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Introduction: Anti-oestrogens have been the mainstay of therapy in patients with oestrogen-receptor (ER) positive breast cancer and have provided significant improvements in survival. However, their benefits are limited by tumour recurrence in a significant proportion of initially drug-responsive breast cancer patients because of acquired anti-oestrogen resistance. Relapse on such therapies clinically presents as local and/or regional recurrences, frequently with distant metastases, and the prognosis for these patients is poor. The selective ER modulator, tamoxifen, classically exerts gene inhibitory effects during the drug-responsive phase in ER-positive breast cancer cells. Paradoxically, this drug is also able to induce the expression of genes, which in the appropriate cell context may contribute to an adverse cell phenotype. Here we have investigated the effects of tamoxifen and fulvestrant treatment on invasive signalling and compared this with the direct effects of oestrogen withdrawal to mimic the action of aromatase inhibitors., Methods: The effect of oestrogen and 4-hydroxy-tamoxifen on the invasive capacity of endocrine-sensitive MCF-7 cells, in the presence or absence of functional E-cadherin, was determined by Matrigel invasion assays. Studies also monitored the impact of oestrogen withdrawal or treatment with fulvestrant on cell invasion. Western blotting using phospho-specific antibodies was performed to ascertain changes in invasive signalling in response to the two anti-oestrogens versus both oestradiol treatment and withdrawal., Results: To the best of our knowledge, we report for the first time that tamoxifen can promote an invasive phenotype in ER-positive breast cancer cells under conditions of poor cell-cell contact and suggest a role for Src kinase and associated pro-invasive genes in this process. Our studies revealed that although this adverse effect is also apparent for further classes of anti-oestrogens, exemplified by the steroidal agent fulvestrant, it is absent during oestrogen withdrawal., Conclusions: These data highlight a previously unreported effect of tamoxifen (and potentially further anti-oestrogens), that such agents appear able to induce breast cancer cell invasion in a specific context (absence of good cell-cell contacts), where these findings may have major clinical implications for those patients with tumours that have inherently poor intercellular adhesion. In such patients oestrogen deprivation with aromatase inhibitors may be more appropriate.

De novo insensitivity and acquired resistance to the selective oestrogen receptor modulator tamoxifen and the pure anti-oestrogen fulvestrant (faslodex) severely limit their effectiveness in breast cancer patients. This is a major clinical problem, since each year upward of 1 million women are dispensed anti-oestrogenic drugs. In order to investigate the phenomenon of anti-oestrogen resistance and to rapidly screen drugs that target the resistance mechanism(s), we have previously established several in vitro breast cancer models that have acquired resistance to anti-hormones. Such cells commonly develop an ability to proliferate after approximately 3 months of exposure to 4-hydroxytamoxifen or fulvestrant, despite an initial endocrine-responsive (i.e. growth-suppressive) phase. The current paper explores the role that growth factor signalling plays in the transition of oestrogen receptor-positive endocrine-responsive breast cancer cells to anti-oestrogen resistance or insensitivity and how we might, in the future, most effectively use anti-growth factor therapies to treat or delay endocrine-resistant states.

Breast cancer models of acquired tamoxifen resistance, oestrogen receptor (ER)+ /ER- de novo resistance and gene transfer studies cumulatively demonstrate the increased importance of growth factor receptor signalling, notably the epidermal growth factor receptor (EGFR)/HER2, in tamoxifen resistance. Our recent in vitro studies also suggest that EGFR signalling productively cross-talks with insulin-like growth factor receptor (IGF-1R) and, where present, activates ER on key AF-1 serine residues to facilitate acquired tamoxifen-resistant growth. This paper presents our immunohistochemical evidence that EGFR/HER2 signalling (i.e. transforming growth factor (TGF)alpha, EGFR and HER2 expression; phosphorylation of EGFR, HER2 and ERK1/2 MAP kinase) is also prominent in clinical de novo resistant and modestly increased in acquired tamoxifen-resistant states, suggesting that anti-EGFR/HER2 strategies may prove valuable treatments. Primary breast cancer samples employed were obtained for (1) patients subsequently treated with tamoxifen for advanced disease where endocrine response and survival data were available and (2) ER+ elderly patients during tamoxifen response and relapse. We also present our clinical immunohistochemical findings that IGF-1R expression, its phosphorylation on tyrosine 1316, and also phosphorylation on serine 118 of ER are not only prominent in ER+ tamoxifen-responsive disease, but are also detectable in ER+ de novo and acquired tamoxifen-resistant breast cancer, where there is evidence of EGFR/ER cross-talk. Our data suggest that agents to deplete effectively ER or IGF-1R signalling may be of value in treating ER+ de novo/acquired tamoxifen resistance in addition to tamoxifen-responsive disease in vivo. IGF-1R inhibitors may also prove valuable in ER- patients, since considerable IGF-1R signalling activity was apparent within approximately 50% of such tumours.

