The effects of melatonin on the proliferative activity of retinoblastoma cell line HXO-RB44

Objective To investigate inhibited effects of melatonin （MLT） on proliferative activity of retinoblastoma cell line HXO-RB44 and its related mechanism. Methods HXO-RB44 cells were treated by MLT of different concentration （10^-10, 10^-9 , 10^-8, 10^-7 mmol/L. Cell counting and tetrazolium dye-reduction assay （MTT） were used to determine the effect of MLT on the survival and proliferation of HXO-RB44 cells. Apoptotic nuclei were further analyzed by Hoechst-PI fluorescence staining. Flow cytometry was used to measure the fluorescent intensity of ROS, cell cycle distribution and apoptosis. Results 10^-6 mmol/L （or exceed） of MLT could inhibit the proliferation of HXO-RB44 cells in vitro while 10^-7 mmol/L （or below） of MLT couldn＇t. With the increase of MLT concentration from 10-^10 mmol/L to 10^-7 mmol/L, HXO-RB44 cells gradually increased the expression of ROS. Hoechst staining showed that 4, 8, 12 and 24 hours after the incubation with MLT, the nuclear pyknosis and nuclear fragmentation increased in HXO-RB44 cells. The extent of apoptosis was proportional to the concentrations of MLT. Flow cytometry revealed that with the increasing of MLT concentration, G0/G1 and G2/M phase cells increased, S phase cells decreased. The apoptotic rate was also increased. Conclusion 10.6 M of MLT could inhibit the proliferation of HXO-RB44 cells. This effect may relate to the increased ROS expression, cell cycle arrest at Go/G1 phase and apoptosis of HXO-RB44 cells. Key words: Retinoblastoma/therapy;  Cell cycle/drug effects;  Apoptosis;  Melatonin