Interstitial photodynamic therapy in the canine prostate with disulfonated aluminum phthalocyanine and 5-aminolevulinic acid-induced protoporphyrin IX

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Abstract
Photodynamic therapy (PDT) is an experimental approach for treating prostate cancer localized to the gland that does not involve surgery or irradiation. Second-generation photosensitizers 5-aminolevulinic acid (ALA) and aluminum disulfonated phthalocyanine (A1S2Pc) were studied in the normal canine prostate. Tissue biodistribution of photosensitizers on serial biopsies was examined using fluorescence microscopy. Photodynamic therapy was done by delivering red light interstitially at 100mW through fibers placed under transrectal ultrasound guidance. Peak levels of A1S2Pc apppeared at 5-24 hr and at 3 hr for ALA. Macroscopic PDT lesions were up to 12 mm in diameter using A1S2Pc, but only 1-2 mm with ALA. Light at 300 mW caused thermal lesions. At 28 days, damaged glands remained atrophic, but the interlobular supporting stroma was well preserved. Urethral lesions healed by 28 days without functional impairment. Although the results with ALA were disappointing, PDT using A1S2Pc looks like a promising modality for treatment of localized prostate cancer. Prostate 32:89–98, 1997.