Preclinical evaluation of the antibody fragment targeting fibronectin EDB in the theranostics of radioactive iodine-resistant thyroid cancer.

Abstract

ObjectiveRadioactive iodine-resistant thyroid cancer (RAIR-TC) poses diagnostic and therapeutic challenges due to the absence of sodium/iodide symporter (NIS) expression. This study aims to evaluate the preclinical value of ⁸⁹Zr-DFO-EDB and ¹⁷⁷Lu-DTPA-EDB, an antibody fragment targeting fibronectin EDB (FN-EDB), in the theranostics of RAIR-TC.MethodsA CAL-62 human iodine-resistant thyroid cancer xenograft mouse model was established. The EDB antibody fragment (approximately 100 kD), selected through phage display technology, was labeled with ⁸⁹Zr and ¹⁷⁷Lu, respectively. The targeting characteristics of ⁸⁹Zr-DFO-EDB and ¹⁷⁷Lu-DTPA-EDB in the CAL-62 and NIS-silenced models were analyzed using dynamic micro-PET/CT imaging and ex vivo biodistribution. The anti-tumor efficacy and safety were assessed by a single treatment with 100 μCi of ¹⁷⁷Lu-DTPA-EDB.ResultsThe labeling efficiency of ⁸⁹Zr-DFO-EDB was 90.9%, with a radiochemical purity (RCP) of >99% and stability >98% at 180 min. Imaging showed that tumor uptake peaked at 72 h (13.8 ± 3.32%ID/g) and the liver was the main metabolic organ. High tumor uptake (16.1 ± 1.85%ID/g) was observed in the NIS-silenced model, confirming that EDB antibody targeting is independent of NIS status. The labeling efficiency of ¹⁷⁷Lu-DTPA-EDB was 87.7%, with an RCP of >98.6% and stability >95% at 48 h. In the treatment group, tumor volume decreased by 78.5%, with a relative proliferation rate T/C of 25.05% (65%, with only transient weight loss (5.2%) and mild hepatocyte degeneration observed.Conclusion⁸⁹Zr-DFO-EDB and ¹⁷⁷Lu-DTPA-EDB achieved precise theranostics of RAIR-TC by targeting EDB-FN, with excellent imaging contrast and significant therapeutic effects, providing an innovative strategy for clinical translation in NIS-negative thyroid cancer.