Due to their favourable tolerability profiles, endocrine therapies have long been considered the treatment of choice for hormone-sensitive metastatic breast cancer. However, the oestrogen agonist effects of the available selective oestrogen receptor modulators, such as tamoxifen, and the development of cross-resistance between endocrine therapies with similar modes of action have led to the need for new treatments that act through different mechanisms. Fulvestrant ('Faslodex') is the first of a new type of endocrine treatment--an oestrogen receptor (ER) antagonist that downregulates the ER and has no agonist effects. This article provides an overview of the current understanding of ER signalling and illustrates the unique mode of action of fulvestrant. Preclinical and clinical study data are presented in support of the novel mechanism of action of this new type of ER antagonist.

Although many estrogen receptor-positive breast cancers initially respond to antihormones, responses are commonly incomplete with resistance ultimately emerging. Delineation of signaling mechanisms underlying these phenomena would allow development of therapies to improve antihormone response and compromise resistance. This in vitro investigation in MCF-7 breast cancer cells examines whether epidermal growth factor receptor (EGFR) signaling limits antiproliferative and proapoptotic activity of antihormones and ultimately supports development of resistance. It addresses whether the anti-EGFR agent gefitinib (ZD1839/Iressa; TKI: 1 mum) combined with the antihormones 4-hydroxytamoxifen (TAM: 0.1 mum) or fulvestrant (Faslodex; 0.1 mum) enhances growth inhibition and prevents resistance. TAM significantly suppressed MCF-7 growth over wk 2-5, reducing proliferation detected by immunocytochemistry and fluorescence-activated cell sorter cell cycle analysis. A modest apoptotic increase was observed by fluorescence-activated cell sorter and fluorescence microscopy, with incomplete bcl-2 suppression. EGFR induction occurred during TAM response, as measured by immunocytochemistry and Western blotting, with EGFR-positive, highly proliferative resistant growth subsequently emerging. Although TKI alone was ineffective on growth, TAM plus TKI cotreatment exhibited superior antigrowth activity vs. TAM, with no viable cells by wk 12. Cotreatment was more effective in inhibiting proliferation, promoting apoptosis, and eliminating bcl-2. Cotreatment blocked EGFR induction, markedly depleted ERK1/2 MAPK and protein kinase B phosphorylation, and prevented emergence of EGFR-positive resistance. Faslodex plus TKI cotreatment was also a superior antitumor strategy. Thus, increased EGFR evolves during treatment with antihormones, limiting their efficacy and promoting resistance. Gefitinib addition to antihormonal therapy could prove more effective in treating estrogen receptor-positive breast cancer and may combat development of resistance.

In patients with estrogen receptor (ER)-negative disease or ER+ hormone-resistant disease, the dominant influence on tumor cell growth is growth factors, e.g., epidermal growth factor (EGF), heregulins, and insulin-like growth factors acting through specific receptor tyrosine kinases at the cell surface. This superfamily of ligand-activated growth factor receptors triggers cascades of biochemical signals that influence tumor cell motility, invasiveness, angiogenesis, and survival, as well as proliferation. In breast tumors, expression of epidermal growth factor receptor (EGFR) and/or erbB2 is associated with poor prognosis; the therapeutic utility of blocking these receptors has been established using trastuzumab (Herceptin), a monoclonal antibody that blocks erbB2 signaling. An alternative therapeutic approach is offered by small molecule inhibitors of EGFR-TK, exemplified by ZD1839 (Iressa), a potent and selective EGFR-TK inhibitor. Resistance to tamoxifen is associated with up-regulation of the EGFR-TK pathway and mitogen-activated protein kinase activity is substantially increased in tamoxifen-resistant MCF-7 cells. ZD1839 treatment of tamoxifen-resistant MCF-7 cells blocks mitogen-activated protein kinase activity. Furthermore, treatment of wild-type MCF-7 cells with tamoxifen and ZD1839 prevents development of tamoxifen resistance. These data support the potential clinical utility of ZD1839 in tamoxifen-resistant breast cancer and suggest the possibility of preventing resistance by the early use of combination ZD1839 with antiestrogenic agents such as tamoxifen or ICI 182,780.

