Photosensitization by synthetic diporphyrins and dichlorins in vivo and in vitro

A group of polycarboxylic diporphyrins, two dichlorins and a porphyrin-chlorine dimer, with rings linked by methylene groups, were examined to help identify structures which can mediate photodynamic tumor eradication in vivo. Among the features sought were short persistence of normal tissue photosensitization and substantial absorbance at wavelengths longer than 630 nm. Both objectives were achieved, with pertinent structure-activity relationships partly characterized. The relative hydrophobicity of the different sensitizers was an important determinant of their accumulation in cell culture, but not of in vivo effectiveness. These compounds showed affinity for protein and high-density lipoprotein components of serum. Their distribution may be mediated by a different mechanism than that which occurs with more hydrophobic sensitizers like hematoporphyrin derivative which have greater affinity for low-density lipoproteins and less for protein components of serum, as compared with the products examined in this study.