Bioactive Streptoglutarimides A-J from the Marine-Derived Streptomyces sp. ZZ741

Marine actinobacteria metabolites: unlocking new treatments for acne vulgaris

Marine-derived actinobacteria isolated from sponge Cliona varians and soft coral Eunicea fusca were screened for antibacterial activity against acne-related bacteria, specifically Staphylococcus epidermidis ATCC 14990, methicillin-resistant Staphylococcus aureus ATCC BAA44, and Cutibacterium acnes ATCC 6919. Cytotoxicity assays were performed on human dermal fibroblast (HDFa) and keratinocyte (HaCaT) cell lines to assess the safety profile of the extracts. Chemical characterization was conducted using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Among the extracts, six derived from Kocuria sp., Rhodococcus sp., Nocardia sp., Micrococcus sp., and Streptomyces sp. demonstrated significant antibacterial activity. Notably, extract Z9.216 from Kocuria sp. exhibited the highest efficacy, inhibiting S. epidermidis by 68%, S. aureus by 93%, and C. acnes by 98.7% at a concentration of 0.003 mg/mL, which was comparable to the standard antibiotics erythromycin and vancomycin, while maintaining over 90% cell viability in both HDFa and HaCaT cell lines. Untargeted metabolomic analysis suggested that antibacterial activity might be associated with compounds from the chemical families of alkaloids, terpenoids, and fatty acids, among others. These findings highlight the therapeutic potential of marine actinobacteria in underexplored environments as a promising strategy for treating acne vulgaris, a chronic inflammatory skin condition.

Prospects of marine-derived compounds as potential therapeutic agents for glioma

CONTEXT

Glioma, the most common primary malignant brain tumour, is a grave health concern associated with high morbidity and mortality. Current treatments, while effective to some extent, are often hindered by factors such as the blood-brain barrier and tumour microenvironment. This underscores the pressing need for exploring new pharmacologically active anti-glioma compounds.

METHODS

This review synthesizes information from major databases, including Chemical Abstracts, Medicinal and Aromatic Plants Abstracts, ScienceDirect, SciFinder, Google Scholar, Scopus, PubMed, Springer Link and relevant books. Publications were selected without date restrictions, using terms such as 'Hymenocrater spp.,' 'phytochemical,' 'pharmacological,' 'extract,' 'essential oil' and 'traditional uses.' General web searches using Google and Yahoo were also performed. Articles related to agriculture, ecology, synthetic work or published in languages other than English or Chinese were excluded.

RESULTS

The marine environment has been identified as a rich source of diverse natural products with potent antitumour properties.

CONCLUSIONS

This paper not only provides a comprehensive review of marine-derived compounds but also unveils their potential in treating glioblastoma multiforme (GBM) based on functional classifications. It encapsulates the latest research progress on the regulatory biological functions and mechanisms of these marine substances in GBM, offering invaluable insights for the development of new glioma treatments.

Penicamins A-L, Polyoxygenated Diterpenes from Penicillium camemberti JSB-7212

Penicamins A-L (1-12), 12 highly oxygenated novel diterpenes, were obtained from the fungus Penicillium camemberti JSB-7212. Compounds 1-12 share the same 7/6/5 tricyclic skeleton as valparane-type diterpenes but differ in the absolute configurations at C-7, C-11, and C-14, as well as in the oxidation levels at C-6 and C-8, which were determined through extensive spectroscopic data interpretation. Stereochemical assignments of compounds 1, 2, and 4-12 were established by single-crystal X-ray diffraction, and the absolute configuration of 3 was determined by analysis of the NOESY data and biogenetic consideration. Compounds 2 and 3 were immunosuppressive against lipopolysaccharide (LPS)-induced B cells, with IC50 values of 3.0 and 7.9 μM, respectively. They also moderately suppressed concanavalin A (ConA)-induced T cell proliferation, with IC50 values of 19 and 20 μM, respectively.

Antiproliferative metabolites against glioma cells from the marine-associated actinomycete Streptomyces sp. ZZ735

Metabolites produced by the genus Streptomyces are the most important resource for discovering bioactive compounds. In this study, chemical investigation on the metabolites produced by the marine-derived Streptomyces sp. ZZ735 in rice solid medium led to the isolation of eighteen compounds (1-18). Chemical structures of the isolated compounds were determined based on their HRESIMS data and the extensive NMR spectral analyses. Streptonaphthothiazines A (1), B (2), 2-(2-hydroxy-2-methylpropanoylamino)-benzoic acid (7), and streptomycinoic acids A (17), B (18) are characterized as five previously undescribed compounds. The structural backbones of streptonaphthothiazines A (1), B (2) and streptomycinoic acids A (17), B (18) are found from a natural resource for the first time. It is also the first report of 2-(2-methylpropanoylamino)-benzoic acid (3), 2-(2-methylpropanoylamino)-benzamide (4), methyl 2-(3-hydroxypropanoylamino)-benzoate (5), 2-propionylaminobenzamide (6), and (2E)-3-(3-hydroxy-4,5-dimethoxyphenyl)-2-propenoic acid (15) as natural products. Streptonaphthothiazines A (1), B (2) and streptomycinoic acids A (17), B (18) have antiproliferative activity against human glioma U87MG or U251 cells with IC50 values ranging from 31.8 to 37.9 μM.

Biotechnological potential of actinomycetes in the 21st century: a brief review

This brief review aims to draw attention to the biotechnological potential of actinomycetes. Their main uses as sources of antibiotics and in agriculture would be enough not to neglect them; however, as we will see, their biotechnological application is much broader. Far from intending to exhaust this issue, we present a short survey of the research involving actinomycetes and their applications published in the last 23 years. We highlight a perspective for the discovery of new active ingredients or new applications for the known metabolites of these microorganisms that, for approximately 80 years, since the discovery of streptomycin, have been the main source of antibiotics. Based on the collected data, we organize the text to show how the cosmopolitanism of actinomycetes and the evolutionary biotic and abiotic ecological relationships of actinomycetes translate into the expression of metabolites in the environment and the richness of biosynthetic gene clusters, many of which remain silenced in traditional laboratory cultures. We also present the main strategies used in the twenty-first century to promote the expression of these silenced genes and obtain new secondary metabolites from known or new strains. Many of these metabolites have biological activities relevant to medicine, agriculture, and biotechnology industries, including candidates for new drugs or drug models against infectious and non-infectious diseases. Below, we present significant examples of the antimicrobial spectrum of actinomycetes, which is the most commonly investigated and best known, as well as their non-antimicrobial spectrum, which is becoming better known and increasingly explored.

Marine Streptomyces-Derived Novel Alkaloids Discovered in the Past Decade

Natural alkaloids originating from actinomycetes and synthetic derivatives have always been among the important suppliers of small-molecule drugs. Among their biological sources, Streptomyces is the highest and most extensively researched genus. Marine-derived Streptomyces strains harbor unconventional metabolic pathways and have been demonstrated to be efficient producers of biologically active alkaloids; more than 60% of these compounds exhibit valuable activity such as antibacterial, antitumor, anti-inflammatory activities. This review comprehensively summarizes novel alkaloids produced by marine Streptomyces discovered in the past decade, focusing on their structural features, biological activity, and pharmacological mechanisms. Future perspectives on the discovery and development of novel alkaloids from marine Streptomyces are also provided.

Streptomyces: a natural source of anti-Candida agents

Introduction. There is an urgent need to source new compounds that can combat the current threat of serious infection caused by Candida spp. and contend with the problem of antimicrobial resistance.

Gap. A synthesis of the evidence available from the current literature is needed to identify promising antifungal chemotherapeutics.

Aim. To highlight anti-Candida compounds derived from Streptomyces spp. (a well-known source of antimicrobial compounds) that could translate to potential candidates for future clinical practice.

Methodology. A comprehensive review was conducted across three scientific literature databases spanning a 13-year period.

Results. We identified 151 compounds with anti-Candida activity. Amongst these, 40 were reported with very strong inhibitory activity, having minimum inhibitory concentrations (MICs) against Candida spp. of <3.5 µg ml−1, 66 compounds were considered strong inhibitors and 45 compounds exhibited moderate inhibitory potential. From an analysis of the MICs, we deduced that the actinomycin-like compounds RSP01 and RSP02 were probably the most promising anti-Candida compounds. Other antifungals of note included filipin-like compounds, which demonstrated superior inhibition to amphotericin B and activity against Candida glabrata and Candida krusei, and bafilomycin derivatives, which had substantial inhibition against Candida parapsilosis.

Conclusion. It is essential to recognize the limitations inherent in the quest for new antifungals, which encompass toxicity, in vivo effectiveness and constraints associated with limited data access. However, further investigation through in-depth study and emerging technologies is of paramount importance, given that there are still many more compounds to discover. This review highlights the importance of antifungal compounds derived from Streptomyces , which demonstrate robust inhibition, and, in many cases, low toxicity, making them promising candidates for the development of novel antifungal agents.

The Genomic-Driven Discovery of Glutarimide-Containing Derivatives from Burkholderia gladioli

Glutarimide-containing polyketides exhibiting potent antitumor and antimicrobial activities were encoded via conserved module blocks in various strains that favor the genomic mining of these family compounds. The bioinformatic analysis of the genome of Burkholderia gladioli ATCC 10248 showed a silent trans-AT PKS biosynthetic gene cluster (BGC) on chromosome 2 (Chr2C8), which was predicted to produce new glutarimide-containing derivatives. Then, the silent polyketide synthase gene cluster was successfully activated via in situ promoter insertion and heterologous expression. As a result, seven glutarimide-containing analogs, including five new ones, gladiofungins D-H (3-7), and two known gladiofungin A/gladiostatin (1) and 2 (named gladiofungin C), were isolated from the fermentation of the activated mutant. Their structures were elucidated through the analysis of HR-ESI-MS and NMR spectroscopy. The structural diversities of gladiofungins may be due to the degradation of the butenolide group in gladiofungin A (1) during the fermentation and extraction process. Bioactivity screening showed that 2 and 4 had moderate anti-inflammatory activities. Thus, genome mining combined with promoter engineering and heterologous expression were proved to be effective strategies for the pathway-specific activation of the silent BGCs for the directional discovery of new natural products.

New Insights on Biological Activities, Chemical Compositions, and Classifications of Marine Actinomycetes Antifouling Agents

Biofouling is the assemblage of undesirable biological materials and macro-organisms (barnacles, mussels, etc.) on submerged surfaces, which has unfavorable impacts on the economy and maritime environments. Recently, research efforts have focused on isolating natural, eco-friendly antifouling agents to counteract the toxicities of synthetic antifouling agents. Marine actinomycetes produce a multitude of active metabolites, some of which acquire antifouling properties. These antifouling compounds have chemical structures that fall under the terpenoids, polyketides, furanones, and alkaloids chemical groups. These compounds demonstrate eminent antimicrobial vigor associated with antiquorum sensing and antibiofilm potentialities against both Gram-positive and -negative bacteria. They have also constrained larval settlements and the acetylcholinesterase enzyme, suggesting a strong anti-macrofouling activity. Despite their promising in vitro and in vivo biological activities, scaled-up production of natural antifouling agents retrieved from marine actinomycetes remains inapplicable and challenging. This might be attributed to their relatively low yield, the unreliability of in vitro tests, and the need for optimization before scaled-up manufacturing. This review will focus on some of the most recent marine actinomycete-derived antifouling agents, featuring their biological activities and chemical varieties after providing a quick overview of the disadvantages of fouling and commercially available synthetic antifouling agents. It will also offer different prospects of optimizations and analysis to scale up their industrial manufacturing for potential usage as antifouling coatings and antimicrobial and therapeutic agents.

Bioactive Metabolites from Terrestrial and Marine Actinomycetes

Actinomycetes inhabit both terrestrial and marine ecosystems and are highly proficient in producing a wide range of natural products with diverse biological functions, including antitumor, immunosuppressive, antimicrobial, and antiviral activities. In this review, we delve into the life cycle, ecology, taxonomy, and classification of actinomycetes, as well as their varied bioactive metabolites recently discovered between 2015 and 2023. Additionally, we explore promising strategies to unveil and investigate new bioactive metabolites, encompassing genome mining, activation of silent genes through signal molecules, and co-cultivation approaches. By presenting this comprehensive and up-to-date review, we hope to offer a potential solution to uncover novel bioactive compounds with essential activities.

Ubiquitin-specific protease 28: the decipherment of its dual roles in cancer development

As significant posttranslational modifications, ubiquitination and deubiquitination, whose balance is modulated by ubiquitin-conjugating enzymes and deubiquitinating enzymes (DUBs), can regulate many biological processes, such as controlling cell cycle progression, signal transduction and transcriptional regulation. Belonging to DUBs, ubiquitin-specific protease 28 (USP28) plays an essential role in turning over ubiquitination and then contributing to the stabilization of quantities of substrates, including several cancer-related proteins. In previous studies, USP28 has been demonstrated to participate in the progression of various cancers. Nevertheless, several reports have recently shown that in addition to promoting cancers, USP28 can also play an oncostatic role in some cancers. In this review, we summarize the correlation between USP28 and tumor behaviors. We initially give a brief introduction of the structure and related biological functions of USP28, and we then introduce some concrete substrates of USP28 and the underlying molecular mechanisms. In addition, the regulation of the actions and expression of USP28 is also discussed. Moreover, we concentrate on the impacts of USP28 on diverse hallmarks of cancer and discuss whether USP28 can accelerate or inhibit tumor progression. Furthermore, clinical relevance, including impacting clinical prognosis, influencing therapy resistance and being the therapy target in some cancers, is depicted systematically. Thus, assistance may be given to future experimental designs by the information provided here, and the potential of targeting USP28 for cancer therapy is emphasized.

Secondary Metabolites from Marine-Derived Bacteria with Antibiotic and Antibiofilm Activities against Drug-Resistant Pathogens

The search for new antibiotics against drug-resistant microbes has been expanded to marine bacteria. Marine bacteria have been proven to be a prolific source of a myriad of novel compounds with potential biological activities. Therefore, this review highlights novel and bioactive compounds from marine bacteria reported during the period of January 2016 to December 2021. Published articles containing novel marine bacterial secondary metabolites that are active against drug-resistant pathogens were collected. Previously described compounds (prior to January 2016) are not included in this review. Unreported compounds during this period that exhibited activity against pathogenic microbes were discussed and compared in order to find the cue of the structure-bioactivity relationship. The results showed that Streptomyces are the most studied bacteria with undescribed bioactive compounds, followed by other genera in the Actinobacteria. We have categorized the structures of the compounds in the present review into four groups, based on their biosynthetic origins, as polyketide derivatives, amino acid derivatives, terpenoids, as well as compounds with mixed origin. These compounds were active against one or more drug-resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE), vancomycin-resistant Enterococci (VRE), multidrug-resistant Mycobacterium tuberculosis (MDR-TB), and amphotericin B-resistant Candida albicans. In addition, some of the compounds also showed activity against biofilm formation of the test bacteria. Some previously undescribed compounds, isolated from marine-derived bacteria during this period, could have a good potential as lead compounds for the development of drug candidates to overcome multidrug-resistant pathogens.

New Hygrocins K-U and Streptophenylpropanamide A and Bioactive Compounds from the Marine-Associated Streptomyces sp. ZZ1956

Marine-derived Streptomyces actinomycetes are one of the most important sources for the discovery of novel bioactive natural products. This study characterized the isolation, structural elucidation and biological activity evaluation of thirty compounds, including twelve previously undescribed compounds, namely hygrocins K-U (5-13, 17 and 18) and streptophenylpropanamide A (23), from the marine-associated actinomycete Streptomyces sp. ZZ1956. Structures of the isolated compounds were determined by a combination of extensive NMR spectroscopic analyses, HRESIMS data, the Mosher's method, ECD calculations, single crystal X-ray diffraction and comparison with reported data. Hygrocins C (1), D (2), F (4), N (8), Q (11) and R (12), 2-acetamide-6-hydroxy-7-methyl-1,4-naphthoquinone (22), echoside C (27), echoside A (28) and 11,11'-O-dimethylelaiophylin (30) had antiproliferative activity (IC50: 0.16-19.39 μM) against both human glioma U87MG and U251 cells with hygrocin C as the strongest active compound (IC50: 0.16 and 0.35 μM, respectively). The analysis of the structure-activity relationship indicated that a small change in the structures of the naphthalenic ansamycins had significant influence on their antiglioma activities. Hygrocins N (8), O (9), R (12), T (17) and U (18), 2-amino-6-hydroxy-7-methyl-1,4-naphthoquinone (21), 2-acetamide-6-hydroxy-7-methyl-1,4-naphthoquinone (22), 3'-methoxy(1,1',4',1″-terphenyl)-2',6'-diol (26), echoside C (27) and echoside A (28) showed antibacterial activity against methicillin-resistant Staphylococcus aureus and Escherichia coli with MIC values of 3-48 μg/mL.

Production of secondary metabolites in stirred tank bioreactor co-cultures of Streptomyces noursei and Aspergillus terreus

The focus of the study was to characterize the bioprocess kinetics and secondary metabolites production in the novel microbial co-cultivation system involving Streptomyces noursei ATCC 11455 (the producer of an antifungal substance known as nystatin) and Aspergillus terreus ATCC 20542 (the source of lovastatin, a cholesterol-lowering drug). The investigated “A. terreus vs. S. noursei” stirred tank bioreactor co-cultures allowed for the concurrent development and observable biosynthetic activity of both species. In total, the production profiles of 50 secondary metabolites were monitored over the course of the study. The co-cultures were found to be effective in terms of enhancing the biosynthesis of several metabolic products, including mevinolinic acid, an acidic form of lovastatin. This work provided a methodological example of assessing the activity of a given strain in the co-culture by using the substrates which can be metabolized exclusively by this strain. Since S. noursei was shown to be incapable of lactose utilization, the observed changes in lactose levels were attributed to A. terreus and thus confirmed its viability. The study was complemented with the comparative microscopic observations of filamentous morphologies exhibited in the co-cultures and corresponding monocultures.

Biocontrol of Candida albicans by Antagonistic Microorganisms and Bioactive Compounds

Candida albicans is an endogenous opportunistic pathogenic fungus that is harmless when the host system remains stable. However, C. albicans could seriously threaten human life and health when the body’s immune function declines or the normal flora is out of balance. Due to the increasing resistance of candidiasis to existing drugs, it is important to find new strategies to help treat this type of systemic fungal disease. Biological control is considered as a promising strategy which is more friendly and safer. In this review, we compare the bacteriostatic behavior of different antagonistic microorganisms (bacteria and fungi) against C. albicans. In addition, natural products with unique structures have attracted researchers’ attention. Therefore, the bioactive nature products produced by different microorganisms and their possible inhibitory mechanisms are also reviewed. The application of biological control strategies and the discovery of new compounds with antifungal activity will reduce the resistance of C. albicans, thereby promoting the development of novel diverse antifungal drugs.

