral drugs against HEV infection.

Pathobiology of Lomentospora prolificans: could this species serve as a model of primary antifungal resistance?

The number of fungal isolates resistant to antifungal drugs has increased dramatically over the last few years and has become an important concern for clinicians. Among these isolates, fungi showing multidrug resistance are particularly worrying because of the difficulties associated with their treatment. These factors hamper the successful recovery of patients and drastically raise mortality rates. Antifungal resistance is multifactorial and several mechanisms in different fungi have been described. There is a need to study these mechanisms in depth; however, the study of antifungal drug resistance separately for each individual species makes progress in the field very slow and tedious. The selection of a multiresistant microorganism as a model for understanding resistance mechanisms and extrapolating the results to other species could help in the search for a solution. In this mini-review, we describe the pathobiology of Lomentospora (Scedosporium) prolificans, paying special attention to its intrinsic resistance to all currently available antifungal agents. The characteristics of L. prolificans offer several advantages: the possibility of using a single microorganism for the study of resistance to different drugs, even cases of double and triple resistance; it is biologically safe for society in general as no new genetically-modified strains are needed for the experiments; it is homologous with other fungal species, and there is repetitiveness between different strains. In conclusion, we propose L. prolificans as a candidate for consideration as a fungal model for the study of resistance mechanisms against antifungal agents.

1,2,3,4,6-Penta-O-galloyl-ß-D-glucose, a bioactive compound in Elaeocarpus sylvestris extract, inhibits varicella-zoster virus replication

The aim of this study was to establish the effect of a 70% ethanol extract of Elaeocarpus sylvestris (ESE) on varicella-zoster virus (VZV) replication and identify the specific bioactive component(s) underlying its activity. ESE induced a significant reduction in replication of the clinical strain of VZV. Activity-guided fractionation indicated that the ethyl acetate (EtOAc) fraction of ESE contains the active compound(s) inhibiting VZV replication. High-Performance Liquid Chromatography coupled to Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (HPLC-Q-TOF-MS/MS) analysis of the EtOAc fraction of ESE facilitated the identification of 13 chemical components. Among these, 1,2,3,4,6-penta-O-galloyl-ß-D-glucose (PGG) markedly suppressed VZV-induced c-Jun N-terminal kinase (JNK) activation, expression of viral immediate-early 62 (IE62) protein and VZV replication. Our results collectively support the utility of PGG as a potential candidate anti-viral drug to treat VZV-associated diseases.

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.

Design, Synthesis and Biological Evaluation of 2-(2-Amino-5(6)-nitro-1H-benzimidazol-1-yl)-N-arylacetamides as Antiprotozoal Agents

Parasitic diseases are a public health problem affecting millions of people worldwide. One of the scaffolds used in several drugs for the treatment of parasitic diseases is the benzimidazole moiety, a heterocyclic aromatic compound. This compound is a crucial pharmacophore group and is considered a privileged structure in medicinal chemistry. In this study, the benzimidazole core served as a model for the synthesis of a series of 2-(2-amino-5(6)-nitro-1H-benzimidazol-1-yl)-N-arylacetamides 1–8 as benznidazole analogues. The in silico pharmacological results calculated with PASS platform exhibited chemical structures highly similar to known antiprotozoal drugs. Compounds 1–8 when evaluated in silico for acute toxicity by oral dosing, were less toxic than benznidazole. The synthesis of compounds 1–8 were carried out through reaction of 5(6)-nitro-1H-benzimidazol-2-amine (12) with 2-chlroactemides 10a–h, in the presence of K₂CO₃ and acetonitrile as solvent, showing an inseparable mixture of two regioisomers with the -NO₂ group in position 5 or 6 with chemical yields of 60 to 94%. The prediction of the NMR spectra of molecule 1 coincided with the experimental chemical displacements of the regioisomers. Comparisons between the NMR prediction and the experimental data revealed that the regioisomer endo-1,6-NO₂ predominated in the reaction. The in vitro antiparasitic activity of these compounds on intestinal unicellular parasites (Giardia intestinalis and Entamoeba histolytica) and a urogenital tract parasite (Trichomonas vaginalis) were tested. Compound 7 showed an IC₅₀ of 3.95 μM and was 7 time more active against G. intestinalis than benznidazole. Compounds 7 and 8 showed 4 times more activity against T. vaginalis compared with benznidazole.

Novel therapeutics for bacterial infections

The relentless increase in antibiotic resistance among all major groups of bacterial pathogens shows no sign of abating. The situation is exacerbated by a marked decline in the number of new antibiotics entering the marketplace. It is essential that new ways to treat severe bacterial infections are investigated before the antibiotic well runs dry. This review covers many promising approaches, some novel and some based on old ideas that were not considered viable when clinicians were able to exploit a wide palette of cheap and effective antibacterial chemotherapeutics. These approaches include the use of photosensitive dyes, bacteriophage and phage-encoded proteins, and agents that compromise virulence and antibiotic-resistance machineries. I also make a case for continuing in some form with tried and trusted platforms for drug discovery that served society well in the past.

Marine Sponge-Derived Streptomyces sp. SBT343 Extract Inhibits Staphylococcal Biofilm Formation

Staphylococcus epidermidis and Staphylococcus aureus are opportunistic pathogens that cause nosocomial and chronic biofilm-associated infections. Indwelling medical devices and contact lenses are ideal ecological niches for formation of staphylococcal biofilms. Bacteria within biofilms are known to display reduced susceptibilities to antimicrobials and are protected from the host immune system. High rates of acquired antibiotic resistances in staphylococci and other biofilm-forming bacteria further hamper treatment options and highlight the need for new anti-biofilm strategies. Here, we aimed to evaluate the potential of marine sponge-derived actinomycetes in inhibiting biofilm formation of several strains of S. epidermidis, S. aureus, and Pseudomonas aeruginosa. Results from in vitro biofilm-formation assays, as well as scanning electron and confocal microscopy, revealed that an organic extract derived from the marine sponge-associated bacterium Streptomyces sp. SBT343 significantly inhibited staphylococcal biofilm formation on polystyrene, glass and contact lens surfaces, without affecting bacterial growth. The extract also displayed similar antagonistic effects towards the biofilm formation of other S. epidermidis and S. aureus strains tested but had no inhibitory effects towards Pseudomonas biofilms. Interestingly the extract, at lower effective concentrations, did not exhibit cytotoxic effects on mouse fibroblast, macrophage and human corneal epithelial cell lines. Chemical analysis by High Resolution Fourier Transform Mass Spectrometry (HRMS) of the Streptomyces sp. SBT343 extract proportion revealed its chemical richness and complexity. Preliminary physico-chemical characterization of the extract highlighted the heat-stable and non-proteinaceous nature of the active component(s). The combined data suggest that the Streptomyces sp. SBT343 extract selectively inhibits staphylococcal biofilm formation without interfering with bacterial cell viability. Due to absence of cell toxicity, the extract might represent a good starting material to develop a future remedy to block staphylococcal biofilm formation on contact lenses and thereby to prevent intractable contact lens-mediated ocular infections.