APOPTOSIS DURING PHOTODYNAMIC THERAPY-INDUCED ABLATION OF RIF-1 TUMORS IN C3H MICE - ELECTRON-MICROSCOPIC, HISTOPATHOLOGIC AND BIOCHEMICAL-EVIDENCE

Very little is known about the applicability of the metabolic and bioc hemical events observed in cell culture systems to in vivo tumor shrin kage following photodynamic therapy (PDT). The purpose of this study w as to assess whether PDT induces apoptosis during tumor ablation in vi vo. We treated radiation-induced fibrosarcoma (RIF-I) tumors grown in C3H/HeN mice with PDT employing three photosensitizers, Photofrin-II, chloroaluminum phthalocyanine tetrasulfonate, or Pc IV (a promising ph thalocyanine developed in this laboratory). Each photosensitizer was i njected intraperitoneally and 24 h later the tumors were irradiated wi th an appropriate wavelength of red light using an argon-pumped dye la ser. During the course of tumor shrinkage, the tumors were removed at 1, 2, 4 and 10 h post-PDT for DNA fragmentation; histopathologic, and electron microscopic studies. Markers of apoptosis, viz. the ladder of nucleosome-size DNA fragments, increased apoptotic bodies, and conden sation of chromatin material around the periphery of the nucleus, were evident in tumor tissue even 1 h post-PDT; the extent of these change s increased during the later stages of tumor ablation. No changes were observed in tumors given photosensitizer alone or irradiation alone. Our data suggest that the damage produced by in vivo PDT may activate endonucleolysis and chromatin condensation, and that apoptosis is an e arly event in tumor shrinkage following PDT.