The potent and selective RIPK2 inhibitor BI 706039 improves intestinal inflammation in the TRUC mouse model of inflammatory bowel disease

Effects of Mycobacterium vaccae NCTC 11659 and Lipopolysaccharide Challenge on Polarization of Murine BV-2 Microglial Cells

Previous studies have shown that the in vivo administration of soil-derived bacteria with anti-inflammatory and immunoregulatory properties, such as Mycobacterium vaccae NCTC 11659, can prevent a stress-induced shift toward an inflammatory M1 microglial immunophenotype and microglial priming in the central nervous system (CNS). It remains unclear whether M. vaccae NCTC 11659 can act directly on microglia to mediate these effects. This study was designed to determine the effects of M. vaccae NCTC 11659 on the polarization of naïve BV-2 cells, a murine microglial cell line, and BV-2 cells subsequently challenged with lipopolysaccharide (LPS). Briefly, murine BV-2 cells were exposed to 100 µg/mL whole-cell, heat-killed M. vaccae NCTC 11659 or sterile borate-buffered saline (BBS) vehicle, followed, 24 h later, by exposure to 0.250 µg/mL LPS (Escherichia coli 0111: B4; n = 3) in cell culture media vehicle (CMV) or a CMV control condition. Twenty-four hours after the LPS or CMV challenge, cells were harvested to isolate total RNA. An analysis using the NanoString platform revealed that, by itself, M. vaccae NCTC 11659 had an "adjuvant-like" effect, while exposure to LPS increased the expression of mRNAs encoding proinflammatory cytokines, chemokine ligands, the C3 component of complement, and components of inflammasome signaling such as Nlrp3. Among LPS-challenged cells, M. vaccae NCTC 11659 had limited effects on differential gene expression using a threshold of 1.5-fold change. A subset of genes was assessed using real-time reverse transcription polymerase chain reaction (real-time RT-PCR), including Arg1, Ccl2, Il1b, Il6, Nlrp3, and Tnf. Based on the analysis using real-time RT-PCR, M. vaccae NCTC 11659 by itself again induced "adjuvant-like" effects, increasing the expression of Il1b, Il6, and Tnf while decreasing the expression of Arg1. LPS by itself increased the expression of Ccl2, Il1b, Il6, Nlrp3, and Tnf while decreasing the expression of Arg1. Among LPS-challenged cells, M. vaccae NCTC 11659 enhanced LPS-induced increases in the expression of Nlrp3 and Tnf, consistent with microglial priming. In contrast, among LPS-challenged cells, although M. vaccae NCTC 11659 did not fully prevent the effects of LPS relative to vehicle-treated control conditions, it increased Arg1 mRNA expression, suggesting that M. vaccae NCTC 11659 induces an atypical microglial phenotype. Thus, M. vaccae NCTC 11659 acutely (within 48 h) induced immune-activating and microglial-priming effects when applied directly to murine BV-2 microglial cells, in contrast to its long-term anti-inflammatory and immunoregulatory effects observed on the CNS when whole-cell, heat-killed preparations of M. vaccae NCTC 11659 were given peripherally in vivo.

Receptor Interacting Ser/Thr-Protein Kinase 2 as a New Therapeutic Target

Receptor interacting serine/threonine protein kinase 2 (RIPK2) is a downstream signaling molecule essential for the activation of several innate immune receptors, including the NOD-like receptors (NOD1 and NOD2). Recognition of pathogen-associated molecular pattern proteins by NOD1/2 leads to their interaction with RIPK2, which induces release of pro-inflammatory cytokines through the activation of NF-κB and MAPK pathways, among others. Thus, RIPK2 has emerged as a key mediator of intracellular signal transduction and represents a new potential therapeutic target for the treatment of various conditions, including inflammatory diseases and cancer. In this Perspective, first, an overview of the mechanisms that underlie RIPK2 function will be presented along with its role in several diseases. Then, the existing inhibitors that target RIPK2 and different therapeutic strategies will be reviewed, followed by a discussion on current challenges and outlook.

