xCT, component of cysteine/glutamate transporter, as an independent prognostic factor in human esophageal squamous cell carcinoma

CACNA2D1 regulates the progression and influences the microenvironment of colon cancer

BACKGROUND

Calcium voltage-gated channel auxiliary subunit alpha 2/delta 1 (CACNA2D1), a gene encoding a voltage-gated calcium channel, has been reported as an oncogene in several cancers. However, its role in colon cancer (CC) remains unclear. This study aimed to investigate the function of CACNA2D1 and its effect on the microenvironment in CC.

METHODS

Immunohistochemistry (IHC) analysis was performed on samples collected from 200 patients with CC who underwent curative colectomy. Knockdown experiments were performed using CACNA2D1 siRNA in the human CC cell lines HCT116 and RKO, and cell proliferation, cycle, apoptosis, and migration were then analyzed. The fibroblast cell line CCD-18Co was co-cultured with CC cell lines to determine the effect of CACNA2D1 on fibroblasts and the relationship between CACNA2D1 and the cancer microenvironment. Gene expression profiles of cells were analyzed using microarray analysis.

RESULTS

IHC revealed that high CACNA2D1 expression was an independent poor prognostic factor in patients with CC and that CACNA2D1 expression and the stroma are correlated. CACNA2D1 depletion decreased cell proliferation and migration; CACNA2D1 knockdown increased the number of cells in the sub-G1 phase and induced apoptosis. CCD-18Co and HCT116 or RKO cell co-culture revealed that CACNA2D1 affects the cancer microenvironment via fibroblast regulation. Furthermore, microarray analysis showed that the p53 signaling pathway and epithelial-mesenchymal transition-associated pathways were enhanced in CACNA2D1-depleted HCT116 cells.

CONCLUSIONS

CACNA2D1 plays an important role in the progression and the microenvironment of CC by regulating fibroblasts and may act as a biomarker for disease progression and a therapeutic target for CC.

Recent advancements in nanomaterial-mediated ferroptosis-induced cancer therapy: Importance of molecular dynamics and novel strategies

Ferroptosis is a novel type of controlled cell death resulting from an imbalance between oxidative harm and protective mechanisms, demonstrating significant potential in combating cancer. It differs from other forms of cell death, such as apoptosis and necrosis. Molecular therapeutics have hard time playing the long-acting role of ferroptosis induction due to their limited water solubility, low cell targeting capacity, and quick metabolism in vivo. To this end, small molecule inducers based on biological factors have long been used as strategy to induce cell death. Research into ferroptosis and advancements in nanotechnology have led to the discovery that nanomaterials are superior to biological medications in triggering ferroptosis. Nanomaterials derived from iron can enhance ferroptosis induction by directly releasing large quantities of iron and increasing cell ROS levels. Moreover, utilizing nanomaterials to promote programmed cell death minimizes the probability of unfavorable effects induced by mutations in cancer-associated genes such as RAS and TP53. Taken together, this review summarizes the molecular mechanisms involved in ferroptosis along with the classification of ferroptosis induction. It also emphasized the importance of cell organelles in the control of ferroptosis in cancer therapy. The nanomaterials that trigger ferroptosis are categorized and explained. Iron-based and noniron-based nanomaterials with their characterization at the molecular and cellular levels have been explored, which will be useful for inducing ferroptosis that leads to reduced tumor growth. Within this framework, we offer a synopsis, which traverses the well-established mechanism of ferroptosis and offers practical suggestions for the design and therapeutic use of nanomaterials.

Blocking SLC7A11 attenuates the proliferation of esophageal squamous cell carcinoma cells

The role of ferroptosis-associated gene SLC7A11 in esophageal cancer progression is largely unknown, therefore, the effects of blocking SLC7A11 on esophageal squamous cell carcinoma (ESCC) cells are evaluated. Results showed that SLC7A11 was overexpressed in ESCC tissues both in mRNA and protein levels. Blocking SLC7A11 using Erastin suppressed the proliferation and colony formation of ESCC cells, decreased cellular ATP levels, and improved ROS production. Sixty-three SLC7A11-binding proteins were identified using the IP-MS method, and these proteins were enriched in four signaling pathways, including spliceosome, ribosome, huntington disease, and diabetic cardiomyopathy. The deubiquitinase inhibitors PR-619, GRL0617, and P 22077 could reduce at least 40% protein expression level of SLC7A11 in ESCC cells, and PR-619 and GRL0617 exhibited suppressive effects on the cell viability and colony formation ability of KYSE30 cells, respectively. Erastin downregulated GPX4 and DHODH and also reduced the levels of β-catenin, p-STAT3, and IL-6 in ESCC cells. In conclusion, SLC7A11 was overexpressed in ESCC, and blocking SLC7A11 using Erastin mitigated malignant phenotypes of ESCC cells and downregulated key ferroptosis-associated molecules GPX4 and DHODH. The therapeutic potential of targeting SLC7A11 should be further evaluated in the future.

Roles of reactive oxygen species in inflammation and cancer

Reactive oxygen species (ROS) constitute a spectrum of oxygenic metabolites crucial in modulating pathological organism functions. Disruptions in ROS equilibrium span various diseases, and current insights suggest a dual role for ROS in tumorigenesis and the immune response within cancer. This review rigorously examines ROS production and its role in normal cells, elucidating the subsequent regulatory network in inflammation and cancer. Comprehensive synthesis details the documented impacts of ROS on diverse immune cells. Exploring the intricate relationship between ROS and cancer immunity, we highlight its influence on existing immunotherapies, including immune checkpoint blockade, chimeric antigen receptors, and cancer vaccines. Additionally, we underscore the promising prospects of utilizing ROS and targeting ROS modulators as novel immunotherapeutic interventions for cancer. This review discusses the complex interplay between ROS, inflammation, and tumorigenesis, emphasizing the multifaceted functions of ROS in both physiological and pathological conditions. It also underscores the potential implications of ROS in cancer immunotherapy and suggests future research directions, including the development of targeted therapies and precision oncology approaches. In summary, this review emphasizes the significance of understanding ROS-mediated mechanisms for advancing cancer therapy and developing personalized treatments.

