Estrogen Receptor Α-positive Breast Cancer Research Articles

Empagliflozin demonstrates cytotoxicity and synergy with tamoxifen in ER-positive breast cancer cells: anti-proliferative and anti-survival effects.

Accumulating evidence suggests that sodium-glucose cotransporter 2 (SGLT2) inhibitors may be effective at eliminating tumor cells. While empagliflozin exhibits nearly the highest selectivity for SGLT2 over SGLT1, its specific impact alone and in combination with tamoxifen remains largely unexplored in estrogen receptor α-positive (ERα +) breast cancer. This study investigated the anticancer effects of empagliflozin and its potential synergy with tamoxifen in MCF-7 breast cancer cells. The individual and combined cytotoxic effects of empagliflozin and tamoxifen were assessed using the xCELLigence system. The activities of AMP-activated protein kinase α (AMPKα), p38 mitogen-activated protein kinase (p38 MAPKα), p70-S6 kinase 1 (p70S6K1), and protein kinase B (Akt) were assessed using Western blotting. The gene expression levels of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) and Forkhead box O3a (FOXO3a) were assessed via qPCR. Our results revealed time- and concentration-dependent cytotoxic effects of empagliflozin and tamoxifen whether administered separately or in combination. While tamoxifen exhibits potency with an IC50 value of 17 μM, approximately ten times greater than that of empagliflozin (IC50 = 177 μM), synergistic effects are observed when the concentrations of the two agents approach their respective IC50 values. Additionally, empagliflozin significantly increases AMPKα activity while concurrently inhibiting Akt, p70S6K1, and p38 MAPKα, and these effects are significantly enhanced when empagliflozin is combined with tamoxifen. Moreover, empagliflozin modulates the gene expression, downregulating PGC-1α while upregulating FOXO3a. Empagliflozin exerts anti-proliferative and anti-survival effects by inhibiting mTOR, Akt, and PGC-1α, and it exhibits synergy with tamoxifen in MCF-7 breast cancer cells.

MCM2 is involved in subtyping and tamoxifen resistance of ERα-positive breast cancer by acting as the downstream factor of ERα.

Tamoxifen (TAM) resistance is finally developed in over 40% of patients with estrogen receptor α-positive breast cancer (ERα+ -BC), documenting that discovering new molecular subtype is needed to confer perception to the heterogeneity of ERα+ -BC. We obtained representative gene sets subtyping ERα+ -BC using gene set variation analysis (GSVA), non-negative matrix factorization (NMF), and COX regression methods on the basis of METABRIC, TCGA, and GEO databases. Furthermore, the risk score of ERα+ -BC subtyping was established using least absolute shrinkage and selection operator (LASSO) regression on the basis of genes in the representative gene sets, thereby generating the two subtypes of ERα+ -BC. We further found that minichromosome maintenance complex component 2 (MCM2) functioned as the hub gene subtyping ERα+ -BC using GO, KEGG, and MCODE. MCM2 expression was capable for specifically predicting 1-year overall survival (OS) of ERα+ -BC and correlated with T stage, AJCC stage, and tamoxifen (TAM) sensitivity of ERα+ -BC. The downregulation of MCM2 expression inhibited proliferation, migration, and invasion of TAM-resistant cells and promoted G0/G1 arrest. Altogether, tamoxifen resistance entails that MCM2 is a hub gene subtyping ERα+ -BC, providing a novel dimension for discovering a potential target of TAM-resistant BC.

Identification of Novel Dual-Target Estrogen Receptor α Degraders with Tubulin Inhibitory Activity for the Treatment of Endocrine-Resistant Breast Cancer.

Endocrine resistance remains a significant problem in the clinical treatment of estrogen receptor α-positive (ERα+) breast cancer (BC). In this study, we developed a series of novel dual-functional ERα degraders based on a bridged bicyclic scaffold with selenocyano (SeCN) side chains. These compounds displayed potent ERα degradation and tubulin depolymerization activity. Among them, compounds 35s and 35t exhibited the most promising antiproliferative and ERα degradation activity in multiple ERα+ BC cell lines bearing either wild-type or mutant ERα. Meanwhile, compounds 35s and 35t disrupted the microtubule network by restraining tubulin polymerization, evidenced by 35t inducing cell cycle arrest in the G2/M phase. In MCF-7 and LCC2 xenograft models, compounds 35s and 35t remarkably suppressed tumor growth without noticeable poisonousness. Finally, this study provided guidance for developing new dual-target antitumor drug candidates for the ERα+ BC therapy, especially for the resistant variant.

Activity of Estrogen Receptor β Agonists in Therapy-Resistant Estrogen Receptor-Positive Breast Cancer.

BackgroundAmong women, breast cancer is the leading cause of cancer-related death worldwide. Estrogen receptor α-positive (ERα+) breast cancer accounts for 70% of all breast cancer subtypes. Although ERα+ breast cancer initially responds to estrogen deprivation or blockade, the emergence of resistance compels the use of more aggressive therapies. While ERα is a driver in ERα+ breast cancer, ERβ plays an inhibitory role in several different cancer types. To date, the lack of highly selective ERβ agonists without ERα activity has limited the exploration of ERβ activation as a strategy for ERα+ breast cancer.MethodsWe measured the expression levels of ESR1 and ESR2 genes in immortalized mammary epithelial cells and different breast cancer cell lines. The viability of ERα+ breast cancer cell lines upon treatments with specific ERβ agonists, including OSU-ERb-12 and LY500307, was assessed. The specificity of the ERβ agonists, OSU-ERb-12 and LY500307, was confirmed by reporter assays. The effects of ERβ agonists on cell proliferation, cell cycle, apoptosis, colony formation, cell migration, and expression of tumor suppressor proteins were analyzed. The expression of ESR2 and genes containing ERE-AP1 composite response elements was examined in ERα+ human breast cancer samples to determine the correlation between ESR2 expression and overall survival and that of putative ESR2-regulated genes.ResultsIn this study, we demonstrate the efficacy of highly selective ERβ agonists in ERα+ breast cancer cell lines and drug-resistant derivatives. ERβ agonists blocked cell proliferation, migration, and colony formation and induced apoptosis and S and/or G2/M cell-cycle arrest of ERα+ breast cancer cell lines. Also, increases in the expression of the key tumor suppressors FOXO1 and FOXO3a were noted. Importantly, the strong synergy between ERβ agonists and ERα antagonists suggested that the efficacy of ERβ agonists is maximized by combination with ERα blockade. Lastly, ESR2 (ERβ gene) expression was negatively correlated with ESR1 (ERα gene) and CCND1 RNA expression in human metastatic ERα+/HER2- breast cancer samples.ConclusionOur results demonstrate that highly selective ERβ agonists attenuate the viability of ERα+ breast cancer cell lines in vitro and suggest that this therapeutic strategy merits further evaluation for ERα+ breast cancer.

Dynamics of estrogen-induced ROS and DNA strand break generation in estrogen receptor α-positive breast cancer

DNA repair machinery is involved in estrogen-dependent transactivation. Mounting evidence suggests that mechanisms underlying estrogen-induced DNA damage are complicated. To date estrogen-induced DNA oxidation and its impact on ERα-mediated transaction remains ambiguous. Herein, we found that the process of 17β-estradiol (E2)-induced ROS production can be approximately divided into two phases according to responding time and generation mechanisms. The intracellular Ca2+ fluctuation and ERα-dependent transcription lead to temporospatially different oxidative DNA damage. Further, we demonstrate that DNA oxidation is dispensable for estrogen-responsive gene expression. Dynamics of estrogen-induced DNA strand break generation also show two-phase pattern and topoisomerase-mediated DNA stand breaks are essential in estrogen signaling. Collectively, our findings have provided new insights into oxidative DNA damage in estrogen signaling.

Abstract BS1-2: A new perspective on androgen receptor action in estrogen receptor-α positive breast cancer

Abstract Resistance to estrogen receptor alpha (ER) target therapies is the major cause of breast cancer death. Therapeutic engagement of steroid receptors that impinge on, but do not ablate, ER signalling is an emerging new treatment strategy. The AR is expressed in the majority of breast tumors and represents an exceptional therapeutic target, especially as a range of drugs including AR agonists, antagonists and selective AR modulators (SARMs) are available. Interest in targeting AR for treatment of breast cancer has escalated over the past decade. Despite clinical correlations and preclinical studies supporting a protective role for AR in breast cancer, especially in ER-positive disease, enthusiasm was largely directed toward antagonizing AR with anti-androgenic drugs used to treat men with prostate cancer, a disease definitively driven by oncogenic AR activity. While some pre-clinical studies supported use of an AR antagonist for ER-positive breast cancer, this strategy has had minimal success in clinical trials. Our most recent preclinical studies using a diverse range of in vivo breast cancer models (Hickey et al, Nature Medicine 2021) provides compelling evidence for (i) AR being a tumor suppressor in ER+ breast cancer, and (ii) an AR agonist, not an antagonist, treatment strategy being the optimal therapeutic approach. Citation Format: W Tilley. A new perspective on androgen receptor action in estrogen receptor-α positive breast cancer. [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 BS1-2.

