THE NEW SENSITIZING AGENTS FOR PHOTODYNAMIC THERAPY - 21-SELENAPORPHYRIN AND 21-THIAPORPHYRIN

Background: Photodynamic therapy may be a promising treatment for pati ents with tumors. The mechanism of its action is poorly understood and different from the cytotoxic effects induced by antitumor drugs. Mate rials and methods: new sensitizers, termed as 21-selenaporphyrin (SEP) and 21-thiaporphyrin (STSP) were studied for their photocytotoxicity in vitro against selected human cancer cell lines. This study was foll owed by in vivo screening of the effect of SEP using an animal tumor m odel. The activity of the new agents was compared with that of a known photosensitizer, namely chlorin e6. In our selection of the cell line s applied for in vitro study, the possible accessibility and effective ness of photodynamic therapy (PDT) for treatment of colon and urinary bladder cancers, was considered. Results: new compounds appeared to be not toxic for tested cells in culture. without exposure to light. The STSP exerted in vitro effects comparable with chlorin e6 photocytotox icity, while SEP appeared to be ineffective. However, in vivo experime nts performed in a BFS1 fibrosarcoma tumor model in mice showed that t he SEP was at least as much effective as chlorin e6 in the induction o f tumor necrosis. In contrast to chlorin e6, SEP-PDT induced no skin s ensitization. Conclusions: both new sensitizers can be applied in PDT at no risk of skin damage. The mechanism of the action of these two co mpounds is probably different i.e. the 21-thiaporphyrin possibly acts directly on tumor cells and the 21-selenaporphyrin via endothelial cel ls of newly formed tumor vasculature.