Anticancer effects of 3,3′-diindolylmethane are associated with G1 arrest and mitochondria-dependent apoptosis in human nasopharyngeal carcinoma cells

The antitumor effects of 3,3'-diindolylmethane (DIM) are exhibited in a number of human cancer cells. However, there have been few studies performed concerning the effect of DIM on nasopharyngeal cancer (NPC) cells. In the present study, we examined the in vitro antitumor activity of DIM on the poorly differentiated NPC cell line CNE-2. The potential molecular mechanisms of the activity were also explored. CNE-2 cells were treated with varying concentrations of DIM for different times. Cell proliferation and apoptosis were detected and the molecular mechanisms involved in these effects were characterized. The results demonstrated that DIM at concentrations of 15-100 μM caused dose- and time-dependent inhibition of CNE-2 cell proliferation. Flow cytometry analysis revealed a high sub-G1 cell peak following treatment with DIM, and the rate of apoptosis increased. DIM may elevate the levels of cleaved Bid and Bax and enhance mitochondrial membrane depolarization, allowing the efflux of cytochrome c, Smac and Omi into the cytosol. The levels of caspases-3, -8 and -9 and cleaved poly (ADP-ribose) polymerase (PARP) were upregulated following DIM treatment in a dose-dependent manner. DIM also inhibits the phosphorylation of IκB-α, and showed dose-dependent inhibition of Bcl-2, XIAP and NF-κB in CNE-2 cells in vitro. These results indicate that DIM inhibits cell proliferation by inducing cell cycle arrest at G0/G1 phase and induces the apoptosis of CNE-2 cells by regulating multiple molecules in a mitochondria-dependent pathway. DIM may be a preventive and therapeutic agent against NPC.