Fungal substances as modulators of NF-κB activation pathway

Development of a High-throughput NanoBRET Screening Platform to Identify Modulators of the RAS/RAF Interaction

Activating mutations in RAS are found in approximately 30% of human cancers, resulting in the delivery of a persistent signal to critical downstream effectors that drive tumorigenesis. RAS-driven malignancies respond poorly to conventional cancer treatments and inhibitors that target RAS directly are limited; therefore, the identification of new strategies and/or drugs to disrupt RAS signaling in tumor cells remains a pressing therapeutic need. Taking advantage of the live-cell bioluminescence resonance energy transfer (BRET) methodology, we describe the development of a NanoBRET screening platform to identify compounds that modulate binding between activated KRAS and the CRAF kinase, an essential effector of RAS that initiates ERK cascade signaling. Using this strategy, libraries containing synthetic compounds, targeted inhibitors, purified natural products, and natural product extracts were evaluated. These efforts resulted in the identification of compounds that inhibit RAS/RAF binding and in turn suppress RAS-driven ERK activation, but also compounds that have the deleterious effect of enhancing the interaction to upregulate pathway signaling. Among the inhibitor hits identified, the majority were compounds derived from natural products, including ones reported to alter KRAS nanoclustering (ophiobolin A), to impact RAF function (HSP90 inhibitors and ROS inducers) as well as some with unknown targets and activities. These findings demonstrate the potential for this screening platform in natural product drug discovery and in the development of new therapeutic agents to target dysregulated RAS signaling in human disease states such as cancer.

Promising Anti-cancer Therapeutics From Mushrooms: Current Findings and Future Perceptions

BACKGROUND

Nowadays, medicines derived from natural sources have drawn much attention as potential therapeutic agents in the suppression and treatment of cancer because of their low toxicity and fewer side effects.

OBJECTIVE

The present review aims to assess the currently available knowledge on the ethnomedicinal uses and pharmacological activities of bioactive compounds obtained from medicinal mushrooms towards cancer treatment.

METHODS

A literature search has been conducted for the collection of research papers from universally accepted scientific databases. These research papers and published book chapters were scrutinized to retrieve information on ethnomedicinal uses of mushrooms, different factors involved in cancer cell proliferation, clinical and in silico pharmaceutical studies made for possible treatments of cancer using mushroom derived compounds. Overall, 241 articles were retrieved and reviewed from the year 1970 to 2020, out of which 98 relevant articles were finally considered for the preparation of this review.

RESULTS

This review presents an update on the natural bioactive substances derived from medicinal mushrooms and their role in inhibiting the factors responsible for cancer cell proliferation. Along with it, the present review also provides information on the ethnomedicinal uses, solvents used for extraction of anti-cancer metabolites, clinical trials, and in silico studies that were undertaken towards anticancer drug development from medicinal mushrooms.

CONCLUSION

The present review provides extensive knowledge on various anti-cancer substances obtained from medicinal mushrooms, their biological actions, and in silico drug designing approaches, which could form a basis for the development of natural anti-cancer therapeutics.

Erinacine A and related cyathane diterpenoids: Molecular diversity and mechanisms underlying their neuroprotection and anticancer activities

