Theranostics 2019; 9(22):6719-6733. doi:10.7150/thno.34857

Research Paper

CMKLR1-targeting peptide tracers for PET/MR imaging of breast cancer

Sarah Erdmann1, Lars Niederstadt1, Eva Jolanthe Koziolek2,3,4, Juan Daniel Castillo Gómez2, Sonal Prasad2,3, Asja Wagener1, Jan Lennart von Hacht1, Sandy Reinicke1, Samantha Exner1, Sebastian Bandholtz1, Nicola Beindorff3, Winfried Brenner2,3,5, Carsten Grötzinger1,4,5,6 ✉

1. Department of Hepatology and Gastroenterology, Campus Virchow-Klinikum, Charité - Universitätsmedizin Berlin, Berlin, Germany
2. Department of Nuclear Medicine, Campus Virchow-Klinikum, Charité - Universitätsmedizin Berlin, Berlin, Germany
3. Berlin Experimental Radionuclide Imaging Center (BERIC), Campus Virchow-Klinikum, Charité - Universitätsmedizin Berlin, Berlin
4. German Cancer Research Center (DKFZ) Heidelberg, Germany
5. German Cancer Consortium (DKTK), partner site Berlin, Germany
6. Molecular Cancer Research Center (MKFZ), Campus Virchow-Klinikum, Charité - Universitätsmedizin Berlin, Berlin, Germany

This is an open access article distributed under the terms of the Creative Commons Attribution License ( See for full terms and conditions.
Erdmann S, Niederstadt L, Koziolek EJ, Gómez JDC, Prasad S, Wagener A, von Hacht JL, Reinicke S, Exner S, Bandholtz S, Beindorff N, Brenner W, Grötzinger C. CMKLR1-targeting peptide tracers for PET/MR imaging of breast cancer. Theranostics 2019; 9(22):6719-6733. doi:10.7150/thno.34857. Available from

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Background: Molecular targeting remains to be a promising approach in oncology. Overexpression of G protein-coupled receptors (GPCRs) in human cancer is offering a powerful opportunity for tumor-selective imaging and treatment employing nuclear medicine. We utilized novel chemerin-based peptide conjugates for chemokine-like receptor 1 (CMKLR1) targeting in a breast cancer xenograft model.

Methods: By conjugation with the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), we obtained a family of five highly specific, high-affinity tracers for hybrid positron emission tomography/magnetic resonance (PET/MR) imaging. A xenograft model with target-positive DU4475 and negative A549 tumors in immunodeficient nude mice enabled CMKLR1-specific imaging in vivo. We acquired small animal PET/MR images, assessed biodistribution by ex vivo measurements and investigated the tracer specificity by blocking experiments.

Results: Five CMKLR1-targeting peptide tracers demonstrated high biological activity and affinity in vitro with EC50 and IC50 values below 2 nM. Our target-positive (DU4475) and target-negative (A549) xenograft model could be validated by ex vivo analysis of CMKLR1 expression and binding. After preliminary PET imaging, the three most promising tracers [68Ga]Ga-DOTA-AHX-CG34, [68Ga]Ga-DOTA-KCap-CG34 and [68Ga]Ga-DOTA-ADX-CG34 with best tumor uptake were further analyzed. Hybrid PET/MR imaging along with concomitant biodistribution studies revealed distinct CMKLR1-specific uptake (5.1% IA/g, 3.3% IA/g and 6.2% IA/g 1 h post-injection) of our targeted tracers in DU4475 tumor tissue. In addition, tumor uptake was blocked by excess of unlabeled peptide (6.4-fold, 5.5-fold and 3.4-fold 1 h post-injection), further confirming CMKLR1 specificity. Out of five tracers, we identified these three tracers with moderate, balanced hydrophilicity to be the most potent in receptor-mediated tumor targeting.

Conclusion: We demonstrated the applicability of 68Ga-labeled peptide tracers by visualizing CMKLR1-positive breast cancer xenografts in PET/MR imaging, paving the way for developing them into theranostics for tumor treatment.

Keywords: Tumor targeting, PET tracer, Chemokine-like receptor 1, peptide ligand, breast cancer