Glutaminolysis and Transferrin Regulate Ferroptosis

Targeting mutant p53 for efficient cancer therapy

The tumour suppressor gene TP53 is the most frequently mutated gene in cancer. Wild-type p53 can suppress tumour development by multiple pathways. However, mutation of TP53 and the resultant inactivation of p53 allow evasion of tumour cell death and rapid tumour progression. The high frequency of TP53 mutation in tumours has prompted efforts to restore normal function of mutant p53 and thereby trigger tumour cell death and tumour elimination. Small molecules that can reactivate missense-mutant p53 protein have been identified by different strategies, and two compounds are being tested in clinical trials. Novel approaches for targeting TP53 nonsense mutations are also underway. This Review discusses recent progress in pharmacological reactivation of mutant p53 and highlights problems and promises with these strategies.

Pin1 Promotes Regulated Necrosis Induced by Glutamate in Rat Retinal Neurons via CAST/Calpain2 Pathway

The purpose of the current study was to investigate whether peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) can interact with calpastatin (CAST) and regulate CAST/calpain2, under excessive glutamate conditions, and subsequently regulate necrosis in rat retinal neurons. Glutamate triggered CAST/calpain2-mediated necrosis regulation in primary cultured retinal neurons, as demonstrated by propidium iodide-staining and lactate dehydrogenase assay. Co-IP results and a computer simulation suggested that Pin1 could bind to CAST. Western blot, real-time quantitative polymerase chain reaction, immunofluorescence, and phosphorylation analysis results demonstrated that CAST was regulated by Pin1, as proven by the application of juglone (i.e., a Pin1 specific inhibitor). The retinal ganglion cell 5 cell line, combined with siRNA approach and flow cytometry, was then used to verify the regulatory pathway of Pin1 in CAST/calpain2-modulated neuronal necrosis that was induced by glutamate. Finally, in vivo studies further confirmed the role of Pin1 in CAST/calpain2-modulated necrosis following glutamate excitation, in the rat retinal ganglion cell and inner nuclear layers. In addition, a flash electroretinogram study provided evidence for the recovery of impaired visual function, which was induced by glutamate, with juglone treatment. Our work aims to investigate the involvement of the Pin1-CAST/calpain2 pathway in glutamate-mediated excitotoxicity.

miR-137 regulates ferroptosis by targeting glutamine transporter SLC1A5 in melanoma

Ferroptosis is a regulated form of cell death driven by small molecules or conditions that induce lipid-based reactive oxygen species (ROS) accumulation. This form of iron-dependent cell death is morphologically and genetically distinct from apoptosis, necroptosis, and autophagy. miRNAs are known to play crucial roles in diverse fundamental biological processes. However, to date no study has reported miRNA-mediated regulation of ferroptosis. Here we show that miR-137 negatively regulates ferroptosis by directly targeting glutamine transporter SLC1A5 in melanoma cells. Ectopic expression of miR-137 suppressed SLC1A5, resulting in decreased glutamine uptake and malondialdehyde (MDA) accumulation. Meanwhile, antagomir-mediated inactivation of endogenous miR-137 increased the sensitivity of melanoma cells to erastin- and RSL3-induced ferroptosis. Importantly, knockdown of miR-137 increased the antitumor activity of erastin by enhancing ferroptosis both in vitro and in vivo. Collectively, these data indicate that miR-137 plays a novel and indispensable role in ferroptosis by inhibiting glutaminolysis and suggest a potential therapeutic approach for melanoma.

The Role of Ferroptosis in Cancer Development and Treatment Response

Ferroptosis is a process driven by accumulated iron-dependent lipid ROS that leads to cell death, which is a distinct regulated cell death comparing to other cell death. The lethal metabolic imbalance resulted from GSH depletion or inactivation of glutathione peroxidase 4 is the executor of ferroptosis within the cancer cell. Small molecules-induced ferroptosis has a strong inhibition of tumor growth and enhances the sensitivity of chemotherapeutic drugs, especially in the condition of drug resistance. These evidences have highlighted the importance of ferroptosis in cancer therapeutics, but the roles of ferroptosis in tumorigenesis and development remain unclear. This article provides an overview of the mechanisms of ferroptosis, highlights the role of ferroptosis in cancer and discusses strategies for therapeutic modulation.

An Overview of Pathways of Regulated Necrosis in Acute Kidney Injury

Necrosis is the predominant form of regulated cell death in acute kidney injury (AKI) and represents results in the formation of casts that appear in the urine sedimentation, referred to as muddy brown casts, which are part of the diagnosis of AKI. Pathologists referred to this typical feature as acute tubular necrosis. We are only beginning to understand the dynamics and the molecular pathways that underlie such typical necrotic morphology. In this review, we provide an overview of candidate pathways and summarize the emerging evidence for the relative contribution of these pathways of regulated necrosis, such as necroptosis, ferroptosis, mitochondrial permeability transition-mediated regulated necrosis, parthanatos, and pyroptosis. Inhibitors of each of these pathways are available, and clinical trials may be started after the detection of the most promising drug targets, which will be discussed here. With the global burden of AKI in mind, inhibitiors of regulated necrosis represent promising means to prevent this disease.

The p53 Tumor Suppressor in the Control of Metabolism and Ferroptosis

The p53 tumor suppressor continues to be distinguished as the most frequently mutated gene in human cancer. It is widely believed that the ability of p53 to induce senescence and programmed cell death underlies the tumor suppressor functions of p53. However, p53 has a number of other functions that recent data strongly implicate in tumor suppression, particularly with regard to the control of metabolism and ferroptosis (iron- and lipid-peroxide-mediated cell death) by p53. As reviewed here, the roles of p53 in the control of metabolism and ferroptosis are complex. Wild-type (WT) p53 negatively regulates lipid synthesis and glycolysis in normal and tumor cells, and positively regulates oxidative phosphorylation and lipid catabolism. Mutant p53 in tumor cells does the converse, positively regulating lipid synthesis and glycolysis. The role of p53 in ferroptosis is even more complex: in normal tissues, WT p53 appears to positively regulate ferroptosis, and this pathway appears to play a role in the ability of basal, unstressed p53 to suppress tumor initiation and development. In tumors, other regulators of ferroptosis supersede p53's role, and WT p53 appears to play a limited role; instead, mutant p53 sensitizes tumor cells to ferroptosis. By clearly elucidating the roles of WT and mutant p53 in metabolism and ferroptosis, and establishing these roles in tumor suppression, emerging research promises to yield new therapeutic avenues for cancer and metabolic diseases.

