Multidrug resistance (MDR) represents a bottleneck in the treatment of breast cancer. Although the potential of aldose reductase inhibitors (ARIs) as sensitizers against MDR has been explored in recent decades, the intrinsic mechanism still needs to be elucidated, and promising agents in the clinic need to be developed. In this study, three novel ARIs (5a-c), characterized by bis-pocket binding, were designed and synthesized. Inhibitory activity is positively correlated with antioxidation and benefits from rigid spacers. Only 5a with less activities in inhibition and antioxidation was demonstrated as a stronger sensitizer against doxorubicin (DOX)-resistant MCF-7 cells (MCF-7/ADR) than epalrestat (EPA). Either 5a or EPA may decrease GSH abundance and increase ROS, Fe