Fatal myocardial infarction in the Scottish adjuvant tamoxifen trial. The Scottish Breast Cancer Committee.

OBJECTIVE--To investigate the incidence of fatal myocardial infarction in women in the two randomised arms of the Scottish adjuvant tamoxifen trial. DESIGN--Retrospective review of hospital notes to determine with the greatest possible certainty women who had died of an acute myocardial infarction. SETTING--Scottish Cancer Trials Office, the University of Edinburgh. PATIENTS--1070 postmenopausal women with operable breast cancer who were randomised to receive either adjuvant tamoxifen for five years or until relapse (539 patients) or tamoxifen for at least six weeks on the confirmation of first recurrence (531 patients). MAIN OUTCOME MEASURES--Incidence of fatal myocardial infarction in women with no known or suspected systemic cancer. RESULTS--Of the 200 women who died in the adjuvant tamoxifen arm of the trial, 44 were free of cancer at death and 10 of these died of myocardial infarction. In the observation arm 251 women died, of whom 61 showed no evidence of systemic cancer and 25 had a fatal myocardial infarction. The incidence of fatal myocardial infarction in the two groups was significantly different (chi 2 = 6.88, p = 0.0087). CONCLUSION--Tamoxifen given for at least five years as adjuvant therapy for breast cancer seems to have a cardioprotective oestrogen-like effect in postmenopausal women.     

Cytotoxicity of tamoxifen in normal and tumoral cell lines and its ability to induce cellular transformation in vitro

Tamoxifen (TAM) is a non-steroidal anti-estrogen used to treat patients with estrogen receptor-positive breast cancer and as a chemopreventive agent against breast cancer in high risk pre- and post-menopausal women. However, recent studies have shown that tamoxifen causes endometrial and hepatic cancer. In this study, we examined the effects of tamoxifen (5, 10, 25 and 50 microM) on the growth and proliferation of nine tumoral cell lines (UACC62, MCF-7, NCI-460, K-562, OVCAR-03, PC-03, HT-29, 786-0, NCI-ADR) and non-tumoral cell lines (3T3, V79, MDCK, VERO). Chinese hamster lung fibroblasts (V79) were the most sensitive lineage to tamoxifen, with 21.6% of the cells showing apoptosis at 50 microM TAM. Microscopic analysis showed that, the cellular transformation caused by TAM in V79 cells was similar to that seen with 7,12-dimethylbenz(a)anthracene, thus indicating the carcinogenicity of TAM.     

A diphenylmethane derivative selective for the anti-estrogen binding site may help define its biological role

By employing as a probe the new compound, N,N-diethyl-2-[(4-phenyl-methyl)-phenoxy]-ethanamine X HC1 (N,N-DPPE), which preferentially binds the anti-estrogen binding site, it is demonstrated that this site appears to contribute to the growth inhibitory action of tamoxifen on MCF-7 human breast cancer cells, even at lower concentrations of this anti-estrogen (1 X 10(-7) M to 1 X 10(-6) M) at which the major effect is clearly mediated via estrogen receptor. The combination of N,N-DPPE and tamoxifen is additive and this effect is not abolished by 17 beta-estradiol. This suggests that the anti-estrogen binding site is not simply a passive reservoir for binding tamoxifen, but may itself mediate the cytotoxic effects of specific ligands.     

Tamoxifen and flaxseed alter angiogenesis regulators in normal human breast tissue in vivo

