Novel Insights into Redox-Based Mechanisms for Auranofin-Induced Rapid Cancer Cell Death

SIMPLE SUMMARY: One of the significant features of cancer cells is a persistent pro-oxidative status. Compared to their normal counterparts, the malignant cells are generally more dependent on antioxidants for cell survival and more vulnerable to further oxidative insults via pharmacological interventions. This is the biological basis of oxidative stress- or redox-based anticancer strategies. Auranofin (AUF) is a promising repositioning anticancer molecule with a multifaceted mode of action that could be cancer cell type- or dose-dependent. Using triple-negative breast cancer cells, we evidenced that thioredoxin reductase inhibition, the best-studied anticancer mechanism of AUF, may not be sufficient to induce efficient cell death. Cytotoxic doses of AUF elicited rapid and global intracellular oxidative stress. Based on the indications from redox proteome data, we showed experimentally that AUF treatment triggered a dose-dependent S-phase arrest and disintegration of the actin cytoskeleton structure. These findings on AUF-induced early effects should provide novel insights into the anticancer mechanisms of this promising molecule. ABSTRACT: Auranofin (Ridaura(®), AUF) is a gold complex originally approved as an antirheumatic agent that has emerged as a potential candidate for multiple repurposed therapies. The best-studied anticancer mechanism of AUF is the inhibition of thioredoxin reductase (TrxR). However, a number of reports indicate a more complex and multifaceted mode of action for AUF that could be cancer cell type- and dose-dependent. In this study, we observed that AUF displayed variable cytotoxicity in five triple-negative breast cancer cell lines. Using representative MDA-MB-231 cells treated with moderate and cytotoxic doses of AUF, we evidenced that an AUF-mediated TrxR inhibition alone may not be sufficient to induce cell death. Cytotoxic doses of AUF elicited rapid and drastic intracellular oxidative stress affecting the mitochondria, cytoplasm and nucleus. A “redoxome” proteomics investigation revealed that a short treatment with a cytotoxic dose AUF altered the redox state of a number of cysteines-containing proteins, pointing out that the cell proliferation/cell division/cell cycle and cell–cell adhesion/cytoskeleton structure were the mostly affected pathways. Experimentally, AUF treatment triggered a dose-dependent S-phase arrest and a rapid disintegration of the actin cytoskeleton structure. Our study shows a new spectrum of AUF-induced early effects and should provide novel insights into the complex redox-based mechanisms of this promising anticancer molecule.