Ascidian Toxins with Potential for Drug Development

Prospects of marine-derived compounds as potential therapeutic agents for glioma

CONTEXT

Glioma, the most common primary malignant brain tumour, is a grave health concern associated with high morbidity and mortality. Current treatments, while effective to some extent, are often hindered by factors such as the blood-brain barrier and tumour microenvironment. This underscores the pressing need for exploring new pharmacologically active anti-glioma compounds.

METHODS

This review synthesizes information from major databases, including Chemical Abstracts, Medicinal and Aromatic Plants Abstracts, ScienceDirect, SciFinder, Google Scholar, Scopus, PubMed, Springer Link and relevant books. Publications were selected without date restrictions, using terms such as 'Hymenocrater spp.,' 'phytochemical,' 'pharmacological,' 'extract,' 'essential oil' and 'traditional uses.' General web searches using Google and Yahoo were also performed. Articles related to agriculture, ecology, synthetic work or published in languages other than English or Chinese were excluded.

RESULTS

The marine environment has been identified as a rich source of diverse natural products with potent antitumour properties.

CONCLUSIONS

This paper not only provides a comprehensive review of marine-derived compounds but also unveils their potential in treating glioblastoma multiforme (GBM) based on functional classifications. It encapsulates the latest research progress on the regulatory biological functions and mechanisms of these marine substances in GBM, offering invaluable insights for the development of new glioma treatments.

An organic extract from ascidian Ciona robusta induces cytotoxic autophagy in human malignant cell lines

The last decades have seen an increase in the isolation and characterization of anticancer compounds derived from marine organisms, especially invertebrates, and their use in clinical trials. In this regard, ascidians, which are included in the subphylum Tunicata, represent successful examples with two drugs, Aplidine© and Yondelis© that reached the market as orphan drugs against several malignancies. Here, we report that an organic extract prepared from homogenized tissues of the Mediterranean ascidian Ciona robusta inhibited cell proliferation in HT-29, HepG2, and U2OS human cells with the former being the most sensitive to the extract (EC50 = 250 μg/mL). We demonstrated that the ascidian organic extract was not cytotoxic on HT-29 cells that were induced to differentiate with sodium butyrate, suggesting a preference for the mixture for the malignant phenotype. Finally, we report that cell death induced by the organic extract was mediated by the activation of a process of cytotoxic autophagy as a result of the increased expression of the LC3-II marker and number of autophagic vacuoles, which almost doubled in the treated HT-29 cells. In summary, although the detailed chemical composition of the Ciona robusta extract is still undetermined, our data suggest the presence of bioactive compounds possessing anticancer activity.

Trabectedin and Lurbinectedin Modulate the Interplay between Cells in the Tumour Microenvironment-Progresses in Their Use in Combined Cancer Therapy

Trabectedin (TRB) and Lurbinectedin (LUR) are alkaloid compounds originally isolated from Ecteinascidia turbinata with proven antitumoral activity. Both molecules are structural analogues that differ on the tetrahydroisoquinoline moiety of the C subunit in TRB, which is replaced by a tetrahydro-β-carboline in LUR. TRB is indicated for patients with relapsed ovarian cancer in combination with pegylated liposomal doxorubicin, as well as for advanced soft tissue sarcoma in adults in monotherapy. LUR was approved by the FDA in 2020 to treat metastatic small cell lung cancer. Herein, we systematically summarise the origin and structure of TRB and LUR, as well as the molecular mechanisms that they trigger to induce cell death in tumoral cells and supporting stroma cells of the tumoral microenvironment, and how these compounds regulate immune cell function and fate. Finally, the novel therapeutic venues that are currently under exploration, in combination with a plethora of different immunotherapeutic strategies or specific molecular-targeted inhibitors, are reviewed, with particular emphasis on the usage of immune checkpoint inhibitors, or other bioactive molecules that have shown synergistic effects in terms of tumour regression and ablation. These approaches intend to tackle the complexity of managing cancer patients in the context of precision medicine and the application of tailor-made strategies aiming at the reduction of undesired side effects.

