Biomarkers of tumour redox status in response to modulations of glutathione and thioredoxin antioxidant pathways

The ability of certain cancer cells to maintain a highly reduced intracellular environment is correlated with aggressiveness and drug resistance. Since the glutathione (GSH) and thioredoxin (TRX) systems cooperate to a tight regulation of ROS in cell physiology, and to a stimulation of tumour initiation and progression, modulation of the GSH and TRX pathways are emerging as new potential targets in cancer. In vivo methods to assess changes in tumour redox status are critically needed to assess the relevance of redox-targeted agents. The current study assesses in vitro and in vivo biomarkers of tumour redox status in response to treatments targeting the GSH and TRX pathways, by comparing cytosolic and mitochondrial redox nitroxide electron paramagnetic resonance (EPR) probes, and cross-validation with redox dynamic fluorescent measurement. For that purpose, the effect of the GSH modulator buthionine sulfoximine (BSO) and of the TRX reductase inhibitor auranofin were measured in vitro using both cytosolic and mitochondrial EPR and roGFP probes in breast and cervical cancer cells. In vivo, mice bearing breast or cervical cancer xenografts were treated with the GSH or TRX modulators and monitored using the mito-TEMPO spin probe. Our data highlight the importance of using mitochondria-targeted spin probes to assess changes in tumour redox status induced by redox modulators. Further in vivo validation of the mito-tempo spin probe with alternative in vivo methods should be considered, yet the spin probe used in vivo in xenografts demonstrated sensitivity to the redox status modulators.