Necroptosis inhibitors as therapeutic targets in inflammation mediated disorders - a review of the current literature and patents

Viral-induced neuronal necroptosis: Detrimental to brain function and regulation by necroptosis inhibitors

Neuronal necroptosis (programmed necrosis) in the CNS naturally occurs through a caspase-independent way and, especially in neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parknson's disease (PD), Amyotrophic Lateral Sclerosis (ALS) and viral infections. Understanding necroptosis pathways (death receptor-dependent and independent), and its connections with other cell death pathways could lead to new insights into treatment. Receptor-interacting protein kinase (RIPK) mediates necroptosis via mixed-lineage kinase-like (MLKL) proteins. RIPK/MLKL necrosome contains FADD, procaspase-8-cellular FLICE-inhibitory proteins (cFLIPs), RIPK1/RIPK3, and MLKL. The necrotic stimuli cause phosphorylation of MLKL and translocate to the plasma membrane, causing an influx of Ca2+ and Na+ ions and, the immediate opening of mitochondrial permeability transition pore (mPTP) with the release of inflammatory cell damage-associated molecular patterns (DAMPs) like mitochondrial DNA (mtDNA), high-mobility group box1 (HMGB1), and interleukin1 (IL-1). The MLKL translocates to the nucleus to induce transcription of the NLRP3 inflammasome complex elements. MLKL-induced NLRP3 activity causes caspase-1 cleavage and, IL-1 activation which promotes neuroinflammation. RIPK1-dependent transcription increases illness-associated microglial and lysosomal abnormalities to facilitate amyloid plaque (Aβ) aggregation in AD. Recent research has linked neuroinflammation and mitochondrial fission with necroptosis. MicroRNAs (miRs) such as miR512-3p, miR874, miR499, miR155, and miR128a regulate neuronal necroptosis by targeting key components of necroptotic pathways. Necroptosis inhibitors act by inhibiting the membrane translocation of MLKL and RIPK1 activity. This review insights into the RIPK/MLKL necrosome-NLRP3 inflammasome interactions during death receptor-dependent and independent neuronal necroptosis, and clinical intervention by miRs to protect the brain from NDDs.

Unwinding the modalities of necrosome activation and necroptosis machinery in neurological diseases

Necroptosis, a regulated form of cell death, is involved in the genesis and development of various life-threatening diseases, including cancer, neurological disorders, cardiac myopathy, and diabetes. Necroptosis initiates with the formation and activation of a necrosome complex, which consists of RIPK1, RIPK2, RIPK3, and MLKL. Emerging studies has demonstrated the regulation of the necroptosis cell death pathway through the implication of numerous post-translational modifications, namely ubiquitination, acetylation, methylation, SUMOylation, hydroxylation, and others. In addition, the negative regulation of the necroptosis pathway has been shown to interfere with brain homeostasis through the regulation of axonal degeneration, mitochondrial dynamics, lysosomal defects, and inflammatory response. Necroptosis is controlled by the activity and expression of signaling molecules, namely VEGF/VEGFR, PI3K/Akt/GSK-3β, c-Jun N-terminal kinases (JNK), ERK/MAPK, and Wnt/β-catenin. Herein, we briefly discussed the implication and potential of necrosome activation in the pathogenesis and progression of neurological manifestations, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, traumatic brain injury, and others. Further, we present a detailed picture of natural compounds, micro-RNAs, and chemical compounds as therapeutic agents for treating neurological manifestations.