Regulated Cell Death

In this chapter, the various subroutines of regulated cell death are neatly described by highlighting apoptosis and subforms of regulated necrosis such as necroptosis, ferroptosis, pyroptosis, and NETosis. Typically, all forms of regulated necrosis are defined by finite rupture of the plasma cell membrane. Apoptosis is characterized by an enzymatic machinery that consists of caspases which cause the morphologic features of this type of cell death. Mechanistically, apoptosis can be instigated by two major cellular signalling pathways: an intrinsic pathway that is initiated inside cells by mitochondrial release of pro-apoptotic factors or an extrinsic pathway that is initiated at the cell surface by various death receptors. In necroptosis, the biochemical processes are distinct from those found in apoptosis; in particular, there is no caspase activation. As such, necroptosis is a kinase-mediated cell death that relies on “receptor-interacting protein kinase 3” which mediates phosphorylation of the pseudokinase “mixed lineage kinase domain-like protein.” While ferroptosis is an iron-dependent, oxidative form of regulated necrosis that is biochemically characterized by accumulation of ROS from iron metabolism, oxidase activity, and lipid peroxidation products, pyroptosis is defined as a form of cell death (predominantly of phagocytes) that develops during inflammasome activation and is executed by caspase-mediated cleavage of the pore-forming protein gasdermin D. Finally, NETosis refers to a regulated death of neutrophils that is characterized by the release of chromatin-derived weblike structures released into the extracellular space. The chapter ends up with a discussion on the characteristic feature of regulated necrosis: the passive release of large amounts of constitutive DAMPs as a consequence of final plasma membrane rupture as well as the active secretion of inducible DAMPs earlier during the dying process. Notably, per cell death subroutine, the active secretion of inducible DAMPs varies, thereby determining different immunogenicity of dying cells.

Pathological Roles of Iron in Cardiovascular Disease

Iron is an essential mineral required for a variety of vital biological functions. Despite being vital for life, iron also has potentially toxic aspects. Iron has been investigated as a risk factor for coronary artery disease (CAD), however, iron's toxicity in CAD patients still remains controversial. One possible mechanism behind the toxicity of iron is "ferroptosis", a newly described form of irondependent cell death. Ferroptosis is an iron-dependent form of regulated cell death that is distinct from apoptosis, necroptosis, and other types of cell death. Ferroptosis has been reported in ischemiareperfusion (I/R) injury and several other diseases. Recently, we reported that ferroptosis is a significant form of cell death in cardiomyocytes. Moreover, myocardial hemorrhage, a major event in the pathogenesis of heart failure, could trigger the release of free iron into cardiac muscle and is an independent predictor of adverse left ventricular remodeling after myocardial infarction. Iron deposition in the heart can now be detected with advanced imaging methods, such as T2 star (T2*) cardiac magnetic resonance imaging, which can non-invasively predict iron levels in the myocardium and detect myocardial hemorrhage, thus existing technology could be used to assess myocardial iron. We will discuss the role of iron in cardiovascular diseases and especially with regard to myocardial I/R injury.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

CHAC1 degradation of glutathione enhances cystine-starvation-induced necroptosis and ferroptosis in human triple negative breast cancer cells via the GCN2-eIF2α-ATF4 pathway

Cancer cells exhibit an abnormal amino acid metabolism and a dependence on specific amino acids, which might provide potential targets for treating cancer patients. In this study, we demonstrated that human triple negative breast cancer (TNBC) cells were highly susceptible to cystine starvation. We found that necrostatin-1 (Nec-1, a RIP1 inhibitor), necrosulfonamide (an MLKL inhibitor), deferoxamine (an ion chelator), ferrostatin-1 (a ferroptosis inhibitor) and RIP1 knockdown can prevent cystine-starvation-induced cell death, suggesting that cystine starvation induces necroptosis and ferroptosis in TNBC cells. Moreover, cystine starvation induced mitochondrial fragmentation, dysfunction, and ROS production. A mitochondrial ROS scavenger, Necrox-5, can prevent cystine-starvation-induced cell death. In addition, cystine starvation was found to activate GCN2, but not PERK, to increase the phosphorylation of eIF2α at serine 51, the protein expression of ATF4, and the expression of ATF4 target genes such as CHAC1, which might be downstream of the RIP1/RIP3-MLKL pathway and contribute to cystine-starvation-induced cell death. Knockdown of CHAC1 rescued the cystine-starvation-induced reduction in glutathione (GSH) levels and cell death. Furthermore, N-acetyl-cysteine (NAC), Trolox, and Nec-1 significantly prevented the cystine-starvation-induced increase in intracellular ROS levels, mitochondrial fragmentation and cell death. In summary, these results suggest that CHAC1 degradation of GSH enhances cystine-starvation-induced necroptosis and ferroptosis through the activated GCN2-eIF2α-ATF4 pathway in TNBC cells. Our findings improve our understanding of the mechanism underlying cystine-starvation-induced TNBC cell death.

Acetylation Is Crucial for p53-Mediated Ferroptosis and Tumor Suppression

Although previous studies indicate that loss of p53-mediated cell cycle arrest, apoptosis, and senescence does not completely abrogate its tumor suppression function, it is unclear how the remaining activities of p53 are regulated. Here, we have identified an acetylation site at lysine K98 in mouse p53 (or K101 for human p53). Whereas the loss of K98 acetylation (p53^K98R) alone has very modest effects on p53-mediated transactivation, simultaneous mutations at all four acetylation sites (p53^4KR: K98R+ 3KR[K117R+K161R+K162R]) completely abolish its ability to regulate metabolic targets, such as TIGAR and SLC7A11. Notably, in contrast to p53^3KR, p53^4KR is severely defective in suppressing tumor growth in mouse xenograft models. Moreover, p53^4KR is still capable of inducing the p53-Mdm2 feedback loop, but p53-dependent ferroptotic responses are markedly abrogated. Together, these data indicate the critical role of p53 acetylation in ferroptotic responses and its remaining tumor suppression activity.

To eat or not to eat-the metabolic flavor of ferroptosis

Ferroptosis is a newly defined iron-dependent, non-apoptotic mode of cell death with necrotic morphology. Distinctive from other death mechanisms, ferroptosis requires cellular iron and lipid peroxides, and is dictated by specific cellular metabolic processes. Importantly, ferroptosis has been implicated in a plethora of human diseases. This paper reviews the recent advances and outstanding questions of the field by focusing on the role of cellular metabolism in ferroptosis. The relevance of ferroptosis to disease and therapy is also discussed.