FoxO3a Inhibits Tamoxifen-Resistant Breast Cancer Progression by Inducing Integrin α5 Expression.

Simple SummaryTamoxifen is a mainstay of adjuvant treatment for estrogen receptor α-positive (ERα+) breast tumors, which account for over 70% of all the diagnosed breast malignancies. Unfortunately, ~30% of patients initially responding to the therapy will eventually relapse with an endocrine-resistant disease. Here, we show that the transcription factor FoxO3a can overcome tamoxifen resistance by inhibiting cell motility and invasiveness, the main features of tumor progression. The underlying mechanism could be ascribed to FoxO3a-dependent transcriptional up-regulation of the integrin α5 subunit of the α5β1 fibronectin receptor, a well-known membrane heterodimer controlling cell adhesion. Indeed, FoxO3a and integrin α5 expression is significantly correlated in ERα+ tumors, and FoxO3a protective effects are lost in cells with reduced levels of integrin α5. Therefore, a pharmacological increase in FoxO3a levels could represent an effective approach to be exploited in combination with tamoxifen treatment in order to restore the sensitivity to the therapy in refractory tumors.Resistance to endocrine therapy is still a major clinical challenge in the management of estrogen receptor α-positive (ERα+) breast cancer (BC). Here, the role of the Forkhead box class O (FoxO)3a transcription factor in tumor progression has been evaluated in tamoxifen-resistant BC cells (TamR), expressing lower levels of FoxO3a compared to sensitive ones. FoxO3a re-expression reduces TamR motility (wound-healing and transmigration assays) and invasiveness (matrigel transwell invasion assays) through the mRNA (qRT-PCR) and protein (Western blot) induction of the integrin α5 subunit of the α5β1 fibronectin receptor, a well-known membrane heterodimer controlling cell adhesion and signaling. The induction occurs through FoxO3a binding to a specific Forkhead responsive core sequence located on the integrin α5 promoter (cloning, luciferase, and ChIP assays). Moreover, FoxO3a failed to inhibit migration and invasion in integrin α5 silenced (siRNA) cells, demonstrating integrin α5 involvement in both processes. Finally, using large-scale gene expression data sets, a strong positive correlation between FoxO3a and integrin α5 in ERα+, but not in ER-negative (ERα−), BC patients emerged. Altogether, our data show how the oncosuppressor FoxO3a, by increasing the expression of its novel transcriptional target integrin α5, reverts the phenotype of endocrine-resistant BC toward a lower aggressiveness.

SETD1A-SOX2 axis is involved in tamoxifen resistance in estrogen receptor α-positive breast cancer cells.

Rationale: Approximately 30-40% of estrogen receptor (ER)-positive breast cancer (BC) cases recur after tamoxifen therapy. Thus, additional studies on the mechanisms underlying tamoxifen resistance and more specific prognostic biomarkers are required. In this study, we investigated the role of the SET domain containing 1A (SETD1A), a histone H3-lysine 4 (H3K4) methyltransferase, in the development of tamoxifen resistance in BC.Methods: The relationship between tamoxifen resistance and SETD1A protein level was investigated using resistant cell lines derived from the parent BC cells. Biochemical and molecular assays, such as RNA-sequencing, reverse transcription-quantitative polymerase chain reaction, chromatin-immunoprecipitation, and protein-binding assays, were used to identify the SETD1A target gene in tamoxifen-resistant BC cells. Additionally, the role of SETD1A in cancer stem cells (CSCs) was investigated using CSCs isolated from tamoxifen-resistant BC cells. Comprehensive transcriptome analysis and immunofluorescence staining using clinical datasets and tissue microarray were performed to determine the correlation between the expression of the SETD1A-SRY-box transcription factor 2 (SOX2) pair and recurrence in tamoxifen-treated patients with BC.Results: SETD1A was expressed at higher levels in tamoxifen-resistant BC cells than in primary BC cells. Notably, SETD1A-depleted tamoxifen-resistant MCF-7 cells showed restored sensitivity to tamoxifen, whereas SETD1A overexpression in MCF-7 cells resulted in decreased sensitivity. SETD1A is recruited to the SOX2 gene via its interaction with SOX2, thereby enhancing the expression of SOX2 genes in tamoxifen-resistant BC cells. The growth of tamoxifen-resistant cells and CSCs was effectively suppressed by SETD1A knockdown. In addition, high levels of SETD1A and SOX2 were significantly correlated with a low survival rate in patients with ER-positive tamoxifen-resistant BC.Conclusion: Our findings provide the first evidence of the critical role of the SETD1A-SOX2 axis in tamoxifen-resistant BC cells, implying that SETD1A may serve as a molecular target and prognostic indicator of a therapeutic response in patients with tamoxifen-resistant BC.

