Prevention of DNA double-strand breaks induced by radioiodide-(131)I in FRTL-5 thyroid cells.

Radioiodine-131 released from nuclear reactor accidents has dramatically increased the incidence of papillary thyroid cancer in exposed individuals. The deposition of ionizing radiation in cells results in double-strand DNA breaks (DSB) at fragile sites, and this early event can generate oncogenic rearrangements that eventually cause cancer. The aims of this study were to develop a method to show DNA DSBs induced by (131)I in thyroid cells; to test monovalent anions that are transported by the sodium/iodide symporter to determine whether they prevent (131)I-induced DSB; and to test other radioprotective agents for their effect on irradiated thyroid cells. Rat FRTL-5 thyroid cells were incubated with (131)I. DSBs were measured by nuclear immunofluorescence using antibodies to p53-binding protein 1 or γH2AX. Incubation with 1-10 µCi (131)I per milliliter for 90 min resulted in a dose-related increase of DSBs; the number of DSBs increased from a baseline of 4-15% before radiation to 65-90% after radiation. GH3 or CHO cells that do not transport iodide did not develop DSBs when incubated with (131)I. Incubation with 20-100 µm iodide or thiocyanate markedly attenuated DSBs. Perchlorate was about 6 times more potent than iodide or thiocyanate(.) The effects of the anions were much greater when each was added 30-120 min before the (131)I. Two natural organic compounds recently shown to provide radiation protection partially prevented DSBs caused by (131)I and had an additive effect with perchlorate. In conclusion, we developed a thyroid cell model to quantify the mitogenic effect of (131)I. (131)I causes DNA DSBs in FRTL-5 cells and had no effect on cells that do not transport iodide. Perchlorate, iodide, and thiocyanate protect against DSBs induced by (131)I.

Stability of recombinant human thyrotropin potency based on bioassay in FRTL-5 cells.

BACKGROUND: Recombinant human thyrotropin (rhTSH; Thyrogen®) is approved for use in a 0.9 mg dose/day for 2 consecutive days for diagnosis and treatment of differentiated thyroid cancer. It is recommended that it be injected immediately after reconstitution in the distilled water diluent supplied by the manufacturer. However, Thyrogen has been used off-label in doses less than the standard 0.9 mg dose for stimulation of radioiodine uptake in the treatment of multinodular goiter. To determine whether the biologic activity of Thyrogen can be preserved after dilution, we designed experiments to assess the biologic stability of Thyrogen under different durations and temperatures of storage. METHODS: rhTSH was diluted in 1% bovine serum albumin in phosphate-buffered saline to a concentration of 0.9 mg /mL and further diluted to 0.1 mg/mL. Aliquots of 0.5 mL were stored at room temperature, 4°C, -11°C, and -60°C for various lengths of time. In addition, rhTSH aliquots were also subjected to incubation for 1 hour at 50°C and to 10 cycles of freezing in dry ice alternating with thawing at 37°C. Bioassays were performed in FRTL-5 cells. rhTSH was added to the media at a final concentration of either 5 ng/mL or 20 ng/mL, and the cells were then incubated for 48 hours. Potency was assessed by measurement of ¹²5I-iodide uptake in comparison to cells treated with perchlorate to block iodide uptake. Samples were immunoassayed at day 185 of storage. RESULTS: Samples stored at 4°C, -11°C, -60°C, and room temperature retained activity after storage periods of up to 204 days. Samples subjected to 10 freeze-thaw cycles or heated to 50°C for 1 hour retained full biologic activity. Immunoassay at day 185 showed no difference in immunoactivity in relation to the storage condition. CONCLUSION: rhTSH kept at 4°C, -11°C, -60°C, and room temperature maintained good biologic potency for more than 6 months of storage when tested in vitro, indicating that the biologic activity is very stable. However, altered sialylation occurring during storage could have altered the half-life of rhTSH. Nevertheless, the data provide reassurance that storage in the cold for a few months does not result in significant loss of biologic activity.