Immuno-PET Imaging and Radioimmunotherapy of 64Cu-/177Lu-Labeled Anti-EGFR Antibody in Esophageal Squamous Cell Carcinoma Model

Immuno-PET provides valuable information about tumor location, phenotype, susceptibility to therapy, and treatment response, especially to targeted radioimmunotherapy. In this study, we prepared antiepidermal growth factor receptor (EGFR) antibody via identical chelator, 3,6,9,15-tetraazabicyclo[9.3.1]-pentadeca-1(15),1 1,13-trience-3,6,9,-triacetic acid (PCTA), labeled with Cu-64 or Lu-177 to evaluate the EGFR expression levels using immuno-PET and the feasibility of radioimmunotherapy in an esophageal squamous cell carcinoma (ESCC) model. Methods: Cetuximab was conjugated with p-SCN-Bn-PCTA and radiolabeled with Cu-64 or Lu-177. In vitro EGFR expression levels were determined and compared using flow cytometry and cell binding assay. In vivo EGFR expression levels were evaluated via immuno-PET imaging of Cu-64-cetuximab and biodistribution analysis. Micro-SPECT/CT imaging, biodistribution, and radioimmunotherapy studies of Lu-177-cetuximab were performed in the ESCC model. Therapeutic responses were monitored using F-18-FDG PET and immunohistochemical staining. Results: Cu-64- or Lu-177-labeled antibodies showed high radiolabeling yield (>98%), stability (>90%), and favorable immunoreactivity. In vitro EGFR status measured by cell binding assay was correlated with the flow cytometry data. Immuno-PET, micro-SPECT/CT, and biodistribution demonstrated specific uptake in ESCC tumors depending on the EGFR expression levels. Tumor accumulation of Cu-64- and Lu-177-cetuximab was peaked at 48 and 120 h, respectively. Radioimmunotherapy with Lu-177-cetuximab showed significant inliibition of tumor growth (P < 0.01) and marked reduction of F-18-FDG SUV compared with that of control (P < 0.05) Terminal deoxynucleotidyl transferase dUTP nick-end labeling positivity and Ki-67 staining indices increased and decreased, respectively, in the radioimmunotherapy group compared with other groups (P < 0.01). Conclusion: Cu-64-cetuximab immuno-PET represented EGFR expression levels in ESCC tumors, and Lu-177-cetuximab radioimmunotherapy effectively inhibited the tumor growth. The diagnostic and therapeutic convergence radiopharmaceutical Cu-64-/Lu-177-PCTA-cetuximab may be useful as a diagnostic tool in patient selection and a potent radioimmunotherapy agent in EGFR-positive ESCC tumors.