Third annual William L. McGuire Memorial Lecture. "Studies on the estrogen receptor in breast cancer"--20 years as a target for the treatment and prevention of cancer

Antiprogestins for breast cancer treatment: We are almost ready

The development of antiprogestins was initially a gynecological purpose. However, since mifepristone was developed, its application for breast cancer treatment was immediately proposed. Later, new compounds with lower antiglucocorticoid and antiandrogenic effects were developed to be applied to different pathologies, including breast cancer. We describe herein the studies performed in the breast cancer field with special focus on those reported in recent years, ranging from preclinical biological models to those carried out in patients. We highlight the potential use of antiprogestins in breast cancer prevention in women with BRCA1 mutations, and their use for breast cancer treatment, emphasizing the need to elucidate which patients will respond. In this sense, the PR isoform ratio has emerged as a possible tool to predict antiprogestin responsiveness. The effects of combined treatments of antiprogestins together with other drugs currently used in the clinic, such as tamoxifen, CDK4/CDK6 inhibitors or pembrolizumab in preclinical models is discussed since it is in this scenario that antiprogestins will be probably introduced. Finally, we explain how transcriptomic or proteomic studies, that were carried out in different luminal breast cancer models and in breast cancer samples that responded or were predicted to respond to the antiprogestin therapy, show a decrease in proliferative pathways. Deregulated pathways intrinsic of each model are discussed, as well as how these analyses may contribute to a better understanding of the mechanisms involved.

Update Breast Cancer 2021 Part 5 – Advanced Breast Cancer

Despite the COVID 19 pandemic and mostly virtual congresses, innovation in the treatment of breast cancer patients continues at an unabated pace. This review summarises the current developments. Initial overall survival data for CDK4/6 inhibitor treatment in combination with an aromatase inhibitor as the first advanced line of therapy in treatment-naive postmenopausal patients have been published. Similarly, a trial comparing trastuzumab-deruxtecan versus trastuzumab-emtansine revealed a clear benefit regarding progression-free survival. Understanding of biomarkers making checkpoint inhibitor therapy particularly effective is increasing, and new compounds such as oral selective estrogen receptor destabilisers (SERDs) are entering clinical development and completing the first phase III trials.

Tristetraprolin: A cytosolic regulator of mRNA turnover moonlighting as transcriptional corepressor of gene expression

Tristetraprolin (TTP) is a nucleocytoplasmic 326 amino acid protein whose sequence is characterized by possessing two CCCH-type zinc finger domains. In the cytoplasm TTP function is to promote the degradation of mRNAs that contain adenylate/uridylate-rich elements (AREs). Mechanistically, TTP promotes the recruitment of poly(A)-specific deadenylases and exoribonucleases. By reducing the half-life of about 10% of all the transcripts in the cell TTP has been shown to participate in multiple cell processes that include regulation of gene expression, cell proliferation, metabolic homeostasis and control of inflammation and immune responses. However, beyond its role in mRNA decay, in the cell nucleus TTP acts as a transcriptional coregulator by interacting with chromatin modifying enzymes. TTP has been shown to repress the transactivation of NF-κB and estrogen receptor suggesting the possibility that it participates in the transcriptional regulation of hundreds of genes in human cells and its possible involvement in breast cancer progression. In this review, we discuss the cytoplasmic and nuclear functions of TTP and the effect of the dysregulation of its protein levels in the development of human diseases. We suggest that TTP be classified as a moonlighting tumor supressor protein that regulates gene expression through two different mechanims; the decay of ARE-mRNAs and a transcriptional coregulatory function.

An H3K4me3 reader, BAP18 as an adaptor of COMPASS-like core subunits co-activates ERα action and associates with the sensitivity of antiestrogen in breast cancer

Estrogen receptor alpha (ERα) signaling pathway is essential for ERα-positive breast cancer progression and endocrine therapy resistance. Bromodomain PHD Finger Transcription Factor (BPTF) associated protein of 18kDa (BAP18) has been recognized as a crucial H3K4me3 reader. However, the whole genomic occupation of BAP18 and its biological function in breast cancer is still elusive. Here, we found that higher expression of BAP18 in ERα-positive breast cancer is positively correlated with poor prognosis. ChIP-seq analysis further demonstrated that the half estrogen response elements (EREs) and the CCCTC binding factor (CTCF) binding sites are the significant enrichment sites found in estrogen-induced BAP18 binding sites. Also, we provide the evidence to demonstrate that BAP18 as a novel co-activator of ERα is required for the recruitment of COMPASS-like core subunits to the cis-regulatory element of ERα target genes in breast cancer cells. BAP18 is recruited to the promoter regions of estrogen-induced genes, accompanied with the enrichment of the lysine 4-trimethylated histone H3 tail (H3K4me3) in the presence of E2. Furthermore, BAP18 promotes cell growth and associates the sensitivity of antiestrogen in ERα-positive breast cancer. Our data suggest that BAP18 facilitates the association between ERα and COMPASS-like core subunits, which might be an essential epigenetic therapeutic target for breast cancer.

IFI27/ISG12 Downregulates Estrogen Receptor α Transactivation by Facilitating Its Interaction With CRM1/XPO1 in Breast Cancer Cells

The estrogen receptor alpha (ERα) is a ligand-activated transcription factor whose activity is modulated by its interaction with multiple protein complexes. In this work, we have identified the protein interferon alpha inducible protein 27 (IFI27/ISG12) as a novel ERα-associated protein. IFI27/ISG12 transcription is regulated by interferon and estradiol and its overexpression is associated to reduced overall survival in ER+ breast cancer patients but its function in mammary gland tissue remains elusive. In this study we showed that overexpression of IFI27/ISG12 in breast cancer cells attenuates ERα transactivation activity and the expression of ERα-dependent genes. Our results demonstrated that IFI27/ISG12 overexpression in MCF-7 cells reduced their proliferation rate in 2-D and 3-D cell culture assays and impaired their ability to migrate in a wound-healing assay. We show that IFI27/ISG12 downregulation of ERα transactivation activity is mediated by its ability to facilitate the interaction between ERα and CRM1/XPO1 that mediates the nuclear export of large macromolecules to the cytoplasm. IFI27/ISG12 overexpression was shown to impair the estradiol-dependent proliferation and tamoxifen-induced apoptosis in breast cancer cells. Our results suggest that IFI27/ISG12 may be an important factor in regulating ERα activity in breast cancer cells by modifying its nuclear versus cytoplasmic protein levels. We propose that IFI27/ISG12 may be a potential target of future strategies to control the growth and proliferation of ERα-positive breast cancer tumors.

Expression pattern of estroprogestinic receptors in sinonasal inverted papilloma

Inverted papilloma (IP) is a locally destructive, benign neoplasm of the nose and paranasal sinuses with a high tendency for recurrence, a significant potential for malignancy, and an etiology that today is still uncertain. The expression of hormonal receptors in neoplastic tissues has been the focus of intensive research for its potential diagnostic, prognostic, and therapeutic significance. The aim of this study was to assess the potential estroprogestinic receptor expression in patients undergoing sinus surgery for IP. A retrospective study was carried out, on surgical specimens of 73 patients who underwent endoscopic sinus surgery for first manifestation of sinonasal IP (primitive IP group) and in 21 subjects who had developed a recurrence (relapsed IP group). The results of the immunohistochemical analysis of the first group showed the absence of receptor expression for PGR in all cases analyzed and the presence of a low positivity for ER in 11 cases (P > 0.082). Similarly, in the second group the results showed a low presence of ER receptors in 3 of the 21 cases (P > 0.068), while there was no evidence of PGR receptors in the examined samples. In addition, in 11 of the cases only 3 were considered positive (27.2%) showing a recurrence during follow-up (P > 0.068).

