Abstract

Tumor cell survival and progression are critically dependent on intracellular redox homeostasis, with mitochondria playing a central role in maintaining this balance via antioxidant defenses. Consequently, therapeutic strategies that target mitochondrial function to disrupt this delicate balance are attracting increasing attention. Natural pro-oxidant drugs exhibit unique biological activities and relatively low systemic toxicity, demonstrating considerable promise compared to conventional chemotherapeutic agents. However, their clinical translation is impeded by poor solubility, rapid clearance, and limited tumor penetration. To overcome these limitations, this study designed a reactive oxygen species (ROS)-responsive amphiphilic block prodrug copolymer (PCC), which was synthesized via polycondensation of a cinnamaldehyde (CA)-functionalized ROS-cleavable thioketal monomer (TCA) with curcumin (Cur) and mPEG. This design enables the codelivery of CA and Cur. The self-assembled PCC nanoparticles demonstrated favorable biocompatibility and high drug delivery efficiency. In vitro, PCC NPs were effectively internalized by 4T1 tumor cells, where they rapidly and continuously released CA and Cur upon intracellular ROS stimulation. The two agents acted synergistically to promote ROS generation, induce calcium ion overload, and reduce mitochondrial membrane potential. This process established a positive feedback loop that amplified oxidative stress, disrupted the redox homeostasis of tumor cells, and ultimately induced apoptosis. Compared with free CA and Cur, PCC exhibited significantly cytotoxicity against 4T1 cells with the half-inhibitory concentration (IC50) of 13.93 μM, which is markedly lower than the 21.66 μM for free Cur and 193.06 μM for free CA. In vivo experiments confirmed that PCC nanoparticles could accumulate at tumor sites via the enhanced permeability and retention (EPR) effect, achieving a tumor inhibition rate of up to 86% and significantly suppressing