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Influence of Macrocyclic Chelators on the Targeting Properties of 68Ga-Labeled Synthetic Affibody Molecules: Comparison with 111In-Labeled Counterparts
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Biomedical Radiation Sciences. (Vladimir Tolmachev)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Biomedical Radiation Sciences. (Vladimir Tolmachev)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Preclinical PET Platform.ORCID iD: 0000-0001-6120-2683
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2013 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 8, no 8, e70028- p.Article in journal (Refereed) Published
Abstract [en]

Affibody molecules are a class of small (7 kDa) non-immunoglobulin scaffold-based affinity proteins, which have demonstrated substantial potential as probes for radionuclide molecular imaging. The use of positron emission tomography (PET) would further increase the resolution and quantification accuracy of Affibody-based imaging. The rapid in vivo kinetics of Affibody molecules permit the use of the generator-produced radionuclide 68Ga (T1/2 = 67.6 min). Earlier studies have demonstrated that the chemical nature of chelators has a substantial influence on the biodistribution properties of Affibody molecules. To determine an optimal labeling approach, the macrocyclic chelators 1,4,7,10-tetraazacylododecane-1,4,7,10-t​etraaceticacid (DOTA), 1,4,7-triazacyclononane-N,N,N-triacetic acid (NOTA) and 1-(1,3-carboxypropyl)-1,4,7- triazacyclononane-4,7-diacetic acid (NODAGA) were conjugated to the N-terminus of the synthetic Affibody molecule ZHER2:S1 targeting HER2. Affibody molecules were labeled with 68Ga, and their binding specificity and cellular processing were evaluated. The biodistribution of 68Ga-DOTA-ZHER2:S1, 68Ga-NOTA-ZHER2:S1 and 68Ga-NODAGA-ZHER2:S1, as well as that of their 111In-labeled counterparts, was evaluated in BALB/C nu/nu mice bearing HER2-expressing SKOV3 xenografts. The tumor uptake for 68Ga-DOTA-ZHER2:S1 (17.9±0.7%IA/g) was significantly higher than for both 68Ga-NODAGA-ZHER2:S1 (16.13±0.67%IA/g) and 68Ga-NOTA-ZHER2:S1 (13±3%IA/g) at 2 h after injection. 68Ga-NODAGA-ZHER2:S1 had the highest tumor-to-blood ratio (60±10) in comparison with both 68Ga-DOTA-ZHER2:S1 (28±4) and 68Ga-NOTA-ZHER2:S1 (42±11). The tumor-to-liver ratio was also higher for 68Ga-NODAGA-ZHER2:S1 (7±2) than the DOTA and NOTA conjugates (5.5±0.6 vs.3.3±0.6). The influence of chelator on the biodistribution and targeting properties was less pronounced for 68Ga than for 111In. The results of this study demonstrate that macrocyclic chelators conjugated to the N-terminus have a substantial influence on the biodistribution of HER2-targeting Affibody molecules labeled with 68Ga.This can be utilized to enhance the imaging contrast of PET imaging using Affibody molecules and improve the sensitivity of molecular imaging. The study demonstrated an appreciable difference of chelator influence for 68Ga and 111In.

Place, publisher, year, edition, pages
2013. Vol. 8, no 8, e70028- p.
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
URN: urn:nbn:se:uu:diva-205597DOI: 10.1371/journal.pone.0070028ISI: 000324518400033PubMedID: 23936372OAI: oai:DiVA.org:uu-205597DiVA: diva2:642149
Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2015-10-01Bibliographically approved
In thesis
1. Affibody Molecules for PET Imaging
Open this publication in new window or tab >>Affibody Molecules for PET Imaging
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Optimization of Affibody molecules would allow for high contrast imaging of cancer associated surface receptors using molecular imaging. The primary aim of the thesis was to develop Affibody-based PET imaging agents to provide the highest possible sensitivity of RTK detection in vivo. The thesis evaluates the effect of radiolabelling chemistry on biodistribution and targeting properties of Affibody molecules directed against HER2 and PDGFRβ. The thesis is based on five published papers (I-V).

Paper I. The targeting properties of maleimido derivatives of DOTA and NODAGA for site-specific labelling of a recombinant HER2-binding Affibody molecule radiolabelled with 68Ga were compared in vivo. Favourable in vivo properties were seen for the Affibody molecule with the combination of 68Ga with NODAGA.

Paper II. The aim was to compare the biodistribution of 68Ga- and 111In-labelled HER2-targeting Affibody molecules containing DOTA, NOTA and NODAGA at the N-terminus. This paper also demonstrated favourable in vivo properties for Affibody molecules in combination with 68Ga and NODAGA placed on the N-terminus.

Paper III.  The influence of chelator positioning on the synthetic anti-HER2 affibody molecule labelled with 68Ga was investigated. The chelator DOTA was conjugated either at the N-terminus, the middle of helix-3 or at the C-terminus of the Affibody molecules. The N-terminus placement provided the highest tumour uptake and tumour-to-organ ratios.

Paper IV. The aim of this study was to evaluate if the 68Ga labelled PDGFRβ-targeting Affibody would provide an imaging agent suitable for PDGFRβ visualization using PET. The 68Ga labelled conjugate provided high-contrast imaging of PDGFRβ-expressing tumours in vivo using microPET as early as 2h after injection.

Paper V. This paper investigated if the replacement of IHPEM with IPEM as a linker molecule for radioiodination of Affibody molecules would reduce renal retention of radioactivity. Results showed that the use of the more lipophilic linker IPEM reduced the renal radioactivity retention for radioiodinated Affibody molecules.

In conclusion, this thesis clearly demonstrates that the labelling strategy is of great importance with a substantial influence on the targeting properties of Affibody molecules and should be taken under serious considerations when developing new imaging agents.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 70 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1125
Affibody molecules, Molecular imaging, PET, Radiolabelling, HER2, PDGFRβ
National Category
Medical and Health Sciences
Research subject
Biomedical Radiation Science
urn:nbn:se:uu:diva-259410 (URN)978-91-554-9299-1 (ISBN)
Public defence
2015-10-03, Fåhraeussalen, Rudbecklaboratoriet, Dag Hammarskjölds väg 20, 751 85, Uppsala, 09:00 (English)
Available from: 2015-09-03 Created: 2015-08-03 Last updated: 2015-10-01

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