Our results suggest that the sinonasal IP is a benign tumor independent of estrogen and progesterone, and the receptors for these hormones are therefore unsuitable as predictors of relapse or possible prognostic indicators and therapeutic targets.

Changes in Serum Lipid and Lipoprotein Levels in Postmenopausal Patients with Node-Positive Breast Cancer Treated with Tamoxifen

Tamoxifen has been used for a long time as an adjuvant hormonal treatment in breast cancer patients. We studied 62 newly diagnosed postmenopausal women, aged 50-79 years, with node-positive breast cancer and receiving adjuvant tamoxifen (20 mg per day). Total serum cholesterol, triglycerides, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol, apo AI, apo AII, apo B and Lp(a) were determined before the surgery and 3, 6, 9, 12 and 24 months after starting tamoxifen treatment. Tamoxifen significantly reduced total serum cholesterol (6.13+/-1.20 mmol/L vs 5.21+/-1.05 mmol/L) (P <0.01), LDL-cholesterol (3.72+/-0.70 mmol/L vs 2.93+/-0.51) (P <0.01) and Lp(a) (0.11+/-0.07 g/L vs 0.02+/-0.01 g/L) (P < 0.01). There were no changes in triglycerides or HDL-cholesterol serum levels during tamoxifen treatment. The results indicate that an additional beneficial effect of adjuvant tamoxifen therapy may be that it decreases cardiovascular risk in such patients.

Hypoxia and Hormone-Mediated Pathways Converge at the Histone Demethylase KDM4B in Cancer

Hormones play an important role in pathophysiology. The hormone receptors, such as estrogen receptor alpha and androgen receptor in breast cancer and prostate cancer, are critical to cancer cell proliferation and tumor growth. In this review we focused on the cross-talk between hormone and hypoxia pathways, particularly in breast cancer. We delineated a novel signaling pathway from estrogen receptor to hypoxia-inducible factor 1, and discussed the role of this pathway in endocrine therapy resistance. Further, we discussed the estrogen and hypoxia pathways converging at histone demethylase KDM4B, an important epigenetic modifier in cancer.

Phosphatidylinositol-3 Kinase Inhibitors, Buparlisib and Alpelisib, Sensitize Estrogen Receptor-positive Breast Cancer Cells to Tamoxifen

Tamoxifen is the standard first-line hormonal therapy for premenopausal women with estrogen receptor (ER)-positive metastatic breast cancer (BC). One of the crucial mechanisms underlying hormonal therapy resistance is the collateral activation of the phosphatidylinositol-3 kinase (PI3K)/AKT pathway. We explored whether PI3K inhibitors, buparlisib and alpelisib, enhance the efficacy of tamoxifen against ER-positive BC cells. We have observed a synergism between alpelisib or buparlisib and tamoxifen in the treatment for ER-positive BC cell lines harboring different PI3K alterations. Immunoblotting analysis showed alpelisib, buparlisib, or either drug in combination with tamoxifen downregulated the PI3K downstream targets in the MCF-7 and ZR75-1 cells. In the MCF-7 cells transfected with a constitutive active (myristoylated) AKT1 construct or mutant ER, the synergistic effect between alpelisib and tamoxifen was markedly attenuated, indicating that synergism depends on AKT inhibition or normally functioning ER. Combining alpelisib or buparlisib with tamoxifen also attenuated MCF-7 tumor growth in Balb/c nude mice. Our data suggest that additional PI3K blockade might be effective in enhancing the therapeutic effect of tamoxifen in ER-positive BC and support the rationale combination in clinical trials.

Nuclear tristetraprolin acts as a corepressor of multiple steroid nuclear receptors in breast cancer cells

Tristetraprolin (TTP) is a 34-kDa, zinc finger-containing factor that in mammalian cells acts as a tumor suppressor protein through two different mechanisms. In the cytoplasm TTP promotes the decay of hundreds of mRNAs encoding cell factors involved in inflammation, tissue invasion, and metastasis. In the cell nucleus TTP has been identified as a transcriptional corepressor of the estrogen receptor alpha (ERα), which has been associated to the development and progression of the majority of breast cancer tumors. In this work we report that nuclear TTP modulates the transactivation activity of progesterone receptor (PR), glucocorticoid receptor (GR) and androgen receptor (AR). In recent years these steroid nuclear receptors have been shown to be of clinical and therapeutical relevance in breast cancer. The functional association between TTP and steroid nuclear receptors is supported by the finding that TTP physically interacts with ERα, PR, GR and AR in vivo. We also show that TTP overexpression attenuates the transactivation of all the steroid nuclear receptors tested. In contrast, siRNA-mediated reduction of endogenous TTP expression in MCF-7 cells produced an increase in the transcriptional activities of ERα, PR, GR and AR. Taken together, these results suggest that the function of nuclear TTP in breast cancer cells is to act as a corepressor of ERα, PR, GR and AR. We propose that the reduction of TTP expression observed in different types of breast cancer tumors may contribute to the development of this disease by producing a dysregulation of the transactivation activity of multiple steroid nuclear receptors.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

Estrogen receptor-α directly regulates the hypoxia-inducible factor 1 pathway associated with antiestrogen response in breast cancer

A majority of breast cancers are driven by estrogen via estrogen receptor-α (ERα). Our previous studies indicate that hypoxia-inducible factor 1α (HIF-1α) cooperates with ERα in breast cancer cells. However, whether ERα is implicated in the direct regulation of HIF-1α and the role of HIF-1α in endocrine therapy response are unknown. In this study we found that a subpopulation of HIF-1α targets, many of them bearing both hypoxia response elements and estrogen response elements, are regulated by ERα in normoxia and hypoxia. Interestingly, the HIF-1α gene itself also bears an estrogen response element, and its expression is directly regulated by ERα. Clinical data revealed that expression of the HIF-1α gene or a hypoxia metagene signature is associated with a poor outcome to endocrine treatment in ERα(+) breast cancer. HIF-1α was able to confer endocrine therapy resistance to ERα(+) breast cancer cells. Our findings define, for the first time to our knowledge, a direct regulatory pathway between ERα and HIF-1α, which might modulate hormone response in treatment.

Novel role for PINX1 as a coregulator of nuclear hormone receptors

Estrogen receptor alpha (ERα) has an established role in breast cancer biology. Transcriptional activation by ERα is a multistep process influenced by coactivator and corepressor proteins. This work shows that Pin2 interacting protein 1 (PINX1) interacts with the N-terminal domain of ERα and functions as a corepressor of ERα. Furthermore, it represses both AF-1 and AF-2 transcriptional activities. Chromatin immunoprecipitation assays verified that the interaction between ERα and PINX1 occurs on E2 regulated promoters and enhanced expression of PINX1 deregulates the expression of a number of genes that have a role in cell growth and proliferation in breast cancer. PINX1 overexpression decreases estrogen mediated proliferation of breast cancer cell lines, while its depletion shows the opposite effect. Taken together, these data show a novel molecular mechanism for PINX1 as an attenuator of estrogen receptor activity in breast cancer cell lines, furthering its role as a tumor suppressor gene in breast cancer.

SIP1/NHERF2 enhances estrogen receptor alpha transactivation in breast cancer cells

The estrogen receptor alpha (ERα) is a ligand-activated transcription factor that possesses two activating domains designated AF-1 and AF-2 that mediate its transcriptional activity. The role of AF-2 is to recruit coregulator protein complexes capable of modifying chromatin condensation status. In contrast, the mechanism responsible for the ligand-independent AF-1 activity and for its synergistic functional interaction with AF-2 is unclear. In this study, we have identified the protein Na+/H+ Exchanger RegulatoryFactor 2 (NHERF2) as an ERα-associated coactivator that interacts predominantly with the AF-1 domain of the nuclear receptor. Overexpression of NHERF2 in breast cancer MCF7 cells produced an increase in ERα transactivation. Interestingly, the presence of SRC-1 in NHERF2 stably overexpressing MCF7 cells produced a synergistic increase in ERα activity. We show further that NHERF2 interacts with ERα and SRC-1 in the promoter region of ERα target genes. The binding of NHERF2 to ERα in MCF7 cells increased cell proliferation and the ability of MCF7 cells to form tumors in a mouse model. We analyzed the expression of NHERF2 in breast cancer tumors finding a 2- to 17-fold increase in its mRNA levels in 50% of the tumor samples compared to normal breast tissue. These results indicate that NHERF2 is a coactivator of ERα that may participate in the development of estrogen-dependent breast cancer tumors.

