Photosensitization and tissue distribution studies of the picket fence porphyrin, 3,1-TPro, a candidate for photodynamic therapy.

From a structurally distinct set of o-substituted tetraphenylporphyrins, the picket fence porphyrin (PFP), 3,1-meso-tetrakis(o-propionamidophenyl)porphyrin (3,1-TPro) has been selected as a potential candidate for use in the photodynamic therapy (PDT) of cancer. In this report, the time-dependent tissue distribution of 14C-labeled 3,1-TPro is described along with the results of various treatment regimens. The tissue distribution of radiolabeled 3,1-TPro is comparable to that of other porphyrin photosensitizers with the advantage of being most effective at 4 h and being cleared rapidly from most tissues. The results of the various treatment regimen experiments, as well as other studies, indicate that the 3,1-TPro mechanism of action is similar to that of other photosensitizers, but may include some minor differences. The conclusion is that 3,1-TPro and other PFP offer a class of effective photosensitizers that may be exploited for their structural versatility, straightforward synthesis leading to a compound of high purity and known structure, and stability (both in terms of shelf-life and in vivo metabolism) as potential candidates for PDT.