Among 834 patients who had primary breast cancer treated by surgery without adjuvant systemic therapy, 363 had relapse treated by endocrine therapy alone. Patients with oestrogen receptor positive tumours (median: 70 vs. 45 months, p < 0.0001) or with non-progression at 6 months of therapy (median: 111 vs. 37 months, p < 0.0001) survived longer than those with oestrogen receptor negative tumours or with disease progression respectively, presumably due to the effect of therapy. On the other hand, the median disease-free interval, uninfluenced by therapy, showed a similar difference: oestrogen receptor positive versus negative = 29 versus 21 months, p < 0.005; non-progression versus progression = 40 versus 19 months, p < 0.0001. Patients with oestrogen receptor-positive tumours and non-progression at 6 months had the longest disease-free interval. The present study has established that there are factors, other than the oestrogen receptor, inherent in the primary tumour as reflected by the disease-free interval, which affect hormone sensitivity. Selection of adjuvant endocrine therapy based on the oestrogen receptor alone would deem inadequate. Further studies to elucidate other possible factors are warranted to refine the use of endocrine therapy, especially in the adjuvant setting when no indication of response is available.

Selective oestrogen receptor downregulators (SERDs) are a class of highly effective steroidal antitumour agents that reduce cellular levels of the oestrogen receptor (ER). In this study, we compared the efficacy by which three novel molecular approaches: (1) antisense oligonucleotides; (2) antisense RNA; and (3) dominant negative mutants are able to act as SERDs. Using transient and, where appropriate, stable gene transfection experiments we found that constitutive overexpression of ER antisense RNA and a hormone-binding domain compromised dominant-negative ER mutant (DNER-1), were most effective at downregulating ER expression and/or activity in vitro.

Expression of oestrogen receptor (ER), epidermal growth factor receptor (EGFR) and transforming growth factor-alpha (TGF alpha) proteins was assessed by immunocytochemistry on primary breast cancer specimens obtained before and following short-term (7-day) presurgical exposure to pure anti-oestrogen (7 alpha- [9- (4,4,5,5,5-pentafluoropentylsulphinyl) nonyl] estra-1,3,5, (10)-triene-3,17 beta-diol, ICI 182780) treatment and compared with no-treatment controls. Paired needle-core and mastectomy samples were obtained from 21 patients. Effects of ICI 182780 (10(-7)M) on MCF7 breast cancer cell ER, EGFR and TGF alpha expression were also examined over 14 days. ER protein was significantly suppressed by ICI 182780 in vivo (P = 0.009) and comparative analysis of short term ICI 182780 effects in vitro, using ER-positive MCF7 cells, gave largely equivalent results. EGFR and TGF alpha protein levels were unaltered by treatment. ICI 182780 suppresses ER without a concomitant rise in either EGFR or TGF alpha.

We have previously reported the early results of a randomized cross-over study of radical radiotherapy vs tamoxifen in patients with locally advanced breast cancer. This study has now recruited 143 patients with a median time from randomization of almost 10 years for both groups. Seventy-three patients received 20 mg tamoxifen twice daily, and 70 had primary radiotherapy at a dose of 40 Gy, which is a lower dose than currently administered. The treatment groups were similar in age, size of tumour and oestrogen receptor status. There was no significant difference between the two treatment groups for the combined initial response and static disease rates (89% for radiotherapy and 78% for tamoxifen, P = 0.15). The median duration of initial response was 12 months for both groups. When patients crossed over to the alternative therapy on local relapse, there was no difference in response/static disease rates (P = 0.34) and duration of response (P = 0.76). A non-significant prolongation of the metastatic-free interval in favour of tamoxifen (P = 0.08) was identified, although there was no difference in survival outcome (P = 0.38). This study shows that in this group of patients primary tamoxifen offers a similar clinical benefit to primary radiotherapy at a dose of 40 Gy, and is therefore an acceptable alternative primary treatment.

