Iakyricidins A–D, Antiproliferative Piericidin Analogues Bearing a Carbonyl Group or Cyclic Skeleton from Streptomyces iakyrus SCSIO NS104

Metabolic Blockade-Based Genome Mining of Saccharopolyspora erythraea SCSIO 07745: Discovery and Biosynthetic Pathway of Aminoquinolinone Alkaloids Bearing 6/6/5 Tricyclic and 6/6/6/5 Tetracyclic Scaffolds

Metabolic blockade-based genome mining of the marine sediment-derived Saccharopolyspora erythraea SCSIO 07745 led to the discovery of 11 novel aminoquinolinone alkaloids, oxazoquinolinones A-J (1-10), characterized by an oxazolidone[3,2-α]quinoline-5,8-dione scaffold, and oxazoquinolinone K (11), featuring an unprecedented fused 6/6/6/5 tetracyclic core ring system. Additionally, 5 new biosynthetic intermediates or shunt products (12-16) and a known metabolite sannanine (17) were identified. Their structures were elucidated by extensive spectroscopic analyses and a comparison of electronic circular dichroism and single-crystal X-ray diffraction. On the basis of the functional gene analyses and structures of the intermediates or shunt products, plausible biosynthetic pathways for compounds 1-17 were proposed. Additionally, oxazoquinolinone K (11) obviously inhibited cell invasion of human glioma cell line LN229 cells at 10 μM.

Beyond traditional screening: Unveiling antibiotic potentials of actinomycetes in extreme environments

Extreme ecosystems are a rich source of specialized metabolites that can overcome multidrug resistance. However, the low efficiency of traditional exploratory research in discovering new antibiotics remains a major limitation. We hypothesized that actinomycetes may have the ability to produce antibiotics in the extremes of a changing natural environment. This study introduces a novel approach to screening natural antibiotic producers from extreme habitats based on the relationship between organisms' adaptive traits and their metabolic activities. The antibacterial and antifungal properties of 667 actinomycete isolates, obtained from 160 samples of Kazakhstan's diverse extreme habitats, were studied under neutral, saline, and alkaline conditions against MRSA, E. coli, C. albicans, and A. niger. Among these isolates, 113 exhibited antibacterial properties, and 109 demonstrated antifungal properties. Notably, one-fifth of the antagonist isolates could produce active substances solely under extreme growth conditions. Fifty-three antagonistic actinomycetes, possessing these characteristics, have been categorized into groups and warrant further investigation as potential producers of new natural antibiotics. Molecular genetic analysis of the selected isolates revealed a high prevalence of Streptomyces and Nocardiopsis strains. Furthermore, 83.4 % of obtained isolates demonstrated the ability to thrive in all studied habitats-neutral, saline, and alkaline. 96.3 % of actinomycetes isolated from extreme environments exhibited adaptation to neutral conditions, highlighting their inherent versatility. Our findings underscore the nearly complete potential (99.7 %) of isolates to overcome the salinity barrier of 3.5 % NaCl, indicating their capacity to inhabit oceanic environments. We assert that actinomycetes should be perceived as a cohesive, globally adaptive group, capable of migrating between changing conditions or remaining stable within them. These studies lay the groundwork for the development of a new platform for screening natural antibiotics.

A novel marine-derived anti-acute kidney injury agent targeting peroxiredoxin 1 and its nanodelivery strategy based on ADME optimization

