Background

[PubMed]

Epidermal growth factor (EGF) is a cytokine that comprises 53 amino acids (6.2 kDa) and is secreted by ectodermic cells, monocytes, kidneys, and duodenal glands (1). EGF stimulates growth of epidermal and epithelial cells. EGF and at least seven other growth factors and their transmembrane receptor kinases play important roles in cell proliferation, survival, adhesion, migration, and differentiation. The EGF receptor (EGFR) family consists of four transmembrane receptors: EGFR (HER1/erbB-1), HER2 (erbB-2/neu), HER3 (erbB-3), and HER4 (erbB-4) (2). HER1, HER3, and HER4 comprise three major functional domains: an extracellular ligand-binding domain, a hydrophobic transmembrane domain, and a cytoplasmic tyrosine kinase domain. No ligand has been clearly identified for HER2; however, HER2 can be activated as a result of ligand binding to other HER receptors with the formation of receptor homodimers and/or heterodimers (3). HER1 and HER2 are overexpressed on many solid tumor cells such as breast, non-small cell lung, head and neck, and colon cancers (4-6). The high levels of HER1 and HER2 expression on cancer cells are associated with a poor prognosis (7-10).

Cetuximab is a humanized IgG₁ monoclonal antibody (mAb) against the extracellular domain of recombinant EGFR (11). Cetuximab was approved by the United States Food and Drug Administration (FDA) to treat patients with advanced colorectal cancer that has metastasized to other parts of the body. Various labeled cetuximab probes have been developed for imaging human breast cancer in small-animal tumor models (12-14). However, the pharmacokinetics of the intact radiolabeled mAb, with high liver uptake and slow blood elimination, are generally not ideal for imaging. Smaller antibody fragments, such as Fab or F(ab´)₂, have better imaging pharmacokinetics because they are rapidly excreted by the kidneys. Wang et al. (15) generated a human Fab antibody fragment against the extracellular domain of EGFR from a human naive Fab phage library. Xu et al. (16) evaluated ¹²⁵I-anti-EGFR human Fab antibody fragment (¹²⁵I-Fab) for single-photon emission computed tomography (SPECT) imaging in nude mice bearing human EGFR-expressing tumors.

Synthesis

[PubMed]

Anti-EGFR Fab (0.2 nmol) was labeled with 74 MBq (2 mCi) ¹²⁵I in the presence of chloramine-T (16). ¹²⁵I-Fab was isolated from the incubation mixture with a PD-10 column. The labeling efficiency was ~75%, and the radiochemical purity was >95%. ¹²⁵I-Fab exhibited an immunoreactivity of 63%. The specific activity was not reported.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

In vitro binding of Fab showed a binding affinity of 30 nM using noncompetitive radioimmunoassay (15). In vitro cell uptake assays were performed using three cell lines with different degree of EGFR expression (A431 > U118 > NIH3T3 cells) (16). The radioactivity levels were 120,000, 40,000, and 8,000 cpm in A431, U118, and NIH3T3 cells, respectively, at 1 h of incubation with 0.06 nM ¹²⁵I-Fab. The radioactivity levels were reduced to 40,000, 20,000, and 7,000 cpm, respectively, by co-incubation with 1.2 nM anti-EGFR Fab.

Animal Studies

Human Studies

[PubMed]

No publication is currently available.

References

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Rubin I., Yarden Y. The basic biology of HER2. Ann Oncol. 2001;12 Suppl 1:S3–8. [PubMed: 11521719]

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Grunwald V., Hidalgo M. Developing inhibitors of the epidermal growth factor receptor for cancer treatment. J Natl Cancer Inst. 2003;95(12):851–67. [PubMed: 12813169]

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Mendelsohn J. Anti-epidermal growth factor receptor monoclonal antibodies as potential anti-cancer agents. J Steroid Biochem Mol Biol. 1990;37(6):889–92. [PubMed: 2285602]

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Yasui W., Sumiyoshi H., Hata J., Kameda T., Ochiai A., Ito H., Tahara E. Expression of epidermal growth factor receptor in human gastric and colonic carcinomas. Cancer Res. 1988;48(1):137–41. [PubMed: 2446740]

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Ang K.K., Berkey B.A., Tu X., Zhang H.Z., Katz R., Hammond E.H., Fu K.K., Milas L. Impact of epidermal growth factor receptor expression on survival and pattern of relapse in patients with advanced head and neck carcinoma. Cancer Res. 2002;62(24):7350–6. [PubMed: 12499279]

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Costa S., Stamm H., Almendral A., Ludwig H., Wyss R., Fabbro D., Ernst A., Takahashi A., Eppenberger U. Predictive value of EGF receptor in breast cancer. Lancet. 1988;2(8622):1258. [PubMed: 2903994]

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Ethier S.P. Growth factor synthesis and human breast cancer progression. J Natl Cancer Inst. 1995;87(13):964–73. [PubMed: 7629883]

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Yarden Y. Biology of HER2 and its importance in breast cancer. Oncology. 2001;61 Suppl 2:1–13. [PubMed: 11694782]

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Kim E.S., Khuri F.R., Herbst R.S. Epidermal growth factor receptor biology (IMC-C225). Curr Opin Oncol. 2001;13(6):506–13. [PubMed: 11673692]

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Cai W., Chen K., He L., Cao Q., Koong A., Chen X. Quantitative PET of EGFR expression in xenograft-bearing mice using 64Cu-labeled cetuximab, a chimeric anti-EGFR monoclonal antibody. Eur J Nucl Med Mol Imaging. 2007;34(6):850–8. [PubMed: 17262214]

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Schechter N.R., Yang D.J., Azhdarinia A., Kohanim S., Wendt R. 3rd, Oh C.S., Hu M., Yu D.F., Bryant J., Ang K.K., Forster K.M., Kim E.E., Podoloff D.A. Assessment of epidermal growth factor receptor with 99mTc-ethylenedicysteine-C225 monoclonal antibody. Anticancer Drugs. 2003;14(1):49–56. [PubMed: 12544258]

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Wen X., Wu Q.P., Ke S., Ellis L., Charnsangavej C., Delpassand A.S., Wallace S., Li C. Conjugation with (111)In-DTPA-poly(ethylene glycol) improves imaging of anti-EGF receptor antibody C225. J Nucl Med. 2001;42(10):1530–7. [PubMed: 11585869]

15.

Wang X., Zhu J., Zhao P., Jiao Y., Xu N., Grabinski T., Liu C., Miranti C.K., Fu T., Cao B.B. In vitro efficacy of immuno-chemotherapy with anti-EGFR human Fab-Taxol conjugate on A431 epidermoid carcinoma cells. Cancer Biol Ther. 2007;6(6):980–7. [PubMed: 17534145]

16.

Xu N., Cai G., Ye W., Wang X., Li Y., Zhao P., Zhang A., Zhang R., Cao B. Molecular imaging application of radioiodinated anti-EGFR human Fab to EGFR-overexpressing tumor xenografts. Anticancer Res. 2009;29(10):4005–11. [PubMed: 19846943]