Rose bengal acetate photodynamic therapy-induced autophagy

Cell deaths in Photodynamic therapy, that is an anticancer therapy requiring exposure of cells or tissue to photosensitizing drug followed by irradiation with visible light of the appropriate wavelength, occur by the efficient induction of apoptotic as well as non-apoptotic cell deaths, like necrosis and autophagy, or by a combination of the three mechanisms. However, the exact role of autophagy in Photodynamic therapy is still a matter of debate. To this purpose, 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 in order to obtain 1.6 J/cm2 as total light dose) and allowed to recover for 72 h. Induction of autophagy and apoptosis was observed with peaks at 8 h and 12 h after irradiation respectively for autophagy and apoptosis. Autophagy was detected by biochemical (Western Blot of LC3B protein) and morphological criteria (TEM, cytochemistry). In addition, the pan-caspases inhibitor z-VAD was not able to completely prevent cell deaths. The simultaneous onset of apoptosis and autophagy following Rose Bengal Acetate Photodynamic therapy is of remarkable interest in consideration of the findings that autophagy can result in class II presentation of antigens and thus explain why low dose Photodynamic therapy can yield anti-tumour vaccines.