Expression of xCT and activity of system xc(-) are regulated by NRF2 in human breast cancer cells in response to oxidative stress

Ginsenoside Rh4 Inhibits Colorectal Cancer Cell Proliferation by Inducing Ferroptosis via Autophagy Activation

Colorectal cancer (CRC) is a severe threat to human health. Ginsenosides such as ginsenoside Rh4 have been widely studied in the antitumor field. Here, we investigated the antiproliferative activity and mechanism of Rh4 against CRC in vivo and in vitro. The CRC xenograft model showed that Rh4 inhibited xenograft tumor growth with few side effects (p < 0.05). As determined by MTT colorimetric assays, Western blotting, and immunohistochemical analysis, Rh4 effectively inhibited CRC cell proliferation through autophagy and ferroptosis (p < 0.05). Rh4 significantly upregulated autophagy and ferroptosis marker expression in CRC cells and xenograft tumor tissues in the present study (p < 0.05). Interestingly, the ferroptosis inhibitor ferrostatin-1 (Fer-1) reversed Rh4-induced ferroptosis (p < 0.05). Moreover, the autophagy inhibitor 3-methyladenine (3-MA) also reversed Rh4-induced ferroptosis (p < 0.05). These results indicate that Rh4-induced ferroptosis is regulated via the autophagy pathway. In addition, Rh4 increased reactive oxygen species (ROS) accumulation, leading to the activation of the ROS/p53 signaling pathway (p < 0.05). Transcriptome sequencing also confirmed this (p < 0.05). Moreover, the ROS scavenger N-acetyl-cysteine (NAC) reversed the inhibitory effect of Rh4 on CRC cells (p < 0.05). Therefore, this study proves that Rh4 inhibits cancer cell proliferation by activating the ROS/p53 signaling pathway and activating autophagy to induce ferroptosis, which provides necessary scientific evidence of the great anticancer potential of Rh4.

Catechin Mediates Ferroptosis to Exert an Anti-Inflammatory Effect on RAW 264.7 Cells

Catechin possesses a potential anti-inflammatory activity, but its anti-inflammatory mechanism is still unclear. Herein, the analysis of network pharmacology showed that catechin might mediate ferroptosis on macrophages to exhibit a significant anti-inflammatory effect on RAW264.7. The metabolomics further indicated that catechin might influence ferroptosis by activating two pathways of cysteine and methionine metabolism and glutathione metabolism, and inhibiting the pathway of ferroptosis to promote the reduction of l-methionine-s-oxide and s-glutathionyl-l-cysteine, and the reduction and synthesis of γ-glutamylcysteine. Furthermore, related proteins (MSRA, CDR, GSR and GCL) in three metabolic pathways and ferroptosis-related proteins (GPX4 and SLC7A11) might be relevant to catechin through molecular docking. Thus, we speculate that catechin plays an anti-inflammatory effect through mediating ferroptosis on RAW264.7, which still needs further focus on the detailed molecular mechanism.

Rho family GTPase 1 (RND1), a novel regulator of p53, enhances ferroptosis in glioblastoma

Background

Ferroptosis is an iron dependent cell death closely associated with p53 signaling pathway and is aberrantly regulated in glioblastoma (GBM), yet the underlying mechanism needs more exploration. Identifying new factors which regulate p53 and ferroptosis in GBM is essential for treatment.

Methods

Glioma cell growth was evaluated by cell viability assays and colony formation assays. Lipid reactive oxygen species (ROS) assays, lipid peroxidation assays, glutathione assays, and transmission electron microscopy were used to assess the degree of cellular lipid peroxidation of GBM. The mechanisms of RND1 in regulation of p53 signaling were analyzed by RT-PCR, western blot, immunostaining, co-immunoprecipitation, ubiquitination assays and luciferase reporter assays. The GBM‐xenografted animal model was constructed and the tumor was captured by an In Vivo Imaging System (IVIS).

Results

From the The Cancer Genome Atlas (TCGA) database, we summarized that Rho family GTPase 1 (RND1) expression was downregulated in GBM and predicted a better prognosis of patients with GBM. We observed that RND1 influenced the glioma cell growth in a ferroptosis-dependent manner when GBM cell lines U87 and A172 were treated with Ferrostatin-1 or Erastin. Mechanistically, we found that RND1 interacted with p53 and led to the de-ubiquitination of p53 protein. Furthermore, the overexpression of RND1 promoted the activity of p53-SLC7A11 signaling pathway, therefore inducing the lipid peroxidation and ferroptosis of GBM.

Conclusions

We found that RND1, a novel controller of p53 protein and a positive regulator of p53 signaling pathway, enhanced the ferroptosis in GBM. This study may shed light on the understanding of ferroptosis in GBM cells and provide new therapeutic ideas for GBM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00791-w.

Ferroptosis is induced by lenvatinib through fibroblast growth factor receptor-4 inhibition in hepatocellular carcinoma

The tyrosine kinase inhibitor lenvatinib is used to treat advanced hepatocellular carcinoma (HCC). Ferroptosis is a type of cell death characterized by the iron‐dependent accumulation of lethal lipid reactive oxygen species (ROS). Nuclear factor erythroid‐derived 2‐like 2 (Nrf2) protects HCC cells against ferroptosis. However, the mechanism of lenvatinib‐induced cytotoxicity and the relationships between lenvatinib resistance and Nrf2 are unclear. Thus, we investigated the relationship between lenvatinib and ferroptosis and clarified the involvement of Nrf2 in lenvatinib‐induced cytotoxicity. Cell viability, lipid ROS levels, and protein expression were measured using Hep3B and HuH7 cells treated with lenvatinib or erastin. We examined these variables after silencing fibroblast growth factor receptor‐4 (FGFR4) or Nrf2 and overexpressing‐Nrf2. We immunohistochemically evaluated FGFR4 expression in recurrent lesions after resection and clarified the relationship between FGFR4 expression and lenvatinib efficacy. Lenvatinib suppressed system X_c⁻ (xCT) and glutathione peroxidase 4 (GPX4) expression. Inhibition of the cystine import activity of xCT and GPX4 resulted in the accumulation of lipid ROS. Silencing‐FGFR4 suppressed xCT and GPX4 expression and increased lipid ROS levels. Nrf2‐silenced HCC cells displayed sensitivity to lenvatinib and high lipid ROS levels. In contrast, Nrf2‐overexpressing HCC cells displayed resistance to lenvatinib and low lipid ROS levels. The efficacy of lenvatinib was significantly lower in recurrent HCC lesions with low‐FGFR4 expression than in those with high‐FGFR4 expression. Patients with FGFR4‐positive HCC displayed significantly longer progression‐free survival than those with FGFR4‐negative HCC. Lenvatinib induced ferroptosis by inhibiting FGFR4. Nrf2 is involved in the sensitivity of HCC to lenvatinib.

Non-coding RNAs in ferroptotic cancer cell death pathway: meet the new masters

Despite the recent advances in cancer therapy, cancer chemoresistance looms large along with radioresistance, a major challenge in dire need of thorough and minute investigation. Not long ago, cancer cells were reported to have proven refractory to the ferroptotic cell death, a newly discovered form of regulated cell death (RCD), conspicuous enough to draw attention from scholars in terms of targeting ferroptosis as a prospective therapeutic strategy. However, our knowledge concerning the underlying molecular mechanisms through which cancer cells gain immunity against ferroptosis is still in its infancy. Of late, the implication of non-coding RNAs (ncRNAs), including circular RNAs (circRNAs), microRNAs (miRNAs), and long non-coding RNAs (lncRNAs) in ferroptosis has been disclosed. Nevertheless, precisely explaining the molecular mechanisms behind the contribution of ncRNAs to cancer radio/chemotherapy resistance remains a challenge, requiring further clarification. In this review, we have presented the latest available information on the ways and means of regulating ferroptosis by ncRNAs. Moreover, we have provided important insights about targeting ncRNAs implicated in ferroptosis with the hope of opening up new horizons for overcoming cancer treatment modalities. Though a long path awaits until we make this ambitious dream come true, recent progress in gene therapy, including gene-editing technology will aid us to be optimistic that ncRNAs-based ferroptosis targeting would soon be on stream as a novel therapeutic strategy for treating cancer.

