Small molecule induced STING degradation facilitated by the HECT ligase HERC4.

Stimulator of interferon genes (STING) is a central component of the cytosolic nucleic acids sensing pathway and as such master regulator of the type I interferon response. Due to its critical role in physiology and its' involvement in a variety of diseases, STING has been a focus for drug discovery. Targeted protein degradation (TPD) has emerged as a promising pharmacology for targeting previously considered undruggable proteins by hijacking the cellular ubiquitin proteasome system (UPS) with small molecules. Here, we identify AK59 as a STING degrader leveraging HERC4, a HECT-domain E3 ligase. Additionally, our data reveals that AK59 is effective on the common pathological STING mutations, suggesting a potential clinical application of this mechanism. Thus, these findings introduce HERC4 to the fields of TPD and of compound-induced degradation of STING, suggesting potential therapeutic applications.

STING Agonists/Antagonists: Their Potential as Therapeutics and Future Developments.

The cGAS STING pathway has received much attention in recent years, and it has been recognized as an important component of the innate immune response. Since the discovery of STING and that of cGAS, many observations based on preclinical models suggest that the faulty regulation of this pathway is involved in many type I IFN autoinflammatory disorders. Evidence has been accumulating that cGAS/STING might play an important role in pathologies beyond classical immune diseases, as in, for example, cardiac failure. Human genetic mutations that result in the activation of STING or that affect the activity of cGAS have been demonstrated as the drivers of rare interferonopathies affecting young children and young adults. Nevertheless, no data is available in the clinics demonstrating the therapeutic benefit in modulating the cGAS/STING pathway. This is due to the lack of STING/cGAS-specific low molecular weight modulators that would be qualified for clinical exploration. The early hopes to learn from STING agonists, which have reached the clinics in recent years for selected oncology indications, have not yet materialized since the initial trials are progressing very slowly. In addition, transforming STING agonists into potent selective antagonists has turned out to be more challenging than expected. Nevertheless, there has been progress in identifying novel low molecular weight compounds, in some cases with unexpected mode of action, that might soon move to clinical trials. This study gives an overview of some of the potential indications that might profit from modulation of the cGAS/STING pathway and a short overview of the efforts in identifying STING modulators (agonists and antagonists) suitable for clinical research and describing their potential as a "drug".

STING regulates peripheral nerve regeneration and colony stimulating factor 1 receptor (CSF1R) processing in microglia.

Inflammatory responses are crucial for regeneration following peripheral nerve injury (PNI). PNI triggers inflammatory responses at the site of injury. The DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream effector stimulator of interferon genes (STING) sense foreign and self-DNA and trigger type I interferon (IFN) immune responses. We demonstrate here that following PNI, the cGAS/STING pathway is upregulated in the sciatic nerve of naive rats and dysregulated in old rats. In a nerve crush mouse model where STING is knocked out, myelin content in sciatic nerve is increased resulting in accelerated functional axon recovery. STING KO mice have lower macrophage number in sciatic nerve and decreased microglia activation in spinal cord 1 week post injury. STING activation regulated processing of colony stimulating factor 1 receptor (CSF1R) and microglia survival in vitro. Taking together, these data highlight a previously unrecognized role of STING in the regulation of nerve regeneration.

TNF leads to mtDNA release and cGAS/STING-dependent interferon responses that support inflammatory arthritis.

Tumor necrosis factor (TNF) is a key driver of several inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel disease, and psoriasis, in which affected tissues show an interferon-stimulated gene signature. Here, we demonstrate that TNF triggers a type-I interferon response that is dependent on the cyclic guanosine monophosphate-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. We show that TNF inhibits PINK1-mediated mitophagy and leads to altered mitochondrial function and to an increase in cytosolic mtDNA levels. Using cGAS-chromatin immunoprecipitation (ChIP), we demonstrate that cytosolic mtDNA binds to cGAS after TNF treatment. Furthermore, TNF induces a cGAS-STING-dependent transcriptional response that mimics that of macrophages from rheumatoid arthritis patients. Finally, in an inflammatory arthritis mouse model, cGAS deficiency blocked interferon responses and reduced inflammatory cell infiltration and joint swelling. These findings elucidate a molecular mechanism linking TNF to type-I interferon signaling and suggest a potential benefit for therapeutic targeting of cGAS/STING in TNF-driven diseases.

Discovery of Orally Active Hydroxyethylamine Based SPPL2a Inhibitors.

