Comparative In Vivo Evaluation of Technetium and Iodine Labels on an Anti-HER2 Affibody for Single-Photon Imaging of HER2 Expression in Tumors

In vivo diagnosis with cancer-specific targeting agents that have optimal characteristics for imaging is an important development in treatment planning for cancer patients. Overexpression of the HER2 antigen is high in several types of carcinomas and has predictive and prognostic value, especially for breast cancer. A new type of targeting agent, the Affibody molecule, was described recently. An Affibody dimer, His6-(ZHER2:4)2 (15.4 kDa), binds to HER2 with an affinity of 3 nmol/L and might be used for the imaging of HER2 expression. The use of 99m Tc might improve the availabilityofthelabeledconjugate,andTc(I)-carbonylchemistry enables the site-specific labeling of the histidine tag on the Affibody molecule. The goals of the present study were to prepare 99m Tc-labeled His6-(ZHER2:4)2 and to evaluate its targeting properties compared with the targeting properties of 125 I-4iodobenzoate-His6-(ZHER2:4)2 [ 125 I-His6-(ZHER2:4)2]. Methods: