Apoptosis is a programmed cell death (type I programmed cell death), primarily mediated by the mitochondrial-dependent endogenous cytochrome c/caspase-9 pathway and caspase-8-related exogenous death receptor pathway [49,50]. When cells are under stress, ROS signaling alters the balance between pro-apoptotic (e.g., Bax/Bak) and anti-apoptotic (e.g., Bcl-2) proteins. This disruption reduces mitochondrial membrane permeability, leading to cytochrome c leakage into the cytoplasm. The released cytochrome c then triggers the caspase cascade, ultimately resulting in mitochondria-dependent apoptosis. It has been proven that bitter melon-derived vesicle extract (BMVE) can induce apoptosis of 4T1 cells by stimulating the production of ROS and destroying the function of mitochondria [51]. ROS mediates MDA-MB-231 and MCF-7 cells apoptosis induced by (-)-Epicatechin [52]. Ligands bind to cell surface death receptors and then activate the exogenous death pathway via caspase 8. The activation and accumulation of ROS are key factors in cell apoptosis [53]. Meanwhile, apoptosis is connected to the interplay between ROS and death signaling pathways, as well as ROS-mediated oxidative stress.

Autophagy and apoptosis can jointly regulate cell death. Under certain conditions, autophagy promotes cell survival by inhibiting apoptosis; however, it can also induce cell death or serve as an alternative cell death mechanism when apoptosis is impaired. Thus, the two processes are closely interrelated and mutually restrictive. Autophagy exhibits a dual role in tumor biology: it can either support tumor progression or contribute to tumor cell death. ROS participates in the formation and degradation of autophagosomes. Some natural compounds induce autophagic tumor cell death by increasing ROS.

Daucosterol, an orally active natural sterol, induces autophagy in MCF-7 cells to inhibit cancer cell proliferation in a ROS-dependent manner. Treatment with ROS scavengers GSH or NAC, as well as the autophagy inhibitor 3-methyladenine (3-MA), counteracts these effects [80]. 6-MDS, a natural benzophenanthridine alkaloid isolated from Hylomecon japonica (Thunb.) Prantl markedly elevates the number of autophagosomes in MCF-7 cells compared with the control group. Autophagy-related protein 5 (Atg5) is a component of the lipid kinase complex essential for autophagosome formation during autophagy initiation. During this process, microtubule-associated protein 1A/1B-light chain 3-I (LC 3-I) is converted to LC 3-II. The detection of LC3 (an autophagy marker) and Atg5 protein levels serves as a reliable method for monitoring autophagy activation. The ratio of LC 3 II/LC 3 I and the expression of ATG 5 protein are evidently increased after 6-MDS treatment. Silencing ATG 5 dramatically enhances the reduction in MCF-7 cell viability induced by 6-MDS. Furthermore, autophagy induction by 6-MDS is promoted by the PI3K inhibitor LY 294002, while pre-treatment with the antioxidant NAC reverses the enhanced autophagy and inhibits the PI3K/AKT/mTOR pathway. These results indicate that 6-MDS regulates the PI3K/AKT/mTOR signaling pathway and increases ROS accumulation, thereby inhibiting autophagy in MCF-7 cells [28].

Rubioncolin C, a natural naphthohydroquinone dimer isolated from the roots and rhizomes of Rubia yunnanensis Diels, significantly enhances the production of hydrogen peroxide, superoxide anions, and mitochondrial superoxide anions in MDA-MB-231 cells. It also increases the expression of LC3 and promotes the conversion of LC3-I to LC3-II. The antioxidant agents NAC and GSH rescue cell viability by scavenging ROS and inhibiting RC-induced cleavage of PARP and LC3. Both chloroquine (CQ, a late-phase autophagy inhibitor) and 3-methyladenine (3-MA, an early-phase autophagy inhibitor) attenuate RC-caused cell death. RC also triggers autophagic death in MDA-MB-231 cells through ROS-mediated inhibition of the Akt/mTOR/p70S6K and NF-κB signaling pathways [30].

