Sibiriline, a new small chemical inhibitor of receptor-interacting protein kinase 1, prevents immune-dependent hepatitis

Necroptosis and autoimmunity

Autoimmunity is a normal physiological state that requires immunological homeostasis and surveillance, whereas necroptosis is a type of inflammatory cell death. When necroptosis occurs, various immune system cells must perform their appropriate duties to preserve immunological homeostasis, whether the consequence is expanding or limiting the inflammatory response and the pathological condition is cleared or progresses to the autoimmune disease stage. This article discusses necroptosis based on RIP homotypic interaction motif (RHIM) interaction under various physiological and pathological situations, with the RIPK1-RIPK3-MLKL necrosome serving as the regulatory core. In addition, the cell biology of necroptosis involved in autoimmunity and its application in autoimmune diseases were also reviewed.

RIPK1 inhibitors: A key to unlocking the potential of necroptosis in drug development

Within the field of medical science, there is a great deal of interest in investigating cell death pathways in the hopes of discovering new drugs. Over the past two decades, pharmacological research has focused on necroptosis, a cell death process that has just been discovered. Receptor-interacting protein kinase 1 (RIPK1), an essential regulator in the cell death receptor signalling pathway, has been shown to be involved in the regulation of important events, including necrosis, inflammation, and apoptosis. Therefore, researching necroptosis inhibitors offers novel ways to treat a variety of disorders that are not well-treated by the therapeutic medications now on the market. The research and medicinal potential of RIPK1 inhibitors, a promising class of drugs, are thoroughly examined in this study. The journey from the discovery of Necrostatin-1 (Nec-1) to the recent advancements in RIPK1 inhibitors is marked by significant progress, highlighting the integration of traditional medicinal chemistry approaches with modern technologies like high-throughput screening and DNA-encoded library technology. This review presents a thorough exploration of the development and therapeutic potential of RIPK1 inhibitors, a promising class of compounds. Simultaneously, this review highlights the complex roles of RIPK1 in various pathological conditions and discusses potential inhibitors discovered through diverse pathways, emphasizing their efficacy against multiple disease models, providing significant guidance for the expansion of knowledge about RIPK1 and its inhibitors to develop more selective, potent, and safe therapeutic agents.

Discovery of Sibiriline derivatives as novel receptor-interacting protein kinase 1 inhibitors

Receptor-interacting protein kinase 1 (RIPK1), a vital protein of the necroptosis pathway, plays a pivotal role in various inflammatory diseases. Sibiriline has been reported to be a potent ATP-competitive RIPK1 inhibitor, but its anti-necroptotic effects are limited. A series of structural analogues of Sibiriline were synthesized and evaluated for their anti-necroptotic activity. Comprehensive structure-activity relationship (SAR) was performed to left azaindole and right substituents of benzene of Sibiriline, respectively. The optimal compound KWCN-41, specifically inhibiting cell necroptosis but not apoptosis, protects cell survival by blocking the necroptotic pathway, which inhibits the phosphorylation of essential proteins of the necroptosis. It also prevented the development of inflammation and reduced the level of inflammatory factors in mice. KWCN-41 is expected to be a lead compound for further studies in inflammatory diseases.

From (Tool)Bench to Bedside: The Potential of Necroptosis Inhibitors

Necroptosis is a regulated caspase-independent form of necrotic cell death that results in an inflammatory phenotype. This process contributes profoundly to the pathophysiology of numerous neurodegenerative, cardiovascular, infectious, malignant, and inflammatory diseases. Receptor-interacting protein kinase 1 (RIPK1), RIPK3, and the mixed lineage kinase domain-like protein (MLKL) pseudokinase have been identified as the key components of necroptosis signaling and are the most promising targets for therapeutic intervention. Here, we review recent developments in the field of small-molecule inhibitors of necroptosis signaling, provide guidelines for their use as chemical probes to study necroptosis, and assess the therapeutic challenges and opportunities of such inhibitors in the treatment of a range of clinical indications.

