Cytotoxic and antibacterial angucycline- and prodigiosin-analogues from the deep-sea derived Streptomyces sp. SCSIO 11594

Decylprodigiosin: a new member of the prodigiosin family isolated from a seaweed-associated Streptomyces

Bioprospecting actinobacterial secondary metabolism from untapped marine sources may lead to the discovery of biotechnologically-relevant compounds. While studying the diversity and bioactive potential of Actinomycetota associated with Codium tomentosum, a green seaweed collected in the northern Portuguese cost, strain CT-F61, identified as Streptomyces violaceoruber, was isolated. Its extracts displayed a strong anticancer activity on breast carcinoma T-47D and colorectal carcinoma HCT116 cells, being effective as well against a panel of human and fish pathogenic bacteria. Following a bioactivity-guided isolation pipeline, a new analogue of the red-pigmented family of the antibiotics prodigiosins, decylprodigiosin (1), was identified and chemically characterized. Despite this family of natural products being well-known for a long time, we report a new analogue and the first evidence for prodigiosins being produced by a seaweed-associated actinomycete.

Anthraquinone metabolites isolated from the rhizosphere soil Streptomyces of Panax notoginseng (Burk.) F. H. Chen target MMP2 to inhibit cancer cell migration

ETHNOPHARMACOLOGICAL RELEVANCE

Panax notoginseng (Burk.) F. H. Chen belongs to the Araliaceae family. It has been used by traditional Chinese people in Northeast Asia for centuries as an antidiabetic, antioxidant, antitumor agent, etc. Endophytic or rhizospheric microorganisms play key roles in plant defense mechanisms, and they are essential in the discovery of pharmaceuticals and valuable new secondary metabolites. In particular, endophytic or rhizospheric microorganisms of traditional medicinal plants.

AIM OF THE STUDY

To discover valuable new secondary metabolites from rhizosphere soil Streptomyces sp. SYP-A7185 of P. notoginseng, and to explore potential bioactivities and targets of metabolites protrusive function.

MATERIALS AND METHODS

The metabolites were obtained via column chromatography and identified by multiple spectroscopic analyses. The antitumor, antioxidant, antibacterial, and antiglycosidases effects of isolated metabolites were tested using 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyltetazolium bromide (MTT), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 96-well turbidimetric, and α-glucosidase inhibitory assays. The potential antitumor targets were predicted through network pharmacological approaches. The interactions between metabolites and target were verified by molecular docking and biolayer interferometry (BLI) assay. The effects of cancer cells migration were detected through wound healing assays in A549 and MCF-7. Other cellular validation experiments including reverse transcription-quantitative PCR (RT‒qPCR) and western blotting (WB) were used to confirm the hypothesis of network pharmacology.

RESULTS

Five different chemotypes of anthraquinone derivatives (1-10), including six new compounds (3, 6-10), were identified from Streptomyces sp. SYP-A7185. Compounds 1-6 and 9 displayed moderate to strong cytotoxicity on five human cancer cell lines (A549, HepG2, MCF-7, MDA-MD-231, and MGC-803). Moreover, matrix metalloproteinase-2 (MMP2) were predicted as a potential antitumor target of metabolites 1-6 and 9 by comprehensive network pharmacology analysis. Later, BLI assays revealed strong intermolecular interactions between MMP2 and antitumor metabolites, and molecular docking results showed the interaction of metabolites 1-6 and 9 with MMP2 was dependent on the crucial amino acid residues of LEU-83, ALA-84, LEU-117, HIS-131, PRO-135, GLY-136, ALA-140, PRO-141, TYR-143, and THR-144. These results implied that metabolites (1-6 and 9) might inhibit cancer cell migration besides cancer cell proliferation. After that, the cell wound healing assay showed that the cell migration processes were also inhibited after the treatments of compounds 1 and 3 in A549 and MCF-7 cells. In addition, the RT‒qPCR and WB results demonstrated that the gene expression levels of MMP2 were decreased after the treatment with compounds 1 and 3 in A549 and MCF-7 cells. Besides, compound 2 displayed moderate antioxidant activity (EC₅₀, 27.43 μM), compounds 3 and 6 exhibited moderate antibacterial activity, and compound 3 inhibited α-glucosidase with an IC₅₀ value of 13.10 μM.

CONCLUSIONS

Anthraquinone metabolites, from rhizosphere soil Streptomyces sp. of P. notoginseng, possess antitumor, antioxidant, antibacterial, and antiglycosidase activities. Moreover, metabolites 1 and 3 inhibit cancer cells migration through downregulating MMP2.

Bacterial Pigments and Their Multifaceted Roles in Contemporary Biotechnology and Pharmacological Applications

Synthetic dyes and colourants have been the mainstay of the pigment industry for decades. Researchers are eager to find a more environment friendly and non-toxic substitute because these synthetic dyes have a negative impact on the environment and people’s health. Microbial pigments might be an alternative to synthetic pigments. Microbial pigments are categorized as secondary metabolites and are mainly produced due to impaired metabolism under stressful conditions. These pigments have vibrant shades and possess nutritional and therapeutic properties compared to synthetic pigment. Microbial pigments are now widely used within the pharmaceuticals, food, paints, and textile industries. The pharmaceutical industries currently use bacterial pigments as a medicine alternative for cancer and many other bacterial infections. Their growing popularity is a result of their low cost, biodegradable, non-carcinogenic, and environmentally beneficial attributes. This audit article has made an effort to take an in-depth look into the existing uses of bacterial pigments in the food and pharmaceutical industries and project their potential future applications.

Transient imine as a directing group for the Pd-catalyzed anomeric C(sp3)-H arylation of 3-aminosugars

The first example of Pd(II)-catalyzed anomeric arylation of 3-aminosugars is reported by using an L,X-type transient directing group (TDG) approach combined with an external 2-pyridone ligand. The released free amine was in situ transformed into an azide function, which was then exploited in a CuAAC to increase the molecular complexity and prepare a variety of complex substituted C3-triazolo C-glycosides in good yields.

