131I-F6 F(ab')2

131I-F6 F(ab')2 is a radiolabeled monoclonal antibody fragment used in a two-step pretargeting radioimmunotherapy approach for cancer treatment. The drug consists of the F(ab')2 fragment of the anti-carcinoembryonic antigen (CEA) monoclonal antibody (F6), which is labeled with radioactive iodine-131. The F(ab')2 format retains two antigen-binding sites but lacks most of the Fc region, reducing non-specific binding and immune activation compared to whole antibodies[3][5]. In clinical studies, this agent has been administered after an initial injection of a bispecific monoclonal antibody targeting both CEA and a hapten, followed by administration of the 131I-labeled hapten to deliver targeted radiation to tumor cells expressing CEA[2]. This strategy aims to improve tumor-to-normal tissue uptake ratios and enhance therapeutic efficacy while minimizing toxicity.