The
epidermal growth factor receptor (EGFR) is a member of the erbB family of receptors and is overexpressed in many
tumor types. A repebody is a newly designed nonantibody
protein scaffold for
tumor targeting that contains
leucine-rich repeat modules. In this study, 3 64Cu-labeled anti-EGFR repebodies with different
chelators were synthesized, and their
biologic characteristics were assessed in cultured cells and
tumor-bearing mice. Methods: Repebodies were synthesized with the
chelators 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-N,N',N,″-triacetic
acid trihydrochloride ([p-SCN-Bn]-
NOTA), 2,2',2″-(10-(2-(2,5-dioxopyrrolidin-1-yloxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl) triacetic
acid (
DOTA-
N-hydroxysuccinimide ester), or 1-(p-isothiocyanatobenzyl)diethylenetriamine pentaacetic
acid trihydrochloride ([p-SCN-Bn]-
DTPA) in 1.0 M NaHCO3
buffer (pH 9.2) for 24 h. Purified
NOTA-,
DOTA-, and
DTPA-conjugated repebody were radiolabeled with 64Cu in 0.1 M NH4OAc
buffer (pH 5.5). To compare the EGFR-binding affinities of the repebodies, cellular uptake studies were performed with the human
non-small cell lung cancer cell line H1650 (high expression of EGFR) and the human
colon adenocarcinoma cell line SW620 (low expression of EGFR). Biodistribution and small-animal PET imaging studies were performed using H1650
tumor-bearing mice. Results: Radiochemical yields of the 64Cu-labeled repebodies were approximately 70%-80%. Cellular uptake of the
NOTA-,
DOTA-, and
DTPA-repebodies was over 4-fold higher in H1650 cells than in SW620 cells at 1 h. The 3 repebodies had accumulated specifically in H1650
tumor-bearing nude mice by 1 h after
intravenous injection and were retained for over 24 h, as measured by the percentage injected dose per gram of tissue (%ID/g).
Tumor uptake of all repebodies increased from 1 to 6 h (at 1 h, 6.28, 8.46, and 6.91 %ID/g for
NOTA-,
DOTA-, and
DTPA-repebody, respectively; at 6 h, 9.4, 8.28, and 10.1 %ID/g, respectively). H1650
tumors were clearly visible after injection of each repebody, with high
tumor-to-background ratios (at 1 h, 3.43, 4.89, and 2.38 for
NOTA-,
DOTA-, and
DTPA-repebody, respectively; at 6 h, 3.05, 4.36, and 2.08; at 24 h, 3.81, 4.58, and 2.86). Conclusion: The 3 64Cu-repebody complexes demonstrated specific and rapid uptake in EGFR-expressing
tumors within 1 h and may have potential as novel EGFR imaging agents for PET.