DELAYED OXIDATIVE PHOTODAMAGE INDUCED BY PHOTODYNAMIC THERAPY

Apoptotic DNA fragmentation was observed 60 min after photodynamic the rapy of murine leukemia cells in culture, using either of two photosen sitizers with predominantly lysosomal targets. When the radical scaven gers trolox or alpha-tocopherol succinate were present during irradiat ion, the subsequent appearance of apoptotic cells was prevented, as wa s phototoxicity. Addition of either scavenger during the 60 min after irradiation provided only partial protection from apoptosis and photot oxicity; this protection was abolished if the addition was delayed for 10 min. These results are consistent with a model whereby long-persis ting photoproducts continue the initiation of apoptosis for approximat ely 10 min after irradiation has ceased.