Chimeric natural products derived from medermycin and the nature-inspired construction of their polycyclic skeletons

Molecular Networking-Guided Discovery of a New Antitumor Pyranonaphthoquinone from Streptomyces tanashiensis DSM 731: Insights from Single-Molecule Stretching Assays

Guided by molecular networking based on single-molecule stretching assay, an unprecedented pyranonaphthoquinone, methyl kalafunginate (1) and five known compounds 2-6 were isolated from Streptomyces tanashiensis DSM 731. Compound 1 was characterized through a combination of spectroscopic techniques, including 1D and 2D NMR analysis, ECD calculation, and X-ray crystallography. Interestingly, we discovered that compound 1 was spontaneously converted from kalafungin (4) in methanol solution. All isolated compounds, except for compound 3, were assessed for their cytotoxic potential against a panel of five human cancer cell lines: A549, HepG2, BxPC-3, SW620, and C4-2B. Compounds 1, 2, 4, and 5 exhibited remarkable cytotoxicity with IC50 values below 2.382 μM, suggesting their potential as promising anticancer agents. These findings highlight the significance of using a combined approach of single-molecule stretching assays and molecular networking for efficiently discovering novel natural products with potential therapeutic applications.

Discovery of a Chimeric Polyketide Family as Cancer Immunogenic Chemotherapeutic Leads

Discovery of cancer immunogenic chemotherapeutics represents an emerging, highly promising direction for cancer treatment that uses a chemical drug to achieve the efficacy of both chemotherapy and immunotherapy. Herein, we report a high-throughput screening platform and the subsequent discovery of a new class of cancer immunogenic chemotherapeutic leads. Our platform integrates informatics-based activity metabolomics for the rapid identification of microbial natural products with both novel structures and potent activities. Additionally, we demonstrate the use of microcrystal electron diffraction (MicroED) for direct structure elucidation of lead compounds from partially purified mixtures. Using this strategy to screen geographically and phylogenetically diverse microbial metabolites against pseudomyxoma peritonei, a rare and severe cancer, we discovered a new class of leads, aspercyclicins. The aspercyclicins feature an unprecedented tightly packed polycyclic polyketide scaffold that comprises continuous fused, bridged, and spiro rings. The biogenesis of aspercyclicins involves two distinct biosynthetic pathways, leading to formation of chimeric compounds that cannot be predicted by bottom-up approaches mining natural product biosynthetic genes. With comparable potency to some clinically used anticancer drugs, aspercyclicins are active against multiple cancer cell types by inducing immunogenic cell death (ICD), including the release of damage-associated molecular patterns and subsequent phagocytosis of cancer cells. The broad-spectrum ICD-inducing activity of aspercyclicins, combined with their low toxicity to normal cells, represents a new class of potential cancer immunogenic chemotherapeutics and, particularly, the first drug lead for pseudomyxoma peritonei treatment.

NRPS-like Gene LYS2 Contributed to the Biosynthesis of Cyclo(Pro-Val) in a Multistress-Tolerant Aromatic Probiotic, Meyerozyma guilliermondii GXDK6

Cyclo(Pro-Val) is a diketopiperazine (DKP) found widespread in marine microbes and resulting food products. With new bioactivities of cyclo(Pro-Val) being continually discovered, its potential applications in agriculture and food are becoming more evident, highlighting the need for efficient and practical methods to produce these compounds. However, the biosynthesis mechanisms of cyclo(Pro-Val), particularly in probiotics, remain unclear, and the functional identification of nonribosomal peptide synthases (NRPS) is still limited. This study presents a new efficient cyclo(Pro-Val) production system using the marine probiotic Meyerozyma guilliermondii (M. guilliermondii) GXDK6 as a chassis cell. We further characterized an NRPS-like gene, LYS2, which spans 3825 bp and encodes an l-2-amino-hexanedioic acid reductase (Lys2p) consisting of 1274 amino acids. A novel macrocyclization mechanism was revealed involving the peptide N-terminal and C-terminal imines mediated by Lys2p through nucleophilic reactions. Overexpressing LYS2 in GXDK6 resulted in a 45.5% increase in cyclo(Pro-Val) production, while knockout LYS2 completely halted its synthesis. This study revealed a novel metabolic regulatory pathway and biosynthetic mechanism for cyclo(Pro-Val) in marine yeast M. guilliermondii GXDK6. Refactoring the biosynthetic pathway in yeast through LYS2 provides an alternative approach for producing cyclo(Pro-Val).