Insufficient therapeutic strategies for acute kidney injury (AKI) necessitate precision therapy targeting its pathogenesis. This study reveals the new mechanism of the marine-derived anti-AKI agent, piericidin glycoside S14, targeting peroxiredoxin 1 (PRDX1). By binding to Cys83 of PRDX1 and augmenting its peroxidase activity, S14 alleviates kidney injury efficiently in Prdx1-overexpression (Prdx1-OE) mice. Besides, S14 also increases PRDX1 nuclear translocation and directly activates the Nrf2/HO-1/NQO1 pathway to inhibit ROS production. Due to the limited druggability of S14 with low bioavailability (2.6%) and poor renal distribution, a pH-sensitive kidney-targeting dodecanamine-chitosan nanoparticle system is constructed to load S14 for precise treatment of AKI. l-Serine conjugation to chitosan imparts specificity to kidney injury molecule-1 (Kim-1)-overexpressed cells. The developed S14-nanodrug exhibits higher therapeutic efficiency by improving the in vivo behavior of S14 significantly. By encapsulation with micelles, the AUC0‒t , half-life time, and renal distribution of S14 increase 2.5-, 1.8-, and 3.1-fold, respectively. The main factors contributing to the improved druggability of S14 nanodrugs include the lower metabolic elimination rate and UDP-glycosyltransferase (UGT)-mediated biotransformation. In summary, this study identifies a new therapeutic target for the marine-derived anti-AKI agent while enhancing its ADME properties and druggability through nanotechnology, thereby driving advancements in marine drug development for AKI.

Discovery of Anti-Hypercholesterolemia Agents Targeting LXRα from Marine Microorganism-Derived Natural Products

A strategy integrating in silico molecular docking with LXRα and phenotypic assays was adopted to discover anti-hypercholesterolemia agents in a small library containing 205 marine microorganism-derived natural products, collected by our group in recent years. Two fumitremorgin derivatives, 12R,13S-dihydroxyfumitremorgin C (1) and tryprostatin A (3), were identified as potential LXRα agonists, by real-time qPCR and Western blot (WB) analysis, together with a surface plasmon resonance (SPR) assay. The anti-hypercholesterolemic effects of 1 and 3, together with their mechanisms, were investigated in depth using different cell and mouse models, among which the study of LXRα is of crucial importance. Compound 1 or 3 exhibited the capacity to effectively reverse excessive lipid accumulation in a hepatic steatosis cell model and significantly reduce liver damage and blood cholesterol levels in high cholesterol diet (HCD)-fed wild-type mice, whereas those beneficial effects were completely nullified in HCD-fed LXRα-knockout mice. Furthermore, 1 and 3 outperformed common LXRα agonists by suppressing the expression of sterol regulatory element-binding protein 1 (SREBP1) in HCD-fed mice, mitigating lipotoxicity. Thus, this study highlights the discovery of two marine microorganism-derived anti-hypercholesterolemia agents targeting LXRα.

Taxonomy and anticancer potential of Streptomyces niphimycinicus sp. nov. against nasopharyngeal carcinoma cells

Streptomyces species are ubiquitous, Gram-positive, spore-forming bacteria with the ability to produce various clinically relevant compounds. The strain 4503 T was isolated from mangrove sediments, showing morphological and chemical properties which were consistent with those of members of the genus Streptomyces. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the isolate was primarily identified as members of the genus Streptomyces, sharing more than 99% sequence identity to Streptomyces yatensis DSM 41771 T, S. antimycoticus NBRC 12839 T, and S. melanosporofaciens NBRC 13061 T. Average nucleotide identities (ANI) and digital DNA-DNA hybridization (dDDH) values between strain 4503 T and its close relatives were all below 95-96% and 75% of the novel species threshold, respectively. Results from phylogenetic, genomic, phenotypic, and chemotaxonomic characteristics analyses confirmed that the isolate represented a novel species of the genus Streptomyces, for which the name Streptomyces niphimycinicus sp. nov. 4503 T (= MCCC 1K04557T = JCM 34996 T) is proposed. The bioassay-guided fractionation of the extract of strain 4503 T resulted in the isolation of a known compound niphimycin C, which showed cytotoxic activity against nasopharyngeal carcinoma (NPC) cell lines TW03 and 5-8F with half maximal inhibitory concentration (IC50) values of 12.24 µg/mL and 9.44 µg/mL, respectively. Further experiments revealed that niphimycin C not only exhibited the capacity of anti-proliferation, anti-metastasis, induction of cell cycle arrest, and apoptosis, but was also able to increase the reactive oxygen species (ROS) production and regulate several signaling pathways in NPC cells. KEY POINTS: • Strain 4503 T was classified as a novel species of Streptomyces. • Niphimycin C correlates with the cytotoxic effect of strain 4503 T against NPC cells. • Niphimycin C induces apoptosis, autophagic flux disruption and cell cycle arrest.