Tristetraprolin represses estrogen receptor α transactivation in breast cancer cells

Estrogen receptor α (ERα) mediates the effects of 17β-estradiol (E2) in normal mammary gland, and it is a key participant in breast cancer tumor development. ERα transactivation activity is mediated by the synergistic interaction of two domains designated AF1 and AF2. The function of AF2 is to recruit coactivator and corepressor proteins that allow ERα to oscillate between the roles of transcriptional activator and repressor. In contrast, the mechanism responsible for AF-1 transcriptional activity is not completely understood. In this study, we identified tristetraproline (TTP) as a novel ERα-associated protein. TTP expression in MCF7 cells repressed ERα transactivation and reduced MCF7 cell proliferation and the ability of the cells to form tumors in a mouse model. We show that TTP transcriptional activity is mediated through its recruitment to the promoter region of ERα target genes and its interaction with histone deacetylases, in particular with HDAC1. TTP expression attenuates the coactivating activity of SRC-1, suggesting that exchange between TTP and other coactivators may play an important role in fine-tuning ERα transactivation. These results indicate that TTP acts as a bona fide ERα corepressor and suggest that this protein may be a contributing factor in the development of E2-dependent tumors in breast cancer.

New insights on the role of hormonal therapy in ovarian cancer

Ovarian cancer (OVCA) is the most lethal gynecological malignancy. It is often diagnosed in advanced stages and despite therapy, 70% relapse within 2years with incurable disease. Regimens with clinical benefit and minimal toxicity are urgently needed. More effective hormonal therapies would be appealing in this setting. Estrogens (E2) are implicated in the etiology of OVCA. Estrogens drive proliferation and anti-estrogens inhibit ovarian cancer growth in vitro and in vivo. Despite estrogen receptor (ER) expression in 67% of OVCAs, small anti-estrogen therapy trials have been disappointing and the benefit of hormonal therapy has not been systematically studied in large well-designed trials. OVCAs often manifest de novo anti-estrogen resistance and those that initially respond invariably develop resistance. Estrogens stimulate ovarian cancer progression by transcriptional activation and cross talk between liganded ER and mitogenic pathways, both of which drive cell cycle progression. Estrogen deprivation and estrogen receptor (ER) blockade cause cell cycle arrest in susceptible OVCAs by increasing the cell cycle inhibitor, p27. This review summarizes and discusses scientific and epidemiological evidence supporting estrogen's role in ovarian carcinogenesis, provides an overview of clinical trials of ER blockade and aromatase inhibitors in OVCA and reviews potential causes of antiestrogen resistance. Anti-estrogen resistance was recently shown to be reversed by dual ER and Src signaling blockade. Blocking cross-talk between ER and constitutively activated kinase pathways may improve anti-estrogen therapeutic efficacy in OVCA, as has been demonstrated in other cancers. Novel strategies to improve benefit from anti-estrogens by combining them with targeted therapies are reviewed.

Degradation of epidermal growth factor receptor mediates dasatinib-induced apoptosis in head and neck squamous cell carcinoma cells

Epidermal growth factor receptor (EGFR) is an important oncoprotein that promotes cell growth and proliferation. Dasatinib, a bcr-abl inhibitor, has been approved clinically for the treatment of chronic myeloid leukemia and demonstrated to be effective against solid tumors in vitro through Src inhibition. Here, we disclose that EGFR degradation mediated dasatinib-induced apoptosis in head and neck squamous cell carcinoma (HNSCC) cells. HNSCC cells, including Ca9-22, FaDu, HSC3, SAS, SCC-25, and UMSCC1, were treated with dasatinib, and cell viability, apoptosis, and underlying signal transduction were evaluated. Dasatinib exhibited differential sensitivities against HNSCC cells. Growth inhibition and apoptosis were correlated with its inhibition on Akt, Erk, and Bcl-2, irrespective of Src inhibition. Accordingly, we found that down-regulation of EGFR was a determinant of dasatinib sensitivity. Lysosome inhibitor reversed dasatinib-induced EGFR down-regulation, and c-cbl activity was increased by dasatinib, indicating that dasatinib-induced EGFR down-regulation might be through c-cbl-mediated lysosome degradation. Increased EGFR activation by ligand administration rescued cells from dasatinib-induced apoptosis, whereas inhibition of EGFR enhanced its apoptotic effect. Estrogen receptor α (ERα) was demonstrated to play a role in Bcl-2 expression, and dasatinib inhibited ERα at the pretranslational level. ERα was associated with EGFR in dasatinib-treated HNSCC cells. Furthermore, the xenograft model showed that dasatinib inhibited HSC3 tumor growth through in vivo down-regulation of EGFR and ERα. In conclusion, degradation of EGFR is a novel mechanism responsible for dasatinib-induced apoptosis in HNSCC cells.

Transcriptional activation of breast cancer-associated gene 2 by estrogen receptor

RNF115, or Breast Cancer-Associated Gene 2 (BCA2), encodes a RING-finger ubiquitin E3 ligase, expression of which was associated with estrogen receptor (ER)-positive status in human breast tumors. Although the BCA2 promoter contains several estrogen response element (ERE) half-sites, the role of ER in the regulation of BCA2 transcription has not been reported. The aim of this study is to investigate the molecular mechanism by which estrogen regulates BCA2 transcription. BCA2 mRNA and protein levels were examined by RT-PCR and Western blot analysis, respectively, and localization was assessed by immunofluorescence. BCA2 promoter activity in response to E(2) was tested by a dual luciferase reporter assay and ER binding to the BCA2 promoter was examined by chromatin immunoprecipitation assay. We found that BCA2 mRNA and protein levels are regulated by estrogen in ER-positive MCF7 breast cancer cells and MDA MB 231 cells stably transfected with ER. Estrogen treatment in hormonal depleted MCF7 and MDA MB 231/ER stably transfected cells resulted in increased nuclear ER and cytoplasmic and nuclear BCA2 staining. Cycloheximide is not able to inhibit BCA2 mRNA levels, suggesting potential BCA2 regulation at the transcriptional level. Anti-estrogens like tamoxifen and ICI 182 178 counteracted E(2)-induced BCA2 protein and knockdown of ER by ER siRNA resulted in a significant decrease in BCA2 protein and a lower nuclear expression pattern. Estrogen treatment lead to a significant increase in BCA2 promoter response, associated with increased binding of ER to the ERE region of the BCA2 promoter. BCA2 is therefore a newly identified transcriptional target of estrogen receptor.

Adjuvant tamoxifen reduces subsequent breast cancer in women with estrogen receptor-positive ductal carcinoma in situ: a study based on NSABP protocol B-24

PURPOSE

The NSABP (National Surgical Adjuvant Breast and Bowel Project) B-24 study demonstrated significant benefit with adjuvant tamoxifen in patients with ductal carcinoma in situ (DCIS) after lumpectomy and radiation. Patients were enrolled without knowledge of hormone receptor status. The current study retrospectively evaluated the relationship between receptors and response to tamoxifen.

