Living on the Edge: ROS Homeostasis in Cancer Cells and Its Potential as a Therapeutic Target

Abstract

Reactive oxygen species (ROS) act as double-edged swords in cancer biology-facilitating tumor growth, survival, and metastasis at moderate levels while inducing oxidative damage and cell death when exceeding cellular buffering capacity. To survive under chronic oxidative stress, cancer cells rely on robust antioxidant systems such as the glutathione (GSH) and thioredoxin (Trx), and superoxide dismutases (SODs). These systems maintain redox homeostasis and sustain ROS-sensitive signaling pathways including MAPK/ERK, PI3K/Akt/mTOR, NF-κB, STAT3, and HIF-1α. Targeting the antioxidant defense mechanisms of cancer cells has emerged as a promising therapeutic strategy. Inhibiting the glutathione system induces ferroptosis, a non-apoptotic form of cell death driven by lipid peroxidation, with compounds like withaferin A and altretamine showing strong preclinical activity. Disruption of the Trx system by agents such as PX-12 and dimethyl fumarate (DMF) impairs redox-sensitive survival signaling. Trx reductase inhibition by auranofin or mitomycin C further destabilizes redox balance, promoting mitochondrial dysfunction and apoptosis. SOD1 inhibitors, including ATN-224 and disulfiram, selectively enhance oxidative stress in tumor cells and are currently being tested in clinical trials. Mounting preclinical and clinical evidence supports redox modulation as a cancer-selective vulnerability. Pharmacologically tipping the redox balance beyond the threshold of cellular tolerance offers a rational and potentially powerful approach to eliminate malignant cells while sparing healthy tissue, highlighting novel strategies for targeted cancer therapy at the interface of redox biology and oncology.

Keywords: antioxidant defense; cancer metabolism; cancer therapy; reactive oxygen species (ROS); redox signaling.

Figure 1

Generation of ROS: (A) Generation of ROS via the Fenton reaction. Intracellular iron (Fe²⁺) can react with H₂O₂ to produce hydroxyl radicals (^•OH), which leads to irreversible lipid peroxidation and cell death. (B) Generation of mitochondrial ROS via leakage of electrons during electron transport. Main sources of ROS are complex I and complex III. Leakage of electrons during electron transport leads to generation of superoxide. SOD1 (intermembrane space) and SOD2 (mitochondrial matrix) convert superoxide into H₂O₂. (C) Generation of ROS via NADPH Oxidase NOX2. NOX2 is inactive until it binds p22phox. After its activation, RAC, p67phox, p47phox, and p40phox were recruited, and NADPH Oxidase is formed. Two electrons are transferred from NADPH to FAD, reducing it to FADH₂. Electrons were then transferred from the inner to the outer heme and finally to oxygen in the extracellular space, where they generate superoxide. Superoxide can be converted to H₂O₂ by SODs. (D) Generation of ROS via Dual Oxidase (DUOX). Superoxide is generated through reduction of oxygen by electrons from NADPH oxidation. Superoxide can be converted to H₂O₂ by SODs. (E) Generation of ROS via Cytochrome p450. The Cytochrome p450 reaction cycle generates ROS via leakage of electrons. ROS lead to enhanced protein modifications, lipid peroxidation, and oxidative DNA damage. (F) Generation of ROS via Xanthine Oxidase (XO). The conversion of Hypoxanthine to Xanthine and the conversion of Xanthine to Uric acid via Xanthine oxidase generate O₂^•−. Superoxide can be converted to H₂O₂ by SOD1. (G) Generation of ROS via arachidonic acid metabolism. Arachidonic acid is generated from glycerophospholipids by cPLA₂ and processed by LOX and COX, generating leukotrienes, prostaglandins, and thromboxanes. ROS are produced as by-products. (H) Additional external factors such as air pollutants, tobacco smoke, radiation, food, and drugs also generate ROS. Ca²⁺ = Calcium ion; COX = Cyclooxygenase; cPLA2 = Cytosolic phospholipase A2; DUOX1/2 = Dual Oxidase 1/2; e- = Electron; FAD = Flavin adenine dinucleotide; Fe²⁺ = Ferrous; Fe³⁺ = Ferric; H⁺ = Proton; H₂O₂ = Hydrogen peroxide; HOO^• = Hydroperoxyl; LOX = Lipoxygenase; NAD⁺ = Nicotinamide adenine dinucleotide (ox.); NADH⁺ = Nicotinamide adenine dinucleotide (red.); NOX2 = Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2; O₂ = Oxygen; O₂^• = Hydroxyl Radical; O₂⁻ = Hydroxyl; O₂^•− = Superoxide; RAC = RAC GTPase; ROS = Reactive oxygen species; SOD = Superoxide dismutases; XDH = Xanthine dehydrogenase; XO = Xanthine Oxidase; The figure was created with the assistance of BioRender.com.

