Localization of experimental submucosal esophageal tumor in rabbits by using mono-L-aspartyl chlorin e6 and long-wavelength photodynamic excitation

Background and Objective: To increase the applicability of photodynamic diagnosis with regard to deep-seated tumor, we illuminated tumors with a long-wavelength laser beam after photosensitization with mono-L-aspartyl chlorin e6 (NPe6). Study Design/Materials and Methods: Rabbits with VX2 esophageal tumors were divided into four groups. The control group was not treated, and the other three groups were injected with 1, 2.5, and 5 mg/kg mono-L-aspartyl chlorin e6 (NPe6), respectively. After excitation with a 664-nm laser beam (10 mW, 10 seconds), the fluorescence image and the relative fluorescence intensity (tumor/normal tissue) were recorded every 2 hours up to 8 hours by a newly developed diode laser endoscopic fluorescence imaging system. The tissue concentration of NPe6 was examined by high performance liquid chromatography at 2, 4, and 6 hours after injection with 1 and 5 mg/kg NPe6. Results: The diode laser endoscopic fluorescence imaging system was able to selectively detect fluorescence from submucosal tumor by comparison with the surrounding normal mucosa after NPe6 injection. The fluorescence intensity correlated with NPe6 dose, selectively accumulated in the tumor tissue and relative intensity peaked at 6 hours after injection. No fluorescent images were detected in controls. Conclusion: Given intravenously, NPe6 at a dose of 5 mg/kg and excited with a 664-nm wavelength laser beam 6 hours later can define experimentally induced deep-seated esophageal carcinoma in rabbits, by using an endoscopic fluorescence imaging system.