Alternol inhibits proliferation and induces apoptosis in mouse lymphocyte leukemia (L1210) cells

Overview of Bioactive Fungal Secondary Metabolites: Cytotoxic and Antimicrobial Compounds

Microorganisms are known as important sources of natural compounds that have been studied and applied for different purposes in distinct areas. Specifically, in the pharmaceutical area, fungi have been explored mainly as sources of antibiotics, antiviral, anti-inflammatory, enzyme inhibitors, hypercholesteremic, antineoplastic/antitumor, immunomodulators, and immunosuppressants agents. However, historically, the high demand for new antimicrobial and antitumor agents has not been sufficiently attended by the drug discovery process, highlighting the relevance of intensifying studies to reach sustainable employment of the huge world biodiversity, including the microorganisms. Therefore, this review describes the main approaches and tools applied in the search for bioactive secondary metabolites, as well as presents several examples of compounds produced by different fungi species with proven pharmacological effects and additional examples of fungal cytotoxic and antimicrobial molecules. The review does not cover all fungal secondary metabolites already described; however, it presents some reports that can be useful at any phase of the drug discovery process, mainly for pharmaceutical applications.

Alternol triggers immunogenic cell death via reactive oxygen species generation

Alternol is a naturally occurring compound that exerts antitumor activity in several cancers. However, whether Alternol induces antitumor immune response remains unknown. In this study, we investigated whether Alternol induced immunogenic cell death (ICD) in prostate cancer cells. Alternol triggered ICD in prostate cancer cells, as evidenced by the release of damage-associated molecular patterns (DAMPs) (i.e., calreticulin, CALR; high mobility group protein B1, HMGB1; and adenosine triphosphate, ATP) and pro-inflammatory cytokine (i.e., interleukin [IL]-1α, IL-1β, IL-6, and IL-8) expression. Alternol facilitated tumor-associated antigen uptake and cross-presentation, CD8 + T-cell priming, and T-cell infiltration in tumor-draining lymph nodes (LNs) and tumors. The presence of Alternol fostered antitumor immune response in vivo, resulting in delayed tumor growth and prolonged survival. Moreover, inhibition of reactive oxygen species (ROS) generation blocked Alternol-induced upregulation of pre-inflammation cytokines, endoplasmic reticulum (ER) stress, and consequent antitumor immune response. Overall, our data indicate that Alternol triggers ICD in prostate cancer cells, which is mediated by ROS generation.

Alternol Sensitizes Renal Carcinoma Cells to TRAIL-Induced Apoptosis

Purpose: Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), a member of the TNF family, can selectively induce cancer cell death while sparing normal cells. However, the application of TRAIL-based antitumor therapies has been hindered due to drug resistance. Alternol is a new compound isolated from microbial fermentation that possesses antitumor activity in different tumors. In our research, we discovered that alternol can sensitize TRAIL-induced apoptosis in renal carcinoma cells (RCCs).

Materials and Methods: Cytotoxic activity was measured by MTT assay. Apoptosis was probed using the PI/annexin V method. Real-time PCR and western blot were used to test the levels of mRNA and protein, respectively. Luciferase assay was used to investigate whether CHOP regulated the expression of death receptor (DR) 5 through transcription. A xenogeneic tumor transplantation model was used to evaluate the anticancer effects of alternol/TRAIL in vivo.

Results: When the mechanisms were investigated, we discovered that alternol increased DR5 expression. DR5 knockdown by siRNA eliminated the enhanced effect of alternol on TRAIL-mediated apoptosis. Alternol reduced the expression of antiapoptotic proteins and increased the levels of proapoptotic proteins. Moreover, alternol increased the level of CHOP, which is necessary for the enhancing effect of alternol on TRAIL-induced apoptosis, given that downregulation of CHOP abrogated the synergistic effect. DR5 upregulation induced by alternol required the production of reactive oxygen species (ROS). Removing ROS inhibited the induction of DR5 and blocked the antiapoptotic proteins induced by alternol.

Conclusion: Taken together, our research suggested that alternol increased TRAIL-mediated apoptosis via inhibiting antiapoptotic proteins and upregulating DR5 levels via ROS generation and the CHOP pathway.

