Hematoporphyrin uptake by experimentally induced cholesteatomas in an animal model

Photodynamic therapy is based on the production of a cytotoxic factor by porphyrins, particularly hematoporphyrin (HP), when exposed to light of a suitable wavelength and intensity. The uptake of HP is notably large in tissues with a high mitotic index. Although cholesteatomas are not malignant tumors, our working hypothesis was that their high lipid content might result in their exhibiting a remarkable affinity to HP, which is normally carried in the blood by lipoproteins. Cholesteatomas were induced in rabbits using the Tübingen procedure (closure of the auditory canal by sutures). Animals were killed 30-40 days later at intervals of 1, 3, 6, 12, and 24 h following intravenous HP administration (5 mg/kg). Specimens were divided into two portions, one for histological examination and the other for biochemical study. The latter revealed that HP accumulates in experimental cholesteatomas, with a maximum uptake after 3 h. The level then gradually decreases, although at a lower rate than in the liver, but remains considerably high even after 24 h. These results suggest that the photodynamic treatment of cholesteatomas should be feasible in our animal model, although such treatment is still speculative in man.