Mechanism of autophagy induction and role of autophagy in antagonizing mitomycin C-induced cell apoptosis in silibinin treated human melanoma A375-S2 cells

Targeting Drug Chemo-Resistance in Cancer Using Natural Products

Cancer is one of the leading causes of death globally. The development of drug resistance is the main contributor to cancer-related mortality. Cancer cells exploit multiple mechanisms to reduce the therapeutic effects of anticancer drugs, thereby causing chemotherapy failure. Natural products are accessible, inexpensive, and less toxic sources of chemotherapeutic agents. Additionally, they have multiple mechanisms of action to inhibit various targets involved in the development of drug resistance. In this review, we have summarized the basic research and clinical applications of natural products as possible inhibitors for drug resistance in cancer. The molecular targets and the mechanisms of action of each natural product are also explained. Diverse drug resistance biomarkers were sensitive to natural products. P-glycoprotein and breast cancer resistance protein can be targeted by a large number of natural products. On the other hand, protein kinase C and topoisomerases were less sensitive to most of the studied natural products. The studies discussed in this review will provide a solid ground for scientists to explore the possible use of natural products in combination anticancer therapies to overcome drug resistance by targeting multiple drug resistance mechanisms.

Evaluation of anti-cancer potency of silibinin on murine renal carcinoma RenCa cells in an animal model with an intact immune system

Silibinin is a flavonoid extract isolated from milk thistle and has been proved to be a promising chemotherapeutic drug for cancer. However, most of those studies were performed on the human cancer cells, where the effects of silibinin could only be observed on an animal model with a deficient immune system. RenCa cells were isolated from a murine spontaneous renal cell carcinoma, which resembles many features of human renal cell carcinoma, and have been used to establish animal models with a sound immune response. Herein, we investigated the anti-cancer effects of silibinin on RenCa cells, revealing that it inhibited cell viability in both dose- and time-dependent manners. Silibinin slightly triggered apoptosis and significantly induced G2-M cell cycle arrest by downregulating cyclin B1 and CDK1 and increasing expression of p21. Furthermore, silibinin significantly inhibited the growth of RenCa cell xenografts in vivo. In addition, we found that silibinin reduced programmed cell death 1 ligand 1 expression of RenCa cells in vivo and in vitro. Our findings demonstrate that silibinin can inhibit the growth of mouse tumor cells in an animal model with an intact immune system, and silibinin may decrease the immunosuppression effect of tumor cells. Our results provide new evidence for evaluation of Silibinin application in cancer therapy.

Bioactive phenolic components and potential health effects of chestnut shell: A review

Chestnut kernels are often used for direct consumption; or processed to produce marron glacé, chestnut purée, and gluten-free products, while chestnut by-products (inner shell and outer shell) are treated as waste residues. Many in vivo and in vitro studies have proved how chestnut shell extract functions as an antioxidant and exhibits anticancer, anti-inflammatory, antidiabetic, and anti-obesity activities. This review introduces the main components of phenolic compounds in chestnut shells, traditional and modern extraction methods, and reported potential health effects. The aim is to have a better understanding of the functional active ingredients in chestnut shells and their value-added uses, to increase understanding of future applications of this agricultural and sideline product in the food, pharmaceutical, and cosmetic industries. PRACTICAL APPLICATIONS: In recent years, chestnut shells have become a hot research topic because of their rich bioactive ingredients. Due to the large amount of phenolic compounds in chestnut shells and their potential health functions (antioxidant, anticancer, antibacterial, anti-inflammatory, hypoglycemic, and treatment of obesity), extracts of chestnut shells have high biological value in the treatment of diseases. Therefore, this review introduces the main components of phenolic compounds in chestnut shells, traditional and modern extraction methods, and the potential health effects of these compounds. The aim of this review is to better understand the functional, active ingredients in chestnut shells and their value-added uses, and to increase understanding of future applications of this agricultural and sideline product in the food, pharmaceutical, and cosmetic industries.

