Localization and phototoxic effect of zinc sulfophthalocyanine photosensitizer in human colon (DLD-1) and lung (A549) carcinoma cells (in vitro)

Background: Photodynamic therapy (PDT) is a therapeutic modality used for treating cancerous cells. It has been previously shown that mixed sulfonated metallophthalocyanine complex, zinc sulfophthalocyanine (ZnPcS _mix) is effective in destroying lung cancer cells. This study aimed to determine subcellular localization of ZnPcS _mix and its effect on two cancer cell lines. Methods: ZnPcS _mix was activated at a wavelength of 680nm with 5J/cm ². Colon (DLD-1) and lung (A549) cancer cell lines were used. Subcellular localization of ZnPcS _mix was determined by fluorescence microscopy. Toxicity of PS alone and combination of light and PS (PDT) was determined by cell morphology, viability, proliferation and cytotoxicity. Cells which received no irradiation (0J/cm ²), irradiation alone (5J/cm ²) or treated with PS alone (no irradiation) served as controls. Results: ZnPcS _mix localized in both lysozomes and mitochondria in both A549 and DLD-1 cells. A549 cells treated with PDT showed a significant decrease in viability and proliferation in all PS concentrations used, while in DLD-1 cells a significant decrease was seen with concentrations of 10, 20 and 40μM. In absence of light, ZnPcS _mix did not result in cellular toxicity in A549 cells whereas in DLD-1 cells it resulted in a reduction in cell proliferation only at a concentration of 40μM. Conclusion: ZnPcS _mix was effective in inducing cell death in both cell lines when localized in vital organelles such mitochondria and lysozomes which are essential for cell functioning. Photoactivated ZnPcS _mix affected the cells at different concentration and yielded good therapeutic results in vitro.