Emodin suppresses maintenance of stemness by augmenting proteosomal degradation of epidermal growth factor receptor/epidermal growth factor receptor variant III in glioma stem cells

Targeting Notch signaling pathways with natural bioactive compounds: a promising approach against cancer

Notch signaling pathway is activated abnormally in solid and hematological tumors, which perform essential functions in cell differentiation, survival, proliferation, and angiogenesis. The activation of Notch signaling and communication among Notch and other oncogenic pathways heighten malignancy aggressiveness. Thus, targeting Notch signaling offers opportunities for improved survival and reduced disease incidence. Already, most attention has been given to its role in the cancer cells. Recent research shows that natural bioactive compounds can change signaling molecules that are linked to or interact with the Notch pathways. This suggests that there may be a link between Notch activation and the growth of tumors. Here, we sum up the natural bioactive compounds that possess inhibitory effects on human cancers by impeding the Notch pathway and preventing Notch crosstalk with other oncogenic pathways, which provoke further study of these natural products to derive rational therapeutic regimens for the treatment of cancer and develop novel anticancer drugs. This review revealed Notch as a highly challenging but promising target in oncology.

New insights into the interaction of emodin with lipid membranes

Emodin is a natural anthraquinone derivative found in nature, widely known as an herbal medicine. Here, the partition, location, and interaction of emodin with lipid membranes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are experimentally investigated with different techniques. Our studies have considered the neutral form of emodin (EMH) and its anionic/deprotonated form (EM-), and their interaction with a more and less packed lipid membrane, DMPC at the gel and fluid phases, respectively. Though DSC results indicate that the two species, EMH and EM-, similarly disrupt the packing of DMPC bilayers, spin labels clearly show that EMH causes a stronger bilayer disruption, both in gel and fluid DMPC. Fluorescence spectroscopy shows that both EMH and EM- have a high affinity for DMPC: the binding of EM- to both gel and fluid DMPC bilayers was found to be quite similar, and similar to that of EMH to gel DMPC, Kp = (1.4 ± 0.3)x103. However, EMH was found to bind twice more strongly to fluid DMPC bilayers, Kp = (3.2 ± 0.3)x103. Spin labels and optical absorption spectroscopy indicate that emodin is located close to the lipid bilayer surface, and suggest that EM- is closer to the lipid/water interface than EMH, as expected. The present studies present a relevant contribution to the current understanding of the effect the two species of emodin, EMH and EM-, present on different microregions of an organism, as local pH values can vary significantly, can cause in a neutral lipid membrane, either more or less packed, liked gel and fluid DMPC, respectively, and could be extended to lipid domains of biological membranes.

Signaling pathways governing glioma cancer stem cells behavior

Glioma is the most common malignant brain tumor that develops in the glial tissue. Several studies have identified that glioma cancer stem cells (GCSCs) play important roles in tumor-initiating features in malignant gliomas. GCSCs are a small population in the brain that presents an essential role in the metastasis of glioma cells to other organs. These cells can self-renew and differentiate, which are thought to be involved in the pathogenesis of glioma. Therefore, targeting GCSCs might be a novel strategy for the treatment of glioma. Accumulating evidence revealed that several signaling pathways, including Notch, TGF-β, Wnt, STAT3, AKT, and EGFR mediated GCSC growth, proliferation, migration, and invasion. Besides, non-coding RNAs (ncRNAs), including miRNAs, circular RNAs, and long ncRNAs have been found to play pivotal roles in the regulation of GCSC pathogenesis and drug resistance. Therefore, targeting these pathways could open a new avenue for glioma management. In this review, we summarized critical signaling pathways involved in the stimulation or prevention of GCSCs tumorigenesis and invasiveness.

