3,3′-Diindolylmethane suppresses growth of human esophageal squamous cancer cells by G1 cell cycle arrest

3,3′-Diindolylmethane (DIM), an active metabolite of indole-3-carbinol, is thought to have antitumor effects in experimental animals and induce apoptosis in various cancer cells. However, the biological functions of DIM in human esophageal cancer cells are unknown. Thus, the purpose of this study was to investigate the cytotoxic effects of DIM in human esophageal squamous cell carcinoma (ESCC) cells to elucidate the molecular mechanism of cell death. Three human ESCC cell lines (TT, TE-8 and TE-12) were used to test the response to DIM. MTT, cell cycle and western blot analyses were conducted. DIM significantly inhibited the proliferation of ESCC cells in a dose- and time-dependent manner. The percentage of G1 phase cells increased 48 h after being treated with DIM. DIM also reduced cyclin D1, cyclin E2, cyclin-dependent kinase (CDK) 4 and CDK 6 activities, and increased p15 and p27 levels. Additionally, DIM diminished pro-caspase-9 protein expression levels and induced increased cleaved poly (ADP-ribose) polymerase levels. These results indicate that DIM leads to G1 phase cell cycle arrest and induces apoptosis by activating caspase-9 in ESCC cells.