Photodynamic diagnosis of a human nasopharyngeal carcinoma xenograft model using the novel Chlorin e6 photosensitizer Fotolon

The current study investigates the potential of the photosensitizer Fotolon as a photodynamic diagnostic agent in an in vivo system of human nasopharyngeal carcinoma (NPC) cells. Fotolon (formerly known as Photolon) represents a complex of trisodium salt Chlorin e6 and polyvinylpyrrolidone (PVP). It is a photosensitizing agent that selectively accumulates in tumour tissues. A poorly differentiated human nasopharyngeal carcinoma cell line CNE-2 was xenografted on 6-8 weeks old male balb/c nude mice for our photodynamic diagnostic (PDD) studies. A fluorescence endoscope system was used to perform the in vivo macroscopic fluorescence digital imaging of tumours on the mice. The macroscopic images were further analyzed for distribution of fluorescence intensity. Laser fluorescence confocal microscopy was used to capture microscopic fluorescence images of the tumour tissue. In our PDD studies, we observed intense fluorescence in the tumour and tumour vasculature of human NPC xenografts on nude mice as early as 15-min post administration of Fotolon. High fluorescence selectivity in the tumour tissue was observed between 3-h and 6-h time points. The tumour to normal tissue selectivity ratio was highest at 6 h. The microfluorescence tumour imaging shows similar trends confirming the macroscopic fluorescence data. Fotolon shows much promise as a good photodiagnostic agent.