Selective cytotoxicity of epidithiodiketopiperazine DC1149B, produced by marine-derived Trichoderma lixii on the cancer cells adapted to glucose starvation

Structural Optimization of Marine Natural Product Pretrichodermamide B for the Treatment of Colon Cancer by Targeting the JAK/STAT3 Signaling Pathway

Marine natural product (MNP) pretrichodermamide B (Pre B, 9) was identified as a novel STAT3 inhibitor in our previous work, while its metabolic instability hindered its further development. To address this drawback, ligand structure-based drug design was adopted leading to a series of Pre B derivatives. Among them, MNP trichodermamide B (tri B, 24) obtained by skeletal rearrangement exhibited more potent antiproliferative activity with an IC50 value of 0.12 μM against HCT116. Notably, 24 stood out with improved metabolic stability (T1/2 = 31 min) and more favorable oral bioavailability (F = 37.5%). Further studies indicated that 24 blocked JAK/STAT3 signaling in dose- and time-dependent manner. In vivo, 24 suppressed tumor growth (TGI = 65%) at a dose of 20 mg/kg in a HCT116-derived xenograft mouse model. Overall, 24 might be a promising lead compound for colon cancer and is worthy of further investigation.

Chemical Constituents and Anticancer Activities of Marine-Derived Fungus Trichoderma lixii

The fungal genus Trichoderma is a rich source of structurally diverse secondary metabolites with remarkable pharmaceutical properties. The chemical constituents and anticancer activities of the marine-derived fungus Trichoderma lixii have never been investigated. In this study, a bioactivity-guided investigation led to the isolation of eleven compounds, including trichodermamide A (1), trichodermamide B (2), aspergillazine A (3), DC1149B (4), ergosterol peroxide (5), cerebrosides D/C (6/7), 5-hydroxy-2,3-dimethyl-7-methoxychromone (8), nafuredin A (9), and harzianumols E/F (10/11). Their structures were identified by using various spectroscopic techniques and compared to those in the literature. Notably, compounds 2 and 5-11 were reported for the first time from this species. Evaluation of the anticancer activities of all isolated compounds was carried out. Compounds 2, 4, and 9 were the most active antiproliferative compounds against three cancer cell lines (human myeloma KMS-11, colorectal HT-29, and pancreas PANC-1). Intriguingly, compound 4 exhibited anti-austerity activity with an IC50 of 22.43 μM against PANC-1 cancer cells under glucose starvation conditions, while compound 2 did not.

Formation of Bridged Disulfide in Epidithiodioxopiperazines

Epidithiodioxopiperazine (ETP) alkaloids, featuring a 2,5-diketopiperazine core and transannular disulfide bridge, exhibit a broad spectrum of biological activities. However, the structural complexity has prevented efficient chemical synthesis and further clinical research. In the past few decades, many achievements have been made in the biosynthesis of ETPs. Here, we discuss the biosynthetic progress and summarize them as two comprehensible metabolic principles for better understanding the complex pathways of α, α'- and α, β'-disulfide bridged ETPs. Specifically, we systematically outline the catalytic machineries to install α, α'- and α, β'-disulfide by flavin-containing oxygenases. This concept would contribute to the medical and industrial applications of ETPs.

The potential of marine-derived piperazine alkaloids: Sources, structures and bioactivities

Marine-derived piperazine alkaloids (MDPAs) constitute a significant group of natural compounds known for their diverse structures and biological activities. Over the past five decades, substantial efforts have been devoted to isolating these alkaloids from marine sources and characterizing their chemical and bioactive profiles. To date, a total of 922 marine-derived piperazine alkaloids have been reported from various marine organisms. These compounds demonstrate a wide range of pharmacological properties, including cytotoxicity, antibacterial, antifungal, antiviral, and various other activities. Notably, among these activities, cytotoxicity emerges as the most prominent characteristic of marine-derived piperazine alkaloids. This review also summarizes the structure-activity relationship (SAR) studies associated with the cytotoxicity of these compounds. In summary, our objective is to provide an overview of the research progress concerning marine-derived piperazine alkaloids, with the aim of fostering their continued development and utilization.

