Radiolabeling of monoclonal anti-CD105 with ¹⁷⁷Lu for potential use in radioimmunotherapy

In this study, we carried out a radioimmunoconjugation using ¹⁷⁷Lu with anti-CD105 (endoglin) monoclonal antibody for an angiogenesis targeting. CD105 has been shown to be a more useful marker to identify proliferating endothelium involved in tumor angiogenesis than panendothelial markers. We optimized the labeling of the anti-CD105 monoclonal antibody with ¹⁷⁷Lu by using cysteine derivative isothiocyanatobenzyl-DTPA (DTPA-NCS) as BFCA. Under the optimal conditions, labeling yield was greater than 99%. Immunoactivity of the radioimmunoconjugate was investigated using combinations of radioanalytical and bioanalytical techniques (ITLC-SG, Cyclone phosphorimager, SDS-PAGE and ELISA). For the biological evaluations we carried out a cell binding assay and a biodistribution study using mice bearing Calu6 lung cancer cell xenografts. The tumor-to-blood ratio was 11.16:1 24 h post-injection. In conclusion, the anti-CD105 monoclonal antibody for an angiogenesis targeting was effectively radioconjugated with ¹⁷⁷Lu. And the biodistribution study showed a high specificity for accumulating in tumor tissues. This radioimmunoconjugate is applicable to detect angiogenesis sites in various diseases and to treat tumors.