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

Torun Engfeldt, Anna Orlova, Thuy Tran, Alexander Bruskin, Charles Widström, Amelie Eriksson Karlström, Vladimir Tolmachev

Research output: Contribution to journalArticlepeer-review

75 Citations (Scopus)

Abstract

Purpose: 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 ZHER2:342. The goal of this study was to develop a method for 99mTc labelling of ZHER2:342 using the MAG3 chelator, which was incorporated into ZHER2:342 using peptide synthesis, and evaluate the targeting properties of the labelled conjugate. Methods: MAG3-ZHER2:342 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 99mTc 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 99mTc-MAG3-ZHER2:342 and 125I-para-iodobenzoate -ZHER2:342 was compared 6 h p.i. Results: Synthetic MAG3-Z HER2:342 possessed an affinity of 0.2 nM for HER2 receptors. The peptide was labelled with 99mTc with an efficiency of about 75-80%. Labelled 99mTc-MAG3-ZHER2:342 retained capacity to bind specifically HER2-expressing SKOV-3 cells in vitro. 99mTc-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. Conclusion: Incorporation of a mercaptoacetyl-containing chelating sequence during chemical synthesis enabled site-specific 99mTc labelling of the ZHER2:342 Affibody molecule with preserved targeting capacity.

Original languageEnglish
Pages (from-to)722-733
Number of pages12
JournalEuropean Journal of Nuclear Medicine and Molecular Imaging
Volume34
Issue number5
DOIs
Publication statusPublished - May 2007
Externally publishedYes

Keywords

  • Biodistribution
  • HER2
  • Peptide
  • Targeting
  • Technetium-99m

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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