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Query: UMLS:C0276241 (MCF)
 28,353 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Androgen and estrogen metabolism was investigated in the hormone-dependent human breast cancer cell line MCF-7 and its two hormone-resistant sublines MCF-7/LCC1 and MCF-7/LCC2. Using the product isolation method, the activity of aromatase, 5alpha-reductase, 3alpha/beta-hydroxysteroid oxidoreductase and 17beta-hydroxysteroid oxidoreductase were investigated isolating the following steroids: estriol (E3), estradiol (E2), estrone (E1), 3alpha/beta-androstanediol (A-diol), testosterone (T), dihydrotestosterone (DHT), androsterone (AND), androstenedion (4-AD) and androstanedione (A-dion). For all experiments, cells were preincubated with cortisol and subsequently incubated with [14C]T or [14C]4-AD as the substrate in medium without phenol red and with serum charcoal stripped of steroids. The results showed no aromatase activity in any of the cell lines under the experimental conditions used, and preincubation with cortisol had no effect on the enzyme activity. With [14C]T as the substrate, the metabolized level of DHT was very similar in the three cell lines, though MCF-7/LCC1 and MCF-7/LCC2 utilized the substrate to a much lesser extent. The amount of DHT and 4-AD produced were comparable in the two hormone-resistant cell lines, while the amount of 4-AD was significantly higher in MCF-7 cells. No differences in enzyme activity were found in the three cell lines when [14C]4-AD was used as the substrate. This study showed an altered androgen metabolism in the MCF-7/LCC1 and MCF-7/LCC2 sublines compared to the parent MCF-7. However, since treatment with DHT and T inhibited cell growth equally well in all three tumor cell lines, it is unlikely that the found differences in steroid metabolism was involved in the acquisition of the endocrine resistance of the two MCF-7 sublines.
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PMID:Steroid metabolism in the hormone dependent MCF-7 human breast carcinoma cell line and its two hormone resistant subpopulations MCF-7/LCC1 and MCF-7/LCC2. 945 94

The high concentrations of estradiol (E2) found in breast tumors of postmenopausal women could be the result of enhanced uptake from plasma or in situ aromatization of androgens to estrogens. To test the relative importance of these two mechanisms, a model system allowing precise distinction between each is required. Such a model was established using aromatase (A+)- and sham (A-)-transfected MCF-7 cells inoculated into ovariectomized (OVX) nude mice. To validate the model, the confounding effect of peripheral aromatization was first excluded experimentally. A- cells were inoculated into OVX mice as homoimplants (A- cells on both flanks) or heteroimplants (A- cells on one flank and A+ cells on the other), and growth of A- cells in response to exogenous aromatase substrate, androstenedione (delta4A), was evaluated. A- cells did not grow in either group during the 8 weeks of observation, indicating the lack of peripheral aromatization in OVX mice. The biological effects of in situ aromatization were then directly examined. We found that A+ cells in the heteroimplant group grew rapidly, and that the average weight of A+ tumor was 7.6-fold larger and tissue E2 concentration was 3-4-fold higher than A- tumors grown in the same animals. These results demonstrate that in situ aromatization rather than uptake can be a determinant of tumor E2 content and growth stimulation. An additional experiment was then designed to evaluate the relative importance of in situ synthesis versus uptake under conditions reflecting postmenopausal physiology. Groups of OVX mice bearing A+ cells received E2 Silastic implants to clamp plasma levels at 5, 7, 10, and 20 pg/ml or delta4A by injection. The highest tumor E2 concentration and growth rate were found in the group receiving delta4A. E2 delivered by Silastic implants always produced lower tissue E2 levels and tumor growth rates than resulted from in situ synthesis. These data provide direct evidence that under physiological conditions reflecting those in postmenopausal women, in situ aromatization in breast tumor makes a major contribution to tissue E2 content. As further validation that our experimental paradigm models the postmenopausal state, we studied OVX animals not given delta4A as substrate. A+ cells also grew under these conditions, and the aromatase inhibitor 4-hydroxyandrostenedione reduced both tumor E2 level and growth rate, providing additional evidence of the importance of in situ synthesis. These studies provide the first direct evidence that in situ synthesis of E2 in breast tumors, as opposed to peripheral aromatization and uptake from plasma, can enhance tissue E2 levels and stimulate tumor growth.
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PMID:In situ aromatization enhances breast tumor estradiol levels and cellular proliferation. 950 Apr 52

