Comparison of conjugation strategies of cross-bridged macrocyclic chelators with cetuximab for copper-64 radiolabeling and PET imaging of EGFR in colorectal tumor-bearing mice.
Epidermal growth-factor receptor (EGFR) is overexpressed in a wide variety of solid tumors and has served as a well-characterized target for cancer imaging and therapy. Cetuximab was the first mAb targeting EGFR approved by the FDA for the treatment of metastatic colorectal and head and neck cancers. Previous studies showed that (64)Cu (T1/2 = 12.7 h; β(+) (17.4%)) labeled DOTA-cetuximab showed promise for PET imaging of EGFR-positive tumors; however the in vivo stability of this compound has been questioned. In this study, two recently developed cross-bridged macrocyclic chelators (CB-TE1A1P and CB-TE1K1P) were conjugated to cetuximab using standard NHS coupling procedures and/or strain-promoted azide-alkyne cycloaddition (SPAAC) methodologies. The radiolabeling and in vitro/vivo evaluation of the resulting cetuximab conjugates were compared. Improved Cu-64 labeling efficiency and high specific activity (684 kBq/μg, decay corrected to the end of bombardment) were obtained with the CB-TE1K1P-PEG4-click-cetuximab conjugate. Saturation binding assays indicated that the prepared cetuximab conjugates had comparable affinity (1.32-2.00 nM) in the HCT116 human colorectal tumor cell membranes. In the subsequent in vivo evaluation, (64)Cu-CB-TE1K1P-PEG4-click-cetuximab demonstrated more rapid renal clearance with a higher tumor/nontumor ratio than other (64)Cu-labeled cetuximab conjugates, and it shows the greatest promise for imaging and therapy of EGFR-positive tumors.
Departments of Radiology, ⊥Pharmacology and Chemical Biology, and #Bioengineering, University of Pittsburgh , Pittsburgh, Pennsylvania, United States.
Dexing
D
Zeng
Yunjun
Y
Guo
Alexander G
AG
White
Zhengxin
Z
Cai
Jalpa
J
Modi
Riccardo
R
Ferdani
Carolyn J
CJ
Anderson
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000493:pharmacokinetics; D061067:Antibodies, Monoclonal, Humanized / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000378:metabolism; D000068818:Cetuximab; D002614:Chelating Agents / Q000378:metabolism*; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D003301:Copper Radioisotopes / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D018796:Immunoconjugates; D051379:Mice; D008819:Mice, Nude; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D002614:Chelating Agents; D003301:Copper Radioisotopes; D018796:Immunoconjugates; D019275:Radiopharmaceuticals; D000068818:Cetuximab
PET imaging; cetuximab; copper-64; cross-bridged chelator; epidermal growth-factor receptor; metal-free click chemistry