Abstract |
METHODS: Functionally active mutants of scVEGF (an engineered single-chain version of pan-receptor VEGF-A with an N-terminal cysteine-containing tag for site-specific conjugation), named scVR1 and scVR2 with enhanced affinity to, respectively, VEGFR-1 and VEGFR-2, were constructed. Parental scVEGF and its receptor-specific mutants were site-specifically derivatized with the 89Zr chelator desferroxamine B via a 3.4-kDa PEG linker. 89Zr labeling of the desferroxamine B conjugates furnished scV/Zr, scVR1/Zr, and scVR2/Zr tracers with high radiochemical yield (>87%), high specific activity (≥9.8 MBq/nmol), and purity (>99%). Tracers were tested in an orthotopic breast cancer model using 4T1luc-bearing syngeneic BALB/c mice. For testing tracer specificity, tracers were coinjected with an excess of cold proteins of the same or opposite receptor specificity or pan-receptor scVEGF. PET imaging, biodistribution, and dosimetry studies in mice, as well as immunohistochemical analysis of harvested tumors, were performed. RESULTS: All tracers rapidly accumulated in orthotopic 4T1luc tumors, allowing for the successful PET imaging of the tumors as early as 2 h after injection. Blocking experiments with an excess of pan-receptor or receptor-specific cold proteins indicated that more than 80% of tracer tumor uptake is VEGFR-mediated, whereas uptake in all major organs is not affected by blocking within the margin of error. Critically, blocking experiments indicated that VEGFR-mediated tumor uptake of scVR1/Zr and scVR2/Zr was mediated exclusively by the corresponding receptor, VEGFR-1 or VEGFR-2, respectively. In contrast, uptake of pan-receptor scV/Zr was mediated by both VEGFR-1 and VEGFR-2 at an approximately 2:1 ratio. CONCLUSION: First-in-class selective PET tracers for imaging VEGFR-1 and VEGFR-2 were constructed and successfully validated in an orthotopic murine tumor model.
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Authors | Jan-Philip Meyer, Kimberly J Edwards, Paul Kozlowski, Marina V Backer, Joseph M Backer, Jason S Lewis |
Journal | Journal of nuclear medicine : official publication, Society of Nuclear Medicine
(J Nucl Med)
Vol. 57
Issue 11
Pg. 1811-1816
(Nov 2016)
ISSN: 1535-5667 [Electronic] United States |
PMID | 27390161
(Publication Type: Journal Article)
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Copyright | © 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc. |
Chemical References |
- Isotopes
- Radiopharmaceuticals
- Vascular Endothelial Growth Factor A
- Zirconium
- Kdr protein, mouse
- Vascular Endothelial Growth Factor Receptor-1
- Vascular Endothelial Growth Factor Receptor-2
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Topics |
- Animals
- Cell Line, Tumor
- Isotope Labeling
- Isotopes
(chemistry, pharmacokinetics)
- Mice
- Mice, Inbred BALB C
- Molecular Imaging
(methods)
- Neoplasms, Experimental
(diagnostic imaging, metabolism)
- Positron-Emission Tomography
(methods)
- Protein Engineering
(methods)
- Radiopharmaceuticals
(chemical synthesis, pharmacokinetics)
- Reproducibility of Results
- Sensitivity and Specificity
- Vascular Endothelial Growth Factor A
(genetics, pharmacokinetics)
- Vascular Endothelial Growth Factor Receptor-1
(metabolism)
- Vascular Endothelial Growth Factor Receptor-2
(metabolism)
- Zirconium
(chemistry, pharmacokinetics)
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