Characterization of GSK'963: a structurally distinct, potent and selective inhibitor of RIP1 kinase

Cytokine Biopharmaceuticals with "Activity-on-Demand" for Cancer Therapy

Cytokines are small proteins that modulate the activity of the immune system. Because of their potent immunomodulatory properties, some recombinant cytokines have undergone clinical development and have gained marketing authorization for the therapy of certain forms of cancer. Recombinant cytokines are typically administered at ultralow doses, as many of them can cause substantial toxicity even at submilligram quantities. In an attempt to increase the therapeutic index, fusion proteins based on tumor-homing antibodies (also called "immunocytokines") have been considered, and some products in this class have reached late-stage clinical trials. While antibody-cytokine fusions, which preferentially localize in the neoplastic mass, can activate tumor-resident leukocytes and may be more efficacious than their nontargeted counterparts, such products typically conserve an intact cytokine activity, which may prevent escalation to curative doses. To further improve tolerability, several strategies have been conceived for the development of antibody-cytokine fusions with "activity-on-demand", acting on tumors but helping spare normal tissues from undesired toxicity. In this article, we have reviewed some of the most promising strategies, outlining their potential as well as possible limitations.

Quantitative target engagement of RIPK1 in human whole blood via the cellular thermal shift assay for potential pre-clinical and clinical applications

The cellular thermal shift assay (CETSA®) is a target engagement method widely used for preclinical characterization of small molecule compounds. CETSA® has been used for semi-quantitative readouts in whole blood with PBMC isolation, and quantitative, plate-based readouts using cell lines. However, there has been no quantitative evaluation of CETSA® in unprocessed human whole blood, which is preferred for clinical applications. Here we report two separate assay formats - Alpha CETSA® and MSD CETSA® - that require less than 100 μL of whole blood per sample without PBMC isolation. We chose RIPK1 as a proof-of-concept target and, by measuring engagement of seven different inhibitors, demonstrate high assay sensitivity and robustness. These quantitative CETSA® platforms enable possible applications in preclinical pharmacokinetic-pharmacodynamic studies, and direct target engagement with small molecules in clinical trials.

Dopaminergic neuronal death via necroptosis in Parkinson's disease: A review of the literature

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive dysfunction and loss of dopaminergic neurons of the substantia nigra pars compacta (SNc). Several pathways of programmed cell death are likely to play a role in dopaminergic neuron death, such as apoptosis, necrosis, pyroptosis and ferroptosis, as well as cell death associated with proteasomal and mitochondrial dysfunction. A better understanding of the molecular mechanisms underlying dopaminergic neuron death could inform the design of drugs that promote neuron survival. Necroptosis is a recently characterized regulated cell death mechanism that exhibits morphological features common to both apoptosis and necrosis. It requires activation of an intracellular pathway involving receptor-interacting protein 1 kinase (RIP1 kinase, RIPK1), receptor-interacting protein 3 kinase (RIP3 kinase, RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL). The potential involvement of this programmed cell death pathway in the pathogenesis of PD has been studied by analysing biomarkers for necroptosis, such as the levels and oligomerization of phosphorylated RIPK3 (pRIPK3) and phosphorylated MLKL (pMLKL), in several PD preclinical models and in PD human tissue. Although there is evidence that other types of cell death also have a role in DA neuron death, most studies support the hypothesis that this cell death mechanism is activated in PD tissues. Drugs that prevent or reduce necroptosis may provide neuroprotection for PD. In this review, we summarize the findings from these studies. We also discuss how manipulating necroptosis might open a novel therapeutic approach to reduce neuronal degeneration in PD.

Design, synthesis and biological evaluation of novel cyclic malonamide derivatives as selective RIPK1 inhibitors

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) plays a key role in cell death and inflammation. RIPK1 is a well-established therapeutic target, due to the presence of a unique kinase-regulating allosteric pocket, which enables selective inhibition. Herein we used GSK2982772 as our starting point in our discovery campaign. Applying isosteric replacement, we successfully identified the malonamide scaffold, instead of the well-established serine template. Further structural optimization led to the design and synthesis of a series of analog inhibitors. The enantiomers of the most promising compound were tested on 97 different kinases. The active enantiomer proved to be kinase selective.

Necroptosis inhibitors: mechanisms of action and therapeutic potential

Necroptosis is a type of programmed cell death that is morphologically similar to necrosis. This type of cell death is involved in various pathophysiological disorders, including inflammatory, neurodegenerative, infectious, and malignant diseases. Receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL) pseudokinase constitute the core components of the necroptosis signaling pathway and are considered the most promising targets for therapeutic intervention. The discovery and characterization of necroptosis inhibitors not only accelerate our understanding of the necroptosis signaling pathway but also provide important drug candidates for the treatment of necroptosis-related diseases. Here, we will review recent research progress on necroptosis inhibitors, mechanisms of action and their potential applications for disease treatment.

Screening of potent RIPK3 inhibitors to attenuate necroptosis and inflammation in mouse traumatic brain injury models

Necroptosis is a type of cell death that occurs when cells are exposed to external stressors such as inflammation, infections, or injury. In necroptosis, cells use a different set of proteins including: receptor-interacting kinase 1 (RIPK1 or RIP1), receptor-interacting kinase 3 (RIPK3 or RIP3) and the phosphorylation of its substrate mixed lineage kinase domain-like protein (MLKL) and pathways to trigger their own death. Mutations in the gene encoding RIPK3 have been associated with many diseases, including neurodegenerative diseases, neuroinflammatory diseases, inflammatory diseases，tumors, and it is being studied as a potential target for inflammatory injury therapy. RIPK3 has also been implicated in the pathology of neuroinflammation following Traumatic brain injury and is currently being explored as a potential therapy. We screened through necroptosis blocking compounds, a library of FDA-approved compounds. We found four compounds:1D6-Foretinib GSK1363089; 15F6-Poziotinib (HM781-36B); 15F9-Dasatinib monohydrate; 15A10-Pexmetinib (ARRY-614); acts as potent inhibitors of necroptosis (Necroptosis Blocking Compounds, NBCs) by blocking the RIPK3 kinase activity. These four compounds effectively block necroptosis induced by death receptor ligands Toll-like receptors as well as viral infections in human, rat and mouse cells. The cellular activation of RIPK3 and MLKL stimulated by necroptosis was strongly inhibited by NBCs. The compounds are promising for targeting RIPK3 kinase activity, thereby preventing necroptosis and inflammatory responses. In our study, we explored the role of NBCs in neuroprotection after traumatic brain injury. It's effectiveness in traumatic brain injury animal models and favorable safety profiles make it a potential candidate for the advances of new therapies for necroptosis-associated neuroinflammatory disorders.

