In Vivo Imaging of Thyroid Cancer with 99mTc-TR1401 and 99mTc-TR1402: A Comparison Study in Dogs

Abstract

Differentiated thyroid cancer (DTC) cells may lose NIS expression and iodine uptake, but usually express TSH receptors (TSHR). Therefore, the aim of our study was to compare two radiolabeled superagonist TSH analogues for DTC imaging. These analogues (namely TR1401 and TR1402) have a higher TSHR binding affinity than recombinant human TSH (Thyrogen®). Radiolabeling was performed with technetium-99m using an indirect method via HYNIC conjugation and was followed by in vitro quality controls and binding assay on TSHR-positive cell lines (ML-1). An in vitro binding assay was also performed and compared with radiolabeled human recombinant TSH. In vivo imaging was performed in four dogs with spontaneous follicular thyroid carcinoma with solid poorly differentiated areas with 99mTc-TR1401 SPECT/CT, 99mTc-TR1402 SPECT/CT, and [18F]FDG PET/CT on different days within 2 weeks. TR1401 and TR1402 were labeled with high specific activity (8.3 ± 1.2 MBq/µg) and retention of their biological activity and structural integrity. Both agonists were able to efficiently bind TSHR receptors expressed by cell lines with dissociation constants (Kd) of 2.7 nM for 99mTc-TR1401 and 0.5 nM for 99mTc-TR1402 compared with 99mTc-Thyrogen (Kd = 8.4 nM). In tumor-targeting experiments, a focal uptake was observed in dogs with spontaneous intraglandular thyroid carcinoma, in which TSHR expression was confirmed by immunohistochemistry. 99mTc-TR1402 provided higher T/B than 99mTc-TR1401 and [18F]FDG (12.9 ± 1.3, 10.2 ± 0.7, and 3.8 ± 0.6, respectively; all p < 0.001). Given these results, 99mTc-TR1402 appears to be a useful tool for in vivo imaging of thyroid cancer.

PET Imaging of Differentiated Thyroid Cancer with TSHR-Targeted [89Zr]Zr-TR1402

“…38 Binding affinity of [ 89 Zr]Zr-TR4102 (Figure 1F) was similar to that previously reported with 99m Tc. 27 In vivo PET imaging in tumor xenograft models showed [ 89 Zr]Zr-TR1402 accumulation in TSHR+ tumors (Figures 2−3 and S2−S7), with a significant difference between TSHR+ and TSHR-THJ529T and FTC133 tumors observed for all S8), limits the benefit of imaging after 24 h postinjection. Methods for improving tumor uptake, including increased tumor vascularization and the use of larger molecular weight constructs to increase circulation time, could be explored to increase tumor retention.…”

“…Recombinant human TSH (rhTSH) analogue TR1402 ,, was supplied by Trophogen, Inc. (Rockville, MD), and Dr. Mariusz Szkudlinski. TR1402 was combined with p-SCN-Bn-deferoxamine (DFO) (Macrocyclics, Plano, TX) at a molar ratio of 3:1 (DFO/TR1402) in 0.1 M, pH 9, sodium carbonate buffer for 2 h at 37 °C , and buffer exchanged into 1 M HEPES using a Zeba Micro Spin Desalting Column 7k MWCO, 75 μL.…”

“…In this study, we assess the uptake of the TSHR-targeted PET radiopharmaceutical [ 89 Zr]­Zr-TR1402 in human DTCs. TR1402 is a 28 kDa bioengineered recombinant human thyroid-stimulating hormone (TSH) analogue, which functions as a TSHR agonist. − …”

The role of companion animal models in radiopharmaceutical development and translation

“…In other studies, dogs were used as a model in gene therapy techniques utilizing the NaI symporter, as well as in the development of imaging agents targeting TSH receptors, which can still be expressed on cancer cells which may lose their NIS expression. 50,66 The interplay between radiopharmaceutical therapy, immunomodulating drugs and tumour response to immunotherapy would be impossible to evaluate in an immune-compromised model, however the tumour-conditioned immune system of companion dogs with naturally-occurring cancer is a highly realistic model that complements small animal discovery work. 40,41 (VRTOG) has published a radiation morbidity scoring scheme which is broadly used in the veterinary radiation oncology literature, and which could be used in the standardized scoring of side effects from radiopharmaceutical therapy.…”

“…This observed uptake heterogeneity could have a profound impact on the delivered dosimetry of 131 I radioiodine therapy (Figure 3). In other studies, dogs were used as a model in gene therapy techniques utilizing the NaI symporter, as well as in the development of imaging agents targeting TSH receptors, which can still be expressed on cancer cells which may lose their NIS expression 50,66 . The interplay between radiopharmaceutical therapy, immunomodulating drugs and tumour response to immunotherapy would be impossible to evaluate in an immune‐compromised model, however the tumour‐conditioned immune system of companion dogs with naturally‐occurring cancer is a highly realistic model that complements small animal discovery work 40,41 .…”