Emerging pharmaceutical therapies of Ascidian-derived natural products and derivatives

In a growing multidrug-resistant environment, the identification of potential new drug candidates with an acceptable safety profile is a substantial crux in pharmaceutical discovery. This review discusses several aspects and properties of approved marine natural products derived from ascidian sources (phylum Chordata, subphylum Tunicata) and/or their deduced analogues including their biosynthetic origin, (bio)chemical preclinical assessments and known efficacy-safety profiles, clinical status in trials, but also translational developments, opportunities and final conclusions. The review also describes the preclinical assessments of a large number of other ascidian compounds that have not been involved in clinical trials yet. Finally, the emerging research on the connectivity of the ascidian hosts and their independent or obligate symbiotic guests is discussed. The review covers the latest information on the topic of ascidian-derived marine natural products over the last two decades including 2022, with the majority of publications published in the last decade.

Depsipeptides Targeting Tumor Cells: Milestones from In Vitro to Clinical Trials

Cancer is currently considered one of the most threatening diseases worldwide. Diet could be one of the factors that can be enhanced to comprehensively address a cancer patient's condition. Unfortunately, most molecules capable of targeting cancer cells are found in uncommon food sources. Among them, depsipeptides have emerged as one of the most reliable choices for cancer treatment. These cyclic amino acid oligomers, with one or more subunits replaced by a hydroxylated carboxylic acid resulting in one lactone bond in a core ring, have broadly proven their cancer-targeting efficacy, some even reaching clinical trials and being commercialized as "anticancer" drugs. This review aimed to describe these depsipeptides, their reported amino acid sequences, determined structure, and the specific mechanism by which they target tumor cells including apoptosis, oncosis, and elastase inhibition, among others. Furthermore, we have delved into state-of-the-art in vivo and clinical trials, current methods for purification and synthesis, and the recognized disadvantages of these molecules. The information collated in this review can help researchers decide whether these molecules should be incorporated into functional foods in the near future.

Antimycobacterial activity and molecular docking of methanolic extracts and compounds of marine fungi from Saldanha and False Bays, South Africa

The number and diversity of drugs in the tuberculosis (TB) drug development process has increased over the years, yet the attrition rate remains very high, signaling the need for continued research in drug discovery. In this study, crude secondary metabolites from marine fungi associated with ascidians collected from Saldanha and False Bays (South Africa) were investigated for antimycobacterial activity. Isolation of fungi was performed by sectioning thin inner-tissues of ascidians and spreading them over potato dextrose agar (PDA). Solid state fermentation of fungal isolates on PDA was then performed for 28 days to allow production of secondary metabolites. Afterwards, PDA cultures were dried and solid-liquid extraction using methanol was performed to extract fungal metabolites. Profiling of metabolites was performed using untargeted liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS). The broth microdilution method was used to determine antimycobacterial activity against Mycobacterium smegmatis mc²155 and Mycobacterium tuberculosis H37Rv, while in silico flexible docking was performed on selected target proteins from M. tuberculosis. A total of 16 ascidians were sampled and 46 fungi were isolated. Only 32 fungal isolates were sequenced, and their sequences submitted to GenBank to obtain accession numbers. Metabolite profiling of 6 selected fungal extracts resulted in the identification of 65 metabolites. The most interesting extract was that of Clonostachys rogersoniana MGK33 which inhibited Mycobacterium smegmatis mc²155 and Mycobacterium tuberculosis H37Rv growth with minimum inhibitory concentrations (MICs) of 0.125 and 0.2 mg/mL, respectively. These results were in accordance with those from in silico molecular docking studies which showed that bionectin F produced by C. rogersoniana MGK33 is a potential inhibitor of M. tuberculosis β-ketoacyl-acyl carrier protein reductase (MabA, PDB ID = 1UZN), with the docking score observed as -11.17 kcal/mol. These findings provided evidence to conclude that metabolites from marine-derived fungi are potential sources of bioactive metabolites with antimycobacterial activity. Even though in silico studies showed that bionectin F is a potent inhibitor of an essential enzyme, MabA, the results should be validated by performing purification of bionectin F from C. rogersoniana MGK33 and in vitro assays against MabA and whole cells (M. tuberculosis).