Recent Advances on Natural Aryl-C-glycoside Scaffolds: Structure, Bioactivities, and Synthesis-A Comprehensive Review

Aryl-C-glycosides, of both synthetic and natural origin, are of great significance in medicinal chemistry owing to their unique structures and stability towards enzymatic and chemical hydrolysis as compared to O-glycosides. They are well-known antibiotics and potent enzyme inhibitors and possess a wide range of biological activities such as anticancer, antioxidant, antiviral, hypoglycemic effects, and so on. Currently, a number of aryl-C-glycoside drugs are on sale for the treatment of diabetes and related complications. This review summarizes the findings on aryl-C-glycoside scaffolds over the past 20 years, concerning new structures (over 200 molecules), their bioactivities-including anticancer, anti-inflammatory, antioxidant, antivirus, glycation inhibitory activities and other pharmacological effects-as well as their synthesis.

Marine Based Natural Products: Exploring the Recent Developments in the Identification of Antimicrobial Agents

The marine ecosystem is the less explored, biologically diverse, and vastest resource to discover novel antimicrobial agents. In recent decades' antimicrobial drugs are losing their effectiveness due to the growing resistance among pathogens, which causes diseases to have considerable death rates across the globe. Therefore, there is a need for the discovery of new antibacterials that can reach the market. There is a gradual growth of compounds from marine sources which are entering the clinical trials. Thus, the prominence of marine natural products in the field of drug design and discovery across the academia and pharmaceutical industry is gaining attention. Herein,  the present review covers nearly 200 marine based antimicrobial agents of 11 structural classes discovered from the year 2010 to 2022. All the discussed compounds have exhibited medium to high antimicrobial activity in inhibiting various microorganisms.

Marine Actinobacteria a New Source of Antibacterial Metabolites to Treat Acne Vulgaris Disease—A Systematic Literature Review

Acne vulgaris is a multifactorial disease that remains under-explored; up to date it is known that the bacterium Cutibacterium acnes is involved in the disease occurrence, also associated with a microbial dysbiosis. Antibiotics have become a mainstay treatment generating the emergence of antibiotic-resistant bacteria. In addition, there are some reported side effects of alternative treatments, which indicate the need to investigate a different therapeutic approach. Natural products continue to be an excellent option, especially those extracted from actinobacteria, which represent a prominent source of metabolites with a wide range of biological activities, particularly the marine actinobacteria, which have been less studied than their terrestrial counterparts. Therefore, this systematic review aimed to identify and evaluate the potential anti-infective activity of metabolites isolated from marine actinobacteria strains against bacteria related to the development of acne vulgaris disease. It was found that there is a variety of compounds with anti-infective activity against Staphylococcus aureus and Staphylococcus epidermidis, bacteria closely related to acne vulgaris development; nevertheless, there is no report of a compound with antibacterial activity or quorum-sensing inhibition toward C. acnes, which is a surprising result. Since two of the most widely used antibiotics for the treatment of acne targeting C. acnes were obtained from actinobacteria of the genus Streptomyces, this demonstrates a great opportunity to pursue further studies in this field, considering the potential of marine actinobacteria to produce new anti-infective compounds.

Integrated Metabolomic, Molecular Networking, and Genome Mining Analyses Uncover Novel Angucyclines From Streptomyces sp. RO-S4 Strain Isolated From Bejaia Bay, Algeria

Multi-omic approaches have recently made big strides toward the effective exploration of microorganisms, accelerating the discovery of new bioactive compounds. We combined metabolomic, molecular networking, and genomic-based approaches to investigate the metabolic potential of the Streptomyces sp. RO-S4 strain isolated from the polluted waters of Bejaia Bay in Algeria. Antagonistic assays against methicillin-resistant Staphylococcus aureus with RO-S4 organic extracts showed an inhibition zone of 20 mm by using the agar diffusion method, and its minimum inhibitory concentration was 16 μg/ml. A molecular network was created using GNPS and annotated through the comparison of MS/MS spectra against several databases. The predominant compounds in the RO-S4 extract belonged to the angucycline family. Three compounds were annotated as known metabolites, while all the others were putatively new to Science. Notably, all compounds had fridamycin-like aglycones, and several of them had a lactonized D ring analogous to that of urdamycin L. The whole genome of Streptomyces RO-S4 was sequenced to identify the biosynthetic gene cluster (BGC) linked to these angucyclines, which yielded a draft genome of 7,497,846 bp with 72.4% G+C content. Subsequently, a genome mining analysis revealed 19 putative biosynthetic gene clusters, including a grincamycin-like BGC with high similarity to that of Streptomyces sp. CZN-748, that was previously reported to also produce mostly open fridamycin-like aglycones. As the ring-opening process leading to these compounds is still not defined, we performed a comparative analysis with other angucycline BGCs and advanced some hypotheses to explain the ring-opening and lactonization, possibly linked to the uncoupling between the activity of GcnE and GcnM homologs in the RO-S4 strain. The combination of metabolomic and genomic approaches greatly improved the interpretation of the metabolic potential of the RO-S4 strain.

Genome-Guided Discovery of Antifungal Filipins from a Deep-Sea-Derived Streptomyces antibioticus

Nine new (1-3, 5-8, 11, and 12; named filipins VI-XIV) and three known (4, 9, and 10) filipin-type polyene macrolides were isolated from the deep-sea-derived Streptomyces antibioticus OUCT16-23 using a genome-guided strategy coupled with bioassay. Their structures were elucidated based on the extensive MS and NMR spectroscopic analyses together with ECD calculations. In an antifungal assay, compounds 4, 5, and 7-10 showed different degrees of growth inhibition against Candida albicans with minimum inhibitory concentrations (MICs) of 1.56-12.5 μg/mL, by which the alkyl side-chain substitution affecting the activity was preliminarily studied. A biosynthetic pathway to 1-12 in S. antibioticus OUCT16-23 is also proposed.

