Antioxidant Mechanisms and ROS-Related MicroRNAs in Cancer Stem Cells. Oxid Med Cell Longev. 2015;2015:425708. [PMID: 26064420 PMCID: PMC4429193 DOI: 10.1155/2015/425708]

The Metabolic Landscape of Cancer Stem Cells: Insights and Implications for Therapy

Cancer stem cells (CSCs) are a subpopulation with self-renewal and differentiation capacities believed to be responsible for tumor initiation, progression, and recurrence. These cells exhibit unique metabolic features that contribute to their stemness and survival in hostile tumor microenvironments. Like non-stem cancer cells, CSCs primarily rely on glycolysis for ATP production, akin to the Warburg effect. However, CSCs also show increased dependence on alternative metabolic pathways, such as oxidative phosphorylation (OXPHOS) and fatty acid metabolism, which provide necessary energy and building blocks for self-renewal and therapy resistance. The metabolic plasticity of CSCs enables them to adapt to fluctuating nutrient availability and hypoxic conditions within the tumor. Recent studies highlight the importance of these metabolic shifts in maintaining the CSC phenotype and promoting cancer progression. The CSC model suggests that a small, metabolically adaptable subpopulation drives tumor growth and therapy resistance. CSCs can switch between glycolysis and mitochondrial metabolism, enhancing their survival under stress and dormant states. Targeting CSC metabolism offers a promising therapeutic strategy; however, their adaptability complicates eradication. A multi-targeted approach addressing various metabolic pathways is essential for effective CSC elimination, underscoring the need for further research into specific CSC markers and mechanisms that distinguish their metabolism from normal stem cells for successful therapeutic intervention.

Deciphering colorectal cancer radioresistance and immune microrenvironment: unraveling the role of EIF5A through single-cell RNA sequencing and machine learning

Background

Radiotherapy (RT) is a critical component of treatment for locally advanced rectal cancer (LARC), though patient response varies significantly. The variability in treatment outcomes is partly due to the resistance conferred by cancer stem cells (CSCs) and tumor immune microenvironment (TiME). This study investigates the role of EIF5A in radiotherapy response and its impact on the CSCs and TiME.

Methods

Predictive models for preoperative radiotherapy (preRT) response were developed using machine learning, identifying EIF5A as a key gene associated with radioresistance. EIF5A expression was analyzed via bulk RNA-seq and single-cell RNA-seq (scRNA-seq). Functional assays and in vivo experiments validated EIF5A's role in radioresistance and TiME modulation.

Results

EIF5A was significantly upregulated in radioresistant colorectal cancer (CRC) tissues. EIF5A knockdown in CRC cell lines reduced cell viability, migration, and invasion after radiation, and increased radiation-induced apoptosis. Mechanistically, EIF5A promoted cancer stem cell (CSC) characteristics through the Hedgehog signaling pathway. Analysis of the TiME revealed that the radiation-resistant group had an immune-desert phenotype, characterized by low immune cell infiltration. In vivo experiments showed that EIF5A knockdown led to increased infiltration of CD8+ T cells and M1 macrophages, and decreased M2 macrophages and Tregs following radiation therapy, thereby enhancing the radiotherapy response.

Conclusion

EIF5A contributes to CRC radioresistance by promoting CSC traits via the Hedgehog pathway and modulating the TiME to an immune-suppressive state. Targeting EIF5A could enhance radiation sensitivity and improve immune responses, offering a potential therapeutic strategy to optimize radiotherapy outcomes in CRC patients.

Mechanisms of traditional Chinese medicine overcoming of radiotherapy resistance in breast cancer

Breast cancer stands as the most prevalent malignancy among women, with radiotherapy serving as a primary treatment modality. Despite radiotherapy, a subset of breast cancer patients experiences local recurrence, attributed to the intrinsic resistance of tumors to radiation. Therefore, there is a compelling need to explore novel approaches that can enhance cytotoxic effects through alternative mechanisms. Traditional Chinese Medicine (TCM) and its active constituents exhibit diverse pharmacological actions, including anti-tumor effects, offering extensive possibilities to identify effective components capable of overcoming radiotherapy resistance. This review delineates the mechanisms underlying radiotherapy resistance in breast cancer, along with potential candidate Chinese herbal medicines that may sensitize breast cancer cells to radiotherapy. The exploration of such herbal interventions holds promise for improving therapeutic outcomes in the context of breast cancer radiotherapy resistance.

The Role of Oxidative Stress in Tumorigenesis and Progression

Oxidative stress refers to the imbalance between the production of reactive oxygen species (ROS) and the endogenous antioxidant defense system. Its involvement in cell senescence, apoptosis, and series diseases has been demonstrated. Advances in carcinogenic research have revealed oxidative stress as a pivotal pathophysiological pathway in tumorigenesis and to be involved in lung cancer, glioma, hepatocellular carcinoma, leukemia, and so on. This review combs the effects of oxidative stress on tumorigenesis on each phase and cell fate determination, and three features are discussed. Oxidative stress takes part in the processes ranging from tumorigenesis to tumor death via series pathways and processes like mitochondrial stress, endoplasmic reticulum stress, and ferroptosis. It can affect cell fate by engaging in the complex relationships between senescence, death, and cancer. The influence of oxidative stress on tumorigenesis and progression is a multi-stage interlaced process that includes two aspects of promotion and inhibition, with mitochondria as the core of regulation. A deeper and more comprehensive understanding of the effects of oxidative stress on tumorigenesis is conducive to exploring more tumor therapies.

Chronic oxidative stress adaptation in head and neck cancer cells generates slow-cyclers with decreased tumour growth in vivo

BACKGROUND

Reactive oxygen species (ROS) are implicated in cancer therapy and as drivers of microenvironmental tumour cell adaptations. Medical gas plasma is a multi-ROS generating technology that has been shown effective for palliative tumour control in head and neck cancer (HNC) patients before tumour cells adapted to the oxidative stress and growth regressed fatally.

METHODS

In a bedside-to-bench approach, we sought to explore the oxidative stress adaptation in two human squamous cell carcinoma cell lines. Gas plasma was utilised as a putative therapeutic agent and chronic oxidative stress inducer.

