131I-sibrotuzumab

131I-sibrotuzumab is a radiolabeled humanized monoclonal antibody targeting fibroblast activation protein alpha (FAP), an inducible tumor stromal antigen highly expressed in the stroma of various epithelial cancers. The drug consists of sibrotuzumab conjugated to radioactive iodine-131 (I-131), enabling both targeted delivery of radiation and imaging. Its mechanism involves binding to FAP on cancer-associated fibroblasts within the tumor microenvironment, delivering cytotoxic radiation directly to the tumor stroma while sparing normal tissues. Developed primarily by Boehringer Ingelheim and Ludwig Institute for Cancer Research, it was investigated for use in advanced or metastatic non-small cell lung cancer and colorectal cancer. Clinical trials demonstrated selective tumor uptake and manageable safety but did not show objective responses; development was discontinued due to lack of efficacy[2][3][5][8].