Molecular confocal laser endomicroscopy: a novel technique for in vivo cellular characterization of gastrointestinal lesions

Abstract

While flexible endoscopy is essential for macroscopic evaluation, confocal laser endomicroscopy (CLE) has recently emerged as an endoscopic method enabling visualization at a cellular level. Two systems are currently available, one based on miniprobes that can be inserted via a conventional endoscope or via a needle guided by endoscopic ultrasound. The second system has a confocal microscope integrated into the distal part of an endoscope. By adding molecular probes like fluorescein conjugated antibodies or fluorescent peptides to this procedure (either topically or systemically administered during on-going endoscopy), a novel world of molecular evaluation opens up. The method of molecular CLE could potentially be used for estimating the expression of important receptors in carcinomas, subsequently resulting in immediate individualization of treatment regimens, but also for improving the diagnostic accuracy of endoscopic procedures by identifying otherwise invisible mucosal lesions. Furthermore, studies have shown that fluorescein labelled drugs can be used to estimate the affinity of the drug to a target organ, which probably can be correlated to the efficacy of the drug. However, several of the studies in this research field have been conducted in animal facilities or in vitro, while only a limited number of trials have actually been carried out in vivo. Therefore, safety issues still needs further evaluations. This review will present an overview of the implications and pitfalls, as well as future challenges of molecular CLE in gastrointestinal diseases.

Keywords: Barrett’s esophagus; Colorectal carcinoma; Confocal laser endomicroscopy; Endoscopy imaging; Gastric carcinoma; Inflammatory bowel disease.

Figure 1

Molecular imaging with labelled antibodies using the confocal laser endomicroscopy system. Antibodies (blue) labelled with a fluorochrome (FITC or Alexa-Fluor 488) (green) bind to a specific target (red triangles) expressed on the plasma membrane of cells in the mucosal layer in the gastrointestinal tract (purple). The confocal laser endomicroscopy (CLE) scope (black and blue tube) excites the fluorochrome with a defined wavelength of 488 nm (yellow). Light is subsequently emitted and detected by the CLE scope.

Figure 2

In vivo epidermal growth factor receptor staining in a human colorectal cancer xenograft (SW480) after intratumoural injection of fluorescein isothiocyanate-labelled anti-epidermal growth factor receptor-antibody. The edge length is 475 μm. Courtesy of Dr. M. Hoetker and Prof. M. Goetz, Tuebingen, Germany.

Figure 3

Molecular confocal laser endomicroscopy staining with Alexa-Fluor 488 labelled anti-CD31 antibodies. As CD31 is an endothelial marker, the structures seen in the image are microvessels in a colonic adenocarcinoma.