Photodynamic Activity of 5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin on the Hep-2 Human Carcinoma Cell Line: Effect of Light Dose and Wavelength Range

Abstract

The photodynamic activity of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (TMP) has been investigated in two systems: reverse micelles of n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water-bearing photooxidizable substrates and on a Hep-2 human carcinoma cell line. The effect of variation in the light dose and wavelength range (360–800, 455–800, and 590–800 nm) was compared in both media. The aerobic singlet oxygen-mediated photooxidation of l-tryptophan (Trp) was used as a model of biological substrate in a micellar system. A considerable increase of the observed rate constants of Trp (kTrpobs) was noted, increasing the irradiated area of the TMP spectrum. In vitro, the survival curves of Hep-2 cells, treated with TMP, were markedly dependent on the light wavelength ranges used for irradiation. A linear behavior between kTrpobs and the photoinactivation rate of Hep-2 cells was found, indicating that the singlet oxygen (1O2 ) is the main species responsible for cell inactivation. These results contributed to an understanding of the photodynamic process yielded by this porphyrin in vitro and the sensitivity of Hep-2 cells to photodamage.