Marine biodiversity as a source of chemical diversity

Marine Invertebrate Peptides: Antimicrobial Peptides

Antimicrobial peptides are an important component of many organisms’ innate immune system, with a good inhibitory or killing effect against the invading pathogens. As a type of biological polypeptide with natural immune activities, antimicrobial peptides have a broad spectrum of antibacterial, antiviral, and antitumor activities. Nevertheless, these peptides cause no harm to the organisms themselves. Compared with traditional antibiotics, antimicrobial peptides have the advantage of not producing drug resistance and have a unique antibacterial mechanism, which has attracted widespread attention. In this study, marine invertebrates were classified into arthropods, annelids, mollusks, cnidarians, and tunicata. We then analyzed the types, sources and antimicrobial activities of the antimicrobial peptides in each group. We also reviewed the immune mechanism from three aspects: membrane-targeted direct killing effects, non-membrane targeting effects and immunomodulatory effects. Finally, we discussed their applications and the existing problems facing antimicrobial peptides in actual production. The results are expected to provide theoretical support for future research and applications of antimicrobial peptides in marine invertebrates.

Application of Networking Approaches to Assess the Chemical Diversity, Biogeography, and Pharmaceutical Potential of Verongiida Natural Products

This study provides a review of all isolated natural products (NPs) reported for sponges within the order Verongiida (1960 to May 2020) and includes a comprehensive compilation of their geographic and physico-chemical parameters. Physico-chemical parameters were used in this study to infer pharmacokinetic properties as well as the potential pharmaceutical potential of NPs from this order of marine sponge. In addition, a network analysis for the NPs produced by the Verongiida sponges was applied to systematically explore the chemical space relationships between taxonomy, secondary metabolite and drug score variables, allowing for the identification of differences and correlations within a dataset. The use of scaffold networks as well as bipartite relationship networks provided a platform to explore chemical diversity as well as the use of chemical similarity networks to link pharmacokinetic properties with structural similarity. This study paves the way for future applications of network analysis procedures in the field of natural products for any order or family.

Marine-derived pipeline anticancer natural products: a review of their pharmacotherapeutic potential and molecular mechanisms

Background

Cancer is a complex and most widespread disease and its prevalence is increasing worldwide, more in countries that are witnessing urbanization and rapid industrialization changes. Although tremendous progress has been made, the interest in targeting cancer has grown rapidly every year. This review underscores the importance of preventive and therapeutic strategies.

Main text

Natural products (NPs) from various sources including plants have always played a crucial role in cancer treatment. In this growing list, numerous unique secondary metabolites from marine sources have added and gaining attention and became potential players in drug discovery and development for various biomedical applications. Many NPs found in nature that normally contain both pharmacological and biological activity employed in pharmaceutical industry predominantly in anticancer pharmaceuticals because of their enormous range of structure entities with unique functional groups that attract and inspire for the creation of several new drug leads through synthetic chemistry. Although terrestrial medicinal plants have been the focus for the development of NPs, however, in the last three decades, marine origins that include invertebrates, plants, algae, and bacteria have unearthed numerous novel pharmaceutical compounds, generally referred as marine NPs and are evolving continuously as discipline in the molecular targeted drug discovery with the inclusion of advanced screening tools which revolutionized and became the component of antitumor modern research.

Conclusions

This comprehensive review summarizes some important and interesting pipeline marine NPs such as Salinosporamide A, Dolastatin derivatives, Aplidine/plitidepsin (Aplidin®) and Coibamide A, their anticancer properties and describes their mechanisms of action (MoA) with their efficacy and clinical potential as they have attracted interest for potential use in the treatment of various types of cancers.

Antimicrobial peptides from marine invertebrates: challenges and perspectives in marine antimicrobial peptide discovery

The emergence of pathogenic bacteria resistance to conventional antibiotics calls for an increased focus on the purification and characterization of antimicrobials with new mechanisms of actions. Antimicrobial peptides are promising candidates, because their initial interaction with microbes is through binding to lipids. The interference with such a fundamental cell structure is assumed to hamper resistance development. In the present review we discuss antimicrobial peptides isolated from marine invertebrates, emphasizing the isolation and activity of these natural antibiotics. The marine environment is relatively poorly explored in terms of potential pharmaceuticals, and it contains a tremendous species diversity which evolved in close proximity to microorganisms. As invertebrates rely purely on innate immunity, including antimicrobial peptides, to combat infectious agents, it is believed that immune effectors from these animals are efficient and rapid inhibitors of microbial growth.

