The antiproliferative effect of tamoxifen in breast cancer cells: mediation by the estrogen receptor

Tamoxifen reduces silicone implant capsule formation in a mouse model

Capsular contracture as a result of the foreign body response (FBR) is a common issue after implant-based breast reconstruction, affecting up to 20% of patients. New evidence suggests that tamoxifen may mitigate the FBR. C57BL/6 female mice were treated with daily tamoxifen or control injections and implanted with bilateral silicone implants in the submammary glandular plane. Implants were removed en bloc after 2 weeks and the implant capsules were evaluated histologically. Tamoxifen treatment decreased capsule thickness, decreased the number of αSMA+ cells (477 ± 156 cells/mm control vs 295 ± 121 cells/mm tamoxifen, p = 0.005 unpaired t test), and decreased CD31+ cells (173.9 ± 96.1 cells/mm2 control vs 106.3 ± 51.8 cells/mm2 tamoxifen, p = 0.043 unpaired t test). There were similar amounts of pro- and anti-inflammatory macrophages (iNOS 336.1 ± 226.3 cells/mm control vs 290.6 ± 104.2 cells/mm tamoxifen, p > 0.999 Mann-Whitney test and CD163 136.6 ± 76.4 cells/mm control vs 94.1 ± 45.9 cells/mm tamoxifen, p = 0.108 unpaired t test). Tamoxifen treatment in the mouse silicone breast implant model decreased capsule formation through modulation of myofibroblasts, neovascularization, and collagen deposition. Tamoxifen may be useful for reducing or preventing capsule formation in clinical breast implantations.

Molecular mechanisms of estrogen action in female genital tract development

The development of the female reproductive tract can be divided into three parts consisting of Müllerian duct organogenesis, pre-sexual maturation organ development, and post-sexual maturation hormonal regulation. In primates, Müllerian duct organogenesis proceeds in an estrogen independent fashion based on transcriptional pathways that are suppressed in males by the presence of AMH and SRY. However, clinical experience indicates that exposure to xenoestrogens such as diethylstilbestrol (DES) during critical periods including late organogenesis and pre-sexual maturational development can have substantial effects on uterine morphology, and confer increased risk of disease states later in life. Recent evidence has demonstrated that these effects are in part due to epigenetic regulation of gene expression, both in the form of aberrant CpG methylation, and accompanying histone modifications. While xenoestrogens and selective estrogen receptor modulators (SERMS) both can induce non-canonical binding confirmations in estrogen receptors, the primate specific fetal estrogens Estriol and Estetrol may act in a similar fashion to alter gene expression through tissue specific epigenetic modulation.

Design, synthesis, and biological evaluation of lipophilically modified bisphenol Z derivatives

In the present study, a small library of bisphenol Z (BPZ) derivatives was synthesized and investigated for anti-proliferative effects in cultured breast and glioblastoma cell lines. Synthesized BPZ derivatives varied in molecular size, polarity, and lipophilicity. Of the 8 derivatives tested, compounds 4 and 6, both of which displayed the highest degree of lipophilicity, were most active at inducing cell death as determined by the XTT assay. Cell membranes were interrogated using trypan blue staining and were shown to remain intact during treatments with 4 and 6. Activation of caspase enzymes (3 and/or 7) was noted to occur following treatment with compound 4. Polar BPZ derivatives, those with a substituted amine or alcohol, were devoid of any inhibitory or proliferative effects. The remaining derivatives seem to lack sufficient lipophilicity to execute an overt toxic effect. Our results suggest that increasing the lipophilic character of BPZ enhances the cytotoxic effects.

Proliferation marker Ki-67 in early breast cancer

Molecular markers have been extensively investigated with a view to providing early and accurate information on long-term outcome and prediction of response to treatment of early breast cancer. Proliferation is a key feature of the progression of tumors and is now widely estimated by the immunohistochemical assessment of the nuclear antigen Ki-67. The expression of Ki-67 correlates with other measurements of proliferation, including S-phase and bromodeoxyuridine uptake. High Ki-67 is a sign of poor prognosis associated with a good chance of clinical response to chemotherapy, but its independent significance is modest and does not merit measurements in most routine clinical scenarios. However, its application as a pharmacodynamic intermediate marker of the effectiveness of medical therapy holds great promise for rapid evaluation of new drugs.

Steroid-free medium discloses oestrogenic effects of the bisphosphonate clodronate on breast cancer cells

Tamoxifen is the standard first-line endocrine therapy for breast cancer, but recent data indicate that it is likely to be replaced by the effective aromatase inhibitors (AIs), in both the metastatic and adjuvant settings. Aromatase inhibitors induce complete oestrogen deprivation that leads to clinically significant bone loss. Several ongoing or planned trials combine AIs with bisphosphonates, even more so that recent data reveal that clodronate may reduce the incidence of bone metastases and prolong survival in the adjuvant setting. Bisphosphonates can inhibit breast cancer cell growth in vitro, but they have never been studied in steroid-free medium (SFM), an in vitro environment that mimics the effects of AIs in vivo. Quite surprisingly, in SFM, clodronate stimulated MCF-7 cell growth in a time- and dose-dependent manner by up to two-fold (crystal violet staining assay), whereas it had no mitogenic activity in complete medium. The bisphosphonate similarly increased the proliferation of IBEP-2 cells, which also express a functional oestrogen receptor (ER), while it weakly inhibited the growth of the ER-negative MDA-MB-231 cells. Expectedly, 17beta-oestradiol stimulated the growth of MCF-7 and IBEP-2 cells cultured in SFM, and had no effect on MDA-MB-231 cells. Moreover, partial (4-OH-tamoxifen) and pure antioestrogens (fulvestrant, ICI 182,780), in combination with clodronate, completely suppressed the mitogenic effect of the bisphosphonate, suggesting that it was mediated by an activation of ER. In accordance with this view, clodronate induced ER downregulation, weakly increased progesterone receptor expression, and stimulated the transcription of an oestrogen-responsive reporter gene. In conclusion, we report a previously unknown stimulatory effect of clodronate on MCF-7 cells grown in SFM, in vitro conditions that are potentially relevant to the use of AIs for breast cancer. Moreover, our data suggest that ER is involved in these effects of clodronate on cancer cell growth.