Alternol/Alteronol: Potent Anti-cancer Compounds With Multiple Mechanistic Actions

Alternol and its oxidate isomer Alteronol are small compounds isolated from the fermentation of a mutant fungus obtained from Taxus brevifolia bark. Preclinical studies showed their potent anti-cancer activities, including attenuating cellular survival pathways, altering protein levels of cell cycle regulators, activating xanthine dehydrogenase to cause accumulation of cellular reactive oxygen species and disrupting cell metabolism by disturbing four Krebs cycle enzymes specifically in malignant cells while having no significant effect on benign cells. In cancer cell culture models, Alternol or Alteronol exert their anti-cancer effect by inducing cell cycle arrest and triggering apoptotic cell death. In mice xenograft models, Alternol or Alteronol potently suppresses tumor growth with no obvious toxicity to the host with a wide therapeutic index over 30-fold. In conclusion, Alternol or Alteronol possess a great potential and feasibility to be developed as an effective anti-tumor therapeutic.

Autophagy inhibition potentiates the anti-EMT effects of alteronol through TGF-β/Smad3 signaling in melanoma cells

Accumulating evidence demonstrated that alteronol, a novel compound that has a similar structure with paclitaxel, exerts anticancer effects against diversified tumors. However, whether alteronol induces autophagy and the relationship between its anticancer effects and autophagy in melanoma remains elusive. In this study, we show that alteronol induces not only anti-proliferation activity and apoptosis but also autophagy in A375 and UACC62 cells. In addition, alteronol inhibits A375 and UACC62 cells invasion and migration by preventing the epithelial–mesenchymal transition (EMT). Blocking autophagy enhances alteronol-induced apoptosis and anti-EMT effects in vitro and in vivo. Mechanistically, we find that alteronol significantly inhibits Akt/mTOR and TGFβ/Smad3 pathways, and co-treatment with autophagy inhibitor 3-MA further potentiate these effects. Our results suggest that alteronol induces cyto-protective autophagy in melanoma cells through inhibition of Akt/mTOR pathway, thus attenuates apoptosis and promotes melanoma cell EMT through TGF-β/Smad3 pathway. Combination with alteronol and autophagy inhibitor 3-MA may be a potential treatment for melanoma as it not only significantly inhibited tumor growth but also suppressed tumor invasion and migration as anti-metastasis agent.

Alteronol Enhances the Anti-tumor Activity and Reduces the Toxicity of High-Dose Adriamycin in Breast Cancer

The first-line chemotherapy drug adriamycin (ADM) is widely used for the treatment of breast cancer, but the acquired drug resistance and the normal tissue toxicity remain clinical challenges. Alteronol has been reported to exert wide-ranging anti-tumor activity. In this study, we firstly examined the synergistic anti-tumor effects and the underlying mechanisms of alteronol combined with ADM in breast cancer. We have found that the combination of alteronol and ADM significantly suppressed the expression levels of the cell cycle-related proteins (CDC2 and Cyclin B1) and induced cell cycle arrest at the G2/M phase, leading to cell proliferation inhibition in breast cancer 4T1 cells. Moreover, co-treatment of alteronol and ADM (i) remarkably activated p38 and JNK kinases, (ii) elevated ROS levels, (iii) triggered mitochondrial dysfunction, (iv) released cytochrome c into the cytoplasm, (v) upregulated apoptosis-related proteins, e.g., cleaved PARP, Bax, and cleaved caspase-3/9, and (vi) downregulated the expression of Bcl-2, followed by apoptosis. Furthermore, our in vivo studies showed that the low-dose combination of alteronol (2 mg/kg) and ADM (1 mg/kg) significantly inhibited tumor growth in tumor bearing mice, and the anti-tumor effect of the combination was the same as that of high-dose ADM (8 mg/kg). In addition, the low-dose combination group showed lower toxicities to major organs than the high-dose ADM group. Taken together, these data demonstrate that the low-dose combination of alteronol and ADM could notably improve the anti-tumor activity and have lower toxicities to major organs than those in high-dose ADM group.

Alteronol induces cell cycle arrest and apoptosis via increased reactive oxygen species production in human breast cancer T47D cells

Objective

Emerging evidence showed that alteronol has a potential antitumour effect in several tumour cells. However, the antitumour effect of alteronol on breast cancer has not been reported. This study investigated the mechanisms of alteronol-induced cell proliferation inhibition in human breast cancer T47D cells.

