3,3′‐Diindolylmethane (DIM) induces cell cycle arrest in HT‐29 human colon cancer cells

Abstract

3,3′-Diindolylmethane (DIM), an indole derivative produced on consumption of broccoli and other cruciferous vegetables, has been shown to have multiple anti-cancer effects in both in vivo and in vitro models. To examine the effects of DIM on of HT-29 human colon cancer cell growth, cells were cultured with various concentrations (0–30 μmol/L) of DIM. Treatment of cells with increasing concentration of DIM led to a dose-dependent decrease in viable cell numbers in HT-29 cells. The decrease in cell growth was due to an increase in apoptosis and a decrease in DNA synthesis. Results from DNA flow cytometric analysis revealed that DIM induced G1 and G2/M phase arrests at 12 h and G2/M phase arrest at 24 h of culture. Western blot analyses of total cell lysates revealed that DIM decreased phosphorylated retinoblastoma proteins (Rb) and E2F-1, and increased hypophosphorylated Rb levels. DIM decreased cyclin A and D1 and increased cyclin-dependent kinase (CDK) 4 levels in a time-related manner. DIM also increased the protein levels of the CDK inhibitors p21 and p27. In addition, DIM decreased the levels of cell division cycle 2 and cyclin B1. These results suggest that DIM inhibits G1 or G2/M phase cell cycle progression by inhibiting CDK activities.