The incidence of breast cancer is increasing in the Western world and there is an urgent need for studies of the mechanisms of sex steroids in order to develop novel preventive strategies. Diet modifications may be among the means for breast cancer prevention. Angiogenesis, key in tumor progression, is regulated by the balance between pro- and anti-angiogenic factors, which are controlled in the extracellular space. Sampling of these molecules at their bioactive compartment is therefore needed. The aims of this study were to explore if tamoxifen, one of the most used anti-estrogen treatments for breast cancer affected some of the most important endogenous angiogenesis regulators, vascular endothelial growth factor (VEGF), angiogenin, and endostatin in normal breast tissue in vivo and if a diet supplementation with flaxseed had similar effects as tamoxifen in the breast. Microdialysis was used for in situ sampling of extracellular proteins in normal breast tissue of women before and after six weeks of tamoxifen treatment or before and after addition of 25 g/day of ground flaxseed to the diet or in control women. We show significant correlations between estradiol and levels of VEGF, angiogenin, and endostatin in vivo, which was verified in ex vivo breast tissue culture. Moreover, tamoxifen decreased the levels of VEGF and angiogenin in the breast whereas endostatin increased significantly. Flaxseed did not alter VEGF or angiogenin levels but similar to tamoxifen the levels of endostatin increased significantly. We conclude that one of the mechanisms of tamoxifen in normal breast tissue include tipping of the angiogenic balance into an anti-angiogenic state and that flaxseed has limited effects on the pro-angiogenic factors whereas the anti-angiogenic endostatin may be modified by diet. Further studies of diet modifications for breast cancer prevention are warranted.     

Endocrine approaches for the treatment of early and advanced breast cancer in postmenopausal women

Preventing clinical progression is the major treatment goal for both early and advanced breast cancer. For hormone-responsive cases (about 70% of the total), this can necessitate the use of sequential hormone therapies at various points during the patient's life. Newer hormonal therapies, such as the third-generation aromatase inhibitor anastrozole, are now competing with tamoxifen as first choice endocrine therapy in breast cancer. In addition, a further non-steroidal aromatase inhibitor letrozole has been shown to be beneficial when given at completion of 5 years adjuvant tamoxifen. In light of these new data, current treatment paradigms need to be reviewed. Already well established as second-line treatments for advanced breast cancer, the improved risk:benefit profiles of anastrozole and letrozole compared with tamoxifen mean that these agents are now also recognised alternative treatments in the first-line relapse setting. More recent studies demonstrate that anastrozole may also have an improved risk:benefit profile compared with tamoxifen when used as initial adjuvant therapy in early breast cancer. Anastrozole is also being evaluated as a preventative treatment in women at high risk of developing breast cancer. A new addition to the endocrine treatment armamentarium is the oestrogen receptor antagonist fulvestrant, which, unlike tamoxifen, has no agonist effects. Fulvestrant is at least as effective as anastrozole in the second-line treatment of advanced breast cancer, and provides similar benefits to tamoxifen when used as first-line therapy in patients with advanced, hormone receptor-positive tumours.     

Faslodex (ICI 182, 780), a novel estrogen receptor downregulator--future possibilities in breast cancer

Tamoxifen is an effective treatment for breast cancer; however, as well as exerting antagonistic effects on the estrogen receptor (ER), tamoxifen acts as a partial agonists in estrogen-sensitive tissues, resulting in stimulation of the endometrium and tumor growth in some patients who become resistant to treatment.

ICI 182, 780 (Faslodex™), a steroidal estrogen antagonist, is the first in a new class of agent—an estrogen receptor downregulator. Pre-clinical breast cancer models show that ICI 182, 780 leads to a prolonged duration of response, and that it exerts its effects via a different mode of action to tamoxifen. This was confirmed in a small clinical study involving 19 post-menopausal advanced breast cancer patients, where ICI 182, 780 was highly effective after tamoxifen failure. Definitive evidence of the differing modes of action of ICI 182, 780 and tamoxifen, were provided in a study involving post-menopausal women with primary breast cancer, where analyses of tumor samples following short-term exposure to both drugs, showed that ICI 182, 780 reduced tumor ER levels in a dose-dependent manner, and to a significantly greater extent than tamoxifen. Additionally, unlike tamoxifen, ICI 182, 780 did not promote ER-mediated progesterone receptor expression, indicating that it lacks estrogen agonist activity.

