Cotreatment with sorafenib and oleanolic acid induces reactive oxygen species-dependent and mitochondrial-mediated apoptotic cell death in hepatocellular carcinoma cells.

Hepatocellular carcinoma (HCC) is the most common liver malignancy, and the lack of effective chemotherapies underlines the need for novel therapeutic approaches for this disease. Recently, we discovered a novel synergistic induction of cell death by combining sorafenib, the only routinely used palliative chemotherapeutic agent, and the triterpenoid oleanolic acid (OA). However, the underlying mechanisms of action have remained obscure. Here, we report that sorafenib and OA acted in concert to trigger mitochondria-mediated apoptotic cell death, which is dependent on reactive oxygen species (ROS). Sorafenib/OA cotreatment significantly increased ROS production, which was prevented by the ROS scavengers α-tocopherol and MnTBAP. Importantly, rescue experiments showed that ROS were required for sorafenib/OA-induced apoptosis as ROS scavengers protected HCC cells against cell death. In addition, sorafenib and OA cotreatment cooperated to decrease myeloid cell leukaemia-1 expression and to activate Bak, two events that were prevented by ROS scavengers. Bak activation was accompanied by the loss of mitochondrial membrane potential, followed by PARP cleavage, DNA fragmentation and, finally, apoptotic cell death in HCC cells. By providing new insights into the molecular regulation of sorafenib/OA-mediated and ROS-dependent cell death, our study contributes toward the development of novel treatment strategies to overcome sorafenib resistance in HCC.

Identification of a novel oxidative stress induced cell death by Sorafenib and oleanolic acid in human hepatocellular carcinoma cells.

The lack of effective chemotherapies in hepatocellular carcinoma (HCC) is still an unsolved problem and underlines the need for new strategies in liver cancer treatment. In this study, we present a novel approach to improve the efficacy of Sorafenib, today's only routinely used chemotherapeutic drug for HCC, in combination with triterpenoid oleanolic acid (OA). Our data show that cotreatment with subtoxic concentrations of Sorafenib and OA leads to highly synergistic induction of cell death. Importantly, Sorafenib/OA cotreatment triggers cell damage in a sustained manner and suppresses long-term clonogenic survival. Sorafenib/OA cotreatment induces DNA fragmentation and caspase-3/7 cleavage and the addition of the pan-caspase inhibitor zVAD.fmk shows the requirement of caspase activation for Sorafenib/OA-triggered cell death. Furthermore, Sorafenib/OA co-treatment stimulates a significant increase in reactive oxygen species (ROS) levels. Most importantly, the accumulation of intracellular ROS is required for cell death induction, since the addition of ROS scavengers (i.e. α-tocopherol, MnTBAP) that prevent the increase of intracellular ROS levels completely rescues cells from Sorafenib/OA-triggered cell death. In conclusion, OA represents a novel approach to increase the sensitivity of HCC cells to Sorafenib via oxidative stress.