RESULTS

Cellular responses of single and multiple treated cells were compared regarding sensitivity, cellular senescence, redox state and cytokine release. Whole transcriptome analysis revealed a strong correlation of cancer cell adaption with increased interleukin 1 receptor type 2 (IL1R2) expression. Using magnetic resonance imaging, tumour growth and gas plasma treatment responses of wild-type (WT) and repeatedly exposed (RE) A431 cells were further investigated in a xenograft model in vivo. RE cells generated significantly smaller tumours with suppressed inflammatory secretion profiles and increased epidermal growth factor receptor (EGFR) activity showing significantly lower gas plasma sensitivity until day 8.

CONCLUSIONS

Clinically, combination treatments together with cetuximab, an EGFR inhibitor, may overcome acquired oxidative stress resistance in HNC.

Molecular mechanisms of tumor resistance to radiotherapy

BACKGROUND

Cancer is the most prevalent cause of death globally, and radiotherapy is considered the standard of care for most solid tumors, including lung, breast, esophageal, and colorectal cancers and glioblastoma. Resistance to radiation can lead to local treatment failure and even cancer recurrence.

MAIN BODY

In this review, we have extensively discussed several crucial aspects that cause resistance of cancer to radiation therapy, including radiation-induced DNA damage repair, cell cycle arrest, apoptosis escape, abundance of cancer stem cells, modification of cancer cells and their microenvironment, presence of exosomal and non-coding RNA, metabolic reprogramming, and ferroptosis. We aim to focus on the molecular mechanisms of cancer radiotherapy resistance in relation to these aspects and to discuss possible targets to improve treatment outcomes.

CONCLUSIONS

Studying the molecular mechanisms responsible for radiotherapy resistance and its interactions with the tumor environment will help improve cancer responses to radiotherapy. Our review provides a foundation to identify and overcome the obstacles to effective radiotherapy.

Nanoparticles for Drug and Gene Delivery in Pediatric Brain Tumors' Cancer Stem Cells: Current Knowledge and Future Perspectives

Primary malignant brain tumors are the most common solid neoplasm in childhood. Despite recent advances, many children affected by aggressive or metastatic brain tumors still present poor prognosis, therefore the development of more effective therapies is urgent. Cancer stem cells (CSCs) have been discovered and isolated in both pediatric and adult patients with brain tumors (e.g., medulloblastoma, gliomas and ependymoma). CSCs are a small clonal population of cancer cells responsible for brain tumor initiation, maintenance and progression, displaying resistance to conventional anticancer therapies. CSCs are characterized by a specific repertoire of surface markers and intracellular specific pathways. These unique features of CSCs biology offer the opportunity to build therapeutic approaches to specifically target these cells in the complex tumor bulk. Treatment of pediatric brain tumors with classical chemotherapeutic regimen poses challenges both for tumor location and for the presence of the blood-brain barrier (BBB). Lastly, the application of chemotherapy to a developing brain is followed by long-term sequelae, especially on cognitive abilities. Novel avenues are emerging in the therapeutic panorama taking advantage of nanomedicine. In this review we will summarize nanoparticle-based approaches and the efficacy that NPs have intrinsically demonstrated and how they are also decorated by biomolecules. Furthermore, we propose novel cargoes together with recent advances in nanoparticle design/synthesis with the final aim to specifically target the insidious CSCs population in the tumor bulk.

The Molecular and Cellular Strategies of Glioblastoma and Non-Small-Cell Lung Cancer Cells Conferring Radioresistance

Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLC). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLC. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.

Wound Healing versus Metastasis: Role of Oxidative Stress

Many signaling pathways, molecular and cellular actors which are critical for wound healing have been implicated in cancer metastasis. These two conditions are a complex succession of cellular biological events and accurate regulation of these events is essential. Apart from inflammation, macrophages-released ROS arise as major regulators of these processes. But, whatever the pathology concerned, oxidative stress is a complicated phenomenon to control and requires a finely tuned balance over the different stages and responding cells. This review provides an overview of the pivotal role of oxidative stress in both wound healing and metastasis, encompassing the contribution of macrophages. Indeed, macrophages are major ROS producers but also appear as their targets since ROS interfere with their differentiation and function. Elucidating ROS functions in wound healing and metastatic spread may allow the development of innovative therapeutic strategies involving redox modulators.

The rs1001179 SNP and CpG methylation regulate catalase expression in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is an incurable disease characterized by an extremely variable clinical course. We have recently shown that high catalase (CAT) expression identifies patients with an aggressive clinical course. Elucidating mechanisms regulating CAT expression in CLL is preeminent to understand disease mechanisms and develop strategies for improving its clinical management. In this study, we investigated the role of the CAT promoter rs1001179 single nucleotide polymorphism (SNP) and of the CpG Island II methylation encompassing this SNP in the regulation of CAT expression in CLL. Leukemic cells harboring the rs1001179 SNP T allele exhibited a significantly higher CAT expression compared with cells bearing the CC genotype. CAT promoter harboring the T -but not C- allele was accessible to ETS-1 and GR-β transcription factors. Moreover, CLL cells exhibited lower methylation levels than normal B cells, in line with the higher CAT mRNA and protein expressed by CLL in comparison with normal B cells. Methylation levels at specific CpG sites negatively correlated with CAT levels in CLL cells. Inhibition of methyltransferase activity induced a significant increase in CAT levels, thus functionally validating the role of CpG methylation in regulating CAT expression in CLL. Finally, the CT/TT genotypes were associated with lower methylation and higher CAT levels, suggesting that the rs1001179 T allele and CpG methylation may interact in regulating CAT expression in CLL. This study identifies genetic and epigenetic mechanisms underlying differential expression of CAT, which could be of crucial relevance for the development of therapies targeting redox regulatory pathways in CLL.

Increased MCL-1 synthesis promotes irradiation-induced nasopharyngeal carcinoma radioresistance via regulation of the ROS/AKT loop

Worldwide, nasopharyngeal carcinoma (NPC) is a rare head and neck cancer; however, it is a common malignancy in southern China. Radiotherapy is the most important treatment strategy for NPC. However, although radiotherapy is a strong tool to kill cancer cells, paradoxically it also promotes aggressive phenotypes. Therefore, we mimicked the treatment process in NPC cells in vitro. Upon exposure to radiation, a subpopulation of NPC cells gradually developed resistance to radiation and displayed cancer stem-cell characteristics. Radiation-induced stemness largely depends on the accumulation of the antiapoptotic myeloid cell leukemia 1 (MCL-1) protein. Upregulated MCL-1 levels were caused by increased stability and more importantly, enhanced protein synthesis. We showed that repeated ionizing radiation resulted in persistently enhanced reactive oxygen species (ROS) production at a higher basal level, further promoting protein kinase B (AKT) signaling activation. Intracellular ROS and AKT activation form a positive feedback loop in the process of MCL-1 protein synthesis, which in turn induces stemness and radioresistance. AKT/MCL-1 axis inhibition attenuated radiation-induced resistance, providing a potential target to reverse radiation therapy-induced radioresistance.

