Execution of RIPK3-regulated necrosis

Oleanolic Acid Acetate Alleviates Cisplatin-Induced Nephrotoxicity via Inhibition of Apoptosis and Necroptosis In Vitro and In Vivo

Cisplatin is a widely used anti-cancer drug for treating solid tumors, but it is associated with severe side effects, including nephrotoxicity. Various studies have suggested that the nephrotoxicity of cisplatin could be overcome; nonetheless, an effective adjuvant drug has not yet been established. Oleanolic acid acetate (OAA), a triterpenoid isolated from Vigna angularis, is commonly used to treat inflammatory and allergic diseases. This study aimed to investigate the protective effects of OAA against cisplatin-induced apoptosis and necroptosis using TCMK-1 cells and a mouse model. In cisplatin-treated TCMK-1 cells, OAA treatment significantly reduced Bax and cleaved-caspase3 expression, whereas it increased Bcl-2 expression. Moreover, in a cisplatin-induced kidney injury mouse model, OAA treatment alleviated weight loss in the body and major organs and also relieved cisplatin-induced nephrotoxicity symptoms. RNA sequencing analysis of kidney tissues identified lipocalin-2 as the most upregulated gene by cisplatin. Additionally, necroptosis-related genes such as receptor-interacting protein kinase (RIPK) and mixed lineage kinase domain-like (MLKL) were identified. In an in vitro study, the phosphorylation of RIPKs and MLKL was reduced by OAA pretreatment in both cisplatin-treated cells and cells boosted via co-treatment with z-VAD-FMK. In conclusion, OAA could protect the kidney from cisplatin-induced nephrotoxicity and may serve as an anti-cancer adjuvant.

Identification of a necroptosis-related gene signature for making clinical predictions of the survival of patients with lung adenocarcinoma

Background

Lung adenocarcinoma (LUAD) is a major pathological subtype of malignant lung cancer with a poor prognosis. Necroptosis is a caspase-independent programmed cell death mode that plays a pivotal role in cancer oncogenesis and metastasis. Here, we explore the prognostic values of different necroptosis-related genes (NRGs) in LUAD.

Methods

mRNA expression data and related clinical information for LUAD samples were obtained from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus databases. NRGs were identified using the GeneCards database. Least absolute shrinkage and selection operator Cox regression and multivariate Cox analysis were used to construct a prognostic risk model. Time-dependent receiver-operating characteristic curves and a nomogram were constructed to validate the predictive values of the prognostic signatures. A necroptosis-related protein-protein interaction network was visualised using the STRING database and Cytoscape software. Functional analyses, including Gene Ontology, Kyoto Encyclopaedia of Genes and Genomes pathway enrichment, gene set enrichment, and gene set variation analyses, were conducted to explore the underlying molecular mechanisms. Finally, the mRNA expression of the prognostic signatures in LUAD cell lines was assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis.

Results

A prognostic model was established for eight NRGs (CALM1, DDX17, FPR1, OGT, PGLYRP1, PRDX1, TUFM, and CPSF3) based on TCGA-cohort data and validated with the GSE68465 cohort. Patients with low-risk scores had better survival outcomes than those with high-risk scores (p = 0.00013). The nomogram was used to predict the prognosis of patients with LUAD. The prediction curves for 1-, 3-, and 5-year OS showed good predictive performance and the accuracy of the nomograms increased over time. RT-qPCR results demonstrated that these eight genes, especially CALM1, PRDX1, and PGLYRP1, were differentially expressed in LUAD cells.

Conclusion

We constructed a reliable eight-NRG signature that provides new insights for guiding clinical practice in the prognosis and treatment of LUAD.

Necrotizing apoptosis-related genes prognosis and treatment effect analysis of osteosarcoma in children

BACKGROUND

Immune cell homeostasis plays a crucial role in cancer research and therapeutic response. While chemotherapy and immunotherapy hold promise in treating osteosarcoma (OS), identifying patients who are likely to respond would significantly improve clinical practices. Necroptosis, a fundamental mechanism mediating chemotherapy and immunotherapy efficacy, offers valuable insights. In this context, subtypes based on necroptosis-related genes have been established to predict the response of OS patients to immunotherapy and chemotherapy.

METHODS

We conducted a high-throughput screening test to identify necroptosis-associated genes that regulate the development of osteosarcoma. Subsequently, the ConsensusClusterPlus package was employed to classify OS patients into subtypes, enabling comparisons of prognosis and clinical information between these subtypes. Patients from the TARGET-OS and GSE21257 datasets were stratified into high-risk and low-risk groups, and their prognoses were compared. Additionally, we assessed the accuracy of the Risk Scoring Model in predicting prognosis, identified independent prognostic factors and explored potential chemotherapeutic agents and immunotherapy drugs.