PATIENTS AND METHODS

Estrogen (ER) and progesterone receptors (PgR) were evaluated in 732 patients with DCIS (41% of original study population). An experienced central laboratory determined receptor status in all patient cases with available paraffin blocks (n = 449) by immunohistochemistry (IHC) using comprehensively validated assays. Results for additional patients (n = 283) determined by various methods (primarily IHC) were available from enrolling institutions. Combined results were evaluated for benefit of tamoxifen by receptor status at 10 years and overall follow-up (median, 14.5 years).

RESULTS

ER was positive in 76% of patients. Patients with ER-positive DCIS treated with tamoxifen (v placebo) showed significant decreases in subsequent breast cancer at 10 years (hazard ratio [HR], 0.49; P < .001) and overall follow-up (HR, 0.60; P = .003), which remained significant in multivariable analysis (overall HR, 0.64; P = .003). Results were similar, but less significant, when subsequent ipsilateral and contralateral, invasive and noninvasive, breast cancers were considered separately. No significant benefit was observed in ER-negative DCIS. PgR and either receptor were positive in 66% and 79% of patients, respectively, and in general, neither was more predictive than ER alone.

CONCLUSION

Patients in NSABP B-24 with ER-positive DCIS receiving adjuvant tamoxifen after standard therapy showed significant reductions in subsequent breast cancer. The use of adjuvant tamoxifen should be considered for patients with DCIS.

Relevance of BCAR4 in tamoxifen resistance and tumour aggressiveness of human breast cancer

Background:

Breast cancer anti-oestrogen resistance 4 (BCAR4) was identified in a search for genes involved in anti-oestrogen resistance in breast cancer. We explored whether BCAR4 is predictive for tamoxifen resistance and prognostic for tumour aggressiveness, and studied its function.

Methods:

BCAR4 mRNA levels were measured in primary breast tumours, and evaluated for association with progression-free survival (PFS) and clinical benefit in patients with oestrogen receptor (ERα)-positive tumours receiving tamoxifen as first-line monotherapy for advanced disease. In a separate cohort of patients with lymph node-negative, ERα-positive cancer, and not receiving systemic adjuvant therapy, BCAR4 levels were evaluated for association with distant metastasis-free survival (MFS). The function of BCAR4 was studied with immunoblotting and RNA interference in a cell model.

Results:

Multivariate analyses established high BCAR4 mRNA levels as an independent predictive factor for poor PFS after start of tamoxifen therapy for recurrent disease. High BCAR4 mRNA levels were associated with poor MFS and overall survival, reflecting tumour aggressiveness. In BCAR4-expressing cells, phosphorylation of v-erb-b2 erythroblastic leukaemia viral oncogene homolog (ERBB)2, ERBB3, and their downstream mediators extracellular signal-regulated kinase 1/2 and v-akt murine thymoma viral oncogene homolog (AKT) 1/2, was increased. Selective knockdown of ERBB2 or ERBB3 inhibited proliferation, confirming their role in BCAR4-induced tamoxifen resistance.

Conclusion:

BCAR4 may have clinical relevance for tumour aggressiveness and tamoxifen resistance. Our cell model suggests that BCAR4-positive breast tumours are driven by ERBB2/ERBB3 signalling. Patients with such tumours may benefit from ERBB-targeted therapy.

CITED2 and NCOR2 in anti-oestrogen resistance and progression of breast cancer

Background:

Endocrine therapies of breast cancer are effective but ultimately fail because of the development of treatment resistance. We have previously revealed several genes leading to tamoxifen resistance in vitro by retroviral insertion mutagenesis. To understand the manner in which these genes yield tamoxifen resistance, their effects on global gene expression were studied and those genes resulting in a distinct gene expression profile were further investigated for their clinical relevance.

Methods:

Gene expression profiles of 69 human breast cancer cell lines that were made tamoxifen resistant through retroviral insertion mutagenesis were obtained using oligonucleotide arrays and analysed with bioinformatic tools. mRNA levels of NCOR2 and CITED2 in oestrogen receptor-positive breast tumours were determined by quantitative RT–PCR. mRNA levels were evaluated for association with metastasis-free survival (MFS) in 620 patients with lymph node-negative primary breast cancer who did not receive systemic adjuvant therapy, and with clinical benefit in 296 patients receiving tamoxifen therapy for recurrent breast cancer.

Results:

mRNA expression profiles of most tamoxifen-resistant cell lines were strikingly similar, except for the subgroups of cell lines in which NCOR2 or CITED2 were targeted by the retrovirus. Both NCOR2 and CITED2 mRNA levels were associated with MFS, that is, tumour aggressiveness, independently of traditional prognostic factors. In addition, high CITED2 mRNA levels were predictive for a clinical benefit from first-line tamoxifen treatment in patients with advanced disease.

Conclusions:

Most retrovirally targeted genes yielding tamoxifen resistance in our cell lines do not impose a distinctive expression profile, suggesting that their causative role in cell growth may be accomplished by post-transcriptional processes. The associations of NCOR2 and CITED2 with outcome in oestrogen receptor-positive breast cancer patients underscore the clinical relevance of functional genetic screens to better understand disease progression, which may ultimately lead to the development of improved treatment options.

Tamoxifen induces pleiotrophic changes in mammary stroma resulting in extracellular matrix that suppresses transformed phenotypes

INTRODUCTION

The functional unit of the mammary gland has been defined as the epithelial cell plus its microenvironment, a hypothesis that predicts changes in epithelial cell function will be accompanied by concurrent changes in mammary stroma. To test this hypothesis, the question was addressed of whether mammary stroma is functionally altered by the anti-oestrogen drug tamoxifen.

METHODS

Forty female rats at 70 days of age were randomised to two groups of 20 and treated with 1.0 mg/kg tamoxifen or vehicle subcutaneously daily for 30 days, followed by a three-day wash out period. Mammary tissue was harvested and effects of tamoxifen on mammary epithelium and stroma determined.

RESULTS

As expected, tamoxifen suppressed mammary alveolar development and mammary epithelial cell proliferation. Primary mammary fibroblasts isolated from tamoxifen-treated rats displayed a three-fold decrease in motility and incorporated less fibronectin in their substratum in comparison to control fibroblasts; attributes indicative of fibroblast quiescence. Immunohistochemistry analysis of CD68, a macrophage lysosomal marker, demonstrated a reduction in macrophage infiltration in mammary glands of tamoxifen-treated rats. Proteomic analyses by mass spectrometry identified several extracellular matrix (ECM) proteins with expression levels with tamoxifen treatment that were validated by Western blot. Mammary tissue from tamoxifen-treated rats had decreased fibronectin and increased collagen 1 levels. Further, ECM proteolysis was reduced in tamoxifen-treated rats as detected by reductions in fibronectin, laminin 1, laminin 5 and collagen 1 cleavage fragments. Consistent with suppression in ECM proteolysis with tamoxifen treatment, matrix metalloproteinase-2 levels and activity were decreased. Biochemically extracted mammary ECM from tamoxifen-treated rats suppressed in vitro macrophage motility, which was rescued by the addition of proteolysed collagen or fibronectin. Mammary ECM from tamoxifen-treated rats also suppressed breast tumour cell motility, invasion and haptotaxis, reduced organoid size in 3-dimensional culture and blocked tumour promotion in an orthotopic xenograft model; effects which could be partially reversed by the addition of exogenous fibronectin.

CONCLUSIONS

These data support the hypothesis that mammary stroma responds to tamoxifen treatment in concert with the epithelium and remodels to a microenvironment inhibitory to tumour cell progression. Reduced fibronectin levels and reduced ECM turnover appear to be hallmarks of the quiescent mammary microenvironment. These data may provide insight into attributes of a mammary microenvironment that facilitate tumour dormancy.

