Flash wave light strongly enhanced the cytocidal effect of photodynamic therapy with acridine orange on a mouse osteosarcoma cell line.

A photodynamic therapy technique with acridine orange (AO-PDT) was experimentally developed and applied clinically to musculoskeletal sarcoma patients to reduce the surgical margin and obtain good limb function. Furthermore, various modalities to enhance and strengthen the cytocidal effect of AO-PDT were investigated. A recent report revealed that the use of stronger unfiltered xenon light in AO-PDT enhanced the cytocidal efficacy of this treatment modality. Therefore, in this study, we investigated whether the use of a flash wave light (FWL) from a xenon lamp, as compared to that of the conventional continuous wave light (CWL), might enhance the cytocidal effect of AO-PDT, using the mouse osteosarcoma cell line, LM8. For an equal energy dose (79.6 joules/cm2), AO-PDT using FWL (10 minutes excitation) was found to exert a significantly stronger cytocidal effect than that using CWL (18 seconds excitation). For the same excitation time (10 minutes' excitation), the use of FWL (79.6 jouleslcm2) was associated with a significantly stronger cytocidal effect of AO-PDT than that of CWL (3,820 joules/cm2). These results reveal that the use of FWL entails the need for a lower excitation energy and shorter excitation time than that of CWL for the cytocidal effect of AO-PDT to be observed against the osteosarcoma cells. In addition, FWL also has the advantage of generating low heat and of having the ability to homogenously illuminate a wider area. We therefore concluded that FWL is more useful for AO-PDT than CWL in terms of saving on the excitation time and of obtaining good efficacy of destruction of the residual tumor in the treatment of musculoskeletal sarcomas.