The marine environment is an excellent resource for natural products with therapeutic potential. Its microbial inhabitants, often associated with other marine organisms, are specialized in the synthesis of bioactive secondary metabolites. Similar to their terrestrial counterparts, marine Actinobacteria are a prevalent source of these natural products. Here, we discuss 77 newly discovered alkaloids produced by such marine Actinobacteria between 2017 and mid-2021, as well as the strategies employed in their elucidation. While 12 different classes of alkaloids were unraveled, indoles, diketopiperazines, glutarimides, indolizidines, and pyrroles were most dominant. Discoveries were mainly based on experimental approaches where microbial extracts were analyzed in relation to novel compounds. Although such experimental procedures have proven useful in the past, the methodologies need adaptations to limit the chance of compound rediscovery. On the other hand, genome mining provides a different angle for natural product discovery. While the technology is still relatively young compared to experimental screening, significant improvement has been made in recent years. Together with synthetic biology tools, both genome mining and extract screening provide excellent opportunities for continued drug discovery from marine Actinobacteria.

Iminosugars have a carbohydrate-like backbone in which the ring oxygen is replaced by nitrogen. They are naturally found in foods such as rice, buckwheat, mulberries, and fermented vegetables, and are reported to exert anti-hyperlipidemic and anti-hyperglycemic effects due to the inhibition of cellular glycosidases. This mechanism suggests their potential role in cancer treatment and prevention. In this study, two natural iminosugars, D-fagomine (FGM) and 1-deoxynojirimycin (DNJ), and their synthetic derivatives were screened for potential anticancer properties using Caco-2 and HCT-116 cells as models for the early and late stages of colon cancer, respectively. Iminosugars were found to decrease cell viability, with effects varying based on the type of iminosugar, cell type, growth condition (glucose concentration), exposure time (1 vs. 13 days), and tissue architecture (monolayer vs. spheroid). The combined use of innovative techniques, such as IncuCyte^® live cell imaging and Seahorse real-time cellular metabolic analysis, and microscopic observation after staining enabled us to detect changes in substrate utilization for energy metabolism, including increased glycolysis and alterations in lipid and glycogen stores. The evidence that iminosugars, both natural and synthetic, influence cellular bioenergetics paves the way for their potential use in various applications, including cancer treatment.

Background: The marine environment hosts the vast majority of living species and marine microbes that produce natural products with great potential in providing lead compounds for drug development. With over 70% of Earth’s surface covered in water and the high interaction rate associated with liquid environments, this has resulted in many marine natural product discoveries. Our improved understanding of the biosynthesis of these molecules, encoded by gene clusters, along with increased genomic information will aid us in uncovering even more novel compounds. Results: We introduce MariClus (https://www.mariclus.com), an online user-friendly platform for mining and visualizing marine gene clusters. The first version contains information on clusters and the predicted molecules for over 500 marine-related prokaryotes. The user-friendly interface allows scientists to easily search by species, cluster type or molecule and visualize the information in table format or graphical representation. Conclusions: This new online portal simplifies the exploration and comparison of gene clusters in marine species for scientists and assists in characterizing the bioactive molecules they produce. MariClus integrates data from public sources, like GenBank, MIBiG and PubChem, with genome mining results from antiSMASH. This allows users to access and analyze various aspects of marine natural product biosynthesis and diversity.