Influence of Estrogen Treatment on ESR1+ and ESR1- Cells in ER+ Breast Cancer: Insights from Single-Cell Analysis of Patient-Derived Xenograft Models.

A 100% ER positivity is not required for an endocrine therapy response. Furthermore, while estrogen typically promotes the progression of hormone-dependent breast cancer via the activation of estrogen receptor (ER)-α, estrogen-induced tumor suppression in ER+ breast cancer has been clinically observed. With the success in establishing estrogen-stimulated (SC31) and estrogen-suppressed (GS3) patient-derived xenograft (PDX) models, single-cell RNA sequencing analysis was performed to determine the impact of estrogen on ESR1+ and ESR1- tumor cells. We found that 17ß-estradiol (E2)-induced suppression of GS3 transpired through wild-type and unamplified ERα. E2 upregulated the expression of estrogen-dependent genes in both SC31 and GS3; however, E2 induced cell cycle advance in SC31, while it resulted in cell cycle arrest in GS3. Importantly, these gene expression changes occurred in both ESR1+ and ESR1- cells within the same breast tumors, demonstrating for the first time a differential effect of estrogen on ESR1- cells. E2 also upregulated a tumor-suppressor gene, IL-24, in GS3. The apoptosis gene set was upregulated and the G2M checkpoint gene set was downregulated in most IL-24+ cells after E2 treatment. In summary, estrogen affected pathologically defined ER+ tumors differently, influencing both ESR1+ and ESR1- cells. Our results also suggest IL-24 to be a potential marker of estrogen-suppressed tumors.

Mammary cell gene expression atlas links epithelial cell remodeling events to breast carcinogenesis.

The female mammary epithelium undergoes reorganization during development, pregnancy, and menopause, linking higher risk with breast cancer development. To characterize these periods of complex remodeling, here we report integrated 50 K mouse and 24 K human mammary epithelial cell atlases obtained by single-cell RNA sequencing, which covers most lifetime stages. Our results indicate a putative trajectory that originates from embryonic mammary stem cells which differentiates into three epithelial lineages (basal, luminal hormone-sensing, and luminal alveolar), presumably arising from unipotent progenitors in postnatal glands. The lineage-specific genes infer cells of origin of breast cancer using The Cancer Genome Atlas data and single-cell RNA sequencing of human breast cancer, as well as the association of gland reorganization to different breast cancer subtypes. This comprehensive mammary cell gene expression atlas ( https://mouse-mammary-epithelium-integrated.cells.ucsc.edu ) presents insights into the impact of the internal and external stimuli on the mammary epithelium at an advanced resolution.

Functional characterization of androgen receptor in two patient-derived xenograft models of triple negative breast cancer.

Extensive efforts, through cell line-based models, have been made to characterize the androgen receptor (AR) signaling pathway in triple-negative breast cancer (TNBC). However, these efforts have not yet reached a consensus with regards to the mechanism of AR in TNBC. Considering that patient-derived xenografts (PDXs) are more appropriate than cell line-based models for recapitulating the structural and molecular features of a patient's tumor, we have identified and molecularly characterized two new AR-positive TNBC PDX models and assessed the impacts of AR agonist [dihydrotestosterone (DHT)] and antagonist (enzalutamide) on tumor growth and gene expression profiles by utilizing immunohistochemistry, western blots, and RNA-Seq analyses. Two PDX models, termed TN1 and TN2, were derived from two grade-3 TNBC tumors, each harboring 1∼5% of AR nuclear positive cancer cells. DHT activated AR in both PDX tumors by increasing nuclear localization and AR protein levels. However, the endpoint tumor volume of DHT-treated TN1 was 3-folds smaller than that of non-treated TN1 tumors. Conversely, the endpoint tumor volume of DHT-treated TN2 was 2-folds larger than that of non-treated TN2. Moreover, enzalutamide failed to antagonize DHT-induced tumor growth in TN2. The RNA-Seq analyses revealed that DHT mainly suppressed gene expression in TN1 (961 down-regulated genes versus 149 up-regulated genes), while DHT promoted gene expression in TN2 (673 up-regulated genes versus 192 down-regulated genes). RNA-Seq data predicted distinct TNBC molecular subtypes for TN1 and TN2. TN1 correlated to a basal-like 1 (BL1) subtype, and TN2 correlated to a basal-like 2 (BL2) subtype. These analyses suggest that TN1 and TN2, which both express functional AR, are two molecularly distinct PDX models. The molecular characterization of these PDX models expands our current knowledge on AR-positive TNBC. Our results do not support that AR is a suitable therapeutic target in TNBC. To our best knowledge, the molecular mechanisms of AR in TNBC are equivocal and should be evaluated using clinically relevant models, considering both the heterogeneous expression of AR in TNBC and the general complexities of AR signaling.