Amino-Based Probe for Natural Products with Covalent Binding Ability to Lysine and Mechanism of Action of Medermycin

A chemoselective amino-based probe was designed for discovering natural products with covalent binding potential to lysine. Using this reactivity-based technique, a marine-derived Streptomyces strain was identified, which could produce medermycin as the major metabolite. A new compound, mederpyrrole A, derived from medermycin and anthranilic acid through nonenzymatic reaction was isolated. Medermycin can react with primary amines under mild conditions to generate chimeric products possessing a naphthoquinone-pyrrole skeleton. It can also covalently bind to proteins.

Discovery of A Chimeric Polyketide Family as Cancer Immunogenic Chemotherapeutic Leads

Discovery of cancer immunogenic chemotherapeutics represents an emerging, highly promising direction for cancer treatment that uses a chemical drug to achieve the efficacy of both chemotherapy and immunotherapy. Herein we report a high-throughput screening platform and the subsequent discovery of a new class of cancer immunogenic chemotherapeutic leads. Our platform integrates informatics-based activity metabolomics for rapid identification of microbial natural products with both novel structures and potent activities. Additionally, we demonstrate the use of microcrystal electron diffraction (MicroED) for direct structure elucidation of the lead compounds from partially purified mixtures. Using this strategy to screen geographically and phylogenetically diverse microbial metabolites against pseudomyxoma peritonei, a rare and severe cancer, we discovered a new class of leads, aspercyclicins. The aspercyclicins feature an unprecedented tightly packed polycyclic polyketide scaffold that comprises continuous fused, bridged, and spiro rings. The biogenesis of aspercyclicins involves two distinct biosynthetic pathways, leading to formation of chimeric compounds that cannot be predicted by bottom-up approaches mining natural products biosynthetic genes. With comparable potency to some clinically used anticancer drugs, aspercyclicins are active against multiple cancer cell types by inducing immunogenic cell death (ICD), including the release of damage-associated molecular patterns and subsequent phagocytosis of cancer cells. The broad-spectrum ICD-inducing activity of aspercyclicins, combined with their low toxicity to normal cells, represents a new class of potential cancer immunogenic chemotherapeutics and particularly the first drug lead for pseudomyxoma peritonei treatment.

Investigation on taxonomy, secondary metabolites and antibacterial activity of Streptomyces sediminicola sp. nov., a novel marine sediment-derived Actinobacteria

BACKGROUND

Marine actinomycetes, especially Streptomyces, are recognized as excellent producers of diverse and bioactive secondary metabolites on account of the multiplicity of marine habitations and unique ecological conditions, which are yet to be explored in terms of taxonomy, ecology, and functional activity. Isolation, culture and genome analysis of novel species of Streptomyces to explore their potential for discovering bioactive compounds is an important approach in natural product research.

RESULTS

A marine actinobacteria, designated strain SCSIO 75703 T, was isolated, and the potential for bioactive natural product discovery was evaluated based on genome mining, compound detection, and antimicrobial activity assays. The phylogenetic, phenotypic and chemotaxonomic analyses indicate that strain SCSIO 75703 T represents a novel species in genus Streptomyces, for which the name Streptomyces sediminicola sp. nov. is proposed. Genome analysis revealed the presence of 25 secondary metabolite biosynthetic gene clusters. The screening for antibacterial activity reveals the potential to produce bioactive metabolites, highlighting its value for in-depth exploration of chemical constituents. Seven compounds (1-7) were separated from the fractions guided by antibacterial activities, including three indole alkaloids (1-3), three polyketide derivatives (4-6), and 4-(dimethylamino)benzoic acid (7). These primarily antibacterial components were identified as anthracimycin (4), 2-epi-anthracimycin (5) and β-rubromycin (6), presenting strong antibacterial activities against Gram-positive bacteria with the MIC value ranged from 0.125 to 16 μg/mL. Additionally,, monaprenylindole A (1) and 3-cyanomethyl-6-prenylindole (2) displayed moderate inhibitory activities against α-glucosidase with the IC50 values of 83.27 and 86.21 μg/mL, respectively.

CONCLUSION

Strain SCSIO 75703 T was isolated from marine sediment and identified as a novel species within the genus Streptomyces. Based on genomic analysis, compounds isolation and bioactivity studies, seven compounds were identified, with anthracimycin and β-rubromycin showing significant biological activity and promising potential for further applications.

Synthesis of aryl enopyranones directly from glycals and aromatic halides to access 2-deoxy-β-C-aryl glycosides

An efficient synthesis of aryl enopyranones via an oxidative Heck-type coupling reaction between ether protected D/L-glycals and different aryl halides is developed. This one-step method attaches an aryl group at the C-1 position keeping the C-1/C-2 double bond intact via the Saegusa-Ito type oxidation, thus facilitating the synthesis of medicinally important 2-deoxy-β-aryl-C-glycosides after Pd/C reduction.