Figure 2

Antioxidative defense. The first line of antioxidative defense comprises SODs, which catalyze the conversion of superoxide into H₂O₂. The second line of defense consists of the enzyme catalase, which converts H₂O₂ into O₂ and H₂O. Catalase is mainly active in peroxisomes, but can also be secreted into the extracellular space. The third line of defense consists of the thioredoxin reductase, converting H₂O₂ into O₂ and H₂O by thioredoxin, which functions as a disulfide reductase. The last line of defense consists of Glutathione (GSH), which also converts H₂O₂ into O₂ and H₂O. GSH acts as a potent ROS scavenger in many cellular compartments such as cytosol, endoplasmic reticulum, mitochondria, vacuoles, and peroxisomes. ER = Endoplasmatic reticulum; GSH = Glutathione; GSSH = Glutathiondisulfide; H₂O₂ = Hydrogen peroxide; O₂^•− = Superoxide; SOD = Superoxide dismutases; Trx = Thioredoxin; TrxR = Thioredoxin Reductase. The figure was created with the assistance of BioRender.com.

Figure 3

Regulation of antioxidative defense. Antioxidant defense is regulated by the transcription factor NRF2. Under physiological conditions KEAP1 controls NRF2 protein levels and promotes its degradation via the proteasome. Under oxidative conditions NRF2 dissociates from KEAP1 and translocates to the nucleus, where it activates the transcription of antioxidant genes via the antioxidant response element. ARE = Antioxidant response element; KEAP1 = Kelch-like ECH-associated protein 1; NRF2 = Nuclear erythroid 2-related factor; ROS = Reactive oxygene species; SOD = Superoxide dismutases; Ub = Ubiquitin. The figure was created with the assistance of BioRender.com.

Figure 4

ROS-mediated modulation of the PI3K/Akt/mTOR pathway. PTEN antagonizes PI3K signaling by dephosphorylating PIP₃ to PIP₂. Reactive oxygen species (ROS) can reversibly inactivate PTEN via oxidation, leading to PIP3 accumulation and constitutive activation of downstream kinases such as Akt and mTOR. In addition, ROS modulate Akt activity through redox-sensitive upstream regulators like PP2A, which normally dephosphorylates and inactivates Akt. Activated Akt promotes tumor progression by enhancing glycolysis, stimulating mTORC1-driven protein synthesis, and inhibiting apoptosis. Beyond direct effects on core PI3K/Akt/mTOR components, ROS also act via stress-responsive regulators such as Sestrin2. Upon oxidative stress, Sestrin2 is induced and attenuates mTORC1 activity by activating AMPK and interacting with the GATOR complex, thereby promoting autophagy and metabolic adaptation. Akt = Protein kinase B; AMPK = AMP-activated protein kinase; GATOR-complex = GAP activity toward rags-complex; mTor = Mammilian target of rapamycin; PI3K = Phosphoinositid-3-kinase; PIP2 = Phosphoinositide-3,4-bisphosphate; PIP3 = Phosphatidylinositol(3,4,5)-trisphosphate; PP2A = Protein phosphatase 2; PTEN = Phosphatase and tensin homolog; ROS = Reactive oxygen species. The figure was created with the assistance of BioRender.com.

Figure 5

ROS-mediated stabilization and activation of HIF-1α. Under normoxic conditions, HIF-1α is hydroxylated by prolyl hydroxylase domain enzymes (PHDs) and subsequently targeted for proteasomal degradation by the von Hippel–Lindau (VHL) ubiquitin ligase complex. Reactive oxygen species (ROS) inhibit PHD activity through oxidation, resulting in HIF-1α stabilization. Stabilized HIF-1α translocates to the nucleus and induces the transcription of target genes involved in glycolysis, angiogenesis, and pH regulation. Additionally, HIF-1α integrates signals from oncogenic pathways such as PI3K/Akt and STAT3, which further enhance the expression of angiogenic genes. HIF-1α = Hypoxia-inducible factor 1 α; OH = Hydroxylation; PHD = Prolyl hydroxylase domain enzymes; PHD = Prolyl hydroxylase domain enzymes; ROS = Reactive oxygen species; STAT3 = Signal transducer and activator of transcription 3; VEGF-A = Vascular endothelial growth factor A; VHL = von Hippel–Lindau tumorsuppressor. The figure was created with the assistance of BioRender.com.

Figure 6

ROS-mediated modulation of NF-κB signaling. Reactive oxygen species (ROS) promote the proteasomal degradation of IκB by oxidizing specific residues, thereby destabilizing the inhibitory NF-κB–IκB complex and enabling NF-κB release. ROS can also oxidize NF-κB subunits themselves, which facilitates their nuclear translocation. However, for efficient DNA binding, NF-κB must be in a reduced state, a condition maintained by thioredoxin (Trx-1). IκB = Inhibitor of NF-κB; IKKα/β = Inhibitor of NF κB kinase subunit α/β; NEMO = NF κB essential modulator; NF κB = Nuclear factor ’kappa-light-chain-enhancer’ of activated B-cells; Ox = Oxidation; P = Phosphorylation; ROS = Reactive oxygen species; Trx1 = Thioredoxin 1. The figure was created with the assistance of BioRender.com.