Cystine Uptake Research Articles

SNF2L maintains glutathione homeostasis by initiating SLC7A11 transcription through chromatin remodeling.

SNF2L encodes an ISWI chromatin remodeling factor that promotes gene transcription and is consistently elevated in cancers. Previous studies have shown that inhibiting SNF2L expression in cancer cells leads to significant growth suppression, DNA damage, and cell death. However, the underlying mechanisms remain poorly understood. In this study, we demonstrated that cancer cells lacking SNF2L show significantly decreased glutathione (GSH) levels, leading to elevated reactive oxygen species (ROS) and increased oxidative stress. SNF2L deficiency also heightened the sensitivity of cancer cells to APR-246, a drug that depletes GSH and induces oxidative stress, consequently decreasing cell viability and increasing ROS levels, regardless of p53 status. Mechanistically, we found that NRF2 recruits SNF2L to the SLC7A11 promoter, leading to increased chromatin accessibility and facilitating SLC7A11 transcription. This results in decreased cystine uptake and impaired GSH biosynthesis. These findings suggest that targeting the SNF2L/SLC7A11 axis could enhance the effectiveness of APR-246 by depleting GSH and increasing ROS level in cancer cells, highlighting SNF2L as a promising therapeutic target.

Engineered nanoplatform mediated gas therapy enhanced ferroptosis for tumor therapy in vivo

The high glutathione (GSH) environment poses a significant challenge for inducing ferroptosis in tumor cells, necessitating the development of nanoplatforms that can deplete intracellular GSH. In this study, we developed an engineered nanoplatform (MIL-100@Era/L-Arg-HA) that enhances ferroptosis through gas therapy. First, we confirmed that the Fe element in the nanoplatform undergoes valence changes under the influence of high GSH and H2O2 in tumor cells. Meanwhile, L-Arg generates NO gas in the presence of intracellular H2O2, which reacts with GSH. Additionally, Erastin depletes GSH by inhibiting the cystine/glutamate antiporter system, reducing cystine uptake and impairing GPX4, while also increasing intracellular H2O2 levels by activating NOX4 protein expression. Through these combined GSH-depletion mechanisms, we demonstrated that MIL-100@Era/L-Arg-HA effectively depletes GSH levels, disrupts GPX4 function, and increases intracellular lipid ROS levels in vitro. Furthermore, this nanoplatform significantly inhibited tumor cell growth and extended the survival time of tumor-bearing mice in vivo. This engineered nanoplatform, which enhances ferroptosis through gas therapy, shows significant promise for ferroptosis-based cancer therapy and offers potential strategies for clinical tumor treatment.

NINJ1 regulates ferroptosis via xCT antiporter interaction and CoA modulation.

Ninjurin-1 (NINJ1), initially identified as a stress-induced protein in neurons, recently emerged as a key mediator of plasma membrane rupture (PMR) during apoptosis, necrosis, and pyroptosis. However, its involvement in ferroptosis is less well elucidated. Here, we demonstrate that NINJ1 also plays a crucial role in ferroptosis, but through a distinct mechanism. NINJ1 knockdown significantly protected cancer cells against ferroptosis induced only by xCT inhibitors but no other classes of ferroptosis-inducing compounds (FINs). Glycine, known to inhibit canonical NINJ1-mediated membrane rupture in other cell deaths, had no impact on ferroptosis. A compound screen revealed that the ferroptosis protective effect caused by NINJ1 knockdown can be abolished by pantothenate kinase inhibitor (PANKi), buthionine sulfoximine (BSO), and diethylmaleate (DEM). These results suggest that this ferroptosis protection is mediated via Coenzyme A (CoA) and glutathione (GSH), both of which were found to be elevated upon NINJ1 knockdown. Furthermore, we discovered that NINJ1 interacts with the xCT antiporter, which is responsible for cystine uptake for the biosynthesis of CoA and GSH. The removal of NINJ1 increased xCT levels and stability, enhancing cystine uptake and thereby providing protection against ferroptosis. Conversely, NINJ1 overexpression reduced xCT levels and sensitized ferroptosis. These findings reveal that NINJ1 regulates ferroptosis via a non-canonical mechanism, distinct from other regulated cell deaths.