Bioprocess Engineering Data on the Cultivation of Marine Prokaryotes and Fungi

The temperature/pressure dependency of marine prokaryotes and fungi, in terms of their growth behaviour as well as their potential to produce new metabolites or enzymes, is evaluated. Advanced shake-flask cultivations and controlled bioreactor cultivations following the batch-type, fed-batch-type and/or continuous-type procedures are summarized. After a summary of the fermentation data available so far, values on maximal biomass, specific growth rates, and (sub)optimal production yields are presented. The application of mesophilic microbes, especially bioactive metabolites, to intensify bioprocess engineering studies, is the goal. Cold-active enzymes and thermostable enzymes are the targets of experiments with psychrophilic and hyperthermophilic enzymes. A special challenge to bioengineers is also provided by barophilic strains originating from depths of, say, nearly 11000 m, or from hydrothermal vents.

Antibacterial activity in Strongylocentrotus droebachiensis (Echinoidea), Cucumaria frondosa (Holothuroidea), and Asterias rubens (Asteroidea)

A search for antibacterial activity in different body parts of the green sea urchin Strongylocentrotus droebachiensis, the common starfish Asterias rubens, and the sea cucumber Cucumaria frondosa was conducted. Antibacterial activity was detected in extracts from several tissues in all species tested, but mainly in the coelomocyte and body wall extracts. Relatively high antibacterial activity could also be detected in gastrointestinal organs and eggs from A. rubens and in eggs from C. frondosa. Differences between active extracts regarding hydrophobicity and sensitivity to heat and proteinase K treatment indicated that several different compounds were responsible for the antibacterial activities detected. Lysozyme-like activity could be detected in several tissues from A. rubens. Haemolytic activity could be detected in all species tested, especially in the body wall extracts. Results from the current study suggest that marine echinoderms are a potential source for the discovery of novel antibiotics.

Strategies for discovering drugs from previously unexplored natural products

Natural products are the most consistently successful source of drug leads. Despite this, their use in drug discovery has fallen out of favour. Natural products continue to provide greater structural diversity than standard combinatorial chemistry and so they offer major opportunities for finding novel low molecular weight lead structures that are active against a wide range of assay targets. As less than 10% of the world's biodiversity has been tested for biological activity, many more useful natural lead compounds are awaiting discovery. The challenge is how to access this natural chemical diversity.

Natural Products as Antiviral Agents

Since the ancient times, natural products have served as a major source of drugs. About fifty percent of today's pharmaceutical drugs are derived from natural origin. Interest in natural products as a source of new drugs is growing due to many factors that will be discussed in this article. Viruses have been resistant to therapy or prophylaxis longer than any other form of life. Currently, there are only few drugs available for the cure of viral diseases including acyclovir which is modeled on a natural product parent. In order to combat viruses which have devastating effects on humans, animals, insects, crop plants, fungi and bacteria, many research efforts have been devoted for the discovery of new antiviral natural products. Recent analysis of the number and sources of antiviral agents reported mainly in the annual reports of medicinal chemistry from 1984 to 1995 indicated that seven out of ten synthetic agents approved by FDA between 1983-1994, are modeled on a natural product parent. It has been estimated that only 5-15% of the approximately 250,000 species of higher plants have been systematically investigated for the presence of bioactive compounds while the potential of the marine environment has barely been tapped. The aim of this review is to provide an overview on the central role of natural products in the discovery and development of new antiviral drugs by displaying 340 structures of plant, marine and microbial origin that show promising in vitro antiviral activity.

Application of a radioreceptor assay to the screening and characterisation of compounds from marine organisms with activity at the phorbol ester binding site of protein kinase C

Protein kinase C is a ubiquitous enzyme with a key role in cellular function, making it an attractive drug target. Utilising a competitive binding assay for the phorbol ester binding site of the enzyme in a rat brain membrane preparation, screening was undertaken on 686 marine macroorganisms representing a broad range of taxa and environments from throughout Australasia. Of these extracts from 28 organisms significantly inhibited [3H]phorbol dibutyrate binding, while two samples enhanced binding. Sponges and echinoderms were particularly well represented in the active specimens. A combination of taxonomic and elution information for individual leads provided a rationale for dereplication and prioritisation. Utilising assay-guided purification, the identity of active compounds from the sponge Agelas axifera was examined in detail. The previously described compounds, the agelasines, were identified. The screening and characterisation methods described provide a method for readily identifying novel probes for protein kinase C.

Fishing for drugs from the sea: status and strategies

Marine organisms represent an enormous, essentially unexploited, resource of natural products. Globally, the race to develop marine-derived drugs is well under way with many pharmaceutical companies positioning themselves to reap large profits by the exploitation of the ocean's rich chemical diversity. Targeted strategies, often in combination with high-throughput screening, are being employed in this hunt for novel pharmacotherapeutic agents. David de Vries and Phil Beart examine the potential, problems and technologies of an international pharmaceutical search that has important ethical considerations.