Background: 

The pineal hormone melatonin (MEL) has diverse physiological functions. Clinical trials indicated that co-application of cisplatin (CDDP) and melatonin improved the 1-year survival rate of cancer patients including breast cancer patients. Several labs have also shown that melatonin has an anti-proliferative effect on MCF-7 cells. We investigated synergy, if any, between melatonin and cisplatin on MCF-7 cell growth.

Method: 

Cell viability was tested using MTT and trypan blue exclusion assays. Early-/ late-apoptosis and necrosis were assessed using flow cytometry (total cytotoxicity kit). Mouse anti-bax and anti-bcl-2 (Santa Cruz Biotechnologies) were used for immunofluorescence and immunoblotting.

Results: 

1) Cisplatin inhibits MCF-7 cell growth concentration dependently (10–100mM) in 24 hrs with a clear rise in late apoptosis. 2) At 1nM, melatonin does not change growth significantly. 3) Co-application of MEL with CDDP significantly (p<=0.05) reverses 100mM CDDP induced growth inhibition over 24h (0.1- 10nM; 21.4±1.8%), while 1nM melatonin reduced total apoptosis significantly. 4) Treatment with melatonin causes Bcl-2 to form discrete puncta in the cytoplasm compared to untreated control. 5) 24h treatment with melatonin (1nM) leads to a significant down regulation of Bax (31±2.3%: p < 0.05).

Conclusion: 

Melatonin at physiological concentration "protects" against cisplatin induced apoptosis. Two possible mechanisms could be discussed. While the punctate appearance of Bcl-2 under melatonin application suggests mitochondrial targeting of Bcl-2, it is also possible that Bax is down-regulated.