Cytotoxic metabolites from the marine-associated Streptomyces sp. ZZ1944

Marine-derived actinomycetes from the genus Streptomycete have a huge potential for the production of metabolites with structural and bioactive uniqueness and diversity. This study described the isolation and structural elucidation of twenty metabolites, including seven previously unreported compounds galbonolide H, galbonolide I, streptophenylpropionic acid A, treptophenylpropyl ester A, streptophenvaleramide A, seco-geldanamycin A and streptorapamycin A, from the marine-associated Streptomycete sp. ZZ1944. Structures of the isolated compounds were elucidated by a combination of extensive NMR spectroscopic analyses, HRESIMS data, optical rotation and ECD calculations. The structure of galbonolide H was also confirmed by a single crystal X-ray diffraction. Both autolytimycin and seco-geldanamycin A showed potent activity against the proliferation of glioma, lung cancer, colorectal cancer and breast cancer cells. Autolytimycin blocked cell cycle of glioma cells and seco-geldanamycin A induced apoptosis of glioma cells.

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.

Streptomyces: Still the Biggest Producer of New Natural Secondary Metabolites, a Current Perspective

There is a real consensus that new antibiotics are urgently needed and are the best chance for combating antibiotic resistance. The phylum Actinobacteria is one of the main producers of new antibiotics, with a recent paradigm shift whereby rare actinomycetes have been increasingly targeted as a source of new secondary metabolites for the discovery of new antibiotics. However, this review shows that the genus Streptomyces is still the largest current producer of new and innovative secondary metabolites. Between January 2015 and December 2020, a significantly high number of novel Streptomyces spp. have been isolated from different environments, including extreme environments, symbionts, terrestrial soils, sediments and also from marine environments, mainly from marine invertebrates and marine sediments. This review highlights 135 new species of Streptomyces during this 6-year period with 108 new species of Streptomyces from the terrestrial environment and 27 new species from marine sources. A brief summary of the different pre-treatment methods used for the successful isolation of some of the new species of Streptomyces is also discussed, as well as the biological activities of the isolated secondary metabolites. A total of 279 new secondary metabolites have been recorded from 121 species of Streptomyces which exhibit diverse biological activity. The greatest number of new secondary metabolites originated from the terrestrial-sourced Streptomyces spp.

Talaromydien a and talaroisocoumarin A, new metabolites from the marine-sourced fungus Talaromyces sp. ZZ1616

New talaromydien A (1) and talaroisocoumarin A (2), together with nine known compounds (3 - 11), were isolated from a culture of the marine-derived Talaromyces sp. ZZ1616 in potato dextrose broth medium. Structures of the new compounds were elucidated based on their HRESIMS data, NMR spectroscopic analyses, the modified Mosher's method, ECD, ¹³C NMR and optical rotation calculations. Talaroisocoumarin A showed antimicrobial activities with MIC values of 36.0 μg/mL against methicillin-resistant Staphylococcus aureus, 32.0 μg/mL against Escherichia coli, and 26.0 μg/mL against Candida albicans.

Novel Alkaloids from Marine Actinobacteria: Discovery and Characterization

The marine environment is an excellent resource for natural products with therapeutic potential. Its microbial inhabitants, often associated with other marine organisms, are specialized in the synthesis of bioactive secondary metabolites. Similar to their terrestrial counterparts, marine Actinobacteria are a prevalent source of these natural products. Here, we discuss 77 newly discovered alkaloids produced by such marine Actinobacteria between 2017 and mid-2021, as well as the strategies employed in their elucidation. While 12 different classes of alkaloids were unraveled, indoles, diketopiperazines, glutarimides, indolizidines, and pyrroles were most dominant. Discoveries were mainly based on experimental approaches where microbial extracts were analyzed in relation to novel compounds. Although such experimental procedures have proven useful in the past, the methodologies need adaptations to limit the chance of compound rediscovery. On the other hand, genome mining provides a different angle for natural product discovery. While the technology is still relatively young compared to experimental screening, significant improvement has been made in recent years. Together with synthetic biology tools, both genome mining and extract screening provide excellent opportunities for continued drug discovery from marine Actinobacteria.

Novel Marine Secondary Metabolites Worthy of Development as Anticancer Agents: A Review

Secondary metabolites from marine sources have a wide range of biological activity. Marine natural products are promising candidates for lead pharmacological compounds to treat diseases that plague humans, including cancer. Cancer is a life-threatening disorder that has been difficult to overcome. It is a long-term illness that affects both young and old people. In recent years, significant attempts have been made to identify new anticancer drugs, as the existing drugs have been useless due to resistance of the malignant cells. Natural products derived from marine sources have been tested for their anticancer activity using a variety of cancer cell lines derived from humans and other sources, some of which have already been approved for clinical use, while some others are still being tested. These compounds can assault cancer cells via a variety of mechanisms, but certain cancer cells are resistant to them. As a result, the goal of this review was to look into the anticancer potential of marine natural products or their derivatives that were isolated from January 2019 to March 2020, in cancer cell lines, with a focus on the class and type of isolated compounds, source and location of isolation, cancer cell line type, and potency (IC₅₀ values) of the isolated compounds that could be a guide for drug development.

