Small-Molecule Inhibitors of Necroptosis: Current Status and Perspectives

Weighted gene co-expression network analysis and single-cell sequence analysis uncover immune landscape and reveal hub genes of necroptosis in macrophages in myocardial ischaemia-reperfusion injury

Myocardial ischaemia-reperfusion injury (MIRI) caused by the treatment of acute myocardial infarction (AMI) is the primary cause of severe ventricular remodelling, heart failure (HF), and high mortality. In recent studies, research on the role of necroptosis in MIRI has focused on cardiomyocytes, but new biomarkers and immunocyte mechanisms of necroptosis are rarely studied. In the present study, weighted gene co-expression network analysis (WGCNA) algorithms were used to establish a weighted gene co-expression network, and Casp1, Hpse, Myd88, Ripk1, and Tpm3 were identified as biological markers of necroptosis using least absolute shrinkage, selection operator (LASSO) regression and support vector machine (SVM) feature selection algorithms. The role and discriminatory power of these five genes in MIRI had never been studied. Single-cell and cell-talk analyses showed that hub genes of necroptosis were focused on macrophages, which mediate the functions of monocytes, fibroblasts, haematopoietic stem cells, and cardiomyocytes, primarily through the TNF/TNFRSF1A interaction. The polarisation and functional activation of macrophages were affected by the MIF signalling network (MIF CD74/CXCR4 and MIF CD74/CD44) of other cells. The results of the immune infiltration assay showed that the five genes involved in necroptosis were significantly related to the infiltration and functional activity of M2 macrophages. TWS-119 is predicted to be a molecular drug that targets key MIRI genes. A mouse model was established to confirm the expression of five hub genes, and ventricular remodelling increased with time after ischaemia-reperfusion injury (IRI). Therefore, Casp1, Hpse, Myd88, Ripk1, and Tpm3 may be key genes regulating necroptosis and polarisation in macrophages, and causing ventricular remodelling.

Discovery of Covalent MLKL PROTAC Degraders via Optimization of a Theophylline Derivative Ligand for Treating Necroptosis

Mixed lineage kinase domain-like pseudokinase (MLKL) initiates necroptosis and could serve as a therapeutic target related to a series of human diseases. Proteolysis-targeting chimeras (PROTACs) are useful tools for degrading pathological proteins and blocking disease processes. Using computer-aided modeling and molecular dynamics simulations, we developed a series of covalent MLKL PROTACs by linking and optimizing a theophylline derivative that covalently targets MLKL. Via structure-activity relationship studies, MP-11 was identified as a potent MLKL PROTAC degrader. Furthermore, MP-11 showed lower toxicity than the original MLKL ligand, exhibiting nanomolar-scale antinecroptotic activity on human cell lines. Xenograft model studies showed that MP-11 effectively degraded MLKL in vivo. Importantly, our study demonstrates that the covalent binding strategy is an effective approach for designing MLKL-targeting PROTACs, serving as a model for developing PROTACs to treat future necroptosis-related human diseases.

Spotlight on necroptosis: Role in pathogenesis and therapeutic potential of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the leading cause of low back pain, which is one of the major factors leading to disability and severe economic burden. Necroptosis is an important form of programmed cell death (PCD), a highly regulated caspase-independent type of cell death that is regulated by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL)-mediated, play a key role in the pathophysiology of various inflammatory, infectious and degenerative diseases. Recent studies have shown that necroptosis plays an important role in the occurrence and development of IDD. In this review, we provide an overview of the initiation and execution of necroptosis and explore in depth its potential mechanisms of action in IDD. The analysis focuses on the connection between NP cell necroptosis and mitochondrial dysfunction-oxidative stress pathway, inflammation, endoplasmic reticulum stress, apoptosis, and autophagy. Finally, we evaluated the possibility of treating IDD by inhibiting necroptosis, and believed that targeting necroptosis may be a new strategy to alleviate the symptoms of IDD.

Small molecule inhibitors targeting heat shock protein 90: An updated review

As a molecular chaperone, heat shock protein 90 (HSP90) plays important roles in the folding, stabilization, activation, and degradation of over 500 client proteins, and is extensively involved in cell signaling, proliferation, and survival. Thus, it has emerged as an important target in a variety of diseases, including cancer, neurodegenerative diseases, and viral infections. Therefore, targeted inhibition of HSP90 provides a valuable and promising therapeutic strategy for the treatment of HSP90-related diseases. This review aims to systematically summarize the progress of research on HSP90 inhibitors in the last five years, focusing on their structural features, design strategies, and biological activities. It will refer to the natural products and their derivatives (including novobiocin derivatives, deguelin derivatives, quinone derivatives, and terpenoid derivatives), and to synthetic small molecules (including resorcinol derivatives, pyrazoles derivatives, triazole derivatives, pyrimidine derivatives, benzamide derivatives, benzothiazole derivatives, and benzofuran derivatives). In addition, the major HSP90 small-molecule inhibitors that have moved into clinical trials to date are also presented here.

