Abstract

Photochemical or photodynamic therapy (PDT) involving the combination processes of dye injection, like hematoporphyrin derivative (HpD), and subsequent exposure to visible laser light has proved effective in the diagnosis and treatment of malignant tumors at the clinical level.¹ In the mechanism of such photosensitized biochemical reactions, excited singlet molecular oxygen (¹O₂) is considered to play an essential role, at least, in starting the reaction. Until now, almost all studies on the generation of ¹O₂ molecules in the photosensitized dye were performed by various chemical methods utilizing scavengers or sensitizers of ¹O₂ molecules during their chemical reactions. However, the spectroscopic technique for the detection of ¹O₂ molecules in the near infrared region based on their transitions around 1.06,1.27, and 1.59 μm is believed to be much more reliable and versatile than the conventional chemical method. Accordingly, we have performed the experimental study on the spectroscopic detection of ¹O₂ molecules in laser-excited photosensitive dye, chlorin-e₆Na, contained in aqueous solution as well as in mouse cultured tumor cells in vitro and in tumor tissues in vivo, employing a highly sensitive near infrared spectrometer system constructed by our project. Chlorin-e₆Na has a structure similar to pheophorbide a, one of the decomposition products from chlorophyll a, which has been demonstrated for the first time by our group to be a more efficient and appropriate dye for the PDT than HpD.² Thus in vitro and in vivo experiments using mouse FM3A cultured tumor cells and C3H mouse tumor tissues in chlorin-e₆Na have indicated the significant spectroscopic evidence for the generation of ¹O₂ molecules with excellent signal-to-noise ratio during laser excitation.

© 1989 Optical Society of America