The presence of a fused 5/6/7 tricyclic core characterizes the group of cyathane diterpene natural products, that include more than 170 compounds, isolated from fungi such as Cyathus africanus and Hericium erinaceus. These compounds have a common biosynthetic precursor (cyatha-3,12-diene) and can be produced bio- or hemi-synthetically, or via total syntheses. Cyathane diterpenes display a range of pharmacological properties, including anti-inflammatory (possibly through binding to the iNOS protein) and neuroprotective effects. Many cyathanes like cyahookerin C, cyathin Q and cyafranines B and G can stimulate neurite outgrowth in cells, whereas conversely a few molecules (such as scabronine M) inhibit NGF-stimulated neurite outgrowth. The main anticancer cyathanes are erinacine A and cyathins Q and R, with a capacity to trigger cancer cell death dependent on the production of reactive oxygen species (ROS). These compounds, active both in vitro and in vivo, activate different signaling pathways in tumor cells to induce apoptosis (and autophagy) and to upregulate the expression of several proteins implicated in the organization and functioning of the actin cytoskeleton. An analysis of the functional analogy between erinacine A and other natural products known to interfere with the actin network in a ROS-dependent manner (notably cucurbitacin B) further supports the idea that erinacine A functions as a perturbator of the cytoskeleton organization. Collectively, we provide an overview of the molecular diversity of cyathane diterpenes and the main mechanisms of action of the lead compounds, with the objective to encourage further research with these fungal products. The anticancer potential of erinacine A deserves further attention but it will be necessary to better characterize the implicated targets and signaling pathways.

Development of an enzyme linked immunosorbent assay for detection of cyathane diterpenoids

Background

So-called cyathane type diterpenoids are produced as secondary metabolites by basidiomycetes. Based on their antibacterial, fungicidal, and cytotoxic properties, cyathane type terpenoids represent interesting target compounds in fungal biotechnology.

Results

An indirect competitive enzyme linked immunosorbent assay has been developed for detection of cyathane type diterpenoids. Rabbit polyclonal antibodies were raised against a mixture of striatal A and B conjugated to bovine serum albumin. The conditions for direct attachment of the hapten striatal B to a solid phase by passive adsorption were optimized. The cross reactivities of the striatals A, C and D, of the striatins A and B, and of the erinacines C and P to striatal B were determined. The validation study showed that the ELISA was precise and sensitive. The average IC₅₀ of striatal B was 36.0 ng mL⁻¹ with an inter-assay coefficient of variation (CV) of 13.2% (n = 5). Recoveries from striatal B spiked samples in the assay were in the range of 97.3 – 125.9%. A good correlation between the striatal B concentration measured by the ELISA and by HPLC-DAD (y = 1.1122× – 0.1585, R² = 0.9942) was obtained from linear regression analysis. The suitability of the ELISA for detection of cyathane type diterpenoids in submerged cultures and fruiting bodies of H. erinaceus was studied. It showed cross reactivity with supernatants from submerged cultures and extracts thereof, but did not show cross reactivity with extracts from fruiting bodies.

Conclusions

The developed method is appropriate for qualitative and quantitative detection of cyathane diterpenoids in complex mixtures. Due to its high sensitivity and specificity, it represents an ideal screening method for discovering new cyathane diterpenoids and new potential producers of them.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-014-0098-4) contains supplementary material, which is available to authorized users.

Analysis of cyathane-type diterpenoids from Cyathus striatus and Hericium erinaceus by high-resolution MALDI MS imaging

Fungal secondary metabolites in both fruiting bodies and pellets from submerged cultures of basidiomycetes were analyzed by atmospheric pressure matrix-assisted laser desorption/ionization-mass spectrometry imaging at a lateral resolution of 15 μm, a mass resolution of 140,000 at m/z 200 and a mass accuracy of better than 2 ppm. The striatals A, B, C, and D, and a number of erinacine type metabolites were detected in the basidiomycetes Cyathus striatus and Hericium erinaceus, respectively. The two fungi were selected as model species, as they are well-known for efficient production of terpenoid secondary metabolites with interesting biological activities, e.g., antibacterial, fungicidal, cytotoxic properties, and stimulating effects on nerve growth factor synthesis. The localization of metabolites revealed a mostly homogeneous distribution of the striatals in the pellets of C. striatus, while a concentration gradient, increasing to the center, was observed in the pellets of H. erinaceus. A mostly homogeneous distribution of metabolites was also found in the fruiting body of H. erinaceus.

