In Vivo Multi-Spectral Wide-Field Fluorescence Detection of Dysplasia in the Mouse

BACKGROUND & AIM: The diagnosis of colitis associated cancer (CAC) remains difficult despite technologic improvements in modern endoscopes. It can be challenging to see a tumor against a background of inflammation. Recently, we demonstrated that ovarian cancer peritoneal implants can be easily visualized In Vivo using a fast reacting gamma-glutamyltransferase (GGT) activatable optical probe, which only fluoresces in the presence of GGT activity. The aim of this study was to test this agent in the context of a colitis associated carcinogenesis model. METHODS: Expression of GGT in colon cancer cell lines was examined with the GGT activatable probe (1 μM) using a fluorescencemicroscopy and a flow cytometry. A mouse model of CAC induced by azoxymethane (AOM) and dextran sulfate sodium (DSS) was then used for the In Vivo experiment. The distal colon up to the splenic flexure was examined with conventional white light and fluorescence micro-colonoscopy before and after intrarectal administration (50 μM/400 μL) of the GGT activatable probe. RESULTS: The GGT activatable probe was activated as early as 5 min after application. Microscopy revealed localization predominantly in the cytosol. Expression of GGT was higher in colon cancer cells than in normal human colon cells. With In Vivo fluorescence micro-colonoscopy, it was possible to detect lesions as early as 5 minutes after intrarectal administration of the probe, and fluorescence lasted at least 30 minutes with high signal-to-background ratios. By switching to white light imaging, fluorescent lesions could be superimposed on sites of tumor. Fluorescence guided biopsy revealed that all fluorescent lesions contained cancer and/or low-to-high grade dysplasia (n = 16), whereas 3 out of 12 non-fluorescent lesions contained low grade dysplasia while the remainder showed no neoplasia/dysplasia. Furthermore, tumor progression in the same mouse could be followed by repeat micro-colonoscopy after application of the GGT activatable probe. CONCLUSIONS: These results indicate that it is possible to enhance the detection of CAC using a GGT activatable probe during endoscopy. This could have broad implications for the early detection of patients with long standing bowel inflammation who are at increased risk for the development of colon cancer.