Triptolide inhibits transcription factor NF-kappaB and induces apoptosis of multiple myeloma cells

Triptolide has been reported to be effective in the treatment of auto-immune diseases. This study investigates the cytotoxic function of triptolide on multiple myeloma (MM) cells. We found that triptolide inhibited the proliferation of both RPMI8226 and U266 cells in a dose-dependent manner (10-80 ng/mL). Triptolide induced apoptosis in MM cells through activation of the cystein protease caspase 8, 9 and 3, and subsequent cleavage of the DNA repair enzyme poly (ADP-ribose) polymerase. Apoptosis was confirmed with cell-cycle analysis and annexin V staining. Moreover, triptolide down-regulated nuclear factor (NF)-kappaB activity in MM cell lines. In addition, triptolide also induced chemosensitivity to doxorubicin and suppressed cell proliferation of fresh MM cells. Therefore, triptolide appears to be a potent inducer of apoptosis in myeloma cells, and might have some benefit in the treatment of myeloma patients.