Tumor suppressor BAP1 suppresses disulfidptosis through the regulation of SLC7A11 and NADPH levels

BAP1, BRCA1-Associated Protein 1, serves as a novel tumor suppressor through the deubiquitination of monoubiquitination of H2A and subsequent gene transcriptional regulation. Regulated cell death like apoptosis or ferroptosis is considered an essential mechanism mediating tumor suppression. Previous reports, including ours, have demonstrated that BAP1 could promote apoptosis and ferroptosis to inhibit tumor development. Whether BAP1 regulated additional types of cell death remains unclear. Disulfidptosis is a recently identified novel cell death mode characterized by aberrant accumulation of intracellular disulfide (e.g., cystine) and depletion of NADPH. In this study, we first demonstrated that BAP1 could significantly protect disulfidptosis induced by glucose starvation, which is validated by various cell death inhibitors and the accumulation of disulfide bonds in the cytoskeleton proteins. BAP1 is known to inhibit SLC7A11 expression. We found that the protective effect of BAP1 against disulfidptosis was counteracted when overexpressing SLC7A11 or adding additional cystine. Conversely, BAP1-mediated suppression of disulfidptosis was largely abrogated when SLC7A11-mediated cystine uptake was inhibited by the knockout of SLC7A11 or erastin treatment. Besides, high BAP1 expression showed lower NADP+/NADPH levels, which might confer resistance to disulfidptosis. Consistent with these observations, the expression level of BAP1 was also positively correlated with NADPH-related genes in KIRC patients, though the underlying mechanism mediating NADPH regulation remains further investigation. In summary, our results revealed the role of BAP1 in the regulation disulfidptosis and provided new insights into the understanding of disulfidptosis in tumor development.

AZD1775 synergizes with SLC7A11 inhibition to promote ferroptosis.

Tumor suppressor p53-mediated cell cycle arrest and DNA damage repair may exert cytoprotective effects against cancer therapies, including WEE1 inhibition. Considering that p53 activation can also lead to multiple types of cell death, the role of this tumor suppressor in WEE1 inhibitor-based therapies remains disputed. In this study, we reported that nucleolar stress-mediated p53 activation enhanced the WEE1 inhibitor AZD1775-induced ferroptosis to suppress lung cancer growth. Our findings showed that AZD1775 promoted ferroptosis by blocking cystine uptake, an action similar to that of Erastin. Meanwhile, inhibition of WEE1 by the WEE1 inhibitors or siRNAs induced compensatory upregulation of SLC7A11, which conferred resistance to ferroptosis. Mechanistically, AZD1775 prevented the enrichment of H3K9me3, a histone marker of transcriptional repression, on the SLC7A11 promoter by repressing the expression of the histone methyltransferase SETDB1, thereby enhancing NRF2-mediated SLC7A11 transcription. This finding was also validated using the H3K9me3 inhibitor BRD4770. Remarkably, we found that the nucleolar stress-inducing agent Actinomycin D (Act. D) inhibited SLC7A11 expression by activating p53, thus augmenting AZD1775-induced ferroptosis. Moreover, the combination of AZD1775 and Act. D synergistically suppressed wild-type p53-harboring lung cancer cell growth both in vitro and in vivo. Altogether, our study demonstrates that AZD1775 promotes ferroptosis by targeting cystine uptake but also mediates the adaptive activation of SLC7A11 through the WEE1-SETDB1 cascade and NRF2-induced transcription, and inhibition of SLC7A11 by Act. D boosts the anti-tumor efficacy of AZD1775 by enhancing ferroptosis in cancers with wild-type p53.

Epigenetic repression of de novo cysteine synthetases induces intra-cellular accumulation of cysteine in hepatocarcinoma by up-regulating the cystine uptake transporter xCT

