Melatonin inhibits aromatase promoter expression by regulating cyclooxygenases expression and activity in breast cancer cells

Background:

Melatonin reduces the development of breast cancer interfering with oestrogen-signalling pathways, and also inhibits aromatase activity and expression. Our objective was to study the promoters through which melatonin modifies aromatase expression, evaluate the ability of melatonin to regulate cyclooxygenases and assess whether the effects of melatonin are related to its effects on intracellular cAMP, in MCF-7 cells.

Methods:

Total aromatase mRNA, aromatase mRNA promoter regions and cyclooxygenases mRNA expression were determined by real-time RT–PCR. PGE₂ and cAMP were measured by kits.

Results:

Melatonin downregulated the gene expression of the two major specific aromatase promoter regions, pII and pI.3, and also that of the aromatase promoter region pI.4. Melatonin 1 nM was able to counteract the stimulatory effect of tetradecanoyl phorbol acetate on PGE₂ production and inhibit COX-2 and COX-1 mRNA expression. Melatonin 1 nM elicited a parallel time-dependent decrease in both cyclic AMP formation and aromatase mRNA expression.

Conclusions:

This study shows that melatonin inhibits aromatase activity and expression by regulating the gene expression of specific aromatase promoter regions. A possible mechanism for these effects would be the regulation by melatonin of intracellular cAMP levels, mediated by an inhibition of cyclooxygenase activity and expression.

Selective estrogen enzyme modulator actions of melatonin in human breast cancer cells

Melatonin exerts oncostatic effects on different kinds of neoplasias, especially on estrogen-dependent mammary tumors. Current knowledge about the mechanisms by which melatonin inhibits the growth of breast cancer cells point to an interaction of melatonin with estrogen-responsive pathways. The intratumoral production of estrogens in breast carcinoma tissue plays a pivotal role in the proliferation of mammary tumoral cells and its blockade is one of the main objectives of the treatment of breast cancer. The aim of the present work is centered on the study of the role of melatonin in the control of some enzymes involved in the formation and transformation of estrogens in human breast cancer cells. The present study demonstrates that melatonin, at physiologic concentrations, modulates the synthesis and transformation of biologically active estrogens in MCF-7 cells, through the inhibition of sulfatase (STS) and 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) activity and expression, enzymes involved in the estradiol formation in breast cancer cells. Physiologic concentrations of melatonin also stimulate the activity and expression of estrogen sulfotransferase (EST), the enzyme responsible for the formation of the biologically inactive estrogen sulfates. The level of EST mRNA steady-state of cells treated with melatonin was three times higher than that in control cells. These findings which document that melatonin has an inhibitory effect on STS and 17beta-HSD1 and a stimulatory effect on EST, in combination with its previously described antiaromatase effect, can open up new and interesting possibilities in clinical applications of melatonin in breast cancer.

Melatonin and estradiol effects on food intake, body weight, and leptin in ovariectomized rats

OBJECTIVE

The study in ovariectomized (Ovx) rats, as a model of menopausal status, of the effects of melatonin (M) and/or estradiol (E), associated or not with food restriction, on body weight (BW) and serum leptin levels.

METHODS

Female SD rats (200-250 g) were Ovx and treated with E, M, E+M or its diluents. Control sham-Ovx rats were treated with E-M diluents. After 7 weeks being fed ad libitum, the animals were exposed for 7 more weeks to a 30% food restriction. We measured: food intake, BW, nocturnal and diurnal urinary excretion of sulphatoxymelatonin (aMT6s), leptin in midday and midnight blood samples, glucose, total cholesterol, LDL, HDL and triglycerides.

RESULTS

Day/night rhythm of aMT6s excretion was preserved in all cases. The increase of aMT6s excretion in M-treated animals basically affected the nocturnal period. In animals fed ad libitum, E fully prevented Ovx-induced increase of BW, leptin and cholesterol. Melatonin reduced food intake and partially prevented the increase of BW and cholesterol, without changing leptin levels. Under food restriction, M was the most effective treatment in reducing BW and cholesterol. Leptin levels were similar in M, E or E+M treated rats, and lower than in untreated Ovx rats.

CONCLUSIONS

Our result gives a preliminary experimental basis for a post-menopausal co-treatment with estradiol and melatonin. It could combine the effectiveness of estradiol (not modified by melatonin) with the positive effects of melatonin (improvement of sleep quality, prevention of breast cancer, etc.). The possible beneficial effects of melatonin which could justify its use, need to be demonstrated in clinical trials.

Inhibitory effects of pharmacological doses of melatonin on aromatase activity and expression in rat glioma cells

Melatonin exerts oncostatic effects on different kinds of neoplasias, especially on oestrogen-dependent tumours. Recently, it has been described that melatonin, on the basis of its antioxidant properties, inhibits the growth of glioma cells. Glioma cells express oestrogen receptors and have the ability to synthesise oestrogens from androgens. In the present study, we demonstrate that pharmacological concentrations of melatonin decreases the growth of C6 glioma cells and reduces the local biosynthesis of oestrogens, through the inhibition of aromatase, the enzyme that catalyses the conversion of androgens into oestrogens. These results are supported by three types of evidence. Firstly, melatonin counteracts the growth stimulatory effects of testosterone on glioma cells, which is dependent on the local synthesis of oestrogens from testosterone. Secondly, we found that melatonin reduces the aromatase activity of C6 cells, measured by the tritiated water release assay. Finally, by (RT)–PCR, we found that melatonin downregulates aromatase mRNA steady-state levels in these glioma cells. We conclude that melatonin inhibits the local production of oestrogens decreasing aromatase activity and expression. By analogy to the implications of aromatase in other forms of oestrogen-sensitive tumours, it is conceivable that the modulation of the aromatase by pharmacological melatonin may play a role in the growth of glioblastomas.

