A novel radionuclide probe targeting FN-EDB: a new strategy for radioactive iodine-refractory differentiated thyroid cancer.

OBJECTIVE: To synthesize a novel 161Tb-DOTA-EDB theranostic probe targeting fibronectin extra-domain B (FN-EDB), and further validate its potential for preclinical translational applications.

METHOD: After synthesis of EDB antibody, p-SCN-Bn-DOTA was used for site-specific modification to construct the DOTA-EDB precursor. Subsequent radiolabeling with 161Tb afforded 161Tb-DOTA-EDB, followed by systematic evaluation of its physicochemical properties. With CAL-62 cells and Radioactive iodine-refractory differentiated thyroid cancer (RAIR-DTC) tumor model, we assessed its targeting, biodistribution, imaging, therapeutic efficacy and biosafety.

RESULTS: The molecular weight of DOTA-EDB was approximately 85 kDa, with a binding affinity of 12.90 nM toward the EDB protein. The radiolabeling yield of 161Tb-DOTA-EDB was 94.6 ± 1.2%, and the radiochemical purity reached 97.9 ± 1.5%, remaining above 92% within 96 h in vitro. The probe exhibited good hydrophilicity with a LogD7.4 value of -2.74 ± 0.52. Micro-SPECT/CT imaging revealed that the tumor uptake reached 7.71 ± 1.23% ID/g at 72 h, and the tumor-to-muscle ratio was 31.19 ± 4.89. In vivo treatment experiments demonstrated that the maximum tumor growth inhibition (TGI) rate reached 87%. Immunohistochemical staining confirmed obvious tumor cell apoptosis in the treatment group in a dose-dependent manner. No significant abnormalities in body weight and hematological parameters were observed in mice during treatment, with only mild to moderate liver damage in non-target organs. Radiation dosimetry showed the tumor absorbed dose was 6.60 ± 1.48 mSv/MBq, and the radiation doses of normal organs were all within the clinical safety range.

CONCLUSION: 161Tb-DOTA-EDB exhibits favorable targeting ability, high stability, prominent tumor uptake, potent antitumor efficacy and good biosafety. It is an ideal theranostic probe for RAIR-DTC.