RESULTS

Through the intersection of expression profiles from the TARGET-OS and GSE21257 datasets, we have identified a total of 92 genes associated with necroptosis. Based on differences in the expression of these genes, patients were divided into three subtypes, and we investigated the differences in tumor-infiltrating immune cells, immune-related pathways, and prognosis among these subtypes. Our nomogram effectively differentiated subtypes with distinct responses to chemotherapy and immunotherapy. The established signature demonstrated superior prediction ability compared with single clinical indicators.

CONCLUSIONS

This pioneering study unveils the prognostic role of necroptosis-related genes in OS patients, providing a promising alternative for prognostic prediction in clinical disease management. Moreover, our findings highlight the significance of immune cell homeostasis in cancer research and therapeutic response, underscoring its relevance in advancing current treatment strategies.

Targeting Cx43 to Reduce the Severity of Pressure Ulcer Progression

In the skin, repeated incidents of ischemia followed by reperfusion can result in the breakdown of the skin and the formation of a pressure ulcer. Here we gently applied paired magnets to the backs of mice to cause ischemia for 1.5 h and then removed them to allow reperfusion. The sterile inflammatory response generated within 4 h causes a stage 1 pressure ulcer with an elevation of the gap junction protein Cx43 in the epidermis. If this process is repeated the insult will result in a more severe stage 2 pressure ulcer with a breakdown of the epidermis 2-3 days later. After a single pinch, the elevation of Cx43 in the epidermis is associated with the inflammatory response with an increased number of neutrophils, HMGB1 (marker of necrosis) and RIP3 (responsible for necroptosis). Delivering Cx43 specific antisense oligonucleotides sub-dermally after a single insult, was able to significantly reduce the elevation of epidermal Cx43 protein expression and reduce the number of neutrophils and prevent the elevation of HMGB1 and RIP3. In a double pinch model, the Cx43 antisense treatment was able to reduce the level of inflammation, necroptosis, and the extent of tissue damage and progression to an open wound. This approach may be useful in reducing the progression of stage 1 pressure ulcers to stage 2.

Profiling of the chemical space on the phenyl group of substituted benzothiazole RIPK3 inhibitors

Necroptosis is confirmed as a precisely programmed cell death that is activated in caspase-deficient conditions. Receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like pseudokinase (MLKL) are the key regulators involved in the signaling pathway. However, accumulating evidence suggests that RIPK1 also works in apoptosis and inflammation pathways independent of necroptosis. Differently, RIPK3 signals necroptosis independent of RIPK1. Thus, identification of specific RIPK3 inhibitors is of great importance for the drug development associated with necroptosis. The benzothiazole carboxamide is a privileged scaffold as RIPK3 inhibitors developed by our group recently. In this study, we work on the phenyl group in-between of benzothiazole and carboxamide to profile the chemical space. Finally, a chlorinated derivative XY-1-127 was found to specifically inhibit necroptosis rather than apoptosis with an EC₅₀ value of 676.8 nM and target RIPK3 with a K_d of 420 nM rather than RIPK1 (K_d = 4300 nM). It was also confirmed to block the formation of necrosome by inhibiting RIPK3 phosphorylation at 1 μM in necroptosis cells. This work discovers the chemical space insights on the phenyl group of the substituted benzothiazole RIPK3 inhibitors and provides a new lead compound for further development.

Global publication trends and research trends of necroptosis application in tumor: A bibliometric analysis

