MCM3 upregulation confers endocrine resistance in breast cancer and is a predictive marker of diminished tamoxifen benefit.

Resistance to endocrine therapy in estrogen receptor-positive (ER) breast cancer is a major clinical problem with poorly understood mechanisms. There is an unmet need for prognostic and predictive biomarkers to allow appropriate therapeutic targeting. We evaluated the mechanism by which minichromosome maintenance protein 3 (MCM3) influences endocrine resistance and its predictive/prognostic potential in ER breast cancer.

Correction: Gene expression profiling identifies FYN as an important molecule in tamoxifen resistance and a predictor of early recurrence in patients treated with endocrine therapy.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Correction: Gene expression profiling identifies FYN as an important molecule in tamoxifen resistance and a predictor of early recurrence in patients treated with endocrine therapy.

Since the online publication of the above article, the authors have noted errors in subfigures 1c and 3b. Therefore, new images of the original immmunocytochemistry stainings have been obtained for Fig. 1c, and the Western blots for siRNA-mediated FYN knockdown in Fig.

A suppressive role of guanine nucleotide-binding protein subunit beta-4 inhibited by DNA methylation in the growth of anti-estrogen resistant breast cancer cells.

Background: Breast cancer is the most common malignancy in women worldwide. Although the endocrine therapy that targets estrogen receptor α (ERα) signaling has been well established as an effective adjuvant treatment for patients with ERα-positive breast cancers, long-term exposure may eventually lead to the development of acquired resistance to the anti-estrogen drugs, such as fulvestrant and tamoxifen. A better understanding of the mechanisms underlying antiestrogen resistance and identification of the key molecules involved may help in overcoming antiestrogen resistance in breast cancer.

Aurora kinase A as a possible marker for endocrine resistance in early estrogen receptor positive breast cancer.

Background: Cell culture studies have disclosed that the mitotic Aurora kinase A is causally involved in both tamoxifen and aromatase inhibitor resistant cell growth and thus may be a potential new marker for endocrine resistance in the clinical setting.

Material And Methods: Archival tumor tissue was available from 1323 Danish patients with estrogen receptor (ER) positive primary breast cancer, who participated in the Breast International Group (BIG) 1-98 trial, comparing treatment with tamoxifen and letrozole and both in a sequence. The expression of Aurora A was determined by immunohistochemistry in 980 tumors and semi quantitively scored into three groups; negative/weak, moderate and high.

Williams syndrome transcription factor (WSTF) acts as an activator of estrogen receptor signaling in breast cancer cells and the effect can be abrogated by 1α,25-dihydroxyvitamin D.

A majority of estrogen receptor positive (ER+) breast cancers are growth stimulated by estrogens. The ability to inhibit the ER signaling pathway is therefore of critical importance in the current treatment of ER+ breast cancers. It has been reported that 1α,25-dihydroxyvitamin D down-regulates the expression of the CYP19A1 gene, encoding the aromatase enzyme that catalyzes the synthesis of estradiol.

A high level of estrogen-stimulated proteins selects breast cancer patients treated with adjuvant endocrine therapy with good prognosis.

Background: Adjuvant endocrine therapy has significantly improved survival of estrogen receptor α (ER)-positive breast cancer patients, but around 20% relapse within 10 years. High expression of ER-stimulated proteins like progesterone receptor (PR), Bcl-2 and insulin-like growth factor receptor I (IGF-IR) is a marker for estrogen-driven cell growth. Therefore, patients with high tumor levels of these proteins may have particularly good prognosis following adjuvant endocrine therapy.

The branched-chain amino acid transaminase 1 sustains growth of antiestrogen-resistant and ERα-negative breast cancer.

Antiestrogen-resistant and triple-negative breast tumors pose a serious clinical challenge because of limited treatment options. We assessed global gene expression changes in antiestrogen-sensitive compared with antiestrogen-resistant (two tamoxifen resistant and two fulvestrant resistant) MCF-7 breast cancer cell lines. The branched-chain amino acid transaminase 1 (BCAT1), which catalyzes the first step in the breakdown of branched-chain amino acids, was among the most upregulated transcripts in antiestrogen-resistant cells.

Expression of transmembrane protein 26 (TMEM26) in breast cancer and its association with drug response.

We have previously shown that stromal cells desensitize breast cancer cells to the anti-estrogen fulvestrant and, along with it, downregulate the expression of TMEM26 (transmembrane protein 26). In an effort to study the function and regulation of TMEM26 in breast cancer cells, we found that breast cancer cells express non-glycosylated and N-glycosylated isoforms of the TMEM26 protein and demonstrate that N-glycosylation is important for its retention at the plasma membrane. Fulvestrant induced significant changes in expression and in the N-glycosylation status of TMEM26.