Cytotoxic compounds from marine actinomycetes: Sources, Structures and Bioactivity

Marine actinomycetes produce a substantial number of natural products with cytotoxic activity. The strains of actinomycetes were isolated from different sources like fishes, coral, sponges, seaweeds, mangroves, sediments etc. These cytotoxic compounds can be categorized briefly into four classes: polyketides, non-ribosomal peptides and hybrids, isoprenoids and hybrids, and others, among which majority are polyketides (146). Twenty two out of the 254 compounds showed potent cytotoxicity with IC₅₀ values at ng/mL or nM level. This review highlights the sources, structures and antitumor activity of 254 natural products isolated from marine actinomycetes, which were new when they were reported from 1989 to 2020.

Investigating Alkylated Prodigiosenes and Their Cu(II)-Dependent Biological Activity: Interactions with DNA, Antimicrobial and Photoinduced Anticancer Activity

Prodigiosenes are a family of red pigments with versatile biological activity. Their tripyrrolic core structure has been modified many times in order to manipulate the spectrum of activity. We have been looking systematically at prodigiosenes substituted at the C ring with alkyl chains of different lengths, in order to assess the relevance of this substituent in a context that has not been investigated before for these derivatives: Cu(II) complexation, DNA binding, self‐activated DNA cleavage, photoinduced cytotoxicity and antimicrobial activity. Our results indicate that the hydrophobic substituent has a clear influence on the different aspects of their biological activity. The cytotoxicity study of the Cu(II) complexes of these prodigiosenes shows that they exhibit a strong cytotoxic effect towards the tested tumor cell lines. The Cu(II) complex of a prodigiosene lacking any alkyl chain excelled in its photoinduced anticancer activity, thus demonstrating the potential of prodigiosenes and their metal complexes for an application in photodynamic therapy (PDT). Two derivatives along with their Cu(II) complexes showed also antimicrobial activity against Staphylococcus aureus strains.

Complete Genome Analysis of Undecylprodigiosin Pigment Biosynthesizing Marine Streptomyces Species Displaying Potential Bioactive Applications

Marine Streptomyces species are underexplored for their pigment molecules and genes. In this study, we report the genome of the undecylprodigiosin biosynthesizing gene cluster carrying Streptomyces sp. strain BSE6.1, displaying antioxidant, antimicrobial, and staining properties. This Gram-positive obligate aerobic bacterium was isolated from the coastal sediment of the Andaman and Nicobar Islands, India. Pink to reddish pigmented colonies with whitish powdery spores on both agar and broth media are the important morphological characteristics of this bacterium. Growth tolerance to NaCl concentrations was 2 to 7%. The assembled genome of Streptomyces sp. BSE6.1 contains one linear chromosome 8.02 Mb in length with 7157 protein-coding genes, 82 tRNAs, 3 rRNAs and at least 11 gene clusters related to the synthesis of various secondary metabolites, including undecylprodigiosin. This strain carries type I, type II, and type III polyketide synthases (PKS) genes. Type I PKS gene cluster is involved in the biosynthesis of red pigment undecylprodigiosin of BSE6.1, similar to the one found in the S. coelicolor A3(2). This red pigment was reported to have various applications in the food and pharmaceutical industries. The genome of Streptomyces sp. BSE6.1 was submitted to NCBI with a BioProject ID of PRJNA514840 (Sequence Read Archive ID: SRR10849367 and Genome accession ID: CP085300).

Marine Anthraquinones: Pharmacological and Toxicological Issues

The marine ecosystem, populated by a myriad of animals, plants, and microorganisms, is an inexhaustible reservoir of pharmacologically active molecules. Among the multiple secondary metabolites produced by marine sources, there are anthraquinones and their derivatives. Besides being mainly known to be produced by terrestrial species, even marine organisms and the uncountable kingdom of marine microorganisms biosynthesize anthraquinones. Anthraquinones possess many different biological activities, including a remarkable antitumor activity. However, due to their peculiar chemical structures, anthraquinones are often associated with toxicological issues, even relevant, such as genotoxicity and mutagenicity. The aim of this review is to critically describe the anticancer potential of anthraquinones derived from marine sources and their genotoxic and mutagenic potential. Marine-derived anthraquinones show a promising anticancer potential, although clinical studies are missing. Additionally, an in-depth investigation of their toxicological profile is needed before advocating anthraquinones as a therapeutic armamentarium in the oncological area.

An Overview on Industrial and Medical Applications of Bio-Pigments Synthesized by Marine Bacteria

Marine bacterial species contribute to a significant part of the oceanic population, which substantially produces biologically effectual moieties having various medical and industrial applications. The use of marine-derived bacterial pigments displays a snowballing effect in recent times, being natural, environmentally safe, and health beneficial compounds. Although isolating marine bacteria is a strenuous task, these are still a compelling subject for researchers, due to their promising avenues for numerous applications. Marine-derived bacterial pigments serve as valuable products in the food, pharmaceutical, textile, and cosmetic industries due to their beneficial attributes, including anticancer, antimicrobial, antioxidant, and cytotoxic activities. Biodegradability and higher environmental compatibility further strengthen the use of marine bio-pigments over artificially acquired colored molecules. Besides that, hazardous effects associated with the consumption of synthetic colors further substantiated the use of marine dyes as color additives in industries as well. This review sheds light on marine bacterial sources of pigmented compounds along with their industrial applicability and therapeutic insights based on the data available in the literature. It also encompasses the need for introducing bacterial bio-pigments in global pigment industry, highlighting their future potential, aiming to contribute to the worldwide economy.

Targeting VEGFR2 protein by marine Streptomyces globosus VITLGK011-derived compound BECA: An in vitro and in silico analysis

This study investigates the anticancer cytotoxic mechanism of action of benzoyloxy-ethyl-carbamic acid (BECA) produced by Streptomyces globosus VITLGK011. Flow cytometry analysis confirmed that BECA (at IC₅₀ : 3.12 µg/ml) treatment for 24 h induced apoptosis in 60% of cells. Schrodinger Maestro tools such as QikProp and DFT were used to confirm that BECA is an eligible drug-like molecule, with suitable physiochemical properties. Glide XP tool was used to perform induced-fit docking between BECA and 30 cancer drug target proteins. The highest significance was observed for VEGFR2 protein (-6.7 kcal/mol). GROMACS tool was used to perform molecular dynamic simulation between BECA and VEGFR2 protein for 40 ns. Root mean square deviation, root mean square fluctuation, H-bond, and trajectory analysis, confirmed that BECA is a suitable inhibitor of VEGFR2 protein. Results conclude that BECA is a valid VEGFR2 inhibitor, and it thus exerts the observed anticancer cytotoxicity against MCF-7 cells.

