Sub-Lethal Hyperthermia Enhances Anticancer Activity of Doxorubicin in Chronically Hypoxic HepG2 Cells Through ROS-Dependent Mechanism

Abstract

Background and aims: Thermal ablation in combination with transarterial chemoembolization (TACE) has been reported to exert a more powerful anti-tumor effect than thermal ablation alone in hepatocellular carcinoma (HCC) patients. However, the underlying mechanisms remain unclear. The purpose of this study was to evaluate whether sub-lethal hyperthermia encountered in the peri-ablation zone during thermal ablation enhances the anticancer activity of doxorubicin in chronically hypoxic (encountered in the tumor area after TACE) liver cancer cells and to explore the underlying mechanisms. Methods HepG2 cells pre-cultured under chronic hypoxic conditions (1% oxygen) were treated in a 42 °C water bath for 15 min or 30 min, followed by incubation with doxorubicin. Assays were then performed to determine intracellular uptake of doxorubicin, cell viability, apoptosis, cell cycle, mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and total antioxidant capacity. Results The results confirmed that sub-lethal hyperthermia enhanced intracellular uptake of doxorubicin into hypoxic HepG2 cells. Hyperthermia combined with doxorubicin led to a greater inhibition of cell viability and increased apoptosis in hypoxic HepG2 cells compared to hyperthermia or doxorubicin alone. In addition, the combination induced apoptosis by increasing ROS and causing disruption of mitochondrial membrane potential. Pretreatment with the ROS scavenger N-acetyl cysteine (NAC) significantly inhibited the apoptotic response suggesting that cell death is ROS-dependent. Conclusions These findings suggest that sub-lethal hyperthermia enhanced the anti-cancer activity of doxorubicin in hypoxic HepG2 cells through ROS-dependent mechanism.