Carolina Alonso-González

Melatonin inhibits the growth of DMBA-induced mammary tumors by decreasing the local biosynthesis of estrogens through the modulation of aromatase activity

Melatonin inhibits the growth of breast cancer cells by interacting with estrogen‐responsive pathways, thus behaving as an antiestrogenic hormone. Recently, we described that melatonin reduces aromatase expression and activity in MCF‐7 human breast cancer cells, thus modulating the local estrogen biosynthesis. To investigate the in vivo aromatase‐inhibitory properties of melatonin in our current study, this indoleamine was administered to rats bearing DMBA‐induced mammary tumors, ovariectomized (ovx) and treated with testosterone. In these castrated animals, the growth of the estrogen‐sensitive mammary tumors depends on the local aromatization of testosterone to estrogens. Ovariectomy significantly reduced the size of the tumors while the administration of testosterone to ovx animals stimulated tumor growth, an effect that was suppressed by administration of melatonin or the aromatase inhibitor aminoglutethimide. Uterine weight of ovx rats, which depends on the local synthesis of estrogens, was increased by testosterone, except in those animals that were also treated with melatonin or aminoglutethimide. The growth‐stimulatory effects of testosterone on the uterus and tumors depend exclusively on locally formed estrogens, since no changes in serum estradiol were appreciated in testosterone‐treated rats. Tumors from animals treated with melatonin had lower microsomal aromatase activity than tumors of animals from other groups, and incubation with melatonin decreased the aromatase activity of microsomal fractions of tumors. Animals treated with melatonin had the same survival probability as the castrated animals and significantly higher survival probability than the uncastrated. We conclude that melatonin could exert its antitumoral effects on hormone‐dependent mammary tumors by inhibiting the aromatase activity of the tumoral tissue.

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

Abstract:  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 ERα. 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 ERα transactivation. We show that melatonin prevents the Cd‐induced growth of synchronized MCF7 breast cancer cells. In transient transfection experiments, we prove that both ERα‐ and ERβ‐mediated transcription are stimulated by Cd. Melatonin is a specific inhibitor of Cd‐induced ERα‐mediated transcription in both estrogen response elements (ERE)‐ and AP1‐containing promoters, whereas ERβ‐mediated transcription is not inhibited by the pineal indole. Moreover, the mutant ERα‐(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 ERα 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 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.

Melatonin as a Selective Estrogen Enzyme Modulator

Melatonin exerts oncostatic effects on different kinds of tumors, especially on hormone-dependent breast cancer. The general conclusion is that melatonin, in vivo, reduces the incidence and growth of chemically-induced mammary tumors in rodents, and, in vitro, inhibits the proliferation and invasiveness of human breast cancer cells. Both studies support the hypothesis that melatonin inhibits the growth of breast cancer by interacting with estrogen-signaling pathways through three different mechanisms: (a) the indirect neuroendocrine mechanism which includes the melatonin down-regulation of the hypothalamic-pituitary-reproductive axis and the consequent reduction of circulating levels of gonadal estrogens, (b) direct melatonin actions at tumor cell level by interacting with the activation of the estrogen receptor, thus behaving as a selective estrogen receptor modulator (SERM), and (c) the regulation of the enzymes involved in the biosynthesis of estrogens in peripheral tissues, thus behaving as a selective estrogen enzyme modulator (SEEM). As melatonin reduces the activity and expression of aromatase, sulfatase and 17beta-hydroxysteroid dehydrogenase and increases the activity and expression of estrogen sulfotransferase, it may protect mammary tissue from excessive estrogenic effects. Thus, a single molecule has both SERM and SEEM properties, one of the main objectives desired for the breast antitumoral drugs. Since the inhibition of enzymes involved in the biosynthesis of estrogens is currently one of the first therapeutic strategies used against the growth of breast cancer, melatonin modulation of different enzymes involved in the synthesis of steroid hormones makes, collectively, this indolamine an interesting anticancer drug in the prevention and treatment of estrogen-dependent mammary tumors.

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.

Regulation of vascular endothelial growth factor by melatonin in human breast cancer cells