Exploring Newer Biosynthetic Gene Clusters in Marine Microbial Prospecting

Marine microbes genetically evolved to survive varying salinity, temperature, pH, and other stress factors by producing different bioactive metabolites. These microbial secondary metabolites (SMs) are novel, have high potential, and could be used as lead molecule. Genome sequencing of microbes revealed that they have the capability to produce numerous novel bioactive metabolites than observed under standard in vitro culture conditions. Microbial genome has specific regions responsible for SM assembly, termed biosynthetic gene clusters (BGCs), possessing all the necessary genes to encode different enzymes required to generate SM. In order to augment the microbial chemo diversity and to activate these gene clusters, various tools and techniques are developed. Metagenomics with functional gene expression studies aids in classifying novel peptides and enzymes and also in understanding the biosynthetic pathways. Genome shuffling is a high-throughput screening approach to improve the development of SMs by incorporating genomic recombination. Transcriptionally silent or lower level BGCs can be triggered by artificially knocking promoter of target BGC. Additionally, bioinformatic tools like antiSMASH, ClustScan, NAPDOS, and ClusterFinder are effective in identifying BGCs of existing class for annotation in genomes. This review summarizes the significance of BGCs and the different approaches for detecting and elucidating BGCs from marine microbes.

Cytotoxic and antimicrobial activities of two new sesquiterpenoids from red sea brittle star Ophiocoma dentata

Bioactive compounds were extracted from a locally available brittle star; Ophiocoma dentata, collected from the Red Sea, Egypt. Two new sesquiterpenoids; 8, 11-epoxy-9(15)-himachaladiene-4-ol (O8-ophiocomane) and, 11-epoxy-9(15)-himachaladiene-4-ol (O7-ophiocomane) were isolated and characterized using appropriate techniques. Structure elucidation was estimated via 1D NMR, 2D NMR, FT-IR and mass spectroscopy analyses. The isolated compounds were tested for cytotoxic, antibacterial and antifungal activities. Pure compounds showed a dose dependent reduction in MCF-7 cells viability with LC50 of 103.5 and 59.5 μg/ml for compounds 1 and 2 respectively compared to the chemotherapeutic drug cisplatin (47.4 µg/ml). In vivo experiments showed that O. dentate extract significantly reduced tumor progression and improved hematological parameters and liver functions of tumor-bearing mice when administered either before or after tumor cells' injection. The most remarkable antimicrobial effects of O. dentate crude extract were against Staphylococcus aureus, Vibrio damsela and Pseudomonas aeruginosa while the pure compounds showed activity against P. aeruginosa alone. Neither the crude extract nor the pure compounds have shown activity against Aeromonas hydrophila. These results indicates that O. dentata extract and newly isolated compounds have shown a promising cytotoxic, antiproliferative and antimicrobial activities that might be useful for pharmaceutical applications.

Bioactive Compounds with Antiglioma Activity from Marine Species

The search for new chemical compounds with antitumor pharmacological activity is a necessary process for creating more effective drugs for each specific malignancy type. This review presents the outcomes of screening studies of natural compounds with high anti-glioma activity. Despite significant advances in cancer therapy, there are still some tumors currently considered completely incurable including brain gliomas. This review covers the main problems of the glioma chemotherapy including drug resistance, side effects of common anti-glioma drugs, and genetic diversity of brain tumors. The main emphasis is made on the characterization of natural compounds isolated from marine organisms because taxonomic diversity of organisms in seawaters significantly exceeds that of terrestrial species. Thus, we should expect greater chemical diversity of marine compounds and greater likelihood of finding effective molecules with antiglioma activity. The review covers at least 15 classes of organic compounds with their chemical formulas provided as well as semi-inhibitory concentrations, mechanisms of action, and pharmacokinetic profiles. In conclusion, the analysis of the taxonomic diversity of marine species containing bioactives with antiglioma activity is performed noting cytotoxicity indicators and to the tumor cells in comparison with similar indicators of antitumor agents approved for clinical use as antiglioblastoma chemotherapeutics.