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.

miR-130-CYLD Axis Is Involved in the Necroptosis and Inflammation Induced by Selenium Deficiency in Pig Cerebellum

Selenium (Se) is an essential trace element in creatures which deficiency can cause necroptosis and inflammation of multiple tissues. MicroRNAs (miRNAs) have been identified to participate multiple biological processes by regulating the expression of target genes. In the present study, the Se-deficient pig cerebellar model was established and conducted by light microscopy, qRT-PCR, and Western blot. Morphological observation exhibited necrosis-like lesions and inflammatory infiltration in the cerebellum of the Se-deficient group. Quantitative analysis result showed that Se deficiency significantly suppressed miR-130 expression, which in turn disinhibited the expression of CYLD. Meanwhile, in comparison to the control group, the expression levels of TNF-α pathway genes (TNF-α, TNFR1, and NF-κB p65) and necroptosis-related genes (RIPK1, RIPK3, and MLKL) in Se deficiency group were obviously increased (P < 0.05). Moreover, Se deficiency induced the occurrence of inflammation by upregulating the expression of inflammatory cytokines (IL-1β, IL-2, IL-8, IL-18, IFN-γ, COX-2, PTGEs, and NLRP3). In conclusion, we proved Se deficiency could induce the deregulation of miR-130-CYLD axis to cause RIPK3-dependent necroptosis and inflammation in pig cerebellum.

Virus-infection in cochlear supporting cells induces audiosensory receptor hair cell death by TRAIL-induced necroptosis

Although sensorineural hearing loss (SHL) is relatively common, its cause has not been identified in most cases. Previous studies have suggested that viral infection is a major cause of SHL, especially sudden SHL, but the system that protects against pathogens in the inner ear, which is isolated by the blood-labyrinthine barrier, remains poorly understood. We recently showed that, as audiosensory receptor cells, cochlear hair cells (HCs) are protected by surrounding accessory supporting cells (SCs) and greater epithelial ridge (GER or Kölliker's organ) cells (GERCs) against viral infections. Here, we found that virus-infected SCs and GERCs induce HC death via production of the tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). Notably, the HCs expressed the TRAIL death receptors (DR) DR4 and DR5, and virus-induced HC death was suppressed by TRAIL-neutralizing antibodies. TRAIL-induced HC death was not caused by apoptosis, and was inhibited by necroptosis inhibitors. Moreover, corticosteroids, the only effective drug for SHL, inhibited the virus-induced transformation of SCs and GERCs into macrophage-like cells and HC death, while macrophage depletion also inhibited virus-induced HC death. These results reveal a novel mechanism underlying virus-induced HC death in the cochlear sensory epithelium and suggest a possible target for preventing virus-induced SHL.

Targeting programmed cell death in metabolic dysfunction-associated fatty liver disease (MAFLD): a promising new therapy

Most currently recommended therapies for metabolic dysfunction-associated fatty liver disease (MAFLD) involve diet control and exercise therapy. We searched PubMed and compiled the most recent research into possible forms of programmed cell death in MAFLD, including apoptosis, necroptosis, autophagy, pyroptosis and ferroptosis. Here, we summarize the state of knowledge on the signaling mechanisms for each type and, based on their characteristics, discuss how they might be relevant in MAFLD-related pathological mechanisms. Although significant challenges exist in the translation of fundamental science into clinical therapy, this review should provide a theoretical basis for innovative MAFLD clinical treatment plans that target programmed cell death.

Gegen Qinlian Decoction Ameliorates Hyperuricemia-Induced Renal Tubular Injury via Blocking the Inflammatory Signaling Pathway

Background: Gegen Qinlian decoction (GGQLD) is a typical traditional Chinese medicine (TCM) prescription documented in Shang Han Lun. Clinically, GGQLD has been utilized to manage the inflammatory symptoms of metabolic diseases and to protect against renal damage in China. In the present study, a hypothesis was proposed that the multi-target solution of GGQLD produced anti-inflammatory effects on ameliorating hyperuricemia (HUA).

Methods: A total of 30 primary HUA patients receiving GGQLD treatment (two doses daily) for 4 weeks were selected. Then, differences in uric acid (UA) levels and expression of peripheral blood mononuclear cells (PBMCs) and urinary exosomes before and after treatment were analyzed. The therapeutic indexes for the active ingredients in GGQLD against HUA were confirmed through pharmacological subnetwork analysis. Besides, the HUA rat model was established through oral gavage of potassium oxonate and treated with oral GGQLD. In addition, proximal tubular epithelial cells (PTECs) were stimulated by UA and intervened with GGQLD for 48 h. Subsequently, RNA-seq, flow cytometry, and confocal immunofluorescence microscopy were further conducted to characterize the differences in UA-mediated inflammation and apoptosis of human renal tubular epithelial cells pre- and post-administration of GGQLD. In the meanwhile, quantitative real-time PCR (qPCR) was carried out to determine gene expression, whereas a western blotting (WB) assay was conducted to measure protein expression.

