Effect of a radiolabel biochemical nature on tumor-targeting properties of EpCAM-binding engineered scaffold protein DARPin Ec1.

Abstract

Radionuclide-based imaging of molecular therapeutic targets might facilitate stratifying patients for specific biotherapeutics. New type of imaging probes, based on designed ankyrin repeat proteins (DARPins), have demonstrated excellent contrast of imaging of human epidermal growth factor type 2 (HER2) expression in preclinical models. We hypothesized that labeling approaches, which result in lipophilic radiometabolites (non-residualizing labels), would provide the best imaging contrast for DARPins that internalize slowly after binding to cancer cells. The hypothesis was tested using DARPin Ec1 that binds to epithelial cell adhesion molecule (EpCAM). EpCAM is a promising therapeutic target. Ec1 was labeled with 125I using two methods to obtain the non-residualizing labels, while residualizing labels were obtained by labeling it with 99mTc. All labeled Ec1 variants preserved target specificity and picomolar binding affinity to EpCAM-expressing pancreatic adenocarcinoma BxPC-3 cells. In murine models, all the variants provided similar tumor uptake. However, 125I-PIB-H6-Ec1 had noticeably lower retention in normal tissues, which provided appreciably higher tumor-to-organ ratios. Furthermore, 125I-PIB-H6-Ec1 demonstrated the highest imaging contrast in preclinical models than any other EpCAM-imaging agent tested so far. In conclusion, DARPin Ec1 in combination with a non-residualizing label is a promising probe for imaging EpCAM expression a few hours after injection.

• Authors: Sergey M Deyev, Anzhelika Vorobyeva, Alexey Schulga, Ayman Abouzayed, Tyran Günther, Javad Garousi, Elena Konovalova, Haozhong Ding, Torbjörn Gräslund, Anna Orlova, Vladimir Tolmachev
• Journal: International journal of biological macromolecules (Int J Biol Macromol) Vol. 145 Pg. 216-225 (Feb 15 2020) ISSN: 1879-0003 [Electronic] Netherlands
• PMID: 31863835 (Publication Type: Journal Article)
• Copyright: Copyright © 2019 Elsevier B.V. All rights reserved.

Chemical References

• Biomarkers, Tumor
• EPCAM protein, human
• Epithelial Cell Adhesion Molecule
• Iodine Radioisotopes
• ERBB2 protein, human
• Receptor, ErbB-2

Topics

• Adenocarcinoma (diagnostic imaging, genetics, metabolism, pathology)
• Animals
• Biological Availability
• Biomarkers, Tumor (genetics, metabolism)
• Endocytosis
• Epithelial Cell Adhesion Molecule (genetics, metabolism)
• Gene Expression
• HT29 Cells
• Heterografts
• Humans
• Iodine Radioisotopes
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Pancreatic Neoplasms (diagnostic imaging, genetics, metabolism, pathology)
• Positron-Emission Tomography
• Protein Binding
• Protein Engineering (methods)
• Receptor, ErbB-2 (genetics, metabolism)
• Tissue Distribution
• Tomography, Emission-Computed, Single-Photon