Iodogen-mediated radiolabeling of Bevacizumab with I-123 for clinical applications

Bevacizumab is a monoclonal antibody, directed against vascular endothelial growth factor (VEGF), and is currently used in various types of cancers (breast, lung, colorectal). In order to administer to humans glioblastomas, we developed its iodine 123 radiolabeling for in vitro and in vivo studies subsequent. The aim of the study is to choose the best radioiodination conditions based on feasibility in a hospital radiopharmacy: Quick one step method under mild condition, reproducible, using materials for pharmaceutical use and in a closed-system. Method Bevacizumab was radiolabeled with ¹²³I using Iodogen, the most widely used oxidants in direct labelling techniques for tyrosyl residues-containing compounds. We have been explored two crucial parameters for clinical transfer: the amount of oxidant required (50μg and 100μg) and the choice of the purification column (size exclusion column or anion exchange resin), respectively. Quality control was performed before and after purification of each condition in order to evaluate the radiochemical purity (RCP) and purification efficiency. The stability of the radiolabeled molecule is evaluated over time and also when the solution is diluted with unlabeled bevacizumab. Moreover, the in vitro stability of ¹²³I-bevacizumab was determined in presence of human blood at 15, 30, 60 and 120 min. Labeling yield before purification was 96.5% for the first condition (50μg Iodogen) and 95.5% for the second one (100μg Iodogen). The radiochemical purity was 99.5% after purification on a size exclusion column and 99% after purification on anion exchange resin. The purification yield with size exclusion column is 75%, compared with 81% of the anionic exchange resin. The stability in the labeling medium of ¹²³I-bevacizumab at 3, 6, 24 and 30 h after labeling showed a RCP at 100%, 93%, 99.8% and 99.8% for condition 1 so that it was found to be 99.2%, 100%, 99.3%, 99.5% for condition 2, respectively. In vitro incubation with human blood, no deiodination of ¹²³I-bevacizumab was observed until 120 min. Bevacizumab was radiolabeled with I-123 with good radiochemical purity and good stability in the labeling medium until 30 h, even when the solution is diluted with unlabeled bevacizumab. Under our experimental conditions, an amount of 50μg oxidant is sufficient. Purification by anion exchange resin seems slightly better and is a commonly used technique to remove free iodine. ¹²³I-bevacizumab remains stable in presence of human blood. These different parameters are easily achievable in a closed system for its clinical transfer. (authors)