Ferroptosis is an iron-catalyzed, nonapoptotic 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 multiorgan 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. In conclusion, 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.

Receptor interacting protein kinase 1 (RIPK1) plays a crucial role in tumor necrosis factor (TNF)-induced necroptosis, suggesting that this pathway might be druggable. Most inhibitors of RIPK1 are classified as either type II or type III kinase inhibitors. This opened up some interesting perspectives for the discovery of novel inhibitors that target the active site of RIPK1. Tozasertib, a type I pan-aurora kinase (AurK) inhibitor, was found to show a very high affinity for RIPK1. Because tozasertib presents the typical structural elements of a type I kinase inhibitor, the development of structural analogues of tozasertib is a good starting point for identifying novel type I RIPK1 inhibitors. In this paper, we identified interesting inhibitors of mTNF-induced necroptosis with no significant effect on AurK A and B, resulting in no nuclear abnormalities as is the case for tozasertib. Compounds 71 and 72 outperformed tozasertib in an in vivo TNF-induced systemic inflammatory response syndrome (SIRS) mouse model.

Ferroptosis is an iron dependent form of necrosis, involved in different pathologies such as kidney failure and neurodegenerative diseases. Glutathione peroxidase 4 (GPX4) is the central enzyme protecting the cell from ferroptosis. High-throughput screening led to the discovery of ferrostatin-1 (Fer-1) as a potent in vitro inhibitor of ferroptosis. In vivo however, the molecule suffers from instability. Therefore, we developed ferrostatin-analogues with improved solubility and in vivo stability. To verify their in vivo efficacy, we established an acute mouse model of iron poisoning-induced organ injury. Both an excess of the natural ferroptosis inhibitor vitamin E in the feed and overexpression of GPX4 have a protective effect on this iron poisoning model, indicating it is a valuable experimental model for ferroptosis-induced organ injury. Interestingly, our novel ferrostatin analogues effectively decrease several markers for organ injury after iron poisoning. Conclusively, 1) ferroptosis is a detrimental factor in acute iron poisoning, 2) our novel ferrostatin-analogues reduce the severity of organ injury due to acute iron poisoning, and 3) our third generation of ferrostatin-analogues might represent potential leads for the treatment of ferroptosis-driven pathologies.

INTRODUCTION:Formation and enlargement of a necrotic core play a pivotal role in atherogenesis. Since the discovery of necroptosis, which is a regulated form of necrosis, prevention of necrotic cell death has become an attractive therapeutic goal to reduce plaque formation. Areas covered: This review highlights the triggers and consequences of (unregulated) necrosis and necroptosis in atherosclerosis. The authors discuss different pharmacological strategies to inhibit necrotic cell death in advanced atherosclerotic plaques. Expert opinion: Addition of a necrosis or necroptosis inhibitor to standard statin therapy could be a promising strategy for primary prevention of cardiovascular disease. However, a necrosis inhibitor cannot block all necrosis stimuli in atherosclerotic plaques. A necroptosis inhibitor could be more effective, because necroptosis is mediated by specific proteins, termed receptor-interacting serine/threonine-protein kinases (RIPK) and mixed lineage kinase domain-like pseudokinase (MLKL). Currently, only RIPK1 inhibitors have been successfully used in atherosclerotic mouse models to inhibit necroptosis. However, because RIPK1 is involved in both necroptosis and apoptosis, and also RIPK1-independent necroptosis can occur, we feel that targeting RIPK3 and MLKL could be a more attractive therapeutic approach to inhibit necroptosis. Therefore, future challenges will consist of developing RIPK3 and MLKL inhibitors applicable in both preclinical and clinical settings.

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.

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.