No abstract

Ferroptosis is a nonapoptotic, iron-catalyzed form of regulated necrosis that is critically dependent on glutathione peroxidase 4 (GPX4). It has been shown to contribute to liver and kidney ischemia reperfusion injury in mice. A chemical inhibitor discovered by high-throughput screening displayed inhibition of ferroptosis with nanomolar activity and was dubbed ferrostatin-1 (fer-1). Ferrostatins inhibit oxidative lipid damage, but suffer from inherent stability problems due to the presence of an ester moiety. This limits the application of these molecules in vivo, due to rapid hydrolysis of the ester into the inactive carboxylic acid. Previous studies highlighted the importance of the ethyl ester and suggested steric modifications of the ester for generating improved molecules. In this study, we report the synthesis of novel ferroptosis inhibitors containing amide and sulfonamide moieties with improved stability, single digit nanomolar antiferroptotic activity, and good ADME properties suitable for application in in vivo disease models.

Ferroptosis is an iron-catalysed, non-apoptotic form of regulated necrosis that results in oxidative lipid damage in cell membranes that can be inhibited by the radical-trapping antioxidant Ferrostatin-1 (Fer-1).Novel inhibitors derived from the Fer-1 scaffold inhibited ferroptosis potently but suffered from solubility issues. In this paper, we report the synthesis of a more stable and readily soluble series of Fer-1 analogues that potently inhibit ferroptosis. The most promising compounds (37, 38 and 39) showed an improved protection compared to Fer-1 against multi-organ injury in mice. No toxicity was observed in mice after daily injection of 39 (UAMC-3203) for 4 weeks. UAMC-3203 inserts rapidly in a phospholipid bilayer in silico, which aligns with the current understanding of the mechanism of action of these compounds. Concludingly, these analogues have superior properties compared to Fer-1, show in vivo efficacy and represent novel lead compounds with therapeutic potential in relevant ferroptosis-driven disease models.

Necroptosis contributes to the pathophysiology of several inflammatory, infectious and degenerative disorders. TNF-induced necroptosis involves activation of the receptor-interacting protein kinases 1 and 3 (RIPK1/3) in a necrosome complex, eventually leading to the phosphorylation and relocation of mixed lineage kinase domain like protein (MLKL). Using a high-content screening of small compounds and FDA-approved drug libraries, we identified the anti-cancer drug Sorafenib tosylate as a potent inhibitor of TNF-dependent necroptosis. Interestingly, Sorafenib has a dual activity spectrum depending on its concentration. In murine and human cell lines it induces cell death, while at lower concentrations it inhibits necroptosis, without affecting NF-κB activation. Pull down experiments with biotinylated Sorafenib show that it binds independently RIPK1, RIPK3 and MLKL. Moreover, it inhibits RIPK1 and RIPK3 kinase activity. In vivo Sorafenib protects against TNF-induced systemic inflammatory response syndrome (SIRS) and renal ischemia–reperfusion injury (IRI). Altogether, we show that Sorafenib can, next to the reported Braf/Mek/Erk and VEGFR pathways, also target the necroptotic pathway and that it can protect in an acute inflammatory RIPK1/3-mediated pathology.

The Aurora kinase family (Aurora A, B and C) are crucial regulators of several mitotic events, including cytokinesis. Increased expression of these kinases is associated with tumorigenesis and several compounds targeting Aurora kinase are under evaluation in clinical trials (a.o. AT9283, AZD1152, Danusertib, MLN8054). Here, we demonstrate that the pan-Aurora kinase inhibitor Tozasertib (VX-680 and MK-0457) not only causes cytokinesis defects through Aurora kinase inhibition, but is also a potent inhibitor of necroptosis, a cell death process regulated and executed by the RIPK1, RIPK3 and MLKL signalling axis. Tozasertib’s potency to inhibit RIPK1-dependent necroptosis and to block cytokinesis in cells is in the same concentration range, with an IC50 of 1.06 µM and 0.554 µM, respectively. A structure activity relationship (SAR) analysis of 67 Tozasertib analogues, modified at 4 different positions, allowed the identification of analogues that showed increased specificity for either cytokinesis inhibition or for necroptosis inhibition, reflecting more specific inhibition of Aurora kinase or RIPK1, respectively. These results also suggested that RIPK1 and Aurora kinases are functionally non-interacting targets of Tozasertib and its analogues. Indeed, more specific Aurora kinase inhibitors did not show any effect in necroptosis and Necrostatin-1s treatment did not result in cytokinesis defects, demonstrating that both cellular processes are not interrelated. Finally, Tozasertib inhibited recombinant human RIPK1, human Aurora A and human Aurora B kinase activity, but not RIPK3. The potency ranking of the newly derived Tozasertib analogues and their specificity profile, as observed in cellular assays, coincide with ADP-Glo recombinant kinase activity assays. Overall, we show that Tozasertib not only targets Aurora kinases but also RIPK1 independently, and that we could generate analogues with increased selectivity to RIPK1 or Aurora kinases, respectively.