pH/ROS Dual-Responsive Self-Amplified ROS-Replenishing Self-Delivery Systems for Tumor-Specific Chemotherapy/Ferroptosis

The heterogeneous and insufficient reactive oxygen species (ROS) level in the tumor microenvironment (TME) limits the effectiveness of conventional ROS-responsive drug delivery systems (DDSs). To overcome this, a pH/ROS dual-responsive amphiphilic copolyprodrug (P(CA-DOX-Fc)-PEG) was designed by integrating cinnamaldehyde (CA), doxorubicin (DOX), and ferrocene dicarbohydrazide (FcDH) via dynamic covalent linkages. The resulting copolymer self-assembled into nanoparticles (P(CA-DOX-Fc)-PEG-NPs) with high DOX and FcDH contents of 64.6 and 15.9%, favorable stability, and a minimal premature leakage of <1% in 160 h. Under acidic and oxidative conditions, the nanoparticles underwent self-amplified degradation, triggered by glutathione (GSH) depletion-induced ROS elevation and Fc-catalyzed hydroxyl radical (·OH) generation, enabling enhanced DOX release and ferroptosis induction. The dual-stimuli responsiveness ensured selective activation in the TME, and cellular uptake studies confirmed effective internalization and nuclei accumulation of DOX in HepG2 cells. In vitro cytotoxicity assays showed a low half-maximal inhibitory concentration (IC₅₀) of 8.91 μg/mL for the HepG2 cells, high viability in normal L02 cells, and a combination index (CI) of 0.92, indicating synergistic chemo- and ferroptosis therapeutic effects. These results demonstrate that P(CA-DOX-Fc)-PEG-NPs offer a promising strategy for precise, tumor-specific, and self-amplified combination therapy through ROS replenishment and environmentally triggered drug release.