Estrogen Receptor β (ERβ) Level but Not Its ERβcx Variant Helps to Predict Tamoxifen Resistance in Breast Cancer

The antiestrogen tamoxifen, a major endocrine therapy of estrogen receptor (ER)-positive breast cancer, is nevertheless inefficient in 30 to 40% of cases for unknown reasons. We retrospectively studied 50 ER-positive primary breast carcinomas. All of the patients had received tamoxifen as the only adjuvant therapy. They were divided into two groups depending on whether they relapsed within 5 years (16 tamoxifen-resistant cases) or did not relapse within 5 years (34 tamoxifen-sensitive cases). The expression of total ER beta protein, and of ER beta cx protein, was estimated anonymously in formalin-fixed, paraffin-embedded tumor sections, by using specific antibodies and quantifiying nuclear immunostaining with a computer image analyzer. All of the tumors were found to be HER-2/neu-negative by immunohistochemistry. Univariate analysis showed that Scarff-Bloom-Richardsson grade modified by Elston (SBR grade; P < 0.001), tumor size (P = 0.042), and MIB-1 proliferation index (P = 0.02) were significantly higher in tamoxifen-resistant tumors. A low level of total ER beta, whether in percentage of positive cells or in quantitative immunocytochemical (QIC) score, was also associated with tamoxifen resistance (P = 0.004). ER beta cx expression and lymph node status were similar between the two groups. The expression of ER beta in the total population was positively correlated with ER beta cx (r = 0.63, P < 0.001), and was independent of the other parameters. In a multivariate analysis, ER beta expression was the most important variable (P = 0.001), followed by SBR grade (I+II versus III; P = 0.008), and MIB-1 (P = 0.016). To conclude, tamoxifen resistance is associated with classical variables of aggressive tumors (high SBR grade, proliferation index, and tumor size) but not with node invasiveness. Low ER beta level is an additional independent marker, better than ER alpha level, to predict tamoxifen resistance.

The effect of the new SERM arzoxifene on growth and gene expression in MCF-7 breast cancer cells

The benzothiophene arzoxifene is a new 3rd generation selective estrogen receptor (ER) modulator (SERM). We have investigated the effect of arzoxifene on growth and gene expression in the estrogen receptor alpha (ERalpha) positive human breast cancer cell line MCF-7. Arzoxifene inhibits cell growth as effectively as the antiestrogen tamoxifen. Northern analysis revealed that arzoxifene exerts a statistically significant inhibition of pS2 and progesterone receptor B mRNA expression. Significant agonistic effect was observed on the antitrypsin mRNA expression. In contrast to estradiol and tamoxifen, arzoxifene does not upregulate cathepsin D mRNA and protein expression. The metabolite of arzoxifene (ARZm) is a more potent growth inhibitor of MCF-7 cells than arzoxifene. A tamoxifen resistant MCF-7 subline displayed a significant dose-dependent growth inhibition to ARZm, whereas an ICI 182,780 resistant cell line only responded to high concentration. Our results indicate that arzoxifene and especially ARZm are efficient growth inhibitors of ER positive human breast cancer cells, including tamoxifen resistant cells. Moreover, arzoxifene displays less estrogen agonistic effects in MCF-7 cells than tamoxifen.

Effect of antiestrogens and aromatase inhibitor on basal growth of the human breast cancer cell line MCF-7 in serum-free medium

Antiestrogens are efficient inhibitors of estrogen-mediated growth of human breast cancer. Besides inhibiting estradiol-stimulated growth, antiestrogens may have a direct growth-inhibitory effect on estrogen receptor (ER) positive cells and thus be more efficient than aromatase inhibitors, which will only abrogate estrogen-dependent tumor growth. To address this issue, we have used the human breast cancer cell line MCF-7/S9 as a model system which is maintained in a chemically defined medium without serum and estrogen. The addition of estradiol results in an increase in cell growth rate. Thus, the MCF-7/S9 cell line is estrogen-responsive but not estrogen-dependent. Three different types of antiestrogens, namely tamoxifen, ICI 182,780 and EM-652 were found to exert a significant and dose-dependent inhibition of basal growth of MCF-7/S9 cells. The growth-inhibitory effect of the three antiestrogens was prevented by simultaneous estradiol treatment. Antiestrogen treatment also reduced the basal pS2 mRNA expression level, thus indicating spontaneous estrogenic activity in the cells. However, treatment with the aromatase inhibitor had no effect on basal cell growth, excluding that endogenous estrogen synthesis is involved in basal growth. These data demonstrate that in addition to their estrogen antagonistic effect, antiestrogens have a direct growth-inhibitory effect which is ER-mediated. Consequently, in the subset of ER positive breast cancer patients with estrogen-independent tumor growth, antiestrogen therapy may be superior to treatment with aromatase inhibitors which only inhibit estrogen formation but do not affect cancer cell growth in the absence of estrogens.

Role of proliferation and apoptosis in net growth rates of human breast cancer cells (MCF-7) treated with oestradiol and/or tamoxifen

Studies on growth regulation in vitro to a large extent rely on comparison of growth curves. However, these do not discriminate between the relative contributions of the mitotic rate and the apoptotic rate to the net growth rate. In the present study, differential effects of 17beta-oestradiol (E2, 10(-8) M) and/or tamoxifen (TAM, 10(-6) M) on proliferation and apoptosis have been examined and related to growth curves of a subline of the human breast cancer cell line MCF-7 adapted to grow at low serum concentrations. Counting of cells and scoring of labelling and apoptotic indices were performed at the start of the experiment and 3, 6 and 9 days after changing the experimental media. The results demonstrate that apoptosis in this subline is constitutively expressed, that E2 protects (at least partly) against apoptosis and stimulates proliferation, resulting in an increased (net) growth rate, and final cell pool size, and that TAM has a weak cytostatic effect and stimulates apoptosis strongly, resulting in a decreased (net) growth rate and final cell pool size. When E2 and TAM are added simultaneously to the medium, the cytotoxic effect of TAM is partly counterbalanced by the protective role of E2, resulting in a reduced apoptotic rate that, however, is at a higher level than in cultures grown with E2 only. As the cytostatic role of TAM is partly abolished by E2, the combined effect of E2 and TAM results in a final (net) growth rate and cell pool size intermediary to cells grown with E2 or TAM alone.