The Double-Edged Sword of Oxidative Stress in Skin Damage and Melanoma: From Physiopathology to Therapeutical Approaches

The skin is constantly exposed to exogenous and endogenous sources of reactive oxygen species (ROS). An adequate balance between ROS levels and antioxidant defenses is necessary for the optimal cell and tissue functions, especially for the skin, since it must face additional ROS sources that do not affect other tissues, including UV radiation. Melanocytes are more exposed to oxidative stress than other cells, also due to the melanin production process, which itself contributes to generating ROS. There is an increasing amount of evidence that oxidative stress may play a role in many skin diseases, including melanoma, being the primary cause or being a cofactor that aggravates the primary condition. Indeed, oxidative stress is emerging as another major force involved in all the phases of melanoma development, not only in the arising of the malignancy but also in the progression toward the metastatic phenotype. Furthermore, oxidative stress seems to play a role also in chemoresistance and thus has become a target for therapy. In this review, we discuss the existing knowledge on oxidative stress in the skin, examining sources and defenses, giving particular consideration to melanocytes. Therefore, we focus on the significance of oxidative stress in melanoma, thus analyzing the possibility to exploit the induction of oxidative stress as a therapeutic strategy to improve the effectiveness of therapeutic management of melanoma.

Iron Dyshomeostasis and Ferroptosis: A New Alzheimer’s Disease Hypothesis?

Iron plays a crucial role in many physiological processes of the human body, but iron is continuously deposited in the brain as we age. Early studies found iron overload is directly proportional to cognitive decline in Alzheimer’s disease (AD). Amyloid precursor protein (APP) and tau protein, both of which are related to the AD pathogenesis, are associated with brain iron metabolism. A variety of iron metabolism-related proteins have been found to be abnormally expressed in the brains of AD patients and mouse models, resulting in iron deposition and promoting AD progression. Amyloid β (Aβ) and hyperphosphorylated tau, two pathological hallmarks of AD, can also promote iron deposition in the brain, forming a vicious cycle of AD development-iron deposition. Iron deposition and the subsequent ferroptosis has been found to be a potential mechanism underlying neuronal loss in many neurodegenerative diseases. Iron chelators, antioxidants and hepcidin were found useful for treating AD, which represents an important direction for AD treatment research and drug development in the future. The review explored the deep connection between iron dysregulation and AD pathogenesis, discussed the potential of new hypothesis related to iron dyshomeostasis and ferroptosis, and summarized the therapeutics capable of targeting iron, with the expectation to draw more attention of iron dysregulation and corresponding drug development.

Loss of LAT1 sex-dependently delays recovery after caerulein-induced acute pancreatitis

BACKGROUND

The expression of amino acid transporters is known to vary during acute pancreatitis (AP) except for LAT1 (slc7a5), the expression of which remains stable. LAT1 supports cell growth by importing leucine and thereby stimulates mammalian target of rapamycin (mTOR) activity, a phenomenon often observed in cancer cells. The mechanisms by which LAT1 influences physiological and pathophysiological processes and affects disease progression in the pancreas are not yet known.

AIM

To evaluate the role of LAT1 in the development of and recovery from AP.

METHODS

AP was induced with caerulein (cae) injections in female and male mice expressing LAT1 or after its knockout (LAT1 Cre/LoxP). The development of the initial AP injury and its recovery were followed for seven days after cae injections by daily measuring body weight, assessing microscopical tissue architecture, mRNA and protein expression, protein synthesis, and enzyme activity levels, as well as by testing the recruitment of immune cells by FACS and ELISA.

RESULTS

The initial injury, evaluated by measurements of plasma amylase, lipase, and trypsin activity, as well as the gene expression of dedifferentiation markers, did not differ between the groups. However, early metabolic adaptations that support regeneration at later stages were blunted in LAT1 knockout mice. Especially in females, we observed less mTOR reactivation and dysfunctional autophagy. The later regeneration phase was clearly delayed in female LAT1 knockout mice, which did not regain normal expression of the pancreas-specific differentiation markers recombining binding protein suppressor of hairless-like protein (rbpjl) and basic helix-loop-helix family member A15 (mist1). Amylase mRNA and protein levels remained lower, and, strikingly, female LAT1 knockout mice presented signs of fibrosis lasting until day seven. In contrast, pancreas morphology had returned to normal in wild-type littermates.

CONCLUSION

LAT1 supports the regeneration of acinar cells after AP. Female mice lacking LAT1 exhibited more pronounced alterations than male mice, indicating a sexual dimorphism of amino acid metabolism.

The hallmarks of cancer metabolism: Still emerging

Metabolism of cancer cells is geared toward biomass production and proliferation. Since the metabolic resources within the local tissue are finite, this can lead to nutrient depletion and accumulation of metabolic waste. To maintain growth in these conditions, cancer cells employ a variety of metabolic adaptations, the nature of which is collectively determined by the physiology of their cell of origin, the identity of transforming lesions, and the tissue in which cancer cells reside. Furthermore, select metabolites not only serve as substrates for energy and biomass generation, but can also regulate gene and protein expression and influence the behavior of non-transformed cells in the tumor vicinity. As they grow and metastasize, tumors can also affect and be affected by the nutrient distribution within the body. In this hallmark update, recent advances are incorporated into a conceptual framework that may help guide further research efforts in exploring cancer cell metabolism.

Ferroptosis: A Potential Target in Cardiovascular Disease

Ferroptosis is a new form of regulatory cell death characterized by iron-dependent and intracellular lipid peroxidation. Ferroptosis can be divided into two stages. The first stage is iron overload in the cell, which generates a large amount of reactive oxygen species through the Fenton reaction, and the second stage results from an imbalance of the intracellular antioxidant system. Excessive phospholipid hydroperoxides cannot be removed by reduction reactions, as this could destroy the cell membrane structure and interfere with mitochondrial function, eventually leading to ferroptosis of the cell. Cardiovascular diseases have gradually become the leading cause of death in modern society. The relationship between ferroptosis and the occurrence and progression of cardiovascular disease has become a research hotspot in recent years. In this review, we summarize the mechanism of ferroptosis and its specific role in cardiovascular disease.

The Potential of Ferroptosis-Targeting Therapies for Alzheimer's Disease: From Mechanism to Transcriptomic Analysis

Alzheimer’s disease (AD), the most common form of dementia, currently affects 40–50 million people worldwide. Despite the extensive research into amyloid β (Aβ) deposition and tau protein hyperphosphorylation (p-tau), an effective treatment to stop or slow down the progression of neurodegeneration is missing. Emerging evidence suggests that ferroptosis, an iron-dependent and lipid peroxidation-driven type of programmed cell death, contributes to neurodegeneration in AD. Therefore, how to intervene against ferroptosis in the context of AD has become one of the questions addressed by studies aiming to develop novel therapeutic strategies. However, the underlying molecular mechanism of ferroptosis in AD, when ferroptosis occurs in the disease course, and which ferroptosis-related genes are differentially expressed in AD remains to be established. In this review, we summarize the current knowledge on cell mechanisms involved in ferroptosis, we discuss how these processes relate to AD, and we analyze which ferroptosis-related genes are differentially expressed in AD brain dependant on cell type, disease progression and gender. In addition, we point out the existing targets for therapeutic options to prevent ferroptosis in AD. Future studies should focus on developing new tools able to demonstrate where and when cells undergo ferroptosis in AD brain and build more translatable AD models for identifying anti-ferroptotic agents able to slow down neurodegeneration.

Metabolic reprogramming in the arsenic carcinogenesis

Chronic exposure to arsenic has been associated with a variety of cancers with the mechanisms undefined. Arsenic exposure causes alterations in metabolites in bio-samples. Recent research progress on cancer biology suggests that metabolic reprogramming contributes to tumorigenesis. Therefore, metabolic reprogramming provides a new clue for the mechanisms of arsenic carcinogenesis. In the present manuscript, we review the latest findings in reprogramming of glucose, lipids, and amino acids in response to arsenic exposure. Most studies focused on glucose reprogramming and found that arsenic exposure enhanced glycolysis. However, in vivo studies observed "reverse Warburg effect" in some cases due to the complexity of the disease evolution and microenvironment. Arsenic exposure has been reported to disturb lipid deposition by inhibiting lipolysis, and induce serine-glycine one-carbon pathway. As a dominant mechanism for arsenic toxicity, oxidative stress is considered to link with metabolism reprogramming. Few studies analyzed the causal relationship between metabolic reprogramming and arsenic-induced cancers. Metabolic alterations may vary with exposure doses and periods. Identifying metabolic alterations common among humans and experiment models with human-relevant exposure characteristics may guide future investigations.

