Sensitization of cells to ionizing radiation by chlorin e6Na

We have investigated whether a hydrophilic photosensitizer, chlorin e6Na (Ce6Na), can sensitize cells to ionizing radiation. When V79‐1 cells were pretreated with Ce6Na for 2 hr before receiving a dose of 2–14 Gy of irradiation, the cells became sensitive to X‐irradiation. The sensitizing effect of Ce6Na depended on the dose of Ce6Na. The sensitizing effect also depended on the length of the treatment period before X‐irradiation up to 4 hr, but not on the length of a treatment period after X‐irradiation. Intracellular concentrations of Ce6Na were increased linearly after incubation with Ce6Na for periods of up to 4 h. The dose‐modifying factor calculated from the survival curve was 1.25. Radiat. Oncol. Invest. 6:151–156, 1998. © 1998 Wiley‐Liss, Inc.