New Antiproliferative Compounds against Glioma Cells from the Marine-Sourced Fungus Penicillium sp. ZZ1750

Seven novel compounds, namely peniresorcinosides A–E (1–5), penidifarnesylin A (6), and penipyridinone A (7), together with the 11 known ones 8–17, were isolated from a culture of the marine-associated fungus Penicillium sp. ZZ1750 in rice medium. The structures of the new compounds were established based on their high-resolution electrospray ionization mass spectroscopy (HRESIMS) data, extensive nuclear magnetic resonance (NMR) spectroscopic analyses, chemical degradation, Mosher’s method, ¹³C-NMR calculations, electronic circular dichroism (ECD) calculations, and single crystal X-ray diffraction. Peniresorcinosides A (1) and B (2) are rare glycosylated alkylresorcinols and exhibited potent antiglioma activity, with IC₅₀ values of 4.0 and 5.6 µM for U87MG cells and 14.1 and 9.8 µM for U251 cells, respectively.

Recent progress on anti-Candida natural products

Candida is an intractable life-threatening pathogen. Candida infection is extremely difficult to eradicate, and thus is the major cause of morbidity and mortality in immunocompromised individuals. Morevover, the rapid spread of drug-resistant fungi has led to significant decreases in the therapeutic effects of clinical drugs. New anti-Candida agents are urgently needed to solve the complicated medical problem. Natural products with intricate structures have attracted great attention of researchers who make every endeavor to discover leading compounds for antifungal agents. Their novel mechanisms and diverse modes of action expand the variety of fungistatic agents and reduce the emergence of drug resistance. In recent decades, considerable effort has been devoted to finding unique antifungal agents from nature and revealing their unusual mechanisms, which results in important progress on the development of new antifungals, such as the novel cell wall inhibitors YW3548 and SCY-078 which are being tested in clinical trials. This review will present a brief summary on the landscape of anti-Candida natural products within the last decade. We will also discuss in-depth the research progress on diverse natural fungistatic agents along with their novel mechanisms.

A Quick Guide to Small-Molecule Inhibitors of Eukaryotic Protein Synthesis

Eukaryotic ribosome and cap-dependent translation are attractive targets in the antitumor, antiviral, anti-inflammatory, and antiparasitic therapies. Currently, a broad array of small-molecule drugs is known that specifically inhibit protein synthesis in eukaryotic cells. Many of them are well-studied ribosome-targeting antibiotics that block translocation, the peptidyl transferase center or the polypeptide exit tunnel, modulate the binding of translation machinery components to the ribosome, and induce miscoding, premature termination or stop codon readthrough. Such inhibitors are widely used as anticancer, anthelmintic and antifungal agents in medicine, as well as fungicides in agriculture. Chemicals that affect the accuracy of stop codon recognition are promising drugs for the nonsense suppression therapy of hereditary diseases and restoration of tumor suppressor function in cancer cells. Other compounds inhibit aminoacyl-tRNA synthetases, translation factors, and components of translation-associated signaling pathways, including mTOR kinase. Some of them have antidepressant, immunosuppressive and geroprotective properties. Translation inhibitors are also used in research for gene expression analysis by ribosome profiling, as well as in cell culture techniques. In this article, we review well-studied and less known inhibitors of eukaryotic protein synthesis (with the exception of mitochondrial and plastid translation) classified by their targets and briefly describe the action mechanisms of these compounds. We also present a continuously updated database (http://eupsic.belozersky.msu.ru/) that currently contains information on 370 inhibitors of eukaryotic protein synthesis.

A critical review on the use of DP4+ in the structural elucidation of natural products: the good, the bad and the ugly. A practical guide

Covering: 2015 up to the end of 2020Even in the golden age of NMR, the number of natural products being incorrectly assigned is becoming larger every day. The use of quantum NMR calculations coupled with sophisticated data analysis provides ideal complementary tools to facilitate the elucidation process in challenging cases. Among the current computational methodologies to perform this task, the DP4+ probability is a popular and widely used method. This updated version of Goodman's DP4 synergistically combines NMR calculations at higher levels of theory with the Bayesian analysis of both scaled and unscaled data. Since its publication in late 2015, the use of DP4+ to solve controversial natural products has substantially grown, with several predictions being confirmed by total synthesis. To date, the structures of more than 200 natural products were determined with the aid of DP4+. However, all that glitters is not gold. Besides its intrinsic limitations, on many occasions it has been improperly used with potentially important consequences on the quality of the assignment. Herein we present a critical revision on how the scientific community has been using DP4+, exploring the strengths of the method and how to obtain optimal results from it. We also analyze the weaknesses of DP4+, and the paths to by-pass them to maximize the confidence in the structural elucidation.