Path of Silibinin from diet to medicine: A dietary polyphenolic flavonoid having potential anti-cancer therapeutic significance

In the last few decades, targeting cancer by the use of dietary phytochemicals has gained enormous attention. The plausible reason and believe or mind set behind this fact is attributed to either lesser or no side effects of natural compounds as compared to the modern chemotherapeutics, or due to their conventional use as dietary components by mankind for thousands of years. Silibinin is a naturally derived polyphenol (a flavonolignans), possess following biochemical features; molecular formula C₂₅H₂₂O₁₀, Molar mass: 482.44 g/mol, Boiling point 793 °C, with strikingly high antioxidant and anti-tumorigenic properties. The anti-cancer properties of Silibinin are determined by a variety of cellular pathways which include induction of apoptosis, cell cycle arrest, inhibition of angiogenesis and metastasis. In addition, Silibinin controls modulation of the expression of aberrant miRNAs, inflammatory response, and synergism with existing anti-cancer drugs. Therefore, modulation of a vast array of cellular responses and homeostatic aspects makes Silibinin an attractive chemotherapeutic agent. However, like other polyphenols, the major hurdle to declare Silibinin a translational chemotherapeutic agent, is its lesser bioavailability. After summarizing the chemistry and metabolic aspects of Silibinin, this extensive review focuses on functional aspects governed by Silibinin in chemoprevention with an ultimate goal of summarizing the evidence supporting the chemopreventive potential of Silibinin and clinical trials that are currently ongoing, at a single platform.

Autophagy: A Potential Therapeutic Target of Polyphenols in Hepatocellular Carcinoma

Autophagy is a conserved biological phenomenon that maintains cellular homeostasis through the clearing of damaged cellular components under cellular stress and offers the cell building blocks for cellular survival. Aberrations in autophagy subsidize to various human pathologies, such as dementia, cardiovascular diseases, leishmaniosis, influenza, hepatic diseases, and cancer, including hepatocellular carcinoma (HCC). HCC is the fifth common mortal type of liver cancer globally, with an inhomogeneous topographical distribution and highest incidence tripled in men than women. Existing treatment procedures with liver cancer patients result in variable success rates and poor prognosis due to their drug resistance and toxicity. One of the pathophysiological mechanisms that are targeted during the development of anti-liver cancer drugs is autophagy. Generally, overactivated autophagy may lead to a non-apoptotic form of programmed cell death (PCD) or autophagic cell death or type II PCD. Emerging evidence suggests that manipulation of autophagy could induce type II PCD in cancer cells, acting as a potential tumor suppressor. Hence, altering autophagic signaling offers new hope for the development of novel drugs for the therapy of resistant cancer cells. Natural polyphenolic compounds, including flavonoids and non-flavonoids, execute their anticarcinogenic mechanism through upregulating tumor suppressors and autophagy by modulating canonical (Beclin-1-dependent) and non-canonical (Beclin-1-independent) signaling pathways. Additionally, there is evidence signifying that plant polyphenols target angiogenesis and metastasis in HCC via interference with multiple intracellular signals and decrease the risk against HCC. The current review offers a comprehensive understanding of how natural polyphenolic compounds exhibit their anti-HCC effects through regulation of autophagy, the non-apoptotic mode of cell death.

Functional Role of p53 in the Regulation of Chemical-Induced Oxidative Stress

The nuclear transcription factor p53, discovered in 1979, has a broad range of biological functions, primarily the regulation of apoptosis, the cell cycle, and DNA repair. In addition to these canonical functions, a growing body of evidence suggests that p53 plays an important role in regulating intracellular redox homeostasis through transcriptional and nontranscriptional mechanisms. Oxidative stress induction and p53 activation are common responses to chemical exposure and are suggested to play critical roles in chemical-induced toxicity. The activation of p53 can exert either prooxidant or antioxidant activity, depending on the context. In this review, we discuss the functional role of p53 in regulating chemical-induced oxidative stress, summarize the potential signaling pathways involved in p53's regulation of chemically mediated oxidative stress, and propose issues that should be addressed in future studies to improve understanding of the relationship between p53 and chemical-induced oxidative stress.

Bidirectional Effects of Pyrrolidine Dithiocarbamate on Severe Acute Pancreatitis in a Rat Model

Introduction

The mechanism by which intestinal mucosal barrier is damaged in severe acute pancreatitis (SAP)-associated impairment is not fully understood.

Methods

We established an l-arginine-induced SAP rat model, pretreated with or without pyrrolidine dithiocarbamate (PDTC). Hematoxylin and eosin staining was performed to evaluate the pathological alterations. Western blotting was conducted to detect the expression of autophagy-related proteins. Oxidative stress was assessed by the levels of malondialdehyde and superoxide dismutase.

Results

We found significant injury of the intestinal mucosal barrier in SAP rats, with overexpression of Beclin-1, LC3, and p65. Pyrrolidine dithiocarbamate showed a bidirectional effect in protecting SAP rats. A high dose of PDTC aggravated disease in rats, while a low or medium dose of PDTC pretreatment, was able to alleviate tissue damage. Pyrrolidine dithiocarbamate changed the expression of Beclin-1, LC3, and p65 in the intestines. The fatty acid-binding protein level was increased in SAP rats with high-dose PDTC or without PDTC pretreatment and was reduced in SAP rats with low- or medium-dose PDTC exposure.

