APOPTOSIS OCCURS IN LYMPHOMA-CELLS BUT NOT IN HEPATOMA-CELLS FOLLOWING IONIZING-RADIATION AND PHOTODYNAMIC THERAPY

The aim of this study was to determine the relative role of apoptosis in photodynamically-induced cytotoxicity or radiation-induced cytotoxi city for hepatoma and lymphoma cells. Human hepatoma cells and mouse l ymphoma cells were treated with either photodynamic therapy (PDT) or i onizing radiation.;Dosimetry studies of immediate cell death following photodynamic therapy in the hepatoma cell line demonstrated second-or der kinetics, similar to that seen in the lymphoma cells. No immediate cell death was noted in the hepatoma or lymphoma cells following ioni zing radiation, but experiments measuring delayed cell death demonstra ted a dose-dependent response. Maximum DNA ladder formation occurred 2 hr after PDT and 24 hr after ionizing radiation in the lymphoma cells , which was consistent with the time courses of cell death for these t reatments. The hepatoma cell line did not demonstrate DNA ladder forma tion despite dosages of PDT or ionizing radiation sufficient to cause high levels of cytotoxicity.