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),11,13-trience-3,6,9,-triacetic acid (PCTA), labeled with ⁶⁴Cu or ¹⁷⁷Lu 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 ⁶⁴Cu or ¹⁷⁷Lu. 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 ⁶⁴Cu-cetuximab and biodistribution analysis. Micro-SPECT/CT imaging, biodistribution, and radioim-munotherapy studies of ¹⁷⁷Lu-cetuximab were performed in the ESCC model. Therapeutic responses were monitored using ¹⁸F-FDG PET and immunohistochemical staining. Results: ⁶⁴Cu-or ¹⁷⁷Lu-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 ⁶⁴Cu- and ¹⁷⁷Lu-cetuximab was peaked at 48 and 120 h, respectively. Radioimmunotherapy with ¹⁷⁷Lu-cetuximab showed significant inhibition of tumor growth (P < 0.01) and marked reduction of ¹⁸F-FDG SUV compared with that of control (P < 0.05). Terminal deoxynucleotidyl transferase dUTP nick-end labeling pos-itivity and Ki-67 staining indices increased and decreased, respectively, in the radioimmunotherapy group compared with other groups (P < 0.01). Conclusion: ⁶⁴Cu-cetuximab immuno-PET represented EGFR expression levels in ESCC tumors, and ¹⁷⁷Lu-cetuximab radioimmunotherapy effectively inhibited the tumor growth. The diagnostic and therapeutic convergence radiopharmaceutical ⁶⁴Cu-/¹⁷⁷Lu-PCTA-cetuximab may be useful as a diagnostic tool in patient selection and a potent radioimmunotherapy agent in EGFR-positive ESCC tumors.