Design, synthesis, molecular docking and biological evaluation of 1,3,5-trisubstituted-1H-pyrazole derivatives as anticancer agents with cell cycle arrest, ERK and RIPK3- kinase activities

The need for new ERK and RIPK3 kinase modulators arises from their central roles in cellular processes, especially in diseases like cancer. This research focused on a ligand-based strategy, incorporating previously documented 1,3,5-trisubstituted-1H-pyrazole derivatives, to craft innovative inhibitors specifically targeting ERK and RIPK3 kinases. Compounds 6, 7, 10a, 10c, and 10d exhibited significant cytotoxicity against PC-3 and MCF-7 cancer cell lines, with IC50 values ranging from 21.9 to 28.6 µM and 3.90-35.5 µM, respectively values surpassing those of the reference compound Doxorubicin. Additionally, cell cycle analysis revealed intriguing results, particularly with 10d inducing cell cycle arrest at the S phase in treated PC-3 cells, indicating potential DNA replication phase inhibition. Moreover, compounds 6, 10a, and 10d exhibited promising results in the in vitro kinase assay supported by molecular docking studies. The core scaffold of these compounds established interactions with vital amino acids within the active pockets of ERK and RIPK3 kinases, thereby securely anchoring them in place. These findings underscore the development of promising modulators for ERK and RIPK3 kinases, suggesting their potential for future contributions to cancer treatments.

Inhibition of Receptor-Interacting Protein Kinase 1 in Chronic Plaque Psoriasis: A Multicenter, Randomized, Double-Blind, Placebo-Controlled Study

INTRODUCTION

Receptor-interacting protein kinase 1 (RIPK1), a key mediator of inflammation through necroptosis and proinflammatory cytokine production, may play a role in the pathogenesis of immune-mediated inflammatory diseases such as chronic plaque psoriasis. An experimental medicine study of RIPK1 inhibition with GSK2982772 immediate-release formulation at doses up to 60 mg three times daily in mild to moderate plaque psoriasis indicated that efficacy may be improved with higher trough concentrations of GSK2982772.

METHODS

This multicenter, randomized, double-blind, placebo-controlled, repeat-dose study (NCT04316585) assessed the efficacy, safety, pharmacokinetics, and pharmacodynamics of 960 mg GSK2982772 (once-daily modified-release formulation) in patients with moderate to severe plaque psoriasis. Twenty-nine patients were randomized 2:1 to GSK2982772 (N = 19) or placebo (N = 10) for 12 weeks.

RESULTS

GSK2982772 was well tolerated with trough concentrations greater than tenfold higher than the previous phase 1 study with immediate release. Despite near complete RIPK1 target engagement in blood and modest reduction in circulating inflammatory cytokines, the proportion of patients achieving 75% improvement from baseline in Psoriasis Area Severity Index score at week 12 was similar between GSK2982772 and placebo (posterior median 1.8% vs 4.9%, respectively), with an estimated median treatment difference of - 2.3%. This analysis incorporated historical placebo data through the use of an informative prior distribution on the placebo arm. Week 4 changes in skin biopsy gene expression suggested sufficient local drug exposure to elicit a pharmacodynamic response.

CONCLUSION

Administration of the RIPK1 inhibitor GSK2982772 to patients with moderate to severe plaque psoriasis did not translate into meaningful clinical improvements.

Therapeutic potential of PANoptosis: innate sensors, inflammasomes, and RIPKs in PANoptosomes

The innate immune system initiates cell death pathways in response to pathogens and cellular stress. Cell death can be either non-lytic (apoptosis) or lytic (PANoptosis, pyroptosis, and necroptosis). PANoptosis has been identified as an inflammatory, lytic cell death pathway driven by caspases and RIPKs that is regulated by PANoptosome complexes, making it distinct from other cell death pathways. Several PANoptosome complexes (including ZBP1-, AIM2-, RIPK1-, and NLRP12-PANoptosomes) have been characterized to date. Furthermore, PANoptosis is implicated in infectious and inflammatory diseases, cancers, and homeostatic perturbations. Therefore, targeting its molecular components offers significant potential for therapeutic development. This review covers PANoptosomes and their assembly, PANoptosome-mediated cell death mechanisms, and ongoing progress in developing therapeutics that target PANoptosis.

Mechanisms of PANoptosis and relevant small-molecule compounds for fighting diseases

Pyroptosis, apoptosis, and necroptosis are mainly programmed cell death (PCD) pathways for host defense and homeostasis. PANoptosis is a newly distinct inflammatory PCD pathway that is uniquely regulated by multifaceted PANoptosome complexes and highlights significant crosstalk and coordination among pyroptosis (P), apoptosis (A), and/or necroptosis(N). Although some studies have focused on the possible role of PANpoptosis in diseases, the pathogenesis of PANoptosis is complex and underestimated. Furthermore, the progress of PANoptosis and related agonists or inhibitors in disorders has not yet been thoroughly discussed. In this perspective, we provide perspectives on PANoptosome and PANoptosis in the context of diverse pathological conditions and human diseases. The treatment targeting on PANoptosis is also summarized. In conclusion, PANoptosis is involved in plenty of disorders including but not limited to microbial infections, cancers, acute lung injury/acute respiratory distress syndrome (ALI/ARDS), ischemia-reperfusion, and organic failure. PANoptosis seems to be a double-edged sword in diverse conditions, as PANoptosis induces a negative impact on treatment and prognosis in disorders like COVID-19 and ALI/ARDS, while PANoptosis provides host protection from HSV1 or Francisella novicida infection, and kills cancer cells and suppresses tumor growth in colorectal cancer, adrenocortical carcinoma, and other cancers. Compounds and endogenous molecules focused on PANoptosis are promising therapeutic strategies, which can act on PANoptosomes-associated members to regulate PANoptosis. More researches on PANoptosis are needed to better understand the pathology of human conditions and develop better treatment.