Protocol for BATTLE-1EX: A High-Resolution Imaging Method to Visualize Whole Synaptic Structures and their Components in the Nervous System.

This protocol describes BATTLE-1EX, which is a combined method of BATTLE-1 and expansion microscopy to obtain high-resolution imaging of whole synaptic structures and their components of hippocampal neural circuits. BATTLE-1 uses two genetically engineered recombinase proteins and competition between two recombinases that can be independently titrated, resulting in a tunable proportion of mCherry+/YFP- and YFP+/mCherry- cells. As a combinational method, BATTLE-1EX has the potential to visualize and dissect whole synaptic structures in numerous regions in the brain. For complete details on the use and execution of this protocol, please refer to Kohara et al. (2020).

Changes in serum estrogenic activity during neoadjuvant therapy with letrozole and exemestane.

The aromatase inhibitors (AIs), letrozole (Femar®/Femara®) and exemestane (Aromasin®), are widely used to treat estrogen receptor (ER) positive breast cancer in postmenopausal patients. In the setting of metastatic breast cancer, these drugs may be used after another causing new responses in selected patients after progressing on the first choice. The precise explanation for this "lack of cross resistance" is still missing. NEOLETEXE is a neoadjuvant, randomized, open-label, cross-over trial. Postmenopausal patients with ER-positive, HER-2 negative, locally advanced breast cancer were enrolled. All patients were randomized to treatment starting with either letrozole or exemestane for at least 2 months followed by another 2 months on the alternative AI. The total estrogenic activities in blood samples were determined using the AroER tri-screen assay developed in the Chen laboratory. Using this highly sensitive assay, estrogenic activity was detected at three time points for all patients. Importantly, a significantly higher total estrogenic activity was found during therapy with exemestane compared to letrozole in 21 out of 26 patients. When letrozole was included in the AroER tri-screen assay, the estrogenic activities in most samples collected during exemestane treatment were further reduced, suggesting that low levels of androgens remained in specimens obtained after exemestane treatment. Our results suggest the AroER tri-screen to be a very sensitive method to estimate the overall estrogen-mediated activity in human samples even during therapy with highly potent aromatase inhibitors. In the present study, serum estrogen activity was significantly higher during exemestane therapy when compared to letrozole therapy.

Single-cell RNA-sequencing analysis of estrogen- and endocrine-disrupting chemical-induced reorganization of mouse mammary gland.

Menopause is a critical window of susceptibility for its sensitivity to endocrine disrupting chemicals due to the decline of endogenous estrogen. Using a surgical menopausal (ovariectomized) mouse model, we assessed how mammary tissue was affected by both 17ß-estradiol (E2) and polybrominated diphenyl ethers (PBDEs). As flame retardants in household products, PBDEs are widely detected in human serum. During physiologically-relevant exposure to E2, PBDEs enhanced E2-mediated regrowth of mammary glands with terminal end bud-like structures. Analysis of mammary gland RNA revealed that PBDEs both augmented E2-facilitated gene expression and modulated immune regulation. Through single-cell RNA sequencing (scRNAseq) analysis, E2 was found to induce Pgr expression in both Esr1+ and Esr1- luminal epithelial cells and Ccl2 expression in Esr1+ fibroblasts. PBDEs promote the E2-AREG-EGFR-M2 macrophage pathway. Our findings support that E2 + PBDE increases the risk of developing breast cancer through the expansion of estrogen-responsive luminal epithelial cells and immune modulation.

