INFLUENCE OF MELATONIN ON INVASIVE AND METASTATIC PROPERTIES OF MCF-7HUMAN BREAST-CANCER CELLS

Melatonin, the principal pineal gland hormone, exerts a direct antipro liferative effect on estrogen-responsive MCF-7 cells in culture. The p urpose of the current study was to investigate the effects of melatoni n on the invasion capacity of MCF-7 cells. In vitro, melatonin at phys iological 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 mu M) of melatonin failed to i nhibit cell invasion. Melatonin was also able to block 17 beta-estradi ol-induced invasion (P < 0.001), Pretreatment of MCF-7 cells with 1 nM melatonin increased the response of tumoral cells to the anti-invasiv e effects of this indolamine. To explore possible mechanisms by which melatonin reduces invasiveness, we measured the attachment of MCF-7 ce lls to a basement membrane, the chemotactic response of the cells, and their type IV collagenolytic activity. The presence of melatonin (1 n M) in the culture medium significantly reduced the ability of MCF-7 ce lls to attach to the basement membrane; this effect was enhanced by pr etreating the cells with the same indolamine (P < 0.001). Melatonin al so counteracts the stimulatory effects of 17 beta-estradiol on cell ad hesion (P < 0.001). The chemotactic response of MCF-7 cells also decre ased in the presence of 1 nM melatonin, and this melatonin-induced red uction of cell migration was more effective on cells that were previou sly incubated for 5 days with melatonin than it was on nonpretreated c ells (P < 0.001). The simultaneous addition of 17 beta-estradiol and m elatonin resulted in a significantly lower chemotactic response than t hat of 17 beta-estradiol-reated cells (P < 0.001). However, type IV co llagenolytic activity was not influenced by melatonin. Our results dem onstrate that melatonin reduces the invasiveness of MCF-7 cells, causi ng a decrease in cell attachment and cell motility, probably by intera cting with the estrogen-mediated mechanisms of MCF-7 cell invasiveness . In addition, we also studied the influence of melatonin on the expre ssion of two cell surface adhesion molecules (E-cadherin and beta(1) i ntegrin) and an intermediate filament protein (vimentin), the expressi on 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 an d beta(1) integrin as well as the number of E-cadherin and beta(1) int egrin immunoreactive cells (P < 0.01). Neither control MCF-7 cells nor those treated with melatonin stained for vimentin. Preliminary in viv o experiments carried out on ovariectomized athymic nude mice implante d with 17 beta-estradiol pellets and inoculated with 5 x 10(6) MCF-7 c ells in the inguinal mammary fat pad suggest that melatonin could decr ease the tumorigenicity of these tumor cells, However, these results n eed further confirmation. Taken together, our results suggest that mel atonin shifts MCF-7 human breast cancer cells to a lower invasive stat us by increasing the beta(1) integrin subunit and E-cadherin expressio n 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.