Intravesical instillation of 5-aminolevulinic acid: the fluorescent metabolite is limited to urothelial cells

Abstract

Objectives: For photodynamic therapy 5-aminolevulinic acid is an attractive compound, since it is a physiologic endogenous substance, and its application in excess results in the accumulation of the metabolite protoporphyrin IX, a very effective photosensitizer. The topical application of 5-aminolevulinic acid in the urinary bladder led to pronounced fluorescence in neoplasias when excited with violet laser light during cystoscopy. The aim of this study was the determination of the transmural distribution of protoporphyrin IX in order to estimate potential efficacy and side effects of a therapeutic application of 5-aminolevulinic acid.

Methods: 5-Aminolevulinic acid was instilled prior to cystoscopy and biopsies were taken of lesions that were either fluorescing or nonfluorescing. Fluorescence distribution was analyzed by fluorescence microscopy on cryostat sections prepared from 72 biopsy specimens. In addition, multicellular spheroids grown from tumor cells and fibroblasts were exposed to 5-aminolevulinic acid and analyzed accordingly.

Results: Biopsy preparations showed that the fluorescence of protoporphyrin IX was limited to normal and neoplastic urothelial cells. Clinical findings were supported by the in vitro data, which showed negative protoporphyrin IX fluorescence in fibroblasts.

Conclusions: Thus, 5-aminolevulinic acid might be superior in selective accumulation to conventional sensitizers known to localize also in endothelial cells of the tumor stroma. The data appear to hold great promise for 5-aminolevulinic acid in photodynamic diagnosis and therapy in bladder cancer, as phototoxicity will be limited to mucosal lesions. Bladder shrinkage due to photodamage of subepithelial structures even in case of high light doses is not expected.