Preclinical study in cats of the pro-photosensitizer 5-aminolevulinic acid

Objective-To determine whether feline cells were able to convert 5-aminolev ulinic acid (ALA) to protoporphyrin IX (PplX) in vivo and in vitro, whether IV administration of ALA to healthy cats resulted in adverse effects, and whether PplX accumulated in a squamous cell carcinoma (SCC) of a cat. Animals-4 healthy adult cats and 1 adult cat with a cutaneous SCC. Procedure-In vitro production of PplX was determined by incubating Crandell feline kidney cells with ALA. Effects of ALA administration and in vivo pr oduction of PplX were determined by administering ALA (100, 200, or 400 mg/ kg of body weight) to healthy cats and collecting skin biopsy specimens for up to 24 hours after drug administration. Blood samples were collected for CBC and serum biochemical analyses, and necropsies were performed. Accumul ation of PplX in a SCC was determined by treating a cat with a facial SCC w ith ALA and collecting specimens of the tumor and adjacent grossly normal s kin. Results-Incubation of ALA with feline cells resulted in time- and dose-depe ndent cytoplasmic accumulation of PplX in vitro. After IV ALA administratio n, PplX was detected in ail tissues examined, with the highest fluorescence intensity in epithelia and in squamous cell carcinoma. The tumor-to-skin f luorescence intensity ratio was 5. All cats developed hepatotoxicoses. Conclusions and Clinical Relevance-Results from this limited number of cats suggest that ALA may be a useful photosensitizer in cats, but that doses > 100 mg/kg, IV, may not be safe.