Divergent Effects of Daidzein and its Metabolites on Estrogen-Induced Survival of Breast Cancer Cells.

Although soy consumption is associated with breast cancer prevention, the low bioavailability and the extensive metabolism of soy-active components limit their clinical application. Here, the impact of daidzein (D) and its metabolites on estrogen-dependent anti-apoptotic pathway has been evaluated in breast cancer cells. In estrogen receptor α-positive breast cancer cells treated with D and its metabolites, single or in mixture, ERα activation and Neuroglobin (NGB) levels, an anti-apoptotic estrogen/ERα-inducible protein, were evaluated. Moreover, the apoptotic cascade activation, as well as the cell number after stimulation was assessed in the absence/presence of paclitaxel to determine the compound effects on cell susceptibility to a chemotherapeutic agent. Among the metabolites, only D-4′-sulfate maintains the anti-estrogenic effect of D, reducing the NGB levels and rendering breast cancer cells more prone to the paclitaxel treatment, whereas other metabolites showed estrogen mimetic effects, or even estrogen independent effects. Intriguingly, the co-stimulation of D and gut metabolites strongly reduced D effects. The results highlight the important and complex influence of metabolic transformation on isoflavones physiological effects and demonstrate the need to take biotransformation into account when assessing the potential health benefits of consumption of soy isoflavones in cancer.

Yuanhuatine from Daphne genkwa selectively induces mitochondrial apoptosis in estrogen receptor α-positive breast cancer cells in vitro.

Breast cancer is one of the most common cancers diagnosed among women worldwide. Estrogen receptor alpha (ERα) is a transcriptional factor that plays an important role in the development and progression of breast cancer. Yuanhuatine, a natural daphnane-type diterpenoid extracted from Daphne genkwa, was reported to exhibit significant cytotoxicity against breast cancer cells. However, the underlying mechanism is still unclear. In this study, we evaluated the cytotoxicity of yuanhuatine on two breast cancer cell lines that are ERα-positive and -negative. The results show that yuanhuatine inhibits the growth of ERα-positive cells (MCF-7) with much stronger inhibitory activity (IC50 = 0.62 µM) compared with positive control tamoxifen (IC50 = 14.43 µM). However, no obvious cytotoxicity was observed in ERα-negative cells (MDA-MB-231). Subsequent experiment also indicated that yuanhuatine markedly induced mitochondrial dysfunction, leading to apoptosis in MCF-7 cells. Molecular docking studies suggest the potential interactions between yuanhuatine and ERα. Immunofluorescence staining and Western blot analysis indicated that yuanhuatine down-regulated the expression of ERα in MCF-7 cells. MPP, a specific ERα inhibitor, significantly enhanced yuanhuatine-induced mitochondrial dysfunction and apoptosis in MCF-7 cells. On the contrary, the treatment with yuanhuatine causes no apoptosis in MM231 cells. Altogether, in vitro and in silico results suggested that ERα down-regulation was involved in yuanhuatine-induced mitochondrial dysfunction and apoptosis in ERα-positive breast cancer cells. Thus, yuanhuatine could be a potential candidate for treating ERα-positive breast cancer.

Abstract 2940: 4-Hydroxytamoxifen enhances sensitivity of estrogen receptor α-positive breast cancer to docetaxel in an estrogen and ZNF423 SNP-dependent fashion

