The nude mouse xenograft system: A model for photodetection and photodynamic therapy in head and neck squamous cell carcinoma

Mechanisms for hematoporphyrin derivative (HPD) localization in malignant tissue and in photodynamic therapy (PDT) have not been established. The authors' experience with human cancer xenografts in nude mice as a tumor system for the experimental study of these mechanisms is described. Human mucosal head and neck squamous cell carcinoma was successfully transplanted to nude mice in 29 per cent of trials and serially passed through multiple generations in three tumor lines. Time required for progressive growth averaged 13.9 days, and 300 mm 3 tumors were obtained in four weeks. Take rates per passage varied, in part because of infection, and exponential growth rates varied among the three lines. However, within a single line exponential growth rates were similar. Average growth constants for the period of exponential growth were 0.14, 0.13, and 0.09 for the three lines. Fluorescent microscopy of excised xenografts revealed HPD fluorescence principally in connective tissue cells. Minimal fluorescence was seen in malignant epithelial cells. Spectrophotometric measures of HPD uptake in homogenized tissue showed highest values in liver. Tumor HPD levels were higher than those for either skin or muscle. The authors conclude that this tumor system can be used effectively to study HPD and PDT in head and neck cancer.