Methods

After treatment with alteronol, T47D cell proliferation was examined by MTT assay. The cell cycle distribution, cell apoptosis, reactive oxygen species level and mitochondrial membrane potential were evaluated via flow cytometry. Next, the protein levels of cyclin B1, cdc2, p21, p-cyclin B1, p-cdc2, p53, Bax, Bcl-2 and cytochrome c were analysed using Western blot analysis. Meanwhile, the mRNA levels of cyclin B1, cdc2, p21 and p53 were examined by qRT-PCR.

Key findings

Our data showed that alteronol inhibited the proliferation of T47D cells via inducing G2-phase arrest and cell apoptosis. Compared with control group, alteronol significantly increased ROS level and triggered mitochondrial dysfunction in alteronol-treated T47D cells. Further studies showed that the mRNA and protein levels of cdc2 and cyclin B1 were downregulated, while the mRNA and protein levels of p21, p53, p-cyclin B1, p-cdc2 and cytochrome c were upregulated. In addition, the expression level of Bax was increased, and the expression level of Bcl-2 was decreased.

Conclusions

Alteronol induced T47D cell cycle arrest and cell apoptosis through increasing ROS production and triggering mitochondrial dysfunction, and subsequently inhibiting T47D cell proliferation.

Alternol, a natural compound, exerts an anti-tumour effect on osteosarcoma by modulating of STAT3 and ROS/MAPK signalling pathways

Osteosarcoma (OS) is the most frequent primary malignant bone tumour. Alternol, a novel compound purified from microbial fermentation products exerts anti-tumour effects across several cancer types. The effect of alternol on human OS remains to be elucidated. We first evaluated the anti-tumour effect of alternol in several human OS cell lines in vitro and investigated its underlying mechanism. Alternol inhibited OS cell proliferation, migration and induced caspase-dependent apoptosis, G2/M cell cycle arrest in a dose and time-dependent manner. Moreover, alternol treatment inhibited signal transducer and activator of transcription-3 (STAT3) phosphorylation in 143B and MG63 human OS cells, as evaluated using a STAT3-dependent dual luciferase reporter system. Exposure to alternol resulted in excessive reactive oxygen species (ROS) generation and Jun amino-terminal kinases (JNK), extracellular signal-regulated kinases (ERK1/2) and p38 activation. Furthermore, alternol-induced cell death was significantly restored in the presence of the ROS scavenger, N-acetyl-l-cysteine (NAC) or a caspase inhibitor Z-VAD-FMK. NAC also prevented G2/M phase arrest and phosphorylation of mitogen-activated protein kinases (MAPK), but did not reverse STAT3 inactivation. Finally, alternol suppressed tumour growth in vivo in the nude mouse OS tibia orthotopic model. Immunohistochemistry revealed that alternol treatment resulted in down-regulation of phosph-STAT3 Tyr705 and up-regulation of cleaved caspase-3 and phosph-SAPK (Stress-activated protein kinases)/JNK expression. Taken together, our results reveal that alternol suppresses cell proliferation, migration and induces apoptosis, cell cycle arrest by modulating of ROS-dependent MAPK and STAT3 signalling pathways in human OS cells. Therefore, alternol is a promising candidate for developing anti-tumour drugs target OS.

Alternol inhibits the proliferation and induces the differentiation of the mouse melanoma B16F0 cell line

High malignant potential and low susceptibility to treatment are characteristics of malignant melanoma. Alternol, a novel compound purified from microbial fermentation products obtained from the bark of the yew tree, exhibits a variety of antitumor activities. Based on these findings, the aim of the present study was to extend the knowledge on the antineoplastic effect of alternol in the mouse melanoma B16F0 cell line. Alternol significantly inhibited the proliferation and colony formation of B16F0 cells in a dose-dependent manner as detected by MTT and soft agar colony formation assays. NaOH alkaline lysis and oxidation of Dopa indicated that alternol enhanced the melanin content and tyrosinase activity of the B16F0 cells and results also showed a dose‑response relationship. Morphologic changes accompanied by extended dendrites were discovered in the B16F0 cells after treatment with alternol. Furthermore, the mRNA levels of tyrosinase, Trp1 and Trp2 were increased by alternol. Our results confirmed that alternol possesses marked antineoplastic properties against melanoma cells, indicating that this microbial fermentation product is a promising agent for the differentiation therapy of cancer. The inhibition of cell proliferation and colony formation by alternol was associated with both cytotoxicity and induction of differentiation.

Growth inhibition and apoptosis induction by alternol in pancreatic carcinoma cells

AIM: To investigate the effect of alternol on pancreatic cancer cells.