Discovery of a cinnamyl piperidine derivative as new neddylation inhibitor for gastric cancer treatment

Targeting neddylation pathway has been recognized as an attractive anticancer therapeutic strategy, thus discovering potent and selective neddylation inhibitors is highly desirable. Our work reported the discovery of novel cinnamyl piperidine compounds and their antitumor activity in vitro and in vivo. Among these compounds, compound 4g was identified as a novel neddylation inhibitor and decreased the neddylation levels of cullin 1, cullin 3 and cullin 5. Mechanistic studies demonstrated that compound 4g could inhibit the migration ability of gastric cancer cells and induce apoptosis partly mediated by the Nrf2-Keap1 pathway. Furthermore, in vivo anti-tumor studies showed that 4g effectively inhibited tumor growth without obvious toxicity. Collectively, the cinnamyl piperidine derivatives could serve as new lead compounds for developing highly effective neddylation inhibitors for gastric cancer therapy.

Oxidative Stress-Related Mechanisms in Melanoma and in the Acquired Resistance to Targeted Therapies

Melanoma is a highly aggressive cancer with the poorest prognosis, representing the deadliest form of skin cancer. Activating mutations in BRAF are the most frequent genetic alterations, present in approximately 50% of all melanoma cases. The use of specific inhibitors towards mutant BRAF variants and MEK, a downstream signaling target of BRAF in the MAPK pathway, has significantly improved progression-free and overall survival in advanced melanoma patients carrying BRAF mutations. Nevertheless, despite these improvements, resistance still develops within the first year of therapy in around 50% of patients, which is a significant problem in managing BRAF-mutated advanced melanoma. Understanding these mechanisms is one of the mainstreams of the research on BRAFi/MEKi acquired resistance. Both genetic and epigenetic mechanisms have been described. Moreover, in recent years, oxidative stress has emerged as another major force involved in all the phases of melanoma development, from initiation to progression until the onsets of the metastatic phenotype and chemoresistance, and has thus become a target for therapy. In the present review, we discuss the current knowledge on oxidative stress and its signaling in melanoma, as well as the oxidative stress-related mechanisms in the acquired resistance to targeted therapies.

Ferroptosis and NRF2: an emerging battlefield in the neurodegeneration of Alzheimer's disease

Ferroptosis is an iron- and lipid peroxidation-dependent cell death modality and emerging evidence indicates that ferroptosis has great explanatory potential for neuronal loss and associated CNS dysfunction in a range of neurodegenerative diseases (e.g., Alzheimer's, Parkinson's and Huntington's diseases, Motor neuron disease, Friedreich ataxia (FRDA)). Ferroptotic death results from lethal levels of phospholipid hydroperoxides that are generated by iron-dependent peroxidation of polyunsaturated fatty acids (PUFAs), such as arachidonic and adrenic acids, which are conjugated to specific phospholipids (e.g., phosphatidylethanolamines (PEs)). The major cellular protector against ferroptosis is glutathione peroxidase 4 (GPX4), a membrane-associated selenoenzyme that reduces deleterious phospholipid hydroperoxides to their corresponding benign phospholipid alcohols in a glutathione-dependent manner. Other complementary protective systems have also been identified that act to bolster cellular defences against ferroptosis. Many pharmacological modulators of the ferroptosis pathway have been identified, targeting proteins involved in iron homoeostasis and autophagy; the production and detoxification of lipid peroxides, and cyst(e)ine/glutathione metabolism. While a growing number of cell signalling pathways converge to regulate the ferroptosis cascade, an emerging understanding of ferroptosis regulation suggests that the ferroptotic 'tone' of cells can be set by the transcription factor, nuclear factor erythroid 2-related factor 2 (NRF2), which transcriptionally controls many key components of the ferroptosis pathway. In this review, we provide a critical overview of the relationship between ferroptosis and NRF2 signalling. With a focus on the role of ferroptosis in Alzheimer's disease (AD), we discuss how therapeutic modulation of the NRF2 pathway is a viable strategy to explore in the treatment of ferroptosis-driven neurodegeneration.

Emerging role of ferroptosis in breast cancer: New dawn for overcoming tumor progression

Breast cancer has become a serious threat to women's health. Cancer progression is mainly derived from resistance to apoptosis induced by procedures or therapies. Therefore, new drugs or models that can overcome apoptosis resistance should be identified. Ferroptosis is a recently identified mode of cell death characterized by excess reactive oxygen species-induced lipid peroxidation. Since ferroptosis is distinct from apoptosis, necrosis and autophagy, its induction successfully eliminates cancer cells that are resistant to other modes of cell death. Therefore, ferroptosis may become a new direction around which to design breast cancer treatment. Unfortunately, the complete appearance of ferroptosis in breast cancer has not yet been fully elucidated. Furthermore, whether ferroptosis inducers can be used in combination with traditional anti- breast cancer drugs is still unknown. Moreover, a summary of ferroptosis in breast cancer progression and therapy is currently not available. In this review, we discuss the roles of ferroptosis-associated modulators glutathione, glutathione peroxidase 4, iron, nuclear factor erythroid-2 related factor-2, superoxide dismutases, lipoxygenase and coenzyme Q in breast cancer. Furthermore, we provide evidence that traditional drugs against breast cancer induce ferroptosis, and that ferroptosis inducers eliminate breast cancer cells. Finally, we put forward prospect of using ferroptosis inducers in breast cancer therapy, and predict possible obstacles and corresponding solutions. This review will deepen our understanding of the relationship between ferroptosis and breast cancer, and provide new insights into breast cancer-related therapeutic strategies.

Ferroptosis and Cancer: Complex Relationship and Potential Application of Exosomes

Cell death induction has become popular as a novel cancer treatment. Ferroptosis, a newly discovered form of cell death, features regulated, iron-dependent accumulation of lipid hydroperoxides. Since this word “ferroptosis” was coined, numerous studies have examined the complex relationship between ferroptosis and cancer. Here, starting from the intrinsic hallmarks of cancer and cell death, we discuss the theoretical basis of cell death induction as a cancer treatment. We review various aspects of the relationship between ferroptosis and cancer, including the genetic basis, epigenetic modification, cancer stem cells, and the tumor microenvironment, to provide information and support for further research on ferroptosis. We also note that exosomes can be applied in ferroptosis-based therapy. These extracellular vesicles can deliver different molecules to modulate cancer cells and cell death pathways. Using exosomes to control ferroptosis occurring in targeted cells is promising for cancer therapy.

Pharmacologic approaches to amino acid depletion for cancer therapy

Cancer cells undergo metabolic reprogramming to support increased demands in bioenergetics and biosynthesis and to maintain reactive oxygen species at optimum levels. As metabolic alterations are broadly observed across many cancer types, metabolic reprogramming is considered a hallmark of cancer. A metabolic alteration commonly seen in cancer cells is an increased demand for certain amino acids. Amino acids are involved in a wide range of cellular functions, including proliferation, redox balance, bioenergetic and biosynthesis support, and homeostatic functions. Thus, targeting amino acid dependency in cancer is an attractive strategy for a number of cancers. In particular, pharmacologically mediated amino acid depletion has been evaluated as a cancer treatment option for several cancers. Amino acids that have been investigated for the feasibility of drug-induced depletion in preclinical and clinical studies for cancer treatment include arginine, asparagine, cysteine, glutamine, lysine, and methionine. In this review, we will summarize the status of current research on pharmacologically mediated amino acid depletion as a strategy for cancer treatment and potential chemotherapeutic combinations that synergize with amino acid depletion to further inhibit tumor growth and progression.

