Potential zinc phthalocyanine-based photosensitizer for photodynamic therapy: Photophysical, theoretical and in vitro studies

The preparation of new photosensitizers and studies on photodynamic therapy (PDT) have provided promising results and realistic expectations for an efficient medical treatment. Phthalocyanines (Pcs) have become extremely attractive for this purpose owing to their molecular versatility and superior physicochemical properties. Motivated by these facts, in this study, non-peripherally substituted zinc(II) Pc (2) was prepared by cyclotetramerization of the phthalonitrile derivative bearing 3-methoxybenzyloxy units. Also, physicochemical and in vitro analyses were completed. In photochemical studies, the obtained singlet oxygen quantum yield (Φ_Δ) values were 0.73 in dimethylsulphoxide (DMSO) and 0.55 in dimethylformamide (DMF). Theoretical calculations based on density functional theory (DFT) provide valuable information on the energies and character of the electronic excitations, thus allowing a prediction of their potential applicability to generate singlet oxygen. The PDT activity of the zinc(II) phthalocyanine bearing 3-methoxybenzyloxy substituents was tested via in vitro studies using the human colon cancer cell lines. In cytotoxicity experiments, the most effective incubation time for cell lines was found to be 24 h, and the most effective concentration was 8 μM. Furthermore, the cell viability rate decreased significantly with the increasing power density. The results suggested that the newly synthesized zinc(II) Pc is an effective photosensitizer with potential use for the treatment of colon cancer.