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5-Aminolevulinic acid (ALA) is a precursor of heme biosynthesis. In the penultimate step of this biosynthesis, protoporphyrin IX (PpIX), an effective photosensitizer, is generated. In this study, the biodistribution and photodynamic effect of ALA-induced PpIX were investigated in an orthotopic rat bladder tumor model. A quantitative comparison of PpIX biodistribution by extraction and fluorescence spectroscopy following intravenous and intravesical administration of ALA was made. The tumor to normal bladder wall ratio was 2:1 at 4 hours for both delivery modes. Fluorescence microscopy demonstrated predominantly cellular rather than stromal PpIX fluorescence. Phototoxicity, evaluated 4 hours after ALA administration, was light dose-dependent with the most efficient tumor necrosis being observed upon 150 J/cm.2 of 630 nm. irradiation. These data suggest that optimized photodynamic therapy with ALA-induced PpIX may be an alternative treatment for superficial bladder carcinoma.

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