Psoralidin (PSO), a phenolic coumarin isolated from psoralidin, significantly induces autophagy in MCF-7 cells, as indicated by the accumulation of autophagic vacuoles and changes in LC3-I expression. Co-treatment with CQ enhances PSO-induced cell death. PSO induces ROS generation, while pretreatment with NAC or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) reverses ROS accumulation, DNA damage, and autophagy. In addition, PSO significantly enhances NOX 4 expression, and NOX 4 knockdown inhibits ROS production, DNA damage, and autophagy activation. These results demonstrate that PSO triggers DNA damage and protective autophagy in MCF-7 cells through a ROS-dependent mechanism mediated by NOX 4 [42]. Euterpe oleracea Mart. (açai), a native Amazon palm species, yields seed extract that exhibits high cytotoxicity against MCF-7 cells. It may induce autophagy by increasing ROS production [81].

In 2012, the term “ferroptosis” was introduced to describe a form of regulated cell death characterized by its dependence on iron and lipid ROS [82]. The labile iron pool (LIP) plays a central role in promoting ferroptosis [83]. Through the Fenton reaction, LIP catalyzes lipid ROS formation, which drives ferroptotic cell death [84]. Meanwhile, excessive ROS production can result in lipid peroxidation, disrupting mitochondrial integrity and function, further contributing to ferroptosis. At the molecular level, the key mechanisms implicated in ferroptosis include: (a) suppression of glutathione peroxidase 4 (GPX4); (b) reduction of the cystine glutamate transporter receptor (system xc-); and (c) inhibition of cysteine uptake via reduced expression of solute carrier family 7 member 11 (SLC7A11), a critical subunit of system Xc⁻, thereby enhancing celluar sensitivity to ferroptosis. Given that many cancer cells resistant to other forms of regulated cell death (RCD) are still sensitive to ferroptosis, targeting this pathway has garnered significant interest as a promising therapeutic strategy for cancer treatment [85]. Isoglycyrrhizin (ISO), a flavonoid glycoside isolated from Glycyrrhiza glabra, concentration- and time-dependently reduces the vitality of MDA-MB-231 and MCF-7 cells. In MDA-MB-231 cells, ISO significantly increases the levels of Fe²⁺, ROS, and MDA, while decreasing GSH levels and downregulating the protein expression of GPX4 and SLC7A-11. GPX4 inhibits lipid peroxidation by reducing small molecule peroxides and lipid peroxides. However, ISO promotes ferroptosis through enhancing ROS accumulation and restraining both GSH synthesis and GPX4 expression [31]. Levistilide (LA), an active compound extracted from Ligusticum chuanxiong Hort., elevates intracellular iron by upregulating heme oxygenase-1 and its upstream molecule Nrf2. Excessive iron disrupts intracellular redox homeostasis, resulting in mitochondrial dysfunction and ROS accumulation, which in turn elicits lipid peroxidation. In MDA-MB-231 cells, LA markedly suppresses GPX4 expression, leading to compensatory upregulation of mRNA related to GSH synthesis-limiting enzymes, enhanced ROS production, and ultimately ferroptosis [86]. 18-β-glycyrrhetinic acid (GA), an active compound from licorice root, promotes the generation of ROS and reactive nitrogen species (RNS) by downregulating system xc-subunit SLC7A11 and reducing the activities of GSH and GPX. This process is mediated through activation of NADPH oxidase and inducible nitric oxide synthase (iNOS), exacerbating lipid peroxidation and eliciting ferroptosis in MDA-MB-231 cells [87].

Besides promoting apoptosis, curcumin can also induce ferroptosis. This process is mediated through solute carrier family 1 member 5 (SLC1A5), and involves enhanced accumulation of lipid ROS, increased production of malondialdehyde (MDA), and elevated intracellular Fe²⁺ levels. As a result, curcumin suppresses the viability of MDA-MB-453 and MCF-7 cells and inhibits tumor growth in vivo [44]. Red ginseng polysaccharide (RGP), an active ingredient from the traditional Chinese medicine Panax ginseng C. A. Meyer (Araliaceae), induces significant accumulation of lipid ROS in MDA-MB231 cells. Overexpression of GPX4 eliminates the anti-viability effects of RGP. Similarly, overexpression of GPX4 reduces the release of lactate dehydrogenase (LDH) in the absence of RGP and attenuates the LDH release induced by RGP, concurrently reversing the accumulation of ROS. RGP likely triggers ferroptosis by inducing ROS production to downregulate GPX4 [39]. Artemisinin (ART) and its derivatives have been investigated as potential anticancer agents for the treatment of highly aggressive cancers due to their ability to induce ferroptosis through iron-mediated cleavage of the endoperoxide bridge. However, their clinical application is limited by poor water solubility and insufficient intracellular iron availability. To overcome these challenges, a zeolitic imidazolate framework-based nanocarrier coordinated with tannic acid and ferrous iron (TA-Fe/ART@ZIF) is developed. This system synergizes Fe²⁺-triggered ART activation with the Fenton reaction to markedly elevate ROS levels in MDA-MB-231 cells, resulting in a 2.5-fold increase in MDA, accumulation of lipid radicals, and potent ferroptosis-mediated suppression of MDA-MB-231 xenograft tumor growth [34]. Shuganning injection (SGNI), a traditional Chinese patent medicine, enhances ROS generation in MDA-MB-231 cells through inducing oxidative stress. This process promotes the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), which translocates into the nucleus and binds to antioxidant response elements (AREs), thereby upregulating the transcription of heme oxygenase-1 (HO-1) and facilitating the accumulation of LIPs through a feedback mechanism. Subsequent degradation of HO-1 leads to increased cytoplasmic Fe²⁺ levels, which induce lipid peroxidation and disrupt cell membrane integrity, ultimately causing ferroptosis in MD-MB 231 cells [88].

Pyroptosis, also known as inflammatory necrosis of cells, is a programmed cell death characterized by continuous swelling of cells until the cell membrane ruptures, resulting in the release of intracellular contents and the initiation of an intense inflammatory response. As a crucial innate immune mechanism, pyroptosis is essential in inhibiting cancer growth. This process is mainly mediated by gasdermin family proteins, especially GSDMD. In the classical pyroptosis pathway, activating stimuli promote inflammasome assembly, which in turn triggers inflammatory caspases that cleave GSDMD. The resulting N-terminal fragment of GSDMD (GSDMDNT) translocates to the cytoplasmic membrane, where it undergoes conformational changes and oligomerizes to form pore-like structures. Through these pores, cells release a large amount of pro-inflammatory factors, triggering an intense inflammatory response and inducing an anti-tumor immune response. ROS can directly regulate caspase activity related to inflammasomes, influence GSDMD cleavage or pore-forming function, and ultimately lead to membrane rupture and necrotic cell death.

Nigericin, an antibiotic derived from Streptomyces species, induces ROS accumulation and mitochondrial dysfunction by promoting potassium efflux in MDA-MB-231 and 4T1 cells. These effects cause an increase in cleaved caspase-3 and activation of the mitochondrial apoptotic pathway. Meanwhile, mitochondrion impairment elicits activation of the caspase-1/GSDMD cascade, resulting in pyroptosis. This further enhances the infiltration and anti-tumor immune response of cluster of differentiation 4 positive (CD4⁺) and cluster of differentiation 8 positive (CD8⁺) T cells [89]. Tetraarsenic hexoxide has been proven to fight cancer by inducing apoptosis. Recent studies have shown that it also inhibits the proliferation of the murine mammary carcinoma 4T1 cells and human MDA-MB-231 cells by triggering pyroptosis. Mechanistically, tetraarsenic hexoxide promotes apoptosis in these cells by inhibiting the phosphorylation of mitochondrial signal transducer and activator of transcription 3 (STAT3), increasing mitochondrial ROS production, and subsequently activating caspase-3. At the same time, cleaved caspase-3 mediates GSDMD cleavage, releasing its N-terminal fragment GSDMDNT. This fragment translocates to the cytoplasmic membrane, where it oligomerizes and forms pore-like structures. These pores facilitate the extensive release of pro-inflammatory cytokines, ultimately causing pyroptosis in 4T1 and MDA-MB-231 cells [90].

Ganoderma lucidum extract (GLE), a traditional Chinese herb known for its excellent antitumor activity, significantly increases ROS levels in MCF-7 cells and activates caspase 3 at concentrations ranging from 50–200 μg/mL. This leads to the cleavage of GSDME proteins, ultimately causing pyroptosis [46]. Similarly, Spatholobus suberectus Dunn has remarkable anticancer efficacy. Treatment with Spatholobus soil percolate (SSP) alone promotes ROS generation and activates caspase-4 and caspase-9 in TNBC cells. The N-terminal fragment of GSDME forms pores in the plasma membrane, leading to pyroptosis in BT 549 and MDA-MB-231 cells. This process occurs independently of canonical inflammasome complexes and is considered to operate through a nonclassical inflammasome pyroptosis signaling pathway. The antioxidant GSH attenuates ROS production and reverses SSP induced pyroptosis [48].

Metastasis is a hallmark of cancer and a primary cause of cancer-related mortality. About 30%–40% of breast cancer patients have already displayed metastasis at the time of diagnosis. Therefore, understanding the metastatic mechanism of breast cancer and developing effective strategies are crucial for improving patient survival. Breast cancer metastasis is mainly related to such factors as epithelial mesenchymal transition (EMT), extracellular matrix (ECM) attachment, blood circulation, and tumor microenvironment. In addition, cancer stem cells (CSC) contribute to metastasis and recurrence. Natural products can inhibit breast cancer metastasis through regulating these processes by ROS modulation.

Dihydrotanshinones (DHTS), a natural compound isolated from Salvia miltiorrhiza Bunge, shows cytotoxicity to various tumor cells. In breast spheroids, DHTS induces ROS generation by increasing NOX5 expression through calcium-mediated signaling. This decreases the nuclear phosphorylation of Stat3 and the secretion of IL-6. Consequently, DHTS suppresses CSC formation and relieves the dynamic balance between non-CSC and CSC transition. Ultimately, DHTS increases CSC death by ROS accumulation and deregulation of the Stat3/IL-6 pathway [35]. Meso-Hannokinol (HA), a diphenylheptane analogue of curcumin, increases the levels of ROS in a dose dependent manner and activates JNK phosphorylation in MDA-MB-231 cells, which are reversed by the antioxidant NAC. MMP-9 and MMP-13 are vital activators of bone metastasis and zinc finger E-box binding homeobox 1(ZEB1) is the promoter of EMT. HA inhibits ZEB1 expression by inducing ROS accumulation to reduce the expression of EMT markers, MMP9 and MMP13 in MDA-MB-231 cells. HA promotes the proliferation of bone marrow-derived mesenchymal stem cells (BMSCs) and reduces bone metastasis of MDA-MB-231 cells [45].

Tetrandrine (TET), a natural plant alkaloid isolated from the dried roots of Stephania tetrandra S. Moore, induces the production of ROS through down-regulating superoxide dismutase 1 (SOD1) and catalase. This causes a reduction in breast cancer stem cells, impairment of EMT properties, and suppression of cell stemness. The inhibitory effects of TET on MDA-MB-231 cells are reversed by either SOD1 overexpression or NAC. Consistent with this, in vivo experiments show that cells overexpressing SOD1 and BCSC-enriched populations are less sensitive to TET treatment compared with vector control cells. These findings demonstrate that TET effectively inhibits BCSC properties and the EMT process via the SOD 1/ROS signaling pathway [32].

Around 70% of newly diagnosed breast tumors express the estrogen receptor (ER)-α. Although targeted therapies such as fulvestrant can effectively reduce ER activity, their clinical utility is often limited by the development of anti-estrogen resistance. In breast cancer cells, knockdown of ER-α can promote autophagy and enhance ROS-triggered cell death [91]. Andrographolide (AD), an active ingredient from Andrographis paniculata (Burm. f.) Nees markedly suppresses the proliferation of ER-positive breast cancer cells. It acts through hindering ER-α transcription and inducing ROS generation, thereby downregulating the forkhead box protein M1 (FOXM1)-ER-α axis and enhancing the efficacy of fulvestrant [37]. In addition, andrographolide induces apoptosis in MCF-7 and MDA-MB-231 cells via inducing inactivation of the ER-α receptor and suppression of the PI3K/AKT/mTOR signaling pathway [92].

Nrf2 is a basic zipper (bZIP) transcription element involved in the regulation of oxidative damage and cellular protection against carcinogens. Overexpression of Nrf2 has been linked to enhanced cancer proliferation. The imbalance between Nrf2 and NF-κB is implicated in many diseases, especially cancer. Many natural products exert anti-breast cancer effects through modulation of Nrf2 and NF-κB pathways. Alpinetin, a major active ingredient derived from Alpinia Katsumadai Hayata, promotes apoptosis in 4T1 and MDA-MB-231 cells through elevating the ratio of Bax/Bcl-2. This leads to the release of cyto-c from mitochondria into the cytoplasm. Meanwhile, alpinetin-induced mitochondrial dysfunction decreases intracellular production of ROS, subsequently repressing NF-κB pathway activation and reducing the transcription of hypoxia inducible factor-1 alpha (HIF-1α). The downregulation of HIF-1α, mediated by impaired NF-κB signaling, inhibits numerous oncogenic target genes, ultimately restraining the migration of cancer cells [94]. Hyperoside, one of the flavonoid glycosides, has anti-inflammatory, antidepressant, and anti-cancer effects. In 4T1 cells, hypericin suppresses NF-κB pathway activation and reduces the nuclear translocation of p-p65 by decreasing ROS generation. The inhibition of NF-κB down-regulates the transcription of anti-apoptotic genes such as Bcl-2 and X-linked inhibitor of apoptosis protein (XIAP), while promoting the accumulation of Bax. These changes result in mitochondrial dysfunction and apoptosis through caspase-3 activation [95]. Lutein, an oxygenated carotenoid widely present in nature, significantly promotes the production of antioxidants and improves the ability of anti-oxidative stress in human breast cancer T47D cells. Meanwhile, it reduces intracellular ROS levels and attenuates oxidative damage. The decline in ROS blocks NF-κB pathway activation and decreases the levels of NF-κB p65. Subsequently, Nrf2 is activated and translocated to the nucleus, where it upregulates the downstream genes encoding cellular antioxidant enzymes, ultimately inhibiting the proliferation of breast cancer cells [96].

Tumor metastasis is the main cause of cancer progression and mortality, driven by complex interactions within the tumor microenvironment. A key mechanism facilitating metastasis is EMT, through which cancer cells acquire invasive and migratory capabilities. ROS can promote EMT progression, thereby accelerating metastatic behavior [101]. Additionally, chronic inflammation is closely associated with the invasion and metastasis of breast cancer [102]. Inflammatory mediators in the tumor microenvironment, including ROS and RNS, contribute to the development of inflammation-related cancers [103]. Natural products can counteract these processes by reducing ROS levels through mitochondrial fusion, thereby inhibiting EMT and inflammasome NLRP3 activation. The suppression of intracellular ROS also downregulates migration-related proteins such as MMP-2 and MMP-9, further reducing metastasis in various cancers.

Silibinin, a natural polyphenol flavone isolated from Silybum marianum, exhibits potential activity against breast cancer. It disrupts mitochondrial dynamics and suppresses the migration of MDA-MB-231 cells by elevating mitochondrial fusion, decreasing the generation of ROS, and inhibiting the activation of inflammatory vesicle NLRP3. Additionally, silibinin downregulates the expression of migration-related proteins MMP-2 and MMP-9. Conversely, treatment with tert-butyl hydroperoxide (tBHP), an exogenous donor of ROS, increases the levels of MMP2 and MMP9, decreases E-cadherin expression, and increases N-cadherin and the EMT-related marker vimentin. This treatment also reverses the anti-migratory effects induced by silibinin [24].

As₄S₄ is an orally administered mineral drug with poor solubility in its raw form (r-As4S4). For the enhancement of its bioavailability, a hydrophilic nanoparticle formulation of As₄S₄ (e-As₄S₄) is developed. When applied to breast cancer cells in both normal and hormonally stimulated mice, e-As₄S₄ exhibits greater cytotoxicity and more strongly inhibits the proliferation of 4T1 cells than r-As4S4. HIF signaling acts as a major regulator of breast cancer metastasis by activating the transcription of genes encoding proteins involved in this process. Oral administration of e-As₄S₄ significantly increases the accumulation of arsenic within tumor tissue, effectively scavenging ROS. This reduction in ROS levels leads to the inhibition of NLRP3 inflammasome activation and suppression of HIF-1α expression. Consequently, angiogenesis and metastasis to the lungs and liver are markedly reduced, ultimately prolonging the survival of the tumor-bearing mice [104].

Calophyllum inophyllum L., commonly known as Laurelwood, is a tropical evergreen tree whose various parts, including leaves, flowers, and stem bark, possess medicinal properties. The extracts derived from different parts of the plant are rich in antioxidants, such as polyphenols, phenolic acids, flavonoids, and other phytochemicals with antioxidant structures. These compounds contribute to the extract’s anti-inflammatory, antibacterial, and anti-cancer activities [105,106]. The extract of Calophyllum inophyllum L. is shown to attenuate intracellular ROS production, eliciting the downregulation of NRF2 and HIF-1α. This results in reduced expression of MMP-2 and MMP-9, inhibition of EMT, and consequent suppression of migration and invasion in MCF-7 and MDA-MB-231 cells. Notably, these effects occur without significant toxicity to normal cells [99]. Elemene, a sesquiterpenoid compound isolated from the rhizomes of Curcuma species, also exhibits anti-metastatic properties. Its nanoemulsion formulation could effectively scavenge ROS and reduce the stability of HIF-1α in vivo and in vitro. These effects lead to diminished angiogenesis within the tumor microenvironment, reduce activation of the NLRP3 inflammasome, and decrease levels of the key pro-inflammatory cytokine IL-1β. Ultimately, elemene nanoemulsion markedly inhibits the metastasis of 4T1 cells to the lungs and liver [98].

Oxidative stress, mediated by ROS, is implicated in the pathogenesis of diverse diseases. Scavenging excess ROS by supplementation with exogenous antioxidants has been recognized as a potential strategy for disease prevention. Many natural products possess excellent antioxidant activities and are useful in the treatment of breast cancer and other conditions. Nevertheless, given the chemical and biochemical diversity of ROS and the different mechanisms of antioxidants, combination approaches may yield greater efficacy than single-agent treatments [107].

Propolis, a resinous mixture produced by bees, has shown protective effects against oxidative stress. Bioactive compounds in Lebanese propolis, in particular, are effective in scavenging free radicals. Thymoquinone (TQ), another natural compound, is a potent ROS scavenger and inhibitor of non-enzymatic lipid peroxidation. When half concentrations of Lebanese propolis and TQ are combined, the treatment is more effective than either agent alone. This combination enhances antioxidant and anticancer activities, improving DPPH radical scavenging capacity and protecting red blood cells from H₂O₂-induced hemolysis. Moreover, TQ enhances the repressive effects of propolis extract on the viability of MDA-MB-231 cells [97]. These findings suggest that combining natural products can synergistically increase antioxidant effects, offering valuable insights for future research [108]. Furthermore, natural antioxidants may also be combined with conventional chemotherapeutic agents to enhance clinical outcomes.