In vitro evaluation of ⁶⁴Cu-labeled GE11-conjugates

The epidermal growth factor receptor (EGFR) is frequently overexpressed in epithelial tumors and consequently represents an important target for cancer diagnosis and therapy. Recently, a novel peptide sequence (GE11, YHWYGYTPQNVI) was identified to bind the EGFR with high affinity in vitro (K_d = 22 nM) as well as in vivo [1]. These promising data suggest that a GE11-conjugate, which is radiolabeled with a positron-emitting radionuclide, may be used for the assessment of EGFR-levels of tumors and metastases by positron emission tomography, thus, identifying patients which can be medicated by anti-EGFR therapy. Therefore, the peptide-conjugates NOTA-linker-GE11, NOTA-linker-GE11-NH₂ and TACN-(linker-GE11-NH₂)₃ (linker = NH-((CH₂)₂-O)₂-(CH₂)₂-NH-CO-CH₂-O-CH₂-CO-βAla) were synthesized and radiolabeled with ⁶⁴Cu at a radiochemical purity of at least 95%. All three radiolabeled GE11-conjugates were stable in buffer as well as in human blood serum. The binding properties of the radiolabeled conjugates were then evaluated in vitro using EGFR-rich (A431, FaDu) and EGFR-negative (MDA-MB-435s) cell preparations. However, as a result of the in vitro studies for all three GE11-conjugates no binding affinity could be determined. These findings may be explained by the highly hydrophobic character of the produced GE11-conjugates with accompanying tendency for aggregation.

Reference
[1] Z. Li, R. Zhao, X. Wu, et al.
FASEB J, 19 (2005), pp. 1978–1985