Cross-Talk between Oxidative Stress and m6A RNA Methylation in Cancer

Oxidative stress is a state of imbalance between oxidation and antioxidation. Excessive ROS levels are an important factor in tumor development. Damage stimulation and excessive activation of oncogenes cause elevated ROS production in cancer, accompanied by an increase in the antioxidant capacity to retain redox homeostasis in tumor cells at an increased level. Although moderate concentrations of ROS produced in cancer cells contribute to maintaining cell survival and cancer progression, massive ROS accumulation can exert toxicity, leading to cancer cell death. RNA modification is a posttranscriptional control mechanism that regulates gene expression and RNA metabolism, and m⁶A RNA methylation is the most common type of RNA modification in eukaryotes. m⁶A modifications can modulate cellular ROS levels through different mechanisms. It is worth noting that ROS signaling also plays a regulatory role in m⁶A modifications. In this review, we concluded the effects of m⁶A modification and oxidative stress on tumor biological functions. In particular, we discuss the interplay between oxidative stress and m⁶A modifications.

Quantitative trait mapping in Diversity Outbred mice identifies novel genomic regions associated with the hepatic glutathione redox system

The tripeptide glutathione (GSH) is instrumental to antioxidant protection and xenobiotic metabolism, and the ratio of its reduced and oxidized forms (GSH/GSSG) indicates the cellular redox environment and maintains key aspects of cellular signaling. Disruptions in GSH levels and GSH/GSSG have long been tied to various chronic diseases, and many studies have examined whether variant alleles in genes responsible for GSH synthesis and metabolism are associated with increased disease risk. However, past studies have been limited to established, canonical GSH genes, though emerging evidence suggests that novel loci and genes influence the GSH redox system in specific tissues. The present study marks the most comprehensive effort to date to directly identify genetic loci associated with the GSH redox system. We employed the Diversity Outbred (DO) mouse population, a model of human genetics, and measured GSH and the essential redox cofactor NADPH in liver, the organ with the highest levels of GSH in the body. Under normal physiological conditions, we observed substantial variation in hepatic GSH and NADPH levels and their redox balances, and discovered a novel, significant quantitative trait locus (QTL) on murine chromosome 16 underlying GSH/GSSG; bioinformatics analyses revealed Socs1 to be the most likely candidate gene. We also discovered novel QTL associated with hepatic NADP⁺ levels and NADP⁺/NADPH, as well as unique candidate genes behind each trait. Overall, these findings transform our understanding of the GSH redox system, revealing genetic loci that govern it and proposing new candidate genes to investigate in future mechanistic endeavors.

Resveratrol attenuates rotenone-induced inflammation and oxidative stress via STAT1 and Nrf2/Keap1/SLC7A11 pathway in a microglia cell line

SCOPE

Resveratrol is abundant in grapes. A protective role for resveratrol in anti-oxidation and anti-inflammatory has been demonstrated. Rotenone is a pesticide, used to make animal models of Parkinson's disease (PD). The aim of our study was to investigate the protective effect of resveratrol on rotenone-induced microglial BV-2 cells and the mechanism.

METHODS

BV-2 cells were pretreated with resveratrol for 1 h and then exposed to rotenone. The level of microglia activation was detected. The Iron content and the production of glutathione, malondialdehyde (MDA), reactive oxygen species(ROS) were detected to reflect the status of oxidative stress. The mRNA levels of interleukin-1β (IL-1β), IL-6 and tumor necrosis factor-α (TNF-α) were measured by qRT-PCR.The expressions of p-STAT1, NF-E2-related factor (Nrf2), Kelch-like ECH-associated protein 1 (Keap1) and SLC7A11 were measured by western blot.

RESULT

Our results showed that resveratrol attenuates microglia activation and M1 polarization in rotenone-induced BV-2 cells. Rotenone induced the production of free iron, ROS and MDA and inhibited the activity of glutathione, while the effects were reserved by resveratrol. Resveratrol also inhibited the induction effect of rotenone on IL-6, IL-1β, and TNF-α. In addition, resveratrol enhanced the protective effect of on rotenone-induced BV-2 cells via the inhibition of STAT1 and Keap1 and the upregulation of Nrf2 and SLC7A11.

CONCLUSION

Resveratrol attenuated rotenone-induced inflammation and oxidative stress in BV-2 cells through enhancing the inhibition of STAT1and Keap1 and the upregulation of Nrf2 and SLC7A11.

Cysteine Boosts Fitness Under Hypoxia-Mimicked Conditions in Ovarian Cancer by Metabolic Reprogramming

Among gynecologic malignancies, ovarian cancer is the third most prevalent and the most common cause of death, especially due to diagnosis at an advanced stage together with resistance to therapy. As a solid tumor grows, cancer cells in the microenvironment are exposed to regions of hypoxia, a selective pressure prompting tumor progression and chemoresistance. We have previously shown that cysteine contributes to the adaptation to this hypoxic microenvironment, but the mechanisms by which cysteine protects ovarian cancer cells from hypoxia-induced death are still to be unveiled. Herein, we hypothesized that cysteine contribution relies on cellular metabolism reprogramming and energy production, being cysteine itself a metabolic source. Our results strongly supported a role of xCT symporter in energy production that requires cysteine metabolism instead of hydrogen sulfide (H2S) per se. Cysteine degradation depends on the action of the H2S-synthesizing enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and/or 3-mercaptopyruvate sulfurtransferase (MpST; together with cysteine aminotransferase, CAT). In normoxia, CBS and CSE inhibition had a mild impact on cysteine-sustained ATP production, pointing out the relevance of CAT + MpST pathway. However, in hypoxia, the concomitant inhibition of CBS and CSE had a stronger impact on ATP synthesis, thus also supporting a role of their hydrogen sulfide and/or cysteine persulfide-synthesizing activity in this stressful condition. However, the relative contributions of each of these enzymes (CBS/CSE/MpST) on cysteine-derived ATP synthesis under hypoxia remains unclear, due to the lack of specific inhibitors. Strikingly, NMR analysis strongly supported a role of cysteine in the whole cellular metabolism rewiring under hypoxia. Additionally, the use of cysteine to supply biosynthesis and bioenergetics was reinforced, bringing cysteine to the plateau of a main carbon sources in cancer. Collectively, this work supports that sulfur and carbon metabolism reprogramming underlies the adaptation to hypoxic microenvironment promoted by cysteine in ovarian cancer.

System Xc-: a key regulatory target of ferroptosis in cancer

Ferroptosis is a type of oxidative stress-dependent regulated necrosis characterized by excessive lipid peroxide accumulation. This novel cell death modality has been implicated in preventing cancer progression. Cancer cells tend to modulate their redox state to prevent excessive peroxidation, eventually facilitating tumor growth. System Xc^- (a cystine/glutamate antiporter system) is a promising target in cancer cells for ferroptosis induction. The overexpression of system Xc^-, especially its core subunit xCT, has been reported in several tumors, and these high expression levels were closely related to cancer cell proliferation, invasion, metastasis and the tumor microenvironment. xCT might serve as a novel biomarker, and its upregulation almost always indicates drug tolerance and poor survival. Therefore, system Xc^- inhibition may enhance chemotherapy sensitivity and optimize patient prognosis. Here, we elaborate on the mediation of ferroptosis by suppressing system Xc^- and the relevant underlying molecular mechanism in cancer cells. The spotlight on this approach to cancer treatment is creating a new horizon and pointing to future opportunities.

Amino acid transporters as emerging therapeutic targets in cancer

Amino acids are indispensable nutrients for both normal and cancer cells. Cancer cells are unable to synthesize essential amino acids as well as some non‐essential amino acids adequately to support rapid proliferation, and must take up amino acids from the surroundings. To meet the increased demand for the amino acid needed for proliferation, high levels of amino acid transporters are expressed on the surface of cancer cells. Cancer cells utilize amino acids to synthesize proteins and nucleotides, as well as to obtain energy. In addition, amino acids are known to play pathological roles in cancer cells. Interestingly, breast cancer cells limit the use of amino acids for cell proliferation based on amino acid availability, which depends on estrogen receptor status. Here, we present a summarized literature review of novel amino acid functions in cancer cells. This review organizes the available knowledge on 2 amino acid transporters, SLC7A5 and SLC7A11, which are considered essential for breast cancer cell growth in a cell‐dependent manner. In particular, we propose the glutamine recycling model to clarify the mechanism underlying aberrant SLC7A5 activation. Finally, we overview the pathological significances of SLC7A5 and SLC7A11 in cancer tissues.

