In vivo resistance to photofrin-mediated photodynamic therapy in radiation-induced fibrosarcoma cells resistant to in vitro Photofrin-mediated photodynamic therapy

The effects of Photofrin-mediated photodynamic therapy ( PDT) on the in vit ro cell survival and in vivo tumor growth of murine radiation-induced fibro sarcoma (RIF) cell tumors have been examined following in vivo PDT treatmen t of tumors. The response to in vivo PDT is examined in tumors derived from RIF-1 mouse fibrosarcoma cells and in tumors derived from RIF-8A cells, wh ich show in vitro resistance to PDT. A significant reduction in tumor volum e is observed over the first three days following in vivo PDT treatment of either 5 or 10 mg/kg. The reduction in tumor volume is greater for a 10 com pared to a 5 mg/ml dose and occurs to a similar extent for both RIF-1 and R IF-8A tumors. The re-growth is significantly delayed for RIF-1 compared to RIF-8A tumors, indicating a greater response for RIF-1 tumors compared to R IF-8A tumors following PDT. A reduced response of the RIF-8A compared to th e RIF-1 tumor cells is also observed in the clonogenic survival of cells fr om tumors that were excised and explanted in vitro immediately following in vivo PDT treatment. These data indicate that the intrinsic cell sensitivit y to PDT is an important component in the mechanism that lends to tumor res ponse following in vivo photodynamic therapy. (C) 1999 Elsevier Science S.A . All rights reserved.