Molecular Mechanisms of Polybrominated Diphenyl Ethers (BDE-47, BDE-100, and BDE-153) in Human Breast Cancer Cells and Patient-Derived Xenografts.

Polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in household materials. Their environmental persistence has led to continuous human exposure and significant tissue levels. Three PBDE congeners (BDE-47, BDE-100, and BDE-153) have been frequently detected in human serum. Although these compounds appear to possess endocrine disrupting activity, studies are largely missing to determine the biological mechanisms of PBDEs in breast cancer cells. Here, we assessed PBDE bioactivities with three complementary strategies: receptor binding/activity assays; nonbiased RNA-sequencing analysis using an estrogen-dependent breast cancer cell line MCF-7aroERE; and in vivo assessments using patient-derived xenograft (PDX) models of human breast cancer. According to the results from in vitro experiments, the PBDE congeners regulate distinct nuclear receptor signaling pathways. BDE-47 acts as a weak agonist of both estrogen receptor α (ERα) and estrogen-related receptor α (ERRα); it could stimulate proliferation of MCF-7aroERE and induced expression of ER-regulated genes (including cell cycle genes). BDE-153 was found to act as a weak antagonist of ERα. BDE-100 could act as (1) an agonist of aryl hydrocarbon receptor (AhR), inducing expression of CYP1A1 and CYP1B1 and (2) as a very weak agonist/antagonist of ERα. In vivo, a mixture of the three congeners with ratios detected in human serum was tested in an ER+ PDX model. The mixture exhibited estrogenic activity through apoptosis/cell cycle regulation and increased the expression of a proliferation marker, Ki-67. These results advance our understanding of the mechanisms of PBDE exposure in breast cancer cells.

Synergistic anti-cancer activity of CDK4/6 inhibitor palbociclib and dual mTOR kinase inhibitor MLN0128 in pRb-expressing ER-negative breast cancer.

PURPOSE: Palbociclib is an approved cyclin-dependent kinase (CDK) 4/6 inhibitor for treatment of patients with ER-positive and HER2-negative breast cancers. While Retinoblastoma protein (pRb), a major substrate of CDK4/6, is a potential target in triple negative breast cancer (TNBC), the usefulness of CDK4/6 inhibitors in this cancer has not been established. This preclinical study investigated the combination effects of palbociclib and the dual mammalian target of rapamycin (mTOR) kinase inhibitor MLN0128 in estrogen receptor (ER)-negative breast cancer in vitro and in vivo. METHODS: The combined effects of two drugs on three TNBC cell lines (MB231, MB468, and CAL148) and an ER-negative and HER2-positive cell line (MB453) were investigated by MTT assay and colony formation analysis. Cell cycle measurements were examined as well as changes in expression of molecules related to G1/S transition and the mTOR pathway. Importantly, a pRb-expressing TNBC patient-derived xenograft (PDX) model was used to assess the effects of the combination in vivo. RESULTS: A combination of palbociclib and MLN0128 synergistically inhibited the proliferation of pRb-expressing cell lines and induced G1 cell cycle arrest. Western blot analysis revealed that CDK4/6-pRb and mTOR pathways were inhibited by these treatments. In pRb-expressing TNBC PDX, the combination treatment drastically suppressed tumor growth compared to either the control or single drug treatments. In addition, the combination treatment significantly reduced the number of Ki67-positive cells. CONCLUSIONS: We revealed that palbociclib and MLN0128 had synergistic anti-cancer activity in both pRb + ER-negative cell lines and a TNBC PDX model. Our results indicate that such combination therapy is worthy of further investigation in a clinical setting.

ERα-mediated cell cycle progression is an important requisite for CDK4/6 inhibitor response in HR+ breast cancer.

