Comparative studies of selected porphyrin photosensitizers

Abstract

We wish to report on PDT simulation studies of a class of compounds, which because of their commercial nonavailability, had hitherto been overlooked: the tetrabenzoporphyrins (TBP5) . We have studied absorption and fluorescence of these compounds in homogeneous solutions and in liposome vesicles. Each substance was examined for its photodynamic effects on 9,lO-dimethylanthracene (DMA, an effective probe for singlet oxygen in PDT simulation) . Since TBPs display absorption in the 630 nm region, a 15 mW He-Ne laser proved convenient for these studies. All our data were intercorrelated and compared with standard HPD and Photofrin samples, as well as studies of self-destruction of these chromophores under similar light irradiation conditions. Despite the fact that some TBPs such as MgTBP and ZnTBP have strong absorption bands in the 630 nixt region (orders of magnitude greater than HPD) , we found that other physical factors may play a dominant role in PDT effectiveness. We followed the photosensitization of DMA in real time by monitoring its fluorescence decrease at 457 nra and found that DMA undergoes an oxygen-mediated (type II) photosensitization reaction. ZnTBP was found to be the most efficient photosensitizer followed by PF-II, MgTBP, HPD and ZnPC. The partition coefficients of the sensitizers to lecithin liposomes are also reported.