Ectopic expression of epidermal growth factor receptors induces hormone independence in ZR-75-1 human breast cancer cells.

Epidermal growth factor (EGF) receptor is inversely related to expression of estrogen receptor (ER) and progesterone receptor in primary breast tumors and is a negative predictor for response to endocrine therapy. To investigate a possible causal role of EGF receptor expression in breast cancer progression to hormone independence, we have created an experimental cell system. Epidermal growth factor receptor complementary DNA was introduced in estrogen-dependent ZR-75-1 breast cancer cells, and the resulting ZR/HERc cells exhibited a mitogenic response to epidermal growth factor, thus bypassing estrogen dependence. This EGF-induced proliferation could not be inhibited by antiestrogens. In addition, we noted changes in cell morphology and keratin expression of EGF-stimulated ZR/HERc cells, suggestive of an altered differentiation state. Furthermore, intolerance of functional ER and EGF receptor signal transduction pathways in ZR/HERc cells was observed during simultaneous activation, which possibly explains the inverse relationship of ER and EGF receptor expression in primary tumors. In contrast to the parental cells, ZR/HERc cells rapidly progressed to a stable ER-negative phenotype when cultured in the presence of the antiestrogen hydroxy-tamoxifen. These results suggest a possible role for EGF receptor in progression of breast cancer to hormone independence.     

Decreased expression of EZH2 is associated with upregulation of ER and favorable outcome to tamoxifen in advanced breast cancer

The purpose of this study is to investigate EZH2 in a large series of breast cancer patients for its prognostic and predictive value, and to evaluate its functional role in treatment response in vitro. EZH2 levels were measured using quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) in primary breast cancer specimens and related to clinicopathologic factors and disease outcome. EZH2 expression was downregulated with siRNAs in MCF7, to assess expression alterations of putative EZH2 downstream genes and to determine cell numbers after treatment with the anti-estrogen ICI 164384. In 688 lymph node-negative patients who did not receive adjuvant systemic therapy, EZH2 was not significantly correlated with metastasis-free survival (MFS). In 278 patients with advanced disease treated with first-line tamoxifen monotherapy, the tertile with highest EZH2 levels was associated with the lowest clinical benefit (OR = 0.48; P = 0.02) and with a shorter progression-free survival (PFS) in both univariate (HR = 1.80; P < 0.001) and multivariate analysis, including traditional factors (HR = 1.61; P = 0.004). In vitro, EZH2 silencing in MCF7 caused a 38% decrease in cell numbers (P < 0.001) whereas ICI 164384 treatment resulted in a 25% decrease (P < 0.001) compared to controls. Combining EZH2 silencing with ICI treatment reduced cell numbers with 67% (P < 0.001) compared to control conditions. EZH2 downregulation was associated with an almost two-fold upregulation of the estrogen receptor alpha (ER) (P = 0.001). In conclusion, EZH2 has no prognostic value in breast cancer. High levels of EZH2 are associated with poor outcome to tamoxifen therapy in advanced breast cancer. Downregulated EZH2 leads to upregulation of the ER and better response to anti-estrogens.     

Aromatase inhibitor versus tamoxifen in postmenopausal woman with advanced breast cancer: a literature-based meta-analysis

Clinical trials have reported conflicting results as to whether Aromatase inhibitors (AIs) as first-line hormonal therapy improve outcome over tamoxifen in postmenopausal women with advanced breast cancer. We performed a meta-analysis comparing primary and secondary endpoints of AIs to tamoxifen as first-line hormonal therapy in postmenopausal women with advanced breast cancer. The event-based odds ratio (OR) with 95% confidence interval (95% CI) were derived, and a test of heterogeneity was applied. Six eligible trials (2560 patients) were selected from 488 studies that initially were identified. A significant difference in favoring AIs over tamoxifen was observed in overall response rate (ORR; OR, 1.56; 95% CI, 1.17-2.07; P = .002) and clinical benefit (CB; OR, 1.70; 95% CI, 1.24-2.33; P = .0009).Whereas the trend toward an improved overall survival (OS) rate was not significant (OR, 1.95; 95% CI, 0.88-4.30; P = .10).Toxicities did not differ significantly except vaginal bleeding (OR, 0.30; 95% CI, 0.16-0.56; P = .0002) and thromboembolic event (OR, 0.47; 95% CI, 0.28-0.77; P = .003). AIs appeared to be effective and feasible compared with tamoxifen as first-line hormonal therapy in postmenopausal women with advanced breast cancer. Further prospective, randomized, controlled trials will be necessary.     