Abstract Background: In early stage, ERα-positive breast cancer, the concurrent use of endocrine therapy and chemotherapy has not been shown to be superior to sequential use. We hypothesized that genetic biomarkers can aid in selecting patients who would benefit from chemo-endocrine therapy. Our previous genome-wide association study (GWAS) and functional studies revealed that a single nucleotide polymorphism (SNP) in ZNF423, rs9940645, determines tamoxifen response. Specifically, 4-hydroxytamoxifen (4-OH-TAM) increases the gene expression of ZNF423, a transcription factor for BRCA1, in cells that are carry the rs9940645 variant, but not the wildtype, genotype. In this study, we set out to identify additional genes regulated by ZNF423, which, upon identifying a relationship between ZNF423 and cell cycle genes, led us to investigate taxane response in a SNP- and tamoxifen-dependent fashion. Method: Gene correlation analysis using The Cancer Genome Atlas (TCGA) breast cancer dataset was used to identify genes with expression correlated with that of ZNF423. Quantitative reverse transcription PCR, chromatin immunoprecipitation, and luciferase reporter assays were used to validate the gene associations. To test ZNF423 rs9940645-specific phenotypes, we used ZR75-1 cells, which are homozygous for the variant SNP, and ZR75-1 cells that were generated to be homozygous wild type (WT) using CRISPR-Cas9 technology, in addition to Hs578T breast cells with ERα overexpression (WT) and HCC1500 cells (variant). Cell cycle was assessed by propidium iodide staining. Cytotoxicity was assessed using a colorimetric assay. Results: Mitosis-related genes VRK1 and PBK, which encode histone H3 kinases, were experimentally validated to be regulated by ZNF423. Specifically, ZNF423 knockdown resulted in decreased VRK1 and PBK expression and activity. Additionally, ZNF423 knockdown resulted in enhanced docetaxel-induced G2/M arrest and cytotoxicity which could be rescued by VRK1 or PBK overexpression. Lastly, breast cancer cells carrying the rs9940645 variant SNP genotype had increased G2-M arrest and decreased cell viability when treated with docetaxel in combination with estradiol and 4-OH-TAM. Conclusion: We identified ZNF423regulated genes involved in the G2/M phase of the cell cycle. We found that 4-OH-TAM sensitized ERα-positive breast cancer cells to docetaxel treatment in a ZNF423 SNP-dependent manner. Our findings suggest that patients with rs9940645 variant genotype may benefit from concurrent tamoxifen endocrine therapy and docetaxel chemotherapy. This would impact a substantial proportion of patients given the minor allele frequency of 0.47 for this SNP. Citation Format: Gen Wang, Sisi QIN, Jacqueline Zayas, James N. Ingle, Mohan Liu, Richard Weinshilboum, Kunwei Shen, Liewei Wang. 4-Hydroxytamoxifen enhances sensitivity of estrogen receptor α-positive breast cancer to docetaxel in an estrogen and ZNF423 SNP-dependent fashion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2940.

4-Hydroxytamoxifen enhances sensitivity of estrogen receptor α-positive breast cancer to docetaxel in an estrogen and ZNF423 SNP-dependent fashion.

In early stage, ERα-positive breast cancer, concurrent use of endocrine therapy and chemotherapy has not been shown to be superior to sequential use. We hypothesized that genetic biomarkers can aid in selecting patients who would benefit from chemo-endocrine therapy. Our previous studies revealed that ZNF423 is a transcription factor for BRCA1 and an intronic single nucleotide polymorphism (SNP) in ZNF423, rs9940645, determines tamoxifen response. Here, we identified mitosis-related genes that are regulated by ZNF423 which led us to investigate taxane response in a rs9940645 SNP- and tamoxifen-dependent fashion. The Cancer Genome Atlas (TCGA) breast cancer dataset was used to identify genes correlated with ZNF423. Quantitative reverse transcription PCR, chromatin immunoprecipitation, and luciferase reporter assays were used to validate the gene regulation. We used CRISPR/Cas9 to engineer paired ZR-75-1 cells which differ only in ZNF423 rs9940645 SNP genotype to test SNP-dependent phenotypes including cell cycle and cell viability. We validated our findings in an additional two breast cancer cell lines, Hs578T-ERα and HCC1500. Mitosis-related genes VRK1 and PBK, which encode histone H3 kinases, were experimentally validated to be regulated by ZNF423. ZNF423 knockdown decreased VRK1 and PBK expression and activity. Additionally, ZNF423 knockdown enhanced docetaxel-induced G2/M arrest and cytotoxicity through VRK1 or PBK regulation. Lastly, cells carrying the rs9940645 variant genotype had increased G2/M arrest and decreased cell viability when treated with docetaxel in combination with estradiol and 4-OH-TAM. We identified ZNF423 regulated genes involved in the G2/M phase of the cell cycle. 4-OH-TAM sensitized ERα-positive breast cancer cells to docetaxel in a ZNF423 SNP-dependent manner. Our findings suggest that patients with rs9940645 variant genotype may benefit from concurrent tamoxifen and docetaxel. This would impact a substantial proportion of patients because this SNP has a minor allele frequency of 0.47.

