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-(omega-methoxypolyethyleneoxyphenyl) porphyrin, H-2-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 H-2-P were compared. It was shown that the H-2-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 H-2-P resulted in non-cytotoxicity in control conditions but, under irradiation, the cytotoxicity increased significantly at 20 mu M of porphyrin; it further increased at 40 mu M, reaching total cell death at 80 mu M. These results suggest that, as already observed for other cellular species, PDT-mediated oxidative stress occurs.