Resistance to different anthracycline chemotherapeutics elicits distinct and actionable primary metabolic dependencies in breast cancer

Chemotherapy resistance is a critical barrier in cancer treatment. Metabolic adaptations have been shown to fuel therapy resistance; however, little is known regarding the generality of these changes and whether specific therapies elicit unique metabolic alterations. Using a combination of metabolomics, transcriptomics, and functional genomics, we show that two anthracyclines, doxorubicin and epirubicin, elicit distinct primary metabolic vulnerabilities in human breast cancer cells. Doxorubicin-resistant cells rely on glutamine to drive oxidative phosphorylation and de novo glutathione synthesis, while epirubicin-resistant cells display markedly increased bioenergetic capacity and mitochondrial ATP production. The dependence on these distinct metabolic adaptations is revealed by the increased sensitivity of doxorubicin-resistant cells and tumor xenografts to buthionine sulfoximine (BSO), a drug that interferes with glutathione synthesis, compared with epirubicin-resistant counterparts that are more sensitive to the biguanide phenformin. Overall, our work reveals that metabolic adaptations can vary with therapeutics and that these metabolic dependencies can be exploited as a targeted approach to treat chemotherapy-resistant breast cancer.

Inhibition of the NRF2/KEAP1 Axis: A Promising Therapeutic Strategy to Alter Redox Balance of Cancer Cells

Significance: The nuclear factor erythroid 2-related factor 2/Kelch-like ECH-associated protein 1 (NRF2/KEAP1) pathway is a crucial and highly conserved defensive system that is required to maintain or restore the intracellular homeostasis in response to oxidative, electrophilic, and other types of stress conditions. The tight control of NRF2 function is maintained by a complex network of biological interactions between positive and negative regulators that ultimately ensure context-specific activation, culminating in the NRF2-driven transcription of cytoprotective genes. Recent Advances: Recent studies indicate that deregulated NRF2 activation is a frequent event in malignant tumors, wherein it is associated with metabolic reprogramming, increased antioxidant capacity, chemoresistance, and poor clinical outcome. On the other hand, the growing interest in the modulation of the cancer cells' redox balance identified NRF2 as an ideal therapeutic target. Critical Issues: For this reason, many efforts have been made to identify potent and selective NRF2 inhibitors that might be used as single agents or adjuvants of anticancer drugs with redox disrupting properties. Despite the lack of specific NRF2 inhibitors still represents a major clinical hurdle, the researchers have exploited alternative strategies to disrupt NRF2 signaling at different levels of its biological activation. Future Directions: Given its dualistic role in tumor initiation and progression, the identification of the appropriate biological context of NRF2 activation and the specific clinicopathological features of patients cohorts wherein its inactivation is expected to have clinical benefits, will represent a major goal in the field of cancer research. In this review, we will briefly describe the structure and function of the NRF2/ KEAP1 system and some of the most promising NRF2 inhibitors, with a particular emphasis on natural compounds and drug repurposing. Antioxid. Redox Signal. 34, 1428-1483.

Targeting SLC3A2 subunit of system XC- is essential for m6A reader YTHDC2 to be an endogenous ferroptosis inducer in lung adenocarcinoma

The m⁶A reader YT521-B homology containing 2 (YTHDC2) has been identified to inhibit lung adenocarcinoma (LUAD) tumorigenesis by suppressing solute carrier 7A11 (SLC7A11)-dependent antioxidant function. SLC7A11 is a major functional subunit of system X_C^-. Inhibition of system X_C^- can induce ferroptosis. However, whether suppressing SLC7A11 is sufficient for YTHDC2 to be an endogenous ferroptosis inducer in LUAD is unknown. Here, we found that induction of YTHDC2 to a high level can induce ferroptosis in LUAD cells but not in lung and bronchus epithelial cells. In addition to SLC7A11, solute carrier 3A2 (SLC3A2), another subunit of system X_C^- was equally important for YTHDC2-induced ferroptosis. YTHDC2 m⁶A-dependently destabilized Homeo box A13 (HOXA13) mRNA because a potential m⁶A recognition site was identified within its 3' untranslated region (3'UTR). Interestingly, HOXA13 acted as a transcription factor to stimulate SLC3A2 expression. Thereby, YTHDC2 suppressed SLC3A2 via inhibiting HOXA13 in an m⁶A-indirect manner. Mouse experiments further confirmed the associations among YTHDC2, SLC3A2 and HOXA13, and demonstrated that SLC3A2 and SLC7A11 were both important for YTHDC2-impaired tumor growth and -induced lipid peroxidation in vivo. Moreover, higher expression of SLC7A11, SLC3A2 and HOXA13 indicate poorer clinical outcome in YTHDC2-suppressed LUAD patients. In conclusion, YTHDC2 is believed to be a powerful endogenous ferroptosis inducer and targeting SLC3A2 subunit of system X_C^- is essential for this process. Increasing YTHDC2 is an alternative ferroptosis-based therapy to treat LUAD.

The intricacies of NRF2 regulation in cancer

The complex role of NRF2 in the context of cancer continues to evolve. As a transcription factor, NRF2 regulates various genes involved in redox homeostasis, protein degradation, DNA repair, and xenobiotic metabolism. As such, NRF2 is critical in preserving cell function and viability, particularly during stress. Importantly, NRF2 itself is regulated via a variety of mechanisms, and the mode of NRF2 activation often dictates the duration of NRF2 signaling and its role in either preventing cancer initiation or promoting cancer progression. Herein, different modes of NRF2 regulation, including oxidative stress, autophagy dysfunction, protein-protein interactions, and epigenetics, as well as pharmacological modulators targeting this cascade in cancer, are explored. Specifically, how the timing and duration of these different mechanisms of NRF2 induction affect tumor initiation, progression, and metastasis are discussed. Additionally, progress in the discovery and development of NRF2 inhibitors for the treatment of NRF2-addicted cancers is highlighted, including modulators that inhibit specific NRF2 downstream targets. Overall, a better understanding of the intricate nature of NRF2 regulation in specific cancer contexts should facilitate the generation of novel therapeutics designed to not only prevent tumor initiation, but also halt progression and ultimately improve patient wellbeing and survival.

Polyamine Homeostasis in Development and Disease

Polycationic polyamines are present in nearly all living organisms and are essential for mammalian cell growth and survival, and for development. These positively charged molecules are involved in a variety of essential biological processes, yet their underlying mechanisms of action are not fully understood. Several studies have shown both beneficial and detrimental effects of polyamines on human health. In cancer, polyamine metabolism is frequently dysregulated, and elevated polyamines have been shown to promote tumor growth and progression, suggesting that targeting polyamines is an attractive strategy for therapeutic intervention. In contrast, polyamines have also been shown to play critical roles in lifespan, cardiac health and in the development and function of the brain. Accordingly, a detailed understanding of mechanisms that control polyamine homeostasis in human health and disease is needed to develop safe and effective strategies for polyamine-targeted therapy.

Enhanced expression of SLC4A11 by tert-Butylhydroquinone is mediated by direct binding of Nrf2 to the promoter of SLC4A11

BACKGROUND

SLC4A11, a Na + dependent OH^- transporter, is highly expressed in the epithelium and endothelium of the cornea. Mutations in SLC4A11 cause congenital hereditary endothelial dystrophy (CHED), a progressive disease with gradual loss of vision and characterized by degeneration and dysfunction of corneal endothelial cells. SLC4A11 expression is also responsive to oxidative stress. Thus, understanding of SLC4A11 gene regulation is of utmost importance for therapeutic interventions. However, it remains elusive how SLC4A11 is regulated at transcriptional and translational level.

