T1/T2 Proportional Magnetic Resonance Nanoprobe Monitoring Tumor Autophagy during Chemotherapy.

Autophagy leads to cellular tolerance of the therapeutic pressure of chemotherapeutic drugs, resulting in treatment resistance. Therefore, the effective monitoring of the autophagy status of tumors in vivo and the regulating of the autophagy level are crucial for improving the efficacy of chemotherapy. In this work, we grafted nitroxide radicals onto the surface of iron oxide nanoparticles (Fe₃O₄ NPs) using dendrimer polymers, yielding Fe₃O₄-NO· NPs that are responsive to reactive oxygen species (ROS) and possess enhanced T1 and T2 signal capabilities in a magnetic resonance imaging (MRI) measurement. The ROS in tumor cells generated by autophagy quenches the nitroxide radicals, thereby weakening the T1 signal. In contrast, Fe₃O₄ NPs are unaffected by intracellular ROS, leading to a stable T2 signal. By comparing the intensity ratio of T1 to T2 in Fe₃O₄-NO· NPs, we can evaluate the in vivo autophagy status within tumors in real time. It also revealed that Fe₃O₄-NO· NPs loaded with doxorubicin (Dox) and combining the autophagy inhibitor exhibited high antitumor activity in cells and tumor-bearing mice. This system, which combines real-time monitoring of tumor cell autophagy with the delivery of chemotherapeutic drugs, provides an innovative and effective strategy for tumor treatment with potential clinical application prospects.