Neoalbaconol induces cell death through necroptosis by regulating RIPK-dependent autocrine TNFα and ROS production

Necroptosis pathway emerged as potential diagnosis markers in spinal cord injury

The present research focused on identifying necroptosis-related differentially expressed genes (NRDEGs) in spinal cord injury (SCI) to highlight potential therapeutic and prognostic target genes in clinical SCI. Three SCI-related datasets were downloaded, including GSE151371, GSE5296 and GSE47681. MSigDB and KEGG datasets were searched for necroptosis-related genes (NRGs). Differentially expressed genes (DEGs) and NRGs were intersected to obtain NRDEGs. The MCC algorithm was employed to select the first 10 genes as hub genes. A protein-protein interaction (PPI) network related to NRDEGs was developed utilizing STRING. Several databases were searched to predict interactions between hub genes and miRNAs, transcription factors, potential drugs, and small molecules. Immunoassays were performed to identify DEGs using CIBERSORTx. Additionally, qRT-PCR was carried out to verify NRDEGs in an animal model of SCI. Combined analysis of all datasets identified 15 co-expressed DEGs and NRGs. GO and KEGG pathway analyses highlighted DEGs mostly belonged to pathways associated with necroptosis and apoptosis. Hub gene expression analysis showed high accuracy in SCI diagnosis was associated with the expression of CHMP7 and FADD. A total of two hub genes, i.e. CHMP7, FADD, were considered potential targets for SCI therapy.

Current evidence and therapeutic implication of PANoptosis in cancer

Regulated cell death (RCD) is considered a critical pathway in cancer therapy, contributing to eliminating cancer cells and influencing treatment outcomes. The application of RCD in cancer treatment is marked by its potential in targeted therapy and immunotherapy. As a type of RCD, PANoptosis has emerged as a unique form of programmed cell death (PCD) characterized by features of pyroptosis, apoptosis, and necroptosis but cannot be fully explained by any of these pathways alone. It is regulated by a multi-protein complex called the PANoptosome. As a relatively new concept first described in 2019, PANoptosis has been shown to play a role in many diseases, including cancer, infection, and inflammation. This study reviews the application of PCD in cancer, particularly the emergence and implication of PANoptosis in developing therapeutic strategies for cancer. Studies have shown that the characterization of PANoptosis patterns in cancer can predict survival and response to immunotherapy and chemotherapy, highlighting the potential for PANoptosis to be used as a therapeutic target in cancer treatment. It also plays a role in limiting the spread of cancer cells. PANoptosis allows for the elimination of cancer cells by multiple cell death pathways and has the potential to address various challenges in cancer treatment, including drug resistance and immune evasion. Moreover, active investigation of the mechanisms and potential therapeutic agents that can induce PANoptosis in cancer cells is likely to yield effective cancer treatments and improve patient outcomes. Research on PANoptosis is still ongoing, but it is a rapidly evolving field with the potential to lead to new treatments for various diseases, including cancer.

The development of necroptosis: what we can learn

Necroptosis is a new type of programmed cell death discovered in recent years, playing an important role in various diseases. Since it was conceptualized in 2005, research on necroptosis has developed rapidly. However, few bibliometric analyses have provided a comprehensive overview of the field. This study aimed to employ a bibliometric analysis to assess necroptosis research's current status and hotspot, highlight landmark findings, and orientate future research. A total of 3993 publications from the WoSCC were collected for this study. Multiple tools were used for bibliometric analysis and data visualization, including an online website, VOSviewer, CiteSpace, and HistCite. Publications related to necroptosis have increased significantly annually, especially in the last 5 years. Globally, the USA and Harvard University are the most outstanding countries and institutions in this field, respectively. The academic groups managed by Peter Vandenabeele and Junying Yuan both have permanent and intensive research on necroptosis. Cell Death and Differentiation is the most vital journal in this field. The molecular mechanisms of necroptosis and its role in disease are the focus of current research, while the crosstalk between programmed cell death is an emerging direction in the field. The "reactive oxygen species", "innate immunity", and "programmed cell death" may be potential research hotspots. Our results present a comprehensive knowledge map and explore research trends. Researchers and funding agencies on necroptosis can obtain helpful references from our study.

Analysis of the Prognosis Prediction Ability of a Necroptosis-Related Gene Signature and its Relationship With the Hepatocellular Carcinoma Immune Microenvironment Using Bioinformatics Analysis and Experimental Validation

Background: Hepatocellular carcinoma (HCC) is one of the most malignant cancers and has a poor prognosis. The immune microenvironment is closely related to the drug sensitivity of a tumor. Necroptosis was reported to be a key factor for HCC. The prognostic value of necroptosis-related genes and their association with the tumor immune microenvironment are still unknown. Methods: Necroptosis-related genes that could comprise a signature for predicting the prognosis of HCC cases were identified using univariate analysis and least absolute shrinkage and selection operator Cox regression analysis. The association between this prognosis prediction signature and HCC immune microenvironment was analyzed. The immunological activities and drug sensitivities were compared between different risk score groups identified using the prognosis prediction signature. The expression levels of the five genes comprising the signature were validated using RT-qPCR. Results: A prognosis prediction signature consisting of five necroptosis-related genes was constructed and validated. Its risk score was = (0.1634 × PGAM5 expression) + (0.0134 × CXCL1 expression) - (0.1007 × ALDH2 expression) + (0.2351 × EZH2 expression) - (0.0564 × NDRG2 expression). The signature was found to be significantly associated with the infiltration of B cells, CD4⁺ T cells, neutrophils, macrophages, and myeloid dendritic cells into the HCC immune microenvironment. The number of infiltrating immune cells and the expression levels of immune checkpoints in the immune microenvironment of high-risk score patients were higher. Sorafenib and immune checkpoint blockade were determined to be ideally suited for treating high-risk score patients and low-risk score patients, respectively. Finally, RT-qPCR results confirmed that the expression levels of EZH2, NDRG2, and ALDH2 were significantly down-regulated in HuH7 and HepG2 cells compared to those in LO2 cells. Conclusion: The necroptosis-related gene signature developed herein can classify patients with HCC according to prognosis risk well and is associated with infiltration of immune cells into the tumor immune microenvironment.

Role of Necroptosis in Central Nervous System Diseases

Necroptosis is a type of precisely regulated necrotic cell death activated in caspase-deficient conditions. Multiple factors initiate the necroptotic signaling pathway, including toll-like receptor 3/4, tumor necrosis factor (TNF), dsRNA viruses, and T cell receptors. Presently, TNF-induced necroptosis via the phosphorylation of three key proteins, receptor-interacting protein kinase 1, receptor-interacting protein kinase 3, and mixed lineage kinase domain-like protein, is the best-characterized process. Necroptosis induced by Z-DNA-binding protein 1 (ZBP-1) and toll/interleukin-1 receptor (TIR)-domain-containing adapter-inducing interferon (TRIF) plays a significant role in infectious diseases, such as influenza A virus, Zika virus, and herpesvirus infection. An increasing number of studies have demonstrated the close association of necroptosis with multiple diseases, and disrupting necroptosis has been confirmed to be effective for treating (or managing) these diseases. The central nervous system (CNS) exhibits unique physiological structures and immune characteristics. Necroptosis may occur without the sequential activation of signal proteins, and the necroptosis of supporting cells has more important implications in disease development. Additionally, necroptotic signals can be activated in the absence of necroptosis. Here, we summarize the role of necroptosis and its signal proteins in CNS diseases and characterize typical necroptosis regulators to provide a basis for the further development of therapeutic strategies for treating such diseases. In the present review, relevant information has been consolidated from recent studies (from 2010 until the present), excluding the patents in this field.