Targeting cancer stem cells by nutraceuticals for cancer therapy

Accumulating evidence has demonstrated that cancer stem cells (CSCs) play an essential role in tumor progression and reoccurrence and drug resistance. Multiple signaling pathways have been revealed to be critically participated in CSC development and maintenance. Emerging evidence indicates that numerous chemopreventive compounds, also known as nutraceuticals, could eliminate CSCs in part via regulating several signaling pathways. Therefore, in this review, we will describe the some natural chemopreventive agents that target CSCs in a variety of human malignancies, including soy isoflavone, curcumin, resveratrol, tea polyphenols, sulforaphane, quercetin, indole-3-carbinol, 3,3'-diindolylmethane, withaferin A, apigenin, etc. Moreover, we discuss that eliminating CSCs by nutraceuticals might be a promising strategy for treating human cancer via overcoming drug resistance and reducing tumor reoccurrence.

PARK7 maintains the stemness of glioblastoma stem cells by stabilizing epidermal growth factor receptor variant III

PARK7 is involved in many key cellular processes, including cell proliferation, transcriptional regulation, cellular differentiation, oxidative stress protection, and mitochondrial function maintenance. Deregulation of PARK7 has been implicated in the pathogenesis of various human diseases, including cancer. Here, we aimed to clarify the effect of PARK7 on stemness and radioresistance of glioblastoma stem cells (GSCs). Serum differentiation and magnetic cell sorting of GSCs revealed that PARK7 was preferentially expressed in GSCs rather than differentiated GSCs. Immunohistochemical staining showed enhanced expression of PARK7 in glioma tissues compared to that in normal brain tissues. shRNA-mediated knockdown of PARK7 inhibited the self-renewal activity of GSCs in vitro, as evidenced by the results of neurosphere formation, limiting dilution, and soft-agar clonogenic assays. In addition, PARK7 knockdown suppressed GSC invasion and enhanced GSC sensitivity to ionizing radiation (IR). PARK7 knockdown suppressed expression of GSC signatures including nestin, epidermal growth factor receptor variant III (EGFRvIII), SOX2, NOTCH1, and OCT4. Contrarily, overexpression of PARK7 in CD133^- non-GSCs increased self-renewal activities, migration, and IR resistance, and rescued the reduction of GSC factors under shPARK7-transfected and serum-differentiation conditions. Intriguingly, PARK7 acted as a co-chaperone of HSP90 by binding to it, protecting EGFRvIII from proteasomal degradation. Knockdown of PARK7 increased the production of reactive oxygen species, inducing partial apoptosis and enhancing IR sensitivity in GSCs. Finally, PARK7 knockdown increased mouse survival and IR sensitivity in vivo. Based on these data, we propose that PARK7 plays a pivotal role in the maintenance of stemness and therapeutic resistance in GSCs.

Emodin inhibiting neutrophil elastase-induced epithelial-mesenchymal transition through Notch1 signalling in alveolar epithelial cells

The transition of alveolar type II epithelial cells into fibroblasts has been reported to cause and/or aggravate pulmonary fibrosis (PF), which is characterized by fibroblast proliferation, an enhanced production and accumulation of ECM (extracellular matrix), alveolar wall damage and functional capillary unit loss. Traditional Chinese medicine Emodin has been reported to inhibit TGF‐β‐induced epithelial‐mesenchymal transition (EMT) in alveolar epithelial cells through Notch signalling. In the present study, neutrophil elastase (NE, also known as ELA2) treatment promoted EMT, Notch1 cleavage (NICD/Notch1 ratio increase) and NICD nuclear translocation in RLE‐6TN cells and A549 cells. The promotive roles of NE treatment in these events were significantly reversed by Notch1 knockdown. Traditional Chinese medicine Emodin treatment remarkably inhibited the enzyme activity of NE, suppressed EMT, Notch1 cleavage and NICD nuclear translocation within RLE‐6TN and A549 cells, while NE treatment significantly reversed the effects of Emodin. Moreover, in RLE‐6TN, the effects of NE on EMT, Notch1 cleavage and NICD nuclear translocation were remarkably attenuated by Emodin treatment and more attenuated by the combination of Emodin and neutrophil elastase inhibitor Sivelestat or notch signal pathway inhibitor DAPT. In conclusion, we revealed the involvement of NE‐induced Notch1 cleavage in the functions of Emodin suppressing NE‐caused EMT in RLE‐6TN cells and A549 cells. This novel mechanism of Emodin inhibiting EMT might extend the application of Emodin in PF treatment.

