The Effect of Irradiation at 670 nm in 5-ALA-mediated PDT.

Abstract

Administered 5-aminolevulinic acid (5-ALA) turns into protoporphyrin IX(Pp-IX) in cells, and the irradiation causes Pp-IX-mediated singlet oxygen generation. It damages surrounding cells and tissue, and, at the same time, Pp-IX itself. When Pp-IX is irradiated at 635 nm, new absorption of photoproducts appears at 670 nm. To increase the effect of 5-ALA-mediated PDT with additional irradiation at 670 nm, we studied its effectiveness using Pp-IX solutions, 5-ALA-administered tumor cells (9L, HeLa), and HeLa tumor-bearing mice.
When a Pp-IX solution was irradiated at 635 nm, singlet oxygen was generated by excitation with nearly 670 nm, indicating the production of photoproducts. Photoproduct-mediated singlet oxygen generation was higher in 9L cells than HeLa cells and photoproducts did not produce an additional PDT effect in HeLa tumors. The cause was suggested as the low uptake of 5-ALA in HeLa cells. Further study is necessary to obtain the irradiation method for the efficient application of 5-ALA-mediated PDT.