Effects of the pure antiestrogen ICI182780 and tamoxifen on ER-protein, ER-mRNA, and estrogen-regulated mRNA expression were analysed using matched pretreatment core-cut biopsies and post-treatment mastectomy samples from 43 ER positive human breast cancers. Sixteen controls received either no preoperative treatment (n = 9) (7 days) or placebo (n = 7) (median 21 days) prior to primary surgery. Nineteen patients received ICI182780 6 mg/day (n = 10) or 18 mg/day (n = 9) for 7 days. Eight patients were given preoperative tamoxifen (4 x 40 mg-day 1, 20 mg/day thereafter, median 21 days). ER-protein expression was assessed on pre and post treatment samples by immunocytochemistry. ER, pS2, pLIV1, and actin-mRNA expression was determined by northern analysis on post-treatment samples only. ER-mRNA levels were similar to controls following ICI182780 or tamoxifen treatment. However ER-protein levels were significantly suppressed by ICI182780, particularly at the higher dosage (p = 0.0013). Tamoxifen had no significant effect on ER-protein levels. The ER-mRNA and ER-protein contents of control tumors were linearly related (Spearman r = 0.719, p = 0.006). A similar relationship between pretreatment protein and post ICI182780 treatment mRNA levels was observed (r = 0.652, p = 0.005). However, comparison of post ICI182780 treatment protein and mRNA results shows a loss of linearity through a reduction in protein without concurrent loss of mRNA (r = 0.28, p = 0.257). pS2 mRNA hybridization was lower in ICI182780 treated samples than controls (Mann-Whitney p = 0.035) but was unaffected by tamoxifen. pLIV1 mRNA hybridization was uninfluenced by either treatment. Short term exposure of breast tumors to ICI182780 appears to produce a greater inhibition of estrogen-induced transcriptional events than tamoxifen. These effects appear to occur without a concurrent reduction in ER mRNA levels.

Several oncogenes and tumour-suppressor genes have been identified that may have an important role in the development of human breast carcinoma. Furthermore, some of these gene alterations may be linked to the development of invasion and subsequent metastasis. Alterations in the expression of ras p21, p53 and c-erbB-2 have all been linked to tumours with rapid cellular proliferation, but the evidence that they are of prognostic importance in patients with breast cancer is conflicting. This study explores the relationship between expression of these oncoproteins and clinical outcome in 92 patients with either locally advanced or metastatic breast cancer treated with primary endocrine therapy. Specimens of the primary carcinoma were available for analysis of hormone receptor, Ki67 labelling index, epidermal growth factor receptor (EGFR), c-erbB-2, p53 and ras p21. Clinical response was measured according to UICC criteria after 6 months of treatment and all patients were followed for time to progression and overall survival. As shown previously, oestrogen receptor (ER) negativity, high Ki67 labelling index and EGFR overexpression were associated with a shorter time to progression and overall survival. However, no statistically significant relationship existed between expression of ras p21, p53 or c-erbB-2 and response to treatment, time to progression or overall survival. We conclude that staining for these three oncoproteins has no role in therapeutic decision-making in patients with advanced breast cancer. The negative finding implies that while abnormal expression of these genes may have an important role in the development of breast cancer, the variations in growth characteristics of advanced breast cancer may be influenced by other factors.

Background: Tamoxifen, a nonsteroidal estrogen antagonist, is the most prescribed drug for the treatment of breast cancer. The use of tamoxifen is limited, however, by the development of resistance to this compound in most patients. Although tamoxifen behaves primarily as an estrogen antagonist, it has agonist (or growth-stimulatory) activity as well. ICI 182,780 is a 7 alpha-alkylsulfinyl analogue of estradiol lacking agonist activity. The absence of agonist activity may make this steroidal antiestrogen superior to tamoxifen in suppressing tumor cell growth., Purpose: We compared the inhibitory effects of ICI 182,780, tamoxifen, and estrogen withdrawal on the growth of established tumors and on tumorigenesis in a model system that uses estrogen-dependent, human MCF-7 breast tumor cells growing in athymic nude mice. We also studied the hormonal responsiveness of tumors that became resistant to the two estrogen antagonists and the effects of these drugs on estrogen-regulated gene expression., Methods: MCF-7 cells were injected subcutaneously into the flanks of castrated, female nude mice. The effects of repeated doses of tamoxifen and ICI 182,780 (500 micrograms and 5 mg, respectively) on the growth of established tumors (8-10 mm in size) were determined after supplemental estrogen was removed. The effects of antiestrogen treatments on the process of tumorigenesis, in the absence of estrogen supplementation, were determined by initiating drug administration on the same day as tumor cell inoculation. To evaluate the hormonal responsiveness of tumors resistant to tamoxifen and ICI 182,780, 1-mm3 segments of the tumors were transplanted onto the flanks of new recipient mice, which were then treated with estrogen or the antiestrogens--alone or in combination. Tumor growth was monitored by measuring tumor volumes twice a week. Expression of the estrogen-responsive genes, pLIV1 and pS2, in the tumors of treated animals was analyzed using blots of total cellular RNA and complementary DNA probes., Results: Treatment with ICI 182,780 suppressed the growth of established tumors twice as long as treatment with tamoxifen or estrogen withdrawal. Tumorigenesis, in the absence of supplemental estrogen, was delayed to a greater extent in ICI 182,780-treated mice than in tamoxifen-treated mice. ICI 182,780 was found to be more effective than tamoxifen in reducing the expression of estrogen-regulated genes. Most tumors eventually became resistant to ICI 182,780 and grew independently of estrogen., Conclusions: ICI 182,780 is a more effective estrogen antagonist than tamoxifen in the MCF-7 tumor cell/nude mouse model system.

