Quercetin-Induced Glutathione Depletion Sensitizes Colorectal Cancer Cells to Oxaliplatin

Quercetin is an antioxidant phytochemical which belongs to the natural flavonoids group. Recently, the compound has been reported to inhibit glutathione reductase responsible for replenishing reduced forms of glutathione and thus leads to glutathione depletion, triggering cell death. In this study, we examined if quercetin sensitizes tumors to oxaliplatin by inhibiting glutathione reductase activity in human colorectal cancer cells, and thereby facilitates apoptotic cell death. A combined treatment with quercetin and oxaliplatin was found to synergistically inhibit glutathione reductase activity, lower intracellular glutathione level, increase reactive oxygen species production, and reduce cell viability, compared to treatment with oxaliplatin alone in human colorectal HCT116 cancer cells. Furthermore, the incorporation of sulforaphane, recognized for its ability to scavenge glutathione, in combination with quercetin and oxaliplatin, substantially suppressed tumor growth in an HCT116 xenograft mouse model. These findings suggest that the depletion of intracellular glutathione by quercetin and sulforaphane could strengthen the anti-cancer efficacy of oxaliplatin.