Pre-clinical evaluation of [111In]-benzyl-DOTA-Z(HER2:342), a potential agent for imaging of HER2 expression in malignant tumors.

ABSTRACT

Imaging of expression of human epidermal growth factor receptor type 2 (HER2) in breast carcinomas may help to select patients eligible for trastuzumab therapy. The Affibody molecule Z(HER2342) is a small (7-kDa) non-immunoglobulin affinity protein, which binds to HER2 with a picomolar affinity. Previously, a benzyl-DTPA conjugate of Z(HER2342) was labeled with 111In and demonstrated good targeting in murine xenografts. We considered that the use of the macrocyclic chelator DOTA could increase the label stability and enhance a choice of nuclides, which could be used as a label for Z(HER2342). The goal of this study was the preparation and pre-clinical evaluation of the indium-111- labeled DOTA-derivative of Z(HER2342). Isothiocyanate-benzyl-DOTA was coupled to recombinant Z(HER2342), and the conjugate was efficiently labeled with 111In at 60 degrees C. The specificity of 111In-benzyl-DOTA-Z(HER2342) binding to HER2 was confirmed in vitro using HER2-expressing breast carcinoma BT474 and ovarian carcinoma SKOV-3 cell lines. Biodistribution of 111In-benzyl-DOTA-Z(HER2342) was performed in nude mice bearing LS174T xenografts and compared directly with the biodistribution of 111In-benzyl-DTPA-Z(HER2342). In vivo, 111In-benzyl-DOTA-Z(HER2342) demonstrated quick clearance from blood and non-specific organs except the kidneys. Four hours post injection (pi), the tumor uptake of 111In-benzyl-DOTA-Z(HER2342) (4.4+/-1.0% IA/g) was specific and the tumor-to-blood ratio was 23. The use of benzyl-DTPA provided higher tumor-to-blood and tumor-to-liver ratios. gamma-camera imaging showed clear visualization of HER2-expressing xenografts using 111In-benzyl-DOTA-Z(HER2342). 111In-benzyl-DOTA-Z(HER2342) has a potential for imaging of HER2 expression in malignant tumors.