In vitro effects of melatonin on cell proliferation in a colon adenocarcinoma line

The effect of melatonin on inhibition of cell growth was studied in CT-26, a murine colon carcinoma-derived cell line. Cells growing in exponential phase were exposed to low (10(-7)-10(-10) M) and high doses (1, 2 and 3 x 10(-3) M) of melatonin during 24 h. Synthesis of DNA was measured by 5-bromo-2'-deoxyuridine incorporation. There was no effect at low doses, but a statistically significant correlation was found between the decrease in DNA synthesis and the dose of melatonin used (r = -0.52, P < 0.001). This implied the following percentages of inhibition: 1 mM, 22%; 2 mM, 25%; 3 mM, 47%. Potential cell membrane damage by high doses of melatonin was investigated by lactate dehydrogenase measurement and no significant levels were observed. Analysis with a single saturation technique showed no detectable oestradiol receptors in this cell type; therefore, we can assume that the effects occurring with the addition of melatonin were not mediated by modulation of this hormone on oestrogen receptors. The decreases in cell growth were attributed to a moderate, but significant antiproliferative action of melatonin on this non-hormone-dependent cell line.