Abstract P2-08-37: The prognostic impact of synaptojanin 2 expression in estrogen receptor α-positive breast cancer patients

Abstract Background: Synaptojanin 2 (SYNJ2) was reported to be a druggable mediator of metastasis. It is overexpressed and amplified in breast cancer, particularly estrogen receptor α (ERα)-positive breast cancer. SYNJ2 was also shown to promote cell migration and invasion in breast cancer xenograft cultures and lung metastasis in mice. Here, we investigated SYNJ2 mRNA expression in breast cancer patients during long-term follow-up. Materials and methods: A total of 434 invasive breast cancer tissues were analyzed for SYNJ2mRNA expression using TaqMan PCR, and the correlation of this expression with patient clinicopathological factors was determined. We also examined the expression of markers associated with tumor-initiating capacity, such as SNAI1, SNAI2, and VIM. Survival curves were analyzed using the Kaplan–Meier method. Cox proportional hazards regression analysis was used for univariate and multivariate analyses of prognostic values. Results: The median follow-up period was 10.7 years. We found positive correlations between high expression of SYNJ2 mRNA and shorter disease-free survival in breast cancer patients (P=0.049), which was limited to ERα-positive patients (P=0.020) and not seen in ERα-negative patients (P=0.863). High SYNJ2 mRNA levels were positively correlated with high tumor grade, ERα negativity, and node positivity. Multivariate analysis indicated that high SYNJ2 mRNA expression was an independent factor for poor disease-free survival in breast cancer patients. Multivariate analysis of poor disease-free survival DFS Mutivariate All patientsp valueHR (95%CI)Tumor size2cm and fewer1540.43151 (Reference) more than 2cm280 1.19 (0.78-1.85)Lymph node metastasisNegative2190.0001 and fewer1 (Reference) Positive184 5.61 (3.59-9.05) Unknown31 2.40 (0.89-5.48)Grade1,22330.38471 (Reference) 3195 1.20 (0.79-1.81) Unknown6 0.17 (1.78-3.49)ER statusPositive3370.02621 (Reference) Negative97 2.06 (1.87-4.07)PgR statusPositive2930.39511 (Reference) Negative141 1.30 (0.70-2.28)SYNJ2 mRNA expressionlow2170.02251 (Reference) high217 1.57 (1.07-2.34) Conclusion:High SYNJ2 expression was shown to be an independent predictive factor of poor prognosis in ERα-positive breast cancer patients. SYNJ2 could therefore be used as a candidate biomarker and therapeutic target in breast cancer. Citation Format: Nishikawa S, Kondo N, Wanifuchi-Endo Y, Hisada T, Uemoto Y, Katagiri Y, Dong Y, Kato H, Takahashi S, Toyama T. The prognostic impact of synaptojanin 2 expression in estrogen receptor α-positive breast cancer patients [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-08-37.

Effects of serum estradiol and progesterone on estrogen-regulated gene expression in breast cancers of premenopausal patients.

Expression of estrogen receptor α in breast cancer is essential for estrogen-dependent growth and partially determines the breast cancer subtype. In premenopausal women, expression of estrogen-regulated genes in estrogen receptor-positive breast cancer tissues are reportedly influenced by the menstrual cycle. We investigated correlations between serum estradiol (E2; tested on the day of surgery) and expression of estrogen-regulated genes and proliferation genes in strongly estrogen receptor α-positive breast cancer tissues from 91 premenopausal women by quantitative reverse transcription-polymerase chain reaction. We also investigated correlations between serum progesterone levels on the day of surgery and mRNA expression of progesterone-regulated genes and proliferation genes. The serum E2 level affected expression of estrogen-regulated genes, including progesterone receptor (P = 0.016, Rs = 0.07) but showed no correlation with expression of genes associated with proliferation. We also observed strong positive correlations between mRNA expression of ESR1 and that of estrogen-regulated genes (P < 0.0001, Rs = 0.329-0.756) and proliferation genes (P < 0.0001, Rs = 0.753-0.843). The serum progesterone level affected expression of RANKL mRNA. However, we observed no correlations between serum progesterone and expression of Wnt-4 or proliferation genes. The serum E2 level on the day of surgery influences estrogen-regulated gene expression moderately in patients found to be strongly positive for estrogen receptor α by immunohistochemistry. Changes in serum E2 levels might influence the results of molecular profiling tests in premenopausal women with breast cancer.

