Epidermal growth factor receptor-2 (EGFR-2) has been implicated in the pathogenesis of breast and other
carcinomas. In this report, we tested the ability of a bacteriophage selected
peptide KCCYSL, radiolabeled with ⁶⁴Cu, to image EGFR-2 expressing
breast tumors in vivo by positron emission tomography (PET). We evaluated and compared the in vivo tissue distribution and imaging properties of ⁶⁴Cu-X-(Gly-Ser-Gly)-KCCYSL
peptide (X = 1,4,7,10, tetraazacyclododecane-N,N',N'',N'''-tetracetic
acid, [
DOTA] 1,4,8,11-tetraazabicyclo[6.6.2]
hexadecane-4,11-diacetic
acid [CB-TE2A], and 1,4,7-
triazacyclononane-1,4,7-triacetic
acid [
NOTA]
chelators) in a human
breast cancer xenograft mouse model using dual modality PET and computed tomography (CT). The synthesized
peptides DO3A-GSG-KCCYSL, CB-TE2A-GSG-KCCYSL, and NO2A-GSG-KCCYSL were purified, radiolabeled with ⁶⁴Cu, and evaluated for human
breast cancer cell (MDA-MB-435) binding, 50% inhibitory concentration, and serum stability. In vivo pharmacokinetic and small animal PET/CT imaging studies were performed using SCID mice bearing MDA-MB-435 xenografts. The radiolabeled
peptides bound with an 50% inhibitory concentration of 42.0 ± 10.2 nM (DO3A), 31 ± 7.9 nM (CB-TE2A), and 44.2 ± 6.6 nM (NO2A) to cultured MDA-MB-435 cells. All of the radiolabeled
peptides were stable in vitro. The
tumor uptake of DO3A, CB-TE2A, and NO2A
peptides were 0.73 ± 0.15 percent injected dose per gram (%ID/g), 0.64 ± 0.08%ID/g, and 0.52 ± 0.04%ID/g, respectively at 1 hour. Liver uptake for the ⁶⁴Cu-DO3A-peptide (1.68 ± 0.42%ID/g) was more than that of the ⁶⁴Cu-CB-TE2A-peptide (0.52 ± 0.02% ID/g) and ⁶⁴Cu-NO2A-peptide (0.48 ± 0.05%ID/g) at 2 hours. PET/CT studies revealed successful
tumor uptake of ⁶⁴Cu-
peptides at 2 hours postinjection. In vivo kidney retention was observed with all of the radiolabeled
peptides. The optimization of bifunctional
chelators improves the pharmacokinetic properties of the ⁶⁴Cu-labeled GSG-KCCYSL
peptide, which enables the selection of a suitable
peptide homolog as a PET imaging agent for EGFR-2 expressing
breast carcinomas.