METHODS

Bioinformatics analysis of the SLC4A11 promoter was performed using TRANSFAC. SLC4A11 promoter constructs were generated and exposed to tert-Butylhydroquinone (tBHQ) or cotransfected with Nuclear factor erythroid 2-related factor 2 (Nrf2) expression plasmid and promoter activity was determined. The expression of SLC4A11 was also determined by quantitative PCR and immunoblot analysis. The binding of Nrf2 to the promoter of SLC4A11 was validated by chromatin immunoprecipitation assay.

RESULTS

Induction of Nrf2 by tBHQ or overexpression of Nrf2 caused increased expression of SLC4A11 in HeLa and human corneal endothelial cells. A conserved Nrf2 binding sequence was found in the promoter of SLC4A11 of several mammalian species. Reporter gene assays showed transcriptional activation of the SLC4A11 promoter in response to tBHQ treatment and Nrf2 overexpression. ChIP analysis validated Nrf2 binding to the conserved sequence of the SLC4A11 promoter. Induction of the Nrf2 pathway also resulted in increased endogenous SLC4A11 protein abundance. On the other hand, depletion of Nrf2 inhibited both transcriptional and translational activities of SLC4A11.

CONCLUSION

In summary, we determined direct Nrf2 binding to antioxidant responsive element site within the SLC4A11 promoter, and observed increased expression of SLC4A11 by Nrf2 inducers. To the best of our knowledge, this is the first study showing Nrf2 exerts an important role in regulation of SLC4A11 gene expression.

Ferroptosis, radiotherapy, and combination therapeutic strategies

Ferroptosis, an iron-dependent form of regulated cell death driven by peroxidative damages of polyunsaturated-fatty-acid-containing phospholipids in cellular membranes, has recently been revealed to play an important role in radiotherapy-induced cell death and tumor suppression, and to mediate the synergy between radiotherapy and immunotherapy. In this review, we summarize known as well as putative mechanisms underlying the crosstalk between radiotherapy and ferroptosis, discuss the interactions between ferroptosis and other forms of regulated cell death induced by radiotherapy, and explore combination therapeutic strategies targeting ferroptosis in radiotherapy and immunotherapy. This review will provide important frameworks for future investigations of ferroptosis in cancer therapy.

Rapamycin Promotes ROS-Mediated Cell Death via Functional Inhibition of xCT Expression in Melanoma Under γ-Irradiation

Although many cancer patients are administered radiotherapy for their treatment, the interaction between tumor cells and macrophages in the tumor microenvironment attenuates the curative effects of radiotherapy. The enhanced activation of mTOR signaling in the tumors promotes tumor radioresistance. In this study, the effects of rapamycin on the interaction between tumor cells and macrophages were investigated. Rapamycin and 3BDO were used to regulate the mTOR pathway. In vitro, tumor cells cocultured with macrophages in the presence of each drug under normoxic or hypoxic conditions were irradiated with γ–rays. In vivo, mice were irradiated with γ–radiation after injection with DMSO, rapamycin and 3BDO into tumoral regions. Rapamycin reduced the secretion of IL-4 in tumor cells as well as YM1 in macrophages. Mouse recombinant YM1 decreased the enhanced level of ROS and the colocalized proportion of both xCT and EEA1 in irradiated tumor cells. Human recombinant YKL39 also induced results similar to those of YM1. Moreover, the colocalized proportion of both xCT and LC3 in tumor tissues was elevated by the injection of rapamycin into tumoral regions. Overall, the suppression of mTOR signaling in the tumor microenvironment might be useful for the improvement of tumor radioresistance.

Glutamine metabolite α-ketoglutarate acts as an epigenetic co-factor to interfere with osteoclast differentiation

Osteoclasts (OCs) have been well-known involved in the exacerbation of bone-related diseases. However, the role of metabolites on osteoclastogenesis has not been well characterized. Herein, we found osteoclastogenesis was negatively regulated by α-ketoglutarate (αKG) in vitro and in vivo (C57BL/6 mouse). Kinetic transcriptome analysis revealed the upregulation of solute carrier family 7 member 11 (Slc7a11), a subunit of the cysteine/glutamate antiporter, as well as the downregulation of typical OC maker genes through αKG treatment. Given that Slc7a11 could control ROS level through glutathione import, we measured intracellular ROS, then RANKL-induced ROS production was inhibited by αKG. Notably, we highlight that αKG plays an epigenetic co-factor at the Slc7a11 promoter by demethylating repressive histone H3K9 methylation and simultaneously increasing the nuclear factor erythroid 2-related factor (Nrf2) binding, a critical transcription factor through chromatin immunoprecipitation (ChIP) analysis. Together, we suggested that αKG could be a therapeutic strategy for OC activated diseases.

xCT/SLC7A11 antiporter function inhibits HIV-1 infection

Human macrophages are protected by intrinsic antiviral defenses that provide moderate protection against HIV-1 infection. Macrophages that do become infected can serve as long-lived reservoirs, to disseminate HIV-1 to CD4+ T cells. Infection of macrophages with HIV-1 and HIV-2 is inhibited by constitutive mobilization of antioxidant response master transcription regulator Nrf2. The downstream mediator of this restriction was not identified. Among the tens of genes controlled directly by Nrf2 in macrophages, we found that xCT/SLC7A11, a 12-transmembrane, cystine-glutamate antiporter promotes antiretroviral activity. We show here that depletion of xCT mRNA increases HIV-1 infection. Reconstitution of xCT knock out cells with wild-type xCT but not a transport-deficient mutant restores anti-HIV-1 activity. Pharmacological inhibitors of xCT amino acid transport also increase infection. The block is independent of known restriction factors and acts against HIV-1 and HIV-2. Like the block triggered through Nrf2, xCT function impedes infection immediately before 2-LTR circle formation.

Molecular pathology underlying the robustness of cancer stem cells

Intratumoral heterogeneity is tightly associated with the failure of anticancer treatment modalities including conventional chemotherapy, radiation therapy, and molecularly targeted therapy. Such heterogeneity is generated in an evolutionary manner not only as a result of genetic alterations but also by the presence of cancer stem cells (CSCs). CSCs are proposed to exist at the top of a tumor cell hierarchy and are undifferentiated tumor cells that manifest enhanced tumorigenic and metastatic potential, self-renewal capacity, and therapeutic resistance. Properties that contribute to the robustness of CSCs include the abilities to withstand redox stress, to rapidly repair damaged DNA, to adapt to a hyperinflammatory or hyponutritious tumor microenvironment, and to expel anticancer drugs by the action of ATP-binding cassette transporters as well as plasticity with regard to the transition between dormant CSC and transit-amplifying progenitor cell phenotypes. In addition, CSCs manifest the phenomenon of metabolic reprogramming, which is essential for maintenance of their self-renewal potential and their ability to adapt to changes in the tumor microenvironment. Elucidation of the molecular underpinnings of these biological features of CSCs is key to the development of novel anticancer therapies. In this review, we highlight the pathological relevance of CSCs in terms of their hallmarks and identification, the properties of their niche—both in primary tumors and at potential sites of metastasis—and their resistance to oxidative stress dependent on system xc (−).

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Intratumoral heterogeneity driven by CSCs is responsible for therapeutic resistance.

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CTCs survive in the distant organs and achieve colonization, causing metastasis.

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E/M hybrid cancer cells due to partial EMT exhibit the highest metastatic potential.

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The CSC niche regulates stemness in metastatic disease as well as in primary tumor.

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Activation of system xc(-) by CD44 variant in CSCs is a promising therapeutic target.

The mTORC1-mediated activation of ATF4 promotes protein and glutathione synthesis downstream of growth signals

The mechanistic target of rapamycin complex 1 (mTORC1) stimulates a coordinated anabolic program in response to growth-promoting signals. Paradoxically, recent studies indicate that mTORC1 can activate the transcription factor ATF4 through mechanisms distinct from its canonical induction by the integrated stress response (ISR). However, its broader roles as a downstream target of mTORC1 are unknown. Therefore, we directly compared ATF4-dependent transcriptional changes induced upon insulin-stimulated mTORC1 signaling to those activated by the ISR. In multiple mouse embryo fibroblast and human cancer cell lines, the mTORC1-ATF4 pathway stimulated expression of only a subset of the ATF4 target genes induced by the ISR, including genes involved in amino acid uptake, synthesis, and tRNA charging. We demonstrate that ATF4 is a metabolic effector of mTORC1 involved in both its established role in promoting protein synthesis and in a previously unappreciated function for mTORC1 in stimulating cellular cystine uptake and glutathione synthesis.

