Cytotoxic gephyromycins from the Streptomyces sp. SS13I

New Alpiniamide-Type Polyketide with Antibiofilm Activities from the Marine-Derived Streptomyces sp. ZS-A65

Two new alpiniamide-type polyketides, alpiniamides H-I (1-2), in addition to four recognized compounds, were discovered in Streptomyces sp. ZSA65 derived from the marine sediments. The planar structure and absolute configuration of alpiniamides H-I were elucidated using a combination of 1D, 2D NMR, HRESIMS data analysis, Mosher's method and ECD calculations. The antibiofilm and antibacterial activities against P. aeruginosa were evaluated using the microdilution method. Notably, Compound 2 exhibited strong antibiofilm property.

Cytotoxic and Antifungal Staurosporine Derivatives from Marine-Derived Actinomycete Streptomyces sp. ZS-A121

A novel staurosporine derivate, streptomholyrine A (1), along with 6 known compounds were identified from the rice-based solid fermentation of marine-derived Streptomyces sp. ZS-A121. The planar structure and absolute configuration of streptomholyrine A were elucidated using a combination of 1D, 2D NMR, HRESIMS data analysis, chemical transformation, ECD and NMR calculations. Screening of all these compounds revealed their cytotoxic activity against HCT-116 cell lines, with IC50 values ranging from 0.012 to 11.67 μM, except for the known 1H-indole-3-hydroxyacetyl, which showed no inhibition activity. Furthermore, streptomholyrine A, along with two known staurosporine derivatives, k252d and staurosporine, exhibited activities against Candida albicans, with MICs of 12.5, 25.0 and 50.0 μg/ml, respectively.

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.

Characterization of Bioactivities and Biosynthesis of Angucycline/Angucyclinone Derivatives Derived from Gephyromycinifex aptenodytis gen. nov., sp. nov

Strain NJES-13^T is the type strain and currently the only species of the newly established actinobacteria genera Aptenodytes in the family Dermatophilaceae isolated from the gut microbiota of the Antarctic emperor penguin. This strain demonstrated excellent bioflocculation activity with bacteria-derived exopolysaccharides (EPSs). Moreover, it produced bioactive angucycline/angucyclinone derivatives (ADs) and contained one type III polyketide synthase (T3PKS), thus demonstrating great potential to produce novel bioactive compounds. However, the low productivity of the potential new AD metabolite was the main obstacle for its chemical structure elucidation. In this study, to increase the concentration of targeted metabolites, the influence of cellular morphology on AD metabolism in strain NJES-13^T was determined using glass bead-enhanced fermentation. Based on the cellular ultra-structural observation driven by bacterial EPSs, and quantitative analysis of the targeted metabolites, the successful increasing of the productivity of three AD metabolites was achieved. Afterward, a new frigocyclinone analogue was isolated and then identified as 2-hydroxy-frigocyclinone, as well as two other known ADs named 2-hydroxy-tetrangomycin (2-HT) and gephyromycin (GPM). Three AD metabolites were found to demonstrate different bioactivities. Both C-2 hydroxyl substitutes, 2-hydroxy-tetrangomycin and 2-hydroxy-frigocyclinone, exhibited variable inhibitory activities against Staphylococcus aureus, Bacillus subtilis and Candida albicans. Moreover, the newly identified 2-hydroxy-frigocyclinone also showed significant cytotoxicity against three tested human-derived cancerous cell lines (HL-60, Bel-7402 and A549), with all obtained IC₅₀ values less than 10 µM. Based on the genetic analysis after genomic mining, the plausible biogenetic pathway of the three bioactive ADs in strain NJES-13^T was also proposed.

