Skip Navigation LinksHome > August 2007 - Volume 2 - Issue 8 > Zirconium-89 labeled Cetuximab: A very promising imaging pro...
Journal of Thoracic Oncology:
doi: 10.1097/01.JTO.0000283397.83216.5f
Poster Discussion Abstracts: Session PD3 and PD5 PD -Thursday, September 6: Session PD3: Thursday, September 6 Novel Therapeutics: Novel Therapeutics, Thu, 12:30 - 14:15

Zirconium-89 labeled Cetuximab: A very promising imaging probe to monitor and quantify EGFR expression non-invasively in vivo: PD3-1-3

Aerts, Hugo1; Dubois, Ludwig1; Straathof, Roel1; Hackeng, Tilman2; Chiu, Roland1; De Ruysscher, Dirk1; Lammering, Guido1; Wouters, Brad1; van Dongen, Guus3; Lambin, Philippe1

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1 Department of Radiation Oncology (MAASTRO), University of Maastricht, Maastricht, The Netherlands 2 Department of Biochemistry, University of Maastricht, Maastricht, The Netherlands 3 Department of Nuclear Medicine and PET Research, VU University Medical Centre, Amsterdam, The Netherlands

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Background:

The epidermal growth factor receptor (EGFR) is highly expressed in a significant percentage of human malignancies and its expression is associated with tumor aggressiveness and treatment resistance. The monoclonal antibody Cetuximab (C225) blocks the ligand binding domain of EGFR with high affinity, preventing downstream signaling which results in tumor growth inhibition. Consequently, Cetuximab has evolved as a promising new targeted agent in oncology and is nowadays increasingly used in clinical trials in combination with chemo- / radiotherapy. Image modalities to monitor the binding of Cetuximab non-invasively in cancer patients could significantly increase our knowledge of the clinical use of Cetuximab as a targeted agent. To contribute to this knowledge, we developed and validated a new imaging probe using Cetuximab labeled with the PET isotope Zirconium-89.

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Methods:

Human A431 epidermoid carcinoma cells were used as high EGFR expressing cells, glioblastoma U373 MG and colorectal adenocarcinoma HT29 cells as intermediate EGFR expressing cells, and T47D breast carcinoma cells as negative control. The in vitro expression of EGFR was assessed using Western blotting. Quantitative validation of specific binding of Cetuximab was done using fluorescence-activated cell sorting (FACS) after incubation with Oregon Green 488 labeled Cetuximab. The in vivo binding of Cetuximab to EGFR was assessed by performing PET imaging from 0 to 96 hours on A431 and T47D tumor bearing NMRI-nu mice after injection of Zirconium-89 (89Zr) - labeled Cetuximab. Immunohistochemistry was used to validate the in vivo findings.

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Results:

Stability of Oregon Green 488 and 89Zr-labeled Cetuximab was confirmed by MALDI-TOF and HPLC respectively. Gammacounting of the 89Zr-cetuximab HPLC fractions demonstrated a radiochemical purity of 98%. Western blot analysis confirmed EGFR expression in the corresponding cell lines. Specific binding of Oregon Green 488 labeled Cetuximab was seen in EGFR expressing cell lines at a nanoMolar saturation concentration.

In mice, PET images showed clear delineation of EGFR-positive xenografts, but not of EGFR-negative xenografts. Tumor-to-blood ratios in the EGFR expressing cell line were significantly higher (P < 0.0015) compared to the negative control starting from 24 hours post injection, and reached an optimum after 72 hours due to the long biologic half-life of Cetuximab in the blood. Histopathology using anti-EGFR monoclonal antibodies confirmed the findings seen non-invasively.

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Conclusions:

Using the newly developed probes, we assessed the binding of Cetuximab to EGFR both in vitro and in vivo. The 89Zr-cetuximab in vivo probe represents a promising tool to evaluate the biologic and pharmacokinetic effects of Cetuximab non-invasively. Monitoring these effects in combination with radiotherapy before, during and after treatment will ultimately result in individualized patient treatment. A phase I trial in patients is underway.

Copyright © 2007 by the European Lung Cancer Conference and the International Association for the Study of Lung Cancer.

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