Positron Emission Tomography Imaging of Platelet-Derived Growth Factor Receptor β in Colorectal Tumor Xenograft Using Zirconium-89 Labeled Dimeric Affibody Molecule.

Platelet-derived growth factor receptor β (PDGFRβ) is overexpressed in a variety of malignant cancers, plays a critical role in tumor angiogenesis, and has been proven as a valuable target for cancer treatment. In this pilot study, a dimeric affibody molecule, Z_PDGFRβ, was prepared and radiolabeled with positron emission radionuclide zirconium-89 for PET imaging of colorectal tumors by targeting PDGFRβ expression in vivo. The PDGFRβ-binding capability of dimeric affibody was evaluated by flow cytometry, immunofluorescent staining, and whole-body optical imaging. Then, Z_PDGFRβ was conjugated with DFO-Bn-NCS and radiolabeled with ⁸⁹Zr. Targeted binding capability of ⁸⁹Zr-DFO-Z_PDGFRβ to PDGFRβ expressing cells was investigated by cellular assay in vitro and microPET/CT imaging in vivo. Dimeric Z_PDGFRβ affibody had specifically higher binding capability with PDGFRβ expressing pericytes rather than LS-174T cancer cells, and well colocalized with tumor neovasculature by flow cytometry and immunofluorescent assay. Z_PDGFRβ was successfully labeled with ⁸⁹Zr by DFO chelating with yield of 94.1 ± 3.53%. ⁸⁹Zr-DFO-Z_PDGFRβ indicated preserved specific binding ability with PDGFRβ expressing cells and effective inhibiting capability to PDGF-β ligands ( P < 0.05) in vitro. Biodistribution indicated that tumor uptake of ⁸⁹Zr-DFO-Z_PDGFRβ reached the peak of 6.93 ± 0.64%ID/g, and the tumor-to-blood ratio was 5.5 ± 0.6 at 2 h post-injection. LS-174T xenografts were clearly visualized by microPET/CT imaging through 1 to 4 h post-injection of ⁸⁹Zr-DFO-Z_PDGFRβ affibody conjugate. In conclusion, the ⁸⁹Zr-DFO-Z_PDGFRβ conjugate demonstrated specific and high binding ability with colorectal tumor, which indicated its use as a potential radiopharmaceutical for diagnostic imaging of tumor associate vasculatures with PET/CT.