Conclusions

Autophagy is involved in the impairment of intestinal mucosal barrier during SAP. A suitable dose of PDTC (1 or 10 mg/kg) may decrease the severity of SAP by inhibiting autophagy in intestinal mucosal cells.

Silibinin to improve cancer therapeutic, as an apoptotic inducer, autophagy modulator, cell cycle inhibitor, and microRNAs regulator

Silibinin is a natural plant polyphenol with high antioxidant and anticancer properties, which causes broad-spectrum efficacy against cancer, including cell cycle arrest and apoptosis in most cancer cell types. Silibinin, by modulating the apoptosis, cell cycle progression and autophagic pathways in various cellular and molecular routs might be used to design more effective anticancer strategies. Silibinin also regulates aberrant miRNAs expression linked to many aspects of cell biology in cancer. Maybe the most interesting aspect of silibinin is its ability to trigger multiple cellular signaling pathways to induce a particular biologic effect in various cell types. This review discusses investigations supporting the ability of silibinin to be as a natural modulator of involved cellular biological events in cancer progression. In this review, we introduce the salient features of silibinin therapy to optimize clinical outcomes for oncology patients. The goal of the treatments is to make it possible to eliminate the tumor with the minimum side effects and cure the patient in the early stage cancer. Therefore, plant extracts such as silibinin can be included in the treatments.

Silibinin Induced Human Glioblastoma Cell Apoptosis Concomitant with Autophagy through Simultaneous Inhibition of mTOR and YAP

Silibinin, also known as silybin, is the major flavonolignan isolated from Silybum marianum. Although previous reports demonstrated that silibinin exhibits significant tumor suppressor activities in various cancers by promoting cell apoptosis, it was also shown to trigger autophagy to counteract apoptosis induced by exogenous stresses in several types of cells. However, there is no report to address the role of silibinin induced autophagy in human A172 and SR glioblastoma cells. Our study showed that silibinin treatment not only inhibited the metabolic activities of glioblastoma cells but also promoted their apoptosis through the regulation of caspase 3 and PARP-1 in concentration- and time-dependent manners. Meanwhile, silibinin induced autophagy through upregulation of microtubule-associated protein a light chain 3- (LC3-) II. And autophagy inhibition with chloroquine, a lysosomotropic agent, significantly enhanced silibinin induced glioblastoma cell apoptosis. Moreover, silibinin dose-dependently downregulated the phosphorylation levels of mTOR at Ser-2448, p70S6K at Thr-389, and 4E-BP1 at Thr-37/46. Furthermore, the expression of YAP, the downstream effector of Hippo signal pathway, was also suppressed by silibinin. These results suggested that silibinin induced glioblastoma cell apoptosis concomitant with autophagy which might be due to simultaneous inhibition of mTOR and YAP and silibinin induced autophagy exerted a protective role against cell apoptosis in both A172 and SR cells.

Silymarin induces a multi-targeted cell death process in the human colon cancer cell line HT-29

This study investigated the Silymarin (SM) effects on growth of HT-29 human colon cancer cell line and its cellular death mechanism. HT-29 cells were treated by 25μM/ml of SM for 48h. HT-29 cells were also pretreated with 10mmol zVAD (apoptosis inhibitor), 10mmol 3-MA (autophagy inhibitor) and 3mmol Nec (necroptosis inhibitor) for evaluation cell death induced by apoptosis, outophagy and necroptosis. MTT and clonogenicity assays revealed that the SM without inhibitors induced a significant decrease in cell viability and proliferation of HT-29 cells (p<0.05). SM in presence of Nec and 3-MA significantly decreased viability and proliferation of HT-29 cells. Apoptotic indexes were significantly increased compare to other groups. SM in presence of zVAD and 3-MA significantly decreased viability and proliferation of HT-29 cells, and expression of RIPK1 and RIPK3 in compare to absence the inhibitors. Necroptotic index was also increased. zVAD could not completely blocked apoptosis. This indicate that SM may stimulate both caspase-dependent and caspase-independent apoptotic pathways. SM in presence of zVAD and Nec significantly decreased cell viability and proliferation of HT-29 cells in compare to control and other experimental groups. LC3-II positive cells were significantly increased in this group in compare to the control and SM without inhibitors treatment. Our results revealed that the high SM toxicity to HT-29 cells depends on multiple cell death pathways, which involved mainly autophagy.

