Recent advances in understanding spleen tyrosine kinase (SYK) in human biology and disease, with a focus on fostamatinib

Spleen tyrosine kinase (SYK) is an important regulatory molecule of signal transduction pathways involved in the pathogenesis of autoimmune diseases such as immune thrombocytopenia (ITP), and the SYK-signaling pathway has emerged as a potential target for the treatment of numerous diseases. The aim of this narrative review is to summarize the biological properties of SYK and its involvement in disease pathways, provide an update on SYK inhibitors in the treatment of ITP, and consider other potential applications. Fostamatinib, the only licensed SYK inhibitor to date, produces clinical response in ITP patients, including those who are refractory to other treatments. It appears to reduce the risk of thrombotic events and may therefore be a drug to consider for patients with an increased thrombotic risk. Encouraging results have also been obtained in the treatment of warm autoimmune hemolytic anemia. Several other SYK inhibitors have entered clinical trials for a range of indications, reflecting the ability of these drugs to affect multiple signaling pathways. SYK inhibitors have the potential to target several aspects of COVID-19 pathogenesis including thrombosis, without affecting normal hemostasis, and data from the first study of fostamatinib in COVID-19 are encouraging. It is hoped that ongoing trials in autoimmune indications other than ITP, as well as in hematological malignancies and other disorders, confirm the promise of SYK inhibitors. Immune thrombocytopenia (ITP) is an autoimmune disease that usually happens when your immune system mistakenly attacks and destroys platelets, which are cells that help blood to clot. Individuals with ITP can experience easy or excessive bruising and bleeding. Scientists have identified that an enzyme called spleen tyrosine kinase (SYK) is involved in numerous biological processes that are associated with the immune system response, inflammation, and some types of cancer in humans. Therefore, it has become a target for new drugs which inhibit the action of SYK. In this review article, the authors provide a summary of the biological properties and actions of SYK and its involvement in various diseases, discuss information about drugs that have been developed as SYK inhibitors for the treatment of ITP, and consider other potential uses for drugs that inhibit SYK. Although several drugs are being developed, the only SYK inhibitor that is currently available for the treatment of ITP is a drug called fostamatinib. In patients with ITP, including those who no longer respond to other treatments, fostamatinib has been shown to improve platelet counts and reduce bleeding events. Researchers are also currently investigating the use of drugs that inhibit SYK, including fostamatinib, for the potential treatment of other diseases associated with inflammation (e.g. rheumatoid arthritis, COVID-19), autoimmunity (e.g. warm autoimmune hemolytic anemia), and blood cancers (e.g. lymphoma, chronic lymphocytic leukemia, and acute myeloid leukemia). eng

Small-molecule screening identifies Syk kinase inhibition and rutaecarpine as modulators of macrophage training and SARS-CoV-2 infection.

Biologically active small molecules can impart modulatory effects, in some cases providing extended long-term memory. In a screen of biologically active small molecules for regulators of tumor necrosis factor (TNF) induction, we identify several compounds with the ability to induce training effects on human macrophages. Rutaecarpine shows acute and long-term modulation, enhancing lipopolysaccharide (LPS)-induced pro-inflammatory cytokine secretion and relieving LPS tolerance in human macrophages. Rutaecarpine inhibits ß-glucan-induced H3K4Me3 marks at the promoters of several pro-inflammatory cytokines, highlighting the potential of this molecule to modulate chromosomal topology. Syk kinase inhibitor (SYKi IV), another screen hit, promotes an enhanced response to LPS similar to that previously reported for ß-glucan-induced training. Macrophages trained with SYKi IV show a high degree of resistance to influenza A, multiple variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and OC43 coronavirus infection, highlighting a potential application of this molecule and other SYKis as prophylactic treatments for viral susceptibility.

Spleen tyrosine kinase mediates innate and adaptive immune crosstalk in SARS-CoV-2 mRNA vaccination.

