MON-512 The Anti-Cancer Agent, Homoharringtonine, Induces the Sodium Iodide Symporter (NIS) Gene Expression in Culture Cells from Papillary Thyroid Cancer, as Well as Non-Thyroid Cancers

BACKGROUND: The therapeutic effect of thyroid cancer by radioiodide treatment is dependent on enhancement of NIS expression by TSH, especially its much greater magnitude in target tissue(s) compared to other healthy tissues. We preliminarily found that a protein synthesis inhibitor cycloheximide (CHX) markedly enhanced NIS mRNA expression, followed by increased iodide uptake, in several cancer cell lines, though CHX is highly toxic for clinical use. Aims: To evaluate the possibility of clinical application of such a pathway to enhance NIS expression, we tried another weak protein synthesis inhibitor, homoharringtonine (HHT), a natural plant alkaloid already utilized as an anti-leukemia agent, in several human cancer cell lines, including thyroid cancer. Methods: BHP 2-7 papillary thyroid cancer cells, MCF7 breast cancer cells, and MKN gastric cancer cells were treated with HHT and/or a p38 inhibitor, and harvested for quantitative RT-PCR of NIS. Results: HHT significantly induced the NIS mRNA expression in all of the cell lines tested, up to 298-fold in BHP cells, 38-fold in MCF7 cells, and 235-fold in MKN cells. Time course experiments indicated a biphasic induction of NIS in BHP cells with two peaks at 48 hours and 96 hours, with the EC(50) of 664 ng/mL and 767 ng/mL, respectively. In contrast, NIS induction by HHT was monophasic in MCF7 cells at 24 hours with EC(50) of 24.6 ng/mL, as well as MKN cells at 96 hours with EC(50) of 255.7 ng/mL. Roles of p38 MAPK in the NIS induction has been reported previously, however, p38 inhibitors, SB239063 (10μM), as well as ML3403 (30μM), did not significantly reduce the NIS expression in HHT-treated BHP cells. Conclusion: These results indicated that HHT has a potential to enhance NIS expression in some NIS-expressing cancer tissues, including papillary thyroid cancer, although its functionality and efficacy are to be validated. The heterogeneity of response in the NIS expression to HHT in three cell lines could be due to differential mechanisms of NIS gene regulation in different tissues.