Aims
We aim to develop and validate a peptide that is specific for epidermal growth factor receptor (EGFR), a cell surface target that is overexpressed in colonic adenomas and is readily accessible for imaging.
Conclusions
We have selected and validated a peptide that can be used as a specific contrast agent to identify colonic adenomas that overexpress EGFR in vivo on fluorescence endoscopy.
Methods
We expressed and purified the extracellular domain of EGFR for use with phage display to identify a peptide QRHKPRE that binds to domain 2 of this target. A near-infrared fluorescence endoscope was used to perform in vivo imaging to validate specific peptide binding to spontaneous colonic adenomas in a mouse model with topical administration. We also validated specific peptide binding to human colonic adenomas on immunohistochemistry and immunofluorescence.
Results
After labeling with Cy5.5, we validated specific peptide binding to EGFR on knockdown and competition studies. Peptide binding to cells occurred within 2.46 min and had an affinity of 50 nm. No downstream signaling was observed. We measured a target-to-background ratio of 4.0±1.7 and 2.7±0.7, for polyps and flat lesions, respectively. On immunofluorescence of human colonic specimens, greater intensity from peptide binding to dysplasia than normal was found with a 19.4-fold difference. Conclusions: We have selected and validated a peptide that can be used as a specific contrast agent to identify colonic adenomas that overexpress EGFR in vivo on fluorescence endoscopy.