Melatonin inhibits the proliferation of human osteosarcoma cell line MG-63

• Melatonin supplementation reduces the human osteosarcoma cell proliferation in a dose-dependent and time-dependent manner.
• Melatonin induced the G1 and G2/M phase arrest in the human osteosarcoma cells.
• Melatonin's inhibitory effect involves the downregulation of cyclin D1, CDK4, cyclin B1 and CDK1.

It seems established that the onset of osteosarcoma and the reduction in melatonin production run in parallel; this suggests that the decline in the cancer-inhibiting agent, melatonin, may contribute to the occurrence of osteosarcoma and that melatonin supplementation may have promise for preventing the development and progression of this condition. There is, however, no direct evidence regarding an antiproliferative effect of melatonin in osteosarcoma cells. In the current study, we examined whether melatonin inhibits the proliferation of human osteosarcoma cell line MG-63. MTT staining showed that at 4 mM–10 mM concentrations, melatonin significantly reduced the MG-63 cell proliferation in a dose-dependent and time-dependent manner. Flow cytometry documented that 4 mM melatonin significantly increased the fraction of cells in the G0/G1 phase of the cell cycle, while simultaneously reducing the proportion in the S and G2/M phases. Western blot and real-time PCR analyses further confirmed that melatonin's inhibitory effect was possibly because of downregulation of cyclin D1 and CDK4, related to the G1 phase, and of cyclin B1 and CDK1, related to the G2/M phase. There was no downregulation of cyclin E, CDK2, and cyclin A, which are related to G1/S transition and S phase. These findings provide evidence that melatonin may significantly inhibit human osteosarcoma cell proliferation in a dose-dependent and time-dependent manner and this inhibition involves the downregulation of cyclin D1, CDK4, cyclin B1 and CDK1.