Receptor-interacting protein kinase 2 (RIPK2) profoundly contributes to post-stroke neuroinflammation and behavioral deficits with microglia as unique perpetrators

BACKGROUND

Receptor-interacting protein kinase 2 (RIPK2) is a serine/threonine kinase whose activity propagates inflammatory signaling through its association with pattern recognition receptors (PRRs) and subsequent TAK1, NF-κB, and MAPK pathway activation. After stroke, dead and dying cells release a host of damage-associated molecular patterns (DAMPs) that activate PRRs and initiate a robust inflammatory response. We hypothesize that RIPK2 plays a damaging role in the progression of stroke injury by enhancing the neuroinflammatory response to stroke and that global genetic deletion or microglia-specific conditional deletion of Ripk2 will be protective following ischemic stroke.

METHODS

Adult (3-6 months) male mice were subjected to 45 min of transient middle cerebral artery occlusion (tMCAO) followed by 24 h, 48 h, or 28 days of reperfusion. Aged male and female mice (18-24 months) were subjected to permanent ischemic stroke and sacrificed 48 h later. Infarct volumes were calculated using TTC staining (24-48 h) or Cresyl violet staining (28d). Sensorimotor tests (weight grip, vertical grid, and open field) were performed at indicated timepoints. Blood-brain barrier (BBB) damage, tight junction proteins, matrix metalloproteinase-9 (MMP-9), and neuroinflammatory markers were assessed via immunoblotting, ELISA, immunohistochemistry, and RT-qPCR. Differential gene expression profiles were generated through bulk RNA sequencing and nanoString®.

RESULTS

Global genetic deletion of Ripk2 resulted in decreased infarct sizes and reduced neuroinflammatory markers 24 h after stroke compared to wild-type controls. Ripk2 global deletion also improved both acute and long-term behavioral outcomes with powerful effects on reducing infarct volume and mortality at 28d post-stroke. Conditional deletion of microglial Ripk2 (mKO) partially recapitulated our results in global Ripk2 deficient mice, showing reductive effects on infarct volume and improved behavioral outcomes within 48 h of injury. Finally, bulk transcriptomic profiling and nanoString data demonstrated that Ripk2 deficiency in microglia decreases genes associated with MAPK and NF-κB signaling, dampening the neuroinflammatory response after stroke injury by reducing immune cell activation and peripheral immune cell invasion.

CONCLUSIONS

These results reveal a hitherto unknown role for RIPK2 in the pathogenesis of ischemic stroke injury, with microglia playing a distinct role. This study identifies RIPK2 as a potent propagator of neuroinflammatory signaling, highlighting its potential as a therapeutic target for post-stroke intervention.

RIPK2: a promising target for cancer treatment

As an essential mediator of inflammation and innate immunity, the receptor-interacting serine/threonine-protein kinase-2 (RIPK2) is responsible for transducing signaling downstream of the intracellular peptidoglycan sensors nucleotide oligomerization domain (NOD)-like receptors 1 and 2 (NOD1/2), which will further activate nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways, leading to the transcription activation of pro-inflammatory cytokines and productive inflammatory response. Thus, the NOD2-RIPK2 signaling pathway has attracted extensive attention due to its significant role in numerous autoimmune diseases, making pharmacologic RIPK2 inhibition a promising strategy, but little is known about its role outside the immune system. Recently, RIPK2 has been related to tumorigenesis and malignant progression for which there is an urgent need for targeted therapies. Herein, we would like to evaluate the feasibility of RIPK2 being the anti-tumor drug target and summarize the research progress of RIPK2 inhibitors. More importantly, following the above contents, we will analyze the possibility of applying small molecule RIPK2 inhibitors to anti-tumor therapy.