Marine Natural Products from Tunicates and Their Associated Microbes

Marine tunicates are identified as a potential source of marine natural products (MNPs), demonstrating a wide range of biological properties, like antimicrobial and anticancer activities. The symbiotic relationship between tunicates and specific microbial groups has revealed the acquisition of microbial compounds by tunicates for defensive purpose. For instance, yellow pigmented compounds, "tambjamines", produced by the tunicate, Sigillina signifera (Sluiter, 1909), primarily originated from their bacterial symbionts, which are involved in their chemical defense function, indicating the ecological role of symbiotic microbial association with tunicates. This review has garnered comprehensive literature on MNPs produced by tunicates and their symbiotic microbionts. Various sections covered in this review include tunicates' ecological functions, biological activities, such as antimicrobial, antitumor, and anticancer activities, metabolic origins, utilization of invasive tunicates, and research gaps. Apart from the literature content, 20 different chemical databases were explored to identify tunicates-derived MNPs. In addition, the management and exploitation of tunicate resources in the global oceans are detailed for their ecological and biotechnological implications.

An Analysis of Biosynthesis Gene Clusters and Bioactivity of Marine Bacterial Symbionts

Symbiotic marine bacteria have a pivotal role in drug discovery due to the synthesis of diverse biologically potential compounds. The marine bacterial phyla proteobacteria, actinobacteria and firmicutes are commonly associated with marine macro organisms and frequently reported as dominant bioactive compound producers. They can produce biologically active compounds that possess antimicrobial, antiviral, antitumor, antibiofilm and antifouling properties. Synthesis of these bioactive compounds is controlled by a set of genes of their genomes that is known as biosynthesis gene clusters (BGCs). The development in the field of biotechnology and bioinformatics has uncovered the potential BGCs of the bacterial genome and its functions. Now-a-days researchers have focused their attention on the identification of potential BGCs for the discovery of novel bioactive compounds using advanced technology. This review highlights the marine bacterial symbionts and their BGCs which are responsible for the synthesis of bioactive compounds.

Symbioses of Cyanobacteria in Marine Environments: Ecological Insights and Biotechnological Perspectives

Cyanobacteria are a diversified phylum of nitrogen-fixing, photo-oxygenic bacteria able to colonize a wide array of environments. In addition to their fundamental role as diazotrophs, they produce a plethora of bioactive molecules, often as secondary metabolites, exhibiting various biological and ecological functions to be further investigated. Among all the identified species, cyanobacteria are capable to embrace symbiotic relationships in marine environments with organisms such as protozoans, macroalgae, seagrasses, and sponges, up to ascidians and other invertebrates. These symbioses have been demonstrated to dramatically change the cyanobacteria physiology, inducing the production of usually unexpressed bioactive molecules. Indeed, metabolic changes in cyanobacteria engaged in a symbiotic relationship are triggered by an exchange of infochemicals and activate silenced pathways. Drug discovery studies demonstrated that those molecules have interesting biotechnological perspectives. In this review, we explore the cyanobacterial symbioses in marine environments, considering them not only as diazotrophs but taking into consideration exchanges of infochemicals as well and emphasizing both the chemical ecology of relationship and the candidate biotechnological value for pharmaceutical and nutraceutical applications.

