Peptide Targeted Imaging of Cancer

Abstract

After the discovery of several specific peptide receptors in a variety of cancer types more than 10 years ago, radiolabeled peptide analogs with adequate stability, receptor binding properties, and biokinetic behavior were introduced for imaging of neuroendocrine tumors, several adenocarcinomas, lymphoma, and melanoma. Although initially ¹²³I or ¹¹¹In were used for labeling, recent efforts have also concentrated on ^99mTc or PET-radionuclides (¹⁸F,⁶⁸Ga), as they result in better image resolution with lower radiation dose to patients. Scintigraphy with labeled somatostatin analogs (^99mTc, ¹¹¹In,¹⁸F,⁶⁸Ga), with ¹²³I-labeled vasoactive intestinal peptide, and recently ^99mTc-bombesin/GRP-or-¹¹¹In gastrin analogs, have shown a mean sensitivity of greater than 85% to localize deposits of tumors, with appropriate receptor expression frequently scarcely visible with other imaging procedures. Moreover, these observations introduced peptide-targeted metabolic radiotherapy for metastatic cancers. This development has produced a considerable amount of preclinical studies to broaden the impact of labeled peptide ligands on the management of cancer.