Melatonin exerts oncostatic effects on breast cancer by interfering with the estrogen‐signaling pathways. Melatonin reduces estrogen biosynthesis in human breast cancer cells, surrounding fibroblasts and peritumoral endothelial cells by regulating cytokines that influence tumor microenvironment. This hormone also exerts antiangiogenic activity in tumoral tissue. In this work, our objective was to study the role of melatonin on the regulation of the vascular endothelial growth factor (VEGF) in breast cancer cells. To accomplish this, we cocultured human breast cancer cells (MCF‐7) with human umbilical vein endothelial cells (HUVECs). VEGF added to the cultures stimulated the proliferation of HUVECs and melatonin (1 mm) counteracted this effect. Melatonin reduced VEGF production and VEGF mRNA expression in MCF‐7 cells. MCF‐7 cells cocultured with HUVECs stimulated the endothelial cells proliferation and increased VEGF levels in the culture media. Melatonin counteracted both stimulatory effects on HUVECs proliferation and on VEGF protein levels in the coculture media. Conditioned media from MCF‐7 cells increased HUVECs proliferation, and this effect was significantly counteracted by anti‐VEGF and 1 mm melatonin. All these findings suggest that melatonin may play a role in the paracrine interactions between malignant epithelial cells and proximal endothelial cells through a downregulatory action on VEGF expression in human breast cancer cells, which decrease the levels of VEGF around endothelial cells. Lower levels of VEGF could be important in reducing the number of estrogen‐producing cells proximal to malignant cells as well as decreasing tumoral angiogenesis.

Melatonin uses in oncology: breast cancer prevention and reduction of the side effects of chemotherapy and radiation

Introduction: The possible oncostatic properties of melatonin on different types of neoplasias have been studied especially in hormone-dependent adenocarcinomas. Despite the promising results of these experimental investigations, the use of melatonin in breast cancer treatment in humans is still uncommon. Areas covered: This article reviews the usefulness of this indoleamine for specific aspects of breast cancer management, particularly in reference to melatonins antiestrogenic and antioxidant properties: i) treatments oriented to breast cancer prevention, especially when the risk factors are obesity, steroid hormone treatment or chronodisruption by exposure to light at night (LAN); ii) treatment of the side effects associated with chemo- or radiotherapy. Expert opinion: The clinical utility of melatonin depends on the appropriate identification of its actions. Because of its SERM (selective estrogen receptor modulators) and SEEM (selective estrogen enzyme modulators) properties, and its virtual absence of contraindications, melatonin could be an excellent adjuvant with the drugs currently used for breast cancer prevention (antiestrogens and antiaromatases). The antioxidant actions also make melatonin a suitable treatment to reduce oxidative stress associated with chemotherapy, especially with anthracyclines, and radiotherapy

Melatonin down-regulates hTERT expression induced by either natural estrogens (17β-estradiol) or metalloestrogens (cadmium) in MCF-7 human breast cancer cells

The goal was to evaluate whether melatonin (Mel) down-regulates hTERT expression induced by 17beta-estradiol (E(2)) or cadmium (Cd) in breast cancer cells. We found that: (a) Mel inhibits E(2) or Cd-induced hTERT transcription in hTERT-Luc transfected MCF-7 cells, (b) Mel significantly reduces E(2)- and Cd-mediated hTERT transactivation triggered by ERalpha in transfected HeLa cells, (c) Mel inhibits hTERT expression induced by E(2) or Cd in MCF-7 cells. Melatonin inhibition of telomerase activity supports a possible role in treatment of estrogen-dependent tumors or carcinogenesis by environmental or occupational exposure to xenoestrogens.

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

Abstract:  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 17β‐hydroxysteroid dehydrogenase type 1 (17β‐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 17β‐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 interferes in the desmoplastic reaction in breast cancer by regulating cytokine production

Abstract:  Melatonin exerts oncostatic effects on breast cancer by interfering with the estrogen signaling pathways. Melatonin inhibits aromatase enzyme in breast cancer cells and fibroblasts. In addition, melatonin stimulates the adipogenic differentiation of fibroblasts. Our objective was to study whether melatonin interferes in the desmoplastic reaction by regulating some factors secreted by malignant cells, tumor necrosis factor (TNF)‐α, interleukin (IL)‐11, and interleukin (IL)‐6. To accomplish this, we co‐cultured 3T3‐L1 cells with MCF‐7 cells. The addition of breast cancer cells to the co‐cultures inhibited the differentiation of 3T3‐L1 preadipocytes to mature adipocytes, by reducing the intracytoplasmic triglyceride accumulation, an indicator of adipogenic differentiation, and also stimulated their aromatase activity. Melatonin counteracted the inhibitory effect on adipocyte differentiation and aromatase activity induced by MCF‐7 cells in 3T3‐L1 cells. The levels of cytokines in the co‐culture media were 10 times those found in culture of 3T3‐L1 cells alone. Melatonin decreased the concentrations of cytokines in the media and counteracted the stimulatory effect induced by MCF‐7 cells on the cytokine levels. One millimolar melatonin induced a reduction in TNF‐α, IL‐6, and IL‐11 mRNA expression in MCF‐7 and 3T3‐L1 cells. The findings suggest that melatonin may play a role in the desmoplastic reaction in breast cancer through a downregulatory action on the expression of antiadipogenic cytokines, which decrease the levels of these cytokines. Lower levels of cytokines stimulate the differentiation of fibroblasts and decrease both aromatase activity and expression, thereby reducing the number of estrogen‐producing cells proximal to malignant cells.