Antimicrobial and Cytotoxic Angucyclic Quinones from Actinomadura miaoliensis

Eight new angucyclic quinones, miaosporones A to H (1-8), along with the previously described metabolites 8-hydroxy-3-methylbenz[a]anthraquinone (9), tetrangulol (10), 5,6-dihydro-1,8-dihydroxy-3-methybenz[a]anthracene-7,12-quinone (11), and SF2315A (12), were isolated from the terrestrial actinomycete Actinomadura miaoliensis TBRC 5172 obtained from sediment collected from the Huai Yang reservoir, Prachuap Khiri Khan Province, Thailand. The relative and absolute configurations of the new compounds were determined from analysis of NMR spectroscopic and X-ray crystallographic data. Miaosporone A exhibited antimalarial activity against Plasmodium falciparum K1 and antibacterial activity against Mycobacterium tuberculosis with respective IC₅₀ values of 2.5 and 2.4 μM and displayed cytotoxic activities against both cancerous (MCF-7 and NCI-H187) and nonmalignant (Vero) cells.

A new indolizinium alkaloid from marine-derived Streptomyces sp. HNA39

A new indolizinium alkaloid, named as cyclizidine J (1), was identified from Gause's liquid fermentation of marine-derived Streptomyces sp. HNA39. Its structure was elucidated by extensive NMR spectroscopic methods, HRESIMS data, and ECD calculations. To our best knowledge, compound 1 was a unique cyclizidine-type alkaloid that contain a chlorine atom substituted at position C-8. Unfortunately, biological evaluation of 1 exhibited no active against PC-3 cancer cell line, BRD4, and ROCK2 protein kinase.

S-Bridged Thioether and Structure-Diversified Angucyclinone Derivatives from the South China Sea-Derived Micromonospora echinospora SCSIO 04089

Angucyclinces belong to the class of aromatic polyketides and display a wide variety of structure diversity and pharmaceutical significance. Herein we report the isolation, structure elucidation, and bioactivity evaluation of structure-diversified angucyclinone derivatives and anthracene from the South China Sea-derived Micromonospora echinospora SCSIO 04089, including a thioether, gephysulfuromycin (1), two new benzo[b]phenanthridines, homophenanthroviridone (2) and homophenanthridonamide (3), a new benzo[b]fluorene, homostealthin D (4), a new naphtho[2,3-b]benzofuran, nenesfuran (5), a new naphthoquinone, WS-5995 D (6) and a new anthracene, nenesophanol (7), together with three known compounds (8-10). Their structures were elucidated by extensive spectroscopic analyses. The structures of 1-3 and 5-8 were confirmed by X-ray crystallographic analyses. Gephysulfuromycin (1) featured a rare single S-bridged 3,12a-epithiotetraphene skeleton. Homophenanthroviridone (2) was found to be cytotoxic to SF-268, MCF-7, and HepG2 cell lines with IC₅₀ values of 5.4 ± 0.4, 6.8 ± 0.3, and 1.4 ± 0.1 μM, respectively. Compound 2 was also active against Gram-positive bacteria with MIC (minimal inhibition concentration) values ranging 2-4 μg mL^-1.

Unusual bridged angucyclinones and potent anticancer compounds from Streptomyces bulli GJA1

Two new unique angucyclinones (1 and 2) with unprecedented ether bridges connecting carbons 5 and 7 were isolated from the cultures of Streptomyces bulli GJA1, an endophyte of Gardenia jasminoides, together with two known ones (3 and 4). The MS²-based molecular networking system facilitated the isolation of compounds with target functionalities. The stereochemistry of 1 was completely established by ROESY and ECD experiments. Compound 3 showed antivirulence activities by inhibiting the peptide toxin (PSMs) production and the biofilm formation of MRSA. Compounds 3 and 4 showed very potent anti-proliferative effects against OV1 and ES2 ovarian cancer cells.

Monacycliones G-K and ent-Gephyromycin A, Angucycline Derivatives from the Marine-Derived Streptomyces sp. HDN15129

Six new angucycline derivatives, named monacycliones G-K (1-5) and ent-gephyromycin A (6), as well as three known ones (7-9) were discovered from the marine sediment-derived actinomycete Streptomyces sp. HDN15129 guided by Global Natural Products Social (GNPS) molecular networking. Structures including absolute configurations were elucidated by extensive NMR, MS, and ECD analyses. Among them, monacyclione G (1) possesses a unique scaffold featuring a xanthone core linked to the aminodeoxysugar ossamine, and monacycliones H-J (2-4) are rare examples of natural angucyclines with an S-methyl group. Monacycliones I and J (3 and 4) showed cytotoxic activity against multiple human cancer cell lines, with IC₅₀ values ranging from 3.5 to 10 μM.