Oncogene-Selective Sensitivity to Synchronous Cell Death following Modulation of the Amino Acid Nutrient Cystine

Cancer cells reprogram their metabolism, altering both uptake and utilization of extracellular nutrients. We individually depleted amino acid nutrients from isogenic cells expressing commonly activated oncogenes to identify correspondences between nutrient supply and viability. In HME (human mammary epithelial) cells, deprivation of cystine led to increased cell death in cells expressing an activated epidermal growth factor receptor (EGFR) mutant. Cell death occurred via synchronous ferroptosis, with generation of reactive oxygen species (ROS). Hydrogen peroxide promoted cell death, as both catalase and inhibition of NADPH oxidase 4 (NOX4) blocked ferroptosis. Blockade of EGFR or mitogen-activated protein kinase (MAPK) signaling similarly protected cells from ferroptosis, whereas treatment of xenografts derived from EGFR mutant non-small-cell lung cancer (NSCLC) with a cystine-depleting enzyme inhibited tumor growth in mice. Collectively, our results identify a potentially exploitable sensitization of some EGFR/MAPK-driven tumors to ferroptosis following cystine depletion.

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A nutrient depletion screen revealed a selective role for cystine in promoting viability

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Cystine was shown to promote viability by preventing ferroptosis

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Sensitivity to depletion of cystine was related to activation of MAPK

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Depletion of cystine inhibited tumor growth in a NSCLC xenograft model

Cysteine Dioxygenase 1 Mediates Erastin-Induced Ferroptosis in Human Gastric Cancer Cells

BACKGROUND

Ferroptosis is a recently discovered form of iron-dependent nonapoptotic cell death. It is characterized by loss of the activity of the lipid repair enzyme, glutathione peroxidase 4 (GPX4), and accumulation of lethal reactive lipid oxygen species. However, we still know relatively little about ferroptosis and its molecular mechanism in gastric cancer (GC) cells. Here, we demonstrate that erastin, a classic inducer of ferroptosis, induces this form of cell death in GC cells and that cysteine dioxygenase 1 (CDO1) plays an important role in this process.

METHODS

We performed quantitative real-time polymerase chain reaction, Western blotting, cell viability assay, reactive oxygen species (ROS) assay, glutathione assay, lipid peroxidation assay, RNAi and gene transfection, immunofluorescent staining, dual-luciferase reporter assay, transmission electron microscopy, and chromatin immunoprecipitation assay to study the regulation of ferroptosis in GC cells. Mouse xenograft assay was used to figure out the mechanism in vivo.

RESULTS

Silencing CDO1 inhibited erastin-induced ferroptosis in GC cells both in vitro and in vivo. Suppression of CDO1 restored cellular GSH levels, prevented ROS generation, and reduced malondialdehyde, one of the end products of lipid peroxidation. In addition, silencing COO1 maintained mitochondrial morphologic stability in erastin-treated cells. Mechanistically, c-Myb transcriptionally regulated CDO1, and inhibition of CDO1 expression upregulated GPX4 expression.

CONCLUSIONS

Our findings give a better understanding of ferroptosis and its molecular mechanism in GC cells, gaining insight into ferroptosis-mediated cancer treatment.

Lipoxygenase-mediated generation of lipid peroxides enhances ferroptosis induced by erastin and RSL3

In cancer cells the small compounds erastin and RSL3 promote a novel type of cell death called ferroptosis, which requires iron-dependent accumulation of lipid reactive oxygen species. Here we assessed the contribution of lipid peroxidation activity of lipoxygenases (LOX) to ferroptosis in oncogenic Ras-expressing cancer cells. Several 12/15-LOX inhibitors prevented cell death induced by erastin and RSL3. Furthermore, siRNA-mediated silencing of ALOX15 significantly decreased both erastin-induced and RSL3-induced ferroptotic cell death, whereas exogenous overexpression of ALOX15 enhanced the effect of these compounds. Immunofluorescence analyses revealed that the ALOX15 protein consistently localizes to cell membrane during the course of ferroptosis. Importantly, treatments of cells with ALOX15-activating compounds accelerated cell death at low, but not high doses of erastin and RSL3. These observations suggest that tumor ferroptosis is promoted by LOX-catalyzed lipid hydroperoxide generation in cellular membranes.

Live or let die: Neuroprotective and anti-cancer effects of nutraceutical antioxidants

Diet sources are closely involved in the pathogenesis of diverse neuropsychiatric disorders and cancers, in addition to inherited factors. Currently, natural products or nutraceuticals (commonly called medical foods) are increasingly employed for adjunctive therapy of these patients. However, the potential molecular mechanisms of the nutrient efficacy remain elusive. In this review, we summarized the neuroprotective and anti-cancer mechanisms of nutraceuticals. It was concluded that the nutraceuticals exerted neuroprotection and suppressed tumor growth possibly through the differential modulations of redox homeostasis. In addition, the balance between reactive oxygen species (ROS) production and ROS elimination was manipulated by multiple molecular mechanisms, including cell signaling pathways, inflammation, transcriptional regulation and epigenetic modulation, which were involved in the therapeutic potential of nutraceutical antioxidants against neurological diseases and cancers. We specifically proposed that ROS scavenging was integral in the neuroprotective potential of nutraceuticals, while alternation of ROS level (either increase or decrease) or disruption of redox homeostasis (ROS addiction) constituted the anti-cancer property of these compounds. We also hypothesized that ROS-associated ferroptosis, a novel type of lipid ROS-dependent regulatory cell death, was likely to be a critical mechanism for the nutraceutical antioxidants. Targeting ferroptosis is advantageous to develop new nutraceuticals with more effective and lower adverse reactions for curing patients with neuropsychiatric diseases or carcinomas.

NRF2 Is a Major Target of ARF in p53-Independent Tumor Suppression

Although ARF can suppress tumor growth by activating p53 function, the mechanisms by which it suppresses tumor growth independently of p53 are not well understood. Here, we identified ARF as a key regulator of nuclear factor E2-related factor 2 (NRF2) through complex purification. ARF inhibits the ability of NRF2 to transcriptionally activate its target genes, including SLC7A11, a component of the cystine/glutamate antiporter that regulates reactive oxygen species (ROS)-induced ferroptosis. As a consequence, ARF expression sensitizes cells to ferroptosis in a p53-independent manner while ARF depletion induces NRF2 activation and promotes cancer cell survival in response to oxidative stress. Moreover, the ability of ARF to induce p53-independent tumor growth suppression in mouse xenograft models is significantly abrogated upon NRF2 overexpression. These results demonstrate that NRF2 is a major target of p53-independent tumor suppression by ARF and also suggest that the ARF-NRF2 interaction acts as a new checkpoint for oxidative stress responses.

How do we fit ferroptosis in the family of regulated cell death?