Marine Natural Products with High Anticancer Activities

This review covers recent literature from 2012-2019 concerning 170 marine natural products and their semisynthetic analogues with strong anticancer biological activities. Reports that shed light on cellular and molecular mechanisms and biological functions of these compounds, thus advancing the understanding in cancer biology are also included. Biosynthetic studies and total syntheses, which have provided access to derivatives and have contributed to the proper structure or stereochemistry elucidation or revision are mentioned. The natural compounds isolated from marine organisms are divided into nine groups, namely: alkaloids, sterols and steroids, glycosides, terpenes and terpenoids, macrolides, polypeptides, quinones, phenols and polyphenols, and miscellaneous products. An emphasis is placed on several drugs originating from marine natural products that have already been marketed or are currently in clinical trials.

Chlorinated bis-indole alkaloids from deep-sea derived Streptomyces sp. SCSIO 11791 with antibacterial and cytotoxic activities

Two new chlorinated bis-indole alkaloids, dionemycin (1) and 6-OMe-7',7″-dichorochromopyrrolic acid (2), along with seven known analogs 3-9, were isolated from the deep-sea derived Streptomyces sp. SCSIO 11791. Their structures were elucidated by extensive HRESIMS, and 1D and 2D NMR data analysis. In vitro antibacterial and cytotoxic assays revealed that, compound 1, shows anti-staphylococcal activity with an MIC range of 1-2 μg/mL against six clinic strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated from human and pig. Additionally, compound 1 displayed cytotoxic activity against human cancer cell lines NCI-H460, MDA-MB-231, HCT-116, HepG2, and noncancerous MCF10A with an IC₅₀ range of 3.1-11.2 μM. Analysis of the structure-activity relationship reveals that the chlorine atom at C-6″ could be pivotal for conferring their bioactivities, thus providing hints on chemical modifications on bis-indole alkaloid scaffold in drug design.

Screening of new cell cycle suppressive compounds from marine-derived microorganisms in Chinese hamster ovary cells

Monoclonal antibodies (mAbs) are active pharmaceutical ingredients in antibody drugs, produced mainly using recombinant Chinese hamster ovary (CHO) cells. The regulation of recombinant CHO cell proliferation can improve the productivity of heterologous proteins. Chemical compound approaches for cell cycle regulation have the advantages of simplicity and ease of use in industrial processes. However, CHO cells have genetic and phenotypic diversity, and the effects of such compounds might depend on cell line and culture conditions. Increasing the variety of cell cycle inhibitors is a promising strategy to overcome the dependency. Marine microorganisms are a vast and largely undeveloped source of secondary metabolites with physiological activity. In this study, we focused on secondary metabolites of marine microorganisms and evaluated their effectiveness as cell cycle inhibitory compounds. Of 720 extracts from microorganisms (400 actinomycetes and 320 filamentous fungi) collected from the Okinawan Sea, we identified nine extracts that decreased the specific growth rate and increased the specific production rate without reducing cell viability. After fractionating the extracts, the components of active fractions were estimated using time-of-flight mass spectrometry analysis. Then, four compounds, including staurosporine and undecylprodigiosin were deduced to be active compounds. These compounds have been reported to exert a cell cycle inhibitory effect on mammalian cells. These compounds might serve as additives to improve mAb production in CHO cells. This study indicates that secondary metabolites of marine microorganisms are a useful source for new cell cycle inhibitory compounds that can increase mAb production in CHO cells.

An Indonesian Marine Bacterium, Pseudoalteromonas rubra, Produces Antimicrobial Prodiginine Pigments

Red pigmented marine bacteria, Pseudoalteromonas rubra strains PS1 and SB14, were isolated from two sampling locations in different ecosystems on Alor Island, Indonesia, and cultured in the laboratory. We analyzed the 16S rRNA gene sequences and examined the pigment composition and found that both strains produced cycloprodigiosin (3), prodigiosin (4), and 2-methyl-3-hexyl-prodiginine (5) as major compounds. In addition, we detected three minor compounds: prodigiosin derivatives 2-methyl-3-propyl prodiginine (1), 2-methyl-3-butyl prodiginine (2), and 2-methyl-3-heptyl-prodiginine (6). To our knowledge, this is the first report that P. rubra synthesizes not only prodigiosin and cycloprodigiosin but also four prodigiosin derivatives that differ in the length of the alkyl chain. The antimicrobial activity of cycloprodigiosin, prodigiosin, and 2-methyl-3-hexyl-prodiginine was examined by a disk-diffusion test against Escherichia coli, Staphylococcus aureus, Salmonella typhi, and Candida albicans. We found that, at a concentration of 20 μg/mL, cycloprodigiosin showed the greatest inhibition (25.1 ± 0.55 mm) against S. aureus.

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.

Marine Actinomycetes-derived Natural Products

Actinomycetes is an abundant resource for discovering a large number of lead compounds, which play an important role in microbial drug discovery. Compared to terrestrial microorganisms, marine actinomycetes have unique metabolic pathways because of their special living environment, which has the potential to produce a variety of bioactive substances. In this paper, secondary metabolites isolated from marine actinomycetes are reviewed (2013-2018), most of which exhibited cytotoxic, antibacterial, and antiviral biological activities.

Deep Hypersaline Anoxic Basins as Untapped Reservoir of Polyextremophilic Prokaryotes of Biotechnological Interest

Deep-sea hypersaline anoxic basins (DHABs) are considered to be among the most extreme ecosystems on our planet, allowing only the life of polyextremophilic organisms. DHABs’ prokaryotes exhibit extraordinary metabolic capabilities, representing a hot topic for microbiologists and biotechnologists. These are a source of enzymes and new secondary metabolites with valuable applications in different biotechnological fields. Here, we review the current knowledge on prokaryotic diversity in DHABs, highlighting the biotechnological applications of identified taxa and isolated species. The discovery of new species and molecules from these ecosystems is expanding our understanding of life limits and is expected to have a strong impact on biotechnological applications.

