The development of [(124)I]iodinated-VG76e: a novel tracer for imaging vascular endothelial growth factor in vivo using positron emission tomography.
The development of anticancer therapies that target the angiogenic process is an area of major growth in oncology. A method of noninvasively measuring tumor vascular endothelial growth factor (VEGF) in vivo could provide important efficacy information for VEGF-dependent antiangiogenic agents and the role of VEGF in cancer biology. We have developed a novel radiotracer for use with positron emission tomography (PET) that enables noninvasive imaging of VEGF. This radiotracer comprises an IgG1 monoclonal antibody, known as VG76e, that binds to human VEGF, labeled with a positron-emitting radionuclide, iodine-124 ([(124)I]-SHPP-VG76e). Three radiolabeling strategies were evaluated to synthesize the radiotracer with optimal radiochemical yield, purity, and immunoreactivity. To evaluate the pharmacokinetics and VEGF-specific localization of [(124)I]-SHPP-VG76e, two subclones of the HT1080 human fibrosarcoma selected on the basis of differing VEGF production (26.6 and 1/3C, the former producing 2-4-fold more in vitro) were established in culture and grown as solid tumor xenografts in immune-deficient mice. A single i.v. injection of the radiotracer into tumor-bearing mice revealed a time dependent and specific localization of [(125)I]-SHPP-VG76e to the tumor tissue. Three validation studies established the VEGF specificity and potential for use of [(124)I]-SHPP-VG76e in vivo: (a) uptake of [(125)I]-SHPP-VG76e was 1.8-fold higher in HT1080-26.6 compared with HT1080-1/3C tumors (P < 0.05); (b) uptake of [(125)I]-SHPP-VG76e in HT1080-26.6 tumors was specifically blocked by prior administration of excess unlabeled VG76e (P < 0.05); and (c) tumor uptake of the IgG1, [(125)I]-SHPP-CIP5, which has a similar molecular weight as [(125)I]-SHPP-VG76e but does not recognize VEGF, was the same for both HT1080-26.6 and HT1080-1/3C (P > 0.05). Other than tumor localization, [(125)I]-SHPP-VG76e was present in urine and blood and to a lesser extent in heart, lungs, liver, kidney, and spleen. Whole-animal PET imaging studies revealed a high tumor-to-background contrast and also revealed [(124)I]-SHPP-VG76e distributions in the major organs. These studies support further development of [(124)I]-SHPP-VG76e as a radiotracer for measuring tumor levels of VEGF in humans.
Collingridge
David R
DR
Cancer Research UK Positron Emission Tomography Oncology Group, Department of Cancer Medicine, Imperial College of Science, Technology and Medicine, Hammersmith Hospital, London W12 0NN.
Carroll
Veronica A
VA
Glaser
Mathias
M
Aboagye
Eric O
EO
Osman
Safiye
S
Hutchinson
Oliver C
OC
Barthel
Henryk
H
Luthra
Sajinder K
SK
Brady
Frank
F
Bicknell
Roy
R
Price
Pat
P
Harris
Adrian L
AL
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D016228:Endothelial Growth Factors / Q000096:biosynthesis / Q000378:metabolism*; D005260:Female; D005354:Fibrosarcoma / Q000000981:diagnostic imaging / Q000378:metabolism; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry / Q000493:pharmacokinetics; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000737:chemistry; D007553:Isotope Labeling; D008222:Lymphokines / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D016228:Endothelial Growth Factors; D018796:Immunoconjugates; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D008222:Lymphokines; D019275:Radiopharmaceuticals; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors