Preclinical ImmunoPET Imaging of Thyroid-Stimulating Hormone Receptor Expression in Thyroid Cancer using [Cu]Cu-NOTA-TSHR-Ab.

Advanced thyroid cancers are aggressive and often refractory to the current standard of care. The thyroid-stimulating hormone receptor (TSHR) is highly expressed in thyroid cancers and rarely expressed outside the thyroid, making it a viable target for developing radiotheranostics for imaging and therapy of advanced thyroid cancer. This study reports the radiosynthesis and preclinical evaluation of a Cu-labeled human antibody for positron emission tomography (PET) imaging of TSHR expression in advanced thyroid cancer mouse models. Human anti-TSHR recombinant antibody K1-70 (TSHR-Ab) was labeled with copper-64, yielding [Cu]Cu-NOTA-TSHR-Ab with a radiochemical yield of 46.89 ± 3.74%, radiochemical purity of 98.77 ± 0.89%, and specific activity >212 GBq/μmol ( = 5). studies on TSHR-positive (THJ529T) and wild-type (THJ529T) cells demonstrated the radiotracer's high specificity and nanomolar binding affinity for THJ529T cells, with a dissociation constant () of 4.74 nM and an inhibition constant () of 0.92 nM. ImmunoPET imaging in mice bearing dual-flank tumors (THJ529T and THJ529T) at multiple time points (1, 2, 4, 18, 24, and 48 h) postinjection (p.i.) revealed rapid tumor targeting and high uptake in TSHR-positive thyroid tumors (SUV: 3.63 ± 0.42, 3.82 ± 0.44, and 4.09 ± 0.56 at 18, 24, and 48 h p.i., respectively). Co-injection studies with varying doses of unlabeled TSHR-Ab (0, 25, 50, 100 μg) demonstrated that the coinjection significantly reduced background signals, especially in the spleen, liver, and bone, with a dose of 25 μg effectively reducing off-target signals without affecting tumor uptake. Biodistribution and immunohistochemistry analyses supported these immunoPET imaging results. Furthermore, a comparison study with traditional [F]FDG PET imaging showed that [Cu]Cu-NOTA-TSHR outperformed [F]FDG in tumor detection. In conclusion, [Cu]Cu-NOTA-TSHR-Ab is a promising radiotracer for PET imaging of TSHR-positive advanced thyroid cancers, with the potential to guide and monitor TSHR-targeted therapies. Further clinical evaluation of [Cu]Cu-NOTA-TSHR-Ab could provide valuable insights for patient stratification and optimization of anti-TSHR treatments.