Purpose: Noninvasive positron emission tomography (PET) imaging of vascular endothelial growth factor receptor 2 (VEGFR-2) expression could be a valuable tool for evaluation of patients with a variety of malignancies, and particularly for monitoring those undergoing antiangiogenic therapies that block VEGF/VEGFR-2 function. The aim of this study was to develop a VEGFR-2-specific PET tracer.
Methods: The D63AE64AE67A mutant of VEGF(121) (VEGF(DEE)) was generated by recombinant DNA technology. VEGF(121) and VEGF(DEE) were purified and conjugated with DOTA for (64)Cu labeling. The DOTA conjugates were tested in vitro for VEGFR-2 specificity and functional activity. In vivo tumor targeting efficacy and pharmacokinetics of (64)Cu-labeled VEGF(121) and VEGF(DEE) were compared using an orthotopic 4T1 murine breast tumor model. Blocking experiments, biodistribution studies, and immunofluorescence staining were carried out to confirm the noninvasive imaging results.
Results: Cell binding assay demonstrated that VEGF(DEE) had about 20-fold lower VEGFR-1 binding affinity and only slightly lower VEGFR-2 binding affinity as compared with VEGF(121). MicroPET imaging studies revealed that both (64)Cu-DOTA-VEGF(121) and (64)Cu-DOTA-VEGF(DEE) had rapid and prominent activity accumulation in VEGFR-2-expressing 4T1 tumors. The renal uptake of (64)Cu-DOTA-VEGF(DEE) was significantly lower than that of (64)Cu-DOTA-VEGF(121) as rodent kidneys expressed high levels of VEGFR-1 based on immunofluorescence staining. Blocking experiments and biodistribution studies confirmed the VEGFR specificity of (64)Cu-DOTA-VEGF(DEE).
Conclusion: We have developed a VEGFR-2-specific PET tracer, (64)Cu-DOTA-VEGF(DEE). It has comparable tumor targeting efficacy to (64)Cu-DOTA-VEGF(121) but much reduced renal toxicity. This tracer may be translated into the clinic for imaging tumor angiogenesis and monitoring antiangiogenic treatment efficacy.