Role of Receptor Interacting Protein (RIP) kinases in cancer

The Receptor Interacting Protein (RIP) kinase family consists of seven Serine/Threonine kinases, which plays a key signaling role in cell survival and cell death. Each RIP family member contains a conserved kinase domain and other domains that determine the specific kinase function through protein-protein interactions. RIP1 and RIP3 are best known for their critical roles in necroptosis, programmed necrosis and a non-apoptotic inflammatory cell death process. Dysregulation of RIP kinases contributes to a variety of pathogenic conditions such as inflammatory diseases, neurological diseases, and cancer. In cancer cells, alterations of RIP kinases at genetic, epigenetic and expression levels are frequently found, and suggested to promote tumor progression and metastasis, escape of antitumor immune response, and therapeutic resistance. However, RIP kinases can be either pro-tumor or anti-tumor depending on specific tumor types and cellular contexts. Therapeutic agents for targeting RIP kinases have been tested in clinical trials mainly for inflammatory diseases. Deregulated expression of these kinases in different types of cancer suggests that they represent attractive therapeutic targets. The focus of this review is to outline the role of RIP kinases in cancer, highlighting potential opportunities to manipulate these proteins in cancer treatment.

Necroptosis: A Pathogenic Negotiator in Human Diseases

Over the past few decades, mechanisms of programmed cell death have attracted the scientific community because they are involved in diverse human diseases. Initially, apoptosis was considered as a crucial mechanistic pathway for programmed cell death; recently, an alternative regulated mode of cell death was identified, mimicking the features of both apoptosis and necrosis. Several lines of evidence have revealed that dysregulation of necroptosis leads to pathological diseases such as cancer, cardiovascular, lung, renal, hepatic, neurodegenerative, and inflammatory diseases. Regulated forms of necrosis are executed by death receptor ligands through the activation of receptor-interacting protein kinase (RIPK)-1/3 and mixed-lineage kinase domain-like (MLKL), resulting in the formation of a necrosome complex. Many papers based on genetic and pharmacological studies have shown that RIPKs and MLKL are the key regulatory effectors during the progression of multiple pathological diseases. This review focused on illuminating the mechanisms underlying necroptosis, the functions of necroptosis-associated proteins, and their influences on disease progression. We also discuss numerous natural and chemical compounds and novel targeted therapies that elicit beneficial roles of necroptotic cell death in malignant cells to bypass apoptosis and drug resistance and to provide suggestions for further research in this field.

Occurrences and phenotypes of RIPK3-positive gastric cells in Helicobacter pylori infected gastritis and atrophic lesions

BACKGROUND

Research evidences suggest that diverse forms of programmed cell death (PCD) are involved in the helicobacter pylori (H. pylori)-induced gastric inflammation and disorders.

AIMS

To characterize occurrences and phenotypes of necroptosis in gastric cells in H. pylori infected gastritis and atrophic specimens.

METHODS

Occurrences and phenotypes of necroptosis in gastric cells were immunohistochemically characterized with receptor-interacting protein kinase 3 (RIPK3) antibody in both human H. pylori infected gastric gastritis, atrophic specimens, and transgenic mice.

RESULTS

Increased populations of RIPK3-positive cells were observed in both gastric glands and lamina propria in H. pylori infected human oxyntic gastritis and atrophic specimens. Phenotypic analysis revealed that many RIPK3-positive cells were H ⁺ K⁺ ATPase-positive parietal cells in the gastric glands and were predominantly CD3-positive T lymphocytes, CD68-positive macrophages, and SMA-alpha-positive stromal cells in the lamina propria. Furthermore, we found an increased expression of RIPK3-positive gastric glandular cells along with the histological process of hyperplasia-atrophy-dysplasia progression in hypergastrinemic INS-GAS mice.

CONCLUSIONS

An increased population of RIPK3-positive cells was observed in several types of gastric cells, future studies that define the effects and mechanisms of PCD implicated in the development of H. pylori induced gastric disorders are needed.

Zinc finger protein 91 mediates necroptosis by initiating RIPK1-RIPK3-MLKL signal transduction in response to TNF receptor 1 ligation

Necroptosis is a form of regulated programmed cell death that is mediated by receptor-interacting protein kinase 1 (RIPK1), receptor-interacting serine/threonine protein kinase-3 (RIPK3), and mixed lineage kinase domain-like protein (MLKL); however, it is not known whether zinc finger protein 91 (ZFP91) is involved in this process. Here, we investigated ZFP91 as a potential mediator of necroptosis. Our mechanistic study demonstrates that ZFP91 promotes RIPK1-RIPK3 interaction, thereby stabilizing the RIPK1 and RIPK3 proteins and facilitating necroptosis. ZFP91 stabilized RIPK1 to promote cell death by inducing RIPK1 de-ubiquitination. ZFP91 also significantly increased production of mitochondrial reactive oxygen species (ROS). Accumulation of ROS promoted RIPK3-independent necroptosis triggered by tumor necrosis factor (TNF). in vivo, ZFP91 knockdown alleviated TNFα-induced systemic inflammatory response syndrome (SIRS). These results provide direct evidence that ZFP91 plays an important role in the initiation of RIPK1/RIPK3-dependent necroptosis in vitro and in vivo. We discussed the potential of ZFP91 as a novel therapeutic target for necroptosis-associated diseases.

Tanshinone IIA Shows Higher Antiproliferative Activities than Sinapic Acid in 4 Cancer Cell Lines and Simultaneously Induces Apoptosis and Necroptosis in Human Lung Cancer A549 Cells

Tanshinone IIA (Tan IIA) and sinapic acid (SA) are 2 components separately isolated from 2 Asian medicinal plants, Hydnophytum formicarum Jack and Salvia miltiorrhiza Bunge. The antitumor activities of them were worth exploring, therefore, we examined their antitumor activities in A549, HCT116, HeLa, and Colo320 cancer cell lines by means of WST-1 assay. The results show that Tan IIA exerted far higher (IC50 from 1.0 ± 0.0 to 166.3 ± 24.0 µg/mL) antiproliferative activities than SA (IC50 from 2236.3 ± 484.1 to >10 000.0 µg/mL). Of the 4 cell lines, A549 cells were the most sensitive to Tan IIA; thus, we used Western blotting to explore the cytotoxic mechanisms of Tan IIA in A549 cells and found that they rely on simultaneous induction of apoptosis and necroptosis in the cells. Apoptosis was hallmarked by the induction of cleaved caspase-3 by Tan IIA and necroptosis by the necroptotic marker proteins cyclophilin A and high mobility group box 1 (HMGB1), as well as increased lactate dehydrogenase (LDH) activities. The necroptotic effect was confirmed by the necroptosis inhibitor necrostatin-1 (Nec-1), which eliminated these effects and restored cell survival rates. The levels of cyclophilin A decreased in response to the pan-caspase inhibitor z-VAD-fmk, and those of cleaved caspase-3 decreased in response to Nec-1. Conclusively, Tan IIA has the potential to prevent lung cancer and the mechanism seems to be apoptosis and necroptosis, of which the relationship is mutually interdependent. This is the first report of Tan IIA eliciting necroptosis in A549 cells. Tan IIA may be used for necroptosis-based cancer therapy, especially to overcome apoptosis resistance.

