Abstract
The photodynamic behavior of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (TMP) has been investigated in solutions containing photo-oxidizable substrates and in the presence of Hep-2 human larynx-carcinoma cell line. It has been found that Hep-2 cells rapidly incorporate TMP until an intracellular concentration of ∼0.018 μmol of TMP/10 6 cells is reached. The survival of the irradiated cells treated with TMP was dependent upon both light exposure level and intracellular sensitizer concentration. In addition, a linear dependence of the photoinactivation rate (1/ D 50, where D 50 represents the light exposure level required to inactivate 50% of the cell population) and TMP intracellular concentration was found, indicating that TMP localizes at unsaturated sites within the cells. TMP photosensitized singlet molecular oxygen ( 1Δ 2) with a quantum yield of 0.65. When the amino acid l-tryptophan was used to assess 1Δ 2-mediated photooxidation in a homogeneous medium, singlet molecular oxygen ( 1Δ g) mediation appeared to be mainly responsible for the cell inactivation. These in vitro results enhance our understanding of the phototoxicity of porphyrins in cellular media and the sensitivity of Hep-2 cells to photodamage.
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