Metabolomics-Guided Discovery of New Dimeric Xanthones from Co-Cultures of Mangrove Endophytic Fungi Phomopsis asparagi DHS-48 and Phomopsis sp. DHS-11.

The co-culture strategy, which mimics natural ecology by constructing an artificial microbial community, is a useful tool for the activation of biosynthetic gene clusters (BGCs) to generate new metabolites, as well as to increase the yield of respective target metabolites. As part of our project aiming at the discovery of structurally novel and biologically active natural products from mangrove endophytic fungi, we selected the co-culture of a strain of Phomopsis asparagi DHS-48 with another Phomopsis genus fungus DHS-11, both endophyted in mangrove Rhizophora mangle considering the impart of the taxonomic criteria and ecological data. The competition interaction of the two strains was investigated through morphology observation and scanning electron microscopy (SEM), and it was found that the mycelia of the DHS-48 and DHS-11 compacted and tangled with each other with an interwoven pattern in the co-culture system. A new approach that integrates HPLC chromatogram, 1HNMR spectroscopy, UPLC-MS-PCA, and molecular networking enabled the targeted isolation of the induced metabolites, including three new dimeric xanthones phomoxanthones L-N (1-3), along with six known analogs (4-9). Their planar structures were elucidated by an analysis of their HRMS, MS/MS, and NMR spectroscopic data and the absolute configurations based on ECD calculations. These metabolites showed broad cytotoxic activity against the cancer cells assessed, of which compounds 7-9 displayed significant cytotoxicity towards human liver cells HepG-2 with IC50 values ranging from 4.83 µM to 12.06 µM. Compounds 1-6 exhibited weak immunosuppressive activity against the proliferation of ConA-induced (T-cell) and LPS-induced (B-cell) murine splenic lymphocytes. Therefore, combining co-cultivation with a metabolomics-guided strategy as a discovery tool will be implemented as a systematic strategy for the quick discovery of target bioactive compounds.

Efomycine U, a new C2-asymmetric elaiophylin derivative from Streptomyces malaysiensis DSM 4137.

Chemical examination of an actinomycete strain Streptomyces malaysiensis DSM 4137 derived from a soil sample derived isolate Streptomyces sp. DSM 3816, yielded a new C2-asymmetric elaiophylin derivative efomycine U (1) and a known analogue halichoblelide D (2). These structures were unambiguously elucidated on the basis of extensive NMR spectroscopic and mass spectrometric analyses. All compounds isolated were subjected to antimicrobial, cytotoxic and immnosuppressive activities evaluation.

Immunosuppressive Cytochalasins from the Mangrove Endophytic Fungus Phomopsis asparagi DHS-48.

Three new cytochalasins, phomoparagins A-C (1-3), along with five known analogs (4-8), were isolated from Phomopsis asparagi DHS-48, a mangrove-derived endophytic fungus. Their structures, including their absolute configurations, were elucidated using a combination of detailed HRESIMS, NMR, and ECD techniques. Notably, 1 possessed an unprecedented 5/6/5/8/5-fused pentacyclic skeleton. These compounds were tested for their inhibitory activity against concanavalin A (ConA)/lipopolysaccharide (LPS)-induced spleen lymphocyte proliferation and calcineurin (CN) enzyme. Several metabolites (2 and 4-6) exhibited fascinating inhibitory activities with a relatively low toxicity. Furthermore, 2 was demonstrated to inhibit ConA-stimulated activation of NFAT1 dephosphorylation and block NFAT1 translocation in vitro, subsequently inhibiting the transcription of interleukin-2 (IL-2). Our results provide evidence that 2 may, at least partially, suppress the activation of spleen lymphocytes via the CN/NFAT signaling pathway, highlighting that it could serve as an effective immunosuppressant that is noncytotoxic and natural.

Novel Isoindolinone-Based Analogs of the Natural Cyclic Peptide Fenestin A: Synthesis and Antitumor Activity.

Small- and medium-sized cyclopeptides have been found to have extensive bioactivities and have drawn much attention from medicinal chemists. In the work described in this paper, various cyclic peptide analogs of Fenestin A were synthesized by intramolecular photoinduced electron-transfer cyclization reactions to study the influence of slight structural changes on the bioactivity of small cyclopeptides. The incorporation of thiazole and rigid isoindolinone fragments was found to improve the bioactivity of the cyclopeptide. Detailed in vitro studies of the apoptosis mechanism, mitochondrial membrane potential, cell cycle, intracellular Ca2+ concentration, and lactate dehydrogenase activity following treatment with a cyclopeptide showed that the cyclopeptide could induce apoptosis of tumor cells and lead to cycle arrest in the G2/M phase. The research also suggested that the photoinduced reaction could be applied to construct cyclic peptides stereoselectively, and the introduction of rigid fragments could enhance the biological activity of cyclopeptide drugs.