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.

The expression of RIPK3 is associated with cell turnover of gastric mucosa in the mouse and human stomach

Necroptosis is a novel manner of programmed cell death and important for tissue development, homeostasis, damage, and repair. Activation of receptor-interacting protein kinase 3 (RIPK3), a key member of receptor-interacting protein family in contributing significantly to necroptosis, in tissues is a hallmark of cells dying by necroptosis. However, there are few studies that examine the expression of RIPK3 in the glandular cells of stomachs under physiological condition. We have therefore conducted this study to immunohistochemically characterize the key element of necroptosis, RIPK3, in the mouse and human stomach. Results showed that RIPK3 positive cells could be observed in the surface mucosal cells, granular cells, and lamina propria cells in both mouse and human stomach tissues. Ratios of PCNA/RIPK3 positive cells in the glandular cells were ~ 2.1 in mouse and ~ 4.15 in human sections respectively. Morphological and double immunofluorescence analysis confirmed that these RIPK3 positive cells were mucous, parietal and lamina propria cells. Our results indicate that the expression of RIPK3 in different cell types might contribute to cell turnover of gastric mucosa in the mouse and human stomach under physiological condition.

Caspase-Independent Regulated Necrosis Pathways as Potential Targets in Cancer Management

Regulated necrosis is an emerging type of cell death independent of caspase. Recently, with increasing findings of regulated necrosis in the field of biochemistry and genetics, the underlying molecular mechanisms and signaling pathways of regulated necrosis are gradually understood. Nowadays, there are several modes of regulated necrosis that are tightly related to cancer initiation and development, including necroptosis, ferroptosis, parthanatos, pyroptosis, and so on. What’s more, accumulating evidence shows that various compounds can exhibit the anti-cancer effect via inducing regulated necrosis in cancer cells, which indicates that caspase-independent regulated necrosis pathways are potential targets in cancer management. In this review, we expand the molecular mechanisms as well as signaling pathways of multiple modes of regulated necrosis. We also elaborate on the roles they play in tumorigenesis and discuss how each of the regulated necrosis pathways could be therapeutically targeted.

Targeting the signaling in Epstein-Barr virus-associated diseases: mechanism, regulation, and clinical study

Epstein–Barr virus-associated diseases are important global health concerns. As a group I carcinogen, EBV accounts for 1.5% of human malignances, including both epithelial- and lymphatic-originated tumors. Moreover, EBV plays an etiological and pathogenic role in a number of non-neoplastic diseases, and is even involved in multiple autoimmune diseases (SADs). In this review, we summarize and discuss some recent exciting discoveries in EBV research area, which including DNA methylation alterations, metabolic reprogramming, the changes of mitochondria and ubiquitin-proteasome system (UPS), oxidative stress and EBV lytic reactivation, variations in non-coding RNA (ncRNA), radiochemotherapy and immunotherapy. Understanding and learning from this advancement will further confirm the far-reaching and future value of therapeutic strategies in EBV-associated diseases.

Targeting necroptosis in anticancer therapy: mechanisms and modulators

Necroptosis, a genetically programmed form of necrotic cell death, serves as an important pathway in human diseases. As a critical cell-killing mechanism, necroptosis is associated with cancer progression, metastasis, and immunosurveillance. Targeting necroptosis pathway by small molecule modulators is emerging as an effective approach in cancer therapy, which has the advantage to bypass the apoptosis-resistance and maintain antitumor immunity. Therefore, a better understanding of the mechanism of necroptosis and necroptosis modulators is necessary to develop novel strategies for cancer therapy. This review will summarize recent progress of the mechanisms and detecting methods of necroptosis. In particular, the relationship between necroptosis and cancer therapy and medicinal chemistry of necroptosis modulators will be focused on.

The Role of Necroptosis in ROS-Mediated Cancer Therapies and Its Promising Applications

Over the past decades, promising therapies targeting different signaling pathways have emerged. Among these pathways, apoptosis has been well investigated and targeted to design diverse chemotherapies. However, some patients are chemoresistant to these therapies due to compromised apoptotic cell death. Hence, exploring alternative treatments aimed at different mechanisms of cell death seems to be a potential strategy for bypassing impaired apoptotic cell death. Emerging evidence has shown that necroptosis, a caspase-independent form of cell death with features between apoptosis and necrosis, can overcome the predicament of drug resistance. Furthermore, previous studies have also indicated that there is a close correlation between necroptosis and reactive oxygen species (ROS); both necroptosis and ROS play significant roles both under human physiological conditions such as the regulation of inflammation and in cancer biology. Several small molecules used in experiments and clinical practice eliminate cancer cells via the modulation of ROS and necroptosis. The molecular mechanisms of these promising therapies are discussed in detail in this review.

Necroptosis in Immuno-Oncology and Cancer Immunotherapy

Immune-checkpoint blockers (ICBs) have revolutionized oncology and firmly established the subfield of immuno-oncology. Despite this renaissance, a subset of cancer patients remain unresponsive to ICBs due to widespread immuno-resistance. To "break" cancer cell-driven immuno-resistance, researchers have long floated the idea of therapeutically facilitating the immunogenicity of cancer cells by disrupting tumor-associated immuno-tolerance via conventional anticancer therapies. It is well appreciated that anticancer therapies causing immunogenic or inflammatory cell death are best positioned to productively activate anticancer immunity. A large proportion of studies have emphasized the importance of immunogenic apoptosis (i.e., immunogenic cell death or ICD); yet, it has also emerged that necroptosis, a programmed necrotic cell death pathway, can also be immunogenic. Emergence of a proficient immune profile for necroptosis has important implications for cancer because resistance to apoptosis is one of the major hallmarks of tumors. Putative immunogenic or inflammatory characteristics driven by necroptosis can be of great impact in immuno-oncology. However, as is typical for a highly complex and multi-factorial disease like cancer, a clear cause versus consensus relationship on the immunobiology of necroptosis in cancer cells has been tough to establish. In this review, we discuss the various aspects of necroptosis immunobiology with specific focus on immuno-oncology and cancer immunotherapy.

Necroptosis in Cholangiocarcinoma

Necroptosis is a type of regulated cell death that is increasingly being recognized as a relevant pathway in different pathological conditions. Necroptosis can occur in response to multiple stimuli, is triggered by the activation of death receptors, and is regulated by receptor-interacting protein kinases 1 and 3 and mixed-lineage kinase domain-like, which form a regulatory complex called the necrosome. Accumulating evidence suggests that necroptosis plays a complex role in cancer, which is likely context-dependent and can vary among different types of neoplasms. Necroptosis serves as an alternative mode of programmed cell death overcoming apoptosis and, as a pro-inflammatory death type, it may inhibit tumor progression by releasing damage-associated molecular patterns to elicit robust cross-priming of anti-tumor CD8+ T cells. The development of therapeutic strategies triggering necroptosis shows great potential for anti-cancer therapy. In this review, we summarize the current knowledge on necroptosis and its role in liver biliary neoplasms, underlying the potential of targeting necroptosis components for cancer treatment.