The kinetics of binding of oestradiol and the steroidal pure antioestrogen ICI 164,384 to the molybdate-stabilized oestrogen receptor, partially purified from pig and human uterine tissue, were determined. ICI 164,384 bound directly to the oestrogen receptor protein and the kinetic parameters of this interaction were, in general, similar to those for the binding of oestradiol, regardless of the source of the receptor protein. However, the rate of association of oestradiol, regardless of the source of the receptor protein. However, the rate of association of the antagonist with the receptor protein was slower when compared to that of oestradiol. Furthermore, the concentration of binding sites for the two ligands was of the same order. The binding of oestradiol resulted in a steroid-receptor complex which could be transformed in vitro, to a form with increased affinity for DNA-cellulose. However, the complex formed between ICI 164,384 and the receptor protein did not show increased affinity for DNA-cellulose when exposed to conditions that transformed agonist-receptor complexes. Therefore, the binding of ICI 164,384 to the oestrogen receptor protein results in a suppression of the transformation process. A similar suppression in vivo may account for the pure antagonist properties of ICI 164,384.

The endocrinological and clinical effects of an LH-RH agonist, Zoladex, and an antiestrogen, Nolvadex, in patients with advanced breast cancer are outlined and their potential in the therapy of nonmalignant diseases of the breast and high-risk states is briefly discussed. Additional data are presented to indicate that new antiestrogens are now available for experimental studies that, unlike tamoxifen, do not possess partial estrogen-like activity and that show favorable antitumor properties against DMBA-induced mammary tumors and MCF-7 human breast cancer cells in culture. The lack of agonistic effects of this new class of pharmacological agents now allows a state of total estrogen deprivation to be approached, a previously unobtainable clinical goal.

The proliferative actions of a series of antioestrogens on the development of the second thoracic mammary gland of ovariectomized immature Sprague-Dawley rats have been investigated. Evidence is presented that shows trans-tamoxifen, LY 117018 and LY 139481, like oestradiol-17 beta and cis-tamoxifen, promote full mammary gland ductal development and induce a high rate of cell proliferation in the undifferentiated epithelial cells of the terminal end buds, the main growth region for ductal growth. Conversely, ICI 164,384, a new antioestrogen, is without effect on ductal elongation. In vivo exposure of trans-tamoxifen and LY 117018 treated glands in medically castrated animals to the carcinogen DMBA, results in a high rate of mammary tumour development. Indeed, the actions of these so-called antioestrogens are equivalent to those observed in oestradiol-treated rats.

The use of partially purified preparations of the human uterine oestrogen receptor has enabled, for the first time, a study of the binding of the steroidal, pure antioestrogen ICI 164,384 [N-n-butyl-11-(3,17 beta-dihydroxy-oestra-1,3,5(10)-trien-7 alpha-yl)N-methyl-undecamide] to the oestrogen receptor. Scatchard analyses of the binding of [3H]oestradiol and [3H]ICI 164,384 to the receptor show that the equilibrium dissociation constants for the interactions of these ligands with the receptor at 0 degrees C are 0.44 and 0.69 nM respectively. The concentration of receptor binding sites for the agonist was 1986 fmol/mg protein whilst that for the antagonist was 1400 fmol/mg protein. The affinity of the antioestrogen-receptor complex for DNA-cellulose does not increase following exposure to conditions that transform the oestrogen-receptor complex.