Effect of 4-hydroxytamoxifen isomers on growth and ultrastructural aspects of normal human breast epithelial (HBE) cells in culture

In the search for a breast cancer prevention strategy which would avoid undesirable effects of orally administered tamoxifen, the percutaneous administration of the highly active metabolite 4OHTamoxifen (4OHTam) has been proposed. Percutaneous 4OHTam penetrates the skin to reach breast tissues. It, thus, avoids the hepatic first pass effect, and offers an optimal local/systemic effect. However, trans-4OHTamoxifen can spontaneously isomerize into the cis-isomer, which may have estrogen agonist action. The aim of this study was to examine the effect of cis-4OHTam on normal human breast epithelial (HBE) cells in culture. Spontaneous isomerization of trans- into cis-4OHTam occurred within 24-48h, but stabilized rapidly at a trans/cis ratio of 70/30, whether in stock solution, culture medium or cultured cells. The cis-4OHTam did not stimulate HBE cell growth according to histometric cell counts and scanning electron microscopy analysis, but inhibited E(2)-induced cell growth, albeit two to three times less than trans-4OHTam. In conclusion, spontaneous isomerization of trans- to cis-4-OHTam is limited and 4OHTam retains a marked antiestrogenic effect. It may prove to be a useful alternative to tamoxifen in breast cancer prevention, especially if administered percutaneously.

Tamoxifen elicits its anti-estrogen effects in growth plate chondrocytes by inhibiting protein kinase C

17 beta-Estradiol (E(2)) regulates growth plate cartilage cells via classical nuclear receptor mechanisms, as well as by direct effects on the chondrocyte membrane. These direct effects are stereospecific, causing a rapid increase in protein kinase C (PKC) specific activity, are only found in cells from female rats and are mimicked by E(2)-bovine serum albumin (BSA), which cannot penetrate the cell membrane. E(2) and E(2)-BSA stimulate alkaline phosphatase specific activity and proteoglycan sulfation in female rat costochondral cartilage cell cultures, but traditional nuclear receptors do not appear to be involved. This study examined the effect of the anti-estrogen tamoxifen on these markers of chondrocyte differentiation; the gender-specificity of tamoxifen's effect on PKC, if tamoxifen has an effect on vitamin D metabolite-stimulated PKC, which is mediated via specific membrane receptors (1,25-mVDR; 24,25-mVDR) and whether the effect of tamoxifen is mediated by nuclear estrogen receptors. Tamoxifen dose-dependently inhibited the effect of E(2)-BSA on PKC, alkaline phosphatase and proteoglycan sulfation in confluent cultures of female resting zone (RC) cells and growth zone (GC) (prehypertrophic/upper hypertrophic zones) cells, suggesting that its action is at the membrane and not cell maturation-dependent. Neither the estrogen receptor (ER) antagonist ICI 182780 nor the ER agonist diethylstilbesterol affected E(2) or E(2)-BSA-stimulated PKC in female chondrocytes. Tamoxifen also inhibited the increase in PKC activity due to 1 alpha,25-(OH)(2)D(3) or 24R,25-(OH)(2)D(3) in growth plate cells derived from either female or male rats. Inhibition of PKC by tamoxifen may be a general property of membrane receptors involved in rapid responses to hormones.

The evolving role of specific estrogen receptor modulators (SERMs)

Estrogens are the most effective therapy for women with postmenopausal problems. However, relatively few women use estrogen and then often for a limited time because of the fear of its carcinogenic effects on the uterus and breast; in addition, estrogen is not advised for women who have had breast cancer. Selective estrogen receptor modulators (SERMs) are agents with antagonist action on the uterus and breast and agonist action on the bones, cardiovascular system, and brain. Unlike estrogens, however, existing SERMs do not help alleviate the vasomotor and urogenital problems associated with menopause. A comprehensive review of the literature published from January 1995 to June 1999 was conducted. Reports were identified using Medline and Cancer Lit. The effect of menopausal problems on the health of women and the socioeconomic effects of menopause are discussed. All currently available and investigational SERMs are reviewed and discussed, including their mechanism of action, metabolism, dose scheduling, antitumor activity, and potential role in maintaining the health of menopausal women and in preventing breast cancer.

Indole-3-carbinol inhibits the expression of cyclin-dependent kinase-6 and induces a G1 cell cycle arrest of human breast cancer cells independent of estrogen receptor signaling

Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables such as cabbage, broccoli, and Brussels sprouts, has been shown to reduce the incidence of spontaneous and carcinogen-induced mammary tumors. Treatment of cultured human MCF7 breast cancer cells with I3C reversibly suppresses the incorporation of [3H]thymidine without affecting cell viability or estrogen receptor (ER) responsiveness. Flow cytometry of propidium iodide-stained cells revealed that I3C induces a G1 cell cycle arrest. Concurrent with the I3C-induced growth inhibition, Northern blot and Western blot analyses demonstrated that I3C selectively abolished the expression of cyclin-dependent kinase 6 (CDK6) in a dose- and time-dependent manner. Furthermore, I3C inhibited the endogenous retinoblastoma protein phosphorylation and CDK6 phosphorylation of retinoblastoma in vitro to the same extent. After the MCF7 cells reached their maximal growth arrest, the levels of the p21 and p27 CDK inhibitors increased by 50%. The antiestrogen tamoxifen also suppressed MCF7 cell DNA synthesis but had no effect on CDK6 expression, while a combination of I3C and tamoxifen inhibited MCF7 cell growth more stringently than either agent alone. The I3C-mediated cell cycle arrest and repression of CDK6 production were also observed in estrogen receptor-deficient MDA-MB-231 human breast cancer cells, which demonstrates that this indole can suppress the growth of mammary tumor cells independent of estrogen receptor signaling. Thus, our observations have uncovered a previously undefined antiproliferative pathway for I3C that implicates CDK6 as a target for cell cycle control in human breast cancer cells. Moreover, our results establish for the first time that CDK6 gene expression can be inhibited in response to an extracellular antiproliferative signal.