Recognition of necroptosis: From molecular mechanisms to detection methods

Necroptosis is a crucial modality of programmed cell death characterized by distinct morphological and biochemical hallmarks, including cell membrane rupture, organelle swelling, cytoplasmic and nuclear disintegration, cellular contents leakage, and release of damage-associated molecular patterns (DAMPs), accompanied by the inflammatory responses. Studies have shown that necroptosis is involved in the etiology and evolution of a variety of pathologies including organ damage, inflammation disorders, and cancer. Despite its significance, the field of necroptosis research grapples with the challenge of non-standardized detection methodologies. In this review, we introduce the fundamental concepts and molecular mechanisms of necroptosis and critically appraise the principles, merits, and inherent limitations of current detection technologies. This endeavor seeks to establish a methodological framework for necroptosis detection, thereby propelling deeper insights into the research of cell necroptosis.

Discovery of 5-(1-benzyl-1H-imidazol-4-yl)-1,2,4-oxadiazole derivatives as novel RIPK1 inhibitors via structure-based virtual screening

RIPK1 plays a key role in necroptosis and is associated with various inflammatory diseases. Using structure-based virtual screening, a novel hit with 5-(1-benzyl-1H-imidazol-4-yl)-1,2,4-oxadiazole scaffold was identified as an RIPK1 inhibitor with an IC50 value of 1.3 μM. Further structure-activity relationship study was performed based on similarity research and biological evaluation. The molecular dynamics simulation of compound 2 with RIPK1 indicated that it may act as a type II kinase inhibitor. This study provides a highly efficient way to discover novel scaffold RIPK1 inhibitors for further development.

Identification of a marine-derived sesquiterpenoid, Compound-8, that inhibits tumour necrosis factor-induced cell death by blocking complex II assembly

BACKGROUND AND PURPOSE

Tumour necrosis factor (TNF) is a pleiotropic inflammatory cytokine that not only directly induces inflammatory gene expression but also triggers apoptotic and necroptotic cell death, which leads to tissue damage and indirectly exacerbates inflammation. Thus, identification of inhibitors for TNF-induced cell death has broad therapeutic relevance for TNF-related inflammatory diseases. In the present study, we isolated and identified a marine fungus-derived sesquiterpenoid, 9α,14-dihydroxy-6β-p-nitrobenzoylcinnamolide (named as Cpd-8), that inhibits TNF receptor superfamily-induced cell death by preventing the formation of cytosolic death complex II.

EXPERIMENTAL APPROACH

Marine sponge-associated fungi were cultured and the secondary metabolites were extracted to yield pure compounds. Cell viability was measured by ATP-Glo cell viability assay. The effects of Cpd-8 on TNF signalling pathway were investigated by western blotting, immunoprecipitation, and immunofluorescence assays. A mouse model of acute liver injury (ALI) was employed to explore the protection effect of Cpd-8, in vivo.

KEY RESULTS

Cpd-8 selectively inhibits TNF receptor superfamily-induced apoptosis and necroptosis. Cpd-8 prevents the formation of cytosolic death complex II and subsequent RIPK1-RIPK3 necrosome, while it has no effect on TNF receptor I (TNFR1) internalization and the formation of complex I in TNF signalling pathway. In vivo, Cpd-8 protects mice against TNF-α/D-GalN-induced ALI.

CONCLUSION AND IMPLICATIONS

A marine fungus-derived sesquiterpenoid, Cpd-8, inhibits TNF receptor superfamily-induced cell death, both in vitro and in vivo. This study not only provides a useful research tool to investigate the regulatory mechanisms of TNF-induced cell death but also identifies a promising lead compound for future drug development.

Development of Biochemical and Cellular Probes to Study RIPK1 Target Engagement

RIPK1 inhibitors have emerged as promising candidates for treating diverse diseases, including inflammatory diseases, autoimmune disorders, Alzheimer's disease, and cancer. However, the previously reported binding assays have limited sensitivity and stability, impeding high-throughput screening and robust characterization of the RIPK1 inhibitors. To address this challenge, we introduced two probes, T2-BDP-FL and T3-BDP-FL, derived from distinct RIPK1 inhibitors with different binding modes to establish time-resolved fluorescence resonance energy transfer (TR-FRET) displacement assays. Employing our TR-FRET displacement assays, we quantified the biochemical binding affinities of a series of RIPK1 inhibitors with diverse structural and binding modes for human RIPK1. Consistent results were obtained with these two probes in the TR-FRET displacement assay. Furthermore, we developed a RIPK1 fluorescent probe, T2-BDP589, for the NanoBRET assay. This assay enabled the characterization of RIPK1 target engagement by various RIPK1 inhibitors for both human and mouse RIPK1 in live cells. Our developed fluorescent probe displacement assays offer a sensitive and high-throughput approach to identify RIPK1 inhibitors based on both biochemical and cellular activities.

Scaffold hopping derived novel benzoxazepinone receptor-interacting protein kinase 1 (RIP1) inhibitors as anti-necroptosis agents: Anti-inflammatory effect in systemic inflammatory response syndrome (SIRS) and epilepsy

Necroptosis is a type of regulated cell death known for its pro-inflammatory nature due to the substantial release of cellular contents. The phosphorylation of key proteins, namely RIP1, RIP3, and mixed lineage kinase domain-like protein (MLKL), plays a pivotal role in the processes associated with necroptosis. Consequently, inhibiting the phosphorylation of any of these three key protein kinases could effectively block necroptosis. Utilizing a scaffold hopping strategy, we have successfully designed and synthesized a series of novel RIP1 inhibitors with selective and anti-necrotic properties, using compound o1 as the lead compound. In comparison to o1, SY1 has demonstrated heightened antinecroptosis activity and binding affinity in vitro studies. Moreover, SY1 has exhibited superior efficacy in both in vivo studies, specifically in the context of SIRS, and pharmacokinetic assessments. Furthermore, SY1 has proven effective in significantly suppressing the central inflammatory response induced by epilepsy.