The expression of iNOS and nitrotyrosine in colitis and colon cancer in humans

Chronic inflammation increases the risk of development of several types of malignancies including colon cancer. It also represents a paradigm for the connection between inflammation and cancer in terms of epidemiology and mechanistic studies in preclinical models. A key component of inflammation promoting cancer is the transcription factor NF-κB, which is known to play a critical role in the regulation of the inducible nitric oxide synthase (iNOS) gene. iNOS is an enzyme dominantly expressed during inflammatory reactions. Although synthesis of high amounts of nitric oxide (NO) by iNOS has been demonstrated in pathophysiological processes, such as acute or chronic inflammation and tumorigenesis, the role of iNOS activity in these diseases is still not well understood. Analysis of human biopsies of colitis and colon cancer using immunohistochemistry revealed elevated iNOS protein expression levels, which were strongly paralleled by increased expression of nitrotyrosine suggesting that iNOS has been highly activated in these tissues. These results were corroborated in an in vitro study showing the presence of high iNOS levels in a colon cancer cell line (HT-29) following inflammatory stimuli (TNF-α, peroxynitrite). In addition, the involvement of metastatic processes in the colon biopsies was assessed by means of in situ zymography of MMP activation. MMP 2 (gelatinase A) activation was higher in histopathological sections of colitis and cancer compared to controls. Overall, these data strengthen the findings that in inflammation and colon cancer in humans, iNOS expression and tyrosine nitration may be an indicator of cancer development and progression.

Anti-leukemic and immunomodulatory effects of fungal metabolites of Pleurotus pulmonarius and Pleurotus ostreatus on benzene-induced leukemia in Wister rats

BACKGROUND

The use of natural bioactive compounds in conventional chemotherapy is a new direction in cancer treatment that is gaining more research attention recently. Bioactive polysaccharides and polysaccharide-protein complexes from some fungi (edible mushrooms) have been identified as sources of effective and non-toxic antineoplastic agents. Selected oyster mushrooms (Pleurotus pulmonarius and P. ostreatus being local [Nigeria] and exotic strains, respectively) were cultured on a novel medium of yeast extract supplemented with an ethanolic extract of Annona senegalensis, and the antileukemic potential of their metabolites was studied.

METHODS

Leukemia was successfully induced in Wister rats by intravenous injection (0.2 mL) of a benzene solution every 2 days for 3 consecutive weeks. The aqueous solution of fungal metabolites (20 mg/mL) produced by submerged fermentation was orally administered (0.2 mL) before, during, and after leukemia induction. Leukemia burden was assessed by comparing the hematological parameters at baseline and after leukemia induction. The immunomodulatory potential of the metabolites was assessed by using a phagocytic assay (carbon clearance method). The ability to enhance leukopoiesis was assessed by using the total leukocyte count.

RESULTS

Leukemia induction resulted in significant anemia indices and leukocytosis (P<0.05) in the experimental rats. Both metabolites equally enhanced leukopoiesis and demonstrated phagocytic actions; P. ostreatus activity was significantly higher than that of P. pulmonarius (P<0.05).

CONCLUSION

The metabolites exhibited profound antileukemic potential by suppressing leukemia and demonstrating immunotherapeutic activities on animals after oral administration in various experimental groups.

