Abstract
Singlet oxygen (1O2) generated in photodynamic therapy (PDT) plays a very important role in killing tumor cells. Using a new near infrared-photomultiplier tube (NIR-PMT) system, we monitored the real-time production of 1O2 during PDT and thus investigated the relationship between the 1O2 production and photodynamic effects. We performed PDT using 5-aminolevulinic acid (ALA) in 9L glioma cells in vitro and in rat in vivo subcutaneous tumor model inoculated 9L glioma cells, and monitored 1O2 production using NIR-PMT system. Moreover, based on the 1O2 monitoring, we investigated how 1O2 production would affect the tumor cell death following PDT. We could observe the temporal changes of 1O2 production during PDT in detail. At a low fluence rate the 1O2 signal gradually decreased with a low peak, while at a high fluence rate it decreased immediately with a high peak. Consequently, the cumulative 1O2 at a low fluence rate tended to be higher, which thus induced a strong photodynamic effect. A low fluence rate tended to induce apoptotic change, while a high fluence rate tended to induce necrotic change. The results of this study suggested that the monitoring of 1O2 enables us to predict the photodynamic effect and then allows us to select the optimal laser conditions for each patient.
