Effects of melatonin combined with Cis-platinum or methotrexate on the proliferation of osteosarcoma cell line SaOS-2.

Objective: To evaluate the effects of melatonin (Mel) combined with cis-platinum (DDP) or methotrexate (MTX) on the proliferation of osteosarcoma cell line SaOS-2, and to explore whether Mel combined with DDP or MTX could play a synergistic antitumor effect.

Methods: SaOS-2 was treated with Mel alone or Mel combined with DDP or MTX. Cell counting kit-8 assay was used to measure the cell activities. Combination index(CI) value was used to evaluate the combined effects: CI<1 indicating synergetic effect, CI=1 additive, and CI>1 antagonistic.Flow cytometry was used to analyze cell cycle distribution and cell apoptosis.

Results: After treated with Mel (0.5,1,2,4,5 mmol/L), DDP (6.67, 16.67, 33.33, 66.66 μmol/L) or MTX(0.1, 0.5, 1, 2, 4 mmol/L)alone,SaOS-2 cell activities decreased in a dose-dependent manner (all P<0.05). The activities of SaOS-2 cell treated with both Mel (1 mmol/L) and DDP or MTX were significantly lower than that of DDP or MTX alone (all P<0.05).CI values of cells exposed to 1 mmol/L Mel plus 6.67, 16.67, 33.33, and 66.66 μmol/L DDP were 1.18, 1.21, 1.09, and 0.84, respectively,and CI values of cells exposed to 1 mmol/L Mel plus 0.1, 0.5, 1, 2, and 4 mmol/L MTX were 0.88, 0.88 ,0.83, 0.78, and 0.81, respectively. The G1-stage cells were increased and the S-stage cells were reduced when the cells were treated with Mel (1 mmol/L) alone or combined with MTX (0.5 mmol/L) (P<0.05). The S-stage cells were increased when the cells treated with MTX (0.5 mmol/L) (P<0.05). The apoptotic cells were increased when they treated with Mel (1 mmol/L) alone or combined with DDP (16.67 μmol/L) or MTX (0.5 mmol/L) (P<0.05). When the cells were treated with Mel combined with DDP or MTX, the apoptotic cells were more than that of DDP or Mel alone(P<0.05).

Conclusions: Mel can inhibit SaOS-2 cells activity,block the cell cycle at G1-stage,and induce apoptosis. Mel has an antagonistic effect with lower concentration of DDP but a synergistic effect with MTX or higher concentration of DDP.