Antiamoebic Activities of Indolocarbazole Metabolites Isolated from Streptomyces sanyensis Cultures

Marine Pharmacology in 2019-2021: 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 current 2019-2021 marine pharmacology literature review provides a continuation of previous reviews covering the period 1998 to 2018. Preclinical marine pharmacology research during 2019-2021 was published by researchers in 42 countries and contributed novel mechanism-of-action pharmacology for 171 structurally characterized marine compounds. The peer-reviewed marine natural product pharmacology literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral mechanism-of-action studies for 49 compounds, 87 compounds with antidiabetic and anti-inflammatory activities that also affected the immune and nervous system, while another group of 51 compounds demonstrated novel miscellaneous mechanisms of action, which upon further investigation, may contribute to several pharmacological classes. Thus, in 2019-2021, a very active preclinical marine natural product pharmacology pipeline provided novel mechanisms of action as well as new lead chemistry for the clinical marine pharmaceutical pipeline targeting the therapy of several disease categories.

A novel glycosylated indolocarbazole derivative LCS1269 effectively inhibits growth of human cancer cells in vitro and in vivo through driving of both apoptosis and senescence by inducing of DNA damage and modulating of AKT/mTOR/S6K and ERK pathways

In recent decades, indolocarbazole glycosides containing sugar moieties have attracted attention due to their diverse anti-tumor activities. In the present study, a series of new indolo [2,3-a]pyrrolo [3,4-c]carbazole derivatives were synthesized for the first time. First of all, we have shown that compound 6e (LCS1269) had the most pronounced effect on inhibiting tumor growth in the transferable solid and non-solid murine tumors as compared with other synthesized indolocarbazole derivatives. The results of the in vivo nude mice xenoraft study also confirmed that LCS1269 treatment strongly suppressed the growth of human colon cancer SW620 xenografts. It is important to note that the antiproliferative activity of LCS1269 against three human cancer cell lines (MCF-7, HCT-116 and A549) was considerably higher than that against the non-tumor cell lines (immortalized breast cells and normal embryonic fibroblasts). Furthermore, the treatment of MCF-7, HCT-116 and A549 cells with LCS1269 caused the statistically significant inhibition of anchorage-dependent and anchorage-independent colony formation. We further revealed that LCS1269 treatment of investigated human cancer cells resulted in the DNA damage and G2/M cell cycle arrest followed by the decrease of mitochondrial membrane potential with subsequent initiation of intrinsic apoptosis and the triggering of senescence via p53-dependent mechanisms. In addition, our western blotting findings and molecular docking data suppose that LCS1269 could at least partially attenuate cancer cells growth by modulation of AKT/mTOR/S6K and ERK signaling pathways. Therefore, we concluded that LCS1269 might be the promising compound for implementation and probable use in the clinical practice.

Novel Alkaloids from Marine Actinobacteria: Discovery and Characterization

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.

Evaluation of Indolocarbazoles from Streptomyces sanyensis as a Novel Source of Therapeutic Agents against the Brain-Eating Amoeba Naegleria fowleri

Naegleria fowleri is an opportunistic pathogenic free-living amoeba which is able to rapidly colonize the central nervous system (CNS) and causes a lethal infection known as primary amoebic meningoencephalitis (PAM). Furthermore, more than 98% of the known cases of PAM are fatal and affect mainly children under 12 and young adults. Until now, no fully effective therapeutic agents against N. fowleri are available and hence the urgent need to find novel agents to treat PAM. At present, PAM therapy is based on the combination of amphotericin B, miltefosine, among others, with unwanted toxic effects. Recently, our team isolated various indolocarbazoles (ICZs) from the culture of a mangrove strain of Streptomyces sanyensis which showed activity against kinetoplastids and the Acanthamoeba genus. Hence, in this study, the activity of the previously isolated ICZs, staurosporine (STS), 7-oxostaurosporine (7OSTS), 4′-demethylamino-4′-oxostaurosporine, and streptocarbazole B, was evaluated against two type strains of N. fowleri. Furthermore, the performed activity assays revealed that STS was the most active ICZ presenting an inhibitory concentration 50 (IC₅₀) of 0.08 ± 0.02 µM (SI 109.3). Moreover, STS induced programmed cell death (PCD) in the treated amoebae by triggering DNA condensation, mitochondrial disfunction, cell membrane disruption, and reactive oxygen species (ROS) generation. Therefore, STS could be a promising therapeutic agent against PAM.

Antikinetoplastid Activity of Indolocarbazoles from Streptomyces sanyensis

Chagas disease and leishmaniasis are neglected tropical diseases caused by kinetoplastid parasites of Trypanosoma and Leishmania genera that affect poor and remote populations in developing countries. These parasites share similar complex life cycles and modes of infection. It has been demonstrated that the particular group of phosphorylating enzymes, protein kinases (PKs), are essential for the infective mechanisms and for parasite survival. The natural indolocarbazole staurosporine (STS, 1) has been extensively used as a PKC inhibitor and its antiparasitic effects described. In this research, we analyze the antikinetoplastid activities of three indolocarbazole (ICZs) alkaloids of the family of staurosporine STS, 2-4, and the commercial ICZs rebeccamycin (5), K252a (6), K252b (7), K252c (8), and arcyriaflavin A (9) in order to establish a plausive approach to the mode of action and to provide a preliminary qualitative structure-activity analysis. The most active compound was 7-oxostaurosporine (7OSTS, 2) that showed IC₅₀ values of 3.58 ± 1.10; 0.56 ± 0.06 and 1.58 ± 0.52 µM against L. amazonensis; L. donovani and T. cruzi, and a Selectivity Index (CC₅₀/IC₅₀) of 52 against amastigotes of L. amazonensis compared to the J774A.1 cell line of mouse macrophages.