Antimicrobial resistance in biofilms: Exploring marine actinobacteria as a potential source of antibiotics and biofilm inhibitors

Antimicrobial resistance (AMR) is one of the serious global public health threats that require immediate action. With the emergence of new resistance mechanisms in infection-causing microorganisms such as bacteria, fungi, and viruses, AMR threatens the effective prevention and treatment of diseases caused by them. This has resulted in prolonged illness, disability, and death. It has been predicted that AMR will lead to over ten million deaths by 2050. The rapid spread of multidrug-resistant bacteria is also causing old antibiotics to become ineffective. Among the diverse factors contributing to AMR, intrinsic biofilm development has been highlighted as an essential contributing facet. Moreover, biofilm-derived antibiotic tolerance leads to serious recurrent chronic infections. Therefore, the discovery of novel bioactive molecules is a potential solution that can help combat AMR. To achieve this, sustained mining of novel antimicrobial leads from actinobacteria, particularly marine actinobacteria, can be a promising strategy. Given their vast diversity and different habitats, the extraordinary capacity of actinobacteria can be tapped to synthesize new antibiotics or bioactive molecules for biofilm inhibition. Advanced screening strategies and novel approaches in the field of modern biochemical and molecular biology can be used to detect such new compounds. In view of this, the present review focuses on understanding some of the recent strategies to inhibit biofilm formation and explores the potential role of marine actinobacteria as sources of novel antibiotics and biofilm inhibitor molecules.

Small Molecules of Marine Origin as Potential Anti-Glioma Agents

Marine organisms are able to produce a plethora of small molecules with novel chemical structures and potent biological properties, being a fertile source for discovery of pharmacologically active compounds, already with several marine-derived agents approved as drugs. Glioma is classified by the WHO as the most common and aggressive form of tumor on CNS. Currently, Temozolomide is the only chemotherapeutic option approved by the FDA even though having some limitations. This review presents, for the first time, a comprehensive overview of marine compounds described as anti-glioma agents in the last decade. Nearly fifty compounds were compiled in this document and organized accordingly to their marine sources. Highlights on the mechanism of action and ADME properties were included. Some of these marine compounds could be promising leads for the discovery of new therapeutic alternatives for glioma treatment.

Evaluation of the antiproliferative activity of 106 marine microbial metabolites against human lung cancer cells and potential antiproliferative mechanism of purpuride G

A total of 106 marine microbial metabolites were evaluated for their antiproliferative activity against human lung cancer cells. Results showed that 23 compounds exhibited activity in inhibiting the proliferation of A549 and H157 cells with IC₅₀ values ranging from 1.5 to 48.2 μM. Pyrrospirone F, chrysophanol, physcion, and purpuride G are the four most active compounds with IC₅₀ values of 1.5-7.3 μM. Further investigation of purpuride G (a newly discovered sesquiterpene lactone) demonstrated its potent antiproliferative activity against six different lung cancer cells of A549, H157, H460, H1299, H1703, and PC9 with IC₅₀ values of 2.1-3.3 μM. The antiproliferative activity of purpuride G against cancer cells is related to block cell cycle, induce apoptosis through regulating the apoptotic proteins Bcl-2 and Bax, and inhibit glycolysis by downregulating two key glycolytic enzymes of hexokinase 2 and pyruvate kinase M2.

Identification of trans-AT polyketide clusters in two marine bacteria reveals cryptic similarities between distinct symbiosis factors

Glutarimide-containing polyketides are known as potent antitumoral and antimetastatic agents. The associated gene clusters have only been identified in a few Streptomyces producers and Burkholderia gladioli symbiont. The new glutarimide-family polyketides, denominated sesbanimides D, E and F along with the previously known sesbanimide A and C, were isolated from two marine alphaproteobacteria Stappia indica PHM037 and Labrenzia aggregata PHM038. Structures of the isolated compounds were elucidated based on 1D and 2D homo and heteronuclear NMR analyses and ESI-MS spectrometry. All compounds exhibited strong antitumor activity in lung, breast and colorectal cancer cell lines. Subsequent whole genome sequencing and genome mining revealed the presence of the trans-AT PKS gene cluster responsible for the sesbanimide biosynthesis, described as sbn cluster. Strikingly, the modular architecture of downstream mixed type PKS/NRPS, SbnQ, revealed high similarity to PedH in pederin and Lab13 in labrenzin gene clusters, although those clusters are responsible for the production of structurally completely different molecules. The unexpected presence of SbnQ homologues in unrelated polyketide gene clusters across phylogenetically distant bacteria, raises intriguing questions about the evolutionary relationship between glutarimide-like and pederin-like pathways, as well as the functionality of their synthetic products.

Antiproliferative Activity and Potential Mechanism of Marine-Sourced Streptoglutarimide H against Lung Cancer Cells

In 2019, streptoglutarimide H (SGH) was characterized as a new glutarimide from the secondary metabolites produced by a marine-derived actinomycete Streptomyces sp. ZZ741 and shown to have in vitro antiglioma activity. However, the antiproliferative activity and potential mechanism of SGH against lung cancer cells have not yet been characterized. This study demonstrated that SGH significantly inhibited the proliferation of different lung cancer cells. In terms of mechanism of action, SGH downregulated cell cycle- and nucleotide synthesis-related proteins to block cell cycle at G0/G1 phase, reduced the expression levels of glycolytic metabolic enzymes to inhibit glycolysis, and downregulated the important cancer transcription factor c-Myc and the therapeutic target deubiquitinase USP28. Potent anticancer activity and multiple mechanisms indicated SGH to be a novel antitumor compound against lung cancer cells.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) 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 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Bioactive Alkaloids from the Actinomycete Actinoalloteichus sp. ZZ1866

