Rituximab Iodination Procedure for Radioiodinated Rituximab (131I-Rituximab) Preparation

Abstract

Rituximab is a chimeric monoclonal antibody which has specific for CD20 antigen expressed by pre-B and mature B-cells. Radiolabelled Rituximab, 131 I-Rituximab, has been sucessfully used for treatment of B-Cell NHL. Due to its short shelf-life, 131 I-Rituximab is commonly freshly prepared in hospitals prior to its used. This study aimed to validate rituximab iodination procedure for 131I-Rituximab preparation in order to find the most suitable procedure to be applied in hospitals which intend to produce 131 I-Rituximab in-house. Three different methods of radiolabelling using three types of oxidizing agents, namely Iodobeads, Iodogen, and Chloramine-T were performed. Prior to the validation, radiochemical purity test and purification procedures were also validated as these procedures are critical for producing an acceptable quality of I-Rituximab. In addition, the shelf-life of 131 I-Rituximab was also studied. This study was conducted at the Centre for Radioisotope and Radiopharmaceutical Technology, Serpong during the period of July 2015 to February 2018. The results showed that the radiochemical purity test of 131 I-Rituximab could be easily performed by using instance thin layer chromatography-silica gel (ITLC-SG) in the stationary phase and 85% methanol or saline in the mobile phase. Purification of 131 I-Rituximab was conducted using a Sephadex G-25 M filled column with 0.1 M PBS, pH 7.2, as the eluent that was found to be quite reliable to give 131 I-Rituximab with radiochemical purity of >95% and recovery of approximately 90%. Radiolabelling efficiency performed using Iodobeads was the lowest (60%) compared to that of Iodogen and Chloramine-T (80-90%). In addition, approximately 30% of I was retained by Iodobeads and this procedure was time consuming(~1 hours). It is concluded that Chloramine-T and Iodogen are better than Iodobeads as the oxidizing agent for radiolabelling of Rituximab with 131 I. The radiochemical purity of 131 I-Rituximab is well maintained when stored at room temperature and in 4 °C temperature up to 6 hours.