Effects of MT1 melatonin receptor overexpression on the aromatase-suppressive effect of melatonin in MCF-7 human breast cancer cells

A major mechanism through which melatonin reduces the development of breast cancer is based on its anti-estrogenic actions by interfering at different levels with the estrogen-signalling pathways. Melatonin inhibits both aromatase activity and expression in vitro (MCF-7 cells) as well as in vivo, thus behaving as a selective estrogen enzyme modulator. The objective of this study was to study the effect of MT1 melatonin receptor overexpression in MCF-7 breast cancer cells on the aromatase-suppressive effects of melatonin. Transfection of the MT1 melatonin receptor in MCF-7 cells significantly decreased aromatase activity of the cells and MT1-transfected cells showed a level of aromatase activity that was 50% of vector-transfected MCF-7 cells. The proliferation of estrogen-sensitive MCF-7 cells in an estradiol-free media but in the presence of testosterone (an indirect measure of aromatase activity) was strongly inhibited by melatonin in those cells overexpressing the MT1 receptor. This inhibitory effect of melatonin on cell growth was higher on MT1 transfected cells than in vector transfected ones. In MT1-transfected cells, aromatase activity (measured by the tritiated water release assay) was inhibited by melatonin (20% at 1 nM; 40% at 10 microM concentrations). The same concentrations of melatonin did not significantly influence the aromatase activity of vector-transfected cells. MT1 melatonin receptor transfection also induced a significant 55% inhibition of aromatase steady-state mRNA expression in comparison to vector-transfected MCF-7 cells (p<0.001). In addition, in MT1-transfected cells melatonin treatment inhibited aromatase mRNA expression and 1 nM melatonin induced a higher and significant down-regulation of aromatase mRNA expression (p<0.05) than in vector-transfected cells. The findings presented herein point to the importance of MT1 melatonin receptor in mediating the oncostatic action of melatonin in MCF-7 human breast cancer cells and confirm MT1 melatonin receptor as a major mediator in the melatonin signalling pathway in breast cancer.

Melatonin prevents the estrogenic effects of sub-chronic administration of cadmium on mice mammary glands and uterus

Cadmium (Cd) is a heavy metal classified as a human carcinogen. Occupational exposure, dietary consumption and cigarette smoking are sources of Cd contamination. Cd-induced carcinogenicity depends on its oxidative and estrogenic actions. A possible role of Cd in breast cancer etiology has been recently suggested. Melatonin, because of its antioxidant and antiestrogenic properties could counteract the toxic effects of this metalloestrogen. Our aim was both to determine the effects of relevant doses of Cd on mice mammary glands and uterus and to test whether melatonin would counteract its effects. Female mice of different ages and estrogenic status (prepuberal, adult intact, adult ovariectomized) were treated with CdCl(2) (2-3 mg/kg, i.p.), melatonin (10 microg/mL in drinking water), CdCl(2) + melatonin, or diluents. Whereas in prepuberal animals Cd disturbs mammary ductal growth and reduces the number of terminal end buds, in adults, regardless of the steroidal milieu, Cd exerts estrogenic effects on mammary glands, increasing lobuloalveolar development and ductal branching. Uterine weight also increased as a result of Cd treatment. The effects of Cd are partially inhibited by melatonin. In adult ovariectomized mice, Cd concentration in blood of animals treated with CdCl(2) + melatonin was lower than in mice receiving only Cd; the opposite effects were found in non-castrated animals. As Cd mimics the effect of estrogens, the high incidence of breast cancer in tobacco smokers and women working in industries related with Cd could be explained because of the properties of this metal. The effects of melatonin point to a possible role of this indoleamine as a preventive agent for environmental or occupational Cd contamination.

Melatonin inhibits both ER alpha activation and breast cancer cell proliferation induced by a metalloestrogen, cadmium