Introduction: Necroptosis is an alternative, caspase-independent programmed cell death that appears when apoptosis is inhibited. A gowing number of studies have reflected the link between necroptosis and tumors. However, only some systematical bibliometric analyses were focused on this field. In this study, we aimed to identify and visualize the cooperation between countries, institutions, authors, and journals through a bibliometric analysis to help understand the hotspot trends and emerging topics regarding necroptosis and cancer research. Methods: The articles and reviews on necroptosis and cancer were obtained from the Web of Science Core Collection on 16 September 2022. Countries, institutions, authors, references, and keywords in this field were visually analyzed by CtieSpace 5.8.R3, VOSviewer 1.6.18, and R package "bibliometrix." Results: From 2006 to 2022, 2,216 qualified original articles and reviews on necroptosis in tumors were published in 685 academic journals by 13,009 authors in 789 institutions from 75 countries/regions. Publications focusing on necroptosis and cancer have increased violently in the past 16 years, while the citation number peaked around 2008-2011. Most publications were from China, while the United States maintained the dominant position as a "knowledge bridge" in necroptosis and cancer research; meanwhile, Ghent University and the Chinese Academy of Sciences were the most productive institutions. Moreover, only a tiny portion of the articles were multiple-country publications. Peter Vandenabeele had the most significant publications, while Alexei Degterev was most often co-cited. Peter Vandenabeele also gets the highest h-index and g-index in this research field. Cell Death and Disease was the journal with the most publications on necroptosis and cancer, which was confirmed to be the top core source by Bradford's Law. At the same time, Cell was the leading co-cited journal, and the focus area of these papers was molecular, biology, and immunology. High-frequency keywords mainly contained those that are molecularly related (MLKL, NF-kB, TNF, RIPK3, RIPK1), pathological process related (necroptosis, apoptosis, cell-death, necrosis, autophagy), and mechanism related (activation, expression, mechanisms, and inhibition). Conclusion: This study comprehensively overviews necroptosis and cancer research using bibliometric and visual methods. Research related to necroptosis and cancer is flourishing. Cooperation and communication between countries and institutions must be further strengthened. The information in our paper would provide valuable references for scholars focusing on necroptosis and cancer.

Comprehensive Analysis of Necroptosis-Related Genes as Prognostic Factors and Immunological Biomarkers in Breast Cancer

Breast cancer (BC) is a lethal malignancy with a poor prognosis. Necroptosis is critical in the progression of cancer. However, the expression of genes involved in necroptosis in BC and their association with prognosis remain unclear. We investigated the predictive potential of necroptosis-related genes in BC samples from the TCGA dataset. We used LASSO regression to build a risk model consisting of twelve necroptosis-related genes in BC. Using the necroptosis-related risk model, we were able to successfully classify BC patients into high- and low-risk groups with significant prognostic differences (p = 4.872 × 10 ^-7). Additionally, we developed a matched nomogram predicting 5, 7, and 10-year overall survival in BC patients based on this necroptosis-related risk model. Our next step was to perform multiple GSEA analyses to explore the biological pathways through which these necroptosis-related risk genes influence cancer progression. For these twelve risk model genes, we analyzed CNV, SNV, OS, methylation, immune cell infiltration, and drug sensitivity in pan-cancer. In addition, immunohistochemical data from the THPA database were used to validate the protein expression of these risk model genes in BC. Taken together, we believe that necroptosis-related genes are considered potential therapeutic targets in BC and should be further investigated.

Apoptosis, autophagic cell death, and necroptosis: different types of programmed cell death in bovine corpus luteum regression

In mammals, the corpus luteum (CL) is a transient organ that secretes progesterone (P4). In the absence of pregnancy, the CL undergoes regression (luteolysis), which is a crucial preparation step for the next estrous cycle. Luteolysis, initiated by uterine prostaglandin F_2α (PGF) in cattle, is usually divided into two phases, namely functional luteolysis characterized by a decline in P4 concentration and structural luteolysis characterized by the elimination of luteal tissues from the ovary. Programmed cell death (PCD) of luteal cells, including luteal steroidogenic cells (LSCs) and luteal endothelial cells (LECs), plays a crucial role in structural luteolysis. The main types of PCD are caspase-dependent apoptosis (type 1), autophagic cell death (ACD) via the autophagy-related gene (ATG) family (type 2), and receptor-interacting protein kinase (RIPK)-dependent programmed necrosis (necroptosis, type 3). However, these PCD signaling pathways are not completely independent and interact with each other. Over the past several decades, most studies on luteolysis have focused on apoptosis as the principal mode of bovine luteal cell death. Recently, ATG family members were reported to be expressed in bovine CL, and their levels increased during luteolysis. Furthermore, the expression of RIPKs, which are crucial mediators of necroptosis, is reported to increase in bovine CL during luteolysis and is upregulated by pro-inflammatory cytokines in bovine LSCs and LECs. Therefore, apoptosis, ACD, and necroptosis may contribute to bovine CL regression. In this article, we present the recent findings regarding the mechanisms of the three main types of PCD and the contribution of these mechanisms to luteolysis.