A Transversal Approach Combining In Silico, In Vitro and In Vivo Models to Describe the Metabolism of the Receptor Interacting Protein 1 Kinase Inhibitor Sibiriline

Sibiriline is a novel drug inhibiting receptor-interacting protein 1 kinase (RIPK1) and necroptosis, a regulated form of cell death involved in several disease models. In this study, we aimed to investigate the metabolic fate of sibiriline in a cross-sectional manner using an in silico prediction, coupled with in vitro and in vivo experiments. In silico predictions were performed using GLORYx and Biotransformer 3.0 freeware; in vitro incubation was performed on differentiated human HepaRG cells, and in vivo experiments including a pharmacokinetic study were performed on mice treated with sibiriline. HepaRG culture supernatants and mice plasma samples were analyzed with ultra-high-performance liquid chromatography, coupled with tandem mass spectrometry (LC-HRMS/MS). The molecular networking bioinformatics tool applied to LC-HRMS/MS data allowed us to visualize the sibiriline metabolism kinetics. Overall, 14 metabolites, mostly produced by Phase II transformations (glucuronidation and sulfation) were identified. These data provide initial reassurance regarding the toxicology of this new RIPK1 inhibitor, although further studies are required.

An Optimized Workflow for the Discovery of New Antimicrobial Compounds Targeting Bacterial RNA Polymerase Complex Formation

Bacterial resistance represents a major health problem worldwide and there is an urgent need to develop first-in-class compounds directed against new therapeutic targets. We previously developed a drug-discovery platform to identify new antimicrobials able to disrupt the protein–protein interaction between the β’ subunit and the σ⁷⁰ initiation factor of bacterial RNA polymerase, which is essential for transcription. As a follow-up to such work, we have improved the discovery strategy to make it less time-consuming and more cost-effective. This involves three sequential assays, easily scalable to a high-throughput format, and a subsequent in-depth characterization only limited to hits that passed the three tests. This optimized workflow, applied to the screening of 5360 small molecules from three synthetic and natural compound libraries, led to the identification of six compounds interfering with the β’–σ⁷⁰ interaction, and thus was capable of inhibiting promoter-specific RNA transcription and bacterial growth. Upon supplementation with a permeability adjuvant, the two most potent transcription-inhibiting compounds displayed a strong antibacterial activity against Escherichia coli with minimum inhibitory concentration (MIC) values among the lowest (0.87–1.56 μM) thus far reported for β’–σ PPI inhibitors. The newly identified hit compounds share structural feature similarities with those of a pharmacophore model previously developed from known inhibitors.

Advances in RIPK1 kinase inhibitors

Programmed necrosis is a new modulated cell death mode with necrotizing morphological characteristics. Receptor interacting protein 1 (RIPK1) is a critical mediator of the programmed necrosis pathway that is involved in stroke, myocardial infarction, fatal systemic inflammatory response syndrome, Alzheimer's disease, and malignancy. At present, the reported inhibitors are divided into four categories. The first category is the type I ATP-competitive kinase inhibitors that targets the area occupied by the ATP adenylate ring; The second category is type Ⅱ ATP competitive kinase inhibitors targeting the DLG-out conformation of RIPK1; The third category is type Ⅲ kinase inhibitors that compete for binding to allosteric sites near ATP pockets; The last category is others. This paper reviews the structure, biological function, and recent research progress of receptor interaction protein-1 kinase inhibitors.

Targeting Necroptosis as a Promising Therapy for Alzheimer's Disease

Alzheimer's disease (AD) is an irreversible and progressive neurodegenerative disorder featured by memory loss and cognitive default. However, there has been no effective therapeutic approach to prevent the development of AD and the available therapies are only to alleviate some symptoms with limited efficacy and severe side effects. Necroptosis is a new kind of cell death, being regarded as a genetically programmed and regulated pattern of necrosis. Increasing evidence reveals that necroptosis is tightly related to the occurrence and development of AD. This review aims to summarize the potential role of necroptosis in AD progression and the therapeutic capacity of targeting necroptosis for AD patients.