Cytotoxicity and antiestrogenicity of a novel series of basic diphenylethylenes

On the premise that it is necessary to develop antiestrogens with a higher cytotoxic component in order to reduce the risks of the development of heterogeneous malignant cell populations in breast cancer, we studied a novel series of basic diphenylethylenes, for the most part devoid of estrogenic activity, with low antiestrogenicity but much enhanced cytotoxicity compared to the reference drug tamoxifen. The main structural features associated with cytotoxicity were E isomery, substituents of five to eight carbons on the ethylene bond, and dibasicity.

The anti-estrogen tamoxifen blocks the stimulatory effects of interleukin-6 on 17 beta-hydroxysteroid dehydrogenase activity in MCF-7 cells

Previous studies have revealed that human breast fibroblasts secrete the cytokine, interleukin-6 (IL-6) which stimulates the ability of MCF-7 human breast carcinoma cells to convert estrone (E1) to the biologically more active 17 beta-estradiol (E2). This is mediated by an increase in reductive 17 beta-hydroxysteroid dehydrogenase (17-HSD) activity. In the studies described here, we have extended our observations using the anti-estrogen, tamoxifen, to demonstrate that in a steady state, endogenous intracellular concentrations of E2 have no effects on reductive 17-HSD activity (E1-->E2), but are already maximally inhibitory for the oxidative reaction (E2-->E1). Increasing intracellular concentrations of E2, however, stimulated the reductive 17-HSD in a dose-dependent manner. IL-6 stimulated the reductive pathway and was synergistic with E2. IL-6 is most likely acting through an E2-dependent mechanism, since tamoxifen completely reversed the effects of E2 and IL-6 separately and in combination. These observations suggest that tamoxifen may reduce intratissular levels of E2 by directly increasing oxidative 17-HSD activity and by blocking the actions of paracrine factors such as IL-6 which increase reductive 17-HSD activity.

Relative involvement of protein kinase C and of the estrogen receptor in the cytotoxic action of a population of triphenylethylenes on MCF7 cells as revealed by correspondence factorial (CF) analysis

A multivariate statistical method, correspondence factorial (CF) analysis, was used to examine the correlations among the protein binding and cell proliferation effects of a series of 36 di- and triphenylethylenes (DPEs and TPEs). The analysis was applied to a study which measured their competition for estradiol binding to cytosol estrogen receptor (ER), their influence on protein kinase C (PKC) activity under different conditions of enzyme activation, their ability to promote the growth of a breast cancer cell line and to inhibit growth at high concentrations (cytotoxicity). The CF analysis revealed several levels of correlation. First, it distinguished those molecules within the population that stimulated rather than inhibited PKC activity. Second, it made apparent a strong correlation between cytotoxicity and inhibition of Ca++ and phosphatidylserine-dependent PKC activity, which was most marked when the enzyme had been activated by diacylglycerol indicating that PKC inhibition under physiological conditions might contribute to the overall cytotoxicity of these compounds. Third, a lower level of correlation was established between competition for ER binding and cytotoxicity. Taken together, the results suggest that MCF7 cells might be most sensitive to a cytotoxic effect of TPEs (via PKC and other targets) when they at the same time decrease estrogen-stimulated proliferation via an ER-mediated antiestrogenic effect.

The influence of a novel cyclopropyl antiestrogen (compound 7a) on human breast cancer cells in culture

Compound 7a ([Z]-1,1,-dichloro-2,3-diphenyl-2-(4-(2- dimethylamino)ethoxy)phenyl) cyclopropane, dihydrogen citrate salt) is a novel cyclopropyl antiestrogen which was shown to be an estrogen antagonist without estrogen agonist activity. The antiproliferative activity of 7a was examined on estrogen receptor (ER) positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells and A-549 human lung cancer cells. Compound 7a inhibited the growth of MCF-7 cells in a dose-related manner over a concentration range of 10(-9) to 10(-5) M, but did not alter the growth of MDA-MB-231 or A-549 cells. The antiproliferative activity of 7a (10(-7) M) on MCF-7 cells was reversed by co-administration of estradiol (10(-8) M). An ER-dependent mechanism of action is also supported by the specific ER binding of 7a in MCF-7 cells observed in this study. A study of cell surface morphology using scanning electron microscopy (SEM) revealed that compound 7a at 10(-6) M reduced the length and density of microvilli (MV) on MCF-7 cells, which was reversed by co-administration of estradiol (10(-8) M). Compound 7a did not alter the cell surface morphology of ER-negative MDA-MB-231 cells. In conclusion, 7a inhibited the growth of ER-positive MCF-7 cells in an estradiol-reversible manner, and had no effect on ER-negative MDA-MB-231 cells or A-549 lung cancer cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell-growth quantitation methods for the evaluation of antiestrogens in human breast cancer cells in culture

The antiproliferative activity of the antiestrogen, tamoxifen, on the growth of MCF-7 human breast cancer cells was evaluated using the hemocytometric trypan blue exclusion method, [3H]-thymidine incorporation, and a total protein determination. Tamoxifen was evaluated over a concentration range from 10(-9) to 10(-6) M. The hemocytometric trypan blue exclusion method and [3H]-thymidine incorporation were sensitive enough to demonstrate the inhibitory influence of tamoxifen on the proliferation of MCF-7 cells at a concentration as low as 10(-9) M. A very good correlation of these two methods was observed in the submicromolar concentration range of tamoxifen. The total protein determination method was only sensitive enough to detect the antiproliferative influence of tamoxifen at concentrations above 10(-6) M. In conclusion, the [3H]-thymidine incorporation method was found to be effective and much less time consuming than the hemocytometric trypan blue exclusion method for evaluating the antiproliferative effects of antiestrogens in cultured MCF-7 cells. However, when evaluating antiestrogens, which are cell-cycle specific, the results of the [3H]-thymidine incorporation method should be interpreted with caution.

Antagonistic effect of triphenylethylenic antiestrogens on the association of estrogen receptor to calmodulin

Binding of (3H)-estradiol labeled estrogen receptor from uterine cytosol to calmodulin was demonstrated by both affinity chromatography and sucrose gradient sedimentation. Triphenylethylene antiestrogens (tamoxifen family) with strong antagonistic activity against the calmodulin-dependent c-AMP phosphodiesterase largely reduced the binding of the receptor. Relevance of this observation with regard to the major antiproliferative activity (cytotoxicity) of these drugs is discussed.

