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At least 811 records · Page 45Linked to original sources
PubMed2004

The effect of doxorubicin and retinoids on proliferation, necrosis and apoptosis in MCF-7 breast cancer cells.

Doxorubicin (Adriamycin) is the most active drug in the treatment of breast cancer. The aim of this study was to investigate the interaction of doxorubicin and retinoids in the inhibition of proliferation of hormone sensitive (ER+) human breast cancer cell line MCF-7 and to find out whether this combination can result in the enhancement of its therapeutic effect. As a comparison we also used estradiol and tamoxifen. We also made an attempt to elucidate the effect of these compounds on the stimulation of the apoptotic pathway in breast cancer cells. Cell proliferation in a 24-hour culture was assessed by [3H] thymidine incorporation into cancer cells and by immunocytochemical analysis of cellular cycle-related PCNA and Ki-67 antigens expression, after the incubation of the cell culture with 10, 20 and 50 nM doxorubicin (DOX), 2 nM estradiol (E2), 10 microM tamoxifen (TAM) and 1 nM, 0.01, 0.1, 1 and 10 microM of all-trans retinoid acid (ATRA). The assessment of cell viability and analysis of apoptotic and necrotic cells were performed after the 72-hour incubation of the culture with the examined substances and following apoptosis induction using acridine orange and ethidine bromide. Of the doxorubicin concentrations used in the study, 20 nM inhibited thymidine incorporation to 84.83 +/- 10.00% (control=100%). In the same culture conditions, 2 nM E2 stimulated cancer cells to 157.09 +/- 8.84%. Concentrations of 10 microM TAM and 10 microM ATRA inhibited the proliferation to 63.16 +/- 7.85% and 52.19 +/- 3.21%, respectively. A statistically significant reduction of these values was observed when 20 nM DOX was added to medium with E2 - 39.24 +/- 7.6%, TAM - 48.34 +/- 2.05% and ATRA - 21.98 +/- 1.69%, respectively; the percentage of PCNA- and Ki-67-positive cells was also reduced. Despite high antiproliferative efficacy of 20 nM DOX and 10 microM ATRA combination, the percentage of apoptotic cells was only 25 +/- 0.81%, being similar to that obtained in the culture with 20 nM DOX. The concentrations of 10, 20 and 50 nM DOX that were used to inhibit the proliferation of MCF-7 cell line were not particulary effective. The inhibitory effect was obtained when 20 nM of DOX and E2, TAM or ATRA were used simultaneously. The use of E2 caused a two-fold decrease in the percentage of proliferating cells. It was also shown that the effectiveness of DOX in combination with ATRA is significantly higher than that of DOX combined with TAM, which might suggest a valuable approach to the treatment of breast cancer.

Apoptosis↗
PubMed2005

[Modulation and function of estrogen receptor isoforms alpha and beta in endometrial carcinoma cells].

OBJECTIVE: To explore an efficient way to modulate the expression of estrogen receptor (ER) alpha and beta, and to build up a model of endometrial cancer cell expressing predominantly one isoform of ER and to verify the roles of ER alpha and beta in the tumorigenesis of endometrial cancer associated with estrogen and tamoxifen (TAM). METHODS: A series of oligodeoxyribonucleotides (ODN) against alpha or beta regions of ER alpha or beta were synthesized and tested in human endometrial cancer cell lines (Ishikawa) that express functional ER alpha and beta. The expressions of two ER isoforms were detected by western blot using specific antibodies. Then we studied the change of Ishikawa proliferation in response to 17beta-estradiol and TAM under the influence of antisense ODN. RESULTS: (1) Transfection with antisense ODN directed against the ERalpha and ERbeta could significantly inhibit target protein production. (2) 17beta-estradiol could increase the proliferation of Ishikawa cells, but they lost the ability to proliferate in response to 17beta-estradiol after transfected with ERalpha antisense ODN especially at hours 24, 48 and 72 (P < 0.05). There was no obvious change in cell numbers of Ishikawa in response to 17beta-estradiol which were transfected with ERbeta antisense ODN. (3) TAM could also increase the growth of Ishikawa cells. After transfected with ERalpha antisense ODN, the cells lost the ability to proliferate in response to TAM at hours 24, 48 and 72 (P < 0.05). The inhibition was also seen in Ishikawa cells transfected with ERbeta antisense ODN at hour 72. CONCLUSIONS: (1) Antisense ODN directed against the ERalpha or ERbeta can inhibit the expression of ERalpha or ERbeta effectively. (2) ERalpha may be the primary receptor in the proliferation of Ishikawa cells in response to 17beta-estradiol. Both ERalpha and ERbeta are involved in agonist impact of TAM on endometrial cancer cells.

Cell Line, Tumor↗
PubMed2005

[The synergistic inhibitory effect of 5-aza-2-deoxycytidine and Tamoxifen on estrogen receptor alpha negative breast cancer cell lines in vitro].

OBJECTIVE: To observe if ER alpha gene can be induced by 5-aza-CdR in ER alpha negative human breast cancer cell lines (MDA-MB-231 and MDA-MB-435) and the synergistic inhibitory effects of 5-aza-CdR and Tamoxifen on these two cell lines in vitro. METHODS: The status of 5'CpG island methylation of ER alpha gene in ER alpha negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines and 20 cases of breast cancer tissue was studied by MSP, the expression of ER alpha mRNA was inspected by using RT-PCR after these two cell lines were treated with 5-aza-CdR. Cell proliferation was evaluated by MTT assay, distribution of cell cycle and rate of apoptosis were determined by flow cytometry after these two cell lines were treated with 5-aza-CdR or TAM alone, or in combination in vitro. RESULTS: The 5'CpG island is methylated in the core promotor of ER alpha gene in ER alpha negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines and the methylating rate is 25.0%, 66.7%, 83.3%, 100% in 20 cases of breast cancer tissue of stage I, II, III, IV, respectively. The expression of ER alpha mRNA was induced in these two cell lines after treated with 5-aza-CdR, MTT array showed the proliferation activity of these two cell lines was obviously reduced in 5-aza-CdR group and the inhibitory effect on proliferation was enhanced when 5-aza-CdR combined with TAM compared with control group, the induction of apoptosis was 11.20% and 8.71% respectively by 5-aza-CdR, while the rate of apoptosis is 48.8% and 53.1% when these two cells were treated with 5-aza-CdR combined with TAM. CONCLUSIONS: 5-aza-CdR can re-express ER alpha by demethylating and sensitive ER alpha negative human breast cancer cell lines to TAM, 5-aza-CdR and TAM synergistically inhibit proliferation and induce apoptosis in ER alpha negative human breast cancer cell lines, thus offer a new way for the treatment of ER alpha negative breast cancer.

Adult↗
PubMed1991

Three amino acid substitutions in domain I of calmodulin prevent the activation of chicken smooth muscle myosin light chain kinase.

TaM-BMI is a genetically engineered chimeric protein consisting of the first 55 amino acids of cardiac troponin C (but with the normally inactive first Ca2+ binding domain reactivated by site- directed mutagenesis) ligated to the last three domains of chicken calmodulin (George, S.E., VanBerkum, M.F., Ono, T., Cook, R., Hanley, R.M., Putkey, J.A., and Means, A. R. (1990) J. Biol. Chem. 265, 9228-9235). This protein binds chicken smooth muscle myosin light chain kinase (smMLCK) but fails to activate the enzyme, thus functioning as a potent competitive inhibitor (Ki = 66 nM). We have created 29 mutants of calmodulin designed to identify the minimal number of alterations which must be introduced in the first domain to convert the protein to a competitive inhibitor of smMLCK. Alterations of three amino acids predicted to lie on the external surface of calmodulin (E14A, T34K, S38M) recapitulated the phenotype of TaM-BMI and exhibited a Ki of 38 nM. Both the triple mutant and TaM-BMI activated phosphodiesterase and bound a synthetic peptide analog of the calmodulin binding region of smMLCK with an affinity similar to that of native calmodulin (Kact and Kd values of approximately 2 and 3 nM respectively). When a synthetic peptide analog of the myosin light chain phosphorylation site was used as substrate rather than the 20-kDa light chains, TaM-BMI and the triple mutant were partial agonists: the Km for peptide substrate was increased 100- and 60-fold, and catalytic activity was 45 and 60%, respectively, relative to calmodulin. These data suggest TaM-BMI and E14A/T34K/S38M may interact with the calmodulin binding domain of smMLCK in a manner similar to calmodulin. However, alterations in electrostatic and hydrophobic interactions created by the three amino acid substitutions prevent the conformational change in the enzyme usually produced by calmodulin binding. Lack of such changes results in loss of catalytic activity and light chain binding. Additionally, our results show that altering only 3 amino acids residues converts calmodulin to an enzyme-selective antagonist, thus demonstrating the ability to separate calmodulin binding to smMLCK from calmodulin-induced activation of the enzyme.

Animals↗
PubMed1991

Monoclonal nature of transient abnormal myelopoiesis in Down's syndrome.

Neonates with Down's syndrome occasionally show an excess of blasts in their peripheral blood. This disorder spontaneously resolves within several months and is called transient abnormal myelopoiesis (TAM) or transient myeloproliferative disorder. It has been uncertain whether the excess of blasts in TAM is a result of a clonal proliferation or a polyclonal reactive condition. The clonality of cells in females can be examined by analysis of the methylation patterns of the X chromosomes of proliferating cells using restriction fragment length polymorphism (RFLP). Using this strategy, we studied three females with Down's syndrome accompanied by TAM who showed heterozygosity in RFLP of either the hypoxanthine phosphoribosyltransferase or phosphoglycerate kinase gene. Analysis of the methylation patterns of these genes demonstrated a clonal nature for blasts in three patients. Thus, TAM is a clonal proliferative disorder. In addition, lymphocytes with a normal appearance contained in analyzed samples from these patients also showed a monoclonal pattern, suggesting that TAM may be a disorder of multipotent stem cells.

Bone Marrow↗
PubMed2006

Modeling end-users' acceptance of a knowledge authoring tool.

OBJECTIVES: Knowledge bases comprise a vital component in the classic medical expert system model, yet the knowledge acquisition process by which they are created has been characterized as highly iterative and labor-intensive. The difficulty of this process underscores the importance of knowledge authoring tools that satisfy the demands of end-users. The authors hypothesize that the acceptability of a knowledge authoring tool for the creation of medical knowledge base content can be predicted by an accepted model in the information technology (IT) field, specifically the Technology Acceptance Model (TAM). METHODS: An online survey was conducted amongst knowledge base authors who had previously established experience with the authoring tool software. The Likert-based questions in the survey were patterned directly after accepted TAM constructs with minor modifications to particularize them to the software being used. The results were analyzed using structural equation modeling. RESULTS: The TAM performed well in predicting endusers' behavioral intentions to use the knowledge authoring tool. Five out of seven goodness-of-fit statistics indicate that the model represents the behavioral intentions of the authors well. All but one of the hypothesized relationships specified by the TAM were significant with p values less than 0.05. CONCLUSIONS: The TAM provides an adequate means by which development teams can anticipate and better understand what aspects of a knowledge authoring tool are most important to their target audience. Further research involving other behavioral models and an expanded user base will be necessary to better understand the scope of issues that factor into acceptability.

Attitude↗
PubMedDate not supplied

Adjuvant hormone treatment and chemotherapy in postmenopausal women with operable breast cancer: a retrospective analysis.

Two hundred consecutive postmenopausal women with operable breast cancer and metastatic axillary nodes were treated during the period January - December 1981 with adjuvant chemotherapy (CMF) or hormonal treatment (tamoxifen). The distribution of receptor status (estrogen or progesterone), number of axillary metastatic nodes (less than = 3 or greater than 3), surgical treatment and size of the primary tumor were homogeneous in both groups. Receptor status and number of axillary lymph nodes were correlated with adjuvant treatment efficacy. Ten-year disease-free survival (DFS) was higher in the TAM-treated (72%) than in the CMF-treated group (52%) (p less than 0.01). In patients with less than = 3 axillary metastatic nodes, those treated with TAM had a higher DFS rate than those treated with CMF (75% vs 59%, p less than 0.01). There was no difference in DFS between CMF-and TAM-treated groups within the greater than 3 metastatic lymph node patients. In ER + primary tumors, DFS was higher in the subset treated with TAM (62%) than with CMF (51%) (p less than 0.05), whereas no difference in DFS was observed in ER- patients between the two treatment groups. Considering the TAM group, DFS was better (p less than 0.01) for ER+ cases than for ER- cases only at 5 years of observation. In the CMF group, DFS was not influenced by ER status. PgR content did not affect DFS in either adjuvant treatment group.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

[Effects of antiestrogenic drug tamoxifen on human placental secretion of progesterone and human chorionic gonadotropin during early gestation].

Placental villus tissue obtained from pregnant women of 6 to 7 weeks was cultured in vitro for four days, with or without addition of tamoxifen (Tam), an antiestrogenic drug. The levels of both progesterone (P) and human chorionic gonadotropin (hCG) in culture medium collected every day were measured by using radio-immuno assay, so as to observe the effects of Tam on the secretion of P and hCG by villus tissue as well as the time course of these effects. The experimental results showed that the levels of both P and hCG in the culture medium collected on the 3rd and 4th days in the Tam-treated group were significantly lower than those in the control group, indicating that Tam could have a direct inhibitory effect on the secretory function of the placental villus tissue during early pregnancy. The slow onset of the inhibitory effect was in correspondence with the clinical observation that the early pregnancy terminating effect of PGS would be potentiated after 4-5 days of Tam medication. In addition, this inhibitory effect of tamoxifen on the placental secretory function was suggested to be associated with a decrease in the responsiveness of placental tissue to GnRH.

Chorionic Gonadotropin↗
PubMedDate not supplied

Identification and distribution in the rat of acidic metabolites of tamoxifen.

Chromatographic analysis of acidic fractions of urinary radioactivity from immature female rats which had received the triarylethylene antiestrogen tamoxifen (TAM), labeled with 14C, resulted in the identification of two new metabolites. These were tamoxifen acid (TA), in which the side chain of TAM was changed to an oxyacetic acid moiety, and 4-hydroxytamoxifen acid (4-HTA), which had a similarly altered side chain plus a phenolic hydroxy group in its structure. In contrast to other TAM metabolites and other arylacetic acids, neither TA nor 4-HTA were eliminated as glucuronic acid or glycine conjugates in urine. Only small amounts of acidic radioactivity were found in liver tissue 24 and 48 hr after dosing, and none was detected in uterine tissue. However, TA plus 4-HTA accounted for 2.8% and 2.9% of the administered dose eliminated within 24 hr in urine and feces, respectively. These results suggest that TA and 4-HTA are important final products of TAM metabolism and that these, unlike other hydroxylated and/or dealkylated metabolites of this drug, may not contribute to the antiuterotrophic effects of TAM.

Animals↗
PubMed1991

[Response to rechallenged tamoxifen of metastatic breast cancer relapsed after surgical adjuvant tamoxifen treatment].

Tamoxifen (TAM), an antiestrogen was administered 20 mg b.i.d. to 20 patients with recurrent breast cancer at the time of first relapse who had been treated with the adjuvant therapy including TAM 10 mg b.i.d.. Patients who had been treated with TAM at least 1 year and in which the relapse had occurred after 3 months or more after the cessation of adjuvant treatment were enrolled in the study. Sixteen patients were evaluated, and a complete response was observed in 3 (19%), partial response in 1 (6%), no change in 5 (31%), and progressive disease in 7 (44%). The response rate was shown to be 25% with 95% confidence interval: 3.8-46.2%. The duration of response ranged from 23+ to 32 weeks. Patients who have received postoperative adjuvant therapy including TAM and have relapsed after the cessation of therapy may retain hormone dependency in responding to a further TAM treatment at the time of relapse of malignancy.

Administration, Oral↗
PubMed1989

[Effects of chemo-endocrine therapy on DMBA-induced rat mammary carcinoma].

The effect of chemo-endocrine therapy (5-FU plus TAM) on 7,12-DMBA-induced rat mammary carcinomas was studied in terms of its antitumor effects and changes in hormone receptors (ER and PgR). The study detected no difference in antitumor effects between combined administration of 5-FU and TAM, and either agent alone. The ER and PgR contents markedly decreased following chemo-endocrine therapy and endocrine therapy (TAM), but no significant decrease was achieved by chemotherapy (5-FU) alone. These results suggest that, in the combined administration of 5-FU and TAM, TAM was more effective than 5-FU. The expected advantage from chemo-endocrine therapy was not observed.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Mechanisms of estrogen action on the proliferation of MCF-7 human breast cancer cells in an improved culture medium.

The effects of 17 beta-estradiol and tamoxifen (TAM) on the proliferation of responsive MCF-7 and unresponsive HBC-4 human breast cancer cells were studied in a defined culture medium containing insulin (2 micrograms/ml), transferrin (2 micrograms/ml), ethanolamine (2 microM), and selenite (25 nM). MCF-7 cells grew at a population-doubling rate of 2.0 days in serum-free medium and at a rate of 1.7 days in the medium containing 1 mg/ml of the 55-70% ammonium sulfate fraction of bovine serum or 1% dextrancoated charcoal-treated fetal bovine serum. Increasing concentrations of the ammonium sulfate fraction and/or dextran-coated charcoal-treated fetal bovine serum increasingly inhibited the growth of MCF-7 cells but did not inhibit HBC-4 cell growth, indicating that such serum preparations contain some growth inhibitor specific for estradiol-responsive MCF-7 cells. A sufficiently high concentration of exogenous estradiol (100 pM) had the dual action of neutralizing the growth inhibition by the 55-70% ammonium sulfate fraction of bovine serum and dextran-treated charcoal-treated fetal bovine: serum and enhancing directly the MCF-7 cell growth maximally 2-fold. Bovine serum albumin fraction V containing globulin remnants also inhibited growth, but globulin-free bovine serum albumin did not. Eliminating growth inhibition by the use of globulin-free bovine serum albumin enabled us to develop an ideal medium for assaying the direct effects of estradiol and TAM on MCF-7 cells. With this medium, we clearly identified (a) a direct mitogenic effect of exogenous estradiol on MCF-7 cells which was initiated at 3 pM and maximized at 0.2 to 10 nM, (b) an acute lethal effect of 1 microM TAM and its prevention by 100 pM estradiol, and (c) a nearly 50-fold increase in the concentration of exogenous estradiol (10 nM) required for maximum growth enhancement in the presence of 1 microM TAM than without TAM (0.2-0.3 nM).

Breast Neoplasms↗
PubMed1988

[Experimental chemo- and chemoendocrine therapy of human breast carcinomas serially transplanted into nude mice].

Four human breast carcinoma strains serially transplanted into nude mice were used for the experimental chemotherapy and combination chemoendocrine therapy. Whereas three of these strains (MCF-7, Br-10, TM-61) possessed cytosol estrogen receptor (ERc) and were dependent on estradiol for the tumor growth, the other strain (MX-1) without ERc was hormone independent. For the chemotherapy, mitomycin C (MMC), adriamycin (ADM), cyclophosphamide (CPM) and 5-fluorouracil (5-FU) were administered 3 times every 4 days. To know the stability of ERc after chemotherapy, binding sites of ERc were measured 4 days after MMC administration at doses of 1, 2 and 4.5 mg/kg. For the chemoendocrine therapy, 1 or 2 mg/kg of MMC was administered once followed by treatment by tamoxifen (TAM). The effect of treatment was evaluated by T/C ratio of the tumor weight. MMC showed the most excellent antitumor effect and CPM and ADM showed a moderate effect. As ERc was found to be stable by MMC treatment, TAM was used after MMC, and this combination of MMC and TAM revealed an additive effect against ERc positive strains and no combination effect was observed in MX-1 without ERc. The dose response curves of 4 strains to MMC alone against 4 strains were made and the effect of combination chemoendocrine therapy was converted to the effect of MMC alone, showing the dose of MMC could be significantly reduced. Binding sites of ERc which were measured 4 days after MMC administration (1, 2 and 4.5 mg/kg) was found to be stable, suggesting TAM treatment after MMC might be reasonable. From these results, chemoendocrine therapy of MMC followed by TAM was considered to be beneficial modality for clinical treatment of the cytotoxic agent and increasing the antitumor effect.

Animals↗
PubMed1987

Chemoendocrine therapy with prolonged estrogen priming in advanced breast cancer: endocrine pharmacokinetics and toxicity.

Recent efforts to improve response rates in advanced breast cancer have used short, alternating courses of antiestrogen therapy followed by estrogen priming to cytokinetically enhance tumor cell sensitivity to antimetabolites. Based on recent in vitro and in vivo studies, we have introduced a chemoendocrine regimen that uses prolonged courses of estrogen priming. The present protocol consists of alternating monthly cycles of tamoxifen (TAM) and estradiol during which sequential (24-hr) methotrexate, 5-fluorouracil, and leucovorin are administered at 2-week intervals. Twenty-five patients with metastatic breast cancer received greater than 80 endocrine cycles and greater than 300 courses of chemotherapy by this protocol; two-thirds of these patients had previously failed other endocrine or chemotherapy regimens. Most patients experienced grade 1 or 2 myelosuppression or gastrointestinal symptoms during at least one treatment cycle; however, overall toxicity was considered to be mild and therapy was very well tolerated. Serum levels of estradiol, estrone, TAM, and TAM metabolites were measured during all phases of the endocrine cycle in five patients on chronic therapy. Concentrations of TAM and its more abundant metabolite, N-desmethyltamoxifen (N-desTAM), rose twofold during antiestrogen therapy and fell during estrogen priming, with mean levels persisting greater than 100 ng/ml throughout the priming interval. Mean estradiol (E2) and estrone (E1) levels rose during priming and were sustained fivefold and tenfold above the basal postmenopausal levels measured during antiestrogen treatment. Calculating the serum molar ratios of [TAM + N-desTAM]/[E2 + E1] during each phase of the treatment cycle confirmed that estrogen priming was achieved pharmacologically by this endocrine schedule. Clinical remissions were observed in this small patient sample with seven of 18 patients achieving either complete (28%) or partial (11%) responses, and an additional 39% obtaining disease stabilization. Further clinical study is necessary to evaluate the optimal response rate of this regimen and to determine whether cyclic estrogen priming by this schedule results in enhanced tumor cell proliferation in vivo.

Adult↗
PubMed1985

[Intratumoral levels and metabolism of 4-hydroxytamoxifen after percutaneous administration at the breast level].

(3H)-4 hydroxytamoxifen (4O H Tam), the active metabolite of the antiestrogen tamoxifen (Tam) was dissolved in ethanol and locally percutaneously administered on 4 human breast carcinomas before surgery. 12, 24, 72 hrs. and 7 days later, (3H)-4O H Tam was recovered in cytosol and nuclear fractions of the tumor. Only traces of radioactivity were recovered in plasma. From these results it appears clearly that the percutaneous administration of 4O H Tam on the mammary gland yields a local antiestrogen effect without the systemic effects observed in case of oral administration of Tam.

Administration, Topical↗
PubMed1985

[Studies on sensitivity test with clonogenic assay against chemo-endocrine therapy for human breast cancer].

The sensitivity of human breast cancer cells against estradiol-17 beta (E2), tamoxifen (TAM) and adriamycin (ADM) was investigated using the modified stem cell assay method by Hamburger and Salmon. Two hundred and six specimens, 145 from primary breast cancer and 61 from metastatic lesions, were placed in culture. Ninety eight specimens of them (47.1%) successfully formed more than 5 colonies per 5 X 10(5) cells plated. In 47 specimens (22.8%), more than 20 colonies were formed, which made it feasible to perform meaningful sensitivity test. Results obtained were as follows: Sensitivity against E2. More than 150% increase of colony formation was observed in the 36.7% cases of ER(+) group and in the 22.1% cases of ER(-) group. Sensitivity against TAM. When more than 60% inhibition in % colony formation was applied to cut off line, response rates for TAM were 21.7% in all cases, 26.7% in ER(+) group and 12.5% in ER(-) group, respectively. Sensitivity against ADM. When more than 50% inhibition in % colony formation was applied to cut off line, response rate for ADM was 26.7% in all cases. Higher response rate was observed in ER(-) group than in ER(+) group. Response rates of sensitivity test for TAM or ADM were very similar to the results obtained in the clinical use of TAM or ADM.

Breast Neoplasms↗
PubMed1984

Effect of estrogen and antiestrogen on the human breast cancer cell line MCF-7 adapted to growth at low serum concentration.

The human breast cancer cell line MCF-7 has been adapted to long-term growth at 0.5 and 0.05% fetal bovine serum. Free cytoplasmic and filled nuclear estrogen receptors were found in cells grown at 5, 0.5, and 0.05% fetal bovine serum. Cells grown in medium with 0.05% dextran-charcoal-treated serum contained cytoplasmic receptors but no filled nuclear receptors, indicating that this medium did not contain biologically active concentrations of estrogen. Addition of estradiol to the medium translocated the cytoplasmic receptor to the nucleus and stimulated progesterone receptor synthesis but did not increase the growth rate. The antiestrogen tamoxifen (TAM) inhibited cell growth at all serum concentrations investigated, at least in part by a reduction of the growth fraction. The sensitivity to TAM was highest at low serum concentrations. The effect of TAM could be reversed by estradiol at TAM concentrations of 10(-6) M or lower. It is concluded that estradiol does not have a direct growth-stimulatory effect on our MCF-7 cells in monolayer cultures although the cells contain functional estrogen receptors and growth of the cells in athymic mice requires estrogens. TAM has an estrogen-competitive, inhibitory effect on the growth of MCF-7 cells at concentrations lower than 10(-6) M. At higher concentrations, the growth inhibition is unspecific and noncompetitive by estradiol.

Adenocarcinoma↗
PubMed1994

Effect of tamoxifen on mammary preneoplasia: relevance to chemopreventive intervention.

The nonsteroidal antiestrogen tamoxifen (TAM) is used to treat receptor-positive breast cancer and is now being evaluated for prophylaxis of "high-risk" population. The present study seeks to examine mechanisms that may be critical for prophylactic effects of TAM on transformation-sensitive mammary tissue. The experimental systems utilized included: in vivo rodent models for mammary tumorigenesis and in vitro cell culture models for preneoplastic transformation. In the in vivo models TAM suppressed constitutive, as well as carcinogen-induced proliferation, expression of mammary tumor virus-associated reverse transcriptase activity and decreased the incidence and frequency of mammary hyperplastic alveolar nodules. In the in vitro models TAM suppressed carcinogen-induced DNA damage, altered cellular metabolism of estradiol favoring the formation of less estrogenic catechols, and down-regulated anchorage-independent growth that is induced by ras oncogene and chemical carcinogen. Effective down-regulation of specific proliferative and metabolic biomarkers that are perturbed in mammary cell prior to tumorigenesis provides evidence that altered cellular metabolism of E2 may, in part, be responsible for antiproliferative and prophylactic properties of TAM against mammary tumorigenesis.

Animals↗