Herb-sourced emodin inhibits angiogenesis of breast cancer by targeting VEGFA transcription

Anti-angiogenesis is an important and promising strategy in cancer therapy. However, the current methods using anti-vascular endothelial growth factor A (VEGFA) antibodies or inhibitors targeting VEGFA receptors are not as efficient as expected partly due to their low efficiencies in blocking VEGFA signaling in vivo. Until now, there is still no method to effectively block VEGFA production in cancer cells from the very beginning, i.e., from the transcriptional level. Here, we aimed to find bioactive small molecules to block VEGFA transcription. Methods: We screened our natural compound pool containing 330 small molecules derived from Chinese traditional herbs for small molecules activating the expression of seryl-tRNA synthetase (SerRS), which is a newly identified potent transcriptional repressor of VEGFA, by a cell-based screening system in MDA-MB-231 cell line. The activities of the candidate molecules on regulating SerRS and VEGFA expression were first tested in breast cancer cells. We next investigated the antiangiogenic activity in vivo by testing the effects of candidate drugs on the vascular development in zebrafish and by matrigel plug angiogenesis assay in mice. We further examined the antitumor activities of candidate drugs in two triple-negative breast cancer (TNBC)-bearing mouse models. Furthermore, streptavidin-biotin affinity pull-down assay, coimmunoprecipitation assays, docking analysis and chromatin immunoprecipitation were performed to identify the direct targets of candidate drugs. Results: We identified emodin that could greatly increase SerRS expression in TNBC cells, consequently reducing VEGFA transcription. Emodin potently inhibited vascular development of zebrafish and blocked tumor angiogenesis in TNBC-bearing mice, greatly improving the survival. We also identified nuclear receptor corepressor 2 (NCOR2) to be the direct target of emodin. Once bound by emodin, NCOR2 got released from SerRS promoter, resulting in the activation of SerRS expression and eventually the suppression of VEGFA transcription. Conclusion: We discovered a herb-sourced small molecule emodin with the potential for the therapy of TNBC by targeting transcriptional regulators NCOR2 and SerRS to suppress VEGFA transcription and tumor angiogenesis.

Molecular Chaperones in Cancer Stem Cells: Determinants of Stemness and Potential Targets for Antitumor Therapy

Cancer stem cells (CSCs) are a great challenge in the fight against cancer because these self-renewing tumorigenic cell fractions are thought to be responsible for metastasis dissemination and cases of tumor recurrence. In comparison with non-stem cancer cells, CSCs are known to be more resistant to chemotherapy, radiotherapy, and immunotherapy. Elucidation of mechanisms and factors that promote the emergence and existence of CSCs and their high resistance to cytotoxic treatments would help to develop effective CSC-targeting therapeutics. The present review is dedicated to the implication of molecular chaperones (protein regulators of polypeptide chain folding) in both the formation/maintenance of the CSC phenotype and cytoprotective machinery allowing CSCs to survive after drug or radiation exposure and evade immune attack. The major cellular chaperones, namely heat shock proteins (HSP90, HSP70, HSP40, HSP27), glucose-regulated proteins (GRP94, GRP78, GRP75), tumor necrosis factor receptor-associated protein 1 (TRAP1), peptidyl-prolyl isomerases, protein disulfide isomerases, calreticulin, and also a transcription heat shock factor 1 (HSF1) initiating HSP gene expression are here considered as determinants of the cancer cell stemness and potential targets for a therapeutic attack on CSCs. Various approaches and agents are discussed that may be used for inhibiting the chaperone-dependent development/manifestations of cancer cell stemness.

Heat Shock Proteins in Glioblastoma Biology: Where Do We Stand?