Celastrol Induces Necroptosis and Ameliorates Inflammation via Targeting Biglycan in Human Gastric Carcinoma

Celastrol, a triterpene isolated from the root of traditional Chinese medicine Thunder of God Vine, possesses anti-cancer and anti-inflammatory activity to treat rheumatoid disease or as health product. Necroptosis is considered as a new approach to overcome chemotherapeutics resistance. However, whether celastrol exerts necroptosis leading to gastric cancer cell death is still unclear. Here, for the first time we showed that celastrol induced necroptosis in HGC27 and AGS gastric cancer cell lines. More importantly, celastrol down-regulated biglycan (BGN) protein, which is critical for gastric cancer migration and invasion. Furthermore, celastrol activated receptor-interacting protein 1 and 3 (RIP1 and RIP3) and subsequently promoted the translation of mixed-lineage kinase domain-like (MLKL) from cytoplasm to plasma membrane, leading to necroptosis of gastric cancer cell, which was blocked by over-expression BGN. In addition, celastrol suppressed the release of pro-inflammatory cytokines TNF-α and IL-8 in HGC27 and AGS cells, which was reversed by over-expression BGN. Taken together, we identified celastrol as a necroptosis inducer, activated RIP1/RIP3/MLKL pathway and suppressed the level of pro-inflammatory cytokines by down-regulating BGN in HGC-27 and AGS cells, which supported the feasibility of celastrol in gastric cancer therapy.

Current translational potential and underlying molecular mechanisms of necroptosis

Cell death has a fundamental impact on the evolution of degenerative disorders, autoimmune processes, inflammatory diseases, tumor formation and immune surveillance. Over the past couple of decades extensive studies have uncovered novel cell death pathways, which are independent of apoptosis. Among these is necroptosis, a tightly regulated, inflammatory form of cell death. Necroptosis contribute to the pathogenesis of many diseases and in this review, we will focus exclusively on necroptosis in humans. Necroptosis is considered a backup mechanism of apoptosis, but the in vivo appearance of necroptosis indicates that both caspase-mediated and caspase-independent mechanisms control necroptosis. Necroptosis is regulated on multiple levels, from the transcription, to the stability and posttranslational modifications of the necrosome components, to the availability of molecular interaction partners and the localization of receptor-interacting serine/threonine-protein kinase 1 (RIPK1), receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Accordingly, we classified the role of more than seventy molecules in necroptotic signaling based on consistent in vitro or in vivo evidence to understand the molecular background of necroptosis and to find opportunities where regulating the intensity and the modality of cell death could be exploited in clinical interventions. Necroptosis specific inhibitors are under development, but >20 drugs, already used in the treatment of various diseases, have the potential to regulate necroptosis. By listing necroptosis-modulated human diseases and cataloging the currently available drug-repertoire to modify necroptosis intensity, we hope to kick-start approaches with immediate translational potential. We also indicate where necroptosis regulating capacity should be considered in the current applications of these drugs.

Medicinal Plants from Brazilian Cerrado: Antioxidant and Anticancer Potential and Protection against Chemotherapy Toxicity

The use of natural antioxidants in cancer therapy has increased: first, due to the potential of natural antioxidants to kill tumour cells and second, because of their capacity to protect healthy cells from the damage caused by chemotherapy. This review article discusses the antioxidant properties of extracts obtained from medicinal plants from the Brazilian Cerrado and the cell death profile induced by each of these extracts in malignant cells. Next, we describe the capacity of other medicinal plants from the Cerrado to protect against chemotherapy-induced cell toxicity. Finally, we focus on recent insights into the cell death profile induced by extracts from Cerrado plants and perspectives for future therapeutic approaches.

Inhibition of Lung Cancer by 2-Methoxy-6-Acetyl-7-Methyljuglone Through Induction of Necroptosis by Targeting Receptor-Interacting Protein 1

Aims: Most chemotherapeutic agents exploit apoptotic signaling to trigger cancer cell death, which frequently results in drug resistance. Necroptosis, a nonapoptotic form of regulated cell death, offers an alternative strategy to eradicate apoptosis-resistant cancer cells. We previously reported a natural necroptosis inducer 2-methoxy-6-acetyl-7-methyljuglone (MAM) in A549 lung cancer cells. The current study is designed to investigate the detailed necroptotic signaling and its cytotoxicity on drug-resistant cancer cells. Furthermore, in vivo anticancer effects were also evaluated in nude mice model. Results: MAM directly targets receptor-interacting protein 1 (RIP1) kinase in A549 and H1299 cells, which is responsible for reactive oxygen species (ROS, mainly hydrogen peroxide) generation. A positive feedback loop between calcium (Ca²⁺) and c-Jun N-terminal kinase (JNK) occurred following ROS generation, leading to lysosomal membrane permeabilization and mitochondrial dysfunction. MAM showed similar cytotoxic potency toward cisplatin-resistant A549 (A549/Cis) cells by inducing necroptosis as confirmed by the protective effect of 7-Cl-O-Nec-1 (Nec-1s) and by the morphological characteristics obtained via transmission electron microscopy. Interestingly, tumor necrosis factor alpha (TNFα) was not involved in this process. Intraperitoneal injection of MAM significantly suppressed tumor growth in A549 tumor xenograft without significant body weight loss and multiorgan toxicities. Innovation and Conclusion: Our findings demonstrate that MAM induces necroptosis in A549 and H1299 lung cancer cells by targeting RIP1 kinase and ROS in a TNFα-independent manner. MAM kills A549/Cis cells with similar potency through induction of necroptosis. MAM shows anticancer effect in animal model. The present study raises the therapeutic possibility and strategy to combat cancer by the induction of necroptosis.

The role of necroptosis in cancer biology and therapy

Apoptosis resistance is to a large extent a major obstacle leading to chemotherapy failure during cancer treatment. Bypassing the apoptotic pathway to induce cancer cell death is considered to be a promising approach to overcoming this problem. Necroptosis is a regulated necrotic cell death modality in a caspase-independent fashion and is mainly mediated by Receptor-Interacting Protein 1 (RIP1), RIP3, and Mixed Lineage Kinase Domain-Like (MLKL). Necroptosis serves as an alternative mode of programmed cell death overcoming apoptosis resistance and may trigger and amplify antitumor immunity in cancer therapy.The role of necroptosis in cancer is complicated. The expression of key regulators of the necroptotic pathway is generally downregulated in cancer cells, suggesting that cancer cells may also evade necroptosis to survive; however, in certain types of cancer, the expression level of key mediators is elevated. Necroptosis can elicit strong adaptive immune responses that may defend against tumor progression; however, the recruited inflammatory response may also promote tumorigenesis and cancer metastasis, and necroptosis may generate an immunosuppressive tumor microenvironment. Necroptosis also reportedly promotes oncogenesis and cancer metastasis despite evidence demonstrating its antimetastatic role in cancer. In addition, necroptotic microenvironments can direct lineage commitment to determine cancer subtype development in liver cancer. A plethora of compounds and drugs targeting necroptosis exhibit potential antitumor efficacy, but their clinical feasibility must be validated.Better knowledge of the necroptotic pathway mechanism and its physiological and pathological functions is urgently required to solve the remaining mysteries surrounding the role of necroptosis in cancer. In this review, we briefly introduce the molecular mechanism and characteristics of necroptosis, the interplay between necroptosis and other cell death mechanisms, crosstalk of necroptosis and metabolic signaling and detection methods. We also summarize the intricate role of necroptosis in tumor progression, cancer metastasis, prognosis of cancer patients, cancer immunity regulation, cancer subtype determination and cancer therapeutics.