Although the antiestrogen tamoxifen has been the mainstay of therapy for estrogen receptor (ER)-positive breast cancer, successful treatment of responsive tumors is often followed by the acquisition of tamoxifen resistance. Subsequently, only 30-40% of patients have a positive response to second hormonal therapies. This lack of response might be explained by mechanisms for tamoxifen resistance that sensitize ER pathways to small amounts of estrogenic activity present in tamoxifen or that bypass ER pathways completely. To elucidate one possible mechanism of tamoxifen resistance, we treated ovariectomized tumor-bearing mice injected with fibroblast growth factor (FGF)-transfected MCF-7 breast carcinoma cells with the steroidal antiestrogen ICI 182,780 or one of two aromatase inhibitors, 4-OHA or letrozole. These treatments did not slow estrogen-independent growth or prevent metastasis of tumors produced by FGF-transfected MCF-7 cells in ovariectomized nude mice. FGF-transfected cells had diminished responses to ICI 182,780 in vitro, suggesting that autocrine activity of the transfected FGF may be replacing estrogen as a mitogenic stimulus for tumor growth. ER levels in FGF transfectants were not down-regulated, and basal levels of transcripts for estrogen-induced genes or of ER-mediated transcription of estrogen response element (ERE) luciferase reporter constructs in the FGF expressing cells were not higher than parental cells, implying that altered hormonal responses are not due to down-regulation of ER or to FGF-mediated activation of ER. These studies indicate that estrogen independence may be achieved through FGF signaling pathways independent of ER pathways. If so, therapies directed at the operative mechanism might produce a therapeutic response or allow a response to a second course of antiestrogen treatment.
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PMID:Tamoxifen-resistant fibroblast growth factor-transfected MCF-7 cells are cross-resistant in vivo to the antiestrogen ICI 182,780 and two aromatase inhibitors. 953 40

To determine the most effective strategies for the treatment of postmenopausal hormone dependent breast cancer, we recently developed a model system in nude mice. In this model, estrogen receptor-positive human breast cancer cells (MCF-7) stably transfected with the aromatase gene are inoculated into ovariectomized, immunosuppressed (nude) mice. These cells synthesize sufficient estrogen from androgen substrate to stimulate their proliferation and the development of tumors. Moreover, estrogen secreted by the tumor cells maintains uterine weight comparable to that of the intact mouse. In the present study, we employed this model to investigate the effects of the aromatase inhibitor, letrozole (CGS 20267 [Femara]) on mammary tumor growth and on the uterus. We also used this model to predict the effects of combining two aromatase inhibitors, letrozole and anastrozole (Arimidex), with the antiestrogen tamoxifen (Nolvadex). Letrozole was found to be a highly potent inhibitor of tumor proliferation and more effective than tamoxifen. No stimulation of uterine growth was observed with the aromatase inhibitors. However, the combination of letrozole or anastrozole and tamoxifen was no more effective than either aromatase inhibitor alone. The agonistic effect of tamoxifen on the uterus was observed when it was given alone and when combined with the aromatase inhibitors. Furthermore, letrozole had the most potent antitumor activity when compared to other aromatase inhibitors and antiestrogens. No additional benefit was observed by combining these agents with tamoxifen over treatment with aromatase inhibitors alone.
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PMID:Preclinical studies using the intratumoral aromatase model for postmenopausal breast cancer. 955 90