Heat shock proteins (HSPs) are evolutionary conserved proteins that work as molecular chaperones and perform broad and crucial roles in proteostasis, an important process to preserve the integrity of proteins in different cell types, in health and disease. Their function in cancer is an important aspect to be considered for a better understanding of disease development and progression. Glioblastoma (GBM) is the most frequent and lethal brain cancer, with no effective therapies. In recent years, HSPs have been considered as possible targets for GBM therapy due their importance in different mechanisms that govern GBM malignance. In this review, we address current evidence on the role of several HSPs in the biology of GBMs, and how these molecules have been considered in different treatments in the context of this disease, including their activities in glioblastoma stem-like cells (GSCs), a small subpopulation able to drive GBM growth. Additionally, we highlight recent works that approach other classes of chaperones, such as histone and mitochondrial chaperones, as important molecules for GBM aggressiveness. Herein, we provide new insights into how HSPs and their partners play pivotal roles in GBM biology and may open new therapeutic avenues for GBM based on proteostasis machinery.

Emodin, a natural anthraquinone, suppresses liver cancer in vitro and in vivo by regulating VEGFR2 and miR-34a

The pharmacokinetic (PK) and potential effects of Emodin on liver cancer were systematically evaluated in this study. Both the intragastric administration (i.g.) and hypodermic injection (i.h.) of Emodin exhibited a strong absorption (absorption rate < 1 h) and elimination capacity (t_1/2 ≈ 2 h). The tissue distribution of Emodin after i.h. was rapid and wide. The stability of Emodin in three species of liver microsomes wasrat >human> beagle dog. These PK data provided the basis for the subsequent animal experiments. In liver cancer patient tissues, the expression of vascular endothelial growth factor (VEGF)-induced signaling pathways, including phosphorylated VEGF receptor 2 (VEGFR₂), AKT, and ERK_1/2,were simultaneously elevated, but miR-34a expression was reduced and negatively correlated with SMAD₂ and SMAD₄. Emodin inhibited the expression of SMAD_2/4 in HepG2 cells by inducing the miR-34a level. Subsequently, BALB/c nude mice received a daily subcutaneous injection of HepG2 cells with or without Emodin treatment (1 mg/kg or 10 mg/kg), and Emodin inhibited tumorigenesis and reduced the mortality rate in a dose-dependent manner. In vivo experiments showed that cell proliferation, migration, and invasion were promoted by VEGF or miR-34a signal treatment but were inhibited when combined with Emodin treatment. All these results demonstrated that Emodin inhibited tumorigenesis in liver cancer by simultaneously inhibiting the VEGFR₂-AKT-ERK_1/2signaling pathway and promoting a miR-34a-mediated signaling pathway.

Saccharina japonica Extract Suppresses Stemness of Glioma Stem Cells by Degrading Epidermal Growth Factor Receptor/Epidermal Growth Factor Receptor Variant III

Cancer stem cells, a small subpopulation of cells with stem cell-like characteristics found within most solid tumors, are widely reported to be responsible for the malignancy of aggressive cancer cells, and targeting these cells presents a sound therapeutic strategy for reducing the risk of tumor relapse. In the present study, we examined the effects of an extract of Saccharina japonica (ESJ) on glioblastoma stem cells (GSCs). Saccharina japonica is a member of the Phaeophyceae (brown algae) family, which displays biological activities, including antitumor effects. ESJ inhibited the sphere-forming ability of GSCs in vitro as evidenced by neurosphere formation and limiting dilution assays. Treatment with ESJ partially induced apoptosis, reduced cell invasiveness, and sensitized GSCs to ionizing radiation. In addition, ESJ inhibited the maintenance of stemness in GSCs by suppressing the expression of epidermal growth factor receptor (EGFR)/EGFR variant III (EGFRvIII) and Notch intracellular domain. Intriguingly, the observed ESJ-induced suppression also appeared to induce the proteasomal degradation of EGFR/EGFRvIII. Our results indicate that ESJ could be considered a potent therapeutic adjuvant that targets GSCs.

