TUMOR-SPECIFIC RESPONSE TO PHOTODYNAMIC THERAPY

The exact mechanism by which photodynamic therapy (PDT) causes tumor d estruction has not been elucidated. Early reports indicated that PDT c auses direct cellular effects probably mediated by unstable oxygen spe cies, resulting in cellular oxidation and death. More recently, PDT ef fects on tumor blood flow have been implicated, and there are question s as to whether the PDT response is specific to tumor tissue. Rats wer e implanted with a window chamber containing either a mammary adenocar cinoma or a piece of inert surgical sponge. After growth of the tumor was ascertained, all rats were given 5 mg/kg Photofrin intraperitoneal ly, and then were irradiated with 630 nm light 24 hours post-injection . Caliper thickness and reflectance measurements were performed before and after irradiation; all animals were sacrificed 72 hours post-PDT and the chambers submitted for histologic analysis. Animals implanted with tumors demonstrated marked edema of the chamber with an associate d decrease in reflectance. No edema response was noted in the chambers containing inert sponge, or in any controls. Nonselective PDT effects (characterized by a marked foreign body response) in chambers contain ing sponge was not seen. Histologic analysis of treated specimens corr oborate the above data. (C) 1993 Wiley-Liss, Inc.