BackgroundThe metabolic reprogramming of amino acids is critical for cancer cell growth and survival. Notably, intracellular accumulation of cysteine is often observed in various cancers, suggesting its potential role in alleviating the oxidative stress associated with rapid proliferation. The liver is the primary organ for cysteine biosynthesis, but much remains unknown about the metabolic alterations of cysteine and their mechanisms in hepatocellular carcinoma cells.MethodsRNA-seq data from patients with hepatocarcinoma were analyzed using the TNMplot database. The underlying mechanism of the oncogenic alteration of cysteine metabolism was studied in mice implanted with BNL 1ME A.7 R.1 hepatocarcinoma.ResultsDatabase analysis of patients with hepatocellular carcinoma revealed that the expression of enzymes involved in de novo cysteine synthesis was down-regulated accompanying with increased expression of the cystine uptake transporter xCT. Similar alterations in gene expression have also been observed in a syngeneic mouse model of hepatocarcinoma. The enhanced expression of DNA methyltransferase in murine hepatocarcinoma cells caused methylation of the upstream regions of cysteine synthesis genes, thereby repressing their expression. Conversely, suppression of de novo cysteine synthesis in healthy liver cells induced xCT expression by up-regulating the oxidative-stress response factor NRF2, indicating that reduced de novo cysteine synthesis repulsively increases cystine uptake via enhanced xCT expression, leading to intracellular cysteine accumulation. Furthermore, the pharmacological inhibition of xCT activity decreased intracellular cysteine levels and suppressed hepatocarcinoma tumor growth in mice.ConclusionsOur findings indicate an underlying mechanism of the oncogenic alteration of cysteine metabolism in hepatocarcinoma and highlight the efficacy of alteration of cysteine metabolism as a viable therapeutic target in cancer.

Ursodeoxycholic acid inhibits the uptake of cystine through SLC7A11 and impairs de novo synthesis of glutathione

Ursodeoxycholic acid (UDCA) is a naturally occurring, low-toxicity, and hydrophilic bile acid (BA) in the human body that is converted by intestinal flora using primary BA. Solute carrier family 7 member 11 (SLC7A11) functions to uptake extracellular cystine in exchange for glutamate, and is highly expressed in a variety of human cancers. Retroperitoneal liposarcoma (RLPS) refers to liposarcoma originating from the retroperitoneal area. Lipidomics analysis revealed that UDCA was one of the most significantly downregulated metabolites in sera of RLPS patients compared with healthy subjects. The augmentation of UDCA concentration (≥25 μg/mL) demonstrated a suppressive effect on the proliferation of liposarcoma cells. [15N2]-cystine and [13C5]-glutamine isotope tracing revealed that UDCA impairs cystine uptake and glutathione (GSH) synthesis. Mechanistically, UDCA binds to the cystine transporter SLC7A11 to inhibit cystine uptake and impair GSH de novo synthesis, leading to reactive oxygen species (ROS) accumulation and mitochondrial oxidative damage. Furthermore, UDCA can promote the anti-cancer effects of ferroptosis inducers (Erastin, RSL3), the murine double minute 2 (MDM2) inhibitors (Nutlin 3a, RG7112), cyclin dependent kinase 4 (CDK4) inhibitor (Abemaciclib), and glutaminase inhibitor (CB839). Together, UDCA functions as a cystine exchange factor that binds to SLC7A11 for antitumor activity, and SLC7A11 is not only a new transporter for BA but also a clinically applicable target for UDCA. More importantly, in combination with other antitumor chemotherapy or physiotherapy treatments, UDCA may provide effective and promising treatment strategies for RLPS or other types of tumors in a ROS-dependent manner.

Discovery of the Inhibitor Targeting the SLC7A11/xCT Axis through In Silico and In Vitro Experiments.

In the development and progression of cervical cancer, oxidative stress plays an important role within the cells. Among them, Solute Carrier Family 7 Member 11 (SLC7A11/xCT) is crucial for maintaining the synthesis of glutathione and the antioxidant system in cervical cancer cells. In various tumor cells, studies have shown that SLC7A11 inhibits ferroptosis, a form of cell death, by mediating cystine uptake and maintaining glutathione synthesis. Additionally, SLC7A11 is also involved in promoting tumor metastasis and immune evasion. Therefore, inhibiting the SLC7A11/xCT axis has become a potential therapeutic strategy for cervical cancer. In this study, through structure-based high-throughput virtual screening, a compound targeting the SLC7A11/xCT axis named compound 1 (PubChem CID: 3492258) was discovered. In vitro experiments using HeLa cervical cancer cells as the experimental cell model showed that compound 1 could reduce intracellular glutathione levels, increase glutamate and reactive oxygen species (ROS) levels, disrupt the oxidative balance within HeLa cells, and induce cell death. Furthermore, molecular dynamics simulation results showed that compound 1 has a stronger binding affinity with SLC7A11 compared to the positive control erastin. Overall, all the results mentioned above indicate the potential of compound 1 in targeting the SLC7A11/xCT axis and treating cervical cancer both in vitro and in silico.