Hypoxia-Induced miR-210 Overexpression Promotes the Differentiation of Human-Induced Pluripotent Stem Cells to Hepatocyte-Like Cells on Random Nanofiber Poly-L-Lactic Acid/Poly (ε-Caprolactone) Scaffolds

An alternative treatment to liver transplantation includes the use of differentiated stem cells. Hypoxia has been shown to endow human-induced pluripotent stem cells (hiPSCs) with enhanced hepatic differentiation. We have investigated a new strategy for hepatocyte differentiation from hiPSCs using a three-step differentiation protocol with lentiviral overexpression of hypoxia-microRNA-210 of cells grown on a hybrid scaffold. We analyzed the transduction of the miR-210 lentiviral and definitive endoderm and pluripotency gene markers, including SRY-box 17 (SOX17), forkhead box A2 (FOXA2), and octamer-binding transcription factor 4 (OCT-4) by Real-Time PCR and fluorescent microscope. The scanning electron microscopy (SEM) examined the 3D cell morphological changes. Immunocytochemistry staining was used together with assays for aspartate aminotransferase, alanine aminotransferase, and urea secretion to analyze hepatocyte biomarkers and functional markers consisting of α-fetoprotein (AFP), low-density lipoprotein (LDL) uptake, fat accumulation, and glycogen. The flow cytometry analyzed the generation of reactive oxygen species (ROS). Compared to cells transfected with the blank lentiviral vectors as a control, overexpressing miR-210 was at higher levels in hiPSCs. The expression of endodermal genes and glycogen synthesis significantly increased in the differentiated lentiviral miR-210 cells without any differences regarding lipid storage level. Additionally, cells containing miR-210 showed a greater expression of ALB, LDL, AST, ALT, urea, and insignificant lower AFP and ROS levels after 18 days. However, SEM showed no significant differences between cells under the differentiation process and controls. In conclusion, the differentiation of hiPSCs to hepatocyte-like cells under hypoxia miR-210 may be a suitable method for cell therapy and regenerative medicine.

Luteolin Inhibits Breast Cancer Stemness and Enhances Chemosensitivity through the Nrf2-Mediated Pathway

Cancer stem cells (CSCs) are subpopulations of tumor masses with unique abilities in self-renewal, stemness maintenance, drug resistance, and the promotion of cancer recurrence. Recent studies have suggested that breast CSCs play essential roles in chemoresistance. Therefore, new agents that selectively target such cells are urgently required. Reactive oxygen species (ROS)-producing enzymes are the reason for an elevated tumor oxidant status. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcriptional factor, which upon detecting cellular oxidative stress, binds to the promoter region of antioxidant genes. By triggering a cytoprotective response, Nrf2 maintains cellular redox status. Cripto-1 participates in the self-renewal of CSCs. Herein, luteolin, a flavonoid found in Taraxacum officinale extract, was determined to inhibit the expressions of stemness-related transcriptional factors, the ATP-binding cassette transporter G2 (ABCG2), CD44, aldehyde dehydrogenase 1 activity as well as the sphere formation properties of breast CSCs. Furthermore, luteolin suppressed the protein expressions of Nrf2, heme oxygenase 1 (HO-1), and Cripto-1 which have been determined to contribute critically to CSC features. The combination of luteolin and the chemotherapeutic drug, Taxol, resulted in enhanced cytotoxicity to breast cancer cells. These findings suggest that luteolin treatment significantly attenuated the hallmarks of breast cancer stemness by downregulating Nrf2-mediated expressions. Luteolin constitutes a potential agent for use in cancer stemness-targeted breast cancer treatments.

Astaxanthin attenuates hepatic steatosis in high-fat diet-fed rats by suppressing microRNA-21 via transactivation of nuclear factor erythroid 2-related factor 2

This study examined whether astaxanthin (ASX) could alleviate hepatic steatosis in rats fed a high-fat diet (HFD) by modulating the nuclear factor erythroid 2-related factor 2 (Nrf2)/miR-21 axis. Rats (n = 8/group) were fed either a standard diet (3.8 kcal/g; 10% fat) or HFD (4.6 kcal/g; 40% fat) and treated orally with either the vehicle or ASX (6 mg/kg) daily for 8 days. Another group was fed HFD and treated with ASX and brusatol (an Nrf2 inhibitor) (2 mg/kg/twice per week/i.p.). ASX prevented the gain in body and liver weights and attenuated hepatic lipid accumulation in HFD-fed rats. In the control and HFD-fed rats, ASX did not affect food intake, serum free fatty acid (FFA) content, and glucose and insulin levels and tolerance. However, serum triglyceride (TG), cholesterol, and low-density lipoprotein-cholesterol levels; hepatic levels of TGs and FFAs; and hepatic levels of Srebp1, Srebp2, HMGCR, and fatty acid synthase mRNAs and miR-21 were reduced and the mRNA levels of Pparα were significantly increased in both the groups. These effects were associated with a reduction in the hepatic levels of reactive oxygen species, malondialdehyde, tumor necrosis factor-α, and interlukin-6 as well as an increase in superoxide dismutase levels, total glutathione content, and nuclear levels and activity of Nrf2. miR-21 levels were strongly correlated with the nuclear activity of Nrf2. Brusatol completely reversed the effects of ASX. In conclusion, ASX prevents hepatic steatosis mainly by transactivating Nrf2 and is associated with the suppression of miR-21 and Srebp1/2 and upregulation of Pparα expression.