In the last few years many new cell death modalities have been described. To classify different types of cell death, the term 'regulated cell death' was introduced to discriminate it from 'accidental cell death'. Regulated cell death involves the activation of genetically encoded molecular machinery that couples the presence of some signal to cell death. These forms of cell death, like apoptosis, necroptosis and pyroptosis have important physiological roles in development, tissue repair, and immunity. Accidental cell death occurs in response to physical or chemical insults and occurs independently of molecular signalling pathways. Ferroptosis, an emerging and recently (re)discovered type of regulated cell death occurs through Fe(II)-dependent lipid peroxidation when the reduction capacity of a cell is insufficient. Ferroptosis is coined after the requirement for free ferrous iron. Here, we will consider the extent to which ferroptosis is similar to other regulated cell deaths and explore emerging ideas about the physiological role of ferroptosis.

Ferroptosis: A Regulated Cell Death Nexus Linking Metabolism, Redox Biology, and Disease

Ferroptosis is a form of regulated cell death characterized by the iron-dependent accumulation of lipid hydroperoxides to lethal levels. Emerging evidence suggests that ferroptosis represents an ancient vulnerability caused by the incorporation of polyunsaturated fatty acids into cellular membranes, and cells have developed complex systems that exploit and defend against this vulnerability in different contexts. The sensitivity to ferroptosis is tightly linked to numerous biological processes, including amino acid, iron, and polyunsaturated fatty acid metabolism, and the biosynthesis of glutathione, phospholipids, NADPH, and coenzyme Q10. Ferroptosis has been implicated in the pathological cell death associated with degenerative diseases (i.e., Alzheimer's, Huntington's, and Parkinson's diseases), carcinogenesis, stroke, intracerebral hemorrhage, traumatic brain injury, ischemia-reperfusion injury, and kidney degeneration in mammals and is also implicated in heat stress in plants. Ferroptosis may also have a tumor-suppressor function that could be harnessed for cancer therapy. This Primer reviews the mechanisms underlying ferroptosis, highlights connections to other areas of biology and medicine, and recommends tools and guidelines for studying this emerging form of regulated cell death.

t-BuOOH induces ferroptosis in human and murine cell lines

Reactive oxygen species (ROS)-induced apoptosis has been extensively studied. Increasing evidence suggests that ROS, for instance, induced by hydrogen peroxide (H₂O₂), might also trigger regulated necrotic cell death pathways. Almost nothing is known about the cell death pathways triggered by tertiary-butyl hydroperoxide (t-BuOOH), a widely used inducer of oxidative stress. The lipid peroxidation products induced by t-BuOOH are involved in the pathophysiology of many diseases, such as cancer, cardiovascular diseases, or diabetes. In this study, we exposed murine fibroblasts (NIH3T3) or human keratinocytes (HaCaT) to t-BuOOH (50 or 200 μM, respectively) which induced a rapid necrotic cell death. Well-established regulators of cell death, i.e., p53, poly(ADP)ribose polymerase-1 (PARP-1), the stress kinases p38 and c-Jun N-terminal-kinases 1/2 (JNK1/2), or receptor-interacting serine/threonine protein kinase 1 (RIPK1) and 3 (RIPK3), were not required for t-BuOOH-mediated cell death. Using the selective inhibitors ferrostatin-1 (1 μM) and liproxstatin-1 (1 μM), we identified ferroptosis, a recently discovered cell death mechanism dependent on iron and lipid peroxidation, as the main cell death pathway. Accordingly, t-BuOOH exposure resulted in a ferrostatin-1- and liproxstatin-1-sensitive increase in lipid peroxidation and cytosolic ROS. Ferroptosis was executed independently from other t-BuOOH-mediated cellular damages, i.e., loss of mitochondrial membrane potential, DNA double-strand breaks, or replication block. H₂O₂ did not cause ferroptosis at equitoxic concentrations (300 μM) and induced a (1) lower and (2) ferrostatin-1- or liproxstatin-1-insensitive increase in lipid peroxidation. We identify that t-BuOOH and H₂O₂ produce a different pattern of lipid peroxidation, thereby leading to different cell death pathways and present t-BuOOH as a novel inducer of ferroptosis.

Antihypertrophic Effects of Small Molecules that Maintain Mitochondrial ATP Levels Under Hypoxia

Since impaired mitochondrial ATP production in cardiomyocytes is thought to lead to heart failure, a drug that protects mitochondria and improves ATP production under disease conditions would be an attractive treatment option. In this study, we identified small-molecule drugs, including the anti-parasitic agent, ivermectin, that maintain mitochondrial ATP levels under hypoxia in cardiomyocytes. Mechanistically, transcriptomic analysis and gene silencing experiments revealed that ivermectin increased mitochondrial ATP production by inducing Cox6a2, a subunit of the mitochondrial respiratory chain. Furthermore, ivermectin inhibited the hypertrophic response of human induced pluripotent stem cell-derived cardiomyocytes. Pharmacological inhibition of importin β, one of the targets of ivermectin, exhibited protection against mitochondrial ATP decline and cardiomyocyte hypertrophy. These findings indicate that maintaining mitochondrial ATP under hypoxia may prevent hypertrophy and improve cardiac function, providing therapeutic options for mitochondrial dysfunction.

Iron accumulation in senescent cells is coupled with impaired ferritinophagy and inhibition of ferroptosis

Cellular senescence is characterised by the irreversible arrest of proliferation, a pro-inflammatory secretory phenotype and evasion of programmed cell death mechanisms. We report that senescence alters cellular iron acquisition and storage and also impedes iron-mediated cell death pathways. Senescent cells, regardless of stimuli (irradiation, replicative or oncogenic), accumulate vast amounts of intracellular iron (up to 30-fold) with concomitant changes in the levels of iron homeostasis proteins. For instance, ferritin (iron storage) levels provided a robust biomarker of cellular senescence, for associated iron accumulation and for resistance to iron-induced toxicity. Cellular senescence preceded iron accumulation and was not perturbed by sustained iron chelation (deferiprone). Iron accumulation in senescent cells was driven by impaired ferritinophagy, a lysosomal process that promotes ferritin degradation and ferroptosis. Lysosomal dysfunction in senescent cells was confirmed through several markers, including the build-up of microtubule-associated protein light chain 3 (LC3-II) in autophagosomes. Impaired ferritin degradation explains the iron accumulation phenotype of senescent cells, whereby iron is effectively trapped in ferritin creating a perceived cellular deficiency. Accordingly, senescent cells were highly resistant to ferroptosis. Promoting ferritin degradation by using the autophagy activator rapamycin averted the iron accumulation phenotype of senescent cells, preventing the increase of TfR1, ferritin and intracellular iron, but failed to re-sensitize these cells to ferroptosis. Finally, the enrichment of senescent cells in mouse ageing hepatic tissue was found to accompany iron accumulation, an elevation in ferritin and mirrored our observations using cultured senescent cells.

