d) Corresponding histology (H&E) at 20X magnification. In Nec-4 animals, probes Nec-4 were studied that GRB2 were activated to emit light in the near infrared (NIR) spectrum by cathepsin B, a cystein protease that is overexpressed by many murine and human colorectal neoplasias(5). impact on future endoscopy in gastroenterology. strong class=”kwd-title” Keywords: Molecular imaging, endoscopy, confocal endomicroscopy, autofluorescence imaging, malignancy, EGFR Introduction Molecular imaging has raised increasing interest in the field of gastrointestinal (GI) endoscopy with the potential to significantly impact on our current diagnostic and therapeutic algorithms and biomedical research. Molecular imaging encompasses modalities that enable minimally-invasive visualization of disease-specific morphologic or functional tissue alterations based on the specific molecular signature of single cells or whole tissue. This discipline has been strongly driven by recent developments to provide individualized molecularly targeted therapies in the field of oncology and C to a lesser extent C inflammatory diseases. At the same time, technological and scientific developments in endoscopy have provided us with new imaging devices to enhance detection and characterization of early neoplastic lesions, such as chromoendoscopy and virtual chromoendoscopy techniques, surface enhancement modalities in conjunction with high-resolution endoscopes and ultrahigh magnification during endoscopy. While subsequent endoscopic therapy usually relies on the detection of lesions at an early stage, recent studies have still reported a significant miss rate throughout the entire GI tract. Molecular imaging Nec-4 in GI endoscopy therefore aims at identification and characterization of lesions based on their molecular fingerprint rather than their morphology and ultimately at increasing the efficiency of endoscopic screening and surveillance. This usually requires detection of biomarkers with a device compatible with use in humans. On the basis of insights gathered from animal experiments most pre-clinical and clinical trials have utilized fluorescent detection of biomarkers. Ideally, molecular endoscopy combines wide-field macroscopic imaging, providing red flag detection of areas of interest within the large surface of the GI mucosa and a modality to provide targeted microscopic characterization of such a lesion. Optical contrast /Contrast brokers for molecular imaging Optical contrast Nec-4 can arise from endogenous fluorophores or exogenously administered contrast brokers. In autofluorescence imaging (AFI), tissue excitation with light of a short wavelength results in emission of a longer wavelength. Alterations in the autofluorescence pattern of neoplastic tissue have been attributed to altered metabolic activity, such as FAD, NADH, and porphyrins as well as hemoglobin content and a breakdown of collagen fiber cross-links. This results in a shift towards red spectrum when such tissue is excited with blue light. In addition, typical morphologic indicators of malignancy such as increased nuclear-to-cytoplasmic ratio influence the propagation of light. The altered autofluorescence signal is usually translated into false colored images, usually depicting neoplasia in purple against a green background of healthy mucosa. Many of these tissue alterations are not specific for neoplasia, and the resultant AFI image is a combination of multiple molecular alterations. Therefore, AFI suffers from a low specificity and a high false-positive rate but benefits from the fact that no contrast agent has to be applied during endoscopy. On the other hand, the intrinsic transmission can be enhanced by the application of precursor molecules that are metabolized to photodynamically active substances. 5-aminolevulinic acid (5-ALA) is the most widely used agent. Much like AFI, inflammation negatively impacts around the specificity. Induced fluorescence is usually several orders of magnitudes more intense than autofluorescence. Exogenous molecular probes usually target a disease-specific biomarker(1). Such probes include antibodies, antibody fragments, peptides, nanoparticles and wise activatable probes (Fig. 1). Several studies have used fluorescently labeled antibodies against epitopes that are commonly overexpressed in most gastrointestinal cancers, such as vascular endothelial growth factor (VEGF) or epidermal growth factor receptor (EGFR) (2, 3). Antibodies bind to their target structure in a highly selective manner, thereby optimizing the signal-to-background ratio. In addition, the biologic relevance of their targets is usually often well established and exploited therapeutically even today, such as by Cetuximab or Panitumumab (against EGFR) or Bevacizumab (against VEGF). Imaging of tumors after a first labeled test dose could potentially predict response to targeted chemotherapy. On the other hand, antibodies may Nec-4 confer allergic reactions after systemic application, and their diffusion across epithelial borders and delivery to target structures is usually slow due to their high molecular excess weight. Peptides are low molecular excess weight molecules that consist of a few amino acids in length and face fewer of these limitations(4). The challenge in developing these peptides is usually to select unique sequences that have high specificity and affinity towards the target structures. Antibody fragments could serve as an alternative. Nanoparticles such as quantum dots and metallic nanoparticles can be coated with significantly stronger fluorophores. In animal and cell culture studies, they allow targeting of even minute amounts of target structures, and can be loaded with ligands to.