Hypoxia-responsive nanoreactors based on self-enhanced photodynamic sensitization and triggered ferroptosis for cancer synergistic therapy

Background: Photodynamic therapy (PDT), a typical reactive oxygen species (ROS)-dependent treatment with high controllability, has emerged as an alternative cancer therapy modality but its therapeutic efficacy is still unsatisfactory due to the limited light penetration and constant oxygen consumption. With the development of another ROS-dependent paradigm ferroptosis, several efforts have been made to conquer the poor efficacy by combining these two approaches; however the biocompatibility, tumor-targeting capacity and clinical translation prospect of current studies still exist great concerns. Herein, a novel hypoxia-responsive nanoreactor BCFe@SRF with sorafenib (SRF) loaded inside, constructed by covalently connecting chlorin e6 conjugated bovine serum albumin (BSA-Ce6) and ferritin through azobenzene (Azo) linker, were prepared to offer unmatched opportunities for high-efficient PDT and ferroptosis synergistic therapy. Results: The designed BCFe@SRF exhibited appropriate size distribution, stable dispersity, excellent ROS generation property, controllable drug release capacity, tumor accumulation ability, and outstanding biocompatibility. Importantly, the BCFe@SRF could be degraded under hypoxia environment to release BSA-Ce6 for laser-triggered PDT, ferritin for iron-catalyzed Fenton reaction and SRF for tumor antioxidative defense disruption. Meanwhile, besides PDT effects, it was found that BCFe@SRF mediated treatment upon laser irradiation in hypoxic environment not only could accelerate lipid peroxidation (LPO) generation but also could deplete intracellular glutathione (GSH) and decrease glutathione peroxidase (GPX4) expression, which was believed as three symbolic events during ferroptosis. All in all, the BCFe@SRF nanoreactor, employing multiple cascaded pathways to promote intracellular ROS accumulation, presented remarkably outstanding antitumor effects both in vitro and in vivo. Conclusion: BCFe@SRF could serve as a promising candidate for synergistic PDT and ferroptosis therapy, which is applicable to boost oxidative damage within tumor site and will be informative to future design of ROS-dependent therapeutic nanoplatforms.