Determination of trace elements in anti-influenza virus mushrooms

We have determined the trace element composition of anti-influenza virus mushrooms using atomic absorption spectrophotometer. The elements present in greater concentration in Ganoderma lucidum samples are selenium, iron, and zinc, with selenium being the element with the highest concentration of all, at 416 ± 38.5 mg/kg; in Cordyceps militaris samples are iron, selenium, and zinc, with iron being the element with the highest concentration of all, at 291 ± 20.9 mg/kg; in Kuehneromyces mutabilis samples are selenium, iron, and manganese, with selenium being the element with the highest concentration of all, at 203 ± 9.8 mg/kg; in Inonotus hispidus samples are zinc, selenium, and iron, with zinc being the element with the highest concentration of all, at 194 ± 16.9mg/kg; in the Collybia maculata samples are iron, selenium, and zinc, with iron being the element with the highest concentration of all, at 274 ± 22.2 mg/kg, respectively. The average metal concentrations in mushrooms decreases in the order: selenium > iron > zinc > chromium > manganese > copper > magnesium > lead. After the mice were administered (orally) with mushroom extracts for 8 weeks and inoculated intranasally with viral suspension, element levels in serum were also measured. Highly significantly increased values of Se, Zn, and Mg in the serum of mice supplemented with anti-influenza virus mushrooms were a characteristic finding. Se, Zn, and Mg present in mushrooms may play a direct or indirect role in their anti-influenza virus nature. They may provide prophylactic protection against influenza infection via stimulation of host innate immune response.

A Hypothesis: Supplementation with Mushroom-Derived Active Compound Modulates Immunity and Increases Survival in Response to Influenza Virus (H1N1) Infection

We hypothesize that the mushroom-derived active compound may be a potential strategy for increasing survival in response to influenza virus (H1N1) infection through the stimulation of host innate immune response. The validity of the hypothesis can be tested by immune response to influenza infection as seen through survival percentage, virus clearance, weight loss, natural killer cell cytotoxicity, Tumor Necrosis Factor-α (TNF-α) and Interferon-gamma (IFN-γ) levels, lytic efficiency in the spleens of mice and inducible nitric oxide synthase mRNA expressions in RAW 264.7 murine macrophage cells. The hypothesis may improve people's quality of life, reduce the medical cost of our healthcare system and eliminate people's fears of influenza outbreak.

The effects of dietary supplementation with Agaricales mushrooms and other medicinal fungi on breast cancer: evidence-based medicine

Breast cancer is the most prevalent cancer in women. The most frequent therapeutic approaches for the treatment of this disease are chemotherapy, radiotherapy, hormone therapy, and surgery. Conventional pharmacological treatments cause many harmful side effects in patients. To improve the quality of life of breast cancer patients, researchers have sought alternative adjuvant treatment strategies. To assess the effects of fungi and other basidiomycetes Agaricales on the co-adjuvant treatment of breast cancer, we conducted a literary review of the available scientific evidence. We selected articles published in refereed journals from 1990 to 2011 in Medline, Lilacs, CAPES, Scielo, and Pubmed. Articles written in English, Spanish, and Portuguese were reviewed. We used the following descriptors: Agaricales, medicinal mushroom/fungus, breast cancer, dietary supplementation, synonyms, and related terms. The pharmacological effects of nutritional and medicinal mushrooms have been reported in several experimental clinical studies and have shown promising results in the adjuvant treatment of breast cancer. Adjuvant treatment with mushrooms is associated with improvements in the immunological and hematologic parameters of breast cancer, as well as in the quality of life of these patients. Randomized clinical studies are needed to elucidate the possible mechanisms of action and clinical benefits of these fungi with respect to survival time, disease progression, and metastasis in breast cancer.

Inhibition of TNFα-induced iNOS expression in HSV-tk transduced 9L glioblastoma cell lines by Marasmius oreades substances through NF-κB- and MAPK-dependent mechanisms