Redox biology of regulated cell death in cancer: A focus on necroptosis and ferroptosis

Redox changes and generation of reactive oxygen species (ROS) are part of normal cell metabolism. While low ROS levels are implicated in cellular signaling pathways necessary for survival, higher levels play major roles in cancer development as well as cell death signaling and execution. A role for redox changes in apoptosis has been long established; however, several new modalities of regulated cell death have been brought to light, for which the importance of ROS production as well as ROS source and targets are being actively investigated. In this review, we summarize recent findings on the role of ROS and redox changes in the activation and execution of two major forms of regulated cell death, necroptosis and ferroptosis. We also discuss the potential of using modulators of these two forms of cell death to exacerbate ROS as a promising anticancer therapy.

The Epstein-Barr virus LMP1 interactome: biological implications and therapeutic targets

The oncogenic potential of Epstein-Barr virus (EBV) is mostly attributed to latent membrane protein 1 (LMP1), which is essential and sufficient for transformation of fibroblast and primary lymphocytes. LMP1 expression results in the activation of multiple signaling cascades like NF-ΚB and MAP kinases that trigger cell survival and proliferative pathways. LMP1 specific signaling events are mediated through the recruitment of a number of interacting proteins to various signaling domains. Based on these properties, LMP1 is an attractive target to develop effective therapeutics to treat EBV-related malignancies. In this review, we focus on LMP1 interacting proteins, associated signaling events, and potential targets that could be exploited for therapeutic strategies.

Hexavalent chromium induces oxidative stress and mitochondria-mediated apoptosis in isolated skin fibroblasts of Indo-Pacific humpback dolphin

The increasing gas emissions and industrial wastewater discharge of anthropogenic hexavalent chromium (Cr(VI)) have been growing health concerns to the high trophic level marine mammals. Our previous studies showed that Indo-Pacific humpback dolphin (Sousa chinensis), stranded on the Pearl River Estuary region, contained exceedingly high levels of Cr in their skin-tissues. Unfortunately, the molecular toxic mechanisms on this mammal are absent, limiting our understanding of the eco-physiological impacts of Cr(VI) on dolphins. Thus, the cytotoxicity effects of Cr(VI) were analyzed on fibroblasts we isolated from the skin of S. chinensis (ScSF). This study showed that Cr(VI) markedly inhibited the viability of ScSF cells via induction of apoptosis accompanied by an increase in the production of reactive oxygen species and the population of G2/M arrest or apoptotic sub-G1 phase cells, up-regulation of p53, and activation of caspase-3. Further investigation on intracellular mechanisms indicated that Cr(VI) induced depletion of mitochondrial membrane potential in cells through regulating the expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) proteins, resulting in decrease of the ATP level, cytochrome c release from mitochondria into cytosol, and the activation of caspase-9. Furthermore, antioxidants N-acetylcysteine and vitamin C displayed chemoprotective activity against Cr(VI) via suppression of p53 expression, indicating that the Cr(VI)-induced cell death may be mediated by oxidative stress. Overall, these results provide insights into the potential mechanisms underlying the cytotoxicity of Cr(VI) in Indo-Pacific humpback dolphin skin cells, offer experimental support for the proposed protective role of antioxidants in Cr(VI)-induced toxicity, and suggest that Cr(VI) contamination is one of key health concern issues for the protection of Indo-Pacific humpback dolphin.

Hydrogen peroxide induces programmed necrosis in rat nucleus pulposus cells through the RIP1/RIP3-PARP-AIF pathway

This study aimed to systematically investigate whether programmed necrosis contributes to H2 O2 -induced nucleus pulposus (NP) cells death and to further explore the underlying mechanism involved. Rat NP cells were subjected to different concentrations of H2 O2 for various time periods. The cell viability was measured using a cell counting kit-8, and the death rate was detected by Hoechst 33258/propidium iodide (PI) staining. The programmed necrosis-related molecules receptor-interacting protein 1 (RIP1), receptor-interacting protein 3 (RIP3), poly (ADP-ribose) polymerase (PARP), and apoptosis inducing factor (AIF) were determined by real-time polymerase chain reaction and Western blotting, respectively. The morphologic and ultrastructural changes were examined by phasecontrast microscopy and transmission electron microscopy (TEM). In addition, the necroptosis inhibitor Necrostatin-1 (Nec-1), the PARP inhibitor diphenyl-benzoquinone (DPQ) and small interfering RNA (siRNA) technology were used to indirectly evaluate programmed necrosis. Our results indicated that H2 O2 induced necrotic morphologic and ultrastructural changes and an elevated PI positive rate in NP cells; these effects were mediated by the upregulation of RIP1 and RIP3, hyperactivation of PARP, and translocation of AIF from mitochondria to nucleus. Additionally, NP cells necrosis was significantly attenuated by Nec-1, DPQ pretreatment and knockdown of RIP3 and AIF, while knockdown of RIP1 produced the opposite effects. In conclusion, these results suggested that under oxidative stress, RIP1/RIP3-mediated programmed necrosis, executed through the PARP-AIF pathway, played an important role in NP cell death. Protective strategies aiming to regulate programmed necrosis may exert a beneficial effect for NP cells survival, and ultimately retard intervertebral disc (IVD) degeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1269-1282, 2018.

Hispidin induces autophagic and necrotic death in SGC-7901 gastric cancer cells through lysosomal membrane permeabilization by inhibiting tubulin polymerization

Hispidin and its derivatives are widely distributed in edible mushrooms. Hispidin is more cytotoxic to A549, SCL-1, Bel7402 and Capan-1 cancer cells than to MRC5 normal cells; by contrast, hispidin protects H9c2 cardiomyoblast cells from hydrogen peroxide-induced or doxorubicin-induced apoptosis. Consequently, further research on how hispidin affects normal and cancer cells may help treat cancer and reduce chemotherapy-induced side effects. This study showed that hispidin caused caspase-independent death in SGC-7901 cancer cells but not in GES-1 normal cells. Hispidin-induced increases in LC3-II occurred in SGC-7901 cells in a time independent manner. Cell death can be partially inhibited by treatment with ATG5 siRNA but not by autophagy or necroptosis inhibitors. Ultrastructural evidence indicated that hispidin-induced necrotic cell death involved autophagy. Hispidin-induced lysosomal membrane permeabilization (LMP) related to complex cell death occurred more drastically in SGC-7901 cells than in GES-1 cells. Ca²⁺ rather than cathepsins from LMP contributed more to cell death. Hispidin induced microtubule depolymerization, which can cause LMP, more drastically in SGC-7901 cells than in GES-1 cells. At 4.1 μM, hispidin promoted cell-free tubulin polymerization but at concentrations higher than 41 μM, hispidin inhibited polymerization. Hispidin did not bind to tubulin. Alterations in microtubule regulatory proteins, such as stathmin phosphorylation at Ser¹⁶, contributed to hispidin-induced SGC-7901 cell death. In conclusion, hispidin at concentrations higher than 41 μM may inhibit tubulin polymerization by modulating microtubule regulatory proteins, such as stathmin, causing LMP and complex SGC-7901 cell death. This mechanism suggests a promising novel treatment for human cancer.

