SENSITIVITY OF 9L GLIOSARCOMAS TO PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) has been used clinically for the treatment of malignant brain gliomas. However, the efficacy of this treatment to date has remained equivocal. This study focused on determining the se nsitivity of 9L gliosarcoma in Fischer 344 rats to PDT with increasing doses of 632 nm light and making a comparison of the responses of nor mal and tumor tissue in the brain at these doses. This sensitivity was then correlated with the concentrations of Photofrin(R) present in th ese tissues at the time of treatment. Our study indicates that the lev el of Photofrin(R) in the tumor was 13 times that present in normal br ain 48 h after injection. However, this selective localization of the photosensitizer was not reflected in a selective tissue response to PD T. There was minimal tumor response to a dose of 35 J cm(-2), which ha s been reported previously to cause necrosis to the normal brain. Incr easing energy dose levels resulted in an increased tumor response to P DT; however, normal tissue remained more sensitive than tumor tissue a t all energy dose levels examined. These data indicate that, although Photofrin(R) is retained to a significantly higher degree in the tumor than in the normal brain tissue, the normal brain is more sensitive t han the tumor to PDT under the conditions outlined in this study. (C) 1996 by Radiation Research Society