Actinoquinolines A and B, anti-inflammatory quinoline alkaloids from a marine-derived Streptomyces sp., strain CNP975

Marine Streptomyces-Derived Novel Alkaloids Discovered in the Past Decade

Natural alkaloids originating from actinomycetes and synthetic derivatives have always been among the important suppliers of small-molecule drugs. Among their biological sources, Streptomyces is the highest and most extensively researched genus. Marine-derived Streptomyces strains harbor unconventional metabolic pathways and have been demonstrated to be efficient producers of biologically active alkaloids; more than 60% of these compounds exhibit valuable activity such as antibacterial, antitumor, anti-inflammatory activities. This review comprehensively summarizes novel alkaloids produced by marine Streptomyces discovered in the past decade, focusing on their structural features, biological activity, and pharmacological mechanisms. Future perspectives on the discovery and development of novel alkaloids from marine Streptomyces are also provided.

Biology of quinoline and quinazoline alkaloids

Quinoline and quinazoline alkaloids, two important classes of N-based heterocyclic compounds, have attracted scientific and popular interest worldwide since the 19th century. More than 600 compounds have been isolated from nature to date. To build on our two prior reviews, we reexamined the promising molecules described in previous reports and provided updated literature on novel quinoline and quinazoline alkaloids isolated over the past 5 years. This chapter reviews and discusses 205 molecules with a broad range of bioactivities, including antiparasitic and insecticidal, antibacterial and antifungal, cardioprotective, antiviral, anti-inflammatory, and other effects. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.

Natural Product Inhibitors of Cyclooxygenase (COX) Enzyme: A Review on Current Status and Future Perspectives

BACKGROUND

Several clinically used COX-1 and COX-2 inhibitor drugs were reported to possess severe side effects like GI ulcers and cardiovascular disturbances, respectively. Natural products being structurally diverse always attracted the attention of chemists/ medicinal chemists as a potential source of lead molecules in the drug discovery process. COX-2 inhibitory natural products also possess potential cancer chemopreventive property against various cancers including that of colon, breast and prostate.

METHODS

Various in vitro, in vivo and in silico standardized methods were used to evaluate COX inhibition property of different secondary metabolites isolated from plant, microbial and marine origin.

RESULTS

We had earlier reported a detailed account of natural product inhibitors of COX reported during 1995-2005, in 2006. In the proposed review, we report 158 natural product inhibitors of COX during 2006 to 2019 belonging to various secondary metabolite classes such as alkaloids, terpenoids, polyphenols as flavonoids, chromones, coumarins, lignans, anthraquinones, naphthalenes, curcuminoids, diarylheptanoids and miscellaneous compounds of plant and marine origin. Further Structure Activity Relationship (SAR) studies of possible leads are also included in the article.

CONCLUSION

COX inhibitors served as a potential source of lead molecules for the discovery and development of anti-inflammatory drugs. Compilation of natural product and semisynthetic inhibitors of COX may serve as valuable information to the researchers who are looking for possible lead molecules from a natural source to conduct further preclinical and clinical studies.

Marine Pharmacology in 2016-2017: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis and Antiviral Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The review of the 2016-2017 marine pharmacology literature was prepared in a manner similar as the 10 prior reviews of this series. Preclinical marine pharmacology research during 2016-2017 assessed 313 marine compounds with novel pharmacology reported by a growing number of investigators from 54 countries. The peer-reviewed literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral activities for 123 marine natural products, 111 marine compounds with antidiabetic and anti-inflammatory activities as well as affecting the immune and nervous system, while in contrast 79 marine compounds displayed miscellaneous mechanisms of action which upon further investigation may contribute to several pharmacological classes. Therefore, in 2016-2017, the preclinical marine natural product pharmacology pipeline generated both novel pharmacology as well as potentially new lead compounds for the growing clinical marine pharmaceutical pipeline, and thus sustained with its contributions the global research for novel and effective therapeutic strategies for multiple disease categories.

Discovery of natural anti-inflammatory alkaloids: Potential leads for the drug discovery for the treatment of inflammation

Inflammation is an adaptive response of the immune system to tissue malfunction or homeostatic imbalance. Corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs) are frequently applied to treat varieties of inflammatory diseases but are associated with gastrointestinal, cardiovascular, and kidney side effects. Developing more effective and less toxic agents remain a challenge for pharmaceutical chemist due to the complexity of the different inflammatory processes. Alkaloids are widely distributed in plants with diverse anti-inflammatory activities, providing various potential lead compounds or candidates for the design and discovery of new anti-inflammatory drug candidates. Therefore, re-examining the anti-inflammatory alkaloid natural products is advisable, bringing more opportunities. In this review, we summarized and described the recent advances of natural alkaloids with anti-inflammatory activities and possible mechanisms in the period from 2009 to 2020. It is hoped that this review of anti-inflammatory alkaloids can provide new ideas for researchers engaged in the related fields and potential lead compounds for the discovery of anti-inflammatory drugs.

