Chromomycins A2 and A3 from marine actinomycetes with TRAIL resistance-overcoming and Wnt signal inhibitory activities

Chromomycins from soil-derived Streptomyces sp. inhibit the growth of human non-small cell lung cancer cells by targeting c-FLIP

Three chromomycin derivatives, chromomycins A3 (1, CA3), A5 (2, CA5), and monodeacetylchromomycin A3 (3, MDA-CA3), were identified from the soil-derived Streptomyces sp. CGMCC 26516. A reinvestigation of the structure of CA5 is reported, of which the absolute configuration was unambiguously determined for the first time to be identical with that of CA3 based on nuclear magnetic resonance (NMR) data analysis as well as NMR and electronic circular dichroism calculations. Compounds 1-3 showed potent cytotoxicity against the non-small-cell lung cancer (NSCLC) cells (A549, H460, H157-c-FLIP, and H157-LacZ) and down-regulated the protein expression of c-FLIP in A549 cells. The IC50 values of chromomycins in H157-c-FLIP were higher than that in H157-LacZ. Furthermore, si-c-FLIP promoted anti-proliferation effect of chromomycins in NSCLC cells. In nude mice xenograft model, 1 and 2 both showed more potent inhibition on the growth of H157-lacZ xenografts than that of H157-c-FLIP xenografts. These results verify that c-FLIP mediates the anticancer effects of chromomycins in NSCLC.

Streptomyces tagetis sp. nov., a chromomycin producing bacteria isolated from the roots of Tagetes patula

A novel halotolerant actinobacterium, designated as RG38T, capable of producing black extracellular melanin pigment on SP2 agar, was isolated from the roots of Tagetes patula. Comparative analysis of the 16S rRNA gene sequence revealed the highest similarity to Streptomyces collinus NBRC 12759T (99.3%). Phylogenetic analysis showed that strain RG38T clustered within the genus Streptomyces forming a monophyletic cluster with its close relatives. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and amino-acid identity (AAI) values between strain RG38T and related species within the genus Streptomyces were below the standard threshold for prokaryotic species delineation. The DNA G + C content of the strain RG38T was determined to be 73.3%. The genome size measured 7,150,598 bp comprising 17 contigs and encompassed 6,053 protein coding genes. AntiSMASH analysis of the whole genome revealed 35 putative biosynthetic gene clusters (BGCs) responsible for various secondary metabolites. Among these clusters, two gene clusters exhibited 100% similarity to the chromomycin A3, albaflavenone, and anthracimycin, respectively. These compounds were reported to possess significant anticancer and antibacterial activities. LC-MS-based analysis, coupled with further isolation studies, confirmed the production of chromomycins A2 (1), A3 (2), and their derivatives, along with their antibiotic activities. These findings underscore the potential of this novel strain as a novel resource for the discovery of diverse antimicrobial compounds. This study is the first to report an antimicrobial compound producing Streptomyces species isolated from medicinal plant T. patula. Based on a polyphasic study, the strain RG38T isolated from an unexplored habitat with a high potential for new natural products represents a novel species within the genus Streptomyces. Accordingly, we propose the name Streptomyces tagetis sp. nov. for this novel species, with the type strain is RG38T (=KCTC 49624T = TBRC 15113T).

Antitumor activity of galaxamide involved in cell apoptosis and stemness by inhibiting Wnt/β-catenin pathway in cervical cancer

Our previous work reported that galaxamide, a cyclopeptide extracted from the seaweed Galaxaura filamentosa, showed antiproliferative activity against HeLa cells by MTT assay. In this study, the growth-inhibitory effects of galaxamide in HeLa cells and xenograft mouse models were investigated. It was found galaxamide significantly inhibited cell growth, colony formation, migration, and invasion and induced cell apoptosis by inhibiting the Wnt signaling pathway in HeLa cells. RNA sequencing revealed that galaxamide regulated stemness by Wnt6 signaling pathway in HeLa cells. By analyzing The Cancer Genome Atlas database, Wnt6 was found to be negatively/positively correlated with stemness- and apoptosis-related genes in human cervical cancer. Cancer stem-like cells (CSCs) isolated and enriched from HeLa cells demonstrated elevated Wnt6 and β-catenin genes compared with nonstem HeLa cells. After galaxamide treatment, CSCs showed abrogation of sphere-forming ability, along with inhibition of stemness-related and Wnt pathway genes. Galaxamide treatment was also accompanied by the induction of apoptosis in HeLa cells, which was consistent with the results in BALB/c nude mice. Our results provide evidence that suppression of stemness by downregulating the Wnt signaling pathway is the molecular mechanism by which galaxamide effectively inhibits cell growth and induces apoptosis in cervical cancer cells.