Cadmium (Cd) is a heavy metal affecting human health both through environmental and occupational exposure. There is evidence that Cd accumulates in several organs and is carcinogenic to humans. In vivo, Cd mimics the effect of estrogens in the uterus and mammary gland. In estrogen-responsive breast cancer cell lines, Cd stimulates proliferation and can also activate the estrogen receptor independent of estradiol. The ability of this metalloestrogen to increase gene expression in MCF7 cells is blocked by anti-estrogens suggesting that the activity of these compounds is mediated by ER alpha. The aims of this work were to test whether melatonin inhibits Cd-induced proliferation in MCF7 cells, and also to study whether melatonin specifically inhibits Cd-induced ER alpha transactivation. We show that melatonin prevents the Cd-induced growth of synchronized MCF7 breast cancer cells. In transient transfection experiments, we prove that both ER alpha- and ER beta-mediated transcription are stimulated by Cd. Melatonin is a specific inhibitor of Cd-induced ER alpha-mediated transcription in both estrogen response elements (ERE)- and AP1-containing promoters, whereas ER beta-mediated transcription is not inhibited by the pineal indole. Moreover, the mutant ER alpha-(K302G, K303G), unable to bind calmodulin, is activated by Cd but becomes insensitive to melatonin treatment. These results proved that melatonin inhibits MCF7 cell growth induced by Cd and abolishes the stimulatory effect of the heavy metal in cells expressing ER alpha at both ERE-luc and AP1-luc sites. We can infer from these experiments that melatonin regulates Cd-induced transcription in both ERE- and AP1 pathways. These results also reinforce the hypothesis of the anti-estrogenic properties of melatonin as a valuable tool in breast cancer therapies.

Melatonin and mammary cancer: a short review

Melatonin is an indolic hormone produced mainly by the pineal gland. The former hypothesis of its possible role in mammary cancer development was based on the evidence that melatonin down-regulates some of the pituitary and gonadal hormones that control mammary gland development and which are also responsible for the growth of hormone-dependent mammary tumors. Furthermore, melatonin could act directly on tumoral cells, as a naturally occurring antiestrogen, thereby influencing their proliferative rate. The first reports revealed a low plasmatic melatonin concentration in women with estrogen receptor (ER)-positive breast tumors. However, later studies on the possible role of melatonin on human breast cancer have been scarce and mostly of an epidemiological type. These studies described a low incidence of breast tumors in blind women as well as an inverse relationship between breast cancer incidence and the degree of visual impairment. Since light inhibits melatonin secretion, the relative increase in the melatonin circulating levels in women with a decreased light input could be interpreted as proof of the protective role of melatonin on mammary carcinogenesis. From in vivo studies on animal models of chemically induced mammary tumorigenesis, the general conclusion is that experimental manipulations activating the pineal gland or the administration of melatonin lengthens the latency and reduces the incidence and growth rate of mammary tumors, while pinealectomy usually has the opposite effects. Melatonin also reduces the incidence of spontaneous mammary tumors in different kinds of transgenic mice (c-neu and N-ras) and mice from strains with a high tumoral incidence. In vitro experiments, carried out with the ER-positive MCF-7 human breast cancer cells, demonstrated that melatonin, at a physiological concentration (1 nM) and in the presence of serum or estradiol: (a) inhibits, in a reversible way, cell proliferation, (b) increases the expression of p53 and p21WAF1 proteins and modulates the length of the cell cycle, and (c) reduces the metastasic capacity of these cells and counteracts the stimulatory effect of estradiol on cell invasiveness; this effect is mediated, at least in part, by a melatonin-induced increase in the expression of the cell surface adhesion proteins E-cadherin and beta(1)-integrin. The direct oncostatic effects of melatonin depends on its interaction with the tumor cell estrogen-responsive pathway. In this sense it has been demonstrated that melatonin down-regulates the expression of ERalpha and inhibits the binding of the estradiol-ER complex to the estrogen response element (ERE) in the DNA. The characteristics of melatonin's oncostatic actions, comprising different aspects of tumor biology as well as the physiological doses at which the effect is accomplished, give special value to these findings and encourage clinical studies on the possible therapeutic value of melatonin on breast cancer.

Direct antiproliferative effects of melatonin on two metastatic cell sublines of mouse melanoma (B16BL6 and PG19)

The effects of melatonin on the growth of two highly tumorigenic rodent melanoma cells were studied in vitro. PG19, an amelanotic mouse melanoma cell line, and B16BL6, a melanotic melanoma cell line selected for its invasive potential in vitro, were cultured in the presence of different concentrations of melatonin (10 microM to 0.1 pM). Five days later, viable cells were determined in a haemocytometer by the trypan blue exclusion test. Melatonin at concentrations of 1 nM and 10 pM (within the range of concentrations that correspond to physiological night-time and daytime levels in human blood) significantly inhibited proliferation in both melanoma cell lines. Subphysiological (0.1 pM) or supraphysiological (10 microM to 100 nM) concentrations of melatonin lacked this effect. These results support the hypothesis that, at physiological concentrations, melatonin exerts a direct inhibitory effect on PG19 and B16BL6 cells proliferation.

Melatonin effects on intercellular junctional communication in MCF-7 human breast cancer cells