RIPK2 as a promising druggable target for autoimmune diseases

Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) is an essential regulator of the inflammatory process and immune response. In innate immunity, the NOD-RIPK2 signaling axis is an important pathway that directly mediates inflammation and immune response. In adaptive immunity, RIPK2 may affect T cell proliferation, differentiation and cellular homeostasis thereby involving T cell-driven autoimmunity, but the exact mechanism remains unclear. Recent advances suggest a key role of RIPK2 in diverse autoimmune diseases (ADs) such as inflammatory bowel diseases, rheumatoid arthritis, multiple sclerosis, systemic lupus erythematosus, and Behcet's disease. This review aims to provide valuable therapeutic direction for ADs by focusing on the function and modulation of RIPK2 in innate and adaptive immunity, its involvement with various ADs and the application of RIPK2-related drugs in ADs. We raise the notion that drug targeting RIPK2 could be a promising therapeutic strategy for the treatment of ADs, though much work remains to be done for clinical application.

Developments of PROTACs technology in immune-related diseases

Traditional chemotherapy and immunotherapy are primary disease-treatment strategies. However, they face numerous challenges, including limited therapeutic benefits, off-target effects, serious adverse effects, drug resistance, long half-life time, poor oral bioavailability, and drugging undruggable proteins. Proteolytic targeted chimeras (PROTACs) were suggested to solve these problems. PROTACs are heterogeneous functional molecules linked by a chemical linker and contain a binding ligand for the protein of interest and a recruiting ligand for the E3 ligand. The binding of a PROTAC to a target protein brings the E3 ligand enzyme into proximity, initiating polyubiquitination of the target protein, followed by protease-mediated degradation. To date, PROTACs against dozens of immunological targets have been successfully developed, many of which have been clinically validated drug targets, and several have entered clinical trials for immune-related diseases. This article reviews the role of PROTACs-mediated degradation of critical proteins in immune disorders and cancer immunotherapy. Chemical structures, cellular and in vivo activities, and pharmacodynamics of these PROTACs are summarized. Lastly, we also discuss the prospects and potential limitations that PROTACs face.

Recent advances in the development of RIPK2 modulators for the treatment of inflammatory diseases

Receptor-interacting serine/threonine kinase 2 (RIPK2) is a vital immunomodulator that plays critical roles in nucleotide-binding oligomerization domain 1 (NOD1), NOD2, and Toll-like receptors (TLRs) signaling. Stimulated NOD1 and NOD2 interact with RIPK2 and lead to the activation of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinases (MAPK), followed by the production of pro-inflammatory cytokines such as TNF-α, IL-6, and IL-12/23. Defects in NOD/RIPK2 signaling are associated with numerous inflammatory diseases, including asthma, sarcoidosis, inflammatory bowel disease (Crohn's disease and ulcerative colitis), multiple sclerosis, and Blau syndrome. As RIPK2 is a crucial element of innate immunity, small molecules regulating RIPK2 functions are attractive to establish novel immunotherapies. The increased interest in developing RIPK2 inhibitors has led to the clinical investigations of novel drug candidates. In this review, we attempt to summarize recent advances in the development of RIPK2 inhibitors and degraders.

Discovery of Potent and Selective Receptor-Interacting Serine/Threonine Protein Kinase 2 (RIPK2) Inhibitors for the Treatment of Inflammatory Bowel Diseases (IBDs)

Receptor-interacting serine/threonine protein kinase 2 (RIPK2) has been demonstrated to be a promising target for treating inflammatory diseases. Herein, we describe the discovery and optimization of a series of RIPK2 inhibitors derived from an FLT3 inhibitor, CHMFL-FLT3-165. Compound 10w was identified to possess an IC₅₀ value of 0.6 nM for RIPK2 and greater than 50,000-fold selectivity over its family homologous kinase RIPK1 (IC₅₀ > 30 μM). It exhibited high kinase selectivity and inhibited RIPK2 to prevent NOD-induced cytokine production following muramyl dipeptide (MDP) stimulation. In an acute colitis model, compound 10w exerted better therapeutic effects than the JAK inhibitor filgotinib and the RIPK2 inhibitor WEHI-345. These robust results of in vitro and in vivo pharmacodynamic experiments demonstrate that RIPK2 as a therapeutic target shows potential abilities for the treatment of inflammatory bowel diseases.