Effects of tamoxifen and protein kinase C inhibitors on hyperthermic cell killing

The effects of the anti-estrogen, tamoxifen, and the protein kinase C inhibitor, 1-(5-isoquinolinylsulfonyl)2-methylpiperazine (H7), on hyperthermic cytotoxicity were studied. Three cell lines were used, a human colon cancer cell line (HT-29), a human mammary carcinoma cell line (MCF-7), and Chinese hamster V79 lung fibroblasts. With all three cell lines, tamoxifen at concentrations greater than 7.5 microM during heating or with a 3-hr exposure prior to heating significantly sensitized cells to heat. When cells were preincubated with 10-20 microM tamoxifen for 1-2 hr at 37 degrees C prior to heat treatment, washed free of extracellular tamoxifen, heated to generate thermoresistance, and examined 18 hr later for thermoresistance, tamoxifen treated HT-29 and MCF-7 cells were significantly more heat sensitive than thermotolerant controls not previously exposed to tamoxifen. In contrast, the degree of induced thermoresistance of V79 cells was unchanged after tamoxifen treatment. H7, but not its structural analogue and low affinity protein kinase C inhibitor, HA1004, also sensitized cells to heat. Neither H7 nor HA1004 had any apparent effect on the degree of heat-induced thermoresistance in the three cell lines tested.

The effects of anti-estrogen therapy on lymphocyte functions in breast cancer patients

The effects of anti-estrogen therapy (tamoxifen or toremifene) on in vitro lymphocyte functions were investigated in breast cancer patients. We found that the amount of DNA synthesis, with or without PWM stimulation, was decreased in all cancer patient groups compared to normal controls. The number of Ig-secreting cells was enhanced in unstimulated peripheral blood lymphocyte cultures but decreased in PWM-stimulated cultures. This occurred in all cancer patient groups investigated, with or without anti-estrogen therapy, as compared to healthy controls. On the other hand, subsequent samples with two-month intervals showed that anti-estrogens can increase PFC responses and inhibit DNA synthesis of peripheral blood lymphocytes in more than half of the patients. Interestingly, the enhancing dexamethasone effect, which usually causes an increase in the number of Ig-secreting cells in PWM-stimulated cultures, was also seen more often in anti-estrogen-treated patients. These results suggest that anti-estrogens may have immunoregulatory effects in vivo.

Effects of melatonin on the cell cycle kinetics and "estrogen-rescue" of MCF-7 human breast cancer cells in culture

Melatonin has been shown to have a direct inhibitory action on the proliferation of estrogen-responsive MCF-7 human breast cancer cells in culture. In the present study, we examined by flow cytometry whether this inhibitory effect might be exerted on the G1 phase of the cell cycle, thus causing a transition delay into the S phase. In order to further verify this hypothesis we tested the ability of estradiol to "rescue" MCF-7 cells from melatonin inhibition, and the potential of this indoleamine to block the ability of estradiol to rescue the cells from tamoxifen inhibition. Following five days of incubation, melatonin (10(-9)M) increased the fraction of cells in G1 of the cell cycle while simultaneously causing a 50% reduction in the proportion of cells in S phase. The antiproliferative effect of melatonin (10(-5)M) was prevented by the simultaneous treatment of the cells with estradiol (10(-8)M) in clonogenic soft agar culture, or reversed by the addition of estradiol to cells previously incubated with and inhibited by melatonin (10(-9)M) in monolayer culture. Additionally, melatonin blocked the estrogen-rescue of tamoxifen-inhibited cells in both types of culture systems. These results support the hypothesis that the antiproliferative effect of melatonin, like tamoxifen, is cell cycle specific by causing a G1-S transition delay. These results also indicate an important interaction of melatonin with estrogen-mediated mechanisms of MCF-7 cell proliferation.

Anti-steroidal and anti-growth factor activities of anti-estrogens

Both steroid hormones, such as estrogens and progestins acting via nuclear receptors, and growth factors, such as EGF, IGF-I and IGF-II acting via transmembrane receptors, are able to modulate the growth of human breast cancer cells. In addition to its anti-estrogenic action requiring estrogen receptor (ER) and leading to growth arrest, we have previously shown that the anti-hormone tamoxifen (Tam) is able to block EGF, insulin and IGF-I mitogenic activities in total absence of estrogens (BBRC, 146,1502,1987). This anti-growth factor activity is observed exclusively in ER + cells and is rescued by estradiol addition, thus suggesting that it is mediated by accessible ER sites. In the same culture conditions, progestins and anti-progestins do not display such an inhibition, whereas retinoic acid does, thus indicating that this anti-growth factor effect is not restricted to ER ligands. To progress in the understanding of this inhibition, we first analyzed how Tam could affect EGF and IGF-I binding in responsive cells. We have shown that Tam neither affects EGF and IGF-I binding to their respective receptors by direct competition nor modulates their affinities. However, our recent data suggest that Tam pretreatment (6 days) of MCF7 cells, which similarly prevents EGF and IGF-I mitogenic activities, results in opposite effects on the concentrations of their binding sites. In conclusion, we propose that some steroid antagonists can inhibit not only the action of agonist ligands of the receptors they are binding to, but can also modulate the action of growth factors by decreasing their receptor concentrations or altering their functionalities.

Multiple mechanisms of protein kinase C inhibition by triphenylacrylonitrile antiestrogens

The activation of type I (gamma), II (beta) and III (alpha) protein kinase C (PKC) subspecies by phosphatidylserine (PS) and diacylglycerol (DAG) is inhibited by micromolar concentrations of triphenylacrylonitrile (TPE) antiestrogens. TPE A (with p-hydroxy and p-diethylaminoethoxy groups on the 3- and 3'-phenyl rings, respectively) interacts with PS-vesicles as well as with the regulatory domain of PKC, probably at a site different from the Ca2+ and DAG binding sites. The interaction of TPE A with the regulatory domain of enzyme is very slow. Apparently, TPE A does not interact with the catalytic domain of PKC. In contrast, another TPE derivative, TPE B (with a p-hydroxy group on each of the three phenyl rings) inhibits the enzyme activity in a competitive manner with respect to ATP, suggesting that this TPE interacts with the catalytically active site of the enzyme. It seems likely that various TPE antiestrogen derivatives may exert their inhibitory action on PKC by multiple different mechanisms.

