Kinetics of endogenous protoporphyrin IX induction by aminolevulinic acid: preliminary studies in the bladder

Photodynamic therapy (PDT) is an experimental treatment for cancer in which cell damage is achieved by the action of light on a photosensitizing drug. Though an effective treatment for superficial bladder cancer, its use has been limited due to complications relating to laser light dosimetry and the tissue specificity of the photosensitizer hematoporphyrin derivative (HPD). Aminolevulinic acid (ALA), a precursor in the biosynthesis of heme, induces the production of the endogenous photosensitizer protoporphyrin IX (PpIX) in a variety of tissues. We have studied the kinetics of PpIX accumulation in the rat bladder following ALA administration using a fluorimetric porphyrin assay. After oral and intravenous administration of ALA a rapid rise in PpIX content occurs followed by a reduction to control values by 24 hours. No increase in bladder PpIX content was detected after topical administration.