Melatonin exerts a direct antiproliferative effect on estrogen-responsive MCF-7 cells in culture. Recently, the importance of the anti-invasive actions of melatonin as a part of the oncostatic action of this indolamine has been reported. Gap junctional intercellular communication is known to be involved in controlling cell proliferation and differentiation, and a decrease in intercellular junctional communication has been described in highly invasive mammary cancer cells. Because melatonin at physiological doses (1 nM) shifts MCF-7 cells to a lower invasive status, we postulate that melatonin could modulate the levels of gap junctional intercellular communication in these tumor cells. To test our hypothesis, we studied gap junctional intercellular communication in MCF-7 human breast cancer cells previously (7-8 days) treated, or not, with melatonin (10 microM or 1 nM). Using the scrape-loading assay dye-transfer technique to introduce 0.05% Lucifer yellow into cells, we measured the ability of the tumor cells to transfer dye to adjacent cells. Rhodamine dextran (0.05%) was used as a control dye to verify that dye-transfer occurs through intercellular junctions. The presence of melatonin (10 microM or 1 nM) in the culture medium significantly increased (P < 0.01) the transfer of the dye to adjacent cells through gap junctions. This increase was greater at 10 microM melatonin, and averaged scan profiles of cells treated with melatonin 10 microM showed a statistically significant increase (P < 0.01) in the integrated optical density values, and a broadening of the densitometric scan. These findings suggest that melatonin could exert its antitumor action, at least in part, by increasing regulatory signals that are passed between adjacent epithelial cells through intercellular junctions.

Low radon doses sensitize MCF-7 human breast cancer cells to taxol

We studied whether human breast cancer cells show increased sensitivity to the chemotherapeutic agent taxol when they have been treated with low radiation doses (1.7-3.2 x 10(-3) Gy) from the gas radon. To this end, MCF-7 cells were cultivated in a medium either with or without dissolved radon for 3 days and then exposed to taxol (50 nM). Cells exposed to low doses of radon and then to a concentration of 50 nM of taxol exhibit a lower proliferation rate and a lower viability than cells treated with the same concentration of taxol but not irradiated. These findings indicate an important interaction of radon and taxol in the inhibition of MCF-7 cell growth.

Influence of serum from healthy or breast tumor-bearing women on the growth of MCF-7 human breast cancer cells

Sera from women healthy (HW) or with breast (BCW), ovarian or endometrial cancer, were added (10%) to the culture media of MCF-7 cells and cell proliferation assessed 4 days later to verify: a) whether sera from BCW, obtained before or 8 days after tumor ablaction, influence the proliferation of these cells, b) whether the effects of serum from BCW are specific for mammary tumor cells. Sera from BCW, but not sera from women with ovarian or endometrial cancer, increased MCF-7 cell proliferation in comparison with sera from HW. After surgical ablation of the breast tumors, serum's ability to increase MCF-7 cell proliferation decreased significantly. These effects cannot be explained by differences on serum levels of estradiol or melatonin. These results suggest the presence of growth-promoting substances of possible tumoral origin in serum of BCW, a fact that should be considered as support for the surgical treatment of tumor masses.

Melatonin and mammary pathological growth

In this article we review the state of the art on the role of the pineal gland and melatonin in mammary cancer tumorigenesis in vivo as well as in vitro. The former hypothesis of a possible role of the pineal gland in mammary cancer development was based on the evidence that the pineal, via its main secretory product, melatonin, downregulates some of the pituitary and gonadal hormones which control mammary gland development and are also responsible for the growth of hormone-dependent mammary tumors. Furthermore, melatonin could act directly on tumoral cells, thereby influencing their proliferative rate. Other possible origins of melatonin's antitumoral actions could be found in its antioxidant or immunoenhancing properties. The working hypotheses of most experiments were that the activation of the pineal gland, or the administration of melatonin, should give rise to antitumoral behavior; conversely, suppression of the pineal gland or melatonin deficits should stimulate mammary tumorigenesis. From in vivo studies on animal models of tumorigenesis, the general conclusion is that experimental manipulations activating the pineal gland, or the administration of melatonin, enlarge the latency and reduce the incidence and growth rate of chemically induced mammary tumors, while pinealectomy usually has the opposite effects. The direct actions of melatonin on mammary tumors have been suggested because of its ability to inhibit, at physiological doses (1 nM), the in vitro proliferation and invasiveness of MCF-7 human breast cancer cells. The fact that most studies have been performed on two models, chemically induced mammary adenocarcinoma in rats (in vivo studies) and the cell tumor line MCF-7 (in vitro studies), makes the generalization of the results somewhat difficult. However, the characteristics of these actions, comprising different aspects of tumor biology such as initiation, proliferation, and metastasis, as well as the doses (physiological range) at which the effect is accomplished, give special value to these findings. On the strength of these data, the small number of clinical studies focusing on the possible therapeutic value of melatonin on breast cancer is surprising.

Melatonin, experimental basis for a possible application in breast cancer prevention and treatment

The role of the pineal as an oncostatic gland has been studied in animal models of tumorigenesis, especially on those concerning the mammary gland. The general conclusion is that experimental manipulations activating pineal gland, or the administration of melatonin, reduce the incidence and growth rate of chemically-induced murine mammary tumors, while pinealectomy or situations which implicate a reduction of melatonin production usually stimulate mammary carcinogenesis. The direct actions of melatonin on mammary tumors have been suggested because of its ability to inhibit, at physiological doses (1nM), the in vitro proliferation of MCF-7 human breast cancer cells. In this article we review the outstanding findings related to melatonin actions on mammary which, taken together, support a possible usefulness of this indoleamine in the prevention and treatment of mammary gland malignancy.