SLC7A11 promotes the progression of gastric cancer and regulates ferroptosis through PI3K/AKT pathway

OBJECTIVE

Ferroptosis is a form of regulated cell death that occurs depending on iron and reactive oxygen species (ROS), but the underlying molecular mechanisms remain poorly understood. The aim of our study was to investigate the role of solute carrier family 7 member 11(SLC7A11) in the progression of gastric cancer (GC) and its molecular mechanism.

METHOD

The expression of SLC7A11 in GC was detected by real-time fluorescence quantitative polymerase chain reaction (RT-PCR), immunohistochemistry (IHC) and western blot. SLC7A11 interference and overexpression vector was constructed in vitro, transfected into GC cells, and the high efficiency plasmid vector fragment was screened.CCK-8 assay was used to detect the effect of cell proliferation. The migration ability of cells was detected by transwell assay. The mitochondrial structure was observed by transmission electron microscopy.CCK-8 assay was also used to detect the effect of SLC7A11 on the growth inhibition rate of ferroptosis in GC cells. The level of malondialdehyde (MDA), the ultimate product of lipid peroxidation, was detected by micro-method. The effect of SLC7A11 on PI3K/AKT signaling pathway was detected by Western blot.

RESULTS

SLC7A11 was significantly overexpressed in GC tissues than that in adjacent tissues. Knockdown of SLC7A11 inhibits cell proliferation, cell migration and invasion of GC, and increases the sensitivity of ferroptosis via moderating ROS and lipid peroxidation. Besides, overexpression of the SLC7A11 in GC cells reverses erastin-induced ferroptosis partially. Mechanistically, we reveal that suppression of SCL7A11 leads to inactivity of PI3K/AKT signaling pathway and further enhancing ferroptosis related lipid peroxidation, and thereby inhibiting GC progression.

CONCLUSION

SLC7A11 plays an oncogene role in malignant progression of GC. SLC7A11 reversely regulates ferroptosis of GC cells by activating PI3K/AKT signaling pathway. Silencing SLC7A11 expression can inhibit the progression of GC.

Role of ferroptosis in esophageal cancer and corresponding immunotherapy

Esophageal cancer (EC) is one of the most common digestive system malignancies in the world. The combined modality treatment of EC is usually surgery and radiation therapy, however, its clinical efficacy for advanced patients is relatively limited. Ferroptosis, a new type of iron-dependent programmed cell death, is different from apoptosis, necrosis and autophagy. In recent years, many studies have further enlightened that ferroptosis plays an essential role in the occurrence, development and metastasis of tumors. Targeting ferroptosis stimulates a new direction for further exploration of oncologic treatment regimens. Furthermore, ferroptosis has a critical role in the immune microenvironment of tumors. This paper reviews the mechanism of ferroptosis and the ferroptosis research progress in the treatment of EC. We further elaborate the interaction between ferroptosis and immunotherapy, and the related mechanisms of ferroptosis participation in the immunotherapy of EC, so as to provide new directions and ideas for the treatment of EC.

The prognostic and clinicopathological significance of SLC7A11 in human cancers: a systematic review and meta-analysis

Objective

It is of great importance to recognize bio-markers for cancer prognosis. However, the association between solute carrier family 7 member 11 (SLC7A11) and prognosis is still controversial. Therefore, we conducted this systematic review and meta-analysis to identify the prognostic and clinicopathological significance of SLC7A11 in human cancers.

Methods

PubMed, Web of Science, Scopus, the Cochrane Library and Embase database were searched from database inceptions to March 19th 2022. Hand searches were also conducted in references. Prognosis and clinicopathological data were extracted and analyzed.

Results

A total of 12 eligible studies with 1,955 patients were included. The results indicated that SLC7A11 expression is associated with unfavorable overall survival (OS), unfavorable recurrence-free survival (RFS) and unfavorable progression free survival (PFS). And SLC7A11 expression is also associated with more advanced tumor stage.

Conclusions

SLC7A11 expression is associated with more unfavorable prognosis and more advanced tumor stage. Therefore, SLC7A11 could be a potential biomarker for human cancer prognosis.

Ferulic Acid Mitigates Growth and Invasion of Esophageal Squamous Cell Carcinoma through Inducing Ferroptotic Cell Death

Objective

Ferroptosis is an iron- and ROS-dependent form of cell death initiated by lipid peroxidation. The rapidly developing study of ferroptosis has facilitated its application in cancer therapeutics. The current study is aimed at investigating the functional property of ferulic acid (FA, a phenolic acid substance) on inducing ferroptosis in antiesophageal squamous cell carcinoma (ESCC).

Methods

ESCC cells were administrated with gradient doses of FA or with ferroptosis inhibitor deferoxamine. Cellular growth was measured with CCK-8 and colony formation experiments. LDH, caspase-3, MDA, SOD, GSH, and iron were assayed with corresponding kits. Apoptotic level was evaluated through Annexin V-FITC apoptosis staining, with migration and invasion utilizing Transwell assays. Through quantitative RT-PCR, angiogenesis-relevant genes VEGFA and PDGFB were detected. ROS generation was measured via DCFH-DA probe. Immunoblotting was conducted for monitoring ACSL4, SLC7A11, HO-1, and GPX4.

