Influence of thyroid-stimulating hormone on 18F-fluorodeoxyglucose and 99mTc-methoxyisobutylisonitrile uptake in human poorly differentiated thyroid cancer cells in vitro

Objective  In poorly differentiated thyroid cancer originating from thyroid follicular cells, the ability to concentrate iodine is lost. This makes recurrence undetectable by ¹³¹I whole-body scan. In this situation, other radiopharmaceuticals, such as ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and technetium-99m-methoxyisobutylisonitrile (^99mTc-MIBI), are used to evaluate recurrence or metastasis. Some reports suggest that ¹⁸F-FDG uptake is increased by thyroid-stimulating hormone (TSH) stimulation. This study aimed to determine the influence of TSH on ¹⁸F-FDG and ^99mTc-MIBI uptake in human poorly differentiated thyroid cancer cells in vitro. Materials and methods  The cells were stimulated with 1000 μU/ml of recombinant human thyroid-stimulating hormone (rhTSH) for 1 day, 3 days, and 5 days. Each cell was incubated with 0.5 MBq/ml-1 MBq/ml of ¹⁸F-FDG or 0.5 MBq/ml-1 MBq/ml of ^99mTc-MIBI for 1 h at 37°C. The uptake of each radiopharmaceutical in the cells was quantified as a percent of whole radioactivity per total viable cell number. The quantification of glucose transporter 1, 2, 3 and 4 mRNA expression was measured using RT-PCR. Results  TSH stimulation increased ¹⁸F-FDG uptake in a time-dependent manner. Following 5 days of rhTSH stimulation, ¹⁸F-FDG uptake was approximately 2.2 times that of the control. The increase in ¹⁸F-FDG uptake following rhTSH stimulation was correlated to the increase in GLUT4 mRNA level. The GLUT1 mRNA level was unchanged. An increased uptake of ^99mTc-MIBI was observed with a pattern similar to that of ¹⁸F-FDG. The ^99mTc-MIBI uptake was approximately 1.5 times that of the control 5 days later. Conclusions  These results suggest that TSH stimulates ¹⁸F-FDG and ^99mTc-MIBI uptake in poorly differentiated papillary thyroid cancer, and therefore ¹⁸F-FDG-PET or ^99mTc-MIBI scans under TSH stimulation may be more accurate than under suppression.