Targeted Delivery Prodigiosin to Choriocarcinoma by Peptide-Guided Dendrigraft Poly-l-lysines Nanoparticles

The available and effective therapeutic means to treat choriocarcinoma is seriously lacking, mainly due to the toxic effects caused by chemotherapy and radiotherapy. Accordingly, we developed a method for targeting delivery of chemotherapeutical drugs only to cancer cells, not normal cells, in vivo, by using a synthetic placental chondroitin sulfate (CSA)-binding peptide (plCSA-BP) derived from malarial protein VAR2CSA. A 28 amino acids placental CSA-binding peptide (plCSA-BP) from the VAR2CSA was synthesized as a guiding peptide for tumor-targeting delivery, dendrigraft poly-L-lysines (DGL) was modified with plCSA-BP and served as a novel targeted delivery carrier. Choriocarcinoma was selected to test the effect of targeted delivery carrier, and prodigiosin isolated from Serratia marcescens subsp. lawsoniana was selected as a chemotherapeutical drug and encapsulated in the DGL modified by the plCSA-BP nanoparticles (DGL/CSA-PNPs). DGL/CSA-PNPs had a sustained slow-release feature at pH 7.4, which could specifically bind to the JEG3 cells and exhibited better anticancer activity than that of the controls. The DGL/CSA-PNPs induced the apoptosis of JEG3 cells through caspase-3 and the P53 signaling pathway. DGL/CSA-PNPs can be used as an excellent targeted delivery carrier for anticancer drugs, and the prodigiosin could be an alternative chemotherapeutical drug for choriocarcinoma.

Chemical constituents of Streptomyces sp. strain Al-Dhabi-97 isolated from the marine region of Saudi Arabia with antibacterial and anticancer properties

BACKGROUND

Unlike the terrestrial region, the microorganisms especially actinomycetes groups existing in the marine environment are important sources for the medically important drugs and other active compounds. Considering the importance of natural compounds from the marine actinomycetes, the present study proceeded to identify and characterize promising antibacterial and anticancer actinomycetes from the marine region of Saudi Arabia and to profile the individual chemical components.

METHODS

Antimicrobial, anticancer and chemical profiling were performed by broth microdilution, mitochondrial membrane potential assays and GC-MS analysis. Investigations were directed towards the isolation and characterization of active Streptomyces sp. strain Al-Dhabi-97.

RESULTS

The obtained results of the morphological, biochemical, physiological and molecular level studies of the isolate Al-Dhabi-97 showed similarity towards the species of Streptomyces. Gram positive bacteria such as Bacillus subtilis, Enterococcus faecalis, Staphylococcus epidermidis and Staphylococcus aureus showed MIC values of 500, 250, 125 and 62.5μg/ml and Gram negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumonia, Escherichia coli and Salmonella paratyphi reported MIC values of 500, 500, 250 and >250μg/ml in the antimicrobial studies. The results of anticancer studies showed that at 100μg/ml, the extract showed maximum cell growth inhibition and exhibited 2.5% necrosis, 62.2% late apoptosis and 20.8% early apoptosis in COLO 320 DM and VERO cell lines respectively. Chemical profiling of the extract authenticated the presence of constituents such as 1-phenanthrenemethanol (46.64%), phthalic acid, di(2-propylpentyl) ester (26.97%), benzenebutanoic acid (3.37%), podocarp-7-en-3-one (2.68%), and indole-3-carboxaldehyde (1.11%) respectively.

CONCLUSION

The present study concluded that Saudi Arabian marine region was a promising area for the identification of medically important natural products producing actinomycetes for antibacterial and anticancer drugs.

Extreme Environment Streptomyces: Potential Sources for New Antibacterial and Anticancer Drug Leads?

Antimicrobial resistance (AR) is recognized as one of the greatest threats to public health and in global concern. Consequently, the increased morbidity and mortality, which are associated with multidrug resistance bacteria, urgently require the discovery of novel and more efficient drugs. Conversely, cancer is a growing complex human disease that demands new drugs with no or fewer side effects. Most of the drugs currently used in the health care systems were of Streptomyces origin or their synthetic forms. Natural product researches from Streptomyces have been genuinely spectacular over the recent years from extreme environments. It is because of technical advances in isolation, fermentation, spectroscopy, and genomic studies which led to the efficient recovering of Streptomyces and their new chemical compounds with distinct activities. Expanding the use of the last line of antibiotics and demand for new drugs will continue to play an essential role for the potent Streptomyces from previously unexplored environmental sources. In this context, deep-sea, desert, cryo, and volcanic environments have proven to be a unique habitat of more extreme, and of their adaptation to extreme living, environments attribute to novel antibiotics. Extreme Streptomyces have been an excellent source of a new class of compounds which include alkaloids, angucycline, macrolide, and peptides. This review covers novel drug leads with antibacterial and cytotoxic activities isolated from deep-sea, desert, cryo, and volcanic environment Streptomyces from 2009 to 2019. The structure and chemical classes of the compounds, their relevant bioactivities, and the sources of organisms are presented.

Ilamycin C induces apoptosis and inhibits migration and invasion in triple-negative breast cancer by suppressing IL-6/STAT3 pathway

BACKGROUND

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with poor prognosis, and its treatment remains a challenge due to few targeted medicines and high risk of relapse, metastasis, and drug resistance. Thus, more effective drugs and new regimens for the therapy of TNBC are urgently needed. Ilamycins are a kind of cyclic peptides and produced by Streptomyces atratus and Streptomyces islandicus with effective anti-tuberculosis activity. Ilamycin C is a novel compound isolated from the deep South China Sea-derived Streptomyces atratus SCSIO ZH16 and exhibited a strong cytotoxic activity against several cancers including breast cancer cell line MCF7. However, the cytotoxic activity of Ilamycin C to TNBC cells and a detailed antitumor mechanism have not been reported.