The new alkaloids marinacarbolines E-Q (1-10, 12-14), caerulomycin N (15), and actinoallonaphthyridine A (16), together with the known marinacarboline C (11) and cyanogramide (17), were isolated from the actinomycete Actinoalloteichus sp. ZZ1866. The structures of the isolated compounds were elucidated based on their HRESIMS data, extensive NMR spectroscopic analyses, Mosher's method, ECD calculations, single-crystal X-ray diffraction analysis, and chemical degradation studies. Marinacarbolines E-L (1-8) share an indole-pyridone-imidazole tetracyclic skeleton, which is the first example of this kind of skeleton. Caerulomycin N (15) and cyanogramide (17) exhibited cytotoxic activity against both human glioma U251 and U87MG cells with IC₅₀ values of 2.0-7.2 μM. Marinacarbolines E (1), G (3), I (5), and M (9) showed cytotoxic activity against U87MG cells with IC₅₀ values of 2.3-8.9 μM.

New Antifungal Metabolites from the Mariana Trench Sediment-Associated Actinomycete Streptomyces sp. SY1965

New streptothiazolidine A (1), streptodiketopiperazines A (2) and B (3), and (S)-1-(3-ethylphenyl)-1,2-ethanediol (4), together with eight known compounds (5–12), were isolated from the Mariana Trench sediment-associated actinomycete Streptomyces sp. SY1965. The racemic mixtures of (±)-streptodiketopiperazine (2 and 3) and (±)-1-(3-ethylphenyl)-1,2-ethanediol (4 and 5) were separated on a chiral high-performance liquid chromatography (HPLC) column. Structures of the new compounds were elucidated by their high-resolution electrospray ionization mass spectroscopy (HRESIMS) data and extensive nuclear magnetic resonance (NMR) spectroscopic analyses. Streptothiazolidine A is a novel salicylamide analogue with a unique thiazolidine-contained side chain and its absolute configuration was established by a combination of nuclear Overhauser effect spectroscopy (NOESY) experiment, electronic circular dichroism (ECD) and ¹³C NMR calculations. New streptothiazolidine A (1) and streptodiketopiperazines A (2) and B (3) showed antifungal activity against Candida albicans with MIC values of 47, 42, and 42 g/mL, respectively.

Antimicrobial compounds from marine actinomycetes

Marine actinomycetes were the main origin of marine natural products in the past 40 years. This review was to present the sources, structures and antimicrobial activities of 313 new natural products from marine actinomycetes reported from 1976 to 2019.

Recent progress of antibacterial natural products: Future antibiotics candidates

The discovery of novel antibacterial molecules plays a key role in solving the current antibiotic crisis issue. Natural products have long been an important source of drug discovery. Herein, we reviewed 256 natural products from 11 structural classes in the period of 2016-01/2020, which were selected by SciFinder with new compounds or new structures and MICs lower than 10 μg/mL or 10 μM as criterions. This review will provide some effective antibacterial lead compounds for medicinal chemists, which will promote the antibiotics research based on natural products to the next level.

Bioactive Metabolites from the Mariana Trench Sediment-Derived Fungus Penicillium sp. SY2107

Mariana Trench sediments are enriched in microorganisms, however, the structures and bioactivities of their secondary metabolites are not very known. In this study, a fungus Penicillium sp. SY2107 was isolated from a sample of Mariana Trench sediment collected at a depth of 11000 m and an extract prepared from the culture of this fungus in rice medium showed antimicrobial activities. Chemical investigation on this active extract led to the isolation of 16 compounds, including one novel meroterpenoid, named andrastone C. Structure of the new compound was elucidated based on high-resolution electrospray ionization mass spectroscopy (HRESIMS) data, extensive nuclear magnetic resonance (NMR) spectroscopic analyses and a single crystal X-ray diffraction. The crystal structure of a known meroterpenoid andrastone B was also reported in this study. Both andrastones B and C exhibited antimicrobial activities against methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Candida albicans with minimum inhibitory concentration (MIC) values in a range from 6 to 13 g/mL.

New metabolites from the marine-derived bacterium Pseudomonas sp. ZZ820R

Six previously undescribed compounds, named monaxanthones A and B, monaphenol A, monathioamide A, monaprenylindole A, and monavalerolactone A, were isolated from the culture of a marine-sourced bacterium Pseudomonas sp. ZZ820R in rice medium. Their structures were elucidated based on the HRESIMS data, NMR and MS-MS spectroscopic analyses, optical rotation and ECD calculations. Monathioamide A is an unprecedented sulfur-contained compound and monavalerolactone A represents the first example of this type of natural products. Monaprenylindole A showed antibacterial activity against methicillin-resistant Staphylococcus 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.