Modulation of Autophagy by a Thioxanthone Decreases the Viability of Melanoma Cells

(1) Background: Our previous studies unveiled the hit thioxanthone TXA1 as an inhibitor of P-glycoprotein (drug efflux pump) and of human tumor cells growth, namely of melanoma cells. Since TXA1 is structurally similar to lucanthone (an autophagy inhibitor and apoptosis inducer) and to N¹⁰-substituted phenoxazines (isosteres of thioxanthones, and autophagy inducers), this study aimed at further assessing its cytotoxic mechanism and evaluating its potential as an autophagy modulator in A375-C5 melanoma cells; (2) Methods: Flow cytometry with propidium iodide (PI) for cell cycle profile analysis; Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, flow cytometry with Annexin V/PI labeling and Western blot for apoptosis analysis were conducted. A pharmacophore approach was used for mapping TXA1 onto pharmacophores for autophagy induction. Autophagy analyses included transmission electron microscopy for visualization of autophagic structures, fluorescence microscopy for observation of monodansylcadaverine (MDC) staining, pattern of LC3 expression in the cells and acridine orange staining, and Western blot for autophagic proteins expression; (3) Results: TXA1 induced autophagy of melanoma cells at the GI₅₀ concentration (3.6 μM) and apoptosis at twice that concentration. Following treatment with TXA1, autophagic structures were observed, together with the accumulation of autophagosomes and the formation of autophagolysosomes. An increase in LC3-II levels was also observed, which was reverted by 3-methyladenine (3-MA) (an early stage autophagy-inhibitor) but further increased by E-64d/pepstatin (late-stage autophagy inhibitors). Finally, 3-MA also reverted the effect of TXA1 in cellular viability; (4) Conclusion: TXA1 decreases the viability of melanoma cells by modulation of autophagy and may, therefore, serve as a lead compound for the development of autophagy modulators with antitumor activity.

Timosaponin AIII induces apoptosis and autophagy in human melanoma A375-S2 cells

Timosaponin AIII (AIII), a steroidal saponin isolated from Anemarrhena asphodeloides Bge. Our study showed that AIII induced both apoptosis and autophagy, and autophagy inhibited apoptosis in A375S2 cells. Furtherly, this study was carried out to investigate what kind of cytokines plays an important role in this process. The results revealed that AIII induced apoptosis through activating c-Jun N-terminal protein kinase (JNK) or extracellular signal related kinase (ERK) signaling pathway and generating NO. However, JNK or ERK inhibited autophagy, while NO had no effect on autophagy. Therefore, JNK, ERK or NO regulates two programmed death processes in different ways. AIII did not show obvious cytotoxic effect on human peripheral blood mononuclear cells, which indicated that AIII has less side effects on normal cells, and could be considered as a leading compound for developing novel anticancer drug.

Isoorientin induces apoptosis and autophagy simultaneously by reactive oxygen species (ROS)-related p53, PI3K/Akt, JNK, and p38 signaling pathways in HepG2 cancer cells

Cell death is closely related to autophagy under some circumstances; however, the effect of isoorientin (ISO) on autophagy and the interplay between apoptosis and autophagy in human hepatoblastoma cancer (HepG2) cells remains poorly understood. The present study showed that ISO induced autophagy, which was correlated with the formation of autophagic vacuoles and the overexpression of Beclin-1 and LC3-II. The autophagy inhibitor 3-methyladenine (3-MA) markedly inhibited apoptosis, and the apoptosis inhibitor ZVAD-fmk also decreased ISO-induced autophagy. In addition, the PI3K/Akt inhibitor LY294002 enhanced Beclin-1, LC3-II, and poly(ADP-ribose) polymerase (PARP) cleavage levels. Also, the reactive oxygen species (ROS) inhibitor N-acetyl-L-cysteine (NAC), the JNK inhibitor SP600125, and the p38 inhibitor SB203580 efficiently downregulated the levels of these proteins. Moreover, the p53 inhibitor pifithrin-α and the nuclear factor (NF)-κB inhibitor pyrrolidinedithiocarbamic acid (PDTC) clearly suppressed Beclin-1 and LC3-II and increased cytochrome c release, caspase-3 activation, and PARP cleavage. These results demonstrated for the first time that ISO simultaneously induced apoptosis and autophagy by ROS-related p53, PI3K/Akt, JNK, and p38 signaling pathways. Furthermore, ISO-induced apoptosis by activating the Fas receptor-mediated apoptotic pathway and suppressing the p53 and PI3K/Akt-dependent NF-κB signaling pathway, with the subsequent increase in the release of cytochrome c, caspase-3 activation, and PARP cleavage.

