In vitro evaluation of the genotoxic and clastogenic potential of photodynamic therapy

Photodynamic therapy (PDT) was recently introduced in clinical practice for the management of cancer. As far as PDT relies on the combined action of a photosensitizer and a laser source, there is a need to evaluate the genoto xic and mutagenic potential of this treatment modality. This paper reports the effects of various photosensitizer and photo-irradiation doses on letha lity to the MIA PaCa cell line using ZnPcS4 as the photosensitizer, The sis ter chromatid exchange (SCE) assay was used to evaluate the genotoxicity of various photosensitizer and photoirradiation doses. Also, chromosomal aber rations at various time intervals post-irradiation were evaluated. The resu lts showed that a combination of 3 J/cm(2) irradiance with 5 mu M ZnPcS4 co ncentration leads to the LD90 72 h post-irradiation. Eight days post-irradi ation the LD90 level was achieved using a light dose of 3 J/cm(2), independ ent of ZnPcS4 concentration. The SCE assay showed that cells treated with v arious light and drug doses presented no genotoxic potential, as SCE levels were not different from untreated (control) cells, Chromosomal analysis af ter PDT treatment at various time intervals post-irradiation showed that th ere was no significant chromosomal damage in cells treated photodynamically compared with untreated controls. The results show that the cell killing m echanism after PDT is not at the chromosome level, but may be at a differen t cellular level, such as plasma membranes, mitochondria, etc.