Aromatase, a cytochrome P450, catalyzes three consecutive hydroxylation reactions converting C19 androgens to aromatic C18 estrogens. The control of human aromatase expression is complex in that several promoters drive aromatase expression in a tissue-specific manner. Promoters I.3 and II are situated within the 700-bp region immediately upstream of exon II of the human aromatase gene, and these promoters have been shown to drive aromatase expression in breast tumors. This paper reports the characterization of a negative regulatory element that is situated between promoters I.3 and II and down regulates the action of these promoters. This negative regulatory element is thought to be a silencer element (S1) because it acts in an orientation- and promoter-independent manner. The position of S1 (5'-CCAAGGTCAGAAATGCTGCAATTCAAGCCA-3') was mapped by DNase I footprinting and DNA deletion analyses. The region contains three pairs of inverted repeats, as indicated by an underline, probably explaining why S1 functions in both orientations. Chloramphenicol acetyltransferase functional analyses indicated that the transcriptional activity of promoter I.3 was suppressed two- to three-fold by S1. Mutations of two inverted repeat segments (i.e., TTC and CC) in S1 destroyed its silencing action and modified the protein binding patterns in DNA mobility shift analysis. UV cross-linking experiments with 32P-labeled bromodeoxyuridine-substituted S1 as the probe and nuclear extracts from MCF-7 breast cancer cells and skin fibroblasts revealed that four major nuclear proteins, with molecular masses of approximately 150, 45, 30, and 25 kDa, bound to this element. Interestingly, two smaller proteins could be competed by an unlabeled fragment which contains promoter I.3. In addition, mutation of S1 at the region CC destroyed the ability to compete with the wild-type S1 for the binding of 30- and 25-kDa proteins. These results led us to propose that S1 down regulates the action of promoter I.3, and the 30- and 25-kDa proteins present in the nuclear extract of MCF-7 cells and skin fibroblasts are involved in the silencer action.
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PMID:Characterization of a silencer element in the human aromatase gene. 960 55

Estrogen receptor activation in hormone dependent cells (MCF-7 and T47D) and hormone independent cells (MDA-MB-231) was measured by bioluminescence in stably transfected human breast cancer MCF-7, T47D and MDA-MB-231 cell lines with a reporter gene which allows expression of the firefly luciferase enzyme under the control of an estrogen regulatory element. Estrogen receptor activation by estrogens and steroid sulfates such as estrone 3-sulfate (E1S), estradiol 3-sulfate (E2S), estriol 3-sulfate (E3S) and dehydroepiandrosterone sulfate (DHEAS) were studied and compared in these cell lines. DHEAS, at a physiological plasma concentration only (1 microM), had a high "estrogen-like" effect in MCF-7 and T47D cells. In contrast, estrogen sulfates did not have any effect on the luciferase activity at their physiological plasma concentration. These results suggest that MCF-7 and T47D cells could convert DHEAS to estrogens by aromatase and/or to estrogen-like compounds by other enzymatic systems. This is the first demonstrahon of the steroid sulfates action through their metabolites on the estrogen receptor. Therefore, at the concentrations observed in physiological conditions, DHEAS could contribute to the pool of compounds having estrogenic activities in human breast cancer hormone dependent cell lines.
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PMID:Dehydroepiandrosterone sulfate estrogenic action at its physiological plasma concentration in human breast cancer cell lines. 967 90

Estrogen is the major hormonal stimulus for growth of the hormonal-dependent type of breast cancer. The rate-limiting step in the conversion of androgens to estrogens in breast tumors is catalyzed by aromatase, one of a series of related P-450 enzymes involved in the production of steroid hormones. An interesting correlation has been found between KGF mRNA and aromatase mRNA expression in human breast tumors. Tumors that express aromatase mRNA exhibit strong KGF expression, while tumors that do not express aromatase are weak or negative for KGF expression. Thus, it is reasonable to theorize that a possible association between KGF and aromatase in controlling human breast tumor growth exists. The purpose of the current study was to establish whether there is any interaction between KGF, which is known to have epithelial-specific mitogenic activity on breast cancer cells in vitro, and the synthesis of estradiol within the hormone-dependent breast cancer epithelial cells. In the present study, we have demonstrated that KGF stimulates aromatase activity in human breast cancer cells (MCF-7) in a dose-dependent manner. Our data shows that recombinant human KGF, at a dose as low as 10 ng/ml, can significantly increase aromatase activity 2-fold over controls. In agreement with this observation, we also found that aromatase mRNA levels were increased after 10 ng/ml KGF treatment in MCF-7 cells. These results indicate that the stimulatory effect of KGF on aromatase activity may be mediated by alterations in aromatase mRNA levels or in the efficiency of the translation of the message in MCF-7 cells. In addition, our results have demonstrated that modulation of aromatase activity appears to correlate with the stimulation of proliferative activity by KGF in MCF-7 cells. These results are consistent with our previous observations that estradiol-17 beta stimulates KGF expression in human breast cancer stromal cells, leading to the speculation that breast malignant transformation is associated with a positive feedback stimulation, whereby estradiol-17 beta stimulates breast cancer stromal cell production of KGF, and KGF subsequently stimulates aromatase activity in breast cancer cells, consequently raising levels of estradiol-17 beta, in turn acts on breast stromal cells to yield more KGF. Such a positive feedback loop could play an important role in the loss of growth control in human breast cancer cells.
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PMID:Keratinocyte growth factor (KGF) induces aromatase activity in cultured MCF-7 human breast cancer cells. 970 7