While ER has multiple biological effects, ER-cyclin D1-CDK4/6-RB is a critical pathway for the action of estrogen on the cell cycle, especially for breast cancers that rely on estrogen for growth. The latest and most efficient CDK4/6 inhibitors target the phosphorylation of retinoblastoma (RB) tumor suppressor gene; thus, altering levels of many cell cycle molecules. Estrogen receptor (ER)+/HER2- breast cancers have shown great progression free survival when CDK4/6 inhibitors are combined with endocrine therapies. Here we report the mechanism of antiestrogen (fulvestrant) combination with CDK4/6 inhibitors is due to synergism in the suppression of ER-mediated cell cycle progression. Furthermore, we performed single cell analysis of cells from an estrogen dependent/hormone receptor-positive patient derived xenograft (PDX) tumor model treated with palbociclib. These single cells expressed various levels of ER and RB which are involved in cell cycle regulation; and the response to palbociclib treatment relies not only on the ER-cyclin D1-CDK4/6-RB pathway but it is also dependent on elevated levels of ER and/or RB. Our preclinical studies show that palbociclib response is dependent on cells with ER, which is directly involved in cell cycle progression in hormone receptor positive (HR+) breast cancer.

Use of dual mTOR inhibitor MLN0128 against everolimus-resistant breast cancer.

PURPOSE: HR+/HER2- aromatase inhibitor-resistant metastatic breast cancer can be treated with everolimus and a second AI until the cancer recurs. Targeting these everolimus-resistant patients with the latest standard of care, CDK4/6 inhibitors, has not been clearly addressed. Understanding the signaling transduction pathways, which everolimus resistance activates, will elucidate the mechanisms and offer treatment strategies of everolimus resistance. METHODS: To mimic the clinical setting, letrozole-resistant cells were used to generate an everolimus-resistant model (RAD-R). Reverse phase protein array (RPPA) was performed to reveal changes in the signaling transduction pathways, and expression levels of key proteins were analyzed. Inhibitors targeting the major signaling pathways, a CDK4/6 inhibitor palbociclib and a mTORC1/2 inhibitor (MLN0128), were evaluated to establish resistance mechanisms of RAD-R. RESULTS: RPPA results from RAD-R indicated changes to significant regulatory pathways and upregulation of p-AKT expression level associating with everolimus resistance. MLN0128, that inhibits the AKT phosphorylation, effectively suppressed the proliferation of RAD-R cells while treatment with palbociclib had no effect. CONCLUSION: Among the many signaling transduction pathways, which are altered post everolimus resistance, targeting dual mTORC1/2 is a possible option for patients who have recurrent disease from previous everolimus treatment.

Identification of Estrogen-Related Receptor α Agonists in the Tox21 Compound Library.

The estrogen-related receptor α (ERRα) is an orphan nuclear receptor (NR) that plays a role in energy homeostasis and controls mitochondrial oxidative respiration. Increased expression of ERRα in certain ovarian, breast, and colon cancers has a negative prognosis, indicating an important role for ERRα in cancer progression. An interaction between ERRα and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) has also recently been shown to regulate an enzyme in the ß-oxidation of free fatty acids, thereby suggesting that ERRα plays an important role in obesity and type 2 diabetes. Therefore, it would be prudent to identify compounds that can act as activators of ERRα. In this study, we screened ∼10,000 (8311 unique) compounds, known as the Tox21 10K collection, to identify agonists of ERRα. We performed this screen using two stably transfected HEK 293 cell lines, one with the ERRα-reporter alone and the other with both ERRα-reporter and PGC-1α expression vectors. After the primary screening, we identified more than five agonist clusters based on compound structural similarity analysis (e.g., statins). By examining the activities of the confirmed ERRα modulators in other Tox21 NR assays, eliminating those with promiscuous NR activity, and performing follow-up assays (e.g., small interfering RNA knockdown), we identified compounds that might act as endocrine disrupters through effects on ERRα signaling. To our knowledge, this study is the first comprehensive analysis in discovering potential endocrine disrupters that affect the ERRα signaling pathway.

Dual mTOR Kinase Inhibitor MLN0128 Sensitizes HR+/HER2+ Breast Cancer Patient-Derived Xenografts to Trastuzumab or Fulvestrant.