Parallel RNAi and compound screens identify the PDK1 pathway as a target for tamoxifen sensitization

Tamoxifen is the most commonly used drug to treat breast cancer and acts by blocking ERalpha (oestrogen receptor alpha) signalling. Although highly effective, its usefulness is limited by the development of resistance. Given this, strategies that limit resistance by sensitizing cells to tamoxifen may be of use in the clinic. To gain insight into how this might be achieved, we used chemical and genetic screens to identify targets and small-molecule inhibitors that cause tamoxifen sensitization. A high-throughput genetic screen, using an RNA interference library targeting 779 kinases and related proteins, identified the PDK1 (phosphoinositide-dependent kinase 1) signalling pathway as a strong determinant of sensitivity to multiple ERalpha antagonists, including tamoxifen. A chemical screen using existing drugs and known kinase inhibitors also identified inhibitors of the PDK1 pathway, including triciribine and tetrandrine. Aside from identifying novel agents and targets for tamoxifen sensitization, this approach also provides evidence that performing chemical and genetic screens in parallel may be useful.

Relevance of breast cancer antiestrogen resistance genes in human breast cancer progression and tamoxifen resistance

PURPOSE

We have previously identified a set of breast cancer antiestrogen resistance (BCAR) genes causing estrogen independence and tamoxifen resistance in vitro using a functional genetic screen. Here, we explored whether these BCAR genes provide predictive value for tamoxifen resistance and prognostic information for tumor aggressiveness in breast cancer patients.

PATIENTS AND METHODS

mRNA levels of 10 BCAR genes (AKT1, AKT2, BCAR1, BCAR3, EGFR, ERBB2, GRB7, SRC, TLE3, and TRERF1) were measured in estrogen receptor-positive breast tumors using quantitative reverse-transcriptase polymerase chain reaction. Normalized mRNA levels were evaluated for association with progression-free survival (PFS) in 242 patients receiving tamoxifen as first-line monotherapy for recurrent disease, and with distant metastasis-free survival (MFS) in 413 lymph node-negative (LNN) primary breast cancer patients who did not receive systemic adjuvant therapy.

RESULTS

Concerning tamoxifen resistance, BCAR3, ERBB2, GRB7, and TLE3 mRNA levels were predictive for PFS, independent of traditional predictive factors. By combining GRB7 (or ERBB2) and TLE3 mRNA levels, patients could be classified in three subgroups with distinct PFS. For the evaluation of tumor aggressiveness, AKT2, EGFR, and TRERF1 mRNA levels were all significantly associated with MFS, independent of traditional prognostic factors. Using the combined AKT2 and EGFR mRNA status, four prognostic groups were identified with different MFS outcomes.

CONCLUSION

The majority of BCAR genes, which were revealed to confer tamoxifen resistance and estrogen independence in vitro by functional screening, have clinical relevance, and associate with tamoxifen resistance and/or tumor aggressiveness in breast cancer patients.

Dual targeting of Src and ER prevents acquired antihormone resistance in breast cancer cells

Acquired resistance to endocrine therapies presents a major obstacle to the successful treatment of breast cancer patients. Previously, we have shown that acquisition of resistance to tamoxifen in breast cancer cells is accompanied by an elevation in Src kinase activity which promotes an aggressive, invasive phenotype in vitro. Here, we have explored the potential therapeutic effects of combining Src inhibition with anti-oestrogen treatment on the development of endocrine insensitivity in breast cancer cells. Treatment of MCF7 and T47D cells with tamoxifen alone resulted in an initial growth inhibitory phase followed by the eventual development of tamoxifen resistance together with an elevation of Src kinase activity, which was central to their increased invasive capacity. Chronic exposure of both cell types to the Src inhibitor, AZD0530, as a monotherapy resulted in outgrowth of AZD0530-resistant cells, in which Src kinase activity remained suppressed as did their in vitro invasive nature. Treatment of both MCF7 and T47D cells with AZD0530 in combination with tamoxifen resulted in a reduction of Src activity together with inhibition of focal adhesion kinase phosphorylation and a complete abrogation of their in vitro invasive behaviour. Furthermore, combination therapy significantly suppressed expression of cyclinD1 and c-myc and prevented cell proliferation and the subsequent emergence of a resistant phenotype, with total cell loss occurring by 12 weeks. These data demonstrate that pharmacological targeting of Src kinase, in conjunction with antihormone therapies, effectively prevents antihormone resistance in breast cancer cells in vitro and suggests a potential novel therapeutic benefit of Src kinase inhibitors clinically.

Decursin and decursinol angelate inhibit estrogen-stimulated and estrogen-independent growth and survival of breast cancer cells

Introduction

Estrogen and estrogen receptor (ER)-mediated signaling are crucial for the etiology and progression of human breast cancer. Attenuating ER activities by natural products is a promising strategy to decrease breast cancer risk. We recently discovered that the pyranocoumarin compound decursin and its isomer decursinol angelate (DA) have potent novel antiandrogen receptor signaling activities. Because the ER and the androgen receptor belong to the steroid receptor superfamily, we examined whether these compounds affected ER expression and signaling in breast cancer cells.

Methods

We treated estrogen-dependent MCF-7 and estrogen-independent MDA MB-231 human breast cancer cells with decursin and DA, and examined cell growth, apoptosis, and ERα and ERβ expression in both cell lines – and, in particular, estrogen-stimulated signaling in the MCF-7 cells. We compared these compounds with decursinol to determine their structure-activity relationship.

Results

Decursin and DA exerted growth inhibitory effects on MCF-7 cells through G₁ arrest and caspase-mediated apoptosis. These compounds decreased ERα in MCF-7 cells at both mRNA and protein levels, and suppressed estrogen-stimulated genes. Decursin and the pure antiestrogen Faslodex™ exerted an additive growth inhibitory effect on MCF-7 cells. In MDA MB-231 cells, these compounds induced cell-cycle arrests in the G₁ and G₂ phases as well as inducing apoptosis, accompanied by an increased expression of ERβ. In contrast, decursinol, which lacks the side chain of decursin and DA, did not have these cellular and molecular activities at comparable concentrations.

Conclusion

The side chain of decursin and DA is crucial for their anti-ER signaling and breast cancer growth inhibitory activities. These data provide mechanistic rationales for validating the chemopreventive and therapeutic efficacy of decursin and its derivatives in preclinical animal models of breast cancer.

Identification of CDK10 as an important determinant of resistance to endocrine therapy for breast cancer

Therapies that target estrogen signaling have transformed the treatment of breast cancer. However, the effectiveness of these agents is limited by the development of resistance. Here, an RNAi screen was used to identify modifiers of tamoxifen sensitivity. We demonstrate that CDK10 is an important determinant of resistance to endocrine therapies and show that CDK10 silencing increases ETS2-driven transcription of c-RAF, resulting in MAPK pathway activation and loss of tumor cell reliance upon estrogen signaling. Patients with ER alpha-positive tumors that express low levels of CDK10 relapse early on tamoxifen, demonstrating the clinical significance of these observations. The association of low levels of CDK10 with methylation of the CDK10 promoter suggests a mechanism by which CDK10 expression is reduced in tumors.

Genetic screening reveals an essential role of p27kip1 in restriction of breast cancer progression

The genetic changes and mechanisms underlying the progression of estrogen-dependent breast cancers to estrogen-independent, antiestrogen-resistant, and metastatic breast cancers are unclear despite being a major problem in endocrine therapy. To identify genes responsible for this progression, we carried out a genetic screening by an enhanced retroviral mutagen (ERM)-mediated random mutagenesis in the estrogen-dependent T47D breast cancer cells. We found that T47D cells contain only one p27kip1 (p27) allele coding for the p27 cyclin-dependent kinase (CDK) inhibitor. An ERM insertion into the p27 locus of T47D cells disrupted the p27 gene and created estrogen-independent and antiestrogen-resistant breast cancer cells that still maintained functional estrogen receptors. Disruption of p27 in T47D cells resulted in several changes, and most of these changes could be rescued by p27 restoration. First, CDK2 activity was increased in the absence of estrogen or in the presence of estrogen antagonists tamoxifen or ICI 182780; second, amplified in breast cancer 1 (AIB1), a cancer overexpressed transcriptional coactivator, was hyperphosphorylated, which made AIB1 a better coactivator for E2F1; and third, growth factor receptor binding protein 2-associated binder 2 (Gab2) and Akt activity were increased following E2F1 overactivation, leading to a significant enhancement of cell migration and invasion. Furthermore, the p27-deficient cells, but not T47D control cells, developed lung metastasis in an ovarian hormone-independent manner when they were i.v. injected into nude mice. In sum, loss of p27 activated AIB1, E2F1, Gab2, and Akt; increased cell migration and invasion; caused antiestrogen insensitivity; and promoted metastasis of breast cancer cells. These findings suggest that p27 plays an essential role in restriction of breast cancer progression.

