PET of vascular endothelial growth factor receptor expression

For solid tumors and metastatic lesions, tumor vascularity is a critical factor in assessing response to therapy. Here we report the first example, to our knowledge, of Cu-64-labeled vascular endothelial growth factor 121 (VEGF(121)) for PET of VEGF receptor (VEGFR) expression in vivo. Methods: VEGF121 was conjugated with 1,4,7,10-tetraazadodecane-NN',N",N"'-tetraacetic acid (DOTA) and then labeled with Cu-64 for small-animal PET of mice bearing different sized U87MG human glioblastoma xenografts. Blocking experiments and ex vivo histopathology were performed to confirm the in vivo results. Results: There were 4.3 +/- 0.2 DOTA molecules per VEGF121, and the VEGFR2 binding affinity of DOTA-VEGF(121) was comparable to VEGF121. Cu-64 labeling of DOTA-VEGF121 was achieved in 90 +/- 10 min and the radiolabeling yield was 87.4% +/- 3.2%. The specific activity of Cu-64-DOTA-VEGF(121) was 3.2 +/- 0.1 GBq/mg with a radiochemical purity of > 98%. Small-animal PET revealed rapid, specific, and prominent uptake of Cu-64-DOTA-VEGF121 in small U87MG tumors (high VEGFR2 expression) but significantly lower and sporadic uptake in large U87MG tumors (low VEGFR2 expression). No appreciable renal clearance of 64Cu-DOTA-VEGF121 was observed, although the kidney uptake was relatively high likely due to VEGFR1 expression. Blocking experiments, immunofluorescence staining, and western blot confirmed the VEGFR specificity of Cu-64-DOTA-VEGF121. Conclusion: Successful demonstration of the ability of Cu-64-DOTA-VEGF121 to visualize VEGFR expression in vivo may allow for clinical translation of this radiopharmaceutical for imaging tumor angiogenesis and guiding antiangiogenic treatment, especially patient selection and treatment monitoring of VEGFR-targeted cancer therapy.