Different modalities of host cell death and their impact on Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) is the pathogen that causes tuberculosis (TB), a leading infectious disease of humans worldwide. One of the main histopathological hallmarks of TB is the formation of granulomas comprised of elaborately organized aggregates of immune cells containing the pathogen. Dissemination of Mtb from infected cells in the granulomas due to host and mycobacterial factors induces multiple cell death modalities in infected cells. Based on molecular mechanism, morphological characteristics, and signal dependency, there are two main categories of cell death: programmed and nonprogrammed. Programmed cell death (PCD), such as apoptosis and autophagy, is associated with a protective response to Mtb by keeping the bacteria encased within dead macrophages that can be readily phagocytosed by arriving in uninfected or neighboring cells. In contrast, non-PCD necrotic cell death favors the pathogen, resulting in bacterial release into the extracellular environment. Multiple types of cell death in the PCD category, including pyroptosis, necroptosis, ferroptosis, ETosis, parthanatos, and PANoptosis, may be involved in Mtb infection. Since PCD pathways are essential for host immunity to Mtb, therapeutic compounds targeting cell death signaling pathways have been experimentally tested for TB treatment. This review summarizes different modalities of Mtb-mediated host cell deaths, the molecular mechanisms underpinning host cell death during Mtb infection, and its potential implications for host immunity. In addition, targeting host cell death pathways as potential therapeutic and preventive approaches against Mtb infection is also discussed.

High Glucose Induces Late Differentiation and Death of Human Oral Keratinocytes

Keratinocytes are essential cells for wound repair. Impaired oral wound healing is common in diabetic patients with periodontal disease. High glucose, or hyperglycemia, impairs the cellular function of different cell types. However, it is unknown whether high glucose has a detrimental effect on the functions of oral keratinocytes. In the current study, a human gingival keratinocyte cell line, telomerase immortalized gingival keratinocytes (TIGK), was treated with high glucose (24 and 48 mM) for up to 120 h. Proliferation, migration, cell viability, and production of markers of differentiation, growth factors and enzymatic antioxidants were assessed after high glucose treatment. The results showed that high glucose significantly inhibited TIGK proliferation and migration. High glucose also induced significant cell death through apoptosis and necrosis as determined by flow cytometry, especially at 120 h after high glucose treatment. Necrosis was the dominant form of cell death induced. Real-time PCR showed that high glucose treatment upregulated mRNA expression of late keratinocyte differentiation makers, such as keratin 1, 10, 13 and loricrin, and downregulated enzymatic antioxidants, including superoxide dismutase 1, catalase, nuclear factor erythroid 2 -related factor 2, heme oxygenase 1. In conclusion, high glucose impairs the proliferation and migration of oral keratinocytes and likely induces cell death through the promotion of late cell differentiation and down-regulation of enzymatic antioxidants.

The regulation of necroptosis by ubiquitylation

Necroptosis is a programmed necrosis that is mediated by receptor-interacting protein kinases RIPK1, RIPK3 and the mixed lineage kinase domain-like protein, MLKL. Necroptosis must be strictly regulated to maintain normal tissue homeostasis, and dysregulation of necroptosis leads to the development of various inflammatory, infectious, and degenerative diseases. Ubiquitylation is a widespread post-translational modification that is essential for balancing numerous physiological processes. Over the past decade, considerable progress has been made in the understanding of the role of ubiquitylation in regulating necroptosis. Here, we will discuss the regulatory functions of ubiquitylation in necroptosis signaling pathway. An enhanced understanding of the ubiquitylation enzymes and regulatory proteins in necroptotic signaling pathway will be exploited for the development of new therapeutic strategies for necroptosis-related diseases.

Neuroimmune Mechanisms Underlying Neuropathic Pain: The Potential Role of TNF-α-Necroptosis Pathway

The neuroimmune mechanism underlying neuropathic pain has been extensively studied. Tumor necrosis factor-alpha (TNF-α), a key pro-inflammatory cytokine that drives cytokine storm and stimulates a cascade of other cytokines in pain-related pathways, induces and modulates neuropathic pain by facilitating peripheral (primary afferents) and central (spinal cord) sensitization. Functionally, TNF-α controls the balance between cell survival and death by inducing an inflammatory response and two programmed cell death mechanisms (apoptosis and necroptosis). Necroptosis, a novel form of programmed cell death, is receiving increasing attraction and may trigger neuroinflammation to promote neuropathic pain. Chronic pain is often accompanied by adverse pain-associated emotional reactions and cognitive disorders. Overproduction of TNF-α in supraspinal structures such as the anterior cingulate cortex (ACC) and hippocampus plays an important role in pain-associated emotional disorders and memory deficits and also participates in the modulation of pain transduction. At present, studies reporting on the role of the TNF-α–necroptosis pathway in pain-related disorders are lacking. This review indicates the important research prospects of this pathway in pain modulation based on its role in anxiety, depression and memory deficits associated with other neurodegenerative diseases. In addition, we have summarized studies related to the underlying mechanisms of neuropathic pain mediated by TNF-α and discussed the role of the TNF-α–necroptosis pathway in detail, which may represent an avenue for future therapeutic intervention.

