Data supporting the publication: Low-Dose-Rate Ionizing Radiation Increases Singlet Oxygen Production by Photosensitizers

Photosensitizers have significant potential as radiosensitizers in cancer treatment, yet the mechanism of ionizing radiation-induced singlet oxygen (1O2) generation remains unclear. Here, we systematically investigated 1O2 production by the photosensitizer Chlorin e6 (Ce6) using SOSG probe and imidazole/RNO detection methods, evaluating effects of photon energy (X-rays up to 310 kV and 60Co gamma rays at 1.17 and 1.33 MeV), dose, and dose rate. Ce6 produced more 1O2 with increasing photon energy. At 5 Gy, the lowest dose rate (0.005 Gy/min) yielded significantly more 1O2 than higher dose rates (7-0.05 Gy/min). Scavenging experiments identified superoxide anions (·O2-) as a key intermediate. We propose that, unlike classical triplet-state photosensitization, ionizing radiation induces Ce6 radical cations (Ce6•+), which react with radiation-induced ·O2- to generate 1O2. These findings suggest potential for photosensitizer–radiation combinations in low dose rate therapies, though further biological validation and consideration of tumor redox status are required.