METHODS

CCK-8 assays were used to examine cell viability and cytotoxic activity of Ilamycin C to TNBC, non-TNBC MCF7, and nonmalignant MCF10A cells. EdU assays and flow cytometry were performed to assess cell proliferation and cell apoptosis. Transwell migration and Matrigel invasion assays were utilized to assess the migratory and invading capacity of TNBC cells following the treatment of Ilamycin C. The expressions of proteins were detected by western blot.

RESULTS

In this study, we found that Ilamycin C has more preferential cytotoxicity in TNBC cells than non-TNBC MCF7 and nonmalignant MCF10A cells. Notably, our studies revealed the mechanism that Ilamycin C can induce Bax/Bcl-2-related caspase-dependent apoptosis and inhibit migration and invasion through MMP2/MMP9/vimentin/fascin in TNBC by suppressing IL-6-induced STAT3 phosphorylation.

CONCLUSIONS

This study provides the first evidence that Ilamycin C has significant implications for the potential as a novel IL-6/STAT3 inhibitor for TNBC treatment in the future.

Metagenomics Approaches in Discovery and Development of New Bioactive Compounds from Marine Actinomycetes

Marine actinomycetes are prolific sources of marine drug discovery system contributing for several bioactive compounds of biomedical prominence. Metagenomics, a culture-independent technique through its sequence- and function-based screening has led to the discovery and synthesis of numerous biologically significant compounds like polyketide synthase, Non-ribosomal peptide synthetase, antibiotics, and biocatalyst. While metagenomics offers different advantages over conventional sequencing techniques, they also have certain limitations including bias classification, non-availability of quality DNA samples, heterologous expression, and host selection. The assimilation of advanced amplification and screening methods such as φ29 DNA polymerase, Next-Generation Sequencing, Cosmids, and recent bioinformatics tools like automated genome mining, anti-SMASH have shown promising results to overcome these constrains. Consequently, functional genomics and bioinformatics along with synthetic biology will be crucial for the success of the metagenomic approach and indeed for exploring new possibilities among the microbial consortia for the future drug discovery process.

Angucycline Glycosides from an Intertidal Sediments Strain Streptomyces sp. and Their Cytotoxic Activity against Hepatoma Carcinoma Cells

Four angucycline glycosides including three new compounds landomycin N (1), galtamycin C (2) and vineomycin D (3), and a known homologue saquayamycin B (4), along with two alkaloids 1-acetyl-β-carboline (5) and indole-3-acetic acid (6), were isolated from the fermentation broth of an intertidal sediments-derived Streptomyces sp. Their structures were established by IR, HR-ESI-MS, 1D and 2D NMR techniques. Among the isolated angucyclines, saquayamycin B (4) displayed potent cytotoxic activity against hepatoma carcinoma cells HepG-2, SMMC-7721 and plc-prf-5, with IC₅₀ values 0.135, 0.033 and 0.244 μM respectively, superior to doxorubicin. Saquayamycin B (4) also induced apoptosis in SMMC-7721 cells as detected by its morphological characteristics in 4′,6-diamidino-2-phenylindole (DAPI) staining experiment.

Biological Potential and Mechanism of Prodigiosin from Serratia marcescens Subsp. lawsoniana in Human Choriocarcinoma and Prostate Cancer Cell Lines

Tripyrrole molecules have received renewed attention due to reports of numerous biological activities, including antifungal, antibacterial, antiprotozoal, antimalarial, immunosuppressive, and anticancer activities. In a screen of bacterial strains with known toxicities to termites, a red pigment-producing strain, HDZK-BYSB107, was isolated from Chamaecyparis lawsoniana, which grows in Oregon, USA. Strain HDZK-BYSB107 was identified as Serratia marcescens subsp. lawsoniana. The red pigment was identified as prodigiosin using ultraviolet absorption, LC-MS, and 1H-NMR spectroscopy. The bacterial prodigiosin had an inhibitory effect on both Gram-negative and Gram-positive bacteria. The main objective of this study was to explore the anticancer activities and mechanism of strain HDZK-BYSB107 prodigiosin by using human choriocarcinoma (JEG3) and prostate cancer cell lines (PC3) in vitro and JEG3 and PC3 tumor-bearing nude mice in vivo. In vitro anticancer activities showed that the bacterial prodigiosin induced apoptosis in JEG3 cells. In vivo anticancer activities indicated that the prodigiosin significantly inhibited the growth of JEG3 and PC3 cells, and the inhibitory activity was dose and time dependent. The anticancer efficacy of the bacterial prodigiosin on JEG3 and PC3 cells, JEG3 and PC3 tumor exhibited a correlation with the down regulation of the inhibitor of IAP family, including XIAP, cIAP-1 and cIAP-2, and the activation of caspase-9 and caspase-3 accompanied by proteolytic degradation of poly (ADP-ribose)-polymerase. The expressions of P53 and Bax/Bcl-2 in JEG3 and PC3 cells were significantly higher than in untreated groups. Our results indicated that the bacterial prodigiosin extracted from C. lawsoniana is a promising molecule due to its potential for therapeutic applications.