METHODS: Pancreatic cancer cells PANC-1 and BxPC3 were treated with various concentrations of alternol for 24, 48 and 72 h. Cell proliferation was measured by cell counting. Cell cycle distribution and mitochondrial membrane potential were determined by flow cytometry. Apoptosis was determined by a TdT-mediated dUTP nick end labeling assay and Hoechst staining. Expression of caspase 3, Bcl-2, p53 and p21 was measured by western blotting.

RESULTS: Alternol showed dose- and time-dependent inhibition of the proliferation of PANC-1 and BxPC3 cells in vitro. Alternol induced apoptosis and cell cycle arrest at S phase and decreased mitochondrial membrane potential. Alternol activated caspase 3, upregulated p53 and p21 expression, and downregulated Bcl-2 expression in a dose-dependent manner.

CONCLUSION: Our results suggested that alternol is a candidate for treatment of pancreatic cancer.

Alternol inhibits migration and invasion of human hepatocellular carcinoma cells by targeting epithelial-to-mesenchymal transition

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related deaths worldwide. Such deaths are due, in large part, to its propensity to metastasize. We have examined the effect of alternol on human HCC cells and the underlying molecular mechanism. Therapeutic effects of alternol on cancer cell migration and invasion were analyzed with Boyden chamber and wound healing assays. Effects of alternol on the levels of various proteins involved in cancer cell migration and invasion were determined with gelatin zymography, immunofluorescence, and Western blotting. As shown, treatment with alternol has resulted in a concentration-dependent inhibition of cell migration and invasion of HepG2 cells. The inhibition of HCC invasion by alternol was associated with the suppression of MMP-9 expression and reversal of epithelial-to-mesenchymal transition (EMT). The above results indicated that alternol has the ability to inhibit the migration and invasion of human HCC cells by reversing the process of EMT, suggesting that alternol may be developed as an alternative drug for the treatment of HCC.

Natural compound Alternol induces oxidative stress-dependent apoptotic cell death preferentially in prostate cancer cells

Prostate cancers at the late stage of castration resistance are not responding well to most of current therapies available in clinic, reflecting a desperate need of novel treatment for this life-threatening disease. In this study, we evaluated the anticancer effect of a recently isolated natural compound, Alternol, in multiple prostate cancer cell lines with the properties of advanced prostate cancers in comparison to prostate-derived nonmalignant cells. As assessed by trypan blue exclusion assay, significant cell death was observed in all prostate cancer cell lines except DU145 but not in nonmalignant (RWPE-1 and BPH1) cells. Further analyses revealed that Alternol-induced cell death was an apoptotic response in a dose- and time-dependent manner, as evidenced by the appearance of apoptosis hallmarks such as caspase-3 processing and PARP cleavage. Interestingly, Alternol-induced cell death was completely abolished by reactive oxygen species scavengers N-acetylcysteine and dihydrolipoic acid. We also demonstrated that the proapoptotic Bax protein was activated after Alternol treatment and was critical for Alternol-induced apoptosis. Animal xenograft experiments in nude mice showed that Alternol treatment largely suppressed tumor growth of PC-3 xenografts but not Bax-null DU-145 xenografts in vivo. These data suggest that Alternol might serve as a novel anticancer agent for patients with late-stage prostate cancer.

Alternol induces an S-phase arrest of melanoma B16F0 cells

Alternol is a novel compound purified from the fermentation products of a microorganism in the yew tree bark. This study looks at the effects of alternol on the proliferation and cell cycle distribution of mouse melanoma cells. The inhibition of cell proliferation and changes in cell cycle distribution were analysed by sulforhodamine B and flow cytometry assays, respectively. mRNA expression of cyclin A, cyclin-dependent kinase 2 (CDK2), proliferating cell nuclear antigen (PCNA) and CDK inhibitor1A (p21) were measured by real-time reverse transcription PCR (RT-PCR). The protein levels of cyclin A, CDK2 and PCNA were analysed by Western blot analysis. p21 was measured by ELISA. Alternol treatment caused a significant decrease in the proliferation rate of B16F0 and B16F10 cells, which were significantly arrested in S phase, but this treatment had less effect on normal human embryonic kidney 293T cells. The mechanism by which alternol inhibits B16F0 proliferation in vitro may be associated with the inhibition of CDK2 and PCNA, and the activation of p21.