Results

FA administration observably mitigated cellular viability and colony formation capacity and motivated LDH release, caspase-3 activity, and apoptosis in EC-1 and TE-4 cells. In addition, migration and invasion together with angiogenesis of ESCC cells were restraint by FA. FA exposure led to the increase of MDA content, ROS production, and iron load as well as the reduction of SOD activity and GSH content. Also, FA augmented the activities of ACSL4 and HO-1, with lessening SLC7A11 and GPX4. Nonetheless, deferoxamine restrained the effect of FA on ESCC ferroptosis.

Conclusion

Altogether, FA may act as a ferroptosis inducer and thus attenuates cell growth and invasion of ESCC, which boosts the clinical application of FA in ESCC therapeutics.

Targeting amino acid metabolism in cancer

Metabolic rewiring is a characteristic hallmark of cancer cells. This phenomenon sustains uncontrolled proliferation and resistance to apoptosis by increasing nutrients and energy supply. However, reprogramming comes together with vulnerabilities that can be used against tumor and can be applied in targeted therapy. In the last years, the genetic background of tumors has been identified thoroughly and new therapies targeting those mutations tested. Nevertheless, we propose that targeting the phenotype of cancer cells could be another way of treatment aiming to avoid drug resistance and non-responsiveness of cancer patients. Amino acid metabolism is part of the altered processes in cancer cells. Amino acids are building blocks and also sensors of signaling pathways regulating main biological processes. In this comprehensive review, we described four amino acids (asparagine, arginine, methionine, and cysteine) which have been actively investigated as potential targets for anti-tumor therapy. Asparagine depletion is successfully used for decades in the treatment of acute lymphoblastic leukemia and there is a strong implication to apply it to other types of tumors. Arginine auxotrophic tumors are great candidates for arginine-starvation therapy. Higher requirement for essential amino acids such as methionine and cysteine point out promising targetable weaknesses of cancer cells.

IFNγ enhances ferroptosis by increasing JAK‑STAT pathway activation to suppress SLCA711 expression in adrenocortical carcinoma

Adrenocortical carcinoma (ACC) is a rare type of tumor with a poor prognosis. Ferroptosis is a relatively novel form of programmed cell death driven by iron-dependent lipid peroxidation accumulation. Recent evidence suggests that IFNγ facilitates erastin-induced ferroptosis, which contributed to anticancer therapy in various types of cancer. However, it has remained elusive whether the regulation of IFNγ on ferroptosis has a positive role in the treatment of ACC. Thus, the aim of the present study was to explore the effects of IFNγ on erastin-induced ferroptosis in the ACC cell line NCI-H295R and investigate the underlying mechanisms. Cell viability was assessed using a Cell Counting Kit-8 assay, an ethynyldioxyuridine proliferation assay and Live/Dead staining. The levels of iron, reactive oxygen species, lipid peroxidation and mitochondrial damage were also assessed. Western blot and reverse transcription-quantitative PCR analyses were used to determine the underlying molecular mechanisms involved in the erastin-induced ferroptosis of NCI-H295R cells. The results suggested that IFNγ promoted erastin-induced ferroptotic cell death. Furthermore, IFNγ enhanced erastin-induced ferroptosis, as evidenced by the accumulation of iron, as well as the increase in lipid peroxidation and promotion of mitochondrial damage. Further analysis suggested that IFNγ enhanced ferroptosis by suppressing the expression of solute carrier family 7 member 11, an important negative regulator of ferroptosis, and this was achieved via activation of the JAK/STAT pathway in NCI-H295R cells. The present study provided experimental evidence on the activity and mechanism of ferroptosis enhanced by IFNγ in ACC and may give critical insight into the immunotherapeutic management of ACC.

Targeting multidrug resistance-associated protein 1 (MRP1)-expressing cancers: Beyond pharmacological inhibition

Resistance to chemotherapy remains one of the most significant obstacles to successful cancer treatment. While inhibiting drug efflux mediated by ATP-binding cassette (ABC) transporters is a seemingly attractive and logical approach to combat multidrug resistance (MDR), small molecule inhibition of ABC transporters has so far failed to confer clinical benefit, despite considerable efforts by medicinal chemists, biologists, and clinicians. The long-sought treatment to eradicate cancers displaying ABC transporter overexpression may therefore lie within alternative targeting strategies. When aberrantly expressed, the ABC transporter multidrug resistance-associated protein 1 (MRP1, ABCC1) confers MDR, but can also shift cellular redox balance, leaving the cell vulnerable to select agents. Here, we explore the physiological roles of MRP1, the rational for targeting this transporter in cancer, the development of small molecule MRP1 inhibitors, and the most recent developments in alternative therapeutic approaches for targeting cancers with MRP1 overexpression. We discuss approaches that extend beyond simple MRP1 inhibition by exploiting the collateral sensitivity to glutathione depletion and ferroptosis, the rationale for targeting the shared transcriptional regulators of both MRP1 and glutathione biosynthesis, advances in gene silencing, and new molecules that modulate transporter activity to the detriment of the cancer cell. These strategies illustrate promising new approaches to address multidrug resistant disease that extend beyond the simple reversal of MDR and offer exciting routes for further research.

