MCF-7 Mammosphere Research Articles

NK3.3-Derived Extracellular Vesicles Penetrate and Selectively Kill Treatment-Resistant Tumor Cells.

Cancer treatments often become ineffective due to the development of tumor resistance, leading to metastasis and relapse. Treatments may also fail because of their inability to access cells deep within the tumor tissue. When this occurs, new therapeutic agents are needed. We previously reported that NK3.3EVs, extracellular vesicles (EVs) derived from the normal human natural killer (NK) cell line, NK3.3, have strong cytotoxic activity against leukemia and breast cancer cell lines, without harming normal cells. Here, we used a three-dimensional (3D) MCF7 breast cancer mammosphere model to reproduce a more physiological environment that NK3.3EVs would encounter in vivo. NK3.3EVs penetrated MCF7 mammospheres, inducing death by apoptosis. We generated an imatinib-resistant K562 chronic myeloid leukemia (CML) cell line to investigate whether NK3.3EVs were able to kill tumor cells resistant to front-line chemotherapy. NK3.3EVs were even more cytotoxic to imatinib-resistant cells than parental cells, inducing apoptosis via caspase-3/-7 activation. The small population of cancer stem cells (CSCs) within tumors also contributes to therapeutic resistance. NK3.3EVs reduced the CSC-like CD34+/CD38- subpopulation in imatinib-resistant and parental K562 cultures and decreased CSC-associated expression of tumor-promoting genes. Our results provide strong evidence that NK3.3EVs may be a potential new immunotherapeutic agent for difficult-to-treat cancers.

(-)-Xanthatin as a Killer of Human Breast Cancer MCF-7 Mammosphere Cells: A Comparative Study with Salinomycin.

Experimental evidence accumulated by our research group and others strongly suggests that (–)-xanthatin, a xanthanolide sesquiterpene lactone, exhibits anti-proliferative effects on human breast cancer cells (in vitro) as well as anti-tumor effects in experimental animals (in vivo). In cancer biology, it is now critically important for anti-cancer agents to selectively target cancer stem cells (CSCs) in order to overcome cancer therapeutic resistance and recurrence. However, it has not yet been established whether (–)-xanthatin abrogates the formation of breast CSCs. In the present study, we utilized chemically synthesized pure (–)-xanthatin and a culture system to obtain mammospheres from human breast cancer MCF-7 cells, which are a CSC-enriched population. We herein demonstrated for the first time that (–)-xanthatin exhibited the ability to kill mammospheres, similar to salinomycin, an established selective killer of CSCs. A possible anti-proliferative mechanism toward mammospheres by (–)-xanthatin is discussed.

Vitamin D3 and Salinomycin synergy in MCF-7 cells cause cell death via endoplasmic reticulum stress in monolayer and 3D cell culture

1α, 25, dihydroxyvitamin D3 (1,25D), the active form of vitamin D3, has antitumor properties in several cancer cell lines in vitro. Salinomycin (Sal) has anticancer activity against cancer cell lines. This study aims to examine the cytotoxic and antiproliferative effect of Sal associated with 1,25D on MCF-7 breast carcinoma cell line cultured in monolayer (2D) and three-dimensional models (mammospheres). We also aim to evaluate the molecular mechanism of Sal and 1,25D-mediated effects. We report that Sal and 1,25D act synergistically in MCF-7 mammospheres and monolayer causing G1 cell cycle arrest, reduction of mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) overproduction with a long-lasting cytotoxic response represented by clonogenic and mammosphere assay. We observed the induction of cell death by apoptosis with upregulation in mRNA levels of apoptosis-related genes (CASP7, CASP9, and BBC3). Extensive cytoplasmic vacuolization, a morphological characteristic found in paraptosis, was also seen and could be triggered by endoplasmic reticulum stress (ER) as we found transcriptional upregulation of genes related to ER stress (ATF6, GADD153, GADD45G, EIF2AK3, and HSPA5). Overall, Sal and 1,25D act synergistically, inhibiting cell proliferation by activating simultaneously multiple death pathways and may be a novel and promising luminal A breast cancer therapy strategy.

Macrophage induced ERK-TGF-β1 signaling in MCF7 breast cancer cells result in reversible cancer stem cell plasticity and epithelial mesenchymal transition

BackgroundBreast cancer is a heterogenous disease composed of multiple clonal populations and the mechanism by which the tumor microenvironment induces cancer stem cell plasticity is not fully understood. MethodsMCF7 breast cancer cells were treated with macrophage conditioned medium (MɸCM). PD98059 and SB431542 were used for ERK and TGF-βR inhibition respectively. Epithelial-mesenchymal transition (EMT) and cancer stem cell markers (CSC) were studied using qRT-PCR and flowcytometry. SCID mice were used for animal experiments. ResultsMɸCM- induced ERK/TGF-β1 signaling led to enrichment of CSC and EMT in MCF7 cells and mammospheres. These effects were abrogated by both MEK inhibitor PD98059 (TGF-β1 synthesis) and SB431542 (TGF-β1 signaling). The increase in CSC was both hybrid (ALDH1+) and mesenchymal (CD44+ CD24− cells). Increase in hybrid E/M state was at a single cell level as confirmed by the increase in both claudin-1 (E) and vimentin (M). This did not have any growth advantage in SCID mice and monitoring of CSC and EMT markers before and after growth in SCID mice indicated reversal of these markers in tumor cells recovered from mice. Removal of MɸCM and neutralization of TNF-α, IL-6 and IL-1β in MɸCM abrogated ERK phosphorylation, TGF-β and CSC enrichment indicating the requirement of continuous signaling for maintenance. ConclusionsERK signaling plays an important role in MɸCM- induced EMT and CSC plasticity which is completely reversible upon withdrawal of signals. General significanceOur experimental observations support the semi-independent nature of EMT-stemness connection which is very dynamic and reversible depending on the microenvironment.