The Role of Necroptosis in Cerebral Ischemic Stroke

Cerebral ischemia, also known as ischemic stroke, accounts for nearly 85% of all strokes and is the leading cause of disability worldwide. Due to disrupted blood supply to the brain, cerebral ischemic injury is trigged by a series of complex pathophysiological events including excitotoxicity, oxidative stress, inflammation, and cell death. Currently, there are few treatments for cerebral ischemia owing to an incomplete understanding of the molecular and cellular mechanisms. Accumulated evidence indicates that various types of programmed cell death contribute to cerebral ischemic injury, including apoptosis, ferroptosis, pyroptosis and necroptosis. Among these, necroptosis is morphologically similar to necrosis and is mediated by receptor-interacting serine/threonine protein kinase-1 and -3 and mixed lineage kinase domain-like protein. Necroptosis inhibitors have been shown to exert inhibitory effects on cerebral ischemic injury and neuroinflammation. In this review, we will discuss the current research progress regarding necroptosis in cerebral ischemia as well as the application of necroptosis inhibitors for potential therapeutic intervention in ischemic stroke.

The pathogenesis of organ fibrosis: Focus on necroptosis

Fibrosis is a common process of tissue repair response to multiple injuries in all chronic progressive diseases, which features with excessive deposition of extracellular matrix. Fibrosis can occur in all organs and tends to be nonreversible with the progress of the disease. Different cells types in different organs are involved in the occurrence and development of fibrosis, that is, hepatic stellate cells, pancreatic stellate cells, fibroblasts and myofibroblasts. Various types of programmed cell death, including apoptosis, autophagy, ferroptosis and necroptosis, are closely related to organ fibrosis. Among these programmed cell death types, necroptosis, an emerging regulated cell death type, is regarded as a huge potential target to ameliorate organ fibrosis. In this review, we summarize the role of necroptosis signalling in organ fibrosis and collate the small molecule compounds targeting necroptosis. In addition, we discuss the potential challenges, opportunities and open questions in using necroptosis signalling as a potential target for antifibrotic therapies. LINKED ARTICLES: This article is part of a themed issue on Translational Advances in Fibrosis as a Therapeutic Target. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.22/issuetoc.

Synthesis and evaluation of a novel PET ligand, a GSK'963 analog, aiming at autoradiography and imaging of the receptor interacting protein kinase 1 in the brain

BACKGROUND

Receptor interacting protein kinase 1 (RIPK1) is a serine/threonine kinase, which regulates programmed cell death and inflammation. Recently, the involvement of RIPK1 in the pathophysiology of Alzheimer's disease (AD) has been reported; RIPK1 is involved in microglia's phenotypic transition to their dysfunctional states, and it is highly expressed in the neurons and microglia in the postmortem brains in AD patients. They prompt neurodegeneration leading to accumulations of pathological proteins in AD. Therefore, regulation of RIPK1 could be a potential therapeutic target for the treatment of AD, and in vivo imaging of RIPK1 may become a useful modality in studies of drug discovery and pathophysiology of AD. The purpose of this study was to develop a suitable radioligand for positron emission tomography (PET) imaging of RIPK1.

RESULTS

(S)-2,2-dimethyl-1-(5-phenyl-4,5-dihydro-1H-pyrazol-1-yl)propan-1-one (GSK'963) has a high affinity, selectivity for RIPK1, and favorable physiochemical properties based on its chemical structure. In this study, since 11C-labeling (half-life: 20.4 min) GSK'963 retaining its structure requiring the Grignard reaction of tert-butylmagnesium halides and [11C]carbon dioxide was anticipated to give a low yield, we decided instead to 11C-label a GSK'963 analog ((S)-2,2-dimethyl-1-(5-(m-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)propan-1-one, GG502), which has a high RIPK1 inhibitory activity equivalent to that of the original compound GSK'963. Thus, we successfully 11C-labeled GG502 using a Pd-mediated cross-coupling reaction in favorable yields (3.6 ± 1.9%) and radiochemical purities (> 96%), and molar activity (47-115 GBq/μmol). On autoradiography, radioactivity accumulation was observed for [11C]GG502 and decreased by non-radioactive GG502 in the mouse spleen and human brain, indicating the possibility of specific binding of this ligand to RIPK1. On brain PET imaging in a rhesus monkey, [11C]GG502 showed a good brain permeability (peak standardized uptake value (SUV) ~3.0), although there was no clear evidence of specific binding of [11C]GG502. On brain PET imaging in acute inflammation model rats, [11C]GG502 also showed a good brain permeability, and no significant increased uptake was observed in the lipopolysaccharide-treated side of striatum. On metabolite analysis in rats at 30 min after administration of [11C]GG502, ~55% and ~10% of radioactivity was from unmetabolized [11C]GG502 in the brain and the plasma, respectively.

CONCLUSIONS

We synthesized and evaluated a 11C-labeled PET ligand based on the methylated analog of GSK'963 for imaging of RIPK1 in the brain. Although in autoradiography of the resulting [11C]GG502 indicated the possibility of specific binding, the actual PET imaging failed to detect any evidence of specific binding to RIPK1 despite its good brain permeability. Further development of radioligands with a higher binding affinity for RIPK1 in vivo and more stable metabolite profiles compared with the current compound may be required.

The therapeutic potential of targeting regulated non-apoptotic cell death

Cell death is critical for the development and homeostasis of almost all multicellular organisms. Moreover, its dysregulation leads to diverse disease states. Historically, apoptosis was thought to be the major regulated cell death pathway, whereas necrosis was considered to be an unregulated form of cell death. However, research in recent decades has uncovered several forms of regulated necrosis that are implicated in degenerative diseases, inflammatory conditions and cancer. The growing insight into these regulated, non-apoptotic cell death pathways has opened new avenues for therapeutic targeting. Here, we describe the regulatory pathways of necroptosis, pyroptosis, parthanatos, ferroptosis, cuproptosis, lysozincrosis and disulfidptosis. We discuss small-molecule inhibitors of the pathways and prospects for future drug discovery. Together, the complex mechanisms governing these pathways offer strategies to develop therapeutics that control non-apoptotic cell death.