Natural products with 1,2-oxazine scaffold: occurrence, chemical diversity, bioactivity, synthesis, and biosynthesis

Covering: up to the end of July, 20231,2-Oxazine is a heterocyclic scaffold rarely found in natural products and is characterized by a directly connected N-O bond in a six-membered ring. Since the discovery of geneserine, the first 1,2-oxazine-containing natural product (1,2-oxazine NP) being isolated from Calabar bean (Physostigma venenosum) in 1925, a total of 76 naturally occurring 1,2-oxazine NPs have been isolated and identified from various sources, which have attracted the attention of researchers in the field of natural product chemistry, organic synthesis, biosynthesis, and pharmacology. This review summarizes the chemical family of 1,2-oxazine NPs, focusing on their source organisms, structural diversities, chemical synthesis, and biosynthesis.

Mechanistic Investigation of the Degradation Pathways of α-β/α-α Bridged Epipolythiodioxopiperazines (ETPs)

Epipolythiodioxopiperazines (ETPs) make up a class of biologically active fungal metabolites with a transannular disulfide bridge. In this work, we used DFT calculations to examine in detail the degradation (desulfurization) pathways of α-β/α-α bridged ETPs. The chemical stability of ETPs is influenced by the type of sulfur bridge, the structural features, and the storage conditions. Our results suggest appropriate protection of the phenolic OH of ETPs would improve various pharmaceutically relevant properties, including bioavailability.

Identification of marine natural product Pretrichodermamide B as a STAT3 inhibitor for efficient anticancer therapy

The Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) regulates the expression of various critical mediators of cancer and is considered as one of the central communication nodes in cell growth and survival. Marine natural products (MNP) represent great resources for discovery of bioactive lead compounds, especially anti-cancer agents. Through the medium-throughput screening of our in-house MNP library, Pretrichodermamide B, an epidithiodiketopiperazine, was identified as a JAK/STAT3 signaling inhibitor. Further studies identified that Pretrichodermamide B directly binds to STAT3, preventing phosphorylation and thus inhibiting JAK/STAT3 signaling. Moreover, it suppressed cancer cell growth, in vitro, at low micromolar concentrations and demonstrated efficacy in vivo by decreasing tumor growth in a xenograft mouse model. In addition, it was shown that Pretrichodermamide B was able to induce cell cycle arrest and promote cell apoptosis. This study demonstrated that Pretrichodermamide B is a novel STAT3 inhibitor, which should be considered for further exploration as a promising anti-cancer therapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00162-x.

Deoxygenative Arylation of 5,6-Dihydro-4H-1,2-oxazine-N-oxides with Arynes

Six-membered cyclic nitronates (5,6-dihydro-4H-1,2-oxazine-N-oxides) react with Kobayashi's aryne precursors producing 3-(2-hydroxyaryl)-substituted 1,2-oxazines via deoxygenative C-H arylation. The process involves a hitherto unknown 1,3-dipolar cycloaddition of nitronate to the aryne to give an unusual tricyclic nitroso acetal, in which the N-O bond of the isoxazoline ring is selectively cleaved upon the action of a base (CsF) or an acid (TFA). The transient cycloadducts were isolated and characterized in some cases. The synthetic potential of the obtained 3-(2-hydroxyaryl)-substituted 1,2-oxazines was demonstrated by their stereoselective reduction to 1,4-amino alcohols and reductive 1,2-oxazine ring contraction to tetrahydrofuran derivatives.

