⁶⁴Cu-based PET Imaging

The increasing understanding of tumor biology has led to better clinical care and improved survival for many cancer patients. Advances in morphologic imaging techniques, particularly magnetic resonance imaging (MRI) and computed tomography (CT), have improved tumor detection and staging, as well as measurement of treatment response. However, the inability to characterize tumor growth and metabolism, i.e., pathophysiology, is a limitation of the application of morphological imaging techniques. As one of the rapidly evolving technologies in medical imaging, positron emission tomography (PET) has created metabolic imaging capabilities to characterize and measure biochemical and physiological aberrations by visualizing them non-invasively and in real time. Positron emission is obtained by injecting a molecular probe into the subject to obtain an imaging signal. The molecular probes must be radiolabeled with positron emission radionuclides. In addition to traditional PET radionuclides (e.g., ¹⁸F and ¹¹C), metallic radionuclides are also used for PET probe construction (e.g., ⁶⁴Cu, 86Y, and 89Zr), which typically have long half-lives and can perform PET imaging continuously on the same subject for hours or even days. As a metallic radionuclide, ⁶⁴Cu has great application due to its inherent half-life decay, low beta energy and commercial availability.

Introduction into ⁶⁴Cu for PET Imaging

⁶⁴Cu has special nuclear properties such as favorable half-life (12.7 hours) and attractive decay properties for imaging and potential therapeutic applications in nuclear medicine. As a positron emitter, ⁶⁴Cu is often used to produce experimental and clinical radiopharmaceuticals, and its beta emission increases the possibility of therapeutic applications. Compared to other typical PET radionuclides, ⁶⁴Cu has a relatively long half-life, which is beneficial for imaging of therapeutic and certain physiological processes.

• Bone metastases: ⁶⁴Cu linked to the methanephosphonate functional group has the potential to be used as a bone imaging agent.
• Neuroendocrine tumors: ⁶⁴Cu-DOTA-TATE is commercially approved for localizing growth hormone receptor-positive neuroendocrine tumors (NETs).
• Prostate Cancer: ⁶⁴Cu can be used for in vitro and in vivo studies of prostate cancer when stably chelated with CB-TE2A.
• Perfusion: ⁶⁴Cu-ethylglyoxal bis(thiosemicarbazone) (ETS) has multiple potential uses as a PET radiopharmaceutical, and ⁶⁴Cu-ETS has been used for experimental preclinical myocardial, brain, and tumor perfusion assessments.
• Cancer therapy: ⁶⁴Cu is thought to kill cancer cells due to its unique decay properties.

⁶⁴Cu-labeled Dendrimers for Cancer PET Imaging

Carrier materials used as PET probes include small molecules, peptides, proteins, and nanoparticles (NPs). Among them, NPs are of particular interest due to their ability to interact with various biomolecules, such as enzymes, receptors, and antibodies. As a radiometal, 64Cu requires a bifunctional chelator (BFC) for radiolabeling of NPs. As a nanoparticle, dendrimers are highly branched, monodisperse synthetic macromolecules with an abundance of surface functional groups. Due to their unique characteristics, dendrimers are considered as favorable platforms for the construction of multimodal imaging probes.

• Dendrimers modified with folate and radiolabeled with 64Cu can be used for PET imaging of tumors that overexpress folate receptors.
• Multifunctional dendrimer nanoprobes labeled with 64Cu have great promise for applications, not only for targeted PET imaging of different types of cancers, but also for molecular imaging of cardiovascular and inflammatory diseases, such as for PET imaging of atherosclerotic platelets.

⁶⁴Cu-DOTA-FA-FI-G5-NHAc dendrimers for tumor-targeted microPET imaging. (Ma W, et al., 2018)

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Reference

1. Ma W.; et al. ⁶⁴Cu-Labeled multifunctional dendrimers for targeted tumor PET imaging. Nanoscale. 2018, 10: 6113-6124.