Vemurafenib inhibits necroptosis in normal and pathological conditions as a RIPK1 antagonist

Necroptosis, a programmed cell death with necrotic-like morphology, has been recognized as an important driver in various inflammatory diseases. Inhibition of necroptosis has shown potential promise in the therapy of multiple human diseases. However, very few necroptosis inhibitors are available for clinical use as yet. Here, we identified an FDA-approved anti-cancer drug, Vemurafenib, as a potent inhibitor of necroptosis. Through direct binding, Vemurafenib blocked the kinase activity of receptor-interacting protein kinases 1 (RIPK1), impeded the downstream signaling and necrosome complex assembly, and inhibited necroptosis. Compared with Necrostain-1, Vemurafenib stabilized RIPK1 in an inactive DLG-out conformation by occupying a distinct allosteric hydrophobic pocket. Furthermore, pretreatment with Vemurafenib provided strong protection against necroptosis-associated diseases in vivo. Altogether, our results demonstrate that Vemurafenib is an effective RIPK1 antagonist and provide rationale and preclinical evidence for the potential application of approved drug in necroptosis-related diseases.

NHWD-1062 ameliorates inflammation and proliferation by the RIPK1/NF-κB/TLR1 axis in Psoriatic Keratinocytes

Psoriasis is a common chronic inflammatory skin disease. RIPK1 plays an important role in inflammatory diseases. At present, the clinical efficacy of the RIPK1 inhibitor is limited and the regulatory mechanism is unclear in the treatment of psoriasis. Therefore, our team developed a new RIPK1 inhibitor, NHWD-1062, which showed a slightly lower IC50 in U937 cells than that of GSK'772 (a RIPK1 inhibitor in clinical trials) (11 nM vs. 14 nM), indicating that the new RIPK1 inhibitor was no less inhibitory than GSK'772. In this study, we evaluated the therapeutic effects of NHWD-1062 using an IMQ-induced mouse model of psoriasis and explored the precise regulatory mechanism involved. We found that gavage of NHWD-1062 significantly ameliorated the inflammatory response and inhibited the abnormal proliferation of the epidermis in IMQ-induced psoriatic mice. We then elucidated the mechanism of NHWD-1062, which was that suppressed the proliferation and inflammation of keratinocytes in vitro and in vivo through the RIPK1/NF-κB/TLR1 axis. Dual-luciferase reporter assay indicated that P65 can directly target the TLR1 promoter region and activate TLR1 expression, leading to inflammation. In summary, our study demonstrates that NHWD-1062 alleviates psoriasis-like inflammation by inhibiting the activation of the RIPK1/NF-κB/TLR1 axis, which has not been previously reported and further provides evidence for the clinical translation of NHWD-1062 in the treatment of psoriasis.

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.

An in vitro evaluation of the antioxidant activities of necroptosis and apoptosis inhibitors: the potential of necrostatin-1 and necrostatin-1i to have radical scavenging activities

BACKGROUND

Necroptosis inhibitors, including necrostatin-1 (Nec-1), are attracting attention as potential therapeutic agents against various diseases, such as acute lung injury, chronic obstructive pulmonary disease, acute kidney injury, nonalcoholic fatty liver, and neurodegenerative disease, where necroptosis is thought to act as a contributing factor. Nec-1 suppresses necroptosis by inhibiting receptor-interacting protein (RIP) 1 kinase and can also reduce reactive oxygen species (ROS) production; however, the underlying molecular mechanisms mediating ROS reduction remain unclear.

METHODS

The antioxidant effects of necroptosis inhibitors, including Nec-1 and apoptosis inhibitors, were quantified by performing a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Nec-1-related compounds were subsequently assayed for cupric ion-reducing capacity and superoxide dismutase (SOD)-like activity.

RESULTS

Considering all examined apoptosis and necroptosis inhibitors, Nec-1and Nec-1i exhibited antioxidant activity in DPPH radical scavenging assay. In the cupric ion-reducing capacity assay, Nec-1i showed stronger antioxidant capacity than Nec-1. In the SOD-like activity assay, both Nec-1 and Nec-1i were found to have stronger antioxidant capacity than ascorbic acid (IC₅₀ = 4.6 ± 0.040 and 61 ± 0.54 µM, respectively).

CONCLUSION

These results suggest that Nec-1 and Nec-1i may exhibit direct radical scavenging ability against superoxide anions, independent of RIP1 inhibition.

A new perspective on the potential application of RIPK1 in the treatment of sepsis

RIPK1 is a global cellular sensor that can determine the survival of cells. Generally, RIPK1 can induce cell apoptosis and necroptosis through TNF, Fas and lipopolysaccharide stimulation, while its scaffold function can sense the fluctuation of cellular energy and promote cell survival. Sepsis is a nonspecific disease that seriously threatens human health. There is some dispute in the literature about the role of RIPK1 in sepsis. In this review, the authors attempt to comprehensively discuss the differential results for RIPK1 in sepsis by summarizing the underlying molecular mechanism and putting forward a tentative idea as to whether RIPK1 can serve as a biomarker for the monitoring of treatment and progression in sepsis.

From PERK to RIPK1: Design, synthesis and evaluation of novel potent and selective necroptosis inhibitors

Receptor-Interacting serine/threonine-Protein Kinase 1 (RIPK1) emerged as an important driver of inflammation and, consequently, inflammatory pathologies. The enzymatic activity of RIPK1 is known to indirectly promote inflammation by triggering cell death, in the form of apoptosis, necroptosis and pyroptosis. Small molecule Receptor-Interacting serine/threonine-Protein Kinase 1 inhibitors have therefore recently entered clinical trials for the treatment of a subset of inflammatory pathologies. We previously identified GSK2656157 (GSK'157), a supposedly specific inhibitor of protein kinase R (PKR)-like ER kinase (PERK), as a much more potent type II Receptor-Interacting serine/threonine-Protein Kinase 1 inhibitor. We now performed further structural optimisation on the GSK'157 scaffold in order to develop a novel class of more selective Receptor-Interacting serine/threonine-Protein Kinase 1 inhibitors. Based on a structure-activity relationship (SAR) reported in the literature, we anticipated that introducing a substituent on the para-position of the pyridinyl ring would decrease the interaction with PERK. Herein, we report a series of novel GSK'157 analogues with different para-substituents with increased selectivity for Receptor-Interacting serine/threonine-Protein Kinase 1. The optimisation led to UAMC-3861 as the best compound of this series in terms of activity and selectivity for Receptor-Interacting serine/threonine-Protein Kinase 1 over PERK. The most selective compounds were screened in vitro for their ability to inhibit RIPK1-dependent apoptosis and necroptosis. With this work, we successfully synthesised a novel series of potent and selective type II Receptor-Interacting serine/threonine-Protein Kinase 1 inhibitors based on the GSK'157 scaffold.

