TrxR Inhibition and Nrf2–FOXO3 Modulation by Repurposed Drugs: A Redox Strategy to Reverse Cancer Multidrug Resistance

A common cause of multidrug-resistant (MDR) cancer is imbalanced redox signaling, which reduces the effectiveness of chemotherapy and promotes regrowth of cancer cells. Amplification of thioredoxin reductase (TrxR) and activation of the Keap1-Nrf2-FOXO3 pathway may contribute to enhanced drug efflux, strengthens antioxidant defenses, and resistance to oxidative stress-induced apoptosis in certain tumors. Redox-based drug repurposing offers a promising strategy to overcome MDR by targeting these shortcomings. Repurposing drugs including metformin, auranofin, brusatol, and natural polyphenols increase reactive oxygen species (ROS) and make MDR cells more sensitive to chemotherapy via modulation and inhibiting Nrf2 or TrxR. Nanotechnology advancements and combination of repurposed drugs with anticancer drugs, ferroptosis inducers may improve tumor selectivity while lowering systemic toxicity. Preclinical experiments show effectiveness by suppressing antioxidant pathways, inhibiting efflux pump function, and delivering drugs in a redox-responsive manner. Next-generation tumor-selective delivery systems, adaptive clinical trial designs, and biomarker-driven patient classification based on TrxR expression or Keap1/Nrf2 mutations are the main areas of focus. Translation into clinical practice could be accelerated by combining specific redox profiling, nanocarrier technologies, and pharmacokinetics. For MDR cancer, redox-targeted drug repurposing is an effective, precision-based strategy for recovering chemosensitivity and enhancing treatment outcomes.