Design, synthesis and anti-necroptosis activity of fused heterocyclic MLKL inhibitors

Necroptosis is an important form of programmed cell death (PCD), which is mediated by a death receptor and independent of the caspase proteolytic enzyme. Mixed lineage kinase domain-like (MLKL) is the final effector of necroptosis, playing an irreplaceable role in the execution of necroptosis. However, the studies on MLKL inhibitors are in their infancy. Necrosulfonamide (NSA) is an early-discovered covalent MLKL inhibitor, possessing medium anti-necroptosis activity and a structure-activity relationship (SAR) not widely disclosed. In this study, with the covalent motif maintained, we aim to improve the activity by introducing the terminal fused heterocycles and meanwhile revealing the SAR on the part. As a result, compounds 9 and 14 showed the best activity (EC50 = 148.4 and 595.9 nM) against necroptosis among the analogues by covalently binding to MLKL. The SAR was also concluded to guide further structural optimization in this field.

Discovery of novel biaryl benzoxazepinones as dual-mode receptor-interacting protein kinase-1 (RIPK1) inhibitors

Systemic inflammatory response syndrome (SIRS), an exaggerated defense response of the organism to a noxious stressor, involves a massive inflammatory cascade that ultimately leads to reversible or irreversible end-organ dysfunction and even death. Suppressing RIPK1, a key protein in necroptosis pathway, has been proven to be an effective therapeutic strategy for inflammation and SIRS. In this study, a series of novel biaryl benzoxazepinone RIPK1 inhibitors were designed and synthesized by introducing different aryl substituents at the C7 position of benzoxazepinone. As a result, p-cyanophenyl substituted analog 19 exhibited the most potent in vitro anti-necroptotic effect in HT-29 cells (EC50 = 1.7 nM) and superior protection against temperature loss and death in mice in the TZ-induced SIRS model compared to GSK'772. What's more, in vivo analysis of the levels of inflammatory factors in mice also revealed that compound 19 had better anti-inflammatory activity than GSK'772.

Discovery of 4-amino-1,6-dihydro-7H-pyrrolo[2,3-d]pyridazin-7-one derivatives as potential receptor-interacting serine/threonine-protein kinase 1 (RIPK1) inhibitors

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is an important regulatory factor in the necroptosis signaling pathway, and is considered an attractive therapeutic target for treating multiple inflammatory diseases. Herein, we describe the design, synthesis, and structure-activity relationships of 4-amino-1,6-dihydro-7H-pyrrolo [2,3-d]pyridazin-7-one derivatives as RIPK1 inhibitors. Among them, 13c showed favorable RIPK1 kinase inhibition activity with an IC50 value of 59.8 nM, and high RIPK1 binding affinity compared with other regulatory kinases of necroptosis (RIPK1 Kd = 3.5 nM, RIPK3 Kd = 1700 nM, and MLKL Kd > 30,000 nM). 13c efficiently blocked TNFα-induced necroptosis in both human and murine cells (EC50 = 1.06-4.58 nM), and inhibited TSZ-induced phosphorylation of the RIPK1/RIPK3/MLKL pathway. In liver microsomal assay studies, the clearance rate and half-life of 13c were 18.40 mL/min/g and 75.33 min, respectively. 13c displayed acceptable pharmacokinetic characteristics, with oral bioavailability of 59.55%. In TNFα-induced systemic inflammatory response syndrome, pretreatment with 13c could effectively protect mice from loss of body temperature and death. Overall, these compounds are promising candidates for future optimization studies.

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

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

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.

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.

The traditional herb Sargentodoxa cuneata alleviates DSS-induced colitis by attenuating epithelial barrier damage via blocking necroptotic signaling

ETHNOPHARMACOLOGICAL RELEVANCE

The traditional Chinese herb, Sargentodoxa cuneata, is primarily utilized as a crucial herb for managing ulcerative colitis (UC), also known as "Da Xue Teng (DXT)" or "Hong Teng" in Chinese. Nevertheless, the chemical composition, prototype, and metabolite constituents of DXT and its pharmacological mechanism of treatment for UC remain unclear.

AIM OF THE STUDY

Necroptosis, a caspase-independent form of programmed cell death, plays a crucial role in the inflammatory pathogenesis of UC. The occurrence of necroptosis in intestinal epithelial cells triggers a robust inflammatory response and disrupts the integrity of both the mucinous barrier and tight junction construction. The objective of our study was to determine the chemical composition of DXT, identify its absorbed active ingredients and metabolites in rat serum, and investigate whether DXT possesses epithelial barrier protective effects by inhibiting necroptosis.