Nigratine as dual inhibitor of necroptosis and ferroptosis regulated cell death

Nigratine (also known as 6E11), a flavanone derivative of a plant natural product, was characterized as highly specific non-ATP competitive inhibitor of RIPK1 kinase, one of the key components of necroptotic cell death signaling. We show here that nigratine inhibited both necroptosis (induced by Tumor Necrosis Factor-α) and ferroptosis (induced by the small molecules glutamate, erastin, RSL3 or cumene hydroperoxide) with EC50 in the µM range. Taken together, our data showed that nigratine is a dual inhibitor of necroptosis and ferroptosis cell death pathways. These findings open potential new therapeutic avenues for treating complex necrosis-related diseases.

Evaluation of the expression of necroptosis pathway mediators and its association with tumor characteristics in functional and non-functional pituitary adenomas

BACKGROUND

Pituitary adenomas impose a burden of morbidity on patients and characterizing the molecular mechanisms underlying its pathogenesis received remarkable attention. Despite the appealing role of necroptosis as an alternative cell death pathway in cancer pathogenesis, its relevance to pituitary adenoma pathogenesis has yet to be determined that is perused in the current study.

METHODS

The total number of 109 specimens including pituitary adenomas and cadaveric healthy pituitary tissues were enrolled in the current study. Tumor and healthy pituitary tissues were subjected to RNA extraction and gene analysis using Real-Time PCR. The expression levels of necroptosis markers (RIP1K, RIP3K and, MLKL) and their association with the patient's demographic features were evaluated, also the protein level of MLKL was assessed using immunohistochemistry in tissues.

RESULTS

Based on our data, the remarkable reduction in RIP3K and MLKL expression were detected in nonfunctional and GH-secreting pituitary tumors compared to pituitary normal tissues. Invasive tumors revealed lower expression of RIP3K and MLKL compared to non-invasive tumors, also the attenuated level of MLKL was associated with the tumor size in invasive NFPA. The simultaneous down-regulation of MLKL protein in pituitary adenoma tissues was observed which was in line with its gene expression. While, RIP1K over-expressed significantly in both types of pituitary tumors which showed no significant correlation with patient's age, gender and tumor size in GHPPA and NFPA group. Notably, MLKL and RIP3K gene expression was significantly correlated in the GHPPA group.

CONCLUSIONS

According to our data, the reduced expression of necroptosis mediators (RIP3K, MLKL) in pituitary adenoma reinforces the hypothesis that the necroptosis pathway can be effective in regulating the proliferation and growth of pituitary tumor cells and tumor recurrence.

A narrative review of the role of necroptosis in liver disease: a double-edged sword

Acute and chronic liver injuries lead to hepatocyte death and turnover. When injuries become chronic, continuous cell death and transformation lead to chronic inflammation, fibrosis, cirrhosis, and eventually carcinoma. A therapeutic strategy of great significance for liver disease is to control hepatocyte death in acute and chronic injuries. This strategy prevents hepatocytes from causing liver failure and inhibits both secondary inflammation and fibrosis. Both apoptosis and necrosis have been proven to occur in the liver, but the role of necroptosis in liver diseases is controversial. Necroptosis, which has features of necrosis and apoptosis, is a regulatory process that occurs in some cell types when caspases are inhibited. The signaling pathway of necroptosis is characterized by the activation of receptor-interacting proteins kinase (RIPK) and mixed lineage kinase domain-like (MLKL). Necroptosis is associated with a variety of inflammatory diseases and has been the focus of research in recent years. The incidence of necroptosis in liver tissues has been studied recently in several liver injury models, but the results of the studies are not consistent. The purpose of this review is to summarize the published data on the involvement of necroptosis in liver injury, focusing on the controversies, issues remaining to be discussed, and potential therapeutic applications in this area.

