Photodynamic therapy of murine skin tumors using Photofrin-II

Photodynamic therapy (PDT) is a new experimental cancer therapy in which a photosensitizing chemical that selectively localizes within tumors is given to a tumor-bearing individual and the tumor is then irradiated by wavelengths within the visible spectrum of the photosensitizer. The only photosensitizer currently approved for human clinical trials is Photofrin-II (Pf-II). In most preclinical studies, the effectiveness of Pf-II has been assessed in implanted tumor models rather than in systems in which tumors are grown in their own connective tissue matrix. In this study, the pharmacokinetics, tumor ablation capability and cutaneous photosensitizing capacity of Pf-II were assessed in mice bearing chemically induced or ultraviolet B radiation (UVB)-induced benign skin neoplasms. Intraperitoneal administration of Pf-II (5 mg/kg body weight) to tumor-bearing animals showed maximum tumor: normal skin ratio of the photosensitizer at 72 h. When SENCAR mice bearing chemically induced tumors were irradiated with visible light corresponding to the absorption spectrum of the photosensitizer, up to 89% ablation in tumor volume at 20 d post-irradiation was observed. Animals treated with Pf-II and exposed to visible light showed significant cutaneous photosensitization for at least 6 d after-irradiation. Treatment of SKH-1 hairless mice bearing UVB-induced cutaneous neoplasms with Pf-II exhibited similar pharmacokinetics, skin tumor ablation effects and cutaneous photosensitivity. Our data indicate that Pf-II has significant activity towards the ablation of murine skin benign tumors grown in their own tissue matrix, suggesting that such a murine skin tumor model system could be valuable in evaluating the photodynamic effects of newly developed photosensitizers.