Characterized mechanism of α-mangostin-induced cell death: Caspase-independent apoptosis with release of endonuclease-G from mitochondria and increased miR-143 expression in human colorectal cancer DLD-1 cells

α-Mangostin, a xanthone from the pericarps of mangosteen (Garcinia mangostana Linn.), was evaluated for in vitro cytotoxicity against human colon cancer DLD-1 cells. The number of viable cells was consistently decreased by the treatment with α-mangostin at more than 20 μM. The cytotoxic effect of 20 μM α-mangostin was found to be mainly due to apoptosis, as indicated by morphological findings. Western blotting, the results of an apoptosis inhibition assay using caspase inhibitors, and the examination of caspase activity did not demonstrate the activation of any of the caspases tested. However, endonuclease-G released from mitochondria with the decreased mitochondrial membrane potential was shown. The levels of phospho-Erk1/2 were increased in the early phase until 1 h after the start of treatment and thereafter decreased, and increased again in the late phase. On the other hand, the level of phospho-Akt was sharply reduced with the process of apoptosis after 6 h of treatment. Interestingly, the level of microRNA-143, which negatively regulates Erk5 at translation, gradually increased until 24 h following the start of treatment. We also examined the synergistic growth suppression in DLD-1 cells by the combined treatment of the cells with α-mangostin and 5-FU which is one of the most effective chemotherapeutic agents for colorectal adenocarcinoma. The co-treatment with α-mangostin and 5-FU, both at 2.5 μM, augmented growth inhibition compared with the treatment with 5 μM of α-mangostin or 5 μM 5-FU alone. These findings indicate unique mechanisms of α-mangostin-induced apoptosis and its action as an effective chemosensitizer.