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Background and Purpose Triphenylethylene ( TPE)-like compounds were the first agents to be used in the treatment of metastatic breast cancer in postmenopausal women. Although structurally related to the anti-oestrogen, 4-hydroxytamoxifen, TPEs possess oestrogenic properties in fully oestrogenized breast cancer cells but do not induce apoptosis with short-term treatment in long-term oestrogen-deprived breast cancer cells. This study determined the differential effects of bisphenol, a TPE, on growth and apoptosis based on the modulation of the shape of the ligand-oestrogen receptor complex. Experimental Approach Apoptotic flow cytometric studies were used to evaluate apoptosis over time. Proliferation of the breast cancer cells was assessed using DNA quantification and cell cycle analysis. Real-time PCR was performed to quantify mRNA levels of apoptotic genes. Regulation of cell cycle and apoptotic genes was determined using PCR-based arrays. Key Results Bisphenol induced an up-regulation of cell cycle genes similar to those induced by 17β oestradiol ( E2). Unlike the changes induced by E2 that occur after 24 h, the apoptosis evoked by bisphenol occurred after 4 days, with quantifiable apoptotic changes noted at 6 days. A prolonged up-regulation of endoplasmic reticulum stress and inflammatory stress response genes was observed with subsequent activation of apoptosis-related genes in the second week of treatment with bisphenol. Conclusions and Implications The bisphenol: ERα complex induces delayed biological effects on the growth and apoptosis of breast cancer cells. Both the shape of the complex and the duration of treatment control the initiation of apoptosis. [ABSTRACT FROM AUTHOR]

Discusses how to subvert the action of tamoxifen, an endocrine therapy of choice for breast cancer. Information on the therapy; Mechanism of action of the therapy.

Selective oestrogen receptor modulators (SERMs) can build bone in the postmenopausal woman and lower circulating cholesterol. These oestrogen-like properties contrast with the anti-oestrogenic properties observed in the breast where SERMs inhibit the oestrogen-mediated development and growth of ER positive breast cancers. The two clinically useful SERMs, tamoxifen and its chemical cousin raloxifene, are currently used successfully either for the treatment and prevention of breast cancer (tamoxifen) or the treatment and prevention of osteoporosis (raloxifene). However, raloxifene has the beneficial side-effect of breast cancer prevention. These multifunction medicines provide proof of concept that novel molecules can be selectively targeted to diseases mediated by the endocrine system. [ABSTRACT FROM AUTHOR]

Tamoxifen (TAM) has both cytostatic and cytotoxic properties for breast cancer. TAM engaged mitochondrial estrogen receptor beta (ERβ) as an antagonist in MCF7-BK cells, increasing reactive oxygen species (ROS) concentrations from the mitochondria that were required for cytotoxicity. In part, this derived from TAM downregulating manganese superoxide dismutase (MnSOD) activity by causing the nitrosylation of tyrosine 34, thereby increasing ROS. ROS-activated protein kinase C delta and c-jun N-terminal kinases, resulting in the mitochondrial translocation of Bax and cytochrome C release. Interestingly, TAM failed to cause high ROS levels or induce cell death in MCF7-BK-TR cells due to stimulation of MnSOD activity through agonistic effects at mitochondrial ERβ. In several mouse xenograft models, lentiviral shRNA-induced knockdown of MnSOD caused tumors that grew in the presence of TAM to undergo substantial apoptosis. Tumor MnSOD and mitochondrial ERβ are therefore targets for therapeutic intervention to reverse TAM resistance and enhance a cell death response. [ABSTRACT FROM AUTHOR]

The link between sex steroids and the development and growth of breast cancer has proved to be an invaluable clue for advances in the prevention and treatment of breast cancer. The identification of the oestrogen receptor (ER) not only allowed advances in the molecular endocrinology of oestrogen action, but also provided a target for antioestrogenic therapeutic agents. However, the application of long-term or indefinite treatment regimens has consequences for the breast cancer. New forms of resistance, based upon enhanced cellular survival networks independent of ER and the suppression of apoptotic mechanisms, develop and then evolve. Remarkably, low concentrations of oestrogen collapse survival pathways and induce apoptosis in completely antihormonally refractory breast cancer. However, recurrent oestrogen-stimulated disease is again sensitive to antihormonal therapy. The novel reapplication of the ER as a therapeutic target for apoptosis is emerging as a new strategy for the long-term targeted maintenance treatment of breast cancer, and in formulating a targeted strategy for endocrine independent cancer. [ABSTRACT FROM AUTHOR]

