Evaluation of Cu-labeled DOTA--Phe-Tyr-octreotide (Cu-DOTA-TOC) for imaging somatostatin receptor-expressing tumors

Hanaoka, Hirofumi*; Tominaga, Hideyuki*; Yamada, Keiichi*; Paudyal, P.*; Iida, Yasuhiko*; Watanabe, Shigeki; Paudyal, B.*; Higuchi, Tetsuya*; Oriuchi, Noboru*; Endo, Keigo*

In-111 (In)-labeled octreotide has been clinically used for imaging somatostatin receptor-positive tumors, and radiolabeled octreotide analogs for positron emission tomography (PET) have been developed. The aim of this study is to produce and fundamentally examine a Cu-labeled octreotide analog, Cu-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid--Phe-Tyr-octreotide (Cu-DOTA-TOC). Cu-DOTA-TOC can be produced in amounts efficient for clinical study with high radiochemical yield. Cu-DOTA-TOC was stable in vitro, but time-dependent transchelation to protein was observed after injection into mice. In biodistribution studies, the radioactivity of Cu was higher than that of In in all organs except kidney. In tumor-bearing mice, Cu-DOTA-TOC showed a high accumulation in the tumors, and the tumor-to-blood ratio reached as high as 8.81 1.17 at 6 h after administration. Cu-DOTA-TOC showed significantly higher accumulation in the tumor than Cu-TETA-OC and Cu-DOTA-OC. PET showed a very clear image of the tumor, which was comparable to that of F-FDG PET and very similar to that of Cu-TETA-OC. Cu-DOTA-TOC clearly imaged a somatostatin receptor-positive tumor and seemed to be a potential PET tracer in the clinical phase.