Synthesis and characterization of potent RIPK3 inhibitors based on a tricyclic scaffold

Background: Necroptosis is an important form of regulated cell death involved in inflammatory diseases, degenerative diseases and cancer. RIPK3 is an interesting target for intervention of necroptosis-associated diseases. Methodology: Herein the authors report the synthesis of a series RIPK3 inhibitors under the guidance of structure-based drug design which leads to the identification of compound 37. Results: Compound 37 potently rescued human and mouse cells from necroptotic stimuli TNFα, Smac mimetic, z-VAD and LPS + z-VAD, displayed high affinity to RIPK3 (Kd = 14 nM) but no observable affinity to RIPK1 and inhibited RIPK3 kinase function. Importantly, compound 37 significantly alleviated TNF-induced systemic inflammatory response syndrome in the mouse model. Conclusion: These results support compound 37 as a prototype RIPK3 inhibitor for lead optimization.

The multitargeted kinase inhibitor KW-2449 ameliorates cisplatin-induced nephrotoxicity by targeting RIPK1-mediated necroptosis

Cisplatin (cis-dichloro-diammine platinum, CDDP) is a well-known chemotherapeutic drug against a broad spectrum of human malignancies. However, the clinical utility of this effective chemotherapy agent is dose limited by its toxic side effects such as nephrotoxicity and ototoxicity. Necroptosis is a form of programmed necrotic cell death that is mediated by serine/threonine kinases, RIPK1 and RIPK3, together with MLKL. In this study, we identified that the multitargeted kinase inhibitor KW-2449 inhibited cisplatin-induced necroptosis, while potentiated cisplatin-induced apoptosis in cancer cells. Mechanistic studies indicated that KW-2449 directly inhibited RIPK1 kinase activity to block necroptosis. Oral administration of KW-2449 attenuated renal cell necrosis and reduced pro-inflammatory responses in mouse models of cisplatin-induced nephrotoxicity. Taken together, our study shows that KW-2449 is a novel necroptosis inhibitor by targeting RIPK1 kinase activity and has great clinic potential for the treatment of cisplatin-induced nephrotoxicity.

Programmed Cell Death in the Left and Right Ventricle of the Late Phase of Post-Infarction Heart Failure

While necroptosis has been shown to contribute to the pathogenesis of post-infarction heart failure (HF), the role of autophagy remains unclear. Likewise, linkage between these two cell death modalities has not been sufficiently investigated. HF was induced by 60-min left coronary occlusion in adult Wistar rats and heart function was assessed 6 weeks later followed by immunoblotting analysis of necroptotic and autophagic proteins in both the left (LV) and right ventricle (RV). HF had no effect on RIP1 and RIP3 expression. PhosphoSer229-RIP3, acting as a pro-necroptotic signal, was increased in LV while deceased in RV of failing hearts. Total MLKL was elevated in RV only. Decrease in pSer555-ULK1, increase in pSer473-Akt and no significant elevation in beclin-1 and LC3-II/I ratio indicated rather a lowered rate of autophagy in LV. No beclin-1 upregulation and decreased LC3 processing also suggested the inhibition of both autophagosome formation and maturation in RV of failing hearts. In contrast, p89 PARP1 fragment, a marker of executed apoptosis, was increased in RV only. This is the first study showing a different signaling in ventricles of the late phase of post-infarction HF, highlighting necroptosis itself rather than its linkage with autophagy in LV, and apoptosis in RV.

Small-Molecule Inhibitors of Necroptosis: Current Status and Perspectives

Necroptosis, an important form of programmed cell death (PCD), is a highly regulated caspase-independent type of cell death that plays a critical role in the pathophysiology of various inflammatory, infectious, and degenerative diseases. Currently, receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL) have been widely recognized as critical therapeutic targets of the necroptotic machinery. Targeting RIPK1, RIPK3, and/or MLKL is a promising strategy for necroptosis-related diseases. Following the identification of the first RIPK1 inhibitor Nec-1 in 2005, the antinecroptosis field is attracting increasing research interest from multiple disciplines, including the biological and medicinal chemistry communities. Herein, we will review the functions of necroptosis in human diseases, as well as the related targets and representative small-molecule inhibitors, mainly focusing on research articles published during the past 10 years. Outlooks and perspectives on the associated challenges are also discussed.