MATERIALS AND METHODS

First, the UPLC-Q-TOF/MS was applied to identify the chemical composition of DXT, as well as the absorption components and metabolites of DXT in rat serum. Second, the network pharmacology analysis was further investigated to elucidate the potential targets for treating UC. Finally, the mechanism of action was validated by necroptosis-based experiment in vitro and an in vivo model of colitis.

RESULTS

A comprehensive analysis revealed the presence of 31 phytochemicals derived from DXT herb, as well as a total of 39 components in rat serum. Network pharmacology analysis indicated that TNF, EGFR, HSP90, etc. are the potential targets. Experimental in vitro and in vivo verified that the DXT could improve disease activity index, body weight, colon length and intestinal barrier permeability in mice with colitis by inhibiting necroptosis of intestinal epithelial cells.

CONCLUSIONS

In this study, the phytochemicals derived from DXT herb and absorption active ingredients and metabolites of DXT in rat serum were analyzed. The biological mechanism of treatment for UC can be elucidated by combining network pharmacology investigation with experimental in vitro and in vivo studies. The findings offered a theoretical basis for comprehending the bioactive substances and the pharmacological process of DXT.

Discovery of novel 5-phenylpyrazol receptor interacting protein 1(RIP1) kinase inhibitors as anti-necroptosis agents by combining virtual screening and in vitro and in vivo experimental evaluations

Necroptosis is one of the modes of cell death, and its occurrence and development are associated with the development of numerous diseases. To prevent the progression of necroptosis, it is crucial to inhibit the phosphorylation of three proteins: receptor-interacting protein kinase 1 (RIP1), RIP3, and mixed lineage kinase domain-like protein (MLKL). Through virtual and experimental screening approaches, we have identified 8 small molecular inhibitors with potent antinecroptotic activity and binding affinity to RIP1. Among these compounds, SY-1 demonstrated the most remarkable antinecroptotic activity (EC50 = 105.6 ± 9.6 nM) and binding affinity (RIP1 Kd = 49 nM). It effectively blocked necroptosis and impeded the formation of necrosomes by inhibiting the phosphorylations of the RIP1/RIP3/MLKL pathway triggered by TSZ (TNFα, Smac mimetic and Z-VAD-fmk). Furthermore, SY-1 exhibited a protective effect against tumor necrosis factor (TNF)-induced hypothermia in mice and significantly improved the survival rate (100 %, 30 mg/kg) of mice with systemic inflammatory response syndrome (SIRS) in a dose-dependent manner. Pharmacokinetic parameters of SY-1 were also collected in vitro and in vivo. These results strongly suggest that SY-1 and its derivatives warrant further investigation for their potential therapeutic applications.

Insight from Linker Investigations: Discovery of a Novel Phenylbenzothiazole Necroptosis Inhibitor Targeting Receptor-Interacting Protein Kinase 1 (RIPK1) from a Phenoxybenzothiazole Compound with Dual RIPK1/3 Targeting Activity

Necroptosis, a regulated cell death form, is a critical contributor in various inflammatory diseases. We previously identified a phenoxybenzothiazole SZM-610 as a RIPK1 and RIPK3 necroptosis inhibitor. We conducted extensive studies to investigate different chemical components' effects on antinecroptosis activity and RIPK1/3 activity. This study focused on replacing the linker in phenoxybenzothiazoles to assess its impact. Remarkably, compound 10, bearing a novel 3,2'-phenylbenzothiazole scaffold, exhibited fourfold more potent nanomolar activity than SZM-610. Unlike SZM-610, this compound inhibited RIPK1 (Kd = 17 nM) and eliminated RIPK3 inhibition at 5000 nM. Various linkages confirmed the 3,2'-phenylbenzothiazole superior potency. Moreover, this compound specifically inhibited necroptosis by inhibiting RIPK1, RIPK3, and MLKL phosphorylation. In a TNF-induced inflammatory model, it dose-dependently (1.25-5 mg/kg) protected mice from hypothermia and death, surpassing SZM-610's effectiveness. These findings highlight 3,2'-phenylbenzothiazole as a promising lead structure for developing drugs targeting necroptosis-related diseases.

Profiling of small-molecule necroptosis inhibitors based on the subpockets of kinase-ligand interactions

Necroptosis is a highly regulated cell death (RCD) form in various inflammatory diseases. Receptor-interacting protein kinase 1 (RIPK1) and RIPK3 are involved in the pathway. Targeting the kinase domains of RIPK1 and/or 3 is a drug design strategy for related diseases. It is generally accepted that essential reoccurring features are observed across the human kinase domains, including RIPK1 and RIPK3. They present common N- and C-terminal domains that are built up mostly by α-helices and β-sheets, respectively. The current RIPK1/3 kinase inhibitors mainly interact with the kinase catalytic cleft. This article aims to present an in-depth profiling for ligand-kinase interactions in the crucial cleft areas by carefully aligning the kinase-ligand cocrystal complexes or molecular docking models. The similarity and differential structural segments of ligands are systematically evaluated. New insights on the adaption of the conserved and selective kinase domains to the diversity of chemical scaffolds are also provided. In a word, our analysis can provide a better structural requirement for RIPK1 and RIPK3 inhibition and a guide for inhibitor discovery and optimization of their potency and selectivity.