SPPL2a (Signal Peptide Peptidase Like 2a) is an intramembrane aspartyl protease engaged in the function of B-cells and dendritic cells. Despite being an attractive target for modulation of the immune system, selective SPPL2a inhibitors are barely described in the literature. Recently, we have disclosed a selective, small molecular weight agent SPL-707 which confirmed that pharmacological inhibition of SPPL2a leads to the accumulation of its substrate CD74/p8 and as a consequence to a reduction in the number of B-cells as well as myeloid dendritic cells in mice. In this paper we describe the discovery of novel hydroxyethylamine based SPPL2a inhibitors. Starting from a rather lipophilic screening hit, several iterative optimization cycles allowed for its transformation into a highly potent and selective compound 15 (SPL-410) which inhibited in vivo CD74/p8 fragment processing in mice at 10 mg/kg oral dose.

Discovery of the First Potent, Selective, and Orally Bioavailable Signal Peptide Peptidase-Like 2a (SPPL2a) Inhibitor Displaying Pronounced Immunomodulatory Effects In Vivo.

Signal peptide peptidase-like 2a (SPPL2a) is an aspartic intramembrane protease which has recently been shown to play an important role in the development and function of antigen presenting cells such as B lymphocytes and dendritic cells. In this paper, we describe the discovery of the first selective and orally active SPPL2a inhibitor (S)-2-cyclopropyl-N1-((S)-5,11-dioxo-10,11-dihydro-1H,3H,5H-spiro[benzo[d]pyrazolo[1,2-a][1,2]diazepine-2,1'-cyclopropan]-10-yl)-N4-(5-fluoro-2-methylpyridin-3-yl)succinamide 40 (SPL-707). This compound shows adequate selectivity against the closely related enzymes γ-secretase and SPP and a good pharmacokinetic profile in mouse and rat. Compound 40 significantly inhibited processing of the SPPL2a substrate CD74/p8 fragment in rodents at doses ≤10 mg/kg b.i.d. po. Oral dosing of 40 for 11 days at ≥10 mg/kg b.i.d. recapitulated the phenotype seen in Sppl2a knockout (ko) and ENU mutant mice (reduced number of specific B cells and myeloid dendritic cells). Thus, we believe that SPPL2a represents an interesting and druggable pharmacological target, potentially providing a novel approach for the treatment of autoimmune diseases by targeting B cells and dendritic cells.

Effective "activated PI3Kδ syndrome"-targeted therapy with the PI3Kδ inhibitor leniolisib.

Pathogenic gain-of-function variants in the genes encoding phosphoinositide 3-kinase δ (PI3Kδ) lead to accumulation of transitional B cells and senescent T cells, lymphadenopathy, and immune deficiency (activated PI3Kδ syndrome [APDS]). Knowing the genetic etiology of APDS afforded us the opportunity to explore PI3Kδ inhibition as a precision-medicine therapy. Here, we report in vitro and in vivo effects of inhibiting PI3Kδ in APDS. Treatment with leniolisib (CDZ173), a selective PI3Kδ inhibitor, caused dose-dependent suppression of PI3Kδ pathway hyperactivation (measured as phosphorylation of AKT/S6) in cell lines ectopically expressing APDS-causative p110δ variants and in T-cell blasts derived from patients. A clinical trial with 6 APDS patients was conducted as a 12-week, open-label, multisite, within-subject, dose-escalation study of oral leniolisib to assess safety, pharmacokinetics, and effects on lymphoproliferation and immune dysregulation. Oral leniolisib led to a dose-dependent reduction in PI3K/AKT pathway activity assessed ex vivo and improved immune dysregulation. We observed normalization of circulating transitional and naive B cells, reduction in PD-1+CD4+ and senescent CD57+CD4- T cells, and decreases in elevated serum immunoglobulin M and inflammatory markers including interferon γ, tumor necrosis factor, CXCL13, and CXCL10 with leniolisib therapy. After 12 weeks of treatment, all patients showed amelioration of lymphoproliferation with lymph node sizes and spleen volumes reduced by 39% (mean; range, 26%-57%) and 40% (mean; range, 13%-65%), respectively. Thus, leniolisib was well tolerated and improved laboratory and clinical parameters in APDS, supporting the specific inhibition of PI3Kδ as a promising new targeted therapy in APDS and other diseases characterized by overactivation of the PI3Kδ pathway. This trial was registered at www.clinicaltrials.gov as #NCT02435173.

Identification of SPPL2a Inhibitors by Multiparametric Analysis of a High-Content Ultra-High-Throughput Screen.