Different signalling in infarcted and non-infarcted areas of rat failing hearts: A role of necroptosis and inflammation

Necroptosis has been recognized in heart failure (HF). In this study, we investigated detailed necroptotic signalling in infarcted and non‐infarcted areas separately and its mechanistic link with main features of HF. Post‐infarction HF in rats was induced by left coronary occlusion (60 minutes) followed by 42‐day reperfusion. Heart function was assessed echocardiographically. Molecular signalling and proposed mechanisms (oxidative stress, collagen deposition and inflammation) were investigated in whole hearts and in subcellular fractions when appropriate. In post‐infarction failing hearts, TNF and pSer229‐RIP3 levels were comparably increased in both infarcted and non‐infarcted areas. Its cytotoxic downstream molecule p‐MLKL, indicating necroptosis execution, was detected in infarcted area. In non‐infarcted area, despite increased pSer229‐RIP3, p‐MLKL was present in neither whole cells nor the cell membrane known to be associated with necroptosis execution. Likewise, increased membrane lipoperoxidation and NOX2 levels unlikely promoted pro‐necroptotic environment in non‐infarcted area. Collagen deposition and the inflammatory csp‐1‐IL‐1β axis were active in both areas of failing hearts, while being more pronounced in infarcted tissue. Although apoptotic proteins were differently expressed in infarcted and non‐infarcted tissue, apoptosis was found to play an insignificant role. p‐MLKL‐driven necroptosis and inflammation while inflammation only (without necroptotic cell death) seem to underlie fibrotic healing and progressive injury in infarcted and non‐infarcted areas of failing hearts, respectively. Upregulation of pSer229‐RIP3 in both HF areas suggests that this kinase, associated with both necroptosis and inflammation, is likely to play a dual role in HF progression.

Role of Retinoic Acid Receptor-γ in DNA Damage-Induced Necroptosis

DNA-damaging compounds, commonly used as chemotherapeutic drugs, are known to trigger cells to undergo programmed cell death such as apoptosis and necroptosis. However, the molecular mechanism of DNA damage-induced cell death is not fully understood. Here, we report that RARγ has a critical role in DNA damage-induced programmed cell death, specifically in necroptosis. The loss of RARγ abolishes the necroptosis induced by DNA damage. In addition, cells that lack RARγ are less susceptible to extrinsic apoptotic pathway activated by DNA-damaging agents whereas the intrinsic apoptotic pathway is not affected. We demonstrate that RARγ is essential for the formation of RIPK1/RIPK3 death complex, known as Ripoptosome, in response to DNA damage. Furthermore, we show that RARγ plays a role in skin cancer development by using RARγ1 knockout mice and human squamous cell carcinoma biopsies. Hence, our study reveals that RARγ is a critical component of DNA damage-induced cell death.

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RARγ plays a key role in DNA damage-induced cell death

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RARγ is essential for RIPK1-mediated necroptosis and apoptosis following DNA damage

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RARγ is required for the formation of Ripoptosome in response to DNA damage

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Loss of RARγ correlates with skin cancer development

N-(7-Cyano-6-(4-fluoro-3-(2-(3-(trifluoromethyl)phenyl)acetamido)phenoxy)benzo[d]thiazol-2-yl)cyclopropanecarboxamide (TAK-632) Analogues as Novel Necroptosis Inhibitors by Targeting Receptor-Interacting Protein Kinase 3 (RIPK3): Synthesis, Structure-Activity Relationships, and in Vivo Efficacy

Necroptosis, a form of programmed cell death, plays a critical role in various diseases, including inflammatory, infectious, and degenerative diseases. We previously identified N-(7-cyano-6-(4-fluoro-3-(2-(3-(trifluoromethyl)phenyl)acetamido)phenoxy)benzo[d]thiazol-2-yl)cyclopropanecarboxamide (TAK-632) (6) as a potent inhibitor of necroptosis by targeting both receptor-interacting protein kinase 1 (RIPK1) and 3 (RIPK3) kinases. Herein, we performed three rounds of structural optimizations of TAK-632 and elucidated structure-activity relationships to generate more potent inhibitors by targeting RIPK3. The analogues with carbamide groups exhibited great antinecroptotic activities, and compound 42 showed >60-fold selectivity for RIPK3 than RIPK1. It blocked necrosome formation by specifically inhibiting the phosphorylation of RIPK3 in necroptotic cells. In a tumor necrosis factor-induced systemic inflammatory response syndrome model, it significantly protected mice from hypothermia and death at a dose of 5 mg/kg, which was much more effective than TAK-632. Moreover, it showed favorable and druglike pharmacokinetic properties in rats with an oral bioavailability of 25.2%. Thus, these RIPK3-targeting small molecules represent promising lead structures for further development.

