In Vitro Efficacy of Water-Soluble Mercaptopyridine-Substituted Oxotitanium (IV) Phthalocyanine Compounds in Photodynamic Therapy of Oral Squamous Cell Carcinoma

<i>Background and Objectives</i>: The efficacy of newly synthesized water-soluble octa-mercaptopyridine-substituted oxotitanium (IV) phthalocyanine (oxo-TiPc) and copper (II) phthalocyanine (CuPc) compounds in photodynamic therapy (PDT) was investigated using human tongue squamous cell cancer cell line (SCC-9, ATCC) cultures. <i>Materials and Methods</i>: A laser light source with a wavelength of 635 nm was used for this study. The cytotoxic values of the cancerous (SCC-9) and healthy (L-929) cell samples to which different Pc concentrations were applied under laser light were evaluated spectroscopically with the XTT method. <i>Results</i>: The oxo-TiPc compound exhibited a significantly lower IC50 value (46.8 µM) for SCC-9 cells compared to the CuPc compound (286.2 µM), indicating higher anticancer activity. This cytotoxicity may be due to decreased aggregation and enhanced reactive oxygen species (ROS) formation. Double-staining tests confirmed that oxo-TiPc-induced cell death included both apoptosis and necrosis. <i>Conclusions</i>: The findings show that the oxo-TiPc compound, unlike the CuPc compound, exhibited more selective toxicity to the SCC-9 cell line and has a higher phototoxic effect.