Melatonin increases p53 and p21WAF1 expression in MCF-7 human breast cancer cells in vitro

The aim of the present work was to study whether melatonin, at physiological concentrations, exerts its antiproliferative effects on MCF-7 human breast cancer cells by inducing the expression of some of the proteins involved in the control of the cell cycle. MCF-7 cells were cultured for 48 h in DMEM media containing either melatonin (1 nM) or the diluent (0.001% ethanol). At this concentration, after 48 hours of incubation, melatonin reduced the number of viable cells in relation to controls. The decreased cell proliferation was coincident with a significant increase in the expression of p53 as well as p21WAF1 proteins. These results demonstrate that melatonin inhibits MCF-7 cell proliferation by inducing an arrest of cell cycle dependent on an increased expression of p21WAF1 protein, which is mediated by the p53 pathway.

Influence of melatonin on invasive and metastatic properties of MCF-7 human breast cancer cells

Melatonin, the principal pineal gland hormone, exerts a direct antiproliferative effect on estrogen-responsive MCF-7 cells in culture. The purpose of the current study was to investigate the effects of melatonin on the invasion capacity of MCF-7 cells. In vitro, melatonin at physiological doses (1 nM) reduced (P < 0.001) the invasiveness of tumoral cells measured in Falcon invasion chambers. Subphysiological (0.1 pM) and pharmacological concentrations (10 microM) of melatonin failed to inhibit cell invasion. Melatonin was also able to block 17beta-estradiol-induced invasion (P < 0.001). Pretreatment of MCF-7 cells with 1 nM melatonin increased the response of tumoral cells to the anti-invasive effects of this indolamine. To explore possible mechanisms by which melatonin reduces invasiveness, we measured the attachment of MCF-7 cells to a basement membrane, the chemotactic response of the cells, and their type IV collagenolytic activity. The presence of melatonin (1 nM) in the culture medium significantly reduced the ability of MCF-7 cells to attach to the basement membrane; this effect was enhanced by pretreating the cells with the same indolamine (P < 0.001). Melatonin also counteracts the stimulatory effects of 17beta-estradiol on cell adhesion (P < 0.001). The chemotactic response of MCF-7 cells also decreased in the presence of 1 nM melatonin, and this melatonin-induced reduction of cell migration was more effective on cells that were previously incubated for 5 days with melatonin than it was on nonpretreated cells (P < 0.001). The simultaneous addition of 17beta-estradiol and melatonin resulted in a significantly lower chemotactic response than that of 17beta-estradiol-treated cells (P < 0.001). However, type IV collagenolytic activity was not influenced by melatonin. Our results demonstrate that melatonin reduces the invasiveness of MCF-7 cells, causing a decrease in cell attachment and cell motility, probably by interacting with the estrogen-mediated mechanisms of MCF-7 cell invasiveness. In addition, we also studied the influence of melatonin on the expression of two cell surface adhesion molecules (E-cadherin and beta1 integrin) and an intermediate filament protein (vimentin), the expression of which has been correlated with the relative invasive capacity of human breast cancer cells. The culture of tumor cells in the presence of melatonin (1 nM) increased the membrane staining for E-cadherin and beta1 integrin as well as the number of E-cadherin and beta1 integrin immunoreactive cells (P < 0.01). Neither control MCF-7 cells nor those treated with melatonin stained for vimentin. Preliminary in vivo experiments carried out on ovariectomized athymic nude mice implanted with 17beta-estradiol pellets and inoculated with 5 x 10(6) MCF-7 cells in the inguinal mammary fat pad suggest that melatonin could decrease the tumorigenicity of these tumor cells. However, these results need further confirmation. Taken together, our results suggest that melatonin shifts MCF-7 human breast cancer cells to a lower invasive status by increasing the beta1 integrin subunit and E-cadherin expression and promoting the differentiation of tumor cells. Finally, our study points out the existence of the anti-invasive actions of melatonin as a part of the oncostatic action of melatonin.

Effects of melatonin on the proliferation and differentiation of human neuroblastoma cells in culture

Since melatonin has direct inhibitory effects on some tumor cells in vitro, the aim of the present work was to study whether the growth and structural characteristics of the human neuroblastoma cell line SK-N-SH in vitro are influenced by this indoleamine. Concentrations of melatonin of 10(-9) and 10(-11) M significantly inhibited (P < 0.05) cell proliferation. Subphysiological (10(-13) M) or supraphysiological (10(-7) and 10(-5) M) concentrations of melatonin lacked this effect. After 8 days of exposure to melatonin (10(-9) M), cells showed significantly smaller cell and nuclear sizes than control cells. Melatonin-treated cells presented greater neurite outgrowth than control cells. These results support the hypothesis that melatonin, at physiological concentrations, exerts a direct antiproliferative effect on SK-N-SH cells, promoting the differentiation of neuroblastoma cells.