Src promotes estrogen-dependent estrogen receptor alpha proteolysis in human breast cancer

Estrogen drives both transcriptional activation and proteolysis of estrogen receptor alpha (ER alpha; encoded by ESR1). Here we observed variable and overlapping ESR1 mRNA levels in 200 ER alpha-negative and 50 ER alpha-positive primary breast cancers examined, which suggests important posttranscriptional ER alpha regulation. Our results indicate that Src cooperates with estrogen to activate ER alpha proteolysis. Inducible Src stimulated ligand-activated ER alpha transcriptional activity and reduced ER alpha t(1/2). Src and ER alpha levels were inversely correlated in primary breast cancers. ER alpha-negative primary breast cancers and cell lines showed increased Src levels and/or activity compared with ER alpha-positive cancers and cells. ER alpha t(1/2) was reduced in ER alpha-negative cell lines. In both ER alpha-positive and -negative cell lines, both proteasome and Src inhibitors increased ER alpha levels. Src inhibition impaired ligand-activated ER alpha ubiquitylation and increased ER alpha levels. Src siRNA impaired ligand-activated ER alpha loss in BT-20 cells. Pretreatment with Src increased ER alpha ubiquitylation and degradation in vitro. These findings provide what we believe to be a novel link between Src activation and ER alpha proteolysis and support a model whereby crosstalk between liganded ER alpha and Src drives ER alpha transcriptional activity and targets ER alpha for ubiquitin-dependent proteolysis. Oncogenic Src activation may promote not only proliferation, but also estrogen-activated ER alpha loss in a subset of ER alpha-negative breast cancers, altering prognosis and response to therapy.

Activation of mitogenic pathways and sensitization to estrogen-induced apoptosis: two independent characteristics of tamoxifen-resistant breast cancer cells?

Paradoxical induction of apoptosis by estrogen has been described previously for estrogen-deprived and antiestrogen-resistant breast cancer cells. In this study we analyzed the possible interrelations between cell sensitization to estrogen apoptotic action and cell ability to (anti)estrogen-independent growth. Using tamoxifen-resistant sublines derived from the parent MCF-7 breast cancer cells by long-term tamoxifen treatment we demonstrated that resistant cells are characterized by increased level of EGF receptor and unexpected increase of VEGF receptor 2 (Flk-1/KDR) and its specific ligand, VEGF-A. The importance of the VEGF signaling in the autocrine regulation of cell growth was indicated by the ability of VEGF inhibitor, soluble fragment of Flt-1/Fc chimera, to suppress the phosphorylation of MAP kinases as well as to inhibit the estrogen-independent growth of MCF-7 cells. Sensitization of tamoxifen-resistant cells to estrogen-induced apoptosis required the additional continuous cultivation in steroid-depleted medium and did not depend on the activity of both EGF and VEGF pathways. Finally, we showed that treatment of the cells with 17beta-estradiol (10(-9) M) resulted in a marked increase in p53 level both in the resistant cells undergoing apoptosis and in the parent MCF-7 cells insensitive to apoptotic estrogen action. These data provide an important support for the existence of a disbalance between pro- and anti-apoptotic machinery in the resistant breast cancer cells that forms independently of the acquired ability to estrogen-independent growth.

Secreted frizzled related protein 2 (sFRP2) decreases susceptibility to UV-induced apoptosis in primary culture of canine mammary gland tumors by NF-kappaB activation or JNK suppression

Tumor formation can result from a decrease in cell death, as well as an increase in cell proliferation. In spite of the high incidence of mammary gland tumors (MGTs) in female dogs, the understanding of its etiology is still poor. Consistent with several proto-oncogenes (such as Wnt) for the mammary gland, sFRP2 is expressed in canine MGTs which is normally silent in the mammary gland. To elucidate the roles of SFRP2 in the tumorigenesis of MGTs, apoptosis regulation mediated by sFRP2 was investigated by overexpression of sFRP2 in MGT cells. DNA fragmentation and TUNEL assays showed a decreased susceptibility of the cells to UV-induced apoptosis in the context of sFRP2 overexpression. To analyze the pathways through which sFRP2 transduces anti-apoptosis signals, multiple-color immunofluorescence staining, immunoprecipitation, and immunoblotting were carried out. sFRP2 was found co-localized in the extracellular matrix of MGTs and the tyrosine phosphorylation of FAK was enhanced. Moreover, JNK was suppressed and NF-kB was activated in the cells expressing sFRP2 after UV-induced apoptosis analyzed by immunoblotting and electrophoretic mobility shift assay (EMSA). Taken together, these results suggest that sFRP2 exerts its anti-apoptotic function in mammary cancer cells through NF-kappaB activation or JNK suppression.

Synthesis of 7alpha-substituted derivatives of 17beta-estradiol

Estrogen receptor (ER) pure antagonists such as ICI-182,780 (fulvestrant) are effective alternatives to tamoxifen (an ER antagonist/weak partial agonist) in the treatment of postmenopausal, receptor-positive human breast cancers. Structurally, these pure antagonists contain the basic core structure of 17beta-estradiol (E(2)) with a long side chain attached to its C-7alpha position. We explored and compared in this study various synthetic routes for preparing a number of C-7alpha-substituted derivatives of E(2), which are highly useful for the design and synthesis of high-affinity ER antagonists, ER-based imaging ligands, and other ER-based multi-functional agents. Using E(2) as the starting material and 1-iodo-6-benzyloxyhexane as a precursor for the C-7alpha side chain, a seven-step synthetic procedure afforded 3,17beta-bis(acetoxy)-7alpha-(6-hydroxyhexanyl)-estra-1,3,5(10)-triene (one of the derivatives prepared) in an overall yield of approximately 45% as compared to other known procedures that afforded substantially lower overall yield (8-27%). The synthetic steps for this representative compound include: (1) protection of the C-3 and C-17beta hydroxyls of E(2) using methoxymethyl groups; (2) hydroxylation of the C-6 position of the bismethoxymethyl ether of E(2); (3) Swern oxidation of the C-6 hydroxy to the ketone group; (4) C-7alpha alkylation of the C-6 ketone derivative of E(2); (5) deprotection of the two methoxymethyl groups; (6) reprotection of the C-3 and C-6 free hydroxyls with acetyl groups; (7) removal of the C-6 ketone and the benzyl group on the side chain by catalytic hydrogenation in acetic acid. As predicted, two of the representative C-7alpha-substituted derivatives of E(2) synthesized in the present study retained strong binding affinities (close to those of E(2) and ICI-182,780) for the human ERalpha and ERbeta subtypes as determined using the radioligand-receptor binding assays.

Substituted phenanthrenes with basic amino side chains: A new series of anti-breast cancer agents

In the course of our search for new anti-breast cancer agents, substituted phenanthrenes with basic amino side chains were synthesized and some of them showed remarkable antiproliferative activity against ER +ve MCF-7 cell line with IC(50) in the range of 3.53-22.25 microM. One of the compounds 15 ca showed anti-breast cancer activity in 7,12-dimethylbenz[a]anthracene (DMBA) induced hormone-dependent mammary tumor in rat and the activity was comparable to that shown by tamoxifen.

