The study of the characteristic of photocytotoxicity under high peak power pulsed irradiation with ATX-S10Na(II) in vitro.

We studied hydrophilic photosensitizer ATX-S10Na(II) mediated photocytotoxicity against macrophage-like cell under pulsed irradiation. We found that photocytotoxicity suppression under high intensity irradiation was directly induced by a decrease in the Type-II photoreaction. We showed that this decrease was not attributable to absorption saturation with the high intensity irradiation. We found the cell lethality change from 70% to 13% with the pulse peak power density ranging from 0.29 MW/cm(2) to 1.36 MW/cm(2), at the light dose of 20 J/cm(2) and the pulse repetition rate at 40 Hz. To investigate the Type-II reaction, we measured the photobleaching, oxygen consumption and singlet oxygen luminescence of the photosensitizer solution. The transient absorption from the photosensitizer during the irradiation was measured with the pump-and-probe technique. We believe that the photocytotoxicity suppression induced by the high intensity irradiation might be useful for the treatment of depth-controlled photodynamic therapy without the wall damage of a hollow organ.