Selective cytotoxicity of ascochlorin in ER-negative human breast cancer cell lines

Enzymology and biosynthesis of the orsellinic acid derived medicinal meroterpenoids

The advent of synthetic biology has yielded fruitful studies on orsellinic acid-derived meroterpenoids, which reportedly possess important biological activities. Genomics and transcriptomics have significantly accelerated the discovery of the biosynthetic genes for orsellinic acid-derived fungal and plant meroterpenoids. Subsequently, a well-developed heterologous host provides a convenient platform to generate a supply of useful natural products. Furthermore, in vitro reconstitution and genome editing tools have been increasingly employed as efficient means to fully understand the enzyme reaction mechanisms. With the knowledge of the biosynthetic machinery, combinatorial and engineered biosyntheses have yielded novel molecules with improved bioactivities. These studies will lay the foundation for the production of meroterpenoids with novel medicinal properties.

Ascochlorin Suppresses MMP-2-Mediated Migration and Invasion by Targeting FAK and JAK-STAT Signaling Cascades

Human glioblastomas express higher levels of matrix metalloprotease-2 (MMP-2) than low-grade brain tumors and normal brain tissues. Ascochlorin (ASC) has anti-metastatic, anti-angiogenic, and synergistic effect in various types of cancer cells. However, it remains unknown whether ASC can affect cell migration and invasion in malignant human glioma cells. In this study, we found that ASC indeed inhibits cell migration and invasion in U373MG and A172. ASC significantly suppresses the MMP-2 gelatinolytic activity and expression in U373MG and A172. To determine the molecular mechanism by which ASC suppressed cell migration and invasion, we investigated whether ASC could modulate metastasis via focal adhesion kinase (FAK) and janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling, a potential drug target. ASC strongly inhibits the phosphorylation of FAK, and treatment with a FAK inhibitor significantly suppresses cancer cell migration in the presence of ASC. In addition, ASC significantly decreased phosphorylation of JAK2/STAT3, cancer cell migration and nuclear translocation of STAT3. Taken together, these results suggest that ASC inhibits cell migration and invasion by blocking FAK and JAK/STAT signaling, resulting in reduced MMP-2 activity. J. Cell. Biochem. 119: 300-313, 2018. © 2017 Wiley Periodicals, Inc.

[Mitochondria as targets of chemotherapy]

Living organisms have developed a wide variety of energy metabolism to survive within the specialized environments. There is a remarkable diversity in mitochondrial electron transport system, which might be potential targets for chemotherapy. Atovaquone, clinically used to treat malaria and pneumocystis pneumonia, is a specific inhibitor of Qo site in the cytochrome bc(1) complex of Plasmodium falciparum and Pneumocystis jirovecii. Phytopathogenic fungus, Ascochyta viciae produces two antibiotics, ascochlorin and ascofuranone. Ascochlorin specifically binds to inhibit the electron transport of both Qi and Qo sites in cytochrome bc(1) complex. Besides the unique respiratory inhibition, further investigation is in progress to elucidate the effects on cancer cells. On the other hand, ascofuranone specifically inhibits cyanide-insensitive trypanosome alternative oxidase, which is a sole terminal oxidase in the mitochondrion of Trypanosoma brucei, causative of African trypanosomiasis. In vivo study suggests that ascofuranone is a promising candidate for chemotherapeutic agents to treat African trypanosomiasis.

HZ08, a great regulator to reverse multidrug resistance via cycle arrest and apoptosis sensitization in MCF-7/ADM

In early studies, it was demonstrated that R-HZ08, S-HZ08 and the racemate had strong reverse efficacy of multidrug resistance in vitro and in vivo (Yan et al., 2008b). The effect was supposed to have direct interaction with multidrug resistance-associated protein (MRP1) in MCF-7/ADM and P-glycoprotein in K562/A02. According to our latest study, we found HZ08 could enhance chemotherapy induced apoptosis by synergistic action on reactive oxygen species generation, GSH depletion, mitochondrial membrane potential depolarization, cytochrome c release and caspase activation. Moreover, the potential selective effect of HZ08 on resistant cells suggested that HZ08 have specific targets for resistance reversal via apoptosis regulation. Therefore, we traced individual influence of HZ08, not only on apoptosis pathway per se but also on apoptosis related intracellular regulation systems. Then we found HZ08 could increase cells in G(0)/G(1) phase and regulate apoptosis related proteins (Bcl-2, Bax) as well as upstream functional molecules (c-Myc and c-Fos), which are usually abnormal in malignancy and responsible for multidrug resistance in MCF-7/ADM. Thereby, chemotherapy induced apoptosis was promoted. R-HZ08 showed better effect than S-HZ08 or the racemate did in most of targets above. Furthermore, HZ08 did not change the concentration of intracellular Ca(2+) which means it would not have side effect as verapamil does. Considering multidrug resistance is multifactorial, HZ08, especially R-HZ08, which could sensitize apoptosis by multiple improvements of upstream malignant characters, will be a promising drug to enhance the effect of chemotherapy in the treatment of multidrug resistant tumor.

p53-independent induction of G1 arrest and p21WAF1/CIP1 expression by ascofuranone, an isoprenoid antibiotic, through downregulation of c-Myc

