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

Two human breast cancer cell lines (MCF-7 and MDA-MB-231) and one cell line derived from normal human breast (HBL-100) were examined for the presence of aromatase activity by determining the amounts of [3H]estradiol ([3H]E2) formed by cell cultures incubated with [3H]testosterone. Aromatase activity was demonstrable in both breast cancer cell lines, but estradiol synthesis was not observed in HBL-100 cultures. The [3H]E2 content of MCF-7 cultures rose as a function of incubation time and substrate concentration. Furthermore, [3H]E2 formation by this cell line was suppressed by several known inhibitors of human placental aromatase. These observations represent the first evidence that some lines of continuously cultured human breast cancer cells, like some human breast tumors, are capable of forming estrogen from an extracellular precursor steroid. Cultured breast cells may provide model systems for investigating the relative importance of intracellular estrogen formation in the regulation of human breast cancer cell growth.
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PMID:Estradiol formation from testosterone by continuously cultured human breast cancer cells. 45 46

Aromatase, a cytochrome P-450, catalyzes the formation of aromatic C18 estrogenic steroids from C19 androgens. DNA sequence analysis of the human aromatase gene has revealed that a putative promoter sequence exists immediately up-stream of the second exon. Chloramphenicol acetyltransferase functional analyses of cells transfected with chloramphenicol acetyltransferase expression plasmids containing various DNA fragments derived from the 3'-end of the first intron of the aromatase gene were performed to show that a promoter indeed exists in this region. However, in all of the cell lines used in this study, MCF-7, JAR, OVCAR-3, and skin fibroblast, the function of this promoter was inhibited by a negative regulatory element situated up-stream from the promoter. The results further suggest that this inhibitory element behaves as a silencer element, in that it could inhibit a simian virus-40 promoter from a distance of several kilobases. This negative element worked in both orientations and inhibited the functions of several promoters, including the newly identified promoter situated in the 3'-end of the first intron of the human aromatase gene. Primer extension analysis has been performed to determine the potential transcription start site. The mechanism of the regulation of aromatase expression is known to be very complex. The presence of a promoter and a silencer at the 3'-end of the first intron may represent one additional way that aromatase expression is controlled in estrogen-producing cells.
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PMID:Identification of a promoter and a silencer at the 3'-end of the first intron of the human aromatase gene. 133 79

Currently there is much interest in the role that growth factors may play in the development of human breast tumours. We have shown previously that growth factors secreted by breast tumours may influence the activity of oestradiol hydroxysteroid dehydrogenase, the enzyme which catalyses the interconversion of oestrone (E1) and oestradiol. As the formation of E1 from its sulphate (E1S) by oestrone sulphatase may be quantitatively more important than production from androstenedione via aromatase, we have studied the effect of insulin-like growth factor-1 (IGF-I) and basic fibroblast growth factor (bFGF) on oestrone sulphatase activity in the hormone-dependent MCF-7 and the hormone-independent MDA-MB-231 breast cancer cell lines. In both these cell types, bFGF (1-200 ng/ml) and IGF-I (25-200 ng/ml) significantly stimulated oestrone sulphatase activity in a dose-dependent manner (by 8-60%) after 48 h. Additionally, cycloheximide significantly inhibited (by 90-120%) this stimulation of oestrone sulphatase activity by the two growth factors in both MCF-7 and MDA-MB-231 cells. Basal oestrone sulphatase activity was higher in the oestrogen receptor, ER-ve MDA-MB-231 cells than in the ER + ve MCF-7 breast cancer cells. We conclude that these growth factors, believed to be secreted by breast tumours, may induce enzymes of oestrogen synthesis and hence increase local production of oestrogens.
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PMID:Modulation of oestrone sulphatase activity in breast cancer cell lines by growth factors. 156 28

Of the total number of breast cancers approx. 30-50% are hormone-dependent and estradiol is one of the main factors of cancerization. Consequently, the control of this hormone inside the cancer cell is of capital importance because it is well established that the inhibition of estradiol biosynthesis can have a positive effect on the evolution of the disease. The blockage of estradiol can be obtained by the action of anti-aromatases, anti-sulfatases, the control of the 17 beta-hydroxysteroid dehydrogenase activity or by the stimulation of the sulfotransferase which converted the estrogens in their sulfates. In breast cancer tissue estrone sulfate is quantitatively the most important source of estradiol. In the intact cell, estrone sulfatase activity is very intense in the hormone-dependent cell lines (e.g. MCF-7, T-47D) but very small activity is observed in the hormone-independent (e.g. MDA-MB-231, MDA-MB-436) cell lines. However, this activity became very strong after homogenization in the hormone-independent cells, suggesting the presence of repressive factor(s) for this enzyme or its sequestering in an inactive form, in the intact cells of these cell lines. In a series of previous studies it was found that in hormone-dependent cell lines different anti-estrogens: tamoxifen and derivatives, ICI 164,384, very significantly decrease the estradiol concentration originated from estrone sulfate, and recently it was observed that Decapeptyl (D-Trp6-gonadotropin-releasing hormone) in the presence of heparin can also decrease the conversion of estrone sulfate into estradiol. No significant effect was obtained in the presence of heparin or Decapeptyl alone. The estrone sulfatase activity can be inhibited by progesterone, the progestagen R-5020, and testosterone. In another series of recent studies the presence of very strong estrogen sulfotransferase activity has been shown in one breast cancer cell line, the MDA-MB-468. We can conclude that: (1) the control of estradiol concentration can be carried out in the breast cancer tissue itself; (2) estrone sulfate can play an important role in the bioavailability of estradiol in the breast cancer cell; and (3) as is the case for the aromatase, the control of: the estrogen sulfatase, estrogen sulfotransferase, and 17 beta-hydroxysteroid dehydrogenase can be new targets for therapeutic applications in breast cancer.
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PMID:Recent data on estrogen sulfatases and sulfotransferases activities in human breast cancer. 158 Sep 21