SOX4-mediated FBW7 transcriptional upregulation confers Tamoxifen resistance in ER+ breast cancers via GATA3 downregulation

AimTamoxifen-mediated endocrine therapy has been standard treatment for ER+ breast cancers; however, majority of them acquire resistance leading to disease relapse. Although numerous substrates of E3 ligase FBW7 are known, only a handful of factors that regulate FBW7 expression and function are reported. In particular, there remains a lack of in-depth understanding of FBW7 transcriptional regulation. Materials and methodsLuciferase reporter assay was performed after cloning full length and truncated FBW7 promoters followed by Chromatin immunoprecipitation assay to validate binding of SOX4 on FBW7 promoter. Transcriptional regulation of FBW7 by SOX4 and their biological consequences with respect to ER+ breast cancer was then evaluated using immunoblotting and other cell based assays. Key findingsSOX4 positively regulates FBW7 at transcriptional level by binding to three putative SOX4 biding sites within 3.1 kb long FBW7 promoter. Analysis of publicly available RNAseq datasets also showed a positive correlation between SOX4 and FBW7 mRNA in cancer cell lines and patient samples. qPCR and Immunoblotting confirmed that transiently or stably expressed SOX4 induced both endogenous FBW7 mRNA and protein levels. Our findings further demonstrated that increased levels of SOX4 and FBW7 in MCF7 mammospheres promoted cancer stemness and tumor cell dormancy. We further showed that both MCF7 mammospheres and MCFTAMR cells had elevated SOX4 levels which apparently enhanced FBW7 to potentiate GATA3 degradation leading to enhanced stemness, tumor dormancy and Tamoxifen resistance in MCF7TAMR as well as patients with ER+ breast cancers. SignificanceTargeting SOX4-FBW7-GATA3 axis may overcome tamoxifen resistance in ER+ breast cancers.

Aminoflavone upregulates putative tumor suppressor miR-125b-2-3p to inhibit luminal A breast cancer stem cell-like properties.

Metastatic breast cancer is incurable and often due to breast cancer stem cell (CSC)-mediated self-renewal. We previously determined that the aryl hydrocarbon receptor (AhR) agonist aminoflavone (AF) inhibits the expression of the CSC biomarker α6-integrin (ITGA6) to disrupt the formation of luminal (hormone receptor-positive) mammospheres (3D breast cancer spheroids). In this study, we performed miRNA-sequencing analysis of luminal A MCF-7 mammospheres treated with AF to gain further insight into the mechanism of AF-mediated anti-cancer and anti-breast CSC activity. AF significantly induced the expression of >70 microRNAs (miRNAs) including miR125b-2–3p, a predicted stemness gene regulator. AF-mediated miR125b-2–3p induction was validated in MCF-7 mammospheres and cells. miR125b-2–3p levels were low in breast cancer tissues irrespective of subtype compared to normal breast tissues. While miR125b-2–3p levels were low in MCF-7 cells, they were much lower in AHR100 cells (MCF-7 cells made unresponsive to AhR agonists). The miR125b-2–3p mimic decreased, while the antagomiR125b-2–3p increased the expression of stemness genes ITGA6 and SOX2 in MCF-7 cells. In MCF-7 mammospheres, the miR125b-2–3p mimic decreased only ITGA6 expression although the antagomiR125b-2–3p increased ITGA6, SOX2 and MYC expression. AntagomiR125b-2–3p reversed AF-mediated suppression of ITGA6. The miR125b-2–3p mimic decreased proliferation, migration, and mammosphere formation while the antagomiR125b-2–3p increased proliferation and mammosphere formation in MCF-7 cells. The miR125b-2–3p mimic also inhibited proliferation, mammosphere formation, and migration in AHR100 cells. AF induced AhR- and miR125b2-3p-dependent anti-proliferation, anti-migration, and mammosphere disruption in MCF-7 cells. Our findings suggest that miR125b-2–3p is a tumor suppressor and AF upregulates miR125b-2–3p to disrupt mammospheres via mechanisms that rely at least partially on AhR in luminal A breast cancer cells.