Protein kinase C subspecies in estrogen receptor-positive and -negative human breast cancer cell lines

Estrogen receptor-positive (MCF7) and -negative (BT20) human breast cancer cell lines, which are frequently used for studies on cancer chemotherapy with triphenylethylene (TPE) anti-estrogens, express at least three protein kinase C subspecies. Two of them are identified as type II PKC having the beta-sequence and type III PKC having the alpha-sequence. The other one shows typical characteristics of PKC which responds to Ca2+, phosphatidylserine and diacylglycerol, but shows kinetic properties subtly different from the previously known PKC subspecies. Immunoblot analysis has shown that this enzyme does not correspond to any of the well defined subspecies with known sequence structures. All of these PKC subspecies are similarly susceptible to the TPE antiestrogens.

Antiestrogenic properties of keoxifene, trans-4-hydroxytamoxifen, and ICI 164384, a new steroidal antiestrogen, in ZR-75-1 human breast cancer cells

The agonistic/antagonistic properties of two non-steroidal antiestrogens, namely trans-4-monohydroxytamoxifen (OH-TAM) and keoxifene (LY156758), and the new steroidal antiestrogen ICI164384, a 7 alpha-alkylamide derivative of estradiol (E2), were assessed by measuring their effect on the proliferation of ZR-75-1 cells, an estrogen-responsive human breast cancer cell line. While subnanomolar concentrations of both OH-TAM and LY156758 had significant estrogenic stimulatory activity on cell growth in the absence of estrogens and higher concentrations were inhibitory, ICI164384 behaved exclusively as a growth inhibitor and more potently so than the two other compounds. The three antiestrogens had similar potency to inhibit the mitogenic effect of E2 and at 300 nM, all antiproliferative effects were completely reversible by the estrogen. ICI164384 was a weaker competitor of 3H-labeled E2 or R2858 (moxestrol) uptake in intact ZR-75-1 cells in a 1-hour assay, partly because of a slower intracellular access to estrogen specific binding sites. Moreover, ICI164384 interacted in a rapidly (approximately 6 h) reversible manner with estrogen-specific binding sites, while the non-steroidal antiestrogens induced a longer-acting (greater than 24 h) down-regulation of specific [3H]R2858 uptake. The present data indicate that, among the antiestrogens studied, ICI164384 is the only compound acting as a pure antiestrogen in ZR-75-1 breast cancer cells, while LY156758 and OH-TAM behave as antiestrogens endowed with partial agonistic activity in this system.

Modes of inhibition of protein kinase C by triphenylacrylonitrile antiestrogens

Protein kinase C (PKC) I (gamma), II (beta) and III (alpha) subspecies' activities are inhibited by three triphenylacrylonitrile (TPE) antiestrogens at micromolar concentrations. TPE 1 (having a p-hydroxy and a p-diethylaminoethoxy group on the 3-, and 3'- phenyl rings respectively) and TPE 2 (having a p-diethylaminoethoxy group on both the 3-, and 3'- phenyl rings) are competitive with the mechanism of activation by phosphatidylserine (PS). TPE 3 (having p-hydroxy groups on each of the three phenyl rings) is non-competitive with PS and inhibits the Ca2+- and PS-independent phosphorylation of protamine sulfate by PKC subspecies. This evidence suggests that PKC activity can be inhibited by different routes depending on the TPE structure: diethylaminoethoxy side chain-substituted TPEs (TPE 1 and 2) interact with PS as well as with the regulatory domain, whereas the trihydroxylated derivative (TPE 3) inhibits the enzyme by interacting with the catalytically active site.

Regulation of epidermal growth factor-receptor by estrogen and antiestrogen in the human breast cancer cell line MCF-7

Regulation of breast tumor proliferation depends in a large part on a variety of hormones and growth factors. In this report we show that estrogen and antiestrogen modulate epidermal growth factor-receptor (EGF-R) level in the human breast cancer MCF-7 cells with opposite mechanisms. Although a short-term treatment (24h to 48h) with estradiol leads to a decrease in EGF-R number, the addition of hormone in cell culture for 5 days increases EGF-R level with a maximal effect observed at 10(-10) M estradiol. In contrast, when cells are treated with the antiestrogen hydroxytamoxifen, a dose-dependent decrease in EGF-R level occurs. We also report that EGF is able to induce estrogen receptors and, to a lesser extent, progesterone receptors when added to MCF-7 cell cultures. These results demonstrate an interaction between both estrogen receptor and EGF receptor growth promoting systems in target cells. The implications of such an interaction in the understanding of human breast cancer hormone responsiveness and, in the development of therapies, are discussed.

Comparative effects of 17 beta-estradiol, progestin R5020, tamoxifen and RU38486 on lactate dehydrogenase activity in MCF-7 human breast cancer cells

The effects of 17 beta-estradiol (estradiol), synthetic progestin R5020 and their antagonists, tamoxifen (Tam) and synthetic RU38486 on lactate dehydrogenase (LDH) activity in MCF-7 human breast cancer cells during the growth period were studied. A specially developed quantitative cytochemical assay was used; LDH activity is expressed per cell, and is thus independent of the positive and negative growth effects of the hormones and antagonists. Estradiol and R5020 stimulated LDH activity after similar exposures (6-48 h) and the stimuli were concentration dependent over the range 10(-7) M to 10(-10) M. As for the antagonists, RU38486 stimulated LDH activity in much the same way as estradiol and R5020; Tam alone, on the other hand, does not stimulate LDH, but when added to estradiol, Tam inhibits estradiol mediated LDH activation. When present at half-stimulant concentration, estradiol + R5020 and estradiol + RU38486 exhibit additive effects on LDH activity. Thus LDH appears to be an interesting tool for the study of hormone and antagonist effects in MCF-7 breast cancer cells.