Purpose: Therapeutic strategies against hormonal receptor-positive (HR+)/HER2+ breast cancers with poor response to trastuzumab need to be optimized.Experimental Design: Two HR+/HER2+ patient-derived xenograft (PDX) models named as COH-SC1 and COH-SC31 were established to explore targeted therapies for HER2+ breast cancers. RNA sequencing and RPPA (reverse phase protein array) analyses were conducted to decipher molecular features of the two PDXs and define the therapeutic strategy of interest, validated by in vivo drug efficacy examination and in vitro cell proliferation analysis.Results: Estrogen acted as a growth driver of trastuzumab-resistant COH-SC31 tumors but an accelerator in the trastuzumab-sensitive COH-SC1 model. In vivo trastuzumab efficacy examination further confirmed the consistent responses between PDXs and the corresponding tumors. Integrative omics analysis revealed that mammalian target of rapamycin (mTOR) and ERα signaling predominantly regulate tumor growth of the two HR+/HER2+ PDXs. Combination of the dual mTOR complex inhibitor MLN0128 and anti-HER2 trastuzumab strongly suppressed tumor growth of COH-SC1 PDX accompanied by increasing ER-positive cell population in vivo Instead, MLN0128 in combination with antiestrogen fulvestrant significantly halted the growth of HR+/HER2+ cancer cells in vitro and trastuzumab-resistant COH-SC31 as well as trastuzumab-sensitive COH-SC1 tumors in vivoConclusions: Compared with the standard trastuzumab treatment, this study demonstrates alternative therapeutic strategies against HR+/HER2+ tumors through establishment of two PDXs coupled with integrative omics analyses and in vivo drug efficacy examination. This work presents a prototype of future "co-clinical" trials to tailor personalized medicine in clinical practice. Clin Cancer Res; 24(2); 395-406. ©2017 AACR.

Characterization of patient-derived tumor xenografts (PDXs) as models for estrogen receptor positive (ER+HER2- and ER+HER2+) breast cancers.

The research was to appraise the utility of the patient-derived tumor xenografts (PDXs) as models of estrogen receptor positive (ER+HER2- and ER+HER2+) breast cancers. We compared protein expression profiles by Reverse Phase Protein Array (RPPA) in tumors that resulted in PDXs compared to those that did not. Our overall PDX intake rate for ER+ breast cancer was 9% (9/97). The intake rate for ER+HER2+ tumors (3/16, 19%) was higher than for ER+HER2- tumors (6/81, 7%). Heat map analyses of RPPA data showed that ER+HER2- tumors were divided into 2 groups by luminal A/B signature [protein expression of ER, AR, Bcl-2, Bim (BCL2L11), GATA3 and INPP4b], and this expression signature was also associated with the rate of PDX intake. Cell survival pathways such as the PI3K/AKT signaling and RAS/ERK pathways were more activated in the specimens that could be established as PDX in both classes. Expression of the ER protein itself may have a bearing on the potential success of an ER+ PDX model. In addition, HER2 and its downstream protein expressions were up-regulated in the ER+HER2+ patient tumors that were successfully established as PDX models. Moreover, the comparison of RPPA data between original and PDX tumors suggested that the selection/adaptation process required to grow the tumors in mice is unavoidable for generation of ER+ PDX models, and we identified differences between patient tumor samples and paired PDX tumors. A better understanding of the biological characteristics of ER+PDX would be the key to using PDX models in assessing treatment strategies in a preclinical setting.

Cell-Based High-Throughput Screening for Aromatase Inhibitors in the Tox21 10K Library.

Multiple mechanisms exist for endocrine disruption; one nonreceptor-mediated mechanism is via effects on aromatase, an enzyme critical for maintaining the normal in vivo balance of androgens and estrogens. We adapted the AroER tri-screen 96-well assay to 1536-well format to identify potential aromatase inhibitors (AIs) in the U.S. Tox21 10K compound library. In this assay, screening with compound alone identifies estrogen receptor alpha (ERα) agonists, screening in the presence of testosterone (T) identifies AIs and/or ERα antagonists, and screening in the presence of 17ß-estradiol (E2) identifies ERα antagonists. Screening the Tox-21 library in the presence of T resulted in finding 302 potential AIs. These compounds, along with 31 known AI actives and inactives, were rescreened using all 3 assay formats. Of the 333 compounds tested, 113 (34%; 63 actives, 50 marginal actives) were considered to be potential AIs independent of cytotoxicity and ER antagonism activity. Structure-activity analysis suggested the presence of both conventional (eg, 1, 2, 4, - triazole class) and novel AI structures. Due to their novel structures, 14 of the 63 potential AI actives, including both drugs and fungicides, were selected for confirmation in the biochemical tritiated water-release aromatase assay. Ten compounds were active in the assay; the remaining 4 were only active in high-throughput screen assay, but with low efficacy. To further characterize these 10 novel AIs, we investigated their binding characteristics. The AroER tri-screen, in high-throughput format, accurately and efficiently identified chemicals in a large and diverse chemical library that selectively interact with aromatase.