Identification of the Raf kinase inhibitor TAK-632 and its analogues as potent inhibitors of necroptosis by targeting RIPK1 and RIPK3

BACKGROUND AND PURPOSE

Necroptosis is a form of programmed, caspase-independent, cell death, mediated by receptor-interacting protein kinases, RIPK1 and RIPK3, and the mixed lineage kinase domain-like (MLKL). Necroptosis contributes to the pathophysiology of various inflammatory, infectious, and degenerative diseases. Thus, identification of low MW inhibitors for necroptosis has broad therapeutic relevance. Here, we identified that the pan-Raf inhibitor TAK-632 was also an inhibitor of necroptosis. We have further generated a more selective, highly potent analogue of TAK-632 by targeting RIPK1 and RIPK3.

EXPERIMENTAL APPROACH

Cell viability was measured by MTT, propidium staining, or CellTiter-Glo luminescent assays. Effects of TAK-632 on necroptosis signalling pathways were investigated by western blotting, immunoprecipitation, and in vitro kinase assays. Downstream targets of TAK-632 were identified by a drug affinity responsive target stability assay and a pull-down assay with biotinylated TAK-632. A mouse model of TNF-α-induced systemic inflammatory response syndrome (SIRS) was further used to explore the role of TAK-632 in protecting against necroptosis-associated inflammation in vivo.

KEY RESULTS

TAK-632 protected against necroptosis in human and mouse cells but did not protect cells from apoptosis. TAK-632 directly bound with RIPK1 and RIPK3 to inhibit kinase activities of both enzymes. In vivo, TAK-632 alleviated TNF-induced SIRS. Furthermore, we performed a structure-activity relationship analysis of TAK-632 analogues and generated SZM594, a highly potent inhibitor of RIPK1/3.

CONCLUSIONS AND IMPLICATIONS

TAK-632 is an inhibitor of necroptosis and represents a new lead compound in the development of highly potent inhibitors of RIPK1 and RIPK3.

Kinase-Based Taming of Brain Microglia Toward Disease-Modifying Therapy

Microglia are the primary immune cells residing in the central nervous system (CNS), where they play essential roles in the health and disease. Depending on the CNS inflammatory milieu, they exist in either resting or activated states. Chronic neuroinflammation mediated by activated microglia is now considered to be a common characteristic shared by many neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis, which currently pose a significant socioeconomic burden to the global healthcare system. Accumulating evidence has indicated protein kinases (PKs) as important drug targets for therapeutic interventions of these detrimental diseases. Here, we review recent findings suggesting that selected PKs potentially participate in microglia-mediated neuroinflammation. Taming microglial phenotypes by modulating the activity of these PKs holds great promise for the development of disease-modifying therapies for many neurodegenerative diseases.

Strong and sustained activation of the anticipatory unfolded protein response induces necrotic cell death

The endoplasmic reticulum stress sensor, the unfolded protein response (UPR), regulates intracellular protein homeostasis. While transient activation of the reactive UPR by unfolded protein is protective, prolonged and sustained activation of the reactive UPR triggers CHOP-mediated apoptosis. In the recently characterized, evolutionarily conserved anticipatory UPR, mitogenic hormones and other effectors pre-activate the UPR; how strong and sustained activation of the anticipatory UPR induces cell death was unknown. To characterize this cell death pathway, we used BHPI, a small molecule that activates the anticipatory UPR through estrogen receptor α (ERα) and induces death of ERα⁺ cancer cells. We show that sustained activation of the anticipatory UPR by BHPI kills cells by inducing depletion of intracellular ATP, resulting in classical necrosis phenotypes, including plasma membrane disruption and leakage of intracellular contents. Unlike reactive UPR activation, BHPI-induced hyperactivation of the anticipatory UPR does not induce apoptosis or sustained autophagy. BHPI does not induce CHOP protein or PARP cleavage, and two pan-caspase inhibitors, or Bcl2 overexpression, have no effect on BHPI-induced cell death. Moreover, BHPI does not increase expression of autophagy markers, or work through recently identified programmed-necrosis pathways, such as necroptosis. Opening of endoplasmic reticulum IP₃R calcium channels stimulates cell swelling, cPLA2 activation, and arachidonic acid release. Notably, cPLA2 activation requires ATP depletion. Importantly, blocking rapid cell swelling or production of arachidonic acid does not prevent necrotic cell death. Rapid cell death is upstream of PERK activation and protein synthesis inhibition, and results from strong and sustained activation of early steps in the anticipatory UPR. Supporting a central role for ATP depletion, reversing ATP depletion blocks rapid cell death, and the onset of necrotic cell death is correlated with ATP depletion. Necrotic cell death initiated by strong and sustained activation of the anticipatory UPR is a newly discovered role of the UPR.

