The photodynamic efficiency of phenothiazinium dyes is aggregation dependent

The evaluation of the IC50 values of phenothiazinium dyes in neoplastic immortalized cells (HeLa) in the dark and under irradiation showed that the effectiveness of the photosensitizers (PSs) increased in the order of Azure A (AA) < Azure B (AB) < Methylene Blue (MB). Singlet oxygen production was similar in all of the compounds and the cell uptake of MB was lower than those of AA and AB. The evaluation of the dimer to monomer ratio showed that aggregation increased in the order of MB < AB < AA. Thus, the photodynamic efficiency of these PSs was dependent on aggregation. In order to improve the effectiveness of photodynamic therapy (PDT), it is important to develop phenothiazinium dyes with structural modifications and/or to design formulations that could reduce aggregation.