Quaternary ammonium-linked glucuronidation of trans-4-hydroxytamoxifen, an active metabolite of tamoxifen, by human liver microsomes and UDP-glucuronosyltransferase 1A4

Tamoxifen (TAM), a nonsteroidal antiestrogen, is the most widely used drug for chemotherapy of hormone-dependent breast cancer in women. Trans-4-hydroxy-TAM (trans-4-HO-TAM), one of the TAM metabolites in humans, has been considered to be an active metabolite of TAM because of its higher affinity toward estrogen receptors (ERs) than the parent drug and other side-chain metabolites. In the present study, we found a new potential metabolic pathway of trans-4-HO-TAM and its geometrical isomer, cis-4-HO-TAM, via N-linked glucuronic acid conjugation for excretion in humans. N+-Glucuronides of 4-HO-TAM isomers were isolated along with O-glucuronides from a reaction mixture consisting of trans- or cis-4-HO-TAM and human liver microsomes fortified with UDP-glucuronic acid and identified with their respective synthetic specimens by high performance liquid chromatography-electrospray ionization time-of-flight mass spectrometry. Although N- and O-glucuronidating activities of human liver microsomes toward trans-4-HO-TAM were nearly comparable, O-glucuronidation was predominant for cis-4-HO-TAM conjugation. Only UGT1A4 catalyzed the N-linked glucuronidation of 4-HO-TAM among recombinant human UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT1A8, UGT1A9, UGT1A10, UGT2B4, UGT2B7, UGT2B15, and UGT2B17) expressed in insect cells. In contrast, all UGT isoforms, except for UGT1A3 and UGT1A4, catalyzed O-glucuronidation of 4-HO-TAM. Although O-glucuronidation of 4-HO-TAM greatly decreased binding affinity for human ERs, 4-HO-TAM N+-glucuronide still had binding affinity similar to 4-HO-TAM itself, suggesting that N+-glucuronide might contribute to the biological activity of TAM in vivo.

Tamoxifen may prevent both ER+ and ER- breast cancers and select for ER- carcinogenesis: an alternative hypothesis

INTRODUCTION

Breast Cancer Prevention Trial (BCPT) and Multiple Outcomes of Raloxifene (MORE) data have been interpreted to indicate that tamoxifen reduces the risk of ER+ but not ER- breast carcinogenesis. We explored whether these data also support an alternative hypothesis, that tamoxifen influences the natural history of both ER+ and ER- cancers, that it may be equally effective in abrogating or delaying ER- and ER+ carcinogenesis, and place selection pressure, in some cases, for the outgrowth of ER- cancers.

METHODS

BCPT and MORE data were used to investigate whether: first, tamoxifen could reduce equally the emergence of ER- and ER+ tumors; and second, tamoxifen could select a fraction of emerging ER+ cancers and promote their transformation to ER- cancers. Assuming that some proportion, Z, of ER+ tumors becomes ER- after tamoxifen exposure and that the risk reduction for both ER- and ER+ tumors is equal, we solved for both the transformation rate and the risk reduction rate.

RESULTS

If tamoxifen equally reduces the incidence of ER+ and ER- tumors by 60%, the BCPT results are achieved with a transformation of approximately Z = 20% of ER+ to ER- tumors. Validation with MORE data using an equal risk reduction of 60% associated with tamoxifen produces an almost identical transformation rate Z of 23%.

CONCLUSION

Data support an alternative hypothesis that tamoxifen may promote ER- carcinogenesis from a precursor lesion that would otherwise have developed as ER+ without tamoxifen selection.

Regulation of parathyroid hormone-related peptide by estradiol: effect on tumor growth and metastasis in vitro and in vivo

We evaluated the capacity of estradiol (E(2)) to regulate PTHrP production, cell growth, tumor growth, and metastasis to the skeleton in breast cancer. In estrogen receptor (ER)-negative human breast cancer cells, MDA-MB-231, and cells transfected with full-length cDNA encoding ER (S-30), E(2) caused a marked decrease in cell growth and PTHrP production, effects that were abrogated by anti-E(2) tamoxifen. E(2) also inhibited PTHrP promoter activity in S-30 cells. For in vivo studies, MDA-MB-231 and S-30 cells were inoculated into the mammary fat pad of female BALB/c nu.nu mice. Animals receiving S-30 cells developed tumors of significantly smaller volume compared with MDA-MB-231 tumor-bearing animals. This change in tumor volume was reversed when S-30 cells were inoculated into ovariectomized (OVX) hosts. Inoculation of MDA-MB-231 cells into the left ventricle resulted in the development of lesions in femora and tibia as determined by x-ray analysis. In contrast, these lesions were significantly smaller in volume and number in animals inoculated with S-30, and this lower incidence was reversed in OVX animals. Bone histological analysis showed that the tumor volume to tissue volume ratio was comparable with that seen by x-ray. Immunohistochemical analysis showed that PTHrP production was inhibited in S-30 group and restored to levels comparable to that seen in MDA-MB-231 tumor-bearing animals when S-30 cells were inoculated in OVX animals. Collectively these studies show that E(2) production is inversely correlated with PTHrP production and that the growth-promoting effect of PTHrP has a direct impact on tumor growth at both nonskeletal and skeletal sites.

Invasive lobular carcinoma: to grade or not to grade

Grading of invasive ductal carcinoma of no special type using the Nottingham combined histologic grading system provides independent prognostic information. The prognostic utility of grading invasive lobular carcinomas, however, has not been fully elucidated. In addition, the relationship between grade in invasive lobular carcinomas and expression of predictive biomarkers is less certain. The purpose of this study was to correlate histologic grade in invasive lobular carcinoma with known prognostic and predictive markers. All primary resections for invasive mammary carcinomas diagnosed in Mount Sinai Hospital, Toronto, between the years 1996 and 2002 were reviewed (n=1053). Of these cases, 50 were pure invasive lobular carcinoma (incidence 4.7%). The median age at diagnosis was 64 years. These tumors were graded using the Nottingham combined histologic grading system and analyzed for estrogen receptor, progesterone receptor, HER2/neu and E-cadherin expression. Tumor grade was correlated with tumor size (P=0.03), and the American Joint Committee on Cancer nodal status (P=0.05). Assessment of the individual components of grade showed that the mitotic score was highly correlated with tumor size (P=0.02), lymph node positivity (P=0.02) and overall American Joint Committee on Cancer stage (P=0.01). Estrogen receptor and progesterone receptor were highly expressed irrespective of the grade of tumor. HER2/neu protein overexpression and E-cadherin protein expression was absent in all invasive lobular carcinomas studied. We conclude that pure invasive lobular carcinoma is uncommon and occurs predominantly in postmenopausal women. Increasing tumor grade is correlated with median tumor size and the American Joint Committee on Cancer nodal stage, but not correlated with the expression of estrogen receptor, progesterone receptor, E-cadherin or HER2/neu protein overexpression.

Mifepristone induces growth arrest, caspase activation, and apoptosis of estrogen receptor-expressing, antiestrogen-resistant breast cancer cells

PURPOSE

A major clinical problem in the treatment of breast cancer is the inherent and acquired resistance to antiestrogen therapy. In this study, we sought to determine whether antiprogestin treatment, used as a monotherapy or in combination with antiestrogen therapy, induced growth arrest and active cell death in antiestrogen-resistant breast cancer cells.

EXPERIMENTAL DESIGN

MCF-7 sublines were established from independent clonal isolations performed in the absence of drug selection and tested for their response to the antiestrogens 4-hydroxytamoxifen (4-OHT) and ICI 182,780 (fulvestrant), and the antiprogestin mifepristone (MIF). The cytostatic (growth arrest) effects of the hormones were assessed with proliferation assays, cell counting, flow cytometry, and a determination of the phosphorylation status of the retinoblastoma protein. The cytotoxic (apoptotic) effects were analyzed by assessing increases in caspase activity and cleavage of poly(ADP-ribose) polymerase.