Repurposing of Ibrutinib and Quizartinib as potent inhibitors of necroptosis

Necroptosis is a form of regulated cell death that has been implicated in multiple diseases. TNF-induced necroptosis is regulated by necrosomes, complexes consisting of RIPK1, RIPK3 and MLKL. In this study, by screening of a small-compound library, we identified dozens of compounds that inhibited TNF-induced necroptosis. According to the mechanisms by which they inhibited necroptosis, these compounds were classified into different groups. We then identified Ibrutinib as an inhibitor of RIPK3 and found that Quizartinib protected against the TNF-induced systemic inflammatory response syndrome in mice by inhibiting the activation of RIPK1. Altogether, our work revealed dozens of necroptosis inhibitors, suggesting new potential approaches for treating necroptosis-related diseases.

PROTACs Targeting MLKL Protect Cells from Necroptosis

Mixed Lineage Kinase domain-Like pseudokinase (MLKL) is implicated in a broad range of diseases due to its role as the ultimate effector of necroptosis and has therefore emerged as an attractive drug target. Here, we describe the development of PROteolysis TArgeting Chimeras (PROTACs) as a novel approach to knock down MLKL through chemical means. A series of candidate degraders were synthesized from a high-affinity pyrazole carboxamide-based MLKL ligand leading to the identification of a PROTAC molecule that effectively degraded MLKL and completely abrogated cell death in a TSZ model of necroptosis. By leveraging the innate ability of these PROTACs to degrade MLKL in a dose-dependent manner, the quantitative relationship between MLKL levels and necroptosis was interrogated. This work demonstrates the feasibility of targeting MLKL using a PROTAC approach and provides a powerful tool to further our understanding of the role of MLKL within the necroptotic pathway.

Scaffold hopping derived novel benzoxazepinone RIPK1 inhibitors as anti-necroptosis agents

Receptor-interacting protein kinase 1 (RIPK1)-mediated necroptosis is believed to have a significant role in contributing to inflammatory diseases. Inhibiting RIPK1 has shown promise in effectively alleviating the inflammation process. In our current study, we employed scaffold hopping to develop a series of novel benzoxazepinone derivatives. Among these derivatives, compound o1 displayed the most potent antinecroptosis activity (EC50=16.17±1.878nM) in cellular assays and exhibited the strongest binding affinity to the target site. Molecular docking analyses further elucidated the mechanism of action of o1, revealing its ability to fully occupy the protein pocket and form hydrogen bonds with the amino acid residue Asp156. Our findings highlight that o1 specifically inhibits necroptosis, rather than apoptosis, by impeding the RIPK1/Receptor-interacting protein kinase 3 (RIPK3)/mixed-lineage kinase domain-like (MLKL) pathway's phosphorylation, triggered by TNFα, Smac mimetic, and z-VAD (TSZ). Additionally, o1 demonstrated dose-dependent improvements in the survival rate of mice with Systemic Inflammatory Response Syndrome (SIRS), surpassing the protective effect observed with GSK'772.

A natural chalcone cardamonin inhibits necroptosis and ameliorates dextran sulfate sodium (DSS)-induced colitis by targeting RIPK1/3 kinases

Necroptosis, a new form of programmed cell death, is involved in the pathogenesis of ulcerative colitis (UC). Inhibition of necroptosis represents an attractive strategy for UC therapy. Herein, cardamonin, a natural chalcone isolated from Zingiberaceae family, was firstly identified as a potent necroptosis inhibitor. In vitro, cardamonin significantly inhibited necroptosis in TNF-α plus Smac mimetic and z-VAD-FMK (TSZ)-, cycloheximide plus TZ (TCZ)-, or lipopolysaccharide plus SZ (LSZ)-stimulated HT29, L929, or RAW264.7 cell lines. Furthermore, TSZ-induced elevated population of necrotic cells, release of LDH and HMGB1 also could be inhibited by cardamonin in HT29 cells. Cellular thermal shift assay (CETSA) and drug affinity responsive target stability (DARTS) assay combined with molecular docking demonstrated that cardamonin interacted with RIPK1/3. Furthermore, cardamonin blocked the phosphorylation of RIPK1/3, thereby disrupting RIPK1-RIPK3 necrosome formation and MLKL phosphorylation. In vivo, orally administration of cardamonin attenuated dextran sulfate sodium (DSS)-induced colitis, which mainly manifested as mitigated intestinal barrier damage, suppressed necroinflammation, and reduced phosphorylation of MLKL. Taken together, our findings revealed that dietary cardamonin is a novel necroptosis inhibitor and has great potential for UC therapy by targeting RIPK1/3 kinases.

Analysis on benzothiazole necroptosis inhibitors with chiral substitutions in the solvent-accessible region of RIP kinase domain

Receptor-interacting protein kinase 1 (RIPK1) and RIPK3, two imperative targets of the necroptosis pathway, are associated with various inflammatory-related diseases. Regulating kinase activity with inhibitors has been confirmed as a promising strategy for inflammation treatment. However, most of the reported type I and II kinase inhibitors of RIPK1 and RIPK3, including benzothiazole compounds discovered by our group, have selective limitations due to interaction with ATP-binding pockets. Fortunately, a solvent exposure E0 region of the kinase domain, which extends into the linker region, has been reported to be related to the potency and selectivity of inhibitors. Hence, based on our previous study, a series of benzothiazole necroptosis inhibitors with chiral substitutions in the linker region were developed to investigate RIPK1/3 inhibitory potency. The results showed a 2-to 6-fold increase in anti-necroptotic activity for these chiral compounds. The improved selectivity on RIPK1 or RIPK3 was demonstrated on different derivatives. Predicted binding conformations of enantiomers with RIPK1/3 gave an explanation for their activity differences, guiding further rational design of chiral necroptosis inhibitors.