RIP3 deficiency ameliorates inflammatory response in mice infected with influenza H7N9 virus infection

Influenza H7N9 virus infection causes an acute, highly contagious respiratory illness that triggers cell death of infected cells and airway epithelial destruction. RIP3 is a key regulator of cell death responses to a growing number of viral and microbial agents. This study aimed to investigate the role of RIP3 in inflammation of influenza H7N9 virus infection. Here, RIP3 knock out (RIP3−/−) mice and littermate wild type mice were infected intranasally with influenza H7N9 virus (A/Fujian/S03/2015) to determine the contribution of RIP3 to the inflammatory response of influenza H7N9 virus infection. It was found that RIP3−/− mice infected with H7N9 virus showed higher survival and less weight loss, compared with wild type littermate mice. In addition, RIP3−/− mice had fewer regions of edema, infiltration with inflammatory cells, and alveolar collapses, and the secretions of IL-1β, IL-6, RANTES and MIP-1 in BALF were significantly decreased on days 3 and 7 p.i. when compared with WT mice. Moreover, caspase 1/IL1β signaling was found to be involved in RIP3 associated inflammation of influenza H7N9 virus, but not RIP3/MLKL dependent necrosis. In the conclusion, our results indicated that RIP3 deficiency can protect mice from the infection of influenza H7N9 virus by downregulating caspase 1/IL1β signaling, which provided evidence of the RIP3 involved necroptosis independent manner.

Shikonin induces glioma cell necroptosis in vitro by ROS overproduction and promoting RIP1/RIP3 necrosome formation

Necroptosis is a type of programmed necrosis regulated by receptor interacting protein kinase 1 (RIP1) and RIP3. Necroptosis is found to be accompanied by an overproduction of reactive oxygen species (ROS), but the role of ROS in regulation of necroptosis remains elusive. In this study, we investigated how shikonin, a necroptosis inducer for cancer cells, regulated the signaling leading to necroptosis in glinoma cells in vitro. Treatment with shikonin (2-10 μmol/L) dose-dependently triggered necrosis and induced overproduction of intracellular ROS in rat C6 and human SHG-44, U87 and U251 glioma cell lines. Moreover, shikonin treatment dose-dependently upregulated the levels of RIP1 and RIP3 and reinforced their interaction in the glioma cells. Pretreatment with the specific RIP1 inhibitor Nec-1 (100 μmol/L) or the specific RIP3 inhibitor GSK-872 (5 μmol/L) not only prevented shikonin-induced glioma cell necrosis but also significantly mitigated the levels of intracellular ROS and mitochondrial superoxide. Mitigation of ROS with MnTBAP (40 μmol/L), which was a cleaner of mitochondrial superoxide, attenuated shikonin-induced glioma cell necrosis, whereas increasing ROS levels with rotenone, which improved the mitochondrial generation of superoxide, significantly augmented shikonin-caused glioma cell necrosis. Furthermore, pretreatment with MnTBAP prevented the shikonin-induced upregulation of RIP1 and RIP3 expression and their interaction while pretreatment with rotenone reinforced these effects. These findings suggest that ROS is not only an executioner of shikonin-induced glioma cell necrosis but also a regulator of RIP1 and RIP3 expression and necrosome assembly.

Murine cytomegalovirus IE3-dependent transcription is required for DAI/ZBP1-mediated necroptosis

DNA-dependent activator of interferon regulatory factors/Z-DNA binding protein 1 (DAI/ZBP1) is a crucial sensor of necroptotic cell death induced by murine cytomegalovirus (MCMV) in its natural host. Here, we show that viral capsid transport to the nucleus and subsequent viral IE3-dependent early transcription are required for necroptosis. Necroptosis induction does not depend on input virion DNA or newly synthesized viral DNA A putative RNA-binding domain of DAI/ZBP1, Zα2, is required to sense virus and trigger necroptosis. Thus, MCMV IE3-dependent transcription from the viral genome plays a crucial role in activating DAI/ZBP1-dependent necroptosis. This implicates RNA transcripts generated by a large double-stranded DNA virus as a biologically relevant ligand for DAI/ZBP1 during natural viral infection.