Durable cell-mediated immune responses require efficient innate immune signaling and the release of pro-inflammatory cytokines. How precisely mRNA vaccines trigger innate immune cells for shaping antigen specific adaptive immunity remains unknown. Here, we show that SARS-CoV-2 mRNA vaccination primes human monocyte-derived macrophages for activation of the NLRP3 inflammasome. Spike protein exposed macrophages undergo NLRP3-driven pyroptotic cell death and subsequently secrete mature interleukin-1ß. These effects depend on activation of spleen tyrosine kinase (SYK) coupled to C-type lectin receptors. Using autologous cocultures, we show that SYK and NLRP3 orchestrate macrophage-driven activation of effector memory T cells. Furthermore, vaccination-induced macrophage priming can be enhanced with repetitive antigen exposure providing a rationale for prime-boost concepts to augment innate immune signaling in SARS-CoV-2 vaccination. Collectively, these findings identify SYK as a regulatory node capable of differentiating between primed and unprimed macrophages, which modulate spike protein-specific T cell responses.

Multi-Arm Trial of Inflammatory Signal Inhibitors (MATIS) for Hospitalised Patients with Mild or Moderate COVID-19 Pneumonia: A Structured Summary of a Study Protocol for a Randomised Controlled Trial

Introduction: Severe COVID-19 pneumonia is characterised by respiratory and multi-organ failure in the context of marked systemic inflammation. This hyperinflammatory syndrome is reflected by the elevation of several inflammatory molecules, such as C-reactive protein (CRP), ferritin, IL-6, troponin, and D-dimer. In a subset of patients, early intervention with signal inhibitors may treat the Covid-19 hyperinflammatory syndrome before the development of acute lung injury and organ failure. We present a summary of a study protocol for a randomised controlled, multi-arm trial with two novel inflammatory signal inhibitors;Ruxolitinib (RUX) and Fostamatinib (FOS) for the treatment of Covid-19 pneumonia. RUX is an oral Janus Associated Kinase (JAK1/JAK2) inhibitor approved for the treatment of splenomegaly, myelofibrosis and polycythaemia vera. Inhibition of STAT3 downregulates IL-6 and IL-23, which are important for the inflammatory effects of Th17 cells. Further, JAK2 inhibition has been shown to reduce levels of TNFa and CRP, as well as reducing viral cellular entry and assembly. FOS is an oral spleen tyrosine kinase (SYK) inhibitor approved for the treatment of chronic immune thrombocytopenia. Studies of severe acute respiratory distress syndrome (ARDS) suggest that the pathogenesis relies on a series of SYK events leading to cytokine and chemokine release. FOS acts by inhibiting SYK activity, blocking the production and release of cytokines induced via C-lectin receptors and Fc receptor activation, ameliorating the cytokine storm which precedes ARDS. Primary Objective: The primary objective of MATIS is to determine the efficacy of RUX or FOS compared to standard of care (SOC) to reduce the proportion of hospitalised patients progressing from mild or moderate to severe COVID-19 pneumonia at 14 days from baseline. Secondary objectives at 7, 14 and 28 days: - Determine the efficacy of RUX or FOS to reduce mortality - Determine the efficacy of RUX or FOS to reduce the need for invasive ventilation or ECMO - Determine the efficacy of RUX or FOS to reduce the need for non-invasive ventilation - Determine the efficacy of RUX or FOS to reduce the proportion of patients suffering significant oxygen desaturation - Determine the efficacy of RUX or FOS to reduce the need for renal replacement therapy - Determine the efficacy of RUX and FOS to reduce the incidence of venous thromboembolism COVID-19 pneumonia - Determine the efficacy of RUX and FOS to reduce the severity of COVID-19 pneumonia [graded by a modified WHO Ordinal Scale] - Determine the efficacy of RUX or FOS to reduce the level of inflammatory biomarkers - Determine the efficacy of RUX or FOS to reduce the duration of hospital admission - Evaluate the safety of RUX and FOS for COVID-19 pneumonia Study Design: This is a multi-arm, two-stage, open-label, randomised (1:1:1) controlled trial. Participants will be recruited during hospitalisation for COVID-19 in multiple centres in the UK. Eligible participants (table 1) are randomised to one of the three interventions (RUX, FOS, SOC) by a central web-based randomisation service. This uses randomisation sequences with random block sizes, stratified by age (<65 and ≥65 years) and site. The treatment duration is 14 days from baseline. Patients receiving RUX will be administered 10mg BD for Day 1-7 and 5mg BD for Day 8-14. FOS will be administered as 150mg BD day 1-7 and 100mg BD day 8-14. Participants receive follow up assessments on days 7, 14 and 28 after the first dose. Outcomes: Primary endpoints will be assessed with a pairwise comparison (FOS vs SOC and RUX vs SOC) of the proportion of participants diagnosed with severe COVID-19 pneumonia within 14 days. Severe COVID-19 pneumonia is defined by a modified WHO COVID-19 Ordinal Score 5, comprising the following indicators of disease severity: - Death - Requirement for invasive ventilation - Requirement for non-invasive ventilation including CPAP or high flow oxygen - O2 saturation < 90% on 60% inspired oxygen Samples size: In stage 1 of this multi-arm study, 171 parti ipants will be randomised (57 per arm). Following an interim analysis, if either intervention shows a signal of efficacy, stage 2 will recruit a further 95 participants per arm (Fig 1). Trial Status: Recruitment is ongoing and commenced 2nd October 2020. Currently 127 patients are recruited and stage 1 is projected to be completed by 1st September 2021. The full protocol can be accessed via the trial's website. [Formula presented] Disclosures: Milojkovic: Novartis: Honoraria, Speakers Bureau;Incyte: Honoraria, Speakers Bureau;Bristol-Myers Squibb: Honoraria, Speakers Bureau;Pfizer: Honoraria, Speakers Bureau. Cooper: Principia and Sanofi: Consultancy;Sanofi and Principia: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations expenses. OffLabel Disclosure: Fostamatanib - is a tyrosine kinase inhibitor with activity against spleen tyrosine kinase (SYK). In the context of treating COVID-19, Fostamatanib acts by inhibiting SYK activist, blocking the production and release of cytokines induced via C-lectin receptors and Fc receptor activation, ameliorating the cytokine storm which precedes ARDS. Studies of severe acute respiratory syndrome induced by coronavirus, suggest that pathogenesis relies on a series of SYK events. SYK medicates ctuokine and chemokine release, induced by the activation of C-lectin receptors and immunoglobulin Fc receptors, resulting in neutrophil and monocyte lung ingress, sequential activation of neutrophil extracellular traps and activation of lung epithelium and multiple myeloid cell. This is followed by inflammation and tissue destruction that contribute to ARDS. Ruxolitinib - A JAK1/JAK2 inhibitor. JAK and STAT molecules are proteins that trance extracellular stimulation into intracellular signalling, leading to expression of host inflammatory cytokines and a variety of immune cells. In the context of MATIS, we use low dose ruxolitinib to treat COVID-19 by targeting key signalling pathways implicated in the hyper-inflammatory response of patients with COVID-19 infection. The mechanisms of Ruxolitinib to act in COVID-19 is through inhibition of STAT3 activation, down regulating IL-6 and IL-23, signalling important for the inflammatory effects of Th17 cells. Furthermore it leads to reductions of TNFa and CRP.

Complement activation and increased expression of Syk, mucin-1 and CaMK4 in kidneys of patients with COVID-19.

Acute and chronic kidney failure is common in hospitalized patients with COVID-19, yet the mechanism of injury and predisposing factors remain poorly understood. We investigated the role of complement activation by determining the levels of deposited complement components (C1q, C3, FH, C5b-9) and immunoglobulin along with the expression levels of the injury-associated molecules spleen tyrosine kinase (Syk), mucin-1 (MUC1) and calcium/calmodulin-dependent protein kinase IV (CaMK4) in the kidney tissues of people who succumbed to COVID-19. We report increased deposition of C1q, C3, C5b-9, total immunoglobulin, and high expression levels of Syk, MUC1 and CaMK4 in the kidneys of COVID-19 patients. Our study provides strong rationale for the expansion of trials involving the use of inhibitors of these molecules, in particular C1q, C3, Syk, MUC1 and CaMK4 to treat patients with COVID-19.