Relaxation Suppressed Exchange Tuning MRI Integrated with Manganese-Based Nanozyme Probes for Ferroptosis Induction and GPX4 Monitoring

Ferroptosis has emerged as a viable approach to enhance therapeutic efficacy in triple-negative breast cancer (TNBC), making monitoring essential for prognostic evaluation. However, conventional MR imaging cannot characterize ferroptosis-related biomarkers. Herein, we propose a Relaxation Suppressed Exchange Tuning (ReSET) MRI strategy for ferroptosis modulation and monitoring, which relies on T1 relaxation and chemical exchange saturation transfer (CEST). ReSET was achieved by a tumor-microenvironment-responsive nanoprobe (SiO₂@FUDR@MnO₂, SiFM), consisting of a mesoporous silica core loaded with chemotherapeutic floxuridine and the MnO₂ shell with nanozyme activities. This structure promotes robust ROS generation, which induces lipid peroxidation and ultimately facilitates chemodynamic therapy (CDT)-sensitized ferroptosis. Notably, ReSET takes advantage of the tumor-responsive release of Mn²⁺ from SiFM, which shortens T1 relaxation and suppresses the saturation transfer efficiency between water and exchangeable endogenous protons reducing magnetization transfer ratio asymmetry (MTRasym). The inverse correlation between the T1 intensity and MTRasym provides a sensitive and specific indicator for visualizing glutathione peroxidase 4 (GPX4) expression, thereby enabling cross-modal monitoring of ferroptosis. Meanwhile, we revealed that the ReSET strategy enables sensitive detection of small lesions in liver micrometastasis models. Overall, we establish a ReSET MRI-guided strategy using a manganese-based nanoplatform, which represents a promising ferroptosis-related theranostic approach for TNBC.