Low Expression of SLC7A11 Confers Drug Resistance and Worse Survival in Ovarian Cancer via Inhibition of Cell Autophagy as a Competing Endogenous RNA

Drug resistance is the main cause of chemotherapy failure in ovarian cancer (OC), and identifying potential druggable targets of autophagy is a novel and promising approach to overcoming drug resistance. In this study, 131 genes associated with autophagy were identified from three autophagy-related databases, and of these, 14 were differentially expressed in 90 drug-resistant OC tissues versus 197 sensitive tissues according to the Cancer Genome Atlas ovarian cancer cohort. Among these 14 genes, SLC7A11 was significantly decreased in two paclitaxel-resistant OC cells (HeyA8-R and SKOV3-R) and in 90 drug-resistant tissues compared with their controls. In vitro overexpression of SLC7A11 significantly increased the sensitivity of HeyA8-R cells to paclitaxel, inhibited colony formation, induced apoptosis, and arrested cell cycle. Further, low SLC7A11 expression was correlated with poor overall survival (OS), progression-free survival (PFS), and post-progression survival (PPS) in 1815 OC patients. Mechanistically, SLC7A11 strongly regulated cell autophagy as a competing endogenous RNA (ceRNA) based on pan-cancer analyses of 32 tumor types. Specifically, as a ceRNA for autophagy genes STX17, RAB33B, and UVRAG, SLC7A11 was strongly and positively co-expressed with these three genes in 20, 12, and 12 different tumors, respectively, in 379 OC tissues and in 90 drug-resistant OC tissues, and the former two were significantly upregulated in SLC7A11-overexpressed HeyA8-R cells. Further, SLC7A11 induced the protein expression of other autophagy genes, such as LC3, Atg16L1, and Atg7, and the expression of the respective proteins was further increased when the cells were treated with paclitaxel. The results strongly suggest that SLC7A11 regulates autophagy via ceRNA interactions with the three abovementioned genes in pan-cancer and in drug-resistant OC. Moreover, low expression of STX17 and UVRAG also significantly predicted low OS, PFS, and PPS. The combination of SLC7A11 with STX17 was more predictive of OS and PFS than either individually, and the combination of SLC7A11 with UVRAG was highly predictive of OS and PPS. The above results indicated that decreased SLC7A11 resulted in drug resistance and effected low rates of survival in OC patients, probably via ceRNA interactions with autophagy genes, and thus the gene could serve as a therapeutic target and potential biomarker in OC.

SLC7A11 regulated by NRF2 modulates esophageal squamous cell carcinoma radiosensitivity by inhibiting ferroptosis

BACKGROUND

Solute carrier family 7 member 11(SLC7A11) is a component of cysteine/glutamate transporter, which plays a key role in tumor growth; however, its underlying effect on radiosensitivity in esophageal squamous cell carcinoma (ESCC) remains unclear. This study aimed to clarify SLC7A11's expression and correlation with nuclear expression of nuclear factor erythroid-2 (NRF2)-associated radioresistance in ESCC.

METHODS

We included 127 ESCC patients who received radical chemoradiotherapy. Immunohistochemical staining was used to detect SLC7A11 and NRF2 nuclear expression, and the relationship between clinicopathological characteristics and survival rates or therapy response were evaluated. Western blot, dual-reporter assays and Chromatin immunoprecipitation (ChIP)-sequencing were used to analyze their relationship in vitro. Their roles in radioresistance were then investigated through multiple validation steps.

RESULTS

NRF2 nuclear expression and SLC7A11 expression were overexpressed in ESCC tissues and were positively correlated with one another. NRF2 nuclear expression was significantly associated with tumor length, lymph node metastasis, and TNM stage, while SLC7A11 expression was associated with lymph node metastasis. Patients with high NRF2 nuclear expression and SLC7A11 expression had significantly shorter overall and progression-free survival, and poor treatment response. The multivariate model showed that NRF2 nuclear expression and SLC7A11 expression, sex and tumor location are independent prognostic factors. In vitro analysis confirmed that hyperactivation of NRF2 induced SLC7A11 expression by directly binding to its promoter region, promoting radioresistance, reducing radiotherapy-induced lipid peroxidation levels, PTGS2 expression, and radiotherapy-related ferroptosis morphologic features.

CONCLUSION

Our study reveals a connection between high SLC7A11 expression and NRF2 nuclear expression in patients with ESCC that was related to worse survival and poorer therapy outcomes. SLC7A11-mediated ferroptosis inhibition induced NRF2-associated radioresistance, highlighting potential of NRF2/SLC7A11/ferroptosis axis as future therapeutic targets against therapy resistance biomarker.

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.

Cyst(e)ine in nutrition formulation promotes colon cancer growth and chemoresistance by activating mTORC1 and scavenging ROS

Weight loss and cachexia are common problems in colorectal cancer patients; thus, parenteral and enteral nutrition support play important roles in cancer care. However, the impact of nonessential amino acid components of nutritional intake on cancer progression has not been fully studied. In this study, we discovered that gastrointestinal cancer patients who received cysteine as part of the parenteral nutrition had shorter overall survival (P < 0.001) than those who did not. Cystine indeed robustly promotes colon cancer cell growth in vitro and in immunodeficient mice, predominately by inhibiting SESN2 transcription via the GCN2-ATF4 axis, resulting in mTORC1 activation. mTORC1 inhibitors Rapamycin and Everolimus block cystine-induced cancer cell proliferation. In addition, cystine confers resistance to oxaliplatin and irinotecan chemotherapy by quenching chemotherapy-induced reactive oxygen species via synthesizing glutathione. We demonstrated that dietary deprivation of cystine suppressed colon cancer xenograft growth without weight loss in mice and boosted the antitumor effect of oxaliplatin. These findings indicate that cyst(e)ine, as part of supplemental nutrition, plays an important role in colorectal cancer and manipulation of cyst(e)ine content in nutritional formulations may optimize colorectal cancer patient survival.