Melatonin inhibits DNA synthesis in MCF-7 human breast cancer cells in vitro

The aim of the present work was to study whether physiological doses of melatonin (1nM) modified DNA synthesis in MCF-7 human breast cancer cells. Exponentially growing MCF-7 cells were incubated for 24 h with thymidine (2mM) for blocking mitosis and synchronizing the cell division cycle. Synchronization was assessed by a flow cytometry study which showed that after release from excess thymidine, 82.3% of the cells were in phase G1. Lots of these synchronized cells were pulsed for 1h with [3H]deoxythymidine ([3H]dThy) or [3H]dThy + melatonin, at 0,3,6,9,12,15 or 24 h from the release of the mitotic arrest. The exposition of these synchronized MCF-7 cells to melatonin for only 1h, significantly inhibited [3H]dThy incorporation when it was at 6 or 9 h. after release from mitotic block, at a time when DNA precursor incorporation was the highest and the number of cells in S phase was maximum. We conclude that, at least in part, melatonin antiproliferative effects on MCF-7 cells could be mediated by a reduction of DNA synthesis.

Influence of low doses of radiation due to 222Rn on proliferation of fibroblasts and MCF-7 human breast cancer cells in vitro

The aim of the present study is to analyze the effects of low doses of radiation due to radon (within the range present in the environment) in the proliferation of normal (fibroblasts) and tumoral (MCF-7 human breast cancer cells) mammalian cells. Both fibroblast and MCF-7 cells were incubated in culture media with different levels of radon (doses of 10-15 000 microGy), or non-radon (control). After incubation the number of cells per plate was measured with a hemocytometer. The dissolution of radon in the culture media decreased the proliferation of MCF-7 cells (not the fibroblasts). Within the range of doses used in this experiment, the lowest as well as the highest doses of radiation had the lowest antiproliferative effects. Intermediate doses strongly decreased the number of final cells with respect to those in the control population.

Modulation of the length of the cell cycle time of MCF-7 human breast cancer cells by melatonin

It has been shown that melatonin has a direct inhibitory effect on the proliferation of MCF-7 human breast cancer cells in culture. In the present work, we studied whether the length of the cell cycle of MCF-7 cells in increased by melatonin. In MCF-7 cells partially synchronized and labelled with [3H]thymidine, melatonin (10(-9)M), added to the culture medium, shifted the period of the labeling index rhythm from 20.36 hours to 23.48 hours. The fact that melatonin significantly increased (p<0.005) the duration of the cell cycle of human breast cancer cells, support the notion that this hormone exerts part of its antitumor effect through a cell-cycle-specific mechanism by delaying the entry of MCF-7 cells into mitosis.

Melatonin inhibition of MCF-7 human breast-cancer cells growth: influence of cell proliferation rate

We have studied whether the cell proliferation rate modifies the inhibitory actions of melatonin on MCF-7 cell growth. The proliferative rate of cells was altered by plating them at different densities (5 x 10(4) to 100 x 10(4) cells/dish) in media with low charcoal-stripped serum concentrations. In this way, population doubling time ranged from 33 h (for density = 100 x 10(4) cells/dish) to 75 h (for density = 5 x 10(4) cells/dish). Melatonin (10(-9)M) only inhibited fast proliferating MCF-7 cells, increasing their cell doubling time, and did not significantly modify the length of doubling time in the cultures with low proliferation rate, in which doubling time was already long. These data clearly show that there is a direct relation between proliferative rate of cells and melatonin inhibitory actions on MCF-7 cells.

Differences between pulsatile or continuous exposure to melatonin on MCF-7 human breast cancer cell proliferation

We studied the different in vitro antiproliferative actions of melatonin on MCF-7 cells, depending on whether the cells are exposed to hormone concentrations which remain constant in culture media (Group I, 10(-9) M; Group II, 10(-11) M melatonin) or varying at 12 h intervals, thus simulating a diurnal rhythm: Group III, 12 h in 10(-9) M melatonin/12 h without melatonin (10(-9) M/0 12/12 h); Group IV, 10(-11) M/0 12/12 h; Group V, 10(-9) M/10(-11) M 12/12 h. After 5 days of culture, cell proliferation appeared significantly inhibited in Groups I and III, but not in Groups II and IV. However, the highest antiproliferative effect was obtained by sequential exposure to 10(-9) M/10(-11) M melatonin (Group V), which mimics the physiological rhythm of serum melatonin concentration.

Melatonin modulates growth factor activity in MCF-7 human breast cancer cells

Melatonin has been shown to have direct oncostatic actions on estrogen-responsive, MCF-7 human breast cancer cells in culture. In the present study, we examined whether these inhibitory actions on cell growth may be mediated through actions on bioassayable growth factor activity. In order to test this hypothesis, we estimated the growth factor activity of conditioned medium (CM) from estradiol (E2), or melatonin-treated cells, in the presence or absence of melatonin on MCF-7 cell growth. We also determined whether melatonin inhibits the action of epidermal growth factor (EGF) action in the absence of E2. The addition of melatonin (10(-9) M) to the cultures of MCF-7 cells with CM from E2 (10(-8) M)-treated cells significantly inhibited the growth stimulatory activity of CM, suggesting that melatonin inhibited cell proliferation by blocking the action of E2-induced autocrine growth stimulatory factors. Conditioned medium from melatonin-treated cells significantly inhibited cell proliferation, while an additional supply of melatonin to these cultures had an even greater inhibitory effect. Melatonin was also active in the complete absence of serum as long as cell growth was stimulated by EGF, an E2-inducible growth factor. The inhibitory effect of melatonin increased as the dose of EGF increased. This non-antiestrogenic inhibitory effect of melatonin was reversed by E2, but not by EGF itself, suggesting that melatonin requires accessible estrogen receptor sites for its inhibitory activity on the growth stimulating action of EGF. Taken together, these findings suggest that melatonin may inhibit the action and/or release of growth stimulatory factors as well as stimulate the release of growth inhibitory factors in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between melatonin and estradiol on morphological and morphometric features of MCF-7 human breast cancer cells