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Altered iron homeostasis in senescent cells is driven by impaired ferritinophagy.

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Impaired ferritinophagy causes functional cellular iron deficiency.

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senescent cells are resistant to iron mediated cell death including ferroptosis.

Ferroptosis and autophagy induced cell death occur independently after siramesine and lapatinib treatment in breast cancer cells

Ferroptosis is a cell death pathway characterized by iron-dependent accumulation of reactive oxygen species (ROS) within the cell. The combination of siramesine, a lysosome disruptor, and lapatinib, a dual tyrosine kinase inhibitor, has been shown to synergistically induce cell death in breast cancer cells mediated by ferroptosis. These treatments also induce autophagy but its role in this synergistic cell death is unclear. In this study, we determined that siramesine and lapatinib initially induced ferroptosis but changes to an autophagy induced cell death after 24 hours. Furthermore, we found that intracellular iron level increased in a time dependent manner following treatment accompanied by an increase in ROS. Using the iron chelator deferoxamine (DFO) or the ROS scavenger alpha-tocopherol decreased both autophagy flux and cell death. We further discovered that decreased expression of the iron storage protein, ferritin was partially dependent upon autophagy degradation. In contrast, the expression of transferrin, which is responsible for the transport of iron into cells, is increased following treatment with lapatinib alone or in combination with siramesine. This indicates that ferroptosis and autophagy induced cell death occur independently but both are mediated by iron dependent ROS generation in breast cancer cells.

Iron, Oxidative Damage and Ferroptosis in Rhabdomyosarcoma

Recent data have indicated a fundamental role of iron in mediating a non-apoptotic and non-necrotic oxidative form of programmed cell death termed ferroptosis that requires abundant cytosolic free labile iron to promote membrane lipid peroxidation. Different scavenger molecules and detoxifying enzymes, such as glutathione (GSH) and glutathione peroxidase 4 (GPX4), have been shown to overwhelm or exacerbate ferroptosis depending on their expression magnitude. Ferroptosis is emerging as a potential weapon against tumor growth since it has been shown to potentiate cell death in some malignancies. However, this mechanism has been poorly studied in Rhabdomyosarcoma (RMS), a myogenic tumor affecting childhood and adolescence. One of the main drivers of RMS genesis is the Retrovirus Associated DNA Sequences/Extracellular signal Regulated Kinases (RAS/ERK)signaling pathway, the deliberate activation of which correlates with tumor aggressiveness and oxidative stress levels. Since recent studies have indicated that treatment with oxidative inducers can significantly halt RMS tumor progression, in this review we covered different aspects, ranging from iron metabolism in carcinogenesis and tumor growth, to mechanisms of iron-mediated cell death, to highlight the potential role of ferroptosis in counteracting RMS growth.

Characterization of ferroptosis in murine models of hemochromatosis

Ferroptosis is a recently identified iron-dependent form of nonapoptotic cell death implicated in brain, kidney, and heart pathology. However, the biological roles of iron and iron metabolism in ferroptosis remain poorly understood. Here, we studied the functional role of iron and iron metabolism in the pathogenesis of ferroptosis. We found that ferric citrate potently induces ferroptosis in murine primary hepatocytes and bone marrow-derived macrophages. Next, we screened for ferroptosis in mice fed a high-iron diet and in mouse models of hereditary hemochromatosis with iron overload. We found that ferroptosis occurred in mice fed a high-iron diet and in two knockout mouse lines that develop severe iron overload (Hjv^-/- and Smad4^Alb/Alb mice) but not in a third line that develops only mild iron overload (Hfe^-/- mice). Moreover, we found that iron overload-induced liver damage was rescued by the ferroptosis inhibitor ferrostatin-1. To identify the genes involved in iron-induced ferroptosis, we performed microarray analyses of iron-treated bone marrow-derived macrophages. Interestingly, solute carrier family 7, member 11 (Slc7a11), a known ferroptosis-related gene, was significantly up-regulated in iron-treated cells compared with untreated cells. However, genetically deleting Slc7a11 expression was not sufficient to induce ferroptosis in mice. Next, we studied iron-treated hepatocytes and bone marrow-derived macrophages isolated from Slc7a11^-/- mice fed a high-iron diet.

CONCLUSION

We found that iron treatment induced ferroptosis in Slc7a11^-/- cells, indicating that deleting Slc7a11 facilitates the onset of ferroptosis specifically under high-iron conditions; these results provide compelling evidence that iron plays a key role in triggering Slc7a11-mediated ferroptosis and suggest that ferroptosis may be a promising target for treating hemochromatosis-related tissue damage. (Hepatology 2017;66:449-465).

EGLN1/c-Myc Induced Lymphoid-Specific Helicase Inhibits Ferroptosis through Lipid Metabolic Gene Expression Changes

Ferroptosis is a newly discovered form of non-apoptotic cell death in multiple human diseases. However, the epigenetic mechanisms underlying ferroptosis remain poorly defined. First, we demonstrated that lymphoid-specific helicase (LSH), which is a DNA methylation modifier, interacted with WDR76 to inhibit ferroptosis by activating lipid metabolism-associated genes, including GLUT1, and ferroptosis related genes SCD1 and FADS2, in turn, involved in the Warburg effect. WDR76 targeted these genes expression in dependent manner of LSH and chromatin modification in DNA methylation and histone modification. These effects were dependent on iron and lipid reactive oxygen species. We further demonstrated that EGLN1 and c-Myc directly activated the expression of LSH by inhibiting HIF-1α. Finally, we demonstrated that LSH functioned as an oncogene in lung cancer in vitro and in vivo. Therefore, our study elucidates the molecular basis of the c-Myc/EGLN1-mediated induction of LSH expression that inhibits ferroptosis, which can be exploited for the development of therapeutic strategies targeting ferroptosis for the treatment of cancer.

Lipid Peroxidation-Dependent Cell Death Regulated by GPx4 and Ferroptosis

Glutathione peroxidase 4 (Phospholipid hydroperoxide glutathione peroxidase, PHGPx) can directly reduce phospholipid hydroperoxide. Depletion of GPx4 induces lipid peroxidation-dependent cell death in embryo, testis, brain, liver, heart, and photoreceptor cells of mice. Administration of vitamin E in tissue specific GPx4 KO mice restored tissue damage in testis, liver, and heart. These results indicate that suppression of phospholipid peroxidation is essential for cell survival in normal tissues in mice. Ferroptosis is an iron-dependent non-apoptotic cell death that can elicited by pharmacological inhibiting the cystine/glutamate antiporter, system Xc^- (type I) or directly binding and loss of activity of GPx4 (Type II) in cancer cells with high level RAS-RAF-MEK pathway activity or p53 expression, but not in normal cells. Ferroptosis by Erastin (Type I) and RSL3 (RAS-selective lethal 3, Type II) treatment was suppressed by an iron chelator, vitamin E and Ferrostatin-1, antioxidant compound. GPx4 can regulate ferroptosis by suppression of phospholipid peroxidation in erastin and RSL3-induced ferroptosis. Recent works have identified several regulatory factors of erastin and RSL3-induced ferroptosis. In our established GPx4-deficient MEF cells, depletion of GPx4 induce iron and 15LOX-independent lipid peroxidation at 26 h and caspase-independent cell death at 72 h, whereas erastin and RSL3 treatment resulted in iron-dependent ferroptosis by 12 h. These results indicated the possibility that the mechanism of GPx4-depleted cell death might be different from that of ferroptosis induced by erastin and RSL3.