Increased SIAH expression predicts ductal carcinoma in situ (DCIS) progression to invasive carcinoma

Hyperactivated HER2/Neu/EGFR/RAS signaling is a major growth-promoting pathway known to drive cellular transformation and oncogenesis in breast cancers. HER2 amplification is detected in ~20% of all human breast cancer and is quite prevalent (up to 49%) in ductal carcinoma in situ (DCIS). The E3 ubiquitin ligase SIAH is considered a key downstream “gatekeeper” required for proper HER2/EGFR/RAS signal transduction. Formalin-fixed, paraffin-embedded resection specimens from 65 patients with DCIS treated with wide excision only were stained with an anti-SIAH antibody, and the percentage of tumor and normal adjacent tissue cells positive for SIAH nuclear staining were recorded. Statistical analysis was performed comparing SIAH staining in tumor cells to disease recurrence, histologic type, necrosis, hormone receptor status, and Her2/neu status, as well as nuclear grade. Correlation of SIAH expression in tumor cells with SIAH expression in normal adjacent tissue and age was also examined. Expression levels of SIAH in tumor cells was significantly higher in specimens from patients with recurrence (median = 19%) as compared to patients without recurrence (7%) (P < 0.001). There was also significantly increased SIAH expression in tumors with more aggressive features including comedo morphology (13.5% in comedo vs. 7% in other histologic types, P = 0.014). No significant association was observed between SIAH expression and estrogen receptor, progesterone receptor, and Her2/neu status. There was a significant correlation between SIAH expression in tumors and normal adjacent tissue (Spearman correlation = 0.58, P < 0.001) as well as between SIAH expression in normal adjacent tissue and patient age (Spearman correlation = −0.59, P < 0.001). No significant correlation was identified between patient age and SIAH expression in tumors (Spearman correlation = −0.23, P = 0.067). In conclusion, SIAH may represent a useful prognostic biomarker that predicts DCIS progression to invasive breast cancer.     

High IKKα expression is associated with reduced time to recurrence and cancer specific survival in oestrogen receptor (ER)‐positive breast cancer

The aim of our study was to examine the relationship between tumour IKKα expression and breast cancer recurrence and survival. Immunohistochemistry was employed in a discovery and a validation tissue microarray to assess the association of tumour IKKα expression and clinico‐pathological characteristics. After siRNA‐mediated silencing of IKKα, cell viability and apoptosis were assessed in MCF7 and MDA‐MB‐231 breast cancer cells. In both the discovery and validation cohorts, associations observed between IKKα and clinical outcome measures were potentiated in oestrogen receptor (ER) positive Luminal A tumours. In the discovery cohort, cytoplasmic IKKα was associated with disease‐free survival (p = 0.029) and recurrence‐free survival on tamoxifen (p < 0.001) in Luminal A tumours. Nuclear IKKα and a combination of cytoplasmic and nuclear IKKα (total tumour cell IKKα) were associated with cancer‐specific survival (p = 0.012 and p = 0.007, respectively) and recurrence‐free survival on tamoxifen (p = 0.013 and p < 0.001, respectively) in Luminal A tumours. In the validation cohort, cytoplasmic IKKα was associated with cancer‐specific survival (p = 0.023), disease‐free survival (p = 0.002) and recurrence‐free survival on tamoxifen (p = 0.009) in Luminal A tumours. Parallel experiment with breast cancer cells in vitro demonstrated the non‐canonical NF‐κB pathway was inducible by exposure to lymphotoxin in ER‐positive MCF7 cells and not in ER‐negative MDA‐MB‐231 cells. Reduction in IKKα expression by siRNA transfection increased levels of apoptosis and reduced cell viability in MCF7 but not in MDA‐MB‐231 cells. IKKα is an important determinant of poor outcome in patients with ER‐positive invasive ductal breast cancer and thus may represent a potential therapeutic target.     

