To overcome the problem of overlooking
colorectal tumors, a new and highly sensitive modality of colonoscopy is needed. Moreover, it is also important to establish a new modality to evaluate viable
tumor volume in primary lesions of
colorectal cancer (CRC) during
chemotherapy. Therefore, we carried out molecular imaging of
colorectal tumors targeting
epidermal growth factor receptor (EGFR), which is highly expressed on
tumor cells, for evaluating chemotherapeutic efficacy and for endoscopic detection of colorectal
adenomas. We first attempted to image five CRC cell lines with various levels of EGFR expression using an Alexa Fluor-labeled anti-EGFR
monoclonal antibody (AF-EGFR-Ab). A strong fluorescence signal was observed in the cells depending on the level of EGFR expression. When nude mice xenografted with LIM1215 CRC cells, which highly express EGFR, were i.v. injected with AF-EGFR-Ab, a strong fluorescence signal appeared in the
tumor with a high signal to noise ratio, peaking at 48 hours after injection and then gradually decreasing, as shown using an IVIS Spectrum system. When the xenografted mice were treated with
5-fluorouracil, fluorescence intensity in the
tumor decreased in proportion to the viable
tumor cell volume. Moreover, when the colorectum of
azoxymethane-treated rats was observed using a thin fluorescent
endoscope with AF-EGFR-Ab, all 10 small colorectal
adenomas (≤3 mm) were detected with a clear fluorescence signal. These preliminary results of animal experiments suggest that EGFR-targeted fluorescent molecular imaging may be useful for quantitatively evaluating cell viability in CRC during
chemotherapy, and also for detecting small
adenomas using a fluorescent
endoscope.