miR‐200c suppresses stemness and increases cellular sensitivity to trastuzumab in HER2+ breast cancer

Resistance to trastuzumab remains a major obstacle in HER2‐overexpressing breast cancer treatment. miR‐200c is important for many functions in cancer stem cells (CSCs), including tumour recurrence, metastasis and resistance. We hypothesized that miR‐200c contributes to trastuzumab resistance and stemness maintenance in HER2‐overexpressing breast cancer. In this study, we used HER2‐positive SKBR3, HER2‐negative MCF‐7, and their CD44⁺CD24^? phenotype mammospheres SKBR3‐S and MCF‐7‐S to verify. Our results demonstrated that miR‐200c was weakly expressed in breast cancer cell lines and cell line stem cells. Overexpression of miR‐200c resulted in a significant reduction in the number of tumour spheres formed and the population of CD44⁺CD24^? phenotype mammospheres in SKBR3‐S. Combining miR‐200c with trastuzumab can significantly reduce proliferation and increase apoptosis of SKBR3 and SKBR3‐S. Overexpression of miR‐200c also eliminated its downstream target genes. These genes were highly expressed and positively related in breast cancer patients. Overexpression of miR‐200c also improved the malignant progression of SKBR3‐S and SKBR3 in vivo. miR‐200c plays an important role in the maintenance of the CSC‐like phenotype and increases drug sensitivity to trastuzumab in HER2+ cells and stem cells.     

A preliminary study of the role of extracellular -5′- nucleotidase in breast cancer stem cells and epithelial-mesenchymal transition

Tumor stem cell theory may well explain a variety of malignant behaviors of tumors. Cells undergoing epithelial-mesenchymal transition (EMT) share many characteristics with tumor stem cells. Our previous studies showed that extracellular -5'- nucleotidase (CD73), one of the important surface markers of mesenchymal stem cells, may promote growth and metastasis of breast cancer cells both in vivo and in vitro. In this study, we assessed breast cancer stem cell (BCSC) markers [acetaldehyde dehydrogenase (ALDH)⁺ and CD44⁺CD24^?] in various breast cancer cell lines with flow cytometry after overexpression (by lentivirus infection) or suppression (by siRNA interference) of CD73. We measured CD73 expression in breast cancer mammospheres with real-time PCR and western blots. Finally, we examined the expression of CD73 and EMT markers in different breast cancer cell lines, as well as in mammary cells (MCF10A) that underwent EMT induced by transforming growth factor beta (TGF-β). We found that CD73 positively correlated with ALDH⁺ or CD44⁺CD24^? subsets of breast cancer cells. CD73 was expressed more in breast cancer mammospheres than in adherent cells. CD73 and mesenchymal marker expression was higher in breast cancer cells with more malignant features, while CD73 was lower in low malignant breast cancer cells with higher epithelial markers. Furthermore, CD73 expression increased during the process of TGF-β-induced EMT. Our results indicate that CD73 may play an important role in BCSCs.     

Effect of Melatonin in Epithelial Mesenchymal Transition Markers and Invasive Properties of Breast Cancer Stem Cells of Canine and Human Cell Lines

Cancer stem cells (CSCs) have been associated with metastasis and therapeutic resistance and can be generated via epithelial mesenchymal transition (EMT). Some studies suggest that the hormone melatonin acts in CSCs and may participate in the inhibition of the EMT. The objectives of this study were to evaluate the formation of mammospheres from the canine and human breast cancer cell lines, CMT-U229 and MCF-7, and the effects of melatonin treatment on the modulation of stem cell and EMT molecular markers: OCT4, E-cadherin, N-cadherin and vimentin, as well as on cell viability and invasiveness of the cells from mammospheres. The CMT-U229 and MCF-7 cell lines were subjected to three-dimensional culture in special medium for stem cells. The phenotype of mammospheres was first evaluated by flow cytometry (CD44⁺/CD24^low/- marking). Cell viability was measured by MTT colorimetric assay and the expression of the proteins OCT4, E-cadherin, N-cadherin and vimentin was evaluated by immunofluorescence and quantified by optical densitometry. The analysis of cell migration and invasion was performed in Boyden Chamber. Flow cytometry proved the stem cell phenotype with CD44⁺/CD24^low/- positive marking for both cell lines. Cell viability of CMT-U229 and MCF-7 cells was reduced after treatment with 1mM melatonin for 24 h (P<0.05). Immunofluorescence staining showed increased E-cadherin expression (P<0.05) and decreased expression of OCT4, N-cadherin and vimentin (P<0.05) in both cell lines after treatment with 1 mM melatonin for 24 hours. Moreover, treatment with melatonin was able to reduce cell migration and invasion in both cell lines when compared to control group (P<0.05). Our results demonstrate that melatonin shows an inhibitory role in the viability and invasiveness of breast cancer mammospheres as well as in modulating the expression of proteins related to EMT in breast CSCs, suggesting its potential anti-metastatic role in canine and human breast cancer cell lines.     