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.

xCT-Driven Expression of GPX4 Determines Sensitivity of Breast Cancer Cells to Ferroptosis Inducers

Inducers of ferroptosis such as the glutathione depleting agent Erastin and the GPX4 inhibitor Rsl-3 are being actively explored as potential therapeutics in various cancers, but the factors that determine their sensitivity are poorly understood. Here, we show that expression levels of both subunits of the cystine/glutamate antiporter xCT determine the expression of GPX4 in breast cancer, and that upregulation of the xCT/selenocysteine biosynthesis/GPX4 production axis paradoxically renders the cancer cells more sensitive to certain types of ferroptotic stimuli. We find that GPX4 is strongly upregulated in a subset of breast cancer tissues compared to matched normal samples, and that this is tightly correlated with the increased expression of the xCT subunits SLC7A11 and SLC3A2. Erastin depletes levels of the antioxidant selenoproteins GPX4 and GPX1 in breast cancer cells by inhibiting xCT-dependent extracellular reduction which is required for selenium uptake and selenocysteine biosynthesis. Unexpectedly, while breast cancer cells are resistant compared to nontransformed cells against oxidative stress inducing drugs, at the same time they are hypersensitive to lipid peroxidation and ferroptosis induced by Erastin or Rsl-3, indicating that they are 'addicted' to the xCT/GPX4 axis. Our findings provide a strategic basis for targeting the anti-ferroptotic machinery of breast cancer cells depending on their xCT status, which can be further explored.

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.

Membrane Transporters for Amino Acids as Players of Cancer Metabolic Rewiring

Cancer cells perform a metabolic rewiring to sustain an increased growth rate and compensate for the redox stress caused by augmented energy metabolism. The metabolic changes are not the same in all cancers. Some features, however, are considered hallmarks of this disease. As an example, all cancer cells rewire the amino acid metabolism for fulfilling both the energy demand and the changed signaling routes. In these altered conditions, some amino acids are more frequently used than others. In any case, the prerequisite for amino acid utilization is the presence of specific transporters in the cell membrane that can guarantee the absorption and the traffic of amino acids among tissues. Tumor cells preferentially use some of these transporters for satisfying their needs. The evidence for this phenomenon is the over-expression of selected transporters, associated with specific cancer types. The knowledge of the link between the over-expression and the metabolic rewiring is crucial for understanding the molecular mechanism of reprogramming in cancer cells. The continuous growth of information on structure-function relationships and the regulation of transporters will open novel perspectives in the fight against human cancers.

ROS Mediate xCT-Dependent Cell Death in Human Breast Cancer Cells under Glucose Deprivation

xCT, also known as solute carrier family 7 member 11 (SLC7A11), the light chain of the cystine/glutamate antiporter, is positively correlated with cancer progression due to antioxidant function. During glucose deprivation, the overexpression of xCT does not protect cancer cells but instead promotes cell death. Further understanding the mechanism of glucose deprivation-induced cell death is important for developing anticancer treatments targeting the glucose metabolism. In this study, we found that breast cancer cells with a high expression of xCT demonstrated increased levels of reactive oxygen species (ROS) and were more sensitive to glucose deprivation than the cells with a low expression of xCT. However, AMP-activated protein kinase (AMPK) did not significantly affect glucose-deprivation-induced cell death. The antioxidant N-acetyl-cysteine prevented glucose-deprivation-induced cell death, and the glutathione biosynthesis inhibitor L-buthionine-S, R-sulfoximine enhanced glucose-deprivation-induced cell death. The inhibition of xCT by sulfasalazine or a knockdown of xCT reduced the glucose-deprivation-increased ROS levels and glucose-deprivation-induced cell death. Glucose deprivation reduced the intracellular glutamate, and supplementation with α-ketoglutarate prevented the glucose-deprivation-increased ROS levels and rescued cell death. The knockdown of sirtuin-3 (SIRT3) further enhanced the ROS levels, and promoted xCT-related cell death after glucose deprivation. In conclusion, our results suggested that ROS play a critical role in xCT-dependent cell death in breast cancer cells under glucose deprivation.

Cysteine as a Carbon Source, a Hot Spot in Cancer Cells Survival

Cancer cells undergo a metabolic rewiring in order to fulfill the energy and biomass requirements. Cysteine is a pivotal organic compound that contributes for cancer metabolic remodeling at three different levels: (1) in redox control, free or as a component of glutathione; (2) in ATP production, via hydrogen sulfide (H₂S) production, serving as a donor to electron transport chain (ETC), and (3) as a carbon source for biomass and energy production. In the present review, emphasis will be given to the role of cysteine as a carbon source, focusing on the metabolic reliance on cysteine, benefiting the metabolic fitness and survival of cancer cells. Therefore, the interplay between cysteine metabolism and other metabolic pathways, as well as the regulation of cysteine metabolism related enzymes and transporters, will be also addressed. Finally, the usefulness of cysteine metabolic route as a target in cancer treatment will be highlighted.

Autophagy activation is required for homocysteine-induced apoptosis in bovine aorta endothelial cells

An elevated level of homocysteine (Hcy) in plasma is an independent risk factor for cardiovascular disease and central nervous system disease. Endothelial dysfunction as a result of apoptosis in endothelial cells is involved in the development and progression of these diseases. In this study, we aimed to investigate the effect of autophagy activation by amino acid starvation on Hcy-induced cytotoxicity in bovine aorta endothelial cells (BAECs). Hcy-induced lactate dehydrogenase (LDH) release was promoted by amino acid starvation. In addition, Hcy increased cleaved caspase-3 level, an indicator of apoptosis, by amino acid starvation. We revealed that oxidative stress is not involved in the Hcy-induced cytotoxicity promoted by amino acid starvation. Salazosulfapyridine (SASP), an SLC7A11 inhibitor, protected against the Hcy-induced LDH release promoted by amino acid starvation. SASP decreased the Hcy-induced cleaved caspase-3 level by amino acid starvation. We demonstrate for the first time that autophagy activation by amino acid starvation promotes Hcy-induced apoptosis in BAECs. Moreover, SLC7A11 inhibitor SASP, which is an amino acid transporter, protects against Hcy-induced apoptosis due to autophagy.