Streptomyces-Derived Metabolites with Potential Photoprotective Properties-A Systematic Literature Review and Meta-Analysis on the Reported Chemodiversity

Sun overexposure is associated with the development of diseases that primarily affect the skin, which can lead to skin cancer. Among the main measures of photoprotection is the use of sunscreens. However, there is currently concern about the reported harmful effects to both humans and the environment due to several of the sunscreen ingredients available on the market. For this reason, the search for and development of new agents with photoprotective properties is required. In searching for these metabolites, researchers have turned their attention to microbial sources, especially the microbiota in unusual hostile environments. Among the diverse microorganisms available in nature, Actinobacteria and specifically Streptomyces, have been shown to be a source of metabolites with various biological activities of interest, such as antimicrobial, antitumor and immunomodulator activities. Herein, we present the results of a systematic review of the literature in which Streptomyces isolates were studied as a source of compounds with photoprotective properties. A meta-analysis of the structure-property and structure-activity relationships of those metabolites identified in the qualitative analysis phase was also carried out. These findings indicate that Streptomyces are a source of metabolites with potential applications in the development of new, safe and more eco-friendly sunscreens.

Screening of chalcone analogs with anti-depressant, anti-inflammatory, analgesic, and COX-2-inhibiting effects

A group of 2-methyl-4-phenylquinoline-chalcone analogs (2a-2x) was synthesized and investigated for anti-depressant, anti-inflammatory, and analgesic effects as cyclooxygenase-2 inhibitors. Pharmacological experiments identified 24 analogs that exhibited anti-depressant, anti-inflammatory, and analgesic activities. In particular, compounds 2c, 2k, and 2w markedly shortened immobility times and exhibited the most anti-depressant activity. In addition, the mechanisms of action of the analogs 2c, 2k, and 2w were likely related to increased serotonin levels in the central nervous system. Compounds 2c, 2k, and 2w displayed reasonable cyclooxygenase-2 inhibitory effects (IC₅₀ values from 0.21 to 0.29 µmol/L) similar to celecoxib (IC₅₀: 0.19 µmol/L) in vitro. A molecular docking study of compound 2k also was conducted.

Marine Alkaloids with Anti-Inflammatory Activity: Current Knowledge and Future Perspectives

Alkaloids are nitrogenous compounds with various biological activities. Alkaloids with anti-inflammatory activity are commonly found in terrestrial plants, but there are few records of the identification and characterization of the activity of these compounds in marine organisms such as fungi, bacteria, sponges, ascidians, and cnidarians. Seaweed are a source of several already elucidated bioactive compounds, but few studies have described and characterized the activity of seaweed alkaloids with anti-inflammatory properties. In this review, we have gathered the current knowledge about marine alkaloids with anti-inflammatory activity and suggest future perspectives for the study and bioprospecting of these compounds.

Marine Actinomycetes-derived Natural Products

Actinomycetes is an abundant resource for discovering a large number of lead compounds, which play an important role in microbial drug discovery. Compared to terrestrial microorganisms, marine actinomycetes have unique metabolic pathways because of their special living environment, which has the potential to produce a variety of bioactive substances. In this paper, secondary metabolites isolated from marine actinomycetes are reviewed (2013-2018), most of which exhibited cytotoxic, antibacterial, and antiviral biological activities.

Exploration and genome mining of natural products from marine Streptomyces

Marine Streptomyces sp. are an important source of bioactive compounds owing to their unique habitats and metabolic pathways. Whole-genome sequencing and bioinformatics analyses have shown that the potential of synthesizing secondary metabolites from marine-derived Streptomyces has been substantially underestimated. Genome mining is an integrated strategy used to discover natural products based on gene cluster sequences and biosynthetic pathways. Its emergence has greatly enhanced the discovery of natural compounds from marine Streptomyces, thereby yielding a large number of bioactive molecules with novel structures and potent activities. In this review, we briefly summarize the current applications of genome mining in marine Streptomyces, such as bioinformatics-based optimization of culture conditions, ribosome engineering, control of regulatory networks, heterologous expression of biosynthetic gene cluster, and combinatorial biosynthesis of natural compounds. Furthermore, we discuss the factors hindering the utilization of marine-derived natural products and conclude with the prospects for this technique.

2-Alkyl-4-hydroxyquinolines from a Marine-Derived Streptomyces sp. Inhibit Hyphal Growth Induction in Candida albicans

Four 2-alkyl-4-hydroxyquinoline derivatives (1⁻4) were isolated from a semisolid rice culture of the marine-derived actinomycete Streptomyces sp. MBTG13. The structures of these compounds were elucidated by a combination of spectroscopic methods, and their data were in good agreement with previous reports. Compounds 1 and 2 exhibited weak to moderate antibacterial activity against pathogenic bacteria. Unexpectedly, we found that compound 1 acted as a potent inhibitor of hyphal growth induction in the dimorphic fungus Candida albicans, with an IC₅₀ value of 11.4 μg/mL. Growth experiments showed that this compound did not inhibit yeast cell growth, but inhibited hyphal growth induction. Semi-quantitative reverse transcription (RT)-PCR analysis of hyphal-inducing signaling pathway components indicated that compound 1 inhibited the expression of mRNAs related to the cAMP-Efg1 pathway. The expression of HWP1 and ALS3 mRNAs (hypha-specific genes positively regulated by Efg1, an important regulator of cell wall dynamics) was significantly inhibited by the addition of compound 1. These results indicate that compound 1 acts on the Efg1-mediated cAMP pathway and regulates hyphal growth in Candida albicans.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.