111In-labeled KCCYSL peptide as an imaging probe for ErbB-2-expressing ovarian carcinomas

Aberrant expression of ErbB-2, a member of the epidermal growth factor family of receptors, has been implicated in the formation of various malignancies including ovarian cancer. The objective of this study was to determine whether the phage display-selected ErbB-2 targeting peptide, KCCYSL, once radiolabeled with In-111 would serve as a tumor targeting and single photon emission computed tomography (SPECT/CT) imaging agent in a mouse model of human ovarian carcinoma expressing ErbB-2. The KCCYSL peptide was synthesized with a chelator 1,4,7,10-tetra-azacyclododecane-N,N',N '',N '''-tetraacetic acid (DOTA), and a Gly-Ser-Gly (GSG) spacer between DOTA and amino terminus of the peptide and radiolabeled with (InCl3)-In-111. In vitro cell binding studies indicated that In-111-DOTA-GSG-KCCYSL bound to cultured ovcar-3 carcinoma cells. Bio-distribution studies in scid mice bearing human ovcar-3 tumor xenografts revealed a tumor uptake of 0.50 +/- 0.05 percent injected dose per gram (%ID/g) at 1 h, and 0.39 +/- 0.1 %ID/g at 2h. Blocking studies with non-radiolabeled counterpart indicated a partial inhibition (41%) (P = 0.04) in tumor uptake of In-111-DOTA-GSG-KCCYSL. In vivo tumor uptake of In-111-DOTA-GSG-KCCYSL was clearly evident through SPECT/CT images after 2 h post injection. These studies suggest the potential of this peptide as a radiopharmaceutical for imaging of ErbB-2-expressing ovarian tumors.