Fungal Prenyltransferase AnaPT and Its F265 Mutants Catalyze the Dimethylallylation at the Nonaromatic Carbon of Phloretin

Phloretin is widely found in fruit and shows various biological activities. Here, we demonstrate the dimethylallylation, geranylation, and farnesylation, particularly the first dimethylallylation at the nonaromatic carbon of phloretin (1) by the fungal prenyltransferase AnaPT and its mutants. F265 was identified as a key amino acid residue related to dimethylallylation at the nonaromatic carbon of phloretin. Mutants AnaPT_F265D, AnaPT_F265G, AnaPT_F265P, AnaPT_F265C, and AnaPT_F265Y were discovered to generally increase prenylation activity toward 1. AnaPT_F265G catalyzes the O-geranylation selectively at the C-2' hydroxyl group, which involves an intramolecular hydrogen bond with the carbonyl group of 1. Seven products, 1D5, 1D7-1D9, 1G2, 1G4, and 1F2, have not been reported prior to this study. Twelve compounds, 1D3-1D9, 1G1-1G3, and 1F1-1F2, exhibited potential inhibitory effects on α-glucosidase with IC50 values ranging from 11.45 ± 0.87 to 193.80 ± 6.52 μg/mL. Among them, 1G1 with an IC50 value of 11.45 ± 0.87 μg/mL was the most potential α-glucosidase inhibitor, which is about 30 times stronger than the positive control acarbose with an IC50 value of 346.63 ± 15.65 μg/mL.

Structurally Diverse Macrolactams from an Antarctic Streptomyces Species

Twelve new polyenic macrolactams, cyclamenols G-R (1 and 3-13), together with the known analogue cyclamenol A (2), were isolated from Streptomyces sp. OUCMDZ-4348. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations, chemical derivatizations, and Mosher's methods. The sequenced genome of OUCMDZ-4348 revealed the putative biosynthetic gene cluster of cyclamenols. It was proposed that the polycyclic natural products, cyclamenols H-R, might be formed from cyclamenols A and G through nonenzymatic intramolecular cycloadditions and oxidative cyclizations.

The Probiotic Potential and Metabolite Characterization of Bioprotective Bacillus and Streptomyces for Applications in Animal Production

Probiotics are increasingly recognized for their potential in managing bacterial challenges in animal production. This study aimed to evaluate the probiotic potential of Bacillus and Streptomyces strains, specifically their bioprotective ability against Salmonella. In agar inhibition assays, these bacteria supported Salmonella-inhibition zones, ranging from 2.5 ± 0.5 to 6.3 ± 2.0 mm. Analyses of antimicrobial metabolites revealed their capacity to produce compounds with anti-Salmonella properties, except for Bacillus subtilis MLB2. When Salmonella was exposed to lyophilized metabolites, inhibition occurred in both liquid (at concentrations between 250 and 500 g/L) and solid cultures (at 500 g/L). To confirm their probiotic potential, the S. griseus and Bacillus strains underwent evaluations for antimicrobial resistance, bile salt tolerance, auto- and co-aggregation, pH resistance, and their ability to adhere to and inhibit Salmonella in Caco-2 cells. These assessments confirmed their probiotic potential. The probiotic strains were further encapsulated and subjected to simulated swine and poultry digestion. They demonstrated survival potential through the gastrointestinal tract and significantly reduced the Salmonella population. Thus, these strains exhibit considerable promise for producing biotechnological products aimed at controlling Salmonella in animal production. This approach ensures the health and hygiene of farming facilities, mitigates the spread of zoonotic bacteria, and contributes positively to public health.

Expanding the Chemical Diversity of Secondary Metabolites Produced by Two Marine-Derived Enterocin- and Wailupemycin-Producing Streptomyces Strains

To expand the chemical diversity of secondary metabolites produced by two marine-derived enterocin- and wailupemycin-producing Streptomyces strains, OUCMDZ-3434 and OUCMDZ-2599, precursor feeding and solid fermentation strategies were used. Two new compounds, wailupemycins Q (1) and R (2), were isolated from the extracts of liquid and solid fermentation of OUCMDZ-3434. Furthermore, during the fermentation of OUCMDZ-3434, p-fluorobenzoic acid was added as the key biosynthetic precursor, which resulted in the isolation of eight new fluorinated enterocin and wailupemycin derivatives (3-10) and 10 previously reported analogues (11-20). From the solid fermentation extract of OUCMDZ-2599, a new sulfur-containing compound thiotetromycin B (21) and its known analogue thiotetromycin (22) were identified. Moreover, the solid fermentation strategy effectively activated the biosynthesis of siderophores (23-25) of strain OUCMDZ-2599. Compound 3 showed moderate antibacterial activity against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus subsp. aureus with MIC values of 4 μg/mL. Compounds 23-25 were significantly capable of binding Fe(III).