Molecular imaging of EGFR kinase activity in tumors with 124I-labeled small molecular tracer and positron emission tomography

Mol Imaging Biol. Sep-Oct 2006;8(5):262-77. doi: 10.1007/s11307-006-0049-0.

Abstract

Positron emission tomography (PET) with epidermal growth factor receptor (EGFR) kinase-specific radiolabeled tracers could provide the means for noninvasive and repetitive imaging of heterogeneity of EGFR expression and signaling activity in tumors in individual patients before and during therapy with EGFR signaling inhibitors. We developed the synthesis and (124)I-radiolabeling of the (E)-But-2-enedioic acid [4-(3-[(124)I]iodoanilino)-quinazolin-6-yl]-amide-(3-morpholin-4-yl-propyl)-amide (morpholino-[(124)I]-IPQA), which selectively, irreversibly, and covalently binds the adenosine-triphosphate-binding site to the activated (phosphorylated) EGFR kinase, but not to the inactive EGFR kinase. The latter was demonstrated using in silico modeling with crystal structures of the wild type and different gain-of-function mutants of EGFR kinases. Also, this was demonstrated by selective radiolabeling of the EGFR kinase domain with morpholino-[(131)I]-IPQA in A431 human epidermoid carcinoma cells and Western blot autoradiography. In vitro radiotracer accumulation and washout studies demonstrated a rapid accumulation and progressive retention postwashout of morpholino-[(131)I]-IPQA in A431 epidermoid carcinoma and in U87 human glioma cells genetically modified to express the EGFRvIII mutant receptor, but not in the wild-type U87MG glioma cells under serum-starved conditions. Using morpholino-[(124)I]-IPQA, we obtained noninvasive PET images of EGFR activity in A431 subcutaneous tumor xenografts, but not in subcutaneous tumor xenografts grown from K562 human chronic myeloid leukemia cells in immunocompromised rats and mice. Based on these observations, we suggest that PET imaging with morpholino-[(124)I]-IPQA should allow for identification of tumors with high EGFR kinase signaling activity, including brain tumors expressing EGFRvIII mutants and nonsmall-cell lung cancer expressing gain-of-function EGFR kinase mutants. Because of significant hepatobiliary clearance and intestinal reuptake of the morpholino-[(124)I]-IPQA, additional [(124)I]-IPQA derivatives with improved water solubility may be required to optimize the pharmacokinetics of this class of molecular imaging agents.

Publication types

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

MeSH terms

  • Animals
  • Brain Neoplasms / diagnosis
  • Carcinoma, Non-Small-Cell Lung / diagnosis
  • ErbB Receptors / analysis*
  • Humans
  • Inhibitory Concentration 50
  • Iodine Radioisotopes* / chemistry
  • Iodine Radioisotopes* / pharmacokinetics
  • K562 Cells
  • Mice
  • Mice, Nude
  • Models, Biological
  • Models, Molecular
  • Neoplasms / diagnostic imaging*
  • Neoplasms / enzymology*
  • Phosphorylation
  • Positron-Emission Tomography / methods*
  • Protein Kinase Inhibitors / analysis
  • Protein-Tyrosine Kinases / analysis
  • Protein-Tyrosine Kinases / antagonists & inhibitors
  • Radioactive Tracers
  • Radionuclide Imaging / methods
  • Rats
  • Sensitivity and Specificity
  • Staining and Labeling
  • Tissue Distribution
  • Tumor Cells, Cultured
  • Xenograft Model Antitumor Assays

Substances

  • Iodine Radioisotopes
  • Protein Kinase Inhibitors
  • Radioactive Tracers
  • ErbB Receptors
  • Protein-Tyrosine Kinases