AroER tri-screen™ is a novel functional assay to estimate both estrogenic and estrogen precursor activity of chemicals or biological specimens.

The purpose of the study is to define AroER tri-screen's utility for identifying endocrine-disrupting chemicals (EDCs) that target aromatase and/or estrogen receptor (ER), and to measure the total estrogenic activity in biological specimens. ER-positive, aromatase-expressing MCF-7 breast cancer cells were stably transfected with an estrogen responsive element (ERE)-driven luciferase reporter plasmid to yield a new high-throughput screening platform-the AroER tri-screen. AroER tri-screen was capable of identifying estrogen precursors, such as cortodoxone, which function as estrogens through a two-step conversion process in aromatase-expressing tissue. Furthermore, the system proved useful for assessing EDC activity in biologically relevant samples. Estimating these activities is critical because natural estrogens and estrogenic EDCs are important factors in ER-positive breast cancer risk. As our research demonstrates, incorporating functionally active aromatase into the AroER tri-screen produces a powerful and unique tool to (1) identify new EDCs targeting aromatase and/or ER; (2) discover novel EDCs activated by aromatase; and (3) estimate overall estrogenic activities in biological samples as a potential intermediate risk factor for breast cancer.

A phase I trial of mushroom powder in patients with biochemically recurrent prostate cancer: Roles of cytokines and myeloid-derived suppressor cells for Agaricus bisporus-induced prostate-specific antigen responses.

BACKGROUND: Each year in the United States, nearly 50,000 prostate cancer patients exhibit a rise in prostate-specific antigen (PSA) levels, which can indicate disease recurrence. For patients with biochemically recurrent prostate cancer, we evaluated the effects of white button mushroom (WBM) powder on serum PSA levels and determined the tolerability and biological activity of WBM. METHODS: Patients with continuously rising PSA levels were enrolled in the study. Dose escalation was conducted in cohorts of 6; this ensured that no more than 1 patient per cohort experienced dose-limiting toxicity (DLT). The primary objective was to evaluate treatment feasibility and associated toxicity. The secondary objectives were to determine WBM's effect on serum PSA/androgen levels; myeloid-derived suppressor cells (MDSCs); and cytokine levels. RESULTS: Thirty-six patients were treated; no DLTs were encountered. The overall PSA response rate was 11%. Two patients receiving 8 and 14 g/d demonstrated complete response (CR): their PSA declined to undetectable levels that continued for 49 and 30 months. Two patients who received 8 and 12 g/d experienced partial response (PR). After 3 months of therapy, 13 (36%) patients experienced some PSA decrease below baseline. Patients with CR and PR demonstrated higher levels of baseline interleukin-15 than nonresponders; for this group, we observed therapy-associated declines in MDSCs. CONCLUSIONS: Therapy with WBM appears to both impact PSA levels and modulate the biology of biochemically recurrent prostate cancer by decreasing immunosuppressive factors.

From bench to bedside: What do we know about hormone receptor-positive and human epidermal growth factor receptor 2-positive breast cancer?

Breast cancer is a heterogeneous disease. Thanks to extensive efforts from research scientists and clinicians, treatment for breast cancer has advanced into the era of targeted medicine. With the use of several well-established biomarkers, such as hormone receptors (HRs) (i.e., estrogen receptor [ER] and progesterone receptor [PgR]) and human epidermal growth factor receptor-2 (HER2), breast cancer patients can be categorized into multiple subgroups with specific targeted treatment strategies. Although therapeutic strategies for HR-positive (HR+) HER2-negative (HER2-) breast cancer and HR-negative (HR-) HER2-positive (HER2+) breast cancer are well-defined, HR+ HER2+ breast cancer is still an overlooked subgroup without tailored therapeutic options. In this review, we have summarized the molecular characteristics, etiology, preclinical tools and therapeutic options for HR+ HER2+ breast cancer. We hope to raise the attention of both the research and the medical community on HR+ HER2+ breast cancer, and to advance patient care for this subtype of disease.

