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Updated: Mar 18, 2026
A Simple Bioassay for the Evaluation of Vascular Endothelial Growth Factors
Published on: March 15, 2016
Selective Imaging of VEGFR-1 and VEGFR-2 Using 89Zr-Labeled Single-Chain VEGF Mutants
Jan-Philip Meyer1, Kimberly J Edwards1, Paul Kozlowski1
1Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, New York.
Abstract:
Vascular endothelial growth factor-A (VEGF-A) acts via 2 vascular endothelial growth factor receptors, VEGFR-1 and VEGFR-2, that play important and distinct roles in tumor biology. We reasoned that selective imaging of these receptors could provide unique information for diagnostics and for monitoring and optimizing responses to anticancer therapy, including antiangiogenic therapy. Herein, we report the development of 2 first-in-class 89Zr-labeled PET tracers that enable the selective imaging of VEGFR-1 and VEGFR-2.
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.
Insights
New PET tracers selectively image VEGFR-1 and VEGFR-2, crucial for understanding tumor biology and guiding cancer therapy. These novel imaging agents offer a promising tool for diagnostics and treatment monitoring in oncology.
Area of Science:
- Oncology
- Molecular Imaging
- Radiochemistry
Background:
- Vascular endothelial growth factor-A (VEGF-A) and its receptors, VEGFR-1 and VEGFR-2, are critical in tumor development and angiogenesis.
- Selective imaging of these receptors could offer unique insights for cancer diagnostics and therapy monitoring.
Purpose of the Study:
- To develop and validate novel positron emission tomography (PET) tracers for the selective imaging of VEGFR-1 and VEGFR-2.
Main Methods:
- Engineered single-chain VEGF variants (scVR1, scVR2) with enhanced affinity for VEGFR-1 and VEGFR-2, respectively, were developed.
- These variants were conjugated to a 89Zr chelator and radiolabeled to create PET tracers (scVR1/Zr, scVR2/Zr).
- Tracer performance was evaluated in an orthotopic breast cancer mouse model using PET imaging, biodistribution, and blocking studies.
Main Results:
- The developed 89Zr-labeled tracers (scV/Zr, scVR1/Zr, scVR2/Zr) enabled rapid and successful PET imaging of orthotopic tumors.
- Blocking experiments confirmed that tracer uptake in tumors was predominantly VEGFR-mediated (>80%).
- Crucially, scVR1/Zr and scVR2/Zr demonstrated exclusive binding to VEGFR-1 and VEGFR-2, respectively, validating their selectivity.
Conclusions:
- First-in-class PET tracers for selective imaging of VEGFR-1 and VEGFR-2 have been successfully developed.
- These tracers were validated in a preclinical tumor model, demonstrating high specificity and potential for clinical applications in oncology.