Ascofuranone has been shown to have antitumor activity, but the precise molecular mechanism by which it inhibits the proliferation of cancer cells remains unclear. Here, we study the effects of ascofuranone on cell cycle progression in human cancer cells and find that ascofuranone induces G(1) arrest without cytoxicity with upregulation of p53 and p21(WAF1/CIP1) while downregulating c-Myc and G(1) cyclins. Chromatin immunoprecipitation assay and RNA interference studies with cells deficient in p53 and p21 show that ascofuranone induces p21(WAF1/CIP1) expression and subsequent G(1) arrest through the release of p21(WAF1/CIP1) promoter from c-Myc-mediated transcriptional repression, independent of p53. Ascofuranone-induced p21(WAF1/CIP1) associates with CDK2 and prevents CDK2-cyclin E complex formation, leading to the inactivation of E2F transcriptional activity. These results suggest that ascofuranone upregulates p21(WAF1/CIP1) through p53-independent suppression of c-Myc expression, leading to cytostatic G(1) arrest. Thus, ascofuranone represents a unique natural antitumor compound that targets c-Myc independent of p53.

Suillin from the mushroom Suillus placidus as potent apoptosis inducer in human hepatoma HepG2 cells

During the search of new anti-cancer agent from high fungi, the ethyl acetate extract of the mushroom Suillus placidus was found to exhibit a significant cytotoxic activity against human hepatoma HepG2 cells. With bioassay-guided fractionation, a cytotoxic component suillin was isolated from the extract. The anti-cancer effect of suillin was subsequently examined in 8 human cancer cell lines by using MTT assay. It is of interest to note that human liver cancer cells (HepG2 cells, Hep3B cells, and SK-Hep-1) were preferentially killed by suillin with an IC(50) of approximately 2microM in a 48h treatment. Mechanistically. suillin was found for the first time to induce apoptosis in HepG2 cells as characterized by DNA fragmentation, phosphatidyl-serine (PS) externalization, activation of caspase-3, -8, -9, depolarization of mitochondrial membrane potential, as well as release of cytochrome c into the cytosol. Moreover, the apoptosis induced by suillin was suppressed by both caspase-8 and -9 inhibitors. Western blot analysis revealed significant increases in the protein levels of Fas death receptor, adaptor FADD protein, pro-apoptotic protein Bad and a decline of Bid. These results suggest that the induction of apoptosis by suillin is through both death receptor and mitochondrial pathways. Taken together, our results suggest that suillin might be an effective agent to treat liver cancer.

Ascochlorin activates p53 in a manner distinct from DNA damaging agents

Ascochlorin, a prenylphenol antitumor antibiotic, profoundly increases the expression of endogenous p53 by increasing protein stability in the human osteosarcoma cells and human colon cancer cells. Ascochlorin also increases DNA binding activity to the p53 consensus sequence in nuclear extract and enhances transcription of p53 downstream targets. Ascochlorin specifically induces p53 phosphorylation at ser 392 without affecting ser 15 or 20, whereas DNA damaging agents typically phosphorylate these serines. Moreover, ascochlorin does not induce phosphorylation of ATM and CHK1, an established substrate of ATR that is activated by genotoxins, nor does it increase DNA strand break, as confirmed by comet assay. The structure-activity relationship suggests that p53 activation by ascochlorin is related to inhibition of mitochondrial respiration, which is further supported by the observation that respiratory inhibitors activate p53 in a manner similar to ascochlorin. These results suggest that ascochlorin, through the inhibition of mitochondrial respiration, activates p53 through a mechanism distinct from genotoxins.

Apoptosis and inactivation of the PI3-kinase pathway by tetrocarcin A in breast cancers

A survival kinase, Akt, is a downstream factor in the phosphatidylinositide-3'-kinase-dependent pathway, which mediates many biological responses including glucose uptake, protein synthesis and the regulation of proliferation and apoptosis, which is assumed to contribute to acquisition of malignant properties of human cancers. Here we find that an anti-tumor antibiotic, tetrocarcin A, directly induces apoptosis of human breast cancer cells. The apoptosis is accompanied by the activation of a proteolytic cascade of caspases including caspase-3 and -9, and concomitantly decreases phosphorylation of Akt, PDK1, and PTEN, a tumor suppressor that regulates the activity of Akt through the dephosphorylation of polyphosphoinositides. Tetrocarcin A affected neither expression of Akt, PDK1, or PTEN, nor did it affect the expression of Bcl family members including Bcl-2, Bcl-X(L), and Bax. These results suggest that tetrocarcin A could be a potent chemotherapeutic agent for human breast cancer targeting the phosphatidylinositide-3'-kinase/Akt signaling pathway.

Induction of mitochondria-dependent apoptosis through the inhibition of mevalonate pathway in human breast cancer cells by YM529, a new third generation bisphosphonate

YM529, a new third generation bisphosphonate, induced apoptosis of a human breast cancer cell line, MX-1. Cytotoxic activity of YM529 was more potent than that of incadronate. YM529 activated caspase-9, but not caspase-8, and induced the release of cytochrome c into cytosol. YM529 increased Bax expression and decreased Bcl-2 expression, while it did not induce caspase-8-dependent Bid truncation. Farnesyl pyrophosphate prevented YM529-mediated cytotoxicity. These results suggest that YM529 is a potent therapeutic agent for human breast cancers, activating the mitochondria-dependent apoptotic pathway through the inhibition of protein farnesylation.