A star polymer based on a polyethylene glycol with a porphyrinic core as a photosensitizing agent for application in photodynamic therapy: tests in vitro on human erythrocytes

In this study, human erythrocytes were used to assess the cytotoxicity of an uncharged, water-soluble and bio-compatible porphyrin system [the 5,10,15,20-tetrakis-p-(ω-methoxypolyethyleneoxyphenyl)porphyrin, H2–P], which has the potential to act as a photosensitizing agent in photodynamic therapy (PDT). By investigating the cytotoxicity effects under controlled conditions, at different porphyrin concentrations and upon increasing irradiation times, the data in the absence and in the presence of H2–P were compared. It was shown that the H2–P system, without the assistance of any additional carrier, is easily internalized into cells, unlike the process which occurs for charged porphyrins. Incubation of red blood cells with H2–P resulted in non-cytotoxicity in control conditions but, under irradiation, the cytotoxicity increased significantly at 20 μM of porphyrin; it further increased at 40 μM, reaching total cell death at 80 μM. These results suggest that, as already observed for other cellular species, PDT-mediated oxidative stress occurs.