Approaches to Evaluating Necroptosis in Virus-Infected Cells

The immune system functions to protect the host from pathogens. To counter host defense mechanisms, pathogens have developed unique strategies to evade detection or restrict host immune responses. Programmed cell death is a major contributor to the multiple host responses that help to eliminate infected cells for obligate intracellular pathogens like viruses. Initiation of programmed cell death pathways during the early stages of viral infections is critical for organismal survival as it restricts the virus from replicating and serves to drive antiviral inflammation immune recruitment through the release of damage-associated molecular patterns (DAMPs) from the dying cell. Necroptosis has been implicated as a critical programmed cell death pathway in a diverse set of diseases and pathological conditions including acute viral infections. This cell death pathway occurs when certain host sensors are triggered leading to the downstream induction of mixed-lineage kinase domain-like protein (MLKL). MLKL induction leads to cytoplasmic membrane disruption and subsequent cellular destruction with the release of DAMPs. As the role of this cell death pathway in human disease becomes apparent, methods identifying necroptosis patterns and outcomes will need to be further developed. Here, we discuss advances in our understanding of how viruses counteract necroptosis, methods to quantify the pathway, its effects on viral pathogenesis, and its impact on cellular signaling.

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.

Bacillus anthracis induces NLRP3 inflammasome activation and caspase-8-mediated apoptosis of macrophages to promote lethal anthrax

Lethal toxin (LeTx)-mediated killing of myeloid cells is essential for Bacillus anthracis, the causative agent of anthrax, to establish systemic infection and induce lethal anthrax. The "LeTx-sensitive" NLRP1b inflammasome of BALB/c and 129S macrophages swiftly responds to LeTx intoxication with pyroptosis and secretion of interleukin (IL)-1β. However, human NLRP1 is nonresponsive to LeTx, prompting us to investigate B. anthracis host-pathogen interactions in C57BL/6J (B6) macrophages and mice that also lack a LeTx-sensitive Nlrp1b allele. Unexpectedly, we found that LeTx intoxication and live B. anthracis infection of B6 macrophages elicited robust secretion of IL-1β, which critically relied on the NLRP3 inflammasome. TNF signaling through both TNF receptor 1 (TNF-R1) and TNF-R2 were required for B. anthracis-induced NLRP3 inflammasome activation, which was further controlled by RIPK1 kinase activity and LeTx-mediated proteolytic inactivation of MAP kinase signaling. In addition to activating the NLRP3 inflammasome, LeTx-induced MAPKK inactivation and TNF production sensitized B. anthracis-infected macrophages to robust RIPK1- and caspase-8-dependent apoptosis. In agreement, purified LeTx triggered RIPK1 kinase activity- and caspase-8-dependent apoptosis only in macrophages primed with TNF or following engagement of TRIF-dependent Toll-like receptors. Consistently, genetic and pharmacological inhibition of RIPK1 inhibited NLRP3 inflammasome activation and apoptosis of LeTx-intoxicated and B. anthracis-infected macrophages. Caspase-8/RIPK3-deficient mice were significantly protected from B. anthracis-induced lethality, demonstrating the in vivo pathophysiological relevance of this cytotoxic mechanism. Collectively, these results establish TNF- and RIPK1 kinase activity-dependent NLRP3 inflammasome activation and macrophage apoptosis as key host-pathogen mechanisms in lethal anthrax.

Ligand-based substituent-anchoring design of selective receptor-interacting protein kinase 1 necroptosis inhibitors for ulcerative colitis therapy

Receptor-interacting protein (RIP) kinase 1 is involved in immune-mediated inflammatory diseases including ulcerative colitis (UC) by regulating necroptosis and inflammation. Our group previously identified TAK-632 (5) as an effective necroptosis inhibitor by dual-targeting RIP1 and RIP3. In this study, using ligand-based substituent-anchoring design strategy, we focused on the benzothiazole ring to obtain a series of TAK-632 analogues showing significantly improving on the anti-necroptosis activity and RIP1 selectivity over RIP3. Among them, a conformational constrained fluorine-substituted derivative (25) exhibited 333-fold selectivity for RIP1 (K_d = 15 nmol/L) than RIP3 (K_d > 5000 nmol/L). This compound showed highly potent activity against cell necroptosis (EC₅₀ = 8 nmol/L) and systemic inflammatory response syndrome (SIRS) induced by TNF-α in vivo. Especially, it was able to exhibit remarkable anti-inflammatory treatment efficacy in a DSS-induced mouse model of UC. Taken together, the highly potent, selective, orally active anti-necroptosis inhibitor represents promising candidate for clinical treatment of UC.

Programmed cell death in aortic aneurysm and dissection: A potential therapeutic target

Rupture of aortic aneurysm and dissection (AAD) remains a leading cause of death. Progressive smooth muscle cell (SMC) loss is a crucial feature of AAD that contributes to aortic dysfunction and degeneration, leading to aortic aneurysm, dissection, and, ultimately, rupture. Understanding the molecular mechanisms of SMC loss and identifying pathways that promote SMC death in AAD are critical for developing an effective pharmacologic therapy to prevent aortic destruction and disease progression. Cell death is controlled by programmed cell death pathways, including apoptosis, necroptosis, pyroptosis, and ferroptosis. Although these pathways share common stimuli and triggers, each type of programmed cell death has unique features and activation pathways. A growing body of evidence supports a critical role for programmed cell death in the pathogenesis of AAD, and inhibitors of various types of programmed cell death represent a promising therapeutic strategy. This review discusses the different types of programmed cell death pathways and their features, induction, contributions to AAD development, and therapeutic potential. We also highlight the clinical significance of programmed cell death for further studies.