Effects of combined radiosurgery and temozolomide therapy on epidermal growth factor receptor and variant III in glioblastoma multiforme

Glioblastoma multiforme (GBM) is a highly malignant and notably aggressive primary tumour. Variant III of the epidermal growth factor receptor (EGFRvIII) is one of the most common types of variants in GBM, and serves an important role in tumour invasion, proliferation and treatment resistance. In the present study, statistical analyses were performed on data from 57 patients with GBM, and polymerase chain reaction detection was conducted on the tumour tissues from 32 of these patients. The results indicated that the EGFRvIII mutation was significantly associated with tumour malignancy. Human GBMU87-EGFRvIII cell lines were cultured and treated with radiosurgery and temozolomide individually, or with combined radiosurgery and temozolomide treatment. In vitro and in vivo experimental methods were used to detect the expression levels of Ki-67 and EGFRvIII. As verified in the present study, the EGFRvIII mutation is positively correlated with the malignancy of tumours, and combined radiosurgery and temozolomide therapy may inhibit the invasion and proliferation abilities of U87-EGFRvIII more effectively than treatment alone.

Evaluation of the Drug-like Properties of Kaempferol, Chrysophanol and Emodin and their Interactions with EGFR Tyrosine Kinase - An in silico Approach

In this study, a molecular docking was performed on EGFR tyrosine kinase with plant phenolic compounds kaempferol, chrysophanol and emodin; identified from Cassia tora, an edible plant employed for eye diseases traditionally. The results illustrated that all the compounds have strong binding abilities with epidermal growth factor receptor and validated the reported anticataractogenic potential of C. tora leaves. Further, the compounds also satisfied the criteria for being a drug through its structural features. Taken together, it was proposed that the compounds; kaempferol, chrysophanol and emodin might be helpful for further drug design and development and could be employed as efficient lead compounds in ophthalmic drug formulations.

Inhibitory effect of emodin on fatty acid synthase, colon cancer proliferation and apoptosis

Fatty acid synthase (FASN) is a key anabolic enzyme for de novo fatty acid synthesis, which is important in the development of colon carcinoma. The high expression of FASN is considered a promising molecular target for colon cancer therapy. Emodin, a naturally occurring anthraquinone, exhibits an anticancer effect in various types of human cancer, including colon cancer; however, the molecular mechanisms remain to be fully elucidated. Cell viability was evaluated using a Cell Counting Kit‑8 assay. The apoptosis rate of cells was quantified via flow cytometry following Annexin V/propidium iodide staining. FASN activity was measured by monitoring oxidation of nicotinamide adenine dinucleotide phosphate at a wavelength of 340 nm, and intracellular free fatty acid levels were detected using a Free Fatty Acid Quantification kit. Western blot analysis and reverse transcription‑polymerase chain reaction were used to detect target gene and protein expression. The present study was performed to investigate whether the gene expression of FASN and its enzymatic activity are regulated by emodin in a human colon cancer cell line. Emodin markedly inhibited the proliferation of HCT116 cells and a higher protein level of FASN was expressed, compared with that in SW480, SNU-C2A or SNU‑C5 cells. Emodin significantly downregulated the protein expression of FASN in HCT116 cells, which was caused by protein degradation due to elevated protein ubiquitination. Emodin also inhibited intracellular FASN enzymatic activity and reduced the levels of intracellular free fatty acids. Emodin enhanced antiproliferation and apoptosis in a dose‑ and time‑dependent manner. The combined treatment of emodin and cerulenin, a commercial FASN inhibitor, had an additive effect on these activities. Palmitate, the final product of the FASN reaction, rescued emodin‑induced viability and apoptosis. In addition, emodin altered FASN‑involved signaling pathways, including phosphatidylinositol 3-kinase/Akt and mitogen‑activated protein kinases/extracellular signal-regulated kinases 1/2. These results suggested that emodin-regulated cell growth and apoptosis were mediated by inhibiting FASN and provide a molecular basis for colon cancer therapy.

