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Severe influenza A virus (IAV) infections can result in hyper-inflammation, lung injury and acute respiratory distress syndrome 1-5 (ARDS), for which there are no effective pharmacological therapies. Necroptosis is an attractive entry point for therapeutic intervention in ARDS and related inflammatory conditions because it drives pathogenic lung inflammation and lethality during severe IAV infection 6-8 and can potentially be targeted by receptor interacting protein kinase 3 (RIPK3) inhibitors. Here we show that a newly developed RIPK3 inhibitor, UH15-38, potently and selectively blocked IAV-triggered necroptosis in alveolar epithelial cells in vivo. UH15-38 ameliorated lung inflammation and prevented mortality following infection with laboratory-adapted and pandemic strains of IAV, without compromising antiviral adaptive immune responses or impeding viral clearance. UH15-38 displayed robust therapeutic efficacy even when administered late in the course of infection, suggesting that RIPK3 blockade may provide clinical benefit in patients with IAV-driven ARDS and other hyper-inflammatory pathologies., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

A large protein complex, containing RIPK1, RIPK3, and caspase-8 and known as Complex II, has emerged as one of the key mediators of cell death downstream from a range of innate immune triggers. This regulatory mechanism plays a prominent role in macrophages, where Complex II has been linked to apoptosis, pyroptosis, and necroptosis as well as the enhancement of inflammatory gene expression. Although core components of this complex are fairly well understood, more subtle proteomic changes that determine the direction of a response once the complex is assembled remain much less clear. In addition, Complex II components undergo a wealth of post-translational changes that modify the functions of the complex components. This necessitates development of robust and efficient methods of isolating Complex II for further interrogation of its composition and the post-translational modifications of its components. This article describes several methods that we have developed for Complex II isolation, which can be used to obtain complementary information about this signaling mechanism. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Isolation of Complex II in necroptotic and pyroptotic macrophages using FADD immunoprecipitation Basic Protocol 2: Isolation of the complexes formed by the conditionally expressed 3XFLAG-RIPK1 protein Alternate Protocol: Alternative methods of immunoprecipitation of RIPK1 and other Complex-II-related factors Support Protocol: Generation of stable macrophage cell lines using lentiviral expression Basic Protocol 3: Use of proximity labeling to identify necrosome components in the detergent-insoluble fraction of the cell lysates., (© 2021 Wiley Periodicals LLC.)

Receptor interacting protein kinase-2 (RIPK2) is an enzyme involved in the transduction of pro-inflammatory nucleotide-binding oligomerization domain (NOD) cell signaling, a pathway implicated in numerous chronic inflammatory conditions. Herein, a pyrido[2,3-d]pyrimidin-7-one based class of RIPK2 kinase and NOD2 cell signaling inhibitors is described. For example, 33 (e.g. UH15-15) inhibited RIPK2 kinase (IC 50  = 8 ± 4 nM) and displayed > 300-fold selectivity versus structurally related activin receptor-like kinase 2 (ALK2). This molecule blocked NOD2-dependent HEKBlue NF-κB activation (IC 50  = 20 ± 5 nM) and CXCL8 production (at concentrations > 10 nM). Molecular docking suggests that engagement of Ser25 in the glycine-rich loop may provide increased selectivity versus ALK2 and optimal occupancy of the region between the gatekeeper and the αC-helix may contribute to potent NOD2 cell signaling inhibition. Finally, this compound also demonstrated favorable in vitro ADME and pharmacokinetic properties (e.g. C max  = 5.7 μM, T max  = 15 min, t 1/2  = 3.4 h and Cl = 45 mL/min/kg following single 10 mg/kg intraperitoneal administration) further supporting the use of pyrido[2,3-d]pyrimidin-7-ones as a new structure class of RIPK2 kinase and NOD cell signaling inhibitors., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: S.N., A.D. and G.D.C. declare the following financial interests/ personal relationships which may be considered as potential competing interests: PCT patent application (Publication Number: US 2020/0172536 A1) assigned to the University of Houston System and Trustees of Tufts College. All other authors declare no conflict of interest about this article. All other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)