<p>To prevent cell death induced by elevated oxidative stress, cancer cells activate a series of antioxidant defense mechanisms to mitigate cytotoxicity, thereby enhancing the resistance to pro-oxidative therapy. However, the underlying antioxidant mechanisms in cancer cells remain inadequately understood. Through co-immunoprecipitation followed by quantitative mass spectrometry analysis, we for the first time identified that cytoplasmic ALDH1L1 translocates into mitochondria and co-localizes with mitochondrial transcription factor TFAM in cancer cells in a ROS-dependent feedback manner. Mitochondria-translocated ALDH1L1 maintains mitochondrial redox homeostasis by producing NADPH. Moreover, our findings revealed that the ROS-mediated oxidative modification of ALDH1L1 is necessary for its interaction with HSP90β and subsequent translocation into mitochondria via TOM70, where it binds to TFAM to prevent degradation by LONP1. Furthermore, we found that mitochondrial ALDH1L1 antagonized the double-edged role of ROS in cancer cell survival, indicating that disruption of ALDH1L1 expression promoted cancer cell proliferation and autophagy but concurrently diminished cellular capacity to counteract ROS-induced apoptosis. Consistently, ALDH1L1 knockout enhanced the anti-tumor effect of low-dose pro-oxidant Elesclomol, thereby achieving better efficacy and safety of pro-oxidant therapy. Furthermore, our results demonstrated that the combination of Elesclomol with HSP90 inhibitor Ganetespib exhibited synergistic anti-tumor effects. In conclusion, our findings that mitochondria-translocated ALDH1L1 functions as a feedback regulator of redox homeostasis in cancer cells to enhance the resistance to pro-oxidative therapy can provide critical insights into developing effective pro-oxidative therapies against tumors.</p><p></p>