PG-Priming Enhances Doxorubicin Influx to Trigger Necrotic and Autophagic Cell Death in Oral Squamous Cell Carcinoma

Synergistic effects between natural compounds and chemotherapy drugs are believed to have fewer side effects with equivalent efficacy. However, the synergistic potential of prodigiosin (PG) with doxorubicin (Dox) chemotherapy is still unknown. This study explores the synergistic mechanism of PG and Dox against oral squamous cell carcinoma (OSCC) cells. Three OSCC cell lines were treated with different PG/Dox combinatory schemes for cytotoxicity tests and were further investigated for cell death characteristics by cell cycle flow cytometry and autophagy/apoptosis marker labelling. When OSCC cells were pretreated with PG, the cytotoxicity of the subsequent Dox-treatment was 30% higher than Dox alone. The cytotoxic efficacy of PG-pretreated was found better than those of PG plus Dox co-treatment and Dox-pretreatment. Increase of Sub-G1 phase and caspase-3/LC-3 levels without poly (ADP-ribose) polymeras (PARP) elevation indicated both autophagy and necrosis occurred in OSCC cells. Dox flux after PG-priming was further evaluated by rhodamine-123 accumulation and Dox transporters analysis to elucidate the PG-priming effect. PG-priming autophagy enhanced Dox accumulation according to the increase of rhodamine-123 accumulation without the alterations of Dox transporters. Additionally, the cause of PG-triggered autophagy was determined by co-treatment with endoplasmic reticulum (ER) stress or AMP-activated protein kinase (AMPK) inhibitor. PG-induced autophagy was not related to nutrient deprivation and ER stress was proved by co-treatment with specific inhibitor. Taken together, PG-priming autophagy could sensitize OSCC cells by promoting Dox influx without regulation of Dox transporter. The PG-priming might be a promising adjuvant approach for the chemotherapy of OSCC.

(-)-Shikimic Acid as a Chiral Building Block for the Synthesis of New Cytotoxic 6-Aza-Analogues of Angucyclinones

We describe the syntheses of nine new angucyclinone 6-aza-analogues, achieved through a hetero Diels-Alder reaction between the shikimic acid derivative-azadiene 13, with different naphthoquinones. The cytotoxic activity of the new synthesized compounds and five angucyclinones, previously reported, was evaluated in vitro against three cancer cell lines: PC-3 (prostate cancer), HT-29 (colon cancer), MCF-7 (breast cancer), and one non-tumoral cell line, human colon epithelial cells (CCD841 CoN). Our results showed that most 6-azadiene derivatives exhibited significant cytotoxic activities, which was demonstrated by their IC₅₀ values (less than 10 μM), especially for the most sensitive cells, PC-3 and HT-29. From a chemical point of view, depending on the protected group of ring A and the pattern of substitution on ring D, cytotoxicity elicited these compounds, in terms of their potency and selectivity. Therefore, according to these chemical features, the most promising agents for every cancer cell line were 7a, 17, and 19c for PC-3 cells; 7a, 17, and 20 for HT-29 cells, and 19a for MCF-7 cells.

Angucycline Glycosides from Mangrove-Derived Streptomycesdiastaticus subsp. SCSIO GJ056

Nine new angucycline glycosides designated urdamycins N1⁻N9 (1⁻9), together with two known congener urdamycins A (10) and B (11), were obtained from a mangrove-derived Streptomycesdiastaticus subsp. SCSIO GJ056. The structures of new compounds were elucidated on the basis of extensive spectroscopic data analysis. The absolute configurations of 6⁻9 were assigned by electronic circular dichroism calculation method. Urdamycins N6 (6) and N9 (9) represent the first naturally occurring (5R, 6R)-angucycline glycosides, which are diastereomers of urdamycins N7 (7) and N8 (8), respectively.

Prodigiosin, Violacein, and Volatile Organic Compounds Produced by Widespread Cutaneous Bacteria of Amphibians Can Inhibit Two Batrachochytrium Fungal Pathogens

Symbiotic bacteria can produce secondary metabolites and volatile compounds that contribute to amphibian skin defense. Some of these symbionts have been used as probiotics to treat or prevent the emerging disease chytridiomycosis. We examined 20 amphibian cutaneous bacteria for the production of prodigiosin or violacein, brightly colored defense compounds that pigment the bacteria and have characteristic spectroscopic properties making them readily detectable, and evaluated the antifungal activity of these compounds. We detected violacein from all six isolates of Janthinobacterium lividum on frogs from the USA, Switzerland, and on captive frogs originally from Panama. We detected prodigiosin from five isolates of Serratia plymuthica or S. marcescens, but not from four isolates of S. fonticola or S. liquefaciens. All J. lividum isolates produced violacein when visibly purple, while prodigiosin was only detected on visibly red Serratia isolates. When applied to cultures of chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), prodigiosin caused significant growth inhibition, with minimal inhibitory concentrations (MIC) of 10 and 50 μM, respectively. Violacein showed a MIC of 15 μM against both fungi and was slightly more active against Bsal than Bd at lower concentrations. Although neither violacein nor prodigiosin showed aerosol activity and is not considered a volatile organic compound (VOC), J. lividum and several Serratia isolates did produce antifungal VOCs. White Serratia isolates with undetectable prodigiosin levels could still inhibit Bd growth indicating additional antifungal compounds in their chemical arsenals. Similarly, J. lividum can produce antifungal compounds such as indole-3-carboxaldehyde in addition to violacein, and isolates are not always purple, or turn purple under certain growth conditions. When Serratia isolates were grown in the presence of cell-free supernatant (CFS) from the fungi, CFS from Bd inhibited growth of the prodigiosin-producing isolates, perhaps indicative of an evolutionary arms race; Bsal CFS did not inhibit bacterial growth. In contrast, growth of one J. lividum isolate was facilitated by CFS from both fungi. Isolates that grow and continue to produce antifungal compounds in the presence of pathogens may represent promising probiotics for amphibians infected or at risk of chytridiomycosis. In a global analysis, 89% of tested Serratia isolates and 82% of J. lividum isolates were capable of inhibiting Bd and these have been reported from anurans and caudates from five continents, indicating their widespread distribution and potential for host benefit.

Biosynthesis of ilamycins featuring unusual building blocks and engineered production of enhanced anti-tuberculosis agents

Tuberculosis remains one of the world’s deadliest communicable diseases, novel anti-tuberculosis agents are urgently needed due to severe drug resistance and the co-epidemic of tuberculosis/human immunodeficiency virus. Here, we show the isolation of six anti-mycobacterial ilamycin congeners (1–6) bearing rare L-3-nitro-tyrosine and L-2-amino-4-hexenoic acid structural units from the deep sea-derived Streptomyces atratus SCSIO ZH16. The biosynthesis of the rare L-3-nitrotyrosine and L-2-amino-4-hexenoic acid units as well as three pre-tailoring and two post-tailoring steps are probed in the ilamycin biosynthetic machinery through a series of gene inactivation, precursor chemical complementation, isotope-labeled precursor feeding experiments, as well as structural elucidation of three intermediates (6–8) from the respective mutants. Most impressively, ilamycins E₁/E₂, which are produced in high titers by a genetically engineered mutant strain, show very potent anti-tuberculosis activity with an minimum inhibitory concentration value ≈9.8 nM to Mycobacterium tuberculosis H37Rv constituting extremely potent and exciting anti-tuberculosis drug leads.