Screening study of cancer-related cellular signals from microbial natural products

To identify bioactive natural products from various natural resources, such as plants and microorganisms, we investigated programs to screen for compounds that affect several cancer-related cellular signaling pathways, such as BMI1, TRAIL, and Wnt. This review summarizes the results of our recent studies, particularly those involving natural products isolated from microbial resources, such as actinomycetes, obtained from soil samples collected primarily around Chiba, Japan.

Antibacterial Activity of Chromomycins from a Marine-Derived Streptomyces microflavus

A marine-derived actinomycete (Streptomyces sp. MBTI36) exhibiting antibacterial activities was investigated in the present study. The strain was identified using genetic techniques. The 16S rDNA sequence of the isolate indicated that it was most closely related to Streptomyces microflavus. Furthermore, a new chromomycin A₉ (1), along with chromomycin Ap (2), chromomycin A₂ (3), and chromomycin A₃ (4), were isolated from the ethyl acetate extract. Their structures were determined using extensive spectroscopic methods including 1D and 2D NMR, and HRMS, as well as comparisons with previously reported data. Compounds 1–4 showed potent antibacterial activities against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). During a passage experiment, minimum inhibitory concentration (MIC) values for compounds 1–4 showed no more than a 4-fold increase from the starting MIC value, indicating that no resistance was detected over the 21 passages.

Targeting β-Catenin Signaling by Natural Products for Cancer Prevention and Therapy

The mutations and deregulation of Wnt signaling pathway occur commonly in human cancer and cause the aberrant activation of β-catenin and β-catenin-dependent transcription, thus contributing to cancer development and progression. Therefore, β-catenin has been demonstrated as a promising target for cancer prevention and therapy. Many natural products have been characterized as inhibitors of the β-catenin signaling through down-regulating β-catenin expression, modulating its phosphorylation, promoting its ubiquitination and proteasomal degradation, inhibiting its nuclear translocation, or other molecular mechanisms. These natural product inhibitors have shown preventive and therapeutic efficacy in various cancer models in vitro and in vivo. In the present review, we comprehensively discuss the natural product β-catenin inhibitors, their in vitro and in vivo anticancer activities, and underlying molecular mechanisms. We also discuss the current β-catenin-targeting strategies and other potential strategies that may be examined for identifying new β-catenin inhibitors as cancer preventive and therapeutic drugs.

Marine Natural Products with High Anticancer Activities

This review covers recent literature from 2012-2019 concerning 170 marine natural products and their semisynthetic analogues with strong anticancer biological activities. Reports that shed light on cellular and molecular mechanisms and biological functions of these compounds, thus advancing the understanding in cancer biology are also included. Biosynthetic studies and total syntheses, which have provided access to derivatives and have contributed to the proper structure or stereochemistry elucidation or revision are mentioned. The natural compounds isolated from marine organisms are divided into nine groups, namely: alkaloids, sterols and steroids, glycosides, terpenes and terpenoids, macrolides, polypeptides, quinones, phenols and polyphenols, and miscellaneous products. An emphasis is placed on several drugs originating from marine natural products that have already been marketed or are currently in clinical trials.