Ongoing studies in post-menopausal women with advanced breast cancer are comparing ICI 182, 780 to anastrozole and tamoxifen, respectively. Future studies being considered are whether ICI 182, 780 may also be effective in breast cancer in pre-menopausal women, in early breast cancer and in ductal carcinoma in situ in the breast, in combination with other hormonals, cytotoxics and biological modifiers.     

Chemoprevention of breast cancer - with special interest of tamoxifen

The adjuvant use of tamoxifen confers a survival advantage for patients with node-positive and node-negative breast cancer and demonstrated benefit when used alone or in combination with chemotherapy to treat advanced breast cancer.Tamoxifen prevents induced mammary cancer in rats, decreases the contralateral breast cancer incidence in humans, and its safety record in clinical practice is excellent. This finding led to the concept that the drug might play role in breast cancer prevention. In 1986 at the Royal Marsden Hospital a small pilot study was started, which would serve as a feasibility assessment for a larger trial to determine if tamoxifen prevents breast cancer. The trial shows no effect, because the study is too small for accurate results. Similarly, in another tamoxifen prevention study performed in Italy, the incidence of breast cancer did not differ between groups of tamoxifen and placebo. The negative finding of the study is readily explained by the relatively low risk of breast cancer development in the study population, the high drop-out rate and the small number of women who completed 5 years of treatment. In the NSABP P-1 prevention trial tamoxifen reduced the risk of invasive breast cancer by 49% and of noninvasive breast cancer by 50% in the increased risk population of 13.388 healthy women. The article summarizes the recent theoretical and practical data of the chemoprevention of breast cancer.     

Accomodation of S-cis-tamoxifen-N(2)-guanine adduct within a bent and widened DNA minor groove

The non-steroidal anti-estrogen tamoxifen [TAM] has been in clinical use over the last two decades as a potent adjunct chemotherapeutic agent for treatment of breast cancer. It has also been given prophylactically to women with a strong family history of breast cancer. However, tamoxifen treatment has also been associated with increased endometrial cancer, possibly resulting from the reaction of metabolically activated tamoxifen derivatives with cellular DNA. Such DNA adducts can be mutagenic and the activities of isomeric adducts may be conformation-dependent. We therefore investigated the high resolution NMR solution conformation of one covalent adduct (cis-isomer, S-epimer of [TAM]G) formed from the reaction of tamoxifen [TAM] to N(2)-of guanine in the d(C-[TAM]G-C).d(G-C-G) sequence context at the 11-mer oligonucleotide duplex level. Our NMR results establish that the S-cis [TAM]G lesion is accomodated within a widened minor groove without disruption of the Watson-Crick [TAM]G. C and flanking Watson-Crick G.C base-pairs. The helix axis of the bound DNA oligomer is bent by about 30 degrees and is directed away from the minor groove adduct site. The presence of such a bulky [TAM]G adduct with components of the TAM residue on both the 5'- and the 3'-side of the modified base could compromise the fidelity of the minor groove polymerase scanning machinery.     

Tamoxifen decreases extracellular TGF-beta1 secreted from breast cancer cells--a post-translational regulation involving matrix metalloproteinase activity

Transforming growth factor-β1 (TGF-β1) promotes cancer progression by regulating tumor cell growth and angiogenesis and high levels of TGF-β1 have been associated with metastatic disease and poor prognosis in breast cancer patients. We have previously reported anti-angiogenic effects of the anti-estrogen tamoxifen in breast cancer, by increased matrix metalloproteinase-9 (MMP-9) activity and generation of endostatin. Here, we show that exposure of tamoxifen to ER-positive breast cancer cells for 7 days, decreased extracellular TGF-β1. Intracellular TGF-β1 levels were unaffected by tamoxifen treatment, indicating a post-translational regulation of TGF-β1. Inhibition of MMP activity restored TGF-β1 levels, suggesting an involvement of MMP activities in the down-regulation of TGF-β1 by tamoxifen. Moreover, using an in vivo model of solid MCF-7 tumors in nude mice, we analyzed tumor levels of TGF-β1 after in vivo treatment with estradiol and tamoxifen. Exposure of tumor-bearing mice to tamoxifen significantly decreased tumor TGF-β1 protein levels, tumor growth and angiogenesis. In conclusion, our findings suggest a novel mechanism of action of tamoxifen in breast cancer via sex steroid dependent modulation of the proteolytic tumor microenvironment resulting in reduced extracellular TGF-β1 levels.     