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.

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

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

Ferroptosis, necroptosis and cuproptosis: Novel forms of regulated cell death in diabetic cardiomyopathy

Diabetes is a common chronic metabolic disease, and its incidence continues to increase year after year. Diabetic patients mainly die from various complications, with the most common being diabetic cardiomyopathy. However, the detection rate of diabetic cardiomyopathy is low in clinical practice, and targeted treatment is lacking. Recently, a large number of studies have confirmed that myocardial cell death in diabetic cardiomyopathy involves pyroptosis, apoptosis, necrosis, ferroptosis, necroptosis, cuproptosis, cellular burial, and other processes. Most importantly, numerous animal studies have shown that the onset and progression of diabetic cardiomyopathy can be mitigated by inhibiting these regulatory cell death processes, such as by utilizing inhibitors, chelators, or genetic manipulation. Therefore, we review the role of ferroptosis, necroptosis, and cuproptosis, three novel forms of cell death in diabetic cardiomyopathy, searching for possible targets, and analyzing the corresponding therapeutic approaches to these targets.

Ferroptosis, necroptosis and cuproptosis: Novel forms of regulated cell death in diabetic cardiomyopathy

Diabetes is a common chronic metabolic disease, and its incidence continues to increase year after year. Diabetic patients mainly die from various complications, with the most common being diabetic cardiomyopathy. However, the detection rate of diabetic cardiomyopathy is low in clinical practice, and targeted treatment is lacking. Recently, a large number of studies have confirmed that myocardial cell death in diabetic cardiomyopathy involves pyroptosis, apoptosis, necrosis, ferroptosis, necroptosis, cuproptosis, cellular burial, and other processes. Most importantly, numerous animal studies have shown that the onset and progression of diabetic cardiomyopathy can be mitigated by inhibiting these regulatory cell death processes, such as by utilizing inhibitors, chelators, or genetic manipulation. Therefore, we review the role of ferroptosis, necroptosis, and cuproptosis, three novel forms of cell death in diabetic cardiomyopathy, searching for possible targets, and analyzing the corresponding therapeutic approaches to these targets.

Structure-Based Design of Novel Alkynyl Thio-Benzoxazepinone Receptor-Interacting Protein Kinase-1 Inhibitors: Extending the Chemical Space from the Allosteric to ATP Binding Pockets

Systemic inflammatory response syndrome (SIRS), characterized by severe systemic inflammation, represents a major cause of health loss, potentially leading to multiple organ failure, shock, and death. Exploring potent RIPK1 inhibitors is an effective therapeutic strategy for SIRS. Recently, we described thio-benzoxazepinones as novel RIPK1 inhibitors and confirmed their anti-inflammatory activity. Herein, we further synthesized novel thio-benzoxazepinones by introducing substitutions on the benzene ring by an alkynyl bridge in order to extend the chemical space from the RIPK1 allosteric to ATP binding pockets. The in vitro cell and kinase assays found that compounds 2 and 29 showed highly potent activity against necroptosis (EC₅₀ = 3.7 and 3.2 nM) and high RIPK1 inhibitory activity (K_d = 9.7 and 70 nM). Prominently, these two analogues possessed better in vivo anti-inflammatory effects than the clinical candidate GSK'772 and effectively blocked hypothermia and deaths in a TNFα-induced SIRS model.

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

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

Necroptosis in CNS diseases: Focus on astrocytes

In the last few years, necroptosis, a recently described type of cell death, has been reported to play an important role in the development of various brain pathologies. Necroptosis is a cell death mechanism that has morphological characteristics similar to necrosis but is mediated by fundamentally different molecular pathways. Necroptosis is initiated by signaling through the interaction of RIP1/RIP3/MLKL proteins (receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein). RIPK1 kinase is usually inactive under physiological conditions. It is activated by stimulation of death receptors (TNFR1, TNFR2, TLR3, and 4, Fas-ligand) by external signals. Phosphorylation of RIPK1 results in the formation of its complex with death receptors. Further, complexes with the second member of the RIP3 and MLKL cascade appear, and the necroptosome is formed. There is enough evidence that necroptosis plays an important role in the pathogenesis of brain ischemia and neurodegenerative diseases. In recent years, a point of view that both neurons and glial cells can play a key role in the development of the central nervous system (CNS) pathologies finds more and more confirmation. Astrocytes play complex roles during neurodegeneration and ischemic brain damage initiating both impair and protective processes. However, the cellular and molecular mechanisms that induce pathogenic activity of astrocytes remain veiled. In this review, we consider these processes in terms of the initiation of necroptosis. On the other hand, it is important to remember that like other types of programmed cell death, necroptosis plays an important role for the organism, as it induces a strong immune response and is involved in the control of cancerogenesis. In this review, we provide an overview of the complex role of necroptosis as an important pathogenetic component of neuronal and astrocyte death in neurodegenerative diseases, epileptogenesis, and ischemic brain damage.

