| Early identification of dysplasia in Barrett's esophagus (BE) and the colon remains a critical issue for clinical diagnostic endoscopy, since early discovery directly improves patient survival. Clinical studies have successfully used tissue autofluorescence (AF) with conventional white light endoscopy (WLE) and biopsy for detecting preneoplastic colonic adenomatous polyps, differentiating benign from preneoplastic polyps and identifying BE mucosa in the esophagus. Despite this, in vivo autofluorescence endoscopic detection of early dysplasia continues to be problematic due to suboptimal fluorescence contrast.; The goal of this PhD thesis was to extend previous AF mechanistic studies and explore means of improving in vivo fluorescence endoscopic contrast. First, the AF of isolated living colonic crypts and primary cell cultures of normal colon, hyperplastic and adenomatous polyps was studied at the cellular level in vitro. For BE, fluorescence microscopy was performed on archived ex vivo frozen human tissues of normal esophagus, BE without and with dysplasia, and stomach to characterize the biological origins and possible differences in mucosal AF. Both studies improved our understanding of the biological origins of colon and BE tissue AF. To address suboptimal detection of dysplasia in AF imaging of BE, aminolevulinic acid (ALA) was evaluated in vivo and ex vivo as a diagnostic pro-drug to enhance the fluorescence contrast of dysplasia in BE. The results of these studies were inconsistent. The limited utility of AF and ALA-induced fluorescence for detecting dysplasia in vivo prompted a new approach, using monoclonal antibody-based fluorescent contrast bioconjugate targeting of a tumor-associated mucin antigen overexpressed in human colorectal adenocarcinomas. This agent was developed and evaluated in vitro and in vivo in a xenograft mouse tumor model, yielding significant enhancement of tumor-to-normal contrast. A novel class of fluorescent semiconductor nanoparticles (quantum dots) were evaluated as alternative immunotargeted fluorescence contrast agents in preliminary in vitro and in vivo animal studies. In conclusion, this thesis has advanced our basic understanding of tissue AF in the GI tract, which may translate into improved AF endoscopic imaging technology for enhancing early detection of GI cancers, and offers the distinct possibility of providing real-time non-invasive "molecular endoscopy" for tumor detection in vivo. |