IGF2BP3 suppresses ferroptosis in lung adenocarcinoma by m6A-dependent regulation of TFAP2A to transcriptionally activate SLC7A11/GPX4.

Ferroptosis is recently discovered as an important player in the initiation, proliferation, and progression of human tumors. Insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) has been reported as an oncogene in multiple types of cancers, including lung adenocarcinoma (LUAD). However, little research has been designed to investigate the regulation of IGF2BP3 on ferroptosis in LUAD. qRT-PCR and western blot were used to measure the mRNA and protein expression of IGF2BP3 and transcription factor AP-2 alpha (TFAP2A). CCK-8 assay was performed to determine cell viability. DCFH-DA and C11-BODIPY staining were used to detect the levels of intracellular reactive oxygen species (ROS) and lipid ROS. The corresponding assay kits were used to analyze the levels of malondialdehyde (MDA) and glutathione (GSH). SRAMP website and m6A RNA immunoprecipitation (Me-RIP) were used to predict and confirm the m6A modification of TFAP2A. RIP experiments were conducted to confirm the binding of IGF2BP3 and TFAP2A. RNA stability assay was performed using actinomycin D. Chromatin immunoprecipitation (ChIP) and dual-luciferase reporter experiments were performed to confirm the interaction between TFAP2A and cystine/glutamate antiporter solute carrier family 7 member 11 (SLC7A11) or glutathione peroxidase 4 (GPX4). Mice xenotransplant model was also constructed to explore the effect of IGF2BP3 on LUAD tumor growth and ferroptosis. IGF2BP3 and TFAP2A were both highly expressed in LUAD. IGF2BP3 or TFAP2A knockdown induced ferroptosis by aggravating erastin-induced cell viability suppression, increasing the production of intracellular ROS, lipid ROS, and MDA, and decreasing GSH synthesis, GSH/GSSG ratio, and cystine uptake. Mechanistically, IGF2BP3 stabilized TFAP2A expression via m6A modification. Moreover, sh-IGF2BP3-mediated ferroptosis was significantly abated by TFAP2A overexpression. Furthermore, TFAP2A binds to the promoters of SLC7A11 and GPX4 to promote their transcription. Also, IGF2BP3 depletion suppressed LUAD tumor growth by inducing ferroptosis in mice. IGF2BP3 suppresses ferroptosis in LUAD by m6A-dependent regulation of TFAP2A to promote the transcription of SLC7A11 and GPX4. Our findings suggest that targeting IGF2BP3/TFAP2A/SLC7A11/GPX4 axis might be a potential therapeutic choice to increase ferroptosis sensitivity in LUAD.

Emergence of large-scale cell death through ferroptotic trigger waves

Large-scale cell death is commonly observed during organismal development and in human pathologies1–5. These cell death events extend over great distances to eliminate large populations of cells, raising the question of how cell death can be coordinated in space and time. One mechanism that enables long-range signal transmission is trigger waves6, but how this mechanism might be used for death events in cell populations remains unclear. Here we demonstrate that ferroptosis, an iron- and lipid-peroxidation-dependent form of cell death, can propagate across human cells over long distances (≥5 mm) at constant speeds (around 5.5 μm min−1) through trigger waves of reactive oxygen species (ROS). Chemical and genetic perturbations indicate a primary role of ROS feedback loops (Fenton reaction, NADPH oxidase signalling and glutathione synthesis) in controlling the progression of ferroptotic trigger waves. We show that introducing ferroptotic stress through suppression of cystine uptake activates these ROS feedback loops, converting cellular redox systems from being monostable to being bistable and thereby priming cell populations to become bistable media over which ROS propagate. Furthermore, we demonstrate that ferroptosis and its propagation accompany the massive, yet spatially restricted, cell death events during muscle remodelling of the embryonic avian limb, substantiating its use as a tissue-sculpting strategy during embryogenesis. Our findings highlight the role of ferroptosis in coordinating global cell death events, providing a paradigm for investigating large-scale cell death in embryonic development and human pathologies.