Nitric oxide (NO) is a gaseous, radical molecule that plays a role in various physiological processes. Previously, we reported that transduction of murine colon cancer cells (MC38) with herpes simplex virus thymidine kinase (HSV-tk) gene resulted in a significant over-expression of cyclooxygenase-2 (COX-2) and activation of NF-kB pathway. In this study we show that TNFα, but not LPS, was significantly able to stimulate the production of NO in HSV-tk transduced 9L glioblastoma cell lines, mediated by the up-regulation of iNOS transcript and iNOS protein. The TNFα-induced up-regulation of iNOS expression was mediated by MAPK and NF-κB signaling pathways as revealed by using selective pharmaceutical inhibitors. A culture liquid extract of the edible and medicinal mushroom Marasmius oreades that was previously shown to inhibit iNOS expression in MCF-7 was utilized to prepare fractions and evaluate their ability to affect TNFα-induced iNOS expression in HSV tk transduced 9L cell lines. While most of the tested fractions were shown to inhibit TNFα-induced iNOS expression, they targeted different signaling pathways in a selective fashion. Here, we report that fraction SiSiF1 interfered with IKBα phosphorylation and consequently interfered with NF-κB activation pathway. SiSiF1 showed minimal interference with the phosphorylation of p38 and JNK proteins. In contrast, fraction SiSiF3 selectively inhibited the phosphorylation of p38 and fractions SiSiF4 and SiSiF5 selectively inhibited the phosphorylation of JNK with no observed effect against IKBα and p38 phosphorylation. Our data illustrate the complexity of iNOS regulation in HSV tk transduced 9L cell lines and also the richness of natural products with bioactive substances that may act synergistically through different signaling pathways to affect iNOS gene expression.

Chemical characterization, antiproliferative and antiadhesive properties of polysaccharides extracted from Pleurotus pulmonarius mycelium and fruiting bodies

Mushroom polysaccharides are potent substances that exhibit antitumor and immunomodulatory properties. Studies comparing the chemical composition and antitumor-related activities of polysaccharides released by fungal strains under different growth conditions are not available. Thus, the present study compared polysaccharides extracts produced by Pleurotus pulmonarius from mycelium grown in liquid culture (ME) or fruiting bodies (FBE). Polysaccharides of both ME and FBE had a relatively high molecular mass. NMR spectroscopy indicated that ME glucan is an alpha-glucan whereas FBE glucan is a mixture of both alpha- and beta-glucans. Glucose and galactose where the most prominent monosaccharide in both glucans. Treatment of several colon cancer cell lines expressing varying amounts of galectin-3 with the two fungal glucans inhibited their viability and significantly reduced their ability to adhere to the key component of the extracellular matrix, fibronectin, and to a human umbilical vein endothelial cell monolayer, in a time- and dose-dependent manner mainly in those cell lines expressing high amounts of galectin-3. We conclude that ME and FBE glucans may exert a direct antiproliferative effect on cancer cells expressing high galectin-3 concentrations and concomitantly downregulate tumor cell adherence, the latter being directly related to cancer progression and metastasis.

Marasmius oreades substances block NF-kappaB activity through interference with IKK activation pathway

The activation pathway of nuclear transcription factor kappa B (NF-kappaB) is a key mechanism for the progression of carcinogenesis at the molecular level. NF-kappaB is related to the promotion of cell proliferation, inhibition of apoptosis, and the enhancement of tumor metastasis and angiogenesis. Marasmius oreades culture liquid extract, which was previously shown to affect NF-kappaB activation through inhibition of the phosphorylation of the inhibitory protein kappa B (IkappaBalpha), was subjected to liquid chromatography in order to investigate the specific mechanism of action of the active moieties present in the extract. Four fractions were obtained and tested for their abilities to block NF-kappaB activation pathway at different molecular levels. All fractions showed an anti-proliferative potential with no apparent cytotoxicity on MCF7 breast cancer cell line. Two out of the four fractions strongly affected the phosphorylation of IkappaBalpha and the NF-kappaB reporter activity in MCF7 breast cancer cell line. In addition, these two fractions prevented the p65 nuclear translocation and seemed to interfere with the IkappaB kinase (IKK) activation pathway. The IKK pathway is a major cellular signaling pathway set at a crossroad leading to NF-kappaB activation by a variety of stimuli. Also, these two fractions induced apoptosis of MCF7 cells. This study adds additional valuable data to our knowledge on the anticancer potential of fungal metabolites. It is the first report showing the medicinal value of M. oreades as a natural source of low-molecular-weight bioactive substances able to affect the process of tumorogenesis through the direct blockage of NF-kappaB activation at the IKK level.