NCTD promotes Birinapant-mediated anticancer activity in breast cancer cells by downregulation of c-FLIP

Second mitochondria-derived activator of caspases (SMAC) mimetics is a class of new anticancer agents. However, most cancers exhibit de novo or acquired resistance to SMAC mimetics, posting a problem for broad applications in clinic, and highlighting the necessity of exploring combinational strategies to circumvent SMAC mimetic-resistance. We here showed that Norcantharidin, a drug that is currently being used in cancer treatment, significantly enhanced SMAC mimetic Birinapant-mediated cell viability inhibition and robustly promoted apoptosis in established breast carcinoma cell lines, as well as in primary breast carcinoma cells. Mechanistically, we revealed that Norcantharidin effectively reduced the levels of two major protein isoforms of cellular FLICE-like inhibitor protein(c-FLIP), namely c-FLIP long (c-FLIPL) and c-FLIP short (c-FLIPS). Moreover, Norcantharidin markedly enhanced Birinapant-triggered caspase-8/caspase-3 cascade. Inhibition of caspase-8 activity by a synthetic peptide Z-IETD-FMK significantly attenuated cell death induction by the combination, suggesting that caspase-8 plays a critical role in the anticancer action. In conclusion, our study suggests that the combination of SMAC mimetics with Norcantharidin represents a novel strategy in breast cancer therapy and warrants further studies.

Shikonin potentiates the effect of arsenic trioxide against human hepatocellular carcinoma in vitro and in vivo

Hepatocellular carcinoma (HCC) is a highly lethal malignancy mostly because of metastasis, recurrence and acquired resistance to conventional chemotherapy. Arsenic trioxide (ATO) is successfully used to treat hematological malignancies, and has been proven to trigger apoptosis in HCC cells. However, the phase II trial evaluating the efficacy and toxicity of ATO in patients with HCC showed that single-agent ATO is poorly active against HCC. Therefore, it is of great importance to develop effective chemosensitization agents to ATO. The aim of the present study was to determine whether shikonin (SHI), a natural product from the root of lithospermum erythrorhizon, could synergistically enhance the anti-HCC efficacy of ATO both in vitro and in vivo. We found that the combination of SHI and ATO exhibited synergistic anticancer efficacy and achieved greater selectivity between cancer cells and normal cells. By inducing intracellular oxidative stress, SHI potentiated ATO-induced DNA damage, followed by increased activation of endoplasmic reticulum stress. In addition, inhibition of ROS reversed the apoptosis induced by SHI and ATO, and recovered the activation of endoplasmic reticulum stress, which revealed the vital role of ROS in the synergism. Moreover, HepG2 xenograft tumor growth in nude mice was more effectively inhibited by combined treatment with SHI and ATO. These data suggest that the combination of SHI with ATO presents a promising therapeutic approach for the treatment of HCC.

Necroptosis in tumorigenesis, activation of anti-tumor immunity, and cancer therapy

While the mechanisms underlying apoptosis and autophagy have been well characterized over recent decades, another regulated cell death event, necroptosis, remains poorly understood. Elucidating the signaling networks involved in the regulation of necroptosis may allow this form of regulated cell death to be exploited for diagnosis and treatment of cancer, and will contribute to the understanding of the complex tumor microenvironment. In this review, we have summarized the mechanisms and regulation of necroptosis, the converging and diverging features of necroptosis in tumorigenesis, activation of anti-tumor immunity, and cancer therapy, as well as attempts to exploit this newly gained knowledge to provide therapeutics for cancer.

RIP3 deficiency protects against traumatic brain injury (TBI) through suppressing oxidative stress, inflammation and apoptosis: Dependent on AMPK pathway

Traumatic brain injury (TBI) is a leading cause of disability and mortality in young adults worldwide. The pathophysiology is not fully understood. Programmed necrosis (necroptosis) is a newly identified mechanism of cell death combining features of both apoptosis and necrosis. Receptor-interacting protein 3 (RIP3) plays an important role in programmed necrosis. However, the effect of RIP3-related pathway in TBI is little to be known. We attempted to explore the significance of RIP3 in regulating TBI in vivo. Significantly, TBI induced over-expression of RIP3 in the hippocampus of mice, as well as RIP1 and phosphorylated mixed lineage kinase domain-like protein (MLKL). Mice after TBI exhibited cognitive dysfunction and activation of glia cells, which were significantly attenuated by RIP3-knockout (KO). Moreover, inflammation and oxidative stress in hippocampus were markedly induced by TBI in wild type (WT) mice. Of note, the reduction of pro-inflammatory cytokines and oxidants was observed in RIP3-deficient mice, which was linked to the blockage of NLR pyrin domain containing 3 (NLRP3)/apoptosis-associated speck-like protein containing a CARD (ASC)/Caspase-1 and kelch-like ECH-associated protein 1 (Keap 1) pathways. Further, TBI induced hippocampus apoptosis, evidenced by the increase of cleaved Caspase-8/-3 and poly (ADP)-ribose polymerase (PARP) in WT mice, whereas being decreased by RIP3-knockout. In addition, RIP3 knockout led to phosphorylation of AMP-activated protein kinase α (AMPKα) in hippocampus of mice after TBI. And of note, the in vitro findings indicated that RIP3-ablation attenuated oxidative stress, inflammation and apoptosis in astrocytes, which was dependent on AMPKα activation. Together, suppressing RIP3 might be served as a therapeutic target against brain injury through inhibiting inflammation, oxidative stress and apoptosis.

RIPK1 Inhibition Enhances Pirarubicin Cytotoxic Efficacy through AKT-P21-dependent Pathway in Hepatocellular Carcinoma

Pirarubicin (THP) is a new generation cell cycle nonspecific anthracycline anticancer drug. Pirarubicin and pirarubicin-based combination therapies have been demonstrated to be effective against HCC in TACE. However, the drug resistance limits its therapeutic efficacy. Receptor-interacting protein kinase 1 (RIPK1) displays a critical role in cell death. Here we found that RIPK1 and p21 may participate in the resistance to pirarubicin. In this study, we first found that inhibition of RIPK1 significantly decreased pAKT and increased p21, accompanied by G0/G1 phase cell cycle arrest and cell anti-proliferation in pirarubicin-treated hepatocellular carcinoma cells. Moreover, phosphorylation of AKT reversed the anti-proliferative effect of RIPK1 inhibitor in HCC, which proved that RIPK1-AKT-P21-dependent pathway played a key role in pirarubicin resistance. Using a mouse xenograft model, we further found that RIPK1 inhibitor combined with pirarubicin exerted synergistic anti-tumor effect in vivo. Upon exposure to pirarubicin treatment, xenografts under RIPK1 inhibition maintained higher levels of p21 than control xenografts. In conclusion, the results in our study demonstrated that RIPK1 inhibition enhances the anti-tumor effect of pirarubicin by overcoming drug resistance. RIPK1 inhibitor might be used as an adjuvant to potentiate the inhibitory effect of pirarubicin against primary hepatocellular carcinoma.

Baicalin hydrate inhibits cancer progression in nasopharyngeal carcinoma by affecting genome instability and splicing

Baicalin hydrate (BH), a natural compound, has been investigated for many years because of its traditional medicinal properties. However, the anti-tumor activities of BH and its epigenetic role in NPC have not been elucidated. In this study, we identified that BH inhibits NPC cell growth in vivo and in vitro by inducing apoptosis and cell cycle arrest. BH epigenetically regulated genome instability by up-regulating the expression of satellite 2 (Sat2), alpha satellite (α-Sat), and major satellite (Major-Sat). BH also increased the level of IKKα, Suv39H1, and H3K9me3 and decreased LSH expression. Interestingly, BH promoted the splicing of Suv39H1 via the enhancement of m6A RNA methylation, rather than DNA methylation. Taken together, our results demonstrated that BH has an anti-tumor role in NPC and revealed a unique role of BH in genome instability and splicing in response to DNA damage.