Dual-Site Chemosensor for Visualizing •OH-GSH Redox and Tracking Ferroptosis-Inducing Pathways In Vivo.

Oxidative stress, characterized by an imbalance between oxidative and antioxidant processes, results in excessive accumulation of intracellular reactive oxygen species. Among these responses, the regulation of intracellular hydroxyl radicals (•OH) and glutathione (GSH) is vital for physiological processes. Real-time in situ monitoring these two opposing bioactive species and their redox interactions is essential for understanding physiological balance and imbalance. In this study, we developed a dual-site fluorescence chemosensor OG-3, which can independently image both exogenous and endogenous •OH and GSH in separate channels both within cells and in vivo, eliminating issues of spatiotemporal inhomogeneous distribution and cross-interference. With its imaging capabilities of monitoring •OH-GSH redox, OG-3 elucidated two different pathways for ferroptosis induction: (i) inhibition of system xc- to block cystine uptake (extrinsic pathway) and (ii) GPX4 inactivation, leading to the loss of antioxidant defense (intrinsic pathway). Moreover, we assessed the antiferroptotic function and effects of ferroptosis inhibitors by monitoring •OH and GSH fluctuations during ferroptosis. This method provides a reliable platform for identifying potential ferroptosis inhibitors, contributing to our understanding of relevant metabolic and physiological mechanisms. It shows potential for elucidating the regulation of ferroptosis mechanisms and investigating further strategies for therapeutic applications.

SLC7A11: the Achilles heel of tumor?

The non-natriuretic-dependent glutamate/cystine inverse transporter-system Xc- is composed of two protein subunits, SLC7A11 and SLC3A2, with SLC7A11 serving as the primary functional component responsible for cystine uptake and glutathione biosynthesis. SLC7A11 is implicated in tumor development through its regulation of redox homeostasis, amino acid metabolism, modulation of immune function, and induction of programmed cell death, among other processes relevant to tumorigenesis. In this paper, we summarize the structure and biological functions of SLC7A11, and discuss its potential role in tumor therapy, which provides a new direction for precision and personalized treatment of tumors.

The CRL3KCTD10 ubiquitin ligase–USP18 axis coordinately regulates cystine uptake and ferroptosis by modulating SLC7A11

SLC7A11 is a cystine transporter and ferroptosis inhibitor. How the stability of SLC7A11 is coordinately regulated in response to environmental cystine by which E3 ligase and deubiquitylase (DUB) remains elusive. Here, we report that neddylation inhibitor MLN4924 increases cystine uptake by causing SLC7A11 accumulation, via inactivating Cullin-RING ligase-3 (CRL-3). We identified KCTD10 as the substrate-recognizing subunit of CRL-3 for SLC7A11 ubiquitylation, and USP18 as SLC7A11 deubiquitylase. Upon cystine deprivation, the protein levels of KCTD10 or USP18 are decreased or increased, respectively, contributing to SLC7A11 accumulation. By destabilizing or stabilizing SLC7A11, KCTD10, or USP18 inversely regulates the cystine uptake and ferroptosis. Biologically, MLN4924 combination with SLC7A11 inhibitor Imidazole Ketone Erastin (IKE) enhanced suppression of tumor growth. In human breast tumor tissues, SLC7A11 levels were negatively or positively correlated with KCTD10 or USP18, respectively. Collectively, our study defines how SLC7A11 and ferroptosis is coordinately regulated by the CRL3KCTD10/E3-USP18/DUB axis, and provides a sound rationale of drug combination to enhance anticancer efficacy.

SLC7A11 promotes EMT and metastasis in invasive pituitary neuroendocrine tumors by activating the PI3K/AKT signaling pathway.

