Preclinical evaluation of anti-HER2 Affibody molecules site-specifically labeled with 111In using a maleimido derivative of NODAGA.

INTRODUCTION

Affibody molecules have demonstrated potential for radionuclide molecular imaging. The aim of this study was to synthesize and evaluate a maleimido derivative of the 1,4,7-triazacyclononane-1-glutaric acid-4,7-diacetic acid (NODAGA) for site-specific labeling of anti-HER2 Affibody molecule.

METHODS

The maleimidoethylmonoamide NODAGA (MMA-NODAGA) was synthesized and conjugated to Z(HER2:2395) Affibody molecule having a C-terminal cysteine. Labeling efficiency, binding specificity to and cell internalization by HER2-expressing cells of [(111)In-MMA-NODAGA-Cys(61)]-Z(HER2:2395) were studied. Biodistribution of [(111)In-MMA-NODAGA-Cys(61)]-Z(HER2:2395) and [(111)In-MMA-DOTA-Cys(61)]-Z(HER2:2395) was compared in mice.

RESULTS

The affinity of [MMA-NODAGA-Cys(61)]-Z(HER2:2395) binding to HER2 was 67 pM. The (111)In-labeling yield was 99.6%±0.5% after 30 min at 60°C. [(111)In-MMA-NODAGA-Cys(61)]-Z(HER2:2395) bound specifically to HER2-expressing cells in vitro and in vivo. Tumor uptake of [(111)In-MMA-NODAGA-Cys(61)]-Z(HER2:2395) in mice bearing DU-145 xenografts (4.7%±0.8% ID/g) was lower than uptake of [(111)In-MMA-DOTA-Cys(61)]-Z(HER2:2395) (7.5%±1.6% ID/g). However, tumor-to-organ ratios were higher for [(111)In-MMA-NODAGA-Cys(61)]-Z(HER2:2395) due to higher clearance rate from normal tissues.

CONCLUSIONS

MMA-NODAGA is a promising chelator for site-specific labeling of targeting proteins containing unpaired cysteine. Appreciable influence of chelators on targeting properties of Affibody molecules was demonstrated.