Resolving a Natural Product Cold Case: Elucidation of Fusapyrone Structure and Absolute Configuration and Demonstration of Their Fungal Biofilm Disrupting Properties

Fusapyrones are fungal metabolites, which have been reported to have broad-spectrum antibacterial and antifungal properties. Despite the first members of this chemical class being described three decades prior, many aspects of their structures have remained unresolved, thereby constraining efforts to fully understand structure-activity relationships within this metabolite family and impeding the design of streamlined syntheses. Among the main challenges posed by fusapyrones is the incorporation of several single and groups of stereocenters separated by atoms with freely rotating bonds, which have proven unyielding to spectroscopic analyses. In this study, we obtained a series of new (2-5 and 7-9) and previously reported fusapyrones (1 and 6), which were subjected to a combination of spectroscopic, chemical, and computational techniques enabling us to offer proposals for their full structures, as well as provide a pathway to reinterpreting the absolute configurations of other published fusapyrone metabolites. Biological testing of the fusapyrones revealed their abilities to inhibit and disrupt biofilms made by the human fungal pathogen, Candida albicans. These results show that fusapyrones reduce hyphae formation in C. albicans, as well as decrease the surface adherence capabilities of planktonic cells and cells transitioning into early-stage biofilm formation.

Investigation of carbonyl amidation and O-methylation during biosynthesis of the pharmacophore pyridyl of antitumor piericidins

Piericidins are a large family of bacterial α-pyridone antibiotics with antitumor activities such as their anti-renal carcinoma activity exhibited recently in nude mice. The backbones of piericidins are derived from β, δ-diketo carboxylic acids, which are offloaded from a modular polyketide synthase (PKS) and putatively undergo a carbonyl amidation before α-pyridone ring formation. The tailoring modifications to the α-pyridone structure mainly include the verified hydroxylation and O-methylation of the C-4' position and an unidentified C-5' O-methylation. Here, we describe a piericidin producer, terrestrial Streptomyces conglobatus, which contains a piericidin biosynthetic gene cluster in two different loci. Deletion of the amidotransferase gene pieD resulted in the accumulation of two fatty acids that should be degraded from the nascent carboxylic acid released by the PKS, supporting the carbonyl amidation function of PieD during α-pyridone ring formation. Deletion of the O-methyltransferase gene pieB1 led to the production of three piericidin analogues lacking C-5' O-methylation, therefore confirming that PieB1 specifically catalyses the tailoring modification. Moreover, bioactivity analysis of the mutant-derived products provided clues regarding the structure-function relationship for antitumor activity. The work addresses two previously unidentified steps involved in pyridyl pharmacophore formation during piericidin biosynthesis, facilitating the rational bioengineering of the biosynthetic pathway towards valuable antitumor agents.

Unusual Secondary Metabolites from the Mangrove Ecosystems: Structures, Bioactivities, Chemical, and Bio-Syntheses

Mangrove ecosystems are widely distributed in the intertidal zone of tropical and subtropical estuaries or coasts, containing abundant biological communities, for example, mangrove plants and diverse groups of microorganisms, featuring various bioactive secondary metabolites. We surveyed the literature from 2010 to 2022, resulting in a collection of 134 secondary metabolites, and classified them into two major families in terms of the biological sources and 15 subfamilies according to the chemical structures. To highlight the structural diversity and bioactivities of the mangrove ecosystem-associated secondary metabolites, we presented the chemical structures, bioactivities, biosynthesis, and chemical syntheses.

Marine-Derived Piericidin Diglycoside S18 Alleviates Inflammatory Responses in the Aortic Valve via Interaction with Interleukin 37

Calcific aortic valve disease (CAVD) is a valvular disease frequently in the elderly individuals that can lead to the valve dysfunction. Osteoblastic differentiation of human aortic valve interstitial cells (HAVICs) induced by inflammation play a crucial role in CAVD pathophysiological processes. To date, no effective drugs for CAVD have been established, and new agents are urgently needed. Piericidin glycosides, obtained from a marine-derived Streptomyces strain, were revealed to have regulatory effects on mitochondria in previous studies. Here, we discovered that 13-hydroxypiericidin A 10-O-α-D-glucose (1→6)-β-D-glucoside (S18), a specific piericidin diglycoside, suppresses lipopolysaccharide- (LPS) induced inflammatory responses of HAVICs by alleviating mitochondrial stress in an interleukin (IL)-37-dependent manner. Knockdown of IL-37 by siRNA not only exaggerated LPS-induced HAVIC inflammation and mitochondrial stress but also abrogated the anti-inflammatory effect of S18 on HAVICs. Moreover, S18 alleviated aortic valve lesions in IL-37 transgenic mice of CAVD model. Microscale thermophoresis (MST) and docking analysis of five piericidin analogues suggested that diglycosides, but not monoglycosides, exert obvious IL-37-binding activity. These results indicate that S18 directly binds to IL-37 to alleviate inflammatory responses in HAVICs and aortic valve lesions in mice. Piericidin diglycoside S18 is a potential therapeutic agent to prevent the development of CAVD.

Bisabolanoic acid A, a new polychiral sesquiterpene with AChE inhibitory activity from a mangrove-derived fungus Colletotrichum sp

A new polychiral bisabolane sesquiterpene, bisabolanoic acid A (1), was isolated from the mangrove-derived fungus Colletotrichum sp. SCSIO KcB3-2. Its planar structure was identified on the basis of spectroscopic data analysis (HRESIMS, 1D, and 2D NMR), and the absolute configurations of three chiral carbons were determined by experimental and calculated electronic circular dichroism (ECD) and optical rotatory dispersion (ORD), together with Mo₂(OAc)₄-induced ECD methods. Bisabolanoic acid A (1) showed moderate inhibitory activity against acetylcholinesterase (AChE) with IC₅₀ value of 2.2 μM, and the in silico molecular docking was also performed.

Cytotoxic Minor Piericidin Derivatives from the Actinomycete Strain Streptomyces psammoticus SCSIO NS126

The mangrove-sediment-derived actinomycete strain Streptomyces psammoticus SCSIO NS126 was found to have productive piericidin metabolites featuring anti-renal cell carcinoma activities. In this study, in order to explore more diverse piericidin derivatives, and therefore to discover superior anti-tumor lead compounds, the NS126 strain was further fermented at a 300-L scale under optimized fermentation conditions. As a result, eight new minor piericidin derivatives (piericidins L-R (1-7) and 11-demethyl-glucopiericidin A (8)) were obtained, along with glucopiericidin B (9). The new structures including absolute configurations were determined by spectroscopic methods coupled with experimental and calculated electronic circular dichroism. We also proposed plausible biosynthetic pathways for these unusual post-modified piericidins. Compounds 1 and 6 showed selective cytotoxic activities against OS-RC-2 cells, and 2-5 exhibited potent cytotoxicity against HL-60 cells, with IC₅₀ values lower than 0.1 μM. The new piericidin glycoside 8 was cytotoxic against ACHN, HL-60 and K562, with IC₅₀ values of 2.3, 1.3 and 5.5 μM, respectively. The ability to arrest the cell cycle and cell apoptosis effects induced by 1 and 6 in OS-RC-2 cells, 2 in HL-60 cells, and 8 in ACHN cells were then further investigated. This study enriched the structural diversity of piericidin derivatives and confirmed that piericidins deserve further investigations as promising anti-tumor agents.

