In vivo VEGF imaging with radiolabeled bevacizumab in a human ovarian tumor xenograft.
Vascular endothelial growth factor (VEGF), released by tumor cells, is an important growth factor in tumor angiogenesis. The humanized monoclonal antibody bevacizumab blocks VEGF-induced 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 gamma-emitting isotope 111In and the PET isotope 89Zr.


METHODS
Labeling, stability, and binding studies were performed. Nude mice with a human SKOV-3 ovarian tumor xenograft were injected with 89Zr-bevacizumab, 111In-bevacizumab, or human 89Zr-IgG. Human 89Zr-IgG served as an aspecific control antibody. Small-animal PET and microCT studies were obtained at 24, 72, and 168 h after injection of 89Zr-bevacizumab and 89Zr-IgG (3.5 +/- 0.5 MBq, 100 +/- 6 microg, 0.2 mL [mean +/- SD]). Small-animal PET and microCT images were fused to calculate tumor uptake and compared with ex vivo biodistribution at 168 h after injection. 89Zr- and 111In-bevacizumab ex vivo biodistribution was compared at 24, 72, and 168 h after injection (2.0 +/- 0.5 MBq each, 100 +/- 4 microg 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 89Zr-bevacizumab-namely, 7.38 +/- 2.06 %ID/g compared with 3.39 +/- 1.16 %ID/g (percentage injected dose per gram) for human 89Zr-IgG (P = 0.011) at 168 h and equivalent to ex vivo biodistribution studies. Tracer uptake in other organs was seen primarily in liver and spleen. 89Zr- and 111In-bevacizumab biodistribution was comparable.


CONCLUSIONS
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.
Nagengast
Wouter B
WB
Department of Medical Oncology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands.
de Vries
Elisabeth G
EG
Hospers
Geke A
GA
Mulder
Nanno H
NH
de Jong
Johan R
JR
Hollema
Harry
H
Brouwers
Adrienne H
AH
van Dongen
Guus A
GA
Perk
Lars R
LR
Lub-de Hooge
Marjolijn N
MN
D000818:Animals; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000068258:Bevacizumab; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007205:Indium Radioisotopes; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010051:Ovarian Neoplasms / Q000737:chemistry*; D011786:Quality Control; D019275:Radiopharmaceuticals; D014183:Transplantation, Heterologous; D042461:Vascular Endothelial Growth Factor A / Q000032:analysis*; D015040:Zirconium
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; D042461:Vascular Endothelial Growth Factor A; D000068258:Bevacizumab; D015040:Zirconium