TNFalpha up‐regulates SLUG via the NF‐kappaB/HIF1alpha axis,which imparts breast cancer cells with a stem cell‐like phenotype

Extracellular and intracellular mediators of inflammation, such as tumor necrosis factor alpha (TNFα) and NF‐kappaB (NF‐κB), play major roles in breast cancer pathogenesis, progression and relapse. SLUG, a mediator of the epithelial–mesenchymal transition process, is over‐expressed in CD44⁺/CD24^? tumor initiating breast cancer cells and in basal‐like carcinoma, a subtype of aggressive breast cancer endowed with a stem cell‐like gene expression profile. Cancer stem cells also over‐express members of the pro‐inflammatory NF‐κB network, but their functional relationship with SLUG expression in breast cancer cells remains unclear. Here, we show that TNFα treatment of human breast cancer cells up‐regulates SLUG with a dependency on canonical NF‐κB/HIF1α signaling, which is strongly enhanced by p53 inactivation. Moreover, SLUG up‐regulation engenders breast cancer cells with stem cell‐like properties including enhanced expression of CD44 and Jagged‐1 in conjunction with estrogen receptor alpha down‐regulation, growth as mammospheres, and extracellular matrix invasiveness. Our results reveal a molecular mechanism whereby TNFα, a major pro‐inflammatory cytokine, imparts breast cancer cells with stem cell‐like features, which are connected to increased tumor aggressiveness. J. Cell. Physiol. 225: 682–691, 2010. © 2010 Wiley‐Liss, Inc.     

Methylome analysis reveals Jak-STAT pathway deregulation in putative breast cancer stem cells

Growing evidence supports the existence of a subpopulation of cancer cells with stem cell characteristics within breast tumors. In spite of its potential clinical implications, an understanding of the mechanisms responsible for retaining the stem cell characteristics in these cells is still lacking. Here, we used the mammosphere model combined with DNA methylation bead arrays and quantitative gene expression to characterize the epigenetic mechanisms involved in the regulation of developmental pathways in putative breast cancer stem cells. Our results revealed that MCF7-derived mammospheres exhibit distinct CpG promoter methylation profiles in a specific set of genes, including those involved in Jak-STAT signaling pathway. Hypomethylation of several gene components of the Jak-STAT pathway was correlated with an increased expression in mammospheres relative to parental cells. Remarkably, cell sorting of the cells with a putative cancer stem cell phenotype (CD44⁺/CD24 low) suggests a constitutive activation of Jak-STAT pathway in these cells. These results show that Jak-STAT activation may represent a characteristic of putative breast cancer stem cells. In addition, they favor the concept that the expression of cancer stem-like pathways and the establishment and maintenance of defining properties of cancer stem cells are orchestrated by epigenetic mechanisms.     

PA‐MSHA inhibits proliferation and induces apoptosis through the up‐regulation and activation of caspases in the human breast cancer cell lines

To investigate the effects of PA‐MSHA (Pseudomonas aeruginosa‐mannose sensitive hemagglutinin) on inhibiting proliferation of breast cancer cell lines and to explore its mechanisms of action in human breast cancer cells. MCF‐10A, MCF‐7, MDA‐MB‐468, and MDA‐MB‐231HM cells were treated with PA‐MSHA or PA (Heat‐killed P. aeruginosa) at different concentrations and different times. Changes of cell super‐microstructure were observed by transmission electron microscopy. Cell cycle distribution and apoptosis induced by PA‐MSHA were measured by flow cytometry (FCM) with PI staining, ANNEXIN V‐FITC staining and Hoechst33258 staining under fluorescence microscopy. Western blot was used to evaluate the expression level of apoptosis‐related molecules. A time‐dependent and concentration‐dependent cytotoxic effect of PA‐MSHA was observed in MDA‐MB‐468 and MDA‐MB‐231HM cells but not in MCF‐10A or MCF‐7 cells. The advent of PA‐MSHA changed cell morphology, that is to say, increases in autophagosomes, and vacuoles in the cytoplasm could also be observed. FCM with PI staining, ANNEXIN V‐FITC and Hoechst33258 staining showed that the different concentrations of PA‐MSHA could all induce the apoptosis and G₀–G₁ cell cycle arrest of breast cancer cells. Cleaved caspase 3, 8, 9, and Fas protein expression levels were strongly associated with an increase in apoptosis of the breast cancer cells. There was a direct relationship with increased concentrations of PA‐MSHA but not of PA. Completely different from PA, PA‐MSHA may impart antiproliferative effects against breast cancer cells by inducing apoptosis mediated by at least a death receptor‐related cell apoptosis signal pathway, and affecting the cell cycle regulation machinery. J. Cell. Biochem. 108: 195–206, 2009. © 2009 Wiley‐Liss, Inc.     