San-Huang-Xie-Xin-Tang Constituents Exert Drug-Drug Interaction of Mutual Reinforcement at Both Pharmacodynamics and Pharmacokinetic Level: A Review

Inflammatory disorders underlie varieties of human diseases. San-Huang-Xie-xin-Tang (SHXXT), composed with Rhizoma Rhei (Rheum palmatum L.), Rhizoma Coptidis (Coptis chinensis Franch), and Radix Scutellaria (Scutellaria baicalensis Georgi), is a famous formula which has been widely used in the fight against inflammatory abnormalities. Mutual reinforcement is one of the basic theories of traditional Chinese medicine. Here this article reviewed and analyzed the recent research on (1) How the main constituents of SHXXT impact on inflammation-associated signaling pathway molecules. (2) The interaction between the main constituents and efflux pumps or intestinal transporters. The goal of this work was to, (1) Provide evidence to support the theory of mutual reinforcement. (2) Clarify the key targets of SHXXT and suggest which targets need further investigation. (3) Give advice for the clinical use of SHXXT to elevated the absorption of main constituents and eventually promote oral bioavailability. We search literatures in scientific databases with key words of “each main SHXXT constituent,” in combination with “each main inflammatory pathway target molecule” or each main intestinal transporter, respectively. We report the effect of five main constituents on target molecules which lies in three main inflammatory signaling pathways, we as well investigate the interaction between constituents and intestinal transporter. We conclude, (1) The synergistic effect of constituents at both levels confirm the mutual reinforcement theory of TCM as it is proven in this work. (2) The effect of main constituents on downstream targets in nuclear need more further investigation. (3) Drug elevating the absorption of rhein, berberine and baicalein can be employed to promote oral bioavailability of SHXXT.

Targeting Deubiquitinating Enzymes in Glioblastoma Multiforme: Expectations and Challenges

Glioblastoma (GBM) is regarded as the most common primary intracranial neoplasm. Despite standard treatment with tumor resection and radiochemotherapy, the outcome remains gloomy. It is evident that a combination of oncogenic gain of function and tumor-suppressive loss of function has been attributed to glioma initiation and progression. The ubiquitin-proteasome system is a well-orchestrated system that controls the fate of most proteins by striking a dynamic balance between ubiquitination and deubiquitination of substrates, having a profound influence on the modulation of oncoproteins, tumor suppressors, and cellular signaling pathways. In recent years, deubiquitinating enzymes (DUBs) have emerged as potential anti-cancer targets due to their targeting several key proteins involved in the regulation of tumorigenesis, apoptosis, senescence, and autophagy. This review attempts to summarize recent studies of GBM-associated DUBs, their roles in various cellular processes, and discuss the relation between DUBs deregulation and gliomagenesis, especially how DUBs regulate glioma stem cells pluripotency, microenvironment, and resistance of radiation and chemotherapy through core stem-cell transcriptional factors. We also review recent achievements and progress in the development of potent and selective reversible inhibitors of DUBs, and attempted to find a potential GBM treatment by DUBs intervention.

Emodin: A Review of its Pharmacology, Toxicity and Pharmacokinetics

Emodin is a natural anthraquinone derivative that occurs in many widely used Chinese medicinal herbs, such as Rheum palmatum, Polygonum cuspidatum and Polygonum multiflorum. Emodin has been used as a traditional Chinese medicine for over 2000 years and is still present in various herbal preparations. Emerging evidence indicates that emodin possesses a wide spectrum of pharmacological properties, including anticancer, hepatoprotective, antiinflammatory, antioxidant and antimicrobial activities. However, emodin could also lead to hepatotoxicity, kidney toxicity and reproductive toxicity, particularly in high doses and with long-term use. Pharmacokinetic studies have demonstrated that emodin has poor oral bioavailability in rats because of its extensive glucuronidation. This review aims to comprehensively summarize the pharmacology, toxicity and pharmacokinetics of emodin reported to date with an emphasis on its biological properties and mechanisms of action. Copyright © 2016 John Wiley & Sons, Ltd.