Macroautophagy inhibition sensitizes tamoxifen-resistant breast cancer cells and enhances mitochondrial depolarization

Macroautophagy (autophagy), a process for lysosomal degradation of organelles and long-lived proteins, has been linked to various pathologies including cancer and to the cellular response to anticancer therapies. In the human estrogen receptor positive MCF7 breast adenocarcinoma cell line, treatment with the endocrine therapeutic tamoxifen was shown previously to induce cell cycle arrest, cell death, and autophagy. To investigate specifically the role of autophagy in tamoxifen treated breast cancer cell lines, we used a siRNA approach, targeting three different autophagy genes, Atg5, Beclin-1, and Atg7. We found that knockdown of autophagy, in combination with tamoxifen in MCF7 cells, results in decreased cell viability concomitant with increased mitochondrial-mediated apoptosis. The combination of autophagy knockdown and tamoxifen treatment similarly resulted in reduced cell viability in the breast cancer cell lines, estrogen receptor positive T-47D and tamoxifen-resistant MCF7-HER2. Together, these results indicate that autophagy has a primary pro-survival role following tamoxifen treatment, and suggest that autophagy knockdown may be useful in a combination therapy setting to sensitize breast cancer cells, including tamoxifen-resistant breast cancer cells, to tamoxifen therapy. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Circumvention of tamoxifen resistance by the pure anti-estrogen ICI 182, 780

Both primary and acquired resistance to the growth-inhibitory effects of anti-estrogens (e.g., tamoxifen) limits the clinical usefulness of these drugs in the treatment of breast cancer. The new, steroidal anti-estrogen ICI 182,780 was tested for its ability to inhibit the proliferation of a tamoxifen-resistant variant of the parental MCF-7 human breast-cancer cell line. Two cell lines cloned from the MCF-7 line were used for these experiments: a tamoxifen-sensitive line, MCF 5-21, and a tamoxifen-resistant line, MCF 5-23. Compared with tamoxifen, ICI 182,780 appeared to be 150 and 1540 times more effective in inhibiting cell growth in the 5-21 and 5-23 sub-lines respectively. ICI 182,780 completely circumvented tamoxifen resistance at a concentration of (5 to 10) × 10^?9 M in this model. Based on IC₅₀ concentrations, the 5-23 line was 22-fold more resistant to tamoxifen than the 5-21 line, but only 2-fold more resistant to ICI 182, 780, reducing relative resistance by 10-fold in the resistant line. There were no differences in ER parameters between the 2 lines. ER numbers/cell were: 40500 and 34800 and the K_D 0.48 and 0.15 × 10^?9 M in the 5-21 and 5-23 cells respectively. In the 5-23 cells, the concentrations of ICI 182, 780 and tamoxifen resulting in a 50% inhibition of ³ H-estradiol binding were 2.3 × 10^?8 M and 1 × 10^?6 M, respectively (cf. estradiol 0.89 × 10^?9 M). Thus, one potential mechanism for the increased effectiveness of ICI 182,780 may relate to the increased affinity of this drug for the estrogen receptor as compared with tamoxifen.     

p53 expression status is a significant molecular marker in predicting the time to endocrine therapy failure in recurrent breast cancer: a cohort study