Melatonin has been shown to have a direct inhibitory effect on the proliferation of estrogen-responsive MCF-7 human breast cancer cells, involving an interaction with estradiol. The anti-proliferative effect of melatonin is reversed by the addition of estradiol to the culture. In the present study, we examined whether inhibition by melatonin and subsequent estrogen rescue of MCF-7 cells are correlated with morphological and morphometric changes in these cells. After 4 days of exposure to melatonin, MCF-7 cells showed significantly smaller cell and nuclear sizes than other groups. These morphometric results were closely related to the ultrastructural features observed in these cells. While control and estradiol-treated cells showed increased tumor characteristics, melatonin-treated cells presented greater differentiation, in keeping with their epithelial origin (presence of cytokeratin filament bundles, conspicuous rough endoplasmic reticulum, and Golgi cisternae together with the presence of prominent nucleoli at the nuclear level). Additionally, some melatonin-treated cells displayed degenerative features (mitochondrial swelling with disruption of cristae, cytoplasmic vacuolation, nuclear chromatin disgregation and cell lysis). The addition of estradiol to cells previously incubated with melatonin reversed the changes induced by the latter and these cells showed the same ultrastructural features as the control cells. Our results support the notion that melatonin exerts its antitumor effect through a cell-cycle-specific mechanism by delaying the entry of MCF-7 cells into mitosis. This allows the tumor cells to achieve greater differentiation. The fact that the morphometric and morphological effects induced by melatonin are counteracted by estrogens suggests a cell-cycle acceleration induced by estradiol.

Ultrastructural changes in hypothalamic supraoptic nucleus neurons of ovariectomized estrogen-deprived young rats

We report the occurrence of neuronal degeneration in the supraoptic nucleus of the hypothalamus of prepubertal female rats as a consequence of ovariectomy followed by estrogen deprivation (OVX-EB). In contrast, no degenerating neurons were observed in ovariectomized rats treated with estrogens (OVX + EB) or sham-operated animals. The altered neurons in the OVX-EB group presented a cytoplasm with dilation of the rough endoplasmic reticulum lumen. The nuclear envelope also appeared dilated. There was mitochondrial swelling with disintegrated cristae, while lysosomes appeared intact. The cell nucleus showed a pattern of chromatin condensation and a nucleolus hardly distinguishable from the nucleoplasm. The neuronal alterations reported here may be due to altered gene expression in the cell nucleus resulting from induced hormonal loss during early postnatal development.

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.

Effects of the pineal hormone melatonin on the anchorage-independent growth of human breast cancer cells (MCF-7) in a clonogenic culture system

Only physiological levels of melatonin exert an antiproliferative effect on MCF-7 breast cancer cells grown in an anchorage-dependent culture system. We investigated melatonin's effect on the anchorage-independent growth of MCF-7 cells as well as the dose-response characteristics of this indoleamine under clonogenic culture conditions. Melatonin's inhibitory effect, with respect to the number and size of colonies formed, exhibit a linear dose-response curve with pharmacological concentrations producing a maximal inhibition while subphysiological levels of melatonin induce minimal inhibition. These results indicate that cellular attachment may modify the sensitivity of MCF-7 cells towards melatonin.

Pineal gland in rats with 7,12-dimethylbenz(a)anthracene-induced mammary tumors subjected to manipulations known as enhancers of pineal actions

The ultrastructure of pinealocytes was studied in rats with 7,12-dimethylbenz(a)anthracene-induced mammary tumors which were subjected to experimental manipulations known as enhancers of pineal actions (anosmia, underfeeding or cold exposure). In these animals we found: (I)--more nuclei with deep nuclear invaginations; (II)--a large number of cytoplasmic organelles, including lipid droplets, myeloid bodies, synaptic ribbons and lysosomes; (III)--numerous degenerative changes. In general, we found an increase in structural features related to pineal photoneuroendocrine activity. Our results indicate that pineal-dependent inhibition of neoplastic growth induced by these experimental manipulations, previously reported, can be mediated through an increase in pineal metabolic activity.

Histopathologic features of DMBA-induced mammary tumors in blind-underfed, blind-anosmic, and blind cold-exposed rats: influence of the pineal gland