Invasive pituitary neuroendocrine tumors (PitNETs) are the most prevalent types of intracranial and neuroendocrine tumors. Their aggressive growth and difficulty in complete resection result in a high recurrence rate. Cystine transporter solute carrier family 7 member 11 (SLC7A11) is overexpressed in various cancers, which contributes to tumor growth, progression, and metastasis by promoting cystine uptake and glutathione biosynthesis. We identified SLC7A11 as an invasive biomarker based on three Gene Expression Omnibus cohorts. This study aimed to investigate the role of SLC7A11 in invasive PitNETs. Cell proliferation was assessed using CCK-8 and colony formation assays, while cell apoptosis was estimated with flow cytometry. Wound healing assays and transwell assays were utilized to evaluate migration and invasion ability. Our findings demonstrated that SLC7A11 was markedly upregulated in invasive PitNETs, and was associated with the invasiveness of PitNETs. Knockdown of SLC7A11 could largely suppress tumor cell proliferation, migration, and invasion, while inducing apoptosis. Furthermore, SLC7A11 depletion was implicated in regulating epithelial-mesenchymal transition and inactivating the PI3K/AKT signaling pathway. These insights suggest SLC7A11 as a potential therapeutic target for invasive PitNETs.

Formyl-Peptide Receptor 2 Signaling Modulates SLC7A11/xCT Expression and Activity in Tumor Cells.

Cancer cells exhibit high levels of oxidative stress and consequently require a high amount of cysteine for glutathione synthesis. Solute Carrier Family 7 Member 11 (SLC7A11), or xCT, mediates the cellular uptake of cystine in exchange for intracellular glutamate; imported extracellular cystine is reduced to cysteine in the cytosol through a NADPH-consuming reduction reaction. SLC7A11/xCT expression is under the control of stress-inducing conditions and of several transcription factors, such as NRF2 and ATF4. Formyl-peptide receptor 2 (FPR2) belongs to the FPR family, which transduces chemotactic signals mediating either inflammatory or anti-inflammatory responses according to the nature of its ligands and/or FPR2 binding with other FPR isoforms. The repertoire of FPR2 agonists with anti-inflammatory activities comprises WKYMVm peptide and Annexin A1 (ANXA1), and the downstream effects of the intracellular signaling cascades triggered by FPR2 include NADPH oxidase (NOX)-dependent generation of reactive oxygen species. Herein, we demonstrate that stimulation of CaLu-6 cells with either WKYMVm or ANXA1: (i) induces the redox-regulated activation of SLC7A11/xCT; (ii) promotes the synthesis of glutathione; (iii) prevents lipid peroxidation; and (iv) favors NRF2 nuclear translocation and activation. In conclusion, our overall results demonstrate that FPR2 agonists and NOX modulate SLC7A11/xCT expression and activity, thereby identifying a novel regulative pathway of the cystine/glutamate antiport that represents a new potential therapeutical target for the treatment of human cancers.

A Role for iNOS in Erastin Mediated Reduction of P-Glycoprotein Transport Activity.

The blood-brain barrier is composed of both a physical barrier and an enzymatic barrier. Tight junction (TJ) proteins expressed between endothelial cells of brain capillaries provide the physical barrier to paracellular movement of ions and molecules to the brain, while luminal-facing efflux transporters enzymatically restrict the entry of blood-borne molecules from entering the brain. The expression and activity of ATP Binding Cassette transporters or "ABC" transporters in endothelial cells of the BBB and in human tumor cells are dynamically regulated by numerous signaling pathways. P-glycoprotein (P-gp), (ABCB1), is arguably the most studied transporter of the BBB, and in human cell lines. P-glycoprotein transport activity is rapidly inhibited by signaling pathways that call for the rapid production of nitric oxide (NO) from the inducible nitric oxide synthase enzyme, iNOS. This study investigated how nano-molar levels of the selective chemotherapeutic erastin affect the activity or expression of P-glycoprotein transporter in brain capillaries and in human tumor cell lines. We chose erastin because it signals to iNOS for NO production at low concentrations. Furthermore, erastin inhibits the cellular uptake of cystine through the XC- cystine/glutamate antiporter. Since previous reports indicate that NO production from iNOS can rapidly inhibit P-gp activity in tumor cells, we wondered if induction of iNOS by erastin could also rapidly reduce P-glycoprotein transport activity in brain endothelial cells and in human tumor cell lines. We show here that low concentrations of erastin (1 nM) can induce iNOS, inhibit the activity of P-glycoprotein, and reduce the intracellular uptake of cystine via the Xc- cystine/glutamate antiporter. Consistent with reduced P-glycoprotein activity in rat brain capillary endothelial cells, we show that human tumor cell lines exposed to erastin become more sensitive to cytotoxic substrates of P-glycoprotein.