Tryptophan derived natural marine alkaloids and synthetic derivatives as promising antimicrobial agents

Antimicrobial resistance has become a major threat to public health worldwide, as pathogenic microorganisms are finding ways to evade all known antimicrobials. Therefore, the demand for new and effective antimicrobial agents is also increasing. Natural products have always played an important role in drug discovery, either by themselves or as inspiration for synthetic compounds. The marine environment is a rich source of bioactive metabolites, and among them, tryptophan-derived alkaloids stand out for their abundance and by displaying a variety of biological activities, with antimicrobial properties being among the most significant. This review aims to reveal the potential of marine alkaloids derived from tryptophan as antimicrobial agents. Relevant examples of these compounds and their synthetic analogues reported in the last decades are presented and discussed in detail, with their mechanism of action and synthetic approaches whenever relevant. Several tryptophan-derived marine alkaloids have shown potent and promising antimicrobial activities, whether against bacteria, fungi, or virus. Synthetic approaches to many of the compounds have been developed and recent methodologies are proving to be efficient. Even though most of the studies regarding the antimicrobial activity are still preliminary, this class of compounds has proven to be worth of further investigation and may provide useful lead compounds for the development of antimicrobial agents. Overall, marine alkaloids derived from tryptophan are revealed as a valuable class of antimicrobials and molecular modifications in order to reduce the toxicity of these compounds and additional studies regarding their mechanism of action are interesting topics to explore in the future.

Chronic exposure to the gibberellin derivative GA-13315 sensitizes breast cancer MCF-7 cells but not colon cancer HCT116 cells to irinotecan

13-Chlorine-3,15-dioxy-gibberellic acid methyl ester (GA-13315) is a gibberellin derivative that exhibits selective cytotoxicity to multidrug resistant MCF-7/ADR cells and reverses drug resistance when administered at subtoxic doses in combination with chemotherapy drugs. The present study aimed to investigate the impact of chronic GA-13315 exposure on the chemosensitivity of MCF-7 and HCT116 cell lines. Cells were administered a subtoxic dose of 1 µM GA-13315 for 12 weeks and the sensitivity of the cells to GA-13315, irinotecan and cisplatin, was assessed. The Cell Counting Kit-8 assay results demonstrated that the chronic exposure did not induce resistance to GA-13315, in either MCF-7 or HCT116 cells. Notably, MCF-7 cells were sensitized to irinotecan following exposure to GA-13315; however, HCT116 cells were not. The sensitizing effect of GA-13315 was associated with the alterations of topoisomerase 1 (Top1) protein expression, tyrosyl DNA phosphodiesterase 1 and checkpoint kinase 1. Further analysis indicated that GA-13315 caused DNA fragmentation; however, DNA damage was not mediated by a Top1-dependent molecular mechanism, as GA-13315 was revealed not to be a Top1 poison, despite inhibiting the catalytic activity of Top1. Taken together, the results of the present study indicated that GA-13315 may be used for sensitizing MCF-7 cells to irinotecan, as the chronic exposure of GA-13315 to MCF-7 cells still showed sensitizing effects to irinotecan.

Seasonal dynamics and starvation impact on the gut microbiome of urochordate ascidian Halocynthia roretzi

Background

Gut microbiota plays important roles in host animal metabolism, homeostasis and environmental adaptation. However, the interplay between the gut microbiome and urochordate ascidian, the most closet relative of vertebrate, remains less explored. In this study, we characterized the gut microbial communities of urochordate ascidian (Halocynthia roretzi) across the changes of season and starvation stress using a comprehensive set of omic approaches including 16S rRNA gene amplicon sequencing, shotgun metagenomics, metabolomic profiling, and transcriptome sequencing.

Results

The 16S rRNA gene amplicon profiling revealed that ascidians harbor indigenous gut microbiota distinctly different to the marine microbial community and significant variations in composition and abundance of gut bacteria, with predominant bacterial orders representing each season. Depressed alpha-diversities of gut microbiota were observed across starvation stress when compared to the communities in aquafarm condition. Synechococcales involving photosynthesis and its related biosynthesis was reduced in abundance while the enrichments of Xanthomonadales and Legionellales may facilitate bile acid biosynthesis during starvation. Metabolomics analysis found that long chain fatty acids, linolenic acid, cyanoamino acid, and pigments derived from gut bacteria were upregulated, suggesting a beneficial contribution of the gut microbiome to the ascidian under starvation stress.

Conclusions

Our findings revealed seasonal variation of ascidian gut microbiota. Defense and energy-associated metabolites derived from gut microbiome may provide an adaptive interplay between gut microbiome and ascidian host that maintains a beneficial metabolic system across season and starvation stress. The diversity-generating metabolisms from both microbiota and host might lead to the co-evolution and environmental adaptation.