We have studied the effects of various steroids on DNA synthesis in MCF-7 human breast carcinoma cells, which have aromatase activity and which exert an oestrogen receptor-mediated growth, to assess the significance of intracellular aromatase on growth stimulation as well as inhibition by aromatase inhibitors. The cells were cultured for 96 h in phenol red-free medium containing 10% charcoal-treated fetal bovine serum and test reagents and pulse-labelled with [3H]thymidine. Physiological concentrations of oestradiol, oestrone, testosterone (T) and androstenedione (AD) stimulated thymidine incorporation. However, oestrone-sulphate and dihydrotestosterone (DHT) only stimulated at concentrations greater than the physiological levels. T and DHT stimulation was blocked by tamoxifen, but not by cyproterone acetate, suggesting that the stimulation was mediated via the oestrogen receptor but not by the androgen receptor. Stimulation by T and AD was reduced by aminoglutethimide and 14 alpha-hydroxy-4-androstene-3,6,17-trione, both of which inhibit aromatase activity, however, stimulation by nonaromatizable DHT was not reduced by the inhibitors, suggesting that androgens were converted by the intracellular aromatase to oestrogens which stimulated the thymidine incorporation. It is suggested that intracellular aromatase significantly contributes to the stimulation of DNA synthesis and that aromatase inhibitors suppress the stimulation.
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PMID:Contribution of aromatase to the deoxyribonucleic acid synthesis of MCF-7 human breast cancer cells and its suppression by aromatase inhibitors. 160 40

MCF-7 cell line is a model for estrogen-dependent tumors that have both aromatase activity and estrogen receptor. We studied the contribution of aromatase to cell growth and DNA synthesis by means of aromatase inhibitors. MCF-7 cells were cultured in phenol red-free medium containing 10% charcoal-treated fetal bovine serum and test reagents for 96 hours and pulse-labeled with [3H]thymidine for 1 hour. Physiological concentrations of estradiol, estrone, testosterone(T) and androstenedione(delta 4A) increased [3H] thymidine incorporation. Stimulation by T or dihydrotestosterone (DHT) was reduced by tamoxifen, but not by androgen receptor blocker cyproterone acetate, suggesting that T and DHT stimulated cellular proliferation via estrogen receptor but not via androgen receptor. Stimulation by T or delta 4A was reduced by aromatase inhibitors (aminoglutethimide and 14 alpha-hydroxy-4-androstene-3,6,17-trione), but stimulation by nonaromatizable DHT was not reduced by aromatase inhibitors. These results have suggested that estrogens which are biosynthesized from androgens by the intracellular aromatase play a significant role in growth stimulation of MCF-7 cells and that aromatase inhibitors block this pathway. These methods are useful in assessing the ability of aromatase inhibitors to suppress cell growth.
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PMID:[Growth inhibition of MCF-7 human breast cancer cells by aromatase inhibitors]. 183

A novel nonsteroidal aromatase inhibitor, TAN-931, was isolated from the culture filtrate of a soil isolate fungus, No. 8974. The strain was identified as Penicillium funiculosum No. 8974. TAN-931 inhibited human placental and rat ovarian aromatase activity, and the IC50 value was 17.2 and 162 microM, respectively. The inhibition of human placental aromatase was uncompetitive with respect to androstenedione conversion with a Ki value of 40 microM. When TAN-931 was subcutaneously administered at doses of 25, 50 and 100 mg/kg (once/day, x4) to 20-day-old female Sprague-Dawley rats treated with gonadotropin, the plasma estradiol-17 beta level and the weight of ovaries and uterus were markedly reduced in a dose-dependent manner. The in vivo inhibitory activity of TAN-931 was more potent than that of 4-hydroxyandrostenedione. Consecutive administration of TAN-931 (100 mg/kg, sc, twice/day, x 7) to 9-week-old male Sprague-Dawley rats did not induce any adrenal hypertrophy even though administration of aminoglutethimide caused 2-fold enlargement of the adrenal under the same conditions. Specific binding of TAN-931 to the estrogen receptor from a human breast cancer cell line, MCF-7, was not detected.
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PMID:TAN-931, a novel nonsteroidal aromatase inhibitor produced by Penicillium funiculosum No. 8974. I. Taxonomy, fermentation, isolation,characterization and biological activities. 207 87