Results: Our network analysis revealed that GGQLD treated HUA via the anti-inflammatory and antiapoptotic pathways. Additionally, NLPR3 expression significantly decreased in PBMCs and urinary exosomes of HUA patients after GGQLD treatment. In vivo, GGQLD treatment alleviated HUA-induced renal inflammation, which was associated with decreased expression of NLRP3 inflammasomes and apoptosis-related mRNAs. Moreover, GGQLD promoted renal UA excretion by inhibiting the activation of GSDMD-dependent pyroptosis induced by NLRP3 inflammasomes and by reducing apoptosis via the mitochondrial apoptosis signaling pathway in vitro.

Conclusion: This study indicates that GGQLD efficiently reduces inflammatory responses while promoting UA excretion in HUA. Our findings also provide compelling evidence supporting the idea that GGQLD protects against the UA-mediated renal tubular epithelial cell inflammation through the mitochondrial apoptosis signaling pathways. Taken together, these findings have demonstrated a novel therapeutic method for the treatment of HUA.

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.

Comparison of the Pharmacokinetics of RIPK1 Inhibitor GSK2982772 in Healthy Western and Japanese Subjects

Background and Objectives

GSK2982772 is an oral small-molecule RIPK1 inhibitor with potential therapeutic efficacy in immune-mediated inflammatory diseases (IMIDs). An inter-ethnic comparison of GSK2982772 pharmacokinetics was conducted based on data from Western (Study 1) and Japanese subjects (Study 2).

Methods

Both studies were single-centre, randomised, double-blind, placebo-controlled studies with objectives to assess the safety and characterise the pharmacokinetics of GSK2982772. Western subjects in Study 1 (NCT03305419), Part A (N = 15), were randomly assigned to receive 120 mg three times daily (TID), 240 mg TID, or 360 mg twice daily (BID) doses of GSK2982772, or placebo (TID or BID) for 1 day. Part B subjects (N = 47) received GSK2982772 120 mg TID, 240 mg TID, or placebo TID for 14 days. Japanese subjects in Study 2 (N = 13) (NCT03590613) were randomly assigned to receive TID doses of GSK2982772 60, 120, 240 mg TID or placebo TID for 1 day.

Results

GSK2982772 was well tolerated and adverse events were generally mild. Maximum observed plasma drug concentration (C_max), time to reach C_max (T_max), area under the plasma drug concentration versus time curve after the first GSK2982772 dose (AUC_(0–7)) of 120 and 240 mg, and (AUC_(0–24)) values for the 120 and 240 mg TID doses over a single day were similar in Japanese and Western subjects.

Conclusions

The pharmacokinetics and tolerability of GSK2982772 were similar between Western and Japanese subjects, justifying inclusion of Japanese subjects in future global clinical studies to assess the therapeutic potential of RIPK1 inhibition for the treatment of IMIDs.

Clinical Trials: NCT03305419 and NCT03590613 available from http://www.clinicaltrials.gov.

Electronic supplementary material

The online version of this article (10.1007/s13318-020-00652-2) contains supplementary material, which is available to authorized users.