The intramembrane protease signal peptide peptidase-like 2a (SPPL2a) is a potential drug target for the treatment of autoimmune diseases due to an essential role in B cells and dendritic cells. To screen a library of 1.4 million compounds for inhibitors of SPPL2a, we developed an imaging assay detecting nuclear translocation of the proteolytically released cytosolic substrate fragment. The state-of-the-art hit calling approach based on nuclear translocation resulted in numerous false-positive hits, mainly interrupting intracellular protein trafficking. To filter the false positives, we extracted 340 image-based readouts and developed a novel multiparametric analysis method that successfully triaged the primary hit list. The identified scaffolds were validated by demonstrating activity on endogenous SPPL2a and substrate CD74/p8 in B cells. The multiparametric analysis discovered diverse cellular phenotypes and provided profiles for the whole library. The principle of the presented imaging assay, the screening strategy, and multiparametric analysis are potentially applicable in future screening campaigns.

Investigating the molecular mechanisms through which FTY720-P causes persistent S1P1 receptor internalization.

BACKGROUND AND PURPOSE: The molecular mechanism underlying the clinical efficacy of FTY720-P is thought to involve persistent internalization and enhanced degradation of the S1P1 receptor subtype (S1P1R). We have investigated whether receptor binding kinetics and ß-arrestin recruitment could play a role in the persistent internalization of the S1P1R by FTY720-P. EXPERIMENTAL APPROACH: [(3) H]-FTY720-P and [(33) P]-S1P were used to label CHO-S1P1/3Rs for binding studies. Ligand efficacy was assessed through [(35) S]-GTPγS binding and ß-arrestin recruitment. Metabolic stability was evaluated using a bioassay measuring intracellular Ca(2+) release. CHO-S1P1/3R numbers were determined, following FTY720-P treatment using flow cytometry. KEY RESULTS: The kinetic off-rate of [(3) H]-FTY720-P from the S1P1R was sixfold slower than from the S1P3R, and comparable to [(33) P]-S1P dissociation from S1P1/3Rs. S1P and FTY720-P stimulated [(35) S]-GTPγS incorporation to similar degrees, but FTY720-P was over 30-fold less potent at S1P3Rs. FTY720-P stimulated a higher level of ß-arrestin recruitment at S1P1Rs, 132% of the total recruited by S1P. In contrast, FTY720-P was a weak partial agonist at S1P3R, stimulating just 29% of the total ß-arrestin recruited by S1P. Internalization experiments confirmed that cell surface expression of the S1P1R but not the S1P3R was reduced following a pulse exposure to FTY720-P, which is metabolically stable unlike S1P. CONCLUSIONS AND IMPLICATIONS: FTY720-P and S1P activation of the S1P1R results in receptor internalization as a consequence of an efficient recruitment of ß-arrestin. The combination of slow off-rate, efficacious ß-arrestin recruitment and metabolic stability all contribute to FTY720-P's ability to promote prolonged S1P1R internalization and may be critical factors in its efficacy in the clinic.

Second generation S1P pathway modulators: research strategies and clinical developments.

Multiple Sclerosis (MS) is a chronic autoimmune disorder affecting the central nervous system (CNS) through demyelination and neurodegeneration. Until recently, major therapeutic treatments have relied on agents requiring injection delivery. In September 2010, fingolimod/FTY720 (Gilenya, Novartis) was approved as the first oral treatment for relapsing forms of MS. Fingolimod causes down-modulation of S1P1 receptors on lymphocytes which prevents the invasion of autoaggressive T cells into the CNS. In astrocytes, down-modulation of S1P1 by the drug reduces astrogliosis, a hallmark of MS, thereby allowing restoration of productive astrocyte communication with other neural cells and the blood brain barrier. Animal data further suggest that the drug directly supports the recovery of nerve conduction and remyelination. In human MS, such mechanisms may explain the significant decrease in the number of inflammatory markers on brain magnetic resonance imaging in recent clinical trials, and the reduction of brain atrophy by the drug. Fingolimod binds to 4 of the 5 known S1P receptor subtypes, and significant efforts were made over the past 5 years to develop next generation S1P receptor modulators and determine the minimal receptor selectivity needed for maximal therapeutic efficacy in MS patients. Other approaches considered were competitive antagonists of the S1P1 receptor, inhibitors of the S1P lyase to prevent S1P degradation, and anti-S1P antibodies. Below we discuss the current status of the field, and the functional properties of the most advanced compounds. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

A potent and selective S1P(1) antagonist with efficacy in experimental autoimmune encephalomyelitis.