RESULTS

All of the clonally derived MCF-7 sublines expressed estrogen receptor and progesterone receptor but showed a wide range of antiestrogen sensitivity, including resistance to physiological levels of 4-OHT. Importantly, all of the clones were sensitive to the antiprogestin MIF, whether used as a monotherapy or in combination with 4-OHT. MIF induced retinoblastoma activation, G(1) arrest, and apoptosis preceded by caspase activation.

CONCLUSIONS

We demonstrate that: (a) estrogen receptor(+)progesterone receptor(+), 4-OHT-resistant clonal variants can be isolated from an MCF-7 cell line in the absence of antiestrogen selection; and (b) MIF and MIF plus 4-OHT combination therapy induces growth arrest and active cell death of the antiestrogen-resistant breast cancer cells. These preclinical findings show potential for a combined hormonal regimen of an antiestrogen and an antiprogestin to combat the emergence of antiestrogen-resistant breast cancer cells and, ultimately, improve the therapeutic index of antiestrogen therapy.

TCDD and PCBs inhibit breast cancer cell proliferation in vitro

The effects on cell proliferation of arylhydrocarbon receptor (AhR) agonists in estrogen-responsive T47D and ZR-75-1 cells were investigated. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and the non-ortho-substituted polychlorinated biphenyl (PCB) congeners, PCB 77, PCB 81, PCB 126, and PCB 169 each inhibited 17beta-estradiol (E(2))-stimulated cell proliferation in a dose-responsive manner. In the absence of added E(2), TCDD, PCB 77, PCB 81, and PCB 169 had no significant effect on cell proliferation, while PCB 126 at high concentrations caused slight elevations. The order of effective inhibition of E(2)-stimulated cell proliferation by the PCB congeners was: PCB 81>PCB 126 approximately = PCB 169>PCB 77. In the comparative literature, mammalian TEFs for these congeners toxic potency are in the order: PCB 126>PCB 169>PCB 81 approximately = PCB 77 [Organohalogen Compd. 34 (1997) 237]. Our results thus show an unexpected different pattern for the inhibitory effects of PCBs congeners on E(2)-mediated cell proliferation.

Aromatase inhibitors and other novel agents in breast cancer treatment

Thirty years after the introduction of tamoxifen, which was expanded from palliation of metastatic cancer to recent application for chemoprevention, the primacy of this drug as the mainline pharmacological intervention is currently being challenged by the third generation aromatase inhibitors and inactivators. In contrast to the oestrogen receptor blockade provided by tamoxifen, aromatase inhibitors result in deprivation of oestrogens in postmenopausal women both through paracrine/intracrine and endocrine modulation. Experimental evidence has shown a significant (97-99%) reduction of in vivo aromatase activity and an equal or sometimes better antitumour activity compared with megestrol acetate when these drugs are used as second-line treatment for metastatic breast cancer. Recent pivotal studies in first-line settings comparing tamoxifen for metastatic breast cancer and preliminary results from the neoadjuvant trials demonstrate that third generation aromatase inhibitors are superior to tamoxifen. With a better understanding of local tissue production of oestrogen through oestrone sulfatase, which hydrolyses oestrone sulfate to oestrone, and 17-beta-hydroxysteroid dehydrogenase Type 1, which in turn catalyses the reduction of oestrone to oestradiol, more powerful tactics for oestrogen starvation of cancer may be realised in future.

The Dual ErbB1/ErbB2 Inhibitor, Lapatinib (GW572016), Cooperates with Tamoxifen to Inhibit Both Cell Proliferation- and Estrogen-Dependent Gene Expression in Antiestrogen-Resistant Breast Cancer

Effective treatment of estrogen receptor (ER)-positive breast cancers with tamoxifen is often curtailed by the development of drug resistance. Antiestrogen-resistant breast cancers often show increased expression of the epidermal growth factor receptor family members, ErbB1 and ErbB2. Tamoxifen activates the cyclin-dependent kinase inhibitor, p27 to mediate G1 arrest. ErbB2 or ErbB1 overexpression can abrogate tamoxifen sensitivity in breast cancer lines through both reduction in p27 levels and inhibition of its function. Here we show that the dual ErbB1/ErbB2 inhibitor, lapatinib (GW572016), can restore tamoxifen sensitivity in ER-positive, tamoxifen-resistant breast cancer models. Treatment of MCF-7pr, T-47D, and ZR-75 cells with lapatinib or tamoxifen alone caused an incomplete cell cycle arrest. Treatment with both drugs led to a more rapid and profound cell cycle arrest in all three lines. Mitogen-activated protein kinase and protein kinase B were inhibited by lapatinib. The two drugs together caused a greater reduction of cyclin D1 and a greater p27 increase and cyclin E-cdk2 inhibition than observed with either drug alone. In addition to inhibiting mitogenic signaling and cell cycle progression, lapatinib inhibited estrogen-stimulated ER transcriptional activity and cooperated with tamoxifen to further reduce ER-dependent transcription. Lapatinib in combination with tamoxifen effectively inhibited the growth of tamoxifen-resistant ErbB2 overexpressing MCF-7 mammary tumor xenografts. These data provide strong preclinical data to support clinical trials of ErbB1/ErbB2 inhibitors in combination with tamoxifen in the treatment of human breast cancer.

Structure-based drug design: synthesis, crystal structure, biological evaluation and docking studies of mono- and bis-benzo[b]oxepines as non-steroidal estrogens

Mono- and bis-benzo[b]oxepine derivatives have been rationally synthesized to meet the molecular requirement for interaction with estrogen receptor. Bis-benzo[b]oxepines (7 and 9) and mono-benzo[b]oxepine (10) acquire geometry with phenolic groups disposed in a fashion to stimulate estrogen receptor. Structure-based investigation, in vivo activity and docking studies have been described and correlated to demonstrate a practical approach for suitable ligand design.

Quaternary ammonium-linked glucuronidation of tamoxifen by human liver microsomes and UDP-glucuronosyltransferase 1A4

Tamoxifen (TAM), a nonsteroidal antiestrogen, is the most widely used drug for chemotherapy of hormone-dependent breast cancer in women. In the present study, we found a new potential metabolic pathway of TAM via N-linked glucuronic acid conjugation for excretion in humans. TAM N(+)-glucuronide was isolated from a reaction mixture consisting of TAM and human liver microsomes fortified with UDP-glucuronic acid (UDPGA) and identified with a synthetic specimen by high-performance liquid chromatography-electrospray ionization-mass spectrometry. However, no TAM-glucuronidating activity was detected in microsomes from rat, mouse, monkey, dog, and guinea pig livers. A strong correlation (r(2) =0.92 ) was observed between N-glucuronidating activities toward TAM and trifluoperazine, a probe substrate for human UDP-glucuronosyltransferase (UGT) 1A4, in human liver microsomes from eight donors (five females, three males). However, no correlation ( (r(2) =0.02 )) was observed in the activities between 7-hydroxy-4-(trifluoromethyl)coumarin and TAM. Only UGT1A4 catalyzed the N-linked glucuronidation of TAM among recombinant UGTs (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B4, UGT2B7, UGT2B15, and UGT2B17) expressed in insect cells. Apparent K(m) values for TAM N-glucuronidation by human liver microsomes and recombinant UGT1A4 were 35.8 and 32.4 microM, respectively. These results strongly suggested that UGT1A4 could play a role in metabolism and excretion of TAM without Phase I metabolism in human liver. TAM N(+)-glucuronide still had binding affinity similar to TAM itself for human estrogen receptors, ERalpha and ERbeta, suggesting that TAM N(+)-glucuronide might contribute to the biological activity of TAM in vivo.