Fluorescence photometric analysis of Photofrin uptake and the detection of precancerous and true epidermoid lesions

Neoplastic tissue can be detected by its increased fluorescence compared to surrounding normal tissue after the injection of the tumor-localizing compound Photofrin^TM. In- vivo fluorescence photometry is a non-imaging photodetector which detects the 690 nm fluorescence of the porphyrin. The sensitivity of the instrumentation has allowed the detection of micrometastases in both pre-clinical and clinical studies using low, non-photosensitizing levels of the drug. The technique is now being applied to the 9,10 dimethyl-1,2-benzanthracene (DMBA)-induced hamster buccal cheek pouch carcinoma model to obtain data on the correlation between Photofrin uptake and tumor development. This model shows consistent time patterns of tumor development as well as precancerous leukoplakia lesions and has been well documented as an animal model of oral epidermoid carcinogenesis. The buccal cheek pouches of Syrian Golden hamsters were exposed to a 0.5% DMBA in acetone thrice weekly for specified time durations. Hamsters were subsequently injected with 1.0 mg/kg of Photofrin within the various stages of tumor development. Twenty-four hours post-injection, fluorescence due to drug uptake was measured by in-vivo fluorescence photometry. Mucosal tissues were subsequently biopsied and used for extraction assays. Results demonstrate that Photofrin is retained in DMBA treated tissue with a linear relationship between length of application and Photofrin uptake and fluorescence. This relationship establishes that premalignant lesions can be distinguished from normal tissue by Photofrin uptake and fluorescence and suggests that Photofrin uptake and fluorescence can be used in a predictive manner to diagnose and determine the progression of individual lesions.