Auranofin induces lethality driven by reactive oxygen species in high-grade serous ovarian cancer cells

Abstract

High-grade serous ovarian cancer (HGSOC) accounts for 70% of ovarian cancer cases in the clinical setting; the survival rate for this disease remains remarkably low due to the lack of long-term consolidation therapies following the standard platinum-based chemotherapy, which is not long lasting as the disease recurs as platinum resistant. The purpose of this study was to explore a novel treatment against HGSOC using the gold complex auranofin (AF). AF primarily functions as a pro-oxidant agent through the inhibition of thioredoxin reductase (TrxR), an antioxidant enzyme that is overexpressed in ovarian cancer. We investigated the effect of AF on TrxR activity and various mechanisms of cytotoxicity using HGSOC cells that are clinically sensitive or resistant to platinum. In addition, we studied the interaction between AF and another pro-oxidant agent, L-buthionine sulfoximine (L-BSO), an anti-glutathione (GSH) compound. We demonstrate that AF potently inhibits TrxR activity and reduces the vitality and viability of HGSOC cells regardless of their sensitivities to platinum. We show that AF induces accumulation of reactive oxygen species (ROS), triggers the depolarization of the mitochondrial membrane, and kills HGSOC cells by inducing apoptosis. Yet, AF-induced cell death is abrogated by the ROS-scavenger N-acetyl cysteine (NAC). In addition, the lethality of AF is associated with the activation of caspases-3/7 and the generation of DNA damage, effects that are also prevented by the presence of NAC. Finally, when AF and L-BSO are combined, we observed a synergistic lethality against HGSOC cells, which is mediated by a further increase in ROS together with a decrease in the levels of the antioxidant GSH. In summary, our results support the concept that AF can be used alone or in combination with L-BSO to kill HGSOC cells regardless of their platinum sensitivities suggesting that depletion of antioxidants is an efficient route for treating this disease.