Integrative analysis of miRNA and gene expression reveals regulatory networks in tamoxifen-resistant breast cancer.

Tamoxifen is an effective anti-estrogen treatment for patients with estrogen receptor-positive (ER+) breast cancer, however, tamoxifen resistance is frequently observed. To elucidate the underlying molecular mechanisms of tamoxifen resistance, we performed a systematic analysis of miRNA-mediated gene regulation in three clinically-relevant tamoxifen-resistant breast cancer cell lines (TamRs) compared to their parental tamoxifen-sensitive cell line. Alterations in the expression of 131 miRNAs in tamoxifen-resistant vs.

High CDK6 Protects Cells from Fulvestrant-Mediated Apoptosis and is a Predictor of Resistance to Fulvestrant in Estrogen Receptor-Positive Metastatic Breast Cancer.

Purpose: Resistance to endocrine therapy in estrogen receptor-positive (ER) breast cancer remains a major clinical problem. Recently, the CDK4/6 inhibitor palbociclib combined with letrozole or fulvestrant was approved for treatment of ER advanced breast cancer. However, the role of CDK4/6 in endocrine resistance and their potential as predictive biomarkers of endocrine treatment response remains undefined.

HIF2α contributes to antiestrogen resistance via positive bilateral crosstalk with EGFR in breast cancer cells.

The majority of breast cancers express estrogen receptor α (ERα), and most patients with ERα-positive breast cancer benefit from antiestrogen therapy. The ERα-modulator tamoxifen and ERα-downregulator fulvestrant are commonly employed antiestrogens. Antiestrogen resistance remains a clinical challenge, with few effective treatments available for patients with antiestrogen-resistant breast cancer.

Gene expression alterations associated with outcome in aromatase inhibitor-treated ER+ early-stage breast cancer patients.

Aromatase inhibitors (AI), either alone or together with chemotherapy, have become the standard adjuvant treatment for postmenopausal, estrogen receptor-positive (ER+) breast cancer. Although AIs improve overall survival, resistance is still a major clinical problem, thus additional biomarkers predictive of outcome of ER+ breast cancer patients treated with AIs are needed. Global gene expression analysis was performed on ER+ primary breast cancers from patients treated with adjuvant AI monotherapy; half experienced recurrence (median follow-up 6.

Aurora kinase B is important for antiestrogen resistant cell growth and a potential biomarker for tamoxifen resistant breast cancer.

Background: Resistance to antiestrogen therapy is a major clinical challenge in the treatment of estrogen receptor α (ER)-positive breast cancer. The aim of the study was to explore the growth promoting pathways of antiestrogen resistant breast cancer cells to identify biomarkers and novel treatment targets.

Methods: Antiestrogen sensitive and resistant T47D breast cancer cell lines were used as model systems.

SRC drives growth of antiestrogen resistant breast cancer cell lines and is a marker for reduced benefit of tamoxifen treatment.

The underlying mechanisms leading to antiestrogen resistance in estrogen-receptor α (ER)-positive breast cancer is still poorly understood. The aim of this study was therefore to identify biomarkers and novel treatments for antiestrogen resistant breast cancer. We performed a kinase inhibitor screen on antiestrogen responsive T47D breast cancer cells and T47D-derived tamoxifen and fulvestrant resistant cell lines.

Altered radiation responses of breast cancer cells resistant to hormonal therapy.

Endocrine therapy agents (the selective estrogen receptor (ER) modulators such as tamoxifen or the selective ER down-regulators such as ICI 182,780) are key treatment regimens for hormone receptor-positive breast cancers. While these drugs are very effective in controlling ER-positive breast cancer, many tumors that initially respond well to treatment often acquire drug resistance, which is a major clinical problem. In clinical practice, hormonal therapy agents are commonly used in combination or sequence with radiation therapy.

Aurora kinase A and B as new treatment targets in aromatase inhibitor-resistant breast cancer cells.

Aromatase inhibitors (AIs) are used for treatment of estrogen receptor α (ER)-positive breast cancer; however, resistance is a major obstacle for optimal outcome. This preclinical study aimed at identifying potential new treatment targets in AI-resistant breast cancer cells. Parental MCF-7 breast cancer cells and four newly established cell lines, resistant to the AIs exemestane or letrozole, were used for a functional kinase inhibitor screen.

New cell culture model for aromatase inhibitor-resistant breast cancer shows sensitivity to fulvestrant treatment and cross-resistance between letrozole and exemestane.

