ROS/JNK/c-Jun axis is involved in oridonin-induced caspase-dependent apoptosis in human colorectal cancer cells

Colorectal cancer (CRC) is one of the most common malignant neoplasms with high mortality worldwide. Oridonin, a diterpenoid isolated from the Chinese medicinal herb Rabdosia rubescens, has been proved to have anticancer effect on various types of cancer cells. However, the detailed mechanisms of oridonin in CRC cells remain unclear and if oridonin can overcome 5-FU resistance have not been investigated yet. In this study, we investigated the anticancer effect of oridonin in both 5-FU sensitive and resistant CRC cells and illuminated the underlying mechanisms. We showed that oridonin induced proliferation inhibition and caspase-dependent apoptosis in both 5-FU sensitive and resistant CRC cells. Oridonin induced reactive oxygen species (ROS) accumulation in both 5-FU sensitive and resistant CRC cells, which resulted in cell apoptosis as oridonin-induced apoptosis was almost abolished when cells were co-treated with the ROS scavenger N-acetyl-L-cysteine (NAC). Moreover, we found that oridonin induced CRC cell apoptosis via the c-Jun N-terminal kinase (JNK)/c-Jun pathway as oridonin activated JNK/c-Jun pathway and the JNK inhibitor SP600125 restored oridonin-induced apoptosis in CRC cells. Interestingly, when CRC cells were co-treated with NAC, the activation of JNK/c-Jun pathway induced by oridonin was nearly reversed, indicating that oridonin induced JNK/c-Jun pathway activation through the accumulation of ROS. Taken together, these data reveal that oridonin induces apoptosis through the ROS/JNK/c-Jun axis in both 5-FU sensitive and resistant CRC cells, suggesting that oridonin could be a potential agent for CRC treatment.