Necroptosis in cancer: An angel or a demon?

In the past few decades, apoptosis has been regarded as the only form of programmed cell death. However, the traditional view has been challenged by the identification of several forms of regulated necrosis, including necroptosis. Necroptosis is typified by a necrotic cell death morphology and is controlled by RIP1, RIP3, and mixed lineage kinase domain-like protein. The physiological role of necroptosis is to serve as a "fail-safe" form of cell death for cells that fail to undergo apoptosis during embryonic development and disease defense. Currently, established studies have indicated that necroptosis is involved in cancer initiation and progression. Although elevated necroptosis contributes to cancer cell death, extensive cell death also increases the risk of proliferation and metastasis of the surviving cells by inducing the generation reactive oxygen species, activation of inflammation, and suppression of the immune response. Thus, questions regarding the overall impact of necroptosis on cancer remain open. In this review, we introduce the basic knowledge regarding necroptosis, summarize its dual effects on cancer progression, and analyze its advantages and disadvantages in clinical applications.

Antioxidants Mediate Both Iron Homeostasis and Oxidative Stress

Oxidative stress is a common denominator in the pathogenesis of many chronic diseases. Therefore, antioxidants are often used to protect cells and tissues and reverse oxidative damage. It is well known that iron metabolism underlies the dynamic interplay between oxidative stress and antioxidants in many pathophysiological processes. Both iron deficiency and iron overload can affect redox state, and these conditions can be restored to physiological conditions using iron supplementation and iron chelation, respectively. Similarly, the addition of antioxidants to these treatment regimens has been suggested as a viable therapeutic approach for attenuating tissue damage induced by oxidative stress. Notably, many bioactive plant-derived compounds have been shown to regulate both iron metabolism and redox state, possibly through interactive mechanisms. This review summarizes our current understanding of these mechanisms and discusses compelling preclinical evidence that bioactive plant-derived compounds can be both safe and effective for managing both iron deficiency and iron overload conditions.

Small molecule probes for cellular death machines

The past decade has witnessed a significant expansion of our understanding about the regulated cell death mechanisms beyond apoptosis. The application of chemical biological approaches had played a major role in driving these exciting discoveries. The discovery and use of small molecule probes in cell death research has not only revealed significant insights into the regulatory mechanism of cell death but also provided new drug targets and lead drug candidates for developing therapeutics of human diseases with huge unmet need. Here, we provide an overview of small molecule modulators for necroptosis and ferroptosis, two non-apoptotic cell death mechanisms, and discuss the molecular pathways and relevant pathophysiological mechanisms revealed by the judicial applications of such small molecule probes. We suggest that the development and applications of small molecule probes for non-apoptotic cell death mechanisms provide an outstanding example showcasing the power of chemical biology in exploring novel biological mechanisms.

Signalome-wide RNAi screen identifies GBA1 as a positive mediator of autophagic cell death

Activating alternative cell death pathways, including autophagic cell death, is a promising direction to overcome the apoptosis resistance observed in various cancers. Yet, whether autophagy acts as a death mechanism by over consumption of intracellular components is still controversial and remains undefined at the ultrastructural and the mechanistic levels. Here we identified conditions under which resveratrol-treated A549 lung cancer cells die by a mechanism that fulfills the previous definition of autophagic cell death. The cells displayed a strong and sustained induction of autophagic flux, cell death was prevented by knocking down autophagic genes and death occurred in the absence of apoptotic or necroptotic pathway activation. Detailed ultrastructural characterization revealed additional critical events, including a continuous increase over time in the number of autophagic vacuoles, in particular autolysosomes, occupying most of the cytoplasm at terminal stages. This was followed by loss of organelles, disruption of intracellular membranes including the swelling of perinuclear space and, occasionally, a unique type of nuclear shedding. A signalome-wide shRNA-based viability screen was applied to identify positive mediators of this type of autophagic cell death. One top hit was GBA1, the Gaucher disease-associated gene, which encodes glucocerebrosidase, an enzyme that metabolizes glucosylceramide to ceramide and glucose. Interestingly, glucocerebrosidase expression levels and activity were elevated, concomitantly with increased intracellular ceramide levels, both of which correlated in time with the appearance of the unique death characteristics. Transfection with siGBA1 attenuated the increase in glucocerebrosidase activity and the intracellular ceramide levels. Most importantly, GBA1 knockdown prevented the strong increase in LC3 lipidation, and many of the ultrastructural changes characteristic of this type of autophagic cell death, including a significant decrease in cytoplasmic area occupied by autophagic vacuoles. Together, these findings highlight the critical role of GBA1 in mediating enhanced self-consumption of intracellular components and endomembranes, leading to autophagic cell death.

Autophagy and Ferroptosis - What's the Connection?

PURPOSE OF REVIEW

Autophagy is a conserved intracellular degradation system and plays a dual role in cell death, depending on context and phase. Ferroptosis is a new form of regulated cell death that mainly depends on iron accumulation and lipid peroxidation. In this review, we summarize the processes of autophagy and ferroptosis and discuss their crosstalk mechanisms at the molecular level.

RECENT FINDINGS

The original study shows that ferroptosis is morphologically, biochemically, and genetically distinct from autophagy and other types of cell death. However, recent studies demonstrate that activation of ferroptosis is indeed dependent on the induction of autophagy. Additionally, many ferroptosis regulators such as SLC7A11, GPX4, NRF2, p53, HSPB1, CISD1, FANCD2, and ACSL4 have been identified as potential regulators of autophagy.

SUMMARY

This review not only highlights the importance of autophagy as an emerging mechanism of ferroptosis, but also raises new insights regarding regulated cell death.