Autophagy induced by silibinin protects human epidermoid carcinoma A431 cells from UVB-induced apoptosis

Ultraviolet B (UVB) in the sun light is a major cause of skin damage, which accompanies complex alterations in irradiated skin cells, including DNA lesions, oxidative stress, inflammation and caspase activation. The protection against UVB damage requires multiple interruptions such as repair of the DNA lesions, scavenging of the reactive oxygen species (ROS), repression of the inflammation and others. Silibinin is suggested as an anti-UVB reagent, but the underlying mechanisms have not been fully elucidated. In this study, we found a role of autophagy in the anti-UVB effect of silibinin in A431 cells. Autophagy was reduced after UVB-irradiation while restored by silibinin through the suppression of the IGF-1R signalling pathway. The protective effect of silibinin in UVB-irradiated A431 cells was further enhanced by pre-treatment with an autophagy inducer, rapamycin, while it was reversed by an autophagy inhibitor, wortmannin, indicating that elevated autophagy contributed to the cell survival. Consistently, cell apoptosis was augmented by siRNAs targeting Beclin 1 and Atg5, supporting the hypothesis that autophagy induced by silibinin plays a protective role against UVB-induced epidermal apoptosis.

The gluttonous side of malignant melanoma: basic and clinical implications of macroautophagy

True to their inherent aggressive behavior, melanomas keep impressing the melanoma community with their ability to bypass tumor suppressor mechanisms. Name a pathway with the potential to control cell survival and melanoma cells will likely have it potentiated by multiple genetic or epigenetic alterations. In the context of progression and chemoresistance, large efforts have been dedicated to the identification of protective mechanisms associated with or linked to apoptotic death programs. These studies have guided the design of targeted anticancer strategies. Still, the promise for pro-apoptotic inducers as lead compounds for drug development has yet to come to fruition. It was then a question of time to identify alternative modulators of cell viability. An ideal candidate that is raising great expectations in the oncology field is autophagy, a catabolic process with multiple roles in cell homeostasis. Here we review the incipient literature on autophagy markers in melanocytic lesions. Intriguingly, histopathological studies are unveiling an intrinsic inter- and intratumor variability in the expression of autophagy modulators. Nonetheless, functional studies support a key role of autopaphagy programs in the response to a variety of stress factors. These include adaptive responses to nutrient deprivation, hypoxia and many anticancer agents, among other stimuli. Strategies are being also developed to mobilize the endocytic machinery and shift autolysosomes into death effectors. The opportunities that lie ahead in this field are exciting. Various authophagy mediators are potentially druggable. Moreover, animal models and the development of sophisticated screening methods offer a platform for multilevel academic-industrial collaborations. These efforts are expected to open avenues of research and, hopefully, lead to a more rational approach to melanoma treatment.

Interruption of mitochondrial complex IV activity and cytochrome c expression activated O₂·⁻-mediated cell survival in silibinin-treated human melanoma A375-S2 cells via IGF-1R-PI3K-Akt and IGF-1R-PLC γ-PKC pathways

Silibinin was reported to have high cyto-toxicity in many malignant cell lines, however, it showed low cyto-toxicity in treatment of human melanoma A375-S2 cells and even protected these cells against certain stress insults. Reactive oxygen species was reported to have controversial effects on cancer chemotherapy. In this study we investigated the mechanism of reactive oxygen species generation and the role of reactive oxygen species in protecting cells against silibinin induced cyto-toxicity in A375-S2 cells. We found that silibinin induced the generation of large amount of superoxide anion (O(2)(∙-)) and small amount of hydrogen peroxide (H(2)O(2)) through down-regulating the activity of mitochondrial complex IV and the protein level of cytochrome c. We also discovered that O(2)(∙-) generation activated insulin like growth factor-1 receptor (IGF-1R) and its down-stream phosphatidylinositol 3-kinases-Akt (PI3K-Akt) and phospholipase C γ-protein kinase C (PLC γ-PKC) signaling pathways, which were augmented by H(2)O(2) scavenger catalase. Scavenging O(2)(∙-) by superoxide dismutase (SOD) or inhibition of IGF-1R-PI3K-Akt and IGF-1R-PLC γ-PKC signaling pathways increased cell apoptosis. Therefore, O(2)(∙-) mediated cell resistance to silibinin via activating IGF-1R-PI3K-Akt and IGF-1R-PLC γ-PKC pathways in silibinin treated A375-S2 cells.