Sdy-1 Executes Antitumor Activity in HepG2 and HeLa Cancer Cells by Inhibiting the Wnt/ß-Catenin Signaling Pathway.

Demethylincisterol A3 (Sdy-1), a highly degraded sterol that we previously isolated from Chinese mangrove Rhizophora mucronata endophytic Pestalotiopsis sp. HQD-6, exhibits potent antitumor activity towards a variety of cancer cells. In this study, we further verified that Sdy-1 effectively inhibited the proliferation and migration of human liver (HepG2) and cervical cancer (HeLa) cells in vitro and it can induce cell apoptosis and arrest the cell cycle in the G1-phase. Mechanistically, we demonstrated that Sdy-1 executes its function via inhibition of the Wnt/ß-catenin signaling pathway. Sdy-1 may not inhibit the Wnt signaling pathway through the cascade reaction from upstream to downstream, but directly acts on ß-catenin to reduce its transcription level, thereby reducing the level of ß-catenin protein and further reducing the expression of downstream related proteins. The possible interaction between Sdy-1 and ß-catenin protein was further confirmed by molecular docking studies. In the nude mouse xenograft model, Sdy-1 can also significantly inhibit tumor growth. These results indicated that Sdy-1 is an efficient inhibitor of the Wnt signaling pathway and is a promising antitumor candidate for therapeutic applications.

Near-Infrared Light-Initiated Upconversion Nanoplatform with Tumor Microenvironment Responsiveness for Improved Photodynamic Therapy.

Photodynamic therapy (PDT) is inflowing the mainstream of the cancer treatments, yet the shallow light penetration, thermal damage to normal cells, poor tumor targeting, and skin phototoxicity compromised the PDT efficacy. This paper designed and prepared an upconversion nanoplatform that could effectively convert 808 nm NIR light to red and green light emission, both of which could excite photosensitizers and exert the PDT curative effects. A thin layer of mesoporous silica covering core-shell nanostructure NaGdF4:Yb,Er@NaGdF4:Yb,Nd upconversion nanoparticles was prepared as the carrier to load the photosensitizer pyropheophorbide-a (PPa), which could be excited by green and red light simultaneously and produce high singlet oxygen (1O2) quantum yield (79.1%). Meanwhile, the chemotherapy drug doxorubicin (DOX) was absorbed in the pores of the SiO2 layer to improve the therapeutic effect, and the folic acid-coupled chitosan (Cs-FA) was modified on the surface of the SiO2 layer to obtain the targeting and biocompatible UCNP@SiO2/PPa&DOX@Cs-FA nanoplatform. The physically adsorbed DOX in the pore channel could be released slowly under faintly acidic or GSH stimuli (84% release of DOX after 16 h), suggesting that the nanoplatform was responsive to the tumor microenvironment. In vitro experiments showed that the combined treatment of PDT and DOX was superior to that of PDT alone or DOX chemotherapy alone, implying a synergistic therapeutic effect. The morphological changes and dye staining research of HeLa cells were consistent with the MTT assay. Therefore, this research provided a strategy for the development of an efficient and safe multifunctional cancer treatment nanoplatform integrating low-intensity light excitation, slow release, targeting, photodynamic therapy, and chemotherapy.

Photo-induced synthesis of Axinastatin 3 analogs, the secondary structures and their in vitro antitumor activities.

Cyclic peptides combine several favorable properties such as good binding affinity, target selectivity and low toxicity that make them an attractive modality for drug development. In an effort to identify what conformation could be accounting for the bioactive disparity of natural and synthetic cyclic peptides, some structurally-constrained analogs of cyclopeptide Axinastatin 3 were prepared by photo-induced single electron transfer (SET) reaction. Detailed stereochemistry study was performed by experimental electronic circular dichroism combined with theoretical calculations. Our study suggested that the cyclopeptide 1 with ßI-turn presented stronger antitumor activity comparing with those without such secondary structures. Moreover, a rare 'π helix unit' (compound 3) was realized because of the constrained cyclic structure, which could be considered an important research object for future study of unique helix secondary structures.

Photo-induced synthesis, structure and in vitro bioactivity of a natural cyclic peptide Yunnanin A analog.

A cyclic analog of natural peptide Yunnanin A was synthesized via photoinduced single electron transfer reaction (SET) in the paper. The resulting compound exhibited potent bioactivity (with IC50 values 29.25 µg mL-1 against HepG-2 cell lines and 65.01 µg mL-1 against HeLa cell lines), but almost have no toxicity to normal cells (with IC50 values 203.25 µg mL-1 against L929 cell lines), which may be served as a potential antitumor drug for medical treatment. The spatial structure was examined by experimental electronic circular dichroism (ECD) and quantum chemistry calculations. Moreover, the theoretical study suggested that special intramolecular hydrogen bonds and γ, ß-turn secondary structures may be possible sources affecting cyclic peptide's bioactivity.