Combined Application of Photofrin II and Ionizing Radiation in an in vitro and in vivo Experiment

The use of photofrin II, which has been approved as a tumor selective photosensitizer, is well established in PDT for tumor treatment. Ionizing irradiation also has a substantial role in tumor therapy. Radiosensitizers are used to increase the efficacy of radiotherapy. In the following work we present the results of in vitro cell survival assay combining the application of Photofrin II and ionizing irradiation.

Experiments using several series of cell lines were performed:human bladder cell line (RT 4), colon adenocarcinoma (HT 29) and the glioblastoma cells (U 373 MG) were investgated, with and without of Photofrin II, before ionizing irradiation. RT 4 and U 373 MG, treated with Photofrin II prior to radiation, showed cell survival significantly lower than cell cultures untreated with Photofrin II. For the HT – cells, the results did not differ between treated and untreated cells. For the in vivo experiments we used nude mice, to which were implanted the tumor material subcutaneously. The mice were injected with different photosensitizing agents and irradiated with 5 to 15Gy using a Siemens X-ray device.

Results: Photofrin II can also act as an effective radiosensitizer. All the other photosensitizers, tested by us, were ineffective due to radiosensitizing.

The possibility to use the same chemical compound (Photofrin II) as both a photo- and a radiosensitizing agent open the possibility to combine the two therapeutic modalities in order to achieve more efficient tumor control.