Methylglyoxal induces ambience for cancer promotion in HepG2 cells via Warburg effect and promotes glycation

Methylglyoxal (MGO) is a toxic, highly reactive metabolite derived mainly from glucose and amino acids degradation. MGO is also one of the prime precursors for advanced glycation end products formation. The present research was performed to check whether MGO has any role in the promotion of cancer in HepG2 cells. For this, cells were incubated with MGO (50 µM) for 24 h and subjected to various analyses. Aminoguanidine (200 µM) was positive control. The various biochemical and protein expression studies, relevant to the MGO detoxification system, oxidative stress, and glycolysis were performed. MGO caused the reduction of expression of GLO 1 (27%) and GLO 2 (11%) causing weakening of the innate detoxification system. This is followed by an increase of RAGE (95%), AGEs or methylglyoxal adducts. We also observed hypoxia via estimation of oxygen consumption rate and surplus reactive oxygen species (ROS) (24%). To investigate the off-target effect of MGO we checked its effect on glucose transport, and its associated proteins. Glucose uptake was found to increase (15%) significantly with overexpression of GLUT 1 (35%). We also found a significant increase of glycolytic enzymes such as hexokinase II, phosphofructokinase 1, and lactate dehydrogenase along with lactate production. Observation of surplus ROS and enhanced glycolysis led us to check the expression of HIF 1α which is their downstream signaling pathway. Interestingly HIF 1α was found to increase significantly (35%). It is known that enhanced glycolysis and oxidative stress are catalysts for the overexpression of HIF 1α which in turn creates an ambience for the promotion of cancer. Aminoguanidine was able to prevent the adverse effect of MGO partially. This is the first study to show the potential of MGO for the promotion of cancer in the non-tumorigenic HepG2 cells via the Warburg effect and glycation.

Biodiversity and Enzyme Activity of Marine Fungi with 28 New Records from the Tropical Coastal Ecosystems in Vietnam

The coastal marine ecosystems of Vietnam are one of the global biodiversity hotspots, but the biodiversity of marine fungi is not well known. To fill this major gap of knowledge, we assessed the genetic diversity (ITS sequence) of 75 fungal strains isolated from 11 surface coastal marine and deeper waters in Nha Trang Bay and Van Phong Bay using a culture-dependent approach and 5 OTUs (Operational Taxonomic Units) of fungi in three representative sampling sites using next-generation sequencing. The results from both approaches shared similar fungal taxonomy to the most abundant phylum (Ascomycota), genera (Candida and Aspergillus) and species (Candida blankii) but were different at less common taxa. Culturable fungal strains in this study belong to 3 phyla, 5 subdivisions, 7 classes, 12 orders, 17 families, 22 genera and at least 40 species, of which 29 species have been identified and several species are likely novel. Among identified species, 12 and 28 are new records in global and Vietnamese marine areas, respectively. The analysis of enzyme activity and the checklist of trophic mode and guild assignment provided valuable additional biological information and suggested the ecological function of planktonic fungi in the marine food web. This is the largest dataset of marine fungal biodiversity on morphology, phylogeny and enzyme activity in the tropical coastal ecosystems of Vietnam and Southeast Asia. Biogeographic aspects, ecological factors and human impact may structure mycoplankton communities in such aquatic habitats.

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.

Asymmetric Formal Synthesis of Trichodermamides B and C

An asymmetric formal synthesis of trichodermamides B and C was achieved in 15 steps based on a tyrosine ester chiral-pool approach. Key features of this synthesis include stereoselective construction of a cis-1,2-oxazadecaline core by an acid-mediated tandem deprotection–intramolecular oxy-Michael reaction, oxime ether formation via an N-bromination–elimination sequence, and diene construction by a palladium-catalyzed demonomethylcarbonation.

Development of Marine-Derived Compounds for Cancer Therapy

Cancer has always been a threat to human health with its high morbidity and mortality rates. Traditional therapy, including surgery, chemotherapy and radiotherapy, plays a key role in cancer treatment. However, it is not able to prevent tumor recurrence, drug resistance and treatment side effects, which makes it a very attractive challenge to search for new effective and specific anticancer drugs. Nature is a valuable source of multiple pharmaceuticals, and most of the anticancer drugs are natural products or derived from them. Marine-derived compounds, such as nucleotides, proteins, peptides and amides, have also shed light on cancer therapy, and they are receiving a fast-growing interest due to their bioactive properties. Their mechanisms contain anti-angiogenic, anti-proliferative and anti-metastasis activities; cell cycle arrest; and induction of apoptosis. This review provides an overview on the development of marine-derived compounds with anticancer properties, both their applications and mechanisms, and discovered technologies.