Role of Necroptosis in Central Nervous System Diseases

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

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.

Discovery of a New Class of Uracil Derivatives as Potential Mixed Lineage Kinase Domain-like Protein (MLKL) Inhibitors

Necroptosis is a form of programmed cell death. Mixed lineage kinase domain-like protein (MLKL) is the necroptosis executor, and it is involved in various diseases such as tissue damage and neurodegeneration-related diseases. Here, we report the development of novel MLKL inhibitors with a uracil nucleus through scaffold morphing from our previously reported xanthine MLKL inhibitor TC13172. After a rational structure-activity relationship study, we obtained the highly potent compounds 56 and 66. Mechanism studies revealed that these compounds partially inhibited MLKL oligomerization and significantly inhibited MLKL translocation to the membrane. Compared with TC13172, 56 and 66 have a different mode of action and, importantly, their reaction rate with glutathione is more than 150-fold lower. This reduction in potential off-target effects and cell toxicity makes this series an attractive starting point for further drug development for MLKL-related disease treatments.

Understanding Necroptosis in Pancreatic Diseases

Intermediate between apoptosis and necrosis, necroptosis is a regulated caspase-independent programmed cell death that induces an inflammatory response and mediates cancer development. As our understanding improves, its role in the physiopathology of numerous diseases, including pancreatic diseases, has been reconsidered, and especially in pancreatitis and pancreatic cancer. However, the exact pathogenesis remains elusive, even though some studies have been conducted on these diseases. Its unique mechanisms of action in diseases are expected to bring prospects for the treatment of pancreatic diseases. Therefore, it is imperative to further explore its molecular mechanism in pancreatic diseases in order to identify novel therapeutic options. This article introduces recent related research on necroptosis and pancreatic diseases, explores necroptosis-related molecular pathways, and provides a theoretical foundation for new therapeutic targets for pancreatic diseases.

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.

Discovery of a chalcone derivative as potent necroptosis inhibitor for the treatment of acute kidney injury

Necroptosis, a form of inflammation-related programmed cell death, is a major mechanism of proximal tubular cell injury in acute kidney injury (AKI). Blockade of necroptosis signaling represents a promising strategy for clinical therapy of AKI. Previously, we identified a small molecular RIPK1 inhibitor Cpd-71 with nephroprotective activities. In order to discover more nephroprotective agents, in this study, twenty chalcone derivatives were synthesized and evaluated for their anti-necroptosis and nephroprotective activities. Among the chalcone derivatives, Cpd-2 exhibited the most potent anti-necroptosis activity (IC₅₀ = 1.08 μM) and protective activity (EC₅₀ = 1.49 μM) through directly binding to RIPK1 and blocking RIPK1-RIPK3-MLKL signaling pathway. Furthermore, Cpd-2 effectively attenuated cisplatin or hypoxia/reoxygenation (H/R)-induced injury and necroptotic inflammation in renal cell models. Moreover, in cisplatin- or ischemia/reperfusion (I/R) induced AKI mouse model, detection of creatinine and urea nitrogen in blood showed that Cpd-2 improved kidney function. PAS staining and immunofluorescence analysis indicated that Cpd-2 also reduced pathological damage and inhibited inflammatory development in kidney tissues. In summary, although some chalcone derivatives have been reported to prevent kidney injury previously, our present study not only discovered a promising leading compound Cpd-2, but also provided a novel and successful practice for the development of necroptosis inhibitors from natural products derivatives as AKI therapeutic agents. This article is protected by copyright. All rights reserved.

Investigation on the chemical space of the substituted triazole thio-benzoxazepinone RIPK1 inhibitors

As a key upstream kinase involved in the activation of necroptosis, receptor-interacting protein kinase 1 (RIPK1) plays a vital role in the treatment of relevant inflammatory diseases. Recently, we described the thio-benzoxazepinones as RIPK1 necroptosis inhibitors. On this basis, we further explored the chemical space of the thio-benzoxazepinones by introducing substitutions on the triazole group and evaluated their anti-necroptotic activity. The structure-activity relationship (SAR) was extended for this series of new derivatives. The best compound 2 with methyl and compound 10 with fluoroethyl were obtained and both specifically inhibited necroptosis rather than apoptosis with EC₅₀ values of 2.5 and 8.9 nM, respectively. They blocked the downstream necroptotic pathway to prevent cell lysis and prevent in vivo inflammation in a dose-dependent manner. This work provides that substituted thio-benzoxazepines can better occupy the hydrophobic cavity and enhance the hydrophobic interaction as promising lead compounds to enhance the in vivo activity of this class of compounds.

