⁶⁸Ga-based PET Imaging

Unlike conventional imaging, molecular imaging holds the promise of more accurate detection in the early stages of disease. A specific target or pathway is imaged based on the signal of a detected molecular imaging agent. Molecular imaging has been described to visualize, characterize and measure bioengineering in vivo at the molecular and cellular levels in real time. With the rapid development of the medical imaging field, various molecular imaging modalities have been developed, including magnetic resonance (MR) imaging, optical imaging, positron emission tomography (PET) and single photon emission computed tomography (SPECT). Positron emission tomography (PET) has gained tremendous interest in the past few years as a tool for molecular imaging of cancer.

Advantages of ⁶⁸Ga for PET Imaging

PET provides researchers with physiological and biological information by imaging the distribution of reagents in the body for disease diagnosis, treatment monitoring and prognosis assessment. In the last decade, PET has become a clinical test tool for disease diagnosis, prognosis assessment and treatment monitoring due to its high sensitivity and quantitative analysis. Positron emission is obtained by injecting a molecular probe into a subject to obtain an imaging signal. The molecular probes must be radiolabeled with positron emission radionuclides. In addition to conventional PET radionuclides (e.g., ¹⁸F and ¹¹C), metallic radionuclides are also used in the construction of PET probes (e.g., ⁶⁴Cu, ⁶⁸Ga, and ⁸⁹Zr).

• ⁶⁸Ga is a popular PET radionuclide because of its favorable properties such as favorable half-life (68 min) and the lack of need for on-site production of cyclotrons.
• Moreover, as a nonphysiological metal positron emitter with low production cost, ⁶⁸Ga (β, 89%; EC, 11%) shows significant superiority over ⁺⁶⁴Cu (β, 17.8%; β^+-, 38.4%; EC, 43.8%), improving the quality of images after PET imaging.
• Several ⁶⁸Ga complexes are available for PET imaging of cancer.

⁶⁸Ga-labeled Dendrimers for PET Imaging

With the continuous advances in nanotechnology, various nanoparticles (NPs) can be used as PET imaging agents, including but not limited to liposomes, micelles, polymers, gold NPs, metal oxide NPs, and dendrimers. Dendrimers, as a class of highly branched, monodisperse synthetic nanomaterials, have well-defined structure and composition, as well as highly controllable size and surface properties. It has many advantages over other nanomaterials.

• For example, the most studied fifth-generation dendrimer is only 5.4 nm in size and can be eliminated directly by the kidney in vivo without degradation.
• The unique characteristics make dendrimers easy to construct contrast agents, especially nanoprobes using different positron-emitting nuclides.
• In addition, dendrimers can be engineered (modified by ligands with targeting functions) and enhanced permeability and retention (EPR) effects to improve tumor targeting.

Like ⁶⁴Cu, ⁶⁸Ga can be chelated with DOTA and NOTA. After radiolabeling with ⁶⁸Ga, the dendrimer is stable in vivo and in serum for about 4h to be effectively retained in tumor tissues by EPR effect and excreted mainly through the kidneys. Due to the unique structural properties of dendrimers allowing simple modification of targeting ligands and radionuclides, dendrimers can be used as versatile scaffolds for the construction of various PET imaging agents, and numerous advances have been made in the past decades.

⁶⁸Ga-DOTA-PAMAM-D for PET imaging. (Ghai A, et al., 2015)

How We Can Help

As a CRO providing innovative dendrimer products and high-quality, cost-effective custom services, CD BioSciences is adept at solving all problems in our clients' dendrimer projects. If you are interested, please feel free to contact us and our distinguished scientists will meet each of your specific needs.

Reference

1. Ghai A.; et al. Radiolabeling optimization and characterization of (68)Ga labeled DOTA-polyamido-amine dendrimer conjugate - Animal biodistribution and PET imaging results. Appl Radiat Isot. 2015, 105: 40-46.