DAMPs in Unilateral Ureteral Obstruction

Damage-associated molecular patterns (DAMPs) are released from tubular and interstitial cells in the kidney after unilateral ureteral obstruction (UUO). DAMPs are recognized by pattern recognition receptors (PRRs), which mediate the initiation of an immune response and the release of inflammatory cytokines. The animal model of UUO is used for various purposes. UUO in adult mice serves as a model for accelerated renal fibrosis, which is a hallmark of progressive renal disease. UUO in adult mice enables to study cell death, inflammation, and extracellular matrix deposition in the kidney. Neonatal UUO is a model for congenital obstructive nephropathies. It studies inflammation, apoptosis, and interstitial fibrosis in the neonatal kidney, when nephrogenesis is still ongoing. Following UUO, several DAMPs as well as DAMP receptors are upregulated. In adult UUO, soluble uric acid is upregulated and activates the NOD-like receptor family, pyrin domain containing-3 (NLRP3) inflammasome, which promotes fibrosis, apoptosis, and reactive oxygen species (ROS) injury. Further DAMPs associated with UUO are uromodulin, members of the IL-1 family, and necrotic cell DNA, all of which promote sterile inflammation. In neonatal UUO, the receptor for advanced glycation endproducts (RAGE) is highly upregulated. RAGE is a ligand for several DAMPs, including high mobility group box 1 (HMGB1) and S100 proteins, which play an important role in renal fibrosis. Additionally, necroptosis is an important mechanism of cell death, besides apoptosis, in neonatal UUO. It is highly inflammatory due to release of cytokines and specific DAMPs. The release and recognition of DAMPs initiate sterile inflammation, which makes them good candidates to develop and improve diagnostic and therapeutic strategies in renal fibrosis and congenital obstructive nephropathies.

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.

Peptidyl Fluoromethyl Ketones and Their Applications in Medicinal Chemistry

Peptidyl fluoromethyl ketones occupy a pivotal role in the current scenario of synthetic chemistry, thanks to their numerous applications as inhibitors of hydrolytic enzymes. The insertion of one or more fluorine atoms adjacent to a C-terminal ketone moiety greatly modifies the physicochemical properties of the overall substrate, especially by increasing the reactivity of this functionalized carbonyl group toward nucleophiles. The main application of these peptidyl α-fluorinated ketones in medicinal chemistry relies in their ability to strongly and selectively inhibit serine and cysteine proteases. These compounds can be used as probes to study the proteolytic activity of the aforementioned proteases and to elucidate their role in the insurgence and progress on several diseases. Likewise, if the fluorinated methyl ketone moiety is suitably connected to a peptidic backbone, it may confer to the resulting structure an excellent substrate peculiarity and the possibility of being recognized by a specific subclass of human or pathogenic proteases. Therefore, peptidyl fluoromethyl ketones are also currently highly exploited for the target-based design of compounds for the treatment of topical diseases such as various types of cancer and viral infections.

Phenotypic high-throughput screening platform identifies novel chemotypes for necroptosis inhibition

Regulated necrosis or necroptosis, mediated by receptor-interacting kinase 1 (RIPK1), RIPK3 and pseudokinase mixed lineage kinase domain-like protein (MLKL), contributes to the pathogenesis of inflammatory, infectious and degenerative diseases. Recently identified necroptosis inhibitors display moderate specificity, suboptimal pharmacokinetics, off-target effects and toxicity, preventing these molecules from reaching the clinic. Here, we developed a cell-based high-throughput screening (HTS) cascade for the identification of small-molecule inhibitors of necroptosis. From the initial library of over 250,000 compounds, the primary screening phase identified 356 compounds that strongly inhibited TNF-α-induced necroptosis, but not apoptosis, in human and murine cell systems, with EC50 < 6.7 μM. From these, 251 compounds were tested for RIPK1 and/or RIPK3 kinase inhibitory activity; some were active and several have novel mechanisms of action. Based on specific chemical descriptors, 110 compounds proceeded into the secondary screening cascade, which then identified seven compounds with maximum ability to reduce MLKL activation, IC50 >100 μM, EC50 2.5-11.5 μM under long-term necroptosis execution in murine fibroblast L929 cells, and full protection from ATP depletion and membrane leakage in human and murine cells. As a proof of concept, compound SN-6109, with binding mode to RIPK1 similar to that of necrostatin-1, confirmed RIPK1 inhibitory activity and appropriate pharmacokinetic properties. SN-6109 was further tested in mice, showing efficacy against TNF-α-induced systemic inflammatory response syndrome. In conclusion, a phenotypic-driven HTS cascade promptly identified robust necroptosis inhibitors with in vivo activity, currently undergoing further medicinal chemistry optimization. Notably, the novel hits highlight the opportunity to identify new molecular mechanisms of action in necroptosis.