An integrated analysis to predict micro‐RNAs targeting both stemness and metastasis in breast cancer stem cells

Several evidences support the idea that a small population of tumour cells representing self‐renewal potential are involved in initiation, maintenance, metastasis, and outcomes of cancer therapy. Elucidation of microRNAs/genes regulatory networks activated in cancer stem cells (CSCs) is necessary for the identification of new targets for cancer therapy. The aim of the present study was to predict the miRNAs pattern, which can target both metastasis and self‐renewal pathways using integration of literature and data mining. For this purpose, mammospheres derived from MCF‐7, MDA‐MB231, and MDA‐MB468 were used as breast CSCs model. They had higher migration, invasion, and colony formation potential, with increasing in stemness‐ and EMT‐related genes expression. Our results determined that miR‐204, ‐200c, ‐34a, and ‐10b contemporarily could target both self‐renewal and EMT pathways. This core regulatory of miRNAs could increase the survival rate of breast invasive carcinoma via up‐regulation of OCT4, SOX2, KLF4, c‐MYC, NOTCH1, SNAI1, ZEB1, and CDH2 and down‐regulation of CDH1. The majority of those target genes were involved in the regulation of pluripotency, MAPK, WNT, Hedgehog, p53, and transforming growth factor β pathways. Hence, this study provides novel insights for targeting core regulatory of miRNAs in breast CSCs to target both self‐renewal and metastasis potential and eradication of breast cancer.     

Osteoprotegerin production by breast cancer cells is suppressed by dexamethasone and confers resistance against TRAIL‐induced apoptosis

Osteoprotegerin (OPG) is a decoy receptor for receptor activator of NF‐κB ligand (RANKL) and TNF‐related apoptosis‐inducing ligand (TRAIL). While RANKL is essential for osteoclastogenesis and facilitates breast cancer migration into bone, TRAIL promotes breast cancer apoptosis. We analyzed the expression of OPG and TRAIL and its modulation in estrogen receptor‐positive MCF‐7 cells and receptor‐negative MDA‐MB‐231 cells. In both cells, OPG mRNA levels and protein secretion were dose‐ and time‐dependently enhanced by interleukin (IL)‐1β and suppressed by dexamethasone. In contrast to MCF‐7 cells, MDA‐MB‐231 abundantly expressed TRAIL mRNA, which was enhanced by IL‐1β and inhibited by dexamethasone. TRAIL activated pro‐apoptotic caspase‐3, ‐7, and poly‐ADP‐ribose polymerase and decreased cell numbers of MDA‐MB‐231, but had no effect on MCF‐7 cells. Gene silencing siRNA directed against OPG resulted in a 31% higher apoptotic rate compared to non‐target siRNA‐treated MDA‐MB‐231 cells. Furthermore, TRAIL induced significantly less apoptosis in cells cultured in conditioned media (containing OPG) compared to cells exposed to TRAIL in fresh medium lacking OPG (P < 0.01) and these protective effects were reversed by blocking OPG with its specific ligand RANKL (P < 0.05). The association between cancer cell survival and OPG production by MDA‐MB‐231 cells was further supported by the finding, that modulation of OPG secretion using IL‐1β or dexamethasone prior to TRAIL exposure resulted in decreased and increased rate of apoptosis, respectively (P < 0.05). Thus, OPG secretion by breast cancer cells is modulated by cytokines and dexamethasone, and may represent a critical resistance mechanism that protects against TRAIL‐induced apoptosis. J. Cell. Biochem. 108: 106–116, 2009. © 2009 Wiley‐Liss, Inc.     

10H‐3,6‐Diazaphenothiazines triggered the mitochondrial‐dependent and cell death receptor‐dependent apoptosis pathways and further increased the chemosensitivity of MCF‐7 breast cancer cells via inhibition of AKT1 pathways

Breast cancer is one of the leading causes of death in cancer categories, followed by lung, colorectal, and ovarian among the female gender across the world. 10H‐3,6‐diazaphenothiazine (PTZ) is a thiazine derivative compound that exhibits many pharmacological activities. Herein, we proceed to investigate the pharmacological activities of PTZ toward breast cancer MCF‐7 cells as a representative in vitro breast cancer cell model. The PTZ exhibited a proliferation inhibition (IC₅₀ = 0.895 µM) toward MCF‐7 cells. Further, cell cycle analysis illustrated that the S‐phase checkpoint was activated to achieve proliferation inhibition. In vitro cytotoxicity test on three normal cell lines (HEK293 normal kidney cells, MCF‐10A normal breast cells, and H9C2 normal heart cells) demonstrated that PTZ was more potent toward cancer cells. Increase in the levels of reactive oxygen species results in polarization of mitochondrial membrane potential (ΔΨm), together with suppression of mitochondrial thioredoxin reductase enzymatic activity suggested that PTZ induced oxidative damages toward mitochondria and contributed to improved drug efficacy toward treatment. The RT² PCR Profiler Array (human apoptosis pathways) proved that PTZ induced cell death via mitochondria‐dependent and cell death receptor‐dependent pathways, through a series of modulation of caspases, and the respective morphology of apoptosis was observed. Mechanistic studies of apoptosis suggested that PTZ inhibited AKT1 pathways resulting in enhanced drug efficacy despite it preventing invasion of cancer cells. These results showed the effectiveness of PTZ in initiation of apoptosis, programmed cell death, toward highly chemoresistant MCF‐7 cells, thus suggesting its potential as a chemotherapeutic drug.     

Phenotypic and Functional Characterization of Human Mammary Stem/Progenitor Cells in Long Term Culture

Background

Cancer stem cells exhibit close resemblance to normal stem cells in phenotype as well as function. Hence, studying normal stem cell behavior is important in understanding cancer pathogenesis. It has recently been shown that human breast stem cells can be enriched in suspension cultures as mammospheres. However, little is known about the behavior of these cells in long-term cultures. Since extensive self-renewal potential is the hallmark of stem cells, we undertook a detailed phenotypic and functional characterization of human mammospheres over long-term passages.

Methodology

Single cell suspensions derived from human breast ‘organoids’ were seeded in ultra low attachment plates in serum free media. Resulting primary mammospheres after a week (termed T1 mammospheres) were subjected to passaging every 7th day leading to the generation of T2, T3, and T4 mammospheres.

Principal Findings

We show that primary mammospheres contain a distinct side-population (SP) that displays a CD24^low/CD44^low phenotype, but fails to generate mammospheres. Instead, the mammosphere-initiating potential rests within the CD44^high/CD24^low cells, in keeping with the phenotype of breast cancer-initiating cells. In serial sphere formation assays we find that even though primary (T1) mammospheres show telomerase activity and fourth passage T4 spheres contain label-retaining cells, they fail to initiate new mammospheres beyond T5. With increasing passages, mammospheres showed an increase in smaller sized spheres, reduction in proliferation potential and sphere forming efficiency, and increased differentiation towards the myoepithelial lineage. Significantly, staining for senescence-associated β-galactosidase activity revealed a dramatic increase in the number of senescent cells with passage, which might in part explain the inability to continuously generate mammospheres in culture.

Conclusions

Thus, the self-renewal potential of human breast stem cells is exhausted within five in vitro passages of mammospheres, suggesting the need for further improvisation in culture conditions for their long-term maintenance.     

3‐O‐Methylfunicone,a metabolite produced by Penicillium pinophilum,modulates ERK1/2 activity,affecting cell motility of human mesothelioma cells

Objectives: 3‐O‐methylfunicone (OMF), a secondary metabolite produced by Penicillium pinophilum, affects cell proliferation and motility in a variety of human solid tumours. The aim of this study was to demonstrate whether OMF has the ability to arrest cell division and motility, in a human mesothelioma cell line. Malignant mesothelioma is an aggressive cancer that does not respond to standard therapies the cells of which are considered to be highly resistant to apoptosis. Material and methods: Cell motility and invasion were measured using a modified Boyden chamber. Gene expression was examined by RT‐PCR, while ERK1/2 was investigated by Western blot analysis. All experiments were also performed on primary cultures of mesothelial cells. Results: The present study shows that OMF inhibited motility of the NCI mesothelioma cell line by modulating ERK signalling activity, and affected αVβ5 integrin and MMP‐2 expression, inducing marked downregulation at both mRNA and protein levels. Substantial downregulation of VEGF gene expression was also demonstrated. These effects were not observed in normal mesothelial cell cultures. Conclusion: OMF may have potential as a naturally derived anti‐tumour drug for treatment of mesothelioma.     

DLG5 suppresses breast cancer stem cell‐like characteristics to restore tamoxifen sensitivity by inhibiting TAZ expression

Tamoxifen (TAM) is a primary drug for treatment of estrogen receptor positive breast cancer. However, TAM resistance remains a serious threat to breast cancer patients and may be attributed to increased stemness of breast cancer. Here, we show that discs large homolog 5 (DLG5) expression is down‐regulated in TAM‐resistant breast cancer and cells. DLG5 silencing decreased the sensitivity to TAM and increased the frequency and stemness of CD44⁺/CD24^? breast cancer stem cells (BCSCs) and TAZ, a transducer of the Hippo pathway, expression in MCF7 cells while DLG5 overexpression had opposite effects. TAZ silencing restored the sensitivity to TAM and reduced the frequency and stemness in TAM‐resistant breast cancer cells. Taken together, our data indicate that down‐regulated DLG5 expression increases the stemness of breast cancer cells by enhancing TAZ expression, contributing to TAM resistance in breast cancer.     

Fibroblasts share mesenchymal phenotypes with stem cells, but lack their differentiation and colony-forming potential

Background information. Although MSCs (mesenchymal stem cells) and fibroblasts have been well studied, differences between these two cell types are not fully understood. We therefore comparatively analysed antigen and gene profiles, colony‐forming ability and differentiation potential of four human cell types in vitro: commercially available skin‐derived fibroblasts [hSDFs (human skin‐derived fibroblasts)], adipose tissue‐derived stem cells [hASCs (human adipose tissue‐derived stem cells)], embryonic lung fibroblasts (WI38) and dermal microvascular endothelial cells [hECs (human dermal microvascular endothelial cells)]. Results. hSDFs, hASCs and WI38 exhibited a similar spindle‐like morphology and expressed same antigen profiles: positive for MSC markers (CD44, CD73 and CD105) and fibroblastic markers [collagen I, HSP47 (heat shock protein 47), vimentin, FSP (fibroblast surface protein) and αSMA (α smooth muscle actin)], and negative for endothelial cell marker CD31 and haemopoietic lineage markers (CD14 and CD45). We further analysed 90 stem cell‐associated gene expressions by performing real‐time PCR and found a more similar gene expression pattern between hASCs and hSDFs than between hSDFs and WI38. The expression of embryonic stem cell markers [OCT4, KLF4, NANOG, LIN28, FGF4 (fibroblast growth factor 4) and REST] in hASCs and hSDFs was observed to differ more than 2.5‐fold as compared with WI38. In addition, hSDFs and hASCs were able to form colonies and differentiate into adipocytes, osteoblasts and chondrocytes in vitro, but not WI38. Moreover, single cell‐derived hSDFs and hASCs obtained by clonal expansion were able to differentiate into adipocytes and osteoblasts. However, CD31 positive hECs did not show differentiation potential. Conclusions. These findings suggest that (i) so‐called commercially available fibroblast preparations from skin (hSDFs) consist of a significant number of cells with differentiation potential apart from terminally differentiated fibroblasts; (ii) colony‐forming capacity and differentiation potential are specific important properties that discriminate MSCs from fibroblasts (WI38), while conventional stem cell properties such as plastic adherence and the expression of CD44, CD90 and CD105 are unspecific for stem cells.     

Inhibition of RelB by 1,25‐dihydroxyvitamin D3 promotes sensitivity of breast cancer cells to radiation

Aberrant constitutive expression of the NF‐κB c‐Rel and RelA subunits in breast cancer cells was shown to promote their survival. Recently, we demonstrated that aggressive breast cancers constitutively express high levels of the RelB subunit, which promotes their more invasive phenotype via induction of the BCL2 gene. As these cancers are frequently resistant to therapy, here we tested the hypothesis that RelB promotes their survival. High RelB expressing Hs578T and MDA‐MB‐231 breast cancer cells were more resistant to γ‐radiation than MCF7 and ZR‐75 cells, which express lower RelB levels. Knockdown of RelB in Hs578T led to decreased survival in response to γ‐irradiation, while conversely ectopic expression of RelB in MCF7 cells protected these cells from radiation. Similar data were obtained upon treatment of Hs578T or MCF7 cells with the chemotherapeutic agent doxorubicin. High serum levels of 25‐hydroxyvitamin D are associated with decreased breast cancer risk and mortality, although, the mechanisms of its protective actions have not been fully elucidated. Treatment of Hs578T and Her‐2/neu‐driven NF639 cells with 1,25‐dihydroxyvitamin D₃ decreased RelB/RELB gene expression and levels of pro‐survival targets Survivin, MnSOD and Bcl‐2, while increasing their sensitivity to γ‐irradiation. Thus, RelB, which promotes survival and a more highly invasive phenotype of breast cancer cells, is a target of 1,25‐dihydroxyvitamin D₃, providing one mechanism for the observed protective role of 25‐hydroxyvitamin D in patients with breast cancer. J. Cell. Physiol. 220: 593–599, 2009. © 2009 Wiley‐Liss, Inc.     

Apoptosis‐inducing effect of garcinol is mediated by NF‐κB signaling in breast cancer cells

Garcinol, obtained from Garcinia indica in tropical regions, is used for its numerous biological effects. Its anti‐cancer activity has been suggested but the mechanism of action has not been studied in‐detail, especially there is no report on its action against breast cancer cells. Here we tested our hypothesis that garcinol may act as an anti‐proliferative and apoptosis‐inducing agent against breast cancer cell lines. Using multiple techniques such as MTT, Histone‐DNA ELISA, Annexin V‐PI staining, Western blot for activated caspases and cleaved PARP, homogenous caspase‐3/7 fluorometric assay and EMSA, we investigated the mechanism of apoptosis‐inducing effect of garcinol in ER‐positive MCF‐7 and ER‐negative MDA‐MB‐231 cells. We found that garcinol exhibits dose‐dependent cancer cell‐specific growth inhibition in both the cell lines with a concomitant induction of apoptosis, and has no effect on non‐tumorigenic MCF‐10A cells. Our results suggested induction of caspase‐mediated apoptosis in highly metastatic MDA‐MB‐231 cells by garcinol. Down‐regulation of NF‐κB signaling pathway was observed to be the mechanism of apoptosis‐induction. Garcinol inhibited constitutive NF‐κB activity, which was consistent with down‐regulation of NF‐κB‐regulated genes. This is the first report on anti‐proliferative and apoptosis‐inducing action of garcinol against human breast cancer cells and the results suggest that this natural compound merits investigation as a potential chemo‐preventive/‐therapeutic agent, especially against breast cancer. J. Cell. Biochem. 109: 1134–1141, 2010. © 2010 Wiley‐Liss, Inc.     

Cardamonin induces G2/M arrest and apoptosis via activation of the JNK–FOXO3a pathway in breast cancer cells

Cardamonin (CD), a naturally occurring chalcone isolated from large black cardamom, was previously reported to suppress the proliferation of breast cancer cells. However, its precise molecular anti‐tumor mechanisms have not been well elucidated. In this study, we found that CD markedly inhibited the proliferation of MDA‐MB 231 and MCF‐7 breast cancer cells through the induction of G2/M arrest and apoptosis. Reactive oxygen species (ROS) plays a pivotal role in the inhibition of CD‐induced cell proliferation. Treatment with N‐acetyl‐cysteine (NAC), an ROS scavenger, blocked CD‐induced G2/M arrest and apoptosis in this study. Quenching of ROS by overexpression of catalase also blocked CD‐induced cell cycle arrest and apoptosis. We showed that CD enhanced the expression and nuclear translocation of Forkhead box O3 (FOXO3a) via upstream c‐Jun N‐terminal kinase, inducing the expression of FOXO3a and its target genes, including p21, p27, and Bim. This process led to the reduction of cyclin D1 and enhancement of activated caspase‐3 expression. The addition of NAC markedly reversed these effects, knockdown of FOXO3a using small interfering RNA also decreased CD‐induced G2/M arrest and apoptosis. In vivo, CD efficiently suppressed the growth of MDA‐MB 231 breast cancer xenograft tumors. Taken together, our data provide a molecular mechanistic rationale for CD‐induced cell cycle arrest and apoptosis in breast cancer cells.