Background:Oestrogen (E2) induces apoptosis in long-term E2-deprived MCF7 cells (MCF7:5C). Taxanes have been used extensively in the treatment of early and advanced breast cancer. We have interrogated the sequence of events that involve the apoptotic signalling pathway induced by E2 in comparison with paclitaxel.Methods:DNA quantification and cell cycle analysis were used to assess proliferation of cancer cells. Apoptosis was evaluated using annexin V and DNA staining methods. Regulation of apoptotic genes was determined by performing PCR-based arrays and RT-PCR.Results:E2-induced apoptosis is a delayed process, whereas paclitaxel immediately inhibits the growth and induces death of MCF7:5C cells. The cellular commitment for E2-triggered apoptosis occur after 24 h. Activation of the intrinsic pathway was observed by 36 h of E2 treatment with subsequent induction of the extrinsic apoptotic pathway by 48 h. Paclitaxel exclusively activated extramitochodrial apoptotic genes and caused rapid G2/M blockade by 12 h of treatment. By contrast, E2 causes an initial proliferation with elevated S phase of cell cycles followed by apoptosis of the MCF7:5C cells. Most importantly, we are the first to document that E2-induced apoptosis can be reversed after 24 h treatment.Conclusions:These data indicate that E2-induced apoptosis involves a novel, multidynamic process that is distinctly different from that of a classic cytotoxic chemotherapeutic drug used in breast cancer. [ABSTRACT FROM AUTHOR]

Objective. Tamoxifen has mixed agonist/antagonist activities, leading to tissue-specific estrogen-like actions and endometrial cancer. The purpose of this study was to evaluate the effects of antiestrogens on the growth of estrogen receptor (ER)-positive ECC-1 endometrial cancer cells in vitro and in vivo.Methods. We performed growth studies and luciferase assays using ERE-tK and AP-1 reporters. ERα protein expression was measured by Western blot after antiestrogen treatments. We investigated the actions of antiestrogens on the transcription of the pS2 gene in situ measured by Northern blot and the actions of antiestrogens on the VEGF protein secreted by ELISA. ERα, ERβ, EGFR, and HER2/neu mRNAs were determined by RT-PCR. Last, ECC-1 tumors were developed by inoculation of cells into ovariectomized athymic mice and treated with estradiol (E2), tamoxifen, raloxifene, and a combination.Results. E2 induced cell proliferation while antiestrogens did not. E2 and raloxifene down regulated ERα protein; in contrast, 4OHT did not. ICI182,780 completely degraded the receptor. ECC-1 cells express ERβ at insignificant levels. Luciferase assays did not show any induction in ERE- nor AP-1-mediated transcription by antiestrogens. E2 caused a concentration-dependent increase in pS2 mRNA but antiestrogens did not. E2 increased VEGF expression in a dose-dependent manner and antiestrogens blocked E2 action. E2 down regulated HER2/neu while 4OHT and raloxifene did not change HER2/neu levels compared to control. In addition, EGFR mRNA was down regulated by E2 but raloxifene did not change it. Tamoxifen and raloxifene did not promote tumor growth in vivo. However, raloxifene (1.5 mg daily) only partially blocked E2-stimulated growth.Conclusions. Tamoxifen and raloxifene are antiproliferative agents and antiestrogens in ECC-1 endometrial cells in vitro and in vivo. The observation that selective estrogen-receptor modulators do not down regulate EGFR and HER2/neu mRNA may provide a potential role for these oncogenes in the development of raloxifene- or tamoxifen-stimulated endometrial cancer. The ECC-1 cell line could provide important new clues about the evolution of drug resistance to tamoxifen and raloxifene. [Copyright &y& Elsevier]

An inverse relationship between protein kinase C (PKC) activity and oestrogen receptor (ER) expression in human breast cell lines and tumours has been firmly established over the past 10 years. To determine whether specific alterations in PKC expression accompany hormone-independence, we examined the expression of PKC isozymes in the hormone-independent human breast cancer cell clones MCF-7 5C and T47D:C42 compared with their hormone-dependent counterparts, MCF-7 A4, MCF-7 WS8 and T47D:A18 respectively. Both hormone-independent cell clones exhibit elevated PKC alpha expression and increased basal AP-1 activity compared with the hormone-dependent cell clones. To determine whether PKC alpha overexpression is sufficient to mediate the hormone-independent phenotype, we stably transfected an expression plasmid containing PKC alpha cDNA to the T47D:A18 and MCF-7 A4 cell lines. This is the first report of PKC alpha transfection in T47D cells. In contrast to MCF-7 cells, T47D has the propensity to lose the ER and more readily forms tamoxifen-stimulated tumours in athymic mice. We find that in T47D:A18/PKC alpha clones, there is concomitant up-regulation of PKC beta I and delta, whereas in the MCF-7 A4/PKC alpha transfectants PKC epsilon is up-regulated. In T47D:A18, but not in MCF-7 A4, PKC alpha stable transfection is accompanied by down-regulation of ER function whilst basal AP-1 activity is elevated. Our results suggest PKC alpha overexpression may play a role in growth signalling during the shift from hormone dependent to hormone-independent breast cancers. [ABSTRACT FROM AUTHOR]

