Development of new radioimmunoconjugates using anti-angiogenic antibody

Abstract

Radioimmunotherapy (RIT) has been used to treat malignant tumors by delivering a sufficient radiation dose to specific receptor antigens that are overexpressed in tumor cells. For the development of new radioimmunotheraputic agents, appropriate targeting antibodies and the effective radiolabeling with radioisotopes are essential.

For this purpose, we have synthesized a cystein based DTPA-NCS (cys-DTPA-NCS) that possesses five free terminal carboxylic acids and isothiocynate for easy conjugation. In this study, we demonstrate that the cys-DTPA-NCS presents excellent chelating ability for radioimmunoconjugation. $^{177}Lu$ labeled immunoconjugate using cys-DTPA-NCS was prepared under ambient conditions with a high radiolabeling yield and was radiochemically stable.

As targeting antibodies, we chose anti-vascular endothelial growth factor receptor 1 (VEGFR 1) and anti-CD105 which identifys proliferating endothelium involved in tumor angiogenesis.

We optimized the labeling of the antibody with $^{177}Lu$ by using cysteine based DTPA-NCS. Under the optimal conditions, labeling yield was greater than 99%. The stability of the $^{177}Lu$ labeled radioimmunoconjugates were investigated using combinations of radioanalytical and bioanalytical techniques (ITLC-SG, Cyclone phosphorimager, SDS-PAGE). For the biological evaluation we carried out the biodistribution studies using mice bearing Calu 6 non small lung cancer cell xenografts. The tumor-to-blood ratios of $^{177}Lu$-cys-DTPA-NCS-anti-CD105 and $^{177}Lu$-cys-DTPA-NCS-anti-VEGFR 1 were 11.16 : 1 and 3.25 : 1 24h post-injection, respectively.

The $^{177}Lu$-cys-DTPA-NCS-anti-VEGFR 1 had affinity on the surface of HUVE cells (Human Umbilical Vein Endothilial Cells) and a VEGFR 1 expressing tumor cell, T98G glioblastoma cell.

Furthermore, it accumulated at a metastatic organ in a metastatic animal model. In addition, Metastasis of B16F10 cells to the lungs was markedly suppressed under treatment of $^{177}Lu$-cys-DTPA-NCS-anti-VEGFR 1 and this was confirmed by $^{18}F$-FDG imaging using small animal PET. $^{177}Lu$-cys-DTPA-NCS-anti VEGFR 1 has a high potential for inhibition of metastasis.

In conclusion, cys-DTPA-NCS is a good bifunctional chelating agent for radioimmunoconjugation, and the prepared $^{177}Lu$ labeled anti-angiogenic antibodies should be considered for further evaluation as potential radiopharmaceuticals for RIT.