Graphical Abstract

Ten-Year Research Update Review: Antiviral Activities from Marine Organisms

Oceans cover more than 70 percent of the surface of our planet and are characterized by huge taxonomic and chemical diversity of marine organisms. Several studies have shown that marine organisms produce a variety of compounds, derived from primary or secondary metabolism, which may have antiviral activities. In particular, certain marine metabolites are active towards a plethora of viruses. Multiple mechanisms of action have been found, as well as different targets. This review gives an overview of the marine-derived compounds discovered in the last 10 years. Even if marine organisms produce a wide variety of different compounds, there is only one compound available on the market, Ara-A, and only another one is in phase I clinical trials, named Griffithsin. The recent pandemic emergency caused by SARS-CoV-2, also known as COVID-19, highlights the need to further invest in this field, in order to shed light on marine compound potentiality and discover new drugs from the sea.

Antitumoral compounds from vertebrate sister group: A review of Mediterranean ascidians

Among the diseases that afflict the human population, cancer is one for which many drug treatments are not yet known or effective. Moreover, the pharmacological treatments used often create serious side effects in sick patients and for this reason, it is essential to find effective and less harmful treatments. To date, marine biodiversity is a real source of metabolites with antitumoral activity and among invertebrates' ascidians have been the main source to obtain them. Mediterranean area is the richest in biodiversity and contains several ascidian species used in drugs development during the years. However, many more Mediterranean ascidian species have not been studied and could be a source of useful bioactive compounds. This review aims to summarize the scientific studies that analyzed the antitumor compounds obtained from different Mediterranean ascidians species, encouraging them to search further compounds in other new species to improve pharmacological treatments and human population life.

A combined analysis of transcriptomics and proteomics of a novel Antarctic Salpa sp. and its potential toxin screenings

BACKGROUND

We successfully captured a kind of gelatinous organism DA-6 from Antarctic water, extracted its total RNAs and proteins, and performed species identification through a combination of transcriptomics and proteomics in this study.

METHODS

The gelatinous organism DA-6 was captured 200 m underwater in Antarctica. Total RNA was extracted to construct the transcriptome and the proteins were identified by LC-MS/MS.

RESULTS

DA-6 was identified as an Antarctic Salpa sp. through morphological examination and MT-CO1 phylogenetic analysis. A total of 47,183 unigenes were harvested through transcriptome. We also successfully annotated 11,954 (25.34%), 10,006 (22.21%), 4469 (9.47%) and 4901 (9.71%) unigenes with NR, SwissProt, GO and KEGG databases, respectively. In the proteomic analysis, a total of 4680 peptides and 1280 proteins were harvested using the transcriptome as the reference database. A number of both 549 (31.98%) proteins reannotated against the GO and KEGG databases. Moreover, a number of 5 toxic proteins matched from the 89 toxin-related unigenes were successfully screened, including 2 metalloproteinases, 1 serine protease, 1 serine protease inhibitor and 1 aflatoxin.

CONCLUSION

Our study is the first to identify an Antarctic Salpa sp. according to the combination of de novo transcriptomics and proteomics, which can further be served as a public database for the identification of potential polar Salpa-derived lead compounds. In addition to morphology and CO1, the combined analysis of transcriptome and proteome can also be used as a value method for new species identify e.g. Salpa sp.

Metabolomic tools used in marine natural product drug discovery

Introduction: The marine environment is a very promising resource for natural product research, with many of these reaching the market as new drugs, especially in the field of cancer therapy as well as the drug discovery pipeline for new antimicrobials. Exploitation for bioactive marine compounds with unique structures and novel bioactivity such as the isoquinoline alkaloid; trabectedin, the polyether macrolide; halichondrin B, and the peptide; dolastatin 10, requires the use of analytical techniques, which can generate unbiased, quantitative, and qualitative data to benefit the biodiscovery process. Metabolomics has shown to bridge this understanding and facilitate the development of new potential drugs from marine sources and particularly their microbial symbionts.Areas covered: In this review, articles on applied secondary metabolomics ranging from 1990-2018 as well as to the last quarter of 2019 were probed to investigate the impact of metabolomics on drug discovery for new antibiotics and cancer treatment.Expert opinion: The current literature review highlighted the effectiveness of metabolomics in the study of targeting biologically active secondary metabolites from marine sources for optimized discovery of potential new natural products to be made accessible to a R&D pipeline.