Preclinical Evidence for the Interplay between Oxidative Stress and RIP1-Dependent Cell Death in Neurodegeneration: State of the Art and Possible Therapeutic Implications

Neurodegenerative diseases are the most frequent chronic, age-associated neurological pathologies having a major impact on the patient’s quality of life. Despite a heavy medical, social and economic burden they pose, no causative treatment is available for these diseases. Among the important pathogenic factors contributing to neuronal loss during neurodegeneration is elevated oxidative stress resulting from a disturbed balance between endogenous prooxidant and antioxidant systems. For many years, it was thought that increased oxidative stress was a cause of neuronal cell death executed via an apoptotic mechanism. However, in recent years it has been postulated that rather programmed necrosis (necroptosis) is the key form of neuronal death in the course of neurodegenerative diseases. Such assumption was supported by biochemical and morphological features of the dying cells as well as by the fact that various necroptosis inhibitors were neuroprotective in cellular and animal models of neurodegenerative diseases. In this review, we discuss the relationship between oxidative stress and RIP1-dependent necroptosis and apoptosis in the context of the pathomechanism of neurodegenerative disorders. Based on the published data mainly from cellular models of neurodegeneration linking oxidative stress and necroptosis, we postulate that administration of multipotential neuroprotectants with antioxidant and antinecroptotic properties may constitute an efficient pharmacotherapeutic strategy for the treatment of neurodegenerative diseases.

Novel insights into RIPK1 as a promising target for future Alzheimer's disease treatment

Alzheimer's disease (AD) is an intractable neurodegenerative disease showing a clinical manifestation with memory loss, cognitive impairment and behavioral dysfunction. The predominant pathological characteristics of AD include neuronal loss, β-amyloid (Aβ) deposition and hyperphosphorylated Tau induced neurofibrillary tangles (NFTs), while considerable studies proved these could be triggered by neuronal death and neuroinflammation. Receptor-interacting protein kinase 1 (RIPK1) is a serine/threonine kinase existed at the cross-point of cell death and inflammatory signaling pathways. Emerging investigations have shed light on RIPK1 for its potential role in AD progression. The present review makes a bird's eye view on the functions of RIPK1 and mainly focus on the underlying linkages between RIPK1 and AD from comprehensive aspects including neuronal death, Aβ and Tau, inflammasome activation, BBB rupture, AMPK/mTOR, mitochondrial dysfunction and O-glcNAcylation. Moreover, the discovery of RIPK1 inhibitors, ongoing clinical trials along with future RIPK1-targeted therapeutics are also reviewed.

Chemogenomics for drug discovery: clinical molecules from open access chemical probes

In recent years chemical probes have proved valuable tools for the validation of disease-modifying targets, facilitating investigation of target function, safety, and translation. Whilst probes and drugs often differ in their properties, there is a belief that chemical probes are useful for translational studies and can accelerate the drug discovery process by providing a starting point for small molecule drugs. This review seeks to describe clinical candidates that have been inspired by, or derived from, chemical probes, and the process behind their development. By focusing primarily on examples of probes developed by the Structural Genomics Consortium, we examine a variety of epigenetic modulators along with other classes of probe.

Necroptosis molecular mechanisms: Recent findings regarding novel necroptosis regulators

Necroptosis is a form of programmed necrosis that is mediated by various cytokines and pattern recognition receptors (PRRs). Cells dying by necroptosis show necrotic phenotypes, including swelling and membrane rupture, and release damage-associated molecular patterns (DAMPs), inflammatory cytokines, and chemokines, thereby mediating extreme inflammatory responses. Studies on gene knockout or necroptosis-specific inhibitor treatment in animal models have provided extensive evidence regarding the important roles of necroptosis in inflammatory diseases. The necroptosis signaling pathway is primarily modulated by activation of receptor-interacting protein kinase 3 (RIPK3), which phosphorylates mixed-lineage kinase domain-like protein (MLKL), mediating MLKL oligomerization. In the necroptosis process, these proteins are fine-tuned by posttranslational regulation via phosphorylation, ubiquitination, glycosylation, and protein-protein interactions. Herein, we review recent findings on the molecular regulatory mechanisms of necroptosis.

Discovery of a Necroptosis Inhibitor Improving Dopaminergic Neuronal Loss after MPTP Exposure in Mice

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, mainly characterized by motor deficits correlated with progressive dopaminergic neuronal loss in the substantia nigra pars compacta (SN). Necroptosis is a caspase-independent form of regulated cell death mediated by the concerted action of receptor-interacting protein 3 (RIP3) and the pseudokinase mixed lineage domain-like protein (MLKL). It is also usually dependent on RIP1 kinase activity, influenced by further cellular clues. Importantly, necroptosis appears to be strongly linked to several neurodegenerative diseases, including PD. Here, we aimed at identifying novel chemical inhibitors of necroptosis in a PD-mimicking model, by conducting a two-step screening. Firstly, we phenotypically screened a library of 31 small molecules using a cellular model of necroptosis and, thereafter, the hit compound effect was validated in vivo in a sub-acute 1-methyl-1-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) PD-related mouse model. From the initial compounds, we identified one hit—Oxa12—that strongly inhibited necroptosis induced by the pan-caspase inhibitor zVAD-fmk in the BV2 murine microglia cell line. More importantly, mice exposed to MPTP and further treated with Oxa12 showed protection against MPTP-induced dopaminergic neuronal loss in the SN and striatum. In conclusion, we identified Oxa12 as a hit compound that represents a new chemotype to tackle necroptosis. Oxa12 displays in vivo effects, making this compound a drug candidate for further optimization to attenuate PD pathogenesis.

Enantiomeric profiling of a chiral benzothiazole necroptosis inhibitor

Necroptosis is a form of programmed cell death that contributes to the pathophysiology of multiple diseases. Development of small-molecule anti-necroptosis agents has great promising clinical therapeutic relevance. The benzothiazole compounds were discovered by our group from an in-house fluorine-containing compound library as potent necroptosis inhibitors. Herein, a chiral dimethylcyclopropyl benzothiazole necroptosis inhibitor was developed and the enantiomeric profiling resulted that the (S) form was generally more potent than the (R) counterpart in 2 ~ 4-fold toward cell necroptosis, receptor-interacting protein (RIP) kinases 1 and 3. The chiral compounds could significantly inhibit the expression of the phosphorylation of RIPK1, RIPK3 and MLKL in necroptotic cells. The molecular modelling studies predicted the binding modes of the enantiomers with RIP and explained their activity differences, guiding further rational design of the chiral necroptosis inhibitors.