Endocrine therapy-resistant breast cancer model cells are inhibited by soybean glyceollin I through Eleanor non-coding RNA

Long-term estrogen deprivation (LTED) of an estrogen receptor (ER) α-positive breast cancer cell line recapitulates cancer cells that have acquired estrogen-independent cell proliferation and endocrine therapy resistance. Previously, we have shown that a cluster of non-coding RNAs, Eleanors (ESR1 locus enhancing and activating non-coding RNAs) formed RNA cloud and upregulated the ESR1 gene in the nuclei of LTED cells. Eleanors were inhibited by resveratrol through ER. Here we prepared another polyphenol, glyceollin I from stressed soybeans, and identified it as a major inhibitor of the Eleanor RNA cloud and ESR1 mRNA transcription. The inhibition was independent of ER, unlike one by resveratrol. This was consistent with a distinct tertiary structure of glyceollin I for ER binding. Glyceollin I preferentially inhibited the growth of LTED cells and induced apoptosis. Our results suggest that glyceollin I has a novel role in LTED cell inhibition through Eleanors. In other words, LTED cells or endocrine therapy-resistant breast cancer cells may be ready for apoptosis, which can be triggered with polyphenols both in ER-dependent and ER-independent manners.

The role of Aurora-A in cancer stem cells.

Aurora kinase A (Aurora-A), a member of the Aurora family of serine/threonine kinases, plays a critical role in multiple steps of mitotic progression, including microtubule stability during the G1 phase of the cell cycle, chromosome alignment and segregation, and cytokinesis and is aberrantly expressed in various types of human cancers. In addition to its classic functions, recent studies have indicated that Aurora-A is critical for controlling self-renewal of embryonic stem cells through negative regulation of p53. Additionally, aberrant expression of Aurora-A contributes to oncogenic transformation and induces stem cell-like properties in estrogen receptor α-positive breast cancer cells. Silencing of Aurora-A has been implicated in elimination of leukemia stem cells in vivo. Therefore, Aurora-A is an attractive target for cancer therapeutics and a growing number of small molecule inhibitors of Aurora-A have been developed. In the present review, we will address the role of Aurora-A in cancer stem cells, as well as the outcomes of clinical trials assessing Aurora-A-specific small molecular inhibitors.

Arctigenin inhibits the activation of the mTOR pathway, resulting in autophagic cell death and decreased ER expression in ER-positive human breast cancer cells.

Arctigenin, a member of the Asteraceae family, is a biologically active lignan that is consumed worldwide due to its several health benefits. However, its use may pose a problem for patients with estrogen receptor (ER)α-positive breast cancer, since studies have shown that arctigenin is a phytoestrogen that exerts a proliferative effect by binding to the ER. Thus, in this study, we examined the effect of arctigenin on ERα-positive MCF-7 human breast cancer cells to determine whether the consumption of arctigenin is safe for patients with breast cancer. First, we found that arctigenin inhibited the viability of the MCF-7 cells, and colony formation assay confirmed that this effect was cytotoxic rather than cytostatic. The cytotoxic effects were not mediated by cell cycle arrest, apoptosis, or necroptosis, despite DNA damage, as indicated by poly(ADP-ribose) polymerase (PARP) cleavage and phosphorylated H2A.X. An increase in lipidated LC3, a marker of autophagosome formation, was observed, indicating that autophagy was induced by arctigenin, which was found to be triggered by the inhibition of the mechanistic target of rapamycin (mTOR) pathway. We then examined the effects of arctigenin on ERα expression and determined whether it affects the sensitivity of the cells to tamoxifen, as tamoxifen is commonly used against hormone-responsive cancers and is known to act via the ERα. We found that treatment with arctigenin effectively downregulated ERα expression, which was found to be a consequence of the inhibition of the mTOR pathway. However, treatment with arctigenin in combination with tamoxifen did not affect the sensitivity of the cells to tamoxifen, but instead, exerted a synergistic effect. On the whole, our data indicate that the phytoestrogen, arctigenin, mainly targeted the mTOR pathway in ERα-positive MCF-7 human breast cancer cells, leading to autophagy-induced cell death and the downregulation of ERα expression. Furthermore, the synergistic effects between arctigenin and tamoxifen suggest that the consumption of arctigenin is not only safe for patients with hormone-sensitive cancers, but may also be an effective co-treatment.

Estradiol suppresses phosphorylation of ERα serine 167 through upregulation of PP2A in breast cancer cells.

