Rose bengal acetate photodynamic therapy-induced autophagy

Photodynamic therapy (PDT), an anticancer therapy requiring the exposure of cells or tissue to a photosensitizing drug followed by irradiation with visible light of the appropriate wavelength, induces cell death by the efficient induction of apoptotic as well as non-apoptotic mechanisms, such as necrosis and autophagy, or a combination of all three mechanisms. However, the exact role of autophagy in photodynamic therapy is still a matter of debate. To understand the role of autophagy in PDT, we investigated the induction of autophagy in HeLa cells photosensitized with Rose Bengal Acetate (RBAc). After incubation with Rose Bengal Acetate (10-5 M), HeLa cells were irradiated for 90 seconds (green LED DPL 305, emitting at 530 +15 nm to obtain 1.6 J/cm2 as the total light dose) and allowed to recover for 72 h. Induction of autophagy and apoptosis were observed with peaks at 8 h and 12 h after irradiation, respectively. Autophagy was detected by biochemical (Western Blotting for the LC3B protein) and morphological criteria (TEM, cytochemistry). In addition, the pan-caspase inhibitor, z-VAD, was unable to completely prevent cell death. The simultaneous onset of apoptosis and autophagy following Rose Bengal Acetate PDT is of remarkable interest in light of the findings that autophagy can result in the class II presentation of antigens and thus, explain why low dose PDT can yield anti-tumor immune responses.