Primidone blocks RIPK1-driven cell death and inflammation

The receptor-interacting serine/threonine protein kinase 1 (RIPK1) is a key mediator of regulated cell death and inflammation. Recent studies suggest that RIPK1 inhibition would fundamentally improve the therapy of RIPK1-dependent organ damage in stroke, myocardial infarction, kidney failure, and systemic inflammatory response syndrome. Additionally, it could ameliorate or prevent multi-organ failure induced by cytokine release in the context of hyperinflammation, as seen in COVID-19 patients. Therefore, we searched for a RIPK1 inhibitor and present the aromatic antiepileptic and FDA-approved drug primidone (Liskantin®) as a potent inhibitor of RIPK1 activation in vitro and in a murine model of TNFα-induced shock, which mimics the hyperinflammatory state of cytokine release syndrome. Furthermore, we detected for the first time RIPK1 activation in the respiratory tract epithelium of hospitalized patients who tested positive for SARS-CoV-2 infection. Our data provide a strong rationale for evaluating the drug primidone in conditions of hyperinflammation in humans.

Recent progress in small-molecule inhibitors for critical therapeutic targets of necroptosis

Nonapoptotic types of regulated cell death have attracted widespread interest since the discovery that certain forms of cell necrosis can be regulated. In particular, research into cell necroptosis has made significant progress in connection with kidney, inflammatory, degenerative and neoplastic diseases. Inhibitors targeting the critical necroptosis-associated proteins RIPK1/3 and MLKL have been in development for more than a decade. Herein the authors compile a list of the known small-molecule inhibitors of these enzymes and representative structures of compounds co-crystallized with these proteins and put forward some thoughts regarding their future development.

A randomized, placebo-controlled experimental medicine study of RIPK1 inhibitor GSK2982772 in patients with moderate to severe rheumatoid arthritis

Background

Receptor-interacting protein kinase 1 (RIPK1) is a key mediator of inflammation through cell death and proinflammatory cytokine production. This multicenter, randomized, double-blind (sponsor-unblinded), placebo-controlled, experimental medicine study evaluated the safety, pharmacokinetics (PK), and preliminary efficacy of GSK2982772, a RIPK1 inhibitor, in moderate to severe rheumatoid arthritis (RA).

Methods

Patients with moderate to severe RA who had received ≥12 weeks’ stable-dose conventional synthetic disease-modifying antirheumatic drug (csDMARD) therapy were randomized (2:1) to GSK2982772 60 mg or placebo orally 2 or 3 times daily for 84 days. Safety, PK, disease activity, joint damage, and pharmacodynamic (PD) biomarkers were assessed at days 43 and 85.

Results

A total of 52 patients were randomized (placebo, 18; GSK2982772, 34). Adverse events (AEs) were reported in 13 (72%) in patients in the placebo group (n = 3 b.i.d; n = 10 t.i.d.) and 20 (61%) in the GSK2982772 group (n = 3 b.i.d; n = 17 t.i.d.). All treatment-related AEs were mild/moderate, except one severe case of alopecia areata at day 49 and retinal vein thrombosis at day 66 (which led to withdrawal from the study) in patients receiving GSK2982772 t.i.d. Disease Activity Score in 28 Joints–C-reactive protein (DAS28-CRP) scores, ACR20/50/70 response, and rates of low disease activity and remission were similar between placebo and GSK2982772 arms.

Conclusions

These results suggest that inhibition of RIPK1 activity at the GSK2982772 exposure levels evaluated do not translate into meaningful clinical improvement of RA.

Trial registration

ClinicalTrials.gov Identifier: NCT02858492. Registered 8 August 2016.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02468-0.

Inhibitors of RIP1 kinase: a patent review (2016-present)

Introduction: RIP1 kinase is a serine/threonine-protein kinase that has recently emerged as a central regulator of TNF-α dependent programmed necrosis (necroptosis), an inflammatory form of cell death, with important roles in inflammation and neurodegeneration. Small molecule RIP1 kinase inhibitors may provide new opportunities for treating a variety of autoimmune, inflammatory, and neurodegenerative diseases, among others, and thus have attracted widespread drug development efforts and a corresponding large amount of patent activity in recent years. Areas covered: This review focuses on the patent literature covering small molecule inhibitors of RIP1 kinase from 2016-present. Expert opinion: Inhibition of programmed necrosis (necroptosis) by RIP1 kinase inhibitors is a new field that has attracted widespread recent interest as a possible therapeutic means to treat a number of diseases in the inflammatory, neurodegenerative, and oncology areas. The interest in the therapeutic potential of RIP1kinase is evidenced by more than 40 small molecule patent applications published since 2016. To date, only a few RIP1 kinase inhibitors have entered the clinic. An understanding of the optimal clinical setting, in terms of dosing and disease indications for RIP1 inhibition, will require further clinical readouts as the current inhibitors progress and additional molecules enter into full development.

A Single-Stranded DNA-Encoded Chemical Library Based on a Stereoisomeric Scaffold Enables Ligand Discovery by Modular Assembly of Building Blocks

A versatile and Lipinski-compliant DNA-encoded library (DEL), comprising 366 600 glutamic acid derivatives coupled to oligonucleotides serving as amplifiable identification barcodes is designed, constructed, and characterized. The GB-DEL library, constructed in single-stranded DNA format, allows de novo identification of specific binders against several pharmaceutically relevant proteins. Moreover, hybridization of the single-stranded DEL with a set of known protein ligands of low to medium affinity coupled to a complementary DNA strand results in self-assembled selectable chemical structures, leading to the identification of affinity-matured compounds.

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.

Potent Inhibition of Necroptosis by Simultaneously Targeting Multiple Effectors of the Pathway

Necroptosis is an inflammatory form of programmed cell death that has been implicated in various human diseases. Compound 2 is a more potent analogue of the published compound 1 and inhibits necroptosis in human and murine cells at nanomolar concentrations. Several target engagement strategies were employed, including cellular thermal shift assays (CETSA) and diazirine-mediated photoaffinity labeling via a bifunctional photoaffinity probe derived from compound 2. These target engagement studies demonstrate that compound 2 binds to all three necroptotic effector proteins (mixed lineage kinase domain-like protein (MLKL), receptor-interacting serine/threonine protein kinase 1 (RIPK1) and receptor-interacting serine/threonine protein kinase 3 (RIPK3)) at different levels in vitro and in cells. Compound 2 also shows efficacy in vivo in a murine model of systemic inflammatory response syndrome (SIRS).