Selective cytotoxicity of marine-derived fungal metabolite (3S,6S)-3,6-dibenzylpiperazine-2,5-dione against cancer cells adapted to nutrient starvation

The cancer cells that are adapted to the hypoxic and nutrient-starved conditions of the tumor microenvironment have become a key target for anticancer therapies. In the course of search for selective cytotoxic substances against cancer cells adapted to nutrient starvation, (3S,6S)-3,6-dibenzylpiperazine-2,5-dione (1) was isolated from culture extract of marine-derived Paecilomyces formous 17D47-2. Compound 1 showed cytotoxic activity on the human pancreatic carcinoma PANC-1 cells adapted to glucose-starved conditions with IC50 value of 28 µM, whereas no effect was observed against PANC-1 cells under general culture conditions up to 1000 µM. Further studies on the mechanism of the selective cytotoxicity of 1 against the glucose-starved PANC-1 cells suggest that it may function via uncoupling of mitochondrial oxidative phosphorylation.

Mitochondrial Targeting in an Anti-Austerity Approach Involving Bioactive Metabolites Isolated from the Marine-Derived Fungus Aspergillus sp

The tumor microenvironment is a nutrient-deficient region that alters the cancer cell phenotype to aggravate cancer pathology. The ability of cancer cells to tolerate nutrient starvation is referred to as austerity. Compounds that preferentially target cancer cells growing under nutrient-deficient conditions are being employed in anti-austerity approaches in anticancer drug discovery. Therefore, in this study, we investigated physcion (1) and 2-(2',3-epoxy-1',3',5'-heptatrienyl)-6-hydroxy-5-(3-methyl-2-butenyl) benzaldehyde (2) obtained from a culture extract of the marine-derived fungus Aspergillus species (sp.), which were isolated from an unidentified marine sponge, as anti-austerity agents. The chemical structures of 1 and 2 were determined via spectroscopic analysis and comparison with authentic spectral data. Compounds 1 and 2 exhibited selective cytotoxicity against human pancreatic carcinoma PANC-1 cells cultured under glucose-deficient conditions, with IC₅₀ values of 6.0 and 1.7 µM, respectively. Compound 2 showed higher selective growth-inhibitory activity (505-fold higher) under glucose-deficient conditions than under general culture conditions. Further analysis of the mechanism underlying the anti-austerity activity of compounds 1 and 2 against glucose-starved PANC-1 cells suggested that they inhibited the mitochondrial electron transport chain.

Cytotoxic Activity of Abietane-Type Diterpenes Isolated From Taxodium distichum Against Cancer Cells Adapted to Nutrient-Starved Conditions

The mechanisms of cancer cell adaptation to tumor microenvironmental conditions, such as hypoxia and nutrient starvation, are currently receiving much attention as possible therapeutic targets. In an attempt to identify selectively cytotoxic substances against cancer cells adapted to nutrient starvation, 4 abietane-type diterpenes, sugiol (1), 6-α-hydroxysugiol (2), cryptojaponol (3), and 6-hydroxy-5,6-dehydrosugiol (4), were isolated from the bark of Taxodium distichum L. Rich var. distichum (bald cypress). Compounds 1, 2, and 4 showed potent cytotoxic activity against PANC-1 cells adapted to nutrient-starved conditions with half-maximal effective concentration (EC50) values of 6.4-9.2 µM, whereas the EC50 values of these compounds against PANC-1 cells under general culture conditions were more than 100 µM. Alternatively, compound 3, which we report for the first time in the genus Taxodium, showed moderate cytotoxicity against PANC-1 cells under nutrient-starved conditions with an EC50 of 37.9 µM. The selective index (S.I.), which compared the activity under nutrient-starved conditions with that under general culture conditions, was low (7.9). Further investigation revealed that the selective cytotoxic activity of compound 2 might be affecting the mitochondria.