Aromatase inhibitors (AIs) are effective endocrine therapeutics for postmenopausal women with estrogen receptor (ER)α-positive breast cancer. However, the efficacy of the treatment is often limited by the onset of AI resistance, owing to the phosphorylation of ERα serine 167 (Ser167). Previous studies have indicated that hyperactivation of the phosphoinositide-3 kinase/RAC serine/threonine-protein kinase signaling pathway occurs in AI-resistant breast cancer models, which coincides with elevated levels of ERα phosphorylation at Ser167. The tumor suppressor serine/threonine-protein phosphatase 2A (PP2A) regulates the phosphatidylinositol 3-kinase/RAC serine/threonine-protein kinase signaling pathway. A previous study indicated that PP2A inhibition decreased ERα Ser167 phosphorylation and estradiol (E2)-independent cell growth. The present study investigated the potential relevance of PP2A in E2 deprivation-resistant MCF-7 cells. E2 depletion reduced the susceptibility of MCF-7 cells to inhibitors of mechanistic target of rapamycin (mTOR) and significantly increased ERα Ser167 phosphorylation and decreased expression of PP2A. Conversely, long-term E2-deprived (LTED) MCF-7 cells, a model of AI-resistant breast cancer, exhibited decreased ERα Ser167 phosphorylation and further upregulation of PP2A in E2-containing medium. The PP2A activator forskolin (FSK) significantly inhibited LTED cell proliferation by increasing the effect of everolimus (Eve), an mTOR inhibitor. In summary, the present study provides further evidence that PP2A represents a therapeutic target for AI-resistant breast cancer.

18F-16α-17β-Fluoroestradiol Binding Specificity in Estrogen Receptor-Positive Breast Cancer.

Purpose To determine the binding specificity of 18F-16α-17β-fluoroestradiol (FES) in estrogen receptor (ER) α-positive breast cancer cells and tumor xenografts. Materials and Methods Protocols were approved by the office of biologic safety and institutional animal care and use committee. By using ER-negative MDA-MB-231 breast cancer cells, clonal lines were created that expressed either wild-type (WT; 231 WT ER) or G521R mutant ERα (231 G521R ER), which is defective in estradiol binding. ERα protein levels, subcellular localization, and transcriptional function were confirmed. FES binding was measured by using an in vitro cell uptake assay. In vivo FES uptake was measured in tumor xenografts by using small-animal positron emission tomographic/computed tomographic imaging of 24 mice (17 WT ER tumors, nine mutant G521R ER tumors, eight MDA-MB-231 tumors, and four MCF-7 ER-positive tumors). Statistical significance was determined by using Mann-Whitney (Wilcoxon rank sum) test. Results ERα transcriptional function was abolished in the mutated 231 G521R ER cells despite appropriate receptor protein expression and nuclear localization. In vitro FES binding in the 231 G521R ER cells was reduced to that observed in the parental cells. Similarly, there was no significant FES uptake in the 231 G521R ER xenografts (percent injected dose [ID] per gram, 0.49 ± 0.042), which was similar to the negative control MDA-MB-231 xenografts (percent ID per gram, 0.42 ± 0.051; P = .20) and nonspecific muscle uptake (percent ID per gram, 0.41 ± 0.0095; P = .06). Conclusion This study showed that FES retention in ER-positive breast cancer is strictly dependent on an intact receptor ligand-binding pocket and that FES binds to ERα with high specificity. These results support the utility of FES imaging for assessing tumor heterogeneity by localizing immunohistochemically ER-positive metastases that lack receptor-binding functionality. © RSNA, 2017 Online supplemental material is available for this article.

Reprimo, a Potential p53-Dependent Tumor Suppressor Gene, Is Frequently Hypermethylated in Estrogen Receptor α-Positive Breast Cancer.

Aberrant DNA methylation is a hallmark of many cancers. Currently, there are four intrinsic molecular subtypes in breast cancer (BC): Luminal A, B, Her2-positive, and triple negative (TNBC). Recently, The Cancer Genome Atlas (TCGA) project has revealed that Luminal subtypes have higher levels of genome-wide methylation that may be a result of Estrogen/Estrogen receptor α (E2/ERα) signaling pathway activation. In this study, we analyze promoter CpG-island (CGIs) of the Reprimo (RPRM) gene in breast cancers (n = 77), cell lines (n = 38), and normal breast tissue (n = 10) using a MBDCap-seq database. Then, a validation cohort (n = 26) was used to confirm the results found in the MBDCap-seq platform. A differential methylation pattern was found between BC and cell lines compared to normal breast tissue. In BC, a higher DNA methylation was observed in tissues that were ERα-positive than in ERα-negative ones; more precisely, subtypes Luminal A compared to TNBC. Also, significant reverse correlation was observed between DNA methylation and RPRM mRNA expression in BC. Our data suggest that ERα expression in BC may affect the DNA methylation of CGIs in the RPRM gene. This approach suggests that DNA methylation status in CGIs of some tumor suppressor genes could be driven by E2 availability, subsequently inducing the activation of the ERα pathway.