Abstract P3-10-03: Enrichment of pro-oncogenic immune miRNAs in exosomes by cyclin D1, promote cancer stem cell expansion

Abstract The cyclin D1 (CCND1) gene, encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the Rb protein. Cyclin D1 overexpression occurs in up to 50% of human breast cancers. Cyclin D1, governs the expression (1,3), processing (2), the secretion and the relative proportion of secreted non-coding RNA subtypes (miRNA, rRNA, tRNA, CDBox, scRNA, HAcaBox. scaRNA, piRNA) in human breast cancer and the secretion of piRNA (4). Through base-pairing to the complementary sequence in 3’ untranslated region (3’ UTR) of mRNA, miRNAs participate in diverse biological processes. A subset of miRNA regulate the ageing of innate and adaptive immune cells, which has been associated with breast cancer initiation, progression and therapy resistance. Immuno-miRs, ( miR-21 and miR-93), bind to the 3′-UTR region of mRNAs, and binding to- and or activate Toll-Like Receptor 8 (TLR8) in surrounding cells of the immune system. Exosomes which contain constituents of their cell of origin, including mRNA and miRNA are found in the tumor microenvironment and participate in therapy resistance, cancer metastasis and the metastatic niche. Herein, tet-inducible cyclin D1 shRNA knock down in MCF-7 breast cancer cells reduced MCF-7 cell proliferation and mammosphere formation. Exosomes isolated from wildtype and cyclin D1 knock-down MCF-7 cell culture media, showed that exosomes from cyclin D1 knock down cells decreased proliferation of both wildtype and cyclin D1 knock-down cells. Furthermore, wildtype exosomes partially reversed the cyclin D1 knock-down effects. Cyclin D1 knock-down exosomes decreased mammosphere formation of wildtype MCF-7 cells and wildtype exosomes increased mammosphere formation of cyclin D1 knock-down cells. miRNA profiles within the exosomes, showed that cyclin D1 regulated the abundance of miRNA within exosomes. >85% of the cyclin D1-induced exosome miRNA transcripts were the immune-mIR, miR21. hsa-mir-21 which has documented tumor promoting function, was the most enriched miRNAs in cyclin D1 knock-down exosomes. In contrast, exosome abundance of the transcripts for hsa-mir-16 and hsa-mir-92a, both of which were showed as tumor suppressor in breast cancer cells, were reduced by cyclin D1 shRNA. The cyclin D1-mediated miRNA exosome content may contribute to tumor initiation and progression through heterotypic expansion of cancer stem cells. 1.Yu, Z., etal ., A cyclin D1/microRNA 17/20 regulatory feedback loop in control of breast cancer cell proliferation. J Cell Biol. 2008 Aug 11; 182(3): p. 509-17. 2.Yu., Z,., et. al. Cyclin D1 induction of Dicer governs microRNA processing and expression in breast cancer. Nat Commun 2013;4:2812.doi: 10.1038/ncomms3812. 3.Yu Z, et al. Cyclin D1- Mediated MicroRNA Expression Signature in Breast Cancer Subtype and Outcome. Theranostics, 2018 Mar 11,8:8, 2251-2263. 4.Lü J, et al. Cyclin D1 promotes secretion of pro-oncogenic immuno-miRNAs and piRNAs. Clin Sci (Lond). 2020 Mar 27. pii: CS20191318. doi: 10.1042/CS20191318. [Epub ahead of print]PMID:32219337 Citation Format: Xuanmao Jiao, Chongwen Xu, Lifeng Tian, Zhao Zhang, Anthony W Ashton, Zhiping Li, Richard G Pestell. Enrichment of pro-oncogenic immune miRNAs in exosomes by cyclin D1, promote cancer stem cell expansion [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-10-03.

Sensitivity of MCF-7 mammosphere CSCs to neutron radiation

Aim: Cancer stem cells (CSCs) are highly resistant to chemotherapy and γ-irradiation. Neutrons have a high linear energy transfer, which can lead to extensive damage to the DNA of tumor cells and CSCs. The aim of this work was to compare the sensitivity of MCF-7 human breast adenocarcinoma cells and CSCs to γ- and γ,n-irradiation. Methods: To increase the number of CSCs, MCF-7 cells were cultured as mammospheres. γ-irradiation was carried out in a GUT-200M device (60Co source) in the dose range of 1-8 Gy at a dose rate of 0.75 Gy/min. γ,n-irradiation was carried out in an IR-8 reactor in the dose range of 0.05-2 Gy at a dose rate of 0.06 Gy/min. DNA DSB formation was assessed by the level of γH2AX foci using fluorescence microscopy and flow cytometry. CSCs were identified by flow cytometry as CD44+/CD24-/low cells. Results: We showed that γ,n-irradiation induced the formation of γH2AX foci of a larger size than did γ-irradiation and led to more severe DNA damage per 1 Gy. Moreover, γ,n-radiation was found to have a high relative biological effectiveness (RBE) as assessed by the cell survival rate, the number of CSCs in culture, and the ability of CSCs to repopulate. The highest RBE of neutron radiation was observed at low doses, when cell survival rate decreased by only 5%-10%. With an increase in the radiation dose, the RBE value decreased for all studied parameters, but it remained as high as 5. Conclusion: γ,n-radiation is highly effective against CSCs. Our results explain the efficacy of neutron therapy for resistant forms of breast cancer.

Development of Dl1.72, a Novel Anti-DLL1 Antibody with Anti-Tumor Efficacy against Estrogen Receptor-Positive Breast Cancer.