The Lck inhibitor, AMG-47a, blocks necroptosis and implicates RIPK1 in signalling downstream of MLKL

Necroptosis is a form of caspase-independent programmed cell death that arises from disruption of cell membranes by the mixed lineage kinase domain-like (MLKL) pseudokinase after its activation by the upstream kinases, receptor interacting protein kinase (RIPK)-1 and RIPK3, within a complex known as the necrosome. Dysregulated necroptosis has been implicated in numerous inflammatory pathologies. As such, new small molecule necroptosis inhibitors are of great interest, particularly ones that operate downstream of MLKL activation, where the pathway is less well defined. To better understand the mechanisms involved in necroptosis downstream of MLKL activation, and potentially uncover new targets for inhibition, we screened known kinase inhibitors against an activated mouse MLKL mutant, leading us to identify the lymphocyte-specific protein tyrosine kinase (Lck) inhibitor AMG-47a as an inhibitor of necroptosis. We show that AMG-47a interacts with both RIPK1 and RIPK3, that its ability to protect from cell death is dependent on the strength of the necroptotic stimulus, and that it blocks necroptosis most effectively in human cells. Moreover, in human cell lines, we demonstrate that AMG-47a can protect against cell death caused by forced dimerisation of MLKL truncation mutants in the absence of any upstream signalling, validating that it targets a process downstream of MLKL activation. Surprisingly, however, we also found that the cell death driven by activated MLKL in this model was completely dependent on the presence of RIPK1, and to a lesser extent RIPK3, although it was not affected by known inhibitors of these kinases. Together, these results suggest an additional role for RIPK1, or the necrosome, in mediating human necroptosis after MLKL is phosphorylated by RIPK3 and provide further insight into reported differences in the progression of necroptosis between mouse and human cells.

Autophagy and cancer treatment: four functional forms of autophagy and their therapeutic applications

Cancer is the leading cause of death worldwide. Drugs play a pivotal role in cancer treatment, but the complex biological processes of cancer cells seriously limit the efficacy of various anticancer drugs. Autophagy, a self-degradative system that maintains cellular homeostasis, universally operates under normal and stress conditions in cancer cells. The roles of autophagy in cancer treatment are still controversial because both stimulation and inhibition of autophagy have been reported to enhance the effects of anticancer drugs. Thus, the important question arises as to whether we should try to strengthen or suppress autophagy during cancer therapy. Currently, autophagy can be divided into four main forms according to its different functions during cancer treatment: cytoprotective (cell survival), cytotoxic (cell death), cytostatic (growth arrest), and nonprotective (no contribution to cell death or survival). In addition, various cell death modes, such as apoptosis, necrosis, ferroptosis, senescence, and mitotic catastrophe, all contribute to the anticancer effects of drugs. The interaction between autophagy and these cell death modes is complex and can lead to anticancer drugs having different or even completely opposite effects on treatment. Therefore, it is important to understand the underlying contexts in which autophagy inhibition or activation will be beneficial or detrimental. That is, appropriate therapeutic strategies should be adopted in light of the different functions of autophagy. This review provides an overview of recent insights into the evolving relationship between autophagy and cancer treatment.

Design, synthesis, and evaluation of potent RIPK1 inhibitors with in vivo anti-inflammatory activity

RIPK1 plays a key role in the necroptosis pathway that regulates inflammatory signaling and cell death in various diseases, including inflammatory and neurodegenerative diseases. Herein, we report a series of potent RIPK1 inhibitors, represented by compound 70. Compound 70 efficiently blocks necroptosis induced by TNFα in both human and mouse cells (EC₅₀ = 17-30 nM). Biophysical assay demonstrates that compound 70 potently binds to RIPK1 (K_d = 9.2 nM), but not RIPK3 (K_d > 10,000 nM). Importantly, compound 70 exhibits greatly improved metabolic stability in human and rat liver microsomes compared to compound 6 (PK68), a RIPK1 inhibitor reported in our previous work. In addition, compound 70 displays high permeability in Caco-2 cells and excellent in vitro safety profiles in hERG and CYP assays. Moreover, pre-treatment of 70 significantly ameliorates hypothermia and lethal shock in SIRS mice model. Lastly, compound 70 possesses favorable pharmacokinetic parameters with moderate clearance and good oral bioavailability in SD rat. Taken together, our work supports 70 as a potent RIPK1 inhibitor and highlights its potential as a prototypical lead for further development in necroptosis-associated inflammatory disorders.

Concise synthesis and biological activity evaluation of novel pyrazinyl–aryl urea derivatives against several cancer cell lines, which can especially induce T24 apoptotic and necroptotic cell death

Based on structural modification of regorafenib, 28 pyrazinyl–aryl urea derivatives were synthesized and the in vitro anti-cancer effects were evaluated. Compound 5-23 possessed the strongest inhibitory activity against bladder cancer T24 cell line.

Discovery and Structure-Based Optimization of Fragments Binding the Mixed Lineage Kinase Domain-like Protein Executioner Domain

Necroptosis is a form of programmed cell death that in case of misregulation can lead to inflammatory diseases. Mixed lineage kinase domain-like protein (MLKL), the effector protein in the canonical necroptosis signaling pathway, becomes activated by phosphorylation. Here, we report the identification of novel reversible binders of the MLKL executioner domain by a protein NMR-detected fragment-based screen. Determination of protein fragment costructures using NMR spectroscopy revealed a small molecule binding site that is distinct from the previously identified binding site of covalent MLKL inhibitors. Affinity optimization of the initially prioritized hit with millimolar affinity was achieved by NMR-guided structure-based design and yielded fragment-like molecules with a K_D of 50 μM. Furthermore, we demonstrate that the improved fragment competes for the same binding site as nonyl-maltoside, a detergent that in conjunction with phytic acid activates the MLKL executioner domain.

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.