Background Hormone receptor status has been one of the most important factors in predicting the response to endocrine therapy in breast cancer patients. However, half of those patients with estrogen receptor-positive tumors do not respond to endocrine therapy. There have been no universal factors for predicting resistance to endocrine therapy in this population. Recently, p53 status has been extensively used as a predictive factor for response to systemic therapy, because tumor cells lacking p53 function do not respond to systemic therapy due to a failure in apoptosis. We therefore studied the relationship between the efficacy of endocrine therapy and biological factors, including p53. Methods The expression of p53, Ki67, and human epidermal growth factor receptor (HER)2 was examined by immunostaining in the primary tumors of 53 patients who received endocrine therapy for recurrent or advanced breast cancer. The following clinical factors were also analyzed: site treated, disease-free interval, and response to first-line endocrine therapy. To evaluate the significance of these factors, time to endocrine therapy failure (TTEF), or the total duration of sequential endocrine therapies was adopted as representing the clinical outcome. Results The median TTEF was 16.1 months (range, 2.5–89.9 months). Multivariate analysis showed significantly reduced TTEF associated with no response to first-line endocrine therapy (P = 0.006 and P = 0.002 in all patients and in recurrent patients, respectively) and associated with positive p53 expression (P = 0.066 and P = 0.004, respectively). Conclusion p53 expression status was a significant molecular marker as well as the response to first-line endocrine therapy for predicting TTEF in recurrent breast cancer with hormone-sensitive disease.     

Tumor‐associated macrophages secrete CC‐chemokine ligand 2 and induce tamoxifen resistance by activating PI3K/Akt/mTOR in breast cancer

Breast cancer is the most prevalent malignancy among women. Although endocrine therapy is effective, the development of endocrine resistance is a major clinical challenge. The tumor microenvironment (TME) promotes tumor malignancy, and tumor‐associated macrophages (TAM) within the TME play a crucial role in endocrine resistance. Herein, we aimed to elucidate the relationship between TAM and the endocrine‐resistant phenotype of breast cancer. Macrophages were cultured with conditioned medium (CM) from tamoxifen‐sensitive (MCF7‐S) or ‐resistant (MCF7‐R) MCF7 breast cancer cells. M2 polarization was detected by CD163 immunofluorescence. To determine the effect on endocrine resistance, MCF7 cells were cultured in the supernatant of different TAM, and then treated with tamoxifen. CC‐chemokine ligand 2 (CCL2) immunohistochemistry was carried out on pathological sections from 100 patients with invasive estrogen receptor‐positive breast cancer. We found that macrophages cultured in the CM of MCF7‐S and MCF7‐R cells were induced into TAM, with a more obvious M2 polarization in the latter. Tamoxifen resistance was increased by culture in TAM medium. TAM secreted CCL2, which increased endocrine resistance in breast cancer cells through activation of the PI3K/Akt/mTOR signaling pathway. High expression of CCL2 was correlated with infiltration of CD163+macrophages (r = 0.548, P < .001), and patients with high CCL2 expression presented shorter progression‐free survival than those with low CCL2 expression (P < .05). We conclude that CCL2 secreted by TAM activates PI3K/Akt/mTOR signaling and promotes an endocrine resistance feedback loop in the TME, suggesting that CCL2 and TAM may be novel therapeutic targets for patients with endocrine‐resistant breast cancer.     

High protein expression of EZH2 is related to unfavorable outcome to tamoxifen in metastatic breast cancer