Simple SummaryOver 70% of breast cancers (BCs) are estrogen receptor-positive (ER+). The development of endocrine therapy has considerably improved patient outcomes. However, there is a clinical need for novel effective therapies against ER+ BCs, since many of these do not respond to standard therapy, and more than one-third of responders acquire resistance, experience relapse and metastasize. The Notch ligand Delta-like 1 (DLL1) is a key player in ER+ BC development and aggressiveness. Contrary to complete Notch pharmacological inhibitors, antibody-targeting of individual Notch components is expected to have superior therapeutic efficacy and be better tolerated. In this study, we developed and characterized a novel specific anti-DLL1 antibody with efficacy in inhibiting BC cell proliferation, mammosphere formation and angiogenesis, as well as anti-tumor and anti-metastatic efficacy in an ER+ BC mouse model without side effects. Thus, our data suggest that this anti-DLL1 antibody is a promising candidate for ER+ BC treatment.The Notch-signaling ligand DLL1 has emerged as an important player and promising therapeutic target in breast cancer (BC). DLL1-induced Notch activation promotes tumor cell proliferation, survival, migration, angiogenesis and BC stem cell maintenance. In BC, DLL1 overexpression is associated with poor prognosis, particularly in estrogen receptor-positive (ER+) subtypes. Directed therapy in early and advanced BC has dramatically changed the natural course of ER+ BC; however, relapse is a major clinical issue, and new therapeutic strategies are needed. Here, we report the development and characterization of a novel monoclonal antibody specific to DLL1. Using phage display technology, we selected an anti-DLL1 antibody fragment, which was converted into a full human IgG1 (Dl1.72). The Dl1.72 antibody exhibited DLL1 specificity and affinity in the low nanomolar range and significantly impaired DLL1-Notch signaling and expression of Notch target genes in ER+ BC cells. Functionally, in vitro treatment with Dl1.72 reduced MCF-7 cell proliferation, migration, mammosphere formation and endothelial tube formation. In vivo, Dl1.72 significantly inhibited tumor growth, reducing both tumor cell proliferation and liver metastases in a xenograft mouse model, without apparent toxicity. These findings suggest that anti-DLL1 Dl1.72 could be an attractive agent against ER+ BC, warranting further preclinical investigation.

Abstract 2356: Cyclin D1 mediated exosomes are enriched for pro-oncogenic miRNAs and promote cancer stem cell expansion

Abstract miRNAs are a class of endogenous noncoding small RNAs that participate in diverse biological processes through base-pairing to the complementary sequence in 3' untranslated region (3' UTR) of mRNA Specific miRNA have been associated with the initiation, progression and therapy resistance and regulate immunological processes including the activation and ageing of innate and adaptive immune cells. Immuno-miRs, including. miR-21 and miR-93, regulate immune function in the tumor microenvironment by binding to the 3′-UTR region of target mRNAs, or by binding to- and activating Toll-Like Receptor 8 (TLR8) in surrounding cells of the immune system. The cyclin D1 (CCND1) gene, which encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the Rb protein, is overexpressed in up to 50% of human breast cancers. Cyclin D1, governs the expression, processing, the secretion and the relative proportion of secreted non-coding RNA subtypes (miRNA, rRNA, tRNA, CDBox, scRNA, HAcaBox. scaRNA, piRNA) in human breast cancer and the secretion of piRNA. Exosomes, which consist of a lipid bilayer membrane surrounding a small cytosol, contain constituents of their cell of origin, including mRNA and miRNA. Exosomes in the tumor microenvironment, participate in therapy resistance, cancer metastasis and the metastatic niche. Herein, knock down of cyclin D1 in MCF-7 cells with tet-inducible cyclin D1 shRNA decreased MCF-7 cell proliferation and mammosphere formation. Exosomes isolated from wild-type and cyclin D1 knock-down MCF-7 cell culture media, showed that exosomes from cyclin D1 knock down cells dramatically decreased proliferation of both wild-type and cyclin D1 knock-down cells, whereas the wild-type exosomes partially reversed the cyclin D1 knock down effects. Cyclin D1 knock-down exosomes decreased mammosphere formation of wild-type MCF-7 cells and wild-type exosomes increased mammosphere formation of cyclin D1 knock-down cells. miRNA profiles within the exosomes, showed that cyclin D1 regulated the abundance of miRNA within exosomes. The pattern of miRNA within exosomes regulated by cyclin D1 were enriched for miRNA governing mesenchymal epithelial transition and the induction of stem cell function. The most enriched miRNA in cyclin D1 wild-type exosomes was hsa-mir-21 which was recognized tumor promoting function, whereas the most enriched miRNAs in cyclin D1 knock-down exosomes were has-mir-16 and has-mir-92a, both of which were shown as tumor suppressor in breast cancer cells. The immune-miR miR-21 represented >85% of the cyclin D1-induced exosome miRNA transcripts, The cyclin D1-mediated miRNA exosome content may contribute to tumor initiation and progression through heterotypic expansion of cancer stem cells. Citation Format: Xuanmao Jiao, Chongwen Xu, Lifeng Tian, Zhao Zhang, Anthony W. Ashton, Zhiping Li, Richard G. Pestell. Cyclin D1 mediated exosomes are enriched for pro-oncogenic miRNAs and promote cancer stem cell expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2356.