Lymphocyte trafficking is critically regulated by the Sphingosine 1-phosphate receptor-1 (S1P(1)), a G protein-coupled receptor that has been highlighted as a promising therapeutic target in autoimmunity. Fingolimod (FTY720, Gilenya) is a S1P(1) receptor agonist that has recently been approved for the treatment of multiple sclerosis (MS). Here, we report the discovery of NIBR-0213, a potent and selective S1P(1) antagonist that induces long-lasting reduction of peripheral blood lymphocyte counts after oral dosing. NIBR-0213 showed comparable therapeutic efficacy to fingolimod in experimental autoimmune encephalomyelitis (EAE), a model of human MS. These data provide convincing evidence that S1P(1) antagonists are effective in EAE. In addition, the profile of NIBR-0213 makes it an attractive candidate to further study the consequences of S1P(1) receptor antagonism and to differentiate the effects from those of S1P(1) agonists.

Oxysterols direct immune cell migration via EBI2.

Epstein-Barr virus-induced gene 2 (EBI2, also known as GPR183) is a G-protein-coupled receptor that is required for humoral immune responses; polymorphisms in the receptor have been associated with inflammatory autoimmune diseases. The natural ligand for EBI2 has been unknown. Here we describe the identification of 7α,25-dihydroxycholesterol (also called 7α,25-OHC or 5-cholesten-3ß,7α,25-triol) as a potent and selective agonist of EBI2. Functional activation of human EBI2 by 7α,25-OHC and closely related oxysterols was verified by monitoring second messenger readouts and saturable, high-affinity radioligand binding. Furthermore, we find that 7α,25-OHC and closely related oxysterols act as chemoattractants for immune cells expressing EBI2 by directing cell migration in vitro and in vivo. A critical enzyme required for the generation of 7α,25-OHC is cholesterol 25-hydroxylase (CH25H). Similar to EBI2 receptor knockout mice, mice deficient in CH25H fail to position activated B cells within the spleen to the outer follicle and mount a reduced plasma cell response after an immune challenge. This demonstrates that CH25H generates EBI2 biological activity in vivo and indicates that the EBI2-oxysterol signalling pathway has an important role in the adaptive immune response.

Pyrazole derived from (+)-3-carene; a novel potent, selective scaffold for sphingosine-1-phosphate (S1P(1)) receptor agonists.

High throughput screening and hit to lead optimization led to the identification of 'carene' as a promising scaffold showing selective S1P(1) receptor agonism. In parallel to this work we have established a pharmacophore model for the S1P(1) receptor highlighting the minimal structural requirement necessary for potent receptor agonism.

Persistent signaling induced by FTY720-phosphate is mediated by internalized S1P1 receptors.

Targeting sphingosine-1-phosphate receptors with the oral immunomodulator drug FTY720 (fingolimod) has demonstrated substantial efficacy in the treatment of multiple sclerosis. The drug is phosphorylated in vivo, and most of the clinical effects of FTY720-phosphate (FTY720P) are thought to be mediated via S1P1 receptors on lymphocytes and endothelial cells, leading to sequestration of lymphocytes in secondary lymphoid organs. FTY720P was described to act as a "functional antagonist" by promoting efficient internalization of S1P1 receptors. We demonstrate here that S1P1 receptors activated by FTY720P retain signaling activity for hours in spite of a quantitative internalization. Structural analogs of FTY720P with shorter alkyl side chains retained potency and efficacy in a functional assay but failed to promote long-lasting receptor internalization and signaling. We show that persistent signaling translates into an increased chemokinetic migration of primary human umbilical vein endothelial cells, which suggests persistent agonism as a crucial parameter in the mechanism of action of FTY720.

The O-linked N-acetylglucosamine modification in cellular signalling and the immune system. 'Protein modifications: beyond the usual suspects' review series.

The intracellular modification of proteins by the addition of a single O-linked N-acetylglucosamine (O-GlcNAc) molecule is a ubiquitous post-translational modification in eukaryotic cells. It is catalysed by O-linked N-acetylglucosaminyltransferase, which attaches O-GlcNAc to serine/threonine residues, and it is counter-regulated by beta-N-acetylglucosaminidase, which is the antagonistic glycosidase that removes the O-GlcNAc group. O-GlcNAc modification competes with phosphorylation by protein kinases at similar sites, thereby affecting important signalling nodes. Accumulating evidence supports a central role for O-GlcNAc modifications and the corresponding enzymes in the regulation of immune cells, particularly in the activation processes of T and B lymphocytes. Here, we discuss recent advances in the field of O-GlcNAc modifications, focusing on the cells of the immune system.

