We performed a feasibility study to determine the optimal dosage and time of administration of the monoclonal antibody zirconium-89 ((89)Zr)-trastuzumab to enable positron emission tomography (PET) imaging of human epidermal growth factor receptor 2 (HER2)-positive lesions. Fourteen patients with HER2-positive metastatic breast cancer received 37 MBq of (89)Zr-trastuzumab at one of three doses (10 or 50 mg for those who were trastuzumab-naive and 10 mg for those who were already on trastuzumab treatment). The patients underwent at least two PET scans between days 2 and 5. The results of the study showed that the best time for assessment of (89)Zr-trastuzumab uptake by tumors was 4-5 days after the injection. For optimal PET-scan results, trastuzumab-naive patients required a 50 mg dose of (89)Zr-trastuzumab, and patients already on trastuzumab treatment required a 10 mg dose. The accumulation of (89)Zr-trastuzumab in lesions allowed PET imaging of most of the known lesions and some that had been undetected earlier. The relative uptake values (RUVs) (mean +/- SEM) were 12.8 +/- 5.8, 4.1 +/- 1.6, and 3.5 +/- 4.2 in liver, bone, and brain lesions, respectively, and 5.9 +/- 2.4, 2.8 +/- 0.7, 4.0 +/- 0.7, and 0.20 +/- 0.1 in normal liver, spleen, kidneys, and brain tissue, respectively. PET scanning after administration of (89)Zr-trastuzumab at appropriate doses allows visualization and quantification of uptake in HER2-positive lesions in patients with metastatic breast cancer.

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Vascular endothelial growth factor (VEGF), released by tumor cells, is an important growth factor in tumor angiogenesis. The humanized monoclonal antibody bevacizumab blocks VEGFinduced tumor angiogenesis by binding, thereby neutralizing VEGF. Our aim was to develop radiolabeled bevacizumab for noninvasive in vivo VEGF visualization and quantification with the single g-emitting isotope 111 In and the PET isotope 89 Zr. Methods: Labeling, stability, and binding studies were performed. Nude mice with a human SKOV-3 ovarian tumor xenograft were injected with 89 Zr-bevacizumab, 111 In-bevacizumab, or human 89 Zr-IgG. Human 89 Zr-IgG served as an aspecific control antibody. Small-animal PET and microCT studies were obtained at 24, 72, and 168 h after injection of 89 Zr-bevacizumab and 89 Zr-IgG (3.5 6 0.5 MBq, 100 6 6 mg, 0.2 mL [mean 6 SD]). Small-animal PET and microCT images were fused to calculate tumor uptake and compared with ex vivo biodistribution at 168 h after injection. 89 In-bevacizumab ex vivo biodistribution was compared at 24, 72, and 168 h after injection (2.0 6 0.5 MBq each, 100 6 4 mg in total, 0.2 mL). Results: Labeling efficiencies, radiochemical purity, stability, and binding properties were optimal for the radioimmunoconjugates. Small-animal PET showed uptake in well-perfused organs at 24 h and clear tumor localization from 72 h onward. Tumor uptake determined by quantification of small-animal PET images was higher for 89 Zr-bevacizumab-namely, 7.38 6 2.06 %ID/g compared with 3.39 6 1.16 %ID/g (percentage injected dose per gram) for human 89 Zr-IgG (P 5 0.011) at 168 h and equivalent to ex vivo biodistribution studies. Tracer uptake in other organs was seen primarily in liver and spleen. 89 In-bevacizumab biodistribution was comparable. Conclusion: Radiolabeled bevacizumab showed higher uptake compared with radiolabeled human IgG in a human SKOV-3 ovarian tumor xenograft. Noninvasive quantitative small-animal PET was similar to invasive ex vivo biodistribution. Radiolabeled bevacizumab is a new tracer for noninvasive in vivo imaging of VEGF in the tumor microenvironment.

NCT01565200.