Microenvironmental Reactive Oxygen Species in Colorectal Cancer: Involved Processes and Therapeutic Opportunities

Colorectal cancer (CRC) is the fourth most common cause of cancer deaths worldwide. Although screening programs have reduced mortality rates, there is a need for research focused on finding the main factors that lead primary CRC to progress and metastasize. During tumor progression, malignant cells modify their habitat, corrupting or transforming cells of different origins and creating the tumor microenvironment (TME). Cells forming the TME like macrophages, neutrophils, and fibroblasts generate reactive oxygen species (ROS) that modify the cancer niche. The effects of ROS in cancer are very diverse: they promote cellular proliferation, epithelial-to-mesenchymal transition (EMT), evasion of cell death programs, migration, and angiogenesis. Due to the multifaceted role of ROS in cancer cell survival and function, ROS-modulating agents such as antioxidants or pro-oxidants could have therapeutic potential in cancer prevention and/or as a complement to systemic treatments. In this review, we will examine the main ROS producer cells and their effects on cancer progression and metastasis. Furthermore, we will enumerate the latest clinical trials where pro-oxidants and antioxidants have therapeutic uses in CRC.

Browsing the oldest antioxidant enzyme: catalase and its multiple regulation in cancer

Aerobic organisms possess numerous antioxidant enzymatic families, including catalases, superoxide dismutases (SODs), peroxiredoxins (PRDXs), and glutathione peroxidases (GPXs), which work cooperatively to protect cells from an excess of reactive oxygen species (ROS) derived from endogenous metabolism or external microenvironment. Catalase, as well as other antioxidant enzymes, plays an important dichotomous role in cancer. Therefore, therapies aimed at either reverting the increased or further escalating catalase levels could be effective, depending on the metabolic landscape and on the redox status of cancer cells. This dichotomous role of catalase in cancers highlights the importance to deepen comprehensively the role and the regulation of this crucial antioxidant enzyme. The present review highlights the role of catalase in cancer and provides a comprehensive description of the molecular mechanisms associated with the multiple levels of catalase regulation.

Quercetin prevents cadmium chloride-induced hepatic steatosis and fibrosis by downregulating the transcription of miR-21

This study investigated if cadmium chloride (CdCl₂ )-induced hepatic steatosis and fibrosis and the protective effect of quercetin (QUR) are mediated modulating the activity of miR-21, a known hepatic lipogenic and fibrotic miRNA. Male rats (n = 8/group) were divided as control, control + QUR (50 mg/kg; orally), CdCl₂ (10 moml/L; drinking water), CdCl₂  + miR-21 antagomir (inhibitor) (16 mg/kg/first 3 days), and CdCl₂  + QUR (50 mg/kg). Treatments were conducted for 20 weeks, daily. All treatments showed no effect on fasting glucose and insulin levels. Administration of either miR-21 or QUR prevented CdCl₂ -induced hepatic damage, as well as lipid droplets and collagen deposition. They also reduced serum levels of ALT and AST and decreased serum and hepatic levels of total cholesterol, triglycerides, and low-density lipoproteins in CdCl₂ -treated rats. Concomitantly, they reduced hepatic levels of reactive oxygen species, malondialdehyde, interleukin-6, and tumor necrosis factor-α, suppressed the activation of NF-kb P65, and increased hepatic levels of nuclear factor erythroid 2-related factor 2 (Nrf2), glutathione (GSH), and superoxide dismutase (SOD). These effects were associated with reduced expression of SREBP1, TGF-β1, Smad3, and collagen1 A and increased expression of PPARα, CPT1, and smad7. Interestingly, QUR significantly lowered levels of miR-21 and increased the protein levels and activity of Nrf2, as well as levels of GSH and SOD in the livers of both the control and CdCl₂ -treated rats. Of note, levels of Nrf2 were negatively correlated with the transcription of miR-21. In conclusion: QUR prevents CdCl₂ -induced hepatic steatosis and fibrosis mainly through attenuating its ability to upregulate miR-21, at least, by upregulation of Nrf2.

Sevoflurane Postconditioning Attenuates Hepatic Ischemia-Reperfusion Injury by Limiting HMGB1/TLR4/NF-κB Pathway via Modulating microRNA-142 in vivo and in vitro

Preconditioning of sevoflurane (Sevo) has been demonstrated to protect the liver from ischemia/reperfusion (I/R) injury. However, it is unknown whether it has hepatoprotective when given at the onset of reperfusion (postconditioning), a protocol with more clinical impact. The present study aimed to explore the hepatoprotective effects of Sevo postconditioning against hepatic IR injury in vivo and in vitro and the possible mechanisms. Using a mouse model of hepatic I/R, Sevo postconditioning significantly improved hepatic injury after reperfusion, as demonstrated by reduced AST, ALT, and LDH serum levels and reduced histologic damage in liver tissues. Furthermore, Sevo postconditioning could suppress the apoptosis, inhibit oxidative stress and inflammatory response in liver tissue of HIRI mice, as well as improve the survival rate of HIRI mice. Through analyzing GSE72314 from the gene expression omnibus (GEO) database, it was demonstrated that microRNA (miR)-142 is downregulated by HIRI, which was reversed by Sevo treatment. Further investigation showed that agomiR-142 injection could enhance the hepatoprotective effects of Sevo postconditioning on I/R injury, while antagomiR-142 reversed these effects in mice. Notably, high mobility group box 1 (HMGB1), an important inflammatory factor, was directly targeted by miR-142 in hepatic cells, and we further found that Sevo could inhibit the expression of HMGB1 through up-regulating miR-142 expression in HIRI mice model. In addition, we found that I/R injury induced the activation of TLR4/NF-κB inflammatory pathway was partially suppressed by Sevo postconditioning, and miR-142 mediated the regulatory role of Sevo postconditioning. In line with the in vivo results, Sevo treatment improved the cell viability, inhibited cell apoptosis, oxidative stress and inflammatory response in vitro HIRI model, while these effects were reversed by antagomiR-142 transfection. Collectively, our findings demonstrated that Sevo postconditioning counteracts the downregulation of miR-142 provoked by I/R, in turn decreased the expression of HMGB1, blocking TLR4/NF-κB pathway activation, thus improving hepatic I/R injury. Our data suggest that Sevo may be a valuable alternative anaesthetic agent in liver transplantation and major liver surgeries.

Oxidative Stress and Cancer Development: Are Noncoding RNAs the Missing Links?