Reversible translocation of p115-RhoGEF by G(12/13)-coupled receptors.

G protein-coupled receptors (GPCRs) are important targets for medicinal agents. Four different G protein families, G(s), G(i), G(q), and G(12), engage in their linkage to activation of receptor-specific signal transduction pathways. G(12) proteins were more recently studied, and upon activation by GPCRs they mediate activation of RhoGTPase guanine nucleotide exchange factors (RhoGEFs), which in turn activate the small GTPase RhoA. RhoA is involved in many cellular and physiological aspects, and a dysfunction of the G(12/13)-Rho pathway can lead to hypertension, cardiovascular diseases, stroke, impaired wound healing and immune cell functions, cancer progression and metastasis, or asthma. In this study, regulator of G protein signaling (RGS) domain-containing RhoGEFs were tagged with enhanced green fluorescent protein (EGFP) to detect their subcellular localization and translocation upon receptor activation. Constitutively active Galpha(12) and Galpha(13) mutants induced redistribution of these RhoGEFs from the cytosol to the plasma membrane. Furthermore, a pronounced and rapid translocation of p115-RhoGEF from the cytosol to the plasma membrane was observed upon activation of several G(12/13)-coupled GPCRs in a cell type-independent fashion. Plasma membrane translocation of p115-RhoGEF stimulated by a GPCR agonist could be completely and rapidly reversed by subsequent application of an antagonist for the respective GPCR, that is, p115-RhoGEF relocated back to the cytosol. The translocation of RhoGEF by G(12/13)-linked GPCRs can be quantified and therefore used for pharmacological studies of the pathway, and to discover active compounds in a G(12/13)-related disease context.

Synthesis and immobilization of erythro-C14-omega-aminosphingosine-1-phosphate as a potential tool for affinity chromatography.

A sphingosine-1-phosphate (S1P) analogue containing a terminal alkyl chain amino group is synthesized in a few steps via olefin cross-metathesis of an optically resolved intermediate and subsequent phosphorylation. Regioselective acylation of this intermediate at its N terminus in solution is demonstrated as a model reaction and provides a biologically active derivative. Finally, the omega-amino intermediate is immobilized on an affinity matrix. The choice of a UV-active phosphate protecting group allows for quantification of resin loading after cleavage which amounted to 66 %.

Requirement for O-linked N-acetylglucosaminyltransferase in lymphocytes activation.

The dynamic modification of nuclear and cytoplasmic proteins with O-linked beta-N-acetylglucosamine (O-GlcNAc) by the O-linked N-acetylglucosaminyltransferase (OGT) is a regulatory post-translational modification that is responsive to various stimuli. Here, we demonstrate that OGT is a central factor for T- and B-lymphocytes activation. SiRNA-mediated knockdown of OGT in T cells leads to an impaired activation of the transcription factors NFAT and NFkappaB. This results in a reduction of IL-2 production consistent with prevention of T-cell activation. OGT is also required for the early activation of B cells mediated by stimulation of the B-cell receptor. Mechanistically, we demonstrate that NFkappaB as well as NFAT are glycosylated with O-GlcNAc after direct binding to OGT. Moreover, kinetic experiments show that O-GlcNAc modification prominently increased shortly after activation of lymphoid cells and it might be required for nuclear translocation of the transcription factors NFkappaB and NFAT.

Phosphorylated FTY720 promotes astrocyte migration through sphingosine-1-phosphate receptors.

Sphingosine-1-phosphate (S1P) receptors are widely expressed in the central nervous system where they are thought to regulate glia cell function. The phosphorylated version of fingolimod/FTY720 (FTY720P) is active on a broad spectrum of S1P receptors and the parent compound is currently in phase III clinical trials for the treatment of multiple sclerosis. Here, we aimed to identify which cell type(s) and S1P receptor(s) of the central nervous system are targeted by FTY720P. Using calcium imaging in mixed cultures from embryonic rat cortex we show that astrocytes are the major cell type responsive to FTY720P in this assay. In enriched astrocyte cultures, we detect expression of S1P1 and S1P3 receptors and demonstrate that FTY720P activates Gi protein-mediated signaling cascades. We also show that FTY720P as well as the S1P1-selective agonist SEW2871 stimulate astrocyte migration. The data indicate that FTY720P exerts its effects on astrocytes predominantly via the activation of S1P1 receptors, whereas S1P signals through both S1P1 and S1P3 receptors. We suggest that this distinct pharmacological profile of FTY720P, compared with S1P, could play a role in the therapeutic effects of FTY720 in multiple sclerosis.