The Role of RIPK1 and RIPK3 in Cardiovascular Disease

Cardiovascular diseases, including peripheral arterial and venous disease, myocardial infarction, and stroke, are the number one cause of death worldwide annually. In the last 20 years, the role of necroptosis, a newly identified form of regulated necrotic cell death, in cardiovascular disease has come to light. Specifically, the damaging role of two kinase proteins pivotal in the necroptosis pathway, Receptor Interacting Protein Kinase 1 (RIPK1) and Receptor Interacting Protein Kinase 3 (RIPK3), in cardiovascular disease has become a subject of great interest and importance. In this review, we provide an overview of the current evidence supporting a pathologic role of RIPK1 and RIPK3 in cardiovascular disease. Moreover, we highlight the evidence behind the efficacy of targeted RIPK1 and RIPK3 inhibitors in the prevention and treatment of cardiovascular disease.

Hair growth promotion by necrostatin-1s

Necrostatins (Necs) have been developed as a receptor-interacting protein kinase 1 (RIPK1) inhibitor, thus inhibiting necroptosis. In this current study, we have investigated the possible involvement of necroptosis in the hair cycle regulation and further examined its underlying molecular mechanisms. Diverse RIPK1/3 inhibitors and siRNA were tested in the human outer-root sheath (ORS) cells and animal models. The expression and hair cycle-dependent expression of RIPK 1, respectively, were investigated in the hair follicles (HF) of human, pig, and the mouse. Resulting from the experiment, Nec-1s was most effective in the hair growth promotion among several inhibitors. Nec-1s induced the ORS cell proliferation and migration, and increased the HF length in mouse and pig organ cultures. In addition, it accelerated the telogen-to-anagen transition and elongated the anagen period in the mouse model. Both apoptosis and necroptosis were detected in hair cycle. RIPK1 and RIPK3 were highly expressed in ORS cells during the hair regression period. Nec-1s upregulated the mRNA expression of Wnt3a and Wnt5b, and the activity of β-catenin. Collectively, Nec-1s promotes hair growth through inhibiting necroptosis and activating the Wnt/β-catenin pathway. Necroptosis is involved in hair cycle regression, and Nec-1s is a promising target for hair-loss treatment.

Inhibitors Targeting RIPK1/RIPK3: Old and New Drugs

The scaffolding function of receptor-interacting protein kinase 1 (RIPK1) regulates prosurvival signaling and inflammatory gene expression, while its kinase activity mediates both apoptosis and necroptosis; the latter involving RIPK3 kinase activity. The mutual transition between the scaffold and kinase functions of RIPK1 is regulated by (de)ubiquitylation and (de)phosphorylation. RIPK1-mediated cell death leads to disruption of epithelial barriers and/or release of damage-associated molecular patterns (DAMPs), cytokines, and chemokines, propagating inflammatory and degenerative diseases. Many drug development programs have pursued targeting RIPK1, and to a lesser extent RIPK3 kinase activity. In this review, we classify existing and novel small-molecule drugs based on their pharmacodynamic (PD) type I, II, and III binding mode. Finally, we discuss their applicability and therapeutic potential in inflammatory and degenerative experimental disease models.

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.

Necroptosis signaling in liver diseases: An update

The apoptosis alternate cell death pathways are extensively studied in recent years and their significance has been well recognized. With identification of newer cell death pathways, the therapeutic opportunities to modulate cell death have indeed further extended. Necroptosis, among other apoptosis alternate pathways, has been immensely studied recently in different hepatic disease models. Receptor-interacting protein 1 (RIPK1), RIPK3 and mixed lineage kinase domain like (MLKL) seemed to be the key players to mediate necroptosis pathway. Initially, necroptosis seemed to be following the typical pathway. But recently diverse pathways and outcomes have been observed. With recent studies reporting diverse outcomes, the necroptosis signalling has become a lot more interesting and intricate. The typical RIPK1 signalling followed by RIPK3 and MLKL might not always be strictly followed. Although, necroptosis signalling has been intensively investigated in various disease conditions; however, there is still a need to further elaborate and understand the unique scaffolding and kinase properties and other signalling interactions of necroptosis signalling molecules.

