Abstract
Expression of the chemokine receptor chemokine C-X-C motif receptor 4 (CXCR4) plays an important role in cancer metastasis, autoimmune diseases and during stem cell based repair processes after stroke and myocardial infarction. Previously reported positron emission tomography (PET) imaging agents targeting CXCR4 suffer from either high non-specific uptake or only bind to the human form of the receptor. The objective of this study is to develop a high stability copper-64 labelled small molecule PET agent for imaging both human and murine CXCR4 chemokine receptors. Methods: Synthesis, radiochemistry, stability and radioligand binding assays were performed for the novel tracer 64Cu-CuCB-Bicyclam. In vivo dynamic PET studies were carried out on mice bearing U87 (CXCR4low) and U87.CXCR4 (CXCR4high) tumors. Biodistribution and receptor blocking studies were carried out on CD1-IGS immunocompetent mice. CXCR4 expression on tumor and liver disaggregates was confirmed using a combination of immunohistochemistry, quantitative polymerase chain reaction (qPCR) and western blot. Results: 64Cu-CuCB-Bicyclam has a high affinity for both the human and murine variants of the CXCR4 receptor (IC50 = 10 nM) and can be obtained from the parent chelator that has low affinity. In vitro and in vivo studies demonstrate specific uptake in CXCR4 expressing cells that can be blocked by >90% using a higher affinity antagonist, with limited uptake in non-CXCR4 expressing organs and high in vivo stability. The tracer was also able to selectively displace the CXCR4 antagonists AMD3100 and AMD3465 from the liver. Conclusions: The application of the tetraazamacrocyclic small molecule 64Cu-CuCB-Bicyclam is demonstrated as an imaging agent for the CXCR4 receptor that is likely to be applicable across a range of species. It has high affinity and stability and is suitable for preclinical research in immunocompetent murine models.
- Copyright © 2019 by the Society of Nuclear Medicine and Molecular Imaging, Inc.