Tuberculosis (TB) remains one of the world’s deadliest communicable diseases, novel anti-TB agents are urgently needed due to severe drug resistance and the co-epidemic of TB/HIV. Here, the authors show that anti-mycobacterial ilamycin congeners bearing unusual structural units possess extremely potent anti-tuberculosis activities.

Inhibitory Growth of Oral Squamous Cell Carcinoma Cancer via Bacterial Prodigiosin

Chemotherapy drugs for oral cancers always cause side effects and adverse effects. Currently natural sources and herbs are being searched for treated human oral squamous carcinoma cells (OSCC) in an effort to alleviate the causations of agents in oral cancers chemotherapy. This study investigates the effect of prodigiosin (PG), an alkaloid and natural red pigment as a secondary metabolite of Serratia marcescens, to inhibit human oral squamous carcinoma cell growth; thereby, developing a new drug for the treatment of oral cancer. In vitro cultured human OSCC models (OECM1 and SAS cell lines) were used to test the inhibitory growth of PG via cell cytotoxic effects (MTT assay), cell cycle analysis, and Western blotting. PG under various concentrations and time courses were shown to effectively cause cell death and cell-cycle arrest in OECM1 and SAS cells. Additionally, PG induced autophagic cell death in OECM1 and SAS cells by LC3-mediated P62/LC3-I/LC3-II pathway at the in vitro level. These findings elucidate the role of PG, which may target the autophagic cell death pathways as a potential agent in cancer therapeutics.

Molecular inter-kingdom interactions of endophytes isolated from Lychnophora ericoides

The importance of microbial natural products has been widely demonstrated in the search for new antibiotics. However, the functional role of microbial metabolites in nature remains to be deciphered. Several natural products are known to mediate microbial interactions through metabolic exchange. One approach to investigate metabolic exchange in the laboratory is through microbial interactions. Here, we describe the chemical study of selected endophytes isolated from the Brazilian medicinal plant Lychnophora ericoides by pairwise inter-kingdom interactions in order to correlate the impact of co-cultivation to their metabolic profiles. Combining mass spectrometry tools and NMR analyses, a total of 29 compounds were identified. These compounds are members of polyene macrocycles, pyrroloindole alkaloids, angucyclines, and leupeptins chemical families. Two of the identified compounds correspond to a new fungal metabolite (29) and a new actinobacterial angucycline-derivative (23). Our results revealed a substantial arsenal of small molecules induced by microbial interactions, as we begin to unravel the complexity of microbial interactions associated with endophytic systems.

Natural Compounds from Herbs that can Potentially Execute as Autophagy Inducers for Cancer Therapy

Accumulated evidence indicates that autophagy is a response of cancer cells to various anti-cancer therapies. Autophagy is designated as programmed cell death type II, and is characterized by the formation of autophagic vacuoles in the cytoplasm. Numerous herbs, including Chinese herbs, have been applied to cancer treatments as complementary and alternative medicines, supplements, or nutraceuticals to dampen the side or adverse effects of chemotherapy drugs. Moreover, the tumor suppressive actions of herbs and natural products induced autophagy that may lead to cell senescence, increase apoptosis-independent cell death or complement apoptotic processes. Hereby, the underlying mechanisms of natural autophagy inducers are cautiously reviewed in this article. Additionally, three natural compounds—curcumin, 16-hydroxycleroda-3,13-dien-15,16-olide, and prodigiosin—are presented as candidates for autophagy inducers that can trigger cell death in a supplement or alternative medicine for cancer therapy. Despite recent advancements in therapeutic drugs or agents of natural products in several cancers, it warrants further investigation in preclinical and clinical studies.

Antimicrobial Spirotetronate Metabolites from Marine-Derived Micromonospora harpali SCSIO GJ089

Two new spirotetronate aglycones, 22-dehydroxymethyl-kijanolide (1) and 8-hydroxy-22-dehydroxymethyl-kijanolide (2), along with seven new spirotetronate glycosides, microsporanates A-F (3-8) and tetrocarcin P (9), together with three known tetrocarcins [tetrocarcins A (10), B (11), and AC6H (12)], were isolated from fermentation broths of the marine-derived Micromonospora harpali SCSIO GJ089. The structures of 1-9 were elucidated on the basis of 1D and 2D NMR and MS spectroscopic data. Compounds 3-8 feature an α,β-unsaturated carbonyl moiety within their spirotetronate skeletons. Moreover, compounds 3-12 displayed strong to moderate antibacterial activities against Gram positive bacteria Bacillus thuringiensis BT01 and B. subtilis BS01 with MIC values ranging from 0.016 to 8.0 μg/mL.

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) 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 (1340 in 429 papers for 2015), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Deep Sea Actinomycetes and Their Secondary Metabolites

Deep sea is a unique and extreme environment. It is a hot spot for hunting marine actinomycetes resources and secondary metabolites. The novel deep sea actinomycete species reported from 2006 to 2016 including 21 species under 13 genera with the maximum number from Microbacterium, followed by Dermacoccus, Streptomyces and Verrucosispora, and one novel species for the other 9 genera. Eight genera of actinomycetes were reported to produce secondary metabolites, among which Streptomyces is the richest producer. Most of the compounds produced by the deep sea actinomycetes presented antimicrobial and anti-cancer cell activities. Gene clusters related to biosynthesis of desotamide, heronamide, and lobophorin have been identified from the deep sea derived Streptomyces.

Cold-water marine natural products, 2006 to 2016

This is an update report on marine natural products isolated from cold-water organisms in the last decade, following the previous review that covered the literature up to 2005. Emphasis is on structural assignments and biological activity.