Post-Remedial Oxygen Supply: A New Perspective on Photodynamic Therapy to Suppress Tumor Metastasis.

Photodynamic therapy (PDT) holds great promise in tumor therapy due to high safety, efficacy, and specificity. However, the risk of increased metastasis in hypoxic tumors after oxygen-dependent PDT remains underestimated. Here, we propose a post-PDT oxygen supply (POS) strategy to reduce the risk of metastasis. Herein, biocompatible and tumor-targeting Ce6@BSA and PFC@BSA nanoparticles were constructed for PDT and POS in a 4T1-orthotropic breast cancer model. PDT with Ce6@BSA nanoparticles increased tumor metastasis via the HIF-1α signaling pathway, whereas POS significantly reduced the PDT-triggered metastasis by blocking this pathway. Furthermore, POS, with clinical protocols and an FDA-approved photosensitizer (hypericin), and oxygen inhalation reduced PDT-induced metastasis. Our study findings indicate that PDT may increase the risk of tumor metastasis and that POS may solve this problem. POS can reduce the metastasis resulting not only from PDT but also from other oxygen-dependent treatments such as radiotherapy and sonodynamic therapy.