Novel Withanolides from Tubocapsicum anomalum Suppress Triple-Negative Breast Cancer by Triggering Apoptosis and p53-ASCT2-SLC7A11-Mediated Ferroptosis.

Triple-negative breast cancer (TNBC) is a malignant breast cancer. There is an urgent need for effective drugs to be developed for TNBC. Tubocapsicum anomalum (T. anomalum) has been reported to have an anti-tumor effect, and six novel withanolides were isolated from it and designated as TAMEWs. However, its anti-TNBC effect is still unknown. The results of an MTT assay indicated a higher sensitivity of TNBC cells to TAMEWs compared to other cells. TAMEWs induced apoptosis via mitochondrial dysfunction. They caused increased levels of lipid ROS and Fe2+, with downregulation of GSH and cystine uptake, and it has been confirmed that TAMEWs induced ferroptosis. Additionally, the results of Western blotting indicate that TAMEWs significantly decrease the expressions of ferroptosis-related proteins. Through further investigation, it was found that the knockdown of the p53 gene resulted in a significant reversal of ferroptosis and the expressions of its associated proteins SLC7A11, ASCT2, and GPX4. In vivo, TAMEWs suppressed TNBC growth with no obvious damage. The IHC results also showed that TAMEWs induced apoptosis and ferroptosis in vivo. Our findings provide the first evidence that TAMEWs suppress TNBC growth through apoptosis and ferroptosis.

NRF2 activation by cysteine as a survival mechanism for triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) is a very aggressive and heterogeneous group of tumors. In order to develop effective therapeutic strategies, it is therefore essential to identify the subtype-specific molecular mechanisms underlying disease progression and resistance to chemotherapy. TNBC cells are highly dependent on exogenous cystine, provided by overexpression of the cystine/glutamate antiporter SLC7A11/xCT, to fuel glutathione synthesis and promote an oxidative stress response consistent with their high metabolic demands. Here we show that TNBC cells of the mesenchymal stem-like subtype (MSL) utilize forced cystine uptake to induce activation of the transcription factor NRF2 and promote a glutathione-independent mechanism to defend against oxidative stress. Mechanistically, we demonstrate that NRF2 activation is mediated by direct cysteinylation of the inhibitor KEAP1. Furthermore, we show that cystine-mediated NRF2 activation induces the expression of important genes involved in oxidative stress response, but also in epithelial-to-mesenchymal transition and stem-like phenotype. Remarkably, in survival analysis, four upregulated genes (OSGIN1, RGS17, SRXN1, AKR1B10) are negative prognostic markers for TNBC. Finally, expression of exogenous OSGIN1, similarly to expression of exogenous NRF2, can prevent cystine depletion-dependent death of MSL TNBC cells. The results suggest that the cystine/NRF2/OSGIN1 axis is a potential target for effective treatment of MSL TNBCs.

Abstract 397: Exploring the role of MDM2-TP53 pathway and ATM in regulation of ferroptosis in dedifferentiated liposarcoma

