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 p resent work, vie studied whether the length of the cell cycle of MCF-7 cells is increased by melatonin. In MCF-7 cells partially synchronize d and labelled with [H-3]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 incr eased (p < 0.005) the duration of the cell cycle of human breast cance r cells, support the notion that this hormone exerts part of its antit umor effect through a cell-cycle-specific mechanism by delaying the en try of MCF-7 cells into mitosis.