Transfer Of The Human Sodium/Iodide Symporter Gene Induces Iodide Uptake In Melanoma Cells

The sodium/iodide symporter (NIS) is an intrinsic membrane protein that mediates the active transport of iodide into the thyroid and other tissues. NIS plays key roles in thyroid pathophysiology as the route by which iodide reaches the gland for thyroid hormone biosynthesis and as a means for diagnostic scintigraphic imaging and for . radioiodide therapy in hyperthyroidism and thyroid cancer. The continued molecular analysis of NIS clearly holds the potential of an even greater impact on the diagnosis and radioiodide treatment of cancer, both in thyroid and beyond.Objective To obtain human sodium/iodide symporter cDNA for studying it' s potential utility as a radioiodide treatment for melanoma.Methods hNIS gene cDNA was amplified with total RNA from human thyroid tissue by RT-PCR. The hNIS cDNA was inserted into coloning vector pUCm-T and subcoloned into eukaryotic expression vector pcDNA3, pcDNA3-hNIS and pcDNA3 were transduced into melanoma cells (B16) by electroporation, and two cell lines named B16-A and B16-Brespectively were established. The uptake and efflux of iodide was examined in vitro. The three cell lines (B16-A, B16-B, B16) were injected subcutaneously into the right flank of C57 mice. Biodistribution study and tumor imaging were performed when the tumor reached approximately 10mm in diameter.Results The cloned hNIS cDNA sequence is identical to the published sequence. Two novel cell lines named 16-A containing pcDNA3-hNIS and B16-B containing pcDNA3 only were established. The resultant cell line B16-A accumulated 17 and 19 times more radioiodide in vitro than B16 and B16-B respectively. The efflux of iodide was also rapid (T1/2eff=10min). The imaging shows in vivo uptake in expected sites including the salivary glands, thyroid, stomach, and hNIS-transduced tumor, whereas the nontransduced tumor is not visual ized. The %ID/g of B16-A tumors at 1, 2, 4, 12, 24h after injection of 125I were 12. 22 ± 0. 71, 10. 91 ± 0.12, 8.73?.99, 1.24 ± 0. 29, and 0. 19 ± 0. 03, respectively, which were significantly higher percentages than those for controlling tumors, P<0. 01. However, biologic T1/2 was about 6 hours.Conclusions Our preliminary data indicate that the transduction of the hNIS gene per se is sufficient to induce iodide transport in melanoma cells both in vitro and in vivo, but T1/2eff is short. With regard to therapeutic application, however, further investigationis necessary to determine a method of maintaining more radioiodide in the cells long enough to produce greater therapeutic effects.