Synthesis and application of a novel cysteine-based DTPA-NCS for targeted radioimmunotherapy.
BACKGROUND
For the development of safe and effective protein-based radiolabeled complexes such as radioimmunotherapy (RIT), the selection of the radionuclides and the chelating agents used for the radiolabeling of tumor-targeting molecules is a critical factor. We aim to synthesize a novel bifunctional chelating agent containing the isothiocyanate group for easy conjugation with antibodies having the characteristics of high stable chelation with therapeutic radionuclides.


METHODS
We have synthesized the DTPA analogue retaining L-cysteine as a core ligand of the thiol group. The chelating power of cysteine-based DTPA-NCS (cys-DTPA-NCS) was compared with that of commercial ρ-SCN-Bn-DTPA. In an application, the cetuximab was radioimmunoconjugated with (177)Lu using cys-DTPA-NCS. The affinity was tested in a cell line overexpressing EGFR. A therapy study was conducted in nude mice with subcutaneous HT-29 xenografts.


RESULTS
The cys-DTPA-NCS presents an excellent ability to chelate as compared to the ρ-SCN-Bn-DTPA. For mean ratio chemical labeling yields of 95%, the result was 0.97. (177)Lu-cys-DTPA-NCS-cetuximab was prepared under ambient condition with a high radiolabeling yield and the radiochemical purity was sustained for at least 6days. The IC50 value of the (177)Lu-labeled cetuximab was 10nM (95% confidence). The stability and therapeutic efficacy of the candidate radiopharmaceutical were verified.


CONCLUSIONS
The new DTPA derivative, cys-DTPA-NCS, is a good bifunctional chelating agent that can be used for protein-based radiopharmaceutical using lanthanides such as (177)Lu and (90)Y. The prepared (177)Lu-cys-DTPA-NCS-cetuximab can be used for the diagnosis and treatment of human colorectal tumor.
Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Republic of Korea.
So-Young
SY
Lee
Young Don
YD
Hong
Hak-Sung
HS
Kim
Sun-Ju
SJ
Choi
D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000627:therapeutic use; D000068818:Cetuximab; D060326:Chemistry Techniques, Synthetic; D003545:Cysteine / Q000737:chemistry* / Q000493:pharmacokinetics; D005260:Female; D019073:HT29 Cells; D006801:Humans; D008187:Lutetium / Q000627:therapeutic use; D051379:Mice; D058990:Molecular Targeted Therapy / Q000379:methods*; D004369:Pentetic Acid / Q000737:chemistry*; D016499:Radioimmunotherapy / Q000379:methods*; D011868:Radioisotopes / Q000627:therapeutic use
D061067:Antibodies, Monoclonal, Humanized; D011868:Radioisotopes; D008187:Lutetium; D004369:Pentetic Acid; D003545:Cysteine; D000068818:Cetuximab