Metabolic Remodeling as a Way of Adapting to Tumor Microenvironment (TME), a Job of Several Holders

The microenvironment depends and generates dependence on all the cells and structures that share the same niche, the biotope. The contemporaneous view of the tumor microenvironment (TME) agrees with this idea. The cells that make up the tumor, whether malignant or not, behave similarly to classes of elements within a living community. These elements inhabit, modify and benefit from all the facilities the microenvironment has to offer and that will contribute to the survival and growth of the tumor and the progression of the disease.The metabolic adaptation to microenvironment is a crucial process conducting to an established tumor able to grow locally, invade and metastasized. The metastatic cancer cells are reasonable more plastic than non-metastatic cancer cells, because the previous ones must survive in the microenvironment where the primary tumor develops and in addition, they must prosper in the microenvironment in the metastasized organ.The metabolic remodeling requires not only the adjustment of metabolic pathways per se but also the readjustment of signaling pathways that will receive and obey to the extracellular instructions, commanding the metabolic adaptation. Many diverse players are pivotal in cancer metabolic fitness from the initial signaling stimuli, going through the activation or repression of genes, until the phenotype display. The new phenotype will permit the import and consumption of organic compounds, useful for energy and biomass production, and the export of metabolic products that are useless or must be secreted for a further recycling or controlled uptake. In the metabolic network, three subsets of players are pivotal: (1) the organic compounds; (2) the transmembrane transporters, and (3) the enzymes.This chapter will present the "Pharaonic" intent of diagraming the interplay between these three elements in an attempt of simplifying and, at the same time, of showing the complex sight of cancer metabolism, addressing the orchestrating role of microenvironment and highlighting the influence of non-cancerous cells.

Ferroptosis Promotes Photodynamic Therapy: Supramolecular Photosensitizer-Inducer Nanodrug for Enhanced Cancer Treatment

The noninvasive nature of photodynamic therapy (PDT) enables the preservation of organ function in cancer patients. However, PDT is impeded by hypoxia in the tumor microenvironment (TME) caused by high intracellular oxygen (O₂) consumption and distorted tumor blood vessels. Therefore, increasing oxygen generation in the TME would be a promising methodology for enhancing PDT. Herein, we proposed a concept of ferroptosis-promoted PDT based on the biochemical characteristics of cellular ferroptosis, which improved the PDT efficacy significantly by producing reactive oxygen species (ROS) and supplying O₂ sustainably through the Fenton reaction. In contrast to traditional strategies that increase O₂ based on decomposition of limited concentration of hydrogen peroxide (H₂O₂), our methodology could maintain the concentration of H₂O₂ and O₂ through the Fenton reaction. Methods: For its association with sensitivity to ferroptosis, solute carrier family 7 member 11 (SLC7A11) expression was characterized by bioinformatics analysis and immunohistochemistry of oral tongue squamous cell carcinoma (OTSCC) specimens. Afterwards, the photosensitizer chlorin e6 (Ce6) and the ferroptosis inducer erastin were self-assembled into a novel supramolecular Ce6-erastin nanodrug through hydrogen bonding and π-π stacking. Then, the obtained Ce6-erastin was extensively characterized and its anti-tumor efficacy towards OTSCC was evaluated both in vitro and in vivo. Results: SLC7A11 expression is found to be upregulated in OTSCC, which is a potential target for ferroptosis-mediated OTSCC treatment. Ce6-erastin nanoparticles exhibited low cytotoxicity to normal tissues. More significantly, The over-accumulated intracellular ROS, increased O₂ concentration and inhibited SLC7A11 expression lead to enhanced toxicity to CAL-27 cells and satisfactory antitumor effects to xenograft tumour mouse model upon irradiation. Conclusion: Our ferroptosis promoted PDT approach markedly enhances anticancer actions by relieving hypoxia and promoting ROS production, thereby our work provides a new approach for overcoming hypoxia-associated resistance of PDT in cancer treatment.

Overexpression of cysteine-glutamate transporter and CD44 for prediction of recurrence and survival in patients with oral cavity squamous cell carcinoma

BACKGROUND

This study analyzed the expression of CD44 and cystine-glutamate transporter SLC7A11 (xCT) in primary oral cavity squamous cell carcinoma (SCC) and the relationships of expression to tumor recurrence and patient survival.

METHODS

Associations between CD44 and xCT expression and clinicopathologic results were analyzed in 231 patients with oral cavity SCC. Cox proportional hazard analyses were used to identify factors associated with recurrence-free survival (RFS), disease-specific survival (DSS), and overall survival (OS).

RESULTS

Overexpression of CD44 and/or xCT was associated with advanced T classification, perineural invasion, and lymphovascular invasion (P < .05 each). High expression of xCT was also associated with nodal metastasis and depth of invasion (P < .01 each). Multivariate analysis indicated that high expression of xCT and both xCT and CD44 were independent predictors of poor RFS, DSS, and OS (P < .05 each).

CONCLUSION

Overexpression of xCT or xCT plus CD44 may predict posttreatment recurrence and survival in patients with oral cavity SCC.

xCT inhibition sensitizes tumors to γ-radiation via glutathione reduction

About 3 million US cancer patients and 1.7 million EU cancer patients received multiple doses of radiation therapy (RT) in 2012, with treatment duration limited by normal adjacent tissue damage. Tumor-specific sensitization could allow treatment with lower radiation doses, reducing normal tissue damage. This is a longstanding, largely unrealized therapeutic goal. The cystine:glutamate exchanger xCT is expressed on poor prognosis subsets of most solid tumors, but not on most normal cells. xCT provides cells with environmental cystine for enhanced glutathione synthesis. Glutathione is used to control reactive oxygen species (ROS), which are therapeutic effectors of RT. We tested whether xCT inhibition would sensitize xCT⁺ tumor cells to ionizing radiation. We found that pretreatment with the xCT inhibitor erastin potently sensitized xCT⁺ but not xCT^- cells, in vitro and in xenograft. Similarly, targeted gene inactivation also sensitized cells, and both modes of sensitization were overcome by glutathione supplementation. Sensitization prolongs DNA damage signaling, increases genome instability, and enhances cell death, revealing an unforeseen role for cysteine in genome integrity maintenance. We conclude that an xCT-specific therapeutic would provide tumor-specific sensitization to RT, allowing treatment with lower radiation doses, and producing far fewer side effects than other proposed sensitizers. Our data speaks to the need for the rapid development of such a drug.