Targeting breast cancer stem cells in triple-negative breast cancer using a combination of LBH589 and salinomycin.

The aim of this study is to investigate the efficacy of combining a histone deacetylase inhibitor (LBH589) and a breast cancer stem cells (BCSC)-targeting agent (salinomycin) as a novel combination therapy for triple-negative breast cancer (TNBC). We performed in vitro studies using the TNBC cell lines to examine the combined effect. We used the mammosphere and ALDEFLUOR assays to estimate BCSC self-renewal capacity and distribution of BCSCs, respectively. Synergistic analysis was performed using CalcuSyn software. For in vivo studies, aldehyde dehydrogenase 1 ALDH1-positive cells were injected into non-obese diabetic/severe combined immunodeficiency gamma (NSG) mice. After tumor formation, mice were treated with LBH589, salinomycin, or in combination. In a second mouse model, HCC1937 cells were first treated with each treatment and then injected into NSG mice. For mechanistic analysis, immunohistochemistry and Western blot analysis were performed using cell and tumor samples. HCC1937 cells displayed BCSC properties including self-renewal capacity, an ALDH1-positive cell population, and the ability to form tumors. Treatment of HCC1937 cells with LBH589 and salinomycin had a potent synergistic effect inhibiting TNBC cell proliferation, ALDH1-positive cells, and mammosphere growth. In xenograft mouse models treated with LBH589 and salinomycin, the drug combination effectively and synergistically inhibited tumor growth of ALDH1-positive cells. The drug combination exerted its effects by inducing apoptosis, arresting the cell cycle, and regulating epithelial-mesenchymal transition (EMT). Combination of LBH589 and salinomycin has a synergistic inhibitory effect on TNBC BCSCs by inducing apoptosis, arresting the cell cycle, and regulating EMT; with no apparent associated severe toxicity. This drug combination could therefore offer a new targeted therapeutic strategy for TNBC and warrants further clinical study in patients with TNBC.

AroER tri-screen is a biologically relevant assay for endocrine disrupting chemicals modulating the activity of aromatase and/or the estrogen receptor.

Endocrine disrupting chemicals (EDCs) interfere with the biosynthesis, metabolism, and functions of steroid hormones, including estrogens and androgens. Aromatase enzyme converts androgen to estrogen. Thus, EDCs against aromatase significantly impact estrogen- and/or androgen-dependent functions, including the development of breast cancer. The current study aimed to develop a biologically relevant cell-based high-throughput screening assay to identify EDCs that act as aromatase inhibitors (AIs), estrogen receptor (ER) agonists, and/or ER antagonists. The AroER tri-screen assay was developed by stable transfection of ER-positive, aromatase-expressing MCF-7 breast cancer cells with an estrogen responsive element (ERE) driven luciferase reporter plasmid. The AroER tri-screen can identify: estrogenic EDCs, which increase luciferase signal without 17ß-estradiol (E2); anti-estrogenic EDCs, which inhibit the E2-induced luciferase signal; and AI-like EDCs, which suppress a testosterone-induced luciferase signal. The assay was first optimized in a 96-well plate format and then miniaturized into a 1536-well plate format. The AroER tri-screen was demonstrated to be suitable for high-throughput screening in the 1536-well plate format, with a 6.9-fold signal-to-background ratio, a 5.4% coefficient of variation, and a screening window coefficient (Z-factor) of 0.78. The assay suggested that bisphenol A (BPA) functions mainly as an ER agonist. Results from screening the 446 drugs in the National Institutes of Health Clinical Collection revealed 106 compounds that modulated ER and/or aromatase activities. Among these, two AIs (bifonazole and oxiconazole) and one ER agonist (paroxetine) were confirmed through alternative aromatase and ER activity assays. These findings indicate that AroER tri-screen is a useful high-throughput screening system for identifying ER ligands and aromatase-inhibiting chemicals.