Gephyromycin C, a novel small-molecule inhibitor of heat shock protein Hsp90, induces G2/M cell cycle arrest and apoptosis in PC3 cells in vitro

Gephyromycin C (GC), a natural compound isolated from a marine-derived actinomycete Streptomyces sp. SS13I, which exerts anti-proliferative effect on PC3 cells. However, its underlying mechanism of the anti-cancer effect remains unknown. The results of SRB assays showed that GC inhibited the proliferation of PC3 cells with an IC₅₀ value of 1.79 ± 0.28 μM. GC also induced G2/M cell cycle arrest which was accompanied by declining levels of cyclin proteins. Possible mechanisms were investigated and it was found that GC bound to Hsp90 and caused the degradation of Hsp90 client proteins (AKT, CHK1, P53, CDK4, Raf-b, and Raf-1). The fluorescent polarization assay with FITC-labeled geldanamycin (FITC-GA) demonstrated that GC was able to compete with FITC-GA in binding to wild type Hsp90 with an IC₅₀ of 2.15 μM. Results of a docking study also suggested that GC interacted with the N-terminal domain of Hsp90. Our results showed that GC could bind to Hsp90, which resulted in down-regulation of Hsp90 client proteins and G2/M arrest in PC3 cells. Since the antitumor effects of this kind of angucycline via targeting Hsp90 has not been reported before, our results indicate that GC is a novel inhibitor of Hsp90 from marine resources and worthy of further study.

A new compound from the marine-derived Streptomyces sp. SS13M

As part of our efforts toward search for structurally new and bioactive natural products from marine-derived microorganisms, one new compound (1) was characterized from a marine-derived actinomycete Streptomyces sp. SS13M. The structure of new compound was elucidated by the analysis of HRESIMS, 1D, and 2D NMR spectroscopic data, and the absolute configuration was determined by ECD calculations.[Formula: see text].

Medermycin-Type Naphthoquinones from the Marine-Derived Streptomyces sp. XMA39

Four new medermycin-type naphthoquinones, strepoxepinmycins A-D (1-4), and one known compound, medermycin (5), were identified from Streptomyces sp. XMA39. Their structures were elucidated by analysis of HRESIMS, 1D and 2D NMR spectroscopic data, and ECD calculations. Among these compounds, strepoxepinmycin A (1) represents a rare 5,10-oxepindione ring system typically formed by a Baeyer-Villiger oxidation, and strepoxepinmycin B (2) is an isolation artifact derived from 1. Bioactivity evaluations of these compounds showed that compounds 3 and 4 exhibited cytotoxicity against HCT-116 and PC-3 cancer cell lines and 4 exhibited moderate inhibition of ROCK 2 protein kinase. In addition, all of the new compounds showed antibacterial activity against Escherichia coli and methicillin-resistant Staphylococcus aureus and antifungal activity against Candida albicans.

Cyclizidine-Type Alkaloids from Streptomyces sp. HNA39

Eight new cyclizidine-type alkaloids (1-8) and one known alkaloid (9) were identified from the chemical investigations of a marine-derived actinomycete, Streptomyces sp. HNA39. Among these alkaloids, compounds 3, 7, and 8 contain a chlorine atom, and the known alkaloid, (+)-ent-cyclizidine (9), is now first reported as a natural product. Their structures were elucidated by extensive NMR-spectroscopic analysis and HRESIMS data. The absolute configurations of all of the compounds were established by ECD calculations. Cytotoxicity evaluations of all of the compounds showed that compound 2 exhibited significant activity against the PC3 and HCT116 human-cancer-cell lines with IC₅₀ values of 0.52 ± 0.03 and 8.3 ± 0.1 μM, respectively. Interestingly, compounds 2, 5, 7, and 8 exhibited moderate inhibition against the ROCK2 protein kinase with IC₅₀ values from 7.0 ± 0.8 to 42 ± 3 μM.