Effect of estradiol and antiestrogens on cholesterol biosynthesis in hormone-dependent and -independent breast cancer cell lines

The effects of estradiol and/or antiestrogens on cholesterol biosynthesis were studied in two breast cancer cell lines. Cholesterogenic activity was evaluated after labeling cells with sodium [14C]acetate for increasing periods of time (up to 24 h) and measuring the incorporation of the radioactivity into nonsaponifiable lipids and into cholesterol, after separation from other labeled metabolites. We compared the effects of estradiol on cholesterogenesis with the well-known effects of this hormone on cell proliferation: estradiol stimulated both cholesterol synthesis and cell growth in MCF-7 cells, but stimulated neither in BT20 cells. The stimulation affected both the 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase step and the post-HMGCoA steps. Only the key enzyme step appeared to be mediated by the estrogen receptor. The hydroxytamoxifen and LY 117018 antiestrogens strongly inhibited cellular cholesterol production in both cell lines. Under the same conditions, cell growth is affected in MCF-7 cells, but not in BT20 (as shown by groups from other laboratories). This demonstrates that de novo synthesis of cholesterol is not essential for cell growth when cells are cultured in the presence of whole serum. The inhibition of cholesterol synthesis by antiestrogens mainly affected the lanosterol demethylation step and the C-27 sterol to cholesterol conversion. This inhibiting effect of antiestrogens was not mediated by the estrogen receptor.

Role of estrogen receptors and antiestrogen binding sites in an early effect of antiestrogens, the inhibition of cholesterol biosynthesis

The effects of estradiol (E2), 4-hydroxy-tamoxifen (OH-Tam), and LY117018 on cholesterogenesis were investigated in two human breast cancer cell lines (MCF-7 and BT20), and in rat hepatoma (HTC) and fibroblastic (NRK-49F) cell lines. It was found that 10(-10) M E2 stimulated and 10(-8) M OH-Tam inhibited cholesterol synthesis in the estrogen-sensitive MCF-7 cell line. The OH-Tam effect occurred in less than 15 min whereas E2 only stimulated after 8 h. The inhibition of cholesterol synthesis was not reversed by E2. E2 was without effect in the HTC and estrogen-resistant BT20 cell lines whereas OH-Tam was as effective as in the MCF-7 cells. LY117018 had nearly as much effect on cholesterol synthesis as OH-Tam, in both MCF-7 and BT20 cells. Neither E2 nor OH-Tam had any effect on the NRK-49F cell line, even at micromolar concentrations. The three lines (MCF-7, BT20, HTC), whose cholesterol synthesis has been shown to be OH-Tam sensitive, appeared to contain high-affinity antiestrogen binding sites (AEBS); since the OH-Tam-resistant line (NRK) only contained low-affinity AEBS, there appears to be some relationship between OH-Tam sensitivity and high-affinity AEBS content. This suggests that the cholesterogenesis inhibition induced by antiestrogens is ER-independent and may involve AEBS. The cholesterogenesis stimulation induced by E2 occurred via a different pathway that appears to be related to the presence of ER in the cells.

Binding of estrogen and antiestrogen in uterine cell nuclei: in vivo autoradiographic studies

The in vivo binding of antiestrogen in nuclei within the uterine stromal, epithelial and myometrial tissue compartments was compared to that of estrogen 2-48 h after injection. Tissue binding and retention of radioactivity was also studied. Immature rats were injected s.c. with 0.36 microgram [3H]hydroxytamoxifen [( 3H]TAM(OH] or 0.24 microgram [3H]estradiol [( 3H]E2) in oil. At 2, 4, 8, 12, 24 and 48 h after injection, uteri were processed for thaw-mount autoradiography and, along with other tissues, for liquid scintillation counting. After [3H]TAM(OH) injection total radioactivity in uterus, cervix, vagina and liver reached peak levels by 8 h then decreased slowly so that by 48 h radioactivity still remained in the tissues. At all time intervals, the levels of radioactivity in heart and muscle remained low. After [3H]E2 injection radioactivity in uterus, cervix and vagina reached peak levels between 2 and 4 h then decreased rapidly so that by 12 h radioactivity was low and essentially the same as in liver, heart and muscle. These results were paralleled by the time course of nuclear binding of [3H]TAM(OH) and [3H]E2 in the uterine cell types: peak levels occurred at 8 h and 4 h, respectively. Nuclear binding was still present 48 h after [3H]TAM(OH) injection but was absent by 24 h after [3H]E2 injection. Different uterine cell types bound different amounts of both the drug and the hormone. After [3H]TAM(OH) injection the decreasing order of labeling intensity in the tissue compartments was stroma, myometrium, epithelium; in contrast, that after [3H]E2 injection was stroma, epithelium, myometrium. The results indicate that the dissimilar nuclear binding kinetics of estrogen and antiestrogen are influenced by the pharmacokinetics but the uterine cell types may also influence binding kinetics.

Growth inhibitory effect of 4-hydroxy-tamoxifen on the BT-20 mammary cancer cell line

The antiestrogenic activities of Tamoxifen have been well documented and this molecule has been successfully used in the treatment of hormone dependent breast cancer. In the present experiments we demonstrate that 4-hydroxy-Tamoxifen (OH-TAM) is able to reduce the growth of the BT-20 cell line which is devoid of estrogen and progesterone receptors. Various parameters have been investigated in growth studies under control conditions and in the presence of OH-TAM. Cell numerations, [3H]thymidine incorporation per cell or per microgram of DNA have shown that OH-TAM reduces the growth rate in proportion to its concentration from 10(-9) M to 10(-6) M. This activity is not reversed by estradiol addition. It is unaffected by the presence or the absence of Phenol Red in the medium. Analysis by flow cytometry suggests that it takes place before the S phase of the cycle. Examination of control and treated cells by Electron Microscopy shows no sign of toxicity. The growth inhibitory activity of OH-TAM on these cell lines appears therefore unrelated to its antiestrogenic properties.