Identification and Characterization of Cadmium-Related Genes in Liver Carcinoma

Evidence indicates that exposure to heavy trace element might be a risk factor for liver carcinoma. Cadmium has been supposed to be a carcinogen that has a correlation with the risk of a number of cancers, including liver cancer. However, the mechanisms underlying Cadmium-induced malignant transformation in liver cells are not fully understood. In the present study, we aimed to screen the differentially expressed genes (DEGs) that might play a role in both the Cadmium-related liver cell transformation and the development of liver cancer. Microarray-based gene expression profiles concerning liver carcinoma vs non-cancerous tissue (GSE64041) and Cadmium-treated liver cells vs controls (GSE8865 and GSE31286), respectively, were retrieved from Gene Expression Omnibus (GEO) database. Then, DEGs of each profile were calculated and screened. The intersection of each DEGs was obtained by Venn analysis. Afterwards, the possible roles of the selected genes in cancer development were evaluated by using Oncomine database and TCGA cohort analysis. Consequently, three DEGs, LRAT, SLC7A11, and ITGA2, were selected for further analysis. SLC7A11 and ITGA2, but not LRAT, were upregulated in liver cancer compared with those in normal tissues, respectively. After using a TCGA cohort analysis, results failed to show a significant correlation between SLC7A11 or ITGA2 expression and clinical parameters. However, the survival analysis showed that patients with high expression levels of SLC7A11 had a shorter overall survival time relative to those of the patients with low levels. In conclusion, SLC7A11 and ITGA2 might play a role in the Cadmium-induced liver cell damage or transformation, and the development of liver carcinoma. SLC7A11 might be a prognostic factor for patients with liver carcinoma. Future validation experiments are needed to verify the results.

Variant isoforms of CD44 involves acquisition of chemoresistance to cisplatin and has potential as a novel indicator for identifying a cisplatin-resistant population in urothelial cancer

BACKGROUND

Cisplatin is the most commonly used chemotherapeutic agent in the treatment of patients with metastatic and/or recurrent urothelial cancer. However, the effectiveness of these treatments is severely limited due to the development of cisplatin resistance. Cancer stem cells have been documented as one of the key hypotheses involved in chemoresistance. CD44v8-10 has been identified as one of the new cancer stem cells markers and was recently shown to enhance the antioxidant system by interaction with xCT, a subunit of the cystine transporter modulating intracellular glutathione synthesis. The aim of the present study was to investigate the clinical role of CD44v8-10 and the molecular mechanism underlying the acquisition of cisplatin resistance through CD44v8-10 in urothelial cancer.

METHODS

We analyzed the clinical significance of the immunohistochemical CD44v9 expression, which detects the immunogen of human CD44v8-10, in 77 urothelial cancer patients treated with cisplatin-based systemic chemotherapy for recurrence and/or metastasis. We then evaluated the biological role of CD44v8-10 in the acquisition of cisplatin resistance using the urothelial cancer cell lines, T24 and T24PR, which were generated to acquire resistance to cisplatin.

RESULTS

The 5-year cancer-specific survival rate was significantly lower in the CD44v9-positive group than in the CD44v9-negative group (P = 0.008). Multivariate analyses revealed that CD44v9 positivity was an independent risk factor of cancer-specific survival (P = 0.024, hazard ratio = 5.16) in urothelial cancer patients who had recurrence and/or metastasis and received cisplatin-based chemotherapy. The expression of CD44v8-10 and xCT was stronger in T24PR cells than in T24 cells. The amount of intracellular glutathione was significantly higher in T24PR cells than in T24 cells (p < 0.001), and intracellular reactive oxygen species production by cisplatin was lower in T24PR cells than in T24 cells. Furthermore, the knockdown of CD44v8-10 by siRNA led to the recovery of cisplatin sensitivity in T24PR cells.

CONCLUSIONS

CD44v9 in tumor specimens has potential as a novel indicator for identifying a cisplatin-chemoresistant population among urothelial cancer patients. CD44v8-10 contributes to reactive oxygen species defenses, which are involved in chemoresistance, by promoting the function of xCT, which adjusts the synthesis of glutathione.

Systemic depletion of L-cyst(e)ine with cyst(e)inase increases reactive oxygen species and suppresses tumor growth

Cancer cells experience higher oxidative stress from reactive oxygen species (ROS) than do non-malignant cells because of genetic alterations and abnormal growth; as a result, maintenance of the antioxidant glutathione (GSH) is essential for their survival and proliferation. Under conditions of elevated ROS, endogenous L-cysteine (L-Cys) production is insufficient for GSH synthesis. This necessitates uptake of L-Cys that is predominantly in its disulfide form, L-cystine (CSSC), via the xCT(-) transporter. We show that administration of an engineered and pharmacologically optimized human cyst(e)inase enzyme mediates sustained depletion of the extracellular L-Cys and CSSC pool in mice and non-human primates. Treatment with this enzyme selectively causes cell cycle arrest and death in cancer cells due to depletion of intracellular GSH and ensuing elevated ROS; yet this treatment results in no apparent toxicities in mice even after months of continuous treatment. Cyst(e)inase suppressed the growth of prostate carcinoma allografts, reduced tumor growth in both prostate and breast cancer xenografts and doubled the median survival time of TCL1-Tg:p53-/- mice, which develop disease resembling human chronic lymphocytic leukemia. It was observed that enzyme-mediated depletion of the serum L-Cys and CSSC pool suppresses the growth of multiple tumors, yet is very well tolerated for prolonged periods, suggesting that cyst(e)inase represents a safe and effective therapeutic modality for inactivating antioxidant cellular responses in a wide range of malignancies.