BackgroundMetastatic breast cancer (MBC) is a highly heterogeneous disease with great differences in outcome to both chemo- and endocrine therapy. Better insight into the mechanisms underlying resistance is essential to better predict outcome to therapy and to obtain a more tailored treatment approach. We have previously described that increased mRNA expression levels of Enhancer of Zeste homolog (EZH2) are associated with worse outcome to tamoxifen therapy in MBC. Here, we explored whether this is also the case for EZH2 protein expression.Patients and methodsA tissue microarray (TMA) was created using formalin-fixed, paraffin-embedded estrogen receptor (ER)-positive primary breast tumor tissues of 250 MBC patients treated with first-line tamoxifen. Quantity and intensity of EZH2 expression were determined by immunohistochemistry (IHC) and both were used to generate and group scores according to a previously described method for scoring EZH2.ResultsIn total, 116 tumors (46%) were considered to be EZH2 positive. The presence of EZH2 protein expression was significantly associated with progression-free survival (PFS) in both univariate [hazard ratio (HR) 1.51, 95% confidence interval (CI) 1.17–1.97, P = 0.002] and multivariate analysis including traditional factors associated with tamoxifen outcome (HR 1.41, 95% CI 1.06–1.88, P = 0.017). Considering quantity irrespective of intensity, tumors with >50% EZH2-positive cells had the worst PFS (HR 2.15, 95% CI 1.42–3.27, P < 0.001), whereas intensity alone did not show a significant association with PFS. Application of other methods of scoring EZH2 positivity resulted in a similar significant association between the amount of EZH2 positive cells and PFS.ConclusionIn addition to EZH2 mRNA levels, these results suggest that protein expression of EZH2 can be used as a marker to predict outcome to tamoxifen therapy. This provides new rationale to explore EZH2 inhibition in the clinical setting and increases the possibilities for a more personalized treatment approach in MBC patients.     

G-protein-coupled estrogen receptor GPR30 and tamoxifen resistance in breast cancer

Recently, we have shown that the new G-protein-coupled estrogen receptor GPR30 plays an important role in the development of tamoxifen resistance in vitro. This study was undertaken to evaluate the correlation between GPR30 and tamoxifen resistance in breast cancer patients. GPR30 protein expression was evaluated by immunohistochemical analysis in 323 patients with primary operable breast cancer. The association between GPR30 expression and tamoxifen resistance was confirmed in a second cohort of 103 patients treated only with tamoxifen. Additionally, we evaluated GPR30 expression in 33 primary tumors and in recurrent tumors from the same patients. GPR30 expression was detected in 56.7% of the breast cancer specimens investigated and it correlated with overexpression of HER-2 (P = 0.021), EGFR (P = 0.024) and lymph node status (P = 0.047). In a first cohort, survival analysis showed that GPR30 was negatively correlated with relapse-free survival (RFS) only in patients treated with tamoxifen (tamoxifen with or without chemotherapy). GPR30 expression was associated with shorter RFS (HR = 1.768; 95% CI, 1.156–2.703; P = 0.009). In a subset of patients treated only with tamoxifen, multivariate analysis revealed that GPR30 expression is an independent unfavorable factor for RFS (HR = 4.440; 95% CI, 1.408–13.997; P = 0.011). In contrast, GPR30 tended to be a favorable factor regarding RFS in patients who did not receive tamoxifen. In 33 paired biopsies obtained before and after adjuvant therapy, GPR30 expression significantly increased only under tamoxifen treatment (P = 0.001). GPR30 expression in breast cancer independently predicts a poor RFS in patients treated with tamoxifen.     

Downregulation of ER-α36 expression sensitizes HER2 overexpressing breast cancer cells to tamoxifen

Tamoxifen provided a successful treatment for ER-positive breast cancer for many years. However, HER2 overexpressing breast cancer cells respond poorly to tamoxifen therapy presumably by pass. The molecular mechanisms underlying development of tamoxifen resistance have not been well established. Recently, we reported that breast cancer cells with high levels of ER-α36, a variant of ER-α, were resistant to tamoxifen and knockdown of ER-α36 expression in tamoxifen resistant cells with the shRNA method restored tamoxifen sensitivity, indicating that gained ER-α36 expression is one of the underlying mechanisms of tamoxifen resistance. Here, we found that tamoxifen induced expression of ER-α36-EGFR/HER2 positive regulatory loops and tamoxifen resistant MCF7 cells (MCF7/TAM) expressed enhanced levels of the loops. Disruption of the ER-α36-EGFR/HER2 positive regulatory loops with the dual tyrosine kinase inhibitor Lapatinib or ER-α36 down-regulator Broussoflavonol B in tamoxifen resistant MCF7 cells restored tamoxifen sensitivity. In addition, we also found both Lapatinib and Broussoflavonol B increased the growth inhibitory activity of tamoxifen in tumorsphere cells derived from MCF7/TAM cells. Our results thus demonstrated that elevated expression of the ER-α36-EGFR/HER2 loops is one of the mechanisms by which ER-positive breast cancer cells escape tamoxifen therapy. Our results thus provided a rational to develop novel therapeutic approaches for tamoxifen resistant patients by targeting the ER-α36-EGFR/HER2 loops.     

