Targeting of HER2-expressing tumors with a site-specifically 99mTc-labeled recombinant affibody molecule, ZHER2:2395, with C-terminally engineered cysteine.

Abstract

UNLABELLED:

The detection of human epidermal growth factor receptor type 2 (HER2) expression in malignant tumors provides important information influencing patient management. Radionuclide in vivo imaging of HER2 may permit the detection of HER2 in both primary tumors and metastases by a single noninvasive procedure. Small (7 kDa) high-affinity anti-HER2 Affibody molecules may be suitable tracers for SPECT visualization of HER2-expressing tumors. The use of generator-produced (99m)Tc as a label would facilitate the prompt translation of anti-HER2 Affibody molecules into use in clinics.

METHODS:

A C-terminal cysteine was introduced into the Affibody molecule Z(HER2:342) to enable site-specific labeling with (99m)Tc. Two recombinant variants, His(6)-Z(HER2:342)-Cys (dissociation constant [K(D)], 29 pM) and Z(HER2:2395)-Cys, lacking a His tag (K(D), 27 pM), were labeled with (99m)Tc in yields exceeding 90%. The binding specificity and the cellular processing of Affibody molecules were studied in vitro. Biodistribution and gamma-camera imaging studies were performed in mice bearing HER2-expressing xenografts.

RESULTS:

(99m)Tc-His(6)-Z(HER2:342)-Cys was capable of targeting HER2-expressing SKOV-3 xenografts in SCID mice, but the liver radioactivity uptake was high. A series of comparative biodistribution experiments indicated that the presence of the His tag caused elevated accumulation in the liver. (99m)Tc-Z(HER2:2395)-Cys, not containing a His tag, showed low uptake in the liver and high and specific uptake in HER2-expressing xenografts. Four hours after injection, the radioactivity uptake values (percentage of injected activity per gram of tissue [%IA/g]) were 6.9 +/- 2.5 (mean +/- SD) %IA/g in LS174T xenografts (moderate level of HER2 expression) and 15 +/- 3 %IA/g in SKOV-3 xenografts (high level of HER2 expression). The corresponding tumor-to-blood ratios were 88 +/- 24 and 121 +/- 24, respectively. Both LS174T and SKOV-3 xenografts were clearly visualized with a clinical gamma-camera 1 h after injection of (99m)Tc-Z(HER2:2395)-Cys.

CONCLUSION:

The Affibody molecule (99m)Tc-Z(HER2:2395)-Cys is a promising tracer for SPECT visualization of HER2-expressing tumors.

• Authors: Sara Ahlgren, Helena Wållberg, Thuy A Tran, Charles Widström, Magnus Hjertman, Lars Abrahmsén, Dietmar Berndorff, Ludger M Dinkelborg, John E Cyr, Joachim Feldwisch, Anna Orlova, Vladimir Tolmachev
• Journal: Journal of nuclear medicine : official publication, Society of Nuclear Medicine (J Nucl Med) Vol. 50 Issue 5 Pg. 781-9 (May 2009) ISSN: 0161-5505 [Print] United States
• PMID: 19372467 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• (99m)Tc-Z(HER2:2395)-Cys
• Organotechnetium Compounds
• Radiopharmaceuticals
• Recombinant Fusion Proteins
• Recombinant Proteins
• Receptor, ErbB-2
• Cysteine

Topics

• Adenocarcinoma (diagnostic imaging, metabolism)
• Animals
• Cysteine (pharmacokinetics)
• Drug Delivery Systems (methods)
• Female
• Metabolic Clearance Rate
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Mice, SCID
• Molecular Probe Techniques
• Organ Specificity
• Organotechnetium Compounds (pharmacokinetics)
• Radiopharmaceuticals (pharmacokinetics)
• Receptor, ErbB-2 (metabolism)
• Recombinant Fusion Proteins (pharmacokinetics)
• Recombinant Proteins (pharmacokinetics)
• Tissue Distribution
• Tomography, Emission-Computed, Single-Photon (methods)