Aromatase inhibitor (AI) treatment is first-line systemic treatment for the majority of postmenopausal breast cancer patients with estrogen receptor (ER)-positive primary tumor. Although many patients benefit from treatment, some will develop resistance, and models mimicking acquired resistance will be valuable tools to unravel the resistance mechanisms and to find new treatments and biomarkers. Cell culture models for acquired resistance to the three clinically relevant AIs letrozole, anastrozole and exemestane were developed by selection and expansion of colonies of MCF-7 breast cancer cells surviving long-term AI treatment under conditions where endogenous aromatase-mediated conversion of androgen to estrogen was required for growth.

A kinase inhibitor screen identifies Mcl-1 and Aurora kinase A as novel treatment targets in antiestrogen-resistant breast cancer cells.

Antiestrogen resistance is a major problem in breast cancer treatment. Therefore, the search for new therapeutic targets and biomarkers for antiestrogen resistance is crucial. In this study, we performed a kinase inhibitor screen on antiestrogen responsive MCF-7 cells and a panel of MCF-7-derived tamoxifen- and fulvestrant-resistant cell lines.

Sorafenib and nilotinib resensitize tamoxifen resistant breast cancer cells to tamoxifen treatment via estrogen receptor α.

Tamoxifen‑resistant breast cancer is a major clinical problem and new treatment strategies are highly warranted. In this study, the multitargeting kinase inhibitors sorafenib and nilotinib were investigated as potential new treatment options for tamoxifen‑resistant breast cancer. The two compounds inhibited cell growth, reduced expression of total estrogen receptor α (ER), Ser118-phosphorylated ER, FOXA1 and AIB1 and resensitized tamoxifen‑resistant cells to tamoxifen.

Differential response to α-oxoaldehydes in tamoxifen resistant MCF-7 breast cancer cells.

Tamoxifen is the standard adjuvant endocrine therapy for estrogen-receptor positive premenopausal breast cancer patients. However, tamoxifen resistance is frequently observed under therapy. A tamoxifen resistant cell line has been generated from the estrogen receptor positive mamma carcinoma cell line MCF-7 and was analyzed for putative differences in the aldehyde defence system and accumulation of advanced glycation end products (AGE).

Gene expression profiling identifies FYN as an important molecule in tamoxifen resistance and a predictor of early recurrence in patients treated with endocrine therapy.

To elucidate the molecular mechanisms of tamoxifen resistance in breast cancer, we performed gene array analyses and identified 366 genes with altered expression in four unique tamoxifen-resistant (TamR) cell lines vs the parental tamoxifen-sensitive MCF-7/S0.5 cell line. Most of these genes were functionally linked to cell proliferation, death and control of gene expression, and include FYN, PRKCA, ITPR1, DPYD, DACH1, LYN, GBP1 and PRLR.

The broad-spectrum metalloproteinase inhibitor BB-94 inhibits growth, HER3 and Erk activation in fulvestrant-resistant breast cancer cell lines.

Breast cancer cells can switch from estrogen receptor α (ER)- to human epidermal growth factor receptor (HER)-driven cell growth upon acquiring antiestrogen resistance. HER ligands are cleaved by metalloproteinases leading to release of active HER ligands, activation of HER receptors and consequently increased cell growth. In this study, we investigated the importance of HER receptors, in particular HER3, and HER ligand shedding for growth and signaling in human MCF-7 breast cancer cells and MCF-7-derived sublines resistant to the antiestrogen fulvestrant.

1α,25-dihydroxyvitamin D3 inhibits cell growth and NFκB signaling in tamoxifen-resistant breast cancer cells.

Resistance to antiestrogens is a major clinical problem in current breast cancer treatment and development of new treatment strategies for these tumors is highly prioritized. In this study, we have investigated the effects of 1α,25-dihydroxyvitamin D3 on the proliferation of tamoxifen-resistant cells. Further, we have investigated on a molecular level the effects of vitamin D on NFkB signaling in tamoxifen-resistant breast cancer cells.

T47D breast cancer cells switch from ER/HER to HER/c-Src signaling upon acquiring resistance to the antiestrogen fulvestrant.

In this study, T47D cell lines resistant to the antiestrogen fulvestrant were established and analyzed to explore, whether a switch to HER signaling, as seen in fulvestrant resistant MCF-7 cell lines, is a general resistance mechanism. We find that parental T47D cells depend on ER and HER signaling for growth. Fulvestrant resistant T47D cells have lost ER expression and, although HER2 was over expressed, growth was only partially driven by HER receptors.