The influence of the pineal gland on the histopathologic changes induced in mammary glands by 7, 12-dimethylbenz(a)-anthracene (DMBA) has been studied. To achieve the maximum expression of pineal action in animals, 28-day-old female Sprague-Dawley rats were subjected to one of the following treatments: blindness + olfactory bulbectomy (BA), blindness + underfeeding (BU), or blindness + cold exposure (BC). Half of the rats in each group were also pinealectomized. Animals that were intact or only pinealectomized served as controls. Each animal received a single intragastrical dose of DMBA (20 mg) 4 weeks after performing the treatments mentioned above. At 28 weeks of age animals were sacrificed, and mammary tumors as well as mammary glands without macroscopic lesions were collected. Animals of the BU group failed to develop any tumors throughout the 20-week control period. In the remaining groups, tumors were found; the relation between number of adenocarcinomas (AC) and fibroadenomas was similar, always with a greater incidence of ACs. Some ACs showed areas with changes in the ductal epithelium that are considered signs of tumoral regression; pinealectomized animals had the lowest incidence of ACs with signs of regression. Ductule hyperplasia, considered as a premalignant lesion, was more frequent in pinealectomized rats than in controls and in animals with enhanced pineal function (BA, BU, and BC). Some nontumoral mammary glands showed dysplastic lesions; these lesions were less frequent in BU rats than in controls. We conclude that suppression of pineal function sensitizes the ductule cells to the initiation of neoplastic processes and hinders the development of regressive changes.

Myeloid bodies associated with lipid droplets in pinealocytes of blind, blind-bulbectomized, blind-underfed or blind cold-exposed rats

The ultrastructure of pinealocytes was studied in rats subjected to manipulations known as enhancers of pineal actions: blindness (B), blindness + olfactory bulbectomy (BObx), blindness + underfeeding (BU), blindness + cold exposure (BC). A large number of myeloid bodies (MBs) were found especially in the light pinealocytes of BObx, BU and BC rats but not in intact controls. These MBs were, in most cases, associated with lipid droplets. The presence of a large number of MBs in rats in which pineal-dependent gonadal impairment has been demonstrated, strongly supports the hypothesis that MBs play a role in pineal photoneuroendocrine activity.

Cold exposure as a potentiating factor of pineal actions in nonhibernating mammals

Twenty-eight-day-old male rats were used in three experiments to study whether cold exposure potentiates pineal actions in nonhibernating mammals. The following questions were considered: (a) Can cold exposure increase the antigonadal effects of light deprivation? (b) Are the effects induced by blindness plus cold exposure pineal dependent? (c) Can cold exposure modify the response of the endocrine-reproductive axis to exogenously administered melatonin? Blind cold-exposed rats showed a significant loss in body weight as well as in weights of pituitary and reproductive tract organs compared with either intact or blind animals kept at 22 degrees C, or intact rats exposed to cold; serum testosterone levels were also lowest in blind cold-exposed rats. These effects were not present in blind cold-exposed animals that were pinealectomized at the beginning of the experiment. When intact animals placed at 22 or 10 degrees C were treated with daily injections of melatonin (50 micrograms) there was a reduction of body weight and weights of the hypophyso-gonadal axis organs. Those effects of melatonin were, however, significantly greater in cold-exposed rats than in rats placed at 22 degrees C. These results suggest that cold exposure should be considered as another state which potentiates the pineal-dependent actions of light deprivation. Cold exposure probably acts by increasing the sensitivity of sites at which pineal melatonin exerts its actions.

Antigonadal actions of olfactory and light deprivation. I. Effects of blindness combined with olfactory bulb deafferentation, transection of vomeronasal nerves, or bulbectomy

Olfactory bulbectomy is known to potentiate the antigonadal effects of light deprivation. However, the physiological interpretation of the effects of bulbar ablation is complex, since it simultaneously implies sequelae like: a) the loss of olfactory sensitivity (anosmia), b) the suppression of the accessory olfactory system (AOS), and c) the suppression of nonsensorial functions of the bulbs. To study the participation of these three mechanisms in the effects of bulbectomy + light deprivation, we compared, in 28-day-old male rats, the effects of olfactory bulb deafferentation (peripheral anosmia) with those induced by either olfactory bulbectomy or blocking the AOS, alone or associated with blindness. As compared to the intact or blinded animals, both blinded deafferented (EA) and blinded bulbectomized (EB) rats showed various reductions in weights of body, testes, accessory sexual glands, and prostates; serum testosterone levels were also depressed. Testes of EA rats showed various degrees of alterations in spermatogenesis. The only difference between EA and EB groups was in the pituitary weight, significantly lower in EA rats.

Antigonadal actions of olfactory and light deprivation. II. Effects of pinealectomy or melatonin injections in olfactory bulb deafferented or bulbectomized male rats

Since olfactory bulb deafferentation (peripheral anosmia) potentiates the antigonadal effects of light deprivation, we studied a) the pineal involvement in this action and b) whether peripheral anosmia might increase the response to melatonin injections. Four-week-old male rats were used in two experimental series. The first included rats in which blindness + peripheral anosmia was associated with either pinealectomy or sham pinealectomy. In the second series, intact, olfactory bulb deafferented and bulbectomized rats received daily injections of either melatonin (50 micrograms) or the vehicle alone. In both experiments animals were killed at 10 weeks of age. The reduction in the weight of accessory sexual glands and prostates, as well as in the serum testosterone levels, induced by blindness + peripheral anosmia was fully prevented by pinealectomy, whereas body and pituitary weight reduction induced by the dual sensory deprivation were only partially prevented. Melatonin produced no effects in intact animals whereas in rats with either peripheral anosmia or bulbectomy it reduced the weight of body, accessory sexual glands, and prostates. Serum testosterone levels were not modified in any case with melatonin treatment.