Correlating EGFR expression with receptor-binding properties and internalization of 64Cu-DOTA-cetuximab in 5 cervical cancer cell lines

The anti-epidermal growth factor receptor (anti-EGFR) antibody cetuximab is clinically approved for the treatment of EGFR-expressing metastatic colorectal cancer and advanced head and neck cancer. Overexpression of EGFR has also been found in more than 70% of carcinomas of the cervix. The overall goal of this study was to determine whether Cu-64-1,4,7,10-tetraazacyclododecane-N,N',N '',N'''-tetraacetic acid (DOTA)-cetuximab has potential as an agent for measuring EGFR concentration by PET imaging in cervical cancer tumors. Methods: Cetuximab was conjugated to the bifunctional chelator DOTA and labeled with Cu-64. EGFR messenger RNA (mRNA) expression was correlated with EGFR densities on the cell surface of 5 different cervical cancer cell lines and with receptor function, measured by internalization of Cu-64-DOTA-cetuximab. Imaging in tumor-bearing mice with small-animal PET was performed using the highest-expressing cervical cancer cell line. Results: The affinity of Cu-64-DOTA-cetuximab binding for the EGIFR was similar in 4 EGFR-positive lines, varying from 0.1 to 0.7 nM. The mRNA expression corresponded well with EGFR densities and levels of internalization, with responses decreasing in the order of CaSki > ME-180 > DoTc2 4510 > HeLa > C-33A. Biodistribution and small-animal PET studies with Cu-64-DOTA-cetuximab in CaSki tumor-bearing nude mice showed relatively high tumor uptake at 24 h after injection (13.2 +/- 1.2 percentage of injected activity per gram), although there was also significant retention of activity in the blood and liver accumulation. Conclusion: Cu-64-DOTA-cetuximab was successfully used to detect and quantify EGFR expression in cervical cancer tumors, and small-animal PET/CT of EGFR-expressing CaSki tumors suggests potential for PET/CT of EGFR-positive tumors.