Response to Inhibition of Receptor-Interacting Protein Kinase 1 (RIPK1) in Active Plaque Psoriasis: A Randomized Placebo-Controlled Study

Receptor-interacting protein kinase 1 (RIPK1), a regulator of inflammation and cell death, is a potential therapeutic target in immune-mediated inflammatory diseases (IMIDs). The objective of this phase IIa multicenter, randomized, double-blind, placebo-controlled study was to evaluate safety, tolerability pharmacokinetics, pharmacodynamics, and preliminary efficacy of GSK2982772, a RIPK1 inhibitor, in plaque-type psoriasis. Psoriasis patients (N = 65) were randomized to 60 mg twice daily (b.i.d.) or three times daily (t.i.d.), or placebo for 84 days. Most adverse events (AEs) were mild with no severe drug-related AEs reported. Plaque Lesion Severity Sum improved with b.i.d. treatment compared with placebo; interpretation of t.i.d. treatment results was complicated by a high placebo response. Reductions in epidermal thickness and infiltration by CD3+ T cells in the epidermis and dermis were observed compared with placebo. Results support the rationale for additional studies on RIPK1 inhibition in IMIDs.

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.

Respiratory Syncytial Virus Infection Promotes Necroptosis and HMGB1 Release by Airway Epithelial Cells

Rationale: Respiratory syncytial virus (RSV) bronchiolitis causes significant infant mortality. Bronchiolitis is characterized by airway epithelial cell (AEC) death; however, the mode of death remains unknown.Objectives: To determine whether necroptosis contributes to RSV bronchiolitis pathogenesis via HMGB1 (high mobility group box 1) release.Methods: Nasopharyngeal samples were collected from children presenting to the hospital with acute respiratory infection. Primary human AECs and neonatal mice were inoculated with RSV and murine Pneumovirus, respectively. Necroptosis was determined via viability assays and immunohistochemistry for RIPK1 (receptor-interacting protein kinase-1), MLKL (mixed lineage kinase domain-like pseudokinase) protein, and caspase-3. Necroptosis was blocked using pharmacological inhibitors and RIPK1 kinase-dead knockin mice.Measurements and Main Results: HMGB1 levels were elevated in nasopharyngeal samples of children with acute RSV infection. RSV-induced epithelial cell death was associated with increased phosphorylated RIPK1 and phosphorylated MLKL but not active caspase-3 expression. Inhibition of RIPK1 or MLKL attenuated RSV-induced HMGB1 translocation and release, and lowered viral load. MLKL inhibition increased active caspase-3 expression in a caspase-8/9-dependent manner. In susceptible mice, Pneumovirus infection upregulated RIPK1 and MLKL expression in the airway epithelium at 8 to 10 days after infection, coinciding with AEC sloughing, HMGB1 release, and neutrophilic inflammation. Genetic or pharmacological inhibition of RIPK1 or MLKL attenuated these pathologies, lowered viral load, and prevented type 2 inflammation and airway remodeling. Necroptosis inhibition in early life ameliorated asthma progression induced by viral or allergen challenge in later life.Conclusions: Pneumovirus infection induces AEC necroptosis. Inhibition of necroptosis may be a viable strategy to limit the severity of viral bronchiolitis and break its nexus with asthma.

Receptor-interacting protein kinase 1 (RIPK1) as a therapeutic target

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a key mediator of cell death and inflammation. The unique hydrophobic pocket in the allosteric regulatory domain of RIPK1 has enabled the development of highly selective small-molecule inhibitors of its kinase activity, which have demonstrated safety in preclinical models and clinical trials. Potential applications of these RIPK1 inhibitors for the treatment of monogenic and polygenic autoimmune, inflammatory, neurodegenerative, ischaemic and acute conditions, such as sepsis, are emerging. This article reviews RIPK1 biology and disease-associated mutations in RIPK1 signalling pathways, highlighting clinical trials of RIPK1 inhibitors and potential strategies to mitigate development challenges.

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) — a key mediator of cell death and inflammation — is activated in human diseases. Here, Yuan and colleagues discuss current understanding of RIPK1 biology and its association with diseases including inflammatory and autoimmune disorders, neurodegenerative diseases and sepsis. The clinical development of small-molecule RIPK1 inhibitors and associated challenges are discussed.

RIPK1: A rising star in inflammatory and neoplastic skin diseases

Skin diseases bring great psychological and physical impacts on patients, however, a considerable number of skin diseases still lack effective treatments, such as psoriasis, systemic lupus erythematosus, melanoma and so on. Receptor-interacting serine threonine kinase 1 (RIPK1) plays an important role in cell death, especially necroptosis, associated with inflammation and tumor. As many molecules modulate the ubiquitination of RIPK1, disruption of this checkpoint can lead to skin diseases, which can be ameliorated by RIPK1 inhibitors. This review will focus on the molecular mechanism of RIPK1 activation in inflammation as well as the current knowledges on the contribution of RIPK1 in skin diseases.

The necroptosis pathway and its role in age-related neurodegenerative diseases: will it open up new therapeutic avenues in the next decade?

INTRODUCTION

Necroptosis is a programmed form of necrotic cell death. Growing evidence demonstrates that necroptosis contributes to cell demise in different pathological conditions including age-dependent neurodegenerative diseases (NDs). These findings open new avenues for understanding the mechanisms of neuronal loss in NDs, which might eventually translate into novel therapeutic interventions.

AREAS COVERED

We reviewed key aspects of necroptosis, in health and disease, focusing on evidence demonstrating its involvement in the pathogenesis of age-related NDs. We then highlight the activation of this pathway in the mechanism of axonal degeneration. We searched on PubMed the literature regarding necroptosis published between 2008 and 2020 and reviewed all publications were necroptosis was studied in the context of age-related NDs.

EXPERT OPINION

Axonal loss and neuronal death are the ultimate consequences of NDs that translate into disease phenotypes. Targeting degenerative mechanisms of the neuron appears as a strategy that might cover a wide range of diseases. Thus, the participation of necroptosis as a common mediator of neuronal demise emerges as a promising target for therapeutic intervention. Considering evidence demonstrating that necroptosis mediates axonal degeneration, we propose and discuss the potential of targeting necroptosis-mediated axonal destruction as a strategy to tackle NDs before neuronal loss occurs.