E-cadherin mediates the aggregation of breast cancer cells induced by tamoxifen and epidermal growth factor

In the present study, we evaluated the ability of 4-hydroxytamoxifen (OHT) and epidermal growth factor (EGF) to regulate homotypic adhesion in MCF7 breast cancer cells. Our results demonstrate that OHT and EGF activate the E-cadherin promoter, increase E-cadherin mRNA and protein expression and enhance homotypic aggregation of MCF7 cells. Interestingly, an ERα and EGFR cross-talk is involved in the E-cadherin expression by OHT and EGF, as demonstrated by knocking down either receptor. On the basis of our findings, the well-established cross-talk between ERα and EGFR could be extended to the modulation of E-cadherin expression by OHT and EGF. Thus, the potential ability of tamoxifen to induce cell–cell aggregation may contribute to the biologic response of pharmacologic intervention in patients with breast cancer.     

Sensitivity to further endocrine therapy is retained following progression on first-line fulvestrant

Summary There is a need for new endocrine agents that lack cross-resistance with currently available treatments to extend the endocrine treatment window and delay the need for cytotoxic chemotherapy. This retrospective analysis evaluated the response of postmenopausal patients with previously untreated metastatic/locally advanced breast cancer to further endocrine treatment following progression on first-line fulvestrant or tamoxifen. Patients received fulvestrant 250 mg (intramuscular injection every 28 days) plus matching tamoxifen placebo (once daily), or tamoxifen 20 mg (orally once daily) plus matching fulvestrant placebo (every 28 days) in a double-blind, randomized, phase III trial. Treatment continued until disease progression or withdrawal, when further endocrine therapy was initiated (at the treating physician’s discretion). Information regarding subsequent therapies and responses was obtained by follow-up questionnaire. Two-hundred-and-forty-five questionnaires were returned (from 587 patients), 149 of which yielded follow-up data on patients receiving second-line endocrine therapy following fulvestrant (n=83) and tamoxifen (n=66). Second-line therapy produced objective responses (OR) in 6/44 (13.6%) and clinical benefit (CB) in 25/44 (56.8%) patients who had CB with fulvestrant and produced OR in 5/41 (12.2%) patients and CB in 27/41 (65.8%) patients who had CB with first-line tamoxifen. For patients deriving no CB from trial therapy, second-line therapy produced OR in 3/39 (7.7%) and CB in 15/39 (38.5%) patients in the fulvestrant group and OR in 4/25 (16.0%) and CB in 12/25 (48.0%) patients in the tamoxifen group. Results from this questionnaire-based study suggest that postmenopausal women with advanced breast cancer who respond to first-line fulvestrant or tamoxifen retain sensitivity to subsequent endocrine therapy.     

Urokinase-type plasminogen activator system in breast cancer: association with tamoxifen therapy in recurrent disease

The prognostic value of components of the urokinase-type plasminogen activator (uPA) system, its receptor uPAR (CD87), and plasminogen activator inhibitors PAI-1 and PAI-2 is well established. We studied the predictive value of these proteolytic factors by evaluating the association of their tumor expression level and the efficacy of tamoxifen therapy in patients with recurrent breast cancer. The antigen levels of the four factors were determined by ELISA in cytosols prepared from estrogen receptor-positive primary breast tumors of 691 hormone-naive breast cancer patients with recurrent disease and treated with tamoxifen as first-line systemic therapy. High tumor levels of uPA (P < 0.001), uPAR (P < 0.01), and PAI-1 (P = 0.01) were associated with a lower efficacy of tamoxifen therapy. In the multivariable analysis, uPA (P < 0.001) provided additional information independent of the traditional predictive factors to predict benefit from tamoxifen therapy. High levels of uPA, uPAR, and PAI-1 predicted a shorter progression-free survival (PFS) on tamoxifen in an analysis of the first 9 months of therapy. However in the analysis during the total follow-up period, high PAI-2 levels (P = 0.01) showed a longer response to tamoxifen. In conclusion, uPA, uPAR, and PAI-1, components of the urokinase system, are predictive for the efficacy of tamoxifen therapy in patients treated for recurrent breast cancer. Knowledge of their tumor expression levels might be helpful for future individualized therapy protocols, including possible new-targeted therapies based on the interference in the urokinase system.     

