Intracellular localization of meso-Tetra(p-sulfophenyl)porphine: a potential tumor localizing agent

The mechanism of meso-tetra (p-sulfophenyl)porphine (TPPS4) localization was examined in Vero and HEp-2 cells in vitro. TPPS4 was found to be relatively nontoxic to both cell types at concentrations up to 200 microgram/ml. However, changes in cellular ultrastructure were observed by electron microscopy, consisting mainly of an increase in membrane-bound vacuoles. The nature of the new structures has not been determined. Both fluorescence microscopy and cellular fractionation indicate that TPPS4 is localized inside the cells studied. Considerable differences in the pattern of localization between the two cell types were found. The TPPS4 in the Vero cells was found to be mainly in the soluble fraction and the red fluorescence was found to be diffuse throughout the cytoplasm. The HEp-2 cells showed TPPS4 fluorescence associated with various cell organelles, predominatly the nucleolus. [14C]-TPPS4 was found in many cellular components but predominantly it was in the soluble and protein fractions. These differences may be significant in the understanding of in vivo localization of this porphyrin in neoplastic tissue.