Photosensitizing action of isomeric zinc N-methylpyridylporphyrins in human carcinoma cells

The success of photodynamic therapy (PDT), as a minimally invasive approach, in treating both neoplastic and non-neoplastic diseases has stimulated the search for new compounds with potential application in PDT. We have previously reported that Zn(II) N-alkylpyridylporphyrins (ZnTM-2(3,4)-PyP4+ and ZnTE-2-PyP4+) can act as photosensitizers and kill antibiotic-resistant bacteria. This study investigated the photosensitizing effects of the isomers of ZnTMPyP4+ (ZnTM-2(3,4)-PyP4+) and respective ligands on a human colon adenocarcinoma cell line. At 10 μM and 30 min of illumination the isomeric porphyrins completely inhibited cell growth, and at 20 μM killed approximately 50% of the cancer cells. All these effects were entirely light-dependent. The isomers of the ZnTMPyP4+ and the respective ligands show high photosensitizing efficiency and no toxicity in the dark. Their efficacy as photosensitizers is comparable to that of hematoporphyrin derivative (HpD).