Bioactive Metabolites from Marine Ascidians: Future Treatment for Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a developmental disorder that influences communication and behavior. Numerous researches propose that genes can act together with manipulations from the environment to affect development in ways that lead to ASD. The broad range of issues facing people with ASD means that there is no single proper drug and treatment for ASD. Numerous shortcomings associated with the present conventional therapeutic strategies have forced researchers to venture into alternative natural sources for effective compounds. The marine environment has emerged as an alternate search environment due to its versatile conditions where organisms employ various biodefense mechanisms for their survival. Ascidians are an excellent source for unique bioactive compounds with nutritive and therapeutic content and it still holds credit for being an underused source from marine animals. Bioactive compounds isolated from ascidians have various commendable biomedical applications due to their unique chemical structures. The present chapter will focus on the potential of bioactive compounds derived from ascidians for the treatment of the neurologic disorder-ASD.

Origins and Bioactivities of Natural Compounds Derived from Marine Ascidians and Their Symbionts

Marine ascidians are becoming important drug sources that provide abundant secondary metabolites with novel structures and high bioactivities. As one of the most chemically prolific marine animals, more than 1200 inspirational natural products, such as alkaloids, peptides, and polyketides, with intricate and novel chemical structures have been identified from ascidians. Some of them have been successfully developed as lead compounds or highly efficient drugs. Although numerous compounds that exist in ascidians have been structurally and functionally identified, their origins are not clear. Interestingly, growing evidence has shown that these natural products not only come from ascidians, but they also originate from symbiotic microbes. This review classifies the identified natural products from ascidians and the associated symbionts. Then, we discuss the diversity of ascidian symbiotic microbe communities, which synthesize diverse natural products that are beneficial for the hosts. Identification of the complex interactions between the symbiont and the host is a useful approach to discovering ways that direct the biosynthesis of novel bioactive compounds with pharmaceutical potentials.

Penicamide A, A Unique N,N'-Ketal Quinazolinone Alkaloid from Ascidian-Derived Fungus Penicillium sp. 4829

Previously unreported N,N′-ketal quinazolinone enantiomers [(−)-1 and (+)-1] and a new biogenetically related compound (2), along with six known compounds, 2-pyrovoylaminobenzamide (3), N-(2-hydroxypropanoyl)-2 amino benzoic acid amide (4), pseurotin A (5), niacinamide (6), citreohybridonol (7), citreohybridone C (8) were isolated from the ascidian-derived fungus Penicillium sp. 4829 in wheat solid-substrate medium culture. Their structures were elucidated by a combination of spectroscopic analyses (1D and 2D NMR and Electron Circular Dichroism data) and X-ray crystallography. The enantiomeric pair of 1 is the first example of naturally occurring N,N′-ketal quinazolinone possessing a unique tetracyclic system having 4-quinazolinone fused with tetrahydroisoquinoline moiety. The enantiomeric mixtures of 1 displayed an inhibitory effect on NO production in lipopolysaccharide-activated RAW264.7 cells, while the optically pure (–)-1 showed better inhibitory effect than (+)-1.

Anti-glioma trichobamide A with an unprecedented tetrahydro-5H-furo[2,3-b]pyrrol-5-one functionality from ascidian-derived fungus Trichobotrys effuse 4729

Trichobamide A (1), a novel pyrrocidine alkaloid with an unprecedented tetrahydro-5H-furo[2,3-b]pyrrol-5-one moiety, was isolated from the ascidian-derived fungus Trichobotrys effuse 4729.