Significance: It is now clear that genetic changes underlie the basis of cancer, and alterations in functions of multiple genes are responsible for the process of tumorigenesis. Besides the classical genes that are usually implicated in cancer, the role of noncoding RNAs (ncRNAs) and reactive oxygen species (ROS) as independent entitites has also been investigated. Recent Advances: The microRNAs and long noncoding RNAs (lncRNAs), two main classes of ncRNAs, are known to regulate many aspects of tumor development. ROS, generated during oxidative stress and pathological conditions, are known to regulate every step of tumor development. Conversely, oxidative stress and ROS producing agents can suppress tumor development. The malignant cells normally produce high levels of ROS compared with normal cells. The interaction between ROS and ncRNAs regulates the expression of multiple genes and pathways implicated in cancer, suggesting a unique mechanistic relationship among ncRNA-ROS-cancer. The mechanistic relationship has been reported in hepatocellular carcinoma, glioma, and malignancies of blood, breast, colorectum, esophagus, kidney, lung, mouth, ovary, pancreas, prostate, and stomach. The ncRNA-ROS regulate several cancer-related cell signaling pathways, namely, protein kinase B (AKT), epidermal growth factor receptor (EGFR), forkhead box O3 (FOXO3), kelch-like ECH-associated protein 1 (Keap1), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), nuclear factor erythroid 2-related factor 2 (Nrf2), p53, phosphatase and tensin homologue (PTEN), and wingless-related integration site (Wnt)/glycogen synthase kinase-3 beta (GSK3β). Critical Issues: To date, most of the reports about ncRNA-oxidative stress-carcinogenesis relationships are based on cell lines. The mechanistic basis for this relationship has not been completely elucidated. Future Directions: Attempts should be made to explore the association of lncRNAs with ROS. The significance of the ncRNA-oxidative stress-carcinogenesis interplay should also be explored through studies in animal models.

Regulatory effects of noncoding RNAs on the interplay of oxidative stress and autophagy in cancer malignancy and therapy

Noncoding RNAs (ncRNAs) regulation of various diseases including cancer has been extensively studied. Reactive oxidative species (ROS) elevated by oxidative stress are associated with cancer progression and drug resistance, while autophagy serves as an ROS scavenger in cancer cells. However, the regulatory effects of ncRNAs on autophagy and ROS in various cancer cells remains complex. Here, we explore how currently investigated ncRNAs, mainly miRNAs and lncRNAs, are involved in ROS production through modulating antioxidant genes. The regulatory effects of miRNAs and lncRNAs on autophagy-related (ATG) proteins to control autophagy activity in cancer cells are discussed. Moreover, differential expression of ncRNAs in tumor and normal tissues of cancer patients are further analyzed using The Cancer Genome Atlas (TCGA) database. This review hypothesizes links between ATG genes- or antioxidant genes-modulated ncRNAs and ROS production, which might result in tumorigenesis, malignancy, and cancer recurrence. A better understanding of the regulation of ROS and autophagy by ncRNAs might advance the use of ncRNAs as diagnostic and prognostic markers as well as therapeutic targets in cancer therapy.

Photodynamic therapy regulates fate of cancer stem cells through reactive oxygen species

Photodynamic therapy (PDT) is an effective and promising cancer treatment. PDT directly generates reactive oxygen species (ROS) through photochemical reactions. This oxygen-dependent exogenous ROS has anti-cancer stem cell (CSC) effect. In addition, PDT may also increase ROS production by altering metabolism, endoplasmic reticulum stress, or potential of mitochondrial membrane. It is known that the half-life of ROS in PDT is short, with high reactivity and limited diffusion distance. Therefore, the main targeting position of PDT is often the subcellular localization of photosensitizers, which is helpful for us to explain how PDT affects CSC characteristics, including differentiation, self-renewal, apoptosis, autophagy, and immunogenicity. Broadly speaking, excess ROS will damage the redox system and cause oxidative damage to molecules such as DNA, change mitochondrial permeability, activate unfolded protein response, autophagy, and CSC resting state. Therefore, understanding the molecular mechanism by which ROS affect CSCs is beneficial to improve the efficiency of PDT and prevent tumor recurrence and metastasis. In this article, we review the effects of two types of photochemical reactions on PDT, the metabolic processes, and the biological effects of ROS in different subcellular locations on CSCs.

CSC Radioresistance: A Therapeutic Challenge to Improve Radiotherapy Effectiveness in Cancer

Radiotherapy (RT) is a modality of oncologic treatment that can be used to treat approximately 50% of all cancer patients either alone or in combination with other treatment modalities such as surgery, chemotherapy, immunotherapy, and therapeutic targeting. Despite the technological advances in RT, which allow a more precise delivery of radiation while progressively minimizing the impact on normal tissues, issues like radioresistance and tumor recurrence remain important challenges. Tumor heterogeneity is responsible for the variation in the radiation response of the different tumor subpopulations. A main factor related to radioresistance is the presence of cancer stem cells (CSC) inside tumors, which are responsible for metastases, relapses, RT failure, and a poor prognosis in cancer patients. The plasticity of CSCs, a process highly dependent on the epithelial–mesenchymal transition (EMT) and associated to cell dedifferentiation, complicates the identification and eradication of CSCs and it might be involved in disease relapse and progression after irradiation. The tumor microenvironment and the interactions of CSCs with their niches also play an important role in the response to RT. This review provides a deep insight into the characteristics and radioresistance mechanisms of CSCs and into the role of CSCs and tumor microenvironment in both the primary tumor and metastasis in response to radiation, and the radiobiological principles related to the CSC response to RT. Finally, we summarize the major advances and clinical trials on the development of CSC-based therapies combined with RT to overcome radioresistance. A better understanding of the potential therapeutic targets for CSC radiosensitization will provide safer and more efficient combination strategies, which in turn will improve the live expectancy and curability of cancer patients.

4-Hydroxy-7-oxo-5-heptenoic acid lactone is a potent inducer of brain cancer cell invasiveness that may contribute to the failure of anti-angiogenic therapies