Deguelin, an Aurora B Kinase Inhibitor, Exhibits Potent Anti-Tumor Effect in Human Esophageal Squamous Cell Carcinoma

Aurora B kinase has emerged as a key regulator of mitosis and deregulation of Aurora B activity is closely related to the development and progression of human cancers. In the present study, we found that Aurora B is overexpressed in human esophageal squamous cell carcinoma (ESCC), high levels of Aurora B protein were associated with a worse overall survival rate in ESCC patients. Depleting of Aurora B blunted the malignant phenotypes in ESCC cells. Importantly, we demonstrated that a natural compound, deguelin, has a profound anti-tumor effect on ESCC via inhibiting Aurora B activity. Deguelin potently inhibited in vitro Aurora B kinase activity. The in silico docking study further indicated that deguelin was docked into the ATP-binding pocket of Aurora B. Inhibition of Aurora B activity attenuated growth of ESCC cells, resulted in G2/M cell cycle arrest, polyploidy cells formation, and apoptosis induction. Knocking down of Aurora B decreased the sensitivity of ESCC cells to deguelin. The in vivo results showed that deguelin blocked the phosphorylation of histone H3 and inhibited the growth of ESCC tumor xenografts. Overall, we identified deguelin as an effective Aurora B inhibitor, which deserves further studies in other animal models and ESCC treatment.

Necroptosis in cancer: An angel or a demon?

In the past few decades, apoptosis has been regarded as the only form of programmed cell death. However, the traditional view has been challenged by the identification of several forms of regulated necrosis, including necroptosis. Necroptosis is typified by a necrotic cell death morphology and is controlled by RIP1, RIP3, and mixed lineage kinase domain-like protein. The physiological role of necroptosis is to serve as a "fail-safe" form of cell death for cells that fail to undergo apoptosis during embryonic development and disease defense. Currently, established studies have indicated that necroptosis is involved in cancer initiation and progression. Although elevated necroptosis contributes to cancer cell death, extensive cell death also increases the risk of proliferation and metastasis of the surviving cells by inducing the generation reactive oxygen species, activation of inflammation, and suppression of the immune response. Thus, questions regarding the overall impact of necroptosis on cancer remain open. In this review, we introduce the basic knowledge regarding necroptosis, summarize its dual effects on cancer progression, and analyze its advantages and disadvantages in clinical applications.

A novel damage mechanism: Contribution of the interaction between necroptosis and ROS to high glucose-induced injury and inflammation in H9c2 cardiac cells

Recently, a novel mechanism known as 'programmed necrosis' or necroptosis has been shown to be another important mechanism of cell death in the heart. In this study, we investigated the role of necroptosis in high glucose (HG)-induced injury and inflammation, as well as the underlying mechanisms. In particular, we focused on the interaction between necroptosis and reactive oxygen species (ROS) in H9c2 cardiac cells. Our results demonstrated that the exposure of H9c2 cardiac cells to 35 mM glucose (HG) markedly enhanced the expression level of receptor-interacting protein 3 (RIP3), a kinase which promotes necroptosis. Importantly, co-treatment of the cells with 100 µM necrostatin-1 (a specific inhibitor of necroptosis) and HG for 24 h attenuated not only the increased expression level of RIP3, but also the HG-induced injury and inflammation, as evidenced by an increase in cell viability, a decrease in ROS generation, the attenuation of the dissipation of mitochondrial membrane potential and a decrese in the secretion levels of inflammatory cytokines, i.e., interleukin (IL)-1β and tumor necrosis factor (TNF)-α. Furthermore, treatment of the cells with 1 mM N-acetyl‑L‑cysteine (a scavenger of ROS) for 60 min prior to exposure to HG significantly reduced the HG-induced increase in the RIP3 expression level, as well as the injury and inflammatory response described above. Taken together, the findings of this study clearly demonstrate a novel damage mechanism involving the positive interaction between necroptosis and ROS attributing to HG-induced injury and inflammation in H9c2 cardiac cells.

Cytosolic calcium mediates RIP1/RIP3 complex-dependent necroptosis through JNK activation and mitochondrial ROS production in human colon cancer cells

Necroptosis is a form of programmed necrosis mediated by signaling complexes with receptor-interacting protein 1 (RIP1) and RIP3 kinases as the main mediators. However, the underlying execution pathways of this phenomenon have yet to be elucidated in detail. In this study, a RIP1/RIP3 complex was formed in 2-methoxy-6-acetyl-7-methyljuglone (MAM)-treated HCT116 and HT29 colon cancer cells. With this formation, mitochondrial reactive oxygen species (ROS) levels increased, mitochondrial depolarization occurred, and ATP concentrations decreased. This process was identified as necroptosis. This finding was confirmed by experiments showing that MAM-induced cell death was attenuated by the pharmacological or genetic blockage of necroptosis signaling, including RIP1 inhibitor necrostatin-1s (Nec-1s) and siRNA-mediated gene silencing of RIP1 and RIP3, but was unaffected by caspase inhibitor z-vad-fmk or necrosis inhibitor 2-(1H-Indol-3-yl)-3-pentylamino-maleimide (IM54). Transmission electron microscopy (TEM) analysis further revealed the ultrastructural features of MAM-induced necroptosis. MAM-induced RIP1/RIP3 complex triggered necroptosis through cytosolic calcium (Ca²⁺) accumulation and sustained c-Jun N-terminal kinase (JNK) activation. Both calcium chelator BAPTA-AM and JNK inhibitor SP600125 could attenuate necroptotic features, including mitochondrial ROS elevation, mitochondrial depolarization, and ATP depletion. 2-thenoyltrifluoroacetone (TTFA), which is a mitochondrial complex II inhibitor, was found to effectively reverse both MAM induced mitochondrial ROS generation and cell death, indicating the complex II was the ROS-producing site. The essential role of mitochondrial ROS was confirmed by the protective effect of overexpression of manganese superoxide dismutase (MnSOD). MAM-induced necroptosis was independent of TNFα, p53, MLKL, and lysosomal membrane permeabilization. In summary, our study demonstrated that RIP1/RIP3 complex-triggered cytosolic calcium accumulation is a critical mediator in MAM-induced necroptosis through sustained JNK activation and mitochondrial ROS production. Our study also provided new insights into the molecular regulation of necroptosis in human colon cancer cells.

Necroptosis: Modules and molecular switches with therapeutic implications

Among the various programmed cell death (PCD) pathways, "Necroptosis" has gained much importance as a novel paradigm of cell death. This pathway has emerged as a backup mechanism when physiologically conserved PCD (apoptosis) is non-functional either genetically or pathogenically. The expanding spectrum of necroptosis from physiological development to diverse patho-physiological disorders, including xenobiotics-mediated toxicity has now grabbed the attention worldwide. The efficient role of necroptosis regulators in disease development and management are under constant examination. In fact, few regulators (e.g. MLKL) have already paved their way towards clinical trials and others are in queue. In this review, emphasis has been paid to the various contributing factors and molecular switches that can regulate necroptosis. Here we linked the overview of current knowledge of this enigmatic signaling with magnitude of therapeutics that may underpin the opportunities for novel therapeutic approaches to suppress the pathogenesis of necroptosis-driven disorders.

