The pineal hormone, melatonin, has been reported to have an inhibitory effect on the cell growth of human breast cancer. We have now assessed the interaction of melatonin with 5-fluorouracil (5-FU) on estrogen-sensitive MCF7 and estrogen-insensitive HBC4 cell lines. Melatonin inhibited MCF7 cell growth dose-dependently, reaching a maximum inhibition of growth of 39% that of control at a concentration of 0.3 nM (this is about equivalent to the physiological concentration of melatonin secreted at 0200 h in humans). 5-FU also demonstrated an inhibitory effect on MCF7 cell growth and a maximal inhibition of growth by 24% was acquired at a concentration of 500 ng/ml. By contrast, the inhibitory effect of melatonin was reduced by the co-administration of 5-FU, independently of 5-FU concentration. Melatonin and/or 5-FU exhibited no effect on HBC4 cells. This preliminary study indicates that 5-FU should be handled with care for treatment of estrogen sensitive-breast cancer.
5-Fluorouracil attenuates an oncostatic effect of melatonin on estrogen-sensitive human breast cancer cells (MCF7)