Curcumin loaded on graphene nanosheets induced cell death in mammospheres from MCF-7 and primary breast tumor cells

Elimination of tumor cells is still a therapeutic challenge for breast cancer (BC) in men and women. Mammospheres serve as valuable in vitro tools for evaluating tumor behavior and sensitivity to anticancer treatments. Graphene nanosheets with unique physicochemical properties have been considered as potential biomedical approaches for drug delivery, bioimaging, and therapy. Graphene oxide (GO) and graphene quantum dots (GQDs) are suitable nanocarriers for hydrophobic and low bioaccessible anti-tumor materials like curcumin. Despite extensive studies on the potential application of graphene nanosheets in medicine, our knowledge of how different cells function and respond to these nanoparticles remains limited. Here, we evaluated cell death in mammospheres from MCF-7 and primary tumor cells in response to curcumin loaded on graphene nanosheets. Mammospheres were exposed to graphene oxide-curcumin (GO-Cur) and graphene quantum dots-curcumin (GQDs-Cur), and the incidence of cell death was evaluated by Hoechst 33342/propidium iodide double staining and flow cytometry. Besides, the expression of miR-21, miR-29a, Bax, and Bcl-2 genes were assessed using RT-qPCR. We observed, GO, and GQDs had no cytotoxic effect on Kerman male breast cancer/71 (KMBC/71) and MCF-7 tumor cells, while curcumin induced death in more than 50% of tumor cells. GO-Cur and GQDs-Cur synergistically enhanced anti-tumor activity of curcumin. Moreover, GQDs-Cur induced cell death in almost all cells of KMBC/71 mammospheres (99%; p < 0.0001). In contrast, GO-Cur induced cell death in only 21% of MCF-7 mammosphere cells (p < 0.0001). Also, the expression pattern of miR-21, miR-29a, and Bax/Bcl-2 ratio in KMBC/71 and MCF-7 mammospheres was different in response to GO-Cur and GQDs-Cur. Although KMBC/71 and MCF-7 tumor cells had similar clinical features and displayed similar responses to curcumin, more investigations are needed to clarify the detailed molecular mechanisms underlying observed differences in response to GO-Cur and GQDs-Cur.

Targeted nanoformulation of C1 inhibits the growth of KB spheroids and cancer stem cell-enriched MCF-7 mammospheres

C1, a synthetic analog of curcumin, has been reported to show potent antiproliferative effects against a variety of cancer cells. Here, we report a strong anticancer activity of the folate receptor-targeted lipid nanoparticle formulation of C1 against cancer cells and cancer stem cells both in 2D culture and 3D spheroids. The size of the C1 encapsulated folic acid functionalized nanoliposomes (Lipos-C1) was determined to be 83 ± 17 nm. Lipos-C1 nanoparticles displayed sustained C1 release kinetics at both pH 7.4 and 5.5. The folate receptor (FR) targeted nanoliposomes were internalized into FR-positive KB cells via the folate receptor-mediated endocytosis process. Lipos-C1 killed KB cells much more efficiently than C1. Lipos-C1 depolymerized microtubules, generated ROS, caused DNA damage, and induced apoptosis in KB cells. Importantly, Lipos-C1 strongly inhibited the growth of the 3D KB spheroids than C1. Interestingly, Lipos-C1 also suppressed cancer stem cells (CSCs) enriched MCF-7 mammosphere growth by impeding breast cancer stem cells (BCSCs) enrichment, growth, and proliferation. The results suggested that Lipos-C1 could be a promising nanoformulation for cancer chemotherapy.

Combination of Doxorubicin and Berberine Generated Synergistic Anticancer Effect on Breast Cancer Cells Through Down-regulation of Nanog and miRNA-21 Gene Expression

Background: Our purpose was to investigate the effect of berberine (BER) and doxorubicin (DOX) on the expression of stem cell markers Nanog and microRNA- 21 in MCF-7 cells. Methods: The study was an in vitro study employing the human breast cancer cell line MCF-7 that was divided into four groups: Group I: MCF-7 cell line maintained in drug-free environment as untreated control, Group II: MCF-7 cell line treated with different concentrations of DOX, Group III: MCF-7 cell line treated with various concentrations of BER. Group IV: MCF-7 cell line treated with different concentrations of combined DOX and BER. MTT assay determined the metabolic activity and viability of MCF-7 cells for all groups. We further extracted total RNA from MCF-7 cells, and RT-PCR assayed the expression of Nanog and miRNA-21. Results: The results revealed that DOX and/or BER decreased the percentage of viable MCF-7 monolayer and mammospheres breast cancer cells in a concentrationdependent manner. Moreover, the combination of DOX and BER generated synergistic anticancer effect on MCF-7 monolayer cells and mammospheres. In addition, DOX alone, BER alone, and their combination significantly reduced Nanog and miRNA- 21 gene expression in MCF-7 mammospheres compared with untreated mammospheres. Conclusions: BER may affect the viability of breast cancer cells through downregulation of Nanog and miRNA-21 gene expression, ultimately enhancing the sensitivity of breast cancer cell line to DOX. BER may be an effective chemotherapeutic agent against breast cancer where the combination of DOX and BER generates synergistic anticancer effects.