Cysteine metabolic circuitries: druggable targets in cancer

To enable survival in adverse conditions, cancer cells undergo global metabolic adaptations. The amino acid cysteine actively contributes to cancer metabolic remodelling on three different levels: first, in its free form, in redox control, as a component of the antioxidant glutathione or its involvement in protein s-cysteinylation, a reversible post-translational modification; second, as a substrate for the production of hydrogen sulphide (H2S), which feeds the mitochondrial electron transfer chain and mediates per-sulphidation of ATPase and glycolytic enzymes, thereby stimulating cellular bioenergetics; and, finally, as a carbon source for epigenetic regulation, biomass production and energy production. This review will provide a systematic portrayal of the role of cysteine in cancer biology as a source of carbon and sulphur atoms, the pivotal role of cysteine in different metabolic pathways and the importance of H2S as an energetic substrate and signalling molecule. The different pools of cysteine in the cell and within the body, and their putative use as prognostic cancer markers will be also addressed. Finally, we will discuss the pharmacological means and potential of targeting cysteine metabolism for the treatment of cancer.

S-allyl cysteine ameliorates heat stress-induced oxidative stress by activating Nrf2/HO-1 signaling pathway in BMECs

Heat stress-induced oxidative stress in bovine mammary epithelial cells (BMECs) threatens the normal growth and development of bovine mammary tissue, resulting in lower milk production of dairy cows. The aim of the present study is to investigate the protective effects of S-allyl cysteine (SAC), an organosulfur component extracted from aged garlic, on heat stress-induced oxidative stress and apoptosis in BMECs and to explore its underlying mechanisms. Our results showed that heat stress treatment considerably decreased cell viability, whereas SAC treatment dose-dependently restored cell viability of BMECs under heat-stress conditions. In addition, SAC protected BMECs from heat stress-induced oxidative damage by inhibiting the excessive accumulation of reactive oxygen species (ROS) and increasing the activity of antioxidant enzymes. It also inhibited heat stress-induced apoptosis by reducing the ratio of Bax/Bcl-2 and blocking proteolytic the cleavage of caspase-3 in BMECs. Interestingly, we found that the protective effect of SAC on heat stress-induced oxidative stress and apoptosis was dependent on the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway. SAC promoted the Nrf2 nuclear translocation in heat stress-induced BMECs. The results were also validated by Nrf2 and Keap1 knockdown experiments further demonstrating that Nrf-2 was indeed involved in the protective effect of SAC on heat stress-induced oxidative damage and apoptosis. In summary, our results showed that SAC could protect BMECs from heat stress-induced injury by mediating the Nrf2/HO-1 signaling pathway, suggesting that SAC could be considered as a therapeutic drug for attenuating heat stress-induced mammary gland diseases.

Administration of N-acetylcysteine Plus Acetylsalicylic Acid Markedly Inhibits Nicotine Reinstatement Following Chronic Oral Nicotine Intake in Female Rats

Background

Nicotine is the major addictive component of cigarette smoke and the prime culprit of the failure to quit smoking. Common elements perpetuating the use of addictive drugs are (i) cues associated with the setting in which drug was used and (ii) relapse/reinstatement mediated by an increased glutamatergic tone (iii) associated with drug-induced neuroinflammation and oxidative stress.

Aims

The present study assessed the effect of the coadministration of the antioxidant N-acetylcysteine (NAC) plus the anti-inflammatory acetylsalicylic acid (ASA) on oral nicotine reinstatement intake following a post-deprivation re-access in female rats that had chronically and voluntarily consumed a nicotine solution orally. The nicotine-induced oxidative stress and neuroinflammation in the hippocampus and its effects on the glutamate transporters GLT-1 and XCT mRNA levels in prefrontal cortex were also analyzed.

Results

The oral coadministration of NAC (40 mg/kg/day) and ASA (15 mg/kg/day) inhibited by 85% of the oral nicotine reinstatement intake compared to control (vehicle), showing an additive effect of both drugs. Acetylsalicylic acid and N-acetylcysteine normalized hippocampal oxidative stress and blunted the hippocampal neuroinflammation observed upon oral nicotine reinstatement. Nicotine downregulated GLT-1 and xCT gene expression in the prefrontal cortex, an effect reversed by N-acetylcysteine, while acetylsalicylic acid reversed the nicotine-induced downregulation of GLT-1 gene expression. The inhibitory effect of N-acetylcysteine on chronic nicotine intake was blocked by the administration of sulfasalazine, an inhibitor of the xCT transporter.

Conclusion

Nicotine reinstatement, following post-deprivation of chronic oral nicotine intake, downregulates the mRNA levels of GLT-1 and xCT transporters, an effect reversed by the coadministration of N-acetylcysteine and acetylsalicylic acid, leading to a marked inhibition of nicotine intake. The combination of these drugs may constitute a valuable adjunct in the treatment of nicotine-dependent behaviors.

System Xc-: a key regulatory target of ferroptosis in cancer

Ferroptosis is a type of oxidative stress-dependent regulated necrosis characterized by excessive lipid peroxide accumulation. This novel cell death modality has been implicated in preventing cancer progression. Cancer cells tend to modulate their redox state to prevent excessive peroxidation, eventually facilitating tumor growth. System Xc^- (a cystine/glutamate antiporter system) is a promising target in cancer cells for ferroptosis induction. The overexpression of system Xc^-, especially its core subunit xCT, has been reported in several tumors, and these high expression levels were closely related to cancer cell proliferation, invasion, metastasis and the tumor microenvironment. xCT might serve as a novel biomarker, and its upregulation almost always indicates drug tolerance and poor survival. Therefore, system Xc^- inhibition may enhance chemotherapy sensitivity and optimize patient prognosis. Here, we elaborate on the mediation of ferroptosis by suppressing system Xc^- and the relevant underlying molecular mechanism in cancer cells. The spotlight on this approach to cancer treatment is creating a new horizon and pointing to future opportunities.

Natural Products as Inducers of Non-Canonical Cell Death: A Weapon against Cancer

Simple Summary

Anticancer therapeutic approaches based solely on apoptosis induction are often unsuccessful due to the activation of resistance mechanisms. The identification and characterization of compounds capable of triggering non-apoptotic, also called non-canonical cell death pathways, could represent an important strategy that may integrate or offer alternative approaches to the current anticancer therapies. In this review, we critically discuss the promotion of ferroptosis, necroptosis, and pyroptosis by natural compounds as a new anticancer strategy.

Abstract

Apoptosis has been considered the main mechanism induced by cancer chemotherapeutic drugs for a long time. This paradigm is currently evolving and changing, as increasing evidence pointed out that antitumor agents could trigger various non-canonical or non-apoptotic cell death types. A considerable number of antitumor drugs derive from natural sources, both in their naturally occurring form or as synthetic derivatives. Therefore, it is not surprising that several natural compounds have been explored for their ability to induce non-canonical cell death. The aim of this review is to highlight the potential antitumor effects of natural products as ferroptosis, necroptosis, or pyroptosis inducers. Natural products have proven to be promising non-canonical cell death inducers, capable of overcoming cancer cells resistance to apoptosis. However, as discussed in this review, they often lack a full characterization of their antitumor activity together with an in-depth investigation of their toxicological profile.

The Taming of Nuclear Factor Erythroid-2-Related Factor-2 (Nrf2) Deglycation by Fructosamine-3-Kinase (FN3K)-Inhibitors-A Novel Strategy to Combat Cancers

Simple Summary

Aim of this review is to provide an overview on (a) Fructosamine-3-Kinase (FN3K) and its role in regulating Nuclear Factor Erythorid-2-Related Factor-2 (Nrf2); (b) the role of glycation and deglycation mechanisms in modulating the functional properties of proteins, in particular, the Nrf2; (c) the dual role of Nrf2 in the prevention and treatment of cancers. Since controlling the glycation of Nrf2 is one of the key mechanisms determining the fate of a cell; whether to get transformed into a cancerous one or to stay as a normal one, it is important to regulate Nrf2 and deglycating FN3K using pharmacological agents. Inhibitors of FN3K are being explored currently to modulate Nrf2 activity thereby control the cancers.

