Imaging of HER2-expressing tumours using a synthetic Affibody molecule containing the 99mTc-chelating mercaptoacetyl-glycyl-glycyl-glycyl (MAG3) sequence

• Published in: European journal of nuclear medicine and molecular imaging 2007-05, Vol.34 (5), p.722-733
• Main Authors: Engfeldt, Torun, Orlova, Anna, Tran, Thuy, Bruskin, Alexander, Widström, Charles, Karlström, Amelie Eriksson, Tolmachev, Vladimir
• Format: Article
• Language: English
• Subjects: Animals; Antibodies; Biodistribution; Biophysics; Biosensing Techniques; Biotechnology; Cell Line, Tumor; Female; Gene expression; HER2; Humans; MEDICIN; Medicin och hälsovetenskap; MEDICINE; Mice; Mice, Inbred BALB C; Neoplasm Transplantation; Neoplasms - diagnosis; Neoplasms - diagnostic imaging; Nuclear medicine; Peptide; Peptides; Peptides - chemistry; Radionuclide Imaging; Radiopharmaceuticals - pharmacokinetics; Receptor, ErbB-2 - metabolism; Spectrometry, Mass, Electrospray Ionization; Targeting; Technetium Tc 99m Mertiatide - pharmacokinetics; Technetium-99m; Tumors
• ISSN: 1619-7070; 1619-7089; 1619-7089
• DOI: 10.1007/s00259-006-0266-4

Expression of human epidermal growth factor receptor type 2 (HER2) in malignant tumours possesses well-documented prognostic and predictive value. Non-invasive imaging of expression can provide valuable diagnostic information, thereby influencing patient management. Previously, we reported a phage display selection of a small (about 7 kDa) protein, the Affibody molecule Z(HER2:342), which binds HER2 with subnanomolar affinity, and demonstrated the feasibility of targeting of HER2-expressing xenografts using radioiodinated Z(HER2:342). The goal of this study was to develop a method for (99m)Tc labelling of Z(HER2:342) using the MAG3 chelator, which was incorporated into Z(HER2:342) using peptide synthesis, and evaluate the targeting properties of the labelled conjugate. MAG3-Z(HER2:342) was assembled using Fmoc/tBu solid phase peptide synthesis. Biochemical characterisation of the agent was performed using RP-HPLC, ESI-MS, biosensor studies and circular dichroism. A procedure for (99m)Tc labelling in the presence of sodium/potassium tartrate was established. Tumour targeting was evaluated by biodistribution study and gamma camera imaging in xenograft-bearing mice. Biodistribution of (99m)Tc-MAG3-Z(HER2:342) and (125)I-para-iodobenzoate -Z(HER2:342) was compared 6 h p.i. Synthetic MAG3-Z(HER2:342) possessed an affinity of 0.2 nM for HER2 receptors. The peptide was labelled with (99m)Tc with an efficiency of about 75-80%. Labelled (99m)Tc-MAG3-Z(HER2:342) retained capacity to bind specifically HER2-expressing SKOV-3 cells in vitro. (99m)Tc-MAG3-Z(HER2:342) showed specific tumour targeting with a contrast similar to a radioiodinated analogue in mice bearing LS174T xenografts. Gamma camera imaging demonstrated clear and specific visualisation of HER2 expression. Incorporation of a mercaptoacetyl-containing chelating sequence during chemical synthesis enabled site-specific (99m)Tc labelling of the Z(HER2:342) Affibody molecule with preserved targeting capacity.