Receptor-Mediated Tumor Targeting with Radiolabeled Peptides: There Is More to It than

the binding and animal biodistribution data of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 (Ahx is aminohexanoic acid; DTPA is diethylenetriaminepen-taacetic acid), an analog of glucagon-like peptide-1 (GLP-1) (1). Their results raise high hopes of actually achieving selective and potent receptor-mediated targeting of tumors with a radiolabeled peptide but, at the same time, revive critical issues on the possi-bility of predicting the clinical success, See page 2025 usefulness, and indications of any newly developed radiopharmaceuti