HSPA5 Regulates Ferroptotic Cell Death in Cancer Cells

Ferroptosis is a form of regulated cell death driven by oxidative injury promoting lipid peroxidation, although detailed molecular regulators are largely unknown. Here, we show that heatshock 70-kDa protein 5 (HSPA5) negatively regulates ferroptosis in human pancreatic ductal adenocarcinoma (PDAC) cells. Mechanistically, activating transcription factor 4 (ATF4) resulted in the induction of HSPA5, which in turn bound glutathione peroxidase 4 (GPX4) and protected against GPX4 protein degradation and subsequent lipid peroxidation. Importantly, the HSPA5-GPX4 pathway mediated ferroptosis resistance, limiting the anticancer activity of gemcitabine. Genetic or pharmacologic inhibition of the HSPA5-GPX4 pathway enhanced gemcitabine sensitivity by disinhibiting ferroptosis in vitro and in both subcutaneous and orthotopic animal models of PDAC. Collectively, these findings identify a novel role of HSPA5 in ferroptosis and suggest a potential therapeutic strategy for overcoming gemcitabine resistance. Cancer Res; 77(8); 2064-77. ©2017 AACR.

Inhibition of neuronal ferroptosis protects hemorrhagic brain

Intracerebral hemorrhage (ICH) causes high mortality and morbidity, but our knowledge of post-ICH neuronal death and related mechanisms is limited. In this study, we first demonstrated that ferroptosis, a newly identified form of cell death, occurs in the collagenase-induced ICH model in mice. We found that administration of ferrostatin-1, a specific inhibitor of ferroptosis, prevented neuronal death and reduced iron deposition induced by hemoglobin in organotypic hippocampal slice cultures (OHSCs). Mice treated with ferrostatin-1 after ICH exhibited marked brain protection and improved neurologic function. Additionally, we found that ferrostatin-1 reduced lipid reactive oxygen species production and attenuated the increased expression level of PTGS2 and its gene product cyclooxygenase-2 ex vivo and in vivo. Moreover, ferrostatin-1 in combination with other inhibitors that target different forms of cell death prevented hemoglobin-induced cell death in OHSCs and human induced pluripotent stem cell-derived neurons better than any inhibitor alone. These results indicate that ferroptosis contributes to neuronal death after ICH, that administration of ferrostatin-1 protects hemorrhagic brain, and that cyclooxygenase-2 could be a biomarker of ferroptosis. The insights gained from this study will advance our knowledge of the post-ICH cell death cascade and be essential for future preclinical studies.

Ferroptosis Inhibition: Mechanisms and Opportunities

The past decade has yielded tremendous insights into how cells die. This has come with our understanding that several distinct forms of cell death are encompassed under the umbrella term necrosis. Among these distinct forms of regulated necrotic cell death, ferroptosis has attracted considerable attention owing to its putative involvement in diverse pathophysiological processes. A key feature of the ferroptosis process is the requirement of phospholipid peroxidation, a process that has been linked with several human pathologies. Now with the establishment of a connection between lipid peroxidation and a distinctive cell death pathway, the search for new small molecules able to suppress lipid peroxidation has gained momentum and may yield novel cytoprotective strategies. We review here advances in our understanding of the ferroptotic process and summarize the development of lipid peroxidation inhibitors with the ultimate goal of suppressing ferroptosis-relevant cell death and related pathologies.

Iron and ferroptosis: A still ill-defined liaison

Ferroptosis is a recently described form of regulated necrotic cell death, which appears to contribute to a number of diseases, such as tissue ischemia/reperfusion injury, acute renal failure, and neurodegeneration. A hallmark of ferroptosis is iron-dependent lipid peroxidation, which can be inhibited by the key ferroptosis regulator glutathione peroxidase 4(Gpx4), radical trapping antioxidants and ferroptosis-specific inhibitors, such as ferrostatins and liproxstatins, as well as iron chelation. Although great strides have been made towards a better understanding of the proximate signals of distinctive lipid peroxides in ferroptosis, still little is known about the mechanistic implication of iron in the ferroptotic process. Hence, this review aims at summarizing recent advances in our understanding to what is known about enzymatic and nonenzymatic routes of lipid peroxidation, the involvement of iron in this process and the identification of novel players in ferroptotic cell death. Additionally, we review early works carried out long time before the term "ferroptosis" was actually introduced but which were instrumental in a better understanding of the role of ferroptosis in physiological and pathophysiological contexts. © 2017 IUBMB Life, 69(6):423-434, 2017.

Reactive oxygen species and cancer paradox: To promote or to suppress?

Reactive oxygen species (ROS), a group of highly reactive ions and molecules, are increasingly being appreciated as powerful signaling molecules involved in the regulation of a variety of biological processes. Indeed, their role is continuously being delineated in a variety of pathophysiological conditions. For instance, cancer cells are shown to have increased ROS levels in comparison to their normal counterparts. This is partly due to an enhanced metabolism and mitochondrial dysfunction in cancer cells. The escalated ROS generation in cancer cells contributes to the biochemical and molecular changes necessary for the tumor initiation, promotion and progression, as well as, tumor resistance to chemotherapy. Therefore, increased ROS in cancer cells may provide a unique opportunity to eliminate cancer cells via elevating ROS to highly toxic levels intracellularly, thereby, activating various ROS-induced cell death pathways, or inhibiting cancer cell resistance to chemotherapy. Such results can be achieved by using agents that either increase ROS generation, or inhibit antioxidant defense, or even a combination of both. In fact, a large variety of anticancer drugs, and some of those currently under clinical trials, effectively kill cancer cells and overcome drug resistance via enhancing ROS generation and/or impeding the antioxidant defense mechanism. This review focuses on our current understanding of the tumor promoting (tumorigenesis, angiogenesis, invasion and metastasis, and chemoresistance) and the tumor suppressive (apoptosis, autophagy, and necroptosis) functions of ROS, and highlights the potential mechanism(s) involved. It also sheds light on a very novel and an actively growing field of ROS-dependent cell death mechanism referred to as ferroptosis.

Iron accumulation, glutathione depletion, and lipid peroxidation must occur simultaneously during ferroptosis and are mutually amplifying events

Ferroptosis is a recently discovered form of regulated necrosis that involves iron-dependent lipid peroxidation. How cells die once ferroptosis is triggered remains unclear. Ferroptosis is hypothesized to require three critical events: (1) accumulation of redox-active iron, (2) glutathione depletion, and (3) lipid peroxidation. It is proposed that these three events must unfold simultaneously because stopping any critical event also stops ferroptosis. These events are hypothesized to amplify in severity through positive feedback loops. The cause of death in ferroptosis is therefore the synergistic combination of antioxidant depletion, iron toxicity, and membrane denaturation. The relevance of these feedback loops for cancer and neurodegenerative therapies is discussed.

