Near-infrared-labeled peptide multimer functions as phage mimic for high affinity, specific targeting of colonic adenomas in vivo

Background: Fluorescent-labeled peptides are being developed to improve the endoscopic detection of colonic dysplasia. Objective: To demonstrate a near-infrared peptide multimer that functions as a phage mimic for in vivo detection of colonic adenomas. Design: A peptide multimer was synthesized by using trilysine as a dendritic wedge to mimic the presentation of peptides on phage, and all peptides, including the multimer, were fluorescent-labeled with Cy5.5. Setting: Small-animal imaging facility. Animal Subjects: Genetically engineered CPC;Apc mice that spontaneously develop colonic adenomas. Intervention: Near-infrared-labeled AKPGYLS peptide multimer was administered topically into the distal colons of the mice, and endoscopic images of adenomas were captured. Fluorescence intensities were quantified by target-to-background (T/B) ratios, and adenoma dimensions were measured with calipers after imaging. Validation of specific peptide binding was performed on cryosectioned specimens and cells by using confocal microscopy and flow cytometry. Main Outcome Measurements: Fluorescence T/B ratios from colonic adenomas and adjacent normal-appearing mucosa. Results: AKP-multimer, monomer, trilysine core, and Cy5.5 resulted in mean (+/- SD) T/B ratios of 3.85 +/- 0.25, 2.21 +/- 0.13, 1.56 +/- 0.12, and 1.19 +/- 0.11, respectively, P < .01 on in vivo imaging. Peptide multimer showed higher contrast and greater specificity for dysplastic crypts as compared with other probes. Peptide multimer demonstrated significantly greater binding to HT29 cells on flow cytometry and fluorescence microscopy in comparison to monomer and trilysine core. A binding affinity of 6.4 nm/L and time constant of 0.1136 minutes(-1) (8.8 minutes) was measured for multimer. Limitations: Only distal colonic adenomas were imaged. Conclusion: Peptide multimers combine strengths of multiple individual peptides to enhance binding interactions and demonstrate significantly higher specificity and affinity for tumor targets. (Gastrointest Endosc 2012;76:1197-206.)