PET Imaging of VEGFR-2 Expression in Lung Cancer with 64Cu-Labeled Ramucirumab

J Nucl Med. 2016 Feb;57(2):285-90. doi: 10.2967/jnumed.115.166462. Epub 2015 Nov 5.

Abstract

Lung cancer accounts for 17% of cancer-related deaths worldwide, and most patients present with locally advanced or metastatic disease. Novel PET imaging agents for assessing vascular endothelial growth factor receptor-2 (VEGFR-2) expression can be used for detecting VEGFR-2-positive malignancies and subsequent monitoring of therapeutic response to VEGFR-2-targeted therapies. Here, we report the synthesis and characterization of an antibody-based imaging agent for PET imaging of VEGFR-2 expression in vivo.

Methods: Ramucirumab (named RamAb), a fully humanized IgG1 monoclonal antibody, was conjugated to 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) and labeled with (64)Cu. Flow cytometry analysis and microscopy studies were performed to compare the VEGFR-2 binding affinity of RamAb and NOTA-RamAb. PET imaging and biodistribution studies were performed in nude mice bearing HCC4006 and A549 xenograft tumors. Ex vivo histopathology was performed to elucidate the expression patterns of VEGFR-2 in different tissues and organs to validate in vivo results.

Results: Flow cytometry examination revealed the specific binding capacity of fluorescein isothiocyanate-RamAb to VEGFR-2, and no difference in VEGFR-2 binding affinity was seen between RamAb and NOTA-RamAb. After being labeled with (64)Cu, PET imaging revealed specific and prominent uptake of (64)Cu-NOTA-RamAb in VEGFR-2-positive HCC4006 tumors (9.4 ± 0.5 percentage injected dose per gram at 48 h after injection; n = 4) and significantly lower uptake in VEGFR-2-negative A549 tumors (4.3 ± 0.2 percentage injected dose per gram at 48 h after injection; n = 3). Blocking experiments revealed significantly lower uptake in HCC4006 tumors, along with histology analysis, further confirming the VEGFR-2 specificity of (64)Cu-NOTA-RamAb.

Conclusion: This study provides initial evidence that (64)Cu-NOTA-RamAb can function as a PET imaging agent for visualizing VEGFR-2 expression in vivo, which may also find potential applications in monitoring the treatment response of VEGFR-2-targeted cancer therapy.

Keywords: 64Cu; molecular imaging; positron emission tomography (PET); ramucirumab; vascular endothelial growth factor receptor-2 (VEGFR-2).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antibodies, Monoclonal* / pharmacokinetics
  • Antibodies, Monoclonal, Humanized
  • Cell Line, Tumor
  • Copper Radioisotopes
  • Heterocyclic Compounds
  • Heterocyclic Compounds, 1-Ring
  • Humans
  • Isotope Labeling
  • Lung Neoplasms / diagnostic imaging*
  • Lung Neoplasms / metabolism*
  • Mice
  • Mice, Nude
  • Molecular Imaging
  • Positron-Emission Tomography
  • Radiopharmaceuticals* / pharmacokinetics
  • Ramucirumab
  • Tissue Distribution
  • Vascular Endothelial Growth Factor Receptor-2 / biosynthesis*
  • Vascular Endothelial Growth Factor Receptor-2 / genetics
  • Xenograft Model Antitumor Assays

Substances

  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Copper Radioisotopes
  • Heterocyclic Compounds
  • Heterocyclic Compounds, 1-Ring
  • Radiopharmaceuticals
  • 1,4,7-triazacyclononane-N,N',N''-triacetic acid
  • KDR protein, human
  • Vascular Endothelial Growth Factor Receptor-2