SAT-725 Alterations in the Phenotype and Epigenomic Landscape of Luminal Breast Cancer Following Long-Term Nanomolar Exposure to Bisphenol a (BPA)

Breast cancer (BCa) is the leading cause of female cancer-related death worldwide. Luminal BCa accounts for at least 70% of all BCa and is characterized by its hormone dependence, particularly to estrogen. Endocrine disruptors may function to exert the pro-tumorigenic effects of estrogen in proxy following environmental exposure. Bisphenol A (BPA) is a ubiquitous endocrine disruptor shown to increase risk towards developing BCa in multiple in vivo mammalian models and in vitro human breast models. Despite this, there is limited information on the phenotypic and epigenetic effects of nanomolar BPA following long-term exposure particularly in the context of BCa stem cell population, which accumulate the ‘cellular insult’ and are likely to pass such information down through epigenetic mechanisms. We hypothesize that BPA affects the epigenome, in part, by altering the regulation of DNA methyltransferases (DNMTs) since BPA disrupts transcriptional and translational regulation of DNMTs in various other tissue types such as the brain, testis and prostate. In this study, MCF7 cells were chronically (>4 weeks) cultured with nanomolar doses of BPA, and subsequently subjected to phenotypic assays and gene expression analysis in monolayer or mammosphere culture. Gene expression analysis revealed a downregulation of DNMT3A and ESR1 following long-term exposure to BPA in mammosphere culture of MCF7 cells, but not in monolayer culture. This is accompanied by alterations in mammosphere morphology, reduction in mammosphere size, an increase in the mammosphere number, and an increase in the CD49f+ population, indicating a positive contribution of BPA to stemness. However, there are no significant changes in proliferation, apoptotic rate, and metastasis in both monolayer and mammosphere culture. Future analysis includes assessment of genome-wide alterations in DNA methylation patterns in these chronically exposed MCF7 mammospheres, as well as identifying estrogen responsiveness, chemotherapeutic response, and self-renewal properties of these cancer cells.

Nuclear Factor Erythroid-Derived 2-Like 2-Induced Reductive Stress Favors Self-Renewal of Breast Cancer Stem-Like Cellsviathe FoxO3a-Bmi-1 Axis

Aims: A subpopulation of cancer cells, termed cancer stem cells (CSCs), has stemness properties, such as self-renewal and differentiation, which drive cancer recurrence and tumor resistance. CSCs possess enhanced protection capabilities to maintain reduced intracellular levels of reactive oxygen species (ROS) compared with nonstem-like cancer cells. This study investigated whether reductive stress could regulate self-renewal activity in breast CSCs. Results: We found that manifestation of stemness in breast cancer stem-like cells was associated with an elevated production of reduced glutathione (GSH) maintained by upregulation of glutamate cysteine ligase catalytic subunit (GCLC) and consequently, lowered ROS levels. This was accompanied by upregulation of phospho-AMP-activated protein kinase, FoxO3a, and Bmi-1. Notably, expression of nuclear factor erythroid-derived 2-like 2 (Nrf2) protein was substantially increased in cells undergoing sphere formation. We noticed that expression of Bmi-1 was inhibited after introduction of Nrf2 short interfering RNA into MCF-7 mammosphere cells. Silencing of Nrf2 expression suppressed the xenograft growth of subcutaneously or orthotopically injected human breast cancer cells. Innovation: Association between Nrf2 and self-renewal signaling in CSCs has been reported, but the underlying molecular mechanism remains largely unresolved. This study demonstrates the Nrf2-mediated signaling pathway in maintenance of reductive stress in breast CSCs. Conclusion: Nrf2 overactivation in breast CSCs upregulates GCLC expression and consequently enhances GSH biosynthesis with concurrent reduction in intracellular ROS accumulation, thereby provoking the reductive stress. The consequent upregulation of nuclear FoxO3a and its binding to the promoter of the gene encoding Bmi-1 account for the self-renewal activity of breast cancer stem-like cells and their growth in a xenograft mouse model.

Characterization of the stemness potency of mammospheres isolated from the breast cancer cell lines.

Stemness phenotype mammospheres established from cell lines and tissues taken from autopsy can be used to test and to identify the most sensitive drugs for chemotherapy. Therefore, the aim of the present study was isolation and characterization of cancer stem cells derived from MCF7, MDA-MB231, and SKBR3 breast cancer cell lines to demonstrate the stemness phenotypes of mammospheres generated for further their applications in therapeutic approaches. In this study, two luminal subtypes of cell lines, MCF7 and SKBR3 and a basal subtype cell line, MDA-MB-231, were chosen. Mammosphere culturing was implemented for breast cancer stem cells isolation and mammosphere formation efficiency. At the next step, CD44+/CD24- cell ratio, Oct4 and Nanog mRNA levels, proliferation rate, migration rate of mammospheres, and drug resistance (in third passage) were evaluated. In addition, tumorigenicity of mammospheres in the chick embryo model was evaluated and compared through the chick chorioallantoic membrane assay. Among mammospheres formed in all three cell lines, MCF7 had the highest mammosphere formation efficiency. CD24 marker (a differentiation marker for the breast cancer cells) was significantly reduced in the mammospheres generated from MCF7 and SKBR3, during three passages. Also, Oct4 and Nanog transcript levels were significantly higher in all three types of mammospheres, as compared with their cell lines. Proliferation, migration rate, and drug resistance of mammospheres generated from all three cell lines were found to be significantly higher. Tumorigenicity of MCF7 mammospheres was confirmed through tumor size measurement. Also, tumorigenicity of MCF7 and SKBR3 mammospheres was confirmed through more migration from ectoderm to mesoderm and endoderm. We succeeded to establish the technology that can be extended to tissue in the future. We have demonstrated a number of mammospheres can be generated from cell lines. Also, cells with different molecular features showed different stemness phenotypes.

Estradiol induces cell proliferation in MCF‑7 mammospheres through HER2/COX‑2.

Cluster of differentiation (CD)44+/CD24- breast cancer cells have stem cell‑like characteristics and are potent initiators of tumorigenesis. Mammosphere cells can partially initiate breast tumorigenesis by inducing estradiol (E2)‑dependent breast cancer cells. However, the mechanisms by which E2 mediates cancer formation in MCF‑7 mammosphere (MS) cells have remained elusive. In the present study, MS cells were isolated by sphere culture. It was possible to maintain these MS cells in culture for long periods of time, while retaining the CD44+/CD24- stem cell marker status. The CD44+/CD24- status was confirmed by flow cytometry. Furthermore, the stem‑cell markers Musashi‑1, cytokeratin (CK)7 and CK19 were identified by immunofluorescence microscopy. It was revealed that treatment of MS cells with E2 increased the expression of CD44, whereas decreased the expression of CD24 on MS cells. In addition, treatment with E2 increased colony formation by MS cells. E2 also induced cyclooxygenase‑2 (COX‑2) expression in MS cells, which promoted their proliferation through the estrogen receptor/human epidermal growth factor receptor 2 (HER2)/mitogen‑activated protein kinase/phosphoinositide‑3 kinase signaling pathway. The results suggested a tumorigenic mechanism by which E2 promotes tumor cell proliferation via HER2/COX‑2 signaling. The present study provided evidence for the molecular impact of E2 on breast tumorigenesis, and suggested possible strategies for preventing and treating human breast cancer.

Abstract 3999: Intracellular redox status determines self-renewal activity of breast cancer stem-like cells through activation of Nrf2-mediated FoxO3a-Bmi-1 signaling

Abstract A subpopulation of cancer cells, termed cancer stem cells (CSCs), has a self-renewal property, which drives cancer recurrence and tumor resistance. It has been reported that CSCs possess enhanced capabilities to protect against oxidative stress caused by reactive oxygen species (ROS) compared with non-stem-like cancer cells. In the present study, we found that the redox-sensitive transcription factor NF-E2-related factor 2 (Nrf2) plays a role in self-renewal activity of human breast cancer cells, and that this was mediated by Bmi-1. The manifestation of stemness in breast CSC-like cells was associated with an elevated ratio of reduced to oxidized glutathione (GSH) and consequently, lowered ROS levels compared with parent breast cancer (MCF-7) cells. We observed that there was a concurrent increase in the expression of CD44, glutamate cysteine ligase (GCLC) and Bmi-1 in CD24low/CD44high breast cancer stem-like cells sorted from MCF-7 mammospheres. Treatment with buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis, led to a decrease in the number and the size of mammospheres, which was accompanied by the reduction of Bmi-1 expression. Conversely, treatment with a membrane permeable GSH ethyl ester (GSH-MEE) enhanced the size and the number of mammospheres. In addition, phosphorylation of AMPK (Thr 172) and FoxO3a (Ser 7) as well as expression of Bmi-1 was increased in mammosphere cells treated with GSH-MEE. When GSH-MEE-treated mammospheres were challenged with hydrogen peroxide, the phosphorylation of AMPK was abolished. Notably, FoxO3a directly bound to the Bmi-1 promoter as assessed by the chromatin immunoprecipitation assay. Moreover, elevated nuclear accumulation of Nrf2 protein was evident in cells growing under sphere-forming conditions. Under physiologic conditions, Nrf2 is sequestered in the cytoplasm as an inactive complex with Keap1. Sphere-forming breast cancer cells exhibited an enhanced interaction between Keap1 and CD44, which may account for an increased translocation of Nrf2 in nucleus. We found that expression of GCLC, FoxO3a and Bmi-1 was inhibited following introduction of Nrf2 siRNA into MCF-7 mammsophere cells. Knockdown of Nrf2 suppressed the xenograft growth of orthotopically injected breast cancer stem-like cells in athymic nude mice, and this was accompanied by decreased expression of GCLC, FoxO3a and Bmi-1. In conclusion, CD44 promotes Nrf2 accumulation in breast cancer stem-like cells, which, in turn, upregulates GCLC expression and consequently enhances GSH biosynthesis with concomitant reduction in intracellular ROS levels. The consequent upregulation of nuclear FoxO3a and its binding to the Bmi-1 promoter may stimulate self-renewal and growth of breast cancer stem-like cells. Citation Format: Do-Hee Kim, Jeong-Hoon Jang, Young-Joon Surh. Intracellular redox status determines self-renewal activity of breast cancer stem-like cells through activation of Nrf2-mediated FoxO3a-Bmi-1 signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3999.

The standardized Korean Red Ginseng extract and its ingredient ginsenoside Rg3 inhibit manifestation of breast cancer stem cell–like properties through modulation of self-renewal signaling

BackgroundThe ginsenoside Rg3, one of active components of red ginseng, has chemopreventive and anticancer potential. Cancer stem cells retain self-renewal properties which account for cancer recurrence and resistance to anticancer therapy. In our present study, we investigated whether the standardized Korean Red Ginseng extract (RGE) and Rg3 could modulate the manifestation of breast cancer stem cell–like features through regulation of self-renewal activity. MethodsThe effects of RGE and Rg3 on the proportion of CD44high/CD24low cells, as representative characteristics of stem-like breast cancer cells, were determined by flow cytometry. The mammosphere formation assay was performed to assess self-renewal capacities of breast cancer cells. Aldehyde dehydrogenase activity of MCF-7 mammospheres was measured by the ALDEFLUOR assay. The expression levels of Sox-2, Bmi-1, and P-Akt and the nuclear localization of hypoxia inducible factor-1α in MCF-7 mammospheres were verified by immunoblot analysis. ResultsBoth RGE and Rg3 decreased the viability of breast cancer cells and significantly reduced the populations of CD44high/CD24low in MDA-MB-231 cells. RGE and Rg3 treatment attenuated the expression of Sox-2 and Bmi-1 by inhibiting the nuclear localization of hypoxia inducible factor-1α in MCF-7 mammospheres. Suppression of the manifestation of breast cancer stem cell–like properties by Rg3 was mediated through the blockade of Akt-mediated self-renewal signaling. ConclusionThis study suggests that Rg3 has a therapeutic potential targeting breast cancer stem cells.

Abstract P2-01-10: Circulating CAF/CTC complexes and breast cancer metastasis

Abstract Background: Metastatic disease in breast cancer (BC) is the leading cause of cancer-related mortality among women worldwide. Synergy between cancer cells and non-cancer cells of the tumor microenvironment (TME) are vital for disease progression. Cancer associated fibroblasts (CAFs) are the major cell type in the stroma of BC and are critical mediators of tumor progression and metastasis. Transport of circulating tumor cells (CTCs) and CTC clusters through the vasculature seeds metastasis and clinical and preclinical studies demonstrate that CTC clusters have a higher metastatic potential than individual CTCs. More recently, circulating cancer stem cells (cCSCs) have been implicated as more metastatic than non-CSC CTCs. In our lab, we have demonstrated that CAFs also circulate (cCAFs). We have observed cCAFs in peripheral blood from breast cancer patients and in murine models of breast cancer. Furthermore, we have observed that cCAFs are present in circulation as both individual cells and as well as in complexes with CTCs. Given the integral role of CAFs in BC metastasis, we hypothesize that cCAFs complex with CTCs/cCSCs to bolster BC metastasis. Methods: cCAF/CTC clusters were identified and enumerated from peripheral blood of patients with BC, and associations with clinical features and disease outcomes were evaluated. Blood was collected by cardiac puncture from PyMT mice from 4 weeks through to the presence of metastases (10 weeks) and cCAF/CTC clusters enumerated. We co-injected CAFs with MCF-7 cellsl into NSG mice, blood collected by cardiac puncture, and cCAF/CTC clusters were enumerated. At time of final sacrifice, tumors were removed and assessed for presence of CSCs. Using our established model of cCAF/CTC clustering in vitro we interrogated cCAF/CTC complexing with both metastatic and poorly metastatic BC cells. Results: Circulating cCAFs/CTCs clusters are significantly increased in the blood of patients with advanced stage BC and associate not only with severity of disease but also with poorer clinical outcomes. In the spontaneous PyMT mouse model, the appearance of circulating cCAF/CTC clusters increased significantly as tumors grew but prior to metastasis. We demonstrate that metastatic BC cells form clusters with CAFs in vitro while non-metastatic BC cells do not form complexes with CAFs in vitro. Enriching for stem cells from MCF7 mammospheres, resulted in CAF/CSC clusters in vitro. In mice that were co-injected with non-metastatic MCF7 cells and CAFs from a TNBC/Basal-like BC (CAF23) we observed disease metastasis, an enrichment for cancer stem cell (CSC)-like CTCs, and the presence of circulating cCAF/MCF7-CSC clusters. Conclusions: Circulating clusters of CTCs and cCAFs are characteristic, and potentially causative, of BC metastasis. Observations of cCAF/CTC clusters from preclinical and clinical samples are corroborated by our determination that the ability of BC cells to form complexes with CAFs in vitro is related to the intrinsic metastatic ability of the breast cancer cells. Both in vitro and in circulation, the BC cells in cCAF/cBC clusters are CSCs, so cCAF/cCSC clusters. Disrupting the formation of cCAF/CTC complexes may be a potential strategy to reduce treat or prevent breast cancer metastasis. Citation Format: Miller P, Sharma U, Medina-Saenz K, Yeasky T, Picon-Ruiz M, Morata-Tarifa C, Seagroves T, Slingerland J, Lippman M, El-Ashry D. Circulating CAF/CTC complexes and breast cancer metastasis [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-01-10.