Alteronol inhibits the invasion and metastasis of B16F10 and B16F1 melanoma cells in vitro and in vivo

AIMS

The purpose of this study is to evaluate the anti-metastatic effects of alteronol on melanoma B16F10 and B16F1 cells in vitro and in vivo.

MAIN METHODS

Melanoma B16F1 and B16F10 cells were cultured in vitro. Cell proliferation was analyzed via 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. The cell migration and invasion were evaluated via wound healing and transwell chamber assays. The activity of matrix metalloproteinase 2 (MMP-2) in culture supernatants was assessed via gelatin zymography. The expression of MMP-2 and TIMP-2 were detected via enzyme-linked immunosorbent assay (ELISA) assay. The anti-metastatic ability in vivo was detected through experimental lung metastasis.

KEY FINDINGS

The data indicate that alteronol can inhibit the proliferation, invasion, and migration of B16F1 and B16F10 cells in vitro and in vivo, decrease the activity and expression of MMP-2, enhance the expression level of Tissue Inhibitor of Metalloproteinase-2 (TIMP-2), and inhibit the experimental lung metastasis of B16F1 and B16F10 cells.

SIGNIFICANCE

Although alteronol and taxol are obtained from the same source, these substances do not destroy the rare resource; the mechanisms of them on tumor growth inhibition are different. Conversely, alteronol treatment had lesser effects on normal cells revealing for a selective property and a strong competitive advantage.

Alternol exerts prostate-selective antitumor effects through modulations of the AMPK signaling pathway

BACKGROUND

Alternol is an original compound purified from the fermentation products of Alternaria alternata var. monosporus, a microorganism from the bark of the yew tree. It has been reported that Alternol can inhibit proliferation of mouse leukemia cells and human gastric carcinoma cells, the aim of this study was to investigate the effects of Alternol on prostate cancer cells in comparison to prostate cells.

METHODS

The MTT assay was utilized to assess cell viability. Cell cycle was analyzed by flow cytometry with propidium iodide staining. Protein expression levels were examined by Western blotting.

RESULTS

Alternol treatment resulted in a significant decrease in the viability of prostate cancer cells but had lesser effects on prostate cells. Alternol inhibited AMP-activated protein kinase (AMPK) phosphorylation in prostate cancer C4-2 cells but stimulated AMPK phosphorylation in prostate RWPE-1 cells. Inhibition of p27 phosphorylation was observed in C4-2 cells whereas a promotion of p27 phosphorylation was seen in RWPE-1 cells. Alternol treatment resulted in a profound increase in the LC3II/LC3I protein ratio in RWPE-1 cells but not in C4-2 cells. A dose-dependent down-regulation of Bcl-2 protein was detected in C4-2 cells but not in RWPE-1 cells. Pretreatment of cells with Compound C (AMPK inhibitor) before Alternol treatment abolished the selective antitumor effect of Alternol.

CONCLUSIONS

These results reveal for the first time that Alternol exerts a selective antitumor effect on prostate cancer cells when compared with RWPE-1 prostate epithelial cells. In addition, the AMPK signaling pathway is responsible for the selective antitumor effects of Alternol.

Biological activities of the fermentation extract of the endophytic fungus Alternaria alternata isolated from Coffea arabica L

A total of 22 endophytic fungi isolated from coffee (Coffea arabica L.) were cultivated in vitro and their crude extracts tested. The screening was carried out using the agar diffusion method against Staphylococcus aureus, Escherichia coli and Candida albicans. The most effective isolate was Alternaria alternata, and subsequently, its extract was assayed. The total phenolic content was 3.44 μg GAE/mg of the crude extract. For the antibacterial and antifungal activity assays, minimum inhibitory concentrations (MIC) and minimum bactericidal and fungicidal concentrations (MBC and MFC) were determined. The ranges of MIC values were 50-100 μg/mL for S. aureus and 400-800 μg/mL for E. coli. The extract did not show activity in the tested concentrations for C. albicans. The fungal crude extract was assayed for antioxidant activities. Its ability to scavenge DPPH radicals and antioxidant activity by β-carotene/linoleic acid system oxidation was not significant. In addition, antitumor activity was studied using the MTT assay. At a dilution of 400 μg/mL, the extract displayed a cytotoxic activity of approximately 50% towards HeLa cells in vitro. The results indicate that endophytic fungi could be a promising source of bioactive compounds and warrant further study.