Previously, we discovered that free radical-induced oxidative fragmentation of the docosahexaenoate ester of 2-lysophosphatidylcholine produces 4-hydroxy-7-oxo-5-heptenoic acid (HOHA) lactone that, in turn, promotes the migration and invasion of endothelial cells. This suggested that HOHA lactone might similarly promote migration and invasion of glioblastoma multiformae (GBM) brain cancer stem cells (CSCs). A bioinformatics analysis of clinical cancer genomic data revealed that matrix metalloproteinase (MMP)1 and three markers of oxidative stress - superoxide dismutase 2, NADPH oxidase 4, and carbonic anhydrase 9 - are upregulated in human mesenchymal GBM cancer tissue, and that MMP1 is positively correlated to all three of these oxidative stress markers. In addition, elevated levels of MMP1 are indicative of GBM invasion, while low levels of MMP1 indicate survival. We also explored the hypothesis that the transition from the proneural to the more aggressive mesenchymal phenotype, e.g., after treatment with an anti-angiogenic therapy, is promoted by the effects of lipid oxidation products on GBM CSCs. We found that low micromolar concentrations of HOHA lactone increase the cell migration velocity of cultured GBM CSCs, and induce the expression of MMP1 and two protein biomarkers of the proneural to mesenchymal transition (PMT): p65 NF-κβ and vimentin. Exposure of cultured GBM CSCs to HOHA lactone causes an increase in phosphorylation of mitogen-activated protein kinases and Akt kinases that are dependent on both protease-activated receptor 1 (PAR1) and MMP1 activity. We conclude that HOHA lactone promotes the PMT in GBM through the activation of PAR1 and MMP1. This contributes to a fatal flaw in antiangiogenic, chemo, and radiation therapies: they promote oxidative stress and the generation of HOHA lactone in the tumor that fosters a change from the proliferative proneural to the migratory mesenchymal GBM CSC phenotype that seeds new tumor growth. Inhibition of PAR1 and HOHA lactone are potential new therapeutic targets for impeding GBM tumor recurrence.

microRNAs Tune Oxidative Stress in Cancer Therapeutic Tolerance and Resistance

Relapsed disease following first-line therapy remains one of the central problems in cancer management, including chemotherapy, radiotherapy, growth factor receptor-based targeted therapy, and immune checkpoint-based immunotherapy. Cancer cells develop therapeutic resistance through both intrinsic and extrinsic mechanisms including cellular heterogeneity, drug tolerance, bypassing alternative signaling pathways, as well as the acquisition of new genetic mutations. Reactive oxygen species (ROSs) are byproducts originated from cellular oxidative metabolism. Recent discoveries have shown that a disabled antioxidant program leads to therapeutic resistance in several types of cancers. ROSs are finely tuned by dysregulated microRNAs, and vice versa. However, mechanisms of a crosstalk between ROSs and microRNAs in regulating therapeutic resistance are not clear. Here, we summarize how the microRNA-ROS network modulates cancer therapeutic tolerance and resistance and direct new vulnerable targets against drug tolerance and resistance for future applications.

The Yin-Yang Regulation of Reactive Oxygen Species and MicroRNAs in Cancer

Reactive oxygen species (ROS) are highly reactive oxygen-containing chemical species formed as a by-product of normal aerobic respiration and also from a number of other cellular enzymatic reactions. ROS function as key mediators of cellular signaling pathways involved in proliferation, survival, apoptosis, and immune response. However, elevated and sustained ROS production promotes tumor initiation by inducing DNA damage or mutation and activates oncogenic signaling pathways to promote cancer progression. Recent studies have shown that ROS can facilitate carcinogenesis by controlling microRNA (miRNA) expression through regulating miRNA biogenesis, transcription, and epigenetic modifications. Likewise, miRNAs have been shown to control cellular ROS homeostasis by regulating the expression of proteins involved in ROS production and elimination. In this review, we summarized the significance of ROS in cancer initiation, progression, and the regulatory crosstalk between ROS and miRNAs in cancer.

Morin Protects Human Respiratory Cells from PM2.5 Induced Genotoxicity by Mitigating ROS and Reverting Altered miRNA Expression

Chronic fine particulate matter (PM2.5) exposure causes oxidative stress and leads to many diseases in human like respiratory and cardiovascular disorders, and lung cancer. It is known that toxic responses elicited by PM2.5 particles depend on its physical and chemical characteristics that are greatly influenced by the source. Dietary polyphenolic compounds that possess antioxidant and free radical scavenging properties could be used for therapeutic or preventive approaches against air pollution related health hazards. This study evaluates characteristics and toxicity of PM2.5 collected from rural, urban, industrial, and traffic regions in and around Coimbatore City, Tamilnadu, India. Traffic PM2.5 particles contained higher amounts of metals and polycyclic aromatic hydrocarbons (PAHs). It also possessed higher levels of oxidative potential, induced more intracellular reactive oxygen species (ROS), and caused more levels of cell death and DNA damage in human respiratory cells. Its exposure up regulated DNA damage response related miR222, miR210, miR101, miR34a, and miR93 and MycN and suppressed Rad52. Pre-treatment with morin significantly decreased the PM2.5 induced toxicity and conferred protection against PM2.5 induced altered miRNA expression. Results of this study showed that cytoprotective effect of morin is due to its antioxidative and free radical scavenging activity.

Redox regulation of cell state and fate

The failure in effective cancer treatment is thought to be attributed to a subpopulation of tumor cells with stem cell-like properties. These cancer stem cells (CSCs) are intimately linked to tumor initiation, heterogeneity, maintenance, recurrence and metastasis. Increasing evidence supports the view that a tight redox regulation is crucial for CSC proliferation, tumorigenicity, therapy resistance and metastasis in many cancer types. Since the distinct metabolic and epigenetic states of CSCs may influence ROS levels, and hence their malignancy, ROS modulating agents hold promise in their utility as anti-CSC agents that may improve the durability of current cancer treatments. This review will focus on (i) how ROS levels are regulated for CSCs to elicit their hallmark features; (ii) the link between ROS and metabolic plasticity of CSCs; and (iii) how ROS may interface with epigenetics that would enable CSCs to thrive in a stressful tumor microenvironment and survive therapeutic insults.

Low‑intensity ultrasound enhances the chemosensitivity of hepatocellular carcinoma cells to cisplatin via altering the miR‑34a/c‑Met axis

Recently, the use of low-intensity ultrasound (LIUS) combined with chemotherapeutic agents is widely used in clinical practice, mainly for the treatment of cancer; however, the mechanisms as to how LIUS enhances the antitumor effects of these agents are not fully understood. The aim of the present study was to explore the synergistic antitumor effects and mechanisms of cisplatin (DDP) combined with LIUS (LIUS-DDP) in hepatocellular carcinoma (HCC). We reported that LIUS effectively enhanced Huh7 and HCCLM3 cell sensitivity to a low concentration of DDP. Reverse transcription-quantitative polymerase chain reaction analysis revealed that LIUS could increase the expression of microRNA-34a (miR-34a) in HCC cells following DDP treatment. In addition, LIUS-DDP significantly increased intracellular reactive oxygen species (ROS) levels in vitro, and the upregulation of miR-34a induced by LIUS-DDP was reversed by the ROS scavenger N-acetylcysteine, suggesting that LIUS upregulates the expression of miR-34a via production of ROS. In addition, knockdown of miR-34a in HCC cells significantly suppressed the synergistic effects of LIUS-DDP treatment. Conversely, overexpression of miR-34a enhanced these synergistic effects. The results of a dual-luciferase assay indicated that c-Met, a well-known oncogene, was a target of miR-34a. We also determined that LIUS-DDP treatment inhibited the expression of c-Met, possibly due to increased ROS production, which upregulated miR-34a expression. Furthermore, overexpression of c-Met reversed the synergistic effects of LIUS-DDP treatment. Our findings suggest that LIUS could enhance the chemosensitivity of HCC cells to DDP by altering the miR-34a/c-Met axis. Therefore, DDP combined with LIUS may be a potential therapeutic application for the clinical treatment of patients with HCC.

