In vitro evaluation of Schiff base-decorated phthalocyanines for photodynamic therapy in PC3 prostate cancer cells

Schiff base-decorated non-ionic phthalocyanine compounds with different metals and a metal-free derivative were synthesized and characterized using different spectroscopic techniques. The influence of the central metal on the photophysicochemical properties was systematically investigated in DMSO. The obtained results reveal that the singlet oxygen quantum yield followed the order In3b > Zn3b > 3bH2Pc in DMSO. The synthesized non-ionic phthalocyanine compounds, except metal-free phthalocyanine (0.12 for 3bH2Pc), have good Φ_Δ values (0.71 for Zn3b and 0.85 for In3b) compared with the unsubstituted ZnPc in DMSO (Φ_Δ = 0.67). In addition to the photophysicochemical studies, in vitro PDT studies were also performed on PC3 prostate cancer cells to evaluate the biological activity of Pcs. All compounds exhibited low dark cytotoxicity at the selected concentration. Upon light irradiation, phthalocyanine-mediated PDT significantly reduced cell viability and induced apoptotic cell death. These effects were accompanied by a pronounced increase in intracellular ROS generation, particularly in the cells treated with metallophthalocyanine-mediated PDT. In particular, In3b- and Zn3b-mediated PDT exhibited markedly enhanced cytotoxic and apoptotic effects compared with metal-free 3bH2Pc. These findings demonstrate a strong correlation between improved photophysical properties, increased ROS generation, and enhanced in vitro PDT efficacy.