Targeting the Oncogenic TBX2 Transcription Factor With Chromomycins

The TBX2 transcription factor plays critical roles during embryonic development and it is overexpressed in several cancers, where it contributes to key oncogenic processes including the promotion of proliferation and bypass of senescence. Importantly, based on compelling biological evidences, TBX2 has been considered as a potential target for new anticancer therapies. There has therefore been a substantial interest to identify molecules with TBX2-modulatory activity, but no such substance has been found to date. Here, we adopt a targeted approach based on a reverse-affinity procedure to identify the ability of chromomycins A₅ (CA₅) and A₆ (CA₆) to interact with TBX2. Briefly, a TBX2-DNA-binding domain recombinant protein was N-terminally linked to a resin, which in turn, was incubated with either CA₅ or CA₆. After elution, bound material was analyzed by UPLC-MS and CA₅ was recovered from TBX2-loaded resins. To confirm and quantify the affinity (K_D) between the compounds and TBX2, microscale thermophoresis analysis was performed. CA₅ and CA₆ modified the thermophoretic behavior of TBX2, with a K_D in micromolar range. To begin to understand whether these compounds exerted their anti-cancer activity through binding TBX2, we next analyzed their cytotoxicity in TBX2 expressing breast carcinoma, melanoma and rhabdomyosarcoma cells. The results show that CA₅ was consistently more potent than CA₆ in all tested cell lines with IC₅₀ values in the nM range. Of the cancer cell types tested, the melanoma cells were most sensitive. The knockdown of TBX2 in 501mel melanoma cells increased their sensitivity to CA₅ by up to 5 times. Furthermore, inducible expression of TBX2 in 501mel cells genetically engineered to express TBX2 in the presence of doxycycline, were less sensitive to CA₅ than the control cells. Together, the data presented in this study suggest that, in addition to its already recognized DNA-binding properties, CA₅ may be binding the transcription factor TBX2, and it can contribute to its cytotoxic activity.

Small Molecule Wnt Pathway Modulators from Natural Sources: History, State of the Art and Perspectives

The Wnt signaling is one of the major pathways known to regulate embryonic development, tissue renewal and regeneration in multicellular organisms. Dysregulations of the pathway are a common cause of several types of cancer and other diseases, such as osteoporosis and rheumatoid arthritis. This makes Wnt signaling an important therapeutic target. Small molecule activators and inhibitors of signaling pathways are important biomedical tools which allow one to harness signaling processes in the organism for therapeutic purposes in affordable and specific ways. Natural products are a well known source of biologically active small molecules with therapeutic potential. In this article, we provide an up-to-date overview of existing small molecule modulators of the Wnt pathway derived from natural products. In the first part of the review, we focus on Wnt pathway activators, which can be used for regenerative therapy in various tissues such as skin, bone, cartilage and the nervous system. The second part describes inhibitors of the pathway, which are desired agents for targeted therapies against different cancers. In each part, we pay specific attention to the mechanisms of action of the natural products, to the models on which they were investigated, and to the potential of different taxa to yield bioactive molecules capable of regulating the Wnt signaling.

Regulated Cell Death Signaling Pathways and Marine Natural Products That Target Them

Our understanding of cell death used to consist in necrosis, an unregulated form, and apoptosis, regulated cell death. That understanding expanded to acknowledge that apoptosis happens through the intrinsic or extrinsic pathways. Actually, many other regulated cell death processes exist, including necroptosis, a regulated form of necrosis, and autophagy-dependent cell death. We also understand that apoptosis occurs beyond the intrinsic and extrinsic pathways with caspase independent forms of apoptosis existing. Our knowledge of the signaling continues to grow, and with that, so does our ability to target different parts of the pathways with small molecules. Marine natural products co-evolve with their targets, and these unique molecules have complex structures with exquisite biological activities and specificities. This article offers a review of our current understanding of the signaling pathways regulating cell death, and highlights marine natural products that can affect these signaling pathways.

Probing insulin secretion with a new tool

JGP study explains how chromomycin A2 affects insulin secretion.

Chromomycin A2 potently inhibits glucose-stimulated insulin secretion from pancreatic β cells

Drugs that target insulin secretion are useful to understand β cell function and the pathogenesis of diabetes. Kalwat et al. investigate an aureolic acid that inhibits insulin secretion and reveal that it disrupts Wnt signaling, interferes with gene expression, and suppresses Ca²⁺ influx in β cells.