Abstract

Glycated stress is mediated by the advanced glycation end products (AGE) and the binding of AGEs to the receptors for advanced glycation end products (RAGEs) in cancer cells. RAGEs are involved in mediating tumorigenesis of multiple cancers through the modulation of several downstream signaling cascades. Glycated stress modulates various signaling pathways that include p38 mitogen-activated protein kinase (p38 MAPK), nuclear factor kappa–B (NF-κB), tumor necrosis factor (TNF)-α, etc., which further foster the uncontrolled proliferation, growth, metastasis, angiogenesis, drug resistance, and evasion of apoptosis in several cancers. In this review, a balanced overview on the role of glycation and deglycation in modulating several signaling cascades that are involved in the progression of cancers was discussed. Further, we have highlighted the functional role of deglycating enzyme fructosamine-3-kinase (FN3K) on Nrf2-driven cancers. The activity of FN3K is attributed to its ability to deglycate Nrf2, a master regulator of oxidative stress in cells. FN3K is a unique protein that mediates deglycation by phosphorylating basic amino acids lysine and arginine in various proteins such as Nrf2. Deglycated Nrf2 is stable and binds to small musculoaponeurotic fibrosarcoma (sMAF) proteins, thereby activating cellular antioxidant mechanisms to protect cells from oxidative stress. This cellular protection offered by Nrf2 activation, in one way, prevents the transformation of a normal cell into a cancer cell; however, in the other way, it helps a cancer cell not only to survive under hypoxic conditions but also, to stay protected from various chemo- and radio-therapeutic treatments. Therefore, the activation of Nrf2 is similar to a double-edged sword and, if not controlled properly, can lead to the development of many solid tumors. Hence, there is a need to develop novel small molecule modulators/phytochemicals that can regulate FN3K activity, thereby maintaining Nrf2 in a controlled activation state.

Tumor-Associated Antigen xCT and Mutant-p53 as Molecular Targets for New Combinatorial Antitumor Strategies

The cystine/glutamate antiporter xCT is a tumor-associated antigen that has been newly identified in many cancer types. By participating in glutathione biosynthesis, xCT protects cancer cells from oxidative stress conditions and ferroptosis, and contributes to metabolic reprogramming, thus promoting tumor progression and chemoresistance. Moreover, xCT is overexpressed in cancer stem cells. These features render xCT a promising target for cancer therapy, as has been widely reported in the literature and in our work on its immunotargeting. Interestingly, studies on the TP53 gene have revealed that both wild-type and mutant p53 induce the post-transcriptional down modulation of xCT, contributing to ferroptosis. Moreover, APR-246, a small molecule drug that can restore wild-type p53 function in cancer cells, has been described as an indirect modulator of xCT expression in tumors with mutant p53 accumulation, and is thus a promising drug to use in combination with xCT inhibition. This review summarizes the current knowledge of xCT and its regulation by p53, with a focus on the crosstalk of these two molecules in ferroptosis, and also considers some possible combinatorial strategies that can make use of APR-246 treatment in combination with anti-xCT immunotargeting.

Non-canonical Glutamate-Cysteine Ligase Activity Protects against Ferroptosis

Cysteine is required for maintaining cellular redox homeostasis in both normal and transformed cells. Deprivation of cysteine induces the iron-dependent form of cell death known as ferroptosis; however, the metabolic consequences of cysteine starvation beyond impairment of glutathione synthesis are poorly characterized. Here, we find that cystine starvation of non-small-cell lung cancer cell lines induces an unexpected accumulation of γ-glutamyl-peptides, which are produced due to a non-canonical activity of glutamate-cysteine ligase catalytic subunit (GCLC). This activity is enriched in cell lines with high levels of NRF2, a key transcriptional regulator of GCLC, but is also inducible in healthy murine tissues following cysteine limitation. γ-glutamyl-peptide synthesis limits the accumulation of glutamate, thereby protecting against ferroptosis. These results indicate that GCLC has a glutathione-independent, non-canonical role in the protection against ferroptosis by maintaining glutamate homeostasis under cystine starvation.

The Harmonious Interplay of Amino Acid and Monocarboxylate Transporters Induces the Robustness of Cancer Cells

There is a growing body of evidence that metabolic reprogramming contributes to the acquisition and maintenance of robustness associated with malignancy. The fine regulation of expression levels of amino acid and monocarboxylate transporters enables cancer cells to exhibit the metabolic reprogramming that is responsible for therapeutic resistance. Amino acid transporters characterized by xCT (SLC7A11), ASCT2 (SLC1A5), and LAT1 (SLC7A5) function in the uptake and export of amino acids such as cystine and glutamine, thereby regulating glutathione synthesis, autophagy, and glutaminolysis. CD44 variant, a cancer stem-like cell marker, stabilizes the xCT antiporter at the cellular membrane, and tumor cells positive for xCT and/or ASCT2 are susceptible to sulfasalazine, a system Xc(-) inhibitor. Inhibiting the interaction between LAT1 and CD98 heavy chain prevents activation of the mammalian target of rapamycin (mTOR) complex 1 by glutamine and leucine. mTOR signaling regulated by LAT1 is a sensor of dynamic alterations in the nutrient tumor microenvironment. LAT1 is overexpressed in various malignancies and positively correlated with poor clinical outcome. Metabolic reprogramming of glutamine occurs often in cancer cells and manifests as ASCT2-mediated glutamine addiction. Monocarboxylate transporters (MCTs) mediate metabolic symbiosis, by which lactate in cancer cells under hypoxia is exported through MCT4 and imported by MCT1 in less hypoxic regions, where it is used as an oxidative metabolite. Differential expression patterns of transporters cause functional intratumoral heterogeneity leading to the therapeutic resistance. Therefore, metabolic reprogramming based on these transporters may be a promising therapeutic target. This review highlights the pathological function and therapeutic targets of transporters including xCT, ASCT2, LAT1, and MCT.

Amino Acid Transporters on the Guard of Cell Genome and Epigenome

Tumorigenesis is driven by metabolic reprogramming. Oncogenic mutations and epigenetic alterations that cause metabolic rewiring may also upregulate the reactive oxygen species (ROS). Precise regulation of the intracellular ROS levels is critical for tumor cell growth and survival. High ROS production leads to the damage of vital macromolecules, such as DNA, proteins, and lipids, causing genomic instability and further tumor evolution. One of the hallmarks of cancer metabolism is deregulated amino acid uptake. In fast-growing tumors, amino acids are not only the source of energy and building intermediates but also critical regulators of redox homeostasis. Amino acid uptake regulates the intracellular glutathione (GSH) levels, endoplasmic reticulum stress, unfolded protein response signaling, mTOR-mediated antioxidant defense, and epigenetic adaptations of tumor cells to oxidative stress. This review summarizes the role of amino acid transporters as the defender of tumor antioxidant system and genome integrity and discusses them as promising therapeutic targets and tumor imaging tools.

Aldo Keto Reductases AKR1B1 and AKR1B10 in Cancer: Molecular Mechanisms and Signaling Networks

Deregulation of metabolic pathways has increasingly been appreciated as a major driver of cancer in recent years. The principal cancer-associated alterations in metabolism include abnormal uptake of glucose and amino acids and the preferential use of metabolic pathways for the production of biomass and nicotinamide adenine dinucleotide phosphate (NADPH). Aldo-keto reductases (AKRs) are NADPH dependent cytosolic enzymes that can catalyze the reduction of carbonyl groups to primary and secondary alcohols using electrons from NADPH. Aldose reductase, also known as AKR1B1, catalyzes the conversion of excess glucose to sorbitol and has been studied extensively for its role in a number of diabetic pathologies. In recent years, however, high expression of the AKR1B and AKR1C family of enzymes has been strongly associated with worse outcomes in different cancer types. This review provides an overview of the catalysis-dependent and independent data emerging on the molecular mechanisms of the functions of AKRBs in different tumor models with an emphasis of the role of these enzymes in chemoresistance, inflammation, oxidative stress and epithelial-to-mesenchymal transition.