Inhibition of Prostaglandin Reductase 2, a Putative Oncogene Overexpressed in Human Pancreatic Adenocarcinoma, Induces Oxidative Stress-Mediated Cell Death Involving xCT and CTH Gene Expressions through 15-Keto-PGE2

Prostaglandin reductase 2 (PTGR2) is the enzyme that catalyzes 15-keto-PGE₂, an endogenous PPARγ ligand, into 13,14-dihydro-15-keto-PGE₂. Previously, we have reported a novel oncogenic role of PTGR2 in gastric cancer, where PTGR2 was discovered to modulate ROS-mediated cell death and tumor transformation. In the present study, we demonstrated the oncogenic potency of PTGR2 in pancreatic cancer. First, we observed that the majority of the human pancreatic ductal adenocarcinoma tissues was stained positive for PTGR2 expression but not in the adjacent normal parts. In vitro analyses showed that silencing of PTGR2 expression enhanced ROS production, suppressed pancreatic cell proliferation, and promoted cell death through increasing 15-keto-PGE₂. Mechanistically, silencing of PTGR2 or addition of 15-keto-PGE₂ suppressed the expressions of solute carrier family 7 member 11 (xCT) and cystathionine gamma-lyase (CTH), two important providers of intracellular cysteine for the generation of glutathione (GSH), which is widely accepted as the first-line antioxidative defense. The oxidative stress-mediated cell death after silencing of PTGR2 or addition of 15-keto-PGE₂ was further abolished after restoring intracellular GSH concentrations and cysteine supply by N-acetyl-_L-cysteine and 2-Mercaptomethanol. Our data highlight the therapeutic potential of targeting PTGR2/15-keto-PGE₂ for pancreatic cancer.

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

Cancer cells adapt to high levels of oxidative stress in order to survive and proliferate by activating key transcription factors. One such master regulator, the redox sensitive transcription factor NF E2 Related Factor 2 (NRF2), controls the expression of cellular defense genes including those encoding intracellular redox-balancing proteins involved in glutathione (GSH) synthesis. Under basal conditions, Kelch-like ECH-associated protein 1 (KEAP1) targets NRF2 for ubiquitination. In response to oxidative stress, NRF2 dissociates from KEAP1, entering the nucleus and binding to the antioxidant response element (ARE) in the promoter of its target genes. Elevated reactive oxygen species (ROS) production may deplete GSH levels within cancer cells. System xc(-), an antiporter that exports glutamate while importing cystine to be converted into cysteine for GSH synthesis, is upregulated in cancer cells in response to oxidative stress. Here, we provided evidence that the expression of xCT, the light chain subunit of system xc(-), is regulated by NRF2 in representative human breast cancer cells. Hydrogen peroxide (H2O2) treatment increased nuclear translocation of NRF2, also increasing levels of xCT mRNA and protein and extracellular glutamate release. Overexpression of NRF2 up-regulated the activity of the xCT promoter, which contains a proximal ARE. In contrast, overexpression of KEAP1 repressed promoter activity and decreased xCT protein levels, while siRNA knockdown of KEAP1 up-regulated xCT protein levels and transporter activity. These results demonstrate the importance of the KEAP1/NRF2 pathway in balancing oxidative stress in breast cancer cells through system xc(-). We have previously shown that xCT is upregulated in various cancer cell lines under oxidative stress. In the current investigation, we focused on MCF-7 cells as a model for mechanistic studies.

Chromosomal aneuploidies and combinational fluorescence in situ hybridization probe panels are useful for predicting prognosis for esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a common cancer type in China. In this study, we aimed to develop aneuploidy markers for diagnosis and prognosis of ESCC.

METHODS

Chromosomal aneuploidies were detected in 493 primary tumors and 61 precancerous lesions by fluorescence in situ hybridization with chromosome enumeration probes (CEP), and cut-off values were set by receiver operating characteristic (ROC) curves.

RESULTS

According to the cut-off values, chromosomes 3, 8, 10, 12, 17 and 20 presented frequent gains, with rates of 70.1, 69.7, 58.9, 66.9, 67.5 and 77.2 % in tumors and of 32.1, 26.8, 33.9, 41.2, 44.0 and 42.0 % in precancerous lesions. Loss of chromosome Y was detected in 72.0 % of male patients. An optimal four-probe panel CEP3/12/17/20 was established for detecting ESCC (sensitivity: 86.1 %), and CEP3/10/12/20 for precancerous lesions (sensitivity: 48.0 %). Gain of CEP8 was significantly correlated with lymph node metastasis (LNM) and late stages (P = 0.002 and 0.001), and loss of CEPY with age (P = 0.002, male). Kaplan-Meier survival curves indicated that patients with positive CEP10/17 (pT1 + T2, P = 0.041) and CEP8/17 (stages IIb + III + IV, P = 0.002) had poor overall survival. Combinations of LNM/stage and CEP panels could divide patients into more subgroups, including LNM + CEP3/17, LNM + CEP10/17, LNM + CEP3/10/17, stage + CEP3/17, stage + CEP10/17 and stage + CEP3/10/17 (P = 0.0004, 0.0003, 0.0001, 0.005, 0.001 and 0.0008, respectively). Multivariate Cox regression analysis confirmed that the above combinational models were independent prognostic factors.

CONCLUSIONS

Our data suggest that the combinational probe sets may have potential for detection and prognostic prediction of ESCC.