Chalcogen bearing tetrasubstituted zinc (II) phthalocyanines for CT26 colon carcinoma cells photodynamic therapy

The synthesis and photochemical properties of six new lipophilic chalcogen tetrasubstituted zinc (II) phthalocyanines and their corresponding water-soluble cationic derivatives were investigated for CT26 colon carcinoma cells photodynamic therapy. Sulfur and selenium phthalocyanines Q-bands are red shifted around 10 nm with respect to the Q-band of oxygen phthalocyanines. The introduction of Se atoms in peripheral position generates non-significant shifts in the absorption spectrum compared to S-bearing phthalocyanine. In addition, Q-band absorption coefficient of selenium phthalocyanines showed to be higher than their respective sulfur and oxygen analogs, which is relevant for dosing in PDT studies. The fluorescence emission maximum wavelength showed the same trend regards to the presence of chalcogen atoms, O < Se < S. All phthalocyanines are efficient singlet oxygen generators with values in the range 0.42–0.75. In most cases, increasing the atomic number of chalcogen atoms produces a rise of singlet oxygen production efficiency. The replacement of O for S or Se atoms cause a red shifting around 20 nm of triplet-triplet maximum absorption wavelength and the introduction of Se atoms causes a significant shortening of τT. The photodynamic effect was evaluated on CT26 colon carcinoma cells. Oxygen phthalocyanines triggered cell death both in the absence or presence of light, whereas sulfur and selenium phthalocyanines diminished cell viability in a concentration dependent manner only after light exposure. S-bearing phthalocyanines showed the best photodynamic efficiency among all novel phthalocyanines.