Progress in the prevention of breast cancer: concept to reality

In 1936, Professor Antoine Lacassagne suggested that breast cancer could be prevented by developing drugs to block estrogen action in the breast. Jensen discovered the physiologic target, the estrogen receptor, that regulates estrogen action in its target tissues and Lerner discovered the first nonsteroidal antiestrogen MER25. However, the success of tamoxifen as a treatment of breast cancer opened the door for the testing of the worth of tamoxifen to reduce breast cancer incidence in high-risk women. In 1998, Fisher showed that tamoxifen could reduce breast cancer incidence by 50%. Nevertheless, only half the women who develop breast cancer have risk factors other than age, so what can be done for women without risk factors? The recognition that nonsteroidal antiestrogens have the ability to modulate estrogen action selectively has advanced the design and development of new drug for multiple diseases. Tamoxifen and raloxifene maintain bone density and raloxifene is now used to prevent osteoporosis and is being tested as a preventive for coronary heart disease and breast cancer. The drug group is now known as selective estrogen receptor modulators (SERMs) and the challenge is to design new agents for multiple applications. If the 20th century was the era of chemotherapy, the 21st century will be the era of chemoprevention.     

乳腺癌细胞表皮生长因子受体、HER-2对雌激素受体的调控及三苯氧胺耐药机制

雌激素受体(ER)在乳腺癌的发生和发展中起重要作用,抗雌激素治疗的内分泌治疗为重要的治疗方案,但易产生三苯氧胺(TAM)的耐药性而使治疗失效,原因之一可能是由于表皮生长因子受体(EGFR)和HER-2高表达引起ER磷酸化所致。本文概述了其中的分子机制和可能涉及的传导通路等。     

Sequential adjuvant hormone therapy in postmenopausal breast cancer: rationale and clinical results

For the past 15 years tamoxifen has been the standard adjuvant hormone therapy for women with early-stage breast cancer and estrogen receptor (ER)-positive tumors, irrespective of nodal status and other clinicopathological parameters. Recent studies provided evidence that the optimal duration of tamoxifen treatment is 5 years. Based on the positive clinical results obtained with the administration of aromatase inhibitors (AIs) in the metastatic setting, several controlled clinical trials have evaluated the efficacy and side effects of AIs versus standard tamoxifen also as adjuvant therapy in postmenopausal breast cancer patients. The results of the above studies, suggest a therapeutic advantage of AIs over tamoxifen with regard to relapse-free survival and the risk of metachronous contralateral breast cancer. We review the rationale and the available clinical data on initial or sequential hormone treatment with AIs and we propose a novel scenario for possible therapeutic strategies based on the clinicopathological characteristics of the patients and on the biology of each single tumor.     

Tamoxifen Inhibition of Ocular Melanoma Cell Attachment to Matrix Proteins

Tamoxifen plays a major role in the management of breast cancer in women and is currently used to a lesser extent in other neoplasias. Many of the pharmacological properties of tamoxifen are consistent with anti-estrogen activity, but it also has significant, although lesser, benefit in patients whose tumours are estrogen-receptor negative. We recently reported that murine B16 melanoma cell attachment to extracellular matrix proteins can be inhibited by calmodulin antagonists. In seeking a calmodulin antagonist that could be used clinically, we investigated tamoxifen, which is known to have calmodulin antagonist activity in vitro, and confirmed that it will inhibit murine melanoma cell attachment in vitro. In the current study, we examined the effect of tamoxifen on the attachment of human ocular melanoma cell lines to a range of extracellular matrix substrates to evaluate the potential relevance of calmodulin antagonists, including tamoxifen, to reducing metastatic spread of these tumours. We report that six ocular melanoma cell lines established from choroidal melanoma tumours showed rapid attachment to a range of substrates and that this attachment can be significantly reduced by an experimental calmodulin antagonist (J8) and by tamoxifen. In summary, we conclude that the ability of calmodulin antagonists, including tamoxifen, to inhibit ocular melanoma cell attachment to matrix proteins in vitro merits further investigation as it may offer another approach to reducing metastatic spread of these tumours.     