Necroptotic Cell Death in Liver Transplantation and Underlying Diseases: Mechanisms and Clinical Perspective

Cell death is a natural process for the turnover of aged cells, but it can also arise as a result of pathological conditions. Cell death is recognized as a key feature in both acute and chronic hepatobiliary diseases caused by drug, alcohol, and fat uptake; by viral infection; or after surgical intervention. In the case of chronic disease, cell death can lead to (chronic) secondary inflammation, cirrhosis, and the progression to liver cancer. In liver transplantation, graft preservation and ischemia/reperfusion injury are associated with acute cell death. In both cases, so-called programmed cell death modalities are involved. Several distinct types of programmed cell death have been described of which apoptosis and necroptosis are the most well known. Parenchymal liver cells, including hepatocytes and cholangiocytes, are susceptible to both apoptosis and necroptosis, which are triggered by distinct signal transduction pathways. Apoptosis is dependent on a proteolytic cascade of caspase enzymes, whereas necroptosis induction is caspase-independent. Moreover, different from the "silent" apoptotic cell death, necroptosis can cause a secondary inflammatory cascade, so-called necroinflammation, triggered by the release of various damage-associated molecular patterns (DAMPs). These DAMPs activate the innate immune system, leading to both local and systemic inflammatory responses, which can even cause remote organ failure. Therapeutic targeting of necroptosis by pharmacological inhibitors, such as necrostatin-1, shows variable effects in different disease models.

The emerging roles of protein homeostasis-governing pathways in Alzheimer's disease

Pathways governing protein homeostasis are involved in maintaining the structural, quantitative, and functional stability of intracellular proteins and involve the ubiquitin-proteasome system, autophagy, endoplasmic reticulum, and mTOR pathway. Due to the broad physiological implications of protein homeostasis pathways, dysregulation of proteostasis is often involved in the development of multiple pathological conditions, including Alzheimer's disease (AD). Similar to other neurodegenerative diseases that feature pathogenic accumulation of misfolded proteins, Alzheimer's disease is characterized by two pathological hallmarks, amyloid-β (Aβ) plaques and tau aggregates. Knockout or transgenic overexpression of various proteostatic components in mice results in AD-like phenotypes. While both Aβ plaques and tau aggregates could in turn enhance the dysfunction of these proteostatic pathways, eventually leading to apoptotic or necrotic neuronal death and pathogenesis of Alzheimer's disease. Therefore, targeting the components of proteostasis pathways may be a promising therapeutic strategy against Alzheimer's disease.

6E11, a highly selective inhibitor of Receptor-Interacting Protein Kinase 1, protects cells against cold hypoxia-reoxygenation injury

Necroptosis is a programmed cell death pathway that has been shown to be of central pathophysiological relevance in multiple disorders (hepatitis, brain and cardiac ischemia, pancreatitis, viral infection and inflammatory diseases). Necroptosis is driven by two serine threonine kinases, RIPK1 (Receptor Interacting Protein Kinase 1) and RIPK3, and a pseudo-kinase MLKL (Mixed Lineage Kinase domain-Like) associated in a multi-protein complex called necrosome. In order to find new inhibitors for use in human therapy, a chemical library containing highly diverse chemical structures was screened using a cell-based assay. The compound 6E11, a natural product derivative, was characterized as a positive hit. Interestingly, this flavanone compound: inhibits necroptosis induced by death receptors ligands TNF-α (Tumor Necrosis Factor) or TRAIL (TNF-Related Apoptosis-Inducing Ligand); is an extremely selective inhibitor, among kinases, of human RIPK1 enzymatic activity with a nM Kd; has a non-ATP competitive mode of action and a novel putative binding site; is weakly cytotoxic towards human primary blood leukocytes or retinal pigment epithelial cells at effective concentrations; protects human aortic endothelial cells (HAEC) from cold hypoxia/reoxygenation injury more effectively than necrostatin-1 (Nec-1) and Nec-1s. Altogether, these data demonstrate that 6E11 is a novel potent small molecular inhibitor of RIPK1-driven necroptosis.