Abstract Background: Ferroptosis, a process involved in accumulation of lipid-based reactive oxygen species (ROS), is a form of cell death with unique morphologic features and regulatory mechanism. Tumor suppressor p53 (TP53) is a key factor in regulation of ferroptosis through multiple pathways. Mouse double minute 2 homolog (MDM2), a key oncogene of dedifferentiated LPS (DDLPS), is one of the negative regulators of the TP53. In our previous study, we had showed that nutlin-3, a MDM2 inhibitor, could exert synergistic cytotoxicity with ferroptosis-inducing agent (erastin and RSL3) on DDLPS in a sequential manner, possibly through upregulation of SLC3A2 with altered cystine/glutamate exchange (AACR Annual Meeting 2023 abstract#4777). Mutated in Ataxia-Telangiectasia gene (ATM) is a critical gene in DNA damage response. ATM could regulate ferroptosis either directly through altered iron pool, or indirectly through activating TP53 by phosphorylation of MDM2. In this study, we explored the role of ATM and MDM2-TP53 pathway, as well as interaction between them, in regulation of ferroptosis of DDLPS. We also studied the potential role of combination of DNA damaging agent (DDA), such as cisplatin, with ferroptosis-inducing agents in the treatment of DDLPS. Methods: We explored the possible synergistically cytotoxic effect of cisplatin and ferroptosis-inducing agents in DDLPS cell lines. We also investigated the role of ATM in this synergistic effect by using siRNA or ATM inhibitor. In addition, we used cystine uptake assay (measurement of altered cystine/glutamate exchange) and iron level assay (measurement of labile iron pool) to study the functional change responsible to ferroptosis-inducing effect of cisplatin. Finally, we used immunoblotting study to reveal the potential molecular mechanism responsible for synergistic effect of cisplatin and ferroptosis-inducing agent. Results: Cisplatin and erastin showed synergistic cytotoxicity in DDLPS cell line, most likely through ferroptosis-inducing effect. Cisplatin could activate ATM, with resultant dissociation of TP53 and MDM2. Cisplatin could exert ferroptosis-inducing effect through down-regulation SLC7A11A with resultant decrease cystine uptake, as well as increase labile iron pool. ATM inhibition could offset the ferroptosis-inducing effect of cisplatin by reversing both effects. Conclusion: Modulation of ferroptosis is a potential treatment strategy in DDLPS. MDM2-TP53 pathway and ATM as well as interaction of both may play an important role in regulation of ferroptosis in DDLPS. Combination of DDA, such as cisplatin, and ferroptosis-inducing agents is a potential strategy in DDLPS treatment. Citation Format: Chueh-Chuan Yen, San-Chi Chen, Chih-Hsueh Chen, Jir-You Wang, Chao-Ming Chen, Po-Kuei Wu, Muh-Hwa Yang, Wei-Ming Chen. Exploring the role of MDM2-TP53 pathway and ATM in regulation of ferroptosis in dedifferentiated liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 397.

Abstract 436: Extracellular glutathione catabolism as an alternative cyst(e)ine source in cancer

Abstract Glutathione (GSH) is the most abundant antioxidant in the human body and plays essential roles in physiology and disease. Unchecked oxidative stress is involved in tumor initiation and progression. Paradoxically, clinical and laboratory data show that ROS-scavenging molecules such as glutathione not only fail to impede tumor growth but, in many cases, accelerate it. Still, preliminary data from our lab show that genetically ablating tumors’ ability to synthesize GSH does not affect their growth. This finding suggests that the favorable influence of glutathione on tumor growth may arise from external sources. Yet, the mechanism cancer cells employ to take advantage of extracellular glutathione in this context is unknown. Here, we show that γ-glutamyl-transpeptidase 1 (GGT1), an enzyme that localizes on the outer side of the cell’s membrane, can break down extracellular GSH, yielding glutamate and the dipeptide cysteinylglycine. Cysteinylglycine can be further metabolized, generating cysteine and glycine to the cells. We found that the addition of exogenous GSH, as well as cysteinylglycine, can mitigate cell death, proliferation arrest, and oxidative stress caused by cystine depletion. The overexpression of human GGT1 in cancer cells significantly reduces the amount of glutathione needed to rescue cell fitness. Accordingly, pharmacologic inhibition of GGT1 activity prevented GSH's ability to rescue cell proliferation. Moreover, an unbiased pharmacological screening revealed that GGT1-mediated cysteine acquisition renders cancer cells resistant to inhibitors of cystine uptake and utilization, supporting the role of GGT1 as a source of cyst(e)ine. Our findings reveal that cancer cells can access cysteine, a vital yet scarce amino acid, through GGT1's ability to break down glutathione, which is present in remarkably high concentrations within the tumor microenvironment. Although the downstream proteins involved in the transport and utilization of GSH breakdown products are yet to be identified, we anticipate this pathway has the potential to uncover novel therapeutic avenues for cancer treatment by targeting alternative pathways of nutrient acquisition that are potentially implicated in cancer progression and therapy resistance. Citation Format: Fabio Hecht, Marco Zocchi, Emily Tuttle, Gloria Asantewaa, TashJaé Scales, Fatemeh Alimohammadi, Nathan Ward, Gina DeNicola, Isaac Harris. Extracellular glutathione catabolism as an alternative cyst(e)ine source in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 436.