Modulators of insulin secretion could be used to treat diabetes and as tools to investigate β cell regulatory pathways in order to increase our understanding of pancreatic islet function. Toward this goal, we previously used an insulin-linked luciferase that is cosecreted with insulin in MIN6 β cells to perform a high-throughput screen of natural products for chronic effects on glucose-stimulated insulin secretion. In this study, using multiple phenotypic analyses, we found that one of the top natural product hits, chromomycin A2 (CMA2), potently inhibited insulin secretion by at least three potential mechanisms: disruption of Wnt signaling, interference of β cell gene expression, and partial suppression of Ca²⁺ influx. Chronic treatment with CMA2 largely ablated glucose-stimulated insulin secretion even after washout, but it did not inhibit glucose-stimulated generation of ATP or Ca²⁺ influx. However, by using the K_ATP channel opener diazoxide, we uncovered defects in depolarization-induced Ca²⁺ influx that may contribute to the suppressed secretory response. Glucose-responsive ERK1/2 and S6 phosphorylation were also disrupted by chronic CMA2 treatment. By querying the FUSION bioinformatic database, we revealed that the phenotypic effects of CMA2 cluster with a number of Wnt–GSK3 pathway-related genes. Furthermore, CMA2 consistently decreased GSK3β phosphorylation and suppressed activation of a β-catenin activity reporter. CMA2 and a related compound, mithramycin, are known to have DNA interaction properties, possibly abrogating transcription factor binding to critical β cell gene promoters. We observed that CMA2 but not mithramycin suppressed expression of PDX1 and UCN3. However, neither expression of INSI/II nor insulin content was affected by chronic CMA2. The mechanisms of CMA2-induced insulin secretion defects may involve components both proximal and distal to Ca²⁺ influx. Therefore, CMA2 is an example of a chemical that can simultaneously disrupt β cell function through both noncytotoxic and cytotoxic mechanisms. Future therapeutic applications of CMA2 and similar aureolic acid analogues should consider their potential effects on pancreatic islet function.

The Antitumor Antibiotics Complex of Aureolic Acids from the Marine Sediment-associated Strain of Streptomyces sp. KMM 9048

A new antibiotic complex of six aureolic acids was isolated from the marine sediment-associated strain Streptomyces sp. KMM 9048. Four of the compounds (3–6) were found to be similar but not identical to the known chromomycins A2, A3, demethyl chromomycin A3 and A4. The two remaining compounds, A2–1 (1) and A3–1 (2), were established as novel chromomycin analogs, which did not contain sugar B. Spectroscopic methods including 1D and 2D NMR, and HRMS and MS/MS were applied for structure elucidation. Compounds 1-5 showed strong antimicrobial activity against Gram-positive indicatory bacteria Enterococcus faecium, Staphylococcus aureus, S. epidermidis, and Bacillus subtilis. Antitumor assay indicated that all tested compounds, in different manners, inhibited colony formation of RPMI-7951 and SK-Mel-28 cancer cells. This is the first study reporting the inhibitory effects of chromomycin analogs 1–5 on the colony formation of the investigated cancer cell lines. Compound 3, in a concentration of 5 nM, inhibited colony formation of RPMI-7951 and SK-Mel-28 cells by 82 % and 72 %, respectively. Our finding indicated that, of the compounds tested, 3 and 4 are promising anticancer and antimicrobial agents.

A harmine-derived beta-carboline displays anti-cancer effects in vitro by targeting protein synthesis

