A simple and safe method for ¹³¹I radiolabeling of rituximab for myeloablative high-dose radioimmunotherapy

The aim of this study was to develop a safe and simple radiolabeling and purification procedure for high-dose ¹³¹I-rituximab for treatment of patients with non-Hodgkin's lymphoma. As the starting point, the conventional Iodogen-coated vial method was applied. After the iodogen-coated monoclonal antibody (mAb) method, a labeling method involving much lower amounts of iodogen was assessed. Subsequently, ¹³¹I-rituximab was purified with a tangential flow filtration system. Quality control of the final product was performed by using size-exclusion chromatography with ultraviolet detection and by instant high-performance thin-layer chromatography. Immunoreactivity was determined by using a cell-binding assay. During the labeling procedure, radiation exposure was monitored. The coated vial method resulted in a low radiation exposure, but immunoreactivity was highly compromised (37%). Also, formation of aggregates was observed. The maximal observed effective dose was 18 μSv, finger thermoluminescence dosemeters revealed a hand-dose measurement of 0.8 mSv. The second method resulted in an immunoreactivity of 70%. Radiochemical purity was >97% after purification. The maximal measured effective dose was 31 μSv, and detected exposure to the hands was 1.9 mSv. We have developed a simple labeling technique for the preparation of high-dose ¹³¹I-rituximab. The method offers a high purity and retained immunoreactivity with minimal radiation exposure for involved personnel.