Cyclopentenone-Containing Tetrahydroquinoline and Geldanamycin Alkaloids from Streptomyces malaysiensis as Potential Anti-Androgens against Prostate Cancer Cells

Malaymycin (1), a new cyclopentenone-containing tetrahydroquinoline alkaloid, and mccrearamycin E (2), a geldanamycin analogue bearing a rare ring-contracted cyclopentenone moiety, and a C₂-symmetric macrodiolide (7) were isolated from Streptomyces malaysiensis SCSIO41397. Their structures including absolute configurations were determined by detailed analyses of NMR and HRMS data and ECD calculations. The occurrence of mccrearamycin E (2) bearing a ring-contracted cyclopentenone is rare in the geldanamycin class. All isolated compounds were evaluated for their cytotoxicities against five cancer cell lines. As a result, compounds 1, 4, 5, and 7 showed cytotoxicity against some or all of the five cancer cell lines with IC₅₀ values ranging from 0.067 to 7.2 μM. In particular, compound 1 inhibited the growth of C42B and H446 cell lines with IC₅₀ values of 67 and 70 nM, respectively. Malaymycin (1) significantly induced cell cycle arrest at the G0/G1 phase in C42B cell lines and caused cell shrinkage and inhibited the expression of the androgen receptor (AR) at both the mRNA and protein levels in a dose-dependent manner. Further examination by qRT-PCR analysis showed that 1 strongly suppressed the expression of AR target genes KLK2 and KLK3 in the C42B and 22RV1 cell lines, which suggested that 1 might be a promising potential lead compound for the development of a treatment for the castration-resistant prostate cancer (CRPC).

Biological insights into the piericidin family of microbial metabolites

Extensively produced by members of the genus Streptomyces, piericidins are a large family of microbial metabolites, which consist of main skeleton of 4-pyridinol with methylated polyketide side chain. Nonetheless, these metabolites show differences in their bioactive potentials against micro-organisms, insects and tumour cells. Due to its close structural similarity with coenzyme Q, piericidins also possess an inhibitory activity against NADH dehydrogenase as well as Photosystem II. This review studied the latest research progress of piericidins, covering the chemical structure and physical properties of newly identified members, bioactivities, biosynthetic pathway with gene clusters and future prospect. With the increasing incidence of drug-resistant human pathogen strains and cancers, this review aimed to provide clues for the development of either new potential antibiotics or anti-tumour agents.

New piericidin derivatives from the marine-derived streptomyces sp. SCSIO 40063 with cytotoxic activity

Two new piericidins A5 (1) and G1 (2), a previously synthesized piericidin G2 (3), and two known piericidins A1 (4) and A2 (5) were isolated from the marine-derived Streptomyces sp. SCSIO 40063. The structures of 1-5 were elucidated by HRESIMS, 1 D, 2 D NMR data analyses and comparisons with the known compounds. Compound 2 showed moderate cytotoxicities against four human tumor cell lines SF-268, MCF-7, HepG2 and A549 with IC₅₀ values between 10.0 and 12.7 μM.

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.

Anticancer Drug Discovery from Microbial Sources: The Unique Mangrove Streptomycetes

Worldwide cancer incidence and mortality have always been a concern to the community. The cancer mortality rate has generally declined over the years; however, there is still an increased mortality rate in poorer countries that receives considerable attention from healthcare professionals. This suggested the importance of the prompt detection, effective treatment, and prevention strategies. The genus Streptomyces has been documented as a prolific producer of biologically active secondary metabolites. Streptomycetes from mangrove environments attract researchers' attention due to their ability to synthesize diverse, interesting bioactive metabolites. The present review highlights research on mangrove-derived streptomycetes and the production of anticancer-related compounds from these microorganisms. Research studies conducted between 2008 and 2019, specifically mentioning the isolation of streptomycetes from mangrove areas and described the successful purification of compound(s) or generation of crude extracts with cytotoxic activity against human cancer cell lines, were compiled in this review. It is anticipated that there will be an increase in prospects for mangrove-derived streptomycetes as one of the natural resources for the isolation of chemotherapeutic agents.