MPP+ induces necrostatin-1- and ferrostatin-1-sensitive necrotic death of neuronal SH-SY5Y cells

Regulation of cell death is potentially a powerful treatment modality for intractable diseases such as neurodegenerative diseases. Although there have been many reports about the possible involvement of various types of cell death in neurodegenerative diseases, it is still unclear exactly how neurons die in patients with these diseases, thus treatment strategies based on cell death regulation have not been established yet. To obtain some insight into the mechanisms of cell death involved in neurodegenerative diseases, we studied the effect of 1-methyl-4-phenylpyridinium (MPP+) on the human neuroblastoma cell line SH-SY5Y (a widely used model of Parkinson’s disease). We found that MPP+ predominantly induced non-apoptotic death of neuronally differentiated SH-SY5Y cells. This cell death was strongly inhibited by necrostatin-1 (Nec-1), a necroptosis inhibitor, and by an indole-containing compound (3,3′-diindolylmethane: DIM). However, it occurred independently of receptor-interacting serine/threonine-protein kinase 1/3 (RIP1/RIP3), indicating that this form of cell death was not necroptosis. MPP+-induced cell death was also inhibited by several inhibitors of ferroptosis, including ferrostatin-1 (Fer-1). Although MPP+-induced death and ferroptosis shared some features, such as occurrence of lipid peroxidation and inhibition by Fer-1, MPP+-induced death seemed to be distinct from ferroptosis because MPP+-induced death (but not ferroptosis) was inhibited by Nec-1, was independent of p53, and was accompanied by ATP depletion and mitochondrial swelling. Further investigation of MPP+-induced non-apoptotic cell death may be useful for understanding the mechanisms of neuronal loss and for treatment of neurodegenerative diseases such as Parkinson’s disease.

mTORC1 inhibition in cancer cells protects from glutaminolysis-mediated apoptosis during nutrient limitation

A master coordinator of cell growth, mTORC1 is activated by different metabolic inputs, particularly the metabolism of glutamine (glutaminolysis), to control a vast range of cellular processes, including autophagy. As a well-recognized tumour promoter, inhibitors of mTORC1 such as rapamycin have been approved as anti-cancer agents, but their overall outcome in patients is rather poor. Here we show that mTORC1 also presents tumour suppressor features in conditions of nutrient restrictions. Thus, the activation of mTORC1 by glutaminolysis during nutritional imbalance inhibits autophagy and induces apoptosis in cancer cells. Importantly, rapamycin treatment reactivates autophagy and prevents the mTORC1-mediated apoptosis. We also observe that the ability of mTORC1 to activate apoptosis is mediated by the adaptor protein p62. Thus, the mTORC1-mediated upregulation of p62 during nutrient imbalance induces the binding of p62 to caspase 8 and the subsequent activation of the caspase pathway. Our data highlight the role of autophagy as a survival mechanism upon rapamycin treatment.

A tale of two glutaminases: homologous enzymes with distinct roles in tumorigenesis

Many cancer cells exhibit an altered metabolic phenotype, in which glutamine consumption is upregulated relative to healthy cells. This metabolic reprogramming often depends upon mitochondrial glutaminase activity, which converts glutamine to glutamate, a key precursor for biosynthetic and bioenergetic processes. Two isozymes of glutaminase exist, a kidney-type (GLS) and a liver-type enzyme (GLS2 or LGA). While a majority of studies have focused on GLS, here we summarize key findings on both glutaminases, describing their structure and function, their roles in cancer and pharmacological approaches to inhibiting their activities.

Non-Canonical Cell Death Induced by p53

Programmed cell death is a vital biological process for multicellular organisms to maintain cellular homeostasis, which is regulated in a complex manner. Over the past several years, apart from apoptosis, which is the principal mechanism of caspase-dependent cell death, research on non-apoptotic forms of programmed cell death has gained momentum. p53 is a well characterized tumor suppressor that controls cell proliferation and apoptosis and has also been linked to non-apoptotic, non-canonical cell death mechanisms. p53 impacts these non-canonical forms of cell death through transcriptional regulation of its downstream targets, as well as direct interactions with key players involved in these mechanisms, in a cell type- or tissue context-dependent manner. In this review article, we summarize and discuss the involvement of p53 in several non-canonical modes of cell death, including caspase-independent apoptosis (CIA), ferroptosis, necroptosis, autophagic cell death, mitotic catastrophe, paraptosis, and pyroptosis, as well as its role in efferocytosis which is the process of clearing dead or dying cells.

Ferroptosis, a new form of cell death, and its relationships with tumourous diseases

Ferroptosis is a newly discovered type of cell death that differs from traditional apoptosis and necrosis and results from iron‐dependent lipid peroxide accumulation. Ferroptotic cell death is characterized by cytological changes, including cell volume shrinkage and increased mitochondrial membrane density. Ferroptosis can be induced by two classes of small‐molecule substances known as class 1 (system X_c⁻ inhibitors) and class 2 ferroptosis inducers [glutathione peroxidase 4 (GPx4) inhibitors]. In addition to these small‐molecule substances, a number of drugs (e.g. sorafenib, artemisinin and its derivatives) can induce ferroptosis. Various factors, such as the mevalonate (MVA) and sulphur‐transfer pathways, play pivotal roles in the regulation of ferroptosis. Ferroptosis plays an unneglectable role in regulating the growth and proliferation of some types of tumour cells, such as lymphocytoma, ductal cell cancer of the pancreas, renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). Here, we will first introduce the discovery of and research pertaining to ferroptosis; then summarize the induction mechanisms and regulatory pathways of ferroptosis; and finally, further elucidate the roles of ferroptosis in human tumourous diseases.

Nanomedicine: An iron age for cancer therapy

Two reports show FDA-approved nanoparticles can kill cancer cells through iron- and reactive oxygen species-dependent mechanisms, offering new strategies for cancer treatment.

Ultrasmall nanoparticles induce ferroptosis in nutrient-deprived cancer cells and suppress tumour growth

The design of cancer-targeting particles with precisely tuned physicochemical properties may enhance the delivery of therapeutics and access to pharmacological targets. However, a molecular-level understanding of the interactions driving the fate of nanomedicine in biological systems remains elusive. Here, we show that ultrasmall (<10 nm in diameter) poly(ethylene glycol)-coated silica nanoparticles, functionalized with melanoma-targeting peptides, can induce a form of programmed cell death known as ferroptosis in starved cancer cells and cancer-bearing mice. Tumour xenografts in mice intravenously injected with nanoparticles using a high-dose multiple injection scheme exhibit reduced growth or regression, in a manner that is reversed by the pharmacological inhibitor of ferroptosis, liproxstatin-1. These data demonstrate that ferroptosis can be targeted by ultrasmall silica nanoparticles and may have therapeutic potential.