In Vivo VEGF Imaging with Radiolabeled Bevacizumab in a Human Ovarian Tumor Xenograft

Abstract

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.

Development of a 124I-labeled version of the anti-PSMA monoclonal antibody capromab for immunoPET staging of prostate cancer: Aspects of labeling chemistry and biodistribution

“…It has been shown for several different antibodies that uptake of 111 In and 89 Zr in normal organs is very similar, with slightly higher uptake in liver and bones for 89 Zr (15,16,18). Comparison of our data for indium-labeled capromab with recently published data for zirconium-labeled capromab showed much higher zirconium concentrations in lung, liver and spleen.…”

“…PET provides better resolution (and, accordingly, lower influence of partial volume effect) and better registration efficiency, which improves imaging quality. Feasibility of antibody-mediated PET imaging (immunoPET) has been demonstrated in a number of preclinical studies using monoclonal antibodies targeting several tumor-associated antigens (6,(15)(16)(17)(18)(19)(20). Preliminary clinical data concerning immunoPET imaging of HER2-expressing breast cancer (21) and renal cell carcinoma (22) are very encouraging.…”

PET-CT Imaging in Breast Cancer Patients: New Tracers, Future Directions

“…Zr-labeled bevacizumab showed clear and specific tumor localization in human ovarian cancer models [75]. Nagengast et al reported similar results with 18 F-labeled ranibizumab, a Fab-fragment binding to VEGF [76,77], and also found good correlation between 89 Zr-bevacizumab uptake and therapeutic response to anti-angiogenic treatment in vivo in mouse-model with ovarian cancer xenografts [78].…”

Nanobodies Targeting the Hepatocyte Growth Factor: Potential New Drugs for Molecular Cancer Therapy

“…Like the 89 Zr-aHGF-Nanobodies, 89 Zrbevacizumab showed selective uptake in VEGF-producing xenografts in mice (35), whereas uptake decreased when VEGF expression was inhibited by treatment with HSP90 inhibitors (36,37), indicating a relationship between 89 Zr-bevacizumab tumor uptake and VEGF expression. What is more, 89 Zr-bevacizumab biodistribution could be imaged quantitatively and at excellent resolution, and in the mean time clinical trials have been started with 89 Zr-bevacizumab, as a follow-up of singlephoton emission computed tomography (SPECT) studies with 111 In-bevacizumab in patients with melanoma (38).…”