Predisposition to Apoptosis in Hepatocellular Carcinoma: From Mechanistic Insights to Therapeutic Strategies

Hepatocellular carcinoma (HCC) ranks among the most rapidly evolving cancers in the Western world. The majority of HCCs develop on the basis of a chronic inflammatory liver damage that predisposes liver cancer development and leads to deregulation of multiple cellular signaling pathways. The resulting dysbalance between uncontrolled proliferation and impaired predisposition to cell death with consecutive failure to clear inflammatory damage is a key driver of malignant transformation. Therefore, resistance to death signaling accompanied by metabolic changes as well as failed immunological clearance of damaged pre-neoplastic hepatocytes are considered hallmarks of hepatocarcinogenesis. Hereby, the underlying liver disease, the type of liver damage and individual predisposition to apoptosis determines the natural course of the disease as well as the therapeutic response. Here, we will review common and individual aspects of cell death pathways in hepatocarcinogenesis with a particular emphasis on regulatory networks and key molecular alterations. We will further delineate the potential of targeting cell death-related signaling as a viable therapeutic strategy to improve the outcome of HCC patients.

The Caspase Inhibitor Z-VAD-FMK Alleviates Endotoxic Shock via Inducing Macrophages Necroptosis and Promoting MDSCs-Mediated Inhibition of Macrophages Activation

Macrophages play a critical role in the pathogenesis of endotoxin shock by producing excessive amounts of pro-inflammatory cytokines. A pan-caspase inhibitor, zVAD, can be used to induce necroptosis under certain stimuli. The role of zVAD in both regulating the survival and activation of macrophages, and the pathogenesis of endotoxin shock remains not entirely clear. Here, we found that treatment of mice with zVAD could significantly reduce mortality and alleviate disease after lipopolysaccharide (LPS) challenge. Notably, in LPS-challenged mice, treatment with zVAD could also reduce the percentage of peritoneal macrophages by promoting necroptosis and inhibiting pro-inflammatory responses in macrophages. In vitro studies showed that pretreatment with zVAD promoted LPS-induced nitric oxide-mediated necroptosis of bone marrow-derived macrophages (BMDMs), leading to reduced pro-inflammatory cytokine secretion. Interestingly, zVAD treatment promoted the accumulation of myeloid-derived suppressor cells (MDSCs) in a mouse model of endotoxin shock, and this process inhibited LPS-induced pro-inflammatory responses in macrophages. Based on these findings, we conclude that treatment with zVAD alleviates LPS-induced endotoxic shock by inducing macrophage necroptosis and promoting MDSC-mediated inhibition of macrophage activation. Thus, this study provides insights into the effects of zVAD treatment in inflammatory diseases, especially endotoxic shock.

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

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

Apoptosis and necroptosis in the liver: a matter of life and death

Cell death represents a basic biological paradigm that governs outcomes and long-term sequelae in almost every hepatic disease condition. Acute liver failure is characterized by massive loss of parenchymal cells but is usually followed by restitution ad integrum. By contrast, cell death in chronic liver diseases often occurs at a lesser extent but leads to long-term alterations in organ architecture and function, contributing to chronic hepatocyte turnover, the recruitment of immune cells and activation of hepatic stellate cells. These chronic cell death responses contribute to the development of liver fibrosis, cirrhosis and cancer. It has become evident that, besides apoptosis, necroptosis is a highly relevant form of programmed cell death in the liver. Differential activation of specific forms of programmed cell death might not only affect outcomes in liver diseases but also offer novel opportunities for therapeutic intervention. Here, we summarize the underlying molecular mechanisms and open questions about disease-specific activation and roles of programmed cell death forms, their contribution to response signatures and their detection. We focus on the role of apoptosis and necroptosis in acute liver injury, nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH) and liver cancer, and possible translations into clinical applications.