Gene expression preferentially regulated by tamoxifen in breast cancer cells and correlations with clinical outcome

The beneficial effect of the selective estrogen receptor (ER) modulator tamoxifen in the treatment and prevention of breast cancer is assumed to be through its ability to antagonize the stimulatory actions of estrogen, although tamoxifen can also have some estrogen-like agonist effects. Here, we report that, in addition to these mixed agonist/antagonist actions, tamoxifen can also selectively regulate a unique set of >60 genes, which are minimally regulated by estradiol (E2) or raloxifene in ERalpha-positive MCF-7 human breast cancer cells. This gene regulation by tamoxifen is mediated by ERalpha and reversed by E2 or ICI 182,780. Introduction of ERbeta into MCF-7 cells reverses tamoxifen action on approximately 75% of these genes. To examine whether these genes might serve as markers of tamoxifen sensitivity and/or the development of resistance, their expression level was examined in breast cancers of women who had received adjuvant therapy with tamoxifen. High expression of two of the tamoxifen-stimulated genes, YWHAZ/14-3-3z and LOC441453, was found to correlate significantly with disease recurrence following tamoxifen treatment in women with ER-positive cancers and hence seem to be markers of a poor prognosis. Our data indicate a new dimension in tamoxifen action, involving gene expression regulation that is tamoxifen preferential, and identify genes that might serve as markers of tumor responsiveness or resistance to tamoxifen therapy. This may have a potential effect on the choice of tamoxifen versus aromatase inhibitors as adjuvant endocrine therapy.     

Selective estrogen receptor modulators: discrimination of agonistic versus antagonistic activities by gene expression profiling in breast cancer cells

Selective estrogen receptor modulators (SERMs) such as tamoxifen are effective in the treatment of many estrogen receptor-positive breast cancers and have also proven to be effective in the prevention of breast cancer in women at high risk for the disease. The comparative abilities of tamoxifen versus raloxifene in breast cancer prevention are currently being compared in the Study of Tamoxifen and Raloxifene trial. To better understand the actions of these compounds in breast cancer, we have examined their effects on the expression of approximately 12,000 genes, using Affymetrix GeneChip microarrays, with quantitative PCR verification in many cases, categorizing their actions as agonist, antagonist, or partial agonist/antagonist. Analysis of gene stimulation and inhibition by the SERMs trans-hydroxytamoxifen (TOT) and raloxifene (Ral) or ICI 182,780 (ICI) and by estradiol (E2) in estrogen receptor-containing MCF-7 human breast cancer cells revealed that (a) TOT was the most E2-like of the three compounds, (b) all three compounds either partially or fully antagonized the action of E2 on most genes, with the order of antagonist activity being ICI > Ral > TOT, (c) TOT and Ral, but not ICI, displayed partial agonist/partial antagonist activity on a number of E2-regulated genes, (d) several stimulatory cell cycle-related genes were down-regulated exclusively by ICI, (e) the estrogen-like activity of Ral nearly always overlapped with that of TOT, indicating that Ral has little unique agonist activity different from that of TOT, and (f) some genes were specifically up-regulated by TOT but not Ral, ICI, or E2. Hence, gene expression profiling can discern fundamental differences among SERMs and provides insight into the distinct biologies of TOT, Ral, and ICI in breast cancer.