The effect of tamoxifen and medroxyprogesterone on giant cell formation by monocytes from patients with breast cancer

Incubation of peripheral blood monocytes from patients with breast cancer under agarose for 6 days at 37 degrees C in a 5% CO2 atmosphere resulted in giant cell formation. This phenomenon appeared to be mediated by retroviruses present in these cells. In this study giant cell formation was investigated in patients with primary stage I and II breast cancer before and 3 months after mastectomy with axillary lymph node clearance. Mastectomy had no significant inhibitory effect on giant cell formation. In vitro incubation of monocytes from patients with breast cancer in the presence of tamoxifen (Nolvadex) resulted in significant inhibition of giant cell formation (P less than 0.000003; paired Student's t-test). In vitro addition of medroxyprogesterone (Farlutal) to monocytes from patients with breast cancer also resulted in significant inhibition of giant cell formation (P less than 0.003: paired Student's t-test). Furthermore, incubation of monocytes from patients treated by mastectomy followed by 3 months treatment with adjuvant tamoxifen, resulted in a significant reduction (P less than 0.00007; paired Student's t-test) in the number of giant cells compared to the same samples tested before the commencement of the treatment. Giant cell formation may be used as a simple test to predicte the response of patients with breast cancer to either tamoxifen or medroxyprogesterone.

Effect of tamoxifen and tamoxifen derivatives on the conversion of estrone sulfate to estradiol in the MCF-7 mammary cancer cell line

The human mammary cancer cell line MCF-7 in culture was used to study the effect of tamoxifen and its derivatives: 4-hydroxytamoxifen (4-OH-Tam), N-desmethyltamoxifen (Dem-Tam) and cis-tamoxifen (cis-Tam) on the uptake and conversion of [3H]estrone sulfate (3H-E1S) to estradiol (E2). When [3H]-E1S (4 X 10(-9) M) was incubated by itself (control) a great proportion of the radioactivity was found as [3H]E2, predominantly in the nuclear fraction. All of the anti-estrogens (10(-6) M - 10(-5) M) studied decreased the total uptake of radioactivity by the cells by 50-60% and the quantity of E2 formed. The calculated concentrations (in pg/mg DNA +/- S.E.M.) of E2 (cytosol + 0.6 M KCl nuclear extract) with the anti-estrogens at 10(-5) M were as follows: control 56 +/- 3; Tam treated cells 4 +/- 1; + 4-OH-Tam 2 +/- 1; + Dem-Tam 5 +/- 2; + cis-Tam 8 +/- 4. A significant decrease in the concentrations of E2 was also observed in the mitochondria-microsomal fractions after the different treatments. It is suggested that the MCF-7 cells can use estrone-3-sulfate as a source of E2 and that the inhibitory effect of tamoxifen and its derivatives on the conversion of this sulfate to E2 could be involved in the anti-estrogenic process of these triphenylethylene derivatives.

Difference between R5020 and the antiprogestin RU486 in antiproliferative effects on human breast cancer cells

We have compared the effects of the progestin R5020 and the antiprogestin RU486 on the growth of the MCF-7 and T47D breast cancer cell lines. Differences between the two compounds were demonstrated in several parameters. 1. Estradiol was required for the efficient inhibition of cell growth of both lines by R5020 but not by RU486. Therefore in the total absence of estrogen (phenol-red free medium), the effects of the two drugs on cell growth were dissociated, RU486 remaining inhibitory while R5020 was inactive. 2. The proteins secreted by cells were differently affected, since R5020 induced a 48K protein and decreased the production of the estrogen-regulated 52K protein, while RU486 had no effect on these two parameters. 3. The morphology of cells treated by R5020 was more altered in the presence of estradiol than in its absence, while that of cells treated by RU486 was not affected whether or not estradiol was present. 4. There was a greater reduction of estrogen receptor sites in MCF-7 cells produced by R5020 than by RU486. Even though the two drugs appear to act through the same progesterone receptor and to inhibit total protein secretion, it is likely that they exert their antiproliferative effects on cultured breast cancer cells by different mechanisms. R5020 antagonizes the stimulation produced by estradiol. RU486 by contrast exerts a more direct progesterone receptor mediated inhibitory effect requiring no synergism by estradiol and therefore does not act through a partial progestin activity.

Antiestrogens inhibit the mitogenic effect of growth factors on breast cancer cells in the total absence of estrogens

The antiproliferative effect of antiestrogens in breast cancer is believed to be entirely due to the inhibition of estrogen induced growth. We show here that non-steroidal antiestrogens inhibit the growth of the human breast cancer MCF7 cells in the complete absence of estrogens (phenol-red-free medium) when cell proliferation is stimulated by insulin or epidermal growth factor. This non-antiestrogenic effect of antiestrogens is, however, mediated by accessible estrogen receptor sites, as it is not observed in receptor negative hormone-independent breast cancers, and is rescued by estradiol but not by insulin. We conclude that antiestrogens inhibit cell proliferation by inhibiting growth factor action as well as estrogen action and that in both cases, accessible estrogen receptors are required.

Human breast cancer in the athymic nude mouse: cytostatic effects of long-term antiestrogen therapy

We have investigated the effects of long-term estrogen withdrawal or tamoxifen therapy of MCF-7 human breast cancer cells growing in the athymic nude mouse to clarify mechanisms by which endocrine therapy inhibits tumor growth. Estrogen withdrawal with or without tamoxifen inhibited MCF-7 tumor growth, but did not cause significant regression, even after 4 months of treatment. Serial histologic studies of treated tumors revealed a reduction in mitotic rate but no significant gross or ultrastructural cytopathic changes. Treated tumors did show a modest increase in stromal fibrosis as well as occasional cytoplasmic or nuclear vacuolization, perhaps indicating early cytopathic effects. Cell viability was confirmed by cloning tumor cells in soft agar; cloning efficiency in treated tumors was similar to that in controls. Tumor fragments from treated mice were also viable and formed tumors when transplanted into estrogen-supplemented but not estrogen-deprived mice indicating continued hormone dependence. When estrogen-deprived or tamoxifen-treated mice were replenished with estrogen, cell proliferation was reactivated and tumor growth resumed. After 3-4 months of endocrine therapy, tumors began to regrow despite continued treatment suggesting the conversion to hormone independence. These studies suggest that in this model system, estrogen withdrawal and antiestrogen therapy work primarily by cytostatic rather than cytocidal mechanisms.

Serum protects HeLa cells from antiestrogen effects in culture

The effect of nafoxidine and tamoxifen on HeLa cells is reported in this study. The two antiestrogens showed no effect on HeLa cells when grown in the presence of fetal calf serum, the cytotoxic effects were observed only under serum-free conditions. BSA also protected the HeLa cells from antiestrogen effects. The effect of nafoxidine and tamoxifen on different established cell lines and a primary culture of rat skin fibroblasts has been studied.