Identification and Characterization of NTB451 as a Potential Inhibitor of Necroptosis

Necroptosis, or caspase-independent programmed cell death, is known to be involved in various pathological conditions, such as ischemia/reperfusion injury, myocardial infarction, atherosclerosis, and inflammatory bowel diseases. Although several inhibitors of necroptosis have been identified, none of them are currently in clinical use. In the present study, we identified a new compound, 4-({[5-(4-aminophenyl)-4-ethyl-4H-1,2,4-triazol-3-yl]sulfanyl}methyl)-N-(1,3-thiazol-2-yl) benzamide (NTB451), with significant inhibitory activity on the necroptosis induced by various triggers, such as tumor necrosis factor-α (TNF-α) and toll-like receptor (TLR) agonists. Mechanistic studies revealed that NTB451 inhibited phosphorylation and oligomerization of mixed lineage kinase domain like (MLKL), and this activity was linked to its inhibitory effect on the formation of the receptor interacting serine/threonine-protein kinase 1 (RIPK1)-RIPK3 complex. Small interfering RNA (siRNA)-mediated RIPK1 knockdown, drug affinity responsive target stability assay, and molecular dynamics (MD) simulation study illustrated that RIPK1 is a specific target of NTB451. Moreover, MD simulation showed a direct interaction of NTB451 and RIPK1. Further experiments to ensure that the inhibitory effect of NTB451 was restricted to necroptosis and NTB451 had no effect on nuclear factor-κB (NF-κB) activation or apoptotic cell death upon triggering with TNF-α were also performed. Considering the data obtained, our study confirmed the potential of NTB451 as a new necroptosis inhibitor, suggesting its therapeutic implications for pathological conditions induced by necroptotic cell death.

Randomized clinical study of safety, pharmacokinetics, and pharmacodynamics of RIPK1 inhibitor GSK2982772 in healthy volunteers

GSK2982772 is a highly selective inhibitor of receptor‐interacting protein kinase 1 (RIPK1) being developed to treat chronic inflammatory diseases. This first‐in‐human study evaluated safety, tolerability, pharmacokinetics (PK), and exploratory pharmacodynamics (PD) of GSK2982772 administered orally to healthy male volunteers. This was a Phase I, randomized, placebo‐controlled, double‐blind study. In Part A, subjects received single ascending doses of GSK2982772 (0.1‐120 mg) or placebo in a crossover design during each of 4 treatment periods. In Part B, subjects received repeat doses of GSK2982772 (20 mg once daily [QD] to up to 120 mg twice daily [BID]) or placebo for 14 days. Part C was an open‐label relative bioavailability study comparing 20‐mg tablets vs capsules. Safety, tolerability, pharmacokinetics (PK), RIPK1 target engagement (TE), and pharmacodynamics (PD) were assessed. The most common adverse events (AEs) were contact dermatitis and headache. Most AEs were mild in intensity, and there were no deaths or serious AEs. The PK of GSK2982772 was approximately linear over the dose range studied (up to 120 mg BID). There was no evidence of drug accumulation upon repeat dosing. Greater than 90% RIPK1 TE was achieved over a 24‐hour period for the 60‐mg and 120‐mg BID dosing regimens. Single and repeat doses of GSK2982772 were safe and well tolerated. PK profiles showed dose linearity. The high levels of RIPK1 TE support progression into Phase II clinical trials for further clinical development.

Regulated Cell Death

In this chapter, the various subroutines of regulated cell death are neatly described by highlighting apoptosis and subforms of regulated necrosis such as necroptosis, ferroptosis, pyroptosis, and NETosis. Typically, all forms of regulated necrosis are defined by finite rupture of the plasma cell membrane. Apoptosis is characterized by an enzymatic machinery that consists of caspases which cause the morphologic features of this type of cell death. Mechanistically, apoptosis can be instigated by two major cellular signalling pathways: an intrinsic pathway that is initiated inside cells by mitochondrial release of pro-apoptotic factors or an extrinsic pathway that is initiated at the cell surface by various death receptors. In necroptosis, the biochemical processes are distinct from those found in apoptosis; in particular, there is no caspase activation. As such, necroptosis is a kinase-mediated cell death that relies on “receptor-interacting protein kinase 3” which mediates phosphorylation of the pseudokinase “mixed lineage kinase domain-like protein.” While ferroptosis is an iron-dependent, oxidative form of regulated necrosis that is biochemically characterized by accumulation of ROS from iron metabolism, oxidase activity, and lipid peroxidation products, pyroptosis is defined as a form of cell death (predominantly of phagocytes) that develops during inflammasome activation and is executed by caspase-mediated cleavage of the pore-forming protein gasdermin D. Finally, NETosis refers to a regulated death of neutrophils that is characterized by the release of chromatin-derived weblike structures released into the extracellular space. The chapter ends up with a discussion on the characteristic feature of regulated necrosis: the passive release of large amounts of constitutive DAMPs as a consequence of final plasma membrane rupture as well as the active secretion of inducible DAMPs earlier during the dying process. Notably, per cell death subroutine, the active secretion of inducible DAMPs varies, thereby determining different immunogenicity of dying cells.

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

Necroptosis is a regulated form of cell death involved in several disease models including in particular liver diseases. Receptor-interacting protein kinases, RIPK1 and RIPK3, are the main serine/threonine kinases driving this cell death pathway. We screened a noncommercial, kinase-focused chemical library which allowed us to identify Sibiriline as a new inhibitor of necroptosis induced by tumor necrosis factor (TNF) in Fas-associated protein with death domain (FADD)-deficient Jurkat cells. Moreover, Sib inhibits necroptotic cell death induced by various death ligands in human or mouse cells while not protecting from caspase-dependent apoptosis. By using competition binding assay and recombinant kinase assays, we demonstrated that Sib is a rather specific competitive RIPK1 inhibitor. Molecular docking analysis shows that Sib is trapped closed to human RIPK1 adenosine triphosphate-binding site in a relatively hydrophobic pocket locking RIPK1 in an inactive conformation. In agreement with its RIPK1 inhibitory property, Sib inhibits both TNF-induced RIPK1-dependent necroptosis and RIPK1-dependent apoptosis. Finally, Sib protects mice from concanavalin A-induced hepatitis. These results reveal the small-molecule Sib as a new RIPK1 inhibitor potentially of interest for the treatment of immune-dependent hepatitis.

Necroptosis as a potential therapeutic target in multiple organ dysfunction syndrome

Purpose

To investigate how necroptosisis, i.e. programmed necrosis, is involved in MODS, and to examine whether Nec-1, a specific necroptosis inhibitor, ameliorates multiorgan injury in MODS.

Experimental Design

A model of MODS was established in six-week old SD rats using fracture trauma followed by hemorrhage. Control animals received sham surgery. Cell death form and necrosome formation were measured by fluorescence-activated cell sorting and western blotting. MODS rats were randomly assigned to receive Nec-1 or saline with pretreatment and once daily. The first end-point was 72 hours survival. Organ injury and dysfunction, inflammatory cytokine levels, and necroptotic execution protein expression were also recorded.

Results

Organ injury and dysfunction were significantly more severe in the MODS group than the sham group (all p<0.01). Furthermore, MODS-induced liver, lung and kidney tissue injury was characterized by necroptosis rather than apoptosis, and accompanied by necrosome formation. Compared to MODS group, Nec-1 administration significantly improved 72 hours survival (p<0.01). Nec-1 administration significantly reduced necroptosis-induced liver, lung and kidney injury and dysfunction, inhibited inflammatory cytokines production, inhibited release of necroptotic execution proteins such as high-mobility group box 1 and mixed-lineage kinase domain-like protein pseudokinase in MODS rats (all p<0.01).

Conclusions

These results suggest that necroptosis is involved the pathology of MODS. Further, a necroptotic inhibitor Nec-1 may be considered as an adjunct treatment for MODS.