A mammalian cell expression plasmid, pH beta-Aro, containing the human placenta aromatase complementary DNA was constructed. The prepared plasmid was used to transfect breast cancer cells (MCF-7), noncancerous breast cells (HBL-100), and Chinese hamster ovary cells by a stable expression method. While the maximum velocities for aromatase expressed in three types of cells were different (10-201 pmol of [3H2O] formed/h/mg) using [1 beta, 2 beta-3H]androst-4-ene-3,17-dione as the substrate, the apparent Michaelis-Menten constants were found to be similar (39.9-57.8 nM) and were within the range determined for the enzyme existing in human placenta. The expressed activities were inhibited by the known aromatase inhibitors, 4-hydroxyandrostenedione and aminoglutethimide, at concentrations that normally inhibit the human placental aromatase. However, it was found that the inhibition profiles were different for aromatase expressed in different types of cells, suggesting that other factors, such as the uptake of the inhibitor, may also play a role in determining the inhibition efficiency. These constructed aromatase expressing mammalian cell lines will be very useful tools for aromatase inhibitor screening.
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PMID:Stable expression of human aromatase complementary DNA in mammalian cells: a useful system for aromatase inhibitor screening. 220 60

Androstenedione analogs containing 7 alpha-substituents have proven to be potent inhibitors of aromatase both in vitro and in vivo. Several of these agents have exhibited higher affinity for the enzyme complex than the substrate. In order to examine further the interaction(s) of 7-substituted steroids with aromatase, biochemical and pharmacological studies were performed on 7 alpha-thiosubstituted androstenediones and 7-substituted 4,6-androstadiene-3,17-diones. Potent inhibition of aromatase activity in human placental microsomes has been observed with several new 7 alpha-thiosubstituted androstenediones. 7-Benzyl- and 7-phenethyl-4,6-androstadiene-3,17-diones effectively inhibited microsomal aromatase, with apparent Kis ranging from 61 to 174 nM. On the other hand, 7-phenyl-4,6-androstadiene-3,17-dione exhibited poor activity, with an apparent Ki of 1.42 microM. Similar inhibitory activity was observed with reconstituted, purified cytochrome P450Arom preparations. Additionally, these agents were evaluated for inhibition of aromatase activity in two human carcinoma cell lines, the MCF-7 human mammary cancer line and the JAr choriocarcinoma line. The 7 alpha-thiosubstituted androstenediones and 7-substituted 4,6-androstadiene-3,17-diones produced dose-dependent inhibitions of aromatase activity in the cell cultures. The most effective inhibitors were the 7 alpha-substituted androstenediones, with EC50 values ranging from 7.3 to 105 nM. Finally, the JAr cell culture system exhibited prolonged inhibition of aromatase activity following exposure to 7 alpha-APTADD, suggesting enzyme inactivation by this inhibitor. Thus, these agents are effective aromatase inhibitors, and the results encourage further development of this group of medicinal agents for the treatment of estrogen-dependent mammary carcinoma.
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PMID:Biochemical and pharmacological development of steroidal inhibitors of aromatase. 225 41

7 alpha-(4'-Amino)phenylthio-1,4-androstadiene-3,17-dione (7 alpha-APTADD), a potent enzyme-activated irreversible inhibitor, was examined in two different human cell culture lines, MCF-7 human mammary carcinoma cells and JAr choriocarcinoma cells. Both the MCF-7 and JAr cell culture systems exhibit aromatase activity, and 7 alpha-APTADD was evaluated for its aromatase-inhibitory activity, for its ability to inactivate the enzyme complex, and for the time course of recovery of enzymatic activity. This inhibitor produced a dose-dependent inhibition of aromatase activity in MCF-7 cells and in JAr cells, with EC50 values of 91 and 7.3 nM, respectively. Two other steroidal inhibitors, 7 alpha-(4'-amino)phenylthio-4-androstene-3,17-dione and 4-hydroxyandrostenedione, produced similar dose-response curves and EC50 values, while the nonsteroidal aminoglutethimide was less effective. Both cell culture systems exhibited prolonged inhibition of aromatase activity following exposure to 7 alpha-APTADD, suggesting enzyme inactivation by this inhibitor. Thus, 7 alpha-APTADD is an effective inhibitor of aromatase in MCF-7 mammary carcinoma cells and in JAr choriocarcinoma cells. These studies encourage further development of this group of medicinal agents for the treatment of estrogen-dependent mammary carcinoma.
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PMID:Aromatase inhibition by an enzyme-activated irreversible inhibitor in human carcinoma cell cultures. 234 May 13


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