Potential roles of microRNAs in redox state: An update

Oxidative stress is an important underlying cause of many disease processes and may arise due to either increasing free radical generation or decreasing antioxidant defense systems. MicroRNAs (miRs) are 22-nucleotide non-coding RNAs that may regulate many intracellular processes; and, more recently, they have been implicated in the pathways for free radical generation leading to oxidative stress. However, conversely, there is evidence that miRs may have an antioxidant effect, thus miR expression may be critical for the maintenance of the normal redox state and cell homeostasis. This review addresses these discrepant and opposing miR actions on how they may modify and regulate the oxidative balance.

Peroxiredoxin II Regulates Cancer Stem Cells and Stemness-Associated Properties of Cancers

Cancer stem cells (CSCs) represent a sub-population of cancer cells with the ability to regulate stemness-associated properties which are specifically responsible for unlimited growth of cancers, generation of diverse cancer cells in differentiated state and resistance to existing chemotherapy and radiotherapy. Even though, current therapies destroy majority of cancer cells, it is believed to leave CSCs without eradicating which may be the conceptualization for chemoresistance and radio-resistance. Reactive oxygen species (ROS) maintain stem cells and regulate the stemness-associated properties of cancers. Beyond the maximum limit, ROS can damage cellular functions of cancers by subjecting them to oxidative stress. Thus, maintenance of ROS level plays an important role in cancers to regulate stemness-associated properties. Peroxiredoxin II (Prx II) is a member of peroxiredoxin antioxidant enzyme family which considers as a regulator of ROS in cellular environments by modulating redox status to maintain CSC phenotype and stemness properties. Prx II has cell type-dependent expression in various types of cancer cells and overexpression or silenced expression of Prx II in cancers is associated with stem cell phenotype and stemness-associated properties via activation or deactivation of various signaling pathways. In this review, we summarized available studies on Prx II expression in cancers and the mechanisms by which Prx II takes parts to regulate CSCs and stemness-associated properties. We further discussed the potential therapeutic effects of altering Prx II expression in cancers for better anticancer strategies by sensitizing cancer cells and stem cells to oxidative stress and inhibiting stemness-associated properties.

Poly(ethylene glycol)-poly(lysine) block copolymer-ubenimex conjugate targets aminopeptidase N and exerts an antitumor effect in hepatocellular carcinoma stem cells

Previous studies highlighted that aminopeptidase N (APN)/CD13 acts as a scavenger in the survival of hepatocellular carcinoma (HCC) stem cells by reducing reactive oxygen species (ROS) levels. Hence, it has been proposed that APN/CD13 inhibition can increase cellular ROS levels and sensitize cells to chemotherapeutic agents. Although ubenimex, also known as bestatin, competitively inhibits proteases such as APN/CD13 on the cellular membrane and it is clinically used for patients with acute myeloid leukemia and lymphedema, research has demonstrated that higher concentrations of the agent induce the death of APN/CD13⁺ HCC stem cells. In this study, we developed a poly(ethylene glycol)-poly(lysine) block copolymer-ubenimex conjugate (PEG-b-PLys(Ube)) to increase the efficacy of reagents in APN/CD13⁺ cancer stem cells. Exposure to PEG-b-PLys(Ube) increased the intracellular ROS concentration by inhibiting APN enzyme activity, permitting the induction of apoptosis and attenuation of HCC cell proliferation. In addition, PEG-b-PLys(Ube) exhibited a relatively stronger antitumor effect in mice than PEG-b-PLys alone or phosphate-buffered saline. Moreover, an isobologram analysis revealed that combinations of fluorouracil, cisplatin, or doxorubicin with PEG-b-PLys(Ube) exhibited synergistic effects. This study demonstrated that PEG-b-PLys(Ube) does not impair the properties of ubenimex and exerts a potent antitumor effect.

MiR200 and miR302: Two Big Families Influencing Stem Cell Behavior

In this review, we described different factors that modulate pluripotency in stem cells, in particular we aimed at following the steps of two large families of miRNAs: the miR-200 family and the miR-302 family. We analyzed some factors tuning stem cells behavior as TGF-β, which plays a pivotal role in pluripotency inhibition together with specific miRNAs, reactive oxygen species (ROS), but also hypoxia, and physical stimuli, such as ad hoc conveyed electromagnetic fields. TGF-β plays a crucial role in the suppression of pluripotency thus influencing the achievement of a specific phenotype. ROS concentration can modulate TGF-β activation that in turns down regulates miR-200 and miR-302. These two miRNAs are usually requested to maintain pluripotency, while they are down-regulated during the acquirement of a specific cellular phenotype. Moreover, also physical stimuli, such as extremely-low frequency electromagnetic fields or high-frequency electromagnetic fields conveyed with a radioelectric asymmetric conveyer (REAC), and hypoxia can deeply influence stem cell behavior by inducing the appearance of specific phenotypes, as well as a direct reprogramming of somatic cells. Unraveling the molecular mechanisms underlying the complex interplay between externally applied stimuli and epigenetic events could disclose novel target molecules to commit stem cell fate.

Cancer stem cells and signaling pathways in radioresistance

Radiation therapy (RT) is one of the most important strategies in cancer treatment. Radioresistance (the failure to RT) results in locoregional recurrence and metastasis. Therefore, it is critically important to investigate the mechanisms leading to cancer radioresistance to overcome this problem and increase patients' survival. Currently, the majority of the radioresistance-associated researches have focused on preclinical studies. Although the exact mechanisms of cancer radioresistance have not been fully uncovered, accumulating evidence supports that cancer stem cells (CSCs) and different signaling pathways play important roles in regulating radiation response and radioresistance. Therefore, targeting CSCs or signaling pathway proteins may hold promise for developing novel combination modalities and overcoming radioresistance. The present review focuses on the key evidence of CSC markers and several important signaling pathways in cancer radioresistance and explores innovative approaches for future radiation treatment.