Aromatase activity is increased in breast tumors and it is possible that this results from stimulation by cytokines and/or prostaglandin E2 (PGE2) which regulate the activity of this enzyme. As different promoters can be used to control aromatase gene expression in normal and malignant breast tissues, which are regulated by different factors, we are currently investigating the relative roles of cytokines and PGE2 in controlling breast tumor aromatase activity. No significant effect of PGE2 on aromatase activity in MCF-7 breast cancer cells has so far been detected. However, preliminary evidence was obtained, from co-cultures of MCF-7 cells and breast tumor-derived fibroblasts, that MCF-7 cells secrete a factor, possibly a cytokine, which can act in a paracrine manner to enhance aromatase activity in stromal cells. Understanding the complex regulation of aromatase activity in breast tumors could lead to novel therapies for specifically inhibiting tumor estrogen synthesis.
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PMID:Biochemical control of breast aromatase. 979 12

Aromatase mRNA in non-malignant breast tissues was mainly transcribed form skin fibroblast/fetal liver-specific exon 1 (exon 1b) of the aromatase gene. However, in half the cases of breast cancers, switching of the alternative exons 1 from exon 1b to ovary-specific exon 1 (exon 1c) was observed, and expression levels of aromatase mRNA in breast cancer tissues were significantly higher than those in the distal regions to tumors or in non-malignant breast tissues. Co-culture or addition of the conditioned medium of breast cancer cells, MCF-7 caused increase of aromatase mRNA in cultured adipose stromal cells from breast tissues together with switching from exon 1b to exon 1c. Removal of fetal calf serum (FCS) from the culture medium or addition of forskolin or phorbol ester (TPA) also induced rapid elevation of aromatase mRNA and switching to exon 1c, whereas TGFbeta almost abolished the expression, suggesting that cancer cells might secret forskolin- or TPA-like stimulatory factors, or consume TGFbeta-like inhibitory factors in serum for expression of aromatase mRNA. The promoter region responsible for transcription from exon 1b and the switching was investigated using a newly developed reporter carrying 4 major alternative exons 1 and promoters. Transcriptional elements responsible for preferential utilization of exon 1b were identified on the promoter region between -300 and -400 of exon 1b. Gel shift assay showed a unique site for a FCS-dependent DNA binding factor just downstream of GRE (glucocorticoid responsive element) in this promoter region.
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PMID:Molecular analysis of aberrant expression of aromatase in breast cancer tissues. 979 13

An intratumoral aromatase model in the ovariectomized nude mouse was developed which simulated the hormone responsive postmenopausal breast cancer patient. MCF-7, human breast cancer cells transfected with the aromatase gene, inoculated into ovariectomized nude mice are able to synthesize sufficient estrogens to enhance cell proliferation and the development of tumors. These tumors are responsive to both antiestrogens and aromatase inhibitors. However, letrozole was found to be more effective than tamoxifen and caused tumor regression, a result not previously noted in nude mice with endocrine treatments. When the aromatase inhibitors were combined with tamoxifen, tumor growth was suppressed to about the same extent as treatment with the aromatase inhibitors alone. Thus, there was no additive or synergistic effects of combining tamoxifen with aromatase inhibitors. These results suggest that letrozole has the potential to be more effective than tamoxifen for achieving greater reduction in estrogenic effects on tumors and uterus in postmenopausal breast cancer patients. In addition, sequential treatment with these agents is likely to be more beneficial to the patient in terms of longer response to treatment.
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PMID:Intratumoral aromatase model: the effects of letrozole (CGS 20267). 979 14


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