Assessing and managing breast cancer risk: clinical tools for advising patients

Using breast cancer risk assessment tools and going through the process of assessing breast cancer risk can answer many women's questions about what puts them at relatively higher or lower risk. This effectively engages both the clinician and the patient in a discussion about breast cancer, the chances of getting it, and the family's involvement--making the process as important as the actual tools. Examples of selected case histories demonstrate risk assessment using available tools such as the Gail-NCI and the Claus models. For some women, such as those considering tamoxifen or prophylactic surgeries, it may be desirable to prescreen for the inheritance of hereditary mutations and to follow with genetic testing, if indicated. Testing for mutations of breast cancer susceptibility genes or for their diminished expression adds to our ability to assess breast cancer risk at an individual level. The literature contains general interventions that are widely accepted to reduce the severity and the burden of breast cancer, and these are brought together here. The risk assessment process is an important part of a risk reduction program and can help motivate women to engage in prevention activities. This paper uses 2 hypothetical but fact-based and typical case histories to discuss the utility of risk assessment tools for informing women about their options.     

Effects of various agents on DNA fragmentation and telomerase enzyme activities in adenocarcinoma cell lines

Natural compounds such as resveratrol, tannic acid, and quercetin may help to treat cancer. Tamoxifen is a non-steroidal anti-estrogen drug widely used in the treatment of patients with estrogen receptor-positive breast cancer. The aim of the study was to compare the effects of these natural compounds and tamoxifen in colon adenocarcinoma (CaCo-2) and breast adenocarcinoma (MCF-7) cell lines, on telomerase enzyme activity, cell viability, number of cells and DNA fragmentation. In this study to determine telomerase enzyme activity was used PCR–ELISA kit. To determine cell viability and number of cells were used tripan blue stain. DNA fragmentation was determined by DNA ladder isolation kit. Tannic acid was more effective than resveratrol, with respect to reduction in telomerase activity, cell viability and cell count in breast adenocarcinoma. Tannic acid and tamoxifen was more effective than resveratrol and quercetin telomerase activity, cell viability and cell count in colon adenocarcinoma. Flavonoids such as resveratrol, tannic acid and quercetin which was studied on, has benefical effects on cancer therapy. These effects such as decreasing telomerase enzyme activity, cell viability and number of cells and inducing DNA fragmentation (apoptosis) must be studied for assist to develop new therapeutic pathways. There should be much more sudies in order to discover resveratrol, tannic acid and quercetin and other potential medicines.     

New insights into the metabolism of tamoxifen and its role in the treatment and prevention of breast cancer

The metabolism of tamoxifen is being redefined in the light of several important pharmacological observations. Recent studies have identified 4-hydroxy N-desmethyltamoxifen (endoxifen) as an important metabolite of tamoxifen necessary for antitumor actions. The metabolite is formed through the enzymatic product of CYP2D6 which also interacts with specific selective serotonin reuptake inhibitors (SSRIs) used to prevent the hot flashes observed in up to 45% of patients taking tamoxifen. Additionally, the finding that enzyme variants of CYP2D6 do not promote the metabolism of tamoxifen to endoxifen means that significant numbers of women might not receive optimal benefit from tamoxifen treatment. Clearly these are particularly important issues not only for breast cancer treatment but also for selecting premenopausal women, at high risk for breast cancer, as candidates for chemoprevention using tamoxifen.