Growing evidence indicates that protein synthesis is deregulated in cancer onset and progression and targeting this process might be a selective way to combat cancers. While harmine is known to inhibit DYRK1A and intercalate into the DNA, tri-substitution was shown previously to modify its activity profile in favor of protein synthesis inhibition. In this study, we thus evaluated the optimized derivative CM16 in vitro anti-cancer effects unfolding its protein synthesis inhibition activity. Indeed, the growth inhibitory profile of CM16 in the NCI 60-cancer-cell-line-panel correlated with those of other compounds described as protein synthesis inhibitors. Accordingly, CM16 decreased in a time- and concentration-dependent manner the translation of neosynthesized proteins in vitro while it did not affect mRNA transcription. CM16 rapidly penetrated into the cell in the perinuclear region of the endoplasmic reticulum where it appears to target translation initiation as highlighted by ribosomal disorganization. More precisely, we found that the mRNA expression levels of the initiation factors EIF1AX, EIF3E and EIF3H differ when comparing resistant or sensitive cell models to CM16. Additionally, CM16 induced eIF2α phosphorylation. Those effects could explain, at least partly, the CM16 cytostatic anti-cancer effects observed in vitro while neither cell cycle arrest nor DNA intercalation could be demonstrated. Therefore, targeting protein synthesis initiation with CM16 could represent a new promising alternative to current cancer therapies due to the specific alterations of the translation machinery in cancer cells as recently evidenced with respect to EIF1AX and eIF3 complex, the potential targets identified in this present study.

Marine Drugs Regulating Apoptosis Induced by Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)

Marine biomass diversity is a tremendous source of potential anticancer compounds. Several natural marine products have been described to restore tumor cell sensitivity to TNF-related apoptosis inducing ligand (TRAIL)-induced cell death. TRAIL is involved during tumor immune surveillance. Its selectivity for cancer cells has attracted much attention in oncology. This review aims at discussing the main mechanisms by which TRAIL signaling is regulated and presenting how marine bioactive compounds have been found, so far, to overcome TRAIL resistance in tumor cells.

Drugs from marine sources: modulation of TRAIL induced apoptosis in cancer cells

There have been overwhelming advances in molecular oncology and data obtained through high-throughput technologies have started to shed light on wide ranging molecular mechanisms that underpin cancer progression. Increasingly it is being realized that marine micro-organisms and the biodiversity of plankton are rich sources of various anticancer compounds. Marine derived compounds play major roles in inducing apoptosis in cancer cells. More importantly, various agents have been noted to enhance TRAIL induced apoptosis in cancer cells by functionalizing intrinsic and extrinsic pathways. In this commentary, a list of marine derived compounds reported to induce apoptosis is discussed.

Natural compounds with Wnt signal modulating activity

This article highlights natural compounds that are reported to modulate the Wnt signalling activity. The plausible mechanisms of action of the natural Wnt modulators are also presented.

Chromomycin A2 induces autophagy in melanoma cells

The present study highlights the biological effects of chromomycin A2 toward metastatic melanoma cells in culture. Besides chromomycin A2, chromomycin A3 and demethylchromomycin A2 were also identified from the extract derived from Streptomyces sp., recovered from Paracuru Beach, located in the northeast region of Brazil. The cytotoxic activity of chromomycin A2 was evaluated across a panel of human tumor cell lines, which found IC50 values in the nM-range for exposures of 48 and 72 h. MALME-3M, a metastatic melanoma cell line, showed the highest sensitivity to chromomycin A2 after 48h incubation, and was chosen as a model to investigate this potent cytotoxic effect. Treatment with chromomycin A2 at 30 nM reduced cell proliferation, but had no significant effect upon cell viability. Additionally, chromomycin A2 induced accumulation of cells in G0/G1 phase of the cell cycle, with consequent reduction of S and G2/M and unbalanced expression of cyclins. Chromomycin A2 treated cells depicted several cellular fragments resembling autophagosomes and increased expression of proteins LC3-A and LC3-B. Moreover, exposure to chromomycin A2 also induced the appearance of acidic vacuolar organelles in treated cells. These features combined are suggestive of the induction of autophagy promoted by chromomycin A2, a feature not previously described for chromomycins.

Isolation of β-Indomycinone Guided by Cytotoxicity Tests from Streptomyces sp. IFM11607 and Revision of its Double Bond Geometry

The antibiotic β-indomycinone was isolated from Streptomyces sp. IFM11607 by cytotoxicity-guided fractionation against human gastric adenocarcinoma AGS cells, and the geometry of its Δ17,18-double bond was revised from E to Z based on the coupling constant.