Background: Tamoxifen has been shown to promote the growth of human endometrial tumors implanted in athymic mice, and it has been associated with a twofold to threefold increase in endometrial cancer. Toremifene, a chlorinated derivative of tamoxifen, and ICI 182,780, a pure antiestrogen, are two new antiestrogens being developed for the treatment of breast cancer. The effects of these drugs on endometrial cancer are currently unknown. Our objective was to evaluate the effects of toremifene and ICI 182,780 on the growth of human endometrial cancer in athymic mice.Methods: Athymic, ovariectomized mice were implanted with human endometrial tumors and treated with estrogen, tamoxifen, or the new antiestrogens.Results: The effects of tamoxifen and toremifene on the growth of either tamoxifen-stimulated or tamoxifen-naive endometrial tumors in athymic mice were not substantially different. ICI 182,780 inhibited the growth of tamoxifen-stimulated endometrial cancer, in both the presence and the absence of estrogen.Conclusions: Toremifene and tamoxifen produce identical effects in our endometrial cancer models. Therefore, it is possible that toremifene, like tamoxifen, may be associated with an increased incidence of endometrial cancer. In contrast, ICI 182,780 inhibited tamoxifen-stimulated endometrial cancer, both in the presence and in the absence of estrogen, suggesting that this drug may be safe with regard to the endometrium, even if it is used following tamoxifen, and that it may not result in an increased incidence of endometrial cancer. Indeed, it is even possible that ICI 182,780 may prove useful as an adjuvant agent in early stage endometrial cancer. [ABSTRACT FROM AUTHOR]

Objective: To determine the effects of tamoxifen on risk factors for cardiovascular disease in disease-free postmenopausal women.Design: Double-blind, placebo-controlled, randomized 2-year clinical trial.Setting: University health sciences center.Patients: Clinically postmenopausal women (140) with a diagnosis of axillary node-negative breast cancer, who were disease-free by laboratory and clinical evaluations.Measurements: Levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, apolipoprotein A-I, apolipoprotein B, glucose, weight, blood pressure, and reported exercise and work activity were measured.Main Results: Postmenopausal women receiving tamoxifen were evaluated at 3- or 6-month intervals during a 2-year assessment period and showed a mean decrease of 12% in total cholesterol levels (at 24 months -0.672 mmol/L; 95% CI, -0.839 to -0.505 mmol/L) and a mean decrease of 20% in calculated low-density lipoprotein (LDL) cholesterol levels (at 24 months, -0.725 mmol/L; 95% CI, -0.868 to -0.583 mmol/L) (P less than 0.001). Women with greater baseline cholesterol levels had greater decreases with tamoxifen treatment. Levels of HDL cholesterol decreased in patients treated with tamoxifen, but this decrease was only statistically significant at one of five measurement times. Apolipoprotein A-I levels increased significantly at the two time points at which it was measured (P = 0.02), and apolipoprotein B levels decreased significantly at these times (P less than 0.01) in patients treated with tamoxifen. Plasma glucose levels, reported exercise and work activity, reported smoking, weight, and systolic and diastolic blood pressures did not change with treatment.Conclusion: During 2 years of treatment, tamoxifen showed generally favorable effects on the lipid and lipoprotein profile of treated postmenopausal women. These effects may partially explain the decrease in adverse events and in mortality related to coronary heart disease seen in patients receiving adjuvant tamoxifen treatment. [ABSTRACT FROM AUTHOR]

Tamoxifen is a well-established adjuvant drug for the treatment and prevention of Estrogen Receptor (ER) positive breast cancer, effective in both pre- and postmenopausal women. However, the metabolic activation of tamoxifen to endoxifen by the CYP2D6 enzyme system still remains controversial to plan the treatment of patients with breast cancer. Since the discovery and description of the pharmacological properties of endoxifen, clinical trials were undertaken to determine the pharmacological relevance of endoxifen. The results of these trials, however, vary. In this study we demonstrate the pharmacological impact of endoxifen in a laboratory simulation of breast cancer therapy with tamoxifen in postmenopausal women in vitro in a panel of human breast cancer cell lines (MCF-7, T47D, ZR-75-1 and BT474). The concentrations of estrogens (E1/E2) used to simulate postmenopausal women treated with tamoxifen, were obtained from published studies, as well as the concentrations of tamoxifen and its metabolites (N-desmethyltamoxifen, 4- hydroxytamoxifen and endoxifen) based on the CYP2D6 genotype in postmenopausal breast cancer patients (Murdter TE et al, Clin Pharmacol Ther, 2011). Our results demonstrate that irrespective of CYP2D6 genotype, tamoxifen and its primary metabolites (N-desmethyltamoxifen and 4-hydroxytamoxifen) are able to inhibit completely the estrogen -stimulated growth of breast cancer cells in vitro. Additional endoxifen in any concentration corresponding to CYP2D6 genotype was not able to increase the antiestrogenic effect of tamoxifen and its primary metabolites. Moreover, we demonstrate that 4-hydroxytamoxifen is absolutely essentialforinhibition of estrogen action. Based on our results, we can conclude that endoxifen is pharmacologically supportive but not essential for any genotype of CYP2D6 in a postmenopausal setting. This study (PYM) was supported by Susan G. Komen for the Cure International Postdoctoral Fellowship under Award number SAC100009(VCJ), and the Department of Defense Breast Program under Award number W81XWH-06-1-0590 (VCJ). [ABSTRACT FROM AUTHOR]