The effects and regulatory mechanism of RIP3 on RGC-5 necroptosis following elevated hydrostatic pressure

Necroptosis is a type of regulated cell death that has been implicated in various diseases. Receptor-interacting protein 3 (RIP3), a member of the RIP family, is an important mediator of the necroptotic pathway. Cleavage of RIP3 at Asp328 by caspase-8 abolishes the kinase activity of RIP3, which is critical for necroptosis. Moreover, RIP3 is significantly upregulated during the early stages of acute high intra-ocular pressure and oxygen glucose deprivation. In this study, the effects of RIP3 during elevated hydrostatic pressure (EHP) were investigated and the possible mechanism through which caspase-8 regulated RIP3 cleavage was explored. Flow cytometry analysis revealed that the number of EHP-induced necrotic retinal ganglion cell 5 (RGC-5) cells was reduced after RIP3-knockdown. Furthermore, malondialdehyde (MDA) levels and glycogen phosphorylase (PYGL) activity in normal RGC-5 cells were much higher than those in RIP3-knockdown cells after EHP. EHP-induced RGC-5 necrosis was significantly reduced after treatment with butylated hydroxyanisole (BHA), a reactive oxygen species (ROS) scavenger. MDA levels and PYGL activity were lower in normal RGC-5 cells than those in cells with caspase-8 inhibition after EHP. Western blot analysis demonstrated that the RIP3 cleavage product was upregulated in cells with caspase-8 inhibition. Additionally, flow cytometry analysis revealed that the number of EHP-induced necrotic RGC-5 cells was increased after caspase-8 inhibition. Our results suggested that RGC-5 necroptosis following EHP was mediated by RIP3 through induction of PYGL activity and subsequent ROS accumulation. Thus, caspase-8 may participate in the regulation of RGC-5 necroptosis via RIP3 cleavage.

Matrine induces RIP3-dependent necroptosis in cholangiocarcinoma cells

The development of acquired resistance to pro-apoptotic antitumor agents is a major impediment to the cure of cholangiocarcinoma (CCA). Antitumor drugs inducing non-apoptotic cell death are considered as a new approach to overcome such drug resistance. Here, we reported for the first time that matrine-induced necroptosis in CCA cell lines, differing from its classical role to induce apoptosis in many other kinds of cancer cells. CCA cells under matrine treatment exhibited typical necrosis-like but not apoptotic morphologic change. These matrine-induced morphologic change and cell death in CCA cells were greatly attenuated by necroptosis inhibitor necrostatin-1, but not apoptosis inhibitor z-VAD-fmk. Unlike many cancer cells with negative receptor-interacting protein 3 (RIP3) expression, moderate expression of RIP3 in CCA cells was observed and was required for matrine to induce necroptosis, which was switched to apoptosis after knocking down endogenous RIP3. Moreover, matrine could increase RIP3 expression level, which may facilitate the necroptosis process. Translocation of mixed lineage kinase-domain like (MLKL) from cytoplasm to plasma membrane as a downstream event of RIP3, as well as the increased production of reactive oxygen species (ROS) by RIP3/MLKL, was critical for matrine to induce necroptosis. In clinical study, we found RIP3 was lower but still moderately expressed in most CCA tissue samples compared with adjacent normal tissues. Taken together, we identified matrine as a necroptosis inducer in CCA by enhancing RIP3 expression and the following RIP3/MLKL/ROS signaling pathway, which provided new individualized strategies based on RIP3 expression to overcome chemoresistance in CCA therapy.

Endosulfan induces apoptosis by activating the negative regulation pathway of cell cycle and death receptor pathway in spermatogenic cells

The male reproductive toxicity of endosulfan has been proved. Nevertheless, the underlying molecular mechanisms of the apoptosis caused by endosulfan in spermatogenic cells remains poorly understood. In order to investigate the reproductive toxicity mechanism caused by endosulfan, there were four groups, which had eight Wistar male rats randomly assigned to them, and the rats in different groups received different doses of endosulfan for a period of 21 days. GC-1 spermatogenic cell lines were divided into four groups, and each group was exposed to different doses of endosulfan for 24 hours. The results of this research showed that endosulfan decreased the cell viability, damaged cell membranes and induced apoptosis in spermatogenic cells. Endosulfan had obviously activated the protein expression of PKC-δ, p53, p^21cip1, p^27kip1, Fas, FasL, Caspase-8, Caspase-3, and inhibited the expression of E₂F-1. Endosulfan also induced oxidative stress and DNA damage in spermatogenic cells. The results of this research suggested that endosulfan could lead to E₂F-1-induced apoptosis of spermatogenic cells by activating the negative regulation factors of the cell cycle, and endosulfan might cause apoptosis by death receptor pathway, causing oxidative stress.

Endosulfan inducing apoptosis and necroptosis through activation RIPK signaling pathway in human umbilical vascular endothelial cells

Endosulfan, an organochlorine pesticide, was found in human blood, and its possible cardiovascular toxicity has been suggested. However, the mechanism about endothelial cell injuries induced by endosulfan has remained unknown. In the present study, human umbilical vein endothelial cells (HUVECs) were chosen to explore the toxicity mechanism and were treated with 0, 1, 6, and 12 μg/mL^-1 endosulfan for 24 h, respectively. The results showed that exposure to endosulfan could inhibit the cell viability, increase the release of lactate dehydrogenase (LDH), damage the ultrastructure, and lead to apoptosis and necroptosis in HUVECs. Furthermore, endosulfan upregulated the expressions of receptor-interacting protein kinase 1 (RIPK1), receptor-interacting protein kinase 3 (RIPK3), mixed lineage kinase domain-like (MLKL), caspase 8, and caspase 3, which means the activation of RIPK1 pathways. In addition, endosulfan promoted the increases of ROS, IL-1α, and IL-33 levels while antioxidant N-acetyl-L-cysteine (NAC) effectively attenuated the cytotoxicity from endosulfan. Taken together, these results have demonstrated that endosulfan induces the apoptosis and necroptosis of HUVECs, where the RIPK pathway plays a pro-necroptotic role and NAC plays an anti-necroptotic role. Our results may contribute to understanding cellular mechanisms for endosulfan-induced cardiovascular toxicity.

Relevance of necroptosis in cancer

Resistance to caspase-dependent apoptosis is often responsible for treatment failures in cancer. Finding novel therapeutic strategies that can activate alternative cell death programs appears to be appealing. Necroptosis is a form of programmed necrosis that occurs under caspase-deficient conditions. This alternative form of cell death has recently emerged as a potential anticancer therapy that could overcome apoptosis resistance. A growing understanding of the molecular events triggering necroptosis helped to examine its implication in cancer development and to define new therapeutic strategies. Genetic and proteomic analysis suggest that necroptosis is deregulated in many cancers. Various preclinical and clinical compounds induced necroptosis and have demonstrated significant therapeutic efficacy. Moreover, accumulating evidence has shown that necroptosis promotes anticancer immune response. A better knowledge of the cascade of events regulating necroptosis is expected to assess the feasibility of its therapeutic exploitation for cancer therapy.