Review on cell models to evaluate the potential antioxidant activity of polysaccharides

Owing to various health functions, natural polysaccharides are becoming a kind of popular dietary nutritional supplement.

Roles of peroxiredoxins in cancer, neurodegenerative diseases and inflammatory diseases

Peroxiredoxins (PRDXs) are antioxidant enzymes, known to catalyze peroxide reduction to balance cellular hydrogen peroxide (H₂O₂) levels, which are essential for cell signaling and metabolism and act as a regulator of redox signaling. Redox signaling is a critical component of cell signaling pathways that are involved in the regulation of cell growth, metabolism, hormone signaling, immune regulation and variety of other physiological functions. Early studies demonstrated that PRDXs regulates cell growth, metabolism and immune regulation and therefore involved in the pathologic regulator or protectant of several cancers, neurodegenerative diseases and inflammatory diseases. Oxidative stress and antioxidant systems are important regulators of redox signaling regulated diseases. In addition, thiol-based redox systems through peroxiredoxins have been demonstrated to regulate several redox-dependent process related diseases. In this review article, we will discuss recent findings regarding PRDXs in the development of diseases and further discuss therapeutic approaches targeting PRDXs. Moreover, we will suggest that PRDXs could be targets of several diseases and the therapeutic agents for targeting PRDXs may have potential beneficial effects for the treatment of cancers, neurodegenerative diseases and inflammatory diseases. Future research should open new avenues for the design of novel therapeutic approaches targeting PRDXs.

The autophagy inhibitor chloroquine targets cancer stem cells in triple negative breast cancer by inducing mitochondrial damage and impairing DNA break repair

Triple negative breast cancer (TNBC), characterized by an abundance of treatment-resistant breast cancer stem cells (CSCs), has a poorer prognosis than other types of breast cancers. Despite its aggressiveness, no effective targeted therapy exists for TNBC. Here, we demonstrate that CQ effectively targets CSCs via autophagy inhibition, mitochondrial structural damage, and impairment of double-stranded DNA break repair. Electron microscopy demonstrates CQ-induced mitochondrial cristae damage, which leads to mitochondrial membrane depolarization with a significant reduction in the activity of cytochrome c oxidase and accumulation of superoxide and double-stranded DNA breaks. CQ effectively diminishes the TNBC cells' ability to metastasize in vitro and in a TNBC xenograft model. When administered in combination with carboplatin, CQ effectively inhibits carboplatin-induced autophagy. This combination treatment significantly diminishes the expression of DNA repair proteins in CSC subpopulations, resulting in tumor growth reduction in carboplatin-resistant BRCA1 wild-type TNBC orthotopic xenografts. As TNBC's high treatment failure rate has been attributed to enrichment of CSCs, CQ, an autophagy inhibitor with anti-CSC effects, may be an effective adjunct to current TNBC chemotherapy regimens with carboplatin.

Multidrug Resistance-associated Protein-1 (MRP-1)-dependent Glutathione Disulfide (GSSG) Efflux as a Critical Survival Factor for Oxidant-enriched Tumorigenic Endothelial Cells

Endothelial cell tumors are the most common soft tissue tumors in infants. Tumor-forming endothelial (EOMA) cells are able to escape cell death fate despite excessive nuclear oxidant burden. Our previous work recognized perinuclear Nox-4 as a key contributor to EOMA growth. The objective of this work was to characterize the mechanisms by which EOMA cells evade oxidant toxicity and thrive. In EOMA cells, compared with in the cytosol, the nuclear GSSG/GSH ratio was 5-fold higher. Compared to the ratio observed in healthy murine aortic endothelial (MAE) cells, GSSG/GSH was over twice as high in EOMA cells. Multidrug resistance-associated protein-1 (MRP-1), an active GSSG efflux mechanism, showed 2-fold increased activity in EOMA compared with MAE cells. Hyperactive YB-1 and Ape/Ref-1 were responsible for high MRP-1 expression in EOMA. Proximity ligand assay demonstrated MRP-1 and YB-1 binding. Such binding enabled the nuclear targeting of MRP-1 in EOMA in a leptomycin-B-sensitive manner. MRP-1 inhibition as well as knockdown trapped nuclear GSSG, causing cell death of EOMA. Disulfide loading of cells by inhibition of GSSG reductase (bischoloronitrosourea) or thioredoxin reductase (auranofin) was effective in causing EOMA death as well. In sum, EOMA cells survive a heavy oxidant burden by rapid efflux of GSSG, which is lethal if trapped within the cell. A hyperactive MRP-1 system for GSSG efflux acts as a critical survival factor for these cells, making it a potential target for EOMA therapeutics.

Oxidative stress enables Epstein-Barr virus-induced B-cell transformation by posttranscriptional regulation of viral and cellular growth-promoting factors

Infection of human B lymphocytes by Epstein-Barr virus (EBV) leads to the establishment of immortalized lymphoblastoid cell lines (LCLs) that are widely used as a model of viral oncogenesis. An early consequence of infection is the induction of DNA damage and activation of the DNA damage response, which limits the efficiency of growth transformation. The cause of the DNA damage remains poorly understood. We have addressed this question by comparing the response of B lymphocytes infected with EBV or stimulated with a potent B-cell mitogen. We found that although the two stimuli induce comparable proliferation during the first 10 days of culture, the EBV-infected blasts showed significantly higher levels of DNA damage, which correlated with stronger and sustained accumulation of reactive oxygen species (ROS). Treatment with ROS scavengers decreased DNA damage in both mitogen-stimulated and EBV-infected cells. However, while mitogen-induced proliferation was slightly improved, the proliferation of EBV-infected cells and the establishment of LCLs were severely impaired. Quenching of ROS did not affect the kinetics and magnitude of viral gene expression but was associated with selective downregulation of the viral LMP1 and phosphorylated cellular transcription factor STAT3 that have key roles in transformation. Analysis of the mechanism by which high levels of ROS support LMP1 expression revealed selective inhibition of viral microRNAs that target the LMP1 transcript. Our study provides novel insights into the role of EBV-induced oxidative stress in promoting B-cell immortalization and malignant transformation.